Biaxially aligned polyester film

Abstract

The objective of this invention is to provide a polyester film with excellent cold-workability and the ability to suppress springback and curling after forming. This invention is a biaxially aligned polyester film, primarily composed of terephthalic acid and ethylene glycol, with a puncture strength of 0.45 N / μm to 0.80 N / μm, a heat shrinkage rate of 2.5% or less in both the MD and TD directions at 150°C, a coefficient of dynamic friction μd between at least one side of the film and a metal plate of 0.10 to 0.50, and a stress attenuation rate of 15.0% or more in both the MD and TD directions in a tensile stress relief test at 25°C, expressed as stress attenuation rate (%) = 100 × (σ0 - σ1) / σ0, relative to the total dicarboxylic acid content in the film of 0.02 mol% to 2.0 mol%.

Description

Technical Field

[0001] This invention relates to a polyester film, specifically a polyester film with excellent cold-workability, particularly suitable for use in battery packaging, pharmaceutical packaging, and other applications where metal foils are laminated and then shaped. Prior Technology

[0002] Aromatic polyesters, represented by polyethylene terephthalate (PET), possess excellent mechanical properties and chemical resistance, and are widely used as molded products for fibers, films, etc. In particular, PET resin is inexpensive and hygienic, making it widely used for food and beverage containers.

[0003] In recent years, laminated lithium-ion battery outer packaging materials or press-through packs have been obtained by cold forming a laminate made of resin film or metal foil. The laminate used for the above-mentioned cold forming is generally composed of polyethylene terephthalate film / biaxially stretched nylon film / aluminum foil / polypropylene film, etc. (see, for example, Patent Document 1).

[0004] Furthermore, regarding pharmaceutical packaging, in order to prevent the deterioration of the contents, there is a growing demand for packaging forms using metal foil, primarily aluminum, and there is a need to improve the formability of the metal foil to match the shape of the contents.

[0005] One factor affecting formability during cold forming is the flexibility of the resin film. If the resin film has low flexibility, it will bear a strong load during elongation in cold forming, potentially leading to pinholes or delamination. Conversely, if the resin film is too flexible, its effectiveness as a substrate protecting the metal foil-containing laminate weakens, resulting in reduced physical properties of the obtained laminate. Therefore, it is crucial that the resin film possesses a flexibility that is neither too high nor too low.

[0006] As a means of solving these problems, for example, according to Patent Document 2, a laminate is disclosed that is formed by sequentially stacking at least a substrate layer, an adhesive layer, a metal layer and a sealant layer. The aforementioned substrate layer can obtain good formability by setting the sum (A+B) of the stress value A when the elongation is 50% in the MD direction / the stress value B when the elongation is 50% in the TD direction to a specific range.

[0007] On the other hand, in the aforementioned cold forming process, after drawing forming, a portion of the formed part tends to return to its original shape (springback), which can be problematic. This springback can lead to insufficient dimensional accuracy in the drawn-formed shape. Furthermore, during the forming process, because the surrounding parts are strongly stretched, the substrate layer surrounding the formed part warps as it tries to return to its original state, potentially reducing yield in subsequent processing. In this regard, as described in the previously cited Patent Document 2, controlling only the F5 or F50 value of the film can improve the forming depth, but it is still insufficient to improve the deterioration of dimensional accuracy caused by the springback after forming or the warping resistance after forming.

[0008] Patent document 3 discloses a biaxially aligned polyester film, which is a biaxially aligned polyethylene terephthalate film using recycled PET bottle raw materials. The film has a melt resistivity of less than 1.0 × 10⁸ Ω·cm at 285°C, and the sodium and potassium content is greater than 0 ppm and less than 150 ppm. Based on this technology, a biaxially aligned polyester film can be obtained, which has low residual components of the washing solution used in the production of recycled PET bottle raw materials, excellent thermal stability, low foreign matter content, and stable melt resistivity, without compromising the film's productivity or appearance quality. [Previous Technical Documents] [Patent Literature]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2008-053133. [Patent Document 2] International Publication No. 2015-125806. [Patent Document 3] Japanese Patent Application Publication No. 2014-65282. Summary of the Invention

[0010] [The problem that the invention aims to solve]

[0011] This invention was developed against the backdrop of the prior art. Specifically, the purpose of this invention is to provide a polyester film that not only possesses excellent cold formability and suppresses the reduction in dimensional accuracy after forming due to springback, but also exhibits excellent warpage resistance, and is an environmentally friendly polyester film containing post-consumer recycled materials. [Methods used to solve problems]

[0012] Through in-depth research, the inventors of this invention discovered that by selecting a specific range of stretching conditions and controlling the mechanical properties of the membrane within a predetermined range, it can achieve excellent cold workability and suppress springback and curling after forming, thus achieving the present invention.

[0013] That is, the present invention is formed by the following components. [1] A biaxially aligned polyester film, which is mainly composed of terephthalic acid and ethylene glycol; has a puncture strength of 0.45 N / μm or more to 0.80 N / μm or less as determined by JIS Z 7102; has a heat shrinkage rate of 2.5% or less in both the MD and TD directions at 150°C; has a coefficient of dynamic friction μd of at least one side of the film with a metal plate of 0.10 or more to 0.50 or less; and has a stress attenuation rate of 15.0% or more in both the MD and TD directions as expressed by the following formula (1) in a tensile stress relief test at 25°C. Equation (1) Stress attenuation rate (%) = 100 × (σ0 - σ1) / σ0 Here, σ0 represents the tensile stress value at the moment after applying a tensile force to the aforementioned membrane at a stretching speed of 200 mm / min and applying 50% tensile strain, and σ1 represents the tensile stress value when σ0 is maintained at 50% tensile strain for 2 seconds. The content of isophthalic acid in the membrane relative to the total dicarboxylic acid content is more than 0.02 mol% and less than 2.0 mol%. [2] As described in [1], when the stress at 3% elongation in the MD and TD directions of the film at 25°C is set as X(MD) and X(TD), respectively, and the stress at 30% elongation in the MD and TD directions is set as Y(MD) and Y(TD), respectively, and the values ​​of Y(MD) / X(MD) and Y(TD) / X(TD) are set as Z(MD) and Z(TD), respectively, all of the following equations (2) to (5) are satisfied. Equation (2) 125MPa≦Y(MD)≦155MPa Equation (3) 140MPa≦Y(TD)≦190MPa Equation (4) 1.3≦Z(MD)≦1.6 Equation (5) 1.7≦Z(TD)≦2.2 [3] Biaxially aligned polyester film as described in [1] or [2], wherein the film contains at least 60% by mass of post-consumer recycled material relative to the total polyester resin. [4] The biaxially aligned polyester film described in any of [1] to [3], wherein the number of defects larger than 1 mm per 1000 square meters of film is less than 1.0. [5] Biaxially aligned polyester film as described in any of [1] to [4], for cold forming applications. [6] A laminate comprising a biaxially aligned polyester film, a gas barrier layer and a sealant layer as described in any one of [1] to [5]. [7] As described in [6], the aforementioned gas barrier layer comprises a metal foil. [8] A battery packaging material comprising a laminate as described in [6] or [7]. [Invention Benefits]

[0014] By using the biaxially aligned polyester film of this invention as the substrate layer, the metal foil can appropriately follow the shape of the mold during molding, thus not only suppressing the occurrence of pinholes or cracks, but also exhibiting excellent springback and warping resistance after molding, resulting in excellent dimensional accuracy and thus contributing to improved productivity. Furthermore, by using an environmentally friendly polyester film made from recycled materials, it helps reduce the environmental burden by not impacting changes in surface carbon dioxide levels. Simple Explanation of the Diagram

[0015] [Figure 1] is a schematic diagram illustrating a method of multi-segment extension in the TD direction during the membrane manufacturing process. Implementation

[0016] The present invention will now be described in detail.

[0017] [Polyester Resin Composition] The biaxially aligned polyester film of this invention is a film formed from a polyester resin composition that includes terephthalic acid as a dicarboxylic acid component and ethylene glycol as a diol component as a main component. Here, "including as a main component" means that the total composition of the polyester resin is set to 100 mol%, and the content of this component in the polyester resin composition is 80 mol% or more, preferably 90 mol% or more, more preferably 95 mol% or more, and most preferably 97 mol% or more.

[0018] Furthermore, other components can also be copolymerized in these polyester resins. Specifically, examples of dicarboxylic acids as copolymerizing components include: isophthalic acid, naphthalene dicarboxylic acid, 4,4-biphenyl dicarboxylic acid, adipic acid, sebacic acid, and ester-forming derivatives of these dicarboxylic acids. Examples of glycols include: diethylene glycol, hexanediol, neopentyl glycol, and cyclohexanediol. Also examples include: polyoxyalkylene glycols such as polyethylene glycol and polypropylene glycol. The copolymerization amount is preferably 10 mol% or less per repeating unit, more preferably 5 mol% or less, and most preferably 3 mol% or less.

[0019] The aforementioned polyester resin composition may include polyester resin obtained through recycling. As recycled raw materials, there are pre-consumer materials of waste plastics generated from the membrane manufacturing process and post-consumer materials of used waste plastics; both can be used, but post-consumer materials are preferred from the perspective of reducing plastic waste and lowering the environmental burden. Examples of post-consumer materials include fibers containing polyester resin as a main component, food and beverage containers, detergent and pharmaceutical containers, other containers and packaging, with PET bottles molded from PET resin being particularly suitable.

[0020] The polyester resin composition used in the biaxially aligned polyester film of the present invention preferably contains at least 60% by mass of post-consumer recycled material relative to the total polyester resin, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0021] There are two main recycling methods: physical recycling and chemical recycling. Both are acceptable. Below are examples of methods for producing post-consumer recyclable materials from PET bottles using physical recycling and chemical recycling.

[0022] [Physically recycled polyester resin] Recycled PET bottles are sorted to remove all other materials and waste. After removing labels, they are shredded into flakes. These flakes often contain foreign matter. Furthermore, the possibility of filling used PET bottles with chemicals such as pharmaceuticals or solvents is also considered. Examples include dishwashing detergents, insecticides, herbicides, pesticides, and various oils. Normal washing is insufficient to remove the chemicals adsorbed on the PET bottle surface; therefore, alkaline washing is preferable. Sodium hydroxide or potassium hydroxide solutions are used as the alkali metal hydroxide solution in this washing step. A pre-wash can also be performed before alkaline washing. Without alkaline washing, foreign matter remains in the resin, causing not only breakage during film formation and reduced productivity, but also affecting the film's appearance or causing print defects in subsequent printing steps.

[0023] The concentration of the aqueous solution of alkali metal hydroxide used in the above-mentioned cleaning steps, although it depends on the temperature, time, and stirring conditions, is generally in the range of 1% to 10% by weight. Furthermore, the cleaning time ranges from 10 minutes to 100 minutes, and to improve efficiency, it is best to perform the cleaning while stirring.

[0024] Following alkaline washing, it is preferable to perform rinsing and drying. Alkaline washing and rinsing can also be repeated several times. Because the components of the aqueous solution of alkali metal hydroxide used in the alkaline washing step remain on the sheet, they can sometimes affect the physical properties of the final film during the melt extrusion steps in the subsequent pelletizing and film-forming processes.

[0025] In this washing process, some of the PET bottle flakes are hydrolyzed by the aqueous solution of alkali metal hydroxide. Furthermore, the degree of polymerization of the resin decreases due to the heating during the molding of the PET bottles. Consequently, the heat and moisture applied during the pulverization, remelting, and pelletizing of recycled PET bottles for reuse further reduce the degree of polymerization. While direct reuse is possible, depending on the intended use, the reduced degree of polymerization results in inferior formability, strength, transparency, or heat resistance, sometimes making direct reuse impossible. In such cases, to restore the reduced degree of polymerization, it is preferable to perform solid-phase polymerization on the pulverized and washed PET bottle flakes or the flakes melted and pelletized from them.

[0026] In the solid-state polymerization step, the washed sheet or the pelletized sheet obtained by melt extrusion can be continuously polymerized in an inert gas such as nitrogen or rare gas at a temperature of 180°C to 245°C, preferably 200°C to 240°C.

[0027] As for the polyester resin ultimately contained in PET bottles, which is recycled from the market or society, it is ideal to adjust the conditions of the flakes or pellets to have an inherent viscosity of 0.55 dl / g to 0.90 dl / g, more preferably 0.60 dl / g to 0.85 dl / g.

[0028] The process of pelletizing the sheet is described below. The sheet is melted, extruded, cooled, and granulated using an extruder equipped with degassing and filtration mechanisms. In the melting step of the extruder, melt mixing can be performed at a temperature typically between 260°C and 300°C, preferably between 265°C and 295°C. The PET bottle flakes, which are pulverized, need to be thoroughly dried beforehand, preferably at a concentration of 5 ppm to 200 ppm, more preferably 10 ppm to 100 ppm, and even more preferably 15 ppm to 50 ppm. If the sheet contains a high amount of moisture, a hydrolysis reaction will occur during the melting step, reducing the intrinsic viscosity of the resulting polyester resin. As a degassing method, it is preferable to have at least one vacuum vent in the molten resin zone. Furthermore, the extruder preferably has a filter capable of filtering and removing solid foreign matter with a particle size of 25 μm or larger, preferably 15 μm or larger, and more preferably 10 μm or larger from the molten resin. Molten resin that has passed through a filter is cooled in water via a mold and then cut into pellets of the desired shape for granulation.

[0029] The sheet or pellets obtained by the above method can be melt-extruded into sheet form by an extruder, either alone or mixed with polyester resin composed of initial raw materials, and extended in the MD and TD directions to obtain a biaxially aligned polyester film.

[0030] [Chemically recycled polyester resin] After the recycled PET bottles are processed through the same sorting, crushing, and washing steps described above to remove foreign matter, they are then depolymerized to break down and refine them into raw or intermediate materials for PET resin. These materials are then polymerized again to produce new PET resin. Because chemical recycling removes foreign matter and impurities through depolymerization / repolymerization, it can regenerate polyester resin of the same high quality as the original resin. Therefore, compared to the aforementioned physically recycled polyester resin, it is particularly suitable for food packaging due to its superior hygiene.

[0031] Examples of depolymerization and repolymerization methods include: refining bis-2-hydroxyethyl terephthalate (BHET), an intermediate raw material used in resin manufacturing, by adding ethylene glycol (EG) and in the presence of a catalyst, and then repolymerizing this component to form PET; or repolymerizing terephthalic acid and ethylene glycol by heating them in a non-aqueous organic solvent in the presence of an oxidized iron catalyst.

[0032] The following describes one aspect of a method for the chemical recovery of bis-2-hydroxyethyl terephthalate (BHET). The crude PET sheets obtained from the above-mentioned crushing and washing steps are depolymerized and melted simultaneously, and then hydrolyzed to become a low-degree-of-polymerization PET melt. Depolymerization is then carried out using excess ethylene glycol to obtain a mixed solution of crude BHET and crude ethylene glycol.

[0033] After the depolymerization reaction is completed, the two mixed solutions of crude BHET and crude ethylene glycol are cooled and filtered to remove unreacted linear and cyclic oligomers, solidified residual plastics other than polyethylene terephthalate, metals and other solid foreign matter, which are high-melting-point precipitates. Then, adsorption and ion exchange treatments are applied to remove colorants and dissolved ions, thereby removing foreign matter contained in crude BHET.

[0034] The obtained crude BHET and crude ethylene glycol mixture is subjected to distillation and evaporation to separate and distill off the ethylene glycol, thereby obtaining concentrated BHET; or, the two mixtures are cooled to below 10°C to allow BHET to crystallize, and then the ethylene glycol and BHET are separated to obtain concentrated BHET. This concentrated BHET is then vacuum evaporated at a temperature between 190°C and 250°C, with a residence time of less than 10 minutes in the evaporator, to obtain refined BHET.

[0035] After obtaining high-purity refined BHET in the above manner, this refined BHET is added to a melt polycondensation reactor to obtain high-purity polyethylene terephthalate polymer. The obtained high-purity polyethylene terephthalate polymer can be granulated into pellets, and then melt-extruded into sheets by an extruder, either alone or mixed with polyester resin composed of the initial raw materials, extending in both the MD and TD directions to obtain a biaxially aligned polyester film.

[0036] In the biaxially aligned polyester film of the present invention, the content of isophthalic acid in the polyester film relative to the total dicarboxylic acid content is preferably in the range of 0.02 mol% to 2.0 mol%. More preferably, it is 0.05 mol% to 1.5 mol%, further preferably 0.1 mol% to 1.0 mol%, and most preferably 0.15 mol% to 0.5 mol%. By having an isophthalic acid content of 0.02 mol% or more, a polyester film with a high content of recycled materials can be obtained. On the other hand, when the isophthalic acid content is high, the crystallinity decreases, and sometimes the mechanical strength of the film may decrease. By setting the isophthalic acid content to the above range, it is easier to produce a film with excellent lamination strength, shrinkage rate, and thickness uniformity.

[0037] In the polyester used in PET bottles, crystallinity is controlled to achieve a good bottle appearance, sometimes resulting in the use of polyesters containing less than 10 mol% isophthalic acid. Therefore, in the polyester film of this invention, the material containing isophthalic acid is included in a certain amount. By containing a specific amount of isophthalic acid in the film, the adhesion strength between the film and a sealant or metal foil can be improved. Although the reason for the improved adhesion between the film and a sealant or metal foil due to the presence of isophthalic acid is not yet clear, it is presumed that because isophthalic acid-ethylene glycol units are less likely to crystallize than terephthalic acid-ethylene glycol units, a large amount of amorphous components remain in the film. As a result, not only does the film become easier to modify through surface treatments such as corona treatment, but the outermost surface of the film also becomes more soluble in solvents, primarily due to increased affinity for the adhesive (used when the film is bonded to a sealant or metal foil).

[0038] The inherent viscosity of the aforementioned polyester resin composition is preferably in the range of 0.50 dl / g to 0.90 dl / g, and more preferably in the range of 0.55 dl / g to 0.80 dl / g, in terms of film-forming properties or recyclability.

[0039] In addition to polyester resin, polyester resin compositions may also contain commonly known additives, such as lubricants, stabilizers, colorants, antioxidants, antistatic agents, and ultraviolet absorbers.

[0040] For example, the aforementioned lubricant can adjust the coefficient of kinetic friction of the film. In addition to inorganic lubricants such as silica, calcium carbonate, and aluminum oxide, organic lubricants can also be mentioned. As inorganic lubricants, silica and calcium carbonate are preferred, and from the viewpoint of balancing transparency and lubricity, porous silica is the best.

[0041] The lower limit of the lubricant content in the biaxially aligned polyester film of the present invention is preferably 400 ppm by mass, more preferably 600 ppm by mass. By setting it to 500 ppm by mass or higher, the film's lubricity can be improved. The upper limit of the lubricant content is preferably 1500 ppm by mass, more preferably 1200 ppm by mass. By setting it to below 1500 ppm by mass, the film's transparency can be improved.

[0042] [Manufacturing method of biaxially aligned polyester film] The method for obtaining the biaxially aligned polyester film of the present invention is not particularly limited, and a T-die method or blow molding method can be appropriately selected. A representative manufacturing step of the T-die method is described here. The T-die method includes the following steps: (1) melting and extruding a polyester resin composition into a sheet and cooling it on a cooling roller to form an unstretched sheet; (2) stretching the unstretched sheet to the MD direction (length direction) and the TD direction (width direction) orthogonal to the MD direction; (3) heating the stretched film to crystallize it; (4) heat-relaxing (sometimes called relaxation) step to remove the residual strain of the heat-fixed film; and (5) cooling step to cool the heat-relaxed film.

[0043] The membrane of the present invention can be a single-layer structure with at least one layer, or a multilayer structure with two or more layers. It can be two, three, four, or five layers.

[0044] The upper limit of the cooling roller temperature is preferably 40°C, and more preferably below 20°C. If it is below 40°C, the crystallinity of the molten polyester resin composition will not become too high during cooling and curing, making it easier to extend and suppressing the reduction in transparency caused by crystallization. The lower limit of the cooling roller temperature is preferably 0°C. If it is above 0°C, the crystallization inhibition effect of the molten polyester resin composition during cooling and curing can be fully utilized. Furthermore, when the cooling roller temperature is set within the above range, in order to prevent condensation, it is preferable to reduce the humidity of the environment near the cooling roller beforehand.

[0045] The thickness of the unstretched sheet is preferably in the range of 15 μm to 2500 μm. More preferably, it is below 600 μm, and optimally below 400 μm.

[0046] The following explains the extension steps. The extension method can be either simultaneous biaxial extension or gradual biaxial extension. The following explanation uses gradual biaxial extension as an example.

[0047] The lower limit of the elongation ratio in the MD direction is preferably 2.5 times, more preferably 2.8 times, and exceptionally preferably 3.1 times. If it is above 2.5 times, not only does the mechanical strength of the film become better, but the thickness unevenness is also improved, which leads to the improvement of the winding quality when making the roll. The upper limit of the elongation ratio in the MD direction is preferably 5.0 times, more preferably 4.5 times, and even more preferably 4.0 times. By setting the elongation ratio in the MD direction to 5.0 times or less, it is possible to suppress the increased springback and curling after forming due to excessively high film alignment.

[0048] The preferred temperature for stretching in the MD direction is in the range of 80°C to 130°C. If the stretching temperature in the MD direction is below 80°C, the springback and curling after forming may increase due to excessively high film alignment. On the other hand, if the stretching temperature in the MD direction is above 130°C, the formability may decrease due to lower MD alignment.

[0049] As a method for extending in the MD direction, methods such as extending between multiple rolls while heating them simultaneously, or extending by heating with an infrared heater, are available. Extending by heating with an infrared heater is advantageous because it easily achieves high temperatures and allows for localized heating, thus reducing scratches and defects caused by the rolls. On the other hand, when extending between multiple rolls while heating them simultaneously, multi-stage extension between multiple rolls is preferable. By using multi-stage extension between multiple rolls, even at high extension ratios, the upward alignment in the MD direction can be suppressed, and springback and curling after forming can be prevented. The number of rolls used for multi-stage extension is preferably 2 or more, and more preferably 3 or more.

[0050] In the extension step, it is preferable that after the extension step in the MD direction, there is a relaxation step in the MD direction (hereinafter also referred to as MD relaxation) between the extension step in the MD direction and the extension step in the TD direction. The lower limit of the MD relaxation rate is preferably 1%, more preferably 3%, and especially preferably 5%. If it is above 1%, the amorphous component in the film is mitigated, which can reduce the stretching stress in the subsequent TD stretching step. As a result, since the alignment of the film can be suppressed from becoming too high, springback and curling after forming can be suppressed. The upper limit of MD relaxation rate is preferably 10%, more preferably 8%, and ideally 6%. If it is below 10%, it can not only suppress wrinkles caused by shrinkage and improve the appearance quality of the membrane, but also suppress the reduction of mechanical strength caused by misalignment. There are no particular limitations on the method of MD relaxation. For example, a method can be given by using a hot air heater to heat the rollers and then applying the relaxation treatment by the speed difference between the rollers.

[0051] The lower limit of the elongation temperature in the TD direction is preferably 90°C, more preferably 100°C, and even more preferably 110°C. If it is above 90°C, springback and curling after forming can be suppressed because the elongation stress can be reduced. The upper limit of the stretching temperature in the TD direction is preferably 140°C, more preferably 130°C, and even more preferably 120°C. If the stretching temperature in the TD direction exceeds 140°C, not only will the film-forming properties decrease, but the alignment of the obtained film in the TD direction will also weaken, thus potentially reducing the formability.

[0052] The lower limit of the elongation ratio in the TD direction is preferably 2.5 times, more preferably 3.0 times, and ideally 3.5 times. If it is above 2.5 times, not only will the mechanical strength and thickness uniformity of the film be improved, but the formability will also be enhanced. The upper limit of the elongation ratio in the TD direction is preferably 5.0 times, more preferably 4.5 times, and especially preferably 4.0 times. By setting it to 5.0 times or less, the upward alignment in the TD direction can be suppressed, and the occurrence of springback and curling after molding can be suppressed.

[0053] In addition to the commonly used linear extension pattern with increased elongation ratio, multi-stage extension can be used more effectively in the TD direction. Multi-stage extension, compared to the usual single-stage extension (i.e., linear extension), as shown in Figure 1, involves two or more extension steps, which reduces the extension stress experienced during TD extension. As a result, even with the same elongation ratio, excessive alignment in the TD direction can be prevented, thus suppressing springback and curling after molding.

[0054] Multi-stage extension in the TD direction is preferably between two and five stages. Multi-stage extension allows for variations in the extension temperature, resulting in changes in extension stress and thus reducing extension stress during TD extension. Two or more stages reduce extension stress, preventing excessive alignment in the TD direction even at the same elongation ratio, thus suppressing springback and curling after forming. Five or fewer stages prevent excessively large equipment. In multi-stage extension, a temperature pattern is preferably established where a temperature difference of 2°C or more is applied to each stage, decreasing the temperature from the first stage to the last. Furthermore, in the case of multi-stage extension, a region of fixed length can be appropriately set after each extension stage. By setting a region of fixed length after each extension stage, the internal stress that occurs during extension is mitigated in the fixed length region, thereby further reducing the extension stress when performing the next extension. Even with the same extension ratio, it can suppress the alignment in the TD direction from becoming too high, and suppress springback and curling after forming.

[0055] The lower limit of the heat-setting temperature in the heat-setting step is preferably 170°C, more preferably 180°C, and particularly preferably 190°C. Temperatures above 170°C can reduce the heat shrinkage rate. The upper limit of the heat-setting temperature is preferably 230°C, more preferably 220°C, and particularly preferably 210°C. Temperatures below 230°C can suppress the decrease in mechanical strength caused by the embrittlement of the biaxially aligned polyester film.

[0056] The lower limit of the relaxation rate in the TD direction during the heat tempering step is preferably 0.5%, more preferably 1.0%, and even more preferably 2.0%. A relaxation rate above 0.5% can keep the thermal shrinkage rate in the TD direction low. The upper limit of the relaxation rate in the TD direction is preferably 10%, more preferably 8%, and even more preferably 6%. A relaxation rate below 10% can prevent sagging and improve flatness.

[0057] [Composition and properties of biaxially aligned polyester films] The lower limit of the thickness of the biaxially aligned polyester film of the present invention is preferably 5 μm, more preferably 10 μm. By setting it to 5 μm or more, good mechanical properties and formability can be obtained. The upper limit of the thickness of the biaxially aligned polyester film of the present invention is preferably 100 μm, more preferably 70 μm, and particularly preferably 40 μm.

[0058] The lower limit of the puncture strength of the biaxially aligned polyester film of the present invention is preferably 0.45 N / μm, and more preferably 0.50 N / μm. Good formability can be obtained if the puncture strength is above 0.45 N / μm. The upper limit of the puncture strength of the biaxially aligned polyester film of the present invention is 0.80 N / μm. If the puncture strength exceeds 0.80 N / μm, the effect of improving formability will saturate. Here, the puncture strength (unit N / μm) referred to in the present invention means the strength (unit N) of the needle penetrating the film when a needle with a tip radius of 0.5 mm punctures the film at a puncture speed of 50 mm / min, divided by the thickness of the film (unit μm).

[0059] The lower limit of the heat shrinkage rate in the MD and TD directions of the biaxially aligned polyester film of the present invention is preferably 0.1%, more preferably 0.2%, and particularly preferably 0.3%. The upper limit of the heat shrinkage rate in the MD and TD directions is preferably 2.5%, more preferably 2.0%, and particularly preferably 1.8%. By keeping it below 2.5%, dimensional changes during heating in the secondary processing step are suppressed, and the occurrence of wrinkles can be reduced.

[0060] The thickness non-uniformity in the TD direction of the biaxially aligned polyester film of the present invention is preferably 18% or less, more preferably 16% or less, and even more preferably 14% or less. When it is below 18%, the winding quality when made into a roll becomes good.

[0061] The haze of the biaxially aligned polyester film of the present invention is preferably 5.0% or less, more preferably 3.0% or less, and even more preferably 2.5% or less. By setting it to 5.0% or less, the printing looks more aesthetically pleasing, which is therefore preferable.

[0062] Secondly, the springback during forming will be explained. In applications such as battery packaging and pharmaceutical packaging, the film is pressed into a mold of a predetermined shape, held in the pressed state for a certain period of time, and then the mold is pulled upwards to create a shaped body. However, if the internal stress in the film is not sufficiently relieved during the holding time and the mold is pulled upwards directly, the film will generate a force that wants to return to its original shape, resulting in greater springback and a risk of reduced dimensional accuracy of the shaped body. The inventors of this case discovered that in the tensile stress relief test of the obtained biaxially aligned polyester film, by setting the stress decay rate after holding for 2 seconds within a specific range, the aforementioned springback can be reduced.

[0063] In the tensile stress relief test at 25°C, the biaxially aligned polyester film of the present invention exhibits a stress attenuation rate of at least 15% in both the MD and TD directions, as shown in the following formula (1), and more preferably at least 16%. Equation (1) Stress attenuation rate (%) after holding for 2 seconds = 100 × (σ0 - σ1) / σ0 Here, σ0 represents the tensile stress of the aforementioned membrane after a tensile force of 50% is applied at a stretching speed of 200 mm / min, and σ1 represents the tensile stress when σ0 is maintained at 50% tensile strain for 2 seconds.

[0064] The biaxially aligned polyester film of the present invention preferably satisfies the following formulas (2) and (3) when the stress (F30 value) when the elongation in the MD direction of the film at 25°C is 30% and the stress (F30 value) when the elongation in the TD direction is 30% and the stress (F30 value) is 30% and the stress (T) when the elongation in the TD direction is 30%. Equation (2) 125MPa≦Y(MD)≦155MPa Equation (3) 140MPa≦Y(TD)≦190MPa

[0065] Excellent formability can be obtained by setting the value of Y(MD) to 125 MPa or higher. On the other hand, by setting the value of Y(MD) to 155 MPa or lower, excessive stress in the formed film is suppressed, reducing springback and warpage after forming, thus achieving good formability. Similarly, excellent formability can be obtained by setting the value of Y(TD) to 140 MPa or higher. By setting the value of Y(TD) to 190 MPa or lower, excessive stress in the formed film is suppressed, reducing springback and warpage after forming, thus achieving good formability.

[0066] The biaxially aligned polyester film of the present invention preferably satisfies the following equations (4) and (5) when the stress (F3 value) when the film elongates by 3% in the MD direction at 25°C is X(MD), the stress (F3 value) when the film elongates by 3% in the TD direction is X(TD), the value of Y(MD) / X(MD) is Z(MD), and the value of Y(TD) / X(TD) is Z(TD). Equation (4) 1.3≦Z(MD)≦1.6 Equation (5) 1.7≦Z(TD)≦2.2

[0067] Setting the Z(MD) value to 1.3 or higher yields excellent formability. Conversely, setting the Z(MD) value to 1.6 or lower prevents excessive stress in the formed film, reducing springback and warpage, thus achieving good formability. Similarly, setting the Z(TD) value to 1.7 or higher yields excellent formability. Setting the Z(TD) value to 2.2 or lower prevents excessive stress in the formed film, reducing springback and warpage, thus achieving good formability.

[0068] From a formability point of view, the biaxially aligned polyester film of the present invention preferably has a coefficient of kinetic friction μd relative to a metal surface of 0.10 or more to 0.50 or less. When the polyester film of the present invention is used for battery packaging or pharmaceutical packaging, these components are formed by compression molding using male and female molds. By setting the coefficient of kinetic friction μd between the film and the metal to 0.10 or more to 0.50 or less, smooth molding is possible due to good sliding properties relative to the compression mold. More preferably, it is 0.20 or more to 0.50 or less, and even more preferably, it is 0.25 or more to 0.40 or less. In the present invention, the coefficient of kinetic friction relative to the metal refers to the coefficient of kinetic friction between any surface of the film and the SUS304-#400 mirror-finished material. The aforementioned coefficient of kinetic friction can be controlled by the content of the lubricant added to the film.

[0069] The biaxially aligned polyester film of the present invention preferably has a defect number of 1 mm or more per 1000 square meters of film of 1.0 or less. By keeping the number of defects below 1.0, the film quality becomes good, and printing defects can also be prevented. Post-consumer materials are prone to contamination by foreign matter and residues of chemicals. In order to set the defect number to 1.0 or less, by performing the above-mentioned alkaline washing step, foreign matter and other substances that cause defects can be removed.

[0070] A printable layer can also be deposited in the biaxially aligned polyester film of the present invention. As the printing ink forming the printable layer, printing inks containing water-based and solvent-based resins are preferable. Examples of resins used as printing inks include acrylic resins, urethane resins, polyester resins, vinyl chloride resins, vinyl acetate copolymer resins, and mixtures of these resins. The printing ink may also contain known additives such as antistatic agents, opacifiers, UV absorbers, plasticizers, lubricants, fillers, colorants, stabilizers, lubricants, defoamers, crosslinking agents, antiblocking agents, and antioxidants.

[0071] There are no particular limitations on the printing method used to set the printing layer; known printing methods such as offset printing, gravure printing, and screen printing can be used. Regarding the drying of the solvent after printing, known drying methods such as hot air drying, hot roller drying, and infrared drying can be used.

[0072] The present invention provides a laminate formed by further providing an inorganic thin film layer or a gas barrier layer such as a metal foil to a biaxially aligned polyester film.

[0073] The aforementioned inorganic thin film layer is a thin film composed of metals or inorganic oxides. There are no particular limitations on the materials forming the inorganic thin film layer, as long as they can form a thin film; however, from the viewpoint of gas barrier properties, inorganic oxides such as aluminum, silicon oxide (silicon oxide), aluminum oxide (aluminum oxide), and mixtures of silicon oxide and aluminum oxide are preferred. In particular, a composite oxide of silicon oxide and aluminum oxide is preferred in terms of balancing the flexibility and density of the thin film layer.

[0074] In this composite oxide, the mixing ratio of silicon oxide to aluminum oxide, by mass ratio of the metal components, is preferably in the range of 20% to 70% for Al. On the other hand, if it is below 70%, the inorganic thin film layer can be softened, and the film can be prevented from being damaged and the gas barrier properties reduced during secondary processing such as printing or lamination. In addition, the silicon oxide referred to here is various silicon oxides such as SiO or SiO2 or mixtures of such silicon oxides, and the aluminum oxide is various aluminum oxides such as AlO or Al2O3 or mixtures of such aluminum oxides.

[0075] The thickness of inorganic thin film layers is typically from 1 nm to 100 nm, preferably from 5 nm to 50 nm. If the thickness of the inorganic thin film layer is greater than 1 nm, it becomes easier to obtain more satisfactory gas barrier properties. On the other hand, if the thickness is less than 100 nm, it becomes advantageous in terms of bending resistance and manufacturing cost.

[0076] There are no particular limitations on the methods for forming inorganic thin film layers. For example, well-known vapor deposition methods such as physical vapor deposition (PVD), sputtering, and ion plating, or chemical vapor deposition (CVD) can be used. Below, a typical method for forming inorganic thin film layers will be explained using a silicon oxide-alumina thin film as an example. For instance, in the case of vacuum vapor deposition, a mixture of SiO₂ and Al₂O₃, or a mixture of SiO₂ and Al, is preferably used as the vapor deposition raw material. These vapor deposition raw materials can typically be particle-sized, ideally to maintain the pressure during vapor deposition, with a preferred particle size of 1 mm to 5 mm. Heating can be achieved using resistance heating, high-frequency induction heating, electron beam heating, laser heating, etc. Furthermore, oxygen, nitrogen, hydrogen, argon, carbon dioxide, water vapor, etc., can be introduced as reactant gases, or reactive vapor deposition can be performed using methods such as adding ozone or ion-assisted deposition. Furthermore, the film formation conditions can be arbitrarily changed, such as applying a bias voltage to the substrate (the deposited film for evaporation) or heating or cooling the substrate. The evaporation material, reactive gas, bias voltage of the substrate, heating / cooling, etc., can also be changed in the case of sputtering or CVD methods. Moreover, a printed layer can also be deposited on the aforementioned inorganic thin film layer.

[0077] In the case where the inorganic thin film layer is provided in the biaxially aligned polyester film of the present invention, it is preferable to provide a protective layer on the inorganic thin film layer. The gas barrier layer composed of metal oxide is not a completely dense film, and is dotted with tiny defects. By coating the metal oxide layer with the specific protective layer resin composition described later to form a protective layer, the resin in the protective layer resin composition is impregnated into the defective portions of the metal oxide layer, thereby achieving the effect of stable gas barrier properties. Furthermore, by using a gas barrier material for the protective layer itself, the gas barrier performance of the laminated film is also greatly improved.

[0078] Examples of the aforementioned protective layer include: a protective layer formed by adding epoxy, isocyanate, or melamine-based curing agents to resins such as urethane, polyester, acrylic, titanium, isocyanate, imide, and polybutadiene. Examples of solvents used in forming the protective layer include: aromatic solvents such as benzene and toluene; alcohol solvents such as methanol and ethanol; ketone solvents such as acetone and methyl ethyl ketone; ester solvents such as ethyl acetate and butyl acetate; and polyol derivatives such as ethylene glycol monomethyl ether.

[0079] The metal foil used as a gas barrier layer can be made of various metal foils such as aluminum and stainless steel. Aluminum foil is preferred in terms of moisture resistance, processability (e.g., ductility), and cost. Ordinary soft aluminum foil can be used. Among these, iron-containing aluminum foil is preferred in terms of excellent pinhole resistance and ductility during forming. The iron content in the iron-containing aluminum foil (100% by mass) is preferably 0.1% to 9.0% by mass, more preferably 0.5% to 2.0% by mass. If the iron content is above the lower limit, the pinhole resistance and ductility are excellent. If the iron content is below 9.0% by mass, the flexibility is excellent. The thickness of the metal foil is preferably 9μm to 200μm, more preferably 15μm to 100μm, in terms of barrier properties, pinhole resistance, and processability.

[0080] Other materials can also be laminated in the laminate of the present invention. As a method, it is possible to use a method of laminating biaxially aligned polyester films after film formation or a method of laminating them during film formation.

[0081] The laminate of the present invention can further form a heat-sealable resin layer (also known as a sealant layer) in the biaxially aligned polyester film and gas barrier layer, which can be used as a cold-formed packaging material. The sealant layer is usually formed by extrusion lamination or dry lamination.

[0082] Examples of sealant layers include resin films composed of polyolefin resins or acid-modified polyolefin resins grafted with acids such as maleic anhydride. Examples of the aforementioned polyolefin resins include: low-density, medium-density, and high-density polyethylene; ethylene-α-olefin copolymers; homopolymer, block copolymer, or atactic copolymers; and propylene-α-olefin copolymers. These polyolefin resins can be used individually or in combination of two or more.

[0083] The sealant layer can be a single-layer film or a multi-layer film, depending on the required function. For example, to provide moisture resistance, a multi-layer film containing resins such as ethylene-cyclic olefin copolymers or polymethylpentene can be used. Furthermore, the sealant layer can also be formulated with various additives such as flame retardants, slip agents, anti-blocking agents, antioxidants, light stabilizers, and tackifiers. The thickness of the sealant layer is preferably 10 μm to 100 μm, more preferably 20 μm to 60 μm.

[0084] The laminate of the present invention can also be formed by providing an adhesive layer, a printing layer, etc. between the biaxially aligned polyester film and the gas barrier layer, and / or between the gas barrier layer and the sealant layer.

[0085] This invention provides a battery outer packaging material comprising a laminate (including a biaxially aligned polyester film, a gas barrier layer, and a sealant layer). It is particularly suitable for battery outer packaging materials for laminated lithium-ion batteries. As another embodiment, this invention provides a pharmaceutical packaging material. [Example]

[0086] The evaluation of membranes and laminates is performed using the following methods. Unless otherwise specified, the measurements are conducted in a testing chamber at 23°C and 65% relative humidity.

[0087] [Membrane thickness] The determination was performed using a needle-plate gauge in accordance with JIS K7130-1999 A method.

[0088] Evaluation of thickness unevenness in the TD direction Samples were taken from the film roller at 800 mm along the TD direction and 40 mm along the length direction. The thickness in the width direction was measured continuously at 5 m / s using a Continuous Film Thickness Tester (manufactured by Fujiwork). The maximum thickness measured was set as Tmax, the minimum thickness as Tmin, and the average thickness as Tave. The thickness non-uniformity in the width direction of the film was calculated from the following formula (6). Equation (6) Thickness non-uniformity = [(Tmax.-Tmin.) / Tave.]×100 (%)

[0089] [Membrane thermal shrinkage rate] The heat shrinkage rate was measured according to the dimensional change test method of JIS-C-2318, except that the test temperature was set at 150°C and the heating time was 15 minutes. The test specimens were cut from the MD direction and the TD direction respectively for measurement.

[0090] [Content of terephthalic acid and isophthalic acid in polyester] A sample solution was prepared by dissolving chloroform D (manufactured by Yurisop) and trifluoroacetic acid D1 (manufactured by Yurisop) in a 10:1 (volume ratio). The proton NMR of the sample solution was measured using NMR (Nuclear Magnetic Resonance) (GEMINI-200; manufactured by Varian) at 23°C with 64 measurements. During the NMR measurement, the peak intensity of the predetermined protons was calculated, and the content (in moles%) of terephthalic acid and isophthalic acid in 100 moles of the acid component was calculated.

[0091] [Number of defects in film] The film rolls are rewound using a rewinding machine. During rewinding, a defect detection machine (model F MAX MR) manufactured by FUTEC is used to investigate defects. Then, for defects larger than 1 mm in either the longitudinal or transverse direction, the number of defects per 1000 square meters of film area is calculated.

[0092] [Puncture strength] The test was conducted according to the "Specifications and Standards for Foods, Additives, etc., Section 3: Utensils and Containers" (Ministry of Health, Labour and Welfare Notice No. 20, 1982) of the Food Sanitation Law, specifically section 2, "Test Method for Strength, etc." A needle with a tip radius of 0.5 mm was used to puncture the membrane at a puncture speed of 50 mm / min. The puncture strength was calculated by dividing the strength (N) of the needle penetrating the membrane by the membrane thickness (μm). The test was performed at room temperature (23°C), and the unit is [N / μm].

[0093] [Coefficient of kinetic friction] According to JIS K-7125, using a tensile testing machine (Tensilon, manufactured by ORIENTEC), at 23°C and 65%RH, the coefficient of dynamic friction μd was determined when the surface of the uncorona-treated film was bonded to SUS304-#400 mirror-finished material. The SUS304-#400 mirror-finished material weighs 1.5 kg and has a base area of ​​63 mm x 63 mm. Furthermore, the tensile speed during the friction test was 200 mm / min.

[0094] [Haze] Following the method of JIS-K-7105, a haze meter (Nippon Denshoku Manufacturing Co., Ltd., NDH2000) was used to measure the haze at three different locations on the sample. The average value of the measurements was set as the haze. The unit is [%).

[0095] [Strength and tensile strength of biaxially aligned membranes] According to JIS K 7127, test specimens with a width of 15 mm and a length of 100 mm were cut along the MD direction of the membrane. Tensile testing was performed on the specimens using a tensile testing machine (Autograph AG-I manufactured by Shimadzu Corporation) at a spacing of 50 mm between test points and a tensile speed of 200 mm / min. The stress at 3% elongation (F3 value) and the stress at 30% elongation (F30 value) were calculated from the obtained stress-strain curves.

[0096] [Stress attenuation rate of biaxially aligned films] Test samples with a width of 15 mm and a length of 100 mm were cut along the MD direction of the membrane. Using a tensile testing machine (Autograph AG-I manufactured by Shimadzu Corporation), a tensile strain of 50% was applied at a spacing of 50 mm between the test points and a tensile speed of 200 mm / min. The tensile strain was maintained from the application of the 50% tensile strain until 100 seconds later, and the stress change was recorded. From the obtained holding time-stress diagram, read the stress value after holding for 2 seconds from the moment 50% strain is applied, and use the following formula (1) to calculate the stress decay rate after holding for 2 seconds.

[0097] Equation (1) Stress attenuation rate (%) after holding for 2 seconds = 100 × (σ0 - σ1) / σ0

[0098] Here, σ0 represents the tensile stress of the aforementioned membrane after a tensile force of 50% is applied at a stretching speed of 200 mm / min, and σ1 represents the stress value after σ0 maintains a tensile strain of 50% for 2 seconds.

[0099] [Cold formability] A biaxially aligned polyester film, a biaxially aligned polyamide film (manufactured by Toyobo, N1102, 15μm thick), an aluminum foil (8079 material, 40μm thick), and an unstretched polypropylene film (manufactured by Toyobo, P1146, 70μm thick) serving as a sealant layer were dry-laminated using a carbamate-based adhesive (dry lamination adhesive manufactured by Toyo Morton, with a mixing ratio of TM-509, CAT10L, and ethyl acetate of 33.6:4.0:62.4 (mass ratio)). This process created a laminate consisting of biaxially aligned polyester film, biaxially aligned polyamide film, aluminum foil, and a sealant layer. The resulting laminate was then placed in a die set mold (90mm x 50mm protrusion shape) and drawn into shape using a press at 23°C. The drawing depth during molding is gradually increased in 0.2 mm increments. The maximum depth to which the above-mentioned laminate will not break is set as the drawing depth, and the evaluation is carried out as follows. A: The drawing depth is 8mm or more. B: The drawing depth is 6mm to less than 8mm. C: The drawing depth is 4mm to less than 6mm D: The drawing depth is less than 4mm.

[0100] [Springback after forming] The aforementioned laminated body was placed in a mold base (90mm × 50mm protrusion shape), and drawn into shape by applying pressure at 23°C using a press. The die insertion speed during drawing was set to 200mm / min, and the holding time after insertion was set to 2 seconds. The container depth after removing the mold was measured, and the retention rate (the ratio of container depth to forming depth) was calculated and evaluated as follows. A: The retention rate is over 90%. B: Retention rate is above 80% but below 90%. C: Retention rate of 70% or higher but less than 80% D: Retention rate not reaching 70%

[0101] [The curled shape after shaping] The test piece that was undamaged and could be formed in the aforementioned cold workability evaluation was placed on a horizontal platform with the convex part facing upwards. The average height of the warp of the four corners of the formed test piece from the aforementioned platform was taken as the average warp height, and the evaluation was carried out according to the following criteria. A: The average warpage height is less than 3mm. B: The average warpage height is 3mm or more but less than 5mm C: The average warpage height is 5mm or more but less than 10mm D: The average warpage height is 10mm or more.

[0102] [Manufacturing Example] The polyester resins used in the examples and comparative examples are as described below.

[0103] Polyester Resin A: Physically Recycled Polyester Resin After the recycled used beverage bottles are rinsed to remove any remaining beverage residue and other foreign matter, they are pulverized to obtain flakes. The flakes are then washed with a 3.5% by weight sodium hydroxide solution at 10% by weight, 85°C, and for 30 minutes with stirring. Following this alkaline washing, the flakes are removed and washed with distilled water at 10% by weight, 25°C, and for 20 minutes with stirring. This washing process is repeated twice, replacing the distilled water. After washing, the flakes are dried and melted using an extruder. Fine foreign matter is further removed by filtering through two separate filters with increasingly smaller screen sizes. A third filter with a minimum screen size of 50 μm is used to remove impurities, yielding polyester resin A with an intrinsic viscosity of 0.69 dl / g and an isophthalic acid content of 1.5 moles.

[0104] Polyester Resin B: Chemically Recycled Polyester Resin The recycled PET bottles are fed into a wet grinder. A solution of 500g of kitchen liquid detergent in 1000 liters of water is circulated and ground within the wet grinder. A gravity separator connected to the grinder causes heavier materials such as metal, sand, and glass to settle, and flakes are taken from the top. These flakes are then rinsed with pure water and centrifuged to produce recycled flakes.

[0105] 30 kg of the sample obtained by melting the above-mentioned recycled flakes in an undried state was placed in an autoclave equipped with a stirrer. A mixture of 150 kg of preheated ethylene glycol and 150 g of zinc acetate dihydrate was added. After removing fractions with boiling points lower than ethylene glycol, such as water and acetic acid, the mixture was reacted for 4 hours at 195°C to 200°C using a reflux condenser. After the reaction, the temperature of the reactor contents was lowered to 97°C to 98°C, and hot filtration was performed to remove suspended solids and precipitates. The filtrate after hot filtration was further cooled until the crude BHET was completely dissolved. Then, it was subjected to a pre-purification treatment at 50°C to 51°C for 30 minutes, passing through an activated carbon bed followed by an anion / cation exchange mixed bed.

[0106] The pre-refined liquid was added back into a stirred autoclave and heated to distill off the remaining ethylene glycol at 198°C, yielding a concentrated BHET melt. The concentrated BHET melt was then cooled naturally under a nitrogen atmosphere with stirring, and removed from the autoclave to obtain concentrated BHET fragments. These fragments were reheated and melted to 130°C, then fed to a thin-film vacuum evaporator using a metering pump for evaporation, cooling, and condensation to obtain refined BHET. This refined BHET was used as a raw material for melt polymerization to obtain a chemically recycled polyester resin B with an intrinsic viscosity of 0.69 dl / g.

[0107] Polyester resin C: Initial polyester resin The PET resin derived from fossil fuels is used with terephthalic acid / ethylene glycol = 100 / 100 (mol%) and a porous silica particle content of 0.72% by mass (intrinsic viscosity 0.62 dl / g).

[0108] Polyester Resin D: Physically Recycled Polyester Resin In the manufacturing steps of the aforementioned polyester resin A, except that alkaline washing is not performed, the process is carried out in the same manner as that of polyester resin A to obtain polyester resin D with an intrinsic viscosity of 0.69 dl / g and an isophthalic acid content of 1.5 moles.

[0109] Polyester resin E: Initial polyester resin The PET resin used is derived from fossil fuels and has a terephthalic acid / ethylene glycol ratio of 100 / 100 (moles%) (intrinsic viscosity 0.62 dl / g).

[0110] [Example 1] Polyester resin A and polyester resin C were fed into an extruder at the ratios shown in Table 1. The resins were melted at 280°C using the extruder and then cast from a T-die. The mixture was then sealed using an electrostatic sealing method on a cooling roller at 10°C to obtain an unstretched film. Next, the obtained unstretched film was preheated on a roller heated to 80°C, and then heated to 120°C using an infrared heater, and stretched in the MD direction at a stretch ratio of 3.7. Next, the film was stretched in the TD direction using a tenter frame at a preheating temperature of 120°C, a stretching temperature of 140°C, and a stretch ratio of 4.6. Afterward, it was heat-fixed at 210°C, subjected to a 5% relaxation treatment in the TD direction, and the surface layer (A) on the side in contact with the cooling roller was corona treated at 40 W·min / m². The film was then wound into a roll using a winding machine to produce a biaxially aligned polyester film with a thickness of 12 μm. The raw material composition and membrane preparation conditions of the obtained membrane, the physical properties of the obtained membrane, and the evaluation results are shown in Table 1.

[0111] [Examples 2 to 3] Except for changing the longitudinal stretch ratio to the ratio shown in Table 1, a biaxially aligned polyester film with a thickness of 12 μm was obtained by film preparation in the same manner as in Example 1. The physical properties and evaluation results are shown in Table 1.

[0112] [Example 4] Except that the longitudinal stretching method was set to three-segment stretching on a roller, and the roller was heated to a temperature of 115°C, and the stretching was carried out in three segments with the first segment set to 1.24 times, the second segment set to 1.4 times, and the third segment set to 2.6 times, with a total stretching ratio of 4.5 times in the length direction, a biaxially aligned polyester film with a thickness of 12 μm was obtained by film preparation in the same manner as in Example 1. The physical properties and evaluation results are shown in Table 1.

[0113] [Example 5] Polyester resin A and polyester resin C were fed into an extruder at the ratios shown in Table 1. The resins were melted at 280°C using the extruder and then cast from a T-die. The mixture was then sealed using an electrostatic sealing method on a cooling roller at 10°C to obtain an unstretched film. Next, the obtained unstretched film was preheated on a roller heated to 80°C, then heated to 120°C using an infrared heater, and stretched in the MD direction at a stretch ratio of 5.0. The film after MD stretching is passed through a heating furnace set at 95°C with a hot air heater. The speed difference between the rollers at the inlet and outlet of the heating furnace is used to perform a 3% relaxation treatment in the MD direction. Secondly, the stretching method of the tenter frame transverse stretching machine was changed to a three-stage stretching process, with a fixed length of 1m between the first and second stages and between the second and third stages. The stretching temperature and the stretching ratio of each stage are shown in Table 1. Afterwards, heat curing was performed at 210°C, followed by a 5% heat relaxation treatment in the width direction. Corona treatment was then applied to the surface in contact with the cooling roller at 40 W·min / m². The film was then wound into a roll using a winding machine to produce a 12μm thick biaxially aligned polyester film. The raw material composition and membrane preparation conditions of the obtained membrane, the physical properties of the obtained membrane, and the evaluation results are shown in Table 1.

[0114] [Examples 6 to 7] Except for changing the ratio of polyester resin A to polyester resin C to the ratio shown in Table 1, a biaxially aligned polyester film with a thickness of 12 μm was obtained by film preparation in the same manner as in Example 1. The physical properties and evaluation results are shown in Table 1.

[0115] [Example 8] Except for replacing polyester resin A with polyester resin B, a biaxially aligned polyester film with a thickness of 12 μm was obtained by film preparation in the same manner as in Example 1. The physical properties and evaluation results are shown in Table 1.

[0116] [Table 1A] unit Example 1 Example 2 Example 3 Example 4 raw material Polyester Resin A quality% 87 87 87 87 Polyester resin B quality% - - - - Polyester resin C quality% 13 13 13 13 Polyester resin D quality% - - - - Polyester resin E quality% - - - - Silicon Oxide Addition ppm 950 950 950 950 MD extension steps Extension method - 1 extension 1 extension 1 extension 3-section extension Heating method - infrared heater infrared heater infrared heater Roller heating Extension ratio Paragraph 1 times 3.7 3.0 4.0 1.24 Paragraph 2 times - - - 1.4 Paragraph 3 times - - - 2.6 total times 3.7 3.0 4.0 4.5 Extended temperature - ℃ 120 120 120 115 relaxation rate - % - - - - TD extension steps Extension ratio Paragraph 1 times 4.6 4.6 4.6 4.6 Paragraph 2 Paragraph 3 Extended temperature Paragraph 1 times 140 140 140 140 Paragraph 2 Paragraph 3 Extended mode - - straight line straight line straight line straight line Heat setting temperature - ℃ 210 210 210 210 thickness - μm 12 12 12 12 Uneven thickness - % 14.4 15.1 13.5 13.5 Haze - % 2.1 2.2 2.4 2.5 Puncture strength - N 6.1 5.5 6.4 6.5 - N / μm 0.51 0.46 0.53 0.54 thermal shrinkage rate MD % 1.7 1.2 1.7 1.8 thermal shrinkage rate TD % 0.4 0.3 0.4 0.4 Stress attenuation rate MD % 18.9 19.8 17.1 17.7 TD % 16.6 16.5 16.7 16.7 X:F3 MD MPa 96 100 94 95 TD MPa 93 94 94 93 Y:F30 MD MPa 133 132 138 137 TD MPa 183 182 183 182 Z:F30 / F3 MD - 1.4 1.3 1.5 1.4 TD - 2.0 1.9 2.0 2.0 coefficient of kinetic friction of metals - - 0.35 0.37 0.39 0.34 isophthalic acid content - % 1.4 1.4 1.4 1.4 Number of defects - Units / 1000m² 0.7 0.6 0.7 0.7 Cold formability - - B C A B Curl after forming - - B A C B Springback after forming - - B A C B

[0117] [Table 1B] unit Example 5 Example 6 Example 7 Example 8 raw material Polyester Resin A quality% 87 83 92 - Polyester resin B quality% - - - 87 Polyester resin C quality% 13 17 8 13 Polyester resin D quality% - - - - Polyester resin E quality% - - - - Silicon Oxide Addition ppm 950 1200 600 950 MD extension steps Extension method - 1 extension 1 extension 1 extension 3-section extension Heating method - infrared heater infrared heater infrared heater Roller heating Extension ratio Paragraph 1 times 3.7 3.0 4.0 1.24 Paragraph 2 times - - - 1.4 Paragraph 3 times - - - 2.6 total times 3.7 3.0 4.0 4.5 Extended temperature - ℃ 120 120 120 115 relaxation rate - % - - - - TD extension steps Extension ratio Paragraph 1 times 4.6 4.6 4.6 4.6 Paragraph 2 Paragraph 3 Extended temperature Paragraph 1 times 140 140 140 140 Paragraph 2 Paragraph 3 Extended mode - - straight line straight line straight line straight line Heat setting temperature - ℃ 210 210 210 210 thickness - μm 12 12 12 12 Uneven thickness - % 14.8 14.4 14.6 14.4 Haze - % 2.2 2.8 1.8 2.1 Puncture strength - N 6.5 6.1 6.1 6.1 - N / μm 0.54 0.51 0.51 0.51 thermal shrinkage rate MD % 1.9 1.5 1.6 1.7 thermal shrinkage rate TD % 0.3 0.4 0.4 0.4 Stress attenuation rate MD % 20.2 18.6 18.4 18.9 TD % 18.8 16.6 16.6 16.6 X:F3 MD MPa 92 97 97 96 TD MPa 94 93 93 93 Y:F30 MD MPa 139 134 134 133 TD MPa 175 183 183 183 Z:F30 / F3 MD - 1.5 1.4 1.4 1.4 TD - 1.9 2.0 2.0 2.0 coefficient of kinetic friction of metals - - 0.35 0.26 0.46 0.35 isophthalic acid content - % 1.4 1.3 1.5 1.4 Number of defects - Units / 1000m² 0.6 0.4 0.8 0.1 Cold formability - - B A C B Curl after forming - - B B B B Springback after forming - - B B B B

[0118] [Comparative Examples 1 to 4] Except for changing the longitudinal and transverse stretching conditions to those shown in Table 2, a biaxially aligned polyester film with a thickness of 12 μm was obtained by film preparation in the same manner as in Example 1. The physical properties and evaluation results are shown in Table 2.

[0119] [Comparative Examples 5 to 6] Except for changing the ratio of polyester resin A to polyester resin C to the ratio shown in Table 2, a biaxially aligned polyester film with a thickness of 12 μm was obtained by film preparation in the same manner as in Example 1. The physical properties and evaluation results are shown in Table 2.

[0120] [Comparative Example 7] Except for replacing polyester resin A with polyester resin D, a biaxially aligned polyester film with a thickness of 12 μm was obtained by film preparation in the same manner as in Example 1. The physical properties and evaluation results are shown in Table 2.

[0121] [Reference Example 1] Except for replacing polyester resin A with polyester resin E, which is derived from fossil fuel polyethylene terephthalate resin, a biaxially aligned polyester film with a thickness of 12 μm was prepared in the same manner as in Example 1. The physical properties and evaluation results are shown in Table 2.

[0122] [Table 2A] unit Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 raw material Polyester Resin A quality% 87 87 87 87 Polyester resin B quality% - - - - Polyester resin C quality% 13 13 13 13 Polyester resin D quality% - - - - Polyester resin E quality% - - - - Silicon Oxide Addition ppm 950 950 950 950 MD extension steps Extension method - 1 extension 1 extension 1 extension 3-section extension Heating method - infrared heater infrared heater Roller heating Roller heating Extension ratio Paragraph 1 times 2.5 5.0 3.7 4.5 Paragraph 2 times - - - Paragraph 3 times - - - total times 2.5 5.0 3.7 4.5 Extended temperature - ℃ 120 120 115 115 relaxation rate - % - - - - TD extension steps Extension ratio Paragraph 1 times 3.0 5.5 4.6 4.6 Paragraph 2 Paragraph 3 Extended temperature Paragraph 1 times 140 140 120 140 Paragraph 2 Paragraph 3 Extended mode - - straight line straight line straight line straight line Heat setting temperature - ℃ 210 210 210 210 thickness - μm 12 12 12 12 Uneven thickness - % twenty two 12.2 13.7 12.2 Haze - % 2.1 2.5 2.1 2.5 Puncture strength - N 4.8 6.8 6.1 6.7 - N / μm 0.40 0.57 0.51 0.56 thermal shrinkage rate MD % 1.1 3.4 1.8 2.5 thermal shrinkage rate TD % 0.2 1.6 0.7 0.5 Stress attenuation rate MD % 25.5 9.3 13.4 11.2 TD % 19.5 8.6 16.4 16.5 X:F3 MD MPa 103 83 94 83 TD MPa 100 88 94 64 Y:F30 MD MPa 118 156 154 155 TD MPa 160 209 182 183 Z:F30 / F3 MD - 1.1 1.9 1.6 1.9 TD - 1.6 2.4 1.9 2.9 coefficient of kinetic friction of metals - - 0.35 0.37 0.36 0.36 isophthalic acid content - % 1.4 1.4 1.4 1.4 Number of defects - Units / 1000m² 0.6 0.5 0.7 0.6 Cold formability - - D A B B Curl after forming - - A D D D Springback after forming - - A D D D

[0123] [Table 2B] unit Comparative Example 5 Comparative Example 6 Comparative Example 7 Reference Example 1 raw material Polyester Resin A quality% 75 96 - - Polyester resin B quality% - - - - Polyester resin C quality% 25 4 13 13 Polyester resin D quality% - - 87 - Polyester resin E quality% - - - 87 Silicon Oxide Addition ppm 1800 300 950 950 MD extension steps Extension method - 1 extension 1 extension 1 extension 3-section extension Heating method - infrared heater infrared heater infrared heater infrared heater Extension ratio Paragraph 1 times 3.7 3.7 3.7 3.7 Paragraph 2 times - - - Paragraph 3 times - - - total times 3.7 3.7 3.7 3.7 Extended temperature - ℃ 120 120 120 120 relaxation rate - % - - - - TD extension steps Extension ratio Paragraph 1 times 4.6 4.6 4.6 4.6 Paragraph 2 Paragraph 3 Extended temperature Paragraph 1 times 140 140 140 140 Paragraph 2 Paragraph 3 Extended mode - - straight line straight line straight line straight line Heat setting temperature - ℃ 210 210 210 210 thickness - μm 12 12 12 12 Uneven thickness - % 14.6 14.4 14.4 14.5 Haze - % 3.6 1.3 2.1 2.2 Puncture strength - N 6.1 6.1 6.1 6.0 - N / μm 0.51 0.51 0.51 0.50 thermal shrinkage rate MD % 1.6 1.7 1.7 1.6 thermal shrinkage rate TD % 0.2 0.3 0.4 0.3 Stress attenuation rate MD % 18.5 18.4 18.9 18.0 TD % 16.4 16.5 16.6 16.1 X:F3 MD MPa 97 97 96 99 TD MPa 93 93 93 95 Y:F30 MD MPa 134 134 133 138 TD MPa 183 183 183 189 Z:F30 / F3 MD - 1.4 1.4 1.4 1.4 TD - 2.0 2.0 2.0 1.9 coefficient of kinetic friction of metals - - 0.10 0.64 0.35 0.31 isophthalic acid content - % 1.2 1.5 1.4 0.0 Number of defects - Units / 1000m² 0.4 0.9 10.0 0.1 Cold formability - - A D C B Curl after forming - - B B B B Springback after forming - - B B B B

Claims

1. A biaxially aligned polyester film, comprising terephthalic acid and ethylene glycol as the main components; having a puncture strength of 0.45 N / μm or more to 0.80 N / μm or less as determined by JIS Z 7102; having a heat shrinkage rate of 2.5% or less in both the MD and TD directions at 150°C; having a coefficient of dynamic friction μd between at least one side of the film and a metal plate of 0.10 or more to 0.50 or less; and having a stress attenuation rate of 15.0% or more in both the MD and TD directions as expressed by the following formula (1) in a tensile stress relief test at 25°C; Formula (1) Stress attenuation rate (%) = 100 × (σ0 - σ1) / σ0; Here, σ0 represents the tensile stress value at the moment after applying a tensile force to the aforementioned film at a tensile speed of 200 mm / min and applying 50% tensile strain, and σ1 represents the tensile stress value when 50% tensile strain is maintained for 2 seconds from σ0. The content of isophthalic acid in the membrane relative to the total dicarboxylic acid content is 0.02 mol% to less than 2.0 mol%; the content of lubricant in the membrane is 400 ppm to less than 950 ppm by mass.

2. As described in claim 1, the biaxially aligned polyester film, wherein the stress at which the film elongates by 3% in the MD and TD directions at 25°C is set as X(MD) and X(TD), respectively, the stress at which the film elongates by 30% in the MD and TD directions is set as Y(MD) and Y(TD), respectively, and the values ​​of Y(MD) / X(MD) and Y(TD) / X(TD) are set as Z(MD) and Z(TD), respectively, satisfies all of the following equations (2) to (5); Equation (2) 125MPa≦Y(MD)≦155MPa; Equation (3) 140MPa≦Y(TD)≦190MPa; Equation (4) 1.3≦Z(MD)≦1.6; Equation (5) 1.7≦Z(TD)≦2.

2.

3. The biaxially aligned polyester film as described in claim 1 or 2, wherein it contains at least 60% by mass of post-consumer recycled material relative to the total polyester resin.

4. The biaxially aligned polyester film as described in claim 1 or 2, wherein the number of defects larger than 1 mm per 1000 square meters of film is less than 1.

0.

5. The biaxially aligned polyester film as described in claim 1 or 2, for use in cold forming applications.

6. A laminate comprising a biaxially aligned polyester film, a gas barrier layer, and a sealant layer as described in any one of claims 1 to 5.

7. The laminate as described in claim 6, wherein the aforementioned gas barrier layer comprises a metal foil.

8. A battery outer packaging material comprising a laminate as described in claim 6 or 7.

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