Biaxially oriented polyamide film

Abstract

To provide a biaxially stretched polyamide film excellent in moldability, and capable of suppressing delamination.SOLUTION: A biaxially stretched polyamide film has a creep deformation ratio in a film longitudinal direction of 1.8% or more when loading a vertical weight of 20 kg / m on a longitudinal end of a film strip suspended at 90°C for 60 sec.. A cell case packaging material for cold molding is a laminate having at least a substrate layer, a barrier layer, and a sealant layer, where the substrate layer is a biaxially stretched polyamide film. A cell case is obtained by molding a cell housing part so that the sealant layer becomes an innermost layer using the cell case packaging material for cold molding.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a biaxially stretched polyamide film. Specifically, the present invention relates to a biaxially stretched polyamide film for cold forming, which is suitably used as a main base material for packaging materials for cold forming, particularly for battery case packaging materials such as lithium ion secondary batteries.

Background Art

[0002] In recent years, lithium ion secondary batteries are used in smartphones, tablet terminals, and various other devices, and lithium ion secondary batteries using a laminated type exterior body are widely popular. As the base material of the laminate, mainly polyamide films are used, and the high strength characteristics of the polyamide film contribute to the forming depth of cold forming.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when a molded body is manufactured using a laminate containing high-strength polyamide film, the molding depth increases, but conversely, the residual stress in the molded body also increases. Therefore, if the adhesion strength between the layers of the laminate is low, there is a risk of delamination. If the polyamide film is exposed to moisture or placed under high humidity conditions, the adhesion strength between the layers of the laminate further decreases, increasing the likelihood of delamination. In particular, lithium-ion secondary batteries have various usage scenarios and are expected to be exposed to harsh environments, so performance evaluation methods include tests such as immersion in hot water. For this reason, in order to keep the residual stress in the molded body below a certain level, the molding depth must be reduced.

[0005] Patent Document 1 proposes a biaxially oriented nylon film that achieves both excellent cold formability and suppression of delamination between layers by adjusting the thermal shrinkage stress and tensile strength of the nylon film within a specific range. Patent Document 2 proposes a biaxially oriented polyamide film that suppresses crack formation and fracture due to degradation under harsh conditions by using a polyamide resin to which a specific antioxidant has been added. However, Patent Documents 1 and 2 do not offer any suggestions or indications regarding the adjustment of physical properties other than thermal shrinkage stress and tensile strength.

[0006] The objective of the present invention is to provide a biaxially oriented polyamide film that exhibits excellent moldability and can suppress delamination. [Means for solving the problem]

[0007] As a result of diligent research to solve the above problems, the inventors of the present invention discovered that by increasing the creep deformation rate of the polyamide film, excellent moldability and delamination can be suppressed, thus completing the present invention.

[0008] In other words, the present invention provides the following [1] to [5]. [1] A biaxially oriented polyamide film in which the creep deformation rate in the longitudinal direction of the film is 1.8% or more when a vertical load of 20 kg / m is applied to the longitudinal end of a film strip suspended at 90°C for 60 seconds. [2] The biaxially oriented polyamide film is a film in which the 50% modulus value in all four directions (0°(MD), 45°, 90°(TD), 135°) in a uniaxial tensile test (sample width 15 mm, distance between chucks 100 mm, tensile speed 200 mm / min) is 140 MPa or more, as described in [1].

[0009] [3] A cold-formable battery case packaging material which is a laminate having at least a base layer, a barrier layer and a sealant layer, wherein the base layer is the biaxially oriented polyamide film described in [1] or [2].

[0010] A battery case in which the battery housing is formed using the cold-forming battery case packaging material described in [4][3], such that the sealant layer is the innermost layer.

[0011] A battery in which the battery body is housed in the battery compartment of the battery case described in [5][4], and the battery body is sealed. [Effects of the Invention]

[0012] The biaxially oriented polyamide film of the present invention has a molding depth of 4.5 mm or more, which provides excellent moldability and the effect of suppressing delamination. Therefore, according to the present invention, it is possible to provide a battery case with a greater molding depth than conventional models. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic diagram of a tubular simultaneous biaxial stretching apparatus. [Modes for carrying out the invention]

[0014] The following describes embodiments for carrying out the present invention. [Biaxially oriented polyamide film] The present invention relates to a biaxially oriented polyamide film in which the creep deformation rate in the longitudinal direction of the film is 1.8% or more when a vertical load of 20 kg / m is applied to the longitudinal end of a film strip suspended at 90°C for 60 seconds.

[0015] (Raw material for biaxially oriented polyamide film) Examples of polyamide resins used as raw materials for the biaxially oriented polyamide film of the present invention include aliphatic polyamide resins, aromatic polyamide resins, or mixtures of aliphatic polyamide resins and aromatic polyamide resins. Examples of the polyamide resins mentioned above include polyamide resins obtained by polycondensation of lactams with three or more membered rings, polymerizable ω-amino acids, dibasic acids, and diamines. Specifically, polymers such as ε-caprolactam, aminocaproic acid, enantractam, 7-aminoheptanoic acid, 11-aminoundecanoic acid, 9-aminononanoic acid, α-pyrrolidone, and α-piperidone, diamines such as hexamethylenediamine, nonamethylenediamine, undecamethylenediamine, dodecamethylenediamine, and metaxylylenediamine, and dicarboxylic acids such as terephthalic acid, isophthalic acid, adipic acid, sebatic acid, dodecadibatic acid, and glutaric acid. Polymers or copolymers thereof obtained by polycondensation of salts include, for example, nylon (polyamide) 6, nylon 6 / 6, nylon 11, nylon 12, nylon 6 / 10, nylon 6 / 12, nylon 6 / 6 / 12 copolymer, other polyamide copolymers, nylon MXD6, aramid, polyamide-imide (PAI), aromatic polyimide, polyetherimide (PEI), polymaleimideamine (PMIA), and polyaminobismaleimide (PABM). Among these, nylon (polyamide) 6 is the most preferred polyamide resin used in the present invention from the viewpoint of productivity, moldability, and film properties, mainly strength.

[0016] In addition, in the case of polyamide resins such as nylon 6, those having a number average molecular weight of 10,000 to 30,000 are preferred, and particularly preferred are those having a number average molecular weight of 22,000 to 24,000. By using a polyamide resin having a number average molecular weight of 10,000 or more, the impact strength and tensile strength of the obtained biaxially stretched polyamide film can be made sufficient. Also, a polyamide resin having a number average molecular weight of 30,000 or less results in an appropriate entanglement of molecular chains, suppressing the generation of excessive strain during stretching processing, suppressing breakage and puncture during stretching processing, and leading to stable production of the biaxially stretched polyamide film.

[0017] In addition, the polyamide resin used in the present invention can contain other resins such as polycarbonate resin and polyester within a range that does not impair the physical properties of the obtained film. Furthermore, the polyamide resin used in the present invention, and the above-mentioned other resins can contain additives such as lubricants, anti-blocking agents, inorganic extenders, antioxidants, ultraviolet absorbers, antistatic agents, flame retardants, plasticizers, colorants, crystallization inhibitors, crystallization accelerators, etc., within a range that does not impair the physical properties of the obtained film.

[0018] (Method for producing a biaxially stretched polyamide film) The biaxially stretched polyamide film of the present invention can be produced by a known method. For example, the biaxially stretched polyamide film of the present invention is obtained by a production method including a step of melt-extruding the polyamide resin and cooling it to obtain an unstretched film, a step of biaxially stretching the unstretched film to obtain a biaxially stretched film, and a step of heat-treating the biaxially stretched film.

[0019] <Melt extrusion and cooling step> This step is a step of melt-extruding the polyamide resin and cooling it to obtain an unstretched film. In the case of T-die film formation, the sheet-like molten resin is directly water-cooled both inside and outside by immersing it in a water tank. On the other hand, in the case of annular film formation, the molten tubular thin film is formed by extruding it downwards through an annular die mounted downwards on the extruder. Next, it is guided to a cooling mandrel connected to the annular die, and cooling water introduced from each nozzle of the cooling mandrel comes into direct contact with the inside of the molten tubular thin film to cool it. At the same time, cooling water is also flowed from an external cooling tank used in combination with the cooling mandrel, and the cooling water comes into direct contact with the outside of the molten tubular thin film to cool it. The temperature of the internal and external water is preferably 30°C or lower, and particularly preferably 20°C or lower from the viewpoint of rapid film formation. If it is higher than 30°C, it may lead to whitening of the unstretched film and poor appearance of the unstretched film due to boiling of the cooling water, and stretching may gradually become more difficult.

[0020] <Biaxial stretching process> This process involves biaxially stretching the obtained unstretched film to obtain a biaxially oriented film. The biaxial stretching method can be appropriately selected from methods such as simultaneous biaxial stretching using a tubular or tenter method, which performs longitudinal and transverse stretching at the same time, or sequential secondary stretching, which performs longitudinal and transverse stretching sequentially. From the viewpoint of the balance of longitudinal and transverse strength of the resulting biaxially oriented polyamide film, simultaneous biaxial stretching using a tubular method is preferred. By performing biaxial stretching in this way, the strength properties, in particular, are dramatically improved, and a biaxially oriented polyamide film with excellent moldability can be obtained. The stretching ratio is preferably in the range of 2.8 to 4.0 times in the flow direction (longitudinal direction) (hereinafter also referred to as "MD") and the perpendicular direction (also referred to as "TD"), and is particularly preferably in the range of 3.0 to 3.4 times. If the stretching ratio is less than 2.8 times, the impact strength and tensile strength of the resulting biaxially oriented polyamide film may be insufficient. Furthermore, if the stretching ratio exceeds 4.0 times, excessive strain on the molecular chains occurs during stretching, which may lead to frequent breakage or punctures during the stretching process, potentially making it impossible to produce film stably. The stretching temperature is preferably in the range of 40 to 80°C, and particularly preferably in the range of 45 to 65°C.

[0021] <Heat treatment process> This step involves heat-treating the obtained biaxially oriented film. Heat treatment using a hot roll method is preferred. By performing heat treatment using a hot roll method, the biaxially oriented polyamide film of the present invention can be obtained. The material of the hot roll in the hot roll method is not particularly limited. Since the film is brought into contact with a heating roll and then with a cooling roll set to a temperature of 50°C or lower, the heating roll and cooling roll together constitute a single heat treatment facility. While it is possible to complete the heat treatment in one stage using a single heat treatment facility, it is preferable to use two or more heat treatment facilities and perform the heat treatment in stages (multiple stages) at temperatures ranging from 60°C to 215°C, from the viewpoint of minimizing sudden changes such as shrinkage to the film and reducing factors that could cause operational problems such as film cutting. The highest heat treatment temperature (hereinafter also referred to as the "main heat treatment temperature") is preferably 185°C to 215°C, and particularly preferably 190°C to 210°C. If the main heat treatment temperature exceeds 215°C, the degree of crystallinity becomes too high, which may reduce the strength and physical properties of the film. On the other hand, if the main heat treatment temperature is below 185°C, the thermal dimensional stability of the film decreases significantly, which may cause practical problems such as the film shrinking easily during lamination or delamination occurring easily during the heat-sealing process after molding.

[0022] There are several heat treatment methods for biaxially oriented films: the hot roll method, the tenter method, or a combination of the hot roll method and the tenter method. In the hot roll method, heat is applied at the moment the hot roll contacts the film. In contrast, the tenter method takes a relatively long time to heat, and because the heat treatment is performed while clamping both ends of the film with tenter clips, the tenter method provides more tension-induced heat fixation compared to the hot roll method. Therefore, heat treatment using the tenter method is thought to result in a film with a larger microcrystalline portion, and as a result, a film with a lower creep deformation rate. Furthermore, the creep deformation rate is reduced not only by the vertical (TD) fixation by the tenter method, but also by the tension-induced heat fixation in the flow direction (MD) during heat treatment. Conversely, by relaxing the film during heat treatment using the hot roll method (performing heat treatment while slightly loosening the film), the creep deformation rate can be increased. Also, in the hot roll method, which involves short-time heat treatment, the amount of microcrystalline material decreases, and as a result, the creep deformation rate is thought to increase. In the present invention, when the film is relaxed in the flow direction (MD) during heat treatment, the relaxation rate is, for example, 0.1% to 15.0%, preferably 3.0% to 12.0%, and more preferably 5.0% to 9.0%.

[0023] Creep deformation is caused by stress and time, and in the case of thermoplastic resins, it is accelerated by heat. Therefore, the creep deformation rate is considered a parameter that is relevant when stress and heat are applied to the substrate and laminate during processes such as printing, lamination, and bag making. Smaller creep deformation results in smaller dimensional changes, which is advantageous in terms of accuracy in printing and bag making. On the other hand, especially when laminating with rigid metal foils, or after molding the resulting laminate, the residual stress on the substrate is considered to be larger because the permanent strain of the formed laminate layer is small. Therefore, it is considered that if the substrate has a large creep deformation rate, the residual stress will be relieved by permanent strain, and delamination will be less likely to occur.

[0024] The biaxially oriented polyamide film of the present invention exhibits creep in the longitudinal direction of the film when a vertical load of 20 kg / m is applied to the longitudinal end of a film strip suspended at 90°C for 60 seconds. The deformation rate is 1.8% or more, more preferably 2.0% or more, even more preferably 2.5% or more, and particularly preferably 3.0% or more. If it is 1.8% or more, the residual stress in the molded article is relaxed, and the delamination suppression effect is stably exhibited. On the other hand, the biaxially oriented polyamide film becomes more stretchable, and from the viewpoint of sufficiently suppressing the occurrence of wrinkles in the biaxially oriented polyamide film during lamination, the creep deformation rate is preferably 10% or less. The creep deformation rate can be determined, for example, by the method described in the examples.

[0025] The biaxially oriented polyamide film of the present invention preferably has a tensile breaking strength of 240 MPa or more in all four directions (0° (MD), 45°, 90° (TD), and 135°), and more preferably 280 MPa or more. This makes it difficult for the biaxially oriented polyamide film and aluminum foil to break during molding, even in mold shapes with large molding depths, which are generally considered difficult to mold, thus ensuring stable and excellent moldability. If the tensile breaking strength in any one of the four directions is less than 240 MPa, the biaxially oriented polyamide film will easily break during molding, and there is a risk that stable moldability cannot be obtained, especially when molding mold shapes with large molding depths that require high tensile strength at high elongation. Furthermore, the biaxially oriented polyamide film of the present invention can have 50% modulus values ​​in its four directions (0° (MD), 45°, 90° (TD), 135°) independently of 140 MPa or higher, 150 MPa or higher, 160 MPa or higher, 170 MPa or higher, 180 MPa or higher, 190 MPa or higher, or 200 MPa or higher. Furthermore, in one embodiment of the biaxially oriented polyamide film of the present invention, the 50% modulus values ​​in all four directions (0° (MD), 45°, 90° (TD), 135°) are preferably 140 MPa or higher, and more preferably 150 MPa or higher. This ensures stable moldability, especially when molding mold shapes with relatively small molding depths. If the 50% modulus value in any one of the four directions is less than 140 MPa, the biaxially oriented polyamide film may easily break during molding, potentially resulting in unstable moldability. The uniaxial tensile breaking strength and 50% modulus value of the biaxially oriented polyamide film of the present invention in four directions (0° (MD), 45°, 90° (TD), 135°) can be determined from the stress-strain curve obtained by a uniaxial tensile test (sample width 15 mm, chuck distance 100 mm, tensile speed 200 mm / min).

[0026] The thickness of the biaxially oriented polyamide film of the present invention is, for example, 5 μm to 50 μm, preferably 10 μm to 30 μm. If the thickness is less than 5 μm, the impact resistance of the laminate packaging material using the biaxially oriented polyamide film of the present invention will be low, and there is a risk that the moldability will be insufficient. On the other hand, if the thickness is greater than 50 μm, although the strength for maintaining shape is improved, the effect on preventing breakage and improving moldability is small, and it only reduces the volumetric energy density of the battery.

[0027] [Battery case packaging material for cold forming] The present invention relates to a cold-formable battery case packaging material which is a laminate having at least a base layer, a barrier layer and a sealant layer, wherein the base layer is the above-mentioned biaxially oriented polyamide film. The base layer may consist solely of the above-mentioned biaxially oriented polyamide film, or it may consist of the above-mentioned biaxially oriented polyamide film in combination with other base materials. Such other base materials include biaxially oriented polybutylene terephthalate film, biaxially oriented polypropylene film, biaxially oriented polyethylene terephthalate film, biaxially oriented ethylene-vinyl alcohol film, biaxially oriented polyethylene naphthalate film, biaxially oriented polystyrene film, biaxially oriented polyvinylidene chloride film, and biaxially oriented polyvinyl alcohol Examples include ethanol film. One or more other substrates can be used. Furthermore, as a barrier layer, a layer made of metal foil is preferred from the viewpoint of providing high moisture resistance to the battery case packaging material, and an aluminum foil layer made of aluminum or a soft material of aluminum-iron alloy is more preferred. Generally, laminate packaging materials containing an aluminum foil layer are not suitable for cold forming because the aluminum foil layer is prone to rupture and pinholes during cold forming. However, the laminate packaging material (battery case packaging material) containing the biaxially oriented polyamide film of the present invention has excellent moldability, impact resistance and pinhole resistance, so it can suppress rupture of the aluminum foil layer during cold stretch forming and deep drawing forming. In addition, from the viewpoint of improving adhesion during lamination, one or both sides of the aluminum foil layer may be subjected to an undercoat treatment with a coupling agent such as a silane coupling agent or a titanium coupling agent, or a surface treatment such as corona discharge treatment. Furthermore, from the viewpoint of imparting heat-sealability, airtightness, and chemical resistance to the battery case packaging material, a sealant layer made of an unstretched film such as polyethylene, polypropylene, maleic acid-modified polypropylene, maleic acid-modified polyethylene, ethylene-acrylate copolymer, ionomer resin, and polyvinyl chloride is preferred as the sealant layer. One or more types of films can be used for the sealant layer.

[0028] The battery case packaging material for cold forming according to the present invention can be manufactured by a dry lamination method, in which a base layer, a barrier layer, and a sealant layer are laminated together via an adhesive. The resin used as an adhesive is not particularly limited, but examples include adhesives using a resin such as polyester resin, epoxy resin, polyurethane resin, or polyester-epoxy copolymer resin as the main component, and one or more of isocyanate resin, melamine resin, oxazoline resin, or phenolic resin as a curing agent. The adhesive layer formed by such an adhesive is suitable for cold forming.

[0029] The thickness of the battery case packaging material for cold forming according to the present invention is preferably 250 μm or less. If the thickness exceeds 250 μm, it becomes difficult to form the corners by cold forming, and a molded product with a sharp shape may not be obtained. The thickness of the substrate layer is preferably 5 μm to 50 μm. The barrier layer thickness is preferably 20 μm to 100 μm. This allows for good maintenance of the molded shape and prevents oxygen, moisture, etc., from entering the packaging material. If the barrier layer thickness is less than 20 μm, the barrier layer is prone to rupture during cold forming of the battery case packaging material, and even if it does not rupture, pinholes are more likely to occur, which may allow oxygen, moisture, etc., to enter the packaging material. On the other hand, if the barrier layer thickness exceeds 100 μm, the effect of preventing rupture and pinhole formation during cold forming is not significantly improved, and it is undesirable as it only increases the thickness of the battery case packaging material. The thickness of the sealant layer is preferably 20 μm to 100 μm.

[0030] The battery case packaging material of the present invention is a packaging material that can be processed by cold (room temperature) molding methods such as stretch molding or deep drawing molding. Despite the thin thickness of the battery case packaging material, it has high strength, allowing for sharp molding, and is a laminate packaging material that is less prone to barrier layer rupture or pinhole formation during molding, as well as delamination after molding.

[0031] The battery case packaging material of the present invention can be used as packaging material for lithium-ion secondary batteries, which use particularly corrosive electrolytes and are extremely sensitive to the intrusion of moisture and oxygen. Furthermore, the battery case packaging material of the present invention can be used not only for lithium-ion secondary batteries, but also for primary batteries, secondary batteries, and other applications where lightweight and sharp moldability are required for the battery case.

[0032] [Battery case] The present invention is a battery case in which the battery storage portion is formed using the above-mentioned cold-forming battery case packaging material so that the sealant layer is the innermost layer. The battery case of the present invention is suitably used as a battery case for secondary batteries, particularly lithium-ion secondary batteries. Furthermore, since the battery case packaging material of the present invention has excellent moldability, the battery case of the present invention can be easily obtained by molding according to known methods. The molding method is not particularly limited, but by cold (room temperature) molding (stretch molding or deep drawing), it is possible to manufacture battery cases with complex shapes and high dimensional accuracy.

[0033] [battery] The present invention relates to a battery in which the battery body is housed in the battery compartment of the above-mentioned battery case, and the battery body is sealed. The battery is not particularly limited, but examples include lithium-ion rechargeable batteries.

[0034] The laminate packaging material containing the biaxially oriented polyamide film of the present invention has excellent heat sealability, chemical resistance, and moldability, and therefore, in addition to being used as a battery case packaging material, it can also be used as a container material for contents containing pharmaceuticals, cosmetics, photographic chemicals, and other highly corrosive organic solvents. [Examples]

[0035] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0036] Example 1 (Production of biaxially oriented polyamide film) Nylon (polyamide) 6 pellets (relative viscosity 3.48) were melted and kneaded in an extruder at 255°C. The molten material was then extruded from a die as a cylindrical film, and subsequently rapidly cooled with water to produce an unstretched film. Next, in a tubular simultaneous biaxial stretching apparatus with the structure shown in Figure 1, this unstretched film was inserted between a pair of nip rolls 1, and while air was injected under pressure, it was heated by a preheating heater 2 and a main heating heater 3, and air was blown from a cooling air ring 4 to the stretching end point, thereby obtaining MD and TD simultaneous biaxially stretched films 5 by the tubular method. The stretching ratios were 3.2 times for MD and 3.2 times for TD, and the stretching temperature was 60°C. Next, this biaxially stretched film 5 was placed in a hot roll type heat treatment apparatus and heat treated at 198°C to obtain a biaxially stretched polyamide film. The thickness of the biaxially stretched polyamide film was 15 μm. During the heat treatment using a hot roll method, the MD of the biaxially oriented film was relaxed, and the final MD stretching ratio was 3.0 times.

[0037] (Method for measuring the 50% modulus value of biaxially oriented polyamide film) The 50% modulus value of biaxially oriented polyamide film was measured using an Orientec Co., Ltd. Tensilon universal tester (model: RTC-1210-A) under the conditions of a sample width of 15 mm, a chuck distance of 100 mm, and a tensile speed of 200 mm / min. Measurements were taken in each of the four directions: 0° (MD), 45°, 90° (TD), and 135°. For the measurements, biaxially oriented polyamide film was used that had been conditioned for 2 hours at 23°C × 50% humidity. Based on the obtained stress-strain curves, the 50% modulus values ​​in each direction were determined. The results are shown in Table 1.

[0038] (Method for measuring the creep deformation rate of biaxially oriented polyamide film) From the obtained biaxially oriented polyamide film, strip-shaped test specimens with an MD of 300 mm and a TD of 50 mm were prepared and conditioned for 2 hours at 23°C and 50% humidity. Two gauge marks were drawn on the MD of the conditioned test specimen so that the distance between the gauge marks was 250 mm, and the distance between the gauge marks was measured (before the test). (Length between gauge marks). One gauge mark position was clamped with a 50 mm wide clip, and the other gauge mark position was clamped with a 50 mm wide clip, and a weight adjusted so that the total weight including the clips was 1 kg was attached to the clips. The test specimen was then suspended in an electric furnace set to 90°C so that the clips with the weights attached were at the bottom (i.e., a vertical load of 20 kg / m was applied). After 1 minute, the specimen was removed from the electric furnace, the weight and clips were removed, and the length between the gauge marks was measured with a scale (length between gauge marks after the test). The value obtained by the following formula was defined as the creep deformation rate (unit: %). Creep deformation rate (%) = (Gauge length after test - Gauge length before test) / Gauge length before test × 100

[0039] (Method for measuring the average crystallization parameter of biaxially oriented polyamide film) The absorbance of biaxially oriented polyamide film at each wavenumber was measured using an infrared spectrophotometer (ATR method, using a Ge prism). The absorbance at 1200 cm² was attributed to the α-crystal structure of nylon 6. -1 Let A be the absorbance of 1370 cm², where the intensity changes monotonically only with respect to the thickness of the sample, independent of structural changes such as crystallization. -1 When the absorbance was denoted as B, the value obtained by dividing A by B was defined as the crystallization parameter. Since crystallization can also occur as a trigger for stretching orientation, the results differ depending on the measurement direction. Therefore, measurements were taken in MD and TD directions, and the average value was defined as the average crystallization parameter. This allowed for a comparative evaluation of the degree of crystallization of biaxially oriented polyamide films.

[0040] (Method for evaluating cold formability and the occurrence of delamination) The cold formability of laminate packaging materials (battery case packaging materials) containing biaxially oriented polyamide film was evaluated. Specifically, the obtained biaxially oriented polyamide film was first used as a base layer (thickness 15 μm), and aluminum foil (thickness 32 μm) and unoriented polypropylene film (thickness 30 μm) were dry laminated to it (dry coating amount 4.0 g / m²). 2Laminated packaging material was obtained by the following process. For the dry lamination, TM-K55 / CAT-10 manufactured by Toyo Morton Co., Ltd. (mixing ratio 100 / 8) was used as the adhesive. The laminated packaging material after dry lamination was aged at 60°C for 72 hours. The laminated packaging material obtained in this way was conditioned for 2 hours in an environment of 23°C × 50%, and then cold-formed (at room temperature) from the unstretched polypropylene film side with a maximum load of 10 MPa using a compression mold (38 mm × 38 mm), and the maximum molding depth at which defects such as pinholes and cracks did not occur was evaluated at 0.5 mm intervals. The presence or absence of delamination between the biaxially oriented polyamide film and aluminum foil was visually confirmed for the cold-formed laminated packaging material using the above method. Furthermore, the packaging material was treated in 100°C hot water for 30 minutes, wiped dry, and then stored at 23°C × 50% RH for 24 hours. The presence or absence of delamination between the biaxially oriented polyamide film and aluminum foil was then visually confirmed.

[0041] Examples 2-6, Comparative Examples 1-8 As shown in Table 1, the procedure was the same as in Example 1, except that the heat treatment method, main heat treatment temperature, MD stretching ratio, MD relaxation rate during heat treatment, and final MD stretching ratio were changed.

[0042] [Table 1]

[0043] As shown in Table 1, biaxially oriented polyamide fiber with a creep deformation rate of 1.8% or higher Laminated packaging materials (battery case packaging materials) using aluminum foil had a molding depth of 4.5 mm or more, and no delamination occurred between the biaxially oriented polyamide film and aluminum foil immediately after molding and after hot water treatment (Examples 1 to 3). In particular, when the creep deformation rate was 2.0% or more, the molding depth was 5.0 mm, and the moldability was even better (Examples 1 and 2). In contrast, laminate packaging materials using a biaxially oriented polyamide film with a creep deformation rate of 1.5% had a molding depth of 4.5 mm, but delamination occurred between the biaxially oriented polyamide film and the aluminum foil after hot water treatment (Comparative Examples 1 and 2). Furthermore, laminate packaging materials using biaxially oriented polyamide film with a creep deformation rate of 1.5% or less and a 50% modulus value of 130 MPa or less in all four directions showed molding cracks at a molding depth of 4.0 mm (Comparative Examples 3 and 4). Therefore, it is clear that the present invention achieves both excellent formability, particularly excellent cold formability and suppression of delamination, by making the creep deformation rate in the longitudinal direction of the film 1.8% or more when a vertical load of 20 kg / m is applied to the longitudinal end of a film strip suspended at 90°C for 60 seconds. [Industrial applicability]

[0044] The biaxially oriented polyamide film of the present invention is suitably used as a main base material for cold-forming packaging materials, particularly for battery case packaging materials such as lithium-ion secondary batteries. [Explanation of symbols]

[0045] 1. Nip Roll 2. Preheating heater 3. Main Heating Element 4. Cooling air ring 5. Biaxially oriented film

Claims

1. When a 15 μm thick film strip is suspended at 90°C and a vertical load of 20 kg / m is applied to its longitudinal end for 60 seconds, the creep deformation rate in the longitudinal direction of the film is 1.8% or more. In a uniaxial tensile test (sample width 15 mm, chuck distance 100 mm, tensile speed 200 mm / min), the 50% modulus values ​​in all four directions (0° (MD), 45°, 90° (TD), 135°) are 140 MPa or higher, and the tensile breaking strength in all directions is 240 MPa or higher. Biaxially oriented polyamide film.

2. A battery case packaging material for cold forming, which is a laminate having at least a base layer, a barrier layer and a sealant layer, A battery case packaging material for cold forming, wherein the base layer is the biaxially oriented polyamide film described in claim 1.

3. A battery case in which a battery storage portion is formed using the cold-forming battery case packaging material described in claim 2, such that the sealant layer is the innermost layer.

4. A battery in which a battery body is housed in the battery compartment of the battery case described in claim 3, and the battery body is sealed.

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