Polyamide films and laminates for molding

Abstract

To provide a polyamide film for molding that exhibits excellent water resistance, isotropic heat shrinkage properties, and good moldability even when made from a single material, and is environmentally friendly as it allows for volume reduction. [Solution] A polyamide film containing a polyamide resin that, when the total constituent units of the polyamide resin are 100 mol%, contains 60 mol% or more of polyamide 66 constituent units, and satisfies the following requirements (1) and (2). (1) The thermal shrinkage rate at 160°C is 3.0% or less in both the flow direction and the width direction. (2) The impact strength retention rate of the polyamide film for molding after treatment with hot water at 120°C for 30 minutes is 35% or more.

Description

Technical Field

[0001] The present invention relates to a polyamide film for molding used in the packaging fields of foods, pharmaceuticals, and industrial products.

Background Art

[0002] In recent years, biaxially stretched films have been adopted as films for molding, particularly for use in the packaging fields of industrial products such as packaging materials for electrochemical cells and exterior materials for lithium-ion batteries. The biaxially stretched film is used as a base material layer located on the outermost side of industrial products. The base material layer is required to have formability, heat resistance, and water resistance.

[0003] For example, in Patent Document 1, a technique for reducing the anisotropy of the base material layer to improve formability has been proposed. Among the 45-degree direction and the 135-degree direction with respect to the stretching direction of one biaxially stretched film, the direction with a large tensile strength and the direction with a small tensile strength among the 45-degree direction and the 135-degree direction with respect to the stretching direction of the other biaxially stretched film are aligned, and it has been proposed to dry laminate and bond the adjacent biaxially stretched films vertically. In addition, in Patent Document 2, for the purpose of imparting water resistance and heat resistance to the outermost layer of the base material layer, it has been proposed to laminate the outermost layer of the base material layer with a polyester film and the inner layer with a polyamide film.

[0004] However, both of the prior art documents 1 and 2 are used on the premise of bonding a plurality of biaxially stretched films, resulting in a lamination process for obtaining the base material layer and complicating the process for obtaining the film for molding. In addition, in recent years, attention has been paid to reducing the volume of plastics for environmental protection, but it is impossible to reduce the volume to obtain a base material layer by bonding a plurality of biaxially stretched films, and there is a problem in that it cannot be said to be environmentally friendly.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] The present invention was devised to solve the problems of the above-mentioned prior art, and its objective is to provide a polyamide film for molding that exhibits excellent water resistance, isotropic heat shrinkage properties, and good moldability, even as a single-material film. Furthermore, it aims to provide an environmentally friendly polyamide film for molding that does not require lamination of multiple biaxially oriented films, thus reducing the volume of the film. [Means for solving the problem]

[0007] The present invention consists of the following configuration. [1] A polyamide film containing a polyamide resin that, when the total constituent units of the polyamide resin are considered to be 100 mol%, contains 60 mol% or more of polyamide 66 constituent units, and satisfies the following requirements (1) and (2). (1) The thermal shrinkage rate at 160°C is 3.0% or less in both the flow direction and the width direction. (2) The impact strength retention rate of the polyamide film for molding after treatment with hot water at 120°C for 30 minutes is 35% or more. [2] The polyamide film for molding according to [1], wherein the impact strength of the polyamide film for molding is 1.00 J / 20 μm or more. [3] A polyamide film for molding according to [1] or [2], wherein the dry heat strain at 160°C, as defined by the following formula (3), is 1.0% or less. Dry heat strain (%) = |ab|... (3) a: Dry heat shrinkage rate at 160°C in the 45-degree direction when the width direction angle is 0 degrees and the flow direction angle is 90 degrees. b: Dry heat shrinkage rate at 160°C in the 135° direction when the width direction angle is 0° and the flow direction angle is 90°. (However, the sample is taken at a position 150 mm from both ends of the film in the width direction toward the center, the 160°C dry heat strain is calculated at both ends of the film in the width direction, and the larger value is taken as the dry heat strain value.) [4] A laminate in which a metal layer is laminated on at least one surface of a polyamide film for molding as described in any of [1] to [3]. [5] The laminate according to [4], wherein the metal layer is an aluminum layer with a thickness of 15 μm to 80 μm. [6] The laminate according to [4] or [5], wherein a sealant layer is laminated on the side opposite to the side on which the molding polyamide film of the metal layer is laminated. [7] A packaging body using a polyamide film for molding as described in any of [1] to [3], or a laminate as described in any of [4] to [6]. [Effects of the Invention]

[0008] The polyamide film for molding according to the present invention possesses isotropic properties in terms of water resistance and heat shrinkage. Therefore, it is suitable for molding using square, rectangular, or other molds in the fields of food, pharmaceutical, and industrial product packaging. In particular, when used as a base layer in industrial products, it can provide excellent water resistance without the need to laminate a polyester film to the outermost layer. Furthermore, because multiple films are not laminated together, the volume of plastic used can be reduced, making it an environmentally friendly polyamide film for molding. [Modes for carrying out the invention]

[0009] The embodiments of the present invention will be described in detail below.

[0010] [Polyamide resin] The polyamide resin contained in the polyester film for molding of the present invention preferably contains 60 mol% or more of polyamide 66 constituent units when the total constituent units constituting the polyamide resin are set to 100 mol%. The polyamide resin may be a polyamide 66 homopolymer or a copolymerized polyamide resin with other amide constituent units. Alternatively, it may be a mixture of a polyamide 66 homopolymer and / or a copolymer containing polyamide 66 constituent units and another polyamide resin other than polyamide 66. In the present invention, the polyamide 66 constituent units refer to constituent units obtained by condensation polymerization of adipic acid and hexamethylenediamine.

[0011] When the polyamide resin is a copolymerized polyamide resin, it is preferable that the polyamide 66 constituent units account for 60 mol% or more of the total constituent units, and more preferably 65 mol% or more. A copolymerized polyamide resin containing 60 mol% or more of polyamide 66 constituent units is preferable because it improves water resistance. There is no upper limit set for the copolymerization ratio of polyamide 66, but it may be, for example, 99 mol%.

[0012] In this invention, water resistance refers to the ability to maintain high impact strength after hot water treatment. Specifically, it refers to the impact strength retention rate of a polyamide film for molding after retort treatment at 120°C for 30 minutes using the test method described later. A higher impact strength retention rate indicates better water resistance.

[0013] When the polyamide resin is a copolymerized polyamide resin, the amide constituent units other than polyamide 66 are not particularly limited, and examples include polyamide 6, polyamide 6 / 10, polyamide 11, polyamide 12, and (poly)metaxylene adipamide. Polyamide 6 is preferred. Furthermore, if 60 mol% or more of the total constituent units of the polyamide resin contained in the polyamide film for molding are polyamide 66 constituent units, it may be a mixture of a polyamide resin having polyamide 66 constituent units alone or copolymerized and a polyamide resin having the aforementioned amide constituent units.

[0014] The melting point of the polyamide resin contained in the polyamide film for molding of the present invention is not particularly limited, but it is preferably 240°C or higher, and more preferably 243°C or higher. A melting point of 240°C or higher is preferable because it maintains mechanical strength during heat treatment of the polyamide film after stretching, resulting in good moldability. There is no upper limit to the melting point, but it is preferably 275°C or lower, and more preferably 270°C or lower, in order to facilitate extrusion molding and film formation.

[0015] The lower limit of the relative viscosity of the polyamide resin contained in the polyamide film for molding according to the present invention is 1.8, and more preferably 2.6. Setting it to 1.8 or higher is preferable because it can increase the impact strength of the polyamide film for molding and reduce the likelihood of pinholes occurring during molding. The upper limit of the relative viscosity of the polyamide resin is 5.0, and more preferably 4.5. Setting it to 5.0 or lower suppresses excessive load on the extruder and stress during film stretching, thereby obtaining good film-forming properties.

[0016] [Auxiliary materials, additives] The polyamide film for molding according to the present invention does not contain auxiliary materials or additives such as lubricants, or it may contain various additives such as other lubricants, heat stabilizers, antioxidants, antistatic agents, antifogging agents, ultraviolet absorbers, dyes, and pigments as needed.

[0017] [Lubricant] In the polyamide film for molding of the present invention, fine particles can be contained as a lubricant for the purpose of improving the lubricity and cold formability. The fine particles can be appropriately selected and used from inorganic fine particles such as silica, kaolin, and zeolite, and polymer-based organic fine particles such as acrylic and polystyrene. In terms of transparency and lubricity, it is preferable to use silica fine particles. The preferable average particle diameter of the fine particles is 0.5 to 5.0 μm, and more preferably 1.0 to 3.0 μm. When the average particle diameter is 0.5 μm or more, good lubricity can be obtained with a small addition amount. On the other hand, when it is 5.0 μm or less, it is possible to prevent the surface roughness of the film from becoming too large and deteriorating the appearance.

[0018] When using the silica fine particles, the pore volume range of silica is preferably 0.5 to 2.0 ml / g, and more preferably 0.8 to 1.6 ml / g. When the pore volume is 0.5 ml / g or more, it is possible to prevent the deterioration of film transparency due to the generation of voids. On the other hand, when the pore volume is 2.0 ml / g or less, sufficient protrusions on the surface can be obtained.

[0019] In the polyamide film for molding of the present invention, fatty acid amide and / or fatty acid bisamide can be contained for the purpose of improving the lubricity. Examples of fatty acid amide and / or fatty acid bisamide include erucic acid amide, stearic acid amide, ethylene bisstearic acid amide, ethylene bisbehenic acid amide, ethylene bisoleic acid amide, and the like. The content of fatty acid amide and / or fatty acid bisamide is preferably 0.01 to 0.40% by mass, and more preferably 0.05 to 0.30% by mass. When the content of fatty acid amide and / or fatty acid bisamide is 0.01% by mass or more, sufficient lubricity can be obtained. On the other hand, when it is 0.40% by mass or less, it is possible to prevent the deterioration of wettability.

[0020] [Antioxidant] The polyamide film for molding according to the present invention may contain an antioxidant. A phenolic antioxidant is preferred. The phenolic antioxidant is preferably a fully hindered phenolic compound or a partially hindered phenolic compound. Examples include tetrakis-[methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionate]methane, stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and 3,9-bis[1,1-dimethyl-2-[β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]2,4,8,10-tetraoxaspiro[5,5]undecane. The inclusion of a phenolic antioxidant improves the film-forming operability of the polyamide film for molding.

[0021] [Physical properties of polyamide films for molding] The thickness of the polyamide film for molding according to the present invention is not particularly limited, but when used as a packaging material, it is usually 100 μm or less, and generally a thickness of 5 to 50 μm is preferred, with a thickness of 8 to 30 μm being particularly preferred.

[0022] The polyamide film for molding in this invention preferably has a heat shrinkage rate of 3.0% or less in both the flow direction and the width direction at 160°C for 10 minutes, and more preferably 2.5% or less. By setting the heat shrinkage rate to 3.0% or less, curling and shrinkage can be suppressed when heat is applied in subsequent processes such as lamination. There is no particular lower limit for the heat shrinkage rate, but for example, it is preferably 0.5% or more.

[0023] The impact strength of the polyamide film for molding in this invention is preferably 1.00 J / 20 μm or more, and more preferably 1.10 J / 20 μm or more, when the film thickness is converted to 20 μm. An impact strength of 1.00 J / 20 μm or more allows for good moldability. While a high impact strength is preferable, a value of 2.00 J / 20 μm or less is also preferable from the viewpoint of dimensional stability and moldability.

[0024] In the present invention, the impact strength retention rate after treating the polyamide film for molding with hot water at 120°C for 30 minutes is preferably 35% or more, and more preferably 40% or more. A retention rate of 35% or more is preferable because it provides good water resistance to the polyamide film for molding. The impact strength retention rate after treatment with hot water at 120°C for 30 minutes is preferably high, preferably 100% or less, and also preferably 90% or less.

[0025] In the present invention, the dry heat strain in the measurement method described later for the polyamide film for molding is preferably 1.0% or less, and more preferably 0.8% or less. A dry heat strain of 1.0% or less is preferable because it reduces the distortion in the width direction of the polyamide film for molding. While a small dry heat strain is preferable, a strain of 0.1% or more is also preferable.

[0026] The molding polyamide film of the present invention is preferably used as a laminate having a metal layer on at least one side, and a sealant layer on a side different from the side on which the molding polyamide film is laminated with the metal layer, as described below. For example, the lower limit of the deep drawing amount of a laminate consisting of molding polyamide film (20 μm) / Al foil (40 μm) / unoriented polypropylene film (70 μm) is preferably 4.0 mm or more, more preferably 4.2 mm or more, and particularly preferably 4.4 mm or more. By setting it to 4.0 mm or more, it can be suitably used even in deep drawing applications.

[0027] [Method for creating polyamide film for molding] The polyamide film for molding according to the present invention can be manufactured by known manufacturing methods, and may be produced by either sequential biaxial stretching or simultaneous biaxial stretching of an unstretched sheet obtained by the T-die method. Alternatively, it may be produced by simultaneous biaxial stretching using the tubular method. Particularly preferred is simultaneous biaxial stretching using the tubular method. Typical manufacturing examples are described below.

[0028] [Simultaneous biaxial stretching using the tubular method] First, the raw resin is melted and extruded using an extruder, and the molten material is extruded from the die as a cylindrical film, which is then rapidly cooled to obtain an unstretched film. The melting temperature of the resin is preferably 240 to 350°C. If the temperature is 240°C or higher, defects such as unmelted material can be suppressed. If the temperature is 350°C or lower, a decrease in strength due to a decrease in molecular weight caused by resin degradation, and defects in appearance due to carbides can be prevented.

[0029] Next, the unstretched film is passed between a pair of nip rolls, and while air is injected into it under pressure, it is heated with a heater. At the same time, air is blown in from the outside through an air ring to expand the unstretched film, thereby performing simultaneous biaxial stretching using the tubular method and obtaining a simultaneously biaxially oriented film.

[0030] The lower limit of the stretching ratio in the flow direction and width direction is preferably 2.2 times, more preferably 2.5 times, and particularly preferably 2.8 times. Setting it to 2.2 times or higher not only ensures sufficient thickness accuracy but also sufficient pinhole resistance, such as impact strength. The upper limit of the stretching ratio in the flow direction and width direction is preferably 5.0 times, more preferably 4.5 times, and particularly preferably 4.0 times. Setting it to 5.0 times or lower can suppress breakage during simultaneous stretching by the tubular method.

[0031] Next, this stretched film is placed in a tenter-type heat treatment machine and heat-treated to obtain a film for molding.

[0032] The lower limit of the heat-setting temperature is preferably 160°C, and more preferably 180°C. Setting it to 160°C or higher can keep the thermal shrinkage rate low, improving processability in subsequent processes such as lamination. The upper limit of the heat-setting temperature is preferably 250°C, and more preferably 240°C. Setting it to 250°C or lower can suppress defects in appearance due to film whitening and a decrease in impact strength.

[0033] Performing a relaxation treatment after heat-setting treatment is preferable from the viewpoint of controlling the thermal shrinkage rate. The temperature during the relaxation treatment is preferably in the range from the glass transition temperature (Tg) of the resin to the heat-setting treatment temperature, and more preferably between "Tg + 10°C" and "heat-setting treatment temperature - 10°C". It is preferable if the relaxation treatment temperature is above Tg, as it is less likely to cause thermal shrinkage distortion. Conversely, it is preferable if the relaxation temperature is below the heat-setting treatment temperature, as the thermal shrinkage suppression effect of the relaxation treatment can be effectively obtained.

[0034] The lower limit of the relaxation rate in the relaxation process is preferably 0.5%, more preferably 1%. Setting it to 0.5% or higher is sufficient to suppress the thermal shrinkage rate and improve processability. The upper limit of the relaxation rate is preferably 20%, more preferably 15%, and particularly preferably 10%. Setting it to 20% or lower prevents wrinkles and deterioration of productivity.

[0035] [Sequential biaxial stretching method for unstretched sheets] For film formation using the T-die method, first, the raw resin is melt-extruded using an extruder, extruded in a film shape from the T-die, cast onto a cooling roll and cooled to obtain an unstretched film. The melting temperature of the resin is preferably 240 to 350°C. If it is 240°C or higher, defects such as unmelted material can be suppressed. If it is 350°C or lower, a decrease in strength due to a decrease in molecular weight due to resin degradation, and defects in appearance due to carbides can be prevented. The T-die temperature is preferably 250 to 350°C.

[0036] The cooling roll temperature is preferably -30 to 80°C, and more preferably 0 to 50°C. To obtain an unstretched film by casting the film-like molten material extruded from the T-die onto a rotating cooling drum and cooling it, methods such as using an air knife or an electrostatic adhesion method using electrostatic charge can be preferably applied. The latter is particularly preferred.

[0037] Furthermore, it is preferable to cool the opposite side of the cooling roll of the cast unstretched film. For example, it is preferable to use a combination of methods such as bringing the cooling liquid in the tank into contact with the opposite side of the cooling roll of the unstretched film, applying a liquid that evaporates with a spray nozzle, or cooling by spraying a high-speed fluid.

[0038] The unstretched film can be stretched using either simultaneous biaxial stretching or sequential biaxial stretching. In either case, multi-stage stretching, such as single-stage or double-stage stretching, can be used as the stretching method in the MD direction. Multi-stage stretching in the flow direction, such as double-stage stretching, is preferable to single-stage stretching in terms of physical properties and uniformity (isotropy) of physical properties in the flow direction and width direction. In sequential biaxial stretching, roll stretching is preferred for stretching in the flow direction.

[0039] In sequential biaxial stretching, the lower limit of the stretching temperature in the flow direction by roll stretching is preferably 50°C, more preferably 55°C, and particularly preferably 60°C. Stretching is possible at temperatures of 50°C or higher. The upper limit of the stretching temperature in the flow direction is preferably 120°C, more preferably 115°C, and particularly preferably 110°C. Stable stretching is possible at temperatures of 120°C or lower.

[0040] The lower limit of the stretching ratio in the flow direction (or the total stretching ratio obtained by multiplying each ratio in the case of multi-stage stretching) is preferably 2.2 times, more preferably 2.5 times, and particularly preferably 2.8 times. Setting it to 2.2 times or higher ensures not only sufficient thickness accuracy in the flow direction but also sufficient impact strength. The upper limit of the stretching ratio in the flow direction is preferably 5.0 times, more preferably 4.5 times, and particularly preferably 4.0 times. Setting it to 5.0 times or lower allows for stretching in the subsequent lateral stretching process.

[0041] Furthermore, when extending the flow direction in multiple stages, the above-described extensions are possible for each stage, but the extension ratios must be adjusted so that the product of the extension ratios in all flow directions is 5.0 or less. For example, in the case of two-stage extension, it is preferable to extend the first stage by 1.5 to 2.23 times and the second stage by 1.5 to 2.23 times.

[0042] The film, stretched in the flow direction, is stretched in the width direction using a tenter, heat-set, and then relaxed (also called a relaxation treatment). The lower limit of the stretching temperature in the width direction is preferably 50°C, more preferably 55°C, and particularly preferably 60°C. Stretching becomes possible at 50°C or higher. The upper limit of the stretching temperature in the width direction is preferably 190°C, more preferably 185°C, and particularly preferably 180°C. Stable stretching is possible by keeping the temperature below 190°C.

[0043] The lower limit of the stretching ratio in the width direction (or the total stretching ratio obtained by multiplying each ratio in the case of multi-stage stretching) is preferably 2.2, more preferably 2.5, and particularly preferably 2.8. Setting it to 2.2 or higher ensures not only sufficient thickness accuracy in the width direction but also sufficient impact strength. The upper limit of the stretching ratio in the width direction is preferably 5.0, more preferably 4.5, and particularly preferably 4.0. Setting it to 5.0 or lower can suppress fracture during width stretching.

[0044] The lower limit of the surface stretching ratio (stretching ratio in the flow direction × stretching ratio in the width direction) is preferably 4.8 times, more preferably 6.3 times, and particularly preferably 7.8 times. Setting it to 4.8 times or higher not only ensures sufficient thickness accuracy but also sufficient impact strength. The upper limit of the surface stretching ratio is preferably 25.0 times, more preferably 20.3 times, and particularly preferably 16.0 times. By setting it to 25.0 times or less, breakage during stretching can be suppressed.

[0045] The lower limit of the heat-setting temperature is preferably 150°C, and more preferably 160°C. Setting it to 150°C or higher allows for lower thermal shrinkage rates, thereby improving processability in subsequent processes such as lamination. The upper limit of the heat-fixing temperature is preferably 250°C, and more preferably 240°C. By keeping it below 250°C, it is possible to suppress defects in appearance due to film whitening and a decrease in impact strength.

[0046] The heat fixation time is preferably 0.5 to 20 seconds, and more preferably 1 to 15 seconds. The heat fixation time can be adjusted to an appropriate time by considering the heat fixation temperature and the airflow speed in the heat fixation zone.

[0047] Performing a relaxation treatment after heat-setting treatment is preferable from the viewpoint of controlling the thermal shrinkage rate. The temperature during the relaxation treatment is preferably in the range from the glass transition temperature (Tg) of the resin to the heat-setting treatment temperature, and more preferably between "Tg + 10°C" and "heat-setting treatment temperature - 10°C". It is preferable if the relaxation treatment temperature is above Tg, as it is less likely to cause thermal shrinkage distortion. Conversely, it is preferable if the relaxation temperature is below the heat-setting treatment temperature, as the thermal shrinkage suppression effect of the relaxation treatment can be effectively obtained.

[0048] The lower limit of the relaxation rate in the relaxation process is preferably 0.5%, more preferably 1%. Setting it to 0.5% or higher is sufficient to suppress the thermal shrinkage rate and improve processability. The upper limit of the relaxation rate is preferably 20%, more preferably 15%, and particularly preferably 10%. Setting it to 20% or lower suppresses sagging within the tenter, preventing wrinkles and deterioration of productivity.

[0049] [Simultaneous biaxial stretching method for unstretched sheets] In the T-die tenter-type simultaneous biaxial stretching method, the raw resin is first melted and extruded using an extruder, extruded in a film form from the T-die, cast onto a cooling roll for cooling, and an unstretched film is obtained. The melting temperature of the resin is preferably 240 to 350°C. If it is 240°C or higher, defects such as unmelted material can be suppressed. If it is 350°C or lower, a decrease in strength due to a decrease in molecular weight due to resin degradation, and defects in appearance due to carbides can be prevented. The T-die temperature is preferably 250 to 350°C.

[0050] The cooling roll temperature is preferably -30 to 80°C, and more preferably 0 to 50°C. To obtain an unstretched film by casting the film-like molten material extruded from the T-die onto a rotating cooling drum and cooling it, methods such as using an air knife or an electrostatic adhesion method using electrostatic charge can be preferably applied. The latter is particularly preferred.

[0051] Furthermore, it is preferable to cool the opposite side of the cooling roll of the cast unstretched film. For example, it is preferable to use a combination of methods such as bringing the cooling liquid in the tank into contact with the opposite side of the cooling roll of the unstretched film, applying a liquid that evaporates with a spray nozzle, or cooling by spraying a high-speed fluid.

[0052] The lower limit of the stretching temperature for simultaneous biaxial stretching of an unstretched film is preferably 50°C, more preferably 55°C, and particularly preferably 60°C. Stretching is possible at temperatures of 50°C or higher. The upper limit of the stretching temperature for simultaneous biaxial stretching is preferably 190°C, more preferably 185°C, and particularly preferably 180°C. Stable stretching is possible at temperatures of 190°C or lower.

[0053] When performing simultaneous biaxial stretching, the lower limit of the stretching ratio in the flow direction and width direction is preferably 2.2 times, more preferably 2.5 times, and particularly preferably 2.8 times. Setting it to 2.2 or higher ensures not only sufficient thickness accuracy but also sufficient impact strength. The upper limit of the stretching ratio in the flow direction and width direction is preferably 5.0 times, more preferably 4.5 times, and particularly preferably 4.0 times. Setting it to 5.0 times or lower can suppress fracture during stretching.

[0054] The lower limit of the surface stretching ratio (stretching ratio in the flow direction × stretching ratio in the width direction) is preferably 4.8 times, more preferably 6.3 times, and particularly preferably 7.8 times. Setting it to 4.8 times or higher not only ensures sufficient thickness accuracy but also sufficient impact strength. The upper limit of the surface stretching ratio is preferably 25.0 times, more preferably 20.3 times, and particularly preferably 16.0 times. By setting it to 25.0 times or less, breakage during stretching can be suppressed.

[0055] The lower limit of the heat-setting temperature is preferably 150°C, and more preferably 160°C. Setting it to 150°C or higher can keep the thermal shrinkage rate low, improving processability in subsequent processes such as lamination. The upper limit of the heat-setting temperature is preferably 250°C, and more preferably 240°C. Setting it to 250°C or lower can suppress defects in appearance due to film whitening and a decrease in impact strength.

[0056] The heat fixation time is preferably 0.5 to 20 seconds, and more preferably 1 to 15 seconds. The heat fixation time can be adjusted to an appropriate time by considering the heat fixation temperature and the airflow speed in the heat fixation zone.

[0057] Performing a relaxation treatment after heat-setting treatment is preferable from the viewpoint of controlling the thermal shrinkage rate. The temperature during the relaxation treatment is preferably in the range from the glass transition temperature (Tg) of the resin to the heat-setting treatment temperature, and more preferably between "Tg + 10°C" and "heat-setting treatment temperature - 10°C". It is preferable if the relaxation treatment temperature is above Tg, as it is less likely to cause thermal shrinkage distortion. Conversely, it is preferable if the relaxation temperature is below the heat-setting treatment temperature, as the thermal shrinkage suppression effect of the relaxation treatment can be effectively obtained.

[0058] The lower limit of the relaxation rate in the relaxation process is preferably 0.5%, more preferably 1%. Setting it to 0.5% or higher is sufficient to suppress the thermal shrinkage rate and improve processability. The upper limit of the relaxation rate is preferably 20%, more preferably 15%, and particularly preferably 10%. Setting it to 20% or lower suppresses sagging within the tenter, preventing wrinkles and deterioration of productivity.

[0059] [Secondary processing of polyamide film for molding] Furthermore, the polyamide film for molding according to the present invention can be subjected to heat treatment or humidity control treatment to improve dimensional stability depending on the application. In addition, corona treatment, coating treatment, flame treatment, etc. can be applied to improve the adhesion of the film surface, and printing, vapor deposition of metals or inorganic oxides, etc. can also be applied.

[0060] A printed layer may be laminated onto the polyamide film for molding according to the present invention. Water-based and solvent-based resin-containing printing inks are preferably used as the printing ink for forming the printed layer. Examples of resins used in the printing ink include acrylic resins, urethane resins, polyester resins, vinyl chloride resins, vinyl acetate copolymer resins, and mixtures thereof. The printing ink may contain known additives such as antistatic agents, light-blocking agents, ultraviolet absorbers, plasticizers, lubricants, fillers, colorants, stabilizers, lubricants, defoaming agents, crosslinking agents, anti-blocking agents, and antioxidants.

[0061] The printing method for creating the printed layer is not particularly limited, and known printing methods such as offset printing, gravure printing, and screen printing can be used. For drying the solvent after printing, known drying methods such as hot air drying, hot roll drying, and infrared drying can be used.

[0062] The polyamide film for molding according to the present invention may have layers of other materials laminated onto it. The lamination method is not particularly limited and can be a method of laminating the polyamide film after it has been manufactured, or a method of laminating it during film formation, etc.

[0063] [Metal layer] The laminate of the present invention is preferably one in which a metal layer is laminated onto the moldable polyamide film of the present invention. The metal layer may be laminated in direct contact with the moldable polyamide film of the present invention, or it may be laminated via other layers such as an adhesive layer.

[0064] Various metallic elements (aluminum, iron, copper, nickel, etc.) can be used as the metal for the metal layer, but an aluminum layer is particularly preferred. From the viewpoint of deep drawing formability, the thickness of the metal layer is preferably 15 μm to 80 μm, and particularly preferably 20 μm to 60 μm.

[0065] [Sealant layer] In the present invention, it is preferable that the laminate has a sealant layer laminated on a surface different from the surface on which the polyamide film for molding the metal layer is laminated. The sealant layer may be laminated in direct contact with the metal layer, or it may be laminated via another layer such as an adhesive layer.

[0066] The sealant layer is preferably an unoriented polyolefin film. The unoriented polyolefin film is preferably a film containing a polyethylene-based resin composition and / or a polypropylene-based resin composition.

[0067] When the sealant layer is mainly formed from a polyethylene-based resin composition, examples of polyethylene-based resin compositions include linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE). The sealant layer may be a single layer or a multilayer structure of two or more layers, and may include at least one layer formed from a polyethylene-based resin composition, and may also include layers made of any other resin.

[0068] The lower limit of the sealant layer thickness is preferably 15 μm, more preferably 20 μm, and particularly preferably 25 μm. A thickness of 15 μm or more makes it easier to obtain heat seal strength. The upper limit of the sealant layer thickness is preferably 80 μm, more preferably 70 μm, and particularly preferably 60 μm. A thickness of 80 μm or less makes the film less stiff and easier to process, and also facilitates the production of suitable laminates for battery packaging. [Examples]

[0069] The evaluation methods for the various physical properties used in this invention are shown below. [Thickness of polyamide film for molding] The obtained film was cut into 100mm lengths in the direction of flow, stacked in a stack of 10 sheets, and conditioned for more than 2 hours in an environment of 23°C and 65% relative humidity. After that, the thickness was measured using a thickness measuring instrument manufactured by Tester Sangyo at positions that divided the width of the film into 10 equal parts (for narrow films, the division was made to ensure a width that could be measured for thickness), and the average value was divided by the number of stacked films to determine the film thickness.

[0070] [Thermal shrinkage rate] The thermal shrinkage rate (%) of the film was measured using the following formula (2), in accordance with the dimensional change test method described in JIS C2151:2019, except that the test temperature was 160°C and the heating time was 10 minutes, for both the flow direction and the width direction. Thermal shrinkage rate (%) = [(Length before treatment - Length after treatment) / Length before treatment] × 100 …(2)

[0071] [Impact strength] The impact punching strength of a polyamide film for molding was measured using a No. 181 film impact tester manufactured by Yasuda Seiki Seisakusho Co., Ltd. under conditions of 23°C and 65% relative humidity. The values ​​were expressed as J (joules) / 20μm, converted to a value per 20μm thickness.

[0072] [Impact strength retention rate] The impact strength described above was defined as the strength before treatment. Next, the polyamide film for molding was subjected to retort treatment at 120°C for 30 minutes using a hot water spray type retort sterilization device (Hisaka Works, Ltd. "RCS-60SPXTG"). After lightly wiping off the moisture from the film surface, the strength against impact punching of the polyamide film for molding was measured in the same manner as above under conditions of 23°C and 65% relative humidity, and this was defined as the strength after treatment. Subsequently, the strength retention rate was calculated using equation (4). Impact strength retention rate (%) = (Strength after treatment / Strength before treatment) × 100 …(4)

[0073] [Dry heat distortion] Circular samples with a diameter of 80 mm were cut from both ends of the film in the width direction, centered 150 mm from each end towards the center. These samples were left to stand for at least 30 minutes at 23°C and 50% relative humidity before heat treatment. The diameter lengths in the 45-degree and 135-degree directions were measured, with the width direction angle being 0 degrees and the flow direction angle being 90 degrees, and these were defined as the lengths before treatment. Subsequently, the samples were heat-treated at 160°C for 10 minutes, and then left to stand for at least 30 minutes at 23°C and 50% relative humidity. The diameter lengths in the 45-degree and 135-degree directions were similarly measured, and these were defined as the lengths after treatment. The 160°C dry heat shrinkage rates in the 45-degree and 135-degree directions were calculated using equation (5). Dry heat shrinkage rate at 160°C (%) = {(Length before treatment - Length after treatment) / Length after treatment} × 100 ... (5) Next, the dry heat strain at both ends of the film in the width direction, as defined by equation (3) below, was calculated, and the larger value was taken as the measured value of the dry heat strain. Dry heat strain (%) = |ab|··· (3) a: Thermal shrinkage rate in the 45-degree direction when the widthwise angle is 0 degrees and the flow direction angle is 90 degrees. b: Thermal shrinkage rate in the 135-degree direction when the widthwise angle is 0 degrees and the flow direction angle is 90 degrees.

[0074] [Fabrication of laminates] A two-component urethane-based adhesive ("Takelac® A525S" and "Takenate® A50" manufactured by Mitsui Chemicals, Inc.) was mixed in a ratio of 13.5:1.0 (by mass) on any surface of the polyamide film for molding according to the present invention, and a 40 μm thick "Aluminum Hak CE 8079" manufactured by Toyo Aluminum Co., Ltd. was laminated to it by dry lamination. Subsequently, a 70 μm thick unoriented polypropylene film ("P1147" manufactured by Toyobo Co., Ltd.) was laminated to the aluminum layer side of the polyamide film / aluminum layer laminate using the same two-component urethane-based adhesive by dry lamination. This polyamide film / aluminum layer / sealant layer laminate was aged at 40°C for 4 days to obtain a three-layer laminate. The film and aluminum layers used were all laminated with the longitudinal and width directions aligned. The thickness of the adhesive layer formed by the two-component urethane-based adhesive after drying was 4 μm in all cases.

[0075] [Draw-molding properties of laminates] A sample measuring 15 cm in the flow direction and 15 cm in the width direction was cut from the aforementioned three-layer laminate. This sample was set in a mold with the flow direction and width direction aligned, and deep drawing was performed by pressing from above. Specifically, the laminate was placed on a mold measuring 54 mm in length and 54 mm in width, and with the laminate held in place by a film retainer, it was pressed at 23°C with a punch shaped to match the mold. The drawing speed was set to 6 mm / s. The drawing depth was increased in increments of 0.2 mm during the drawing process, and the maximum drawing depth at which the laminate was not damaged was defined as the drawing depth. judgement molding depth ○: 8mm or larger △: 4mm to less than 8mm ×: Less than 4mm

[0076] <Manufacturing example> The raw materials used are listed below. (1) Polyamide resin A It uses polyamide 66 resin manufactured by Ascend. (2) Polyamide resin B Polyamide 66 / 6 resin, manufactured by Ascend, was used, in which the mole fraction of polyamide 66 constituent units relative to the total amide constituent units is 73 mol%. (3) Polyamide resin C It uses polyamide 6 resin manufactured by Toyobo Co., Ltd.

[0077] [Example 1] Polyamide resin A [100% by mass] was fed into an extruder. The resin was melted at 280°C in the extruder and melt-extruded, and the molten material was extruded from the die as a cylindrical film, which was then rapidly cooled to obtain an unstretched film. Next, the unstretched film was passed between a pair of nip rolls, and while air was injected into it under pressure, it was heated with a heater, and at the same time, air was blown from the outside through an air ring to expand the unstretched film, and simultaneous biaxial stretching was performed by the tubular method, stretching it 3.0 times in the flow direction and 3.0 times in the width direction to obtain a simultaneously biaxially oriented film. Subsequently, the simultaneously biaxially oriented film was fed into a tenter-type heat treatment machine and subjected to a heat setting treatment at 230°C and a 1.5% relaxation treatment to obtain a polyamide film for molding with a thickness of 20 μm.

[0078] [Example 2] A polyamide film for molding was obtained in the same manner as in Example 1, except that the raw material fed into the extruder was changed to polyamide resin B [100% by mass].

[0079] [Example 3] A polyamide film for molding was obtained in the same manner as in Example 1, except that the stretching ratio of the simultaneous biaxial stretching method using the tubular method was changed to 3.5 times in the flow direction and 3.5 times in the width direction.

[0080] [Example 4] A polyamide film for molding was obtained in the same manner as in Example 1, except that the stretching ratio in the simultaneous biaxial stretching method using the tubular method was changed to 2.5 times in the flow direction and 2.5 times in the width direction.

[0081] [Example 5] A polyamide film for molding was obtained in the same manner as in Example 1, except that the temperature of the heat setting treatment was changed to 225°C.

[0082] [Example 6] A polyamide film for molding was obtained in the same manner as in Example 1, except that the stretching ratio in the simultaneous biaxial stretching method using the tubular method was changed to 3.0 times in the flow direction and 3.5 times in the width direction.

[0083] [Example 7] Polyamide resin A [100% by mass] was fed into an extruder. It was melted at 280°C and extruded by melt extrusion, cast from a T-die at 280°C, and adhered to a cooling roll at 20°C by electrostatic adhesion to obtain an unstretched sheet. Next, the obtained unstretched sheet was stretched at a temperature of 170°C using a simultaneous biaxial stretching method, with a stretch ratio of 3.0 times in the flow direction and 3.0 times in the width direction, to obtain a simultaneously biaxially oriented film. Next, the simultaneously biaxially oriented film was subjected to a heat-setting treatment at 215°C for 3 seconds and a relaxation treatment of 1.5% for 1 second to obtain a polyamide film for molding with a thickness of 20 μm.

[0084] [Example 8] Polyamide resin A [100% by mass] was fed into an extruder. It was melted at 280°C and extruded by melt extrusion, cast from a T-die at 280°C, and adhered to a cooling roll at 20°C by electrostatic adhesion to obtain an unstretched sheet. Next, the obtained unstretched sheet was stretched at a temperature of 170°C using a simultaneous biaxial stretching method, with a stretching ratio of 3.3 times in the flow direction and 3.3 times in the width direction, to obtain a simultaneously biaxially oriented film. Next, the simultaneously biaxially oriented film was subjected to a heat-setting treatment at 235°C for 3 seconds and a relaxation treatment at 6% for 1 second to obtain a polyamide film for molding with a thickness of 20 μm.

[0085] [Example 9] Polyamide resin A [100% by mass] was fed into an extruder. It was melted at 280°C and extruded by melt extrusion, cast from a T-die at 280°C, and adhered to a cooling roll at 20°C by electrostatic adhesion to obtain an unstretched sheet. Next, the obtained unstretched sheet was roll-stretched at 100°C to a ratio of 1.73 in the flow direction, and then roll-stretched again at 95°C to a ratio of 1.73. Then it was passed through a tenter and stretched to a ratio of 3.0 in the width direction at 170°C. After transverse stretching, it was immediately subjected to a heat-setting treatment at 215°C for 3 seconds and a relaxation treatment of 1.5% for 1 second to obtain a 20 μm thick polyamide film for molding.

[0086] Table 1 shows the physical properties and various evaluation results of the laminated films obtained in Examples 1 to 9. As shown in Table 1, by using a copolymerized polyamide resin in which the copolymerization ratio of polyamide 66 is 60 mol% or more, the impact strength retention rate is increased, and water resistance close to or equivalent to that of polyethylene terephthalate resin can be provided, resulting in excellent water resistance. Furthermore, by achieving the specified thermal shrinkage rate, impact strength, and dry heat strain, the film exhibited excellent isotropy in thermal shrinkage characteristics in both the longitudinal and transverse directions, as well as excellent cold formability.

[0087] [Comparative Example 1] A polyamide film for molding was obtained in the same manner as in Example 1, except that the raw material fed into the extruder was changed to polyamide resin C [100% by mass] and the resin was melted and extruded at 260°C in the extruder. Because the raw material used was a copolymerized polyamide resin with a polyamide 66 copolymerization ratio of 60 mol% or more, or not a polyamide 66 resin, the impact strength retention rate decreased and the water resistance was poor.

[0088] [Comparative Example 2] A polyamide film for molding was obtained in the same manner as in Example 8, except that the raw material fed into the extruder was changed to polyamide resin C [100% by mass], melted at 260°C and extruded by melt extrusion, cast from a T-die at 260°C, and the stretching temperature was changed to 145°C. Because the raw material used was a copolymerized polyamide resin with a polyamide 66 copolymerization ratio of 60 mol% or more, or not a polyamide 66 resin, the impact strength retention rate decreased and water resistance was poor. In addition, the mechanical strength decreased during heat treatment and moldability decreased.

[0089] [Comparative Example 3] A polyamide film for molding was obtained in the same manner as in Example 1, except that the temperature of the heat setting treatment was changed to 210°C. However, the heat setting treatment was insufficient, resulting in a high thermal shrinkage rate, which caused curling and made molding difficult, resulting in poor cold formability.

[0090] [Comparative Example 4] Polyamide resin A [100% by mass] was fed into an extruder. It was melted at 280°C and extruded by melt extrusion, cast from a T-die at 280°C, and adhered to a cooling roll at 20°C by electrostatic adhesion to obtain an unstretched sheet. Next, the obtained unstretched sheet was roll-stretched at 100°C to a ratio of 1.73 in the flow direction, and then roll-stretched again at 95°C to a ratio of 1.73. Next, it was passed through a tenter and stretched 3.5 times in the width direction at 170°C. Immediately after transverse stretching, a heat-setting treatment was performed at 215°C for 3 seconds, followed by a relaxation treatment of 1.5% for 1 second, to obtain a 20 μm thick polyamide film for molding. The large difference in thermal shrinkage rates between the flow direction and the width direction, the non-isotropic orientation of the molecular chains in both the longitudinal and transverse directions, and the resulting deterioration of dry heat strain resulted in poor cold-formability using a square mold.

[0091] [Reference example 1] A laminated film with a thickness of 27 μm was obtained by laminating the base material layers, with the outermost layer being Toyobo Ester® Film E5104-12 μm (polyethylene terephthalate film) and the inner layer being Toyobo Harden® Film N1104-15 μm (polyamide 6 film). Because the outermost layer is a polyester film, it has excellent heat resistance and good cold-formability.

[0092] Table 1 shows the physical properties and various evaluation results of the polyamide films for molding obtained in Comparative Examples 1 to 4 and the laminated films of the Reference Examples.

[0093] [Table 1] [Industrial applicability]

[0094] The present invention provides a polyamide film for molding with excellent water resistance and isotropic heat shrinkage properties. Therefore, it is suitable for use in packaging for food, pharmaceuticals, and industrial products, particularly for molding using square, rectangular, or other molds. When used as a base layer in industrial products, it provides excellent heat resistance without the need to laminate a polyester film to the outermost layer. Furthermore, because multiple films are not laminated, the volume of plastic used can be reduced, providing an environmentally friendly polyamide film for molding. It is particularly suitable as a molding film for packaging industrial products such as electrochemical cell packaging materials and lithium-ion battery casings, and can be suitably used as a laminated film with a metal layer or sealant layer.

Claims

1. A polyamide film containing a polyamide resin that, when the total constituent units of the polyamide resin are 100 mol%, contains 60 mol% or more of polyamide 66 constituent units, and satisfies the following requirements (1) and (2). (1) The thermal shrinkage rate at 160°C is 3.0% or less in both the flow direction and the width direction. (2) The impact strength retention rate of the polyamide film for molding after treatment with hot water at 120°C for 30 minutes is 35% or more.

2. The polyamide film for molding according to claim 1, wherein the impact strength of the polyamide film for molding is 1.00 J / 20 μm or more.

3. The polyamide film for molding according to claim 1, wherein the dry heat strain at 160°C, as defined by the following formula (3), is 1.0% or less. Dry heat strain (%) = |a - b| ... (3) a: Dry heat shrinkage rate at 160°C in the 45-degree direction when the width direction angle is 0 degrees and the flow direction angle is 90 degrees. b: Dry heat shrinkage rate at 160°C in the 135° direction when the width direction angle is 0° and the flow direction angle is 90°. (However, the sample is taken at a position 150 mm from both ends of the film in the width direction toward the center, the 160°C dry heat strain is calculated at both ends of the film in the width direction, and the larger value is taken as the dry heat strain value.)

4. A laminate comprising a metal layer laminated on at least one surface of a polyamide film for molding as described in claim 1.

5. The laminate according to claim 4, wherein the metal layer is an aluminum layer with a thickness of 15 μm to 80 μm.

6. The laminate according to claim 5, wherein a sealant layer is laminated on the side opposite to the side on which the polyamide film for molding the metal layer is laminated.

7. A packaging body using a polyamide film for molding according to claim 1 or 2, or a laminate according to any one of claims 4 to 6.

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