Polyamide film for molding and laminate

Abstract

Provided is a polyamide film which is for molding and which, even when the film is made of a single material, has excellent heat resistance, dimensional stability during moisture absorption, orientation of molecular chains and isotropy of thermal shrinkage characteristics, has good moldability, and can reduce film volume and thus be environmentally friendly. The polyamide film for molding satisfies the following requirements.　(1) A polyamide resin constituting the polyamide film for molding has a melting point of at least 240 °C (2) The thermal shrinkage at 160 °C is at most 3.0% in both the flow direction and the width direction (3) With regard to the thermal shrinkage at 160 °C, the difference between the flow direction and the width direction is at most 0.3% (4) Nx, which is the refractive index of the film in the flow direction, and Ny, which is the refractive index of the film in the width direction, are each 1.55 to 1.58 as measured by an Abbe refractometer (5) The moisture absorption elongation rate is 1.5% or less in both the flow direction and the width direction (6) The moisture absorption strain is 0.8% or less

Description

Polyamide film for forming and laminate

[0001] The present invention relates to a polyamide film for forming used in packaging of foods, pharmaceuticals, industrial products, etc.

[0002] In recent years, as a film for forming used in packaging of industrial products, such as a film for forming, particularly a packaging material for an electrochemical cell or an exterior material for a lithium-ion battery, a biaxially stretched film has been adopted. The biaxially stretched film is used as a base material layer of a film for packaging industrial products. The base material layer is required to have formability, heat resistance, chemical resistance, and water resistance.

[0003] For example, in Patent Document 1, a method of reducing the anisotropy of the base material layer in order to improve the formability of the exterior material for a lithium-ion battery 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 biaxially stretched films adjacent to each other vertically. Further, in Patent Document 2, in order to impart 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 as a polyester film and the inner layer as a polyamide film.

[0004] However, both Patent Documents 1 and 2 bond 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 forming. Further, in recent years, reduction of the volume of plastics has been attracting attention for environmental protection, but it is not possible to reduce the volume in order to obtain the 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.

[0005] Japanese Patent No. 6036880 Japanese Patent No. 6127394

[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 heat resistance, dimensional stability when absorbing moisture, isotropy in molecular chain orientation and thermal shrinkage characteristics, and good moldability, even when made from a single material. 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.

[0007] The present invention comprises the following configurations: [1] A polyamide film for molding that satisfies the following requirements: (1) The melting point of the polyamide resin constituting the polyamide film for molding is 240°C or higher. (2) The thermal shrinkage rate at 160°C is 3.0% or less in both the flow direction and the width direction. (3) The difference between the thermal shrinkage rate at 160°C in the flow direction and the width direction is 0.3% or less. (4) The refractive index of the film in the flow direction and the refractive index of the film in the width direction, as determined by an Abbe refractometer, are 1.55 or more and 1.58 or less. (5) The moisture-absorbing elongation rate is 1.5% or less in both the flow direction and the width direction. (6) The moisture-absorbing strain is 0.8% or less. [2] The polyamide film for molding according to [1], wherein the impact strength is 1.00 J / 20 μm or more. [3] A laminate comprising the polyamide film for molding according to [1] or [2] and a metal layer, wherein the metal layer is laminated on one or both sides of the polyamide film for molding. [4] The laminate according to [3], wherein the metal layer is an aluminum layer with a thickness of 15 μm or more and 80 μm or less. [5] The laminate according to [3] or [4], wherein the metal layer is laminated on one side of the molding polyamide film and the sealant layer is laminated on the other side. [6] A package containing the molding polyamide film according to [1] or [2], or the laminate according to any one of [3] to [5].

[0008] The polyamide film for molding according to the present invention possesses heat resistance, dimensional stability when absorbing moisture, and isotropic molecular chain orientation and heat shrinkage properties. Therefore, it is suitable for molding using square, rectangular, or other molds for packaging food, pharmaceuticals, and industrial products. In particular, when used as a base layer in packaging films for industrial products, it can provide excellent heat resistance without laminating 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.

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

[0010] 1. Polyamide Resin The polyamide resin constituting the polyamide film for molding according to the present invention preferably has a melting point of 240°C or higher, and more preferably 243°C or higher. A melting point of 240°C or higher results in a melting point close to or equivalent to that of polyethylene terephthalate resin, thereby improving the heat resistance of the polyamide film for molding. For this reason, for example, when the polyamide film for molding is used as packaging, it is not necessary to laminate a film made of polyethylene terephthalate resin as the outermost layer, which reduces the volume of plastic used and is preferable for environmental reasons. Furthermore, a melting point of 240°C or higher maintains mechanical strength even during heat treatment of the polyamide film after stretching, thus maintaining high moldability. There is no upper limit set for the melting point, but it is preferable to set it to 275°C or lower, and more preferably 270°C or lower, as this facilitates extrusion molding and film formation.

[0011] The lower limit of the relative viscosity of the polyamide resin used in this invention is 1.8, and more preferably 2.6. By setting it to 1.8 or higher, the relative viscosity of the resulting polyamide film for molding can be maintained at a high level, improving the pinhole resistance, such as the impact strength of the film, and thus making it less likely for pinholes to occur during molding. The upper limit of the relative viscosity of the polyamide resin used in this invention is 5.0, and more preferably 4.5. By setting it to 5.0 or lower, it is possible to suppress excessive load on the extruder and stress during film stretching, and good film-forming properties can be obtained. Relative viscosity refers to the ratio of the viscosity of the polyamide resin solution to the viscosity of the solvent.

[0012] 2. Auxiliary Materials and Additives The polyamide film for molding of the present invention may 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.

[0013] 2 (1) Lubricant The polyamide film for molding of the present invention may contain fine particles as a lubricant for the purpose of improving slipperiness and cold formability. The fine particles can be appropriately selected from inorganic fine particles such as silica, kaolin, and zeolite; and polymeric organic fine particles such as acrylic and polystyrene. It is preferable to use silica fine particles in terms of transparency and slipperiness. The preferred average particle size of the fine particles is 0.5 μm or more and 5.0 μm or less, and more preferably 1.0 μm or more and 3.0 μm or less. If the average particle size is 0.5 μm or more, good slipperiness can be obtained with a small amount of additive. On the other hand, if it is 5.0 μm or less, it is possible to prevent the surface roughness of the film from becoming too large and the appearance from becoming poor.

[0014] When using the aforementioned silica fine particles, the pore volume range of the silica is preferably 0.5 ml / g or more and 2.0 ml / g or less, and more preferably 0.8 ml / g or more and 1.6 ml / g or less. When the pore volume is 0.5 ml / g or more, deterioration of film transparency due to void formation can be prevented. On the other hand, when the pore volume is 2.0 ml / g or less, sufficient surface protrusions can be obtained.

[0015] The polyamide film for molding according to the present invention may contain fatty acid amides and / or fatty acid bisamides for the purpose of improving slipperiness. Examples of fatty acid amides and / or fatty acid bisamides include erucic acid amide, stearic acid amide, ethylenebisstearate amide, ethylenebisbehenic acid amide, and ethylenebisoleic acid amide. The content of fatty acid amides and / or fatty acid bisamides is preferably 0.01% by mass or more and 0.40% by mass or less, and more preferably 0.05% by mass or more and 0.30% by mass or less. If the content of fatty acid amides and / or fatty acid bisamides is 0.01% by mass or more, sufficient slipperiness can be obtained. On the other hand, if it is 0.40% by mass or less, deterioration of wettability can be prevented.

[0016] 2 (2) Antioxidants The polyamide film for molding of the present invention may contain antioxidants. Phenolic antioxidants are preferred. Phenolic antioxidants are preferably fully hindered phenolic compounds or partially hindered phenolic compounds. Examples include tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane, stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 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, etc. By including phenolic antioxidants, the film-forming operability of the polyamide film for molding is improved.

[0017] 3. Physical Properties of the Polyamide Film for Molding The polyamide film for molding of the present invention exhibits excellent moldability. The polyamide film for molding of the present invention has properties that make it particularly suitable for deep drawing and cold forming. Deep drawing is a molding technique in which a laminate in which a metal layer is laminated on one or both sides of the polyamide film for molding of the present invention is sandwiched between a punch and a die, and pressure is applied to plastically deform it, thereby creating hollow parts such as cylindrical or rectangular tubes. Deep drawing may be performed cold or warm. Cold forming is a general term for processing methods in which the laminate according to the present invention is plastically deformed at a low temperature below the recrystallization temperature of the metal layer, for example, at room temperature. The polyamide film for molding and the laminate according to the present invention are useful, for example, as exterior materials for lithium-ion batteries and materials for press-through packs.

[0018] 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 μm to 50 μm is preferred, with a thickness of 8 μm to 30 μm being particularly preferred.

[0019] The polyamide film for molding in the present invention preferably has a heat shrinkage rate of 3.0% or less in both the flow direction (MD) and the width direction (TD) at 160°C for 10 minutes, and more preferably 2.5% or less. By setting the heat shrinkage rate to 3.0% or less, it is possible to suppress the occurrence of curling and shrinkage 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.

[0020] In the present invention, the polyamide film for molding preferably has a difference of 0.3% or less between the flow direction and the width direction in terms of heat shrinkage rate at 160°C for 10 minutes, and more preferably 0.2% or less. By making the difference between the flow direction and the width direction in terms of heat shrinkage rate 0.3% or less, the isotropic properties of the heat shrinkage are excellent, and the cold formability using square or rectangular molds, in particular the cold formability of square molds, is improved. There is no particular lower limit set for the difference between the flow direction and the width direction in terms of heat shrinkage rate, but for example, it is preferably 0.05% or more.

[0021] In the present invention, the refractive index Nx in the MD direction and the refractive index Ny in the TD direction of the polyamide film for molding, as determined by an Abbe refractometer, are preferably 1.55 or more and 1.58 or less, and more preferably 1.555 or more and 1.575 or less. A value of 1.55 or more is preferable because it provides sufficient orientation of the molecular chains of the polyamide film for molding, improving cold formability. On the other hand, a value of 1.58 or less is preferable because it allows for appropriate heat shrinkage and provides a film with excellent dimensional stability.

[0022] In the present invention, the moisture-absorbing elongation of the polyamide film for molding, as measured by the method described later, is preferably 1.5% or less in both the flow direction (MD) and the width direction (TD), and more preferably 1.3% or less. Setting it to 1.5% or less prevents the film from stretching under high humidity conditions, thereby suppressing deformation due to the stretching of the packaging. Furthermore, setting it to 1.5% or less is preferable because, for example, when the polyamide film for molding is used as packaging, it is not necessary to laminate a film made of polyethylene terephthalate resin as the outermost layer. While a low moisture-absorbing elongation is preferable, it is also preferable if it is 0.05% or more.

[0023] In the present invention, the moisture-absorbing strain of the polyamide film for molding, as measured by the method described later, is preferably 0.8% or less, and more preferably 0.6% or less. This is preferable because it reduces the distortion in the width direction of the polyamide film for molding. While a small moisture-absorbing strain is preferable, it is also preferable if it is 0.1% or more.

[0024] The impact strength of the polyamide film for molding in the present 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.

[0025] The molding polyamide film of the present invention is preferably used as a laminate having a metal layer on one side and a sealant layer on the side opposite to the side with the metal layer, as described later. For example, the lower limit of the deep drawing amount of a laminate consisting of molding polyamide film (25 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.

[0026] 4. Method for Preparing Polyamide Film for Molding The polyamide film for molding of 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, simultaneous biaxial stretching by the tubular method may also be used. Particularly preferred is simultaneous biaxial stretching by the tubular method. Typical manufacturing examples are described below.

[0027] 4 (1) Simultaneous biaxial stretching by 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°C or higher and 350°C or lower. 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 due to resin degradation, and defects such as carbides can be prevented.

[0028] 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.

[0029] 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. By setting the stretching ratio to 2.2 times or higher, not only is sufficient thickness accuracy achieved, but pinhole resistance such as impact strength is also sufficiently achieved. 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. By setting the stretching ratio to 5.0 times or lower, breakage during simultaneous stretching by the tubular method can be suppressed.

[0030] Next, this stretched film is placed in a tenter-type heat treatment machine and heat-treated to obtain a film for molding.

[0031] The lower limit of the heat-setting temperature is preferably 160°C, and more preferably 180°C. Setting the heat-setting temperature to 160°C or higher can suppress the thermal shrinkage rate and improve the processability of subsequent processes such as lamination. The upper limit of the heat-setting temperature is preferably 250°C, and more preferably 240°C. Setting the heat-setting temperature to 250°C or lower can suppress defects in appearance due to film whitening and a decrease in impact strength.

[0032] From the viewpoint of controlling the thermal shrinkage rate, it is preferable to perform a relaxation treatment after the heat-setting treatment. The temperature in 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". A relaxation treatment temperature of "Tg + 10°C" or higher is preferable as it is less likely to cause thermal shrinkage distortion. Conversely, a relaxation temperature of "heat-setting treatment temperature - 10°C" or lower is preferable as it effectively suppresses thermal shrinkage due to the relaxation treatment.

[0033] The lower limit of the relaxation rate in the relaxation treatment is preferably 0.5%, more preferably 1%. By setting the relaxation rate to 0.5% or higher, the thermal shrinkage rate can be sufficiently suppressed, and the processability is improved. The upper limit of the relaxation rate is preferably 20%, more preferably 15%, and particularly preferably 10%. By setting the relaxation rate to 20% or lower, wrinkles and deterioration of productivity can be prevented.

[0034] 4(2) Sequential biaxial stretching method for unstretched sheets For film formation by the T-die method, first, the raw resin is melted and 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°C or higher and 350°C or lower. If the melting temperature 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°C or higher and 350°C or lower.

[0035] The cooling roll temperature is preferably between -30°C and 80°C, and more preferably between 0°C and 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 that applies an electrostatic charge can be preferably applied. The latter is particularly preferred.

[0036] 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.

[0037] 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 of physical properties such as isotropy in the flow direction and width direction. In sequential biaxial stretching, roll stretching is preferred for stretching in the flow direction.

[0038] 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 becomes possible by setting the stretching temperature to 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 can be achieved by setting the stretching temperature in the flow direction to 120°C or lower.

[0039] The lower limit of the stretching ratio in the flow direction is preferably 2.2 times, more preferably 2.5 times, and particularly preferably 2.8 times. By setting the stretching ratio in the flow direction to 2.2 times or more, not only is sufficient thickness accuracy in the flow direction achieved, but impact strength is also achieved. 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. By setting the stretching ratio in the flow direction to 5.0 times or less, stretching in the subsequent lateral stretching process becomes possible. Note that when stretching in multiple stages, the stretching ratio refers to the total stretching ratio obtained by multiplying each respective ratio.

[0040] Furthermore, when extending the flow direction in multiple stages, the above-described extensions are possible for each stage, but it is preferable to adjust the extension ratios 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 set the extension ratio for the first stage to 1.5 times or more and 2.23 times or less, and the extension ratio for the second stage to 1.5 times or more and 2.23 times or less.

[0041] The film stretched in the flow direction is preferably stretched in the width direction with a tenter, heat-set, and relaxed. The relaxation treatment is also called a relaxation process. The lower limit of the stretching temperature in the width direction is preferably 50 °C, more preferably 55 °C, and particularly preferably 60 °C. When the stretching temperature in the width direction is 50 °C or higher, stretching becomes possible. The upper limit of the stretching temperature in the width direction is preferably 190 °C, more preferably 185 °C, and particularly preferably 180 °C. By setting the stretching temperature in the width direction to 190 °C or lower, stable stretching can be achieved.

[0042] The lower limit of the stretching ratio in the width direction is preferably 2.2 times, more preferably 2.5 times, and particularly preferably 2.8 times. By setting the stretching ratio in the width direction to 2.2 times or more, not only the thickness accuracy in the width direction becomes sufficient, but also the impact strength becomes sufficient. The upper limit of the stretching ratio in the width direction is preferably 5.0 times, more preferably 4.5 times, and particularly preferably 4.0 times. By setting the stretching ratio in the width direction to 5.0 times or less, breakage during width stretching can be suppressed.

[0043] The lower limit of the surface stretching ratio is preferably 4.8 times, more preferably 6.3 times, and particularly preferably 7.8 times. By setting the surface stretching ratio to 4.8 times or more, not only the thickness accuracy becomes sufficient, but also the impact strength becomes sufficient. 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 the surface stretching ratio to 25.0 times or less, breakage during stretching can be suppressed. The surface stretching ratio can be calculated by (stretching ratio in the flow direction) × (stretching ratio in the width direction).

[0044] The lower limit of the heat-setting temperature is preferably 150 °C, more preferably 160 °C. By setting the heat-setting temperature to 150 °C or higher, the heat shrinkage rate can be kept low, and the processability in subsequent processes such as the lamination process can be improved. The upper limit of the heat-setting temperature is preferably 250 °C, more preferably 240 °C. By setting the heat-setting temperature to 250 °C or lower, appearance defects due to film whitening and a decrease in impact strength can be suppressed.

[0045] The heat fixing time is preferably 0.5 seconds or more and 20 seconds or less, more preferably 1 second or more and 15 seconds or less. The heat fixing time can be set to an appropriate time in consideration of the heat fixing temperature and the wind speed in the heat fixing zone.

[0046] It is preferable to perform a relaxation treatment after the heat fixing treatment from the viewpoint of controlling the heat shrinkage rate. The temperature in the relaxation treatment preferably falls within the temperature range from the glass transition temperature (Tg) of the resin to the heat fixing treatment temperature, and more preferably is from “Tg + 10°C” to “heat fixing treatment temperature - 10°C”. When the temperature of the relaxation treatment is “Tg + 10°C” or higher, it is preferable because it is less likely to cause heat shrinkage distortion. Conversely, when the relaxation temperature is “heat fixing treatment temperature - 10°C” or lower, it is preferable because the heat shrinkage suppression effect by the relaxation treatment can be effectively obtained.

[0047] The lower limit of the relaxation rate in the relaxation treatment is preferably 0.5%, more preferably 1%. By setting the relaxation rate to 0.5% or more, the heat shrinkage rate can be sufficiently suppressed and the workability is improved. The upper limit of the relaxation rate is preferably 20%, more preferably 15%, and particularly preferably 10%. By setting the relaxation rate to 20% or less, sagging in the tenter can be suppressed, and wrinkles and productivity deterioration can be prevented.

[0048] 4(3) Simultaneous biaxial stretching method for an unstretched sheet In the tenter-type simultaneous biaxial stretching method using the T-die method, first, the raw material resin is melt-extruded using an extruder, extruded in film form from the T-die, cast on a cooling roll and cooled to obtain an unstretched film. The melting temperature of the resin is preferably 240°C or higher and 350°C or lower. When the resin melting temperature is 240°C or higher, appearance defects due to drawbacks such as unmelted matter can be suppressed. When the resin melting temperature is 350°C or lower, strength reduction accompanying molecular weight reduction due to resin deterioration, appearance defects due to carbide, etc. can be prevented. The T-die temperature is preferably 250°C or higher and 350°C or lower.

[0049] The cooling roll temperature is preferably between -30°C and 80°C, and more preferably between 0°C and 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 that applies an electrostatic charge can be preferably applied. The latter is particularly preferred.

[0050] 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.

[0051] 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 becomes possible by setting the stretching temperature to 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 can be achieved by setting the stretching temperature to 190°C or lower.

[0052] 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. By setting the stretching ratio to 2.2 times or higher, not only is sufficient thickness accuracy achieved, but impact strength is also sufficient. 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. By setting the stretching ratio to 5.0 times or lower, fracture during stretching can be suppressed.

[0053] The lower limit of the surface stretching ratio is preferably 4.8 times, more preferably 6.3 times, and particularly preferably 7.8 times. By setting the surface stretching ratio to 4.8 times or higher, not only is sufficient thickness accuracy achieved, but sufficient impact strength is also achieved. 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 the surface stretching ratio to 25.0 times or lower, fracture during stretching can be suppressed. The surface stretching ratio can be calculated by (stretching ratio in the flow direction) × (stretching ratio in the width direction).

[0054] The lower limit of the heat-setting temperature is preferably 150°C, and more preferably 160°C. Setting the heat-setting temperature to 150°C or higher can suppress the rate of thermal shrinkage, thereby improving the processability of subsequent processes such as lamination. The upper limit of the heat-setting temperature is preferably 250°C, and more preferably 240°C. Setting the heat-setting temperature to 250°C or lower can suppress defects in appearance due to film whitening and a decrease in impact strength.

[0055] The heat fixation time is preferably 0.5 seconds to 20 seconds, and more preferably 1 second 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.

[0056] From the viewpoint of controlling the thermal shrinkage rate, it is preferable to perform a relaxation treatment after the heat-setting treatment. The temperature in 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". A relaxation treatment temperature of "Tg + 10°C" or higher is preferable as it is less likely to cause thermal shrinkage distortion. Conversely, a relaxation temperature of "heat-setting treatment temperature - 10°C" or lower is preferable as it effectively suppresses thermal shrinkage due to the relaxation treatment.

[0057] The lower limit of the relaxation rate in the relaxation process is preferably 0.5%, more preferably 1%. By setting the relaxation rate to 0.5% or higher, the thermal shrinkage rate can be sufficiently suppressed, improving processability. The upper limit of the relaxation rate is preferably 20%, more preferably 15%, and particularly preferably 10%. By setting the relaxation rate to 20% or lower, sagging within the tenter can be suppressed, preventing wrinkles and deterioration of productivity.

[0058] 5. Secondary Processing of Polyamide Films for Molding Furthermore, the polyamide film for molding of 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 6. Metal Layer The laminate of the present invention preferably has a metal layer laminated on one or both sides of 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 another layer such as an adhesive layer.

[0063] Various metallic elements such as aluminum, iron, copper, and nickel can be used as the metal for the metal layer, but aluminum 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.

[0064] 7. Sealant Layer The laminate of the present invention preferably 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 polyamide film or the metal layer, or it may be laminated via another layer such as an adhesive layer.

[0065] 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.

[0066] 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.

[0067] The lower limit of the sealant layer thickness is preferably 15 μm, more preferably 20 μm, and particularly preferably 25 μm. When the sealant layer thickness is 15 μm or more, heat seal strength is easily obtained. The upper limit of the sealant layer thickness is preferably 80 μm, more preferably 70 μm, and particularly preferably 60 μm. When the sealant layer thickness is 80 μm or less, the film does not become too stiff, making it easier to process, and it is easier to manufacture a suitable laminate for battery packaging.

[0068] This application claims the benefit of priority based on Japanese Patent Application No. 2024-164146, filed on September 20, 2024. The entire specification of Japanese Patent Application No. 2024-164146, filed on September 20, 2024, is incorporated herein by reference.

[0069] The evaluation methods for the various physical properties used in this invention are shown below. Test Example 1: Thickness of the polyamide film for molding Ten sheets of the obtained film were stacked in the flow direction to a length of 100 mm and cut out. The film was then conditioned for more than two hours in an environment of 23°C and 65% relative humidity. After that, the thickness was measured at 10 points, dividing the width direction of the film into 10 equal parts, using a film thickness measuring instrument ("TH-102", manufactured by Tester Sangyo Co., Ltd.). The average value was divided by the number of stacked films to obtain the film thickness.

[0070] Test Example 2: The heat shrinkage rate (%) of the heat shrinkage rate of the film was measured according to 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, using the following formula (1): Heat shrinkage rate (%) = [(Length before treatment - Length after treatment) / Length before treatment] × 100 ... (1)

[0071] Test Example 3: Difference in Heat Shrinkage Rate between Flow Direction and Width Direction The heat shrinkage rate (%) of the film was measured, and the difference between the heat shrinkage rate in the flow direction and the width direction was expressed as an absolute value using the following formula (2). Difference in heat shrinkage rate (%) = (Heat shrinkage rate in flow direction) - (Heat shrinkage rate in width direction) ... (2) However, if the difference in heat shrinkage rate (%) ≥ 0, the calculated value obtained from formula (2) is taken as the measured value. If the difference in heat shrinkage rate (%) < 0, the calculated value obtained from formula (2) multiplied by -1 is taken as the measured value.

[0072] Test Example 4: A 5 mm square sample was cut from a polyamide film for refractive index molding. The refractive index (Nx) in the longitudinal direction of the film, the refractive index (Ny) in the width direction, and the refractive index (Nz) in the thickness direction were measured using an Abbe refractometer ("NAR-1T" manufactured by Atago Corporation) according to JIS K7142-1996 Method A, with sodium D line as the light source and diiodomethane as the contact liquid.

[0073] Test Example 5: An impact strength film impact tester ("No. 181," manufactured by Yasuda Seiki Seisakusho Co., Ltd.) was used to measure the impact punching strength of a polyamide film for molding under conditions of 23°C and 65% relative humidity. The values ​​were expressed in J (joules) / 20 μm, converted to a value per 20 μm thickness.

[0074] Test Example 6: Moisture-absorbing elongation A circular sample with a diameter of 80 mm was cut from the center of the obtained film. This sample was left to stand for more than 2 hours in an environment of 30°C and 87% relative humidity, and the length of the diameter in the flow direction and width direction was measured and defined as the diameter at high humidity. Subsequently, after being left to stand for more than 2 hours in an environment of 20°C and 44% relative humidity, the length of the diameter in the flow direction and width direction was similarly measured and defined as the diameter at low humidity. The moisture-absorbing elongation was calculated using the following formula (3): Moisture-absorbing elongation (%) = [(Diameter at high humidity - Diameter at low humidity) / Diameter at low humidity] × 100 ... (3)

[0075] Test Example 7: After winding a film obtained by simultaneous biaxial stretching using the moisture-strain tubular method, or by sequential or simultaneous biaxial stretching of an unstretched sheet, circular samples with a diameter of 80 mm were cut from both ends of the film roll in the width direction, centered at a position 150 mm toward the center. These samples were left to stand for more than two hours at 30°C and 87% relative humidity. The lengths of the diameters 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 diameters at high humidity. Subsequently, after leaving the samples to stand for more than two hours at 20°C and 44% relative humidity, the lengths of the diameters in the 45-degree and 135-degree directions were similarly measured, and these were defined as the diameters at low humidity. The moisture-strain elongation in the 45-degree and 135-degree directions were calculated in the same manner as in formula (1). Next, the moisture-strain at both ends of the film in the width direction was calculated using the following formula (4), and the larger value was taken as the measured value of the moisture-strain. In the case of simultaneous biaxial stretching using the tubular method, two film rolls are obtained. Therefore, the moisture strain was calculated at four points, both ends in the width direction of each film roll, and the larger value was taken as the measured moisture strain. Moisture strain (%) = (Moisture elongation in the 45-degree direction) - (Moisture elongation in the 135-degree direction) ... (4) If moisture strain (%) ≥ 0, the calculated value obtained from equation (4) is taken as the measured value. If moisture strain (%) < 0, the calculated value obtained from equation (4) multiplied by -1 is taken as the measured value.

[0076] Test Example 8: Laminate Preparation "Takelac® A525S" (manufactured by Mitsui Chemicals, Inc.) and "Takenate® A50" (manufactured by Mitsui Chemicals, Inc.), both polyurethane adhesives, were mixed in a ratio of 13.5:1.0 (mass ratio) and applied to one side of a polyamide film for molding. A 40 μm thick aluminum foil ("CE8079" manufactured by Toyo Aluminum Co., Ltd.) was then laminated using the dry lamination method. Subsequently, the same adhesive was applied to the aluminum layer side of the resulting laminate, and a 70 μm thick unoriented polypropylene film ("P1147" manufactured by Toyobo Co., Ltd.) was laminated using the dry lamination method. The resulting laminate was aged at 40°C for 4 days to obtain the final laminate. When laminating the films and aluminum layers, the longitudinal and width directions were aligned in all cases. The thickness of the adhesive layer after drying was 4 μm in all cases.

[0077] Test Example 9: Draw-Formability of Laminate A sample measuring 15 cm in the flow direction and 15 cm in the width direction was cut from the aforementioned laminate. This sample was set in a mold with the flow direction and width direction aligned, and draw-formed 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 holder, it was pressed at 23°C with a punch of a shape corresponding to the mold. The draw speed was set to 6 mm / s. The draw depth during molding was increased in increments of 0.2 mm, and the maximum depth at which the laminate was not damaged was defined as the draw depth, and the formability was evaluated according to the following criteria: ○: Draw depth of 8 mm or more △: Draw depth of 4 mm or more and less than 8 mm ×: Draw depth less than 4 mm

[0078] The raw materials used are listed below. (1) Polyamide resin A: Polyamide 66 resin manufactured by Ascend, with a melting point of 263°C was used. (2) Polyamide resin B: Polyamide 66 / 6 resin manufactured by Ascend, with a melting point of 245°C was used. (3) Polyamide resin C: Polyamide 6 resin manufactured by Toyobo, with a melting point of 220°C was used.

[0079] Example 1 Polyamide resin A [100% by mass] was put 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 and 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 air was blown from the outside 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. Then, the simultaneously biaxially oriented film was put 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.

[0080] 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].

[0081] 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.

[0082] Example 4 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 2.5 times in the flow direction and 2.5 times in the width direction.

[0083] 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.

[0084] Example 6 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 3.0 times in the flow direction and 3.5 times in the width direction.

[0085] Example 7 Polyamide resin A [100% by mass] was put into an extruder. It was melted at 280°C and melt-extruded, 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 by simultaneous biaxial stretching 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.

[0086] Example 8 Polyamide resin A [100% by mass] was put into an extruder. It was melted at 280°C and melt-extruded, 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 by simultaneous biaxial stretching with a stretch ratio of 3.3 times in the flow direction and 3.3 times in the width direction to obtain a simultaneously biaxially stretched film. Next, the simultaneously biaxially stretched film was subjected to a heat setting treatment at 235°C for 3 seconds and a relaxation treatment of 6% for 1 second to obtain a polyamide film for molding with a thickness of 20 μm.

[0087] Example 9 Polyamide resin A [100% by mass] was put into an extruder. It was melted at 280°C and melt-extruded, 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 by 1.73 times in the flow direction, and then roll-stretched again at 95°C by 1.73 times. Next, it was passed through a tenter and stretched 3.0 times 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 polyamide film for molding with a thickness of 20 μm.

[0088] 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 polyamide resin with a high melting point, the laminated films of Examples 1 to 9 have a melting point close to or equivalent to that of polyethylene terephthalate resin, and therefore exhibit excellent heat resistance. Furthermore, by achieving the specified thermal shrinkage rate, refractive index, impact strength, moisture elongation rate, and moisture strain, the laminated films of Examples 1 to 9 exhibited excellent molecular orientation in both longitudinal and transverse directions, isotropic thermal shrinkage characteristics, and cold formability.

[0089] 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. Due to the low melting point of the raw material used, the heat resistance was poor, as shown in Table 1. In addition, the moisture elongation rate was high.

[0090] 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. Due to the low melting point of the raw material used, the heat resistance was poor, as shown in Table 1. In addition, because a resin with a low melting point was used, the mechanical strength decreased during heat treatment, and the moldability decreased. Furthermore, the moisture elongation rate was high.

[0091] 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. The laminated film of Comparative Example 3 had insufficient heat-setting treatment and a high thermal shrinkage rate, resulting in curling and poor molding performance, and thus poor cold-formability.

[0092] Comparative Example 4 Polyamide resin A [100% by mass] was fed into an extruder. It was melted at 280°C and melt-extruded, 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 by 1.73 times in the flow direction, and then roll-stretched again at 95°C by 1.73 times. Next, it was passed through a tenter and stretched 3.5 times 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 polyamide film for molding with a thickness of 20 μm. The laminated film of Comparative Example 4 had a large difference in thermal shrinkage rate between the flow direction and the width direction, and the orientation of the molecular chains in both the longitudinal and transverse directions was not isotropic, resulting in poor cold-formability using a square mold. In addition, the moisture-absorbing elongation rate in the width direction deteriorated.

[0093] Reference Example 1: The outermost layer of the base material was made of a PET biaxially oriented film ("Toyobo Ester® Film E5104," manufactured by Toyobo Co., Ltd., 12 μm thick), and the inner layer was made of a nylon biaxially oriented film ("Toyobo Harden® Film N1104," manufactured by Toyobo Co., Ltd., 15 μm thick), resulting in a laminated film with a thickness of 27 μm. The laminated film in Reference Example 1 had excellent heat resistance because the outermost layer was a polyester film, and also exhibited good cold formability.

[0094] 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.

[0095]

[0096] The present invention provides a polyamide film for molding that exhibits excellent heat resistance, dimensional stability during moisture absorption, and isotropic properties in molecular chain orientation and heat shrinkage. Therefore, it is suitable for use in molding using square, rectangular, or other molds for packaging food, pharmaceuticals, and industrial products. When used as a base layer in packaging films for 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 cells and lithium-ion batteries, and can be suitably used as a laminated film with a metal layer or sealant layer.

Claims

1. A polyamide film for molding that meets the following requirements: (1) The polyamide resin constituting the polyamide film for molding has a melting point of 240°C or higher. (2) The thermal shrinkage rate at 160°C is 3.0% or less in both the flow direction and the width direction. (3) The difference between the thermal shrinkage rate at 160°C in the flow direction and the width direction is 0.3% or less. (4) The refractive index of the film in the flow direction (Nx) and the refractive index of the film in the width direction (Ny), as determined by an Abbe refractometer, are 1.55 or higher and 1.58 or lower. (5) The moisture-absorbing elongation is 1.5% or less in both the flow direction and the width direction. (6) The moisture-absorbing strain is 0.8% or less.

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

3. A laminate comprising a moldable polyamide film and a metal layer as described in claim 1, wherein the metal layer is laminated on one or both sides of the moldable polyamide film.

4. The laminate according to claim 3, wherein the metal layer is an aluminum layer with a thickness of 15 μm or more and 80 μm or less.

5. The laminate according to claim 3, wherein the metal layer is laminated on one side of the molding polyamide film and the sealant layer is laminated on the other side.

6. A packaging body comprising a polyamide film for molding according to claim 1 or 2, or a laminate according to any one of claims 3 to 5.

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