TW202444803A - Biaxially stretched polyamide film, food packaging material, and ethanol evaporator packaging material - Google Patents

Abstract

The purpose of the present invention is to provide a biaxially stretched polyamide film having excellent bending pinhole resistance, puncture strength, dimensional stability and ethanol permeability. The present invention is a biaxially stretched polyamide film, which contains polyamide 6 as a main component. In the biaxially stretched polyamide film, the ethanol permeability is 6000g. μm/m ^{2 .} 24hr to 10000g. μm/m ^{2 .} 24hr (50%RH/40℃), the thickness is less than 15μm, the thermal shrinkage rate in the traveling direction and the width direction of the film is less than 2.0%, the surface crystallization parameter is in the range of 1.0 to 1.5, and the puncture strength is more than 6.0N.

Description

Biaxially stretched polyamide film, food packaging material, and ethanol evaporator packaging material

The present invention relates to a biaxially stretched polyamide film which can be suitably used as a food packaging film and a packaging material for an alcohol transpiration agent.

Biaxially stretched films made of aliphatic polyamides represented by polyamide 6 have excellent impact resistance and bending pinhole resistance and are widely used as various packaging material films. In Patent Documents 1 and 2, since polyamide films generally have high alcohol permeability, they are also used as base films for alcohol evaporative packaging bags and freshness-retaining packaging bags that require specific gas permeability. Patent Document 3 shows the following description: By making the thickness of the biaxially stretched polyamide film thin, the desired gas permeability can be obtained. [Prior Art Document] [Patent Document]

[Patent Document 1] Japanese Patent Publication No. 2003-211604. [Patent Document 2] Japanese Patent Publication No. 2002-204652. [Patent Document 3] Japanese Patent Publication No. 2010-167652.

[The problem that the invention wants to solve]

Patent document 3 shows that reducing the thickness of the nylon membrane is effective in improving ethanol permeability, but the inventors found that the bending pinhole resistance and puncture strength would decrease as the thickness of the membrane was reduced. Furthermore, in Patent document 3, the inventors also found that there is room for improvement in the dimensional stability of the membrane.

The purpose of the present invention is to provide a biaxially stretched polyamide film having excellent bending pinhole resistance, puncture strength, dimensional stability, and ethanol permeability. [Means for solving the problem]

The inventors have conducted intensive research to achieve the above-mentioned goal, and have found that in a biaxially stretched polyamide film, a resin other than polyamide 6 having a maximum dispersion diameter of 1 μm or more is dispersed in the polyamide 6 resin, and the polyamide 6 resin has a specific plane orientation and a specific crystallinity, so that a biaxially stretched polyamide film having good bending pinhole resistance, puncture strength, dimensional stability, and ethanol permeability can be obtained. The inventors have repeatedly conducted further research and improvements, thereby completing the invention represented by the following.

[1] A biaxially stretched polyamide film comprises polyamide 6 as a main component, wherein the biaxially stretched polyamide film has an ethanol permeability of 6000 g. μm/m ² . 24 hr to 10000 g. μm/m ² . 24 hr (50% RH/40°C), a thickness of less than 15 μm, a thermal shrinkage rate of less than 2.0% in both the travel direction and the width direction of the film when heat treated at 160°C for 10 minutes, a surface crystallization parameter in the range of 1.0 to 1.5, and a puncture strength of more than 6.0 N. [2] A biaxially stretched polyamide film as described in [1], wherein the biaxially stretched polyamide film has at least one layer containing 60% by mass to 98% by mass of a polyamide 6 resin (a) and 2% by mass to 40% by mass of a resin other than polyamide 6 (b). [3] The biaxially stretched polyamide film as described in [2], wherein the resin (b) other than the polyamide 6 is at least one selected from the group consisting of thermoplastic elastomers such as polyolefins, ionic polymers, polyester elastomers, polyamide elastomers, polyolefin elastomers, polystyrene elastomers, polyurethane elastomers, polyvinyl chloride elastomers, etc.; aliphatic polyester resins; aliphatic aromatic polyester resins; aliphatic polyamide resins; and aliphatic aromatic polyamide resins. [4] The biaxially stretched polyamide film as described in [2] or [3], wherein the aliphatic aromatic polyester resin is a polybutylene adipate terephthalate resin. [5] The biaxially stretched polyamide film as described in [2], wherein the resin (b) other than polyamide 6 is derived from biomass and is at least one polyamide selected from the group consisting of polyamide 11, polyamide 410, polyamide 610, and polyamide 1010. [6] The biaxially stretched polyamide film as described in any one of [2] to [5], wherein the maximum dispersion diameter of the resin (b) other than polyamide 6 is greater than 1 μm. [7] The biaxially stretched polyamide film as described in any one of [1] to [6], wherein the stress at 5% elongation in the travel direction and the width direction of the film is less than 70.0 MPa. [8] A biaxially stretched polyamide film as described in any one of [1] to [7], wherein the surface orientation (ΔP) is greater than or equal to 0.050. [9] A biaxially stretched polyamide film as described in any one of [1] to [8], wherein a laminate of the biaxially stretched polyamide film and a polyethylene film having a thickness of 40 μm is subjected to 1000 bending treatments at a temperature of 1° C. using a Gelbo Flex Tester, and the number of pinholes generated is less than 20. [10] A food packaging material comprising a biaxially stretched polyamide film as described in any one of [1] to [9], and a sealant film. [11] A packaging material for ethanol evaporative agent, comprising a laminate of at least two layers including a biaxially stretched polyamide film as described in any one of [1] to [9] and a breathable resin film or non-woven fabric. [Effect of the invention]

According to the present invention, a biaxially stretched polyamide film having excellent bending pinhole resistance, puncture strength, dimensional stability and ethanol permeability, a food packaging material using the biaxially stretched polyamide film, and a packaging material for ethanol evaporative can be provided.

The biaxially stretched polyamide film of the present invention is described in detail below. In addition, in this specification, the numerical range represented by "to" means a range including the numerical values described before and after "to" as the lower limit and the upper limit.

The biaxially stretched polyamide film of the present invention preferably contains polyamide 6 as a main constituent. Here, "containing as a main constituent" means that when the total constituent components of the polyester resin are set to 100% by mass, the content of the component in the polyester resin composition constituting the film is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and further preferably 80% by mass or more. The biaxially stretched polyamide film of the present invention is preferably a biaxially stretched polyamide film having a functional layer on at least one area of the substrate layer. The biaxially stretched polyamide film of the present invention preferably has at least two layers of a substrate layer and a functional layer, and may also have a two-layer structure of substrate layer/functional layer, or a three-layer structure of functional layer/substrate layer/functional layer. The details of each layer are described below.

[Substrate layer A] The first resin composition forming the substrate layer contains at least polyamide 6 resin (a). The first resin composition preferably contains 60% by mass or more of polyamide 6, more preferably 80% by mass or more, and further preferably 85% by mass or more, with the first resin composition being 100% by mass. If the content of polyamide 6 is less than 60% by mass, the impact resistance may be reduced and the gas permeability may be significantly increased. By containing 80% by mass or more of polyamide 6, a polyamide film having mechanical strength such as impact strength and gas barrier properties can be obtained. The upper limit of the content of polyamide 6 is preferably 98% by mass or less, and more preferably 97% by mass or less, when the first resin composition is set to 100% by mass. That is, the content of polyamide 6 is preferably 60% by mass to 98% by mass, more preferably 80% by mass to 98% by mass, and further preferably 85% by mass to 97% by mass. In addition, in this specification, the upper and lower limits of the numerical range can be appropriately combined to set a suitable numerical range (hereinafter, the same applies to the numerical range).

The first resin composition forming the substrate layer includes at least one resin (b) other than polyamide 6. The resin (b) is not particularly limited as long as it has the effect of imparting flexibility to the substrate layer and is immiscible with polyamide 6. It is preferably at least one selected from the group consisting of thermoplastic elastomers such as polyolefins, ionomers, polyester elastomers, polyamide elastomers, polyolefin elastomers, polystyrene elastomers, polyurethane elastomers, polyvinyl chloride elastomers, etc.; aliphatic polyester resins; aliphatic aromatic polyester resins; aliphatic polyamide resins; and aliphatic aromatic polyamide resins.

Examples of polyolefins include homopolymers of olefins, copolymers of olefins and other monomers, and mixtures thereof, and copolymers obtained by graft-polymerizing unsaturated carboxylic acids onto polyolefins. Examples of homopolymers of olefins include polyethylene (high density, low density) and polypropylene. Examples of copolymers of olefins and other monomers include ethylene/vinyl acetate copolymers, ethylene/propylene copolymers, ethylene/butene copolymers, ethylene/acrylic acid copolymers, and ethylene/methacrylic acid copolymers. Examples of unsaturated carboxylic acids used for copolymers obtained by graft-polymerizing unsaturated carboxylic acids onto polyolefins include carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and citric acid; and acid anhydrides such as maleic anhydride, citric anhydride, and itaconic anhydride. Unsaturated carboxylic acids can be used alone or in combination.

The so-called ionic polymer refers to an α,β-ethylenic unsaturated monomer having a polyolefin and a carboxyl portion, wherein the carboxyl portion is neutralized by a metal ion having a valence of 1 to 3. Examples of the polyolefin include copolymers of polyethylene or ethylene, at least one α-olefin having a carbon number of usually 3 to 8, and a diene (e.g., 1,4-hexadiene). Examples of the α,β-ethylenic unsaturated monomer having a carboxyl portion include methacrylic acid, acrylic acid, maleic acid, maleic anhydride, and fumaric acid. Examples of the metal ion include zinc ion, sodium ion, lithium ion, potassium ion, and magnesium ion. Ionic polymers can be produced by a direct synthesis method of polymerizing an α-olefin and an olefin monomer having a carboxyl group, or by a method of grafting a monomer having a carboxyl group onto an olefin skeleton.

Examples of the thermoplastic elastomer include thermoplastic elastomers such as polyolefins, ionomers, polyester elastomers, polyamide elastomers, polyolefin elastomers, polystyrene elastomers, polyurethane elastomers, and polyvinyl chloride elastomers; aliphatic polyester resins; aliphatic aromatic polyester resins; aliphatic polyamide resins; and aliphatic aromatic polyamide resins. For example, polyamide elastomers, polyester elastomers, polyurethane elastomers, acrylic thermoplastic elastomers, polystyrene elastomers, and hydrogenated products thereof may also be used.

Examples of the polyamide elastomer include polyetheramide, polyetheresteramide, and polyesteramide. Furthermore, dicarboxylic acids such as dodecanedicarboxylic acid, adipic acid, and terephthalic acid may be copolymerized with the polyamide elastomer as an optional component.

The polyester elastomer refers to a block copolymer composed of a crystalline hard segment and a flexible soft segment. Among them, a block copolymer having a hard segment composed of a cyclic polyester and a soft segment composed of a polyalkylene ether, and a block copolymer having a hard segment composed of a cyclic polyester and a soft segment composed of a chain aliphatic polyester are preferred, and a cyclic polyester/polyalkylene ether block copolymer is more preferred. In addition, in the present invention, the so-called "cyclic polyester" refers to a polyester formed by using a dicarboxylic acid or its alkyl ester as a raw material containing a dicarboxylic acid or its alkyl ester having a cyclic structure.

As polyurethane thermoplastic elastomers, from the viewpoint of molding processability, there can be cited polyurethane thermoplastic elastomers having a hard segment composed of a diisocyanate compound and a glycol having a molecular weight of about 50 to 500, and a soft segment composed of a diisocyanate compound and a long-chain diol. As the aforementioned long-chain diol, a polyether-based long-chain diol such as polyalkylene glycol having a molecular weight of about 500 to 10,000, or a polyester-based long-chain diol such as polyalkylene adipate, polycaprolactone, polycarbonate, etc. can be used. Examples of the diisocyanate compound include phenylene diisocyanate, toluene diisocyanate, xylene diisocyanate, 4,4-diphenylmethane diisocyanate, and hexamethylene diisocyanate. The diisocyanate compound may be the same or different in the soft segment and the hard segment.

Examples of acrylic thermoplastic elastomers include ethylene/acrylate copolymer elastomers, ethylene/methacrylate copolymer elastomers, and acrylic ABA type triblock copolymers composed of acrylate and methacrylate.

Examples of the polystyrene-based elastomer include styrene/butadiene copolymer rubber and styrene/isoprene copolymer rubber.

As the aliphatic polyester resin, polybutylene succinate and polybutylene succinate adipate are preferably used. As the aliphatic aromatic polyester resin, an aliphatic aromatic polyester resin containing adipic acid is preferred, and polybutylene adipate terephthalate is particularly preferred. More preferred is an aliphatic or aliphatic aromatic polyester resin having a glass transition temperature (Tg) of -30°C or less. By using a polyester copolymer having a glass transition temperature of -30°C or less, excellent bending pinhole resistance can be exhibited even in a refrigerated environment.

As the aliphatic polyamide resin, polyamide 11, polyamide 610, polyamide 1010, and polyamide 410 can be preferably used. Furthermore, it can also be a polyamide resin of which at least a part of the raw materials are derived from biomass. By containing a polyamide resin containing raw materials derived from biomass, the bending pinhole resistance can be further improved. As the aliphatic aromatic polyamide resin, polymexylene diamide (MXD6), polyamide 6T, polyamide 6I, polyamide 6T6I, polyamide 9T, etc. can be cited. Among them, MXD6 is preferred from the viewpoint of improving elongation and adhesion.

Regarding the content of the resin (b) other than polyamide 6 contained in the first resin composition forming the substrate layer, the first resin composition is set to 100 mass%, and the content of the resin (b) other than polyamide 6 is 2 mass% to 40 mass% or 2 mass% to 20 mass%, preferably 4 mass% to 15 mass%. By including 2 mass% or more of the resin (b) other than polyamide 6, the effect of bending pinhole resistance can be obtained. By including 40 mass% or less (preferably 20 mass% or less) of the resin (b) other than polyamide 6, the film can be prevented from becoming soft and the puncture strength and impact strength can be prevented from decreasing. Furthermore, it is also possible to prevent the film from being easily stretched and causing pitch deviation during processing such as printing.

The first resin composition forming the substrate layer may contain thermoplastic resins other than polyamide 6 resins within the scope of not impairing the purpose of the present invention. For example, polyamide resins such as polyamide 12 resin, polyamide 66 resin, polyamide 6/12 copolymer resin, polyamide 6/66 copolymer resin, polyamide MXD6 resin, polyamide MXD10 resin, and polyamide 11/6T copolymer resin may be cited. Thermoplastic resins other than polyamide resins may be contained as needed, such as polyester polymers such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene 2,6-naphthalate; and polyolefin polymers such as polyethylene and polypropylene.

The substrate layer may contain other additives such as thermoplastic resins, lubricants, heat stabilizers, antioxidants, antistatic agents, antifogging agents, ultraviolet absorbers, dyes, pigments, etc. as needed.

[Functional layer B] The second resin composition forming the functional layer preferably contains at least polyamide 6. When the second resin composition is set to 100 mass%, the second resin composition preferably contains 70 mass% or more of polyamide 6, more preferably 80 mass% or more, and particularly preferably 90 mass% or more. By containing 70 mass% or more of polyamide 6, a polyamide film having mechanical strength such as impact strength and gas barrier properties can be obtained. When the second resin composition is set to 100 mass%, the upper limit of the content of polyamide 6 is preferably 99 mass% or less, and more preferably 96 mass% or less. That is, the content of polyamide 6 is preferably 70% to 99% by mass, more preferably 80% to 96% by mass, and further preferably 90% to 96% by mass. The polyamide 6 may be the same polyamide 6 as that used in the first resin composition.

The second resin composition forming the functional layer may include a polyamide resin other than polyamide 6. Examples of the polyamide resin other than polyamide 6 include polyamide MXD6 resin, polyamide 11, polyamide 12, and polyamide 66. When the second resin composition includes a polyamide resin other than polyamide 6, the second resin composition is set to 100 mass%, and the content of the polyamide resin other than polyamide 6 is preferably 1 mass% to 30 mass%, more preferably 3 mass% to 20 mass%, and even more preferably 5 mass% to 10 mass%. By including 1 mass% or more, the film can be given slippery properties. On the other hand, if it is more than 30% by mass, there is a risk that the effect of improving the slipperiness of the film may be saturated. As the polyamide resin other than polyamide 6, polyamide MXD6 resin is preferably used.

The second resin composition forming the functional layer may contain microparticles, organic lubricants, etc. as lubricants to improve the film's lubricity. By improving the lubricity, the film's operability is improved and the rupture of the packaging bag due to friction can be reduced.

As the aforementioned fine particles, inorganic fine particles such as silica, kaolin, and zeolite, and polymer organic fine particles such as acrylic and polystyrene can be appropriately selected and used. In addition, from the perspective of transparency and slipperiness, silica fine particles are preferably used.

The preferred average particle size of the microparticles is 0.5 μm to 5.0 μm, more preferably 1.0 μm to 3.0 μm. When the average particle size is 0.5 μm or more, good lubricity can be expected, and when it is 5.0 μm or less, poor appearance due to increased surface roughness of the film can be prevented.

When silicon dioxide particles are used as the particles, the pore volume of silicon dioxide is preferably in the range of 0.5 ml/g to 2.0 ml/g, and more preferably in the range of 0.8 ml/g to 1.6 ml/g.

As the aforementioned organic lubricant, fatty acid amide and/or fatty acid diamide can be used. Examples of fatty acid amide and/or fatty acid diamide include erucic acid amide, stearic acid amide, ethylene distearyl amide, ethylene dioleic acid amide, etc. When the second resin composition is set to 100 mass%, the content of fatty acid amide and/or fatty acid diamide contained in the second resin composition forming the functional layer is preferably 0.01 mass% to 0.40 mass%, and more preferably 0.05 mass% to 0.30 mass%. By being 0.01 mass% or more, the effect of lubricity can be expected. By setting the content to 0.40 mass % or less, the wettability of the printing ink can be ensured when the printing layer is provided on the functional layer side.

The functional layer may contain various additives such as other thermoplastic resins, lubricants, thermal agents, antioxidants, antistatic agents, antifogging agents, ultraviolet absorbers, dyes, pigments, etc.

[Biaxially stretched polyamide film] The biaxially stretched polyamide film of the present invention is preferably a film having at least two layers, namely a substrate layer and a functional layer, and may also be a two-layer structure of substrate layer/functional layer, or a three-layer structure of functional layer/substrate layer/functional layer.

The ethanol permeability of the biaxially stretched polyamide film of the present invention is preferably 6000 g. μm/m ² . 24hr (50% RH/40°C) or more. When the biaxially stretched polyamide film of the present invention is used as a packaging material for an ethanol evaporator, the ethanol impregnated in the nonwoven fabric as the ethanol evaporator slowly evaporates, and a sufficient ethanol gas concentration for maintaining the freshness of the food in the food package can be obtained. When the ethanol permeability is lower than 6000 g. μm/m ² . 24hr (50% RH/40°C), the penetration of the alcohol gas evaporated from the alcohol evaporator is hindered, and there is a possibility that a sufficient alcohol gas concentration for maintaining the freshness of the food in the food package cannot be obtained, which is not preferred. The ethanol penetration rate is preferably 10000g. μm/m ^{2 .} 24hr (50%RH/40℃) or less. By setting the ethanol penetration rate to 10000g. μm/m ^{2 .} 24hr (50%RH/40℃) or less, condensation of ethanol in the package due to increased ethanol penetration can be prevented.

The thickness of the biaxially stretched polyamide film of the present invention is preferably 15 μm or less, more preferably 5 μm to 12 μm. When the thickness of the biaxially stretched polyamide film is 15 μm or less, the alcohol permeability is excellent, and it helps to save resources and reduce waste. When the thickness of the biaxially stretched polyamide film is 5 μm or more, the mechanical strength required for secondary processing such as lamination, coating, and slitting can be fully obtained, so it is better.

The total thickness of the substrate layer and the functional layer (when there are multiple substrate layers and functional layers, the total thickness of each layer) is set to 100%, and the thickness of the substrate layer is preferably 50% to 90%, and more preferably 60% to 80%. By setting the thickness of the substrate layer to 50% or more, bending pinhole resistance can be imparted. By setting the thickness of the substrate layer to 90% or less, friction pinhole resistance can be imparted to the functional layer.

The biaxially stretched polyamide film of the present invention has a stress at 5% elongation obtained by a tensile test in the traveling direction and the width direction of the film, that is, the F5 value is preferably 70 MPa or less, more preferably 60 MPa or less, and further preferably 50 MPa or less. By setting the F5 value to 70 MPa or less, the film becomes soft and is less likely to be damaged by bending fatigue. As the lower limit of the F5 value, it is preferably 20 MPa or more. In terms of preventing the printing spacing deviation caused by the elongation of the film during the secondary processing, it is preferred to set the F5 value to 20 MPa or more. That is, the F5 value is preferably 20 MPa to 70 MPa, more preferably 20 MPa to 60 MPa, and further preferably 20 MPa to 50 MPa. As means for adjusting the F5 value to 20 MPa or more and 70 MPa or less, low-multiple stretching, high-temperature stretching, and addition of resins other than nylon 6 are exemplified. However, from the viewpoint of productivity, addition of resins other than nylon 6 is preferred.

The biaxially stretched polyamide film of the present invention has excellent bending pinhole resistance. When the torsional bending test is performed 1000 times at a temperature of 1°C using a Gelbo bend tester, the number of pinhole defects is 20 or less, preferably 15 or less, and further preferably 10 or less. The fewer the number of pinhole defects after the bending test, the better the bending pinhole resistance. As long as the number of pinholes is preferably 20 or less, and more preferably 15 or less, a packaging bag that is not prone to pinholes can be obtained even when a load is applied to the packaging bag during transportation.

The crystallization parameter (1200cm ^{-1 /1370cm -1 ) of the biaxially stretched polyamide film of the present invention obtained from the intensity ratio of the peak near 1200cm -1} and the peak near 1370cm ^-1 in the spectrum obtained by ATR (Attenuated Total Reflection) measurement of FT ^- IR (Fourier-transform infrared ray spectrophotometer) is preferably 1.0 or more. Here, the peak of 1200cm ^-1 is the absorption derived from the α crystal of nylon ⁶ , and 1370cm ^-1 is the absorption unrelated to crystallization. By setting the crystallization parameter to the range of 1.0 to 1.5, dimensional stability can be obtained. By setting the crystallization parameter to 1.0 or more, dimensional stability is improved, and by setting the crystallization parameter to 1.5 or less, mechanical strength can be obtained.

The heat shrinkage rate of the biaxially stretched polyamide film of the present invention at 160°C for 10 minutes is preferably in the range of 0.6% to 3.0% in both the traveling direction (hereinafter sometimes referred to as MD (Mechanical Direction) direction) and the width direction (hereinafter sometimes referred to as TD (Transverse Direction) direction), and more preferably in the range of 0.5% to 2.0%. By setting the heat shrinkage rate to 3.0% or less, the occurrence of curling and shrinkage can be suppressed when heat is applied in subsequent steps such as lamination and printing. When the heat shrinkage rate is set to 0.6% or more, it is better in terms of excellent impact resistance.

The plane orientation (ΔP) of the biaxially stretched polyamide film of the present invention is preferably 0.050 to 0.070. The plane orientation is obtained by using a refractometer to obtain birefringence, and the refractive index in the length direction is set as Nx, the refractive index in the width direction is set as Ny, and the refractive index in the thickness direction is set as Nz, and is obtained by the following formula. ΔP=(Nx+Ny)/2-Nz By increasing the biaxial stretching ratio, especially the stretching ratio in the TD direction, the plane orientation can be increased. By making the plane orientation greater than 0.05, the mechanical strength of the film such as puncture strength can be obtained. Furthermore, by making the plane orientation less than 0.07, the reduction in productivity can be suppressed.

The impact strength of the biaxially stretched polyamide film of the present invention is preferably 0.6 J or more, more preferably 0.7 J or more.

The puncture strength of the film of the present invention is preferably 6.0 N or more. By setting the puncture strength to 6.0 N or more, even when filling solid contents, it is possible to prevent the bag from being pierced by the contents and causing a hole in the bag, or to prevent the bag from being pierced by external factors during transportation. The upper limit of the puncture strength is not particularly limited, and may be 100 N or less, or 50 N or less.

The maximum dispersion diameter of the resin (b) other than polyamide 6 contained in the substrate layer is preferably 1.0 μm or more. Here, the maximum dispersion diameter refers to the maximum length of the long axis of the resin (b) dispersed in the substrate layer when the substrate layer is observed by a transmission electron microscope (TEM): the unit is μm. An example is shown in Figure 1. Figure 1 is a photograph obtained by observing the cross-section of the film in the direction of travel at a magnification of 2000 times by a transmission electron microscope. The area (domain) with a higher concentration after dyeing is the resin (b). When the dispersion diameter of the resin (b) is 1.0 μm or more, good bending pinhole resistance and ethanol penetration can be obtained. As a reason for obtaining good bending pinhole resistance, it is believed that the reason is that the soft resin (b) is dispersed in polyamide 6 in an immiscible manner, thereby improving the flexibility of the entire film and not being easily damaged by bending fatigue. As a reason for obtaining good ethanol permeability, it is believed that the reason is that the resin (b) is dispersed in polyamide 6 in an immiscible manner, thereby forming a weak interface between polyamide 6 and resin (b), and ethanol permeates the film through the interface. When the maximum dispersion diameter of the resin (b) is less than 1.0μm, mutual solubility is promoted and the characteristics of polyamide 6 as the base material are prominent, so the bending pinhole resistance and ethanol permeability are reduced.

[Method for producing biaxially stretched polyamide film] The method for producing the biaxially stretched polyamide film of the present invention is described. First, the raw resin is melt-extruded using an extruder, extruded from a T-die in a film-like state, cast on a cooling roll for cooling, and an unstretched film having at least a substrate layer and a functional layer laminated thereon is obtained. In order to obtain an unstretched laminated film, a co-extrusion method using a feed block, a multi-manifold, etc. is preferably used. In addition to the co-extrusion method, a dry lamination method, an extrusion lamination method, etc. may also be selected. When lamination is performed by co-extrusion, it is desirable to reduce the difference in melt viscosity between the first resin composition forming the substrate layer and the second resin composition forming the functional layer.

The melting temperature of the resin is preferably 220°C to 350°C. If the melting temperature is below the above, unmelted materials may be produced, resulting in defects and other poor appearance. If the melting temperature is exceeded, deterioration of the resin may be observed, and molecular weight may be reduced and the appearance may deteriorate. The mold temperature is preferably 250°C to 350°C. The cooling roller temperature is preferably -30°C to 80°C, and further preferably 0°C to 50°C. In order to cast the film-like melt extruded from the T-die onto a rotating cooling drum for cooling to obtain an unstretched film, for example, a method using an air knife, an electrostatic sealing method by applying an electrostatic charge, etc. may be preferably applied. In addition, it is preferred that the surface of the unstretched film formed by casting that is opposite to the cooling roll is also cooled. For example, it is preferred to use a method of making the cooling liquid in the tank contact the surface of the unstretched film that is opposite to the cooling roll, a method of applying liquid evaporated by a spray nozzle, or a method of cooling by blowing a high-speed fluid. The unstretched film obtained in the above manner is stretched in biaxial directions to obtain the biaxially stretched polyamide film of the present invention.

As a stretching method, it can be any of a synchronous biaxial stretching method and a step-by-step biaxial stretching method. The step-by-step biaxial stretching method is preferred because it is easy to increase the surface orientation to obtain the puncture strength, easy to adjust the crystallization parameters to obtain the desired dimensional stability, and easy to increase the film forming speed to reduce the manufacturing cost. In any case, one-stage stretching or two-stage stretching or other multi-stage stretching methods can be used as the stretching method in the MD direction. As described below, in terms of physical properties and the uniformity of physical properties in the MD direction and TD direction (isotropy), two-stage stretching or other multi-stage MD direction stretching is better rather than one-stage stretching. The stretching in the MD direction in the step-by-step biaxial stretching method is preferably roller stretching.

The lower limit of the stretching temperature in the MD direction is preferably 50°C, more preferably 55°C, and further preferably 60°C. If the stretching temperature in the MD direction is less than 50°C, the resin may not soften and may be difficult to stretch. The upper limit of the stretching temperature in the MD direction is preferably 120°C, more preferably 115°C, and further preferably 110°C. If the stretching temperature in the MD direction exceeds 120°C, the resin may become too soft and may not be stably stretched. Stretching below 120°C is better in preventing adhesion and breakage to the roller. That is, the stretching temperature in the MD direction is preferably 50°C to 120°C, more preferably 55°C to 115°C, and further preferably 60°C to 110°C.

The lower limit of the stretching ratio in the MD direction (when stretching is performed in multiple stages, the total stretching ratio obtained by multiplying the respective ratios) is preferably 2.2 times, more preferably 2.5 times, and further preferably 2.8 times. If the stretching ratio in the MD direction is less than 2.2 times, sometimes the thickness accuracy in the MD direction is reduced, and the crystallinity becomes too low, resulting in a reduction in impact strength. The upper limit of the stretching ratio in the MD direction is preferably 5.0 times, more preferably 4.5 times, and most preferably 4.0 times. Setting the stretching ratio to 5.0 times or less is preferred from the perspective of both productivity and film stability. That is, the stretching ratio in the MD direction is preferably 2.2 to 5.0 times, more preferably 2.5 to 4.5 times, and further preferably 2.8 to 4.0 times.

In addition, when the stretching in the MD direction is performed in multiple stages, the stretching as described above can be performed in each stage, but the stretching ratio is preferably adjusted so that the sum of the stretching ratios in all MD directions is 5.0 or less. For example, in the case of two-stage stretching, it is preferred to set the stretching ratio in the first stage to between 1.5 and 2.1 times, and the stretching ratio in the second stage to between 1.5 and 1.8 times.

The film stretched in the MD direction is stretched in the TD direction using a tenter, heat-fixed and relaxed (also called a relaxation treatment). The lower limit of the stretching temperature in the TD direction is preferably 50°C, more preferably 55°C, and further preferably 60°C. If it is less than 50°C, the resin may not soften and stretching may become difficult. The upper limit of the stretching temperature in the TD direction is preferably 190°C, more preferably 185°C, and further preferably 180°C. From the viewpoint of inhibiting film crystallization and thus inhibiting fracture, it is preferred to set the stretching temperature in the TD direction to 190°C or less. That is, the stretching temperature in the TD direction is preferably 50°C to 190°C, more preferably 55°C to 185°C, and further preferably 60°C to 180°C.

The lower limit of the stretching ratio in the TD direction (when stretching is performed in multiple stages, the total stretching ratio obtained by multiplying the respective ratios) is preferably 2.8, more preferably 3.2, further preferably 3.5, and particularly preferably 3.8. If it is less than 2.8, in addition to sometimes reducing the thickness accuracy in the TD direction, the crystallinity becomes too low, resulting in reduced impact strength. The upper limit of the stretching ratio in the TD direction is preferably 5.5, more preferably 5.0, further preferably 4.7, particularly preferably 4.5, and most preferably 4.3. From the viewpoint of preventing fracture, it is preferred to set the stretching ratio in the TD direction to 5.5 or less. That is, the stretching ratio in the TD direction is preferably 2.8 to 5.5 times, more preferably 3.2 to 5.0 times, further preferably 3.5 to 4.7 times, particularly preferably 3.8 to 4.5 times, and most preferably 3.8 to 4.3 times.

The lower limit of the heat fixing temperature is preferably 210°C, more preferably 212°C. If the heat fixing temperature is low, the thermal shrinkage rate becomes too large, and the appearance after lamination tends to deteriorate and the lamination strength decreases. The upper limit of the heat fixing temperature is preferably 220°C, more preferably 218°C. If the heat fixing temperature is too high, the impact strength tends to decrease. The heat fixing time is preferably 0.5 seconds to 20 seconds, and further preferably 1 second to 15 seconds. The heat fixing time can be set to an appropriate time taking into account the heat fixing temperature and the wind speed in the heat fixing area. From the viewpoint of preventing the embrittlement of the film, it is better to set the heat fixing temperature to 220°C or less. From the viewpoint of improving dimensional stability and laminate strength, the heat setting temperature is preferably set to 210°C or higher. That is, the heat setting temperature is preferably 210°C to 220°C, more preferably 212°C to 218°C.

Relaxation after heat setting is effective for controlling thermal shrinkage. The temperature of the relaxation treatment is selected from the range of the heat setting temperature to the Tg of the resin, preferably (heat setting temperature (℃) - 10)℃ or more and (Tg (℃) + 10)℃ or less. If the relaxation temperature is too high, the shrinkage rate becomes too fast and causes strain, etc., which is not good. On the contrary, if the relaxation temperature is too low, it will not become a relaxation treatment, but only become a droop, the thermal shrinkage rate will not decrease, and the dimensional stability will deteriorate. The lower limit of the relaxation rate of the relaxation treatment is preferably 0.5%, and more preferably 1%. If it does not reach 0.5%, the thermal shrinkage rate may not be sufficiently reduced. The upper limit of the relaxation rate is preferably 20%, more preferably 15%, and further preferably 10%. If it exceeds 20%, relaxation may occur in the tenter and production may become difficult. In terms of reducing the thermal shrinkage rate, it is preferred to set the relaxation rate to 0.5% or more. In terms of preventing the film from sagging, it is preferred to set the relaxation rate to 20% or less. That is, the relaxation rate is preferably 0.5% to 20%, more preferably 1% to 15%, and further preferably 1% to 10%.

Furthermore, the biaxially stretched polyamide film of the present invention may be subjected to heat treatment or moisture conditioning treatment according to the application to improve the dimensional stability. In addition, in order to improve the adhesion of the film surface, it may be subjected to corona treatment, coating treatment, flame treatment, etc., or printing processing, and evaporation processing of metals, inorganic oxides, etc. may be performed.

One embodiment of the present invention is to process the biaxially stretched polyamide film of the present invention into a laminated film laminated with a sealant film to provide a packaging material. Examples of the sealant film include: unstretched linear low-density polyethylene (LLDPE; Linear Low Density Polyethylene) film, unstretched polypropylene (CPP (Cast Polypropylene; Cast Polypropylene)) film, ethylene/vinyl alcohol copolymer (EVOH; Ethylene vinyl alcohol) film, etc. The sealant film can be laminated in a manner of directly contacting the biaxially stretched polyamide film, and can also be laminated via other layers such as a bonding agent layer. The aforementioned packaging material may include a printing layer. The packaging material of the present invention is bagged and processed into a packaging bag.

Another embodiment of the present invention provides a packaging material for ethanol evaporator, which is composed of a laminate of at least two layers including the biaxially stretched polyamide film of the present invention and a breathable resin film or a non-woven fabric. The breathable resin film is not particularly limited as long as it is a film that is breathable or ethanol permeable, and examples thereof include: unstretched linear low-density polyethylene (LLDPE) film, unstretched polypropylene (CPP) film, ethylene/vinyl alcohol copolymer (EVOH) film, ethylene/vinyl acetate copolymer (EVA; Ethylene Vinyl Acetate) film, etc. Furthermore, a non-woven fabric may be used instead of the breathable resin film, or the non-woven fabric may be used in combination with the breathable resin film. As the nonwoven fabric substrate, for example, polyester, polypropylene, rayon, nylon, biodegradable fiber, pulp, cotton, etc. can be used, and polypropylene can also be used appropriately. As the nonwoven fabric, any of short-fiber nonwoven fabric and long-fiber nonwoven fabric can also be used. The above nonwoven fabric can be a paper substrate.

This application is based on the priority claim of Japanese Special Application No. 2023-055926 filed on March 30, 2023. All contents of the specification of Japanese Special Application No. 2023-055926 filed on March 30, 2023 are incorporated into this application for reference. [Example]

The evaluation of the membrane was performed by the following measurement method. Unless otherwise specified, the measurement was performed in a measurement room at 23°C and a relative humidity of 65%.

(1) Film thickness The film was divided into 10 equal parts in the TD direction (for narrow films, the film was divided into 10 equal parts in a way that ensures the width of the film can be measured), 10 sheets were overlapped and 100 mm of the film was cut in the MD direction, and the film was conditioned for more than 2 hours at a temperature of 23°C and a relative humidity of 65%. The thickness of the center of each sample was measured using a thickness tester manufactured by TESTER SANGYO, and the average value was set as the thickness.

(2) Thermal shrinkage of film In addition to setting the test temperature to 160°C and the heating time to 10 minutes, the thermal shrinkage was measured using the following formula in accordance with the dimensional change test method described in JIS C2318. Thermal shrinkage = [(length before treatment - length after treatment) / length before treatment] × 100 (%)

(3) F5 value of film The obtained biaxially stretched polyamide film was left to stand for 2 hours in a room adjusted to 23°C and a relative humidity of 50% RH, and then cut into elongated pieces with a length of 150 mm (100 mm between points) in the measuring direction of the MD and TD of the film and a length of 15 mm in the direction perpendicular to the measuring direction to obtain a sample. A tensile tester (AG-1I manufactured by Shimadzu Corporation) equipped with a 1 kN load cell and a sample chuck was used to perform the tensile test at a test speed of 200 mm/min. Based on the obtained stress-elongation curve, the stress at which the film was elongated by 5% was set as the F5 value and treated as a substitute value for the elastic modulus. The number of samples was measured as 3, and the average value of each was calculated.

(4) Impact strength of film Measured using a film impact tester manufactured by Toyo Seiki Seisaku-sho Co., Ltd.

(5) Puncture strength of film The test is carried out in accordance with "2. Strength test method" of "Standards for food, additives, etc. Part 3: Utensils and containers and packaging" in the Food Sanitation Law (Notice No. 20 of the Ministry of Health, Labor and Welfare of Japan in 1982 (Showa 57)). A needle with a tip diameter of 0.7 mm is pierced through the film at a piercing speed of 50 mm/min, and the strength of the needle when it penetrates the film is measured as the puncture strength. The measurement is carried out at room temperature (23°C), and the value obtained is set as the puncture strength of the film (unit: N).

(6) Crystallization parameters FT-IR ATR measurement was performed on the front and back sides of the sample under the following conditions. FT-IR device: FTS-60A/896 manufactured by Bio Rad DIGILAB Co., Ltd. 1st reflection ATR accessory: golden gate MKII (manufactured by SPECAC) Internal reflection element: diamond Incident angle: 45° Resolution: 4 cm ^-1 Accumulated times: 128 times The crystallinity is calculated by the intensity ratio of the absorption appearing near 1200 cm ^-1 to the absorption appearing near 1370 cm ^-1 (1200 cm ^-1 /1370 cm ^-1 ). Here, 1200 cm ^-1 is the absorption of α crystal of nylon 6, and 1370 cm ^-1 is the absorption not related to crystallization.

(7) Planar orientation of the film For the sample, the refractive index in the length direction (nx), the refractive index in the width direction (ny), and the refractive index in the thickness direction (nz) of the film were measured by Abbe refractometer using the sodium D line as the light source according to JIS K 7142-1996 A method, and the planar orientation coefficient was calculated by the calculation formula of formula (1). Planar orientation coefficient (ΔP) = (nx + ny) / 2 − nz

(8) Ethanol penetration rate Put degreased cotton soaked in ethanol into a cup, cover the cup with a film, and measure the ethanol penetration rate based on the weight loss after leaving it at a relative humidity of 50% and 40°C for 24 hours.

(9) Dispersion diameter of resin A cross section of the membrane in any direction is cut out in a manner that allows observation, and the cross section is embedded in epoxy resin. The embedded sample is cut into ultrathin sections using a microtome equipped with an ultrasonic knife. In order to confirm the dispersion shape of the resin (b), an appropriate staining treatment is performed according to the type of resin (b). The test piece is carbon-evaporated to prepare a sample for TEM observation. The JEM2100 transmission electron microscope manufactured by JEOL Ltd. is used at an accelerating voltage of 200 kV for observation and photographing. When photographing, the magnification is adjusted so that the entire substrate layer falls within the photographing range. In the obtained photograph, the longest length among the lengths of the long axis of the resin dispersed in the base layer is set as the maximum dispersion diameter.

(10) Film resistance to bending pinholes The number of bending fatigue pinholes was measured using a Gelbo bend tester manufactured by TESTER SANGYO Co., Ltd. by the following method. Specifically, a polyester adhesive was applied to the biaxially stretched polyamide film prepared in the embodiment, and then a 40 μm thick linear low-density polyethylene film (L-LDPE film: manufactured by Toyobo Co., Ltd.; L4102) was dry-laminated and aged for 3 days at 40°C to prepare a laminated film. The obtained laminated film was cut into 12 inches × 8 inches and made into a cylinder with a diameter of 3.5 inches. One end of the cylindrical film was fixed to the fixed head side of the Gelbo bending tester, and the other end was fixed to the movable head side. The initial holding interval was set to 7 inches. A 440-degree twist was applied within the first 3.5 inches of the stroke, and the subsequent 2.5 inches were completed by a straight horizontal motion. This bending fatigue was performed 1000 times at a speed of 40 times/minute, and the number of pinholes generated in the laminated film was counted. In addition, the measurement was performed in an environment of 1°C. Place the L-LDPE film side of the test film as the lower surface on the filter paper (Advantec; No.50), and fix the four corners with Cellotape (registered trademark). Apply ink (Pilot ink (product number INK-350-Blue) diluted 5 times with pure water) on the test film and use a rubber roller to extend it to the entire surface. Wipe off the excess ink, then remove the test film and measure the number of ink dots attached to the filter paper.

The resin compositions of the base layer and the functional layer are as follows. Resin composition constituting the base material layer A: Polyamide 6 (manufactured by Toyobo Co., Ltd.; relative viscosity 2.8; melting point 220°C) Resin other than polyamide 6 (b) ・Polybutylene adipate terephthalate PBAT (ecoflex F-Blend C1200 manufactured by BASF) ・Polyethylene Elastomer PEE (Tefabloc TPC A1400N manufactured by Mitsubishi Chemical Co., Ltd.) ・Polyamide Elastomer PAE (PEBAX 4033 SA01 manufactured by Arkema) ・Polyolefin Elastomer POE (MELTHENE H6051 manufactured by Tosoh Co., Ltd.) ・Polybutylene succinate PBS (Showa High Polymer Co., Ltd.; Bionolle 1001) ・Polyamide 11 (Rilsan manufactured by Arkema; melting point 186°C)

Resin composition constituting functional layer B: Polyamide 6 (manufactured by Toyobo Co., Ltd.; relative viscosity 2.8; melting point 220°C) 90 parts by mass; Polyamide MXD6 (manufactured by Mitsubishi Gas Chemical Co., Ltd.; relative viscosity 2.1; melting point 237°C) 10 parts by mass; Porous silica particles (manufactured by Fuji Silysia Chemical Co., Ltd.; average particle size 2.0μm; pore volume 1.6ml/g) 0.54 parts by mass; Fatty acid diamide (ethylene distearylamide manufactured by Kyoeisha Chemical Co., Ltd.) 0.15 parts by mass

(Example 1 to Example 7) The raw materials of the substrate layer: layer A and the functional layer: layer B are mixed by the formulation listed in Table 1. Using an apparatus consisting of two extruders and a 380 mm wide co-extrusion T-die, the layers are laminated by the feed block method in the structure of functional layer: layer B/substrate layer: layer A/functional layer: layer B, and the molten resin of the resin composition listed in Table 1 is extruded from the T-die into a film, cast on a cooling roll regulated at 20°C to make it electrostatically close, so as to obtain an unstretched film with a thickness of 100 μm to 200 μm.

The obtained unstretched film was guided to a roll stretching machine, and stretched 1.73 times in the MD direction at 80°C by using the circumferential speed difference of the rolls, and then further stretched 1.85 times at 70°C. Next, the uniaxially stretched film was guided to a tenter-type stretching machine, preheated at 60°C, stretched 1.2 times at 120°C, stretched 1.7 times at 130°C, stretched 2.0 times at 160°C in the TD direction, and heat-fixed at 218°C, and then 7% relaxation treatment was performed at 218°C, and the surface of one side was subjected to corona discharge treatment to obtain a biaxially stretched polyamide film. The discharge rate of the extruder was adjusted so that the thickness of the base layer became 8 μm and the thickness of the functional layer became 1 μm on the front and back sides respectively, with respect to the thickness of the biaxially stretched polyamide film of 10 μm.

(Example 8, Example 9) By adjusting the composition of the feed block and the discharge amount of the extruder according to the formulation described in Table 1, the biaxially stretched polyamide film was obtained by the same method as in Examples 1 to 7, with the total thickness of the biaxially stretched polyamide film being 15 μm, the thickness of the substrate layer being 12 μm, and the thickness of the functional layer being 1.5 μm on the surface and back.

(Comparative Examples 1 to 4, Comparative Example 6) Except that the resin compositions of the substrate layer and the functional layer were changed as shown in Table 2, a biaxially stretched polyamide film was obtained by the same method as in Example 1. The evaluation results of the obtained film are shown in Table 2.

(Comparative Example 5) The rotation speed of the extruder for discharging the resin composition constituting the substrate layer was increased within a range where the target thickness did not increase, and adjustments were made to enhance mixing. In addition, a biaxially stretched polyamide film was obtained by the same method as in Examples 1 to 7, Comparative Examples 1 to 4, and Comparative Example 6.

The evaluation results of the films obtained in Examples and Comparative Examples are shown in Table 1.

[Table 1A] Unit Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Substrate (A) Layer Composition Polyamide 6(a) Quality 96 92 80 90 Resins other than polyamide 6 (b) Type − PBAT PBAT PBAT PBS Addition amount Quality 4 8 20 10 Function (B) Layer Composition Polyamide 6 Quality 90 90 90 90 Polyamide MXD6 Quality 10 10 10 10 Silicon dioxide particles Quality 0.54 0.54 0.54 0.54 Fatty acid diamide Quality 0.15 0.15 0.15 0.15 Overall thickness μm 10 10 10 10 Substrate layer thickness μm 8.0 8.0 8.0 8.0 Layered structure − B/A/B B/A/B B/A/B B/A/B Extension method − Step by step Step by step Step by step Step by step MD stretching temperature ℃ 80 80 80 80 MD stretch ratio times 3.15 3.15 3.15 3.15 TD preheating temperature ℃ 60 60 60 60 TD stretching temperature ℃ 130 130 130 130 TD stretch ratio times 4.0 4.0 4.0 4.0 TD heat fixation temperature ℃ 216 216 216 216 TD relaxation temperature ℃ 216 216 216 216 TD relaxation rate % 7 7 7 7 Fog % 3.7 4.1 5.6 4.2 friction Static friction coefficient − 0.40 0.46 0.48 0.48 Dynamic friction coefficient − 0.37 0.44 0.46 0.46 Stress at 5% elongation MD direction MPa 52.0 46.0 41.0 44.0 TD Direction MPa 43.0 40.0 37.0 36.0 Thermal shrinkage MD direction % 1.0 1.1 0.9 1.1 TD Direction % 1.0 1.2 1.0 1.2 Impact strength J 0.83 0.78 0.72 0.75 Puncture strength N 8.0 8.2 7.2 7.9 Crystallization parameters − 1.10 1.12 1.15 1.12 Surface orientation (ΔP) − 0.058 0.057 0.054 0.055 Ethanol penetration g． μm/ m ² ． 24hr 7000 7500 9000 7800 Maximum dispersion diameter of resin (b) other than polyamide 6 μm 4.0 4.1 4.0 3.6 Bend pinhole Piece 10 2 0 1

[Table 1B] Unit Embodiment 5 Embodiment 6 Embodiment 7 Embodiment 8 Substrate (A) Layer Composition Polyamide 6(a) Quality 88 96 94 92 Resins other than polyamide 6 (b) Type − PEE PAE POE PBAT Addition amount Quality 12 4 6 8 Function (B) Layer Composition Polyamide 6 Quality 90 90 90 90 Polyamide MXD6 Quality 10 10 10 10 Silicon dioxide particles Quality 0.54 0.54 0.54 0.54 Fatty acid diamide Quality 0.15 0.15 0.15 0.15 Overall thickness μm 10 10 10 15 Substrate layer thickness μm 8.0 8.0 8.0 12.0 Layered structure − B/A/B B/A/B B/A/B B/A/B Extension method − Step by step Step by step Step by step Step by step MD stretching temperature ℃ 80 80 80 80 MD stretch ratio times 3.15 3.15 3.15 3.15 TD preheating temperature ℃ 60 60 60 60 TD stretching temperature ℃ 130 130 130 130 TD stretch ratio times 4.0 4.0 4.0 4.0 TD heat fixation temperature ℃ 216 216 216 217 TD relaxation temperature ℃ 216 216 216 217 TD relaxation rate % 7 7 7 7 Fog % 4.2 3.0 5.0 2.5 friction Static friction coefficient − 0.53 0.53 0.53 0.63 Dynamic friction coefficient − 0.51 0.51 0.51 0.65 Stress at 5% elongation MD direction MPa 43.0 43.0 43.0 54.0 TD Direction MPa 35.0 35.0 35.0 44.0 Thermal shrinkage MD direction % 1.3 1.3 1.3 0.9 TD Direction % 1.2 1.2 1.2 1.1 Impact strength J 0.76 0.82 0.74 1.12 Puncture strength N 7.6 7.9 7.4 13.2 Crystallization parameters − 1.15 1.14 1.10 1.12 Surface orientation (ΔP) − 0.056 0.056 0.055 0.057 Ethanol penetration g． μm/ m ² ． 24hr 8000 6800 7000 6500 Maximum dispersion diameter of resin (b) other than polyamide 6 μm 4.4 2.0 4.2 4.3 Bend pinhole Piece 2 2 2 1

[Table 1C] Unit Embodiment 9 Comparison Example 1 Comparison Example 2 Comparison Example 3 Substrate (A) Layer Composition Polyamide 6(a) Quality 86 100 100 100 Resins other than polyamide 6 (b) Type − PA11 − − − Addition amount Quality 14 − − − Function (B) Layer Composition Polyamide 6 Quality 90 90 90 90 Polyamide MXD6 Quality 10 10 10 10 Silicon dioxide particles Quality 0.54 0.54 0.54 0.54 Fatty acid diamide Quality 0.15 0.15 0.15 0.15 Overall thickness μm 15 10 15 25 Substrate layer thickness μm 12.0 8.0 12.0 20.0 Layered structure − B/A/B B/A/B B/A/B B/A/B Extension method − Step by step Step by step Step by step Step by step MD stretching temperature ℃ 80 80 80 80 MD stretch ratio times 3.15 3.15 3.15 3.15 TD preheating temperature ℃ 60 60 60 60 TD stretching temperature ℃ 130 130 130 130 TD stretch ratio times 4.0 4.0 4.0 4.0 TD heat fixation temperature ℃ 217 216 217 218 TD relaxation temperature ℃ 217 216 217 218 TD relaxation rate % 7 7 7 7 Fog % 2.8 3.1 2.2 3.5 friction Static friction coefficient − 0.62 0.32 0.60 0.50 Dynamic friction coefficient − 0.61 0.30 0.58 0.48 Stress at 5% elongation MD direction MPa 54.0 54.0 53.0 53.0 TD Direction MPa 44.0 44.0 42.0 42.0 Thermal shrinkage MD direction % 0.9 1.1 1.1 1.1 TD Direction % 1.1 1.2 1.2 1.2 Impact strength J 1.15 0.83 1.20 2.00 Puncture strength N 13.8 8.2 14.5 24.0 Crystallization parameters − 1.08 1.13 1.09 1.08 Surface orientation (ΔP) − 0.057 0.055 0.056 0.057 Ethanol penetration g． μm/ m ² ． 24hr 6700 5700 5300 3700 Maximum dispersion diameter of resin (b) other than polyamide 6 μm 3.0 − − − Bend pinhole Piece 12 16 18 25

[Table 1D] Unit Comparison Example 4 Comparison Example 5 Comparison Example 6 Substrate (A) Layer Composition Polyamide 6(a) Quality 98 92 60 Resins other than polyamide 6 (b) Type − PBAT PBAT PBAT Addition amount Quality 2 8 40 Function (B) Layer Composition Polyamide 6 Quality 90 90 90 Polyamide MXD6 Quality 10 10 10 Silicon dioxide particles Quality 0.54 0.54 0.54 Fatty acid diamide Quality 0.15 0.15 0.15 Overall thickness μm 10 10 10 Substrate layer thickness μm 8.0 8.0 8.0 Layered structure − B/A/B B/A/B B/A/B Extension method − Step by step Step by step Step by step MD stretching temperature ℃ 80 80 80 MD stretch ratio times 3.15 3.15 3.15 TD preheating temperature ℃ 60 60 60 TD stretching temperature ℃ 130 130 130 TD stretch ratio times 4.0 4.0 4.0 TD heat fixation temperature ℃ 216 216 216 TD relaxation temperature ℃ 216 216 216 TD relaxation rate % 7 7 7 Fog % 3.5 3.5 7.2 friction Static friction coefficient − 0.25 0.25 0.62 Dynamic friction coefficient − 0.25 0.25 0.61 Stress at 5% elongation MD direction MPa 53.0 53.0 38.0 TD Direction MPa 42.0 42.0 36.0 Thermal shrinkage MD direction % 1.1 1.1 0.8 TD Direction % 1.2 1.2 0.9 Impact strength J 0.82 0.80 0.65 Puncture strength N 8.3 8.5 5.5 Crystallization parameters − 1.12 1.14 1.13 Surface orientation (ΔP) − 0.056 0.056 0.055 Ethanol penetration g． μm/ m ² ． 24hr 5700 5700 16000 Maximum dispersion diameter of resin (b) other than polyamide 6 μm 4.0 0.5 4.0 Bend pinhole Piece 12 18 0

The films described in Examples 1 to 9 have good bending pinhole resistance, dimensional stability, puncture strength, and ethanol permeability, and are suitable for use as alcohol evaporators. It is believed that the film has a high orientation with a plane orientation of 0.5 or more, a high crystallization with a crystallization parameter of 1.0 or more, and the resin (b) has a dispersion diameter of 1 μm or more, so that an interface with low adhesion strength is formed with the polyamide resin, and the ethanol permeability is improved by utilizing this interface. Furthermore, it is believed that the flexibility of the substrate layer A itself is improved by the dispersion of the resin (b), and the bending pinhole resistance is improved.

The film described in Comparative Example 1 has excellent dimensional stability and puncture strength, but poor bending pinhole resistance and ethanol penetration resistance. It is believed that when the plane orientation ΔP is greater than 0.05 and the crystallization parameter is in the range of 1 to 1.5, the dimensional stability and puncture strength are good, but as crystallization progresses, the brittleness of the film increases, and the bending pinhole resistance and ethanol penetration decrease.

Although the thickness of the film described in Comparative Example 2 is 15 μm, no resin other than polyamide 6 is added to the substrate layer, so a dispersed structure achieved by phase separation is not generated, and ethanol penetration achieved by utilizing the dispersed interface does not occur, and the ethanol penetration rate cannot meet the requirements for use as an alcohol evaporator.

The film described in Comparative Example 3 has a relatively thick thickness of 25 μm, and no resin other than polyamide 6 is added to the base layer, so the bending pinhole resistance and ethanol permeability cannot satisfy the application of alcohol evaporation agent.

In the film described in Comparative Example 4, the amount of PBAT added as the resin (b) is small, the interface between polyamide 6 and PBAT is small, and the ethanol permeability is insufficient.

The maximum dispersion diameter of the resin (b) of the film described in Comparative Example 5 is 0.5 μm, which is relatively small, and the miscibility with polyamide 6 is progressing, and good ethanol permeability and good bending pinhole resistance cannot be obtained.

The membrane described in Comparative Example 6 was added with 40% by mass of PBAT. As a result, the ethanol permeability increased to 16000 g. μm/m ² . 24hr (50% RH/40°C). As for the use as an ethanol evaporator, the ethanol evaporated quickly.

[Figure 1] is a transmission electron microscope photograph obtained by observing the dispersion state of the polyamide 6 resin (a) and the resin other than polyamide 6 (b) contained in the film.

Claims (11)

A biaxially stretched polyamide film comprises polyamide 6 as a main component. In the biaxially stretched polyamide film, the ethanol permeability is 6000g.μm/ ^m2.24hr to 10000g.μm/ ^m2.24hr (50%RH/40℃), the thickness is less than 15μm, the thermal shrinkage rate of the film in the traveling direction and the width direction when heat-treated at 160℃ for 10 minutes is less than 2.0%, the crystallization parameter of the surface is in the range of 1.0 to 1.5, and the puncture strength is more than 6.0N. The biaxially stretched polyamide film as described in claim 1, wherein the biaxially stretched polyamide film has at least one layer containing 60 mass % to 98 mass % of a polyamide 6 resin (a) and 2 mass % to 40 mass % of a resin other than polyamide 6 (b). The biaxially stretched polyamide film as described in claim 2, wherein the resin (b) other than the aforementioned polyamide 6 is at least one selected from the group consisting of polyolefins, ionic polymers, polyester elastomers, polyamide elastomers, polyolefin elastomers, polystyrene elastomers, polyurethane elastomers, polyvinyl chloride elastomers; aliphatic polyester resins; aliphatic aromatic polyester resins; aliphatic polyamide resins; and aliphatic aromatic polyamide resins. The biaxially stretched polyamide film as recited in claim 3, wherein the aliphatic aromatic polyester resin is polybutylene adipate terephthalate resin. The biaxially stretched polyamide film as described in claim 2, wherein the resin (b) other than the polyamide 6 is derived from biomass and is at least one polyamide selected from the group consisting of polyamide 11, polyamide 410, polyamide 610, and polyamide 1010. The biaxially stretched polyamide film as recited in claim 2, wherein the maximum dispersion diameter of the resin (b) other than the polyamide 6 is 1.0 μm or more. The biaxially stretched polyamide film as recited in claim 1, wherein the stress at 5% elongation in both the traveling direction and the width direction of the biaxially stretched polyamide film is 70.0 MPa or less. The biaxially stretched polyamide film as recited in claim 1 has a plane orientation (ΔP) of greater than 0.050. The biaxially stretched polyamide film as described in claim 1, wherein a laminated film of the biaxially stretched polyamide film and a polyethylene film having a thickness of 40 μm is prepared, and when the laminated film is bent 1000 times at a temperature of 1° C. using a Gelbo bend tester, the number of pinholes generated is less than 20. A food packaging material comprises a biaxially stretched polyamide film as described in any one of claims 1 to 9, and a sealant film. A packaging material for ethanol transpiration agent, comprising a laminate of at least two layers including a biaxially stretched polyamide film as described in any one of claims 1 to 9 and a breathable resin film or non-woven fabric.