JP7543779B2 - Method for producing gas barrier polyamide film - Google Patents

Description

The present invention relates to a gas-barrier polyamide film that has excellent impact resistance and abrasion pinhole resistance and uses polyamide 6 chemically recycled from waste polyamide products. The gas-barrier polyamide film of the present invention is suitable for use as a food packaging film, etc.

In recent years, along with the growing calls for the creation of a recycling-oriented society, there is a desire to move away from fossil fuels in the materials sector, just as in the energy sector.
In recent years, marine plastic pollution has become a major problem.
When plastics from marine litter flow into the ocean, they break down into tiny plastic particles (microplastics) due to ultraviolet light and physical wear. When marine organisms eat these particles, they may be exposed to chemicals contained in or adsorbed to them, and this may have an impact on top predators through the food chain, making this a global problem.
Much of the marine plastic waste mentioned above has washed up from land, and while most of it is disposable plastic containers and packaging, it also includes fishing lines and nets.
Given this background, in order to reduce marine plastic waste, it is important to reduce plastic waste by recycling and making effective use of this plastic waste.

On the other hand, biaxially oriented films made of aliphatic polyamides, such as polyamide 6, have been widely used as various packaging film materials due to their excellent impact resistance and resistance to pinholes caused by bending. However, these polyamide films used for packaging also contribute to the plastic waste mentioned above, so there is a demand for the use of recycled materials.

There are three ways to recycle nylon 6: thermal recycling, in which it is incinerated and the heat energy is recovered; material recycling, in which it is melted and remolded for reuse; and chemical recycling, in which it is chemically depolymerized to return it to the raw nylon material and reused in nylon production, etc.

Of these, the chemical recycling method is an industrially useful recycling method because it breaks down nylon 6 into its raw material, caprolactam, which is then recovered and reused as a raw material for nylon 6.

For example, Patent Document 1 discloses a recycling method in which used nylon clothing products are collected, depolymerized to recover ε-caprolactam, which is then purified, polymerized, and melt-spun or molded into nylon fibers or nylon molded products.
This technology makes it possible to recycle collected clothing products by returning them to their raw materials and reusing them. In addition, by disassembling and refining collected clothing products, high-purity, high-quality raw materials (raw monomers) can be obtained, which can be recycled to produce high-quality nylon 6 products and can be recycled repeatedly. Furthermore, the work of collecting and sorting collected clothing products can be greatly reduced.

Nylon resin recycled using the above-mentioned chemical recycling method has been used primarily as a raw material for fibers and molded products, but has not been put to practical use as food packaging film.

In addition, gas barrier films made by laminating thin films of aluminum, aluminum oxide, silicon oxide, etc. onto polyamide films by vapor deposition or other methods are widely used in the food packaging field, and there is a demand for these to also have a reduced environmental impact.

Japanese Patent Application Publication No. 7-310204

The present invention was devised in light of the above-mentioned conventional techniques. The object of the present invention is to provide a gas-barrier polyamide film that has excellent impact resistance and abrasion pinhole resistance and is made from polyamide 6 that is chemically recycled from waste polyamide products.

That is, the present invention comprises the following:
[1] A gas barrier polyamide film, comprising a biaxially oriented polyamide film made of a polyamide resin containing 70% by mass or more of polyamide 6, in which 4 to 90% by mass of the polyamide 6 is chemically recycled polyamide 6, and an inorganic thin film layer is laminated on at least one side of the biaxially oriented polyamide film.
[2] The gas barrier polyamide film according to [1], wherein the biaxially oriented polyamide film contains 5 to 60% by mass of mechanically recycled polyamide 6.
[3] A gas barrier polyamide film comprising a biaxially oriented polyamide film having a surface layer (B layer) laminated on at least one side of a base layer (A layer), and an inorganic thin film layer laminated on at least one side of the biaxially oriented polyamide film, wherein the base layer (A layer) is the biaxially oriented polyamide film, and the B layer is made of a polyamide resin composition containing 70% by mass or more of polyamide 6.
[4] The gas barrier polyamide film according to [3], characterized in that the base layer (A layer) contains 5 to 80 mass % of mechanically recycled polyamide 6 and the surface layer (B layer) contains 0 to 30 mass % of mechanically recycled polyamide 6. [5] The gas barrier polyamide film according to any one of [1] to [4], characterized in that the gas barrier polyamide film satisfies the following (a) to (c):
(a) a puncture strength of 0.65 N/μm or more;
(b) Impact strength is 0.9 J/15 μm or more.
(c) In the abrasion pinhole resistance test, the distance until pinholes appear is 2,900 cm or more.
[6] The gas barrier polyamide film according to any one of [1] to [5] above, which satisfies the following (d) and (e):
(d) haze of 2.6% or less;
(e) The coefficient of kinetic friction is 1.0 or less.
[7] The gas barrier polyamide film according to any one of [1] to [6], characterized in that after being laminated with a polyethylene sealant film, the gas barrier polyamide film has a water-resistant laminate strength of 4.0 N/15 mm or more.
[8] A laminated film obtained by laminating a sealant film on the gas barrier polyamide film according to any one of [1] to [7].
[9] A packaging bag using the laminated film described in [8].

According to the present invention, by laminating an inorganic thin film layer onto biaxially oriented polyamide blended with polyamide 6 chemically recycled from waste polyamide products, a polyamide film that has excellent impact resistance, bending pinhole resistance, and gas barrier properties and can reduce the environmental load can be obtained.

Schematic diagram of a friction pinhole resistance evaluation device

1: Head of fastness tester 2: Cardboard board 3: Mount for holding sample 4: Film sample folded in four 5: Direction of rubbing amplitude

The gas barrier polyamide film of the present invention will be described in detail below.
The gas barrier polyamide film of the present invention is a gas barrier polyamide film comprising a biaxially oriented polyamide film (layer A) made of a polyamide resin containing 70% by mass or more of polyamide 6, with 5 to 90% by mass of the polyamide 6 being chemically recycled polyamide 6. The gas barrier polyamide film is also a gas barrier polyamide film comprising a biaxially oriented polyamide film having a layer B laminated on at least one side of the biaxially oriented polyamide film, and an inorganic thin film layer laminated on at least one side of the biaxially oriented polyamide film, with the layer B containing 70% by mass or more of polyamide 6 resin.

[Biaxially oriented polyamide film or substrate layer (A layer)]
The biaxially oriented polyamide film or base layer (layer A) in the present invention contains 70% by mass or more of polyamide 6 resin, thereby obtaining excellent mechanical strength such as impact strength and gas barrier properties such as oxygen, which are inherent to biaxially oriented polyamide films made of polyamide 6 resin.
The biaxially oriented polyamide film or base layer (layer A) in the present invention is a polyamide resin layer containing at least 70% by mass or more of polyamide 6, and 5 to 90% by mass of the polyamide 6 is polyamide 6 chemically recycled from waste polyamide 6 products such as waste plastic products, waste tire rubber, fibers, and fishing nets.
The biaxially oriented polyamide film or layer A in the present invention contains 5 to 90% by mass of polyamide 6 chemically recycled from waste polyamide 6 products such as waste plastic products, waste tire rubber, fibers, and fishing nets, and is therefore a biaxially oriented polyamide film with reduced environmental impact that uses raw materials recycled from polyamide products that were previously discarded as garbage. In addition, by selecting a specific stretching method, a gas barrier polyamide film that simultaneously has excellent puncture resistance and abrasion pinhole resistance can be obtained.
[Polyamide 6]
The polyamide 6 used in the present invention is usually produced by ring-opening polymerization of ε-caprolactam. The polyamide 6 obtained by ring-opening polymerization is usually subjected to removal of lactam monomer with hot water, followed by drying and melt extrusion in an extruder.
The relative viscosity of the polyamide 6 used in the present invention is preferably 1.8 to 4.5, and more preferably 2.6 to 3.2. If the relative viscosity is less than 1.8, the impact strength of the film is insufficient. If the relative viscosity is more than 4.5, the load on the extruder increases, making it difficult to obtain an unstretched film before stretching.

[Chemically recycled polyamide 6]
The polyamide 6 used in the A layer may be polyamide 6 polymerized from commonly used monomers derived from fossil fuels, or polyamide 6 chemically recycled from waste polyamide 6 products such as waste plastic products, waste tire rubber, fibers, and fishing nets.

As a method for obtaining chemically recycled polyamide 6 from waste polyamide 6 products, for example, the method disclosed in the above-mentioned Patent Document 1 can be used. That is, a method can be used in which used nylon (polyamide) products are collected, depolymerized to recover ε-caprolactam, which is then purified and polymerized.

<Depolymerization conditions>
In the depolymerization carried out in producing the chemically recycled polyamide 6 used in the A layer, the polyamide 6 fiber is usually depolymerized by heating. The depolymerization may or may not use a catalyst. The depolymerization may be carried out in the absence (dry process) or in the presence (wet process) of water.

The pressure of depolymerization carried out when producing the chemically recycled polyamide 6 used in layer A may be reduced pressure, normal pressure, or increased pressure. The temperature of depolymerization is usually 100°C to 400°C, preferably 200°C to 350°C, and more preferably 220°C to 300°C. If the temperature is low, the polyamide 6 product does not melt, and the depolymerization rate is slow. If the temperature is high, decomposition of unnecessary polyamide 6 monomer (i.e., caprolactam) occurs, which may reduce the purity of the recovered caprolactam.

When a catalyst is used in the depolymerization carried out in producing the chemically recycled polyamide 6 used in the A layer, an acid catalyst or a base catalyst is usually used. Examples of acid catalysts include phosphoric acid, boric acid, sulfuric acid, organic acids, organic sulfonic acids, solid acids, and salts thereof, and examples of base catalysts include alkali hydroxides, alkali salts, alkaline earth hydroxides, alkaline earth salts, organic bases, and solid bases. Preferred examples include phosphoric acid, boric acid, organic acids, alkali hydroxides, and alkali salts. More preferred examples include phosphoric acid, sodium phosphate, potassium phosphate, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate.

The amount of acid catalyst used in the above depolymerization is usually preferably 0.01 to 50% by mass relative to the polyamide 6 fiber component. More preferably, it is 0.01 to 20% by mass, and even more preferably, it is 0.5 to 10% by mass. If the amount of catalyst used is small, the reaction rate will be slow, and if it is large, side reactions will increase and the catalyst cost will increase, which is economically disadvantageous.

The above depolymerization can be carried out in the absence (dry) or presence (wet) of water. In the case of wet depolymerization, the amount of water used is preferably 0.1 to 50 times by mass relative to the polyamide 6 product components such as fibers. More preferably, it is 0.5 to 20 times by mass, and even more preferably, it is 1 to 10 times by mass. If the amount of water used is small, the reaction rate will be slow, and if it is large, the concentration of the recovered caprolactam aqueous solution will be low, which is disadvantageous in obtaining caprolactam.

The method for recovering the caprolactam recovered by the above method is not particularly limited. For example, when dry depolymerization is performed, the generated caprolactam is distilled from the reactor by vacuum distillation to obtain recovered caprolactam. After the depolymerization reaction is completed, the caprolactam may be taken out by vacuum distillation. Alternatively, the caprolactam may be taken out continuously as the reaction proceeds.
In the case of wet depolymerization, the produced caprolactam is distilled together with water from the reactor to obtain a recovered aqueous caprolactam solution. After the depolymerization reaction is completed, the caprolactam may be extracted by vacuum distillation or continuously as the reaction proceeds.
In order to obtain caprolactam of even higher purity, the recovered caprolactam can be combined with other purification methods, such as precision distillation of the recovered caprolactam, distillation under reduced pressure with the addition of a small amount of sodium hydroxide, treatment with activated carbon, ion exchange treatment, and recrystallization.

[Mechanically recycled polyamide 6]
Polyamide 6, which is mechanically recycled waste material generated during the manufacturing and processing of biaxially oriented polyamide films, can be further added to layer A.

The mechanically recycled polyamide 6 referred to above is a raw material made by recovering scrap material generated during the manufacture of biaxially oriented polyamide film, such as non-standard, unshippable film and offcuts (edge trims), and pelletizing them through melt extrusion or compression molding.

The lower limit of the amount of mechanically recycled polyamide 6 added to layer A is preferably 10% by mass, more preferably 15% by mass, and even more preferably 20% by mass. If the amount of mechanically recycled polyamide 6 added is less than the above range, the recycled ratio in the film will be low.
The upper limit of the amount of mechanically recycled polyamide 6 added to layer A is preferably 50% by mass, more preferably 40% by mass, and even more preferably 30% by mass. If the amount of mechanically recycled polyamide added exceeds the above range, the film may be colored more strongly or have a higher haze value, which may impair the appearance of the film. Alternatively, the amount of degraded material may increase during the production of the film, which may deteriorate the film formability.

[Secondary materials, additives]
The biaxially oriented polyamide film or the base layer (A layer) in the present invention may contain various additives such as other thermoplastic resins, lubricants, heat stabilizers, antioxidants, antistatic agents, antifogging agents, ultraviolet absorbers, dyes, pigments, etc., as necessary.

<Other thermoplastic resins>
The biaxially oriented polyamide film or base layer (A layer) in the present invention may contain a thermoplastic resin in addition to the polyamide 6 and the polyamide resin at least partly derived from biomass as raw materials, within the scope of the present invention. Examples of the polyamide resin include polyamide 12, polyamide 66, polyamide 6-12 copolymer, polyamide 6-66 copolymer, polyamide MXD6, and other polyamide-based resins.
If necessary, thermoplastic resins other than polyamides, for example, polyester polymers such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate, and polyolefin polymers such as polyethylene and polypropylene, may be contained.
It is preferable that the raw materials for these thermoplastic resins are derived from biomass, since they do not affect the increase or decrease in carbon dioxide on the ground and therefore the environmental load can be reduced.

<Lubricant>
In the present invention, the biaxially oriented polyamide film or the base layer (layer A) preferably contains fine particles or an organic lubricant such as a fatty acid amide as a lubricant in order to improve the slipperiness and make it easy to handle.

The fine particles can be appropriately selected from inorganic fine particles such as silica, kaolin, zeolite, etc., polymeric organic fine particles such as acrylic and polystyrene, etc. From the viewpoints of transparency and lubricity, it is preferable to use silica fine particles.
The average particle size of the fine particles is preferably 0.5 to 5.0 μm, more preferably 1.0 to 3.0 μm. If the average particle size is less than 0.5 μm, a large amount of the fine particles is required to obtain good slip properties. On the other hand, if the average particle size exceeds 5.0 μm, the surface roughness of the film tends to become too large, resulting in poor appearance.

When using the silica fine particles, the pore volume of the silica is preferably in the range of 0.5 to 2.0 ml/g, and more preferably 0.8 to 1.6 ml/g. If the pore volume is less than 0.5 ml/g, voids are likely to occur and the transparency of the film will deteriorate, and if the pore volume exceeds 2.0 ml/g, the fine particles will tend to be less likely to form surface protrusions.

In the present invention, the biaxially oriented polyamide film or the base layer (layer A) may contain a fatty acid amide and/or a fatty acid bisamide for the purpose of improving the slip property. Examples of the fatty acid amide and/or the fatty acid bisamide include erucic acid amide, stearic acid amide, ethylene bisstearic acid amide, ethylene bisbehenic acid amide, and ethylene bisoleic acid amide.
The content of fatty acid amide and/or fatty acid bisamide in the biaxially stretched polyamide film or base layer (A layer) in the present invention is preferably 0.01 to 0.40% by mass, more preferably 0.05 to 0.30% by mass. If the content of fatty acid amide and/or fatty acid bisamide is less than the above range, the slipping property tends to be deteriorated. On the other hand, if it exceeds the above range, the wettability tends to be deteriorated.

In the present invention, polyamide resins such as polyamide MXD6, polyamide 12, polyamide 66, polyamide 6-12 copolymer, and polyamide 6-66 copolymer can be added to the biaxially stretched polyamide film or substrate layer (layer A) to improve slipperiness. Polyamide MXD6 is particularly preferred, and it is preferable to add 1 to 10 mass %.

<Antioxidants>
The biaxially oriented polyamide film or the substrate layer (layer A) in the present invention may contain an antioxidant.
The antioxidant is preferably a phenol-based antioxidant. The phenol-based antioxidant is preferably a completely hindered phenol-based compound or a partially hindered phenol-based compound. Examples of the phenol-based antioxidant include tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane, stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and 3,9-bis[1,1-dimethyl-2-[β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]2,4,8,10-tetraoxaspiro[5,5]undecane.
By including the phenol-based antioxidant, the film-forming operability of the biaxially oriented polyamide film or the base layer (A layer) is improved. In particular, when using recycled film as a raw material, the resin is prone to thermal degradation, which tends to cause film-forming operational problems and increase production costs. On the other hand, by including the antioxidant, the thermal degradation of the resin is suppressed and the operability is improved.

[Layer B (surface layer)]
The layer B in the present invention is a layer containing polyamide 6 in an amount of 70% by mass or more.
In the present invention, layer B contains 70% by mass or more of polyamide 6, so that a biaxially oriented polyamide film having excellent mechanical strength such as impact strength and gas barrier properties such as oxygen can be obtained.
As the polyamide 6, polyamide 6 polymerized from new raw materials, chemically recycled polyamide 6, and mechanically recycled polyamide 6 can be used, similar to the polyamide 6 used in the layer A.
Layer B in the present invention may contain various additives such as other thermoplastic resins, lubricants, heat stabilizers, antioxidants, antistatic agents, antifogging agents, ultraviolet absorbers, dyes, pigments, etc., depending on the functions to be imparted to the surface of layer B.
When layer B is used on the outside of a packaging bag, it is necessary to have friction pinhole resistance, so it is not preferable to contain soft resins such as polyamide elastomers and polyolefin elastomers or substances that generate a large amount of voids. Also, when it is desired to improve friction pinhole resistance, it is better to reduce the content of mechanically recycled polyamide 6 to less than 30% by mass, and more preferably to 15% by mass or less.

The layer B in the present invention may contain a thermoplastic resin other than the above-mentioned polyamide 6, provided that the object of the present invention is not impaired. Examples of such polyamide-based resins include polyamide MXD6, polyamide 11, polyamide 12, polyamide 66, polyamide 6-12 copolymer, and polyamide 6-66 copolymer.
If necessary, thermoplastic resins other than polyamides, for example, polyester polymers such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate, and polyolefin polymers such as polyethylene and polypropylene, may be contained.

In the present invention, it is preferred that layer B contains fine particles or an organic lubricant as a lubricant in order to improve the film slipping property.
By improving the slipperiness, the film becomes easier to handle and the risk of packaging bags breaking due to friction is reduced.

The above-mentioned 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 fine particles. From the standpoint of transparency and slipperiness, it is preferable to use silica fine particles.

The preferred average particle size of the above fine particles is 0.5 to 5.0 μm, and more preferably 1.0 to 3.0 μm. If the average particle size is less than 0.5 μm, a large amount is required to obtain good slip properties. On the other hand, if it exceeds 5.0 μm, the surface roughness of the film tends to become too large, resulting in a poor appearance.

When using the above silica fine particles, the silica pore volume range is preferably 0.5 to 2.0 ml/g, and more preferably 0.8 to 1.6 ml/g. If the pore volume is less than 0.5 ml/g, voids are more likely to occur, and the transparency of the film will deteriorate. If the pore volume exceeds 2.0 ml/g, the fine particles tend not to form surface protrusions.

The organic lubricant may contain a fatty acid amide and/or a fatty acid bisamide, such as erucic acid amide, stearic acid amide, ethylene bisstearic acid amide, ethylene bisbehenic acid amide, or ethylene bisoleic acid amide.
The content of the fatty acid amide and/or fatty acid bisamide added to the layer B is preferably 0.01 to 0.40% by mass, and more preferably 0.05 to 0.30% by mass. If the content of the fatty acid amide and/or fatty acid bisamide is less than the above range, the slipping property tends to be deteriorated. On the other hand, if it exceeds the above range, the wettability tends to be deteriorated.

In the present invention, polyamide resins other than polyamide 6, such as polyamide MXD6, polyamide 11, polyamide 12, polyamide 66, polyamide 6-12 copolymer, polyamide 6-66 copolymer, etc., can be added to layer B for the purpose of improving the slipperiness of the film. Polyamide MXD6 is particularly preferred, and it is preferable to add 1 to 10% by mass. If it is less than 1% by mass, the effect of improving the slipperiness of the film is small. If it is more than 10% by mass, the effect of improving the slipperiness of the film becomes saturated.
Polyamide MXD6 resin is produced by the polycondensation of metaxylylenediamine and adipic acid.
The relative viscosity of the polyamide MXD6 is preferably 1.8 to 4.5, and more preferably 2.0 to 3.2. If the relative viscosity is less than 1.8 or more than 4.5, it may be difficult to knead it with the polyamide resin in the extruder.

In addition, polyamide resins other than polyamide 6 can be added to layer B to improve adhesion. In this case, copolymer polyamide resins such as polyamide 6-12 copolymer and polyamide 6-66 copolymer are preferred.

Additives and auxiliary materials such as lubricants and antioxidants can be added to layer A and/or layer B of the gas barrier polyamide film of the present invention during resin polymerization or melt extrusion in an extruder. A high-concentration master batch can be prepared and added to the polyamide resin during film production. These known methods can be used.

[Inorganic thin film layer]
The gas barrier polyamide film of the present invention can be imparted with gas barrier properties by providing an inorganic thin film layer (C layer) on the surface of the biaxially stretched polyamide film.
The inorganic thin film layer is a thin film made of a metal or an inorganic oxide. There is no particular restriction on the material forming the inorganic thin film layer as long as it can be made into a thin film, but from the viewpoint of gas barrier properties, inorganic oxides such as silicon oxide (silica), aluminum oxide (alumina), and a mixture of silicon oxide and aluminum oxide are preferred. In particular, a composite oxide of silicon oxide and aluminum oxide is preferred from the viewpoint of achieving both flexibility and denseness of the thin film layer. In this composite oxide, the mixture ratio of silicon oxide and aluminum oxide is preferably in the range of 20 to 70 mass% Al in terms of the mass ratio of the metal content. If the Al concentration is less than 20 mass%, the water vapor barrier property may be reduced. On the other hand, if it exceeds 70 mass%, the inorganic thin film layer tends to become hard, and there is a risk that the film will be destroyed during secondary processing such as printing or lamination, resulting in a decrease in gas barrier property. Note that silicon oxide here refers to various silicon oxides such as SiO and SiO2 or a mixture thereof, and aluminum oxide refers to various aluminum oxides such as AlO and Al2O3 or a mixture thereof.

The thickness of the inorganic thin film layer is usually 1 to 100 nm, preferably 5 to 50 nm. If the thickness of the inorganic thin film layer is less than 1 nm, it may be difficult to obtain satisfactory gas barrier properties. On the other hand, if the thickness is made excessively thick, exceeding 100 nm, the corresponding improvement in gas barrier properties cannot be obtained, and it is actually disadvantageous in terms of bending resistance and manufacturing costs.

There are no particular limitations on the method for forming the inorganic thin film layer, and any known deposition method may be used, such as physical deposition methods (PVD methods) such as vacuum deposition, sputtering, and ion plating, or chemical deposition (CVD). Below, a typical method for forming an inorganic thin film layer will be described using a silicon oxide/aluminum oxide thin film as an example. For example, when using vacuum deposition, a mixture of SiO2 and Al2O3, or a mixture of SiO2 and Al, is preferably used as the deposition raw material. Particles are usually used as these deposition raw materials, and in this case, it is desirable that the size of each particle is large enough that the pressure during deposition does not change, and the preferred particle diameter is 1 mm to 5 mm. Heating can be performed by resistance heating, high-frequency induction heating, electron beam heating, laser heating, or other methods. It is also possible to introduce oxygen, nitrogen, hydrogen, argon, carbon dioxide, water vapor, or other reactive gases, or to use means such as ozone addition and ion assist to employ reactive deposition. Furthermore, the deposition conditions can be changed as desired, such as by applying a bias to the deposition target (the laminated film used for deposition) or by heating or cooling the deposition target. Such deposition materials, reactive gases, bias, heating/cooling of the deposition target, etc. can also be changed in the same way when using the sputtering method or CVD method.

[Protective Layer]
In the present invention, a protective layer can also be formed on the inorganic thin film layer (layer C). The inorganic thin film layer may not be a completely dense film, but may have minute defects scattered therein. Therefore, by forming a protective layer by applying a specific resin composition for protective layer described later onto the inorganic thin film layer, the resin in the resin composition for protective layer penetrates into the defective parts of the inorganic thin film layer, resulting in an effect of stabilizing the gas barrier properties. In addition, by using a material having gas barrier properties for the protective layer itself, the gas barrier performance of the laminated film is also greatly improved.

Examples of the resin composition used for the protective layer formed on the surface of the inorganic thin film layer of the gas barrier polyamide film of the present invention include resins such as urethane-based resins, polyester-based resins, acrylic-based resins, titanate-based resins, isocyanate-based resins, imine-based resins, and polybutadiene-based resins to which a curing agent such as an epoxy-based curing agent, an isocyanate-based curing agent, or a melamine-based curing agent has been added.
The urethane resin is preferred because the polar group of the urethane bond interacts with the inorganic thin film layer and the presence of amorphous portions gives it flexibility, so that damage to the inorganic thin film layer can be suppressed even when a bending load is applied.
The acid value of the urethane resin is preferably within the range of 10 to 60 mgKOH/g, more preferably within the range of 15 to 55 mgKOH/g, and even more preferably within the range of 20 to 50 mgKOH/g. When the acid value of the urethane resin is within the above range, the liquid stability is improved when the resin is made into an aqueous dispersion, and the protective layer can be uniformly deposited on the highly polar inorganic thin film, resulting in a good coat appearance.

The urethane resin preferably has a glass transition temperature (Tg) of 80°C or higher, more preferably 90°C or higher. By making the Tg 80°C or higher, it is possible to reduce swelling of the protective layer due to molecular motion during the moist heat treatment process (heating - keeping the temperature - cooling).

From the viewpoint of improving gas barrier properties, it is more preferable to use a urethane resin containing an aromatic or araliphatic diisocyanate component as a main constituent component as the urethane resin.
Among these, it is particularly preferable to contain a metaxylylene diisocyanate component. By using the above resin, the cohesive strength of the urethane bond can be further increased due to the stacking effect between aromatic rings, and as a result, good gas barrier properties can be obtained.

In the present invention, the proportion of aromatic or araliphatic diisocyanate in the urethane resin is preferably 50 mol% or more (50 to 100 mol%) out of 100 mol% of the polyisocyanate component (F). The total proportion of aromatic or araliphatic diisocyanate is preferably 60 to 100 mol%, more preferably 70 to 100 mol%, and even more preferably 80 to 100 mol%. As such a resin, the "Takelac (registered trademark) WPB" series available from Mitsui Chemicals, Inc. can be suitably used. If the total proportion of aromatic or araliphatic diisocyanate is less than 50 mol%, good gas barrier properties may not be obtained.

The urethane resin preferably has a carboxylic acid group (carboxyl group) from the viewpoint of improving the affinity with the inorganic thin film layer. In order to introduce a carboxylic acid (salt) group into the urethane resin, for example, a polyol compound having a carboxylic acid group, such as dimethylolpropionic acid or dimethylolbutanoic acid, may be introduced as a copolymerization component as a polyol component. In addition, after synthesizing the urethane resin containing a carboxylic acid group, the urethane resin in a water dispersion can be obtained by neutralizing it with a salt forming agent. Specific examples of the salt forming agent include ammonia, trialkylamines such as trimethylamine, triethylamine, triisopropylamine, tri-n-propylamine, and tri-n-butylamine, N-alkylmorpholines such as N-methylmorpholine and N-ethylmorpholine, and N-dialkylalkanolamines such as N-dimethylethanolamine and N-diethylethanolamine. These may be used alone or in combination of two or more.
Examples of the solvent include aromatic solvents such as benzene and toluene; alcohol solvents such as methanol and ethanol; ketone solvents such as acetone and methyl ethyl ketone; ester solvents such as ethyl acetate and butyl acetate; and polyhydric alcohol derivatives such as ethylene glycol monomethyl ether.

[Method of producing gas barrier polyamide film]
The gas barrier polyamide film of the present invention is produced by forming an inorganic thin film layer on the biaxially oriented polyamide film of the present invention by the above-mentioned method.
<Method for producing biaxially oriented polyamide film>
The biaxially stretched polyamide film of the present invention can be produced by a known production method. For example, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be mentioned. The sequential biaxial stretching method is preferable because it can increase the film production speed and is advantageous in terms of production costs.
The method for producing the biaxially stretched polyamide film of the present invention will now be described in further detail.
First, a raw material resin is melt-extruded using an extruder, extruded from a T-die into a film, and cast onto a cooling roll for cooling to obtain an unstretched film.
The melting temperature of the resin is preferably 200 to 300° C. If it is lower than the above, unmelted matter may occur, resulting in defects and other poor appearance, whereas if it exceeds the above, deterioration of the resin may be observed, resulting in a decrease in molecular weight and a decrease in appearance.
When a surface layer (layer B) is laminated onto a base layer (layer A), it is preferable to obtain an unstretched film by coextrusion using a feed block, a multi-manifold, or the like.

The cooling roll temperature is preferably from -30 to 80°C, and more preferably from 0 to 50°C.
In order to obtain an unstretched film by casting the film-like molten material extruded from a T-die onto a rotating cooling drum and cooling it, for example, a method using an air knife or an electrostatic adhesion method in which a static charge is applied can be preferably used. The latter method is particularly preferably used.

It is also preferable to cool the side of the cast unstretched film opposite the cooling roll. For example, it is preferable to use a combination of a method of contacting the side of the unstretched film opposite the cooling roll with a cooling liquid in a tank, a method of applying a liquid that evaporates with a spray nozzle, and a method of cooling by spraying a high-speed fluid. The unstretched film obtained in this manner is stretched biaxially to obtain a biaxially stretched polyamide film.

As a method for stretching in the MD direction, multi-stage stretching such as one-stage stretching or two-stage stretching can be used. As described later, multi-stage MD stretching such as two-stage stretching is preferred in terms of physical properties and uniformity of physical properties in the MD direction and the TD direction (isotropy) rather than one-stage stretching.
In the sequential biaxial stretching method, stretching in the MD direction is preferably performed by roll stretching.

The lower limit of the MD stretching temperature is preferably 50° C., more preferably 55° C., and further preferably 60° C. If the temperature is less than 50° C., the resin does not soften, and stretching may become difficult.
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 temperature exceeds 120° C., the resin becomes too soft and stable stretching may not be possible.

The lower limit of the stretch ratio in the MD direction (when stretching in multiple stages, the total stretch ratio multiplied by each stretch ratio) is preferably 2.2, more preferably 2.5, and even more preferably 2.8. If it is less than 2.2, the thickness accuracy in the MD direction decreases, and the crystallinity becomes too low, which may reduce the 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. If it exceeds 5.0 times, the subsequent stretching may become difficult.

When stretching in the MD direction is performed in multiple stages, the above-mentioned stretching is possible for each stretch, but the stretching ratios must be adjusted so that the product of all stretching ratios in the MD direction is 5.0 or less. For example, in the case of two-stage stretching, it is preferable to stretch the first stage at 1.5 to 2.1 times and the second stage at 1.5 to 1.8 times.

The film stretched in the MD direction is stretched in the TD direction by a tenter, heat-set, and then subjected to a relaxation treatment (also called a relaxation treatment).
The lower limit of the TD stretching temperature is preferably 50° C., more preferably 55° C., and further preferably 60° C. If the temperature is less than 50° C., the resin does 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. If the temperature exceeds 190° C., crystallization may occur, making stretching difficult.

The lower limit of the stretch ratio in the TD direction (when stretching in multiple stages, the total stretch ratio multiplied by each stretch ratio) is preferably 2.8, more preferably 3.2, even more preferably 3.5, and particularly preferably 3.8. If it is less than 2.8, the thickness accuracy in the TD direction decreases, and the crystallinity becomes too low, which may reduce the impact strength.
The upper limit of the stretching ratio in the TD direction is preferably 5.5 times, more preferably 5.0 times, still more preferably 4.7 times, particularly preferably 4.5 times, and most preferably 4.3 times. If it exceeds 5.5 times, the productivity may be significantly reduced.

The selection of the heat setting temperature is an important factor in the present invention. As the heat setting temperature is increased, the crystallization and orientation relaxation of the film progresses, improving the impact strength and reducing the heat shrinkage rate. On the other hand, if the heat setting temperature is low, the crystallization and orientation relaxation are insufficient and the heat shrinkage rate cannot be sufficiently reduced. ) Also, if the heat setting temperature is too high, the resin deteriorates and the film rapidly loses its toughness, such as its impact strength.

The lower limit of the heat setting temperature is preferably 180° C., more preferably 200° C. If the heat setting temperature is too low, the heat shrinkage rate becomes too large, which tends to deteriorate the appearance after lamination and to reduce the laminate strength.
The upper limit of the heat setting temperature is preferably 230° C., more preferably 220° C. If the heat setting temperature is too high, the impact strength tends to decrease.

The heat setting time is preferably 0.5 to 20 seconds. More preferably, it is 1 to 15 seconds. The heat setting time can be set appropriately by balancing the heat setting temperature and the wind speed in the heat setting zone. If the heat setting conditions are too weak, crystallization and orientation relaxation will be insufficient, causing the above problems. If the heat setting conditions are too strong, the film toughness will decrease.

Relaxation treatment after heat setting is effective in controlling the thermal shrinkage rate. The temperature for relaxation treatment can be selected in the range from the heat setting temperature to the glass transition temperature (Tg) of the resin, but it is preferably from the heat setting temperature -10°C to Tg +10°C. If the relaxation temperature is too high, the shrinkage rate will be too fast, which is undesirable and can cause distortion. Conversely, if the relaxation temperature is too low, relaxation treatment will not occur and the material will simply slacken, the thermal shrinkage rate will not decrease, and dimensional stability will deteriorate.

The lower limit of the relaxation rate in the relaxation treatment is preferably 0.5%, more preferably 1%. If it is less than 0.5%, the heat shrinkage rate may not be reduced sufficiently.
The upper limit of the relaxation rate is preferably 20%, more preferably 15%, and further preferably 10%. If it exceeds 20%, sagging occurs in the tenter, which may make production difficult.

To increase the adhesive strength with the inorganic thin film layer or the sealant film, the surface of the laminated stretched polyamide film and/or the surface of the adhesive modification layer may be subjected to corona treatment, flame treatment, etc. Also, to increase the adhesive strength between the laminated stretched polyamide film and the adhesive modification layer, the surface of the laminated stretched polyamide film on the adhesive modification layer side may be subjected to corona treatment, flame treatment, etc.

[Gas Barrier Film Thickness Configuration]
The thickness of the gas barrier polyamide film in the present invention is not particularly limited, but when used as a packaging material, it is usually 100 μm or less, and generally, a thickness of 5 to 50 μm is used, and particularly, a thickness of 8 to 30 μm is used.

When the gas barrier polyamide film of the present invention has a laminated structure of a base layer and a surface layer, and when the B layer is to be imparted with slipperiness and abrasion pinhole resistance, the thickness of the surface layer (B layer) is preferably 0.5 to 8 μm in order to realize these functions. In addition, in order to increase the recycling rate, the thickness of the base layer (A layer) is preferably 50 to 93%, and more preferably 70 to 93%, of the total thickness of the A layer and the B layer.

[Properties of gas barrier polyamide film]
The gas barrier polyamide film of the present invention preferably has less than 20 pinhole defects when a twist bending test is performed 1000 times at a temperature of 1° C. using a Gelbo flex tester according to the measurement method described in the Examples. More preferably, the number of pinhole defects is less than 10. The fewer the number of pinhole defects after the bending test, the better the bending pinhole resistance is. If the number of pinholes is 10 or less, a packaging bag that is less likely to develop pinholes even when a load is applied to the packaging bag during transportation, etc. can be obtained.

Furthermore, the gas barrier polyamide film of the present invention preferably has a distance until pinholes appear in a friction pinhole resistance test of 2000 cm or more, more preferably 2900 cm or more, and even more preferably 3000 cm or more. The longer the distance until pinholes appear, the better the friction pinhole resistance is, and if the distance until pinholes appear is 2900 cm or more, a packaging bag that is less likely to have pinholes even if the packaging bag rubs against a cardboard box or the like during transportation can be obtained.
In the present invention, a gas barrier polyamide film having excellent properties in both bending pinhole resistance and friction pinhole resistance can be obtained by optimizing the raw material compositions of layers A and B. The gas barrier polyamide film of the present invention having these properties is highly useful as a packaging film because it is less likely to develop pinholes during transportation.

The gas barrier polyamide film of the present invention preferably has a heat shrinkage rate at 160°C for 10 minutes in the range of 0.6 to 5.0% in both the machine direction (hereinafter abbreviated as MD direction) and the width direction (hereinafter abbreviated as TD direction), more preferably 0.6 to 3.0%. If the heat shrinkage rate exceeds 5.0%, curling or shrinkage may occur when heat is applied in the next process, such as lamination or printing. Furthermore, the lamination strength with the sealant film may be weakened. Although it is possible to reduce the heat shrinkage rate to less than 0.6%, it may become mechanically fragile. Furthermore, this is not preferable because it reduces productivity.

Since excellent impact resistance is a feature of biaxially oriented polyamide films, the impact strength of the highly adhesive polyamide film of the present invention is preferably 0.7 J/15 μm or more. More preferably, the impact strength is 0.9 J/15 μm or more. Although a higher impact strength is preferable, it is difficult to make it higher than 1.5 J/15 μm.
The puncture strength of the highly adhesive polyamide film of the present invention is preferably 0.65 N/μm or more. The more preferable puncture resistance strength is 0.70 N/μm or more. Although a higher puncture strength is preferable, it is difficult to make the puncture strength higher than 1.0 N/μm.
The plane orientation coefficient of the highly adhesive polyamide film of the present invention is preferably 0.045 or more. More preferably, the plane orientation coefficient is 0.050 or more. The larger the plane orientation coefficient, the greater the impact strength and puncture strength, which is preferable. However, in order to make the plane orientation coefficient greater than 0.080, the stretch ratio must be increased, which is difficult because the film is prone to breakage during the stretching process.

The haze value of the gas barrier polyamide film of the present invention is preferably 10% or less, more preferably 5% or less, and further preferably 2.6% or less.
A small haze value means good transparency and gloss, so when used for packaging bags, beautiful printing is possible and the product value is increased.
Adding fine particles to improve the slipperiness of the film increases the haze value, so it is preferable to add fine particles only to the surface layer, layer B, or to contain a larger amount of fine particles therein and to reduce the content in layer A, since this will result in a film with good slipperiness and a small haze value.

The gas barrier polyamide film of the present invention preferably has a laminate strength of 4.0 N/15 mm or more after being laminated with the polyethylene sealant described in the Examples.
The gas barrier polyamide film of the present invention is usually laminated with a sealant film and then processed into a packaging bag. If the laminate strength is 4.0 N/15 mm or more, when a packaging bag is produced using the gas barrier polyamide film of the present invention in various lamination configurations, the strength of the seal portion is sufficient, and a strong packaging bag that is difficult to tear can be obtained.
In order to increase the lamination strength to 4.0 N/15 mm or more, the gas barrier polyamide film of the present invention can be subjected to corona treatment, coating treatment, flame treatment, or the like.

The gas barrier polyamide film of the present invention can be subjected to heat treatment or humidity conditioning treatment to improve dimensional stability depending on the application. In addition, to improve the adhesion of the film surface, corona treatment, coating treatment, flame treatment, printing, deposition of metals, inorganic oxides, etc. are also possible. As the deposition film formed by deposition processing, aluminum deposition film, and deposition film of silicon oxide or aluminum oxide alone or a mixture are preferably used. Furthermore, by coating a protective layer on these deposition films, oxygen and hydrogen barrier properties can be improved.

The gas barrier polyamide film of the present invention is laminated with a sealant film or the like to form a laminate film, and then processed into packaging bags such as bottom-sealed bags, side-sealed bags, three-side-sealed bags, pillow bags, standing pouches, gusseted bags, and square-bottom bags.
Examples of the sealant film include an unstretched linear low density polyethylene film, an unstretched polypropylene film, and an ethylene-vinyl alcohol copolymer resin film.
The layer structure of the laminated film using the gas barrier polyamide film of the present invention is not particularly limited as long as the gas barrier polyamide film according to the embodiment of the present invention is contained in the laminated film. The film used for the laminated film may be made of either petrochemically derived raw materials or biomass-derived raw materials, but polylactic acid, polyethylene terephthalate, polybutylene succinate, polyethylene, polyethylene furanoate, etc., polymerized using biomass-derived raw materials are preferred in terms of reducing environmental load.

Examples of layer configurations of the laminated film of the present invention, where the boundary between layers is represented by /, include ONY/joint/LLDPE, ONY/joint/CPP, ONY/joint/Al/joint/CPP, ONY/joint/Al/joint/LLDPE, ONY/PE/Al/joint/LLDPE, ONY/joint/Al/PE/LLDPE, PET/joint/ONY/joint/LLDPE, PET/joint/ONY/PE/LLDPE, PET/joint/ONY/joint/Al/joint/LLDP. E, PET/Contact/Al/Contact/ONY/Contact/LLDPE, PET/Contact/Al/Contact/ONY/PE/LLDPE, PET/PE/Al/PE/ONY/PE/LLDPE, PET/Contact/ONY/Contact/CPP, PET/Contact/ONY/Contact/Al/Contact/CPP, PET/Contact/Al/ Contact/ONY/Contact/CPP, ONY/Contact/PET/Contact/LLDPE, ONY/Contact/PET/PE/LLDPE, ONY/Contact/PET/Contact/CPP , ONY//Al//PET//LLDPE, ONY/bond/Al/bond/PET/PE/LLDPE, ONY/PE/LLDPE, ONY/PE/CPP, ONY/PE/Al/PE, ONY/PE/Al/PE/LLDPE, OPP/bond/ONY/bond/LLDPE, ONY/bond/EVOH/bond/LLDPE, ONY/bond/EVOH/bond/CPP, ONY/bond/aluminum or inorganic oxide vapor-deposited PET/bond/LLDPE, Examples include ONY/bond/aluminum-vapor-deposited PET/bond/ONY/bond/LLDPE, ONY/bond/aluminum-vapor-deposited PET/PE/LLDPE, ONY/PE/aluminum-vapor-deposited PET/PE/LLDPE, ONY/bond/aluminum-vapor-deposited PET/bond/CPP, PET/bond/aluminum-vapor-deposited PET/bond/ONY/bond/LLDPE, CPP/bond/ONY/bond/LLDPE, ONY/bond/aluminum-vapor-deposited LLDPE, ONY/bond/aluminum-vapor-deposited CPP, etc.
The abbreviations used in the above layer structure are as follows:
ONY: gas barrier polyamide film of the present invention, PET: stretched polyethylene terephthalate film, LLDPE: unstretched linear low density polyethylene film, CPP: unstretched polypropylene film, OPP: stretched polypropylene film, PE: extrusion laminate or unstretched low density polyethylene film, Al: aluminum foil, EVOH: ethylene-vinyl alcohol copolymer resin, Ad: adhesive layer for bonding films together, aluminum or inorganic oxide vapor deposition means that aluminum or inorganic oxide is vapor-deposited.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. The films were evaluated using the following measurement methods. Unless otherwise specified, measurements were performed in a measurement room with an environment of 23°C and a relative humidity of 65%.

(1) Recycled film ratio The recycled film ratio is calculated as the proportion of chemically recycled and mechanically recycled materials to the total raw materials of the film, and expressed as a percentage.
(2) Film Thickness Divide the film into 10 equal parts in the TD direction (for narrow films, divide them so that the width is sufficient to measure the thickness), cut out 10 pieces of 100 mm film in the MD direction, and condition them for 2 hours or more in an environment of 23°C and 65% relative humidity. The thickness of the center of each sample was measured using a thickness measuring device manufactured by Tester Sangyo, and the average value was taken as the thickness.

(3) Haze Value of Film: Measured using a direct-reading haze meter manufactured by Toyo Seiki Seisakusho Co., Ltd. in accordance with JIS-K-7105.
(4) Dynamic Friction Coefficient of Film The dynamic friction coefficient between the outer surfaces of the film rolls was evaluated under the following conditions in accordance with JIS-C2151. The test specimen had a width of 130 mm and a length of 250 mm, and the test speed was 150 mm/min.

(5) Impact strength of film: Measured using a film impact tester manufactured by Toyo Seiki Seisakusho Co., Ltd. The measured value was converted to a value per 15 μm thickness and expressed as J (joule)/15 μm.
(6) Planar Orientation Degree of Film For a sample, the refractive index in the longitudinal direction (Nx), the refractive index in the width direction (Ny), and the refractive index in the thickness direction (Nz) of the film were measured using an Abbe refractometer with sodium D line as a light source according to JIS K 7142-1996, Method A, and the planar orientation coefficient was calculated according to the calculation formula (1).
Planar orientation coefficient (ΔP) = (Nx+Ny)/2-Nz (1)
(7) Puncture strength of film The obtained polyester film was sampled into a 5 cm square, and the puncture strength of the film was measured in accordance with JIS Z1707 using a digital force gauge "ZTS-500N", an electric measuring stand "MX2-500N" and a puncture jig "TKS-250N" manufactured by Imada Co., Ltd. The unit was N/μm.

(8) Bending Fatigue Pinhole Resistance of Film The number of pinholes due to bending fatigue was measured by the following method using a Gelbo Flex Tester manufactured by Rigaku Kogyosha.
After applying a polyester adhesive to the surface of the inorganic thin film layer of the gas barrier polyamide film prepared in the examples, a linear low density polyethylene film (L-LDPE film: Toyobo Co., Ltd., L4102) having a thickness of 40 μm was dry laminated and aged for 3 days in an environment of 40° C. to obtain a laminate film. The obtained laminate film was cut into 12 inches x 8 inches to form a cylindrical shape with a diameter of 3.5 inches, one end of the cylindrical film was fixed to the fixed head side of the Gelbo flex tester and the other end was fixed to the movable head side, and the initial gripping distance was set to 7 inches. A flex fatigue was performed 1000 times at a speed of 40 times/min, in which a 440 degree twist was given in the first 3.5 inches of the stroke, and the entire stroke was completed in a linear horizontal motion for the next 2.5 inches, and the number of pinholes generated in the laminate film was counted. The measurement was performed in an environment of 1° C. The test film was placed on a filter paper (Advantec, No. 50) with the L-LDPE film side facing down, and the four corners were fixed with Cellophane Tape (registered trademark). Ink (Pilot ink (product number INK-350-Blue) diluted 5 times with pure water) was applied to the test film and spread over the entire surface using a rubber roller. After wiping off unnecessary ink, the test film was removed, and the number of ink dots on the filter paper was counted.

(9) Resistance to Pinholes Caused by Abrasion of Film A friction test was carried out by the following method using a fastness tester (manufactured by Toyo Seiki Seisakusho) to measure the distance at which pinholes appeared.
A test sample was prepared by folding the same laminate film as that prepared in the above-mentioned evaluation of pinhole resistance against bending in four to make sharp corners, and rubbing it against the inner surface of a cardboard with a fastness tester at an amplitude of 25 cm, an amplitude speed of 30 times/min, and a weight of 100 g. The cardboard used was K280 x P180 x K210 (AF) = (surface liner x core material x backing liner (type of flute)).
The pinhole occurrence distance was calculated according to the following procedure. The longer the pinhole occurrence distance, the better the abrasion pinhole resistance.
First, a friction test was performed with an amplitude of 100 times and a distance of 2500 cm. If no pinholes were found, the friction test was performed with an amplitude of 20 times and a distance of 500 cm increased. If no pinholes were found, the friction test was performed with an amplitude of 20 times and a distance of 500 cm increased. This was repeated, and the distance at which a pinhole was found was marked with an X, and the test was set to level 1. If a pinhole was found with an amplitude of 100 times and a distance of 2500 cm, the friction test was performed with an amplitude of 20 times and a distance of 500 cm reduced. If a pinhole was found, the friction test was performed with an amplitude of 20 times and a distance of 500 cm reduced. This was repeated, and the distance at which a pinhole was not found was marked with an O, and the test was set to level 1.
Next, for level 2, if the final result in level 1 was ○, the number of amplitudes was increased by 20, and a friction test was conducted. If no pinholes were formed, a ○ was marked, and if a pinhole was formed, a × was marked. If the final result in level 1 was ×, the number of amplitudes was decreased by 20, and a friction test was conducted. If no pinholes were formed, a ○ was marked, and if a pinhole was formed, a × was marked.
Furthermore, for levels 3 to 20, if the previous level was rated as ○, increase the number of amplitudes by 20 and conduct a friction test; if no pinholes are created, mark it as ○, if a pinhole is created, mark it as ×. If the previous level was rated as ×, reduce the number of amplitudes by 20 and conduct a friction test; if no pinholes are created, mark it as ○, if a pinhole is created, mark it as ×. Repeat this process and mark levels 3 to 20 as ○ or ×.
For example, the results shown in Table 1 were obtained. Using Table 1 as an example, a method for determining the pinhole occurrence distance will be explained.
Count the number of O and X trials for each distance.
The distance with the most tests was used as the median, and the coefficient was set to 0. For distances longer than that, the coefficient was set to +1, +2, +3... for every 500 cm, and for distances shorter than that, the coefficient was set to -1, -2, -3... for every 500 cm.
In all tests from levels 1 to 20, the number of tests in which no holes were formed was compared with the number of tests in which holes were formed, and the friction pinhole generation distance was calculated for each of the following cases A and B using the respective formulas.
A: In all tests, the number of tests in which no holes were formed is equal to or greater than the number of tests in which holes were formed. Distance at which pinholes were generated by friction = median + 500 x (Σ (coefficient x number of tests in which no holes were formed) / number of tests in which no holes were formed) + 1/2)
B: In all tests, the number of tests without holes is less than the number of tests with holes. Distance at which pinholes occur due to friction = median + 500 x (Σ (coefficient x number of tests with holes) / number of tests with holes) - 1/2)

(10) Heat Shrinkage of Film The heat shrinkage of film was measured according to the following formula in accordance with the dimensional change test method described in JIS C2318, except that the test temperature was 160° C. and the heating time was 10 minutes.
Heat shrinkage rate = [(length before treatment - length after treatment) / length before treatment] x 100 (%)

(11) Laminate strength with polyethylene sealant A laminate film prepared in the same manner as described in the evaluation of pinhole resistance was cut into a strip of 15 mm width × 200 mm length, and one end of the laminate film was peeled off at the interface between the polyamide film and the linear low-density polyethylene film. Using an autograph (manufactured by Shimadzu Corporation), the laminate strength was measured three times in each of the MD and TD directions under the conditions of a temperature of 23°C, a relative humidity of 50%, a pulling speed of 200 mm/min, and a peel angle of 90°, and the average value was used to evaluate.

(12) Water-resistant laminate strength (laminate strength under water adhesion conditions)
(11) When measuring the laminate strength, water was dropped onto the peeled interface of the strip-shaped laminate film with a dropper, and the laminate strength was measured. Measurements were made three times in each of the MD and TD directions, and the average value was used for evaluation.

(13) Relative Viscosity of Raw Material Polyamide 0.25 g of polyamide was dissolved in 96% sulfuric acid in a 25 ml measuring flask to a concentration of 1.0 g/dl, and the relative viscosity of the polyamide solution was measured at 20° C.
(14) Melting Point of Raw Material Polyad In accordance with JIS K7121, a differential scanning calorimeter SSC5200 manufactured by Seiko Instruments Inc. was used in a nitrogen atmosphere at a sample weight of 10 mg, a heating start temperature of 30° C., and a heating rate of 20° C./min. The endothermic peak temperature (Tmp) was determined as the melting point.

(15) Coating amount of adhesive modification layer A gas barrier polyamide film was cut into an area of 10 cm x 10 cm, and the adhesive modification layer surface of the film was wiped with a cloth soaked in a mixed organic solvent of methyl ethyl ketone/toluene = 1/1, and the weight before and after wiping was measured with a precision balance (AUW120D manufactured by Shimadzu Corporation). The coating amount (g/ ^m2 ) was calculated by converting the measured weight difference into per square meter.

[Polyamide 6 (a-1) newly polymerized from petrochemical-derived raw materials]
As the polyamide 6 (a-1) newly polymerized from petrochemical-derived raw materials, polyamide 6 having a relative viscosity of 2.8 and a melting point of 220° C. manufactured by Toyobo Co., Ltd. was used.
[Production of chemically recycled polyamide 6 (a-2)]
The polyamide 6 fibers recovered from the waste materials and a 75% by mass aqueous phosphoric acid solution as a depolymerization catalyst were charged into a depolymerization apparatus and heated to 260°C under a nitrogen atmosphere. The reaction was started while blowing superheated steam into the depolymerization apparatus, and the ε-caprolactam and steam continuously distilled from the depolymerization apparatus were cooled to recover an ε-caprolactam distillate. The recovered distillate was concentrated with an evaporator, and the resulting ε-caprolactam was repolymerized to obtain chemically recycled polyamide 6. The relative viscosity of polyamide 6 (a-2) was 2.7, and the melting point was 221°C.

[Production of mechanically recycled polyamide 6 (a-3)]
Off-standard films and scraps generated as cut ends (edge trims) from stretched films obtained by the method shown in Example 1 described later were collected and pulverized, kneaded in an extruder with a cylinder temperature of 270°C, pelletized, and then dried at 100°C under reduced pressure to obtain mechanically recycled polyamide 6. Polyamide 6 (a-3) had a relative viscosity of 2.6 and a melting point of 221°C.

Example 1
Using an apparatus consisting of one extruder and a 380 mm wide single layer T-die, a molten resin of the following resin composition was extruded from the T-die into a film, which was then cast onto a cooling roll whose temperature was controlled at 20°C and electrostatically adhered to obtain an unstretched film having a thickness of 200 µm.
The resin composition is a polyamide resin composition consisting of 85 parts by mass of polyamide A (polyamide 6, manufactured by Toyobo Co., Ltd., relative viscosity 2.8, melting point 220°C), 5.0 parts by mass of polyamide B, 0.45 parts by mass of porous silica fine particles (manufactured by Fuji Silysia Chemical Ltd., average particle size 2.0 μm, pore volume 1.6 ml/g), and 0.15 parts by mass of fatty acid bisamide (ethylene bisstearic acid amide, manufactured by Kyoeisha Chemical Co., Ltd.).
The extrusion rate of the extruder was adjusted so that the biaxially oriented polyamide film had a total thickness of 15 μm.
The unstretched film obtained was introduced into a roll-type stretching machine, and by utilizing the difference in peripheral speed of the rolls, it was stretched 1.73 times in the MD direction at 80° C., and then further stretched 1.85 times at 70° C. Then, it was continuously introduced into a tenter-type stretching machine, preheated at 110° C., and then stretched 1.2 times in the TD direction at 120° C., 1.7 times at 130° C., and 2.0 times at 160° C., heat-set at 218° C., and then relaxed by 7% at 218° C., and then the surface on the side on which the inorganic thin film layer was to be laminated was corona discharge-treated, and the film was wound into a roll and slit to obtain a film roll having a width of 400 mm.

A composite oxide layer of silicon dioxide and aluminum oxide was formed as an inorganic thin film layer on the slit film by electron beam deposition. Particulate SiO ₂ (purity 99.9%) and Al ₂ O ₃ (purity 99.9%) of about 3 mm to 5 mm were used as deposition sources. The inorganic thin film layer (SiO ₂ /A1 ₂ O ₃ composite oxide layer) in the film thus obtained (inorganic thin film layer/adhesive layer-containing film) had a thickness of 13 nm. The composition of this composite oxide layer was SiO ₂ /A1 ₂ O ₃ (mass ratio) = 60/40.

Furthermore, a water/alcohol-based coating liquid consisting of a dispersion of a metaxylylene group-containing urethane resin ("Takelac (registered trademark) WPB341" manufactured by Mitsui Chemicals, Inc.; solid content 30%) was applied by wire bar coating method onto the inorganic thin film layer formed by the above vapor deposition, and dried at 200°C for 15 seconds to laminate a protective layer. The coating amount after drying was 0.19 g/ ^m2 in terms of solid content.
In this manner, a gas barrier polyamide film having a biaxially oriented polyamide film, an inorganic thin film layer and a protective layer laminated in this order was produced.

(Examples 2 to 7)
A gas barrier polyamide film was obtained in the same manner as in Example 1, except that the film-forming conditions such as the polyamide resin composition, the stretching ratio, and the heat setting temperature were changed as shown in Table 2. The evaluation results of the obtained gas barrier polyamide film are shown in Table 2.

In Example 7, however, an inorganic thin film layer made of aluminum oxide was laminated as the inorganic thin film layer by the following method.
The film was set on the unwinding side of a continuous vacuum deposition machine, the continuous vacuum deposition machine was depressurized to 10 ⁻⁴ Torr or less, and the machine was run over a cooled metal drum. Aluminum metal with a purity of 99.99% was loaded into an alumina crucible from the bottom of the cooling drum, and the aluminum metal was heated and evaporated. Oxygen was supplied into the vapor to cause an oxidation reaction, which caused the aluminum metal to adhere and accumulate on the film, forming an aluminum oxide film with a thickness of 30 nm.

(Example 8)
In Example 8, a gas barrier polyamide film was obtained using the following simultaneous biaxial stretching method.
Using an apparatus consisting of one extruder and a single-layer T-die with a width of 380 mm, the molten resin of the same resin composition as in Example 4 was extruded from the T-die into a film shape, cast onto a cooling roll adjusted to 20°C, and electrostatically adhered to obtain a sheet with a thickness of 160 μm. The obtained sheet was sent to a hot water bath adjusted to 50°C and subjected to a water immersion treatment for 2 minutes to adjust the moisture content to about 4%. The end of the width direction of this sheet was held by the clip of a tenter-type simultaneous biaxial stretching machine, stretched 3.3 times in both the longitudinal and transverse directions at 180°C, heat-set at 210°C, and further relaxed in the transverse direction by 5% at 210°C. Then, the surface on the side on which the inorganic thin film layer was laminated was corona discharge-treated, and the film was wound into a roll shape and slit to obtain a film roll with a width of 400 mm.

(Comparative Example 1)
A biaxially oriented polyamide film without an inorganic thin film layer was obtained using only polyamide 6(a-1) newly polymerized from petrochemical raw materials in the same manner as in Example 1, except that the film-forming conditions such as the polyamide resin composition, the stretching ratio, and the heat setting temperature were changed as shown in Table 2.

As shown in Table 2, the gas barrier polyamide films using the chemically recycled polyamide 6 (a-2) shown in the Examples or the gas barrier polyamide films using the chemically recycled polyamide 6 (a-2) and the mechanically recycled polyamide 6 (a-3) had good properties such as impact resistance, puncture strength, bending pinhole resistance, and gas barrier properties, and were excellent as packaging films requiring gas barrier properties.
On the other hand, in Comparative Example 1, a biaxially oriented polyamide film without an inorganic thin film layer was obtained using only polyamide 6 (a-1) newly polymerized from non-recycled petrochemical-derived raw materials as the raw material. Although a biaxially oriented polyamide film having impact strength and puncture strength equivalent to those of the Examples was obtained, it was not suitable for use as a packaging film, which requires high oxygen permeability and gas barrier properties.

Example 9
Using an apparatus consisting of two extruders and a 380 mm wide co-extrusion T-die, the layers were laminated in a B layer/A layer/B layer configuration using the feed block method, and the molten resin was extruded from the T-die into a film. This was then cast onto a cooling roll whose temperature was controlled at 20°C and electrostatically adhered to obtain an unstretched film with a thickness of 200 μm.
The resin compositions of layers A and B are as follows.
Resin composition constituting layer A: a polyamide resin composition consisting of 95 parts by mass of polyamide 6 (manufactured by Toyobo Co., Ltd., relative viscosity 2.8, melting point 220°C) as polyamide resin (a-1) and 5 parts by mass of polyamide resin (a-2).
Resin composition constituting layer B: A resin composition consisting of 95 parts by mass of polyamide 6 (manufactured by Toyobo Co., Ltd., relative viscosity 2.8, melting point 220°C) as polyamide resin (a-1), 5.0 parts by mass of polyamide resin (a-2), 0.45 parts by mass of porous silica fine particles (manufactured by Fuji Silysia Chemical Ltd., average particle size 2.0 μm, pore volume 1.6 ml/g), and 0.15 parts by mass of fatty acid bisamide (ethene bisstearic acid amide, manufactured by Kyoeisha Chemical Co., Ltd.).

The feed block configuration and the extrusion rate of the extruder were adjusted so that the biaxially oriented polyamide film had a total thickness of 15 μm, a thickness of the base layer (A layer) of 12 μm, and a thickness of each of the front and back surface layers (B layer) of 1.5 μm.
The obtained unstretched film was introduced into a roll-type stretching machine, and by utilizing the difference in peripheral speed of the rolls, it was stretched 1.73 times in the MD direction at 80° C., and then further stretched 1.85 times at 70° C. Subsequently, the following coating solution (A) was applied to this uniaxially stretched film by a roll coater, and then it was continuously introduced into a tenter-type stretching machine while drying with hot air at 70° C., and after preheating at 110° C., it was stretched 1.2 times at 120° C., 1.7 times at 130° C., and 2.0 times at 160° C. in the TD direction, heat-set at 218° C., and then relaxed by 7% at 218° C., and then the surface on the side on which the inorganic thin film layer was to be laminated was corona discharge-treated, and the film was wound into a roll and slit to obtain a film roll having a width of 400 mm.

An inorganic thin film layer and a protective layer were laminated on the slit film in the same manner as in Example 1, producing a gas barrier polyamide film laminated in the order of biaxially oriented polyamide film/inorganic thin film layer/protective layer.

(Examples 10 to 17)
A gas barrier polyamide film was obtained in the same manner as in Example 9, except that the film-forming conditions such as the polyamide resin composition, the stretching ratio, and the heat setting temperature were changed as shown in Table 3. The evaluation results of the obtained gas barrier polyamide film are shown in Table 3.
However, in Example 16, an aluminum oxide thin film layer was laminated as the inorganic thin film layer, as in Example 7.
In Example 17, a gas barrier polyamide film was obtained by using the simultaneous biaxial stretching method as in Example 8.

(Comparative Example 1)
A biaxially oriented polyamide film without an inorganic thin film layer was obtained using only polyamide 6(a-1) newly polymerized from petrochemical-derived raw materials in the same manner as in Example 1, except that the film-forming conditions such as the polyamide resin composition, the stretching ratio, and the heat setting temperature were changed as shown in Table 3.

(Reference Examples 1 and 2)
A gas barrier polyamide film containing a large amount of mechanically recycled polyamide 6 (a-3) in the surface layer (B layer) was obtained in the same manner as in Example 9, except that the film-forming conditions such as the polyamide resin composition, the stretching ratio, and the heat setting temperature were changed as shown in Table 3. The evaluation results of the obtained gas barrier polyamide film are shown in Table 3.

As shown in Table 3, the gas barrier polyamide films using the chemically recycled polyamide 6 (a-2) shown in the Examples or the gas barrier polyamide films using the chemically recycled polyamide 6 (a-2) and the mechanically recycled polyamide 6 (a-3) had good properties such as impact resistance, puncture strength, bending pinhole resistance, and gas barrier properties, and were excellent as packaging films requiring gas barrier properties.
On the other hand, in Comparative Example 2, a biaxially oriented polyamide film without an inorganic thin film layer was obtained using only polyamide 6 (a-1) newly polymerized from non-recycled petrochemical-derived raw materials as the raw material. Although a biaxially oriented polyamide film having impact strength and puncture strength equivalent to those of the Examples was obtained, it was not suitable for use as a packaging film, which requires high oxygen permeability and gas barrier properties.

In addition, in Reference Examples 1 and 2, a large amount of mechanically recycled polyamide 6 was used in the surface layer (layer B). In this case, the transparency (haze) and abrasion pinhole resistance were inferior to the films in Examples 8 to 15, in which the content of mechanically recycled polyamide 6 in the surface layer was 10 mass % or less.

(Example 18)
The gas barrier polyamide film produced in Example 1-2 was used to produce laminates having the following configurations (1) to (9), and the laminates (1) to (9) were used to produce three-side sealed and pillow-type packaging bags. The packaging bags had good appearance and were resistant to tearing in a drop impact test.
(1) Gas barrier polyamide film layer/printed layer/polyurethane adhesive layer/linear low density polyethylene film sealant layer.
(2) Gas barrier polyamide film layer/printed layer/polyurethane adhesive layer/unoriented polypropylene film sealant layer.
(3) Biaxially oriented PET film layer/printed layer/polyurethane-based adhesive layer/gas barrier polyamide film layer/polyurethane-based adhesive layer/unoriented polypropylene film sealant layer.
(4) Biaxially oriented PET film layer/printed layer/polyurethane adhesive layer/gas barrier polyamide film layer/polyurethane adhesive layer/linear low density polyethylene film sealant layer.

The gas barrier polyamide film of the present invention has excellent impact resistance, bending pinhole resistance, and abrasion pinhole resistance, and also has excellent gas barrier properties, so it can be suitably used as a food packaging material and an industrial packaging material that require various gas barrier properties. Furthermore, by using polyamide 6 that is chemically recycled from waste polyamide products, it can contribute to reducing the environmental load.

Claims (7)

A method for producing a gas barrier polyamide film, comprising: a biaxially oriented polyamide film made of a polyamide resin containing 70% by mass or more of polyamide 6, wherein 4 to 90% by mass of said polyamide 6 is chemically recycled polyamide 6; and a method for producing a gas barrier polyamide film, comprising laminating an inorganic thin film layer on at least one side of said biaxially oriented polyamide film containing 5 to 60% by mass of mechanically recycled polyamide 6. A method for producing a gas barrier polyamide film, comprising laminating an inorganic thin film layer on at least one side of a biaxially oriented polyamide film having a surface layer (B layer) laminated on at least one side of a base layer (A layer), the base layer (A layer) being made of a polyamide resin containing 100% by mass of polyamide 6, of which 5 to 90% by mass is chemically recycled polyamide 6, the biaxially oriented polyamide film containing 5 to 80% by mass of mechanically recycled polyamide 6, and the B layer being made of a polyamide resin composition containing 70% by mass or more of polyamide 6 and 0 to 30% by mass of mechanically recycled polyamide 6. 3. The method for producing a gas barrier polyamide film according to claim 1, wherein the gas barrier polyamide film satisfies the following (a) to (c):
(a) a puncture strength of 0.65 N/μm or more;
(b) Impact strength is 0.9 J/15 μm or more.
(c) In the abrasion pinhole resistance test, the distance until pinholes appear is 2,900 cm or more. The method for producing a gas barrier polyamide film according to any one of claims 1 to 3 , wherein the gas barrier polyamide film satisfies the following (d) and (e):
(d) haze of 2.6% or less;
(e) The coefficient of kinetic friction is 1.0 or less. 5. The method for producing a gas barrier polyamide film according to claim 1, wherein the gas barrier polyamide film has a water-resistant laminate strength of 4.0 N/15 mm or more after being laminated with a polyethylene sealant film. A method for producing a laminated film, comprising laminating a sealant film on the gas barrier polyamide film obtained by the method for producing a gas barrier polyamide film according to any one of claims 1 to 5 . A method for producing a packaging bag using the laminated film obtained by the method for producing a laminated film according to claim 6 .