JP7567907B2 - Method for producing biaxially oriented polyamide film - Google Patents

Description

The present invention relates to a biaxially oriented polyamide film that is excellent in impact resistance, bending pinhole resistance, and abrasion pinhole resistance, and is made from raw materials derived from biomass (organic resources derived from living organisms such as plants) and polyamide 6 chemically recycled from waste polyamide products. The biaxially oriented polyamide film of the present invention is suitable for use as a food packaging film, etc.

Traditionally, biaxially oriented films made of aliphatic polyamides, such as polyamide 6, have been widely used as various packaging material films due to their excellent impact resistance and pinhole resistance against bending.

As a means of improving the above-mentioned pinhole resistance, a film in which an aliphatic polyamide is mixed with a polyamide-based elastomer is known (see, for example, Patent Document 1). This film has good pinhole resistance and impact resistance in low-temperature environments, and pinholes due to bending fatigue are unlikely to occur even in low-temperature environments. However, it has been found that the polyamide-based elastomer added during film production is thermally degraded, and is prone to producing a degraded product called "eye plaster" at the outlet of the die lip, which causes a deterioration in the accuracy of the film thickness. In addition, the degraded product itself falls, resulting in defective products, which reduces the production efficiency during continuous film production.

Pinholes are generated not only by bending but also by friction (rubbing). Methods for improving pinholes caused by bending and pinholes caused by friction are often contradictory. For example, increasing the flexibility of a film makes it less likely for pinholes to occur due to bending, but the softer the film is, the more likely it is that pinholes caused by friction will occur. In response to this, a packaging laminate has been proposed that has excellent resistance to bending and pinholes caused by friction by providing a surface coating agent on the outer surface of a biaxially oriented polyamide film (see, for example, Patent Document 2). However, this method is not very effective at preventing pinholes caused by friction. In addition, a coating process is required.

In recent years, in order to build a recycling-oriented society, the use of biomass as an alternative to fossil fuel raw materials has been attracting attention in the field of materials. Biomass is an organic compound produced by photosynthesis from carbon dioxide and water, and by using it, it becomes carbon dioxide and water again, making it a so-called carbon-neutral raw material (the amount of carbon dioxide emitted and absorbed in the environment is the same, so the increase of carbon dioxide, a greenhouse gas, can be suppressed). Recently, the practical application of biomass plastics made from these biomass raw materials has progressed rapidly, and there are also attempts to produce polyester, a general-purpose polymer material, from these biomass raw materials.

In addition, there is a demand for the use of recycled materials to reduce the amount of plastic waste generated. Methods for recycling polyamide 6 include the thermal recycling method, in which it is incinerated and the heat energy is recovered, the material recycling method, in which it is melted and remolded for reuse, and the chemical recycling method, in which it is chemically depolymerized to return it to the raw materials for polyamide, and then reused in polyamide production, etc.

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

For example, Patent Document 3 discloses a recycling method in which used polyamide clothing products are collected, depolymerized to recover ε-caprolactam, which is then purified, polymerized, and melt spun or molded into polyamide fibers or polyamide 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 breaking down and refining collected clothing products, high-purity, high-quality raw materials (raw monomers) can be obtained, which allows for recycling to produce high-quality polyamide 6 products and enables repeated recycling. Furthermore, the work of collecting and sorting collected clothing products is significantly reduced.

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

Japanese Patent Application Publication No. 11-254615 JP 2001-205761 A Japanese Patent Application Publication No. 7-310204

The present invention was devised in consideration of the problems of the conventional technology. The object of the present invention is to provide a biaxially oriented polyamide film that is excellent in impact resistance, bending pinhole resistance, and abrasion pinhole resistance, and that can reduce the environmental load.

That is, the present invention comprises the following:
[1] The polyamide resin contains 70 to 99% by mass of polyamide 6 and 1 to 30% by mass of a polyamide whose raw material is at least partially derived from biomass;
The polyamide 6 comprises 5 to 100 parts by mass of polyamide 6 obtained by chemical recycling, based on 100 parts by mass of polyamide 6.
[2] The biaxially stretched polyamide film according to [1], wherein the polyamide 6 contains, per 100 parts by mass of polyamide 6, polyamide 6 obtained by chemical recycling and 5 to 50 parts by mass of polyamide 6 obtained by mechanical recycling.
[3] The biaxially oriented polyamide film according to [1] or [2], characterized in that the content of biomass-derived carbon as determined by radioactive carbon (C ¹⁴ ) measurement is 1 to 15% of the total carbon in the biaxially oriented polyamide film.
[4] The biaxially stretched polyamide film according to any one of [1] to [3], wherein the polyamide resin at least a part of which is derived from biomass is at least one polyamide resin selected from the group consisting of polyamide 11, polyamide 410, polyamide 610, and polyamide 1010.
[5] A biaxially oriented polyamide film according to any one of [1] to [4], wherein the biaxially oriented polyamide film has one or more layers laminated on at least one side of the biaxially oriented polyamide film, the laminated layers containing 70 to 100 mass% of polyamide 6, and the polyamide 6 contains 5 to 100 mass parts of polyamide 6 obtained by chemical recycling, based on 100 mass parts of polyamide 6.
[6] The biaxially stretched polyamide film according to [5], wherein the polyamide 6 contains, per 100 parts by mass of polyamide 6, polyamide 6 obtained by chemical recycling and 5 to 50 parts by mass of polyamide 6 obtained by mechanical recycling.
[7] The biaxially oriented polyamide film according to [5] or [6], wherein the thickness of the laminated layer is 7 to 50% of the total thickness of the film.
[8] The biaxially oriented polyamide film according to any one of [1] to [7], which satisfies the following (a) and (b):
(a) The number of pinhole defects is 10 or less when a twisting and bending test using a Gelbo flex tester is performed 1,000 times at a temperature of 1° C.;
(b) The distance until pinholes appear in a pinhole resistance test is 2,900 cm or more. [9] The biaxially stretched polyamide film according to any one of [1] to [8], characterized in that the haze is 10% or less and the dynamic friction coefficient is 1.0 or less.
[10] The biaxially oriented polyamide film according to any one of [1] to [8], characterized in that a laminate strength after being laminated with a polyethylene sealant film is 4.0 N/15 mm or more.
[11] A laminated film comprising a sealant film laminated on at least one surface of the biaxially oriented polyamide film according to any one of [1] to [10].
[12] A packaging bag using the laminated film described in [11].

The biaxially oriented polyamide film of the present invention is primarily composed of polyamide 6 resin, and by blending it with polyamide resin polymerized from specific biomass-derived raw materials and adopting specific film-forming conditions, it is possible to obtain a polyamide film that exhibits impact resistance, flexure pinhole resistance, abrasion pinhole resistance, and adhesion to sealant films, as well as being carbon-neutral.

The biaxially oriented polyamide film of the present invention can further be produced using or blending polyamide 6 that has been chemically recycled from waste polyamide products, thereby reducing the environmental impact of the resulting polyamide film.

Furthermore, according to the present invention, since the biomass-derived polyamide is effective in improving pinhole resistance, there is no need to add a polyamide-based elastomer. This makes it possible to suppress adhesion of deterioration products to the inner surface of the die caused by polyamide-based elastomers and adhesion of resin to the die slip outlet. As a result, it is possible to prevent the thickness unevenness of the film from worsening and to enable long-term continuous production.

Schematic diagram of a friction pinhole resistance evaluation device

[Biaxially oriented polyamide film]
The biaxially stretched polyamide film of the present invention contains, as polyamide resins, 70 to 99% by mass of polyamide 6 and 1 to 30% by mass of polyamide at least partly derived from biomass. The polyamide 6 further contains 5 to 100 parts by mass of polyamide 6 obtained by chemical recycling, based on 100 parts by mass of polyamide 6. By containing 70% by mass or more of polyamide 6, excellent mechanical strength such as impact strength and gas barrier properties such as oxygen, which are inherent to biaxially stretched polyamide films made of polyamide 6, can be obtained.

The biaxially stretched polyamide film of the present invention has improved flex pinhole resistance and abrasion pinhole resistance due to the inclusion of 1 to 30% by mass of polyamide resin, at least a portion of which is derived from biomass. Conventionally used flex pinhole resistance improvers such as polyamide elastomers and polyolefin elastomers improve flex pinhole resistance but deteriorate abrasion pinhole resistance. By including polyamide resin, at least a portion of which is derived from biomass, a biaxially stretched polyamide film having excellent flex pinhole resistance and abrasion pinhole resistance at the same time can be obtained. In addition, a carbon-neutral film is obtained that is less affected by increases and decreases in terrestrial carbon dioxide.

The polyamide 6 used in the biaxially stretched polyamide film of the present invention is preferably polyamide 6 obtained from chemical recycling, with 5 to 100 parts by mass being polyamide 6 obtained from chemical recycling, based on 100 parts by mass of all polyamide 6. Examples of raw materials for chemical recycling include, but are not limited to, discarded polyamide 6 products such as discarded plastic products, discarded tire rubber, fibers, and fishing nets. By using chemically recycled polyamide 6, a polyamide film that can reduce the environmental load can be obtained.

[Polyamide 6]
The polyamide 6 resin used in the present invention is usually produced by ring-opening polymerization of ε-caprolactam. The polyamide 6 resin 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 polyamide 6 resin 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 will be insufficient. If it is more than 4.5, the load on the extruder will be too great, making it difficult to obtain an unstretched film before stretching.

The polyamide 6 used in the biaxially stretched polyamide film of the present invention includes polyamide 6 polymerized from commonly used monomers derived from fossil fuels, as well as polyamide 6 chemically recycled from waste polyamide 6 products such as waste plastic products, waste tire rubber, fibers, and fishing nets. A method for obtaining chemically recycled polyamide 6 from waste polyamide 6 products can be, for example, to collect used polyamide products, depolymerize them to obtain ε-caprolactam, purify the ε-caprolactam, and then polymerize polyamide 6.

<Depolymerization conditions>
In the depolymerization carried out in producing the chemically recycled polyamide 6 used in the biaxially oriented polyamide film of the present invention, the polyamide 6 product is usually depolymerized by heating. The depolymerization may or may not be performed using a catalyst.

The pressure of the depolymerization may be reduced, normal, or increased. The temperature of the 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) may occur, resulting in a decrease in the purity of the recovered caprolactam.

When a catalyst is used in the above depolymerization, 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 0.01 to 50% by mass relative to the polyamide 6 component. It is preferably 0.01 to 20% by mass, and more preferably 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 0.1 to 50 times by mass relative to the polyamide 6 product components such as fibers. Preferably, it is 0.5 to 20 times by mass, and 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. In the case of wet depolymerization, the generated caprolactam is distilled out of the reactor together with water to obtain a recovered caprolactam aqueous solution. After the depolymerization reaction is completed, caprolactam can be extracted by vacuum distillation. Alternatively, it can be extracted continuously as the reaction proceeds. In the case of dry depolymerization, the generated caprolactam is distilled out of the reactor by vacuum distillation to obtain recovered caprolactam. After the depolymerization reaction is completed, caprolactam can be extracted by vacuum distillation. Alternatively, it can be removed continuously as the reaction proceeds.

To obtain caprolactam of even higher purity, the recovered caprolactam can be combined with other purification methods, such as precision distillation, distillation under reduced pressure with the addition of a small amount of sodium hydroxide, treatment with activated carbon, ion exchange treatment, and recrystallization.

The biaxially oriented polyamide film of the present invention can further be used in combination with polyamide 6 which is mechanically recycled waste material generated during the manufacturing process of the biaxially oriented polyamide film.

The above-mentioned mechanically recycled polyamide 6 is a raw material made by recovering scrap material generated during the production of biaxially oriented polyamide film, such as non-standard, unshippable film or cut off pieces (edge trim), and pelletizing it through melt extrusion or compression molding.

The lower limit of the proportion of mechanically recycled polyamide 6 added to the biaxially stretched polyamide film of the present invention is not particularly limited. The upper limit is preferably 50 parts by mass, more preferably 40 parts by mass, and even more preferably 30 parts by mass, based on 100 parts by mass of all polyamide 6. If the proportion of mechanically recycled polyamide added exceeds the above, the film may become more colored or have a high haze value, which may impair the appearance of the film. Alternatively, the amount of degraded material may increase during film production, which may deteriorate the film formability.

[Polyamide resin in which at least a part of the raw material is derived from biomass]
Examples of the polyamide resin used in the present invention, at least a part of which is derived from biomass, include polyamide 11, polyamide 410, polyamide 610, polyamide 1010, polyamide MXD10 resin, and polyamide 11-6T copolymer resin.

Polyamide 11 is a polyamide resin having a structure in which monomers having 11 carbon atoms are bonded via amide bonds. Usually, polyamide 11 is obtained by using aminoundecanoic acid or undecane lactam as a monomer. In particular, aminoundecanoic acid is a monomer obtained from castor oil, and is therefore desirable from the viewpoint of carbon neutrality. The constituent units derived from these monomers having 11 carbon atoms preferably account for 50 mol% or more of the total constituent units in polyamide 11, more preferably 80 mol% or more, and may even be 100 mol%. Polyamide 11 is usually produced by the ring-opening polymerization of the undecane lactam described above. Polyamide 11 obtained by ring-opening polymerization is usually subjected to removal of the lactam monomer with hot water, then dried and melt-extruded with an extruder. The relative viscosity of polyamide 11 is preferably 1.8 to 4.5, more preferably 2.4 to 3.2. If the relative viscosity is less than 1.8, the impact strength of the film is insufficient. If it is more than 4.5, the load on the extruder becomes large, making it difficult to obtain an unstretched film before stretching.

Polyamide 610 is a polyamide resin having a structure in which a diamine having 6 carbon atoms and a dicarboxylic acid having 10 carbon atoms are polymerized. Hexamethylenediamine and sebacic acid are usually used. Of these, sebacic acid is a monomer obtained from castor oil, and is therefore desirable from the viewpoint of carbon neutrality. The total of the constituent units derived from these monomers having 6 carbon atoms and the constituent units derived from monomers having 10 carbon atoms in PA610 is preferably 50 mol % or more of the total constituent units, more preferably 80 mol % or more, and may be 100 mol %.

Polyamide 1010 is a polyamide resin having a structure in which a diamine having 10 carbon atoms and a dicarboxylic acid having 10 carbon atoms are polymerized. Typically, 1,10-decanediamine (decamethylenediamine) and sebacic acid are used in polyamide 1010. Decamethylenediamine and sebacic acid are monomers obtained from castor oil, and are therefore desirable from the viewpoint of carbon neutrality. The total of the structural units derived from these diamines having 10 carbon atoms and the structural units derived from dicarboxylic acids having 10 carbon atoms in PA1010 is preferably 50 mol% or more of the total structural units, more preferably 80 mol% or more, and may be 100 mol%.

Polyamide 410 is a polyamide resin having a structure in which a monomer having four carbon atoms is copolymerized with a diamine having ten carbon atoms. Sebacic acid and tetramethylenediamine are usually used for polyamide 410. From an environmental perspective, it is preferable to use sebacic acid made from castor oil, a vegetable oil. The sebacic acid used here is preferably obtained from castor oil from the standpoint of environmental protection (especially from the standpoint of carbon neutrality).

In the biaxially stretched polyamide film of the present invention, the lower limit of the content of the polyamide resin at least partly derived from biomass is not particularly limited, but is preferably 1% by mass, and more preferably 3% by mass or more. The upper limit of the content is 30% by mass, and more preferably 20% by mass. If the content of the polyamide resin at least partly derived from biomass exceeds 30% by mass, the molten film may become unstable when cast, making it difficult to obtain a homogeneous unstretched film.

[Secondary materials, additives]
The biaxially oriented polyamide film of 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 stretched polyamide film of the present invention may contain a thermoplastic resin in addition to the polyamide 6 and the polyamide resin whose raw material is at least partially derived from biomass, as long as the object of the present invention is not impaired. Examples of the polyamide resin include polyamide 12 resin, polyamide 66 resin, polyamide 6-12 copolymer resin, polyamide 6-66 copolymer resin, and polyamide MXD6 resin. If necessary, a thermoplastic resin other than a polyamide resin, for example, a polyester polymer such as polyethylene terephthalate, polybutylene terephthalate, or polyethylene-2,6-naphthalate, or a polyolefin polymer such as polyethylene or polypropylene, may be contained. If the raw material of these thermoplastic resins is derived from biomass, it is preferable because it does not affect the increase or decrease of carbon dioxide on the ground, thereby reducing the environmental load.

<Lubricant>
In order to improve the slipperiness and make the biaxially oriented polyamide film of the present invention easy to handle, it is preferable to contain an organic lubricant such as fine particles or fatty acid amide as a lubricant. By improving the slipperiness of the biaxially oriented polyamide film of the present invention, it is also effective in reducing the breakage of packaging bags due to friction.

The fine particles can be appropriately selected from inorganic fine particles such as silica, kaolin, and zeolite, and polymeric organic fine particles such as acrylic and polystyrene. From the viewpoints of transparency and slipperiness, it is preferable to use silica fine particles. The preferred average particle size of the 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 slipperiness. 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 the silica fine particles are used, 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 is deteriorated, and if the pore volume exceeds 2.0 ml/g, the fine particles tend not to form surface protrusions.

The biaxially stretched polyamide film of the present invention 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 of 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 the content exceeds the above range, the wettability tends to be deteriorated.

To improve slip properties, polyamide resins such as polyamide MXD6 resin, polyamide 12 resin, polyamide 66 resin, polyamide 6-12 copolymer resin, and polyamide 6-66 copolymer resin can be added to the biaxially stretched polyamide film of the present invention. Polyamide MXD6 resin is particularly preferred, and it is preferable to add it in an amount of 1 to 10 mass %.

<Antioxidants>
The biaxially stretched polyamide film of 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 containing a phenol-based antioxidant, the film-forming operability of the biaxially stretched polyamide film is improved. In particular, when recycled films are used as raw materials, the resin is prone to thermal degradation, which tends to cause operational problems in film production and increase production costs. On the other hand, by adding an antioxidant, the thermal degradation of the resin is suppressed and operationality is improved.

[Surface layer]
In the present invention, one or more surface layers made of the same or different resin compositions can be laminated on one or both sides of the biaxially stretched polyamide film. By laminating at least one surface layer, the surface properties can be improved.

The surface layer is preferably a layer made of a resin composition containing 70 to 100% by mass of polyamide 6. Preferably, polyamide 6 is 80% by mass or more. More preferably, polyamide 6 is 90% by mass or more. The upper limit is 100% by mass, preferably 99% by mass, and more preferably 97% by mass. By containing 70% by mass or more of polyamide 6, a biaxially oriented polyamide film having excellent mechanical strength such as impact strength and gas barrier properties such as oxygen can be obtained.

Furthermore, it is preferable that the polyamide 6 obtained by chemical recycling is contained in an amount of 5 to 100 parts by mass per 100 parts by mass of polyamide 6. In addition to the polyamide 6 obtained by chemical recycling, polyamide 6 obtained by mechanical recycling can be used in combination. The proportion of polyamide 6 obtained by mechanical recycling is preferably 0 to 50 parts by mass per 100 parts by mass of polyamide 6. If the proportion of mechanically recycled polyamide used exceeds the above, the film may become more colored or the haze value may be high, 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.

The surface layer can contain various additives such as other thermoplastic resins, lubricants, heat stabilizers, antioxidants, antistatic agents, anti-fogging agents, UV absorbers, dyes, pigments, etc., depending on the function to be imparted to the surface of the surface layer. When the surface layer is used on the outside of a packaging bag, it needs to be resistant to abrasion and pinholes, so it is not preferable to contain soft resins such as polyamide elastomers or polyolefin elastomers, or substances that generate a large amount of voids.

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

It is preferable that the surface layer contains fine particles or an organic lubricant as a lubricant to improve the slipperiness of the film. By improving the slipperiness, the film becomes easier to handle and the risk of packaging bags breaking due to friction is reduced.

The fine particles can be appropriately selected from inorganic fine particles such as silica, kaolin, and zeolite, and polymeric organic fine particles such as acrylic and polystyrene fine particles. From the standpoint of transparency and slipperiness, it is preferable to use silica fine particles.

The preferred average particle size of the microparticles 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-mentioned silica microparticles, the range of the silica pore volume 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 likely to occur and the transparency of the film will deteriorate. If the pore volume exceeds 2.0 ml/g, the microparticles tend not to form surface protrusions.

The organic lubricant may contain fatty acid amide and/or fatty acid bisamide. Examples of fatty acid amide and/or fatty acid bisamide include erucic acid amide, stearic acid amide, ethylene bisstearic acid amide, ethylene bisbehenic acid amide, and ethylene bisoleic acid amide. The content of fatty acid amide and/or fatty acid bisamide added to the surface layer is preferably 0.01 to 0.40% by mass, and 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 slipperiness tends to deteriorate. On the other hand, if it exceeds the above range, the wettability tends to deteriorate.

In order to improve the slipperiness of the film, polyamide resins other than polyamide 6, such as polyamide MXD6 resin, polyamide 11, polyamide 12 resin, polyamide 66 resin, polyamide 6-12 copolymer resin, polyamide 6-66 copolymer resin, etc., can be added to the surface layer. Polyamide MXD6 resin 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 polycondensation of metaxylylenediamine and adipic acid. The relative viscosity of 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 polyamide resin in an extruder.

When adding fine particles, organic lubricants, or polyamide resins such as polyamide MXD6 resin to the surface layer for the purpose of improving the slipperiness of the film, it is preferable to reduce the amount of these added to the biaxially oriented polyamide film that serves as the base material, as this results in a film that is both highly transparent and has excellent slipperiness.

In addition, in order to improve adhesion, a polyamide resin other than polyamide 6 can be added to the surface layer. In this case, copolymer polyamide resins such as polyamide 6-12 copolymer resin and polyamide 6-66 copolymer resin are preferred.

As a method for adding auxiliary materials and additives such as lubricants and antioxidants to the biaxially oriented polyamide film and surface layer that serve as the substrate of the present invention, they can be added during resin polymerization or melt extrusion in an extruder. A high-concentration master batch may be prepared and added to the polyamide resin during film production. These known methods can be used.

[Biaxially oriented polyamide film]
The thickness of the biaxially oriented polyamide film of 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 one or more layers that become surface layers are laminated on at least one side of the biaxially oriented polyamide film of the present invention to form a laminated film, if the thickness of the surface layer accounts for a large proportion of the total thickness of the film, the bending pinhole resistance decreases. The thickness of the laminated layer is preferably 7 to 50% of the total thickness of the film, and more preferably 7 to 30%.

The biaxially stretched polyamide film of the present invention has 10 or less pinhole defects when a twist bending test is performed 1,000 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 is 5 or less. 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 the packaging bag is subjected to a load during transportation, etc. can be obtained.

Furthermore, in the biaxially stretched polyamide film of the present invention, in the friction pinhole resistance test described in the Examples, the distance until pinholes appear is 2900 cm or more. More preferably, it is 3100 cm or more, and even more preferably, it is 3300 cm or more. The longer the distance at which pinholes appear, the better the friction pinhole resistance is, and if the distance at which pinholes appear is 2900 cm or more, a packaging bag that is less likely to develop pinholes even if the packaging bag rubs against a cardboard box or the like during transportation, etc., can be obtained.

The biaxially oriented polyamide film of the present invention is characterized by having excellent properties in both bending pinhole resistance and friction pinhole resistance. The biaxially oriented polyamide film of the present invention, which has these properties, is extremely useful as a packaging film because it is less likely to develop pinholes during transportation.

The heat shrinkage rate of the film of the present invention at 160°C for 10 minutes is in the range of 0.6 to 3.0% in both the machine direction (hereinafter abbreviated as MD direction) and the width direction (hereinafter abbreviated as TD direction), and is preferably 0.6 to 2.5%. If the heat shrinkage rate exceeds 3.0%, curling or shrinkage may occur when heat is applied in the next process, such as lamination or printing. In addition, the lamination strength with the sealant film may be weakened. Although it is possible to make the heat shrinkage rate less than 0.6%, it may become mechanically fragile. In addition, this is not preferable because it deteriorates productivity.

Since excellent impact resistance is a feature of biaxially oriented polyamide films, the impact strength of the biaxially oriented 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.

The haze value of the biaxially stretched polyamide film of the present invention is preferably 10% or less. More preferably, it is 7% or less, and even more preferably, it is 5% or less. A small haze value means good transparency and gloss, so when used for packaging bags, beautiful printing can be achieved and the product value is increased. Since the haze value increases when fine particles are added to improve the slipperiness of the film, when the film has two or more layers, the haze value can be reduced by adding fine particles only to the surface layer.

The dynamic friction coefficient of the biaxially oriented polyamide film of the present invention is preferably 1.0 or less. More preferably, it is 0.7 or less, and even more preferably, it is 0.5 or less. If the dynamic friction coefficient of the film is small, the film has good slipperiness and is easy to handle. If the dynamic friction coefficient of the film is too small, it becomes too slippery and difficult to handle, so the dynamic friction coefficient of the biaxially oriented polyamide film of the present invention is preferably 0.15 or more.

The biaxially stretched polyamide film of the present invention preferably contains 1 to 15% of biomass-derived carbon (also called biomass ratio) based on the total carbon in the polyamide film as measured by radiocarbon (C ¹⁴ ) according to ASTM D6866-16. Carbon dioxide in the atmosphere contains a certain proportion of C ¹⁴ (105.5 pMC), and it is known that the C ¹⁴ content in plants that grow by absorbing carbon dioxide from the atmosphere, such as corn, is also about 105.5 pMC. It is also known that fossil fuels contain almost no C ^14. Therefore, the proportion of biomass-derived carbon can be calculated by measuring the proportion of C ¹⁴ in the total carbon atoms in the polyester.

The biaxially oriented polyamide film of the present invention has a laminate strength of 4.0 N/15 mm or more after being bonded with the polyethylene sealant described in the examples. The biaxially oriented polyamide film 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 biaxially oriented 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 make the laminate strength 4.0 N/15 mm or more, the biaxially oriented polyamide film of the present invention can be subjected to corona treatment, coating treatment, flame treatment, etc.

[Film preparation method]
The biaxially oriented polyamide film of the present invention can be produced by a known production method.
For example, sequential biaxial stretching and simultaneous biaxial stretching can be used. The sequential biaxial stretching is preferable because it can increase the film-forming 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.
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.

When producing a biaxially oriented polyamide film in which a surface layer is laminated on at least one side of a base film, a coextrusion method using a feed block or multi-manifold is preferred to obtain a laminated unstretched film. In addition to the coextrusion method, dry lamination, extrusion lamination, etc. can also be selected. When laminating by the coextrusion method, it is desirable to use polyamide resin compositions used for each layer such that the difference in melt viscosity is small.

The melting temperature of the resin is preferably 220 to 350°C. If it is less than the above, unmelted material may occur, resulting in defects and other poor appearance, while if it exceeds the above, deterioration of the resin may be observed, resulting in a decrease in molecular weight and a deterioration in appearance. The die temperature is preferably 250 to 350°C.

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 surface of the cast unstretched film opposite the cooling roll. For example, it is preferable to use a combination of a method of contacting the surface 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-velocity fluid. The unstretched film thus obtained is stretched in biaxial directions to obtain the biaxially stretched polyamide film of the present invention.

The stretching method may be either a simultaneous biaxial stretching method or a sequential biaxial stretching method. In either case, multi-stage stretching such as one-stage stretching or two-stage stretching can be used as the stretching method in the MD direction. As described later, multi-stage MD stretching such as two-stage stretching is preferable in terms of physical properties and uniformity of physical properties in the MD and TD directions (isotropy) rather than one-stage stretching. Roll stretching is preferable for stretching in the MD direction in the sequential biaxial stretching method.

The lower limit of the MD stretching temperature is preferably 50°C, more preferably 55°C, and even more preferably 60°C. If it is less than 50°C, the resin does not soften and stretching may be difficult. The upper limit of the MD stretching temperature is preferably 120°C, more preferably 115°C, and even more preferably 110°C. If it exceeds 120°C, the resin may become 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 times, more preferably 2.5 times, and even more preferably 2.8 times. If it is less than 2.2 times, the thickness accuracy in the MD direction decreases, and the crystallinity may become too low, resulting in a decrease in impact strength. The upper limit of the stretch 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, subsequent stretching may become difficult.

In addition, when stretching in the MD direction is performed in multiple stages, the above-mentioned stretching is possible in each stretching, 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 using a tenter, heat-set, and relaxed (also called relaxation). The lower limit of the stretching temperature in the TD direction is preferably 50°C, more preferably 55°C, and even more 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 even more 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 may become too low, resulting in a decrease in impact strength. The upper limit of the stretch ratio in the TD direction is preferably 5.5, more preferably 5.0, even more preferably 4.7, particularly preferably 4.5, and most preferably 4.3. If it exceeds 5.5, productivity may decrease significantly.

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 210°C, more preferably 212°C. If the heat setting temperature is too low, the thermal shrinkage rate becomes too large, which deteriorates the appearance after lamination and tends to reduce the laminate strength. The upper limit of the heat setting temperature is preferably 220°C, more preferably 218°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. It is preferably 1 to 15 seconds. The heat setting time can be adjusted 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 a heat setting temperature of -10°C to Tg + 10°C is preferable. 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%, and more preferably 1%. If it is less than 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 even more preferably 10%. If it exceeds 20%, sagging may occur in the tenter, making production difficult.

Furthermore, the biaxially stretched 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, in order to improve the adhesion of the film surface, corona treatment, coating treatment, flame treatment, etc., printing processing, and deposition processing of metal objects, inorganic oxides, etc. can be performed. As the deposition film formed by deposition processing, an aluminum deposition film, or a deposition film of silicon oxide or aluminum oxide alone or a mixture thereof is preferably used. Furthermore, by coating a protective layer on these deposition films, oxygen barrier properties, etc. can be improved.

[Laminated films and bags]
The biaxially stretched polyamide film of the present invention is laminated with a sealant film or the like to form a laminate film, which is then processed into packaging bags such as bottom-sealed bags, side-sealed bags, three-side-sealed bags, pillow bags, standing pouches, gusseted bags, square-bottom bags, etc. Examples of the sealant film include unstretched linear low-density polyethylene films, unstretched polypropylene films, and ethylene-vinyl alcohol copolymer resin films.

The layer structure of the laminated film of the present invention using the biaxially oriented polyamide film of the present invention is not particularly limited as long as it contains the biaxially oriented polyamide film of the present invention in the laminated film. In addition, 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 the environmental load.

Examples of layer configurations of the laminated film of the present invention include ONY/adhesive/LLDPE, ONY/adhesive/CPP, ONY/adhesive/Al/adhesive/CPP, ONY/adhesive/Al/adhesive/LLDPE, ONY/PE/Al/adhesive/LLDPE, ONY/adhesive/Al/PE/LLDPE, PET/adhesive/ONY/adhesive/LLDPE, PET/adhesive/ONY/PE/LLDPE, PET/adhesive/ONY/adhesive/Al/adhesive/LLDPE, PET/adhesive/ONY/PE/LLDPE, PET/adhesive/ONY/adhesive/Al/adhesive/LLDPE, PET/adhesive adhesive/Al/adhesive/ONY/adhesive/LLDPE, PET/adhesive/Al/adhesive/ONY/PE/LLDPE, PET/PE/Al/PE/ONY/PE/LLDPE, PET/adhesive/ONY/adhesive/CPP, PET/adhesive/ONY/adhesive/Al/adhesive/CPP, PET/adhesive/Al/adhesive/ONY/adhesive/CPP, ONY/adhesive/PET/adhesive/LLDPE, ONY/adhesive/PET/PE/LLDPE, ONY/adhesive/PET/adhesive/ CPP, ONY/adhesive/Al/adhesive/PET/adhesive/LLDPE, ONY/adhesive/Al/v/PET/PE/LLDPE, ONY/PE/LLDPE, ONY/PE/CPP, ONY/PE/Al/PE, ONY/PE/Al/PE/LLDPE, OPP/adhesive/ONY/adhesive/LLDPE, ONY/adhesive/EVOH/adhesive/LLDPE, ONY/adhesive/EVOH/adhesive/CPP, ONY/adhesive/aluminum-deposited PET/adhesive/LLDPE, ON Examples of adhesives include Y/adhesive/aluminum-vapor-deposited PET/adhesive/ONY/adhesive/LLDPE, ONY/adhesive/aluminum-vapor-deposited PET/PE/LLDPE, ONY/PE/aluminum-vapor-deposited PET/PE/LLDPE, ONY/adhesive/aluminum-vapor-deposited PET/adhesive/CPP, PET/adhesive/aluminum-vapor-deposited PET/adhesive/ONY/adhesive/LLDPE, CPP/adhesive/ONY/adhesive/LLDPE, ONY/adhesive/aluminum-vapor-deposited LLDPE, ONY/adhesive/aluminum-vapor-deposited CPP, etc.
The abbreviations used in the above layer structure are as follows:
/ : indicates the boundary between layers ONY: biaxially oriented polyamide film PET: oriented polyethylene terephthalate film LLDPE: unoriented linear low density polyethylene film CPP: unoriented polypropylene film OPP: oriented polypropylene film PE: extrusion laminate or unoriented low density polyethylene film Al: aluminum foil EVOH: ethylene-vinyl alcohol copolymer resin adhesive: adhesive layer that bonds films together Aluminum vapor deposition: indicates that aluminum 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) Haze Value of Film: The haze value was measured using a direct-reading haze meter manufactured by Toyo Seiki Seisakusho Co., Ltd. in accordance with JIS K7105.
(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) Biomass Degree of Film The biomass degree of the obtained film was measured by radioactive carbon (C ¹⁴ ) measurement according to ASTM D6866-16 Method B (AMS).
(4) Heat Shrinkage of Film The heat shrinkage of the 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 (%)
(5) Impact strength of film: Measured using a film impact tester manufactured by Toyo Seiki Seisakusho Co., Ltd. The measured value was converted per 15 μm thickness and expressed as J (joule)/15 μm.
(6) 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.

(7) Bending Fatigue Pinhole Resistance of Film The number of pinholes caused by bending fatigue was measured by the following method using a Gelbo Flex Tester manufactured by Rigaku Kogyosha.
After applying a polyester adhesive to the 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 at 40° C. to obtain a laminate film. The obtained laminate film was cut into 12 inches by 8 inches, and made into 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, with an initial gripping distance of 7 inches. A flex fatigue test 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 at 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.

(8) 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 pinhole resistance evaluation in 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.
Further, 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 ×. This process is repeated, and levels 3 to 20 are marked 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 occurrence 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 developed is equal to or greater than the number of tests in which holes were developed. Distance at which pinholes were generated by friction = median + 500 x (Σ (coefficient x number of tests in which no holes were developed) / number of tests in which no holes were developed) + 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)

(9) Laminate strength with polyethylene sealant A laminate film prepared in the same manner as described in the explanation of the pinhole resistance evaluation 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 biaxially oriented 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.

(10) Film-forming stability during casting The process of extruding a molten resin into a film from a T-die, casting it onto a cooling roll and cooling it to obtain an unstretched film was visually observed, and the film-forming stability was evaluated as follows.
A: The film formation was stable and a homogeneous unstretched film was obtained.
B: Film formation was a little unstable, and fluctuations were observed in the width of the unstretched film, but biaxial stretching was possible.
C: The film formation was unstable and the unstretched film was inhomogeneous, so that a biaxially stretched film could not be obtained.
In addition, a rating of B or higher indicates practical use.
(11) Generation Cycle of Thermally Degraded Products Formed at the Die Lip Exit After cleaning of the die lip, film production was started, and the time until thermally degraded products formed on the die lip was observed.

(12) 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.
(13) Melting Point of Raw Polyamide The melting point was determined as the endothermic peak temperature (Tmp) in a nitrogen atmosphere using a differential scanning calorimeter, SSC5200 type, manufactured by Seiko Instruments Inc., in accordance with JIS K7121, with a sample weight of 10 mg, a heating start temperature of 30° C., and a heating rate of 20° C./min.

[Polyamide 6]
The polyamide 6 used in the examples and comparative examples is as follows.
Polyamide 6 (a-1)
Relative viscosity 2.8, melting point 220°C, manufactured by Toyobo Co., Ltd.

Polyamide 6 (a-2) obtained by chemical recycling
Relative viscosity 2.7, melting point 221°C
The polyamide 6 fibers recovered from the waste materials and a 75% by mass aqueous phosphoric acid solution serving 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 a chemically recycled polyamide resin.

Polyamide 6 (a-3) obtained by mechanical recycling
Relative viscosity: 2.6, melting point: 221°C
The non-standard film and scrap materials generated as cut ends (edge trims) from the stretched film produced in Example 1 were collected and crushed, 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.

[Example 1-1]
Using an apparatus consisting of an extruder and a 380 mm wide T-die, the following molten 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 the roll to obtain an unstretched film having a thickness of 200 μm.
(Resin composition)
Polyamide 6 (a-1): 92 parts by weight Polyamide 6 (a-2): 5 parts by weight Polyamide 11 (manufactured by Arkema, relative viscosity 2.5, melting point 186° C.): 3 parts by weight Porous silica fine particles (manufactured by Fuji Silysia Chemical Ltd., average particle size 2.0 μm, pore volume 1.6 ml/g): 0.45% by weight
Fatty acid bisamide (ethylene bisstearic acid amide manufactured by Kyoeisha Chemical Co., Ltd.): 0.15% by mass

The unstretched film obtained was introduced into a roll-type stretching machine, and using 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, this uniaxially stretched film 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 7% at 200°C. The surface on the side to be dry-laminated with the linear low-density polyethylene film was then corona discharge-treated to obtain a biaxially stretched polyamide film. The evaluation results of the obtained biaxially stretched film are shown in Table 2.

[Examples 1-2 to 1-12]
A biaxially stretched film was obtained in the same manner as in Example 1-1, except that the raw material resin composition and the film-forming conditions such as the heat setting temperature were changed as shown in Table 2. The evaluation results of the obtained biaxially stretched film are also shown in Table 2. In the examples and comparative examples, the following polyamide resins at least a part of which is derived from biomass were used as raw materials.
Polyamide 410: (manufactured by DSM, ECOPaXX Q150-E, melting point 250° C.)
Polyamide 610: (Arkema, Rilsan S SMNO, melting point 222° C.)
Polyamide 1010: (Arkema, RilsanT TMNO, melting point 202° C.)

As shown in Table 2, the films of the examples had both good pinhole resistance due to bending and good pinhole resistance due to friction. In addition, the films had low haze and good transparency, high impact strength, and high lamination strength with the sealant film, making them excellent as packaging films.

[Comparative Examples 1-1 to 1-5]
A biaxially stretched film was obtained in the same manner as in Example 1-1, except that the raw material resin composition and the film-forming conditions such as the heat setting temperature were changed as shown in Table 3. The evaluation results of the obtained biaxially stretched film are shown in Table 3. However, in Comparative Example 1-4, the molten resin could not be stably extruded from the T-die into a film shape, and a homogeneous unstretched film could not be obtained, so biaxial stretching was not possible.

As shown in Table 3, the biaxially stretched polyamide films of Comparative Examples 1-1 and 1-2, which do not contain a material that modifies the pinhole resistance of bending, and the biaxially stretched polyamide film of Comparative Example 1-3, which contains too little polyamide 11, had poor pinhole resistance of bending. In Comparative Example 1-4, the polyamide 11 content was too high, so the molten resin could not be stably extruded into a film from the T-die, and a homogeneous unstretched film was not obtained, and a biaxially stretched polyamide film was not obtained. In Comparative Example 1-5, when a polyamide elastomer that is conventionally used as a material that modifies the pinhole resistance of bending was used, the pinhole resistance of bending was good, but the pinhole resistance of abrasion was poor. In addition, there was a drawback that deterioration materials were easily attached to the die during long-term production, making it impossible to perform long-term continuous production.

[Example 2-1]
Using an apparatus consisting of two extruders and a 380 mm wide coextrusion T-die, the layers were laminated in a B layer/A layer/B layer configuration by the feed block method, and the molten resin 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 feed block configuration and the extrusion rate of the extruder were adjusted so that the biaxially stretched polyamide film had a total thickness of 15 μm, a base layer (A layer) thickness of 12 μm, and front and back surface layers (B layers) thicknesses of 1.5 μm each.

The resin compositions of the layers A and B used in Example 2 were as follows.
(Resin composition constituting layer A)
Polyamide 6 (a-1): 92 parts by mass Chemically recycled polyamide 6 (a-2): 5 parts by mass Polyamide 11 (manufactured by Shuseisha, relative viscosity 2.5, melting point 186° C.): 3 parts by mass (resin composition constituting layer B)
Polyamide 6 (a-1): 90 parts by mass Chemically recycled polyamide 6 (a-2): 5 parts by mass Polyamide MXD6 (manufactured by Mitsubishi Gas Chemical Co., Ltd., relative viscosity 2.1, melting point 237 ° C.): 5 parts by mass Porous silica fine particles (manufactured by Fuji Silysia Chemical Co., Ltd., average particle size 2.0 μm, pore volume 1.6 ml / g): 0.54 mass%
Fatty acid bisamide (ethylene bisstearic acid amide manufactured by Kyoeisha Chemical Co., Ltd.): 0.15% by mass

The unstretched film obtained was introduced into a roll-type stretching machine, and using 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, this uniaxially stretched film 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. The surface on the side to be dry-laminated with the linear low-density polyethylene film was then corona discharge-treated to obtain a biaxially stretched polyamide film. The evaluation results of the obtained biaxially stretched film are shown in Table 4.

[Examples 2-2 to 2-12]
A biaxially stretched film was obtained in the same manner as in Example 2-1, except that the resin compositions of the A layer and the B layer, the heat setting temperature, and other film-forming conditions were changed as shown in Table 4. The evaluation results of the obtained biaxially stretched film are also shown in Table 4.

As shown in Table 4, the films of the examples had both good pinhole resistance due to bending and good pinhole resistance due to friction. In addition, the films had low haze and good transparency, high impact strength, and high lamination strength with the sealant film, making them excellent as packaging films.

[Comparative Examples 2-1 to 2-7]
A biaxially stretched film was obtained in the same manner as in Example 2-1, except that the film-forming conditions such as the resin compositions of Layer A and Layer B and the heat setting temperature were changed as shown in Table 5. The evaluation results of the obtained biaxially stretched film are also shown in Table 5. However, in Comparative Example 2-4, the molten resin could not be stably extruded from the T-die into a film shape, and a homogeneous unstretched film could not be obtained, so biaxial stretching was not possible.

The biaxially stretched polyamide films of Comparative Examples 2-1 and 2-2, which do not contain a material for modifying pinhole resistance, and the biaxially stretched polyamide film of Comparative Example 2-3, which contains too little polyamide 11, were inferior in pinhole resistance. In Comparative Example 2-4, the content of polyamide 11 was too high, so the molten resin could not be stably extruded from the T-die into a film, and a homogeneous unstretched film was not obtained, and a biaxially stretched polyamide film was not obtained. In Comparative Example 2-5, the thickness and thickness ratio of the A layer were small, so the film had poor pinhole resistance. In Comparative Example 2-6, the amount of polyamide MXD6 in the B layer was large and the amount of polyamide 6 resin was small, so the film had poor pinhole resistance and abrasion pinhole resistance. In Comparative Example 2-7, a polyamide elastomer that has been conventionally used as a material for modifying pinhole resistance was used, and the film had good pinhole resistance but poor abrasion pinhole resistance. Furthermore, there was a drawback in that deterioration materials were likely to adhere to the die during long periods of production, making it impossible to carry out long periods of continuous production.

[Examples 3 and 4]
The biaxially stretched polyamide films produced in Examples 1-2 and 2-2 were used to produce laminated films having the following configurations (1) to (9), and the laminated films (1) to (9) were used to produce three-sided sealed and pillow-type packaging bags. The packaging bags had good appearance and were resistant to tearing in a drop impact test.
(1) Biaxially oriented polyamide film layer/printed layer/polyurethane adhesive layer/linear low density polyethylene film sealant layer (2) Biaxially oriented polyamide film layer/printed layer/polyurethane adhesive layer/unstretched polypropylene film sealant layer (3) Biaxially oriented PET film layer/printed layer/polyurethane adhesive layer/biaxially oriented polyamide film layer/polyurethane adhesive layer/unstretched polypropylene film sealant layer (4) Biaxially oriented PET film layer/printed layer/polyurethane adhesive layer/biaxially oriented polyamide film layer/polyurethane adhesive layer/linear low density polyethylene film sealant layer (5) Biaxially oriented polyamide film layer/anchor coat layer/inorganic thin film layer/inorganic thin film protective layer/printed layer/polyurethane adhesive layer/linear low density polyethylene film sealant layer (6) Linear low density polyethylene film sealant layer/polyurethane adhesive adhesive layer/biaxially oriented polyamide film layer/anchor coat layer/inorganic thin film layer/polyurethane adhesive layer/linear low density polyethylene film sealant layer (7) linear low density polyethylene film layer/polyurethane adhesive layer/biaxially oriented polyamide film layer/anchor coat layer/inorganic thin film layer/polyurethane adhesive layer/linear low density polyethylene film layer/low density polyethylene/paper/low density polyethylene/linear low density polyethylene film sealant layer (8) biaxially oriented polyamide film layer/anchor coat layer/inorganic thin film layer/inorganic thin film protective layer/printed layer/polyurethane adhesive layer/non-oriented polypropylene film sealant layer (9) biaxially oriented PET film layer/inorganic thin film layer/inorganic thin film protective layer/printed layer/polyurethane adhesive layer/biaxially oriented polyamide film layer/polyurethane adhesive layer/easy peel type non-oriented polypropylene film sealant layer

The biaxially oriented polyamide film of the present invention is excellent in impact resistance, bending pinhole resistance, and abrasion pinhole resistance at the same time, and therefore can be suitably used as a packaging material such as food packaging. Furthermore, since the film uses a resin polymerized from raw materials derived from biomass that is originally on the ground, it is a carbon-neutral film and has little impact on the increase or decrease of carbon dioxide on the ground, thereby reducing the environmental load. Furthermore, since the film contains polyamide 6 chemically recycled from waste polyamide products, plastic products that were previously discarded can be reused, reducing the environmental load and contributing to reducing the amount of plastic waste discharged.

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

Claims (9)

The resin contains only a polyamide resin, and the polyamide resin contains only 70 to 99% by mass of polyamide 6 and 1 to 30% by mass of polyamide 11 , at least a part of which is derived from biomass as a raw material;
A method for producing a biaxially oriented polyamide film, wherein the polyamide 6 contains 5 to 100 parts by mass of polyamide 6 obtained by chemical recycling, and more than 0 part by mass but not more than 50 parts by mass of polyamide 6 obtained by mechanical recycling, based on 100 parts by mass of polyamide 6. The method for producing a biaxially oriented polyamide film according to claim 1, characterized in that the content of biomass-derived carbon as determined by radioactive carbon (C ¹⁴ ) measurement is 1 to 15% of the total carbon in the biaxially oriented polyamide film. 3. A method for producing a biaxially oriented polyamide film in which one or more layers are laminated on both sides of a biaxially oriented polyamide film obtained by the method for producing a biaxially oriented polyamide film according to claim 1 or 2, wherein the laminated layers contain 70 to 100 mass% of polyamide 6, and the polyamide 6 contains 5 to 100 parts by mass of polyamide 6 obtained by chemical recycling , and more than 0 parts by mass and 50 parts by mass or less of polyamide 6 obtained by mechanical recycling, based on 100 parts by mass of polyamide 6. The method for producing a biaxially oriented polyamide film according to claim 3 , wherein the thickness of the laminated layer is 7 to 50% of the total thickness of the film. A method for producing a biaxially oriented polyamide film, characterized in that the biaxially oriented polyamide film obtained by the method for producing a biaxially oriented polyamide film according to any one of claims 1 to 4 satisfies the following (a) and (b):
(a) The number of pinhole defects is 10 or less when a twisting and bending test using a Gelbo flex tester is performed 1,000 times at a temperature of 1° C.;
(b) The distance until pinholes appear in the friction pinhole resistance test is 2900 cm or more. A method for producing a biaxially oriented polyamide film, characterized in that the biaxially oriented polyamide film obtained by the method for producing a biaxially oriented polyamide film according to any one of claims 1 to 5 has a haze of 10% or less and a dynamic friction coefficient of 1.0 or less. A method for producing a biaxially oriented polyamide film, characterized in that the biaxially oriented polyamide film obtained by the method for producing a biaxially oriented polyamide film according to any one of claims 1 to 5 and a polyethylene sealant film are laminated together to have a laminate strength of 4.0 N/15 mm or more. A method for producing a laminated film, comprising laminating a sealant film on at least one side of the biaxially oriented polyamide film obtained by the method for producing a biaxially oriented polyamide film according to any one of claims 1 to 7 . A method for producing a packaging bag using the laminated film obtained by the method for producing a laminated film according to claim 8 .