Biaxially oriented polyamide film

Abstract

[Problem] To provide a biaxially stretched polyamide film having excellent resistance against pinholes due to bending and resistance against pinholes due to repeated contact, and having excellent puncture resistance, and further making it possible to inhibit generation of foreign matter during film formation. [Solution] A biaxially stretched polyamide film obtained by laminating a functional layer (layer B) on at least one surface of a substrate layer (layer A), the biaxially stretched polyamide film being characterized in that: the substrate layer (layer A) contains at least (a) 70-99 mass% of a polyamide 6 resin and (b) 1-20 mass% of an aliphatic or an aromatic aliphatic polyester resin, and the functional layer (layer B) contains at least 70 mass% or more of a polyamide 6 resin.

Description

Technical Field

[0001] The present invention relates to a biaxially stretched polyamide film excellent in impact resistance, flexural pinhole resistance, and friction pinhole resistance. The biaxially stretched polyamide film of the present invention is suitably used for films for food packaging and the like.

Background Art

[0002] Conventionally, a biaxially stretched film made of an aliphatic polyamide typified by polyamide 6 has excellent impact resistance and flexural pinhole resistance and is widely used as various packaging material films.

[0003] Also, for liquid filling packaging such as soups and seasonings, in order to further improve flexural pinhole resistance and impact resistance, a biaxially stretched polyamide film in which various elastomers (rubber components) are mixed with an aliphatic polyamide to be more flexible and improve flexural pinhole resistance is used.

[0004] As a means for improving the above flexural pinhole resistance, a film in which a polyamide-based elastomer is mixed with an aliphatic polyamide is known (see, for example, Patent Document 1). This film has good flexural pinhole resistance and impact resistance in a low-temperature environment, and pinholes due to flexural fatigue are less likely to occur even in a low-temperature environment. However, in the case of a film in which a polyamide-based elastomer is mixed with an aliphatic polyamide, since the polyamide-based elastomer added during film production thermally deteriorates, it is easy to generate a deteriorated product called a lip at the die lip outlet. The deteriorated product itself drops to produce defective products, and there is a problem of reducing the production efficiency during continuous film production.

[0005] Pinholes are generated not only by bending but also by friction (rubbing). The methods for improving pinholes caused by bending and those caused by friction often conflict with each other. For example, increasing the flexibility of the film makes it less likely to generate bending pinholes, but on the other hand, the softer the film becomes, the more likely it is to generate pinholes due to friction. In contrast, a laminated body for packaging has been proposed that improves the generation of pinholes caused by bending and friction by providing a surface coating agent on the outer surface of a biaxially stretched polyamide film (see, for example, Patent Document 2). However, this method has little effect on preventing the generation of friction pinholes. In addition, a coating process is required.

[0006] Furthermore, for example, Patent Documents 3 and 4 disclose a stretched film made of a polyamide-based resin composition containing 1 to 10% by mass of a polyester-based thermoplastic elastomer. According to such a technique, it is said to have excellent bend resistance even in a low-temperature environment. However, also in these techniques, since an elastomer component with low heat resistance exists on the surface layer, there is still room for improvement in the problem that it is easy to generate a deteriorated product called a die lip deposit at the die lip outlet.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention was created in view of the problems of such prior art. The object of the present invention is to provide a biaxially stretched polyamide film that is excellent in pinhole resistance due to bending and pinhole resistance due to repeated contact, excellent in puncture resistance, and capable of suppressing the generation of foreign matters during film formation. Furthermore, in addition to the above, it is excellent in water-resistant adhesion strength with a sealant film, and further to provide an easily adhesive polyamide film capable of suppressing the generation of foreign matters during film formation, or a biaxially stretched polyamide film excellent in gas barrier properties.

Means for Solving the Problems

[0009] The present invention comprises the following configuration. 〔1〕 A biaxially stretched polyamide film in which a functional layer (B layer) is laminated on at least one side of a base material layer (A layer), wherein the base material layer (A layer) contains at least (a) 70 to 99% by mass of polyamide 6 resin and (b) 1 to 20% by mass of an aliphatic or aromatic aliphatic polyester resin, and the functional layer (B layer) contains at least 70% by mass or more of polyamide 6 resin. 〔2〕 The biaxially stretched polyamide film according to 〔1〕, wherein the (b) aliphatic or aromatic aliphatic polyester resin is at least one polyester resin selected from the group consisting of polybutylene succinate, polybutylene succinate adipate, and polybutylene adipate terephthalate. 〔3〕 The biaxially stretched polyamide film according to 〔1〕 or 〔2〕, wherein the base material layer (A layer) contains a polyamide resin at least part of the raw material of which is derived from biomass. 〔4〕 The biaxially stretched polyamide film according to 〔3〕, wherein the polyamide resin at least part of the raw material 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〕 The biaxially stretched polyamide film according to any one of 〔1〕 to 〔4〕, characterized in that the biaxially stretched polyamide film satisfies the following (a) to (c). When the number of bending fatigue pinholes is 5 or less when the bending test using a gelboflex tester is carried out 1000 times at a temperature of 1 °C When the distance until pinholes occur in the friction resistance pinhole test is 2900 cm or more When the piercing strength of the film is 0.67 N / μm or more A biaxially stretched polyamide film having a coating layer containing at least one resin selected from the group consisting of a polyester resin, a polyurethane resin, a polyacrylic resin, and an acrylic graft copolymer polyester resin in an amount of 0.01 to 3 g / m2 as a solid content on at least one side of the biaxially stretched polyamide film according to any one of [1] to [5]. A polyamide film having an inorganic thin film layer on at least one side of the biaxially stretched polyamide film according to any one of [1] to [6]. A laminated film in which a sealant film is laminated on the biaxially stretched polyamide film according to any one of [1] to [7]. A packaging bag using the laminated film according to [8].

Advantages of the Invention

[0010] The biaxially stretched polyamide film of the present invention is mainly composed of a polyamide 6 resin, and by disposing a layer blended with a specific polyester-based resin on the inner layer of the film, it is excellent in impact resistance, bending pinhole resistance, and friction pinhole resistance.

[0011] In addition, since the elastomer component does not deteriorate inside the die in the film forming process of the film, it is possible to suppress the adhesion of deteriorated products to the inner surface of the die and the adhesion of eye varnish to the die lip outlet over a long period of time. It is possible to suppress the film thickness unevenness caused by the adhesion of deteriorated products to the inner surface of the die or the die lip outlet. In addition, since the number of times of cleaning the die lip by stopping production can be reduced, the biaxially stretched polyamide film of the present invention enables continuous production for a long time.

Brief Description of the Drawings

[0012]

Figure 1

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the biaxially stretched polyamide film of the present invention will be described in detail. The biaxially stretched polyamide film of the present invention is a biaxially stretched polyamide film in which a functional layer (B) is laminated on at least one side of an A layer (base material layer). Hereinafter, the details of each layer will be described.

[0014] [A layer (base material layer)] The base material layer (A layer) is composed of a resin composition containing at least (a) 70 to 99% by mass of polyamide 6 resin and (b) 1 to 20% by mass of an aliphatic or aromatic aliphatic polyester resin.

[0015] By containing 70% by mass or more of polyamide 6 resin in the base material layer (A layer), a biaxially stretched polyamide film having excellent mechanical strength such as impact strength and gas barrier properties such as oxygen can be obtained. Polyamide 6 used for the base material layer (A layer) is usually produced by ring-opening polymerization of ε-caprolactam. The polyamide 6 obtained by ring-opening polymerization is usually dried after removing the lactam monomer with hot water and then melt-extruded with an extruder.

[0016] The relative viscosity of polyamide 6 is preferably 1.8 to 4.5, more preferably 2.6 to 3.2. When the relative viscosity is less than 1.8, the impact strength of the film is insufficient. When it is greater than 4.5, the load on the extruder increases and it becomes difficult to obtain an unstretched film before stretching.

[0017] When the base material layer (layer A) contains 1 to 20% by mass of an aliphatic or aromatic aliphatic polyester resin, a biaxially stretched polyamide film excellent in flexing pinhole resistance can be obtained. As the aliphatic or aromatic aliphatic polyester resin contained in the base material layer (layer A), those having a glass transition temperature (Tg) of minus 30°C or lower are preferred. By using a polyester copolymer having a glass transition temperature of minus 30°C or lower, excellent pinhole resistance can be exhibited even in a frozen environment. Among them, as the preferred aliphatic polyester resin, polybutylene succinate and polybutylene succinate adipate are preferred, and as the aromatic aliphatic polyester resin, polybutylene adipate terephthalate is preferred in terms of having flexible characteristics.

[0018] The lower limit of the aliphatic or aromatic aliphatic polyester resin contained in the base material layer (layer A) is preferably 1% by mass, more preferably 2% by mass, and most preferably 3% by mass. When the addition amount of the aliphatic or aromatic aliphatic polyester resin contained in the base material layer (layer A) is less than 1% by mass, the effect of improving the flexing pinhole resistance cannot be obtained. The upper limit of the aliphatic or aromatic aliphatic polyester resin contained in the base material layer (layer A) is preferably 20% by mass, more preferably 15% by mass. When the addition amount of the aliphatic or aromatic aliphatic polyester resin contained in the base material layer (layer A) exceeds 20% by mass, the film becomes too soft, not only the puncture strength and impact strength decrease, but also the film becomes easy to stretch, so that pitch deviation and the like are likely to occur during processing such as printing.

[0019] The base material layer (layer A) can further improve the flexing pinhole resistance by containing a specific polyamide resin containing a biomass-derived raw material. The upper limit of the content of the polyamide resin in which at least a part of the raw material contained in the base material layer (layer A) is derived from biomass is preferably 30% by mass, more preferably 20% by mass. When the content of the polyamide resin in which at least a part of the raw material is derived from biomass exceeds 30% by mass, the molten film becomes unstable when casting the molten film, and it becomes difficult to obtain a homogeneous unstretched film.

[0020] As the polyamide resin in which at least a part of the raw materials that can be used for the base material layer (A layer) is derived from biomass, polyamide 11, polyamide 610, polyamide 1010, and polyamide 410 are preferable from the viewpoint of availability.

[0021] The 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 undecanolactam as a monomer. In particular, aminoundecanoic acid is a monomer obtained from castor oil, and thus is desirable from the viewpoint of environmental protection (especially from the viewpoint of carbon neutrality). The structural units derived from these monomers having 11 carbon atoms are preferably 50% or more of all the structural units in polyamide 11, and may be 100%. The polyamide 11 is usually produced by ring-opening polymerization of the aforementioned undecanolactam. The polyamide 11 obtained by ring-opening polymerization is usually dried after removing the lactam monomer with hot water, and then 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. When the relative viscosity is less than 1.8, the impact strength of the film is insufficient. When it is greater than 4.5, the load on the extruder increases and it becomes difficult to obtain an unstretched film before stretching.

[0022] The polyamide 610 is a polyamide resin having a structure in which a monomer having 6 carbon atoms and a monomer having 10 carbon atoms are bonded via an amide bond. Usually, polyamide 610 is obtained by copolymerization of diamine and dicarboxylic acid, and hexamethylenediamine and sebacic acid are used respectively. Among these, sebacic acid is a monomer obtained from castor oil, and thus is desirable from the viewpoint of environmental protection (especially from the viewpoint of carbon neutrality). The total of the structural units derived from these monomers having 6 carbon atoms and the structural units derived from the monomers having 10 carbon atoms is preferably 50% or more of all the structural units in polyamide 610, and may be 100%.

[0023] The above 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 copolymerized. Usually, 1,10-decanediamine (decamethylenediamine) and sebacic acid are used for polyamide 1010. Since decamethylenediamine and sebacic acid are monomers obtained from castor oil, they are desirable from the viewpoint of environmental protection (especially 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 the dicarboxylic acid having 10 carbon atoms is preferably 50% or more of all the structural units in polyamide 1010, and may be 100%.

[0024] The above polyamide 410 is a polyamide resin having a structure in which a monomer having 4 carbon atoms and a diamine having 10 carbon atoms are copolymerized. Usually, sebacic acid and tetramethylenediamine are used for polyamide 410. As sebacic acid, those using castor oil derived from vegetable oil are preferred from the environmental aspect. The sebacic acid used here is desirable from the viewpoint of environmental protection (especially from the viewpoint of carbon neutrality) as it is obtained from castor oil.

[0025] The base material layer (A layer) can contain various additives such as other thermoplastic resins, lubricants, heat stabilizers, antioxidants, antistatic agents, antifogging agents, ultraviolet absorbers, dyes, and pigments as necessary.

[0026] The base material layer (A layer) can contain a thermoplastic resin other than polyamide 6 resin within a range that does not impair the object of the present invention. Examples include polyamide-based resins such as polyamide 12 resin, polyamide 66 resin, polyamide 6·12 copolymer resin, polyamide 6·66 copolymer resin, polyamide MXD6 resin, polyamide MXD10 resin, and polyamide 11·6T copolymer resin. If necessary, thermoplastic resins other than polyamide resins, such as polyester polymers such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate, and polyolefin polymers such as polyethylene and polypropylene, may be contained.

[0027] [Functional layer (layer B)] The functional layer (layer B) is characterized by containing 70 to 100% by mass or more of polyamide 6 resin. By containing 70% by mass or more of polyamide 6 resin in the functional layer (layer B), a biaxially stretched polyamide film having excellent mechanical strength such as impact strength and gas barrier properties such as oxygen can be obtained. As the polyamide 6 resin, the same resin as the polyamide 6 resin used in the base material layer (layer A) can be used.

[0028] In the functional layer (layer B), various additives such as other thermoplastic resins, lubricants, heat stabilizers, antioxidants, antistatic agents, antifogging agents, ultraviolet absorbers, dyes, and pigments can be contained according to the function of having them on the surface of the functional layer (layer B). When the functional layer (layer B) is used on the outside of the packaging bag, since friction-resistant pinhole resistance is required, it is not preferable to contain soft resins such as polyamide-based elastomers and polyolefin-based elastomers or substances that generate a large amount of voids.

[0029] In the functional layer (layer B), within a range not impairing the object of the present invention, a thermoplastic resin can be contained in addition to the polyamide 6 resin. Examples include polyamide-based resins such as 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, thermoplastic resins other than polyamide resins, such as polyester polymers such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate, and polyolefin polymers such as polyethylene and polypropylene, may be contained.

[0030] In the functional layer (layer B), in order to improve the film slipperiness, it is preferable to contain fine particles, organic lubricants, etc. as lubricants. By improving the slipperiness, the handleability of the film is improved, and the breakage of the packaging bag due to rubbing is reduced.

[0031] As the above-mentioned fine particles, it is possible to appropriately select and use from among inorganic fine particles such as silica, kaolin, zeolite, and polymer-based organic fine particles such as acrylic-based and polystyrene-based fine particles. From the viewpoints of transparency and slipperiness, it is preferable to use silica fine particles.

[0032] The preferable average particle diameter of the above-mentioned fine particles is 0.5 to 5.0 μm, and more preferably 1.0 to 3.0 μm. If the average particle diameter is less than 0.5 μm, a large amount of addition 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 and the appearance tends to deteriorate.

[0033] When using the above-mentioned silica fine particles, the pore volume range of silica is preferably 0.5 to 2.0 ml / g, and more preferably 0.8 to 1.6 ml / g. If the pore volume is less than 0.5 ml / g, voids are likely to occur and the transparency of the film deteriorates. If the pore volume exceeds 2.0 ml / g, the formation of protrusions on the surface by the fine particles tends to be difficult.

[0034] As the above-mentioned organic lubricant, fatty acid amide and / or fatty acid bisamide can be contained. Examples of fatty acid amide and / or fatty acid bisamide include erucic acid amide, stearic acid amide, ethylene bisstearic acid amide, ethylene bisbehenic acid amide, ethylene bisoleic acid amide, etc. The content of fatty acid amide and / or fatty acid bisamide added to the functional layer (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 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.

[0035] In the functional layer (layer B), 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 for the purpose of improving the slipperiness of the film. In particular, polyamide MXD6 resin is preferable, and it is preferably added in an amount of 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 saturates.

[0036] 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, more preferably 2.0 to 3.2. When the relative viscosity is less than 1.8 or more than 4.5, it may be difficult to knead with the polyamide resin in an extruder.

[0037] Also, polyamide resins other than polyamide 6 can be added to the functional layer (layer B) for the purpose of improving adhesiveness. In this case, copolymer polyamide resins such as polyamide 6·12 copolymer resin and polyamide 6·66 copolymer resin are preferable.

[0038] As a method of adding auxiliary materials and additives such as lubricants and antioxidants to the base material layer (layer A) and the functional layer (layer B) of the biaxially stretched polyamide film of the present invention, it can be added during resin polymerization or during melt extrusion in an extruder. A high-concentration masterbatch may be prepared and the masterbatch may be added to the polyamide resin during film production. It can be carried out by such known methods.

[0039] The thickness of the biaxially stretched 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 those with a thickness of 5 to 50 μm are used, and particularly those with a thickness of 8 to 30 μm are used.

[0040] In the thickness configuration of the base material layer (A layer) and the functional layer (B layer) of the biaxially stretched polyamide film of the present invention, when the thickness of the functional layer (B layer) occupies most of the total film thickness, the flexural pinhole resistance decreases. Therefore, in the present invention, it is preferable that the thickness of the base material layer (A layer) is 50 to 93%, particularly 60 to 93%, of the total thickness of the base material layer (A layer) and the functional layer (B layer).

[0041] When using a polyamide resin in which at least a part of the raw materials of the biaxially stretched polyamide film of the present invention is derived from biomass, the content of carbon derived from biomass by the above radiocarbon (C14) measurement is preferably 1 to 15% with respect to the total carbon in the polyamide film.

[0042] The biaxially stretched polyamide film of the present invention has 5 or less pinhole defects when the torsion bending test using a gelbo flex tester by the measurement method described in the examples is carried out 1000 times at a temperature of 1°C. More preferably, it is 3 or less. The fewer the number of pinhole defects after the bending test, the better the flexural pinhole resistance. If the number of pinholes is 5 or less, a packaging bag in which pinholes are less likely to occur even when a load is applied to the packaging bag during transportation can be obtained.

[0043] Furthermore, the biaxially stretched polyamide film of the present invention has a distance to pinhole generation of 2900 cm or more in the friction-resistant pinhole test by the measurement method described in the examples. More preferably, it is 3100 cm or more, and still more preferably 3300 cm or more. The longer the distance at which pinholes occur, the better the friction-resistant pinhole resistance. If the distance at which pinholes occur is 2900 cm or more, a packaging bag in which pinholes are less likely to occur even when the packaging bag rubs against a cardboard box or the like during transportation can be obtained.

[0044] The biaxially stretched polyamide film of the present invention is characterized in that both the above flexural pinhole resistance and friction-resistant pinhole resistance are excellent. The biaxially stretched polyamide film of the present invention having these characteristics is extremely useful as a packaging film because pinholes are less likely to occur during transportation.

[0045] The film of the present invention preferably has a heat shrinkage rate at 160°C for 10 minutes in both the flow direction (hereinafter abbreviated as the MD direction) and the width direction (hereinafter abbreviated as the TD direction) in the range of 0.6 to 3.0%, more preferably 0.6 to 2.5%. When 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. Also, the lamination strength with the sealant film may become weak. Although it is possible to make the heat shrinkage rate less than 0.6%, it may become mechanically brittle. Also, productivity may deteriorate.

[0046] Since excellent impact resistance is a characteristic of the biaxially stretched polyamide film, the impact strength of the biaxially stretched polyamide film of the present invention is preferably 0.7 J / 15 μm or more. A more preferable impact strength is 0.9 J / 15 μm or more.

[0047] The puncture strength of the film of the present invention is preferably 0.67 N / μm or more. By setting the puncture strength to 0.67 N / μm or more, even when a solid content or the like is filled, it is possible to suppress the content from piercing the bag and opening a hole in the bag, or the bag from being opened by external factors during transportation.

[0048] The haze value of the biaxially stretched polyamide film of the present invention is preferably 10% or less. More preferably 7% or less, and even more preferably 5% or less. When the haze value is small, the transparency and gloss are good. Therefore, when used for a packaging bag, beautiful printing can be performed, enhancing the commercial value. Since adding fine particles to improve the slipperiness of the film increases the haze value, it is possible to reduce the haze value by adding the fine particles only to the functional layer (B layer) of the surface layer.

[0049] The biaxially oriented polyamide film of the present invention preferably has a laminating strength of 4.0 N / 15 mm or more after being laminated with the polyethylene-based sealant film 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 above laminating 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 laminated configurations, sufficient strength of the seal portion can be obtained, and a packaging bag that is difficult to break can be obtained. In order to make the laminating 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.

[0050] [Method for producing biaxially oriented polyamide film] The biaxially oriented polyamide film of the present invention can be produced by a known production method. For example, a sequential biaxial stretching method and a simultaneous biaxial stretching method can be mentioned. The sequential biaxial stretching method is preferable because the film production speed can be increased, which is advantageous in terms of production cost.

[0051] The method for producing the biaxially oriented polyamide film of the present invention will be described. First, the raw material resin is melt-extruded using an extruder, extruded in a film shape from a T-die, cast on a cooling roll and cooled to obtain an unstretched film. In the present invention, in order to obtain an unstretched film in which a base material layer (A layer) and a functional layer (B layer) are laminated, a co-extrusion method using a feed block, a multi-manifold, etc. is preferable. In addition to the co-extrusion method, a dry lamination method, an extrusion lamination method, etc. can also be selected. When laminating by the co-extrusion method, it is desirable that the difference in melt viscosity between the polyamide resin compositions used for the base material layer (A layer) and the functional layer (B layer) is reduced.

[0052] The melting temperature of the resin is preferably 220 to 350 °C. If it is less than the above, unmolten materials may occur, and appearance defects such as flaws may occur. If it exceeds the above, resin deterioration etc. may be observed, and molecular weight reduction and appearance deterioration may occur. The die temperature is preferably 250 to 350 °C. The cooling roll temperature is preferably -30 to 80 °C, and more preferably 0 to 50 °C. To cast and cool the film-like melt extruded from the T-die onto a rotating cooling drum to obtain an unstretched film, for example, a method using an air knife or an electrostatic adhesion method for applying an electrostatic charge can be preferably applied. In particular, the latter is preferably used. Also, it is preferable to cool the opposite side of the cooling roll of the cast unstretched film. For example, it is preferable to use in combination a method of bringing the cooling liquid in the tank into contact with the opposite side of the cooling roll of the unstretched film, a method of applying a liquid that evaporates with a spray nozzle, a method of cooling by spraying a high-speed fluid, etc. The unstretched film thus obtained is stretched in a biaxial direction to obtain the biaxially stretched polyamide film of the present invention.

[0053] As the stretching method, either a simultaneous biaxial stretching method or a sequential biaxial stretching method may be used. The sequential biaxial stretching method is preferable because the film-forming speed can be increased, which is advantageous in terms of manufacturing cost. In any case, as the stretching method in the MD direction, multi-stage stretching such as single-stage stretching or two-stage stretching can be used. As will be described later, multi-stage stretching in the MD direction such as two-stage stretching, rather than single-stage stretching, is preferable in terms of physical properties and the uniformity (isotropy) of the physical properties in the MD direction and the TD direction. The stretching in the MD direction in the sequential biaxial stretching method is preferably roll stretching.

[0054] The lower limit of the stretching temperature in the MD direction is preferably 50 °C, more preferably 55 °C, and even more preferably 60 °C. If it is less than 50 °C, the resin may not soften, and stretching may be difficult. The upper limit of the stretching temperature in the MD direction 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.

[0055] The lower limit of the draw ratio in the MD direction (in the case of multi-stage drawing, the total draw ratio obtained by multiplying each 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, not only will the thickness accuracy in the MD direction decrease, but the degree of crystallinity may become too low and the impact strength may decrease. The upper limit of the draw 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 drawing may become difficult.

[0056] Also, when performing multi-stage drawing in the MD direction, such drawing as described above is possible for each drawing, but regarding the ratio, it is necessary to adjust the draw ratio so that the product of the total draw ratios in the entire MD direction is 5.0 or less. For example, in the case of two-stage drawing, the first-stage drawing is preferably 1.5 to 2.1 times, and the second-stage drawing is preferably 1.5 to 1.8 times.

[0057] The film drawn in the MD direction is drawn in the TD direction using a tenter, heat-fixed, and subjected to a relaxation treatment (also referred to as a relaxation treatment). The lower limit of the drawing temperature in the TD direction is preferably 50 °C, more preferably 55 °C, and even more preferably 60 °C. If it is less than 50 °C, the resin may not soften and drawing may become difficult. The upper limit of the drawing temperature in the TD direction is preferably 190 °C, more preferably 185 °C, and even more preferably 180 °C. If it exceeds 190 °C, crystallization may occur and drawing may become difficult.

[0058] The lower limit of the draw ratio in the TD direction (in the case of multi-stage drawing, the total draw ratio obtained by multiplying each ratio) is preferably 2.8, more preferably 3.2 times, even more preferably 3.5 times, and particularly preferably 3.8 times. If it is less than 2.8, not only will the thickness accuracy in the TD direction decrease, but the degree of crystallinity may become too low and the impact strength may decrease. The upper limit of the draw ratio in the TD direction is preferably 5.5 times, more preferably 5.0 times, even more preferably 4.7, particularly preferably 4.5, and most preferably 4.3 times. If it exceeds 5.5 times, productivity may decrease significantly.

[0059] The selection of the heat setting temperature is an important factor in the present invention. As the heat setting temperature increases, the crystallization and orientation relaxation of the film progress, the impact strength can be improved, and the heat shrinkage rate can be reduced. On the other hand, when the heat setting temperature is low, the crystallization and orientation relaxation are insufficient and the heat shrinkage rate cannot be sufficiently reduced.) Also, when the heat setting temperature becomes too high, the resin deteriorates and the toughness of the film such as the impact strength is rapidly lost.

[0060] The lower limit of the heat setting temperature is preferably 210 °C, more preferably 212 °C. When the heat setting temperature is low, the heat shrinkage rate becomes too large and the appearance after lamination deteriorates, and the lamination strength tends to decrease. The upper limit of the heat setting temperature is preferably 220 °C, more preferably 218 °C. When 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 to an appropriate time in consideration of the heat setting temperature and the wind speed in the heat setting zone. If the heat setting conditions are too weak, the crystallization and orientation relaxation will be insufficient and the above problems will occur. If the heat setting conditions are too strong, the film toughness will decrease.

[0061] Performing a relaxation treatment after the heat setting treatment is effective for controlling the heat shrinkage rate. The temperature for the relaxation treatment can be selected in the range from the heat setting treatment temperature to the Tg of the resin, but preferably the heat setting treatment temperature - 10 °C to Tg + 10 °C is preferred. If the relaxation temperature is too high, the shrinkage rate is too fast and it may cause distortion, etc., which is not preferable. On the contrary, if the relaxation temperature is too low, it will not be a relaxation treatment, but simply slacken and the heat shrinkage rate will not decrease, and the dimensional stability will deteriorate. The lower limit of the relaxation rate of the relaxation treatment is preferably 0.5%, more preferably 1%. If it is less than 0.5%, the heat shrinkage rate may not decrease sufficiently. 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 and production may become difficult.

[0062] Furthermore, the biaxially oriented polyamide film of the present invention can be heat-treated or humidity-conditioned to improve dimensional stability according to the intended use. In addition, it is also possible to perform corona treatment, coating treatment, flame treatment, etc. to improve the adhesiveness of the film surface, or to perform printing, vapor deposition of metal objects, inorganic oxides, etc.

[0063] [Coating layer (C)] Another aspect of the biaxially oriented polyamide film of the present invention is a film having a coating layer (C) on at least one side of a biaxially oriented polyester film in order to impart easy adhesiveness to the film. The coating layer (C) can contain at least one resin selected from the group consisting of polyester resin, polyurethane resin, polyacrylic resin, and acrylic graft copolymer polyester resin in an amount of 0.01 to 3 g / m2 as a solid content. The coating layer (C) is preferably provided by applying and drying a coating solution before winding the film as a mill roll in the film manufacturing process. The coating solution can be applied to an unstretched film, a uniaxially oriented film, and / or a biaxially oriented film. When the film is manufactured by the sequential biaxial stretching method, usually, the coating solution is applied to and dried on the uniaxially oriented film. When the film is manufactured by simultaneous biaxial stretching, usually, the coating solution is applied to and dried on the unstretched film.

[0064] Since the coating layer (C) in the present invention is provided by applying and drying a coating solution before winding the film as a mill roll in the film manufacturing process, it is preferable to use an aqueous dispersion of resin for the coating solution in order to ensure safety and hygiene in manufacturing.

[0065] [Polyester resin used for coating layer (C)] When using a polyester resin as the coating layer (C), a copolyester resin can be selected as the polyester resin. The copolyester resin is a polycondensate of a dicarboxylic acid component, a diol component, and other ester-forming components. Examples of the dicarboxylic acid component contained as a constituent in the copolyester resin include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, and 5-sodium sulfoisophthalic acid; aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, and sebacic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and 1,2-cyclohexanedicarboxylic acid; and unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and tetrahydrophthalic acid, etc. can be mentioned.

[0066] In addition to the above dicarboxylic acid components, salts of 5-sulfoisophthalic acid, sulfoterephthalic acid, 4-sulfoisophthalic acid, 4-sulfonaphthalene-2,6-dicarboxylic acid, and 5(4-sulfophenoxy)isophthalic acid can be used to impart water dispersibility. Among them, it is preferable to use 5-sodium sulfoisophthalic acid in the range of 1 to 10 mol%.

[0067] Examples of the diol component contained in the copolyester resin include aliphatic diols such as ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, and polyethylene glycol; alicyclic diols such as 1,4-cyclohexanedimethanol; aromatic diols such as 4,4'-bis(hydroxyethyl)bisphenol A; and further bis(polyoxyethylene glycol)bisphenol ether, etc.

[0068] <Polyurethane resin used for the coating layer> When using a polyurethane resin as the coating layer (C), examples of the polyurethane resin include those obtained by reacting polyols having two or more active hydrogens with organic polyisocyanates. Examples of the polyols include saturated polyester polyols; polyether polyols (such as polyethylene glycol, polytetramethylene glycol, etc.); amino alcohols (such as ethanolamine, diethanolamine, triethanolamine, etc.); unsaturated polyester polyols (such as those obtained by polycondensing an unsaturated polyvalent carboxylic acid alone or a mixture thereof with a saturated polyvalent carboxylic acid, and a mixture of a saturated polyvalent alcohol and an unsaturated polyvalent alcohol), polybutadiene polyols (such as 1,2-polybutadiene polyol, 1,4-polybutadiene polyol, etc.), and polyols having an unsaturated double bond such as acrylic polyols (acrylic polyols having a hydroxyl group in the side chain obtained by copolymerizing various acrylic monomers and an acrylic acid monomer having a hydroxyl group). Examples of the organic polyisocyanates include aromatic polyisocyanates (such as diphenylmethane diisocyanate, toluene diisocyanate, etc.), aliphatic polyisocyanates (such as hexamethylene diisocyanate, etc.), alicyclic polyisocyanates (such as isophorone diisocyanate, etc.), aromatic-aliphatic polyisocyanates (such as xylylene diisocyanate), and further polyisocyanates obtained by previously reacting these isocyanates with a low molecular weight polyol.

[0069] <Polyacrylic resin used for the coating layer> When using a polyacrylic resin as the coating layer (C), examples of the polyacrylic resin include acrylic polymers obtained by polymerizing acrylic acid or methacrylic acid, or salts or esters thereof. Examples of acrylic ester-based and methacrylic ester-based monomers include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, glycidyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, etc. Examples of salts of acrylic acid and methacrylic acid include sodium acrylate, sodium methacrylate, potassium acrylate, potassium methacrylate, ammonium acrylate, ammonium methacrylate, etc. In addition to these essential components, acrylic acid-based monomers such as acrylamide, methacrylamide, aminoethyl methacrylate, aminomethyl methacrylate, N-methylolacrylamide, N-methoxymethylacrylamide, etc. may be added.

[0070] In addition, monomers such as vinyl chloride, vinyl acetate, styrene, vinyl ether, butadiene, isoprene, sodium vinyl sulfonate, etc. can also be used as copolymerization components in the polyacrylic resin. Note that for the acrylic polymer, it is preferable that hydrophilic components such as acrylate components, methacrylate components, acrylic acid components, acrylamide components, 2-hydroxyethyl acrylate components, N-methylolacrylamide components, etc. are included as copolymerization components to enhance the functionality of the coating film. Also, a copolymer having a functional group in the molecular side chain may be used. Further, this acrylic polymer can be obtained by using a hard component such as methyl methacrylate or ethyl methacrylate as the main component and copolymerizing a soft component such as an acrylic ester as the copolymerization component.

[0071] <Acrylic graft copolymer polyester resin used for the coating layer> An acrylic graft copolymerized polyester resin can be used as the coating layer (C), and in the present invention, an acrylic graft copolymerized polyester aqueous dispersion is cited as a preferred example. It contains grafted polyester particles, water, an aqueous solvent or an organic solvent, and exhibits a semi-transparent to milky white appearance. This grafted polyester has a main chain made of polyester and a graft portion (side chain) formed by a polymer of a radically polymerizable monomer containing a radically polymerizable monomer having a hydrophilic group.

[0072] The average particle diameter of the grafted polyester particles in the acrylic graft copolymerized polyester aqueous dispersion, measured by the laser light scattering method, is 500 nm or less, preferably 10 nm to 500 nm, more preferably 10 nm to 300 nm. When the average particle diameter exceeds 500 nm, the strength of the coating film after coating decreases.

[0073] The content of the acrylic graft copolymerized polyester particles in the acrylic graft copolymerized polyester aqueous dispersion is usually 1% by mass to 50% by mass, preferably 3% by mass to 30% by mass. The particles in the acrylic graft copolymerized polyester aqueous dispersion that can be used in the present invention can take a core-shell structure with the polyester main chain as the core in the aqueous dispersion medium.

[0074] The coating film obtained from the above acrylic graft copolymerized polyester aqueous dispersion has extremely excellent adhesiveness to a polyamide film. Furthermore, since the blocking resistance is extremely excellent, it can be used without problems even in a film substrate with a relatively low glass transition temperature. Also, when forming a laminate, the adhesiveness to the adhesive used when laminating a printing ink or a sealant layer is also very good. The resulting laminated film (also referred to as a laminate film) can have significantly improved durability in retort treatment and boiling water treatment. Furthermore, when using a flexible grafted polyester such that the glass transition temperature of the grafted polyester in the copolymerized polyester aqueous dispersion is 30°C or lower, preferably 10°C or lower, the durability of the laminate is further improved.

[0075] (Polyester main chain of acrylic graft copolymer polyester) In the present invention, the polyester that can be used as the main chain of the grafted polyester is preferably a saturated or unsaturated polyester synthesized from at least a dicarboxylic acid component and a diol component, and the obtained polyester can be a polymer of one kind or a mixture of two or more kinds of polymers. And a polyester that is not inherently dispersed or dissolved in water is preferred. The weight average molecular weight of the polyester that can be used in the present invention is 5,000 to 100,000, preferably 5,000 to 50,000. If the weight average molecular weight is less than 5,000, the physical properties of the coating film such as the post-processability of the dry coating film will deteriorate. Further, if the weight average molecular weight is less than 5,000, the polyester itself as the main chain is easily solubilized in water, so that the formed grafted polyester cannot form the core-shell structure described later. When the weight average molecular weight of the polyester exceeds 100,000, it becomes difficult to disperse in water. From the viewpoint of water dispersion, 100,000 or less is preferred. The glass transition point is 30°C or lower, preferably 10°C or lower.

[0076] The dicarboxylic acid component is preferably a dicarboxylic acid mixture containing at least one aromatic dicarboxylic acid, at least one aliphatic and / or alicyclic dicarboxylic acid, and at least one dicarboxylic acid having a radically polymerizable unsaturated double bond. As the aromatic dicarboxylic acid, terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, etc. can be used. Further, sodium 5-sulfoisophthalate can also be used as necessary. As the aliphatic dicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, dimer acid, acid anhydrides thereof, etc. can be used. As the alicyclic dicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, acid anhydrides thereof, etc. can be used. Examples of the dicarboxylic acid containing a radically polymerizable unsaturated double bond include α,β-unsaturated dicarboxylic acids such as fumaric acid, maleic acid, maleic anhydride, itaconic acid, citraconic acid, and alicyclic dicarboxylic acids containing an unsaturated double bond such as 2,5-norbornene dicarboxylic anhydride and tetrahydrophthalic anhydride. Among these, fumaric acid, maleic acid, and 2,5-norbornene dicarboxylic acid (endo-bicyclo-(2,2,1)-5-heptene-2,3-dicarboxylic acid) are preferred.

[0077] The above diol component is composed of at least one of aliphatic glycols having 2 to 10 carbon atoms, alicyclic glycols having 6 to 12 carbon atoms, and glycols containing an ether bond. Examples of the aliphatic glycol having 2 to 10 carbon atoms include ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,9-nonanediol, 2-ethyl-2-butylpropanediol, and the like. Examples of the alicyclic glycol having 6 to 12 carbon atoms include 1,4-cyclohexanedimethanol and the like. Examples of the glycol containing an ether bond include diethylene glycol, triethylene glycol, dipropylene glycol, and glycols obtained by adding 1 to several moles of ethylene oxide or propylene oxide to two phenolic hydroxyl groups of bisphenols, such as 2,2-bis(4-hydroxyethoxyphenyl)propane. Polyethylene glycol, polypropylene glycol, and polytetramethylene glycol can also be used as needed.

[0078] In addition to the above dicarboxylic acid component and diol component, polycarboxylic acids and / or polyols having a functionality of 3 or more can be copolymerized. Examples of polycarboxylic acids having three or more functional groups include (anhydrous) trimellitic acid, (anhydrous) pyromellitic acid, (anhydrous) benzophenone tetracarboxylic acid, trimesic acid, ethylene glycol bis(anhydrotrimellitate), glycerol tris(anhydrotrimellitate), and the like. Examples of polyols having three or more functional groups include glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, and the like. The polycarboxylic acid and / or polyol having three or more functional groups can be used in the range of 0 to 5 mol%, preferably 0 to 3 mol%, based on the total polycarboxylic acid component containing the dicarboxylic acid component or the total polyol component containing the diol component.

[0079] (Graft portion of acrylic graft copolymerized polyester) The graft portion of the grafted polyester that can be used in the present invention can be a polymer derived from a monomer mixture containing at least one radically polymerizable monomer having a hydrophilic group or a group that can be changed to a hydrophilic group later.

[0080] The weight average molecular weight of the polymer constituting the graft portion is 500 to 50,000, preferably 4000 to 50,000. When the weight average molecular weight is less than 500, the grafting rate decreases, so the imparting of hydrophilicity to the polyester is not sufficiently carried out, and generally it is difficult to control the weight average molecular weight of the graft portion to less than 500. The graft portion forms a hydration layer of dispersed particles. In order to give the particles a sufficiently thick hydration layer and obtain a stable dispersion, it is desirable that the weight average molecule of the graft portion derived from the radically polymerizable monomer is 500 or more. The upper limit of the weight average molecular weight of the graft portion of the radically polymerizable monomer is preferably 50,000 as described above from the viewpoint of polymerizability in solution polymerization. The control of the molecular weight within this range can be achieved by appropriately selecting the amount of polymerization initiator, monomer dropping time, polymerization time, reaction solvent, and monomer composition, and appropriately combining a chain transfer agent and a polymerization inhibitor as necessary. The glass transition point is 30°C or lower, preferably 10°C or lower.

[0081] As the hydrophilic group of the radically polymerizable monomer, a carboxyl group, a hydroxyl group, a sulfonic acid group, an amide group, a quaternary ammonium salt, a phosphoric acid group, etc. can be used. As the group that can be changed into a hydrophilic group, an acid anhydride, glycidyl, chlorine, etc. can be used. The dispersibility of the graft polyester in water can be controlled by the hydrophilic group introduced into the polyester by grafting. Among the above hydrophilic groups, the carboxyl group is preferable for controlling the dispersibility of the graft polyester in water because the amount of introduction thereof into the graft polyester can be accurately determined using the acid value known in the art.

[0082] Examples of the carboxyl group-containing radically polymerizable monomer include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, etc., and further maleic anhydride, itaconic anhydride, methacrylic anhydride, etc. that easily generate carboxylic acid upon contact with water / amine can be used. Preferred carboxyl group-containing radically polymerizable monomers are acrylic anhydride, methacrylic anhydride and maleic anhydride.

[0083] In addition to the above hydrophilic group-containing radically polymerizable monomer, it is preferable to copolymerize at least one radically polymerizable monomer that does not contain a hydrophilic group. In the case of only the hydrophilic group-containing monomer, grafting onto the polyester main chain does not occur smoothly, and it is difficult to obtain a good copolymerized polyester aqueous dispersion. Efficient grafting can be carried out for the first time by copolymerizing at least one radically polymerizable monomer that does not contain a hydrophilic group.

[0084] As the radical polymerizable monomer not containing a hydrophilic group, one or more combinations of monomers having an ethylenically unsaturated bond and not containing the above-described hydrophilic group are used. Examples of such monomers include acrylic esters such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, and hydroxypropyl acrylate; methacrylic esters such as methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and hydroxypropyl methacrylate; acrylic acid or methacrylic acid derivatives such as acrylamide, N-methylolacrylamide, and diacetoneacrylamide; nitriles such as acrylonitrile and methacrylonitrile; vinyl esters such as vinyl acetate, vinyl propionate, and vinyl benzoate; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, and vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and methyl isopropenyl ketone; N-vinyl compounds such as N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole, and N-vinyl pyrrolidone; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl bromide, and vinyl fluoride; and aromatic vinyl compounds such as styrene, α-methylstyrene, t-butylstyrene, vinyltoluene, and vinylnaphthalenes. These monomers can be used alone or in combination of two or more.

[0085] The usage ratio of the hydrophilic group-containing monomer and the monomer not containing a hydrophilic group is determined in consideration of the amount of the hydrophilic group introduced into the graft polyester. Usually, the mass ratio (hydrophilic group-containing monomer: monomer not containing a hydrophilic group) is in the range of 95:5 to 5:95, preferably 90:10 to 10:90, and more preferably 80:20 to 40:60.

[0086] When a carboxyl group-containing monomer is used as the hydrophilic group-containing monomer, the total acid value of the grafted polyester is 600 to 4000 eq. / 10 6 g, preferably 700 to 3000 eq. / 10 6 g, most preferably 800 to 2500 eq. / 10 6 g. When the acid value is 600 eq. / 10 6 g or less, it is difficult to obtain a copolymerized polyester aqueous dispersion with a small particle size when the grafted polyester is dispersed in water, and furthermore, the dispersion stability of the copolymerized polyester aqueous dispersion decreases. When the acid value is 4000 eq. / 10 6 g or more, the water resistance of the easy-adhesion layer formed from the copolymerized polyester aqueous dispersion becomes low.

[0087] The mass ratio of the polyester main chain to the graft portion in the acrylic graft copolymerized polyester (polyester: radically polymerizable monomer) is in the range of 40:60 to 95:5, preferably 55:45 to 93:7, and more preferably 60:40 to 90:10.

[0088] When the mass ratio of the polyester main chain is 40% by mass or less, the excellent performance of the base polyester already described, namely high processability, excellent water resistance, and excellent adhesion to various substrates, cannot be fully exhibited. On the contrary, undesirable properties of the acrylic resin, namely low processability, gloss, water resistance, etc., are added. When the mass ratio of the polyester is 95% by mass or more, the amount of hydrophilic groups in the graft portion that imparts hydrophilicity to the grafted polyester is insufficient, and a good aqueous dispersion cannot be obtained.

[0089] <Crosslinking agent added to the coating solution> The above coating solution can be used as a coating agent for forming a coating layer as it is, but by further blending a crosslinking agent (curing resin) for curing, a high degree of water resistance can be imparted to the coating layer. As the crosslinking agent, a phenol formaldehyde resin which is a condensate of alkylated phenols, cresols, etc. and formaldehyde; an amino resin such as an adduct of urea, melamine, benzoguanamine, etc. and formaldehyde, and an alkyl ether compound composed of this adduct and an alcohol having 1 to 6 carbon atoms; a polyfunctional epoxy compound; a polyfunctional isocyanate compound; a blocked isocyanate compound; a polyfunctional aziridine compound; an oxazoline compound, etc. can be used.

[0090] In the coating layer used in the present invention, additives such as an antistatic agent, an inorganic lubricant, and an organic lubricant can be contained in order to impart antistatic properties and slipperiness within a range that does not impair the effects of the present invention. When applying an antistatic agent, an inorganic lubricant, an organic lubricant, etc. to the film surface, it is preferable to contain these additives in the coating layer in order to prevent the desorption of these additives.

[0091] As a method for applying a coating agent to a polyamide film substrate to form a coating layer, known coating methods such as a gravure method, a reverse method, a die method, a bar method, and a dip method can be used.

[0092] The coating amount of the coating agent is 0.01 to 3 g / m as a solid content with respect to the polyamide film after biaxial stretching. 2 Preferably, it is applied so as to be 0.04 to 0.5 g / m. 2 When the coating amount is 0.01 g / m or less, sufficient adhesive strength between the coating layer and other layers cannot be obtained. When it exceeds 3 g / m, blocking occurs and there are practical problems. 2 2 2 When it exceeds 3 g / m, blocking occurs and there are practical problems.

[0093] The coating layer can be prepared by applying a coating agent to a biaxially stretched polyamide film substrate, or by applying a coating agent to an unstretched or uniaxially stretched polyamide film substrate, drying, and then, if necessary, further performing uniaxial stretching or heat fixing after biaxial stretching. As the drying temperature after coating the coating agent, drying and heat fixing are performed at 150°C or higher, preferably 200°C or higher, so that the coating film becomes strong and the adhesiveness between the easy adhesion layer and the polyamide film substrate is improved.

[0094] When stretching is performed after coating, the drying after coating needs to control the moisture content of the coating film in the range of 0.1 to 2% in order not to impair the stretchability of the coating film. After stretching, drying and heat fixing are carried out at 200 °C or higher, so that the coating film becomes strong and the adhesiveness between the coating layer and the polyamide film substrate is improved dramatically.

[0095] [Inorganic thin film layer (D)] The biaxially stretched polyamide film of the present invention can impart gas barrier properties by providing an inorganic thin film layer on at least one side of the film.

[0096] The inorganic thin film layer and its forming method according to the embodiment of the present invention will be described. The inorganic thin film layer is a thin film made of a metal or an inorganic oxide. The material for forming the inorganic thin film layer is not particularly limited as long as it can form a thin film, but from the viewpoints of transparency and gas barrier properties, inorganic oxides such as silicon oxide (silica), aluminum oxide (alumina), and a mixture of silicon oxide and aluminum oxide are preferably mentioned. In particular, from the viewpoint of achieving both flexibility and denseness of the inorganic thin film layer, a composite oxide of silicon oxide and aluminum oxide is preferable. In this composite oxide, the mixing ratio of silicon oxide and aluminum oxide is preferably in the range of 20 to 70% by mass of Al in terms of the mass ratio of the metal components. When the Al concentration is less than 20% by mass, the water vapor barrier property may be lowered. On the other hand, when it exceeds 70% by mass, the inorganic thin film layer tends to become hard, and the film may be broken during secondary processing such as printing and laminating, resulting in a decrease in the gas barrier property. Here, the silicon oxide referred to herein is various silicon oxides such as SiO and SiO2 or a mixture thereof, and the aluminum oxide is various aluminum oxides such as AlO and A12O3 or a mixture thereof.

[0097] The film thickness of the inorganic thin film layer is generally 1 to 100 nm, preferably 5 to 50 nm. If the film 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, even if it is excessively thick exceeding 100 nm, the corresponding improvement effect in gas barrier properties cannot be obtained, and it is rather disadvantageous in terms of bending resistance and manufacturing cost.

[0098] There is no particular limitation on the method for forming the inorganic thin film layer. For example, known vapor deposition methods such as physical vapor deposition methods (PVD methods) such as vacuum evaporation method, sputtering method, ion plating method, or chemical vapor deposition method (CVD method) can be appropriately adopted. Hereinafter, a typical method for forming the inorganic thin film layer will be described taking a silicon oxide-aluminum oxide-based thin film as an example. For example, when adopting the vacuum evaporation method, a mixture of SiO2 and A12O3, or a mixture of SiO2 and Al, etc. is preferably used as the evaporation raw material. Usually, particles are used as these evaporation raw materials. At that time, it is desirable that the size of each particle is such that the pressure during evaporation does not change, and the preferable particle diameter is 1 mm to 5 mm. For heating, methods such as resistance heating, high-frequency induction heating, electron beam heating, laser heating, etc. can be adopted. Also, reactive evaporation using means such as introduction of oxygen, nitrogen, hydrogen, argon, carbon dioxide gas, water vapor, etc. as reaction gases, ozone addition, ion assist, etc. can be adopted. Furthermore, the film formation conditions such as applying a bias to the object to be evaporated (the laminated film to be subjected to evaporation), heating or cooling the object to be evaporated can be arbitrarily changed. Such evaporation materials, reaction gases, bias of the object to be evaporated, heating and cooling, etc. can be similarly changed when adopting the sputtering method or CVD method.

[0099] [Laminated film laminated with a sealant film] The biaxially stretched polyamide film of the present invention is processed into a laminated film laminated with a sealant film or the like, and then processed into a packaging bag. Examples of the sealant film include an unstretched linear low-density polyethylene (LLDPE) film, an unstretched polypropylene (CPP) film, an ethylene-vinyl alcohol copolymer resin (EVOH) film, etc.

[0100] Examples of the layer structure of the laminated film of the present invention include, for example, 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 / 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 / adhesive / 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 vapor-deposited PET / adhesive / LLDPE, ONY / 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, and the like. Each abbreviation used in the above layer structure is as follows. / : Represents the boundary of the layer. ONY: Biaxially stretched polyamide film or biaxially stretched polyester film having a coating layer 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 for bonding films Aluminum vapor deposition: Indicates that aluminum is vapor deposited

[0101] Examples of the layer structure of the laminated film using the biaxially oriented polyamide film having the inorganic thin film layer (D) of the present invention include, for example, ONY / inorganic thin film layer / adhesive / CPP, PET / adhesive / ONY / inorganic thin film layer / adhesive / LLDPE, PET / adhesive / ONY / inorganic thin film layer / PE / LLDPE, PET / adhesive / ONY / inorganic thin film layer / adhesive / CPP, ONY / inorganic thin film layer / adhesive / PET / adhesive / LLDPE, ONY / inorganic thin film layer / adhesive / PET / PE / LLDPE, ONY / inorganic thin film layer / adhesive / PET / adhesive / CPP, ONY / inorganic thin film layer / PE / LLDPE, ONY / inorganic thin film layer / PE / CPP, OPP / adhesive / ONY / inorganic thin film layer / adhesive / LLDPE, ONY / inorganic thin film layer / adhesive / EVOH / adhesive / LLDPE, ONY / inorganic thin film layer / adhesive / EVOH / adhesive / CPP, CPP / adhesive / ONY / inorganic thin film layer / adhesive / LLDPE, and the like. In addition, each abbreviation used in the above layer structure is as follows. / : Represents the boundary of the layer ONY / inorganic thin film layer: Biaxially oriented polyamide film having the inorganic thin film layer (D) PET: Oriented polyethylene terephthalate film LLDPE: Unoriented linear low density polyethylene film CPP: Unoriented polypropylene film OPP: Oriented polypropylene film PE: Extruded laminate or unstretched low-density polyethylene film EVOH: Ethylene-vinyl alcohol copolymer resin Adhesive: Adhesive layer for bonding films together

Examples

[0102] 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 evaluation of the film was carried out by the following measurement methods. Unless otherwise specified, the measurement was carried out in a measurement room at 23°C and 65% relative humidity.

[0103] (1) Haze value of the film Measured using a direct-reading haze meter manufactured by Toyo Seiki Seisaku-sho, Ltd., in accordance with JIS-K-7105.

[0104] (2) Film thickness The film was divided into 10 equal parts in the TD direction (for films with a narrow width, the width was adjusted to ensure a width where the thickness could be measured). Ten 100-mm films in the MD direction were stacked and cut out, and conditioned for 2 hours or more in an environment at 23°C and 65% relative humidity. The thickness at the center of each sample was measured using a thickness measuring instrument manufactured by Tester Sangyo, and the average value was taken as the thickness.

[0105] (3) Measurement of film biomass content The obtained film biomass content was measured by radioactive carbon (C14) measurement as shown in ASTM D6866-16 Method B (AMS). (4) Thermal shrinkage rate of the film The thermal shrinkage rate was measured by 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. Thermal shrinkage rate = [(length before treatment - length after treatment) / length before treatment] × 100 (%) (5) Impact strength of the film The measurement was carried out using a film impact tester manufactured by Toyo Seiki Seisaku-sho, Ltd. The measured value was expressed as J (Joule) / 15μm in terms of per 15μm thickness. (6) Coefficient of kinetic friction of the film In accordance with JIS-C2151, the coefficient of kinetic friction between the outer surfaces of the film rolls was evaluated under the following conditions. The size of the test piece was 130 mm in width and 250 mm in length, and the test speed was 150 mm / min. (7) Puncture strength of the film The measurement was carried out in accordance with "2. Strength test method" of "Food, Additives, etc. Standard 3: Utensils and Containers / Packaging" (Ministry of Health and Welfare Notification No. 20 of 1982) in the Food Sanitation Law. A needle with a tip diameter of 0.7 mm was punctured into the film at a puncture speed of 50 mm / min, and the strength when the needle penetrated the film was measured as the puncture strength. The measurement was carried out at room temperature (23°C), and the value obtained by dividing the puncture strength of the film (unit: N) by the actual thickness of the film was defined as the puncture strength (unit: N / μm).

[0106] (8) Degree of surface orientation of the film Samples were obtained from the central position in the width direction of the film. For the samples, in accordance with JIS K 7142-1996 Method A, using a sodium D line as the light source, the refractive index (nx) in the longitudinal direction of the film and the refractive index (ny) in the width direction were measured with an Abbe refractometer, and the surface orientation coefficient was calculated by the calculation formula of Equation (1). Surface orientation coefficient (ΔP) = (nx + ny) / 2 - nz (1) (9) Elastic modulus of the film After the obtained biaxially stretched polyamide film was allowed to stand in a room adjusted to 23 degrees and 50% RH for 2 hours, it was cut into strip shapes 150 mm (gauge length 100 mm) in the MD and TD measurement directions of the film and 15 mm in the direction perpendicular to the measurement direction to obtain samples. Using a tensile tester (AG-1 manufactured by Shimadzu Corporation) equipped with a 1 kN load cell and sample holders, a tensile test was carried out at a test speed of 200 mm / min. The elastic modulus was calculated from the slope of the obtained load-elongation curve. The measurement was carried out with 3 samples, and the average value of each was calculated.

[0107] (10) Pinhole resistance to bending of the film Using a Gelboflex tester manufactured by Rikagaku Kogyo Co., Ltd., the number of pinholes due to bending fatigue was measured by the following method. After applying a polyester-based adhesive to the film produced in the example, a linear low-density polyethylene film (L-LDPE film: manufactured by Toyobo Co., Ltd., L4102) with a thickness of 40 μm was dry laminated, and aging was performed for 3 days in an environment at 40 °C to obtain a laminated film. The obtained laminated film was cut into a size of 12 inches × 8 inches, formed 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 Gelboflex tester, and the other end was fixed to the movable head side, with an initial gripping interval of 7 inches. A twist of 440 degrees was applied in the first 3.5 inches of the stroke, and then the remaining 2.5 inches was a linear horizontal movement to complete the full stroke, and bending fatigue was performed 1000 times at a speed of 40 times / minute. The number of pinholes generated in the laminated film was counted. The measurement was carried out in an environment at 1 °C. The L-LDPE film side of the test film was placed on the lower surface on filter paper (Advantec, No. 50), 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 onto the test film and spread evenly over one side using a rubber roller. After wiping off the unnecessary ink, the test film was removed, and the number of ink dots on the filter paper was measured.

[0108] (11) Pinhole resistance to friction of the film Using a fastness tester (manufactured by Toyo Seiki Seisaku-sho, Ltd.), a friction test was performed by the following method to measure the pinhole generation distance. A laminated film similar to that produced in the above pinhole resistance to bending evaluation was made into a test sample by folding it four times and sharpening the corners, and was rubbed against the inner surface of corrugated cardboard with an amplitude of 25 cm, an amplitude speed of 30 times / minute, and a weight of 100 g using a fastness tester. The corrugated cardboard used was K280×P180×K210(AF) = (face material liner × core material × back material liner (type of flute)). The pinhole generation distance was calculated according to the following procedure. The longer the pinhole generation distance, the better the friction resistance pinhole property. First, a friction test was conducted at an amplitude of 100 times and a distance of 2500 cm. If no pinhole opened, the friction test was conducted with the amplitude increased by 20 times and the distance increased by 500 cm. Also, if no pinhole opened, the friction test was further conducted with the amplitude increased by 20 times and the distance increased by 500 cm. This was repeated, and the distance at which the pinhole opened was marked with an "×" as level 1. If a pinhole opened at an amplitude of 100 times and a distance of 2500 cm, the friction test was conducted with the amplitude decreased by 20 times and the distance decreased by 500 cm. Also, if a pinhole opened, the friction test was further conducted with the amplitude decreased by 20 times and the distance decreased by 500 cm. This was repeated, and the distance at which no pinhole opened was marked with an "○" as level 1. Next, as level 2, if the last one at level 1 was "○", the friction test was conducted with the amplitude increased by 20 times. If no pinhole opened, it was marked with an "○", and if a pinhole opened, it was marked with an "×". If the last one at level 1 was "×", the friction test was conducted with the amplitude decreased by 20 times. If no pinhole opened, it was marked with an "○", and if a pinhole opened, it was marked with an "×". Furthermore, as levels 3 to 20, if the previous level was "○", the friction test was conducted with the amplitude increased by 20 times. If no pinhole opened, it was marked with an "○", and if a pinhole opened, it was marked with an "×". If the previous level was "×", the friction test was conducted with the amplitude decreased by 20 times. If no pinhole opened, it was marked with an "○", and if a pinhole opened, it was marked with an "×". This was repeated to mark "○" or "×" for levels 3 to 20. For example, results as shown in Table 1 were obtained. Taking Table 1 as an example, the method for obtaining the pinhole generation distance will be explained. Count the number of "○" and "×" tests for each distance. The distance with the most test times was taken as the median value, and the coefficient was set to zero. 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 the tests from level 1 to level 20, the number of tests where no hole opened and the number of tests where a hole opened were compared, and the friction pinhole generation distance was calculated using the respective formulas for the following cases A and B. A; In all tests, when the number of tests in which holes did not open is greater than or equal to the number of tests in which holes opened Friction pinhole generation distance = Median + 500×(Σ(Coefficient × Number of tests in which holes did not open) / Number of tests in which holes did not open) + 1 / 2) B: In all tests, when the number of tests in which holes did not open is less than the number of tests in which holes opened Friction pinhole generation distance = Median + 500×(Σ(Coefficient × Number of tests in which holes opened) / Number of tests in which holes opened) - 1 / 2)

[0109]

Table 1

[0110] (12) Laminating strength with polyethylene-based sealant The laminated film prepared in the same manner as described in the method for evaluating flexural pinhole resistance was cut into strips with a width of 15 mm and a length of 200 mm. One end of the laminated film was peeled at the interface between the biaxially stretched polyamide film and the linear low-density polyethylene film. Using an autograph (manufactured by Shimadzu Corporation), the laminating strength was measured three times in the MD direction and the TD direction under the conditions of a temperature of 23°C, a relative humidity of 50%, a tensile speed of 200 mm / min, and a peeling angle of 90°, and evaluated by the average value.

[0111] (13) Water-resistant laminating strength (laminating strength under water adhesion conditions) When measuring the laminating strength in (12), the laminating strength was measured while dropping water on the peeling interface of the strip-shaped laminated film with a dropper. It was measured three times in the MD direction and the TD direction respectively and evaluated by the average value. (13) Generation cycle of heat degradation products generated at the die lip outlet After cleaning the die lip, film formation was started, and the time until heat degradation products were generated on the die lip was observed. A: Even in film formation for 36 hours or more, no heat degradation products are generated and there is no foreign matter adhesion to the film. B: Heat degradation products adhere to the die lip between 24 and 36 hours. C: Thermal degradation products adhere to the die lip within 24 hours, and foreign matter appears in the film.

[0112] (14) Relative viscosity of the raw polyamide A polyamide solution was prepared by dissolving 0.25 g of polyamide in 25 ml of a volumetric flask with 96% sulfuric acid to a concentration of 1.0 g / dl, and the relative viscosity was measured at 20°C. (15) Melting point of the raw polyamide In accordance with JIS K7121, using a SSC5200 type differential scanning calorimeter manufactured by Seiko Instruments Inc., in a nitrogen atmosphere, sample weight: 10 mg, starting temperature for temperature rise: 30°C, heating rate: 20°C / min, the endothermic peak temperature (Tmp) was determined as the melting point.

[0113] [Example 1-1] An apparatus consisting of two extruders and a 380 mm wide coextrusion T-die was used. The functional layer (B layer) / substrate layer (A layer) / functional layer (B layer) was laminated by the feed block method, and the molten resin of the following resin composition was extruded in film form from the T-die, cast onto a cooling roll adjusted to 20°C, and electrostatically adhered to obtain an unstretched film with a thickness of 200 μm. The resin compositions of the substrate layer (A layer) and the functional layer (B layer) are as follows. Resin composition constituting the substrate layer (A layer): 89.5 parts by mass of polyamide 6 (manufactured by Toyobo Co., Ltd., relative viscosity 2.8, melting point 220°C), and 10.5 parts by mass of polybutylene terephthalate adipate (trade name "EcoFlex" manufactured by BASF, glass transition temperature -31.3°C, melting point 120°C), a polyamide resin composition. Resin composition constituting the functional layer (B layer): 95 parts by mass of polyamide 6 (manufactured by Toyobo Co., Ltd., relative viscosity 2.8, melting point 220°C), 5.0 parts by mass of polyamide MXD6 (manufactured by Mitsubishi Gas Chemical Co., Ltd., relative viscosity 2.1, melting point 237°C), 0.54 parts by mass of porous silica fine particles (manufactured by Fuji Silysia Chemical Ltd., average particle diameter 2.0 μm, pore volume 1.6 ml / g), and 0.15 parts by mass of fatty acid bisamide (ethylene bis stearic acid amide manufactured by Kyoeisha Chemical Co., Ltd.), a resin composition. The configuration of the feed block and the discharge rate of the extruder were adjusted so that the total thickness of the biaxially stretched polyamide film was 15 μm, the thickness of the substrate layer (layer A) was 9 μm, and the thickness of the functional layer (layer B) was 3 μm each on the front and back sides.

[0114] The obtained unstretched film was led to a roll-type stretching machine and stretched 1.73 times in the MD direction at 80 °C using the peripheral speed difference of the rolls, and then further stretched 1.85 times at 70 °C. Subsequently, this uniaxially stretched film was continuously led to a tenter-type stretching machine, preheated at 110 °C, and then 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, then subjected to a 7% relaxation treatment at 218 °C, and then the surface on the side to be dry-laminated with the linear low-density polyethylene film was subjected to corona discharge treatment to obtain a biaxially stretched polyamide film. The evaluation results of the obtained biaxially stretched film are shown in Table 2.

[0115] [Examples 1-2 to 1-11] The resin compositions of the substrate layer (layer A) and the functional layer (layer B), and the film-forming conditions such as the heat-setting temperature were changed as shown in Table 2, and a biaxially stretched film was obtained in the same manner as in Example 1. The evaluation results of the obtained biaxially stretched film are shown in Table 2.

[0116] The following aliphatic or aromatic aliphatic polyester resins were used respectively. ·PBAT: Polybutylene adipate terephthalate (manufactured by BASF, Ecoflex) ·PBS: Polybutylene succinate (manufactured by Showa Highpolymer Co., Ltd., Bionolle 1001) ·PBSA: Polybutylene succinate adipate (manufactured by Showa Highpolymer Co., Ltd., Bionolle 3001) ·PAE: Polyamide elastomer (manufactured by Arkema, nylon 12 / polytetramethylene glycol copolymer, Pebax SA01) ·PEE: Maleic anhydride-modified polyester elastomer (manufactured by Mitsubishi Chemical Corporation, Tefabloc)

[0117] In addition, polyamide resins in which at least part of the raw materials is derived from biomass were used, respectively, as follows. · Polyamide 11: (manufactured by Jusho Co., relative viscosity 2.5, melting point 186 °C, biomass content 100%) · Polyamide 410: (manufactured by DSM, ECOPaXX Q150-E, melting point 250 °C, biomass content 70%) · Polyamide 610: (manufactured by Arkema, RilsanS SMNO, melting point 222 °C, biomass content 63%) · Polyamide 1010: (manufactured by Arkema, RilsanT TMNO, melting point 202 °C, biomass content 100%)

[0118]

Table 2A

[0119]

Table 2B

[0120] As shown in Table 2, films of the examples were films with good flexural pinhole resistance and friction pinhole resistance. In addition, they had low haze, good transparency, high impact strength, high piercing strength, high laminating strength with the sealant film, and were excellent as packaging films. Also, even in long-term film formation, stable film formation was possible without deposition of degraded products on the die lip.

[0121] [Comparative Example 1] According to the resin compositions and conditions shown in Table 3, a biaxially stretched polyamide film was produced in the same manner as in Example 1-1. The raw materials used in the resin composition were the same as those in Example 1. For Comparative Examples 1-5, biaxially stretched polyamide films were produced by the following methods.

[0122] [Comparative Examples 1-5] An apparatus consisting of one extruder and a 380 mm wide single-layer T-die was used. The molten resin of the following resin composition was extruded in film form from the T-die, cast onto a cooling roll temperature-controlled at 20 °C, and electrostatically adhered to obtain an unstretched film with a thickness of 180 μm. Resin composition constituting the layer: A polyamide resin composition consisting of 97 parts by mass of polyamide 6 (manufactured by Toyobo Co., Ltd., relative viscosity 2.8, melting point 220 °C) and 3.0 parts by mass of maleic anhydride-modified polyester elastomer (manufactured by Mitsubishi Chemical Corporation, Primalloy AP GQ131). 0.09 parts by mass of porous silica fine particles (manufactured by Fuji Silysia Chemical Ltd., average particle diameter 2.0 μm, pore volume 1.6 ml / g). 300 ppm of ethylene bisstearamide. Next, the obtained unstretched film was longitudinally stretched 3.0 times by a roll stretching machine at 65 °C, then laterally stretched 4.0 times by a tenter stretching machine in an atmosphere of 110 °C, and further heat-treated in the same tenter in an atmosphere of 210 °C to prepare a single-layer polyamide-based film with a thickness of 15 μm.

[0123] Table 3 shows the physical properties and various evaluation results of the biaxially stretched polyamide film produced in Comparative Example 1.

[0124]

Table 3

[0125] As shown in Table 3, the biaxially stretched polyamide film containing no material for improving the flexing pinhole resistance in Comparative Example 1-1 had poor flexing pinhole resistance. In Comparative Example 1-2, since there was too much material for improving the flexing pinhole resistance, although the flexing pinhole resistance was excellent, the haze value of the film was high, and the film impact strength, piercing strength, and friction pinhole resistance were poor. In Comparative Examples 1-3, 1-4, and 1-5, since the surface layer side also contained a material for improving the flexing pinhole resistance, the friction pinhole resistance was poor. Also, deposition of deteriorated products occurred on the lip of the die in the extrusion process.

[0126] [Example 2] Using the biaxially oriented polyamide film produced in Example 1-1, laminates having the following configurations (1) to (9) were produced, and using the laminates of (1) to (9), three-side seal type and pillow type packaging bags were produced. Packaging bags with good appearance and difficult to break in the drop impact test were able to be produced. (1) Biaxially oriented polyamide film layer / printing layer / polyurethane-based adhesive layer / linear low density polyethylene film sealant layer. (2) Biaxially oriented polyamide film layer / printing layer / polyurethane-based adhesive layer / unoriented polypropylene film sealant layer. (3) Biaxially oriented PET film layer / printing layer / polyurethane-based adhesive layer / biaxially oriented polyamide film layer / polyurethane-based adhesive layer / unoriented polypropylene film sealant layer (4) Biaxially oriented PET film layer / printing layer / polyurethane-based adhesive layer / biaxially oriented polyamide film layer / polyurethane-based 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 / printing layer / polyurethane-based adhesive layer / linear low density polyethylene film sealant layer (6) Linear low density polyethylene film sealant layer / polyurethane-based adhesive layer / biaxially oriented polyamide film layer / anchor coat layer / inorganic thin film layer / polyurethane-based adhesive layer / linear low density polyethylene film sealant layer (7) Linear low density polyethylene film layer / polyurethane-based adhesive layer / biaxially oriented polyamide film layer / anchor coat layer / inorganic thin film layer / polyurethane-based 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 / printing layer / polyurethane-based adhesive layer / unoriented polypropylene film sealant layer (9) Biaxially oriented PET film layer / Inorganic thin film layer / Inorganic thin film protective layer / Printing layer / Polyurethane-based adhesive layer / Biaxially oriented polyamide film layer / Polyurethane-based adhesive layer / Easy peel type unoriented polypropylene film sealant layer

[0127] [Example 3] (Biaxially oriented polyamide film with a coating layer) Using an apparatus consisting of two extruders and a 380 mm wide coextrusion T-die, for the resin composition shown in Table 4, it was laminated in the configuration of functional layer (B layer) / base material layer (A layer) / functional layer (B layer) by the feed block method, and the molten resin was extruded in film form from the T-die, cast onto a cooling roll temperature-controlled at 20°C, and electrostatically adhered to obtain an unstretched film with a thickness of 200 μm. The raw materials used in the resin composition were the same as those in Example 1 and Comparative Example 1.

[0128] The obtained unstretched film was led to a roll type stretching machine and stretched 1.73 times in the MD direction at 80°C using the peripheral speed difference of the rolls, and then further stretched 1.85 times at 70°C. Subsequently, the following coating solution (A) was applied to this uniaxially stretched film with a roll coater and then dried with warm air at 70°C. Continuously, this uniaxially stretched film was led to a tenter type stretching machine, preheated at 110°C, then 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-fixed at 218°C, and then subjected to a 7% relaxation treatment at 218°C. Next, the surface on the side to be dry laminated with a linear low density polyethylene film was subjected to corona discharge treatment to obtain a biaxially oriented polyamide film. However, in Examples 3-4, the following coating solution (B): an aqueous dispersion of a polyurethane resin was used as the coating solution.

[0129] The physical properties and various evaluation results of the biaxially oriented polyamide film produced in Example 3 are shown in Table 4.

[0130]

Table 4A

[0131]

Table 4B

[0132] As shown in Table 4, films of the examples were films with good flexing pinhole resistance and rubbing pinhole resistance. Also, they had low haze, good transparency, high impact strength and puncture strength, and high water-resistant laminating strength with a sealant film, and were excellent as packaging films. Also, even in long-term film formation, stable film formation was possible without deposits of degraded products on the die lip.

[0133] [Comparative Example 3] A biaxially stretched polyamide film having a coating layer was produced in the same manner as in Example 3 according to the resin composition and conditions shown in Table 5.

[0134] For the comparative example 3-5 a biaxially stretched polyamide film was produced by the following method. An apparatus consisting of one extruder and a 380 mm-wide single-layer T-die was used. The molten resin of the resin composition described in Table 5 was extruded in film form from the T-die, cast onto a cooling roll with temperature controlled at 20°C, and electrostatically adhered to obtain an unstretched film with a thickness of 180 μm. Next, the obtained unstretched film was longitudinally stretched 3.0 times in the MD direction by a roll stretching machine at 65°C. Subsequently, after applying the following coating solution (A) to this uniaxially stretched film with a roll coater, it was dried with warm air at 70°C. Continuously, this uniaxially stretched film was led to a tenter stretching machine, transversely stretched 4.0 times by a tenter stretching machine in an atmosphere of 110°C, and further heat-treated in an atmosphere of 210°C by the same tenter to produce a single-layer polyamide-based film with a thickness of 15 μm.

[0135] Coating solution (A): An aqueous dispersion of an acrylic graft copolymer polyester 466 parts by mass of dimethyl terephthalate, 466 parts by mass of dimethyl isophthalate, 401 parts by mass of neopentyl glycol, 443 parts by mass of ethylene glycol, and 0.52 parts by mass of tetra-n-butyl titanate were charged into a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial reflux condenser, and a transesterification reaction was carried out at 160 to 220°C for 4 hours. Next, 23 parts by mass of fumaric acid was added, and the temperature was raised from 200°C to 220°C over 1 hour to carry out an esterification reaction. Then, the temperature was raised to 255°C, and after gradually reducing the pressure of the reaction system, the reaction was carried out with stirring for 1 hour and 30 minutes under a reduced pressure of 0.2 mmHg to obtain a polyester. The obtained polyester was pale yellow and transparent, had a glass transition temperature of 60°C, and a weight average molecular weight of 12,000. The composition obtained by NMR measurement and the like was as follows. ·Dicarboxylic acid component Terephthalic acid 48 mol% Isophthalic acid 48 mol% Fumaric acid 4 mol% ·Diol component Neopentyl glycol 50 mol% Ethylene glycol 50 mol%

[0136] 75 parts by mass of the above polyester resin, 56 parts by mass of methyl ethyl ketone, and 19 parts by mass of isopropyl alcohol were placed in a reactor equipped with a stirrer, a thermometer, a reflux device, and a metering dropping device, heated and stirred at 65°C to dissolve the resin. After the resin was completely dissolved, a solution prepared by dissolving a mixture of 17.5 parts by mass of methacrylic acid and 7.5 parts by mass of ethyl acrylate, and 1.2 parts by mass of azobis(dimethylvaleronitrile) in 25 parts by mass of methyl ethyl ketone was dropped into the polyester solution at 0.2 ml / min, and stirring was continued for another 2 hours after the dropping was completed. After sampling (5 g) for analysis was carried out from the reaction solution, 300 parts by mass of water and 25 parts by mass of triethylamine were added to the reaction solution, and the mixture was stirred for 1 hour to prepare a dispersion of grafted polyester. Then, the temperature of the obtained dispersion was raised to 100°C, and methyl ethyl ketone, isopropyl alcohol, and excess triethylamine were distilled off to obtain a copolymerized polyester aqueous dispersion.

[0137] The resulting dispersion was white, had an average particle size of 300 nm, and a Brookfield viscosity at 25 °C of 50 centipoise. 1.25 g of heavy water was added to 5 g of this dispersion to adjust the solid content concentration to 20% by mass, and then DSS was added, and 13 13 125 MHz C-NMR was measured. The half-width of the signal (160 - 175 ppm) of the carbonyl carbon in the polyester main chain was ∞ (no signal was detected), and the half-width of the signal (181 - 186 ppm) of the carbonyl carbon of methacrylic acid in the graft portion was 110 Hz. The solution sampled at the end of the grafting reaction was dried at 100 °C for 8 hours under vacuum, and the solid content was measured for acid value, polyester graft efficiency (NMR measurement), and the molecular weight of the graft portion by hydrolysis. The acid value of the solid content was 2300 eq. / 10 6 g. 1 In the measurement of 1H-NMR, since no signal (δ = 6.8 - 6.9 ppm, doublet) derived from fumaric acid was detected at all, it was confirmed that the graft efficiency of the polyester was 100%. The molecular weight of the graft portion was a weight average molecular weight of 10,000. Subsequently, the aqueous dispersion obtained as described above was diluted with water to a solid content concentration of 5% by mass to obtain a coating solution (A).

[0138] Coating solution (B): An aqueous dispersion of a polyurethane resin Preparation of polyurethane and aqueous dispersion; Adipic acid was used as the dicarboxylic acid component; and 1,4-butanediol 60 mol% (of the glycol component) and 40 mol% of the propylene oxide (1 mol) adduct of bisphenol A were used as the glycol components to obtain a polyester (polyester polyol) with a Tg of -5 °C. Toluene diisocyanate was allowed to act on this polyester to obtain a urethane polymer. This was used as a prepolymer, and 1,6-hexanediol was allowed to act on it for chain extension and an aminocarboxylate was reacted at the end to obtain a water-insoluble and water-dispersible polyurethane. This was dispersed in hot water while stirring to obtain a 25% aqueous dispersion. The aqueous dispersion of the polyurethane was added to an equal mixture of ion-exchanged water and isopropyl alcohol and diluted so that the solid content became 5% by mass to obtain a coating solution (B).

[0139] Table 5 shows the physical properties and various evaluation results of the biaxially stretched polyamide film prepared in Comparative Example 3.

[0140]

Table 5

[0141] As shown in Table 5, the biaxially stretched polyamide film containing no material for improving the flex resistance pinhole resistance of Comparative Example 3-1 had poor flex resistance pinhole resistance. In Comparative Example 3-2, since there was too much material for improving the flex resistance pinhole resistance, although the flex resistance pinhole resistance was excellent, the haze value of the film was high, and the film impact strength, puncture strength, and friction resistance pinhole resistance were poor. In Comparative Examples 3-3, 3-4, and 3-5, since the surface layer side also contained a material for improving the flex resistance pinhole resistance, they were inferior in friction pinhole resistance. Also, deposition of deteriorated products occurred on the die lip during the extrusion process.

[0142] [Example 4] (Biaxially stretched polyamide film having an inorganic thin film layer) The resin compositions of the base material layer (A layer) and the functional layer (B layer), and the film-forming conditions such as the heat setting temperature were changed as shown in Table 6, and a biaxially stretched film was obtained in the same manner as in Example 1-1. The raw materials used in the resin compositions were the same as those in Example 1 and Comparative Example 1.

[0143] Next, a composite oxide thin film layer of silicon dioxide and aluminum oxide was formed on the surface of the obtained biaxially stretched polyamide film subjected to corona treatment by the following method. <Formation of a composite oxide (SiO2 / A12O3) inorganic thin film layer of silicon dioxide and aluminum oxide> An inorganic thin film layer of a composite oxide of silicon dioxide and aluminum oxide was formed by electron beam evaporation on the surface of the obtained biaxially stretched polyamide film that had been subjected to corona treatment. The deposition method was to set the film on the unwinding side of a continuous vacuum evaporator, run it through a cooling metal drum, and wind up the film. At this time, the continuous vacuum evaporator was evacuated to 10-4 Torr or less, and particulate SiO2 (purity 99.9%) and A12O3 (purity 99.9%) of about 3 mm to 5 mm were used as evaporation sources in an alumina crucible below the cooling drum. The film thickness of the obtained inorganic thin film layer (SiO2 / A12O3 composite oxide layer) was 13 nm. Also, the composition of this composite oxide layer was SiO2 / A12O3 (mass ratio) = 60 / 40.

[0144] However, in Examples 4-5, an inorganic thin film layer of aluminum oxide was formed by the following method as the inorganic thin film layer. <Formation of Aluminum Oxide (A12O3) Inorganic Thin Film Layer> An inorganic thin film layer of aluminum oxide was formed by electron beam evaporation on the surface of the obtained biaxially stretched polyamide film that had been subjected to corona treatment. The method of evaporating aluminum oxide was to set the film on the unwinding side of a continuous vacuum evaporator, run it through a cooling metal drum, and wind up the film. At this time, the continuous vacuum evaporator was evacuated to 10 -4 Torr or less, 99.99% pure metallic aluminum was loaded into an alumina crucible below the cooling drum, the metallic aluminum was heated and evaporated, oxygen was supplied into its vapor to cause an oxidation reaction, and it was deposited and adhered onto the film to form an aluminum oxide film with a thickness of 30 nm.

[0145] The physical properties and various evaluation results of the biaxially stretched polyamide film produced in Example 4 are shown in Table 6.

[0146]

Table 6A

[0147]

Table 6B

[0148] [Table 6C]

[0149] As shown in Table 6, a film with good flexing pinhole resistance and rubbing pinhole resistance was obtained for the film of the example. Also, a film with low haze, good transparency, and high gas barrier properties was obtained. Further, the impact strength and puncture strength were also high, and it was excellent as a packaging film. Also, even in film formation over a long period of time, film formation of a stable film was possible without deposits of degraded products on the die lip.

[0150] [Comparative Example 4] The resin compositions of the base material layer (A layer) and the functional layer (B layer), and film formation conditions such as the heat setting temperature were changed as shown in Table 7, and a biaxially stretched film was obtained in the same manner as in Comparative Example 1. Next, a composite oxide thin film layer of the above-mentioned silicon dioxide and aluminum oxide was formed on the surface of the obtained biaxially stretched polyamide film that had been subjected to corona treatment. Note that Reference Example In 4-3, no inorganic thin film layer was formed.

[0151] The physical properties and various evaluation results of the biaxially stretched polyamide film produced in Comparative Example 4 are shown in Table 7.

[0152] [Table 7]

[0153] As shown in Table 7, the biaxially stretched polyamide film containing no material for improving the flexing pinhole resistance of Comparative Example 4-1 was inferior in flexing pinhole resistance. In Comparative Example 4-2, since there was too little material for improving the flexing pinhole resistance, the flexing pinhole resistance of the film was inferior. Reference ExampleIn Comparative Example 4-3, an inorganic thin film layer was not formed, resulting in a large oxygen permeability and making it unsuitable as a gas barrier film. In Comparative Example 4-4, there were too many materials for modifying the flexural pinhole resistance. Although the flexural pinhole resistance was excellent, the film's impact strength, puncture strength, and friction pinhole resistance were inferior. In Comparative Example 4-5, since the functional layer on the surface contained a material for modifying the flexural pinhole resistance, it was inferior in friction pinhole resistance. Also, deposition of deteriorated products on the die lip occurred during the extrusion process. In Comparative Examples 4-6 and 4-7, polyamide elastomer and polyester elastomer, which have been conventionally used as materials for modifying the flexural pinhole resistance, were used. Although the flexural pinhole resistance was excellent, the film's impact strength, puncture strength, and friction pinhole resistance were inferior.

Industrial Applicability

[0154] The biaxially stretched polyamide film of the present invention is excellent in impact resistance, flexural pinhole resistance, and friction pinhole resistance at the same time, and thus can be suitably used for applications such as packaging materials for food packaging. Furthermore, since the elastomer component does not deteriorate inside the die, it is possible to suppress the adhesion of deteriorated products to the inner surface of the die and the adhesion of eye varnish to the die lip outlet over a long period of time, reduce the frequency of cleaning the die lip by stopping production, and enable continuous production for a long time.

Explanation of Signs

[0155] 1: Head part of the durability tester 2: Corrugated cardboard 3: Mounting board for sample holding 4: Four-folded film sample 5: Rubbing amplitude direction

Claims

1. A biaxially stretched polyamide film in which a functional layer (B layer) is laminated on at least one side of a base material layer (A layer), the thickness of the biaxially stretched polyamide film is 5 to 100 μm, and the thickness of the base material layer (A layer) is 50 to 93% of the total thickness of the base material layer (A layer) and the functional layer (B layer). The base material layer (A layer) contains at least (a) 70 to 99% by mass of polyamide 6 resin and (b) 1 to 20% by mass of an aliphatic or aromatic aliphatic polyester resin. The (b) aliphatic or aromatic aliphatic polyester resin is at least one polyester resin selected from the group consisting of polybutylene succinate, polybutylene succinate adipate, and polybutylene adipate terephthalate. The functional layer (B layer) contains at least 70% by mass or more of polyamide 6 resin, contains 1 to 10% by mass of polyamide MXD6 resin, contains silica fine particles, and further contains fatty acid amide and / or fatty acid bisamide, and does not contain a material for modifying flexural pinhole resistance. A biaxially stretched polyamide film characterized by this.

2. The biaxially stretched polyamide film according to claim 1, wherein the base material layer (A layer) contains a polyamide resin in which at least a part of the raw material is derived from biomass.

3. The biaxially stretched polyamide film according to claim 2, wherein the polyamide resin in which at least a part of the raw material 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.

4. The biaxially stretched polyamide film according to any one of claims 1 to 3, characterized in that the biaxially stretched polyamide film satisfies the following (a) to (c). (a) The number of flexural fatigue pinholes when a flexure test using a gelbo flex tester is performed 1000 times at a temperature of 1°C is 5 or less. (b) The distance until pinholes occur in the friction resistance pinhole test is 2900 cm or more. (c) The puncture strength of the film is 0.67 N / μm or more.

5. On at least one side of the biaxially oriented polyamide film according to any one of claims 1 to 4, a coating layer containing at least one resin selected from the group consisting of a polyester resin, a polyurethane resin, a polyacrylic resin, and an acrylic graft copolymer polyester resin having a solid content of 0.01 to 3 g / m ２ 2. A biaxially oriented polyamide film having a coating layer containing at least one resin selected from the group consisting of a polyester resin, a polyurethane resin, a polyacrylic resin, and an acrylic graft copolymer polyester resin having a solid content of 0.01 to 3 g / m

6. A polyamide film having an inorganic thin film layer on at least one side of the biaxially stretched polyamide film according to any one of claims 1 to 5.

7. A laminated film in which a sealant film is laminated on the biaxially stretched polyamide film according to any one of claims 1 to 6.

8. A packaging bag using the laminated film according to claim 7.

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