JP2021130770A - Polyamide-based resin film and packaging using the film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyamide-based resin film having excellent bending pinhole resistance and transparency in a wide temperature range from a low temperature environment to a normal temperature environment.
SOLUTION: The film has at least one A layer containing an aliphatic polyamide resin (a1) and a styrene block copolymer (a2), and when the A layer is 100% by mass, the styrene block copolymer weight. The content of the coalescence (a2) is 1 to 20% by mass, and the styrene-based block copolymer (a2) contains a styrene monomer unit and an isobutylene monomer unit as a copolymerization component, and is a styrene monomer. The unit content is 5% by mass or more and less than 30% by mass, the weight average molecular weight is 20,000 or more and 130,000 or less, the haze of the film is 10% or less, the temperature is 5 ° C., and the relative humidity is 50. %, Polypolymer-based resin film characterized in that the number of pinholes is 15.0 / 481 cm ^{2 or less in a gelboflex test of 500 times of bending.}
[Selection diagram] None

Description

The present invention relates to a polyamide resin film used for packaging food products, pharmaceutical medical products, industrial parts, etc., and a package using the film.

A film made of a polyamide resin is used for various purposes because it has excellent mechanical properties such as impact resistance and strength, heat resistance, and molding processability such as biaxial stretching.

In addition, polyamide-based resin films are superior to other resins in impact resistance, mechanical strength, etc., but in the current market where low-temperature transportation and thinning of packaging materials have progressed, transportation during distribution, transportation, and other materials It is an urgent issue to further reduce the occurrence of pinholes due to friction and impact with the food packaging market and industry, and further improvement of toughness of polyamide resin films, especially pinholes, has occurred. It is strongly desired to improve the bending pinhole resistance in a wide temperature range from the easy low temperature environment to the normal temperature environment.

In response to such problems, Patent Document 1 describes a polyamide 6-layer as the outermost layer, which contains a flexible modifier, an ethylene-vinyl acetate copolymer saponified layer, and a polyamide that does not contain a flexible modifier. A biaxially stretched polyamide-based laminated film in which six layers are co-extruded is disclosed, and polyolefins, polyamide elastomers, and polyester elastomers are exemplified as the softening modifier.
Further, Patent Document 2 describes a layer A containing an aliphatic polyamide, a layer B containing 55 to 95% by mass of an ethylene-vinyl acetate copolymer saponified product, and 5 to 45% by mass of a soft polymer. , A polyamide-based multilayer film in which a C layer containing an aliphatic polyamide is laminated in this order is disclosed, and examples of the soft polymer include a polyolefin resin, a modified polyolefin resin, an ionomer resin, a polyamide-based elastomer, and a (meth) acrylic-based elastomer. , Polyamide-based elastomers are exemplified.
However, these technologies alone cannot meet the market demand for bending pinhole resistance, which has been increasing in recent years, and also have insufficient transparency.

Japanese Unexamined Patent Publication No. 2010-023242 JP-A-2010-131950

In view of the above circumstances, an object of the present invention is to provide a polyamide resin film having excellent bending pinhole resistance and transparency in a wide temperature range from a low temperature environment to a normal temperature environment.

As a result of diligent studies to achieve the above object, the present inventors have made at least a layer A containing an aliphatic polyamide resin (a1) and a styrene-based block copolymer (a2) having a specific composition and molecular weight. It has been found that the above-mentioned problems can be solved by using a film having one layer, and the following invention has been completed.

The first invention is a film having at least one A layer containing an aliphatic polyamide resin (a1) and a styrene-based block copolymer (a2), and is styrene-based when the A layer is 100% by mass. The content of the block copolymer (a2) is 1 to 20% by mass, and the styrene-based block copolymer (a2) contains a styrene monomer unit and an isobutylene monomer unit as a copolymerization component, and is styrene. The content of the monomer unit is 5% by mass or more and less than 30% by mass, the weight average molecular weight is 20,000 or more and 130,000 or less, the haze of the film is 10% or less, and the temperature is 5 ° C. It is a polyamide-based resin film characterized in that the ^{number of pinholes is 15.0 / 481 cm 2} or less in a gelboflex test in which the relative humidity is 50% and the bending is 500 times.

The first film of the present invention is a biaxially stretched film having at least two layers, the A layer and the B layer containing a gas barrier resin, and has a gelboflex test at 23 ° C. and a relative humidity of 50% and bending 3000 times. Under the conditions, the number of pinholes is preferably less than ^{4.0 / 481 cm 2.}

In the first invention, the gas barrier resin of the B layer is preferably an ethylene-vinyl acetate copolymer saponified product (b1), and the B layer contains the styrene block copolymer (a2). When the B layer is 100% by mass, the content of the styrene-based block copolymer (a2) is preferably 1 to 20% by mass.

In the first invention, it is preferable that the styrene-based block copolymer (a2) is a styrene-isobutylene-styrene block copolymer.

In the first aspect of the present invention, in a cross-sectional observation parallel to the flow direction (MD) or width direction (TD) of the film, the horizontal particles of the dispersed particles of the styrene-based block copolymer (a2) in the A layer of MD or TD. The maximum diameter in the direction is preferably 3.0 μm or less.

In the first invention, it is preferable that the A layer is arranged on the outermost layer.

The second invention is a package using the polyamide resin film of the first invention.

The polyamide-based resin film of the present invention has an excellent balance of transparency and bending pinhole resistance. In particular, since it can have good bending pin pole resistance in the temperature range from low temperature to room temperature, the package using the film of the present invention can be used for storage, distribution, display, and consumer use of the packaged product. Until the start, the quality of the package can be maintained well.

FIG. 1A is a schematic view of a cross section parallel to the TD of the layer A and perpendicular to the film thickness direction (hereinafter, may be referred to as a cross section in the TD parallel direction), and FIG. 1B is a schematic view of the layer A. It is a schematic diagram of the cross section parallel to MD and perpendicular to the film thickness direction (hereinafter, may be referred to as MD parallel direction cross section).

Hereinafter, the present invention will be described in detail.
When "X to Y" (X and Y are arbitrary numbers) is described, it means "X or more and Y or less", and "preferably larger than X" and "preferably smaller than Y". It includes the meaning of ".
The polyamide-based resin film of the present invention (hereinafter, may be referred to as "film of the present invention") contains at least one layer A containing an aliphatic polyamide-based resin (a1) and a styrene-based block copolymer (a2). Has layers.

<Layer A>
(Aliphatic polyamide resin (a1))
As the aliphatic polyamide resin (a1) used in the present invention, the following ring-opening polymer of cyclic lactam can be preferably used. Specifically, acetolactam (polyamide 2), propiolactam (polyamide 3), butyloractam (polyamide 4), valerolactam (polyamide 5), caprolactam (polyamide 6), enantractam (polyamide 7), caprilolactam (polyamide 7). Polyamide 8), pelargolactam (polyamide 9), caprinolactam (polyamide 10), laurolactam (polyamide 12) and the like.
Further, the following polycondensate of aminocarboxylic acid can also be preferably used. Specifically, aminopropionic acid (polyamide 3), aminobutylic acid (polyamide 4), aminovaleric acid (polyamide 5), aminocaproic acid (polyamide 6), aminoenantic acid (polyamide 7), aminocapric acid (polyamide 8). ), Aminopelargonic acid (polyamide 9), aminocapric acid (polyamide 10), aminolauric acid (polyamide 12) and the like.

Further, the following polycondensate of dicarboxylic acid and diamine can also be preferably used. Specifically, polytetramethylene adipamide (polyamide 46), polytetramethylene sebacamide (polyamide 410), polytetramethylene dodecamide (polyamide 412), polyhexamethylene adipamide (polyamide 66), polyhexa. Methylene sebacamide (polyamide 610), polyhexamethylene dodecamide (polyamide 612), polynonamethylene adipamide (polyamide 96), polynonamethylene sebacamide (polyamide 910), polynonamethylene dodecamide (polyamide 912) , Polydecamethylene adipamide (polyamide 106), polydecamethylene sebacamide (polyamide 1010), polydecamethylene dodecamide (polyamide 1012) and the like. These may be copolymerized by one component alone or in combination of multiple components. Moreover, any copolymerization method such as random copolymerization, block copolymerization, and graft copolymerization may be used.
Among these aliphatic polyamide-based resins, polyamide 6, polyamide 66, and polyamide 6, 66 are preferable because they have an excellent balance of heat resistance, moldability, water absorption, and mechanical strength, and polyamide 6 has high versatility and economy. Is particularly preferable.

(Styrene-based block copolymer (a2))
The styrene-based block copolymer (a2) used in the present invention contains a styrene monomer unit and an isobutylene monomer unit as a copolymerization component, and the content of the styrene monomer unit is 5% by mass or more and 30% by mass. It is less than, and the weight average molecular weight is 20,000 or more and 130,000 or less.

The styrene-based block copolymer (a2) may have at least one styrene block and at least one isobutylene block in the molecule, and its structure is not particularly limited. For example, it may have a linear ABA-type triblock structure, an AB-type diblock structure, or a branched-chain or star-shaped (radial-type) molecular chain form branched into two or more. Among them, from the viewpoint of the adhesion between the sea / island phase with the aliphatic polyamide resin (a1) and the adhesion with other layers, the linear ABA type triblock structure, the AB type diblock structure, and a mixture thereof are used. Preferably, a linear ABA type triblock structure is more preferable.

Examples of the monomers constituting the styrene block include styrene, α-methylstyrene, 2-methylstyrene, 4-methylstyrene, 4-propylstyrene, 4-t-butylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, and the like. Styrenes such as 2-ethyl-4-benzylstyrene, 4- (phenylbutyl) styrene, 2,4,6-trimethylstyrene, monofluorostyrene, difluorostyrene, monochlorostyrene, dichlorostyrene, methoxystyrene, t-butoxystyrene, etc. Vinyl group-containing aromatic compounds such as vinyl naphthalenes such as 1-vinylnaphthalene and 2-vinylnaphthalene; vinylene group-containing aromatic compounds such as inden and acetylene can be mentioned. The monomer unit constituting the styrene block may be only one type or two or more types, but among them, styrene or a unit derived from styrene is particularly preferable.

Further, the styrene block may be a hydrogenated aromatic ring, and can generally be obtained by hydrogenating the block copolymer after producing the block copolymer. The hydrogenation rate of the aromatic ring is preferably 50% by mass or more, more preferably 80% by mass or more, from the viewpoint of improving the gas barrier property of the present film. The hydrogenation method and reaction form of the aromatic ring are not particularly limited, but a method having a high hydrogenation rate and a small polymer chain cleavage reaction is preferable.

An example of the monomer constituting the isobutylene block is isobutylene.
Specific examples of the styrene block and isobutylene block copolymer include styrene-isobutylene block copolymer (SIB), styrene-isobutylene-styrene block copolymer (SIBS), and SIBS / SIB that combines these. It is preferable because it has excellent thermal stability.

The styrene-based block copolymer (a2) contains at least one functional group selected from an acid anhydride group, a carboxyl group, a hydroxyl group, an amino group, an isocyanate group and an epoxy group. It may be united. Further, a mixture of the modified copolymer and the unmodified copolymer can also be used.

The copolymer composition ratio of the styrene-based block copolymer (a2) is 5% by mass or more and less than 30% by mass of the styrene monomer unit. The lower limit is preferably 10% by mass or more, and more preferably 15% by mass or more. The upper limit is preferably 28% by mass or less, more preferably 25% by mass or less.
When the styrene monomer unit is less than 30% by mass, the rubber hardness becomes low, and when blended with the aliphatic polyamide resin (a1), excellent impact resistance can be imparted. On the other hand, when it is 5% by mass or more, the styrene-based block copolymers (a2) can be dry-blended without blocking each other, and the moldability is excellent.
The isobutylene monomer unit is preferably 70% by mass or more and less than 95% by mass, and the lower limit is more preferably 72% by mass or more and further preferably 75% by mass or more. The upper limit is preferably 90% by mass or less, more preferably 85% by mass or less.
When a plurality of styrene blocks and isobutylene blocks are provided, the total composition ratio (mass%) is used.

The weight average molecular weight of the styrene-based block copolymer (a2) is 20,000 or more and 130,000 or less. The lower limit is preferably 40,000 or more, and more preferably 60,000 or more. The upper limit is preferably 11,000,000 or less, and more preferably 100,000 or less.
When the weight average molecular weight is 130,000 or less, the fluidity of the styrene-based block copolymer (a2) becomes good, and the formability and processability of the film when mixed with the fatty acid polyamide resin (a1) are good. Become. In particular, since fine dispersed particles of the styrene-based block copolymer (a2) can be formed, bending pinhole resistance can be improved in a wide temperature range from low temperature to room temperature. On the other hand, when it is 20,000 or more, the mechanical properties such as impact resistance and moldability of this film are good.

The styrene-based block copolymer (a2) preferably has a type A durometer hardness of 15 or more and 50 or less. The lower limit is more preferably 18 or more, and even more preferably 20 or more. The upper limit is more preferably less than 45, and even more preferably less than 40.
The type A durometer hardness of the styrene-based block copolymer (a2) depends on the copolymer composition ratio, the molecular weight, and the block structure, and flexibility can be imparted to the film by 50 or less. Further, when the type A durometer hardness is 15 or more, the styrene-based block copolymers (a2) are less likely to block each other, and the productivity is improved.
The hardness of the type A durometer can be measured by reading and measuring the value 15 seconds after the pressure plate is brought into contact with the test piece by the method described in JIS K6253-3.

When the total amount of the aliphatic polyamide resin (a1) and the styrene block copolymer (a2) in the layer A is 100% by mass, the content of the styrene block copolymer (a2) is 1 to 20% by mass. Is preferable, 2 to 15% by mass is more preferable, and 3 to 12% by mass is further preferable. If it is 1% by mass or more, a sufficient bending pinhole resistance improving effect can be obtained. If it is 20% by mass or less, the oxygen gas barrier property and mechanical strength of this film can be sufficiently maintained.

In the A layer of this film, the styrene block copolymer (a2) is dispersed in the form of particles with respect to the aliphatic polyamide resin (a1), (a1) is in the form of sea, and (a2) is in the form of islands. (See FIGS. 1 (a) and 1 (b)).
In the cross-sectional observation parallel to the flow direction (MD) or width direction (TD) of this film, the maximum horizontal diameter of the dispersed particles of the styrene-based block copolymer (a2) in the A layer of MD or TD is 3.0 μm. The following is preferable, and 2.0 μm or less is more preferable.
The maximum diameter in the horizontal direction means the maximum diameter of dispersed particles observed when the film is cut perpendicular to the thickness direction and observed at a magnification of 2000 times by the cross-section dyeing TEM method. By dispersing a large number of particles of 3.0 μm or less, both the transparency of the film and the bending pinhole resistance are improved.

Further, the aspect ratio (major axis / minor axis) of the length (major axis) in the horizontal direction of the film to the length (minor axis) in the film thickness direction of the dispersed particles of the styrene-based block copolymer (a2) in the A layer is 2. The above is preferable, and 5 or more is more preferable. There is no particular upper limit. When the aspect ratio is 2 or more, the particles become thin in the horizontal direction and are dispersed in large numbers, so that the styrene-based block copolymer (a2) is present on the entire surface in the horizontal direction of the film, so that stress concentration due to film bending occurs. However, pinholes are unlikely to occur.
In particular, when the above-mentioned maximum diameter and aspect ratio are satisfied in the form of a biaxially stretched film in a low temperature environment, the effect of pinhole resistance is remarkably exhibited.

Further, the maximum horizontal diameter of the dispersed particles of the styrene-based block copolymer (a2) in the A layer is 3.0 μm when observed in either the flow direction (MD) or the width direction (TD) of the film. When the diameter is 4.0 μm or more, preferably 5.0 μm or more in the cross-sectional observation in the other film direction, the linear cut property in the other film direction is good. For example, when the maximum diameter of the dispersed particles in the width direction (TD) is 3.0 μm or less and the maximum diameter of the dispersed particles in the flow direction (MD) is 4.0 m or more, the pinhole resistance and transparency of the film are determined. The linear cut property in the film flow direction (MD) is improved (see FIGS. 1 (a) and 1 (b)).
In particular, by combining pinhole resistance, transparency, and linear cutability in the form of a biaxially stretched film, when this film is used as a packaging material, the storage stability and visibility of the contents are improved, as well as The ease of opening the package by the user is improved and the convenience is improved.

(Other ingredients)
The layer A contains the above-mentioned components (a1) and (a2) as main components, and may also contain other components such as an aromatic polyamide resin as long as the characteristics of the film of the present invention are not impaired. ..
Here, the main component is based on the layer containing it (100% by mass), and the component is 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 95% by mass or more. It means to include.

Examples of the aromatic polyamide resin and the alicyclic polyamide resin that may be contained in the A layer include polytetramethylene terephthalamide (polyamide 4T), polypentamethylene terephthalamide (polyamide 5T), and poly-2-methylpentamethylene terephthalamide. Amid (polyamide M-5T), polyhexamethylene hexahydroterephthalamide (polyamide 6T), polynonamethylene terephthalamide (polyamide 9T), polydecamethylene terephthalamide (polyamide 10T), polyundecamethylene terephthalamide (polyamide 11T) , Polydodecamethylene terephthalamide (polyamide 12T), polymetaxylylene adipamide (polyamide MXD6), polyparaxylylene adipamide (polyamide PXD6), polymetaxylylene sebacamide (polyamide MXD10), polyparaxylylene Semi-crystalline polyamide resin such as bacamide (polyamide PXD6), polyhexamethylene isophthalamide (polyamide 6I), polybis (3-methyl-4-aminohexyl) methaneterephthalamide (polyamide PACMT), polybis (3-methyl- 4-Aminohexyl) methaneisophthalamide (polyamide PACMI), polybis (3-methyl-4-aminohexyl) methadodecamide (polyamide PACM12), polybis (3-methyl-4-aminohexyl) methanetetradecamide (polyamide PACM14) ) And the like can be preferably used. These may be copolymerized individually by one component or in combination of a plurality of components. Moreover, any copolymerization method such as random copolymerization, block copolymerization, and graft copolymerization may be used.

Further, the layer A is a heat stabilizer, an antioxidant, an ultraviolet absorber, a weather resistant agent, a lubricant, a filler, a nucleating agent, a plasticizer, a foaming agent, and an antiblocking agent within a range that does not impair the physical properties of the film of the present invention. , Antifogging agent, flame retardant, dye, pigment, stabilizer, coupling agent, impact resistance improving material and other additives can be contained.

<B layer>
The film of the present invention can be imparted with gas barrier properties by providing a B layer made of a gas barrier resin, and when used as a packaging film, it prevents the contents from spoiling and enhances long-term storage. It is useful.
Known resins can be used as the gas barrier resin, and examples thereof include polyvinyl alcohol (PVA), ethylene-vinyl acetate copolymer saponified product (EVOH), metaxylylene diadipamide (MXD6 nylon), and polyvinylidene chloride (polyvinylidene chloride). PVDC). Of these, ethylene-vinyl acetate copolymer saponified product (EVOH) is preferable from the viewpoint of oxygen gas barrier property.

(Ethylene-vinyl acetate copolymer saponified product (b1))
The ethylene-vinyl acetate copolymer saponified product (b1) (EVOH) used in the present invention is a copolymer obtained by saponifying a copolymer of ethylene and vinyl acetate with an alkali catalyst or the like. The ethylene content in the ethylene-vinyl acetate copolymer saponified product is not particularly limited, but is generally preferably 20 mol% or more, more preferably 24 mol% or more, from the viewpoint of film film formation stability. be. On the other hand, the upper limit of the ethylene content is preferably 48 mol% or less, more preferably 38 mol% or less, and further preferably 30 mol% or less from the viewpoint of gas barrier properties. The degree of saponification of the ethylene-vinyl acetate copolymer saponified product (b1) is preferably 96% or more, more preferably 98% or more. In the film of the present invention, when the ethylene content in the ethylene-vinyl acetate copolymer saponified product (b1) and the degree of saponification are within the above ranges, the balance between film forming property and gas barrier property is excellent. .. Therefore, coextrusion with an aliphatic polyamide resin and molding processing such as biaxial stretching become possible.

Further, the ethylene-vinyl acetate copolymer saponified product (b1) may be variously modified as needed, and the modified ethylene-vinyl acetate copolymer saponified product and the ethylene-vinyl acetate copolymer saponified product May be a mixture of. Examples of the modified ethylene-vinyl acetate copolymer saponified product include a modified ethylene-vinyl acetate copolymer saponified product made of propylene, isobutene, etc., and a modified ethylene-vinyl acetate copolymer made of at least one α-olefin having 3 to 30 carbon atoms. Obtained by saponifying a ternary copolymer consisting of a modified ethylene-vinyl acetate copolymer saponified product obtained by graft-polymerizing a copolymer saponified product and an acrylic acid ester, and a (meth) acrylic acid ester-ethylene-vinyl acetate. Modified ethylene-vinyl acetate copolymer saponified product, modified ethylene-vinyl acetate copolymer saponified product in which the hydroxyl group of the ethylene-vinyl acetate copolymer saponified product is modified with a cyanoethyl group, and polyester is depolymerized with vinyl alcohol. A modified ethylene-vinyl acetate copolymer obtained by saponifying a copolymer of a modified ethylene-vinyl acetate copolymer saponified product containing a polyester graft and an olefinically unsaturated monomer containing vinyl acetate-ethylene-silicon. Modified ethylene-vinyl acetate copolymer obtained by saponifying a ternary copolymer composed of a saponified product and a pyrrolidone ring-containing monomer-ethylene-vinyl acetate. Ethylene-vinyl acetate copolymer saponified product obtained by saponification of coalescence, modified ethylene-vinyl acetate copolymer saponified product obtained by saponification of ternary copolymer composed of allyl acetate-ethylene-vinyl acetate, isoacetate Ethylene-vinyl acetate copolymer saponified product obtained by saponifying a ternary copolymer composed of propenyl-ethylene-vinyl acetate, and modification in which a polyether component is added to the end of the ethylene-vinyl acetate copolymer saponified product. Ethylene-vinyl acetate copolymer saponified product, modified ethylene-vinyl acetate copolymer saponified product in which the polyether component is added in a graft form as a branch polymer of ethylene-vinyl acetate copolymer saponified product, alkylene oxide is ethylene- Examples thereof include a modified ethylene-vinyl acetate copolymer saponified product added to the vinyl acetate copolymer saponified product.

(Other ingredients)
The B layer contains a gas barrier resin as a main component, and may contain other resins and components as long as the characteristics of the film of the present invention are not impaired.
Here, the main component means that the component is contained in an amount of 50% by mass or more, preferably 80% by mass or more, based on the layer containing the component (100% by mass).

-Thermoplastic elastomer (b2)
For example, a thermoplastic elastomer (b2) can be mixed in order to improve the flexibility of the B layer and the pinhole resistance of the film. For example, known polyolefin-based elastomers, polyamide-based elastomers, (meth) acrylic-based elastomers, polyester-based elastomers, styrene-based elastomers, and modified products thereof can be mentioned, and one or more of them may be used. Examples of the modifying component include unsaturated carboxylic acids such as maleic anhydride and / or anhydrides thereof, glycidyl acid, amines, epoxies, isocyanates and the like, and the modification rate is preferably 0.01 to 10% by mass. Further, a block copolymer using polyalkylene ether glycol as a soft segment of a polyamide-based elastomer or a polyester-based elastomer is preferable.

Examples of the styrene-based elastomer include styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene / propylene copolymer (SEP), and styrene-ethylene / propylene. -Styrene block copolymer (SEPS), styrene-ethylene / butylene-styrene block copolymer (SEBS), styrene-ethylene-ethylene / propylene-styrene block copolymer (SEEPS), styrene-isobutylene block copolymer (SEEPS) SIB), styrene-isobutylene-styrene block copolymer (SIBS) and the like.

Soft segment from the viewpoint of good compatibility with the ethylene-vinyl acetate copolymer saponified product (b1) of layer B, fine dispersion, less decrease in transparency of the film, and improvement of impact resistance and pinhole resistance. As the above, polyamide-based block copolymers and polyester-based block copolymers using polyalkylene ether glycol, and maleic anhydride-modified products thereof, SIB, and SIBS are preferable.
Among them, as the elastomer (b2) of the B layer, SIB and SIBS having the characteristics of the styrene block copolymer (a2) used for the A layer are used, and the same type of styrene block copolymer (a2) is used for the A layer and the B layer. When a2) is blended, it is preferable in terms of the productivity of the coextruded film that arranges the A layer and the B layer.

When the total amount of the ethylene-vinyl acetate copolymer saponified product (b1) and the thermoplastic elastomer (b2) in the layer B is 100% by mass, the content of the thermoplastic elastomer (b2) is 1 to 20% by mass. It is preferable, 2 to 15% by mass is more preferable, and 3 to 10% by mass is further preferable. Bending resistance is improved by 1% by mass or more. When it is 20% by mass or less, deterioration of gas barrier property and transparency of this film can be suppressed. Further, when the content is low, gel generation in film formation is suppressed, which is preferable in terms of film productivity.

In the B layer of this film, the thermoplastic elastomer (b2) is dispersed in the form of particles with respect to the ethylene-vinyl acetate copolymer saponified product (b1), (b1) is dispersed in the form of sea, and (b2) is dispersed in the form of islands. Make a form.
As for the dispersed form, the maximum horizontal diameter of the particles (b2) in the horizontal direction is preferably 3.0 μm or less, more preferably 2.0 μm or less, still more preferably 1.0 μm or less. The maximum diameter means the maximum diameter of the dispersed particles observed when the film is cut perpendicularly in the thickness direction and observed at a magnification of 2000 times by the cross-section dyeing TEM method.
The thermoplastic elastomer (b2) is mainly composed of an ethylene-vinyl acetate copolymer saponified product (b1) having poor flexibility and impact resistance because the particles are dispersed in the B layer with a maximum diameter of 3.0 μm or less. It is possible to significantly improve the mechanical strength such as the flexibility, impact resistance, and bending pinhole resistance of the B layer, and also to have transparency.

Further, even when a stretched film is produced, the thermoplastic elastomer (b2) in the ethylene-vinyl acetate copolymer saponified product (b1) is not strongly stretched, and the length (short) of the dispersed particles in the film thickness direction is short. The aspect ratio (major axis / minor axis) of the length (major axis) in the horizontal direction of the film with respect to the diameter) is preferably 1 to 3.
When this film has an A layer and a B layer, the dispersion of the styrene block copolymer (a2) in the aliphatic polyamide resin (a1) of the A layer and the ethylene-vinyl acetate copolymer saponified product of the B layer (a2) Combined with the dispersion of the thermoplastic elastomer (b2) in b1), the flexibility is improved in a transparent state, and the bending pinhole resistance against local stress concentration due to bending is increased, which is severe at low temperature. It can also exhibit good physical properties in the environment.

-General-purpose resin, additives, etc. In addition to the above-mentioned components (b1) and (b2), the B layer contains other components such as general-purpose resins and additives as long as the characteristics of the film of the present invention are not impaired. You may.
The definition of the main component, additives, etc. are the same as those for the A layer.

<Layer structure>
This film may have at least one layer A containing an aliphatic polyamide resin (a1) and a styrene block copolymer (a2), and may have another layer. For example, it is also possible to arrange the B layer containing the gas barrier resin described above, the aliphatic polyamide resin layer (C layer) not containing the styrene block copolymer (a2), and the like.

For example, in the case of a film structure having an A layer and a B layer, a three-layer structure such as A layer / B layer / A layer can be mentioned, and in the case of further having a C layer, A layer / B layer / C layer / A A four-layer structure such as a layer and a five-layer structure such as A layer / C layer / B layer / C layer / A layer and C layer / A layer / B layer / A layer / C layer are preferable.
Further, the A layer / in which a plurality of A layers having different types and contents of the styrene block copolymer (a2) and a plurality of B layers having different types and contents of the thermoplastic elastomer (b2) are arranged. Five-layer structure such as B layer / B layer / B layer / A layer, A layer / A layer / B layer / A layer / A layer, C layer / A layer / B layer / B layer / B layer / A layer / A seven-layer structure such as a C layer, a C layer / A layer / A layer / B layer / A layer / A layer / C layer, etc. is preferably mentioned, but is not limited to these exemplified ones.
Further, an adhesive layer or another layer may be further provided between the layers. Of the above layer structures, from the viewpoint of improving the bending resistance of the film and the recycling production efficiency, it is preferable to use a layer structure having the A layer as the outermost layer.

Further, from the viewpoint of bending pinhole resistance and oxygen gas barrier property, the thickness ratio of the A layer to the total film thickness is preferably 30 to 90%, and the thickness ratio of the B layer is preferably 10 to 70%. When there are a plurality of A layers and / or B layers, these are ratios of the total thickness of each A layer and / or B layer to the total thickness.
The thickness of each of the A layer, the B layer, and the C layer is not particularly limited, but is preferably 1 to 15 μm, respectively. It is more preferably 2 to 10 μm, still more preferably 3 to 8 μm. When there are a plurality of A layer, B layer, and C layer, each layer may have a different layer thickness or the same layer thickness.
The total thickness of this film is not particularly limited, but for example, when workability and practicality are taken into consideration, the lower limit is preferably 10 μm or more, and more preferably 12 μm or more. The upper limit value is preferably 50 μm or less, more preferably 30 μm or less. When the total thickness of this film is within the above range, the film has sufficient rigidity, is excellent in mechanical properties such as bending pinhole resistance and impact resistance, and is also excellent in gas barrier property.

This film is preferably a biaxially stretched film from the viewpoint of mechanical properties and gas barrier properties. As the biaxial stretching method, conventionally known stretching methods such as tenter-type sequential biaxial stretching, tenter-type simultaneous biaxial stretching, and tubular simultaneous biaxial stretching can be adopted.

This film can generally be used by being laminated with a polyolefin-based sealant film such as polyethylene. In this case, the layer located on the outermost layer side in the layer structure of the present film may be laminated by applying a surface treatment such as a corona treatment. In addition, an adhesive layer, metal foil, paper, etc. can be laminated. An existing laminating method can be used for laminating, and examples thereof include a dry laminating method, a wet laminating method, a sand laminating method, and an extrusion laminating method. In addition to corona treatment, this film can also be subjected to surface treatment such as printing, coating, and thin film deposition, as well as surface treatment.

From the viewpoint of maintaining the quality of the contents and preventing spoilage, the film of the present invention is made of polyvinyl, which is further laminated with a gas barrier resin layer or vapor-deposited with a metal such as aluminum or a metal oxide such as silicon oxide or alumina. By applying a gas barrier coating agent such as alcohol (PVA), the gas barrier property and moisture resistance can be further improved.

<Manufacturing method>
The present film can be produced by various methods, and for example, it is preferably produced by the following method.
Both the aliphatic polyamide resin (a1) and the ethylene-vinyl acetate copolymer saponified product (b1) have high hygroscopicity, and when the hygroscopic material is used, water vapor and oligomers are generated when the raw material is thermally melted and extruded. Inhibits film formation. Therefore, in preparing the raw materials, it is preferable to dry them in advance so that the water content is 0.1% by mass or less. Further, various additives such as lubricants, antistatic agents, antioxidants, antiblocking agents, stabilizers, dyes, pigments, and inorganic fine particles can be appropriately used as long as they do not affect the properties of the film.

Then, in the case of a multilayer film, the raw materials of each layer are melt-extruded by different extruders, and a substantially amorphous and non-oriented film (hereinafter referred to as "unstretched film") is produced by a coextrusion method. In the production of this unstretched film, for example, the resin obtained by melting the above raw materials with a number of extruders corresponding to the types of raw materials is merged with a feed block, a multi-manifold flat die, or an annular die, and then a multilayer is produced. A coextrusion method can be adopted in which a flat or annular unstretched film is formed by extruding as a film and then quenching. In the case of a single-layer film, it is possible to produce an unstretched film by extruding using a known flat die or cyclic die.

Next, the above-mentioned unstretched film is usually 2.0 to 5.0 times in one direction, preferably 2.0 to 5.0 times in the flow direction (longitudinal direction, MD) of the film and the width direction (horizontal direction, TD) perpendicular to the flow direction. , More preferably 2.0 to 5.0 times in each of the vertical and horizontal biaxial directions, and more preferably 2.5 to 4.5 times in each of the vertical and horizontal biaxial directions. When the stretching ratios in the longitudinal and horizontal biaxial stretching directions are smaller than 2.0 times, the effect of orientation due to stretching is small, the mechanical properties such as film strength are inferior, and the stretching ratio in the biaxial stretching direction. When each is greater than 5.0 times, the multilayer film is likely to break during stretching.

As the biaxial stretching method, conventionally known stretching methods such as tenter-type sequential biaxial stretching, tenter-type simultaneous biaxial stretching, and tubular simultaneous biaxial stretching can be adopted. For example, in the case of the tenter type sequential biaxial stretching method, the unstretched film is heated to a temperature range of 40 to 100 ° C. and stretched 2.0 to 5.0 times in the longitudinal direction by a roll type longitudinal stretching machine. Subsequently, it can be produced by stretching 2.0 to 5.0 times in the lateral direction within a temperature range of 60 to 140 ° C. by a tenter type transverse stretching machine. Further, in the case of the tenter type simultaneous biaxial stretching method or the tubular type simultaneous biaxial stretching method, for example, in the temperature range of 60 to 200 ° C., stretching is performed 2.0 to 5.0 times in each axial direction at the same time in the vertical and horizontal directions. Can be manufactured by

Subsequently, the biaxially stretched film obtained to impart dimensional stability is heat-fixed. The heat fixing temperature is preferably 200 ° C. to 225 ° C., more preferably in the range of 205 to 220 ° C. As a result, a stretched film having good room temperature dimensional stability and having an arbitrary heat shrinkage rate can be obtained. The biaxially stretched film sufficiently heat-fixed by the heat treatment operation can be cooled and wound by a conventional method.
When the heat fixing temperature is within the above range, heat fixing is sufficiently performed and the laminate strength is maintained. Further, a film having sufficient impact resistance and bending pinhole resistance can be obtained, and an excellent film without troubles such as breakage and whitening of the film surface can be obtained.

In the present invention, in order to relieve the stress of crystallization shrinkage due to heat fixing, the film shrinks by relaxing in the width direction of 0 to 15%, preferably 3 to 10% during heat fixing. Since the follow-up relaxation is sufficiently performed and the film relaxes uniformly in the width direction, the shrinkage ratio in the width direction becomes uniform and a film having excellent room temperature dimensional stability can be obtained.

In the present invention, after the above relaxation, retransstretching can be performed at a temperature of 140 ° C. to 200 ° C. in the range of 2 to 9%, preferably 3 to 7%, and more preferably 4 to 7%. .. When the re-transverse stretching temperature is within the above range, an appropriate stress at the time of stretching is obtained and uniform stretching is possible, so that the lateral shrinkage ratio in the width direction becomes uniform. In addition, heat fixation is not applied after stretching, and the lateral shrinkage rate is likely to occur. Further, when the re-transverse stretching ratio is within the above range, a lateral shrinkage ratio sufficient to follow the solidification shrinkage of the sealant can be obtained, the appearance of the sealed portion is good, and an appropriate shrinkage ratio can be obtained. It is possible to prevent troubles such as wrinkles and pattern misalignment in the printing and laminating processes. The stretched film formed by the above method is cooled and rolled by a conventional method.

<Physical characteristics of film>
(Oxygen gas barrier property)
The film, 23 ° C., it is ^{preferably, 1.5cc / m 2 / 24h /} atm or less oxygen permeability at 50% relative humidity is not more than 2.0cc ^/ m 2 ^/ 24h ^/ atm it is more ^preferred, and more preferably not more than 1.0cc / m 2 / 24h / atm , it is desired a lower value. If oxygen permeability 2.0cc / m 2 / 24h / ^atm or less, as a packaging film, to prevent the deterioration of the contents, preferable since it is possible to maintain sufficient oxygen gas barrier properties to keep fresh ..

(Pinhole resistance (bending pinhole resistance))
This film uses a gelboflex tester to perform bending tests under each condition of 3000 times under 50% relative humidity at 23 ° C, 500 times under 50% relative humidity at 5 ° C, and 3000 times under 50% relative humidity at 5 ° C. And the number of pinholes generated was measured. The test was performed three times under each condition, and the average value was calculated. Number Pinholes in any conditions, preferably 15.0 cells / 481cm ² or less, more preferably 13.0 pieces / 481cm ² or less, still more preferably less than 4.0 pieces / 481cm ^2, 3.0 units / 481 cm ² or less is more preferable, 1.0 piece / 481 cm ² or less is particularly preferable, and less is preferable. Further, the lower the environmental temperature, the less flexible the film is, so that the number of pinholes under low temperature conditions is small, which means that the pinhole resistance is better. If it is less than 15.0 pieces / 481 cm ² , bending during transportation as a food packaging film and pinholes due to collisions between the films are unlikely to occur, and it is easy to suppress oxidative deterioration of the contents due to a decrease in gas barrier property. ..

When this film is a multilayer including a B layer, the number of pinholes is preferably less than ^{4.0 / 481 cm 2 and} more preferably ^{3.0 / 481 cm 2 or less under any condition.} .0 pieces / 481 cm ² or less is more preferable, and less is preferable.

(transparency)
In the film of the present invention, the haze value measured based on JIS K7136 is 10% or less, preferably 8% or less, more preferably 5% or less, and preferably a smaller value. As long as the value of all haze is within the relevant range, this film is excellent in transparency, designability, and visibility of the contents when used as a packaging film.

(Hot water shrinkage rate)
The hot water shrinkage rate of this film for 5 minutes at 95 ° C. is preferably 0.1% or more and 15% or less in both the flow direction (MD) and the width direction (TD). The lower limit is more preferably 0.3% or more, further preferably 0.5% or more. The upper limit is more preferably 10% or less, further preferably 5% or less. The hot water shrinkage rate at 127 ° C. for 5 minutes is preferably 1% or more and 30% or less in both the vertical direction (MD) and the horizontal direction (TD). The lower limit is more preferably 3% or more, further preferably 5% or more. The upper limit is more preferably 25% or less, further preferably 23% or less.
If the hot water shrinkage rate is less than the above range, the heat fixing temperature may be too high, and the impact resistance and bending pinhole resistance of the biaxially stretched film tend to decrease. If the hot water shrinkage rate exceeds the above range, heat fixing may be insufficient, causing shrinkage due to heat applied in post-processing such as printing, laminating, and bag making, and during printing. It may cause slippage, wrinkles during laminating, and distortion of bag-making products.
A higher hot water shrinkage rate is advantageous for low temperature pin pole resistance, but the film mechanical strength and the above-mentioned post-workability tend to be insufficient. The present invention has the effect that sufficient film mechanical strength can be obtained even at a low hot water shrinkage rate.

(Tensile breaking stress, tensile breaking elongation)
This film has excellent mechanical strength, and the tensile breaking stress under the test speeds of 200 mm / min, -10 ° C, and 23 ° C measured based on JIS K7127: 1999 is in the longitudinal direction (MD) and lateral direction (TD). ) Are preferably in the range of 100 to 400 MPa, the lower limit is more preferably 150 MPa or more, and even more preferably 200 MPa or more. If the film has a tensile stress at break in this range, pinholes and breaks due to bending are unlikely to occur while maintaining the rigidity of the film when the contents are packaged.
In addition, the tensile elongation at break under the test speeds of 200 mm / min, -10 ° C, and 23 ° C measured based on JIS K7127: 1999 is 50% or more in either the vertical direction (MD) or the horizontal direction (TD). % Or less is preferable, the lower limit is more preferably 60% or more, and even more preferably 75% or more. Further, it is particularly preferable that the film has excellent toughness in the range in which both the vertical direction (MD) and the horizontal direction (TD) are concerned.

(Impact resistance)
This film has excellent impact resistance, and the fracture energy measured by the Hydroshot high-speed tester under the conditions of -10 ° C and 23 ° C measured based on ASTM D3763 is preferably 0.3 J or more, preferably 0.5 J. The above is more preferable. A film having a breaking energy within such a range is less likely to break or pinhole even when the contents are packaged and, for example, an impact generated during transportation is generated.

(Straight line cutability)
It is preferable that a straight line is drawn in the flow direction (MD) of the film with a magic pen, and the absolute value of the amount of deviation from the straight line when the film is torn by 200 mm along the straight line is 5.0 mm or less.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. The obtained film was evaluated by the following method.

(1) Oxygen gas barrier properties Oxygen gas barrier property, JIS K7126 compliance with 23 ° C. to Method B, the oxygen permeability at 50% ^RH: was measured (units cc / m 2 / 24h / atm ).

(2) Pinhole resistance (bending resistance)
A film cut into a size of 20 cm × 28 cm was allowed to stand for 24 hours or more under the conditions of a predetermined temperature and a relative humidity of 50% as shown below to adjust the temperature and humidity, and conformed to the MIL-B-131C standard. Gelboflex tester No. made by Rigaku Kogyo Co., Ltd. Using the 901 type, the bending test was repeated as follows, and the number of pinholes per ^{481 cm 2 was measured.} The film is formed into a cylindrical shape with a length of 20 cm and a circumference of 28 cm, and one end of the wound cylindrical film is on the outer circumference of the disk-shaped fixed head of the tester, and the other end is on the outer circumference of the disk-shaped movable head of the tester. 5 mm pieces were overlapped and fixed respectively. The fixed head and the movable head face each other with a distance of 17.5 cm.

The movable head is then rotated 440 ° in the direction of the fixed head while approaching 8.8 cm along the axes of both parallel heads, followed by a 6.3 cm straight run without rotation. , These operations were performed in reverse, and a bending test in which the stroke until the movable head was returned to the initial position was performed once was continuously performed at a speed of 40 times per minute for a predetermined number of times. After that, the number of pinholes (unit) generated in ^{the area of 481 cm 2} between the length of 17.5 cm between the fixed head and the movable head and the circumference of 27.5 cm excluding the overlap when forming a cylinder. : Number / 481 cm ² ) was measured by applying a voltage of 1 kV using a pinhole tester TRD type manufactured by Sanko Electronics Laboratory.
The temperature, humidity, and the number of bending tests are as follows: (i) temperature 5 ° C. relative humidity 50%, bending 500 times, (ii) temperature 5 ° C. relative humidity 50%, bending 3000 times, (iii) temperature 23 ° C. relative humidity 50%, The bending was performed under three conditions of 3000 times. The test was performed three times under each condition, and the average value was calculated.

(3) Transparency Transparency was evaluated by measuring haze (unit:%) in accordance with JIS K7136.

(4) Hot water shrinkage rate Cut out from the three points at both ends and the center of the film in the vertical direction 120 mm x horizontal direction 120 mm, and three reference lines exceeding 100 mm in the vertical and horizontal directions (MD direction and TD direction) of this sample. I pulled it. This sample was allowed to stand in an atmosphere of 23 ° C. and 50% relative humidity for 24 hours to measure the reference line. Let F be the measured length before heat treatment. The sample was removed after immersion in hot water at 95 ° C. for 5 minutes or after an autoclave test at 127 ° C. for 5 minutes. Further, after allowing to stand in an atmosphere of 23 ° C. and 50% relative humidity for 30 minutes, the length of the reference line is measured, and the length after heat treatment is defined as G. Using the following formula, the average value of the three hot water shrinkage rates (unit:%) in the vertical direction and the horizontal direction was calculated.
(Formula) (FG) / F × 100 (%)

(5) Tensile breaking stress, tensile breaking elongation Based on JIS K7127: 1999, tensile breaking stress (unit: MPa) and tensile breaking elongation in the vertical and horizontal directions (MD direction, TD direction) at a test speed of 200 mm / min. (Unit:%) was measured under the conditions of −10 ° C. and 23 ° C.

(6) Impact resistance The fracture energy (unit: J) measured by the Hydroshot high-speed tester measured based on ASTM D3763 was measured in an atmosphere of −10 ° C. and 23 ° C.

(7) Straight line cutability From the three points at both ends and the center of the obtained film, cut out two sheets each of 300 mm for MD x 180 mm for TD, and draw straight lines that are exactly parallel to the MD at intervals of 30 mm. Next, use a feather blade to make a cut on this line up to 50 mm from the end, make it into a strip, and prepare a test piece. The test piece is then placed in front of the measurer on a flat frosted glass in such a way that the MD faces straight forward. Here, in the case of the right hand guide, the right hand holds the strip portion at the right end of the test piece, and the left hand holds the strip portion next to it. Slowly and straightly pull your right hand holding the strip part toward you. This operation is performed 5 times in order from the right end. In the case of left-handed pull, the reverse operation is performed.
A straight line at 200 mm from the start of tearing, that is, a width deviated from the straight line previously drawn parallel to the MD, that is, a straight line is drawn on the MD, and the absolute value of the amount of deviation from the straight line when the 200 mm is torn is L (mm). It was used as an index of cutability.
The above tests are conducted for each of the right and left guides, the average value (rounded to the second minority of the average value) is taken, and the following is used using the maximum value of the 6 points at both ends and in the center. Evaluation was performed.
〇; When L (mm) is 5.0 mm or less ×; When L (mm) exceeds 5.0 mm

(8) Dispersion form of elastomer The film is cut in parallel in the flow direction (MD) and width direction (TD) and perpendicular to the film thickness direction. × 8 μm was observed at each of three locations, and the maximum horizontal diameter (unit: μm) of the observed dispersed particles was measured. In addition, the aspect ratio (major axis / minor axis) of the length (major axis) in the film horizontal direction to the length (minor axis) in the film thickness direction of the dispersed particles was calculated.

<Raw materials used>
(Aliphatic polyamide resin)
N1: Polyamide 6 (relative viscosity (96% sulfuric acid) 3.34)

(Gas barrier resin)
V1: Ethylene-vinyl acetate copolymer saponified product (EVOH) (ethylene content 25 mol%, saponification degree 99% or more)
V2: Ethylene-vinyl acetate copolymer saponified product (EVOH) (ethylene content 32 mol%, saponification degree 99% or more)

(Thermoplastic elastomer)
E1: Styrene-based elastomer, styrene-isobutylene-styrene block copolymer (SIBS) (styrene content 23% by mass, weight average molecular weight 95,000, type A durometer hardness 33)
E2: Styrene-based elastomer, styrene-isobutylene-styrene block copolymer (SIBS) (styrene content 23% by mass, weight average molecular weight 93,000, type A durometer hardness 33)
E3: Styrene-based elastomer, styrene-isobutylene-styrene block copolymer (SIBS) (styrene content 30% by mass, weight average molecular weight 88,000, type A durometer hardness 45)
E4: Styrene-based elastomer, styrene-isobutylene-styrene block copolymer (SIBS) (styrene content 15% by mass, weight average molecular weight 146,000, type A durometer hardness 25)
E5: Styrene-based elastomer, styrene-ethylene / butylene-styrene block copolymer (SEBS) (styrene content 20% by mass)
E6: Polyamide-based elastomer, polyamide 12-polytetramethylene ether glycol copolymer E7: Polyolefin-based elastomer, maleic anhydride-modified-ethylene-butene 1-4-methylpentene copolymer

(Examples 1 and 2, Comparative Examples 1 and 4, Reference Examples 1 and 2)
The resin represented by the above abbreviation was blended with a φ40 mm single-screw extruder and extruded at a temperature of 250 ° C. to prepare a 50 μm-thick single-layer non-stretched film, and the evaluation results are shown in Table 1.

(Examples 3 to 5, Comparative Examples 5 to 7, Reference Examples 3 to 4)
The resin composition of layer A containing the raw materials in the mass ratio shown in Table 2 was charged into a φ40 mm single-screw extruder, and the resin composition of layer B was charged into a φ32 mm single-screw extruder and melted by both extruders. The resin is divided by a distribution block and multi-layered in a co-extruded T-die, and a molten film having a three-layer structure of A layer / B layer / A layer is extruded and rapidly cooled on a cooling roll at 30 ° C. to form an unstretched multilayer film. Was produced.
Next, the obtained unstretched multilayer film was stretched 3 times in the longitudinal direction by a roll type longitudinal stretching machine under 55 ° C. conditions, and further stretched 3.5 times in the transverse direction by a tenter type transverse stretching machine under 120 ° C. conditions. .. Subsequently, the obtained biaxially stretched film was heat-fixed under 220 ° C. conditions, and then laterally relaxed by 5%. After that, the film is cooled to room temperature, both ends corresponding to the grips of the clips are trimmed, and the trimmed product film is wound into a roll, and the thickness of each layer of the A layer / B layer / A layer is 5.5 μm / 4. A biaxially stretched multilayer film having a total thickness of 15.0 μm and 0 μm / 5.5 μm was obtained. The evaluation results are shown in Table 2.

(Example 6)
The resin composition of the A layer or the C layer in which the raw materials are mixed in the mass ratio shown in Table 2 is put into the extruder of φ65 mm, the resin composition of the A layer is put into the extruder of φ50 mm, and the resin composition of the B layer is put into the extruder. Was put into an extruder of φ50 mm, and the melted resin compositions were distributed by a distribution block and multi-layered in a co-extruded T-die, and (A layer or C layer) / A layer / B layer / A layer / ( A five-layer molten film (A layer or C layer) was extruded and rapidly cooled on a cooling roll at 30 ° C. to prepare an unstretched multilayer film.
Next, the obtained unstretched multilayer film was stretched 3 times in the longitudinal direction using a roll-type longitudinal stretching machine under 50 ° C. conditions, and further stretched 3.5 times in the transverse direction using a tenter-type transverse stretching machine under 120 ° C. conditions. bottom. Subsequently, the obtained biaxially stretched film was heat-fixed under the condition of 210 ° C. After that, the film is cooled to room temperature, both ends corresponding to the grips are trimmed on the clip, and the trimmed film is wound into a roll to form (A layer or C layer) / A layer / B layer / A layer / (A). A biaxially stretched multilayer film having a layer thickness of 3.5 / 2.0 / 4.0 / 2.0 / 3.5 μm and a total thickness of 15.0 μm was obtained. The evaluation results are shown in Table 2.

(Non-stretched single layer film; Examples 1 and 2, Comparative Examples 1 to 4)
In Examples 1 and 2 of the single-layer film, nylon 6 which is an aliphatic nylon, the content of the styrene monomer unit is 5% by mass or more and less than 30% by mass, and the weight average molecular weight is 20,000 or more and 13. It contained SIBS of 0,000 or less, and was able to achieve both good transparency and low temperature bending resistance.
Comparative Example 1 containing no SIBS and Comparative Example 2 using SIBS having a styrene monomer content of 30% by mass or more had poor low-temperature bending resistance. Comparative Example 3 using SIBS having a weight average molecular weight of more than 130,000 and Comparative Example 4 using SEBS had poor transparency.

(Biaxially stretched multilayer film; Examples 3 to 6, Comparative Examples 5 to 7)
In Examples 3 to 6 of the multilayer film in which the B layer containing EVOH, which is a gas barrier resin, is arranged, the haze is 10.0% or less, the temperature is 5 ° C. and the relative humidity is 50%, and the number of bending-resistant pinholes is 1.0 / With less than 481 cm ² and oxygen permeability of 1.0 cc / m ² / 24h / atm or less, it has transparency, bending pinhole resistance, and oxygen gas barrier properties, and also has good tensile properties, impact resistance, and linear cut properties. A film with excellent balance could be obtained.
Further, in Examples 3 to 6, the maximum horizontal diameter of the elastomer-dispersed particles in the A layer having a cross section parallel to the TD and perpendicular to the film thickness direction is 3.0 μm or less, the aspect ratio is 2 or more, and is parallel to the MD. Moreover, the maximum horizontal diameter of the elastomer-dispersed particles in the layer A having a cross section perpendicular to the film thickness direction was 4.0 μm or more. FIG. 1A shows a schematic view of the TD parallel cross section of the layer A, and FIG. 1B shows a schematic view of the MD parallel cross section of the layer A.
^{Among them, in Example 6, the number of pinholes was only 0.2 / 481 cm 2} even in the bending resistance pinhole test under the harsh conditions of a temperature of 5 ° C. and a relative humidity of 50% and bending of 3000 times, and the oxygen gas barrier. It was a very excellent film that had both property and transparency. It is self-evident that under the conditions of a temperature of 5 ° C. and a relative humidity of 50% and bending of 500 times, the number is 0.2 / 481 cm ^{2 or less.}
On the other hand, the three-layer films shown in Comparative Examples 5 to 7 are inferior in bending pinhole resistance, and Comparative Example 7 using SIBS having a weight average molecular weight of more than 130,000 is in a dispersed state of the A layer. The film was poor and the appearance of the film was poor.

(Reference Examples 1 to 4)
When a polyamide-based elastomer was used, Reference Example 1 of the single-layer film had high haze and poor transparency, but Reference Example 3 of the multilayer film had haze due to thinning of the film and elastomer by biaxial stretching. It has decreased.
When a polyolefin-based elastomer was used, Reference Example 2 of the single-layer film had good transparency and low-temperature bending resistance, but since the affinity between the aliphatic nylon and the polyolefin-based elastomer was low, the multilayer film In Reference Example 4, voids were generated at the phase interface between the dispersed particles (islands) of the polyolefin-based elastomer and nylon 6 (sea) due to biaxial stretching, and the haze increased.

Since the film of the present invention has excellent transparency and excellent bending pinhole resistance in a wide temperature range from a low temperature environment to a normal temperature environment, the long-term storage stability of the packaged contents can be improved, and the package can be packaged. It is effective in maintaining the quality of the contents such as food and industrial parts and reducing waste loss.

a1: Aliphatic polyamide resin a2: Styrene block copolymer

Claims (7)

A film having at least one A layer containing an aliphatic polyamide resin (a1) and a styrene-based block copolymer (a2).
When the A layer is 100% by mass, the content of the styrene-based block copolymer (a2) is 1 to 20% by mass.
The styrene-based block copolymer (a2) contains a styrene monomer unit and an isobutylene monomer unit as a copolymerization component, and the content of the styrene monomer unit is 5% by mass or more and less than 30% by mass. And the weight average molecular weight is 20,000 or more and 130,000 or less.
A polyamide-based resin film characterized in that the haze of the film is 10% or less, the temperature is 5 ° C., the relative humidity is 50%, and the number of pinholes is 15.0 / 481 cm ^{2 or less in a gelboflex test of 500 times of bending.} .. A biaxially stretched film having at least two layers, the A layer and the B layer containing a gas barrier resin.
The polyamide-based resin film according to claim 1, ^{wherein the number of pinholes is less than 4.0 / 481 cm 2} under the gelboflex test conditions of 23 ° C. and 50% relative humidity and 3000 times of bending. When the gas barrier resin of the B layer is an ethylene-vinyl acetate copolymer saponified product (b1), the B layer contains the styrene block copolymer (a2), and the B layer is 100% by mass, the above. The polyamide-based resin film according to claim 2, wherein the content of the styrene-based block copolymer (a2) is 1 to 20% by mass. The polyamide-based resin film according to any one of claims 1 to 3, wherein the styrene-based block copolymer (a2) is a styrene-isobutylene-styrene block copolymer. In the cross-sectional observation parallel to the flow direction (MD) or width direction (TD) of the film, the maximum horizontal diameter of the dispersed particles of the styrene-based block copolymer (a2) in the A layer of MD or TD is 3. The polyamide-based resin film according to any one of claims 1 to 4, which is 0 μm or less. The polyamide-based resin film according to any one of claims 1 to 5, wherein the A layer is arranged on the outermost layer. A package using the polyamide resin film according to any one of claims 1 to 6.

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