Polyamide resin film and packaging material

Abstract

To provide a polyamide resin film that is excellent in low water absorption and has sufficient impact resistance.SOLUTION: A polyamide resin film includes a layer (A) including at least an aliphatic polyamide resin and a layer (B) including a gas barrier resin. When the total mass of the layer (A) is 100 mass%, the layer (A) contains a polyamide resin (a) of 1-100 mass%. The polyamide resin (a) includes at least one selected from a polyamide including a C10 diamine and / or a C10 dicarboxylic acid and a polyamide having the molecular structure of polyamide 11.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a low water-absorbent polyamide resin film and a package using the film. [Background technology]

[0002] BACKGROUND ART Films made of polyamide resins are resin materials used in a variety of applications due to their excellent mechanical properties such as impact resistance and strength, heat resistance, and moldability such as biaxial orientation. Furthermore, although polyamide resins have superior gas barrier properties against oxygen and other gases compared to general-purpose plastics such as polyolefin resins, they are known to have insufficient gas barrier properties to meet the level required for long-term storage of contents such as food and pharmaceutical packaging. Therefore, polyamide resin films that combine mechanical properties, moldability, gas barrier properties, etc., by multi-layering them with layers of resins with high gas barrier properties, such as saponified ethylene-vinyl acetate copolymer (EVOH) and metaxylylenediadipamide (MXD6 nylon), have become widely used.

[0003] On the other hand, biaxially oriented films made from polyamide resins generally use polyamide 6 as the main component for its versatility and productivity, but due to the relatively high water absorption properties of polyamide 6, there is a potential problem of it easily elongating and changing dimensions when absorbed in high-humidity environments, which can easily cause problems in secondary processes in packaging material production, such as printing, laminating, boiling, and retort processing. Furthermore, there is a demand for polyamide biaxially oriented films with excellent low water absorption, including the ability to prevent water absorption in the gas barrier resin layer. Furthermore, polyamide 6 film is highly valued for packaging applications that require impact resistance, such as puncture resistance, due to its high tensile properties. However, films that are multilayered with a gas barrier resin layer are also required to have the same high impact resistance as polyamide 6 film.

[0004] Patent Document 1 discloses a technology for producing a polyamide resin film having good dimensional stability against water and excellent flex fatigue resistance, which includes a low moisture absorption polyamide resin and a flex fatigue resistance improver. However, nylon 6T, nylon 6T / 6, nylon MXD, nylon 12, and the like, which are listed as suitable low moisture absorption polyamide resins, produce films with insufficient impact resistance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-121136 Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above circumstances, an object of the present invention is to provide a polyamide resin film having excellent low water absorption and sufficient impact resistance. [Means for solving the problem]

[0007] As a result of intensive research into achieving the above object, the present inventors have found that the above-mentioned problems can be solved by using a layer (A) containing a specific aliphatic polyamide resin, or by combining a layer (A) containing a specific aliphatic polyamide resin with a layer (B) containing a gas barrier resin, and have thus completed the present invention.

[0008] The first invention is a polyamide-based resin film having at least a layer (A) containing an aliphatic polyamide resin and a layer (B) containing a gas barrier resin, wherein, when the total mass of the layer (A) is taken as 100 mass%, the layer (A) contains 1 to 100 mass% of a polyamide resin (a), and the polyamide resin (a) is at least one selected from polyamides containing a diamine having 10 carbon atoms and / or a dicarboxylic acid having 10 carbon atoms, and polyamides having a molecular structure of polyamide 11.

[0009] In the first aspect of the present invention, the polyamide resin (a) is preferably polyamide 10,10 and / or polyamide 11.

[0010] In the first aspect of the present invention, when the total mass of the layer (A) is taken as 100 mass %, the layer (A) preferably contains 1 to 40 mass % of the polyamide resin (a).

[0011] In the first aspect of the present invention, the layer (A) preferably contains the polyamide resin (a) and polyamide 6.

[0012] The polyamide resin film of the first aspect of the present invention preferably has a water absorption rate of 5.0% or less in a 24-hour water immersion test at 23°C.

[0013] The polyamide resin film of the first aspect of the present invention is preferably biaxially stretched.

[0014] The second invention of the present invention is a package made using the polyamide resin film of the first invention of the present invention.

[0015] The third invention of the present invention is a polyamide-based resin film having at least a layer (A) containing an aliphatic polyamide resin, characterized in that, when the total mass of the layer (A) is taken as 100 mass%, the layer (A) contains 1 to 100 mass% of a polyamide resin (a), and the polyamide resin (a) is at least one selected from polyamides containing a diamine having 10 carbon atoms and / or a dicarboxylic acid having 10 carbon atoms, and polyamides having a molecular structure of polyamide 11.

[0016] In the third aspect of the present invention, the polyamide resin (a) is preferably polyamide 10,10 and / or polyamide 11.

[0017] In the third aspect of the present invention, when the total mass of the layer (A) is taken as 100 mass %, the layer (A) preferably contains 50 mass % or more of the polyamide resin (a).

[0018] The polyamide resin film of the third aspect of the present invention preferably has a water absorption rate of 2.8% or less in a 24-hour water immersion test at 23°C.

[0019] The polyamide resin film of the third aspect of the present invention is preferably biaxially stretched. [Effects of the Invention]

[0020] According to the present invention, a polyamide resin film having excellent low water absorption and sufficient impact resistance can be provided. Due to these characteristics, the polyamide resin film of the present invention is suitable for use in a relatively high humidity environment and can be suitably used as packaging for food, medicine, clothing, industrial parts, etc. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described in detail below. The "polyamide resin film of the present invention" may be referred to as the "film of the present invention," the "layer (A) containing an aliphatic polyamide resin" may be referred to as the "layer (A)," and the "layer (B) containing a gas barrier resin" may be referred to as the "layer (B)." In the case of a layer containing both an aliphatic polyamide resin and a gas barrier resin, the layer is designated as Layer (A) when the content of the aliphatic polyamide resin in the layer is 50% by mass or more, and the layer is designated as Layer (B) when the content of the aliphatic polyamide resin in the layer is less than 50% by mass. Polyamide resin films can absorb moisture (water) from the air or absorb the water contained in food products that they package. In the description of this invention, the terms hygroscopicity and water absorption are used synonymously. When written as "X to Y" (X and Y are any numbers), unless otherwise specified, it means "X or more and Y or less," as well as "preferably greater than X" and "preferably smaller than Y."

[0022] <Layer (A) Containing Aliphatic Polyamide Resin> The polyamide resin film of the present invention has at least one layer (A) containing an aliphatic polyamide resin, and the layer (A) contains 1 to 100 mass % of a polyamide resin (a) when the total mass of the layer (A) is taken as 100 mass %. The aliphatic polyamide resin in the present invention refers to a polyamide resin produced by ring-opening polymerization of various known lactams, and a polyamide resin produced by condensation polymerization of known aliphatic diamines and aliphatic dicarboxylic acids. The polyamide resin (a) is at least one selected from polyamides containing a diamine having 10 carbon atoms and / or a dicarboxylic acid having 10 carbon atoms, and polyamides having a molecular structure of polyamide 11, and may be either an aliphatic polyamide resin or a semi-aromatic polyamide resin. Therefore, among the aliphatic polyamide resins, the aliphatic polyamide resins other than the polyamide resin (a) will be referred to as the polyamide resin (b) in the following description. Accordingly, the aliphatic polyamide resin used in the film of the present invention may be the polyamide resin (a) alone, both the polyamide resin (a) and the polyamide resin (b), or the polyamide resin (b) alone. The layer (A) containing the aliphatic polyamide resin may be one layer or multiple layers, and in the case of multiple layers, the resin composition of each layer may be different.

[0023] (Polyamide resin (a)) The polyamide resin (a) used in the present invention is at least one selected from polyamides containing a C10 diamine (e.g., 1,10-decanediamine) and / or a C10 dicarboxylic acid (e.g., sebacic acid), and polyamides having the molecular structure of polyamide 11. The molecular structures of these polyamides have longer alkyl chains than polyamide 6, which is commonly used in polyamide-based resin films. Therefore, polyamide resin (a) is highly hydrophobic, reducing the water absorption of the film and, in turn, reducing dimensional changes due to water absorption. Note that "a polyamide containing a C10 diamine and / or a C10 dicarboxylic acid" refers to the polyamide containing a residue resulting from condensation polymerization of a C10 diamine and / or a C10 dicarboxylic acid, and "a polyamide having the molecular structure of polyamide 11" refers to, for example, polyamide 11,T, and copolymers of polyamide 11 and polyalkylene ether glycol, in addition to polyamide 11 shown below.

[0024] Examples of the polyamide resin (a) include aliphatic polyamides such as polyamide 10, polyamide 11, polyamide 4,10, polyamide 5,10, polyamide 6,10, polyamide 8,10, polyamide 9,10, polyamide 10,10, and polyamide 10,12, semi-aromatic polyamides such as polyamide 10,T and polyamide 11,T, and copolymers of polyamide 10 or polyamide 11 with polyalkylene ether glycol. These may be used alone or in combination of two or more.

[0025] Examples of the polyalkylene ether glycol in the copolymer of polyamide 10 or polyamide 11 and polyalkylene ether glycol include polyoxyethylene glycol, polyoxytetramethylene glycol, and polyoxypropylene glycol, with polyoxytetramethylene glycol being preferred from the viewpoint of pinhole resistance due to bending. Furthermore, in order to contribute the molecular structural characteristics of polyamide 10 or polyamide 11 to the film, the copolymerization composition ratio of polyamide 10 or polyamide 11 is preferably 65% ​​by mass or more, more preferably 70% by mass or more. By setting the copolymerization composition ratio of polyamide 10 or polyamide 11 within this range, the contribution of long-chain alkyl chains increases, resulting in excellent low water absorption.

[0026] The polyamide resin (a) is preferably polyamide 10, polyamide 11, polyamide 10,10, or polyamide 10,12 from the viewpoint of low water absorption, and more preferably polyamide 10,10 or polyamide 11 from the viewpoint of impact resistance.

[0027] When the polyamide resin (a) is at least one selected from polyamides containing a diamine having 10 carbon atoms and / or a dicarboxylic acid having 10 carbon atoms, and polyamides having a molecular structure of polyamide 11, the film can be imparted with excellent low water absorption and sufficient impact resistance. The molecular structure of polyamide resin (a) has a longer hydrocarbon chain than polyamide 6, a typical polyamide resin (b) described below. This results in a lower concentration of amide bond groups per unit mass, resulting in low water absorption. Furthermore, because polyamide resin (a) has a lower concentration of amide bond groups per unit mass than polyamide 6, the proportion of hydrogen bonds between polyamide resins during film formation, particularly when biaxially stretched, is reduced, reducing the elasticity of the film and increasing its impact resistance. Furthermore, compared to polyamide 12, which is known as a low-water-absorbency resin, polyamide resin (a) is less likely to gel due to thermal degradation when melt-extruded with a high-melting-point resin. Its low elastic modulus also contributes to its excellent impact resistance.

[0028] Furthermore, polyamide 10,10 and polyamide 11 have high affinity with polyamide 6, so when polyamide 6 is used as polyamide resin (b), it is possible to design minute domain diameters (islands) in the sea / island structure of an incompatible mixture of polyamide resin (a) and polyamide 6. This is advantageous because it suppresses void formation at the sea / island phase interface during biaxial stretching and allows the production of a biaxially stretched nylon film with excellent transparency.

[0029] Furthermore, in terms of reducing the environmental burden, which has become a social issue in recent years, among the polyamide resins (a), polyamide 10, polyamide 11, polyamide 4,10, polyamide 5,10, polyamide 6,10, polyamide 8,10, polyamide 9,10, polyamide 10,10, polyamide 10,12, polyamide 10,T, polyamide 11,T, and polyamide 11-polyoxytetramethylene glycol, which are derived from biomass, are preferred. Among these, polyamide 11 and polyamide 10,10 are preferred because they are 100% plant-derived resins. Polyamide 10,10 is obtained by co-condensation polymerization of sebacic acid and 1,10-decanediamine obtained by amminating sebacic acid. Polyamide 11 is obtained by condensation polymerization of 11-aminoundecanoic acid obtained from castor oil.

[0030] The polyamide resin (a) preferably has a melting point of 180° C. or higher, more preferably 185° C. or higher, from the viewpoint of heat resistance of the film. The polyamide resin (a) has a density of 1100 kg / m 3 Preferably less than 1080 kg / m 3 The following is more preferred:

[0031] (Polyamide resin (b)) The polyamide resin (b) is an aliphatic polyamide resin other than the polyamide resin (a). There are no particular limitations on the resin component, but polyamide 6, polyamide 6,6, polyamide 6,66, and polyamide 12 are preferred in terms of meeting market specifications as a polyamide-based resin film, particularly in terms of the mechanical properties of the film, and polyamide 6 is more preferred in terms of economy and versatility. One type of polyamide resin (b) may be used, or two or more types may be used.

[0032] Polyamide 6 can be a known resin obtained by ring-opening polymerization of ε-caprolactam. From the viewpoint of film-forming properties, the relative viscosity, measured according to JIS K6920-2:2009 in 96% sulfuric acid, is preferably 1.0 to 5.0, more preferably 2.0 to 4.5, and particularly preferably 2.5 to 4.0. This range of viscosity provides good miscibility with the polyamide resin (a) in layer (A), facilitates stable co-extrusion with other layers (A), layers (B) containing a gas barrier resin such as a saponified ethylene-vinyl acetate copolymer or metaxylenediadipamide, and other layers (C) composed of polyolefin resins, polyester resins, or other resins, and minimizes flow unevenness due to viscosity differences between layers. The melting point of polyamide 6 is preferably 200 to 250° C., more preferably 210 to 240° C. If the melting point of polyamide 6 is within this range, it will have excellent heat resistance and extrusion moldability, and will be easy to mold into a biaxially stretched film. The density of polyamide 6 is 1100 to 1200 kg / m3 in terms of film toughness. 3 is preferable, and 1110 to 1150 kg / m 3 is more preferred.

[0033] (Other ingredients) The layer (A) containing an aliphatic polyamide resin may contain other resins, thermoplastic elastomers, additives, etc., within the range that does not impair the effects of the present invention. Examples of other resins include semi-crystalline aromatic polyamides and amorphous aromatic polyamides. Polyamide MXD6 is preferred in terms of gas barrier properties, etc. Amorphous aromatic PA is preferred in terms of reducing crystallinity and improving stretchability. The content of the other resins is preferably 10% by mass or less relative to the total mass of the layer (A) (100% by mass).

[0034] Examples of the thermoplastic elastomer include polyamide elastomers, polyester elastomers, polystyrene elastomers, and polyolefin elastomers. These are resins that have a molecular skeleton of polyamide, polyester, polystyrene, or polyolefin as a hard segment and a polyalkylene ether glycol or rubber component as a soft segment, and exhibit elasticity. Here, polyamide elastomers refer to those with a soft segment content of 50% by mass or more. Furthermore, when the polyamide elastomer, polyester elastomer, or polyolefin elastomer is modified with an unsaturated carboxylic acid such as maleic anhydride or its derivative or anhydride, the affinity with the polyamide resins (a) and (b) is increased, the dispersion miscibility is good, and the pinhole resistance and transparency of the film are improved, which is preferable. Suitable thermoplastic elastomers include, for example, block copolymers of polyamide 11 or polyamide 12 with polyoxytetramethylene glycol and acid-modified products thereof, block copolymers of polybutylene terephthalate with polyoxytetramethylene glycol and acid-modified products thereof, and styrene-isobutylene-styrene block copolymers (SIBS). When the total mass of the layer (A) is taken as 100% by mass, the content of the thermoplastic elastomer is preferably 10% by mass or less from the viewpoints of film formability, high transparency, and low water absorption.

[0035] Examples of additives that may be included include heat stabilizers, antioxidants, ultraviolet absorbers, weathering agents, lubricants, fillers, nucleating agents, plasticizers, antiblocking agents, anti-fogging agents, flame retardants, dyes, pigments, stabilizers, coupling agents, and impact resistance improvers. The content of the additives is preferably 5% by mass or less relative to 100% by mass of the total of the constituent components of the layer (A) from the viewpoints of film formability, high transparency, and low water absorption.

[0036] (Composition of Layer (A)) In the film of the present invention, when the total mass of the layers (A) containing aliphatic polyamide resins is taken as 100 mass%, the layers (A) contain 1 to 100 mass% of polyamide resin (a). When there are multiple layers (A), the total amount of polyamide resin (a) in each layer is 1 to 100 mass% relative to 100 mass% of the total of the layers (A). This configuration enables the polyamide resin film to have low water absorption and impact resistance, and to reduce the environmental impact. In terms of low water absorption, impact resistance, and reduced environmental impact of the polyamide resin film, the higher the content of polyamide resin (a) the better, with the upper limit being 100% by mass and the lower limit being preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more. From the viewpoint of the balance between the elastic modulus and impact resistance of the polyamide film, the content of the polyamide resin (a) has an upper limit of 100% by mass, preferably 80% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less, and a lower limit of, for example, preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more. When the polyamide resin (b) is, for example, polyamide 6, polyamide 66, or polyamide 6,66, a high content of polyamide resin (b) is preferable in terms of the elastic modulus, chemical resistance, and heat resistance of the film. Therefore, when the total of polyamide resin (a) and polyamide resin (b) is 100% by mass, the mass content ratio of polyamide resin (a) to polyamide resin (b) is preferably 1-50:50-99, and more preferably 1-40:60-99. The content of the polyamide resin (a) in the total of the layers (A) can be set depending on the layer structure of the film of the present invention and the composition of each layer (A).

[0037] When polyamide resin (a) and polyamide resin (b) are contained in layer (A), they form an incompatible dispersion, forming a sea / island structure in which the component with a higher composition ratio forms the sea (matrix) and the component with a lower composition ratio forms islands (domains). When the composition ratio of the polyamide resin (a) or polyamide resin (b) with the lower composition ratio is 30 mass% or less, the domain diameter tends to be small, which is preferable in terms of film transparency, as it reduces film haze. Furthermore, void generation originating from the sea / island phase interface tends to be suppressed, which is also effective for stable film formation.

[0038] <Layer (B) Containing Gas Barrier Resin> The film of the present invention is preferably provided with a layer (B) containing a gas barrier resin, which can impart gas barrier properties and is useful for preventing deterioration and spoilage of contents and improving long-term storage stability when used as a packaging material. Known resins can be used as the gas barrier resin, including, for example, polyvinyl alcohol (PVA)-based resins, saponified ethylene-vinyl acetate copolymer (EVOH)-based resins, semi-aromatic polyamides containing metaxylylenediamine such as polymetaxylylenediadipamide (polyamide MXD6), polyvinylidene chloride (PVDC)-based resins, etc. Among these, saponified ethylene-vinyl acetate copolymer (EVOH)-based resins and semi-aromatic polyamides containing metaxylylenediamine are preferred in terms of oxygen gas barrier properties and moldability, and semi-aromatic polyamides containing metaxylylenediamine are more preferred in terms of interlayer adhesion with layer (A) containing an aliphatic polyamide resin.

[0039] (Saponified ethylene-vinyl acetate copolymer) The saponified ethylene-vinyl acetate copolymer (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, and may contain, in addition to ethylene structural units and vinyl alcohol structural units (including unsaponified vinyl ester structural units), structural units derived from the following comonomers: α-olefins such as propylene, isobutene, α-octene, α-dodecene, and α-octadecene; hydroxy-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, and 3-butene-1,2-diol, as well as hydroxy-containing α-olefin derivatives such as their esters and acylation products; unsaturated carboxylic acids or their salts, partial alkyl esters, complete alkyl esters, nitriles, amides, or anhydrides; unsaturated sulfonic acids or their salts; vinylsilane compounds; vinyl chloride; and styrene. Furthermore, it is also possible to use EVOH-based resins that have been post-modified by urethanization, acetalization, cyanoethylation, oxyalkylenation, etc. These EVOHs may be used alone or in combination of two or more. The ethylene content in the saponified ethylene-vinyl acetate copolymer is not particularly limited, but from the viewpoint of film formation stability, it is generally preferably 5 mol% or more, more preferably 10 mol% or more, and particularly preferably 20 mol% or more. From the viewpoint of gas barrier properties, the upper limit of the ethylene content is preferably 48 mol% or less, more preferably 38 mol% or less, and even more preferably 30 mol% or less. Furthermore, the saponified ethylene-vinyl acetate copolymer has a saponification degree of preferably 96% or more, more preferably 98% or more. In the film of the present invention, when the ethylene content and saponification degree in the saponified ethylene-vinyl acetate copolymer are within the above ranges, an excellent balance between film formability and gas barrier properties is achieved, making the film suitable for molding processes such as coextrusion with layer (A) and biaxial stretching.

[0040] (Semi-aromatic polyamide containing metaxylylenediamine) Examples of semi-aromatic polyamides containing metaxylylenediamine used in the present invention include polymetaxylylene adipamide (polyamide MXD6), metaxylylene / paraxylylene adipamide copolymers, and copolymers thereof copolymerized with aliphatic diamines, alicyclic diamines, aromatic diamines other than metaxylylenediamine and paraxylylenediamine, aromatic dicarboxylic acids, lactams, ω-aminocarboxylic acids, aromatic aminocarboxylic acids, etc. Among these, polymetaxylylene adipamide (polyamide MXD6) is preferred from the viewpoints of gas barrier properties and moldability.

[0041] Polymetaxylylene adipamide (polyamide MXD6) refers to a polymerization product of primarily metaxylylene diamine and adipic acid. When the diamine components constituting polymetaxylylene adipamide are taken as 100 mol %, metaxylylene diamine accounts for 70 mol % or more, preferably 80 mol % or more, and more preferably 90 mol % or more. It may contain up to 30 mol % of an isomer of orthoxylylene diamine, paraxylylene diamine, or an aliphatic diamine having 6 to 12 carbon atoms, but from the viewpoints of gas barrier properties and heat resistance, it is preferable that these are not included. When the dicarboxylic acid components constituting polymetaxylylene adipamide (polyamide MXD6) are taken as 100 mol %, adipic acid accounts for 70 mol % or more, preferably 80 mol % or more, and more preferably 90 mol % or more. The film may contain 30 mol% or less of an aliphatic dicarboxylic acid having 7 to 12 carbon atoms, an aromatic dicarboxylic acid such as terephthalic acid or isophthalic acid, or a cyclic aliphatic dicarboxylic acid such as 1,4-cyclohexanedicarboxylic acid, but from the viewpoint of gas barrier properties and stretchability, it is preferable that these are not contained.

[0042] (Other ingredients) The layer (B) containing the gas barrier resin can contain a thermoplastic elastomer to the extent that the effects of the present invention are not impaired. The inclusion of a thermoplastic elastomer improves the flexibility of the layer (B) and makes it possible to improve the pinhole resistance of the film. As the thermoplastic elastomer, the same types that can be contained in the layer (A) described above can be used. When the layer (B) is taken as 100% by mass, the content of the thermoplastic elastomer is preferably 20% by mass or less, more preferably 1 to 15% by mass. A thermoplastic elastomer content of 20% by mass or less can prevent deterioration of the gas barrier properties and transparency of the film and also suppresses gel generation during film production, which is preferable in terms of film productivity.

[0043] <Layer configuration> The film of the present invention is a film having at least a layer (A) containing a polyamide resin, and preferably further has a layer (B) containing a gas barrier resin. When a plurality of layers (A) are provided, the layers (A) may have the same composition or different compositions. In the case of a layer structure such as layer (A1) / layer (A2) / layer (B), in order to improve the interlayer adhesion between layer (A1) and layer (B), layer (A2) preferably contains a resin common to layer (A1) and / or layer (B). For example, layer (A2) preferably contains polyamide resin (a) and / or polyamide resin (b) and a gas barrier resin (e.g., polyamide MXD6). When a plurality of layers (B) are disposed, the layers (B) may have the same composition or different compositions.

[0044] In addition to the layer (A) and the layer (B), another layer (C) may be present. The components of the other layer (C) are not particularly limited, but when layer (C) is disposed between layer (A) and layer (B), it is preferable to use an adhesive resin, such as an acid-modified polyolefin resin, to improve interlayer adhesion. When layer (C) is disposed on the surface of the film, it is preferable to provide a layer made of polyamide 6, polyamide 6,6, polyamide 6,66, polyamide MXD6, polyester, etc., to improve the pinhole resistance and friction / abrasion resistance of the film.

[0045] The order of the layers is not particularly limited, but for example, a two-layer structure such as [A / B], a three-layer structure such as [A / B / A], [A / B / C], [A / C / B], or a five-layer structure such as [A / A / B / A / A], [A / C / B / C / A], [C / A / B / A / C], or [A / B / C / B / A] is preferred in terms of film formation stability. Among these, a structure in which low-water-absorbent layers (A) are disposed on both sides of layer (B), such as [A / B / A], [A / A / B / A / A], [A / C / B / C / A], or [C / A / B / A / C], is preferred in terms of preventing water absorption by layer (B) and improving the gas barrier properties of the film, and imparting sufficient impact resistance to the film, including layer (B).

[0046] Hereinafter, polyamide resin (a) will be abbreviated as resin (a), polyamide MXD6 as MXD6, polyamide 6 as PA6, amorphous aromatic polyamide as amorphous PA, saponified ethylene-vinyl acetate copolymer as EVOH, and thermoplastic elastomer as elastomer, and examples of layer compositions will be shown. Preferred examples of the layer structure [A / B / A] include the following. [Resin (a)] / [EVOH] / [Resin (a)] [Resin (a)] / [MXD6 + Elastomer] / [Resin (a)] ·[Resin (a) + Amorphous PA] / [EVOH] / [Resin (a) + Amorphous PA] [Resin (a) + amorphous PA] / [MXD6 + elastomer] / [Resin (a) + amorphous PA] ·[PA6+Resin(a)] / [EVOH] / [PA6+Resin(a)] [PA6 + resin (a)] / [MXD6 + elastomer] / [PA6 + resin (a)]

[0047] Preferred examples of the layer structure [A / A / B / A / A] include the following. ·[Resin (a)] / [PA6+Resin (a)] / [EVOH] / [PA6+Resin (a)] / [Resin (a)] ·[PA6+Resin(a)] / [Resin(a)] / [EVOH] / [Resin(a)] / [PA6+Resin(a)] [Resin (a)] / [PA6+MXD6] / [MXD6+Elastomer] / [PA6+MXD6] / [Resin (a)] [Resin (a)] / [PA6 + Resin (a) + MXD6] / [MXD6 + Elastomer] / [PA6 + Resin (a) + MXD6] / [Resin (a)]

[0048] [PA6 + resin (a)] / [PA6 + resin (a) + MXD6] / [MXD6 + elastomer] / [PA6 + resin (a) + MXD6] / [PA6 + resin (a)] [PA6 + resin (a)] / [PA6 + MXD6] / [MXD6 + elastomer] / [PA6 + MXD6] / [PA6 + resin (a)] [PA6 + resin (a)] / [PA6 + resin (a) + MXD6 + elastomer] / [MXD6 + elastomer] / [PA6 + resin (a) + MXD6 + elastomer] / [PA6 + resin (a)]

[0049] Furthermore, by combining A layers or C layers of the various compositions described above, layer configurations such as [A / A], [A / A / A], [A / A / A / A], [A / A / A / A / A], [A / C / A], [A / A / C / A / A], [C / A / C], and [A / C / A / C / A] may be given.

[0050] The total thickness of the film of the present invention is not particularly limited, but from the viewpoints of processability, transparency, and handleability, it is preferably 5 to 50 μm, more preferably 10 to 30 μm, and even more preferably 12 to 25 μm. If the total thickness is within the above range, the film will have good mechanical properties as a polyamide-based biaxially stretched film and excellent gas barrier properties.

[0051] From the viewpoint of the mechanical properties and oxygen gas barrier properties of the film, it is preferable that the thickness ratio of layer (A) to the total film thickness (100%) is 25 to 90%, and that of layer (B) to 10 to 75%. When there are multiple layers (A) and / or layers (B), the thickness ratio refers to the ratio of the total thickness of layer (A) or layer (B) to the total thickness. The thickness of each of Layer (A), Layer (B), and Layer (C) is not particularly limited, but is preferably 1 to 15 μm, more preferably 2 to 10 μm, and even more preferably 3 to 8 μm. When there are multiple Layers (A), Layers (B), and Layers (C), the thicknesses may be different for each layer or the same for each layer.

[0052] The film of the present invention can be subjected to surface treatments or finishes such as printing, coating, and vapor deposition. It can also be used by laminating it with other resin layers such as polyolefins and polyesters, other films or adhesive layers, metal foils, paper, etc. Known lamination methods can be used, such as dry lamination, wet lamination, sand lamination, and extrusion lamination. During lamination, the surface of the film of the present invention can also be subjected to surface treatments such as corona discharge and anchor coating. Furthermore, when the film of the present invention is used as a packaging material, from the viewpoint of maintaining the quality of the contents and preventing spoilage, the gas barrier properties and moisture resistance can be further improved by vapor deposition of aluminum, silicon oxide, alumina, diamond-like carbon, etc., or by applying a gas barrier coating agent such as a polyvinyl alcohol (PVA)-based resin or a polyvinylidene chloride (PVDC)-based resin.

[0053] <Manufacturing method> The film of the present invention may have a film configuration having at least a layer (A) containing an aliphatic polyamide resin and a layer (B) containing a gas barrier resin, and can be produced by known methods. When using raw material polyamides and gas barrier resins that have absorbed water, water vapor and oligomers are generated during the thermal melting and extrusion process, hindering film formation. Therefore, when preparing the raw materials, it is preferable to dry the resin in advance to reduce the moisture content to 0.1% by mass or less. The resins are fed into extruders for each layer, and the molten resins are joined in a feed block, or a multi-manifold flat die, or an annular die, and then co-extruded as a multilayer film, which is then rapidly cooled to obtain a flat or annular unstretched film.

[0054] To obtain a biaxially stretched film, an unstretched film is biaxially stretched in the film's machine direction (longitudinal direction, MD) and its transverse direction (transverse direction, TD) using a known method such as tenter-type sequential biaxial stretching, tenter-type simultaneous biaxial stretching, or tubular-type simultaneous biaxial stretching. For example, in the case of the tenter-type sequential biaxial stretching method, the unstretched film can be produced by heating the film to a temperature range of 40 to 100°C, stretching it in the machine direction using a roll-type machine-type stretching machine, and then stretching it in the transverse direction using a tenter-type transverse stretching machine at a temperature range of 80 to 230°C. In addition, in the case of the tenter-type simultaneous biaxial stretching method or the tubular-type simultaneous biaxial stretching method, the film can be produced by simultaneously stretching it in both the machine and transverse directions at a temperature range of 40 to 230°C. The stretching ratio is preferably 2.0 to 5.0 times, more preferably 2.5 to 4.5 times, in each of the machine direction (machine direction, MD) and width direction (transverse direction, TD) of the film. When the stretching ratio in each of the biaxial stretching directions is 2.0 times or more, stretching orientation proceeds and mechanical properties such as film strength become good, and when the stretching ratio is 5.0 times or less, the film is less likely to break during stretching and productivity is good.

[0055] Furthermore, to improve the dimensional stability of the film, the biaxially stretched film can be heat-set. The heat-setting temperature is preferably 170° C. to 225° C., more preferably 180° C. to 220° C. This makes it possible to obtain a biaxially stretched film with good dimensional stability at room temperature. In order to alleviate the stress of crystallization shrinkage due to heat setting, a relaxation treatment can be carried out in the width direction during heat setting in the range of 0 to 15%, preferably 3 to 10%. After the relaxation treatment, the film can be re-stretched in the width direction by 2 to 9%, preferably 3 to 7%, and more preferably 4 to 7% at a temperature of 140 to 200° C. If the re-stretching temperature is within the above range, an appropriate stress is obtained during stretching, resulting in uniform stretching and making it easier to achieve a uniform transverse shrinkage rate in the width direction.

[0056] <Film properties> (Low water absorption) The water absorption is preferably 5.00% or less, more preferably 4.00% or less, even more preferably 3.00 or less, particularly preferably 2.50 or less, and most preferably 2.20 or less. Biaxially stretched films are preferred because they have a lower water absorption than unstretched films due to the increased crystal orientation of the resin. The water absorption rate is determined by the following water absorption test. A circular film test piece with a diameter of 100 mm is stored at 23°C and a relative humidity of 50% for at least 24 hours, and then its mass (s) is weighed. The film test piece is then immersed in distilled water at 23°C for 24 hours, after which the water adhering to the surface is wiped off and the mass (e) of the film test piece is weighed, and the water absorption rate is calculated using the following formula 1. Four film test pieces are tested and the average value is calculated. {(e)-(s)} / (s)×100(%) (Formula 1)

[0057] (shock resistance) The impact resistance of the film of the present invention can be evaluated by the puncture impact strength when a hole is made in a film test piece at the penetration portion, and is preferably at least 0.3 J, more preferably at least 0.4 J. If the puncture impact strength is within this range, the film has excellent impact resistance and is good in that it is less likely to develop holes when used as a packaging material. The impact resistance of the film of the present invention is measured by the impact hole opening strength test of JIS P8134: 1998. The stand of the device is installed on a solid foundation so as not to cause loss of work, and the pendulum has an arm in a 90-degree arc, with a penetrating part attached to the tip of the arm, allowing it to oscillate freely.

[0058] (tensile stress at break, tensile elongation at break) The tensile breaking stress is preferably 150 MPa or more, more preferably 200 MPa or more, in both the machine direction (MD) and the transverse direction (TD) at both temperatures of -20°C and 23°C. There is no particular upper limit, but it is about 500 MPa. A film with a tensile breaking stress in this range will maintain the rigidity of the film when packaging contents, and will be less likely to develop pinholes or break due to bending. The tensile breaking elongation is preferably 35% or more, and more preferably 40% or more, in both the machine direction (MD) and cross direction (TD) of the film, and at both temperatures of -20°C and 23°C. The lower the temperature, the more difficult the film is to stretch, and the lower its puncture resistance when packaging frozen foods, so a tensile breaking elongation of 35% or more at -20°C is useful. There is no particular upper limit to the tensile breaking elongation, but it is about 150%. The tensile elongation at break and the tensile stress at break are measured in accordance with JIS K7127:1999, at a test speed of 200 mm / min, at temperatures of -20°C and 23°C.

[0059] (transparency) The film of the present invention preferably has a haze of 10.0% or less, more preferably 8.0% or less, and the lower the haze, the better. When the haze value is within this range, the film has excellent transparency, and is excellent in design and visibility of contents when used as a packaging film. The haze is measured in accordance with JIS K7136:2000.

[0060] (Bending pinhole resistance) The film of the present invention was subjected to a flex test using a Gelbo flex tester under the following conditions: 3,000 flexes at 23°C and 50% relative humidity, and 500 flexes at 5°C and 50% relative humidity, and the number of pinholes that occurred was counted. Three tests were conducted under each condition, and the average value was calculated. The number of pinholes was 10.0 / 481 cm under both conditions. 2 The following is preferable: 5.0 pieces / 481cm 2 The following is more preferable, and the fewer the number of pinholes, the better. Generally, the lower the environmental temperature, the more the film loses flexibility, so it is desirable that the number of pinholes is small under low temperature conditions. 10.0 pieces / 481cm 2 If the film is below this level, pinholes are less likely to occur due to bending of the film during transport and storage of the package, or due to collisions between packages, and oxidation degradation of the contents due to a decrease in gas barrier properties is more easily prevented.

[0061] (Oxygen gas barrier properties) The film of the present invention has an oxygen permeability of 10 cc / m under conditions of 23°C and 50% relative humidity. 2 / 24h / atm or less is preferable, and 5cc / m 2 It is more preferable that the oxygen permeability is 10 cc / m / 24h / atm or less, and it is desirable that the value is even lower. 2 / 24h / atm or less is preferable because the packaging film can maintain sufficient oxygen gas barrier properties to prevent deterioration of the contents and keep them fresh.

[0062] (Biomass ratio) When a biomass-derived polyamide resin (a) is used in layer (A), the biomass content of the film can be calculated from the composition ratio of the layer and the layer thickness ratio to the total film thickness. From the viewpoint of recent environmental issues, it is desirable to increase the biomass content of the film, and for example, 1% or more is preferable, 5% or more is more preferable, 10% or more is even more preferable, and 50% or more is particularly preferable, and the higher the better.

[0063] The biomass content can be determined by measuring the percentage of carbon (14C), which is only found in organic matter derived from biomass, using an accelerator mass spectrometer (AMS).

[0064] To distinguish between organic matter derived from biomass and organic matter derived from fossil fuels, a standardization method is known that uses the abundance ratio of radioactive 14C as of 1950 as a reference standard, such as (Determining the Biobased Control of Solid, Liquid, and Gaseous Samples Using Radiocarbon Analysis) by the US National Bureau of Standards (NIST). Specifically, the sample to be measured is combusted to generate carbon dioxide, which is then purified in a vacuum line and reduced with hydrogen using iron as a catalyst to produce graphite. This graphite is then loaded into a dedicated 14C-AMS instrument based on a tandem accelerator to measure 14C counts, 13C concentrations (13C / 12C), and 14C concentrations (14C / 12C). From these measurements, the 14C concentration ratio (%) of the sample carbon to standard modern carbon can be calculated. Oxalic acid (HOxII) provided by the National Institute of Standards (NIST) can be used as the standard sample.

[0065] The biomass ratio of the film of the present invention can be calculated by multiplying the "biomass ratio of the resin made from biomass-derived resources" (%) by the "mass proportion of the resin made from biomass-derived resources."

[0066] <Package> The film of the present invention can be laminated with a sealant film or the like by a known lamination method and formed into a package such as a bag, a tube, or a container combining a lid and a base. [Example]

[0067] The present invention will be specifically explained below using examples, but the present invention is not limited to these. <Ingredients> The abbreviations, components, physical properties, etc. of the resins used in the examples and comparative examples are as follows:

[0068] (Polyamide resin (b)) PA6: Polyamide 6, relative viscosity 3.4, melting point 220°C, density 1140 kg / m 3 , biomass content 0% (Polyamide resin (a)) PA11: Polyamide 11, melting point 190°C, density 1030kg / m 3 , 100% biomass PA10,10: Polyamide 10,10, melting point 189°C, density 1040kg / m 3 , 100% biomass (thermoplastic elastomer) PA12-PTMG: Polyamide 12-polytetramethylene ether glycol (PTMG) block copolymer, PTMG copolymer composition ratio 70% by mass (gas barrier resin) MXD6: Polymetaxylylenediadipamide

[0069] <Film production, film layer structure> (Examples 1 to 7, Comparative Example 1) The resin compositions for Layer (A1) and Layer (A2), in which the raw materials were blended in the mass ratios shown in Table 1, were each fed into a φ40 mm extruder, and the resin composition for Layer (B) was fed into a φ32 mm extruder. Each was melted at 250°C, distributed using a distribution block, and multilayered in a coextrusion T-die to extrude a molten film, which was then quenched on a cooling roll at 30°C to produce an unstretched multilayer film. The resulting unstretched multilayer film was stretched 3.0 times in the machine direction at 56°C using a roll-type longitudinal stretching machine, then stretched 4.9 times in the width direction at 120°C using a tenter-type transverse stretching machine, followed by heat setting at 215°C and 8% relaxation in the width direction. The film was then cooled to room temperature, and both ends corresponding to the gripping portions of the clips were trimmed. The trimmed film was wound into a roll to obtain a biaxially stretched multilayer film with a layer structure of [Layer (A1) 3.4 μm / Layer (A2) 2.6 μm / Layer (B) 3.0 μm / Layer (A2) 2.6 μm / Layer (A1) 3.4 μm] and a total thickness of 15.0 μm. The thickness of each layer was measured by microscopic observation of a vertical cross section of the film.

[0070] <Evaluation> The biaxially stretched multilayer film obtained was subjected to the following evaluations, and the results are summarized in Table 1. (1) Water absorption (water absorption rate (%)) A circular film test piece with a diameter of 100 mm was stored at 23°C and a relative humidity of 50% for at least 24 hours and then its mass (s) was weighed. After immersing the film test piece in distilled water at 23°C for 24 hours, the water adhering to the surface was wiped off and the mass (e) of the film test piece was weighed, and the water absorption rate (unit: %) was calculated using the following formula 1. Four film test pieces were tested and the average value was calculated. {(e)-(s)} / (s)×100 (Formula 1) Water absorption rate 2.8% or less ◎ Water absorption rate: Over 2.8% and 5.0% or less Water absorption rate exceeds 5.0% ×

[0071] (2) Impact resistance (puncture impact strength (J)) The puncture impact strength (unit: J) was measured using the impact hole opening strength test of JIS P8134:1998. The stand of the device was set on a solid foundation to prevent loss of work volume, and the pendulum had an arm with a 90-degree arc, with a penetrating part attached to the tip of the arm, allowing it to oscillate freely.

[0072] (3) Tensile breaking stress (MPa), tensile breaking elongation (%) Based on JIS K7127:1999, the tensile breaking stress (unit: MPa) and tensile breaking elongation (unit: %) in the machine direction (MD) and transverse direction (TD) were measured at a test speed of 200 mm / min and at temperatures of -20°C and 23°C.

[0073] (4) Transparency (haze (%)) The haze (unit: %) was measured in accordance with JIS K7136:2000.

[0074] (5) Biomass content (%) The biomass ratio (%) was calculated from the biomass ratio of the raw material polyamide resin, the layer composition ratio, and the layer thickness ratio.

[0075] [Table 1]

[0076] The biaxially stretched multilayer films of Examples 1 to 5 contained 1% by mass or more of polyamide 11 or polyamide 10,10 corresponding to polyamide resin (a) relative to 100% by mass of the total of Layer (A1) and Layer (A2), and had lower film water absorption than Comparative Example 1. The impact resistance, expressed as puncture impact strength, was sufficient for a polyamide film. The tensile stress at break and tensile elongation at break were also good.

[0077] The biaxially stretched multilayer films of Examples 6 and 7 contained 50% by mass or more of polyamide 10,10 or polyamide 11 corresponding to polyamide resin (a) relative to 100% by mass of the total of Layer (A1) and Layer (A2), and had lower water absorption than Comparative Example 1 and better water absorption than Examples 1 to 5. Furthermore, the impact resistance, expressed as puncture impact strength, was sufficient for a polyamide film, and the tensile stress at break and tensile elongation at break were also good. [Industrial Applicability]

[0078] The film of the present invention is a polyamide resin film with excellent low water absorption and sufficient impact resistance, and is suitable for packaging food, medicine, clothing, industrial parts, etc. It is particularly useful for applications under high humidity and for packaging contents containing moisture. Furthermore, the use of a biomass-derived resin raw material greatly contributes to reducing environmental impact.

Claims

1. A biaxially stretched film having at least a layer (A) containing an aliphatic polyamide resin and a layer (B) containing a gas barrier resin, the biaxially stretched film being heat-set at 170°C or higher, The layer (A) has at least three layers in the order of the layer (A), the layer (B), and the layer (A), Both outermost layers are the layer (A), the layer (A) contains a polyamide resin (a) in an amount of 1 to 100% by mass, where the total mass of the layer (A) is 100% by mass; the polyamide resin (a) is at least one selected from the group consisting of polyamides containing a diamine having 10 carbon atoms and / or a dicarboxylic acid having 10 carbon atoms, and polyamides having a molecular structure of polyamide 11; a gas barrier resin of the layer (B) that is at least one selected from a saponified ethylene-vinyl acetate copolymer (EVOH) resin and a semi-aromatic polyamide containing metaxylylenediamine;

2. The biaxially stretched polyamide-based resin film according to claim 1, wherein the layer (B) further contains a thermoplastic elastomer.

3. 3. The biaxially stretched polyamide resin film according to claim 1, wherein the polyamide resin (a) is polyamide 10,10 and / or polyamide 11.

4. 4. The biaxially stretched polyamide resin film according to claim 1, wherein the layer (A) contains 1 to 40% by mass of the polyamide resin (a), where the total mass of the layer (A) is 100% by mass.

5. 5. The biaxially stretched polyamide resin film according to claim 1, wherein the layer (A) contains the polyamide resin (a) and polyamide 6.

6. 6. The biaxially stretched polyamide resin film according to claim 1, which has a water absorption rate of 5.0% or less in a 24-hour water immersion test at 23°C.

7. A packaging material comprising the biaxially stretched polyamide resin film according to any one of claims 1 to 6.

8. A method for producing a biaxially stretched polyamide resin film as described in claim 1, which method sequentially comprises a stretching step in which the film is stretched by 2.0 times or more in both the flow direction (longitudinal direction, MD) and the width direction (transverse direction, TD) of the film, and a heat setting step in which the film is heat set at 170°C or higher.

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