Biaxially oriented polyamide resin film and method for manufacturing the same

Abstract

The present invention provides a biaxially oriented polyamide resin film that exhibits excellent pinhole resistance in low-temperature environments and dimensional stability in high-temperature environments. [Solution] A biaxially oriented polyamide resin film having at least two layers: an A layer containing an aliphatic polyamide resin (a1) and a polyolefin resin (a2), and a B layer containing at least one selected from the group consisting of ethylene-vinyl alcohol copolymer and polymetaxylylenediadipamide. (a2) is an ethylene / 1-hexene copolymer having a group derived from maleic anhydride with a melting peak temperature of 70 to 120°C; the content of (a1) is 88 to 98% by mass and the content of (a2) is 1 to 10% by mass relative to 100% by mass of the A layer. The film exhibits a hot water shrinkage rate of 5% or less at 95°C for 5 minutes; a hot water shrinkage rate of 15% or less at 127°C for 5 minutes under a pressure of 0.15 MPa; and a pinhole count of 30 / 500cm in a Gelboflex test at -25°C 50% with 1,000 bending cycles. 2 The following applies:

Description

[Technical Field]

[0001] The present invention relates to a biaxially oriented polyamide resin film and a method for producing the same. [Background technology]

[0002] Films made from polyamide resin compositions (hereinafter referred to as "polyamide films") exhibit excellent properties such as gas barrier properties, toughness, pinhole resistance, heat resistance, and transparency. For this reason, polyamide films are widely used in various fields. Specifically, polyamide films are used, for example, as food packaging materials. In particular, in the distribution of food, there has been an increase in cases where products are transported at low temperatures to maintain freshness and then displayed in convenience stores and supermarkets. In this context, mechanical strength during low-temperature transport is required, and pinhole resistance is a particularly important requirement. Furthermore, bag making and filling processes are becoming faster, and dimensional stability of the film when subjected to heat during bag making and filling is required.

[0003] Patent Document 1 discloses a polyamide resin composition having a predetermined molecular weight, comprising an aliphatic polyamide resin (A) and an ethylene / α-olefin copolymer having 3 to 8 carbon atoms (B) having functional groups in predetermined proportions, and showing that a film with excellent appearance, transparency, puncture strength, and pinhole resistance can be obtained, and that material recycling is possible. Patent Document 2 discloses a polyamide resin composition containing a polyamide resin, an olefin-based elastomer, an antioxidant, and an ionomer resin in predetermined proportions, and shows that a polyamide film with excellent thermal durability can be obtained. Patent Document 3 discloses a composition containing polyamide, a prepolymer for imparting fluidity, an impact resistance modifier such as a polyolefin, and additives in predetermined proportions, and shows that fluidity or rheological behavior suitable for the intended molding method, such as injection molding, can be obtained.

[0004] Furthermore, films are known that laminate a polyamide resin layer and a gas barrier layer in order to further enhance gas barrier properties while taking advantage of the excellent properties of polyamide resin. For example, Patent Document 4 discloses a biaxially oriented polyamide laminated film in which polyamide A / polyamide B / polyamide C / polyamide B / polyamide A are laminated in that order, polyamide A contains polyamide 6 and polyamide 6 / 66 copolymer in predetermined proportions, polyamide B contains polyamide 6 and aromatic polyamide in predetermined proportions, and polyamide C mainly contains aromatic polyamide, and is heat-fixed so that the hot water shrinkage rate at 95°C for 5 minutes is within a predetermined range, and it is shown that the film has physical strength such as impact strength and tensile strength, as well as sufficient lamination strength with sealant films such as CPP. Patent Document 5 discloses a gas barrier polyamide resin film having a layer order of outer layer (A) / middle layer (B) / inner layer (C) / middle layer (B) / outer layer (A), wherein the outer layer (A) contains 99-100% by mass of aliphatic polyamide resin, the middle layer (B) contains 70-85% by mass of aliphatic polyamide resin and 15-30% by mass of thermoplastic elastomer, and the inner layer (C) contains a gas barrier resin, with the thickness of each layer of the middle layer (B) being 2.0-20.0% of the total film thickness. This film is shown to have high resistance to bending pinholes from room temperature to low temperature conditions, as well as good transparency and puncture resistance, and is less prone to manufacturing problems. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2024 / 010008 [Patent Document 2] International Publication No. 2017 / 073559 [Patent Document 3] Special Publication No. 2017-509763 [Patent Document 4] Japanese Patent Publication No. 2010-269557 [Patent Document 5] Japanese Patent Publication No. 2022-147469 [Overview of the project] [Problems that the invention aims to solve]

[0006] The films obtained from the polyamide resin compositions described in Patent Documents 1 to 3 have insufficient gas barrier properties as food packaging materials, and further improvements are needed in pinhole resistance at low temperatures and dimensional stability at high temperatures. The polyamide laminated films described in Patent Documents 4 and 5 have excellent properties due to the provision of a gas barrier layer, possessing pinhole resistance under certain low-temperature environments and dimensional stability under high-temperature environments. However, further improvements are needed in terms of pinhole resistance and dimensional stability.

[0007] The present invention aims to provide a biaxially oriented polyamide resin film and a method for manufacturing the same, which exhibits excellent pinhole resistance in low-temperature environments and dimensional stability in high-temperature environments. [Means for solving the problem]

[0008] The present invention relates to the following [1] to [9]. [1] A biaxially oriented polyamide resin film having at least two layers: an A layer containing an aliphatic polyamide resin (a1) and a polyolefin resin (a2), and a B layer containing at least one selected from the group consisting of ethylene-vinyl alcohol copolymer and polymetaxylylenediadipamide, The polyolefin resin (a2) is an ethylene / 1-hexene copolymer having a group derived from maleic anhydride, and its melting peak temperature, as measured from the DSC curve when heated from 0°C to 280°C at a rate of 20°C / min in an air atmosphere, is 70-120°C; when layer A is considered to be 100% by mass, the content of the aliphatic polyamide resin (a1) is 88-98% by mass, and the content of the polyolefin resin (a2) is 1-10% by mass. For the biaxially stretched polyamide resin film, the hot water shrinkage rate at 95°C for 5 minutes is 5% or less; the hot water shrinkage rate at 127°C for 5 minutes under a pressure of 0.15 MPa is 15% or less; and in the gelbo flex test at an environmental temperature of -25°C, a relative humidity of 50%, and 1,000 flexures, the number of pinholes is 30 per 500 cm 2 The following biaxially stretched polyamide resin film. [2] The biaxially stretched polyamide resin film according to [1], wherein the aliphatic polyamide resin (a1) is at least one selected from the group consisting of polyamide 6, polyamide 11, and polyamide 12. [3] The biaxially stretched polyamide resin film according to [1] or [2], wherein the ratio of the thickness of the A layer to the thickness of the biaxially stretched polyamide resin film is 10 to 95%. [4] The biaxially stretched polyamide resin film according to any one of [1] to [3], wherein when the A layer is 100% by mass, the content of the polyolefin resin (a2) is 2.0 to 8.0% by mass. [5] The biaxially stretched polyamide resin film according to any one of [1] to [4], having at least three layers in the order of A layer, B layer, and A layer. [6] The biaxially stretched polyamide resin film according to any one of [1] to [5], further having a polyolefin resin layer on the A layer. [7] A package containing the biaxially stretched polyamide resin film according to [6]. [8] A method for producing a biaxially stretched polyamide resin film having at least two layers, including an A layer containing an aliphatic polyamide resin (a1) and a polyolefin resin (a2), and a B layer containing at least one selected from the group consisting of an ethylene-vinyl alcohol copolymer and polymetaxylylene diadipamide, the method comprising: Step 1 of feeding the raw materials constituting the A layer and the raw materials constituting the B layer into the extruders of each layer and co-extruding to obtain a laminated film; and Step 2 of biaxially stretching the obtained laminated film. The polyolefin resin (a2) is an ethylene / 1-hexene copolymer having a group derived from maleic anhydride, and the melting peak temperature measured from the DSC curve when the temperature is raised from 0°C to 280°C at a rate of 20°C / min in an air atmosphere is 70 to 120°C; when the A layer is 100% by mass, the content of the aliphatic polyamide resin (a1) is 88 to 98% by mass, and the content of the polyolefin resin (a2) is 1 to 10% by mass. For the biaxially stretched polyamide resin film, the hot water shrinkage rate at 95°C for 5 minutes is 5% or less; the hot water shrinkage rate at 127°C for 5 minutes under a pressure of 0.15 MPa is 15% or less, and the number of pinholes is 30 / 500 cm in the gelbo flex test at an environmental temperature of -25°C, a relative humidity of 50%, and 1,000 flexures. 2 The following is a method for producing a biaxially stretched polyamide resin film. [9] The method for producing a biaxially stretched polyamide resin film according to [8], further including a step of attaching a polyolefin resin layer on the A layer by a laminating method.

Effects of the Invention

[0009] According to the present invention, it is possible to provide a biaxially stretched polyamide resin film excellent in pinhole resistance in a low-temperature environment and dimensional stability in a high-temperature environment, and a method for producing the same.

Embodiments for Carrying Out the Invention

[0010] In this specification, the content of each component in each layer means the total amount of the plurality of substances corresponding to each component in the composition, unless otherwise specified when there are a plurality of substances corresponding to each component in the composition. In this specification, the term "polyamide resin film" means a film having at least one layer containing 50% by mass or more of polyamide resin. Hereinafter, the biaxially stretched polyamide resin film and the method for producing the same according to the present invention will be described in detail.

[0011] The biaxially oriented polyamide resin film of the present invention has at least two layers: an A layer containing an aliphatic polyamide resin (a1) and a polyolefin resin (a2), and a B layer containing at least one selected from the group consisting of ethylene-vinyl alcohol copolymer and polymetaxylylenediadipamide; the polyolefin resin (a2) is an ethylene / 1-hexene copolymer having a group derived from maleic anhydride, and is measured from a DSC curve when the temperature is raised from 0°C to 280°C at a rate of 20°C / min in an air atmosphere. The melting peak temperature is 70-120°C; when layer A is considered to be 100% by mass, the content of the aliphatic polyamide resin (a1) is 88-98% by mass, and the content of the polyolefin resin (a2) is 1-10% by mass; for the biaxially oriented polyamide resin film, the hot water shrinkage rate at 95°C for 5 minutes is 5% or less; the hot water shrinkage rate at 127°C for 5 minutes under a pressure of 0.15 MPa is 15% or less; and in a Gelboflex test with an ambient temperature of -25°C, relative humidity of 50%, and 1,000 bending cycles, the number of pinholes is 30 / 500cm. 2 The biaxially oriented polyamide resin film of the present invention exhibits excellent pinhole resistance in low-temperature environments and dimensional stability in high-temperature environments.

[0012] [A layer] Layer A contains an aliphatic polyamide resin (a1) and a polyolefin resin (a2).

[0013] <Aliphatic polyamide resin (a1)> Aliphatic polyamide resin (a1) contains aliphatic groups in its constituent repeating units and has amide bonds (-CONH-) in its main chain. Examples of aliphatic polyamide resin (a1) include aliphatic homopolyamides and aliphatic copolymer polyamides, which may be used individually or in combination of two or more. From the viewpoint of film strength and heat resistance, aliphatic polyamide resin (a1) is preferably an aliphatic homopolyamide.

[0014] Aliphatic homopolyamides are polyamide resins composed of a single type of structural unit derived from an aliphatic monomer. Aliphatic homopolyamides may consist of at least one of a lactam and an aminocarboxylic acid which is a hydrolysate of the lactam, or they may consist of a combination of one diamine and one dicarboxylic acid. Here, a combination of a diamine and a dicarboxylic acid is considered as one type of monomer.

[0015] Examples of lactams include ε-caprolactam, enantractam, undecanelactam, dodecanelactam (ω-laurolactam), α-pyrrolidone, and α-piperidone. Among these, one selected from the group consisting of ε-caprolactam, undecanelactam, and dodecanelactam is preferred from the viewpoint of polymerization productivity. Examples of aminocarboxylic acids include ε-aminocaproic acid, 7-aminoheptanoic acid, 9-aminononanoic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid.

[0016] Examples of diamines include aliphatic diamines such as ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, peptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, tridecanediamine, tetradecanediamine, pentadecanediamine, hexadecanediamine, heptadecanediamine, octadecanediamine, nonadecanediamine, eicosanediamine, 2-methyl-1,8-octanediamine, and 2,2,4 / 2,4,4-trimethylhexamethylenediamine.

[0017] Examples of dicarboxylic acids include aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedionic acid, dodecanedionic acid, tridecanedionic acid, tetradecanedionic acid, pentadecanedionic acid, hexadecanedionic acid, octadecanedionic acid, and eicosanedionic acid.

[0018] From the viewpoint of pinhole resistance in low-temperature environments and dimensional stability in high-temperature environments, the aliphatic polyamide resin (a1) is preferably at least one selected from the group consisting of polyamide 6, polyamide 11, and polyamide 12, and more preferably polyamide 6.

[0019] Examples of known polyamide manufacturing apparatuses for producing aliphatic polyamide resin (a1) include batch reaction vessels, single-tank or multi-tank continuous reaction apparatuses, tubular continuous reaction apparatuses, single-screw kneading extruders, twin-screw kneading extruders, and other kneading reaction extruders. Polymerization can be carried out using known methods such as melt polymerization, solution polymerization, and solid-phase polymerization, by repeatedly operating under atmospheric pressure, reduced pressure, and increased pressure. These polymerization methods can be used individually or in appropriate combinations.

[0020] (Physical properties of aliphatic polyamide resin (a1)) From the viewpoint of moldability, the relative viscosity of the aliphatic polyamide resin (a1) is preferably 2.0 to 5.0, more preferably 2.0 to 4.5, and even more preferably 2.1 to 3.5. By setting the relative viscosity of the aliphatic polyamide resin (a1) within the above range, it becomes easier to ensure the moldability of the film and the mechanical strength of the resulting film.

[0021] The relative viscosity of the aliphatic polyamide resin (a1) is a value measured at 25°C by dissolving 1 g of the aliphatic polyamide resin (a1) in 100 ml of 96% sulfuric acid in accordance with JIS K 6920. When the aliphatic polyamide resin (a1) is a combination of two or more types, it is preferable to measure the relative viscosity by the above method. However, when the relative viscosity of each polyamide resin and its mixing ratio are known, the average value calculated by summing the values obtained by multiplying each relative viscosity by its mixing ratio may also be used as the relative viscosity of the aliphatic polyamide resin (a1).

[0022] From the viewpoint of reducing film gel, the terminal amino group concentration of the aliphatic polyamide resin (a1) is preferably -5 ~5.5×10 -5 eq / g, more preferably -5 ~5.0×10 -5 eq / g, and even more preferably -5 ~4.8×10 -5 eq / g. The terminal amino group concentration can be expressed as the equivalent of amino groups per 1 g of the polymer, and can be measured by dissolving the polyamide resin in a phenol / methanol mixed solution and titrating with 1 / 50N hydrochloric acid.

[0023] When the aliphatic polyamide resin (a1) contains two or more polyamide resin components with different terminal amino group concentrations, the terminal amino group concentration in the polyamide resin is preferably measured by the above neutralization titration. However, when the terminal amino group concentration of each polyamide resin component and its mixing ratio are known, the average value calculated by summing the values obtained by multiplying each terminal amino group concentration by its mixing ratio may also be used as the terminal amino group concentration of the polyamide resin.

[0024] From the viewpoint of mechanical properties, the number-average molecular weight Mn of the aliphatic polyamide resin (a1), as measured by GPC, is preferably 25,000 to 65,000, and the ratio of weight-average molecular weight Mw to Mn (Mw / Mn) is preferably 1.0 to 4.0. The number-average molecular weight Mn is more preferably 30,000 to 65,000, even more preferably 33,000 to 63,000, and even more preferably 35,000 to 60,000. The number-average molecular weight Mn can also be 25,000 to 60,000. Furthermore, the Mw / Mn ratio is more preferably 1.0 to 3.0, and even more preferably 1.0 to 2.5. The values ​​of Mn and Mw are measured by gel permeation chromatography (GPC).

[0025] From the viewpoint of moldability, the melting point of the aliphatic polyamide resin (a1) is preferably 150 to 260°C, more preferably 160 to 250°C, and even more preferably 180 to 240°C. The melting point is the melting peak temperature in the DSC curve when the aliphatic polyamide resin (a1) is heated to 280°C in an air atmosphere, held at this temperature for 5 minutes, then cooled to 0°C at a rate of 20°C / min, and then heated from 0°C to 280°C at a rate of 20°C / min.

[0026] From the viewpoint of moldability, the aliphatic polyamide resin (a1) preferably has a melt flow rate (MFR) of 1 to 100 g / 10 min, more preferably 2 to 90 g / 10 min, and even more preferably 3 to 80 g / 10 min, as measured in accordance with ASTM D1238 at 230°C and a load of 2.16 kg.

[0027] (Content of aliphatic polyamide resin (a1)) When layer A is considered to be 100% by mass, the content of aliphatic polyamide resin (a1) is 88 to 98% by mass. By setting the content of aliphatic polyamide resin (a1) within the above range, the aliphatic polyamide resin (a1) and the polyolefin resin (a2) exhibit good compatibility, improving the melt stability of the composition of layer A and the moldability of the film. Furthermore, the pinhole resistance of the resulting biaxially oriented polyamide resin film in low-temperature environments and dimensional stability in high-temperature environments can be improved. The content of aliphatic polyamide resin (a1) is preferably 90.0 to 98.0% by mass, and more preferably 91.0 to 97.0% by mass, of 100% by mass of layer A.

[0028] <Polyolefin resin (a2)> The polyolefin resin (a2) is a component that contributes to improving the pinhole resistance of the resulting biaxially oriented polyamide resin film in low-temperature environments. The polyolefin resin (a2) is an ethylene / 1-hexene copolymer having a group derived from maleic anhydride. The polyolefin resin (a2) may be one type or a combination of two or more types.

[0029] Methods for introducing groups derived from maleic anhydride into polyolefin resin (a2) include (i) copolymerizing maleic anhydride during polymerization of the copolymer, (ii) introducing groups derived from maleic anhydride into the molecular chains or molecular ends of the ethylene / 1-hexene copolymer using polymerization initiators, chain transfer agents, etc., and (iii) grafting maleic anhydride onto the ethylene / 1-hexene copolymer. These introduction methods can be used individually or in appropriate combinations. In particular, from the viewpoint of suppressing deterioration of appearance caused by the film gel of layer A and maintaining the transparency and good pinhole resistance of layer A, it is preferable that the polyolefin resin (a2) be manufactured by method (ii) or (iii).

[0030] From the viewpoint of compatibility between aliphatic polyamide resin (a1) and polyolefin resin (a2) and reduction of film gel formation, the functional group concentration in the polyolefin resin (a2) is 1.0 × 10⁻⁶.-5 ~60×10 -5 It is preferable that the ratio is eq / g, and 2.0 × 10 -5 ~40×10 -5 It is more preferable that the value be eq / g, and 3.0 × 10 -5 ~30×10 -5 It is even more preferable that the concentration is eq / g. The functional group concentration of the polyolefin resin (a2) can be expressed as the equivalent amount of carboxyl groups per gram of polymer, and is measured by neutralization titration with a 0.1 N KOH ethanol solution using a sample solution prepared with a solvent such as xylene and phenolphthalein as an indicator.

[0031] When the polyolefin resin (a2) is a copolymer having groups derived from maleic anhydride by the method of (ii) or (iii) above, the maleic anhydride modification rate (content of groups derived from maleic anhydride (mass%)) is preferably 0.1% to 3% by mass, more preferably 0.3% to 2% by mass, and particularly preferably 0.5% to 1.5% by mass. By setting the maleic anhydride modification rate within the above range, the compatibility between the aliphatic polyamide resin (a1) and the polyolefin resin (a2) can be improved, and film gel formation can be reduced. Methods for measuring the maleic anhydride modification rate include converting the equivalent amount of carboxyl groups obtained by the neutralization titration above into the maleic anhydride modification rate, and FT-IR at a wavenumber of 1780 cm² to which carbonyl groups are attributed. -1 Methods include measuring based on the peak intensity using a calibration curve created separately.

[0032] From the viewpoint of compatibility between aliphatic polyamide resin (a1) and polyolefin resin (a2), in the polyolefin resin (a2), the proportion of 1-hexene monomer in the total 100 mol% of ethylene monomer and 1-hexene monomer constituting the copolymer is preferably 1 to 99 mol%, more preferably 5 to 95 mol%, and even more preferably 10 to 90 mol%.

[0033] The molecular structure of the polyolefin resin (a2) may be linear or branched, having long or short side chains. The polyolefin resin (a2) may be 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 1,4-octadiene, 1,5-octadiene, 1,6-octadiene, 1,7-octadiene, 2-methyl-1,5-hexadiene, 6-methyl-1,5-heptadiene, 7-methyl-1,6-octadiene, 4-ethylidene-8-methyl-1,7-nonadiene, 4,8-dimethyl-1,4,8-decatriene (DMDT), dicyclopentadiene Polyenes such as dienes, cyclohexadiene, cyclooctadiene, 5-vinylnorbornene, 5-ethlylidene-2-norbornene, 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene, 6-chloromethyl-5-isopropenyl-2-norbornene, 2,3-diisopropylidene-5-norbornene, 2-ethlylidene-3-isopropylidene-5-norbornene, and 2-propenyl-2,5-norbornadiene, as well as non-conjugated dienes and non-conjugated trienes, may be copolymerized. One or more of these can be used.

[0034] From the viewpoint of moldability, the melting point of the polyolefin resin (a2) is 70 to 120°C, preferably 75 to 120°C, and more preferably 80 to 115°C. The melting point is the melting peak temperature in the DSC curve when the polyolefin resin (a2) is heated to 280°C in an air atmosphere, held at this temperature for 5 minutes, then cooled to 0°C at a rate of 20°C / min, and then heated from 0°C to 280°C at a rate of 20°C / min.

[0035] (Content of polyolefin resin (a2)) When layer A is considered to be 100% by mass, the content of polyolefin resin (a2) is 1 to 10% by mass. By setting the content of polyolefin resin (a2) within the above range, the aliphatic polyamide resin (a1) and the polyolefin resin (a2) exhibit good compatibility, improving the melt stability of the composition of layer A and the moldability of the film. Furthermore, the pinhole resistance of the resulting biaxially oriented polyamide resin film in low-temperature environments and the dimensional stability in high-temperature environments can be improved. The content of polyolefin resin (a2) is preferably 2.0 to 8.0% by mass, and more preferably 3.0 to 8.0% by mass, of 100% by mass of layer A. When layer A is considered to be 100% by mass, if the content of polyolefin resin (a2) is less than 1% by mass, the pinhole resistance of the biaxially oriented polyamide resin film in low-temperature environments does not improve. If the content exceeds 10% by mass, the film strength of layer A decreases.

[0036] <Other ingredients (C)> The composition of layer A may also contain other components (C) in addition to components (a1) and (a2). Examples of other components include polyamide resins other than component (a1), such as polyamide resins having alicyclic or aromatic groups in the main chain or side chains; thermoplastic resins other than component (a2); flexibility modifiers, antioxidants, antiblocking agents, lubricants, nucleating agents, plasticizers, foaming agents, stabilizers, UV absorbers, weathering agents, antifogging agents, antistatic agents, colorants, etc.

[0037] Each layer of the biaxially oriented polyamide resin film may contain a flexibility modifier to improve flexural pinhole resistance. Examples of flexibility modifiers include polyolefins, polyamide elastomers, and polyester elastomers. The flexibility modifier may be one type or a combination of two or more types.

[0038] The aforementioned polyolefins contain 50% by mass or more of polyethylene units and polypropylene units in their main chain. Examples of constituent units other than polyethylene units and polypropylene units of the aforementioned polyolefins include vinyl acetate or its partially saponified products; acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters or partially metal neutralized products thereof (ionomers); 1-alkenes such as butene; alkadienes; styrene, etc. Polyolefins containing multiple of these constituent units can also be used.

[0039] The aforementioned polyamide elastomers belong to polyamide-based block copolymers such as polyetheramides and polyether esteramides. Examples of polyamide components include polyamide 6, polyamide 66, and polyamide 12. Examples of polyether components include polyoxytetramethylene glycol, polyoxyethylene glycol, and polyoxy-1,2-propylene glycol. From the viewpoint of compatibility between the polyamide and polyether components, thermal stability during extrusion, and flexibility modification effect, copolymers mainly composed of polyoxytetramethylene glycol and polylauryl lactam (polyamide 12) are most preferred. In addition, those containing small amounts of dicarboxylic acid units such as dodecanedicarboxylic acid, adipic acid, and terephthalic acid as optional components can also be used.

[0040] Examples of the aforementioned polyester elastomers include polyether ester elastomers made by combining polybutylene terephthalate and polyoxytetramethylene glycol, and polyester ester elastomers made by combining polybutylene terephthalate and polycaprolactone.

[0041] From the viewpoint of improving the handling properties of the molded film, the composition of layer A may include an antiblocking agent. Examples of antiblocking agents include minerals such as diatomaceous earth, calcium carbonate, feldspars, and quartz, as well as synthetic silica and cross-linked resin beads. The antiblocking agent may be one type or a combination of two or more types.

[0042] From the perspective of reducing the generation amount of the film gel, the composition of the A layer can contain an antioxidant. Examples of the antioxidant include organic antioxidants such as phenolic compounds, phosphorus compounds, sulfur compounds, and inorganic antioxidants such as metal halide compounds. The antioxidant may be one kind or a combination of two or more kinds.

[0043] From the perspectives of improving the slipperiness between pellets before molding, improving the slipperiness between the processing machine and the pellets, improving the slipperiness between the molded films, etc., the composition of the A layer can contain a lubricant. Examples of the lubricant include end-modified polyalkylene glycols, phosphate esters or phosphite esters, higher fatty acid monoesters, higher fatty acids or their metal salts, carboxylic acid amides, low molecular weight polyethylene, magnesium silicate, substituted benzylidene sorbitols and other compounds. These may be one kind or a combination of two or more kinds.

[0044] The aliphatic polyamide resin (a1) has the property of high hygroscopicity. Therefore, when the raw materials are melt-melted and extruded, water vapor and oligomers may be generated, which may inhibit film formation. Therefore, it is preferable that these raw materials are dried in advance so that the moisture content is 0.1% by mass or less.

[0045] When the A layer is 100% by mass, the content of the other component (C) is preferably 0 to 5% by mass, more preferably 0 to 3.0% by mass, and even more preferably 0 to 2.0% by mass.

[0046] <Manufacturing method of the composition of the A layer> The method for producing the composition of layer A is not particularly limited. For example, the composition of layer A can be obtained by melt-kneading an aliphatic polyamide resin (a1), a polyolefin resin (a2), and an optional other component (C) in a kneader. Examples of kneaders include single-screw and twin-screw extruders, Banbury mixers, kneaders, and mixing rolls. For example, any method may be used, such as a method in which all raw materials are blended using a twin-screw extruder and then melt-kneaded, or a method in which some of the raw materials are blended and the remaining raw materials are mixed using a side feeder during melt-kneading. Furthermore, the polyolefin resin (a2) and other components (C) may each be melt-kneaded with a predetermined amount of aliphatic polyamide resin (a1), and the resulting melt-kneaded mixture may be uniformly dry-blended with the remaining amount of aliphatic polyamide resin (a1). The resulting dry-blended mixture can be further melted and mixed and used as layer A. A tumbler, mixer, or the like can be used for dry-blending. When melting the composition of layer A in a film molding machine or the like and forming it into a film, it is preferable to process it into pellet form from the viewpoint of the manufacturing stability of the film and the dispersibility of each component in the composition.

[0047] [B layer] Layer B comprises at least one selected from the group consisting of ethylene-vinyl alcohol copolymer (EVOH) and polymetaxylylenediadipamide (MXD6). Layer B is a layer for further improving the gas barrier properties of the biaxially oriented polyamide resin film. Ethylene-vinyl alcohol copolymer and polymetaxylylenediadipamide may be used individually or in combination of two or more.

[0048] <Ethylene-vinyl alcohol copolymer> Ethylene-vinyl alcohol copolymer (EVOH) is obtained by saponifying a copolymer of ethylene and vinyl acetate with an alkaline catalyst or the like. The ethylene content in the ethylene-vinyl alcohol copolymer is not particularly limited, but from the viewpoint of film formation stability, it is generally preferred to be 20 mol% or more, and more preferably 24 mol% or more. On the other hand, from the viewpoint of gas barrier properties, the upper limit of the ethylene content is preferably 50 mol% or less, more preferably 40 mol% or less, and even more preferably 35 mol% or less. Furthermore, the degree of saponification of the ethylene-vinyl alcohol copolymer is preferably 96 mol% or more, and more preferably 98 mol% or more. By having the ethylene content and degree of saponification in the ethylene-vinyl alcohol copolymer within the above ranges, layer B has an excellent balance of film formation properties and gas barrier properties. Therefore, it is possible to perform molding processes such as co-extrusion with layer A and biaxial stretching.

[0049] The ethylene-vinyl alcohol copolymer may be modified in various ways as needed, or it may be a mixture of a modified ethylene-vinyl alcohol copolymer and an unmodified ethylene-vinyl alcohol copolymer. Examples of modified ethylene-vinyl alcohol copolymers include: a modified ethylene-vinyl alcohol copolymer obtained by copolymerizing at least one α-olefin having 3 to 30 carbon atoms, such as propylene or isobutene; a modified ethylene-vinyl alcohol copolymer obtained by graft polymerization of an acrylic acid ester; a modified ethylene-vinyl alcohol copolymer obtained by saponifying a ternary copolymer consisting of (meth)acrylic acid ester-ethylene-vinyl acetate; a modified ethylene-vinyl alcohol copolymer obtained by modifying the hydroxyl groups of the ethylene-vinyl alcohol copolymer with cyanoethyl groups; a modified ethylene-vinyl alcohol copolymer containing a polyester graft obtained by depolymerizing polyester with vinyl alcohol; a modified ethylene-vinyl alcohol copolymer obtained by saponifying a copolymer of vinyl acetate-ethylene-silicon-containing olefinic unsaturated monomers; and a pyrrolidone ring-containing monomer-ethylene-vinyl acetate. Examples include modified ethylene-vinyl alcohol copolymers obtained by saponifying a ternary copolymer consisting of nyl, modified ethylene-vinyl alcohol copolymers obtained by saponifying a ternary copolymer consisting of acrylamide-ethylene-vinyl acetate, modified ethylene-vinyl alcohol copolymers obtained by saponifying a ternary copolymer consisting of allyl acetate-ethylene-vinyl acetate, modified ethylene-vinyl alcohol copolymers obtained by saponifying a ternary copolymer consisting of isopropenyl acetate-ethylene-vinyl acetate, modified ethylene-vinyl alcohol copolymers in which a polyether component is attached to the end of the ethylene-vinyl alcohol copolymer, modified ethylene-vinyl alcohol copolymers in which a polyether component is attached in a graft-like manner as a branch polymer of the ethylene-vinyl alcohol copolymer, and modified ethylene-vinyl alcohol copolymers in which alkylene oxide is attached to the ethylene-vinyl alcohol copolymer.

[0050] <Polymetaxylylenediadipamide> From the viewpoint of achieving high gas barrier properties, polymetaxylylenediadipamide (MXD6) containing polyamide units composed of metaxylylenediamine and adipic acid in its molecular chain is preferably used. Polymetaxylylenediadipamide in which a portion of the adipic acid is replaced with isophthalic acid or terephthalic acid can also be used.

[0051] Other polyamide structural units in polymetaxylylenediadipamide include: structural units consisting of metaxylylenediamine and α,ω aliphatic dicarboxylic acid having 7 to 12 carbon atoms; structural units consisting of paraxylylenediamine and α,ω aliphatic dicarboxylic acid having 6 to 12 carbon atoms; structural units consisting of lactam or aminocarboxylic acid; structural units consisting of aliphatic diamine and dicarboxylic acid; structural units consisting of alicyclic diamine or dicarboxylic acid and aliphatic diamine or dicarboxylic acid; structural units consisting of aromatic diamine or aromatic dicarboxylic acid other than xylylenediamine and aliphatic diamine or dicarboxylic acid, etc.

[0052] Specific examples of structural units consisting of metaxylylenediamine and α,ω aliphatic dicarboxylic acids having 7 to 12 carbon atoms include polymetaxylylenedipimeramide, polymetaxylylenediazeramide, and polymetaxylylenediosebaamide. Specific examples of constituent units consisting of paraxylylenediamine and α,ω aliphatic dicarboxylic acids having 6 to 12 carbon atoms include polyparaxylylenediadipamide, polyparaxylylenedipimeramide, polyparaxylylenediazeramide, and polyparaxylylenediosebaamide.

[0053] As the lactams, aminocarboxylic acids, aliphatic diamines, and dicarboxylic acids that constitute the other polyamide structural units, the compounds exemplified in <Aliphatic Polyamide Resin (a1)> can be used. In addition, heterocyclic or heteroatom-containing diamines such as piperazine bispropylamine and neopentyl glycol bispropylamine; aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid; cycloaliphatic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, etc. can also be used.

[0054] From the viewpoint of gas barrier properties, the B layer is preferably an ethylene-vinyl alcohol copolymer (EVOH). In the case of polymetaxylylene diadipamide (MXD6), in addition to gas barrier properties, it also has hot water resistance, so it has the advantage of being usable not only for boiling but also for packaging materials for retort applications.

[0055] (Content of ethylene-vinyl alcohol copolymer and polymetaxylylene diadipamide) From the viewpoint of gas barrier properties, when the B layer is 100% by mass, the total content of the ethylene-vinyl alcohol copolymer and polymetaxylylene diadipamide is preferably 90 to 100% by mass, more preferably 93 to 100% by mass, and even more preferably 95 to 100% by mass.

[0056] <Other components> The B layer may contain other components other than the ethylene-vinyl alcohol copolymer and polymetaxylylene diadipamide. As the other components, the components exemplified in <Other components (C)> of the A layer can be used.

[0057] When the B layer is 100% by mass, the content of the other components is preferably 0 to 10% by mass, more preferably 0 to 7% by mass, and even more preferably 0 to 5% by mass. Among them, when the B layer contains polymetaxylylene diadipamide, it is preferable to add 1 to 10% by weight of a softening modifier to the B layer.

[0058] <Method for producing the composition of the B layer> The manufacturing method of the composition of the B layer is not particularly limited. For example, the composition of the B layer can be obtained by melt-kneading at least one selected from the group consisting of an ethylene-vinyl alcohol copolymer and polymetaxylylene diadipamide and optionally other components using a kneader. As the kneader, those exemplified in <the manufacturing method of the composition of the A layer> can be used.

[0059] [Biaxially stretched polyamide resin film] The biaxially stretched polyamide resin film has at least two layers of an A layer and a B layer. The A layer and the B layer may each be used alone as one layer or in combination of two or more layers. When the A layer and the B layer are each a combination of two or more layers, the formulations of the respective layers constituting the A layer and the B layer may be the same or different, and the respective layers constituting the A layer and the B layer may be adjacent or there may be other layers in between.

[0060] The biaxially stretched polyamide resin film is manufactured by stretching a film in which at least two layers of an A layer and a B layer are laminated in the longitudinal direction (MD) and the transverse direction (TD), respectively. From the viewpoint of imparting sufficient film strength and improving dimensional stability in a high-temperature environment, the stretching ratios in the longitudinal direction and the transverse direction are preferably 2.0 to 5.0 times, more preferably 2.2 to 5.0 times, and even more preferably 2.5 to  4.5 times.

[0061] [Physical properties of biaxially stretched polyamide resin film] (Hot water shrinkage rate) The biaxially oriented polyamide resin film has a hot water shrinkage rate of 5% or less at 95°C for 5 minutes, and a hot water shrinkage rate of 15% or less at 127°C for 5 minutes under a pressure of 0.15 MPa. By keeping the hot water shrinkage rate within the above range, the biaxially oriented polyamide resin film is less susceptible to thermal shrinkage even when subjected to boiling or retort treatment, thus minimizing damage to its physical properties and appearance. The hot water shrinkage rate at 95°C for 5 minutes is preferably 5.0% or less for both MD and TD, more preferably 4.5% or less, and even more preferably 4.0% or less. The hot water shrinkage rate at 127°C for 5 minutes under a pressure of 0.15 MPa is preferably 15.0% or less for both MD and TD, more preferably 12.0% or less, and even more preferably 10.0% or less.

[0062] (Pinhole resistance in low-temperature environments) In a Gelboflex test conducted at an ambient temperature of -25°C, relative humidity of 50%, and 1,000 bending cycles, the biaxially oriented polyamide resin film showed a pinhole count of 30 per 500 cm. 2 The following applies: By setting the number of pinholes within the above range, the biaxially oriented polyamide resin film exhibits good pinhole resistance in low-temperature environments. The number of pinholes is preferably 20 or less, more preferably 10 or less, and particularly preferably 5 or less. The lower limit of the number of pinholes is 0.

[0063] <Layer structure of biaxially oriented polyamide resin film> From the viewpoint of film strength and pinhole resistance, the ratio of the thickness of layer A to the total thickness of the biaxially oriented polyamide resin film is preferably 10 to 95%, more preferably 15 to 92%, and even more preferably 20 to 90%. If there are two or more layers of layer A, the ratio of the thickness of layer A refers to the sum of the thicknesses of all layers A.

[0064] From the viewpoint of gas barrier properties, the ratio of the thickness of layer B to the total thickness of the biaxially oriented polyamide resin film is preferably 2 to 50%, more preferably 3 to 40%, and even more preferably 5 to 30%. If there are two or more layers of layer B, the ratio of the thickness of layer B refers to the sum of the thicknesses of all layers B.

[0065] The total thickness of the biaxially oriented polyamide resin film is preferably 8 to 30 μm. A total thickness of 8 μm or more increases the physical strength of the biaxially oriented polyamide resin film. However, considering cost, a total thickness of 30 μm or less is preferable. A total thickness of 9 to 22 μm is more preferable, and 10 to 18 μm is even more preferable.

[0066] From the viewpoint of improving pinhole resistance in low-temperature environments, when the biaxially oriented polyamide resin film is considered as 100% by mass, the content of polyolefin resin (a2) is preferably 1.0 to 9.0% by mass, more preferably 1.5 to 8.0%, and even more preferably 2.0 to 7.0%.

[0067] From the viewpoint of film strength, pinhole resistance, and gas barrier properties, it is preferable that the biaxially oriented polyamide resin film has at least three layers in the order of layer A, layer B, and layer A.

[0068] A biaxially oriented polyamide resin film may not have layers other than layers A and B. Other layers include polyamide resin layers other than layer A, polyolefin resin layers, and adhesive layers. Note that the polyolefin resin layer and adhesive layer are not layers A and B. The upper limit of the ratio of the thickness of other layers to the thickness of the biaxially oriented polyamide resin film is preferably 50% or less, more preferably 45% or less, and even more preferably 40% or less. The lower limit of the ratio of the thickness of other layers is preferably 3% or more, more preferably 5% or more, and even more preferably 8% or more. If there are two or more other layers, the ratio of the thickness of other layers refers to the sum of the thicknesses of all other layers.

[0069] The biaxially oriented polyamide resin film preferably further has a polyolefin resin layer on top of layer A. When there are two or more polyolefin resin layers, the composition of each polyolefin resin layer may be the same or different.

[0070] Examples of polyolefins constituting the polyolefin resin layer include low-density polyethylene, linear low-density polyethylene, high-density polyethylene, ethylene / α-olefin copolymer with 3 or more carbon atoms, propylene homopolymer, propylene / α-olefin copolymer with 4 or more carbon atoms, and other non-polar polyolefins, as well as ethylene / acrylic acid copolymer, ethylene / vinyl acetate copolymer, ethylene / acrylic acid ester copolymer, and ethylene / methacrylic acid copolymer. Among these, from the viewpoint of food packaging applications, non-polar polyolefins and ethylene / vinyl acetate copolymers are preferred, and linear low-density polyethylene is more preferred. When the polyolefin resin layer is a non-polar polyolefin layer, the water vapor barrier properties of the biaxially oriented polyamide resin film tend to be further improved. When the polyolefin resin layer is an ethylene / vinyl acetate copolymer layer, the oxygen gas permeability of the biaxially oriented polyamide resin film tends to be further reduced. A biaxially oriented polyamide resin film having a polyolefin resin layer further on layer A can be suitably used for food packaging.

[0071] [Method for manufacturing biaxially oriented polyamide resin film] A biaxially oriented polyamide resin film can be manufactured by a manufacturing method that includes step 1, in which raw materials constituting layer A and raw materials constituting layer B are fed into extruders for each layer and co-extruded to obtain a laminated film, and step 2, in which the obtained laminated film is biaxially oriented.

[0072] Step 1 is the process of feeding the raw materials constituting layer A and layer B into the respective extruders and co-extruding them to obtain a laminated film. This laminated film is manufactured, for example, by co-extrusion, in which the raw materials for each layer are fed into 2 to 5 extruders, the molten resin is extruded with a flat die or a round die, and then rapidly cooled to obtain a flat or tubular laminated unstretched film. The melting temperature of layer A is preferably 210 to 280°C, and more preferably 220 to 270°C. The melting temperature of layer B is preferably 200 to 260°C, and more preferably 210 to 230°C.

[0073] Step 2 is a step of biaxially stretching the laminated film obtained in Step 1. The stretching ratios in the longitudinal (MD) and transverse (TD) directions are preferably 2.0 to 5.0 times, more preferably 2.2 to 5.0 times, and even more preferably 2.5 to 4.5 times. The biaxial stretching method can be any known method, such as tenter-type sequential biaxial stretching, tenter-type simultaneous biaxial stretching, or tubular-type simultaneous biaxial stretching. For example, in the tenter-type sequential biaxial stretching method, the laminated film obtained in step 1 is heated to a temperature range of 50 to 110°C, stretched 2.0 to 5.0 times in the longitudinal direction using a roll-type longitudinal stretcher, and then stretched 2.0 to 5.0 times in the transverse direction using a tenter-type transverse stretcher at a temperature range of 60 to 140°C. In the case of tenter-type simultaneous biaxial stretching or tubular-type simultaneous biaxial stretching, for example, the film is stretched 2.0 to 5.0 times in both the longitudinal and transverse directions simultaneously at a temperature range of 60 to 130°C.

[0074] The improvement in strength due to stretching is due to the orientation of aliphatic polyamide resin (a1) molecules. However, if stretching alone is not performed, the biaxially oriented polyamide resin film will shrink when heat is applied during processing such as printing, lamination with sealant film, or bag making. Therefore, it is preferable to perform heat fixing. In other words, the method for manufacturing a biaxially oriented polyamide resin film preferably further includes a step 3 in which the laminated film obtained in step 2 is heat-fixed. The heat-fixing temperature is preferably 180 to 230°C, and more preferably 200 to 220°C. Heat setting involves applying heat to the main raw material, aliphatic polyamide resin (a1), to near its melting point after stretching, as described in the heat treatment operation above, to suppress shrinkage. The hot water shrinkage rate at 95°C for 5 minutes is preferably 5% or less in both the longitudinal and transverse directions, more preferably 5.0% or less, more preferably 4.5% or less, and even more preferably 4.0% or less. If heat setting is insufficient and the hot water shrinkage rate in either the longitudinal or transverse direction exceeds 5%, shrinkage will occur during post-processing, adversely affecting dimensions and appearance. Furthermore, insufficient heat setting leads to stronger surface orientation of the film, making it more prone to peeling in the thickness direction. In other words, when a biaxially oriented polyamide resin film is laminated with a polyolefin resin layer, it becomes weaker against forces that peel the polyolefin resin layer, making it difficult to achieve sufficient laminate strength on the laminated surface. In particular, if the biaxially oriented polyamide resin film is a multilayer film with 3 or 5 layers, the thickness of each layer decreases, and the strength of each layer weakens, making it easier for delamination to occur, which greatly affects the laminate strength. Increasing the heat setting temperature and relaxing the surface orientation is effective in increasing the laminate strength, but this weakens the orientation of the aliphatic polyamide resin (a1), which tends to lead to a decrease in film strength.

[0075] The biaxially oriented polyamide resin film, which has been sufficiently heat-fixed by the heat treatment operation, can be cooled and wound up by conventional methods. Furthermore, to improve the adhesion strength with other base films, surface treatments such as corona discharge treatment can be applied to one or both sides of the biaxially oriented polyamide resin film.

[0076] The biaxially oriented polyamide resin film obtained in this manner is used as a base material, preferably by further laminating it with a polyolefin resin layer such as polypropylene or polyethylene.

[0077] The method for producing a biaxially oriented polyamide resin film preferably further includes step 4, in which a polyolefin-based resin layer is attached to layer A by lamination. The biaxially oriented polyamide resin film thus obtained can be suitably used for food packaging applications. In this specification, "attachment" means laminating another resin layer on top of a resin layer.

[0078] The method for laminating a polyolefin resin layer onto layer A is not particularly limited, and examples include the co-extrusion method, extrusion lamination method, and dry lamination method described in Japanese Patent Application Publication No. 2011-225870, among which the dry lamination method is preferred.

[0079] <Package> The packaging comprises a biaxially oriented polyamide resin film having at least two layers, an A layer and a B layer, and further having a polyolefin resin layer on the A layer. Preferably, the packaging has at least four layers in the order of A layer, B layer, A layer, and polyolefin resin layer. The packaging material has high gas barrier properties, high pinhole resistance even at low temperatures, sufficient puncture resistance, and good transparency, resulting in good film aesthetics and visibility of the packaged contents. Therefore, it can be suitably used as packaging for various foods under room temperature, refrigerated, and frozen conditions. There are no particular restrictions on the packaging material, but examples include bags, lids, bottoms, tubes, tanks, labels, etc. When using biaxially oriented polyamide resin film in packaging, it may be laminated with other thermoplastic resin films such as sealant films or polyester resin films, or decorated with printing or other processes, using known methods. There are no particular restrictions on the number or composition of the laminations. [Examples]

[0080] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples and can be implemented with appropriate modifications without changing the essence of the invention.

[0081] [Measurement of physical properties of each raw material and biaxially oriented polyamide resin film] The following physical properties were evaluated for each raw material and the biaxially oriented polyamide resin film.

[0082] 1.DSC measurement Aliphatic polyamide resin (a1) and polyolefin resin (a2) were measured using differential scanning calorimeter (DSC). The sample was heated to 280°C in an air atmosphere, held at this temperature for 5 minutes, then cooled to 0°C at a rate of 20°C / min, and the top temperature of the endothermic peak when the temperature was then raised from 0°C to 280°C at a rate of 20°C / min was defined as the melting peak temperature (melting point).

[0083] 2. Haze The total haze (in %) of the biaxially oriented polyamide resin films of the examples and comparative examples was measured in accordance with JIS K 7136:2000. The total haze is preferably 10.0% or less, more preferably 8.0% or less, and particularly preferably 5.0% or less.

[0084] 3. Resistance to flexural pinholes in low-temperature environments (Gelboflex test) The biaxially oriented polyamide resin films of the examples and comparative examples were cut to a size of 20 cm x 28 cm, left to stand for more than 24 hours under ambient temperature of -25°C and relative humidity of 50%, and then repeatedly subjected to bending tests using a Gelboflex tester as follows, until 481 cm. 2 The number of pinholes was measured. The film was rolled into a cylindrical shape with a length of 20 cm and a circumference of 28 cm. One end of the rolled cylindrical film was fixed to the outer circumference of the disc-shaped fixed head of the tester, and the other end was fixed to the outer circumference of the disc-shaped movable head of the tester.

[0085] Next, the movable head was rotated 440° while moving 15.2 cm closer to the fixed head along the axes of the two parallel heads in the direction of the fixed head. Then, these movements were reversed, and the movable head was returned to its original position. This bending test, which constituted one cycle, was performed continuously 1,000 times at a speed of 42 times per minute. After the test, the area of ​​the film, excluding the parts fixed to the outer circumference of the fixed and movable heads, was 481 cm² (17.5 cm × 27.5 cm). 2 Number of pinholes in the interior (unit: number of pinholes / 481cm) 2 The pinhole count was measured using an immersion method with dyed canola oil. The number of pinholes measured was 500 cm². 2 The number of winning entries was converted to a number, and evaluated according to the following criteria. The number of pinholes is 30 per 500cm. 2 The following is preferable: 20 pieces / 500cm 2 The following is more preferable: 10 pieces / 500cm 2 The following are particularly preferable.

[0086] 4. Hydrothermal contraction rate For the biaxially oriented polyamide resin films of the examples and comparative examples, cuts were made from three points: both ends and the center, measuring MD120mm × TD120mm. Three reference lines exceeding 100mm were drawn on these samples in the MD, TD, and diagonal directions (at 45° from each of the MD and TD directions). These samples were left standing for 24 hours at 23°C and 50% relative humidity, and the lengths of the reference lines were measured. The measured length before heat treatment was denoted as F. The sample was immersed in 95°C hot water and 127°C hot water under a pressure of 0.15 MPa for 5 minutes each, and then removed. Next, it was left to stand for 30 minutes in an atmosphere of 23°C and 50% relative humidity, and the length of the aforementioned reference line was measured, and the length after heat treatment was defined as G. Using the following formula, the average value of the three hot water shrinkage rates (in %) was calculated for the MD, TD, and oblique directions for the sample after immersion in 95°C hot water, and for the MD and TD directions for the sample after immersion in 127°C hot water under a pressure of 0.15 MPa. (Formula) (FG) / F×100 (%) The shrinkage rate after immersion in hot water at 95°C for 5 minutes is preferably 5.0% or less in the MD, TD, and oblique directions, more preferably 4.5% or less, and particularly preferably 4.0% or less. The shrinkage rate after immersion in hot water at 127°C for 5 minutes under a pressure of 0.15 MPa is preferably 15.0% or less for both MD and TD, more preferably 12.0% or less, and particularly preferably 10.0% or less.

[0087] [Raw materials used] The raw materials used in the examples and comparative examples are as follows: (1) Aliphatic polyamide resin (a1) Polyamide 6: Manufactured by UBE Corporation (Relative viscosity: 2.2; Melting point: 220°C; MFR measured at 230°C and a load of 2.16 kg in accordance with ASTM D1238: 60.0 g / 10 min; Terminal amino group concentration: 3.3 × 10⁻⁶ -5 eq / g) (2) Polyolefin resin (a2) Maleic anhydride-modified ethylene / 1-hexene copolymer: Manufactured by Ube Maruzen Polyethylene Co., Ltd., F3000 (Melting point: 115℃; MFR: 8.5g / 10min measured at 230℃ and a load of 2.16kg in accordance with ASTM D1238; Maleic anhydride modification rate: 1% by mass) (3) Antiblocking agents Silica (manufactured by Mizusawa Chemical Co., Ltd., Mizukasil® registered trademark, average particle size: 2.8 μm) (4) Ethylene-vinyl alcohol copolymer (b) Ethylene-vinyl alcohol copolymer: Manufactured by Mitsubishi Chemical Corporation, Soanol® (Ethylene content: 25 mol%, Saponification degree: 99 mol% or higher)

[0088] Example 1 As the first aliphatic polyamide resin (a1), polyamide 6 and maleic anhydride-modified ethylene / 1-hexene copolymer were melt-kneaded using a twin-screw kneader ZSK32McPlus (manufactured by Coperion Co., Ltd., screw diameter 32 mm) at a cylinder temperature of 230°C, a screw rotation speed of 500 rpm, and a discharge rate of 75 kg / h to produce the first pellet. Similarly, as the second aliphatic polyamide resin (a1), polyamide 6 and silica were melt-kneaded using a twin-screw kneader ZSK32McPlus (manufactured by Coperion Co., Ltd., screw diameter 32 mm) at a cylinder temperature of 230°C, a screw rotation speed of 500 rpm, and a discharge rate of 75 kg / h to produce the second pellet. The first pellet, the second pellet, and polyamide 6 as the third aliphatic polyamide resin (a1) were dry-blended to a final composition of 95.02% by mass of polyamide 6, 4.83% by mass of maleic anhydride-modified ethylene / 1-hexene copolymer, and 0.15% by mass of silica, thereby preparing the material for layer A.

[0089] The dry blend obtained in this way was used as layer A, and an ethylene-vinyl alcohol copolymer as layer B, and co-extruded. The thickness ratios of layer A and layer B were 45.0% and 10.0%, respectively, and a laminated film consisting of three layers, A / B / A, was prepared. The resulting unstretched laminated film was then stretched to a total of 10 times its original length by 2.9 times in the lengthwise and 3.5 times in the widthwise in a sequential biaxial stretching process, and the resulting biaxially oriented film was heat-set at 215°C. After trimming the ends of the film that would be gripped by the clips while it was running on the film guide unit, the film was wound into a roll to obtain a biaxially oriented film with a thickness of 15 μm.

[0090] Examples 2 and 3 and Comparative Example 1 Except for changing the composition of layer A as shown in Table 1, the biaxially oriented polyamide resin films of Examples 2 and 3 and Comparative Example 1 were obtained in the same manner as in Example 1.

[0091] Example 4 The first and second pellets were prepared in the same manner as in Example 1. The first pellet and the third aliphatic polyamide resin (a1), polyamide 6, were dry-blended so that the final composition was 92.80% by mass of polyamide 6 and 7.20% by mass of maleic anhydride-modified ethylene / 1-hexene copolymer, thereby preparing the material for layer A.

[0092] Separately, the second pellet and polyamide 6 as the fourth aliphatic polyamide resin (a1) were dry-blended so that the final composition was 99.85% by mass of polyamide 6 and 0.15% by mass of silica, thereby preparing the material for layer C.

[0093] Co-extrusion was performed using the dry blend of layer A as layer A, the ethylene-vinyl alcohol copolymer as layer B, and the dry blend of layer C as layer C. The thickness ratios of layers C, A, and B were 28.3%, 16.7%, and 10.0%, respectively, and a laminated film consisting of five layers (C / A / B / A / C) was prepared. The resulting unstretched laminated film was then sequentially stretched in a biaxial stretching process to a total of 10 times its original length (2.9 times in the lengthwise direction and 3.5 times in the widthwise direction), and the resulting biaxially oriented film was heat-set at 215°C. After trimming the ends of the film that would be gripped by the clips during cooling while the film was running on the film guide unit, the film was wound into a roll to obtain a biaxially oriented film with a thickness of 15 μm.

[0094] Examples 5 and 6 Biaxially oriented polyamide resin films of Examples 5 and 6 were obtained in the same manner as in Example 4, except that the composition of layer A was changed as shown in Table 1.

[0095] Table 1 shows the formulations of Examples 1-6 and Comparative Example 1, the thickness of each layer, and the various physical properties of the resulting biaxially oriented polyamide resin films.

[0096] [Table 1]

[0097] In Table 1, the content of each component in layers A, B, and C is expressed as the mass-based percentage of the total content of layers A, B, and C, respectively. On the other hand, the content (mass%) of maleic anhydride-modified ethylene / 1-hexene copolymer in the entire film refers to the content of maleic anhydride-modified ethylene / 1-hexene copolymer when the biaxially oriented polyamide resin film is considered as 100% by mass. This content is calculated from the content of maleic anhydride-modified ethylene / 1-hexene copolymer contained in each layer and the thickness ratio of each layer, assuming that the specific gravity of each layer is the same.

[0098] Table 1 shows that the biaxially oriented polyamide resin films of Examples 1-6 exhibited a hot water shrinkage rate of 5% or less at 95°C for 5 minutes; a hot water shrinkage rate of 15% or less at 127°C for 5 minutes under a pressure of 0.15 MPa; and in a Gelboflex test at an ambient temperature of -25°C, relative humidity of 50%, and 1,000 bending cycles, the number of pinholes was 30 / 500cm. 2 The following demonstrates excellent resistance to pinholes in low-temperature environments and superior dimensional stability in high-temperature environments.

[0099] Comparative Example 1, a biaxially oriented polyamide resin film in which layer A does not contain maleic anhydride-modified ethylene / 1-hexene copolymer, showed a pinhole count of 30 / 500cm in the Gelboflex test. 2 It exceeded this limit and had poor resistance to pinholes in low-temperature environments. [Industrial applicability]

[0100] The biaxially oriented polyamide resin film of the present invention is suitable for use in food packaging and other applications, and is useful.

Claims

1. A biaxially oriented polyamide resin film having at least two layers: an A layer containing an aliphatic polyamide resin (a1) and a polyolefin resin (a2), and a B layer containing at least one selected from the group consisting of ethylene-vinyl alcohol copolymer and polymetaxylylenediadipamide, The polyolefin resin (a2) is an ethylene / 1-hexene copolymer having a group derived from maleic anhydride, and the melting peak temperature measured from the DSC curve when the temperature is raised from 0°C to 280°C at a rate of 20°C / min in an air atmosphere is 70 to 120°C. When layer A is considered to be 100% by mass, the content of the aliphatic polyamide resin (a1) is 88 to 98% by mass, and the content of the polyolefin resin (a2) is 1 to 10% by mass. For the aforementioned biaxially oriented polyamide resin film, the hot water shrinkage rate at 95°C for 5 minutes is 5% or less; the hot water shrinkage rate at 127°C for 5 minutes under a pressure of 0.15 MPa is 15% or less; and in a Gelboflex test at an ambient temperature of -25°C, relative humidity of 50%, and 1,000 bending cycles, the number of pinholes is 30 / 500 cm. ２ The following is a biaxially oriented polyamide resin film.

2. The biaxially oriented polyamide resin film according to claim 1, wherein the aliphatic polyamide resin (a1) is at least one selected from the group consisting of polyamide 6, polyamide 11, and polyamide 12.

3. The biaxially oriented polyamide resin film according to claim 1, wherein the ratio of the thickness of the A layer to the total thickness of the biaxially oriented polyamide resin film is 10 to 95%.

4. The biaxially oriented polyamide resin film according to claim 1, wherein when the A layer is considered to be 100% by mass, the content of the polyolefin resin (a2) is 2.0 to 8.0% by mass.

5. The biaxially oriented polyamide resin film according to claim 1, having at least three layers in the order of layer A, layer B, and layer A.

6. A biaxially oriented polyamide resin film according to any one of claims 1 to 5, further comprising a polyolefin resin layer on layer A.

7. A packaging body comprising the biaxially oriented polyamide resin film described in claim 6.

8. A method for producing a biaxially oriented polyamide resin film having at least two layers: an A layer containing an aliphatic polyamide resin (a1) and a polyolefin resin (a2), and a B layer containing at least one selected from the group consisting of ethylene-vinyl alcohol copolymer and polymetaxylylenediadipamide. The process includes step 1, which involves feeding the raw materials constituting layer A and the raw materials constituting layer B into the respective extruders and co-extruding them to obtain a laminated film, and step 2, which involves biaxial stretching the obtained laminated film. The polyolefin resin (a2) is an ethylene / 1-hexene copolymer having a group derived from maleic anhydride, and the melting peak temperature measured from the DSC curve when the temperature is raised from 0°C to 280°C at a rate of 20°C / min in an air atmosphere is 70 to 120°C. When layer A is considered to be 100% by mass, the content of the aliphatic polyamide resin (a1) is 88 to 98% by mass, and the content of the polyolefin resin (a2) is 1 to 10% by mass. For the aforementioned biaxially oriented polyamide resin film, the hot water shrinkage rate at 95°C for 5 minutes was 5% or less; the hot water shrinkage rate at 127°C for 5 minutes under a pressure of 0.15 MPa was 15% or less; and in a Gelboflex test at an ambient temperature of -25°C, relative humidity of 50%, and 1,000 bending cycles, the number of pinholes was 30 / 500 cm. ２ The following is a method for manufacturing a biaxially oriented polyamide resin film.

9. A method for producing a biaxially oriented polyamide resin film according to claim 8, further comprising the step of attaching a polyolefin resin layer to layer A by lamination.

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