Laminated film and method for producing same

Abstract

A laminated film in which a resin layer is provided on at least one surface of a polyamide film, wherein the laminated film is characterized in that the polyamide film is a stretched film comprising a polyamide resin composition containing 1.0-10.0 mass% of a polyester-based thermoplastic elastomer, the resin layer contains a polyvinylidene chloride resin, and the laminated film satisfies conditions (A)-(C). (A) The haze of the laminated film is 10% or lower. (B) The adhesive strength of the resin layer and the polyamide film in a 5°C, 55% RH atmosphere is 0.5 N / cm or higher. (C) The laminated film has a pinhole count in a 1000× repeated flexural fatigue test in a 5°C, 55% RH atmosphere of 5 / 500 cm2 or lower.

Description

[Technical field]

[0001] The present invention relates to a laminated film in which a resin layer containing a polyvinylidene chloride resin is laminated on a film made of a polyamide resin composition containing a polyester thermoplastic elastomer, and to a method for producing the same. [Background technology]

[0002] Films made of polyamide resins such as nylon 6 and nylon 66 have excellent mechanical properties such as tensile strength, puncture strength, pinhole strength, and impact strength, as well as excellent gas barrier properties and heat resistance. For this reason, laminated films made by laminating a sealant made of a polyolefin film to a polyamide resin film substrate by methods such as dry lamination or extrusion lamination are used in a wide range of fields, including packaging materials for sterilization processes such as boiling and retorting.

[0003] In recent years, packaging materials have been required to maintain the quality of the packaged goods and contents without deterioration, and improvements in this area are being sought. In particular, for pharmaceuticals, food, and other contents, in order to maintain quality, logistics methods that maintain low-temperature environments such as refrigeration and freezing (cold chains) have become widely used during the production, transportation, and consumption processes, and there is an increasing demand for packaging materials to improve their pinhole resistance, especially in low-temperature environments.

[0004] Examples of pinholes that occur in packaging materials include puncture pinholes that occur when a sharp corner of a packaging material pierces a mating packaging material, bending pinholes that occur when a packaging material is repeatedly bent due to vibration during transportation, and friction pinholes that occur due to repeated contact with cardboard. Polyamide resin films are considered to be packaging materials with high pinhole resistance that are less susceptible to pinholes caused by puncture, bending, friction, etc. However, polyamide resin films become hard when the environmental temperature is low, and therefore the number of pinholes that occur, particularly due to bending, tends to increase significantly.

[0005] In order to improve the flex resistance in a low-temperature environment, a method of adding an olefin copolymer or a polyamide copolymer to a polyamide resin has been proposed. For example, JP 2014-014976 A discloses a polyamide resin film having improved flex resistance in a low-temperature environment by adding a ternary copolymer of ethylene, n-butyl acrylate, and maleic anhydride as an olefin copolymer, and JP 2003-012921 A discloses a polyamide resin having improved flex resistance in a low-temperature environment by adding a polyether ester amide elastomer, which is a polyamide thermoplastic elastomer, as a polyamide copolymer.

[0006] However, none of the polyamide films has been sufficiently improved in flex resistance in a low-temperature environment, and has low transparency, making it impossible to use the polyamide films in applications requiring transparency as a packaging material. Thus, a packaging material that is excellent in both flex resistance and transparency even in a low-temperature environment has yet to be provided.

[0007] Furthermore, in packaging materials, particularly food packaging materials, oxygen barrier properties and water vapor barrier properties are required in order to enhance the storage stability of the contents. As a method for achieving this, a method of laminating a resin layer having barrier properties on a base film is known. However, a laminate film in which the above-mentioned resin layer is laminated on a base film does not have sufficient adhesion between the base film and the resin layer in a low-temperature environment, and does not have sufficient bending resistance in a low-temperature environment, and the resulting package sometimes does not have sufficient bag-breaking resistance in a low-temperature environment. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made to solve the above-mentioned problems, and has an object to provide a polyamide-based laminate film which has excellent adhesion between a base film and a resin layer in a low-temperature environment, excellent flexural resistance so as to reduce the number of pinholes generated, and further has excellent barrier properties and transparency, and when used as a package, has excellent bag-breaking resistance in a low-temperature environment, and a method for producing the same. [Means for solving the problem]

[0009] As a result of investigations aimed at solving the above-mentioned problems, the present inventors have found that a film made of a polyamide resin composition containing a specific amount of a polyester-based thermoplastic elastomer, and a resin layer containing a polyvinylidene chloride resin are laminated, formed, and stretched by a specific method, has excellent bending resistance in a low-temperature environment, and also has excellent adhesion and transparency at low temperatures, thereby completing the present invention.

[0010] The laminate film of the present invention is a laminate film having a resin layer provided on at least one surface of a polyamide film, The polyamide film is a stretched film made of a polyamide resin composition containing 1.0 to 10.0% by mass of a polyester thermoplastic elastomer, The resin layer contains a polyvinylidene chloride resin, It is characterized by satisfying the following conditions (A) to (C). (A) The haze of the laminate film is 10% or less. (B) The adhesive strength between the resin layer and the polyamide film in an atmosphere of 5° C. and 55% RH is 0.5 N / cm or more. (C) The number of pinholes in the laminated film after 1000 repeated bending fatigue tests at 5°C and 55% RH is 5 / 500cm. 2 The following is the result. According to the laminated film of the present invention, the amount of extractable caprotactam monomer is preferably 0.1% by mass or less. According to the laminate film of the present invention, in a bag drop test under an atmosphere of 5° C. and 55% RH, a laminate in which a sealant resin layer is laminated on a laminate film can be dropped preferably 70 times or more before breaking. The method for producing a laminated film of the present invention is characterized by carrying out the following steps (a), (b), and (c) in this order. (a) A step of allowing an unstretched film made of a polyamide resin composition containing 1.0 to 10.0% by mass of a polyester thermoplastic elastomer to absorb water so that the moisture content is 2 to 10%. (b) A step of applying a resin layer forming liquid containing a polyvinylidene chloride resin to at least one surface of the water-absorbed unstretched film. (c) A process of biaxially stretching the unstretched film coated with the resin layer forming liquid so that the MD stretch ratio (X) and the TD stretch ratio (Y) are each in the range of 2.2 to 3.8 times and the stretch ratio ratio (X / Y) is 0.8 to 1.2. Effect of the Invention

[0011] The laminated film of the present invention has high adhesion strength between the polyamide film as the base film and the resin layer in a low-temperature environment, has excellent bending resistance at low temperatures, can reduce the number of pinholes generated, and is also excellent in barrier properties and transparency. The package obtained from the laminated film of the present invention has excellent resistance to rupture not only in a refrigerated environment but also in a freezer environment, and can be suitably used for medical containers such as food and infusion bags distributed in a low-temperature environment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will be described in detail below. The laminated film of the present invention comprises a polyamide film and a resin layer provided on at least one surface of the polyamide film. In the present invention, the polyamide film constituting the laminated film is a stretched film made of a polyamide resin composition containing a polyester thermoplastic elastomer. The polyamide film may have either a single layer structure or a multilayer structure, but the single layer structure is more excellent in productivity.

[0013] Examples of the polyamide resin that constitutes the resin composition include nylon 6, nylon 66, nylon 46, nylon 69, nylon 610, nylon 612, nylon 1010, nylon 11, nylon 12, polymetaxylylene adipamide (nylon MXD6), nylon 6T, nylon 9T, nylon 10T, and mixtures and copolymers thereof. In particular, nylon 6 is preferable in terms of productivity and performance, and has excellent cost performance. When nylon 6 is used as a film raw material, other polyamide components may be contained in an amount of 30 mass% or less by copolymerization, mixing, or the like, from among the above-mentioned polyamide resins.

[0014] The polyamide resin preferably contains an end-blocking agent such as an organic glycidyl ester, a dicarboxylic anhydride, a monocarboxylic acid such as benzoic acid, or a diamine in order to suppress the generation of monomers during melting.

[0015] The relative viscosity of the polyamide resin is not particularly limited, but the relative viscosity measured using 96% sulfuric acid as a solvent under the conditions of a temperature of 25°C and a concentration of 1 g / dl is preferably 1.5 to 5.0, more preferably 2.5 to 4.5, and even more preferably 2.8 to 4.0. If the relative viscosity of the polyamide resin is less than 1.5, the mechanical properties of the obtained film tend to be significantly reduced. Moreover, if the relative viscosity of the polyamide resin exceeds 5.0, the film production tends to be hindered.

[0016] If necessary, the polyamide resin may contain one or more of various additives such as pigments, antioxidants, UV absorbers, preservatives, antistatic agents, antiblocking agents, inorganic fine particles, etc., within the scope of not adversely affecting the performance of the film.

[0017] The polyamide resin may contain one or more of various inorganic or organic lubricants in order to improve the slip properties of the film, etc. Examples of lubricants include clay, talc, calcium carbonate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, calcium aluminate, magnesium aluminosilicate, glass balloons, carbon black, zinc oxide, antimony trioxide, zeolite, hydrotalcite, layered silicate, ethylene bisstearic acid amide, etc.

[0018] In the present invention, the resin composition constituting the polyamide film must contain 1.0 to 10.0 mass % of a polyester thermoplastic elastomer, preferably 1.3 to 8.0 mass %, and most preferably 2.0 to 6.0 mass %. If the content of the polyester-based thermoplastic elastomer is less than 1% by mass, the resulting film will have a high elastic modulus and poor bending resistance in a low-temperature environment. Furthermore, if the content of the polyester-based thermoplastic elastomer exceeds 10% by mass, the resulting laminate film may have reduced transparency or poor adhesion between the polyamide-based film and the resin layer in a low-temperature environment, and may have poor seal strength, falling resistance, and tear resistance when used as a package.

[0019] The polyester-based thermoplastic elastomer in the present invention is preferably composed mainly of a crystalline polymer segment consisting of a crystalline aromatic polyester unit and a polymer segment consisting of an aliphatic polyether unit.

[0020] The crystalline polymer segment consisting of a crystalline aromatic polyester unit is a unit consisting of a crystalline aromatic polyester formed from an aromatic dicarboxylic acid or an ester-forming derivative thereof and an aliphatic diol, and is preferably a polybutylene terephthalate unit derived from terephthalic acid and / or dimethyl terephthalate and 1,4-butanediol. Other examples of polyester units include dicarboxylic acid components such as terephthalic acid, isophthalic acid, phthalic acid, naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid, diphenyl-4,4'-dicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-sulfoisophthalic acid, and ester-forming derivatives thereof, and diols having a molecular weight of 300 or less, for example, aliphatic diols such as 1,4-butanediol, ethylene glycol, trimethylene glycol, pentamethylene glycol, hexamethylene glycol, neopentyl glycol, and decamethylene glycol, 1,4-cyclohexanedimethanol, and tricyclohexanedimethanol. It may be a polyester unit derived from an alicyclic diol such as decanedimethylol, an aromatic diol such as xylylene glycol, bis(p-hydroxy)diphenyl, bis(p-hydroxyphenyl)propane, 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane, bis[4-(2-hydroxy)phenyl]sulfone, 1,1-bis[4-(2-hydroxyethoxy)phenyl]cyclohexane, 4,4'-dihydroxy-p-terphenyl, or 4,4'-dihydroxy-p-quaterphenyl, or a copolymerized polyester unit using two or more of these dicarboxylic acid components and diol components in combination. It is also possible to copolymerize a polyfunctional carboxylic acid component having three or more functionalities, a polyfunctional oxyacid component, and a polyfunctional hydroxy component in a range of 5 mol % or less.

[0021] The polymer segment consisting of aliphatic polyether units is a unit whose main constituent is aliphatic polyether. Specific examples of aliphatic polyethers include poly(ethylene ether) glycol, poly(propylene ether) glycol, poly(tetramethylene ether) glycol, poly(hexamethylene ether) glycol, copolymers of ethylene oxide and propylene oxide, ethylene oxide addition polymers of poly(propylene ether) glycol, and copolymers of ethylene oxide and tetrahydrofuran. Among these aliphatic polyethers, poly(tetramethylene ether) glycol is preferred because the resulting polyester block copolymer has good elastic properties. The number average molecular weight of this polymer segment in the copolymerized state is preferably about 300 to 6000.

[0022] The content of the polymer segment consisting of an aliphatic polyether unit in the polyester-based thermoplastic elastomer is preferably 10 to 80% by mass, more preferably 15 to 75% by mass. If the content of the polymer segment is less than 10% by mass, the resulting resin composition tends to be hard, whereas if the content exceeds 80% by mass, the resin composition may be too flexible and not exhibit physical properties.

[0023] The polyester thermoplastic elastomer can be produced by a commonly used method, for example, a method of subjecting a lower alcohol diester of a dicarboxylic acid, an excess amount of a low molecular weight glycol, and a component constituting a polymer segment to an ester exchange reaction in the presence of a catalyst and polycondensing the resulting reaction product, a method of subjecting a dicarboxylic acid, an excess amount of a glycol, and a component constituting a polymer segment to an esterification reaction in the presence of a catalyst and polycondensing the resulting reaction product, or a method of adding a polymer segment component to a previously prepared crystalline segment and subjecting it to an ester exchange reaction to randomize the resulting product.

[0024] Commercially available polyester thermoplastic elastomers include "Primalloy AP (MODIC)" manufactured by Mitsubishi Chemical Corporation, "Pelprene" manufactured by Toyobo Co., Ltd., and "Hytrel" manufactured by Toray DuPont Co., Ltd.

[0025] The laminate film of the present invention has a resin layer containing a polyvinylidene chloride resin (hereinafter sometimes abbreviated as PVDC) provided on at least one surface of a polyamide film from the viewpoint of improving the barrier property and also from the viewpoint of improving adhesion to the polyamide film, which is a base film.

[0026] PVDC is obtained as a latex dispersed in a medium by polymerizing 50-99% by mass of vinylidene chloride as raw materials and 1-50% by mass of one or more other monomers copolymerizable with vinylidene chloride by a known emulsion polymerization method. The average particle size of PVDC in the latex is preferably 0.05-0.5 μm, and particularly preferably 0.07-0.3 μm. PVDC may be used in combination with various additives such as antiblocking agents and antistatic agents within the scope of the present invention.

[0027] The thickness of the resin layer is preferably 0.5 to 3.5 μm, more preferably 0.7 to 3.0 μm, and most preferably 1.0 to 2.5 μm. If the resin layer is less than 0.5 μm thick, sufficient gas barrier properties cannot be obtained, and if it exceeds 3.5 μm, the film-forming properties are reduced and the appearance of the film is easily damaged. In addition, if the resin layer is thick, the laminated film tends to become hard, and pinholes are easily generated when the film is bent in a low-temperature environment.

[0028] The laminated film of the present invention contains the above-mentioned polyamide resin composition and polyvinylidene chloride resin as constituent components, and can be produced by the method for producing the laminated film of the present invention described below.

[0029] The haze, which is a characteristic value indicating the transparency of the laminated film of the present invention, must be 10% or less, preferably 8% or less, and most preferably 6% or less. A laminated film with a haze of more than 10% is difficult to use in applications requiring transparency. In addition, a laminated film with a haze of more than 10% may have a poor dispersion state of the polyester thermoplastic elastomer in the polyamide film or may have insufficient preheating before the stretching process during film production, which may result in reduced bending resistance in a low-temperature environment and poor drop resistance.

[0030] In the laminated film of the present invention, the adhesion strength between the polyamide film and the resin layer in an atmosphere of 5° C. and 55% RH must be 0.5 N / cm or more, and is preferably 1.5 N / cm or more. If the adhesion strength is less than 0.5 N / cm, the adhesion between the polyamide film and the resin layer of the laminated film decreases when the film is stored in a refrigerated or frozen environment, making it impossible to obtain a sufficient seal strength, and the resulting package may break when dropped.

[0031] The adhesion strength between the polyamide-based film and the resin layer can be improved, for example, by reducing the amount of caprolactam monomer in the laminated film, as described below, or by forming a resin layer on a polyamide-based film at a stage after the moisture content adjustment step and before stretching, when producing the laminated film, as described below, where the amount of monomer is small.

[0032] The flex resistance of the laminated film of the present invention in a low-temperature environment is evaluated by the number of pinholes in a 1000-time repeated flex fatigue test in an atmosphere of 5°C and 55% RH using a Gelbo flex tester. 2 It is necessary that the number of pieces is less than 4.0 / 500cm. 2 Preferably less than 3.5 pieces / 500cm 2 It is preferable that the number of pieces is less than 3.0 pieces / 500 cm. 2 It is most preferable that the number of pinholes is less than 5 / 500cm. 2 A laminated film exceeding this value does not have sufficient strength when used as a package, and in particular, when the contents are liquid, problems such as leakage due to pinholes formed as a result of bending fatigue in a low-temperature environment can occur.

[0033] As described above, the laminated film of the present invention is also excellent in puncture strength and abrasion resistance, which are properties that affect pinhole resistance in a low-temperature environment. First, the puncture strength of the laminated film of the present invention in a low temperature environment is evaluated based on the puncture strength in an atmosphere of 5°C and 55% RH. The laminated film of the present invention preferably has this strength per 1 μm of 0.60 N / μm or more, more preferably 0.65 N / μm or more. A laminated film having a puncture strength of less than 0.60 N / μm may be difficult to use in applications requiring pinhole resistance.

[0034] The abrasion resistance of the laminated film of the present invention in a low temperature environment is evaluated by the number of times of sliding until pinholes are generated by repeated contact in an atmosphere of 5°C and 55% RH using a Gakushin type friction tester. For the laminated film of the present invention, this number is preferably 200 times or more, and more preferably 250 times or more. If the number of times of sliding until pinholes are generated is less than 200 times, it may be difficult to use the film in applications requiring pinhole resistance.

[0035] The laminated film of the present invention has a caprolactam monomer extraction amount of preferably 0.1% by mass or less, more preferably 0.05% by mass or less. If the caprolactam monomer extraction amount of the laminated film exceeds 0.1% by mass, the adhesive strength between the polyamide film and the resin layer in an atmosphere of 5° C. and 55% RH may decrease to less than 0.5 N / cm.

[0036] The elastic modulus of the laminated film of the present invention in MD (length direction) and TD (width direction) is preferably 1.0 to 2.3 GPa, and the ratio of the elastic modulus of MD to TD (MD / TD) is preferably 0.9 to 1.5. When the elastic modulus and the elastic modulus ratio in MD and TD are within the above ranges, the laminated film of the present invention can have improved bending resistance in a low-temperature environment and excellent transparency. In general, in order to reduce the occurrence of pinholes in a polyamide laminate film, the properties of puncture strength and abrasion resistance are important as well as bending resistance. The laminate film of the present invention exhibits excellent pinhole resistance even in a low temperature environment because the polyamide film constituting the film also has excellent puncture strength and abrasion resistance that are specific to the film.

[0037] The elastic modulus in the MD and TD of the laminated film of the present invention is preferably 1.0 to 2.3 GPa, more preferably 1.2 to 2.1 GPa, and even more preferably 1.4 to 1.9 GPa, as described above. If the elastic modulus of the laminated film is lower than 1.0 GPa, the film will have poor bending resistance and transparency in a low-temperature environment, and the puncture strength and abrasion resistance will also decrease. On the other hand, if the elastic modulus of the laminated film is higher than 2.3 GPa, the film will have poor bending resistance and poor transparency in a low-temperature environment, even if the polyamide film contains a polyester elastomer within the range specified in the present invention.

[0038] The ratio of the elastic modulus in MD to TD (MD / TD) of the laminated film of the present invention is preferably 0.9 to 1.5, more preferably 1.0 to 1.4, and even more preferably 1.1 to 1.35, as described above. If the elastic modulus ratio is out of the above range, the film will have poor bending resistance and transparency in a low-temperature environment, and will also have reduced puncture strength and abrasion resistance.

[0039] When used for packaging purposes, the thickness of the laminated film is preferably 10 to 50 μm, and more preferably 10 to 30 μm.

[0040] The laminate obtained by laminating a sealant resin layer on the laminate film of the present invention can be used as a package. As described above, the laminate film of the present invention has high adhesion strength between the polyamide film and the resin layer, has excellent flex resistance at low temperatures, and can reduce the number of pinholes, so the resulting package has excellent resistance to bag breakage. For example, a package filled with water can be dropped many times before the bag breaks even if it is dropped repeatedly in a refrigerated or frozen environment. In a drop bag test of a laminate obtained by laminating a sealant resin layer on a laminate film under an atmosphere of 5°C and 55% RH, the laminate film of the present invention is preferably dropped 70 times or more before the bag breaks, more preferably 150 times or more, and even more preferably 200 times or more. The drop bag test is performed by dropping a package filled with 1000 ml of water (a package heat-sealed at a width of 10 mm using two laminates of 200 mm x 300 mm) from a height of 1.2 m.

[0041] Next, the method for producing the laminated film of the present invention will be described. The method for producing the laminated film of the present invention is a method which sequentially carries out the following steps (a), (b) and (c). (a) A step of allowing an unstretched film made of a polyamide resin composition containing 1.0 to 10.0% by mass of a polyester thermoplastic elastomer to absorb water so that the moisture content is 2 to 10%. (b) A step of applying a resin layer forming liquid containing a polyvinylidene chloride resin to at least one surface of the water-absorbed unstretched film. (c) A process of biaxially stretching the unstretched film coated with the resin layer forming liquid so that the MD stretch ratio (X) and the TD stretch ratio (Y) are each in the range of 2.2 to 3.8 times and the stretch ratio ratio (X / Y) is 0.8 to 1.2.

[0042] The above step (a) will now be described. First, a polyamide resin and a polyester-based thermoplastic elastomer are melt-kneaded to produce a polyamide-based resin composition containing 1.0 to 10.0% by mass of the polyester-based thermoplastic elastomer. The extruder used for melt kneading may be either a single screw extruder having one screw in a cylinder or a multi-screw extruder having multiple screws. When feeding the polyester thermoplastic elastomer and the polyamide resin into the cylinder, it is preferable to feed them simultaneously from near the inlet of the cylinder, but it is also possible to feed the polyester thermoplastic elastomer from the middle of the cylinder after feeding the polyamide resin from near the inlet of the cylinder. In either case, it is preferable to set the cylinder temperature at the start of kneading immediately after both resins are added to 180 to 200°C, and set the cylinder temperature near the outlet of the composition in which both resins are kneaded to (melting point of polyamide resin + 10°C) to (melting point of polyamide resin + 30°C), and perform melt kneading. By carrying out the melt kneading at such a temperature setting, the dispersibility of the polyester thermoplastic elastomer added in the polyamide resin is improved. If the cylinder temperature at the start of kneading is less than 180°C, the polyamide resin melts and moves to the rear half of the cylinder, resulting in insufficient kneading with the polyester thermoplastic elastomer, and the dispersed particle size of the polyester thermoplastic elastomer increases, which may result in insufficient bending resistance or increased haze in the resulting film. On the other hand, if the cylinder temperature at the start of kneading exceeds 200°C, the polyester thermoplastic elastomer melts immediately after being added and wraps around the cylinder, making the extrusion of the polyamide resin unstable and making it difficult to obtain an unstretched film with a uniform thickness. In addition, if the cylinder temperature near the outlet of the composition in which both resins are kneaded is less than (melting point of polyamide resin + 10°C), unmelted polyamide resin may be present, making it difficult to obtain a continuous unstretched film. On the other hand, if the cylinder temperature near the outlet exceeds (melting point of polyamide resin + 30°C), the polyamide resin and polyester-based thermoplastic elastomer may thermally decompose, making it difficult to obtain a continuous unstretched film.

[0043] Next, the resin composition containing both resins is heated and melted in an extruder and extruded into a film from a T-die, and then cooled and solidified on a rotating cooling drum using a known casting method such as air knife casting or electrostatic casting to form an unstretched film. The average thickness of the unstretched film is not particularly limited, but is generally about 15 to 500 μm, and preferably 50 to 300 μm. By setting the thickness within such a range, the stretching step can be carried out more efficiently.

[0044] Furthermore, the obtained unstretched film is allowed to absorb water so that the moisture content becomes 2 to 10% by mass. The unstretched film before absorbing water usually has a moisture content of 0.1% by mass, and in the conventional technology, unstretched films with such a moisture content are stretched. In contrast, the present invention is characterized in that moisture is added to the unstretched film to adjust the moisture content to the above range. That is, in the present invention, the moisture content of the unstretched film must be 2 to 10% by mass as described above, and is preferably 3.5 to 8.5% by mass. If the moisture content of the unstretched film is less than 2% by mass, the amount of moisture that acts as a plasticizer is small, and the stress during stretching is high. As a result, large or numerous voids are generated between the polyamide resin in the film and the polyester-based thermoplastic elastomer particles dispersed therein, resulting in high film haze and frequent breakage of the film. On the other hand, if the moisture content exceeds 10% by mass, the unstretched film will have large thickness unevenness, and the stretched film obtained through the stretching process will also have large thickness unevenness and will have poor bending resistance.

[0045] The method for adjusting the moisture content is not particularly limited as long as it can increase the moisture content of the unstretched film. For example, any of a method of spraying water or steam onto the unstretched film, a method of applying water to the unstretched film with a roller, a method of immersing the unstretched film in water, etc. can be used. For example, a method of immersing the unstretched film in a water tank for a certain period of time can be preferably used. The water used to adjust the moisture content may be any of pure water, tap water, etc., and is not particularly limited. In addition, other components may be dispersed or dissolved in the water as long as they do not impede the effects of the present invention. The pH of the water used to adjust the moisture content is preferably 6.5 to 9.0. The temperature of the water is preferably 20 to 70° C., more preferably 30 to 65° C., and even more preferably 40 to 55° C. If the temperature of the water is less than 20° C., it may be difficult to adjust the moisture content in a short time. If the temperature of the water exceeds 70° C., the unstretched film is likely to wrinkle, the stretching becomes non-uniform, the quality of the stretched film is reduced, and problems such as the film being cut during stretching and the film end coming off the grip are likely to occur, resulting in reduced operability. The unstretched film is preferably immersed in the water tank for 0.5 to 10 minutes.

[0046] Next, the step (b) will be described. Step (b) is a step of applying a resin layer forming liquid containing a polyvinylidene chloride resin to at least one surface of an unstretched film that has been allowed to absorb water so that the moisture content is 2 to 10% by mass. A resin layer forming liquid containing polyvinylidene chloride resin is applied to at least one surface of an unstretched film whose moisture content has been adjusted to the above range, and the film is then stretched in the next step, whereby the adhesion strength between the polyamide film and the resin layer can be made 0.5 N / cm or more.

[0047] The method for applying a resin layer-forming liquid to provide a resin layer containing a polyvinylidene chloride resin on a polyamide film is not particularly limited, but a conventional method such as gravure roll coating, reverse roll coating, wire bar coating, air knife coating, die coating, or curtain die coating can be used. The polyamide film may be subjected to a corona discharge treatment or the like immediately before the above coating.

[0048] The unstretched film coated with the resin layer-forming liquid containing polyvinylidene chloride resin is preferably subjected to a preheating (drying) step prior to the stretching step. The preheating temperature is preferably 180 to 250°C, more preferably 190 to 240°C, even more preferably 200 to 230°C, and most preferably 210 to 230°C. If the preheating temperature is less than 180°C, the unstretched film will be difficult to obtain the film temperature required for stretching, resulting in high stretching stress, which will cause the polyamide resin in close contact with the polyester-based thermoplastic elastomer to suddenly peel off due to the stretching stress, resulting in large or numerous voids in the film, which may increase the porosity and the haze. In addition, neck stretching may occur, bowing may become prominent, and breakage may occur frequently. On the other hand, if the preheating temperature exceeds 250°C, the evaporation rate of the absorbed water in the unstretched film will be too high, and as a result, the film will be draw-stretched and molecular orientation will be difficult, so that the obtained stretched film will tend to have uneven thickness and will also tend to have poor bending resistance.

[0049] The method of preheating the unstretched film is not limited. For example, it is preferable to preheat the unstretched film by setting the temperature of hot air blown onto the film traveling through the preheating zone of the stretching machine to the above-mentioned temperature range. The time during which the unstretched film travels through the preheating zone (preheating time) is preferably 0.5 to 5 seconds.

[0050] Step (c) will now be described. The unstretched film produced as described above is stretched in a stretching step. The stretching method is not particularly limited, and any of the following methods can be applied: tubular method, tenter type simultaneous biaxial stretching method, tenter type sequential biaxial stretching method, etc. The tubular method is advantageous in that the equipment cost is lower than other methods, but it is difficult to improve the thickness accuracy of the film, and the tenter type biaxial stretching method is superior in terms of quality stability, dimensional stability, and productivity. Therefore, the tenter type biaxial stretching method is preferred as a method for producing the laminated film of the present invention, and the tenter type simultaneous biaxial stretching method is particularly preferred as a method for producing a film having the above elastic modulus and elastic modulus ratio, since the variation in physical property values ​​and distortion at the center and ends of the film tend to be small.

[0051] As described above, by adjusting the unstretched film to a specific moisture content and then stretching and heat setting the film, the stretching stress during stretching can be suppressed, and the polyamide resin that is in close contact with the polyester-based thermoplastic elastomer can be stretched without peeling due to the stretching stress, and the formation of large or numerous voids in the film can be effectively suppressed or prevented.

[0052] In the stretching step, the unstretched film coated with the resin layer forming liquid containing polyvinylidene chloride resin is biaxially stretched so that the stretching ratio in the length direction (MD stretching ratio, X) and the stretching ratio in the width direction (TD stretching ratio, Y) are each in the range of 2.2 to 3.8 times, and the stretching ratio ratio (X / Y) is 0.8 to 1.2. In particular, it is preferable that X and Y are each 2.3 to 3.7 times, and X / Y is preferably 0.9 to 1.1. If either X or Y is less than 2.2 times, the unstretched film is not stretched sufficiently, and the resulting laminated film has a low elastic modulus and large thickness unevenness as a result of insufficient crystallization of the film. As a result, the film has poor bending resistance, and may also have poor impact strength, tensile strength, tensile elongation, etc. On the other hand, if either X or Y is more than 3.8 times, the film is oriented and crystallized too much, and the resulting laminated film tends to have a high elastic modulus and is prone to breaking during the stretching process. If the stretching ratio (X / Y) is outside the above range, the resulting laminated film will tend to have large anisotropy in elastic modulus, and will have reduced bending resistance and abrasion resistance. The product of the stretching ratios (X×Y) is preferably 8.5 to 11.0, and more preferably 9.0 to 10.0. If the product of the stretching ratios (X×Y) is less than 8.5, the resulting laminated film may have a low elastic modulus and reduced abrasion resistance. On the other hand, if the product of the stretching ratios (X×Y) is more than 11.0, the resulting laminated film may have a high elastic modulus and reduced bending resistance.

[0053] The stretching temperature is preferably 170 to 230° C., and more preferably 180 to 220° C. If the stretching temperature is less than 170° C., it is difficult to obtain the film temperature required for stretching, so that the stretching stress increases, and the physical properties of the laminated film, such as flex resistance and impact strength, decrease, and breakage occurs frequently. On the other hand, if the stretching temperature exceeds 230° C., the film temperature becomes too high, resulting in draw stretching, which makes it difficult to achieve molecular orientation, and therefore the physical properties of the resulting laminated film, such as impact strength, decrease.

[0054] The biaxially stretched laminate film is preferably heat-set at a temperature of 150 to 220°C in the tenter in which the stretching process was performed, and, if necessary, is subjected to a relaxation process in the MD and / or TD in the range of 0 to 10%, preferably 2 to 6%. EXAMPLES

[0055] The present invention will now be described in detail with reference to examples. The methods for evaluating various physical properties in the following examples and comparative examples are as follows.

[0056] <Relative viscosity> Polyamide resin pellets were dissolved in 96% sulfuric acid to a concentration of 1 g / dl, and the measurement was carried out at a temperature of 25°C.

[0057] <Moisture percentage> The unstretched film before stretching was sampled, placed in a weighing bottle, and then dried at 150° C. for 20 hours, and the mass was calculated from the change in mass before and after drying.

[0058] <Operability> The state of the unstretched film passing through the water tank was visually observed to judge the occurrence of wrinkles, meandering, etc. The film was rated on the following three-level scale of "○", "△", and "×". "○" and "△" are considered acceptable, with "○" being preferred. ◯: No wrinkles or meandering occurs in the unstretched film during travel △: Stretching is possible, but wrinkles, meandering, etc. occur in the unstretched film during running. ×: The unstretched film frequently develops wrinkles, meanders, etc. during travel, and the stretched film frequently breaks.

[0059] <Caprolactam monomer extraction amount in film> [Preparation of measurement samples] The obtained laminated film was freeze-pulverized, 0.5 g was precisely weighed, and placed in a 10 ml headspace bottle, 10 ml of ultrapure water was added, and the bottle was sealed with a butyl rubber stopper and an aluminum cap, after which extraction was carried out in a boiling water bath (100°C) for 2 hours. After cooling, the bottle was filtered through a 0.45 μm disk filter to prepare a measurement sample. [Creating a calibration curve] 0.1 g of caprolactam was dissolved in 100 ml of ultrapure water to make a 1000 ppm solution, which was then further diluted to prepare standard solutions of 100, 50, 20, 10, 5, and 2 ppm. [HPLC conditions] Apparatus: Hewlett Packard HP1100 HPLC system, column: Waters Pureisil 5 μm C18 120 Å 4.6 mm × 250 mm (40 ° C), detector: UV 210 nm, injection volume: 10 μl, flow rate: 0.7 ml / min, elution: methanol / water (volume ratio: 35 / 75) solution for 12 minutes, then switched to methanol / water (volume ratio: 100 / 0) solution over 3 minutes and run for 30 minutes, then switched to methanol / water (volume ratio: 35 / 75) solution over 5 minutes and run for 20 minutes. [Calculation method] The mass of the monomer in the sample was calculated from the monomer concentration of the sample detected under the above conditions, and the value divided by the mass of the film was determined as the amount of monomer extracted (mass %).

[0060] <Elastic modulus, elastic modulus ratio> The obtained laminated film was left for 2 hours in an environmental test room adjusted to 23°C and 50% RH, and then cut into strips of 150 mm length (gauge distance 100 mm) and 10 mm width in the measurement direction of the MD and TD of the film to obtain samples. A tensile test was performed at a test speed of 500 mm / min using a tensile tester (AG-IS manufactured by Shimadzu Corporation) equipped with a load cell for measuring 1 kN and a sample chuck. The elastic modulus was calculated from the gradient of the load-elongation curve, and the elastic modulus ratio (MD / TD) was calculated. Measurements were performed on 5 samples, and the average value of each was calculated.

[0061] <Cloudy> The haze was measured according to JIS K7136 using a haze meter manufactured by Nippon Denshoku Industries Co., Ltd. Measurements were performed on three samples, and the average value was calculated.

[0062] <Flexibility (Pinhole Resistance 1) (Flex Fatigue Test)> The obtained laminated film was left for 2 hours in an environmental test room adjusted to 5°C and 55% RH, and then subjected to a 1000-cycle bending fatigue test (torsion angle: 440°) using a Gelbo Flex Tester (BE-1005, manufactured by Tester Sangyo Co., Ltd.). The number of pinholes in the film sample (chuck distance 178 mm, diameter 89 mm) was determined by counting the number of places where ink penetrated on filter paper. Measurements were carried out on three samples, and the number of pinholes was measured at 500 cm 2 The average number of pinholes per sample was calculated.

[0063] <Puncture strength (pinhole resistance 2)> The obtained laminated film was left for 2 hours in an environmental test room adjusted to 5℃ and 55% RH, and then the film was tensioned and fixed to a doughnut-shaped plate frame with an inner diameter of 30 mm, and a semicircular needle with a diameter of 1.0 mm and a tip radius of 0.5 mm was placed perpendicularly to the sample surface and pierced into the center of the sample at a speed of 50 mm / min, and the maximum load until the needle penetrated was measured as the strength at which the film broke. Measurements were performed on 5 samples, and the average strength value per 1 μm of film thickness was calculated.

[0064] <Abrasion resistance (pinhole resistance 3)> The laminate film prepared by the method described in the <Adhesion Strength> section below was left for 2 hours in an environmental test room adjusted to 5°C and 55% RH, then folded in four so that the polyamide film surface was on the outside, and the top of the folded film was rubbed with a basis weight of 400 g / m2 in a Gakushin type friction tester. 2 After contacting the film vertically with a piece of cardboard, a load of 50 g was applied to the film and it was fixed to a jig. The cardboard was slid 120 mm in the lengthwise direction of the folded film at 30 times per minute, and the occurrence of pinholes was checked every 10 times, and the number of times of sliding at which a pinhole occurred was recorded. The test was carried out on three samples, and the wear resistance was evaluated based on the number of times of sliding with the smallest number of times. In practice, the number of times of sliding until pinholes occur is required to be 150 or more, and 250 or more is preferable. The occurrence of pinholes was judged by dropping ethyl acetate onto the apex of the folded film that had been in contact with the cardboard and observing whether or not the ethyl acetate penetrated onto the white paper.

[0065] <Thickness unevenness> The thickness was measured across the entire width of the laminated film at 10 cm intervals along the width direction using a β-ray transmission thickness meter, and the thickness unevenness was calculated using the following formula and rated on a three-level scale as follows: "○" and "△" are acceptable, with "○" being preferred. Thickness unevenness = (maximum thickness along the width direction - minimum thickness along the width direction) ÷ average thickness × 100 ○: 10% or less △: Over 10% and 15% or less ×: More than 15%

[0066] <Oxygen permeability> The gas barrier properties were evaluated by measuring the oxygen permeability of the laminated film in an atmosphere of 20°C and 90% RH using an oxygen barrier measuring device (OX-TRAN 2 / 20) manufactured by Mocon. The measurements were carried out on two samples, and the average value was calculated. 2 ·d·MPa) is considered to be acceptable. 2 It is preferable that the compressive strength is less than 1.0 MPa.

[0067] <Strong adhesion> A urethane adhesive (DIC Corporation, Dick Dry LX-401A / SP-60) was applied to the surface of the resin layer of the laminated film at a dry coating weight of 3.0 g / m 2 After that, a heat treatment was performed at 80° C. Then, an unstretched polyethylene film (TUX MCS, 50 μm, manufactured by Mitsui Chemicals Tocello Co., Ltd.) was dry laminated on the adhesive surface after the heat treatment at a nip pressure of 490 kPa on a metal roll heated to 80° C. Furthermore, the adhesive was subjected to aging as recommended to obtain a laminate film. A 15 mm wide test piece was taken from the obtained laminate film, and the interface between the polyethylene film and the resin layer at the end of the test piece was peeled off in an atmosphere of 5°C and 55% RH.Then, the laminate strength was measured using a tensile tester (Shimadzu Corporation AGS-100G) at a tensile speed of 300 mm / min, with the polyethylene film and the laminate film forming a T-shape. In this laminate strength measurement, peeling occurs at the interface between the resin layer and the polyamide film, or at the interface between the polyethylene film and the resin layer. When there is no peeling between the polyamide film and the resin layer in the sample after strength measurement, the peel strength between the polyamide film and the resin layer is considered to be at least equal to or greater than this measured value. An adhesive strength of 0.5 N / cm or more is considered to be acceptable.

[0068] <Strong seal> The laminate film prepared by the method described above in <Adhesion strength> was cut into two pieces measuring 200 mm x 300 mm, and the polyethylene films were joined together and the three sides were heat sealed at a width of 10 mm to prepare a three-sided bag. The sealing conditions were 160°C x 1 second. A 15mm wide test piece of the sealed portion was cut out from the obtained three-sided bag, and the seal strength of the end of the test piece (laminated film portion) was measured at a tension speed of 300mm / min using a tensile tester (Shimadzu Corporation AGS-100G) in an atmosphere of 5°C and 55% RH. The seal strength was evaluated on the following three-level scale. "○" and "△" are acceptable (i.e., 25N / cm or more is acceptable), and "○" is preferable (i.e., 35N / cm or more is preferable). ○:35N / cm or more △: 25N / cm or more, less than 35N / cm ×: Less than 25N / cm

[0069] <Drop resistance (bag breakage resistance)> The three-sided bag prepared by the method described above in <Seal strength> was filled with 1000 ml of water, the air inside the bag was released, and the remaining side was heat-sealed at a width of 10 mm to prepare a sealed test sample. The sealing conditions were 160°C x 1 second. Test A was performed by dropping a test sample from a height of 1.2 m above a horizontally placed 0.5 mm thick smooth SUS plate so that one film side of the test sample hits the SUS plate, and then test B was performed by dropping the test sample so that one short side of the test sample hits the SUS plate, alternately until the test sample broke, and the number of times tests A and B were dropped until the test sample broke was measured. Note that the test sample has two film sides and two short sides, and the same film side and the same short side were dropped so that they hit the SUS plate. Three samples were evaluated, and the average value was calculated. The test was performed in a 5°C, 55% RH atmosphere and a -2°C atmosphere, and the test sample was left to stand in the atmosphere for 3 hours before the test was performed. In a refrigerated environment of 5°C and 55% RH, the number of times required until the bag breaks is essentially 70 or more, preferably 150 or more, and more preferably 200 or more. In a freezer environment of -2°C, the number of times required until the bag breaks is essentially 50 or more, preferably 100 or more, and more preferably 150 or more.

[0070] The raw materials used in the examples and comparative examples are as follows.

[0071] [Polyamide resin] 100 parts by mass of ε-caprolactam, 0.12 parts by mass of benzoic acid (10 mmol / kg relative to ε-caprolactam), and 3 parts by mass of water were added to a sealed reaction vessel equipped with a stirrer, and the temperature was raised to carry out a polycondensation reaction at a pressure of 0.5 MPa and a temperature of 260°C. The mixture was discharged from the reaction vessel, cut into chips, refined, and dried to obtain a polyamide resin. The relative viscosity of the polyamide resin chips was 3.03. [Master Chip] A master chip was prepared by melt-mixing 100 parts by mass of polyamide resin and 6 parts by mass of silica fine particles (Syloid SY-150, manufactured by Mizusawa Industrial Chemicals).

[0072] [Polyester-based thermoplastic elastomer] Primalloy: Mitsubishi Chemical Primalloy AP GQ131 (MODIC GQ131) Hytrel: Hytrel 5577 manufactured by Toray DuPont [Polyamide-based thermoplastic elastomer] PEBAX: Arkema PEBAX 3533 [Olefin copolymer] · Rexpearl: Rexpearl ET230X manufactured by Japan Polyethylene Corporation

[0073] Example 1 Polyamide resin, Primalloy, a polyester-based thermoplastic elastomer, and master chips were blended so that the Primalloy content was 4.0% by mass and the inorganic microparticle content was 0.05% by mass. The blend was then placed in an extruder and melted in a cylinder heated to a mixing start temperature of 190°C and a cylinder outlet temperature of 230°C. The mixture was extruded into a sheet from a T-die orifice and rapidly cooled by contacting it with a rotating drum cooled to 10°C, obtaining an unstretched film with a thickness of 250 μm. Next, as a moisture content adjustment step, the unstretched film was introduced into a water bath set at pH 7.9 and temperature 53° C. and immersed in water for 1 minute to absorb water, thereby adjusting the moisture content of the film to 5.8% by mass. Next, PVDC latex (Saran Latex L536B (solid content concentration 49 mass%) manufactured by Asahi Kasei Corporation) was applied to one side of the water-absorbed unstretched film by air knife coating, and the film was dried for 30 seconds by an infrared irradiator at a temperature of 110°C to evaporate the water in the latex. The unstretched film laminated with a resin layer containing PVDC was introduced into a simultaneous biaxial stretching machine, preheated at 220°C for 2 seconds, and then subjected to simultaneous biaxial stretching at 195°C with an MD stretch ratio (X) of 3.0 and a TD stretch ratio (Y) of 3.3. Subsequently, the film was heat-treated at a temperature of 210°C and relaxed by 5% in the transverse direction to obtain a laminated film with a polyamide film thickness of 25 μm and a resin layer thickness of 1.5 μm.

[0074] Examples 2 to 14, 16 to 19, Comparative Examples 1 to 5, 7, 9 to 11, 13 A laminated film was obtained in the same manner as in Example 1, except that the type and content of the elastomer and the film production conditions were changed as shown in Tables 1 and 3. In Example 9, Saran Latex L549B (solid content concentration 48% by mass) manufactured by Asahi Kasei Corporation was used as the PVDC latex.

[0075] Example 15 In the same manner as in Example 1, an unstretched film having a thickness of 250 μm was obtained. Next, as a moisture content adjustment step, the unstretched film was introduced into a water bath set at pH 7.9 and temperature 53° C. and immersed in water for 1 minute to absorb water, thereby adjusting the moisture content of the film to 5.8% by mass. Next, the water-absorbed unstretched film was longitudinally stretched at 55°C with an MD stretching machine consisting of a group of heating rollers with different peripheral speeds at an MD stretching ratio (X) of 3.0 times. After that, PVDC latex (Saran latex L536B (solid content concentration 49 mass%) manufactured by Asahi Kasei Corporation) was applied to one side of the longitudinally stretched film by gravure coating. Furthermore, this longitudinally stretched film was preheated at 180°C for 1 second, and then transversely stretched at 180°C with a TD stretching ratio (Y) of 3.3 times, thereby performing a successive stretching process. After that, the temperature was gradually increased in the tenter, and the film was heat-treated at a maximum temperature of 210° C., and then 2% relaxation was performed in the TD at 210° C. After that, the film was cooled to 100° C., and a laminated film having a thickness of 25 μm and a resin layer having a thickness of 1.5 μm was obtained.

[0076] Comparative Example 6 A laminated film having a thickness of 25 μm and a resin layer having a thickness of 1.5 μm was obtained in the same manner as in Example 1, except that an aqueous PVA solution (polyvinyl alcohol JF-05 manufactured by Japan Vinyl Acetate & Poval Co., Ltd., saponification degree 98 to 99 mol%, concentration 10 mass%) was applied to one side of the water-absorbed unstretched film instead of applying PVDC latex.

[0077] Comparative Example 8 The water-absorbed unstretched film was dried using an infrared irradiator at 110°C for 30 seconds to adjust the moisture content of the unstretched film to 1.3 mass%. In the same manner as in Example 1, except that, a 25 μm-thick laminated film having a 1.5 μm-thick resin layer laminated thereon was obtained.

[0078] Comparative Example 12 After the moisture adjustment step, a polyamide-based film having a thickness of 25 μm was obtained without laminating a polyvinylidene chloride resin layer in the same manner as in Example 1. The obtained film was coated with PVDC latex to a thickness of 1.5 μm, and dried at a drying temperature of 110° C. for 15 seconds to obtain a laminated film.

[0079] The configurations, production conditions, and evaluation results of the laminated films obtained in Examples 1 to 19 and Comparative Examples 1 to 13 are shown in Tables 1 to 4.

[0080] [Table 1]

[0081] [Table 2]

[0082] [Table 3]

[0083] [Table 4]

[0084] As is clear from Tables 1 to 4, the laminate films of Examples 1 to 19 have a polyamide film containing a polyester thermoplastic elastomer within the range specified in the present invention and a resin layer containing PVDC laminated thereon, and therefore even in a low-temperature environment, they have excellent adhesion between the polyamide film and the resin layer, excellent pinhole resistance such as bending resistance, puncture strength, and abrasion resistance, and also have excellent gas barrier properties and transparency. In addition, packages using the laminate films have excellent bag rupture resistance.

[0085] On the other hand, the laminated film of Comparative Example 1 had poor bending resistance and bag-breaking resistance in a low-temperature environment because the polyamide film did not contain a polyester thermoplastic elastomer, and the laminated film of Comparative Example 2 had a polyester thermoplastic elastomer content lower than the range specified in the present invention. The laminated film of Comparative Example 3 had a polyester thermoplastic elastomer content higher than the range specified in the present invention, so the haze value was high and the transparency was poor, and the adhesion between the polyamide film and the resin layer in a low-temperature environment was poor, resulting in poor bag-breaking resistance. The polyamide film of Comparative Example 4 contains an olefin copolymer instead of a polyester thermoplastic elastomer, so wrinkles occurred in the unstretched film during the moisture content adjustment process, and the laminated film was stretched non-uniformly, resulting in very large thickness unevenness and frequent breaks, which led to poor operability, so the physical properties were not evaluated. The laminated film of Comparative Example 5 contains an amide thermoplastic elastomer instead of a polyester thermoplastic elastomer, so the adhesion between the polyamide film and the resin layer in a low-temperature environment was poor, and the bag-break resistance was poor. The laminated film of Comparative Example 6 had a resin layer containing PVA instead of PVDC, and therefore had poor gas barrier properties. Furthermore, the adhesion between the polyamide film and the resin layer in a low-temperature environment was poor, resulting in poor bag-rupture resistance. The laminated film of Comparative Example 7 was inferior in transparency because the polyamide film did not pass through the moisture content adjustment process, and the amount of caprolactam monomer extracted was large, so the adhesion between the polyamide film and the resin layer in a low-temperature environment was low, and further, the flex resistance and bag-breaking resistance were poor. The laminated film of Comparative Example 8 was produced by stretching an unstretched film with a moisture content lower than the range specified in the present invention, so the transparency was poor and the flex resistance and bag-breaking resistance in a low-temperature environment were poor. The laminated film of Comparative Example 9 was produced by stretching a film with a moisture content higher than the range specified in the present invention, so the thickness was large and the flex resistance, puncture strength, abrasion resistance, and bag-breaking resistance in a low-temperature environment were poor. The laminated film of Comparative Example 10 had a small longitudinal stretch ratio, and therefore had large thickness unevenness, and was inferior in bending resistance, puncture strength, abrasion resistance, and bag breakage resistance in a low-temperature environment. The laminated film of Comparative Example 11 had a large longitudinal stretch ratio, and therefore was frequently broken during the widthwise stretching process, resulting in poor operability, and therefore the physical properties were not evaluated. In the laminated film of Comparative Example 12, a polyvinylidene chloride resin layer was laminated onto a moisture-adjusted and stretched polyamide film by a post-coating method, and therefore the adhesion between the polyamide film and the resin layer was poor, resulting in poor resistance to bag rupture. The laminated film of Comparative Example 13, like Comparative Example 1, had poor bending resistance and bag rupture resistance in a low temperature environment because the polyamide film did not contain a polyester thermoplastic elastomer.

Claims

1. A laminated film having a resin layer provided on at least one surface of a polyamide film, The polyamide-based film is a stretched film made of a polyamide-based resin composition containing 1.0 to 10.0% by mass of a polyester-based thermoplastic elastomer, The resin layer contains a polyvinylidene chloride resin, A laminated film characterized by satisfying the following conditions (A) to (C). (A) The haze of the laminated film is 10% or less. (B) The adhesive strength between the resin layer and the polyamide film in an atmosphere of 5° C. and 55% RH is 0.5 N / cm or more. (C) The number of pinholes in the laminated film after 1000 repeated bending fatigue tests in an atmosphere of 5° C. and 55% RH is 5 / 500 cm ２ The following is the result.

2. 2. The laminated film according to claim 1, wherein the amount of caprotactam monomer extracted is 0.1% by mass or less.

3. 3. The laminate film according to claim 1, wherein the laminate, in which a sealant resin layer is laminated on the laminate film, can be dropped 70 or more times before breaking in a bag drop test under an atmosphere of 5° C. and 55% RH.

4. A method for producing the laminated film according to any one of claims 1 to 3, comprising the steps of: (a) A step of allowing an unstretched film made of a polyamide resin composition containing 1.0 to 10.0% by mass of a polyester thermoplastic elastomer to absorb water so that the moisture content is 2 to 10%. (b) A step of applying a resin layer forming liquid containing a polyvinylidene chloride resin to at least one surface of the water-absorbed unstretched film. (c) A process of preheating the unstretched film coated with the resin layer-forming liquid at 180 to 250°C, and then biaxially stretching the preheated film at 170 to 230°C so that the MD stretch ratio (X) and the TD stretch ratio (Y) are each in the range of 2.2 to 3.8 times and the stretch ratio ratio (X / Y) is 0.8 to 1.2.

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