Composite multilayer film and multilayer structure using the same, and packaging material for retort

Abstract

To provide a composite multilayer film which is excellent in gas barrier property under a high humidity condition immediately after retort treatment at high temperature for a long period of time.SOLUTION: A composite multilayer film has a barrier layer (A) on the outermost layer, and has a protective layer (P) and an inorganic layer (I) adjacent to each other provided on the exposed surface of the barrier layer (A) of the multilayer film having such a structure that the barrier layer (A), an adhesive layer (B) and a core layer (C) are adjacently stacked in this order, wherein the barrier layer (A) is composed of only a resin composition (a) which contains EVOH (a1) and PA (a2) and has a mass ratio (a1 / a2) of 55 / 45 to 98 / 2, the adhesive layer (B) contains an adhesive resin (b) having a melting point of 130 to 170°C as a main component, the core layer (C) contains a polyolefin resin (c) having a melting point of 130 to 170°C as a main component, the resin composition (a) contains 40 to 500 ppm of alkali metal ions (d), and the composite multilayer film does not have a layer containing a resin having a melting point lower than 130°C as a main component, and a metal layer having average thickness of 1 μm or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a composite multilayer film, a multilayer structure including the composite multilayer film, and a packaging material for retort including the multilayer structure.

[0002] Packaging materials for long-term preservation of foods often require gas barrier properties such as oxygen barrier properties. By using a packaging material with high gas barrier properties, oxidation of foods by oxygen and propagation of microorganisms can be suppressed. As foods with an extended edible period, the number of retort foods, which are obtained by filling foods into a packaging material and then performing heat sterilization treatment under pressure (hereinafter sometimes simply abbreviated as "retort treatment"), is increasing. For the gas barrier layer for retort packaging materials, a property that the gas barrier property does not deteriorate after heat treatment (hereinafter sometimes simply abbreviated as "retort resistance") is required, and gas barrier films obtained by laminating a transparent vapor deposition layer of silica (silicon oxide) or alumina (aluminum oxide) on an aluminum foil or a polyester film with high heat resistance are generally used. When using an aluminum foil, light-shielding properties can be imparted in addition to gas barrier properties, and when using a gas barrier film laminated with a vapor deposition layer of silica or alumina, visibility of the contents can be imparted (Patent Documents 1 and 2).

[0003] Ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as "EVOH"), which is widely used as a gas barrier resin for packaging materials, exhibits gas barrier properties by crystallization and densification due to hydrogen bonding between hydroxyl groups in the molecule, but there are problems such as a decrease in gas barrier properties due to EVOH absorbing water during retort treatment. As a means for suppressing a decrease in gas barrier properties due to retort treatment, Patent Document 3 reports that a resin composition produced by mixing EVOH and polyamide (hereinafter sometimes abbreviated as "PA") has improved retort resistance compared to EVOH alone and can be preferably used as a packaging material for retort. Further, Patent Document 4 reports that a resin composition produced by mixing a specific modified EVOH and polyamide has excellent retort resistance and bending resistance.

[0004] On the one hand, in recent years, due to environmental problems and waste problems, the demand for so-called post-consumer recycling (hereinafter sometimes simply abbreviated as recycling), which involves collecting and recycling packaging materials consumed in the market, has been increasing globally. In recycling, the general process is to cut the collected packaging materials, separate and wash them if necessary, and then melt and mix them using an extruder. In this regard, it is required that the packaging material be composed of a single material as much as possible (monomaterialization), so that high-purity and high-quality recycled raw materials can be obtained. In particular, aluminum foil and polyester film are known to inhibit recyclability because they are inferior in compatibility and dispersibility with polyolefin-based resins widely used as packaging materials. Patent Document 5 describes that a multilayer structure having a structure in which a resin layer composed of a resin composition containing specific EVOH and PA and an inorganic layer typified by vapor deposition are laminated adjacent to each other has excellent gas barrier properties and appearance even after stretching treatment and retort treatment followed by bending treatment. Furthermore, a multilayer structure with a high thickness ratio of polypropylene-based resin considering monomaterialization is described.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the multilayer structure with a high thickness ratio of the polypropylene-based resin described in Patent Document 5, although the gas barrier property tends to recover over time after retort treatment, particularly when the retort treatment temperature is high (e.g., 135 °C) and the retort treatment time is long (e.g., 120 minutes), there is a problem that the gas barrier property immediately after retort treatment significantly decreases. Furthermore, when the packaging material is stored in a wet state or under high humidity conditions after retort treatment, there is a problem that the recovery of the gas barrier property is delayed and the storability of the contents is inferior. Since the edible period of retort foods largely depends on the cumulative amount of oxygen invading through the packaging material, even when the gas barrier property recovers over time after retort treatment, if the gas barrier property immediately after retort treatment significantly decreases or if it takes a long time for the gas barrier property to recover, the extension of the edible period of retort foods may be restricted.

[0007] The present invention has been made to solve the above problems, and provides a composite multilayer film excellent in gas barrier property under high humidity conditions immediately after retort treatment at high temperature (e.g., 135 °C) and for a long time (e.g., 120 minutes), even if it is a composite multilayer film having a high thickness ratio (e.g., 75% or more) of a polyolefin-based resin, a multilayer structure including the composite multilayer film, and a retort packaging material including the multilayer structure.

Means for Solving the Problems

[0008] The inventors of the present invention have found that a composite multilayer film having a protective layer and an inorganic layer adjacent to each other on the surface side of the barrier layer of a multilayer film having a barrier layer made of a resin composition containing specific EVOH and polyamide on the outermost surface has excellent gas barrier property even immediately after high-temperature and long-time retort treatment, and have also found that its excellent gas barrier property is exhibited even under high humidity conditions. Furthermore, by specifying the materials and configuration to be used, it has been found that in addition to the above characteristics, the appearance characteristics and recyclability are also excellent, and the present invention has been completed. That is, the above problems are [1] A multilayer film having a barrier layer (A) on the outermost surface, with the barrier layer (A), adhesive layer (B), and core layer (C) laminated adjacent to each other in this order, is provided with a protective layer (P) and an inorganic layer (I) adjacent to each other on the surface side of the barrier layer (A). The barrier layer (A) consists only of a resin composition (a) containing an ethylene-vinyl alcohol copolymer (a1) (hereinafter may be abbreviated as "EVOH (a1)") with an ethylene unit content of 20 to 50 mol% and a saponification degree of 90 mol% or more, and a polyamide (a2) (hereinafter may be abbreviated as "PA (a2)"), where the mass ratio (a1 / a2) of EVOH (a1) to PA (a2) is 55 / 45 to 98 / 2. The adhesive layer (B) mainly contains an adhesive resin (b) with a melting point of 130 to 170°C, and the core layer (C) mainly contains a polyolefin resin (c) with a melting point of 130 to 170°C. The resin composition (a) contains 40 to 500 ppm of alkali metal ions (d) and does not have a layer mainly composed of a resin with a melting point of less than 130°C and a metal layer with an average thickness of 1 μm or more; [2] The composite multilayer film of [1], wherein the protective layer (P) in the adjacent protective layer (P) and inorganic layer (I) is a protective layer (Pa) laminated at a position closer to the surface side of the barrier layer (A) of the multilayer film than the inorganic layer (I); [3] The composite multilayer film of [1], wherein the protective layer (P) in the adjacent protective layer (P) and inorganic layer (I) is a protective layer (Pb) laminated at a position farther from the surface side of the barrier layer (A) of the multilayer film than the inorganic layer (I); [4] The composite multilayer film of [1], wherein the protective layer (P) in the adjacent protective layer (P) and inorganic layer (I) includes a protective layer (Pa) laminated at a position closer to the surface side of the barrier layer (A) of the multilayer film than the inorganic layer (I), and a protective layer (Pb) laminated at a position farther from the surface side of the barrier layer (A) of the multilayer film than the inorganic layer (I), and is provided with a structure in which the protective layer (Pa), inorganic layer (I), and protective layer (Pb) are laminated adjacent to each other in this order on the surface side of the barrier layer (A); [5] The composite multilayer film of any one of [1] to [4], wherein the adhesive resin (b) mainly contains acid-modified polypropylene; [6] The composite multilayer film of any one of [1] to [5], wherein the polyolefin resin (c) contains polypropylene as a main component; [7] The composite multilayer film of any one of [1] to [6], wherein the inorganic layer (I) is an inorganic oxide vapor deposition layer mainly composed of alumina or silica; [8] The composite multilayer film of any one of [1] to [7], wherein the protective layer (P) is mainly composed of a water-soluble polyvinyl alcohol-based resin (K) or a water-dispersible polyurethane-based resin (L); [9] The composite multilayer film of any one of [1] to [8], wherein the protective layer (P) contains at least one selected from the group consisting of at least one metal compound (M) selected from the group consisting of metal alkoxides, hydrolyzates of metal alkoxides, and hydrolytic condensates of metal alkoxides, and at least one selected from the group consisting of layered inorganic compounds (N), and the total content thereof is 5 to 40% by mass;

[10] The composite multilayer film of any one of [1] to [9], wherein the resin composition (a) contains at least one polyvalent metal ion (e) selected from the group consisting of magnesium ions, calcium ions, and zinc ions in an amount of 10 to 500 ppm;

[11] The composite multilayer film of any one of [1] to

[10] , wherein the EVOH (a1) has a modified group containing a primary hydroxyl group represented by the following general formula (I); [Chemical formula] [In the formula, X represents a hydrogen atom, a methyl group, or a group represented by R 2 -OH. R 1 , R 2 each independently represents a single bond, an alkylene group having 1 to 9 carbon atoms, or an alkyleneoxy group having 1 to 9 carbon atoms, and the alkylene group and the alkyleneoxy group may contain a hydroxyl group, an alkoxy group, or a halogen atom.

[12] The composite multilayer film of

[11] , wherein R 1 in the general formula (I) is a single bond and X is a hydroxymethyl group;

[13] The composite multilayer film of

[11] or

[12] , wherein the content of the modified group containing the primary hydroxyl group in the EVOH (a1) is 0.3 mol% or more and less than 10 mol%;

[14] The multilayer film is any one of the composite multilayer films of [1] to

[13] that is not substantially stretched;

[15] The multilayer film is any one of the composite multilayer films of [1] to

[13] that is stretched 3 times or more and less than 12 times only in the substantially uniaxial direction;

[16] The multilayer film is any one of the composite multilayer films of [1] to

[13] that is stretched 3 times or more and less than 12 times in each of the biaxial directions;

[17] The adhesive resin (b) contains acid-modified polypropylene as a main component, the polyolefin resin (c) contains polypropylene as a main component, and the total average thickness ratio of the layers mainly composed of polypropylene-based resins to the average thickness of the composite multilayer film is 0.75 or more, any one of the composite multilayer films of [1] to

[16] ;

[18] A multilayer structure obtained by laminating any one of the composite multilayer films of [1] to

[17] and at least one resin layer (R) mainly composed of a thermoplastic resin (r);

[19] The thermoplastic resin (r) contains polypropylene resin as a main component, the multilayer structure of

[18] ;

[20] A packaging material for retort having the multilayer structure of

[18] or

[19] ;

[21] After retort treatment at 135 °C for 120 minutes, the oxygen transmission rate (under the conditions of 20 °C and 100% RH) measured by the method described in JIS K 7126-2:2006 is less than 2 cc / (m 2 ·day·atm), the packaging material for retort of

[20] ; is solved by providing the above.

Effects of the Invention

[0009] According to the present invention, even a composite multilayer film having a high thickness ratio of polyolefin-based resin can provide a composite multilayer film excellent in gas barrier properties immediately after high-temperature and long-time retort treatment. Further, by including the composite multilayer film, a multilayer structure excellent in gas barrier properties immediately after high-temperature and long-time retort treatment and a packaging material for retort using the same can be provided.

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described. In the following description, specific materials (such as compounds) may be exemplified as those that exhibit specific functions, but the present invention is not limited to embodiments using such materials. Further, unless otherwise specified, the exemplified materials may be used alone or in combination.

[0011] The composite multilayer film of the present invention has a barrier layer (A) on the outermost surface, and a protective layer (P) and an inorganic layer (I) adjacent to each other are provided on the surface side of the barrier layer (A) of the multilayer film having a structure in which the barrier layer (A), the adhesive layer (B), and the core layer (C) are laminated adjacent to each other in this order. The barrier layer (A) contains EVOH (a1) and PA (a2) having an ethylene unit content of 20 to 50 mol% and a saponification degree of 90 mol% or more, and the mass ratio (a1 / a2) of EVOH (a1) to PA (a2) is 55 / 45 to 98 / 2. The adhesive layer (B) mainly contains an adhesive resin (b) having a melting point of 130 to 170°C, and the core layer (C) mainly contains a polyolefin resin (c) having a melting point of 130 to 170°C. The resin composition (a) contains 40 to 500 ppm of alkali metal ions (d), and does not have a layer mainly composed of a resin having a melting point of less than 130°C and a metal layer having an average thickness of 1 μm or more.

[0012] The barrier layer (A) has gas barrier properties and can effectively block oxygen permeation from minute defects in the inorganic layer (I). Therefore, the composite multilayer film of the present invention can achieve high gas barrier properties. Further, on the surface side of the barrier layer (A), the protective layer (P) and the inorganic layer (I) are laminated adjacent to each other, so that high gas barrier properties are exhibited even immediately after retort treatment at high temperature for a long time. Also, both the adhesive layer (B) and the core layer (C) contain a resin having a melting point of 130 to 170°C as a main component. The polyolefin resin (c) contained in the core layer (C) and EVOH (a1) can be easily melt-mixed, and the adhesive resin (b) contained in the adhesive layer (B) also functions as a compatibilizer for EVOH (a1) and the polyolefin resin (c). Therefore, the composite multilayer film of the present invention having a structure in which the barrier layer (A), the adhesive layer (B), and the core layer (C) are laminated adjacent to each other in this order tends to have good recyclability. At this time, by containing 40 to 500 ppm of alkali metal ions (d) in the resin composition (a), the interlayer adhesiveness between the barrier layer (A) and the adhesive layer (B) and the gas barrier properties immediately after retort treatment at high temperature for a long time are improved, and the recyclability also tends to be good. Also, by specifying the materials and configuration to be used, it is possible to provide a composite multilayer film excellent in appearance characteristics and recyclability.

[0013] In the present specification, "adjacent" means that adjacent layers are directly laminated. Specifically, in the expression "the barrier layer (A), the adhesive layer (B), and the core layer (C) are laminated adjacent to each other in this order", the barrier layer (A), the adhesive layer (B), and the core layer (C) are laminated in this order, and it means that the barrier layer (A) and the adhesive layer (B) are directly laminated, and the adhesive layer (B) and the core layer (C) are directly laminated. "Main component" means a component contained in an amount exceeding 50% by mass. The "average thickness" of each layer other than the inorganic layer (I) means the average value of the thicknesses measured at any five locations. "ppm" means the content based on mass (mass ppm). "Polypropylene" means a homopolymer of propylene and a copolymer having 70 mol% or more of propylene units. "Acid-modified polypropylene" refers to a polymer obtained by modifying polypropylene with an acid. The acid-modified polypropylene may be a polymer in which at least one of an acidic group and an acid anhydride group is introduced into the polypropylene. "Polypropylene-based resin" refers to polypropylene and modified polypropylene (such as acid-modified polypropylene). Modified polypropylene refers to a polymer obtained by modifying polypropylene. "Acid-modified polyolefin" refers to a polyolefin obtained by modifying a polyolefin with an acid. "Polyolefin-based resin" refers to polyolefin and modified polyolefin (such as acid-modified polyolefin). Modified polyolefin refers to a polymer obtained by modifying a polyolefin. In a composite multilayer film or a multilayer structure, the "uppermost layer" or "outermost surface" does not mean to distinguish between the front and back, but refers to the exposed surface. That is, a multilayer film or a multilayer structure has two uppermost layers or outermost surfaces, respectively. In this specification, "consisting essentially of only" allows the inclusion of optional components within a range that does not affect the effects of the present invention, and "consisting of only" in this specification means excluding optional components other than unavoidably contained impurities. In this specification, the numerical range described using "~" means including the numerical values described before and after "~" as the lower limit value and the upper limit value. That is, "α~β" means "α or more and β or less". Also, in this specification, the upper limit value and the lower limit value of the numerical range (content, physical properties, etc.) can be combined as appropriate. "Recyclability" in this specification means that when the recovered product of the composite multilayer film, multilayer structure or retort packaging material of the present invention is melt-kneaded to produce a recovered composition, the coloring of the resin, the generation of lumps due to gelation, and the viscosity change of the resin are suppressed, and a recovered composition with excellent appearance can be efficiently produced, which can be evaluated by the recovery test described in the examples. As used herein, "immediately after retort treatment" means several hours later. For example, in the examples, measurement samples were prepared immediately after the retort treatment, and the measurement results "4 hours later" were used as the evaluation results of the barrier properties immediately after the retort treatment.

[0014] <Barrier layer (A) and resin composition (a)> The multilayer film constituting the composite multilayer film of the present invention contains EVOH (a1) with an ethylene unit content of 20 to 50 mol% and a saponification degree of 90 mol% or more, and PA (a2), and the mass ratio (a1 / a2) of EVOH (a1) to PA (a2) is 55 / 45 to 98 / 2. It has a barrier layer (A) consisting only of the resin composition (a) on the outermost layer, and the resin composition (a) contains 40 to 500 ppm of alkali metal ions (d). The content of EVOH (a1) in the resin composition (a) is preferably more than 50% by mass. Further, the resin composition (a) may contain at least one polyvalent metal ion (e) selected from the group consisting of magnesium ions, calcium ions, and zinc ions, and other components described later as optional components. Details will be described below.

[0015] <EVOH (a1)> The resin composition (a) contains a specific amount of EVOH (a1). By containing a specific amount of EVOH (a1) in the resin composition (a), the gas barrier property becomes good. EVOH (a1) is usually obtained by saponifying an ethylene-vinyl ester copolymer obtained by polymerizing ethylene and a vinyl ester. The ethylene unit content of EVOH (a1) is 20 to 50 mol%. When the ethylene unit content is 20 mol% or more, the melt moldability of EVOH (a1) and the pulverized product of the composite multilayer film containing EVOH (a1) is improved. The ethylene unit content is preferably 25 mol% or more, more preferably 30 mol% or more. On the other hand, when the ethylene unit content is 50 mol% or less, the gas barrier property of the composite multilayer film of the present invention is improved. The ethylene unit content is preferably 45 mol% or less, more preferably 40 mol% or less. Further, the saponification degree of EVOH (a1) is 90 mol% or more. The saponification degree means the ratio of the number of vinyl alcohol units to the total number of vinyl alcohol units and vinyl ester units in EVOH (a1). When the saponification degree is 90 mol% or more, the gas barrier property of the composite multilayer film of the present invention is improved. The saponification degree is preferably 95 mol% or more, more preferably 99 mol% or more, and even more preferably 99.9 mol% or more. The ethylene unit content and the saponification degree of EVOH (a1) are 1 determined by 1H-NMR measurement.

[0016] EVOH (a1) may be a mixture of two or more types of EVOH having different ethylene unit contents. In this case, the difference in ethylene unit contents between the EVOHs with the most different ethylene unit contents is preferably 30 mol% or less, more preferably 20 mol% or less, still more preferably 15 mol% or less, and may be 3 mol% or more. Similarly, EVOH (a1) may be a mixture of two or more types of EVOH having different saponification degrees. In this case, the difference in saponification degrees between the most different EVOHs is preferably 7 mol% or less, more preferably 5 mol% or less, and may be 0.5 mol% or more. When it is desired to achieve both high thermoformability and gas barrier properties at a higher level, EVOH (a1-1) having an ethylene unit content of 24 mol% or more and less than 34 mol% and a saponification degree of 99 mol% or more, and EVOH (a1-2) having an ethylene unit content of 34 mol% or more and less than 50 mol% and a saponification degree of 99 mol% or more are mixed so that the blending mass ratio (a1-1 / a1-2) is 60 / 40 to 90 / 10, and it is preferably used as EVOH (a1).

[0017] EVOH (a1) preferably has a modified group containing a primary hydroxyl group represented by the following general formula (I). The reason for this is that by having a modified group containing a primary hydroxyl group represented by the general formula (I), the fluidity of the polymer chain of EVOH is improved, so that during melt molding or secondary processing such as stretching, the stress in the resin can be effectively relaxed, and the adhesive reaction activity with the adjacent layer can be maintained. Thereby, especially when the multilayer film is a stretched film, the gas barrier property immediately after high-temperature and long-time retort treatment can be improved. From the viewpoint of making the effects of the present invention more remarkable, it is preferable that R1 in the general formula (I) is a single bond and X is a hydroxymethyl group. Further, the content of the modified group containing a primary hydroxyl group represented by the general formula (I) is preferably 0.3 mol% or more and less than 10 mol%. The modified group containing a primary hydroxyl group can be introduced by copolymerization or a polymer reaction.

Chemical formula

[0018] EVOH (a1) may contain monomer units other than ethylene units, vinyl ester units, vinyl alcohol units, and modified groups containing the primary hydroxyl group, as long as the effects of the present disclosure are not inhibited. The content of other monomer units is preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 1% by mass or less, and particularly preferably not substantially contained.Examples of such other monomers include α-olefins such as propylene, n-butene, isobutylene, 1-hexene; acrylic acid and its salts; unsaturated monomers having an acrylate group; methacrylic acid and its salts; unsaturated monomers having a methacrylate group; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts (e.g., quaternary salts); methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid and its salts, methacrylamidopropyldimethylamine and its salts (e.g., quaternary salts); vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, 2,3-diacetoxy-1-vinyloxypropane; vinyl cyanides such as acrylonitrile, methacrylonitrile; vinyl halides such as vinyl chloride, vinyl fluoride; vinylidene halides such as vinylidene chloride, vinylidene fluoride; allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane, allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, fumaric acid and their salts or esters; vinyl silane compounds such as vinyltrimethoxysilane; alkenes having an ester group such as isopropenyl acetate, 3-acyloxy-1-propene, 3-acyloxy-1-butene, 4-acyloxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4-acyloxy-2-methyl-1-butene, 4-acyloxy-3-methyl-1-butene, 3,4-diacyloxy-2-methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, 4,5-diacyloxy-1-pentene, 4-acyloxy-1-hexene, 5-acyloxy-1-hexene, 6-acyloxy-1-hexene, 5,6-diacyloxy-1-hexene, 1,3-diacetoxy-2-methylenepropane or their enolates, etc.

[0019] The MFR (at 190°C under a load of 2.16 kg) measured in accordance with JIS K7210 (2014) for EVOH(a1) is preferably 0.2 to 20 g / 10 min. The MFR of EVOH(a1) is more preferably 0.5 g / 10 min or more, and even more preferably 0.8 g / 10 min or more. On the other hand, the MFR of EVOH(a1) is more preferably 15 g / 10 min or less, even more preferably 10 g / 10 min or less, particularly preferably 5 g / 10 min or less, and may even be 3 g / 10 min or less. When the MFR of EVOH(a1) is within the above range, the melt moldability of EVOH(a1) and the pulverized product of the composite multilayer film containing EVOH(a1) is also improved.

[0020] <PA(a2)> The resin composition (a) contains a specific amount of PA (a2). When the resin composition (a) contains a specific amount of PA (a2), the retort resistance and the appearance after retort treatment tend to be good. Specific examples of PA (a2) used in the present invention include polycaproamide (nylon 6), poly-ω-aminoheptanoic acid (nylon 7), poly-ω-aminononanoic acid (nylon 9), polyundecanamide (nylon 11), polylauryl lactam (nylon 12), polyethylene diamine adipamide (nylon 26), polytetramethylene adipamide (nylon 46), polyhexamethylene adipamide (nylon 66), polyhexamethylene sebacamide (nylon 610), polyhexamethylene dodecamide (nylon 612), polyoctamethylene adipamide (nylon 86), polydecamethylene adipamide (nylon 106), caprolactam / lauryl lactam copolymer (nylon 6 / 12), caprolactam / ω-aminononanoic acid copolymer (nylon 6 / 9), caprolactam / hexamethylene diammonium adipate copolymer (nylon 6 / 66), lauryl lactam / hexamethylene diammonium adipate copolymer (nylon 12 / 66), ethylenediammonium adipate / hexamethylene diammonium adipate copolymer (nylon 26 / 66), caprolactam / hexamethylene diammonium adipate / hexamethylene diammonium sebacate copolymer (nylon 6 / 66 / 610), ethylenediammonium adipate / hexamethylene diammonium adipate / hexamethylene diammonium sebacate copolymer (nylon 26 / 66 / 610), polyhexamethylene isophthalamide (nylon 6I), polyhexamethylene terephthalamide (nylon 6T), hexamethylene isophthalamide / hexamethylene terephthalamide copolymer (nylon 6I / 6T), 11-aminoundecanamide / hexamethylene terephthalamide copolymer, polynonamethylene terephthalamide (nylon 9T), polydecamethylene terephthalamide (nylon 10T), polyhexamethylene cyclohexylamide, polynonamethylene cyclohexylamide, or those obtained by modifying these polyamides with aromatic amines such as methylene benzylamine and metaxylylenediamine.In addition, examples include metaxylylenediammonium adipate and the like. Among these, from the viewpoint of particularly improving the gas barrier property and appearance immediately after high-temperature and long-time retort treatment, it is preferably a polyamide resin mainly composed of caproamide. Specifically, it is preferable that 75 mol% or more of the structural units of PA(a2) are caproamide units. Among them, from the viewpoint of compatibility with EVOH(A), PA(a2) is preferably nylon 6.

[0021] The degree of polymerization of PA(a2) is preferably 1.7 to 5.0, more preferably 2.0 to 5.0, in terms of relative viscosity measured in accordance with JIS K6920-1(2018).

[0022] As the polymerization method of PA(a2), melt polymerization, interfacial polymerization, solution polymerization, bulk polymerization, solid-phase polymerization, or a combination of these methods can be adopted.

[0023] The mass ratio (a1 / a2) of EVOH(a1) to PA(a2) is 55 / 45 to 98 / 2, preferably 65 / 35 to 96 / 4, more preferably 75 / 25 to 94 / 6, and even more preferably 80 / 20 to 92 / 8. When the mass ratio (a1 / a2) is less than 55 / 45, the gas barrier property tends to be insufficient, and when the mass ratio (a1 / a2) exceeds 98 / 2, the gas barrier property immediately after retort treatment tends to be insufficient.

[0024] <Alkali metal ion (d)> The resin composition (a) contains 40 to 500 ppm of alkali metal ions (d). When the resin composition (a) contains alkali metal ions (d) within the above range, the interlayer adhesiveness with the adhesive layer (B) described later and the gas barrier property immediately after retort treatment at high temperature for a long time tend to improve, and the recyclability also tends to be good. When the alkali metal ions (d) are less than 40 ppm, the resin composition (a) tends to thicken during melt molding, which may cause appearance defects due to lumps and may also reduce the interlayer adhesiveness with the adhesive layer (B) described later. On the other hand, when the alkali metal ions (d) exceed 500 ppm, the resin composition (a) may decompose excessively or coloring may become a problem during melt molding. Also, when manufacturing a recovered composition by melt-kneading the recovered materials of the composite multilayer film, multilayer structure, and retort packaging material of the present invention, when the content of alkali metal ions (d) is 40 ppm or more, the generation of lumps can be suppressed, and the recyclability tends to improve. On the other hand, when the content of alkali metal ions (d) is 500 ppm or less, an excessive decomposition reaction during the production of the recovered composition can be suppressed, and the recyclability tends to improve. From this perspective, the lower limit of the content of alkali metal ions (d) is preferably 80 ppm, more preferably 120 ppm. The upper limit of the content of alkali metal ions (d) is preferably 400 ppm, more preferably 300 ppm. Also, by controlling the content ratio of alkali metal ions (d) and the carboxylic acid described later, the melt moldability and coloring resistance of the obtained resin composition (a) can be further improved.

[0025] Examples of the alkali metal ions (d) include ions of lithium, sodium, potassium, rubidium, and cesium. From the perspective of industrial availability, sodium or potassium ions are preferred. In particular, by using potassium ions, it may be possible to achieve both a high level of hue of the resin composition (a) and interlayer adhesiveness with the adhesive layer (B) described later. These may be used alone or in combination of two or more.

[0026] Examples of the alkali metal compound that provides the alkali metal ion (d) include aliphatic carboxylates, aromatic carboxylates, carbonates, hydrochlorides, nitrates, sulfates, phosphates, hydroxides, and metal complexes of alkali metals such as lithium, sodium, and potassium. Among them, aliphatic carboxylates and phosphates are more preferred because they are easy to obtain and handle. Preferred aliphatic carboxylates include acetates, caprylate salts, and stearate salts.

[0027] <Polyvalent metal ion (e)> The resin composition (a) preferably contains at least one polyvalent metal ion (e) selected from the group consisting of magnesium ions, calcium ions, and zinc ions in an amount of 10 to 500 ppm. When the polyvalent metal ion (e) is contained in an amount of 10 ppm or more, it tends to suppress appearance defects such as thickening and the generation of lumps during the melt molding of the resin composition (a). On the other hand, when the content of the polyvalent metal ion (e) is 500 ppm or less, it tends to suppress excessive decomposition and coloring during the melt molding of the resin composition (a). Further, in the case of producing the composite multilayer film, multilayer structure, and recovered composition of the packaging material for retort of the present invention, a crosslinking reaction of the resin may proceed during the production of the recovered composition, resulting in thickening and gelation. However, by containing the polyvalent metal ion (e) in an amount of 10 ppm or more, thickening, gelation, and adhesion of the resin to the screw are suppressed. On the other hand, when the content of the polyvalent metal ion (e) is 500 ppm or less, it tends to suppress the generation of lumps during recycling and suppress the deterioration of the hue during recycling. From this viewpoint, the content of the polyvalent metal ion (e) is preferably 40 to 400 ppm, more preferably 70 to 300 ppm, and even more preferably 100 to 200 ppm. The resin composition (a) preferably contains magnesium ions or calcium ions as the polyvalent metal ion (e), and more preferably contains magnesium ions. Further, by controlling the content ratio of the polyvalent metal ion (e) and the carboxylic acid described below, the melt moldability and coloring resistance of the obtained resin composition (a) can be further improved.

[0028] Examples of the polyvalent metal compound that provides the polyvalent metal ion (e) include aliphatic carboxylates, aromatic carboxylates, carbonates, hydrochlorides, nitrates, sulfates, phosphates, hydroxides, and metal complexes of magnesium, calcium, and zinc. Among them, aliphatic carboxylates and hydroxides are more preferred because they are easily available and easy to handle. Preferred aliphatic carboxylates include acetates, caprylate salts, and stearate salts.

[0029] The resin composition (a) may contain other components other than EVOH (a1), PA (a2), alkali metal ion (d), and polyvalent metal ion (e) as long as the effects of the present invention are not inhibited. Examples of other components include alkaline earth metal ions and transition metal ions other than polyvalent metal ion (e), higher aliphatic carboxylic acids, carboxylic acids other than higher aliphatic carboxylic acids (monocarboxylic acids, polyvalent carboxylic acids), thermoplastic resins other than EVOH (a1) and PA (a2), phosphate compounds, boron compounds, oxidation accelerators, antioxidants (hindered phenol-based compounds, etc.), plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorants, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, fillers, pigments, dyes, processing aids, flame retardants, antifogging agents, etc. From the viewpoint of suppressing coloring when melt-molding the pulverized product of the composite multilayer film and multilayer structure containing the resin composition (a), it is preferable to contain a higher aliphatic carboxylic acid, a carboxylic acid other than a higher aliphatic carboxylic acid, and / or a phosphate compound. Further, by containing a boron compound, the melt viscosity of the resin composition (a) and the pulverized product of the composite multilayer film and multilayer structure containing the resin composition (a) can be controlled.

[0030] <Higher aliphatic carboxylic acid> The resin composition (a) may further contain a higher aliphatic carboxylic acid having 8 to 30 carbon atoms. The higher aliphatic carboxylic acid may be contained in part or in whole in the form of a salt, and may also be contained as a salt of an alkali metal ion (d) or a polyvalent metal ion (e). As the higher aliphatic carboxylic acid, caprylic acid or stearic acid is preferably used. The multilayer film constituting the composite multilayer film of the present invention has a barrier layer (A) consisting only of the resin composition (a) on the outermost layer. However, in the die, the higher aliphatic carboxylic acid acts as a lubricant with the die metal surface, and it is considered that appearance defects due to uneven film thickness of the multilayer film and the generation of gels and bumps due to the remaining resin can be suppressed. For this reason, it is preferable that the resin composition (a) contains 100 ppm or more of the higher aliphatic carboxylic acid. On the other hand, when the content of the higher aliphatic carboxylic acid is 4000 ppm or less, thickening during melt molding of the resin composition (a) is suppressed, and the interlayer adhesiveness with the adhesive layer (B) described later tends to be maintained. From these viewpoints, the content of the higher aliphatic carboxylic acid is more preferably 200 to 3000 ppm, and even more preferably 300 to 2500 ppm.

[0031] <Carboxylic acid> The resin composition (a) may further contain a carboxylic acid other than the higher aliphatic carboxylic acid. The lower limit of the content of the carboxylic acid is preferably 50 ppm, more preferably 100 ppm. On the other hand, the upper limit of the content of the carboxylic acid is preferably 500 ppm, more preferably 450 ppm. When the content of the carboxylic acid is 50 ppm or more, the coloring resistance tends to be good. On the other hand, when the content of the carboxylic acid is 500 ppm or less, the interlayer adhesiveness can be maintained and the generation of odor can be suppressed.

[0032] The pKa of the carboxylic acid is preferably 3.5 to 5.5. When the pKa of the carboxylic acid is within the above range, the pH buffering ability of the resulting resin composition (a) is enhanced, the melt moldability is further improved, and the coloring due to acidic substances and basic substances is further improved.

[0033] The carboxylic acid may be a monocarboxylic acid. These may be used individually or in combination of two or more. A monocarboxylic acid is a compound having one carboxyl group in the molecule. The monocarboxylic acid having a pKa in the range of 3.5 to 5.5 is not particularly limited, and examples include formic acid (pKa = 3.77), acetic acid (pKa = 4.76), propionic acid (pKa = 4.85), acrylic acid (pKa = 4.25), and the like. These carboxylic acids may further have substituents such as a hydroxyl group, an amino group, and a halogen atom. Among them, acetic acid is preferred because of its high safety and easy availability and handling.

[0034] The carboxylic acid may be a polycarboxylic acid. When the carboxylic acid is a polycarboxylic acid, the coloring resistance of the resin composition (a) at high temperatures and the coloring resistance of the melt-molded product of the crushed product of the obtained composite multilayer film or multilayer structure may be further improved in some cases. Also, it is preferable that the polycarboxylic acid compound has three or more carboxyl groups. In this case, the coloring resistance may be more effectively improved in some cases. A polycarboxylic acid is a compound having two or more carboxyl groups in the molecule. In this case, it is preferable that the pKa of at least one carboxyl group is in the range of 3.5 to 5.5. Examples include oxalic acid (pKa2 = 4.27), succinic acid (pKa1 = 4.20), fumaric acid (pKa2 = 4.44), malic acid (pKa2 = 5.13), glutaric acid (pKa1 = 4.30, pKa2 = 5.40), adipic acid (pKa1 = 4.43, pKa2 = 5.41), pimelic acid (pKa1 = 4.71), phthalic acid (pKa2 = 5.41), isophthalic acid (pKa2 = 4.46), terephthalic acid (pKa1 = 3.51, pKa2 = 4.82), citric acid (pKa2 = 4.75), tartaric acid (pKa2 = 4.40), glutamic acid (pKa2 = 4.07), aspartic acid (pKa = 3.90), and the like.

[0035] <Phosphate compound> The resin composition (a) may further contain a phosphate compound. The lower limit of the content of the phosphate compound is preferably 5 ppm in terms of phosphate radical. On the other hand, the upper limit of the content of the phosphate compound is preferably 100 ppm in terms of phosphate radical. By containing the phosphate compound within this range, the coloring of the obtained resin composition (a) and the melt-molded product of the pulverized composite multilayer film or multilayer structure can be suppressed, and the thermal stability may be improved.

[0036] As the phosphate compound, for example, various acids such as phosphoric acid and phosphorous acid and their salts are used. The phosphate may be any of primary phosphate, secondary phosphate, and tertiary phosphate. The cation species of the phosphate is not particularly limited, but alkali metals and alkaline earth metals are preferred as the cation species. Among them, sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate are preferred as the phosphate compound.

[0037] <Boron compound> The resin composition (a) may further contain a boron compound. When the boron compound is contained, the lower limit of the content in the resin composition (a) is preferably 50 ppm in terms of boron element, and more preferably 100 ppm. On the other hand, the upper limit of the content of the boron compound in the resin composition (a) is preferably 400 ppm in terms of boron element, and more preferably 200 ppm. By containing the boron compound within this range, the thermal stability during the melt molding of the resin composition (a) and the pulverized product of the obtained composite multilayer film or multilayer structure can be improved, and the generation of gels and lumps may be suppressed. Also, the drawdown resistance and the neck-in resistance during film formation may be improved, or the mechanical properties of the obtained film may be improved. These effects are presumably due to the occurrence of a chelate interaction between EVOH (a1) and the boron compound.

[0038] Examples of the boron compound include boric acid, boric acid ester, borate, and boron hydride. Specifically, boric acids such as orthoboric acid (H3BO3), metaboric acid, and tetraboric acid; boric acid esters such as trimethyl borate and triethyl borate; alkali metal salts or alkaline earth metal salts of the boric acid, borates such as borax, etc. Among them, orthoboric acid is preferred.

[0039] <Hindered phenol-based compound> The resin composition (a) may further contain a hindered phenol-based compound as an antioxidant. When the hindered phenol-based compound is contained, the content of the hindered phenol-based compound in the resin composition (a) is preferably 1000 to 10000 ppm. When the content is 1000 ppm or more, coloring, thickening, and gelation of the resin can be suppressed when melt-molding the pulverized product of the composite multilayer film or multilayer structure. The content of the hindered phenol-based compound is more preferably 2000 ppm or more. On the other hand, when the content of the hindered phenol-based compound is 10000 ppm or less, coloring and bleed-out derived from the hindered phenol-based compound can be suppressed. The content of the hindered phenol-based compound is more preferably 8000 ppm or less.

[0040] The hindered phenol-based compound has at least one hindered phenol group. The hindered phenol group refers to a group in which a bulky substituent is bonded to at least one of the carbons adjacent to the carbon to which the hydroxyl group of phenol is bonded. As the bulky substituent, an alkyl group having 1 to 10 carbon atoms is preferred, and a t-butyl group is more preferred.

[0041] The hindered phenol compound is preferably in a solid state near room temperature. From the viewpoint of suppressing the bleed-out of the compound, the melting point or softening temperature of the hindered phenol compound is preferably 50°C or higher, more preferably 60°C or higher, and still more preferably 70°C or higher. From the same viewpoint, the molecular weight of the hindered phenol compound is preferably 200 or higher, more preferably 400 or higher, and still more preferably 600 or higher. On the other hand, the molecular weight is usually 2000 or lower. Further, from the viewpoint of facilitating the mixing with EVOH(a1) or PA(a2), the melting point or softening temperature of the hindered phenol compound is preferably 200°C or lower, more preferably 190°C or lower, and still more preferably 180°C or lower.

[0042] From the viewpoint of more easily facilitating the mixing with EVOH(a1) or PA(a2), the hindered phenol compound preferably has an ester bond or an amide bond. Examples of the hindered phenol compound having an ester bond include esters of aliphatic carboxylic acids having a hindered phenol group and aliphatic alcohols. Examples of the hindered phenol compound having an amide bond include amides of aliphatic carboxylic acids having a hindered phenol group and aliphatic amines. Among them, it is preferable that the hindered phenol compound has an amide bond.

[0043] Specific structures of hindered phenolic compounds having an ester bond or an amide bond include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], which is commercially available from BASF as Irganox 1010; stearyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, which is commercially available as Irganox 1076; 2,2'-thiodiethyl bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], which is commercially available as Irganox 1035; octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, which is commercially available as Irganox 1135; ethylene bis(oxyethylene) bis(3-tert-butyl-4-hydroxy-5-methylbenzenepropanoate), which is commercially available as Irganox 245; 1,6-hexanediol bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], which is commercially available as Irganox 259; and N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide], which is commercially available as Irganox 1098. Among them, N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide], which is commercially available as Irganox 1098, and pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], which is commercially available as Irganox 1010, are preferred, and the former is more preferred.

[0044] The resin composition (a) may further contain a thermoplastic resin other than EVOH (a1) and PA (a2). Examples of the thermoplastic resin other than EVOH (a1) and PA (a2) include various polyolefins (such as polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, copolymer of ethylene and an α-olefin having 4 or more carbon atoms, copolymer of polyolefin and maleic anhydride, ethylene-vinyl ester copolymer, ethylene-acrylic ester copolymer, or modified polyolefin obtained by graft-modifying these with an unsaturated carboxylic acid or its derivative, etc.), various polyesters (such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate, and modified polyvinyl alcohol resin, etc. The content of the thermoplastic resin in the resin composition (a) is usually less than 40% by mass, preferably less than 30% by mass, more preferably less than 20% by mass, still more preferably less than 10% by mass, and may even be less than 5% by mass or less than 1% by mass, and it is particularly preferred that it is substantially absent.

[0045] From the perspective that the effects of the present invention can be more significantly achieved, the total proportion of EVOH (a1) and PA (a2) in the resin constituting the resin composition (a) is preferably 60% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and may be 97% by mass or more, or even 99% by mass or more. The resin constituting the resin composition (a) may be substantially only EVOH (a1) and PA (a2), may consist only of EVOH (a1) and PA (a2), and may also be 100% by mass or less. Also, from the perspective that the effects of the present invention can be more significantly achieved, the total proportion of EVOH (a1) and PA (a2) in the resin composition (a) is preferably 60% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and may be 98% by mass or more, or even 99% by mass or more. The resin composition (a) may also consist substantially only of EVOH (a1), PA (a2), and alkali metal ions (d).

[0046] The production method of the resin composition (a) is not particularly limited, but it can be produced by melt-kneading EVOH (a1), PA (a2), and other components and additives such as alkali metal ions (d) and, if necessary, polyvalent metal ions (e). The alkali metal ions (d) and polyvalent metal ions (e) may be blended in a solid state such as powder or as a melt, or may be blended as a solute contained in a solution or a dispersoid contained in a dispersion. As the solution and the dispersion, an aqueous solution and an aqueous dispersion are respectively preferable. For melt-kneading, known mixing devices or kneading devices such as a kneader extruder, an extruder, a mixing roll, and a Banbury mixer can be used. The temperature range during melt-kneading can be appropriately adjusted according to the melting points of the EVOH (a1) and PA (a2) used, and usually, 190 to 250 °C is adopted. Also, it may be produced by previously adding some components to EVOH (a1) or PA (a2) and then melt-kneading the other components that are additionally required as described above. As a method of previously adding some components to EVOH (a1) or PA (a2), a method of immersing EVOH (a1) or PA (a2) as pellets or powder in a solution in which the added components are dissolved can be exemplified. As the solution, an aqueous solution is preferable.

[0047] <Adhesive layer (B) and adhesive resin (b)> The composite multilayer film of the present invention has an adhesive layer (B) containing an adhesive resin (b) having a melting point of 130 to 170°C. By including the adhesive layer (B) in the composite multilayer film of the present invention, a composite multilayer film excellent in appearance and interlayer adhesiveness tends to be obtained. Further, by including the adhesive layer (B), the compatibility between the barrier layer (A) and the core layer (C) is improved during recycling, and thus the recyclability tends to be improved. Examples of the adhesive resin (b) include acid-modified polyolefins obtained by graft-polymerizing an unsaturated carboxylic acid such as maleic anhydride or a derivative thereof onto a polyolefin, and it is preferable to contain, as a main component, an acid-modified polypropylene obtained by graft-polymerizing an unsaturated carboxylic acid such as maleic anhydride or a derivative thereof onto polypropylene. The melting point of the adhesive resin (b) mainly depends on the polyolefin before acid modification. Regarding the polyolefin, the content described for the polyolefin resin (c) described later can be applied as it is.

[0048] The melting point of the adhesive resin (b) is 130 to 170°C, preferably 140 to 167°C, and more preferably 150 to 164°C. When the melting point of the adhesive resin (b) is within the above range, the gas barrier property immediately after retort treatment tends to be excellent.

[0049] The proportion of the acid-modified polyolefin in the adhesive resin (b) is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 95% by mass or more, and may be substantially composed only of the acid-modified polyolefin. When the adhesive resin (b) contains acid-modified polypropylene, the proportion of the acid-modified polypropylene in the adhesive resin (b) is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 95% by mass or more, and may be substantially composed only of the acid-modified polypropylene. Further, the proportion of the adhesive resin (b) in the adhesive layer (B) is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 95% by mass or more, and may be substantially composed only of the adhesive resin (b).

[0050] <Core layer (C) and polyolefin resin (c)> The composite multilayer film of the present invention has a core layer (C) containing a polyolefin resin (c) having a melting point of 130 to 170°C. The polyolefin resin (c) is not particularly limited as long as it is a polyolefin having a melting point of 130 to 170°C. However, from the viewpoint of improving the recyclability of the composite multilayer film and multilayer structure containing the polyolefin resin (c), the polyolefin resin (c) preferably contains polypropylene as a main component. Polypropylene is widely used as a packaging material regardless of the presence or absence of gas barrier properties, and its recycling infrastructure is relatively well-established in various countries. Examples of polypropylene include polypropylene; propylene-based copolymers obtained by copolymerizing propylene with α-olefins such as ethylene, 1-butene, 1-hexene, and 4-methyl-1-pentene. The content of propylene units in the propylene-based copolymer is 70 mol% or more, preferably 80 mol% or more, and may be 90 mol% or more.

[0051] From the viewpoint of making the effects of the present invention more remarkable, the melt flow rate (MFR) (at 230°C under a load of 2160 g) measured according to the method described in JIS K7210 (2014) of the polyolefin resin (c) is preferably 0.1 to 30 g / 10 min, more preferably 0.3 to 25 g / 10 min, and even more preferably 0.5 to 20 g / 10 min.

[0052] The melting point of the polyolefin resin (c) is 130 to 170°C, preferably 140 to 167°C, and more preferably 150 to 164°C. When the melting point of the polyolefin resin (c) is within the above range, it tends to have excellent gas barrier properties immediately after retort treatment.

[0053] The proportion of polyolefin in the polyolefin resin (c) is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 95% by mass or more, and may be substantially composed of only polyolefin, or may be 100% by mass or less. Further, when the polyolefin resin (c) contains polypropylene, the proportion of polypropylene in the polyolefin resin (c) is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 95% by mass or more, and may be substantially composed of only polypropylene. Also, the proportion of the polyolefin resin (c) in the core layer (C) is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 95% by mass or more, and may be substantially composed of only the polyolefin resin (c), or may be 100% by mass or less.

[0054] The adhesive layer (B) and the core layer (C) each contain an adhesive resin (b) and a polyolefin resin (c) as main components. In these layers, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorants, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, fillers, pigments, dyes, processing aids, flame retardants, antifogging agents and other components may be contained as long as the effects of the present invention are not impaired. However, the total amount is less than 50% by mass for each layer, preferably less than 40% by mass, more preferably less than 30% by mass, still more preferably less than 20% by mass, particularly preferably less than 10% by mass, and may be less than 5% by mass, less than 3% by mass, or less than 1% by mass.

[0055] <Multilayer film> The multilayer film that constitutes the composite multilayer film of the present invention has a barrier layer (A) on the outermost layer, and has a structure in which at least the barrier layer (A), the adhesive layer (B), and the core layer (C) are laminated adjacent to each other in this order. The barrier layer (A), the adhesive layer (B), and the core layer (C) may each have a plurality of layers. As the layer structure of the multilayer film of the present invention, when the barrier layer (A) is represented by A, the adhesive layer (B) is represented by B, and the core layer (C) is represented by C, and " / " represents that they are directly laminated, examples include A / B / C, A / B / C / B / A, A / B / C / B / A / B / C, A / B / C / B / A / B / C / B / A, etc.

[0056] From the viewpoints of gas barrier property, recyclability, and economy, the average thickness of the barrier layer (A) of the multilayer film is preferably 0.2 μm or more and less than 10 μm, more preferably 0.4 μm or more and less than 8 μm, and even more preferably 0.6 μm or more and less than 6 μm. From the viewpoint of further emphasizing recyclability, the average thickness of the barrier layer (A) is particularly preferably less than 3 μm, and may be less than 2 μm or less than 1 μm. Also, from the viewpoints of gas barrier property, recyclability, and economy, the ratio of the average thickness of the barrier layer (A) to the total average thickness of the multilayer film is preferably 3% or more and less than 25%. From the viewpoint of further emphasizing recyclability, the ratio of the average thickness of the barrier layer (A) to the total average thickness of the multilayer film is more preferably less than 15%, and may be less than 10% or less than 5%.

[0057] From the viewpoints of interlayer adhesiveness, recyclability, and economy, the average thickness of the adhesive layer (B) of the multilayer film is preferably 0.2 μm or more and less than 10 μm. The average thickness of the adhesive layer (B) is more preferably 0.4 μm or more and less than 8 μm, and even more preferably 0.6 μm or more and less than 6 μm. Also, from the viewpoints of interlayer adhesiveness, recyclability, and economy, the ratio of the average thickness of the adhesive layer (B) to the total average thickness of the multilayer film is preferably 3% or more and less than 25%. The ratio of the average thickness of the adhesive layer (B) to the total average thickness of the multilayer film is more preferably less than 15%, and may be less than 10% or less than 5%.

[0058] From the viewpoints of resource efficiency and recyclability, the average thickness of the core layer (C) of the multilayer film is preferably 1 μm or more and less than 200 μm. The average thickness of the core layer (C) is more preferably 5 μm or more, still more preferably 10 μm or more, and may be 15 μm or more or 20 μm or more. Further, the average thickness of the core layer (C) is more preferably less than 100 μm, still more preferably less than 60 μm, particularly preferably less than 40 μm, and may be less than 30 μm or less than 20 μm. Further, for the same reason, it is also preferable that the ratio of the average thickness of the core layer (C) to the total average thickness of the multilayer film exceeds 60%. The ratio of the average thickness of the core layer (C) to the total average thickness of the multilayer film is more preferably more than 70%, and may be more than 75% or more than 80%.

[0059] The average thickness of the multilayer film is preferably 10 μm or more and less than 200 μm, and more preferably 12 μm or more and less than 100 μm. In the case of the stretched multilayer film described later, the average thickness of the multilayer film is preferably 10 μm or more and less than 55 μm, more preferably 12 μm or more and less than 45 μm, still more preferably 14 μm or more and less than 35 μm, and may be 16 μm or more and less than 25 μm.

[0060] The multilayer film may be an unstretched multilayer film that is not substantially stretched, or it may be a stretched multilayer film stretched in a uniaxial direction or a biaxial direction. In the case of an unstretched multilayer film, it has excellent impact resistance and can also be suitably used as a heat-sealable film. On the other hand, by stretching in a uniaxial direction or a biaxial direction, the mechanical properties and gas barrier properties of the obtained multilayer film can be improved. From the viewpoints of economy and ease of tearing the multilayer film (easy to open the packaging material when used as a packaging material), the multilayer film is preferably a uniaxially stretched multilayer film. From the viewpoint of obtaining a film with less anisotropy in mechanical properties and being tough, the multilayer film is preferably a biaxially stretched multilayer film. From the viewpoints of the thickness uniformity and mechanical strength of the obtained multilayer film, it is preferably stretched at least 3 times or more and less than 12 times in at least one uniaxial direction. In the case of a uniaxially stretched multilayer film, it is preferably stretched substantially only in the uniaxial direction 3 times or more and less than 12 times, and more preferably 4 times or more and less than 10 times. In the case of a biaxially stretched multilayer film, it is preferably stretched 3 times or more and less than 12 times in each biaxial direction, and more preferably 4 times or more and less than 12 times. In the case of a tenter-type sequential biaxially stretched film, it is common to stretch 4 to 6 times in the film flow direction (MD direction) and then 8 to 12 times in the width direction (TD direction).

[0061] The method for forming the multilayer film is not particularly limited. Generally, a conventional coextrusion method in which each resin is extruded from a separate die or a common die and laminated can be used. As the die, either an annular die or a T-die can be used. The method of stretching in the uniaxial direction or the biaxial direction is also not particularly limited, and the film can be produced by performing stretching treatment in the flow direction of the film and / or in the direction perpendicular to the flow direction, that is, the width direction, by a conventionally known stretching method such as roll-type uniaxial stretching, tubular simultaneous biaxial stretching, tenter-type sequential biaxial stretching, tenter-type simultaneous biaxial stretching, etc. Among them, the effects of the present invention are particularly remarkable in the case of a multilayer film produced by tenter-type sequential biaxial stretching. The temperature during stretching is usually 70 to 180°C, more preferably 80 to 170°C, and may be 90 to 160°C from the viewpoint of processability. If necessary, after the stretching treatment, it is preferable to perform a so-called heat setting operation by heating at a temperature equal to or higher than the glass transition point and lower than the melting point to increase the crystallinity and fix the orientation of the molecular chains.

[0062] <Composite multilayer film> The composite multilayer film of the present invention includes an inorganic layer (I) and a protective layer (P) adjacent to each other on the surface side of the barrier layer (A) of the multilayer film. That is, the inorganic layer (I) or the protective layer (P) may be adjacent to the barrier layer (A), or the barrier layer (A) and the inorganic layer (I) or the protective layer (P) may be laminated via other layers, but it is preferable that the inorganic layer (I) or the protective layer (P) is laminated adjacent to the barrier layer (A). As the layer structure of the composite multilayer film, assuming that the inorganic layer (I) is I, the protective layer (P) is P, and " / / " means being laminated via an adhesive layer, examples include multilayer film / I / P, multilayer film / / I / P, multilayer film / P / I, multilayer film / / P / I, multilayer film / P / I / P, multilayer film / / P / I / P, etc. In the above layer structure, it is assumed that the inorganic layer (I) and the protective layer (P) adjacent to each other are laminated on the surface side of the barrier layer (A) of the multilayer film. The barrier layer (A) and the inorganic layer (I) are preferably laminated directly.

[0063] <Inorganic layer (I)> The inorganic layer (I) is composed of inorganic substances such as metals and inorganic oxides, and means a layer having gas barrier properties against oxygen and water vapor. Since the barrier layer (A) has a higher affinity for metals and inorganic oxides compared to ordinary thermoplastic resins, when the inorganic layer (I) is laminated adjacent to the barrier layer (A), a dense and defect-free inorganic layer (I) can be formed, and the interlayer adhesion thereof is good. Further, since the barrier layer (A) has gas barrier properties, even when defects occur in the inorganic layer (I) due to bending or the like, a decrease in gas barrier properties can be suppressed.

[0064] The inorganic layer (I) is preferably an inorganic oxide vapor deposition layer. The inorganic oxide vapor deposition layer is excellent not only in hot water resistance but also in terms of visibility of the contents as a packaging material, proper oven performance, and suppression of coloring, generation of gels and lumps when melt-molding pulverized materials. The inorganic oxide vapor deposition layer includes inorganic oxides, for example, oxides of silicon, aluminum, magnesium, calcium, potassium, tin, sodium, boron, titanium, lead, zirconium, yttrium, etc., preferably a vapor deposition film of alumina (aluminum oxide) or silica (silicon oxide). From the viewpoint of economy, a vapor deposition film of alumina is preferable, but from the viewpoint of gas barrier properties, a vapor deposition film of silica is preferable.

[0065] The average thickness of the inorganic layer (I) is generally 10 nm or more and less than 150 nm. When the average thickness is within the above range, the gas barrier property is excellent, and the viscosity stability is excellent when melt-molding the pulverized product of the composite multilayer film or multilayer structure containing the inorganic layer (I), and the generation of gels and lumps can be suppressed. The average thickness of the inorganic oxide vapor deposition layer is preferably 120 nm or less, more preferably 90 nm or less, and even more preferably 60 nm or less. Also, the average thickness of the inorganic oxide vapor deposition layer is preferably 12 nm or more, more preferably 14 nm or more, and even more preferably 16 nm or more. From the viewpoint of particularly emphasizing the gas barrier property, the average thickness of the inorganic oxide vapor deposition layer is preferably 25 nm or more, more preferably 35 nm or more, and even more preferably 45 nm or more. The average thickness of the inorganic oxide vapor deposition layer is the average value of the thicknesses at any 10 points of the cross-section of the inorganic oxide vapor deposition layer measured by an electron microscope. When the composite multilayer film of the present invention has an inorganic oxide vapor deposition layer, the light transmittance at a wavelength of 600 nm can be 80% or more, and the visibility of the contents when used as a packaging material is excellent. From the viewpoint of further improving the visibility, the light transmittance at a wavelength of 600 nm is more preferably 90% or more. The light transmittance can be increased, for example, by suppressing the thickness unevenness of the multilayer film used in the production of the composite multilayer film. As a means for further suppressing the thickness unevenness of the multilayer film, for example, a means of stretching in at least one axial direction can be mentioned. The light transmittance of the multilayer film at a wavelength of 600 nm is preferably 80% or more, and more preferably 90% or more.

[0066] The inorganic layer (I) can be formed into a film by known physical vapor deposition methods or chemical vapor deposition methods. Specifically, examples include vacuum vapor deposition method, sputtering method, ion plating method, ion beam mixing method, plasma CVD method, laser CVD method, MO-CVD method, thermal CVD method, etc. Among them, it is preferable to use a physical vapor deposition method, and particularly preferably the vacuum vapor deposition method. The upper limit of the surface temperature of the multilayer film during the film formation of the inorganic layer (I) is preferably 80°C, more preferably 70°C, and even more preferably 60°C. Also, the lower limit of the surface temperature of the multilayer film during the film formation of the inorganic layer (I) is not particularly limited, but 0°C is preferable, 10°C is more preferable, and 20°C is even more preferable. Before film formation, the surface of the multilayer film may be subjected to plasma treatment. A known method can be used for the plasma treatment, and atmospheric pressure plasma treatment is preferable. In the atmospheric pressure plasma treatment, as the discharge gas, nitrogen, helium, neon, argon, krypton, xenon, radon, etc. are used. Among them, nitrogen, helium, and argon are preferably used, and particularly nitrogen is preferable because the cost can be reduced.

[0067] <Protective layer (P)> The composite multilayer film of the present invention comprises a protective layer (P) and an inorganic layer (I) adjacent to each other on the front surface side of the barrier layer (A) of the multilayer film. The protective layer (P) may be a protective layer (Pa) laminated at a position closer to the front surface side of the barrier layer (A) of the multilayer film than the inorganic layer (I), or may be a protective layer (Pb) laminated at a position farther from the front surface side of the barrier layer (A) of the multilayer film than the inorganic layer (I). Further, the protective layer (P) includes a protective layer (Pa) laminated at a position closer to the front surface side of the barrier layer (A) of the multilayer film than the inorganic layer (I), and a protective layer (Pb) laminated at a position farther from the front surface side of the barrier layer (A) of the multilayer film than the inorganic layer (I), and may have a structure in which the protective layer (Pa), the inorganic layer (I), and the protective layer (Pb) are laminated adjacent to each other in this order on the front surface side of the multilayer film (X). From the viewpoint of exhibiting water vapor barrier properties in addition to gas barrier properties, it is preferable that the composite multilayer film of the present invention has a structure in which the barrier layer (A), the inorganic layer (I), and the protective layer (P) are laminated adjacent to each other in this order. The protective layer (P) itself may not have gas barrier properties, but preferably has gas barrier properties. By providing the protective layer (P) and the inorganic layer (I) adjacent to each other on the front surface side of the barrier layer (A) of the composite multilayer film of the present invention, the gas barrier properties immediately after high-temperature and long-time retort treatment tend to be significantly excellent. The reason is not clear, but it is considered that not only can the protective layer (P) suppress the occurrence of defects in the inorganic layer (I), but also the moisture that penetrates by the retort treatment, particularly the moisture around the barrier layer (A) and the inorganic layer (I), can be effectively discharged due to the presence of the protective layer (P). The point that the protective layer (P) can effectively discharge moisture is a surprising effect not known so far and is a finding discovered as a result of the inventors' intensive studies.

[0068] In one aspect of the present invention, the protective layer (P) preferably contains a water-soluble resin as a main component. Examples of the water-soluble resin include resins having a hydroxyl group such as polyvinyl alcohol and poly(2-hydroxyethyl methacrylate), resins having a carboxyl group such as polyacrylic acid and carboxymethyl cellulose, resins having an amino group such as polyallylamine and polyethyleneimine, resins having an amide group such as polyacrylamide, poly(N,N-dimethylacrylamide) and poly(N-isopropylacrylamide), resins having a sulfonic acid group such as polystyrene sulfonic acid and polyvinyl sulfonic acid, resins having a polyether group such as polyethylene oxide and polyethylene glycol, and polyvinyl pyrrolidone, polyoxazoline, etc. Among the above-mentioned water-soluble resins, polymers having a hydrogen bonding group are preferable, water-soluble resins having a hydroxyl group, polyamides, polyethers, polyvinyl pyrrolidone, polyoxazoline, etc. are more preferable, water-soluble resins having a hydroxyl group are even more preferable, and polyvinyl alcohol-based resins (K) are particularly preferable. The polyvinyl alcohol-based resin (K) may be a homopolymer of vinyl alcohol or one or more compounds selected from the group consisting of copolymers containing vinyl alcohol units such as EVOH. These may be used alone or in combination of two or more. From the viewpoint of gas barrier properties, the higher the saponification degree is, the closer it is to 100%, but usually it is 90% or more, preferably 95% or more. The number average degree of polymerization is usually 50 or more and 5000 or less.

[0069] In another aspect of the present invention, the protective layer (P) preferably contains a water-dispersible resin as a main component, and more preferably contains a water-dispersible polyurethane resin (L) (hereinafter may be abbreviated as "polyurethane resin (L)") as a main component. The protective layer (P) containing the polyurethane resin (L) as a main component has little adverse effect on recyclability and tends to be able to produce a high-quality recovered resin. Since the polar group of the urethane bond in the polyurethane resin (L) interacts with the inorganic layer (I) and has flexibility due to the presence of the amorphous portion, damage to the inorganic layer (I) can be suppressed even when dimensional changes or bending loads are applied. The acid value of the polyurethane resin (L) is preferably in the range of 10 to 60 mgKOH / g. More preferably, it is in the range of 15 to 55 mgKOH / g, and even more preferably in the range of 20 to 50 mgKOH / g. When the acid value of the polyurethane resin (L) is within the above range, the liquid stability is improved when made into an aqueous dispersion, and the protective layer (P) can be uniformly laminated on the inorganic layer (I), resulting in a good appearance. Further, the polyurethane resin (L) preferably has a glass transition temperature (Tg) of 80°C or higher, more preferably 90°C or higher. By setting Tg to 80°C or higher, a decrease in the gas barrier property of the composite multilayer film in the converting process can be efficiently suppressed.

[0070] From the viewpoint of improving the gas barrier property, the polyurethane resin (L) more preferably contains an aromatic or araliphatic diisocyanate component as a main constituent component. Here, with respect to the urethane resin, "component" means a structural unit (constituent component) constituting the urethane resin. Among them, it is particularly preferable to include a urethane resin containing a metaxylylene diisocyanate component. By using such a resin, the cohesive force of the urethane bond can be further enhanced by the stacking effect between aromatic rings, and as a result, a good gas barrier property can be obtained.

[0071] In the present invention, it is preferable that the proportion of the aromatic or araliphatic diisocyanate in the polyurethane-based resin (L) is in the range of 50 mol% or more (50 to 100 mol%) in 100 mol% of the polyisocyanate component. The proportion of the total amount of the aromatic or araliphatic diisocyanate is preferably 60 to 100 mol%, more preferably 70 to 100 mol%, and still more preferably 80 to 100 mol%. As such a resin, the "Takelac (registered trademark) WPB" series commercially available from Mitsui Chemicals, Inc. can be preferably used. When the proportion of the total amount of the aromatic or araliphatic diisocyanate is 50 mol% or more, the protective layer (P) itself tends to exhibit good gas barrier properties.

[0072] The polyurethane-based resin (L) preferably has a carboxylic acid group (carboxyl group) from the viewpoint of improving the affinity with the inorganic layer (I). In order to introduce a carboxylic acid (salt) group into the urethane resin, for example, as a polyol component, a polyol compound having a carboxylic acid group such as dimethylolpropionic acid or dimethylolbutanoic acid may be introduced as a copolymerization component. Further, after synthesizing the carboxylic acid group-containing urethane resin and neutralizing it with a salt-forming agent, a water-dispersed urethane resin can be obtained. Specific examples of the salt-forming agent include trialkylamines such as ammonia, trimethylamine, triethylamine, triisopropylamine, tri-n-propylamine, and tri-n-butylamine; N-alkylmorpholines such as N-methylmorpholine and N-ethylmorpholine; and N-dialkylalkanolamines such as N-dimethylethanolamine and N-diethylethanolamine. These may be used alone or in combination of two or more.

[0073] The protective layer (P) preferably contains at least one selected from the group consisting of at least one metal compound (M) selected from the group consisting of metal alkoxides, hydrolyzates of metal alkoxides, and hydrolytic condensates of metal alkoxides, and a layered inorganic compound (N). The total content of the metal compound (M) and the layered inorganic compound (N) in the protective layer (P) is preferably 5 to 45% by mass, more preferably 7 to 40% by mass, and even more preferably 9 to 35% by mass. By containing the metal compound (M) and the layered inorganic compound (N) within this range, the gas barrier property of the protective layer (P) can be further improved, and the interlayer adhesiveness with the inorganic layer (I) may also be improved. When the protective layer (P) contains the metal compound (M), the protective layer (P) preferably contains a water-soluble polyvinyl alcohol-based resin (K) as a main component. Further, when the protective layer (P) contains the layered inorganic compound (N), the protective layer (P) preferably contains a water-dispersible polyurethane-based resin (L) as a main component.

[0074] <Metal compound (M)> The metal compound (M) is at least one selected from the group consisting of metal alkoxides, hydrolyzates of metal alkoxides, and hydrolytic condensates of metal alkoxides. The metal alkoxide has the general formula: R 1 n M(OR2) m (wherein M is a metal atom, R 1 , R 2 is an organic group having 1 to 8 carbon atoms, n is 0 or more, m is 1 or more, and n + m represents the valence of M). At least one or more of this metal alkoxide, a partial hydrolyzate of the metal alkoxide, or a hydrolytic condensate of the metal alkoxide can be used. As the metal atom represented by M in the above general formula: R 1 n M(OR2) m , silicon, zirconium, titanium, aluminum, etc. can be used as the metal atom, and silicon is preferred. As for the usage of these alkoxides, they can be used alone or by mixing alkoxides of two or more different metal atoms in the same solution.

[0075] The organic group R 1Specific examples thereof include, for example, alkyl groups such as methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, sec-butyl group, t-butyl group, n-hexyl group, n-octyl group, etc. Further, the organic group R 2 Specific examples thereof include, for example, methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, sec-butyl group, etc. These alkyl groups in the same molecule may be the same or different.

[0076] Among the alkoxides, alkoxysilanes in which M is silicon (Si) are preferred, and the alkoxysilane is represented by Si(ORa)4. Ra is a lower alkyl group, and methyl group, ethyl group, n-propyl group, n-butyl group, etc. are used. Specific examples of the alkoxysilane include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, etc. Further, an alkylalkoxysilane Rb m Si(ORc) 4-m can be used (m is an integer of 1, 2, or 3). As Rb and Rc, methyl group, ethyl group, etc. are used, and specific examples of the alkylalkoxysilane include methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, etc. These alkoxysilanes and alkylalkoxysilanes can be used alone or in a mixture of two or more. Furthermore, condensates of alkoxysilanes can also be used, specifically, polytetramethoxysilane, polytetraethoxysilane, etc. are included.

[0077] Two or more of these alkoxides may be mixed and used. In particular, by mixing and using an alkoxysilane and a zirconium alkoxide, the toughness, heat resistance, etc. of the obtained protective layer (P) may be improved. In the present invention, a silane coupling agent may be used in combination with the above alkoxide. As the silane coupling agent, a known organoalkoxysilane containing an organic reactive group can be used. In particular, an organoalkoxysilane having an epoxy group or an amino group is preferable. Examples thereof include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-aminopropyltrimethoxysilane, and γ-aminopropyltriethoxysilane. Two or more of such silane coupling agents may be mixed and used. The amount of such a silane coupling agent used is in the range of 0.1 to 20 parts by mass with respect to 100 parts by mass of the above alkoxysilane.

[0078] <Layered inorganic compound (N)> The layered inorganic compound (N) is a plate-like inorganic compound having a layer structure. Those that become a plate-like structure by treatments such as swelling, splitting, and interlayer delamination are also included. An inorganic compound in which unit crystal layers are stacked on each other to form a layered structure is preferred, and cations or anions can also be included between the unit crystal layers. The layered inorganic compound (N) preferably has swelling properties. Here, the layered inorganic compound having swelling properties means a layered inorganic compound that swells, splits, or disperses when added to a solvent such as water or alcohol. Specific examples of the layered inorganic compound (N) include layered inorganic silicates such as mica, montmorillonite, kaolinite, dickite, nacrite, halloysite, antigorite, chrysotile, pyrophyllite, beidellite, nontronite, saponite, sauconite, stevensite, hectorite, tetrasilicic mica, sodium teniolite, muscovite, margarite, talc, vermiculite, phlogopite, zansorphyllite, chlorite; graphenes such as graphene, graphene oxide, reduced graphene oxide; etc. Among them, layered inorganic silicates and graphenes are preferred, and layered inorganic silicates are more preferred. As the layered inorganic silicate, clay minerals are preferred, and among them, clay minerals of the mica group, smectite group, and vermiculite group are more preferred, and the mica group and smectite group are particularly preferred. Examples of the mica group include mica, and examples of the smectite group include montmorillonite, beidellite, nontronite, saponite, sauconite, stevensite, hectorite. Mica and montmorillonite are preferred, and mica is more preferred. Also, two or more types of the layered inorganic compound (N) may be used.

[0079] The aspect ratio of the layered inorganic compound (N) is not particularly limited as long as it does not inhibit the effects of the present invention, but is preferably 50 to 10,000. From the viewpoint of improving the gas barrier property, the aspect ratio is more preferably 100 or more, further preferably 200 or more, particularly preferably 300 or more, and may be 400 or more or 500 or more. On the other hand, from the viewpoint of improving the formulation and coating properties of the solution or dispersion, the aspect ratio is more preferably 7,000 or less, further preferably 5,000 or less, particularly preferably 3,000 or less, and may be 2,000 or less or 1,000 or less. The aspect ratio (Z) of the layered inorganic compound (N) is a value defined by Z = L / a. Here, L is the average particle size of the layered inorganic compound, and a represents the unit thickness of the layered inorganic compound, that is, the thickness of the unit crystal layer of the layered inorganic compound, which is determined by X-ray diffraction method. Also, the average particle size of the layered inorganic compound (N) is not particularly limited as long as it does not inhibit the effects of the present invention, but is preferably 20 nm to 200 μm. The average particle size is more preferably 100 nm or more, further preferably 500 nm or more, particularly preferably 1 μm or more, and may be 5 μm or more or 8 μm or more. On the other hand, the average particle size is more preferably 100 μm or less, further preferably 50 μm or less, particularly preferably 30 μm or less, and may be 20 μm or less or 15 μm or less. The average particle size of the layered inorganic compound (N) is the particle size (volume-based median diameter) obtained by dispersing the layered inorganic compound in a liquid medium such as water and measuring it with a laser diffraction / scattering type particle size distribution measuring device.

[0080] The interlayer spacing of the layered inorganic compound (N) alone is not particularly limited as long as it does not inhibit the effects of the present invention, but is preferably 0.1 nm to 100 nm. The interlayer spacing is preferably 50 nm or less, more preferably 10 nm or less. The interlayer spacing refers to the spacing d obtained based on Bragg's equation (nλ = 2dsinθ, n = 1, 2, 3 ···) from the angle θ corresponding to the peak on the low-angle side among the peaks obtained by X-ray diffraction.

[0081] The interlayer spacing of the layered inorganic compound (N) in the protective layer (P) is preferably wider than the interlayer spacing of the layered inorganic compound (N) alone. By swelling, splitting, or dispersing the layered inorganic compound (N) in a solvent, the interlayer spacing of the layered inorganic compound (N) is widened, and then it is mixed with a water-soluble polyvinyl alcohol-based resin (K) or a water-dispersible polyurethane-based resin (L), or a solution or dispersion thereof. As a result, the water-soluble polyvinyl alcohol-based resin (K) or the water-dispersible polyurethane-based resin (L) enters between the unit crystal layers of the layered inorganic compound (N), causing the interlayer spacing to widen. The widening of the interlayer spacing can be confirmed by the shift of the angle θ corresponding to the low-angle side peak derived from the layered inorganic compound (N) to the low-angle side among the peaks obtained by X-ray diffraction of the protective layer (P), or by the non-observation of the low-angle side peak derived from the layered inorganic compound (N).

[0082] When the water-soluble polyvinyl alcohol-based resin (K) or the water-dispersible polyurethane-based resin (L) enters between the unit crystal layers of the layered inorganic compound (N), the gas barrier property of the protective layer (P) is improved. This is because the gas molecules to be permeated cannot permeate through the unit crystal layers of the layered inorganic compound (N) and instead go around and diffuse, resulting in a longer effective distance for permeating through the protective layer (P). Since the layered inorganic compound (N) has a high aspect ratio of the unit crystal layer, that is, the ratio of width to thickness, it can efficiently improve the gas barrier property compared with spherical and fibrous inorganic compounds.

[0083] In the present invention, the protective layer (P) composed of the above composition is specifically laminated as follows. First, a coating liquid is prepared by mixing at least one metal compound (M) or layered inorganic compound (N) selected from the group consisting of a water-soluble polyvinyl alcohol-based resin (K) or a water-dispersible polyurethane-based resin (L), a metal alkoxide, a hydrolyzate of the metal alkoxide, and a hydrolytic condensate of the metal alkoxide, water and / or an organic solvent as a solvent, and minor components such as a sol-gel catalyst and an acid as required. Here, when the above coating liquid contains at least one metal compound (M) selected from the group consisting of a metal alkoxide, a hydrolyzate of the metal alkoxide, and a hydrolytic condensate of the metal alkoxide, the hydrolysis and polycondensation reactions of the metal alkoxide gradually proceed in the coating liquid. Next, it can be laminated by applying and drying the above coating liquid to the surface side of the barrier layer (A) or the surface side of the inorganic layer (I) by a conventional method.

[0084] The protective layer (P) may contain a crosslinking agent, other polymers, tackifiers, pigments, dyes, etc. in order to further improve the performance according to the purpose.

[0085] As the crosslinking agent, a crosslinking agent having self-crosslinking properties, a compound having a plurality of reactive functional groups in the molecule, a metal having a polyvalent coordination site, etc. can be used. Specifically, an oxazoline group-containing compound, an isocyanate group-containing compound, an epoxy group-containing compound, a carbodiimide group-containing compound, a melamine compound, a urea compound, a zirconium salt compound, etc. can be mentioned, and a plurality of them may be mixed and used as required. Among them, from the viewpoint of ease of handling, an oxazoline group-containing compound, an isocyanate group-containing compound, and an epoxy group-containing compound are preferable.

[0086] The oxazoline group-containing compound is not particularly limited as long as it has at least two or more oxazoline groups in the molecule. For example, compounds having an oxazoline group such as 2,2'-bis(2-oxazoline), 2,2'-ethylene-bis(4,4'-dimethyl-2-oxazoline), 2,2'-p-phenylene-bis(2-oxazoline), bis(2-oxazolinylcyclohexane) sulfide, and oxazoline group-containing polymers can be mentioned. One or more of these can be used. Among these, an oxazoline group-containing polymer is preferred because of its ease of handling.

[0087] The oxazoline group-containing polymer can be obtained, for example, by polymerizing addition-polymerizable oxazolines such as 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline. Other monomers may be copolymerized with the oxazoline group-containing polymer as needed. The polymerization method of the oxazoline group-containing polymer is not particularly limited, and a known polymerization method can be adopted.

[0088] Examples of commercially available oxazoline group-containing polymers include the Epocros series manufactured by Nippon Shokubai Co., Ltd., such as the water-soluble types "WS-500" and "WS-700"; and the emulsion types "K-1010E", "K-1020E", "K-1030E", "K-2010E", "K-2020E", "K-2030E", etc.

[0089] The isocyanate group-containing compound is not particularly limited as long as it has at least two or more isocyanate groups in the molecule. For example, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane 2,4'- or 4,4'-diisocyanate, polymethylene polyphenyl diisocyanate, tolidine diisocyanate, 1,4-diisocyanatobutane, hexamethylene diisocyanate, 1,5-diisocyanato-2,2-dimethylpentane, 2,2,4- or 2,4,4-trimethyl-1,6-diisocyanatohexane, 1,10-diisocyanatodecane, 1,3- or 1,4-diisocyanatocyclohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane, 4,4'-diisocyanatodicyclohexylmethane, hexahydrotoluene 2,4- or 2,6-diisocyanate, perhydro-2,4'- or 4,4'-diphenylmethane diisocyanate, naphthalene 1,5-diisocyanate, xylylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, tetramethylxylylene diisocyanate and other polyfunctional isocyanate compounds, or modified products thereof can be mentioned. Here, the modified product is obtained by modifying the diisocyanate in the polyfunctional isocyanate compound by a known method. For example, polyfunctional isocyanate compounds having an allophanate group, a biuret group, a carbodiimide group, a uretonimine group, a uretdione group, an isocyanurate group, etc., and further, adduct-type polyfunctional isocyanate compounds modified with polyfunctional alcohols such as trimethylolpropane can be mentioned. In addition, the isocyanate group-containing compound may contain monoisocyanate in the range of 20% by mass or less. Also, one or more of these can be used.

[0090] Isocyanate group-containing compounds can usually be obtained by reacting polyfunctional isocyanate compounds with monovalent or polyvalent nonionic polyalkylene ether alcohols. Commercially available products of such aqueous polyfunctional isocyanate compounds include, for example, Bayhydur 3100, Bayhydur VPLS 2150 / 1, SBU Isocyanate L801, Desmodur N3400, Desmodur VPLS 2102, Desmodur VPLS 2025 / 1, SBU Isocyanate 0772, Desmodur DN manufactured by Sumitomo Bayer Urethane Co., Ltd.; Takenate WD720, Takenate WD725, Takenate WD730 manufactured by Takeda Pharmaceutical Company Limited; Duranate WB40-100, Duranate WB40-80D, Duranate WX-1741 manufactured by Asahi Kasei Corporation; Basonat HW-100, Basonat LR-9056 manufactured by BASF Corporation, etc.

[0091] The epoxy group-containing compound is not particularly limited as long as it has at least two or more epoxy groups in the molecule. For example, bisphenol A diglycidyl ether, bisphenol A β-dimethylglycidyl ether, bisphenol F diglycidyl ether, tetrahydroxyphenylmethane tetraglycidyl ether, resorcinol diglycidyl ether, brominated bisphenol A diglycidyl ether, chlorinated bisphenol A diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, diglycidyl ether of bisphenol A alkylene oxide adduct, novolac glycidyl ether, polyalkylene glycol diglycidyl ether, glycerin triglycidyl ether, pentaerythritol diglycidyl ether, glycidyl ether type such as epoxy urethane resin; glycidyl ether-ester type such as glycidyl ether-ester of p-oxybenzoic acid; glycidyl ester type such as diglycidyl phthalate, diglycidyl tetrahydrophthalate, diglycidyl hexahydrophthalate, diglycidyl acrylate, diglycidyl dimer acid; glycidyl amine type such as glycidyl aniline, tetraglycidyl diaminodiphenylmethane, triglycidyl isocyanurate, triglycidyl aminophenol; linear aliphatic epoxy resins such as epoxidized polybutadiene, epoxidized soybean oil; alicyclic epoxy resins such as 3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate, 3,4-epoxycyclohexylmethyl(3,4-epoxycyclohexane)carboxylate, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, vinylcyclohexene diepoxide, dicyclopentadiene monoxide, bis(2,3-epoxycyclopentyl)ether, limonene dioxide, etc. One or more of these can be used.

[0092] Examples of commercially available epoxy group-containing compounds suitable for the present invention and being aqueous systems include, for example, the Denacol series (EX-313, EM-150, EM-101, etc.) manufactured by Nagase ChemteX Corporation, and the Adeka Resin series (EM-0517, EM-0526, EM-11-50B, EM-051R, etc.) manufactured by ADEKA Corporation.

[0093] The melamine compound is not particularly limited as long as it has a melamine skeleton in the molecule. For example, an alkylolated melamine derivative, a compound obtained by reacting an alkylolated melamine derivative with an alcohol to be partially or completely etherified, and a mixture thereof can be used. As the alcohol used for etherification, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, isobutanol, etc. are preferably used. Further, the melamine compound may be either a monomer or a multimer of dimer or higher, and a mixture thereof may also be used.

[0094] Examples of commercially available melamine compounds include Cymel 323, Cymel 325, Cymel 327, Cymel 328, Cymel 370, etc. manufactured by Nippon Cytec Industries Co., Ltd.

[0095] The carbodiimide group-containing compound is not particularly limited as long as it has at least two or more carbodiimide groups in the molecule. For example, compounds having a carbodiimide group such as p-phenylene-bis(2,6-xylylcarbodiimide), tetramethylene-bis(t-butylcarbodiimide), cyclohexane-1,4-bis(methylene-t-butylcarbodiimide), and polycarbodiimide which is a polymer having a carbodiimide group can be mentioned. One or more of these can be used. Among these, polycarbodiimide is preferable because of its ease of handling. Examples of commercially available polycarbodiimides include the Carbodilite series manufactured by Nisshinbo. Specific products include, for example, water-soluble types such as "SV-02", "V-02", "V-02-L2", "V-04"; emulsion types such as "E-01", "E-02"; organic solution types such as "V-01", "V-03", "V-07", "V-09"; and solvent-free types such as "V-05".

[0096] From the viewpoint of improving the heat resistance or water resistance of the coating film, etc., the content of the crosslinking agent is preferably 0.01 to 30 parts by mass, more preferably 0.1 to 20 parts by mass, and even more preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of the water-soluble polyvinyl alcohol-based resin (K) or the water-dispersible polyurethane-based resin (L). When the content of the crosslinking agent is 0.01 part by mass or more, the coating film performance of the protective layer (P) is improved, and when it is 30 parts by mass or less, the coating stability of the protective layer (P) etc. may be improved. From the viewpoint of the recyclability of the multilayer structure of the present invention, there may be cases where it is preferable that the protective layer (P) does not contain a crosslinking agent.

[0097] Other polymers and tackifiers are not particularly limited. For example, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyvinyl chloride, polyvinylidene chloride, ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylate-maleic anhydride copolymer, styrene-maleic acid resin, styrene-butadiene resin, butadiene resin, acrylonitrile-butadiene resin, poly(meth)acrylonitrile resin, (meth)acrylamide resin, chlorinated polyethylene-based resin, chlorinated polypropylene resin, polyester resin, modified nylon resin, tackifying resins such as rosin, phenol resin, silicone resin, epoxy resin, etc. may be mentioned, and a plurality of them may be mixed and used as necessary. These polymers may be used as they are in a solid state, but from the viewpoint of maintaining stability in the coating liquid, it is preferable to use those processed into an aqueous dispersion.

[0098] Examples of pigments and dyes include titanium oxide, zinc white, carbon black, etc., and any of disperse dyes, acid dyes, cationic dyes, reactive dyes, etc. can be used. In the protective layer (P) of the present invention, various agents such as a leveling agent, an antifoaming agent, an anti-wicking agent, a pigment dispersant, an ultraviolet absorber, a thickener, a weathering agent, a flame retardant, etc. can also be added as necessary.

[0099] From the viewpoint of further improving recyclability, the protective layer (P) preferably contains a polyurethane-based resin (L) as a main component, and more preferably contains a metal compound (M) or a layered inorganic compound (N) in addition to the polyurethane-based resin (L), and even more preferably contains a layered inorganic compound (N) in addition to the polyurethane-based resin (L). On the other hand, from the viewpoint of further improving the gas barrier property, the protective layer (P) preferably contains a water-soluble polyvinyl alcohol-based resin (K) as a main component, and more preferably contains a metal compound (M) or a layered inorganic compound (N) in addition to the water-soluble polyvinyl alcohol-based resin (K), and even more preferably contains a metal compound (M) in addition to the water-soluble polyvinyl alcohol-based resin (K).

[0100] In the protective layer (P), the proportion occupied by the water-soluble polyvinyl alcohol-based resin (K), the water-dispersible polyurethane-based resin (L), the metal compound (M) and / or the layered inorganic compound (N) is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, particularly preferably 99% by mass or more. The protective layer (P) may substantially consist only of the water-soluble polyvinyl alcohol-based resin (K), the water-dispersible polyurethane-based resin (L), the metal compound (M) and / or the layered inorganic compound (N), and may also be 100% by mass or less.

[0101] In the resin constituting the protective layer (P), the proportion occupied by the water-soluble polyvinyl alcohol-based resin (K) or the water-dispersible polyurethane-based resin (L) is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, particularly preferably 99% by mass or more. The resin constituting the protective layer (P) may substantially consist only of the water-soluble polyvinyl alcohol-based resin (K) or the water-dispersible polyurethane-based resin (L), and may also be 100% by mass or less.

[0102] In the protective layer (P), the proportion occupied by the water-soluble polyvinyl alcohol-based resin (K) or the water-dispersible polyurethane-based resin (L) may be 55% by mass to 95% by mass.

[0103] From the viewpoints of gas barrier properties, recyclability and economy, the average thickness of the protective layer (P) of the composite multilayer film is preferably 0.05 μm or more and less than 10 μm. The average thickness of the protective layer (P) is more preferably 0.1 μm or more and less than 6 μm, still more preferably 0.3 μm or more and less than 4 μm, particularly preferably 0.5 μm or more and less than 2 μm.

[0104] As the lower limit of the total average thickness ratio of the layers mainly composed of polyolefin resins in the composite multilayer film of the present invention, 0.75 is preferable, 0.85 is more preferable, 0.88 is still more preferable, and 0.90 may also be used. By increasing the total average thickness ratio of the layers mainly composed of polyolefin resins in the composite multilayer film, the recyclability can be improved. As the upper limit of the total average thickness ratio of the layers mainly composed of polyolefin resins in the composite multilayer film, 0.995 is preferable, 0.99 is more preferable, and 0.98 may also be used. When the polyolefin resin in the composite multilayer film of the present invention contains a polypropylene resin, as the lower limit of the total average thickness ratio of the layers mainly composed of the polypropylene resin, 0.75 is preferable, 0.85 is more preferable, 0.88 is still more preferable, and 0.90 may also be used. By increasing the total average thickness ratio of the layers mainly composed of the polypropylene resin in the composite multilayer film, the recyclability can be improved. As the upper limit of the total average thickness ratio of the layers mainly composed of the polypropylene resin in the composite multilayer film, 0.995 is preferable, 0.99 is more preferable, and 0.98 may also be used. Examples of the layer mainly composed of the polypropylene resin include the adhesive layer (B) when the adhesive resin (b) is, for example, acid-modified polypropylene, and the core layer (C) when the polyolefin resin (c) is polypropylene.

[0105] The composite multilayer film of the present invention does not have a layer containing a resin having a melting point of less than 130°C as a main component and a metal layer having an average thickness of 1 μm or more. That is, it does not have a layer containing a resin having a melting point of less than 130°C as a main component and does not have a metal layer having an average thickness of 1 μm or more. By not having a layer containing a resin having a melting point of less than 130°C as a main component and a metal layer having an average thickness of 1 μm or more, the heat resistance and recyclability of the composite multilayer film tend to be improved. Here, the metal layer is a layer having continuous and discontinuous surfaces made of a metal such as aluminum foil. Further, from the viewpoint of further improving recyclability, it is preferable that the composite multilayer film of the present invention does not have a layer containing a polyester or polyamide having a melting point of 200°C or higher as a main component. The barrier layer (A), protective layer (P), resin layer (R), and adhesive layer are not layers containing a resin having a melting point of less than 130°C as a main component.

[0106] The composite multilayer film of the present invention preferably has an oxygen transmission rate (under the conditions of 20°C and 100% RH) measured according to the method described in JIS K 7126-2 (isobaric method; 2006) of less than 0.5 cc / (m 2 ·day·atm), more preferably less than 0.3 cc / (m 2 ·day·atm), even more preferably less than 0.1 cc / (m 2 ·day·atm), still more preferably less than 0.05 cc / (m 2 ·day·atm), and particularly preferably less than 0.02 cc / (m 2 ·day·atm) or less than 0.01 cc / (m 2 ·day·atm). A composite multilayer film having an oxygen transmission rate within the above range has excellent gas barrier properties, so that the storability of the contents is good.

[0107] The composite multilayer film of the present invention preferably has an oxygen transmission rate (under the conditions of 20°C and 100% RH) measured according to the method described in JIS K 7126-2 (isobaric method; 2006) immediately after retort treatment of less than 2 cc / (m 2 ·day·atm), preferably 1 cc / (m 2·day·atm) is more preferably less than, 0.7 cc / (m 2 ·day·atm) is even more preferably less than, 0.5 cc / (m 2 ·day·atm) is even more preferably less than, 0.3 cc / (m 2 ·day·atm) or less than 0.2 cc / (m 2 ·day·atm) is particularly preferably less than. The composite multilayer film having an oxygen transmission rate within the above range has excellent gas barrier properties even immediately after retort treatment, so that the preservability of the contents is good. Note that the retort treatment shall be carried out according to the method described in the examples.

[0108] <Multilayer structure> The composite multilayer film of the present invention itself can be used as a packaging material having gas barrier properties. However, by forming a multilayer structure in which at least one resin layer (R) containing a thermoplastic resin (r) as a main component is laminated, various functions as a packaging material such as designability and heat sealability can be imparted. The thermoplastic resin (r) is not particularly limited, and examples include linear low-density polyethylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, vinyl ester resin, ethylene-propylene copolymer, polypropylene, propylene-α-olefin copolymer (α-olefin having 4 to 20 carbon atoms), polybutene, polypentene, and other olefins alone or copolymers thereof, polyamides such as nylon 6 and nylon 6,6, polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polystyrene, polyvinyl chloride, polyvinylidene chloride, acrylic resin, polycarbonate, chlorinated polyethylene, chlorinated polypropylene, and the like. Among them, polyolefins are preferable from the viewpoints of excellent moisture resistance, mechanical properties, economy, heat sealability, etc., and polyamides and polyesters are preferable from the viewpoints of excellent mechanical properties, heat resistance, etc. In particular, in order to obtain a multilayer structure with excellent recyclability, it is preferable that the melting point is less than 200°C, and the thermoplastic resin (r) is of the same type as the above-mentioned polyolefin resin (c), that is, a polyolefin resin with a melting point of 130 to 170°C is more preferable, it is further preferable to contain a polypropylene-based resin as a main component, it is even more preferable to be a polypropylene-based resin, and it is particularly preferable to be a polypropylene resin. Regarding the content of the polypropylene resin in the resin layer (R), the same mode as the core layer (C) is a preferable mode. Therefore, in order to obtain a multilayer structure with excellent recyclability, it is preferable that both the polyolefin resin (c) and the thermoplastic resin (r) contain a polypropylene-based resin as a main component, and it is more preferable to be a polypropylene-based resin. Such a resin layer (R) may be unstretched, or may be stretched or rolled in a uniaxial or biaxial direction. From the viewpoint of improving mechanical strength, it is preferably a biaxially stretched layer, and from the viewpoint of improving heat sealability, it is preferably an unstretched layer.That is, a multilayer structure in which a resin layer (R) stretched or rolled in a uniaxial or biaxial direction is provided on one surface of the composite multilayer film and an unstretched resin layer (R) is provided on the other surface is also one of the preferred embodiments, with improved mechanical strength and heat sealability.

[0109] The method for forming the resin layer (R) is not particularly limited, but it is generally formed by melt extrusion using an extruder. As the die, either an annular die or a T-die can be used. The method for stretching in the uniaxial or biaxial direction is also not particularly limited, and it can be manufactured by performing stretching treatment in the flow direction of the film and / or the direction perpendicular to the flow direction, that is, the width direction, by a conventionally known stretching method such as roll-type uniaxial stretching, tubular simultaneous biaxial stretching, tenter-type sequential biaxial stretching, tenter-type simultaneous biaxial stretching, etc. From the viewpoint of the thickness uniformity and mechanical strength of the resulting layer, the area magnification is preferably 8 to 60 times. The area magnification is more preferably 55 times or less, and even more preferably 50 times or less. Also, the area magnification is more preferably 9 times or more. If the area magnification is less than 8 times, stretching marks may remain, and if it exceeds 60 times, the layer is likely to break during stretching.

[0110] From the viewpoint of industrial productivity, the average thickness of the resin layer (R) is preferably 10 to 200 μm. Specifically, the average thickness in the case of the unstretched layer is more preferably 10 to 150 μm, and the average thickness in the case of the biaxially stretched layer is more preferably 10 to 50 μm.

[0111] Also, the average thickness of the multilayer structure of the present invention is preferably 300 μm or less. Since the multilayer structure of the present invention is lightweight and flexible when the average thickness is within the above range, it is preferably used for flexible packaging applications. In addition, the amount of resin used in the multilayer structure is small, and the environmental load is suppressed. From the viewpoint of improving recyclability, the ratio of the total average thickness of the layers containing a polyolefin-based resin as the main component to the average thickness of the multilayer structure is preferably 0.85 or more, more preferably 0.88 or more, further preferably 0.90 or more, even more preferably 0.91 or more, and particularly preferably 0.92 or more. On the other hand, from the viewpoint of improving gas barrier properties, the ratio is preferably 0.995, more preferably 0.990, and may be 0.985.

[0112] The average thickness of each layer in the multilayer structure of the present invention may be appropriately adjusted according to the application. However, from the viewpoints of suppressing coloring during melt molding of the pulverized material, improving the thermal stability during melt molding, and suppressing the generation of defects, at least one of the core layer (C) and the resin layer (R) contains a polypropylene-based resin as the main component. The ratio of the total average thickness of the layers containing a polypropylene-based resin as the main component to the average thickness of the multilayer structure is preferably 0.85 or more, more preferably 0.88 or more, further preferably 0.90 or more, even more preferably 0.91 or more, and particularly preferably 0.92 or more. On the other hand, from the viewpoint of improving gas barrier properties, the ratio is preferably 0.995, more preferably 0.990, and may be 0.985.

[0113] The method of laminating the resin layer (R) on the composite multilayer film of the present invention is not particularly limited, and examples thereof include extrusion lamination, co-extrusion lamination, dry lamination, and the like. When laminating the resin layer (R) on the composite multilayer film, an adhesive layer may be provided. Further, each layer constituting the multilayer structure of the present invention may be laminated via an adhesive layer as necessary. However, there is no adhesive layer between the barrier layer (A) and the adhesive layer (B) of the multilayer film and between the adhesive layer (B) and the core layer (C). Further, there is no adhesive layer between the barrier layer (A) and the protective layer (P) or the inorganic layer (I). Furthermore, there is no adhesive layer between the protective layer (P) and the inorganic layer (I). The adhesive layer can be formed by applying a known adhesive and drying it. The adhesive is preferably a two-component reaction type polyurethane-based adhesive obtained by mixing and reacting a polyisocyanate component and a polyol component. The average thickness of the adhesive layer is not particularly limited, but is preferably 1 to 6 μm, more preferably 2 to 5 μm.

[0114] The multilayer structure of the present invention is not particularly limited, and for example, the following layer configuration is preferable from the viewpoint of obtaining a multilayer structure excellent in gas barrier properties and recyclability. In the following layer configuration, the barrier layer (A) is represented as A, the adhesive layer (B) is represented as B, the core layer (C) is represented as C, the inorganic layer (I) is represented as I, the protective layer (P) is represented as P, and the layer (R) is represented as R. " / " means being directly laminated, and " / / " means being laminated via an adhesive layer or being directly laminated, but being laminated via an adhesive layer is a preferable aspect. (1) C / B / A / I / P / / R (2) C / B / A / P / I / / R (3) R / / C / B / A / I / P / / R (4) R / / C / B / A / P / I / / R As in the above (3) and (4), when the resin layers (R) are arranged on both sides, it is preferable that one resin layer (R) is stretched in the uniaxial direction or the biaxial direction and the other resin layer (R) is unstretched. Although the preferable aspect varies depending on the content stored and the environment used when used as a packaging material, it is preferable that the resin layer (R) laminated on the core layer (C) side is stretched in the uniaxial direction or the biaxial direction.

[0115] The multilayer structure of the present invention may have other layers other than those described above, as long as the effects of the present invention are not inhibited. Examples of other layers include a recovery layer. In particular, it is preferable to reuse, as part or all of the recovery layer, a recovery composition containing the recovered product of the multilayer structure of the present invention described later. Another example of other layers is, for example, a printing layer. The printing layer may be included at any position of the multilayer structure of the present invention. Examples of the printing layer include a film obtained by applying and drying a solution containing, for example, a pigment or a dye and, if necessary, a binder resin. Examples of the coating method for the printing layer include various coating methods using a gravure printing method, a wire bar, a spin coater, a die coater, etc., in addition to the gravure printing method. The average thickness of the ink layer is not particularly limited, but is preferably 0.5 to 10 μm, and more preferably 1 to 4 μm.

[0116] It is preferable to reuse the recovered product (scrap) obtained by recovering the ends and defective products generated during the production of the multilayer structure of the present invention. A method for recovering a multilayer structure that is melt-molded after pulverizing the multilayer structure of the present invention, and a recovery composition containing the recovered product of the multilayer structure of the present invention are also preferred embodiments of the present invention.

[0117] In recovering the multilayer structure of the present invention, first, the recovered product of the multilayer structure of the present invention is pulverized. The pulverized recovered product may be directly melt-molded to obtain a recovery composition, or may be melt-molded together with other components as necessary to obtain a recovery composition. A preferable component to be added to the recovered product is a polyolefin resin, and a polypropylene-based resin is more preferable. As the polyolefin resin, the same type as the polyolefin resin (c) described above used in the multilayer film of the present invention is used. The pulverized recovered product may be directly used for the production of molded articles such as multilayer structures, or after the pulverized recovered product is melt-molded to obtain pellets made of a recovery composition, the pellets may be used for the production of molded articles.

[0118] Since the multilayer structure of the present invention is excellent in gas barrier properties under high humidity conditions immediately after retort treatment, it can be suitably used as a material for various packages such as food packaging, pharmaceutical packaging, industrial chemical packaging, and agricultural chemical packaging. In particular, the packaging material provided with the multilayer structure of the present invention can be suitably used as a packaging material having excellent recyclability.

Example

[0119] Hereinafter, the present invention will be described more specifically using examples, but the present invention is not limited by these examples at all.

[0120] Example 1 (1) Preparation of an EVOH (a1) and PA (a2) - containing resin composition (a) for the barrier layer (A) (1-1) Synthesis of EVAc Into a 250 L pressurized reaction tank equipped with a jacket, a stirrer, a nitrogen inlet, an ethylene inlet, and an initiator addition port, 100 kg of vinyl acetate, 10 kg of methanol, and 2.9 kg of 2 - methylene - 1,3 - propanediol diacetate (hereinafter referred to as MPDAc) were charged. After heating to 60 °C, nitrogen bubbling was carried out for 30 minutes to replace the inside of the reaction tank with nitrogen. Then, ethylene was introduced so that the reaction tank pressure (ethylene pressure) became 4.9 MPa. After adjusting the temperature inside the reaction tank to 60 °C, 36 g of 2,2’ - azobis(2,4 - dimethylvaleronitrile) (“V - 65” manufactured by Wako Pure Chemical Industries, Ltd.) as an initiator was added as a methanol solution to start the polymerization. During the polymerization, the ethylene pressure was maintained at 4.9 MPa and the polymerization temperature was maintained at 60 °C. After 6 hours, when the polymerization rate of vinyl acetate reached 45%, cooling was carried out to stop the polymerization. After opening the reaction tank to remove ethylene, nitrogen gas was bubbled to completely remove ethylene. Then, unreacted vinyl acetate was removed under reduced pressure, and methanol was added to the modified ethylene - vinyl acetate copolymer (hereinafter sometimes referred to as modified EVAc) in which the structural unit derived from MPDAc was introduced by copolymerization to obtain a 20 mass% methanol solution.

[0121] (1-2) Saponification of EVAc A 500 L reaction tank equipped with a jacket, a stirrer, a nitrogen inlet, a reflux condenser, and a solution addition port was charged with a 20% by mass methanol solution of the modified EVAc obtained in (1-1). While blowing nitrogen into this solution, the temperature was raised to 60 °C, and 0.5 equivalents of sodium hydroxide with respect to the vinyl acetate units in the modified EVAc was added as a 2 N methanol solution. After the addition of the sodium hydroxide methanol solution was completed, the reaction mixture was stirred for 2 hours while maintaining the temperature in the system at 60 °C to allow the saponification reaction to proceed. Then, acetic acid was added to stop the saponification reaction. Next, while heating and stirring at 60 to 80 °C, ion-exchanged water was added, methanol was distilled out of the reaction tank, and modified EVOH was precipitated. The precipitated modified EVOH was collected and pulverized with a mixer. The obtained modified EVOH powder was put into a 1 g / L aqueous acetic acid solution (bath ratio 20: 20 L of the aqueous solution per 1 kg of the powder) and stirred and washed for 2 hours. This was drained, and then put into a 1 g / L aqueous acetic acid solution (bath ratio 20) and stirred and washed for 2 hours. The drained product was put into ion-exchanged water (bath ratio 20), and the operation of stirring and washing for 2 hours and then draining was repeated 3 times for purification. Next, it was immersed in an aqueous solution containing 0.5 g / L of acetic acid and 0.1 g / L of sodium acetate (bath ratio 20) with stirring for 4 hours, then drained, and dried at 60 °C for 16 hours to obtain a crude dried product of modified EVOH.

[0122] (1-3) Production of Hydrous Pellets of EVOH An 80 L stirring tank equipped with a jacket, a stirrer, and a reflux condenser was charged with the crude dried product of modified EVOH, water, and methanol obtained in (1-2), and the temperature was raised to 80 °C to dissolve them. This solution was extruded through a tube with a diameter of 4 mm into a mixed solution of water / methanol = 90 / 10 cooled to 5 °C to precipitate it in a strand shape, and this strand was cut into pellets with a strand cutter to obtain hydrous pellets of modified EVOH. When the water content rate of the obtained hydrous pellets of modified EVOH was measured with a halogen moisture meter "HR73" manufactured by METTLER, it was 60% by mass.

[0123] (1-4) Production of EVOH Composition Pellets The water-containing pellets of the modified EVOH obtained in the above (3) were put into an aqueous acetic acid solution of 1 g / L (bath ratio 20) and stirred and washed for 2 hours. This was drained, and then put into an aqueous acetic acid solution of 1 g / L (bath ratio 20) again and stirred and washed for 2 hours. After draining, the aqueous acetic acid solution was renewed and the same operation was carried out. The one drained after washing with the aqueous acetic acid solution was put into ion-exchanged water (bath ratio 20), and the operation of stirring and washing for 2 hours and then draining was repeated 3 times for purification, and water-containing pellets of modified EVOH with the catalyst residue during the saponification reaction removed were obtained. The water-containing pellets were put into an aqueous solution (bath ratio 20) of sodium acetate (concentration 0.5 g / L), acetic acid (concentration 0.8 g / L), and phosphoric acid (concentration 0.005 g / L), and immersed for 4 hours while stirring periodically. This was drained and dried at 80 °C for 3 hours and at 105 °C for 16 hours to obtain pellets of the modified EVOH composition (EVOH(1)).

[0124] (1-5) Content and saponification degree of each structural unit of EVOH By the method described in WO2014 / 024912A1, the modified EVAc and the modified EVOH after saponification were 1 each subjected to 1H-NMR measurement to determine the ethylene unit content, saponification degree, and MPDAc unit content (content of modified group units containing primary hydroxyl groups represented by the general formula (I)) of the modified EVOH. The results are shown in Table 1. In addition, the "MPDAc unit" described above and in the table means that it was an MPDAc unit during copolymerization modification, and the MPDAc unit of the obtained EVOH has been saponified in the saponification step of the above (1-2), and the R1 in the general formula (I) is a single bond and X is a hydroxymethyl group, which has become a 2-methylene-1,3-propanediol unit, but it shall be referred to as the "MPDAc unit".

[0125] (1-6) MFR of EVOH Regarding the pellets of the modified EVOH composition obtained in the above (1-4), in accordance with JIS K7210 (1999), the MFR at a temperature of 210 °C and a load of 2160 g was measured. The MFR was 4.0 g / 10 min.

[0126] (1-7) Sodium salt content and phosphate compound content in the EVOH composition 0.5 g of the modified EVOH composition pellets obtained in (1-4) above were placed in a pressure vessel made of Teflon (registered trademark), and 5 mL of concentrated nitric acid was added thereto, followed by decomposition at room temperature for 30 minutes. After 30 minutes, the lid was closed, and decomposition was carried out by heating at 150 °C for 10 minutes and then at 180 °C for 5 minutes using a wet decomposition apparatus (manufactured by Actak Co., Ltd.: "MWS-2"), and then cooled to room temperature. This treatment solution was transferred to a 50 mL volumetric flask (made of TPX) and made up to the mark with pure water. For this solution, analysis of the contained metals was performed using an ICP emission spectroscopic analyzer (PerkinElmer "OPTIMA4300DV") to determine the sodium salt content and phosphate compound content in the modified EVOH composition pellets. The sodium salt content was 250 ppm in terms of sodium element conversion value, and the phosphate compound content was 15 ppm in terms of phosphate radical conversion value.

[0127] (1-8) Production of the resin composition 85 parts by mass of the modified EVOH composition pellets obtained in (1-4) above, 15 parts by mass of Nylon 6 "SF1018A" pellets manufactured by Ube Industries, Ltd. (hereinafter abbreviated as "PA6": relative viscosity [ηr] 3.0, melting point 221 °C), and magnesium hydroxide powder (150 ppm in terms of magnesium ion conversion) were mixed and then supplied to a twin-screw extruder "TEX30α" (screw diameter 30 mm) manufactured by Japan Steel Works, Ltd. Using a screw having a sequential offset kneading disk with L (screw length) / D (screw diameter) = 3, melt extrusion was carried out under the conditions of a melting temperature of 230 to 240 °C and an extrusion rate of 20 kg / hr to obtain strands. The obtained strands were cooled and solidified in a cooling tank and then cut to obtain pellets of a resin composition (EVOH (a1) and PA (a2) - containing resin composition (a) for the barrier layer (A)).

[0128] (2) Resin composition containing an adhesive resin (b) for the adhesive layer (B) Maleic anhydride-modified polypropylene manufactured by Mitsui Chemicals, Inc. ("Admer (trademark) QF500" (MFR (230 °C, under a load of 2.16 kg) 3.0 g / 10 min, melting point 161 °C) It was used as it was as resin composition pellets for the adhesive layer (B) with the adhesive resin (b).

[0129] (3) Resin composition containing polyolefin resin (c) for the core layer (C) Polypropylene manufactured by Nippon Polypropylene Corporation (「Novatech (trademark) PP EA7AD」 (MFR (under 230 °C, 2.16 kg load) 1.4 g / 10 min, melting point 161 °C)) was used as it was as resin composition pellets for the core layer (C).

[0130] (4) Production of multilayer film Using each of the resin composition pellets in (1) to (3) above, a multilayer film with an average thickness and layer structure of (A) / (B) / (C) = 2 μm / 2 μm / 16 μm = EVOH2 / Tie2 / PP16 was produced using coextrusion film production equipment. All the extruders were single-screw extruders with D (mm) = 30, and a full-flight screw with L / D = 28 and a compression ratio of 3.0 was used. As the die, a T-die of the feed block lamination type with a width of 350 mm was used. The temperature conditions at this time are shown below. Extrusion temperature of resin composition (a): Feeding section / Compression section / Measuring section / Adapter = 190 / 230 / 230 / 230 °C Extrusion temperature of resin composition containing adhesive resin (b): Feeding section / Compression section / Measuring section / Adapter = 175 / 220 / 230 / 230 °C Extrusion temperature of resin composition containing polyolefin resin (c): Feeding section / Compression section / Measuring section / Adapter = 175 / 220 / 230 / 230 °C Die temperature: 230 °C Cooling roll temperature: 80 °C

[0131] (5) Production of composite multilayer film On the surface of the barrier layer (A) of the multilayer film obtained in (4), a silica (SiOx) vapor deposition layer (inorganic layer (I)) with an average thickness of 30 nm was laminated by a known vacuum vapor deposition method. Next, on the surface of the inorganic layer (I), 30 parts by mass of a polyurethane dispersion "Takelac (trademark) WPB341" manufactured by Mitsui Chemicals, Inc. (an aqueous dispersion of a polyester urethane resin having metaxylylene diisocyanate as a monomer component, solid content 30%), 12.5 parts by mass of a swellable synthetic mica (Somashif (trademark) ME-300B4T, aspect ratio 330, average particle size 10 μm) manufactured by Katakura Koppe Agrí Co., Ltd., and 57.5 parts by mass of pure water were mixed to prepare a coating liquid (P1). The coating liquid was applied with a wire bar so that the average thickness after drying was 1 μm, and dried at 100 °C for 5 minutes to laminate a protective layer (P). In this way, a composite multilayer film having an average thickness and layer structure of (P) / (I) / (A) / (B) / (C) = 1 μm / 30 nm / 2 μm / 2 μm / 16 μm = PL1 / SiOx(30 nm) / EVOH2 / Tie2 / PP16 was produced.

[0132] (6) Fabrication of Multilayer Structure A two-component reactive polyurethane-based adhesive (24 parts by mass of "Takelac (trademark) A-520" and 4 parts by mass of "Takenate (trademark) A-50" manufactured by Mitsui Chemicals, Inc.) was mixed with 37 parts by mass of ethyl acetate to prepare an adhesive solution. Next, the adhesive solution was applied with a wire bar on the corona-treated surface of a polypropylene film (RXC-22 manufactured by Mitsui Chemicals Toatsu Chemicals, Inc.) (resin layer (R)) having an average thickness of 50 μm so that the average thickness after drying was 4 μm, dried at 100 °C for 5 minutes, and laminated with the composite multilayer film obtained in (5) above to produce a multilayer structure having an average thickness and layer structure of (R) / adhesive / (P) / (I) / (A) / (B) / (C) = 50 μm / 4 μm / 1 μm / 30 nm / 2 μm / 2 μm / 16 μm. The adhesion temperature (heating roll temperature) during lamination was 80 °C, and then aging was performed at 40 °C for 3 days.

[0133] (7) Oxygen Permeation Rate of Multilayer Structure Before Retort Treatment Using the multilayer structure obtained in (6), the oxygen transmission rate was measured with the composite multilayer film side as the oxygen supply side and the polypropylene film side as the carrier gas side. Specifically, an oxygen transmission rate measuring device (MOCON OX-TRAN2 / 21 manufactured by Modern Controls) was used, and the oxygen transmission rate (unit: cc / (m 2 ·day·atm)) was measured under the conditions of a temperature of 20°C, a humidity of 100% RH on the oxygen supply side, a humidity of 100% RH on the carrier gas side, an oxygen pressure of 1 atm, and a carrier gas pressure of 1 atm. Nitrogen gas containing 2% by volume of hydrogen gas was used as the carrier gas. When the oxygen transmission rate exceeded 0.5 cc / (m 2 ·day·atm), it was determined that the gas barrier property was poor. The results are shown in Table 3.

[0134] (8) Oxygen transmission rate immediately after retort treatment of the multilayer structure After cutting out two pieces of the multilayer structure obtained in (6) to A4 size, they were overlapped so that the polypropylene film sides faced each other, and three sides were heat-sealed to produce a pouch. Next, 900 g of water was filled from the opening of the pouch, and the opening was heat-sealed to produce a water-filled pouch. This was subjected to a retort treatment at 135°C for 120 minutes using a retort apparatus (a high-temperature and high-pressure cooking sterilization tester "RCS-40RTGN" manufactured by Nisaka Seisakusho Co., Ltd.). After the retort treatment, the water on the surface of the pouch was wiped off, the pouch was immediately opened to remove the water, a 9 cm square measurement sample was cut out from the center part (non-heat-sealed part) of the pouch, and the oxygen transmission rate was measured with the composite multilayer film side as the oxygen supply side and the polypropylene film side as the carrier gas side. Specifically, an oxygen transmission rate measuring device (MOCON OX-TRAN2 / 21 manufactured by Modern Controls) was used, and the oxygen transmission rate (unit: cc / (m 2 ·day·atm)) was measured under the conditions of a temperature of 20°C, a humidity of 100% RH on the oxygen supply side, a humidity of 100% RH on the carrier gas side, an oxygen pressure of 1 atm, and a carrier gas pressure of 1 atm. Nitrogen gas containing 2% by volume of hydrogen gas was used as the carrier gas. The measured value 4 hours after the start of measurement was taken as the oxygen transmission rate immediately after the retort treatment. When the oxygen transmission rate was 2 cc / (m 2When it exceeded ·day·atm), it was determined that the decrease in gas barrier properties immediately after retort treatment could not be suppressed. The results are shown in Table 3.

[0135] (9) Water vapor transmission rate of the multilayer structure before retort treatment (6) Using the multilayer structure obtained in (6), with the polypropylene film side as the water vapor supply side and the composite multilayer film side as the carrier gas side, the water vapor transmission rate was measured. Specifically, using a water vapor transmission rate measuring device ("MOCON PERMATRAN W3 / 33" manufactured by Modern Controls), in accordance with JIS K 7129-2 (infrared sensor method; 2019), at a temperature of 40 °C, a humidity of 90% RH on the water vapor supply side, and a humidity of 0% RH on the carrier gas side, the water vapor transmission rate (unit: g / (m 2 ·day)) was measured. Nitrogen gas was used as the carrier gas. The results are shown in Table 3.

[0136] (10) Water vapor transmission rate of the multilayer structure immediately after retort treatment (6) For the multilayer structure obtained in (6), retort treatment was performed in the same manner as in (8) above. After retort treatment, the water on the surface of the pouch was wiped off, the pouch was immediately opened to remove the water, a 9 cm square measurement sample was cut out from the center part (non-heat-sealed part) of the pouch, and with the polypropylene film side as the water vapor supply side and the composite multilayer film side as the carrier gas side, the water vapor transmission rate was measured. Specifically, using a water vapor transmission rate measuring device ("MOCON PERMATRAN W3 / 33" manufactured by Modern Controls), in accordance with JIS K 7129-2 (infrared sensor method; 2019), at a temperature of 40 °C, a humidity of 90% RH on the water vapor supply side, and a humidity of 0% RH on the carrier gas side, the water vapor transmission rate (unit: g / (m 2 ·day)) was measured. Nitrogen gas was used as the carrier gas. The measured value 4 hours after the start of measurement was taken as the water vapor transmission rate immediately after retort treatment. The results are shown in Table 3.

[0137] (11) Appearance immediately after retort treatment The multilayer structure obtained in (6) was subjected to retort treatment in the same manner as in (8) above. After the retort treatment, the water on the surface of the pouch was wiped off, and visual observation was immediately performed. The appearance characteristics of the pouch were evaluated in five grades A to E as follows. The results are shown in Table 3. Judgment criteria A: Almost no change in appearance was observed compared to before the retort treatment B: Slight whitening was observed C: Slight whitening or / and deformation was observed D: Moderate whitening or / and deformation was observed, or partial delamination was observed E: Severe whitening or / and deformation was observed, or extensive delamination was observed

[0138] (12) Bumps and coloring of the melt-molded product of the pulverized multilayer structure The multilayer structure obtained in (6) was pulverized into a size of 4 mm square or less. This pulverized product and polypropylene manufactured by Nippon Polypropylene Co., Ltd. (「Novatech (trademark) PP EA7AD」 (MFR (under 230 °C, 2.16 kg load) 1.4 g / 10 min, melting point 161 °C)) were blended at a mass ratio (pulverized product / polypropylene resin) of 30 / 70, and a single-layer film with a thickness of 100 μm was obtained by performing single-layer film formation under the extrusion conditions shown below. The thickness of the single-layer film was adjusted by appropriately changing the screw rotation speed and the take-up roll speed. Also, as a control, a single-layer film with a thickness of 100 μm was obtained using only the polypropylene resin in the same manner. Extruder: Single-screw extruder manufactured by Toyo Seiki Seisakusho Screw diameter: 20 mm φ (L / D = 20, compression ratio = 3.5, full flight type) Extrusion temperature: Feeding section / Compression section / Metering section / Die C1 / C2 / C3 / D = 235 / 235 / 235 / 235 °C Take-up roll temperature: 80 °C The bumps and coloring status of the obtained single-layer film were evaluated in five grades A to E as follows. The results are shown in Table 3. Judgment criteria for bumps A: The amount of bumps was almost unchanged compared to the control B: There was slightly more amount of small lumps compared to the control. C: There was more amount of small lumps compared to the control. D: There was more amount of large lumps compared to the control. E: There was much more amount of large lumps compared to the control. Judgment criteria for coloring A: The degree of hue change was small compared to the control. B: Slight coloring was observed compared to the control. C: Moderate coloring was observed compared to the object. D: Significant coloring was observed compared to the object, but it was uniform as a whole. E: Significant coloring was observed compared to the object, and unevenness by location was also observed.

[0139] (13) Melting viscosity stability of the pulverized product of the multilayer structure (6) The multilayer structure obtained in (6) was pulverized to a size of 4 mm square or less. This pulverized product and polypropylene manufactured by Nippon Polypro Co., Ltd. ("Novatec (trademark) PP EA7AD" (MFR (at 230 °C, under a load of 2.16 kg) 1.4 g / 10 min, melting point 161 °C)) were blended at a mass ratio (pulverized product / polypropylene resin) of 30 / 70 and weighed 75 g in total. Using a lab plastomill (biaxial anisotropic), kneading was carried out for 30 minutes under a nitrogen atmosphere at 235 °C and 100 rpm. Also, as a control, kneading was carried out in the same manner using only the polypropylene resin. Evaluation was performed in 5 grades of A to E below according to the ratio (TR / TP) of the torque value (TR) of the blended resin after 30 minutes of kneading and the torque value (TP) of the polypropylene resin. The results are shown in Table 3. Judgment criteria A: 90 / 100 or more and less than 110 / 100 B: 80 / 100 or more and less than 90 / 100, or 110 / 100 or more and less than 120 / 100 C: 70 / 100 or more and less than 80 / 100, or 120 / 100 or more and less than 130 / 100 D: 60 / 100 or more and less than 70 / 100, or 130 / 100 or more and less than 140 / 100 E: Less than 60 / 100, or 140 / 100 or more

[0140] Example 2 A coextruded film having an average thickness and layer structure of (A) / (B) / (C) = 10 μm / 10 μm / 80 μm = EVOH10 / Tie10 / PP80 was produced in the same manner as in Example 1 except for changing the average thickness. After that, stretching 5 times in the longitudinal direction was applied in an atmosphere of 120 °C to produce a stretched multilayer film having an average thickness and layer structure of 2 μm / 2 μm / 16 μm = EVOH2 / Tie2 / PP16. Resin composition pellets, a composite multilayer film, and a multilayer structure were produced in the same manner as in Example 1 except that the obtained stretched multilayer film was used instead of the multilayer film of Example 1, and various measurements and evaluations were performed. The results are shown in Table 3.

[0141] Example 3 Resin composition pellets, a multilayer film, a composite multilayer film, and a multilayer structure were produced in the same manner as in Example 2 except that EVOH(2) (ethylene unit content 38 mol%, saponification degree 99.9 mol% or more, not containing MPDAc units, MFR (210 °C, 2.16 kg load) 4.0 g / 10 min, containing 250 ppm of sodium acetate in terms of sodium ions, 25 ppm of phosphate ions in terms of phosphate radicals, 150 ppm of boric acid in terms of boron element, and no polyvalent metal ions) was used instead of EVOH(1), and various measurements and evaluations were performed. The results are shown in Table 3.

[0142] Example 4 Resin composition pellets, a multilayer film, a composite multilayer film, and a multilayer structure were produced in the same manner as in Example 2 except that EVOH(3) (ethylene unit content 38 mol%, saponification degree 99.9 mol% or more, MPDAc unit content 5 mol%, MFR (210 °C, 2.16 kg load) 4.0 g / 10 min, containing 250 ppm of sodium acetate in terms of sodium ions, 25 ppm of phosphate ions in terms of phosphate radicals, 200 ppm of boric acid in terms of boron element, and no polyvalent metal ions) was used instead of EVOH(1), and various measurements and evaluations were performed. The results are shown in Table 3.

[0143] Example 5 Except that EVOH(4) (ethylene unit content 27 mol%, saponification degree 99.9 mol% or more, does not contain MPDAc unit, MFR (210 °C, 2.16 kg load) 3.7 g / 10 min, contains 220 ppm of sodium acetate in terms of sodium ion, 15 ppm of phosphate ion in terms of phosphate radical, 150 ppm of boric acid in terms of boron element, and does not contain polyvalent metal ions) was used instead of EVOH(1), resin composition pellets, multilayer films, composite multilayer films and multilayer structures were produced in the same manner as in Example 2, and various measurements and evaluations were carried out. The results are shown in Table 3.

[0144] Example 6 Except that EVOH(5) (ethylene unit content 44 mol%, saponification degree 99.9 mol% or more, does not contain MPDAc unit, MFR (210 °C, 2.16 kg load) 4.5 g / 10 min, contains 280 ppm of sodium acetate in terms of sodium ion, 30 ppm of phosphate ion in terms of phosphate radical, 250 ppm of boric acid in terms of boron element, and does not contain polyvalent metal ions) was used instead of EVOH(1), resin composition pellets, multilayer films, composite multilayer films and multilayer structures were produced in the same manner as in Example 2, and various measurements and evaluations were carried out. The results are shown in Table 3.

[0145] Example 7 A coextruded film having an average thickness and layer structure of (A) / (B) / (C) = 100 μm / 100 μm / 800 μm = EVOH100 / Tie100 / PP800 was produced in the same manner as in Example 1 except for changing the average thickness. Then, stretching was applied 5 times in the longitudinal direction in an atmosphere of 120 °C and then 10 times in the width direction in an atmosphere of 150 °C to produce a stretched multilayer film having an average thickness and layer structure of 2 μm / 2 μm / 16 μm = EVOH2 / Tie2 / PP16. Except that the obtained stretched multilayer film was used instead of the multilayer film of Example 1, resin composition pellets, composite multilayer films and multilayer structures were produced in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 3.

[0146] Examples 8 to 22, Comparative Examples 2 to 5 The resin composition pellets, multilayer films, composite multilayer films, and multilayer structures were produced and subjected to various measurements and evaluations in the same manner as in Example 7, except that the composition of the resin composition, the layer configuration, and the average thickness of the composite multilayer film were changed as shown in Tables 1 and 2. In Examples 13, 14, and 15, magnesium stearate, calcium stearate, and zinc stearate were used instead of magnesium hydroxide, respectively. In Example 19, an alumina (AlOx) vapor deposition layer was used instead of the silica (SiOx) vapor deposition layer. The results are shown in Tables 3 and 4.

[0147] Example 23 A coating liquid (P2) adjusted in the same manner as in Example 1 except that a swellable synthetic mica (Somashif (trademark) ME-200B4T, aspect ratio 230, average particle size 7 μm) manufactured by Katakura Koppu Agri Co., Ltd. was used instead of the swellable synthetic mica (Somashif (trademark) ME-300B4T, aspect ratio 330, average particle size 10 μm) manufactured by Katakura Koppu Agri Co., Ltd. used as the material for the protective layer (P) was used in place of the coating liquid (P1). The resin composition pellets, composite multilayer films, and multilayer structures were produced and subjected to various measurements and evaluations in the same manner as in Example 7. The results are shown in Table 4.

[0148] Example 24 A coating liquid (P3) adjusted in the same manner as in Example 1 except that the swellable synthetic mica (Somashif (trademark) ME-300B4T, aspect ratio 330, average particle size 10 μm) manufactured by Katakura Koppu Agri Co., Ltd. used as the material for the protective layer (P) was not used was used in place of the coating liquid (P1). The resin composition pellets, composite multilayer films, and multilayer structures were produced and subjected to various measurements and evaluations in the same manner as in Example 7. The results are shown in Table 4.

[0149] Example 25 To 10.4 g of tetraethoxysilane, 89.6 g of hydrochloric acid (0.1 N) was added, and the mixture was stirred for 30 minutes for hydrolysis and condensation to obtain 30 parts by mass of a hydrolysis and condensation solution having a solid content of 3% by mass (in terms of SiO₂) and 70 parts by mass of a 3% by mass aqueous solution of polyvinyl alcohol. A coating liquid (P4) was prepared by mixing them, and a resin composition pellet, a multilayer film, a composite multilayer film, and a multilayer structure were produced in the same manner as in Example 7 except that the coating liquid (P4) was used instead of the coating liquid (P1), and various measurements and evaluations were carried out. The results are shown in Table 4.

[0150] Comparative Example 1 In Example 1, when forming the multilayer film, only the resin composition containing the polyolefin resin (c) was extruded without simultaneously extruding the resin compositions containing the resin composition (a) and the adhesive resin (b), and a single-layer film (core layer (C)) having an average thickness of 1000 μm was produced by adjusting the average thickness. A stretched single-layer film (average thickness 20 μm), a composite multilayer film, and a multilayer structure were produced in the same manner as in Example 7 except that the obtained single-layer film was used instead of the multilayer film, and various measurements and evaluations were carried out. The results are shown in Table 4.

[0151]

Table 1

[0152]

Table 2

[0153]

Table 3

[0154]

Table 4

Claims

1. On the surface side of the barrier layer (A) of a multilayer film having a structure in which a barrier layer (A), an adhesive layer (B), and a core layer (C) are laminated adjacent to each other in this order with the barrier layer (A) on the outermost surface, a protective layer (P) and an inorganic layer (I) adjacent to each other are provided. The barrier layer (A) consists only of a resin composition (a) containing an ethylene-vinyl alcohol copolymer (a1) having an ethylene unit content of 20 to 50 mol% and a saponification degree of 90 mol% or more and a polyamide (a2), and the mass ratio (a1 / a2) of the ethylene-vinyl alcohol copolymer (a1) to the polyamide (a2) is 55 / 45 to 98 / 2. The adhesive layer (B) contains, as a main component, an adhesive resin (b) having a melting point of 130 to 170°C. The core layer (C) contains, as a main component, a polyolefin resin (c) having a melting point of 130 to 170°C. The resin composition (a) contains 40 to 500 ppm of an alkali metal ion (d). A composite multilayer film having no layer containing a resin having a melting point of less than 130°C as a main component and no metal layer having an average thickness of 1 μm or more.

2. The composite multilayer film according to claim 1, wherein the protective layer (P) in the protective layer (P) and the inorganic layer (I) adjacent to each other is a protective layer (Pa) laminated at a position closer to the surface side of the barrier layer (A) of the multilayer film than the inorganic layer (I).

3. The composite multilayer film according to claim 1, wherein the protective layer (P) in the protective layer (P) and the inorganic layer (I) adjacent to each other is a protective layer (Pb) laminated at a position farther from the surface side of the barrier layer (A) of the multilayer film than the inorganic layer (I).

4. The composite multilayer film according to claim 1, wherein the protective layer (P) in the protective layer (P) and the inorganic layer (I) adjacent to each other includes a protective layer (Pa) laminated at a position closer to the surface side of the barrier layer (A) of the multilayer film than the inorganic layer (I) and a protective layer (Pb) laminated at a position farther from the surface side of the barrier layer (A) of the multilayer film than the inorganic layer (I), and has a structure in which the protective layer (Pa), the inorganic layer (I), and the protective layer (Pb) are laminated adjacent to each other in this order on the surface side of the barrier layer (A).

5. The composite multilayer film according to claim 1, wherein the adhesive resin (b) contains acid-modified polypropylene as a main component.

6. The composite multilayer film according to claim 1, wherein the polyolefin resin (c) contains polypropylene as a main component.

7. The composite multilayer film according to claim 1, wherein the inorganic layer (I) is an inorganic oxide vapor deposition layer mainly composed of alumina or silica.

8. The composite multilayer film according to claim 1, wherein the protective layer (P) is mainly composed of a water-soluble polyvinyl alcohol-based resin (K) or a water-dispersible polyurethane-based resin (L).

9. The composite multilayer film according to claim 1, wherein the protective layer (P) contains at least one selected from the group consisting of at least one metal compound (M) selected from the group consisting of metal alkoxides, hydrolysis products of metal alkoxides, and hydrolysis condensates of metal alkoxides, and a layered inorganic compound (N), and the total content thereof is 5 to 40% by mass.

10. The composite multilayer film according to claim 1, wherein the resin composition (a) contains at least one polyvalent metal ion (e) selected from the group consisting of magnesium ions, calcium ions, and zinc ions in an amount of 10 to 500 ppm.

11. The composite multilayer film according to claim 1, wherein the ethylene-vinyl alcohol copolymer (a1) has a modified group containing a primary hydroxyl group represented by the following general formula (I). 【Chemical 1】 [wherein X represents a hydrogen atom, a methyl group or a group represented by R ２ -OH. R １ , R ２ each independently represents a single bond, an alkylene group having 1 to 9 carbon atoms or an alkyleneoxy group having 1 to 9 carbon atoms, and the alkylene group and the alkyleneoxy group may contain a hydroxyl group, an alkoxy group or a halogen atom.]

12. R in the general formula (I) above １ The composite multilayer film according to claim 11, wherein is a single bond and X is a hydroxymethyl group.

13. The composite multilayer film according to claim 11, wherein the content of the modified group containing a primary hydroxyl group in the ethylene-vinyl alcohol copolymer (a1) is 0.3 mol% or more and less than 10 mol%.

14. The composite multilayer film according to claim 1, wherein the multilayer film is substantially not stretched.

15. The composite multilayer film according to claim 1, wherein the multilayer film is stretched 3 times or more and less than 12 times only in a substantially uniaxial direction.

16. The composite multilayer film according to claim 1, wherein the multilayer film is stretched 3 times or more and less than 12 times in each of the biaxial directions.

17. The composite multilayer film according to claim 1, wherein the adhesive resin (b) contains acid-modified polypropylene as a main component, the polyolefin resin (c) contains polypropylene as a main component, and the total average thickness ratio of the layers mainly composed of polypropylene-based resins to the average thickness of the composite multilayer film is 0.75 or more.

18. A multilayer structure obtained by laminating the composite multilayer film according to any one of claims 1 to 17 and at least one resin layer (R) mainly composed of a thermoplastic resin (r).

19. The multilayer structure according to claim 18, wherein the thermoplastic resin (r) contains polypropylene resin as a main component.

20. A packaging material for retort having the multilayer structure according to Claim 18.

21. Immediately after retort treatment at 135°C for 120 minutes, the oxygen transmission rate (under the conditions of 20°C and 100% RH) measured by the method described in JIS K 7126-2:2006 is less than 2 cc / (m ２ ·day·atm), the packaging material for retort according to claim 20.

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