Multilayer structure and packaging material

Abstract

Provided is a multilayer structure having a sealant layer (X) and a base material layer (Y). The sealant layer (X) has a barrier layer (A) which contains, as a main component, an EVOH (a) having an ethylene unit content of 20-50 mol% and a saponification degree of 90 mol% or more, an adhesive layer (B) which contains an adhesive resin (b) as a main component, and a thermal bonding layer (C) which contains an ethylene-α-olefin copolymer resin (c) having a density of 0.880-0.930 g / cm3. The base material layer (Y) contains, as a main component, polypropylene (y) having a melting point of 150°C or higher as measured by a differential scanning calorimeter (DSC) and is stretched in biaxial directions. The multilayer structure has an elastic modulus of 2000 MPa or more under conditions of 23°C and 50% RH in the biaxial directions, in which the thermal bonding layer (C) of the sealant layer (X) serves as the outermost surface.

Description

[Technical Field]

[0001] The present invention relates to multilayer structures and packaging materials. [Background technology]

[0002] Packaging materials for long-term food storage often require gas barrier properties, including oxygen barrier properties. Using packaging materials with high gas barrier properties can prevent oxidative deterioration of food due to oxygen intrusion and microbial growth. Metal foils (e.g., aluminum foils), metal vapor deposition layers, and inorganic vapor deposition layers (e.g., silicon oxide and aluminum oxide) are commonly used to improve gas barrier properties. Meanwhile, resin layers with gas barrier properties, such as vinyl alcohol polymers and polyvinylidene chloride, are also widely used. Vinyl alcohol polymers exhibit gas barrier properties through crystallization and densification due to hydrogen bonding between hydroxyl groups in the molecules. Among these, ethylene-vinyl alcohol copolymers (hereinafter sometimes abbreviated as "EVOH") are suitable for melt molding due to their excellent thermal stability. With the development of coextrusion technology, multilayer structures with an EVOH layer as an intermediate layer have become widely used as gas barrier packaging materials.

[0003] In recent years, environmental and waste issues have led to a growing global demand for post-consumer recycling (hereinafter simply referred to as "recycling"). This involves collecting and recycling packaging materials consumed in the market. Recycling typically involves shredding collected packaging materials, sorting and cleaning them as necessary, and then melt-mixing them using an extruder. In this regard, packaging materials must be composed of as few materials as possible (mono-materialization), which allows for the production of high-purity, high-quality recycled raw materials. For example, gas-barrier packaging materials containing a polyamide layer and an EVOH layer are commonly used due to their excellent mechanical strength. However, chemical reactions between the polyamide resin and the EVOH can produce particles, which can reduce recyclability. Taking these challenges into account, it is necessary to achieve mono-materialization to provide gas-barrier packaging materials with excellent recyclability while maintaining gas barrier properties and mechanical strength.

[0004] Patent Document 1 describes that a multilayer structure having a hard layer with a puncture strength of 40 N / mm or more and 150 N / mm or less and (1) a resin composition layer containing EVOH having a melting point of 170°C or more and EVOH having a melting point of less than 170°C, or (2) a resin composition layer containing modified EVOH containing a modifying group with a specific primary hydroxyl group, has excellent mechanical strength and thermoformability despite not having a polyamide layer, and when the recovered material is melt-molded, the generation of lumps due to resin deterioration (gelation) is suppressed, and it also has excellent recyclability. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 071513 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when used as a packaging material for heavy contents, there is a tendency for higher resistance to bag breakage due to dropping, and the multilayer structure described in Patent Document 1 sometimes has insufficient resistance to bag breakage due to dropping. In particular, when the temperature of the contents is high, such as when the contents are filled with heat, sterilized by heat, or cooked by heat, the resistance to bag breakage due to dropping may be particularly insufficient.

[0007] The present invention has been made to solve the above problems, and an object of the present invention is to provide a multilayer structure and a packaging material that are excellent in gas barrier properties, resistance to bag breakage due to dropping, and recyclability. [Means for solving the problem]

[0008] According to the present invention, the above object is to [1] A sealant layer (X) and a base layer (Y) are provided, wherein the sealant layer (X) comprises a barrier layer (A) containing, as a main component, an ethylene-vinyl alcohol copolymer (a) (hereinafter sometimes abbreviated as "EVOH (a)") having an ethylene unit content of 20 to 50 mol% and a saponification degree of 90 mol% or more, an adhesive layer (B) containing, as a main component, an adhesive resin (b), and a base layer (Y) having a density of 0.880 to 0.930 g / cm 3 a multilayer structure having a heat-sealable layer (C) containing as a main component an ethylene-α-olefin copolymer resin (c) (hereinafter, sometimes simply referred to as "ethylene-α-olefin copolymer resin (c)") represented by the formula (I), a base layer (Y) containing as a main component a polypropylene (y) (hereinafter, sometimes simply referred to as "polypropylene (y)") having a melting point measured by a differential scanning calorimeter (DSC) of 150°C or higher, the base layer (Y) being a biaxially stretched layer having an elastic modulus of 2000 MPa or higher in both directions under conditions of 23°C and 50% RH, and the heat-sealable layer (C) of the sealant layer (X) on the outermost surface; [2] The puncture strength S measured according to JIS Z 1707:2019 under conditions of 23°C and 50% RH, and the puncture strength S of the base layer (Y) measured according to JIS Z 1707:2019 under conditions of 23°C and 50% RH Y Difference with (SS Y ) is 3.5N or more; [3] The multilayer structure according to [2], wherein the puncture strength S is 12 N or more; [4] The multilayer structure of any one of [1] to [3], wherein when the base layer (Y) is heated from 20°C to 220°C at 10°C / min and then cooled to -50°C at 10°C / min using a differential scanning calorimeter (DSC), the difference (T1-T2) between the maximum endothermic peak temperature (T1) during heating and the maximum exothermic peak temperature (T2) during cooling is 56°C or less; [5] The multilayer structure of any one of [1] to [4], wherein the sealant layer (X) and the base layer (Y) are laminated via an adhesive layer (Z), and the thickness of the adhesive layer (Z) is 2 to 7 μm; [6] The multilayer structure of any one of [1] to [5], wherein the ethylene-α-olefin copolymer resin (c) is a linear low-density polyethylene copolymerized with ethylene and an α-olefin having 6 or more carbon atoms; [7] A multilayer structure according to any one of [1] to [6], wherein the barrier layer (A) contains a boron compound in an amount of 50 to 400 ppm in terms of elemental boron; [8] The multilayer structure of any one of [1] to [7], wherein the ethylene unit content of the EVOH (a) is 22 mol% or more and 28 mol% or less; [9] The multilayer structure of any one of [1] to [8], wherein the thickness of the barrier layer (A) is 5 μm or less;

[10] The oxygen transmission rate measured according to the method described in JIS K 7126-2:2006 under conditions of 20°C and 65% RH is 5 cc / (m 2 A multilayer structure of any of [1] to [9], which has a thermal conductivity of 0.1 MPa or less (·day·atm);

[11] The water vapor transmission rate measured according to the method described in JIS K 7129-2:2019 under conditions of 40 ° C and 90% RH is 3 g / (m 2 A multilayer structure of any one of [1] to

[10] , wherein the maximum permissible ...

[12] A packaging material comprising any one of the multilayer structures described in [1] to

[11] ; This is achieved by providing [Effects of the Invention]

[0009] The multilayer structure and packaging material of the present invention are excellent in gas barrier properties, resistance to bag breakage due to dropping, and recyclability. DETAILED DESCRIPTION OF THE INVENTION

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

[0011] The multilayer structure of the present invention has a sealant layer (X) and a substrate layer (Y), wherein the sealant layer (X) comprises a barrier layer (A) containing, as a main component, EVOH (a) having an ethylene unit content of 20 to 50 mol% and a saponification degree of 90 mol% or more, an adhesive layer (B) containing, as a main component, an adhesive resin (b), and a cellulose ester resin (C) having a density of 0.880 to 0.930 g / cm 3 The heat-sealable layer (C) comprises, as a main component, an ethylene-α-olefin copolymer resin (c) represented by the formula (I), and the base layer (Y) comprises, as a main component, a polypropylene (y) having a melting point of 150°C or higher as measured by differential scanning calorimetry (DSC), and is a biaxially stretched layer having an elastic modulus of 2000 MPa or higher in both directions at 23°C and 50% RH. The heat-sealable layer (C) of the sealant layer (X) is located on the outermost surface. "Containing as a main component" means containing more than 50% by mass, preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, and may also be 95% by mass or more, 97% by mass or more, or 99% by mass or more.

[0012] The multilayer structure of the present invention tends to be able to improve gas barrier properties while maintaining recyclability by providing the barrier layer (A). The multilayer structure of the present invention tends to be able to improve mechanical strength including resistance to bag breakage due to dropping and recyclability by providing the adhesive layer (B). The main component of the heat-sealable layer (C) has a density of 0.880 to 0.930 g / cm. 3The ethylene-α-olefin copolymer resin (c) tends to achieve excellent mechanical strength, including resistance to bag drop rupture, while maintaining heat sealability. The multilayer structure of the present invention tends to achieve excellent mechanical strength, including resistance to bag drop rupture, even under high-temperature conditions, when the base layer (Y) contains, as a main component, polypropylene (y) having a melting point of 150°C or higher as measured by differential scanning calorimetry (DSC), and is a biaxially stretched layer, and when the biaxial modulus of elasticity at 23°C and 50% RH is 2000 MPa or higher.

[0013] "Bag drop resistance" can be evaluated by the number of tests conducted before water leakage occurs when a bag made using the multilayer structure of the present invention is filled with contents and dropped from a certain height, and can be evaluated specifically by the method described in the Examples. When expressed as "bag drop resistance," it basically means resistance to bag drop at room temperature and at high temperatures. "Recyclability" can be evaluated by the occurrence of lumps in a melt-molded product obtained by melt-kneading crushed material of the multilayer structure, and can be evaluated specifically by the method described in the Examples. "Barrier properties" refer to oxygen barrier properties and water vapor barrier properties, and "gas barrier properties" refer to oxygen barrier properties.

[0014] "ppm" means the content by mass (ppm by mass).

[0015] The term "surface (or surface layer)" in a multilayer film or multilayer structure does not refer to the front or back, but refers to the exposed surface. In other words, a multilayer film or multilayer structure has two surfaces. Similarly, a multilayer film or multilayer structure has two outermost surfaces.

[0016] The phrase "consisting essentially of" allows for the inclusion of optional components to the extent that the effects of the present invention are not affected, and "consisting only of" means excluding optional components other than impurities that are inevitably contained.

[0017] <Barrier layer (A)> The multilayer structure of the present invention has a barrier layer (A) containing EVOH (a) as a main component. EVOH (a) has excellent gas barrier properties, so a multilayer structure having a layer containing EVOH (a) as a main component is preferably used as a packaging material with excellent content preservation properties. EVOH (a) can be easily melt-mixed with polyolefin-based resins, providing a packaging material with excellent recyclability.

[0018] EVOH (a) is usually obtained by saponifying an ethylene-vinyl ester copolymer obtained by polymerizing ethylene and a vinyl ester. A representative vinyl ester is vinyl acetate, but other fatty acid vinyl esters (vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate, etc.) can also be used.

[0019] The ethylene unit content of EVOH (a) is 20 to 50 mol%. When the ethylene unit content is 20 mol% or more, the melt moldability of EVOH (a) and the pulverized product of the multilayer structure containing EVOH (a) is improved. The ethylene unit content is preferably 21 mol% or more, more preferably 22 mol% or more, and may be 25 mol% or more. On the other hand, when the ethylene unit content is 50 mol% or less, the gas barrier property of the multilayer structure of the present invention is improved. The ethylene unit content is preferably 46 mol% or less, more preferably 42 mol% or less, even more preferably 39 mol% or less, even more preferably 33 mol% or less, and particularly preferably 28 mol% or less. The saponification degree of EVOH (a) 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 (a). When the saponification degree is 90 mol% or more, the gas barrier property of the multilayer structure 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 saponification degree may be 100 mol% or less. The ethylene unit content and saponification degree of EVOH (a) are as follows: 1 It can be determined by H-NMR measurement.

[0020] EVOH (a) may be a mixture of two or more EVOHs having different ethylene unit contents. In this case, the difference in ethylene unit content between the EVOHs having the most different ethylene unit contents is preferably 30 mol% or less, more preferably 25 mol% or less, even more preferably 20 mol% or less, and may be 3 mol% or more. Similarly, EVOH (a) may be a mixture of two or more EVOHs having different degrees of saponification. In this case, the difference in saponification degree between the EVOHs having the most different degrees of saponification 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 thermoformability and gas barrier properties at a higher level, it is preferred to use as EVOH (a) an EVOH (a1) having an ethylene unit content of 22 mol% or more and less than 34 mol% and a degree of saponification of 99 mol% or more and an EVOH (a2) having an ethylene unit content of 34 mol% or more and less than 50 mol% and a degree of saponification of 99 mol% or more, mixed in a blending mass ratio (a1 / a2) of 60 / 40 to 90 / 10.

[0021] EVOH (a) may contain other monomer units in addition to ethylene, vinyl ester, and vinyl alcohol, as long as the effects of the present invention are not impaired. In particular, by introducing a modifying group containing a primary hydroxyl group having a specific structure, it may be possible to achieve high levels of both gas barrier properties and moldability of EVOH (a). The content of other monomer units is preferably 10 mol% or less, more preferably 5 mol% or less, even more preferably 1 mol% or less, and particularly preferably substantially none. Examples of such other monomers include alkenes such as propylene, butylene, pentene, and hexene; 3-acyloxy-1-propene, 3-acyloxy-1-butene, 4-acyloxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-methyl ...4-methyl-1-butene, 4-methyl-1-butene, 4-methyl-1-butene, 4-methyl-1-butene, 4-methyl-1-butene, 4-methyl-1-butene, 4-methyl-1-butene, 4-methyl-1-butene, 4-methyl-1-butene, 4 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 Examples of suitable vinyl silane compounds include ester group-containing alkenes such as siloxy-1-hexene and 1,3-diacetoxy-2-methylenepropane, or saponified products thereof; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, and itaconic acid, or their anhydrides, salts, or mono- or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, and methallylsulfonic acid, or their salts; vinyl silane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxyethoxy)silane, and γ-methacryloxypropylmethoxysilane; and alkyl vinyl ethers, vinyl ketone, N-vinylpyrrolidone, vinyl chloride, and vinylidene chloride.

[0022] EVOH (a) may be modified as necessary by urethanization, acetalization, cyanoethylation, oxyalkylenation, etc. Oxyalkylenation can be carried out using an epoxy compound, such as epoxyethane (ethylene oxide), epoxypropane, 1,2-epoxybutane, 2,3-epoxybutane, 3-methyl-1,2-epoxybutane, 1,2-epoxypentane, 3-methyl-1,2-epoxypentane, 1,2-epoxyhexane, 2,3-epoxyhexane, 3,4-epoxyhexane, 3-methyl-1,2-epoxyhexane, 3-methyl-1,2-epoxyheptane, 4-methyl-1,2-epoxyheptane, 1, Examples include 2-epoxyoctane, 2,3-epoxyoctane, 1,2-epoxynonane, 2,3-epoxynonane, 1,2-epoxydecane, 1,2-epoxydodecane, epoxyethylbenzene, 1-phenyl-1,2-propane, 3-phenyl-1,2-epoxypropane, various alkyl glycidyl ethers, various alkylene glycol monoglycidyl ethers, various alkenyl glycidyl ethers, various epoxy alkanols such as glycidol, various epoxy cycloalkanes, and various epoxy cycloalkenes. Among these, 1,2-epoxybutane, 2,3-epoxybutane, epoxypropane, epoxyethane, or glycidol is preferred, and epoxypropane or glycidol is more preferred.

[0023] The MFR (190°C, under a load of 2.16 kg) of EVOH (a), measured in accordance with JIS K 7210 (2014), is preferably 0.2 to 20 g / 10 min. The MFR of EVOH (a) 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 (a) is more preferably 15 g / 10 min or less, even more preferably 10 g / 10 min or less, even more preferably 5 g / 10 min or less, and particularly preferably 3 g / 10 min or less. When the MFR of EVOH (a) is within the above range, the melt moldability of EVOH (a) and the pulverized product of the multilayer structure containing EVOH (a) (the multilayer structure of the present invention) is improved.

[0024] The barrier layer (A) may contain components other than the EVOH (a), as long as the effects of the present invention are not impaired. Examples of other components include alkali metal ions, polyvalent metal ions, carboxylic acids, phosphate compounds, boron compounds, prooxidants, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, UV absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, bulking agents, pigments, dyes, processing aids, flame retardants, and antifogging agents. The content of other components in the barrier layer (A) is usually 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less.

[0025] The barrier layer (A) preferably contains 10 to 400 ppm of alkali metal ions. The lower limit of the alkali metal ion content is more preferably 100 ppm, and even more preferably 150 ppm. On the other hand, the upper limit of the alkali metal ion content is more preferably 350 ppm, and may be 250 ppm. When the alkali metal ion content is 10 ppm or more, the interlayer adhesion in the multilayer structure of the present invention including a layer obtained by molding EVOH (a) is good. On the other hand, when the alkali metal ion content is 400 ppm or less, discoloration tends to be suppressed. By controlling the content ratio of the alkali metal ions to the carboxylic acid described below, the melt moldability and discoloration resistance can be further improved.

[0026] Examples of alkali metal ions include lithium, sodium, potassium, rubidium, and cesium ions, but sodium or potassium ions are preferred from the viewpoint of industrial availability. In particular, the use of sodium ions can sometimes achieve high levels of both color and interlayer adhesion with the adhesive layer. These ions may be used alone or in combination of two or more.

[0027] Examples of alkali metal salts that provide alkali metal ions include aliphatic carboxylates, aromatic carboxylates, carbonates, hydrochlorides, nitrates, sulfates, phosphates, and metal complexes of alkali metals such as sodium and potassium. Among these, at least one selected from the group consisting of sodium acetate, potassium acetate, sodium phosphate, and potassium phosphate is more preferred from the viewpoint of easy availability.

[0028] The barrier layer (A) preferably contains 10 to 200 ppm of at least one polyvalent metal ion selected from the group consisting of magnesium ions, calcium ions, and zinc ions. The inclusion of a certain amount of polyvalent metal ions suppresses thickening, gelation, and resin adhesion to the screw during melt molding of the EVOH (a) and the pulverized product of the multilayer structure containing the EVOH (a). The barrier layer (A) more preferably contains magnesium ions or calcium ions as the polyvalent metal ions, and even more preferably magnesium ions. The polyvalent metal ions are preferably contained as carboxylates. The carboxylic acids used here may be either aliphatic or aromatic carboxylic acids, with aliphatic carboxylic acids being preferred. Examples of aliphatic carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, lauric acid, stearic acid, myristic acid, behenic acid, and montanic acid, with higher fatty acids having 10 to 25 carbon atoms being more preferred. To suppress coloration during melt molding, the polyvalent metal ions are preferably contained as salts of the polycarboxylic acids described below.

[0029] The content of polyvalent metal ions in the barrier layer (A) is preferably 10 to 200 ppm in terms of metal atoms. When the content is 10 ppm or more, the viscosity stability of the EVOH (a) and the pulverized product of the multilayer structure containing EVOH (a) is improved, and gelation of the resin and adhesion of the resin to the extruder screw are suppressed. The lower limit of the content of polyvalent metal ions is more preferably 20 ppm. On the other hand, when the content of polyvalent metal ions is 200 ppm or less, excessive decomposition of the pulverized product of the multilayer structure containing EVOH (a) is suppressed, and the color of the recovered composition is improved. The upper limit of the content of polyvalent metal ions is more preferably 160 ppm, and even more preferably 120 ppm.

[0030] The barrier layer (A) preferably further contains a boron compound. The lower limit of the content of the boron compound is preferably 50 ppm, more preferably 100 ppm, in terms of elemental boron. On the other hand, the upper limit of the content of the boron compound is preferably 400 ppm, more preferably 300 ppm, in terms of elemental boron. By containing the boron compound within this range, the mechanical properties of the multilayer structure may be improved. Furthermore, the thermal stability of the EVOH (a) and the pulverized product of the multilayer structure during melt molding may be improved, and the occurrence of gels and lumps may be suppressed. Drawdown resistance and neck-in resistance during film formation may be improved. These effects are presumably due to the occurrence of chelating interaction between the EVOH (a) and the boron compound.

[0031] Examples of boron compounds include boric acid, boric acid esters, borate salts, and boron hydrides. Specific examples include boric acids such as orthoboric acid (HBO), 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 above boric acids; and borate salts such as borax. Among these, orthoboric acid is preferred.

[0032] The barrier layer (A) preferably contains a carboxylic acid. The lower limit of the carboxylic acid content is preferably 50 ppm, more preferably 100 ppm. On the other hand, the upper limit of the carboxylic acid content is preferably 400 ppm, more preferably 350 ppm. When the carboxylic acid content is within the above range, deterioration of the hue tends to be suppressed. The carboxylic acid content is determined by extracting 10 g of the resin composition constituting the barrier layer (A) with 50 ml of pure water at 95°C for 8 hours, and then titrating the resulting extract. Note that the carboxylic acid content in the resin composition does not take into account carboxylic acids present as salts in the extract. When the resin composition contains acidic compounds other than carboxylic acids, the carboxylic acid content in the resin composition can be determined by subtracting the contribution of these acidic compounds from the measured value obtained by titration.

[0033] 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 in the weakly acidic range is increased, further improving the melt moldability and further reducing the influence of coloration due to acidic or basic substances.

[0034] The carboxylic acid may be a monocarboxylic acid. These may be used alone or in combination of two or more. A "monocarboxylic acid" is a compound having one carboxy group in the molecule. Monocarboxylic acids having a pKa in the range of 3.5 to 5.5 are not particularly limited, and examples thereof include formic acid (pKa = 3.77), acetic acid (pKa = 4.76), propionic acid (pKa = 4.85), and acrylic acid (pKa = 4.25). These carboxylic acids may further have a substituent such as a hydroxyl group, an amino group, or a halogen atom. Among these, acetic acid is preferred because of its high safety and ease of availability and handling.

[0035] The carboxylic acid may be a polycarboxylic acid. When the carboxylic acid is a polycarboxylic acid, the discoloration resistance of the EVOH (a) at high temperatures and the discoloration resistance of a melt-molded product of crushed material of a multilayer structure containing the EVOH (a) may be further improved. The polycarboxylic acid compound preferably has three or more carboxy groups. In this case, discoloration resistance may be more effectively improved. The "polycarboxylic acid" is a compound having two or more carboxy groups in the molecule. In this case, it is preferable that the pKa of at least one carboxy group is in the range of 3.5 to 5.5, and examples thereof 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=5.50), and the like. =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), etc.

[0036] The barrier layer (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 radicals. On the other hand, the upper limit of the content of the phosphate compound is preferably 100 ppm in terms of phosphate radicals. By containing the phosphate compound in this range, coloration of the melt-molded product of the EVOH (a) and the pulverized product of the multilayer structure may be suppressed, and thermal stability may be improved. "In terms of phosphate radicals" refers to the content of phosphorus element (P) in terms of phosphate ions (PO4 3- ) is the value converted into the content.

[0037] Examples of the phosphate compound include various acids such as phosphoric acid and phosphorous acid, and salts thereof. The phosphate may be any of primary, secondary, and tertiary phosphates. The cation species of the phosphate is not particularly limited, but alkali metals or alkaline earth metals are preferred. Among these, sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate are preferred as the phosphate compound.

[0038] The barrier layer (A) may further contain, as an antioxidant, for example, a hindered phenol compound having an ester bond or an amide bond. The content of the hindered phenol compound is preferably 1,000 to 10,000 ppm. When the content is 1,000 ppm or more, coloration, thickening, and gelation of the resin can be suppressed when the pulverized product of the multilayer structure is melt-molded. The content of the hindered phenol compound is more preferably 2,000 ppm or more. On the other hand, when the content of the hindered phenol compound is 10,000 ppm or less, coloration and bleed-out resulting from the hindered phenol compound can be suppressed. The content of the hindered phenol compound is more preferably 8,000 ppm or less.

[0039] The hindered phenol 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 carbon atom adjacent to the carbon atom to which the hydroxyl group of the phenol is bonded. The bulky substituent is preferably an alkyl group having 1 to 10 carbon atoms, more preferably a t-butyl group.

[0040] The hindered phenol compound is preferably in a solid state at around room temperature. From the viewpoint of suppressing 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 even more preferably 70°C or higher. From the viewpoint of suppressing bleed-out, the molecular weight of the hindered phenol compound is preferably 200 or higher, more preferably 400 or higher, and even more preferably 600 or higher. Meanwhile, the molecular weight is usually 2000 or lower. From the viewpoint of facilitating mixing with EVOH (a), the melting point or softening temperature of the hindered phenol compound is preferably 200°C or lower, more preferably 190°C or lower, and even more preferably 180°C or lower.

[0041] The hindered phenol compound 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, and 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 these, it is preferable that the hindered phenol compound has an amide bond, from the viewpoint of facilitating mixing with EVOH (a).

[0042] Specific structures of the hindered phenolic compounds include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] commercially available from BASF as Irganox 1010, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)stearylpropionate commercially available as Irganox 1076, 2,2'-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] commercially available as Irganox 1035, and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate commercially available as Irganox 1135. octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate, ethylene bis(oxyethylene) bis(3-tert-butyl-4-hydroxy-5-methylbenzenepropanoate) commercially available as Irganox 245, 1,6-hexanediol bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] commercially available as Irganox 259, and N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide] commercially available as Irganox 1098. Among these, N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide] commercially available as Irganox 1098 and pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] commercially available as Irganox 1010 are preferred, with Irganox 1098 being more preferred.

[0043] The barrier layer (A) may further contain a thermoplastic resin other than EVOH (a). Examples of thermoplastic resins other than EVOH (a) include various polyolefins (polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymers, copolymers of ethylene and an α-olefin having 4 or more carbon atoms, copolymers of polyolefins and maleic anhydride, ethylene-vinyl ester copolymers, ethylene-acrylic acid ester copolymers, and modified polyolefins obtained by graft-modifying these with unsaturated carboxylic acids or their derivatives), various polyamides (nylon 6, nylon 6 / 6, nylon 6 / 66 copolymer, nylon 11, nylon 12, polymetaxylylene adipamide, etc.), various polyesters (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate, and modified polyvinyl alcohol resins. The content of the thermoplastic resin in the barrier layer (A) is less than 50% by mass, preferably 30% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and may be 1% by mass or less.

[0044] The proportion of EVOH (a) in the resin constituting the barrier layer (A) is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, or the resin constituting the barrier layer (A) may consist solely of EVOH (a). The proportion of EVOH (a) in the barrier layer (A) is more than 50% by mass, preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, or the barrier layer (A) may consist essentially of EVOH (a) alone.

[0045] When the barrier layer (A) contains components other than EVOH (a), the method for producing the resin composition constituting the barrier layer (A) is not particularly limited. The barrier layer (A) can be produced by melt-kneading EVOH (a) and, if necessary, other additives (e.g., metal ions). The other additives may be blended in a solid state, such as powder, or as a melt. They may also be blended as solutes in a solution or dispersoids in a dispersion. The solution and dispersion are preferably aqueous solutions and aqueous dispersions, respectively. For melt-kneading, known mixing or kneading devices such as kneader-ruders, extruders, mixing rolls, and Banbury mixers can be used. The temperature range during melt-kneading can be adjusted appropriately depending on the melting point of the EVOH (a) used, and is typically 150 to 300°C.

[0046] In another embodiment, a masterbatch containing a high concentration of other additives relative to EVOH(a) can be produced by melt-kneading, and the masterbatch can be dry-blended with EVOH(a) substantially free of other additives for use in producing a multilayer structure. In yet another embodiment, EVOH(a) and other additives can be dry-blended for use in producing a multilayer structure. "Dry-blending" refers to mechanically mixing EVOH(a) in granular or pelletized form. Mixing may be performed using a mixing device such as a tumbler, ribbon mixer, or Henschel mixer, or by manual stirring, shaking, or the like in a sealed container. The mixing temperature may be from room temperature to below the melting point of EVOH(a), and mixing can be performed under an air or nitrogen atmosphere. The multilayer structure may also be produced by pre-adding some components to EVOH(a) and then melt-kneading additional components as described above. An example of a method for pre-adding some components to EVOH(a) is immersing EVOH(a) in the form of pellets or powder in a solution in which the additional components are dissolved. An aqueous solution is preferred as the solution.

[0047] <Adhesive layer (B)> The multilayer structure of the present invention has an adhesive layer (B) containing an adhesive resin (b) as a main component. The adhesive layer (B) functions to bond the barrier layer (A) and the thermal seal layer (C). Therefore, the adhesive layer (B) is preferably provided between the barrier layer (A) and the thermal seal layer (C), and is preferably directly laminated on the barrier layer (A) and the thermal seal layer (C).

[0048] Examples of adhesive resin (b) include carboxyl-containing modified olefin polymers obtained by chemically bonding an unsaturated carboxylic acid or its anhydride to an olefin polymer via addition reaction, graft reaction, or the like. Examples of unsaturated carboxylic acids or their anhydrides include maleic acid, maleic anhydride, fumaric acid, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, citraconic acid, and hexahydrophthalic anhydride, with maleic anhydride being preferred. Specifically, preferred examples include one or a mixture of two or more selected from maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, maleic anhydride-grafted ethylene-propylene copolymer, maleic anhydride-grafted ethylene-ethyl acrylate copolymer, and maleic anhydride-grafted ethylene-vinyl acetate copolymer, with maleic anhydride-grafted polyethylene being more preferred. The acid value of such adhesive resin (b) is preferably 0.5 to 5 mgKOH / g, more preferably 1 to 4 mgKOH / g. The acid value of the adhesive resin (b) can be measured in accordance with JIS K 0070:1992 using xylene as a solvent.

[0049] The adhesive resin (b) may be a mixture of an unmodified resin (bx) and an acid-modified resin (by). In this case, from the viewpoint of further increasing mechanical strength, the unmodified resin (bx) preferably contains an ethylene-α-olefin copolymer resin (c) described later, and more preferably is an ethylene-α-olefin copolymer resin (c). When the unmodified resin (bx) contains an ethylene-α-olefin copolymer resin (c), the ethylene-α-olefin copolymer resin (c) contained in the adhesive layer (B) and the ethylene-α-olefin copolymer resin (c) contained in the heat-sealable layer (C) may be the same or different, but are preferably the same. The ratio (bx / by) of the unmodified resin (bx) to the acid-modified resin (by) in the adhesive resin (b) is preferably 55 / 45 to 95 / 5, and more preferably 65 / 35 to 90 / 10. In this case, a resin with a relatively high degree of acid modification can be preferably used as the acid-modified resin (by), and its acid value is preferably 5 to 30 mgKOH / g, more preferably 8 to 20 mgKOH / g. This may further improve the mechanical strength of the resulting multilayer structure while maintaining the required interlayer adhesive strength. When the adhesive resin (b) of the present invention is a mixture of an unmodified resin (bx) and an acid-modified resin (by), the unmodified resin (bx) and the acid-modified resin (by) may be melt-kneaded in advance, or a dry blend of the unmodified resin (bx) and the acid-modified resin (by) may be used. For melt-kneading, known mixing or kneading devices such as a kneader / ruder, extruder, mixing roll, or Banbury mixer can be used. The temperature range during melt-kneading can be appropriately adjusted depending on the melting points of the unmodified resin (bx) and the acid-modified resin (by) used, and is typically 150 to 300°C. The mixing may be carried out using a mixing device such as a tumbler, ribbon mixer, or Henschel mixer, or may be carried out in a sealed container by manually stirring, shaking, etc. The mixing temperature may be from room temperature to below the melting points of the unmodified resin (bx) and the acid-modified resin (by), and the mixing may be carried out in an air atmosphere or a nitrogen atmosphere.

[0050] The adhesive layer (B) may contain components other than the adhesive resin (b) as long as the effects of the present invention are not impaired. Examples of such components include alkali metal ions, polyvalent metal ions, carboxylic acids, phosphate compounds, boron compounds, prooxidants, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, UV absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, bulking agents, pigments, dyes, processing aids, flame retardants, and antifogging agents. The content of such components in the adhesive layer (B) is typically 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less. The adhesive layer (B) may further contain a thermoplastic resin other than the adhesive resin (b). Examples of such thermoplastic resins that may be contained in the barrier layer (A) include the resins listed above. The content of the thermoplastic resin in the adhesive layer (B) is less than 50% by mass, preferably less than 30% by mass, more preferably less than 10% by mass, even more preferably 5% by mass or less, and may be 1% by mass or less.

[0051] The proportion of adhesive resin (b) in the resin constituting adhesive layer (B) is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, or the resin constituting adhesive layer (B) may consist solely of adhesive resin (b). The proportion of adhesive resin (b) in adhesive layer (B) is more than 50% by mass, preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, or the adhesive layer (B) may be substantially composed of adhesive resin (b) alone.

[0052] <Thermal adhesive layer (C)> The multilayer structure of the present invention has a density of 0.880 to 0.930 g / cm 3 The heat-sealable layer (C) contains, as its main component, an ethylene-α-olefin copolymer resin (c), which is a polyolefin copolymer having a thermal seal function. The heat-sealable layer (C) functions as a sealing layer when forming the packaging material, and also enhances various mechanical strengths such as resistance to bag breakage due to dropping, puncture strength, and tensile strength.

[0053] The density of the ethylene-α-olefin copolymer resin (c) is 0.880 to 0.930 g / cm 3 When the density is within the above range, the resulting multilayer structure is flexible and has excellent handleability, and in addition to drop-breakage resistance, various mechanical strengths such as puncture strength and elongation and tensile strength and elongation are improved. The lower limit of the density is 0.890 g / cm 3 is preferred, and 0.900 g / cm 3 More preferably, 0.905 g / cm 3 is more preferably 0.910 g / cm 3 The upper limit of the density is 0.925 g / cm 3 is preferred, and 0.920 g / cm 3 is more preferred.

[0054] The MFR (190°C, under a load of 2.16 kg) of the ethylene-α-olefin copolymer resin (c) is preferably 0.5 to 5.0 g / 10 min. When the MFR is within the above range, the ethylene-α-olefin copolymer resin (c) has excellent melt processability, and the resulting multilayer structure has improved mechanical strengths such as drop-breakage resistance, puncture strength and elongation, and tensile strength and elongation. The lower limit of the MFR is more preferably 0.7 g / 10 min. The upper limit of the MFR is more preferably 4.0 g / 10 min, and even more preferably 2.0 g / 10 min. The MFR is measured at 190°C under a load of 2.16 kg in accordance with JIS K 7210 (2014).

[0055] The ethylene-α-olefin copolymer resin (c) is a resin obtained by polymerizing ethylene with an α-olefin having 3 or more carbon atoms. Examples of the α-olefin having 3 or more carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, and 4-methyl-1-pentene. The ethylene-α-olefin copolymer resin (c) is preferably a linear low-density polyethylene obtained by polymerizing ethylene with an α-olefin having 6 or more carbon atoms, or may be a linear low-density polyethylene obtained by polymerizing ethylene with an α-olefin having 8 or more carbon atoms. When the α-olefin copolymerized with ethylene has a relatively large number of carbon atoms, various mechanical strengths such as pin puncture strength and tensile strength and elongation may be particularly improved. There is no particular upper limit on the number of carbon atoms in the α-olefin having 3 or more carbon atoms, but it is generally 12 or less.

[0056] A metallocene catalyst is preferably used as the polymerization catalyst. Linear low-density polyethylene polymerized using a metallocene catalyst is produced by copolymerizing ethylene and an α-olefin in the presence of a catalyst formed from a compound of a transition metal of Group 4 of the periodic table, preferably zirconium, having at least one ligand having a cyclopentadienyl skeleton, an organoaluminum oxy compound, and various other components added as needed. Linear low-density polyethylene polymerized using a metallocene catalyst has excellent melt moldability, and the resulting multilayer structure has an excellent balance of heat resistance, flexibility, and mechanical strength.

[0057] Linear low-density polyethylene obtained by polymerizing ethylene and an α-olefin having 6 or more carbon atoms using a metallocene catalyst is commercially available as an industrially produced product, and examples of such products include "Evolue (trademark)" (manufactured by Prime Polymer Co., Ltd.), "Sumikasen (trademark)" (manufactured by Sumitomo Chemical Co., Ltd.), "Yumerit (trademark)" (manufactured by Ube Maruzen Polyethylene Co., Ltd.), and "Elite (trademark)" (manufactured by The Dow Chemical Company).

[0058] The heat-sealable layer (C) may contain components other than the ethylene-α-olefin copolymer resin (c) as long as the effects of the present invention are not impaired. Examples of other components include alkali metal ions, polyvalent metal ions, carboxylic acids, phosphate compounds, boron compounds, oxidation promoters, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, UV absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, bulking agents, pigments, dyes, processing aids, flame retardants, and anti-fogging agents. The content of other components in the heat-sealable layer (C) is usually 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less. The heat-sealable layer (C) may further contain a thermoplastic resin other than the ethylene-α-olefin copolymer resin (c). Examples of the thermoplastic resin that may be contained in the barrier layer (A) include the resins listed above. The content of the thermoplastic resin in the heat-sealable layer (C) is less than 50% by mass, preferably less than 30% by mass, more preferably less than 10% by mass, even more preferably 5% by mass or less, and may be 1% by mass or less.

[0059] The proportion of the ethylene-α-olefin copolymer resin (c) in the resin constituting the heat-sealable layer (C) is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, or the resin constituting the heat-sealable layer (C) may consist solely of the ethylene-α-olefin copolymer resin (c). The proportion of the ethylene-α-olefin copolymer resin (c) in the heat-sealable layer (C) is more than 50% by mass, preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, or the heat-sealable layer (C) may be substantially composed of the ethylene-α-olefin copolymer resin (c) alone.

[0060] The method for producing the resin composition constituting the heat-sealable layer (C) is not particularly limited, but it can be produced by melt-kneading the ethylene-α-olefin copolymer resin (c) and, if necessary, other additives. For melt-kneading, known mixing or kneading devices such as a kneader-ruder, extruder, mixing roll, or Banbury mixer can be used. The temperature range during melt-kneading can be appropriately adjusted depending on the melting point of the ethylene-α-olefin copolymer resin (c) used, and is usually 150 to 300°C.

[0061] In another embodiment, a masterbatch containing a high concentration of other additives, if necessary, is prepared by melt-kneading the ethylene-α-olefin copolymer resin (c), and the masterbatch is dry-blended with an ethylene-α-olefin copolymer resin (c) that is substantially free of other additives, and used to prepare a multilayer structure. In yet another embodiment, the ethylene-α-olefin copolymer resin (c) and other additives can be dry-blended to prepare the heat-sealable layer (C). Mixing may be performed using a mixing device such as a tumbler, ribbon mixer, or Henschel mixer, or by manual stirring, shaking, or the like in a sealed container. The mixing temperature may be from room temperature to below the melting point of the ethylene-α-olefin copolymer resin (c), and mixing may be performed in an air or nitrogen atmosphere.

[0062] The sealant layer (X) has a barrier layer (A), an adhesive layer (B), and a heat-sealing layer (C). At least one pair of the barrier layer (A) and the adhesive layer (B) is preferably laminated adjacent to each other. This makes it possible to obtain a multilayer structure that has high gas barrier properties and recyclability, as well as excellent mechanical strength and stability.

[0063] The lamination method for producing the sealant layer (X) can be a conventional coextrusion method in which each resin is extruded through separate dies or a common die and laminated. The die can be either a circular die or a T-die. The molding temperature during melt molding can be adjusted appropriately based on the melting point and melt viscosity of the resin used, and is often selected from the range of 150 to 300°C. From the viewpoint of maintaining the heat seal strength when molding the multilayer structure of the present invention into a flexible packaging material, the sealant layer (X) is preferably a non-oriented layer.

[0064] The total thickness of the sealant layer (X) is preferably 15 to 300 μm, more preferably 25 to 250 μm, even more preferably 35 to 200 μm, and particularly preferably 45 to 150 μm. When the total thickness is within the above range, the sealant layer (X) is lightweight and flexible, and is therefore preferably used for flexible packaging. The amount of resin used in the sealant layer (X) is small, and the environmental load is reduced.

[0065] The lower limit of the thickness of the barrier layer (A) is preferably 1 μm. When the lower limit of the thickness of the barrier layer (A) is within the above range, the multilayer film exhibits sufficient gas barrier properties. The upper limit of the thickness of the barrier layer (A) is preferably 30 μm, more preferably 25 μm, even more preferably 20 μm, and particularly preferably 15 μm. When the upper limit of the thickness of the barrier layer (A) is within the above range, the recyclability is improved when the sealant layer (X) or the multilayer structure is recovered and reused. In particular, from the viewpoint of improving resistance to drop rupture of a bag at high temperatures, the thickness of the barrier layer (A) may be preferably 5 μm or less, more preferably 4 μm or less. When the thickness of the barrier layer (A) is 5 μm or less, the ethylene unit content of the EVOH (a) is preferably 33 mol% or less, more preferably 28 mol% or less, in order to maintain good gas barrier properties. When the sealant layer (X) has multiple barrier layers (A), the thickness of the barrier layer (A) mentioned above means the total thickness of the multiple barrier layers (A).

[0066] The thickness of the adhesive layer (B) is preferably 1 to 20 μm, more preferably 2 to 10 μm. When the thickness of the adhesive layer (B) is within the above range, the interlayer adhesion between the barrier layer (A) and the heat-sealing layer (C) is increased, and the recyclability when the sealant layer (X) or the multilayer structure is recovered and reused is improved. When the sealant layer (X) has multiple adhesive layers (B), the thickness of the adhesive layer (B) mentioned above means the total thickness of the multiple adhesive layers (B).

[0067] The thickness of the heat-sealing layer (C) is preferably 15 to 300 μm, more preferably 30 to 200 μm, and even more preferably 40 to 150 μm. When the thickness of the heat-sealing layer (C) is within the above range, recyclability, mechanical strength, and water vapor barrier property are improved. When the sealant layer (X) has multiple heat-sealing layers (C), the thickness of the heat-sealing layer (C) mentioned above means the total thickness of the multiple heat-sealing layers (C).

[0068] In the sealant layer (X), the ratio of the thickness of the barrier layer (A) to the total thickness of all layers is preferably 0.10 or less. When this ratio is within the above range, recyclability and mechanical strength are improved. The upper limit of the ratio of the thickness of the barrier layer (A) to the total thickness of all layers is more preferably 0.08, even more preferably 0.05, and particularly preferably 0.04. The lower limit of the ratio of the thickness of the barrier layer (A) to the total thickness of all layers is not particularly limited, but is preferably 0.005 in order to achieve sufficient gas barrier properties. Meanwhile, in the multilayer structure of the present invention, the ratio of the thickness of the heat-sealable layer (C) to the total thickness of all layers is preferably 0.60 or more, more preferably 0.70 or more, even more preferably 0.80 or more, and may be 0.99 or less. When this ratio is within the above range, recyclability, mechanical strength, and water vapor barrier properties are improved.

[0069] The layer structure of the sealant layer (X) is not particularly limited as long as it has a barrier layer (A), an adhesive layer (B), and a heat-sealing layer (C), and the heat-sealing layer (C) is exposed. If the heat-sealing layer (C) is represented as (C), the adhesive resin layer (B) as (B), and the barrier layer (A) as (A), and " / " indicates direct lamination, examples of layer structures include (C) / (B) / (A) / (B) / (C), (C) / (B) / (A), etc. In addition to the above layer structure, other layers may be further included, and when multiple barrier layers (A), adhesive layers (B), and heat-sealing layers (C) are used, different types of resins may be used for each.

[0070] <Base material layer (Y)> The multilayer structure of the present invention has a base layer (Y) that is biaxially stretched and contains, as its main component, a polypropylene (y) having a melting point of 150°C or higher as measured by differential scanning calorimetry (DSC). The base layer (Y) has a modulus of elasticity in both directions of 2000 MPa or higher at 23°C and 50% RH. "Polypropylene" refers to a propylene homopolymer, a copolymer of 80 mol% or more propylene and 20 mol% or less ethylene or α-olefin monomer, or a copolymer of 90 mol% or more propylene and less than 10 mol% non-olefin monomers whose functional groups contain atoms other than carbon, oxygen, and hydrogen atoms. By including, as its main component, a polypropylene (y) having a melting point of 150°C or higher as measured by differential scanning calorimetry (DSC), the multilayer structure of the present invention can have improved resistance to bag breakage due to dropping under high temperature conditions. The melting point is preferably 155°C or higher, more preferably 160°C or higher, and even more preferably 165°C or higher. The melting point may be 170°C or lower. When the base layer (Y) is a biaxially stretched layer and the biaxial modulus of elasticity at 23°C and 50% RH is 2000 MPa or higher in both directions, a multilayer structure having excellent portability and improved resistance to bag breakage due to dropping at high temperatures can be obtained. The biaxial stretching ratio is not particularly limited, but is preferably 3 times or more but less than 12 times in each direction, more preferably 4 times or more but less than 10 times, and even more preferably 4 times or more but less than 6 times in the machine direction (MD) and 8 times or more but less than 12 times in the transverse direction (TD). The modulus of elasticity in the MD direction is preferably 2400 MPa or more, and may be 2600 MPa or more. The modulus of elasticity in the MD direction may be 4000 MPa or lower. The modulus of elasticity in the TD direction is preferably 3500 MPa or more, and may be 5000 MPa or higher. The modulus of elasticity in the TD direction may be 7000 MPa or lower. When the substrate layer (Y) is heated from 20°C to 220°C at 10°C / min using a differential scanning calorimeter (DSC) and then cooled to -50°C at 10°C / min, it is preferable that the difference (T1-T2) between the maximum endothermic peak temperature (T1) during heating and the maximum exothermic peak temperature (T2) during cooling is 56°C or less.When the difference (T1-T2) from the maximum exothermic peak temperature (T2) during cooling is 56°C or less, the water vapor barrier properties of the resulting multilayer structure are significantly improved, and the drop-breakage resistance of the bag under high-temperature conditions may be further improved. The difference (T1-T2) is preferably 55°C or less, more preferably 54°C or less, even more preferably 53°C or less, and particularly preferably 52°C or less. The difference (T1-T2) may be 50°C or more, or 51°C or more.

[0071] The proportion of polypropylene (y) in the resin constituting the base layer (Y) is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and may be 97% by mass or more or 99% by mass or more, and the resin constituting the base layer (Y) may consist solely of polypropylene (y). The content of polypropylene (y) in the base layer (Y) must be more than 50% by mass, and is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may be 97% by mass or more or 99% by mass or more, and the base layer (Y) may be composed essentially of polypropylene (y) only.

[0072] The method for producing the base layer (Y) is not particularly limited, but it is generally produced by melt extrusion using an extruder. Either a circular die or a T-die can be used as the die. The method for biaxial stretching is also not particularly limited, and the film can be produced by stretching in the machine direction and / or the direction perpendicular to the machine direction, i.e., the width direction, using a conventionally known stretching method such as tubular simultaneous biaxial stretching, tenter type sequential biaxial stretching, or tenter type simultaneous biaxial stretching.

[0073] From the viewpoint of industrial productivity, the thickness of the base layer (Y) is preferably 10 to 100 μm. Furthermore, from the viewpoint of achieving a balance between the mechanical strength, water vapor barrier property, and production costs of the multilayer structure, the thickness of the base layer (Y) is more preferably 12 to 55 μm, even more preferably 14 to 35 μm, and particularly preferably 16 to 25 μm. Note that, while a thick multilayer structure generally tends to have higher drop-breakage resistance, when the base layer (Y) has a certain thickness or more, drop-breakage resistance, particularly at room temperature, tends to decrease.

[0074] The layer structure of the base layer (Y) is not particularly limited as long as it contains polypropylene (y) as the main component, and may be a single layer or multiple layers, but from the viewpoints of production costs and imparting functionality, it is generally a single layer to five layers.

[0075] <Multilayer structure> The multilayer structure of the present invention is a multilayer structure in which a sealant layer (X) and a base layer (Y) are laminated, and has a heat-sealable layer (C) of the sealant layer (X) on the outermost surface. Since the heat-sealable layer (C) is disposed on the outermost surface of the multilayer structure, the multilayer structure of the present invention can be easily heat-sealed when used as a packaging material, etc. The multilayer structure of the present invention preferably does not have a resin layer with a thickness of 10 μm or more containing a resin with a melting point of 200°C or more as its main component, or a metal layer with a thickness of 1 μm or more. That is, it is preferable that the EVOH (a), adhesive resin (b), ethylene-α-olefin copolymer (c), and polypropylene (y) all have melting points below 200°C. The phrase "does not have a resin layer with a thickness of 10 μm or more containing a resin with a melting point of 200°C or more as its main component, or a metal layer with a thickness of 1 μm or more" means that the multilayer structure does not have a resin layer with a thickness of 10 μm or more containing a resin with a melting point of 200°C or more as its main component, and does not have a metal layer with a thickness of 1 μm or more. By not having a resin layer having a thickness of 10 μm or more and containing a resin having a melting point of 200°C or more as a main component, or a metal layer having a thickness of 1 μm or more, it is possible to prevent uneven mixing with other components when the pulverized product of the multilayer structure is melt-molded. In other words, recyclability is improved. A "metal layer" is a layer having continuous and discontinuous surfaces made of metal, such as aluminum foil. From the viewpoint of further improving recyclability, the thickness of each layer containing a resin having a melting point of 200°C or more as a main component is preferably 7 μm or less, and may be 5 μm or less.

[0076] The upper limit of the total thickness of the multilayer structure of the present invention is preferably 300 μm. With a total thickness within the above range, the multilayer structure of the present invention is lightweight and flexible, making it suitable for flexible packaging applications. The amount of resin used in the multilayer structure is small, thereby reducing the environmental impact. The upper limit of the total thickness of the multilayer structure of the present invention is more preferably 250 μm, and even more preferably 200 μm. From the viewpoint of maintaining the mechanical strength and water vapor barrier property of the multilayer structure of the present invention, the lower limit of the total thickness is preferably 30 μm, more preferably 50 μm, even more preferably 100 μm, and particularly preferably 150 μm. While drop-breakage resistance can usually be improved by increasing the total thickness of the multilayer structure, the present invention makes it possible to increase drop-breakage resistance without increasing the total thickness of the multilayer structure. It has been found that increasing the thickness of the base layer (Y) results in a decrease in drop-breakage resistance, particularly at room temperature, which is the opposite of the usual trend, and that adjusting the thickness of each layer can produce a multilayer structure with specifically superior drop-breakage resistance. It has generally been thought that the presence of a barrier layer (A) reduces resistance to drop rupture of a bag, but we have discovered the surprising effect that when the thickness of the barrier layer (A) is very thin (for example, 5 μm or less), it tends to further improve resistance to drop rupture, especially at high temperatures.

[0077] The thickness of each layer in the multilayer structure of the present invention may be adjusted appropriately depending on the application, but from the viewpoints of suppressing discoloration when the pulverized material is melt-molded, improving thermal stability during melt-molding, and suppressing the occurrence of lumps, the ratio of the total thickness of the layers containing a polyolefin resin as a main component to the total thickness of the multilayer structure is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.90 or more, and particularly preferably 0.95 or more. Preferred polyolefin resins are polyethylene, ethylene-α-olefin copolymer resins, polypropylene, and acid-modified resins thereof. For example, ethylene-α-olefin copolymer resin (c), polypropylene (y), and adhesive resin (b) in the case of a polyolefin resin, etc., correspond to polyolefin resins.

[0078] The multilayer structure of the present invention has a puncture strength S measured according to JIS Z 1707:2019 under conditions of 23°C and 50% RH, and a puncture strength S of the base layer (Y) measured according to JIS Z 1707:2019 under conditions of 23°C and 50% RH. Y Difference with (SS Y The difference (SS ) is preferably 3.5 N or more, and more preferably 4.0 N or more. Y ) may be 10 N or less. By satisfying this condition, the drop-breakage resistance of the obtained multilayer structure tends to be further improved. For the same reason, the puncture strength S of the multilayer structure of the present invention is preferably 12 N or more, more preferably 15 N or more, and even more preferably 18 N or more. The puncture strength S may be 30 N or less. The puncture strength can be adjusted, for example, by the type of polypropylene (y) used in the base layer (Y), the thickness of each layer of the multilayer structure, the layer configuration of the multilayer structure, etc.

[0079] The oxygen transmission rate (OTR) of the multilayer structure of the present invention under conditions of 20°C and 65% RH is not particularly limited and may be adjusted depending on the application, but is preferably 5 cc / (m 2 A multilayer structure having an OTR in this range has excellent gas barrier properties and is suitable for use as a packaging material. The OTR is preferably 2 cc / (m 2 ·day·atm) or less is more preferable, and 1.5cc / (m 2 ·day·atm) or less is more preferable, and 0.5cc / (m 2 ·day·atm) or less. OTR is 0.1cc / (m 2 The OTR may be equal to or greater than 1000 kJ / day atm. The OTR is measured in accordance with JIS K 7126-2 (isobaric method; 2006), and specifically, the method described in the examples is employed.

[0080] The water vapor transmission rate (WVTR) of the multilayer structure of the present invention under conditions of 40°C and 90% RH is not particularly limited and may be adjusted depending on the application. 2·day) or less is preferable. Multilayer films with a WVTR in this range have excellent water vapor barrier properties and are suitable for use as packaging materials. WVTR is 3.5g / (m 2 ·day) or less is preferable, and 3.0g / (m 2 ·day) or less is more preferable, and 2.5g / (m 2 ·day) or less. WVTR is 1g / (m 2 ·day) or more. WVTR is measured in accordance with JIS K 7129-2 (infrared sensor method; 2019), and specifically, the method described in the examples is employed.

[0081] The method for laminating the base layer (Y) on the sealant layer (X) is not particularly limited, and examples thereof include extrusion lamination, coextrusion lamination, and dry lamination. However, from the viewpoint of handleability, dry lamination is preferred. When laminating the base layer (Y) on the sealant layer (X), an adhesive layer may be provided. The adhesive layer may be an adhesive layer (B), or an adhesive layer (Z) that can be formed by applying and drying a known adhesive. As the known adhesive, for example, a two-component reactive polyurethane adhesive in which a polyisocyanate component and a polyol component are mixed and reacted is preferred. The thickness of the adhesive layer (Z) is not particularly limited, but is preferably 2 to 7 μm, more preferably 3 to 5 μm.

[0082] The multilayer structure of the present invention may include layers other than those described above, provided that the effects of the present invention are not impaired. The other layers are preferably other than a resin layer having a thickness of 10 μm or more and containing a resin having a melting point of 200°C or higher as a primary component, or a metal layer having a thickness of 1 μm or more. Examples of such layers include a resin layer containing a thermoplastic resin as a primary component. The thermoplastic resin is not particularly limited, and examples include polyolefin, polyamide, polyester, polystyrene, polyvinyl chloride, polyvinylidene chloride, acrylic resin, polycarbonate, chlorinated polyethylene, and chlorinated polypropylene. Another example of the other layer is a recovered layer. It is particularly preferable to reuse a recovered composition containing the recovered material from the multilayer structure of the present invention, as described below, as part or all of the recovered layer. Another example of the other layer is a printed layer. The printed layer may be included at any position in the multilayer structure of the present invention. Examples of the printed layer include a film obtained by applying and drying a solution containing a pigment or dye, and optionally a binder resin. Coating methods for the printed layer include gravure printing and various coating methods using a wire bar, spin coater, die coater, etc. The thickness of the printed layer is not particularly limited, but is preferably 0.5 to 10 μm, more preferably 1 to 4 μm.

[0083] It is preferable to recover and reuse end portions and defective products generated during the production of the multilayer structure of the present invention. It is also preferable to recover and reuse multilayer structures distributed on the market. In this case, a common recovery method is to crush the multilayer structure and then melt-molde it.

[0084] When recovering the multilayer structure of the present invention, the recovered multilayer structure of the present invention is first pulverized. The pulverized recovered material may be melt-molded directly to obtain a recovered composition, or may be melt-molded together with other components as needed to obtain a recovered composition. When the recovered composition is obtained by melt-molding together with other components, the other components are preferably polyolefin resins, more preferably polypropylene resins, polyethylene resins, or mixtures thereof. The pulverized recovered material may be directly used to produce a molded product such as a multilayer structure, or the pulverized recovered material may be melt-pelletized to obtain pellets of the recovered composition, which may then be used to produce a molded product. Possible melt-molding methods for the recovered composition include extrusion molding, inflation molding, blow molding, melt spinning, and injection molding. The molding temperature during melt molding may be adjusted appropriately based on the melting point and melt viscosity of the resin used and is often selected from the range of 150 to 300°C. The recovered composition may contain unused resin, but the content of the recovered material in the recovered composition is preferably 10% by mass or more, more preferably 20% by mass or more, and may even be 30% by mass or more. The content of EVOH (a) in the recovered composition is preferably 20% by mass or less, more preferably 10% by mass or less, and may be 5% by mass or less.

[0085] The multilayer structure of the present invention is preferably produced by coextrusion molding, since this reduces the amount of particles in the recovered layer after the multilayer structure of the present invention is recovered.

[0086] The multilayer structure of the present invention has excellent gas barrier properties, resistance to bag breakage due to dropping, and recyclability, and therefore can be suitably used as a variety of packaging materials such as food packaging, pharmaceutical packaging, industrial chemical packaging, and agricultural chemical packaging. However, it can also be used for a wider range of applications and is not limited to these applications.

[0087] A suitable embodiment of the packaging material is a package obtained by filling the packaging material with contents. The contents that can be filled include, but are not limited to, beverages such as wine and fruit juice; foods such as fruits, nuts, vegetables, meat products, baby foods, coffee, jam, mayonnaise, ketchup, cooking oil, dressings, sauces, foods boiled in soy sauce, and dairy products; and other contents that are susceptible to deterioration in the presence of oxygen, such as pharmaceuticals, cosmetics, and gasoline. [Example]

[0088] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples in any way.

[0089] <Materials used> ·Base material layer (Y) Y-1: Biaxially stretched PP film "U-1 (20 μm)" manufactured by Mitsui Chemicals Tocello Co., Ltd. Y-2: Biaxially stretched PP film "U-1 (40 μm)" manufactured by Mitsui Chemicals Tocello Co., Ltd. Y-3: Biaxially stretched PP film "WH-OP-HE-1 (20 μm)" manufactured by Mitsui Chemicals Tocello Co., Ltd. YC-1: Unstretched PP film "SC (40 μm)" manufactured by Mitsui Chemicals Tocello Co., Ltd. YC-2: Biaxially oriented HDPE film "Ethy-Lyte 25HD200" manufactured by Jindal Poly Films Ltd. EVOH(a) a-1: EVOH, ethylene unit content 32 mol%, saponification degree 99.9 mol%, sodium acetate 250 ppm in sodium ion equivalent, magnesium acetate 40 ppm in magnesium ion equivalent, phosphate ion 20 ppm in phosphate radical equivalent, boric acid 200 ppm in boron element equivalent, MFR (190°C, 2.16 kg load) 1.6 g / 10 min a-2: EVOH, ethylene unit content 32 mol%, saponification degree 99.9 mol%, sodium acetate 250 ppm (calculated as sodium ions), magnesium acetate 40 ppm (calculated as magnesium ions), phosphate ions 20 ppm (calculated as phosphate radicals), MFR (190°C, 2.16 kg load) 1.6 g / 10 min a-3: EVOH, ethylene unit content 24 mol%, saponification degree 99.9 mol%, sodium acetate 250 ppm (calculated as sodium ions), magnesium acetate 40 ppm (calculated as magnesium ions), phosphate ions 20 ppm (calculated as phosphate radicals), MFR (210°C, 2.16 kg load) 2.5 g / 10 min a-4: EVOH, ethylene unit content 27 mol%, saponification degree 99.9 mol%, sodium acetate 250 ppm (calculated as sodium ions), magnesium acetate 40 ppm (calculated as magnesium ions), phosphate ions 20 ppm (calculated as phosphate radicals), MFR (210°C, 2.16 kg load) 3.0 g / 10 min a-5: EVOH, ethylene unit content 44 mol%, saponification degree 99.9 mol%, sodium acetate 250 ppm (calculated as sodium ions), magnesium acetate 40 ppm (calculated as magnesium ions), phosphate ions 20 ppm (calculated as phosphate radicals), MFR (190°C, 2.16 kg load) 5.0 g / 10 min ·Adhesive resin (b) b-1: Maleic anhydride-modified polyethylene "Admer™ NF518" manufactured by Mitsui Chemicals, Inc. (MFR (190°C, 2.16 kg load) 3.1 g / 10 min, density 0.91 g / cm 3 , acid value 1.10mgKOH / g) b-2: Maleic anhydride-modified polypropylene "Admer™ QF500" manufactured by Mitsui Chemicals, Inc. (MFR (230°C, 2.16 kg load) 3.0 g / 10 min, density 0.90 g / cm 3 , acid value 1.12mgKOH / g) Ethylene-α-olefin copolymer resin (c) c-1: Linear low-density polyethylene "Evolue™ SP1510" manufactured by Prime Polymer Co., Ltd. (ethylene and 1-hexene polymerized with a metallocene catalyst, MFR (190°C, 2.16 kg load) 1.0 g / 10 min, density 0.915 g / cm 3 ) c-2: Linear low-density polyethylene "Evolue™ SP0510" manufactured by Prime Polymer Co., Ltd. (ethylene and 1-hexene polymerized with a metallocene catalyst, MFR (190°C, 2.16 kg load) 1.2 g / 10 min, density 0.903 g / cm 3 ) c-3: Linear low-density polyethylene "Evolue™ SP2510" manufactured by Prime Polymer Co., Ltd. (ethylene and 1-hexene polymerized with a metallocene catalyst, MFR (190°C, 2.16 kg load) 1.5 g / 10 min, density 0.923 g / cm 3 ) cC-1: Linear low-density polyethylene "Evolue™ SP4030" manufactured by Prime Polymer Co., Ltd. (ethylene and 1-hexene polymerized with a metallocene catalyst, MFR (190°C, 2.16 kg load) 3.8 g / 10 min, density 0.938 g / cm 3 ) cC-2: Polypropylene "Novatec™ PP EA7AD" manufactured by Japan Polypropylene Corporation (MFR (230°C, 2.16 kg load) 1.4 g / 10 min, density 0.90 g / cm 3 )

[0090] <Evaluation method> (1) Differential scanning calorimetry of the base layer (Y) The base layer (Y) used in the examples and comparative examples was heated from 20°C to 220°C at 10°C / min and then cooled to -50°C at 10°C / min using a differential scanning calorimeter DSC (TA Instruments "Q2000"), and the difference (T1-T2) between the maximum endothermic peak temperature (T1) during heating and the maximum exothermic peak temperature (T2) during cooling was calculated. The maximum endothermic peak temperature (T1) during heating was taken as the melting point of the polypropylene (y) constituting the base layer (Y).

[0091] (2) Elastic modulus measurement of the base layer (Y) The substrate layer (Y) used in the examples and comparative examples was conditioned at 23°C and 50% RH for 24 hours, then cut into a 15 mm width and measured for modulus at a tensile speed of 5 mm / min in accordance with ASTM D-638. Measurements were performed on 10 samples each in the machine direction (MD) and cross direction (TD), and the average values ​​were calculated.

[0092] (3) Measurement of puncture strength of base layer (Y) and multilayer structure The substrate layer (Y) used in the examples and comparative examples and the multilayer structures obtained in the examples and comparative examples were conditioned at 23°C and 50% RH for 24 hours, and then the breaking strength was measured when a needle with a tip diameter of 1 mm was pierced at a speed of 50 mm / min under the same conditions. The measurement was performed 10 times at different locations, and the average value was used as the measurement result. Note that the needle was pierced from the substrate layer (Y) side of the multilayer structures.

[0093] (4) Measurement of oxygen permeability of multilayer structure The oxygen transmission rate was measured using the multilayer structures obtained in the examples and comparative examples, with one side being the oxygen supply side and the other side being the carrier gas side. Specifically, the oxygen transmission rate (unit: cc / (m)) was measured using an oxygen transmission rate measuring device ("MOCON OX-TRAN2 / 21" manufactured by Modern Controls) in accordance with JIS K 7126-2 (isobaric method; 2006) under the conditions of a temperature of 20°C, a humidity of 65% RH on the oxygen supply side, a humidity of 65% RH on the carrier gas side, an oxygen pressure of 1 atmosphere, and a carrier gas pressure of 1 atmosphere. 2 The oxygen permeability (%) was measured. During the measurement, the substrate layer (Y) side of the multilayer structure was used as the oxygen supply side. Nitrogen gas containing 2% by volume of hydrogen gas was used as the carrier gas. The oxygen permeability was 5.0 cc / (m 2 When the gas barrier strength was 1000 kJ / h or more (1000 kJ / h), it was determined that the gas barrier properties were insufficient.

[0094] (5) Measurement of water vapor transmission rate of multilayer structure Using the multilayer structures obtained in the examples and comparative examples, the water vapor transmission rate was measured with one side as the water vapor supply side and the other side as the carrier gas side. Specifically, using a water vapor transmission rate measuring device ("MOCON PERMATRAN W3 / 33" manufactured by Modern Controls), the water vapor transmission rate (unit: g / (m)) was measured in accordance with JIS K 7129-2 (infrared sensor method; 2019) under the conditions of 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. 2 The time (day) was measured. During the measurement, the base layer (Y) side of the multilayer structure was set as the carrier gas side. Nitrogen gas was used as the carrier gas.

[0095] (6) Drop-break resistance of multilayer structure (room temperature) Two A4-sized sheets were cut out from the multilayer structures obtained in the Examples and Comparative Examples, and the sealant layers (X) were stacked together, followed by heat sealing along three sides at a width of 5 mm. Next, 1.2 L of water was filled through the opening, and the remaining side was heat sealed to create a water-filled bag. This water-filled bag was repeatedly dropped upright from a height of 1.5 m under conditions of 25°C and 70% RH, and the number of times water leakage was confirmed was counted. The same test was performed five times, and the average value was used as the measurement result. The results were evaluated according to the following criteria. D and E are unacceptable criteria. Judgment criteria A: 12 or more times B: 8 to less than 12 times C: 4 to less than 8 times D: 2 or more times but less than 4 times E: Less than twice

[0096] (7) Drop-break resistance of multilayer structure (high temperature) Two A4-sized sheets were cut from the multilayer structures obtained in the Examples and Comparative Examples, and the sealant layers (X) were stacked together. Three sides were heat-sealed at a width of 5 mm. Next, 1.2 L of water was filled through the opening, and the remaining side was heat-sealed to create a water-filled bag. This water-filled bag was immersed in hot water at 95°C for 15 minutes, and then repeatedly dropped upright from a height of 1.5 m under conditions of 25°C and 70% RH. The number of times water leakage was confirmed was counted. The same test was performed five times, and the average value was used as the measurement result. The results were evaluated according to the following criteria. D and E are unacceptable criteria. Judgment criteria A: 8 or more times B: 5 to less than 8 times C: 3 or more times but less than 5 times D: 2 or more times but less than 3 times E: Less than twice

[0097] (8) Evaluation of recyclability of multilayer structures The multilayer structures obtained in the examples and comparative examples were crushed into pieces of 4 mm square or less. The crushed pieces were mixed with a low-density polyethylene resin "Novatec LD LJ400" (MFR (190°C, 2.16 kg load) 1.5 g / 10 min, density 0.921 g / cm) manufactured by Japan Polyethylene Corporation. 3 ) and polypropylene "Novatec™ PP EA7AD" manufactured by Japan Polypropylene Corporation (MFR (230°C, 2.16 kg load) 1.4 g / 10 min, density 0.90 g / cm 3 ) were blended in a mass ratio (ground material / polyethylene resin / polypropylene resin) of 40 / 30 / 30, and a monolayer film with a thickness of 50 μm was obtained by extruding the material under the extrusion conditions shown below. The thickness of the monolayer film was adjusted by appropriately changing the screw rotation speed and take-up roll speed. As a control, a monolayer film with a thickness of 50 μm was similarly obtained without blending the ground material ((polyethylene resin / polypropylene resin) 50 / 50). Extruder: Toyo Seiki Seisakusho single screw extruder Screw diameter: 20mmφ (L / D=20, compression ratio=3.5, full flight type) Extrusion temperature: feeding section / compression section / metering section / die = 180 / 230 / 230 / 230℃ Take-off roll temperature: 80℃ The occurrence of lumps in the obtained monolayer film was evaluated on the following 5-level scale of A to E, where E is an unacceptable standard. Judgment criteria A: The amount of lumps was almost the same as the control. B: The amount of small particles was slightly more than the control. C: Compared to the control, there were more small particles. D: Compared to the control, there were more large particles. E: The amount of large particles was significantly greater than in the control group.

[0098] <Example> Example 1 EVOH (a-1) was used as the material for the barrier layer (A), adhesive resin (b-1) as the material for the adhesive layer (B), and ethylene-α-olefin copolymer resin (c-1) as the material for the heat-sealing layer (C). A 300 mm wide 5-layer co-extrusion cast film-making equipment was used to produce a multilayer film (sealant layer (X-1)) with a layer thickness and layer structure of (C) / (B) / (A) / (B) / (C) = 60 μm / 4 μm / 6 μm / 4 μm / 60 μm. The film-making conditions at this time are shown below. Extrusion temperature of barrier layer (A): feeding zone / compression zone / metering zone / die = 170 / 220 / 220 / 220°C Extrusion temperature of adhesive layer (B): feeding section / compression section / metering section / die = 170 / 220 / 220 / 220°C Extrusion temperature of heat-sealing layer (C): Feeding section / compression section / metering section / die = 170 / 220 / 220 / 220°C Cooling roll temperature: 40℃ Take-up speed: 1.5m / min

[0099] A two-component reactive polyurethane adhesive (24 parts by mass of "Takelac A-520" manufactured by Mitsui Chemicals, Inc. and 4 parts by mass of "Takenate A-50") was mixed with 37 parts by mass of ethyl acetate to prepare an adhesive solution. The adhesive solution was then applied to a substrate layer (Y-1) using a bar coater so that the thickness after drying would be 4 μm, and dried at 80 ° C for 3 minutes to form an adhesive layer (Z). This was then laminated with the multilayer film (sealant layer (X-1)) obtained above to produce a multilayer structure having a layer thickness and layer structure of (Y-1) / adhesive layer (Z) / (C) / (B) / (A) / (B) / (C) = 20 μm / 4 μm / 60 μm / 4 μm / 6 μm / 4 μm / 60 μm.

[0100] The substrate layer (Y-1) used and the resulting multilayer structure were evaluated according to the evaluation methods described above. The results are shown in Table 1.

[0101] Examples 2 to 14, Comparative Examples 3 to 6 Multilayer structures were produced and evaluated in the same manner as in Example 1, except that the type of substrate layer (Y), the type of EVOH (a), the thickness of the barrier layer (A), the type of ethylene-α-olefin copolymer resin (c) and the thickness of the adhesive layer (Z) were changed as shown in Table 1. The results are shown in Tables 1 and 2.

[0102] Example 15 Using EVOH (a-1) as the material for the barrier layer (A), adhesive resin (b-1) as the material for the adhesive layer (B), and ethylene-α-olefin copolymer resin (c-1) as the material for the heat-sealable layer (C), a multilayer film (sealant layer (X-2)) having a layer thickness and layer structure of (A) / (B) / (C)=6 μm / 8 μm / 120 μm was produced using a 300 mm wide 5-layer coextrusion cast film production equipment under the same film formation conditions as in Example 1. Then, using the same method as in Example 1, a multilayer structure having a layer thickness and layer structure of (Y-1) / adhesive layer (Z) / (A) / (B) / (C)=20 μm / 4 μm / 6 μm / 8 μm / 120 μm was produced and evaluated. The results are shown in Table 1.

[0103] Comparative Example 1 A multilayer structure was produced and evaluated in the same manner as in Example 1, except that the base layer (Y-1) was not laminated and the sealant layer (X-1) was used as it was as a multilayer structure. The results are shown in Table 2.

[0104] Comparative Example 2 A multilayer structure was produced and evaluated in the same manner as in Example 1, except that a single-layer film having a thickness of 134 μm was produced as the heat-sealable layer (C) instead of the multilayer film. The results are shown in Table 2.

[0105] [Table 1]

[0106] [Table 2]

Claims

1. A sealant layer (X) and a substrate layer (Y) are included. The sealant layer (X) comprises a barrier layer (A) containing, as a main component, an ethylene-vinyl alcohol copolymer (a) having an ethylene unit content of 20 to 50 mol% and a saponification degree of 90 mol% or more, an adhesive layer (B) containing, as a main component, an adhesive resin (b), and a film having a density of 0.880 to 0.930 g / cm ３ a heat-sealable layer (C) containing, as a main component, an ethylene-α-olefin copolymer resin (c) represented by the formula: the base layer (Y) is a biaxially stretched layer containing, as a main component, polypropylene (y) having a melting point of 150°C or higher as measured by a differential scanning calorimeter (DSC), and the biaxially stretched layer has an elastic modulus of 2000 MPa or higher under conditions of 23°C and 50% RH; A multilayer structure having a heat-sealable layer (C) of a sealant layer (X) on the outermost surface.

2. The puncture strength S measured according to JIS Z 1707:2019 under conditions of 23°C and 50% RH, and the puncture strength S of the base material layer (Y) measured according to JIS Z 1707:2019 under conditions of 23°C and 50% RH Ｙ Difference with (S-S Ｙ 2. The multilayer structure according to claim 1, wherein the piercing strength S is 3.5 N or more, and the piercing strength S is measured by piercing the multilayer structure from the base layer (Y) side.

3. 3. The multilayer structure according to claim 2, wherein the puncture strength S is 12 N or more.

4. The multilayer structure according to any one of claims 1 to 3, wherein when the temperature of the base layer (Y) is increased from 20°C to 220°C at 10°C / min and then decreased to -50°C at 10°C / min using a differential scanning calorimeter (DSC), the difference (T1-T2) between the maximum endothermic peak temperature (T1) during temperature increase and the maximum exothermic peak temperature (T2) during temperature decrease is 56°C or less.

5. The multilayer structure according to any one of claims 1 to 3, wherein the sealant layer (X) and the base layer (Y) are laminated via an adhesive layer (Z), and the thickness of the adhesive layer (Z) is 2 to 7 µm.

6. The multilayer structure according to any one of claims 1 to 3, wherein the ethylene-α-olefin copolymer resin (c) is a linear low-density polyethylene copolymerized with ethylene and an α-olefin having 6 or more carbon atoms.

7. 4. The multilayer structure according to claim 1, wherein the barrier layer (A) contains a boron compound in an amount of 50 to 400 ppm in terms of elemental boron.

8. 4. The multilayer structure according to claim 1, wherein the ethylene-vinyl alcohol copolymer (a) has an ethylene unit content of 22 mol % or more and 28 mol % or less.

9. The multilayer structure according to any one of claims 1 to 3, wherein the barrier layer (A) has a thickness of 5 µm or less.

10. The oxygen transmission rate measured by the method described in JIS K 7126-2:2006 under conditions of 20°C and 65% RH is 5 cc / (m ２ The multilayer structure according to any one of claims 1 to 3, wherein the viscosity is 1000 kJ / min or less.

11. The water vapor transmission rate measured by the method described in JIS K 7129-2:2019 under conditions of 40°C and 90% RH is 3 g / (m ２ The multilayer structure according to any one of claims 1 to 3, wherein the average particle size is 100 nm or less.

12. A packaging material comprising the multilayer structure according to any one of claims 1 to 3.

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