Multilayer structure and packaging material

Abstract

A multilayer structure having a sealant layer (X) and a base material layer (Y), the sealant layer (X) having a barrier layer (A) containing, as a main component, EVOH (a) having an ethylene unit content of 20-50 mol% and a degree of saponification of 90 mol% or more, an adhesive layer (B) containing, as a main component, an adhesive resin (b), and a heat-melting layer (C), the adhesive layer (B) containing, as a main component, an adhesive resin (a) having an ethylene unit content of 20-50 mol% and a degree of saponification of 90 mol% or more; the thermally fused layer (C) contains, as a main component, an ethylene-alpha-olefin copolymer resin (c) having a density of 0.880-0.930 g / cm3, and the base material layer (Y) contains, as a main component, a polypropylene (y) having a melting point of 150 DEG C or higher as measured by a differential scanning calorimeter (DSC), and is stretched in each of the biaxial directions. And a heat-welded layer (C) having a sealant layer (X) on the outermost surface of the multilayer structure, the elastic modulus in each of the biaxial directions under conditions of 23 DEG C and 50% RH being 2000 MPa or more.

Description

Technical Field

[0001] This invention relates to multi-layer structures and packaging materials. Background Technology

[0002] For packaging materials used for long-term food preservation, gas barrier properties, primarily oxygen barrier properties, are generally required. By using packaging materials with high gas barrier properties, it is possible to inhibit oxidative deterioration and / or microbial growth caused by oxygen intrusion. As layers that enhance gas barrier properties, metal foils such as aluminum and / or metal vapor-deposited layers, and inorganic vapor-deposited layers such as silicon dioxide and / or alumina are widely used. On the other hand, resin layers with gas barrier properties, such as vinyl alcohol polymers and / or polyvinylidene chloride, are also widely used. Vinyl alcohol polymers exhibit characteristics such as crystallization, high density, and gas barrier properties achieved through hydrogen bonding of hydroxyl groups within the molecules. Among them, ethylene-vinyl alcohol copolymers (hereinafter sometimes abbreviated as "EVOH") are suitable for melt molding due to their excellent thermal stability. With the development of co-extrusion technology, multilayer structures with an EVOH layer in the middle layer are widely used as gas barrier packaging materials.

[0003] Furthermore, in recent years, driven by environmental and / or waste issues, the demand for post-consumer recycling (hereinafter sometimes abbreviated as reuse) of packaging materials consumed in the market has been increasing worldwide. Reuse typically involves cutting the recycled packaging materials, sorting / washing them as needed, and then melt-blending them using an extruder. From this perspective, there is a need for packaging materials to be composed of as few as possible (single-material packaging), thereby obtaining high-purity and high-quality reusable raw materials. For example, from the viewpoint of excellent mechanical strength, gas barrier packaging materials with polyamide and EVOH layers are commonly used. However, polyamide resins react chemically with EVOH to produce particulate matter, thus sometimes reducing reusability. In view of this issue, there is a need to achieve single-material packaging materials that provide gas barrier packaging materials that maintain gas barrier properties and mechanical strength while offering excellent reusability.

[0004] Patent document 1 describes a multilayer structure having a resin composition layer and a hard layer with a puncture strength of 40 N / mm or more and 150 N / mm or less. Although it does not have a polyamide layer, it has excellent mechanical strength and thermoforming properties. When its recycled material is melt-molded, the generation of particulate matter caused by resin deterioration (gelation) is suppressed, and its reusability is also excellent. The resin composition layer is (1) a resin composition layer having EVOH with a melting point of 170°C or more and EVOH with a melting point of less than 170°C or (2) a resin composition layer having a specific modified EVOH containing a modified group with a primary hydroxyl group.

[0005] Existing technical documents Patent documents Patent document 1: International Publication No. 2020 / 071513. Summary of the Invention

[0006] The problem that the invention aims to solve However, when used as packaging material for heavy contents, there is a tendency to require higher drop resistance, and the multi-layer structure described in Patent Document 1 sometimes lacks sufficient drop resistance. Especially when the contents are at high temperatures, such as during heat filling, heat sterilization, or heat cooking, the drop resistance is sometimes significantly insufficient.

[0007] This invention was made to solve the above-mentioned problems, and its purpose is to provide a multilayer structure and packaging material with excellent gas barrier properties, drop damage resistance and reusability.

[0008] Methods for solving problems According to the present invention, the above-mentioned objective is achieved by providing the following technical solution.

[0009] [1] A multilayer structure having a sealant layer (X) and a substrate layer (Y), the sealant layer (X) having a barrier layer (A), an adhesive layer (B) and a heat-fusion layer (C), the barrier layer (A) comprising an ethylene-vinyl alcohol copolymer (a) (hereinafter sometimes abbreviated as "EVOH(a)") with an ethylene unit content of 20-50 mol% and a saponification degree of 90 mol% or more as the main component, the adhesive layer (B) comprising an adhesive resin (b) as the main component, and the heat-fusion layer (C) comprising a resin with a density of 0.880-0.930 g / cm³. 3 The main component is ethylene-α-olefin copolymer resin (c) (hereinafter sometimes referred to as "ethylene-α-olefin copolymer resin (c)"). The substrate layer (Y) is a layer containing polypropylene (y) (hereinafter sometimes referred to as "polypropylene (y)") with a melting point of 150°C or higher as measured by differential scanning calorimetry (DSC) as the main component, and is stretched along the biaxial direction. The elastic modulus in the aforementioned biaxial direction is 2000 MPa or higher under the conditions of 23°C and 50%RH. The outermost surface of the multilayer structure has a heat-fused layer (C) with a sealant layer (X). [2] According to the multilayer structure of [1], the puncture strength S measured by JIS Z 1707:2019 under conditions of 23°C and 50%RH is the same as the puncture strength S of the substrate layer (Y) measured by JIS Z 1707:2019 under conditions of 23°C and 50%RH. Y The difference (SS) Y The value is 3.5N or higher; [3] According to the multilayer structure of [2], wherein the aforementioned puncture strength S is 12N or more; [4] According to any one of [1] to [3], in which 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, the difference (T1-T2) between the maximum endothermic peak temperature (T1) during heating and the maximum exothermic peak temperature (T2) during cooling is less than 56°C; [5] According to any one of [1] to [4], the multilayer structure wherein the sealant layer (X) and the substrate layer (Y) are laminated by means of an adhesive layer (Z) and the thickness of the adhesive layer (Z) is 2 to 7 μm; [6] According to any one of [1] to [5], the multilayer structure wherein the ethylene-α-olefin copolymer resin (c) is a linear low-density polyethylene obtained by copolymerizing ethylene with α-olefins having 6 or more carbon atoms; [7] According to any one of [1] to [6], the multilayer structure wherein the barrier layer (A) contains 50 to 400 ppm of boron compound in terms of boron element; [8] According to any one of [1] to [7], the ethylene unit content of EVOH(a) is more than 22 mol% and less than 28 mol%; [9] According to any one of [1] to [8], the thickness of the barrier layer (A) is less than 5 μm;

[10] According to any one of [1] to [9], the multilayer structure wherein the oxygen permeability at 20°C and 65%RH, measured using the method described in JIS K 7126-2:2006, is 5cc / (m²). 2 ·day·atm) and below;

[11] A multilayer structure according to any one of [1] to

[10] , wherein the water vapor permeation rate at 40°C and 90%RH, measured using the method described in JIS K 7129-2:2019, is 3 g / (m²). 2 · Days and below;

[12] Packaging material comprising a multilayer structure of any one of [1] to

[11] .

[0010] Invention Effects The multi-layer structure and packaging material of the present invention have excellent gas barrier properties, drop damage resistance and reusability. Detailed Implementation

[0011] The following describes embodiments of the present invention. It should be noted that in the following description, specific materials (compounds, etc.) are sometimes exemplified as substances exhibiting specific functions, but the present invention is not limited to the manner in which such materials are used. The exemplified materials may be used alone or in combination unless otherwise specified.

[0012] The multilayer structure of the present invention has a sealant layer (X) and a substrate layer (Y). The sealant layer (X) has a barrier layer (A), an adhesive layer (B), and a heat-fusion layer (C). The barrier layer (A) contains EVOH (a) with an ethylene unit content of 20-50 mol% and a saponification degree of 90 mol% or more as the main component. The adhesive layer (B) contains an adhesive resin (b) as the main component. The heat-fusion layer (C) contains a resin with a density of 0.880-0.930 g / cm³. 3 The ethylene-α-olefin copolymer resin (c) is used as the main component. The substrate layer (Y) is a layer containing polypropylene (y) with a melting point of 150°C or higher as measured by differential scanning calorimetry (DSC) as the main component, and stretched along the biaxial direction. The elastic modulus in the aforementioned biaxial direction is 2000 MPa or higher under the conditions of 23°C and 50% RH. The outermost surface of the multilayer structure has a heat-fused layer (C) with a sealant layer (X). "Containing...as the main component" means containing more than 50% by mass, preferably more than 70% by mass, more preferably more than 80% by mass, and even more preferably more than 90% by mass. It can be in the form of more than 95% by mass, more than 97% by mass, or more than 99% by mass.

[0013] The multilayer structure of the present invention exhibits a tendency to maintain reusability and improve gas barrier properties by including a barrier layer (A). It also exhibits a tendency to improve mechanical strength, including drop resistance, and reusability by including an adhesive layer (B). The main component of the heat-fused layer (C) has a density of 0.880~0.930 g / cm³. 3 The ethylene-α-olefin copolymer resin (c) exhibits a tendency to maintain heat-sealing properties and achieve excellent mechanical strength, including drop resistance. In the multilayer structure of the present invention, by making the substrate layer (Y) a layer containing polypropylene (y) with a melting point of 150°C or higher as measured by differential scanning calorimetry (DSC) as the main component, and stretching it along the biaxial direction, the elastic modulus in the aforementioned biaxial direction at 23°C and 50%RH conditions is 2000 MPa or higher, thereby exhibiting a tendency to achieve excellent mechanical strength, including drop resistance, even under high temperature conditions.

[0014] "Drop resistance" can be evaluated by the number of tests conducted after filling a bag made using the multi-layer structure of the present invention with contents and dropping it from a specified height to the point of leakage. Specifically, it can be evaluated using the methods described in the examples. When described as drop resistance, it basically refers to drop resistance at room temperature and high temperature. "Reusability" can be evaluated by the generation of particulate matter in the melt-molded article obtained by melting and mixing fragments of the multi-layer structure. Specifically, it can be evaluated using the methods described in the examples. "Barrier properties" refer to oxygen barrier properties and water vapor barrier properties; "gas barrier properties" refer to oxygen barrier properties.

[0015] "ppm" refers to the content of a quality standard (mass ppm).

[0016] The term "surface (or surface layer)" in multilayer films and / or multilayer structures does not imply a distinction between the front and back surfaces, but rather refers to the exposed surface. That is, multilayer films and / or multilayer structures have two surfaces. Similarly, multilayer films and / or multilayer structures have two outermost surfaces.

[0017] "Constitutes substantially only of ~" means that the inclusion of optional components is accepted to the extent that it does not affect the effects of the invention, and "Constitutes only of ~" means that optional components are excluded except for unavoidably included impurities.

[0018] <Barrier Layer (A)> The multilayer structure of the present invention has a barrier layer (A) comprising EVOH(a) as a main component. EVOH(a) has excellent gas barrier properties; therefore, the multilayer structure having a layer comprising EVOH(a) as a main component is preferably used as a packaging material with high content preservation. EVOH(a) can be readily melt-mixed with polyolefin-based resins, thus providing a packaging material with excellent reusability.

[0019] EVOH(a) is usually obtained by saponifying an ethylene-vinyl ester copolymer obtained by polymerizing ethylene with ethylene ester. Vinyl acetate is a representative example of an ethylene ester, but other fatty acid ethylene esters (vinyl formate, vinyl propionate, vinyl valerate, vinyl decanoate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl neopentanoate, and vinyl tert-carbonate, etc.) can also be used.

[0020] The ethylene unit content of EVOH(a) is 20-50 mol%. If the ethylene unit content is 20 mol% or more, the melt-forming properties of EVOH(a) and the pulverized multilayer structure containing EVOH(a) are improved. The ethylene unit content is preferably 21 mol% or more, more preferably 22 mol% or more, and can be 25 mol% or more. On the other hand, if the ethylene unit content is 50 mol% or less, the gas barrier properties of the multilayer structure of the present invention are improved. The ethylene unit content is preferably 46 mol% or less, more preferably 42 mol% or less, further 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. "Saponification degree" refers to the ratio of the number of ethylene alcohol units in EVOH(a) to the total number of ethylene alcohol units and ethylene ester units. If the saponification degree is 90 mol% or more, the gas barrier properties of the multilayer structure of the present invention are 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 degree of saponification can be below 100 mol%. The ethylene unit content and degree of saponification of EVOH(a) are determined by... 1 The result is obtained by H-NMR measurement.

[0021] EVOH(a) can be a mixture of two or more EVOHs with different ethylene unit contents. In this case, the difference in ethylene unit content between the EVOHs with the largest difference in ethylene unit content is preferably 30 mol% or less, more preferably 25 mol% or less, even more preferably 20 mol% or less, and can be 3 mol% or more. Similarly, EVOH(a) can be a mixture of two or more EVOHs with different degrees of saponification. In this case, the difference in degree of saponification between the EVOHs with the largest difference in ethylene unit content is preferably 7 mol% or less, more preferably 5 mol% or less, and can be 0.5 mol% or more. When it is desirable to balance thermoforming properties and gas barrier properties to a higher level, it is preferable to mix EVOH(a1) with an ethylene unit content of 22 mol% or more and less than 34 mol% and a saponification degree of 99 mol% or more with EVOH(a2) with an ethylene unit content of 34 mol% or more and less than 50 mol% and a saponification degree of 99 mol% or more with a mixing mass ratio (a1 / a2) of 60 / 40 to 90 / 10, and use it in the form of EVOH(a).

[0022] EVOH(a) may contain monomer units other than ethylene, ethylene ester, and vinyl alcohol, provided that it does not impair the effects of the present invention. In particular, by introducing modified groups containing primary hydroxyl groups with specific structures, it is sometimes possible to achieve a high level of gas barrier properties and processability of EVOH(a). The content of other monomer units is preferably 10 mol% or less, more preferably 5 mol% or less, further preferably 1 mol% or less, and particularly preferably substantially non-existent. Other examples of such monomers include olefins such as propylene, butene, pentene, and hexene; 3-acyloxy-1-propene, 3-acyloxy-1-butene, 4-acyloxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4-acyloxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4-acyloxy-2-methyl-1-butene, 4-acyloxy-3-methyl-1-butene, 3,4-diacyloxy-2-methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, 4,5-diacyloxy-1-pentene, 4-acyloxy-1-hexene, 5-acyloxy-1-hexene, 6-acyloxy Alkenes containing ester groups, such as 1-hexene, 5,6-diacyloxy-1-hexene, and 1,3-diacetoxy-2-methylenepropane, or their saponifications; unsaturated acids, such as acrylic acid, methacrylic acid, crotonic acid, and itaconic acid, or their anhydrides, salts, or monoalkyl 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 methyl allyl sulfonic acid, or their salts; vinyl silane compounds, such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxy-ethoxy)silane, and γ-methacryloyloxypropylmethoxysilane; alkyl vinyl ethers, vinyl ketones, N-vinylpyrrolidone, vinyl chloride, and vinylidene chloride.

[0023] EVOH(a) can be modified as needed through urethane esterification, acetalization, cyanoethylation, oxoalkylation, etc. Oxyalkylation can be performed using epoxides, such as ethylene oxide, propylene oxide, 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, The mixture includes 2-epoxyheptane, 1,2-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, glycidyl and other epoxyalkanols, various epoxycycloalkanes, and various epoxycycloolefins. Preferably, it contains 1,2-epoxybutane, 2,3-epoxybutane, propylene oxide, ethylene oxide, or glycidyl, more preferably propylene oxide or glycidyl.

[0024] The melt flow rate (MFR) of EVOH(a) measured according to JIS K 7210 (2014) (at 190°C and a load of 2.16 kg) 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. If the MFR of EVOH(a) is within the above range, the melt-forming properties of EVOH(a) and the pulverized product containing the multilayer structure (the multilayer structure of the present invention) are improved.

[0025] The barrier layer (A) may contain components other than EVOH (a), provided that it does not impair the effects of the present invention. Examples of such components include alkali metal ions, polyvalent metal ions, carboxylic acids, phosphoric acid compounds, boron compounds, oxidation promoters, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorants, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, pigments, dyes, processing aids, flame retardants, and antifogging agents. The content of other components in the barrier layer (A) is typically 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less.

[0026] 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 can be 250 ppm. If the alkali metal ion content is 10 ppm or more, the interlayer adhesion of the multilayer structure of the present invention, including the layer obtained by molding EVOH(a), becomes good. On the other hand, if the alkali metal ion content is 400 ppm or less, it tends to suppress coloring. By controlling the ratio of alkali metal ions to the carboxylic acid described later, melt formability and / or colorfastness can be further improved.

[0027] Examples of alkali metal ions include lithium, sodium, potassium, rubidium, and cesium ions. From an industrial point of view, sodium or potassium ions are preferred. In particular, by using sodium ions, it is sometimes possible to achieve a high level of balance between hue and interlayer adhesion to the adhesive layer. One type can be used alone, or two or more can be used in combination.

[0028] 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. From the viewpoint of easy availability, at least one salt selected from sodium acetate, potassium acetate, sodium phosphate, and potassium phosphate is more preferred.

[0029] The barrier layer (A) preferably contains 10 to 200 ppm of at least one polyvalent metal ion selected from magnesium, calcium, and zinc ions. By containing a specified amount of polyvalent metal ions, thickening, gelation, and / or resin adhesion to the screw are suppressed during the melt molding of EVOH(a) and the pulverized material containing EVOH(a). Magnesium or calcium ions are more preferably contained in the barrier layer (A) as polyvalent metal ions, and magnesium ions are even more preferred. The polyvalent metal ion is preferably contained as a carboxylate. The carboxylic acid can be any of aliphatic or aromatic carboxylic acids, preferably aliphatic carboxylic acids. Examples of aliphatic carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, lauric acid, stearic acid, myristic acid, behenic acid, and linalic acid, and more preferably higher fatty acids with 10 to 25 carbon atoms. From the viewpoint of suppressing coloring during melt molding, the polyvalent metal ion is also preferably contained in the form of a salt of the polyvalent carboxylic acid described below.

[0030] The content of polyvalent metal ions in the barrier layer (A) is preferably 10 to 200 ppm in terms of metal atoms. If the content is 10 ppm or more, the viscosity stability of EVOH(a) and the pulverized material containing the multilayer structure of EVOH(a) becomes good, and resin gelation and / or resin adhesion to the extruder screw are suppressed. The lower limit of the polyvalent metal ion content is more preferably 20 ppm. On the other hand, if the content of polyvalent metal ions is 200 ppm or less, excessive decomposition of the pulverized material containing the multilayer structure of EVOH(a) is suppressed, and the color of the recovery composition becomes good. The upper limit of the polyvalent metal ion content is more preferably 160 ppm, and even more preferably 120 ppm.

[0031] The barrier layer (A) preferably also contains a boron compound. The lower limit of the boron compound content, converted to boron element, is preferably 50 ppm, more preferably 100 ppm. On the other hand, the upper limit of the boron compound content, converted to boron element, is preferably 400 ppm, more preferably 300 ppm. By containing a boron compound within this range, the mechanical properties of the multilayer structure are sometimes improved. Furthermore, the thermal stability of EVOH (a) and the pulverized multilayer structure during melt molding is sometimes improved, suppressing the formation of gels and particles. Resistance to flow and / or resistance to necking during film formation are sometimes improved. It can be inferred that these effects are due to chelate interactions between EVOH (a) and the boron compound.

[0032] Examples of boron compounds include boric acid, borate esters, borates, and boron hydride. Specifically, examples include orthoboric acid (H3BO3), metaboric acid, tetraboric acid, and other boric acids; trimethyl borate, triethyl borate, and other borate esters; alkali metal or alkaline earth metal salts of the aforementioned boric acids; and borates such as borax. Orthoboric acid is preferred.

[0033] The barrier layer (A) preferably contains 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. If the carboxylic acid content is within the above range, it tends to suppress color deterioration. The carboxylic acid content is determined by titrating the resulting extract after extracting 10 g of the resin composition constituting the barrier layer (A) with 50 ml of pure water at 95°C for 8 hours. It should be noted that the carboxylic acid content in the resin composition does not consider carboxylic acid present in the aforementioned extract in the form of salts. If the resin composition contains acidic compounds other than carboxylic acid, the carboxylic acid content in the resin composition can be determined by subtracting the contribution of these acidic compounds from the titration-based measurement value.

[0034] The pKa of carboxylic acids is preferably 3.5 to 5.5. If the pKa of carboxylic acids is within the above range, the pH buffering capacity in the weakly acidic range is improved, which can further improve melt formability and further reduce the coloring effect caused by acidic and / or alkaline substances.

[0035] Carboxylic acids can be monocarboxylic acids. They can be used alone or in combination of two or more. A "monocarboxylic acid" refers to a compound having one carboxyl group in its molecule. Monocarboxylic acids with a pKa in the range of 3.5 to 5.5 are not particularly limited, but examples 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 also have substituents such as hydroxyl, amino, or halogen atoms. Among these, acetic acid is preferred from the perspectives of high safety, ease of acquisition, and processing.

[0036] The carboxylic acid can be a polycarboxylic acid. If the carboxylic acid is a polycarboxylic acid, it can sometimes further improve the colorfastness of EVOH(a) at high temperatures and / or the colorfastness of melt-molded fragments containing multilayer structures of EVOH(a). Polycarboxylic acid compounds also preferably have three or more carboxyl groups. In this case, colorfastness can sometimes be improved more effectively. "Polycarboxylic acid" refers to a compound having two or more carboxyl groups within its molecule. In this case, it is preferable that the pKa of at least one carboxyl group is in the range of 3.5 to 5.5. Examples include oxalic acid (pKa2=4.27), succinic acid (pKa1=4.20), fumaric acid (pKa2=4.44), malic acid (pKa2=5.13), glutaric acid (pKa1=4.30, pKa2=5.40), adipic acid (pKa1=4.43, pKa2=5.41), pimelic acid (pKa1=4.71), phthalic acid (pKa2=5.41), isophthalic acid (pKa2=4.46), terephthalic acid (pKa1=3.51, pKa2=4.82), citric acid (pKa2=4.75), tartaric acid (pKa2=4.40), glutamic acid (pKa2=4.07), and aspartic acid (pKa=3.90).

[0037] The barrier layer (A) may also contain a phosphoric acid compound. The lower limit of the phosphoric acid compound content, expressed in terms of phosphate ions, is preferably 5 ppm. On the other hand, the upper limit of the phosphoric acid compound content, expressed in terms of phosphate ions, is preferably 100 ppm. By containing the phosphoric acid compound within this range, the coloring of EVOH(a) and the melt-molded form of the multilayer structure is sometimes suppressed, thus improving thermal stability. "Phosphate ion conversion" refers to converting the content of elemental phosphorus (P) into phosphate ions (PO4). 3- The value is obtained by measuring the content of ).

[0038] Examples of phosphoric acid compounds include various acids such as phosphoric acid and phosphorous acid, and / or their salts. Phosphates can be any of dihydrogen phosphate, monohydrogen phosphate, or other 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 phosphoric acid compounds.

[0039] The barrier layer (A) may also contain, as an antioxidant, a hindered phenolic compound having, for example, ester or amide bonds. The content of the hindered phenolic compound is preferably 1000 to 10000 ppm. If the content is 1000 ppm or more, coloring, thickening, and gelation of the resin can be suppressed when the pulverized material of the multilayer structure is melt-molded. The content of the hindered phenolic compound is more preferably 2000 ppm or more. On the other hand, if the content of the hindered phenolic compound is 10000 ppm or less, coloring and / or exudation originating from the hindered phenolic compound can be suppressed. The content of the hindered phenolic compound is more preferably 8000 ppm or less.

[0040] Hindered phenolic compounds have at least one hindered phenolic group. A "hindered phenolic group" refers to a group in which at least one carbon atom adjacent to the carbon atom bonded to the phenolic hydroxyl group is bonded to a bulky substituent. The bulky substituent is preferably an alkyl group with 1 to 10 carbon atoms, and more preferably a tert-butyl group.

[0041] The hindered phenolic compound is preferably in a solid state near room temperature. From the viewpoint of suppressing the exudation of this compound, the melting point or softening temperature of the hindered phenolic 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 exudation, the molecular weight of the hindered phenolic compound is preferably 200 or higher, more preferably 400 or higher, and even more preferably 600 or higher. On the other hand, this molecular weight is typically 2000 or lower. From the viewpoint of easy miscibility with EVOH(a), the melting point or softening temperature of the hindered phenolic compound is preferably 200°C or lower, more preferably 190°C or lower, and even more preferably 180°C or lower.

[0042] Hindered phenolic compounds possess either ester bonds or amide bonds. Examples of hindered phenolic compounds with ester bonds include esters of aliphatic carboxylic acids and aliphatic alcohols containing hindered phenolic groups; examples of hindered phenolic compounds with amide bonds include amides of aliphatic carboxylic acids and aliphatic amines containing hindered phenolic groups. From the viewpoint of easy miscibility with EVOH(a), hindered phenolic compounds preferably possess amide bonds.

[0043] Examples of specific structures of hindered phenolic compounds include pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] sold by BASF as Irganox 1010, stearate of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate sold as Irganox 1076, 2,2'-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] sold as Irganox 1035, octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate sold as Irganox 1135, bis(3-tert-butyl-4-hydroxy-5-methylphenylpropionate) ethylene bis(oxyethylene) ester sold as Irganox 245, and others sold as Irganox... The products are 1,6-hexanediol bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] sold in the form of 259, and N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propaneamide] sold in the form of Irganox 1098. Preferably, N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propaneamide] sold in the form of Irganox 1098 and pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] sold in the form of Irganox 1010 are used, with Irganox 1098 being more preferred.

[0044] The barrier layer (A) may also contain thermoplastic resins 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 with α-olefins having 4 or more carbon atoms, copolymers of polyolefins with maleic anhydride, ethylene-vinyl ester copolymers, ethylene-acrylate copolymers, or modified polyolefins obtained by grafting them with unsaturated carboxylic acids or their derivatives), various polyamides (nylon 6, nylon 6 / 6, nylon 6 / 66 copolymers, nylon 11, nylon 12, poly(m-phenylene adipamide), etc.), various polyesters (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate), polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate, and modified polyvinyl alcohol resins, etc. The content of the aforementioned 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 can be 1% by mass or less.

[0045] The resin constituting the barrier layer (A) preferably contains 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. It can also contain 95% by mass or more, 97% by mass or more, or 99% by mass or more. The resin constituting the barrier layer (A) may consist solely of EVOH (a). The proportion of EVOH (a) in the barrier layer (A) exceeds 50% by mass, preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. It can also contain 95% by mass or more, 97% by mass or more, or 99% by mass or more. The barrier layer (A) may substantially consist solely of EVOH (a).

[0046] When the barrier layer (A) contains components other than EVOH (a), the method for manufacturing the resin composition constituting the barrier layer (A) is not particularly limited, and it can be manufactured by melt-blending EVOH (a) with other additives (metal ions, etc.) as needed. Other additives can be blended in solid form such as powder or in the form of melts, or in the form of solutes contained in solutions or dispersed phases contained in dispersions. As solutions and dispersions, aqueous solutions and aqueous dispersions are suitable, respectively. Melt blending can be performed using known mixing or blending equipment such as KNEADER-RUDER, extruders, open mill rolls, and Banbury mixers. The temperature range during melt blending can be appropriately adjusted according to the melting point of the EVOH (a) used, and is typically 150–300°C.

[0047] In other methods, a masterbatch containing a high concentration of other additives in EVOH(a) can be produced by melt blending. This masterbatch is then dry-blended with EVOH(a) that does not contain other additives and used to manufacture multilayer structures. Furthermore, in other methods, EVOH(a) and other additives can be dry-blended to manufacture multilayer structures. "Dry blending" refers to mechanical mixing in powder or granular form. Mixing can be performed using mixing devices such as rotary drums, ribbon mixers, or Henschel mixers, and can be done by manual stirring or shaking in a closed container. The mixing temperature can be maintained between room temperature and below the melting point of EVOH(a), and can be performed in an air atmosphere or a nitrogen atmosphere. It can be manufactured by adding other necessary melt-blending components to EVOH(a) in addition to several pre-added components. An example of pre-adding several components to EVOH(a) is impregnating EVOH(a) in granular or powder form with a solution containing the additives. An aqueous solution is suitable as the solution.

[0048] <Adhesive Layer (B)> The multilayer structure of the present invention has an adhesive layer (B) comprising an adhesive resin (b) as the main component. The adhesive layer (B) functions to bond the barrier layer (A) to the heat-fused layer (C). Therefore, it is preferable to have an adhesive layer (B) between the barrier layer (A) and the heat-fused layer (C), and it is preferable to directly laminate the barrier layer (A) and the heat-fused layer (C).

[0049] As the adhesive resin (b), examples include modified olefin polymers containing carboxyl groups obtained by chemically bonding unsaturated carboxylic acids or their anhydrides to olefin polymers through addition reactions and / or grafting reactions. 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, among which maleic anhydride is particularly suitable. Specifically, suitable materials include one or more mixtures selected from maleic anhydride-grafted modified polyethylene, maleic anhydride-grafted modified polypropylene, maleic anhydride-grafted modified ethylene-propylene copolymer, maleic anhydride-grafted modified ethylene-ethyl acrylate copolymer, and maleic anhydride-grafted modified ethylene-vinyl acetate copolymer, among which maleic anhydride-grafted modified polyethylene is more preferred. The acid value of this adhesive resin (b) is preferably 0.5 to 5 mg KOH / g, more preferably 1 to 4 mg KOH / g. The acid value of adhesive resin (b) can be determined using xylene as a solvent, in accordance with JIS K 0070:1992.

[0050] The adhesive resin (b) may be a mixture of unmodified resin (bx) and acid-modified resin (by). In this case, from the viewpoint of further improving mechanical strength, the unmodified resin (bx) preferably includes ethylene-α-olefin copolymer resin (c) described later, and more preferably ethylene-α-olefin copolymer resin (c). When the unmodified resin (bx) includes ethylene-α-olefin copolymer resin (c), the ethylene-α-olefin copolymer resin (c) included in the adhesive layer (B) and the ethylene-α-olefin copolymer resin (c) included in the heat-fusion layer (C) may be the same or different, but 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 high degree of acid modification (by) is preferably used as the acid-modified resin (by), with an acid value preferably of 5 to 30 mg KOH / g, more preferably 8 to 20 mg KOH / g. This allows for the maintenance of necessary interlayer bond strength while further improving the mechanical strength of the resulting multilayer structure. When the adhesive resin (b) of the present invention is a mixture of unmodified resin (bx) and acid-modified resin (by), a substance prepared by pre-melt-blending the unmodified resin (bx) and acid-modified resin (by) can be used, or a substance prepared by dry-blending the unmodified resin (bx) and acid-modified resin (by) separately can be used. Melt-blending can be performed using known mixing or blending equipment such as a KNEADER-RUDER, extruder, open mill roll, or Banbury mixer. The temperature range during melt-blending can be appropriately adjusted according to the melting points of the unmodified resin (bx) and acid-modified resin (by) used, and is typically 150 to 300°C. Mixing can be performed using mixing devices such as rotary drums, ribbon agitators, or Henschel mixers, or by manually stirring or shaking in a closed container. The mixing temperature can be maintained at room temperature or below the melting points of the unmodified resin (BX) and the acid-modified resin (BY), and can be carried out in an air or nitrogen atmosphere.

[0051] The adhesive layer (B) may contain components other than the adhesive resin (b), provided that it does not impair the effects of the present invention. Examples of such components include alkali metal ions, polyvalent metal ions, carboxylic acids, phosphoric acid compounds, boron compounds, oxidation accelerators, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, pigments, dyes, processing aids, flame retardants, and antifogging agents. The content of other 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 also contain a thermoplastic resin other than the adhesive resin (b). The above-described resins, which can be included in the barrier layer (A), can be used as thermoplastic resins. The content of the aforementioned 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, and even more preferably less than 5% by mass, and can be less than 1% by mass.

[0052] The proportion of adhesive resin (b) constituting the adhesive layer (B) is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. It can be 95% by mass or more, 97% by mass or more, or 99% by mass or more. The resin constituting the adhesive layer (B) may consist of adhesive resin (b) alone. The proportion of adhesive resin (b) in the adhesive layer (B) is more than 50% by mass, preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. It can be 95% by mass or more, 97% by mass or more, or 99% by mass or more. The adhesive layer (B) may consist substantially of adhesive resin (b) alone.

[0053] <Thermal Fusion Layer (C)> The multilayer structure of the present invention has a heat-fusion layer (C), said heat-fusion layer (C) having a density of 0.880~0.930 g / cm³. 3 The ethylene-α-olefin copolymer resin (c) is the main component. The heat-fused layer (C) not only functions as a sealing layer when forming packaging materials and provides resistance to drop damage, but also has the function of improving various mechanical strengths such as puncture strength and / or tensile strength.

[0054] The density of the ethylene-α-olefin copolymer resin (c) is 0.880~0.930 g / cm³. 3 If the density is within the above range, the resulting multilayer structure is flexible and has excellent manufacturability, while improving various mechanical strengths such as puncture strength and / or tensile strength, in addition to drop resistance. The lower limit of the density is preferably 0.890 g / cm³. 3 More preferably, it is 0.900 g / cm³.3 Further preferred value is 0.905 g / cm³. 3 It can be 0.910 g / cm³. 3 The upper limit of density is preferably 0.925 g / cm³. 3 More preferably, it is 0.920 g / cm³. 3 .

[0055] The melt flow rate (MFR) of the ethylene-α-olefin copolymer resin (c) at 190°C and a load of 2.16 kg is preferably 0.5 to 5.0 g / 10 min. If the MFR is within the above range, the ethylene-α-olefin copolymer resin (c) exhibits excellent melt processability, and the resulting multilayer structure exhibits improved mechanical strengths such as drop breakage resistance, puncture strength, and / or tensile strength. 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 determined according to JIS K 7210 (2014) at 190°C and a load of 2.16 kg.

[0056] 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 α-olefins with 3 or more carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, and 4-methyl-1-pentene. 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, but it can also be a linear low-density polyethylene obtained by polymerizing ethylene with an α-olefin having 8 or more carbon atoms. When the number of carbon atoms in the α-olefin copolymerized with ethylene is large, various mechanical strengths such as puncture strength and / or tensile strength are sometimes significantly improved. There is no particular upper limit on the number of carbon atoms in the aforementioned α-olefins with 3 or more carbon atoms, and the number of carbon atoms is usually 12 or less.

[0057] Metallocene catalysts are preferred as polymerization catalysts. Linear low-density polyethylene obtained by polymerization using metallocene catalysts is manufactured by copolymerizing ethylene with α-olefins in the presence of a catalyst comprising at least one coordinating group having a cyclopentadienyl backbone, a transition metal of Group 4 of the periodic table, preferably a zirconium compound, an organoaluminum oxide compound, and various other components added as needed. Linear low-density polyethylene obtained by polymerization using metallocene catalysts exhibits excellent melt-forming properties, and the resulting multilayer structures demonstrate an excellent balance of heat resistance, flexibility, and mechanical strength.

[0058] Regarding linear low-density polyethylene obtained by polymerizing ethylene with α-olefins having 6 or more carbon atoms using metallocene catalysts, industrially manufactured products are already available. Examples include "Evolue" (manufactured by Prime Polymer), "SUMIKATHENE" (manufactured by Sumitomo Chemical), "UMERIT" (manufactured by Ube Maruzen Polyethylene), and "ELITE" (manufactured by Dow Chemical).

[0059] The heat-fused layer (C) may contain other components besides the ethylene-α-olefin copolymer resin (c), provided that the effects of the present invention are not impaired. Examples of such other components include alkali metal ions, polyvalent metal ions, carboxylic acids, phosphoric acid compounds, boron compounds, oxidation accelerators, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, pigments, dyes, processing aids, flame retardants, and antifogging agents. The content of other components in the heat-fused layer (C) is typically 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less. The heat-fused layer (C) may also contain thermoplastic resins other than the ethylene-α-olefin copolymer resin (c). The above-described resins, which can be included in the barrier layer (A), can be used as thermoplastic resins. The content of the aforementioned thermoplastic resin in the heat-fusion layer (C) is less than 50% by mass, preferably less than 30% by mass, more preferably less than 10% by mass, and even more preferably less than 5% by mass, and can be less than 1% by mass.

[0060] The proportion of ethylene-α-olefin copolymer resin (c) constituting the heat-fusion layer (C) is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. It can be 95% by mass or more, 97% by mass or more, or 99% by mass or more. The resin constituting the heat-fusion layer (C) can be composed solely of ethylene-α-olefin copolymer resin (c). The proportion of ethylene-α-olefin copolymer resin (c) in the heat-fusion layer (C) is more than 50% by mass, preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. It can be 95% by mass or more, 97% by mass or more, or 99% by mass or more. The heat-fusion layer (C) can be substantially composed solely of ethylene-α-olefin copolymer resin (c).

[0061] The method for manufacturing the resin composition constituting the heat-bonding layer (C) is not particularly limited, and it can be manufactured by melt-blending an ethylene-α-olefin copolymer resin (C) with other additives as needed. Melt-blending can be performed using known mixing or blending equipment such as a Kneader-Ruder, extruder, open mill roll, or Banbury mixer. The temperature range during melt-blending can be appropriately adjusted according to the melting point of the ethylene-α-olefin copolymer resin (C) used, and is typically 150–300 °C.

[0062] In other methods, a masterbatch containing a high concentration of other additives relative to the ethylene-α-olefin copolymer resin (c) can be produced by melt blending. This masterbatch is then dry-blended with ethylene-α-olefin copolymer resin (c) that is substantially free of other additives and used to manufacture multilayer structures. Furthermore, in other methods, the ethylene-α-olefin copolymer resin (c) and other additives can be dry-blended to manufacture a heat-fused layer (C). Mixing can be performed using mixing devices such as rotary drums, ribbon agitators, or Henschel mixers, and can be done by manual stirring or agitation in a closed container. As for the mixing temperature, it can be carried out at room temperature to below the melting point of the ethylene-α-olefin copolymer resin (c), and can be performed under an air atmosphere or a nitrogen atmosphere.

[0063] The sealant layer (X) comprises a barrier layer (A), an adhesive layer (B), and a heat-bonding layer (C). Preferably, at least one set of barrier layers (A) and adhesive layers (B) are stacked adjacent to each other. This results in a multilayer structure with high gas barrier properties, reusability, mechanical strength, and stability.

[0064] As a lamination method for manufacturing the sealant layer (X), conventional co-extrusion methods can be used, in which various resins are extruded and laminated from different or common molds. As the mold, either a ring mold or a T-mold can be used. The molding temperature during melt molding can be appropriately adjusted according to the melting point and / or melt viscosity of the resin used, and is mostly selected from the range of 150 to 300°C. It should be noted that, from the viewpoint of maintaining the heat-sealing strength when the multilayer structure of the present invention is molded for use as a flexible packaging material, the sealant layer (X) is preferably a non-stretchable layer.

[0065] The total thickness of the sealant layer (X) is preferably 15-300 μm, more preferably 25-250 μm, even more preferably 35-200 μm, and particularly preferably 45-150 μm. By achieving a total thickness within the above range, the sealant layer (X) is lightweight and flexible, thus making it ideal for use in flexible packaging. The low amount of resin used in the sealant layer (X) helps to minimize environmental impact.

[0066] The minimum thickness of the barrier layer (A) is preferably 1 μm. If the minimum thickness of the barrier layer (A) is within the above range, the multilayer film exhibits sufficient gas barrier properties. The maximum thickness of the barrier layer (A) is preferably 30 μm, more preferably 25 μm, further preferably 20 μm, and particularly preferably 15 μm. If the maximum thickness of the barrier layer (A) is within the above range, the reusability when recycling the sealant layer (X) or the multilayer structure is improved. In particular, from the viewpoint of improving drop resistance at high temperatures, the thickness of the barrier layer (A) is sometimes preferably 5 μm or less, and sometimes more preferably 4 μm or less. When the thickness of the barrier layer (A) is 5 μm or less, in order to maintain good gas barrier properties, the ethylene unit content of EVOH(a) is preferably 33 mol% or less, more preferably 28 mol% or less. When the sealant layer (X) has multiple barrier layers (A), the thickness of the barrier layer (A) mentioned above refers to the total thickness of the multiple barrier layers (A).

[0067] The thickness of the adhesive layer (B) is preferably 1 to 20 μm, more preferably 2 to 10 μm. If the thickness of the adhesive layer (B) is within the above range, the interlayer adhesion between the barrier layer (A) and the heat-fused layer (C) becomes stronger, and the reusability when recycling the sealant layer (X) or the multilayer structure is improved. When the sealant layer (X) has multiple adhesive layers (B), the thickness of the adhesive layer (B) refers to the total thickness of the multiple adhesive layers (B).

[0068] The thickness of the heat-fusion bonding layer (C) is preferably 15 to 300 μm, more preferably 30 to 200 μm, and even more preferably 40 to 150 μm. If the thickness of the heat-fusion bonding layer (C) is within the above range, reusability, mechanical strength, and water vapor barrier properties are improved. When the sealant layer (X) has multiple heat-fusion bonding layers (C), the thickness of the heat-fusion bonding layer (C) refers to the total thickness of the multiple heat-fusion bonding layers (C).

[0069] The ratio of the thickness of the barrier layer (A) in the sealant layer (X) to the total thickness of all layers is preferably 0.10 or less. If this ratio is within the above range, reusability 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, further 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 to exhibit sufficient gas barrier properties, it is preferably 0.005. On the other hand, the ratio of the thickness of the heat-fusion layer (C) in the multilayer structure of the present invention to the total thickness of all layers is preferably 0.60 or more, more preferably 0.70 or more, further preferably 0.80 or more, and can be 0.99 or less. If this ratio is within the above range, reusability, mechanical strength, and water vapor barrier properties are improved.

[0070] The sealant layer (X) can be composed of a barrier layer (A), an adhesive layer (B), and a heat-fused layer (C), and there is no particular limitation on the exposed surface of the heat-fused layer (C). If the heat-fused layer (C) is represented as (C), the adhesive resin layer (B) as (B), and the barrier layer (A) as (A), and " / " indicates direct lamination, then layer compositions such as (C) / (B) / (A) / (B) / (C) and (C) / (B) / (A) can be listed. In addition to the above layer compositions, other layers may also be included. When multiple barrier layers (A), adhesive layers (B), and heat-fused layers (C) are used, different types of resins may also be used.

[0071] <Substrate layer (Y)> The multilayer structure of the present invention has a substrate layer (Y), which is a layer containing polypropylene (y) with a melting point of 150°C or higher as measured by differential scanning calorimetry (DSC) as the main component, and stretched along the biaxial direction. The elastic modulus in the aforementioned biaxial direction is 2000 MPa or higher under conditions of 23°C and 50% RH. "Polypropylene" refers to: homopolymers of propylene, copolymers of 80 mol% or more of propylene with 20 mol% or less of ethylene or α-olefin monomers, and copolymers of 90 mol% or more of propylene with less than 10 mol% of non-olefin monomers whose functional groups do not contain atoms other than carbon, oxygen, and hydrogen atoms. By including polypropylene (y) with a melting point of 150°C or higher as the main component in the substrate layer (Y), the drop breakage resistance of the multilayer structure of the present invention under high-temperature conditions can be improved. This 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 can be below 170°C. The substrate layer (Y) is a layer stretched along both biaxial directions. By ensuring that the elastic modulus in both biaxial directions at 23°C and 50%RH is 2000 MPa or more, a multilayer structure with excellent handling convenience and improved drop resistance under high-temperature conditions can be obtained. The stretching ratio in the biaxial directions is not particularly limited, but it is preferable to stretch it by 3 times or more and less than 12 times in both biaxial directions, more preferably by 4 times or more and less than 10 times, and even more preferably by 4 times or more and less than 6 times in the flow direction (MD) and 8 times or more and less than 12 times in the width direction (TD). The elastic modulus in the MD direction is preferably 2400 MPa or more, and can be 2600 MPa or more. The elastic modulus in the MD direction can be 4000 MPa or less. The elastic modulus in the TD direction is preferably 3500 MPa or more, and can be 5000 MPa or more. The elastic modulus in the TD direction can be 7000 MPa or less. When the substrate layer (Y) is heated from 20°C to 220°C at a rate of 10°C / min using a differential scanning calorimeter (DSC), and then cooled to -50°C at a rate of 10°C / min, the difference (T1-T2) between the maximum endothermic peak temperature (T1) during heating and the maximum exothermic peak temperature (T2) during cooling is preferably 56°C or less. When the difference (T1-T2) between the maximum exothermic peak temperature (T2) during cooling and the substrate layer (Y) is 56°C or less, the water vapor barrier properties of the resulting multilayer structure are sometimes significantly improved, and the drop breakage resistance under high-temperature conditions is further improved. The aforementioned 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 aforementioned difference (T1-T2) can be 50°C or more, or 51°C or more.

[0072] The proportion of polypropylene (y) in the resin constituting the substrate layer (Y) is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, particularly preferably 95% by mass or more, and can be 97% by mass or more, or 99% by mass or more. The resin constituting the substrate layer (Y) may consist of only polypropylene (y). The content of polypropylene (y) in the substrate layer (Y) must exceed 50% by mass, preferably 70% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and can be 97% by mass or more, or 99% by mass or more. The substrate layer (Y) may substantially consist of only polypropylene (y).

[0073] There is no particular limitation on the film-forming method of the substrate layer (Y), and it is generally formed by melt extrusion using an extruder. As the mold, either a ring mold or a T-mold can be used. There is also no particular limitation on the method of stretching along the biaxial direction; it can be manufactured by using existing known stretching methods such as tubular simultaneous biaxial stretching, tenter frame successive biaxial stretching, and tenter frame simultaneous biaxial stretching, stretching along the film flow direction and / or in a direction perpendicular to the flow direction, i.e., the width direction.

[0074] From the viewpoint of industrial productivity, the thickness of the substrate layer (Y) is preferably 10 to 100 μm. Furthermore, from the viewpoint of balancing the mechanical strength, water vapor barrier properties, and manufacturing cost of the multilayer structure, the thickness of the substrate layer (Y) is more preferably 12 to 55 μm, even more preferably 14 to 35 μm, and particularly preferably 16 to 25 μm. It should be noted that, generally, a larger thickness in the multilayer structure tends to improve drop resistance, but when the substrate layer (Y) has a thickness greater than a specified value, it tends to decrease drop resistance at room temperature, especially.

[0075] The composition of the substrate layer (Y) is not particularly limited as long as it contains polypropylene (y) as the main component. It can be a single layer or multiple layers. From the point of view of manufacturing cost and functionality, it is usually a single layer to five layers.

[0076] <Multi-layer structure> The multilayer structure of the present invention is a multilayer structure in which a sealant layer (X) and a substrate layer (Y) are stacked, and a heat-sealing layer (C) of the sealant layer (X) is provided on the outermost surface. In the multilayer structure, by providing a heat-sealing layer (C) on the outermost surface, the multilayer structure of the present invention can be easily heat-sealed when used as 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 higher as the main component, and a metal layer with a thickness of 1 μm or more. That is, the EVOH (a) adhesive resin (b), ethylene-α-olefin copolymer (c), and polypropylene (y) all preferably have melting points below 200°C. "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 higher as the main component, and a metal layer with a thickness of 1 μm or more" means: 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 higher as the main component, and does not have a metal layer with a thickness of 1 μm or more. By eliminating the presence of a resin layer with a thickness of 10 μm or more containing a resin with a melting point of 200°C or higher as the main component, and a metal layer with a thickness of 1 μm or more, uneven mixing with other components can be suppressed during the melting and molding of pulverized multilayer structures. This improves reusability. The "metal layer" refers to a layer such as aluminum foil that has continuous and discontinuous surfaces formed of metal. From the viewpoint of further improving reusability, the thickness of each layer containing a resin with a melting point of 200°C or higher as the main component is preferably 7 μm or less, and can be 5 μm or less.

[0077] The upper limit of the total thickness of the multilayer structure of the present invention is preferably 300 μm. By making the total thickness within the above range, the multilayer structure of the present invention is lightweight and flexible, and therefore preferably used for flexible packaging applications. The amount of resin used in the multilayer structure is small, which can reduce environmental burden. 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 properties 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. Generally, it is possible to improve drop resistance by increasing the total thickness of the multilayer structure, but according to the present invention, drop resistance can be improved without increasing the total thickness of the multilayer structure. It has been found that when the thickness of the substrate layer (Y) is increased, there is a tendency, in particular, to decrease drop resistance at room temperature, contrary to the usual trend, and it has been found that by adjusting the thickness of each layer, a multilayer structure with superior drop resistance can be specifically obtained. It is generally assumed that the presence of the barrier layer (A) would reduce drop resistance, but the following surprising effect was found: in areas where the barrier layer (A) is very thin (e.g., less than 5 μm), there is a tendency to further improve drop resistance at high temperatures.

[0078] The thickness of each layer in the multilayer structure of the present invention can be adjusted appropriately according to the application. From the viewpoint of suppressing coloration when melting and molding pulverized material, improving thermal stability during melting and molding, and suppressing particulate matter generation, the ratio of the total thickness of the layer containing polyolefin resin as the main component to the total thickness of the multilayer structure is preferably 0.80 or more, more preferably 0.85 or more, further preferably 0.90 or more, and particularly preferably 0.95 or more. As the polyolefin resin, polyethylene, ethylene-α-olefin copolymer resin and polypropylene, and their acid-modified resins are preferred, such as ethylene-α-olefin copolymer resin (c), polypropylene (y), and adhesive resin (b) when it is a polyolefin resin, etc.

[0079] The puncture strength S of the multilayer structure of the present invention, measured using JIS Z 1707:2019 at 23°C and 50%RH, and the puncture strength S of the substrate layer (Y), measured using JIS Z 1707:2019, at 23°C and 50%RH, are compared. Y The difference (SS) Y The preferred value is 3.5N or more, more preferably 4.0N or more. The aforementioned difference (SS) Y The puncture strength S can be 10N or less. By satisfying this condition, the drop damage resistance of the resulting 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 12N or more, more preferably 15N or more, and even more preferably 18N or more. The aforementioned puncture strength S can be 30N or less. The aforementioned puncture strength can be adjusted according to, for example, the type of polypropylene (y) used in the substrate layer (y), the thickness of each layer of the multilayer structure, the layer composition of the multilayer structure, etc.

[0080] The oxygen permeability (OTR) of the multilayer structure of the present invention under conditions of 20°C and 65%RH can be adjusted according to the application and is not particularly limited, but is preferably 5cc / (m 2 OTR with a gas barrier value of 2 cc / (atm) or less. Multilayer structures in this range exhibit excellent gas barrier properties, making them suitable for use as packaging materials. More preferably, OTR has a gas barrier value of 2 cc / (atm). 2 ·day·atm) or less, further preferably 1.5cc / (m 2 For doses below 1.5 cc / (m³), the limit is 0.5 cc / (m³). 2 Below 0.1 cc / (m·atm). OTR can be 0.1 cc / (m·at ... 2 The OTR was measured according to JIS K 7126-2 (isobaric method; 2006), specifically using the method described in the examples.

[0081] The water vapor transmission rate (WVTR) of the multilayer structure of the present invention under conditions of 40°C and 90%RH can be adjusted according to the application and is not particularly limited, but is preferably 4 g / (m²). 2 • Less than 1 day. WVTR multilayer films in this range have excellent water vapor barrier properties and are suitable for use as packaging materials. WVTR is preferably 3.5 g / (m³). 2 ·days or less, more preferably 3.0g / (m 2 For doses below 2.5 g / (m²), the dosage can be 2.5 g / (m²). 2 • days) or less. WVTR can be 1g / (m 2 • Days or more. WVTR was measured in accordance with JIS K 7129-2 (Infrared sensor method; 2019), specifically using the method described in the examples.

[0082] The method for laminating the substrate layer (Y) onto the sealant layer (X) is not particularly limited, and examples include extrusion lamination, co-extrusion lamination, and dry lamination. From an operational point of view, dry lamination is preferred. When laminating the substrate layer (Y) onto the sealant layer (X), an adhesive layer may be provided. The adhesive layer can be an adhesive layer (B), or an adhesive layer (Z) that can be formed by applying a known adhesive and drying it. As a known adhesive, 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.

[0083] In the multilayer structure of the present invention, other layers besides those described above may be included without impairing the effects of the present invention. Preferably, in addition to resin layers with a thickness of 10 μm or more containing a resin with a melting point of 200°C or higher as the main component, or metal layers with a thickness of 1 μm or more, examples include resin layers containing thermoplastic resins as the main component. The aforementioned thermoplastic resins are not particularly limited, and examples include polyolefins, polyamides, polyesters, polystyrene, polyvinyl chloride, polyvinylidene chloride, acrylic resins, polycarbonate, chlorinated polyethylene, and chlorinated polypropylene. Another example of other layers is a recycling layer. It is particularly preferable to reuse a recycling composition containing the recycled material of the multilayer structure described later as part or all of the recycling layer. Another example of other layers is a printing layer. The printing layer can exist at any location in the multilayer structure of the present invention. Examples of printing layers include, for instance, a coating obtained by applying a solution containing pigments or dyes and, as needed, an adhesive resin, and then drying it. Besides gravure printing, various coating methods using wire rods, spin coaters, and die coaters can be listed as methods for applying the printing layer. The thickness of the printing layer is not particularly limited, but is preferably 0.5 to 10 μm, more preferably 1 to 4 μm.

[0084] End pieces and / or defective products generated during the manufacture of the multilayer structure of the present invention are preferably recycled and reused. It is also preferable to recycle and reuse multilayer structures already in circulation in the market. In this case, a typical recycling method is to crush the multilayer structure and then melt it down for molding.

[0085] When recycling the multilayer structure of the present invention, the recycled material of the multilayer structure of the present invention is first pulverized. The pulverized recycled material can be directly melt-molded to obtain a recycled composition, or it can be melt-molded together with other components as needed to obtain a recycled composition. When obtaining a recycled composition by melt-molding together with other components, polyolefin resin is preferred, more preferably polypropylene resin, polyethylene resin, or a mixture thereof. The pulverized recycled material can be directly used to manufacture molded articles such as multilayer structures, or the pulverized recycled material can be melt-stacked to obtain granules formed from the recycled composition, which are then used to manufacture molded articles. The melt-molding method for the recycled composition can be extrusion molding, blow molding, blow molding, melt spinning, injection molding, etc. The molding temperature during melt molding can be adjusted appropriately according to the melting point and / or melt viscosity of the resin used, and is mostly selected from the range of 150 to 300°C. The aforementioned recycled composition may contain unused resin, and the content of recycled material in the aforementioned recycled composition is preferably 10% by mass or more, more preferably 20% by mass or more, and can be 30% by mass or more. The content of EVOH(a) in the aforementioned recycled composition is preferably 20% by mass or less, more preferably 10% by mass or less, and can be 5% by mass or less.

[0086] Since the recycled layer of the multilayer structure of the present invention contains less particulate matter, the multilayer structure of the present invention is preferably manufactured by co-extrusion molding.

[0087] The multilayer structure of the present invention has excellent gas barrier properties, drop damage resistance and reusability. Therefore, it can be used as a variety of packaging materials such as food packaging, chemical packaging, industrial pharmaceutical packaging, and pesticide packaging. It can be further used in a wide range of applications, but is not limited to these applications.

[0088] A suitable embodiment of the aforementioned packaging material is a package formed by filling the aforementioned packaging material with contents. Examples of possible contents include beverages such as alcohol and fruit juice; food items such as fruits, nuts, vegetables, meat products, baby food, coffee, jam, mayonnaise, ketchup, cooking oil, seasonings, sauces, seafood, and dairy products; other examples include chemicals, cosmetics, gasoline, and other contents that are prone to deterioration in the presence of oxygen, but are not limited to these. Example

[0089] The present invention will now be described in more detail with reference to specific examples. However, the present invention is not limited to these examples.

[0090] <Materials Used> • Substrate layer (Y) Y-1: Biaxially stretched PP film "U-1 (20μm)" manufactured by Mitsui Chemicals Tohcello. Y-2: Biaxially stretched PP film "U-1 (40μm)" manufactured by Mitsui Chemicals Tohcello. Y-3: Biaxially stretched PP film "WH-OP-HE-1 (20μm)" manufactured by Mitsui Chemicals Tohcello. YC-1: Unstretched PP film "SC (40μm)" manufactured by Mitsui Chemicals Tohcello. YC-2: Biaxially stretched HDPE film "Ethy-Lyte 25HD200" manufactured by Jindal Poly Films Ltd. ·EVOH(a) a-1: EVOH and ethylene unit content are 32 mol%, saponification degree is 99.9 mol%, containing sodium acetate (250 ppm in sodium ion conversion), magnesium acetate (40 ppm in magnesium ion conversion), phosphate ions (20 ppm in phosphate ion conversion), boric acid (200 ppm in boron element conversion), and MFR (190℃, 2.16 kg load) is 1.6 g / 10 minutes. a-2: EVOH and ethylene unit content are 32 mol%, saponification degree is 99.9 mol%, containing sodium acetate (250 ppm sodium ion equivalent), magnesium acetate (40 ppm magnesium ion equivalent), and phosphate ions (20 ppm phosphate ion equivalent). MFR (190℃, 2.16 kg load) is 1.6 g / 10 min. a-3: EVOH and ethylene unit content are 24 mol%, saponification degree is 99.9 mol%, containing sodium acetate (250 ppm sodium ion equivalent), magnesium acetate (40 ppm magnesium ion equivalent), and phosphate ions (20 ppm phosphate ion equivalent). MFR (210℃, 2.16 kg load) is 2.5 g / 10 minutes. a-4: EVOH and ethylene unit content are 27 mol%, saponification degree is 99.9 mol%, containing sodium acetate (250 ppm sodium ion equivalent), magnesium acetate (40 ppm magnesium ion equivalent), and phosphate ions (20 ppm phosphate ion equivalent). MFR (210℃, 2.16 kg load) is 3.0 g / 10 minutes. a-5: EVOH and ethylene unit content are 44 mol%, saponification degree is 99.9 mol%, containing sodium acetate (250 ppm sodium ion equivalent), magnesium acetate (40 ppm magnesium ion equivalent), phosphate ions (20 ppm phosphate ion equivalent), and MFR (190℃, 2.16 kg load) is 5.0 g / 10 minutes. • Adhesive resin (b) b-1: Mitsui Chemicals' maleic anhydride-modified polyethylene "ADMER (trademark) NF518" (MFR (190℃, 2.16kg load) 3.1g / 10min, density 0.91g / cm³) 3 (Acid value: 1.10 mg KOH / g) b-2: Mitsui Chemicals' maleic anhydride-modified polypropylene "ADMER (trademark) QF500" (MFR (230℃, 2.16kg load) 3.0g / 10min, density 0.90g / cm³) 3 (Acid value: 1.12 mg KOH / g) · Ethylene-α-olefin copolymer resin (c) c-1: Prime Polymer's linear low-density polyethylene "Evolue (trademark) SP1510" (polymerized from ethylene and 1-hexene using a metallocene catalyst, MFR (190°C, 2.16 kg load) 1.0 g / 10 min, density 0.915 g / cm³). 3 ) c-2: Prime Polymer's linear low-density polyethylene "Evolue (trademark) SP0510" (polymerized from ethylene and 1-hexene using a metallocene catalyst, MFR (190°C, 2.16 kg load) 1.2 g / 10 min, density 0.903 g / cm³). 3 ) c-3: Prime Polymer's linear low-density polyethylene "Evolue (trademark) SP2510" (polymerized from ethylene and 1-hexene using a metallocene catalyst, MFR (190°C, 2.16 kg load) 1.5 g / 10 min, density 0.923 g / cm³). 3 ) cC-1: Evolue (trademark) SP4030, a linear low-density polyethylene manufactured by Prime Polymer (polymerized from ethylene and 1-hexene using a metallocene catalyst; MFR (190°C, 2.16 kg load) 3.8 g / 10 min; density 0.938 g / cm³). 3 ) cC-2: Polypropylene "NOVATEC (trademark) PP EA7AD" manufactured by Nippon Polypropylene Co., Ltd. (MFR (230℃, 2.16kg load) 1.4g / 10min, density 0.90g / cm³) 3 ) <Evaluation Methods> (1) Differential scanning calorimetry analysis of the substrate layer (Y) For the substrate layer (Y) used in the examples and comparative examples, a differential scanning calorimeter (DSC) (TA Instruments Q2000) was used to heat the substrate from 20°C to 220°C at a rate of 10°C / min, and then cooled it to -50°C at a rate of 10°C / min. 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 substrate layer (Y).

[0091] (2) Determination of the elastic modulus of the substrate layer (Y) After conditioning the substrate layer (Y) used in the examples and comparative examples at 23°C and 50%RH for 24 hours, a 15mm wide section was cut out, and the elastic modulus was determined according to ASTM D-638 at a tensile speed of 5mm / min. Measurements were performed in both the flow direction (MD) and width direction (TD) for 10 samples each, and the average value was calculated.

[0092] (3) Puncture strength determination of substrate layer (Y) and multilayer structure After conditioning the substrate layer (Y) used in the examples and comparative examples and the multilayer structures obtained in the examples and comparative examples at 23°C and 50%RH for 24 hours, the fracture strength was measured when a needle with a tip diameter of 1 mm was punctured at a speed of 50 mm / min under the same conditions. The measurement was performed 10 times while changing the location, and the average value was used as the measurement result. It should be noted that, for the multilayer structure, the needle was punctured from the substrate layer (Y) side.

[0093] (4) Determination of oxygen permeation rate of multilayer structures Using the multilayer structure obtained in the examples and comparative examples, one side was designated as the oxygen supply side and the other side as the carrier gas side, and the oxygen permeation rate was measured. Specifically, using an oxygen permeation measuring device (Modern Control's "MOCONOX-TRAN2 / 21"), according to JIS K 7126-2 (isobaric method; 2006), the oxygen permeation rate (unit: cc / (m³)) was measured under the following conditions: temperature 20°C, humidity of 65%RH on both the oxygen supply and carrier gas sides, oxygen pressure of 1 atmosphere, and carrier gas pressure of 1 atmosphere. 2• Days • atm)). During the measurement, the substrate layer (Y) side of the multilayer structure was designated as the oxygen supply side. Nitrogen gas containing 2% hydrogen by volume was used as the carrier gas. It should be noted that the oxygen permeation rate was 5.0 cc / (m²). 2 If the gas barrier is above 100 atm, it is judged to be insufficient.

[0094] (5) Measurement of water vapor permeation rate of multi-layered structures Using the multilayer structure obtained in the examples and comparative examples, one side was designated as the water vapor supply side and the other side as the carrier gas side, and the water vapor transmission rate was measured. Specifically, using a water vapor transmission rate measuring device (ModernControl's "MOCON PERMATRAN W3 / 33"), according to JIS K 7129-2 (infrared sensor method; 2019), the water vapor transmission rate (unit: g / (m³)) was measured 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 • (day). During the measurement, the substrate layer (Y) side of the multilayer structure was designated as the carrier gas side. Nitrogen gas was used as the carrier gas.

[0095] (6) Drop resistance of multi-layer structures (room temperature) Two A4-sized pieces were cut from the multilayer structure obtained in the examples and comparative examples. The sealant layer (X) was overlapped, and three sides were heat-sealed with a width of 5 mm. Next, 1.2 L of water was filled through the opening, and the remaining sides were heat-sealed to create a water-filled bag. This water-filled bag was repeatedly dropped vertically from a height of 1.5 m at 25°C and 70% RH to determine the number of times leakage occurred. Five such tests were performed, and the average value was used as the result. The results were judged according to the following criteria. It should be noted that criteria D and E are unacceptable.

[0096] Judgment: Benchmark A: More than 12 times B: 8 or more but less than 12 times C: 4 or more but less than 8 times D: More than 2 times but less than 4 times E: Less than 2 times (7) Drop damage resistance (high temperature) of multi-layer structures Two A4-sized pieces were cut from the multilayer structure obtained in the examples and comparative examples. The sealant layer (X) was overlapped, and three sides were heat-sealed with a width of 5 mm. Next, 1.2 L of water was filled through the opening, and the remaining sides were 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 vertically from a height of 1.5 m at 25°C and 70% RH to determine the number of times leakage occurred. This test was performed five times, and the average value was used as the result. The results were judged according to the following criteria. It should be noted that criteria D and E are unacceptable.

[0097] Judgment: Benchmark A: More than 8 times B: 5 or more but less than 8 times C: More than 3 times but less than 5 times D: More than 2 times but less than 3 times E: less than 2 times.

[0098] (8) Evaluation of the reusability of multi-layer structures The multilayer structures obtained in the examples and comparative examples were pulverized to a size of less than 4 mm square. This pulverized material was then mixed with NOVATEC LD LJ400 low-density polyethylene resin (MFR 190°C, 2.16 kg load) manufactured by Nippon Polyethylene Co., Ltd., with a density of 0.921 g / cm³ and a mass fraction of 1.5 g / 10 minutes. 3 The polypropylene "NOVATEC (trademark) PPEA7AD" manufactured by Japan Polypropylene Corporation (MFR (230℃, 2.16kg load) is 1.4g / 10min, and the density is 0.90g / cm³) is compared with that of "NOVATEC (trademark) PPEA7AD" manufactured by Japan Polypropylene Corporation. 3 A single-layer film with a thickness of 50 μm was obtained by blending the pulverized material (polyethylene resin / polypropylene resin) in a mass ratio of 40 / 30 / 30 and extruding it under the conditions shown below. The thickness of the single-layer film was adjusted by appropriately changing the screw speed and traction roller speed. As a control, a single-layer film with a thickness of 50 μm was also obtained without blending the pulverized material (polyethylene resin / polypropylene resin 50 / 50).

[0099] Extruder: Single-screw extruder manufactured by Toyo Seiki Co., Ltd. Screw diameter: 20mmφ (L / D=20, compression ratio=3.5, full thread type) Extrusion temperature: Supply section / Compression section / Metering section / Die = 180 / 230 / 230 / 230℃ Traction roller temperature: 80℃ The particulate matter generation of the obtained monolayer membrane is evaluated according to the five stages A through E below. It should be noted that E is an unacceptable benchmark.

[0100] Judgment: Benchmark A: Compared to the control, the amount of particulate matter remained almost unchanged. B: The amount of small particulate matter was slightly higher compared to the control. C: The amount of small particulate matter was greater compared to the control. D: Compared with the control, there was a greater amount of large particulate matter. E: The amount of large particles is much greater than that of the control.

[0101] <Example> Example 1 EVOH (a-1) was used as the material for the barrier layer (A), the adhesive resin (b-1) was used as the material for the adhesive layer (B), and the ethylene-α-olefin copolymer resin (c-1) was used as the material for the heat-fusion layer (C). A multilayer film (sealant layer (X-1)) with a layer thickness and layer composition of (C) / (B) / (A) / (B) / (C) = 60μm / 4μm / 6μm / 4μm / 60μm was produced using a 300mm wide five-layer co-extrusion casting film-making machine. The film-making conditions at this time are shown below.

[0102] Extrusion temperature of barrier layer (A): Supply section / Compression section / Metering section / Die = 170 / 220 / 220 / 220℃ Extrusion temperature of adhesive layer (B): Supply section / Compression section / Metering section / Die = 170 / 220 / 220 / 220℃ Extrusion temperature of the heat-fusion layer (C): Supply section / Compression section / Metering section / Die = 170 / 220 / 220 / 220℃ Temperature of cooling roller: 40℃ Traction speed: 1.5 m / min A two-component reactive polyurethane adhesive (24 parts by mass of "TAKELAC A-520" and 4 parts by mass of "TAKENATE A-50" manufactured by Mitsui Chemicals) was mixed with 37 parts by mass of ethyl acetate to prepare an adhesive solution. Next, the adhesive solution was applied to a substrate layer (Y-1) using a rod coater to a dried thickness of 4 μm. The substrate layer (Z) was dried at 80°C for 3 minutes to form an adhesive layer. This layer was then laminated with the previously obtained multilayer film (sealant layer (X-1)) to create a multilayer structure with a layer thickness and composition 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.

[0103] The substrate layer (Y-1) and the resulting multilayer structure were evaluated according to the evaluation method described above. The results are shown in Table 1.

[0104] Examples 2-14, Comparative Examples 3-6 As described in Table 1, the type of substrate layer (Y), the type of EVOH (a), the thickness of barrier layer (A), the type of ethylene-α-olefin copolymer resin (c), and the thickness of adhesive layer (Z) were varied. Otherwise, a multilayer structure was fabricated using the same method as in Example 1, and the results were evaluated. The results are shown in Tables 1-2.

[0105] 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-fusion layer (C), a multilayer film (sealant layer (X-2)) with a layer thickness and layer composition of (A) / (B) / (C) = 6 μm / 8 μm / 120 μm was fabricated using a 300 mm wide five-layer co-extrusion casting film-forming apparatus under the same film-forming conditions as in Example 1. Subsequently, using the same method as in Example 1, a multilayer structure with a layer thickness and layer composition of (Y-1) / adhesive layer (Z) / (A) / (B) / (C) = 20 μm / 4 μm / 6 μm / 8 μm / 120 μm was fabricated and evaluated. The results are shown in Table 1.

[0106] Comparative Example 1 Without laminating the substrate layer (Y-1), the sealant layer (X-1) was used directly as the multilayer structure. Otherwise, the multilayer structure was fabricated using the same method as in Example 1, and the results were evaluated. The results are shown in Table 2.

[0107] Comparative Example 2 Instead of a multilayer film, a 134 μm thick thermally bonded layer (C) monolayer film was fabricated and used. Otherwise, a multilayer structure was fabricated using the same method as in Example 1, and the results were evaluated. The results are shown in Table 2.

[0108] [Table 1]

[0109] [Table 2]

Claims

1. A multilayer structure having a sealant layer (X) and a substrate layer (Y). The sealant layer (X) comprises a barrier layer (A), an adhesive layer (B), and a heat-fusion layer (C). The barrier layer (A) contains an ethylene-vinyl alcohol copolymer (a) with an ethylene unit content of 20-50 mol% and a saponification degree of 90 mol% or more as the main component. The adhesive layer (B) contains an adhesive resin (b) as the main component. The heat-fusion layer (C) contains a resin with a density of 0.880-0.930 g / cm³. 3 The ethylene-α-olefin copolymer resin (c) is used as the main component. The substrate layer (Y) is a layer containing polypropylene (y) with a melting point of 150°C or higher as measured by differential scanning calorimetry (DSC) as the main component, and which has been stretched along the biaxial direction. The elastic modulus in the aforementioned biaxial direction is 2000 MPa or higher under the conditions of 23°C and 50% RH. The outermost surface of the multilayer structure has a heat-fused layer (C) with a sealant layer (X).

2. The multilayer structure according to claim 1, wherein the puncture strength S measured using JIS Z 1707:2019 at 23°C and 50%RH and the puncture strength S of the substrate layer (Y) measured using JIS Z 1707:2019 at 23°C and 50%RH are respectively... Y The difference (SS) Y The value is above 3.5N.

3. The multi-layer structure according to claim 2, wherein, The aforementioned puncture intensity S is 12N or higher.

4. The multi-layer structure according to any one of claims 1 to 3, wherein, The substrate layer (Y) was heated from 20°C to 220°C at a rate of 10°C / min using a differential scanning calorimeter (DSC), and then cooled to -50°C at a rate of 10°C / min. The difference between the maximum endothermic peak temperature (T1) during the heating and the maximum exothermic peak temperature (T2) during the cooling (T1-T2) was less than 56°C.

5. The multi-layer structure according to any one of claims 1 to 3, wherein, The sealant layer (X) and the substrate layer (Y) are laminated together by means of an adhesive layer (Z), the thickness of which is 2~7μm.

6. The multi-layer structure according to any one of claims 1 to 3, wherein, Ethylene-α-olefin copolymer resin (c) is a linear low-density polyethylene obtained by copolymerizing ethylene with α-olefins having 6 or more carbon atoms.

7. The multi-layer structure according to any one of claims 1 to 3, wherein, The barrier layer (A) contains 50 to 400 ppm of boron compounds.

8. The multi-layer structure according to any one of claims 1 to 3, wherein, The ethylene-vinyl alcohol copolymer (a) has an ethylene unit content of more than 22 mol% and less than 28 mol%.

9. The multi-layer structure according to any one of claims 1 to 3, wherein, The thickness of the barrier layer (A) is less than 5 μm.

10. The multilayer structure according to any one of claims 1 to 3, wherein, The oxygen permeability measured using the method described in JIS K 7126-2:2006 at 20°C and 65% RH was 5 cc / (m²). 2 (ATM) and below.

11. The multilayer structure according to any one of claims 1 to 3, wherein, The water vapor permeation rate at 40°C and 90% RH, measured using the method described in JIS K 7129-2:2019, was 3 g / (m²). 2 (Heaven) and below.

12. Packaging material comprising a multilayer structure as described in any one of claims 1 to 3.

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