Multilayer structure and packaging material using the same

Abstract

To provide a multilayer structure having excellent barrier properties, mechanical properties and recyclability.SOLUTION: There is provided a multilayer structure obtained by laminating a layer (X) and a layer (Y), in which the layer (X) has a barrier layer (A) mainly composed of EVOH (a) having an ethylene unit content of 20 to 50 mol% and a saponification degree of 90 mol% or more, an adhesive layer (B) mainly composed of an adhesive resin (b), and a heat-sealing layer (C) mainly composed of an ethylene-α-olefin copolymer resin (c) having a density of 0.880 to 0.920 g / cm3, and does not have a layer mainly composed of a resin with a melting point of 200°C or higher and a metal layer with a thickness of 1 μm or more, and the layer (Y) contains polyethylene as a main component, and when the layer (Y) is heated by DSC from -50°C to 220°C at 10°C / min (first heating), cooled to -50°C, and then heated again to 220°C (second heating), a ratio (H1 / H2) of a total heat of fusion (H1) to a total heat of fusion (H2) at 0 to 150°C during a first temperature rise and a second temperature rise is 1.01 to 1.10.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a multilayer structure having excellent barrier properties, mechanical properties and recyclability, and to a packaging material, a recycled composition and a recycling method each using the same. [Background technology]

[0002] Packaging materials for long-term food storage are often required to have gas barrier properties, including oxygen barrier properties. By using packaging materials with high gas barrier properties, it is possible to suppress oxidative deterioration of food caused by oxygen intrusion and the proliferation of microorganisms. Metal foils such as aluminum and inorganic vapor deposition layers such as silicon oxide and aluminum oxide are widely used as layers that improve gas barrier properties. On the other hand, resin layers with gas barrier properties such as vinyl alcohol polymers and polyvinylidene chloride are also widely used. Vinyl alcohol polymers have the characteristic that they crystallize and become highly densified by hydrogen bonding between hydroxyl groups in the molecules, thereby exhibiting gas barrier properties. Among them, ethylene-vinyl alcohol copolymers (hereinafter sometimes abbreviated as "EVOH") are suitable for melt molding due to their excellent thermal stability, and with the development of coextrusion technology, multilayer structures with an EVOH layer as an intermediate layer are widely used as gas barrier packaging materials.

[0003] In recent years, environmental and waste problems have led to a growing global demand for post-consumer recycling (hereinafter sometimes abbreviated to simply "recycling"), which involves collecting and recycling packaging materials consumed in the market. In recycling, the process generally adopted is to cut the collected packaging materials, separate and wash them as necessary, and then melt and mix them using an extruder. In this regard, there is a demand for packaging materials to be composed of a single material as much as possible (mono-materialization), which allows for the production of recycled raw materials with high purity and high quality.

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

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

[0006] However, when used as a packaging material for a heavy content, there is a tendency for higher mechanical strength to be required, and the multilayer structure described in Patent Document 1 sometimes lacks mechanical strength. In addition, although mechanical strength can be improved by increasing the thickness of the multilayer structure, the amount of resin used in the packaging material increases, so there is a demand for efficiently improving mechanical strength while keeping the thickness as small as possible. In addition, for example, when a barrier film is used as a packaging material for food such as soup or liquid such as detergent, or as a packaging material for powder or other substances that solidify when absorbing moisture, it is necessary to suppress the permeation of moisture, etc., in order to maintain quality, but the multilayer structure described in Patent Document 1 sometimes lacks water vapor barrier properties.

[0007] The present invention has been made to solve the above-mentioned problems, and has an object to provide a multilayer structure having excellent barrier properties (oxygen barrier properties and water vapor barrier properties), mechanical properties and recyclability, as well as a packaging material, a recovered composition and a recovery method each using the same. [Means for solving the problem]

[0008] According to the present invention, the above object is [1] A multilayer structure in which a sealant layer (X) and a base layer (Y) are laminated, the sealant layer (X) comprising a barrier layer (A) (hereinafter may be simply referred to as "barrier layer (A)") containing, as a main component, an ethylene-vinyl alcohol copolymer (a) (hereinafter may be abbreviated as "EVOH (a)") having an ethylene unit content of 20 to 50 mol% and a saponification degree of 90 mol% or more, an adhesive layer (B) (hereinafter may be simply referred to as "adhesive layer (B)") containing, as a main component, an adhesive resin (b), and a polyimide resin (P) having a density of 0.880 to 0.920 g / cm 3 The thermal adhesive layer (C) (hereinafter may be simply referred to as "thermal adhesive layer (C)") contains, as a main component, an ethylene-α-olefin copolymer resin (c) (hereinafter may be abbreviated as "ethylene-α-olefin copolymer resin (c)"), and does not have a layer containing, as a main component, a resin having a melting point of 200°C or more and a metal layer having a thickness of 1 μm or more. The base layer (Y) contains polyethylene as a main component, and the base a multilayer structure in which, when the layer (Y) is heated from -50°C to 220°C at 10°C / min (first heating) in a differential scanning calorimeter (DSC), then cooled to -50°C at 10°C / min, and further heated to 220°C at 10°C / min (second heating), the ratio (H1 / H2) of the total heat of fusion (H1) at 0 to 150°C during the first heating to the total heat of fusion (H2) at 0 to 150°C during the second heating is 1.01 to 1.10; [2] The multilayer structure according to [1], wherein the base layer (Y) is a layer containing, as a main component, high-density polyethylene having a melting point of 128°C or higher as measured by a differential scanning calorimeter (DSC); [3] The multilayer structure of [1] or [2], in which the sealant layer (X) and the base layer (Y) are laminated by dry lamination; [4] The multilayer structure according to any one of [1] to [3], wherein the base layer (Y) is stretched at least uniaxially; [5] The multilayer structure of [4], wherein the base layer (Y) is uniaxially stretched in the machine direction (MD); [6] The multilayer structure of [4], in which the base layer (Y) is biaxially stretched; [7] The multilayer structure of any one of [1] to [6], wherein the sealant layer (X) is not stretched; [8] A multilayer structure according to any one of [1] to [7], wherein the barrier layer (A) contains a boron compound (g) in an amount of 50 to 400 ppm in terms of elemental boron; [9] The multilayer structure of any of [1] to [8], wherein the barrier layer (A) contains 0.01 to 7.00 ppm of at least one aldehyde (d) selected from the group consisting of 2,4-hexadienal (d1) and 2,4,6-octatrienal (d2);

[10] The multilayer structure of any one of [1] to [9], wherein the ethylene-α-olefin copolymer resin (c) has an MFR (190°C, under a load of 2.16 kg) of 0.5 to 5.0 g / 10 min, as measured in accordance with JIS K7210 (2014);

[11] The multilayer structure of any of [1] to

[10] , wherein the ethylene-α-olefin copolymer resin (c) is a linear low-density polyethylene copolymerized with ethylene and an α-olefin having 6 or more carbon atoms;

[12] The multilayer structure of any of [1] to

[11] , wherein the barrier layer (A) contains 10 to 200 ppm of at least one polyvalent metal ion (e) selected from the group consisting of magnesium ions, calcium ions, and zinc ions;

[13] The multilayer structure of any one of [1] to

[12] , wherein the barrier layer (A) contains 10 to 400 ppm of alkali metal ions (f);

[14] The multilayer structure of any of [1] to

[13] , wherein the ethylene-vinyl alcohol copolymer (a) contains EVOH (a1) having an ethylene unit content of 22 mol% or more and less than 34 mol% and a degree of saponification of 99 mol% or more, and EVOH (a2) having an ethylene unit content of 34 mol% or more and less than 50 mol% and a degree of saponification of 99 mol% or more;

[15] The multilayer structure of any one of [1] to

[14] , in which the barrier layer (A) and the base layer (Y) are laminated via an adhesive layer;

[16] A packaging material comprising any one of the multilayer structures of [1] to

[15] ;

[17] A recovered composition comprising a recovered multilayer structure of any one of [1] to

[15] ;

[18] A method for recovering a multilayer structure comprising crushing any one of the multilayer structures described in [1] to

[15] and then melt-molding the resulting multilayer structure; This is achieved by providing Effect of the Invention

[0009] The multilayer structure of the present invention and the packaging material using the same are excellent in barrier property, mechanical properties and recyclability. In addition, since the multilayer structure of the present invention and the packaging material using the same are excellent in recyclability, a recovered composition obtained by melt-kneading the multilayer structure and a recovery method thereof can also be provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0011] In this specification, "polyethylene" refers to a homopolymer of ethylene, a copolymer of 80 mol% or more ethylene and 20 mol% or less α-olefin monomer, and a copolymer of 90 mol% or more ethylene and less than 10 mol% of a non-olefin monomer whose functional group does not contain atoms other than carbon atoms, oxygen atoms, and hydrogen atoms. "Polyethylene-based resin" refers to polyethylene and acid-modified polyethylene. "Acid-modified polyethylene" refers to a polymer obtained by modifying polyethylene with an acid. The acid-modified polyethylene may be a polymer in which at least one of an acid group and an acid anhydride group is introduced into polyethylene.

[0012] The multilayer structure of the present invention is a multilayer structure in which a sealant layer (X) and a base layer (Y) are laminated together, and the sealant layer (X) comprises a barrier layer (A) containing, as a main component, EVOH (a) having an ethylene unit content of 20 to 50 mol% and a saponification degree of 90 mol% or more, an adhesive layer (B) containing, as a main component, an adhesive resin (b), and a cellulose acylate having a density of 0.880 to 0.920 g / cm.3 The thermal adhesive layer (C) has an ethylene-α-olefin copolymer resin (c) as a main component, and does not have a layer containing a resin having a melting point of 200°C or more as a main component and a metal layer with a thickness of 1 μm or more. The base layer (Y) contains polyethylene as a main component. When the base layer (Y) is heated from -50°C to 220°C at 10°C / min in a differential scanning calorimeter (DSC) (first heating), then cooled to -50°C at 10°C / min, and further heated to 220°C at 10°C / min (second heating), the ratio (H1 / H2) of the total heat of fusion (H1) at 0 to 150°C during the first heating to the total heat of fusion (H2) at 0 to 150°C during the second heating is 1.01 to 1.10. Here, "containing as a main component" means containing more than 50% by mass, preferably containing 70% by mass or more, more preferably containing 80% by mass or more, even more preferably containing 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more. By providing the barrier layer (A), the multilayer structure of the present invention tends to be able to improve gas barrier properties while maintaining recyclability. Furthermore, by providing the adhesive layer (B), mechanical strength and recyclability tend to be improved. Furthermore, when the main component of the heat-sealing layer (C) has a density of 0.880 to 0.920 g / cm 3By using the ethylene-α-olefin copolymer resin (c) having the above-mentioned formula (I), excellent mechanical strength tends to be realized. In addition, the multilayer structure of the present invention can exhibit good recyclability by not having a layer containing a resin having a melting point of 200° C. or more as a main component and a metal layer having a thickness of 1 μm or more. Furthermore, by setting the ratio of the heats of fusion (H1 / H2) of the base layer (Y) of the multilayer structure of the present invention to 1.01 to 1.10, the water vapor barrier property can be efficiently improved even if the thickness of the multilayer structure is thin (for example, 200 μm or less). The recyclability in this specification can be evaluated by evaluating the amount of lumps and coloring in a melt-molded product obtained by melt-kneading the crushed multilayer structure, and the melt viscosity stability during melt-kneading of the crushed multilayer structure, and specifically, can be evaluated by the method described in the Examples. The mechanical strength in this specification can be evaluated by evaluating the puncture breaking strength and elongation and the drop-breakage resistance, and specifically, can be evaluated by the method described in the Examples. In this specification, the term "barrier property" means oxygen barrier property and water vapor barrier property, and the term "gas barrier property" means oxygen barrier property.

[0013] <Barrier layer (A)> The multilayer structure of the present invention has a barrier layer (A) containing EVOH (a) as a main component. Since EVOH (a) has excellent gas barrier properties, a multilayer structure having a layer containing EVOH (a) as a main component is preferably used as a packaging material with excellent content preservation properties. In addition, since EVOH (a) can be easily melt-mixed with polyethylene-based resins, a packaging material with excellent recyclability can be provided.

[0014] EVOH (a) is usually obtained by saponifying an ethylene-vinyl ester copolymer obtained by polymerizing ethylene and a vinyl ester. A representative vinyl ester is vinyl acetate, but other fatty acid vinyl esters (vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate, etc.) can also be used.

[0015] The ethylene unit content of EVOH(a) is 20 to 50 mol%. When the ethylene unit content is 20 mol% or more, the melt moldability of EVOH(a) and the pulverized product of the multilayer structure containing EVOH(a) is improved. The ethylene unit content is preferably 23 mol% or more, more preferably 26 mol% or more, and may be 29 mol% or more. On the other hand, when the ethylene unit content is 50 mol% or less, the gas barrier property of the multilayer structure of the present invention is improved. The ethylene unit content is preferably 46 mol% or less, more preferably 42 mol% or less, and may be 38 mol% or less. In addition, the saponification degree of EVOH(a) is 90 mol% or more. The saponification degree means the ratio of the number of vinyl alcohol units to the total number of vinyl alcohol units and vinyl ester units in EVOH(a). When the saponification degree is 90 mol% or more, the gas barrier property of the multilayer structure of the present invention is improved. The saponification degree is preferably 95 mol% or more, more preferably 99 mol% or more, and even more preferably 99.9 mol% or more. The degree of saponification may be 100 mol % or less. The ethylene unit content and the degree of saponification of EVOH (a) are 1 It can be determined by H-NMR measurement.

[0016] EVOH (a) may be a mixture of two or more EVOHs having different ethylene unit contents. In this case, the difference in ethylene unit content between the EVOHs having the most different ethylene unit contents is preferably 30 mol% or less, more preferably 25 mol% or less, even more preferably 20 mol% or less, and may be 3 mol% or more. Similarly, EVOH (a) may be a mixture of two or more EVOHs having different saponification degrees. In this case, the difference in saponification degree between the EVOHs having the most different ethylene unit contents is preferably 7 mol% or less, more preferably 5 mol% or less, and may be 0.5 mol% or more. When it is desired to achieve both thermoformability and gas barrier property at a higher level, it is preferable to mix EVOH (a1) having an ethylene unit content of 22 mol% or more and less than 34 mol% and a degree of saponification of 99 mol% or more with EVOH (a2) having an ethylene unit content of 34 mol% or more and less than 50 mol% and a degree of saponification of 99 mol% or more in a blending mass ratio (a1 / a2) of 60 / 40 to 90 / 10 and use the mixture as EVOH (a).

[0017] EVOH (a) may contain other monomer units other than ethylene, vinyl ester and vinyl alcohol, so long as the effects of the present invention are not impaired. In particular, by introducing a modified group containing a primary hydroxyl group having a specific structure, the gas barrier properties and moldability of EVOH (a) may be compatible at a high level. The content of other monomer units is preferably 10 mol% or less, more preferably 5 mol% or less, even more preferably 1 mol% or less, and particularly preferably substantially not contained. Examples of such other monomers include alkenes such as propylene, butylene, pentene, and hexene; 3-acyloxy-1-propene, 3-acyloxy-1-butene, 4-acyloxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4-acyloxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-methyl -1-butene, 4-acyloxy-2-methyl-1-butene, 4-acyloxy-3-methyl-1-butene, 3,4-diacyloxy-2-methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, 4,5-diacyloxy-1-pentene, 4-acyloxy-1-hexene, 5-acyloxy-1-hexene, 6-acyloxy-1-hexene, 5,6-diacyloxy ester group-containing alkenes or saponification products thereof, such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, or other unsaturated acids or their anhydrides, salts, or mono- or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids or salts thereof, such as vinyl sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid; vinyl silane compounds such as vinyl trimethoxy silane, vinyl triethoxy silane, vinyl tri(β-methoxy-ethoxy) silane, and γ-methacryloxypropyl methoxy silane; alkyl vinyl ethers, vinyl ketones, N-vinyl pyrrolidone, vinyl chloride, and vinylidene chloride.

[0018] EVOH (a) may be modified as necessary by urethanization, acetalization, cyanoethylation, oxyalkylenation, etc. Oxyalkylenation can be carried out using an epoxy compound, such as epoxyethane (ethylene oxide), epoxypropane, 1,2-epoxybutane, 2,3-epoxybutane, 3-methyl-1,2-epoxybutane, 1,2-epoxypentane, 3-methyl-1,2-epoxypentane, 1,2-epoxyhexane, 2,3-epoxyhexane, 3,4-epoxyhexane, 3-methyl-1,2-epoxyhexane, 3-methyl-1,2-epoxyheptane, 4-methyl-1,2-epoxyheptane, 1, Examples of such epoxy alkanols include 2-epoxyoctane, 2,3-epoxyoctane, 1,2-epoxynonane, 2,3-epoxynonane, 1,2-epoxydecane, 1,2-epoxydodecane, epoxyethylbenzene, 1-phenyl-1,2-propane, 3-phenyl-1,2-epoxypropane, various alkyl glycidyl ethers, various alkylene glycol monoglycidyl ethers, various alkenyl glycidyl ethers, various epoxy alkanols such as glycidol, various epoxy cycloalkanes, and various epoxy cycloalkenes. Among these, 1,2-epoxybutane, 2,3-epoxybutane, epoxypropane, epoxyethane, or glycidol is preferred, and epoxypropane or glycidol is more preferred.

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

[0020] The barrier layer (A) preferably contains 0.01 ppm or more and 7.00 ppm or less of an aliphatic aldehyde (d), which is at least one selected from the group consisting of 2,4-hexadienal (d1) and 2,4,6-octatrienal (d2). The lower limit of the content of the aliphatic aldehyde (d) in the barrier layer (A) is preferably 0.01 ppm, more preferably 0.02 ppm, even more preferably 0.04 ppm, and particularly preferably 0.10 ppm. The upper limit of the content of the aliphatic aldehyde (d) in the barrier layer (A) is preferably 7.00 ppm, more preferably 4.00 ppm, even more preferably 3.00 ppm, even more preferably 2.50 ppm, and particularly preferably 0.50 ppm. When the content of the aliphatic aldehyde (d) is within this range, the amount of lumps is reduced when the melt-molded product of the EVOH (a) and the pulverized product of the multilayer structure is molded into a film.

[0021] The barrier layer (A) preferably contains 10 to 200 ppm of at least one polyvalent metal ion (e) selected from the group consisting of magnesium ion, calcium ion, and zinc ion. By containing a certain amount of polyvalent metal ion (e), thickening, gelation, and resin adhesion to the screw are suppressed when pulverized EVOH (a) and the multilayer structure containing EVOH (a) are melt-molded. The barrier layer (A) more preferably contains magnesium ion or calcium ion as the polyvalent metal ion (e), and further preferably contains magnesium ion. In addition, it is preferable to contain the polyvalent metal ion (e) as a carboxylate. The carboxylic acid in this case may be either an aliphatic carboxylic acid or an aromatic carboxylic acid, but an aliphatic carboxylic acid is preferable. Examples of the aliphatic carboxylic acid include formic acid, acetic acid, propionic acid, butyric acid, lauric acid, stearic acid, myristic acid, behenic acid, and montanic acid, and higher fatty acids having 10 to 25 carbon atoms are more preferable. From the viewpoint of suppressing coloration during melt molding, it is also preferable that the polyvalent metal ion (e) is contained as a salt of a polyvalent carboxylic acid, which will be described later.

[0022] The content of the polyvalent metal ion (e) in the barrier layer (A) is preferably 10 to 200 ppm in terms of metal atom. When the content is 10 ppm or more, the viscosity stability of the EVOH (a) and the ground product of the multilayer structure containing EVOH (a) is improved, and the gelation of the resin and the adhesion of the resin to the extruder screw are suppressed. The lower limit of the content of the polyvalent metal ion (e) is more preferably 20 ppm. On the other hand, when the content of the polyvalent metal ion (e) is 200 ppm or less, the excessive decomposition of the ground product of the multilayer structure containing EVOH (a) is suppressed, and the color of the recovered composition is improved. The upper limit of the content of the polyvalent metal ion (e) is more preferably 160 ppm, and even more preferably 120 ppm.

[0023] The barrier layer (A) may contain other components other than EVOH (a) and polyvalent metal ions (e) as long as the effects of the present invention are not impaired. Examples of other components include alkali metal ions (f), polyvalent metal ions other than polyvalent metal ions (e), carboxylic acids, phosphoric acid compounds, boron compounds, oxidation promoters, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorants, UV absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, bulking agents, pigments, dyes, processing aids, flame retardants, and antifogging agents. In particular, from the viewpoint of improving the interlayer adhesion and melt moldability of a laminate containing EVOH (a), it is preferable to contain alkali metal ions. In addition, from the viewpoint of suppressing coloration during melt molding of EVOH (a) and recycled resin containing EVOH (a), it is preferable to contain carboxylic acids and / or phosphoric acid compounds. Furthermore, by containing a boron compound, it is possible to control the melt viscosity of EVOH (a) and the recycled resin containing EVOH (a), and it may be possible to improve the mechanical strength of the multilayer structure of the present invention. The content of other components in the barrier layer (A) is usually 5 mass% or less, preferably 3 mass% or less, and more preferably 1 mass% or less.

[0024] The barrier layer (A) preferably contains 10 to 400 ppm of alkali metal ions (f). The lower limit of the content of alkali metal ions (f) is more preferably 100 ppm, and further preferably 150 ppm. On the other hand, the upper limit of the content of alkali metal ions (f) is more preferably 350 ppm, and may be 250 ppm. When the content of alkali metal ions (f) is 10 ppm or more, the interlayer adhesion in the multilayer structure of the present invention including the layer obtained by molding EVOH (a) is good. On the other hand, when the content of alkali metal ions (f) is 400 ppm or less, coloration tends to be suppressed. In addition, by controlling the content ratio of alkali metal ions (f) and carboxylic acid described later, melt moldability and coloration resistance can be further improved.

[0025] Examples of the alkali metal ion (f) include lithium, sodium, potassium, rubidium, and cesium ions, but sodium or potassium ions are preferred from the viewpoint of industrial availability. In particular, by using sodium ions, it may be possible to achieve high levels of both hue and interlayer adhesion with the adhesive layer (B). These may be used alone or in combination of two or more.

[0026] Examples of alkali metal salts that provide the alkali metal ion (f) include aliphatic carboxylates, aromatic carboxylates, carbonates, hydrochlorides, nitrates, sulfates, phosphates, and metal complexes of alkali metals such as sodium and potassium. Among these, at least one selected from the group consisting of sodium acetate, potassium acetate, sodium phosphate, and potassium phosphate is more preferred from the viewpoint of easy availability.

[0027] The barrier layer (A) preferably further contains a boron compound (g). The lower limit of the content of the boron compound (g) is preferably 50 ppm, more preferably 100 ppm, in terms of boron element. On the other hand, the upper limit of the content of the boron compound is preferably 400 ppm, more preferably 200 ppm, in terms of boron element. By containing the boron compound (g) in this range, the mechanical properties of the multilayer structure are improved. Furthermore, the thermal stability during melt molding of the EVOH (a) and the pulverized product of the multilayer structure may be improved, and the occurrence of gels and bumps may be suppressed. In addition, the drawdown resistance and the neck-in resistance during film formation may be improved. It is presumed that these effects are due to the occurrence of a chelate interaction between the EVOH (a) and the boron compound.

[0028] Examples of the boron compound (g) include boric acid, boric acid esters, borate salts, and boron hydrides.Specific examples include boric acid such as orthoboric acid (H3BO3), metaboric acid, and tetraboric acid; boric acid esters such as trimethyl borate and triethyl borate; alkali metal salts or alkaline earth metal salts of the boric acid, and borate salts such as borax.Of these, orthoboric acid is preferred.

[0029] The barrier layer (A) preferably contains a carboxylic acid. The lower limit of the content of the carboxylic acid is preferably 50 ppm, more preferably 100 ppm. On the other hand, the upper limit of the content of the carboxylic acid is preferably 400 ppm, more preferably 350 ppm. When the content of the carboxylic acid is within the above range, the deterioration of the hue tends to be suppressed. The content of the carboxylic acid is obtained by extracting 10 g of the resin composition constituting the barrier layer (A) with 50 ml of pure water at 95 ° C for 8 hours, and then titrating the obtained extract. Note that the content of the carboxylic acid in the resin composition does not take into account the carboxylic acid present as a salt in the extract. In addition, when the resin composition contains acidic compounds other than the carboxylic acid, the content of the carboxylic acid in the resin composition can be obtained by subtracting the contribution of these acidic compounds from the measured value by titration.

[0030] The pKa of the carboxylic acid is preferably 3.5 to 5.5. When the pKa of the carboxylic acid is within the above range, the pH buffering ability in the weak acid range is increased, the melt moldability is further improved, and the coloring effect due to acidic or basic substances can be further reduced.

[0031] The carboxylic acid may be a monobasic carboxylic acid. These may be used alone or in combination of two or more. The monobasic carboxylic acid is a compound having one carboxyl group in the molecule. Examples of monobasic carboxylic acids having a pKa in the range of 3.5 to 5.5 include, but are not limited to, formic acid (pKa=3.77), acetic acid (pKa=4.76), propionic acid (pKa=4.85), and acrylic acid (pKa=4.25). These carboxylic acids may further have a substituent such as a hydroxyl group, an amino group, or a halogen atom. Among these, acetic acid is preferred because of its high safety and ease of availability and handling.

[0032] The carboxylic acid may be a polycarboxylic acid. When the carboxylic acid is a polycarboxylic acid, the coloring resistance of EVOH (a) at high temperatures and the coloring resistance of a melt-molded product of a crushed material of a multilayer structure containing EVOH (a) may be further improved. The polycarboxylic acid compound preferably has three or more carboxyl groups. In this case, the coloring resistance may be more effectively improved. The polycarboxylic acid is a compound having two or more carboxyl groups in the molecule. In this case, it is preferable that the pKa of at least one carboxyl group is in the range of 3.5 to 5.5, and examples of the polycarboxylic acid 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, pKa 2=5.41), pimelic acid (pKa1=4.71), phthalic acid (pKa2=5.41), isophthalic acid (pKa2=4.46), terephthalic acid (pKa1=3.51, pKa2=4.82), citric acid (pKa2=4.75), tartaric acid (pKa2=4.40), glutamic acid (pKa2=4.07), aspartic acid (pKa=3.90), etc.

[0033] The barrier layer (A) may further contain a phosphate compound. The lower limit of the content of the phosphate compound is preferably 5 ppm in terms of phosphate radicals. On the other hand, the upper limit of the content of the phosphate compound is preferably 100 ppm in terms of phosphate radicals. By containing the phosphate compound in this range, coloration of the melt-molded product of the EVOH (a) and the pulverized product of the multilayer structure may be suppressed, and thermal stability may be improved.

[0034] As the phosphoric acid compound, various acids such as phosphoric acid and phosphorous acid and their salts can be used. The phosphate may be any of primary phosphate, secondary phosphate, and tertiary phosphate. The cationic species of the phosphate is not particularly limited, but the cationic species is preferably an alkali metal or an alkaline earth metal. Among them, the phosphoric acid compound is preferably sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate.

[0035] The barrier layer (A) may further contain, as an antioxidant, for example, a hindered phenol-based compound having an ester bond or an amide bond. The content of the hindered phenol-based compound is preferably 1000 to 10000 ppm. When the content is 1000 ppm or more, coloring, thickening, and gelation of the resin can be suppressed when the pulverized product of the multilayer structure is melt-molded. The content of the hindered phenol-based compound is more preferably 2000 ppm or more. On the other hand, when the content of the hindered phenol-based compound is 10000 ppm or less, coloring and bleeding out derived from the hindered phenol-based compound can be suppressed. The content of the hindered phenol-based compound is more preferably 8000 ppm or less.

[0036] The hindered phenol compound has at least one hindered phenol group. The hindered phenol group refers to a bulky substituent bonded to at least one carbon atom adjacent to the carbon atom bonded to the hydroxyl group of phenol. The bulky substituent is preferably an alkyl group having 1 to 10 carbon atoms, more preferably a t-butyl group.

[0037] The hindered phenol compound is preferably in a solid state at around room temperature. From the viewpoint of suppressing bleed-out of the compound, the melting point or softening temperature of the hindered phenol compound is preferably 50° C. or higher, more preferably 60° C. or higher, and even more preferably 70° C. or higher. From the viewpoint of suppressing bleed-out, the molecular weight of the hindered phenol compound is preferably 200 or higher, more preferably 400 or higher, and even more preferably 600 or higher. Meanwhile, the molecular weight is usually 2000 or lower. From the viewpoint of facilitating mixing with EVOH (a), the melting point or softening temperature of the hindered phenol compound is preferably 200° C. or lower, more preferably 190° C. or lower, and even more preferably 180° C. or lower.

[0038] The hindered phenol compound has an ester bond or an amide bond. Examples of the hindered phenol compound having an ester bond include esters of aliphatic carboxylic acids having a hindered phenol group and aliphatic alcohols, and examples of the hindered phenol compound having an amide bond include amides of aliphatic carboxylic acids having a hindered phenol group and aliphatic amines. Among these, it is preferable that the hindered phenol compound has an amide bond from the viewpoint of facilitating mixing with EVOH (a).

[0039] Specific structures of the hindered phenol compounds include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] commercially available from BASF as Irganox 1010, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)stearylpropionate commercially available as Irganox 1076, 2,2'-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] commercially available as Irganox 1035, and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate commercially available as Irganox 1135. octadecyl-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate, ethylene bis(oxyethylene) bis(3-tert-butyl-4-hydroxy-5-methylbenzenepropanoate) available commercially as Irganox 245, 1,6-hexanediol bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] available commercially as Irganox 259, and N,N'-hexamethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide] available commercially as Irganox 1098. Among these, N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide], commercially available as Irganox 1098, and pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], commercially available as Irganox 1010, are preferred, with Irganox 1098 being more preferred.

[0040] The barrier layer (A) may further contain a thermoplastic resin other than EVOH (a). Examples of the thermoplastic resin other than EVOH (a) include various polyolefins (polyethylene, polypropylene, poly1-butene, poly4-methyl-1-pentene, ethylene-propylene copolymers, copolymers of ethylene and α-olefins having 4 or more carbon atoms, copolymers of polyolefins and maleic anhydride, ethylene-vinyl ester copolymers, ethylene-acrylic acid ester copolymers, or modified polyolefins obtained by graft-modifying these with unsaturated carboxylic acids or their derivatives, etc.), various polyamides (nylon 6, nylon 6 / 6, nylon 6 / 66 copolymers, nylon 11, nylon 12, polymetaxylylene adipamide, etc.), various polyesters (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate, and modified polyvinyl alcohol resins, etc. The content of the thermoplastic resin in the barrier layer (A) is less than 50% by mass, preferably 30% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and may be 1% by mass or less.

[0041] The proportion of EVOH (a) in the resin constituting the barrier layer (A) is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, or the resin constituting the barrier layer (A) may be composed only of EVOH (a). The proportion of EVOH (a) in the barrier layer (A) is more than 50% by mass, preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, or the barrier layer (A) may be composed substantially only of EVOH (a).

[0042] When the barrier layer (A) contains a component other than EVOH (a), the method for producing the resin composition constituting the barrier layer (A) is not particularly limited, but the barrier layer (A) can be produced by melt-kneading EVOH (a) and other additives (polyvalent metal ions (e), etc.) as necessary. The other additives may be blended in a solid state such as powder or as a melt, or may be blended as a solute contained in a solution or a dispersoid contained in a dispersion. As the solution and dispersion, an aqueous solution and an aqueous dispersion are preferable, respectively. For the melt-kneading, a known mixing or kneading device such as a kneader-ruder, an extruder, a mixing roll, or a Banbury mixer can be used. The temperature range during melt-kneading can be appropriately adjusted depending on the melting point of the EVOH (a) used, and a temperature of 150 to 300°C is usually adopted.

[0043] In another embodiment, a master batch containing other additives at a high concentration relative to EVOH(a) can be produced by melt kneading, and the master batch can be dry blended with EVOH(a) that does not substantially contain other additives to produce a multilayer structure. In yet another embodiment, EVOH(a) and other additives can be dry blended to produce a multilayer structure. Dry blending refers to mechanical mixing in the form of powder or pellets. Mixing may be performed using a mixing device such as a tumbler, ribbon mixer, or Henschel mixer, or may be performed by manually stirring, shaking, or the like in a closed container. The mixing temperature may be from room temperature to less than the melting point of EVOH(a), and mixing can be performed under an air atmosphere or a nitrogen atmosphere. Alternatively, the multilayer structure may be produced by adding some components to EVOH(a) in advance and then melt kneading other components that are required as described above. An example of a method of adding some components to EVOH(a) in advance is a method of immersing EVOH(a) as pellets or powder in a solution in which the additive components are dissolved. The solution is preferably an aqueous solution.

[0044] <Adhesive layer (B)> The multilayer structure of the present invention has an adhesive layer (B) containing an adhesive resin (b) as a main component. The adhesive layer (B) has a function of bonding the barrier layer (A) and the thermal adhesive layer (C). Therefore, the adhesive layer (B) is preferably provided between the barrier layer (A) and the thermal adhesive layer (C), and is preferably directly laminated to the barrier layer (A) and the thermal adhesive layer (C).

[0045] The adhesive resin (b) may be, for example, a modified olefin polymer containing a carboxyl group obtained by chemically bonding an unsaturated carboxylic acid or its anhydride to an olefin polymer by addition reaction or graft reaction. Examples of the unsaturated carboxylic acid or its anhydride 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 preferably used. Specifically, one or a mixture of two or more selected from maleic anhydride graft-modified polyethylene, maleic anhydride graft-modified polypropylene, maleic anhydride graft-modified ethylene-propylene copolymer, maleic anhydride graft-modified ethylene-ethyl acrylate copolymer, and maleic anhydride graft-modified ethylene-vinyl acetate copolymer are preferably used, among which maleic anhydride graft-modified polyethylene is more preferable. The acid value of such adhesive resin (b) is preferably 0.5 to 5 mgKOH / g, more preferably 1 to 4 mgKOH / g. The acid value of the adhesive resin (b) can be measured in accordance with JIS K 0070:1992 using xylene as a solvent.

[0046] The adhesive resin (b) may be a mixture of an unmodified resin (bx) and an acid-modified resin (by). In this case, from the viewpoint of further increasing the mechanical strength, the unmodified resin (bx) preferably contains an ethylene-α-olefin copolymer resin (c) described later, and more preferably is an ethylene-α-olefin copolymer resin (c). Here, when the unmodified resin (bx) contains an ethylene-α-olefin copolymer resin (c), the ethylene-α-olefin copolymer resin (c) contained in the adhesive layer (B) and the ethylene-α-olefin copolymer resin (c) contained in the heat-sealing layer (C) may be the same or different, but are preferably the same. In addition, the ratio (bx / by) of the unmodified resin (bx) and 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, as the acid-modified resin (by), a resin having a relatively high degree of acid modification can be preferably used, and its acid value is preferably 5 to 30 mgKOH / g, more preferably 8 to 20 mgKOH / g. In this way, the mechanical strength of the multilayer structure obtained may be further improved while maintaining the necessary interlayer adhesive strength. When the adhesive resin (b) of the present invention is a mixture of the unmodified resin (bx) and the acid-modified resin (by), the unmodified resin (bx) and the acid-modified resin (by) may be melt-kneaded in advance, or the unmodified resin (bx) and the acid-modified resin (by) may be dry-blended. For the melt-kneading, a known mixing or kneading device such as a kneader-ruder, an extruder, a mixing roll, or a Banbury mixer may be used. The temperature range during melt-kneading can be appropriately adjusted depending on the melting points of the unmodified resin (bx) and the acid-modified resin (by) used, and is usually 150 to 300°C. Dry blending refers to mechanically mixing in the form of powder or pellets. The mixing may be performed using a mixing device such as a tumbler, a ribbon mixer, or a Henschel mixer, or may be performed in a sealed container by manually stirring, shaking, etc. The mixing temperature may be from room temperature to below the melting points of the unmodified resin (bx) and the acid-modified resin (by), and the mixing may be performed in an air atmosphere or a nitrogen atmosphere.

[0047] The adhesive layer (B) may contain other components other than the adhesive resin (b) as long as the effect of the present invention is not impaired. Examples of other 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, UV absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, bulking agents, pigments, dyes, processing aids, flame retardants, and antifogging agents. The content of other components in the adhesive layer (B) is usually 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less. In addition, the adhesive layer (B) may further contain a thermoplastic resin other than the adhesive resin (b). As the thermoplastic resin, the above-mentioned resins exemplified as the thermoplastic resin that may be contained in the barrier layer (A) can be used. The content of the thermoplastic resin in the adhesive layer (B) is less than 50% by mass, preferably less than 30% by mass, more preferably less than 10% by mass, further preferably 5% by mass or less, and may be 1% by mass or less.

[0048] The proportion of the adhesive resin (b) in the resin constituting the adhesive layer (B) is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, and the resin constituting the adhesive layer (B) may be composed only of the adhesive resin (b). The proportion of the 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, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, and the adhesive layer (B) may be substantially composed only of the adhesive resin (b).

[0049] The multilayer structure of the present invention has a density of 0.880 to 0.920 g / cm 3 The heat-sealing layer (C) contains as its main component an ethylene-α-olefin copolymer resin (c), which is a thermosealing layer having a function as a sealing layer when forming a packaging material, and also has a function of increasing various mechanical strengths such as puncture strength and elongation and tensile strength and elongation, and can particularly increase puncture breaking elongation.

[0050] The density of the ethylene-α-olefin copolymer resin (c) is 0.880 to 0.920 g / cm 3 When the density is within the above range, the resulting multilayer structure is flexible and has excellent handleability, and various mechanical strengths such as puncture strength and tensile strength are improved. The lower limit of the density is 0.885 g / cm 3 is preferred, and 0.890 g / cm 3 More preferably, 0.895 g / cm 3 The upper limit of the density is 0.917 g / cm 3 is preferred.

[0051] The MFR (190°C, under a load of 2.16 kg) of the ethylene-α-olefin copolymer resin (c) is preferably 0.5 to 5.0 g / 10 min. When the MFR is within the above range, the ethylene-α-olefin copolymer resin (c) has excellent melt processability, and the obtained multilayer structure has improved mechanical strengths such as puncture strength and 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 measured at 190°C under a load of 2.16 kg in accordance with JIS K 7210 (2014).

[0052] The ethylene-α-olefin copolymer resin (c) is a resin obtained by polymerizing ethylene with an α-olefin having 3 or more carbon atoms. Examples of the α-olefin having 3 or more carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, and 4-methyl-1-pentene. The ethylene-α-olefin copolymer resin (c) is preferably a linear low-density polyethylene obtained by polymerizing ethylene with an α-olefin having 6 or more carbon atoms, and more preferably a linear low-density polyethylene obtained by polymerizing ethylene with an α-olefin having 8 or more carbon atoms. When the carbon number of the α-olefin copolymerized with ethylene is relatively large, various mechanical strengths such as pin puncture strength and tensile strength may be particularly improved.

[0053] In addition, it is preferable to use a metallocene catalyst as the polymerization catalyst. The linear low-density polyethylene polymerized using a metallocene catalyst is produced by copolymerizing ethylene and an α-olefin in the presence of a catalyst formed from a compound of a transition metal of Group 4 of the periodic table, preferably zirconium, having at least one ligand having a cyclopentadienyl skeleton, an organoaluminum oxy compound, and various components added as necessary. The linear low-density polyethylene polymerized using a metallocene catalyst has excellent melt moldability, and the multilayer structure obtained has an excellent balance of heat resistance, flexibility, and mechanical strength.

[0054] Linear low-density polyethylene obtained by polymerizing ethylene and an α-olefin having 6 or more carbon atoms using a metallocene catalyst is commercially available as industrially produced polyethylene, such as "Evolue (trademark)" (Prime Polymer Co., Ltd.), "Sumikasen (trademark)" (Sumitomo Chemical Co., Ltd.), "Yumerit (trademark)" (Ube Maruzen Polyethylene Co., Ltd.), and "Elite (trademark)" (Dow Chemical Co., Ltd.).

[0055] The heat-sealing layer (C) may contain other components other than the ethylene-α-olefin copolymer resin (c) as long as the effects of the present invention are not impaired. Examples of other components include alkali metal ions, polyvalent metal ions, carboxylic acids, phosphoric acid compounds, boron compounds, oxidation promoters, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorants, UV absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, bulking agents, pigments, dyes, processing aids, flame retardants, and antifogging agents. The content of other components in the heat-sealing layer (C) is usually 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less. The heat-sealing layer (C) may further contain a thermoplastic resin other than the ethylene-α-olefin copolymer resin (c). As the thermoplastic resin, the above-mentioned resins exemplified as the thermoplastic resin that may be contained in the barrier layer (A) can be used. The content of the thermoplastic resin in the heat-sealing layer (C) is less than 50% by mass, preferably less than 30% by mass, more preferably less than 10% by mass, further preferably 5% by mass or less, and may be 1% by mass or less.

[0056] The proportion of the ethylene-α-olefin copolymer resin (c) in the resin constituting the heat-sealing layer (C) is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, and the resin constituting the heat-sealing layer (C) may be composed only of the ethylene-α-olefin copolymer resin (c). The proportion of the ethylene-α-olefin copolymer resin (c) in the heat-sealing layer (C) is more than 50% by mass, preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, and the heat-sealing layer (C) may be substantially composed only of the ethylene-α-olefin copolymer resin (c).

[0057] The method for producing the resin composition constituting the heat-sealing layer (C) is not particularly limited, but it can be produced by melt-kneading the ethylene-α-olefin copolymer resin (c) and, if necessary, other additives. For the melt-kneading, a known mixing or kneading device such as a kneader-ruder, an extruder, a mixing roll, or a Banbury mixer can be used. The temperature range during melt-kneading can be appropriately adjusted depending on the melting point of the ethylene-α-olefin copolymer resin (c) used, and is usually 150 to 300°C.

[0058] In another embodiment, a master batch containing other additives at a high concentration as necessary for the ethylene-α-olefin copolymer resin (c) is produced by melt kneading, and the master batch is dry-blended with an ethylene-α-olefin copolymer resin (c) that does not substantially contain other additives, and can be used to produce a multilayer structure. In yet another embodiment, the ethylene-α-olefin copolymer resin (c) and other additives can be dry-blended to produce the heat-sealable layer (C). Dry blending refers to mechanical mixing in the form of powder or pellets. Mixing may be performed using a mixing device such as a tumbler, ribbon mixer, or Henschel mixer, or may be performed by manually stirring, shaking, or the like in a sealed container. The mixing temperature may be from room temperature to less than the melting point of the ethylene-α-olefin copolymer resin (c), and mixing can be performed under an air atmosphere or a nitrogen atmosphere.

[0059] The sealant layer (X) of the present invention has a barrier layer (A), an adhesive layer (B) and a heat-sealing layer (C). It is preferable that at least one pair of the barrier layer (A) and the adhesive layer (B) are laminated adjacent to each other. This makes it possible to obtain a multilayer structure having high gas barrier properties and recyclability, as well as excellent mechanical strength and stability.

[0060] The lamination method for producing the sealant layer (X) may be a conventional co-extrusion method in which each resin is extruded from a separate die or a common die and laminated. As the die, either a circular die or a T-die may be used. The molding temperature during melt molding may be appropriately adjusted based on the melting point and melt viscosity of the resin used, and is often selected from the range of 150 to 300°C. From the viewpoint of maintaining the heat seal strength when the multilayer structure of the present invention is molded for use as a soft packaging material, it is preferable that the sealant layer (X) is a non-oriented layer.

[0061] The total thickness of the sealant layer (X) of the present invention is preferably 15 to 300 μm, more preferably 25 to 250 μm, further preferably 35 to 200 μm, and particularly preferably 45 to 150 μm. When the total thickness is within the above range, the sealant layer (X) of the present invention is lightweight and flexible, and is therefore preferably used for flexible packaging. In addition, the amount of resin used in the sealant layer (X) is small, and the environmental load is suppressed.

[0062] The lower limit of the thickness of the barrier layer (A) is preferably 1 μm, more preferably 2 μm. When the lower limit of the thickness of the barrier layer (A) is within the above range, the multilayer film exhibits sufficient gas barrier properties. The upper limit of the thickness of the barrier layer (A) is preferably 30 μm, more preferably 25 μm, further preferably 20 μm, and particularly preferably 15 μm. When the upper limit of the thickness of the barrier layer (A) is within the above range, the recyclability is improved when the sealant layer (X) or the multilayer structure is recovered and reused.

[0063] The thickness of the adhesive layer (B) is preferably 1 to 20 μm, more preferably 2 to 10 μm. When the thickness of the adhesive layer (B) is within the above range, the interlayer adhesion between the barrier layer (A) and the thermal adhesive layer (C) is increased, and the recyclability when the sealant layer (X) or the multilayer structure is recovered and reused is improved.

[0064] The thickness of the heat-sealing layer (C) is preferably 15 to 300 μm, more preferably 30 to 200 μm, and even more preferably 40 to 150 μm. When the thickness of the heat-sealing layer (C) is within the above range, the recyclability, mechanical strength, and water vapor barrier property are improved.

[0065] In the sealant layer (X) of the present invention, the ratio of the thickness of the barrier layer (A) to the total thickness of all layers is preferably 0.10 or less. When this ratio is within the above range, the recyclability and mechanical strength are improved. The upper limit of the ratio of the thickness of the barrier layer (A) to the total thickness of all layers is more preferably 0.08, even more preferably 0.05, and particularly preferably 0.04. The lower limit of the ratio of the thickness of the barrier layer (A) to the total thickness of all layers is not particularly limited, but is preferably 0.005 in order to exhibit sufficient gas barrier properties. On the other hand, in the multilayer structure of the present invention, the ratio of the thickness of the heat-sealing layer (C) to the total thickness of all layers is preferably 0.60 or more, more preferably 0.70 or more, even more preferably 0.80 or more, and may be 0.99 or less. When this ratio is within the above range, the recyclability, mechanical strength, and water vapor barrier properties are improved.

[0066] The layer structure of the sealant layer (X) of the present invention is not particularly limited as long as it has a barrier layer (A), an adhesive layer (B) and a heat-sealing layer (C). If the heat-sealing layer (C) is expressed as (C), the adhesive resin layer (B) as (B), and the barrier layer (A) as (A), and " / " indicates direct lamination, examples of the layer structure include (C) / (B) / (A) / (B) / (C) and (C) / (B) / (A). It is preferable that the heat-sealing layer (C) of the sealant layer (X) is exposed. Therefore, when laminating the substrate layer (Y) and the sealant layer (X) described later, it is preferable to laminate them so that the heat-sealing layer (C) of the sealant layer (X) is exposed. In addition to the above layer structure, another layer may be further included, and the other layer may be present as the outermost layer of the sealant layer (X) or between each layer. When a plurality of barrier layers (A), adhesive layers (B) and thermal adhesive layers (C) are used, different types of resins may be used for each of them.

[0067] <Base material layer (Y)> The multilayer structure of the present invention has a base layer (Y) containing polyethylene as a main component, and when the base layer (Y) is heated from -50°C to 220°C at 10°C / min (first heating) in a differential scanning calorimeter (DSC), then cooled to -50°C at 10°C / min, and further heated to 220°C at 10°C / min (second heating), the ratio (H1 / H2) of the total heat of fusion (H1) at 0 to 150°C during the first heating to the total heat of fusion (H2) at 0 to 150°C during the second heating is 1.01 to 1.10. By setting the heat of fusion ratio (H1 / H2) within the above range, it is possible to achieve both high levels of mechanical strength and water vapor barrier property while keeping the total thickness low. The heat of fusion ratio (H1 / H2) means that the crystallinity of the base layer (Y) is slightly higher than that of a resin obtained by simply melt-molding a similar resin. From the viewpoint of further improving the mechanical strength, the upper limit of the ratio of heats of fusion (H1 / H2) is preferably 1.08, more preferably 1.05. On the other hand, from the viewpoint of improving the water vapor barrier property of the multilayer structure, the lower limit of the ratio of heats of fusion (H1 / H2) is preferably 1.02, more preferably 1.03. Here, the total heat of fusion at 0 to 150°C means the total heat of fusion of the resin having a melting point at 0 to 150°C in the base layer (Y), and in one embodiment of the present invention, for example, means the total heat of fusion of polyethylene. The ratio of heats of fusion (H1 / H2) can be controlled by the set temperatures of the extruder and die when producing the base layer (Y), the cooling rate after extrusion from the die, the presence or absence of a stretching step, the stretching temperature, the stretching ratio, and the heat treatment temperature.

[0068] The substrate layer (Y) of the present invention is preferably composed of at least one resin layer containing polyethylene as a main component. Examples of polyethylene include linear low-density polyethylene, low-density polyethylene, medium-density polyethylene, and high-density polyethylene. Among them, high-density polyethylene (HDPE) is preferred from the viewpoint of water vapor barrier properties.

[0069] The proportion of polyethylene in the resin constituting the base layer (Y) is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, may be 97% by mass or more or 99% by mass or more, and the resin constituting the base layer (Y) may be composed of polyethylene only. The content of polyethylene in the base layer (Y) must be more than 50% by mass, is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, may be 97% by mass or more, 99% by mass or more, and the base layer (Y) may be composed substantially of only a thermoplastic resin.

[0070] The lower limit of the melting point of the thermoplastic resin in the base layer (Y) measured by a differential scanning calorimeter (DSC) is preferably 128° C. When the melting point is within the above range, the processability is improved. On the other hand, from the viewpoint of recyclability, the upper limit of the melting point of the thermoplastic resin in the base layer (Y) measured by a differential scanning calorimeter (DSC) is preferably 140° C.

[0071] The substrate layer (Y) of the present invention is preferably stretched at least uniaxially, more preferably uniaxially in the machine direction (MD) in some cases, and preferably stretched biaxially in some cases. By stretching the substrate layer (Y) at least uniaxially, the mechanical strength and water vapor barrier property of the multilayer structure are improved. In particular, from the viewpoint of improving the mechanical strength, a biaxially stretched layer is preferable.

[0072] The method for forming the base layer (Y) is not particularly limited, but it is generally formed by melt extrusion using an extruder. As the die, either a circular die or a T-die can be used. The method for stretching in the uniaxial or biaxial direction is also not particularly limited, and the film can be produced by stretching in the flow direction and / or the direction perpendicular to the flow direction, i.e., the width direction, using a conventionally known stretching method such as roll-type uniaxial stretching, tubular-type simultaneous biaxial stretching, tenter-type sequential biaxial stretching, and tenter-type simultaneous biaxial stretching. The stretching ratio is preferably 8 to 60 times in area from the viewpoint of the uniformity of the thickness of the obtained layer and mechanical strength. The area ratio is more preferably 55 times or less, and even more preferably 50 times or less. The area ratio is more preferably 9 times or more. If the area ratio is less than 8 times, stretching unevenness may remain, and if it exceeds 60 times, the layer may easily break during stretching.

[0073] From the viewpoint of industrial productivity, the thickness of the base layer (Y) is preferably 10 to 100 μm, and from the viewpoint of achieving a balance between the mechanical strength, water vapor barrier property, and production costs of the multilayer structure, the thickness of the base layer (Y) is more preferably 15 to 75 μm, and further preferably 30 to 55 μm.

[0074] The layer structure of the base layer (Y) of the present invention is not particularly limited as long as it contains polyethylene as a main component, and may be a single layer or multiple layers, but is preferably a single layer from the viewpoint of production costs.

[0075] <Multilayer structure> The multilayer structure of the present invention is a multilayer structure in which a sealant layer (X) and a base layer (Y) are laminated, and does not have a layer containing a resin having a melting point of 200°C or more as a main component and a metal layer having a thickness of 1 μm or more. That is, the melting points of EVOH (a), adhesive resin (b) and ethylene-α-olefin copolymer (c) are all less than 200°C. By not having a layer containing a resin having a melting point of 200°C or more as a main component and a metal layer having a thickness of 1 μm or more, it is possible to suppress uneven mixing with other components when melt-molding the pulverized product of the multilayer structure. That is, recyclability is improved. Here, the metal layer is a layer having continuous and discontinuous surfaces made of metal, such as aluminum foil. It is also preferable that at least one pair of the barrier layer (A) and adhesive layer (B) are laminated adjacent to each other. In this way, a multilayer structure having high gas barrier properties and recyclability, and excellent mechanical strength and stability can be obtained.

[0076] In addition, the upper limit of the total thickness of the multilayer structure of the present invention is preferably 300 μm. When the total thickness is in the above range, the multilayer structure of the present invention is lightweight and flexible, and is therefore preferably used for soft packaging applications. In addition, the amount of resin used in the multilayer structure is small, and the environmental load is suppressed. 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. In addition, from the viewpoint of maintaining the mechanical strength and water vapor barrier property of the multilayer structure of the present invention, the lower limit of the total thickness is preferably 30 μm. The lower limit of the total thickness of the multilayer structure of the present invention is more preferably 50 μm, more preferably 100 μm, and particularly preferably 150 μm.

[0077] The thickness of each layer in the multilayer structure of the present invention may be appropriately adjusted depending on the application, but from the viewpoints of suppressing coloration during melt molding of the pulverized material, improving thermal stability during melt molding, and suppressing the occurrence of bumps, the ratio of the total thickness of the layers containing a polyethylene resin as a main component to the total thickness of the multilayer structure is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.90 or more, and particularly preferably 0.95 or more. The layers containing a polyethylene resin as a main component include the base layer (Y), the adhesive layer (B) containing a polyethylene adhesive resin as a main component, and the heat-sealing layer (C).

[0078] The method of laminating the base layer (Y) on the sealant layer (X) is not particularly limited, and examples thereof include extrusion lamination, coextrusion lamination, dry lamination, etc., but dry lamination is preferable from the viewpoint of handling. When laminating the base layer (Y) on the multilayer structure, an adhesive layer may be provided. The adhesive layer may be an adhesive layer (B), or may be formed by applying a known adhesive and drying it. As the known adhesive, for example, a two-liquid reactive polyurethane adhesive in which a polyisocyanate component and a polyol component are mixed and reacted is preferable. The thickness of the adhesive layer is not particularly limited, but is preferably 1 to 5 μm, more preferably 2 to 4 μm. When laminating the base layer (Y) on the sealant layer (X), it is preferable that the barrier layer (A) and base layer (Y) constituting the sealant layer (X) are laminated via an adhesive layer. That is, it is preferable to have a layer structure of barrier layer (A) / adhesive layer / base layer (Y).

[0079] The multilayer structure of the present invention may have layers other than those described above, provided that the effects of the present invention are not impaired. Examples of the other layers include a resin layer containing a thermoplastic resin other than EVOH (a), adhesive resin (b), and ethylene-α-olefin copolymer resin (c) as a main component. The thermoplastic resin is not particularly limited, and examples thereof include olefins such as polypropylene, propylene-α-olefin copolymer (α-olefins having 4 to 20 carbon atoms), polybutene, and polypentene, or copolymers thereof, polyamides such as nylon 6 and nylon 6 / 6, polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polystyrene, polyvinyl chloride, polyvinylidene chloride, acrylic resins, polycarbonate, chlorinated polyethylene, and chlorinated polypropylene. When the multilayer structure of the present invention includes a resin layer containing the thermoplastic resin as a main component, it is preferable that the thermoplastic resin is polypropylene, but from the viewpoint of recyclability, it is preferable that the multilayer structure does not include a resin layer containing the thermoplastic resin as a main component. Another example of the other layer includes a recovery layer. In particular, it is preferable to reuse a recovered composition containing a recovered material of the multilayer structure of the present invention described later as a part or the whole of the recovered layer. Another example of the other layer is a printed layer. The printed layer may be included at any position of the multilayer structure of the present invention. The printed layer may be, for example, a film obtained by applying a solution containing a pigment or dye and, if necessary, a binder resin, and drying it. Examples of the coating method of the printed layer include gravure printing and various coating methods using a wire bar, a spin coater, a die coater, etc. The thickness of the printed layer is not particularly limited, but is preferably 0.5 to 10 μm, more preferably 1 to 4 μm.

[0080] It is preferable to recover and reuse the end portions and defective products generated during the production of the multilayer structure of the present invention. It is also a suitable embodiment to recover and reuse the multilayer structures distributed on the market. A method for recovering the multilayer structure of the present invention by crushing the multilayer structure of the present invention and then melt-molding it, and a recovered composition containing the recovered multilayer structure of the present invention are also suitable embodiments of the present invention. Here, the recovered multilayer structure of the present invention also includes recovered packaging materials containing the multilayer structure of the present invention.

[0081] In the recovery of the multilayer structure of the present invention, the recovered material of the multilayer structure of the present invention is first pulverized. The pulverized recovered material may be melt-molded as it is to obtain a recovered composition, or may be melt-molded together with other components as necessary to obtain a recovered composition. A preferred component to be added to the recovered material is a polyolefin resin, more preferably a polyethylene resin. The pulverized recovered material may be directly used to manufacture a molded product such as a multilayer structure, or the pulverized recovered material may be melt-pelletized to obtain pellets of the recovered composition, and the pellets may be used to manufacture a molded product. The melt molding method of the recovered composition may include extrusion molding, inflation molding, blow molding, melt spinning, injection molding, etc. The molding temperature during melt molding may be appropriately adjusted based on the melting point and melt viscosity of the resin used, and is often selected from the range of 150 to 300 ° C. The recovered composition may contain unused resin, but the content of the recovered material in the recovered composition is preferably 10 mass % or more, more preferably 20 mass % or more, and may be 30 mass % or more. The content of EVOH (a) in the recovered composition is preferably 20% by mass or less, more preferably 10% by mass or less, and may be 5% by mass or less.

[0082] Since the multilayer structure of the present invention has excellent appearance characteristics, gas barrier properties, mechanical properties, and recyclability, it can be suitably used as various packaging materials such as food packaging, pharmaceutical packaging, industrial chemical packaging, and agricultural chemical packaging, but it can also be used in a wider range of applications and is not limited to these applications.

[0083] A package obtained by filling the packaging material with contents is a preferred embodiment of the packaging material. Contents that can be filled include, but are not limited to, beverages such as wine and fruit juice, foods such as fruits, nuts, vegetables, meat products, baby foods, coffee, jams, mayonnaise, ketchup, edible oils, dressings, sauces, foods boiled in soy sauce, dairy products, and other contents that are prone to deterioration in the presence of oxygen, such as medicines, cosmetics, and gasoline. EXAMPLES

[0084] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples in any way.

[0085] <Materials used> ·Base material layer (Y) Y-1: Biaxially oriented HDPE "Ethy-Lyte (trademark) 40HD200" (melting point 130°C) manufactured by Jindal Poly Films Ltd. Y-2: MD uniaxially oriented HDPE "Hibron (trademark) P25" (melting point 133°C) manufactured by Tokyo Ink Co., Ltd. Y-3: MD-direction uniaxially oriented HDPE "Hibron (trademark) FMQK25" (melting point 1) manufactured by Tokyo Ink Co., Ltd. Y-4: Biaxially oriented HDPE "Ethy-Lyte (trademark) 25HD200" (melting point 130°C) manufactured by Jindal Poly Films Ltd. Y-4: Biaxially oriented HDPE "Ethy-Lyte (trademark) 25HD200" (melting point 130°C) manufactured by Jindal Poly Films Ltd. Y-5: TD-oriented uniaxially stretched HDPE "Kararyan (trademark) Y18" (melting point 132°C) manufactured by Denka Co., Ltd. Y-6: Biaxially oriented LDPE film with a thickness of 40 μm (melting point 125°C) Y-7: High-density polyethylene "Novatec (trademark) HD ​​HY540" manufactured by Japan Polyethylene Co., Ltd. (MFR (190°C, 2.16 kg load) 1.0 g / 10 min, density 0.960 g / cm 3 ) was used as the raw material to produce a 40μm thick non-oriented HDPE film by T-die single layer film formation under the following conditions. Extruder: Single-screw extruder manufactured by Toyo Seiki Co., Ltd. Screw diameter: 20mmφ (L / D=20, compression ratio=3.5, full flight type) Extrusion temperature: feeding section / compression section / metering section / die = 180 / 220 / 220 / 220℃ Take-off roll temperature: 50℃ Take-off speed: 1.5m / min Y-8: High-density polyethylene "Novatec (trademark) HD ​​HY540" manufactured by Japan Polyethylene Co., Ltd. (MFR (190°C, 2.16 kg load) 1.0 g / 10 min, density 0.960 g / cm 3 ) was used as the raw material and produced by T-die single layer film formation under the following conditions, and then heat-treated at 120°C for 5 minutes to produce a 40μm thick non-oriented HDPE film. Extruder: Single-screw extruder manufactured by Toyo Seiki Co., Ltd. Screw diameter: 20mmφ (L / D=20, compression ratio=3.5, full flight type) Extrusion temperature: feeding section / compression section / metering section / die = 180 / 220 / 220 / 220℃ Take-off roll temperature: 50℃ Take-off speed: 1.5m / min EVOH(a) a-1: EVOH, ethylene unit content 32 mol%, saponification degree 99.9 mol%, MFR after drying (190°C, 2.16 kg load) 1.6 g / 10 min a-2: EVOH, ethylene unit content 27 mol%, saponification degree 99.9 mol%, MFR after drying (190°C, 2.16 kg load) 1.5 g / 10 min a-3: EVOH, ethylene unit content 44 mol%, saponification degree 99.9 mol%, MFR after drying (190°C, 2.16 kg load) 1.7 g / 10 min ·Adhesive resin (b) b-1: Maleic anhydride modified polyethylene "Admer (trademark) NF518" manufactured by Mitsui Chemicals Inc. (MFR (190°C, 2.16 kg load) 3.1 g / 10 min, density 0.91 g / cm 3 , acid value 1.10mgKOH / g) Ethylene-α-olefin copolymer resin (c) c-1: Linear low-density polyethylene "Evolue (trademark) SP1510" manufactured by Prime Polymer Co., Ltd. (ethylene and 1-hexene polymerized with a metallocene catalyst, MFR (190°C, 2.16 kg load) 1.0 g / 10 min, density 0.915 g / cm 3 ) c-2: Linear low-density polyethylene "Evolue (trademark) SP0510" manufactured by Prime Polymer Co., Ltd. (ethylene and 1-hexene polymerized with a metallocene catalyst, MFR (190°C, 2.16 kg load) 1.2 g / 10 min, density 0.903 g / cm 3 ) c-3: Linear low-density polyethylene "Evolue (trademark) SP1540" manufactured by Prime Polymer Co., Ltd. (ethylene and 1-hexene polymerized with a metallocene catalyst, MFR (190°C, 2.16 kg load) 3.8 g / 10 min, density 0.915 g / cm 3 ) Polyvalent metal ions (e) Mg-St: Magnesium stearate Ca-St: Calcium stearate Zn-St: Zinc stearate MgOAc: Magnesium acetate Alkali metal ions (f) AcONa: Sodium acetate AcOK: Potassium acetate

[0086] <Evaluation method> (1) Heat of fusion For the base material layer (Y) used in the examples and comparative examples, a differential scanning calorimeter DSC ("Q2000" manufactured by TA Instruments) was used to raise the temperature from -50°C to 220°C at 10°C / min (first heating), then lower the temperature to -50°C at 10°C / min, and further raise the temperature to 220°C at 10°C / min (second heating), and the total heat of fusion (H1) from 0 to 150°C during the first heating and the ratio (H1 / H2) of the total heat of fusion (H1) from 0 to 150°C during the first heating to the total heat of fusion (H2) from 0 to 150°C during the second heating were calculated.

[0087] (2) Oxygen permeability The oxygen transmission rate was measured using the multilayer structures obtained in the examples and comparative examples, with one side being the oxygen supply side and the other side being the carrier gas side. Specifically, using an oxygen transmission rate measuring device ("MOCON OX-TRAN2 / 21" manufactured by Modern Controls), the oxygen transmission rate (unit: cc / (m)) was measured under the conditions of temperature 20°C, humidity 65% ​​RH on the oxygen supply side, humidity 65% ​​RH on the carrier gas side, oxygen pressure 1 atm, and carrier gas pressure 1 atm in accordance with JIS K 7126-2 (isobaric method; 2006). 2 The carrier gas used was nitrogen gas containing 2% by volume of hydrogen gas.

[0088] (3) Water vapor transmission rate Using the multilayer structures obtained in the examples and comparative examples, the water vapor transmission rate was measured with one side being the water vapor supply side and the other side being the carrier gas side. Specifically, using a water vapor transmission rate measuring device ("MOCON PERMATRAN W3 / 33" manufactured by Modern Controls), the water vapor transmission rate (unit: g / (m)) was measured under 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 in accordance with JIS K 7129-2 (infrared sensor method; 2019). 2 The water vapor transmission rate was 4.0 g / (m 2 ·days) or more, the water vapor barrier property was judged to be insufficient.

[0089] (4) Seal strength The multilayer structures obtained in the examples and comparative examples were cut into two pieces with a width of 15 mm, then stacked with the sealant layer (X) side on the inside and heat sealed. The film was conditioned for 24 hours under conditions of 23°C and 50% RH, and then subjected to T-peel using an autograph (tensile speed 250 mm / min) manufactured by Shimadzu Corporation under the same conditions to measure the seal strength. If the seal strength was less than 20 N / 15 mm, it was determined that the seal strength was insufficient.

[0090] (5) Puncture breaking strength and elongation The multilayer structures obtained in the examples and comparative examples were conditioned for 24 hours under conditions of 23°C and 50% RH, and then the breaking elongation and breaking strength were measured under the same conditions when a needle with a tip diameter of 1 mm was pierced at a speed of 50 mm / min. The measurement was performed 10 times at different locations, and the average value was used as the measurement result. If the puncture breaking elongation was less than 3.0 mm, it was determined that the mechanical properties were insufficient. Also, if the puncture breaking strength was less than 9.0 N, it was determined that the mechanical properties were insufficient.

[0091] (6) Drop-break resistance The multilayer structures obtained in the examples and comparative examples were cut into two pieces of A4 size, the sealant layers (X) were stacked together, and three sides were heat-sealed at a width of 5 mm. Next, 1 L of water was filled from the opening, and the remaining sides were heat-sealed to create a water-filled bag. This water-filled bag was allowed to freely fall upright from a height of 1 m under conditions of 20°C and 70% RH. After 20 drops, those that did not show water leakage or peeling between layers were deemed to have passed, and those that showed leakage or peeling between layers were deemed to have failed. The same test was performed five times, and the results were judged according to the following criteria. D is an unacceptable criterion. Judgment criteria A: Passed all five times B: Passed 4 times out of 5, failed 1 time (minor peeling between layers) C: 4 out of 5 passes, 1 fail (large leaks or delamination) D: 2 or more failures

[0092] (7) Lumps and coloring of melt-molded products of crushed multilayer structures The multilayer structures obtained in the examples and comparative examples were crushed into pieces of 4 mm square or less. The crushed pieces were mixed with a low-density polyethylene resin "Novatec LD LJ400" (MFR (190°C, 2.16 kg load) 1.5 g / 10 min, density 0.921 g / cm) manufactured by Japan Polyethylene Corporation. 3) was blended in a mass ratio (ground material / polyethylene resin) of 40 / 60, and a monolayer film with a thickness of 50 μm was obtained by performing monolayer film formation under the extrusion conditions shown below. The thickness of the monolayer film was adjusted by appropriately changing the screw rotation speed and the take-up roll speed. As a control, a monolayer film with a thickness of 50 μm was similarly obtained using only polyethylene resin. Extruder: Toyo Seiki Co., Ltd. single screw extruder Screw diameter: 20mmφ (L / D=20, compression ratio=3.5, full flight type) Extrusion temperature: feeding section / compression section / metering section / die = 180 / 230 / 230 / 230℃ Take-off roll temperature: 80℃ The degree of lumps and coloring of the obtained monolayer film was evaluated on the following 5-level scale of A to E, where E is an unacceptable standard. Criteria for determining the quality of goods A: Compared to the control, the amount of pimples was almost the same. B: The amount of small particles was slightly more than in the control. C: Compared to the control, the amount of small bumps was greater. D: Compared to the control, there was a greater amount of large bumps. E: The amount of large particles was significantly greater than in the control. Coloring criteria A: The degree of color change was small compared to the control. B: Slight discoloration was observed compared to the control. C: Moderate coloring was observed compared to the control. D: Significant coloring was observed compared to the control. E: Compared to the target, significant coloring and unevenness were observed.

[0093] (8) Viscosity stability of melt-molded multilayer structure pulverized material The multilayer structures obtained in the examples and comparative examples were pulverized to a size of 4 mm square or less. 60 g of this pulverized material was kneaded using a Labo Plastomill (biaxial counter-rotating) under nitrogen atmosphere at 230°C and 100 rpm, and the torque change was measured. The torque values ​​(TI and TF, respectively) were calculated 10 minutes and 90 minutes after the start of kneading, and the ratio of these values ​​(TF / TI) was used to evaluate the results on a 5-level scale of A to E below. E is an unacceptable standard. Judgment criteria A: 80 / 100 or more and less than 120 / 100 B: 70 / 100 or more but less than 80 / 100, or 120 / 100 or more but less than 130 / 100 C: 60 / 100 or more but less than 70 / 100, or 130 / 100 or more but less than 140 / 100 D: 50 / 100 or more but less than 60 / 100, or 140 / 100 or more but less than 150 / 100 E: Less than 50 / 100 or more than 150 / 100

[0094] (Example) Example 1 The EVOH (a-1) hydrous pellets (moisture content: 55% by mass) were immersed in an aqueous solution containing sodium acetate, phosphoric acid, and boric acid at 25°C for 6 hours while stirring, then deliquored, dried at 80°C for 4 hours in a hot air dryer ("DN6101" manufactured by Yamato Scientific Co., Ltd.), and then dried at 120°C for 40 hours to obtain dried EVOH pellets (moisture content: 0.25%). The concentrations of sodium acetate, phosphoric acid, and boric acid were adjusted so that the contents in the obtained dried EVOH pellets were 200 ppm sodium acetate in terms of sodium ions, 30 ppm phosphate ions in terms of phosphate radicals, and 150 ppm boric acid in terms of boron element. The obtained dried EVOH pellets and magnesium stearate were melt-kneaded so that the content of magnesium ions in the obtained resin composition was 50 ppm, to obtain resin composition pellets for the barrier layer (A). The melt kneading was carried out using a twin-screw extruder manufactured by Toyo Seiki Seisakusho (D (mm) = 25, L / D = 30, screws: same direction fully intermeshing type) so that the resin temperature was 220°C.

[0095] The resin composition pellets obtained above were used as the material for the barrier layer (A), maleic anhydride modified polyethylene (b-1) was used as the material for the adhesive layer (B), and ethylene-α-olefin copolymer resin (c-1) was used as the material for the thermoplastic resin layer (C), and a multilayer film (sealant layer (X-1)) having a layer thickness and layer structure of (C) / (B) / (A) / (B) / (C)=51μm / 6μm / 6μm / 6μm / 51μm was produced using a 5-layer coextrusion cast film production equipment with a width of 300mm. The film production conditions at this time are shown below. Extrusion temperature of barrier layer (A): feeding section / compression section / metering section / die = 170 / 220 / 220 / 220℃ Extrusion temperature of adhesive layer (B): feeding section / compression section / metering section / die = 170 / 220 / 220 / 220°C Extrusion temperature of thermoplastic resin layer (C): feeding section / compression section / metering section / die = 170 / 220 / 220 / 220°C Cooling roll temperature: 40℃ Take-off speed: 1.5m / min

[0096] A two-liquid reactive polyurethane adhesive (24 parts by mass of "Takelac A-520" and 4 parts by mass of "Takenate A-50" manufactured by Mitsui Chemicals, Inc.) was mixed with 37 parts by mass of ethyl acetate to prepare an adhesive solution. Next, the adhesive solution was applied to the substrate layer (Y-1) by a bar coater so that the thickness after drying was 2 μm, dried at 100 ° C. for 5 minutes, and laminated with the multilayer film (sealant layer (X-1)) obtained above to prepare a multilayer structure having a layer thickness and layer structure of (Y-1) / adhesive / (C) / (B) / (A) / (B) / (C) = 40 μm / 2 μm / 51 μm / 6 μm / 6 μm / 6 μm / 51 μm. The heat of fusion of the substrate layer (Y-1) was measured according to the method described in the above evaluation method 1. The results are shown in Table 1.

[0097] The obtained multilayer structure was evaluated for oxygen transmission rate, water vapor transmission rate, seal strength, puncture breaking strength / elongation, drop bag breakage resistance, bumps and coloring of the melt-molded product of the pulverized multilayer structure, and melt viscosity stability of the pulverized multilayer structure according to the methods described in the above evaluation methods (2) to (8). The results are shown in Table 3. The stretching state shown in Table 1 is expressed as BO for biaxial stretching, MDO for uniaxial stretching in MD, TDO for uniaxial stretching in TD, and Cast for non-stretching.

[0098] Examples 2 to 8, 10 to 20, 23, 24, 26, Comparative Examples 2, 3, 5) A multilayer structure was produced in the same manner as in Example 1, except that the type of substrate layer (Y), the type of EVOH (a), the type and content of polyvalent metal ion (e), the type and content of alkali metal ion (f), the content of boron compound (g), and the type of thermal adhesive layer (C) were changed as shown in Table 1 or Table 2, and various measurements and evaluations were performed. The results are shown in Tables 1 to 4.

[0099] Example 9 A multilayer structure was produced in the same manner as in Example 1, except that 20 parts by mass of the dry EVOH pellets having an ethylene unit content of 44 mol% obtained in Example 8, 80 parts by mass of the dry EVOH pellets having an ethylene unit content of 32 mol% obtained in Example 1, and magnesium stearate were melt-kneaded so that the magnesium ion content in the resulting resin composition was 50 ppm to produce resin composition pellets for the barrier layer (A). Various measurements and evaluations were performed. The results are shown in Tables 1 and 3.

[0100] Example 21 EVOH (a-1) was used as the material for the barrier layer (A), maleic anhydride modified polyethylene (b-1) manufactured by Mitsui Chemicals, Inc. was used as the material for the adhesive layer (B), and ethylene-α-olefin copolymer resin (c-1) was used as the material for the thermoplastic resin layer (C). A multilayer film having a layer thickness and layer structure of (C) / (B) / (A) / (B) / (C)=204μm / 24μm / 24μm / 24μm / 204μm was produced using a 5-layer co-extrusion cast film production equipment with a width of 300mm. The obtained multilayer film was subjected to simultaneous biaxial stretching at a stretching temperature of 80°C and a stretching ratio of 2 x 2 using a stretching device (SDR-506WK) manufactured by Eto Corporation, and the obtained stretched multilayer film ((C) / (B) / (A) / (B) / (C) = 51 μm / 6 μm / 6 μm / 6 μm / 51 μm) was used as the sealant layer (X-2).

[0101] A multilayer structure was produced in the same manner as in Example 1, except that the sealant layer (X-2) was used instead of the sealant layer (X-1), and various measurements and evaluations were carried out. The results are shown in Tables 2 and 4.

[0102] Example 22 A multilayer film (sealant layer (X-3)) having a layer thickness and layer structure of (C) / (B) / (A)=108 μm / 6 μm / 6 μm was produced using a 300 mm wide 5-layer co-extrusion cast film production equipment, and a multilayer structure ((Y-1) / adhesive / (A) / (B) / (C)=40 μm / 2 μm / 6 μm / 6 μm / 108 μm) was produced in the same manner as in Example 1, except that the multilayer structure was produced, and various measurements and evaluations were carried out. The results are shown in Tables 2 and 4. A 3-layer multilayer film was produced without using some of the extruders of the 5-layer co-extrusion cast film production equipment.

[0103] Example 25 A multilayer structure was produced in the same manner as in Example 1, except that the multilayer structure produced in the same manner as in Example 1 was subjected to a heat treatment at a temperature of 110° C. for 5 minutes, and various measurements and evaluations were carried out. The results are shown in Tables 2 and 4.

[0104] Comparative Example 1 Except for using the sealant layer (X-1) as it is as a multilayer structure without laminating the base layer (Y-1), various measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 2 and 4.

[0105] Comparative Example 4 Except for using the sealant layer (X-1) as it was as a multilayer structure, various measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 2 and 4.

[0106] [Table 1]

[0107] [Table 2]

[0108] [Table 3]

[0109] [Table 4]

[0110] Example 27 In a 60L stirring tank equipped with a jacket, a stirrer and a reflux condenser, 2 kg of crude dried EVOH obtained by a known method, 0.8 kg of water and 2.2 kg of MeOH were charged and stirred at 60°C for 5 hours to completely dissolve. 2,4-hexadienal and 2,4,6-octatrienal were added to the obtained solution. This solution was extruded through a 4 mm diameter gold plate into a mixture of water / MeOH = 90 / 10 cooled to -5°C to precipitate in the form of strands, and the strands were cut into pellets with a strand cutter to obtain hydrous pellets of EVOH. The moisture content of the obtained hydrous pellets of EVOH was measured with a Mettler halogen moisture meter "HR73" and found to be 52% by mass.

[0111] The obtained EVOH hydrous pellets were placed in a 1 g / L aqueous acetic acid solution (bath ratio 20) and washed with stirring for 2 hours. The pellets were deliquinated and then placed in a 1 g / L aqueous acetic acid solution (bath ratio 20) and washed with stirring for 2 hours. After deliquification, the aqueous acetic acid solution was renewed and the same operation was carried out. The pellets were washed with an aqueous acetic acid solution, deliquinated, placed in ion-exchanged water (bath ratio 20), washed with stirring for 2 hours, and then deliquinated. This operation was repeated three times, and the electrical conductivity of the washing solution was 3 μS / cm or less (measured with "CM-30ET" by Toa Denpa Kogyo Co., Ltd.), and hydrous pellets of EVOH (a-4) (ethylene unit content 32 mol%, saponification degree 99.9 mol%, MFR (190°C, 2.16 kg load) when dried) from which the catalyst residue from the saponification reaction had been removed were obtained.

[0112] The obtained EVOH (a-4) hydrous pellets were immersed in an aqueous solution containing sodium acetate, phosphoric acid and boric acid at 25 ° C. for 6 hours while stirring, then deliquored, dried at 80 ° C. for 4 hours in a hot air dryer (Yamato Scientific Co., Ltd. "DN6101"), and then dried at 120 ° C. for 40 hours to obtain dried EVOH pellets (water content 0.25%). The concentrations of sodium acetate, phosphoric acid and boric acid were adjusted so that the contents in the obtained dried EVOH pellets were 200 ppm sodium acetate in terms of sodium ions, 30 ppm phosphate ions in terms of phosphate radicals, 150 ppm boric acid in terms of boron elements, 0.20 ppm 2,4-hexadienal (d1), and 0.06 ppm 2,4,6-octatrienal (d2). The obtained dried EVOH pellets and magnesium stearate were melt-kneaded so that the magnesium ion content in the obtained resin composition was 50 ppm, to obtain resin composition pellets for the barrier layer (A). The melt-kneading was performed using a twin-screw extruder (D (mm) = 25, L / D = 30, screws: same direction fully intermeshing type) manufactured by Toyo Seiki Seisakusho, Ltd., so that the resin temperature was 220°C.

[0113] A multilayer structure was produced and evaluated in the same manner as in Example 1, except that the obtained resin composition pellets were used as the material for the barrier layer (A). The results are shown in Table 5. The evaluation result for the lumps in the melt-molded product of the pulverized multilayer film was B, the same as in Example 1, but the amount of lumps was less than that in Example 1.

[0114] Examples 28 and 29 Dry EVOH pellets and multilayer structures were produced and evaluated in the same manner as in Example 27, except that the content of aldehyde (d) was changed as shown in Table 5. The results are shown in Table 5.

[0115] [Table 5]

Claims

1. A multilayer structure in which a sealant layer (X) and a substrate layer (Y) are laminated, The sealant layer (X) comprises a barrier layer (A) containing, as a main component, an ethylene-vinyl alcohol copolymer (a) having an ethylene unit content of 20 to 50 mol% and a saponification degree of 90 mol% or more, an adhesive layer (B) containing, as a main component, an adhesive resin (b), and a film having a density of 0.880 to 0.920 g / cm ３ a heat-sealable layer (C) containing, as a main component, an ethylene-α-olefin copolymer resin (c) represented by the formula: It does not have a layer containing as a main component a resin having a melting point of 200°C or higher and a metal layer having a thickness of 1 μm or more, The base layer (Y) contains polyethylene as a main component, A multilayer structure in which, when the substrate layer (Y) is heated in a differential scanning calorimeter (DSC) from -50°C to 220°C at 10°C / min (first heating), then cooled to -50°C at 10°C / min, and further heated to 220°C at 10°C / min (second heating), the ratio (H1 / H2) of the total heat of fusion (H1) from 0 to 150°C during the first heating to the total heat of fusion (H2) from 0 to 150°C during the second heating is 1.01 to 1.

10.

2. 2. The multilayer structure according to claim 1, wherein the substrate layer (Y) is a layer containing, as a main component, high-density polyethylene having a melting point of 128°C or higher as measured by differential scanning calorimetry (DSC).

3. 2. The multilayer structure according to claim 1, wherein the sealant layer (X) and the substrate layer (Y) are laminated by dry lamination.

4. 2. The multilayer structure according to claim 1, wherein the substrate layer (Y) is stretched at least uniaxially.

5. 5. The multilayer structure according to claim 4, wherein the substrate layer (Y) is uniaxially stretched in the machine direction (MD).

6. The multilayer structure according to claim 4, wherein the substrate layer (Y) is biaxially stretched.

7. 2. The multilayer structure of claim 1, wherein the sealant layer (X) is unoriented.

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

9. 2. The multilayer structure according to claim 1, wherein the barrier layer (A) contains 0.01 to 7.00 ppm of an aldehyde (d) which is at least one selected from the group consisting of 2,4-hexadienal (d1) and 2,4,6-octatrienal (d2).

10. The multilayer structure according to claim 1, wherein the ethylene-α-olefin copolymer resin (c) has an MFR (190°C, under a load of 2.16 kg) measured in accordance with JIS K7210 (2014) of 0.5 to 5.0 g / 10 min.

11. 2. The multilayer structure according to claim 1, wherein the ethylene-α-olefin copolymer resin (c) is a linear low-density polyethylene obtained by copolymerizing ethylene with an α-olefin having 6 or more carbon atoms.

12. 2. The multilayer structure according to claim 1, wherein the barrier layer (A) contains 10 to 200 ppm of at least one polyvalent metal ion (e) selected from the group consisting of magnesium ions, calcium ions, and zinc ions.

13. 2. The multilayer structure according to claim 1, wherein the barrier layer (A) contains 10 to 400 ppm of alkali metal ions (f).

14. 2. The multilayer structure according to claim 1, wherein the ethylene-vinyl alcohol copolymer (a) comprises: EVOH (a1) having an ethylene unit content of 22 mol% or more and less than 34 mol% and a degree of saponification of 99 mol% or more; and EVOH (a2) having an ethylene unit content of 34 mol% or more and less than 50 mol% and a degree of saponification of 99 mol% or more.

15. The multilayer structure according to claim 1, wherein the barrier layer (A) and the substrate layer (Y) are laminated via an adhesive layer.

16. A packaging material comprising the multilayer structure of any one of claims 1 to 15.

17. A reclaimed composition comprising a reclaimed multilayer structure according to any one of claims 1 to 15.

18. A method for recovering a multilayer structure, comprising pulverizing the multilayer structure according to any one of claims 1 to 15 and then melt-molding the pulverized multilayer structure.