Multilayer structure, method for separating and recycling thereof

Abstract

Provided is a multilayer structure, etc., which is excellent in interlayer adhesion under high humidity and separation of a barrier layer in water, and even in the case where the barrier layer is exposed to water in a separation and recovery process, the viscosity stability of the resin constituting the barrier layer after separation and recovery is excellent. The multilayer structure of the present invention is a multilayer structure comprising a barrier layer (A), a water-soluble layer (B), and an adhesive layer (C), the adhesive layer (C) being laminated on one or both faces of the barrier layer (A) via the water-soluble layer (B), the barrier layer (A) having a polyamide or an ethylene-vinyl alcohol copolymer (a1) as a main component, and the water-soluble layer (B) containing 100 ppm or more and 2000 ppm or less of an alkali metal ion (b1).

Description

Technical Field

[0001] This invention relates to multilayer structures, methods for separating them, and methods for reusing them. Background Technology

[0002] Gas barrier resin films containing ethylene-vinyl alcohol copolymers (hereinafter sometimes referred to as EVOH) have long been used as transparent packaging materials with high oxygen barrier properties. Furthermore, EVOH is also used in applications such as laminated packaging materials, taking advantage of its thermoforming properties in addition to its high gas barrier properties. As laminated packaging materials, known examples include multilayer structures containing layers comprising resin compositions, wherein the resin compositions contain EVOH, components containing at least one of nitric acid and nitrate ions, metal ions, and carboxylic acid or carboxylate ions only in specific amounts (Patent Document 1).

[0003] In addition, for the purpose of improving the strength and secondary processing of laminated films, laminated packaging materials containing polyamides are sometimes used as gas barrier layers. As laminated packaging materials, multilayer films, for example, having a polyamide layer and a polyolefin layer laminated together are known (Patent Document 2).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2017 / 047806

[0007] Patent Document 2: Japanese Patent Application Publication No. 2005-088344 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] The multilayer structures described in Patent Documents 1 and 2 have the following problems: when they are recycled and reused, cross-linking or decomposition occurs due to repeated heating of EVOH or polyamide, resulting in particulate matter, thus reducing their reusability.

[0010] The present invention was made to solve the above-mentioned problems, and its purpose is to provide a multilayer structure, a separation method thereof and a recycling method thereof, wherein the multilayer structure has excellent interlayer adhesion under high humidity and excellent separation of the barrier layer in water, and even when the barrier layer is exposed to water in the separation and recycling process, the resin constituting the barrier layer has excellent viscosity stability after separation and recycling.

[0011] Methods for solving problems

[0012] The above-mentioned problem is solved by providing the following technical solution.

[0013] [1] A multilayer structure comprising a barrier layer (A), a water-soluble layer (B) and an adhesive layer (C), wherein the adhesive layer (C) is laminated on one or both sides of the barrier layer (A) by means of the water-soluble layer (B), the barrier layer (A) having polyamide or ethylene-vinyl alcohol copolymer (a1) as the main component, and the water-soluble layer (B) containing alkali metal ions (b1) of more than 10 ppm and less than 2000 ppm;

[0014] [2] According to the multilayer structure of [1], the water-soluble layer (B) has a vinyl alcohol polymer (b2) as the main component;

[0015] [3] According to the multilayer structure of [2], the viscosity-average degree of polymerization of the vinyl alcohol polymer (b2) is 400 or more and 2000 or less;

[0016] [4] According to the multilayer structure of [2] or [3], wherein the degree of saponification of the vinyl alcohol polymer (b2) is more than 70 mol% and less than 95 mol%;

[0017] [5] According to any one of [2] to [4], the total content of vinyl alcohol units and vinyl ester units in the vinyl alcohol polymer (b2) is more than 95 mol%;

[0018] [6] According to any one of [1] to [5], the alkali metal ion (b1) contained in the water-soluble layer (B) is sodium ion;

[0019] [7] According to any one of [1] to [6], the multilayer structure wherein the water-soluble layer (B) further contains a plasticizer (b3), wherein the component constituting the plasticizer (b3) is selected from at least one of glycerol, polyethylene glycol, polypropylene glycol, polyglycerol, mannitol, sorbitol and pentaerythritol;

[0020] [8] According to any one of [1] to [7], the solubility parameter of the resin constituting the main component of the barrier layer (A) is 11.0 (cal / cm³). 3 ) 1 / 2 Furthermore, the solubility parameter (SP) of the barrier layer (A) A The solubility parameter (SP) relative to the resin that constitutes the main component of the water-soluble layer (B). B The ratio of SP to ) A / SP B () is above 0.60 and below 0.95;

[0021] [9] A multilayer structure according to any one of [1] to [8], wherein the barrier layer (A) has an ethylene-vinyl alcohol copolymer as the main component;

[0022]

[10] According to any one of [1] to [9], the multilayer structure wherein the barrier layer (A) further contains alkali metal ions (a2) of more than 50 ppm and less than 500 ppm;

[0023]

[11] According to any one of [1] to

[10] , the multilayer structure wherein the barrier layer (A) further contains more than 1 ppm and less than 5000 ppm of higher fatty acids or their salts;

[0024]

[12] According to any one of [1] to

[11] , the multilayer structure, wherein the barrier layer (A) further contains a boron compound of more than 1 ppm and less than 300 ppm in terms of boron element conversion;

[0025]

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

[12] , wherein the adhesive layer (C) has a carboxylic acid modified polyolefin as the main component;

[0026]

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

[13] further contains other thermoplastic resin layers (D), the density of which is 1.0 g / cm³. 3 the following;

[0027]

[15] According to any one of [1] to

[14] , the density of the barrier layer (A) is 1.0 g / cm³. 3 Furthermore, the overall density of the layers excluding the barrier layer (A) and the water-soluble phase (B) is 1.0 g / cm³. 3 the following;

[0028]

[16] Separation method, wherein a portion or all of the water-soluble layer (B) is dissolved by contacting the multilayer structure of any one of [1] to

[15] with water (W) at 20°C to 95°C, causing the substance (X) containing the barrier layer (A) to settle in the water (W), and causing the substance (Y) containing the adhesive layer (C) to float.

[0029]

[17] A method for reusing multilayer structures, wherein substances (X) and (Y) recovered by the separation method of

[16] are each independently melt-formed.

[0030] Invention Effects

[0031] The multilayer structure of the present invention exhibits excellent interlayer adhesion under high humidity and excellent separation of the barrier layer in water. Furthermore, even when the barrier layer is exposed to water during the separation and recycling process, the resin constituting the barrier layer maintains excellent viscosity stability when reused after separation and recycling. Specifically, a separation method can be provided, for example, to cause the adhesive resin to float and the ethylene-vinyl alcohol copolymer and polyamide to settle. Additionally, a reuse method can be provided to allow the separated substances to be melt-formed independently. Thus, the degradation of the performance and quality of packaging materials can be suppressed, and the reusability of packaging materials can be improved, contributing to the realization of a circular economy. Detailed Implementation

[0032] The multilayer structure of the present invention comprises a barrier layer (A), a water-soluble layer (B), and an adhesive layer (C). The adhesive layer (C) is laminated on one or both sides of the barrier layer (A) by means of the water-soluble layer (B). The barrier layer (A) has polyamide or ethylene-vinyl alcohol copolymer as the main component (a1), and the water-soluble layer (B) contains alkali metal ions (b1) of more than 10 ppm and less than 2000 ppm.

[0033] It should be noted that in this specification, the main component refers to the component with the highest content on a mass basis. Additionally, "ppm" refers to the content ratio on a mass basis.

[0034] (Barrier layer (A))

[0035] The resin constituting the main component of the barrier layer (A) is polyamide or EVOH. By having polyamide or EVOH as the main component, the oxygen barrier properties of the multilayer structure are improved. From the viewpoint of reusability after separation and recycling, the resin constituting the main component of the barrier layer (A) is more preferably EVOH.

[0036] Examples of the aforementioned polyamides include, for instance, polyhexamethylene adipamide (Nylon 6), poly-ω-aminoheptanoic acid (Nylon 7), poly-ω-aminononanoic acid (Nylon 9), polyundecylamide (Nylon 11), polylaurolamide (Nylon 12), polyethylene adipamide (Nylon 26), polybutylene adipamide (Nylon 46), polyhexamethylene adipamide (Nylon 66), polyhexamethylene adipamide (Nylon 610), polyhexamethylene dodecyl diamide (Nylon 612), polyoctyl adipamide (Nylon 86), polydecyl adipamide (Nylon 106), caprolactam / laurolactam copolymer (Nylon 6 / 12), caprolactam / ω-aminononanoic acid copolymer (Nylon 6 / 9), caprolactam / hexamethylene diamine adipate copolymer (Nylon 6 / 66), lauryl lactam / hexamethylene diamine adipate copolymer (Nylon 12 / 66), and ethylenediamine hexamethylene adipate. The following polyamides are available: Nylon 26 / 66, Nylon 6 / 66 / 610, Nylon 26 / 66 / 610, Nylon ...910, Nylon 92, Nylon 10, Nylon 10, Nylon 92, Nylon 10, Nylon 92, Nylon 10, Nylon 92, Nylon 10, Nylon 92, Nylon 10, Nylon 92, Nylon 92, Nylon 10, Nylon 92, Nylon 92, Nylon 92, Nylon 92, Nylon 92, Nylon 92, Nylon 92, Nylon 92 Other examples include isophthalic acid adipate. Among these, nylon 6 / 66 or nylon 6 is preferred, considering its superior economic efficiency, melt-forming properties, and mechanical properties.

[0037] EVOH is a copolymer containing ethylene units and vinyl alcohol units. EVOH is typically a polymer obtained by saponifying an ethylene-vinyl ester copolymer. The lower limit of the ethylene unit content in the EVOH is preferably 20 mol%, more preferably 25 mol%. If the ethylene unit content of the EVOH is above the lower limit, the flexibility and thermoformability of the EVOH are improved, and the thermoformability of the resulting multilayer structure is improved. Furthermore, the upper limit of the ethylene unit content is preferably 55 mol%, more preferably 50 mol%. If the ethylene unit content of the EVOH is below the upper limit, the gas barrier properties of the EVOH and the resulting multilayer structure are improved.

[0038] The degree of saponification of EVOH is preferably 90 mol% or more, more preferably 95 mol% or more, and even more preferably 98 mol% or more. If the degree of saponification is within the above range, the thermal stability of the resulting resin composition is improved.

[0039] The EVOH may contain units derived from monomers other than ethylene, vinyl esters, and vinyl ester saponins, without impairing the effects of the present invention. When the EVOH contains units derived from other monomers, their content relative to all monomer units in the EVOH is preferably 10 mol% or less, more preferably 5 mol% or less, and even more preferably 3 mol% or less. Furthermore, the content of other monomer units may be 0.05 mol% or more. Examples of other monomers include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxy-ethoxy)silane, γ-methacryloyloxypropylmethoxysilane, and other vinylsilane compounds.

[0040] The EVOH may have at least one of the structural unit (I) shown in formula (I), the structural unit (II) shown in formula (II), and the structural unit (III) shown in general formula (III) without prejudice to the purpose of the present invention. By giving the EVOH such structural units, the thermoformability of the resulting multilayer structure can be improved.

[0041] [Chemistry 1]

[0042]

[0043] In equation (I), R 1 R 2 and R 3 Each can independently represent a hydrogen atom, an aliphatic hydrocarbon group with 1 to 10 carbon atoms, an alicyclic hydrocarbon group with 3 to 10 carbon atoms, an aromatic hydrocarbon group with 6 to 10 carbon atoms, or a hydroxyl group. Additionally, R... 1 R 2 and R 3 One of the optional bonds. In addition, some or all of the hydrogen atoms in the aforementioned aliphatic hydrocarbon groups with 1 to 10 carbon atoms, alicyclic hydrocarbon groups with 3 to 10 carbon atoms, and aromatic hydrocarbon groups with 6 to 10 carbon atoms may be substituted with hydroxyl, carboxyl, or halogen atoms.

[0044] In equation (II), R 4 R 5 R 6 and R 7 Each can independently represent a hydrogen atom, an aliphatic hydrocarbon group with 1 to 10 carbon atoms, an alicyclic hydrocarbon group with 3 to 10 carbon atoms, an aromatic hydrocarbon group with 6 to 10 carbon atoms, or a hydroxyl group. Additionally, R... 4 With R 5 Optional bonding, or, R 6 With R 7Optional bonding. In addition, some or all of the hydrogen atoms in the aforementioned aliphatic hydrocarbon groups with 1 to 10 carbon atoms, alicyclic hydrocarbon groups with 3 to 10 carbon atoms, and aromatic hydrocarbon groups with 6 to 10 carbon atoms may be substituted with hydroxyl, alkoxy, carboxyl, or halogen atoms.

[0045] In equation (III), R 8 R 9 R 10 and R 11 Each of these groups independently represents a hydrogen atom, an aliphatic hydrocarbon group with 1 to 10 carbon atoms, an alicyclic hydrocarbon group with 3 to 10 carbon atoms, an aromatic hydrocarbon group with 6 to 10 carbon atoms, or a hydroxyl group. Furthermore, some or all of the hydrogen atoms in the aforementioned aliphatic hydrocarbon groups with 1 to 10 carbon atoms, alicyclic hydrocarbon groups with 3 to 10 carbon atoms, and aromatic hydrocarbon groups with 6 to 10 carbon atoms may optionally be substituted with a hydroxyl, alkoxy, carboxyl, or halogen atom. R 北 and R 13 Each can independently represent a hydrogen atom, a formyl group, or an alkanoyl group with 2 to 10 carbon atoms.

[0046] When the EVOH contains the structural units shown in formulas (I) to (III) above, the lower limit of its content is preferably 0.1 mol%, more preferably 0.5 mol%, and even more preferably 1 mol%. In addition, the upper limit of this content is preferably 30 mol%, more preferably 15 mol%, and even more preferably 10 mol%. If the content of the structural units shown in the above formula is within the above range, the softness and processing characteristics of the resin composition are improved, and the thermoforming properties of the resulting multilayer structure are improved.

[0047] In the structural units shown in the above formula, aliphatic hydrocarbon groups with 1 to 10 carbon atoms can be alkyl, alkenyl, etc.; alicyclic hydrocarbon groups with 3 to 10 carbon atoms can be cycloalkyl, cycloalkenyl, etc.; and aromatic hydrocarbon groups with 6 to 10 carbon atoms can be phenyl, etc.

[0048] In structural unit (I), R 1 R 2 and R 3 Each of the following is preferably a hydrogen atom, methyl, ethyl, hydroxyl, hydroxymethyl, and hydroxyethyl, and from the viewpoint of further improving the thermoformability of the obtained multilayer structure, each of the following is preferably a hydrogen atom, methyl, hydroxyl, and hydroxymethyl.

[0049] In structural unit (II), R 4 and R 5 Preferably, both are hydrogen atoms. In particular, R is more preferred. 4 and R 5 Both are hydrogen atoms, the aforementioned R 6 and R 7One of them is an aliphatic hydrocarbon group with 1 to 10 carbon atoms, and the other is a hydrogen atom. The aliphatic hydrocarbon group is preferably alkyl or alkenyl. From the viewpoint of particularly emphasizing the gas barrier properties of the resulting multilayer structure, R is particularly preferred. 6 and R 7 One of them is a methyl or ethyl group, and the other is a hydrogen atom. Furthermore, the aforementioned R is particularly preferred. 6 and R 7 One of them is (CH2). h The substituents shown are OH (where h is an integer from 1 to 8), and the other is a hydrogen atom. In this (CH2) h In the substituents represented by OH, h is preferably an integer from 1 to 4, more preferably 1 or 2, and particularly preferably 1.

[0050] In structural unit (III), R 8 R 9 R 10 and R 11 Suitable for use is an aliphatic hydrocarbon group with 1 to 5 hydrogen atoms or carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, or n-pentyl.

[0051] Polyamide and EVOH can be used alone or in combination of two or more.

[0052] The lower limit for the content of polyamide or EVOH in the barrier layer (A) is sometimes preferably 80% by mass, more preferably 90% by mass, and even more preferably 95% by mass, 97% by mass, or 99% by mass. By setting the content of polyamide or EVOH in the barrier layer (A) to the above-mentioned lower limit or above, the barrier properties can be improved. The upper limit for the content of polyamide or EVOH in the barrier layer (A) can be 100% by mass or 99.99% by mass.

[0053] The barrier layer (A) preferably contains alkali metal ions (a2) of 50 ppm to 500 ppm. Especially when the main component of the barrier layer (A) is EVOH, the barrier layer (A) preferably contains alkali metal ions (a2). By ensuring the content of alkali metal ions (a2) is 50 ppm or more, the viscosity stability of the resin constituting the barrier layer (A) after the multilayer structure is separated and recycled is improved. This can be attributed to the fact that even if alkali metal ions (a2) dissolve from the barrier layer (A) exposed to water during the separation and recycling process of the multilayer structure described later, a sufficient amount of alkali metal ions (a2) can remain. The content of alkali metal ions (a2) is more preferably 80 ppm or more, and even more preferably 100 ppm or more. On the other hand, by ensuring the content of alkali metal ions (a2) is 500 ppm or less, the viscosity reduction during long-term melt mixing can be suppressed, and melt formability can be improved. The content of alkali metal ions (a2) is more preferably 300 ppm or less, and even more preferably 270 ppm or less.

[0054] There are no particular limitations on the alkali metal ion (a2), but sodium ion or potassium ion is preferred.

[0055] The alkali metal ions (a2) contained in the barrier layer (A) can exist in a state of dissociation as anions that self-constitute alkali metal salts, or in a state of salts formed by bonding with anions. Alternatively, they can exist in a state of coordination with groups (e.g., carboxyl groups, hydroxyl groups, etc.) present in EVOH, polyamide, and other optional components.

[0056] Alkali metal ions (a2) are usually derived from alkali metal salts. That is, the barrier layer (A) can contain alkali metal salts. There are no particular limitations on the components containing alkali metal ions (a2), and fatty acid salts (acetates, propionates, etc.) and salts other than fatty acid metal salts (nitrates, sulfates, etc.) can be used.

[0057] The barrier layer (A) preferably further contains a higher fatty acid or its salt at a concentration of 1 ppm or more and 5000 ppm or less, calculated as higher fatty acids. Particularly when the main component of the barrier layer (A) is EVOH, the barrier layer (A) preferably contains a higher fatty acid or its salt. By containing a higher fatty acid or its salt, the leaching of alkali metal ions (a2) from the barrier layer (A) during the separation of the multilayer structure in water (W) can be suppressed, and as a result, the viscosity stability of the resin constituting the barrier layer (A) after separation and recovery can be maintained. The content of the higher fatty acid or its salt is more preferably 5 ppm or more and 4000 ppm or less, and even more preferably 10 ppm or more and 2500 ppm or less, calculated as higher fatty acids.

[0058] Examples of higher fatty acid salts include alkali metal salts such as sodium and potassium salts of higher fatty acids, and alkaline earth metal salts such as magnesium and calcium salts of higher fatty acids. It should be noted that, in the case of alkali metal salts containing higher fatty acids, the content of alkali metal ions (a2) in the barrier layer (A) is calculated in the form of alkali metal ions that also include higher fatty acids.

[0059] As higher fatty acids or their salts, higher fatty acids or their salts with 12 or more carbon atoms are preferred, and examples include lauric acid, lauric acid, tridecyl acid, myristic acid, pentadecyl acid, palmitic acid, heptadecanoic acid, stearic acid, basic stearic acid, hydroxystearic acid, basic hydroxystearic acid, nonadecanoic acid, oleic acid, behenic acid, linoleic acid, linoleic acid, and other fatty acids or their salts. From the viewpoint of dispersibility in the barrier layer (A), one or more of these are appropriately used.

[0060] The barrier layer (A) preferably also contains a boron compound with a content of 1 ppm or more and 300 ppm or less based on boron element conversion. Especially when the main component of the barrier layer (A) is EVOH, the barrier layer (A) preferably contains a boron compound. By forming the barrier layer (A) from a resin composition containing a boron compound, torque variation during heating and melting can be suppressed. The boron compound used in this invention is not particularly limited, and examples include boric acids, borate esters, borates, boron hydrides, etc. Specifically, examples of boric acids include orthoboric acid, metaboric acid, tetraboric acid, etc. Examples of borate esters include triethyl borate, trimethyl borate, etc., and examples of borates include alkali metal salts, alkaline earth metal salts, borax, etc. Among these compounds, orthoboric acid (hereinafter sometimes abbreviated as boric acid) is preferred. By making the content of the boron compound 1 ppm or more, torque variation during heating and melting can be sufficiently suppressed. The lower limit of the aforementioned boron compound content is more preferably 10 ppm. On the other hand, by keeping the boron compound content at 300 ppm or less (based on boron element conversion), the leaching of boric acid compounds from the barrier layer (A) is suppressed during the separation of the multilayer structure. As a result, the viscosity stability of the resin constituting the barrier layer (A) after separation and recovery is improved. The upper limit of the boron compound content is more preferably 250 ppm, and even more preferably 200 ppm.

[0061] The barrier layer (A) may contain components other than alkali metal ions (a2), higher fatty acids, higher fatty acid salts, and boron compounds, as long as it does not impede the effects of the present invention. Examples of such components include resins other than polyamides and EVOH, polyvalent metal ions, carboxylic acids, phosphoric acid compounds, oxidation accelerators, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, pigments, dyes, processing aids, flame retardants, surfactants, crosslinking agents, fiber reinforcing agents, and antifogging agents. From the viewpoint of suppressing coloring when the resin constituting the barrier layer (A), especially EVOH and resin compositions containing EVOH, is melt-molded, it is preferable to include carboxylic acids or phosphoric acid compounds. The content of other components in the barrier layer (A) is typically 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less.

[0062] The barrier layer (A) may contain any resin other than polyamide and EVOH, and examples include thermoplastic resins such as polyolefin, polyester, polystyrene, polyvinyl chloride, acrylic resin, polyurethane, polycarbonate, and polyvinyl acetate.

[0063] The method for including alkali metal ions (a2), higher fatty acids, higher fatty acid salts, boron compounds, and other additives as needed in the barrier layer (A) is not particularly limited. Examples include methods such as melting polyamide or EVOH and mixing it with the aforementioned compounds; methods of melt-blending polyamide or EVOH with the aforementioned compounds in an extruder; and methods of mixing polyamide or EVOH powder, granules, spheres, cylindrical flakes, or other granules with solid, liquid, or solution forms of the aforementioned compounds to impregnate or spread them onto the polyamide or EVOH granules. Appropriate methods can be selected considering the physical properties of the aforementioned compounds and the permeability to the polyamide or EVOH. Furthermore, these methods can be used in combination. The temperature range during melt blending can be appropriately adjusted according to the melting point of the polyamide or EVOH used, typically between 150 and 250°C. It should be noted that commercially available EVOH resin granules containing alkali metal ions (a2) can also be used.

[0064] The average thickness of each barrier layer (A) is not particularly limited, but a lower limit is preferably 0.5 μm, more preferably 1 μm, and even more preferably 3 μm. Setting the average thickness of the barrier layer (A) to the lower limit or above improves barrier properties, etc. On the other hand, an upper limit for this average thickness is preferably 100 μm, more preferably 60 μm, even more preferably 40 μm, and even more preferably 20 μm. Setting the average thickness of the barrier layer (A) to the lower limit or below improves flexibility, etc. It should be noted that the average thickness of the layer refers to the average of the thicknesses measured at any five locations. The same applies to other layers.

[0065] (Water-soluble layer (B))

[0066] The water-soluble layer (B) contains alkali metal ions (b1) of 10 ppm to 2000 ppm. If the content of alkali metal ions (b1) is within this range, during the separation of the multilayer structure, some of the alkali metal ions (b1) in the water-soluble layer (B) are transferred to the barrier layer (A). Even when the barrier layer is exposed to water during the separation and recovery process, the resin constituting the barrier layer exhibits excellent viscosity stability after separation and recovery. If the content of alkali metal ions (b1) is less than 10 ppm, the transfer of alkali metal ions (b1) from the water-soluble layer (B) to the barrier layer (A) is not sufficient during the separation of the multilayer structure. As a result, the viscosity stability of the resin constituting the barrier layer (A) decreases after separation and recovery. The lower limit of the alkali metal ion (b1) content is preferably 100 ppm, more preferably 200 ppm, and particularly preferably 500 ppm. On the other hand, if the content of alkali metal ions (b1) exceeds 2000 ppm, the viscosity decreases sharply during prolonged melt mixing, and melt formability sometimes deteriorates. The upper limit of the content of alkali metal ions (b1) is preferably 1500 ppm, more preferably 1200 ppm, and particularly preferably 1000 ppm.

[0067] Examples of alkali metal ions (b1) included in the water-soluble layer (B) include lithium ions, sodium ions, and potassium ions. From the viewpoint of color and viscosity stability of the resin composition, sodium ions are preferred.

[0068] The alkali metal ions (b1) contained in the water-soluble layer (B) of the present invention can exist in a state of dissociation from the anions that constitute alkali metal salts, or in a state of salts formed by bonding with anions. Additionally, they can exist in a state of coordination with groups (e.g., carboxyl groups, hydroxyl groups, etc.) of the vinyl alcohol polymer (b2) described later, or other optional components.

[0069] Alkali metal ions (b1) are usually derived from alkali metal salts. That is, the water-soluble layer (B) can contain alkali metal salts. There are no particular limitations on the components containing alkali metal ions (b1), and fatty acid metal salts, metal salts other than fatty acid metal salts (nitrates, sulfates, etc.) can be used.

[0070] The aforementioned fatty acid metal salts can be higher fatty acid metal salts with 12 or more carbon atoms, or fatty acid metal salts with 11 or fewer carbon atoms. From the viewpoint of ease of transfer from the water-soluble layer (B) to the barrier layer (A), aliphatic metal salts with 11 or fewer carbon atoms are preferred. Examples of higher fatty acid metal salts with 12 or more carbon atoms include metal salts of fatty acids such as lauryl acid, lauric acid, tridecyl acid, myristic acid, pentadecyl acid, palmitic acid, heptadecanoic acid, stearic acid, basic stearic acid, hydroxystearic acid, basic hydroxystearic acid, nonadecanoic acid, oleic acid, behenic acid, linoleic acid, etc. Examples of fatty acid metal salts with 11 or fewer carbon atoms include acetates and propionates. From the viewpoint of dispersibility in the water-soluble layer (B), any one or two or more of these salts are appropriately used.

[0071] Resins that form the main component of the water-soluble layer (B) can include starch-based components such as corn starch and their polymer components; cellulose-based polymers such as carboxymethyl cellulose and carboxyethyl cellulose; acrylic polymers such as sodium polyacrylate; and vinyl alcohol-based polymers such as polyvinyl alcohol. Among these, a vinyl alcohol-based polymer (b2) is preferred from the viewpoint of melt-forming properties and adhesion to the barrier layer (A). By having a vinyl alcohol-based polymer as the main component of the water-soluble layer (B), the gas barrier properties and separability of the multilayer structure are improved. The vinyl alcohol-based polymer (b2) is a polymer containing vinyl alcohol units. It should be noted that, from the viewpoint of water solubility, the vinyl alcohol-based polymer (b2) is preferably a vinyl alcohol-based polymer other than EVOH (A), which can be used as the barrier layer (A).

[0072] The viscosity-to-polymerization degree of the vinyl alcohol polymer (b2) is preferably 400 or more and 2000 or less. The lower limit of the viscosity-to-polymerization degree is more preferably 500, and even more preferably 700. By setting the viscosity-to-polymerization degree to the lower limit or above, the adhesiveness and thermal stability of the vinyl alcohol polymer (b2) are improved. The upper limit of the viscosity-to-polymerization degree is more preferably 1500, and even more preferably 1000. By setting the viscosity-to-polymerization degree to the upper limit or below, the melt-forming properties of the vinyl alcohol polymer (b2) are improved.

[0073] The viscosity-uniform degree of polymerization of the vinyl alcohol polymer (b2) was determined according to JIS K 6726:1994. Specifically, the intrinsic viscosity [η] (L / g) of the vinyl alcohol polymer (b2) was measured in water at 30°C. Using the value of the intrinsic viscosity [η], the viscosity-uniform degree of polymerization P was calculated using the following formula. It should be noted that when the degree of saponification of the vinyl alcohol polymer (b2) is less than 99.5 mol%, the intrinsic viscosity [η] was measured after saponification to a degree of saponification of 99.5 mol% or more.

[0074] P=([η]×10 4 / 8.29) (1 / 0.62)

[0075] The degree of saponification of the vinyl alcohol polymer (b2) is preferably 70 mol% or more, more preferably 75 mol% or more, and even more preferably 85 mol% or more. If the degree of saponification is 70 mol% or more, the vinyl alcohol polymer (b2) exhibits excellent water solubility and improved separability of multilayer structures. The degree of saponification of the vinyl alcohol polymer (b2) is preferably 95 mol% or less, more preferably 93 mol% or less, and even more preferably 90 mol% or less. If the degree of saponification is 95 mol% or less, the vinyl alcohol polymer (b2) exhibits excellent melt-forming properties. The degree of saponification of the vinyl alcohol polymer (b2) is determined according to JIS K6726:1994.

[0076] Examples of vinyl alcohol-based polymers (b2) include polyvinyl alcohol (hereinafter sometimes referred to as "PVA") and modified PVA. Among these, PVA is more preferred from the viewpoint of solubility in water. The vinyl alcohol-based polymer (b2) may contain one or more types.

[0077] The total content of vinyl alcohol units and vinyl ester units in the vinyl alcohol polymer (b2) is preferably 95 mol% or more. By making the above total content 95 mol% or more, the solubility of the vinyl alcohol polymer (b2) in water is improved, and as a result, the separability of the multilayer structure in water is improved. The total content of vinyl alcohol units and vinyl ester units is more preferably 97 mol% or more, even more preferably 98 mol% or more, and particularly preferably 99 mol% or more.

[0078] In the vinyl alcohol polymer (b2), monomer units other than vinyl alcohol units and vinyl ester units may be contained, provided that the effects of the present invention are not impaired. Examples of such monomers include α-olefins such as ethylene, propylene, n-butene, and isobutene; acrylic acid and its salts; acrylates; methacrylic acid and its salts; methacrylates; acrylamide; N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetone acrylamide, acrylamide propanesulfonic acid and its salts, acrylamide propyl dimethylamine and its salts or quaternary ammonium salts thereof, N-hydroxymethylacrylamide and its derivatives, etc.; methacrylamide; N-methylmethylacrylamide, N-ethylmethylacrylamide, methacrylamide propanesulfonic acid and its salts, methacrylamide propyl dimethylamine and its salts or quaternary ammonium salts thereof, N- Methacrylamide derivatives such as hydroxymethyl methacrylamide and its derivatives; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc.; nitriles such as acrylonitrile and methacrylonitrile; halogenated vinylides such as vinyl chloride and vinyl fluoride; vinylidene halogenated vinylides such as vinylidene chloride and vinylidene fluoride; allyl acetate, allyl chloride, etc.; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, fumaric acid, and their salts or esters; vinyltrimethoxysilane and other vinylsilyl compounds; isopropyl acetate, etc. The content of units (monomer units) derived from these monomers varies depending on the purpose and use, preferably less than 10 mol%, more preferably less than 5 mol%, further preferably less than 1 mol%, particularly preferably less than 0.5 mol%, and can be 0 mol%. It should be noted that when the vinyl alcohol polymer (b2) is an ethylene-modified PVA containing ethylene units, the total number of ethylene units in all monomer units can be up to 10 mol% or less.

[0079] The lower limit for the content of the vinyl alcohol polymer (b2) in the water-soluble layer (B) is preferably 60% by mass, more preferably 70% by mass, and even more preferably 80% by mass. By setting the content of the vinyl alcohol polymer (b2) in the water-soluble layer (B) to the above lower limit or above, interlayer adhesion and separation in water can be improved. The upper limit for the content of the vinyl alcohol polymer (b2) in the water-soluble layer (B) can be 99.9% by mass, 99% by mass, or 95% by mass.

[0080] The water-soluble layer (B) preferably also contains a plasticizer (b3). By containing the plasticizer (b3), the melt-forming properties of resins such as vinyl alcohol polymers (b2) and their solubility in water (W) are improved. The molecular weight of the plasticizer (b3) is not particularly limited, but from the viewpoint of peelability, it is preferably 10,000 or less, more preferably 2,000 or less, even more preferably 200 or less, and particularly preferably 100 or less. As a lower limit for the content of plasticizer (b3) in the water-soluble layer (B), it is preferably 3% by mass, more preferably 5% by mass, and even more preferably 8% by mass. As an upper limit for the content of plasticizer (b3), it is preferably 45% by mass, more preferably 30% by mass, and even more preferably 20% by mass. The components constituting the plasticizer (b3) are preferably selected from at least one of glycerol, polyethylene glycol, polypropylene glycol, polyglycerol, mannitol, sorbitol and pentaerythritol, more preferably selected from at least one of glycerol, polyethylene glycol, mannitol and sorbitol, and particularly preferably selected from at least one of glycerol, mannitol and sorbitol.

[0081] In the water-soluble layer (B), other components besides alkali metal ions (b1), vinyl alcohol polymers (b2), or other water-soluble resins and plasticizers (b3) may be contained, as long as they do not impede the effects of the present invention. Examples of such other components include, for instance, polyvalent metal ions, carboxylic acids, phosphoric acid compounds, oxidation promoters, antioxidants, heat stabilizers (melt stabilizers), photoinitiators, deodorants, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, pigments, dyes, processing aids, flame retardants, and antifogging agents. The content of other components in the water-soluble layer (B) is typically 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less.

[0082] The water-soluble layer (B) is preferably composed of a resin composition containing a vinyl alcohol polymer (b2). The method for preparing the resin composition containing the vinyl alcohol polymer (b2) is not particularly limited; it can be prepared by any method as long as the alkali metal ions (b1), the vinyl alcohol polymer (b2), the plasticizer (b3), and other components as needed can be uniformly mixed. Vinyl alcohol polymer compositions can be prepared by, for example, the following methods: a method of melting and granulating after blending alkali metal ions (b1), vinyl alcohol polymer (b2), and plasticizer (b3); a method of mixing and granulating while adding alkali metal ions (b1), vinyl alcohol polymer (b2), and plasticizer (b3) to a melt mixer in specified proportions; a method of melting and granulating after pre-introducing alkali metal ions (b1) into vinyl alcohol polymer (b2) and blending with plasticizer (b3); and a method of mixing and granulating while pre-introducing alkali metal ions (b1) into vinyl alcohol polymer (b2) and adding vinyl alcohol polymer (b2) and plasticizer (b3) to a melt mixer in specified proportions.

[0083] The water-soluble layer (B) used in this invention is a layer in which part or all of the main components are dissolved in water (W). It can be a layer in which part or all of the main components are dissolved by contacting water (W) at 20°C to 95°C. Alternatively, the water-soluble layer (B) can be a layer in which part or all of the main components are dissolved when 1 part by mass of the water-soluble layer (B) is stirred in 100 parts by mass of hot pure water at 80°C for 30 minutes.

[0084] The average thickness of each water-soluble layer (B) is not particularly limited, but a lower limit is preferably 0.1 μm, more preferably 0.3 μm, further preferably 0.5 μm, and even more preferably 1 μm. On the other hand, an upper limit for this average thickness is preferably 100 μm, more preferably 60 μm, further preferably 40 μm, and even more preferably 20 μm. By setting the average thickness of the water-soluble layer (B) within the above range, interlayer adhesion under high humidity and separation in water can be improved.

[0085] (Adhesive layer (C))

[0086] The adhesive layer (C) is typically an adhesive layer that bonds to the water-soluble layer (B) and, optionally, another thermoplastic resin layer (D). The adhesive layer (C) is, for example, a layer with an adhesive resin as its main component. The adhesive layer (C) preferably has a carboxylic acid-modified polyolefin as its main component. Examples of carboxylic acid-modified polyolefins include, for example, modified olefin polymers containing carboxyl groups obtained by chemically bonding unsaturated carboxylic acids or their anhydrides to an olefin polymer through addition reactions, grafting reactions, etc. Examples of unsaturated carboxylic acids or their anhydrides include maleic acid, maleic anhydride, fumaric acid, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, citraconic acid, hexahydrophthalic anhydride, etc., among which maleic anhydride is suitable. Specifically, suitable materials may include one or more mixtures selected from maleic anhydride-grafted modified polyethylene, maleic anhydride-grafted modified polypropylene, maleic anhydride-grafted modified ethylene-propylene copolymer, maleic anhydride-grafted modified ethylene-ethyl acrylate copolymer, maleic anhydride-grafted modified ethylene-vinyl acetate copolymer, etc.

[0087] If rubber / elastomer components such as polyisobutylene and ethylene-propylene rubber, or polyolefin resins different from the parent polyolefin resin of the adhesive resin, are mixed into the adhesive resin, the adhesiveness may sometimes be improved.

[0088] The adhesive layer (C) can be a layer formed from an anchoring coating agent, an adhesive, etc. Alternatively, the adhesive layer (C) can be formed by treating the surface of a single layer (e.g., a water-soluble layer (B)) of the two layers to be bonded with a known anchoring coating agent, or by applying a known adhesive to the surface of a single layer. As this adhesive, a two-component reactive polyurethane adhesive, in which a polyisocyanate component and a polyol component are mixed and reacted, is preferred. Furthermore, by adding a small amount of a known silane coupling agent or other additive to the anchoring coating agent or adhesive, the adhesion can sometimes be further improved. Examples of silane coupling agents include, but are not limited to, silane coupling agents having reactive groups such as isocyanate groups, epoxy groups, amino groups, urea groups, and mercapto groups.

[0089] The average thickness of each adhesive layer (C) is preferably 0.01 μm or more and 20 μm or less, more preferably 0.03 μm or more and 10 μm or less, and even more preferably 1 μm or more and 5 μm or less.

[0090] (Other thermoplastic resin layers (D))

[0091] The multilayer structure of the present invention preferably further comprises other thermoplastic resin layers (D). Other thermoplastic resin layers (D) are layers in which thermoplastic resin is the main component. The thermoplastic resin constituting other thermoplastic resin layers (D) is not particularly limited, and examples include homopolymers or copolymers of linear low-density polyethylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, vinyl ester resins, ethylene-propylene copolymers, polypropylene, propylene-α-olefin copolymers (α-olefins with 4 to 20 carbon atoms), polybutene, polypentene, and other olefins; polyesters such as polyethylene terephthalate; polystyrene, polyvinyl chloride, polyvinylidene chloride, acrylic resins, polycarbonate, chlorinated polyethylene, chlorinated polypropylene, etc. From the viewpoint of reusability, polyolefins are preferred. The content of thermoplastic resin in other thermoplastic resin layers (D) is preferably 80% by mass or more and 100% by mass or less, and can be 90% by mass or more or 99% by mass or less.

[0092] From the viewpoint of separability from the barrier layer (A) in water, the density of the other thermoplastic resin layer (D) is preferably 1.0 g / cm³. 3 Below, less than 1.0 g / cm³ is preferred. 3 Further preferred is 0.95 g / cm³ 3 The following applies. For example, the lower density limit of other thermoplastic resin layers (D) can be 0.8 g / cm³. 3 It can also be 0.85 g / cm³. 3 .

[0093] Other thermoplastic resin layers (D) may contain additives, such as heat stabilizers, antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, stabilizers, surfactants, crosslinking agents, and fiber reinforcing agents. Preferably, at least one is selected from antioxidants, ultraviolet absorbers, and colorants.

[0094] The average thickness of each other thermoplastic resin layer (D) is preferably 1 μm or more and 1,000 μm or less, more preferably 3 μm or more and 500 μm or less, and even more preferably 5 μm or more and 200 μm or less.

[0095] (Multi-layer structure)

[0096] In the multilayer structure of the present invention, an adhesive layer (C) is laminated on one or both surfaces of the barrier layer (A) using a water-soluble layer (B). In this case, in addition to the barrier layer (A), water-soluble layer (B), adhesive layer (C), and other thermoplastic resin layers (D), other optional layers can be used. When other thermoplastic resin layers (D) are provided, the water-soluble layer (B) and the other thermoplastic resin layers (D) are preferably bonded together using the adhesive layer (C). It should be noted that the number of layers is not particularly limited; there can be one layer or two or more layers.

[0097] When manufacturing the above-mentioned multilayer structure, it is sufficient to obtain a multilayer structure composed of layers having (C) / (B) / (A). A multilayer structure composed of layers having (D) / (C) / (B) / (A) / (B) / (C) / (D) is particularly preferred. As a lamination method, the following methods can be listed as examples: (1) a method of co-extruding various resins; (2) a method of pre-fabricating multilayer films having a barrier layer (A) and a water-soluble layer (B) [e.g., a multilayer film with a layer structure of (B) / (A) / (B)], a multilayer film having a barrier layer (A), a water-soluble layer (B) and an adhesive layer (C) [e.g., a multilayer film with a layer structure of (C) / (B) / (A) / (B) / (C)], etc., and then melt-extruding other resins onto them; and (3) a method of dry laminating a single-layer film or a multilayer film containing other resins onto the aforementioned multilayer film using a known adhesive, etc. Furthermore, in the case of co-extrusion via blow molding, it can also be obtained by melting the inner sides of the cylindrical film together using heat after forming a multilayer film consisting of an outer layer (D) / (C) / (B) / (A) / (B) / (C) [inner layer]. The forming temperature during melt forming is mostly selected from the range of 150 to 300°C.

[0098] The multilayer structure of the present invention is not limited to having the layer configuration described above (D) / (C) / (B) / (A) / (B) / (C) / (D). It can have nine or more layers, such as (D) / (X) / (C) / (B) / (A) / (B) / (C) / (X) / (D), (X) / (D) / (C) / (B) / (A) / (B) / (C) / (D) / (X), or (X) / (D) / (X) / (C) / (B) / (A) / (B) / (C) / (X) / (D) / (X). The resins and compositions used in layers with the same symbols in the layer configuration can be the same or different. It should be noted that when multiple adhesive layers (C) and other thermoplastic resin layers (D) are used in the multilayer structure of the present invention, resins of different types can also be used. Furthermore, the multilayer structure of the present invention preferably does not contain paper. In the multilayer structure of the present invention, it is also preferable that all layers are made primarily of resin.

[0099] The lower limit for the number of layers in the multilayer structure of the present invention is 3, preferably 5, and more preferably 7. The upper limit for the number of layers is, for example, 15, 11, 9, or 7. The layer configuration of the multilayer structure of the present invention can be, for example, a symmetrical layer configuration centered on the barrier layer (A), or an asymmetrical layer configuration. A symmetrical layer configuration can be a layer configuration where only the arrangement order of the layers is symmetrical, or a layer configuration that also includes the thickness of each layer being symmetrical.

[0100] The solubility parameter (SP) of the resin, which is the main component of the barrier layer (A) in the multilayer structure of the present invention. A The preferred value is 11.0 (cal / cm³). 3 ) 1 / 2 The above applies. If the solubility parameter of the barrier layer (A) is within the above range, the barrier layer (A) readily accepts alkali metal ions (b1) transferred from the water-soluble layer (B), resulting in improved viscosity stability of the resin in the separated and recovered barrier layer (A). This solubility parameter (SP) A More preferably 12.5 (cal / cm) 3 ) 1 / 2 The above is further preferred to be 13.0 (cal / cm). 3 ) 1 / 2 That's all. This solubility parameter (SP) A The upper limit can be, for example, 15.0 (cal / cm³). 3 ) 1 / 2 It can also be 14.0 (cal / cm³). 3 ) 1 / 2 .

[0101] It should be noted that in this specification, the solubility parameter is set to the value obtained by Fedors formula (Polym.Eng.Sci., 14[2], 147(1974)).

[0102] Solubility parameter (SP) of barrier layer (A) A The solubility parameter (SP) of the resin relative to the main component of the water-soluble layer (B) in the multilayer structure of the present invention. B The ratio of SP to ) A / SP B The solubility parameter ratio is preferably 0.60 or higher and 0.95 or lower. By setting the ratio of the above solubility parameters to 0.60 or higher, the alkali metal ions (b1) transferred from the water-soluble layer (B) are rapidly absorbed into the barrier layer (A), resulting in improved viscosity stability of the resin in the separated and recovered barrier layer (A). The lower limit of the above solubility parameter ratio is more preferably 0.70, and even more preferably 0.80. On the other hand, by setting the above solubility parameter ratio to 0.95 or lower, the affinity of the water-soluble layer (B) for water increases, resulting in improved separability of the multilayer structure in water. The upper limit of the above solubility parameter ratio is more preferably 0.94, and even more preferably 0.92. The solubility parameter (SP) of the resin constituting the main component of the water-soluble layer (B) is... B For example, a preferred value is 13.0 (cal / cm³). 3 ) 1 / 2 Above and 18.0 (cal / cm) 3 ) 1 / 2 The following is more preferably 14.0 (cal / cm³) 3 ) 1 / 2 Above and 16.5 (cal / cm) 3 ) 1 / 2 the following.

[0103] Preferably, the density of the barrier layer (A) in the multilayer structure of the present invention is 1.0 g / cm³. 3 Furthermore, the overall density of the layers excluding the barrier layer (A) and the water-soluble layer (B) is 1.0 g / cm³. 3 Below. If the density is within the above range, after the multilayer structure is separated in water, the barrier layer (A) will sink to the water, while the layers other than the barrier layer (A) and the water-soluble layer (B) (e.g., the adhesive layer (C) and other thermoplastic resin layers (D)) will float in the water, thus improving the separability. The density of the barrier layer (A) is more preferably greater than 1.00 g / cm³. 3 Further preferred value is 1.05 g / cm³. 3 The above is further preferred to be 1.10 g / cm³. 3 That's all. The upper limit of the density of the barrier layer (A) can be, for example, 1.4 g / cm³.3 It can also be 1.3 g / cm³. 3 The overall density of the layers other than the barrier layer (A) and the water-soluble layer (B) (e.g., the adhesive layer (C) and other thermoplastic resin layers (D)) is preferably less than 1.00 g / cm³. 3 Further preferred is 0.98 g / cm³ 3 The following is a further preferred value: 0.95 g / cm³ 3 The lower limit of the overall density of the layers other than the barrier layer (A) and the water-soluble layer (B) can be 0.8 g / cm³. 3 It can also be 0.85 g / cm³. 3 .

[0104] The oxygen permeability (OTR) of the multilayer structure of the present invention can be adjusted according to the application and is not particularly limited, but is preferably 5 cc / (m 2 (day.atm) or less. OTR in this range of multi-layered structures is suitable for use as packaging materials, etc. More preferably, OTR is 4cc / (m 2 For doses below .day.atm), OTR is further preferably 3cc / (m 2 Below .day.atm), 2cc / (m 2 The measurement was performed according to JIS K7126-2 (isobaric method; 2006), specifically using the method described in the examples.

[0105] In addition, to improve the formability and various physical properties, the aforementioned additives, modifiers, fillers, other resins, etc., can be added to each layer of the multilayer structure of the present invention, without hindering the effect of the present invention.

[0106] (Separation methods and reuse methods)

[0107] The separation method of the present invention achieves this by contacting the multilayer structure with water (W) at a temperature of 20°C to 95°C, causing partial or complete dissolution of the water-soluble layer (B), causing the substance (X) containing the barrier layer (A) to settle in the water (W), and causing the substance (Y) containing the adhesive layer (C) to float. While increasing the temperature of the water (W) is expected to remove attached contaminants, the separation efficiency may decrease due to water (W) convection. Furthermore, when the multilayer structure of the present invention includes other thermoplastic resin layers (D), the substance (Y) preferably includes both the adhesive layer (C) and other thermoplastic resin layers (D). The size of the multilayer structure added to the water (W) is not particularly limited, but in the case of a multilayer structure, it is preferably less than 10 cm square to promote interlayer delamination. Additionally, vigorous stirring immediately after addition promotes interlayer delamination, followed by settling, thereby achieving effective separation. After separation, the settled material (X) and the floated material (Y) can be recovered separately. After washing and drying with pure water or the like as needed, they are melt-formed using an extruder to re-granulate as recycled resin. Various molded articles are manufactured using the granules obtained in this manner. In other words, the recycling method for the multilayer structure of the present invention is achieved by independently melt-forming the material (X) and material (Y) recovered using the above separation method.

[0108] It should be noted that when substances (X) and (Y) form a multi-layered structure, fragments can be obtained by crushing the multi-layered structure before or in water (W), thereby effectively separating substances (X) and (Y).

[0109] Here, the water (W) may contain dissolved chloride salts such as sodium chloride and potassium chloride as solutes. That is, the water (W) can be an aqueous solution containing solutes or pure water without solutes.

[0110] When chloride salts or the like are dissolved as solutes in water (W), substances with a higher specific gravity than water can be stably and economically separated by using an aqueous solution within a specific concentration range. From an economic and operational point of view, the concentration of chloride salts or the like, which is necessary for the required specific gravity w of water (W), is preferably 40% by mass or less. By setting this concentration to 40% by mass or less, the supply cost of chloride salts or the like can be suppressed, and the post-separation cleaning process can also be performed efficiently.

[0111] Furthermore, from the viewpoint of the stability of the separation process, the concentration of chloride salts, etc., necessary for the required specific gravity w of water (W) is preferably at least 10% by mass less than the saturation concentration of such chloride salts. By setting the difference between the concentration of chloride salts, etc., necessary for the required specific gravity w of water (W) and the saturation concentration of such chloride salts, the time required for the dissolution of chloride salts, etc., can be shortened. In addition, the precipitation of chloride salts, etc., into the separation tank and the separated material can be suppressed, thereby stabilizing the process.

[0112] Example

[0113] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0114] Example 1

[0115] (1) Preparation of EVOH resin composition granules

[0116] The EVOH resin granules (ethylene content 38 mol%, saponification degree 99.6 mol%, MFR (190℃, 2.16 kg load) 1.69 g / 10 min, oxygen permeability (20℃, 65% RH) 0.71 cc·20 μm / (m) were tested. 2 The resin composition contains 250 ppm sodium ions and 90 ppm phosphate ions. As a boron compound, it contains orthoboric acid (calculated as 180 ppm based on boron element conversion) and stearic acid (manufactured by Fujifilm and Koujun Pharmaceutical Co., Ltd.). The mixture is melt-blended to achieve a stearic acid content of 1100 ppm in the resulting resin composition, yielding EVOH resin composition granules. The melt blending is performed using a 25mm extruder (D(mm)=25, L / D=25, compression ratio=2.0, screw: co-rotating fully meshing type) manufactured by Toyo Seiki Co., Ltd., at a resin temperature of 220°C. It should be noted that the specific gravity of the resulting EVOH resin composition granules is 1.2. Furthermore, the solubility parameter of EVOH contained in this EVOH resin composition granules is 13.5 (cal / cm³). 3 ) 1 / 2 .

[0117] (2) Preparation of PVA resin composition granules

[0118] [Viscosity-uniform polymerization degree and saponification degree]

[0119] The viscosity-uniform polymerization degree and saponification degree of vinyl alcohol polymers were determined by the method described in JIS K6726 (1994).

[0120] The vinyl acetate polymer obtained by conventional polymerization of vinyl acetate was saponified to obtain PVA with a viscosity-average degree of polymerization of 800 and a saponification degree of 88 mol%. 87 parts by weight of the obtained PVA and 13 parts by weight of glycerol as a plasticizer were mixed using a planetary mixer. An aqueous solution of sodium acetate was added at a sodium ion content of 800 ppm, and the mixture was melt-blended to obtain PVA resin composition granules. The melt-blending was performed using a 25mm extruder (D(mm)=25, L / D=25, compression ratio=2.0, screw: co-rotating fully meshing type) manufactured by Toyo Seiki Co., Ltd., at a resin temperature of 220°C.

[0121] (3) Fabrication of multi-layer structures

[0122] Using a co-extrusion multilayer casting film forming apparatus, a multilayer structure was obtained, comprising a barrier layer (A) containing the aforementioned EVOH resin composition, a water-soluble layer (B) containing the aforementioned PVA resin composition, an adhesive layer (C) containing maleic anhydride modified polyethylene (Mitsui Chemicals Co., Ltd.'s "Adoma-NF518"), and other thermoplastic resin layers (D) containing low-density polyethylene (LDPE; Nippon Polyester Co., Ltd.'s "Nobatetsuku LJ400"). This structure (having an average layer thickness of (D) / (C) / (B) / (A) / (B) / (C) / (D) = 50 μm / 5 μm / 5 μm / 5 μm / 5 μm / 50 μm and consisting of 7 co-extruded multilayer casting films) is shown below.

[0123] Co-extrusion conditions

[0124] Extrusion temperature of barrier layer (A): Supply section / Compression section / Metering section / Die = 170 / 210 / 210 / 210℃

[0125] Extrusion temperature of water-soluble layer (B): Feed section / Compression section / Metering section / Die = 170 / 200 / 200 / 210℃

[0126] Extrusion temperature of adhesive layer (C): Feed section / Compression section / Metering section / Die = 170 / 210 / 210 / 210℃

[0127] Extrusion temperatures for other thermoplastic resin layers (D): Feed section / Compression section / Metering section / Die = 170 / 210 / 210 / 210℃

[0128] Extruder:

[0129] • Barrier layer (A) 32φ extruder UT-32-H type (manufactured by Plastics Engineering Research Institute Co., Ltd.)

[0130] • Water-soluble layer (B) 40φ extruder GT-40-A type (manufactured by Plastics Engineering Research Institute, Ltd.)

[0131] • Adhesive layer (C) 40φ extruder GT-40-L type (manufactured by Plastics Engineering Research Institute Co., Ltd.)

[0132] Other thermoplastic resin layers (D) 65φ extruder SZW65GT-22MG-STD type (manufactured by Technobel Co., Ltd.)

[0133] T-die: 600mm wide, 4 types, 7 layers, for various applications (Made by Cloeren Incorporated)

[0134] Temperature of the cooling roller: 60℃

[0135] Traction speed: 4.5 m / min

[0136] (4) Adhesion evaluation

[0137] As an indicator of the interlayer adhesion between the water-soluble layer (B) and the adhesive layer (C) in the multilayer structure prepared in (3), the adhesive strength under high humidity conditions was determined using the following conditions. After conditioning for 7 days at 40°C and 90% RH, short strips of 15 mm × 200 mm were cut out. For the obtained test strips, the T-peel strength (gf / 15 mm) was measured using an "Autograph AGS-H type" manufactured by Shimadzu Corporation, with a chuck spacing of 50 mm and a tensile speed of 250 mm / min. The measurement was performed on 5 test strips, and the average value was taken as the adhesive strength. The judgment criteria are shown below. The results are shown in Table 1.

[0138] A: Strong adhesion, impossible to peel off, or adhesion strength of 150g / 15mm or higher.

[0139] B: Bond strength is ≥50g / 15mm and <150g / 15mm

[0140] C: Bond strength is ≥15g / 15mm and <50g / 15mm

[0141] D: Bond strength less than 15g / 15mm

[0142] (5) Separability evaluation

[0143] (5-1) Evaluation of peelability

[0144] The multilayer structure prepared in (3) was cut into 10 square pieces of 1 cm each to obtain test pieces. The obtained test pieces were stirred in pure water (W) at a temperature of 80°C for 30 minutes and then allowed to stand to evaluate the peelability. The judgment criteria are shown below. The results are shown in Table 1.

[0145] A: During stirring, separation is achieved rapidly, and the remaining membrane, which is not peeled off but exists in a multi-layered form, consists of two or fewer sheets.

[0146] B: During stirring, separation is achieved rapidly, leaving 3-4 layers of membrane that remain unpeeled in a multi-layered form.

[0147] C: During stirring, separation is carried out slowly, leaving 5-6 layers of membrane that remain in a multi-layered form without being peeled off.

[0148] D: During stirring, if more than 7 membranes remain in a multi-layered form without complete separation or peeling, the mixture takes a considerable amount of time to separate.

[0149] (5-2) Discrimination Evaluation

[0150] The test pieces were prepared and tested in the same manner as in (5-1). The distinguishability of the membrane on the barrier layer (A) side and the membrane on the adhesive layer (C) side after settling was evaluated according to the following criteria: that is, whether they could be distinguished by settling or floating. The results are shown in Table 1.

[0151] A: After stirring stops, the membrane on the barrier layer (A) side and the membrane on the adhesive layer (C) side settle or float in the water (W), respectively, appearing as the lower or upper part of the water (W).

[0152] B: After stirring stops, both the membrane on the barrier layer (A) side and the membrane on the adhesive layer (C) side settle or float in the water (W), appearing to accumulate in either the lower or upper part of the water (W).

[0153] (6) Viscosity stability of the separated and recycled barrier layer (A)

[0154] First, in order to determine the torque value before separation, the EVOH resin composition prepared in (1) was mixed using a roller agitator R60 manufactured by Toyo Seiki Co., Ltd. under the following conditions, and the torque value (T1) was measured 60 minutes after mixing.

[0155] Next, to determine the torque value after separation, the multilayer structure prepared in (3) was cut into 200 square pieces of 1 cm each to obtain test pieces. The obtained test pieces were stirred in pure water at a temperature of 80°C (water (W)) for 1 hour and then allowed to stand, thereby separating the multilayer structure. Afterward, only the membrane that settled in the water (W) was taken out and dried to remove the water from the membrane. The same operation was repeated to obtain 100 g of dried membrane of barrier layer (A). Using the obtained membrane, it was mixed under the following conditions using a roller mixer R60 manufactured by Toyo Seiki Co., Ltd., and the torque value after 60 minutes was taken as T2.

[0156] Based on the obtained T1 and T2, the viscosity stability of the separated barrier layer (A) is determined as follows.

[0157] A better rating indicates higher viscosity stability after separation and recovery. The results are shown in Table 1.

[0158] <Agitator Conditions>

[0159] Screw speed: 100 rpm

[0160] Temperature setting: 230℃

[0161] Time: 60 minutes

[0162] Atmosphere: Nitrogen

[0163] A: 0.8 < T2 / T1 ≤ 1.2

[0164] B: 0.5≤T2 / T1≤0.8, 1.2<T2 / T1≤1.5

[0165] C: 0.3≤T2 / T1<0.5, 1.5<T2 / T1≤2

[0166] D: T2 / T1 < 0.3, 2 < T2 / T1

[0167] Examples 2-10, 14, and Comparative Examples 1-3

[0168] Except for changing the components constituting the barrier layer (A) and the water-soluble layer (B) as shown in Tables 1 and 2, the same procedure as in Example 1 was followed to prepare EVOH resin composition granules and multilayer structures, and various physical properties were evaluated. It should be noted that in Example 2, as the vinyl alcohol polymer (b2), a substance obtained by blending PVA with a viscosity-average polymerization degree of 600 and a saponification degree of 80 mol% with PVA with a viscosity-average polymerization degree of 800 and a saponification degree of 74 mol% at a weight ratio of 70 / 30 was used. In Example 3, regarding the plasticizer (b3), PEG (molecular weight 1,000, (Dow Chemical Company's "CARBOWAX" 1000)) was used instead of glycerol. In Example 4, regarding the plasticizer (b3), mannitol was used instead of glycerol. In Example 5, regarding the plasticizer (b3), sorbitol was used instead of glycerol. In Example 9, a potassium hydroxide / methanol solution (4% by mass) was used instead of a sodium hydroxide / methanol solution (4% by mass) for the saponification catalyst solution in the PVA saponification process. In Example 10, ethylene-modified PVA (8 mol% ethylene modification) was used instead of PVA. Furthermore, in Comparative Example 1, the water-soluble layer (B) was not provided, resulting in a multilayer structure of a 5-layer co-extruded multilayer cast film with an average layer thickness of (D) / (C) / (A) / (C) / (D) = 50 μm / 5 μm / 5 μm / 5 μm / 50 μm. The results are shown in Tables 1 and 2. Additionally, in Comparative Example 3, severe gelation occurred during film formation, making it impossible to produce a suitable multilayer structure.

[0169] Example 11

[0170] As the barrier layer (A), polyamide 6 / 66 (BASF's "Ultramid C40L") was used. The co-extrusion temperature was varied as shown below. Otherwise, the same procedure as in Example 1 was followed to fabricate multilayer structures and evaluate various physical properties. The results are shown in Table 2.

[0171] Co-extrusion conditions

[0172] Extrusion temperature of barrier layer (A): Supply section / Compression section / Metering section / Die = 200 / 220 / 220 / 220℃

[0173] Extrusion temperature of water-soluble layer (B): Feed section / Compression section / Metering section / Die = 170 / 200 / 200 / 220℃

[0174] Extrusion temperature of adhesive layer (C): Feed section / Compression section / Metering section / Die = 170 / 210 / 210 / 220℃

[0175] Extrusion temperatures for other thermoplastic resin layers (D): Feed section / Compression section / Metering section / Die = 170 / 210 / 210 / 220℃

[0176] Example 12

[0177] As the barrier layer (A), polyamide 12 (UBESTA 3030XA manufactured by Ube Industries, Ltd.) was used. The co-extrusion temperature was varied as shown below. Otherwise, the same procedure as in Example 1 was followed to fabricate a multilayer structure and evaluate various physical properties. The results are shown in Table 2.

[0178] Co-extrusion conditions

[0179] Extrusion temperature of barrier layer (A): Supply section / Compression section / Metering section / Die = 215 / 220 / 220 / 220℃

[0180] Extrusion temperature of water-soluble layer (B): Feed section / Compression section / Metering section / Die = 170 / 200 / 200 / 220℃

[0181] Extrusion temperature of adhesive layer (C): Feed section / Compression section / Metering section / Die = 170 / 220 / 220 / 220℃

[0182] Extrusion temperatures for other thermoplastic resin layers (D): Feed section / Compression section / Metering section / Die = 170 / 220 / 220 / 220℃

[0183] Example 13

[0184] Instead of melt-blending the EVOH resin granules with sodium stearate, the aforementioned EVOH resin granules were used to replace the aforementioned EVOH resin composition granules to form a barrier layer (A). Otherwise, the same procedure as in Example 1 was followed to fabricate a multilayer structure, and various physical properties were evaluated. The results are shown in Table 2.

[0185] Example 15

[0186] Resin was not allowed to flow into the extruder of the adhesive layer (C). Otherwise, the same procedure as in Example 1 was followed to prepare a multilayer structure ((D) / (B) / (A) / (B) / (D)). Other thermoplastic resin layers (D) were removed from the obtained multilayer structure to obtain two types of three-layer multilayer structures ((B) / (A) / (B)). The obtained two types of three-layer multilayer structure films and biaxially stretched polyethylene terephthalate film ("Lumira-P60" manufactured by Toray Industries, Inc., with an average thickness of 12 μm) were cut into A4 size. Dry lamination adhesive was applied to both sides of the multilayer film. Dry lamination was performed with the outer layer being a polyester film and the inner layer being the two types of three-layer multilayer structures. The film was dried at 80°C for 3 minutes to obtain a transparent laminated film containing 7 layers. As the adhesive used for the aforementioned dry lamination, a two-component adhesive (Mitsui Chemicals' "Takeratsuku A-520" and Mitsui Chemicals' "Takeito A-50") was used. The coating weight of this adhesive was set to 4.0 g / m². 2 After lamination, the laminate was cured at 40°C for 3 days to obtain the laminated film. The physical properties of the obtained laminated film were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0187] Example 16

[0188] The procedure was the same as in Example 15, except that the water (W) used in evaluating the separability of the resulting laminate and the viscosity stability of the separated and recovered barrier layer (A) was changed to a 25% by mass sodium chloride aqueous solution (specific gravity 1.20). The membrane that floated after settling was recovered. Otherwise, the procedure was the same as in Example 1, and various physical properties were evaluated. The results are shown in Table 2.

[0189] [Table 1]

[0190]

[0191] [Table 2]

[0192]

[0193] According to the results in Tables 1 and 2, the multilayer structures of each embodiment exhibit excellent interlayer adhesion under high humidity, separation in water, and viscosity stability after separation and recovery. On the other hand, the multilayer structure of Comparative Example 1, which does not have a water-soluble layer (B), shows poor separation in water and poor viscosity stability after separation and recovery. The multilayer structure of Comparative Example 2, which forms a water-soluble layer (B) with low alkali metal ions (b1), exhibits poor interlayer adhesion under high humidity, and its viscosity stability after separation and recovery is also reduced. The multilayer structure of Comparative Example 3, which forms a water-soluble layer (B) with high alkali metal ions (b1), experiences severe gelation during film formation, resulting in an unsuitable multilayer structure. It should be noted that in Example 16, the chloride ion liquid phase barrier layer (A) in water (W) is transferred; therefore, the viscosity stability after recovery can be considered as evaluation B.

[0194] Industrial utilization

[0195] The multilayer structure of the present invention is suitable for use as a food packaging material and other packaging materials. Furthermore, when the separated barrier layers are recycled and reused, a multilayer structure with excellent viscosity stability can be achieved. Therefore, the multilayer structure of the present invention is suitable for use in recycling methods that involve a recycling process in which the layers are separated by exposure to water and reused separately.

Claims

1. A multi-layered structure comprising a barrier layer A, a water-soluble layer B, and an adhesive layer C. An adhesive layer C is laminated on one or both surfaces of the barrier layer A using a water-soluble layer B. Barrier layer A has polyamide or ethylene-vinyl alcohol copolymer a1 as its main component. The water-soluble layer B has a vinyl alcohol polymer b2 as its main component and contains alkali metal ions b1 at a concentration of more than 10 ppm and less than 2000 ppm.

2. The multi-layer structure according to claim 1, wherein, The viscosity-average degree of polymerization of the vinyl alcohol polymer b2 is above 400 and below 2000.

3. The multi-layer structure according to claim 1 or 2, wherein, The degree of saponification of the vinyl alcohol polymer b2 is above 70 mol% and below 95 mol%.

4. The multi-layer structure according to claim 1 or 2, wherein, The total content of vinyl alcohol units and vinyl ester units in vinyl alcohol polymer b2 is more than 95 mol%.

5. The multi-layer structure according to claim 1 or 2, wherein, The alkali metal ion b1 contained in the water-soluble layer B is sodium ion.

6. The multi-layer structure according to claim 1 or 2, wherein, Water-soluble layer B also contains plasticizer b3. The components constituting plasticizer b3 are selected from at least one of glycerol, polyethylene glycol, polypropylene glycol, polyglycerol, mannitol, sorbitol and pentaerythritol.

7. The multi-layer structure according to claim 1 or 2, wherein, The solubility parameter SP of the resin constituting the main component of the barrier layer A A is 11.0 (cal / cm 3 ) 1 / 2 The solubility parameter SP of the resin constituting the main component of the barrier layer A A The solubility parameter SP of the resin constituting the main component of the water-soluble layer B B The ratio SP A / SP B is 0.60 or more and 0.95 or less.

8. The multi-layer structure according to claim 1 or 2, wherein, Barrier layer A has ethylene-vinyl alcohol copolymer as its main component.

9. The multilayer structure according to claim 1 or 2, wherein, Barrier layer A also contains alkali metal ions a2 at a concentration of 50 ppm to 500 ppm.

10. The multilayer structure according to claim 1 or 2, wherein, Barrier layer A also contains higher fatty acids or their salts, which are calculated to be more than 1 ppm and less than 5000 ppm based on higher fatty acid content.

11. The multilayer structure according to claim 1 or 2, wherein, Barrier layer A also contains boron compounds with a concentration of more than 1 ppm and less than 300 ppm in terms of boron element content.

12. The multilayer structure according to claim 1 or 2, wherein, The adhesive layer C has a carboxylic acid-modified polyolefin as its main component.

13. The multilayer structure according to claim 1 or 2, further comprising other thermoplastic resin layers D, The density of other thermoplastic resin layer D is 1.0 g / cm³. 3 the following.

14. The multilayer structure according to claim 1 or 2, wherein, The density of barrier layer A is 1.0 g / cm³. 3 Furthermore, the overall density of the layers excluding barrier layer A and water-soluble layer B is 1.0 g / cm³. 3 the following.

15. Separation methods, wherein, By contacting the multilayer structure according to any one of claims 1 to 14 with water at a temperature of 20°C to 95°C, part or all of the water-soluble layer B is dissolved. The substance X, which contains the barrier layer A, settles in the water, while the substance Y, which contains the adhesive layer C, floats.

16. Reuse methods for multi-layered structures, among which, The substances X and Y recovered by the separation method of claim 15 are each independently melt-formed.

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