Multilayer structure, method for separating the same, and method for recycling it

Abstract

A multilayer structure in which a layer structure (X) and a layer structure (Y) are laminated with a water-soluble layer (A) interposed therebetween, the layer structure (X) being provided with a substrate layer (B) containing at least one selected from the group consisting of thermoplastic resins and metals, the layer structure (Y) being provided with a polyolefin layer (D) or a paper layer, the difference in density (X−Y) between the layer structure (X) and the layer structure (Y) being 0.2 g / cm3 or greater, the oxygen transmission rate (OTR) of at least one of the layer structure (X) and the layer structure (Y) at 20°C and 65% RH as measured in conformance with JIS K7126-2 (uniform pressure method; 2006) being 20 cc / (m2·day·atm) or less, the water-soluble layer (A) containing a hydroxyl-group-containing resin (a1) and alkali metal ions (a2), and the alkali metal ion (a2) content of the water-soluble layer (A) being 10-2000 ppm (inclusive).

Description

Technical Field

[0001] The present invention relates to a multilayer structure excellent in oxygen barrier properties, adhesiveness under high humidity, and peelability in a separation step, a separation method thereof, and a recycling method thereof.

Background Art

[0002] For plastic packaging materials such as food packaging, various materials having various functions such as mechanical properties, heat resistance, gas barrier properties, and heat sealability are laminated and used. For example, polyamide is used to enhance mechanical properties, polyester is used to enhance heat resistance, ethylene-vinyl alcohol copolymer or polyvinylidene chloride is used to enhance gas barrier properties, and various polyolefins such as polyethylene and polypropylene are widely used to enhance heat sealability.

[0003] In recent years, due to environmental problems and waste problems, the demand for so-called post-consumer recycling (hereinafter sometimes simply abbreviated as recycling), which recovers and reuses packaging materials consumed in the market, has been increasing globally. In recycling, a process of crushing and cutting the collected packaging materials, separating, sorting, and washing them as necessary, and then melt-molding them using an extruder and re-pelletizing them as recycled resin is generally adopted. Using the pellets thus obtained, various molded bodies are manufactured.

[0004] As the separation and sorting method, for example, Patent Document 1 describes a separation method including contacting waste with an aqueous liquid selected so that a part of the waste settles, and obtaining a selectate containing 90% by weight or more of a material (waste) having a specific gravity within a previously selected range. Non-Patent Document 1 also describes that in the mutual separation of general-purpose plastics, the addition of a wetting-agent to remove the hydrophobicity of the plastic surface improves the separability when applying the flotation and sedimentation separation method.

[0005] In addition, Patent Document 2 describes that in a packaging film in which at least two base material layers made of different materials are laminated, an intervening layer having solvent solubility provided between the base material layers is dissolved by solvent immersion, so that each base material layer can be easily separated.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0007] [[ID=2s]]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] As described above, various materials are used for plastic packaging materials including food packaging, and many combinations of materials are difficult to recycle as they are. For example, polyesters such as polyethylene terephthalate often have high melting points and are difficult to recycle when mixed with other materials widely used as packaging materials. In addition, chlorine-based resins such as polyvinylidene chloride are difficult to recycle when mixed with other materials widely used as packaging materials due to concerns about their impact on processing equipment and quality deterioration of recycled resins.

[0009] Therefore, it is necessary to interpose a solvent-soluble layer to separate dissimilar materials used as packaging materials. However, the multilayer structure described in Patent Document 2 has insufficient interlayer adhesion under high humidity or insufficient peelability when stirred in solution. In the separation process involving the dissolution of the solvent-soluble layer, it is important that dissimilar materials can be easily separated, but if the solvent solubility is high, the adhesion under high humidity becomes insufficient. Therefore, it is difficult to achieve both interlayer adhesion under high humidity and peelability in the separation process.

[0010] The present invention aims to solve the aforementioned problems, and its objective is to provide a multilayer structure and a method for separating the same that exhibits excellent oxygen barrier properties, interlayer adhesion under high humidity, and peelability in the separation process. Furthermore, it aims to provide a recycling method for independently melt-molding the materials separated in this manner. [Means for solving the problem]

[0011] The aforementioned problem is, [1] A layer structure (X) and a layer structure (Y) are laminated via a water-soluble layer (A), wherein the layer structure (X) comprises a base layer (B) (hereinafter sometimes abbreviated as "base layer (B)") which includes at least one selected from the group consisting of thermoplastic resin and metal, and the layer structure (Y) comprises a polyolefin layer (D) (hereinafter sometimes abbreviated as "PO layer (D)") or a paper layer, and the density difference (XY) between the layer structure (X) and the layer structure (Y) is 0.2 g / cm³. 3 The above conditions are met, and the oxygen permeability rate (OTR) of at least one of the layer structure (X) and the layer structure (Y), measured in accordance with JIS K7126-2 (isobaric method; 2006) at 20°C and 65%RH, is 20 cc / (m³). 2 A multilayer structure having a pH of less than or equal to (day·atm), wherein the water-soluble layer (A) contains a hydroxyl group-containing resin (a1) and alkali metal ions (a2), and the content of alkali metal ions (a2) in the water-soluble layer (A) is 10 ppm or more and 2000 ppm or less; [2] The density of the layer structure (X) is 1.0 g / cm³ 3The above is true, and the density of the layer structure (Y) is 1.0 g / cm³. 3 The following is a multilayer structure of [1]; [3] A multilayer structure of [1] or [2], wherein the hydroxyl group-containing resin (a1) is polyvinyl alcohol (hereinafter sometimes abbreviated as "PVA"); [4] A multilayer structure of [3] wherein the viscosity-average degree of polymerization of the PVA is 400 or more and 2000 or less; [5] A multilayer structure of [3] or [4] wherein the degree of saponification of the PVA is 70 mol% or more and 95 mol% or less; [6] A multilayer structure of any of [3] to [5], wherein the total content of vinyl alcohol units and vinyl ester units in all monomer units of the PVA is 95 mol% or more; [7] A multilayer structure of any of [1] to [6] wherein the water-soluble layer (A) further comprises a plasticizer (a3) ​​(hereinafter sometimes abbreviated as "plasticizer (a3)") selected from the group consisting of glycerin, polyethylene glycol, polypropylene glycol, polyglycerin, mannitol, sorbitol, and pentaerythritol; [8] A multilayer structure of any of [1] to [7] wherein the base layer (B) contains polyester resin as the main component; [9] A multilayer structure of any of [1] to [8], wherein the layer structure (X) comprises an adhesive layer (C) in direct contact with the water-soluble layer (A);

[10] A multilayer structure of any of [1] to [9], wherein the ratio of the mass of the PO layer (D) to the total mass of the layer structure (Y) is 0.90 or more;

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

[10] wherein the layer structure (Y) comprises a barrier layer (E) (hereinafter sometimes abbreviated as "barrier layer (E)") mainly composed of at least one selected from the group consisting of polyamide (hereinafter sometimes abbreviated as "PA") and ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as "EVOH");

[12] A multilayer structure of

[11] wherein the barrier layer (E) contains the EVOH as the main component;

[13] A multilayer structure of any of the [1] to

[12] , in which one of the layers is printed; A method for separating multilayer structures, comprising the step of dissolving part or all of the water-soluble layer (A) by bringing one of the multilayer structures [1] to

[13] into contact with water (W) at 20°C to 95°C, wherein in the dissolution step, the layer structure (X) is made to settle and the layer structure (Y) is made to float in the water (W); A method for recycling a multilayer structure, comprising the step of independently melt-molding the layer structure (X) and the layer structure (Y) recovered by the separation method of the multilayer structure of

[15]

[14] ; This is resolved by providing [the solution]. [Effects of the Invention]

[0012] The present invention provides a multilayer structure with excellent oxygen barrier properties, excellent interlayer adhesion under high humidity conditions, and excellent delamination properties in the separation process, as well as a method for separating the same. Furthermore, it provides a recycling method for independently melt-molding the separated materials. [Modes for carrying out the invention]

[0013] In this specification, "layered structure" means a structure that may be single-layered or multi-layered. Furthermore, "contains as a main component" means that the content exceeds 50% by mass. Also, "water-soluble" means soluble in pure water at 80°C.

[0014] The multilayer structure of the present invention comprises a layer structure (X) and a layer structure (Y) laminated via a water-soluble layer (A), wherein the layer structure (X) comprises a base layer (B) containing at least one selected from the group consisting of thermoplastic resins and metals, the layer structure (Y) comprises a PO layer (D) or a paper layer, and the density difference (XY) between the layer structure (X) and the layer structure (Y) is 0.2 g / cm³. 3 The above conditions are met, and the oxygen permeability rate (OTR) of at least one of the layer structure (X) and the layer structure (Y) at 20°C and 65%RH, as measured in accordance with JIS K7126-2 (isobaric method; 2006), is 20 cc / (m³).2 ·day·atm) or less, the water-soluble layer (A) contains a hydroxyl group-containing resin (a1) and an alkali metal ion (a2), and the content of the alkali metal ion (a2) in the water-soluble layer (A) is 10 ppm or more and 2000 ppm or less, which is a multilayer structure. The density difference (X - Y) between the layer structure (X) and the layer structure (Y) is 0.2 g / cm 3 or more, that is, the density of the layer structure (X) is 0.2 g / cm higher than the density of the layer structure (Y) 3 or more, which tends to result in excellent peelability in the separation process. Here, in the present specification, "peelability in the separation process" means the peelability in the separation process of dissolving a part or all of the water-soluble layer (A) with water (W) described later to separate the layer structure (X) and the layer structure (Y), and specifically, it can be evaluated by the method described in the examples. Further, the OTR of at least one of the layer structure (X) and the layer structure (Y) is 20 cc / (m 2 ·day·atm) or less, which results in excellent oxygen barrier properties, and for example, when the multilayer structure of the present invention is used as a food packaging material, it tends to suppress the deterioration of the contents. Furthermore, the water-soluble layer (A) contains a hydroxyl group-containing resin (a1) and an alkali metal ion (a2), and the content of the alkali metal ion (a2) in the water-soluble layer (A) is 10 ppm or more and 2000 ppm or less, which tends to achieve both good interlayer adhesion under high humidity and peelability in the separation process.

[0015] In the multilayer structure of the present invention, the density difference (X - Y) between the layer structure (X) and the layer structure (Y) is 0.2 g / cm 3 or more. When the density difference is 0.2 g / cm 3If the density difference is less than 0.25 g / cm³, the peelability in the separation process tends to be insufficient. The reason for this is not clear, but it is presumed that the difference in buoyancy caused by the density difference between layer structure (X) and layer structure (Y) in the separation process, combined with the appropriate solubility of the water-soluble layer (A) described later, affects the peelability in the separation process. This finding was only discovered when the properties of the water-soluble layer (A) described later and the density difference (XY) were within an appropriate range. Furthermore, it is presumed that when external forces such as stirring are applied in the separation process, a force in the peeling direction due to the density difference between layer structure (X) and layer structure (Y) acts, affecting the peelability. The density difference (XY) is 0.25 g / cm³. 3 The above is preferable, 0.3 g / cm³ 3 The above is more preferable. The density difference (XY) is 2.0 g / cm³. 3 It may also be less than 1.0 g / cm³. 3 The following is also acceptable. From the viewpoint of separating the layered structure (X) by allowing it to settle and the layered structure (Y) to float during the separation process, it is preferable that the density difference (XY) be within the aforementioned range.

[0016] In the multilayer structure of the present invention, at least one of the layer structure (X) and layer structure (Y) has an OTR of 20 cc / (m³) at 20°C and 65% RH. 2 The OTR is less than or equal to (day·atm). If the OTR of both layer structure (X) and layer structure (Y) is higher than the above, spoilage and deterioration of the contents are more likely to occur. The OTR of at least one of layer structure (X) and layer structure (Y) is 10 cc / (m 2 (day·atm) or less is more preferable, 3cc / (m 2 A value of less than or equal to (day·atm) is even more preferable. The lower limit of the OTR of at least one of the layered structure (X) and layered structure (Y) is 0.01 cc / (m 2 It may also be 0.1cc / (m) 2 It may also be 0.5cc / (m) 2 It may also be (day·atm). OTR is measured in accordance with JIS K7126-2 (isobaric method; 2006), and specifically the method described in the examples is adopted.

[0017] [Layer structure (X)] The layered structure (X) comprises a base layer (B) and has a density of 0.2 g / cm³ compared to the layered structure (Y) described later. 3 The above is larger. The density of the layered structure (X) used in this invention is 1.0 g / cm³. 3 The above is preferable. The density of the layered structure (X) is 1.0 g / cm³. 3 As described above, the layered structure (X) can be settled when the solvent (water (W)) used in the recovery process is water. The density of the layered structure (X) is 1.05 g / cm³. 3 The above is more preferable, 1.10 g / cm³ 3 The above is even more preferable, 1.20 g / cm³ 3 The above is particularly preferable. The density of the layered structure (X) is 3.0 g / cm³. 3 The following may also be acceptable: 2.0 g / cm³ 3 It may also be less than 1.6 g / cm³. 3 The following is also acceptable.

[0018] (Base material layer (B)) The base layer (B) contains at least one selected from the group consisting of thermoplastic resins and metals. Preferably, the base layer (B) is a layer whose main component is at least one selected from the group consisting of thermoplastic resins and metals. The content of at least one selected from the group consisting of thermoplastic resins and metals in the base layer (B) is preferably 80% by mass or more and 100% by mass or less, more preferably 95% by mass or more and 100% by mass or less, and may even be 98% by mass or more and 100% by mass or less.

[0019] If the base layer (B) contains a thermoplastic resin, examples of the thermoplastic resin include polyolefins (polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, copolymer of ethylene and α-olefins having 4 or more carbon atoms, copolymer of polyolefin and maleic anhydride, ethylene-vinyl ester copolymer, ethylene-vinyl alcohol copolymer, ethylene-acrylic acid ester copolymer, or modified polyolefins obtained by grafting these with unsaturated carboxylic acids or their derivatives), polyamides (nylon 6, nylon 66, nylon 6 / 66 copolymer, nylon 11, nylon 12, polymetaxylylene adipamide, etc.), polyester resins (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate, etc. In particular, from the viewpoint of having an excellent balance of heat resistance and mechanical properties and being able to increase the density of the layer structure (X), it is preferable that the base layer (B) mainly contains polyester resin, more preferably that the base layer (B) is polyester resin, and even more preferably that the base layer (B) is polyethylene terephthalate. Furthermore, if the layer structure (Y) includes a paper layer, it is preferable that the base layer (B) includes a polyolefin layer and a barrier layer. The preferred embodiment of the polyolefin described later in the PO layer (D) section is preferably used. Furthermore, the preferred embodiment of the barrier layer described later in the barrier layer (E) section is preferably used.

[0020] The base layer (B) containing a thermoplastic resin may contain various additives, as long as the effects of the present invention are not hindered. Examples of such additives include heat stabilizers, antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, stabilizers, surfactants, desiccants, crosslinking agents, and fiber reinforcing agents. The content of these additives in the base layer (B) is usually 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less.

[0021] If the base layer (B) contains a metal, it is preferable that the base layer (B) contains a metal foil, and may be a layer made of metal foil. Examples of metal foils include at least one metal selected from the group consisting of gold, silver, copper, nickel, stainless steel, magnesium alloy, and aluminum, and aluminum foil is preferred from the viewpoint of economy and gas barrier properties.

[0022] The base layer (B) may consist of a single layer or multiple layers. The average thickness of the base layer (B) may be, for example, 10 μm to 300 μm, 25 μm to 150 μm, or 75 μm to 150 μm. The average thickness of the base layer (B) is the average value of the thicknesses measured at any 10 points on the cross-section using various microscopes, etc. The average thickness of the other layers is also the average value of the thicknesses measured at any 10 points on the cross-section using various microscopes, etc.

[0023] (Inorganic vapor deposited layer (I)) The layered structure (X) has an OTR of 20 cc / (m³) at 20°C and 65% RH. 2 From the viewpoint of keeping the temperature below (day·atm), it is sometimes preferable to have an inorganic vapor-deposited layer (I) on the surface of the base layer (B). The inorganic vapor-deposited layer (I) is a layer made of inorganic materials such as metals and inorganic oxides formed by vapor deposition. The inorganic vapor-deposited layer (I) has good gas barrier properties against oxygen and water vapor. The average thickness of the inorganic vapor-deposited layer (I) is generally less than 500 nm. Having an average thickness of less than 500 nm results in excellent viscosity stability when melt-molding pulverized multilayer structures containing the inorganic vapor-deposited layer (I), suppressing the generation of gels and lumps, and thus tending to have excellent recyclability. The average thickness of the inorganic vapor-deposited layer (I) may be 1 nm or more. From the viewpoint of maintaining high quality of the layer structure (X) after recycling, it is sometimes preferable that the layer structure (X) does not contain the inorganic vapor-deposited layer (I). On the other hand, if the layer structure (X) has high gas barrier properties, it may be easier to monomaterialize the layer structure (Y), and the recyclability of the layer structure (Y) may be improved. In such cases, it is preferable that the layer structure (X) contains the inorganic vapor-deposited layer (I).

[0024] The inorganic vapor-deposited layer (I) is preferably either a metal vapor-deposited layer or an inorganic oxide vapor-deposited layer. A metal vapor-deposited layer is preferred when light-shielding properties are to be provided, while an inorganic oxide vapor-deposited layer is preferred from the viewpoint of visibility of the contents as a packaging material, suitability for the range, and suppression of the generation of gels and lumps when melt-molding crushed material.

[0025] The metal vapor-deposited layer may be an aluminum vapor-deposited layer. The aluminum vapor-deposited layer is a layer containing aluminum as its main component. The aluminum atom content in the metal vapor-deposited layer is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more. The average thickness of the metal vapor-deposited layer is preferably 120 nm or less, more preferably 100 nm or less, and even more preferably 90 nm or less. Furthermore, the average thickness of the metal vapor-deposited layer is preferably 25 nm or more, more preferably 35 nm or more, and even more preferably 45 nm or more. When the substrate layer (B) has a metal vapor-deposited layer, the light transmittance at a wavelength of 600 nm can be set to, for example, 10% or less, and the light shielding properties are excellent.

[0026] The inorganic oxide vapor-deposited layer is a vapor-deposited film of an inorganic oxide, such as an oxide of silicon, aluminum, magnesium, calcium, potassium, tin, sodium, boron, titanium, lead, zirconium, or yttrium, preferably alumina (aluminum oxide) or silica (silicon oxide). The average thickness of the inorganic oxide vapor-deposited layer is preferably 80 nm or less, more preferably 60 nm or less, and even more preferably 50 nm or less. Furthermore, the average thickness of the inorganic oxide vapor-deposited layer is preferably 10 nm or more, more preferably 15 nm or more, and even more preferably 20 nm or more. When the substrate layer (B) has an inorganic oxide vapor-deposited layer, the light transmittance at a wavelength of 600 nm can be set to, for example, 80% or more, resulting in excellent visibility of the contents when used as packaging material.

[0027] The inorganic vapor-deposited layer (I) can be formed by known physical vapor deposition methods or chemical vapor deposition methods. Specifically, examples include vacuum vapor deposition, sputtering, ion plating, ion beam mixing, plasma CVD, laser CVD, MO-CVD, and thermal CVD. Physical vapor deposition methods are preferred, and vacuum vapor deposition is particularly preferred. A protective layer (topcoat layer) may be provided on the inorganic vapor-deposited layer (I) as needed, provided that it does not hinder the effects of the present invention. The upper limit of the surface temperature during film formation of the inorganic vapor-deposited layer (I) is preferably 60°C, more preferably 55°C, and even more preferably 50°C. The lower limit of the surface temperature during film formation of the inorganic vapor-deposited layer (I) is not particularly limited, but is preferably 0°C, more preferably 10°C, and even more preferably 20°C. The film formation surface may be plasma-treated before film formation. Known methods can be used for the plasma treatment, and atmospheric pressure plasma treatment is preferred. In atmospheric pressure plasma treatment, nitrogen, helium, neon, argon, krypton, xenon, radon, etc., are used as discharge gases. Among these, nitrogen, helium, and argon are preferred, and nitrogen is particularly preferred because it can reduce costs.

[0028] (Adhesive layer (C)) The layer structure (X) may include an adhesive layer (C) to enhance interlayer adhesion. When the layer structure (X) includes an adhesive layer (C), it is preferable that the adhesive layer (C) is in direct contact (adjacent) with the water-soluble layer (A) in the multilayer structure of the present invention, from the viewpoint of further enhancing interlayer adhesion under high humidity. That is, by laminating the water-soluble layer (A) to the substrate layer (B) via the adhesive layer (C), interlayer adhesion is improved, the quality as a packaging material, etc., is improved, and interlayer adhesion under high humidity is also improved. In the multilayer structure of the present invention, it is preferable that the water-soluble layer (A), adhesive layer (C), and substrate layer (B) are directly laminated in this order. It is also preferable that the water-soluble layer (A), adhesive layer (C), inorganic vapor-deposited layer (I), and substrate layer (B) are directly laminated in this order. The average thickness of the adhesive layer (C) is preferably 10 nm to 25 μm, and more preferably 20 nm to 15 μm. For example, if the adhesive layer (C) is mainly composed of an adhesive resin as described later, the average thickness of the adhesive layer (C) may be, for example, 0.5 μm to 25 μm, or 1 μm to 15 μm. If the adhesive layer (C) is formed from an anchor coating agent or an adhesive other than an adhesive resin as described later, the average thickness of the adhesive layer (C) may be, for example, 10 nm to 1 μm, or 20 nm to 200 nm.

[0029] The adhesive layer (C) preferably has an adhesive resin as its main component, such as a carboxylic acid-modified polyolefin or a carboxylic acid-modified polyester, and more preferably consists of an adhesive resin. Examples of carboxylic acid-modified polyolefins include modified olefin polymers containing carboxyl groups, obtained by chemically bonding an unsaturated carboxylic acid or its anhydride to an olefin polymer by addition reaction or graft reaction. 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., with maleic anhydride being particularly preferred. Specifically, one or more mixtures selected from the group consisting of maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, maleic anhydride-grafted ethylene-propylene copolymer, maleic anhydride-grafted ethylene-ethyl acrylate copolymer, maleic anhydride-grafted ethylene-vinyl acetate copolymer, etc., are preferred. The amount of ethylenically unsaturated carboxylic acid or its anhydride added to or grafted (degree of modification) onto the olefin polymer is 0.01 to 15% by mass, preferably 0.02 to 10% by mass, relative to the olefin polymer. Adding rubber / elastomer components such as polyisobutylene or ethylene-propylene rubber, or a polyolefin resin different from the base polyolefin resin of the adhesive resin, to the adhesive resin may improve its adhesion.

[0030] The adhesive layer (C) can also be formed by treating it with a known anchor coating agent or by applying a known adhesive. A two-component reactive polyurethane adhesive, which involves mixing and reacting a polyisocyanate component and a polyol component, is preferred as the anchor coating agent or adhesive. Furthermore, the adhesion can sometimes be further enhanced by adding a small amount of additive, such as a known silane coupling agent, to the anchor coating agent or adhesive. The silane coupling agent is not particularly limited, but examples include silane coupling agents having reactive groups such as isocyanate groups, epoxy groups, amino groups, ureido groups, and mercapto groups.

[0031] (Layer structure of layered structure (X)) The layer structure (X) may consist only of a base layer (B), or only of a base layer (B) and an inorganic vapor-deposited layer (I), or only of a base layer (B) and an adhesive layer (C), or only of a base layer (B), an inorganic vapor-deposited layer (I), and an adhesive layer (C). The layer structure (X) may also have other layers besides the base layer (B), the inorganic vapor-deposited layer (I), and the adhesive layer (C). From the viewpoint of being able to impart various functions such as heat resistance, mechanical properties, and gas barrier properties as required depending on the type of base layer (B), it is preferable that the layer structure (X) has a base layer (B) as at least one of its outermost layers. From a similar viewpoint, it is preferable that the multilayer structure of the present invention has a base layer (B) as one of its outermost layers.

[0032] The layer structure (X) may consist of a single layer or multiple layers. If the layer structure (X) is a multilayer structure, the number of layers is preferably 2 to 6 from the viewpoint of economically providing functions such as gas barrier properties and adhesive properties. Furthermore, the average thickness of the layer structure (X) is preferably 10 μm to 300 μm, more preferably 25 μm to 150 μm, and may be 75 μm to 150 μm, from the viewpoint of handling and resource conservation as a packaging material. Suitable configurations of the layer structure (X) include, for example, polyethylene terephthalate layer (hereinafter sometimes abbreviated as "PET layer"), PET layer / inorganic vapor-deposited layer (I), PET layer / adhesive layer (C), PET layer / inorganic vapor-deposited layer (I) / adhesive layer (C), PET layer / adhesive layer (C) / aluminum foil layer, PET layer / adhesive layer (C) / aluminum foil layer / adhesive layer (C), aluminum foil layer, aluminum foil layer / adhesive layer (C), etc. When the layer structure (Y) includes a paper layer, suitable configurations for the layer structure (X) include, for example, a polyolefin layer (hereinafter sometimes abbreviated as "PO layer"), a PO layer / adhesive layer (C), a PO layer / adhesive layer (C) / barrier layer, a PO layer / adhesive layer (C) / barrier layer / adhesive layer (C), a PO layer / adhesive layer (C) / barrier layer / adhesive layer (C) / PO layer, a PO layer / adhesive layer (C) / barrier layer / adhesive layer (C) / PO layer / adhesive layer (C), etc. In the layer configuration of the example layer structure (X), the "PET layer," "aluminum foil layer," "PO layer," and "barrier layer" correspond to the base layer (B).

[0033] [Layer structure (Y)] The layered structure (Y) comprises a PO layer (D) or a paper layer, and has a density of 0.2 g / cm³ higher than the layered structure (X). 3 The above is small. The layered structure (Y) preferably comprises a PO layer (D). The density of the layered structure (Y) is 1.0 g / cm³. 3 Preferably, the following conditions apply: The density of the layered structure (Y) is 1.0 g / cm³. 3 The following conditions must be met to allow the layered structure (Y) to suspend when the solvent (water (W)) used in the recovery process is water. The density of the layered structure (Y) is 0.98 g / cm³. 3 The following is more preferable: 0.95 g / cm³ 3The following is even more preferable: The density of the layered structure (Y) is 0.8 g / cm³. 3 It may be greater than or equal to 0.85 g / cm³. 3 It may be greater than or equal to 0.90 g / cm³. 3 That's fine too.

[0034] (PO layer(D)) The PO layer (D) is typically a layer mainly composed of polyolefin. Since polyolefin is a resin with excellent recyclability, the layer structure (Y) can be made recyclable after the separation process by including the PO layer (D). The polyolefin constituting the PO layer (D) is not particularly limited and includes linear low-density polyethylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, vinyl ester resin, ethylene-propylene copolymer, ethylene-α-olefin copolymer (α-olefin with 4 to 20 carbon atoms), polypropylene, propylene-α-olefin copolymer (α-olefin with 4 to 20 carbon atoms), polybutene, polypentene, and other olefins alone or copolymers thereof. Among these, at least one selected from the group consisting of linear low-density polyethylene, low-density polyethylene, and polypropylene is preferred from the viewpoint of melt moldability, separability, and economic efficiency.

[0035] The PO layer (D) may contain additives. Examples of additives include heat stabilizers, antioxidants, UV absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, stabilizers, surfactants, crosslinking agents, and fiber reinforcing agents. In particular, it is preferable to include at least one selected from the group consisting of antioxidants, UV absorbers, and colorants. It is preferable that the PO layer (D) is a layer in which the resin constituting the PO layer (D) is composed solely of polyolefins. The proportion of polyolefins in the PO layer (D) may be 80% by mass or more, 90% by mass or more, 95% by mass or more, or 99% by mass or more.

[0036] From the viewpoint of providing heat-sealability to the resulting multilayer structure, it is preferable that the layer structure (Y) has a PO layer (D) as its outermost layer. Similarly, it is preferable that the multilayer structure of the present invention has a PO layer (D) as one of its outermost layers.

[0037] The average thickness of one PO layer (D) is preferably 1 μm to 100 μm, and more preferably 5 μm to 50 μm.

[0038] (paper layer) The layered structure (Y) includes a paper layer, which reduces the weight of the multilayer structure and thus lowers the transportation costs of the packaging material. The paper layer is not particularly limited and can be made from various types of paper, such as natural paper, synthetic paper, kraft paper, fine paper, imitation paper, glassine paper, parchment paper, synthetic paper, white cardboard, Manila cardboard, milk carton base paper, cup base paper, ivory paper, silver paper, etc.

[0039] (Barrier layer (E)) The layered structure (Y) has an OTR of 20 cc / (m³) at 20°C and 65% RH. 2 From the viewpoint of keeping the oxygen barrier properties below (day·atm), it is preferable to include a barrier layer (E) mainly composed of at least one selected from the group consisting of PA and EVOH. Having a barrier layer (E) mainly composed of polyamide or EVOH improves the oxygen barrier properties of the multilayer structure. Furthermore, from the viewpoint of recyclability after the separation process, EVOH is more preferable as the main component constituting the barrier layer (E).

[0040] Examples of PAs include polycaproamide (nylon 6), poly-ω-aminoheptanoic acid (nylon 7), poly-ω-aminononanoic acid (nylon 9), polyundecaneamide (nylon 11), polylauryl lactam (nylon 12), polyethylenediamine adipamide (nylon 26), polytetramethylene adipamide (nylon 46), polyhexamethylene adipamide (nylon 66), polyhexamethylene sevacamide (nylon 610), polyhexamethylene dodecamide (nylon 612), and polyoctamethylene. Nylon adipamide (Nylon 86), Polydecamethylene adipamide (Nylon 106), Caprolactam / Lauryl Lactam Copolymer (Nylon 6 / 12), Caprolactam / ω-Aminonanoic Acid Copolymer (Nylon 6 / 9), Caprolactam / Hexamethylenediammonium Adipate Copolymer (Nylon 6 / 66), Lauryl Lactam / Hexamethylenediammonium Adipate Copolymer (Nylon 12 / 66), Ethylenediammonium Adipate / Hexamethylenediammonium Adipate Copolymer (Nylon 26 / 66), Caprolactam / Hexamethylenediammonium adipate / Hexamethylenediammonium sebacate copolymer (Nylon 6 / 66 / 610), Ethylenediammonium adipate / Hexamethylenediammonium adipate / Hexamethylenediammonium sebacate copolymer (Nylon 26 / 66 / 610), Polyhexamethylene isophthalamide (Nylon 6I), Polyhexamethylene terephthalamide (Nylon 6T), Hexamethylene isophthalamide / Hexamethylene terephthalamide Examples include nylon 6I / 6T copolymers, 11-aminoundecaneamide / hexamethylene terephthalamide copolymers, metaxylenediamine / adipic acid copolymers (nylon MXD6), polynonamethylene terephthalamide (nylon 9T), polydecamethylene terephthalamide (nylon 10T), polyhexamethylene cyclohexylamide, polynonamethylene cyclohexylamide, or these polyamides modified with aromatic amines such as methylenebenzylamine and metaxylenediamine. Modified polyamides such as metaxylylenediammonium adipate are also examples.In particular, PA is preferably nylon 6 / 66 or nylon 6 because it is superior in terms of economy, melt moldability, and mechanical properties. Furthermore, from the viewpoint of gas barrier properties, aromatic polyamides (polyamides having monomer units with aromatic rings or polyamides modified with a modifying agent having aromatic rings) are preferred, and nylon MXD6 is more preferred.

[0041] If the barrier layer (E) contains PA, the barrier layer (E) may also contain other additives besides PA, as long as the effects of the present invention are not hindered. Examples of such other additives include resins other than PA, heat stabilizers, antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, stabilizers, surfactants, desiccants, crosslinking agents, and fiber reinforcing agents. The content of other additives in the barrier layer (E) is usually 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less.

[0042] The ethylene content of EVOH is 20 mol% or more, preferably 25 mol% or more. When the ethylene content of EVOH is 20 mol% or more, the flexibility and thermoformability of the resin composition of the layer structure (Y) are improved, and the thermoformability of the resulting multilayer structure is improved. Furthermore, the ethylene content is preferably 55 mol% or less, and more preferably 50 mol% or less. When the ethylene content of EVOH is 55 mol% or less, the gas barrier properties are improved.

[0043] The degree of saponification of EVOH is preferably 95 mol% or higher, more preferably 98 mol% or higher, and even more preferably 99 mol% or higher, from the viewpoint of gas barrier properties and thermal stability. The degree of saponification of EVOH may be 100 mol% or lower.

[0044] The melt flow rate (MFR) of EVOH at 210°C under a 2160g load is preferably 0.1g / 10 min to 50g / 10 min from the viewpoint of melt moldability and extrusion moldability. The MFR is more preferably 0.5g / 10 min or more, and even more preferably 1g / 10 min or more. Furthermore, the MFR is more preferably 20g / 10 min or less, and even more preferably 10g / 10 min or less.

[0045] EVOH may have units derived from monomers other than ethylene, vinyl esters, and their saponifies, to the extent that the objectives of the present invention are not hindered. When EVOH has the aforementioned other monomer units, the content of each of these other monomer units relative to the total monomer units of EVOH is preferably 30 mol% or less, more preferably 20 mol% or less, even more preferably 10 mol% or less, and particularly preferably 5 mol% or less. Furthermore, when EVOH has units derived from the aforementioned other monomers, the lower limit may be 0.05 mol% or 0.10 mol%. Other monomers include, for example, alkenes such as propylene, butylene, pentene, and hexene; 3-acyloxy-1-propene, 3-acyloxy-1-butene, 4-acyloxy-1-butene, 3,4-diasiloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4-acyloxy-2-methyl-1-butene, and 4-acyloxy-3-methyl -1-butene, 3,4-diasiloxy-2-methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, 4,5-diasiloxy-1-pentene, 4-acyloxy-1-hexene, 5-acyloxy-1-hexene, 6-acyloxy-1-hexene, 5,6-diasiloxy-1-hexene, 1,3-diacetoxy-2-methyl Examples include alkenes having ester groups such as npropane or their saponides; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, and itaconic acid, or their anhydrides, salts, or mono- or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid, or their salts; vinylsilane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxy-ethoxy)silane, and γ-methacryloxypropylmethoxysilane; alkyl vinyl ethers, vinyl ketones, N-vinylpyrrolidone, vinyl chloride, and vinylidene chloride.

[0046] EVOH may be post-modified by methods such as urethaneization, acetalization, cyanoethylation, or oxyalkyleneization.

[0047] EVOH can be used alone or in combination of two or more types.

[0048] If the barrier layer (E) contains EVOH, the barrier layer (E) may also contain other additives other than EVOH, as long as the effects of the present invention are not hindered. Examples of such other additives include antiblocking agents, processing aids, resins other than EVOH, carboxylic acid compounds, phosphoric acid compounds, boron compounds, metal salts, stabilizers, antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, surfactants, desiccants, crosslinking agents, and reinforcing agents such as various fibers.

[0049] Other resins used as additives besides PA or EVOH are not particularly limited and include thermoplastic resins such as polyolefins, polyesters, polystyrenes, polyvinyl chlorides, acrylic resins, polyurethanes, polycarbonates, and polyvinyl acetates.

[0050] When the barrier layer (E) contains PA and EVOH, the proportion of PA and EVOH in the resin constituting the barrier layer (E) is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more. When the barrier layer (E) contains PA and EVOH, the proportion of PA and EVOH in the barrier layer (E) is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more. Furthermore, when the barrier layer (E) contains PA, the proportion of PA in the resin constituting the barrier layer (E) is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more. If the barrier layer (E) contains PA, the proportion of PA in the barrier layer (E) is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more. Furthermore, if the barrier layer (E) contains EVOH, the proportion of EVOH in the resin constituting the barrier layer (E) is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more. If the barrier layer (E) contains EVOH, the proportion of EVOH in the barrier layer (E) is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more.

[0051] The average thickness of each layer of the barrier layer (E) is preferably 0.5 μm or more and 10 μm or less, and more preferably 1 μm or more and 5 μm or less.

[0052] (Other layers) The layer structure (Y) may include the adhesive layer (C) described above. If the layer structure (Y) includes the adhesive layer (C), the adhesive layer (C) may be laminated between the PO layer (D) or paper layer and the barrier layer (E), or it may be laminated between the PO layer (D), paper layer or barrier layer (E) and other layers described later, or it may be in contact with the water-soluble layer (A). A configuration in which the layer structure (Y) includes the adhesive layer (C) and the PO layer (D) or paper layer and other layers (water-soluble layer (A), barrier layer (E) or other layers) are laminated via the adhesive layer (C), or a configuration in which the layer structure (Y) includes the adhesive layer (C) and layers other than the PO layer (D) or paper layer and the water-soluble layer (A) are laminated via the adhesive layer (C), etc., are also preferred embodiments. When the layer structure (Y) includes the adhesive layer (C), the interlayer adhesion under high humidity conditions may be further improved.

[0053] The layer structure (Y) may include layers other than the adhesive layer (C), PO layer (D), paper layer, and barrier layer (E). The layer structure (Y) can be given desired performance by including the other layers. On the other hand, from the viewpoint of recyclability, it may be preferable that the layer structure (Y) does not have the other layers. Examples of the other layers include an inorganic vapor deposition layer (I); metal foil such as gold, silver, copper, nickel, stainless steel, magnesium alloy, and aluminum; polyester resin layers such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; and layers such as polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, and polyacrylate.

[0054] (Layer structure (Y) layer configuration, etc.) The ratio of the mass of the PO layer (D) to the total mass of the layer structure (Y) (D / Y) is preferably 0.90 or greater. When the mass ratio is within the above range, the recyclability of the layer structure (Y) after the multilayer structure of the present invention is separated into layer structure (X) and layer structure (Y) by the separation process described later is improved. The mass ratio (D / Y) may be 1.00 or less, or 0.99 or less.

[0055] The layered structure (Y) may consist of a single layer or multiple layers. If the layered structure (Y) is a multilayer structure, the number of layers is preferably 2 to 7 from the viewpoint of economically providing functions such as gas barrier properties, adhesive properties, and heat sealability. Furthermore, the average thickness of the layered structure (Y) is preferably 10 μm to 500 μm from the viewpoint of handling as a packaging material and resource conservation.

[0056] Examples of the layer configuration of the layered structure (Y) include a PO layer (D), adhesive layer (C) / PO layer (D), barrier layer (E) / adhesive layer (C) / PO layer (D), adhesive layer (C) / barrier layer (E) / adhesive layer (C) / PO layer (D), PO layer (D) / adhesive layer (C) / barrier layer (E) / adhesive layer (C) / PO layer (D), adhesive layer (C) / PO layer (D) / adhesive layer (C) / barrier layer (E) / adhesive layer (C) / PO layer (D), paper layer, adhesive layer (C) / paper layer, and so on.

[0057] [Water-soluble layer (A)] The water-soluble layer (A) contains a hydroxyl group-containing resin (a1) and alkali metal ions (a2), with the alkali metal ion (a2) content in the water-soluble layer (A) being between 10 ppm and 2000 ppm. The water-soluble layer (A) having the above configuration allows it to exhibit interlayer adhesion under high humidity conditions while also exhibiting good peelability in the separation process. The reason for this is unclear, but it is presumed to be due to the efficient attraction of water via the alkali metal ions (a2) and its high solubility in water. Because the water-soluble layer (A) has such properties, the density difference (XY) is 0.2 g / cm³. 3 It is presumed that when the above conditions are met, an unpredictable and advantageous effect of good peelability can be achieved. The water-soluble layer (A) is usually a layer in which some or all of the main components that make up the layer dissolve in water (W), and may also be a layer in which some or all of the main components that make up the layer dissolve when brought into contact with water (W) at 20°C to 95°C.

[0058] (Hydroxygroup-containing resin (a1)) The water-soluble layer (A) contains a hydroxyl group-containing resin (a1). It is preferable that the water-soluble layer (A) mainly contains a hydroxyl group-containing resin (a1). A hydroxyl group-containing resin (a1) means a resin that contains hydroxyl groups. From the viewpoint of improving solubility in water (W), as described later, the proportion of monomer units having hydroxyl groups in the total monomer units of the hydroxyl group-containing resin (a1) is preferably 80 mol% or more, more preferably 85 mol% or more, and may be 90 mol% or more or 95 mol% or more. On the other hand, the proportion of monomer units having hydroxyl groups in the total monomer units of the hydroxyl group-containing resin (a1) may be 100 mol% or less, or 99 mol% or less.

[0059] Examples of hydroxyl group-containing resins (a1) include starch-based components such as corn starch and their polymer components, cellulosic polymers such as carboxymethylcellulose and carboxyethylcellulose, acrylic acid polymers such as sodium polyacrylate, and PVA. Among these, PVA is preferred from the viewpoint of melt moldability and adhesion to the barrier layer (E). By having PVA as the main component, the gas barrier properties of the multilayer structure under high humidity and the peelability in the separation process are improved. Note that EVOH means that the ethylene unit content is 20 mol% or more, and PVA means that it has vinyl alcohol units and the ethylene unit content is less than 20 mol%.

[0060] The viscosity-average degree of polymerization of PVA is preferably 400 or more and 2000 or less. The lower limit of the viscosity-average degree of polymerization is more preferably 500, and even more preferably 700. When the viscosity-average degree of polymerization is 400 or more, the adhesion and thermal stability of the PVA are improved. The upper limit of the viscosity-average degree of polymerization is more preferably 1500, and even more preferably 1000. When the viscosity-average degree of polymerization is 2000 or less, the melt moldability of the PVA is improved.

[0061] The viscosity-average degree of polymerization of PVA is measured in accordance with JIS K6726 (1994). Specifically, the intrinsic viscosity [η] (liters / g) of PVA is measured in water at 30°C, and the viscosity-average degree of polymerization P is calculated using the following formula based on this intrinsic viscosity [η] value. If the degree of saponification of PVA is less than 99.5 mol%, the intrinsic viscosity [η] is measured after saponification until the degree of saponification reaches 99.5 mol% or higher. P = ([η] × 10 4 (8.29) (1 / 0.62)

[0062] The degree of saponification of PVA is preferably 70 mol% or more, more preferably 75 mol%, and more preferably 85 mol% or more. When the degree of saponification is 70 mol% or more, the water solubility of PVA is excellent, and the peelability in the separation process of the multilayer structure is improved. The degree of saponification of PVA is preferably 95 mol% or less, more preferably 93 mol% or less, and even more preferably 90 mol% or less. When the degree of saponification is 95 mol% or less, the melt moldability of PVA is excellent. The degree of saponification of PVA is measured in accordance with JIS K6726 (1994).

[0063] The total content of vinyl alcohol units and vinyl ester units in all monomer units constituting PVA is preferably 95 mol% or more. When the total content is 95 mol% or more, the solubility of PVA in water is further improved, and as a result, the separability of the multilayer structure is further 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.

[0064] PVA may contain monomer units other than vinyl alcohol units and vinyl ester units, as long as the effects of the present invention are not impaired. Such monomers include ethylene units, α-olefins such as propylene, n-butene, and isobutylene; acrylic acid and its salts; acrylic acid esters; methacrylic acid and its salts; methacrylic acid esters; acrylamide; acrylamide derivatives such as N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts or quaternary salts, N-methylolacrylamide and its derivatives; methacrylamide; methacrylamide derivatives such as N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamidopropyldimethylamine and its salts or quaternary salts, N-methylolmethacrylamide and its derivatives; Examples include vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and fumaric acid, and their salts or esters; vinylsilyl compounds such as vinyltrimethoxysilane; and isopropenyl acetate. The content of these monomers varies depending on the purpose and application, but is preferably 10 mol% or less, more preferably less than 5 mol%, even more preferably less than 1 mol%, particularly preferably less than 0.5 mol%, and may be 0 mol%. PVA may be used alone or in combination of two or more types.

[0065] (Alkali metal ions (a2)) The water-soluble layer (A) contains alkali metal ions (a2) in an amount of 10 ppm to 2000 ppm. When the alkali metal ion (a2) content is within the above range, it exhibits excellent adhesion under high humidity and excellent peelability in the separation process. If the alkali metal ion (a2) content is less than 10 ppm, water does not penetrate sufficiently into the water-soluble layer (A) during the separation process, resulting in insufficient water solubility of the water-soluble layer (A), and consequently, reduced peelability in the separation process. The alkali metal ion (a2) content is more preferably 100 ppm or more, even more preferably 200 ppm or more, and particularly preferably 500 ppm or more. On the other hand, if the alkali metal ion (a2) content exceeds 2000 ppm, water penetrates the water-soluble layer (A) severely under high humidity, which may reduce adhesion under high humidity. The alkali metal ion (a2) content is more preferably 1500 ppm or less, even more preferably 1200 ppm or less, and particularly preferably 1000 ppm or less.

[0066] Examples of alkali metal ions (a2) contained in the water-soluble layer (A) include lithium ions, sodium ions, and potassium ions. From the viewpoint of the hue and viscosity stability of the resin composition, sodium ions are preferred.

[0067] The alkali metal ions (a2) contained in the water-soluble layer (A) of the present invention may exist in a state dissociated from the anions constituting the alkali metal salt, or they may exist in a state of salt bonded to the anions. Alternatively, they may exist in a state coordinated to groups (e.g., carboxyl groups, hydroxyl groups, etc.) of a hydroxyl group-containing resin (a1) such as PVA or other optional components.

[0068] Alkali metal ions (a2) are usually derived from salts, but the components that make up alkali metal ions (a2) are not particularly limited, and fatty acid metal salts, metal salts other than fatty acid metal salts (nitrates, sulfates, etc.) can also be used.

[0069] The fatty acid metal salt may be a higher fatty acid metal salt having 12 or more carbon atoms, or a fatty acid metal salt having 11 or fewer carbon atoms, but an aliphatic metal salt having 11 or fewer carbon atoms is preferred from the viewpoint of solubility in water (W) of the water-soluble layer (A). Examples of higher fatty acid metal salts having 12 or more carbon atoms include metal salts of fatty acids such as lauric acid, lauric acid, tridecyl acid, myristic acid, pentadecyl acid, palmitic acid, heptadecyl acid, stearic acid, basic stearic acid, hydroxystearic acid, basic hydroxystearic acid, nonadecanoic acid, oleic acid, behenic acid, montanic acid, and linoleic acid. Examples of fatty acid metal salts having 11 or fewer carbon atoms include acetate and propionate. From the viewpoint of dispersibility in PVA, one or more of these may be used as appropriate.

[0070] The water-soluble layer (A) preferably further contains a plasticizer (a3). The inclusion of a plasticizer (a3) ​​improves the melt-moldability and solubility in water (W) of the hydroxyl group-containing resin (a1) such as PVA. The molecular weight of the plasticizer (a3) ​​is not particularly limited, but from the viewpoint of release properties, 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. The content of the plasticizer (a3) ​​is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more. The content of the plasticizer (a3) ​​is preferably 45% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less. The components constituting the plasticizer (a3) ​​are preferably at least one selected from the group consisting of glycerin, polyethylene glycol, polypropylene glycol, polyglycerin, mannitol, sorbitol, and pentaerythritol, more preferably at least one selected from the group consisting of glycerin, polyethylene glycol, mannitol, and sorbitol, and particularly preferably at least one selected from the group consisting of glycerin, mannitol, and sorbitol.

[0071] The water-soluble layer (A) may contain other components besides the hydroxyl group-containing resin (a1), alkali metal ions (a2), and plasticizer (a3), as long as the effects of the present invention are not hindered. Examples of other components include polyvalent metal ions, carboxylic acids, phosphoric acid compounds, oxidation accelerators, antioxidants, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, fillers, pigments, dyes, processing aids, flame retardants, and antifogging agents. The content of other components in the water-soluble layer (A) is usually 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less.

[0072] The proportion of hydroxyl group-containing resin (a1) in the water-soluble layer (A) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and may also be 95% by mass or more, 97% by mass or more, 98% by mass or more, or 99% by mass or more. Furthermore, the proportion of hydroxyl group-containing resin (a1) in the total resin constituting the water-soluble layer (A) is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more, and the total resin constituting the water-soluble layer (A) may consist substantially of only hydroxyl group-containing resin (a1). In the water-soluble layer (A), the proportion of hydroxyl group-containing resin (a1) and alkali metal ions (a2) is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more. The water-soluble layer (A) may be substantially composed only of hydroxyl group-containing resin (a1) and alkali metal ions (a2). In the water-soluble layer (A), the proportion of hydroxyl group-containing resin (a1) and alkali metal ions (a2) may be 100% by mass or less, or 99% by mass or less. Furthermore, if the water-soluble layer (A) contains a plasticizer (a3), the proportion of hydroxyl group-containing resin (a1), alkali metal ions (a2), and plasticizer (a3) ​​in the water-soluble layer (A) is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more. The water-soluble layer (A) may be substantially composed only of hydroxyl group-containing resin (a1), alkali metal ions (a2), and plasticizer (a3). The proportion of hydroxyl group-containing resin (a1), alkali metal ions (a2), and plasticizer (a3) ​​in the water-soluble layer (A) may be 100% by mass or less.

[0073] The average thickness of one layer of the water-soluble layer (A) is preferably 1 μm to 20 μm, more preferably 2 μm to 10 μm, and in some cases even more preferably 3 μm to 8 μm.

[0074] The method for preparing the resin composition constituting the water-soluble layer (A) is not particularly limited, and any method is acceptable as long as it allows for the uniform mixing of a hydroxyl group-containing resin (a1), alkali metal ions (a2), and optionally a plasticizer (a3) ​​and other components. For example, it can be prepared by blending a hydroxyl group-containing resin (a1), alkali metal ions (a2), and optionally a plasticizer (a3) ​​and other components, then melt-kneading and pelletizing them; by separately adding the hydroxyl group-containing resin (a1), alkali metal ions (a2), and optionally a plasticizer (a3) ​​and other components in a fixed proportion to a melt-kneading machine and then kneading and pelletizing them; by first introducing alkali metal ions (a2) into the hydroxyl group-containing resin (a1), then blending in optionally a plasticizer (a3) ​​and other components, and then melt-kneading and pelletizing them; or by first introducing alkali metal ions (a2) into the hydroxyl group-containing resin (a1), and then separately adding these, along with optionally a plasticizer (a3) ​​and other components in a fixed proportion to a melt-kneading machine and then kneading and pelletizing them.

[0075] [Multilayer structure] In the multilayer structure of the present invention, printing may be applied to any of the layers. The printing may be applied to any of the layers constituting the layer structure (X), the layers constituting the layer structure (Y), or the water-soluble layer (A). Printing may be applied to two or more layers. If printing is applied, the transparency of the molded article obtained by recycling the multilayer structure of the present invention may decrease. Therefore, if transparency is required for the molded article obtained by recycling, it is preferable that no printing is applied. More specifically, if high transparency is required for the molded article obtained by recycling the layer structure (X), but high transparency is not required for the molded article obtained by recycling the layer structure (Y), it is preferable that the printing be applied to the layers constituting the layer structure (Y) or the water-soluble layer (A). That is, from the viewpoint of the recyclability of the layer structure (X), it is preferable that the printing be applied to the layers constituting the layer structure (Y) or the water-soluble layer (A). Furthermore, from the viewpoint of the recyclability of both the layer structure (X) and the layer structure (Y), it is preferable that the printing be applied to the water-soluble layer (A). The printing is formed by directly printing known inks onto a layer constituting a layer structure (X), a layer constituting a layer structure (Y), or a water-soluble layer (A) using a known printing method.

[0076] The multilayer structure of the present invention is formed by laminating layer structure (X) and layer structure (Y) via a water-soluble layer (A). In this case, layer structure (X) and layer structure (Y) may each be a single layer, or they may be a multilayer structure consisting of multiple layers. The water-soluble layer (A) may be directly laminated onto the base layer (B), or the water-soluble layer (A) may be laminated onto the base layer (B) via an adhesive layer (C). The water-soluble layer (A), adhesive layer (C), and base layer (B) may each be manufactured in separate processes and then laminated in a subsequent process such as dry lamination, or they may be laminated sequentially by a solution coating method, or some or all of them may be manufactured simultaneously by a co-extrusion molding method. The molding temperature during melt molding in co-extrusion molding is often selected from the range of 150 to 300°C.

[0077] As a method for laminating the multilayer structure of the present invention, for example, a water-soluble layer (A) is first laminated onto a base layer (B) by a solution coating method, and a layer structure (Y') [PO layer (D) / adhesive resin layer (adhesive layer (C)) / barrier layer (E) / adhesive resin layer (adhesive layer (C)) / PO layer (D), etc.] separately produced by co-extrusion is dry laminated thereon using a known adhesive (such as the adhesive listed for adhesive layer (C)). Note that layer structure (Y') refers to layer structure (Y) before the adhesive layer (C) for dry lamination is provided. That is, in the multilayer structure obtained in the above example, layer structure (X) consists of a base layer (B), and layer structure (Y) consists of a layer configuration of adhesive layer (C) / PO layer (D) / adhesive layer (C) / barrier layer (E) / adhesive layer (C) / PO layer (D).

[0078] From the viewpoint of economically providing functions such as gas barrier properties and mechanical properties, the number of layers in the multilayer structure is preferably 3 to 11. Furthermore, from the viewpoint of handling and resource conservation as a packaging material, the average thickness of the multilayer structure is preferably 20 μm to 500 μm, more preferably 30 μm to 200 μm, and may also be 75 μm to 160 μm.

[0079] The following are examples of the layer configurations of the multilayer structure of the present invention. In this specification, " / " indicates direct lamination, and " / / " indicates direct lamination or lamination via an adhesive layer (C). Furthermore, it is preferable that " / / " is laminated via an adhesive layer (C). In addition, each layer may consist of multiple layers or may include other layers. PET layer / / Water-soluble layer (A) / / PO layer (D) / / Barrier layer (E) / / PO layer (D) PET layer / / Water-soluble layer (A) / / Barrier layer (E) / / PO layer (D) PET layer / Inorganic vapor-deposited layer (I) / / Water-soluble layer (A) / / PO layer (D) / / Barrier layer (E) / / PO layer (D) PET layer / Inorganic vapor-deposited layer (I) / / Water-soluble layer (A) / / Barrier layer (E) / / PO layer (D) ·PET layer / Inorganic vapor deposited layer (I) / / Water-soluble layer (A) / / PO layer (D) PET layer / / Aluminum foil layer / / Water-soluble layer (A) / / PO layer (D) / / Barrier layer (E) / / PO layer (D) PET layer / / Aluminum foil layer / / Water-soluble layer (A) / / Barrier layer (E) / / PO layer (D) • PET layer / / Aluminum foil layer / / Water-soluble layer (A) / / PO layer (D) PET layer / / Water-soluble layer (A) / / Aluminum foil layer / / PO layer (D) / / Barrier layer (E) / / PO layer (D) PET layer / / Water-soluble layer (A) / / Aluminum foil layer / / Barrier layer (E) / / PO layer (D) • PET layer / / Water-soluble layer (A) / / Aluminum foil layer / / PO layer (D) PET layer / / Water-soluble layer (A) / / Inorganic vapor-deposited layer (I) / Barrier layer (E) / / PO layer (D) Aluminum foil layer / / Water-soluble layer (A) / / PO layer (D) / / Barrier layer (E) / / PO layer (D) • Aluminum foil layer / / Water-soluble layer (A) / / Barrier layer (E) / / PO layer (D) • Aluminum foil layer / / Water-soluble layer (A) / / PO layer (D) • PO layer / / Barrier layer / / PO layer / / Water-soluble layer (A) / / Paper layer • PO layer / / Barrier layer / / Water-soluble layer (A) / / Paper layer

[0080] The multilayer structure of the present invention may have a plurality of water-soluble layers (A). In the multilayer structure of the present invention, when the water-soluble layer (A) dissolves in water, it separates into a plurality of layer structures. Among these plurality of layer structures, those that have the predetermined layers described above and satisfy the predetermined density conditions correspond to layer structure (X) and layer structure (Y). There may be one layer structure (X) and one layer structure (Y). A multilayer structure having a portion in which layer structure (X) and layer structure (Y) are laminated via a water-soluble layer (A) corresponds to the multilayer structure of the present invention. If layer structure (X) is denoted as X, layer structure (Y) as Y, water-soluble layer (A) as A, and other layer structures as Z, then an example of the multilayer structure of the present invention having a plurality of water-soluble layers (A) is one having the following layer configuration. ·X / A / Y / A ·X / A / Y / A / Z Z / A / X / A / Y ·Z / A / X / A / Y / A / Z

[0081] In other words, the multilayer structure of the present invention can be said to include a "X / A / Y" laminated structure. Other layer structures may satisfy the conditions of layer structure (X) or layer structure (Y). That is, multiple layers of layer structure (X) and layer structure (Y) may be provided. The multilayer structure of the present invention preferably has only one water-soluble layer (A). Furthermore, the multilayer structure of the present invention preferably consists of an "X / A / Y" laminated structure.

[0082] The oxygen permeability rate of the multilayer structure of the present invention is not particularly limited and can be adjusted according to the application, but an oxygen permeability rate of 10 cc / (m³) at a temperature of 20°C and a relative humidity of 65% is an example. 2 Preferably less than 1 cc / (m³) 2 (day·atm) or less is more preferable, and 0.1cc / (m 2 A value of less than or equal to (day·atm) is even more preferable. Multilayer structures with oxygen permeability in this range can suppress spoilage and deterioration of the contents and maintain the quality of the contents over a long period of time. Oxygen permeability is measured in accordance with JIS K7126-2 (isobaric method; 2006), and specifically the method described in the examples is employed.

[0083] The moisture permeability of the multilayer structure of the present invention is not particularly limited and can be adjusted according to the application, but the moisture permeability at a temperature of 40°C and a relative humidity of 90% is 50 g / (m²). 2 It is preferable that it is less than or equal to 10 g / (m 2 ・day) or less is more preferable, 1g / (m 2 A value of less than or equal to 1 day is even more preferable. Multilayer structures with a moisture permeability within this range can suppress the spoilage and deterioration of the contents and maintain the quality of the contents over a long period of time. Moisture permeability is measured in accordance with JIS Z0208 (1976).

[0084] The multilayer structure of the present invention preferably has a peeling rate of 70% or more, more preferably 80% or more, even more preferably 85% or more, and particularly preferably 90% or 95% or more, which can be evaluated by cutting 100 1 cm squares of the multilayer structure of the present invention, stirring them in 80°C pure water (water (W)) for 60 minutes, and then letting them stand. The peeling rate is expressed as the ratio (%) of the number of multilayer structures from which the layer structure (X) and layer structure (Y) have been peeled off for 100 1 cm squares of the multilayer structure, and can be specifically measured by the method described in the examples.

[0085] Furthermore, in order to improve moldability and various physical properties, the aforementioned additives, modifiers, fillers, other resins, etc., may be added to each layer of the multilayer structure of the present invention, to the extent that they do not hinder the effects of the present invention.

[0086] [Separation and Recycling Methods] The separation method (separation step) of the present invention comprises a step of dissolving part or all of the water-soluble layer (A) by contacting the multilayer structure of the present invention with water (W) at 20°C to 95°C, and the dissolution step is achieved by allowing the layer structure (X) to settle and the layer structure (Y) to float in the water (W). Here, "dissolving part or all" means that the layer structure (X) and layer structure (Y) should be dissolved to the extent that they peel off, but it is preferable that 75% or more by mass of the water-soluble layer (A) is dissolved, more preferably 90% or more by mass is dissolved, and even more preferably it is completely dissolved. The separation method of the multilayer structure of the present invention is expected to have the effect of removing attached contaminants by raising the water temperature, but the separation efficiency may decrease due to water convection, etc. There are no particular restrictions on the size of the multilayer structure to be dropped into the water (W), but in the case of a multilayer structure, it is preferable that it be smaller than 10 cm square in order to promote interlayer delamination. Furthermore, separation can be efficiently achieved by vigorously stirring immediately after dropping the multilayer structure of the present invention into the water to promote interlayer delamination, and then allowing it to stand.

[0087] After separation is complete, the settling layer structure (X) and the floating layer structure (Y) are recovered, washed with pure water or the like as necessary, dried, and then melt-molded using an extruder to be re-pelletized as recycled resin. Various molded products can be manufactured using the pellets thus obtained. In other words, the multilayer structure recycling method of the present invention comprises the step of independently melt-molding the layer structure (X) and the layer structure (Y) recovered by the multilayer structure separation method of the present invention.

[0088] Furthermore, in the separation method for multilayer structures of the present invention, cases where the layer structure (X) and layer structure (Y) are not completely separated, and some layer structure (Y) is contained within the recovered layer structure (X) (in the settled portion), or where some layer structure (X) is contained within the recovered layer structure (Y) (in the suspended portion), are also included in the separation method of the present invention. In the separation method of the present invention, the extent to which the layer structure (X) and layer structure (Y) have been separated can be evaluated by the separation rate, which can be specifically evaluated by the method described in the examples. In the separation method of the present invention, the separation rate is preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and particularly preferably 95% or more.

[0089] (Water) Water (W) may be an aqueous solution containing chloride salts such as sodium chloride and potassium chloride as solutes, or it may be water without solutes (pure water). There are no particular restrictions on the pH range of water (W), but the pH of water (W) is preferably in the range of 5 to 9, and may also be in the range of 6 to 8 or 6.5 to 7.5, as this greatly simplifies the equipment and processes required for dissolution and removal. The water-soluble layer (A) of the multilayer structure of the present invention has excellent solubility even in a near-neutral pH range, for example, pH 5 to 9, and can be easily dissolved and removed. From the viewpoint of economy and handling in the process of recovering the separated film, it is preferable that water (W) is pure water.

[0090] Whether the film (layer structure) from which the water-soluble layer (A) has been removed floats or sinks in water (W) depends on the relative specific gravity of the film and the water (W). In the case of materials with a specific gravity greater than 1, such as polyester or ethylene-vinyl alcohol copolymer, they will sink in ordinary water. However, if it is preferable to recover them by floating, chloride salts such as sodium chloride, potassium chloride, or calcium chloride are added to the water (W) to increase the specific gravity of the water (W), making it possible to recover them by floating. In this case, from the viewpoint of economy and handling, it is preferable that the concentration of chloride salts etc. required to achieve the desired specific gravity of the water (W) is 40% by mass or less. When the concentration is 40% by mass or less, the procurement cost of chloride salts etc. can be reduced, and the washing process after separation can also be carried out efficiently.

[0091] Furthermore, from the viewpoint of the stability of the separation process, it is preferable that the concentration of chloride salts, etc., required to achieve the required specific gravity of water (W) is 10% by mass or more less than the saturation concentration of said chloride salts. When the difference between the concentration of chloride salts, etc., required to achieve the required specific gravity of water (W) and the saturation concentration of said chloride salts is 10% by mass or more, the dissolution of the chloride salts, etc. can be carried out in a relatively short time, the precipitation of chloride salts, etc., in the separation tank and the separated substance is suppressed, and the stability of the process is enhanced.

[0092] From the viewpoint of improving peelability in the separation process, it is preferable that the specific gravity of water (W) lies between the specific gravity of layer structure (X) and the specific gravity of layer structure (Y). When the specific gravity of water (W) lies between the specific gravity of layer structure (X) and the specific gravity of layer structure (Y), the effect on peelability due to the difference in buoyancy caused by the difference in specific gravity (density difference) between layer structure (X) and layer structure (Y) becomes more pronounced when layer structure (X) and layer structure (Y) are separated after a portion of the water-soluble layer (A) has been dissolved and removed, and handling in the recovery process after separation is improved.

[0093] A packaging material comprising a multilayer structure of the present invention is a preferred embodiment of the present invention. This packaging material can be processed into forms such as tubes or bags and is useful as a packaging material for various products such as food, beverages, pharmaceuticals, cosmetics, industrial chemicals, pesticides, and detergents, but it can be used in a wide range of applications and is not limited to these applications. [Examples]

[0094] The present invention will be described in more detail below using examples, but the present invention is not limited in any way by these examples.

[0095] Example 1 (1) Preparation of EVOH resin composition pellets EVOH-38 (ethylene content 38 mol%, degree of saponification 99.6 mol%, MFR (190℃, 2.16 kg load) 1.69 g / 10 min, density 1.2 g / cm³) 3 , oxygen permeability (20℃, 65%RH condition) 0.71cc 20μm / (m 2 EVOH resin composition pellets were obtained by melt-kneading a mixture containing 250 ppm sodium acetate (calculated as sodium ions), 90 ppm phosphoric acid (calculated as phosphate ions), and 180 ppm orthoboric acid (calculated as boron elements) as a boron compound. The melt-kneading was performed using a 25 mm extruder manufactured by Toyo Seiki Seisakusho Co., Ltd. (D(mm)=25, L / D=30, screw: fully meshed in the same direction) to achieve a resin temperature of 220°C.

[0096] (2) Preparation of PVA resin composition pellets Vinyl acetate polymer was obtained by polymerizing vinyl acetate by a conventional method, and the resulting vinyl acetate polymer was saponified by a conventional method to obtain PVA with a viscosity-average degree of polymerization of 800, a degree of saponification of 88 mol%, and a total content of vinyl alcohol units and vinyl acetate units relative to the total monomer units of 99.9 mol%. 87 parts by mass of the obtained PVA and 13 parts by mass of glycerin as a plasticizer were mixed using a planetary mixer. Then, an aqueous sodium acetate solution was added to achieve a sodium ion (alkali metal ion (a2)) content of 800 ppm, and the mixture was melt-kneaded to obtain PVA resin composition pellets. The melt-kneading was performed using a 25 mm extruder manufactured by Toyo Seiki Seisakusho Co., Ltd. (D (mm) = 25, L / D = 30, screw: fully meshed in the same direction), and the resin temperature was set to 220°C. The viscosity-average degree of polymerization and degree of saponification of the obtained PVA were determined by the method described in JIS K6726 (1994).

[0097] (3) Preparation of coating solution 10 parts by mass of PVA resin composition pellets obtained in (2) above were added to 90 parts by mass of distilled water, and the temperature was raised to 80°C while stirring to obtain a PVA coating solution.

[0098] (4) Fabrication of a laminate of a layered structure (X) and a water-soluble layer (A) The base layer (B) is a PET film with an average thickness of 100 μm (Toyobo Co., Ltd.'s "Toyobo Ester (trademark) E5101", density 1.38 g / cm³). 3 A substrate layer (B) was prepared. An anchor coating agent was applied to this substrate layer (B) using a bar coater so that the average thickness after drying was 80 nm. A two-component adhesive ("Takelac® A-626" and "Takenate® A-50" manufactured by Mitsui Chemicals, Inc.) was used as the anchor coating agent. The coated film was dried at 80°C for 2 minutes to form an adhesive layer (C) on the PET layer (substrate layer (B)) and create a layer structure (X). The density of the layer structure (X) was measured using an automatic dry densimeter ("Accubic 1330" manufactured by Shimadzu Corporation) and was found to be 1.38 g / cm³. 3Next, the PVA coating liquid obtained in (3) above was applied to the adhesive layer (C) using a bar coater so that the average thickness after drying was 4 μm. The coated film was dried at 100°C for 3 minutes to form a water-soluble layer (A) on the adhesive layer (C) of the layer structure (X). In this way, a laminate was obtained in which a water-soluble layer (A) was laminated on a layer structure (X) having the structure of base material layer (B) / adhesive layer (C) / water-soluble layer (A) (PET layer / anchor coat layer / PVA resin composition layer).

[0099] (5) Fabrication of the layered structure (Y') Using a co-extrusion multilayer casting apparatus, the PO layer (D) is made of low-density polyethylene (LDPE; Novatec® LJ400 manufactured by Nippon Polyethylene Co., Ltd., density 0.92 g / cm³). 3 ) consists of the barrier layer (E) made of the EVOH resin composition obtained in (1) above, and the adhesive layer (C) is made of maleic anhydride-modified polyethylene (Mitsui Chemicals, Inc. "Admer (trademark) NF518", density 0.91 g / cm³). 3 A layered structure (Y') consisting of (LDPE layer / maleic anhydride-modified polyethylene layer / EVOH resin composition layer / maleic anhydride-modified polyethylene layer / LDPE layer = PO layer (D) / adhesive layer (C) / barrier layer (E) / adhesive layer (C) / PO layer (D) = 21 μm / 2 μm / 2 μm / 2 μm / 21 μm) was fabricated. The film fabrication conditions at this time are shown below. The density of the layered structure (Y') was measured using an automatic dry densimeter (Shimadzu Corporation "Accubic 1330") and was found to be 0.95 g / cm³. 3 That was the case. Co-extrusion conditions Extrusion temperature of PO layer (D): Feed section / Compression section / Measuring section / Die = 170 / 210 / 210 / 210℃ Extrusion temperature of barrier layer (E): Feed section / Compression section / Measuring section / Die = 170 / 210 / 210 / 210℃ Extrusion temperature of adhesive layer (C): Feed section / Compression section / Measuring section / Die = 170 / 210 / 210 / 210℃ Extruder: • PO layer (D) 32φ extruder GT-32-A type (manufactured by Plastics Engineering Research Institute Co., Ltd.) • Barrier layer (E) 20φ extruder, laboratory type ME CO-EXT (manufactured by Toyo Seiki Seisakusho Co., Ltd.) • Adhesive layer (C) 25φ extruder P25-18-AC type (manufactured by Osaka Seiki Kogyo Co., Ltd.) T-die: 300mm width, 3 types, 5 layers (manufactured by Plastics Engineering Laboratory Co., Ltd.) Cooling roll temperature: 80℃ Pickup speed: 3.0m / min

[0100] (6) Hydrophilic treatment One surface of the layered structure (Y') prepared in (5) above was subjected to hydrophilic treatment using the following apparatus. The hydrophilic treatment strength was 130 W·min / m 2 The table speed scale and the output settings of the high-frequency power supply were adjusted accordingly. Equipment: TEC-4AC corona treatment device manufactured by Kasuga Electric Co., Ltd.

[0101] (7) Fabrication of multilayer structures The laminate obtained in (4) above, in which a water-soluble layer (A) is laminated on a layer structure (X), and the layer structure (Y') obtained in (6) above, with one side treated with a hydrophilic coating, were both cut to A4 size. Dry laminating adhesive was applied to the hydrophilic coated side of the layer structure (Y'), and the layer structure (X) and the layer structure (Y') were laminated by dry lamination so that the structure was layer structure (X) / water-soluble layer (A) / adhesive layer (C) / layer structure (Y') (PET layer / anchor coat layer / PVA resin composition layer / dry laminate layer / LDPE layer (surface treated) / maleic anhydride modified polyethylene layer / EVOH resin composition layer / maleic anhydride modified polyethylene layer / LDPE layer), and dried at 80°C for 3 minutes to obtain a multilayer structure (laminate film). As the adhesive for the dry lamination, a two-component adhesive ("Takelac A-520" and "Takenate A-50" from Mitsui Chemicals, Inc.) was used. The application amount of the adhesive was 4.0 g / m². 2 After lamination, the film was cured at 40°C for 3 days to obtain the laminate film. Furthermore, the "adhesive layer (C) / layer structure (Y')" portion of the obtained multilayer structure (dry laminate layer / LDPE layer (surface treated) / maleic anhydride modified polyethylene layer / EVOH resin composition layer / maleic anhydride modified polyethylene layer / LDPE layer) corresponds to layer structure (Y). In other words, the obtained multilayer structure has a layer configuration of "layer structure (X) / water-soluble layer (A) / layer structure (Y)". Since the adhesive layer (C) provided for dry lamination is much thinner than layer structure (Y'), the density of layer structure (Y) is the same as that of layer structure (Y'), at 0.95 g / cm³. 3 In other examples 2 to 17 and comparative examples 1 to 5 described later, the density of the layer structure (Y) was equal to the density of the layer structure (Y') before the adhesive layer (C) for dry lamination was applied.

[0102] (8) Evaluation of interlayer adhesion under high humidity As an indicator of interlayer adhesion between layer structure (X) and layer structure (Y) in the multilayer structure prepared in (7) above, the adhesive strength under high humidity conditions was measured under the following conditions. After conditioning the material in an atmosphere of 20°C and 90%RH for 7 days, strip-shaped test pieces measuring 15 mm × 200 mm were cut out. The T-type peel strength (gf / 15 mm) was measured on the obtained test pieces using a Shimadzu Autograph AGS-H type under the conditions of a chuck spacing of 50 mm and a tensile speed of 250 mm / min. Measurements were performed on five test pieces, and the average value was taken as the adhesive strength. The judgment criteria were as follows. The results are shown in Table 1. A: Adhesive strength 100gf / 15mm or more B: Adhesion strength 50gf / 15mm or more, less than 100gf / 15mm C: Adhesion strength 25gf / 15mm or more, less than 50gf / 15mm D: Adhesion strength less than 25gf / 15mm

[0103] (9) Evaluation of peelability and separation properties (9-1) Evaluation of delamination properties of layered structure (X) and layered structure (Y) The PET layer surface on the X side of the multilayer structure prepared in (7) above was colored with a blue oil-based pen, and the LDPE layer surface on the Y side was colored with a red oil-based pen. Then, 100 1 cm squares were cut out to obtain test specimens. The obtained test specimens were stirred in pure water (water (W)) at 80°C for 60 minutes, and then allowed to stand to evaluate their peelability. The peelability rate (%) was defined as the ratio of the number of multilayer structures from which the X and Y layers were peeled off to 100 test specimens, and the criteria for determining peelability were as follows. The determination of whether or not peeling was possible was made by looking at the color of the film pieces. Film pieces that had been peeled off appeared blue and red, respectively, while film pieces that had not been peeled off appeared purple. The results are shown in Table 1. A: The peeling rate after 5 minutes of standing was 95% or higher. B: The peeling rate after 5 minutes of standing was between 90% and 95%. C: The peeling rate 5 minutes after standing was between 80% and 90%. D: The peeling rate 5 minutes after standing was between 70% and 80%. E: The peeling rate after 5 minutes of standing was less than 70%.

[0104] (9-2) Separability evaluation Test specimens were prepared and tested in the same manner as in (9-1). After the test, the separability of the layered structure (X) and layered structure (Y) was evaluated by allowing them to stand, that is, whether they could be separated by one settling and the other floating, according to the following criteria. The results are shown in Table 1. A: The separation rate after 5 minutes of standing was 95% or higher. B: The separation rate after 5 minutes of standing was between 90% and 95%. C: The separation rate after 5 minutes of standing was between 80% and 90%. D: The separation rate after 5 minutes of standing was less than 80%.

[0105] (10) Oxygen barrier performance assessment (OTR) The layered structures (X), (Y'), and multilayer structures obtained in (4), (5), and (7) above were conditioned for 24 hours at a temperature of 20°C and a relative humidity of 65%. Then, under the same conditions, the oxygen permeability rate (cc / (m³) was measured using a Mocon OX-TRANMODEL2 / 21 oxygen permeability measuring device according to the method described in JIS K7126-2 (isobaric method; 2006). 2 The OTR (Oxygen Temperature Range) was measured (day atm). It was confirmed that the OTR of layer structure (Y) was equal to that of layer structure (Y') before the application of the adhesive layer (C) for dry lamination. In other examples 2 to 17 and comparative examples 1 to 5 described later, the OTR of layer structure (Y) was also equal to that of layer structure (Y'). The oxygen barrier properties of the multilayer structures were evaluated according to the following criteria. The results are shown in Table 1. A: Oxygen permeability 3 cc / (m) 2 Less than (day / atm) B: Oxygen permeation rate 3cc / (m 2 ·day · atm) or more 7.5cc / (m 2 Less than (day / atm) C: Oxygen permeation rate 7.5cc / (m 2 ·day · atm) or more 15cc / (m) 2 Less than (day / atm) D: Oxygen permeation rate 15cc / (m 2 ·day · atm) or more

[0106] Example 2 As the hydroxyl group-containing resin (a1), a blend was used of PVA with a viscosity-average degree of polymerization of 600, a degree of saponification of 80 mol%, and a total content of vinyl alcohol units and vinyl acetate units relative to the total monomer units of 99.9 mol%, and PVA with a viscosity-average degree of polymerization of 800, a degree of saponification of 74 mol%, and a total content of vinyl alcohol units and vinyl acetate units relative to the total monomer units of 99.9 mol%, blended in a mass ratio of 70 / 30. A sodium acetate aqueous solution was added without the addition of a plasticizer (glycerin) to achieve a sodium ion (alkali metal ion (a2)) content of 400 ppm. PVA resin composition pellets were prepared in the same manner as in Example 1, and layered structures (X) and multilayer structures were prepared and evaluated. The results are shown in Table 1.

[0107] Examples 3-5 PVA resin composition pellets were prepared in the same manner as in Example 1, except that a plasticizer listed in Table 1 was added instead of glycerin. Layered structures (X) and multilayer structures were then prepared and evaluated. In Example 3, Dow's "CARBOWAX" 1000 (molecular weight 1000) was used as the PEG. The results are shown in Table 1.

[0108] Examples 6-9 Except for changing the amount of sodium acetate aqueous solution added so that the sodium ion (alkali metal ion (a2)) content was as shown in Tables 1 and 2, PVA resin composition pellets were prepared in the same manner as in Example 1, and layered structures (X) and multilayer structures were prepared and evaluated. The results are shown in Tables 1 and 2.

[0109] Example 10 PVA resin composition pellets were prepared in the same manner as in Example 1, except that PVA with a viscosity-average degree of polymerization of 350, a degree of saponification of 88 mol%, and a total content of vinyl alcohol units and vinyl acetate units relative to the total monomer units of 99.9 mol% was used as the hydroxyl group-containing resin (a1). Layered structures (X) and multilayer structures were then prepared and evaluated. The results are shown in Table 2.

[0110] Example 11 PVA resin composition pellets were prepared in the same manner as in Example 1, except that a potassium acetate aqueous solution was used instead of a sodium acetate aqueous solution. Layered structures (X) and multilayer structures were then fabricated and evaluated. The results are shown in Table 2.

[0111] Example 12 As the hydroxyl group-containing resin (a1), ethylene-modified PVA with an ethylene modification amount of 8 mol%, viscosity-average degree of polymerization of 350, degree of saponification of 98 mol%, and a total content of vinyl alcohol units and vinyl acetate units relative to the total monomer units of 92 mol% was used. Except for the absence of glycerin, PVA resin composition pellets were prepared in the same manner as in Example 1, and layered structures (X) and multilayer structures were prepared and evaluated. The results are shown in Table 2.

[0112] Example 13 The barrier layer (E) is made of nylon MXD6 (S6007, manufactured by Mitsubishi Gas Chemical Company, Inc., with a density of 1.2 g / cm³). 3 Using the same method as in Example 1, layered structures (X) and multilayer structures were fabricated and evaluated, except that the co-extrusion temperature was changed as follows and the average thickness of the barrier layer (E) was changed to 10 μm. The results are shown in Table 3. Co-extrusion conditions Extrusion temperature of adhesive layer (C): Feed unit / Compression unit / Measuring unit / Die = 200 / 250 / 250 / 250℃ Extrusion temperature of PO layer (D): Feeding section / Compression section / Measuring section / Die = 200 / 250 / 250 / 250℃ Extrusion temperature of barrier layer (E): Feed section / Compression section / Measuring section / Die = 220 / 250 / 250 / 250℃

[0113] Example 14 The EVOH resin composition is EVOH-48 (ethylene content 48 mol%, degree of saponification 99.6 mol%, MFR (190℃, 2.16 kg load) 6.40 g / 10 min, density 1.1 g / cm³). 3 , oxygen permeability (20℃, 65%RH condition) 3.5cc 20μm / (m 2 Except for using a EVOH resin composition pellet (containing 200 ppm sodium acetate in terms of sodium ions, 120 ppm phosphoric acid in terms of phosphate ions, and 150 ppm orthoboric acid as a boron compound in terms of boron element), EVOH resin composition pellets were prepared in the same manner as in Example 1, and layered structures (X) and multilayer structures were prepared and evaluated. The results are shown in Table 3.

[0114] Example 15 Instead of LDPE, high-density polyethylene (HDPE; Novatec® HD HY331, manufactured by Nippon Polyethylene Co., Ltd., density 0.95 g / cm³) is used for the PO layer (D). 3 Layered structures and multilayer structures were fabricated and evaluated using the same method as in Example 1, except that the following was used. The results are shown in Table 3.

[0115] Example 16 The layered structure (X) and multilayer structures were manufactured and evaluated in the same manner as in Example 1, except that the PET film was used directly as the layered structure (X) without providing an anchor coat layer. The results are shown in Table 3.

[0116] Example 17 Instead of the PET film (substrate layer (B)), a PET film with an average thickness of 100 μm (Toyobo Co., Ltd.'s "Toyobo Ester (trademark) E5101", density 1.38 g / cm³) is used. 3 A transparent vapor-deposited PET film (a laminate of a substrate layer (B) and an inorganic vapor-deposited layer (I)) was used, on one surface of the film, with an alumina vapor-deposited layer having an average thickness of 50 nm, prepared by a known vacuum deposition method. Layer structures (X) and multilayer structures were then fabricated and evaluated in the same manner as in Example 1, except that an anchor coating agent was applied to the alumina vapor-deposited layer. The results are shown in Table 3.

[0117] Example 18 Using a co-extrusion multilayer casting apparatus, the water-soluble layer (A) consists of PVA resin composition pellets obtained in Example 1, the substrate layer (B) consists of polyethylene terephthalate (PET; "Bellpet EFG70" manufactured by Bell Polyester Products Co., Ltd.), and the adhesive layer (C1) consists of maleic anhydride-modified ethylene acrylate copolymer ("Bynel" manufactured by Dow Chemical Company). The multilayer structure consists of (B) / (C1) / (A) / (C2) / (D) / (C2) / (E) / (C2) / (D) = PET layer / maleic anhydride-modified ethylene acrylate copolymer layer / PVA resin composition layer / maleic anhydride-modified polyethylene layer / LDPE layer / maleic anhydride-modified polyethylene layer / EVOH resin composition layer / maleic anhydride-modified polyethylene layer / LDPE layer = 100 μm / 2 μm / 4 μm / 2 μm / A 300 mm wide, 9-layer co-extruded multilayer cast film with layer thicknesses (average thickness) and layer structure of 21 μm / 2 μm / 2 μm / 2 μm / 21 μm was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 3. The densities of layer structure (X) and layer structure (Y) were measured by preparing films of layer structure (X) (PET layer / maleic anhydride-modified ethylene acrylate layer = 100 μm / 2 μm) and layer structure (Y) (maleic anhydride-modified polyethylene layer / LDPE layer / maleic anhydride-modified polyethylene layer / EVOH resin composition layer / maleic anhydride-modified polyethylene layer / LDPE layer = 2 μm / 21 μm / 2 μm / 2 μm / 2 μm / 21 μm) and measuring them using an automatic dry densimeter (Shimadzu Corporation "Accubic 1330"). The density of layer structure (X) was 1.38 g / cm³ 3 The density of the layered structure (Y) is 0.95 g / cm³. 3 That was the case.

[0118] Comparative Example 1 Except for not providing an anchor coat layer (adhesive layer (C)) for the water-soluble layer (A) and the layer structure (X), the layer structure (X) and the multilayer structure (PET layer / dry laminate layer / LDPE layer (surface treated) / maleic anhydride modified polyethylene layer / EVOH resin composition layer / maleic anhydride modified polyethylene layer / LDPE layer) were prepared or fabricated and evaluated in the same manner as in Example 1. The results are shown in Table 4.

[0119] Comparative Example 2, Comparative Example 3 PVA resin composition pellets were prepared in the same manner as in Example 1, except that the amount of sodium acetate aqueous solution added was changed so that the sodium ion (alkali metal ion (a2)) content was as shown in Table 4. Layered structures (X) and multilayer structures were then prepared and evaluated. The results are shown in Table 4.

[0120] Comparative Example 4 The barrier layer (E) is made of polyamide 6 / 66 (BASF's "Ultramid C40L", density 1.1 g / cm³). 3 Using the same method as in Example 1, layered structures (X) and multilayer structures were fabricated and evaluated, except that the co-extrusion temperature was changed as follows and the average thickness of the barrier layer (E) was changed to 25 μm. The results are shown in Table 4. Co-extrusion conditions Extrusion temperature of adhesive layer (C): Feed unit / Compression unit / Measuring unit / Die = 170 / 210 / 210 / 220℃ Extrusion temperature of PO layer (D): Feeding section / Compression section / Measuring section / Die = 170 / 210 / 210 / 220℃ Extrusion temperature of barrier layer (E): Feed section / Compression section / Measuring section / Die = 200 / 220 / 220 / 220℃

[0121] Comparative Example 5 Layered structures (X) and multilayer structures were fabricated and evaluated in the same manner as in Example 1, except that a single-layer film made of polyamide 12 prepared by the following method was used as the base layer (B) instead of PET film. The results are shown in Table 4. Polyamide 12 (UBESTA 3030XA, manufactured by Ube Industries, Ltd., density 1.01 g / cm³) 3Using a 20mm extruder "D2020" manufactured by Toyo Seiki Seisakusho Co., Ltd. (D(mm)=20, L / D=20, compression ratio=2.0, screw: full flight), a single-layer film was produced under the following conditions to obtain a single-layer film made of polyamide 12. Cylinder temperature: Feed section 215°C, Compression section 230°C, Metering section 230°C Die temperature: 230℃ Screw rotation speed: 100 rpm Take-up roll temperature: 80℃ Roller retrieval speed: 1.5 m / min Average film thickness: 100 μm One surface of the obtained film was subjected to hydrophilic treatment using the aforementioned apparatus to obtain a substrate layer (B) made of polyamide 12.

[0122] [Table 1]

[0123] [Table 2]

[0124] [Table 3]

[0125] [Table 4]

[0126] Example 19 A multilayer structure was prepared in the same manner as in Example 1, except that the surface of the water-soluble layer (A) of the "laminated structure (X) with a water-soluble layer (A) laminated on top of a layered structure (X) was printed with ink. The obtained multilayer structure was cut into 1 cm squares of 100 pieces to obtain test specimens. The obtained test specimens were stirred in water at 80°C for 60 minutes, then left to stand for 5 minutes, and the 100 settled films were collected. 98 of the films were transparent films from which the printed ink had peeled off, and the remaining 2 films were multilayer structures in which the layered structure (X) and layered structure (Y) had settled without separating.

[0127] Example 20 A multilayer structure was fabricated in the same manner as in Example 1, except that after printing on the surface of a PET film (substrate layer (B)) with ink, an anchor coating agent was applied to the printed surface of the substrate layer (B) using a bar coater to create a layer structure (X) with an adhesive layer (C) so that the average thickness after drying was 80 nm. 100 1 cm squares of the obtained multilayer structure were cut out to obtain test specimens. The obtained test specimens were stirred in water at 80°C for 60 minutes, then allowed to stand for 5 minutes, and the 100 settled films were collected. 98 films showed separation between layer structure (X) and layer structure (Y), and 2 multilayer structures showed no separation between layer structure (X) and layer structure (Y). However, there were no transparent films from which the printed ink had peeled off.

[0128] The results from Examples 19 and 20 show that, as in Example 19, printing on the surface of the water-soluble layer (A) of the layered structure (X) allows for the acquisition of a transparent substrate layer (B) by agitation and washing in water, making recycling easier. On the other hand, when printing is applied to the surface of the substrate layer (B), as in Example 20, the transparent substrate layer (B) cannot be recovered, and since PET is often used in applications where transparency is required, recycling for such applications may become difficult. Polyesters, including polyethylene terephthalate, have high melting points and are difficult to recycle when mixed with other materials widely used as packaging materials. However, by using this technology, even combinations of materials that are difficult to recycle can be recycled. [Industrial applicability]

[0129] The multilayer structure of the present invention exhibits sufficient oxygen barrier properties and interlayer adhesion under normal use conditions as a packaging material, while after use as a packaging material, it exhibits excellent peelability in the separation process, allowing for the separation and recovery of each layer structure (X) and layer structure (Y). This improves the recyclability of the packaging material without degrading its performance or quality, thereby contributing to the realization of a circular economy.

Claims

1. Layered structures (X) and (Y) are laminated with a water-soluble layer (A) in between. The layer structure (X) comprises a base layer (B) which includes at least one selected from the group consisting of thermoplastic resins and metals. The aforementioned layer structure (Y) comprises a polyolefin layer (D) or a paper layer, The density difference (X-Y) between the layer structure (X) and the layer structure (Y) is 0.2 g / cm³. ３ That's all. The oxygen permeability rate (OTR) of at least one of the layer structure (X) and the layer structure (Y), measured in accordance with JIS K7126-2 (isobaric method; 2006), at 20°C and 65% RH, is 20 cc / (m³). ２ (day ATM) is less than or equal to, A multilayer structure in which the water-soluble layer (A) contains a hydroxyl group-containing resin (a1) and alkali metal ions (a2), and the content of alkali metal ions (a2) in the water-soluble layer (A) is 10 ppm or more and 2000 ppm or less.

2. The density of the aforementioned layer structure (X) is 1.0 g / cm³ ３ The above is true, and the density of the layer structure (Y) is 1.0 g / cm³. ３ The multilayer structure according to claim 1, which is as follows:

3. The multilayer structure according to claim 1, wherein the hydroxyl group-containing resin (a1) is polyvinyl alcohol.

4. The multilayer structure according to claim 3, wherein the viscosity-average degree of polymerization of the polyvinyl alcohol is 400 or more and 2000 or less.

5. The multilayer structure according to claim 3, wherein the degree of saponification of the polyvinyl alcohol is 70 mol% or more and 95 mol% or less.

6. The multilayer structure according to claim 3, wherein the total content of vinyl alcohol units and vinyl ester units in the total monomer units of the polyvinyl alcohol is 95 mol% or more.

7. The multilayer structure according to claim 1, wherein the water-soluble layer (A) further comprises a plasticizer (a3) ​​consisting of at least one selected from the group consisting of glycerin, polyethylene glycol, polypropylene glycol, polyglycerin, mannitol, sorbitol, and pentaerythritol.

8. The multilayer structure according to claim 1, wherein the base material layer (B) mainly contains polyester resin.

9. The multilayer structure according to claim 1, wherein the layer structure (X) comprises an adhesive layer (C) in contact with the water-soluble layer (A).

10. The multilayer structure according to claim 1, wherein the ratio of the mass of the polyolefin layer (D) to the total mass of the layer structure (Y) is 0.90 or more.

11. The multilayer structure according to claim 1, wherein the layer structure (Y) comprises a barrier layer (E) mainly composed of at least one selected from the group consisting of polyamide and ethylene-vinyl alcohol copolymer.

12. The multilayer structure according to claim 11, wherein the barrier layer (E) mainly comprises the ethylene-vinyl alcohol copolymer.

13. The multilayer structure according to claim 1, wherein one of the layers is printed.

14. The method comprises a step of dissolving part or all of the water-soluble layer (A) by bringing the multilayer structure according to any one of claims 1 to 13 into contact with water (W) at 20°C to 95°C, A method for separating multilayer structures, wherein in the dissolution step, the layer structure (X) is allowed to settle and the layer structure (Y) is allowed to float in the water (W).

15. A method for recycling a multilayer structure, comprising the step of independently melt-molding the layer structure (X) and the layer structure (Y) recovered by the method for separating a multilayer structure according to claim 14.

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