Multilayer structure and packaging material containing the same

Abstract

To provide a multilayer structure that suppresses migration of a compound having 30 or less carbon atoms and having an SP value lower than that of an ethylene-vinyl alcohol copolymer from a recycled resin layer, and that has excellent bending resistance.SOLUTION: There is provided a multilayer structure that at least comprises: a recycled resin layer (A) containing a recycled resin (a) as a main component; a layer (B) containing a polyolefin resin (b) as a main component; and two or more barrier layers (C) containing ethylene-vinyl alcohol copolymer resin (c) as a main component, in which the barrier layers (C) are arranged on outside and inside of the recycled resin layer (A), and the recycled resin layer(A) comprises a compound having 30 or less carbon atoms and having an SP value lower than that of the ethylene-vinyl alcohol copolymer resin (c).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a multilayer structure having a recycled resin layer mainly made of recycled resin, a layer mainly made of polyolefin resin, and two or more barrier layers mainly made of ethylene-vinyl alcohol copolymer resin, and a packaging material containing the same. [Background technology]

[0002] Multilayer structures containing a polyolefin layer and an ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as EVOH) layer having excellent barrier properties are used in various applications such as food packaging containers and fuel containers by taking advantage of their barrier properties. Such multilayer structures are used as various molded products such as films, sheets, cups, trays, and bottles. In this case, the ends and defective products generated when obtaining the various molded products are sometimes collected and melt-molded to be reused as at least one layer of a multilayer structure containing a polyolefin layer and an EVOH layer. Such a recovery technology is useful in terms of waste reduction and economic efficiency, and is widely adopted.

[0003] Patent Document 1 describes a resin composition including (A) a saponified ethylene-vinyl ester copolymer having an ethylene content of 20 to 60 mol%, (B) a polyolefin resin, and (C) a fully dehydrated or partially dehydrated polyvalent metal sulfate hydrate, the resin composition containing 0.1 to 30 parts by weight of the saponified ethylene-vinyl ester copolymer with respect to 100 parts by weight of the polyolefin resin, and the fully dehydrated or partially dehydrated polyvalent metal sulfate hydrate with respect to 100 parts by weight of the saponified ethylene-vinyl ester copolymer ...

[0004] Patent Document 2 describes a laminate consisting of a three-layer film composite, which has a recycled material between a first barrier layer and a second barrier layer, and lists examples of the first and second barrier layers as follows: aluminum; plastic films having ceramic barriers such as silicon oxide and aluminum oxide; plastic films having metal vapor deposition barriers; ethylene-vinyl alcohol copolymers (EVOH), cycloolefin copolymers (COC), amorphous, aromatic, or partially aromatic polyamides (PA), polyacrylonitrile (PAN), polyethylene terephthalate (PET), and the like. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2012-193327 A [Patent Document 2] DE102017123135A1 Summary of the Invention [Problem to be solved by the invention]

[0006] However, Patent Document 1 does not state that a compound having 30 or less carbon atoms and a lower SP value than an ethylene-vinyl alcohol copolymer may be contained in the recovered product of the multilayer structure, and there is no mention of the problem of odor generation when the compound with a low SP value migrates from the multilayer structure. In addition, Patent Document 2 describes a laminate having a recycled material between aluminum foils as a laminate consisting of a three-layer film composite, but the laminate has a problem with bending resistance, and some of the listed barrier layers may not sufficiently suppress odors derived from the recycled material, so improvement is desired. In addition, as a more specific problem, when used as a food packaging material, if the food contains a food containing a relatively low-polarity long-chain fatty acid, etc., compounds with a low SP value may easily migrate into the food, so improvement is desired.

[0007] The present invention has been made to solve the above-mentioned problems, and aims to provide a multilayer structure that inhibits the migration of a compound having a carbon number of 30 or less and a lower SP value than an ethylene-vinyl alcohol copolymer from a recycled resin layer, and that has excellent flex resistance. [Means for solving the problem]

[0008] The above-mentioned problem is solved by providing a multilayer structure having at least a recycled resin layer (A) containing a recycled resin (a) as a main component, a layer (B) containing a polyolefin resin (b) as a main component, and two or more barrier layers (C) containing an ethylene-vinyl alcohol copolymer resin (c) as a main component, wherein the barrier layers (C) are located on the outer and inner sides of the recycled resin layer (A), and the recycled resin layer (A) further contains a compound (X) having a carbon number of 30 or less and a lower SP value than the ethylene-vinyl alcohol copolymer resin (c).

[0009] In this case, it is preferable that the SP value of the compound (X) is 11.5 or less, and the recycled resin layer (A) is made of a post-consumer recycled product mainly composed of a thermoplastic resin. It is preferable that the compound (X) is at least one selected from the group consisting of aliphatic saturated hydrocarbons and aromatic hydrocarbons, and it is preferable that the barrier layer (C) is made only of an ethylene-vinyl alcohol copolymer resin (c). It is preferable that the polyolefin resin (b) contains at least one resin selected from the group consisting of polyethylene resins and polypropylene resins, and it is preferable that the thickness of the recycled resin layer (A) is 10% or more of the total thickness. It is preferable that an adhesive resin layer (D) is further provided between the barrier layer (C) and the recycled resin layer (A), and it is preferable that a layer (B) is further provided on the surface of the barrier layer (C) opposite to the recycled resin layer (A) via the adhesive resin layer (D).

[0010] The above-mentioned problems can also be solved by providing a multilayer structure having at least a resin layer (E), a layer (B) mainly composed of a polyolefin resin (b), and two or more barrier layers (C) mainly composed of an ethylene-vinyl alcohol copolymer resin (c), in which the barrier layers (C) are located on the outer and inner sides of the resin layer (E), the resin layer (E) further contains a compound (X) having a carbon number of 30 or less and a lower SP value than the ethylene-vinyl alcohol copolymer resin (c), and the proportion of the resin layer (E) to the total thickness is 20% or more.

[0011] A packaging material including the multilayer structure is a preferred embodiment, and a packaging product using the packaging material, in which the packaging material surrounds a content, is also a preferred embodiment. Also, a packaging product in which the content is a food product is also a preferred embodiment. Effect of the Invention

[0012] The multilayer structure of the present invention has barrier layers mainly composed of an ethylene-vinyl alcohol copolymer arranged on the outer and inner sides of a recycled resin layer containing a compound having a carbon number of 30 or less and a lower SP value than that of an ethylene-vinyl alcohol copolymer, and therefore can inhibit migration of the compound from the recycled resin layer and provide a multilayer structure with excellent flex resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The multilayer structure of the present invention has at least a recycled resin layer (A) containing a recycled resin (a) as a main component, a layer (B) containing a polyolefin resin (b) as a main component, and two or more barrier layers (C) containing an ethylene-vinyl alcohol copolymer resin (c) (hereinafter sometimes abbreviated as "EVOH (c)") as a main component.

[0014] In the multilayer structure of the present invention, it is important that two or more barrier layers (C) mainly composed of EVOH (c) are located on the outer and inner sides of the recycled resin layer (A), which can suppress the migration of the compound (X) having a carbon number of 30 or less and a lower SP value than EVOH (c) from the recycled resin layer (A) and provide a multilayer structure with excellent flex resistance.

[0015] As a result of the study by the present inventor in the examples described later, in a multilayer structure in which a barrier layer (C) mainly composed of EVOH (c) is arranged only on one side of the recycled layer (A), or in a multilayer structure in which the barrier layer (C) is not provided, the odor cannot be suppressed in a packaging material produced using the multilayer structure, and migration from the recycled resin layer (A) cannot be suppressed. In particular, in a multilayer structure in which the barrier layer (C) is not provided, the amount of elution from the multilayer structure into a solvent is large, and the value of the oxygen transmission rate (OTR) is also very high. In a multilayer structure in which 6 nylon or polyacrylonitrile (PAN) is arranged as a barrier layer on the outer and inner sides of the recycled resin layer (A) instead of EVOH (c), the odor can be suppressed in a packaging material produced using the multilayer structure, but the amount of elution from the multilayer structure into a solvent is large, and migration from the recycled resin layer (A) cannot be suppressed. In addition, the value of the oxygen transmission rate (OTR) is also high, and the number of pinholes is large in a bending test, and it was confirmed that the multilayer structure has poor bending resistance. In addition, in a multilayer structure in which aluminum foil was placed on the outside and inside of the recycled resin layer (A) as a barrier layer instead of EVOH (c), the odor could not be suppressed in the packaging material produced using the multilayer structure, and migration from the recycled resin layer (A) could not be suppressed. In addition, the oxygen transmission rate (OTR) was high, and there were many pinholes in the bending test, confirming that the multilayer structure had poor bending resistance.

[0016] In contrast, in a multilayer structure in which a barrier layer (C) mainly composed of EVOH (c) is arranged on the outside and inside of a recycled resin layer (A), odor can be suppressed in a packaging material produced using the multilayer structure, the amount of elution from the multilayer structure into a solvent is small, and migration from the recycled resin layer (A) can be suppressed. In addition, the oxygen transmission rate (OTR) value is low, and the number of pinholes in a bending test is small, confirming that the multilayer structure has excellent bending resistance. This fact was made clear by the inventor's investigation, and it can be seen that there is great significance in adopting the configuration of the present invention.

[0017] The recycled resin layer (A) in the present invention is mainly composed of recycled resin (a). The term "mainly composed" means that the content of recycled resin (a) in the resin constituting the layer (A) is 80% by mass or more, and preferably 90% by mass or more. In particular, a preferred embodiment is that the recycled resin layer (A) is composed only of recycled resin (a). The recycled resin (a) in the present invention is not a thermoplastic resin obtained by recovering trim or off-spec products during the manufacturing process, but is composed of a thermoplastic resin obtained by recovering products distributed in the market. That is, a preferred embodiment is that the recycled resin layer (A) is composed of a post-consumer recycled product mainly composed of a thermoplastic resin. The thermoplastic resin obtained by recovering products distributed in the market may contain components such as printing ink, antiblocking (AB) agents, antioxidants, oils, lubricants, antistatic agents, crystal nucleating agents, adhesives, pigments, light stabilizers, tackifiers, foaming agents, and plasticizers. When a thermoplastic resin containing such components is reused, there is a problem that the components migrate and generate odors, etc. In particular, when the recycled resin is reused as a packaging material, if the components migrate to the inside, they contaminate the contents contained in the packaging material, and if the components migrate to the outside, they deteriorate the heat sealability of the surface layer. The multilayer structure of the present invention can suppress the migration of the components from the recycled resin layer (A), and therefore can solve such problems.

[0018] Specifically, the recycled resin (a) used in the present invention includes thermoplastic resins such as polyolefin resin (b) and ethylene-vinyl alcohol copolymer resin (c) described later, as well as thermoplastic resins such as polyolefin, polyamide, polyester, polystyrene, polyvinyl chloride, acrylic resin, polyurethane, polycarbonate, and polyvinyl acetate. Among them, the recycled resin (a) is preferably a recovered multilayer structure containing polyolefin resin (b) and ethylene-vinyl alcohol copolymer resin (c). As a method for obtaining the recycled resin (a), it is preferable to recover products distributed in the market, crush the products, and then melt mold them. The crushing method is not particularly limited, and includes a method using a ball mill, a vibration mill, a jet crusher, or the like. The melt molding method is not particularly limited, and includes an extrusion molding method, an injection molding method, and the like, and the melt molding temperature is preferably 180 to 280°C.

[0019] The recycled resin layer (A) in the present invention contains a compound (X) having a carbon number of 30 or less and an SP value lower than that of the ethylene-vinyl alcohol copolymer (c). The inventors' investigations have revealed that the migration of the compound (X) with a low SP value can be suppressed by disposing EVOH (c) with a higher SP value than the compound (X) that is subject to migration on the outer and inner sides of the recycled resin layer (A). The SP value of EVOH (c) is usually 11.6 to 16.2, and migration can be suppressed when the SP value of the compound (X) is lower than that of such EVOH (c). In particular, when the packaging material containing the multilayer structure of the present invention is used as a food packaging material, when the food contains a relatively low-polarity long-chain fatty acid or the like, the migration of the compound with a low SP value to the food can be effectively suppressed. The SP value of the compound (X) is preferably 11.5 or less, more preferably 11.4 or less. On the other hand, the SP value of the compound (X) is usually 5 or more. Specific examples of the compound (X) include aliphatic saturated hydrocarbons and derivatives thereof such as n-hexane, n-heptane, and n-octane; aliphatic unsaturated hydrocarbons and derivatives thereof such as hexene, heptene, and octene; alicyclic saturated hydrocarbons and derivatives thereof such as cyclohexane, cycloheptane, and cyclooctane; alicyclic unsaturated hydrocarbons and derivatives thereof such as cyclohexene, cycloheptene, and cyclooctene; aromatic hydrocarbons such as benzene, toluene, xylene, naphthalene, and phenol; halogenated hydrocarbons such as dichloromethane and chloroform; ethers such as diethyl ether and diisopropyl ether; alcohols such as butanol and pentanol; ketones such as acetone and methyl ethyl ketone; and aldehydes such as acetaldehyde and propionaldehyde. Among these, the compound (X) is preferably at least one selected from the group consisting of aliphatic saturated hydrocarbons, alicyclic unsaturated hydrocarbons, aromatic hydrocarbons, and alcohols, and more preferably at least one selected from the group consisting of aliphatic saturated hydrocarbons, alicyclic unsaturated hydrocarbons, and aromatic hydrocarbons. For example, limonene (a carbon atom-containing alicyclic unsaturated hydrocarbon) contained as a fragrance in detergents and other products remains in the recycled resin layer (A) and may migrate into the contents during recycling or leak to the outside as an odor.The carbon number of the compound (X) is preferably 25 or less, more preferably 20 or less, and even more preferably 15 or less. The carbon number is usually 5 or more. In particular, when the compound (X) that can be contained in the recycled resin layer (A) is a saturated hydrocarbon or an alicyclic unsaturated hydrocarbon having 8 or more carbon atoms, migration can be effectively suppressed. The compound (X) contained in the recycled resin layer (A) may be one type or two or more types.

[0020] The content of the compound (X) in the recycled resin layer (A) in the present invention varies depending on the product distributed on the market, which is the raw material of the recycled resin, but for example, the concentration detected when the recycled resin layer (A) is separated and measured by gas chromatography may be 10 ppm or more. Thus, the multilayer structure of the present invention can effectively suppress migration even when the concentration of the compound (X) is relatively high, such as when the recycled resin layer (A) is made of a post-consumer recycled product.

[0021] The layer (B) in the present invention is mainly composed of polyolefin resin (b). The term "mainly composed" means that the content of polyolefin resin (b) in the resin constituting layer (B) is 80% by mass or more, and preferably 90% by mass or more. Examples of the polyolefin resin (b) used in the present invention include polyethylene resins such as polyethylene (low density, linear low density, medium density, high density, etc.), ethylene-based copolymers obtained by copolymerizing ethylene with α-olefins such as 1-butene, 1-hexene, 4-methyl-1-pentene, or acrylic acid esters; polypropylene resins such as polypropylene, propylene-based copolymers obtained by copolymerizing α-olefins such as ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene, or 4-methyl-1-pentene; poly(1-butene), poly(4-methyl-1-pentene), modified polyolefins obtained by reacting maleic anhydride with the above-mentioned polyolefins; ionomer resins, etc. Among them, a preferred embodiment is that the polyolefin resin (b) contains at least one resin selected from the group consisting of polyethylene resins and polypropylene resins. In a preferred embodiment, the polyethylene resin is a polyethylene resin polymerized with a metallocene catalyst. The polyolefin resin (b) may be used alone or in combination of two or more kinds.

[0022] The barrier layer (C) in the present invention is mainly composed of an ethylene-vinyl alcohol copolymer resin (c). The term "mainly composed" means that the content of the ethylene-vinyl alcohol copolymer resin (c) in the resin constituting the barrier layer (C) is 80% by mass or more, and preferably 90% by mass or more. Among these, a preferred embodiment is one in which the barrier layer (C) is composed only of an ethylene-vinyl alcohol copolymer resin (c), since this can effectively suppress migration of the compound (X).

[0023] EVOH (c) is obtained by saponifying an ethylene-vinyl ester copolymer. A representative vinyl ester is vinyl acetate, but other fatty acid vinyl esters (vinyl propionate, vinyl pivalate, etc.) can also be used. The ethylene content of EVOH (c) is preferably 20 to 60 mol%. If the ethylene content is less than 20 mol%, the thermal stability may decrease. The ethylene content is more preferably 23 mol% or more. If the ethylene content exceeds 60 mol%, the barrier property may decrease. From the viewpoint of reducing the amount of elution of the compound (X) from the multilayer structure, the ethylene content is more preferably 55 mol% or less, even more preferably 50 mol% or less, and particularly preferably 43 mol% or less. On the other hand, from the viewpoint of barrier property, the saponification degree of the vinyl ester unit of EVOH (c) is preferably 80% or more, more preferably 98% or more, and even more preferably 99% or more. The ethylene content and saponification degree of EVOH (c) are determined by a nuclear magnetic resonance (NMR) method.

[0024] EVOH (c) may be copolymerized with polymerizable monomers other than ethylene and vinyl esters within a range that does not impair the effects of the present invention, generally within a range of 5 mol% or less. Examples of such polymerizable monomers include α-olefins such as propylene, 1-butene, 1-hexene, and 4-methyl-1-pentene; (meth)acrylic acid esters; alkyl vinyl ethers; N-(2-dimethylaminoethyl)methacrylamide or its quaternary derivatives, N-vinylimidazole or its quaternary derivatives, N-vinylpyrrolidone, N,N-butoxymethylacrylamide, vinyltrimethoxysilane, vinylmethyldimethoxysilane, and vinyldimethylmethoxysilane.

[0025] The barrier layer (C) may contain a resin other than EVOH (c) to the extent that the effect of the present invention is not impaired. Examples of the resin other than EVOH (c) include thermoplastic resins such as polyolefin, polyamide, polyester, polystyrene, polyvinyl chloride, acrylic resin, polyurethane, polycarbonate, and polyvinyl acetate.

[0026] The barrier layer (C) may contain various additives within the range that does not impair the effects of the present invention. Examples of such additives include antioxidants, plasticizers, heat stabilizers, UV absorbers, antistatic agents, lubricants, colorants, fillers, other resins, etc., and specifically include the following. The content of additives in EVOH (c) is usually 10% by mass or less, preferably 5% by mass or less, and more preferably 1% by mass or less.

[0027] Antioxidants: 2,5-di-t-butylhydroquinone, 2,6-di-t-butyl-p-cresol, 4,4'-thiobis-(6-t-butylphenol), 2,2'-methylene-bis-(4-methyl-6-t-butylphenol), octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, 4,4'-thiobis-(6-t-butylphenol), etc. Ultraviolet absorbers: ethylene-2-cyano-3,3'-diphenylacrylate, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)5-chlorobenzotriazole, 2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-oxybenzophenone, etc. Plasticizers: dimethyl phthalate, diethyl phthalate, dioctyl phthalate, wax, liquid paraffin, phosphate esters, etc. Antistatic agents: pentaerythritol monostearate, sorbitan monopalmitate, sulfated polyolefins, polyethylene oxide, carbowax, etc. Lubricants: ethylene bisstearamide, butyl stearate, etc. Colorants: carbon black, phthalocyanine, quinacridone, indoline, azo pigments, red iron oxide, etc. Fillers: glass fiber, asbestos, ballastonite, calcium silicate, talc, montmorillonite, etc.

[0028] The multilayer structure of the present invention has at least a recycled resin layer (A) mainly made of recycled resin (a), a layer (B) mainly made of polyolefin resin (b), and two or more barrier layers (C) mainly made of EVOH (c). The two or more barrier layers (C) may use the same EVOH (c) or different EVOH (c), and the EVOH (c) described above is preferably used.

[0029] In the multilayer structure of the present invention, two or more barrier layers (C) mainly composed of EVOH (c) are located on the outside and inside of the recycled resin layer (A), and from the viewpoint of increasing adhesive strength, it is preferable to further have an adhesive resin layer (D) between the barrier layer (C) and the recycled resin layer (A). As the adhesive resin layer (D), a modified polyolefin resin modified with an unsaturated carboxylic acid or a derivative thereof is preferably used. As the polyolefin resin, those mentioned in the explanation of the polyolefin resin (b) above can be preferably used. As the unsaturated carboxylic acid or a derivative thereof, maleic acid, fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride, maleic acid monomethyl ester, maleic acid monoethyl ester, maleic acid diethyl ester, fumaric acid monomethyl ester, etc. are mentioned. Among them, maleic anhydride-modified polyolefin is more preferably used. These may be used alone or in combination of two or more.

[0030] In the multilayer structure of the present invention, a preferred embodiment is that the barrier layer (C) on the surface opposite to the recycled resin layer (A) further has a layer (B) via an adhesive resin layer (D). This has the advantage of increasing the mechanical strength. The multilayer structure of the present invention preferably has 4 to 15 layers, and for example, the following structure is preferably adopted. Any other layer may be added.

[0031] 4 layers B / C / A / C, C / B / A / C

[0032] 5 layers B / C / A / C / B, C / B / A / C / B, C / B / A / B / C, B / C / D / A / C, C / B / A / D / C

[0033] 6 layers B / C / B / A / C / B, C / B / C / A / C / B, B / C / D / A / C / B, B / C / D / A / B / C, B / C / D / A / D / C,

[0034] 7 layers B / C / B / A / B / C / B, C / B / C / B / A / C / B, B / C / D / A / D / C / B, B / C / D / A / B / D / C, B / D / C / D / A / C / B

[0035] 8 layers B / C / B / A / B / C / B / C, C / B / C / B / A / C / B / C, B / C / D / A / D / C / D / B, B / C / D / A / B / D / C / B, B / D / C / D / A / D / C / B

[0036] 9 layers B / C / B / A / B / C / B / C / B, C / B / C / B / A / C / B / C / B, B / C / D / A / D / C / B / D / B, B / C / D / A / C / B / D / C / B, B / D / C / D / A / D / C / D / B

[0037] Examples of the method for producing the multilayer structure of the present invention include, but are not limited to, lamination methods such as dry lamination, co-injection molding, co-extrusion molding, etc. Examples of the co-extrusion molding method include co-extrusion lamination, co-extrusion sheet molding, co-extrusion inflation molding, co-extrusion blow molding, etc.

[0038] The thickness of the recycled resin layer (A) in the multilayer structure of the present invention (thickness per layer) is preferably 20 to 200 μm. If the thickness of the recycled resin layer (A) is less than 20 μm, the recycling efficiency may decrease, and the thickness is more preferably 30 μm or more, even more preferably 45 μm or more, and particularly preferably 60 μm or more. On the other hand, if the thickness of the recycled resin layer (A) exceeds 200 μm, migration may increase, and the thickness is more preferably 180 μm or less, even more preferably 150 μm or less, and particularly preferably 130 μm or less. In addition, in the multilayer structure of the present invention, the thickness of the recycled resin layer (A) is preferably 10% or more of the total thickness. Even if the ratio of the recycled resin layer (A) to the total thickness is high, the migration of the compound (X) is effectively suppressed. The ratio may be 20% or more, 40% or more, or 60% or more.

[0039] The thickness of layer (B) in the multilayer structure of the present invention (thickness per layer) is preferably 5 to 65 μm. If the thickness of layer (B) is less than 5 μm, the mechanical strength may be insufficient, and the thickness is more preferably 8 μm or more, even more preferably 12 μm or more, and particularly preferably 15 μm or more. On the other hand, if the thickness of layer (B) exceeds 65 μm, the recycling efficiency may decrease, and the thickness is more preferably 60 μm or less, even more preferably 55 μm or less, and particularly preferably 50 μm or less.

[0040] The thickness of the barrier layer (C) in the multilayer structure of the present invention (thickness per layer) is preferably 0.5 to 20 μm. If the thickness of the barrier layer (C) is less than 0.5 μm, the barrier properties may be insufficient, and the thickness is more preferably 1 μm or more. On the other hand, if the thickness of the barrier layer (C) is more than 20 μm, the flexibility may decrease and the cost may increase, and the thickness is more preferably 16 μm or less, further preferably 12 μm or less, and particularly preferably 8 μm or less.

[0041] When the multilayer structure of the present invention has an adhesive resin layer (D), the thickness (thickness per layer) is preferably 0.5 to 20 μm. When the thickness of the adhesive resin layer (D) is less than 0.5 μm, the mechanical strength may be insufficient, so the thickness is more preferably 1 μm or more, and even more preferably 2 μm or more. On the other hand, when the thickness of the adhesive resin layer (D) exceeds 20 μm, the cost may be high, so the thickness is more preferably 16 μm or less, even more preferably 12 μm or less, and particularly preferably 10 μm or less.

[0042] The total thickness of the multilayer structure of the present invention can be appropriately set depending on the capacity and application. From the viewpoint of cost, the total thickness is preferably 300 μm or less, more preferably 250 μm or less, and even more preferably 200 μm or less. On the other hand, from the viewpoint of ensuring mechanical strength, the total thickness is preferably 30 μm or more, and more preferably 50 μm or more.

[0043] Another embodiment of the multilayer structure of the present invention is a multilayer structure having at least a resin layer (E), a layer (B) mainly composed of a polyolefin resin (b), and two or more barrier layers (C) mainly composed of an ethylene-vinyl alcohol copolymer resin (c), in which the barrier layers (C) are located on the outer and inner sides of the resin layer (E), the resin layer (E) further contains a compound (X) having a carbon number of 30 or less and a lower SP value than the ethylene-vinyl alcohol copolymer resin (c), and the proportion of the resin layer (E) to the total thickness is 20% or more.

[0044] The multilayer structure according to the other embodiment is characterized in that the thickness of the resin layer (E) is 20% or more of the total thickness. Thus, the multilayer structure according to the other embodiment can effectively suppress migration of the compound (X) even when the ratio of the resin layer (E) to the total thickness is high. The ratio may be 40% or more, or 60% or more.

[0045] The layer (B), the barrier layer (C), the compound (X), other resins and additives, and the configuration of each layer and the multilayer structure in the multilayer structure in the other embodiment can be the same as those described above. In addition, the resin layer (E) in the multilayer structure in the other embodiment may be mainly composed of recycled resin (a). That is, the resin layer (E) may have the same configuration as the recycled resin layer (A), and the same one as that used in the above-mentioned recycled resin layer (A) can be used.

[0046] The multilayer structure of the present invention is preferably used as a packaging material for films, sheets, cups, etc. As is clear from the examples described later, in the packaging material produced using the multilayer structure of the present invention, odor is suppressed, the amount of elution from the multilayer structure into a solvent is small, and migration of the compound (X) from the recycled resin layer (A) can be suppressed. Furthermore, the oxygen transmission rate (OTR) value is low and the flex resistance is excellent. Therefore, a packaging product using a packaging material containing the multilayer structure of the present invention, in which the packaging material surrounds the contents, is a more preferred embodiment, and is particularly suitable for packaging products in which the contents are food. EXAMPLES

[0047] The present invention will be described in detail below with reference to examples. In the examples, "parts" and "%" are by weight unless otherwise specified.

[0048] (Example 1) 20 commercially available packaging trays for frozen fried chicken were collected, washed, crushed, and then melt extrusion molded at 210°C to obtain recycled resin (a). Compound (X) contained in recycled resin (a) was eluted with isooctane and separated and identified by LC-MS. The SP value of the detected components was calculated using Fedors' formula (Polym. Eng. Sci., 14[2], 147 (1974)), and the SP value (14.0) of EVOH in the barrier layer (C) was calculated in the same manner. As a result, n-octane (SP value 7.5) and butyl alcohol (SP value 11.4) were included as components with SP values ​​lower than that of the EVOH.

[0049] Using a coextrusion multilayer cast film-forming apparatus, a multilayer structure was obtained in which layer (B) was made of low-density polyethylene (LDPE; "Novatec LC600" manufactured by Japan Polyethylene Corporation), adhesive resin layer (D) was made of maleic anhydride-modified polyethylene ("Admer NF500" manufactured by Mitsui Chemicals, Inc.), barrier layer (C) was made of EVOH ("Eval F171" manufactured by Kuraray Co., Ltd., ethylene content 32 mol%), and recycled resin layer (A) was made of the above-mentioned recycled resin (a) (a 9-layer coextrusion multilayer cast film having a layer thickness configuration of (B) / (D) / (C) / (D) / (A) / (D) / (C) / (D) / (B)=20 μm / 4 μm / 4 μm / 4 μm / 100 μm / 4 μm / 4 μm / 4 μm / 20 μm from the inner layer side).

[0050] The properties of the resulting multilayer structure and packaging material were evaluated in the following manner.

[0051] (Amount of elution) The amount of eluted components in a solvent was measured for the multilayer structures obtained in each of the Examples and Comparative Examples according to EN 1186-15:2002 (E). 2 After exposing the material to an isooctane solution at 40°C for one day, the amount of elution was calculated by measuring the weight of the residue after the solvent was evaporated.

[0052] (OTR) The oxygen transmission rate (OTR) of the multilayer structures obtained in each of the Examples and Comparative Examples was measured using a MOCON OX-TRAN2 / 20 model manufactured by MOCON under conditions of 20°C and 65% RH in accordance with JIS K 7126-2 (isobaric method; 2006), and the average value was calculated.

[0053] (Pinhole after bending) The multilayer structures obtained in each of the Examples and Comparative Examples were repeatedly bent 100 times in an environment of 23°C using a "BE1006 Thermostatic Gelbo Flex Tester" manufactured by Tester Sangyo Co., Ltd. in accordance with ASTM F392-74. The number of pinholes after bending was measured within an A4 size (210 mm x 297 mm). The measurement was performed on two samples each, and the average value was calculated. The fewer the number of pinholes after bending, the more excellent the flexibility (flex resistance).

[0054] (Odor) The multilayer structure obtained after bending as described above was cut into two pieces of 10 cm square, and the four sides were heat-sealed at 100° C. to prepare a packaging material. The packaging material was placed in an aluminum bag and stored at 40° C. for 10 days, after which the aluminum bag was opened and the odor was subjected to a sensory evaluation according to the following criteria. A: There was no odor. B: There was a faint odor. C: There was a clear odor.

[0055] (Examples 2 to 5, Comparative Examples 1 to 5) A multilayer structure was obtained in the same manner as in Example 1, except that the recycled resin layer (A), polyolefin layer (B), barrier layer (C), and adhesive resin layer (D) were as shown in Table 1. Table 1 shows various evaluation results of the obtained multilayer structure and packaging material. As the resin constituting the barrier layer (C), EVOH ("Eval E171" manufactured by Kuraray Co., Ltd., ethylene content 44 mol%) was used in Example 3, 6-nylon (6-Ny) was used in Comparative Example 3, and polyacrylonitrile (PAN) was used in Comparative Example 4. Furthermore, in Comparative Example 1, no barrier layer (C) was provided on the outer layer side, and in Comparative Example 2, no barrier layer (C) was used at all. In Comparative Example 5, aluminum foil was laminated instead of providing a barrier layer (C).

[0056] [Table 1]

Claims

1. A multilayer structure having at least a recycled resin layer (A) containing a recycled resin (a) as a main component, a layer (B) containing a polyolefin resin (b) as a main component, and two or more layers of a barrier layer (C) containing an ethylene-vinyl alcohol copolymer resin (c) as a main component, The barrier layer (C) is located on the outer side and the inner side of the recycled resin layer (A), A multilayer structure in which the recycled resin layer (A) further contains a compound (X) having a carbon number of 30 or less and an SP value lower than that of the ethylene-vinyl alcohol copolymer resin (c).

2. 2. The multilayer structure according to claim 1, wherein the SP value of the compound (X) is 11.5 or less.

3. 3. The multilayer structure according to claim 1, wherein the recycled resin layer (A) is made of a post-consumer recycled product containing a thermoplastic resin as a main component.

4. 4. The multilayer structure according to claim 1, wherein the compound (X) is at least one selected from the group consisting of aliphatic saturated hydrocarbons and aromatic hydrocarbons.

5. 5. The multilayer structure according to claim 1, wherein the barrier layer (C) consists solely of an ethylene-vinyl alcohol copolymer resin (c).

6. The multilayer structure according to any one of claims 1 to 5, wherein the polyolefin resin (b) comprises at least one resin selected from the group consisting of polyethylene resins and polypropylene resins.

7. The multilayer structure according to any one of claims 1 to 6, wherein the thickness of the recycled resin layer (A) is 10% or more of the total thickness.

8. 8. The multilayer structure according to claim 1, further comprising an adhesive resin layer (D) between the barrier layer (C) and the recycled resin layer (A).

9. 9. The multilayer structure according to claim 1, further comprising a layer (B) on a surface of the barrier layer (C) opposite to the recycled resin layer (A) via an adhesive resin layer (D).

10. 10. The multilayer structure according to claim 1, further comprising a layer (B) on a surface of the barrier layer (C) opposite to the resin layer (A) via an adhesive resin layer (D).

11. A multilayer structure having at least a resin layer (E), a layer (B) containing a polyolefin resin (b) as a main component, and two or more layers of a barrier layer (C) containing an ethylene-vinyl alcohol copolymer resin (c) as a main component, The barrier layer (C) is located on the outer side and the inner side of the resin layer (E), the resin layer (E) further contains a compound (X) having a carbon number of 30 or less and an SP value lower than that of the ethylene-vinyl alcohol copolymer resin (c); A multilayer structure in which the proportion of the resin layer (E) to the total thickness is 20% or more.

12. A packaging material comprising the multilayer structure according to any one of claims 1 to 11.

13. 13. A packaged product using the packaging material of claim 12, wherein the packaging material surrounds the contents.

14. 14. The packaged product of claim 13, wherein the contents are a food product.

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