Multilayer structure

Abstract

The present invention relates to a multilayer structure comprising a paper layer (A), an inorganic vapor deposition layer (B) that has a specific average thickness on one surface side of the paper layer (A), which has a specific basis weight, a barrier resin layer (C) that contains a specific ethylene-vinyl alcohol copolymer (c) as the main component, an adhesive resin layer (D), and a thermal fusion layer (E) that contains a polyolefin (e) which has a specific melting point as the main component, wherein: the layer (B), the layer (C), and the layer (D) are all directly laminated in this order; the layer (E) is one outermost layer; the ratio of the total average thickness of layers that have a polyolefin-based resin as a main component to the total value of the average thickness of each layer other than the paper layer (A) is not less than 0.50; and there is no layer containing, as a main component, a resin having a melting point of 200°C or higher, nor a metal layer having an average thickness of 1 μm or more.

Description

multilayer structure

[0001] The present invention relates to a multilayer structure and a packaging container formed from the multilayer structure.

[0002] For example, paper containers are widely used as packaging containers for containing foods and various non-food solids. In particular, multilayer structures in which a resin layer, a vapor-deposited layer, a metal foil, or the like is laminated on a paper layer are widely used as materials for food packaging containers from the viewpoints of barrier properties, heat-sealing properties, and the like. For example, Patent Document 1 discloses a paper container for liquids formed by molding a laminate having a paper layer as a main component, a surface thermoplastic resin layer on the front side, and a barrier film layer and a sealant layer, in this order, on the back side, wherein the barrier film layer has an inorganic vapor-deposited layer formed by vapor-depositing a metal oxide on the EVOH surface of a base film composed of an ethylene-vinyl alcohol copolymer (EVOH) layer and a polypropylene resin layer, the back side of the paper layer and the inorganic vapor-deposited layer being bonded by a polyolefin-based resin layer, and the sealant layer is formed by extrusion-molding a polypropylene resin layer on the polypropylene resin surface of the barrier film layer. Furthermore, Patent Document 2 discloses a simultaneous biaxially oriented multilayer polymer barrier film having gas barrier properties and comprising a polyolefin core layer and at least one barrier surface layer of ethylene vinyl alcohol (EVOH) on at least one side of the core layer, wherein the EVOH barrier layer has a thickness of less than 1.5 μm and an ethylene content of 36 mol % or less, and the film can be heated to 10 cm at 23° C. and 50% RH for 24 hours. ３ / m ２ A simultaneously biaxially oriented multilayer polymer barrier film is disclosed having an oxygen transmission rate (OTR) of less than 1 atm / 1 day.

[0003] JP 2022-16880 A Patent No. 6486104 A

[0004] Packaging containers for storing foods and the like are required to have high gas barrier properties from the viewpoint of maintaining quality. In particular, paper containers are formed by folding a multilayer structure including a paper layer and heat-sealing it, etc., which can easily cause pinholes to form at the bent portions, resulting in a decrease in gas barrier properties. Furthermore, if the gas barrier properties of heat-sealed or other similar areas decrease, gases such as oxygen and water vapor may pass through those areas. Therefore, it is necessary to ensure good gas barrier properties even in areas that have undergone heat-sealing or other heat-pressing treatments. Furthermore, from the viewpoint of reducing costs during packaging container production and minimizing the effects of heat on packaged items during heat-sealing, it is desirable to be able to heat-seal at lower temperatures. However, the conventional paper containers described above sometimes exhibit insufficient low-temperature sealing properties and gas barrier properties after heat-pressing.

[0005] Furthermore, packaging materials such as paper containers are desired to be materials that are easy to collect and reuse (high recyclability). However, in a multilayer structure in which various resin layers and the like are provided in addition to a paper layer, when the resin layers from which the paper layers have been removed are melt-molded, defects may occur in the resulting recycled product (melt-molded product), resulting in deterioration in appearance and quality, due to differences in the melting temperatures of the resins, crosslinking reactions of the resins, and the like.

[0006] Therefore, an object of the present invention is to provide a multilayer structure that has good gas barrier properties and low-temperature sealing properties before and after bending and after hot pressing, and that can suppress the occurrence of defects during recycling.

[0007] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by forming a multilayer structure that satisfies specific requirements. That is, the present invention encompasses the following inventions: [1] A paper layer (A), and an inorganic vapor deposition layer (B), a barrier resin layer (C), an adhesive resin layer (D), and a thermal seal layer (E) on one side of the paper layer (A), wherein the inorganic vapor deposition layer (B), the barrier resin layer (C), and the adhesive resin layer (D) are all directly laminated in this order, and the thermal seal layer (E) is one of the outermost layers, and the paper layer (A) has a basis weight of 30 to 150 g / m ２[2] A multilayer structure according to item [1], wherein the inorganic vapor deposition layer (B) has an average thickness of 5 to 200 nm, the barrier resin layer (C) contains, as a main component, an ethylene-vinyl alcohol copolymer (c) having an ethylene unit content of 20 to 50 mol% and a saponification degree of 90 mol% or more, the heat-sealable layer (E) contains, as a main component, a polyolefin (e) having a melting point of 175°C or less, the ratio of the total average thickness of the layers containing a polyolefin resin as a main component to the total value of the average thicknesses of the layers other than the paper layer (A) is 0.50 or more, and the multilayer structure does not contain a layer containing, as a main component, a resin having a melting point of 200°C or more and a metal layer having an average thickness of 1 μm or more. [2] The multilayer structure according to item [1], wherein the paper layer (A) is provided on the side of the inorganic vapor deposition layer (B) opposite to the barrier resin layer (C). [3] The multilayer structure according to [1] or [2], further comprising a thermoplastic resin layer (F) present between the adhesive resin layer (D) and the heat-sealing layer (E), the thermoplastic resin layer (F) containing polyolefin (f) as a main component. [4] The multilayer structure according to [3], wherein the average thickness (Ft) of the thermoplastic resin layer (F) is greater than the average thickness (Et) of the heat-sealing layer (E). [5] The multilayer structure according to any one of [1] to [4], further comprising a thermoplastic resin layer (G) present between the paper layer (A) and the inorganic vapor deposition layer (B), the thermoplastic resin layer (G) containing polyolefin-based resin (g) as a main component. [6] The multilayer structure according to any one of [1] to [5], wherein the adhesive resin layer (D) contains adhesive resin (d) having a melting point of 175°C or less as a main component. [7] The multilayer structure according to the above [6], wherein the adhesive resin (d) is at least one selected from the group consisting of acid-modified polyethylene (d1) and acid-modified polypropylene (d2). [8] The polyolefin (e) is polyethylene (e1), and the density of the polyethylene (e1) is 0.880 to 0.940 g / cm ３[9] The multilayer structure according to any one of [1] to [7] above, wherein the polyolefin (e) is polypropylene (e2).

[10] The multilayer structure according to [9] above, wherein the heat-sealable layer (E) contains, as the polypropylene (e2), polypropylene (e2-1) having a melting point of more than 110°C and polypropylene (e2-2) having a melting point of 110°C or less, and the mass ratio (e2-1 / e2-2) of the polypropylene (e2-1) to the polypropylene (e2-2) is 55 / 45 to 96 / 4.

[11] The density of the polypropylene (e2-2) is 0.860 to 0.905 g / cm ３

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

[11] above, wherein the minimum temperature at which the heat seal strength exceeds 3 N / 15 mm, obtained by placing the heat-sealable layers (E) face to face and pressing them together using a hot plate heat sealer at a pressure of 0.1 MPa for 1 second, is less than 110°C.

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

[12] above, wherein the inorganic vapor-deposited layer (B) is a metal vapor-deposited layer containing aluminum as a main component, or an inorganic oxide vapor-deposited layer containing alumina or silica as a main component.

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

[13] above, wherein the barrier resin layer (C) contains 10 to 200 ppm of at least one polyvalent metal ion selected from the group consisting of magnesium ions, calcium ions, and zinc ions.

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

[14] above, wherein the barrier resin layer (C) contains two or more ethylene-vinyl alcohol copolymers (c) having different ethylene unit contents.

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

[15] above, wherein the ethylene unit content of the ethylene-vinyl alcohol copolymer (c) is 22 to 30 mol%.

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

[16] above, wherein the multilayer structure has a coextruded film comprising a barrier resin layer (C) and an adhesive resin layer (D), and wherein the coextruded film has an average thickness of 8 to 120 μm.

[18] The multilayer structure according to

[17] above, wherein the coextruded film further comprises a heat-sealing layer (E).

[19] The multilayer structure according to

[17] or

[18] above, wherein the thickness of the barrier resin layer (C) is 0.1 to 30 μm, and the ratio of the thickness of the barrier resin layer (C) to the total thickness of all layers of the coextruded film is 25% or less.

[20] The multilayer structure according to any one of

[17] to

[19] above, wherein the coextruded film is substantially unstretched.

[21] The multilayer structure according to any one of

[17] to

[19] above, wherein the coextruded film is stretched 3 to 12 times in at least one axial direction.

[22] The multilayer structure according to any one of

[17] to

[19] above, wherein the coextruded film is stretched 3 to 12 times in each of two axial directions.

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

[22] above, which does not have an adhesive layer consisting solely of a curing adhesive.

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

[23] above, wherein the mass ratio of the paper layer (A) to the entire multilayer structure is 0.55 or more.

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

[24] above, which does not have a thermal seal layer on the side of the paper layer (A) opposite to the barrier resin layer (C).

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

[25] above, wherein the paper layer (A) is one of the outermost layers.

[27] The oxygen transmission rate measured under conditions of 20°C and 65% RH using the method described in JIS K 7126-2 (isobaric method: 2006), with the paper layer (A) side as the oxygen supply side and the thermal seal layer (E) as the carrier gas side, is 0.5 cc / (m ２

[28] The multilayer structure according to any one of the above [1] to

[26] , wherein the multilayer structure is folded in four so that the heat-sealable layer (E) is on the inside, and the folding is performed by folding in half lengthwise and then in half widthwise, and in this state, a load of 5 kg is applied from above and left to stand for 1 minute, and then the oxygen transmission rate is measured under conditions of 20°C and 65% RH according to the method described in JIS K 7126-2 (isobaric method: 2006) with the paper layer (A) side as the oxygen supply side and the heat-sealable layer (E) as the carrier gas side, and the oxygen transmission rate is 1.0 cc / (m ２

[29] A packaging container formed from the multilayer structure according to any one of [1] to

[28] .

[0008] According to the present invention, it is possible to provide a multilayer structure that has good gas barrier properties and low-temperature sealing properties before and after bending and after hot pressing, and that can further suppress the occurrence of defects during recycling.

[0009] The following describes examples of embodiments of the present invention (hereinafter also referred to as "one aspect of the present invention"). However, each embodiment described below is merely an example for embodying the technical concept of the present invention, and the present invention is not limited to the following description. The present invention also includes embodiments in which the details described herein are arbitrarily selected or arbitrarily combined. Although preferred embodiments are described herein, combinations of two or more of the individual preferred embodiments are also preferred. Preferred specifications can be selected arbitrarily; for example, combinations of preferred specifications can be considered more preferable. Unless otherwise specified, the term "XX to YY" used herein as a numerical range means "XX or more and YY or less" (XX represents the lower limit and YY represents the upper limit). For example, simply describing a numerical range as "10 to 90" means a range of 10 or more and 90 or less. In this specification, the lower and upper limits described in stages for numerical ranges (such as each characteristic value, each component content, each structural unit content, each production condition, and values ​​calculated therefrom, each characteristic, and each condition) can be independently combined. For example, from a description of "preferably 10 to 90, more preferably 30 to 60" for the same item, the "preferable lower limit (10)" and the "more preferable upper limit (60)" can be combined to form "10 to 60." Furthermore, for a numerical range, for example, based on the description of "preferably 10 to 90, more preferably 30 to 60," the upper limit can be specified as "10 or more" or "30 or more" without a particular upper limit. Similarly, the upper limit can be specified as "90 or less" or "60 or less" without a particular lower limit. The same applies when the upper end of the numerical range is "less than" or when the lower limit is "over." Similarly, for example, from a description of "preferably 10 or more, more preferably 30 or more" for the same item and "preferably 90 or less, more preferably 60 or less," the "preferable lower limit (10)" and the "more preferable upper limit (60)" can be combined to form "10 or more and 60 or less." Similarly, the lower limit value alone can be specified as "10 or more" or "30 or more," and similarly, the upper limit value alone can be specified as "90 or less" or "60 or less."The same applies when the expressions "more than or equal to" and "less than or equal to" in the above description are written as "more than" and "less than," respectively. That is, for example, based on the description "preferably more than 10 and less than 90, more preferably 30 or more and 60 or less," the upper and lower limits can be combined to form "more than 10 and 60 or less" or "30 or more and less than 90."

[0010] In this specification, the following terms have the following meanings unless otherwise specified. "Major component" refers to the component with the highest content by mass. "Average thickness" of each layer refers to the average thickness measured at any five locations. "ppm" refers to the content by mass (ppm by mass). "Polyethylene" refers to a homopolymer of ethylene; a copolymer of 80 mol% or more of ethylene and 20 mol% or less of α-olefin monomer, based on 100 mol% of the total amount of monomers; and a copolymer obtained by copolymerizing 90 mol% or more of ethylene with 10 mol% or less of a non-olefin monomer whose functional group contains atoms other than carbon, oxygen, and hydrogen atoms, based on 100 mol% of the total amount of monomers. "Acid-modified polyethylene" refers to a polymer obtained by modifying polyethylene with an acid. Acid-modified polyethylene may be a polymer in which at least one of an acid group and an acid anhydride group has been introduced into polyethylene. "Polyethylene-based resin" refers to polyethylene and modified polyethylene (such as acid-modified polyethylene). Modified polyethylene refers to a polymer obtained by modifying polyethylene. "Polypropylene" refers to a propylene homopolymer; a copolymer of propylene with at least one selected from the group consisting of ethylene and α-olefin monomers having 4 or more carbon atoms (excluding the polyethylene); and a copolymer of propylene with a non-olefin monomer whose functional group does not contain atoms other than carbon atoms, oxygen atoms, and hydrogen atoms. "Acid-modified polypropylene" refers to a polymer obtained by modifying polypropylene with acid. Acid-modified polypropylene may be a polymer in which at least one of an acidic group and an acid anhydride group has been introduced into polypropylene. "Polypropylene-based resin" refers to polypropylene and modified polypropylene (such as acid-modified polypropylene). Modified polypropylene refers to a polymer obtained by modifying polypropylene. "Polyolefin" refers to a polymer having structural units derived from olefin monomers, such as the polyethylene and polypropylene described above. "Acid-modified polyolefin" refers to a polymer obtained by modifying polyolefin with acid.The acid-modified polyolefin may be a polymer in which at least one of an acid group and an acid anhydride group is introduced into a polyolefin. "Polyolefin-based resin" refers to polyolefin and modified polyolefin (such as acid-modified polyolefin). Modified polyolefin refers to a polymer obtained by modifying a polyolefin. The "surface" of a multilayer structure does not mean a distinction between the front and back, but refers to the exposed surface. In other words, the multilayer structure has two surfaces. Similarly, the multilayer structure has two outermost layers.

[0011] Furthermore, in this specification, "ZZ unit" (ZZ is replaced with the name of the monomer) refers to a structural unit derived from the monomer ZZ that constitutes a polymer; for example, "ethylene unit" refers to a structural unit derived from ethylene that constitutes a polymer. Furthermore, in this specification, "MD direction" refers to the flow direction of the film during film formation, and MD is also an abbreviation for Machine Direction. Usually, the MD direction is the longitudinal direction of the film. Furthermore, in this specification, "TD direction" refers to the direction perpendicular to the MD direction, and TD is also an abbreviation for Transverse Direction. Usually, the TD direction is the transverse direction of the film.

[0012] Furthermore, in this specification, unless otherwise specified, the terms "gas barrier property," "low-temperature sealability," "heat resistance," and "recyclability" refer to the properties of the multilayer structure of one embodiment of the present invention. These properties are measured and evaluated by the methods described in the Examples. Therefore, more strictly, the term "recyclability" refers to the properties when the portion of the multilayer structure from which the paper layer (A) has been removed is melt-molded and reused (recycled). In the multilayer structure, the paper layer (A) can be recycled as a paper material such as raw pulp. Therefore, if the recyclability of the portion from which the paper layer (A) has been removed is good, this means that the entire multilayer structure can be effectively recycled. Similarly, in this specification, unless otherwise specified, the terms "defects during recycling" and "coloration during recycling" refer to the defects or coloration, respectively, that occur when recycling the portion from which the paper layer (A) has been removed from the multilayer structure of one embodiment of the present invention. Furthermore, in this specification, unless otherwise specified, the term "recyclability" refers to the properties that include both "defects during recycling" and "coloration during recycling." In addition, in this specification, the term "gas barrier properties after heat pressing" refers to the gas barrier properties of the multilayer structure evaluated in the severe sealing test described in the examples below.

[0013] [Multilayer structure] A multilayer structure according to one embodiment of the present invention (also referred to as "the multilayer structure" in this specification) comprises: a paper layer (A); and an inorganic vapor deposition layer (B), a barrier resin layer (C), an adhesive resin layer (D), and a heat-sealing layer (E) on one side of the paper layer (A), the inorganic vapor deposition layer (B), the barrier resin layer (C), and the adhesive resin layer (D) are all directly laminated in this order, with the heat-sealing layer (E) being one of the outermost layers; and the paper layer (A) has a basis weight of 30 to 150 g / m ２the average thickness of the inorganic vapor deposition layer (B) is 5 to 200 nm; the barrier resin layer (C) contains, as a main component, an ethylene-vinyl alcohol copolymer (c) having an ethylene unit content of 20 to 50 mol% and a saponification degree of 90 mol% or more; the heat-sealable layer (E) contains, as a main component, a polyolefin (e) having a melting point of 175°C or less; the ratio of the total average thickness of the layers containing a polyolefin resin as a main component to the total value of the average thicknesses of the layers other than the paper layer (A) is 0.50 or more; and the multilayer structure does not contain a layer containing, as a main component, a resin having a melting point of 200°C or more and a metal layer having an average thickness of 1 μm or more. The multilayer structure having the above-mentioned aspect can achieve the excellent effects of the present invention. In this specification, the term "direct lamination" means that the layers to be laminated are laminated without any other layers interposed between them.

[0033] Therefore, the phrase "the inorganic vapor deposition layer (B), the barrier resin layer (C), and the adhesive resin layer (D) are all directly laminated in this order" means that the inorganic vapor deposition layer (B), the barrier resin layer (C), and the adhesive resin layer (D) are laminated in this order, with no other layers interposed between the inorganic vapor deposition layer (B) and the barrier resin layer (C), and between the barrier resin layer (C) and the adhesive resin layer (D). Hereinafter, each layer and the layer configuration of the multilayer structure according to one embodiment of the present invention will be described in detail.

[0014] <Paper layer (A)> The paper layer (A) (also referred to as "layer (A)" in this specification) has a basis weight (mass per unit area) of 30 to 150 g / m ２ The basis weight of the layer (A) is 30 g / m ２ By satisfying the above, the processability when manufacturing a multilayer structure can be further improved, and the strength of the resulting multilayer structure can be further increased. Furthermore, since it becomes easier to increase the mass ratio of the paper layer (A) in the multilayer structure, the impact of recovery loss that can inevitably occur during operations when recycling the paper layer (A) can be reduced, and as a result, it is expected that the recycling rate of the paper layer (A) itself (mass of recovered paper / mass of paper layer (A)) will be improved. Furthermore, when the basis weight of the layer (A) is 150 g / m ２By ensuring that the basis weight of the layer (A) is not more than 40 g / m, it is possible to improve the low-temperature sealing property and also to suppress the deterioration of the gas barrier property of the resulting multilayer structure after hot pressing. ２ , more preferably 50 to 120 g / m ２ , more preferably 60 to 100 g / m ２ The basis weight of the layer (A) is a value measured in accordance with JIS P8124:2011.

[0015] The density of the layer (A) is preferably, for example, 0.5 to 1.5 g / cm ３ , more preferably 0.7 to 1.3 g / cm ３ is.

[0016] In addition, common paper containing plant-derived pulp as a main component can be used for the layer (A). In addition to pulp, the layer (A) may contain sizing agents, fillers, paper strength agents, retention aids, pH adjusters, drainage improvers, water-resistant agents, softeners, antistatic agents, antifoaming agents, slime control agents, dyes, pigments, etc. Examples of paper constituting the layer (A) include kraft paper, fine paper, medium-quality paper, alkaline paper, glassine paper, semi-glassine paper, and parchment paper, with fine paper being preferred. The paper used for the layer (A) can be produced by a known method. In addition, commercially available paper can be used for the layer (A).

[0017] <Inorganic Vapor Deposited Layer (B)> The inorganic vapor deposited layer (B) (also referred to as "layer (B)" in this specification) is a layer that primarily contributes to the gas barrier property of the multilayer structure. The average thickness of layer (B) is 5 to 200 nm. When the average thickness of layer (B) is 5 nm or more, the gas barrier property can be further improved. When the average thickness of layer (B) is 200 nm or less, the occurrence of coloration when the resulting multilayer structure is recycled can be further suppressed. A recycled product (melt-molded product) with suppressed coloration is preferred because it has a good appearance. From the viewpoint of obtaining the above-mentioned advantages, the average thickness of layer (B) is preferably 10 to 150 nm, more preferably 20 to 120 nm, and even more preferably 30 to 80 nm. The average thickness can be measured specifically by the method described in the Examples below.

[0018] The layer (B) can be formed by vapor deposition of an inorganic substance. Typically, the layer (B) is formed by vapor deposition of an inorganic substance on the surface of the barrier resin layer (C). Examples of the inorganic substance include metals (e.g., aluminum, copper, etc.), oxides (e.g., alumina, silica, etc.), nitrides (e.g., silicon nitride, etc.), nitride oxides (e.g., silicon oxynitride, etc.), and carbonitrides (e.g., silicon carbonitride, etc.).

[0019] Layer (B) is preferably a metal vapor deposition layer or an inorganic oxide vapor deposition layer. When emphasis is placed on light blocking properties and gas barrier properties after bending treatment, layer (B) is more preferably a metal vapor deposition layer, even more preferably a metal vapor deposition layer mainly composed of aluminum, and may be an aluminum vapor deposition layer. On the other hand, when emphasis is placed on preventing discoloration during recycling, layer (B) is more preferably an inorganic oxide vapor deposition layer, even more preferably an inorganic oxide vapor deposition layer mainly composed of alumina (aluminum oxide) or silica (silicon oxide), and may be an alumina vapor deposition layer or a silica vapor deposition layer. Therefore, in one embodiment of the multilayer structure, layer (B) is more preferably a metal vapor deposition layer mainly composed of aluminum, or an inorganic oxide vapor deposition layer mainly composed of alumina or silica. In this specification, the term "metal vapor deposition layer" refers to a layer containing metal atoms as a main component. For example, in one embodiment of the multilayer structure, the content of metal atoms in layer (B) is preferably 50% by mass or more, and may also be 80% by mass or more, or 90% by mass or more, based on the total amount (100% by mass) of layer (B). In this specification, the term "inorganic oxide vapor-deposited layer" refers to a layer containing an inorganic oxide as a main component. For example, in one embodiment of the multilayer structure, the content of the inorganic oxide in 100% by mass of the total amount of layer (B) is preferably 50% by mass or more, and may also be 80% by mass or more, or 90% by mass or more.

[0020] In the metal vapor deposition layer containing aluminum as the main component, oxidation occurs irreversibly, and aluminum oxide may be partially contained. In the metal vapor deposition layer containing aluminum as the main component, the molar ratio of the content of oxygen atoms to the content of aluminum atoms (O ｍｏｌ / Al ｍｏｌ ) is preferably 0.5 or less, more preferably 0.3 or less, and even more preferably 0.1 or less. ｍｏｌ / Al ｍｏｌ ) is preferably 0 to 0.5, more preferably 0 to 0.3, and even more preferably 0 to 0.1.

[0021] The layer (B) can be provided by a known physical vapor deposition method or chemical vapor deposition method, specifically, a vacuum vapor deposition method, a sputtering method, an ion plating method, an ion beam mixing method, a plasma CVD method, a laser CVD method, an MO-CVD method, a thermal CVD method, etc., and a physical vapor deposition method is preferred, and a vacuum vapor deposition method is more preferred.

[0022] Before vapor deposition, the surface of the layer to be vapor deposited (for example, the barrier resin layer (C)) may be plasma-treated. A known method can be used for the plasma treatment, and atmospheric pressure plasma treatment is preferred. Examples of discharge gases used in atmospheric pressure plasma treatment include nitrogen gas, helium, neon, argon, krypton, xenon, and radon. Among these, nitrogen, helium, and argon are preferred, and nitrogen is more preferred from the viewpoint of cost reduction.

[0023] The layer (B) may consist of a single layer or multiple layers.

[0024] The multilayer structure may include only one layer (B), or may include multiple layers (B). When the multilayer structure includes multiple layers (B), the layers (B) may be identical to or different from one another in composition and thickness. When the multilayer structure includes multiple layers (B), the average thickness of the layers (B) refers to the total average thickness of all the layers (B). When the multilayer structure includes multiple layers (B) and is a laminate in which the layers (B) are directly laminated to one another, the above-mentioned embodiment of "the inorganic vapor deposition layer (B), the barrier resin layer (C), and the adhesive resin layer (D) are all directly laminated in this order" may be such that the layer (B) closest to the layer (C) in the laminate is directly laminated to the layer (C). Furthermore, when a plurality of layers (B) are present but the layers (B) are not directly laminated to one another, it is sufficient that any one of the layers (B) satisfies the above-mentioned aspect that "the inorganic vapor deposition layer (B), the barrier resin layer (C), and the adhesive resin layer (D) are all directly laminated to one another in this order."

[0025] <Barrier Resin Layer (C)> The barrier resin layer (C) (also referred to as "layer (C)" in this specification) contains, as a main component, an ethylene-vinyl alcohol copolymer (c) having an ethylene unit content of 20 to 50 mol% and a saponification degree of 90 mol% or more. Because the multilayer structure includes layer (C), it can exhibit high gas barrier properties both before and after bending. It can also exhibit good gas barrier properties after hot pressing. In particular, layer (C) has good affinity with the inorganic vapor deposition layer (B) described below. Therefore, direct lamination of the inorganic vapor deposition layer (B) and layer (C) tends to result in significantly improved gas barrier properties before and after bending. Furthermore, in this specification, "ethylene-vinyl alcohol copolymer" is also abbreviated as "EVOH."

[0026] (Ethylene-Vinyl Alcohol Copolymer (c)) Ethylene-vinyl alcohol copolymer (c) (hereinafter also referred to as "EVOH (c)") has an ethylene unit content of 20 mol% or more and 50 mol% or less and a degree of saponification of 90 mol% or more. The "ethylene unit content" in the EVOH (c) refers to the content (mol%) of units derived from ethylene monomers in 100 mol% of the total amount of structural units constituting the EVOH (c). The "degree of saponification" in the EVOH (c) refers to the ratio of vinyl alcohol units to the total number of vinyl alcohol units and vinyl ester units in the EVOH (c). EVOH (c) is a copolymer having ethylene units and vinyl alcohol units. EVOH (c) is usually obtained by saponifying an ethylene-vinyl ester copolymer. EVOH (c) may have residual vinyl ester units.

[0027] By having the ethylene unit content of EVOH (c) be 20 mol% or more, defects and coloration during recycling can be further suppressed. From the same viewpoint, the ethylene unit content is preferably 22 mol% or more, more preferably 24 mol% or more, and even more preferably 26 mol% or more or 28 mol% or more, and may be 30 mol% or more. On the other hand, by having the ethylene unit content of EVOH (c) be 50 mol% or less, the gas barrier properties before and after bending treatment and the gas barrier properties after hot pressing can be further improved. From the same viewpoint, the ethylene unit content is preferably 46 mol% or less, more preferably 42 mol% or less, even more preferably 38 mol% or less, and even more preferably 34 mol% or less, and may be 30 mol% or less. As described above, these stepwise lower and upper limits can be independently combined. For example, in one embodiment of the multilayer structure, from the viewpoint of achieving a good balance between the above-mentioned advantages, the ethylene unit content of EVOH (c) is preferably 22 to 46 mol%, more preferably 24 to 42 mol%, even more preferably 26 to 38 mol%, and even more preferably 28 to 34 mol%. Furthermore, for example, when emphasis is placed on further suppressing defects and coloration during recycling, in one embodiment of the multilayer structure, the ethylene unit content of EVOH (c) is preferably 30 to 50 mol%, more preferably 30 to 46 mol%. Furthermore, for example, when emphasis is placed on achieving even better gas barrier properties, in one embodiment of the multilayer structure, the ethylene unit content of EVOH (c) is preferably 20 to 30 mol%, more preferably 22 to 30 mol%.

[0028] When the saponification degree of EVOH (c) is 90 mol% or more, gas barrier properties and the like tend to be further improved. From the viewpoint of further improving the gas barrier properties, the saponification degree is preferably 95 mol% or more, more preferably 99 mol% or more, and even more preferably 99.9 mol% or more. The saponification degree of EVOH (c) is 100 mol% or less. In other words, the saponification degree of EVOH (c) is 90 to 100 mol%, preferably 95 to 100 mol%, more preferably 99 to 100 mol%, and even more preferably 99.9 to 100 mol%. The ethylene unit content and saponification degree of EVOH (c) are １ It can be determined by H-NMR measurement. Specifically, it can be measured by the method described in the examples below.

[0029] The production and saponification of the ethylene-vinyl ester copolymer can be carried out by known methods. Examples of the vinyl ester include vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl pivalate, vinyl versatate, and other aliphatic carboxylic acid vinyl esters. Among these vinyl esters, vinyl acetate is preferred.

[0030] The total content of ethylene units, vinyl alcohol units, and vinyl ester units in EVOH (c) is preferably 90 to 100 mol %, more preferably 95 to 100 mol %, even more preferably 97 to 100 mol %, and still more preferably 99 to 100 mol %, based on 100 mol % of the total amount of structural units constituting EVOH (c). Alternatively, it may be 100 mol %.

[0031] EVOH (c) may contain structural units other than ethylene units, vinyl alcohol units, and vinyl ester units, provided that the objectives of the present invention are not impaired. In particular, the introduction of a modifying group containing a primary hydroxyl group having a specific structure may enable EVOH (c) to achieve both high levels of gas barrier properties and moldability. The content of other monomer units, based on 100 mol% of the total structural units constituting EVOH (c), is preferably 0 to 10 mol%, more preferably 0 to 5 mol%, even more preferably 0 to 3 mol%, even more preferably 0 to 1 mol%, and even more preferably 0 to 1 mol%, and is even more preferably substantially free. The term "substantially free" specifically means that the content of other monomer units, based on 100 mol% of the total structural units constituting EVOH (c), is 0 to 0.5 mol%, preferably 0 to 0.1 mol%, more preferably 0 to 0.05 mol%, and even more preferably 0 to 0.01 mol%.

[0032] Examples of the other monomers include α-olefins such as propylene, n-butene, isobutylene, and 1-hexene; acrylic acid and its salts; unsaturated monomers having an acrylic ester group; methacrylic acid and its salts; unsaturated monomers having a methacrylic ester group; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts (e.g., quaternary salts); methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid and its salts, methacrylamidopropyldimethylamine and its salts (e.g., quaternary salts); vinyl ethers such as ethyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, and 2,3-diacetoxy-1-vinyloxypropane; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane, and allyl chloride; unsaturated dicarboxylic acids and salts or esters thereof such as maleic acid, itaconic acid, and fumaric acid; vinylsilane compounds such as vinyltrimethoxysilane;isopropenyl acetate, 3-acyloxy-1-propene, 3-acyloxy-1-butene, 4-acyloxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4-acyloxy-2-methyl-1-butene, 4-acyloxy-3-methyl-1-butene, 3,4-diacyloxy-2-methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, Examples of such alkenes include ester groups such as 4,5-diacyloxy-1-pentene, 4-acyloxy-1-hexene, 5-acyloxy-1-hexene, 6-acyloxy-1-hexene, 5,6-diacyloxy-1-hexene, 1,3-diacetoxy-2-methylenepropane, or saponified products thereof, 1,3-dipropionyloxy-2-methylenepropane, and 1,3-dibutyronyloxy-2-methylenepropane;

[0033] The melt flow rate (MFR) (190°C, 2.16 kg load) of EVOH (c) measured in accordance with ISO1133-1:2011 is preferably 0.5 to 12 g / 10 min, more preferably 0.8 to 8.0 g / 10 min, and even more preferably 1.0 to 6.0 g / 10 min.

[0034] The EVOH (c) may be used alone or in combination of two or more kinds.

[0035] The barrier resin layer (C) may contain two or more types of EVOH (c) with different ethylene unit contents. In this case, the gas barrier properties before and after bending, the gas barrier properties after hot pressing, and the low-temperature sealability can be improved in a more balanced manner. The two or more types of EVOH (c) with different ethylene unit contents may be two or more types of EVOH (c) with different melting points. For example, when the melting point is measured by differential scanning calorimetry (DSC), peak temperatures corresponding to each EVOH (c) may be confirmed. In measuring the melting point by DSC, the melting point is determined from the peak temperature measured during the second heating step, in which the sample is heated from 30°C to 250°C at a rate of 10°C / min, held at 250°C for 3 minutes, cooled to 30°C at 50°C / min, held at 30°C for 3 minutes, and then heated again from 30°C to 250°C at a rate of 10°C / min.

[0036] For example, when layer (C) contains two or more types of EVOH (c) having different ethylene unit contents, the ethylene unit content of the EVOH (c) having the lower ethylene unit content (hereinafter also referred to as "EVOH (c1)") among the two types of EVOH (c) is preferably 20 to 40 mol%, more preferably 24 to 32 mol%, and the ethylene unit content of the EVOH (c) having the higher ethylene unit content (hereinafter also referred to as "EVOH (c2)") among the two types of EVOH (c) is preferably 32 to 50 mol%, more preferably 38 to 48 mol%.

[0037] The difference (c2-c1) in the ethylene unit content between EVOH (c2) and EVOH (c1), i.e., the value obtained by subtracting the ethylene unit content of EVOH (c1) from the ethylene unit content of EVOH (c2), is preferably 4 to 40 mol%, more preferably 8 to 30 mol%, even more preferably 12 to 25 mol%, and even more preferably 15 to 20 mol%.

[0038] The mass ratio (c1 / c2) of EVOH (c1) to EVOH (c2), i.e., the mass ratio of the content of EVOH (c1) to the content of EVOH (c2) in layer (C) is preferably 50 / 50 to 95 / 5, more preferably 60 / 40 to 90 / 10, and even more preferably 70 / 30 to 85 / 15.

[0039] The proportion of EVOH (c) in the resins constituting layer (C) is preferably 70 to 100 mass%, more preferably 80 to 100 mass%, even more preferably 90 to 100 mass%, and may be 95 to 100 mass%, 99 to 100 mass%, or 99.9 to 100 mass%, based on 100 mass% of the total amount of resins constituting layer (C). From the viewpoint of gas barrier properties, etc., the content of EVOH (c) in layer (C) is preferably 70 mass% or more, more preferably 80 mass% or more, even more preferably 90 mass% or more, based on 100 mass% of the total amount of layer (C), and may also be 95 mass% or more, 99 mass% or more, or 99.9 mass% or more. Furthermore, the content of EVOH (c) in layer (C) is 100 mass% or less, and may be 99.99 mass% or less, based on 100 mass% of the total amount of layer (C). For example, in one embodiment of the multilayer structure, the content of EVOH (c) in Layer (C) is preferably 70 to 100 mass%, more preferably 80 to 100 mass%, and even more preferably 90 to 100 mass%, based on 100 mass% of the total amount of Layer (C), and may also be 95 to 100 mass%, 99 to 100 mass%, 99.9 to 100 mass%, 70 to 99.99 mass%, 80 to 99.99 mass%, 90 to 99.99 mass%, 95 to 99.99 mass%, 99 to 99.99 mass%, or 99.9 to 99.99 mass%.

[0040] Layer (C) preferably contains at least one polyvalent metal ion selected from the group consisting of magnesium ions, calcium ions, and zinc ions. The content of the polyvalent metal ions in layer (C) is preferably 10 ppm or more, more preferably 30 ppm or more, and even more preferably 40 ppm. When particularly important is to suppress defects in the recycled resin, 80 ppm or more may be even more preferable. Having layer (C) contain the polyvalent metal ions at or above the lower limit is preferred because the occurrence of defects during recycling is further suppressed. On the other hand, the content of the polyvalent metal ions in layer (C) may be, for example, 300 ppm or less, but is preferably 200 ppm or less, more preferably 150 ppm or less, and even more preferably 120 ppm or less. When particularly important is to suppress discoloration of the recycled resin, 80 ppm or less may be even more preferable. Having the content of the polyvalent metal ions in layer (C) at or below the upper limit is preferred because the occurrence of discoloration during recycling is suppressed. As described above, these stepwise lower and upper limits can be independently combined. For example, in one embodiment of the multilayer structure, Layer (C) may contain 10 to 300 ppm, preferably 10 to 200 ppm, more preferably 30 to 150 ppm, and even more preferably 50 to 120 ppm, of at least one polyvalent metal ion selected from the group consisting of magnesium ions, calcium ions, and zinc ions. Furthermore, in one embodiment of the multilayer structure, the content of the polyvalent metal ion in Layer (C) may be 10 to 80 ppm, 30 to 80 ppm, 80 to 200 ppm, or 80 to 120 ppm.

[0041] The polyvalent metal ions preferably contain magnesium ions, and more preferably are magnesium ions, from the viewpoint of further suppressing the occurrence of defects during recycling.

[0042] The polyvalent metal ions are preferably present in layer (C) as cations constituting a salt, and more preferably as cations constituting a carboxylate in layer (C). In the salt such as the carboxylate, the polyvalent metal ions and anions may be bonded or free.

[0043] The carboxylate salt containing the polyvalent metal ion is preferably a higher fatty acid salt. Specifically, it is preferably a salt of a carboxylic acid having 12 or more carbon atoms. When the polyvalent metal ion is present in the form of such a higher fatty acid salt, the occurrence of coloration during recycling is further suppressed. Examples of carboxylic acids having 12 or more carbon atoms include lauric acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, basic stearic acid, hydroxystearic acid, basic hydroxystearic acid, nonadecanoic acid, oleic acid, behenic acid, montanic acid, and linoleic acid. The number of carbon atoms of the carboxylic acid may be 12 to 30, 14 to 26, or 16 to 22.

[0044] The polyvalent metal ions may be present in layer (C) as cations constituting fatty acid salts having 11 or less carbon atoms (acetates, propionates, etc.), salts other than fatty acid salts (nitrates, sulfates, etc.), etc. Some or all of the polyvalent metal ions may be present in a state of being coordinated to hydroxyl groups, etc. of EVOH (c), for example.

[0045] The layer (C) may contain, as optional components other than the EVOH (c) and the polyvalent metal ions or salts containing the polyvalent metal ions, boron compounds, carboxylic acids, phosphorus compounds, metal ions other than the polyvalent metal ions, antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, heat stabilizers, resins other than the EVOH (c), etc. The layer (C) may contain two or more of these optional components.

[0046] Examples of the boron compound include boric acids such as orthoboric acid, metaboric acid, and tetraboric acid; boric acid esters such as triethyl borate and trimethyl borate; alkali metal salts or alkali earth metal salts of the boric acids, and boric acid salts such as borax; and boron hydrides. The content of the boron compound in layer (C) is preferably 10 to 1,000 ppm, and more preferably 50 to 400 ppm, in layer (C). By setting the content of the boron compound within the above range, the melt-formability, appearance, and the like of layer (C) are improved, which is preferable. The content of the boron compound is the content calculated as elemental boron.

[0047] Examples of the carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, lactic acid, and salts thereof. The carboxylic acids are preferably carboxylic acids having 4 or less carbon atoms or saturated carboxylic acids, and more preferably acetic acid. The carboxylic acids may also include the carboxylic acid salts containing the polyvalent metal ions.

[0048] Examples of the phosphorus compound include phosphates such as phosphoric acid and phosphorous acid. The phosphate may be in the form of a primary phosphate, a secondary phosphate, or a tertiary phosphate. The cation species of the phosphate is not particularly limited, but alkali metal salts or alkaline earth metal salts are preferred, and among these, sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, or dipotassium hydrogen phosphate is more preferred. The content of the phosphorus compound in layer (C) is preferably 1 to 200 ppm, more preferably 10 to 100 ppm, in layer (C). Setting the content of the phosphorus compound within the above range is preferable because it improves thermal stability and suppresses defects and coloration during recycling. The content of the phosphorus compound is the content calculated as a phosphate ion.

[0049] Examples of the metal ions other than the polyvalent metal ions include monovalent metal ions and polyvalent metal ions other than the polyvalent metal ions, with monovalent metal ions being preferred. As the monovalent metal ions, alkali metal ions are preferred. Examples of the alkali metal ions include lithium ions, sodium ions, and potassium ions, with sodium ions and potassium ions being preferred from the viewpoint of industrial availability. Examples of alkali metal salts containing alkali metal ions include aliphatic carboxylates, aromatic carboxylates, carbonates, hydrochlorides, nitrates, sulfates, phosphates, and metal complexes. Among these, aliphatic carboxylates or phosphates are preferred from the viewpoint of availability, and specifically, sodium acetate, potassium acetate, sodium phosphate, or potassium phosphate is preferred. The content of the alkali metal ions in layer (C) is preferably 10 to 1,000 ppm, more preferably 100 to 400 ppm. By setting the content of the alkali metal ions within the above range, interlayer adhesion and other properties are improved, and coloration during recycling is suppressed, which is preferable.

[0050] Examples of the antioxidant include 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), and octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate.

[0051] Examples of the ultraviolet absorber include ethyl-2-cyano-3,3'-diphenylacrylate, 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, and 2-hydroxy-4-octoxybenzophenone.

[0052] Examples of the plasticizer include dimethyl phthalate, diethyl phthalate, dioctyl phthalate, wax, liquid paraffin, and phosphate esters. Examples of the antistatic agent include pentaerythritol monostearate, sorbitan monopalmitate, sulfated polyolefins, polyethylene oxide, and polyethylene glycol (trade name: Carbowax (registered trademark)). Examples of the lubricant include ethylene bisstearamide and butyl stearate. Examples of the colorant include carbon black, phthalocyanine, quinacridone, indoline, azo pigments, and red iron oxide. Examples of the filler include glass fiber, wollastonite, calcium silicate, talc, and montmorillonite. Examples of the heat stabilizer include hindered phenol compounds and hindered amine compounds. Examples of resins other than the EVOH (c) include polyamides and polyolefins.

[0053] The layer (C) may be a non-stretched layer or a stretched layer. When the layer (C) is a stretched layer, it is preferable because good gas barrier properties can be exhibited even when the layer (C) is relatively thin.

[0054] The average thickness of layer (C) is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.4 μm or more, even more preferably 0.6 μm or more, even more preferably 0.8 μm or more, and may be 2 μm or more, from the viewpoint of further improving gas barrier properties, etc. Furthermore, the average thickness of layer (C) is preferably 30 μm or less, more preferably 20 μm or less, even more preferably 15 μm or less, even more preferably 10 μm or less, even more preferably 5 μm or less, and may even be 3 μm or less, from the viewpoint of suppressing defects and coloration during recycling, etc. As described above, these stepwise lower and upper limits can be independently combined. For example, in one embodiment of the multilayer structure, the average thickness of layer (C) is preferably 0.1 to 30 μm, more preferably 0.2 to 20 μm, even more preferably 0.4 to 15 μm, even more preferably 0.6 to 10 μm, and even more preferably 0.8 to 5 μm.

[0055] The multilayer structure may include only one layer (C), or may include multiple layers (C). When the multilayer structure includes multiple layers (C), the layers (C) may be identical to or different from one another in composition and thickness. When the multilayer structure includes multiple layers (C), the aforementioned average thickness of the layers (C) refers to the total average thickness of all the layers (C). When the multilayer structure includes multiple layers (C) and is a laminate in which the layers (C) are directly laminated to one another, the aforementioned embodiment of "the inorganic vapor deposition layer (B), the barrier resin layer (C), and the adhesive resin layer (D) are all directly laminated in this order" may be such that the layer (C) closest to layer (B) in the laminate is directly laminated to layer (B), and the layer (C) closest to layer (D) is directly laminated to layer (D). Furthermore, when a plurality of layers (C) are present but the layers (C) are not directly laminated to one another, it is sufficient that any one of the layers (C) satisfies the above-mentioned aspect that "the inorganic vapor deposition layer (B), the barrier resin layer (C), and the adhesive resin layer (D) are all directly laminated to one another in this order."

[0056] <Adhesive Resin Layer (D)> The adhesive resin layer (D) (also referred to as "layer (D)" in this specification) is a layer that bonds the layer (C) to another layer, and may be, for example, a layer that bonds the layer (C) to the heat-sealing layer (E) described later, or a layer that bonds the layer (C) to the thermoplastic resin layer (F) described later. Furthermore, the layer (D) preferably contains, as a main component, an adhesive resin having a melting point of less than 200°C, and more preferably contains, as a main component, an adhesive resin (d) having a melting point of 175°C or less.

[0057] The adhesive resin (d) may be any resin having adhesiveness and a melting point of 175° C. or less, and examples thereof include acid-modified polyolefins (carboxylic acid-modified polyolefins, sulfonic acid-modified polyolefins, etc.), epoxy-modified polyolefins, etc. The adhesive resin (d) is preferably a thermoplastic resin.

[0058] The adhesive resin (d) is preferably an acid-modified polyolefin (such as acid-modified polyethylene or acid-modified polypropylene), and more preferably at least one selected from acid-modified polyethylene (d1) and acid-modified polypropylene (d2). In addition, from the viewpoint of further suppressing defects during recycling, when the heat-sealable layer (E) described below contains polyethylene (e1) as the polyolefin (e) as the main component, it is more preferable that the layer (D) contains acid-modified polyethylene (d1) as the main component. Similarly, from the viewpoint of further suppressing defects during recycling, when the heat-sealable layer (E) contains polypropylene (e2) as the polyolefin (e) as the main component, it is more preferable that the layer (D) contains acid-modified polypropylene (d2) as the main component.

[0059] The adhesive resin (d) is also preferably a carboxylic acid-modified polyolefin (a polyolefin having a carboxy group or an anhydride group thereof), and more preferably at least one selected from carboxylic acid-modified polyethylene and carboxylic acid-modified polypropylene.

[0060] The carboxylic acid-modified polyolefin may be a polyolefin having a carboxy group or an anhydride group thereof. The carboxylic acid-modified polyolefin can be obtained, for example, by chemically bonding an ethylenically unsaturated carboxylic acid or an anhydride thereof to an unmodified polyolefin by an addition reaction, a graft reaction, or the like. The unmodified polyolefin used in the production of the carboxylic acid-modified polyolefin is preferably at least one selected from polyethylene and polypropylene.

[0061] Examples of the ethylenically unsaturated carboxylic acid and its anhydride include monocarboxylic acid, monocarboxylic acid ester, dicarboxylic acid, dicarboxylic acid monoester, dicarboxylic acid diester, and dicarboxylic acid anhydride. Specific examples include maleic acid, fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride, maleic acid monomethyl ester, maleic acid monoethyl ester, maleic acid diethyl ester, and fumaric acid monomethyl ester. Among these, dicarboxylic acid anhydrides such as maleic anhydride and itaconic anhydride are preferred, and maleic anhydride is more preferred. That is, the adhesive resin (d) is also preferably a maleic anhydride-modified polyolefin, and more preferably at least one selected from maleic anhydride-modified polyethylene and maleic anhydride-modified polypropylene. Therefore, in one embodiment of the adhesive resin (d), the acid-modified polyethylene (d1) is preferably a carboxylic acid-modified polyethylene, more preferably a maleic anhydride-modified polyethylene, and the acid-modified polypropylene (d2) is preferably a carboxylic acid-modified polypropylene, more preferably a maleic anhydride-modified polypropylene.

[0062] Carboxylic acid-modified polyolefins can be obtained, for example, by introducing an ethylenically unsaturated carboxylic acid or its anhydride into an unmodified polyolefin by addition reaction or graft reaction in the presence of a solvent such as xylene and a catalyst such as a peroxide. The amount of carboxylic acid or its anhydride added or grafted to the unmodified polyolefin (modification degree) is preferably 0.01 to 15% by mass, more preferably 0.02 to 10% by mass, based on 100% by mass of the unmodified polyolefin.

[0063] The acid value of the acid-modified polyolefin such as the carboxylic acid-modified polyolefin is preferably 0.3 to 5.0 mgKOH / g, more preferably 1.0 to 3.0 mgKOH / g.

[0064] The melting point of the adhesive resin (d) is preferably 50 to 175°C, more preferably 55 to 170°C, even more preferably 60 to 170°C, and even more preferably 70 to 165°C. Having the upper limit of the melting point of the adhesive resin (d) within the above range is preferred from the viewpoint of further suppressing defects during recycling, and having the lower limit within the above range is preferred from the viewpoint of improving heat resistance. Furthermore, from the same viewpoint as described above, in one embodiment of the multilayer structure, when the adhesive resin (d) is acid-modified polyethylene (d1), the melting point of the acid-modified polyethylene (d1) is preferably 50 to 140°C, more preferably 55 to 135°C, even more preferably 60 to 130°C, and even more preferably 70 to 125°C. Furthermore, from the same viewpoint as described above, in one embodiment of the multilayer structure, when the adhesive resin (d) is an acid-modified polypropylene (d2), the melting point of the acid-modified polypropylene (d2) is preferably 50 to 175°C, more preferably 65 to 170°C, and even more preferably 80 to 165°C.

[0065] The adhesive resin (d) may have an MFR (190°C, 2.16 kg load) of, for example, 0.2 to 12 g / 10 min, or 0.5 to 8.0 g / 10 min, as measured in accordance with ISO 1133-1: 2011. In one embodiment of the multilayer structure, when the adhesive resin (d) is an acid-modified polyethylene (d1), the MFR (190°C, 2.16 kg load) of the acid-modified polyethylene (d1) is preferably 0.2 to 12.0 g / 10 min, more preferably 0.5 to 8.0 g / 10 min, and even more preferably 1.0 to 5.0 g / 10 min. In one embodiment of the multilayer structure, when the adhesive resin (d) is an acid-modified polypropylene (d2), the MFR (230°C, 2.16 kg load) of the acid-modified polypropylene (d2) is preferably 0.2 to 12.0 g / 10 min, more preferably 0.5 to 8.0 g / 10 min, and even more preferably 1.0 to 5.0 g / 10 min.

[0066] The adhesive resin (d) may be used alone or in combination of two or more kinds.

[0067] The proportion of the adhesive resin (d) in the resins constituting layer (D) is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and even more preferably 97 to 100% by mass, based on 100% by mass of the total amount of the resins constituting layer (D). The content of the adhesive resin (d) in layer (D) is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and even more preferably 97 to 100% by mass, based on 100% by mass of the total amount of layer (D). Layer (D) may contain components other than the adhesive resin (d), such as antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, heat stabilizers, and resins other than the adhesive resin (d).

[0068] Layer (D) may be an unstretched layer or a stretched layer.

[0069] The average thickness of layer (D) is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 0.8 μm or more, and may be 2 μm or more, from the viewpoint of easily exhibiting sufficient adhesiveness. Furthermore, the average thickness of layer (D) is preferably 20 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, and may be 3 μm or less, from the viewpoint of further suppressing defects and coloration during recycling. As described above, these stepwise lower and upper limits can be independently combined. For example, in one embodiment of the multilayer structure, the average thickness of layer (D) is preferably 0.1 to 20 μm, more preferably 0.5 to 10 μm, and even more preferably 0.8 to 5 μm.

[0070] The multilayer structure may include only one layer (D), or may include multiple layers (D). When the multilayer structure includes multiple layers (D), the layers (D) may be identical to or different from one another in composition, thickness, etc. Furthermore, when the multilayer structure includes multiple layers (D), the aforementioned average thickness of the layers (D) refers to the total average thickness of all the layers (D). When the multilayer structure includes multiple layers (D) and is a laminate in which the layers (D) are directly laminated to one another, the aforementioned embodiment in which "the inorganic vapor deposition layer (B), the barrier resin layer (C), and the adhesive resin layer (D) are all directly laminated in this order" may be the same as long as the layer (D) located closest to the layer (C) in the laminate is directly laminated to the layer (C). Furthermore, when a plurality of layers (D) are present but the layers (D) are not directly laminated to one another, it is sufficient that any one of the layers (D) satisfies the above-mentioned aspect that "the inorganic vapor deposition layer (B), the barrier resin layer (C), and the adhesive resin layer (D) are all directly laminated to one another in this order."

[0071] <Heat-sealing layer (E)> The heat-sealing layer (E) (also referred to as "layer (E)" in this specification) is one of the two outermost layers of the multilayer structure. Furthermore, since the layer (E) contains a polyolefin (e) having a melting point of 175°C or less as a main component, it has good low-temperature sealing properties and is more likely to prevent defects from occurring during recycling.

[0072] (Polyolefin (e)) The melting point of the polyolefin (e) is 175° C. or lower, preferably 50 to 175° C., more preferably 55 to 170° C., even more preferably 60 to 170° C., and still more preferably 70 to 165° C. It is preferable that the upper limit of the melting point of the polyolefin (e) is within the above range from the viewpoint of improving low-temperature sealability, and it is preferable that the lower limit is within the above range from the viewpoint of improving heat resistance.

[0073] In one embodiment of the multilayer structure, the polyolefin (e) is preferably polyethylene (e1). For example, from the viewpoint of improving low-temperature sealability and further suppressing defects during recycling, when the layer (D) contains a polyethylene-based resin as the adhesive resin (d) as the main component, the layer (E) preferably contains polyethylene (e1) as the main component.

[0074] In one embodiment of the multilayer structure, the polyolefin (e) is preferably polypropylene (e2). For example, from the viewpoint of improving low-temperature sealing properties and further suppressing defects during recycling, when the layer (D) contains a polypropylene-based resin as the adhesive resin (d) as the main component, the layer (E) preferably contains polypropylene (e2) as the main component. Furthermore, when the polyolefin (e) is polypropylene (e2), this is also preferable from the viewpoint of further improving heat resistance.

[0075] The proportion of polyolefin (e) in the resins constituting layer (E) is preferably 80 to 100 mass%, more preferably 90 to 100 mass%, and even more preferably 97 to 100 mass%, based on 100 mass% of the total amount of resins constituting layer (E). The content of polyolefin (e) in layer (E) is preferably 80 to 100 mass%, more preferably 90 to 100 mass%, and even more preferably 97 to 100 mass%, based on 100 mass% of the total amount of layer (E). Furthermore, when layer (E) contains multiple polyolefins as polyolefin (e), the content of polyolefin (e) is the total amount of the multiple polyolefins. Therefore, in this case, layer (E) can be said to contain polyolefin (e) as a major component if the total amount of the multiple polyolefins is greater than the respective contents of the other components.

[0076] [Polyethylene (e1)] The type of polyethylene (e1) is not particularly limited as long as it has a melting point of 175°C or less, and examples include high-density polyethylene, low-density polyethylene, and linear low-density polyethylene. Of these, linear low-density polyethylene, low-density polyethylene, or a mixture thereof is preferred. Linear low-density polyethylene is a resin obtained by polymerizing ethylene with an α-olefin having 3 or more carbon atoms. Examples of α-olefins having 3 or more carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 4-methyl-1-pentene, 4-methyl-hexene-1, and 4,4-dimethylpentene-1. Of these, the linear low-density polyethylene is preferably a linear low-density polyethylene obtained by polymerizing ethylene with an α-olefin having 6 or more carbon atoms, and more preferably a linear low-density polyethylene obtained by polymerizing ethylene with an α-olefin having 8 or more carbon atoms. When the α-olefin copolymerized with ethylene has a relatively large number of carbon atoms, various mechanical strengths such as puncture strength and elongation of the layer (E) may be particularly improved. The number of carbon atoms of the α-olefin having 3 or more carbon atoms may be, for example, 20 or less, 14 or less, or 10 or less.

[0077] Furthermore, a metallocene catalyst is preferably used as the polymerization catalyst for polymerizing polyethylene (e1). Linear low-density polyethylene polymerized using a metallocene catalyst is produced by copolymerizing ethylene and an α-olefin in the presence of a catalyst formed from a compound having at least one ligand having a cyclopentadienyl skeleton and having a transition metal of Group 4 of the periodic table as the central metal atom (preferably a compound having zirconium as the central metal atom), an organoaluminum oxy compound, and various other components added as needed. Linear low-density polyethylene polymerized using a metallocene catalyst has excellent melt moldability, and the resulting layer (E) has an excellent balance of heat resistance, flexibility, and mechanical strength. Use of such polyethylene is preferred because it can further increase the strength of packaging containers molded from the multilayer structure.

[0078] The density of polyethylene (e1) is, for example, 0.960 g / cm ３ or less, and preferably 0.880 to 0.940 g / cm ３ , more preferably 0.890 to 0.930 g / cm ３ and 0.900 to 0.930 g / cm ３ , or 0.910 to 0.940 g / cm ３ The use of a polyethylene having a relatively low density as the polyethylene (e1) is preferable because it is possible to further increase the strength of the packaging container formed from the multilayer structure. As the polyethylene (e1) satisfying the density range, it is preferable to use, for example, linear low-density polyethylene, low-density polyethylene, or a mixture thereof.

[0079] The melting point of the polyethylene (e1) is preferably 70 to 140° C., more preferably 75 to 135° C., even more preferably 85 to 130° C., and still more preferably 100 to 125° C. It is preferable that the upper limit of the melting point of the polyethylene (e1) is within the above range from the viewpoint of improving low-temperature sealability, and it is preferable that the lower limit is within the above range from the viewpoint of improving heat resistance.

[0080] The MFR (190°C, 2.16 kg load) of the polyethylene (e1), measured in accordance with ISO1133-1:2011, is preferably 0.2 to 12.0 g / 10 min, more preferably 0.5 to 8.0 g / 10 min, even more preferably 1.0 to 5.0 g / 10 min, still more preferably 1.0 to 4.0 g / 10 min, and still more preferably 1.0 to 2.0 g / 10 min.

[0081] In one embodiment of the multilayer structure, the proportion of polyethylene (e1) in the resins constituting layer (E) is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and even more preferably 97 to 100% by mass, based on 100% by mass of the total amount of resins constituting layer (E). In one embodiment of the multilayer structure, the content of polyethylene (e1) in layer (E) is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and even more preferably 97 to 100% by mass, based on 100% by mass of the total amount of layer (E). One type of polyethylene (e1) may be used alone, or two or more types may be used in combination. Furthermore, as described above, when layer (E) contains multiple polyethylenes (e1) as the polyethylene (e1), the content of the polyethylene (e1) is the total amount of the multiple polyethylenes (e1). Therefore, in this case, if the layer (E) contains a plurality of polyethylenes (e1) in a total amount that is greater than the content of each of the other components, it can be said that the layer (E) contains polyethylene (e1) as a main component.

[0082] [Polypropylene (e2)] The type of polypropylene (e2) is not particularly limited as long as it has a melting point of 175°C or less, and examples thereof include propylene homopolymers and copolymers of propylene with at least one selected from the group consisting of ethylene and α-olefin monomers having 4 or more carbon atoms. Examples of the α-olefins having 4 or more carbon atoms include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 4-methyl-1-pentene, 4-methyl-hexene-1, and 4,4-dimethylpentene-1. The copolymer may be a random copolymer, a block copolymer, or a random block copolymer. The number of carbon atoms in the α-olefins having 4 or more carbon atoms may be, for example, 20 or less, 14 or less, or 10 or less. Specific examples of the copolymer include a propylene-ethylene random copolymer, a propylene-ethylene block copolymer, a propylene-1-butene random copolymer, a propylene-1-butene block copolymer, a propylene-ethylene-1-butene random copolymer, a propylene-ethylene-1-butene block copolymer, a propylene-ethylene random block copolymer, and a propylene-ethylene-1-butene random block copolymer.

[0083] The polypropylene (e2) can be produced by a known production method. The polymerization catalyst that can be used when polymerizing the polypropylene (e2) is not particularly limited as long as the effects of the present invention are achieved, and examples thereof include catalysts such as Ziegler-Natta catalysts, Phillips catalysts, metallocene catalysts, and post-metallocene catalysts. The polypropylenes (e2-1) and (e2-2) described below can also be produced by the same production method.

[0084] The density of polypropylene (e2) is, for example, 0.860 to 0.915 g / cm ３ , 0.865-0.915g / cm ３ , 0.870-0.915g / cm ３ , 0.875-0.915g / cm ３ , or 0.880 to 0.910 g / cm ３ may be.

[0085] The melting point of the polypropylene (e2) is preferably 50 to 175° C., more preferably 55 to 170° C., even more preferably 60 to 170° C., and still more preferably 70 to 165° C. It is preferable that the upper limit of the melting point of the polypropylene (e2) is within the above range from the viewpoint of improving low-temperature sealability, and it is preferable that the lower limit is within the above range from the viewpoint of improving heat resistance.

[0086] The MFR (230°C, 2.16 kg load) of the polypropylene (e2) measured in accordance with ISO1133-1:2011 is preferably 0.2 to 12.0 g / 10 min, more preferably 0.5 to 8.0 g / 10 min, and even more preferably 1.0 to 5.0 g / 10 min.

[0087] The content of structural units derived from propylene (hereinafter also referred to as "propylene units") in polypropylene (e2) is not particularly limited, and may be, for example, 8 to 100 mol%, 10 to 100 mol%, 40 to 100 mol%, 50 to 100 mol%, or 60 to 100 mol% relative to 100 mol% of the total amount of structural units constituting polypropylene (e2).

[0088] The polypropylene (e2) may be used alone or in combination of two or more kinds.

[0089] In one embodiment of the multilayer structure, layer (E) preferably contains polypropylene (e2) as the polyolefin (e), and further contains, as the polypropylene (e2), polypropylene (e2-1) having a melting point greater than 110°C and polypropylene (e2-2) having a melting point of 110°C or lower. Layer (E) preferably contains, as the polyolefin (e), polypropylene (e2-1) having a melting point greater than 110°C and polypropylene (e2-2) having a melting point of 110°C or lower, because this further improves low-temperature sealability. Furthermore, for example, even when layer (E) is thinner, sufficient low-temperature sealability can be achieved, making it possible to further reduce the overall thickness of the multilayer structure. Therefore, for example, when the coextruded film described below is a coextruded film having layer (C) and layer (E), stretching the coextruded film to improve the gas barrier properties of layer (C) usually results in a decrease in low-temperature sealability due to the thickness of layer (E), but this can also suppress the decrease in low-temperature sealability. Therefore, this is also preferable from the viewpoint that a multilayer structure having a good balance of gas barrier properties and low-temperature sealability can be easily obtained.

[0090] [Polypropylene (e2-1)] The polypropylene (e2-1) is not particularly limited as long as it has a melting point of greater than 110°C, and the various polypropylenes described above in the section on polypropylene (e2) can be used. The melting point of polypropylene (e2-1) is preferably greater than 110°C and not greater than 175°C, more preferably 115 to 175°C, even more preferably 120 to 170°C, and even more preferably 125 to 165°C, and may be, for example, 140 to 165°C, 145 to 165°C, or 150 to 165°C. It is preferable that the upper limit of the melting point of polypropylene (e2-1) be within the above range from the viewpoint of improving low-temperature sealability, and it is preferable that the lower limit be within the above range from the viewpoint of improving heat resistance.

[0091] The density of polypropylene (e2-1) is, for example, 0.895 to 0.915 g / cm ３ or 0.900 to 0.910 g / cm ３ may be.

[0092] The MFR (230°C, 2.16 kg load) of polypropylene (e2-1) measured in accordance with ISO1133-1:2011 is preferably 0.2 to 12.0 g / 10 min, more preferably 0.5 to 8.0 g / 10 min, and even more preferably 1.0 to 5.0 g / 10 min.

[0093] The content of propylene units in polypropylene (e2-1) is not particularly limited as long as the melting point of polypropylene (e2-1) is greater than 110°C. The content of propylene units is preferably 50 to 100 mol%, more preferably 60 to 100 mol%, even more preferably 70 to 100 mol%, and still more preferably 80 to 100 mol%, or may be 85 to 100 mol%, or 90 to 100 mol%, based on 100 mol% of the total amount of structural units constituting polypropylene (e2-1).

[0094] The polypropylene (e2-1) may be used alone or in combination of two or more kinds.

[0095] [Polypropylene (e2-2)] The polypropylene (e2-2) is not particularly limited as long as it has a melting point of 110°C or less, and the various polypropylenes described above in the section on polypropylene (e2) can be used. Among these, preferred examples of polypropylene (e2-2) include copolymers of propylene and at least one selected from the group consisting of ethylene and α-olefin monomers having 4 or more carbon atoms, and more preferred examples include copolymers of propylene and at least one selected from the group consisting of α-olefin monomers having 4 or more carbon atoms. Examples of the α-olefins having 4 or more carbon atoms include the various α-olefins described above in the section on polypropylene (e2). Of these, at least one selected from 1-butene, 1-pentene, 1-hexene, and 1-octene is preferred, with 1-butene being more preferred. When polypropylene (e2-2) is a copolymer, the copolymer may be a random copolymer, a block copolymer, or a random block copolymer. The carbon number of the α-olefin having 4 or more carbon atoms may be, for example, 20 or less, 14 or less, or 10 or less, preferably 8 or less, and more preferably 6 or less. Specific examples of the copolymer include the various copolymers described above in the section on polypropylene (e2). Among these, one or more copolymers selected from the group consisting of a propylene-1-butene random copolymer, a propylene-1-butene block copolymer, and a propylene-1-butene random block copolymer are preferred. Therefore, it is more preferred to use a propylene-1-butene copolymer as the polypropylene (e2-2).

[0096] The melting point of the polypropylene (e2-2) is preferably 50 to 110° C., more preferably 55 to 100° C., even more preferably 60 to 90° C., and still more preferably 70 to 80° C. It is preferable that the upper limit of the melting point of the polypropylene (e2-2) is within the above range from the viewpoint of improving low-temperature sealability, and it is preferable that the lower limit is within the above range from the viewpoints of improving moldability by preventing adhesion to the molding machine and preventing a decrease in the strength of the obtained film.

[0097] The density of the polypropylene (e2-2) is preferably 0.860 to 0.905 g / cm ３ , more preferably 0.865 to 0.900 g / cm ３ , more preferably 0.870 to 0.895 g / cm ３ and 0.875 to 0.890 g / cm ３ Or 0.880 to 0.890 g / cm ３ may be.

[0098] The MFR (230°C, 2.16 kg load) of polypropylene (e2-2) measured in accordance with ISO1133-1:2011 is preferably 0.5 to 12.0 g / 10 min, more preferably 1.0 to 10.0 g / 10 min, and even more preferably 2.0 to 8.0 g / 10 min.

[0099] The content of propylene units in polypropylene (e2-2) is not particularly limited as long as the melting point of polypropylene (e2-2) is 110°C or lower, but may be, for example, 8 to 100 mol%, 10 to 100 mol%, 40 to 100 mol%, 50 to 100 mol%, or 60 to 100 mol%, relative to the total amount (100 mol%) of structural units constituting polypropylene (e2-2). Furthermore, when the polypropylene (e2-2) is a copolymer of propylene and at least one selected from the group consisting of ethylene and α-olefin monomers having 4 or more carbon atoms, the content of propylene units is not particularly limited as long as the melting point of the polypropylene (e2-2) is 110°C or lower, but is preferably 10 to 95 mol%, more preferably 50 to 95 mol%, and even more preferably 60 to 90 mol%, based on the total 100 mol% of the propylene units and structural units derived from at least one selected from the group consisting of ethylene and α-olefin monomers having 4 or more carbon atoms that constitute the polypropylene (e2-2). Furthermore, when polypropylene (e2-2) is a copolymer of propylene and at least one selected from the group consisting of ethylene and α-olefin monomers having 4 or more carbon atoms, the content of structural units derived from at least one selected from the group consisting of ethylene and α-olefin monomers having 4 or more carbon atoms is not particularly limited as long as the melting point of polypropylene (e2-2) is 110°C or lower, but is preferably 5 to 90 mol%, more preferably 5 to 50 mol%, and even more preferably 10 to 40 mol%, based on 100 mol% of the total amount of propylene units and structural units derived from at least one selected from the group consisting of ethylene and α-olefin monomers having 4 or more carbon atoms constituting polypropylene (e2-2).Furthermore, when the polypropylene (e2-2) is a copolymer of propylene and at least one selected from the group consisting of ethylene and α-olefin monomers having 4 or more carbon atoms, the total content of structural units derived from at least one selected from the group consisting of ethylene and α-olefin monomers having 4 or more carbon atoms is not particularly limited, as long as the melting point of the polypropylene (e2-2) is 110°C or lower, and may be, for example, 80 to 100 mol%, 90 to 100 mol%, 95 to 100 mol%, or 98 to 100 mol%, relative to the total amount (100 mol%) of the structural units constituting the polypropylene (e2-2).

[0100] The polypropylene (e2-2) may be used alone or in combination of two or more kinds.

[0101] The mass ratio (e2-1 / e2-2) of polypropylene (e2-1) to polypropylene (e2-2) is preferably 55 / 45 to 96 / 4, more preferably 60 / 40 to 90 / 10, and even more preferably 70 / 30 to 80 / 20. A mass ratio (e2-1 / e2-2) within the above range is preferred from the viewpoint of facilitating the production of a film that exhibits a good balance of low-temperature sealability, gas barrier properties after heat pressing, moldability due to prevention of adhesion to a molding machine, and the strength of the resulting film.

[0102] In one embodiment of the multilayer structure, the proportion of polypropylene (e2) in the resins constituting layer (E) is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and even more preferably 97 to 100% by mass, based on 100% by mass of the total amount of resins constituting layer (E). In one embodiment of the multilayer structure, the content of polypropylene (e2) in layer (E) is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and even more preferably 97 to 100% by mass, based on 100% by mass of the total amount of layer (E). Furthermore, in one embodiment of the multilayer structure, when layer (E) contains polypropylene (e2-1) and polypropylene (e2-2) as polyolefins (e), the total content of polypropylene (e2-1) and polypropylene (e2-2) in layer (E) is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and even more preferably 97 to 100% by mass, based on 100% by mass of the total amount of layer (E).

[0103] As described above, when layer (E) contains multiple polypropylenes (e2) as polypropylene (e2) (for example, when layer (E) contains polypropylenes (e2-1) and (e2-2)), the content of polypropylene (e2) is the total amount of the multiple polypropylenes (e2). Therefore, in this case, layer (E) can be said to contain polypropylene (e2) as a main component if the total amount of the multiple polypropylenes (e2) is greater than the content of each of the other components. Furthermore, with regard to the content of polypropylene (e2-1) when calculating the mass ratio (e2-1 / e2-2), for example, when multiple polypropylenes (e2-1) are contained, the content of polypropylene (e2-1) used in calculating the mass ratio is the total amount of the multiple polypropylenes (e2-1). The same applies to the content of polypropylene (e2-2) when calculating the mass ratio (e2-1 / e2-2).

[0104] Furthermore, the layer (E) may contain, as components other than the polyolefin (e), antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, heat stabilizers, resins other than the polyolefin (e), etc. As these other components, the same agents as those described above for the layer (C) can be used.

[0105] Layer (E) may be an unstretched layer or a stretched layer.

[0106] The average thickness (Et) of the layer (E) is preferably 1 to 100 μm, more preferably 2 to 50 μm, even more preferably 3 to 25 μm, and still more preferably 4 to 10 μm. Having the lower limit of the average thickness (Et) of the layer (E) within this range is preferable from the viewpoints of improving low-temperature sealing properties and improving gas barrier properties after hot pressing, and having the upper limit within this range makes it easier to increase the mass ratio of the paper layer (A) in the multilayer structure, thereby reducing the impact of recovery losses that can inevitably occur during operations when recycling the paper layer (A). As a result, an improvement in the recycling rate of the paper layer (A) (mass of recovered paper / mass of paper layer (A)) can be expected.

[0107] <Thermoplastic Resin Layer (F)> The multilayer structure preferably further includes a thermoplastic resin layer (F) (also referred to as "layer (F)" in this specification) directly laminated to the adhesive resin layer (D). The layer (F) is preferably present between the adhesive resin layer (D) and the heat-sealing layer (E). In addition, as one embodiment of the multilayer structure, it is more preferable that the layer (D), the layer (F), and the layer (E) are all directly laminated in this order. That is, it is preferable that the layer (B), the layer (C), the layer (D), the layer (F), and the layer (E) are all directly laminated in this order.

[0108] Layer (F) contains a thermoplastic resin as a main component. The thermoplastic resin is not particularly limited as long as it is a thermoplastic resin having a melting point of less than 200°C, and examples thereof include polyolefins, polystyrenes, polycarbonates, acrylic resins, and the adhesive resins described above (such as acid-modified polyolefins). Among these, polyolefins or acid-modified polyolefins are preferred, and polyolefins are more preferred. In this specification, the polyolefin contained in layer (F) is also referred to as "polyolefin (f)." Therefore, it is more preferred that the multilayer structure further includes a layer (F) present between layer (D) and layer (E), and that layer (F) contains polyolefin (f) as a main component. It is preferred that the multilayer structure further includes a layer (F) present between layer (D) and layer (E), and that layer (F) contains polyolefin (f) as a main component, from the viewpoints of improving low-temperature sealing properties, improving gas barrier properties after hot pressing, and further suppressing the occurrence of defects during recycling.

[0109] (Polyolefin (f)) The polyolefin (f) is more preferably at least one selected from polyethylene and polypropylene. Furthermore, from the viewpoint of further suppressing defects during recycling, when at least one layer selected from layer (D) and layer (E) contains a polyethylene-based resin as a main component, preferably when both layers (D) and (E) contain a polyethylene-based resin as a main component, it is even more preferable that the polyolefin (f) be polyethylene. Similarly, from the viewpoint of further suppressing defects during recycling, when at least one layer selected from layer (D) and layer (E) contains a polypropylene-based resin as a main component, preferably when both layers (D) and (E) contain a polypropylene-based resin as a main component, it is even more preferable that the polyolefin (f) be polypropylene. The polyethylene that can be used as the polyolefin (f) is not particularly limited as long as the effects of the present invention are achieved, and may be, for example, the polyethylene (e1) described above. Similarly, the polypropylene that can be used as the polyolefin (f) is not particularly limited as long as the effects of the present invention are achieved, and may be, for example, the polypropylene (e2) described above.

[0110] The melting point of the polyolefin (f) is preferably 50 to 175°C, more preferably 55 to 170°C, even more preferably 60 to 170°C, and even more preferably 70 to 165°C. The upper limit of the melting point of the polyolefin (f) is preferably within the above range from the viewpoints of improving low-temperature sealability and further suppressing defects during recycling, and the lower limit is preferably within the above range from the viewpoint of improving heat resistance. Furthermore, from the same viewpoint as described above, in one embodiment of the multilayer structure, when the polyolefin (f) is polyethylene, the melting point of the polyethylene is preferably 70 to 140°C, more preferably 75 to 135°C, even more preferably 85 to 130°C, and even more preferably 100 to 125°C. Furthermore, from the same viewpoint as described above, in one embodiment of the multilayer structure, when the polyolefin (f) is polypropylene, the melting point of the polypropylene is preferably 50 to 175°C, more preferably 55 to 170°C, even more preferably 60 to 170°C, and even more preferably 70 to 165°C. In one embodiment of the multilayer structure, when the polyolefin (f) is polypropylene, the melting point of the polypropylene may be, for example, greater than 110°C and not greater than 175°C, 115 to 175°C, 120 to 170°C, 125 to 165°C, 140 to 165°C, 145 to 165°C, or 150 to 165°C.

[0111] The content of the thermoplastic resin in the layer (F) is preferably 80 to 100 mass%, more preferably 90 to 100 mass%, and even more preferably 97 to 100 mass%, based on 100 mass% of the total amount of the layer (F).

[0112] Layer (F) may also contain, as components other than the thermoplastic resin, antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, heat stabilizers, resins other than thermoplastic resins, etc. As these other components, the same agents as those described above for layer (C) can be used.

[0113] The average thickness (Ft) of layer (F) is preferably 1 to 100 μm, more preferably 3 to 50 μm, even more preferably 5 to 40 μm, and even more preferably 10 to 30 μm. Having the lower limit of the average thickness (Ft) within the above range is preferred from the viewpoints of improving low-temperature sealability, improving gas barrier properties after hot pressing, and further suppressing the occurrence of defects during recycling. Furthermore, having the upper limit of the average thickness of layer (F) within the above range is preferred from the viewpoint of improving the flexibility of the resulting film. Furthermore, from the viewpoint of further suppressing the occurrence of coloration during recycling, the average thickness of layer (F) is even more preferably 17 to 30 μm, and may be 18 to 25 μm.

[0114] In the multilayer structure, the average thickness (Ft) of the thermoplastic resin layer (F) is preferably greater than the average thickness (Et) of the thermal adhesive layer (E). The thickness ratio [(Ft) / (Et)] of the average thickness (Ft) of the thermoplastic resin layer (F) to the average thickness (Et) of the thermal adhesive layer (E) is preferably greater than 1, more preferably greater than 2, even more preferably greater than 3, and even more preferably greater than 4. The upper limit of the thickness ratio [(Ft) / (Et)] is not particularly limited, but is preferably 20 or less, more preferably 15 or less, even more preferably 10 or less, and even more preferably 8 or less. These stepwise lower and upper limits can be independently combined. For example, in one embodiment of the multilayer structure, the thickness ratio [(Ft) / (Et)] is preferably greater than 1 and less than 20, more preferably 2 to 15, even more preferably 3 to 10, and even more preferably 4 to 8.

[0115] The multilayer structure may include only one layer (F), or may include multiple layers (F). When the multilayer structure includes multiple layers (F), the compositions and thicknesses of the multiple layers (F) may be the same or different. When the multilayer structure includes multiple layers (F), the average thickness (Ft) of the layers (F) refers to the total average thickness of all the layers (F). In one embodiment of the multilayer structure, when the multilayer structure includes multiple layers (F), the layer on the layer (E) side of the multiple layers (F), preferably the layer (F) directly laminated to the layer (E), may be a layer composed of the same composition as the layer (E). For example, among the multiple laminated layers (F), the layer on the layer (E) side may be a layer (F) formed from a resin composition containing the aforementioned polypropylene (e2) and a propylene-α-olefin copolymer.

[0116] <Thermoplastic Resin Layer (G)> The multilayer structure preferably further includes a thermoplastic resin layer (G) (also referred to as "layer (G)" in this specification) present between the paper layer (A) and the inorganic vapor deposition layer (B). In one embodiment of the multilayer structure, it is more preferable that the layers (A), (G), and (B) are all directly laminated in this order. That is, it is more preferable that the layers (A), (G), (B), (C), and (D) are directly laminated in this order. Having the layer (G) is preferable because it can further improve the adhesion between the layers (A) and (B).

[0117] Layer (G) contains a thermoplastic resin as a main component. The thermoplastic resin is not particularly limited as long as it is a thermoplastic resin having a melting point of less than 200°C, and examples thereof include polyolefin, polystyrene, polycarbonate, acrylic resin, and the adhesive resins described above (such as acid-modified polyolefin). The thermoplastic resin is preferably a polyolefin-based resin. Among polyolefin-based resins, polyolefin and acid-modified polyolefin are more preferred, and polyolefin is even more preferred. In this specification, the polyolefin-based resin contained in layer (G) is also referred to as "polyolefin-based resin (g)." Therefore, it is more preferable that the multilayer structure further includes a layer (G) present between layer (A) and layer (B), and that layer (G) contains polyolefin-based resin (g) as a main component. It is preferable that the multilayer structure further includes a layer (G) present between layer (A) and layer (B), and that layer (G) contains polyolefin-based resin (g) as a main component, in terms of further suppressing defects and coloration during recycling.

[0118] (Polyolefin-based resin (g)) As described above, polyolefins and acid-modified polyolefins are more preferred as the polyolefin-based resin (g), and polyolefins are even more preferred. Examples of the polyolefin include the same polyolefins as the polyolefin (f) described above, and their preferred embodiments are also similar, so a description thereof will be omitted here. Examples of the acid-modified polyolefin include the same resins as the acid-modified polyolefins described as suitable examples of the adhesive resin (d) described in the section on the adhesive resin layer (D), and their preferred embodiments are also similar, so a description thereof will be omitted here.

[0119] The content of the thermoplastic resin in layer (G) is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and even more preferably 97 to 100% by mass, based on 100% by mass of the total amount of layer (G). When layer (G) contains polyolefin-based resin (g), the proportion of polyolefin-based resin (g) in the resins constituting layer (G) is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and even more preferably 97 to 100% by mass, based on 100% by mass of the total amount of resins constituting layer (G). When layer (G) contains polyolefin-based resin (g), the content of polyolefin-based resin (g) in layer (G) is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and even more preferably 97 to 100% by mass, based on 100% by mass of the total amount of layer (G).

[0120] Layer (G) may also contain other components besides the thermoplastic resin, such as antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, heat stabilizers, and other resins other than thermoplastic resins. The same agents as those described above for layer (C) can be used as these other components.

[0121] The average thickness of Layer (G) is preferably 1 to 100 μm, more preferably 3 to 50 μm, even more preferably 5 to 40 μm, and even more preferably 10 to 30 μm, and may be 10 to 20 μm. Having the lower limit of the average thickness of Layer (G) within the above range is preferred from the viewpoint of further improving the adhesion between Layer (A) and Layer (B), for example, when Layer (A), Layer (G), and Layer (B) are directly laminated together. Also, having the upper limit of the average thickness of Layer (G) within the above range is preferred from the viewpoint of improving the flexibility of the resulting film.

[0122] Layer (G) is preferably an extruded resin layer. That is, layer (A) and layer (B) (or a co-extruded film having layer (B) described later on one side) are preferably laminated by sandwich lamination. Layer (A) and layer (B) (or a co-extruded film having layer (B) described later on one side) may also be laminated by other methods, such as dry lamination. In this case, the layer interposed between layer (A) and layer (B) may be an adhesive layer using a curable adhesive. However, from the viewpoint of further suppressing defects in recycling and the occurrence of coloration, it is preferable that the multilayer structure use layer (G) as the layer interposed between layer (A) and layer (B), as described above, and it is more preferable that the multilayer structure does not have an adhesive layer using a curable adhesive.

[0123] The multilayer structure may include only one layer (G), or may include multiple layers (G). When the multilayer structure includes multiple layers (G), the compositions and thicknesses of the multiple layers (G) may be the same or different. When the multilayer structure includes multiple layers (G), the average thickness of the layer (G) refers to the sum of the average thicknesses of all the layers (G).

[0124] <Co-extruded Film> The multilayer structure has a co-extruded film, which preferably comprises a barrier resin layer (C) and an adhesive resin layer (D), and may more preferably comprise a barrier resin layer (C), an adhesive resin layer (D), and a heat-sealing layer (E), or may more preferably comprise a barrier resin layer (C), an adhesive resin layer (D), and a thermoplastic resin layer (F), and may even more preferably comprise a barrier resin layer (C), an adhesive resin layer (D), a thermoplastic resin layer (F), and a heat-sealing layer (E). That is, in the multilayer structure, it is preferable that layers (C) and (D) are formed by co-extrusion, and it may be more preferable that layers (C), (D), and (E) are formed by co-extrusion, or it may be more preferable that layers (C), (D), and (F) are formed by co-extrusion, and it may even be more preferable that layers (C), (D), (F), and (E) are formed by co-extrusion. The multilayer structure, having the coextruded film of the above configuration, can achieve a high level of balance between film properties such as gas barrier property and flexibility, and processability and economic efficiency. Since the multilayer structure has a structure in which Layer (B), Layer (C), and Layer (D) are all directly laminated in this order, it is preferable that the multilayer structure has the coextruded film and further has a composite film in which an inorganic vapor deposition layer (B) is provided on the surface of the coextruded film facing the barrier resin layer (C). Use of such a composite film can improve the productivity, gas barrier property, etc. of the multilayer structure.

[0125] The average thickness of the coextruded film is preferably 8 to 120 μm, more preferably 15 to 80 μm, and even more preferably 25 to 60 μm. When the average thickness of the coextruded film is equal to or greater than the lower limit, the gas barrier properties and the like can be further improved. When the average thickness of the coextruded film is equal to or less than the upper limit, the thickness of the multilayer structure can be reduced. The average thickness of the coextruded film is equal to the sum of the average thicknesses of all layers of the coextruded film.

[0126] From the viewpoints of improving gas barrier properties and recyclability, and from the viewpoint of economy, the average thickness of the barrier resin layer (C) of the co-extruded film is preferably 0.1 to 30 μm. Furthermore, the ratio of the average thickness of the barrier resin layer (C) to the average thickness of the co-extruded film is preferably 25% or less. The average thickness of layer (C) is more preferably 0.2 to 20 μm, even more preferably 0.4 to 15 μm, still more preferably 0.6 to 10 μm, and even more preferably 0.8 to 5 μm.

[0127] The ratio of the average thickness of layer (C) to the average thickness of the coextruded film is more preferably less than 25%, even more preferably 20% or less, and even more preferably 15% or less. Furthermore, the ratio of the average thickness of layer (C) to the average thickness of the coextruded film is preferably 1% or more, more preferably 2% or more, and even more preferably 3% or more. As described above, these stepwise lower and upper limits can be independently combined. For example, in one embodiment of the multilayer structure, the ratio of the average thickness of layer (C) to the average thickness of the coextruded film may be, for example, 1 to 25%, 1% or more but less than 25%, 1 to 20%, 1 to 15%, 2 to 25%, 2% or more but less than 25%, 2 to 20%, 2 to 15%, 3 to 25%, 3% or more but less than 25%, 3 to 20%, or 3 to 15%.

[0128] The coextruded film may be a non-stretched film that is not substantially stretched, or may be a stretched film that is stretched uniaxially or biaxially. When the coextruded film is a non-stretched film, the seal strength tends to be increased. When the coextruded film is a stretched film, the gas barrier property tends to be further increased. The "non-stretched film that is not substantially stretched" may be a film that is obtained without undergoing a stretching process during or after normal film formation by extrusion molding or the like, for example, a film that has not been stretched using a stretching machine or the like. Therefore, a film that has not undergone a stretching process and is only affected by the tension that inevitably occurs in the film during the cooling process, winding process, etc. that are required during normal film formation is considered to be "substantially unstretched."

[0129] The coextruded film is preferably stretched at least uniaxially by 3 to 12 times, and more preferably by 4 to 10 times. When the coextruded film is stretched uniaxially, it is preferably stretched in the MD direction of the film. The coextruded film is also preferably stretched biaxially by 3 to 12 times, and more preferably by 3.5 to 10 times. Stretching the coextruded film at such stretch ratios can further enhance the gas barrier properties of the multilayer structure. The coextruded film can be produced by known methods, and either a circular die or a T-die can be used as the die. The molding temperature during melt molding can be adjusted appropriately based on the melting point and melt viscosity of the resin used, and is often selected from the range of 150 to 300°C. The method of uniaxial or biaxial stretching is not particularly limited, and the film can be produced by stretching in the machine direction (MD) and / or the direction perpendicular to the machine direction (TD, i.e., the width direction of the film) using a conventionally known stretching method such as roll-type uniaxial stretching, tubular-type simultaneous biaxial stretching, tenter-type sequential biaxial stretching, or tenter-type simultaneous biaxial stretching. The effects of the present invention are particularly pronounced in the case of multilayer films produced by tenter-type sequential biaxial stretching. From the viewpoint of processability, the temperature during stretching is usually 70 to 180°C, more preferably 80 to 170°C, and may be 90 to 160°C. If necessary, it is preferable to perform a so-called heat setting operation after stretching at a temperature equal to or higher than the glass transition point and lower than the melting point to increase the crystallinity and fix the orientation of the molecular chains.

[0130] <Other Layers> The multilayer structure may have layers other than the paper layer (A), inorganic vapor deposition layer (B), barrier resin layer (C), adhesive resin layer (D), heat-sealing layer (E), thermoplastic resin layer (F), and thermoplastic resin layer (G). Examples of other layers that the multilayer structure may have include other thermoplastic resin layers, adhesive layers using curable adhesives, and printed layers. However, the multilayer structure does not have a layer containing, as a main component, a resin having a melting point of 200°C or higher, or a metal layer having an average thickness of 1 μm or higher. In other words, the multilayer structure does not have a layer containing, as a main component, a resin having a melting point of 200°C or higher, and does not have a metal layer having an average thickness of 1 μm or higher. Furthermore, the barrier resin layer (C), adhesive resin layer (D), heat-sealing layer (E), thermoplastic resin layer (F), and thermoplastic resin layer (G) are layers containing, as a main component, a resin having a melting point of less than 200°C. Since the multilayer structure does not include a layer containing a resin having a melting point of 200°C or higher as a main component (e.g., a layer containing polyethylene terephthalate as a main component) and a metal layer having an average thickness of 1 μm or higher (e.g., a metal foil layer having an average thickness of 1 μm or higher), defects are unlikely to occur in the recycled product during melt molding for recycling, and the multilayer structure has excellent recyclability. Here, a resin without a melting point does not fall under the category of a resin having a melting point of 200°C or higher, and for example, an adhesive layer containing a curable adhesive as a main component does not usually have a melting point and therefore does not fall under the category of a layer containing a resin having a melting point of 200°C or higher as a main component.

[0131] Furthermore, it may be preferable that the multilayer structure does not have an adhesive layer using a curable adhesive. The adhesive layer using a curable adhesive may be a layer consisting of only a curable adhesive, a layer containing 90% by mass or more of a curable adhesive, or a layer containing 80% by mass or more of a curable adhesive. By not having such an adhesive layer, defects during recycling can be further suppressed.

[0132] <Layer Configuration, etc.> As described above, the multilayer structure has at least layer (A), layer (B), layer (C), layer (D), and layer (E). Layer (B), layer (C), and layer (D) are all directly laminated in this order. Layer (E) is one of the outermost layers. From the viewpoint of more easily achieving the effects of the present invention, the multilayer structure preferably has layer (A), layer (B), layer (C), layer (D), and layer (E) in this order. Therefore, the multilayer structure preferably has paper layer (A) on the side of inorganic vapor deposition layer (B) opposite barrier resin layer (C). Layers (A) and (B) may be directly laminated, but are preferably laminated via another layer. For example, the layer between layers (A) and (B) may be layer (G) or an adhesive layer using a curable adhesive, and layers (A) and (B) are preferably laminated via layer (G). Furthermore, the multilayer structure preferably has a layer (F) laminated directly on the layer (D), more preferably has the layer (F) between the layer (D) and the layer (E), and further preferably has the layer (D), the layer (F), and the layer (E) all laminated directly in this order.

[0133] In the multilayer structure, it is preferable that the paper layer (A) does not have a layer containing a polyolefin resin as a main component on the side opposite the barrier resin layer (C), and it is more preferable that the paper layer (A) does not have a thermoplastic resin layer such as a heat-sealing layer on the side opposite the barrier resin layer (C). That is, it is preferable that the paper layer (A) is one of the outermost layers. In other words, it is preferable that the multilayer structure has the paper layer (A) as one of the outermost layers and the heat-sealing layer (E) as the other outermost layer. In this multilayer structure, other layers can be peeled off from only one side of the paper layer (A), and one side of the paper layer (A) is exposed when dissolving the paper layer (A) in a pulper solution or the like for recycling the paper layer (A), which makes it easier for water to penetrate into the layer (A) and improves recyclability. Furthermore, when the multilayer structure is molded into a packaging container, it is preferable that the side on which the paper layer (A) is exposed is the outer surface. When the multilayer structure has the paper layer (A) as the outermost layer, it is easy to detect the paper, specifically, to detect the paper by measuring the infrared spectrum using, for example, total reflection measurement. Therefore, in such a multilayer structure, the paper recycling rate (detected and recovered paper packaging material / total paper packaging material) can be increased. Furthermore, when using the multilayer structure, a heat sealer or the like is used to heat and pressurize the multilayer structure from the layer (A) side to perform a heat sealing treatment of the heat-sealable layer (E), etc., it is also preferable because it is easier to prevent problems (e.g., contamination of equipment, damage to the multilayer structure, etc.) caused by adhesion of resin to the heat sealer.

[0134] Specific layer configurations of the multilayer structure are exemplified below. However, the layer configuration of the multilayer structure is not limited to the following configurations. In the examples of each layer configuration below, " / " indicates direct lamination, and " / / " indicates direct lamination or lamination via layer (G) or an adhesive layer using a curable adhesive. In the layer configurations below, layer (X) represents the other layer described above. (1) Layer (A) / / Layer (B) / Layer (C) / Layer (D) / / Layer (E) (2) Layer (A) / / Layer (B) / Layer (C) / Layer (D) / Layer (F) / / Layer (E) (3) Layer (A) / / Layer (D) / Layer (C) / Layer (B) / / Layer (E) (4) Layer (A) / / Layer (F) / Layer (D) / Layer (C) / Layer (B) / / Layer (E) (5) Layer (X) / / Layer (A) / / Layer (B) / Layer (C) / Layer (D) / / Layer (E) (6) Layer (X) / / Layer (A) / / Layer (B) / Layer (C) / Layer (D) / Layer (F) / / Layer (E) (7) Layer (X) / / Layer (A) / / Layer (D) / Layer (C) / Layer (B) / / Layer (E) (8) Layer (X) / / Layer (A) / / Layer (F) / / Layer (D) / / Layer (C) / / Layer (B) / / Layer (E) Among these, the following layer configurations are preferred: Layer (A) / / Layer (G) / / Layer (B) / / Layer (C) / / Layer (D) / / Layer (E), Layer (A) / / Layer (G) / / Layer (B) / / Layer (C) / / Layer (D) / / Layer (F) / / Layer (E), Layer (A) / / Layer (G) / / Layer (B) / / Layer (C) / / Layer (D) / / Layer (F) / / Ad / / Layer (E), Layer (A) / / Ad / / Layer (B) / / Layer (C) / / Layer (D) / / Layer (E), Layer (A) / / Ad / / Layer (B) / / Layer (C) / / Layer (D) / / Layer (F) / / Ad / / Layer (E). The term "Ad" refers to an adhesive layer that uses a curing adhesive. From the viewpoint of prioritizing recyclability, a layer structure that does not contain Ad is preferred.

[0135] The mass ratio of the paper layer (A) in the multilayer structure may be, for example, 0.40 or more or 0.50 or more relative to the entire multilayer structure, but is preferably 0.55 or more, more preferably 0.60 or more, and even more preferably 0.65 or more. Having the mass ratio of the layer (A) above the lower limit makes it easier to increase the mass ratio of the paper layer (A) in the multilayer structure, thereby reducing the impact of recovery losses that may inevitably occur during recycling of the paper layer (A). As a result, the recycling rate of the paper layer (A) (mass of recovered paper / mass of paper layer (A)) can be further increased. Meanwhile, the mass ratio of the paper layer (A) relative to the entire multilayer structure is preferably 0.95 or less, more preferably 0.90 or less, even more preferably 0.80 or less, and even more preferably 0.75 or less. Having the mass ratio of the paper layer (A) below the upper limit can further improve low-temperature sealing properties and gas barrier properties after heat pressing. As described above, these stepwise lower and upper limits can be independently combined. For example, in one embodiment of the multilayer structure, the mass ratio of the paper layer (A) is preferably 0.55 to 0.95, more preferably 0.55 to 0.90, even more preferably 0.60 to 0.80, and still more preferably 0.65 to 0.75.

[0136] The total average thickness ratio of the layers mainly composed of polyolefin resin in the portions other than the paper layer (A) of the multilayer structure (the ratio of the total average thickness of the layers mainly composed of polyolefin resin to the sum of the average thicknesses of the layers other than the paper layer (A)) is 0.50 or more. Having a total average thickness ratio of the layers mainly composed of polyolefin resin in the portions other than the paper layer (A) of 0.50 or more can suppress the occurrence of defects during recycling. Furthermore, increasing the total average thickness ratio of the layers mainly composed of polyolefin resin in the portions other than the paper layer (A) is preferable because it makes it easier to suppress the occurrence of coloring during recycling. In other words, it is preferable because it makes it easier to improve recyclability. Therefore, the total average thickness ratio of the layers mainly composed of polyolefin resin in the portions other than the paper layer (A) of the multilayer structure is preferably 0.60 or more, more preferably 0.70 or more, even more preferably 0.75 or more, still more preferably 0.80 or more, still more preferably 0.85 or more, and still more preferably 0.90 or more. Furthermore, the total average thickness ratio of the layers containing a polyolefin resin as a main component in the portion of the multilayer structure other than the paper layer (A) is preferably 0.995 or less, more preferably 0.99 or less, and may be 0.98 or less. As described above, these stepwise lower limit values ​​and upper limit values ​​can be independently combined. For example, in one embodiment of the multilayer structure, the total average thickness ratio of the layers containing a polyolefin resin as a main component in the portion of the multilayer structure other than the paper layer (A) can be, for example, 0.50 to 0.995, 0.50 to 0.99, 0.50 to 0.98, 0.60 to 0.995, 0.60 to 0.99, 0.60 to 0.98, 0.70 to 0.995 ... It may be 0 to 0.99, 0.70 to 0.98, 0.75 to 0.995, 0.75 to 0.99, 0.75 to 0.98, 0.80 to 0.995, 0.80 to 0.99, 0.80 to 0.98, 0.85 to 0.995, 0.85 to 0.99, 0.85 to 0.98, 0.90 to 0.995, 0.90 to 0.99, or 0.90 to 0.98.Examples of layers containing a polyolefin resin as a main component include a layer (E) containing a polyolefin (e) as a main component, and also include the layer (D) containing an acid-modified polyolefin as a main component, the layer (F) containing a polyolefin (f) as a main component, and the layer (G) containing a polyolefin resin (g) as a main component, as described above.

[0137] In one embodiment of the multilayer structure, the total average thickness ratio of the layers primarily composed of a polyethylene-based resin in the portions other than the paper layer (A) of the multilayer structure (the ratio of the total average thickness of the layers primarily composed of a polyethylene-based resin to the sum of the average thicknesses of the layers other than the paper layer (A)) is preferably 0.50 or more. Having a total average thickness ratio of the layers primarily composed of a polyethylene-based resin in the portions other than the paper layer (A) of 0.50 or more can suppress the occurrence of defects during recycling. In addition, increasing the total average thickness ratio of the layers primarily composed of a polyethylene-based resin in the portions other than the paper layer (A) is preferable because it further facilitates the suppression of discoloration during recycling. In other words, it is preferable because it facilitates improved recyclability. Therefore, the total average thickness ratio of the layers primarily composed of a polyethylene-based resin in the portions other than the paper layer (A) of the multilayer structure is more preferably 0.60 or more, even more preferably 0.70 or more, even more preferably 0.75 or more, even more preferably 0.80 or more, even more preferably 0.85 or more, and even more preferably 0.90 or more. As described above, the lower limit and upper limit values ​​described in stages can be independently combined. For example, in one embodiment of the multilayer structure, the total average thickness ratio of the layers containing a polyethylene resin as a main component in the portion other than the paper layer (A) of the multilayer structure can be, for example, 0.50 to 0.995, 0.50 to 0.99, 0.50 to 0.98, 0.60 to 0.995, 0.60 to 0.99, 0.60 to 0.98, 0.70 to 0.995 ...5 The total average thickness ratio of layers containing a polyethylene resin as a main component in portions other than the paper layer (A) of the multilayer structure is preferably 0.995 or less, more preferably 0.99 or less, and may be 0.98 or less.Examples of the layer containing a polyethylene-based resin as a main component include the layer (E) containing polyethylene (e1) as a main component, the layer (D) containing acid-modified polyethylene as a main component, the layer (F) containing polyethylene as a main component, and the layer (G) containing a polyethylene-based resin as a main component, as described above.

[0138] In one embodiment of the multilayer structure, the total average thickness ratio of the polypropylene-based resin-based layers in the portion other than the paper layer (A) of the multilayer structure (the ratio of the total average thickness of the polypropylene-based resin-based layers to the sum of the average thicknesses of the layers other than the paper layer (A)) is preferably 0.50 or more. Having a total average thickness ratio of the polypropylene-based resin-based layers in the portion other than the paper layer (A) of 0.50 or more can suppress the occurrence of defects during recycling. In addition, increasing the total average thickness ratio of the polypropylene-based resin-based layers in the portion other than the paper layer (A) is preferable because it further facilitates suppressing the occurrence of coloration during recycling. In other words, it is preferable because it facilitates improving recyclability. Therefore, the total average thickness ratio of the polypropylene-based resin-based layers in the portion other than the paper layer (A) of the multilayer structure is more preferably 0.60 or more, even more preferably 0.70 or more, even more preferably 0.75 or more, even more preferably 0.80 or more, even more preferably 0.85 or more, and even more preferably 0.90 or more. Furthermore, the total average thickness ratio of the layers containing a polypropylene-based resin as a main component in the portion of the multilayer structure other than the paper layer (A) is preferably 0.995 or less, more preferably 0.99 or less, and may be 0.98 or less. As described above, these stepwise lower limit values ​​and upper limit values ​​can be independently combined. For example, in one embodiment of the multilayer structure, the total average thickness ratio of the layers containing a polypropylene-based resin as a main component in the portion of the multilayer structure other than the paper layer (A) can be, for example, 0.50 to 0.995, 0.50 to 0.99, 0.50 to 0.98, 0.60 to 0.995, 0.60 to 0.99, 0.60 to 0.98, 0.70 to 0.995 ... It may be 0 to 0.99, 0.70 to 0.98, 0.75 to 0.995, 0.75 to 0.99, 0.75 to 0.98, 0.80 to 0.995, 0.80 to 0.99, 0.80 to 0.98, 0.85 to 0.995, 0.85 to 0.99, 0.85 to 0.98, 0.90 to 0.995, 0.90 to 0.99, or 0.90 to 0.98.Examples of the layer containing a polypropylene-based resin as a main component include the layer (E) containing polypropylene (e2) as a main component, the layer (D) containing acid-modified polypropylene as a main component, the layer (F) containing polypropylene as a main component, and the layer (G) containing a polypropylene-based resin as a main component, as described above.

[0139] In one embodiment of the multilayer structure, the total average thickness ratio of layers containing a thermoplastic resin having a melting point of less than 200°C as a main component in the portions other than the paper layer (A) of the multilayer structure is preferably 0.95 or more, more preferably 0.98 or more, and even more preferably 0.99 or more. Increasing the total average thickness ratio of the thermoplastic resin having a melting point of less than 200°C in the portions other than the paper layer (A) improves melt moldability during recycling, thereby further suppressing the occurrence of defects and coloration. The total average thickness ratio of layers containing a thermoplastic resin having a melting point of less than 200°C as a main component in the portions other than the paper layer (A) may be, for example, 0.9999 or less. Examples of layers containing a thermoplastic resin having a melting point of less than 200°C as a main component include the above-mentioned layers (C), (D), (E), (F), and (G).

[0140] The average thickness of the multilayer structure (average thickness of the entire multilayer structure) is preferably 30 μm or more, more preferably 50 μm or more, even more preferably 80 μm or more, and even more preferably 100 μm or more. Having an average thickness of the multilayer structure equal to or greater than the lower limit allows for increased strength, etc. On the other hand, the average thickness of the multilayer structure is preferably 600 μm or less, more preferably 450 μm or less, even more preferably 300 μm or less, and even more preferably 250 μm or less. Having an average thickness of the multilayer structure equal to or less than the upper limit allows for increased flexibility and moldability, etc. As described above, these stepwise lower and upper limits can be independently combined. For example, in one embodiment of the multilayer structure, the average thickness of the multilayer structure is preferably 30 to 600 μm, more preferably 50 to 450 μm, even more preferably 80 to 300 μm, and even more preferably 100 to 250 μm.

[0141] In one embodiment of the multilayer structure, the oxygen transmission rate of the multilayer structure measured under conditions of 20°C and 65% RH according to the method described in JIS K 7126-2 (isobaric method: 2006), with the paper layer (A) side as the oxygen supply side and the heat-sealable layer (E) as the carrier gas side, is preferably 0.5 cc / (m ２ ·day·atm), more preferably less than 0.1 cc / (m ２ ·day·atm), more preferably less than 0.05 cc / (m ２ When the oxygen transmission rate is less than the upper limit, the material can be particularly suitably used as a molding material for packaging containers. On the other hand, the oxygen transmission rate is less than 0.001 cc / (m ２ As described above, the lower limit and upper limit values ​​described in stages can be independently combined. For example, in one embodiment of the multilayer structure, the oxygen transmission rate may be, for example, 0.001 cc / (m ２ ・day・atm) or more 0.5cc / (m ２ · day · atm), less than 0.001 cc / (m ２ ・day・atm) or more 0.1cc / (m ２ · day · atm), less than 0.001 cc / (m ２ ・day・atm) or more 0.05cc / (m ２ The oxygen permeability may be less than 1000 kJ / day. More specifically, the oxygen permeability is measured by the method described in the examples.

[0142] In one embodiment of the multilayer structure, the multilayer structure is folded in four so that the heat-sealable layer (E) is on the inside, and the folding in four is performed by folding in half lengthwise and then in half widthwise. In this state, a load of 5 kg is applied from above and left to stand for 1 minute to perform the folding treatment. After that, the oxygen transmission rate measured under conditions of 20°C and 65% RH according to the method described in JIS K 7126-2 (isobaric method: 2006) with the paper layer (A) side as the oxygen supply side and the heat-sealable layer (E) as the carrier gas side is preferably 1.0 cc / (m ２ ·day·atm), more preferably less than 0.2 cc / (m ２·day·atm), more preferably less than 0.1 cc / (m ２ Since the oxygen transmission rate after the folding treatment is less than the upper limit, the material can be particularly suitably used as a molding material for a packaging container that is to be folded. On the other hand, the oxygen transmission rate after the folding treatment is less than 0.002 cc / (m ２ As described above, the lower limit and upper limit values ​​described in stages can be independently combined. For example, in one embodiment of the multilayer structure, the oxygen transmission rate after the bending treatment may be, for example, 0.002 cc / (m ２ ・day・atm) or more 1.0cc / (m ２ · day · atm), less than 0.002 cc / (m ２ ・day・atm) or more 0.2cc / (m ２ · day · atm), less than 0.002 cc / (m ２ ・day・atm) or more 0.1cc / (m ２ The oxygen permeability after the folding treatment may be less than 1 / 2 day / atm. More specifically, the oxygen permeability after the folding treatment is measured by the method described in the examples.

[0143] In one embodiment of the multilayer structure, the oxygen transmission rate after heat pressing treatment evaluated by the severe seal test described in the examples below is preferably 1.0 cc / (m ２ ·day·atm), more preferably less than 0.2 cc / (m ２ ·day·atm), more preferably less than 0.1 cc / (m ２ Since the oxygen transmission rate after the heat press treatment is less than the upper limit, the composition can be particularly suitably used as a molding material for packaging containers to be heat-sealed. On the other hand, the oxygen transmission rate after the heat press treatment is less than 0.002 cc / (m ２ As described above, the lower limit and upper limit values ​​described in stages can be independently combined. For example, in one embodiment of the multilayer structure, the oxygen transmission rate after the heat press treatment may be, for example, 0.002 cc / (m２ ・day・atm) or more 1.0cc / (m ２ · day · atm), less than 0.002 cc / (m ２ ・day・atm) or more 0.2cc / (m ２ · day · atm), less than 0.002 cc / (m ２ ・day・atm) or more 0.1cc / (m ２ The oxygen transmission rate after the heat press treatment may be less than 1 / 2 day / atm. More specifically, the oxygen transmission rate after the heat press treatment is measured by the method described in the examples.

[0144] In one embodiment of the multilayer structure, the minimum temperature at which the heat seal strength obtained by placing the heat-sealable layers (E) face to face and pressing them together using a hot plate heat sealer at a pressure of 0.1 MPa for 1 second exceeds 3 N / 15 mm is preferably less than 110°C, more preferably less than 90°C. When the temperature is below the upper limit, the structure can be suitably used as a molding material for packaging containers that require heat sealing at lower temperatures, for example, when the contents are heat-sensitive. On the other hand, the temperature may be, for example, 50°C or higher, or 60°C or higher. As described above, these stepwise lower and upper limits can be independently combined. For example, in one embodiment of the multilayer structure, the temperature may be, for example, 50°C or higher but lower than 110°C, 50°C or higher but lower than 90°C, 60°C or higher but lower than 110°C, or 60°C or higher but lower than 90°C. Whether the temperature range is satisfied can be more specifically confirmed by the method described in the Examples.

[0145] For the purpose of reuse, the multilayer structure can be crushed and separated into the paper layer (A) and the portion other than the paper layer (A), and the portion other than the paper layer (A) can be used as a melt-molding material and melt-kneaded for recycling. By using the portion of the multilayer structure other than the paper layer (A) as a melt-molding material, a melt-molded product (recycled product) with few defects can be obtained. The portion of the multilayer structure other than the paper layer (A) can be mixed with other melt-molding materials (other recycled resins, unused resins, etc.). The separated paper layer (A) can also be reused.

[0146] The method for producing the multilayer structure is not particularly limited. As one embodiment of the method for producing the multilayer structure, for example, the multilayer structure can be obtained by the following steps. Step (1): A coextruded film of a barrier resin layer (C), an adhesive resin layer (D), and a heat-sealing layer (E) is produced by coextrusion. Here, it is preferable to produce a coextruded film that also contains a thermoplastic resin (F) between layers (D) and (E). Step (2): An inorganic vapor deposition layer (B) is provided on the surface of the coextruded film facing the barrier resin layer (C), thereby producing a composite film. Step (3): Paper, which is the paper layer (A), and the composite film are laminated by a known means such as sandwich lamination or dry lamination, so that the paper layer (A) and the inorganic vapor deposition layer (B) face each other.

[0147] Alternatively, for example, a composite film may be produced by providing an inorganic vapor deposition layer (B) on a monolayer film of a barrier resin layer (C), and then laminating an adhesive resin layer (D) (preferably a thermoplastic resin (F)) and a heat-sealing layer (E) thereon by extrusion lamination, dry lamination, etc. Alternatively, a two-layer film of an inorganic vapor deposition layer (B) and a barrier resin layer (C) with a paper layer (A) may be bonded together by sandwich lamination or dry lamination (preferably via a thermoplastic resin (G)), and then an adhesive resin layer (D) (preferably a thermoplastic resin (F)) and a heat-sealing layer (E) may be laminated together by extrusion lamination, sandwich lamination, or dry lamination.

[0148] The multilayer structure is suitably used as a molding material for packaging containers, preferably paper containers. The use of the packaging container is not particularly limited, and it is preferably a container for storing solids such as food. The multilayer structure may also be used for purposes other than as a molding material for packaging containers. For example, it can be suitably used for industrial purposes, construction purposes, and the like.

[0149] Furthermore, when a packaging container is formed from the multilayer structure, it is preferable that the surface on which the paper layer (A) is exposed is the outer surface. In this case, paper detection, specifically, detection of paper by infrared spectrum measurement using, for example, total reflectance measurement, is facilitated. Therefore, in such a multilayer structure, the paper recycling rate (detected and recovered paper packaging material / total paper packaging material) can be increased. Furthermore, when a packaging container is formed from the multilayer structure, it is preferable that the surface on which layer (E) is exposed is the inner surface. For example, when the multilayer structure is folded, a packaging container can be formed by bringing parts of the layers (E) into contact with each other and heat-sealing them, with the surface on which layer (E) is exposed being the inner surface. The multilayer structure also has excellent gas barrier properties after folding, so that the packaging container obtained by this molding can also have good gas barrier properties.

[0150] [Packaging Container] A packaging container according to one embodiment of the present invention is formed from the multilayer structure. The multilayer structure has good gas barrier properties and low-temperature sealing properties before and after folding and after heat pressing, and can also suppress defects during recycling. Therefore, the multilayer structure can be suitably used as a packaging container. Applications of the packaging container are not particularly limited, but examples include packaging containers for storing gases; packaging containers for storing liquids (e.g., beverages; non-beverage liquids such as detergents and medicines); and packaging containers for storing solids such as food (e.g., dried foods, snacks, confectionery, etc.) or non-food daily necessities. The multilayer structure can be more suitably used as a packaging container for storing solids.

[0151] The packaging container can be formed by using one or more of the multilayer structures, folding them as necessary, and bonding the overlapping portions of the heat-sealable layers (E) together by heat sealing or the like, so as to form, for example, a bag-like shape without any folds, such as a flat pouch, or a bag-like shape with folds, such as a stand-up pouch or a gusseted bag. For the reasons mentioned above, it is preferable that the paper layer (A) be located on the outer surface of the packaging container. Furthermore, it is preferable that the heat-sealable layer (E) be located on the inner surface of the packaging container, for the reasons mentioned above.

[0152] The shape of the packaging container is not limited to a bag shape and may be other shapes (for example, a box shape, etc.). The packaging container may be bonded by a method other than heat sealing, and may have a portion bonded by heat sealing and a portion bonded by another method. Furthermore, the packaging container may further include a member other than the multilayer structure.

[0153] The present embodiment will be described in more detail below with reference to examples, but the present embodiment is not limited to these examples.

[0154] The physical properties of each resin used in the examples and comparative examples were measured or evaluated by the following methods.

[0155] [Melting point] For the resin used in each resin layer, a differential scanning calorimeter (TA Instruments "Q2000") was used. The resin was heated from 30 ° C. to 250 ° C. at a rate of 10 ° C. / min under a nitrogen atmosphere (nitrogen flow rate 50 mL / min), then held at 250 ° C. for 3 minutes, then cooled at a rate of 10 ° C. / min to 30 ° C., held at 30 ° C. for 3 minutes, and then heated again from 30 ° C. to 250 ° C. at a rate of 10 ° C. / min. The vertical axis of the chart obtained during the second heating is the heat flow, the horizontal axis is the temperature, and the shape of the melting peak was confirmed. The apex temperature of the melting peak was read, and that temperature was used as the melting point of the measured resin.

[0156] [Density] Measured in accordance with ISO 1183-3:1999.

[0157] [Ethylene unit content and degree of saponification] Dried pellets of EVOH were dissolved in deuterated dimethyl sulfoxide (DMSO-d6) containing tetramethylsilane (TMS) as an internal standard substance and trifluoroacetic acid (TFA) as an additive, and the solution was analyzed by a 500 MHz １ Measurement was performed at 80°C using a H-NMR (manufactured by JEOL Ltd.: "GX-500"), and the ethylene unit content and the degree of saponification were determined from the peak intensity ratio of the ethylene unit, the vinyl alcohol unit, and the vinyl ester unit from the obtained NMR spectrum.

[0158] [MFR] Measured in accordance with ISO 1133-1:2011.

[0159] Example 1 (1) Preparation of EVOH (c)-Containing Resin Composition for Barrier Resin Layer (C) EVOH (c-1) (ethylene unit content: 32 mol%, degree of saponification: 99.99 mol%, MFR (190°C, 2.16 kg load): 1.6 g / 10 min, sodium acetate (220 ppm in terms of sodium ions), phosphoric acid (30 ppm in terms of phosphate ions), boric acid (150 ppm in terms of elemental boron), and no polyvalent metal ions) and magnesium stearate were melt-kneaded and pelletized so that the magnesium ion content in the resulting resin composition was 50 ppm, thereby obtaining resin composition pellets for the barrier layer (C). The extruder used for melt-kneading was a twin-screw extruder with D (mm) = 25 and co-rotating, fully intermeshing screws with L / D = 25. The resin temperature was set to 220°C.

[0160] (2) Adhesive resin (d) for adhesive resin layer (D) Maleic anhydride-modified polypropylene "ADMER (registered trademark) QF500" manufactured by Mitsui Chemicals, Inc. (MFR (230 ° C, 2.16 kg load) 3.0 g / 10 min, density 0.90 g / cm ３ , melting point 161°C, hereinafter also abbreviated as "MAhPP") was used as an adhesive resin (d-1) as pellets for the adhesive layer (D).

[0161] (3) Polyolefin (e) for the heat-sealing layer (E) Polypropylene "Novatec (registered trademark) FL203D" (MFR (230 ° C, 2.16 kg load) 3.0 g / 10 min, density 0.90 g / cm) manufactured by Japan Polypropylene Corporation ３ , melting point 162°C, hereinafter also abbreviated as "PP.") was used as polypropylene (e2-1), and a propylene-butene random copolymer "Tafmer (registered trademark) XM7070" (MFR (230°C, 2.16 kg load) 7.0 g / 10 min, density 0.885 g / cm) manufactured by Mitsui Chemicals, Inc. ３, melting point 75°C, hereinafter also abbreviated as "PBR") as polypropylene (e2-2) so as to have a mass ratio (e2-1 / e2-2) (hereinafter also referred to as "mass ratio PP / PBR") of 75 / 25, and the pellets were dry-blended and used as they were as pellets for the heat-sealable layer (E).

[0162] (4) Polyolefin (f) for thermoplastic resin layer (F) Polypropylene "Novatec (registered trademark) FL203D" (MFR (230 ° C, 2.16 kg load) 3.0 g / 10 min, density 0.90 g / cm) manufactured by Japan Polypropylene Corporation ３ , melting point 162°C) was used as polyolefin (f) as pellets for the thermoplastic resin layer (F).

[0163] (5) Preparation of Coextruded Films Using each of the pellets (1) to (4) above, a coextruded film having a layer thickness and layer structure of Layer (C) / Layer (D) / Layer (F) / Layer (E) = 4 μm / 4 μm / 20 μm / 5 μm = EVOH4 / MAhPP4 / PP20 / PP+PBR (hereinafter, the layer consisting of a dry blend of PP and PBR will also be abbreviated as "PP'"). In the description of this example, when a specific layer is referred to as "ZZ5," the abbreviation in "ZZ" represents the main component that forms that layer, and the number following ZZ represents the thickness of that layer (units are μm unless otherwise specified). For example, "EVOH4" represents a 4 μm-thick layer whose main component is EVOH. The extruders in the coextrusion film-forming equipment were all single-screw extruders with a D (mm) of 30 and a full-flight screw with an L / D of 28 and a compression ratio of 3.0. A 350 mm wide feedblock lamination type T-die was used as the die. The temperature conditions were as follows: - Extrusion temperature of barrier resin layer (C): feeding section / compression section / metering section / adapter = 175 / 220 / 220 / 220°C - Extrusion temperature of adhesive resin layer (D): feeding section / compression section / metering section / adapter = 175 / 220 / 220 / 220°C - Extrusion temperature of heat-sealing layer (E): feeding section / compression section / metering section / adapter = 175 / 220 / 220 / 220°C - Extrusion temperature of thermoplastic resin layer (F): feeding section / compression section / metering section / adapter = 175 / 220 / 220 / 220°C - Die temperature: 220°C - Chill roll temperature: 80°C

[0164] (6) Preparation of Composite Film A 50 nm-thick aluminum metal vapor-deposited layer (inorganic vapor-deposited layer (B)) (Al) was laminated by a known vacuum vapor deposition method on the surface of the barrier resin layer (C) of the co-extruded film obtained in (5) above, to prepare a composite film having the following layer thickness and layer structure: Layer (B) / Layer (C) / Layer (D) / Layer (F) / Layer (E) = Al (50 nm) / EVOH4 / MAhPP4 / PP20 / PP'5.

[0165] (7) Preparation of multilayer structure As the paper layer (A), a basis weight of 80 g / m ２White paper (wood-free paper) of 100g was prepared. In addition, polypropylene "Novatec (registered trademark) FL203D" (MFR (230°C, 2.16 kg load) 3.0g / 10min, density 0.90g / cm3) manufactured by Japan Polypropylene Corporation was used as the extrusion lamination resin (polyolefin resin (g)). ３ Next, the white paper (free-quality paper) was fed from the first paper feed section of the extrusion laminating equipment, the composite film obtained in (6) was fed from the second paper feed section, and the PP was extruded between them at 270°C to sandwich laminate the film with a 15 μm-thick polypropylene layer (thermoplastic resin layer (G)) interposed therebetween, resulting in a laminate of paper (80 g / m) with a thickness of Layer (A) / Layer (G) / Layer (B) / Layer (C) / Layer (D) / Layer (F) / Layer (E). ２ A multilayer structure having the following layer thickness and layer structure was prepared: PP15 / Al (50 nm) / EVOH4 / MAhPP4 / PP20 / PP'5.

[0166] Example 2 Resin composition pellets, a co-extruded film, a composite film, and a multilayer structure were prepared in the same manner as in Example 1, except that EVOH (c-2) (ethylene unit content: 27 mol%, degree of saponification: 99.99 mol%, MFR (210°C, 2.16 kg load): 4.0 g / 10 min, containing 220 ppm of sodium acetate in terms of sodium ions, 30 ppm of phosphoric acid in terms of phosphate ions, and 150 ppm of boric acid in terms of elemental boron, and containing no polyvalent metal ions) was used instead of EVOH (c-1).

[0167] Example 3 Resin composition pellets, a co-extruded film, a composite film, and a multilayer structure were prepared in the same manner as in Example 1, except that EVOH (c-3) (ethylene unit content: 44 mol%, degree of saponification: 99.99 mol%, MFR (190°C, 2.16 kg load): 5.7 g / 10 min, containing 220 ppm of sodium acetate in terms of sodium ions and 30 ppm of phosphate ions in terms of phosphate radicals, and containing no polyvalent metal ions) was used instead of EVOH (c-1).

[0168] [Example 4] Resin composition pellets, a composite film, and a multilayer structure were prepared in the same manner as in Example 1, except that no polyolefin (f) was used and the thickness of the coextruded film was changed to prepare a coextruded film having a layer thickness and layer structure of Layer (C) / Layer (D) / Layer (E) = 4 μm / 4 μm / 10 μm = EVOH4 / MAhPP4 / PP'10.

[0169] [Example 5] As the material for the heat-sealing layer (E), the thermoplastic resin layer (F), and the thermoplastic resin layer (G), low-density polyethylene "INNATE (registered trademark) TF80" manufactured by Dow Corporation (MFR (190°C, 2.16 kg load) 1.6 g / 10 min, density 0.926 g / cm ３ 124°C, melting point 124°C, hereinafter also abbreviated as "PE") was used, and maleic anhydride modified polyethylene "ADMER (trademark) NF518" (MFR (190°C, 2.16 kg load) 3.1 g / 10 min, density 0.91 g / cm) manufactured by Mitsui Chemicals, Inc. was used as the material for the adhesive resin layer (D). ３ Resin composition pellets, a co-extruded film, a composite film, and a multilayer structure were prepared in the same manner as in Example 1, except that a 1,2-dichloro-2,4-diphenyl-2,4-diene (MAhPE) having a melting point of 122°C (hereinafter also abbreviated as "MAhPE") was used, and various measurements and evaluations were carried out. The results are shown in Table 2.

[0170] [Example 6] Resin composition pellets, a co-extruded film, a composite film, and a multilayer structure were produced in the same manner as in Example 1, except that the mass ratio PP / PBR of the dry blend of PP and PBR used as the material of the heat-sealable layer (E) was changed to 90 / 10.

[0171] [Example 7] Resin composition pellets, a co-extruded film, a composite film and a multilayer structure were produced in the same manner as in Example 1, except that PBR was not used as the material for the heat-sealable layer (E) and only PP was used.

[0172] Example 8 Resin composition pellets, a coextruded film, a composite film and a multilayer structure were produced in the same manner as in Example 1, except that the aluminum metal vapor-deposited layer was changed to an alumina (AlOx) vapor-deposited layer.

[0173] Example 9 Resin composition pellets, a coextruded film, a composite film and a multilayer structure were produced in the same manner as in Example 1, except that the aluminum metal vapor deposition layer was changed to a silica (SiOx) vapor deposition layer.

[0174] [Example 10] Resin composition pellets, a co-extruded film, a composite film, and a multilayer structure were produced in the same manner as in Example 1, except that the amount of magnesium stearate kneaded with EVOH (c-1) was changed so that the magnesium ion content was 20 ppm.

[0175] [Example 11] Resin composition pellets, a co-extruded film, a composite film, and a multilayer structure were produced in the same manner as in Example 1, except that the amount of magnesium stearate kneaded with EVOH (c-1) was changed so that the magnesium ion content was 100 ppm.

[0176] Example 12 Resin composition pellets, a co-extruded film, a composite film and a multilayer structure were produced in the same manner as in Example 1, except that the magnesium stearate kneaded with EVOH (c-1) was changed to calcium stearate.

[0177] Example 13 Resin composition pellets, a co-extruded film, a composite film and a multilayer structure were produced in the same manner as in Example 1, except that the magnesium stearate kneaded with EVOH (c-1) was changed to zinc stearate.

[0178] Example 14 Resin composition pellets, a co-extruded film, a composite film, and a multilayer structure were prepared in the same manner as in Example 1, except that EVOH (c-2) and EVOH (c-3) were mixed (dry blended) in a weight ratio of 75 / 25 instead of EVOH (c-1).

[0179] Example 15 Resin composition pellets, a coextruded film, a composite film, and a multilayer structure were produced in the same manner as in Example 1, except that the thickness structure of the coextruded film was changed to Layer (C) / Layer (D) / Layer (F) / Layer (E) = 10 μm / 4 μm / 25 μm / 5 μm = EVOH10 / MAhPP4 / PP25 / PP'5.

[0180] Example 16: An unstretched coextruded film having a layer thickness and layer structure of Layer (C) / Layer (D) / Layer (F) / Layer (E) = 5 μm / 5 μm / 75 μm / 15 μm = EVOH5 / MAhPP5 / PP75 / PP'15 was prepared in the same manner as in Example 1. This unstretched coextruded film was stretched 5 times in the MD direction (longitudinal direction) to produce a stretched coextruded film of Layer (C) / Layer (D) / Layer (F) / Layer (E) = 1 μm / 1 μm / 15 μm / 3 μm = EVOH1 / MAhPP1 / PP15 / PP'3. Resin composition pellets, composite films, and multilayer structures were prepared in the same manner as in Example 1, except that this stretched coextruded film was used instead of the coextruded film of Example 1.

[0181] [Example 17] Resin composition pellets, a composite film, and a multilayer structure were prepared in the same manner as in Example 16, except that EVOH (c-2) was used instead of EVOH (c-1), and various measurements and evaluations were carried out. The results are shown in Table 2.

[0182] Example 18 Regarding the coextruded film, an unstretched coextruded film having layer thicknesses and a layer structure of Layer (C) / Layer (D) / Layer (F) / Layer (E) = 32 μm / 32 μm / 480 μm / 96 μm = EVOH32 / MAhPP32 / PP480 / PP'96 was prepared in the same manner as in Example 1. This unstretched coextruded film was stretched 4 times in the MD direction (longitudinal direction) and then 8 times in the TD direction (transverse direction) to produce a stretched coextruded film of Layer (C) / Layer (D) / Layer (F) / Layer (E) = 1 μm / 1 μm / 15 μm / 3 μm = EVOH1 / MAhPP1 / PP15 / PP'3. Resin composition pellets, a composite film, and a multilayer structure were produced in the same manner as in Example 1, except that the stretched co-extruded film was used instead of the co-extruded film of Example 1.

[0183] Example 19 Resin composition pellets, a coextruded film, a composite film, and a multilayer structure were produced in the same manner as in Example 17, except that the thickness structure of the coextruded film after stretching was changed to Layer (C) / Layer (D) / Layer (F) / Layer (E) = 1 μm / 1 μm / 20 μm / 5 μm = EVOH1 / MAhPP1 / PP20 / PP'5.

[0184] Example 20 Resin composition pellets, a composite film and a multilayer structure were prepared in the same manner as in Example 19, except that EVOH (c-2) was used instead of EVOH (c-1).

[0185] [Example 21] Paper layer (A) with a basis weight of 145 g / m ２ Resin composition pellets, co-extruded films, composite films, and multilayer structures were produced in the same manner as in Example 1, except that the paper layer (A) was changed to white paper (high-quality paper) of 100g, and the average thickness of each layer other than the paper layer (A) was changed as shown in Tables 1 and 2.

[0186] [Example 22] Resin composition pellets, a co-extruded film, a composite film, and a multilayer structure were produced in the same manner as in Example 19, except that the thickness of the barrier resin layer (C) was changed to 2 µm as shown in Tables 1 and 2.

[0187] [Example 23] Resin composition pellets, co-extruded films, composite films, and multilayer structures were prepared in the same manner as in Example 1, except that the average thickness of each layer other than the paper layer (A) was changed as shown in Tables 1 and 2.

[0188] Example 24 A coextruded film having a layer thickness and layer structure of Layer (C) / Layer (D) / Layer (F) / Layer (E) = 3 μm / 10 μm / 40 μm / 15 μm = EVOH3 / MAhPP10 / PP40 / PP'15 was prepared, and instead of extrusion lamination, a paper layer and composite film were laminated using a known dry lamination method to create a multilayer structure (paper / Ad3 / Al (50 nm) / EVOH3 / MAhPP10 / PP40 / PP'15) (Ad is the adhesive layer formed with the adhesive used in dry lamination). Resin composition pellets, coextruded film, composite film, and multilayer structure were prepared in the same manner as in Example 1. A two-component reactive polyurethane adhesive was used as the adhesive for dry lamination, and was used so that the thickness after drying would be 3 μm.

[0189] [Example 25] For the multilayer structure, a polypropylene film "Novatec (registered trademark) FL203D" (MFR (230°C, 2.16 kg load) 3.0 g / 10 min, density 0.90 g / cm) manufactured by Japan Polypropylene Corporation was laminated on the side opposite to the composite film laminated with the paper layer (A). ３ A resin composition pellet, a co-extruded film, a composite film, and a multilayer structure were prepared in the same manner as in Example 1, except that a 20 μm-thick polypropylene layer was laminated on the resin composition (a copolymer of 1,2-dichloroisopropyl methyl acrylate and 1,2-dichloroisopropyl methyl acrylate, melting point 162° C.) by extrusion at 270° C.

[0190] [Comparative Example 1] Resin composition pellets, a composite film, and a multilayer structure were produced in the same manner as in Example 1, except that a single-layer film of a 25 μm-thick heat-sealable layer (E) (mass ratio PP / PBR = 75 / 25) was used instead of the coextruded film, and aluminum was vapor-deposited on the heat-sealable layer (E). The single-layer film of the heat-sealable layer (E) was produced using a single-screw extruder (die width 300 mm) using a full-flight screw with D (mm) = 20, L / D = 20, and a compression ratio of 3.5. (Extrusion conditions) Extrusion temperature of the heat-sealable layer (E): feeding section / compression section / metering section / adapter = 175 / 220 / 220 / 220 ° C. Die temperature: 220 ° C. Chill roll temperature: 80 ° C.

[0191] Comparative Example 2 A resin composition pellet and a multilayer structure were prepared in the same manner as in Comparative Example 1, except that the aluminum metal vapor deposition layer was not provided.

[0192] Comparative Example 3 A multilayer structure was produced in the same manner as in Comparative Example 2, except that PE was used instead of PP.

[0193] Comparative Example 4 A resin composition pellet, a co-extruded film, and a multilayer structure were prepared in the same manner as in Example 1, except that no aluminum metal vapor deposition layer was laminated.

[0194] [Comparative Example 5] Paper layer (A) with a basis weight of 250 g / m ２ Resin composition pellets, a coextruded film, a composite film and a multilayer structure were prepared in the same manner as in Example 1, except that white paperboard (high-quality paperboard) of 100g was used.

[0195] Comparative Example 6 A 50 nm thick aluminum metal vapor deposition layer (inorganic vapor deposition layer (B)) (Al) was laminated on the surface of a biaxially oriented polyethylene terephthalate film (PET) "Lumirror (registered trademark) P60" (melting point 256°C, thickness 12 μm) manufactured by Toray Industries, Inc., by a known vacuum deposition method, to produce an Al (50 nm) / PET12 composite film. A 20 μm thick heat-sealing layer (E) (mass ratio PP / PBR = 75 / 25) and the paper layer (A) used in Example 1 were bonded to both sides of the composite film using a dry lamination adhesive to produce a multilayer structure (paper / Ad3 / Al (50 nm) / PET12 / Ad3 / PP'20) (Ad is the adhesive layer formed with the adhesive used in dry lamination). A multilayer structure was produced in the same manner as in Example 1. Note that a two-component reactive polyurethane adhesive was used as the dry lamination adhesive, and was used so that the thickness after drying would be 3 μm. The monolayer film of the heat-sealable layer (E) was produced using a single-screw extruder (die width 300 mm) using a full-flight screw with D (mm) = 20, L / D = 20, and a compression ratio of 3.5. (Extrusion conditions) Extrusion temperature of the heat-sealable layer (E): feeding section / compression section / metering section / adapter = 175 / 220 / 220 / 220 ° C. Die temperature: 220 ° C. Chill roll temperature: 80 ° C.

[0196] Comparative Example 7 Resin composition pellets, a co-extruded film, a composite film, and a multilayer structure were prepared in the same manner as in Example 1, except that the average thickness of each layer other than the paper layer (A) was changed as shown in Tables 3 and 4.

[0197] The multilayer structures obtained in each of the Examples and Comparative Examples were measured or evaluated by the following methods. The results are shown in Tables 1 to 4 below.

[0198] [Average Thickness] A thin section of the multilayer structure was cut using a microtome, and the cross section was observed under an optical microscope (Nikon Corporation, ECLIPSE (registered trademark) Ci-E) to measure the thickness of each layer.

[0199] [PO Ratio (Thickness Ratio) Other Than Paper Layer] The total average thickness ratio of layers containing polyolefin resin as a main component in the portion other than the paper layer (A) (hereinafter also referred to as "PO ratio other than paper layer") was calculated using the average thickness of each layer other than the paper layer (A) measured by the above method. For example, in the case of the multilayer structure of Example 1, the layers other than the paper layer (A) containing polyolefin resin as a main component are the adhesive resin layer (D), the heat-sealing layer (E), the thermoplastic resin layer (F), and the thermoplastic resin layer (D). Therefore, the thickness ratio was calculated using the sum (μm) of the average thicknesses of each layer other than the paper layer (A) as the denominator and the sum (μm) of the average thicknesses of the layers (D), (E), (F), and (E) as the numerator. For other multilayer structures, the thickness ratio was calculated using the following formula based on the same concept. Total average thickness ratio of layers mainly composed of polyolefin resin in the portion other than the paper layer (A) = [total average thickness of layers mainly composed of polyolefin resin (μm) / total average thickness of layers other than the paper layer (A) (μm)]

[0200] [Paper layer ratio (mass ratio)] The average thickness of each layer is multiplied by the density of the material of each layer to obtain the mass per unit area (g / cm ２ ), and the sum of the converted masses of each layer is used as the denominator to calculate the mass (g / cm) of the paper layer (A). ２ The paper layer ratio was calculated using the mass of the paper layer (A) as the numerator. The paper layer ratio (mass ratio) of the other multilayer structures was calculated using the following formula based on the same concept: Paper layer ratio (mass ratio) = Mass of the paper layer (A) (g / cm ２ ) / total mass of all layers (g / cm ２ )

[0201] [Oxygen Transmission Rate (OTR)] The oxygen transmission rate of the multilayer structure was measured in accordance with the method described in JIS K 7126-2 (isobaric method: 2006), with the paper layer side as the oxygen supply side and the composite film as the carrier gas side. Specifically, the oxygen transmission rate (unit: cc / (m)) was measured using an oxygen transmission rate measuring device (MOCON Corporation's "MOCON (registered trademark) OX-TRAN (registered trademark) 2 / 21") under the conditions of a temperature of 20°C, a humidity of 65% RH on the oxygen supply side, a humidity of 65% RH on the carrier gas side, an oxygen pressure of 1 atmosphere, and a carrier gas pressure of 1 atmosphere. ２The gas barrier properties were determined to be insufficient when the carrier gas was rated D or E. [Rating: Criteria] A: 0.05 cc / (m ２ · day · atm). B: 0.05 cc / (m ２ ・day・atm) or more, 0.1cc / (m ２ ・day・atm). C: 0.1cc / (m ２ ・day・atm) or more, 0.5cc / (m ２ · day · atm) or less. D: 0.5 cc / (m ２ ・day・atm) or more, 2.0cc / (m ２ · day · atm) or less. E: 2.0 cc / (m ２ ・day・atm) or more.

[0202] [Oxygen Transmission Rate After Folding (OTR After Folding)] The multilayer structure was cut into a 10 cm square and folded in four so that the paper layer was on the outside. The four-folding was performed by folding in half lengthwise and then in half widthwise. In this state, a 5 kg load was applied from above and left to stand for 1 minute, thereby performing a folding treatment. After the folding treatment, the 5 kg load was removed, and the multilayer structure was opened with the folds. The oxygen transmission rate was measured in accordance with the method described in JIS K 7126-2 (isobaric method: 2006) with the paper layer as the oxygen supply side and the heat-sealed layer as the carrier gas side. Specifically, the oxygen transmission rate (unit: cc / (m)) was measured using an oxygen transmission amount measuring device (MOCON Corporation, "MOCON (registered trademark) OX-TRAN (registered trademark) 2 / 21") under conditions of a temperature of 20°C, a humidity of 65% RH on the oxygen supply side, a humidity of 65% RH on the carrier gas side, an oxygen pressure of 1 atmosphere, and a carrier gas pressure of 1 atmosphere. ２ The gas barrier properties were determined to be insufficient for the following criteria: A: 0.1 cc / (m³ / day·atm) and B: 0.1 cc / (m³ / day·atm) were measured and rated according to the following criteria. Nitrogen gas containing 2% by volume of hydrogen gas was used as the carrier gas. Ratings D and E indicated that the gas barrier properties were insufficient. [Rating: Criteria] A: 0.1 cc / (m³ / day·atm) and B: 0.1 cc / (m³ / day·atm) were measured and rated according to the following criteria. ２ ・day・atm). B: 0.1cc / (m ２ ・day・atm) or more, 0.2cc / (m２ ・day・atm). C: 0.2cc / (m ２ ・day・atm) or more, 1.0cc / (m ２ · day · atm) or less. D: 1.0 cc / (m ２ ・day・atm) or more, 4.0cc / (m ２ · day · atm) or less. E: 4.0 cc / (m ２ ・day・atm) or more.

[0203] [Low-Temperature Sealing Test] The multilayer structure was cut into two pieces measuring 15 mm wide x 150 mm long. The two cut-out multilayer structures were placed with the heat-sealable layers (E) facing each other and pressure-bonded for 1 second using a hot plate heat sealer set to various temperatures at a pressure of 0.1 MPa. The heat-sealed test pieces were measured for heat-seal strength at the heat-sealed portion using an Autograph (registered trademark) (Shimadzu Corporation, "DCS-50M") at a tensile speed of 250 mm / min in a T-peel mode. The minimum temperature at which this heat-sealing strength exceeded 3 N / 15 mm was measured, and this temperature was used to evaluate low-temperature sealing property, which was then rated according to the following criteria. A rating of C indicated insufficient low-temperature sealing property. [Rating: Criteria] A: Less than 90°C. B: 90°C or higher, but less than 110°C. C: 110°C or higher.

[0204] [Severe Seal Test (Gas Barrier Property After Severe Seal Test)] The multilayer structure was cut into two 10 cm square pieces. The two cut-out multilayer structures were placed with the heat-sealable layers (E) facing each other, and a Teflon® sheet was sandwiched between the facing heat-sealable layers (E) to prevent fusion, creating a test sample. At the minimum temperature measured in the low-temperature seal test, the test sample was placed with a hot plate heat sealer (sealer width 10 mm) under a pressure of 0.1 MPa for 1 second, with the center of the test sample positioned at the center of the sealer. The same location was pressed three times. The test sample was then rotated 90 degrees and pressed three times under the same conditions, resulting in a total of six press tests on the same test sample. After pressing, cross-shaped press marks were observed on the multilayer structure in the test sample, and the heat-sealable layers of the two multilayer structures were not fused to each other. One of the two multilayer structures after pressing was placed with the paper layer side as the oxygen supply side, with the center of the multilayer structure positioned at the center of the measuring device, and the oxygen transmission rate was measured in accordance with the method described in JIS K 7126-2 (isobaric method: 2006). Specifically, an oxygen transmission rate measuring device ("MOCON (registered trademark) OX-TRAN (registered trademark) 2 / 21" manufactured by Modern Control) was used to measure the oxygen transmission rate (unit: cc / (m)) under conditions of a temperature of 20°C, a humidity of 65% RH on the oxygen supply side, a humidity of 65% RH on the carrier gas side, an oxygen pressure of 1 atmosphere, and a carrier gas pressure of 1 atmosphere. ２ The gas barrier properties after heat pressing were judged to be insufficient. [Judgment: Criteria] A: 0.1 cc / (m) ２ ・day・atm). B: 0.1cc / (m ２ ・day・atm) or more, 0.2cc / (m ２ ・day・atm). C: 0.2cc / (m ２ ・day・atm) or more, 1.0cc / (m ２ · day · atm) or less. D: 1.0 cc / (m ２ ・day・atm) or more, 2.0cc / (m ２· day · atm) or less. E: 2.0 cc / (m ２ ・day・atm) or more.

[0205] [Paper detectability] The infrared spectrum of each multilayer structure was measured on both sides using a total reflection measurement method. If paper was detected on either side, the sample was rated as "OK." If paper was not detected on either side, the sample was rated as "NG." A Fourier transform infrared spectrophotometer ("Spectrum One" manufactured by PerkinElmer) was used for the measurement.

[0206] [Heat resistance] The multilayer structure was cut into a 10 cm square and left to stand in a hot air dryer set to 120°C for 10 minutes. After the test, the cut-out multilayer structure was visually inspected for appearance and its dimensions were measured, and it was judged according to the following criteria. [Judgment: Criteria] The judgment was made according to the following criteria. A: No change in appearance and almost no change in dimensions. B: A slight change in dimensions was observed, but no change in appearance. C: Some wrinkles were observed in the appearance.

[0207] [Evaluation of recyclability of portions other than the paper layer separated from the multilayer structure] The multilayer structure obtained in (8) was crushed into pieces of 4 mm square or less, and stirred in a 90°C aqueous sodium hydroxide solution (1 mol / L) for 30 minutes to remove the paper layer from the multilayer structure. The portions other than the paper layer floating in the aqueous solution were then recovered, washed with water at room temperature, and dried at 60°C for 24 hours to obtain a recovered material. This recovered material was mixed with polypropylene "Novatec (trademark) FL203D" (MFR (230°C, 2.16 kg load) 3.0 g / 10 min, density 0.90 g / cm) manufactured by Japan Polypropylene Corporation. ３, melting point 162°C) were blended in a mass ratio (recycled material / PP) of 40 / 60, and a monolayer film with a thickness of 50 μm was obtained by extrusion under the following conditions. As a control, a monolayer film with a thickness of 50 μm was similarly obtained using only PP. The extruder was a single-screw extruder with D (mm) = 20 and a full-flight screw with L / D = 20 and a compression ratio of 3.5. A 300 mm wide T-die was used as the die. The thickness of the monolayer film was adjusted by appropriately changing the screw rotation speed and take-up roll speed. The temperature conditions used are as follows: Extrusion temperature: feed section / compression section / metering section / adapter = 175 / 220 / 220 / 220°C Die temperature: 220°C Chill roll temperature: 80°C The coloration and defects of the obtained monolayer film were visually evaluated and judged according to the following criteria. In judging defects, ratings E and F were given to indicate that the occurrence of defects during recycling was not suppressed. [Defect Judgment: Criteria] A: The degree of change in hue was small compared to the control. B: Slight coloring was observed compared to the control. C: Moderate coloring was observed compared to the control. D: Significant coloring was observed compared to the control. E: Significant coloring was observed compared to the control, and unevenness was also observed. [Defect Judgment: Criteria] A: The amount of particles was almost the same compared to the control. B: The amount of small particles was slightly higher compared to the control. C: The amount of small particles was higher compared to the control. D: The amount of small particles was higher and the amount of large particles was slightly higher compared to the control. E: The amount of small particles was higher and the amount of large particles was higher compared to the control. F: The amount of small particles was higher and the amount of large particles was significantly higher compared to the control.

[0208]

[0209]

[0210]

[0211]

[0212] In Tables 2 and 4, "MD x TD" in the "Stretching ratio of coextruded film" column represents the stretching ratio in the MD direction and the stretching ratio in the TD direction. For example, the notation "4 x 8" indicates that the film was stretched 4 times in the MD direction and 8 times in the TD direction.

[0213] The results in Tables 1 and 2 confirm that the multilayer structures of Examples 1 to 25 have good gas barrier properties and low-temperature sealing properties before and after bending and after hot pressing, and furthermore, can suppress the occurrence of defects during recycling. Furthermore, it was confirmed that the multilayer structures of Examples 1 to 25 also have good heat resistance.

[0214] On the other hand, from the results of Tables 3 and 4, it was confirmed that the multilayer structure of Comparative Example 1 had an inorganic vapor deposition layer (B) but no barrier resin layer (C), and therefore was significantly inferior in various gas barrier properties. Furthermore, the multilayer structures of Comparative Examples 2 and 3 had neither an inorganic vapor deposition layer (B) nor a barrier resin layer (C), and therefore were significantly inferior in various gas barrier properties. Furthermore, the multilayer structure of Comparative Example 4 had a barrier resin layer (C) but no inorganic vapor deposition layer (B), and therefore was significantly inferior in various gas barrier properties. Furthermore, the multilayer structure of Comparative Example 5 had a paper layer (A) with a basis weight of 150 g / m². ２ Since the thickness exceeded 0.50, it was confirmed that the low-temperature sealability was poor. Furthermore, since the multilayer structure of Comparative Example 5 required a higher heat press temperature during the severe seal test due to its poor low-temperature sealability, it was also confirmed that the gas barrier properties after heat press treatment were poor. Furthermore, since the multilayer structure of Comparative Example 6 uses a layer containing polyethylene terephthalate (a resin with a melting point of 200°C or higher) as the barrier resin layer instead of EVOH (c), it was confirmed that various gas barrier properties were significantly poor. Furthermore, it was confirmed that defects during recycling increased. Furthermore, it was confirmed that the multilayer structure of Comparative Example 7 had an increased number of defects during recycling and worsened coloration because the total average thickness ratio of layers containing polyolefin resin as the main component in the parts other than the paper layer (A) was less than 0.50.

Claims

1. A paper layer (A) and an inorganic vapor deposition layer (B), a barrier resin layer (C), an adhesive resin layer (D), and a heat-sealing layer (E) on one side of the paper layer (A), the inorganic vapor deposition layer (B), the barrier resin layer (C), and the adhesive resin layer (D) are all directly laminated in this order, the heat-sealing layer (E) is one of the outermost layers, and the paper layer (A) has a basis weight of 30 to 150 g / m ２ the average thickness of the inorganic vapor deposition layer (B) is 5 to 200 nm; the barrier resin layer (C) contains, as a main component, an ethylene-vinyl alcohol copolymer (c) having an ethylene unit content of 20 to 50 mol% and a saponification degree of 90 mol% or more; the heat-sealable layer (E) contains, as a main component, a polyolefin (e) having a melting point of 175°C or less; the ratio of the total average thickness of the layers containing a polyolefin resin as a main component to the total value of the average thicknesses of the layers other than the paper layer (A) is 0.50 or more; and the multilayer structure does not have a layer containing, as a main component, a resin having a melting point of 200°C or more and a metal layer having an average thickness of 1 μm or more.

2. The multilayer structure according to claim 1, which has a paper layer (A) on the side of the inorganic vapor deposition layer (B) opposite to the barrier resin layer (C).

3. The multilayer structure according to claim 1, further comprising a thermoplastic resin layer (F) present between the adhesive resin layer (D) and the heat-sealable layer (E), the thermoplastic resin layer (F) containing polyolefin (f) as a main component.

4. The multilayer structure according to claim 3, wherein the average thickness (Ft) of the thermoplastic resin layer (F) is greater than the average thickness (Et) of the heat-sealable layer (E).

5. The multilayer structure according to claim 1, further comprising a thermoplastic resin layer (G) present between the paper layer (A) and the inorganic vapor deposition layer (B), the thermoplastic resin layer (G) containing a polyolefin resin (g) as a main component.

6. The multilayer structure according to claim 1, wherein the adhesive resin layer (D) contains, as a main component, an adhesive resin (d) having a melting point of 175°C or less.

7. The multilayer structure according to claim 6, wherein the adhesive resin (d) is at least one selected from the group consisting of acid-modified polyethylene (d1) and acid-modified polypropylene (d2).

8. The polyolefin (e) is polyethylene (e1), and the density of the polyethylene (e1) is 0.880 to 0.940 g / cm ３ 2. The multilayer structure of claim 1, wherein:

9. The multilayer structure according to claim 1, wherein the polyolefin (e) is polypropylene (e2).

10. The multilayer structure according to claim 9, wherein the heat-sealable layer (E) contains, as the polypropylene (e2), a polypropylene (e2-1) having a melting point of more than 110°C and a polypropylene (e2-2) having a melting point of 110°C or less, and the mass ratio (e2-1 / e2-2) of the polypropylene (e2-1) to the polypropylene (e2-2) is 55 / 45 to 96 / 4.

11. Polypropylene (e2-2) has a density of 0.860 to 0.905 g / cm ３ 11. The multilayer structure of claim 10, wherein:

12. The multilayer structure according to claim 1, wherein the minimum temperature at which the heat seal strength obtained by placing the heat-sealable layers (E) face to face and pressing them together using a hot plate heat sealer at a pressure of 0.1 MPa for 1 second exceeds 3 N / 15 mm is less than 110°C.

13. The multilayer structure according to claim 1, wherein the inorganic vapor-deposited layer (B) is a vapor-deposited metal layer containing aluminum as a main component, or a vapor-deposited inorganic oxide layer containing alumina or silica as a main component.

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

15. The multilayer structure according to claim 1, wherein the barrier resin layer (C) contains two or more types of ethylene-vinyl alcohol copolymers (c) having different ethylene unit contents.

16. The multilayer structure according to claim 1, wherein the ethylene unit content of the ethylene-vinyl alcohol copolymer (c) is 22 to 30 mol %.

17. The multilayer structure according to claim 1, wherein the multilayer structure has a coextruded film, the coextruded film comprising a barrier resin layer (C) and an adhesive resin layer (D), and the average thickness of the coextruded film is 8 to 120 μm.

18. The multilayer structure of claim 17, wherein the coextruded film further comprises a heat-sealable layer (E).

19. The multilayer structure according to claim 17 or 18, wherein the thickness of the barrier resin layer (C) is 0.1 to 30 μm, and the ratio of the thickness of the barrier resin layer (C) to the total thickness of all layers of the coextruded film is 25% or less.

20. The multilayer structure of claim 17 or 18, wherein the coextruded film is substantially unoriented.

21. The multilayer structure of claim 17 or 18, wherein the coextruded film is stretched at least uniaxially by 3 to 12 times.

22. The multilayer structure according to claim 17 or 18, wherein the coextruded film is biaxially stretched 3 to 12 times.

23. The multilayer structure of claim 1, which does not have an adhesive layer consisting solely of a curable adhesive.

24. The multilayer structure according to claim 1, wherein the mass ratio of the paper layer (A) to the entire multilayer structure is 0.55 or more.

25. The multilayer structure according to claim 1, wherein the paper layer (A) does not have a heat-sealing layer on the side opposite to the barrier resin layer (C).

26. The multilayer structure according to claim 1, wherein the paper layer (A) is one of the outermost layers.

27. The oxygen transmission rate measured under conditions of 20°C and 65% RH using the method described in JIS K 7126-2 (isobaric method: 2006) with the paper layer (A) side as the oxygen supply side and the heat-sealable layer (E) as the carrier gas side is 0.5 cc / (m ２ 10. The multilayer structure of claim 1, wherein the viscosity is less than 1000 kJ / day.

28. The sheet was folded in four so that the heat-sealable layer (E) was on the inside, and in this state, a load of 5 kg was applied from above and left to stand for 1 minute to perform a folding treatment. After that, the oxygen transmission rate was measured under the conditions of 20°C and 65% RH using the method described in JIS K 7126-2 (constant pressure method: 2006) with the paper layer (A) side as the oxygen supply side and the heat-sealable layer (E) as the carrier gas side, and the oxygen transmission rate was 1.0 cc / (m ２ 10. The multilayer structure of claim 1, wherein the viscosity is less than 1000 kJ / day.

29. A packaging container formed from the multilayer structure according to claim 1.

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