Multilayer film, vapor-deposited multilayer film, multilayer structure, and packaging material

Abstract

Provided is a multilayer film having a configuration in which at least a skin layer (A), a core layer (C), an adhesive layer (D), and a barrier layer (E) are laminated in the stated order, wherein: the skin layer (A) is positioned on one outermost layer of the multilayer film; the barrier layer (E) is positioned on the other outermost layer of the multilayer film; the core layer (C) is the layer having the greatest thickness in the multilayer film; the skin layer (A) contains a polyethylene-based resin (a) as a main component; the core layer (C) contains a polyethylene-based resin (c) as a main component; the density (dA) of the skin layer (A) is greater than the density (dC) of the core layer (C); the adhesive layer (D) contains an adhesive resin (d) having a melting point of less than 150°C as a main component; the barrier layer (E) contains an ethylene-vinyl alcohol copolymer (e) having an ethylene unit content of 20-30 mol% and a saponification degree of 90 mol% or higher as a main component; and the multilayer film does not have any layer containing a resin having a melting point of 220°C or higher as a main component, and is stretched by a factor of at least three times or more in a uniaxial direction.

Description

Multilayer film, vapor-deposited multilayer film, multilayer structure and packaging material

[0001] The present disclosure relates to multilayer films, vapor deposited multilayer films, or multilayer structures and packaging materials.

[0002] Ethylene-vinyl alcohol copolymers (hereinafter, sometimes abbreviated as "EVOH") are excellent in transparency, gas barrier properties, aroma retention, solvent resistance, oil resistance, and the like, and by taking advantage of these properties, they are used in a wide range of applications, including various types of packaging such as food packaging, pharmaceutical packaging, industrial chemical packaging, and agricultural chemical packaging, as well as industrial films, agricultural films, floor heating pipes, and fuel containers.

[0003] In recent years, driven by environmental and waste problems, there has been a worldwide increase in demand for so-called post-consumer recycling (hereinafter sometimes simply abbreviated as "recycling"), which involves collecting and recycling packaging materials consumed in the market, and there is a demand for packaging materials with excellent recyclability. For example, attempts have been made to produce packaging films based solely on polyethylene or polypropylene, which have poor gas barrier properties, and packaging films with excellent recyclability that are mixed with or laminated with a small amount of a gas barrier material that can be mixed with polyethylene or polypropylene.

[0004] Patent Document 1 describes that by providing an EVOH layer of a specific thickness on the outermost layer of a laminate, the heat sealing speed can be increased when the laminate is used as a packaging film without impairing recyclability, and that by uniaxially stretching the laminate, a multilayer film with excellent transparency and gas barrier properties can be obtained.

[0005] Patent Document 2 describes that in a multilayer film having an EVOH layer as the outermost layer, by using a mixture of at least two types of EVOH having different ethylene unit contents as the EVOH, it is possible to obtain a multilayer film in which blocking between the EVOH layers is suppressed even during stretching after inflation molding.

[0006] International Publication No. 2019 / 243456 International Publication No. 2021 / 210606

[0007] However, in the multilayer films described in Patent Documents 1 and 2, which have an EVOH layer as the outermost layer and are stretched at least uniaxially, the film has a tendency to curl strongly, which can cause process defects such as wrinkles, folds, and peeling of the adhesive during converting processes such as printing and lamination. Although such process defects can be reduced to some extent if a symmetrical layer structure is used, having polyolefin layers as both outermost layers and an EVOH layer as an intermediate layer, in this case, the adhesive strength with the adhesive or printing ink decreases, and the barrier property decreases when the film is made into a vapor-deposited multilayer film having an inorganic vapor-deposited layer on the polyolefin layer, so a layer structure having an EVOH layer as at least one outermost layer is essential.

[0008] The present disclosure has been made to solve the above-mentioned problems, and its object is to provide a multilayer film that has an EVOH layer as one outermost layer, is stretched at least uniaxially, and exhibits both gas barrier properties and low curl. It also provides a vapor-deposited multilayer film using the multilayer film, a multilayer structure using the multilayer film or the vapor-deposited multilayer film, and a packaging material including the multilayer structure. In this specification, a reduced degree of curl in a film may be referred to as "low curl," and the property of being able to suppress process defects such as wrinkling, bending, and adhesive peeling during converting, such as printing or lamination, may be referred to as "convertibility."

[0009] According to the present disclosure, the above object is achieved by providing: [1] a multilayer film having a configuration in which a skin layer (A), a core layer (C), an adhesive layer (D), and a barrier layer (E) are laminated at least in this order, wherein the skin layer (A) is located as one outermost layer of the multilayer film, and the barrier layer (E) is located as the other outermost layer of the multilayer film, the core layer (C) is the thickest layer in the multilayer film, the skin layer (A) contains a polyethylene-based resin (a) as a main component, the core layer (C) contains a polyethylene-based resin (c) as a main component, the density (dA) of the skin layer (A) is greater than the density (dC) of the core layer (C), the adhesive layer (D) contains an adhesive resin (d) having a melting point of less than 150°C as a main component, and the barrier layer (E) contains an ethylene-vinyl alcohol copolymer (e) as a main component having an ethylene unit content of 20 mol% or more and 30 mol% or less and a saponification degree of 90 mol% or more, [2] A multilayer film that does not have a layer containing, as a main component, a resin having a melting point of 220°C or higher, and is stretched at least uniaxially by 3 times or more; [2] A multilayer film of [1], which further has a subskin layer (B) containing, as a main component, a polyethylene-based resin (b) between the skin layer (A) and the core layer (C), and the density (dB) of the subskin layer (B) is smaller than the density (dA) of the skin layer (A) and larger than the density (dC) of the core layer (C); [3] A multilayer film of [1] or [2], in which the density (dD) of the adhesive layer (D) is smaller than the density (dC) of the core layer (C); [4] A multilayer film of [1] or [2], in which the density (dA) of the skin layer (A) is 0.940 g / cm ３ [5] The multilayer film of any one of [1] to [3], wherein the density (dC) of the core layer (C) is 0.910 g / cm or more; ３ Above, 0.940g / cm ３[6] Any of the multilayer films of [1] to [5], in which the ratio of the thickness of the core layer (C) to the total thickness of the multilayer film is 0.3 to 0.8; [7] Any of the multilayer films of [1] to [6], in which the ratio of the thickness of the skin layer (A) to the total thickness of the multilayer film is 0.05 to 0.2; [8] Any of the multilayer films of [1] to [7], in which the ratio of the thickness of the barrier layer (E) to the total thickness of the multilayer film is 0.05 to 0.2; [9] Any of the multilayer films of [1] to [8], in which the adhesive resin (d) is an acid-modified polyethylene resin;

[10] Any of the multilayer films of [1] to [9], in which the barrier layer (E) contains 10 to 300 ppm of at least one polyvalent metal ion (f) selected from the group consisting of magnesium ions, calcium ions, and zinc ions;

[11] The multilayer film of any one of [1] to

[10] , wherein the barrier layer (E) contains 100 to 4000 ppm of a higher aliphatic carboxylic acid (g) having 8 to 30 carbon atoms;

[12] The multilayer film of any one of [1] to

[11] , wherein the multilayer film is stretched three times or more in the longitudinal direction and is not substantially stretched in the transverse direction;

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

[12] , wherein the multilayer film is an inflation-molded product;

[14] The multilayer film of any one of [1] to

[13] , wherein the multilayer film has an inorganic vapor-deposited layer (I) on the exposed surface side of the barrier layer (E);

[15] The vapor-deposited multilayer film of

[14] , wherein the inorganic vapor-deposited layer (I) 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;

[16] a multilayer structure comprising the multilayer film of any one of [1] to

[13] or the vapor-deposited multilayer film of

[14] or

[15] , further comprising a resin layer (R) containing a thermoplastic resin (r) as a main component;

[17] the multilayer structure of

[16] , in which the thermoplastic resin (r) contains a polyethylene resin as a main component;

[18] a packaging material having the multilayer structure of

[16] or

[17] .

[0010] According to the present disclosure, it is possible to provide a multilayer film that has an EVOH layer as one outermost layer, is stretched at least uniaxially, and has both gas barrier properties and low curling properties. It is also possible to provide a vapor-deposited multilayer film using the multilayer film, a multilayer structure using the multilayer film or the vapor-deposited multilayer film, and a packaging material including the multilayer structure.

[0011] The multilayer film of the present disclosure has a configuration in which a skin layer (A), a core layer (C), an adhesive layer (D), and a barrier layer (E) are laminated at least in this order, the skin layer (A) is located as one outermost layer of the multilayer film, and the barrier layer (E) is located as the other outermost layer of the multilayer film, the skin layer (A) and the core layer (C) both contain a polyethylene-based resin as a main component, the density (dA) of the skin layer (A) is greater than the density (dC) of the core layer (C), the adhesive layer (D) contains as a main component an adhesive resin (d) having a melting point of less than 150°C, the barrier layer (E) contains as a main component an ethylene-vinyl alcohol copolymer (e) having an ethylene unit content of 20 mol% or more and 30 mol% or less and a degree of saponification of 90 mol% or more, the multilayer film does not have a layer containing as a main component a resin having a melting point of 220°C or more, and is stretched at least uniaxially by 3 times or more.

[0012] The phrase "skin layer (A), core layer (C), adhesive layer (D), and barrier layer (E) are laminated in this order" is not particularly limited as long as the layer structure has a skin layer (A), core layer (C), adhesive layer (D), and barrier layer (E) laminated in this order. For example, it does not preclude the inclusion of other layers between the layers. The "outermost layer" or "outermost surface" of a multilayer film or multilayer structure does not refer to the front or back, but rather to the exposed surface. In other words, each multilayer film or multilayer structure has two outermost layers or surfaces. "Major component" refers to a component contained in an amount exceeding 50% by mass. "ppm" refers to the mass-based content (ppm by mass). "Polyethylene-based resin" refers to an ethylene homopolymer or a copolymer of 80 mol% or more ethylene and less than 20 mol% of a non-ethylene monomer. Typical non-ethylene monomers include, but are not limited to, α-olefins such as propylene, n-butene, isobutylene, 1-hexene, and 1-octene. Numerical ranges described using "to" include the numerical values ​​before and after "to" as the lower and upper limits. In other words, "α to β" means "α or more and β or less." The upper and lower limits of numerical ranges (content, physical properties, etc.) can be combined as appropriate.

[0013] <Skin layer (A)> The multilayer film of the present disclosure has a skin layer (A) containing a polyethylene-based resin (a) as a main component on one outermost surface. Polyethylene-based resins are widely used in packaging materials, regardless of whether they have gas barrier properties or not, and therefore recycling infrastructure for them has been widely established in various countries. Therefore, by having a skin layer (A) containing a polyethylene-based resin (a) as a main component, the recyclability of the multilayer film of the present disclosure can be improved.

[0014] Examples of the polyethylene resin (a) include ethylene homopolymers and copolymers of 80 mol% or more ethylene and less than 20 mol% non-ethylene monomers, and specific examples include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer (EVA), ethylene-acrylic acid copolymer (EAA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-butyl acrylate copolymer (EBA), ethylene-methacrylic acid copolymer (EMAA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl methacrylate copolymer (EEMA), and ethylene-butyl methacrylate copolymer (EBMA). The polyethylene resin (a) is preferably at least one selected from high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene, or a mixture thereof, and more preferably is substantially high-density polyethylene or a mixture of high-density polyethylene and at least one selected from low-density polyethylene and linear low-density polyethylene. The polyethylene-based resin (a) preferably contains 60% by mass or more of high-density polyethylene, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more of high-density polyethylene, and may consist essentially of high-density polyethylene. In this way, when the polyethylene-based resin (a) has a relatively high content of high-density polyethylene, the low curl property, heat resistance, moisture resistance, and mechanical properties of the multilayer film of the present disclosure can be further improved.

[0015] The polyethylene resin (a) can be appropriately selected from those having a unimodal or multimodal molecular weight distribution, and the use of a multimodal one may sometimes enable a high level of balance between melt moldability and mechanical properties. When the polyethylene resin (a) contains an ethylene-α-olefin copolymer such as linear low-density polyethylene, the α-olefin copolymerized with ethylene is preferably an α-olefin having 4 or more carbon atoms, more preferably an α-olefin having 6 or more carbon atoms, and may also be 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 pin puncture strength and tensile strength and elongation may be particularly improved. There is no particular upper limit on the number of carbon atoms in the α-olefin, but it is generally 12 or less carbon atoms.

[0016] A metallocene catalyst may also be used as the polymerization catalyst for the polyethylene resin (a). The polyethylene resin (a) polymerized using a metallocene catalyst has excellent melt moldability, and the resulting multilayer film has an excellent balance between flexibility and mechanical strength.

[0017] The density (dA) of the skin layer (A) may be larger than the density (dC) of the core layer, for example, 0.920 g / cm ３ Above, 0.930g / cm ３ or more than 0.935 g / cm ３ or more, but from the viewpoint of making the effects of the present disclosure more pronounced, 0.940 g / cm ３ More preferably, 0.945 g / cm ３ More preferably, 0.950 g / cm or more ３ More preferably, 0.955 g / cm ３ More than 0.960 g / cm ３ More preferably, 0.965 g / cm ３ The density (dA) of the skin layer (A) may be in the above range, thereby improving the low-curl property. In particular, even when the barrier layer (E) located on one outermost layer of the multilayer film is made of a material that tends to curl, the skin layer (A) located on the other outermost layer of the multilayer film can provide the low-curl property.

[0018] The melting point of the polyethylene resin (a) is preferably 120° C. or higher, more preferably 123° C. or higher, even more preferably 125° C. or higher, particularly preferably 130° C. or higher, and in some cases preferably 133° C. or higher or 135° C. or higher. From the viewpoint of improving the melt moldability and the mechanical properties of the multilayer film, the melt flow rate (hereinafter sometimes referred to as MFR) of the polyethylene resin (a) (190° C., under a load of 2160 g) measured in accordance with the method described in JIS K 7210 (2014) is preferably 0.1 to 10 g / 10 min, more preferably 0.3 to 5.0 g / 10 min, and even more preferably 0.5 to 2.0 g / 10 min.

[0019] The skin layer (A) may contain other components besides the polyethylene resin (a) as long as the effects of the present disclosure are not impaired. Examples of other components include alkali metal ions, polyvalent metal ions, carboxylic acids, phosphate compounds, boron compounds, prooxidants, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, UV absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, bulking agents, pigments, dyes, processing aids, flame retardants, and antifogging agents. The content of other components in the skin layer (A) is usually 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less. The skin layer (A) may further contain a resin other than the polyethylene resin (a). Examples of resins other than the polyethylene-based resin (a) include thermoplastic resins other than the polyethylene-based resin (a), such as polyolefin, polyamide, polyester, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate, and polyvinyl alcohol resin. The content of the resin other than the polyethylene-based resin (a) in the skin layer (A) is less than 50% by mass, preferably less than 30% by mass, more preferably less than 20% by mass, and even more preferably less than 10% by mass, and may be 5% by mass or less, 3% by mass or less, 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less.

[0020] The proportion of the polyethylene resin (a) in the resin constituting the skin layer (A) is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, or the resin constituting the skin layer (A) may consist solely of the polyethylene resin (a). The content of the polyethylene resin (a) in the skin layer (A) is more than 50% by mass, preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, or the skin layer (A) may be substantially composed of the polyethylene resin (a) alone.

[0021] The method for producing the resin composition constituting the skin layer (A) is not particularly limited, but it can be produced by melt-kneading the polyethylene resin (a) and, if necessary, other additives. For melt-kneading, a known mixing or kneading device such as a kneader-ruder, extruder, mixing roll, or Banbury mixer can be used. The temperature range during melt-kneading can be appropriately adjusted depending on the melting point of the polyethylene resin (a) used, and is usually 150 to 300°C.

[0022] In another embodiment, a masterbatch containing other additives at a high concentration as needed for the polyethylene resin (a) is produced by melt kneading, and the masterbatch is dry-blended with a polyethylene resin (a) that is substantially free of other additives and used to produce the skin layer (A). In yet another embodiment, the polyethylene resin (a) and other additives can be dry-blended to produce the skin layer (A). Dry blending refers to mechanical mixing in the form of powder or pellets. Mixing may be performed using a mixing device such as a tumbler, ribbon mixer, or Henschel mixer, or by manual stirring, shaking, or the like in a sealed container. The mixing temperature may be from room temperature to below the melting point of the polyethylene resin (a), and mixing can be performed in an air or nitrogen atmosphere.

[0023] <Core Layer (C)> The multilayer film of the present disclosure has a core layer (C) containing a polyethylene-based resin (c) as a main component, and the core layer (C) is the thickest layer in the multilayer film. Polyethylene-based resins are widely used in packaging materials, regardless of whether they have gas barrier properties or not, and therefore recycling infrastructures for them have been widely established in various countries. Therefore, by having a core layer (C) containing a polyethylene-based resin (c) as a main component, the recyclability of the multilayer film of the present disclosure can be improved. Examples of the polyethylene resin (c) include ethylene homopolymers and copolymers of 80 mol% or more ethylene and less than 20 mol% non-ethylene monomers, and specific examples include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer (EVA), ethylene-acrylic acid copolymer (EAA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-butyl acrylate copolymer (EBA), ethylene-methacrylic acid copolymer (EMAA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl methacrylate copolymer (EEMA), and ethylene-butyl methacrylate copolymer (EBMA). The polyethylene resin (c) is preferably at least one selected from high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene, or a mixture thereof, more preferably at least one selected from low-density polyethylene and linear low-density polyethylene, or a mixture thereof, and even more preferably substantially linear low-density polyethylene. The polyethylene resin (c) preferably contains 60% by mass or more of linear low-density polyethylene, more preferably 70% by mass or more of linear low-density polyethylene, even more preferably 80% by mass or more of linear low-density polyethylene, and particularly preferably 90% by mass or more of linear low-density polyethylene, and may consist essentially of linear low-density polyethylene. In this way, when the polyethylene resin (c) has a relatively high content of linear low-density polyethylene, the curl resistance and mechanical strength of the multilayer film of the present disclosure can be further improved.

[0024] The polyethylene resin (c) can be appropriately selected from those having a unimodal or multimodal molecular weight distribution, and the use of a multimodal one may sometimes enable a high level of balance between melt moldability and mechanical properties. When the polyethylene resin (c) contains an ethylene-α-olefin copolymer such as linear low-density polyethylene, the α-olefin copolymerized with ethylene is preferably an α-olefin having 4 or more carbon atoms, more preferably an α-olefin having 6 or more carbon atoms, and may also be 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 pin puncture strength and tensile strength and elongation may be particularly improved. There is no particular upper limit on the number of carbon atoms in the α-olefin, but it is generally 12 or less carbon atoms.

[0025] A metallocene catalyst can also be used as the polymerization catalyst for the polyethylene resin (c). The polyethylene resin (c) polymerized using a metallocene catalyst has excellent melt moldability, and the resulting multilayer film has an excellent balance between flexibility and mechanical strength.

[0026] The density (dC) of the core layer (C) is, for example, 0.90 g / cm ３ 0.94g / cm or more ３ Less than or 0.905 g / cm ３ 0.940g / cm or more ３ However, from the viewpoint of making the effects of the present disclosure more pronounced, ３ 0.940g / cm or more ３ Preferably less than 0.915 g / cm ３ 0.935g / cm or more ３ More preferably, less than 0.916 g / cm ３ 0.930g / cm or more ３ On the other hand, in order to improve the anti-curl property, the density (dA) of the skin layer (A) needs to be larger than the density (dC) of the core layer (C). The difference between the density (dA) of the skin layer (A) and the density (dC) of the core layer (C) should be 0.005 g / cm or less. ３ More than 0.01 g / cm ３More preferably, 0.02 g / cm ３ More preferably, 0.03 g / cm ３ More preferably, 0.04 g / cm ３ More than 0.045 g / cm is particularly preferred. ３ or more or 0.05 g / cm ３ There is no particular upper limit to the difference between the density (dA) of the skin layer (A) and the density (dC) of the core layer (C), but it may be, for example, 0.5 g / cm ３ Below, 0.3g / cm ３ or less than 0.1 g / cm ３ It may be the following:

[0027] The melting point of the polyethylene resin (c) is preferably 100 to 130° C., more preferably 110 to 127° C., and in some cases, preferably 115 to 125° C. From the viewpoint of improving the melt moldability and the mechanical properties of the multilayer film, the polyethylene resin (c) has an MFR (190° C., under a load of 2160 g) measured in accordance with the method described in JIS K 7210 (2014) of preferably 0.1 to 10 g / 10 min, more preferably 0.3 to 5.0 g / 10 min, and even more preferably 0.5 to 2.0 g / 10 min.

[0028] The core layer (C) may contain other components besides the polyethylene-based resin (c) as long as the effects of the present disclosure are not impaired. Examples of other components include alkali metal ions, polyvalent metal ions, carboxylic acids, phosphate compounds, boron compounds, prooxidants, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, UV absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, bulking agents, pigments, dyes, processing aids, flame retardants, and antifogging agents. The content of other components in the core layer (C) is usually 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less. The core layer (C) may further contain a resin other than the polyethylene-based resin (c). Examples of resins other than the polyethylene-based resin (c) include thermoplastic resins other than the polyethylene-based resin (c), such as polyolefin, polyamide, polyester, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate, and polyvinyl alcohol resin. The content of the resin other than the polyethylene-based resin (c) in the core layer (C) is less than 50% by mass, preferably less than 30% by mass, more preferably less than 20% by mass, even more preferably less than 10% by mass, particularly preferably 5% by mass or less, and may be 3% by mass or less, 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less.

[0029] The proportion of the polyethylene resin (c) in the resin constituting the core layer (C) is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, or the resin constituting the core layer (C) may consist solely of the polyethylene resin (c). The content of the polyethylene resin (c) in the core layer (C) is more than 50% by mass, preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, or the core layer (C) may be substantially composed of the polyethylene resin (c) alone.

[0030] The method for producing the resin composition constituting the core layer (C) is not particularly limited, but it can be produced by melt-kneading the polyethylene resin (c) and, if necessary, other additives. For melt-kneading, known mixing or kneading devices such as a kneader-ruder, extruder, mixing roll, or Banbury mixer can be used. The temperature range during melt-kneading can be appropriately adjusted depending on the melting point of the polyethylene resin (c) used, and is usually 150 to 300°C.

[0031] In another embodiment, a masterbatch containing a high concentration of other additives, as needed, for the polyethylene resin (c) is produced by melt kneading, and the masterbatch is dry-blended with a polyethylene resin (c) that is substantially free of other additives and used to produce the core layer (C). In yet another embodiment, the polyethylene resin (c) and other additives can be dry-blended to produce the core layer (C). Dry blending refers to mechanical mixing in the form of powder or pellets. Mixing may be performed using a mixing device such as a tumbler, ribbon mixer, or Henschel mixer, or by manual stirring, shaking, or the like in a sealed container. The mixing temperature may be from room temperature to below the melting point of the polyethylene resin (c), and mixing may be performed in an air or nitrogen atmosphere.

[0032] <Subskin Layer (B)> The multilayer film of the present disclosure preferably further includes a subskin layer (B) between the skin layer (A) and the core layer (C) that contains a polyethylene-based resin (b) as a primary component. Polyethylene-based resins are widely used in packaging materials, regardless of whether they have gas barrier properties, and recycling infrastructure for them is widely established in various countries. Therefore, by including a subskin layer (B) that contains a polyethylene-based resin (b) as a primary component, the recyclability of the multilayer film of the present disclosure can be improved. Examples of the polyethylene-based resin (b) include ethylene homopolymers and copolymers of 80 mol% or more ethylene and less than 20 mol% non-ethylene monomers, and specific examples include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer (EVA), ethylene-acrylic acid copolymer (EAA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-butyl acrylate copolymer (EBA), ethylene-methacrylic acid copolymer (EMAA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl methacrylate copolymer (EEMA), and ethylene-butyl methacrylate copolymer (EBMA). The polyethylene-based resin (b) is preferably at least one selected from high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene, or a mixture thereof, and more preferably is substantially high-density polyethylene or medium-density polyethylene, or a mixture of at least one selected from low-density polyethylene and linear low-density polyethylene with at least one selected from high-density polyethylene or medium-density polyethylene. The polyethylene resin (b) preferably contains 30% by mass or more of high-density polyethylene or medium-density polyethylene, more preferably 40% by mass or more of high-density polyethylene or medium-density polyethylene, even more preferably 50% by mass or more of high-density polyethylene or medium-density polyethylene, and may contain 60% by mass or more of high-density polyethylene or medium-density polyethylene.In this way, when the polyethylene resin (b) has a relatively high content of high-density polyethylene or medium-density polyethylene, the multilayer film of the present disclosure can have further improved low curl properties, heat resistance, moisture resistance, and mechanical properties.

[0033] The polyethylene resin (b) can be appropriately selected from those having a unimodal or multimodal molecular weight distribution, and the use of a multimodal one may sometimes enable a high level of balance between melt moldability and mechanical properties. When the polyethylene resin (b) contains an ethylene-α-olefin copolymer such as linear low-density polyethylene, the α-olefin copolymerized with ethylene is preferably an α-olefin having 4 or more carbon atoms, more preferably an α-olefin having 6 or more carbon atoms, and may also be 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 pin puncture strength and tensile strength and elongation may be particularly improved. There is no particular upper limit on the number of carbon atoms in the α-olefin, but it is generally 12 or less carbon atoms.

[0034] A metallocene catalyst can also be used as the polymerization catalyst for the polyethylene resin (b). The polyethylene resin (b) polymerized using a metallocene catalyst has excellent melt moldability, and the resulting multilayer film has an excellent balance between flexibility and mechanical strength.

[0035] From the viewpoint of making the effects of the present disclosure more pronounced, it is preferable that the density (dB) of the subskin layer (B) is smaller than the density (dA) of the skin layer (A) and larger than the density (dC) of the core layer (C), and is, for example, 0.91 to 0.96 g / cm ３ and 0.915 to 0.955 g / cm ３ is preferably 0.920 to 0.950 g / cm ３ More preferably, 0.925 to 0.945 g / cm ３ may be.

[0036] The melting point of the polyethylene resin (b) may be, for example, 115 to 135° C. or 118 to 130° C. From the viewpoint of improving the melt moldability and the mechanical properties of the multilayer film, the polyethylene resin (b) preferably has an MFR (190° C., under a load of 2160 g) measured in accordance with the method described in JIS K 7210 (2014) of 0.1 to 10 g / 10 min, more preferably 0.3 to 5.0 g / 10 min, and even more preferably 0.5 to 2.0 g / 10 min.

[0037] The subskin layer (B) may contain components other than the polyethylene-based resin (b), as long as the effects of the present disclosure are not impaired. Examples of other components include alkali metal ions, polyvalent metal ions, carboxylic acids, phosphate compounds, boron compounds, prooxidants, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, UV absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, bulking agents, pigments, dyes, processing aids, flame retardants, and antifogging agents. The content of other components in the subskin layer (B) is typically 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less. The subskin layer (B) may further contain a resin other than the polyethylene-based resin (b). Examples of resins other than the polyethylene-based resin (b) include thermoplastic resins other than the polyethylene-based resin (b), such as polyolefin, polyamide, polyester, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate, and polyvinyl alcohol resin. The content of the resin other than the polyethylene-based resin (b) in the subskin layer (B) is less than 50% by mass, preferably less than 30% by mass, more preferably less than 20% by mass, even more preferably less than 10% by mass, particularly preferably 5% by mass or less, and may be 3% by mass or less, 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less.

[0038] The proportion of the polyethylene resin (b) in the resin constituting the subskin layer (B) is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more. The resin constituting the subskin layer (B) may consist solely of the polyethylene resin (b). The content of the polyethylene resin (b) in the subskin layer (B) is more than 50% by mass, preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more. The subskin layer (B) may be composed essentially of the polyethylene resin (b) alone.

[0039] The method for producing the resin composition constituting the subskin layer (B) is not particularly limited, and it can be produced by melt-kneading the polyethylene resin (b) and, if necessary, other additives. For melt-kneading, a known mixing or kneading device such as a kneader-ruder, extruder, mixing roll, or Banbury mixer can be used. The temperature range during melt-kneading can be appropriately adjusted depending on the melting point of the polyethylene resin (b) used, and is usually 150 to 300°C.

[0040] In another embodiment, a masterbatch containing a high concentration of other additives, as needed, for the polyethylene resin (b) can be produced by melt-kneading, and the masterbatch can be dry-blended with a polyethylene resin (b) that is substantially free of other additives and used to produce the subskin layer (B). In yet another embodiment, the polyethylene resin (b) and other additives can be dry-blended to produce the subskin layer (B). Dry blending refers to mechanical mixing in the form of powder or pellets. Mixing can be performed using a mixing device such as a tumbler, ribbon mixer, or Henschel mixer, or by manual stirring, shaking, or the like in a sealed container. The mixing temperature may be from room temperature to below the melting point of the polyethylene resin (b), and mixing can be performed in an air or nitrogen atmosphere.

[0041] <Adhesive Layer (D)> The multilayer film of the present disclosure has an adhesive layer (D) containing, as a main component, an adhesive resin (d) having a melting point of less than 150°C. By including the adhesive layer (D), the multilayer film of the present disclosure tends to have excellent appearance and interlayer adhesion. Examples of the adhesive resin (d) include acid-modified polyolefin resins, and acid-modified polyethylene resins are preferred. As the acid-modified polyolefin resin, carboxylic acid-modified polyolefin resins are preferred, polyolefin resins modified with unsaturated carboxylic acids or derivatives thereof are more preferred, carboxylic acid-modified polyolefin resins obtained by graft polymerizing unsaturated carboxylic acids such as maleic anhydride or derivatives thereof onto polyolefin resins are even more preferred, and carboxylic acid-modified polyethylene resins obtained by graft polymerizing unsaturated carboxylic acids such as maleic anhydride or derivatives thereof onto polyethylene resins are preferred. In this case, the polyethylene resins exemplified as polyethylene resins (a), polyethylene resins (b), and polyethylene resins (c) can be preferably used.

[0042] The content of the acid-modified polyolefin resin in the adhesive resin (d) is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 95% by mass or more, and the adhesive resin (d) may be substantially composed of the modified polyolefin resin alone. The proportion of the adhesive resin (d) in the adhesive layer (D) is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 95% by mass or more, and may be 97% by mass or more, 98% by mass or more, or 99% by mass or more, and may be substantially composed of the adhesive resin (d) alone.

[0043] From the viewpoint of making the effects of the present disclosure more pronounced, the density (dD) of the adhesive layer (D) is preferably smaller than the density (dC) of the core layer (C), and is, for example, 0.945 g / cm ３ less than 0.850 g / cm ３ 0.935g / cm or more ３ Preferably less than 0.880 g / cm ３ 0.925g / cm or more ３The melting point of the adhesive resin (d) is preferably less than 150°C, and more preferably 100 to 130°C. From the viewpoint of improving the melt moldability and the mechanical properties of the multilayer film, the MFR (190°C, under a load of 2160 g) of the adhesive resin (d) measured in accordance with the method described in JIS K 7210 (2014) is preferably 0.1 to 10 g / 10 min, more preferably 0.3 to 5.0 g / 10 min, and even more preferably 0.5 to 3.0 g / 10 min. The density, melting point, and MFR of the adhesive resin (d) depend mainly on the density, melting point, and MFR of the polyolefin resin before carboxylic acid modification.

[0044] <Barrier Layer (E)> The multilayer film of the present disclosure has a barrier layer (E) containing EVOH (e) as a main component in one of its outermost layers. This configuration provides the multilayer film of the present disclosure with good gas barrier properties. Because the barrier layer (E) has good affinity with the inorganic vapor-deposited layer (I) described below, a vapor-deposited multilayer film in which the inorganic vapor-deposited layer (I) is adjacent to the exposed surface of the barrier layer (E) exhibits even better barrier properties, and tends to maintain its gas barrier properties even when subjected to physical stress, particularly bending. From the perspective of producing such a vapor-deposited multilayer film, the multilayer film of the present disclosure must have a barrier layer (E) in its outermost layer. Multiple barrier layers (E) may be provided, and in this case, it is sufficient that at least one barrier layer (E) is provided in the outermost layer.

[0045] EVOH (e) is typically obtained by saponifying an ethylene-vinyl ester copolymer obtained by polymerizing ethylene and a vinyl ester. The ethylene unit content of EVOH (e) is 20 mol% or more and 30 mol% or less. An ethylene unit content of 20 mol% or more improves the melt moldability of EVOH (e) and improves the recyclability of the multilayer film of the present disclosure. The ethylene unit content is preferably 21 mol% or more, more preferably 22 mol% or more, and in some cases, 23 mol% or more. On the other hand, an ethylene unit content of 30 mol% or less improves the gas barrier properties and low curl properties of the multilayer film of the present disclosure, even when the barrier layer (E) has a relatively small thickness, and therefore tends to improve converting properties. The ethylene unit content is preferably 28 mol% or less, more preferably 27 mol% or less, and may be 26 mol% or less.

[0046] The saponification degree of EVOH (e) is 90 mol% or more. The saponification degree means the ratio of the number of vinyl alcohol units to the total number of vinyl alcohol units and vinyl ester units in EVOH (e). When the saponification degree is 90 mol% or more, the gas barrier property of the multilayer film of the present disclosure is improved. The saponification degree is preferably 95 mol% or more, more preferably 99 mol% or more, and even more preferably 99.9 mol% or more. The saponification degree of EVOH (e) is usually 100 mol% or less. The ethylene unit content and saponification degree of EVOH (e) are １ It is determined by H-NMR measurement.

[0047] The EVOH (e) may be a mixture of two or more types of EVOH having different ethylene unit contents, or may be a mixture of two or more types of EVOH having different degrees of saponification.

[0048] EVOH (e) may contain other monomer units other than ethylene, vinyl ester, and vinyl alcohol, as long as the effects of the present disclosure are not impaired. In particular, by introducing a modifying group containing a primary hydroxyl group having a specific structure, EVOH (e) may be able to achieve high levels of both gas barrier properties and moldability. The content of other monomer units is preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, even more preferably 0.1% by mass or less, and particularly preferably substantially none. Examples of such 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); methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether 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, 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane and 1,3-dibutyronyloxy-2-methylenepropane.

[0049] The melt flow rate (MFR) of EVOH(e) measured in accordance with JIS K 7210 (2014) (210°C, under a load of 2.16 kg) is preferably 0.2 to 10 g / 10 min. The MFR of EVOH(e) is more preferably 0.4 g / 10 min or more, and even more preferably 0.6 g / 10 min or more. On the other hand, the MFR of EVOH(e) is more preferably 8 g / 10 min or less, even more preferably 6 g / 10 min or less, even more preferably 5 g / 10 min or less, and in some cases, 4 g / 10 min or less, 3 g / 10 min or less, or 2.5 g / 10 min or less is preferred. When the MFR of EVOH(e) is within the above range, the melt moldability of EVOH(e) and pulverized products of multilayer films containing EVOH(e) is improved.

[0050] <Polyvalent Metal Ion (f)> The barrier layer (E) preferably contains at least one polyvalent metal ion (f) selected from the group consisting of magnesium ions, calcium ions, and zinc ions, and the content thereof is preferably 10 to 300 ppm. A content of polyvalent metal ions (f) of 10 ppm or more tends to suppress appearance defects such as thickening and the generation of gels or lumps during melt molding. On the other hand, a content of polyvalent metal ions (f) of 300 ppm or less tends to suppress excessive decomposition and coloration during melt molding. When recycling the multilayer film of the present disclosure, a crosslinking reaction of the resin may progress during melt molding of pulverized material of the multilayer film, causing thickening and gelation. However, by containing a certain amount of polyvalent metal ions (f), thickening, gelation, and adhesion of the resin to the screw are suppressed. From this viewpoint, the content of the polyvalent metal ion (f) is preferably 15 to 240 ppm, more preferably 20 to 200 ppm, more preferably 30 to 150 ppm, and in some cases, preferably 30 to 100 ppm. Among these, the barrier layer (E) preferably contains magnesium ions or calcium ions as the polyvalent metal ions (f), more preferably magnesium ions. By controlling the content ratio of the polyvalent metal ions (f) to the carboxylic acid described below, the melt-formability and coloration resistance can be further improved.

[0051] Examples of polyvalent metal compounds that provide the polyvalent metal ions (f) include aliphatic carboxylates, aromatic carboxylates, carbonates, hydrochlorides, nitrates, sulfates, phosphates, hydroxides, and metal complexes of magnesium, calcium, and zinc. Among these, aliphatic carboxylates and hydroxides are more preferred because of their ease of availability and handling. Preferred aliphatic carboxylates are acetates, caprylates, and stearates.

[0052] <Higher Aliphatic Carboxylic Acid (g)> The barrier layer (E) preferably contains a higher aliphatic carboxylic acid (g) having 8 to 30 carbon atoms, preferably in a content of 100 to 6,000 ppm. The higher aliphatic carboxylic acid (g) may be contained in part or in whole in the form of a salt, or as a salt of a polyvalent metal ion (f) or an alkali metal ion, as described below. The higher aliphatic carboxylic acid (g) is preferably a higher aliphatic carboxylic acid having 8 to 20 carbon atoms, more preferably caprylic acid or stearic acid. The multilayer film of the present disclosure has a barrier layer (E) as one of the outermost layers. It is believed that the higher aliphatic carboxylic acid (g) acts as a lubricant for the die metal surface in the die, thereby suppressing poor appearance due to thickness unevenness of the multilayer film and the occurrence of gels and bumps due to retained resin. For this reason, the barrier layer (E) preferably contains 100 ppm or more of the higher aliphatic carboxylic acid (g). On the other hand, if the content of the higher aliphatic carboxylic acid (g) is 6000 ppm or less, thickening of the barrier layer (E) during melt molding tends to be suppressed and interlayer adhesion with the adhesive layer (D) tends to be maintained. From these viewpoints, the content of the higher aliphatic carboxylic acid (g) is more preferably 200 to 4000 ppm, even more preferably 300 to 3000 ppm, and in some cases is preferably 400 to 2500 ppm, 500 to 2200 ppm, 600 to 2000 ppm, or 700 to 1500 ppm.

[0053] The barrier layer (E) may contain other components in addition to the EVOH (e), polyvalent metal ions (f), and higher aliphatic carboxylic acids (g), as long as the effects of the present disclosure are not impaired. Examples of other components include alkali metal ions, alkaline earth metal ions and transition metal ions other than the polyvalent metal ions (f), carboxylic acids (monocarboxylic acids and polycarboxylic acids) other than the higher aliphatic carboxylic acids (g), thermoplastic resins other than the EVOH (e), phosphate compounds, boron compounds, antioxidants (hindered phenol compounds, etc.), plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, UV absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, bulking agents, pigments, dyes, processing aids, flame retardants, and antifogging agents. From the viewpoint of suppressing the formation of particles and coloration during melt molding of the pulverized multilayer film containing the barrier layer (E), it is preferable for the barrier layer (E) to contain alkali metal ions, carboxylic acids, and / or phosphate compounds. By including a boron compound, the melt viscosity of the barrier layer (E) and the pulverized product of the multilayer film including the barrier layer (E) can be controlled.

[0054] <Alkali Metal Ions> The barrier layer (E) may contain 40 to 500 ppm of alkali metal ions. When the barrier layer (E) contains alkali metal ions in the above range, the interlayer adhesion with the adhesive layer (D) tends to be significantly improved. From this viewpoint, the lower limit of the alkali metal ion content is preferably 80 ppm, more preferably 120 ppm. The upper limit of the alkali metal ion content is preferably 450 ppm, more preferably 400 ppm. When the alkali metal ion content is equal to or greater than the above lower limit, the layer is less likely to thicken during melt molding, and appearance defects such as gels and lumps are less likely to occur, and the interlayer adhesion with the adhesive layer (D) is further improved. On the other hand, when the alkali metal ion content is equal to or less than the above upper limit, excessive decomposition during melt molding is more likely to be suppressed, and discoloration is less likely to become a problem. By controlling the content ratio of the alkali metal ions to the carboxylic acid described below, the melt moldability and discoloration resistance can be further improved.

[0055] Examples of alkali metal ions include lithium, sodium, potassium, rubidium, and cesium ions. From the viewpoint of industrial availability, sodium or potassium ions are preferred, and sodium ions are more preferred. By using potassium ions, it may be possible to achieve high levels of both the hue of the barrier layer (E) and interlayer adhesion with the adhesive layer (D). These ions may be used alone or in combination of two or more.

[0056] Examples of alkali metal compounds that provide alkali metal ions include aliphatic carboxylates, aromatic carboxylates, carbonates, hydrochlorides, nitrates, sulfates, phosphates, hydroxides, and metal complexes of alkali metals such as lithium, sodium, and potassium. Among these, aliphatic carboxylates and phosphates are more preferred because of their ease of availability and handling. Preferred aliphatic carboxylates are acetates, caprylates, and stearates.

[0057] <Carboxylic Acid> The barrier layer (E) preferably contains a carboxylic acid other than the higher aliphatic carboxylic acid (g). The lower limit of the carboxylic acid content is preferably 50 ppm, more preferably 100 ppm. On the other hand, the upper limit of the carboxylic acid content is preferably 400 ppm, more preferably 350 ppm. When the carboxylic acid content is 50 ppm or more, the coloring resistance tends to be improved. On the other hand, when the carboxylic acid content is 400 ppm or less, the interlayer adhesion tends to be maintained and the generation of odor tends to be suppressed.

[0058] The pKa of the carboxylic acid is preferably 3.5 to 5.5. When the pKa of the carboxylic acid is within the above range, the pH buffering ability of the resulting barrier layer (E) is enhanced, further improving the melt moldability and further improving the coloration caused by acidic or basic substances.

[0059] The carboxylic acid may be a monocarboxylic acid. These may be used alone or in combination of two or more. A monocarboxylic acid is a compound having one carboxyl group in the molecule. Monocarboxylic acids having a pKa in the range of 3.5 to 5.5 are not particularly limited, and examples thereof include formic acid (pKa = 3.77), acetic acid (pKa = 4.76), propionic acid (pKa = 4.85), and acrylic acid (pKa = 4.25). These carboxylic acids may further have a substituent such as a hydroxyl group, an amino group, or a halogen atom. Among these, acetic acid is preferred because of its high safety and ease of availability and handling.

[0060] The carboxylic acid may be a polycarboxylic acid. When the carboxylic acid is a polycarboxylic acid, discoloration resistance at high temperatures and discoloration resistance of the resulting melt-molded product of crushed multilayer film may be further improved. The polycarboxylic acid compound preferably has three or more carboxyl groups. In this case, discoloration resistance may be more effectively improved. The polycarboxylic acid is a compound having two or more carboxyl groups in the molecule. In this case, it is preferable that the pKa of at least one carboxyl group is in the range of 3.5 to 5.5, and examples thereof include oxalic acid (pKa2=4.27), succinic acid (pKa1=4.20), fumaric acid (pKa2=4.44), malic acid (pKa2=5.13), glutaric acid (pKa1=4.30, pKa2=5.40), adipic acid (pKa1=4.43, pKa2=5.50), and the like. 2=5.41), pimelic acid (pKa1=4.71), phthalic acid (pKa2=5.41), isophthalic acid (pKa2=4.46), terephthalic acid (pKa1=3.51, pKa2=4.82), citric acid (pKa2=4.75), tartaric acid (pKa2=4.40), glutamic acid (pKa2=4.07), aspartic acid (pKa=3.90), etc.

[0061] <Phosphate Compound> The barrier layer (E) may further contain a phosphate compound. The lower limit of the content of the phosphate compound is preferably 5 ppm in terms of phosphate radicals. On the other hand, the upper limit of the content of the phosphate compound is preferably 100 ppm in terms of phosphate radicals. By containing the phosphate compound in this range, coloration of the resulting barrier layer (E) and the melt-molded product of the pulverized product of the resulting multilayer film may be suppressed, and thermal stability may be improved. "Phosphate radical equivalent" refers to the content of phosphorus element (P) in terms of phosphate ions (PO ４ ３－ ) is the value converted into the content.

[0062] As the phosphate compound, various acids such as phosphoric acid and phosphorous acid and their salts can be used. The phosphate may be any of primary phosphate, secondary phosphate, and tertiary phosphate. The cation species of the phosphate is not particularly limited, but alkali metals and alkaline earth metals are preferred. Among them, sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate are preferred as the phosphate compound.

[0063] <Boron Compound> The barrier layer (E) may further contain a boron compound. When a boron compound is contained, the lower limit of the content in the barrier layer (E) is preferably 50 ppm, more preferably 100 ppm, in terms of elemental boron. On the other hand, the upper limit of the content of the boron compound in the barrier layer (E) is preferably 400 ppm, more preferably 300 ppm, and even more preferably 200 ppm, in terms of elemental boron. By containing the boron compound within this range, the thermal stability of the barrier layer (E) and the pulverized product of the resulting multilayer film during melt molding may be improved, and the occurrence of gels and lumps may be suppressed. Drawdown resistance and neck-in resistance during film formation may be improved, and the mechanical properties of the resulting molded product may be improved. These effects are presumed to be due to the occurrence of a chelating interaction between the EVOH (e) and the boron compound.

[0064] Examples of boron compounds include boric acid, boric acid esters, borate salts, and boron hydrides. ３ BO ３boric acid such as tetraboric acid, metaboric acid, and the like; boric acid esters such as trimethyl borate and triethyl borate; alkali metal salts or alkaline earth metal salts of the above boric acids; and boric acid salts such as borax. Of these, orthoboric acid is preferred.

[0065] The barrier layer (E) may further contain a thermoplastic resin other than EVOH (e). Examples of thermoplastic resins other than EVOH (e) include various polyolefins (polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymers, copolymers of ethylene and an α-olefin having 4 or more carbon atoms, copolymers of polyolefins and maleic anhydride, ethylene-vinyl ester copolymers, ethylene-acrylic acid ester copolymers, and modified polyolefins obtained by graft-modifying these with unsaturated carboxylic acids or derivatives thereof), various polyamides (nylon 6, nylon 6.6, nylon 6 / 66 copolymer, nylon 11, nylon 12, polymetaxylylene adipamide, etc.), various polyesters (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate, and modified polyvinyl alcohol resins. The content of the thermoplastic resin in the barrier layer (E) is usually less than 40% by mass, preferably less than 30% by mass, more preferably less than 20% by mass, even more preferably less than 10% by mass, and may be less than 5% by mass or less than 1% by mass, and it is particularly preferable that the barrier layer (E) is substantially free of the thermoplastic resin.

[0066] From the viewpoint of more significantly achieving the effects of the present disclosure, the proportion of EVOH (e) in the resin constituting the barrier layer (E) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and may be 98% by mass or more or 99% by mass or more, and the resin constituting the barrier layer (E) may be substantially EVOH (e). From the viewpoint of more significantly achieving the effects of the present disclosure, the proportion of EVOH (e) in the barrier layer (E) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and may be preferably 98% by mass or more or 99% by mass or more, and the barrier layer (E) may consist essentially of EVOH (e).

[0067] The barrier layer (E) can be produced by melt-kneading EVOH (e), and, if necessary, polyvalent metal ions (f), higher aliphatic carboxylic acids (g), and / or other components. Each component may be blended in a solid state, such as a powder, or as a melt. Alternatively, the components may be blended as solutes in a solution or dispersoids in a dispersion. Suitable solutions and dispersions are aqueous solutions and aqueous dispersions, respectively. For melt-kneading, known mixing or kneading devices, such as a kneader-ruder, extruder, mixing roll, or Banbury mixer, can be used. The temperature range during melt-kneading can be adjusted appropriately depending on the EVOH (e) used and the melting points of each component, and is typically 150 to 250°C. The barrier layer (E) may also be produced by pre-adding some components to EVOH (e), and then melt-kneading additional components as described above. One method for pre-adding some components to EVOH (e) is to immerse EVOH (e) in the form of pellets or powder in a solution in which the additional components are dissolved.

[0068] <Multilayer Film> The layer configuration of the multilayer film of the present disclosure has a configuration in which a skin layer (A), a core layer (C), an adhesive layer (D), and a barrier layer (E) are laminated at least in this order, with the skin layer (A) located as the outermost layer on one side of the multilayer film and the barrier layer (E) located as the outermost layer on the other side of the multilayer film. It is also preferable that a subskin layer (B) be further present between the skin layer (A) and the core layer (C). Examples of the configuration of the multilayer film include the following: The skin layer (A) is represented as "layer (A)," the subskin layer (B) as "layer (B)," the core layer (C) as "layer (C)," the adhesive layer (D) as "layer (D)," and the barrier layer (E) as "layer (E)." A " / " sign means that the layers on both sides are directly laminated. Examples of the layer configuration of the multilayer film of the present disclosure include layer (A) / layer (C) / layer (D) / layer (E), layer (A) / layer (B) / layer (C) / layer (D) / layer (E), layer (A) / layer (C) / layer (D) / layer (E) / layer (D) / layer (E), layer (A) / layer (B) / layer (C) / layer (D) / layer (E) / layer (D) / layer (E), and the like. Among these, layer (A) / layer (C) / layer (D) / layer (E) or layer (A) / layer (B) / layer (C) / layer (D) / layer (E) is preferred from the viewpoint of industrial productivity, and layer (A) / layer (B) / layer (C) / layer (D) / layer (E) is more preferred from the viewpoint of industrial productivity and in which the effects of the present disclosure become more pronounced. In the layer structure, it is particularly preferred that at least Layer (C) and Layer (D) are laminated in direct contact with each other, and it is also preferred that at least Layer (D) and Layer (E) are laminated in direct contact with each other, and it is even more preferred that at least Layer (C), Layer (D), and Layer (E) are laminated in direct contact with each other in this order.

[0069] The total thickness of the multilayer film of the present disclosure can be appropriately set depending on the application. The total thickness is preferably 10 μm or more, more preferably 12 μm or more. A total thickness of 10 μm or more tends to improve industrial productivity and mechanical properties. The total thickness is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 30 μm or less, and in some cases 25 μm or less, 20 μm or less, or 15 μm or less is preferred. A total thickness of 100 μm or less tends to improve industrial productivity and economic efficiency. The preferred total thickness of the multilayer film means the thickness after stretching.

[0070] The core layer (C) is the thickest layer in the multilayer film of the present disclosure, and the ratio of the thickness of the core layer (C) to the total thickness of the multilayer film of the present disclosure is preferably 0.3 to 0.8 from the viewpoints of industrial productivity, low curling, and mechanical properties. This ratio is preferably 0.35 to 0.80, more preferably 0.40 to 0.75, and in some cases, 0.45 to 0.73 or 0.50 to 0.70.

[0071] The ratio of the thickness of the skin layer (A) to the total thickness of the multilayer film of the present disclosure is preferably 0.05 to 0.2 from the viewpoints of industrial productivity, heat resistance, moisture resistance, low curling, and mechanical properties, more preferably 0.05 to 0.20, and even more preferably 0.05 to 0.15.

[0072] The ratio of the thickness of the barrier layer (E) to the total thickness of the multilayer film of the present disclosure is preferably 0.05 to 0.2 from the viewpoints of industrial productivity, heat resistance, gas barrier properties, low curling properties, and mechanical properties, more preferably 0.05 to 0.20, even more preferably 0.05 to 0.18, and particularly preferably 0.05 to 0.15.

[0073] The multilayer film of the present disclosure is stretched at least uniaxially by 3 times or more. If the multilayer film of the present disclosure is stretched less than 3 times, thickness unevenness due to stretching tends to occur and gas barrier properties tend to be reduced. On the other hand, the upper limit of the stretching ratio of the multilayer film of the present disclosure is usually 12 times. The multilayer film of the present disclosure is preferably stretched at least uniaxially by 4 times or more, more preferably by 5 times or more. The multilayer film of the present disclosure is preferably stretched at least uniaxially by 10 times or less, more preferably by 8 times or less. The multilayer film of the present disclosure may be stretched uniaxially or biaxially. However, from the viewpoint of economy and ease of tearing the multilayer film (ease of opening packaging materials when used as packaging materials), uniaxial stretching is preferred, and uniaxial stretching in the machine direction (machine direction, MD direction) is more preferred, and stretching of 3 times in the machine direction (preferably 3 times to 12 times, more preferably 4 times to 10 times, and even more preferably 5 times to 8 times) is even more preferred. In this case, it is preferable that the film is not substantially stretched in the width direction (TD direction).

[0074] The multilayer film of the present disclosure is preferably an inflation-molded article. When the multilayer film of the present disclosure is an inflation-molded article, the effects of the present disclosure are more effectively exhibited.

[0075] The method for producing a multilayer film of the present disclosure preferably includes, for example, a step (I) of producing an unstretched multilayer film having at least a skin layer (A), a core layer (C), an adhesive layer (D), and a barrier layer (E) laminated in this order, and a step (II) of stretching the obtained unstretched multilayer film at least uniaxially to produce the multilayer film of the present disclosure. A preferred production method of the present disclosure will be described in detail below, but aspects of the present disclosure are not limited thereto.

[0076] In step (I), an unstretched multilayer film is formed in which a skin layer (A), a core layer (C), an adhesive layer (D), and a barrier layer (E) are laminated at least in this order. The method for producing the unstretched multilayer film is not particularly limited, and generally, a conventional coextrusion method in which each resin is extruded from a separate die or a common die and laminated can be used. As the die, either a circular die or a T-die can be used. Examples of the method include inflation molding and cast molding, but inflation molding is preferred in terms of productivity.

[0077] In step (II), the unstretched multilayer film obtained in step (I) is stretched at least uniaxially. The stretching method is not particularly limited, and examples thereof include tenter stretching, tubular stretching, and roll stretching. In terms of productivity, uniaxial stretching by roll stretching is preferred. When the unstretched multilayer film of the present disclosure is an inflation-molded product, roll stretching is preferred from the viewpoint of easily uniaxially stretching the folded cylindrical unstretched multilayer film after inflation molding. The temperature used for stretching is generally in the range of 50°C to 140°C, with 100°C to 130°C being more preferred.

[0078] The multilayer film of the present disclosure does not have a layer containing, as a main component, a resin having a melting point of 220°C or higher. The absence of a layer containing, as a main component, a resin having a melting point of 220°C or higher makes it easier to prevent uneven mixing with other components when melt-molding a recycled multilayer film, vapor-deposited multilayer film, or multilayer structure of the present disclosure, as described below. The multilayer film of the present disclosure preferably does not have a layer containing, as a main component, a resin having a melting point of 210°C or higher, and preferably does not have a layer containing, as a main component, a resin having a melting point of 200°C or higher. For the same reason, it is also preferable not to have a metal layer having a thickness of 1 μm or higher.

[0079] <Inorganic Vapor Deposition Layer (I)> The present disclosure also includes a vapor-deposited multilayer film having an inorganic vapor deposition layer (I) on the exposed surface side of the barrier layer (E) of the multilayer film of the present disclosure. The inorganic vapor deposition layer (I) is preferably laminated on the exposed surface side of the barrier layer (E) of the multilayer film directly or via another layer such as an anchor coat layer, and more preferably laminated directly on the exposed surface side of the barrier layer (E). The inorganic vapor deposition layer (I) can be formed by vapor-depositing an inorganic substance such as a metal or an inorganic oxide, and is usually a layer that has barrier properties against oxygen and water vapor. Because the barrier layer (E) has a higher affinity for metals and inorganic oxides than ordinary thermoplastic resins, laminating the inorganic vapor deposition layer (I) directly on the exposed surface side of the barrier layer (E) can form a dense, defect-free inorganic vapor deposition layer (I), and the interlayer adhesion between the barrier layer (E) and the inorganic vapor deposition layer (I) in the resulting vapor-deposited multilayer film is particularly good. Since the barrier layer (E) has high gas barrier properties, deterioration of the gas barrier properties can be suppressed even when defects occur in the inorganic vapor deposition layer (I) due to bending, etc. The average thickness of the inorganic vapor deposition layer (I) is preferably less than 500 nm. When the average thickness is less than 500 nm, the viscosity stability is excellent when the pulverized product of the multilayer structure including the inorganic vapor deposition layer (I) is melt-molded, and the generation of gels and lumps can be suppressed.

[0080] The inorganic vapor deposition layer (I) is preferably either a metal vapor deposition layer containing aluminum as a main component or an inorganic oxide vapor deposition layer containing an inorganic oxide as a main component. A metal vapor deposition layer is preferred when light-shielding properties are to be imparted, but an inorganic oxide vapor deposition layer is preferred from the viewpoints of visibility of the contents as a packaging material, microwave suitability, and suppression of the generation of gels and lumps when pulverized materials are melt-molded. An inorganic oxide vapor deposition layer is preferred from the viewpoint of suppressing coloration during recycling of the vapor-deposited multilayer film.

[0081] The metal vapor deposition layer is a layer containing aluminum as a main component. The aluminum atom content in the metal vapor deposition layer is preferably more than 50 mol%, more preferably 60 mol% or more, even more preferably 70 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and in some cases 98 mol% or more, 99 mol% or more, or 99.9 mol% or more is preferred. The average thickness of the metal vapor deposition layer is preferably 120 nm or less, more preferably 100 nm or less, and even more preferably 90 nm or less. The average thickness of the metal vapor deposition layer is preferably 25 nm or more, more preferably 35 nm or more, and even more preferably 45 nm or more. The "average thickness of the metal vapor deposition layer" refers to the average thickness at any 10 points on the cross section of the metal vapor deposition layer measured using an electron microscope. When the multilayer film of the present disclosure has a metal vapor deposition layer, the light transmittance at a wavelength of 600 nm can be 10% or less, resulting in excellent light-blocking properties.

[0082] In a metal vapor deposition layer containing aluminum as a main component, oxidation inevitably occurs, and aluminum oxide may be partially contained. In a metal vapor deposition layer containing aluminum as a main component, the molar ratio of the oxygen atom content to the aluminum atom content (O mol / Al mol) is preferably 0.5 or less, more preferably 0.3 or less, and even more preferably 0.1 or less.

[0083] The inorganic oxide vapor deposition layer is a layer containing an inorganic oxide as a main component. The content of the inorganic oxide in the metal vapor deposition layer is preferably more than 50 mol%, more preferably 60 mol% or more, even more preferably 70 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and in some cases, 98 mol% or more, 99 mol% or more, or 99.9 mol% or more is preferred. Examples of inorganic oxides include oxides of silicon, aluminum, magnesium, calcium, potassium, tin, sodium, boron, titanium, lead, zirconium, and yttrium, with alumina or silica being preferred. The average thickness of the inorganic oxide vapor deposition layer is preferably 60 nm or less, more preferably 50 nm or less, and even more preferably 40 nm or less. The average thickness of the inorganic oxide vapor deposition layer is preferably 8 nm or more, more preferably 12 nm or more, and even more preferably 16 nm or more. The "average thickness of the inorganic oxide vapor deposition layer" refers to the average thickness at any 10 points on the cross section of the inorganic oxide vapor deposition layer measured using an electron microscope. When the multilayer film of the present disclosure has an inorganic oxide vapor-deposited layer, it can have a light transmittance of 80% or more at a wavelength of 600 nm, and when used as a packaging material, it has excellent visibility of the contents. From the viewpoint of further improving visibility, the light transmittance at a wavelength of 600 nm is more preferably 90% or more.

[0084] The inorganic vapor deposition layer (I) can be formed by a known physical vapor deposition method or chemical vapor deposition method. Specific examples include vacuum deposition, sputtering, ion plating, ion beam mixing, plasma CVD, laser CVD, MO-CVD, and thermal CVD. Physical vapor deposition is preferred, and vacuum vapor deposition is particularly preferred. The upper limit of the surface temperature of the barrier layer (E) during the formation of the inorganic vapor deposition layer (I) is preferably 60°C, more preferably 55°C, and even more preferably 50°C. The lower limit of the surface temperature of the barrier layer (E) during the formation of the inorganic vapor deposition layer (I) is not particularly limited, but is preferably 0°C, more preferably 10°C, and even more preferably 20°C. The exposed surface of the barrier layer (E) may be plasma-treated before the film formation. The plasma treatment can be performed by a known method, and atmospheric pressure plasma treatment is preferred. In atmospheric pressure plasma treatment, nitrogen, helium, neon, argon, krypton, xenon, radon, or the like is used as a discharge gas. Among these, nitrogen, helium, and argon are preferably used, and nitrogen is particularly preferred because it can reduce costs.

[0085] <Multilayer Structure> The present disclosure also includes a multilayer structure comprising the multilayer film or vapor-deposited multilayer film of the present disclosure and a resin layer (R) containing a thermoplastic resin (r) as a main component. The content of the thermoplastic resin (r) in the resin layer (R) is more than 50 mol%, preferably 60 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and in some cases, 98 mol% or more, 99 mol% or more, or 99.9 mol% or more is preferred. The multilayer film or vapor-deposited multilayer film of the present disclosure itself can be used as a packaging material with gas barrier properties, but by laminating at least one resin layer (R) containing a thermoplastic resin (r) as a main component to form a multilayer structure, various functions as a packaging material, such as designability and heat sealability, can be imparted. The thermoplastic resin (r) is not particularly limited, and examples thereof include linear low-density polyethylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, vinyl ester resin, ethylene-propylene copolymer, polypropylene, propylene-α-olefin copolymer (α-olefin having 4 to 20 carbon atoms), polybutene, polypentene, and other olefin homopolymers or copolymers thereof, polyamides such as nylon 6 and nylon 6,6, polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polystyrene, polyvinyl chloride, polyvinylidene chloride, acrylic resins, polycarbonate, chlorinated polyethylene, and chlorinated polypropylene. Among these, polyolefins are preferred from the viewpoints of excellent moisture resistance, mechanical properties, economic efficiency, heat sealability, and the like, and polyamides and polyesters are preferred from the viewpoints of excellent mechanical properties, heat resistance, and the like. In particular, to obtain a multilayer structure with excellent recyclability, it is more preferable that the thermoplastic resin (r) be the same type as the polyethylene-based resin described above. Such a resin layer (R) may be unstretched, or may be stretched or rolled uniaxially or biaxially. From the viewpoint of improving mechanical strength, a biaxially oriented layer is preferred, and from the viewpoint of improving heat sealability, a non-oriented layer is preferred.

[0086] When the multilayer structure of the present disclosure has multiple resin layers (R), the resin layers (R) may be the same as or different from each other, but are generally different, and the resin layers (R) may be thicker or thinner than the core layer (C).

[0087] The method for producing the resin layer (R) is not particularly limited, but it is generally produced by melt extrusion using an extruder. Either a circular die or a T-die can be used as the die. The method for uniaxial or biaxial stretching is also not particularly limited, and the film can be produced by stretching in the machine direction and / or width direction 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. In the case of a uniaxially stretched layer, the area ratio is preferably 3 to 10 times from the viewpoint of the uniformity of the thickness of the resulting layer and mechanical strength. An area ratio of 4 times or more is more preferred. An area ratio of 9 times or less is more preferred, and an area ratio of 8 times or less is even more preferred. An area ratio of 3 times or more makes it difficult for stretching unevenness to remain, while an area ratio of 10 times or less makes it difficult for layer breakage to occur during stretching. In the case of a biaxially stretched layer, the area ratio is preferably 10 to 60 times from the viewpoint of the uniformity of the thickness of the resulting layer and mechanical strength. The area ratio is more preferably 20 times or more, even more preferably 30 times or more, and may be 40 times or more. The area ratio is more preferably 55 times or less, and even more preferably 50 times or less. When the area ratio is 10 times or more, stretching unevenness is unlikely to remain, and when it is 60 times or less, layer breakage is unlikely to occur during stretching.

[0088] The thickness of the resin layer (R) is preferably 10 to 200 μm from the viewpoint of industrial productivity. Specifically, the thickness is more preferably 10 to 150 μm in the case of an unstretched layer, and more preferably 10 to 50 μm in the case of a uniaxially stretched layer or a biaxially stretched layer.

[0089] The total thickness of the multilayer structure of the present disclosure is preferably 300 μm or less, preferably 200 μm or less, and in some cases, 150 μm or less, 130 μm or less, 100 μm or less, or 80 μm or less. When the total thickness is within the above range, the multilayer structure of the present disclosure is lightweight and flexible, and therefore is preferably used for flexible packaging applications. The amount of resin used in the multilayer structure is small, thereby reducing the environmental impact.

[0090] The thickness of each layer in the multilayer structure of the present disclosure may be adjusted appropriately depending on the application, but from the viewpoints of suppressing coloration during melt molding of the pulverized material, improving thermal stability during melt molding, and suppressing the occurrence of lumps, the ratio of the total thickness of the layers containing a polyethylene-based resin as a main component to the total thickness of the multilayer structure is preferably 0.75 or more, more preferably 0.80 or more, even more preferably 0.85 or more, particularly preferably 0.90 or more, and may even be 0.95 or more. On the other hand, from the viewpoint of improving gas barrier properties, the ratio is preferably 0.99 or less.

[0091] The method for laminating the resin layer (R) on the multilayer film of the present disclosure is not particularly limited, and examples thereof include extrusion lamination, co-extrusion lamination, dry lamination, etc. When laminating the resin layer (R) on the multilayer film, an adhesive layer may be provided between the layers. The adhesive layer can be formed by applying a known adhesive and drying it. The adhesive is preferably a two-component reactive polyurethane adhesive in which a polyisocyanate component and a polyol component are mixed and reacted. The thickness of the adhesive layer is not particularly limited, but is preferably 1 to 5 μm, more preferably 2 to 4 μm.

[0092] The layer configuration of the multilayer structure of the present disclosure is not particularly limited, and examples thereof include the following multilayer structure configurations. In the following, the multilayer film of the present disclosure will be referred to as film (A-E), and the resin layer (R) will be referred to as "layer (R)." " / / " means that the layers on both sides are laminated directly or via an adhesive layer. Examples of layer configurations of the multilayer structure of the present disclosure include layer (R) / / film (A-E), film (A-E) / / layer (R), layer (R) / / film (A-E) / / layer (R), etc.

[0093] The multilayer structure of the present disclosure may have layers other than those described above, provided that the effects of the present disclosure are not impaired. An example of such layers is a recovery layer. It is particularly preferable to reuse a recovered composition containing recovered materials from the multilayer structure of the present disclosure, as described below, as part or all of the recovery layer. Another example of such layers is a printed layer. The printed layer may be included at any position in the multilayer structure of the present disclosure. Examples of the printed layer include a film obtained by applying a solution containing a pigment or dye, and optionally a binder resin, followed by drying. Examples of methods for applying the printed layer include gravure printing and various other application methods using a wire bar, spin coater, die coater, etc. The thickness of the ink layer is not particularly limited, but is preferably 0.5 to 10 μm, more preferably 1 to 4 μm.

[0094] The oxygen transmission rate (OTR) of the multilayer structure of the present disclosure under conditions of 20°C and 65% RH is not particularly limited and may be adjusted depending on the application. The multilayer structure of the present disclosure is preferably applicable to high-barrier applications when it does not have an inorganic vapor deposition layer (I), and to applications requiring even higher barrier properties when it has an inorganic vapor deposition layer (I). In the former case, the OTR is 1 cc / (m ２ ·day·atm) or less, and 0.4 cc / (m ２ ·day·atm) or less is more preferable, and 0.1 cc / (m ２ In the latter case, the OTR is 0.1 cc / (m ２ ·day·atm) or less, and 0.05 cc / (m ２ ·day·atm) or less is more preferable, and 0.03 cc / (m ２ It is more preferable that the OTR is equal to or less than 1 / 2 day atm. In particular, maintaining a low OTR even after physical damage such as bending or stretching will further improve the applicability as a packaging material. The OTR is measured in accordance with JIS K 7126-2 (isobaric method; 2006), and specifically, the method described in the examples is employed.

[0095] The water vapor transmission rate (WVTR) of the multilayer structure of the present disclosure under conditions of 40°C and 90% RH is not particularly limited and may be adjusted depending on the application. The multilayer structure of the present disclosure is preferably applicable to high-barrier applications when it does not have an inorganic vapor deposition layer (I), and to applications requiring even higher barrier properties when it has an inorganic vapor deposition layer (I). In the former case, the WVTR is 5 g / (m ２ ·day) or less, and 4 g / (m ２ ·day) or less is more preferable, and 3 g / (m ２ In the latter case, the WVTR is 1 g / (m ２ ·day) or less, and 0.5 g / (m ２ ·day) or less is more preferable, and 0.3 g / (m ２ It is even more preferable that the WVTR is maintained at a low level even after physical damage such as bending or stretching, which further improves the applicability as a packaging material. WVTR is measured in accordance with JIS K 7129-2 (infrared sensor method; 2019).

[0096] It is preferable to reuse recycled materials from the multilayer film, vapor-deposited multilayer film, or multilayer structure of the present disclosure. Examples of such recycled materials include scrap (ends or defective products) generated during the production of the multilayer film, vapor-deposited multilayer film, or multilayer structure of the present disclosure. A method for recovering a multilayer film, vapor-deposited multilayer film, or multilayer structure, which includes a step of crushing the recycled material and then melt-molding it, and a recycled composition containing the recycled material are also preferred embodiments of the present disclosure. A method for producing a film using the recycled composition as a raw material is also preferred embodiments of the present disclosure.

[0097] In the method for producing the recovered composition, the recovered material is first pulverized. The pulverized recovered material may be melt-molded as is to obtain the recovered composition, or may be melt-molded together with other components as needed to obtain the recovered composition. A preferred component to be added to the recovered material is a polyolefin resin, and the above-mentioned polyethylene-based resin is more preferred. The pulverized recovered material may be directly used to produce a molded product such as a multilayer structure, or the pulverized recovered material may be melt-molded to obtain pellets of the recovered composition, and the pellets may then be used to produce a molded product.

[0098] The mass ratio of EVOH(e) to polyolefin resin in the recovered composition [EVOH(e) / polyolefin resin] is preferably 0.01 / 99.99 to 20 / 80. If the mass ratio is less than 0.01 / 99.99, the proportion of recovered material used may be reduced. On the other hand, if the mass ratio exceeds 20 / 80, the melt moldability and mechanical properties of the recovered composition may be reduced. From the viewpoint of improving the melt moldability and mechanical properties of the resulting recovered composition, the mass ratio is more preferably 15 / 85 or less, even more preferably 10 / 90 or less, and may even be 5 / 95 or less.

[0099] The multilayer structure of the present disclosure has high barrier properties and excellent converting properties, and therefore can be suitably used as a material for various types of packaging, such as food packaging, pharmaceutical packaging, industrial chemical packaging, and pesticide packaging. In particular, packaging materials comprising the multilayer structure of the present disclosure can be suitably used as packaging materials with excellent recyclability.

[0100] The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples in any way.

[0101] <Materials used> Polyethylene resin (a) a-1: High-density polyethylene "Elite (trademark) AT6900" (ethylene and 1-octene copolymer, density 0.969 g / cm 3) manufactured by The Dow Chemical Company ３ a-2: High-density polyethylene "Elite (trademark) 5538G" manufactured by Dow Chemical Company (ethylene and 1-octene copolymer, density 0.941 g / cm 3) ３a-3: Medium density polyethylene "Elite (trademark) 5110G" (ethylene and 1-octene copolymer, density 0.926 g / cm3) manufactured by Dow Chemical Company, melting point 129°C, MFR (190°C, 2.16 kg load) 1.3 g / 10 min ３ ac-1: Linear low-density polyethylene "Elite (trademark) 5400G" (ethylene and 1-octene copolymer, density 0.916 g / cm 3) manufactured by Dow Chemical Company, melting point 123°C, MFR (190°C, 2.16 kg load) 0.85 g / 10 min ３ , melting point 123 ° C., MFR (190 ° C., 2.16 kg load) 1.0 g / 10 min,) Polyethylene resin (b) b-1: High-density polyethylene "Elite (trademark) 5538G" manufactured by Dow Chemical Company (ethylene and 1-octene copolymer, density 0.941 g / cm ３ b-2: Medium density polyethylene "Elite (trademark) 5110G" (ethylene and 1-octene copolymer, density 0.926 g / cm 3) manufactured by Dow Chemical Company, melting point 129 ° C., MFR (190 ° C., 2.16 kg load) 1.3 g / 10 min. ３ , melting point 123 ° C., MFR (190 ° C., 2.16 kg load) 0.85 g / 10 min,) Polyethylene resin (c) c-1: Linear low-density polyethylene "Elite (trademark) 5400G" manufactured by Dow Chemical Company (ethylene and 1-octene copolymer, density 0.916 g / cm ３ , melting point 123 ° C., MFR (190 ° C., 2.16 kg load) 1.0 g / 10 min,) cc-1: High-density polyethylene "Elite (trademark) AT6900" manufactured by Dow Chemical Company (ethylene and 1-octene copolymer, density 0.969 g / cm ３ , melting point 134 ° C., MFR (190 ° C., 2.16 kg load) 1.2 g / 10 min,) Adhesive resin (d) d-1: maleic anhydride modified polyethylene "ADMER (trademark) AT1955E" (density 0.89 g / cm 3) manufactured by Mitsui Chemicals, Inc. ３EVOH (e), polyvalent metal ions (f), and higher aliphatic carboxylic acids (g). e-1: EVOH, ethylene unit content 24 mol%, saponification degree 99.9 mol%, sodium acetate 250 ppm (calculated as sodium ions), phosphate ions 20 ppm (calculated as phosphate radicals), magnesium stearate 50 ppm (calculated as magnesium ions), MFR (210°C, 2.16 kg load) 2.2 g / 10 min. e-2: EVOH, ethylene unit content 27 mol%, saponification degree 99.9 mol%, sodium acetate 250 ppm (calculated as sodium ions), phosphate ions 20 ppm (calculated as phosphate radicals), boric acid 150 ppm (calculated as boron element), magnesium stearate 50 ppm (calculated as magnesium ions), MFR (210°C, 2.16 kg load) 4.0 g / 10 min e-3: EVOH, ethylene unit content 24 mol%, saponification degree 99.9 mol%, sodium acetate 250 ppm (calculated as sodium ions), phosphate ions 20 ppm (calculated as phosphate radicals), MFR (210°C, 2.16 kg load) 2.2 g / 10 min e-4: EVOH, ethylene unit content 24 mol%, saponification degree 99.9 mol%, sodium acetate 250 ppm (calculated as sodium ions), phosphate ions 20 ppm (calculated as phosphate radicals), magnesium stearate 25 ppm (calculated as magnesium ions), MFR (210°C, 2.16 kg load) 2.2 g / 10 min e-5: EVOH, ethylene unit content 24 mol%, saponification degree 99.9 mol%, sodium acetate 250 ppm (calculated as sodium ions), phosphate ions 20 ppm (calculated as phosphate radicals), magnesium stearate 250 ppm (calculated as magnesium ions), MFR (210°C, 2.16 kg load) 2.2 g / 10 min e-6: EVOH, ethylene unit content 24 mol%, saponification degree 99.9 mol%, sodium acetate 250 ppm (calculated as sodium ions), phosphate ions 20 ppm (calculated as phosphate radicals), calcium stearate 50 ppm (calculated as calcium ions), MFR (210°C, 2.16 kg load) 2.2 g / 10 mine-7: EVOH, ethylene unit content 24 mol%, saponification degree 99.9 mol%, sodium acetate 250 ppm (calculated as sodium ions), phosphate ions 20 ppm (calculated as phosphate radicals), zinc stearate 50 ppm (calculated as zinc ions), MFR (210°C, 2.16 kg load) 2.2 g / 10 min. ec-1: EVOH, ethylene unit content 32 mol%, saponification degree 99.9 mol%, sodium acetate 300 ppm (calculated as sodium ions), phosphate ions 30 ppm (calculated as phosphate radicals), boric acid 200 ppm (calculated as boron element), magnesium stearate 50 ppm (calculated as magnesium ions), MFR (210°C, 2.16 kg load) 3.7 g / 10 min. ec-2: EVOH, ethylene unit content 48 mol%, saponification degree 99.9 mol%, sodium acetate 150 ppm in terms of sodium ion, phosphate ion 30 ppm in terms of phosphate radical, boric acid 250 ppm in terms of boron element, magnesium stearate 50 ppm in terms of magnesium ion, MFR (210°C, 2.16 kg load) 6.5 g / 10 min <Evaluation method>

[0102] (1) Measurement of oxygen transmission rate of multilayer film or vapor-deposited multilayer film Using the multilayer films or vapor-deposited multilayer films obtained in the examples and comparative examples, the oxygen transmission rate was measured with the skin layer (A) side as the oxygen supply side and the other side as the carrier gas side. Specifically, the oxygen transmission rate (unit: cc / (m)) was measured in accordance with JIS K 7126-2 (isobaric method; 2006) 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 using an oxygen transmission rate measuring device ("MOCON OX-TRAN2 / 21" manufactured by Modern Controls). ２ The oxygen permeability was measured. Nitrogen gas containing 2% by volume of hydrogen gas was used as the carrier gas. Based on the obtained oxygen permeability, a rating was made according to the following criteria. If the rating was D or E, the gas barrier properties were judged to be insufficient. The results are shown in Table 1. Rating: Criteria A: 0.1 cc / (m ２ ・day・atm) B: 0.1cc / (m ２ ・day・atm) or more, 0.4cc / (m ２ · day · atm) or less C: 0.4 cc / (m２ ・day・atm) or more, 1.0cc / (m ２ · day · atm) or less D: 1.0 cc / (m ２ ・day・atm) or more, 10cc / (m ２ ・day・atm) Less than E: 10cc / (m ２ ・day・atm) or more

[0103] (2) Evaluation of anti-curl properties of multilayer films or vapor-deposited multilayer films A 10 cm square film was cut out from the multilayer films or vapor-deposited multilayer films obtained in the Examples and Comparative Examples, and the state of curling after leaving it to stand for 10 minutes in an atmosphere of 20°C and 65% RH was observed and rated according to the following criteria. A rating of D or E was judged to be insufficient anti-curl properties. The results are shown in Table 1. Rating: Criteria A: Almost no curling observed B: Slight curling observed C: Moderate curling observed D: Severe curling observed E: Extremely severe curling observed

[0104] (3) Evaluation of heat resistance of multilayer structure Two A4 size sheets were cut out from the multilayer structures obtained in the examples and comparative examples, and the resin layers (R) were stacked together. One side was heat-sealed at 120°C for 2 seconds using a hot plate sealer, and the sealed area was visually observed and judged according to the following criteria. Judgment: Criteria A: Good appearance B: Slight whitening was observed C: Mild whitening or voids were observed D: Considerable whitening, voids or deformation was observed E: Severe whitening, voids or deformation was observed

[0105] (4) Evaluation of recyclability of multilayer structure The multilayer structures obtained in the examples and comparative examples were crushed into pieces of 4 mm square or less, and the crushed pieces were mixed with low-density polyethylene (LDPE) "Novatec (trademark) LD LJ400" (density 0.921 g / cm) manufactured by Japan Polyethylene Co., Ltd. ３, melting point 111°C, MFR (190°C, 2.16 kg load) 1.5 g / 10 min) were dry-blended in a mass ratio (recycled material / low-density polyethylene) of 50 / 50, and monolayer film formation was carried out under the extrusion conditions shown below to obtain a monolayer film with an average thickness of 50 μm. As a control, a monolayer film with an average thickness of 50 μm was similarly obtained using only the low-density polyethylene (hereinafter sometimes simply referred to as "control"). 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 was used. A 300 mm wide T-die was used as the die. The average thickness of the monolayer film was adjusted by appropriately changing the screw rotation speed and take-up roll speed. The temperature conditions used here are shown below. : Extrusion temperature: feeding section / compression section / metering section / adapter = 175 / 230 / 230 / 230°C Die temperature: 220°C Chill roll temperature: 80°C The coloration and defects of the obtained monolayer film were visually compared with the control and judged according to the following criteria. The results are shown in Table 2. Coloration judgment: Criteria A: The degree of color change was small compared to the control B: Slight coloration was observed compared to the control C: Moderate coloration was observed compared to the control D: Significant coloration was observed compared to the control E: Significant coloration was observed and unevenness was also observed compared to the control 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 large particles was higher compared to the control E: The amount of large particles was significantly higher compared to the control

[0106] Example 1 Using polyethylene resin (a-1) as the raw material for the skin layer (A), polyethylene resin (b-1) as the raw material for the subskin layer (B), polyethylene resin (c-1) as the raw material for the core layer (C), adhesive resin (d-1) as the raw material for the adhesive layer (D), and resin composition (e-1) as the raw material for the barrier layer (E), an unstretched multilayer film having layer thicknesses and a layer structure of (A) / (B) / (C) / (D) / (E) = 12 μm / 12 μm / 72 μm / 12 μm / 12 μm was produced using an inflation extrusion molding machine under the film formation conditions shown below. Apparatus: Dr. Collin 5-type 5-layer inflation extrusion molding machine Die temperature: 210°C, blow-up ratio: 2.7, take-up speed: 4m / min, film folded diameter width: 25cm <Conditions for skin layer (A) extruder> Extruder: 30φ single screw extruder (Dr. Collin), extrusion temperature: feed section / compression section / metering section = 170°C / 190°C / 210°C. <Conditions for sub-skin layer (B) extruder> Extruder: 20φ single screw extruder (Dr. Collin), extrusion temperature: feed section / compression section / metering section = 170°C / 190°C / 210°C. <Conditions for core layer (C) extruder> Extruder: 20φ single screw extruder (Dr. Collin), extrusion temperature: feed section / compression section / metering section = 170°C / 190°C / 210°C. <Conditions of Extruder for Adhesive Layer (D)> Extruder: 20φ single screw extruder (manufactured by Dr Collin), extrusion temperature: feeding zone / compression zone / metering zone=170°C / 190°C / 210°C. <Conditions of Extruder for Barrier Layer (E)> Extruder: 30φ single screw extruder (manufactured by Dr Collin), extrusion temperature: feeding zone / compression zone / metering zone=190°C / 210°C / 210°C.

[0107] From the obtained cylindrical unstretched multilayer film, an unstretched multilayer film measuring 4 cm in the machine direction (MD direction) and 10 cm in the width direction (TD direction) was cut out, and using a stretching device (SDR-506WK) manufactured by Eto Corporation, it was uniaxially stretched 5 times in the machine direction (MD direction) at 125°C to produce a multilayer film having layer thicknesses and a layer structure of (A) / (B) / (C) / (D) / (E) = 2 μm / 2 μm / 12 μm / 2 μm / 2 μm.

[0108] A two-component reactive polyurethane adhesive (24 parts by mass of "Takelac (trademark) A-520" and 4 parts by mass of "Takenate (trademark) A-50" manufactured by Mitsui Chemicals, Inc.) was mixed with 37 parts by mass of ethyl acetate to prepare an adhesive solution. Next, one side of a polyethylene film ("T.U.X™ FCD," a non-oriented polyethylene film made of linear low-density polyethylene manufactured by Mitsui Chemicals Tohcello, Inc.) (resin layer (R)) having an average thickness of 40 μm was subjected to a corona treatment by a known method, and the above adhesive solution was applied to the corona-treated surface with a wire bar so that the average thickness after drying would be 3 μm. This was then dried at 100°C for 5 minutes and laminated to the exposed surface of the barrier layer (E) of the multilayer film to produce a multilayer structure having a layer thickness and layer structure of (A) / (B) / (C) / (D) / (E) / adhesive layer / (R) = 2 μm / 2 μm / 12 μm / 2 μm / 2 μm / 3 μm / 40 μm. The adhesion temperature (heating roll temperature) during lamination was 80°C, and the laminate was then aged at 40°C for 3 days.

[0109] Examples 2 to 12 and Comparative Examples 1 to 10 Multilayer films and multilayer structures were produced and evaluated in the same manner as in Example 1, except that the types of resin raw materials used in the production of the multilayer films, the layer configurations, and thicknesses were changed as shown in Tables 1 and 2. The results are shown in Tables 1 and 2.

[0110] Example 13 A vapor-deposited multilayer film and a multilayer structure were produced and evaluated in the same manner as in Example 3, except that an alumina (AlOx) vapor-deposited layer (inorganic vapor-deposited layer (I)) having an average thickness of 30 nm was laminated by a known vacuum vapor deposition method on the exposed surface of the barrier layer (E) of the stretched multilayer film obtained in Example 3. The results are shown in Tables 1 and 2.

[0111] Example 14 A vapor-deposited multilayer film and a multilayer structure were prepared and evaluated in the same manner as in Example 13, except that the alumina vapor-deposited layer was changed to a silica (SiOx) vapor-deposited layer. The results are shown in Tables 1 and 2.

[0112] Example 15 A vapor-deposited multilayer film and a multilayer structure were prepared and evaluated in the same manner as in Example 13, except that the alumina vapor-deposited layer was replaced with an aluminum metal (Al) vapor-deposited layer and the thickness of the inorganic vapor-deposited layer (I) was changed to 50 nm. The results are shown in Tables 1 and 2.

[0113] Example 16 A vapor-deposited multilayer film and a multilayer structure were produced and evaluated in the same manner as in Example 1, except that a silica (SiOx) vapor-deposited layer (inorganic vapor-deposited layer (I)) having an average thickness of 30 nm was laminated by a known vacuum vapor deposition method on the exposed surface of the barrier layer (E) of the stretched multilayer film obtained in Example 1. The results are shown in Tables 1 and 2.

[0114] Example 17 A vapor-deposited multilayer film and a multilayer structure were prepared and evaluated in the same manner as in Example 16, except that the average thickness of the layer (R) was changed to 80 μm. The results are shown in Tables 1 and 2.

[0115]

[0116]

[0117] The multilayer films and vapor-deposited multilayer films of Examples 1 to 17 exhibit both gas barrier properties and low curl. On the other hand, the multilayer film of Comparative Example 1, which does not have a barrier layer (E), exhibits poor gas barrier properties. The multilayer films of Comparative Examples 2 to 4, in which the ethylene unit content of the EVOH contained in the barrier layer (E) exceeds 30 mol%, do not exhibit both gas barrier properties and low curl. The multilayer films of Comparative Examples 5 to 7, 9, and 10, in which the density (dA) of the skin layer (A) is the same as the density (dC) of the core layer (C), do not exhibit low curl. The multilayer film of Comparative Example 8, in which the thickness of the skin layer (A) is greater than the thickness of the core layer (C), does not exhibit low curl.

Claims

1. A multilayer film having a structure in which a skin layer (A), a core layer (C), an adhesive layer (D) and a barrier layer (E) are laminated at least in this order, wherein the skin layer (A) is located on one surface of the multilayer film, and the barrier layer (E) is located on the other surface of the multilayer film, the core layer (C) is the thickest layer in the multilayer film, the skin layer (A) contains a polyethylene resin (a) as a main component, the core layer (C) contains a polyethylene resin (c) as a main component, the density (dA) of the skin layer (A) is greater than the density (dC) of the core layer (C), the adhesive layer (D) contains an adhesive resin (d) having a melting point of less than 150°C as a main component, and the barrier layer (E) contains an ethylene-vinyl alcohol copolymer (e) having an ethylene unit content of 20 mol% or more and 30 mol% or less and a saponification degree of 90 mol% or more as a main component, A multilayer film that does not have a layer containing, as a main component, a resin having a melting point of 220°C or higher, and that is stretched at least 3 times in one axial direction.

2. The multilayer film according to claim 1, further comprising a subskin layer (B) between the skin layer (A) and the core layer (C), the subskin layer (B) containing a polyethylene resin (b) as a main component, and the density (dB) of the subskin layer (B) is smaller than the density (dA) of the skin layer (A) and larger than the density (dC) of the core layer (C).

3. The multilayer film of claim 1, wherein the density (dD) of the adhesive layer (D) is less than the density (dC) of the core layer (C).

4. The density (dA) of the skin layer (A) is 0.940 g / cm ３ The multilayer film according to claim 1 .

5. The density (dC) of the core layer (C) is 0.910 g / cm ３ Above, 0.940g / cm ３ The multilayer film of claim 1 , wherein the thickness of the multilayer film is less than 10 μm.

6. The multilayer film according to claim 1, wherein the ratio of the thickness of the core layer (C) to the total thickness of the multilayer film is 0.3 to 0.

8.

7. The multilayer film according to claim 1, wherein the ratio of the thickness of the skin layer (A) to the total thickness of the multilayer film is 0.05 to 0.

2.

8. The multilayer film according to claim 1, wherein the ratio of the thickness of the barrier layer (E) to the total thickness of the multilayer film is 0.05 to 0.

2.

9. The multi-layer film according to claim 1, wherein the adhesive resin (d) is an acid-modified polyethylene resin.

10. The multilayer film according to claim 1, wherein the barrier layer (E) contains 10 to 300 ppm of at least one polyvalent metal ion (f) selected from the group consisting of magnesium ions, calcium ions, and zinc ions.

11. The multilayer film according to claim 1, wherein the barrier layer (E) contains 100 to 4,000 ppm of a higher aliphatic carboxylic acid (g) having 8 to 30 carbon atoms.

12. The multilayer film of claim 1, wherein the multilayer film is stretched at least three times in the machine direction and is substantially unstretched in the cross direction.

13. The multilayer film according to claim 1, which is an inflation-molded product.

14. A vapor-deposited multilayer film comprising an inorganic vapor-deposited layer (I) on the exposed surface side of the barrier layer (E) in the multilayer film according to any one of claims 1 to 13.

15. The vapor-deposited multilayer film according to claim 14, wherein the inorganic vapor-deposited layer (I) is a vapor-deposited metal layer mainly composed of aluminum or a vapor-deposited inorganic oxide layer mainly composed of alumina or silica.

16. A multilayer structure comprising the multilayer film according to any one of claims 1 to 13, and further comprising a resin layer (R) containing a thermoplastic resin (r) as a main component.

17. A multilayer structure comprising the vapor-deposited multilayer film according to claim 14, and further comprising a resin layer (R) containing a thermoplastic resin (r) as a main component.

18. The multilayer structure according to claim 16, wherein the thermoplastic resin (r) contains a polyethylene resin as a main component.

19. The multilayer structure according to claim 17, wherein the thermoplastic resin (r) contains a polyethylene resin as a main component.

20. A packaging material comprising the multi-layer structure of claim 16.

21. A packaging material comprising the multi-layer structure of claim 17.

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