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

Abstract

A multilayer film having a structure in which at least a skin layer (A), a core layer (C), an adhesive layer (D), and a barrier layer (E) are laminated in this order, the skin layer (A) being located on one outermost layer of the multilayer film, the barrier layer (E) being located on the other outermost layer of the multilayer film, the core layer (C) being a layer having the largest thickness in the multilayer film, the skin layer (A) containing a polyethylene resin (a) as the main component, the adhesive layer (D) being a layer having the largest thickness in the multilayer film, and the barrier layer (E) being a layer having the largest thickness in the multilayer film. 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 DEG C as a main component, and 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 more as a main component. The film does not have a layer containing, as a main component, a resin having a melting point of 220 DEG C or higher, and is stretched by at least three times in at least a uniaxial direction.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a multilayer film, an evaporation multilayer film, or a multilayer structure and a packaging material. BACKGROUND

[0002] Ethylene-vinyl alcohol copolymer (hereinafter, sometimes simply referred to as "EVOH") is excellent in transparency, gas barrier property, aroma retention property, solvent resistance, oil resistance, and the like, and is widely used for various packaging such as food packaging, pharmaceutical packaging, industrial chemical packaging, pesticide packaging, industrial films, agricultural films, floor heating pipes, fuel containers, and the like, by utilizing these properties.

[0003] In recent years, in response to environmental problems and waste problems, the demand for so-called post-consumer recycling (hereinafter, sometimes simply referred to as "recycling") of packaging materials after consumption for resource recycling in the recycling market is increasing worldwide, and packaging materials having excellent recyclability are desired. For example, a gas barrier packaging film having excellent recyclability is attempted to be manufactured, which is obtained by mixing or laminating a small amount of a gas barrier material such as polyethylene, polypropylene, which is a base material having low gas barrier property, or a gas barrier material that allows mixing with polyethylene or polypropylene, to a packaging film having polyethylene or polypropylene as a base material.

[0004] Patent Document 1 describes that by providing an EVOH layer having a specific thickness at the surface layer of a laminate, the heat sealing speed when used as a packaging film can be improved without impairing the recyclability. It is described that by stretching these laminates in a uniaxial direction, a multilayer film having excellent transparency and gas barrier property can be obtained.

[0005] Patent Document 2 describes that in a multilayer film having an EVOH layer at the surface layer, by mixing and using at least two kinds of EVOH having different ethylene unit contents as EVOH, a multilayer film in which the adhesion between EVOH layers can be suppressed even at the time of stretching after blow molding is obtained.

[0006] PRIOR ART DOCUMENTS PATENT DOCUMENTS Patent Document 1: International Publication No. 2019 / 243456 Patent Document 2: International Publication No. 2021 / 210606. SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION However, in the multilayer film having an EVOH layer in the outermost layer and being stretched at least in a uniaxial direction described in Patent Literature 1 and Patent Literature 2, since the film has a strong curl, there are sometimes problems in the process such as wrinkles, bending, and adhesive peeling at the time of printing, lamination, and the like. Note that if it is a symmetric layer structure having a polyolefin layer in both of the outermost layers and an EVOH layer as the intermediate layer, such problems in the process can be somewhat alleviated, but in this case, the adhesion strength to the adhesive, printing ink is reduced, or the barrier property is reduced when a vapor deposition multilayer film having an inorganic vapor deposition layer formed on the polyolefin layer, and thus a layer structure having an EVOH layer in at least one of the outermost layers is indispensable.

[0008] The present disclosure was completed in order to solve the above-described problems, and aims to provide a multilayer film having an EVOH layer in one of the outermost layers, being stretched at least in a uniaxial direction, and having both gas barrier property and low curling property. In addition, a vapor deposition multilayer film using the above-described multilayer film, and a multilayer structure using the above-described multilayer film or the above-described vapor deposition multilayer film, and a packaging material having the above-described multilayer structure are also provided. Note that in the present specification, the case where the degree of curling of the film is alleviated is sometimes expressed as "low curling property", and the property capable of suppressing process problems such as wrinkles, bending, and adhesive peeling at the time of printing, lamination, and the like is expressed as "conversion process property".

[0009] Technical means for solving the problems According to the present disclosure, the above-described object is achieved by the following means: [1] A multilayer film having a structure obtained by laminating at least a skin layer (A), a core layer (C), an adhesive layer (D), and a barrier layer (E) in this order, the skin layer (A) is located in one of the outermost layers of the multilayer film, and the barrier layer (E) is located in the other of the outermost layers of the multilayer film, the core layer (C) is the layer having the largest 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 mol% or more and 30 mol% or less and a saponification degree of 90 mol% or more as a main component, which does not have a layer containing a resin having a melting point of 220°C or more as a main component, stretched by 3 times or more in at least a uniaxial direction; [2] The multilayer film according to [1], further having a sub-skin layer (B) containing a polyethylene-based resin (b) as a main component between the skin layer (A) and the core layer (C), the density (dB) of the sub-skin layer (B) being 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 according to [1] or [2], wherein the density (dD) of the adhesive layer (D) is smaller than the density (dC) of the core layer (C); [4] The multilayer film according to any one of [1] to [3], wherein the density (dA) of the skin layer (A) is 0.940 g / cm3 or more; [5] The multilayer film according to any one of [1] to [4], wherein the density (dC) of the core layer (C) is 0.910 g / cm3 or more and less than 0.940 g / cm3; [6] The multilayer film according to any one of [1] to [5], 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 any one of [1] to [6], 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 any one of [1] to [7], 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 multilayer film according to any one of [1] to [8], wherein the adhesive resin (d) is an acid-modified polyethylene-based resin;

[10] The multilayer film according to any one of [1] to [9], wherein the barrier layer (E) contains 10 to 300 ppm of at least one multivalent metal ion (f) selected from the group consisting of magnesium ions, calcium ions and zinc ions;

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

[11] , wherein the multilayer film is stretched by 3 times or more in a longitudinal direction and is not substantially stretched in a width direction;

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

[12] , wherein the multilayer film is a blow-molded body;

[14] A vapor-deposited multilayer film provided with an inorganic vapor-deposited layer (I) on the exposed surface side of the barrier layer (E) of the multilayer film according to any one of [1] to

[13] ;

[15] According to the vapor-deposited multilayer film described in

[14] , the inorganic vapor-deposited layer (I) is a metal vapor-deposited layer with aluminum as the main component, or an inorganic oxide vapor-deposited layer with aluminum oxide or silicon dioxide as the main component.

[16] A multilayer structure having, on the multilayer film described in any one of [1] to

[13] , or the vapor-deposited multilayer film described in

[14] or

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

[17] According to the multilayer structure described in

[16] , the thermoplastic resin (r) comprises polyethylene resin as the main component;

[18] Packaging material having the multi-layered structure described in

[16] or

[17] .

[0010] Invention Effects According to this disclosure, a multilayer film can be provided, which has an EVOH layer on its outermost layer, is stretched at least in a uniaxial direction, and possesses both gas barrier properties and low curl-off properties. Furthermore, vapor-deposited multilayer films using the aforementioned multilayer film, multilayer structures using the aforementioned multilayer film or vapor-deposited multilayer films, and packaging materials having the aforementioned multilayer structures can be provided. Detailed Implementation

[0011] The multilayer film disclosed herein has a structure in which a skin layer (A), a core layer (C), an adhesive layer (D), and a barrier layer (E) are stacked in at least this order. The skin layer (A) is located at one of the outermost layers of the multilayer film, and the barrier layer (E) is located at the other outermost layer of the multilayer film. Both the skin layer (A) and the core layer (C) are mainly composed of polyethylene resin. 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) with a melting point below 150°C as its main component. The barrier layer (E) contains an ethylene-vinyl alcohol copolymer (e) with an ethylene unit content of 20 mol% or more and 30 mol% or less and a saponification degree of 90 mol% or more as its main component. It does not have a layer containing a resin with a melting point above 220°C as its main component, and it is stretched at least 3 times in the uniaxial direction.

[0012] The phrase "the skin layer (A), core layer (C), adhesive layer (D), and barrier layer (E) are stacked in at least this order" means that as long as the layer structure has a skin layer (A), core layer (C), adhesive layer (D), and barrier layer (E) stacked in this order, there are no particular limitations; for example, it does not preclude the inclusion of other layers between each layer. In multilayer films or multilayer structures, "outermost layer" or "outermost surface" does not distinguish between inside and outside, but rather refers to the exposed surface. That is, multilayer films or multilayer structures each have two outermost layers or outermost surfaces.

[0013] "Main component" refers to a component that contains more than 50% by mass.

[0014] "ppm" refers to the content of a quality standard (mass ppm).

[0015] "Polyethylene resins" refer to homopolymers of ethylene, as well as copolymers of ethylene with more than 80 mol% and less than 20 mol% non-ethylene monomers. Representative non-ethylene monomers include α-olefins such as propylene, n-butene, isobutene, 1-hexene, and 1-octene, but are not limited to these.

[0016] The numerical range recorded using "~" indicates that the values ​​before and after "~" are the lower and upper limits. That is, "α~β" means "above α and below β". The upper and lower limits of the numerical range (content, physical property, etc.) can be appropriately combined.

[0017] <Epidermal layer (A)> The multilayer film of this disclosure has a skin layer (A) on its outermost surface comprising a polyethylene resin (a) as the main component. Polyethylene resins are widely used in packaging materials, regardless of their gas barrier properties, and their recycling infrastructure is widely established in various countries. Therefore, by having a skin layer (A) comprising a polyethylene resin (a) as the main component, the reusability of the multilayer film of this disclosure can be improved.

[0018] Examples of polyethylene resins (a) include homopolymers of ethylene and copolymers of 80 mol% or more of ethylene with less than 20 mol% of non-ethylene monomers. 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). Preferably, the polyethylene resin (a) is selected from at least one of high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene, or a mixture thereof. More preferably, it is substantially high-density polyethylene, or a mixture of at least one of low-density polyethylene and linear low-density polyethylene with high-density polyethylene. The polyethylene resin (a) preferably contains 60% by mass or more high-density polyethylene, more preferably 70% by mass or more high-density polyethylene, even more preferably 80% by mass or more high-density polyethylene, and particularly preferably 90% by mass or more high-density polyethylene. It may also be substantially composed of only high-density polyethylene. Thus, by including high-density polyethylene in the polyethylene resin (a) at a high content, the low curl resistance, heat resistance, moisture resistance, and mechanical properties of the multilayer film of this disclosure can be further improved.

[0019] As for polyethylene resin (a), resins with a unimodal or multimodal molecular weight distribution can be appropriately selected. By using multimodal resins, melt molding properties and mechanical properties can sometimes be achieved at a high level of uniformity. When 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 with 4 or more carbon atoms, more preferably an α-olefin with 6 or more carbon atoms, and can also be an α-olefin with 8 or more carbon atoms. When the number of carbon atoms in the α-olefin copolymerized with ethylene is large, various mechanical strengths such as puncture resistance and elongation at break can sometimes be particularly improved. There is no particular upper limit to the number of carbon atoms in the α-olefin, but it is usually 12 or less.

[0020] Metallocene catalysts are also suitable as polymerization catalysts for polyethylene resins (a). Polyethylene resins (a) polymerized using metallocene catalysts exhibit excellent melt moldability, and the resulting multilayer films achieve an excellent balance between flexibility and mechanical strength.

[0021] The density (dA) of the skin layer (A) only needs to be greater than the density (dC) of the core layer. For example, it can be 0.920 g / cm³ or more, 0.930 g / cm³ or more, or 0.935 g / cm³ or more. However, from the viewpoint of making the effects of this disclosure more significant, it is preferable to be 0.940 g / cm³ or more, more preferably 0.945 g / cm³ or more, even more preferably 0.950 g / cm³ or more, particularly preferably 0.955 g / cm³ or more, most preferably 0.960 g / cm³ or more, and it can also be 0.965 g / cm³ or more. By making the density (dA) of the skin layer (A) meet the above range, the low curling property can be improved. In particular, even if the barrier layer (E) present in one of the outermost layers of the multilayer film is a curling material, the low curling property can still be achieved through the skin layer (A) located in the other outermost layer of the multilayer film.

[0022] 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 sometimes preferably 133°C or higher or 135°C or higher. From the viewpoint of improving melt moldability and the mechanical properties of multilayer films, the melt flow rate (hereinafter, sometimes referred to as MFR) (at 190°C and 2160g load) of the polyethylene resin (a) as measured according to 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.

[0023] The skin layer (A) may contain other components besides polyethylene resin (a) as long as it does not impair the effects of this disclosure. Examples of such other components include alkali metal ions, polyvalent metal ions, carboxylic acids, phosphoric acid compounds, boron compounds, oxidation accelerators, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, pigments, dyes, processing aids, flame retardants, and antifogging agents. The content of other components in the skin layer (A) is typically 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 resins other than polyethylene resin (a). Examples of resins other than polyethylene resin (a) include thermoplastic resins such as polyolefins, polyamides, polyesters, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate, and polyvinyl alcohol resin. The content of the resin other than polyethylene 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. It can be less than 5% by mass, less than 3% by mass, less than 1% by mass, less than 0.5% by mass, or less than 0.1% by mass.

[0024] Of the resin constituting the skin layer (A), the proportion of polyethylene resin (a) is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and can be 95% by mass or more, 97% by mass or more, or 99% by mass or more. The resin constituting the skin layer (A) may also be composed solely of polyethylene resin (a). The content of polyethylene resin (a) in the skin layer (A) is greater 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 can be 95% by mass or more, 97% by mass or more, or 99% by mass or more. The skin layer (A) may also be substantially composed solely of polyethylene resin (a).

[0025] The method for manufacturing the resin composition constituting the skin layer (A) is not particularly limited, and it can be manufactured by melt-blending a polyethylene resin (a) with other additives added as needed. Melt-blending can be performed using known mixing or blending equipment such as kneaders, extruders, mixing rollers, and Banbury mixers. The temperature range during melt-blending can be appropriately adjusted according to the melting point of the polyethylene resin (a) used, and is typically 150–300°C.

[0026] In another approach, polyethylene resin (a) can be melt-blended to produce a masterbatch containing a high concentration of other additives as needed. This masterbatch is then dry-blended with polyethylene resin (a) that is substantially free of other additives for use in manufacturing the skin layer (A). Alternatively, polyethylene resin (a) and other additives can be dry-blended for manufacturing the skin layer (A). Dry blending refers to mechanical mixing in powder or granular form. Mixing can be performed using mixing devices such as drum mixers, ribbon mixers, and Henschel mixers, or by manual stirring or vibration in a closed container. The mixing temperature only needs to be between room temperature and a temperature below the melting point of polyethylene resin (a), and mixing can be performed in an air atmosphere or a nitrogen atmosphere.

[0027] <Core Layer (C)> The multilayer film disclosed herein has a core layer (C) comprising polyethylene resin (C) as the main component, and the core layer (C) is the thickest layer in the multilayer film. Polyethylene resin, regardless of its gas barrier properties, is widely used in packaging materials, and its recycling infrastructure has been widely established in various countries. Therefore, by having a core layer (C) comprising polyethylene resin (C) as the main component, the reusability of the multilayer film of this disclosure can be improved. Examples of polyethylene resins (c) include homopolymers of ethylene and copolymers of 80 mol% or more of ethylene with less than 20 mol% of non-ethylene monomers. 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). Preferably, the polyethylene resin (c) is selected from at least one of high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene, or a mixture thereof. More preferably, it is selected from at least one of low-density polyethylene and linear low-density polyethylene, or a mixture thereof. Even more preferably, it is 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. It may also be substantially composed of only linear low-density polyethylene. Thus, by including linear low-density polyethylene in the polyethylene resin (c) at a high content, the low curl resistance and mechanical strength of the multilayer film of this disclosure can be further improved.

[0028] As for polyethylene resin (c), resins with a unimodal or multimodal molecular weight distribution can be appropriately selected. By using multimodal resins, melt molding properties and mechanical properties can sometimes be achieved at a high level of uniformity. When polyethylene resin (c) contains linear low-density polyethylene or other ethylene-α-olefin copolymers, the α-olefin copolymerized with ethylene is preferably an α-olefin with 4 or more carbon atoms, more preferably an α-olefin with 6 or more carbon atoms, and can also be an α-olefin with 8 or more carbon atoms. When the number of carbon atoms in the α-olefin copolymerized with ethylene is large, various mechanical strengths such as puncture resistance and elongation at break can sometimes be particularly improved. There is no particular upper limit to the number of carbon atoms in α-olefins, but it is usually 12 or less.

[0029] Metallocene catalysts can also be used as polymerization catalysts for polyethylene resins (c). Polyethylene resins (c) polymerized using metallocene catalysts exhibit excellent melt moldability, and the resulting multilayer films achieve an excellent balance between flexibility and mechanical strength.

[0030] The density (dC) of the core layer (C) can be, for example, 0.90 g / cm³ or more and less than 0.94 g / cm³, or 0.905 g / cm³ or more and less than 0.940 g / cm³, but from the viewpoint of making the effects of this disclosure more significant, it is preferably 0.910 g / cm³ or more and less than 0.940 g / cm³, more preferably 0.915 g / cm³ or more and less than 0.935 g / cm³, and sometimes preferably 0.916 g / cm³ or more and less than 0.930 g / cm³. On the other hand, in order to improve low curling, the density (dA) of the skin layer (A) needs to be greater than the density (dC) of the core layer (C). The difference between the density (dA) of the epidermis (A) and the density (dC) of the core layer (C) is preferably 0.005 g / cm³ or more, more preferably 0.01 g / cm³ or more, even more preferably 0.02 g / cm³ or more, even more preferably 0.03 g / cm³ or more, particularly preferably 0.04 g / cm³ or more, and may also be 0.045 g / cm³ or more or 0.05 g / cm³ or more. There is no particular upper limit to the difference between the density (dA) of the epidermis (A) and the density (dC) of the core layer (C), for example, it may be 0.5 g / cm³ or less, 0.3 g / cm³ or less, or 0.1 g / cm³ or less.

[0031] The melting point of polyethylene resin (c) is preferably 100-130°C, more preferably 110-127°C, and sometimes preferably 115-125°C. From the viewpoint of improving melt-forming properties and the mechanical properties of multilayer films, the MFR (at 190°C and 2160g load) of polyethylene resin (c) measured according to the method described in JIS K7210 (2014) is preferably 0.1-10 g / 10 min, more preferably 0.3-5.0 g / 10 min, and even more preferably 0.5-2.0 g / 10 min.

[0032] The core layer (C) may contain other components besides polyethylene resin (c) as long as it does not impair the effects of this disclosure. Examples of such other components include alkali metal ions, polyvalent metal ions, carboxylic acids, phosphoric acid compounds, boron compounds, oxidation accelerators, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, pigments, dyes, processing aids, flame retardants, and antifogging agents. The content of other components in the core layer (C) is typically 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 resins other than polyethylene resin (c). Examples of resins other than polyethylene resin (c) include thermoplastic resins such as polyolefins, polyamides, polyesters, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate, and polyvinyl alcohol resin. The content of the resin other than polyethylene 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 less than 5% by mass, and may be less than 3% by mass, less than 1% by mass, less than 0.5% by mass or less than 0.1% by mass.

[0033] In the resin constituting the core layer (C), the proportion of polyethylene resin (c) is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. It can be 95% by mass or more, 97% by mass or more, or 99% by mass or more. The resin constituting the core layer (C) may also be composed solely of polyethylene resin (c). The content of polyethylene resin (c) in the core layer (C) is greater than 50% by mass, preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. It can be 95% by mass or more, 97% by mass or more, or 99% by mass or more. The core layer (C) may also be substantially composed solely of polyethylene resin (c).

[0034] The method for manufacturing the resin composition constituting the core layer (C) is not particularly limited, and it can be manufactured by melt-blending polyethylene resin (C) with other additives added as needed. Melt-blending can be performed using known mixing or blending equipment such as kneaders, extruders, mixing rollers, and Banbury mixers. The temperature range during melt-blending can be appropriately adjusted according to the melting point of the polyethylene resin (C) used, and is typically 150–300°C.

[0035] In another approach, polyethylene resin (c) can be melt-blended to produce a masterbatch containing a high concentration of other additives as needed. This masterbatch is then dry-blended with polyethylene resin (c) that is substantially free of other additives for use in manufacturing the core layer (C). Alternatively, polyethylene resin (c) and other additives can be dry-blended for use in manufacturing the core layer (C). Dry blending refers to mechanical mixing in powder or granular form. Mixing can be performed using mixing devices such as drum mixers, ribbon mixers, and Henschel mixers, or by manual stirring or vibration in a closed container. The mixing temperature only needs to be between room temperature and a temperature below the melting point of polyethylene resin (c), and mixing can be performed in an air atmosphere or a nitrogen atmosphere.

[0036] <Subepidermis (B)> The multilayer film of this disclosure preferably further comprises a secondary skin layer (B) containing polyethylene resin (b) as a main component between the skin layer (A) and the core layer (C). Polyethylene resin, regardless of its gas barrier properties, is widely used in packaging materials, and its recycling infrastructure has been widely established in various countries. Therefore, by having a secondary skin layer (B) containing polyethylene resin (b) as a main component, the reusability of the multilayer film of this disclosure can be improved. Examples of polyethylene resins (b) include homopolymers of ethylene and copolymers of 80 mol% or more of ethylene with less than 20 mol% of non-ethylene monomers. 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). Preferably, the polyethylene resin (b) is selected from at least one of high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene, or a mixture thereof. More preferably, it is substantially high-density polyethylene or medium-density polyethylene, or a mixture of at least one of low-density polyethylene and linear low-density polyethylene with at least one of high-density polyethylene or medium-density polyethylene. The polyethylene resin (b) preferably contains 30% or more by mass of high-density polyethylene or medium-density polyethylene, more preferably 40% or more by mass of high-density polyethylene or medium-density polyethylene, even more preferably 50% or more by mass of high-density polyethylene or medium-density polyethylene, and may also contain 60% or more by mass of high-density polyethylene or medium-density polyethylene. Thus, by including high-density polyethylene or medium-density polyethylene in the polyethylene resin (b) at a higher content, the low curl resistance, heat resistance, moisture resistance, and mechanical properties of the multilayer film of this disclosure can be further improved.

[0037] As for polyethylene resin (b), resins with a unimodal or multimodal molecular weight distribution can be appropriately selected. By using multimodal resins, melt molding properties and mechanical properties can sometimes be achieved at a high level of uniformity. When polyethylene resin (b) contains linear low-density polyethylene or other ethylene-α-olefin copolymers, the α-olefin copolymerized with ethylene is preferably an α-olefin with 4 or more carbon atoms, more preferably an α-olefin with 6 or more carbon atoms, and can also be an α-olefin with 8 or more carbon atoms. When the number of carbon atoms in the α-olefin copolymerized with ethylene is large, various mechanical strengths such as puncture resistance and elongation at break can sometimes be particularly improved. There is no particular upper limit to the number of carbon atoms in the α-olefin, but it is usually 12 or less.

[0038] Metallocene catalysts can also be used as polymerization catalysts for polyethylene resins (b). Polyethylene resins (b) polymerized using metallocene catalysts exhibit excellent melt moldability, and the resulting multilayer films achieve an excellent balance between flexibility and mechanical strength.

[0039] From the viewpoint of making the effects of this disclosure more significant, the density (dB) of the subepidermal layer (B) is preferably less than the density (dA) of the epidermal layer (A) and greater than the density (dC) of the core layer (C), for example, 0.91 to 0.96 g / cm³, preferably 0.915 to 0.955 g / cm³, more preferably 0.920 to 0.950 g / cm³, and may also be 0.925 to 0.945 g / cm³.

[0040] The melting point of the polyethylene resin (b) can be, for example, 115~135°C or 118~130°C. From the viewpoint of improving melt moldability and the mechanical properties of multilayer films, the MFR (at 190°C and 2160g load) of the polyethylene resin (b) measured according to the method described in JIS K 7210 (2014) is preferably 0.1~10g / 10min, more preferably 0.3~5.0g / 10min, and even more preferably 0.5~2.0g / 10min.

[0041] The subskin layer (B) may contain other components besides the polyethylene resin (b), provided that it does not impair the effects of this disclosure. Examples of such other components include alkali metal ions, polyvalent metal ions, carboxylic acids, phosphoric acid compounds, boron compounds, oxidation accelerators, antioxidants, plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, pigments, dyes, processing aids, flame retardants, 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 resins other than the polyethylene resin (b). Examples of resins other than polyethylene resin (b) include thermoplastic resins such as polyolefins, polyamides, polyesters, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate, and polyvinyl alcohol resin. The content of the aforementioned resins other than polyethylene resin (b) in the sub-skin 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.

[0042] Of the resin constituting the subskin layer (B), the proportion of polyethylene resin (b) is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and can 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 also be composed solely of polyethylene resin (b). The content of polyethylene resin (b) in the subskin layer (B) is greater 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 can be 95% by mass or more, 97% by mass or more, or 99% by mass or more. The subskin layer (B) may also be substantially composed solely of polyethylene resin (b).

[0043] The method for manufacturing the resin composition constituting the sub-skin layer (B) is not particularly limited, and it can be manufactured by melt-blending a polyethylene resin (b) with other additives added as needed. Melt-blending can be performed using known mixing or blending equipment such as kneaders, extruders, mixing rollers, and Banbury mixers. The temperature range during melt-blending can be appropriately adjusted according to the melting point of the polyethylene resin (b) used, and is typically 150–300°C.

[0044] In another approach, polyethylene resin (b) can be melt-blended to produce a masterbatch containing a high concentration of other additives as needed. This masterbatch is then dry-blended with polyethylene resin (b) that is substantially free of other additives to produce the sub-skin layer (B). Alternatively, polyethylene resin (b) and other additives can be dry-blended to produce the sub-skin layer (B). Dry blending refers to mechanical mixing in powder or granular form. Mixing can be performed using mixing devices such as drum mixers, ribbon mixers, and Henschel mixers, or by manual stirring or vibration in a closed container. The mixing temperature only needs to be between room temperature and below the melting point of polyethylene resin (b), and mixing can be performed in an air atmosphere or a nitrogen atmosphere.

[0045] <Adhesive Layer (D)> The multilayer film disclosed herein has an adhesive layer (D) comprising an adhesive resin (d) with a melting point below 150°C as the main component. By including the adhesive layer (D) in the multilayer film of this disclosure, a multilayer film with excellent appearance and interlayer adhesion is tended to be obtained. As the adhesive resin (d), examples include acid-modified polyolefin resins, with acid-modified polyethylene resins being preferred. As the acid-modified polyolefin resin, a carboxylic acid-modified polyolefin resin is preferred, more preferably a polyolefin resin obtained by modification with unsaturated carboxylic acids or their derivatives, and even more preferably a carboxylic acid-modified polyolefin resin obtained by grafting and polymerizing unsaturated carboxylic acids or their derivatives, such as maleic anhydride, onto a polyolefin resin. A carboxylic acid-modified polyethylene resin obtained by grafting and polymerizing unsaturated carboxylic acids or their derivatives, such as maleic anhydride, onto a polyethylene resin is also preferred. In this case, as the polyethylene resin, substances exemplified as polyethylene resin (a), polyethylene resin (b), or polyethylene resin (c) can preferably be used.

[0046] The content of 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. The adhesive resin (d) may also be substantially composed of only modified polyolefin resin. The proportion of 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. It may be 97% by mass or more, 98% by mass or more, or 99% by mass or more, and may also be substantially composed of only adhesive resin (d).

[0047] From the viewpoint of making the effects of this disclosure more significant, the density (dD) of the adhesive layer (D) is preferably less than the density (dC) of the core layer (C), for example, less than 0.945 g / cm³, preferably 0.850 g / cm³ or more and less than 0.935 g / cm³, more preferably 0.880 g / cm³ or more and less than 0.925 g / cm³. The melting point of the adhesive resin (d) is below 150°C, preferably 100 to 130°C. From the viewpoint of improving melt-forming properties and the mechanical properties of the multilayer film, the MFR (at 190°C and 2160 g load) of the adhesive resin (d) measured according to 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 primarily on the density, melting point, and MFR of the polyolefin resin before carboxylic acid modification.

[0048] <Barrier Layer (E)> The multilayer film of this disclosure has a barrier layer (E) comprising EVOH(e) as a main component in its outermost layer. With this configuration, the gas barrier properties of the multilayer film of this disclosure are excellent. Because the barrier layer (E) has good affinity with the inorganic vapor-deposited layer (I) described later, the vapor-deposited multilayer film with the inorganic vapor-deposited layer (I) adjacent to the exposed surface of the barrier layer (E) exhibits further excellent barrier properties, particularly tending to maintain gas barrier properties even after being subjected to physical stresses such as bending. From the viewpoint of manufacturing such a vapor-deposited multilayer film, the multilayer film of this disclosure also needs to have a barrier layer (E) in its outermost layer. Multiple barrier layers (E) can be provided; in this case, it is sufficient that at least one barrier layer (E) is provided in the outermost layer.

[0049] EVOH(e) is typically obtained by polymerizing ethylene-ethylene esters with saponified ethylene. The ethylene unit content of EVOH(e) is 20 mol% or more and 30 mol% or less. If the ethylene unit content is 20 mol% or more, the melt-forming properties of EVOH(e) are improved, and the reusability of the multilayer film disclosed herein is improved. The ethylene unit content is preferably 21 mol% or more, more preferably 22 mol% or more, and sometimes preferably 23 mol% or more. On the other hand, if the ethylene unit content is 30 mol% or less, even with a small barrier layer (E) thickness, the gas barrier properties of the multilayer film disclosed herein are improved, and the low curling property is also improved, thus the conversion processability tends to become better. The ethylene unit content is preferably 28 mol% or less, more preferably 27 mol% or less, and may also be 26 mol% or less.

[0050] The degree of saponification of EVOH(e) is 90 mol% or more. The degree of saponification refers to the proportion of ethylene alcohol units in EVOH(e) relative to the total number of ethylene alcohol units and ethylene ester units. If the degree of saponification is 90 mol% or more, the gas barrier properties of the multilayer film of this disclosure are improved. The degree of saponification is preferably 95 mol% or more, more preferably 99 mol% or more, and even more preferably 99.9 mol% or more. The degree of saponification of EVOH(e) is typically 100 mol% or less. The ethylene unit content and degree of saponification of EVOH(e) are determined by ¹H-NMR.

[0051] EVOH(e) can be a mixture of two or more EVOHs with different ethylene unit contents, or a mixture of two or more EVOHs with different degrees of saponification.

[0052] EVOH(e) may contain monomer units other than ethylene, ethylene esters, and vinyl alcohol, provided that this does not impair the effects of the present disclosure. In particular, by introducing modifying groups containing primary hydroxyl groups with specific structures, it is sometimes possible to achieve a high level of both gas barrier properties and molding processability of EVOH(e). 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 absent. Other such monomers include, for example, α-olefins such as propylene, n-butene, isobutene, and 1-hexene; acrylic acid and its salts; unsaturated monomers having acrylate groups; methacrylic acid and its salts; unsaturated monomers having methacrylate groups; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetone acrylamide, acrylamide propanesulfonic acid and its salts, acrylamide propanedimethylamine and its salts (e.g., quaternary salts); methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamide propanesulfonic acid and its salts, methacrylamide propanedimethylamine and its salts (e.g., quaternary salts); methyl vinyl ethers, ethyl vinyl ethers, n-propyl vinyl ethers, isopropyl vinyl ethers, etc. Vinyl ethers such as n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, and 2,3-diacetoxy-1-vinyloxypropane; vinyl cyanide compounds such as acrylonitrile and methacrylonitrile; vinyl haloethylene compounds such as vinylidene chloride and vinylidene fluoride; vinylidene dihaloethylene compounds such as vinylidene chloride and vinylidene fluoride; allyl acetate, 2,3-diacetoxy-1-allyloxypropane, and allyl chloride; unsaturated dicarboxylic acids and their salts or esters such as maleic acid, itaconic acid, and fumaric acid; vinyl silane compounds such as vinyltrimethoxysilane; isopropyl acetate, 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, and 1,3-dibutyryloxy-2-methylenepropane, etc.

[0053] The melt flow rate (MFR) of EVOH(e) as measured according to JIS K 7210 (2014) (at 210°C and 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 sometimes preferably 4 g / 10 min or less, 3 g / 10 min or less, or 2.5 g / 10 min or less. If the MFR of EVOH(e) is within the above range, the melt formability of EVOH(e) and the pulverized product containing the multilayer film of EVOH(e) is improved.

[0054] <Polyvalent metal ions (f)> The barrier layer (E) preferably contains at least one polyvalent metal ion (f) selected from magnesium ions, calcium ions, and zinc ions, and its content is preferably 10 to 300 ppm. If the content of the polyvalent metal ion (f) is 10 ppm or more, it tends to suppress thickening and appearance defects such as gelation or foreign matter formation during melt molding. On the other hand, if the content of the polyvalent metal ion (f) is 300 ppm or less, it tends to suppress excessive decomposition and coloring during melt molding. When reusing the multilayer film of this disclosure, when melt molding the pulverized multilayer film, the cross-linking reaction of the resin sometimes occurs, causing thickening and gelation. However, by containing a certain amount of polyvalent metal ions (f), thickening, gelation, and resin adhesion to the screw can be suppressed. From this point of view, the content of polyvalent metal ions (f) is preferably 15 to 240 ppm, more preferably 20 to 200 ppm, even more preferably 30 to 150 ppm, and sometimes preferably 30 to 100 ppm. The barrier layer (E) preferably contains magnesium or calcium ions as the polyvalent metal ion (f), and more preferably magnesium ions. By controlling the ratio of the polyvalent metal ion (f) to the carboxylic acid described later, melt formability and colorfastness can be further improved.

[0055] Examples of polyvalent metal compounds that provide polyvalent metal ions (f) include aliphatic carboxylates, aromatic carboxylates, carbonates, hydrochlorides, nitrates, sulfates, phosphates, hydroxides, and metal complexes of magnesium, calcium, and zinc. Aliphatic carboxylates and hydroxides are preferred from the viewpoint of ease of acquisition and processing. Acetates, octanoates, and stearates are preferred as aliphatic carboxylates.

[0056] <Higher aliphatic carboxylic acids (g)> The barrier layer (E) preferably contains a higher aliphatic carboxylic acid (g) having 8 to 30 carbon atoms, and its content is preferably 100 to 6000 ppm. The higher aliphatic carboxylic acid (g) may be contained in its salt form, either partially or entirely, or in the form of a salt of a polyvalent metal ion (f) or an alkali metal ion described later. As the higher aliphatic carboxylic acid (g), a higher aliphatic carboxylic acid having 8 to 20 carbon atoms is preferred, and octanoic acid or stearic acid is more preferred. The multilayer film of this disclosure has a barrier layer (E) on its outermost layer, which can be considered to act as a lubricant for the metal surface of the die head, thereby suppressing appearance defects caused by uneven thickness of the multilayer film, gelation caused by retained resin, and the generation of foreign matter. Therefore, the barrier layer (E) preferably contains more than 100 ppm of higher aliphatic carboxylic acid (g). On the other hand, if the content of higher aliphatic carboxylic acids (g) is below 6000 ppm, it tends to suppress thickening during melt molding of the barrier layer (E) or maintain interlayer adhesion with the adhesive layer (D). From these points of view, the content of higher aliphatic carboxylic acids (g) is more preferably 200 to 4000 ppm, more preferably 300 to 3000 ppm, and sometimes preferably 400 to 2500 ppm, 500 to 2200 ppm, 600 to 2000 ppm or 700 to 1500 ppm.

[0057] The barrier layer (E) may contain other components besides EVOH(e), polyvalent metal ions (f), and higher aliphatic carboxylic acids (g), provided that it does not impair the effects of this disclosure. Examples of such other components include: alkali metal ions, alkaline earth metal ions (excluding polyvalent metal ions (f)) and transition metal ions, carboxylic acids (monocarboxylic acids, polycarboxylic acids) other than higher aliphatic carboxylic acids (g), thermoplastic resins other than EVOH(e), phosphoric acid compounds, boron compounds, oxidation accelerators, antioxidants (hindered phenolic compounds, etc.), plasticizers, heat stabilizers (melt stabilizers), photoinitiators, deodorizers, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, fillers, pigments, dyes, processing aids, flame retardants, antifogging agents, etc. From the viewpoint of suppressing foreign matter and coloring during the melt-forming of pulverized multilayer films containing the barrier layer (E), it is preferable to contain alkali metal ions, carboxylic acids, and / or phosphoric acid compounds. By using boron compounds, the melt viscosity of the pulverized material containing the barrier layer (E) and the multilayer film containing the barrier layer (E) can be controlled.

[0058] Alkali metal ions The barrier layer (E) may contain 40 to 500 ppm of alkali metal ions. By including alkali metal ions in the barrier layer (E) within this range, the interlayer adhesion with the adhesive layer (D) tends to be significantly improved. From this perspective, 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. If the alkali metal ion content is above the lower limit, it is less likely to thicken during melt molding, less likely to produce appearance defects such as gels or foreign matter, or further improves the interlayer adhesion with the adhesive layer (D). On the other hand, if the alkali metal ion content is below the upper limit, it is easier to suppress excessive decomposition during melt molding, and coloring is less likely to become a problem. By controlling the ratio of alkali metal ions to the carboxylic acid described later, melt moldability and colorfastness can be further improved.

[0059] Examples of alkali metal ions include lithium, sodium, potassium, rubidium, and cesium ions. From an industrial point of view, sodium or potassium ions are preferred, and sodium ions are more preferred. By using potassium ions, it is sometimes possible to achieve a high level of balance between the hue of the barrier layer (E) and the interlayer adhesion with the adhesive layer (D). They can be used individually or in combination of two or more.

[0060] Alkali metal compounds that provide alkali metal ions include, for example, aliphatic carboxylates, aromatic carboxylates, carbonates, hydrochlorides, nitrates, sulfates, phosphates, hydroxides, and metal complexes of alkali metals such as lithium, sodium, and potassium. Aliphatic carboxylates and phosphates are preferred from the viewpoint of ease of acquisition and processing. As aliphatic carboxylates, acetates, octanoates, and stearates are preferred.

[0061] <Carboxylic acid> The barrier layer (E) preferably contains carboxylic acids other than higher aliphatic carboxylic acids (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, there is a tendency for improved colorfastness. On the other hand, when the carboxylic acid content is 400 ppm or less, there is a tendency to maintain interlayer adhesion and suppress odor generation.

[0062] The pKa of the carboxylic acid is preferably 3.5 to 5.5. If the pKa of the carboxylic acid is within the above range, the pH buffering capacity of the resulting barrier layer (E) is improved, which can further improve melt formability and further improve coloring caused by acidic and / or alkaline substances.

[0063] Carboxylic acids can be monocarboxylic acids. These can be used alone or in combination of two or more. A monocarboxylic acid is a compound having only one carboxyl group within its molecule. Monocarboxylic acids with a pKa in the range of 3.5 to 5.5 are not particularly limited; examples 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 substituents such as hydroxyl, amino, or halogen atoms. Acetic acid is preferred from the viewpoint of high safety, ease of acquisition, and processing.

[0064] The carboxylic acid can be a polycarboxylic acid. When the carboxylic acid is a polycarboxylic acid, it can sometimes further improve the colorfastness at high temperatures and the colorfastness of the resulting multilayer film fragments and melt-molded parts. Polycarboxylic acid compounds preferably have three or more carboxyl groups. In this case, the colorfastness can sometimes be improved more effectively. A polycarboxylic acid is a compound having two or more carboxyl groups within its molecule. In this case, it is preferable that at least one carboxyl group has a pKa in the range of 3.5 to 5.5. Examples 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=5.41), 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), and aspartic acid (pKa=3.90).

[0065] <Phosphoric compounds> The barrier layer (E) may further contain a phosphoric acid compound. The lower limit of the phosphoric acid compound content, expressed in terms of phosphate ions, is preferably 5 ppm. On the other hand, the upper limit of the phosphoric acid compound content, expressed in terms of phosphate ions, is preferably 100 ppm. By containing a phosphoric acid compound within this range, it is sometimes possible to suppress the coloring of the resulting barrier layer (E) and the melt-molded fragments of the resulting multilayer film, thereby improving thermal stability. "Phosphate ion conversion" refers to converting the content of phosphorus element (P) into phosphate ions (PO4). 3- The value after the content of ).

[0066] As a phosphoric acid compound, various acids such as phosphoric acid and phosphorous acid and their salts can be used. The phosphate can be any of dihydrogen phosphate, monohydrogen phosphate, or phosphate. The type of cation in the phosphate is not particularly limited, but alkali metals and alkaline earth metals are preferred. Among these, sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate are preferred as phosphoric acid compounds.

[0067] <Boron compounds> The barrier layer (E) may further contain boron compounds. When boron compounds are present, the lower limit of the boron content in the barrier layer (E), calculated in boron elemental form, is preferably 50 ppm, more preferably 100 ppm. On the other hand, the upper limit of the boron content in the barrier layer (E), calculated in boron elemental form, is preferably 400 ppm, more preferably 300 ppm, and even more preferably 200 ppm. By containing boron compounds within this range, the thermal stability of the barrier layer (E) and the resulting multilayer film fragments during melt molding can sometimes be improved, suppressing the formation of gels and foreign matter. Sometimes, it can improve sag resistance, resistance to necking during film formation, and sometimes improve the mechanical properties of the resulting molded article. It is presumed that these effects are due to the chelating interaction between EVOH(e) and the boron compounds.

[0068] Examples of boron compounds include boric acid, borate esters, borates, and borohydrides. Specifically, examples include orthoboric acid (H3BO3), metaboric acid, tetraboric acid, and other boric acids; trimethyl borate, triethyl borate, and other borate esters; alkali metal salts or alkaline earth metal salts of the above boric acids; and borates such as borax. Orthoboric acid is preferred.

[0069] The barrier layer (E) may further contain thermoplastic resins 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 with α-olefins having 4 or more carbon atoms, copolymers of polyolefins with maleic anhydride, ethylene-vinyl ester copolymers, ethylene-acrylate copolymers, or modified polyolefins obtained by grafting them with unsaturated carboxylic acids or their derivatives), various polyamides (nylon 6, nylon 6,6, nylon 6 / 66 copolymers, nylon 11, nylon 12, poly(hexamethylene isophthalamide), etc.), various polyesters (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate), polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate, and modified polyvinyl alcohol resins, etc. The content of the above-mentioned thermoplastic resin in the barrier layer (E) is generally 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, may be less than 5% by mass or less than 1% by mass, and is particularly preferably substantially free of it.

[0070] From the viewpoint of maximizing the effects of this 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. The resin constituting the barrier layer (E) may also be substantially composed of only EVOH(e). From the viewpoint of maximizing the effects of this 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 sometimes preferably 98% by mass or more or 99% by mass or more. The barrier layer (E) may also be substantially composed of only EVOH(e).

[0071] The method for manufacturing the barrier layer (E) is not particularly limited, and it can be manufactured by melt-blending EVOH(e), and, as needed, polyvalent metal ions (f), higher aliphatic carboxylic acids (g), and / or other components. The components can be in solid form such as powder or in a melt, or in the form of solutes contained in a solution or dispersed phases contained in a dispersion. As solutions and dispersions, aqueous solutions and aqueous dispersions are preferred, respectively. Melt-blending can be performed using known mixing or blending equipment such as kneaders, extruders, mixing rollers, and Banbury mixers. The temperature range during melt-blending can be appropriately adjusted according to the EVOH(e) used and the melting points of each component, typically between 150 and 250°C. Alternatively, several components can be pre-added to EVOH(e), and then other desired components can be further added via melt-blending as described above. One method for pre-adding several components to EVOH(e) is to impregnate EVOH(e) in granular or powder form in a solution containing the added components.

[0072] Multilayer film The multilayer film disclosed herein has a layer structure consisting of a skin layer (A), a core layer (C), an adhesive layer (D), and a barrier layer (E) stacked in at least this order, with the skin layer (A) located as one of the outermost layers of the multilayer film and the barrier layer (E) located as another outermost layer. Preferably, a sub-skin layer (B) is further provided between the skin layer (A) and the core layer (C). Examples of configurations for the multilayer film include the following. It should be noted that the skin layer (A) is referred to as "layer (A)", the sub-skin 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 " / " indicates that the layers on either side are directly stacked. Examples of the layer configurations of the multilayer film disclosed herein 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), etc. From the viewpoint of industrial productivity, 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 greater industrial productivity and more significant effects of the present disclosure, layer (A) / layer (B) / layer (C) / layer (D) / layer (E) is more preferred. In the layer configuration, it is particularly preferred that at least layer (C) and layer (D) are in direct contact and stacked, and it is even more preferred that at least layer (D) and layer (E) are in direct contact and stacked. More preferably, at least layer (C), layer (D), and layer (E) are in direct contact and stacked in this order.

[0073] The overall thickness of the multilayer film disclosed herein can be appropriately set according to the application. The overall thickness is preferably 10 μm or more, more preferably 12 μm or more. With an overall thickness of 10 μm or more, industrial productivity and mechanical properties tend to improve. The overall thickness is preferably 100 μm or less, more preferably 50 μm or less, further preferably 30 μm or less, and sometimes preferably 25 μm or less, 20 μm or less, or 15 μm or less. With an overall thickness of 100 μm or less, industrial productivity and economic efficiency tend to improve. It should be noted that the preferred overall thickness of the multilayer film described above refers to the thickness after stretching.

[0074] The core layer (C) is the thickest layer in the multilayer film of this disclosure. From the viewpoints of industrial productivity, low curling, and mechanical properties, the ratio of the thickness of the core layer (C) to the overall thickness of the multilayer film of this disclosure is preferably 0.3 to 0.8. This ratio is preferably 0.35 to 0.80, more preferably 0.40 to 0.75, and sometimes preferably 0.45 to 0.73 or 0.50 to 0.70.

[0075] From the viewpoints of industrial productivity, heat resistance, moisture resistance, low curling, and mechanical properties, the ratio of the thickness of the skin layer (A) to the overall thickness of the multilayer film of this disclosure is preferably 0.05 to 0.2. This ratio is more preferably 0.05 to 0.20, and even more preferably 0.05 to 0.15.

[0076] From the viewpoints of industrial productivity, heat resistance, gas barrier properties, low curling, and mechanical properties, the ratio of the thickness of the barrier layer (E) to the overall thickness of the multilayer film of this disclosure is preferably 0.05 to 0.2. This ratio is more preferably 0.05 to 0.20, even more preferably 0.05 to 0.18, and particularly preferably 0.05 to 0.15.

[0077] The multilayer film of this disclosure is stretched at least 3 times in the uniaxial direction. If the stretch ratio of the multilayer film of this disclosure is less than 3 times, uneven thickness caused by stretching or reduced gas barrier properties tend to occur. On the other hand, the upper limit of the stretch ratio of the multilayer film of this disclosure is generally 12 times. The multilayer film of this disclosure is preferably stretched at least 4 times in the uniaxial direction, more preferably at least 5 times. The multilayer film of this disclosure is preferably stretched at least 10 times or less in the uniaxial direction, more preferably at least 8 times. The multilayer film of this disclosure can be stretched in the uniaxial direction or in the biaxial direction, but from the viewpoint of economy and the ease with which the multilayer film is torn (easy to open when used as packaging material), uniaxial stretching is preferred, more preferably uniaxial stretching in the longitudinal direction (flow direction, MD direction), and even more preferably stretched at 3 times in the longitudinal direction (preferably 3 times or more and 12 times or less, more preferably 4 times or more and 10 times or less, and even more preferably 5 times or more and 8 times or less). In this case, it is preferable that it is not substantially stretched in the width direction (TD direction).

[0078] The multilayer film disclosed herein is preferably a blow-molded body. When the multilayer film of this disclosure is a blow-molded body, the effects of this disclosure can be more effectively realized.

[0079] The preferred method for manufacturing the multilayer film disclosed herein includes, for example, a step (I) of manufacturing an unstretched multilayer film by laminating a skin layer (A), a core layer (C), an adhesive layer (D), and a barrier layer (E) in at least this order, and a step (II) of stretching the obtained unstretched multilayer film at least in a uniaxial direction to manufacture the multilayer film of this disclosure. The preferred manufacturing method of this disclosure will be described in detail below, but the scope of this disclosure is not limited thereto.

[0080] In step (I), an unstretched multilayer film is formed by stacking the skin layer (A), core layer (C), adhesive layer (D), and barrier layer (E) in at least this order. The method for manufacturing the unstretched multilayer film is not particularly limited; conventional co-extrusion methods, in which each resin is extruded from individual dies or a shared die and then stacked, are generally used. As the die, either a ring die or a T-die can be used; examples include blow molding and casting, but blow molding is preferred from a productivity perspective.

[0081] In step (II), the unstretched multilayer film obtained in step (I) is stretched at least in a uniaxial direction. The stretching method is not particularly limited; examples include tenter frame stretching, tubular stretching, and roller stretching. From a productivity perspective, uniaxial stretching by roller stretching is preferred. When the unstretched multilayer film of this disclosure is a blow-molded body, roller stretching is also preferred from the viewpoint that it is easy to stretch the folded cylindrical unstretched multilayer film after blow molding in a uniaxial direction. The stretching temperature is typically in the range of 50°C to 140°C, but more preferably 100°C to 130°C.

[0082] The multilayer film of this disclosure does not have a layer containing a resin with a melting point of 220°C or higher as a main component. Because it does not have a layer containing a resin with a melting point of 220°C or higher as a main component, it is easier to prevent uneven mixing with other components during the melt-forming process of the multilayer film, vapor-deposited multilayer film, or recycled multilayer structure described above. Preferably, the multilayer film of this disclosure does not have a layer containing a resin with a melting point of 210°C or higher as a main component, and more preferably, it does not have a layer containing a resin with a melting point of 200°C or higher as a main component. For the same reason, it is also preferable not to have a metal layer with a thickness of 1 μm or more.

[0083] <Inorganic vapor deposition layer (I)> Another aspect of this disclosure is a vapor-deposited multilayer film in which an inorganic vapor-deposited layer (I) is present on the exposed side of the barrier layer (E) of the multilayer film. The inorganic vapor-deposited layer (I) is preferably laminated directly or indirectly through other layers such as an anchor coating onto the exposed side of the barrier layer (E) of the multilayer film, and more preferably directly onto the exposed side of the barrier layer (E). The inorganic vapor-deposited layer (I) can be formed by vapor-depositing inorganic materials such as metals and inorganic oxides, and is typically a layer that provides barrier properties against oxygen and water vapor. Since the barrier layer (E) has a higher affinity for metals and inorganic oxides than conventional thermoplastic resins, by directly laminating the inorganic vapor-deposited layer (I) onto the exposed side of the barrier layer (E), a dense and defect-free inorganic vapor-deposited layer (I) can be formed, and the interlayer adhesion between the barrier layer (E) and the inorganic vapor-deposited layer (I) in the resulting vapor-deposited multilayer film becomes particularly good. Because the barrier layer (E) has high gas barrier properties, even when defects occur in the inorganic vapor-deposited layer (I) due to bending or other reasons, the reduction in gas barrier properties can be suppressed. The average thickness of the inorganic vapor-deposited layer (I) is preferably less than 500 nm. With an average thickness of less than 500 nm, excellent viscosity stability is achieved when pulverizing a multilayer structure containing the inorganic vapor-deposited layer (I), thus suppressing the formation of gels and foreign matter.

[0084] The inorganic vapor-deposited layer (I) is preferably either a metal vapor-deposited layer containing aluminum as the main component or an inorganic oxide vapor-deposited layer containing inorganic oxides as the main component. While a metal vapor-deposited layer is preferred for providing light-shielding properties, an inorganic oxide vapor-deposited layer is preferred from the viewpoints of ensuring the visibility of the contents as packaging material, microwave oven applicability, and suppressing the formation of gels and foreign matter during melt-forming and crushing. An inorganic oxide vapor-deposited layer is also preferred from the viewpoint of suppressing coloration during the reuse of the vapor-deposited multilayer film.

[0085] The metal vapor-deposited layer is a layer containing aluminum as the main component. The aluminum atom content in the metal vapor-deposited layer is preferably greater than 50 mol%, more preferably 60 mol% or more, further preferably 70 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and sometimes preferably 98 mol% or more, 99 mol% or more, or 99.9 mol% or more. The average thickness of the metal vapor-deposited layer is preferably less than 120 nm, more preferably less than 100 nm, and further preferably less than 90 nm. The average thickness of the metal vapor-deposited layer is preferably more than 25 nm, more preferably more than 35 nm, and further preferably more than 45 nm. "Average thickness of the metal vapor-deposited layer" refers to the average thickness of any 10 points on the cross-section of the metal vapor-deposited layer measured by an electron microscope. When the multilayer film of this disclosure has a metal vapor-deposited layer, the light transmittance at a wavelength of 600 nm can be less than 10%, exhibiting excellent light-shielding properties.

[0086] In metal vapor-deposited layers with aluminum as the main component, oxidation is inevitable, and sometimes aluminum oxide is partially present. In metal vapor-deposited layers with aluminum as the main component, the molar ratio of oxygen atom content to 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.

[0087] An inorganic oxide vapor-deposited layer is a layer containing inorganic oxides as the main component. The content of inorganic oxides in the metal vapor-deposited layer is preferably greater than 50 mol%, more preferably 60 mol% or more, further preferably 70 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and sometimes preferably 98 mol% or more, 99 mol% or more, or 99.9 mol% or more. Examples of inorganic oxides include oxides of silicon, aluminum, magnesium, calcium, potassium, tin, sodium, boron, titanium, lead, zirconium, yttrium, etc., with alumina or silicon dioxide being preferred. The average thickness of the inorganic oxide vapor-deposited layer is preferably 60 nm or less, more preferably 50 nm or less, and further preferably 40 nm or less. The average thickness of the inorganic oxide vapor-deposited layer is preferably 8 nm or more, more preferably 12 nm or more, and further preferably 16 nm or more. "The average thickness of the inorganic oxide vapor-deposited layer" refers to the average thickness of any 10 points on the cross-section of the inorganic oxide vapor-deposited layer measured by an electron microscope. When the multilayer film of this disclosure has an inorganic oxide vapor-deposited layer, the light transmittance at a wavelength of 600 nm can be 80% or more, resulting in excellent visibility of the contents when used as a packaging material. From the viewpoint of further improving visibility, the light transmittance at a wavelength of 600 nm is more preferably 90% or more.

[0088] The inorganic vapor-deposited layer (I) can be formed by known physical vapor deposition or chemical vapor deposition methods. Specific examples include vacuum vapor deposition, sputtering, ion plating, ion beam mixing, plasma CVD, laser CVD, MO-CVD, and thermal CVD, with physical vapor deposition being preferred, and vacuum vapor deposition being particularly preferred. The upper limit of the surface temperature of the barrier layer (E) during the formation of the inorganic vapor-deposited layer (I) is preferably 60°C, more preferably 55°C, and even more preferably 50°C. The lower limit of the surface temperature of the barrier layer (E) during the formation of the inorganic vapor-deposited layer (I) is not particularly limited, but is preferably 0°C, more preferably 10°C, and even more preferably 20°C. Before forming the film, the exposed surface of the barrier layer (E) can be subjected to plasma treatment. The plasma treatment can use known methods, with atmospheric pressure plasma treatment being preferred. In atmospheric pressure plasma treatment, nitrogen, helium, neon, argon, krypton, xenon, radon, etc., are used as discharge gases. Nitrogen, helium, and argon are preferred, with nitrogen being particularly preferred due to its cost-effectiveness.

[0089] <Multi-layer structure> Another aspect of this disclosure is the formation of a multilayer structure comprising a resin layer (R) containing a thermoplastic resin (r) as a main component on the multilayer film or vapor-deposited multilayer film. The content of thermoplastic resin (r) in the resin layer (R) is greater than 50 mol%, preferably 60 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, particularly preferably 95 mol% or more, and sometimes preferably 98 mol% or more, 99 mol% or more, or 99.9 mol% or more. While the multilayer film or vapor-deposited multilayer film of this disclosure can be used on its own as a packaging material with gas barrier properties, by forming a multilayer structure having at least one resin layer (R) containing a thermoplastic resin (r) as a main component, various functions as a packaging material, such as design and heat-sealing properties, can be imparted. Thermoplastic resin(r) is not particularly limited, and examples 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 with 4 to 20 carbon atoms), homopolymers or copolymers of olefins such as polybutene and polypentene, 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 resin, polycarbonate, chlorinated polyethylene, and chlorinated polypropylene. Among these, polyolefins are preferred from the viewpoint of superior moisture resistance, mechanical properties, economy, and heat-sealing properties; polyamides and polyesters are preferred from the viewpoint of superior mechanical properties and heat resistance. In particular, for obtaining a multilayer structure with excellent reusability, the thermoplastic resin(r) is more preferably the same as the aforementioned polyethylene resin. The resin layer (R) can be unstretched, or it can be stretched or calendered in a uniaxial or biaxial direction. From the viewpoint of improving mechanical strength, a biaxially stretched layer is preferred; from the viewpoint of improving heat-sealing properties, an unstretched layer is preferred.

[0090] When the multilayer structure of this disclosure has multiple resin layers (R), they may be the same as or different from each other, but are generally different. In addition, the resin layer (R) may be thicker or thinner than the core layer (C).

[0091] The method for forming the resin layer (R) is not particularly limited, but it is usually formed by melt extrusion using an extruder. As the die, either a ring die or a T-die can be used. The method of stretching in the uniaxial or biaxial direction is also not particularly limited; conventional and well-known stretching methods such as roller uniaxial stretching, tubular simultaneous biaxial stretching, tenter frame successive biaxial stretching, and tenter frame simultaneous biaxial stretching can be used to stretch the film in the flow direction and / or width direction. In the case of a uniaxially stretched layer, from the viewpoint of uniformity of the resulting layer thickness and mechanical strength, a stretching ratio of 3 to 10 times is preferred. An area ratio of 4 times or more is more preferred. An area ratio of 9 times or less is more preferred, and 8 times or less is even more preferred. If the area ratio is 3 times or more, stretching spots are less likely to remain; if it is 10 times or less, the layer is less likely to break during stretching. In the case of a biaxially stretched layer, from the viewpoint of uniformity of the resulting layer thickness and mechanical strength, a stretching ratio of 10 to 60 times is preferred. The area ratio is more preferably 20 times or more, even more preferably 30 times or more, and can also be 40 times or more. The area ratio is more preferably 55 times or less, even more preferably 50 times or less. If the area ratio is 10 times or more, stretch marks are less likely to remain; if it is 60 times or less, the layer is less likely to break during stretching.

[0092] From the viewpoint of industrial productivity, the thickness of the resin layer (R) is preferably 10 to 200 μm. 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.

[0093] The total thickness of the multilayer structure disclosed herein is preferably 300 μm or less, more preferably 200 μm or less, and sometimes more preferably 150 μm or less, 130 μm or less, 100 μm or less, or 80 μm or less. By keeping the total thickness within the above range, the multilayer structure of this disclosure is lightweight and flexible, and therefore preferably used for flexible packaging applications. The multilayer structure uses a small amount of resin, thus suppressing environmental load.

[0094] The thickness of each layer in the multilayer structure disclosed herein can be appropriately adjusted according to the application. However, from the viewpoint of suppressing coloration during melt molding of pulverized material, improving thermal stability during melt molding, and suppressing the generation of foreign matter, the ratio of the total thickness of the multilayer structure to the total thickness of the layers containing polyethylene resin as the main component 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 also be 0.95 or more. On the other hand, from the viewpoint of improving gas barrier properties, the above ratio is preferably 0.99 or less.

[0095] The method for laminating resin layers (R) on the multilayer film disclosed herein is not particularly limited, and examples include extrusion lamination, co-extrusion lamination, and dry lamination. When laminating resin layers (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 then drying it. The adhesive is preferably a two-component reactive polyurethane adhesive that reacts a polyisocyanate component with a polyol component. The thickness of the adhesive layer is not particularly limited, but is preferably 1 to 5 μm, more preferably 2 to 4 μm.

[0096] The layer composition of the multilayer structure disclosed herein is not particularly limited, but the following multilayer structure compositions can be exemplified, for example. It should be noted that, hereinafter, the multilayer film of this disclosure will be referred to as film (AE), and the resin layer (R) will be referred to as layer (R)". " / / " indicates that the layers on both sides are stacked directly or through an adhesive layer. Examples of layer compositions for the multilayer structure of this disclosure include layer (R) / / film (AE), film (AE) / / layer (R), layer (R) / / film (AE) / / layer (R), etc.

[0097] Without impairing the effects of this disclosure, the multilayer structure of this disclosure may have other layers besides those described above. Examples of other layers include a recycling layer. It is particularly preferred to reuse the recycling composition containing the recyclable material of the multilayer structure of this disclosure (described later) as part or all of the recycling layer. Another example of other layers is a printing layer. The printing layer may be included at any location within the multilayer structure of this disclosure. As a printing layer, for example, a film obtained by coating and drying a solution containing pigments or dyes and, if necessary, a binder resin can be used. Besides gravure printing, various coating methods using wire rods, spin coaters, die coaters, etc., can be used for coating the printing layer. The thickness of the ink layer is not particularly limited, but is preferably 0.5 to 10 μm, more preferably 1 to 4 μm.

[0098] The oxygen permeability (OTR) of the multilayer structure disclosed herein under conditions of 20°C and 65%RH can be appropriately adjusted according to the application, without particular limitation. The multilayer structure of this disclosure is preferably used for high-barrier applications without the inorganic vapor-deposited layer (I), and is preferably used for applications requiring even higher barrier properties when the inorganic vapor-deposited layer (I) is present. In the former case, the OTR is preferably 1 cc / (m²·day·atm) or less, more preferably 0.4 cc / (m²·day·atm) or less, and even more preferably 0.1 cc / (m²·day·atm) or less. In the latter case, the OTR is preferably 0.1 cc / (m²·day·atm) or less, more preferably 0.05 cc / (m²·day·atm) or less, and even more preferably 0.03 cc / (m²·day·atm) or less. In particular, the OTR remains at a low level even after physical damage such as bending and stretching, which further improves its suitability as a packaging material. OTR was measured according to JIS K 7126-2 (isobaric method; 2006), specifically using the method described in the examples.

[0099] The water vapor transmission rate (WVTR) of the multilayer structure disclosed herein under conditions of 40°C and 90%RH can be appropriately adjusted according to the application, without particular limitation. The multilayer structure of this disclosure is preferably used for high-barrier applications without the inorganic vapor-deposited layer (I), and is preferably used for applications requiring even higher barrier properties when the inorganic vapor-deposited layer (I) is present. In the former case, the WVTR is preferably 5 g / (m²·day) or less, more preferably 4 g / (m²·day) or less, and even more preferably 3 g / (m²·day) or less. In the latter case, the WVTR is preferably 1 g / (m²·day) or less, more preferably 0.5 g / (m²·day) or less, and even more preferably 0.3 g / (m²·day) or less. In particular, the WVTR remains at a low level even after physical damage such as bending and stretching, which further improves its suitability as a packaging material. The WVTR is measured according to JIS K 7129-2 (infrared sensor method; 2019).

[0100] It is preferable to reuse the recycled materials of the multilayer films, vapor-deposited multilayer films, or multilayer structures disclosed herein. Examples of such recycled materials include end products or defective products generated during the manufacture of the multilayer films, vapor-deposited multilayer films, or multilayer structures disclosed herein, which are then recycled (waste). Methods for recycling multilayer films, vapor-deposited multilayer films, or multilayer structures that include the process of pulverizing the aforementioned recycled materials and then melt-forming them, as well as recycled compositions containing the aforementioned recycled materials, are also preferred embodiments of this disclosure. Methods for manufacturing films using the aforementioned recycled compositions as raw materials are also preferred embodiments of this disclosure.

[0101] As a method for manufacturing the above-mentioned recycled composition, firstly, the recycled material is pulverized. The pulverized recycled material can be directly melt-molded to obtain the recycled composition, or it can be melt-molded together with other components as needed to obtain the recycled composition. As a preferred component to be added to the recycled material, a polyolefin resin is preferred, and the above-mentioned polyethylene resin is more preferred. The pulverized recycled material can be directly used to manufacture molded articles such as multilayer structures, or the pulverized recycled material can be melt-molded to obtain granules composed of the recycled composition, and then the granules can be used to manufacture molded articles.

[0102] In the recycled composition, the mass ratio of EVOH(e) to polyolefin resin [EVOH(e) / polyolefin resin] is preferably 0.01 / 99.99 to 20 / 80. When the mass ratio is less than 0.01 / 99.99, there is a risk of a decrease in the utilization rate of the recycled material. On the other hand, when the mass ratio is greater than 20 / 80, the melt-forming properties and mechanical properties of the recycled composition may sometimes decrease. From the viewpoint of improving the melt-forming properties and mechanical properties of the obtained recycled composition, the mass ratio is more preferably 15 / 85 or less, even more preferably 10 / 90 or less, and may also be 5 / 95 or less.

[0103] Because the multilayer structure disclosed herein has high barrier properties and excellent processability, it is suitable for use as a material for various packaging such as food packaging, pharmaceutical packaging, industrial drug packaging, and pesticide packaging. In particular, packaging materials with the multilayer structure disclosed herein are suitable for use as packaging materials with excellent reusability. Example

[0104] The present invention will now be described in more detail using examples. These examples do not limit the scope of the invention.

[0105] <Materials Used> • Polyethylene resins (a) a-1: High-density polyethylene "Erite (trademark) AT6900" manufactured by Dooke Mikael Co., Ltd. (copolymer of ethylene and 1-octene, density 0.969 g / cm³, melting point 134℃, MFR (190℃, 2.16 kg load) 1.2 g / 10 minutes) a-2: High-density polyethylene "Elite (trademark) 5538G" manufactured by Dooke Mikael Co., Ltd. (copolymer of ethylene and 1-octene, density 0.941 g / cm³, melting point 129°C, MFR (190°C, 2.16 kg load) 1.3 g / 10 minutes). a-3: Medium-density polyethylene "Elite (trademark) 5110G" manufactured by Dooke Mikael Co., Ltd. (copolymer of ethylene and 1-octene, density 0.926 g / cm³, melting point 123°C, MFR (190°C, 2.16 kg load) 0.85 g / 10 minutes). AC-1: Dookemical Co., Ltd. manufactures linear low-density polyethylene "Elite (trademark) 5400G" (a copolymer of ethylene and 1-octene, density 0.916 g / cm³, melting point 123°C, MFR (190°C, 2.16 kg load) 1.0 g / 10 minutes). • Polyethylene resins (b) b-1: High-density polyethylene "Elite (trademark) 5538G" manufactured by Dooke Mikael Co., Ltd. (copolymer of ethylene and 1-octene, density 0.941 g / cm³, melting point 129°C, MFR (190°C, 2.16 kg load) 1.3 g / 10 minutes) b-2: Medium-density polyethylene "Elite (trademark) 5110G" manufactured by Dooke Mikael Co., Ltd. (copolymer of ethylene and 1-octene, density 0.926 g / cm³, melting point 123°C, MFR (190°C, 2.16 kg load) 0.85 g / 10 minutes). • Polyethylene resins (c) c-1: Dookemical Co., Ltd. manufactures linear low-density polyethylene "Elite (trademark) 5400G" (a copolymer of ethylene and 1-octene, density 0.916 g / cm³, melting point 123°C, MFR (190°C, 2.16 kg load) 1.0 g / 10 minutes). cc-1: High-density polyethylene "Elite (trademark) AT6900" manufactured by Dooke Mikael Co., Ltd. (copolymer of ethylene and 1-octene, density 0.969 g / cm³, melting point 134°C, MFR (190°C, 2.16 kg load) 1.2 g / 10 minutes) • Adhesive resin (d) d-1: Maleic anhydride modified polyethylene "Admirer (trademark) AT1955E" manufactured by Mitsui Chemicals Co., Ltd. (density 0.89 g / cm³, melting point 111°C, MFR (190°C, 2.16 kg load) 2.6 g / 10 minutes) • EVOH (e), polyvalent metal ions (f), and higher aliphatic carboxylic acids (g) e-1: EVOH, ethylene unit content 24 mol%, saponification degree 99.9 mol%, contains sodium acetate (250 ppm based on sodium ions), phosphate ions (20 ppm based on phosphate ions), and magnesium stearate (50 ppm based on magnesium ions), MFR (210℃, 2.16 kg load) 2.2 g / 10 min e-2: EVOH, ethylene unit content 27 mol%, saponification degree 99.9 mol%, contains sodium acetate (250 ppm based on sodium ions), phosphate ions (20 ppm based on phosphate ions), boric acid (150 ppm based on boron element), and magnesium stearate (50 ppm based on magnesium ions), MFR (210℃, 2.16 kg load) 4.0 g / 10 minutes e-3: EVOH, ethylene unit content 24 mol%, saponification degree 99.9 mol%, contains sodium acetate (equivalent to 250 ppm sodium ions) and phosphate ions (equivalent to 20 ppm phosphate ions), MFR (210℃, 2.16 kg load) 2.2 g / 10 min e-4: EVOH, ethylene unit content 24 mol%, saponification degree 99.9 mol%, contains sodium acetate (250 ppm based on sodium ions), phosphate ions (20 ppm based on phosphate ions), and magnesium stearate (25 ppm based on magnesium ions), MFR (210℃, 2.16 kg load) 2.2 g / 10 min e-5: EVOH, ethylene unit content 24 mol%, saponification degree 99.9 mol%, contains sodium acetate (250 ppm based on sodium ions), phosphate ions (20 ppm based on phosphate ions), and magnesium stearate (250 ppm based on magnesium ions), MFR (210℃, 2.16 kg load) 2.2 g / 10 min e-6: EVOH, ethylene unit content 24 mol%, saponification degree 99.9 mol%, contains sodium acetate (250 ppm based on sodium ions), phosphate ions (20 ppm based on phosphate ions), and calcium stearate (50 ppm based on calcium ions), MFR (210℃, 2.16 kg load) 2.2 g / 10 min e-7: EVOH, ethylene unit content 24 mol%, saponification degree 99.9 mol%, contains sodium acetate (250 ppm based on sodium ions), phosphate ions (20 ppm based on phosphate ions), and zinc stearate (50 ppm based on zinc ions), MFR (210℃, 2.16 kg load) 2.2 g / 10 min EC-1: EVOH, ethylene unit content 32 mol%, saponification degree 99.9 mol%, contains sodium acetate (300 ppm based on sodium ions), phosphate ions (30 ppm based on phosphate ions), boric acid (200 ppm based on boron element), and magnesium stearate (50 ppm based on magnesium ions), MFR (210℃, 2.16 kg load) 3.7 g / 10 minutes ec-2: EVOH, ethylene unit content 48 mol%, saponification degree 99.9 mol%, contains sodium acetate (150 ppm based on sodium ions), phosphate ions (30 ppm based on phosphate ions), boric acid (250 ppm based on boron elements), magnesium stearate (50 ppm based on magnesium ions), MFR (210℃, 2.16 kg load) 6.5 g / 10 min.

[0106] <Evaluation Methods> (1) Measurement of oxygen permeation 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, with the skin layer (A) side as the oxygen supply side and the other side as the carrier gas side, the oxygen permeation rate was measured. Specifically, using an oxygen permeation rate measuring device (MOCON OX-TRAN 2 / 21 manufactured by Modan Control Co., Ltd.), the oxygen permeation rate (unit: cc / (m²·day·atm)) was measured according to 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. The carrier gas used was nitrogen gas containing 2% hydrogen by volume. Based on the obtained oxygen permeation rate, the following criteria were used for judgment. It should be noted that a judgment of D or E indicates insufficient gas barrier properties. The results are shown in Table 1.

[0107] Judgment: Benchmark A: Less than 0.1 cc / (m²·day·atm) B: 0.1cc / (m²·day·atm) or higher, but less than 0.4cc / (m²·day·atm) C: 0.4cc / (m²·day·atm) or higher, but less than 1.0cc / (m²·day·atm) D: 1.0cc / (m²·day·atm) or higher, but less than 10cc / (m²·day·atm) E: 10cc / (m²·day·atm) or more (2) Evaluation of low curling properties of multilayer films or vapor-deposited multilayer films A 10cm square film was cut from the multilayer film or vapor-deposited multilayer film obtained in the examples and comparative examples. After standing for 10 minutes at 20°C and 65%RH, the curling state was observed and judged according to the following criteria. It should be noted that a judgment of D or E indicates insufficient curling. The results are shown in Table 1.

[0108] Judgment: Benchmark A: The curls are almost invisible. B: Slight curling observed C: Moderate curling was observed. D: Severe curling was observed. E: Extreme curling was observed. (3) Evaluation of the heat resistance of multilayer structures The multilayer structure obtained in the examples and comparative examples was cut into two A4-sized sheets, with the resin layers (R) overlapping each other. After heat sealing one side for 2 seconds at 120°C using a hot plate sealing machine, the sealed part was visually observed and judged according to the following criteria.

[0109] Judgment: Benchmark A: Good appearance B: Slight whitening was observed. C: Mild whitening or voids were observed. D: Significant degree of whitening, voids, or deformation was observed. E: Extreme whitening, voids, or deformation were observed. (4) Evaluation of the reusability of multi-layer structures The multilayer structures obtained in the examples and comparative examples were pulverized into particles smaller than 4 mm square. These particles were then dry-blended with low-density polyethylene (LDPE) "Nobatek (trademark) LD LJ400" (density 0.921 g / cm³, melting point 111°C, MFR (190°C, 2.16 kg load) 1.5 g / 10 min) manufactured by Nippon Polyethylene Co., Ltd. at a mass ratio of 50 / 50 (recycled material / LDPE). A single-layer film with an average thickness of 50 μm was obtained under the extrusion conditions shown below. As a control, a single-layer film with an average thickness of 50 μm was also obtained using only the aforementioned LDPE (hereinafter sometimes simply referred to as the "control"). A single-screw extruder with a D (mm) of 20 and a fully threaded screw with an L / D of 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 a single film layer is adjusted by appropriately changing the screw speed and the traction roller speed. The temperature conditions at this time are shown below.

[0110] Extrusion temperature: Supply section / Compression section / Metering section / Adapter = 175 / 230 / 230 / 230℃ Die head temperature: 220℃ Cooling roller temperature: 80℃ The coloring and defects of the obtained monolayer film were judged by visual inspection and comparison with the control, according to the following criteria. The results are shown in Table 2.

[0111] Coloring determination: baseline A: Compared to the control, the degree of hue change is small. B: Mild staining was observed compared to the control. C: Moderate staining was observed compared to the control. D: Significant staining was observed compared to the control. E: Significant staining and unevenness were observed compared to the control. Defect Judgment: Benchmark A: Compared to the control, the amount of foreign matter remained almost unchanged. B: Compared to the control group, there were slightly more small-sized foreign objects. C: Compared with the control group, there were more small-sized foreign objects. D: Compared with the control group, there were more large-sized foreign objects. E: Compared to the control, the amount of large-sized foreign objects is much greater.

[0112] Example 1 Polyethylene resin (a-1) was used as the raw material for the skin layer (A), polyethylene resin (b-1) as the raw material for the sub-skin 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). Unstretched multilayer films with a layer thickness and layer composition of (A) / (B) / (C) / (D) / (E) = 12μm / 12μm / 72μm / 12μm / 12μm were fabricated using a blow molding extrusion machine. The film-forming conditions are shown below.

[0113] Equipment: Five types of 5-layer blow extrusion molding machines manufactured by Dr. Collin. Die head temperature: 210℃, blow-up ratio: 2.7, traction speed: 4m / min, film fold width: 25cm <Conditions of the skin layer (A) extruder> Extruder: 30φ single screw extruder (Dr. Collins), extrusion temperature: feed section / compression section / metering section = 170℃ / 190℃ / 210℃.

[0114] <Conditions of the sub-skin layer (B) extruder> Extruder: 20φ single screw extruder (Dr. Collins), extrusion temperature: feed section / compression section / metering section = 170℃ / 190℃ / 210℃.

[0115] <Conditions of the core (C) extruder> Extruder: 20φ single screw extruder (Dr. Collins), extrusion temperature: feed section / compression section / metering section = 170℃ / 190℃ / 210℃.

[0116] <Conditions of the Adhesive Layer (D) Extruder> Extruder: 20φ single screw extruder (Dr. Collins), extrusion temperature: feed section / compression section / metering section = 170℃ / 190℃ / 210℃.

[0117] <Barrier Layer (E) Extruder Conditions> Extruder: 30φ single screw extruder (Dr. Collins), extrusion temperature: feed section / compression section / metering section = 190℃ / 210℃ / 210℃.

[0118] An unstretched multilayer membrane with a flow direction (MD direction) of 4 cm and a width direction (TD direction) of 10 cm was cut from the obtained cylindrical unstretched multilayer membrane. Using the stretching apparatus (SDR-506WK) of Eto Co., Ltd., a multilayer membrane with a layer thickness and layer composition of (A) / (B) / (C) / (D) / (E) = 2μm / 2μm / 12μm / 2μm / 2μm was produced.

[0119] A two-component reactive polyurethane adhesive (24 parts by weight of "Takelac (trademark) A-520" and 4 parts by weight of "Takenet (trademark) A-50" manufactured by Mitsui Chemicals Co., Ltd.) was mixed with 37 parts by weight of ethyl acetate to prepare an adhesive solution. Next, a single side of a polyethylene film (an unstretched polyethylene film made of linear low-density polyethylene, manufactured by Mitsui Chemicals Tosero Co., Ltd., entitled "TUX (trademark) FCD") (resin layer (R)) with an average thickness of 40 μm was corona treated using a known method. On this corona-treated surface, the aforementioned adhesive solution was applied using a wire rod to a dried average thickness of 3 μm. After drying at 100°C for 5 minutes, the film was laminated with the exposed surface of the barrier layer (E) of the multilayer film, thus creating a multilayer structure with a layer thickness and layer composition of (A) / (B) / (C) / (D) / (E) / adhesive layer / (R) = 2 μm / 2 μm / 12 μm / 2 μm / 2 μm / 3 μm / 40 μm. The bonding temperature (heating roller temperature) during lamination was set to 80°C, followed by an aging treatment at 40°C for 3 days.

[0120] Examples 2-12, Comparative Examples 1-10 Except for changes to the type, layer composition, and thickness of the resin raw materials used to manufacture the multilayer film as described in Tables 1 and 2, the multilayer film and multilayer structure were prepared and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0121] Example 13 Except for the exposed surface of the barrier layer (E) of the stretched multilayer film obtained in Example 3, an aluminum oxide (AlOx) vapor-deposited layer (inorganic vapor-deposited layer (I)) with an average thickness of 30 nm was deposited by a known vacuum vapor deposition method. The vapor-deposited multilayer film and multilayer structure were fabricated and evaluated in the same manner as in Example 3. The results are shown in Tables 1 and 2.

[0122] Example 14 Except that the alumina vapor deposition layer was replaced with a silicon dioxide (SiOx) vapor deposition layer, the vapor deposition multilayer film and multilayer structure were prepared and evaluated in the same manner as in Example 13. The results are shown in Tables 1 and 2.

[0123] Example 15 Except for changing the alumina vapor deposition layer to an aluminum metal (Al) vapor deposition layer and setting the thickness of the inorganic vapor deposition layer (I) to 50 nm, the vapor deposition multilayer film and multilayer structure were fabricated and evaluated in the same manner as in Example 13. The results are shown in Tables 1 and 2.

[0124] Example 16 Except for the exposed surface of the barrier layer (E) of the stretched multilayer film obtained in Example 1, a silicon dioxide (SiOx) vapor-deposited layer (inorganic vapor-deposited layer (I)) with an average thickness of 30 nm was deposited by a known vacuum evaporation method. The vapor-deposited multilayer film and multilayer structure were fabricated and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0125] Example 17 Except for changing the average thickness of layer (R) to 80 μm, the vapor-deposited multilayer film and multilayer structure were fabricated and evaluated in the same manner as in Example 16. The results are shown in Tables 1 and 2.

[0126] [Table 1] [Table 2]

[0127] The multilayer films of Examples 1-17 and the vapor-deposited multilayer films possess both gas barrier properties and low curl-up properties. On the other hand, the multilayer film of Comparative Example 1, which does not have a barrier layer (E), has low gas barrier properties. The multilayer films of Comparative Examples 2-4, whose barrier layer (E) contains ethylene units of EVOH with a content greater than 30 mol%, cannot simultaneously possess both gas barrier properties and low curl-up properties. The multilayer films of Comparative Examples 5-7, 9, and 10, whose skin layer (A) has the same density (dA) and core layer (C) density (dC), do not have low curl-up properties. The multilayer film of Comparative Example 8, whose skin layer (A) has a thickness greater than that of the core layer (C), does not have low curl-up properties.

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 stacked in this order, the skin layer (A) is located at one of the outermost layers of the multilayer film, and the barrier layer (E) is located at the other of the outermost layers of the multilayer film, the core layer (C) is the layer having the largest 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 to 30 mol% and a saponification degree of 90 mol% or more as a main component, it does not have a layer containing a resin having a melting point of 220°C or more as a main component, and it is stretched by 3 times or more in at least a uniaxial direction.

2. The multilayer film according to claim 1, further having a sub-skin layer (B) containing a polyethylene-based resin (b) as a main component between the skin layer (A) and the core layer (C), the density (dB) of the sub-skin layer (B) being less than the density (dA) of the skin layer (A) and greater 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 multilayer film of claim 1, wherein, the density (dA) of the skin layer (A) is 0.940 g / cm3 or more.

5. The multilayer film of claim 1, wherein, the density (dC) of the core layer (C) is 0.910 g / cm3 or more and less than 0.940 g / cm3.

6. The multilayer film of 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 of 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 of 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 multilayer film of claim 1, wherein, the adhesive resin (d) is an acid-modified polyethylene-based resin.

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

11. The multilayer film of claim 1, 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 claim 1, wherein, the multilayer film is stretched by 3 times or more in the longitudinal direction and is not substantially stretched in the width direction.

13. The multilayer film of claim 1, wherein, the multilayer film is a blow-molded body.

14. An evaporation multilayer film provided with an inorganic evaporation layer (I) on the exposed surface side of the barrier layer (E) of the multilayer film according to any one of claims 1 to 13.

15. The vapor-deposited multilayer film of claim 14, wherein, the inorganic evaporation layer (I) is a metal evaporation layer having aluminum as a main component, or an inorganic oxide evaporation layer having aluminum oxide or silicon dioxide as a main component.

16. A multilayer structure provided with a resin layer (R) containing a thermoplastic resin (r) as a main component on the multilayer film according to any one of claims 1 to 13.

17. A multilayer structure provided with a resin layer (R) containing a thermoplastic resin (r) as a main component on the evaporation multilayer film according to claim 14.

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

19. The multilayer structure of claim 17, wherein, The thermoplastic resin (r) contains a polyethylene-based resin as a main component.

20. A packaging material having the multilayer structure of claim 16.

21. A packaging material having the multilayer structure of claim 17.

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