Multilayer structure, container, and food packaging container

Abstract

The present invention provides a multilayer structure having an ethylene-vinyl alcohol copolymer layer (A) and a polyethylene resin layer (B) and having excellent distinctness of image. A multilayer structure having an ethylene-vinyl alcohol copolymer layer (A) and a polyethylene resin layer (B), in which the density of a polyethylene resin contained in the polyethylene resin layer (B) is 0.850 g / cm3 to 0.920 g / cm3, the content of the polyethylene resin in the polyethylene resin layer (B) is more than 80 mass%, the impact strength A of the multilayer structure is 350 g or more, and the impact strength B of the polyethylene resin contained in the polyethylene resin layer (B) is more than 80 mass%. The impact strength A is a value obtained by a dart impact A method calculated by measurement in accordance with JIS K7124-1.

Description

Technical Field

[0001] The present invention relates to a multilayer structure having an ethylene-vinyl alcohol copolymer (hereinafter sometimes referred to as "EVOH") layer (A) and a polyethylene resin layer (B), and the multilayer structure has excellent image distinctness. Background Art

[0002] EVOH has very strong intermolecular forces due to hydrogen bonds between hydroxyl groups on the polymer side chains. Therefore, it has high crystallinity, and in addition, the intermolecular forces are also high in the amorphous part, so it is difficult for gas molecules and the like to pass through the film using EVOH, showing excellent gas barrier properties. Therefore, in a wide range of fields such as food packaging, EVOH is used as a gas barrier layer for imparting gas barrier properties to multilayer structures having a polyethylene resin layer such as films and containers.

[0003] For example, Patent Document 1 discloses a multilayer structure including a surface resin layer, a substrate, a gas barrier layer, and a heat seal layer, wherein the surface resin layer, the substrate, and the heat seal layer are formed of polyethylene, and the gas barrier layer is formed of EVOH.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2021-53993 Summary of the invention

[0007] Problem that the invention aims to solve

[0008] The image distinctness of conventional multilayer structures including an EVOH layer and a polyethylene-based resin layer still has room for improvement.

[0009] The present invention has been made in view of the above-mentioned technical problems, and provides a multilayer structure having excellent image distinctness and comprising an EVOH layer and a polyethylene-based resin layer.

[0010] Solutions for solving problems

[0011] The present inventors have conducted intensive studies to solve the above technical problems and have found that the image distinctness of a multilayer structure including an EVOH layer and a polyethylene resin layer can be improved by setting the impact strength of the multilayer structure within a specific range.

[0012] That is, the present invention provides the following [1] to

[10] .

[0013] [1] A multilayer structure comprising an ethylene-vinyl alcohol copolymer layer (A) and a polyethylene resin layer (B),

[0014] The density of the polyethylene resin contained in the polyethylene resin layer (B) is 0.850 g / cm 3 ~0.920g / cm 3 ,

[0015] The content of the polyethylene resin in the polyethylene resin layer (B) exceeds 80% by mass,

[0016] The impact strength A of the multilayer structure is 350 g or more,

[0017] The impact strength A is a value obtained by a dart impact A method and calculated by measurement in accordance with JIS K7124-1.

[0018] [2] A multilayer structure comprising an ethylene-vinyl alcohol copolymer layer (A) and a polyethylene resin layer (B),

[0019] The density of the polyethylene resin contained in the polyethylene resin layer (B) is 0.850 g / cm 3 ~0.920g / cm 3 ,

[0020] The content of the polyethylene resin in the polyethylene resin layer (B) exceeds 80% by mass,

[0021] The weight average molecular weight of the polyethylene resin contained in the polyethylene resin layer (B) is 230,000 or more in terms of polystyrene.

[0022] [3] A multilayer structure comprising an ethylene-vinyl alcohol copolymer layer (A) and a polyethylene resin layer (B),

[0023] The density of the polyethylene resin contained in the polyethylene resin layer (B) is 0.850 g / cm 3 ~0.920g / cm 3 ,

[0024] The content of the polyethylene resin in the polyethylene resin layer (B) exceeds 80% by mass,

[0025] The impact strength B of the polyethylene resin layer (B) is 500 g or more,

[0026] The impact strength B is a value calculated by a dart impact B method based on JIS K7124-1 by measuring a test piece consisting of a single-layer film having the same composition as that of the polyethylene-based resin layer (B) and a thickness of 30 μm.

[0027] [4] The multilayer structure according to any one of [1] to [3], wherein the polyethylene-based resin is a linear low-density polyethylene.

[0028] [5] The multilayer structure according to any one of [1] to [4], wherein the polyethylene resin contains a copolymer component, and the number of carbon atoms of the copolymer component is 4 or more.

[0029] [6] The multilayer structure according to any one of [1] to [5], further comprising an adhesive resin layer (C).

[0030] [7] A multilayer structure according to any one of [1] to [6], wherein the multilayer structure further has another layer (D) on at least one of the outermost layers, and the polyethylene resin layer (B) is arranged between the other layer (D) and the ethylene-vinyl alcohol copolymer layer (A).

[0031] [8] The multilayer structure according to any one of [1] to [7], which does not have a layer containing a polyamide-based resin as a main component.

[0032] [9] A container using the multilayer structure according to any one of [1] to [8].

[0033]

[10] A food packaging container using the multilayer structure described in any one of [1] to [9].

[0034] Effects of the Invention

[0035] According to the present invention, there is provided a multilayer structure comprising an EVOH layer (A) and a polyethylene resin layer (B), wherein the density of the polyethylene resin contained in the polyethylene resin layer (B) is 0.850 g / cm 3 ~0.920g / cm 3 The polyethylene resin layer (B) has a content of the polyethylene resin exceeding 80% by mass and has specific physical properties, thereby forming a multilayer structure having excellent image distinctness. DETAILED DESCRIPTION

[0036] Hereinafter, the embodiments of the present invention will be described in detail, but the present invention is not limited to the following description, and can be arbitrarily modified and implemented without departing from the gist of the present invention. It should be noted that in this specification, when "to" is used and numerical values ​​or physical property values ​​are recorded before and after it for expression, it is used in a manner that includes the values ​​before and after it.

[0037] Hereinafter, a monomer unit contained in a copolymer resin may be simply referred to as a “unit.” For example, a monomer unit based on ethylene may be referred to as an “ethylene unit.”

[0038] A multilayer structure according to one embodiment of the present invention (hereinafter sometimes referred to as "the present multilayer structure") comprises an EVOH layer (A) and a polyethylene resin layer (B), wherein the density of the polyethylene resin contained in the polyethylene resin layer (B) is 0.850 g / cm 3 ~0.920g / cm 3 The polyethylene resin layer (B) has a content of the polyethylene resin exceeding 80% by mass and has specific physical properties as described below.

[0039] Hereinafter, each configuration will be described.

[0040] [EVOH layer (A)]

[0041] The EVOH layer (A) is a layer formed of a resin composition containing EVOH. EVOH is generally a resin obtained by saponifying an ethylene-vinyl ester copolymer, which is a copolymer of ethylene and a vinyl ester monomer, and is a water-insoluble thermoplastic resin. It should be noted that a plurality of EVOH layers (A) may be provided in the multilayer structure.

[0042] The content of EVOH contained in the EVOH layer (A) is not particularly limited, but preferably EVOH is the main component (i.e., the content of EVOH contained in the EVOH layer (A) is 50% by mass or more). The content of EVOH in the EVOH layer (A) is more preferably 60% by mass or more, further preferably 70% by mass or more, particularly preferably 80% by mass or more, 90% by mass or more, 95% by mass or more, or 100% by mass.

[0043] The EVOH layer (A) may contain ingredients other than EVOH within the scope that does not impair the effects of the present invention. For example, it may contain other ingredients such as anti-blocking agents, processing aids, resins other than EVOH, carboxylic acid compounds, phosphoric acid compounds, boron compounds, metal salts, stabilizers, antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, surfactants, desiccants, cross-linking agents, various fibers and other reinforcing agents. These may be used alone or in combination of two or more.

[0044] [EVOH]

[0045] EVOH is a resin generally obtained by saponifying an ethylene-vinyl ester copolymer, which is a copolymer of ethylene and vinyl ester monomers, and is a water-insoluble thermoplastic resin. As a vinyl ester monomer, vinyl acetate is generally used from an economical point of view. As a polymerization method of ethylene and vinyl ester monomers, any known polymerization method such as solution polymerization, suspension polymerization, and emulsion polymerization can be used, and solution polymerization using methanol as a solvent is generally used. The saponification of the obtained ethylene-vinyl ester copolymer can also be carried out by a known method. The EVOH manufactured in this way is mainly composed of structural units derived from ethylene and vinyl alcohol structural units, and generally contains a certain amount of vinyl ester structural units that remain without saponification.

[0046] As the vinyl ester monomer, vinyl acetate is typically used from the viewpoint of market availability and good impurity treatment efficiency during production. As other vinyl ester monomers, for example, aliphatic vinyl esters such as vinyl formate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, and vinyl versatate, and aromatic vinyl esters such as vinyl benzoate can be cited. Generally, aliphatic vinyl esters having 3 to 20 carbon atoms, preferably 4 to 10 carbon atoms, and particularly preferably 4 to 7 carbon atoms can be used. These can be used alone or in combination of two or more.

[0047] EVOH generally uses raw materials derived from petroleum such as naphtha, but can also use raw materials derived from natural gas such as shale gas, or raw materials derived from plants obtained by purifying components such as sugar and starch contained in sugar cane, beets, corn, potatoes, etc., or components such as cellulose contained in plants such as rice, wheat, and millet.

[0048] The content of ethylene units in EVOH can be controlled by the pressure of ethylene when copolymerizing vinyl ester monomers with ethylene, preferably 20 mol% to 60 mol%. More preferably, it is 25 mol% to 55 mol%, further preferably 30 mol% to 50 mol%, particularly preferably 35 mol% to 45 mol%, and particularly preferably 38 mol% to 45 mol%. In addition, from the perspective of further improving mechanical properties and secondary moldability, the EVOH layer (A) preferably contains EVOH having a content of 38 mol% or more. When the content is too low, there is a tendency for gas barrier properties and melt moldability to decrease under high humidity, and on the contrary, when the content is too high, there is a tendency for gas barrier properties to decrease. It should be noted that the content of ethylene units can be measured, for example, based on ISO 14663.

[0049] In addition, the saponification degree of the vinyl ester component in EVOH can be controlled by the amount of the saponification catalyst (usually an alkaline catalyst such as sodium hydroxide is used) when saponifying the ethylene-vinyl ester copolymer, the temperature, the time, etc. From the viewpoint of gas barrier properties, thermal stability, and moisture resistance, it is preferably 80 mol% or more, more preferably 90 mol% or more, more preferably 98 mol% or more, particularly preferably 99 mol% or more, and can also be 100 mol%.

[0050] The saponification degree of the vinyl ester unit of the EVOH is a value measured in accordance with JIS K6726 (wherein EVOH is uniformly dissolved in a water / methanol solvent).

[0051] The melt flow rate (MFR) of EVOH (210°C, load 2160g) is usually 0.5g / 10min to 100g / 10min, preferably 1g / 10min to 50g / 10min, and particularly preferably 3g / 10min to 35g / 10min. When the MFR is too large, the film forming property tends to become unstable, and when the MFR is too small, the viscosity tends to become too high and melt extrusion tends to become difficult.

[0052] MFR is an index of the degree of polymerization of EVOH, and can be adjusted by the amount of the polymerization initiator and the amount of the solvent when ethylene and the vinyl ester monomer are copolymerized.

[0053] EVOH can also be copolymerized with polymerizable monomers other than ethylene and vinyl esters within a range that does not hinder the effect of the present invention, usually within a range of 5 mol% or less. Examples of such polymerizable monomers include: α-olefins such as propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; α-olefins containing hydroxyl groups such as 3-butene-1-ol, 4-pentene-1-ol, and 3-butene-1,2-diol, or α-olefin derivatives containing hydroxyl groups such as esters and acylates thereof; hydroxymethylvinylidene diacetates such as 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, and 1,3-dibutyryloxy-2-methylenepropane; unsaturated carboxylic acids or their salts, partial alkyl esters, complete alkyl esters, nitriles, amides, or anhydrides; unsaturated sulfonic acids or their salts; vinyl silane compounds; vinyl chloride; styrene, etc. These can be used alone or in combination of two or more.

[0054] As the EVOH used in the present invention, any EVOH having a primary hydroxyl group in a side chain can be used. Examples of the EVOH having a primary hydroxyl group in a side chain include EVOH obtained by copolymerizing hydroxyl-containing α-olefins and EVOH having a 1,2-diol structure in a side chain.

[0055] When EVOH having a primary hydroxyl group in a side chain is used, the content of the structural unit derived from the monomer having the primary hydroxyl group is usually preferably 0.1 to 20 mol %, more preferably 0.5 to 15 mol %, particularly preferably 1 to 10 mol % of EVOH.

[0056] In the present invention, EVOH having no primary hydroxyl group in the side chain is preferred from the viewpoint of image distinctness.

[0057] Furthermore, as EVOH, EVOH “post-modified” by urethanization, acetalization, cyanoethylation, oxyalkyleneization, etc. may also be used.

[0058] Only one kind of EVOH may be used, or two or more kinds of EVOH different in the type of vinyl ester, ethylene unit content, physical properties, etc. may be mixed and used.

[0059] In view of compatibility, EVOH is preferably composed of only one type, or when using a plurality of types, EVOH is preferably composed of EVOH having a melting point of 170°C or higher, or EVOH having a melting point of less than 170°C.

[0060] In the present invention, the melting point is measured by the method described in JIS K7121, wherein the sample is temporarily heated to 200°C using a differential scanning calorimeter (DSC), then cooled at a cooling rate of 30°C / min to a temperature about 50°C lower than the glass transition temperature, and then heated at a heating rate of 10°C / min to measure the melting point (second run).

[0061] [Polyethylene resin layer (B)]

[0062] The present multilayer structure has a polyethylene resin layer (B). The polyethylene resin layer (B) is a layer formed of a resin composition containing a polyethylene resin having a specific density. A plurality of polyethylene resin layers (B) may be provided in the multilayer structure.

[0063] The density of the polyethylene resin is 0.850 g / cm 3 ~0.920g / cm 3 , preferably 0.860 g / cm 3 ~0.920g / cm 3 , more preferably 0.870 g / cm 3 ~0.920g / cm 3 , more preferably 0.880 g / cm 3 ~0.920g / cm 3 By setting the density within the above range, the effects of the present invention can be obtained. The density can be measured by a densitometer.

[0064] As a specific polyethylene resin, there is no particular limitation as long as it has the above-mentioned density, and examples thereof include: polyethylene resins such as linear low-density polyethylene, low-density polyethylene, ultra-low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-propylene (block and random) copolymers, ethylene-α-olefin (α-olefin with 4 to 20 carbon atoms) copolymers, and polyethylene resins in a broad sense including modified polyethylene resins such as unsaturated carboxylic acid-modified polyethylene resins obtained by grafting these polyethylenes with unsaturated carboxylic acids or their esters, or combinations thereof. Among them, linear low-density polyethylene is preferred from the perspective of ease of adjusting the above-mentioned impact strength. In addition, the raw materials of the above-mentioned polyethylene resins may be derived from petroleum or from plants. As the above-mentioned polyethylene resin, it is preferred that the halogen-free polyethylene is not contained.

[0065] The above-mentioned polyethylene resin can be a homopolymer resin of ethylene or a copolymer resin. In the case where the polyethylene resin is a copolymer resin, the impact strength can be improved by using a copolymer component with a large number of carbon atoms. As copolymer components other than ethylene, for example, α-olefins having preferably 4 or more carbon atoms, more preferably 6 or more carbon atoms, and further preferably 8 or more carbon atoms can be listed. Specifically, for example, butene, hexene, octene, etc. can be listed, preferably hexene and octene. It should be noted that the carbon number of the copolymer component can be measured by C-NMR.

[0066] When polyethylene resin is copolymer resin, there is the tendency that can improve impact strength by improving the ratio of copolymer components.The ratio of copolymer components is preferably more than 0.5 mol %, more preferably more than 1 mol %, further preferably more than 2 mol %, particularly preferably more than 3 mol %.In addition, the upper limit is usually 20 mol %.The ratio of copolymer components can be measured by NMR.

[0067] The weight average molecular weight of the polyethylene resin is preferably 230,000 or more, more preferably 235,000 or more, further preferably 240,000 or more, particularly preferably 245,000 or more, especially preferably 250,000 or more, and most preferably 253,000 or more. It should be noted that the upper limit is not particularly limited, but is generally 400,000. By making the weight average molecular weight of the polyethylene resin be 230,000 or more, there is a tendency to form a multilayer structure having excellent distinctness of image. The molecular weight of the polyethylene resin can be measured by GPC.

[0068] The melt flow rate (MFR, MFR at 190°C and a load of 2160 g measured in accordance with JIS K7210:2014) of the polyethylene resin is not particularly limited, but is generally 0.01 g / 10 min to 50 g / 10 min, more preferably 0.1 g / 10 min to 10 g / 10 min, from the viewpoint of moldability. The MFR can be measured by a melt indexer.

[0069] Examples of commercially available polyethylene resins preferred in the present invention include Innate (registered trademark) manufactured by The Dow Chemical Company and Exceed (registered trademark) manufactured by ExxonMobil Corporation.

[0070] The content of the polyethylene resin in the polyethylene resin layer (B) exceeds 80% by mass, preferably 85% by mass or more, more preferably 90% by mass or more, and particularly preferably 95% by mass or more. By making the content of the polyethylene resin within the above range, the effect of the present invention can be obtained.

[0071] In the polyethylene resin layer (B), as long as the effect of the present invention is not impaired (for example, the polyethylene resin layer (B) is less than 20% by mass), components other than the polyethylene resin may be contained. As components other than the polyethylene resin, for example, anti-blocking agents, processing aids, resins other than the polyethylene resin, carboxylic acid compounds, phosphoric acid compounds, boron compounds, metal salts, stabilizers, antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, surfactants, desiccants, cross-linking agents, various fibers and other reinforcing agents may be contained. These may be used alone or in combination of two or more.

[0072] As resins other than polyethylene resins that may be contained in the polyethylene resin layer (B), for example, polypropylene, propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers and other polypropylene resins, polybutene, polypentene, etc., cycloolefin resins, ionomers, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylic acid ester copolymers, polyester resins, polyamide resins (including copolymerized polyamides), polyvinyl chloride, polyvinylidene chloride, acrylic resins, polystyrene, vinyl ester resins, polyester elastomers, polyurethane elastomers, chlorinated polyethylene, chlorinated polypropylene and other halogenated polyolefins, aromatic or aliphatic polyketones, etc., or combinations thereof. It should be noted that, from the viewpoint of recyclability, the resins other than polyethylene resins preferably do not contain a polyamide resin as a main component.

[0073] The impact strength (referred to as "impact strength B") of the polyethylene resin layer (B) formed by the resin composition containing these components is not particularly limited, and is preferably more than 500g, more preferably more than 600g, further preferably more than 700g, particularly preferably more than 800g, and especially preferably more than 900g. It should be noted that the upper limit is not particularly limited, and is usually 10000g, preferably less than 9000g, more preferably less than 7000g, further preferably less than 5000g, and particularly preferably less than 3000g.

[0074] When the impact strength B of the polyethylene resin layer (B) is 500 g or more, there is a tendency that a multilayer structure having better distinctness of image can be formed.

[0075] The impact strength B is a value (g) calculated by a dart impact B method by measuring a test piece consisting of a single-layer film having the same composition as the polyethylene resin layer (B) and a thickness of 30 μm in accordance with JIS K7124-1.

[0076] Since the impact strength B is affected by the surface state of the film, it is presumed that by setting the impact strength B within the above range, the polyethylene resin layer (B) can form a smoother surface, thereby enhancing the effect of the present invention.

[0077] As a method for adjusting the impact strength B, for example, there can be listed: a method of adjusting the molecular weight and molecular weight distribution of the polyethylene resin contained in the polyethylene resin layer (B); or a method of adjusting the number of carbon atoms in the copolymer components, the ratio of the copolymer components, etc. when the polyethylene resin is a copolymer resin, etc.

[0078] [Adhesive resin layer (C)]

[0079] The present multilayer structure preferably has an adhesive resin layer (C). The adhesive resin layer (C) contains an adhesive resin and can be provided, for example, as a layer for bonding the EVOH layer (A) and the polyethylene resin layer (B). The adhesive resin layer (C) can be provided as one layer in the multilayer structure or multiple layers.

[0080] The adhesive resin constituting the adhesive resin layer (C) is not particularly limited, and examples thereof include: modified polyolefin polymers containing carboxyl groups obtained by chemically bonding unsaturated carboxylic acids or their anhydrides to polyolefin resins by addition reaction or grafting reaction. Examples of modified polyolefin polymers containing carboxyl groups include: maleic anhydride-grafted modified polyethylene, maleic anhydride-grafted modified polypropylene, maleic anhydride-grafted modified ethylene-propylene (block and random) copolymers, maleic anhydride-grafted modified ethylene-ethyl acrylate copolymers, maleic anhydride-grafted modified ethylene-vinyl acetate copolymers, maleic anhydride-modified polycycloolefin resins, maleic anhydride-grafted modified polyolefin resins and other maleic anhydride-modified polymers.

[0081] These may be used alone or as a mixture of two or more.

[0082] The melt flow rate (MFR, MFR at 190°C and a load of 2160 g measured in accordance with JIS K7210:2014) of the adhesive resin constituting the adhesive resin layer (C) is not particularly limited, but is preferably 0.1 g / 10 min to 20.0 g / 10 min, and more preferably 1.0 g / 10 min to 10.0 g / 10 min. When the MFR of the adhesive resin is within the above range, molding stability tends to be better.

[0083] As the adhesive resin, maleic anhydride-modified polymers such as maleic anhydride-modified polyethylene and maleic anhydride-modified ethylene-α-olefin copolymers are particularly preferred because they not only contribute to the adhesiveness of the resin but also contribute to the suppression of gel formation during melt heating and the suppression of transparency reduction.

[0084] The acid value of maleic anhydride modified polymer is usually 50mgKOH / g or less, preferably 30mgKOH / g or less, and particularly preferably 20mgKOH / g or less. When the acid value is too high, the reaction sites with the hydroxyl groups in EVOH increase, a high degree of polymerization product is generated during melt mixing, and the stability during extrusion processing is reduced, and there is a tendency to be difficult to obtain a good molded product. It should be noted that the lower limit of the acid value is usually 1mgKOH / g, preferably 2mgKOH / g or more. In addition, the acid value is measured based on JISK0070.

[0085] When maleic anhydride-modified polyethylene is used as the maleic anhydride-modified polymer, the MFR (190° C., load 2160 g) is generally 0.01 g / 10 min to 150 g / 10 min, preferably 0.1 g / 10 min to 50 g / 10 min, more preferably 1 g / 10 min to 25 g / 10 min, and further preferably 3 g / 10 min to 10 g / 10 min.

[0086] In addition, the MFR (230°C, load 2160g) when using maleic anhydride modified ethylene-α-olefin copolymer as the maleic anhydride modified polymer is usually 0.1g / 10min to 150g / 10min, preferably 0.5g / 10min to 100g / 10min, more preferably 1g / 10min to 50g / 10min, and further preferably 5g / 10min to 35g / 10min. When the MFR is too large or too small, there is a tendency for poor molding when molding a multilayer structure, so it is not preferred.

[0087] It should be noted that any additive may be appropriately added to the adhesive resin layer (C) within the scope of not impairing the effects of the present invention. Examples of such additives include heat stabilizers, ultraviolet light absorbers, light stabilizers, antioxidants, antistatic agents, neutralizers, rust inhibitors, pigments, etc. These may be used alone or in combination of two or more.

[0088] Then, by mixing the adhesive resin and any additives, a resin composition for obtaining the adhesive resin layer (C) can be prepared.

[0089] The content of the adhesive resin in the adhesive resin layer (C) is not particularly limited, but preferably the adhesive resin is the main component (i.e., the content of the adhesive resin contained in the adhesive resin layer (C) is 50% by mass or more). The content of the adhesive resin is more preferably 60% by mass or more, further preferably 70% by mass or more, particularly preferably 80% by mass or more, 90% by mass or more, 95% by mass or more, or 100% by mass.

[0090] [Other layers (D)]

[0091] The present multilayer structure may have another layer (D) in addition to the above-mentioned layers (A) to (C). Examples of the other layer (D) include a base material layer for imparting strength to the multilayer structure.

[0092] <Base material layer>

[0093] As the material used in the substrate layer, various thermoplastic resins (hereinafter referred to as "substrate resins") can be used. In addition, recycled resins obtained by remelting and molding the ends and defective products generated during the production of the multilayer structure can also be used. Such recycled resins include a mixture of an EVOH layer (A), a polyethylene resin layer (B), an adhesive resin layer (C), and other layers (D).

[0094] Examples of the base resin used in the base layer include linear low-density polyethylene, low-density polyethylene, ultra-low-density polyethylene, medium-density polyethylene, high-density polyethylene, polyethylene resins such as ethylene-propylene (block and random) copolymers, and ethylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers, polypropylene resins such as polypropylene and propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers, (unmodified) polyolefin resins such as polybutene and polypentene, and polyolefin resins including those obtained by grafting and modifying these polyolefins with unsaturated carboxylic acids or their esters. The invention relates to polyolefin resins in a broad sense, including modified olefin resins such as unsaturated carboxylic acid-modified polyolefin resins, cycloolefin resins, ionomers, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylate copolymers, polyester resins, polyamide resins (including copolymerized polyamides), polyvinyl chloride, polyvinylidene chloride, acrylic resins, polystyrene, vinyl ester resins, polyester elastomers, polyurethane elastomers, halogenated polyolefins such as chlorinated polyethylene and chlorinated polypropylene, aromatic or aliphatic polyketones, or combinations thereof.

[0095] It should be noted that the thermoplastic resin used in the substrate layer may be mixed with conventionally known plasticizers, fillers, clay (montmorillonite, etc.), colorants, antioxidants, antistatic agents, lubricants, nucleating agents, antiblocking agents, ultraviolet absorbers, waxes, etc., within a range that does not impair the gist of the present invention (e.g., 30% by mass or less, preferably 10% by mass or less).

[0096] [Multilayer structure]

[0097] The present multilayer structure is a multilayer structure comprising an EVOH layer (A) and a polyethylene-based resin layer (B).

[0098] The present multilayer structure may contain an EVOH layer (A) and a polyethylene resin layer (B), and the other layer structures are not particularly limited. For example, there may be a structure (A / C / B) in which a polyethylene resin layer (B) is laminated on an EVOH layer (A) via an adhesive resin layer (C), and a structure (B / C / A / C / B) in which a polyethylene resin layer (B) is laminated on both sides of an EVOH layer (A) via an adhesive resin layer (C).

[0099] Furthermore, in the present invention, another layer (D) may be provided between these layers or on the outermost layer of the multilayer structure.

[0100] The multilayer structure preferably further comprises another layer (D) on at least one of the outermost layers, and the polyethylene-based resin layer (B) is provided between the other layer (D) and the EVOH layer (A).

[0101] In addition, from the viewpoint of recyclability, the present multilayer structure preferably does not contain a polyamide layer (a layer containing polyamide, a layer containing polyamide as a main component, or a layer formed of polyamide).

[0102] The lamination method of the multilayer structure can be carried out by a known method. For example, the following methods can be cited: a method of melt-extrusion laminating an adhesive resin layer (C) and a polyethylene resin layer (B) on a film or sheet that becomes the EVOH layer (A); a method of melt-extrusion laminating a resin composition that becomes the EVOH layer (A) on an adhesive resin layer (C) and a polyethylene resin layer (B); or a method of co-extruding the three layers (A), (B), and (C). In addition, the following methods can be cited: a method of coating a solution of a resin composition that becomes the EVOH layer (A) on a polyethylene resin layer (B) provided with an adhesive resin layer (C), and then removing the solvent. Among them, the co-extrusion method is preferred from the perspective of cost and environment.

[0103] Furthermore, when the present multilayer structure contains at least one other layer (D), for example, the following production method can be mentioned.

[0104] (i) A method of laminating all layers by coextruding the resins constituting the EVOH layer (A) and the polyethylene resin layer (B), and the resin constituting the adhesive resin layer (C) and the resin constituting the other layer (D) as required;

[0105] (ii) a method of dry laminating a film, sheet or the like formed separately to become another layer (D) and a multilayer structure having an EVOH layer (A), a polyethylene resin layer (B) and, if necessary, an adhesive resin layer (C);

[0106] (iii) a method of laminating by melt-coextruding the resins constituting the EVOH layer (A) and the polyethylene resin layer (B), and the resin constituting the adhesive resin layer (C) included as required, onto the surface of a film, sheet, etc. formed separately to become the other layer (D), or a laminated body composed of a suitable combination of films, sheets, etc.; and

[0107] (iv) A method of applying a solution of a resin to be another layer (D) onto a multilayer structure having an EVOH layer (A), a polyethylene resin layer (B), and, if necessary, an adhesive resin layer (C), and then removing the solvent.

[0108] Among them, method (i) is preferred from the viewpoint of productivity.

[0109] The impact strength (referred to as "impact strength A") of the multilayer structure thus obtained is not particularly limited, and is preferably 350 g or more, more preferably 370 g or more, further preferably 390 g or more, and particularly preferably 410 g or more. It should be noted that the upper limit is not particularly limited, and is usually 10000 g, preferably 9000 g or less, more preferably 7000 g or less, further preferably 5000 g or less, and particularly preferably 3000 g or less. The impact strength A is a value obtained by measuring a test piece formed by a multilayer structure in accordance with JIS K7124-1 and calculated using the dart impact A method.

[0110] It should be noted that the impact strength A is preferably a value calculated by a dart impact A method by measuring a test piece composed of a multilayer film of the polyethylene resin layer (B) (40 μm) / an adhesive resin layer (5 μm) formed by Modic (registered trademark) M512 / an EVOH layer (10 μm) formed by Soarnol (registered trademark) ET3803RB / an adhesive resin layer (5 μm) formed by Modic (registered trademark) M512 / the polyethylene resin layer (B) (40 μm) in accordance with JIS K7124-1.

[0111] It is presumed that since the impact strength A is affected by the surface state of the film and the interface state between the layers of the multilayer structure, by setting the impact strength A within the above range, the multilayer structure can form a smooth surface, thereby enhancing the effect of the present invention.

[0112] The thickness of the multilayer structure is not particularly limited, but is usually 5 μm to 300 μm, preferably 20 μm to 200 μm, and particularly preferably 50 μm to 150 μm.

[0113] The thickness of each layer of the multilayer structure is not particularly limited, and the thickness of the EVOH layer (A) is preferably 1 μm to 50 μm, and more preferably 2 μm to 30 μm. The thickness of the polyethylene resin layer (B) is preferably 5 μm to 200 μm, and more preferably 10 μm to 100 μm. By making the thickness of the polyethylene resin layer (B) within the above range, the effect of the present invention can be improved. The thickness of the adhesive resin layer (C) is preferably 1 μm to 50 μm, and more preferably 2 μm to 20 μm. In the case where there are multiple layers, it is preferred that the total thickness of the multiple layers is within the range of the above thickness.

[0114] In addition, the ratio of the thickness of the EVOH layer (A) to the thickness of the polyethylene resin layer (B) (both are single layer thicknesses) A / B is usually 1 / 50 to 10 / 1, preferably 1 / 30 to 5 / 1, and particularly preferably 1 / 10 to 3 / 1. When the A / B is too small, the gas barrier properties tend to be insufficient, and conversely, when the A / B is too large, the film tends to become brittle.

[0115] The ratio of the thickness of the EVOH layer (A) to the thickness of the adhesive resin layer (C) (both are single layer thicknesses) A / C is usually 1 / 10 to 10 / 1, preferably 1 / 5 to 5 / 1, and particularly preferably 1 / 3 to 3 / 1. When the A / C is too small, the gas barrier properties tend to be insufficient, and conversely, when the A / C is too large, the adhesiveness tends to be insufficient.

[0116] The multilayer structure may also be subjected to (heating) stretching treatment as required. The stretching treatment may be any of uniaxial stretching and biaxial stretching. In the case of biaxial stretching, it may be simultaneous stretching or sequential stretching. In addition, as a stretching method, a method with a high stretching ratio such as a roller stretching method, a tenter stretching method, a tubular stretching method, a stretch blow molding method, and a vacuum pressure forming method may be adopted. The stretching temperature is a temperature near the melting point of the multilayer structure, and is usually selected from a range of about 40°C to 170°C, preferably about 60°C to 160°C. When the stretching temperature is too low, there is a tendency for poor stretchability, and when the stretching temperature is too high, there is a tendency for difficulty in maintaining a stable stretched state.

[0117] It should be noted that after stretching, heat fixing may be further performed for the purpose of imparting dimensional stability. Heat fixing may be performed by a known method, for example, a method in which a multilayer structure (in the form of a stretched film) is heat treated at a temperature of usually 80°C to 180°C, preferably 100°C to 165°C, for usually 2 seconds to 600 seconds while maintaining the multilayer structure (in the form of a stretched film) in a tensioned state.

[0118] [Application of multilayer structure]

[0119] The multilayer structure can be suitably used as packaging materials such as packaging containers and packaging films for various packaging materials such as mayonnaise, seasonings such as sauces, fermented foods such as soybean paste, oily foods such as salad oil, beverages, cosmetics, and pharmaceuticals, in addition to general foods.

[0120] Example

[0121] Hereinafter, the specific embodiments of the present invention will be further described in detail using examples, but the present invention is not limited to the following examples as long as it does not exceed its purport. It should be noted that the values ​​of various manufacturing conditions and evaluation results in the following examples have the meaning of preferred values ​​as the upper or lower limits in the embodiments of the present invention, and the preferred range can be the range specified by the combination of the above-mentioned upper or lower limit values ​​and the values ​​of the following examples or the values ​​between the examples.

[0122] The materials used in the following Examples and Comparative Examples are as follows.

[0123] <evoh>

[0124] "Soarnol (registered trademark) ET3803RB" manufactured by Mitsubishi Chemical Corporation (ethylene unit content 38 mol%, MFR (210°C, load 2160 g) 4.0 g / 10 min, density 1.17 g / cm 3 )

[0125] <Polyethylene resin>

[0126] B1: "Innate (registered trademark) ST50" manufactured by The Dow Chemical Company (linear low-density polyethylene, the number of carbon atoms of the copolymer component is 8, and the density is 0.918 g / cm 3 , MFR (190°C, load 2160g) is 0.85g / 10min, weight average molecular weight (polystyrene conversion) is 251000)

[0127] B2: "Innate (registered trademark) TH60" manufactured by The Dow Chemical Company (linear low-density polyethylene, the number of carbon atoms of the copolymer component is 8, and the density is 0.912 g / cm 3 , MFR (190°C, load 2160g) is 0.85g / 10min, weight average molecular weight (polystyrene conversion) is 253000)

[0128] B3: Exceed (registered trademark) XP 8784 manufactured by ExxonMobil Corporation (linear low-density polyethylene, the number of carbon atoms of the copolymer component is 6, and the density is 0.914 g / cm 3 , MFR (190°C, load 2160g) is 0.80g / 10min, weight average molecular weight (polystyrene conversion) is 269000)

[0129] B4: ExxonMobil "Exceed (registered trademark) 1012MA" (linear low-density polyethylene, the number of carbon atoms of the copolymer component is 6, and the density is 0.912 g / cm 3 , MFR (190°C, load 2160g) is 1.0g / 10min, weight average molecular weight (polystyrene conversion) is 258000)

[0130] B5: "Elite (registered trademark) 5400G" manufactured by The Dow Chemical Company (linear low-density polyethylene, the number of carbon atoms of the copolymer component is 8, and the density is 0.916 g / cm 3 , MFR (190°C, load 2160g) is 1.0g / 10min, weight average molecular weight (polystyrene conversion) is 228000)

[0131] B6: ExxonMobil "Exceed (registered trademark) 2018MA" (linear low-density polyethylene, the number of carbon atoms in the copolymer component is 6, and the density is 0.918 g / cm 3 , MFR (190°C, load 2160g) is 2.0g / 10min, weight average molecular weight (polystyrene conversion) is 208000)

[0132] B7: NOVATEC (registered trademark) UF641 manufactured by Japan Polyethylene Corporation (linear low-density polyethylene, the number of carbon atoms of the copolymer component is 4, and the density is 0.927 g / cm 3 , MFR (190°C, load 2160g) is 2.1g / 10min, weight average molecular weight (polystyrene conversion) is 220000)

[0133] B8: Borouge "Anteo FK2715" (linear low-density polyethylene, the number of carbon atoms of the copolymer components is 4 and 6, density is 0.927 g / cm 3 , MFR (190°C, load 2160g) is 1.3g / 10min, weight average molecular weight (polystyrene conversion) is 240000)

[0134] It should be noted that the weight average molecular weights of the polyethylene resins B1 to B8 are values ​​measured by the following method.

[0135] (Measurement of weight average molecular weight of polyethylene resin)

[0136] Weigh polyethylene resins B1 to B8 respectively, stir them in 1,2,4-trichlorobenzene solvent at 140°C for 1 hour to dissolve them. Use the dissolved sample to perform high-temperature GPC measurement at 140°C. It should be noted that the calibration curve is made using standard polystyrene "Model: 0005204, 0005205, 0005206, 0005207, 0005208, 0005209, 0005210, 0005211, 0005212, 0005213, 0005214, 0005215, 0005218, 0005220, 0005221" manufactured by Tosoh Corporation. Therefore, the value obtained is the polystyrene conversion molecular weight.

[0137] <Adhesive resin>

[0138] ·Mitsubishi Chemical Corporation's "Modic (registered trademark) M512" (density 0.90 g / cm 3 , MFR (190℃, load 2160g) 1.0g / 10min)

[0139] [Example 1]

[0140] [Manufacturing of Multilayer Structure]

[0141] Using the EVOH, B1 and adhesive resin, a four-layer five-layer multilayer casting machine is used to produce a multilayer structure (film) of B1 layer (40μm) / adhesive resin layer (5μm) / EVOH layer (10μm) / adhesive resin layer (5μm) / B1 layer (40μm).

[0142] The molding conditions are as follows.

[0143] (Molding conditions)

[0144] B1 layer: Φ40mm single screw extruder (barrel temperature 210℃)

[0145] Adhesive resin layer: Φ32mm single screw extruder (barrel temperature 210℃)

[0146] EVOH layer: Φ40mm single screw extruder (barrel temperature 220℃)

[0147] Die: Four types of five-layer feed head T-die (die temperature 220℃)

[0148] ·Traction speed: 6.5m / min

[0149] Roller temperature: 80℃

[0150] [Manufacturing of a 30 μm-thick single-layer film]

[0151] Using the above-mentioned B1, a 30 μm single-layer film (polyethylene-based resin layer) of B1 was produced using five types of five-layer inflation molding machines.

[0152] The film forming conditions are as follows.

[0153] (Film Forming Conditions)

[0154] Φ20mm single screw extruder × 5 (barrel temperature 230℃)

[0155] Die head temperature: 220℃

[0156] ·Traction speed: 2.5m / min

[0157] [Examples 2 to 4 and Comparative Examples 1 to 4]

[0158] A multilayer structure and a single-layer film were prepared in the same manner as in Example 1 except that the type of polyethylene resin was changed to the type shown in Table 1 below.

[0159] The multilayer structures and single-layer films of Examples 1 to 4 and Comparative Examples 1 to 4 were evaluated for impact strength and image clarity by the following methods. The evaluation results are shown in Table 1 below.

[0160] <Impact Strength (Dart Impact)>

[0161] (Impact strength B of polyethylene resin layer)

[0162] According to JIS K7124-1, a dart impact tester (manufactured by Toyo Seiki Co., Ltd.) was used to apply a weight to a stainless steel dart (Φ50 mm, 250 g), and the dart was dropped from a height of 1.50 m onto the monolayer film. The appearance of the monolayer film after the dart was dropped was visually confirmed, and the mass of the maximum weight that was not broken was taken as the dart impact strength of the monolayer film.

[0163] (Impact Strength A of Multilayer Structure)

[0164] According to JIS K7124-1, a dart impact tester (manufactured by Toyo Seiki Co., Ltd.) was used to apply a weight to an aluminum dart (Φ38 mm, 32 g) and drop it from a height of 0.66 m onto the multilayer structure. The appearance of the multilayer structure after the dart was dropped was visually confirmed, and the mass of the maximum weight that was not broken was taken as the dart impact strength of the multilayer structure.

[0165] <Image clarity (brightness)>

[0166] The image clarity of the multilayer structure was measured by the transmission method in accordance with JIS K 7374 "Plastics - Method for determination of image clarity". The film test piece was measured with the film machine direction as the vertical direction. The measuring instrument used was the ICM-1 type image clarity measuring instrument manufactured by SUGA Testing Instruments Co., Ltd. A 0.25 mm optical comb was used.

[0167] [Table 1]

[0168]

[0169] *"-" is not determined

[0170] It is understood that the multilayer structures of Examples 1 to 4 are within the range specified by the present invention, as compared with Comparative Examples 1 to 4 which are outside the range specified by the present invention, and therefore the multilayer structures are excellent in distinctness of image.

[0171] It is presumed that by setting the physical properties of the multilayer structure to be within the ranges specified in the present invention, the moldability becomes good and the image distinctness of the multilayer structure is excellent.

[0172] The above embodiments show specific aspects of the present invention, but the above embodiments are merely examples and are not to be construed as limiting. Various modifications obvious to those skilled in the art are intended to be within the scope of the present invention.

[0173] Industrial Applicability

[0174] Since the multilayer structure has excellent image clarity, it can be suitably used as packaging materials such as packaging containers and packaging films for various packaging materials such as mayonnaise, seasonings such as sauces, fermented foods such as soybean paste, oily foods such as salad oil, beverages, cosmetics, and pharmaceuticals, in addition to general foods.< / evoh>

Claims

1. A multilayer structure comprising an ethylene-vinyl alcohol copolymer layer (A) and a polyethylene resin layer (B), The density of the polyethylene resin contained in the polyethylene resin layer (B) is 0.850 g / cm 3 ~0.920g / cm 3 , The content of the polyethylene resin in the polyethylene resin layer (B) exceeds 80% by mass, The impact strength A of the multilayer structure is 350 g or more, The impact strength A is a value obtained by a dart impact A method and calculated by measurement in accordance with JIS K7124-1.

2. A multilayer structure comprising an ethylene-vinyl alcohol copolymer layer (A) and a polyethylene resin layer (B), The density of the polyethylene resin contained in the polyethylene resin layer (B) is 0.850 g / cm 3 ~0.920g / cm 3 , The content of the polyethylene resin in the polyethylene resin layer (B) exceeds 80% by mass, The weight average molecular weight of the polyethylene resin contained in the polyethylene resin layer (B) is 230,000 or more in terms of polystyrene.

3. A multilayer structure comprising an ethylene-vinyl alcohol copolymer layer (A) and a polyethylene resin layer (B), The density of the polyethylene resin contained in the polyethylene resin layer (B) is 0.850 g / cm 3 ~0.920g / cm 3 , The content of the polyethylene resin in the polyethylene resin layer (B) exceeds 80% by mass, The impact strength B of the polyethylene resin layer (B) is 500 g or more, The impact strength B is a value calculated by a dart impact B method based on JIS K7124-1 by measuring a test piece consisting of a single-layer film having the same composition as that of the polyethylene-based resin layer (B) and a thickness of 30 μm.

4. The multilayer structure according to any one of claims 1 to 3, in, The polyethylene resin is a linear low-density polyethylene.

5. The multilayer structure according to any one of claims 1 to 3, in, The polyethylene-based resin includes a copolymer component, and the copolymer component has 4 or more carbon atoms.

6. The multilayer structure according to any one of claims 1 to 3, in, It further includes an adhesive resin layer (C).

7. The multilayer structure according to any one of claims 1 to 3, in, The multilayer structure further comprises another layer (D) on at least one of the outermost layers, and the polyethylene resin layer (B) is provided between the other layer (D) and the ethylene-vinyl alcohol copolymer layer (A).

8. The multilayer structure according to any one of claims 1 to 3, in, There is no layer containing a polyamide-based resin as a main component.

9. A container using the multilayer structure according to any one of claims 1 to 3.

10. A food packaging container using the multilayer structure according to any one of claims 1 to 3.

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