Multilayer structure, and multilayer packaging material

Abstract

To provide a multilayer structure which has less thickness unevenness, low adsorptivity of an organic solvent, and sufficient barrier property.SOLUTION: A multilayer structure has a layer (A) containing a polyolefin resin, and a layer (B) containing an ethylene-vinyl alcohol copolymer, wherein the multilayer structure has two or more layers (B), and the layer (B) is positioned at the innermost layer and the intermediate layer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a multilayer structure, and more particularly to a multilayer structure having little thickness unevenness, low adsorption of organic solvents and the like, and excellent barrier properties, and a multilayer packaging material formed from the multilayer structure. [Background technology]

[0002] Ethylene-vinyl alcohol copolymer (hereinafter sometimes referred to as "EVOH") has very strong intermolecular forces due to hydrogen bonds between hydroxyl groups present in the polymer side chains. Therefore, it is highly crystalline, and the intermolecular forces are strong even in the amorphous parts. Therefore, structures using EVOH exhibit excellent gas barrier properties, with gas molecules being difficult to pass through. Therefore, EVOH is used as a gas barrier layer to impart gas barrier properties to multilayer structures such as films and containers in a wide range of fields, including food packaging.

[0003] For example, Patent Document 1 discloses a multilayer structure that contains a specific compound and has at least a recycled layer containing a recycled resin as a main component, a layer containing a polyolefin resin as a main component, and two or more barrier layers containing EVOH as a main component, the barrier layers being located on the outer and inner sides of the recycled resin layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-28167 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology disclosed in Patent Document 1 uses a barrier layer containing EVOH as a main component as an intermediate layer, which has uneven thickness, high adsorption of organic solvents, etc., and does not provide sufficient barrier properties, so there is room for further improvement.

[0006] Under these circumstances, an object of the present invention is to provide a multilayer structure having little thickness unevenness, low adsorption of organic solvents and the like, and sufficient barrier properties. [Means for solving the problem]

[0007] However, in view of the above circumstances, the present inventors have conducted extensive research and have found that the problems of the present invention can be solved by using a layer containing EVOH as the innermost layer and an intermediate layer in a multilayer structure having a layer containing a polyolefin resin and a layer containing EVOH, and have completed the present invention.

[0008] That is, the present invention has the following aspects. [1] A multilayer structure having a layer (A) containing a polyolefin resin and a layer (B) containing EVOH, The multilayer structure has two or more layers (B), and the layers (B) are located as an innermost layer and an intermediate layer. [2] The multilayer structure according to [1], wherein the content of ethylene structural units in the EVOH contained in the layer (B) is 20 to 47 mol %. [3] The multilayer structure according to [1] or [2], wherein the polyolefin resin contained in the layer (A) is a polyethylene resin. [4] The multilayer structure according to any one of [1] to [3], wherein the thickness of the layer (B) is 0.1 to 50% of the thickness of the multilayer structure. [5] The multilayer structure according to any one of [1] to [4], wherein the multilayer structure has a thickness of 1 to 10,000 μm. [6] The multilayer structure according to any one of [1] to [5], wherein the melting point of the EVOH contained in the layer (A) is 150°C or higher. [7] A multilayer packaging material formed from the multilayer structure according to any one of [1] to [6]. [Effects of the Invention]

[0009] The multilayer structure of the present invention has little thickness unevenness, low adsorption of organic solvents, etc., and excellent barrier properties, and therefore can be suitably used as a multilayer packaging material. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below based on examples of embodiments for carrying out the present invention, but the present invention is not limited to the embodiments described below.

[0011] In the present invention, "X and / or Y (X and Y are any configurations)" means at least one of X and Y, and means three possibilities: X only, Y only, and X and Y. When expressed as "X to Y" (X and Y are any numbers), unless otherwise specified, it means "X or more and Y or less," as well as "preferably greater than X" or "preferably smaller than Y." When expressed as "X or more" (X is any number) or "Y or less" (Y is any number), it also means that "it is preferably greater than X" or "it is preferably less than Y."

[0012] In the present invention, the term "main component" refers to a component that has a significant effect on the properties of the target object, and the content of the component is usually 50% by mass or more in the target object, preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and especially preferably 95% by mass or more, and may be 100% by mass.

[0013] <Multilayer structure> A multilayer structure according to one embodiment of the present invention (hereinafter referred to as "the multilayer structure") is a multilayer structure having a layer (A) containing a polyolefin resin (hereinafter referred to as "PO layer (A)") and a layer (B) containing EVOH (hereinafter referred to as "EVOH layer (B)"). The multilayer structure has two or more layers (B), and the layers (B) are located as the innermost layer and an intermediate layer. In the present invention, the "innermost layer" refers to the layer that comes into contact with the contents when the multilayer packaging material is formed using the multilayer structure, the "outermost layer" refers to the layer that comes into contact with the outside air, and the "intermediate layer" refers to the layer between the innermost layer and the outermost layer.

[0014] In addition to the PO layer (A) and the EVOH layer (B), the multilayer structure may also have a layer (C) containing an adhesive resin (hereinafter referred to as "adhesive resin layer (C)") and a substrate layer (D).

[0015] The layer configuration of the multilayer structure is not particularly limited as long as the EVOH layer (B) is located as the innermost layer and the intermediate layer. The multilayer structure may have a plurality of PO layers (A), EVOH layers (B), adhesive resin layers (C), and substrate layers (D). By using the EVOH layer (B) as the innermost layer, the multilayer structure can reduce the adsorption of organic solvents and the like released from the contents and the like.

[0016] In particular, in terms of the layer configuration of the present multilayer structure, it is preferable that the PO layer (A) be the outermost layer from the viewpoints of thickness stability and heat sealability, and from the viewpoint of barrier properties, it is preferable that both sides of the PO layer (A) are sandwiched between EVOH layers (B) via adhesive resin layers (C).

[0017] An example of a preferred layer configuration of the present multilayer structure is, from the innermost layer side, EVOH layer (B) / adhesive resin layer (C) / PO layer (A) / adhesive resin layer (C) / EVOH layer (B) / adhesive resin layer (C) / PO layer (A). However, the layer configuration of the present multilayer structure is not limited to this configuration. Each layer of the multilayer structure will now be described.

[0018] [PO layer (A)] The PO layer (A) is a layer formed from a resin composition containing a polyolefin resin.

[0019] The content of the polyolefin resin contained in the PO layer (A) is not particularly limited, but the PO layer (A) usually contains a polyolefin resin as a main component. The PO layer (A) may contain one type of polyolefin resin or multiple types of polyolefin resins.

[0020] Examples of the polyolefin resin include homopolymers of α-olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene, and copolymers of the α-olefins with other copolymerization components. Among these, from the viewpoint of transparency, polyethylene resins such as homopolymers of ethylene and copolymers of ethylene with other copolymerization components, and polypropylene resins such as homopolymers of propylene and copolymers of propylene with other copolymerization components are preferred, with polyethylene resins being particularly preferred.

[0021] (Polyethylene resin) As mentioned above, the polyethylene resin may be a homopolymer of ethylene or a copolymer of ethylene with another copolymer component.

[0022] Examples of the other copolymerization components include α-olefins having 3 to 20 carbon atoms, such as propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, and 1-octene; vinyl esters, such as vinyl acetate and vinyl propionate; unsaturated carboxylic acid esters and ionomers thereof, such as methyl (meth)acrylate and ethyl (meth)acrylate; and unsaturated compounds, such as conjugated dienes and non-conjugated dienes. These may be used alone or in combination of two or more. Among these, α-olefins having 4 to 10 carbon atoms are preferred, more preferably 1-butene, 1-hexene, and 1-octene, and particularly preferably 1-hexene and 1-octene, from the viewpoint of increasing impact strength. The number of carbon atoms of the other copolymerization components is 13 It can be determined by C-NMR measurement.

[0023] When the polyethylene resin is a copolymer, the ratio of other copolymerization components is usually 0.5 mol% or more, preferably 1 mol% or more, more preferably 2 mol% or more, and particularly preferably 3 mol% or more. The upper limit is usually 20 mol%. When the ratio of other copolymerization components is within the above range, impact strength tends to be increased. The ratio of the other copolymerization components can be determined by NMR measurement.

[0024] The method for producing the polyethylene resin is not particularly limited, and examples thereof include known polymerization methods using known olefin polymerization catalysts, such as slurry polymerization, solution polymerization, bulk polymerization, and gas phase polymerization using multi-site catalysts represented by Ziegler-Natta catalysts or single-site catalysts represented by metallocene catalysts, as well as bulk polymerization using a radical initiator.

[0025] Specific examples of the polyethylene resin include polyethylene resins in the broad sense, including modified polyethylene resins such as linear low-density polyethylene, low-density polyethylene, very low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-propylene (block and random) copolymers, and ethylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers, or combinations thereof. Of these, linear low-density polyethylene is preferred from the viewpoint of stretchability.

[0026] The polyethylene resin may be made from petroleum-derived or plant-derived raw materials, and preferably does not contain halogenated polyethylene.

[0027] The density of the polyethylene resin is usually 0.850 to 0.980 g / cm 3 and preferably 0.87 to 0.97 g / cm 3 , more preferably 0.88 to 0.95 g / cm 3 , particularly preferably 0.89 to 0.93 g / cm 3If the density is within the above range, the balance between transparency, strength, and flexibility tends to be excellent. Here, the density is a value measured in accordance with JIS K7112 (1999).

[0028] The melt flow rate (MFR) of the polyethylene resin (measured at 190°C under a load of 2160 g according to JIS K7210:2014) is usually 0.001 to 50 g / 10 min, and preferably 0.1 to 10 g / 10 min. If the MFR is within the above range, extrusion processability is stable, and there is a tendency for thickness unevenness and reduction or variation in mechanical strength to be reduced.

[0029] (polypropylene resin) The polypropylene resin is not particularly limited, and may be a homopolymer of propylene or a copolymer of propylene and another copolymerizable component.

[0030] Examples of the other copolymerization components include α-olefins having 2 to 20 carbon atoms, such as ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, and 1-octene, dienes such as divinylbenzene, 1,4-cyclohexadiene, dicyclopentadiene, cyclooctadiene, and ethylidene norbornene, vinyl acetate, (meth)acrylic acid, (meth)acrylic acid esters, glycidyl (meth)acrylate, vinyl alcohol, ethylene glycol, maleic anhydride, styrene, and cyclic olefins. These may be used alone or in combination of two or more.

[0031] The polypropylene resin may be a block copolymer, a random copolymer, or a graft copolymer.

[0032] The melt flow rate (MFR) of the polypropylene resin (measured at 190°C under a load of 2160 g according to JIS K7210:2014) is usually 0.2 g / 10 min or more, preferably 0.5 to 18 g / 10 min, and more preferably 1 to 15 g / 10 min. If the MFR is within the above range, extrusion processability is stable, and there is a tendency for thickness unevenness and reduction or variation in mechanical strength to be reduced.

[0033] The PO layer (A) may contain components other than the polyolefin resin, as long as the components do not impair the effects of the present invention (for example, typically 50% by mass or less of the PO layer (A), preferably 30% by mass or less, more preferably 20% by mass or less, and particularly preferably 10% by mass or less). Examples of the other components include resins other than polyolefin resins, antiblocking agents, processing aids, carboxylic acid compounds, phosphoric acid compounds, boron compounds, metal salts, stabilizers, antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, surfactants, desiccants, crosslinking agents, reinforcing agents such as various fibers, etc. These may be used alone or in combination of two or more.

[0034] Examples of resins other than the polyolefin resin include cyclic olefin resins, ionomers, 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, and polyketone resins such as aromatic polyketones and aliphatic polyketones. These may be used alone or in combination of two or more.

[0035] [EVOH layer (B)] The multilayer structure has two or more, preferably two, EVOH layers (B), which are located as an innermost layer and an intermediate layer, and which are formed from a resin composition containing EVOH. The EVOH layer (B) used as the innermost layer and the EVOH layer (B) used as the intermediate layer may be the same or different.

[0036] The content of EVOH contained in the EVOH layer (B) is not particularly limited, but the EVOH layer (B) usually contains EVOH as a main component.

[0037] The EVOH is 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.

[0038] As the vinyl ester monomer used in the EVOH, vinyl acetate is typically used because of its commercial availability and the efficiency of impurity removal during production. Other vinyl ester monomers include, 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. Aliphatic vinyl esters having typically 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 types.

[0039] The polymerization of ethylene and vinyl ester monomers can be carried out by any known polymerization method, such as solution polymerization, suspension polymerization, or emulsion polymerization, and solution polymerization using methanol as a solvent is generally used. The saponification of the resulting ethylene-vinyl ester copolymer can also be carried out by a known method. The EVOH produced in this manner is mainly composed of structural units derived from ethylene and vinyl alcohol structural units, and usually contains a small amount of vinyl ester structural units that remain unsaponified.

[0040] The content of ethylene structural units in the EVOH is usually 20 to 60 mol%, preferably 20 to 47 mol%, more preferably 22 to 46 mol%, and particularly preferably 25 to 45 mol%. If this content is too low, the gas barrier properties and melt moldability under high humidity conditions tend to decrease, while if it is too high, the gas barrier properties tend to decrease. The content of the ethylene structural units can be controlled by the ethylene pressure when copolymerizing the vinyl ester monomer with ethylene. The content of the ethylene structural unit can be measured based on ISO14663.

[0041] The saponification degree of the EVOH is usually 90 to 100 mol%, preferably 95 to 100 mol%, and more preferably 99 to 100 mol%. The saponification degree can be controlled by the amount, temperature, time, etc. of the saponification catalyst (usually an alkaline catalyst such as sodium hydroxide) used when saponifying the ethylene-vinyl ester copolymer. If the saponification degree is too low, the gas barrier properties, thermal stability, moist heat resistance, etc. tend to decrease. The degree of saponification of EVOH can be measured based on JIS K6726 (wherein EVOH is used as a solution uniformly dissolved in a water / methanol solvent).

[0042] The melt flow rate (MFR) of the EVOH (210°C, load 2160 g) is usually 0.5 to 100 g / 10 min, preferably 1 to 50 g / 10 min, and more preferably 3 to 35 g / 10 min. If the MFR is too high, stability during film formation tends to be impaired, while if it is too low, the viscosity tends to be too high, making melt extrusion difficult. The MFR is an index of the degree of polymerization of EVOH, and can be adjusted by the amount of polymerization initiator and the amount of solvent used when copolymerizing ethylene and vinyl ester monomers.

[0043] The melting point of the EVOH, preferably the EVOH used in the innermost layer, is preferably 150° C. or higher, more preferably 155° C. or higher, even more preferably 158° C. or higher, and particularly preferably 160° C. or higher, in order to achieve excellent heat seal resistance. The upper limit is usually 230° C. or lower, and preferably 220° C. or lower. The melting point of such EVOH can be measured, for example, using a differential scanning calorimeter (DSC) in accordance with the method of measuring the melting temperature after a certain heat treatment as specified in JIS K7121, and the melting peak temperature is taken as the melting point.

[0044] The EVOH may further contain structural units derived from the comonomers shown below (for example, 10 mol % or less of the EVOH) within the range that does not impair the effects of the present invention. Examples of the comonomer include olefins such as propylene, 1-butene, and isobutene; hydroxyl group-containing α-olefins such as 3-butene-1-ol, 3-butene-1,2-diol, 4-pentene-1-ol, and 5-hexene-1,2-diol, and derivatives thereof such as esters and acylates; hydroxyalkylvinylidenes such as 2-methylenepropane-1,3-diol and 3-methylenepentane-1,5-diol; 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, and 1,3-dibutyloxy. hydroxyalkylvinylidene diacetates such as hydroxy-2-methylenepropane; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, (anhydrous) phthalic acid, (anhydrous) maleic acid, (anhydrous) itaconic acid, or their salts or mono- or dialkyl esters in which the alkyl group has 1 to 18 carbon atoms; acrylamide, N-alkylacrylamide in which the alkyl group has 1 to 18 carbon atoms, N,N-dimethylacrylamide, 2-acrylamidopropanesulfonic acid or its salts, acrylamidopropyldimethylamine or its acid salts or its quaternary salts acrylamides such as methacrylamide, N-alkylmethacrylamides in which the alkyl group has 1 to 18 carbon atoms, N,N-dimethylmethacrylamide, 2-methacrylamidopropanesulfonic acid or its salt, methacrylamidepropyldimethylamine or its acid salt or its quaternary salt; N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide; vinyl cyanides such as acrylonitrile and methacrylonitrile; alkyl vinyl ethers in which the alkyl group has 1 to 18 carbon atoms, hydrochloric acid vinyl ethers such as alkoxyalkyl vinyl ether and alkoxyalkyl vinyl ether; halogenated vinyl compounds such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride and vinyl bromide; vinyl silanes such as trimethoxyvinylsilane; halogenated allyl compounds such as allyl acetate and allyl chloride; allyl alcohols such as allyl alcohol and dimethoxyallyl alcohol; and comonomers such as trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride and acrylamido-2-methylpropanesulfonic acid.These may be used alone or in combination of two or more.

[0045] Among these, hydroxyl group-containing α-olefins are preferred, and 3-butene-1,2-diol and 5-hexene-1,2-diol are particularly preferred. When the hydroxyl group-containing α-olefins are copolymerized, the resulting EVOH has primary hydroxyl groups in the side chains. Such EVOH having primary hydroxyl groups in the side chains, particularly EVOH having a 1,2-diol structure in the side chain, is preferred because it maintains gas barrier properties while providing good secondary moldability.

[0046] When the EVOH has a primary hydroxyl group in a side chain, the content of structural units derived from a monomer having the primary hydroxyl group is usually 0.1 to 20 mol %, preferably 0.5 to 15 mol %, particularly preferably 1 to 10 mol % of the EVOH.

[0047] Furthermore, as the EVOH, EVOH that has been "post-modified" by esterification, urethanization, acetalization, cyanoethylation, oxyalkylenation, or the like can also be used.

[0048] When the post-modified EVOH is used, the modification rate is usually 10 mol% or less, and preferably 4 mol% or less. The lower limit is 0.1 mol%. If the modification rate of the EVOH is too high, the EVOH tends to be prone to thermal degradation, and if it is too low, the long-run properties tend to decrease.

[0049] The EVOH may be a mixture of EVOHs having different ethylene structural unit contents, saponification degrees, polymerization degrees, copolymerization components, and the like.

[0050] The EVOH layer (B) may contain components other than EVOH as long as the components do not impair the effects of the present invention (for example, typically 50% by mass or less of the EVOH layer (B), preferably 30% by mass or less, more preferably 20% by mass or less, and particularly preferably 10% by mass or less). Examples of the other components include antiblocking 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, crosslinking agents, reinforcing agents such as various fibers, etc. These may be used alone or in combination of two or more.

[0051] [Adhesive resin layer (C)] The multilayer structure preferably has an adhesive resin layer (C) to improve the adhesion between the layers. The adhesive resin layer (C) is a layer formed from a resin composition containing an adhesive resin.

[0052] The content of the adhesive resin in the adhesive resin layer (C) is not particularly limited, but it is usually one containing the adhesive resin as the main component.

[0053] The adhesive resin is not particularly limited, but examples thereof include modified polyolefin resins containing carboxy groups obtained by chemically bonding an unsaturated carboxylic acid or its anhydride to a polyolefin resin by an addition reaction, a graft reaction, or the like.

[0054] Examples of the modified polyolefin containing a carboxy group include maleic anhydride-grafted polyethylene resin, maleic anhydride-grafted polypropylene resin, maleic anhydride-grafted ethylene-propylene (block and random) copolymer, maleic anhydride-grafted ethylene-ethyl acrylate copolymer, maleic anhydride-grafted ethylene-α-olefin copolymer, maleic anhydride-grafted ethylene-vinyl acetate copolymer, maleic anhydride-grafted polycyclic olefin resin, and other maleic anhydride-grafted polyolefin resins. These may be used alone or as a mixture of two or more kinds.

[0055] As the adhesive resin, maleic anhydride-grafted polyethylene resin and maleic anhydride-grafted ethylene-α-olefin copolymer are particularly preferred, since they contribute not only to interlayer adhesion but also to the effect of suppressing gel formation during melt heating and the effect of suppressing a decrease in transparency.

[0056] The melt flow rate (MFR) of the adhesive resin (measured according to JIS K7210:2014 at 190°C and a load of 2160 g) is usually 0.1 to 20.0 g / 10 min, and preferably 1.0 to 10.0 g / 10 min. If the MFR is too high, the stretchability of the multilayer structure tends to decrease, while if it is too low, the film-forming ability tends to decrease.

[0057] When maleic anhydride grafted modified polyethylene is used as the adhesive resin, the MFR (190°C, load 2160 g) is usually 0.01 to 150 g / 10 min, preferably 0.1 to 50 g / 10 min, more preferably 1 to 25 g / 10 min, and even more preferably 3 to 10 g / 10 min.

[0058] The acid value of the adhesive resin is usually 50 mgKOH / g or less, preferably 30 mgKOH / g or less, and particularly preferably 20 mgKOH / g or less. If the acid value is too high, the number of reaction sites with the hydroxyl groups in the EVOH increases, resulting in the formation of highly polymerized products during the melt-kneading process, which reduces stability during extrusion processing and makes it difficult to obtain good molded products. The lower limit of the acid value is usually 1 mgKOH / g, and preferably 2 mgKOH / g or more. The acid value is measured in accordance with JIS K0070.

[0059] The adhesive resin layer (C) may contain other components in addition to the adhesive resin, as long as the components do not impair the effects of the present invention (for example, typically 50% by mass or less of the adhesive resin layer (C), preferably 30% by mass or less, more preferably 20% by mass or less, and particularly preferably 10% by mass or less). Examples of the other components include antiblocking agents, processing aids, resins other than adhesive resins, carboxylic acid compounds, phosphoric acid compounds, boron compounds, metal salts, stabilizers, antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, surfactants, desiccants, crosslinking agents, reinforcing agents such as various fibers, etc. These may be used alone or in combination of two or more.

[0060] [Base material layer (D)] The multilayer structure may have a substrate layer (D) in addition to the PO layer (A), the EVOH layer (B), and the adhesive resin layer (C). The substrate layer (D) is a layer formed from a resin composition containing, as a main component, a thermoplastic resin other than a polyolefin resin and EVOH.

[0061] Examples of thermoplastic resins other than the polyolefin resins and EVOH include cyclic olefin 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, halogenated polyolefins such as chlorinated polyethylene and chlorinated polypropylene, polyketone resins such as aromatic polyketones and aliphatic polyketones, etc. These may be used alone or in combination of two or more.

[0062] The base layer (D) may also contain a recycled resin obtained by remelting and molding edges, defective products, etc., generated during the production process of the present multilayer structure. Such recycled resin usually contains a mixture of a PO layer (A) and an EVOH layer (B).

[0063] In addition, the base layer (D) may contain components other than the thermoplastic resin, as long as the components do not impair the effects of the present invention (for example, typically 50% by mass or less of the base layer (D), preferably 30% by mass or less, more preferably 20% by mass or less, and particularly preferably 10% by mass or less). Examples of the other components include conventionally known plasticizers, fillers, clays (montmorillonite, etc.), colorants, antioxidants, antistatic agents, lubricants, core materials, antiblocking agents, ultraviolet absorbers, waxes, etc. These may be used alone or in combination of two or more.

[0064] It is preferable that the present multilayer structure does not include a layer containing a polyamide resin (a layer formed from a resin composition containing a polyamide resin as a main component) as the substrate layer (D).

[0065] [Method of manufacturing the present multilayer structure] The multilayer structure has a PO layer (A) and two or more EVOH layers (B), and is obtained by laminating the EVOH layers (B) so that they are positioned as the innermost and intermediate layers. When the multilayer structure has an adhesive resin layer (C) or a substrate layer (D), these layers may be laminated with the PO layer (A) and the EVOH layer (B).

[0066] The lamination method can be a known method. Examples include a method of melt-extrusion laminating a resin composition forming another layer onto any one of the layers included in the multilayer structure, a method of co-extruding the resin compositions forming each layer, a method of dry-laminating each layer using a known adhesive such as an organic titanium compound, an isocyanate compound, a polyester compound, or a polyurethane compound, and a method of applying a solution of a resin composition forming another layer onto any one of the layers included in the multilayer structure and then removing the solvent. Among these, the co-extrusion method is preferred in consideration of cost and environmental impact.

[0067] The multilayer structure is preferably unstretched from the viewpoint of thickness stability, but may be subjected to a (heat) stretching treatment if necessary.

[0068] The stretching may be uniaxial stretching or biaxial stretching, and the biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching.

[0069] Examples of the stretching method include roll stretching, tenter stretching, tubular stretching, stretch-blow method, and vacuum / compressed air forming. Among these, tenter stretching is preferred from the viewpoint of productivity. The stretched state of the multilayer structure can be confirmed by using a general method for analyzing the orientation of a resin (for example, wide-angle X-ray scattering (WAXS)).

[0070] The stretching temperature of the present multilayer structure is usually 100 to 200° C., preferably 110 to 190° C., and more preferably 120 to 180° C. If the stretching temperature is too low, the stretching tends to be poor, and if it is too high, it tends to be difficult to maintain a stable stretched state.

[0071] When the multilayer structure is uniaxially stretched, the stretching direction may be the machine direction (MD) which is parallel to the running direction of the multilayer structure, or the transverse direction (TD) which is perpendicular to the running direction of the multilayer structure. When the present multilayer structure is uniaxially stretched, the stretching ratio is usually 2 to 10 times, preferably 2.5 to 7 times, and more preferably 3 to 6 times.

[0072] When the present multilayer structure is biaxially stretched, the stretching ratio in MD is usually 2 to 10 times, preferably 2.5 to 7 times, and more preferably 3 to 6 times, and the stretching ratio in TD is usually 2 to 10 times, preferably 2.5 to 7 times, and more preferably 3 to 6 times. The order of stretching is not particularly limited, but from the viewpoint of productivity, stretching is preferably performed in the order from MD to TD.

[0073] Furthermore, when the present multilayer structure is biaxially stretched, the areal stretching ratio (MD stretching ratio × TD stretching ratio) is preferably 5 times or more, more preferably 6 to 100 times, even more preferably 7 to 80 times, particularly preferably 8 to 50 times, and especially preferably 8 to 30 times. If the stretching ratio and areal stretching ratio are too large, the film surface after stretching tends to deteriorate.

[0074] To impart dimensional stability to the stretched film, the film may be further heat-set by known means, such as a method of subjecting the multilayer structure to heat treatment while maintaining tension at typically 80 to 180°C, preferably 100 to 165°C, for typically 2 to 600 seconds.

[0075] The multilayer structure thus obtained has an EVOH layer (B) in the innermost layer and the intermediate layer, and therefore has low adsorption of organic solvents and excellent barrier properties.

[0076] From the viewpoint of thickness stability, the thickness of the present layer structure is preferably 1 to 10,000 μm, more preferably 5 to 5,000 μm, and particularly preferably 10 to 1,000 μm.

[0077] The thickness of each layer of the present multilayer structure is not particularly limited, but the thickness of the PO layer (A) is usually 3 to 3000 μm, preferably 5 to 2000 μm, and particularly preferably 10 to 1000 μm. The thickness of the EVOH layer (B) is usually 0.5 to 200 μm, preferably 1 to 100 μm. The thickness of the adhesive resin layer (C) is usually 0.5 to 250 μm, preferably 0.5 to 150 μm, and more preferably 1 to 100 μm. The thickness of the substrate layer (D) is usually 3 to 3000 μm, preferably 5 to 2000 μm, and particularly preferably 10 to 1000 μm. When a plurality of layers of each type are present, it is preferable that the total thickness of the plurality of layers is within the above thickness range.

[0078] The ratio of the thickness of the EVOH layer (B) to the thickness of the present multilayer structure is preferably 0.1 to 50%, more preferably 0.5 to 40%, and particularly preferably 1 to 30%. When the thickness of the EVOH layer (B) is within this range, the gas barrier property tends to be excellent. The thickness of the EVOH layer (B) is the total thickness of all the EVOH layers (B).

[0079] The ratio A / B of the thickness of the EVOH layer (B) to the thickness of the PO layer (A) (both are single layer thicknesses) is usually 50 / 1 to 1 / 10, preferably 30 / 1 to 1 / 5, and particularly preferably 10 / 1 to 1 / 3. If A / B is too small, the gas barrier properties tend to be insufficient, and conversely, if it is too large, the multilayer structure tends to be brittle.

[0080] The ratio B / C of the thickness of the EVOH layer (B) to the thickness of the adhesive resin layer (C) (both are single layer thicknesses) is usually 1 / 10 to 10 / 1, preferably 1 / 5 to 5 / 1, and particularly preferably 1 / 3 to 3 / 1. If the B / C ratio is too small, the gas barrier properties tend to be insufficient, and conversely, if it is too large, the adhesiveness tends to be insufficient.

[0081] The multilayer structure has excellent barrier properties, and the oxygen permeability of the multilayer structure (cc. 20 μm / m 2 ·day·atm) is usually 10cc.20μm / m 2 ·day·atm or less, preferably 5cc.20μm / m 2 ·day·atm or less, particularly preferably 2cc.20μm / m 2 ·day·atm or less. The oxygen permeability (cc. 20 μm / m 2 ·day·atm) is a value measured using Ox-tran2 / 21 at 20°C and 90% RH.

[0082] The present multilayer structure has little thickness variation, low adsorption of organic solvents and the like, and excellent barrier properties, and therefore can be suitably used as a multilayer packaging material for packaging general foods, as well as multilayer structures for packaging, such as seasonings such as mayonnaise and dressings, fermented foods such as miso, oily foods such as salad oil, snacks, beverages, cosmetics, pharmaceuticals, etc., or as a part of the multilayer structures used to form these.

[0083] The multilayer packaging material may be in the form of a bag, a tube, or a bottle, and may also be formed into a cup or tray using the multilayer structure. In such cases, a drawing method is usually employed, specifically, a vacuum forming method, a pressure forming method, a vacuum pressure forming method, a plug-assisted vacuum pressure forming method, etc. Furthermore, when using this multilayer structure to obtain a tubular or bottle-shaped multilayer packaging material from a multilayer parison (a hollow tubular preform before blowing), a blow molding method is employed. Specific examples include extrusion blow molding (two-head, mold-moving, parison-shift, rotary, accumulator, horizontal parison, etc.), cold parison blow molding, injection blow molding, and biaxial stretch blow molding (extrusion cold parison biaxial stretch blow molding, injection cold parison biaxial stretch blow molding, injection molding in-line biaxial stretch blow molding, etc.). The resulting molded article can be subjected to heat treatment, cooling treatment, rolling treatment, printing treatment, dry lamination treatment, solution or melt coating treatment, bag making, deep drawing, box processing, tube processing, splitting, etc., as needed. [Example]

[0084] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. In the examples, "parts" and "%" are by mass.

[0085] Prior to the examples, the following ingredients were prepared: [Polyolefin resin] Polyethylene (PE): Mitsubishi Chemical Corporation "Novatec UF641", density 0.927 g / cm 3 , MFR 2.1g / 10min (190℃, load 2160g) Polypropylene (PP): Mitsubishi Chemical Corporation "Novatec FB3B", density 0.90 g / cm 3 , MFR 7.5g / 10min (190℃, load 2160g) [EVOH] EVOH1: Ethylene unit content 29 mol%, MFR 3.8 g / 10 min (210°C, load 2160 g), density 1.21 g / cm 3 , Saponification degree 99.9 mol%, Melting point 188℃ EVOH2: Ethylene unit content 44 mol%, MFR: 3.8 g / 10 min (210 °C, load 2160 g), density 1.19 g / cm 3 , Saponification degree 99.9 mol%, Melting point 164℃ EVOH3: Ethylene unit content 48 mol%, MFR: 15 g / 10 min (210 °C, load 2160 g), density 1.12 g / cm 3 , Saponification degree 99.9 mol%, Melting point 158℃ [Adhesive resin] Adhesive resin (tie): Mitsubishi Chemical Corporation "Modic M533", density 0.92 g / cm 3 , MFR 2.5g / 10min (190℃, load 2160g)

[0086] <Examples 1 to 5, Comparative Examples 1 to 4> Polyolefin resin, EVOH, and adhesive resin were supplied to a multilayer film device (manufactured by Plastics Engineering Research Institute) so as to form the layer structure shown in Table 1 below, and co-extruded under the multilayer co-extrusion molding conditions shown below to obtain the multilayer structures of Examples 1 to 5 and Comparative Examples 1 to 4. [Multi-layer co-extrusion molding conditions] PO layer (A): Single screw extruder, barrel temperature 210°C EVOH layer (B): Single screw extruder, barrel temperature 230℃ Adhesive resin layer (C): Single screw extruder, barrel temperature 200°C Die: Multilayer die, set temperature 230℃

[0087] The following evaluations were carried out using the obtained multilayer structures of Examples 1 to 5 and Comparative Examples 1 to 4. The results are shown in Table 1 below.

[0088] [Thickness stability] The thickness of the multilayer structure was measured at five points at 2 cm intervals, the difference between the maximum and minimum thicknesses was calculated, and the ratio of this difference to the total thickness was calculated and evaluated according to the following evaluation criteria. [Evaluation criteria] ○: 10% or less △: Over 10% and 20% or less ×: More than 20%

[0089] [Adsorption] A 10cm x 10cm multilayer laminate was heat-sealed at three points to create a pouch, and its mass (W1) was measured. Next, toluene was placed in the pouch, and after storing it for three days, the toluene was removed from the pouch and the mass (W2) of the pouch was measured. The adsorption rate (%) was then calculated using the following formula, and the results were evaluated according to the following criteria. Adsorption rate (%) = (W2 - W1) / W1 x 100 [Evaluation criteria] ○: 1% or less △: Over 1% and 5% or less ×: More than 5%

[0090] [Barrier properties] Using OX-TRAN2 / 21, oxygen permeability (cc. 20 μm / m) was measured under the conditions of 23°C, 90% external humidity, and 50% internal humidity. 2 The oxygen permeability (O2 / day / atm) was measured and evaluated according to the following criteria. The smaller the oxygen permeability value, the better the barrier properties. [Evaluation criteria] 〇: 5cc.20μm / m 2 ·day · atm or less △: 5cc.20μm / m 2 ·day·atm exceeding 10cc.20μm / m 2 ·day · atm or less ×:10cc.20μm / m 2 Exceeding the ATM limit

[0091] 〔comprehensive evaluation〕 Based on the evaluation results of the thickness stability, heat sealability, glossiness, and barrier property, a comprehensive evaluation was made according to the following evaluation criteria. [Evaluation criteria] ◎: All evaluation results are "〇" 〇: All evaluation results are "△" or higher ×: Any evaluation result is "×"

[0092] [Table 1]

[0093] From the results in Table 1, the multilayer structures of Examples 1 to 5 had high thickness stability and excellent adsorption and barrier properties. On the other hand, the multilayer structure of Comparative Example 1, which had the EVOH layer (B) only in the innermost layer, had poor barrier properties, and the multilayer structures of Comparative Examples 2 and 3, which had the EVOH layer (B) in the intermediate layer, had poor adsorption properties. Furthermore, the multilayer structure of Comparative Example 4, which had the EVOH layer (B) in the innermost and outermost layers, had poor thickness stability. [Industrial Applicability]

[0094] The present multilayer structure can be suitably used as a multilayer packaging material for packaging general foods, as well as seasonings such as mayonnaise and dressings, fermented foods such as miso, oily foods such as salad oil, snacks, beverages, cosmetics, pharmaceuticals, etc., or as a packaging material such as a multilayer structure for packaging, or as a part of a multilayer structure for forming these.

Claims

1. A multilayer structure having a layer (A) containing a polyolefin resin and a layer (B) containing an ethylene-vinyl alcohol copolymer, The multilayer structure has two or more layers (B), and the layers (B) are located as an innermost layer and an intermediate layer.

2. 2. The multilayer structure according to claim 1, wherein the ethylene-vinyl alcohol copolymer contained in said layer (B) has an ethylene structural unit content of 20 to 47 mol %.

3. 2. The multilayer structure according to claim 1, wherein the polyolefin resin contained in said layer (A) is a polyethylene resin.

4. 2. The multilayer structure according to claim 1, wherein the thickness of said layer (B) is 0.1 to 50% of the thickness of said multilayer structure.

5. 2. The multilayer structure according to claim 1, wherein the thickness of the multilayer structure is 1 to 10,000 μm.

6. 2. The multilayer structure according to claim 1, wherein the melting point of the ethylene-vinyl alcohol copolymer contained in the layer (A) is 150° C. or higher.

7. A multilayer packaging material formed from the multilayer structure according to any one of claims 1 to 6.

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