Biaxially oriented multilayer structure and method for producing same

Abstract

To provide a sequentially biaxially oriented multilayer structure having excellent barrier properties.SOLUTION: A sequentially biaxially oriented multilayer structure comprises an ethylene-vinyl alcohol copolymer layer (A) and a polyethylene resin layer (B).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a biaxially oriented multilayer structure, and more particularly to a biaxially oriented multilayer structure having excellent barrier properties and a method for producing the same. [Background technology]

[0002] Ethylene-vinyl alcohol copolymers (hereinafter sometimes referred to as "EVOH") have very strong intermolecular forces due to hydrogen bonds between hydroxyl groups present in the polymer side chains. As a result, they are highly crystalline and have strong intermolecular forces even in the amorphous parts, so structures using EVOH are difficult for gas molecules to pass through and exhibit excellent gas barrier properties. For this reason, 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, such as food packaging.

[0003] For example, Patent Document 1 discloses a method for producing a biaxially stretched film, in which a film mainly made of EVOH having a specific composition is simultaneously biaxially stretched at a specific temperature, cooled, and heat-treated.

[0004] Patent Document 2 discloses a film in which a first resin layer formed from polyethylene and a second resin layer formed from EVOH are adjacent to each other by coextrusion and stretched in the same direction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-321278 A [Patent Document 2] JP 2023-37857 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the techniques disclosed in Patent Documents 1 and 2 above have insufficient barrier properties, and there is room for further improvement in the barrier properties.

[0007] Under such circumstances, an object of the present invention is to provide a biaxially oriented multilayer structure having an EVOH layer having excellent barrier properties and a polyethylene-based resin layer. [Means for solving the problem]

[0008] However, in view of the above circumstances, the present inventors conducted extensive research and discovered that sequential biaxial stretching of a multilayer structure having an EVOH layer (A) and a polyethylene-based resin layer (B) results in excellent barrier properties, and thus completed the present invention.

[0009] That is, the present invention has the following aspects. [1] A sequentially biaxially oriented multilayer structure having an ethylene-vinyl alcohol copolymer layer (A) and a polyethylene resin layer (B). [2] The sequentially biaxially stretched multilayer structure according to [1], wherein the ethylene-vinyl alcohol-based copolymer contained in the ethylene-vinyl alcohol-based copolymer layer (A) contains two or more types of ethylene-vinyl alcohol-based copolymers. [3] The sequentially biaxially stretched multilayer structure according to [1] or [2], wherein the ethylene structural unit content of the ethylene-vinyl alcohol copolymer contained in the ethylene-vinyl alcohol copolymer layer (A) is 43 mol % or less. [4] The sequentially biaxially oriented multilayer structure according to any one of [1] to [3], wherein the sequentially biaxially oriented multilayer structure has an areal magnification of 5 times or more. [5] The sequentially biaxially oriented multilayer structure according to any one of [1] to [4], wherein the sequentially biaxially oriented multilayer structure has a stretching temperature of 115 to 140°C. [6] The sequentially biaxially oriented multilayer structure according to any one of [1] to [5], wherein the sequentially biaxially oriented multilayer structure has at least three layers, namely, an outer layer, an intermediate layer, and an inner layer, and the intermediate layer is the ethylene-vinyl alcohol-based copolymer layer (A). [7] The sequentially biaxially oriented multilayer structure according to [6], wherein the outer layer and / or the inner layer of the sequentially biaxially oriented multilayer structure is the polyethylene-based resin layer (B). [8] A multilayer structure having an ethylene-vinyl alcohol copolymer layer (A) and a polyethylene resin layer (B), A method for producing a multilayer structure, comprising the step of sequentially biaxially stretching the multilayer structure. Effect of the Invention

[0010] The sequentially biaxially oriented multilayer structure of the present invention having an EVOH layer (A) and a polyethylene-based resin layer (B) has excellent barrier properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described below based on examples of the mode for carrying out the present invention. However, the present invention is not limited to the embodiment described below.

[0012] In the present invention, "x and / or y (x and y are optional configurations)" means at least one of x and y, and means three possibilities: only x, only y, and both x and y. When expressed as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it includes the meaning of "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 includes the meaning that "greater than X is preferable" or "less than Y is preferable."

[0013] <Sequentially biaxially stretched multilayer structure> The sequentially biaxially oriented multilayer structure according to one embodiment of the present invention (hereinafter, sometimes referred to as "the sequentially biaxially oriented multilayer structure") has an EVOH layer (A) and a polyethylene resin layer (B). In addition, the sequentially biaxially oriented multilayer structure is preferably provided with an adhesive resin layer (C).

[0014] The sequentially biaxially stretched multilayer structure may contain an EVOH layer (A) and a polyethylene-based resin layer (B), and other layer configurations are not particularly limited. For example, the structure (A / C / B) in which the polyethylene-based resin layer (B) is laminated on the EVOH layer (A) via the adhesive resin layer (C), and the structure (B / C / A / C / B) in which the polyethylene-based resin layer (B) is laminated on both sides of the EVOH layer (A) via the adhesive resin layer (C) can be mentioned. In particular, the present sequentially biaxially oriented multilayer structure has at least three layers, namely, an outer layer, an intermediate layer, and an inner layer, and it is preferable that the intermediate layer is an EVOH layer (A), and it is more preferable that the outer layer and / or the inner layer of the present sequentially biaxially oriented multilayer structure is a polyethylene-based resin layer (B).

[0015] In the present invention, a base layer (D) may be provided between these layers or as the outermost layer of the multilayer structure. The layers (A) to (D) may be provided in plurality in the present sequentially biaxially oriented multilayer structure. Each component will be described below.

[0016] [EVOH layer (A)] The EVOH layer (A) is a layer formed of a resin composition containing EVOH. 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.

[0017] The content of EVOH contained in the EVOH layer (A) is not particularly limited, but EVOH is preferably 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, and particularly preferably 100% by mass.

[0018] As the vinyl ester monomer used for the EVOH, vinyl acetate is typically used because of its good market availability and efficiency in treating impurities 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. Usually, 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 kinds.

[0019] 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 generally, solution polymerization using methanol as a solvent is used. The saponification of the obtained 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.

[0020] The EVOH may further contain structural units derived from the comonomers shown below (for example, 10 mol % or less of the EVOH) to the extent that the effects of the present invention are not impaired. Examples of the comonomer include olefins such as propylene, 1-butene, and isobutene; hydroxyl-containing α-olefins such as 3-buten-1-ol, 3-butene-1,2-diol, 4-penten-1-ol, and 5-hexene-1,2-diol, and derivatives thereof such as esters and acylation products; 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-2-methylenepropane; hydroxyalkylvinylidene diacetates such as hydroxyalkyl-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 having an alkyl group with 1 to 18 carbon atoms; acrylamide, N-alkylacrylamide having an alkyl group with 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-alkyl methacrylamides having an alkyl group with 1 to 18 carbon atoms, N,N-dimethyl methacrylamide, 2-methacrylamidopropanesulfonic acid or its salt, methacrylamidepropyldimethylamine or its acid salt or its quaternary salt; N-vinyl amides such as N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide; vinyl cyanides such as acrylonitrile and methacrylonitrile; alkyl vinyl ethers having an alkyl group with 1 to 18 carbon atoms, hydrochloride, etc. 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 can be used alone or in combination of two or more.

[0021] Among them, in this embodiment, since EVOH having a primary hydroxyl group in the side chain is preferable, it is preferable to use a hydroxyl group-containing α-olefin as the comonomer, and in particular, 3-butene-1,2-diol and 5-hexene-1,2-diol are preferable. Such EVOH having a primary hydroxyl group in the side chain, in particular, EVOH having a 1,2-diol structure in the side chain, is preferable in that it has good secondary moldability while maintaining gas barrier properties.

[0022] In the case of EVOH having a primary hydroxyl group in the 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 %, and particularly preferably 1 to 10 mol % of the EVOH.

[0023] Furthermore, as the EVOH, EVOH that has been "post-modified" by esterification, urethanization, acetalization, cyanoethylation, oxyalkylenation, or the like can also be used.

[0024] 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, it tends to be easily thermally deteriorated, and if it is too low, the long-run property tends to decrease.

[0025] The EVOH contained in the EVOH layer (A) preferably contains two or more kinds of EVOH. The EVOH may differ in ethylene structural unit content, saponification degree, polymerization degree, copolymerization component, etc., and preferably contains two or more kinds of EVOH having different ethylene structural unit contents.

[0026] When EVOH having different ethylene structural unit contents is contained in the EVOH layer (A), the number of types is usually 2 to 4, preferably 2 to 3, and particularly preferably 2. As the number of types increases, the productivity and economic efficiency tend to decrease. The number of EVOHs with different ethylene structural unit contents contained in the EVOH layer (A) can be determined from the number of peaks measured using a differential scanning calorimeter (DSC).

[0027] The difference between EVOH (a1) having the maximum ethylene structural unit content in the EVOH layer (A) and EVOH (a2) having the minimum ethylene structural unit content in the EVOH is usually 4 mol% or more, preferably 5 to 30 mol%, more preferably 6 to 25 mol%, and further preferably 7 to 20 mol%. If the difference in the ethylene structural unit content is too small, uneven thickness and cracks tend to occur easily during molding of the multilayer container, whereas if it is too large, the gas barrier properties and appearance tend to deteriorate.

[0028] The difference in the ethylene structural unit content of the two or more EVOHs contained in the EVOH layer (A) can be determined, for example, by measuring the melting peak temperature. That is, since the ethylene structural unit content of EVOH generally correlates with the melting point of EVOH, the ethylene structural unit content of each of the two or more EVOHs contained in the EVOH layer (A) can be calculated by measuring the melting peak temperature of the EVOH layer (A). The melting peak temperature means the peak temperature measured using a differential scanning calorimeter (DSC) when the temperature is increased from -50 to 230°C at 10°C / min, decreased from 230 to -50°C at 10°C / min, and then increased again from -50 to 230°C at 10°C / min.

[0029] The ethylene structural unit content of the EVOH contained in the EVOH layer (A) is usually 20 to 60 mol%, preferably 43 mol% or less, more preferably 24 to 43 mol%, and further preferably 25 to 40 mol%. The ethylene structural unit content can be controlled by the ethylene pressure when copolymerizing the vinyl ester monomer with ethylene. If the content is too low, the gas barrier properties and melt moldability under high humidity tend to decrease, and conversely, if the content is too high, the gas barrier properties tend to decrease. The ethylene structural unit content can be measured based on ISO14663.

[0030] The saponification degree of the EVOH contained in the EVOH layer (A) is usually 90 to 100 mol%, preferably 95 to 100 mol%, 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 is used) used when saponifying the ethylene-vinyl ester copolymer. If the saponification degree is too low, the gas barrier property, 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).

[0031] The melt flow rate (MFR) (210°C, load 2160g) of the EVOH contained in the EVOH layer (A) is usually 0.5 to 100g / 10min, preferably 1 to 50g / 10min, more preferably 3 to 35g / 10min. If the MFR is too high, the stability during film formation tends to be impaired, whereas 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 with a vinyl ester monomer.

[0032] The melting point of the EVOH contained in the EVOH layer (A) is usually 240° C. or lower, preferably 150 to 230° C., and particularly preferably 160 to 220° C. If the melting point is too high, the EVOH tends to be easily decomposed during molding, and if it is too low, the extrusion moldability tends to be unstable. 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.

[0033] The EVOH layer (A) may contain components other than EVOH as long as the effects of the present invention are not impaired. For example, it may contain other components such as antiblocking agents, processing aids, resins other than EVOH, carboxylic acid compounds, phosphoric acid compounds, boron compounds, metal salts, stabilizers, antioxidants, UV absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, surfactants, drying agents, crosslinking agents, and reinforcing agents such as various fibers. These may be used alone or in combination of two or more.

[0034] [Polyethylene resin layer (B)] The polyethylene resin layer (B) is a layer formed from a resin composition containing a polyethylene resin.

[0035] The content of the polyethylene resin in the polyethylene resin layer (B) is not particularly limited, but it is preferable that the polyethylene resin is the main component (i.e., the content of the polyethylene resin in the polyethylene resin layer (B) is 50% by mass or more). The content of the polyethylene resin in the polyethylene resin layer (B) 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, and 100% by mass.

[0036] 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 polyethylene resins such as ethylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers, or combinations thereof. Among these, linear low-density polyethylene is preferred from the viewpoint of stretchability. The raw material of the polyethylene resin may be derived from petroleum or plants. The polyethylene resin preferably does not contain halogenated polyethylene.

[0037] The polyethylene resin may be a homopolymer resin of ethylene or a copolymer resin. When the polyethylene resin is a copolymer resin, the impact strength can be increased by using a copolymer component having a large carbon number. Examples of the copolymer component other than ethylene include α-olefins having preferably 4 or more carbon atoms, more preferably 6 or more carbon atoms, and even more preferably 8 or more carbon atoms. Specific examples include butene, hexene, octene, etc., and preferably hexene and octene. The carbon number of the copolymer component can be measured by C-NMR.

[0038] When the polyethylene resin is a copolymer resin, there is a tendency that the impact strength can be increased by increasing the ratio of the copolymerization component. The ratio of the copolymerization component is preferably 0.5 mol% or more, more preferably 1 mol% or more, even more preferably 2 mol% or more, and particularly preferably 3 mol% or more. The upper limit is usually 20 mol%. The ratio of the copolymerization component can be measured by NMR.

[0039] The density of the polyethylene resin is usually 0.85 to 0.98 g / cm 3 and preferably 0.87 to 0.97 g / cm 3 , more preferably 0.88 to 0.95 g / cm 3 , and more preferably 0.89 to 0.93 g / cm 3If the density is too high, the stretchability of the multilayer structure tends to decrease, whereas if the density is too low, the mechanical strength tends to be poor.

[0040] The melt flow rate (MFR) of the polyethylene resin (measured according to JIS K7210:2014 at 190°C and 2160g) is usually 0.001 to 50g / 10min, and more preferably 0.1 to 10g / 10min. If the MFR is too high, the stretchability of the multilayer structure tends to decrease, whereas if it is too low, the film formability tends to decrease. The MFR can be measured by a melt indexer.

[0041] The polyethylene resin layer (B) may contain components other than polyethylene resins as long as the effects of the present invention are not impaired (for example, the polyethylene resin layer (B) is less than 20% by mass). Examples of components other than polyethylene resins include antiblocking agents, processing aids, resins other than polyethylene resins, carboxylic acid compounds, phosphoric acid compounds, boron compounds, metal salts, stabilizers, antioxidants, UV absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, surfactants, desiccants, crosslinking agents, reinforcing agents such as various fibers, and other components. These may be used alone or in combination of two or more.

[0042] Examples of resins other than polyethylene-based resins that may be included in the polyethylene-based resin layer (B) include polypropylene-based resins such as polypropylene and propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers, polybutene, polypentene, and other cyclic olefin-based resins, ionomers, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylic acid ester copolymers, polyester-based resins, polyamide resins (including copolymerized polyamides), polyvinyl chloride, polyvinylidene chloride, acrylic resins, polystyrene, vinyl ester-based resins, polyester elastomers, polyurethane elastomers, halogenated polyolefins such as chlorinated polyethylene and chlorinated polypropylene, aromatic or aliphatic polyketones, and the like, or combinations thereof. From the viewpoint of recyclability, it is preferable that the resins other than polyethylene-based resins do not contain polyamide resins.

[0043] A commercially available polyethylene resin suitable for this embodiment is, for example, "INNATE TF80" (registered trademark) manufactured by Dow Chemical.

[0044] [Adhesive resin layer (C)] The present sequentially biaxially oriented 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 adhering the EVOH layer (A) and the polyethylene resin layer (B).

[0045] The content of the adhesive resin in the adhesive resin layer (C) is not particularly limited, but the adhesive resin is preferably the main component (i.e., the content of the adhesive resin contained in the adhesive resin layer is 50% by mass or more). The content of the adhesive resin is more preferably 60% by mass or more, even more preferably 70% by mass or more, particularly preferably 80% by mass or more, 90% by mass or more, 95% by mass or more, and 100% by mass is particularly preferred.

[0046] The adhesive resin constituting the adhesive resin layer (C) is not particularly limited, but examples thereof include modified polyolefin polymers containing carboxy groups obtained by chemically bonding an unsaturated carboxylic acid or its anhydride to a polyolefin resin by addition reaction, graft reaction, etc. Examples of modified polyolefin polymers containing carboxy groups include maleic anhydride-modified polymers such as maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene, maleic anhydride grafted ethylene-propylene (block and random) copolymers, maleic anhydride grafted ethylene-ethyl acrylate copolymers, maleic anhydride grafted ethylene-vinyl acetate copolymers, maleic anhydride-modified polycyclic olefin resins, and maleic anhydride grafted polyolefin resins. These may be used alone or in combination of two or more.

[0047] As the adhesive resin, maleic anhydride-modified polymers such as maleic anhydride-modified polyethylene and maleic anhydride-modified ethylene-α-olefin copolymer are particularly preferred, since they contribute not only to the adhesiveness of the resin but also to the effect of suppressing gel generation during melting and heating and the effect of suppressing a decrease in transparency.

[0048] The adhesive resin constituting the adhesive resin layer (C) has a melt flow rate (MFR) (measured according to JIS K7210:2014 at 190°C and a load of 2160 g) of usually 0.1 to 20.0 g / 10 min, preferably 1.0 to 10.0 g / 10 min. If the MFR is too high, the stretchability of the multilayer structure tends to decrease, whereas if it is too low, the film formability tends to decrease.

[0049] When maleic anhydride modified polyethylene is used as the adhesive resin constituting the adhesive resin layer (C), 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.

[0050] The acid value of the adhesive resin constituting the adhesive resin layer (C) 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 EVOH increases, and high polymerization products are generated during the melt-kneading process, which reduces the stability during extrusion processing and tends to make 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 based on JIS K0070.

[0051] The adhesive resin layer (C) may contain other components other than the adhesive resin, such as antiblocking agents, processing aids, resins other than adhesive resins, carboxylic acid compounds, phosphoric acid compounds, boron compounds, metal salts, stabilizers, antioxidants, UV absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, surfactants, desiccants, crosslinking agents, reinforcing agents such as various fibers, etc., within a range that does not impair the effects of the present invention, generally within a range of 20 mass % or less.

[0052] A commercially available adhesive resin suitable for this embodiment is, for example, "Modic M545" (registered trademark) manufactured by Mitsubishi Chemical Corporation.

[0053] [Base material layer (D)] The present sequentially biaxially oriented multilayer structure may have a substrate layer (D) in addition to the above-mentioned Layers (A) to (C).

[0054] As the material used for the base layer (D), various thermoplastic resins (hereinafter referred to as "base resins") are used. Specific examples include polyolefin resins in the broad sense including polypropylene resins such as polypropylene and propylene-α-olefin (α-olefins having 4 to 20 carbon atoms) copolymers, modified olefin resins such as (unmodified) polyolefin resins such as polybutene and polypentene, 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, aromatic or aliphatic polyketones, and the like, or combinations thereof.

[0055] The base layer (D) may be made of a recycled resin obtained by remelting and molding the ends or defective products generated during the manufacturing process of the present sequentially biaxially oriented multilayer structure. Such recycled resin includes a mixture of the EVOH layer (A) and the polyethylene resin layer (B).

[0056] The thermoplastic resin used in the base layer (D) may contain conventionally known plasticizers, fillers, clays (montmorillonite, etc.), colorants, antioxidants, antistatic agents, lubricants, core materials, antiblocking agents, UV absorbers, waxes, etc., within a range that does not impair the spirit of the present invention (for example, 30% by mass or less, preferably 10% by mass or less).

[0057] In addition, it is preferable that the present sequentially biaxially stretched multilayer structure does not include a polyamide-based resin layer [a layer formed from a resin composition containing a polyamide-based resin as a main component (i.e., a layer in which the content of polyamide-based resin in the resin composition is 50 mass% or more)] as the base layer (D).

[0058] [Method of manufacturing a multilayer structure (unstretched multilayer structure)] This sequentially biaxially oriented multilayer structure is obtained by sequentially biaxially stretching a multilayer structure (unstretched multilayer structure) having an EVOH layer (A) and a polyethylene-based resin layer (B).

[0059] The lamination method of the multilayer structure can be a known method. For example, a method of melt extrusion laminating an adhesive resin layer (C) and a polyethylene resin layer (B) on a film or sheet that will become the EVOH layer (A), a method of melt extrusion laminating a resin composition that will become the EVOH layer (A) on the adhesive resin layer (C) or the polyethylene resin layer (B), or a method of co-extrusion of three layers (A), (B) and (C). In addition, a method of applying a solution of a resin composition that will become the EVOH layer (A) on the polyethylene resin layer (B) provided with an adhesive resin layer (C) and then removing the solvent, etc., can be mentioned. Among these, the co-extrusion method is preferable in terms of cost and environment.

[0060] When the multilayer structure contains at least one substrate layer (D), the following production method can be mentioned, for example.

[0061] (i) A method of laminating and forming all layers by co-extruding a resin composition constituting the EVOH layer (A) and the polyethylene resin layer (B), and, if necessary, a resin composition constituting the adhesive resin layer (C) and a resin to be the substrate layer (D); (ii) A method of dry laminating a separately formed film, sheet, etc., which will become the base layer (D) with a multilayer structure having an EVOH layer (A), a polyethylene resin layer (B), and, if necessary, an adhesive resin layer (C); (iii) A method of laminating a resin composition constituting the EVOH layer (A) and the polyethylene resin layer (B) and, if necessary, a resin composition constituting the adhesive resin layer (C) by melt co-extruding onto the surface of a film, sheet, etc., which will become a separately formed base layer (D), or a laminate obtained by appropriately combining these; (iv) A method in which a solution of a resin that will become the base layer (D) is applied to a multilayer structure having an EVOH layer (A), a polyethylene resin layer (B), and, if necessary, an adhesive resin layer (C), and then the solvent is removed. Among these, method (i) is preferred from the viewpoint of productivity.

[0062] [Method for producing sequentially biaxially stretched multilayer structure] The present sequentially biaxially stretched multilayer structure is obtained by sequentially biaxially stretching the multilayer structure (unstretched multilayer structure). In the following description, "MD" refers to the machine direction parallel to the running direction of the multilayer structure, and "TD" refers to the transverse direction perpendicular to the running direction of the multilayer structure.

[0063] Examples of the stretching method include roll stretching, tenter stretching, tubular stretching, stretch blowing, vacuum and compressed air molding, and among these, tenter stretching is preferred from the viewpoint of productivity. The stretched state of the present sequentially biaxially stretched 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) or the like).

[0064] The stretching temperature of the present sequentially biaxially stretched multilayer structure is usually 115 to 140° C., preferably 117 to 138° C., and more preferably 120 to 135° 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.

[0065] The stretch ratio of the present sequentially biaxially stretched multilayer structure is usually 2 to 10 times, preferably 2.5 to 7 times, and more preferably 3 to 6 times in MD, and 2 to 10 times, preferably 2.5 to 7 times, and more preferably 3 to 6 times in TD. The order of stretching is not particularly limited, but from the viewpoint of productivity, stretching is preferably performed from MD to TD.

[0066] The areal stretch ratio (MD stretch ratio x TD stretch ratio) of the present sequentially biaxially stretched multilayer structure 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 stretch ratio and areal stretch ratio are too large, the film surface after stretching tends to deteriorate.

[0067] In order to impart dimensional stability after stretching, heat setting may be further performed. Heat setting can be performed by known means, for example, a method of subjecting a multilayer structure (in the form of a stretched multilayer structure) to heat treatment usually at 80 to 180°C, preferably 100 to 165°C, for usually about 2 to 600 seconds while maintaining the multilayer structure in a tensioned state.

[0068] The thickness of the present sequentially biaxially stretched multilayer structure is not particularly limited, but is usually 1 to 1000 μm, preferably 5 to 500 μm, and particularly preferably 10 to 100 μm.

[0069] The thickness of each layer of the present sequentially biaxially oriented multilayer structure is not particularly limited, but the thickness of the EVOH layer (A) is usually preferably 0.5 to 200 μm, more preferably 1 to 100 μm. The thickness of the polyethylene resin layer (B) is usually preferably 3 to 3000 μm, more preferably 5 to 2000 μm, and even more preferably 10 to 1000 μm. The effect of the present invention can be enhanced by having the thickness of the polyethylene resin layer (B) within the above range. 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. When a plurality of layers are present, it is preferable that the total thickness of the plurality of layers is within the above thickness range.

[0070] The ratio A / B of the thickness of the EVOH layer (A) to the thickness of the polyethylene resin layer (B) (both are single layer thicknesses) is usually 1 / 50 to 10 / 1, preferably 1 / 30 to 5 / 1, and particularly preferably 1 / 10 to 3 / 1. If the A / B is too small, the gas barrier property tends to be insufficient, and conversely, if it is too large, the multilayer structure tends to be brittle.

[0071] The ratio A / C of the thickness of the EVOH layer (A) 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 A / C is too small, the gas barrier properties tend to be insufficient, and conversely, if it is too large, the adhesive properties tend to be insufficient.

[0072] The sequentially biaxially oriented multilayer structure thus obtained has excellent barrier properties, The oxygen permeability of this sequentially biaxially stretched multilayer structure (cc.20μm / m 2 ·day · atm) is usually 1.1 (cc.20μm / m 2 ·day·atm) or less, and preferably 1.0 (cc.20μm / m 2 ·day·atm) or less, and particularly preferably 0.8 (cc.20μm / m 2 ·day·atm). The oxygen permeability (cc.20μm / m 2 ·day·atm) was measured using Ox-tran2 / 21 at 20℃ and 90% RH.

[0073] The barrier property improvement ratio of the present sequentially biaxially oriented multilayer structure is usually 5 or more, preferably 6 or more, and more preferably 7 or more.

[0074] The barrier property improvement rate was calculated by comparing the oxygen permeability (cc.20 μm / m 2 The oxygen permeability was calculated from the oxygen permeability of the stretched multilayer structure relative to the oxygen permeability of the unstretched multilayer structure (oxygen permeability of the unstretched multilayer structure / oxygen permeability of the stretched multilayer structure) using the oxygen permeability of the stretched multilayer structure (oxygen permeability of the stretched multilayer structure / oxygen permeability of the stretched multilayer structure).

[0075] Although the reason why the present sequentially biaxially stretched multilayer structure has such excellent effects is unclear, it is presumed that the barrier properties are improved because sequential biaxial stretching has a higher orientation effect than simultaneous biaxially stretched multilayer structures.

[0076] The present sequentially biaxially stretched multilayer structure can be suitably used as a molding 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, medicines, etc., as well as a packaging material such as a multilayer structure for packaging, or as a part of a multilayer structure for forming these.

[0077] [Multilayer structure] The multilayer structure is obtained by laminating another layer on the present sequentially biaxially oriented multilayer structure. The other layer to be laminated on the present sequentially biaxially oriented multilayer structure is not particularly limited, and may be a layer formed from a resin composition containing the thermoplastic resin exemplified above as the thermoplastic resin or the adhesive resin exemplified as the adhesive resin (C).

[0078] As a method for producing the multilayer structure, various known production methods such as a dry lamination method, a sand lamination method, an extrusion lamination method, a coextrusion lamination method, a solution coating method, etc. can be used.

[0079] [Molded body] It is also possible to obtain a cup- or tray-shaped molded article using the present sequentially biaxially stretched multilayer structure or the multilayer structure. In this case, a drawing method is usually adopted, specifically, a vacuum molding method, a pressure molding method, a vacuum pressure molding method, a plug-assisted vacuum pressure molding method, etc. Furthermore, when using the multilayer structure to obtain a tube- or bottle-shaped multilayer container (laminate structure) from a multilayer parison (a hollow tubular preform before blowing), a blow molding method is adopted. Specific examples include extrusion blow molding (double-head type, mold moving type, parison shift type, rotary type, accumulator type, horizontal parison type, etc.), cold parison type blow molding, injection blow molding, and biaxial stretch blow molding (extrusion type cold parison biaxial stretch blow molding, injection type cold parison biaxial stretch blow molding, injection molding in-line type biaxial stretch blow molding, etc.). The obtained laminate 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, split processing, etc. as necessary. EXAMPLES

[0080] 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 based on mass.

[0081] Prior to the examples, the following components were prepared.

[0082] [EVOH(A)] EVOH (A1): Ethylene structural unit content 29 mol%, MFR 3.8 g / 10 min (210°C, load 2160 g), saponification degree 99.9 mol%, melting point 188°C EVOH (A2): Ethylene structural unit content 38 mol%, MFR 4.0 g / 10 min (210°C, load 2160 g), saponification degree 99.9 mol%, melting point 173°C EVOH (A3): Ethylene structural unit content 44 mol%, MFR 3.5 g / 10 min (210°C, load 2160 g), saponification degree 99.9 mol%, melting point 164°C EVOH (A4): Ethylene structural unit content 38 mol%, side chain 1,2-diol modification rate 1.5 mol%, MFR 4.0 g / 10 min (210°C, load 2160 g), saponification degree 99.6 mol%, melting point 160°C EVOH (A5): Ethylene structural unit content 33 mol%, side chain 1,2-diol modification rate 1.0 mol%, MFR 4.0 g / 10 min (210°C, load 2160 g), saponification degree 99.6 mol%, melting point 170°C

[0083] [Polyethylene (B)] Polyethylene (B1): Dow Chemical [INNATE TF80], MFR 1.7g / 10min (190℃, load 2160g), density 0.926g / cm 3

[0084] [Adhesive resin (C)] Adhesive resin (C1): Mitsubishi Chemical Corporation [Modic M545], MFR 6.0g / 10min (190℃, load 2160g)

[0085] <Example 1> EVOH (A4) with an ethylene structural unit content of 38 mol%, polyethylene (B1), and adhesive resin (C1) were fed into a multilayer cast film device (manufactured by Plastics Engineering Research Institute), and a multilayer structure with a three-type, five-layer structure of polyethylene layer / adhesive resin layer / EVOH layer / adhesive resin layer / polyethylene layer was obtained under the following multilayer coextrusion molding conditions. The thicknesses (μm) of each layer of the obtained multilayer structure were 480 / 60 / 120 / 60 / 480.

[0086] [Multi-layer co-extrusion molding conditions] EVOH layer: 40mmφ single screw extruder (barrel temperature: 210℃) Polyethylene layer: 40mmφ single screw extruder (barrel temperature: 230℃) Adhesive resin layer: 32mmφ single screw extruder (barrel temperature: 200℃) Die: 4-type 5-layer feed block type T die (die temperature: 230℃) - Take-off speed: 1.2m / min

[0087] Next, the obtained multilayer structure was heated to a stretching temperature of 120°C using a tenter-type biaxial stretching device (manufactured by BRUKNER) and sequentially biaxially stretched from MD to TD to an areal stretching ratio of 20 times, i.e., 4 times in MD and 5 times in TD, to obtain a sequentially biaxially stretched multilayer structure.

[0088] <Example 2> A sequentially biaxially stretched multilayer structure was obtained in the same manner as in Example 1, except that the stretching temperature was changed to 130°C.

[0089] <Example 3> A sequentially biaxially stretched multilayer structure was obtained in the same manner as in Example 1, except that EVOH (A5) was used instead of EVOH (A4) and the areal magnification was 12 times (MD 3 times, TD 4 times).

[0090] <Example 4> A sequentially biaxially stretched multilayer structure was obtained in the same manner as in Example 3, except that in Example 3, a mixture of EVOH (A1) and EVOH (A3) in a mass ratio of 75 / 25 was used instead of EVOH (A5) (ethylene structural unit content: 33 mol%).

[0091] <Example 5> A sequentially biaxially stretched multilayer structure was obtained in the same manner as in Example 4, except that the stretching temperature was changed to 130°C.

[0092] <Example 6> A sequentially biaxially stretched multilayer structure was obtained in the same manner as in Example 1, except that EVOH (A2) was used instead of EVOH (A4) and the areal magnification was 8 times (MD 2 times, TD 4 times).

[0093] <Comparative Example 1> A sequentially biaxially stretched multilayer structure was obtained in the same manner as in Example 1, except that simultaneous biaxial stretching was performed.

[0094] <Comparative Example 2> A simultaneously biaxially stretched multilayer structure was obtained in the same manner as in Example 4, except that the stretching method was changed to simultaneous biaxial stretching.

[0095] <Comparative Example 3> A simultaneous biaxially stretched multilayer structure was obtained in the same manner as in Comparative Example 2, except that the stretching temperature was 100°C.

[0096] The following barrier property evaluation was carried out using the obtained stretched multilayer structures of Examples 1 to 6 and Comparative Examples 1 to 3. The results are shown in Table 1 below.

[0097] [Oxygen permeability] The oxygen permeability was measured at 20° C. and 90% RH using Ox-tran 2 / 21 for the obtained stretched multilayer structures of Examples 1 to 6 and Comparative Examples 1 to 3, and for the unstretched multilayer structures that were not stretched in Examples 1 to 6 and Comparative Examples 1 to 3. A smaller oxygen permeability value indicates better barrier properties.

[0098] [Barrier property improvement rate] The oxygen permeability values ​​of the stretched multilayer structure and the unstretched multilayer structure obtained above were compared to determine the barrier property improvement rate (barrier property improvement rate = oxygen permeability value of unstretched multilayer structure / oxygen permeability value of stretched multilayer structure). A higher barrier property improvement rate means a more excellent barrier property.

[0099] [Table 1]

[0100] As can be seen from Table 1, Examples 1 and 2 obtained by successive biaxial stretching had smaller oxygen permeability values ​​and were superior in barrier properties compared to Comparative Examples 1 and 2 obtained by simultaneous biaxial stretching. In addition, the simultaneously biaxially stretched multilayer structure of Comparative Example 3 obtained by simultaneous biaxial stretching at a stretching temperature of 100° C. had pinholes in the film after stretching, and the oxygen permeability exceeded the upper limit and could not be measured. Furthermore, the sequentially biaxially stretched multilayer structures of Examples 1 to 6 obtained by sequential biaxial stretching had a higher barrier property improvement rate than the simultaneous biaxially stretched multilayer structures of Comparative Examples 1 and 2 obtained by simultaneous biaxial stretching, and therefore had excellent barrier properties. Therefore, the sequentially biaxially oriented multilayer structure has superior barrier properties compared to the simultaneously biaxially oriented multilayer structure. [Industrial Applicability]

[0101] The present multilayer structure can be suitably used as a molding 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., as well 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 sequentially biaxially stretched multilayer structure having an ethylene-vinyl alcohol copolymer layer (A) and a polyethylene resin layer (B).

2. The sequentially biaxially stretched multilayer structure according to claim 1, wherein the ethylene-vinyl alcohol copolymer contained in the ethylene-vinyl alcohol copolymer layer (A) contains two or more types of ethylene-vinyl alcohol copolymers.

3. The sequentially biaxially stretched multilayer structure according to claim 1 or 2, wherein the ethylene structural unit content of the ethylene-vinyl alcohol copolymer contained in the ethylene-vinyl alcohol copolymer layer (A) is 43 mol% or less.

4. The sequentially biaxially stretched multilayer structure according to claim 1 or 2, wherein the surface magnification of the sequentially biaxially stretched multilayer structure is 5 times or more.

5. The sequentially biaxially stretched multilayer structure according to claim 1 or 2, wherein the stretching temperature of the sequentially biaxially stretched multilayer structure is 115 to 140°C.

6. The sequentially biaxially stretched multilayer structure according to claim 1 or 2, wherein the sequentially biaxially stretched multilayer structure has at least three layers: an outer layer, an intermediate layer, and an inner layer, and the intermediate layer is the ethylene-vinyl alcohol copolymer layer (A).

7. The sequentially biaxially stretched multilayer structure according to claim 6, wherein the outer layer and / or inner layer of the sequentially biaxially stretched multilayer structure is the polyethylene resin layer (B).

8. A multilayer structure having an ethylene-vinyl alcohol copolymer layer (A) and a polyethylene resin layer (B), A method for manufacturing a multilayer structure, comprising the step of sequentially biaxially stretching the multilayer structure.

9. The method for manufacturing a multilayer structure according to claim 8, wherein in the sequential biaxial stretching, the stretching is performed in the order from MD to TD.

10. The method for manufacturing a multilayer structure according to claim 8 or 9, wherein the surface magnification of the multilayer structure is 5 times or more.

11. The method for manufacturing a multilayer structure according to claim 8 or 9, wherein the surface magnification of the multilayer structure is 6 to 100 times.

12. The method for manufacturing a multilayer structure according to claim 8 or 9, wherein the stretching ratio of the MD of the multilayer structure is 2 to 10 times.

13. The method for manufacturing a multilayer structure according to claim 8 or 9, wherein the stretching ratio of the TD of the multilayer structure is 2 to 10 times.

14. The method for manufacturing a multilayer structure according to claim 8 or 9, wherein the stretching temperature in the sequential biaxial stretching step is 115 to 140°C.

15. The method for producing a multilayer structure according to claim 8 or 9, wherein the multilayer structure has at least three layers: an outer layer, an intermediate layer, and an inner layer, and the intermediate layer is the ethylene-vinyl alcohol copolymer layer (A).