Multilayer structure

Abstract

The present invention provides a multilayer structure having sufficient gas barrier properties and excellent interlayer adhesion. This multilayer structure comprises: a gas barrier layer (A) containing a modified ethylene-vinyl alcohol copolymer and inorganic particles; and a polyurethane layer (B) containing thermoplastic polyurethane. The modified ethylene-vinyl alcohol copolymer contains monomer units (a), (b), and (c), which are represented by the formulas (a), (b), and (c), respectively.

Description

multilayer structure

[0001] The present invention relates to a multilayer structure.

[0002] Films using resins with gas barrier properties, such as ethylene-vinyl alcohol copolymers, are widely used for various applications, such as packaging materials for food, medical products, etc. Recently, various multilayer structures in which multiple resin layers are laminated have been proposed for the purpose of improving various performances, such as gas barrier properties.

[0003] As a conventional multilayer structure in which layers of ethylene-vinyl alcohol copolymer are laminated, Patent Document 1 describes a multilayer structure having a total of eight or more layers, including layers made of a resin composition containing a gas barrier resin such as an ethylene-vinyl alcohol copolymer and layers made of a thermoplastic resin such as a thermoplastic polyurethane. Patent Document 1 also describes that the interlayer adhesion of the multilayer structure is improved by incorporating a metal salt into one of the adjacent layers.

[0004] International Publication No. 2011 / 068105

[0005] In recent years, there has been a demand for the development of multilayer structures that have better interlayer adhesion than conventional multilayer structures and that also have sufficient performance, such as gas barrier properties, that are equivalent to or superior to conventional multilayer structures.

[0006] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a multilayer structure having sufficient gas barrier properties and excellent interlayer adhesion.

[0007] The object is to provide a multilayer structure comprising: [1] a gas barrier layer (A) containing a modified ethylene-vinyl alcohol copolymer and inorganic particles; and a polyurethane layer (B) containing a thermoplastic polyurethane, wherein the modified ethylene-vinyl alcohol copolymer has monomer units (a), (b) and (c) represented by the following formulas (a), (b) and (c), respectively; the contents of the monomer units (a), (b) and (c) in the modified ethylene-vinyl alcohol copolymer satisfy the following formulas (1) to (3); the modified ethylene-vinyl alcohol copolymer has a degree of saponification (DS) defined by the following formula (4) of 90 mol% or more; the content of the inorganic particles in the gas barrier layer (A) is 5 ppm or more and 5,000 ppm or less relative to the modified ethylene-vinyl alcohol copolymer; and at least one pair of the gas barrier layer (A) and the polyurethane layer (B) are directly laminated together; (In formulas (a) to (c), R ａ is a hydrogen atom, a methyl group, or R ｅ It is a group represented by —O—Y. ｂ and R ｅ are each independently a single bond, an alkylene group having 1 to 9 carbon atoms, or an alkyleneoxy group having 1 to 9 carbon atoms, and some or all of the hydrogen atoms in the alkylene group and the alkyleneoxy group may be substituted with a hydroxy group, an alkoxy group, or a halogen atom. ｃ and R ｄare each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and some or all of the hydrogen atoms of the alkyl group may be substituted with a hydroxy group, an alkoxy group, or a halogen atom. X, Y, and Z are each independently a hydrogen atom, a formyl group, or an alkanoyl group having 2 to 10 carbon atoms. ) 18≦a≦55 (1) [100−(a+c)]×0.9≦b≦[100−(a+c)] (2) 0.01≦c≦20 (3) (In the formulas (1) to (3), a, b, and c represent the respective contents (mol %) of the monomer unit (a), the monomer unit (b), and the monomer unit (c) relative to the total monomer units of the modified ethylene-vinyl alcohol copolymer.) DS=[(total number of moles of X, Y, and Z that are hydrogen atoms) / (total number of moles of X, Y, and Z)]×100 (4) [2] The multilayer structure of [1], wherein the monomer unit (c) is represented by the following formula (c1): (In formula (c1), R １ , R ２ , R ３ and R ４ are each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and some or all of the hydrogen atoms of the alkyl group may be substituted with a hydroxy group, an alkoxy group, or a halogen atom. Y and Z have the same meanings as Y and Z in formula (c). [3] R １ , R ２ , R ３ and R ４ and X, Y, and Z are each independently a hydrogen atom; [4] the multilayer structure of any of [1] to [3], wherein X, Y, and Z are each independently a hydrogen atom or an acetyl group; [5] the multilayer structure of any of [1] to [4], wherein the outermost layer is a polyurethane layer (B).

[0008] According to the present invention, it is possible to provide a multilayer structure having sufficient gas barrier properties and excellent interlayer adhesion.

[0009] In this specification, a numerical range described using "to" means that the numerical values ​​described before and after "to" are included as the lower and upper limits. In other words, "α to β" means "not less than α and not more than β." In addition, in this specification, the upper and lower limit values ​​of numerical ranges (content, physical properties, etc.) can be combined as appropriate.

[0010] A multilayer structure according to one embodiment of the present invention comprises a gas barrier layer (A) (hereinafter also referred to as "layer A") containing a modified ethylene-vinyl alcohol copolymer (hereinafter also referred to as "modified EVOH") and inorganic particles, and a polyurethane layer (B) (hereinafter also referred to as "layer B") containing thermoplastic polyurethane (hereinafter also referred to as "TPU"), wherein the modified EVOH has monomer units (a), (b) and (c) represented by the following formulas (a), (b) and (c), respectively, the contents of the monomer units (a), (b) and (c) in the modified EVOH satisfy the following formulas (1) to (3), the modified EVOH has a degree of saponification (DS) defined by the following formula (4) of 90 mol % or more, the content of the inorganic particles in the layer A is 5 ppm or more and 5,000 ppm or less relative to the modified EVOH, and at least one pair of the layer A and the layer B are directly laminated together. (In formulas (a) to (c), R ａ is a hydrogen atom, a methyl group, or R ｅ It is a group represented by —O—Y. ｂ and R ｅ are each independently a single bond, an alkylene group having 1 to 9 carbon atoms, or an alkyleneoxy group having 1 to 9 carbon atoms, and some or all of the hydrogen atoms in the alkylene group and the alkyleneoxy group may be substituted with a hydroxy group, an alkoxy group, or a halogen atom. ｃ and R ｄare each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and some or all of the hydrogen atoms of the alkyl group may be substituted with a hydroxy group, an alkoxy group, or a halogen atom. X, Y, and Z are each independently a hydrogen atom, a formyl group (—CHO), or an alkanoyl group having 2 to 10 carbon atoms. ) 18≦a≦55 (1) [100 - (a + c)] × 0.9≦b≦[100 - (a + c)] (2) 0.01≦c≦20 (3) (In formulas (1) to (3), a, b, and c represent the respective contents (mol %) of the monomer unit (a), the monomer unit (b), and the monomer unit (c) relative to the total monomer units of the modified EVOH.) DS = [(Total number of moles of hydrogen atoms among X, Y, and Z) / (Total number of moles of X, Y, and Z)] × 100 (4)

[0011] The multilayer structure according to one embodiment of the present invention has sufficient gas barrier properties and excellent interlayer adhesion. Although the reason for this is not clear, the following reason is presumed. ａ When at least one of Y and Z, which may be included in the formula (1), is a hydrogen atom, the monomer unit (c) has a hydroxy group at the end of the side chain. Such a hydroxy group has superior reactivity compared to, for example, a hydroxy group directly bonded to the main chain. Therefore, the hydroxy group contained in the monomer unit (c) of the modified EVOH in the A layer can effectively react and bond with the isocyanate group (—NCO) contained in the TPU in the B layer. Furthermore, the isocyanate group contained in the TPU in the B layer can also bond well with the inorganic particles in the A layer. These bonds are presumably responsible for the enhanced adhesion between the A layer and the B layer in the multilayer structure. Furthermore, because the A layer contains the above-described modified EVOH, the multilayer structure can exhibit sufficient gas barrier properties and also exhibit good flex resistance. The configuration of a multilayer structure according to one embodiment of the present invention will be described in detail below.

[0012] <Layer A> Layer A contains modified EVOH and inorganic particles. Layer A has gas barrier properties. The oxygen transmission rate of one layer A measured in accordance with the method described in JIS K7126-2 (constant pressure method; 2006) under conditions of 20°C and 85% RH is 50 cc·20 μm / (m ２ ·day·atm) or less, and 10cc·20μm / (m ２ ·day·atm) or less, and 5 cc·20 μm / (m ２ It is more preferable that the oxygen permeability is 0 cc·20 μm / (m ２ ·day·atm) or more, and 0.01 cc·20 μm / (m ２ ・day・atm) or more or 0.1cc・20μm / (m ２ ·day·atm) or more.

[0013] (Modified EVOH) The modified EVOH has the monomer units (a), (b), and (c) represented by the above formulas (a), (b), and (c), respectively. The modified EVOH may be a random copolymer of these monomer units. One or more types of modified EVOH may be used.

[0014] The monomer unit (a) is an ethylene unit. The content of the monomer unit (a) in the modified EVOH satisfies the following formula (1): 18≦a≦55 (1) (In formula (1), a is the content (mol %) of the monomer unit (a) relative to all the monomer units in the modified EVOH.)

[0015] When a in formula (1) (i.e., the content of the monomer unit (a)) is not less than the above lower limit, bending resistance, flexibility, melt moldability, gas barrier properties under high humidity, etc. can be improved. On the other hand, when a in formula (1) is not more than the above upper limit, gas barrier properties, etc. can be improved. The lower limit of a is preferably 20, more preferably 25, and may be 30 or 35. The upper limit of a is preferably 50, more preferably 45, and may be 40.

[0016] The content of each monomer unit in the modified EVOH is a value measured by the method described in the examples.

[0017] Regarding the monomer unit (b) and the monomer unit (c), the alkanoyl group having 2 to 10 carbon atoms represented by X, Y, and Z in the formula (b) and the formula (c) includes an acetyl group (ethanoyl group: CH ３ —CO—), propionyl group (propanoyl group: CH ３ CH ２ -CO-), benzoyl group (C ６ H ５ —CO—), acrylyl group (propenoyl group: CH ２ ═CH—CO—) and the like.

[0018] It is preferred that X, Y, and Z each independently represent a hydrogen atom or an acetyl group, which can further improve the gas barrier properties and interlayer adhesion.

[0019] The monomer unit (b) is generally a unit derived from a vinyl ester. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, and vinyl caproate, with vinyl acetate being preferred. Specifically, the monomer unit (b) may be a vinyl ester unit or a vinyl alcohol unit formed by saponification of the vinyl ester unit.

[0020] The content of the monomer unit (b) in the modified EVOH satisfies the following formula (2): [100 - (a + c)] x 0.9≦b≦[100 - (a + c)] (2) (In formula (2), a, b, and c represent the respective contents (mol %) of the monomer unit (a), the monomer unit (b), and the monomer unit (c) relative to the total monomer units in the modified EVOH.)

[0021] When b in formula (2) (i.e., the content of the monomer unit (b)) is within the above range, it is possible to improve the gas barrier property, flex resistance, melt moldability, etc. The lower limit of b may be [100-(a+c)]×0.95 or [100-(a+c)]×0.99.

[0022] Regarding the monomer unit (c), R in formula (c) ａ As for R ｅ A group represented by —O—Y is preferred. ｅ As R, an alkylene group having 1 to 9 carbon atoms is preferred, an alkylene group having 1 to 3 carbon atoms is more preferred, and an alkylene group having 1 carbon atom (i.e., a methylene group) is even more preferred. Some or all of the hydrogen atoms in these alkylene groups may be substituted, but it is preferred that they are not substituted. That is, R ａ As for CH ２ A group represented by —O—Y is particularly preferred. ａ is such a group and Y is a hydrogen atom, the monomer unit (c) has a primary hydroxy group at the end of the side chain. Since primary hydroxy groups have particularly excellent reactivity, in such cases, the adhesion between the gas barrier layer (A) and the polyurethane layer (B) can be further improved.

[0023] R ｂ is preferably a single bond.

[0024] R ｃ and R ｄ Examples of the alkyl group having 1 to 10 carbon atoms represented by R include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, and a pentyl group. ｃ and R ｄ R are each independently preferably a hydrogen atom or an unsubstituted alkyl group having 1 to 10 carbon atoms, more preferably a hydrogen atom or an unsubstituted alkyl group having 1 to 3 carbon atoms, and even more preferably a hydrogen atom. ｃ and R ｄ

[0046] When R is a hydrogen atom and Z is a hydrogen atom, the monomer unit (c) has a primary hydroxy group at the end of the side chain. Since primary hydroxy groups have particularly excellent reactivity, in such cases, the adhesion between the gas barrier layer (A) and the polyurethane layer (B) can be further improved.

[0025] The monomer unit (c) is preferably a monomer unit represented by the following formula (c1). (In formula (c1), R １ , R ２ , R ３and R ４ are each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and some or all of the hydrogen atoms of the alkyl group may be substituted with a hydroxy group, an alkoxy group, or a halogen atom. Y and Z have the same meanings as Y and Z in formula (c).

[0026] R １ , R ２ , R ３ and R ４ are each independently preferably a hydrogen atom or an unsubstituted alkyl group having 1 to 10 carbon atoms, more preferably a hydrogen atom or an unsubstituted alkyl group having 1 to 3 carbon atoms, and even more preferably a hydrogen atom. １ and R ２ Both or R ３ and R ４ It is also preferred that both of R are hydrogen atoms. １ and R ２ is a hydrogen atom and Y is a hydrogen atom, or R ３ and R ４

[0046] When R is a hydrogen atom and Z is a hydrogen atom, the monomer unit (c) has a primary hydroxy group at the end of the side chain. Since primary hydroxy groups have particularly excellent reactivity, in such cases, the adhesion between the gas barrier layer (A) and the polyurethane layer (B) can be further improved.

[0027] The monomer unit (c) represented by the above formula (c1) is typically a unit derived from a monomer represented by the following formula (5).

[0028] (In formula (5), R １ , R ２ , R ３ , R ４ , Y and Z are R in formula (c1). １ , R ２ , R ３ , R ４ , Y and Z are synonymous.)

[0029] Examples of the monomer represented by the above formula (5) include 2-methylene-1,3-propanediol diacetate, 2-methylene-1,3-propanediol dipropionate, 2-methylene-1,3-propanediol dibutyrate, 2-methylene-1,3-propanediol, and 2-methylene-1,3-butanediol. Among these, 2-methylene-1,3-propanediol diacetate is preferred from the viewpoint of ease of production. In the case of 2-methylene-1,3-propanediol diacetate, R in formula (5) １ , R ２ , R ３ and R ４ is a hydrogen atom, and Y and Z are acetyl groups.

[0030] The monomer unit (c) may be a monomer unit represented by the following formula (c2) or a monomer unit represented by the following formula (c3). (In formula (c2), R ａ and R ｃ is R in formula (c). ａ and R ｃ is synonymous with

[0031] (In formula (c3), R ５ and R ６ each independently represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, or a hydroxy group. Some or all of the hydrogen atoms in the alkyl group having 1 to 10 carbon atoms and the cycloalkyl group having 3 to 10 carbon atoms may be substituted with a hydroxy group, an alkoxy group, a carboxy group, or a halogen atom.

[0032] The content of the monomer unit (c) in the modified EVOH satisfies the following formula (3): 0.01≦c≦20 (3) (In formula (3), c is the content (mol %) of the monomer unit (c) relative to all the monomer units in the modified EVOH.)

[0033] When c in formula (3) (i.e., the content of the monomer unit (c)) is equal to or greater than the lower limit, interlayer adhesion, flex resistance, and the like can be improved. On the other hand, when c in formula (3) is equal to or less than the upper limit, gas barrier properties, and the like can be improved. The lower limit of c is preferably 0.1, more preferably 0.5, and even more preferably 1.0. The upper limit of c is preferably 12, more preferably 8, and even more preferably 5.

[0034] The modified EVOH usually contains a monomer unit (c) in which at least one of Y and Z is a hydrogen atom. Of all the monomer units (c) contained in the modified EVOH, the proportion of the monomer units (c) in which at least one of Y and Z is a hydrogen atom is preferably 50 mol % or more, more preferably 70 mol % or more, and even more preferably 90 mol % or more. When the modified EVOH contains a sufficient amount of monomer units (c) in which at least one of Y and Z is a hydrogen atom, the adhesion between the A layer and the B layer can be further improved.

[0035] The lower limit of the degree of saponification (DS) of the modified EVOH, as defined by the following formula (4), is 90 mol%, preferably 95 mol%, more preferably 99 mol%, and even more preferably 99.5 mol%. When the degree of saponification of the modified EVOH is equal to or greater than the above lower limit, the gas barrier property, interlayer adhesion, melt moldability, etc. can be improved. The upper limit of the degree of saponification may be 100 mol%. DS = [(total number of moles of hydrogen atoms among X, Y, and Z) / (total number of moles of X, Y, and Z)] × 100 (4) Here, R in the modified EVOH ｂ , R ｃ , R ｄ and R ｅ does not have a hydroxy group, "the total number of moles of hydrogen atoms among X, Y, and Z" represents the number of moles of hydroxy groups contained in the monomer units (b) and (c) of the modified EVOH. In this case, "the total number of moles of X, Y, and Z" represents the total number of moles of hydroxy groups and ester groups contained in the monomer units (b) and (c) of the modified EVOH.

[0036] The degree of saponification of the modified EVOH can be determined by the method described in the examples.

[0037] The lower limit of the total content of the monomer units (a), (b), and (c) relative to all monomer units in the modified EVOH is preferably 95 mol%, more preferably 98 mol%, even more preferably 99 mol%, and particularly preferably 99.9 mol%. When the modified EVOH is substantially composed of only the monomer units (a), (b), and (c), the effects of the present invention are more fully exhibited. The upper limit of the total content may be 100 mol%.

[0038] The modified EVOH may contain other monomer units in addition to the monomer units (a), (b), and (c) to the extent that the effects of the present invention are not impaired. Examples of monomers that provide other monomer units include α-olefins such as propylene, n-butene, isobutylene, and 1-hexene; acrylic acid and its salts; unsaturated monomers having an acrylic ester group; methacrylic acid and its salts; unsaturated monomers having a methacrylic ester group; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts (e.g., quaternary salts); methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid and its salts, methacrylamidopropyldimethylamine and its salts (e.g., quaternary salts); and methyl vinyl ether. vinyl ethers such as ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, 2,3-diacetoxy-1-vinyloxypropane; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane, and allyl chloride; unsaturated dicarboxylic acids and salts or esters thereof such as maleic acid, itaconic acid, and fumaric acid; vinylsilane compounds such as vinyltrimethoxysilane; and isopropenyl acetate.

[0039] The melting point of the modified EVOH is preferably 140° C. or higher and 200° C. or lower, and more preferably 150° C. or higher and 180° C. or lower. When the melting point of the modified EVOH is within the above range, it can exhibit good melt moldability, etc. The melting point of the modified EVOH is measured in accordance with JIS K7121 (2012).

[0040] The lower limit of the content of the modified EVOH in Layer A is, for example, preferably 80% by mass, more preferably 90% by mass, and even more preferably 95% by mass, and may be 98%, 99%, or 99.5% by mass. When the content of the modified EVOH in Layer A is equal to or greater than the above lower limit, the effects of the present invention are particularly satisfactorily exhibited. The upper limit of the content may be 99.999% by mass, or may be 99.99%, 99.9%, or 99% by mass.

[0041] The method for producing the modified EVOH is not particularly limited, and the modified EVOH can be produced, for example, by the method described in paragraphs

[0068] to

[0128] of JP 2021-104579 A. The modified EVOH described in JP 2021-104579 A may be used. The modified EVOH may be a commercially available product.

[0042] A method for producing a modified EVOH having the monomer unit (c) represented by the above formula (c1) includes copolymerizing ethylene, a vinyl ester, and a monomer represented by the above formula (5), and saponifying the resulting modified ethylene-vinyl ester copolymer. The copolymerization and saponification can be carried out by known methods.

[0043] The polymerization method may be batch polymerization, semi-batch polymerization, continuous polymerization, semi-continuous polymerization, etc. Furthermore, the polymerization method may be any known method such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc. Bulk polymerization or solution polymerization, in which polymerization proceeds without a solvent or in a solvent such as alcohol, is usually used.

[0044] The solvent used in the solution polymerization method is not particularly limited, but examples thereof include alcohols, and lower alcohols such as methanol, ethanol, and propanol are preferred. The amount of solvent used in the polymerization reaction solution may be selected taking into consideration the degree of polymerization of the desired modified EVOH, chain transfer of the solvent, and the like. The mass ratio of the solvent to the total monomers (solvent / total monomers) contained in the reaction solution is, for example, in the range of 0.01 to 10, and preferably in the range of 0.05 to 3.

[0045] The polymerization initiator (hereinafter also referred to as "initiator") used in the copolymerization is selected from known initiators, such as azo initiators, peroxide initiators, and redox initiators. Examples of azo initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Examples of peroxide initiators include percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; perester compounds such as t-butyl peroxyneodecanate, α-cumyl peroxyneodecanate, and acetyl peroxide; acetylcyclohexylsulfonyl peroxide; and 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate. Potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like may be combined with the above initiator. Redox initiators are polymerization initiators that combine, for example, the above peroxide initiators with a reducing agent such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, or Rongalit. The amount of initiator used is adjusted depending on the polymerization rate. The amount of initiator used is preferably 0.01 to 0.2 mol %, more preferably 0.02 to 0.15 mol %, based on the vinyl ester. The polymerization temperature is not particularly limited, but is suitably from room temperature to approximately 150°C, and preferably 40°C or higher and lower than the boiling point of the solvent used.

[0046] The copolymerization may be carried out in the presence of a chain transfer agent, as long as the effects of the present invention are not impaired. Examples of chain transfer agents include aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethanethiol; and phosphinates such as sodium phosphinate monohydrate, with aldehydes or ketones being preferred. The amount of chain transfer agent added to the polymerization reaction solution is determined depending on the chain transfer coefficient of the chain transfer agent and the degree of polymerization of the desired modified ethylene-vinyl ester copolymer, but is generally preferably 0.1 to 10 parts by mass per 100 parts by mass of vinyl ester monomer.

[0047] The resulting modified ethylene-vinyl ester copolymer can be saponified to obtain modified EVOH. During this process, the vinyl ester units in the copolymer are converted to vinyl alcohol units. At the same time, the ester bonds in the monomer units derived from the monomer represented by formula (5) are also hydrolyzed and converted to a 1,3-diol structure. In this way, different types of ester groups can be simultaneously hydrolyzed in a single saponification reaction.

[0048] Known methods can be used to saponify the modified ethylene-vinyl ester copolymer. The saponification reaction is usually carried out in an alcohol or aqueous alcohol solution. The alcohol preferably used in this case is a lower alcohol such as methanol or ethanol, with methanol being preferred. The alcohol or aqueous alcohol used in the saponification reaction may contain other solvents such as acetone, methyl acetate, ethyl acetate, or benzene, as long as the amount is, for example, 40% by mass or less. The catalyst used in the saponification is, for example, an alkali metal hydroxide such as potassium hydroxide or sodium hydroxide, an alkali catalyst such as sodium methylate, or an acid catalyst such as a mineral acid. The temperature at which the saponification is carried out is not limited, but a temperature in the range of 20 to 120°C is preferred. If a gel-like product precipitates as the saponification proceeds, the product can be pulverized, washed, and dried to obtain the modified EVOH.

[0049] Examples of methods for producing modified EVOH having the monomer unit (c) represented by formula (c2) include a method of copolymerizing 3,4-diol-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-ol-1-butene, 4-acyloxy-3-ol-1-butene, 3,4-diacyloxy-2-methyl-1-butene, or the like with a vinyl ester and ethylene, and then saponifying the resulting copolymer. Other examples include a method of polymerizing 4,5-diol-1-pentene, 4,5-diacyloxy-1-pentene, 4,5-diol-3-methyl-1-pentene, 4,5-diol-3-methyl-1-pentene, 5,6-diol-1-hexene, 5,6-diacyloxy-1-hexene, or the like with a vinyl ester and ethylene, and then saponifying the resulting copolymer. In this case, conventionally known methods can be appropriately adopted as the copolymerization method and saponification method, and the conditions for preparing the modified EVOH having the monomer unit (c) represented by the above formula (c1) can also be adopted.

[0050] Furthermore, examples of methods for producing modified EVOH having the monomer unit (c) represented by the above formula (c3) include a method of reacting EVOH with a monofunctional epoxy compound. The reaction method is not particularly limited, but examples include a production method in which EVOH and a monofunctional epoxy compound are reacted in a solution, and a production method in which EVOH and a monofunctional epoxy compound are reacted in an extruder. The monofunctional epoxy compound is preferably an epoxy compound having only one epoxy group in the molecule. Furthermore, the number of carbon atoms in the monofunctional epoxy compound is preferably 2 to 8. Specific examples of monofunctional epoxy compounds include 1,2-epoxybutane, epoxypropane, epoxyethane, and glycidol.

[0051] (Inorganic particles) Layer A contains inorganic particles. Inorganic particles are particles whose main component is an inorganic compound. In this specification, the main component refers to a component that is 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, and may be a component that is 99% by mass or more. The inorganic particles may be particles that are essentially composed of only an inorganic compound.

[0052] In the multilayer structure according to one embodiment of the present invention, Layer A contains inorganic particles in addition to modified EVOH, and therefore, the multilayer structure can exhibit the effects of having sufficient gas barrier properties and excellent interlayer adhesion.

[0053] The average particle size of the inorganic particles is preferably more than 0.3 μm and not more than 20 μm, more preferably 0.7 μm or more and 12 μm or less, even more preferably 1.0 μm or more and 8 μm or less, and even more preferably 1.5 μm or more and 4 μm or less. Having the average particle size of the inorganic particles within the above range can further improve the gas barrier properties and interlayer adhesion of the multilayer structure. The average particle size of the inorganic particles refers to the average particle size of secondary particles observed with a field emission scanning electron microscope. The particle size of the secondary particles refers to the major axis. Specifically, the particle size of the inorganic particles is measured by the method described in the examples.

[0054] The inorganic compound constituting the inorganic particles preferably contains a metal element (including a metalloid element), and preferably contains at least one metal element selected from the group consisting of silicon, aluminum, magnesium, zirconium, cerium, tungsten, and molybdenum. Among these, it is more preferable to contain at least one element selected from the group consisting of silicon, aluminum, and magnesium, because they are easily available, and it is even more preferable to contain silicon element.

[0055] Examples of inorganic compounds constituting the inorganic particles include oxides, nitrides, hydroxides, and oxynitrides of the elements exemplified above, with oxides or hydroxides being preferred, oxides being more preferred, metal oxides being even more preferred, silicon dioxide, magnesium oxide, or zirconium dioxide being even more preferred, and silicon dioxide being particularly preferred. When the inorganic particles contain an oxide, the reactivity between the isocyanate groups (—NCO) of the thermoplastic polyurethane and the inorganic particles is further enhanced, thereby further improving the adhesion between Layer A and Layer B. From the perspective of reactivity with isocyanate groups, the inorganic particles may have hydroxy groups on their surfaces.

[0056] The inorganic particles may contain one or more types of particles, and each inorganic particle may be formed from one or more types of inorganic compounds.

[0057] The lower limit of the content of inorganic particles relative to the modified EVOH in Layer A is 5 ppm, preferably 20 ppm, more preferably 50 ppm, even more preferably 100 ppm, even more preferably 300 ppm, even more preferably 500 ppm, and may be 1,000 ppm, 1,500 ppm, or 2,000 ppm. When the content of inorganic particles is equal to or greater than the above lower limit, the adhesion between Layer A and Layer B is improved. The upper limit of the content of inorganic particles relative to the modified EVOH in Layer A is 5,000 ppm, preferably 4,000 ppm, or may be 3,500 ppm, 3,000 ppm, 2,500 ppm, or 2,000 ppm. When the content of inorganic particles is equal to or less than the above upper limit, the multilayer structure can exhibit sufficient gas barrier properties, etc. Note that "ppm" refers to the content by mass.

[0058] The lower limit of the total content of the modified EVOH and inorganic particles in Layer A is, for example, preferably 80% by mass, more preferably 90% by mass, and even more preferably 95% by mass, and may be 98%, 99%, 99.5%, or 99.9% by mass. When the total content of the modified EVOH and inorganic particles in Layer A is equal to or greater than the above lower limit, the effects of the present invention are particularly satisfactorily exhibited. The upper limit of the total content may be 100% by mass, or may be 99.99%, 99.9%, or 99% by mass.

[0059] Layer A may contain a resin other than the above-described modified EVOH. Examples of the other resin include modified or unmodified EVOH other than the above-described modified EVOH, polyolefin, polyamide, polyester, polystyrene, polyvinyl chloride, acrylic resin, polyurethane, polycarbonate, polyvinyl acetate, and other thermoplastic resins.

[0060] Layer A may further contain additives other than the modified EVOH, inorganic particles, and other resins, to the extent that the effects of the present invention are not impaired. Examples of other additives include metal salts, heat stabilizers, antioxidants, UV absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, stabilizers, surfactants, crosslinking agents, and fiber reinforcing agents.

[0061] Layer A preferably contains an alkali metal salt as the metal salt. When Layer A contains an alkali metal salt, interlayer adhesion is improved. The cation species of the alkali metal salt is not particularly limited, but sodium salt or potassium salt is preferred. The anion species of the alkali metal salt is also not particularly limited, and can be added as a carboxylate, carbonate, hydrogencarbonate, phosphate, hydrogenphosphate, borate, hydroxide, etc. The content of the alkali metal salt in Layer A is preferably 10 to 500 ppm, and more preferably 50 to 300 ppm, calculated as the alkali metal element.

[0062] Layer A also preferably contains a boron compound as a thermal stabilizer. Forming Layer A from a resin composition containing a boron compound can suppress torque fluctuations during heat melting. The boron compound is not particularly limited, and examples thereof include boric acids, borate esters, borate salts, and boron hydrides. Specific examples of boric acids include orthoboric acid, metaboric acid, and tetraboric acid. Examples of borate esters include triethyl borate and trimethyl borate, and examples of borates include alkali metal salts, alkaline earth metal salts, and borax of the various boric acids listed above. Among these compounds, orthoboric acid (hereinafter sometimes simply referred to as boric acid) is preferred. The content of the boron compound in Layer A is preferably 20 to 2,000 ppm, and more preferably 50 to 1,000 ppm, in terms of elemental boron.

[0063] It is also preferable that Layer A contains a phosphate compound as a heat stabilizer. Forming Layer A from a resin composition containing a phosphate compound can suppress coloration during melt molding. The phosphate compound is not particularly limited, and various acids such as phosphoric acid and phosphorous acid, and salts thereof, can be used. The phosphate may be contained in the form of primary phosphate, secondary phosphate, or tertiary phosphate, with primary phosphate being preferred. The cation species is also not particularly limited, but alkali metal salts are preferred. Among these, sodium dihydrogen phosphate or potassium dihydrogen phosphate is preferred. The content of the phosphate compound in Layer A is preferably 5 to 200 ppm, more preferably 10 to 160 ppm, calculated as phosphate radical.

[0064] The lower limit of the average thickness of one A layer is preferably 0.1 μm, more preferably 1 μm, even more preferably 3 μm, and may be 5 μm, 10 μm, 20 μm, or 30 μm. On the other hand, the upper limit is preferably 200 μm, more preferably 100 μm, and may be 60 μm, 30 μm, 10 μm, or 5 μm. When the average thickness of one A layer is equal to or greater than the lower limit, the gas barrier properties and durability thereof are improved. When the average thickness of one A layer is equal to or less than the upper limit, the flexibility is improved, and as a result, the flex resistance is improved. The average thickness is the average value of thicknesses measured at any five locations.

[0065] <Layer B> Layer B contains TPU. By including Layer B containing TPU, the multilayer structure according to one embodiment of the present invention can exhibit good stretchability, flex resistance, moldability, and the like.

[0066] TPU is typically a linear multi-block copolymer or the like having (1) a polyurethane portion as a hard segment obtained by reacting a short-chain glycol (low-molecular-weight polyol) with an isocyanate, and (2) a polyurethane portion as a soft segment obtained by reacting a long-chain glycol (high-molecular-weight polyol) with an isocyanate. Polyurethane is a general term for compounds having a urethane bond (-NHCOO-) obtained by a polyaddition reaction (urethanization reaction) between an isocyanate group (-NCO) and a hydroxy group (-OH). One or more types of TPU can be used.

[0067] TPU is generally composed of a polymer polyol, an organic polyisocyanate, a chain extender, and the like.

[0068] Polymer polyols are substances having multiple hydroxy groups and are obtained by polycondensation, addition polymerization (e.g., ring-opening polymerization), polyaddition, or the like. Examples of polymer polyols include polyester polyols, polyether polyols, polycarbonate polyols, and co-condensates thereof (e.g., polyester-ether-polyols). Of these, polyester polyols or polycarbonate polyols are preferred, and polyester polyols are more preferred. These polymer polyols may be used alone or in combination of two or more.

[0069] The polyester polyol can be produced, for example, by condensing an ester-forming derivative such as a dicarboxylic acid, its ester, or its anhydride with a low-molecular-weight polyol by a direct esterification reaction or an ester exchange reaction, or by ring-opening polymerization of a lactone, according to a conventional method.

[0070] Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, poly(methyltetramethylene) glycol, etc. Among these, polytetramethylene glycol is preferred.

[0071] Examples of polycarbonate polyols include those obtained by reacting an aliphatic diol having 2 to 12 carbon atoms, such as 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, or 1,10-decanediol, or a mixture thereof, with diphenyl carbonate or phosgene to cause condensation polymerization.

[0072] The lower limit of the number average molecular weight of the polymer polyol is preferably 500, more preferably 600, and even more preferably 700. On the other hand, the upper limit of the number average molecular weight of the polymer polyol is preferably 8,000, more preferably 5,000, and even more preferably 3,000. The number average molecular weight of the polymer polyol is measured in accordance with JIS K1577 and calculated based on the hydroxyl group value.

[0073] The organic polyisocyanate is not particularly limited, and known organic diisocyanates commonly used in the production of TPU can be used. Examples of organic polyisocyanates include aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate, phenylene diisocyanate, xylylene diisocyanate, 1,5-naphthylene diisocyanate, 3,3'-dichloro-4,4'-diphenylmethane diisocyanate, and toluylene diisocyanate; and aliphatic diisocyanates (including alicyclic diisocyanates) such as hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and hydrogenated xylylene diisocyanate. Among these, aromatic diisocyanates are preferred, and 4,4'-diphenylmethane diisocyanate is more preferred, in that they can improve the strength, flex resistance, and the like of the resulting multilayer structure. These organic diisocyanates may be used alone or in combination of two or more.

[0074] As the chain extender, any chain extender commonly used in the production of TPU can be used, and for example, a low molecular weight compound having two or more active hydrogen atoms in the molecule capable of reacting with an isocyanate group and a molecular weight of 300 or less is preferably used. Examples of chain extenders include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-bis(β-hydroxyethoxy)benzene, and 1,4-cyclohexanediol. Among these, from the viewpoints of the stretchability and moldability of the resulting multilayer structure, aliphatic diols having 2 to 10 carbon atoms are preferred, and 1,4-butanediol is particularly preferred. These chain extenders may be used alone or in combination of two or more.

[0075] The TPU can be produced by using the above-mentioned high molecular weight polyol, organic polyisocyanate, and chain extender, utilizing a known urethane reaction technique. The TPU can be produced by either the prepolymer method or the one-shot method. Among these, melt polymerization in the substantial absence of solvent is preferred, and continuous melt polymerization using a multi-screw extruder is particularly preferred.

[0076] Layer B may be composed solely of TPU, or may contain components other than TPU. The lower limit of the TPU content in Layer B is, for example, preferably 80% by mass, more preferably 90% by mass, and even more preferably 95% by mass, and may be 98%, 99%, 99.5%, or 99.9% by mass. When the TPU content in Layer B is equal to or greater than the above lower limit, the effects of the present invention are particularly sufficiently achieved. The upper limit of the content may be 100%, 99%, or 95% by mass.

[0077] Examples of components other than TPU that may be contained in Layer B include resins other than TPU, heat stabilizers, ultraviolet absorbers, antioxidants, colorants, antistatic agents, lubricants, and fillers.

[0078] The lower limit of the average thickness of one B layer is preferably 0.1 μm, more preferably 1 μm, and even more preferably 3 μm, and may be 5 μm, 10 μm, 20 μm, or 30 μm. On the other hand, the upper limit is preferably 200 μm, more preferably 100 μm, and may be 60 μm, 30 μm, 10 μm, or 5 μm. When the average thickness of one B layer is equal to or greater than the above lower limit, durability and the like are improved. When the average thickness of one B layer is equal to or less than the above upper limit, the multilayer structure can be made thinner.

[0079] <Other Layers> The multilayer structure according to one embodiment of the present invention may be composed of only layer A and layer B, or may include layers other than layer A and layer B. Examples of other layers include resin layers other than layer A and layer B (thermoplastic resin layers other than layer A and layer B, adhesive resin layers, rubber layers, etc.). The other layers may be layers other than resin layers, such as paper layers and metal layers. In one embodiment of the present invention, the multilayer structure may be composed of only resin layers. A resin layer refers to a layer containing a resin as the main component. Examples of multilayer structures composed of only resin layers include multilayer structures composed of only layer A and layer B, and multilayer structures composed of layer A, layer B, and other resin layers.

[0080] <Layer Structure> The layer structure of the multilayer structure according to one embodiment of the present invention is not particularly limited as long as it comprises at least one layer A and at least one layer B, and at least one pair of layer A and layer B is directly laminated together. In the multilayer structure, the directly laminated layer A and layer B have high adhesion between them.

[0081] The lower limit of the number of layers A in the multilayer structure according to one embodiment of the present invention may be 1, 2, or 3. The upper limit of the number of layers A may be 100, 20, 10, 5, 3, or 2. The lower limit of the number of layers B may be 1, 2, or 3. The upper limit of the number of layers B may be 200, 50, 10, 5, 3, or 2. The lower limit of the total number of layers in the multilayer structure is 2, 3, or 4. The upper limit of the total number of layers may be 300, 100, 20, 10, or 5.

[0082] Examples of the layer structure of the multilayer structure according to one embodiment of the present invention include the following layer structures. In the following layer structures, A represents layer A, B represents layer B, and X represents a layer other than layer A and layer B. A / B B / A / B X / A / B B / A / B / A / B X / A / B / A / B X / A / B / A / X B / A / B / A / B / A / B B / B / A / B / A / B / A / B / B B / A / B / A / B / A / B / A / B / B B / A / B / A / B / A / B / A / B / A / B

[0083] A multilayer structure according to one embodiment of the present invention may be an alternating laminate of layers A and layers B. The cross section of the multilayer structure may have a symmetrical structure with the layer A or the layer B as the axis of symmetry. A symmetrical structure has the advantage that the multilayer structure can be particularly efficiently molded by coextrusion.

[0084] In a multilayer structure according to one embodiment of the present invention, it is preferable that at least one outermost layer is a B layer. The outermost layer is a layer that is not in contact with another layer on one side, and the multilayer structure has two outermost layers. When at least one outermost layer of the multilayer structure is a B layer, good adhesion to a rubber material (e.g., a diene rubber) can be achieved on the surface where the B layer, which is the outermost layer, is located. In the multilayer structure, both outermost layers may be B layers. In this case, good adhesion to a rubber material can be achieved on both sides.

[0085] The multilayer structure according to one embodiment of the present invention may be a multilayer film or a molded article formed into a predetermined shape such as a container. The multilayer structure may be a non-stretched film or a stretched film. The average thickness of the multilayer structure is preferably 1 μm or more and 2,000 μm or less, more preferably 10 μm or more and 1,000 μm or less, and even more preferably 50 μm or more and 500 μm or less.

[0086] <Applications, etc.> The multilayer structure according to one embodiment of the present invention has sufficient gas barrier properties and excellent interlayer adhesion. Furthermore, the multilayer structure also has good flex resistance, stretchability, etc., and when the outermost layer is Layer B, the surface of this outermost layer can be well bonded to rubber materials, etc., through a crosslinking reaction. Therefore, the multilayer structure can be used for food packaging materials, medical container packaging materials, other container packaging materials, industrial sheet materials, construction sheet materials, agricultural sheet materials, geomembranes, radon barrier films, other sheet materials, cushioning materials with a gas-tight structure such as air soles, various pipes, etc. In particular, the multilayer structure having Layer B as the outermost layer has good adhesion to rubber materials, etc., as described above, and is therefore suitable for use as a gas barrier film laminated on film-like rubber products such as accumulator inner bags, air-filled balls, inner liners, air springs, etc.

[0087] <Production Method> The method for producing the multilayer structure according to one embodiment of the present invention is not particularly limited as long as it is a method that allows the A layer and the B layer to be laminated and bonded well, and known methods such as coextrusion, lamination, coating, bonding, adhesion, etc. can be used.

[0088] The multilayer structure according to one embodiment of the present invention can be preferably produced by a production method including a step of co-extruding a resin material forming layer A and a resin material forming layer B. The resin material forming layer A contains modified EVOH and inorganic particles. The specific and preferred compositions of the resin material forming layer A are the same as those of layer A. The resin material forming layer B contains TPU. The specific and preferred compositions of the resin material forming layer B are the same as those of layer B.

[0089] In the multilayer coextrusion method, the resin material forming Layer A and the resin material forming Layer B are heated and melted, and then fed to an extrusion die through respective flow paths from different extruders or pumps. After being extruded into multiple layers from the extrusion die, the layers are laminated and bonded to form the multilayer structure. Examples of the extrusion die that can be used include a multi-manifold die, a field block, and a static mixer.

[0090] The viscosity of each resin material forming the A layer and the B layer is preferably in the following melt viscosity ratio: That is, the melt viscosity (η Ａ ) and the melt viscosity (η Ｂ ) and the ratio (η Ｂ / η Ａ The lower limit of the melt viscosity ratio (η Ｂ / η Ａ The upper limit of the melt viscosity ratio (η Ｂ / η Ａ ) in the above range, the appearance of the multilayer structure can be improved when it is molded by multilayer coextrusion, and the adhesion between the A layer and the B layer can be improved, thereby improving the durability of the multilayer structure.

[0091] The method for producing a multilayer structure may include a step of irradiating the structure (multilayer structure) obtained by coextrusion with an electron beam. The electron beam irradiation causes a crosslinking reaction between layers, thereby increasing the interlayer adhesive strength of the resulting multilayer structure. As the electron beam source, various electron beam accelerators such as a Cockcroft-Walton type, a Van de Graaf type, a resonant transformer type, an insulating core transformer type, a Dynamitron type, and a high-frequency type can be used.

[0092] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples in any way.

[0093] Example 1 (1) Synthesis of modified ethylene-vinyl acetate copolymer Into a 50 L pressure reactor equipped with a jacket, a stirrer, a nitrogen inlet, an ethylene inlet, and an initiator addition port, 21 kg of vinyl acetate (hereinafter also referred to as "VAc"), 3.8 kg of methanol (hereinafter also referred to as "MeOH"), and 2-methylene-1,3-propanediol diacetate (R １ , R ２ , R ３ and R ４ A monomer in which Y is a hydrogen atom, and Y and Z are acetyl groups. Hereinafter, this may be referred to as "MPDAc." 0.6 kg of MPDAc was charged, the temperature was raised to 60°C, and nitrogen bubbling was performed for 30 minutes to replace the atmosphere inside the reaction vessel with nitrogen. Ethylene was then introduced so that the reaction vessel pressure (ethylene pressure) was 4.7 MPa. After adjusting the temperature inside the reaction vessel to 60°C, 12.6 g of 2,2'-azobis(2,4-dimethylvaleronitrile) ("V-65" manufactured by Wako Pure Chemical Industries, Ltd.) was added as a methanol solution as an initiator to initiate polymerization. During polymerization, the ethylene pressure was maintained at 4.7 MPa, and the polymerization temperature was maintained at 60°C. After 6.0 hours, when the conversion of VAc reached 45%, the polymerization was terminated by cooling. The reaction vessel was opened to remove ethylene, and then nitrogen gas was bubbled through to completely remove ethylene. Next, unreacted VAc was removed under reduced pressure, and then MeOH was added to the modified ethylene-vinyl acetate copolymer (hereinafter also referred to as "modified EVAc") into which monomer units derived from MPDAc had been introduced to prepare a 20% by mass MeOH solution.

[0094] (2) Saponification of Modified EVAc 4715 g of a 20% by mass MeOH solution of the modified EVAc obtained in (1) was charged into a 10 L reaction vessel equipped with a jacket, a stirrer, a nitrogen inlet, a reflux condenser, and a solution addition port. The solution was heated to 60°C while nitrogen was blown into it, and a 2N MeOH solution of sodium hydroxide was added at a rate of 14.7 mL / min for 2 hours. After the addition of the sodium hydroxide MeOH solution was completed, the saponification reaction was allowed to proceed with stirring for 2 hours while maintaining the temperature in the system at 60°C. 254 g of acetic acid was then added to terminate the saponification reaction. 3 L of ion-exchanged water was then added while heating and stirring at 80°C, and MeOH was drained out of the reaction vessel, resulting in the precipitation of modified EVOH. The precipitated modified EVOH was collected by decantation and pulverized in a mixer. The obtained modified EVOH powder was added to a 1 g / L aqueous acetic acid solution (bath ratio 20: 20 L of aqueous solution per 1 kg of powder) and washed with stirring for 2 hours. The powder was drained and then added to a 1 g / L aqueous acetic acid solution (bath ratio 20) and washed with stirring for 2 hours. The drained powder was then poured into ion-exchanged water (bath ratio 20), washed with stirring for 2 hours, and then drained. This procedure was repeated three times for purification. The powder was then immersed in 10 L of an aqueous solution containing 0.5 g / L of acetic acid and 0.1 g / L of sodium acetate with stirring for 4 hours, drained, and dried at 60°C for 16 hours to obtain 503 g of a crude dried modified EVOH.

[0095] (3) Production of modified EVOH hydrous pellets A 3-L stirring tank equipped with a jacket, a stirrer, and a reflux condenser was charged with 758 g of the crude dried modified EVOH obtained by repeating the procedure in (2) twice, 398 g of water, and 739 g of MeOH, and the mixture was heated to 85°C to dissolve. The resulting solution was extruded through a 4-mm diameter glass tube into a 90 / 10 water / MeOH mixture cooled to 5°C to precipitate strands, which were then cut into pellets with a strand cutter to obtain hydrous pellets of modified EVOH. The moisture content of the obtained hydrous pellets of modified EVOH was measured using a Mettler Halogen Moisture Analyzer "HR73" and found to be 55% by mass.

[0096] (4) Production of Modified EVOH Composition Pellets 1,577 g of the modified EVOH hydrous pellets obtained in (3) above were placed in a 1 g / L aqueous acetic acid solution (bath ratio: 20) and washed with stirring for 2 hours. The pellets were drained and then placed in a 1 g / L aqueous acetic acid solution (bath ratio: 20) and washed with stirring for 2 hours. After draining, the aqueous acetic acid solution was renewed and the same procedure was repeated. The pellets washed with the aqueous acetic acid solution and then drained were placed in ion-exchanged water (bath ratio: 20) and washed with stirring for 2 hours, followed by draining. This procedure was repeated three times for purification. This yielded hydrous modified EVOH pellets with a sufficiently reduced amount of catalyst residue from the saponification reaction. The hydrous pellets were placed in an aqueous solution (bath ratio: 20) containing sodium acetate at a concentration of 0.525 g / L, acetic acid at a concentration of 0.8 g / L, and phosphoric acid at a concentration of 0.007 g / L, and immersed for 4 hours with periodic stirring. The pellets were dewatered and dried at 80° C. for 3 hours and then at 105° C. for 16 hours to obtain pellets of a modified EVOH composition containing acetic acid, a sodium salt, and a phosphoric acid compound.

[0097] (5) Content of each structural unit in modified EVAc The content of monomer unit (a) (a: content of ethylene unit), the content of monomer unit (b) (b: content of monomer unit derived from vinyl acetate), and the content of monomer unit (c) (c: content of monomer unit derived from MPDAc) in modified EVAc were determined by the following procedure for modified EVAc before saponification. １ Calculation was performed by H-NMR measurement.

[0098] First, a small amount of the MeOH solution of modified EVAc obtained in (1) was sampled, and the modified EVAc was precipitated in ion-exchanged water. The precipitate was collected and dried at 60°C under vacuum to obtain a dried product of modified EVAc. Next, the dried product of modified EVAc was dissolved in dimethyl sulfoxide (DMSO)-d6 containing tetramethylsilane as an internal standard substance, and analyzed by a 500 MHz spectrometer. １ Measurement was performed at 80°C using a H-NMR (manufactured by JEOL Ltd.: "GX-500").

[0099] The resulting modified EVAc １The peaks in the H-NMR spectrum are assigned as follows: 0.6 to 1.0 ppm: methylene protons (4H) of terminal ethylene units; 1.0 to 1.85 ppm: methylene protons (4H) of intermediate ethylene units, methylene protons (2H) of main chain units of monomer units derived from MPDAc, and methylene protons (2H) of monomer units derived from vinyl acetate; 1.85 to 2.1 ppm: methyl protons (6H) of monomer units derived from MPDAc and methyl protons (3H) of monomer units derived from vinyl acetate; 3.7 to 4.1 ppm: methylene protons (4H) of side chain units of monomer units derived from MPDAc; 4.4 to 5.3 ppm: methine protons (1H) of monomer units derived from vinyl acetate.

[0100] According to the above assignments, when the integral value from 0.6 to 1.0 ppm is defined as x, the integral value from 1.0 to 1.85 ppm as y, the integral value from 3.7 to 4.1 ppm as z, and the integral value from 4.4 to 5.3 ppm as w, the ethylene unit content (a: mol %), the content of vinyl acetate-derived monomer units (b: mol %), and the content of MPDAc-derived monomer units (c: mol %) are each calculated by the following formulas. a = {(2x + 2y - z - 4w) / (2x + 2y + z + 4w)} × 100 b = {8w / (2x + 2y + z + 4w)} × 100 c = {2z / (2x + 2y + z + 4w)} × 100 As a result of calculation using the above methods, the content of ethylene units (a) was 38.0 mol%, the content of monomer units derived from vinyl acetate (b) was 60.4 mol%, and the content of monomer units derived from MPDAc (c) was 1.6 mol%. The values ​​of a, b, and c in the modified EVAc are the same as the values ​​of a, b, and c in the modified EVOH after saponification.

[0101] (6) Degree of saponification of modified EVOH The same applies to the modified EVOH after saponification. １ The crude dried modified EVOH obtained in (2) above was dissolved in dimethyl sulfoxide (DMSO)-d6 containing tetramethylsilane as an internal standard and tetrafluoroacetic acid (TFA) as an additive, and subjected to H-NMR measurement at 500 MHz. １ Measurement was performed at 80°C using a H-NMR (manufactured by JEOL Ltd.: "GX-500"). １In the H-NMR spectrum, the peak intensity between 1.85 and 2.1 ppm was significantly reduced, confirming that not only the ester groups contained in the vinyl acetate-derived monomer units but also the ester groups contained in the MPDAc-derived monomer units were saponified to hydroxy groups. The degree of saponification was calculated from the peak intensity ratio of the methyl protons of the vinyl acetate-derived monomer units and the MPDAc-derived monomer units (1.85 to 2.1 ppm) to the methine protons of the vinyl alcohol units (3.15 to 4.15 ppm). The degree of saponification (DS) of the modified EVOH was 99.9 mol% or more.

[0102] (7) Melting Point of Modified EVOH The modified EVOH composition pellets obtained in (4) above were heated from 30°C to 215°C at a rate of 10°C / min, then rapidly cooled to -35°C at 100°C / min, and then measured again at a heating rate of 10°C / min from -35°C to 195°C (Seiko Electronics Industries Co., Ltd., differential scanning calorimeter (DSC) "RDC220 / SSC5200H"). Indium and lead were used for temperature calibration. The melting peak temperature (Tpm) was determined from the chart of the second run according to the JIS standard, and this was taken as the melting point of the modified EVOH. The melting point was 160°C.

[0103] (8) Production of Resin Composition Pellets Containing Inorganic Particles To the modified EVOH composition pellets obtained in (4) above, inorganic particles (silicon dioxide particles with an average primary particle size of 30 nm and an average secondary particle size of 2 μm) were added in an amount such that the content relative to the modified EVOH was 1,500 ppm, and the mixture was mixed in a tumbler (manufactured by Nissui Kako Co., Ltd.) for 5 minutes to thoroughly mix the modified EVOH and inorganic particles. The resulting mixture was then fed into the raw material supply section of a twin-screw extruder at a rate of 10 kg / hour, kneaded at a resin temperature of 250°C in the extruder, and extruded to obtain resin composition pellets containing modified EVOH and inorganic particles. The secondary particle size of the inorganic particles in the resulting resin composition pellets was determined as follows. Platinum-palladium-deposited resin composition pellets were observed using a Hitachi field emission scanning electron microscope (FE-SEM) "SU8010" at an acceleration voltage of 1.0 kV and a focal length of 32 mm. The particle diameters of all secondary particles (aggregates) that could be observed in one field of view were determined. The longest diameter of the secondary particles (aggregates) was used as the particle diameter of the secondary particles (aggregates). The particle diameters (secondary particle diameters) of the measured silicon dioxide particles were in the range of 2 to 20 μm.

[0104] (9) Film Production Using the resin composition pellets obtained in (8) above, a single layer film was produced using a 20 mm extruder "D2020" (D (mm) = 20, L / D = 20, compression ratio = 2.0, screw: full flight) manufactured by Toyo Seiki Seisaku-sho, Ltd. under the following conditions to obtain a single layer film. Cylinder temperature: supply section 175°C, compression section 190°C, metering section 190°C Die temperature: 190°C Screw rotation speed: 40 to 100 rpm Discharge rate: 0.4 to 1.5 kg / hour Take-up roll temperature: 80°C Take-up roll speed: 0.8 to 3.2 m / min Film thickness: 20 μm

[0105] In other comparative examples, the temperature conditions of the extruder when producing a monolayer film were set according to the melting point of the modified EVOH or EVOH as follows: Cylinder temperature: Feeding section: 175°C Compression section: Melting point of modified EVOH or EVOH + 30 to 45°C Metering section: Melting point of modified EVOH or EVOH + 30 to 45°C Die temperature: Melting point of modified EVOH or EVOH + 30 to 45°C

[0106] (10) Measurement of Oxygen Transmission Rate The monolayer film having an average thickness of 20 μm obtained in (9) above was conditioned for 3 days under conditions of 20°C and 85% RH, and then the oxygen transmission rate was measured under the same conditions (using "OX-TORAN MODEL 2 / 21" manufactured by Mocon). As a result, the oxygen transmission rate (OTR) was 1.6 cc 20 μm / (m ２ In this measurement, the oxygen transmission rate (OTR) was 10 cc 20 μm / (m ２ ·day·atm) or less, it was determined that the gas barrier properties were sufficient.

[0107] (11) Preparation of Multilayer Structure (I) Using the resin composition pellets obtained in (8) above, a single-layer film (average thickness 100 μm) was prepared by hot pressing under conditions of 210°C and 200 kN. Similarly, a single-layer film of polyurethane resin (BASF, Elastollan E685) was prepared. The obtained gas barrier layer and polyurethane layer were laminated together, and a multilayer structure (I) (multilayer film) having a gas barrier layer and a polyurethane layer was prepared using a heat sealer "HSE 3" manufactured by RDM TEST EQUIPMENT at a temperature of 210°C, a pressure of 0.12 kPa, and a time of 10 seconds. The interlayer adhesion strength of the obtained multilayer structure (I) was evaluated by the method described in (12) below. The average value of three measurements is shown in Table 1.

[0108] (12) Measurement of Interlayer Adhesion Strength of Multilayer Structure (I) The multilayer structure (I) obtained in (11) above was stored in an atmosphere of 20 to 23°C, and 15 mm strips were cut into measurement samples. Using this measurement sample, T-peel strength was measured at a pulling rate of 100 mm / min using an autograph "AGS-H" manufactured by Shimadzu Corporation in an atmosphere of 20 to 23°C. The obtained value (unit: N) was taken as the interlayer adhesion strength between the gas barrier layer and the polyurethane layer. When the interlayer adhesion strength in this measurement was 20 N or more, it was determined that the interlayer adhesion was excellent.

[0109] (13) Preparation of Multilayer Structure (II) A multilayer structure (multilayer film) [layer structure: polyethylene layer / polyurethane layer / modified EVOH composition layer (gas barrier layer) / polyurethane layer / polyethylene layer, average thickness (μm): 170 / 60 / 60 / 60 / 170] was prepared using the resin composition pellets obtained in (8) above, and the polyethylene layers on both sides were peeled off. Japan Polyethylene Corporation's "Novatec LD LJ400" was used as the polyethylene, and Lubrizol Japan Corporation's "Estane 2103-90AE" was used as the polyurethane. The co-extrusion equipment and conditions used were as follows. After peeling off the polyethylene layer, the multilayer structure (II) had an average thickness of 60 μm for each of the outermost polyurethane layers, and an average thickness of 60 μm for the gas barrier layer. The obtained multilayer structure (II) was evaluated by the method described in (14) below. The results are shown in Table 2. (Co-extrusion molding conditions) Extrusion temperature of each resin: Feeding section / compression section / metering section / die = 170°C / 170°C / melting point of modified EVOH or EVOH + 30 to 45°C / melting point of modified EVOH or EVOH + 30 to 45°C Extruder: Polyethylene 32φ extruder GT-32-A type (manufactured by Plastics Technology Research Institute Co., Ltd.) Polyurethane 25φ extruder P25-18-AC type (manufactured by Osaka Seiki Kogyo Co., Ltd.) Resin composition 20φ extruder Lab machine ME type CO-EXT (manufactured by Toyo Seiki Co., Ltd.) T-die: 300 mm wide for 3 types and 5 layers (manufactured by Plastics Technology Research Institute Co., Ltd.) Cooling roll temperature: 80°C Take-up speed: 1.2 m / min

[0110] (14) Measurement of Interlayer Adhesion of Multilayer Structure (II) The interlayer adhesion of the multilayer structure (II) obtained in (13) above was measured as follows. The obtained multilayer structure (II) was stored in an atmosphere of 23°C and 50% RH, and on the day after production, 15 mm strips were prepared to serve as measurement samples. Using this measurement sample, T-peel strength was measured at a pulling rate of 250 mm / min using an autograph "AGS-H" manufactured by Shimadzu Corporation in an atmosphere of 23°C and 50% RH. The obtained value (unit: g / 15 mm) was taken as the interlayer adhesion between the gas barrier layer and the polyurethane layer. In this measurement, an interlayer adhesion strength of 450 g / 15 mm or more was determined to be excellent.

[0111] [Example 2] Resin composition pellets containing inorganic particles were produced in the same manner as in Example 1, except that the amount of inorganic particles was changed to 700 ppm in the above (8) of Example 1, and evaluated by the above methods (13) and (14). The results are shown in Table 2.

[0112] [Example 3] Resin composition pellets containing inorganic particles were produced in the same manner as in Example 1, except that the amount of inorganic particles was changed to 3,000 ppm in (8) of Example 1, and evaluated by the methods in (13) and (14) above. The results are shown in Table 2.

[0113] [Example 4] Polymerization was carried out in the same manner as in Example 1 (1), except that the amount of MeOH was 2.1 kg, the amount of MPDAc was 1.1 kg, the ethylene pressure was 4.3 MPa, and the amount of initiator was 16.8 g, to obtain modified EVAc. After 4.5 hours, when the conversion of VAc reached 32%, the polymerization was stopped by cooling. Resin composition pellets containing inorganic particles were produced in the same manner as in Example 1, except for the above points, and were measured and evaluated using the methods (13) and (14) above. The results are shown in Table 2.

[0114] [Example 5] In the above (8) of Example 1, the inorganic particles were replaced with Al ２ O ３ Resin composition pellets containing inorganic particles and the like were produced in the same manner as in Example 1, except for changing the procedure from Example 1 to Example 1, and evaluated by the methods (13) and (14) above. The results are shown in Table 2.

[0115] [Example 6] Resin composition pellets containing inorganic particles were produced in the same manner as in Example 1, except that in the above (8) of Example 1, the inorganic particles were changed to MgO and the content was changed to 700 ppm, and the pellets were evaluated by the above methods (13) and (14). The results are shown in Table 2.

[0116] [Example 7] In the above (8) of Example 1, the inorganic particles were replaced with ZrO ２ and the content was changed to 700 ppm, and resin composition pellets containing inorganic particles were produced in the same manner as in Example 1, and evaluated by the methods (13) and (14) above. The results are shown in Table 2.

[0117] Comparative Example 1 Polymerization was carried out in the same manner as in Example 1 (1), except that the amount of MeOH was 8.0 kg, the ethylene pressure was 3.6 MPa, the amount of initiator was 4.2 g, and MPDAc was not added, yielding unmodified EVAc. After 4.5 hours, when the VAc conversion reached 44%, the polymerization was terminated by cooling. In Example 1 (8), inorganic particles were not added. Except for these points, unmodified EVOH composition pellets were produced in the same manner as in Example 1. The obtained unmodified EVOH resin composition pellets were reacted with epoxybutane in the presence of a catalyst using a Toshiba Machine Co., Ltd. twin-screw extruder "TEM-35BS" (37 mmφ, L / D = 52.5). Unreacted epoxybutane was removed via a vent. Next, an 8.2 mass% aqueous solution of ethylenediaminetetraacetic acid trisodium hydrate was added as a catalyst deactivator, and pelletization was carried out. The pellets were then dried to yield modified EVOH composition pellets with an ethylene unit content of 32.0 mol%. In addition, the epoxy butane modification rate is １ Measurement by H-NMR (internal standard: tetramethylsilane, solvent: d6-DMSO) revealed that the content was 5.8 mol%. The modified EVOH composition pellets (resin composition pellets) obtained were measured and evaluated by the methods (7) and (9) to (12) above. The results are shown in Table 1.

[0118] Comparative Example 2 Polymerization was carried out in the same manner as in Example 1 (1), except that the amount of MeOH was 9.5 kg, the amount of initiator was 3.2 g, the ethylene pressure was 2.9 MPa, and no MPDAc was added, to obtain unmodified EVAc. After 5.5 hours, when the conversion of VAc reached 46%, the polymerization was terminated by cooling. In Example 1 (8), no inorganic particles were added. Except for these points, unmodified EVOH composition pellets (resin composition pellets) were produced in the same manner as in Example 1, and measurements and evaluations were performed using the methods (5) to (7) and (9) to (12) above. The results are shown in Table 1.

[0119] Comparative Example 3 Polymerization was carried out in the same manner as in Example 1 (1), except that the amount of MeOH was 2.3 kg, the amount of initiator was 4.2 g, the ethylene pressure was 5.6 MPa, and no MPDAc was added, to obtain unmodified EVAc. After 6 hours, when the conversion of VAc reached 44%, the polymerization was terminated by cooling. In Example 1 (8), no inorganic particles were added. Except for these points, unmodified EVOH composition pellets (resin composition pellets) were produced in the same manner as in Example 1, and measurements and evaluations were performed using the methods (5) to (7), (13), and (14) above. The results are shown in Table 2.

[0120] [Comparative Example 4] Modified EVOH composition pellets (resin composition pellets) were produced in the same manner as in Example 1, except that inorganic particles were not added in the above (8) of Example 1, and the pellets were measured and evaluated by the above methods (5) to (7), (13), and (14). The results are shown in Table 2.

[0121] Comparative Example 5 Unmodified EVOH composition pellets (resin composition pellets) were produced in the same manner as in Example 1, except that in (1) of Example 1, the amount of MeOH was changed to 2.3 kg, the amount of initiator was changed to 4.2 g, the ethylene pressure was changed to 5.6 MPa, and MPDAc was not added, and the pellets were measured and evaluated by the methods (5) to (7), (13), and (14) above. The results are shown in Table 2.

[0122] Comparative Example 6 Unmodified EVOH composition pellets (resin composition pellets) were produced in the same manner as in Example 1, except that in (1) of Example 1, the amount of MeOH was changed to 6.3 kg, the amount of initiator was changed to 4.2 g, the ethylene pressure was changed to 4.4 MPa, and MPDAc was not added, and the pellets were measured and evaluated by the methods (5) to (7), (13), and (14) above. The results are shown in Table 2.

[0123]

[0124]

[0125] As shown in Tables 1 and 2, each of the multilayer structures of the Examples had sufficient gas barrier properties and excellent interlayer adhesion.

[0126] The multilayer structure of the present invention can be suitably used for container packaging materials, sheet materials, cushion materials, pipes, etc.

Claims

1. A multilayer structure comprising: a gas barrier layer (A) containing a modified ethylene-vinyl alcohol copolymer and inorganic particles; and a polyurethane layer (B) containing a thermoplastic polyurethane, wherein the modified ethylene-vinyl alcohol copolymer has monomer units (a), (b) and (c) represented by the following formulas (a), (b) and (c), respectively; the contents of the monomer units (a), (b) and (c) in the modified ethylene-vinyl alcohol copolymer satisfy the following formulas (1) to (3); the modified ethylene-vinyl alcohol copolymer has a degree of saponification (DS) defined by the following formula (4) of 90 mol % or more; the content of the inorganic particles in the gas barrier layer (A) is 5 ppm or more and 5,000 ppm or less relative to the modified ethylene-vinyl alcohol copolymer; and at least one pair of the gas barrier layer (A) and the polyurethane layer (B) are directly laminated together. (In formulas (a) to (c), R ａ is a hydrogen atom, a methyl group or R ｅ R is a group represented by —O—Y. ｂ and R ｅ are each independently a single bond, an alkylene group having 1 to 9 carbon atoms, or an alkyleneoxy group having 1 to 9 carbon atoms, and some or all of the hydrogen atoms in the alkylene group and the alkyleneoxy group may be substituted with a hydroxy group, an alkoxy group, or a halogen atom. ｃ and R ｄ are each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and some or all of the hydrogen atoms of the alkyl group may be substituted with a hydroxy group, an alkoxy group, or a halogen atom. X, Y, and Z are each independently a hydrogen atom, a formyl group, or an alkanoyl group having 2 to 10 carbon atoms.) 18≦a≦55 ... (1) [100-(a+c)]×0.9≦b≦[100-(a+c)] ... (2) 0.01≦c≦20 ... (3) (In the formulas (1) to (3), a, b, and c are the respective contents (mol %) of the monomer unit (a), the monomer unit (b), and the monomer unit (c) relative to the total monomer units of the modified ethylene-vinyl alcohol copolymer.) DS=[(total number of moles of X, Y, and Z that are hydrogen atoms) / (total number of moles of X, Y, and Z)]×100 ... (4) 2. The multilayer structure according to claim 1, wherein the monomer unit (c) is represented by the following formula (c1): (In formula (c1), R １ , R ２ , R ３ and R ４ are each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and some or all of the hydrogen atoms of the alkyl group may be substituted with a hydroxy group, an alkoxy group or a halogen atom. Y and Z have the same meaning as Y and Z in formula (c).

3. R １ , R ２ , R ３ and R ４ 3. The multilayer structure of claim 2, wherein each of is a hydrogen atom.

4. The multilayer structure according to any one of claims 1 to 3, wherein X, Y and Z are each independently a hydrogen atom or an acetyl group.

5. The multilayer structure according to any one of claims 1 to 3, wherein the outermost layer is a polyurethane layer (B).