Modified ethylene-vinyl alcohol resin and gas barrier material

Abstract

As an EVOH-based resin having excellent biodegradability and excellent gas barrier properties, a modified EVOH-based resin is provided, which is a modified EVOH-based resin having a primary hydroxyl group in the side chain. The content of the ethylene structural unit in the above-mentioned modified EVOH-based resin is 1 to 16.5 mol%, and the content of the structural unit having a primary hydroxyl group in the side chain is 2.5 mol% or more.

Description

Technical Field

[0001] The present invention relates to a modified ethylene-vinyl alcohol resin, and more particularly to a modified ethylene-vinyl alcohol resin having a specific amount of primary hydroxyl groups in the side chain. Background Art

[0002] Conventionally, ethylene-vinyl alcohol resins (hereinafter, sometimes referred to as "EVOH resins") having an ethylene structural unit content of 20 to 60 mol% have been used for food packaging materials (Non-Patent Document 1) because of their transparency, gas barrier property, fragrance retention property, solvent resistance, and oil resistance, and they can reduce food loss by utilizing these properties.

[0003] On the other hand, in recent years, there has been a demand to reduce the environmental burden. However, from the viewpoint of the low biodegradability of EVOH resins having an ethylene structural unit content of 20 to 60 mol% and further reducing the environmental burden (such as marine problems), there is a demand for a gas barrier resin having excellent biodegradability.

[0004] As the above-mentioned gas barrier resin having biodegradability, in Non-Patent Document 2, for example, with respect to an EVOH resin having an ethylene structural unit content of 4 to 10 mol%, the substrate specificity of an enzyme derived from a microorganism, that is, polyvinyl alcohol dehydrogenase, was reported.

[0005] Non-Patent Document 3 shows that the mechanism of biodegradation of polyvinyl alcohol achieved by the above polyvinyl alcohol dehydrogenase is that the biodegradation is carried out by oxidizing the site where vinyl alcohol units are connected.

[0006] In addition, Patent Document 1 reported the following example: By setting the structure of the EVOH resin to have an ethylene structural unit content of 2 to 19 mol%, a degree of polymerization of 200 to 2000, a saponification degree of 80 to 99.99 mol%, and a total content of carboxyl groups and lactone rings of 0.02 to 0.4 mol%, moderate hydrophilicity was imparted, and an attempt was made to improve biodegradability.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2000-309607

[0010] Non-Patent Documents

[0011] Non-Patent Document 1: New Applications of Gas Barrier / Fragrance Retention Packaging Materials (Japanese: ガスバリア性·保香性包装材料の新展開), Toray Research Center, Inc., 1997, Chapter 2, Ethylene-Vinyl Alcohol Copolymer Resin

[0012] Non-patent document 2: Biosci. Biotech Biochem. Magazine, Vol. 59, No. 7, p. 1229 (1995)

[0013] Non-patent document 3: Macromolecule magazine, Vol. 32, p. 7753 (1999) Summary of the Invention

[0014] Problems to be solved by the invention

[0015] However, in the above-mentioned non-patent document 2, although the reaction rate (Vmax) and Michaelis constant (Km) when the matrix is ​​infinite are evaluated, there is no report on how much the biodegradability of EVOH-based resins decreases after a few days, and further improvement of the actual biodegradability is sought.

[0016] Furthermore, when attempts were made to improve biodegradability, based on the biodegradation mechanism disclosed in Non-Patent Document 3, the only solution was to increase the number of vinyl alcohol unit chains, and therefore, copolymerization with other structural units was not considered.

[0017] Furthermore, the structure and content of carboxyl groups or lactone rings disclosed in Patent Document 1 lack the ability to impart hydrophilicity to EVOH-based resins and require a long time until biodegradation begins, and further improvements are sought.

[0018] Therefore, in this context, the present invention provides an EVOH-based resin having excellent biodegradability and excellent gas barrier properties.

[0019] Solutions for solving problems

[0020] Therefore, in view of the above situation, the present inventors have repeatedly conducted in-depth research and found that by setting the content of ethylene structural units in EVOH-based resins to a specific range and then introducing a specific amount of structural units having primary hydroxyl groups in the side chains, the hydrophilicity of the modified EVOH-based resins can be controlled, making it easy for bacteria that trigger biodegradation to approach, thereby solving the above-mentioned problems.

[0021] This is presumably because: in EVOH-based resins, hydroxyl groups are directly bonded to the polymer main chain in the form of secondary hydroxyl groups, so a three-dimensional cluster structure is formed around the hydroxyl groups, making it difficult for bacteria to access. However, in the case of a structure with primary hydroxyl groups in the side chain, the hydroxyl groups are located away from the main chain. Moreover, compared with secondary hydroxyl groups and tertiary hydroxyl groups, primary hydroxyl groups have less steric hindrance around them, making it easy for bacteria to access them. Therefore, this helps to solve the above-mentioned problem.

[0022] That is, the present invention provides the following [1] to [5].

[0023] [1] A modified EVOH-based resin having primary hydroxyl groups in side chains, wherein the content of ethylene structural units in the modified EVOH-based resin is 1 to 16.5 mol%, and the content of structural units having primary hydroxyl groups in side chains is 2.5 mol% or more.

[0024] [2] The modified EVOH-based resin according to [1], wherein the degree of saponification of the modified EVOH-based resin is 99 mol% or more.

[0025] [3] The modified EVOH-based resin according to [1] or [2], wherein the amount of sodium acetate contained in the EVOH-based resin is less than 0.7% by mass.

[0026] [4] A modified EVOH-based resin according to any one of [1] to [3], wherein the transmittance at 430 nm at 30°C and an optical path length of 20 mm when the modified EVOH-based resin is prepared as a solution having a concentration of 4% by mass using water and 2-propanol as a solvent in a mixing ratio calculated by the following formula (1) is 70% or more.

[0027] Water: 2-propanol = 100 - X: X (mass ratio)... (1)

[0028] X=3.4×(content of ethylene structural units)-5×(content of structural units having primary hydroxyl groups)-20.

[0029] When X is negative, X=0.

[0030] [5] A gas barrier material comprising a layer formed of the modified EVOH-based resin according to any one of [1] to [4].

[0031] Effects of the Invention

[0032] The modified EVOH resin of the present invention is a modified EVOH resin having primary hydroxyl groups in the side chain. The content of ethylene structural units in the above-mentioned modified EVOH resin is 1 to 16.5 mol%, and the content of structural units having primary hydroxyl groups in the side chain is more than 2.5 mol%. Therefore, it has gas barrier properties and excellent biodegradability. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The modified EVOH resin of Example 1 is shown in FIG. 1 H-NMR spectrum.

[0034] Figure 2 The modified EVOH resin of Example 1 is shown in FIG. 13 C-NMR spectrum.

[0035] Figure 3The intermediate of the modified EVOH resin of Example 6, namely the modified ethylene-vinyl ester copolymer 1 H-NMR spectrum.

[0036] Figure 4 The modified EVOH resin of Example 6 is shown in FIG. 1 H-NMR spectrum. DETAILED DESCRIPTION

[0037] Hereinafter, the configuration of the present invention will be described in detail, but this is merely an example of a preferred embodiment.

[0038] In the present invention, “α and / or β (α and β are arbitrary structures or components)” means only α, only β, or a combination of α and β.

[0039] EVOH-based resins are generally thermoplastic resins obtained by saponifying a copolymer of ethylene and a vinyl ester-based monomer, that is, an ethylene-vinyl ester-based copolymer.

[0040] The modified EVOH-based resin of the present invention has a specific amount of primary hydroxyl groups in the side chain, and specifically is an EVOH-based resin having a structural unit represented by the following general formula (1).

[0041]

[0042] (Where R 1 ~R 3 Each independently represents a hydrogen atom or an organic group, and X represents a single bond or a bond chain.

[0043] As R 1 ~R 3 , as long as it is a hydrogen atom or an organic group, there is no particular limitation. Examples of the organic group include hydrocarbon groups such as alkyl, alkenyl, alkynyl, phenyl, and naphthyl (these hydrocarbon groups may optionally have hydroxyl, fluorine, chlorine, and bromine as substituents).

[0044] X connecting the polymer main chain to the primary hydroxyl structure represents a single bond or a bonded chain. As a bonded chain, there is no particular limitation, and in addition to hydrocarbons such as alkylene, alkenylene, alkynylene, phenylene, naphthylene (these hydrocarbons optionally have hydroxyl, fluorine, chlorine and bromine as substituents), oxyalkylene, oxyalkenylene, oxyalkynylene, oxyphenylene, oxynaphthylene and the like bonded to the polymer main chain by means of an ether bond (these hydrocarbons optionally have hydroxyl, fluorine, chlorine and bromine as substituents), -CO-, -CO(CH2)mCO-, -CO(CH2)mCOR 4 -、-NR 5 -、-CONR 5 - etc. 4 、R5 (where m represents a natural number) is independently an arbitrary substituent, preferably a hydrogen atom or an alkyl group.

[0045] In order to obtain the modified EVOH-based resin of the present invention, for example:

[0046] (I) A method in which a monomer having a primary hydroxyl group in a side chain and / or a monomer whose primary hydroxyl group in a side chain is protected by an ester or the like is copolymerized with ethylene and a vinyl ester monomer, followed by deprotection by saponification or the like;

[0047] (II) A method in which a copolymer of ethylene and a vinyl ester monomer is first saponified to obtain an EVOH resin, and then the EVOH resin is post-modified to generate primary hydroxyl groups in the side chains.

[0048] Among them, the above-mentioned method (I) is preferred from the viewpoint of productivity.

[0049] Hereinafter, the method for producing the modified EVOH-based resin of the present invention will be described.

[0050] First, in the case of the above-mentioned method (I), ethylene and vinyl ester monomers may be copolymerized with monomers having primary hydroxyl groups in side chains and / or monomers in which the hydroxyl groups are protected with esters or the like.

[0051] Examples of the vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl versatate, and vinyl trifluoroacetate. These monomers may be used alone or in combination of two or more. Among these, vinyl acetate is preferred from the perspective of economic efficiency.

[0052] Examples of monomers having a primary hydroxyl group in the side chain in the above method (I) include monomers containing a monohydroxyalkyl group such as allyl alcohol, 3-butene-1-ol, 4-pentene-1-ol, 5-hexene-1-ol, 6-heptene-1-ol, and methacrylic alcohol; and monomers containing a dihydroxyalkyl group such as 2-methylene-1,3-propanediol, 3,4-butene-1-diol, 4,5-pentene-1-diol, 4,5-methylpentene-1-diol, 5,6-hexene-1-diol, and glycerol monoallyl ether. These monomers may be used alone or in combination of two or more.

[0053] In addition, examples of monomers in which the primary hydroxyl group of the side chain is protected with an ester or the like (hereinafter sometimes referred to as "a monomer in which the hydroxyl group is protected with an ester or the like") in the above-mentioned method (I) include, for example, acetate esters of the above-mentioned monomers having a primary hydroxyl group of the side chain. Specifically, examples include monomers containing a monoacetoxyalkyl group, such as allyl acetate, 3-butenyl acetate, 4-pentenyl acetate, 5-hexenyl acetate, 6-heptenyl acetate, and methylpropenyl acetate; and monomers containing a diacetoxyalkyl group, such as 2-methylene-1,3-propanediol diacetate, 3,4-diacetoxy-1-butene, 4,5-diacetoxy-1-pentene, 4,5-diacetoxy-3-methyl-1-pentene, 5,6-diacetoxy-1-hexene, and 3-allyloxy-1,2-propanediol diacetate. These monomers can be used alone or in combination of two or more.

[0054] In the above method (I), a monomer having a primary hydroxyl group in a side chain and a monomer in which the hydroxyl group is protected by an ester or the like may be used in combination, and copolymerized with ethylene or a vinyl ester monomer.

[0055] Among them, from the viewpoint of productivity, monomers in which the hydroxyl group is protected by an ester or the like are preferred, monomers containing a diacetoxyalkyl group are more preferred, 3,4-diacetoxy-1-butene and 2-methylene-1,3-propanediol diacetate are further preferred, and 3,4-diacetoxy-1-butene is particularly preferred.

[0056] In the above method (I), for example, when 3,4-diacetoxy-1-butene is used as a copolymerization component, the modified EVOH resin obtained by deprotection by saponification or the like has a structural unit having a primary hydroxyl group in a side chain represented by the following general formula (2).

[0057]

[0058] In the above method (I), for example, when 2-methylene-1,3-propanediol diacetate is used as a copolymerization component, the obtained modified EVOH-based resin has a structural unit having a primary hydroxyl group in a side chain represented by the following general formula (3).

[0059]

[0060] In the above methods (I) and (II), a copolymerizable ethylenically unsaturated monomer may be copolymerized as a copolymerization component within a range not impairing the effects of the present invention.

[0061] Examples of the ethylenically unsaturated monomer include olefins such as propylene, 1-butene, and isobutylene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, phthalic acid (anhydride), maleic acid (anhydride), and itaconic acid (anhydride), or salts thereof, or monoalkyl esters or dialkyl esters in which the alkyl group has 1 to 18 carbon atoms; acrylamide, N-alkylacrylamide in which the alkyl group has 1 to 18 carbon atoms, N,N-dimethylacrylamide, 2-acrylamidopropanesulfonic acid or salts thereof; acrylamides such as acrylamidopropyldimethylamine or its acid salts or quaternary salts thereof; methacrylamide, carbon atoms of alkyl group; Methacrylamides such as N-alkylmethacrylamide, N,N-dimethylmethacrylamide, and 2-methacrylamidopropanesulfonic acid or its salts having 1 to 18 carbon atoms; N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, and N-vinylacetamide; acrylonitriles such as acrylonitrile and methacrylonitrile; vinyl ethers such as alkyl vinyl ethers, hydroxyalkyl vinyl ethers, and alkoxyalkyl vinyl ethers having 1 to 18 carbon atoms in the alkyl group; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, and vinyl bromide; and vinylsilanes. These may be used alone or in combination of two or more.

[0062] For the copolymerization reaction, known methods such as bulk polymerization, solution polymerization, suspension polymerization, dispersion polymerization, or emulsion polymerization can be used. Among them, solution polymerization is preferably used because the copolymerization can be easily controlled.

[0063] When conducting the copolymerization via solution polymerization, the solvent used includes lower alcohols having 1 to 5 carbon atoms, such as methanol, ethanol, propanol, and butanol; and ketones, such as acetone and 2-butanone. These can be used alone or in combination of two or more. Methanol is preferably used because it facilitates control of the polymerization reaction. Furthermore, 2-propanol is preferably used when synthesizing copolymers with a low degree of polymerization.

[0064] The amount of the solvent used can be appropriately selected in consideration of the desired degree of polymerization of the modified EVOH-based resin and the solvent's chain transfer constant. For example, when the solvent is methanol or 2-propanol, the mass ratio (S / M) of the solvent (S) to the monomer (M) is preferably S / M = 0.01 to 10, more preferably S / M = 0.05 to 7.

[0065] As a method for feeding the copolymerization components in solution polymerization, any method may be adopted, such as initial all-in-one feeding, divided feeding, or continuous feeding such as the Hanna method taking into consideration the reactivity ratio of the monomers.

[0066] A polymerization initiator is used in the copolymerization. Examples of the polymerization initiator include azo-based initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile); and peroxide-based initiators such as acetyl peroxide, benzoyl peroxide, lauroyl peroxide, t-butyl peroxyneodecanoate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, diisopropyl peroxydicarbonate, and di(2-ethylhexyl) peroxydicarbonate.

[0067] The amount of the polymerization initiator used varies depending on the type of polymerization initiator and cannot be generalized. It should be selected arbitrarily based on the polymerization rate. For example, when using 2,2'-azobisisobutyronitrile or t-butyl peroxyneodecanoate, the amount is generally 10 to 2000 ppm, preferably 50 to 1000 ppm, relative to the vinyl ester monomer.

[0068] The polymerization temperature of the copolymerization is preferably selected within the range of 40° C. to the boiling point depending on the solvent used and the ethylene pressure.

[0069] In addition, during the copolymerization, the copolymerization can be carried out in the presence of a chain transfer agent within a range that does not impair the effects of the present invention. Examples of chain transfer agents include aldehydes such as acetaldehyde, propionaldehyde, and crotonaldehyde; and thiols such as 2-hydroxyethanethiol. These can be used alone or in combination of two or more. Among them, aldehydes are preferably used. The amount of the chain transfer agent added during the copolymerization is determined based on the chain transfer constant of the chain transfer agent and the degree of polymerization of the target modified EVOH-based resin. Generally, it is preferably 0.1 to 10 parts by mass relative to 100 parts by mass of the vinyl ester-based monomer.

[0070] By saponifying the ethylene-vinyl ester copolymer obtained in this manner, an EVOH resin can be obtained.

[0071] The saponification method can be a known method. For example, the saponification can be carried out by dissolving the ethylene-vinyl ester copolymer obtained above in alcohol or aqueous alcohol using a saponification catalyst.

[0072] Examples of the alcohol include lower alcohols having 1 to 5 carbon atoms, such as methanol, ethanol, and propanol. These can be used alone or in combination of two or more. Of these, methanol is preferred.

[0073] The concentration of the ethylene-vinyl ester copolymer in the alcohol is appropriately selected depending on the viscosity and is usually 5 to 60% by mass.

[0074] Examples of the saponification catalyst include base catalysts such as alkali metal hydroxides and alkoxides such as sodium hydroxide, potassium hydroxide, sodium methoxide, sodium ethoxide, potassium methoxide, and potassium ethoxide; and acid catalysts such as sulfuric acid, hydrochloric acid, nitric acid, methanesulfonic acid, zeolite, and cation exchange resins.

[0075] The saponification temperature is not critical, but is preferably within the range of 20-140°C. As shown in the present invention, when the ethylene structural unit content is 1-16.5 mol%, granules are generated as saponification proceeds, and the reaction proceeds. If a gel-like product gradually precipitates, it can be pulverized. The resulting granules can then be neutralized, washed, and dried as needed to obtain a modified EVOH-based resin.

[0076] The above-mentioned washing is performed to reduce the catalyst used in saponification and the salts generated during the neutralization. For example, when sodium hydroxide, sodium methoxide, sodium ethoxide, etc. are used as saponification catalysts and neutralized with acetic acid, sodium acetate is generated during the neutralization. Therefore, by washing the generated granular material, the amount of sodium acetate remaining in the resulting modified EVOH-based resin can be adjusted. The degree of washing is determined by considering the desired quality of the modified EVOH-based resin and the increased number of steps and costs associated with washing.

[0077] Examples of the cleaning liquid used in the above cleaning process include lower alcohols having 1 to 5 carbon atoms, such as methanol, ethanol, and propanol; and water. These can be used alone or in combination of two or more. Among them, methanol is preferred.

[0078] In addition, the amount of the cleaning liquid used in the cleaning is preferably 4 to 8 parts by mass (bath ratio of 4 to 8) relative to 1 part by mass of the generated granules. As the cleaning temperature, it is preferably 20 to 70°C. As the cleaning time, it is preferably 0.5 to 3 hours. As the number of cleanings, it is preferably 2 to 6 times. As a combination of cleaning conditions, it is more preferred to effectively utilize the cleaning liquid by setting, for example, a bath ratio of 4 and a number of cleanings of 4 to 6 times, a bath ratio of 5 and a number of cleanings of 3 to 5 times, a bath ratio of 8 and a number of cleanings of 2 to 3 times, etc.

[0079] EVOH resins generally have a lower affinity for water than conventional vinyl alcohol resins by an amount corresponding to the amount of ethylene modification. Taking advantage of the water-soluble nature of sodium acetate, washing with a solvent containing water can reduce sodium acetate levels even with a small amount of washing solution. In contrast, the modified EVOH resin of the present invention not only contains less ethylene structural units than conventional EVOH resins but also has structural units with primary hydroxyl groups in their side chains. Consequently, the resin has a higher affinity for water, making washing with a solvent containing water undesirable. Therefore, by employing the aforementioned washing solution, bath ratio, washing temperature, washing time, and number of washing cycles, a modified EVOH resin containing the desired amount of sodium acetate can be obtained.

[0080] In the present invention, there is a tendency that the transparency of a solution of a modified EVOH-based resin described later, and in particular, the gas barrier properties under high humidity, can be adjusted by adjusting the degree of washing after the saponification and neutralization.

[0081] In the present invention, in order to increase the degree of saponification, the once-produced granules may be washed and then dispersed again in alcohol or the like, and an alkali catalyst may be added to further react.

[0082] By the saponification, the vinyl ester units in the ethylene-vinyl ester copolymer are converted into vinyl alcohol units, thereby obtaining an EVOH resin.

[0083] Furthermore, in the aforementioned method (I), when copolymerizing monomers whose hydroxyl groups are protected with esters or the like, the esters or the like in the protected monomers are simultaneously deprotected by saponification, converting them into primary hydroxyl groups in the side chains, thereby producing the modified EVOH-based resin of the present invention. It should be noted that the modified EVOH-based resin of the present invention only needs to have a specific number of primary hydroxyl groups in the side chains, and may not be completely deprotected, but may contain a small amount of ester groups.

[0084] In the case of the aforementioned method (II), for example, the obtained EVOH-based resin can be reacted with a monovalent epoxy group-containing compound. The reaction method is not particularly limited, and suitable methods include, for example, methods in which the reaction is carried out in a solution and methods in which the reaction is carried out in an extruder. Furthermore, when using the method in which the reaction is carried out in an extruder, it is also preferred to use a catalyst containing ions of metals belonging to Groups 3 to 12 of the Periodic Table.

[0085] Preferred examples of the monovalent epoxy group-containing compound include propylene oxide, butylene oxide, and glycidol. These can be used alone or in combination of two or more. Among them, propylene oxide is preferred.

[0086] For example, when propylene oxide is used as the monovalent epoxy group-containing compound, the obtained modified EVOH-based resin has a structural unit having a primary hydroxyl group in a side chain, as represented by the following general formula (4).

[0087]

[0088] By doing so, the modified EVOH-based resin of the present invention having primary hydroxyl groups in the side chains can be obtained. Specifically, a modified EVOH-based resin having a structural unit represented by the following general formula (1) can be obtained. It should be noted that in the present invention, as long as the modified EVOH-based resin has a specific amount of primary hydroxyl groups in the side chains, it may have other hydroxyl structures (secondary hydroxyl groups, tertiary hydroxyl groups) in the side chains.

[0089]

[0090] (Where R 1 ~R 3 Each independently represents a hydrogen atom or an organic group, and X represents a single bond or a bond chain.

[0091] As R 1 ~R 3 , as long as it is a hydrogen atom or an organic group, there is no particular limitation. Examples of the organic group include hydrocarbon groups such as alkyl, alkenyl, alkynyl, phenyl, and naphthyl (these hydrocarbon groups may optionally have hydroxyl, fluorine, chlorine, and bromine as substituents).

[0092] X connecting the polymer main chain to the primary hydroxyl structure represents a single bond or a bonded chain. As a bonded chain, there is no particular limitation, and in addition to hydrocarbons such as alkylene, alkenylene, alkynylene, phenylene, naphthylene (these hydrocarbons optionally have hydroxyl, fluorine, chlorine and bromine as substituents), oxyalkylene, oxyalkenylene, oxyalkynylene, oxyphenylene, oxynaphthylene and the like bonded to the polymer main chain by means of an ether bond (these hydrocarbons optionally have hydroxyl, fluorine, chlorine and bromine as substituents), -CO-, -CO(CH2)mCO-, -CO(CH2)mCOR 4 -、-NR 5 -、-CONR 5 - etc. 4 、R 5 (where m represents a natural number) is independently an arbitrary substituent, preferably a hydrogen atom or an alkyl group.

[0093] The content of ethylene structural units in the modified EVOH-based resin of the present invention is 1 to 16.5 mol%, preferably 3 to 16 mol%, more preferably 5 to 15.5 mol%, and particularly preferably 6 mol% or more and less than 15.0 mol%.

[0094] If the content of ethylene structural units is too low, the viscosity stability of the solution will decrease when attempting to form a layer containing the modified EVOH-based resin using a solution of the modified EVOH-based resin described below. On the other hand, if the content of ethylene structural units is too high, the hydrophilicity decreases, making it difficult for biodegradable bacteria to access the material, resulting in reduced biodegradability and decreased gas barrier properties.

[0095] The content of the ethylene structural unit in the modified EVOH-based resin can be controlled by adjusting the ethylene pressure during copolymerization.

[0096] The content of the structural unit having a primary hydroxyl group in the side chain in the modified EVOH-based resin of the present invention is 2.5 mol% or more, preferably 2.5 to 10 mol%, particularly preferably 3 to 6 mol%.

[0097] If the content of the structural unit having a primary hydroxyl group in the side chain is too low, the hydrophilicity of the modified EVOH-based resin is insufficient and the biodegradability becomes low. In addition, if the content of the structural unit having a primary hydroxyl group in the side chain is too high, the production cost becomes high, which becomes economically disadvantageous.

[0098] The content of the ethylene structural unit of the modified EVOH resin of the present invention and the content of the structural unit having a primary hydroxyl group in the side chain in the modified EVOH resin can be determined by dissolving the modified EVOH resin in dimethyl sulfoxide-d6 containing trifluoroacetic acid-d as an additive and measuring the content of the ethylene structural unit at 50°C. 1 H-NMR, 13 C-NMR and determined from the integration ratio of the spectrum obtained therefrom.

[0099] As a specific example, a modified EVOH-based resin having a structural unit represented by the following general formula (2) and having a primary hydroxyl group in a side chain will be described.

[0100] Figure 1 and Figure 2 The NMR measurement of the modified EVOH resin having a structural unit represented by the general formula (2) and having a primary hydroxyl group in the side chain was performed at 50°C. 1 H-NMR spectrum ( Figure 1 )and 13 C-NMR spectrum ( Figure 2 ).

[0101]

[0102] above 1 H-NMR spectrum ( Figure 1 ) are assigned as follows.

[0103] 0.7-0.9 ppm: Methyl protons (3H) of the terminal ethylene structural unit

[0104] 0.9-1.7 ppm: Methylene protons (4H) of the intermediate ethylene structural unit, methylene protons (2H) of the vinyl alcohol structural unit, methylene protons (2H) of the unsaponified vinyl acetate structural unit, and methylene protons (2H) of the main chain of the 1,2-butanediol structural unit

[0105] 1.7 to 1.9 ppm: methine protons (1H) in the main chain of the 1,2-butanediol structural unit

[0106] 1.9-2.0 ppm: Methyl protons (3H) of unsaponified vinyl acetate structural units

[0107] 3.2 to 4.2 ppm: methine protons (1H) of the vinyl alcohol structural unit, methylene protons (2H) adjacent to the hydroxyl group of the 1,2-butanediol structural unit, and methine protons (1H)

[0108] in addition, 13 C-NMR spectrum ( Figure 2 ) are assigned as follows.

[0109] 8-10 ppm: methyl carbon of the terminal ethylene structural unit

[0110] 20-48 ppm: methylene carbons in the middle ethylene structural unit, methylene carbons in the vinyl alcohol structural unit, methylene carbons and methyl carbons in the unsaponified vinyl acetate structural unit, and main chain methylene carbons and main chain methine carbons in the 1,2-butanediol structural unit.

[0111] 63-64 ppm: Methylene carbon adjacent to the primary hydroxyl group of the 1,2-butanediol structural unit

[0112] 64-75 ppm: methine carbons in vinyl alcohol structural units, methine carbons in unsaponified vinyl acetate structural units, and methine carbons adjacent to the secondary hydroxyl moiety in 1,2-butanediol structural units

[0113] By following the above 1 H-NMR spectroscopy and 13 The content of the ethylene structural unit in the modified EVOH-based resin and the content of the structure having a primary hydroxyl group in the side chain in the modified EVOH-based resin can be determined by solving the following simultaneous equations based on the attribution in the C-NMR spectrum.

[0114] a=4E+2V+3D

[0115] b=V+3D

[0116] c=(V+D) / D

[0117] a:1 H-NMR spectrum ( Figure 1 ) is the integral value of the signal from 0.9 to 1.7 ppm

[0118] b: 1 H-NMR spectrum ( Figure 1 ) is the integral value of the signal between 3.2 and 4.2 ppm

[0119] c: Pass 13 C-NMR spectrum ( Figure 2 ) is obtained by dividing the integral value of the signal at 64 to 75 ppm by the integral value of the signal at 63 to 64 ppm.

[0120] E: molar ratio of ethylene units

[0121] V: molar ratio of vinyl alcohol units

[0122] D: molar ratio of 1,2-butanediol (structure having a primary hydroxyl group in the side chain) unit

[0123] Regarding the content of the structural unit having a primary hydroxyl group in the side chain, in the case of the aforementioned method (I), it can be controlled by the amount of the monomer having a primary hydroxyl group in the side chain or the monomer in which the hydroxyl group is protected by an ester or the like as described above, which is used as a comonomer. Alternatively, in the case of the aforementioned method (II), it can be controlled by the amount of the monovalent epoxy group-containing compound used in the modification.

[0124] The amount of sodium acetate contained in the modified EVOH-based resin is preferably less than 0.7% by mass, particularly preferably less than 0.4% by mass, and even more preferably less than 0.2% by mass. If the amount of sodium acetate exceeds 0.7% by mass, a transparent solution cannot be obtained when preparing the modified EVOH-based resin solution for the barrier material described below, and the appearance of the resulting gas barrier material tends to be reduced. Furthermore, if the amount of sodium acetate is high, the gas barrier material tends to interact with water, particularly under high humidity, leading to a decrease in gas barrier properties. The amount of sodium acetate contained in the modified EVOH-based resin can be determined by titrating the sample solution with hydrochloric acid in accordance with JIS K6726.

[0125] The modified EVOH-based resin has a viscosity of typically 2.50 to 600 mPa·s, preferably 2.90 to 270 mPa·s, and particularly preferably 3.30 to 110 mPa·s, when prepared as a 4% by mass aqueous solution and measured using the falling ball viscometer method of JIS K6726. If the viscosity is too high, coating defects tend to occur when attempting to apply the modified EVOH-based resin solution to a thin film of a substrate resin to obtain a gas barrier material. If the viscosity is too low, the resulting gas barrier material tends to have low strength and durability.

[0126] The viscosity of a 4% by mass aqueous solution of the modified EVOH resin serves as an indicator of the degree of polymerization of the modified EVOH resin. It should be noted that the less a 4% by mass aqueous solution of the modified EVOH resin can be prepared, the more the melt flow rate (MFR) described below can be used as an indicator of the degree of polymerization, if the modified EVOH resin contains ethylene structural units and side chain primary hydroxyl structural units.

[0127] The melt flow rate (MFR) of the modified EVOH-based resin (at 210°C and under a load of 2160 g) is typically 0.1 to 100 g / 10 min, preferably 1 to 50 g / 10 min, and particularly preferably 3 to 35 g / 10 min. If the MFR is too high, it may be difficult to control the thickness of the layer formed from the modified EVOH-based resin during melt molding of the barrier material. If the MFR is too low, a high load may be placed on the molding machine during melt molding.

[0128] The MFR serves as an indicator of the degree of polymerization of the modified EVOH-based resin and can be adjusted by adjusting the amount of the polymerization catalyst and the amount of the solvent when copolymerizing the copolymerization components.

[0129] The modified EVOH resin of the present invention generally has a saponification degree of 85 mol% or greater, preferably 90 mol% or greater, particularly preferably 95 mol% or greater, and even more preferably 99 mol% or greater. If the saponification degree is too low, as described below, gas barrier properties tend to decrease, particularly under high humidity conditions.

[0130] The saponification degree of the modified EVOH-based resin of the present invention can be determined based on JIS K6726 using the alkali consumption associated with the hydrolysis of the residual vinyl acetate units.

[0131] The modified EVOH-based resin of the present invention preferably has a biodegradability of 20% or greater, more preferably 25% or greater, and particularly preferably 30% or greater. The biodegradability can be determined by referring to the method described in JIS K6950, using the biochemical oxygen consumption and theoretical oxygen requirement when tested under the following conditions.

[0132] · Equipment: BOD TESTER 200F (manufactured by TAITEC)

[0133] Plant source: Return sludge from sewage treatment plants that treat domestic sewage

[0134] Standard test culture medium: 100mL

[0135] Planting concentration: 90mg / L

[0136] Temperature: 25±1℃

[0137] Duration: 28 days

[0138] The modified EVOH-based resin of the present invention may be blended with other components to form a resin composition. Examples of these other components include other thermoplastic resins, plasticizers, lubricants, stabilizers, surfactants, colorants, UV absorbers, antistatic agents, desiccants, crosslinking agents, metal salts, fillers, and various fibers. These may be used alone or in combination of two or more.

[0139] The content of the modified EVOH-based resin in the resin composition is usually 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more, with an upper limit of 100% by mass.

[0140] The modified EVOH-based resin of the present invention can be suitably used as a gas barrier material, such as a food packaging material. Methods for producing the modified EVOH-based resin of the present invention into a gas barrier material are not particularly limited, and examples thereof include: (i) applying a solution of the modified EVOH-based resin to a thin film of a substrate resin and drying to form a layer comprising the modified EVOH-based resin; and (ii) melt-molding the modified EVOH-based resin into a gas barrier material.

[0141] In the above-mentioned method (I), examples of the solvent used in the solution of the modified EVOH-based resin include lower alcohols having 1 to 5 carbon atoms, such as water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol. These can be used alone or in combination of two or more. Among them, water, 2-propanol, and a mixed solvent of water and 2-propanol are preferred, and a solvent in which water and 2-propanol have a mixing ratio calculated by the following formula (1) is particularly preferred.

[0142] Water: 2-propanol = 100 - X: X (mass ratio)... (1)

[0143] X=3.4×(content of ethylene structural units)-5×(content of structural units having primary hydroxyl groups)-20.

[0144] When X is negative, X=0

[0145] The present inventors have discovered that when a mixed solvent of water and 2-propanol is used to obtain a uniform solution, the presence of structural units having primary hydroxyl groups in their side chains can reduce the required 2-propanol content. Furthermore, the above formula (1) was discovered based on the relationship between the content of ethylene structural units in the modified EVOH-based resin and the content of structural units having primary hydroxyl groups in their side chains.

[0146] 2-Propanol is an organic solvent. Therefore, when a modified EVOH resin solution is prepared using 2-propanol, it must be recovered during coating. Therefore, in order to minimize the amount of 2-propanol, it is preferable to use a solvent having a mixing ratio calculated by the above formula (1).

[0147] In order to improve the appearance of the gas barrier material, the modified EVOH resin solution is preferably transparent. The transparency of the modified EVOH resin solution can be measured by measuring the transmittance of the solution at a concentration of 4% by mass.

[0148] When the modified EVOH-based resin is prepared as a 4% by mass solution using a solvent having a mixing ratio calculated by the above formula (1), the transmittance at 430 nm at 30°C and an optical path length of 20 mm is preferably 70% or greater, more preferably 75% or greater, and particularly preferably 80% or greater. If the transmittance is less than the above values, the appearance of the resulting gas barrier material tends to be hazy.

[0149] The transmittance was measured and evaluated in accordance with JIS K 6726. However, when water alone is used as a solvent, a uniform aqueous solution cannot be obtained for a modified EVOH resin having a high content of ethylene structural units. Therefore, a solvent having a mixing ratio calculated by the above formula (1) was used.

[0150] The transmittance when the above-mentioned modified EVOH resin is made into a solution with a concentration of 4% by mass can be controlled by the following methods: changing the content of ethylene structural units, the content of primary hydroxyl structural units in the side chain, temperature, solid content concentration of the solution, type of solvent, and mixing ratio of the modified EVOH resin; reducing the amount of salts such as sodium acetate generated by neutralization after saponification, etc.

[0151] Examples of methods for applying the modified EVOH resin solution include known methods such as bar coating, roll coating, die coating, gravure coating, comma coating, and screen printing, among which bar coating is preferred.

[0152] After coating, the coating is dried by, for example, a heat treatment at 60 to 105° C. for 0.5 to 10 minutes, thereby obtaining a gas barrier material having a layer formed of the modified EVOH-based resin.

[0153] Examples of the melt molding method in the method (II) include extrusion molding, injection molding, inflation molding, press molding, and blow molding.

[0154] In this manner, a gas barrier material comprising a layer formed from the modified EVOH-based resin of the present invention can be obtained. This gas barrier material can be a single-layer or multi-layer structure, preferably a multi-layer structure. This multi-layer barrier material preferably comprises at least one layer formed from the modified EVOH-based resin of the present invention. Furthermore, this multi-layer gas barrier material can be laminated with layers formed from the modified EVOH-based resin of the present invention or with other base resins.

[0155] Examples of the base resin include polyethylene resins such as linear low-density polyethylene, low-density polyethylene, ultra-low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-propylene (block and random) copolymers, and ethylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers; polypropylene resins such as polypropylene and propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers; (unmodified) polyolefin resins such as polybutene, polypentene, and polycyclic olefin resins (polymers having a cyclic olefin structure in at least one of the main chain and the side chain); and polyolefin resins such as these. The polyolefin resins include polyolefin resins in a broad sense, such as unsaturated carboxylic acid-modified polyolefin resins obtained by grafting unsaturated carboxylic acids or their esters, modified olefin resins such as polyolefin resins, ionomers, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylate copolymers, polyester resins, polyamide resins (including copolyamides), polyvinyl chloride, polyvinylidene chloride, acrylic resins, polystyrene, vinyl ester resins, polyester elastomers, polyurethane elastomers, polystyrene elastomers, chlorinated polyethylene, chlorinated polypropylene, halogenated polyolefins, aromatic polyketones, or aliphatic polyketones. These can be used alone or in combination of two or more. In addition, the layer of these base resins can be surface treated by corona treatment or the like.

[0156] The thickness of the modified EVOH resin layer is generally 1 to 200 μm, preferably 1 to 100 μm, and particularly preferably 1 to 50 μm. When the gas barrier material has a multilayer structure, this refers to the total thickness of all modified EVOH resin layers included in the gas barrier material.

[0157] The oxygen permeability of the layer formed of the modified EVOH resin measured at 23°C and 0% RH is preferably 5cc·3μm / m 2 ·day·atm or less, more preferably 1cc·3μm / m 2 ·day·atm or less, particularly preferably 0.1cc·3μm / m 2 ·day·atm or less. It should be noted that the lower limit of oxygen permeability is usually 0.003cc·3μm / m 2·day·atm. The above oxygen permeability can be determined using an oxygen permeability measuring device.

[0158] In addition, the environment in which gas barrier materials are used covers a wide range of conditions, from low humidity to high humidity. Therefore, it is preferred that the oxygen permeability is low even under high humidity, and the change in oxygen permeability with respect to humidity changes is small. From this point of view, the oxygen permeability measured under an environment of 23°C and 65% RH is preferably 30cc·3μm / m 2 ·day·atm or less, more preferably 15cc·3μm / m 2 ·day·atm or less, particularly preferably 5cc·3μm / m 2 ·day·atm or less

[0159] The ratio of the oxygen permeability measured at 23°C and 65% RH to the oxygen permeability measured at 23°C and 0% RH is preferably 500 or less, more preferably 300 or less, and particularly preferably 200 or less.

[0160] Example

[0161] The present invention will be described in more detail below with reference to Examples. However, the present invention is not limited to the following Examples unless otherwise specified. In the examples, "parts" refer to weights.

[0162] <Example 1>

[0163] [Synthesis of modified ethylene-vinyl ester copolymer]

[0164] A temperature-controlled autoclave was charged with 460 parts of vinyl acetate, 48 parts of 3,4-diacetoxy-1-butene (a monomer whose hydroxyl group was protected with an ester or the like), and 75 parts of methanol. The system (the interior of the autoclave) was temporarily purged with nitrogen and then purged with ethylene. The temperature was raised to 67°C while stirring. After the temperature was raised, ethylene was introduced under pressure to a partial pressure of 1.0 MPa. A solution of 0.082 parts of 2,2'-azobisisobutyronitrile dissolved in 10 parts of methanol was added. The internal temperature was maintained at 67°C for 4 hours while stirring to allow polymerization to proceed. Subsequently, a solution of 0.98 parts of sorbic acid dissolved in 100 parts of methanol was added. The reaction was cooled to room temperature (23°C) to terminate polymerization. Unreacted monomers were then distilled off to obtain a methanol solution of an ethylene-vinyl acetate-3,4-diacetoxy-1-butene copolymer, which was a modified ethylene-vinyl ester copolymer.

[0165] [Synthesis of modified EVOH-based resin]

[0166] Next, the solution was diluted with methanol to adjust the concentration to 10% by mass, stirred, and saponified by adding a 5% by mass methanol solution of sodium hydroxide in an amount corresponding to 10 mmol% of the vinyl acetate units in the copolymer while maintaining the solution temperature at 45°C. As the reaction proceeded, the saponified product precipitated and eventually became granular. Furthermore, for saponification, the resulting granular saponified product was temporarily filtered out and then dispersed again in 20 times the amount of methanol of the saponified product. A 5% by mass methanol solution of sodium hydroxide in an amount corresponding to 50 mmol% of the initial vinyl acetate units in the copolymer was added, and the product was reacted at 50°C for 3 hours. After the reaction, the product was neutralized with acetic acid and filtered out again to obtain a granular saponified product. Next, in order to reduce the sodium acetate adhering to the saponified product in this state, it was washed with methanol. As a washing method, the granular saponified product was dispersed in 5 times its mass of methanol, stirred at 45°C for 1 hour, and then filtered. The above operation was repeated 3 times. The saponified product thus obtained was dried in a hot air dryer to obtain the modified EVOH-based resin of Example 1. The obtained modified EVOH-based resin had the following 1,2-diol structure as a structure having a primary hydroxyl group in a side chain.

[0167]

[0168] The saponification degree of the obtained modified EVOH-based resin was 99.9 mol % as analyzed based on the alkali consumption associated with the hydrolysis of the residual vinyl acetate units in accordance with JIS K6726.

[0169] The amount of sodium acetate in the modified EVOH resin was determined by titrating the sample solution with hydrochloric acid in accordance with JIS K6726 and found to be 0.097% by mass.

[0170] The obtained modified EVOH-based resin was dissolved in dimethyl sulfoxide-d6 containing trifluoroacetic acid-d as an additive and NMR measurement was performed at 50°C. 1 H-NMR spectrum (refer to Figure 1 ), 13 C-NMR spectrum (refer to Figure 2 ), and the content of ethylene structural units and the content of structural units having primary hydroxyl groups in the side chains were determined according to the above method. The results showed that the content of ethylene structural units was 7.7 mol%, and the content of 1,2-diol structural units (structural units having primary hydroxyl groups in the side chains) was 4.7 mol%.

[0171] The viscosity of a 4% aqueous solution determined by the falling ball viscometer method of JIS K6726 was 8.76 mPa·s.

[0172] <Examples 2 to 6, Comparative Examples 1 to 6>

[0173] By modifying the polymerization conditions in Example 1 as shown in Table 1 below, methanol solutions were obtained from which various unreacted monomers were removed from the modified ethylene-vinyl ester copolymers of Examples 2 to 6 and Comparative Examples 3 to 6, and the ethylene-vinyl ester copolymers of Comparative Examples 1 and 2. For Examples 2 to 6 and Comparative Examples 2 to 6, saponification, washing, and drying were performed in the same manner as in Example 1 to obtain the modified EVOH-based resins and EVOH-based resins shown in Table 2.

[0174] The viscosity of a 4% aqueous solution of the modified EVOH resin of Example 4 measured by the falling ball viscometer method of JIS K6726 was 13.94 mPa·s, and the viscosity of a 4% aqueous solution of the modified EVOH resin of Example 6 was 9.03 mPa·s.

[0175] In Comparative Example 1, methanol was added to the methanol solution of the ethylene-vinyl ester copolymer obtained above, from which unreacted monomers had been distilled off, to adjust the solution to a 15% by mass methanol solution. A 5% by mass methanol solution of sodium hydroxide was added to the solution in an amount equal to 50 mmol of the vinyl acetate units in the copolymer, and the solution was refluxed for 1 hour to effect saponification. At this point, no saponified product precipitated, but remained in solution. Methanol was then further added, and the solution was distilled at 60°C to concentrate the contents. To further promote saponification, a 5% by mass methanol solution of sodium hydroxide was added to an amount equal to 50 mmol of the vinyl acetate units in the copolymer, and the solution was refluxed for 1 hour. At this point, no saponified product precipitated, but remained in solution. Methanol was then further added, and the solution was distilled at 60°C to concentrate the contents, and the solution was solidified in an ice bath. The solidified product was pulverized, repeatedly washed with a 2% by mass aqueous acetic acid solution and further washed with ion-exchanged water, and then dried to obtain the EVOH-based resin of Comparative Example 1.

[0176] The modified EVOH resins of Examples 2 to 5, Comparative Examples 3 to 6, and the EVOH resins of Comparative Examples 1 and 2 were tested for ethylene structural unit content, structural unit content having primary hydroxyl groups in side chains, degree of saponification, and sodium acetate content using the same method as in Example 1. The results are shown in Table 2 below.

[0177] In addition, the content of ethylene structural units and the content of structural units having primary hydroxyl groups in the side chains of the modified EVOH-based resin of Example 6 were determined according to Japanese Patent Application Laid-Open No. 2019-182947. 1H-NMR spectrum (solvent: dimethyl sulfoxide-d6) is shown in Figure 3 The modified EVOH resin of Example 6 was measured at 50°C. 1 H-NMR spectrum (solvent: dimethyl sulfoxide-d6, containing trifluoroacetic acid-d as an additive) is shown in Figure 4 .

[0178] [Table 1]

[0179]

[0180] The resins of Examples and Comparative Examples obtained above were used to evaluate transparency, oxygen permeability, humidity dependence of gas barrier properties, and biodegradability using the following evaluation methods. The results are shown in Table 2 below.

[0181] 〔transparency〕

[0182] For the resins of Examples and Comparative Examples, solutions having a concentration of 4% by mass were prepared using a solvent in which the mixing ratio of water to 2-propanol was set to a value calculated by the following formula (1).

[0183] Water: 2-propanol = 100 - X: X (mass ratio)... (1)

[0184] X=3.4×(content of ethylene structural units)-5×(content of structural units having primary hydroxyl groups)-20.

[0185] When X is negative, X=0.

[0186] The transmittance of the solution having a concentration of 4% by mass prepared above at 30° C. and an optical path length of 20 mm at 430 nm was measured and defined as the transparency of the solution.

[0187] The 2-propanol content in the transparency in Table 2 described later is a value obtained from the above-mentioned formula (1).

[0188] [Production of Gas Barrier Materials]

[0189] Using the solvent obtained according to the above formula (1), the resins of the examples and comparative examples are made into solutions with a concentration of 10 mass%, coated on a corona-treated PET film (38 μm thick) using a rod coater, and dried at 80°C for 5 minutes to obtain a gas barrier material having a 3 μm layer formed by a modified EVOH resin or EVOH-based resin.

[0190] [Gas barrier properties and their humidity dependence]

[0191] The gas barrier material obtained above was measured for oxygen permeability at 23°C and 0% and 65% RH using an oxygen permeability meter (MOCON "OXTRAN 2 / 20"). This was used as a value indicating gas barrier properties and converted to a value for a 3 μm thickness of the modified EVOH resin or EVOH-based resin. The oxygen permeabilities at 0% and 65% RH were denoted as T0% and T65%, respectively, and the value of T65% / T0% was used as an indicator of the humidity dependence of the gas barrier properties.

[0192] 〔Biodegradation〕

[0193] The biodegradability was evaluated using the modified EVOH-based resins or EVOH-based resins of Examples and Comparative Examples, with reference to the method described in JIS K6950, under the following conditions.

[0194] · Equipment: BOD TESTER 200F (manufactured by TAITEC)

[0195] Plant source: Return sludge from sewage treatment plants that treat domestic sewage

[0196] Standard test culture medium: 100mL

[0197] Planting concentration: 90mg / L

[0198] Temperature: 25±1℃

[0199] Duration: 28 days

[0200] The biodegradability is calculated based on the biochemical oxygen consumption and the theoretical oxygen requirement.

[0201] [Table 2]

[0202]

[0203] As shown in Table 2, the modified EVOH-based resins of Examples 1 to 6, in which the ethylene structural unit content is within a specific range and a specific amount of structural units having primary hydroxyl groups in the side chains are introduced, exhibit high transparency in the solution. Consequently, gas barrier materials having excellent appearance can be produced. These materials also exhibit excellent biodegradability, low oxygen permeability, and excellent humidity dependence of gas barrier properties.

[0204] On the other hand, compared to the modified EVOH resins of the Examples, the modified EVOH resins of Comparative Example 1, which is a general EVOH resin, and Comparative Example 3, which has an ethylene structural unit content exceeding the range specified in the present invention, exhibited inferior biodegradability and gas barrier properties. Furthermore, compared to the modified EVOH resins of the Examples, the EVOH resin of Comparative Example 2, which has an ethylene structural unit content within the range specified in the present invention but lacks primary hydroxyl groups in its side chains, exhibited lower biodegradability.

[0205] In contrast, compared with the modified EVOH-based resins of the examples, the modified EVOH-based resins of Comparative Example 4, which does not have an ethylene structure although the content of the structural unit having a side chain primary hydroxyl group is within the range specified in the present invention, and Comparative Examples 5 and 6, which have both ethylene structural units and structural units having a side chain primary hydroxyl group but the contents thereof are outside the range specified in the present invention, have low biodegradability.

[0206] In the above embodiments, specific aspects of the present invention are exemplified, but the above embodiments are merely illustrative and are not to be construed as limiting. It should be understood that various modifications obvious to those skilled in the art fall within the scope of the present invention.

[0207] Industrial applicability

[0208] The modified EVOH-based resin of the present invention has gas barrier properties and excellent biodegradability, and is therefore useful as a packaging material, and can be particularly suitably used as a packaging material for foods, pharmaceuticals, and the like.

Claims

1. A modified ethylene-vinyl alcohol resin, characterized in that, it is a modified ethylene-vinyl alcohol resin having a primary hydroxyl group in the side chain, the content of ethylene structural units in the modified ethylene-vinyl alcohol resin is 1 to 16.5 mol%, and the content of structural units having a primary hydroxyl group in the side chain is 2.5 mol% to 10 mol%, the modified ethylene-vinyl alcohol resin contains sodium acetate, and the amount of sodium acetate contained in the modified ethylene-vinyl alcohol resin is less than 0.7% by mass.

2. The modified ethylene-vinyl alcohol resin according to claim 1, characterized in that, the saponification degree of the modified ethylene-vinyl alcohol resin is 99 mol% or more.

3. The modified ethylene-vinyl alcohol resin according to claim 1 or 2, characterized in that, when using a solvent in which water and 2-propanol have a mixing ratio calculated by the following formula (1) to prepare a 4% by mass solution of the modified ethylene-vinyl alcohol resin, the transmittance at 430 nm at 30 °C and a light path length of 20 mm is 70% or more, water: 2-propanol = 100 - X: X (mass ratio)... (1) X = 3.4 × (content of ethylene structural units) - 5 × (content of structural units having a primary hydroxyl group) - 20... (2), where, when X calculated by the foregoing formula (2) is negative, X = 0 is taken when substituting X into the foregoing formula (1).

4. A gas barrier material, characterized in that, it has a layer formed of the modified ethylene-vinyl alcohol resin according to any one of claims 1 to 3.

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