Modified ethylene-vinyl alcohol resins and gas barrier materials

Abstract

This invention provides a modified EVOH resin, which, in the case of an EVOH resin with excellent biodegradability and excellent gas barrier properties, is a modified EVOH resin with primary hydroxyl groups on its side chains. The modified EVOH resin is characterized by having an ethylene structural unit content of 1 to 16.5 mol%, and a content of structural units with primary hydroxyl groups on their side chains of 2.5 mol% or more.

Description

Technical Field

[0001] This invention relates to a modified ethylene-vinyl alcohol resin, and more specifically to a modified ethylene-vinyl alcohol resin having a specific amount of primary hydroxyl groups on its side chains. Prior Technology

[0002] Ethylene-vinyl alcohol resins (hereinafter sometimes referred to as "EVOH resins") with an ethylene structural unit content of 20-60 mol% have long been used in food packaging materials because they possess transparency, gas barrier properties, aroma retention, solvent resistance, and oil resistance (Non-Patent Document 1). These properties can reduce food spoilage. On the other hand, in recent years there has been a demand for reducing environmental impact, but EVOH-based resins with an ethylene structural unit content of 20-60 mol% have low biodegradability. Considering the need to further reduce environmental impact (such as marine issues), gas barrier resins with excellent biodegradability are required.

[0003] Regarding the aforementioned biodegradable gas barrier resins, for example, Non-Patent Literature 2 reports the matrix specificity of polyvinyl alcohol dehydrogenase, an enzyme derived from microorganisms, for EVOH-based resins with an ethylene structural unit content of 4-10 mol%. Regarding the mechanism of polyvinyl alcohol biodegradation using polyvinyl alcohol dehydrogenase, Non-Patent Literature 3 discloses that it is carried out by oxidizing the bonding sites of the ethylene alcohol units. Furthermore, Patent Document 1 reports an example of attempting to impart appropriate hydrophilicity to the structure of EVOH-based resins and improve biodegradability by setting the content of ethylene structural units to 2-19 mol%, the degree of polymerization to 200-2000, the degree of saponification to 80-99.99 mol%, and the total content of carboxyl groups and lactone rings to 0.02-0.4 mol%. [Previous Technical Documents] [Patent Literature]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2000-309607 [Non-patent literature]

[0005] [Non-Patent Literature 1] New Developments in Gas Barrier and Aroma-Retaining Packaging Materials Toray Research Center, Inc. 1997 Chapter 2 Ethylene-Vinyl Alcohol Copolymer Resins [Non-Patent Literature 2] Biosci. Biotech Biochem. Vol. 59, No. 7, p. 1229 (1995) [Non-Patent Literature 3] Macromolecule, Vol. 32, p. 7753 (1999) Summary of the Invention

[0006] [The problem that the invention aims to solve]

[0007] However, although the aforementioned non-patent literature 2 evaluates the reaction rate (Vmax) and Michaelis constant (Km) when the matrix is ​​infinitely large, it does not report the biodegradability of EVOH-based resins after a few days, and further improvements are still sought for the actual biodegradability. Then, in an attempt to improve biodegradability, according to the biodegradation mechanism disclosed in Non-Patent Literature 3, only the bonding of the vinyl alcohol unit was increased, and therefore the copolymerization with other structural units was not considered.

[0008] Furthermore, the structure and content of the carboxyl or lactone ring disclosed in the aforementioned patent document 1 are poor in imparting hydrophilicity to EVOH-based resins, and it takes a long time for biodegradation to begin, thus requiring further improvement.

[0009] Therefore, under this background, the present invention provides an EVOH-based resin that has both excellent biodegradability and excellent gas barrier properties. [Methods for solving problems]

[0010] On the other hand, the inventors of this case have made repeated efforts to study this matter and found that by setting the content of ethylene structural units in EVOH-based resin to a specific range and then introducing a specific amount of structural units with primary hydroxyl groups on the side chain, the hydrophilicity of the modified EVOH-based resin can be controlled, making it easier for it to access bacteria that cause biodegradation, thereby solving the above-mentioned problem. It is believed that this is because the hydroxyl groups of EVOH-based resins are directly bonded to the polymer backbone in the form of secondary hydroxyl groups. Therefore, the structure around the hydroxyl groups is crowded in three-dimensional space, making it difficult for bacteria to access them. However, because the side chains have primary hydroxyl groups, the hydroxyl groups are located far away from the backbone. Moreover, primary hydroxyl groups have fewer steric barriers around them compared to secondary and tertiary hydroxyl groups, making it easier for bacteria to access them. Therefore, this approach contributes to solving the above problem.

[0011] That is, the present invention provides the following [1]~[5]. [1] A modified EVOH resin, which is a modified EVOH resin with primary hydroxyl groups on the side chain, characterized in that: the content of ethylene structural units in the modified EVOH resin is 1~16.5 mol%, and the content of structural units with primary hydroxyl groups on the side chain is 2.5 mol% or more. [2] The modified EVOH resin as in [1], wherein the degree of saponification of the modified EVOH resin is 99 mol% or more. [3] The modified EVOH resins such as [1] or [2], wherein the amount of sodium acetate contained in the above-mentioned EVOH resins is less than 0.7 by mass. [4] The modified EVOH resin of any one of [1] to [3], wherein when the modified EVOH resin is prepared into a solution with a concentration of 4% by mass using a solvent of water and 2-propanol in a mixing ratio calculated according to the following formula (1), the transmittance at 430 nm is 70% or more under the conditions of 30°C and an optical path length of 20 mm. [Mode] Water:2-propanol = 100 - X:X (mass ratio) ･･･(1) X = 3.4 × (content of ethylene structural units) - 5 × (content of structural units with primary hydroxyl groups) - 20, but when X is negative, let X = 0. [5] A gas barrier material, characterized in that it has a layer composed of a modified EVOH resin as described in any one of [1] to [4]. [Effects of the Invention]

[0012] The modified EVOH resin of the present invention is a modified EVOH resin with primary hydroxyl groups on the side chain. Because the content of the ethylene structural unit in the above modified EVOH resin is 1~16.5 mol%, and the content of the structural unit with primary hydroxyl groups on the side chain is 2.5 mol% or more, it has excellent gas barrier properties and biodegradability. Simple Explanation of the Diagram

[0013] [Figure 1] shows the 1H-NMR spectrum of the modified EVOH resin of Example 1. [Figure 2] shows the 13 C-NMR spectrum of the modified EVOH resin of Example 1. [Figure 3] shows the 1H-NMR spectrum of the modified ethylene-ethylene ester copolymer, which is an intermediate of the modified EVOH resin in Example 6. [Figure 4] shows the 1H-NMR spectrum of the modified EVOH resin of Example 6. Implementation

[0014] The following is a detailed description of the structure of the present invention, but these descriptions only represent one example of an ideal embodiment. Furthermore, in this invention, "α and / or β (α and β are arbitrary components or elements)" refers to combinations of only α, only β, and α and β.

[0015] EVOH-based resins are thermoplastic resins obtained by saponifying ethylene-ethylene ester copolymers, which are copolymers of ethylene and ethylene ester monomers.

[0016] The modified EVOH resin of the present invention has a specific amount of primary hydroxyl groups on its side chain, specifically an EVOH resin having the structural unit of the following general formula (1).

[0017] [Chemistry 1]

[0018] For R1 to R3, there are no particular limitations as long as they are hydrogen atoms or organic groups. Examples of organic groups include alkyl, alkenyl, alkynyl, phenyl, naphthyl, and other hydrocarbon groups (these hydrocarbon groups may also have hydroxyl, fluorine, chlorine, and bromine as substituents). The X series, representing a single bond or a bonded chain, indicates the polymer backbone bonded to a primary hydroxyl group. The bonded chain is not particularly limited; examples include hydrocarbons such as alkyl, alkenyl, alkyne, phenyl, and naphthyl (these hydrocarbons may also have hydroxyl, fluorine, chlorine, and bromine as substituents); hydrocarbons such as alkyl, alkenyl, alkyne, phenyl, and naphthyl bonded to the polymer backbone by ether bonds (these hydrocarbons may also have hydroxyl, fluorine, chlorine, and bromine as substituents); others include -CO-, -CO(CH2)mCO-, -CO(CH2)mCOR4-, -NR5-, and -CONR5- (R4 and R5 are independent substituents, ideally hydrogen atoms or alkyl groups; the m series represents a natural number).

[0019] To obtain the modified EVOH-based resin of this invention, the following methods can be used: (I) A method of deprotection by saponification or the like after copolymerizing monomers with primary hydroxyl groups on the side chains and / or monomers with primary hydroxyl groups on the side chains protected by esters or the like with ethylene and vinyl ester monomers; (II) A method of first saponifying the copolymer of ethylene and ethylene ester monomers to obtain EVOH resin, and then modifying the above EVOH resin to generate primary hydroxyl groups in the side chain. Among the perspectives considering productivity, the method described in (I) above is more ideal. The following describes the manufacturing method of the modified EVOH-based resin of the present invention.

[0020] First, in the case of the method described in (I) above, it is sufficient to copolymerize ethylene and ethylene ester monomers with monomers having primary hydroxyl groups on the side chains and / or monomers in which the hydroxyl groups are protected by esters or the like.

[0021] Regarding the aforementioned vinyl ester monomers, examples include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, trimethylvinyl acetate, vinyl decanoate, vinyl laurate, vinyl stearate, vinyl benzoate, neodecanoate, and vinyl trifluoroacetate. These can be used individually or in combination of two or more. Among these, vinyl acetate is the most economically viable option.

[0022] Regarding monomers with a primary hydroxyl group in the side chain used in method (I) above, examples include monomers containing a single hydroxyl group such as allyl alcohol, 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 6-hepten-1-ol, and methyl allyl alcohol; and monomers containing a dihydroxyl group such as 2-methylene-1,3-propanediol, 3,4-diol-1-butene, 4,5-diol-1-pentene, 4,5-diol-3-methyl-1-pentene, 5,6-diol-1-hexene, and glyceryl monoallyl ether. These can be used alone or in combination of two or more.

[0023] Furthermore, regarding the monomers in method (I) above that protect the primary hydroxyl group of the side chain with an ester or the like (hereinafter, sometimes referred to as "monomers that protect the hydroxyl group with an ester or the like"), examples include acetates of monomers having a primary hydroxyl group in the side chain, as described above. 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 methyl allyl 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 can be used alone, or two or more can be used together.

[0024] In the method described in (I) above, monomers with primary hydroxyl groups on their side chains and monomers whose hydroxyl groups are protected by esters or the like can also be copolymerized with ethylene or vinyl ester monomers.

[0025] From a production perspective, monomers that protect hydroxyl groups with esters are more ideal, monomers containing diethoxyalkyl groups are even more ideal, 3,4-diethoxy-1-butene and 2-methylene-1,3-propanediol diacetate are even more ideal, and 3,4-diethoxy-1-butene is particularly ideal.

[0026] In the method described above (I), for example, when using the above-mentioned 3,4-diethoxy-1-butene, the modified EVOH resin obtained by deprotection by saponification or the like has a primary hydroxyl group represented by the following general formula (2) in its side chain.

[0027] [Chemistry 2]

[0028] Furthermore, in the method described above (I), for example, when using the above-mentioned 2-methylene-1,3-propanediol diacetate, the modified EVOH resin obtained has a primary hydroxyl group represented by the following general formula (3) in its side chain.

[0029] [Chemistry 3]

[0030] Furthermore, in the methods described in (I) and (II) above, without impairing the effect of the present invention, vinyl unsaturated monomers capable of copolymerization can also be used as copolymerization components for copolymerization. Examples of vinyl unsaturated monomers include olefins such as propylene, 1-butene, and isobutene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, phthalic acid (anhydride), maleic acid (anhydride), and itaconic acid (anhydride), or their salts or mono- or dialkyl esters with 1 to 18 carbon atoms; acrylamides, N-alkylmethacrylamide with 1 to 18 carbon atoms, N,N-dimethylacrylamide, 2-acrylamide propane sulfonic acid, or their salts; acrylamide propyl dimethylamine or its acid salts or their fourth-order salts; methacrylamide, N,N-dimethylacrylamide, and other acrylamides with 1 to 18 carbon atoms. Methacrylamides, such as N-alkylmethacrylamide, N,N-dimethylmethacrylamide, 2-methacrylamide propane sulfonic acid or their salts, with a carbon number of 18; N-vinylamines, such as N-vinylpyrrolidone, N-vinylmethylamine, and N-vinylacetamide; cyanide vinyl ethers, such as acrylonitrile and methacrylonitrile; vinyl ethers, such as alkyl vinyl ethers, hydroxyalkyl vinyl ethers, and alkoxyalkyl vinyl ethers with carbon numbers of 1 to 18; halogenated vinyl ethers, such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, and vinyl bromide; and vinyl silanes, etc. These can be used alone or in combination of two or more.

[0031] In their copolymerization reactions, known methods such as bulk polymerization, solution polymerization, suspension polymerization, dispersion polymerization, or emulsion polymerization can be employed. Among these, solution polymerization, which allows for easy control of the copolymerization process, is ideally preferred.

[0032] When performing this copolymerization using solution polymerization, solvents such as methanol, ethanol, propanol, and butanol (lower alcohols with 1 to 5 carbon atoms) and ketones such as acetone and 2-butanone can be used. These can be used alone or in combination. Methanol is ideally used from the perspective of easy control of the polymerization reaction. Furthermore, 2-propanol is ideally used when synthesizing copolymers with low degrees of polymerization.

[0033] Regarding the amount of solvent used, it can be appropriately selected by considering the degree of polymerization of the target modified EVOH resin and the chain transfer constant of the solvent. For example, when the solvent is methanol or 2-propanol, S(solvent) / M(monomer) = 0.01~10 (mass ratio) is more ideal, and S / M = 0.05~7 (mass ratio) is even more ideal.

[0034] Regarding the feeding method of the copolymer components in solution polymerization, any method can be adopted, such as one-time feeding at the beginning, batch feeding, continuous feeding such as the Hanna method which takes into account the reactivity ratio of monomers.

[0035] In the above copolymerization, polymerization initiators can be used. Examples of such polymerization initiators include azo initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylpentanonitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylpentanonitrile), as well as peroxide initiators such as acetyl peroxide, benzoyl peroxide, lauryl peroxide, tert-butyl peroxyneodecanate, 1,1,3,3-tetramethylbutyl peroxyneodecanate, diisopropyl peroxydicarbonate, and di(2-ethylhexyl) peroxydicarbonate.

[0036] The amount of polymerization initiator used varies depending on the type of initiator and cannot be generalized, but can be arbitrarily selected according to the polymerization rate. For example, when using 2,2'-azobisisobutyronitrile or tributyl peroxyneodecanate, the amount relative to ethylene ester monomers is usually 10~2000 ppm, and 50~1000 ppm is more ideal.

[0037] Regarding the polymerization temperature of copolymerization, it is ideal to select a temperature within the range of 40°C to the boiling point, depending on the solvent used and the ethylene pressure.

[0038] Furthermore, copolymerization can also be carried out in the presence of a chain transfer agent without impairing 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. Aldehydes are particularly desirable. The amount of chain transfer agent added during copolymerization is determined based on the chain transfer constant of the chain transfer agent and the degree of polymerization of the target modified EVOH resin. Generally, 0.1 to 10 parts by mass relative to 100 parts by mass of the vinyl ester monomer is ideal.

[0039] EVOH-based resins can be obtained by saponifying the ethylene-vinyl ester copolymer obtained in this manner.

[0040] The above-mentioned saponification method can be carried out using known methods, such as dissolving the obtained ethylene-ethylene ester copolymer in an alcohol or an aqueous alcohol and then using a saponification catalyst.

[0041] Regarding the alcohols mentioned above, examples include lower alcohols with 1 to 5 carbon atoms, such as methanol, ethanol, and propanol. These can be used alone or in combination of two or more. Methanol is considered the most ideal among them.

[0042] The concentration of ethylene-ethylene ester copolymer in alcohol is appropriately selected according to viscosity, usually 5 to 60% by mass.

[0043] Regarding the saponification catalysts mentioned above, examples include alkaline catalysts such as hydroxides and alcohols of alkali metals 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.

[0044] The saponification temperature is not limited, but a range of 20–140°C is ideal. When the content of ethylene structural units is 1–16.5 mol%, as in this invention, granules will be generated as saponification proceeds, indicating that the reaction has occurred. At this point, when the gel-like product precipitates, the product can be pulverized. Subsequently, the generated granules can be neutralized, washed, and dried as needed to obtain the modified EVOH resin.

[0045] The aforementioned washing process aims to reduce the amount of catalyst used during saponification and the salts generated during neutralization. For example, when using sodium hydroxide, sodium methoxide, or sodium ethoxide as saponification catalysts and neutralizing with acetic acid, sodium acetate is generated during neutralization. Therefore, the amount of sodium acetate remaining in the obtained modified EVOH resin can be adjusted by washing away the generated granules. Furthermore, the degree of washing can be determined by considering the quality of the target modified EVOH resin, as well as the additional steps and costs associated with washing.

[0046] Regarding the cleaning solutions used in the above-mentioned cleaning processes, examples include lower alcohols with 1 to 5 carbon atoms such as methanol, ethanol, and propanol, as well as water. These can be used alone or in combination of two or more. Methanol is considered the most ideal among them.

[0047] Furthermore, regarding the liquor ratio in the washing process, a ratio of 4 to 8 parts by mass relative to 1 part by mass of the generated particulate matter (liquor ratio 4 to 8) is ideal. Regarding the washing temperature, 20 to 70°C is ideal. Regarding the washing time, 0.5 to 3 hours is ideal. Regarding the number of washes, 2 to 6 times is ideal. For example, by setting the washing conditions to a liquor ratio of 4 for 4 to 6 washes, a liquor ratio of 5 for 3 to 5 washes, and a liquor ratio of 8 for 2 to 3 washes, the washing solution can be utilized more efficiently, resulting in a more ideal outcome. Typically, ethylene-modified EVOH resins have a lower affinity for water compared to conventional vinyl alcohol resins. Furthermore, due to the easy solubility of sodium acetate in water, they can be washed with water-containing solvents, thereby reducing sodium acetate content even with a small amount of washing solution. However, the modified EVOH resin of this invention has a lower content of ethylene structural units than conventional EVOH resins and contains structural units with primary hydroxyl groups in the side chains. Therefore, the resin has a high affinity for water, making washing with water-containing solvents less than ideal. Thus, by using the aforementioned washing solution, bath ratio, washing temperature, washing time, and number of washing cycles, a modified EVOH resin containing the target amount of sodium acetate can be obtained.

[0048] In this invention, there is a tendency to adjust the transparency of the solution, especially the gas barrier properties at high humidity, by adjusting the degree of washing after saponification and neutralization. Furthermore, in order to improve the degree of saponification, the generated granules can be temporarily washed and then dispersed again in alcohol or the like, and an alkaline catalyst can be added to allow them to react.

[0049] By using the above saponification, EVOH-based resins in which the ethylene ester units in ethylene-ethylene ester copolymers are converted into ethylene alcohol units can be obtained.

[0050] Furthermore, in the method described in (I) above, when copolymerizing monomers in which hydroxyl groups are protected by esters or the like, the modified EVOH resin of the present invention can be obtained by simultaneously deprotecting the esters or the like of the protected monomers and converting them into primary hydroxyl structures in the side chains through saponification. Additionally, the modified EVOH resin of the present invention only needs to have a specific amount of primary hydroxyl groups in the side chains, and may also retain a small amount of ester groups even if the protection has not been completely removed.

[0051] In the case of method (II) above, for example, it is sufficient to react the obtained EVOH-based resin with a monovalent epoxy-containing compound. The above reaction method is not particularly limited, and preferred methods include reacting the resin in solution and reacting the resin in an extruder. Furthermore, when using the method of reacting the resin in an extruder, it is also ideal to use a catalyst containing ions of metals belonging to groups 3 to 12 of the periodic table.

[0052] Preferred examples of monovalent epoxy-containing compounds include propylene oxide, butane oxide, and glycidyl ether. These can be used alone or in combination of two or more. Propylene oxide is the most desirable among them.

[0053] Regarding the aforementioned monovalent epoxy-containing compounds, for example, when using propylene oxide, the resulting modified EVOH resin system has a primary hydroxyl group represented by the following general formula (4) in the side chain.

[0054] [Chemistry 4]

[0055] By doing so, the modified EVOH resin with primary hydroxyl groups on the side chain of the present invention can be obtained. Specifically, it is a modified EVOH resin having structural units of the following general formula (1). In addition, in the present invention, it is only necessary for the side chain of the modified EVOH resin to have a specific amount of primary hydroxyl groups, but other hydroxyl structures (secondary hydroxyl groups, tertiary hydroxyl groups) may also be present on the side chain.

[0056] [Chemistry 5]

[0057] For R1 to R3, there are no particular limitations as long as they are hydrogen atoms or organic groups. Examples of organic groups include alkyl, alkenyl, alkynyl, phenyl, naphthyl, and other hydrocarbon groups (these hydrocarbon groups may also have hydroxyl, fluorine, chlorine, and bromine as substituents). The X series, representing a single bond or a bonded chain, indicates the polymer backbone bonded to a primary hydroxyl group. The bonded chain is not particularly limited; examples include hydrocarbons such as alkyl, alkenyl, alkyne, phenyl, and naphthyl (these hydrocarbons may also have hydroxyl, fluorine, chlorine, and bromine as substituents); hydrocarbons such as alkyl, alkenyl, alkyne, phenyl, and naphthyl bonded to the polymer backbone by ether bonds (these hydrocarbons may also have hydroxyl, fluorine, chlorine, and bromine as substituents); others include -CO-, -CO(CH2)mCO-, -CO(CH2)mCOR4-, -NR5-, and -CONR5- (R4 and R5 are independent substituents, ideally hydrogen atoms or alkyl groups; the m series represents a natural number).

[0058] The modified EVOH resin of this invention contains 1~16.5 mol% of ethylene structural units, 3~16 mol% is more ideal, 5~15.5 mol% is even more ideal, and 6~15.0 mol% is particularly ideal. If the content of ethylene structural units is too low, the viscosity stability of the solution will decrease when using the modified EVOH-based resin solution to form a layer composed of the modified EVOH-based resin. Conversely, if the content of ethylene structural units is too high, the hydrophilicity will decrease, making it difficult for biodegradable bacteria to access the solution, thus reducing biodegradability. Furthermore, the gas barrier properties will also decrease. The content of ethylene structural units in the modified EVOH resin can be controlled by adjusting the ethylene pressure during copolymerization.

[0059] The modified EVOH resin of this invention has a content of 2.5 mol% or more in the side chain with primary hydroxyl groups, which is more ideal between 2.5 and 10 mol%, and particularly ideal between 3 and 6 mol%. If the content of structures with primary hydroxyl groups in the side chain is too low, the modified EVOH resin will have insufficient hydrophilicity and lower biodegradability. Conversely, if the content of structures with primary hydroxyl groups in the side chain is too high, the production cost will increase, which is economically disadvantageous.

[0060] The content of ethylene structural units in the modified EVOH resin of the present invention, and the content of structures with primary hydroxyl groups in the side chain in the modified EVOH resin, can be determined by the integral ratio of the spectra obtained by dissolving it in dimethyl sulfoxide-d6 containing trifluoroacetic acid-d as an additive and measuring it at 50°C using 1H-NMR and 13C-NMR.

[0061] For a specific example, a modified EVOH resin with a side chain having a primary hydroxyl group represented by the following general formula (2) will be used for illustration. Figures 1 and 2 are the 1H-NMR spectra (Figure 1) and 13C-NMR spectra (Figure 2) obtained by NMR determination of modified EVOH resin with primary hydroxyl groups represented by the following general formula (2) on the side chain at 50℃.

[0062] [Chemistry 6]

[0063] The signals in the above 1H-NMR spectrum (Figure 1) are classified as follows. • 0.7~0.9ppm: Methyl proton (3H) in the terminal ethylene structural unit ･0.9~1.7ppm: Methylene protons (4H) in the intermediate ethylene structural unit, methylene protons (2H) in the vinyl alcohol structural unit, methylene protons (2H) in the unsaponified vinyl acetate structural unit, and methylene protons (2H) in the main linear portion of the 1,2-butenediol structural unit. • 1.7~1.9ppm: The methylene proton (1H) in the main linear portion of the 1,2-butenediol structural unit. • 1.9~2.0 ppm: Methyl proton (3H) in the structural unit of unsaponifiable vinyl acetate • 3.2~4.2ppm: Methylene proton (1H) of the vinyl alcohol structural unit, methylene proton (2H) and methylene proton (1H) adjacent to the hydroxyl group of the 1,2-butenediol structural unit.

[0064] Furthermore, the signals in the 13C-NMR spectrum (Figure 2) are classified as follows. • 8~10 ppm: Methyl carbon in the terminal ethylene structural unit • 20~48ppm: Methylene carbon of the intermediate ethylene structural unit, methylene carbon of the vinyl alcohol structural unit, methylene carbon and methyl carbon of the unsaponified vinyl acetate structural unit, and methylene carbon and methine carbon of the main linear portion of the 1,2-butenediol structural unit. 63~64ppm: Methylene carbon adjacent to the primary hydroxyl group of the 1,2-butenediol structural unit • 64~75ppm: methylene carbon of vinyl alcohol structural unit, methylene carbon of unsaponifiable vinyl acetate structural unit, and methylene carbon adjacent to the secondary hydroxyl moiety of 1,2-butenediol structural unit

[0065] By solving the following simultaneous equations based on the classification in the above 1H-NMR and 13C-NMR spectra, the content of ethylene structural units in the modified EVOH resin and the content of structures with primary hydroxyl groups in the side chains of the modified EVOH resin can be obtained. a = 4E + 2V + 3D b=V+3D c=(V+D) / D Integration values ​​of the 0.9–1.7 ppm signal in the a:1 H-NMR spectrum (Figure 1) b: Integral values ​​of the 3.2–4.2 ppm signal in the 1H-NMR spectrum (Figure 1) c: The value obtained by dividing the integrated value of the 64-75 ppm signal in the 13C-NMR spectrum (Figure 2) by the integrated value of the 63-64 ppm signal. E: Mohr's of the ethylene unit V: Mohr's of the vinyl alcohol unit D: Mohr's ratio of 1,2-butenediol (a structure with a primary hydroxyl group in the side chain) units

[0066] In the case of method (I) above, the content of structural units with primary hydroxyl groups in the side chain can be controlled by the amount of monomers with primary hydroxyl groups in the side chain used as comonomers, or by the amount of monomers in which the hydroxyl groups are protected by esters or the like. Furthermore, in the case of method (II) above, the content can be controlled by the amount of the monovalent epoxy-containing compound used for modification.

[0067] Ideally, the modified EVOH resin should contain less than 0.7% by mass, less than 0.4% by mass is particularly ideal, and less than 0.2% by mass is even better. If the amount of sodium acetate exceeds 0.7% by mass, a transparent solution cannot be prepared when making the modified EVOH resin solution for the purpose of producing the barrier material described below, and there is a tendency for the appearance of the gas barrier material to deteriorate. Furthermore, if the amount of sodium acetate is too high, moisture and sodium acetate will easily interact during the formation of the gas barrier material, especially under high humidity conditions, leading to a tendency for reduced gas barrier properties. In addition, the amount of sodium acetate in the modified EVOH resin can be determined by titrating the sample solution with hydrochloric acid according to JIS K6726.

[0068] The viscosity of the modified EVOH resin prepared as a 4% (w / w) aqueous solution and determined using the falling ball viscometer method according to JIS K6726 is typically 2.50~600 mPa·s, with 2.90~270 mPa·s being more ideal and 3.30~110 mPa·s being particularly ideal. If the viscosity is too high, coating defects may occur when applying the modified EVOH resin solution to a substrate resin film to obtain a gas barrier material. If the viscosity is too low, the resulting gas barrier material may have reduced strength and lack durability.

[0069] The viscosity of the modified EVOH resin when it is prepared into a 4% by mass aqueous solution is used as an indicator of the degree of polymerization of the modified EVOH resin. Additionally, when the modified EVOH resin contains ethylene structural units that cannot be adjusted to a 4% by mass aqueous solution, or structural units with primary hydroxyl groups on the side chains, the following melt flow rate (MFR) can also be used as an indicator of the degree of polymerization.

[0070] The melt flow rate (MFR) of the aforementioned modified EVOH resin [210°C, 2160g load] is typically 0.1~100g / 10min, with 1~50g / 10min being more ideal, and 3~35g / 10min being particularly ideal. When the MFR is too high, it tends to become difficult to control the thickness of the layer composed of the modified EVOH resin when manufacturing barrier materials using melt molding; when it is too low, it tends to place a high load on the molding machine during melt molding. This MFR system serves as an indicator of the degree of polymerization of modified EVOH resins, which can be adjusted by the amount of polymerization catalyst and solvent used during copolymerization of the copolymer components.

[0071] The degree of saponification of the modified EVOH resin of this invention is generally above 85 mol%, ideally above 90 mol%, particularly ideal above 95 mol%, and even more ideal above 99 mol%. If the saponification is too low, there is a tendency for reduced gas barrier properties, especially under high humidity conditions. The degree of saponification of the modified EVOH resin of this invention can be determined according to JIS K6726 and the amount of alkali consumption related to the hydrolysis of the remaining vinyl acetate units.

[0072] The biodegradability of the modified EVOH resin of this invention is ideally above 20%, more ideally above 25%, and particularly ideally above 30%. Furthermore, the above biodegradability was obtained by referring to the method described in JIS K6950, based on the biochemical oxygen demand and theoretical oxygen demand under the following test conditions. • Device: BOD TESTER 200F (manufactured by TIETECH) • Inoculation source: Return sludge from wastewater treatment plants that treat domestic sewage. • Standard test culture medium: 100mL • Inoculation concentration: 90 mg / L Temperature: 25±1℃ Period: 28 days

[0073] Furthermore, the modified EVOH resin of this invention can be blended with other components to form resin compositions. Examples of these other components include other thermoplastic resins, plasticizers, lubricants, stabilizers, surfactants, colorants, ultraviolet absorbers, antistatic agents, desiccants, crosslinking agents, metal salts, fillers, and various fibers. These can be used individually or in combination of two or more.

[0074] The content of modified EVOH resin in the above-mentioned resin composition is usually 80% by mass or more, with 90% by mass or more being ideal, and 95% by mass or more being even more ideal. Furthermore, the upper limit is 100% by mass.

[0075] The modified EVOH-based resin of the present invention can be ideally used as a gas barrier material for food packaging materials, etc. There are no particular limitations on the method of using the modified EVOH-based resin of the present invention as a gas barrier material, and examples include: (i) coating a solution of the modified EVOH-based resin onto a thin film of a base resin and drying it to form a layer composed of the modified EVOH-based resin, and then using it as a gas barrier material; (ii) melt-forming the modified EVOH-based resin and then using it as a gas barrier material, etc.

[0076] In the method described above (i), the solvents used for the solution of the modified EVOH resin can include lower alcohols with 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 these, water, 2-propanol, or a mixture of water and 2-propanol are more ideal solvents, and the use of water and 2-propanol in the mixing ratio calculated according to the following formula (1) is particularly ideal. [Mode] Water:2-propanol = 100 - X:X (mass ratio) ･･･(1) X = 3.4 × (content of ethylene structural units) - 5 × (content of structural units with primary hydroxyl groups) - 20. However, when X is negative, let X = 0.

[0077] The inventors of this case discovered the following effect: when a homogeneous solution is obtained using a mixed solvent of water and 2-propanol, the required content of 2-propanol can be reduced by structural units with primary hydroxyl groups in the side chain. Furthermore, the relationship of the above formula (1) was found in the relationship between the content of ethylene structural units and the content of structural units with primary hydroxyl groups in the side chain of the modified EVOH resin. Since 2-propanol is an organic solvent, it must be recovered during coating when using 2-propanol to prepare a solution of modified EVOH-based resin. Therefore, it is ideal to use a solvent with a mixing ratio calculated according to the above formula (1) in a way that minimizes the amount of 2-propanol.

[0078] Furthermore, considering the desire for a better appearance of the gas barrier material, a transparent solution of the aforementioned modified EVOH resin is preferable. The transparency of the aforementioned modified EVOH resin solution can be expressed by measuring the transmittance of a 4% by mass solution.

[0079] When the modified EVOH resin is prepared into a 4% by mass solution using a solvent with the mixing ratio calculated according to formula (1) above, a transmittance of 70% or more at 430 nm is ideal under conditions of 30°C and a light path length of 20 mm, 75% or more is even more ideal, and 80% or more is particularly ideal. If the transmittance does not reach the above values, the gas barrier material produced may have a tendency to appear foggy.

[0080] The above-mentioned transmittance was evaluated in accordance with JIS K6726. However, when using water as the solvent alone, the modified EVOH resin with a higher content of ethylene structural units cannot obtain a uniform aqueous solution, so a solvent with the mixing ratio calculated according to the above formula (1) is used.

[0081] The transmittance of the modified EVOH resin when it is prepared into a solution with a concentration of 4% by mass can be controlled by changing the content of ethylene structural units, the content of structural units with primary hydroxyl groups in the side chain, the temperature, the concentration of solid components in the solution, the type of solvent, and the mixing ratio; and by reducing the amount of salts such as sodium acetate generated by neutralization after saponification.

[0082] Regarding methods for coating the above-mentioned modified EVOH resin solution, known methods such as applicator stick coating, roller coating, mold coating, gravure coating, corner-cut roller coating, and screen printing can be listed. Among these, applicator stick coating is more ideal.

[0083] After coating, the material can be dried by, for example, by heat treatment at 60-105°C for 0.5-10 minutes to obtain a gas barrier material with a layer composed of modified EVOH resin.

[0084] Furthermore, regarding the melt forming method in the above (ii) method, examples include extrusion forming, injection forming, blow molding, compression molding, blow molding, etc.

[0085] This method yields a gas barrier material having a layer composed of the modified EVOH-based resin of the present invention. The aforementioned gas barrier material can be fabricated as a single-layer gas barrier material or a multi-layer gas barrier material, but a multi-layer structure is preferred. Ideally, the aforementioned multi-layer gas barrier material should have at least one layer composed of the modified EVOH-based resin of the present invention. Furthermore, the aforementioned multi-layer gas barrier material can be formed by stacking layers composed of the modified EVOH-based resin of the present invention, or by stacking with other substrate resins.

[0086] Examples of the aforementioned base resins include linear low-density polyethylene, low-density polyethylene, ultra-low-density polyethylene, medium-density polyethylene, high-density polyethylene, polyethylene-propylene (block and random) copolymers, ethylene-α-olefin (α-olefin with 4 to 20 carbon atoms) copolymers, polypropylene-based resins such as polypropylene and propylene-α-olefin (α-olefin with 4 to 20 carbon atoms), polybutene, polypentene, polycyclic olefin resins (polymers in which at least one of the main chain and side chain has a cyclic olefin structure), and unmodified polyolefin resins such as unsaturated carboxylic acids or their esters. These include graft-modified polyolefin resins, such as unsaturated carboxylic acid-modified polyolefin resins, and a broad range of polyolefin resins including modified olefin resins, ionomers, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylate copolymers, polyester resins, polyamide resins (including copolymerized polyamides), polyvinyl chloride, polyvinylidene chloride, acrylic resins, polystyrene, vinyl ester resins, polyester elastomers, polyurethane elastomers, polystyrene elastomers, halogenated polyolefins such as chlorinated polyethylene and chlorinated polypropylene, and aromatic or aliphatic polyketides. These can be used alone or in combination. Furthermore, these base resins can also undergo surface treatments such as corona treatment.

[0087] The thickness of the layer composed of the modified EVOH resin is typically 1~200 μm, with 1~100 μm being more ideal and 1~50 μm being particularly ideal. Furthermore, when the gas barrier material is a multilayer structure, the thickness of all layers composed of the modified EVOH resin contained in the gas barrier material is summed.

[0088] Furthermore, for layers composed of modified EVOH resin, an oxygen transmittance of 5 cc·3 μm / m²·day·atm or less, measured at 23°C and 0%RH, is ideal; 1 cc·3 μm / m²·day·atm or less is even more ideal; and 0.1 cc·3 μm / m²·day·atm or less is particularly ideal. The lower limit of oxygen transmittance is typically 0.003 cc·3 μm / m²·day·atm. The aforementioned oxygen transmittance can be obtained using an oxygen transmittance measuring device.

[0089] Furthermore, because the environment in which gas barrier materials are used spans a wide range of conditions from low to high humidity, oxygen permeability remains low even at high humidity, and it is ideal for changes in oxygen permeability to correspond little to changes in humidity. Considering this, an oxygen permeability of 30cc･3μm / m²･day･atm or less, measured at 23°C and 65%RH, is ideal; 15cc･3μm / m²･day･atm or less is even more ideal; and 5cc･3μm / m²･day･atm or less is particularly ideal.

[0090] For oxygen transmittance measured at 23°C and 65%RH, a ratio of less than 500 to that measured at 23°C and 0%RH is ideal, less than 300 is even more ideal, and less than 200 is particularly ideal. [Example]

[0091] The present invention will be described in more detail below with examples, but the invention is not limited to the following examples as long as it does not depart from its spirit. In addition, the term "part" in the examples refers to a mass standard unless otherwise specified.

[0092] <Example 1> Synthesis of Modified Ethylene-Ethylene Ester Copolymer 460 parts of vinyl acetate, 48 parts of 3,4-diethoxy-1-butene (a monomer with hydroxyl groups protected by esters, etc.), and 75 parts of methanol were fed into a temperature-controlled autoclave. The system was temporarily purged with nitrogen and then purged with ethylene, while stirring and heating to 67°C. After heating, ethylene was forced in to a partial pressure of 1.0 MPa, and 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 carry out the polymerization reaction. Then, a solution of 0.98 parts of sorbic acid dissolved in 100 parts of methanol was added, and the polymerization was stopped by cooling to room temperature (23°C). Unreacted monomers were distilled off to obtain a methanol solution of ethylene-vinyl acetate-3,4-diethoxy-1-butene copolymer, which is a modified ethylene-vinyl ester copolymer.

[0093] Synthesis of Modified EVOH-Based Resins Next, the above solution was diluted with methanol to a concentration of 10% by mass and stirred. While maintaining the solution temperature at 45°C, a 5% by mass methanol solution of sodium hydroxide was added to make the sodium hydroxide amount 10 mmol% relative to the vinyl acetate unit system in the copolymer, and saponification was carried out. The saponified product precipitated as the reaction proceeded, eventually forming particles. For further saponification, the generated particulate saponified product was temporarily filtered and then dispersed again in 20 times the amount of methanol of the saponified product. A 5% by mass methanol solution of sodium hydroxide was added to make it 50 mmol% relative to the initial vinyl acetate unit system in the copolymer, and the reaction was carried out at 50°C for 3 hours. After the reaction, it was neutralized with acetic acid and filtered again to obtain particulate saponified product. Then, in order to reduce the sodium acetate adhering to the saponified product in this state, it was washed with methanol. For the washing method, the particulate saponified product was dispersed in 5 times its mass of methanol, stirred at 45°C for 1 hour, and the filtration operation was repeated 3 times. The saponified product obtained in this manner was dried in a hot air dryer to obtain the modified EVOH resin of Example 1. The obtained modified EVOH resin has the following 1,2-diol structure as a structure with primary hydroxyl groups on the side chain.

[0094] [Chemistry 7]

[0095] Regarding the degree of saponification of the obtained modified EVOH resin, it was analyzed according to JIS K6726 based on the alkali consumption related to the hydrolysis of the residual vinyl acetate unit, and was 99.9 mol. Furthermore, 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 was 0.097 by mass. The obtained modified EVOH resin was dissolved in dimethyl sulfoxide-d6 containing trifluoroacetic acid-d as an additive. Based on the 1H-NMR spectrum (see Figure 1) and 13C-NMR spectrum (see Figure 2) obtained by NMR determination at 50°C, the content of ethylene structural units and the content of structural units with primary hydroxyl groups in the side chain were determined using 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 with primary hydroxyl groups in the side chain) was 4.7 mol%. Furthermore, the viscosity of the 4% concentration aqueous solution obtained by the falling ball viscometer method according to JIS K6726 is 8.76 mPa·s.

[0096] <Examples 2-6, Comparative Examples 1-6> By modifying the polymerization conditions of Example 1 as shown in Table 1 below, methanol solutions of the modified ethylene-ethylene copolymers of Examples 2-6 and Comparative Examples 3-6, and the ethylene-ethylene copolymers of Comparative Examples 1 and 2 after the unreacted monomers have been distilled off were obtained. For Examples 2-6 and Comparative Examples 2-6, the modified EVOH resins and EVOH-based resins shown in Table 2 were obtained by saponification, washing, and drying as in Example 1. Furthermore, the viscosity of the 4% aqueous solution of the modified EVOH resin in Example 4, obtained by the falling ball viscometer method according to JIS K6726, was 13.94 mPa·s, and the viscosity of the 4% aqueous solution of the modified EVOH resin in Example 6 was 9.03 mPa·s.

[0097] Furthermore, regarding Comparative Example 1, methanol was added to adjust the methanol solution obtained by distilling off unreacted monomers from the ethylene-vinyl acetate copolymer obtained by the above method to a concentration of 15% by mass. Here, a 5% by mass methanol solution of sodium hydroxide was added to make the sodium hydroxide concentration 50 mmol% relative to the vinyl acetate unit system in the copolymer, and the solution was refluxed for 1 hour for saponification. At this point, no saponified product precipitated, and the solution remained in a solution state. Then, methanol was added again, and the solution was distilled at 60°C to concentrate the contents. Here, to further saponify, a 5% by mass methanol solution of sodium hydroxide was added again to make the sodium hydroxide concentration 50 mmol% relative to the vinyl acetate unit system in the copolymer, and the solution was refluxed for 1 hour. At this point, no saponified product precipitated, and the solution remained in a solution state. Then, methanol was added again, and the solution was distilled at 60°C to concentrate the contents. The solution was then solidified in an ice bath. The resin cured in this manner was crushed and repeatedly washed with a 2% acetic acid aqueous solution and then with deionized water, and then dried to obtain the EVOH resin of Comparative Example 1.

[0098] For the modified EVOH resins of Examples 2-5, Comparative Examples 3-6, and Comparative Examples 1 and 2, the content of ethylene structural units, the content of structural units with primary hydroxyl groups in the side chains, the degree of saponification, and the amount of sodium acetate were determined using the same method as in Example 1. The results are shown in Table 2 below.

[0099] Furthermore, following Japanese Patent Application Publication No. 2019-182947, the content of ethylene structural units and the content of structural units with primary hydroxyl groups in the side chains of the modified EVOH resin of Example 6 were determined. The 1H-NMR spectrum (solvent: dimethyl sulfoxide-d6) of the modified ethylene-ethylene ester copolymer intermediate of Example 6 measured at 50°C is shown in Figure 3, and the 1H-NMR spectrum (solvent: dimethyl sulfoxide-d6, containing trifluoroacetic acid-d as an additive) of the modified EVOH resin of Example 6 measured at 50°C is shown in Figure 4.

[0100] [Table 1] Acetic acid Ethylene ester (share) Monomers in which hydroxyl groups are protected by esters, etc. methanol (share) ethylene partial pressure (MPa) 2,2'-Azobis Isobutyronitrile (share) peroxide Tributyl neodecanoate (share) Aggregation Time (Hour) type Blending amount (parts) Example 1 460 3,4-Diethoxy-1-butene 48 75 1.0 0.082 - 4 Example 2 460 3,4-Diethoxy-1-butene 42 75 2.0 0.352 - 4 Example 3 460 3,4-Diethoxy-1-butene 32 75 1.0 0.082 - 1 Example 4 460 3,4-Diethoxy-1-butene 48 75 0.3 0.082 - 2 Example 5 460 3,4-Diethoxy-1-butene 36 132 1.4 - 0.129 4 Example 6 460 2-Methylene-1,3- Propylene glycol diacetate 18 75 1.0 0.082 - 2 Comparative Example 1 460 - - 75 3.8 0.082 - 1 Comparative Example 2 460 - - 75 1.0 0.082 - 1 Comparative Example 3 460 3,4-Diethoxy-1-butene 48 75 2.8 0.176 - 4 Comparative Example 4 460 3,4-Diethoxy-1-butene 74 151 - 0.108 - 4 Comparative Example 5 460 3,4-Diethoxy-1-butene 48 75 2.8 0.082 - 4 Comparative Example 6 460 3,4-Diethoxy-1-butene 16 75 1.5 0.176 - 2

[0101] Using the resins obtained in the examples and comparative examples described above, the transparency, oxygen permeability, humidity dependence of gas barrier properties, and biodegradability were evaluated using the following evaluation methods. These results are shown in Table 2 below.

[0102] [transparency] For the resins of the Examples and Comparative Examples, a solution with a concentration of 4% by mass was prepared using a solvent in which the mixing ratio of water and 2-propanol was set to the value calculated according to the following formula (1). [Mode] Water:2-propanol = 100 - X:X (mass ratio) ･･･(1) X = 3.4 × (content of ethylene structural units) - 5 × (content of structural units with primary hydroxyl groups) - 20. However, when X is negative, let X = 0. The transmittance at 430 nm of the 4% by mass solution prepared above was measured at 30°C and with an optical path length of 20 mm, and this transmittance was taken as the transparency of the solution. In the transparency of Table 2 below, the 2-propanol content is the value obtained according to the above formula (1).

[0103] [Fabrication of Gas Barrier Materials] Using the solvent obtained according to the above formula (1), the resins of the examples and comparative examples were prepared into a solution with a concentration of 10% by mass, and coated onto a corona-treated PET film (38 μm thick) with a smearing stick. The film was then dried at 80°C for 5 minutes to obtain a gas barrier material with a 3 μm layer made of modified EVOH resin or EVOH-based resin.

[0104] [Gas barrier properties and their humidity dependence] The oxygen permeability of the aforementioned gas barrier material was measured using an oxygen permeability measuring device (MOCON "OXTRAN2 / 20") at a temperature of 23°C and humidity levels of 0%RH and 65%RH. The value for a thickness of 3μm of modified EVOH resin or EVOH-based resin was then calculated as the value representing the gas barrier performance. Furthermore, the oxygen permeability at 0%RH and 65%RH was defined as T0% and T65%, respectively, and the value of T65% / T0% was used as an indicator of the humidity dependence of the gas barrier performance.

[0105] [Biodegradability] The evaluation of biodegradability was conducted using the modified EVOH resin or EVOH resin of the examples and comparative examples, under the following conditions, in accordance with the method described in JIS K6950. • Device: BOD TESTER 200F (manufactured by TIETECH) • Inoculation source: Return sludge from wastewater treatment plants that treat domestic sewage. • Standard test culture medium: 100mL • Inoculation concentration: 90 mg / L Temperature: 25±1℃ Period: 28 days Biodegradability is determined from biochemical oxygen demand and theoretical oxygen demand.

[0106] [Table 2] Content of ethylene structural units (mol%) Side chain with primary hydroxyl group Structural unit degree of saponification (mol%) Acetic acid Sodium content (quality%) transparency Gas barrier properties (cc･3μm / m2 ･day･atm) Humidity dependence of gas barrier properties Biodegradability (%) structure※ content (mol%) 2-Propanol content (quality%) transmittance (%) 0%RH (T0%) 65%RH (T65%) T65% / T0% Example 1 7.7 (1) 4.7 99.9 0.097 0 96.6 0.06 3.5 58 65 Example 2 15.7 (1) 3.7 99.8 0.076 14.9 80.8 0.05 2.3 46 36 Example 3 7.5 (1) 3.3 99.8 0.034 0 81.3 0.02 1.5 75 72 Example 4 2 (1) 5.3 99.9 0.086 0 92.5 0.02 3.2 160 65 Example 5 11.4 (1) 3.2 99.9 0.08 2.8 76.9 0.03 1.7 57 51 Example 6 7.6 (2) 3.9 99.7 0.085 0 83.8 0.03 1.9 63 64 Comparative Example 1 25 - - 99.8 0.018 65 91.2 0.26 2.6 10 5 Comparative Example 2 6.6 - - 99.9 0.033 2.4 5 0.03 1.5 50 11 Comparative Example 3 20.2 (1) 4.2 99.9 0.103 27.7 97.1 0.2 2.6 13 14 Comparative Example 4 0 (1) 8 99.8 0.035 0 94.4 0.02 5.8 290 15 Comparative Example 5 16.8 (1) 4.4 99.9 0.09 15.1 84.3 0.1 2.4 twenty four 10 Comparative Example 6 11.5 (1) 1.7 99.8 0.076 10.6 72.9 0.07 1.6 twenty three 19 * (1) ... (2) ...

[0107] As can be understood from Table 2 above, the modified EVOH resins of Examples 1 to 6, which set the ethylene structural unit to a specific range and further introduced a specific amount of structural units with primary hydroxyl side chains, can be used to make gas barrier materials with excellent appearance because the solution has high transparency. They are excellent in terms of biodegradability, low oxygen permeability, and excellent humidity dependence of gas barrier properties. On the other hand, the modified EVOH resins of Comparative Example 1 (a general EVOH resin) and Comparative Example 3 (with a higher content of ethylene structural units than specified in this invention) exhibited poorer biodegradability and gas barrier properties compared to the modified EVOH resins of the examples. Furthermore, although the content of ethylene structural units fell within the range specified in this invention, the EVOH resin of Comparative Example 2 (which lacked primary hydroxyl groups in its side chains) had lower biodegradability compared to the modified EVOH resins of the examples. In contrast, the modified EVOH resins of Comparative Example 4, which have a primary hydroxyl group in the side chain and fall within the range specified in this invention but do not have an ethylene structure, and Comparative Examples 5 and 6, which have both ethylene structural units and structural units with primary hydroxyl groups in the side chain but whose content is outside the range specified in this invention, have lower biodegradability compared to the modified EVOH resins of the examples.

[0108] While the above embodiments illustrate specific aspects of the present invention, they are merely illustrative and not intended to be limiting. Various modifications known to those skilled in the art are intended to be included within the scope of this invention. [Industrial applicability]

[0109] The modified EVOH resin of this invention is useful as a packaging material because it has gas barrier properties and excellent biodegradability, and is particularly suitable for use as a packaging material for food, pharmaceuticals and the like.

[0110] none

Claims

1. A modified ethylene-vinyl alcohol resin, wherein the modified ethylene-vinyl alcohol resin has primary hydroxyl groups on its side chains, characterized in that: the content of ethylene structural units in the modified ethylene-vinyl alcohol resin is 1-16.5 mol%, and the content of structural units with primary hydroxyl groups on their side chains is 2.5 mol%-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 as described in claim 1, wherein, The degree of saponification of the modified ethylene-vinyl alcohol resin is above 99 mol%.

3. The modified ethylene-vinyl alcohol resin as claimed in claim 1 or 2, wherein, When the modified ethylene-vinyl alcohol resin is prepared into a solution with a concentration of 4% by mass using water and 2-propanol as solvents in the mixing ratio calculated according to the following formula (1), the transmittance at 430 nm under the conditions of 30°C and a light path length of 20 mm is 70% or more; [Formula] Water: 2-propanol = 100 - X: X (mass ratio) ･･･ (1) X = 3.4 × (content of ethylene structural units) - 5 × (content of structural units with primary hydroxyl groups) - 20, but when X is negative, let X = 0.

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

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