Ethylene-vinyl alcohol copolymer, use thereof for improving heat stability, use thereof for enhancing resistance to pyrolysis, resin composition, molding material, multilayer structure, molded body, film, food package, method for producing multilayer structure, and method for producing molded body

Abstract

Provided is an ethylene-vinyl alcohol copolymer excellent in thermal stability.　This ethylene-vinyl alcohol copolymer has a bio-based degree of 0.0001% or more and less than 3%.

Description

Ethylene-vinyl alcohol copolymer, use for improving thermal stability, use for increasing resistance to thermal decomposition, resin composition, molding material, multilayer structure, molded body, film, food packaging body, method for manufacturing multilayer structure, and method for manufacturing molded body

[0001] The present invention relates to an ethylene-vinyl alcohol copolymer, its use for improving thermal stability, its use for increasing resistance to thermal decomposition, a resin composition, a molding material, a multilayer structure, a molded article, a film, a food packaging material, a method for producing a multilayer structure, and a method for producing a molded article.

[0002] Ethylene-vinyl alcohol copolymers (hereinafter, sometimes referred to as "EVOH resins") are excellent in transparency, gas barrier properties such as oxygen and other gases, aroma retention, solvent resistance, oil resistance, mechanical strength, and the like, and are formed into films, sheets, bottles, and the like, and are widely used as various packaging materials such as food packaging materials, pharmaceutical packaging materials, industrial chemical packaging materials, and agricultural chemical packaging materials.

[0003] Meanwhile, in recent years, there has been an increasing demand for bioplastics made from carbon-neutral biomass-derived raw materials, with the aim of realizing a recycling-oriented society. Therefore, research is being conducted into the development of biomass-derived resins that are comparable in performance to fossil fuel-derived resins by combining biomass-derived raw materials with fossil fuel-derived raw materials.

[0004] For example, Patent Document 1 discloses a gas barrier resin composition containing an EVOH resin in which ethylene and vinyl ester are partly derived from biomass, and an EVOH resin derived from fossil fuel.

[0005] Japanese Patent Application Laid-Open No. 2022-027730

[0006] The gas barrier resin composition disclosed in Patent Document 1 has gas barrier properties and long-run properties comparable to those of fossil fuel-derived resins, but its thermal stability is insufficient compared to those of fossil fuel-derived resins, and there is a demand for better thermal stability.

[0007] In view of this background, the present invention provides an EVOH resin having superior thermal stability to those derived from fossil fuels.

[0008] However, in light of these circumstances, the present inventors have conducted extensive research and have found that by adjusting the bio-based content of an EVOH resin to a specific low range, it is possible to obtain an EVOH resin with superior thermal stability compared to conventional petroleum-derived EVOH resins derived from fossil fuels.

[0009] That is, the present invention has the following aspects. [1] An EVOH resin having a biobased content of 0.0001% or more and less than 3%. [2] The EVOH resin according to [1], having a biobased content of 0.0005% or more and less than 3%. [3] The EVOH resin according to [1], having a biobased content of more than 1% and less than 3%. [4] The EVOH resin according to [1], having a biobased content of 1.1% or more and less than 3%. [5] The EVOH resin according to [1], having a biobased content of 1.1% or more and less than 2.9%. [6] The EVOH resin according to [1], having a biobased content of 1.1% or more and less than 2.8%. [7] The EVOH resin according to [1], having a biobased content of 1.1% or more and less than 2.7%. [8] The EVOH resin according to [1], having a biobased content of 1.1% or more and less than 2%. [9] The EVOH resin according to [1], wherein the biobased content is 1.3% or more and less than 3%.

[10] The EVOH resin according to [1], wherein the biobased content is 1.3% or more and less than 2.9%.

[11] The EVOH resin according to [1], wherein the biobased content is 1.3% or more and less than 2.8%.

[12] The EVOH resin according to [1], wherein the biobased content is 1.3% or more and less than 2.7%.

[13] The EVOH resin according to [1], wherein the biobased content is 1.3% or more and less than 2%.

[14] The EVOH resin according to [1], wherein the biobased content is more than 1% and less than 2.9%.

[15] The EVOH resin according to [1], wherein the biobased content is more than 1% and less than 2.8%.

[16] The EVOH resin according to [1], wherein the biobased content is more than 1% and less than 2.7%.

[17] The EVOH resin according to [1], wherein the biobased content is more than 1% and not more than 2%.

[18] The EVOH resin according to [1], wherein the biobased content is 0.0001% or more and not more than 2%.

[19] The EVOH resin according to [1], wherein the biobased content is 0.0001% or more and less than 1%.

[20] The EVOH resin according to [1], wherein the biobased content is 0.0001% or more and not more than 0.9%.

[21] The EVOH resin according to [1], wherein the biobased content is 0.0001% or more and not more than 0.7%.

[22] The EVOH resin according to any one of [1] to

[21] , having a content of ethylene structural units of 20 mol% or more and 60 mol% or less.

[23] Use of the EVOH resin according to any one of [1] to

[22] for improving thermal stability.

[24] Use of the EVOH resin according to any one of [1] to

[22] for increasing resistance to thermal decomposition.

[25] A resin composition comprising the EVOH resin according to any one of [1] to

[22] .

[26] A molding material comprising the EVOH resin according to any one of [1] to

[22] .

[27] A multilayer structure comprising a layer formed by molding the molding material according to

[26] .

[28] The multilayer structure according to

[27] , further comprising an adhesive resin layer.

[29] A molded article formed by molding the multilayer structure according to

[27] or

[28] .

[30] A film comprising the multilayer structure according to

[27] or

[28] .

[31] A food packaging article formed by molding the multilayer structure according to

[27] or

[28] .

[32] A method for producing the multilayer structure according to

[27] or

[28] , comprising a step of co-extruding a resin composition.

[33] A method for producing the molded article according to

[29] , comprising a step of molding the multilayer structure.

[0010] The EVOH resin of the present invention has excellent thermal stability, even compared to conventional petroleum-derived EVOH resins derived from fossil fuels.

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

[0012] As used herein, "x and / or y (x and y are any configuration)" refers to at least one of x and y, and can mean three things: x only, y only, or x and y. In this specification, when "X to Y" (X and Y are any numbers) is used, unless otherwise specified, it also means "X or more and Y or less," as well as "preferably more than X" or "preferably less than Y." In this specification, when "X or more" (X is any number) or "Y or less" (Y is any number) is used, it also means "preferably more than X" or "preferably less than Y." For numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. Furthermore, in the numerical ranges described herein, the upper or lower limit of the numerical range can also be replaced with the values ​​shown in the examples.

[0013] As used herein, the term "main component" refers to a component that significantly affects the properties of the target object, and the content of the component is typically 50% by mass or more, preferably 55% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, and may be 100% by mass. As used herein, the term "film" also refers to "tape" and "sheet." Furthermore, as used herein, the term "layer" refers to a thick layer as well as a relatively thin layer such as a "film," "tape," or "sheet."

[0014] EVOH resin is a water-insoluble thermoplastic resin obtained by saponifying an ethylene-vinyl ester copolymer, which is a copolymer of ethylene and a vinyl ester, and has ethylene structural units and vinyl alcohol structural units (if the saponification degree of the EVOH resin is not 100 mol %, it also has vinyl ester structural units). In an EVOH resin according to one embodiment of the present invention (hereinafter referred to as "the present EVOH resin"), at least a portion of the ethylene and / or vinyl ester is derived from biomass, and the EVOH resin has a specific bio-based content.

[0015] The term "biomass" refers to organic resources derived from plants and animals, excluding fossil fuels (fossil resources). In particular, biomass is preferably organic resources derived from plants.

[0016] Whether the ethylene and / or vinyl ester used as the raw material for the present EVOH resin is derived from biomass or fossil fuel can be confirmed by measuring the biobased content.

[0017] The "bio-based content" is an index that indicates the proportion of biomass-derived raw materials, and in this specification, it is defined as the percentage of radiocarbon ( 14 The biobased carbon content is determined by measuring the concentration of carbon dioxide (CO2) and carbon dioxide (C). Specifically, the biobased carbon content can be measured according to the method described in ASTM D6866-18. That is, when the biobased carbon content of an EVOH resin is more than 0% but less than 100%, it can generally be said that the raw materials contain both biomass-derived and fossil fuel-derived carbon.

[0018] The present EVOH resin has a biobased content of 0.0001% or more, preferably 0.0005% or more, more preferably 0.001%, even more preferably 0.005% or more, particularly preferably 0.01% or more, especially preferably more than 1%, most preferably 1.1% or more, and even more preferably 1.3% or more. The biobased content is less than 3%, preferably 2.9% or less, more preferably 2.8% or less, even more preferably 2.7% or less, especially preferably 2.5% or less, especially preferably 2.3% or less, most preferably 2% or less, even more preferably less than 1%, even more especially preferably 0.9% or less, and even especially preferably 0.7% or less. The biobased content ranges, for example, from 0.0001% to less than 3%. Since the biobased content is within the above range, the present EVOH resin has excellent thermal stability. It is generally believed that when EVOH resin is produced using biomass-derived raw materials, its physical properties are inferior to those of petroleum-derived EVOH resin due to the influence of impurities derived from the biomass. However, in the present invention, it has been discovered that by setting the bio-based content of the EVOH resin to a specific low range, thermal stability is improved compared to petroleum-derived EVOH resin, contrary to conventional common technical knowledge. The reason for this is that the present EVOH resin, having a specific bio-based content, contains carbon-14 ( 14 It is presumed that the presence of this carbon 14 in the main chain of the EVOH resin can strengthen the bond energy of the EVOH resin itself. 14 Biomass EVOH resin containing carbon-14 has stronger bond energy than petroleum EVOH resin that does not contain carbon-14 due to the primary isotope effect. Therefore, the inclusion of trace amounts of carbon-14 in the main chain of the EVOH resin may further increase the bond energy of the main chain of the EVOH resin, which is inherently resistant to decomposition, and thereby improve its heat resistance. This action is thought to suppress decomposition of the EVOH resin itself and improve its thermal stability. Furthermore, by setting the biobased content within a specific low range, the improvement in thermal stability due to carbon-14 outweighs the decrease in thermal stability caused by impurities derived from biomass, resulting in particularly excellent thermal stability.

[0019] The content of ethylene structural units in the present EVOH resin is usually 20 to 60 mol%, preferably 25 to 50 mol%, and particularly preferably 25 to 35 mol%. When the content of ethylene structural units is equal to or less than the upper limit, the gas barrier property tends to be excellent, and when the content is equal to or more than the lower limit, the gas barrier property under high humidity and the melt moldability tend to be excellent. In this specification, the content of the ethylene structural units usually means 1 It is measured by H-NMR measurement. For example, 1 The measurement method employs H-NMR measurement, using DMSO-d as the measurement solvent and setting the measurement temperature at 50°C.

[0020] The saponification degree of the present EVOH resin is usually 90 to 100 mol%, preferably 95 to 100 mol%, and more preferably 99 to 100 mol%. When the saponification degree is equal to or greater than the lower limit, the EVOH resin tends to have excellent gas barrier properties, thermal stability, and moisture resistance. In this specification, the saponification degree is usually defined as 1 It is measured by H-NMR measurement. For example, 1 The measurement method employs H-NMR measurement, using DMSO-d as the measurement solvent and setting the measurement temperature at 50°C.

[0021] The melt flow rate (MFR) (210°C, 2160 g load) of the present EVOH resin is typically 0.5 to 100 g / 10 min, preferably 1 to 50 g / 10 min, and more preferably 3 to 35 g / 10 min. When the MFR is below the upper limit, excellent stability during film formation is achieved, while when the MFR is above the lower limit, the viscosity tends to be kept from becoming too high and melt extrusion tends to be facilitated. The MFR is an indicator of the degree of polymerization of the EVOH resin and can be adjusted by the amount of polymerization initiator and the amount of solvent used when copolymerizing ethylene and vinyl ester. In this specification, the MFR is a value measured in accordance with JIS K 7120.

[0022] The present EVOH resin can be obtained by a production method including a step of copolymerizing ethylene and a vinyl ester, at least a part of which is derived from biomass.

[0023] The biobased content of the EVOH resin can be adjusted to fall within the above range by, for example: (1) adjusting the biobased content of the raw materials used to directly produce an EVOH resin having a biobased content within the above range; or (2) mixing a biomass EVOH resin having a desired biobased content with a petroleum EVOH resin made from fossil fuel-derived raw materials to produce an EVOH resin having a biobased content within the above range. Among these, method (2) is preferred from the viewpoint of production efficiency. The production method (2) will be described in detail below.

[0024] [Biomass EVOH Resin] The ethylene used in the production of the biomass EVOH resin may be derived from biomass or fossil fuel. The biomass-derived ethylene can be produced, for example, by producing bioethanol from a biomass raw material and then subjecting the bioethanol to a dehydration reaction or the like.

[0025] Examples of the biomass raw material include waste materials, unused materials, and resource crop materials, such as cellulosic crops (pulp, kenaf, wheat straw, rice straw, waste paper, papermaking residues, etc.), wood, charcoal, compost, natural rubber, cotton, sugarcane, soybean lees, oils and fats (rapeseed oil, cottonseed oil, soybean oil, coconut oil, castor oil, etc.), carbohydrate crops (corn, potatoes, wheat, rice, rice husks, rice bran, used rice, cassava, sago palm, etc.), bagasse, buckwheat, soybeans, essential oils (pine oil, orange oil, eucalyptus oil, etc.), pulp black liquor, and vegetable oil cakes. These materials can be used alone or in combination of two or more.

[0026] Examples of the method for producing bioethanol include a method in which the biomass raw material is pretreated as needed (compressed hot water treatment, acid treatment, alkali treatment, saccharification treatment using a saccharifying enzyme), then fermented with yeast to produce bioethanol, and then purified through a distillation process and a dehydration process. Furthermore, when the saccharification treatment is performed, it may be sequential saccharification and fermentation in which saccharification and fermentation are performed in stages, or parallel saccharification and fermentation in which saccharification and fermentation are performed simultaneously, but parallel saccharification and fermentation is preferred from the viewpoint of production efficiency.

[0027] The proportion of biomass-derived ethylene in the ethylene structural units of the biomass EVOH resin may be entirely biomass-derived, but is usually 1 to 99 mol %, preferably 5 to 95 mol %, more preferably 15 to 85 mol %, and even more preferably 35 to 65 mol %. As the proportion of biomass-derived ethylene in the ethylene structural units increases, the biobased content increases, which tends to reduce the environmental impact.

[0028] The proportion of fossil fuel-derived ethylene in the ethylene structural units of the biomass EVOH resin is usually 99 mol % or less, preferably 75 mol % or less, more preferably 55 mol % or less, even more preferably 30 mol % or less, and particularly preferably 10 mol % or less. The biomass EVOH resin does not necessarily contain fossil fuel-derived ethylene in the ethylene structural units.

[0029] Vinyl acetate is typically used as the vinyl ester used in the production of the biomass EVOH resin because of its availability on the market and the efficiency of impurity removal during production. Examples of vinyl esters other than vinyl acetate include aliphatic vinyl esters such as vinyl formate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, and vinyl versatate, and aromatic vinyl esters such as vinyl benzoate. Aliphatic vinyl esters having typically 3 to 20 carbon atoms, preferably 4 to 10 carbon atoms, and particularly preferably 4 to 7 carbon atoms, can be used. These can be used alone or in combination of two or more.

[0030] The vinyl ester may be derived from biomass or fossil fuel, but is preferably derived from biomass.

[0031] The biomass-derived vinyl ester can be obtained, for example, in the case of vinyl acetate, by a general industrial method of reacting ethylene with acetic acid using a palladium catalyst, etc. Alternatively, the biomass-derived vinyl ester may be produced using a biomass-derived carboxylic acid.

[0032] The proportion of biomass-derived vinyl ester in the vinyl alcohol structural units (vinyl ester structural units) of the biomass EVOH resin is usually 1 to 99 mol %, preferably 5 to 95 mol %, more preferably 15 to 85 mol %, even more preferably 25 to 75 mol %, and particularly preferably 35 to 65 mol %. As the proportion of biomass-derived vinyl ester in the vinyl alcohol structural units increases, the biobased content increases, which tends to reduce the environmental impact.

[0033] The proportion of fossil fuel-derived vinyl esters in the vinyl alcohol structural units (vinyl ester structural units) of the biomass EVOH resin is usually 99 mol % or less, preferably 75 mol % or less, more preferably 55 mol % or less, even more preferably 30 mol % or less, and particularly preferably 10 mol % or less. The biomass EVOH resin does not necessarily contain petroleum-derived vinyl esters in the vinyl alcohol structural units.

[0034] The biomass EVOH resin may further contain structural units derived from the comonomers shown below (for example, 10 mol % or less of the biomass EVOH resin) within the range that does not impair the effects of the present invention.Examples of the comonomer include olefins such as propylene, 1-butene, and isobutene; hydroxy group-containing α-olefins such as 3-butene-1-ol, 3-butene-1,2-diol, 4-pentene-1-ol, and 5-hexene-1,2-diol, and derivatives thereof such as esters and acylation products; hydroxyalkylvinylidenes such as 2-methylenepropane-1,3-diol and 3-methylenepentane-1,5-diol; 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, and 1,3-dibutyl hydroxyalkylvinylidene diacetates such as methyloxy-2-methylenepropane; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, (anhydrous) phthalic acid, (anhydrous) maleic acid, (anhydrous) itaconic acid, or their salts or mono- or di-alkyl esters in which the alkyl group has 1 to 18 carbon atoms; acrylamide, N-alkylacrylamide in which the alkyl group has 1 to 18 carbon atoms, N,N-dimethylacrylamide, 2-acrylamidopropanesulfonic acid or its salts, acrylamidopropyldimethylamine or its acid salts or its quaternary salts. acrylamides such as methacrylamide, N-alkylmethacrylamides in which the alkyl group has 1 to 18 carbon atoms, N,N-dimethylmethacrylamide, 2-methacrylamidopropanesulfonic acid or a salt thereof, methacrylamidepropyldimethylamine or an acid salt or a quaternary salt thereof; N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, and N-vinylacetamide; vinyl cyanides such as acrylonitrile and methacrylonitrile; alkyl vinyl ethers in which the alkyl group has 1 to 18 carbon atoms, hydrochloric acid vinyl ethers such as alkoxyalkyl vinyl ether and alkoxyalkyl vinyl ether; halogenated vinyl compounds such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride and vinyl bromide; vinyl silanes such as trimethoxyvinylsilane; halogenated allyl compounds such as allyl acetate and allyl chloride; allyl alcohols such as allyl alcohol and dimethoxyallyl alcohol; and comonomers such as trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride and acrylamido-2-methylpropanesulfonic acid.These may be used alone or in combination of two or more.

[0035] Among these, hydroxy group-containing α-olefins are preferred, with 3-butene-1,2-diol and 5-hexene-1,2-diol being particularly preferred. When the hydroxy group-containing α-olefins are copolymerized, the resulting EVOH resin has primary hydroxyl groups in the side chains. Such biomass EVOH resins having primary hydroxyl groups in the side chains, particularly biomass EVOH resins having a 1,2-diol structure in the side chains, are preferred because they exhibit good secondary moldability while maintaining gas barrier properties.

[0036] When the biomass EVOH resin has a primary hydroxyl group in a side chain, the content of structural units derived from hydroxy group-containing α-olefins is usually 0.1 to 20 mol %, preferably 0.5 to 15 mol %, and particularly preferably 1 to 10 mol % of the biomass EVOH resin.

[0037] The biomass EVOH resin is obtained by saponifying an ethylene-vinyl ester copolymer in which at least a portion of the ethylene and / or vinyl ester is derived from biomass. The polymerization method for copolymerizing ethylene and vinyl ester can be any known polymerization method, such as solution polymerization, suspension polymerization, or emulsion polymerization, with solution polymerization being preferred.

[0038] Examples of the polymerization solvent used in the solution polymerization include lower alcohols such as methanol, ethanol, propanol, and butanol, and ketones such as acetone and methyl ethyl ketone. These may be used alone or in combination of two or more. Among these, methanol is preferred.

[0039] The amount of the polymerization solvent used may be appropriately selected in accordance with the degree of polymerization of the target copolymer, taking into consideration the chain transfer constant of the polymerization solvent. For example, when the polymerization solvent is methanol, the amount is selected from the range of S (polymerization solvent) / M (monomer)=0.01 to 10 (mass ratio), preferably about 0.05 to 7 (mass ratio).

[0040] Examples of the polymerization catalyst used in the solution polymerization include radical polymerization catalysts and low-temperature active radical polymerization catalysts. These polymerization catalysts may be used alone or in combination of two or more. The low-temperature active radical polymerization catalyst refers to an organic compound having a half-life of 10 to 300 minutes at 60°C.

[0041] Examples of the radical polymerization catalyst include azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide, lauryl peroxide, etc. Examples of the low-temperature active radical polymerization catalyst include peroxyesters such as t-butylperoxyneodecanoate, t-butylperoxypivalate, α,α'-bis(neodecanoylperoxy)diisopropylbenzene, cumylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, t-hexylperoxyneodecanoate, and t-hexylperoxypivalate; di-n-propylperoxydicarbonate, di-iso-propylperoxydicarbonate, di-sec-butylperoxydicarbonate, bis(4-methyl-1,2-dimethyl-2,3-diphenylmethane); peroxydicarbonates such as di(2-t-butylcyclohexyl)peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate, di(2-ethylhexyl)peroxydicarbonate, dimethoxybutyl peroxydicarbonate, and di(3-methyl-3-methoxybutylperoxy)dicarbonate; organic peroxides such as diacyl peroxides such as 3,3,5-trimethylhexanoyl peroxide, diisobutyryl peroxide, and lauroyl peroxide; and azo compounds such as 2,2'-azobis-(2,4-dimethylvaleronitrile) and 2,2'-azobis-(4-methoxy-2,4-dimethylvaleronitrile).

[0042] The amount of the polymerization catalyst used varies depending on the type and cannot be generally determined, but is selected as appropriate depending on the polymerization rate. For example, when azobisisobutyronitrile or acetyl peroxide is used, the amount is preferably 0.001 to 0.2 parts by mass, more preferably 0.005 to 0.1 parts by mass, per 100 parts by mass of the vinyl ester.

[0043] As a method for introducing ethylene into the copolymer, ordinary pressurized ethylene polymerization may be carried out, and the amount of ethylene introduced can be controlled by the pressure of ethylene. Although it depends on the intended content of ethylene structural units and cannot be generally determined, it is usually preferable to select the pressure from the range of 2 to 8 MPa.

[0044] The reaction temperature of the solution polymerization cannot be generally determined depending on the polymerization solvent and pressure used, but is usually below the boiling point of the polymerization solvent, preferably 40 to 80° C., particularly preferably 55 to 80° C. When the temperature is below the upper limit, polymerization control becomes easy, and when the temperature is above the lower limit, the polymerization time tends to be shortened.

[0045] When the solution polymerization is a batch system, the polymerization time is usually 4 to 10 hours, preferably 6 to 9 hours. When the polymerization time is equal to or less than the upper limit, productivity tends to be excellent, and when the polymerization time is equal to or greater than the lower limit, polymerization control tends to be easy. When the solution polymerization is a continuous system, the average residence time in the polymerization vessel is preferably 2 to 8 hours, more preferably 2 to 6 hours. When the residence time is equal to or less than the upper limit, productivity tends to be excellent, and when the residence time is equal to or greater than the lower limit, polymerization control tends to be easy.

[0046] The polymerization rate in the solution polymerization is set as high as possible within the range where polymerization control is possible from the viewpoint of productivity, and is preferably 30 to 60%. When the polymerization rate is equal to or less than the upper limit, polymerization control becomes easy, and when the polymerization rate is equal to or more than the lower limit, unpolymerized vinyl ester tends to be reduced.

[0047] The ethylene-vinyl ester copolymer thus obtained can be saponified to obtain a biomass EVOH resin. The saponification is carried out using a saponification catalyst while the ethylene-vinyl ester copolymer thus obtained is dissolved in alcohol or aqueous alcohol.

[0048] Examples of the alcohol include lower alcohols having 1 to 5 carbon atoms, such as methanol, ethanol, and propanol. These may be used alone or in combination of two or more. Of these, methanol is preferred.

[0049] The concentration of the ethylene-vinyl ester copolymer in the alcohol or water-containing alcohol is appropriately selected depending on the viscosity, and is usually 5 to 60% by mass.

[0050] Examples of the saponification catalyst include alkali catalysts such as hydroxides and alcoholates of alkali metals, such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, potassium methylate, and potassium ethylate; and acid catalysts such as sulfuric acid, hydrochloric acid, nitric acid, metasulfonic acid, zeolite, and cation exchange resins. Among these, alkali catalysts such as hydroxides and alcoholates of alkali metals are preferred.

[0051] The temperature at which the saponification is carried out is not limited, but is preferably 20 to 140° C., and the saponification time is preferably 1 to 5 hours.

[0052] Furthermore, as the biomass EVOH resin, a biomass EVOH resin that has been "post-modified" by esterification, urethanization, acetalization, cyanoethylation, oxyalkylenation, or the like can also be used.

[0053] Furthermore, the biomass EVOH resin may be a mixture of biomass EVOH resins having different ethylene structural unit contents, saponification degrees, polymerization degrees, copolymerization components, and the like.

[0054] When the post-modified biomass EVOH resin is used, the modification rate is usually 15 mol % or less, and preferably 10 mol % or less. If the modification rate of the EVOH resin is too high, it tends to be prone to thermal degradation and the long-run properties tend to be reduced.

[0055] The biomass EVOH resin produced in this manner is mainly composed of ethylene structural units and vinyl alcohol structural units, at least a part of which are derived from biomass, and may optionally contain a small amount of vinyl ester structural units remaining without being saponified. When other comonomers are copolymerized, the resin further contains structural units derived from the comonomers.

[0056] The biomass EVOH resin is obtained as a biomass EVOH resin solution containing the polymerization solvent, and it is preferable to produce pellets from this biomass EVOH resin solution.

[0057] From the viewpoint of producing pellets, the content of the biomass EVOH resin in the biomass EVOH resin solution is preferably 10 to 50 mass %.

[0058] The method for producing pellets from the biomass EVOH resin solution is not particularly limited, and any known pellet production method may be used.

[0059] The obtained biomass EVOH resin pellets are preferably subjected to a chemical treatment such as immersion in an aqueous solution containing an agent such as an acid and / or its salt. Examples of the agent include formic acid, acetic acid, adipic acid, phosphoric acid, boric acid, or salts thereof, with acetic acid being preferred. After the chemical treatment in the aqueous solution containing the agent, the biomass EVOH resin pellets are preferably washed with water or the like and dried.

[0060] The drying method may be a known drying method, for example, drying using a fluidized hot air dryer or a stationary hot air dryer.

[0061] The bio-based content of the biomass EVOH resin obtained in this manner is usually 1 to 99.999%, preferably 20 to 86%, more preferably 38 to 76%, and particularly preferably 58 to 66%.

[0062] The content of ethylene structural units in the biomass EVOH resin is usually 20 to 60 mol%, preferably 25 to 50 mol%, and particularly preferably 25 to 35 mol%. When the content of ethylene structural units is equal to or less than the upper limit, the gas barrier property tends to be excellent, and when the content is equal to or more than the lower limit, the gas barrier property under high humidity conditions and melt moldability tend to be excellent.

[0063] The saponification degree of the biomass EVOH resin is usually 90 to 100 mol%, preferably 95 to 100 mol%, and more preferably 99 to 100 mol%. When the saponification degree is equal to or greater than the lower limit, the biomass EVOH resin tends to have excellent gas barrier properties, thermal stability, and moisture resistance.

[0064] The melt flow rate (MFR) (210°C, 2160 g load) of the biomass EVOH resin is usually 0.5 to 100 g / 10 min, preferably 1 to 50 g / 10 min, and more preferably 3 to 35 g / 10 min. When the MFR is equal to or less than the upper limit, the stability during film formation is excellent, and when the MFR is equal to or greater than the lower limit, the viscosity does not become too high and melt extrusion tends to be facilitated.

[0065] [Petroleum EVOH Resin] The petroleum EVOH resin can be obtained by producing it in the same manner as described above for the biomass EVOH resin, except that ethylene derived from a fossil fuel and vinyl ester derived from a fossil fuel are used.

[0066] As the fossil fuel-derived vinyl ester, any of the vinyl esters described above for the biomass EVOH resin that are derived from fossil fuels can be used, and among these, vinyl acetate is preferred.

[0067] The content of ethylene structural units in the petroleum EVOH resin is usually 20 to 60 mol%, preferably 25 to 50 mol%, and particularly preferably 25 to 35 mol%. When the content of ethylene structural units is equal to or less than the upper limit, the gas barrier property tends to be excellent, and when the content is equal to or more than the lower limit, the gas barrier property under high humidity conditions and melt moldability tend to be excellent.

[0068] The saponification degree of the vinyl ester component of the petroleum EVOH resin is usually 90 to 100 mol%, preferably 95 to 100 mol%, and particularly preferably 99 to 100 mol%. When the saponification degree is equal to or greater than the lower limit, the resin tends to have excellent gas barrier properties, thermal stability, and moisture resistance.

[0069] The melt flow rate (MFR) (210°C, 2160 g load) of the petroleum EVOH resin is usually 0.5 to 100 g / 10 min, preferably 1 to 50 g / 10 min, and particularly preferably 3 to 35 g / 10 min. When the MFR is equal to or less than the upper limit, the stability during film formation is excellent, and when the MFR is equal to or more than the lower limit, the viscosity does not become too high and melt extrusion tends to be easy.

[0070] The present EVOH resin is obtained by uniformly mixing the biomass EVOH resin and the petroleum EVOH resin so that the bio-based content falls within the above range.

[0071] The mixing method includes, for example, known methods such as dry blending, melt mixing, and solution mixing, and these can be used in any combination. Among these, the melt kneading method is preferred from the viewpoint of uniformity.

[0072] So far, the present EVOH resin production method (2) has been explained. However, in the method (1), the present EVOH resin can be obtained by selecting ethylene and vinyl ester so that the biobased content falls within the above-mentioned range during the production of the biomass EVOH resin.

[0073] The EVOH resin thus obtained has high resistance to thermal decomposition and high thermal stability.

[0074] <Resin Composition> A resin composition according to one embodiment of the present invention (hereinafter referred to as "the resin composition") contains the EVOH resin of the present invention, and may further contain a thermoplastic resin other than the EVOH resin, compounding agents, etc. Furthermore, the EVOH resin of the present invention is preferably the main component of the resin composition.

[0075] As the thermoplastic resin, known thermoplastic resins can be used, such as polyester resins, polystyrene resins, polyvinyl chloride resins, polycarbonate resins, ionomers, polyvinylidene chloride, polyester elastomers, polyurethane elastomers, chlorinated polyethylene, chlorinated polypropylene, etc. These can be used alone or in combination of two or more.

[0076] When the resin composition contains a thermoplastic resin, the content of the thermoplastic resin is usually 30% by mass or less, preferably 20% by mass or less, and particularly preferably 10% by mass or less of the resin composition. The lower limit is usually 0.1% by mass or more, and the content is, for example, 0.1 to 30% by mass.

[0077] Examples of the compounding agents include inorganic double salts (e.g., hydrotalcite, etc.), plasticizers (e.g., aliphatic polyhydric alcohols such as ethylene glycol, glycerin, and hexanediol), oxygen absorbers [e.g., inorganic oxygen absorbers such as aluminum powder and potassium sulfite; polyhydric phenols such as ascorbic acid, its fatty acid esters and metal salts, gallic acid, and hydroxyl group-containing phenol aldehyde resins; terpene compounds; blends of tertiary hydrogen-containing resins and transition metals (e.g., a combination of polypropylene and cobalt); blends of carbon-carbon unsaturated bond-containing resins and transition metals; Polymeric oxygen absorbers such as polymers containing hydroxyapatite (e.g., a combination of polybutadiene and cobalt), photooxidatively degradable resins (e.g., polyketones), anthraquinone polymers (e.g., polyvinyl anthraquinone), and combinations thereof to which photoinitiators (e.g., benzophenone), antioxidants other than those mentioned above, and deodorants (e.g., activated carbon) may also be added, heat stabilizers (boric acid, phosphoric acid), light stabilizers, ultraviolet absorbers, colorants, antistatic agents, surfactants (excluding those used as lubricants), antibacterial agents, antiblocking agents, fillers (e.g., aluminum, inorganic fillers), etc. These compounds may be used alone or in combination of two or more.

[0078] When the resin composition contains a compounding agent, the content of the compounding agent is usually 10% by mass or less, preferably 5% by mass or less, of the resin composition. The lower limit is usually 0.1% by mass or more, and the content ratio is, for example, 0.1 to 10% by mass.

[0079] The present resin composition can be produced, for example, by mixing the present EVOH resin with a thermoplastic resin, compounding ingredients, etc., by a known method, such as a dry blending method, a melt mixing method, a solution mixing method, an impregnation method, etc. These production methods can also be combined in any manner. The present EVOH resin can also be suitably used to improve the thermal stability of the present resin composition and to increase its resistance to thermal decomposition.

[0080] The present resin composition and the present EVOH resin thus obtained are usually used as raw materials for molding materials. The molding material may be in any form, for example, in a solid form such as pellets or powder, or in a liquid form, but is preferably in a solid form, and more preferably in the form of pellets.

[0081] The pellets may be, for example, spherical, oval, cylindrical, die-shaped, rectangular, or the like, but are typically oval or cylindrical. From the viewpoint of convenience when subsequently used as a molding material, the pellets typically have a minor axis of 1 to 10 mm, preferably 2 to 6 mm, and more preferably 2.5 to 5.5 mm, and a major axis of 1.5 to 30 mm, preferably 3 to 20 mm, and more preferably 3.5 to 10 mm, in the case of an oval shape. Furthermore, the diameter of the base of the cylindrical pellets is typically 1 to 6 mm, preferably 2 to 5 mm, and the length is typically 1 to 6 mm, preferably 2 to 5 mm. Furthermore, the length of each side of the die-shaped pellets is typically 1 to 6 mm, preferably 2 to 5 mm.

[0082] When the present EVOH resin or the present resin composition is solid, its water content is usually 0.01 to 0.5% by mass, preferably 0.05 to 0.35% by mass, and particularly preferably 0.1 to 0.3% by mass.

[0083] The moisture content is measured and calculated by the following method: The mass (W1) of the EVOH resin or resin composition before drying is weighed on an electronic balance, dried in a hot air dryer at 150°C for 5 hours, and then cooled in a desiccator for 30 minutes, after which the mass (W2) is weighed and calculated using the following formula: [Formula] Moisture content (mass%) = [(W1 - W2) / W1] x 100

[0084] When the present EVOH resin or the present resin composition is in the form of pellets, it is also preferable to adhere a known lubricant to the surface of the pellets in order to stabilize the feedability during melt molding. Examples of types of lubricants include higher fatty acids having 12 or more carbon atoms (e.g., lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, etc.), higher fatty acid esters (methyl esters, isopropyl esters, butyl esters, octyl esters of higher fatty acids, etc.), higher fatty acid amides (e.g., saturated higher fatty acid amides such as lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, etc.; unsaturated higher fatty acid amides such as oleic acid amide, erucic acid amide, etc.; bis-higher fatty acid amides such as ethylene bisstearic acid amide, ethylene bisoleic acid amide, ethylene biserucic acid amide, ethylene bislauric acid amide, etc.), low-molecular-weight polyolefins (e.g., low-molecular-weight polyethylene or low-molecular-weight polypropylene having a molecular weight of about 500 to 10,000, or acid-modified products thereof), higher alcohols having 6 or more carbon atoms, ester oligomers, and fluorinated ethylene resins. These compounds can be used alone or in combination of two or more. The content of such lubricants is usually 5% by mass or less, preferably 1% by mass or less, of the present EVOH resin or resin composition. The lower limit is usually 0% by mass, and the content is, for example, 0 to 5% by mass.

[0085] The present EVOH resin or the present resin composition, preferably pellets of the present EVOH resin or the present resin composition, is provided as a molding material for various molded articles. In particular, in the present invention, when the EVOH resin or the present resin composition is provided as a material for melt molding, the effects of the present invention tend to be more efficiently obtained, which is preferred.

[0086] Examples of the molded article include containers such as bags, cups, trays, tubes, and bottles, as well as lids. A drawing method is usually used to mold the containers and lids, and specific examples include vacuum molding, pressure molding, vacuum-pressure molding, and plug-assisted vacuum-pressure molding. Furthermore, blow molding is used to obtain tube- or bottle-shaped containers from parisons (hollow tubular preforms before blowing). Specific examples include extrusion blow molding (double-head, mold-moving, parison-shift, rotary, accumulator, horizontal parison, etc.), cold parison blow molding, injection blow molding, and biaxial stretch blow molding (extrusion-type cold parison biaxial stretch blow molding, injection-type cold parison biaxial stretch blow molding, injection-molding in-line biaxial stretch blow molding, etc.). The resulting molded article may be subjected to heat treatment, cooling treatment, rolling treatment, printing treatment, dry lamination treatment, solution or melt coating treatment, bag making, deep drawing, box processing, tube processing, split processing, etc. as required.

[0087] Examples of the molded article include a monolayer film molded from the present EVOH resin or the present resin composition, as well as a multilayer structure having a layer containing the present EVOH resin or the present resin composition.

[0088] <Multilayer Structure> A multilayer structure according to one embodiment of the present invention (hereinafter referred to as "the multilayer structure") includes a layer containing the present EVOH resin or the present resin composition. The layer containing the present EVOH resin or the present resin composition (hereinafter simply referred to as "the resin layer") can be laminated with another substrate containing a thermoplastic resin other than the present EVOH resin as a main component (hereinafter the resin used for the substrate may be abbreviated as "substrate resin") to impart additional strength, protect the present resin layer from the effects of moisture, etc., or impart other functions.

[0089] Examples of the base resin include polyethylene resins such as linear low-density polyethylene, low-density polyethylene, very low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-propylene (block and random) copolymers, and ethylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers; 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 side chain); and polyolefins containing unsaturated carboxylic acid or modified olefin resins such as unsaturated carboxylic acid-modified polyolefin resins graft-modified with its esters; ionomers; ethylene-vinyl acetate copolymers; ethylene-acrylic acid copolymers; ethylene-acrylic acid ester copolymers; polyester resins; polyamide resins (including copolymerized polyamides); polyvinyl chloride; polyvinylidene chloride; acrylic resins; polystyrene resins; vinyl ester resins; polyester elastomers; polyurethane elastomers; polystyrene elastomers; halogenated polyolefins such as chlorinated polyethylene and chlorinated polypropylene; aromatic or aliphatic polyketones; and the like. These may be used alone or in combination of two or more. The terms linear low-density polyethylene, low-density polyethylene, very low-density polyethylene, medium-density polyethylene, and high-density polyethylene are commonly used terms to represent types of polyethylene.

[0090] Of these, hydrophobic resins such as polyamide resins, polyolefin resins, polyester resins, and polystyrene resins are preferred, and more preferred are polyolefin resins such as polyethylene resins, polypropylene resins, polycyclic olefin resins, and unsaturated carboxylic acid-modified polyolefin resins thereof.

[0091] The layer structure of the present multilayer structure can be any combination, such as a / b, b / a / b, a / b / a, a1 / a2 / b, a / b1 / b2, b2 / b1 / a / b1 / b2, or b2 / b1 / a / b1 / a / b1 / b2, where a represents the present resin layer and b represents the base resin layer. Furthermore, when R represents a recycled layer containing the present EVOH resin or a mixture of the present resin composition and a thermoplastic resin other than the present EVOH resin, obtained by remelting and molding edges or defective products generated during the manufacturing process of the present multilayer structure, the layer structure can also be b / R / a, b / R / a / b, b / R / a / R / b, b / a / R / a / b, b / R / a / R / a / R / b, or b / R / a / R / a / R / b. The total number of layers in the present multilayer structure is usually 2 to 15, and preferably 3 to 10. In the above layer structure, it is also preferable to interpose an adhesive resin layer containing an adhesive resin between the respective layers, if necessary.

[0092] Known adhesive resins can be used, and may be selected appropriately depending on the type of thermoplastic resin used in the base resin layer "b". Representative examples include carboxyl group-containing modified polyolefin polymers obtained by chemically bonding an unsaturated carboxylic acid or its anhydride to a polyolefin resin via addition reaction, graft reaction, or the like. Examples of the carboxyl group-containing modified polyolefin polymers include maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, maleic anhydride-grafted ethylene-propylene (block and random) copolymers, maleic anhydride-grafted ethylene-ethyl acrylate copolymers, maleic anhydride-grafted ethylene-vinyl acetate copolymers, maleic anhydride-modified polycyclic olefin resins, and maleic anhydride-grafted polyolefin resins. These may be used alone or in combination of two or more.

[0093] In the present multilayer structure, when an adhesive resin layer is used between the present resin layer and the base resin layer, since the adhesive resin layers are located on both sides of the present resin layer, it is preferable to use an adhesive resin with excellent hydrophobicity.

[0094] The base resin and adhesive resin may contain conventionally known plasticizers, fillers, clays (montmorillonite, etc.), colorants, antioxidants, antistatic agents, lubricants, core materials, antiblocking agents, waxes, etc., within the range that does not impair the spirit of the present invention (for example, 30% by mass or less, preferably 10% by mass or less, based on the total mass of the resin). These may be used alone or in combination of two or more.

[0095] The lamination of the present resin layer and the substrate resin layer (including the case where an adhesive resin layer is interposed) can be performed by a known method. Examples include a method of melt-extrusion laminating the substrate resin onto a film, sheet, etc. containing the present EVOH resin or the present multilayer structure, a method of melt-extrusion laminating the present EVOH resin or the present resin composition onto the substrate resin layer, a method of co-extruding the present EVOH resin or the present resin composition with the substrate resin, a method of dry-laminating the present resin layer and the substrate resin layer using a known adhesive such as an organic titanium compound, an isocyanate compound, a polyester compound, or a polyurethane compound, and a method of applying a solution of the present EVOH resin or the present resin composition onto the substrate resin and then removing the solvent. Among these, from the viewpoints of cost and the environment, it is preferable to produce the present multilayer structure by including a step of melt-molding a layer containing the present resin layer, and specifically, a co-extrusion method is preferred. That is, it is preferable that the method of producing the present multilayer structure includes a step of co-extruding a resin composition.

[0096] The multilayer structure may be subjected to a (heat) stretching treatment as needed. The stretching treatment may be either uniaxial stretching or biaxial stretching, and in the case of biaxial stretching, it may be simultaneous stretching or sequential stretching. Furthermore, the stretching method may be a roll stretching method, tenter stretching method, tubular stretching method, stretch-blow method, vacuum pressure forming, or the like, whichever provides a higher stretch ratio. The stretching temperature is a temperature near the melting point of the multilayer structure, and is usually selected from the range of 40 to 170°C, preferably about 60 to 160°C. By keeping the stretching temperature at or below the upper limit, a stable stretched state can be maintained, while by keeping the stretching temperature at or above the lower limit, good stretchability tends to be obtained.

[0097] The stretched multilayer structure may be heat-set to provide dimensional stability. Heat-setting can be performed by known means, for example, by subjecting the stretched multilayer structure to heat treatment while maintaining tension, typically at 80 to 180°C, preferably 100 to 165°C, for typically 2 to 600 seconds.

[0098] When the stretched multilayer structure is to be used as a shrink film, the heat-shrinkability can be imparted by, for example, applying cold air to the stretched multilayer structure to cool and fix it, without carrying out the heat-setting process described above.

[0099] The thickness of the present multilayer structure (including a stretched structure), and further the thickness of the present resin layer, base resin layer, and adhesive resin layer constituting the multilayer structure, cannot be generally determined depending on the layer configuration, type of base resin, type of adhesive resin, intended use, packaging form, required physical properties, etc., but the thickness of the present multilayer structure (including a stretched structure) is usually 10 to 5,000 μm, preferably 30 to 3,000 μm, and particularly preferably 50 to 2,000 μm. The present resin layer is usually 1 to 500 μm, preferably 3 to 300 μm, and particularly preferably 5 to 200 μm; the base resin layer is usually 5 to 3,000 μm, preferably 10 to 2,000 μm, and particularly preferably 20 to 1,000 μm; and the adhesive resin layer is usually 0.5 to 250 μm, preferably 1 to 150 μm, and particularly preferably 3 to 100 μm.

[0100] Furthermore, the thickness ratio of the present resin layer to the base resin layer in the present multilayer structure (present resin layer / base resin layer), expressed as the ratio between the thickest layers when there are multiple layers of each type, is usually 1 / 99 to 50 / 50, preferably 5 / 95 to 45 / 55, and particularly preferably 10 / 90 to 40 / 60. Furthermore, the thickness ratio of the present resin layer to the adhesive resin layer in the present multilayer structure (present resin layer / adhesive resin layer), expressed as the ratio between the thickest layers when there are multiple layers of each type, is usually 10 / 90 to 99 / 1, preferably 20 / 80 to 95 / 5, and particularly preferably 50 / 50 to 90 / 10.

[0101] <Molded Article> The multilayer structure can also be used to obtain molded articles such as cup- or tray-shaped multilayer containers. That is, the multilayer structure can be molded to obtain a molded article. In this case, a drawing method is usually used, and specific examples include vacuum forming, pressure forming, vacuum pressure forming, and plug-assisted vacuum pressure forming. Furthermore, blow molding is used to obtain a tube- or bottle-shaped multilayer container (laminate structure) from a multilayer parison (a hollow tubular preform before blowing). Specific examples include extrusion blow molding (two-head type, mold-moving type, parison shift type, rotary type, accumulator type, horizontal parison type, etc.), cold parison blow molding, injection blow molding, and biaxial stretch blow molding (extrusion type cold parison biaxial stretch blow molding, injection type cold parison biaxial stretch blow molding, injection molding in-line biaxial stretch blow molding, etc.). The resulting molded article may be subjected to heat treatment, cooling treatment, rolling treatment, printing treatment, dry lamination treatment, solution or melt coating treatment, bag making, deep drawing, box processing, tube processing, split processing, etc. as required.

[0102] The present EVOH resin, a single layer film formed from the present resin composition, and molded articles such as bags, cups, trays, tubes, bottles, and other containers and lids made from the present multilayer structure are useful as packaging materials for a variety of items, including general foods, as well as seasonings such as mayonnaise and dressings, fermented foods such as miso, oily foods such as salad oil, beverages, cosmetics, and pharmaceuticals, and are particularly suitable for food packaging. That is, they are particularly suitable as food packaging formed from a multilayer structure.

[0103] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. In the examples, "parts" refers to parts by mass.

[0104] Prior to the Examples, biomass EVOH resin and petroleum EVOH resin were produced by the following methods.

[0105] [Production of Biomass EVOH Resin] A polymerization vessel was charged with 100 parts of vinyl acetate, the carbon of which was derived from biomass, and 16 parts of methanol. The system was first purged with nitriding gas, and then with ethylene, until the ethylene pressure reached 4.12 MPa. Under ethylene pressure, the temperature was raised to 67°C with stirring, and peroxyester was added at a rate of 0.05 parts / hour for 4 hours, allowing the reaction to proceed for a total of 6 hours to obtain an ethylene-vinyl acetate copolymer. To 100 parts of a methanol solution containing 50% by mass of the ethylene-vinyl acetate copolymer, 70 parts of a methanol solution containing 0.02 equivalents of sodium hydroxide relative to the remaining vinyl acetate groups in the copolymer was added, and the saponification reaction was carried out at 80°C for 80 minutes. Next, 100 parts of a 50% by weight methanol solution was azeotropically added to the EVOH resin methanol solution, and the methanol was distilled off until the resin concentration in the biomass EVOH resin methanol / water solution reached 40% by weight, resulting in a completely transparent, homogeneous methanol / water solution of EVOH resin. The resulting biomass EVOH resin methanol / water solution was then solidified into a thin plate and cut with a knife to obtain diced pellets with a side length of 3 mm. The resulting diced pellets were washed for 30 minutes with 250 parts of treated water containing 5 parts of acetic acid per 100 parts of pellets. The water was replaced and the washing was repeated twice. The resulting diced pellets were then dried at 118°C for 8 hours in a nitrogen gas stream with an oxygen concentration of 0.5% by volume or less to obtain pellets of biomass EVOH resin (ethylene structural unit content: 32 mol%, saponification degree: 99.7 mol%, biobased content: 64%).

[0106] [Production of Petroleum EVOH Resin] Pellets of petroleum EVOH resin (ethylene structural unit content: 32 mol%, saponification degree: 99.9 mol%, bio-based content: 0%) were obtained in the same manner as in the production of the biomass EVOH resin, except that vinyl acetate derived from fossil fuel was used.

[0107] <Examples 1 to 5, Comparative Examples 1 and 2> The obtained biomass EVOH resin and petroleum EVOH resin were kneaded under the following conditions using a Plastograph EC-plus (manufactured by Brabender) so that the biobased content would be the value shown in Table 1 below, to obtain the EVOH resins of Examples 1 to 3 and Comparative Examples 1 and 2. [Kneading conditions] Small kneader temperature: 210°C Screw rotation: counter-rotation Kneading time: 5 minutes

[0108] The following thermal stability evaluation was carried out using the obtained EVOH resins of Examples 1 to 5 and Comparative Examples 1 and 2. The results are shown in Table 1 below.

[0109] [Evaluation of Thermal Stability] Using a thermogravimetric analyzer (Pyris 1 TGA, manufactured by Perkin Elmer), 5 mg of EVOH resin was subjected to a nitrogen atmosphere at an air flow rate of 20 mL / min, a temperature rise rate of 10°C / min, and a temperature range of 30 to 550°C to calculate the decomposition peak temperature (°C). Note that the decomposition peak temperature is the temperature at which decomposition progresses most rapidly in thermal decomposition, and therefore, the higher the decomposition peak temperature, the slower the thermal decomposition and the better the thermal stability.

[0110]

[0111] The EVOH resins of Examples 1 to 5, which had a biobased content of 0.0001% or more but less than 3%, had higher peak decomposition temperatures and better thermal stability than the EVOH resin of Comparative Example 2, which had a biobased content of 3%. Furthermore, the EVOH resins of Examples 1 to 5 also had higher peak decomposition temperatures and better thermal stability than the petroleum-derived EVOH resin of Comparative Example 1, which had a biobased content of 0%. In particular, the EVOH resins of Examples 1 to 3, which had a biobased content within a specific lower range, had better thermal stability than the EVOH resins of Comparative Examples 1 and 2. When EVOH resins are continuously produced industrially over a long period of time, EVOH resins with lower peak decomposition temperatures are more susceptible to decomposition than EVOH resins with higher peak decomposition temperatures, resulting in a greater amount of thermal decomposition products. These thermal decomposition products have a significant impact on production efficiency and quality. Therefore, even a difference of just a few degrees in peak decomposition temperature can have a significant effect on thermal stability, and ultimately on production efficiency and quality.

[0112] Although the above examples show specific embodiments of the present invention, the examples are merely illustrative and should not be construed as limiting. Various modifications that are obvious to those skilled in the art are intended to fall within the scope of the present invention.

[0113] The present EVOH resin and the present resin composition have excellent thermal stability and are therefore useful as packaging materials for a variety of foods, as well as seasonings such as mayonnaise and dressings, fermented foods such as miso, oily foods such as salad oil, beverages, cosmetics, pharmaceuticals, and the like.

Claims

1. Ethylene-vinyl alcohol copolymer with a bio-based content of 0.0001% or more and less than 3%.

2. The ethylene-vinyl alcohol copolymer according to claim 1, wherein the bio-based content is 0.0005% or more and less than 3%.

3. The ethylene-vinyl alcohol copolymer according to claim 1, wherein the bio-based content is 0.0001% or more and 2% or less.

4. The ethylene-vinyl alcohol copolymer according to claim 1, wherein the bio-based content is 0.0001% or more and less than 1%.

5. The ethylene-vinyl alcohol copolymer according to claim 1, wherein the bio-based content is 0.0001% or more and 0.9% or less.

6. The ethylene-vinyl alcohol copolymer according to claim 1, wherein the bio-based content is 0.0001% or more and 0.7% or less.

7. The ethylene-vinyl alcohol copolymer according to any one of claims 1 to 6, wherein the content of ethylene structural units is 20 mol % or more and 60 mol % or less.

8. Use of the ethylene-vinyl alcohol copolymer according to any one of claims 1 to 6 for improving thermal stability.

9. Use of the ethylene-vinyl alcohol copolymer according to any one of claims 1 to 6 for increasing resistance to thermal decomposition.

10. A resin composition comprising the ethylene-vinyl alcohol copolymer according to any one of claims 1 to 6.

11. A molding material comprising the ethylene-vinyl alcohol copolymer according to any one of claims 1 to 6.

12. A multilayer structure comprising a layer formed from the molding material according to claim 11.

13. The multilayer structure of claim 12, further comprising an adhesive resin layer.

14. A molded article obtained by molding the multilayer structure according to claim 12.

15. A film comprising the multilayer structure of claim 12.

16. A food packaging product formed from the multilayer structure according to claim 12.

17. A method for producing the multilayer structure according to claim 12, comprising the step of co-extruding the resin composition.

18. A method for producing the molded article according to claim 14, comprising the step of molding a multilayer structure.

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