Ethylene-vinyl alcohol copolymer, and multilayer film and vapor-deposited multilayer film using same

Abstract

Provided is an ethylene-vinyl alcohol copolymer containing 20-60 mol% of an ethylene unit and having a saponification degree of 95 mol% or more. For an ethylene-vinyl acetate copolymer obtained by esterifying the ethylene-vinyl alcohol copolymer with acetic anhydride, the absolute value of the slope in the log M range of 5.00-5.75 is 0.130 or less in a curve obtained by plotting the ratio (UV / RI) of a signal intensity UV to a signal intensity RI against the logarithmic value (log M) of the molecular weight M, as obtained by gel permeation chromatography using a differential refractive index detector and an absorbance detector. The log M is a logarithmic value of the molecular weight M measured by the differential refractive index detector, the signal intensity RI is a signal intensity measured by the differential refractive index detector, and the signal intensity UV is a signal intensity measured by the absorbance detector (measurement wavelength: 210 nm).　According to the ethylene-vinyl alcohol copolymer, die build-up is less likely to occur during the formation of a multilayer film in which an EVOH layer is the outermost layer, and a vapor-deposited multilayer film having excellent barrier properties can be obtained even when film formation is continued for a long time.

Description

Ethylene-vinyl alcohol copolymer, and multilayer film and vapor-deposited multilayer film using the same

[0001] The present invention relates to an ethylene-vinyl alcohol copolymer, and a multilayer film and a vapor-deposited multilayer film using the copolymer.

[0002] Ethylene-vinyl alcohol copolymers (hereinafter, sometimes abbreviated as "EVOH") are excellent in transparency, gas barrier properties, aroma retention, solvent resistance, oil resistance, and the like, and by taking advantage of these properties, they are used in a wide range of applications, including various types of packaging such as food packaging, pharmaceutical packaging, industrial chemical packaging, and agricultural chemical packaging, as well as industrial films, agricultural films, floor heating pipes, and fuel containers.

[0003] In recent years, environmental and waste issues have led to a growing global demand for post-consumer recycling (hereinafter simply referred to as "recycling"), which involves recovering and recycling packaging materials consumed in the market. Recycling typically involves shredding recovered packaging materials, separating and cleaning them as necessary, and then melt-mixing them using an extruder. The resulting pellets are then used to manufacture various molded products. To obtain high-purity, high-quality recycled resins, packaging materials must be composed of as few materials as possible (mono-materialization). To achieve this, there is growing demand for barrier films primarily made of polyolefins, which are widely used as packaging materials. To obtain high-purity, high-quality recycled resins while also achieving extremely high gas barrier properties, a vapor-deposited stretched multilayer film has been proposed (Patent Document 1), in which an inorganic vapor-deposited layer is laminated on the surface of an EVOH layer of a polyolefin-based multilayer film, the outermost layer of which is EVOH.

[0004] WO2020 / 071513

[0005] However, as described in Patent Document 1, when a polyolefin-based multilayer film having an EVOH layer as the outermost layer is produced by a melt molding method, EVOH, which has a high affinity for metals, tends to remain inside the die, causing viscosity changes and degradation. In addition, the EVOH expands in volume and tends to come into contact with the die outlet, causing deposits (die buildup) at the die outlet. Therefore, cleaning is required to remove the die buildup. Furthermore, when film production is continued for a long period of time, the resulting vapor-deposited stretched multilayer film, in which an inorganic vapor-deposited layer is laminated on the surface of the EVOH layer, has the problem of insufficient gas barrier properties.

[0006] The present invention has been made to solve the above-mentioned problems, and has an object to provide an ethylene-vinyl alcohol copolymer that is less likely to cause die buildup during the production of a multilayer film in which an EVOH layer is the outermost layer, and that can provide a vapor-deposited multilayer film that has excellent barrier properties even when produced over a long period of time. It is also an object of the present invention to provide a multilayer film using this ethylene-vinyl alcohol copolymer. It is also an object of the present invention to provide a vapor-deposited multilayer film that includes this multilayer film and a vapor-deposited layer.

[0007] As a result of extensive research aimed at solving the above problems, the present inventors have found that by carrying out polymerization of EVOH under specified conditions, etc., so that ethylene units are uniformly contained in each molecular weight component of EVOH, it is possible to suppress the occurrence of die build-up during film production and to obtain a vapor-deposited multilayer film that has excellent barrier properties even when film production is continued for a long period of time.

[0008] That is, the present invention is as follows: [1] An EVOH having an ethylene unit content of 20 to 60 mol% and a degree of saponification of 95 mol% or more, wherein an ethylene-vinyl acetate copolymer obtained by esterifying the EVOH with acetic anhydride is subjected to gel permeation chromatography using a differential refractive index detector and an absorptiometry detector. In the curve obtained by plotting the ratio of signal intensity UV to signal intensity RI (UV / RI) against the logarithm of molecular weight M (logM), the absolute value of the slope in the logM range of 5.00 to 5.75 is 0.130 or less, where: logM is the logarithm of molecular weight M measured with the differential refractive index detector; signal intensity RI is the signal intensity measured with the differential refractive index detector; and signal intensity UV is the signal intensity measured with the absorptiometry detector (measurement wavelength 210 nm). [2] The EVOH according to [1], wherein the content of monomer units derived from a silane compound having an ethylenic double bond is 0.001 to 0.3 mol %. [3] The EVOH according to [1] or [2], wherein the content of ethylene units is 40 to 50 mol %. [4] A multilayer film comprising a barrier resin layer (A) containing the EVOH according to any one of [1] to [3] as a main component. [5] The multilayer film according to [4], wherein the barrier resin layer (A) is at least uniaxially stretched. [6] The multilayer film according to [4] or [5], wherein the barrier resin layer (A) has a thickness of 0.5 to 20 μm. [7] The multilayer film according to any one of [4] to [6], wherein the barrier resin layer (A) is the outermost layer. [8] The multilayer film according to any one of [4] to [7], wherein the barrier resin layer (A) and the other thermoplastic resin layer (B) are co-extruded films having a thickness of 10 to 100 μm. [9] The multilayer film according to [8], wherein the other thermoplastic resin layer (B) is mainly composed of a polyolefin.

[10] A vapor-deposited multilayer film having the multilayer film according to any one of [4] to [9] and a vapor-deposited layer.

[11] The vapor-deposited multilayer film according to

[10] , wherein the vapor-deposited layer is located on the exposed surface side of the barrier resin layer (A).

[0009] The EVOH of the present invention makes it possible to obtain a vapor-deposited multilayer film that is less susceptible to die buildup during the production of a multilayer film in which the EVOH layer is the outermost layer, and that has excellent barrier properties even when the film production is continued for a long period of time.

[0010] 1 is a curve obtained by plotting the ratio of signal intensity UV to signal intensity RI (UV / RI) obtained by GPC measurement of an ethylene-vinyl acetate copolymer obtained by esterifying EVOH in Example 1 with acetic anhydride against the logarithm of molecular weight M (logM).

[0011] The EVOH of the present invention has an ethylene unit content of 20 to 60 mol% and a degree of saponification of 95 mol% or more, and is an ethylene-vinyl acetate copolymer obtained by esterifying the EVOH with acetic anhydride. When gel permeation chromatography is performed using a differential refractive index detector and an absorptiometry detector to obtain an ethylene-vinyl acetate copolymer, the ratio of signal intensity UV to signal intensity RI (UV / RI) is plotted against the logarithm of molecular weight M (logM). The absolute value of the slope in the logM range of 5.00 to 5.75 is 0.130 or less. This EVOH is less likely to cause die buildup during the production of a multilayer film in which the EVOH layer is the outermost layer, and a vapor-deposited multilayer film with excellent barrier properties can be obtained, even when a vapor-deposited layer is formed on the surface of the EVOH layer of the multilayer film obtained after long-term film production.

[0012] The content of ethylene units in the EVOH is 20 to 60 mol% based on the total monomer units. When the content of ethylene units is 20 mol% or more, the melt moldability of the EVOH is improved. The content is preferably 22 mol% or more, more preferably 25 mol% or more, even more preferably 30 mol% or more, even more preferably 35 mol% or more, and particularly preferably 40 mol% or more. On the other hand, when the content of ethylene units is 60 mol% or less, the gas barrier properties of the EVOH are improved. The content is preferably 55 mol% or less, more preferably 52 mol% or less, and even more preferably 50 mol% or less. The content of ethylene units in the EVOH is １ It can be determined by H-NMR measurement.

[0013] The EVOH has a saponification degree of 95 mol% or more. A saponification degree of 95 mol% or more improves the gas barrier properties of the EVOH. The saponification degree is preferably 97 mol% or more, more preferably 98 mol% or more, even more preferably 99 mol% or more, even more preferably 99.5 mol% or more, particularly preferably 99.8 mol% or more, and in some cases 99.9 mol% or more is preferred. The saponification degree means the ratio of the number of vinyl alcohol units to the total number of vinyl alcohol units and vinyl ester units in the EVOH. The saponification degree of the EVOH is １ It can be determined by H-NMR measurement.

[0014] The EVOH preferably contains monomer units derived from a silane compound having an ethylenic double bond. When the EVOH contains monomer units derived from a silane compound having an ethylenic double bond, the content of the monomer units (hereinafter, the content of the monomer units derived from a silane compound having an ethylenic double bond may be referred to as the "silane-modified amount") is preferably 0.001 to 0.3 mol% relative to the total monomer units. The monomer units derived from the silane compound react with hydroxyl groups in the EVOH to form crosslinked structures. When the content is 0.001 mol% or more, the hydroxyl groups in the EVOH are consumed by forming crosslinked structures, thereby further reducing the occurrence of die buildup during film formation. Furthermore, the formation of crosslinked structures further improves the barrier properties of the vapor-deposited multilayer film obtained when film formation is continued for a long period of time. The content is more preferably 0.005 mol% or more, even more preferably 0.008 mol% or more, even more preferably 0.01 mol% or more, and particularly preferably 0.015 mol% or more. On the other hand, when the content is 0.3 mol% or less, die buildup during film formation is even less likely to occur. The content is more preferably 0.25 mol% or less, even more preferably 0.2 mol% or less, even more preferably 0.15 mol% or less, particularly preferably 0.1 mol% or less, and in some cases 0.07 mol% or less is preferred. The content of monomer units derived from a silane compound having an ethylenic double bond in the EVOH can be determined by ICP atomic emission spectroscopy, and specifically, the method described in the Examples is employed.

[0015] The silane compound is preferably at least one selected from the group consisting of vinyl silane compounds and allyl silane compounds, and examples thereof include vinyl trimethoxysilane, vinyl methyl dimethoxysilane, vinyl dimethyl methoxysilane, vinyl triethoxysilane, vinyl methyl diethoxysilane, vinyl dimethyl ethoxysilane, allyl trimethoxysilane, allyl methyl dimethoxysilane, allyl dimethyl methoxysilane, allyl triethoxysilane, allyl dimethyl ethoxysilane, vinyl tris(β-methoxyethoxy)silane, vinyl isobutyl dimethoxysilane, vinyl More preferably, the silane is at least one selected from the group consisting of ethyldimethoxysilane, vinylmethoxydibutoxysilane, vinyldimethoxybutoxysilane, vinyltributoxysilane, vinylmethoxydihexyloxysilane, vinyldimethoxyhexyloxysilane, vinyltrihexyloxysilane, vinylmethoxydioctyloxysilane, vinyldimethoxyoctyloxysilane, vinyltrioctyloxysilane, vinylmethoxydilauryloxysilane, vinyldimethoxylauryloxysilane, vinylmethoxydioleyloxysilane, and vinyldimethoxyoleyloxysilane. Of these, vinyltrimethoxysilane and allyltrimethoxysilane are even more preferred.

[0016] Using a differential refractive index detector and an absorptiometry detector, gel permeation chromatography (hereinafter sometimes abbreviated as GPC) of the ethylene-vinyl acetate copolymer obtained by esterifying the EVOH with acetic anhydride is performed. The ratio of signal intensity UV to signal intensity RI (UV / RI) obtained by the GPC is plotted against the logarithm of molecular weight M (logM). The absolute value of the slope in the logM range of 5.00 to 5.75 (M is 100,000 to 562,341) must be 0.130 or less. Here, logM is the logarithm of molecular weight M measured with the differential refractive index detector, signal intensity RI is the signal intensity measured with the differential refractive index detector, and signal intensity UV is the signal intensity measured with the absorptiometry detector (measurement wavelength 210 nm).

[0017] In the present invention, GPC measurement of the ethylene-vinyl acetate copolymer obtained by esterifying the EVOH with acetic anhydride is performed using a differential refractive index detector and an absorptiometric detector. Polymethyl methacrylate is used as the standard substance, and HFIP with sodium trifluoroacetate added to a concentration of 20 mM is used as the mobile phase. The flow rate is 0.2 mL / min and the temperature is 40°C. The sample used for GPC measurement is the EVOH reacetylated (ethylene-vinyl acetate copolymer). Specifically, the EVOH is esterified and GPC measurement is performed according to the method described in the Examples. FIG. 1 shows a portion of the curve (logM range of 5.00 to 5.75) obtained by GPC of the EVOH in Example 1 of the present application, which will be described later. The signal intensity RI is the signal intensity measured with the differential refractive index detector, and the signal intensity UV is the signal intensity measured with the absorptiometric detector (measurement wavelength 210 nm). Here, the absorption at 210 nm detected by the absorptiometric detector is derived from vinyl ester units, and the ratio of signal intensity UV to signal intensity RI (UV / RI) corresponds to the amount (mol%) of vinyl ester units in each molecular weight component. In FIG. 1 , the horizontal axis represents the logarithm (Log M) of the molecular weight M of each molecular weight component in the ethylene-vinyl acetate copolymer. The molecular weight M was calculated from the elution time detected by the differential refractive index detector using a calibration curve obtained using polymethyl methacrylate as a standard substance. The curve is obtained by plotting the ratio of signal intensity UV to signal intensity RI (UV / RI) against the logarithm (Log M) of the molecular weight M.

[0018] The absolute value of the slope of the curve thus obtained in the logM range of 5.00 to 5.75 must be 0.130 or less. Here, the slope is the slope of a straight line obtained by linearly approximating the curve in the logM range of 5.00 to 5.75, and is specifically determined by the method described in the Examples. The more uniform the content (mol %) of vinyl ester units in each molecular weight component in the ethylene-vinyl acetate copolymer, the smaller the absolute value of the slope of the curve. A uniform content (mol %) of vinyl ester units in each molecular weight component in the ethylene-vinyl acetate copolymer means that the content of ethylene units in each molecular weight component in the EVOH before esterification is uniform. When the absolute value of the slope of the curve is 0.130 or less, die buildup is further suppressed during film formation, and the barrier properties of the vapor-deposited multilayer film obtained when film formation is continued for a long period of time are further improved. Furthermore, the stretchability of the obtained film is also improved. The absolute value of the slope is preferably 0.1 or less, more preferably 0.05 or less, even more preferably 0.02 or less, particularly preferably 0.01 or less, and may be 0.008 or less.

[0019] The MFR (190°C, under a load of 2.16 kg) of the EVOH measured in accordance with JIS K7210 (2014) is preferably 0.2 to 20 g / 10 min. The MFR of the EVOH is more preferably 0.5 g / 10 min or more, and even more preferably 0.8 g / 10 min or more. On the other hand, the MFR of the EVOH is more preferably 15 g / 10 min or less, even more preferably 10 g / 10 min or less, even more preferably 7 g / 10 min or less, and particularly preferably 3 g / 10 min or less.

[0020] The method for producing the EVOH is not particularly limited, but a preferred method involves reacting ethylene, a vinyl ester, and, if necessary, the silane compound having an ethylenic double bond and other monomers described below to obtain an ethylene-vinyl ester copolymer, and then saponifying the ethylene-vinyl ester copolymer. The production method will be described in detail below.

[0021] (Polymerization Step) In the polymerization step, ethylene, a vinyl ester, and, if necessary, the silane compound having an ethylenic double bond, and other monomers described below are reacted (copolymerized) to obtain an ethylene-vinyl ester copolymer. The method for copolymerizing ethylene, vinyl ester, and the like may be any of solution polymerization, suspension polymerization, emulsion polymerization, and bulk polymerization. Furthermore, either a continuous method or a batch method may be used, but a solution polymerization method in which polymerization is performed in a solvent is preferred. Hereinafter, this method will be described.

[0022] The solvent used is preferably an alcohol having a boiling point of 100°C or less, from the viewpoints of solubility of the ethylene-vinyl ester copolymer and EVOH, ease of handling, and ability to efficiently replace alcohol with water. The boiling point is more preferably 80°C or less, and even more preferably 70°C or less. Examples of alcohols having a boiling point of 100°C or less include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, and t-butyl alcohol, with methanol being particularly preferred.

[0023] Examples of initiators that can be used in the polymerization include azonitrile initiators such as 2,2-azobisisobutyronitrile, 2,2-azobis-(2,4-dimethylvaleronitrile), 2,2-azobis-(4-methoxy-2,4-dimethylvaleronitrile), and 2,2-azobis-(2-cyclopropylpropionitrile), and organic peroxide initiators such as isobutyryl peroxide, cumyl peroxy neodecanoate, diisopropyl peroxycarbonate, di-n-propyl peroxydicarbonate, t-butyl peroxy neodecanoate, lauroyl peroxide, benzoyl peroxide, and t-butyl hydroperoxide.

[0024] Examples of vinyl esters include fatty acid vinyl esters such as vinyl acetate, vinyl propionate, and vinyl pivalate, with vinyl acetate being preferred. In addition to vinyl esters, ethylene, and silane compounds having an ethylenic double bond, monomers copolymerizable therewith, for example, α-olefins such as propylene, butylene, isobutylene, pentene, hexene, α-octene, and α-dodecene; 3-acyloxy-1-propene, 3-acyloxy-1-butene, 4-acyloxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4-acyloxy-2-methyl-1-butene, 4-acyloxy-3-methyl-1-butene, 3,4-diacyloxy-2-methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, 4,5-diacyloxy-1-pentene, 4-acyloxy-1-hexene, It is also possible to carry out polymerization in the presence of small amounts of alkenes having an ester group such as acene, 5-acyloxy-1-hexene, 6-acyloxy-1-hexene, 5,6-diacyloxy-1-hexene, and 1,3-diacetoxy-2-methylenepropane; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, and itaconic acid, and their anhydrides, salts, and mono- or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallylsulfonic acid, or salts thereof; alkyl vinyl ethers; vinyl ketones; N-vinylpyrrolidone; vinyl chloride; vinylidene chloride, etc. The content of other monomer units in the EVOH other than vinyl alcohol, vinyl ester, ethylene, and silane compounds having an ethylenic double bond is preferably 5 mol % or less, and in some cases, 3 mol % or less, 1 mol % or less, or 0.1 mol % or less is preferred. The EVOH may not contain the other monomer units.

[0025] The polymerization conditions are preferably as follows: Temperature: preferably 20 to 90°C, more preferably 40 to 70°C. Time (average residence time in the case of a continuous polymerization system): preferably 2 to 15 hours, more preferably 3 to 11 hours. Conversion rate: preferably 10 to 90%, more preferably 30 to 80%, based on the vinyl ester charged. Resin content in the solution after polymerization: preferably 5 to 85% by mass, more preferably 20 to 70% by mass.

[0026] The shape of the polymerization vessel used for polymerization is not particularly limited, but a roughly cylindrical vessel is usually used. In this case, the stirring blade is placed in the roughly cylindrical vessel so that the rotation axis of the vessel coincides with the rotation axis of the stirring blade. The stirring blade diameter d (m) is usually 0.01 to 3 m. In order to further uniformly distribute the ethylene unit content in each molecular weight component in the EVOH, the blade tip peripheral speed is preferably 1.0 to 7.0 m / s. The ratio (d / D) of the stirring blade diameter d (m) to the inner diameter D (m) of the vessel is not particularly limited and may be adjusted appropriately depending on the vessel used, but is usually 0.4 to 0.9. The capacity of the polymerization vessel is not particularly limited, but is usually 0.005 to 200 kL.

[0027] In the saponification step, the ethylene-vinyl ester copolymer is saponified in methanol, and the solvent is then replaced to obtain the EVOH hydrous product having a moisture content of 10 to 75% by mass. Specifically, the process can be carried out as follows. An alkali catalyst is added to the ethylene-vinyl ester copolymer solution from which unreacted vinyl ester has been removed, and the vinyl ester component in the copolymer is saponified. The saponification method can be either continuous or batchwise. Examples of alkali catalysts that can be used include sodium hydroxide, potassium hydroxide, and alkali metal alcoholates. For example, the saponification conditions are as follows: Concentration of ethylene-vinyl ester copolymer in the solution: 10 to 50% by mass; Reaction temperature: 30 to 150°C; Amount of catalyst used: 0.005 to 0.6 moles per mole of vinyl ester; Time (average residence time in the case of a continuous process): 10 minutes to 6 hours

[0028] In general, when saponification is carried out in a continuous system, methyl acetate produced by saponification can be removed more efficiently, and therefore a resin with a high degree of saponification can be obtained with a smaller amount of catalyst than in a batch system. Furthermore, in the case of a continuous system, saponification must be carried out at a higher temperature to prevent the precipitation of EVOH produced by saponification. Therefore, in a continuous system, it is preferable to set the reaction temperature and catalyst amount within the following ranges: Reaction temperature: 70 to 150°C Amount of catalyst used: 0.005 to 0.1 mole per mole of vinyl ester

[0029] As described above, a water-containing EVOH product is obtained by replacing the solvent in a solution containing the saponified ethylene-vinyl ester copolymer obtained by saponifying the ethylene-vinyl ester copolymer. Examples of the method for this include the following. Water is added to the solution containing the saponified ethylene-vinyl ester copolymer while stirring it at 40 to 90°C, and methanol is distilled out of the reaction vessel to precipitate the saponified product. The precipitated saponified product is washed as necessary, and then dried at 50 to 90°C for 1 to 30 hours to obtain a crude dried product of the saponified product. The crude dried product is dissolved in a mixed liquid containing water and methanol [water / methanol mass ratio: 0 / 100 to 70 / 30], and the resulting solution is extruded from a tube into a poor solvent [for example, a mixed liquid containing water, water, and methanol in a water / methanol mass ratio: 100 / 0 to 80 / 20] cooled to -10 to 10°C to precipitate in the form of strands. The strands are cut into pellets with a strand cutter and then washed by immersion in water, an aqueous acetic acid solution, or the like, to obtain pellets of a hydrous EVOH. The moisture content of the hydrous EVOH is usually 10 to 75% by mass.

[0030] The EVOH may contain additives as long as the effects of the present invention are not impaired. The method for incorporating the additives into the EVOH is not particularly limited, and examples thereof include immersing the EVOH hydrous material in an aqueous solution or aqueous dispersion in which the additives are dissolved or dispersed. Examples of the additives include boron compounds, carboxylic acids, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts, with boron compounds, carboxylic acids, and phosphoric acid compounds being preferred. The content of the additives in the EVOH is preferably 30% by mass or less, more preferably 5% by mass or less, even more preferably 2% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0.5% by mass or less.

[0031] Examples of boron compounds include boric acid, boric acid esters, borate salts, and boron hydrides. ３ BO ３ Examples of suitable boron compounds include boric acids such as metaboric acid and tetraboric acid; boric acid esters such as trimethyl borate and triethyl borate; alkali metal or alkaline earth metal salts of the boric acids, and boric acid salts such as borax. Among these, orthoboric acid is preferred. When the EVOH contains a boron compound, the content is preferably 20 to 2,000 ppm in terms of elemental boron. This allows the boron compound to react with hydroxyl groups in the EVOH to form a crosslinked structure. Hydroxyl groups in the EVOH are consumed by forming the crosslinked structure, further reducing the likelihood of die buildup during film formation. Furthermore, the formation of the crosslinked structure further improves the barrier properties of the vapor-deposited multilayer film obtained when film formation is continued for a long period of time. The content is more preferably 70 ppm or more, and even more preferably 100 ppm or more. On the other hand, the content is more preferably 350 ppm or less, and may be 300 ppm or less. In this specification, "ppm" means "ppm by mass."

[0032] Examples of the carboxylic acid include acetic acid, lactic acid, oxalic acid, succinic acid, benzoic acid, and citric acid. It is also preferable that the carboxylic acid has four or fewer carbon atoms. Among these, acetic acid is preferred from the standpoints of cost, availability, and the like. When the EVOH contains a carboxylic acid, the content is preferably 50 to 800 ppm. The carboxylic acid content is more preferably 100 ppm or more. The carboxylic acid content is more preferably 700 ppm or less, and even more preferably 500 ppm or less.

[0033] Examples of the phosphate compound include various acids such as phosphoric acid and phosphorous acid, and salts thereof. The phosphate may be contained in the form of any of primary phosphate, secondary phosphate, and tertiary phosphate, and the cation species is not particularly limited, but alkali metal salts and alkaline earth metal salts are preferred. Among these, phosphoric acid is preferred as the phosphate compound. When the EVOH contains a phosphate compound, the content thereof is preferably 10 to 800 ppm. The content of the phosphate compound is more preferably 20 ppm or more. Furthermore, the content of the phosphate compound is more preferably 700 ppm or less, and even more preferably 500 ppm or less.

[0034] Examples of the alkali metal salt include aliphatic carboxylates, aromatic carboxylates, and phosphates. Examples include sodium acetate, potassium acetate, sodium phosphate, lithium phosphate, sodium stearate, potassium stearate, and the sodium salt of ethylenediaminetetraacetic acid. Of these, sodium acetate, potassium acetate, and sodium phosphate are preferred. When the EVOH contains an alkali metal salt, the content thereof is preferably 5 to 5,000 ppm, more preferably 20 to 1,000 ppm, and even more preferably 30 to 750 ppm, calculated as the alkali metal element.

[0035] Examples of the alkaline earth metal salt include magnesium salt, calcium salt, barium salt, and beryllium salt, with magnesium salt and calcium salt being particularly preferred. The anion species of the alkaline earth metal salt is not particularly limited, but acetate and phosphate are preferred. When the EVOH contains an alkaline earth metal salt, the content thereof is preferably 10 to 1,000 ppm, more preferably 20 to 500 ppm, calculated as the metal element.

[0036] The EVOH of the present invention is obtained by drying the EVOH hydrous product. The drying conditions are not particularly limited, but are usually at 40 to 150° C. for 3 to 15 hours.

[0037] A multilayer structure including a barrier resin layer (A) primarily composed of EVOH is a preferred embodiment of the present invention. Because EVOH has excellent gas barrier properties, multilayer structures having a barrier resin layer (A) primarily composed of EVOH are preferably used as packaging materials with excellent content preservation properties. Furthermore, because EVOH can be easily melt-mixed with polyolefin-based resins, packaging materials with excellent recyclability can be provided. In this specification, the term "main component" refers to the component with the highest content by mass. The content of the EVOH in the barrier resin layer (A) is typically 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, and may even be 95% by mass or more, 97% by mass or more, or 99% by mass or more. The barrier resin layer (A) may be composed essentially of the EVOH. Furthermore, the barrier resin layer (A) may contain an EVOH other than the EVOH. In this case, the total content of the EVOH and the EVOH other than the EVOH contained in the barrier resin layer (A) is usually 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, 99% by mass or more, or even substantially 100% by mass.

[0038] The barrier resin layer (A) may further contain a thermoplastic resin other than EVOH. Examples of the thermoplastic resin other than EVOH include various polyolefins (polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymers, copolymers of ethylene and an α-olefin having 4 or more carbon atoms, copolymers of polyolefins and maleic anhydride, ethylene-vinyl ester copolymers, ethylene-acrylic acid ester copolymers, and modified polyolefins obtained by graft-modifying these with unsaturated carboxylic acids or derivatives thereof), various polyamides (nylon 6, nylon 6 / 6, nylon 6 / 66 copolymer, nylon 11, nylon 12, polymetaxylylene adipamide, etc.), various polyesters (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate, and modified polyvinyl alcohol resins. The content of the other thermoplastic resin in the barrier resin layer (A) is less than 50% by mass, preferably 30% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. It may be 1% by mass or less, or the barrier resin layer (A) may be substantially free of the other thermoplastic resin.

[0039] It is also preferable that the multilayer structure has another thermoplastic resin layer (B) made of a thermoplastic resin other than EVOH. Such a multilayer structure has excellent gas barrier properties. The multilayer structure may further have a layer formed from a component other than resin, such as a layer formed from paper, a metal layer, or an inorganic vapor deposition layer. Examples of the multilayer structure include a multilayer film, a multilayer sheet, a multilayer pipe, and a multilayer fiber, with a multilayer film being preferred.

[0040] The layer structure of the multilayer structure is not particularly limited, and examples thereof include the barrier resin layer (A) as A, the adhesive resin layer as Ad, and the other thermoplastic resin layer (B), with " / " indicating direct lamination, such as B / A / B, A / Ad / B, B / Ad / A / Ad / B, A / Ad / B / Ad / A, and A / Ad / B / Ad / A / Ad / B / Ad / A. Each of these layers may be a single layer or multiple layers. The multilayer structure may also have a layer containing an EVOH other than the EVOH of the present invention.

[0041] Examples of thermoplastic resins other than EVOH contained in the other thermoplastic resin layer (B) include polyolefins such as linear low-density polyethylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, polypropylene, propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymer, polybutene, and polypentene; polyesters such as polyethylene terephthalate; polyester elastomers; polyamides such as nylon-6 and nylon-66; polystyrene; polyvinyl chloride, polyvinylidene chloride, acrylic resins, vinyl ester resins, polyurethane elastomers, polycarbonate, chlorinated polyethylene, and chlorinated polypropylene. Among these, it is preferable that the other thermoplastic resin layer (B) contains polyolefin as a main component. In this case, the content of polyolefin in the other thermoplastic resin layer (B) is usually 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, and may be 95% by mass or more, 97% by mass or more, or 99% by mass or more, and the other thermoplastic resin layer (B) may be composed essentially of polyolefin only.

[0042] The adhesive resin is not particularly limited as long as it has adhesive properties with the barrier resin layer (A) and other thermoplastic resin layers (B), but an adhesive resin containing a carboxylic acid-modified polyolefin is preferred. The carboxylic acid-modified polyolefin is preferably a modified olefin polymer containing a carboxyl group formed by chemically bonding an ethylenically unsaturated carboxylic acid, its ester, or its anhydride to an olefin polymer. Here, the term "olefin polymer" refers to polyolefins such as polyethylene, linear low-density polyethylene, polypropylene, and polybutene, as well as copolymers of olefins with other monomers. Among these, polypropylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, and ethylene-ethyl acrylate copolymer are preferred, with linear low-density polyethylene and ethylene-vinyl acetate copolymer being particularly preferred.

[0043] It is preferable that at least one of the outermost layers of the multilayer structure is a barrier resin layer (A). Conventionally, when EVOH is coextruded as the outermost layer of a multilayer structure, EVOH with high metal affinity tends to remain inside the die, causing viscosity changes and degradation. Furthermore, EVOH volumetric expansion at the die exit tends to cause contact with the die exit, resulting in the formation of deposits (die buildup) at the die exit, which has been problematic. Furthermore, prolonged film production has been problematic in that the gas barrier properties of the resulting vapor-deposited stretched multilayer film, in which an inorganic vapor-deposited layer is laminated on the surface of the EVOH layer, are insufficient. In contrast, the EVOH makes it difficult for die buildup to occur during film production of a multilayer film in which the barrier resin layer (A) is the outermost layer, and a vapor-deposited multilayer film with excellent barrier properties can be obtained even after prolonged film production. The outermost layer refers to a layer that is in contact with other layers of the multilayer structure on only one side. When a multilayer structure has an inner and outer surface, the outermost layer may be the layer on the outer surface (outermost layer) or the layer on the inner surface (innermost layer). The multilayer structure is preferably a multilayer film obtained by co-extrusion molding the EVOH and another thermoplastic resin. In this case, the outermost layer of the multilayer film is preferably a barrier resin layer (A). The multilayer structure may be obtained by laminating a layer composed of another component onto the barrier resin layer (A). Layer configurations having a barrier resin layer (A) as the outermost layer include A for the barrier resin layer (A), Ad for the layer composed of an adhesive resin, and B for the other thermoplastic resin layer (B), and examples of directly laminated layers represented by " / " include A / Ad / B, A / Ad / B / Ad / A, and A / Ad / B / Ad / A / Ad / B / Ad / A. In the case of a multilayer structure having a barrier resin layer (A) as the outermost layer, B is preferably a polyolefin layer from the viewpoint of improving recyclability.

[0044] In the multilayer structure, the thickness of the barrier resin layer (A) is preferably 0.5 to 20 μm. The thickness is more preferably 1 μm or more, even more preferably 1.5 μm or more, and particularly preferably 2 μm or more. On the other hand, the thickness is more preferably 10 μm or less, even more preferably 8 μm or less, and particularly preferably 5 μm or less. The total thickness of the multilayer structure is preferably 10 to 100 μm. Furthermore, the ratio of the thickness of the barrier resin layer (A) to the total thickness of all layers of the multilayer structure is preferably 25% or less, more preferably 20% or less, and even more preferably 15% or less.

[0045] The method for producing the multilayer structure is not particularly limited, and examples thereof include a method of melt-extruding other components onto a molded article (film, sheet, etc.) made of the EVOH, a method of co-extruding the EVOH with other thermoplastic resins, a method of coinjection molding the EVOH with other thermoplastic resins, and a method of laminating the barrier resin layer (A) and a layer made of other components using a known adhesive such as an organic titanium compound, an isocyanate compound, or a polyester-based compound.

[0046] The method for co-extruding the EVOH and the other thermoplastic resin is not particularly limited, and examples thereof include a multi-manifold confluence type T-die method, a feed block confluence type T-die method, and an inflation method. The multilayer structure is preferably a co-extruded film having a barrier resin layer (A) and another thermoplastic resin layer (B). The thickness of the co-extruded film is preferably 10 to 100 μm.

[0047] The multilayer structure has excellent thermoformability and can therefore be suitably used as a material for thermoforming of thermoformed containers and the like.

[0048] The multilayer structure may be in the form of a film or a sheet, and may be molded into various shapes. Methods for further molding a molded article using the film- or sheet-like multilayer structure include, for example, heat-stretch molding, vacuum molding, pressure molding, vacuum-pressure molding, and blow molding. The multilayer structure subjected to various secondary moldings may be a multilayer sheet. The multilayer structure can be used for packaging materials, containers, tubes, etc. The multilayer structure may be a non-stretched multilayer sheet or a stretched multilayer sheet.

[0049] The multilayer structure is preferably one that has been stretched at least uniaxially, and particularly preferably a multilayer film that has been stretched at least uniaxially. The stretching ratio may be 2 to 12 times, 3 to 10 times, or 4 to 8 times. Such multilayer structures that have been stretched at least uniaxially have excellent gas barrier properties, break resistance, etc., and are less susceptible to film surface defects and defects, making them suitable for use as packaging materials, etc. The multilayer structure can be stretched uniaxially or biaxially by a conventionally known method.

[0050] The multilayer structure can be molded by vacuum pressure molding to obtain a container. Vacuum pressure molding is a method in which the multilayer structure is heated and molded using a combination of vacuum and pressure. Containers molded from the multilayer structure by vacuum pressure molding can be produced simply and reliably, and are excellent in appearance, gas barrier properties, etc.

[0051] In the vacuum / pressure molding method, for example, a multilayer structure is heated to soften it and then molded into the shape of a mold. Examples of molding methods include methods using vacuum or compressed air, and optionally a plug, to mold the structure into the shape of a mold (straight method, drape method, air slip method, snapback method, plug assist method, etc.), and press molding. Various molding conditions, such as molding temperature, degree of vacuum, compressed air pressure, and molding speed, are appropriately set depending on the plug shape, mold shape, and properties of the raw material film and multilayer structure.

[0052] The molding temperature is not particularly limited, and may be any temperature at which the resin is softened sufficiently for molding. For example, when thermoforming a multilayer structure, it is desirable not to use a temperature so high that the multilayer structure melts due to heating or that the unevenness of the metal surface of the heater plate is transferred to the multilayer sheet, but also not to use a temperature so low that the shaping is insufficient. Specifically, the temperature of the multilayer structure is 50°C to 180°C, preferably 60°C to 160°C.

[0053] The multilayer structure is preferably a vapor-deposited multilayer film having the multilayer film and a vapor-deposited layer, and more preferably a vapor-deposited multilayer film in which the vapor-deposited layer is located on the exposed surface of the barrier resin layer (A). In this case, the vapor-deposited layer may be formed on the uniaxially or biaxially stretched multilayer film by the method described below. The vapor-deposited layer is preferably a layer formed by vapor deposition, and is preferably a layer formed by vapor deposition of an inorganic substance (inorganic vapor-deposited layer). The EVOH of the present invention has a high affinity with vapor-deposited layers, particularly vapor-deposited layers of aluminum or aluminum oxide, and therefore tends to exhibit good interlayer adhesion between the barrier resin layer (A) and the inorganic vapor-deposited layer.

[0054] The inorganic vapor-deposited layer used as the vapor-deposited layer of the vapor-deposited multilayer film is preferably either a metal vapor-deposited layer containing aluminum as a main component or an inorganic oxide vapor-deposited layer containing alumina or silica as a main component. While a metal vapor-deposited layer is preferred for imparting light-shielding properties, an inorganic oxide vapor-deposited layer is preferred from the viewpoints of visibility of the contents as a packaging material, microwave suitability, and suppression of gels and lumps when pulverized materials are melt-molded.

[0055] The metal vapor deposition layer is generally a layer containing aluminum as a main component. The aluminum atom content in the metal vapor deposition layer is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more. The inorganic oxide vapor deposition layer is a vapor deposition film of an inorganic oxide, such as an oxide of silicon, aluminum, magnesium, calcium, potassium, tin, sodium, boron, titanium, lead, zirconium, or yttrium, preferably alumina or silica. The average thickness of the vapor deposition layer is usually 10 to 120 nm, preferably 20 to 80 nm. The average thickness of the vapor deposition layer is the average value of thicknesses at any 10 points on the cross section of the vapor deposition layer measured using an electron microscope.

[0056] The inorganic vapor deposition layer can be formed by a known physical vapor deposition method or chemical vapor deposition method, such as vacuum vapor deposition, sputtering, ion plating, ion beam mixing, plasma CVD, laser CVD, MO-CVD, and thermal CVD. Of these, physical vapor deposition is preferred, and vacuum vapor deposition is particularly preferred.

[0057] The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples in any way.

[0058] Example 1 (1) Synthesis of Silane-Modified EVAc: A 250 L pressurized reactor equipped with a jacket, a stirrer, a nitrogen inlet, an ethylene inlet, and an initiator addition port was charged with 100 kg of vinyl acetate, 18 kg of methanol, and 0.04 kg of vinyltrimethoxysilane (hereinafter sometimes referred to as VMS). The temperature was raised to 60°C, and nitrogen bubbling was performed for 30 minutes to replace the atmosphere inside the reactor with nitrogen. Ethylene was then introduced so that the reactor pressure (ethylene pressure) was 6.2 MPa. After adjusting the temperature inside the reactor to 60°C, 36 g of 2,2'-azobis(2,4-dimethylvaleronitrile) ("V-65" manufactured by Wako Pure Chemical Industries, Ltd.) was added as an initiator as a methanol solution, and the mixture was stirred at a blade tip peripheral speed of 4.6 m / s to initiate polymerization. During the polymerization, the ethylene pressure was maintained at 6.2 MPa, and the polymerization temperature was maintained at 60°C. After 6 hours, when the conversion of vinyl acetate to polymerization reached 45%, the polymerization was stopped by cooling. The reaction vessel was opened to remove ethylene, and then nitrogen gas was bubbled through to completely remove ethylene. Next, unreacted vinyl acetate was removed under reduced pressure, and methanol was added to the modified ethylene-vinyl acetate copolymer in which structural units derived from VMS had been copolymerized (hereinafter, sometimes referred to as silane-modified EVAc) to prepare a 20% by mass methanol solution.

[0059] (2) Saponification of Silane-Modified EVAc A 20% by mass methanol solution of the silane-modified EVAc obtained in (1) was charged into a 500 L reactor equipped with a jacket, a stirrer, a nitrogen inlet, a reflux condenser, and a solution addition port. The solution was heated to 60°C while nitrogen was blown into it, and a 2 mol / L methanol solution of 0.5 mol of sodium hydroxide per mol of vinyl acetate units in the silane-modified EVAc was added. After the addition of the sodium hydroxide methanol solution was completed, the saponification reaction was allowed to proceed for 2 hours while maintaining the temperature in the system at 60°C and stirring. Thereafter, acetic acid was added to terminate the saponification reaction. Next, ion-exchanged water was added while heating and stirring at 60 to 80°C, and methanol was distilled out of the reactor, resulting in the precipitation of a modified EVOH in which structural units derived from VMS were copolymerized (hereinafter, sometimes referred to as "silane-modified EVOH"). The precipitated silane-modified EVOH was collected and pulverized in a mixer. The obtained silane-modified EVOH powder was poured into a 1 g / L aqueous acetic acid solution (bath ratio 20: 20 L of aqueous solution per 1 kg of powder) and washed with stirring for 2 hours. The powder was dewatered and then poured into a 1 g / L aqueous acetic acid solution (bath ratio 20) and washed with stirring for 2 hours. The dewatered powder was poured into ion-exchanged water (bath ratio 20), washed with stirring for 2 hours, and then drained. This procedure was repeated three times for purification. The powder was then immersed in an aqueous solution containing 0.5 g / L of acetic acid and 0.1 g / L of sodium acetate (bath ratio 10) with stirring for 4 hours, then drained, and dried at 60°C for 16 hours to obtain a crude dried silane-modified EVOH.

[0060] (3) Production of Silane-Modified EVOH Hydrous Pellets: The crude dried modified EVOH obtained in (2), water, and methanol were charged into an 80 L stirring tank equipped with a jacket, a stirrer, and a reflux condenser, and the mixture was heated to 80°C to dissolve. The resulting solution was extruded through a 4 mm diameter tube into a 90 / 10 water / methanol mixture cooled to 5°C to precipitate strands. The strands were cut into pellets with a strand cutter to obtain hydrous pellets of modified EVOH. The moisture content of the resulting hydrous pellets of silane-modified EVOH was measured and found to be 50% by mass. In the examples herein, the moisture content was calculated by measuring 10 g of the sample at 180°C for 18 minutes using a Mettler Halogen Moisture Analyzer "HR73."

[0061] (4) Production of Silane-Modified EVOH Pellets The hydrous modified EVOH pellets obtained in (3) above were placed in a 1 g / L aqueous acetic acid solution (bath ratio: 20), washed with stirring for 2 hours, and then deliquified. This procedure was repeated two more times. The hydrous pellets washed with the aqueous acetic acid solution and then deliquified were placed in ion-exchanged water (bath ratio: 20), washed with stirring for 2 hours, and then deliquified. This procedure was repeated three times for purification, yielding hydrous modified EVOH pellets from which the catalyst residue from the saponification reaction had been removed. The hydrous pellets were placed in an aqueous solution containing 0.5 g / L sodium acetate, 0.8 g / L acetic acid, and 0.005 g / L phosphoric acid (bath ratio: 20), immersed for 4 hours with periodic stirring, and then deliquified. The hydrous pellets were roughly dried by hot air drying at 80°C for 3 hours. Further drying at 110°C for 15 hours in a hot air dryer yielded silane-modified EVOH pellets. The water content of the obtained silane-modified EVOH pellets was 0.15% by mass. The obtained silane-modified EVOH pellets were measured and evaluated by the following methods.

[0062] [Ethylene unit content and degree of saponification] The obtained EVOH pellets were dissolved in deuterated dimethyl sulfoxide (DMSO-d6) containing tetramethylsilane (TMS) as an internal standard substance and trifluoroacetic acid as an additive, and analyzed by a 500 MHz １ Measurement was performed at 80°C using H-NMR (JEOL Ltd. "GX-500"), and the ethylene unit content and degree of saponification were determined from the peak intensity ratio of ethylene units, vinyl alcohol units, and vinyl ester units. The results are shown in Table 2.

[0063] [Content of Monomer Units Derived from Silane Compounds Having Ethylenic Double Bonds] 0.5 g of the EVOH pellets was placed in a Teflon (registered trademark) pressure vessel, and 5 mL of concentrated nitric acid was added thereto and decomposed at room temperature for 30 minutes. After decomposition, the vessel was capped and further decomposed by heating in a wet decomposition apparatus at 150°C for 10 minutes and then at 180°C for 5 minutes, followed by cooling to room temperature. This treated solution was transferred to a 50 mL measuring flask and made up to the desired volume with pure water. The silicon atom content in the silane-modified EVOH pellets was quantified by measuring this solution using a PerkinElmer ICP atomic emission spectrometer "Avio500," and the content of monomer units derived from silane compounds having ethylenic double bonds was calculated using this value. The results are shown in Table 2.

[0064] [GPC Measurement] 0.25 g of the EVOH pellets were placed in a screw tube, and 2.25 g of dimethyl sulfoxide was added. The mixture was then heated at 90°C for 1 hour to dissolve. After cooling to room temperature, 0.014 g of dimethylaminopyridine and 0.65 g of pyridine were added. 1.15 g of acetic anhydride was then added and stirred at room temperature for 1 hour. The resulting solution was added dropwise to 100 mL of ion-exchanged water, and the precipitate was filtered. The filter cake was placed in a screw tube, and 5 mL of tetrahydrofuran was added, followed by heating and stirring at 40°C for 1 hour. After dissolution, the mixture was cooled to room temperature and added dropwise to 100 mL of ion-exchanged water. The precipitate was filtered, and the resulting filter cake was vacuum-dried at 60°C for 16 hours. 0.01 g of the dried filter cake was placed in a screw tube, and 10 g of hexafluoroisopropanol (HFIP) was added, followed by heating and stirring at 40°C for 2 hours. The resulting solution was filtered using a PTFE filter (mesh opening: 0.45 μm) to obtain a filtrate. The resulting filtrate was subjected to GPC measurement of the ethylene-vinyl acetate copolymer obtained by esterifying EVOH using a Tosoh GPC system "HLC-8320GPC" at a flow rate of 0.2 mL / min and a temperature of 40°C, using polymethyl methacrylate as the standard substance and HFIP supplemented with sodium trifluoroacetate to a concentration of 20 mM as the mobile phase. The ratio (UV / RI) of the signal intensity RI measured with a spectrophotometer (measurement wavelength 210 nm) to the signal intensity RI measured with a refractive index detector was plotted against the logarithm of the molecular weight M (LogM). The molecular weight M was calculated from the elution time detected with a refractive index detector using a calibration curve obtained using polymethyl methacrylate as the standard substance. Figure 1 shows a portion of a curve (logM range of 5.00 to 5.75) obtained by GPC measurement of an ethylene-vinyl acetate copolymer, in which the signal intensity ratio (UV / RI) was plotted against the logarithm of the molecular weight M (LogM). A line obtained by linearly approximating the curve in the logM range of 5.00 to 5.75 was determined by the least squares method, and the slope of the line was taken as the slope of the curve (Figure 1, Table 2).

[0065] [Quantification of Sodium Ions, Phosphate, and Boron Compounds] 0.5 g of the EVOH pellets was placed in a Teflon (registered trademark) pressure vessel, and 5 mL of concentrated nitric acid was added and decomposed at room temperature for 30 minutes. After 30 minutes, the vessel was capped and heated at 150°C for 10 minutes and then at 180°C for 5 minutes using a wet decomposition apparatus (MWS-2, manufactured by Actac Corporation) for decomposition, followed by cooling to room temperature. This treated solution was transferred to a 50 mL volumetric flask (TPX (registered trademark)) and made up to the desired volume with purified water. The resulting solution was analyzed for contained metals using an ICP atomic emission spectrometer (OPTIMA 4300DV, manufactured by PerkinElmer), and the amount of sodium ions (sodium element), the amount of phosphoric acid in terms of phosphate radicals, and the content of boron compounds in terms of boron element were calculated. For this quantification, calibration curves prepared using commercially available standard solutions were used. The amount of sodium ions was 500 ppm, and the amount of phosphoric acid in terms of phosphate radicals was 25 ppm.

[0066] [Quantitative Determination of Acetic Acid] 20 g of the obtained EVOH pellets were added to 100 ml of ion-exchanged water and heated and extracted at 95° C. for 6 hours. The extract was neutralized with 1 / 50 N NaOH using phenolphthalein as an indicator to quantify the acetic acid content, which was found to be 20 ppm. The acetic acid content was calculated taking into account the phosphoric acid content.

[0067] [Stretchability] The obtained EVOH pellets were used as a material for the barrier resin layer (A) of a maleic anhydride-modified polypropylene "Admer (trademark) QF500" manufactured by Mitsui Chemicals, Inc. (MFR (230°C, 2.16 kg load) 3.0 g / 10 min, density 0.90 g / cm ３ The adhesive layer was made of polypropylene "Novatec™ PP EA7AD" (MFR (230°C, 2.16 kg load) 1.4 g / 10 min, density 0.90 g / cm) manufactured by Japan Polypropylene Corporation. ３) was used as the material for the other thermoplastic resin layer (B), and a multilayer film having a layer thickness and layer structure of (A) / adhesive layer / (B) = 36 μm / 36 μm / 648 μm was produced using a 300 mm wide three-layer coextrusion cast film-forming equipment, and the obtained film was cut into a size of 5.5 cm × 5.5 cm and subjected to simultaneous biaxial stretching at 80 ° C. using an Eto biaxial stretching machine to confirm the maximum stretching ratio that could be stretched without breaking. The film-forming conditions at this time are shown below. Extrusion temperature (°C) of barrier resin layer (A): feeding section / compression section / metering section / die = 170 / 220 / 220 / 220 Extrusion temperature (°C) of adhesive layer: feeding section / compression section / metering section / die = 170 / 220 / 220 / 220 Extrusion temperature (°C) of other thermoplastic resin layer (B): feeding section / compression section / metering section / die = 170 / 220 / 220 / 220 Chill roll temperature: 40°C Take-up speed: 1.5 m / min

[0068] [Die build-up] The obtained EVOH pellets were used as a material for the barrier resin layer (A) of a maleic anhydride-modified polypropylene "Admer (trademark) QF500" manufactured by Mitsui Chemicals, Inc. (MFR (230°C, 2.16 kg load) 3.0 g / 10 min, density 0.90 g / cm ３ The adhesive layer was made of polypropylene "Novatec™ PP EA7AD" (PP, MFR (230°C, 2.16 kg load) 1.4 g / 10 min, density 0.90 g / cm) manufactured by Japan Polypropylene Corporation. ３ ) was used as the material for the other thermoplastic resin layer (B), and a multilayer film having a layer thickness and layer structure of (A) / adhesive layer / (B) = 9 μm / 9 μm / 162 μm was produced using a three-layer co-extrusion cast film-forming equipment with a width of 300 mm. The die buildup (dye build-up) occurrence time was visually confirmed. The results are shown in Table 2. The film-forming conditions used here are as follows: Extrusion temperature (°C) of barrier resin layer (A): feed section / compression section / metering section / die = 170 / 220 / 220 / 220 Extrusion temperature (°C) of adhesive layer: feed section / compression section / metering section / die = 170 / 220 / 220 / 220 Extrusion temperature (°C) of other thermoplastic resin layer (B): feed section / compression section / metering section / die = 170 / 220 / 220 / 220

[0069] [Oxygen Permeability] Multilayer films were produced using the same method as in the die build-up evaluation, and samples were taken 0.5 hours and 12 hours after the start of film production. Each film was cut into a size of 5.5 cm x 5.5 cm and stretched 3 times in the MD direction at 160°C using an Eto biaxial stretching machine, and then stretched 3 times in the TD direction. The thickness of each layer in the stretched multilayer film is shown in Table 2. An aluminum vapor-deposited layer with an average thickness of 60 nm was laminated on the surface of the barrier resin layer (A) of the obtained biaxially stretched film by a known vacuum deposition method to produce a vapor-deposited multilayer film, and the oxygen permeability was measured. Specifically, an oxygen transmission rate measuring device ("MOCON OX-TRAN2 / 21" manufactured by Modern Control) was used to measure the oxygen transmission rate (cc / (m)) in accordance with JIS K 7126-2 (isobaric method; 2006) under the conditions of a temperature of 20°C, humidity of 65% RH on the oxygen supply side, humidity of 65% RH on the carrier gas side, oxygen pressure of 1 atmosphere, and carrier gas (nitrogen gas containing 2% by volume of hydrogen gas) pressure of 1 atmosphere, with the deposition surface on the oxygen supply side and the other on the carrier gas side. ２ The oxygen permeability of the vapor-deposited multilayer film obtained from a film sampled 0.5 hours after the start of film formation was designated the "oxygen permeability immediately after film formation," and the oxygen permeability of the vapor-deposited multilayer film obtained from a film sampled 12 hours after the start of film formation was designated the "oxygen permeability after long-run." The results are shown in Table 2.

[0070] Example 2: Hydrous EVOH pellets, from which catalyst residue from the saponification reaction had been removed, were obtained in the same manner as in Example 1, except that no VMS was added during EVAc synthesis and the blade tip peripheral speed was set to 1.5 m / s. The moisture content of the obtained hydrous EVOH pellets was measured and found to be 49% by mass. The pellets were placed in an aqueous boric acid solution (concentration: 0.15 g / L, bath ratio: 5), immersed for 6 hours with periodic stirring, and then dewatered. The obtained hydrous EVOH pellets were placed in an aqueous solution (bath ratio: 20) of sodium acetate (concentration: 0.5 g / L), acetic acid (concentration: 0.8 g / L), and phosphoric acid (concentration: 0.005 g / L), immersed for 4 hours with periodic stirring, and then dewatered. The pellets were roughly dried by hot air drying at 80°C for 3 hours. Further drying at 110°C for 15 hours in a hot air dryer yielded EVOH pellets. The resulting EVOH pellets had a water content of 0.12% by mass, a sodium ion content of 500 ppm, a phosphoric acid content converted to phosphate radicals of 25 ppm, and a boron compound content (converted to elemental boron) of 139 ppm. The resulting EVOH pellets were measured and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0071] [Examples 3 to 6, Comparative Example 1] Silane-modified EVOH pellets were obtained in the same manner as in Example 1, except that the amount of VMS added and the blade tip peripheral speed were changed as shown in Table 1. The obtained silane-modified EVOH pellets were subjected to various measurements and evaluations in the same manner as in Example 1. The results are shown in Table 2.

[0072] Examples 7 to 11, Comparative Example 2 Silane-modified EVOH pellets were obtained in the same manner as in Example 1, except that the amount of VMS added, the ethylene pressure, and the blade tip peripheral speed were changed as shown in Table 1. The ethylene unit content, degree of saponification, vinylsilane unit content, and GPC measurement, as well as stretchability evaluation, were carried out for the obtained silane-modified EVOH pellets in the same manner as in Example 1. In addition, the die buildup and oxygen permeability of the obtained silane-modified EVOH pellets were evaluated by the following methods. The results are shown in Table 3.

[0073] [Die Build-up] The silane-modified EVOH pellets obtained in each Example and Comparative Example were used as the material for the barrier resin layer (A). A maleic anhydride-modified polyethylene "Admer (trademark) AT1955E" (density 0.89 g / cm) manufactured by Mitsui Chemicals, Inc. was used. ３ The adhesive layer was made of a high-density polyethylene "Elite™ AT6900" (PE, a copolymer of ethylene and 1-octene, density 0.969 g / cm 3 ) manufactured by Dow Chemical Company. ３ A multilayer film having a layer thickness and layer structure of (A) / adhesive layer / (B) = 5 μm / 5 μm / 90 μm was produced using a 300 mm wide three-layer co-extrusion cast film-forming equipment. The die buildup (dye build-up) occurrence time was visually confirmed. The results are shown in Table 3. The film-forming conditions were as follows: Extrusion temperature of barrier resin layer (A): feed section / compression section / metering section / die = 170 / 220 / 220 / 220°C Extrusion temperature of adhesive layer: feed section / compression section / metering section / die = 170 / 220 / 220 / 220°C Extrusion temperature of other thermoplastic resin layer (B): feed section / compression section / metering section / die = 170 / 220 / 220 / 220°C

[0074] [Oxygen Permeability] Multilayer films were produced using the same method as in the die build-up evaluation, and samples were taken 0.5 hours and 12 hours after the start of film production. Each film was cut into a size of 5.5 cm x 5.5 cm and stretched 5 times in the MD direction at 80°C using an Eto biaxial stretching machine. The thickness of each layer in the stretched multilayer film is shown in Table 3. An aluminum (Al) vapor-deposited layer with an average thickness of 60 nm was laminated on the surface of the barrier resin layer (A) of each of the obtained uniaxially stretched films by a known vacuum deposition method to produce a vapor-deposited multilayer film, and the oxygen permeability was measured. Specifically, an oxygen transmission rate measuring device ("MOCON OX-TRAN2 / 21" manufactured by Modern Control) was used to measure the oxygen transmission rate (cc / (m)) in accordance with JIS K 7126-2 (isobaric method; 2006) under the conditions of a temperature of 20°C, humidity of 65% RH on the oxygen supply side, humidity of 65% RH on the carrier gas side, oxygen pressure of 1 atmosphere, and carrier gas (nitrogen gas containing 2% by volume of hydrogen gas) pressure of 1 atmosphere, with the deposition surface on the oxygen supply side and the other on the carrier gas side. ２ The oxygen permeability of the vapor-deposited multilayer film obtained from a film sampled 0.5 hours after the start of film formation was designated the "oxygen permeability immediately after film formation," and the oxygen permeability of the vapor-deposited multilayer film obtained from a film sampled 12 hours after the start of film formation was designated the "oxygen permeability after long-run." The results are shown in Table 3.

[0075]

[0076]

[0077]

Claims

1. An ethylene-vinyl alcohol copolymer having an ethylene unit content of 20 to 60 mol% and a degree of saponification of 95 mol% or more, wherein the ethylene-vinyl acetate copolymer obtained by esterifying the ethylene-vinyl alcohol copolymer with acetic anhydride is subjected to gel permeation chromatography using a differential refractive index detector and an absorptiometry detector. In the curve obtained by plotting the ratio of signal intensity UV to signal intensity RI (UV / RI) against the logarithm of molecular weight M (logM), the absolute value of the slope in the logM range of 5.00 to 5.75 is 0.130 or less, where: logM is the logarithm of molecular weight M measured with the differential refractive index detector; signal intensity RI is the signal intensity measured with the differential refractive index detector; and signal intensity UV is the signal intensity measured with the absorptiometry detector (measurement wavelength 210 nm).

2. The ethylene-vinyl alcohol copolymer according to claim 1, wherein the content of monomer units derived from a silane compound having an ethylenic double bond is 0.001 to 0.3 mol %.

3. The ethylene-vinyl alcohol copolymer according to claim 1 or 2, wherein the content of ethylene units is 40 to 50 mol %.

4. A multilayer film comprising a barrier resin layer (A) containing the ethylene-vinyl alcohol copolymer according to claim 1 or 2 as a main component.

5. The multilayer film according to claim 4, wherein the barrier resin layer (A) is at least uniaxially stretched.

6. The multilayer film according to claim 4, wherein the thickness of the barrier resin layer (A) is 0.5 to 20 μm.

7. The multilayer film according to claim 4, wherein the barrier resin layer (A) is the outermost layer.

8. The multilayer film according to claim 4, which is a coextruded film having a barrier resin layer (A) and another thermoplastic resin layer (B) and a thickness of 10 to 100 μm.

9. The multilayer film according to claim 8, wherein the other thermoplastic resin layer (B) is mainly composed of polyolefin.

10. A vapor-deposited multilayer film comprising the multilayer film of claim 4 and a vapor-deposited layer.

11. The vapor-deposited multilayer film according to claim 10, wherein the vapor-deposited layer is located on the exposed surface side of the barrier resin layer (A).