Modified ethylene-vinyl alcohol copolymer, and resin composition and molded article each using same

Abstract

Disclosed is a modified ethylene-vinyl alcohol copolymer which contains, with respect to all monomer units, 20-55 mol% of an ethylene unit and 0.005-0.5 mol% of a monomer unit that is derived from a silane compound having an ethylenic double bond, and has a saponification degree of 88 mol% or more, wherein the total of silicon atoms forming a crosslinked structure represented by formula (I) or (II) is 10-60 mol% with respect to all silicon atoms. Such silane-modified ethylene-vinyl alcohol copolymer makes it possible to suppress the development of deposits during melt molding and obtain a molded body which has a good appearance after stretching.

Description

Modified ethylene-vinyl alcohol copolymer, and resin composition and molded article using the same

[0001] The present invention relates to a modified ethylene-vinyl alcohol copolymer containing a monomer unit derived from a silane compound having an ethylenic double bond, a resin composition containing the modified ethylene-vinyl alcohol copolymer as a main component, and a molded article using the resin composition.

[0002] Ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as "EVOH") has excellent gas barrier properties and melt moldability, and is molded into films, sheets, pipes, tubes, bottles, etc. by various melt molding methods, and is widely used as a packaging material in the food and industrial fields where gas barrier properties are required. Furthermore, as legal restrictions on the recycling of packaging materials are becoming more stringent in various countries these days, EVOH is widely accepted as an environmentally friendly gas barrier packaging resin because it does not affect the recyclability of polyolefins even when mixed with them.

[0003] Methods widely known for controlling melt-moldability-related physical properties such as melt viscosity, melt tension, and elongational viscosity, and for improving the mechanical properties of molded products, such as tensile strength and elongation, include adding boric acid to hydrous EVOH resin and then drying it, and copolymerizing EVOH with a vinylsilane compound. Boric acid is a highly polluting substance, requiring strict management and disposal, including of wastewater. On the other hand, vinylsilane compounds are added during polymerization and copolymerized, thereby immobilizing them in the polymer, thereby reducing their concentration in wastewater, making them environmentally preferable. Furthermore, vinylsilane compounds undergo a dehydration reaction during the drying process (usually hot air drying at approximately 110°C for 48 to 72 hours) during EVOH resin production, forming crosslinked structures. However, adding too much vinylsilane compound is known to result in poor appearance and reduced quality of molded products (Patent Documents 1 and 2).

[0004] Japanese Patent Application Laid-Open No. 1988-196645 Japanese Patent Application Laid-Open No. 1991-115447 Japanese Patent Application Laid-Open No. 1991-99842

[0005] The crosslinking reaction of monomer units derived from silane compounds with ethylenic double bonds in EVOH involves dehydration, and multiple crosslinking modes exist depending on the combination of condensation between silanol and vinyl alcohol, condensation between silanols, and the number of crosslinking structures per silicon atom. During the EVOH production process, when EVOH is in a highly hydrated state, the bonds are reversible, but become irreversible and fixed after drying. It has been found that multiple crosslinking structures tend to form per silicon atom, and that conventional drying methods, which result in a continuous decrease in moisture content, can easily cause poor appearance in molded products.

[0006] Furthermore, in recent years, due to the diversification of layer configurations, there has been an increasing trend in producing multilayer structures by co-extrusion and co-stretching an EVOH layer as the outermost layer, with the aim of obtaining a synergistic effect of improving barrier properties through lamination with an inorganic vapor-deposited layer. When EVOH is co-extruded as the outermost layer of a multilayer structure or when EVOH is extruded as a monolayer film, if pitting (meaning deposits on the outer surface of the die lip) occurs on the outer surface of the discharge port of the molten resin composition, the film is prone to develop bumps and streaks due to the pitting, which makes it more likely to form surface defects and defects during co-stretching. Furthermore, performing inorganic vapor deposition on a film with bumps and streaks is likely to cause defects and tend to reduce the adhesion of the inorganic vapor-deposited layer, which is undesirable. It has been found that the EVOH composition described in Patent Document 3 is also insufficient in terms of die buildup, leaving room for improvement. It has also been found that the method of stretching a film co-extruded with an EVOH layer as the outermost layer is particularly susceptible to bumps and streaks.

[0007] The present invention has been made to solve the above-mentioned problems, and provides a modified EVOH that not only suppresses the generation of die deposits during melt molding but also enables the production of molded articles that have good appearance after stretching, and a molded article such as a multilayer structure using the same.

[0008] The present inventors conducted extensive research into the silicon bonds that serve as crosslinking points in modified ethylene-vinyl alcohol copolymers containing monomer units derived from silane compounds having ethylenic double bonds (hereinafter sometimes abbreviated as "silane-modified EVOH"). As a result, they discovered that by heating silane-modified EVOH in a sealed environment with no water inflow or outflow during the drying process at a specific moisture content and for a specific time, it is possible to suppress the generation of die buildup and obtain a multilayer film with excellent appearance properties after stretching, even when the silane-modified EVOH is used as the outermost layer. On the other hand, the effects were limited when silane-modified EVOH was heated in a sealed environment at a moisture content or for a time outside the specific range, or when silane-modified EVOH was heated under conditions where the moisture content continuously decreased by hot air drying without sealing.

[0009] That is, the present invention is as follows: [1] A modified EVOH containing, relative to all monomer units, 20 to 55 mol % of ethylene units and 0.005 to 0.5 mol % of monomer units derived from a silane compound having an ethylenic double bond, having a degree of saponification of 88 mol % or more, and in which the total amount of silicon atoms forming a crosslinked structure represented by the following formula (I) or (II) is 10 to 60 mol % relative to all silicon atoms: [In formula (I), R １ and R ２ are each independently a hydroxyl group or a hydrocarbon group having 1 to 8 carbon atoms, and X １ is a single bond or an alkylene group having 1 to 3 carbon atoms. [In formula (II), R ３ ~R ６ are each independently a hydroxyl group or a hydrocarbon group having 1 to 8 carbon atoms, and X ２ and X ３ are each independently a single bond or an alkylene group having 1 to 3 carbon atoms.

[0010] [2] The silane compound is vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, allyltrimethoxysilane, allylmethyldimethoxysilane, allyldimethylmethoxysilane, allyltriethoxysilane, allyldimethylethoxysilane, vinyltris(β-methoxyethoxy)silane, vinylisobutyldimethoxysilane, vinylethyldimethoxysilane, vinylmethoxydibutoxysilane The EVOH according to [1], which is at least one selected from the group consisting of vinyl silane, vinyl dimethoxybutoxysilane, vinyl tributoxysilane, vinyl methoxydihexyloxysilane, vinyl dimethoxyhexyloxysilane, vinyl trihexyloxysilane, vinyl methoxydioctyloxysilane, vinyl dimethoxyoctyloxysilane, vinyl trioctyloxysilane, vinyl methoxydilauryloxysilane, vinyl dimethoxylauryloxysilane, vinyl methoxydioleyloxysilane, and vinyl dimethoxyoleyloxysilane. [3] A resin composition containing the EVOH according to [1] or [2]. [4] The resin composition according to [3], wherein the eluate obtained by heating 10 g of the resin composition in 50 mL of ion-exchanged water at 95°C under reflux for 12 hours has a pH of 3.5 to 6.0. [5] The resin composition according to [3] or [4], which contains 50 to 800 ppm in total of carboxylic acid or phosphoric acid. [6] A molded article comprising the resin composition according to any one of [3] to [5]. [7] A multilayer structure having at least one layer made of the resin composition according to any one of [3] to [5]. [8] The multilayer structure according to [7], wherein the layer made of the resin composition is at least one outermost layer. [9] A method for producing modified EVOH, comprising: a pre-drying step (3) of pre-drying a hydrous modified EVOH having a moisture content of 10 to 75% by mass, which contains a monomer unit derived from a silane compound having an ethylenic double bond, to obtain a pre-dried product having a moisture content of 0.4 to 1.5% by mass; an aging step (4) of heating the pre-dried product in a sealed state at 80 to 150°C for 12 to 48 hours to obtain an aged product; and a main drying step (5) of drying the aged product with hot air to obtain a dried product having a moisture content of 0.3% by mass or less.

[10] A method for producing a modified EVOH according to [9], further comprising: a polymerization step (1) of copolymerizing a vinyl ester, ethylene, and a silane compound having an ethylenic double bond to obtain a modified ethylene-vinyl ester copolymer; and a saponification step (2) of saponifying the modified ethylene-vinyl ester copolymer in methanol and then replacing the solvent to obtain the hydrous modified EVOH having a water content of 10 to 75% by mass, wherein the hydrous modified EVOH is subjected to a preliminary drying step (3).

[0011] The silane-modified EVOH of the present invention can suppress the generation of die deposits during melt molding, and can also provide a molded article with a good appearance after stretching.

[0012] The modified EVOH of the present invention contains 20 to 55 mol % of ethylene units and 0.005 to 0.5 mol % of monomer units derived from a silane compound having an ethylenic double bond, based on all monomer units, has a degree of saponification of 88 mol % or more, and the total amount of silicon atoms forming the crosslinked structure represented by the following formula (I) or (II) is 10 to 60 mol % based on all silicon atoms. Such modified EVOH suppresses the generation of die buildup during melt molding and enables the production of molded articles, particularly multilayer films, that have good appearance after stretching.

[0013] [In formula (I), R １ and R ２ are each independently a hydroxyl group or a hydrocarbon group having 1 to 8 carbon atoms, and X １ is a single bond or an alkylene group having 1 to 3 carbon atoms.

[0014] [In formula (II), R ３ ~R ６ are each independently a hydroxyl group or a hydrocarbon group having 1 to 8 carbon atoms, and X ２ and X ３ are each independently a single bond or an alkylene group having 1 to 3 carbon atoms.

[0015] The crosslinked structure represented by the formula (I) is formed by condensation of a monomer unit derived from a silane compound having an ethylenic double bond contained in the modified EVOH with a vinyl alcohol unit, and the crosslinked structure represented by the formula (II) is formed by condensation of silane compounds having an ethylenic double bond contained in the modified EVOH with each other.

[0016] In formula (I), R １ and R ２ are each independently a hydroxyl group or a hydrocarbon group having 1 to 8 carbon atoms. Examples of the hydrocarbon group include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, n-hexyl, isohexyl, 2-ethylhexyl, n-heptyl, and n-octyl, and aryl groups such as phenyl and tolyl. Among these, alkyl groups are preferred, and methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, and tert-butyl groups are more preferred, with methyl and ethyl groups being even more preferred. The hydrocarbon group may have a substituent such as a hydroxyl group or a halogen group. The number of carbon atoms is preferably 1 to 6, more preferably 1 to 4, even more preferably 1 to 3, and particularly preferably 1 to 2. Among these, R １ and R ２ is preferably a hydroxyl group.

[0017] In formula (I), X １ is a single bond or an alkylene group having 1 to 3 carbon atoms. Examples of the alkylene group include a methylene group, an ethylene group, and a propylene group. １ is preferably a single bond or a methylene group, and more preferably a single bond.

[0018] In formula (II), R ３ ~R ６ is R in formula (I). １ and R ２ The same as X ２ and X ３ represents X in formula (I). １The same is used.

[0019] The content of ethylene units in the modified EVOH is 20 to 55 mol% based on the total monomer units. When the content of ethylene units is 20 mol% or more, the melt moldability of the modified 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 55 mol% or less, the gas barrier properties of the modified EVOH are improved. The content is preferably 52 mol% or less, more preferably 50 mol% or less. The content of ethylene units in the modified EVOH is １ It can be determined by H-NMR measurement.

[0020] The saponification degree of the modified EVOH is 88 mol% or more. When the saponification degree is 88 mol% or more, defects are less likely to be formed in the obtained film, and surface defects are less likely to occur during co-stretching. In addition, the gas barrier properties and thermal stability of the modified EVOH are improved. The saponification degree is preferably 90 mol% or more, more preferably 95 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 of the modified EVOH is １ It can be determined by H-NMR measurement.

[0021] The content of the monomer units derived from a silane compound having an ethylenic double bond in the modified EVOH is 0.005 to 0.5 mol % relative to the total monomer units. When the content of the monomer units derived from the silane compound is 0.005 mol % or more, the occurrence of die buildup on the outer surface of the discharge port during extrusion molding is reduced. Furthermore, the occurrence of bumps, streaks, and the like due to die buildup is suppressed in the resulting film, making it less likely for film surface defects to occur during co-stretching. Furthermore, the resulting film is less likely to have defects. The content is preferably 0.008 mol % or more, more preferably 0.01 mol % or more, even more preferably 0.02 mol % or more, and particularly preferably 0.03 mol % or more. On the other hand, when the content of the monomer units derived from the silane compound is 0.5 mol % or less, the occurrence of die buildup on the outer surface of the discharge port during extrusion molding is reduced. In the resulting film, the occurrence of bumps, streaks, etc. caused by the die deposits is suppressed, and film surface defects are less likely to occur during co-stretching. The content is preferably 0.45 mol% or less, more preferably 0.3 mol% or less, even more preferably 0.2 mol% or less, even more preferably 0.1 mol% or less, particularly preferably 0.08 mol% or less, and in some cases 0.07 mol% or less is preferred. The content of the monomer units derived from the silane compound having an ethylenic double bond in the modified EVOH can be determined by ICP emission spectroscopy.

[0022] The silane compound is not particularly limited as long as it is capable of forming the crosslinked structure represented by the above formula (I) or (II), but 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, More preferably, the silane is at least one selected from the group consisting of vinylisobutyldimethoxysilane, vinylethyldimethoxysilane, vinylmethoxydibutoxysilane, vinyldimethoxybutoxysilane, vinyltributoxysilane, vinylmethoxydihexyloxysilane, vinyldimethoxyhexyloxysilane, vinyltrihexyloxysilane, vinylmethoxydioctyloxysilane, vinyldimethoxyoctyloxysilane, vinyltrioctyloxysilane, vinylmethoxydilauryloxysilane, vinyldimethoxylauryloxysilane, vinylmethoxydioleyloxysilane, and vinyldimethoxyoleyloxysilane. Of these, vinyltrimethoxysilane and allyltrimethoxysilane are even more preferred.

[0023] In the modified EVOH, the total number of silicon atoms forming the crosslinked structure represented by formula (I) or (II) must be 10 to 60 mol % of the total silicon atoms. When the total number of silicon atoms forming the crosslinked structure represented by formula (I) or (II) is 10 mol % or more, the occurrence of die buildup on the outer surface of the extrusion nozzle is reduced during extrusion molding. The resulting film is less susceptible to the occurrence of bumps, streaks, and other defects due to die buildup, making it less likely to develop surface defects during co-stretching. The resulting film is also less susceptible to defects. The total number of silicon atoms forming the crosslinked structure is preferably 15 mol % or more, more preferably 20 mol % or more, and in some cases, 24 mol % or more or 28 mol % or more is preferred. On the other hand, when the total number of silicon atoms forming the crosslinked structure is 60 mol % or less, the occurrence of die buildup on the outer surface of the extrusion nozzle is reduced. The resulting film is less susceptible to the occurrence of bumps, streaks, and other defects due to die buildup, making it less likely to develop surface defects during co-stretching. The total of silicon atoms forming the crosslinked structure is preferably 57 mol % or less, and in some cases, 53 mol % or less, 50 mol % or less, 43 mol % or less, or 40 mol % or less. The total of silicon atoms forming the crosslinked structure represented by formula (I) or (II) relative to all silicon atoms contained in the modified EVOH is ２９ It can be determined by Si-NMR measurement.

[0024] In the modified EVOH, the total of silicon atoms forming the crosslinked structure represented by formula (I) or (II) and silicon atoms contained in monomer units derived from a silane compound having an ethylenic double bond that do not form a crosslinked structure is preferably 95 mol % or more, more preferably 98 mol % or more, and even more preferably 99 mol % or more, based on the total silicon atoms.

[0025] The production method of the present invention is a method for producing a modified EVOH, comprising the steps of: a pre-drying step (3) of pre-drying a hydrous modified EVOH having a moisture content of 10 to 75% by mass, which contains a monomer unit derived from a silane compound having an ethylenic double bond, to obtain a pre-dried product having a moisture content of 0.4 to 1.5% by mass; an aging step (4) of heating the pre-dried product in a sealed state at 80 to 150°C for 12 to 48 hours to obtain an aged product; and a main drying step (5) of drying the aged product with hot air to obtain a dried product having a moisture content of 0.3% by mass or less. This production method makes it possible to produce the modified EVOH of the present invention having the predetermined crosslinked structure described above.

[0026] The method for producing the modified EVOH preferably further comprises a polymerization step (1) of copolymerizing a vinyl ester, ethylene, and a silane compound having an ethylenic double bond to obtain a modified ethylene-vinyl ester copolymer, and a saponification step (2) of saponifying the modified ethylene-vinyl ester copolymer in methanol and then replacing the solvent to obtain the hydrous modified EVOH having a moisture content of 10 to 75 mass %, and further comprising subjecting the hydrous modified EVOH to a preliminary drying step (3).

[0027] In the polymerization step (1), the copolymerization of ethylene, a vinyl ester, and a silane compound having an ethylenic double bond may be carried out by any of solution polymerization, suspension polymerization, emulsion polymerization, and bulk polymerization. Furthermore, the copolymerization may be carried out by any of continuous and batch polymerization. An example of the polymerization conditions for solution polymerization is shown below.

[0028] 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.

[0029] 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.

[0030] 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 modified 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 modified EVOH may not contain the other monomer units.

[0031] 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.

[0032] After polymerization for a predetermined time, when a predetermined polymerization rate is reached, a polymerization inhibitor is added as necessary, unreacted ethylene gas is evaporated and removed, and then unreacted vinyl ester is purged. Examples of methods for purging the unreacted vinyl ester include a method of purging the unreacted vinyl ester from the polymerization solution under reduced pressure, and a method of continuously feeding the polymerization solution from which ethylene has been removed at a constant rate through the top of a column packed with Raschig rings, blowing vapor of an organic solvent, preferably an alcohol having a boiling point of 100°C or less, and most preferably methanol, into the bottom of the column, distilling a mixed vapor of the organic solvent and unreacted vinyl ester from the top of the column, and withdrawing the copolymer solution from which unreacted vinyl ester has been removed through the bottom of the column.

[0033] In the saponification step (2), the modified ethylene-vinyl ester copolymer is saponified in methanol, followed by solvent substitution to obtain the modified EVOH hydrous product having a moisture content of 10 to 75% by mass. Specifically, this process can be carried out as follows. An alkali catalyst is added to the modified ethylene-vinyl ester copolymer solution from which unreacted vinyl ester has been removed, to saponify the vinyl ester component in the copolymer. During this process, alkoxy groups bonded to silicon atoms in the monomer units derived from the silane compound having an ethylenic double bond are replaced with hydroxy groups through dealcoholization. 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 modified ethylene-vinyl ester copolymer in 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

[0034] 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 modified 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

[0035] As described above, the solvent of the solution containing the saponified ethylene-vinyl ester copolymer obtained by saponifying the modified ethylene-vinyl ester copolymer is replaced to obtain the modified EVOH hydrous product having a moisture content of 10 to 75% by mass. Examples of the method for this include the following: While stirring the solution containing the saponified ethylene-vinyl ester copolymer at 40 to 90°C, water is added, and methanol is distilled out of the reaction vessel to precipitate the saponified product. If necessary, the precipitated saponified product is washed, 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 [e.g., 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 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 modified EVOH hydrous product. The size of the resulting pellets can be, for example, a diameter of 1 mm to 10 mm and a length of 1 mm to 10 mm in the case of a cylindrical shape, or a diameter of 1 mm to 10 mm in the case of a spherical shape. The modified EVOH hydrous product pellets thus obtained are subjected to a preliminary drying step (3).

[0036] In the pre-drying step (3), a modified EVOH hydrous material having a moisture content of 10 to 75% by mass and containing a monomer unit derived from a silane compound having an ethylenic double bond is pre-dried to obtain a pre-dried material having a moisture content of 0.4 to 1.5% by mass. When the modified EVOH hydrous material to be pre-dried has a moisture content of 10% by mass or more, the modified EVOH hydrous material can be produced with good productivity without excessively high viscosity. The moisture content is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. On the other hand, when the moisture content is 75% by mass or less, agglutination of the modified EVOH hydrous material during pre-drying is suppressed, and the time and cost required for pre-drying are reduced. The moisture content is preferably 65% ​​by mass or less, more preferably 60% by mass or less, and even more preferably 55% by mass or less. The methanol content in the modified EVOH hydrous material to be pre-dried is preferably 10% by mass or less, more preferably 5% by mass or less.

[0037] The pre-drying method employed in the pre-drying step (3) is not particularly limited, but a hot air dryer or the like can be used. The drying method can be fluidized drying using a fluidized dryer or static drying using a static dryer, but fluidized drying is preferred to prevent pellets from sticking together. A combination of these methods can also be used, or a method can be used in which the pellets are first dried using fluidized drying and then dried using static drying. The pre-drying temperature is not particularly limited, but 40 to 150°C is preferred. The pre-drying temperature is more preferably 50°C or higher, and even more preferably 60°C or higher. The drying temperature is more preferably 130°C or lower, and even more preferably 120°C or lower. The drying time varies depending on the drying temperature and the desired moisture content, but is typically 1 to 25 hours. Drying can be performed in air or in an inert gas such as nitrogen. When drying in an inert gas, thermal degradation is less likely to occur even if the drying temperature is set higher. Pre-drying can also be performed multiple times. For example, a method may be employed in which a first preliminary drying is carried out at a relatively low temperature (for example, at 40 to 110°C for 1 to 5 hours), and then a second preliminary drying is carried out at a temperature higher than the first temperature (for example, at 90 to 140°C for 1 to 20 hours).

[0038] The pre-dried product thus obtained is subjected to the aging step (4). The moisture content of the pre-dried product subjected to the aging step (4) must be 0.4 to 1.5% by mass. When the moisture content is 0.4% by mass or more, the crosslinking reaction proceeds efficiently without restricting the movement of the molecular chains of the modified EVOH or the acid that serves as a catalyst for the crosslinking reaction (dehydration reaction) during aging. On the other hand, when the moisture content is 1.5% by mass or less, the crosslinking reaction (dehydration reaction), which is a reversible reaction, proceeds more easily. The moisture content is preferably 1.4% by mass or less, more preferably 1.3% by mass or less, even more preferably 1.2% by mass or less, and particularly preferably 1.1% by mass or less.

[0039] In the aging step (4), the pre-dried product is heated in a sealed state at 80 to 150°C for 12 to 48 hours to obtain an aged product. Specifically, the pre-dried product is packed into a container such as a stainless steel container so that there is no headspace, sealed, and then heated (aged) at 80 to 150°C for 12 to 48 hours. By sealing the pre-dried product, the moisture content of the pre-dried product is maintained constant during heating (aging). As a result, crosslinking reactions between monomer units derived from a silane compound having an ethylenic double bond or between a monomer unit derived from a silane compound having an ethylenic double bond and a vinyl alcohol unit are thought to proceed efficiently, resulting in an increased proportion of monomer units derived from a silane compound having an ethylenic double bond that form the crosslinked structure represented by formula (I) or (II).

[0040] In the aging step (4), the heating (aging) temperature is 80°C or higher, whereby the crosslinking reaction of the monomer units derived from the silane compound having an ethylenic double bond proceeds efficiently. The temperature is preferably 90°C or higher, more preferably 100°C or higher, and even more preferably 105°C or higher. On the other hand, the heating (aging) temperature is 150°C or lower, whereby thermal degradation of the pre-dried product is suppressed. The temperature is preferably 140°C or lower, more preferably 130°C or lower, and even more preferably 120°C or lower.

[0041] By setting the heating (aging) time in the aging step (4) to 12 hours or more, the proportion of monomer units derived from a silane compound having an ethylenic double bond that form the crosslinked structure represented by formula (I) or (II) increases. The heating (aging) time is preferably 14 hours or more, more preferably 16 hours or more, and even more preferably 18 hours or more. On the other hand, by setting the heating (aging) time to 48 hours or less, thermal degradation of the pre-dried product is suppressed. The heating (aging) time is preferably 40 hours or less, more preferably 35 hours or less, even more preferably 30 hours or less, and particularly preferably 25 hours or less.

[0042] The aged product thus obtained is dried with hot air in the main drying step (5) to obtain a dried product with a moisture content of 0.3% by mass or less. The drying method employed is the same as that employed in the preliminary drying step (3). The drying temperature in the main drying step (5) is not particularly limited, but is preferably 90 to 150°C. A drying temperature of 90°C or higher allows the aged product to be dried efficiently to the desired moisture content. The drying temperature is more preferably 100°C or higher, and even more preferably 105°C or higher. Furthermore, a drying temperature of 150°C or lower can suppress thermal degradation of the aged product. The drying temperature is more preferably 140°C or lower, and even more preferably 130°C or lower. The drying time varies depending on the drying temperature and the desired moisture content, but is typically 12 to 36 hours. Drying may be performed in air or in an inert gas such as nitrogen. When drying in an inert gas, thermal degradation is less likely to occur even if the drying temperature is set higher. According to the production method of the present invention, the proportion of monomer units derived from a silane compound having an ethylenic double bond that form the crosslinked structure represented by formula (I) or (II) can be increased in the aging step (4) described above, making it possible to easily obtain a silane-modified EVOH in which the total number of silicon atoms forming these crosslinked structures falls within the above-mentioned range. The shape of the dried silane-modified EVOH thus obtained is not particularly limited, but pellets are preferred. The size of the pellets can be, for example, a diameter of 0.8 mm to 9.8 mm in the case of a spherical (or nearly spherical) shape, or a diameter of 0.8 mm to 9.8 mm and a length of 0.8 mm to 9.8 mm in the case of a cylindrical shape.

[0043] A resin composition containing the modified EVOH is a preferred embodiment of the present invention. Components other than the modified EVOH contained in the resin composition include carboxylic acids, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts, with carboxylic acids and phosphoric acid compounds being preferred. The content of the other components in the resin composition 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.

[0044] 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 less carbon atoms. Among these, acetic acid is preferred from the standpoints of cost, ease of availability, and the like. When the resin composition contains a carboxylic acid, the content thereof is preferably 50 to 800 ppm. The content of the carboxylic acid is more preferably 100 ppm or more. The content of the carboxylic acid is more preferably 700 ppm or less, and even more preferably 500 ppm or less. In this specification, "ppm" means "ppm by mass."

[0045] 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 resin composition contains a phosphate compound, its content 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.

[0046] From the viewpoint of further facilitating the formation of the crosslinked structure represented by formula (I) or (II), the resin composition preferably contains 50 to 800 ppm in total of carboxylic acid or phosphoric acid. This total is more preferably 100 ppm or more. Furthermore, this total is more preferably 700 ppm or less, and even more preferably 500 ppm or less. From the same viewpoint, it is also preferable that the pH of the eluate obtained by heating and refluxing 10 g of the resin composition in 50 mL of ion-exchanged water at 95°C for 12 hours is 3.5 to 6.0. The pH of the eluate is more preferably 3.5 to 5.5.

[0047] From the viewpoint of safety, the content of boron compounds in the resin composition is preferably 10 ppm or less, and more preferably the resin composition contains substantially no boron compounds.

[0048] Examples of the alkali metal salt include alkali metal salts of aliphatic carboxylic acids, alkali metal salts of aromatic carboxylic acids, and alkali metal salts of phosphoric acid. 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 resin composition 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.

[0049] 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 resin composition 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.

[0050] The method for producing the resin composition is not particularly limited, but examples thereof include a method in which the modified EVOH hydrous product before being subjected to the preliminary drying step (3) is immersed in an aqueous solution or aqueous dispersion in which the other components are dissolved or dispersed. In this manner, the modified EVOH of the present invention is preferably produced as a resin composition.

[0051] A molded article containing the resin composition is a preferred embodiment of the present invention. Examples of such molded articles include films, sheets, tubes, bags, bottles, packaging materials, and containers. When the resin composition of the present invention is used, the generation of eye boogers during melt molding is suppressed. Furthermore, the resulting molded article has a good appearance and excellent gas barrier properties. The molded article may have a portion formed from the resin composition. That is, the molded article may be a molded article consisting solely of the resin composition, or a molded article consisting solely of the resin composition and other portions. Methods for melt molding the resin composition include, for example, extrusion molding, cast molding, inflation extrusion molding, blow molding, melt spinning, injection molding, injection blow molding, and co-extrusion blow molding. Among these, extrusion molding, injection molding, and blow molding are preferred. Molded articles obtained by molding the resin composition using these methods are also preferred embodiments of the present invention. The melt molding temperature varies depending on the melting point of the resin composition, but is preferably approximately 150 to 270°C. These molded articles can also be crushed and remolded for reuse. Furthermore, films, sheets, etc. can be uniaxially or biaxially stretched.

[0052] The molded article is preferably a multilayer structure having at least one layer made of the resin composition. It is also preferable that the multilayer structure has a layer 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 made of a component other than resin, such as a layer made of 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.

[0053] The layer structure of the multilayer structure is not particularly limited, and examples thereof include a layer made of the resin composition as E, a layer made of an adhesive resin as Ad, a layer made of another thermal adhesive resin as T, and structures such as T / E / T, E / Ad / T, T / Ad / E / Ad / T, E / Ad / T / Ad / E, and E / Ad / T / Ad / E / Ad / T / Ad / E / Ad / E / Ad / E. 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 modified EVOH.

[0054] Examples of thermoplastic resins other than EVOH include 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, polypentene, and other olefin homopolymers or copolymers thereof; polyethylene terephthalate, and other polyesters; 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, chlorinated polypropylene, etc. Among these, polypropylene, polyethylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, polyamide, polystyrene, and polyester are preferably used.

[0055] The adhesive resin is not particularly limited as long as it has adhesive properties with the layer made of the resin composition and other thermoplastic resin layers, 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 such as ethylene-vinyl acetate copolymer and ethylene-ethyl acrylate copolymer. Among these, linear low-density polyethylene, ethylene-vinyl acetate copolymer, and ethylene-ethyl acrylate copolymer are preferred as the polyolefin polymer, with linear low-density polyethylene and ethylene-vinyl acetate copolymer being particularly preferred.

[0056] It is preferable that at least one outermost layer of the multilayer structure is a layer made of the resin composition. Conventionally, when EVOH is co-extruded as the outermost layer of a multilayer structure, if a die deposit (meaning a deposit on the outer surface of the die lip) is formed on the outer surface of the discharge port of the molten resin composition, problems such as the occurrence of bumps and streaks due to the die deposit on the film and the formation of surface defects and defects during co-stretching have been encountered. In contrast, the use of the resin composition suppresses the occurrence of die deposits during melt molding, and a multilayer structure with a good appearance after stretching can be obtained. 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 side (outermost layer) or the layer on the inner surface side (innermost layer). The multilayer structure is preferably a multilayer film obtained by co-extrusion molding the resin composition and other thermoplastic resin pellets. In this case, it is preferable that the outermost layer of the multilayer film is a layer made of the resin composition. The multilayer structure may be a vapor-deposited multilayer film in which an inorganic vapor-deposited layer is formed on a layer of the resin composition of the multilayer film. In this case, the inorganic vapor-deposited layer may be formed on the uniaxially or biaxially stretched multilayer film by the method described below. The multilayer structure may also be formed by laminating a layer of another component on the layer of the resin composition. Because modified EVOH has a high affinity with inorganic vapor-deposited layers, particularly vapor-deposited layers of aluminum or aluminum oxide, the interlayer adhesion between the layer of the resin composition and the inorganic vapor-deposited layer tends to be good. Examples of layer configurations in which the outermost layer is a layer of the resin composition include E for the layer of the resin composition, Ad for the layer of an adhesive resin, and T for the layer of a thermoplastic resin. Examples of direct laminations represented by " / " include E / Ad / T, E / Ad / T / Ad / E, and E / Ad / T / Ad / E / Ad / T / Ad / E. In the case of a multilayer structure in which the outermost layer is a layer of the resin composition, T is preferably a polyolefin from the viewpoint of improving recyclability.

[0057] In the multilayer structure, the thickness of the layer made of the resin composition is preferably 0.2 μm or more and 20 μm or less, more preferably 0.4 μm or more and 16 μm or less, and even more preferably 0.6 μm or more and 12 μm or less, and the ratio of the thickness of the layer made of the resin composition 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.

[0058] 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 resin composition, a method of co-extruding the resin composition and other thermoplastic resin pellets, a method of coinjection molding the resin composition and other thermoplastic resin pellets, and a method of laminating a layer made of the resin composition 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.

[0059] The method for co-extruding the resin composition and other thermoplastic resin pellets 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.

[0060] The multilayer structure has excellent thermoformability and can therefore be suitably used as a material for thermoforming of thermoformed containers and the like.

[0061] 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.

[0062] The multilayer structure may be uniaxially stretched by 2 times or more and 12 times or less. This stretching ratio may be 3 times or more and 10 times or less, or 4 times or more and 8 times or less. Such uniaxially stretched multilayer structures have excellent gas barrier properties, break resistance, etc., and also have few film surface defects or defects. Such uniaxially stretched multilayer structures can be suitably used for packaging materials, etc. The uniaxial stretching of the multilayer structure can be carried out by a conventionally known method.

[0063] The multilayer structure may be biaxially stretched by 2 times or more and 12 times or less. This stretching ratio may be 10 times or less, 8 times or less, or 6 times or less. Such biaxially stretched multilayer structures have excellent gas barrier properties, break resistance, etc., and also have few film surface defects or defects. Such biaxially stretched multilayer structures can be suitably used for packaging materials, etc. Biaxial stretching of the multilayer structure can be carried out by a conventionally known method.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. In the examples and comparative examples described below, analyses and evaluations were carried out by the methods shown below.

[0068] (1) Measurement of ethylene unit content and degree of saponification of EVOH Dried pellets of silane-modified EVOH obtained in each Example and Comparative Example were dissolved in deuterated dimethyl sulfoxide (DMSO-d6) containing tetramethylsilane (TMS) as an internal standard substance and trifluoroacetic acid (TFA) as an additive, and subjected to 500 MHz １ Measurement was performed at 80°C using H-NMR (JEOL Ltd. "GX-500"), and the ethylene unit content and the degree of saponification (the proportion (mol %) of vinyl alcohol units to the total of vinyl alcohol units and vinyl ester units) were determined from the peak intensity ratio of ethylene units, vinyl alcohol units, and vinyl ester units.

[0069] (2) Measurement of the content of monomer units derived from silane compounds having ethylenic double bonds: 0.5 g of dried pellets of silane-modified EVOH obtained in each Example and Comparative Example 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, and then cooled 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 content of silicon compounds in the dried pellets was measured using a PerkinElmer ICP atomic emission spectrometer "Avio500," and then converted to the content (mol%) of monomer units derived from silane compounds having ethylenic double bonds in the silane-modified EVOH.

[0070] (3) Measurement of the crosslinked structure represented by the above formula (I) or (II) Dried pellets of silane-modified EVOH obtained in each Example and Comparative Example were dissolved in deuterated dimethyl sulfoxide (DMSO-d6) containing tetramethylsilane (TMS) as an internal standard substance and chromium (III) acetate as a relaxation reagent, and measured using an NMR apparatus (JEOL Ltd. "ECZ-600") at a resonance frequency of 119 MHz and 80°C to determine the crosslinked structure (R １ ~R ６ is a hydroxyl group, X １ ~X ３ The ratio (mol %) of the total silicon atoms forming the crosslinked structure represented by formula (I) or (II) to the total silicon atoms forming a crosslinked structure represented by formula (I) or (II) relative to the total silicon atoms forming a crosslinked structure represented by formula (I) or (II) relative to the total silicon atoms in the modified EVOH was determined, and this ratio was taken as the total silicon atoms forming the crosslinked structure represented by formula (I) or (II) relative to the total silicon in the modified EVOH. Note that no peaks corresponding to methoxy groups bonded to silicon atoms in the monomer units derived from the silane compound having an ethylenic double bond were observed, and it is believed that these groups were all replaced with hydroxyl groups due to the removal of methanol.

[0071] (4) pH Measurement of Water Immersion Solution of Silane-Modified EVOH Dried Pellets 10 g of the silane-modified EVOH dried pellets obtained in each Example and Comparative Example and 50 mL of ion-exchanged water were placed in a 100 mL Erlenmeyer flask with a stopper, and the flask was fitted with a cooling condenser and stirred for 12 hours at 95° C. The resulting extract was cooled to 20° C., and then the pH was measured using a pH measuring device (Mettler Toledo "MA235pH").

[0072] (5) Measurement of Moisture Content of Pellets The moisture content of 10 g of pellets was measured using a Mettler halogen moisture meter "HR73" under conditions of a drying temperature of 180°C and a drying time of 18 minutes. The value was taken as the moisture content of the pellets. The moisture content of the pellets was calculated using the following formula: Moisture content (mass%) = [(mass before drying - mass after drying) / mass before drying] x 100

[0073] (6) Preparation of multilayer film Using dried pellets of each silane-modified EVOH (resin composition) obtained in the examples and comparative examples, low-density polyethylene "INNATE (trademark) TF80" (PE) as the material for the other thermoplastic resin layer, and maleic anhydride-modified polyethylene "Admer (trademark) NF518" (Ad) as the adhesive layer, a three-kind, three-layer multilayer structure (resin composition / Ad / PE = 10 μm / 10 μm / 100 μm) was produced under the following conditions. Extruder for resin composition: single-screw extruder (Toyo Seiki Co., Ltd., Lab Machine ME Type CO-EXT), caliber 20 mmφ, L / D 20, full-flight screw, feed section / compression section / metering section / die = 175 / 220 / 220 / 220°C. Extruder for Ad: single-screw extruder (Technovel Co., Ltd., SZW20GT-20MG-STD), caliber 20 mmφ, L / D 20, full-flight screw, feed section / compression section / metering section / die = 175 / 220 / 220 / 220°C. Extruder for PE: single-screw extruder (Plastic Technology Research Institute Co., Ltd., GT-32-A), caliber 32 mmφ, L / D 28, full-flight screw, feed section / compression section / metering section / die = 175 / 220 / 220 / 220°C. Die: 300 mm wide, 3-type, 3-layer coat hanger die (manufactured by Plastic Technology Research Institute Co., Ltd.).

[0074] (7) Evaluation of Die Density The above multilayer film was produced continuously for 2 hours, and after 2 hours, the deposits (die density) on the die lip on the EVOH layer side were visually inspected and evaluated according to the following criteria. If it was rated A or B, it was determined that die density was suppressed. (Evaluation: Evaluation criteria) A: No die density was observed over the entire width even after 2 hours of operation. B: Very little die density was observed after 2 hours of operation. C: Die density was observed over 20% or more of the die width after 2 hours of operation.

[0075] (8) Evaluation of appearance (transparency) of multilayer film The multilayer film obtained above was stretched 5 times in the machine direction (MD direction) to obtain a multilayer film with an average thickness of resin composition / Ad / PE = 2 μm / 2 μm / 20 μm. The appearance characteristics of the uniaxially stretched co-extruded film were evaluated according to the following criteria. A or B was judged to be good in appearance. (Evaluation: Criteria) A: No streaks or film surface irregularities were observed B: Slight streaks or film surface irregularities were observed C: Three or more streaks or film surface irregularities were observed

[0076] (9) Evaluation of Appearance Characteristics (Number of Defects) The results of visual inspection of the multilayer film obtained above were taken as appearance characteristics (defects) and evaluated according to the following criteria. A or B was judged to be good appearance. (Evaluation: Criteria) A: A few small defects were observed B: A small number of small defects were observed over the entire surface of the film C: Many large and small defects were observed over the entire surface of the film [Example 1]

[0077] (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, 10 kg of methanol, and 0.08 kg of vinyltrimethoxysilane (hereinafter sometimes referred to as VMS). The temperature was raised to 60°C, and then 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 3.0 MPa. The temperature inside the reactor was adjusted to 60°C, and 36 g of 2,2'-azobis(2,4-dimethylvaleronitrile) ("V-65" manufactured by Wako Pure Chemical Industries, Ltd.) was added as a methanol solution as an initiator to initiate polymerization. The ethylene pressure was maintained at 3.0 MPa, and the polymerization temperature was maintained at 60°C during the polymerization. After 6 hours, when the conversion of vinyl acetate reached 45%, the polymerization was terminated by cooling. The reaction vessel was opened to remove ethylene, and then nitrogen gas was bubbled through to completely remove ethylene. Next, unreacted 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 were copolymerized (hereinafter, sometimes referred to as silane-modified EVAc) to prepare a 20% by mass methanol solution.

[0078] (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.

[0079] (3) Production of hydrous pellets of silane-modified EVOH: 40 parts by mass of the crude dried modified EVOH obtained in (2), 40 parts by mass of water, and 20 parts by mass of 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 tube with an inner diameter of 4 mm into a mixed solution with a mass ratio (water / methanol) of 90 / 10 cooled to 5°C to precipitate in the form of strands. The strands were cut with a strand cutter into cylindrical shapes with a diameter of 2 mm and a length of 3 mm to obtain hydrous pellets of modified EVOH. The moisture content of the obtained hydrous pellets of silane-modified EVOH was measured and found to be 50% by mass.

[0080] (4) Preparation of Dried 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 (bath ratio: 20) containing 0.5 g / L sodium acetate, 0.8 g / L acetic acid, and 0.005 g / L phosphoric acid, immersed for 4 hours with periodic stirring, and then deliquified. The moisture content of the hydrous silane-modified EVOH pellets obtained at this stage was measured and found to be 50% by mass. The hydrous pellets were subjected to preliminary drying 1 using a hot air dryer at 80°C for 3 hours. Further, pre-drying 2 was performed using a hot air dryer at 110°C for 12 hours until the moisture content reached 0.5% by mass. The resulting pre-dried material was then packed into a stainless steel container, ensuring no headspace, sealed with a lid, and heated (aged) at 110°C for 24 hours. The aged pellets (aged product) were removed from the sealed container and dried in a hot air dryer at 110°C for 20 hours to obtain cylindrical dried pellets of silane-modified EVOH (resin composition) with a diameter of 1.2 mm and a length of 2.3 mm. The resulting dried pellets had a moisture content of 0.15% by mass, a phosphoric acid content of 50 ppm, and an acetic acid content of 250 ppm. The dried pellets were evaluated as described above in (1) to (9). The results are shown in Table 1.

[0081] Examples 2 to 13 and Comparative Examples 1 to 12 Dried pellets of silane-modified EVOH (resin compositions) were produced and evaluated in the same manner as in Example 1, except that the polymerization conditions, saponification conditions, bath composition of the aqueous solution in which the hydrous pellets of modified EVOH were immersed, or pre-drying time were changed so that the composition of the silane-modified EVOH, pH of the eluate, and moisture content after pre-drying would be as shown in Table 1, and the aging time and main drying time were changed as shown in Table 1. The results are shown in Table 1.

[0082]

Claims

1. A modified ethylene-vinyl alcohol copolymer containing 20 to 55 mol% of ethylene units and 0.005 to 0.5 mol% of monomer units derived from a silane compound having an ethylenic double bond, based on the total monomer units; having a degree of saponification of 88 mol% or more; and having a total of 10 to 60 mol% of silicon atoms forming a crosslinked structure represented by the following formula (I) or (II), based on the total silicon atoms: [In formula (I), R １ and R ２ are each independently a hydroxyl group or a hydrocarbon group having 1 to 8 carbon atoms, and X １ is a single bond or an alkylene group having 1 to 3 carbon atoms. [In formula (II), R ３ ~R ６ are each independently a hydroxyl group or a hydrocarbon group having 1 to 8 carbon atoms, and X ２ and X ３ are each independently a single bond or an alkylene group having 1 to 3 carbon atoms.

2. The silane compound is vinyltrimethoxysilane, vinylmethyldimethoxysilane, vinyldimethylmethoxysilane, vinyltriethoxysilane, vinylmethyldiethoxysilane, vinyldimethylethoxysilane, allyltrimethoxysilane, allylmethyldimethoxysilane, allyldimethylmethoxysilane, allyltriethoxysilane, allyldimethylethoxysilane, vinyltris(β-methoxyethoxy)silane, vinylisobutyldimethoxysilane, vinylethyldimethoxysilane, vinylmethoxydibutoxysilane, vinyldimethoxy The modified ethylene-vinyl alcohol copolymer according to claim 1, which is at least one selected from the group consisting of butoxysilane, vinyl tributoxysilane, vinyl methoxydihexyloxysilane, vinyl dimethoxyhexyloxysilane, vinyl trihexyloxysilane, vinyl methoxydioctyloxysilane, vinyl dimethoxyoctyloxysilane, vinyl trioctyloxysilane, vinyl methoxydilauryloxysilane, vinyl dimethoxylauryloxysilane, vinyl methoxydioleyloxysilane, and vinyl dimethoxyoleyloxysilane.

3. A resin composition containing the modified ethylene-vinyl alcohol copolymer according to claim 1 or 2.

4. The resin composition according to claim 3, wherein the pH of the eluate obtained by heating 10 g of the resin composition in 50 mL of ion-exchanged water under reflux at 95°C for 12 hours is 3.5 to 6.

0.

5. The resin composition according to claim 3, which contains 50 to 800 ppm in total of carboxylic acid or phosphoric acid.

6. A molded article comprising the resin composition according to claim 3.

7. A multilayer structure having at least one layer made of the resin composition according to claim 3.

8. The multilayer structure according to claim 7, wherein the layer made of the resin composition is at least one outermost layer.

9. A method for producing a modified ethylene-vinyl alcohol copolymer, comprising: a pre-drying step (3) of pre-drying a modified ethylene-vinyl alcohol copolymer hydrous material having a moisture content of 10 to 75% by mass, which contains a monomer unit derived from a silane compound having an ethylenic double bond, to obtain a pre-dried product having a moisture content of 0.4 to 1.5% by mass; an aging step (4) of heating the pre-dried product in a sealed state at 80 to 150°C for 12 to 48 hours to obtain an aged product; and a main drying step (5) of drying the aged product with hot air to obtain a dried product having a moisture content of 0.3% by mass or less.

10. A method for producing a modified ethylene-vinyl alcohol copolymer according to claim 9, further comprising: a polymerization step (1) of copolymerizing a vinyl ester, ethylene, and a silane compound having an ethylenic double bond to obtain a modified ethylene-vinyl ester copolymer; and a saponification step (2) of saponifying the modified ethylene-vinyl ester copolymer in methanol and then replacing the solvent to obtain the modified ethylene-vinyl alcohol copolymer hydrate having a water content of 10 to 75% by mass, wherein the modified ethylene-vinyl alcohol copolymer hydrate is subjected to a preliminary drying step (3).

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