Vinyl alcohol based copolymer, and gas barrier film comprising the same

Abstract

The present invention provides a vinyl alcohol-based copolymer comprising an olefin-derived first repeating unit, a second repeating unit, and a third repeating unit formed by the reaction of the hydroxyl group-containing repeating unit with an unsaturated nitrile-based compound, wherein the content of the third repeating unit is 2 mol% or more and less than 10 mol% relative to the total sum of the second repeating unit and the third repeating unit, 100 mol%; a method for manufacturing the same; and a gas barrier film comprising the same. The vinyl alcohol-based copolymer has excellent moisture stability and can exhibit excellent gas barrier properties even in a humid environment.

Description

Technology Field

[0001] The present invention relates to a vinyl alcohol-based copolymer having excellent gas barrier properties and moisture penetration prevention effects, and excellent adhesion to a polymer substrate such as a polyolefin, and a gas barrier film containing the same. Background Technology

[0003] Saponified vinyl alcohol copolymers, such as ethylene-vinyl acetate copolymers, are used in various applications including films, sheets, and containers based on their excellent gas barrier properties.

[0004] In the case of conventional gas barrier films using saponified ethylene vinyl acetate copolymers, they are manufactured by a method of hydrolyzing the copolymer of ethylene and vinyl acetate after preparation. The film manufactured by the above method contains a vinyl alcohol-based polymer, such as ethylene vinyl alcohol copolymer (EVOH), which is produced by the hydrolysis of the ethylene vinyl acetate copolymer, and the vinyl alcohol-based polymer exhibits gas barrier properties by crystallizing through hydrogen bonding between hydroxyl groups contained within the molecule. However, although the vinyl alcohol-based polymer exhibits high gas barrier properties in a dry state, under humid conditions it absorbs moisture from water vapor, etc., and the hydrogen bonds loosen, causing a problem in which gas permeability increases rapidly.

[0005] Various methods have been proposed to solve this problem. Specifically, Japanese Patent Publication No. 2015-093389 (Patent Document 1) discloses a method of preservation in a humid environment by modifying a modified ethylene-vinyl ester copolymer saponified product with caprolactone, etc. In addition, Japanese Patent Publication No. 2002-138109 (Patent Document 2) discloses a vinyl alcohol-based polymer composition with improved gas barrier properties in a humid environment by introducing a metal alkoxide, such as tetramethoxysilane, as a functional group, a coating agent containing the same, and a laminate.

[0006] In addition, U.S. Patent No. 4,746,700 (Patent Document 3) discloses a film material that exhibits transparency along with gas barrier properties by reducing the copolymer content as a method for manufacturing a vinyl alcohol-based copolymer.

[0007] However, even the proposed method was not sufficient to prevent the degradation of the gas barrier performance of the gas barrier film under humid environments. The problem to be solved

[0009] The present specification aims to provide a vinyl alcohol-based copolymer that has excellent gas barrier properties and moisture penetration prevention effects, as well as excellent adhesion to polymer substrates such as polyolefins.

[0010] In addition, the present specification aims to provide a gas barrier film capable of achieving excellent gas barrier properties by including the vinyl alcohol-based copolymer. means of solving the problem

[0012] The present specification provides a vinyl alcohol-based copolymer comprising: a first repeating unit represented by the following chemical formula 1; a second repeating unit represented by the following chemical formula 2; a third repeating unit represented by the following chemical formula 3; and a fourth repeating unit represented by the following chemical formula 4.

[0013] [Chemical Formula 1]

[0014]

[0015] In the above chemical formula 1, R1 is hydrogen, or an alkyl having 1 to 3 carbon atoms, and

[0016] [Chemical Formula 2]

[0017]

[0018] [Chemical Formula 3]

[0019]

[0020] In the above chemical formula 3, L is an alkylene having 2 to 5 carbon atoms, R is hydrogen or R2-O-CO-, and R2 is an alkyl group having 1 to 5 carbon atoms.

[0021] [Chemical Formula 4]

[0022] .

[0024] According to one embodiment of the invention, the third repeating unit in the vinyl alcohol-based copolymer may be included in an amount of about 1 mol% to about 20 mol% with respect to the total sum of the second repeating unit and the third repeating unit, which is 100 mol%.

[0026] And, in the above chemical formula 3, L is ethylene, 1-methylethylene, or n-propylene, R is hydrogen or R2-O-CO-, and R2 may be a methyl group, an ethyl group, or a propyl group.

[0028] Specifically, the third repeating unit may be represented by the following chemical formula 3-1 or chemical formula 3-2.

[0029] [Chemical Formula 3-1]

[0030]

[0031] [Chemical Formula 3-2]

[0032]

[0034] According to one embodiment of the invention, the first repeating unit in the vinyl alcohol-based copolymer may be included in an amount of about 10 mol% to about 50 mol% with respect to the total amount of the first to fourth repeating units of 100 mol%.

[0036] And, the first repeating unit may be an ethylene-derived repeating unit.

[0038] According to one embodiment of the invention, the second repeating unit may be included in an amount of about 30 mol% to about 80 mol% with respect to the total sum of the first to fourth repeating units of 100 mol%.

[0040] According to one embodiment of the invention, the third repeating unit may be included in an amount of about 1 mole% to about 30 mole% with respect to the total sum of the first to fourth repeating units of 100 mole%.

[0042] According to one embodiment of the invention, the fourth repeating unit may be included in an amount of about 1 mole% to about 30 mole% with respect to the total sum of the first to fourth repeating units of 100 mole%.

[0044] And, according to another aspect of the present invention, a gas barrier film comprising the vinyl alcohol-based copolymer described above is provided.

[0046] In the present invention, terms such as first, second, etc. are used to describe various components, and these terms are used solely for the purpose of distinguishing one component from another component.

[0047] Furthermore, the terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention.

[0048] Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0049] In this specification, terms such as “comprising,” “comprising,” or “having” are used to describe features, numbers, steps, components, or combinations thereof that are implemented, and do not exclude one or more other features, numbers, steps, components, combinations thereof, or the possibility of addition.

[0050] Additionally, in this specification, where each layer or element is referred to as being formed "on" or "above" each layer or element, it means that each layer or element is formed directly on each layer or element, or that another layer or element may be additionally formed between each layer, on an object, or on a substrate.

[0051] The present invention is capable of various modifications and may take various forms, and specific embodiments are illustrated and described in detail below. However, this is not intended to limit the invention to the specific disclosed forms, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0053] The present invention will be described in detail below.

[0055] According to one aspect of the present invention, a vinyl alcohol-based copolymer is provided, comprising a first repeating unit represented by the following chemical formula 1; a second repeating unit represented by the following chemical formula 2; a third repeating unit represented by the following chemical formula 3; and a fourth repeating unit represented by the following chemical formula 4.

[0056] [Chemical Formula 1]

[0057]

[0058] In the above chemical formula 1, R1 is hydrogen, or an alkyl having 1 to 3 carbon atoms, and

[0059] [Chemical Formula 2]

[0060]

[0061] [Chemical Formula 3]

[0062]

[0063] In the above chemical formula 3, L is an alkylene having 2 to 5 carbon atoms, R is hydrogen or R2-O-CO-, and R2 is an alkyl group having 1 to 5 carbon atoms.

[0064] [Chemical Formula 4]

[0065] .

[0067] Ethylene-vinyl alcohol-based copolymers can be bonded to a polyethylene substrate and used for purposes such as packaging for long-term preserved foods. Foods packaged in this way undergo a high-pressure steam sterilization process. During this process, the adhesion between the ethylene-vinyl alcohol-based copolymer and the polyethylene substrate may weaken, which in turn reduces oxygen barrier properties and can cause problems with the long-term preservation of the food.

[0068] A conventional gas barrier film using a vinyl alcohol-based copolymer, represented by a saponified product of an ethylene-vinyl acetate copolymer, is manufactured by copolymerizing an olefin such as ethylene with a vinyl carboxylic acid compound such as vinyl acetate, then hydrolyzing the copolymer with a basic substance to produce a vinyl alcohol-based copolymer, and using the film.

[0069] The inventors of the present invention discovered that when a specific repeating unit containing a cyano group and a specific repeating unit containing a carboxyl group are introduced into such existing ethylene-vinyl alcohol-based copolymers, the adhesion to polyolefin substrates such as polyethylene and polypropylene can be significantly improved, and thus completed the present invention.

[0070] If the adhesion between the ethylene-vinyl alcohol-based copolymer and a polyolefin substrate such as polyethylene or polypropylene is improved, it is possible to prevent the degradation of physical properties, such as oxygen barrier properties, caused by moisture in the aforementioned high-pressure sterilization process.

[0072] A vinyl alcohol-based copolymer according to one aspect of the present invention can achieve excellent adhesion to a polyolefin substrate in the form of a quaternary copolymer comprising, in addition to the olefin-derived repeating unit (first repeating unit) and vinyl alcohol-derived repeating unit (second repeating unit) that were previously commonly used, a repeating unit including a cyano group (third repeating unit) and a repeating unit including a carboxyl group (fourth repeating unit), as described above.

[0075] The above-mentioned first repeating unit is a repeating unit derived from an olefin monomer having 2 to 10 carbon atoms, such as ethylene, propylene, butylene, pentene, hexene, or octene, and acts to increase the mechanical properties of the vinyl alcohol copolymer and to increase hydrophobicity to reduce hygroscopicity.

[0076] In addition, the first repeating unit can improve processability by lowering the glass transition temperature of the vinyl alcohol-based copolymer. Furthermore, the first repeating unit can improve the bonding properties between the vinyl alcohol-based copolymer and the polyolefin substrate by helping the ethylene copolymer-based adhesive used when bonding the vinyl alcohol-based copolymer and the polyolefin substrate to be dispersed within the vinyl alcohol-based copolymer.

[0077] Specifically, the first repeating unit may include a repeating unit derived from ethylene, and optionally, may further include one or more repeating units derived from olefin monomers having 3 to 20 carbon atoms or 3 to 10 carbon atoms, such as propylene, butylene, pentene, hexene, or octene.

[0079] According to one embodiment of the invention, the third repeating unit in the vinyl alcohol-based copolymer may be included in an amount of about 1 mol% to about 20 mol% with respect to the total sum of the second repeating unit and the third repeating unit, which is 100 mol%.

[0080] If the content of the third repeating unit relative to the total amount of the second repeating unit and the third repeating unit, that is, the substitution rate of the vinyl alcohol series being substituted with a cyano group, is too low compared to the above range, a problem may arise in which the adhesion to polyolefins, etc. is reduced, and if the cyano group substitution rate is too high, a problem may arise in which the gas barrier performance is significantly reduced.

[0082] In addition, in the above chemical formula 3, L may be ethylene, 1-methylethylene, or n-propylene, R may be hydrogen or R2-O-CO-, and R2 may be an alkyl group having 1 to 5 carbon atoms.

[0084] Specifically, the third repeating unit may be represented by the following chemical formula 3-1 or chemical formula 3-2.

[0085] [Chemical Formula 3-1]

[0086]

[0087] [Chemical Formula 3-2]

[0088]

[0090] According to one embodiment of the invention, the first repeating unit in the vinyl alcohol-based copolymer may be about 10 mol% to about 50 mol%, or about 10 mol% or more, or about 15 mol% or more, with respect to the total sum of the first to fourth repeating units of 100 mol%, and may be about 50 mol% or less, or about 48 mol% or less.

[0091] If the content of the first repeating unit, i.e., the olefin-derived repeating unit, is too low, problems such as reduced mechanical properties and increased hygroscopicity may occur during film manufacturing, and if the content of the first repeating unit is too high, problems such as significantly reduced gas barrier properties may occur.

[0093] In the present invention, the content of each repeating unit in the copolymer can be calculated from the results of 1H-nuclear magnetic resonance spectroscopy (1H-NMR) analysis. Specifically, using a Bruker Avance III HD 700 MHz 1H-NMR analyzer, the sample is dissolved in a dimethyl sulfoxide solvent (DMSO-d6), the 1H spectrum is measured at room temperature, and the content of each repeating unit can be calculated from the analysis results.

[0095] And, the first repeating unit may be an ethylene-derived repeating unit.

[0097] The above second repeating unit is derived from a monomer of the vinyl carboxylate series, such as vinyl acetate, and is subsequently formed by the hydrolysis reaction of the carboxyl group, and can increase the crystallinity of the copolymer and thereby play a role in improving gas barrier properties.

[0098] According to one embodiment of the invention, the second repeating unit may be about 30 mol% to about 80 mol%, or about 30 mol% or more, or about 40 mol% or more, or about 45 mol% or more, with respect to the total sum of the first to fourth repeating units of 100 mol%, and may be about 80 mol% or less, or about 75 mol% or less.

[0099] If the content of the second repeating unit, i.e., the vinyl alcohol-derived repeating unit, is too low, a problem may arise in which gas barrier properties are significantly reduced, and if the content of the second repeating unit is too high, a problem may arise in which mechanical properties are reduced during film manufacturing.

[0101] The above third repeating unit is a repeating unit formed by adding the hydroxyl group of the above second repeating unit to the unsaturated bond of the unsaturated nitrile-based compound, which can prevent a decrease in gas barrier properties and can play a role in improving adhesion to the polyolefin-based substrate.

[0102] Examples of the above unsaturated nitrile compounds include acrylonitrile, methacrylonitrile, 2-cyanoprofen, or 3-cyanoprofen, and any one or more of these may be used.

[0103] According to one embodiment of the invention, the third repeating unit may be included in an amount of about 1 mol% to about 30 mol%, or about 1 mol% or more, or about 0.02 mol% or more, or about 0.03 mol% or more, or about 0.04 mol% or more, or about 30 mol% or less, or less than about 30 mol%, or about 25 mol% or less, with respect to the total sum of the first to fourth repeating units of 100 mol%.

[0104] If the content of the third repeating unit, that is, the repeating unit including a cyano group, is too high, a problem may arise in which the gas barrier performance is significantly reduced, and if the content of the third repeating unit is too low, a problem may arise in which the adhesion to polyolefins, etc. is reduced.

[0105] In the present invention, the content of the third repeating unit can be calculated by determining the nitrogen content by the Kjeldahl method and inversely calculating using the molecular weight of each repeating unit, etc.

[0107] The above-mentioned fourth repeating unit is a repeating unit formed by the decomposition of nitrile (cyano) groups through hydrolysis after originating from an unsaturated nitrile-based monomer, and can play a role in improving adhesion to a polyolefin-based substrate by increasing the polarity of the vinyl alcohol-based copolymer.

[0108] Examples of the above unsaturated nitrile monomers include acrylonitrile, methacrylonitrile, 2-cyanoprofen, or 3-cyanoprofen, and any one or more of these may be used.

[0109] Here, the above-mentioned unsaturated nitrile monomer is included in the polymerization step of the copolymer and is included in the main chain of the copolymer, and in subsequent processes, all nitrile groups are hydrolyzed and converted into carboxyl groups, which are added to the hydroxyl group of the second repeating unit and connected to the side branch of the copolymer, and the cyano group remains in the final copolymer product, and is distinguished from the aforementioned unsaturated nitrile compound.

[0110] According to one embodiment of the invention, the fourth repeating unit may be included in an amount of about 1 mol% to about 30 mol%, or about 1 mol% or more, or about 0.02 mol% or more, or about 0.03 mol% or more, or about 0.04 mol% or more, or about 30 mol% or less, or less than about 30 mol%, or about 25 mol% or less, with respect to the total sum of the first to fourth repeating units of 100 mol%.

[0111] If the content of the fourth repeating unit, that is, the repeating unit including a cyano group, is too high, a problem may arise in which the gas barrier performance is significantly reduced, and if the content of the fourth repeating unit is too low, a problem may arise in which the adhesion to polyolefins, etc. is reduced.

[0113] A vinyl alcohol-based copolymer according to one embodiment of the invention can be manufactured through a series of reactions described below.

[0115] (polymerization)

[0116] First, a main chain constituting the basic form of a vinyl alcohol-based copolymer according to one embodiment of the present invention is formed by a polymerization reaction.

[0117] (Monomer)

[0118] A first monomer, which is an olefin-based monomer, can be used in the polymerization reaction.

[0119] The first monomer may include an olefin monomer having 3 to 20 carbon atoms or 3 to 10 carbon atoms, such as ethylene, propylene, butylene, pentene, hexene, or octene; more specifically, it may include ethylene and optionally one or more of propylene, butylene, pentene, hexene, and octene, and may form a first repeating unit within the copolymer by polymerization.

[0121] In addition, a second monomer, which is a vinyl acetate monomer, can be used in the polymerization reaction.

[0122] The above vinyl acetate monomer participates in a polymerization reaction to form a copolymer main chain containing acetate as a side branch, after which the carboxyl group of acetate is hydrolyzed. Subsequently, a hydroxyl group remains on the side branch of the copolymer main chain and can form a second repeating unit.

[0124] In addition, a fourth monomer, which is an unsaturated nitrile monomer, can be used in the polymerization reaction.

[0125] Examples of the above unsaturated nitrile monomers include acrylonitrile, methacrylonitrile, 2-cyanoprofen, or 3-cyanoprofen, and any one or more of these may be used.

[0126] The above unsaturated nitrile monomer participates in a polymerization reaction to form a copolymer main chain containing nitrile groups (or cyano groups) as side branches, after which the nitrile groups are hydrolyzed. Subsequently, carboxyl groups remain on the side branches of the copolymer main chain to form a fourth repeating unit.

[0128] (polymerization)

[0129] The above polymerization reaction can be carried out according to conventional methods used in the technical field to which the present invention belongs, and specifically, can be carried out using a radical initiator in a solvent.

[0130] During the polymerization described above, the amount of each monomer added can be determined by considering the content of each repeating unit in the final copolymer produced.

[0131] The above initiators include azo compounds such as 2,2'-azobis-(2,4-dimethylvaleronitrile), 2,2'-azobis-isobutyronitrile, 2,2'-azobis-(4-methoxy-2,4-dimethylvaleronitrile), and 2,2'-azobis-(2-methyl isobutyrate); peroxy-dicarbonates such as bis-(4-t-butylcyclohexyl) peroxy-di-carbonate, di-cyclohexyl peroxy-di-carbonate, bis(2-ethylhexyl) di-sec-butylperoxy-di-carbonate, and di-isopropylperoxy-di-carbonate; Radical initiators such as acetyl peroxide, lauroyl peroxide, di-lauroyl peroxide, di-decanoyl peroxide, and di-octanoyl peroxide may be used, and any one or a mixture of two or more of these may be used.

[0132] The above initiator may be added in a molar ratio of about 0.001 to about 1 mole relative to a total monomer amount of 100 moles, and more specifically, in a molar ratio of about 0.001 or more, or about 0.01 or more, and in a molar ratio of about 1 or less, or about 0.1 or less.

[0133] As the above solvent, a solvent having high solubility for the monomer compound may be used. Specifically, examples include alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, t-butyl alcohol, n-pentyl alcohol, etc.; ketones such as methyl ethyl ketone, acetone, etc.; or sulfoxides such as dimethyl sulfoxide, etc., and any one or more of these may be used. Among these, an alcohol exhibiting superior solubility may be used, and more specifically, t-butyl alcohol may be used.

[0134] The above solvent may be added in an amount of about 30 to about 60 parts by weight per 100 parts by weight of the total amount of the monomer, and more specifically, in an amount of about 30 parts by weight or more, or about 40 parts by weight or more, and about 60 parts by weight or less, or about 50 parts by weight or less. When added within the above-mentioned range, a polymer can be produced with excellent polymerization efficiency through the complete dissolution of the monomer materials.

[0135] The above polymerization reaction can be carried out at about 50 to about 80°C, and more specifically at about 50°C or higher, or about 60°C or higher, and at about 80°C or lower, or about 70°C or lower. When the reaction is carried out within the above temperature range, there is no concern about a decrease in polymerization efficiency due to the occurrence of unreacted or over-reacted reactions.

[0136] As described above, by polymerizing a monomer mixture comprising the first, second, and fourth monomers, a polymer comprising a repeating unit derived from the first monomer (ethylene-based monomer), a repeating unit derived from the second monomer (vinyl acetate), and a repeating unit derived from the fourth monomer (unsaturated nitrile-based monomer) can be prepared, so-called a prepolymer.

[0138] (Hydrolysis)

[0139] Subsequently, an acid or a base is added to the above prepolymer to carry out a hydrolysis reaction.

[0140] Through a hydrolysis reaction, the carboxyl group of the vinyl acetate-derived repeating unit is hydrolyzed to separate the acetate group, leaving the hydroxyl group on the prepolymer. The copolymer finally formed therefrom may include a second repeating unit.

[0141] In addition, through a hydrolysis reaction, the nitrile (cyano) group of the repeating unit derived from the unsaturated nitrile monomer is also hydrolyzed and converted into a carboxyl group, and the copolymer finally formed therefrom may include a fourth repeating unit.

[0142] As mentioned above, this hydrolysis can proceed under acidic or basic conditions, but if it proceeds under basic conditions, the reaction can be further promoted by the saponification of the acetate group, and the esterification reaction in which the separated acetate and hydroxyl group recombine to form an ester can be prevented.

[0143] In the case of basic conditions, it can be performed by adding a basic substance such as caustic soda.

[0144] The above basic substance may be added in a molar ratio of about 5 to about 15 with respect to about 100 moles of the second monomer used in polymerization, and more specifically, in an amount of about 5 molar ratio or more, or about 7 molar ratio or more, and about 15 molar ratio or less, or about 12 molar ratio or less.

[0145] The above basic substance may be introduced in a solution form dissolved in an alcohol-based solvent to increase reaction efficiency.

[0146] The above hydrolysis can be carried out at a temperature of about 50 to about 70°C, more specifically at about 50°C or higher, or about 60°C or higher, and about 70°C or lower, or about 65°C or lower. When carried out within the above temperature range, the hydrolysis reaction can sufficiently occur at an appropriate reaction rate.

[0148] (Michael added)

[0149] Subsequently, an addition reaction is carried out in which a hydroxyl group formed by hydrolysis is added to the unsaturated bond of an unsaturated nitrile compound under basic conditions to introduce a cyano group into the side chain of the prepolymer.

[0150] When preparing a copolymer of an olefin and a vinyl carboxylate compound using an unsaturated monomer containing a cyano group as a comonomer to introduce a cyano group into the copolymer, there is a high possibility that the cyano group will be hydrolyzed during the polymerization process, and there is a concern that the physical properties of the copolymer may deteriorate, such as failing to sufficiently obtain the desired moisture barrier effect.

[0152] Accordingly, in the present invention, after the saponification reaction of the prepolymer is performed to a certain level or higher, an addition reaction with an unsaturated nitrile-based compound is carried out to bond a cyanoalkyl group to the side chain of the copolymer, thereby enabling the improvement effect resulting from the introduction of the cyanoalkyl group while maintaining the excellent physical properties of the copolymer.

[0153] In addition, the timing of the addition of the above-mentioned unsaturated nitrile compound affects the degree of saponification and cyanoalkylation of the prepolymer. As previously mentioned, the addition reaction proceeds after a hydroxyl group is formed from an acetate group through the hydrolysis of the prepolymer, with the anion of this hydroxyl group attacking the double bond of the unsaturated nitrile compound. Therefore, if the content of the above-mentioned intermediate in the reaction system is insufficient or excessively high, it is difficult to satisfy the above-mentioned cyanoalkyl substitution rate.

[0154] Specifically, if the degree of saponification of the prepolymer is less than 95%, there is a risk that thermal stability will be reduced and mechanical strength and gas barrier properties will be reduced when manufacturing a film through melt molding.

[0155] In addition, as described above, since unsaturated nitrile compounds, such as acrylonitrile as a representative example, react with intermediates existing in the form of salts of hydroxyl anions and cations derived from basic substances, which are generated by the hydrolysis of prepolymers, when acrylonitrile is introduced as an unsaturated nitrile compound when the saponification reaction is less than 95%, the basic substance used in the saponification reaction reacts with acrylonitrile in advance to form by-products such as cyanoethanol (Cyanoethanol; HO-CH2-CH2-CN), 2-cyanoethyl ether (2-Cyanoethyl ether; (CN-CH2-CH2)2-O), cyanohexanone, or dicyanoethylated acetone, and as a result, the above intermediates are not sufficiently generated, and cyanoalkylation may be reduced.

[0156] In this case, it is difficult to obtain the effects of increased moisture stabilization and reduced moisture penetration due to cyanoalkylation, and the amount of byproduct generated increases due to the above side reaction.

[0157] Meanwhile, after the saponification reaction is completely finished, cyanoalkyl substitution is difficult because it exists as a saponified prepolymer having a hydroxyl group at the terminal, rather than as an intermediate existing in the form of a salt of a hydroxyl anion and a cation derived from a basic substance.

[0158] Therefore, for cyanoalkyl substitution, cationic substitution of the saponified prepolymer, such as NaOH substitution through the addition of basic substances like caustic soda, must be performed first. However, because the saponified prepolymer has low solubility in solvents, NaOH reacts with unsaturated nitrile compounds to produce by-products before the saponified prepolymer is substituted with NaOH. Consequently, an additional purification process is required to remove by-products, which leads to the problem of generating a large amount of wastewater.

[0159] Accordingly, it is preferable that the above-mentioned unsaturated nitrile compound be introduced when an intermediate existing in the form of a salt of a hydroxyl anion and a cation derived from a basic substance is present in the reaction system at an optimal content. Specifically, it is preferable that the compound be introduced when the saponification reaction is 95% or more and up to the point of completion of the saponification reaction, i.e., up to the point of reaching 100% of the saponification reaction, or when the saponification reaction is 95% or more and just before completion of the saponification reaction, i.e., when it is less than 100% or 99% or less.

[0160] In this case, the generation of by-products caused by free NaOH can be prevented by introducing an unsaturated nitrile compound when NaOH is substituted into the copolymer chain. More specifically, the unsaturated nitrile compound can be introduced 3 hours after the completion of the introduction of the reactants for the saponification reaction, and even more specifically, 3 to 4 hours after the completion of the introduction of the reactants.

[0161] In the present invention, the progress of the saponification reaction can be confirmed through 1H-nuclear magnetic resonance spectroscopy analysis from changes in the intensity of functional group peaks that are generated or extinguished as a result of the saponification reaction, and the progress of the saponification reaction can be estimated as reaction time from repeated analysis results. Specifically, the point at which the saponification reaction is about 50% is about 1 hour after the completion of reactant input, and the point at which it is about 95% is about 3 hours after the completion of reactant input.

[0162] Examples of the above unsaturated nitrile compounds include acrylonitrile, methacrylonitrile, 1-cyanoprofen, and 3-cyanoprofen, and any one or more of these may be used.

[0163] In addition, the amount of the above-mentioned unsaturated nitrile compound added can be determined by considering the cyanoalkyl substitution rate in the final copolymer produced, that is, the content of the third repeating unit.

[0164] In addition, the reaction after adding the above-mentioned unsaturated nitrile compound can be carried out at a temperature range of about 0°C or higher, or about 40°C or higher and about 60°C or lower, for about 2 hours or more, or about 24 hours or more and about 48 hours or less, or about 30 hours or less.

[0165] As a result of the above reaction, product particles are prepared in a dispersed form in a solvent, and subsequently, the vinyl alcohol-based copolymer of the present invention can be obtained by optionally performing further processes such as blowing in steam to volatilize and remove the solvent, precipitating the particles dispersed in water, and separating and washing.

[0166] In the above vinyl alcohol-based copolymer, as cyanoalkyl groups are bonded to the side chains of the copolymer, a peak of the cyanoethyl group (-CH2-CN) bonded to the side chain appears at about 2.7 ppm during 1H-nuclear magnetic resonance spectroscopy analysis.

[0167] In addition, as the timing of the addition of the unsaturated nitrile-based compound is controlled, the content of by-products in the vinyl alcohol-based copolymer being produced can be minimized. Specifically, the vinyl alcohol-based copolymer may contain by-products in an amount of 20% or less of the total weight of the copolymer, more specifically, in an amount greater than 0% by weight and 15% or less by weight, or 12% or less by weight, and the by-products may be cyano group-containing compounds such as cyanoethanol, 2-cyanohexanone, cyanoethyl ether, dicyanoethylated acetone, or mixtures thereof.

[0168] The vinyl alcohol-based copolymer produced by the above-described manufacturing method has cyanoalkyl groups with excellent moisture stability bonded to the side chains, thereby reducing moisture penetration and enabling it to exhibit excellent gas barrier properties against gases such as oxygen, water vapor, carbon dioxide, and nitrogen even in humid environments. Accordingly, it can be used in various applications such as films, sheets, containers, and fibers where gas barrier properties are required.

[0170] And, according to another aspect of the present invention, a gas barrier film comprising the vinyl alcohol-based copolymer described above is provided.

[0171] The above film can be manufactured according to conventional molding methods such as injection molding, compression molding, and extrusion molding. Examples of extrusion molding methods include the T-die method, blow molding, pipe extrusion, line extrusion, release die extrusion, and inflation method. Additionally, co-extrusion molding between the vinyl alcohol-based copolymer and another thermoplastic resin layer is also possible.

[0172] Accordingly, the above-mentioned gas barrier film-forming composition may be included without special limitations as long as it is used in a film-forming composition applied to a conventional film molding method, except that it includes the above-mentioned vinyl alcohol-based copolymer as a base resin.

[0173] The above film-forming composition may further include known additives such as reinforcing materials like glass fibers and carbon fibers, fillers, colorants, stabilizers like hydrotalcite, foaming agents, drying agents, and thermoplastic resins as needed.

[0174] The above film may be used in the form of an independent film, in the form of a coating film on a substrate, or in the form of a multilayer structure with other films.

[0175] In the case of a multilayer structure, it may include the aforementioned vinyl alcohol-based copolymer layer, a polyolefin layer, and a tie-resin for bonding the two.

[0176] Since the above film can maintain excellent gas barrier properties even under high humidity conditions, it can be utilized as packaging materials such as food packaging films, sheets, cosmetic containers, gasoline tank containers, etc. Specifically, the above film has a 95% RH oxygen permeability of approximately 0.05 cc / 20 µm / m² 2 24hr / atm or less, more specifically, about 0.03 cc / 20 µm / m2 It is 24 hr / atm or less, and approximately 0.001 cc / 20 µm / m² 2 24hr / atm or more, or about 0.01 cc / 20 µm / m² 2 It may be more than 24hr / atm. Effects of the invention

[0178] The vinyl alcohol-based copolymer according to the present invention has cyanoalkyl groups with excellent moisture stability bonded to its side chains, thereby reducing moisture penetration and enabling it to exhibit excellent gas barrier properties even in humid environments. Accordingly, the vinyl alcohol-based copolymer is useful as a gas barrier film. Specific details for implementing the invention

[0180] The operation and effects of the invention will be explained in more detail below through specific embodiments. However, these are presented as examples of the invention and do not limit the scope of the invention in any way.

[0182] Example 1

[0183] polymerization

[0184] 100 parts by weight of vinyl acetate and 5 parts by weight of acrylonitrile were added to a 2L reactor containing 100 parts by weight of methanol, and 20 parts by weight of ethylene were added, and then the change in internal pressure of the reactor was stopped.

[0185] Subsequently, the temperature was raised to 70 ℃, 0.3 parts by weight of azobisisobutyronitrile (AIBN) was dissolved in 5 parts by weight of methanol as an initiator and introduced into a reactor, and the polymerization reaction was carried out for 5 hours while stirring at 200 rpm.

[0186] Afterward, the reactor was cooled to room temperature to obtain a copolymer containing the following repeating units.

[0187] , ,

[0189] hydrolysis

[0190] 100 parts by weight of the above prepolymer were introduced into a reactor containing 500 parts by weight of methanol, and dissolved at a temperature of 80 ℃ at 200 rpm.

[0191] Subsequently, 1 part by weight of NaOH dissolved in 10 parts by weight of water and 50 parts by weight of methanol was introduced into a reactor and the reaction was carried out for 5 hours to obtain a copolymer containing the following repeating units.

[0192] , ,

[0194] Addition reaction

[0195] 10 parts by weight of acrylonitrile were added to the reactor relative to 100 parts by weight of the polymer.

[0196] The reaction was carried out by stirring at 200 rpm for 2 hours while maintaining the temperature at approximately 80 ℃.

[0197] Afterward, the reaction was terminated and cooled to room temperature to obtain a copolymer containing the following repeating units.

[0198] , , ,

[0200] Example 2

[0201] A copolymer comprising the following repeating units was obtained by proceeding in the same manner as in Example 1, except that methyl-cyanoacrylate was used instead of acrylonitrile in the addition reaction of Example 1 above.

[0203] Example 3

[0204] A copolymer comprising the following repeating units was obtained by proceeding in the same manner as in Example 1, except that 150 parts by weight of vinyl acetate, 15 parts by weight of ethylene, 20 parts by weight of acrylonitrile, and 0.1 parts by weight of AIBN as an initiator were used in the polymerization reaction of Example 1 above.

[0205] , , ,

[0207] Example 4

[0208] A copolymer comprising the following repeating units was obtained by proceeding in the same manner as in Example 1, except that T-butanol was used instead of methanol in the polymerization reaction of Example 1 above.

[0209] , , ,

[0211] Example 5

[0212] Except for setting the temperature of the polymerization reaction of Example 1 to 60 ℃ and the temperature of the hydrolysis reaction to 100 ℃, the process was carried out in the same manner as Example 1 to obtain a copolymer comprising the following repeating units.

[0213] , , ,

[0215] Reference Example 1

[0216] A copolymer comprising the following repeating units was obtained by proceeding in the same manner as in Example 1, except that 40 parts by weight of vinyl acetate, 35 parts by weight of ethylene, 25 parts by weight of acrylonitrile, and 0.1 parts by weight of AIBN as an initiator were used relative to 100 parts by weight of methanol in the polymerization reaction of Example 1 above.

[0217] , , ,

[0219] Reference Example 2

[0220] A copolymer comprising the following repeating units was obtained by proceeding in the same manner as in Example 1, except that 300 parts by weight of vinyl acetate, 20 parts by weight of ethylene, 25 parts by weight of acrylonitrile, and 0.1 parts by weight of AIBN as an initiator were used relative to 100 parts by weight of methanol in the polymerization reaction of Example 1 above.

[0221] , , ,

[0223] Reference Example 3

[0224] Except for using 50 parts by weight of acrylonitrile in the addition reaction of Example 1, the process was carried out in the same manner as Example 1 to obtain a copolymer comprising the following repeating units.

[0225] , , ,

[0227] Comparative Example 1

[0228] polymerization

[0229] 100 parts by weight of vinyl acetate and 20 parts by weight of ethylene were added to a 2L reactor containing 100 parts by weight of methanol, and then waited until there was no change in the internal pressure of the reactor.

[0230] Afterwards, the temperature was raised to 70 ℃, 0.3 parts by weight of AIBN were dissolved in 5 parts by weight of methanol as an initiator and introduced into a reactor, and the polymerization reaction was carried out for 5 hours while stirring at 200 rpm.

[0231] Then, the reactor was cooled to room temperature to obtain an ethylene-vinyl acetate copolymer containing the following repeating units.

[0232] ,

[0234] Comparative Example 2

[0235] A copolymer comprising the following repeating units was obtained by proceeding in the same manner as in Example 1, except that acetonitrile was used instead of acrylonitrile in the addition reaction of Example 1.

[0236] For reference, acetonitrile is non-reactive, does not participate in addition reactions, and is not included in copolymers.

[0237] , ,

[0239] Comparative Example 3

[0240] Except for setting the temperature of the polymerization reaction in Example 1 to 45 ℃ and the temperature of the hydrolysis reaction to 50 ℃, the process was carried out in the same manner as Example 1.

[0241] However, in this case, it was impossible to manufacture vinyl alcohol-based copolymers.

[0243] The copolymers prepared in the following examples and comparative examples were analyzed by the following method:

[0244] Weight average molecular weight (Mw) and molecular weight distribution (MWD; Mw / Mn)

[0245] <Analysis Conditions>

[0246] - Column: PL mixed B x 2

[0247] - Solvent: DMF / 0.05M LiBr (0.45 μm filtered)

[0248] - Flow rate: 1.0 ml / min

[0249] - Sample concentration: 1.0 mg / ml

[0250] - Injection volume: 100 μl

[0251] - Column temperature: 65 ℃

[0252] -Detector: Waters refractive index detector

[0253] -Standard: Polystyrene (PS) (corrected by a cubic function)

[0254] Six types of polystyrene standards with molecular weights (g / mol) of 9,600 / 31,420 / 113,300 / 327,300 / 1,270,000 / 4,230,000 were used.

[0255] -Data processing:

[0256] 1) The copolymer sample was dissolved in dimethylformamide (DMF) at a concentration of 1 mg / ml and filtered through a 0.45 μm syringe filter. 2) A GPC chromatogram was obtained by injecting the sample solution. 3) A GPC chromatogram was obtained by injecting the standard solution. 4) A calibration curve and an equation were derived from the chromatogram of the standard solution, and the weight-average molecular weight and number-average molecular weight of the sample were obtained by substituting the retention time of the sample solution into the equation. The molecular weight distribution (Mw / Mn) was calculated from the measured weight-average molecular weight (Mw) and number-average molecular weight (Mn) values.

[0258] Cyanoethyl substitution rate

[0259] The nitrogen content of the prepared copolymer was determined by the Kjeldahl method, and from that value, the cyanoethyl substitution rate, that is, the content of the third repeating unit (mol%) relative to the total sum of the second and third repeating units in the final prepared vinyl alcohol-based copolymer (100 mol%), was calculated according to the following mathematical formula 1.

[0260] [Mathematical Formula 1]

[0261] Cyanoalkyl substitution rate = [(Molar% of 3rd repeating unit) / (Molar% of 2nd repeating unit + Molar% of 3rd repeating unit)] X 100

[0262] In the above mathematical formula 1, the mole% of the second repeating unit and the third repeating unit is a value based on 100 mole% of the total sum of repeating units in the vinyl alcohol-based copolymer produced at the end.

[0264] Content of each derived repeating unit in the copolymer

[0265] Using a 1H NMR (Bruker Avance III HD 700Mhz) as an analytical instrument, the sample was dissolved in dimethyl sulfoxide solvent (DMSO-d6), and the 1H-NMR spectrum was measured at room temperature.

[0266] The content of each repeating unit was estimated from the peak positions and areas in the measured spectrum.

[0268] Film Manufacturing

[0269] Using the copolymer compounds prepared in the above examples and comparative examples, three types of 5-layer co-extruded films of LDPE / adhesive resin / ethylene-vinyl alcohol copolymer composition / adhesive resin / LDPE (thickness 50 / 10 / 10 / 10 / 50: unit is μm) were prepared.

[0270] Here, LG Chem FB0300 (MI=3.0g / 10 min; 190℃, 2160g load) was used as the LDPE, and Dow's BYNEL 40E1053 tie resin, an anhydride-based resin, was used as the adhesive resin.

[0271] Molding was carried out at extrusion temperatures of 210°C, 160°C, and 170°C for the ethylene-vinyl alcohol copolymer composition, LDPE, and adhesive resin, respectively, and at a die temperature of 220°C.

[0272] The specifications of the extruder and T-die for each resin are as follows.

[0273] LDPE; 30ø extruder

[0274] Adhesive resin; 26ø extruder

[0275] EVOH; 20ø extruder

[0276] T-die; width 300mm

[0277] In addition, the temperature of the cooling roll was set to 55℃ and the drawing speed to 4m / min.

[0279] Bond strength

[0280] Using the film prepared above, the peel strength value was measured using an autograph at a tensile speed of 250 mm / min under conditions of 20℃ and 80% relative humidity.

[0281] Measurements were performed twice: immediately after manufacturing the film, and after manufacturing the film and exposing it to conditions of 20°C and 80% relative humidity for about 5 days.

[0283] 95% RH oxygen permeability

[0284] Using the MOCON OX-TRAN 2 / 20 from Modern Control as an oxygen permeability measuring device, five samples taken from random locations on the film were tested at a temperature of 20°C, humidity of 95%RH, and oxygen pressure of 2.5 kg / cm² 2 Oxygen permeability (unit: cc / 20μm / m²) under the conditions 2 (24hr / atm) was measured, and the minimum value among them was cited as the oxygen permeability value.

[0286] The above measurement values ​​are summarized in the table below.

[0287] division Interlayer bonding strength (unit: g / 15mm) Weight-average molecular weight* Oxygen evaporation** 1st / 2nd / 3rd / 4th (Unit: mol%) After manufacturing 5 days later Example 1 800 920 1.6 0.4 25 / 65 / 5 / 5 Example 2 780 880 1.7 0.6 25 / 65 / 6 / 4 Example 3 750 820 1.3 0.7 20 / 68 / 6 / 6 Example 4 770 900 1.5 0.4 22 / 68 / 5 / 5 Example 5 700 810 1.8 0.5 22 / 64 / 4 / 10 Comparative Example 1 330 420 1.6 0.4 30 / 70 / 0 / 0 Reference Example 1 560 620 1.0 3.5 54 / 32 / 1 / 13 Reference Example 2 460 600 1.1 2.0 12 / 78 / 2 / 8 Reference Example 3 550 610 1.1 0.5 25 / 35 / 35 / 5 Comparative Example 2 (Use of acetonitrile instead of AN) 330 400 1.5 1.7 30 / 65 / 0 / 5 Comparative Example 3 Copolymer not manufactured

[0288] *Unit: 100,000

[0289] **Unit: cc / m 2 ·20μm·atm·day

[0290] Referring to Table 1 above, it can be clearly seen that the film prepared with the composition according to the embodiment of the present invention has excellent bonding strength and oxygen permeability compared to the comparative example.

Claims

Claim 1 A first repeating unit represented by the following chemical formula 1; a second repeating unit represented by the following chemical formula 2; A vinyl alcohol-based copolymer comprising: a third repeating unit represented by the following chemical formula 3; and a fourth repeating unit represented by the following chemical formula 4, wherein the fourth repeating unit is included in an amount of 1 to 30 mol% with respect to the total sum of the first to fourth repeating units of 100 mol%: [Chemical Formula 1] In the above Chemical Formula 1, R1 is hydrogen, or an alkyl having 1 to 3 carbon atoms, and [Chemical Formula 2] [Chemical Formula 3] In the above Chemical Formula 3, L is an alkylene having 2 to 5 carbon atoms, R is hydrogen or R2-O-CO-, and R2 is an alkyl group having 1 to 5 carbon atoms [Chemical Formula 4]. . Claim 2 A vinyl alcohol-based copolymer according to claim 1, wherein the third repeating unit is included in an amount of 1 mol% to 20 mol% with respect to the total sum of the second repeating unit and the third repeating unit in the copolymer of 100 mol%. Claim 3 A vinyl alcohol-based copolymer according to claim 1, wherein in the above formula 3, L is ethylene, 1-methylethylene, or n-propylene, R is hydrogen or R2-O-CO-, and R2 is a methyl group, ethyl group, or propyl group. Claim 4 In claim 1, the third repeating unit is a vinyl alcohol-based copolymer represented by the following chemical formula 3-1 or chemical formula 3-2. [Chemical Formula 3-1] [Chemical Formula 3-2] Claim 5 A vinyl alcohol-based copolymer according to claim 1, wherein the first repeating unit is included in an amount of 10 to 50 mol% relative to the total sum of the first to fourth repeating units of 100 mol%. Claim 6 In claim 1, the first repeating unit is a vinyl alcohol-based copolymer, which is an ethylene-derived repeating unit. Claim 7 A vinyl alcohol-based copolymer according to claim 1, wherein the second repeating unit is included in an amount of 30 to 80 mol% relative to the total sum of the first to fourth repeating units of 100 mol%. Claim 8 A vinyl alcohol-based copolymer according to claim 1, wherein the third repeating unit is included in an amount of 1 to 30 mol% with respect to the total sum of the first to fourth repeating units of 100 mol%. Claim 9 delete Claim 10 A gas barrier film comprising a vinyl alcohol-based copolymer according to any one of claims 1 to 8.

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