Pellets comprising modified ethylene-vinylalcohol copolymer and method for producing the same

Abstract

To provide a method for producing pellets containing a modified EVOH which is less likely to cause blocking, and to provide the pellets containing the modified EVOH.SOLUTION: There is provided a method for producing pellets containing a modified EVOH, the method including: a melt-kneading step of feeding a water-containing modified ethylene-vinylalcohol copolymer (EVOH) to an extruder and melt-kneading the same to obtain a molten material having a water content of 4 to 35 mass%; a coagulation step of extruding the molten material into a coagulation bath to obtain a strand-like coagulated product; a cutting step of cutting the coagulated product to obtain a cylindrical water-containing pellet; and a drying step of drying the water-containing pellet, wherein the modified EVOH is represented by the following formula (I), the content (mol%) of a, b, and c with respect to all monomer units satisfies a specific range, and the degree of saponification (DS) is 90 mol% or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to pellets containing a modified ethylene-vinyl alcohol copolymer and a method for producing the same. [Background technology]

[0002] Ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as EVOH) has excellent gas barrier properties, transparency, aroma retention, solvent resistance, oil resistance, etc., and is used in a wide range of applications, including various packaging containers such as food packaging containers, pharmaceutical packaging containers, industrial chemical packaging containers, and agricultural chemical packaging containers, as well as fuel containers, taking advantage of these properties. When producing such molded products, secondary processing is often performed after melt molding of EVOH. For example, it is widely practiced to stretch the EVOH to improve its mechanical strength, or to thermoform a film or sheet containing an EVOH layer to form it into a container shape.

[0003] In recent years, there has been an increasing demand for higher stretching ratios and for thermoforming molded products with deeper draw shapes. Furthermore, since EVOH is a resin with a high elastic modulus, there is also an increasing demand for resins with greater flexibility.

[0004] For these reasons, there is a demand for resins that have improved secondary processability and flexibility without impairing as much as possible the inherent properties of EVOH, such as gas barrier properties, transparency, aroma retention, solvent resistance, and oil resistance.

[0005] Patent Document 1 describes a modified EVOH in which 2-methylene-1,3-propanediol units are copolymerized, which is obtained by copolymerizing ethylene, vinyl acetate, and 2-methylene-1,3-propanediol diacetate and then saponifying the copolymer. The modified EVOH is described as having excellent barrier properties, flexibility, and secondary processability. However, the modified EVOH has problems in that pellets block each other during the drying process during production, and molded products such as films and sheets obtained from the modified EVOH block each other when stacked or rolled for storage.

[0006] On the other hand, Patent Document 2 describes a modified EVOH containing an anti-blocking agent made of specific inorganic particles. However, although the modified EVOH was found to improve blocking of films, it was insufficient in improving blocking between pellets. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] WO2014 / 024912 publication [Patent Document 2] JP 2019-182947 A Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made to solve the above problems, and provides a method for producing pellets containing a modified ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as pellets containing modified EVOH) that are less susceptible to blocking, and pellets containing modified EVOH. [Means for solving the problem]

[0009] The above-mentioned problems are solved by providing a method for producing pellets containing modified EVOH, the method comprising: a melt-kneading step of supplying hydrous modified EVOH to an extruder and melt-kneading it to obtain a molten material having a moisture content of 4 to 35 mass %, a coagulation step of extruding the molten material into a coagulation bath to obtain a strand-shaped coagulated material, a cutting step of cutting the coagulated material to obtain cylindrical hydrous pellets, and a drying step of drying the hydrous pellets, the modified EVOH being represented by the following formula (I), the contents (mol %) of a, b, and c relative to the total monomer units satisfy the following formulas (1) to (3), and the degree of saponification (DS) defined by the following formula (4) is 90 mol % or more.

[0010] [ka] [In formula (I), W is a hydrogen atom, a methyl group, or R 2 R represents a group represented by the formula -OY, and X, Y and Z each independently represent a hydrogen atom, a formyl group or an alkanoyl group having 2 to 10 carbon atoms. 1 , R 2 each independently represents a single bond, an alkylene group having 1 to 9 carbon atoms, or an alkyleneoxy group having 1 to 9 carbon atoms, and the alkylene group and the alkyleneoxy group may contain a hydroxyl group, an alkoxy group, or a halogen atom.] 24≦a≦55 (1) 0.01≦c≦10 (2) [100-(a+c)]×0.9≦b≦[100-(a+c)] (3) DS = [(total number of moles of X, Y, and Z that are hydrogen atoms) / (total number of moles of X, Y, and Z)] × 100 (4)

[0011] In this case, in the melt kneading step, it is preferable to supply a water-containing modified EVOH having a water content of 10 to 60% by mass to the extruder. It is also preferable that the melting point of the pellets containing the modified EVOH is 120 to 163° C. It is also preferable that the temperature T0 of the melt in the extruder is 70 to 180° C., the cylinder temperature T1 of the extruder is 65 to 175° C., and T0 and T1 satisfy the following formula (5). 5≦T0-T1≦100 (5)

[0012] R in formula (I) 1 It is also preferred that is a single bond and W is a hydroxymethyl group.

[0013] The above-mentioned problem is solved by a pellet containing a cylindrical modified EVOH, the modified EVOH being represented by the following formula (I), the contents (mol %) of a, b, and c relative to all monomer units satisfying the following formulas (1) to (3), and a degree of saponification (DS) defined by the following formula (4) being 90 mol % or more, The problem is also solved by providing a pellet containing modified EVOH that satisfies the following formulas (6) and (7).

[0014] [ka]

[0015] [In formula (I), W is a hydrogen atom, a methyl group, or R 2 R represents a group represented by the formula -OY, and X, Y and Z each independently represent a hydrogen atom, a formyl group or an alkanoyl group having 2 to 10 carbon atoms. 1 , R 2 each independently represents a single bond, an alkylene group having 1 to 9 carbon atoms, or an alkyleneoxy group having 1 to 9 carbon atoms, and the alkylene group and the alkyleneoxy group may contain a hydroxyl group, an alkoxy group, or a halogen atom.] 24≦a≦55 (1) 0.01≦c≦10 (2) [100-(a+c)]×0.9≦b≦[100-(a+c)] (3) DS = [(total number of moles of X, Y, and Z that are hydrogen atoms) / (total number of moles of X, Y, and Z)] × 100 (4) ΔHma / ΔHmb≦1.05 (6) A B ≧ 0.3 (7) [In the formula (6), ΔHma (J / g) is the crystalline melting enthalpy of the pellets containing the modified EVOH, and ΔHmb is the crystalline melting enthalpy (J / g) of cylindrical comparative pellets having the same diameter and length as the pellets containing the modified EVOH, which are obtained by extruding the molten material obtained by holding the pellets containing the modified EVOH at 210° C. for 6 minutes into water and then cutting the extruded material. In addition, in the formula (7), A is the water absorption rate (mass%) of the pellets containing the modified EVOH after holding them at 40° C. and 90% RH for 300 hours, and B is the water absorption rate (mass%) of the comparative pellets after holding them at 40° C. and 90% RH for 300 hours.] Effect of the Invention

[0016] In the manufacturing method of the present invention, pellets containing hydrous modified EVOH are unlikely to block with each other during the drying process, so that pellets containing modified EVOH are manufactured with good productivity. Moreover, pellets containing modified EVOH are excellent in extrusion stability and thermal stability during molding. By using such pellets containing modified EVOH, molded products with excellent flexibility and gas barrier properties are manufactured with good productivity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention is a method for producing pellets containing modified EVOH, comprising a melt-kneading step of supplying hydrous modified EVOH to an extruder and melt-kneading it to obtain a molten material having a moisture content of 4 to 35 mass%, a coagulation step of extruding the molten material into a coagulation bath to obtain a strand-shaped coagulated material, a cutting step of cutting the coagulated material to obtain cylindrical hydrous pellets, and a drying step of drying the hydrous pellets, wherein the modified EVOH is represented by the following formula (I), the contents (mol %) of a, b, and c relative to the total monomer units satisfy the following formulas (1) to (3), and the saponification degree (DS) defined by the following formula (4) is 90 mol % or more.

[0018] [ka]

[0019] [In formula (I), W is a hydrogen atom, a methyl group, or R 2 R represents a group represented by the formula -OY, and X, Y and Z each independently represent a hydrogen atom, a formyl group or an alkanoyl group having 2 to 10 carbon atoms. 1 , R 2 each independently represents a single bond, an alkylene group having 1 to 9 carbon atoms, or an alkyleneoxy group having 1 to 9 carbon atoms, and the alkylene group and the alkyleneoxy group may contain a hydroxyl group, an alkoxy group, or a halogen atom.] 24≦a≦55 (1) 0.01≦c≦10 (2) [100-(a+c)]×0.9≦b≦[100-(a+c)] (3) DS = [(total number of moles of X, Y, and Z that are hydrogen atoms) / (total number of moles of X, Y, and Z)] × 100 (4)

[0020] In the past, modified EVOH was known to improve flexibility, but blocking, in which the modified EVOH adheres to each other, was a problem. Although an improvement was observed by adding a blocking inhibitor made of a specific inorganic particle to the modified EVOH, blocking between the pellets occurred when producing pellets containing the more flexible modified EVOH, and this still caused problems. In contrast, in the method for producing pellets containing modified EVOH of the present invention, a melt-kneading step for melt-kneading the modified EVOH, a solidifying step for solidifying the molten material, and a cutting step for cutting the strand-shaped solidified material are performed under specific conditions, so that blocking of the pellets containing modified EVOH is suppressed in the subsequent drying step, and pellets containing modified EVOH are produced with good productivity. Moreover, the pellets containing modified EVOH have excellent extrusion stability and thermal stability during molding. By using such pellets containing modified EVOH, molded products with excellent flexibility and gas barrier properties are produced with good productivity.

[0021] The modified EVOH used as a raw material is represented by the following formula (I), the contents (mol %) of a, b, and c relative to the total monomer units satisfy the following formulas (1) to (3), and the degree of saponification (DS) defined by the following formula (4) is 90 mol % or more. This modified EVOH contains, in addition to ethylene units and vinyl alcohol units, monomer units having a primary hydroxyl group (W, Z, and R in formula (I)). 1 By containing the monomer unit (the monomer unit at the right end including ...

[0022] [ka]

[0023] [In formula (I), W is a hydrogen atom, a methyl group, or R 2 R represents a group represented by the formula -OY, and X, Y and Z each independently represent a hydrogen atom, a formyl group or an alkanoyl group having 2 to 10 carbon atoms. 1 , R 2 each independently represents a single bond, an alkylene group having 1 to 9 carbon atoms, or an alkyleneoxy group having 1 to 9 carbon atoms, and the alkylene group and the alkyleneoxy group may contain a hydroxyl group, an alkoxy group, or a halogen atom.]

[0024] R 1 , R 2 each independently represents a single bond, an alkylene group having 1 to 9 carbon atoms, or an alkyleneoxy group having 1 to 9 carbon atoms. The alkylene group and alkyleneoxy group may contain a hydroxyl group, an alkoxy group, or a halogen atom. The number of carbon atoms in the alkylene group is preferably 5 or less, more preferably 3 or less, and even more preferably 2 or less. The number of carbon atoms in the alkyleneoxy group is preferably 5 or less, more preferably 3 or less, and even more preferably 2 or less.

[0025] W is preferably a hydrogen atom or R 2 More preferably, R 2 R is a group represented by -OH. 2 The group represented by -OH is preferably a hydroxyalkyl group (R 2 is an alkylene group).

[0026] Specific examples of the monomer unit having a primary hydroxyl group in the above formula (I) include monomer units represented by the following formulas (II) to (IV), and among these, the structural unit represented by formula (II) is preferred.

[0027] [ka]

[0028] [In formula (II), R 3 and R 4 each independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and the alkyl group may contain a hydroxyl group, an alkoxy group, or a halogen atom.]

[0029] [ka]

[0030] [In formula (III), R 5 has the same meaning as W in formula (I). 6 represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, and the alkyl group may contain a hydroxyl group, an alkoxy group, or a halogen atom.]

[0031] [ka]

[0032] [In formula (IV), R 7 and R 8each independently represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a cycloalkyl group having 3 to 8 carbon atoms, or a hydroxyl group, and the alkyl group and the cycloalkyl group may contain a hydroxyl group, an alkoxy group, or a halogen atom.

[0033] In the present invention, (1) R in the above formula (I) 1 is a single bond, W is a hydroxymethyl group (R 3 , R 4 (2) R in the above formula (I) is a hydrogen atom. 1 is a hydroxymethylene group, W is a hydrogen atom (R 5 , R 6 is a hydrogen atom), or (3) R 1 is a methylmethyleneoxy group, W is a hydrogen atom (R 7 , R 8 one of which is a methyl group and the other is a hydrogen atom), and among these, (1) is preferred.

[0034] In the above formula (I), X, Y and Z each independently represent a hydrogen atom, a formyl group or an alkanoyl group having 2 to 10 carbon atoms. When X, Y or Z is a hydrogen atom, the above formula (I) has a hydroxyl group, and when X, Y or Z is a formyl group or an alkanoyl group, the above formula (I) has an ester group. The alkanoyl group is preferably an alkanoyl group having 2 to 5 carbon atoms, more preferably an acetyl group, a propanoyl group, a butanoyl group, etc., and even more preferably an acetyl group. It is preferable that X, Y and Z are all hydrogen atoms or a mixture containing hydrogen atoms.

[0035] The monomer unit containing X is usually obtained by saponifying a vinyl ester. Therefore, X is preferably a mixture of a hydrogen atom and a formyl group or an alkanoyl group having 2 to 10 carbon atoms. Considering the availability of the monomer (vinyl acetate) and the production cost, it is more preferable that X is a mixture of a hydrogen atom and an acetyl group.

[0036] On the other hand, the monomer unit containing Y and Z can be produced by copolymerizing a monomer having an ester group, such as an unsaturated monomer having a 1,3-diester structure, and then saponifying the copolymer, or by directly copolymerizing a monomer having a hydroxyl group, such as an unsaturated monomer having a 1,3-diol structure. Therefore, Y and Z may each be a hydrogen atom only, or a mixture of a hydrogen atom and a formyl group or an alkanoyl group having 2 to 10 carbon atoms, or more preferably a mixture of a hydrogen atom and an acetyl group.

[0037] The modified EVOH may contain structural units derived from other ethylenically unsaturated monomers copolymerizable with ethylene, the vinyl ester represented by formula (V) and the unsaturated monomer represented by formula (VI) or (VIII) described below, within the scope of not impairing the effects of the present invention. Examples of such other ethylenically unsaturated monomers include α-olefins such as propylene, n-butene, isobutylene, and 1-hexene; acrylic acid and its salts; unsaturated monomers having an acrylic acid ester group; methacrylic acid and its salts; unsaturated monomers having a methacrylic acid ester group; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts (e.g., quaternary salts); methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid and its salts, methacrylamidopropyldimethylamine and its salts (e.g., quaternary salts); methyl vinyl ether, vinyl ethers such as ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, 2,3-diacetoxy-1-vinyloxypropane; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane, and allyl chloride; unsaturated dicarboxylic acids and salts or esters thereof such as maleic acid, itaconic acid, and fumaric acid; vinyl silane compounds such as vinyltrimethoxysilane; and isopropenyl acetate.

[0038] In the modified EVOH, the contents (mol %) of a, b and c relative to the total monomer units satisfy the following formulas (1) to (3). 24≦a≦55 (1) 0.01≦c≦10 (2) [100-(a+c)]×0.9≦b≦[100-(a+c)] (3)

[0039] a indicates the content (mol%) of ethylene units relative to all monomer units, and is 24 to 55 mol%. If the ethylene unit content is less than 24 mol%, the melt moldability of pellets containing modified EVOH deteriorates. a is preferably 26 mol% or more, and more preferably 30 mol% or more. On the other hand, if the ethylene unit content exceeds 55 mol%, the barrier property of the modified EVOH becomes insufficient. a is preferably 52 mol% or less, and more preferably 49 mol% or less.

[0040] c indicates the content (mol%) of the monomer unit having a primary hydroxyl group shown at the right end in the above formula (I) relative to the total monomer units, and is 0.01 to 10 mol%. If c is less than 0.01 mol%, the moldability and secondary processability of pellets containing the modified EVOH become insufficient. c is preferably 0.05 mol% or more, more preferably 0.1 mol% or more, and even more preferably 0.5 mol% or more. On the other hand, if c exceeds 10 mol%, the barrier property of the modified EVOH decreases. c is preferably 5 mol% or less.

[0041] b indicates the content (mol %) of vinyl alcohol units and vinyl ester units relative to the total monomer units, which satisfies the following formula (3). [100-(a+c)]×0.9≦b≦[100-(a+c)] (3) That is, in the modified EVOH, 90% or more of the monomer units other than the ethylene units and the monomer units having a primary hydroxyl group shown at the right end in the above formula (I) are vinyl alcohol units or vinyl ester units. If the above formula (3) is not satisfied, the gas barrier property will be insufficient. Preferably, the following formula (3') is satisfied, and more preferably, the following formula (3") is satisfied. [100-(a+c)]×0.95≦b≦[100-(a+c)](3') [100-(a+c)]×0.98≦b≦[100-(a+c)](3”)

[0042] The modified EVOH has a degree of saponification (DS) defined by the following formula (4) of 90 mol % or more. DS = [(total number of moles of X, Y, and Z that are hydrogen atoms) / (total number of moles of X, Y, and Z)] × 100 (4) Here, "the total number of moles of hydrogen atoms among X, Y, and Z" refers to the number of moles of hydroxyl groups, and "the total number of moles of X, Y, and Z" refers to the total number of moles of hydroxyl groups and ester groups. If the saponification degree (DS) is less than 90 mol%, not only is sufficient barrier performance not obtained, but the thermal stability of the modified EVOH becomes insufficient, and gels and bumps are likely to occur during melt molding. In addition, the long-run moldability during high-temperature molding tends to decrease due to the decrease in thermal stability. The saponification degree (DS) is preferably 95 mol% or more, more preferably 98 mol% or more, and even more preferably 99 mol% or more. In order to have particularly excellent barrier properties and thermal stability, the saponification degree (DS) is preferably 99 mol% or more, more preferably 99.5 mol% or more, and even more preferably 99.8 mol% or more.

[0043] The degree of saponification (DS) can be obtained by the nuclear magnetic resonance (NMR) method. The contents of the monomer units represented by a, b, and c above can also be obtained by the NMR method. The modified EVOH used in the present invention is usually a random copolymer. It can be confirmed that it is a random copolymer by the measurement results of NMR or melting point.

[0044] The melt flow rate (MFR) of the modified EVOH (190°C, under a load of 2160 g) is preferably 0.1 to 30 g / 10 min, more preferably 0.3 to 25 g / 10 min, and further preferably 0.5 to 20 g / 10 min. However, for those having a melting point near or exceeding 190°C, the MFR is measured under a load of 2160 g at multiple temperatures equal to or higher than the melting point, and is plotted on a semi-logarithmic graph with the reciprocal of absolute temperature on the horizontal axis and the logarithm of MFR on the vertical axis, and expressed as a value extrapolated to 190°C.

[0045] The modified EVOH may be a mixture with unmodified EVOH. From the viewpoint of reducing costs, the mass ratio of the modified EVOH to unmodified EVOH in the mixture (modified EVOH / unmodified EVOH) is preferably 1 / 9 to 9 / 1. On the other hand, from the viewpoint of more significantly achieving the effects of the present invention, the mass ratio (modified EVOH / unmodified EVOH) is preferably more than 9 / 1, and more preferably the mixture does not substantially contain unmodified EVOH.

[0046] When the modified EVOH is a mixture of two or more different types of modified EVOH or a mixture of the modified EVOH and the unmodified EVOH, the content, degree of saponification and MFR of each monomer unit are average values ​​calculated from the blending mass ratio.

[0047] The method for producing the modified EVOH containing the monomer unit represented by the formula (II) as the monomer unit having a primary hydroxyl group shown at the right end in the above formula (I) is not particularly limited, and an example thereof includes a method in which ethylene, a vinyl ester represented by the following formula (V), and an unsaturated monomer represented by the following formula (VI) are radically polymerized to obtain a modified ethylene-vinyl ester copolymer represented by the following formula (VII), and then the resulting copolymer is saponified.

[0048] [ka]

[0049] In formula (V), R 9 represents a hydrogen atom or an alkyl group having 1 to 9 carbon atoms. The number of carbon atoms in the alkyl group is preferably 1 to 4. Examples of the vinyl ester represented by formula (V) include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, and vinyl caproate. From an economical viewpoint, vinyl acetate is more preferable.

[0050] [ka]

[0051] In formula (VI), R 3 and R 4 is the same as in formula (II). 10 and R 11 each independently represents a hydrogen atom or an alkyl group having 1 to 9 carbon atoms. The number of carbon atoms in the alkyl group is preferably 1 to 4. Examples of the unsaturated monomer represented by formula (VI) include 2-methylene-1,3-propanediol diacetate, 2-methylene-1,3-propanediol dipropionate, and 2-methylene-1,3-propanediol dibutyrate. Among them, 2-methylene-1,3-propanediol diacetate is preferably used because of its ease of production. In the case of 2-methylene-1,3-propanediol diacetate, R 3 and R 4 is a hydrogen atom, and R 10 and R 11 is a methyl group.

[0052] [ka]

[0053] In formula (VII), R 3 , R 4 , R 9 , R 10 and R 11 are the same as in formulas (II), (V), and (VI). In formula (VII), a, b, and c respectively represent the content (mol%) of ethylene units, vinyl ester units, and units derived from the unsaturated monomer represented by formula (VI) relative to the total monomer units. The modified ethylene-vinyl ester copolymer thus obtained is then saponified.

[0054] In place of the unsaturated monomer represented by the above formula (VI), an unsaturated monomer represented by the following formula (VIII) may be copolymerized. In this case, the unsaturated monomer represented by the following formula (VIII) may be copolymerized by saponification treatment. 9 Only the vinyl ester units containing

[0055] [ka]

[0056] In formula (VIII), R 3 and R 4 is the same as the formula (II). The unsaturated monomer represented by the formula (VIII) includes 2-methylene-1,3-propanediol and 2-methylene-1,3-butanediol.

[0057] The unsaturated monomers represented by the formulas (VI) and (VIII) have high copolymerization reactivity with vinyl ester monomers, so that the copolymerization reaction proceeds easily. Therefore, it is easy to increase the modification amount and polymerization degree of the resulting modified ethylene-vinyl ester copolymer. In addition, even if the polymerization reaction is stopped at a low polymerization rate, the amount of unreacted unsaturated monomer remaining at the end of the polymerization is small, so it is also excellent in terms of environment and cost. In this respect, the unsaturated monomers represented by the formulas (VI) and (VIII) are superior to other monomers having only one carbon atom having a functional group at the allyl position, such as allyl glycidyl ether and 3,4-diacetoxy-1-butene. Here, the unsaturated monomer represented by the formula (VI) is more reactive than the unsaturated monomer represented by the formula (V).

[0058] The polymerization method for producing a modified ethylene-vinyl ester copolymer by copolymerizing ethylene, a vinyl ester represented by the above formula (V), and an unsaturated monomer represented by the above formula (VI) or (VIII) may be any of batch polymerization, semi-batch polymerization, continuous polymerization, and semi-continuous polymerization. In addition, known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization can be adopted as the polymerization method. Bulk polymerization or solution polymerization, in which polymerization is carried out without a solvent or in a solvent such as alcohol, is usually adopted. When a modified ethylene-vinyl ester copolymer with a high degree of polymerization is to be obtained, the adoption of an emulsion polymerization method is one of the options.

[0059] The solvent used in the solution polymerization method is not particularly limited, but may be, for example, an alcohol, more preferably a lower alcohol such as methanol, ethanol, or propanol. The amount of the solvent used in the polymerization reaction solution may be selected in consideration of the viscosity average degree of polymerization of the desired modified EVOH and chain transfer of the solvent, and the mass ratio of the solvent to the total monomers (solvent / total monomers) contained in the reaction solution is usually in the range of 0.01 to 10, preferably in the range of 0.03 to 3, and more preferably in the range of 0.05 to 1.

[0060] The polymerization initiator used in copolymerizing ethylene, the vinyl ester represented by the above formula (V), and the unsaturated monomer represented by the above formula (VI) or (VIII) is selected from known polymerization initiators, such as azo initiators, peroxide initiators, and redox initiators, depending on the polymerization method. Examples of the azo initiator include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Examples of the peroxide initiator include percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; perester compounds such as t-butyl peroxyneodecanate, α-cumyl peroxyneodecanate, and acetyl peroxide; acetylcyclohexylsulfonyl peroxide; and 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate. Potassium persulfate, ammonium persulfate, and hydrogen peroxide may be combined with the above initiator. The redox initiator is, for example, a polymerization initiator obtained by combining the above peroxide initiator with a reducing agent such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, and Rongalite. The amount of the polymerization initiator used is adjusted according to the polymerization rate. The amount of the polymerization initiator used is preferably 0.01 to 0.2 mol, and more preferably 0.02 to 0.15 mol, relative to 100 mol of the vinyl ester monomer. The polymerization temperature is not particularly limited, but is suitably from room temperature to about 150°C, and preferably from 40°C to 100°C.

[0061] When copolymerizing ethylene, a vinyl ester represented by the above formula (V), and an unsaturated monomer represented by the above formula (VI) or (VIII), the copolymerization may be carried out in the presence of a chain transfer agent within a range in which the effects of the present invention are not impaired. Examples of the chain transfer agent include aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethanethiol; and phosphinates such as sodium phosphinate monohydrate. Among them, aldehydes and ketones are preferred. The amount of the chain transfer agent added to the polymerization reaction solution is determined according to the chain transfer coefficient of the chain transfer agent and the polymerization degree of the desired modified ethylene-vinyl ester copolymer, but is generally preferably 0.1 to 10 parts by mass relative to 100 parts by mass of the vinyl ester monomer.

[0062] After polymerization for a predetermined time has reached a predetermined polymerization rate, a polymerization inhibitor is added as necessary, unreacted ethylene gas is removed by evaporation, and unreacted vinyl ester and unsaturated monomers represented by the above formula (VI) or (VIII) are expelled. For example, a method of expelling these may be used in which the polymerization solution from which ethylene has been removed is continuously fed at a constant rate from the top of a tower packed with Raschig rings, and an organic solvent, preferably an alcohol having a boiling point of 100° C. or less, and most preferably methanol vapor is blown into the bottom of the tower, and a mixed vapor of the organic solvent and unreacted vinyl ester, etc. is distilled from the top of the tower, and the copolymer solution from which unreacted vinyl ester, etc. have been removed is taken out from the bottom of the tower.

[0063] An alkali catalyst is added to the copolymer solution from which unreacted vinyl esters and the like have been removed, and the vinyl ester components in the copolymer are saponified. The saponification method can be either continuous or batchwise. As the alkali catalyst, sodium hydroxide, potassium hydroxide, alkali metal alcoholate, etc. are used. Moreover, methanol is preferred as the solvent used for saponification. For example, the saponification conditions are as follows: (1) Concentration of ethylene-vinyl ester copolymer in solution: 10 to 50% by mass (2) Reaction temperature: 30 to 150°C (3) Amount of catalyst used: 0.005 to 0.6 equivalents (per vinyl ester component) (4) Time (average residence time in the case of continuous type): 10 minutes to 6 hours

[0064] In general, when saponification is performed in a continuous system, methyl acetate produced by saponification can be removed more efficiently, so a resin with a high degree of saponification can be obtained with a smaller amount of catalyst than in the batch system. In addition, in the case of a continuous system, saponification must be performed at a higher temperature to prevent the precipitation of EVOH produced by saponification. Therefore, in the continuous system, it is preferable to set the reaction temperature and catalyst amount in the following ranges. Reaction temperature: 70~150℃. Amount of catalyst used: 0.005 to 0.1 equivalent (per vinyl ester component).

[0065] By saponifying the modified ethylene-vinyl ester copolymer in this way, a solution or paste containing modified EVOH is obtained. At this time, the vinyl ester units in the copolymer are converted to vinyl alcohol units. At the same time, the ester bonds derived from the unsaturated monomer represented by formula (VI) are also hydrolyzed and converted to a 1,3-diol structure. In this way, different types of ester groups can be hydrolyzed simultaneously by a single saponification reaction.

[0066] The modified EVOH after the saponification reaction contains an alkali catalyst, by-product salts such as sodium acetate and potassium acetate, and other impurities, which may be removed by neutralization and washing as necessary. When the modified EVOH after the saponification reaction is washed with ion-exchanged water or the like containing almost no metal ions, chloride ions, etc., some catalyst residues such as sodium acetate and potassium acetate may remain in the modified EVOH.

[0067] The EVOH solution or paste thus obtained usually contains at least 50 parts by weight of alcohol per 100 parts by weight of EVOH, and the alcohol is preferably methanol.

[0068] The method for washing the EVOH solution or paste and the method for adjusting the water content are not particularly limited, but can be carried out as follows. Water is added to the EVOH solution or paste while heating and stirring it, and the alcohol is distilled off to precipitate the modified EVOH. The temperature at this time is preferably 50 to 100°C. The precipitated modified EVOH is washed with water, an aqueous acetic acid solution, or the like. The temperature at this time is preferably 5 to 50°C. The washed modified EVOH is dried as necessary. For example, it is dried at 50 to 100°C for 1 to 24 hours. The water content of the modified EVOH can be adjusted depending on the washing and drying conditions at this time.

[0069] The method for producing modified EVOH containing a monomer unit represented by the formula (III) as the monomer unit having a primary hydroxyl group shown at the right end in formula (I) is not particularly limited, and examples thereof include a method for saponifying a copolymer obtained by copolymerizing 3,4-diol-1-butene, a vinyl ester monomer, and ethylene, a method for saponifying a copolymer obtained by copolymerizing 3,4-diacyloxy-1-butene, a vinyl ester monomer, and ethylene, a method for saponifying a copolymer obtained by copolymerizing 3-acyloxy-4-ol-1-butene, a vinyl ester monomer, and ethylene, a method for saponifying a copolymer obtained by copolymerizing 4-acyloxy-3-ol-1-butene, a vinyl ester monomer, and ethylene, and a method for saponifying a copolymer obtained by copolymerizing 3,4-diacyloxy-2-methyl-1-butene, a vinyl ester monomer, and ethylene. The modified EVOH containing the monomer unit represented by formula (III) can be obtained in the same manner as the modified EVOH containing the monomer unit represented by formula (II), except that the monomer used to form the monomer unit having the primary hydroxyl group at the right end in formula (I) is different.

[0070] The 3,4-diol-1-butene is represented by the following formula (IX), the 3,4-diacyloxy-1-butene by the following formula (X), the 3-acyloxy-4-ol-1-butene by the following formula (XI), and the 4-acyloxy-3-ol-1-butene by the following formula (XII).

[0071] [ka]

[0072] [ka]

[0073] Here, R 12 is an alkyl group, preferably a methyl group.

[0074] [ka]

[0075] Here, R 13 is an alkyl group, preferably a methyl group.

[0076] [ka]

[0077] Here, R 14 is an alkyl group, preferably a methyl group.

[0078] The method for producing modified EVOH containing a monomer unit represented by the formula (IV) as the monomer unit having a primary hydroxyl group shown at the right end in formula (I) is not particularly limited, and examples thereof include a method of reacting EVOH having an ethylene unit content of 24 to 55 mol% with a monofunctional epoxy compound described below. The reaction method is not particularly limited, and preferred methods include a production method in which EVOH and a monofunctional epoxy compound are reacted in a solution, and a production method in which EVOH and a monofunctional epoxy compound are reacted in an extruder.

[0079] In the solution reaction production method, a monofunctional epoxy compound is reacted with a solution of EVOH in the presence of an acid catalyst or an alkali catalyst to obtain a modified EVOH. Alternatively, a modified EVOH can be produced by dissolving EVOH and a monofunctional epoxy compound in a reaction solvent and performing a heat treatment. As the reaction solvent, a polar aprotic solvent that is a good solvent for EVOH, such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and N-methylpyrrolidone, is preferable. The modified EVOH obtained after the reaction is appropriately washed and dried, and then fed to an extruder described below. The washing and drying methods are the same as those used in the production method of the modified EVOH containing the monomer unit represented by the above formula (II).

[0080] Examples of reaction catalysts include acid catalysts such as p-toluenesulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, sulfuric acid, and boron trifluoride, and alkali catalysts such as sodium hydroxide, potassium hydroxide, lithium hydroxide, and sodium methoxide. Of these, it is preferable to use an acid catalyst. The amount of catalyst is preferably about 0.0001 to 10 parts by mass per 100 parts by mass of EVOH. The reaction temperature is preferably from room temperature to 150°C.

[0081] In the production method in which EVOH and a monofunctional epoxy compound are reacted in an extruder, the extruder to be used is not particularly limited, and examples thereof include a single-screw extruder, a twin-screw extruder, and a multi-screw extruder with two or more screws. It is also preferable to react EVOH and a monofunctional epoxy compound at a temperature of about 200°C to 300°C. When a twin-screw extruder or a multi-screw extruder with two or more screws is used, it is easy to increase the pressure in the reaction section by changing the screw configuration, and the reaction between EVOH and a monofunctional epoxy compound can be efficiently carried out. In the case of a single-screw extruder, the pressure in the reaction section can be increased by connecting two or more extruders and arranging a valve in the resin flow path between them. Similarly, two or more twin-screw extruders or multi-screw extruders with two or more screws may be connected to produce the modified EVOH. The extruded pellets of modified EVOH are washed as necessary and then fed to an extruder described later. The washing method and drying method are the same as those used in the production method of modified EVOH containing a monomer unit represented by the formula (II) described above.

[0082] A monofunctional epoxy compound is an epoxy compound having only one epoxy group in the molecule.

[0083] The monofunctional epoxy compound used in the present invention is not particularly limited, but specifically, the compounds represented by the following formulae (XIII) to (XV) are preferably used.

[0084] [ka]

[0085] [ka]

[0086] [ka]

[0087] In the formula, R 15 , R 16 and R 17R represents a hydrogen atom, an alkyl group having 1 to 7 carbon atoms, or a cycloalkyl group having 3 to 7 carbon atoms. 16 and R 17 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a cycloalkyl group having 3 to 6 carbon atoms. Also, i represents an integer of 1 to 7.

[0088] The number of carbon atoms in the monofunctional epoxy compound is particularly preferably 2 to 8. From the viewpoint of the gas barrier property of the obtained modified EVOH, the monofunctional epoxy compound is more preferably 1,2-epoxybutane, epoxypropane, epoxyethane and glycidol, and further preferably epoxypropane and glycidol.

[0089] Modified EVOH can be obtained by reacting EVOH with a monofunctional epoxy compound. The mixing ratio of the monofunctional epoxy compound to 100 parts by mass of EVOH is preferably 1 to 50 parts by mass.

[0090] In the melt kneading step, the water content of the hydrous modified EVOH fed to the extruder is preferably 10 to 60% by mass. When the water content is 10% by mass or more, pellets containing modified EVOH having a better hue can be obtained. The water content is more preferably 15% by mass or more, and even more preferably 20% by mass or more. On the other hand, when the water content is less than 60% by mass, foaming of the pellets containing modified EVOH is further suppressed. The water content is more preferably 40% by mass or less, even more preferably 35% by mass or less, and particularly preferably 30% by mass or less. The water content of the hydrous modified EVOH is measured by the method described in the Examples.

[0091] The temperature of the hydrous modified EVOH fed to the extruder is preferably 0°C or higher, more preferably 10°C or higher, and even more preferably 25°C or higher. If the temperature of the hydrous modified EVOH fed to the extruder is lower than 0°C, problems with feeding are likely to occur, and the modified EVOH may not completely melt, resulting in an increase in foamed pellets and a deterioration in color. The temperature of the hydrous modified EVOH fed to the extruder is preferably 80°C or lower, more preferably 75°C or lower, and even more preferably 65°C or lower. If the temperature of the modified EVOH fed to the extruder exceeds 80°C, the water content of the hydrous modified EVOH fed is not stable, and the modified EVOH may not completely melt in the extruder, resulting in an increase in foamed pellets and a deterioration in color. The temperature of the hydrous modified EVOH fed to the extruder can be appropriately adjusted under the conditions before being fed to the extruder.

[0092] The hydrous modified EVOH fed to the extruder may contain alcohol as long as the effects of the present invention are not impaired. The alcohol content in the hydrous modified EVOH is usually 10% by mass or less, preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.1% by mass or less.

[0093] It is preferable to feed an additive to the extruder. The additive is preferably at least one selected from the group consisting of carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts. By adding such an additive, pellets containing modified EVOH with a better color can be obtained.

[0094] Examples of the carboxylic acid include oxalic acid, succinic acid, benzoic acid, citric acid, acetic acid, propionic acid, and lactic acid. Among these, acetic acid, propionic acid, or lactic acid is preferred from the viewpoints of cost and availability. When the pellet containing the modified EVOH contains a carboxylic acid, the content is preferably 1 to 500 ppm based on the total solid content. The lower limit of the carboxylic acid content is more preferably 10 ppm or more, and even more preferably 50 ppm or more. The upper limit of the carboxylic acid content is preferably 400 ppm or less, and more preferably 300 ppm or less. The content of the carboxylic acid in the modified EVOH is measured by the method described in the examples. When the content of the carboxylic acid is 1 ppm or more, coloring during melt molding tends to be suppressed. When the content of the carboxylic acid is 500 ppm or less, the thermal stability tends to be good.

[0095] Examples of boron compounds include, but are not limited to, boric acids, boric acid esters, borate salts, and boron hydrides. Specifically, examples of boric acids include orthoboric acid, metaboric acid, and tetraboric acid. Examples of borate esters include triethyl borate and trimethyl borate. Examples of borates include alkali metal salts, alkaline earth metal salts, and borax of the above-mentioned various borates. Among these compounds, orthoboric acid (hereinafter simply referred to as boric acid) is preferred. When the pellets containing modified EVOH contain a boron compound, the content is preferably 10 to 2000 ppm, more preferably 50 to 1500 ppm, in terms of boron, relative to the total solid content. When the content of the boron compound is within the above range, the thermal stability and moldability tend to be good. The content of the boron compound, the phosphoric acid compound, the alkali metal salt, or the alkaline earth metal salt in the pellets containing modified EVOH is measured by the method described in the Examples.

[0096] Examples of the phosphoric acid compound include various acids such as phosphoric acid and phosphorous acid and their salts. The phosphate may be contained in the form of any of primary phosphate, secondary phosphate, and tertiary phosphate, and the cationic species is not particularly limited, but is preferably an alkali metal salt or an alkaline earth metal salt. Among them, it is preferable to add the phosphoric acid compound in the form of sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, or dipotassium hydrogen phosphate. When the pellet containing the modified EVOH contains a phosphoric acid compound, the content is preferably 1 to 1000 ppm in terms of phosphorus element relative to the total solid content. By adding it in such a range, it is possible to suppress coloring of the molded product and the occurrence of gels and bumps.

[0097] Examples of the alkali metal salt include aliphatic carboxylates, aromatic carboxylates, phosphates, and metal complexes of monovalent metals. For example, sodium acetate, potassium acetate, sodium phosphate, lithium phosphate, sodium stearate, potassium stearate, and sodium salt of ethylenediaminetetraacetic acid are listed. Among them, sodium acetate, potassium acetate, and sodium phosphate are preferred. When the pellets containing modified EVOH contain an alkali metal salt, the content is preferably 5 to 5000 ppm, more preferably 20 to 1000 ppm, and even more preferably 30 to 750 ppm in terms of the alkali metal element relative to the total solid content. By containing 5 ppm or more of the alkali metal element, it is possible to effectively improve interlayer adhesion and compatibility, and by making it 5000 ppm or less, the thermal stability during melt molding is further improved.

[0098] Examples of alkaline earth metal salts include magnesium salts, calcium salts, barium salts, and beryllium salts, and magnesium salts and calcium salts are particularly preferred. The anion species of the alkaline earth metal salt is not particularly limited, but acetates and phosphates are preferred. When the pellets containing modified EVOH contain an alkaline earth metal salt, the content is preferably 10 to 1000 ppm, more preferably 20 to 500 ppm, calculated as alkaline earth metal element, relative to the total solid content. When the content of alkaline earth metal is 10 ppm or more, the long-run property tends to be good. Also, when it is 1000 ppm or less, coloring during resin melting tends to be suppressed.

[0099] The water-containing modified EVOH, and optionally the additives, are fed to an extruder and melt-kneaded to obtain a melt having a water content of 4 to 35% by mass. A twin-screw extruder is preferably used as the extruder for melt-kneading the water-containing modified EVOH. A block cylinder or the like is used as the cylinder. A segment type screw or the like is used as the screw. The screw rotation speed is preferably 10 to 1000 rpm. By setting the screw rotation speed within this range, it becomes easier to adjust the temperature of the melt in the extruder.

[0100] The hydrous modified EVOH is fed into a raw material supply section of an extruder. When the additive is added, it is preferable to add the additive to the hydrous and molten modified EVOH. The extruder preferably has a kneading section, and it is particularly preferable that the additive is added to the kneading section of the extruder, because the additive is easily and uniformly mixed with the modified EVOH.

[0101] The form of addition of the additive is not particularly limited. Examples of the additive include a method of adding the additive as a dry powder in the extruder, a method of adding the additive as a paste impregnated with a solvent, a method of adding the additive in a suspended state in a liquid, and a method of adding the additive as a solution by dissolving the additive in a solvent. From the viewpoint of controlling the amount of the additive and uniformly dispersing the additive in the modified EVOH, the method of adding the additive as a solution by dissolving the additive in a solvent is particularly preferable. The solvent is not particularly limited, but water is preferable from the viewpoints of the solubility of the additive, cost benefits, ease of handling, and safety of the working environment. That is, it is preferable that the additive is an aqueous solution containing at least one selected from the group consisting of carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts. In addition, as a method of addition, it is preferable to add the additive to the extruder from one or more than two places.

[0102] When the additive is added to the modified EVOH as a solution, the lower limit of the amount of the solution added is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 4 parts by mass or more, per 100 parts by mass of the dry mass of the modified EVOH. The upper limit of the amount of the solution added is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of the dry mass of the EVOH. When the amount of the solution added is 1 part by mass or more, the concentration of the solution tends to be easily adjusted, and the dispersibility of the additive in the hydrous EVOH tends to be good. When the amount is 50 parts by mass or less, the moisture content of the resulting pellets containing hydrous modified EVOH tends to be easily controlled.

[0103] The extruder may be simultaneously fed with EVOH pellets different from the hydrous modified EVOH, as long as the effects of the present invention are not impaired. The hydrous modified EVOH pellets different from the hydrous modified EVOH may be dry-blended in advance with the hydrous modified EVOH and fed into the raw material feed section of the extruder, or may be simultaneously fed into the raw material feed section 1 without being dry-blended with the hydrous modified EVOH, or may be fed separately from a raw material feed section different from the hydrous modified EVOH (using an extruder equipped with two raw material feed sections). Among these, the method of feeding the hydrous modified EVOH and the EVOH pellets different from the hydrous modified EVOH separately from different raw material feed sections is superior in terms of quantitative feeding and reducing quality variation.

[0104] In addition, other components can be added to the extruder within a range that does not impair the effects of the present invention. Examples of other components include inorganic substances, plasticizers, lubricants, stabilizers, surfactants, coloring agents, antioxidants, UV absorbers, antistatic agents, drying agents, crosslinking agents, metal salts, fillers, and reinforcing agents such as various fibers. The other components may be introduced into the extruder as solids such as powders or as melts, but from the viewpoint of uniformly dispersing them in the pellets containing the modified EVOH obtained and suppressing the variation in the amount added, it is preferable to add them as solutes contained in a solution or dispersoids contained in a dispersion. As the solution and dispersion, an aqueous solution and an aqueous dispersion are preferable, respectively. When the other components are in a solid state such as powders, they may be dry-blended in advance with the hydrous modified EVOH and then fed into the raw material feed section of the extruder, or they may be simultaneously fed without dry-blending. When they are mixed as solutes contained in a solution or dispersoids contained in a dispersion, they may be added together with the additives, or the other components may be added separately from the additives.

[0105] The temperature T0 of the molten material containing the modified EVOH and water in the extruder is preferably 70 to 180°C. If the temperature T0 is less than 70°C, the fluidity of the water-containing EVOH becomes insufficient, causing gelation or blockage in the container. The temperature T0 is preferably 80°C or higher, more preferably 90°C or higher, and even more preferably 100°C or higher. On the other hand, if the temperature T0 exceeds 180°C, the color of the pellets containing the modified EVOH is significantly deteriorated. The temperature T0 is more preferably 175°C or lower, even more preferably 170°C or lower, and particularly preferably 165°C or lower. Here, the temperature T0 of the molten material refers to the temperature detected by a temperature sensor installed in the cylinder of the extruder in contact with the molten material, and the detection point is near the discharge port at the tip of the extruder. The temperature T0 can be adjusted by the temperature of the water-containing modified EVOH fed to the extruder, the cylinder temperature of the extruder, the screw rotation speed of the extruder, and the like.

[0106] In the production method of the present invention, the cylinder temperature T1 of the extruder is preferably 65 to 175°C. If the cylinder temperature T1 is less than 65°C, the fluidity of the water-containing EVOH is insufficient, and there is a risk of gelation or blockage in the container. The temperature T1 is more preferably 70°C or higher, even more preferably 75°C or higher, even more preferably 80°C or higher, and particularly preferably 85°C or higher. On the other hand, when the temperature T1 is 175°C or lower, pellets containing modified EVOH with good color are obtained. The temperature T1 is more preferably 165°C or lower, even more preferably 150°C or lower, even more preferably 135°C or lower, particularly preferably 130°C or lower, and most preferably 125°C or lower. Here, the cylinder temperature T1 means the highest temperature among the temperatures of the cylinder at a position downstream of the portion where the raw material is supplied to the extruder.

[0107] In the production method of the present invention, it is preferable that the temperature T0 (° C.) of the melt in the extruder and the cylinder temperature T1 (° C.) of the extruder satisfy the following formula (5). 5≦T0-T1≦100 (5)

[0108] As shown in the above formula (5), when the temperature T0 is 5°C or more higher than the temperature T1, pellets containing modified EVOH with little foaming are obtained. T0-T1 is more preferably 15 or more. On the other hand, when T0-T1 is 100 or less, pellets containing modified EVOH with good color are obtained. T0-T1 is more preferably 90 or less, even more preferably 85 or less, even more preferably 80 or less, particularly preferably 75 or less, and most preferably 65 or less. Temperature T0-T1 can be adjusted by changing the screw configuration, cylinder configuration, temperature of the water-containing modified EVOH to be fed, cylinder temperature, and screw rotation speed, etc.

[0109] It is also preferable to dehydrate the modified EVOH in a water-containing state in the extruder. It is also preferable to degas the modified EVOH. Specifically, it is preferable to discharge water and / or water vapor from at least one location in the extruder. The method of discharging is not particularly limited, but examples thereof include a method of discharging from a dehydration slit, a dehydration hole, or a vent port arranged in the cylinder of the extruder. As the dehydration slit, a wedge wire type dehydration slit and a screen mesh type dehydration slit are preferable. As the vent port, a vacuum vent that removes water vapor under reduced pressure and an open vent that removes water vapor under normal pressure are preferable.

[0110] The above-mentioned dehydration operation is carried out to adjust the moisture content of the modified EVOH in the extruder and after extrusion. In order to prevent the moisture content of the EVOH from becoming lower than necessary, water may be supplied to the extruder in addition to the above-mentioned dehydration operation or without the above-mentioned dehydration operation. There is no particular restriction on the method of supplying water to the extruder, but examples thereof include a method of pressurizing water using a plunger pump or the like.

[0111] In the present invention, the moisture content of the molten material containing modified EVOH and water immediately after being discharged from the extruder must be 4 to 35% by mass. When the moisture content is 4% by mass or more, the cuttability of pellets containing modified EVOH tends to be stable. The moisture content is preferably 6% by mass or more, more preferably 8% by mass or more, even more preferably 10% by mass or more, and even more preferably 12% by mass or more. When the moisture content is 35% by mass or less, foaming in pellets containing modified EVOH is suppressed. The moisture content is preferably 32% by mass or less, more preferably 28% by mass or less, even more preferably 26% by mass or less, even more preferably 24% by mass or less, and particularly preferably 22% by mass or less. The moisture content of the molten material is measured by the method described in the Examples.

[0112] In the present invention, it is preferable that the moisture content of the molten material immediately after being discharged from the extruder is lower than the moisture content of the water-containing modified EVOH supplied to the extruder, and the difference between the moisture content of the water-containing modified EVOH and the moisture content of the molten material (moisture content of water-containing modified EVOH - moisture content of molten material) is more preferably 1 mass% or more, even more preferably 3 mass% or more, particularly preferably 5 mass% or more, and most preferably 7 mass% or more.

[0113] In the solidification step, the molten material discharged from the extruder is extruded into a coagulation bath to obtain a strand-shaped coagulation. Water is used as the coagulation bath, but it may contain a small amount of alcohol. The temperature of the coagulation bath is preferably 0 to 50°C, and the temperature of the hydrous modified EVOH during extrusion is usually 60 to 80°C. This temperature difference allows the hydrous EVOH to be solidified in a short time. From the viewpoint of easy handling of the pellets, the aperture of the die is preferably 1 to 10 mmφ.

[0114] In the cutting step, the strand-like coagulated material is cut to obtain cylindrical water-containing pellets. The strand-like coagulated material is cut with a cutter, and a strand cutter is preferable as the cutter. The strand-like coagulated material is preferably cut into lengths (in the extrusion direction) of about 1 to 10 mm.

[0115] The obtained water-containing pellets are subjected to a drying step. The moisture content of the pellets containing the modified EVOH after drying is preferably 1.0% by mass or less, more preferably 0.5% by mass or less. The drying method is not particularly limited, but preferred examples include a static drying method and a fluidized drying method, and it is also possible to adopt a multi-stage drying step in which several drying methods are combined. Among these, a method in which drying is first performed by a fluidized drying method and then by a static drying method is preferred.

[0116] The diameter of the thus obtained cylindrical pellets containing the modified EVOH is preferably 1 to 10 mm. The length of the pellets is also preferably 1 to 10 mm. By forming the pellets into such cylindrical pellets, blocking resistance is further improved.

[0117] In the resin constituting the pellet containing modified EVOH, the proportion of EVOH is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and it is particularly preferable that the resin is composed of EVOH alone. In addition, in the pellet containing modified EVOH, the proportion of the modified EVOH is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more.

[0118] The melting point of the pellets containing the modified EVOH obtained is preferably 120 to 163°C. If the melting point is less than 120°C, the blocking resistance may be insufficient. The melting point is more preferably 130°C or higher, even more preferably 140°C or higher, even more preferably 145°C or higher, and particularly preferably 150°C or higher. On the other hand, if the melting point exceeds 163°C, the temperature during molding processing increases, resulting in poor thermal stability and poor extrusion stability during low-temperature extrusion. The melting point is measured by the method described in the examples.

[0119] It is preferable that the obtained pellets containing modified EVOH satisfy the following formula (6). ΔHma / ΔHmb≦1.05 (6)

[0120] [In the formula (6), ΔHma (J / g) is the crystalline melting enthalpy of the pellets containing the modified EVOH, and ΔHmb is the crystalline melting enthalpy (J / g) of cylindrical comparative pellets having the same diameter and length as the pellets containing the modified EVOH, which are obtained by holding the pellets containing the modified EVOH at 210° C. for 6 minutes, extruding the resulting molten material into water, and then cutting the pellets.]

[0121] When the crystalline melting enthalpy ΔHma of the pellets containing the modified EVOH after the drying step and the crystalline melting enthalpy ΔHmb of the comparative pellets satisfy the above formula (6), low-temperature extrusion becomes possible, and extrusion processability is further improved. The comparative pellets are obtained by melting the pellets containing the modified EVOH and then pelletizing them again, and are obtained by the method described in the Examples. The comparative pellets and the pellets containing the modified EVOH after the drying step must have the same diameter and length. The crystalline melting enthalpy ΔHma of the pellets containing the modified EVOH and the crystalline melting enthalpy ΔHmb of the comparative pellets are also determined by the method described in the Examples. It is more preferable that the crystalline melting enthalpy ΔHma and the crystalline melting enthalpy ΔHmb satisfy the following formula (6'), and even more preferable that they satisfy the following formula (6''). ΔHma / ΔHmb≦1.04 (6') ΔHma / ΔHmb≦1.03 (6'')

[0122] It is also preferable that the pellets containing the modified EVOH satisfy the following formula (7). A B ≧ 0.3 (7) [In the formula (7), A is the water absorption rate (mass%) of the pellets containing the modified EVOH after the drying step, which was kept at 40°C and 90% RH for 300 hours, and B is the water absorption rate (mass%) of the comparative pellets, which was kept at 40°C and 90% RH for 300 hours.]

[0123] The melt flow rate (MFR) (190° C., under a load of 2160 g) of the pellets containing the modified EVOH is preferably in the same range as that of the raw material modified EVOH described above.

[0124] The water absorption rate A of the pellets containing the modified EVOH and the water absorption rate B of the comparative pellets satisfy the above formula (7), thereby further improving the extrusion processability. The pellets containing the modified EVOH that satisfy the above formula (7) are considered to have a relatively high water absorption rate and a large surface area. This is considered to result in the pellets containing the modified EVOH melting at low temperature and low stress, thereby further improving the extrusion processability. Meanwhile, the difference (AB) between the water absorption rate A and the water absorption rate B is usually 0.8 or less, and preferably 0.7 or less. If the difference in water absorption rate exceeds 0.8, the pellets containing the modified EVOH are likely to absorb moisture during long-term storage, which may cause the resin to foam easily during molding.

[0125] The pellets containing the modified EVOH may be used alone, or may be used together with other resin pellets as mixed pellets. Examples of other resin pellets include EVOH pellets other than the pellets containing the modified EVOH, various thermoplastic resins, etc. The content of the pellets containing the modified EVOH of the present invention in the mixed pellets is not particularly limited, but is usually 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0126] In the method for producing pellets containing modified EVOH of the present invention, pellets containing water-containing modified EVOH are unlikely to block with each other during the drying process, so that pellets containing modified EVOH are produced with good productivity. Moreover, the pellets containing modified EVOH are excellent in extrusion stability and thermal stability during molding. Therefore, by using such pellets containing modified EVOH, molded products with excellent flexibility and gas barrier properties are produced with good productivity. The pellets containing modified EVOH are used in a wide range of applications, including various packaging containers such as food packaging containers, pharmaceutical packaging containers, industrial chemical packaging containers, and agricultural chemical packaging containers, fuel containers, transport pipes, and resin wallpaper, taking advantage of the inherent properties of the modified EVOH, such as gas barrier properties, transparency, aroma retention, solvent resistance, and oil resistance.

[0127] A preferred embodiment of the present invention is a pellet containing a cylindrical modified EVOH, the modified EVOH being represented by the following formula (I), the contents (mol %) of a, b, and c relative to the total monomer units satisfying the following formulas (1) to (3), the degree of saponification (DS) defined by the following formula (4) being 90 mol % or more, and satisfying the following formulas (6) and (7).

[0128] [ka]

[0129] [In formula (I), W is a hydrogen atom, a methyl group, or R 2 R represents a group represented by the formula -OY, and X, Y and Z each independently represent a hydrogen atom, a formyl group or an alkanoyl group having 2 to 10 carbon atoms. 1 , R 2 each independently represents a single bond, an alkylene group having 1 to 9 carbon atoms, or an alkyleneoxy group having 1 to 9 carbon atoms, and the alkylene group and the alkyleneoxy group may contain a hydroxyl group, an alkoxy group, or a halogen atom.] 24≦a≦55 (1) 0.01≦c≦10 (2) [100-(a+c)]×0.9≦b≦[100-(a+c)] (3) DS = [(total number of moles of X, Y, and Z that are hydrogen atoms) / (total number of moles of X, Y, and Z)] × 100 (4) ΔHma / ΔHmb≦1.05 (6) A B ≧ 0.3 (7) [In the formula (6), ΔHma (J / g) is the crystalline melting enthalpy of the pellets containing the modified EVOH, and ΔHmb is the crystalline melting enthalpy (J / g) of cylindrical comparative pellets having the same diameter and length as the pellets containing the modified EVOH, which are obtained by extruding the molten material obtained by holding the pellets containing the modified EVOH at 210° C. for 6 minutes into water and then cutting the extruded material. In addition, in the formula (7), A is the water absorption rate (mass%) of the pellets containing the modified EVOH after holding them at 40° C. and 90% RH for 300 hours, and B is the water absorption rate (mass%) of the comparative pellets after holding them at 40° C. and 90% RH for 300 hours.] EXAMPLES

[0130] The present invention will now be described in more detail with reference to examples.

[0131] Synthesis Example 1 (1) Synthesis of modified EVAc In a 250 L pressurized reactor equipped with a jacket, a stirrer, a nitrogen inlet, an ethylene inlet, and an initiator addition inlet, vinyl acetate (R 9 100 kg of 2-methylene-1,3-propanediol diacetate (wherein R is a methyl group; hereinafter referred to as VAc), 10 kg of methanol (hereinafter sometimes referred to as MeOH), and 3 and R 4 is a hydrogen atom, and R 10 and R 112.9 kg of MPDAc (wherein the methyl group is methyl group: hereinafter referred to as MPDAc) was charged and heated to 60°C, and then nitrogen was bubbled for 30 minutes to replace the inside of the reactor with nitrogen. Then, ethylene was introduced so that the reactor pressure (ethylene pressure) was 4.9 MPa. After adjusting the temperature inside the reactor to 60°C, 60 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 start polymerization. During polymerization, the ethylene pressure was maintained at 4.9 MPa and the polymerization temperature at 60°C. After 6 hours, when the polymerization rate of VAc reached 45%, the polymerization was stopped by cooling. The reactor was opened to remove ethylene, and then nitrogen gas was bubbled in to completely remove ethylene. Next, unreacted VAc was removed under reduced pressure, and then MeOH was added to a modified ethylene-vinyl acetate copolymer (hereinafter sometimes referred to as modified EVAc) in which structural units derived from MPDAc had been introduced by copolymerization to prepare a 20 mass% MeOH solution.

[0132] [ka]

[0133] (2) Saponification of denatured EVAc A 500L reaction vessel equipped with a jacket, a stirrer, a nitrogen inlet, a reflux condenser, and a solution addition port was charged with a 20% by mass MeOH solution of the modified EVAc obtained in (1). The temperature of this solution was raised to 60°C while blowing in nitrogen, and 0.5 equivalents of sodium hydroxide relative to the vinyl acetate units in the modified EVAc were added as a 2N MeOH solution. After the addition of the sodium hydroxide MeOH solution was completed, the temperature in the system was kept at 60°C, and the saponification reaction was allowed to proceed by stirring for 2 hours while distilling off methyl acetate and MeOH. Then, acetic acid was added to stop the saponification reaction. Then, while heating and stirring at 60 to 80°C, ion-exchanged water was added, MeOH was distilled out of the reaction vessel, and modified EVOH was precipitated. The precipitated modified EVOH was collected and pulverized in a mixer. The obtained modified EVOH powder was put into a 1g / L aqueous acetic acid solution (bath ratio 20: 20L of aqueous solution per 1kg of powder) and washed by stirring for 2 hours. The product was deliquinated, and then placed in a 1 g / L aqueous acetic acid solution (bath ratio 20) and washed with stirring for 2 hours. The deliquinated product was placed in ion-exchanged water (bath ratio 20), washed with stirring for 2 hours, and then deliquinated. This operation was repeated three times for purification. The product was then immersed in 10 L of an aqueous solution containing 0.5 g / L acetic acid and 0.1 g / L sodium acetate with stirring for 4 hours, then deliquinated, and dried at 60°C for 16 hours to obtain a crude dried product of modified EVOH.

[0134] (3) Content of each structural unit in modified EVAc The ethylene unit content (a mol % in formula (VII)), the content of structural units derived from vinyl acetate (b mol % in formula (VII)), and the content of structural units derived from MPDAc (c mol % in formula (VII)) in the modified EVAc before saponification were calculated. 1 Calculation was performed using H-NMR.

[0135] First, a small amount of the MeOH solution of modified EVAc obtained in (1) was sampled, and the modified EVAc was precipitated in ion-exchanged water. The precipitate was collected and dried at 60°C under vacuum to obtain a dried product of modified EVAc. Next, the dried product of modified EVAc obtained was dissolved in dimethylsulfoxide (DMSO)-d6 containing tetramethylsilane as an internal standard substance, and the solution was analyzed by a 500 MHz NMR spectrometer.1 Measurements were performed at 80°C using H-NMR (JEOL Ltd.: "GX-500").

[0136] Denaturing EVAc 1 The peaks in the H-NMR spectrum are assigned as follows: 0.6-1.0 ppm: methylene protons (4H) of terminal ethylene units 1.0 to 1.85 ppm: methylene protons (4H) of the ethylene unit in the middle part, methylene protons (2H) of the main chain part of the structural unit derived from MPDAc, methylene protons (2H) of the vinyl acetate unit 1.85-2.1 ppm: Methyl protons (6H) of the structural units derived from MPDAc and methyl protons (3H) of the vinyl acetate units 3.7-4.1 ppm: Methylene protons (4H) in the side chain of the structural unit derived from MPDAc 4.4-5.3 ppm: methine proton (1H) of vinyl acetate unit

[0137] According to the above attribution, assuming that the integral value from 0.6 to 1.0 ppm is x, the integral value from 1.0 to 1.85 ppm is y, the integral value from 3.7 to 4.1 ppm is z, and the integral value from 4.4 to 5.3 ppm is w, the content of ethylene units (a: mol %), the content of vinyl ester units (b: mol %), and the content of structural units derived from MPDAc (c: mol %) are each calculated according to the following formulas. a=(2x+2y-z-4w) / (2x+2y+z+4w)×100 b = 8w / (2x+2y+z+4w) x 100 c = 2z / (2x+2y+z+4w) × 100

[0138] As a result of calculation by the above method, the content (a) of ethylene units in the modified EVAc in Synthesis Example 1 was 38.0 mol%, the content (b) of vinyl ester units was 60.5 mol%, and the content (c) of structural units derived from MPDAc was 1.5 mol%. The values ​​of a, b, and c in the modified EVAc are the same as the values ​​of a, b, and c in the modified EVOH after saponification treatment.

[0139] (4) Degree of saponification of modified EVOH The same is true for modified EVOH after saponification. 1 H-NMR measurement was performed. The crude dried modified EVOH obtained in (2) above was dissolved in dimethylsulfoxide (DMSO)-d6 containing tetramethylsilane as an internal standard and tetrafluoroacetic acid (TFA) as an additive, and the NMR spectrum was measured using a 500 MHz NMR spectrometer. 1 Measurements were performed at 80°C using H-NMR (JEOL Ltd.: "GX-500"). 1 As a result of H-NMR measurement, the peak intensity at 1.85 to 2.1 ppm was significantly reduced, which clearly shows that in addition to the ester groups derived from vinyl acetate in the modified EVOH, the ester groups contained in the structural units derived from MPDAc were also saponified to hydroxyl groups. 1 The decrease in the peak intensity at 1.85 to 2.1 ppm was also observed in the H-NMR spectrum. The saponification degree was calculated from the peak intensity ratio of the methyl protons of the vinyl acetate unit (1.85 to 2.1 ppm) and the methine protons of the vinyl alcohol unit (3.15 to 4.15 ppm). The saponification degree of the modified EVOH of Synthesis Example 1 was 99.9 mol% or more.

[0140] Synthesis Examples 2-6 EVAc and EVOH were produced and analyzed in the same manner as in Synthesis Example 1, except that the polymerization conditions in Synthesis Example 1 were changed as shown in Table 1. The results are shown in Table 1.

[0141] [Table 1]

[0142] Example 1 The crude modified EVOH obtained in Synthesis Example 1 was dried at 60°C for 6 hours, and the raw material hydrous modified EVOH (ethylene content 38 mol%, saponification degree 99.99 mol%, content of structural units derived from MPDAc (c) 1.5 mol%) adjusted to a moisture content of 25 mass% was fed into a twin-screw extruder and melt-kneaded under the conditions shown below. In addition, at the C4 portion of the extruder, an additive consisting of an acetic acid / boric acid / sodium acetate aqueous solution was added by a plunger pump so that the content in the pellets containing the modified EVOH finally obtained was 100 ppm acetic acid, 1400 ppm boric acid, and 150 ppm sodium equivalent. (Melting and kneading conditions) Extruder: Twin-screw extruder "Labo Plastomill" manufactured by Toyo Seiki Seisakusho Co., Ltd. Screw diameter: 25mmφ Screw rotation speed: 50 rpm Discharge rate: 2.0 kg / hr (including water mass) Cylinder and die temperature settings: C1 / C2 / C3 / C4 / C5 / Die=80 / 100 / 100 / 100 / 100 / 150(℃)

[0143] The temperature T0 of the melt in the twin-screw extruder was 130°C. The temperature T0 was measured using a temperature sensor attached to the end of the cylinder in contact with the melt. The melt discharged from the twin-screw extruder was extruded into water to obtain a strand-shaped coagulation. The obtained coagulation was then cut with a strand cutter to obtain cylindrical water-containing pellets. The moisture content of the melt immediately after being discharged from the twin-screw extruder and the pellets containing water-containing modified EVOH were measured according to the method described in (1) below, and the moisture content was 15% by mass. The obtained pellets containing water-containing modified EVOH were dried at 60°C for 3 hours, at 80°C for 3 hours, and at 110°C for 20 hours to obtain cylindrical pellets containing modified EVOH with a moisture content of 0.2% by mass, a diameter of 3 mm, and a length of 4 mm. The pellets containing modified EVOH were subjected to the quantitative determination of carboxylic acid, the quantitative determination of metal salts and boron compounds, and the evaluation of crystalline fusion enthalpy, melting point, water absorption rate, extrusion stability, thermal stability, and blocking resistance during drying according to the methods described in (1) to (9). For evaluation of blocking resistance during drying, pellets containing water-containing modified EVOH before drying with a water content of 15% by mass were used. The results are shown in Table 2.

[0144] (1) Measurement of moisture content of pellets, etc. The moisture content of the raw material hydrous modified EVOH, the pellets containing hydrous modified EVOH, and the melt was measured by a heating and drying mass measurement method using a Mettler halogen moisture meter "HR73" under the conditions of a drying temperature of 180°C, a drying time of 20 minutes, and a sample weight of 10 g. These moisture contents were calculated using the following formula. In the following formula, X is the mass of the sample before drying, and Y is the mass of the sample after drying. Moisture content (mass%)=(XY) / X×100

[0145] (2) Determination of carboxylic acids 20 g of the resulting pellets containing modified EVOH were placed in 100 mL of ion-exchanged water and extracted by heating for 6 hours at 95° C. The resulting extract was neutralized with a 0.01 mol / L sodium hydroxide solution using phenolphthalein as an indicator to calculate the carboxylic acid content in the pellets containing modified EVOH.

[0146] (3) Determination of metal salts and boron compounds 0.5 g of the pellets containing the modified EVOH obtained 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 pressure vessel was covered and further decomposed by heating at 150°C for 10 minutes and then at 180°C for 5 minutes using a wet decomposition device (Actac's "MWS-2"), and then cooled to room temperature. This treatment liquid was transferred to a 50 mL measuring flask and made up to 10 mL with ion-exchanged water to prepare a measurement sample solution. The contents of metal elements and boron elements in the sample solution were measured using an ICP emission spectrometer (PerkinElmer's "OPTIMA4300DV"). From the obtained values, the metal salt content in terms of metal elements and the boron compound content in terms of boron elements in the pellets containing the modified EVOH were calculated.

[0147] (4) Crystal fusion enthalpy (ΔH) (4-1) Measurement of ΔHma A 3 mg sample cut from the pellet containing modified EVOH obtained in Example 1 was sealed in an aluminum pan (manufactured by TA Instruments) and heated from 30°C to 200°C at a rate of 10°C / min using a differential scanning calorimeter "Q2000" (manufactured by TA Instruments). The melting enthalpy (ΔHma: J / g) was calculated from the peak area in the temperature range from the start to the end of melting in the obtained DSC curve. The results are shown in Table 2. (4-2) Measurement of ΔHmb The pellets containing the modified EVOH obtained were filled into a cylinder of Melt Indexer L244 (manufactured by Takara Kogyo Co., Ltd.) with an inner diameter of 9.55 mm and a length of 162 mm, and then held at 210°C for 6 minutes. A load was evenly applied to the molten modified EVOH using a plunger with a mass of 10.9 kg and a diameter of 9.48 mm. The resulting molten material was extruded into water, cut, and then dried at 80°C for 10 hours to obtain cylindrical comparative pellets having the same diameter and length as the pellets containing the modified EVOH. The fusion enthalpy (ΔHmb: J / g) of the obtained comparative pellets was determined in the same manner as in (4-1). The results are shown in Table 2.

[0148] (5) Melting point The pellets containing the modified EVOH obtained were heated from 30°C to 200°C at a rate of 10°C / min in accordance with JIS K 7121, then rapidly cooled to 0°C at 10°C / min, and again measured at a heating rate of 10°C / min from 0°C to 200°C (TA Instruments' differential scanning calorimeter (DSC) "Q2000"). Indium was used for temperature calibration. The melting peak temperature (Tpm) was determined from the chart of the 2nd run in accordance with the JIS, and this was taken as the melting point of the pellets containing the modified EVOH. The melting point was 161°C.

[0149] (6)MFR The pellets containing the modified EVOH obtained were filled into a cylinder of Melt Indexer L244 (manufactured by Takara Kogyo Co., Ltd.) with an inner diameter of 9.55 mm and a length of 162 mm, and melted at 190°C. Then, a load was evenly applied to the molten resin composition using a plunger with a mass of 2,160 g and a diameter of 9.48 mm. The amount of resin composition extruded per unit time (g / 10 min) from an orifice with a diameter of 2.1 mm provided in the center of the cylinder was measured, and this was taken as the MFR.

[0150] (7) Water absorption rate The pellets containing the modified EVOH obtained were dried at 80°C for 10 hours, and the mass α before storage was measured. The pellets containing the modified EVOH after drying were then kept at 40°C and 90% RH for 300 hours, and the mass β after storage was measured. The water absorption rate (mass%) was calculated using the following formula. Water absorption rate (mass%)=(β-α) / β×100

[0151] (8) Extrusion stability The pellets containing the modified EVOH obtained were extruded under the following two conditions, and the difference in the discharge amount when the temperature of the supply section was changed was evaluated. It was judged that the smaller the difference in the discharge amount when the temperature of the supply section was changed, the higher the extrusion stability. (Extrusion conditions) Extrusion temperature: Feeding section / Compression section / Metering section / Die =140 or 180 / 200 / 200 / 200(℃) Screw rotation speed: 40 rpm Die: 1 hole, 3mm diameter

[0152] (9) Thermal stability The pellets containing the modified EVOH were used to form a film under the following conditions to obtain a single-layer film of 20 μm. The appearance of the film was visually observed 8 hours after the start of film formation and evaluated according to the following criteria. (Film forming conditions) Supply section: 150℃ Compression section: Melting point of modified EVOH + 20℃ Measuring section: Melting point of modified EVOH + 20℃ Die temperature: 250℃ Screw rotation speed: 20 rpm Take-off roll temperature: 80℃ Take-off roll speed: 1.5m / min (evaluation) A: No streaks were observed on the film. B: Slight streaks were observed on the film. C: Significant streaks were observed on the film.

[0153] (10) Evaluation of blocking resistance of water-modified EVOH when dry (10-1) Evaluation of blocking resistance during drying of pellets containing water-containing modified EVOH at a drying temperature of 70°C 3 kg of pellets containing hydrous modified EVOH before drying, obtained through the melting and kneading process, solidification process, and cutting process, were placed in a 30 cm cube stainless steel mesh basket and dried for 2 hours at 70°C in a precision incubator "DH410" manufactured by Yamato Scientific Co., Ltd. The pellets containing modified EVOH after drying were passed through a sieve with 5 mm openings for 1 minute, and the mass γ (Kg) of the modified EVOH remaining in the sieve was measured as pellets where blocking had occurred, and the blocking occurrence rate at 70°C was calculated using the following formula and evaluated according to the following criteria. The results are shown in Table 2. Blocking incidence rate (mass%) = γ / 3 × 100 (evaluation) A: Blocking rate is less than 10% by mass B: Blocking rate is 10% by mass or more and less than 20% by mass C: Blocking rate is 20% by mass or more

[0154] (10-2) Evaluation of blocking resistance during drying of pellets containing water-containing modified EVOH at a drying temperature of 90°C The entire amount of the pellets containing the hydrous modified EVOH used in the evaluation of (10-1) was placed again in the stainless steel mesh basket and dried for 2 hours at 90°C in a precision incubator "DH410" manufactured by Yamato Scientific Co., Ltd. The same operation as in (10-1) was carried out to calculate the blocking occurrence rate at 90°C. The results are shown in Table 2.

[0155] (10-3) Evaluation of blocking resistance during drying of pellets containing water-containing modified EVOH at a drying temperature of 110°C The entire amount of the pellets containing the hydrous modified EVOH used in the evaluation of (10-2) was placed again in the stainless steel mesh basket and dried for 2 hours at 110°C in a precision incubator "DH410" manufactured by Yamato Scientific Co., Ltd. The same operation as in (10-1) was carried out to calculate the blocking occurrence rate at 110°C. The results are shown in Table 2.

[0156] In the series of drying steps, the smaller the amount of blocked pellets, the higher the yield of pellets containing modified EVOH, and the better the blocking resistance of the pellets was evaluated to be.

[0157] (Examples 2 to 5, Comparative Example 4) Pellets containing modified EVOH were prepared and evaluated in the same manner as in Example 1, except that the synthesis conditions were changed as shown in Table 1. The results are shown in Table 2.

[0158] Example 6 Pellets containing modified EVOH were prepared and evaluated in the same manner as in Example 1, except that the saponification time was changed so that the degree of saponification became 93 mol %. The results are shown in Table 2.

[0159] Comparative Example 1 Pellets containing modified EVOH were prepared in the same manner as in Example 1, except that the molten material discharged from the twin-screw extruder was cut with a hot cutter to form spheres, and then evaluated. The results are shown in Table 2.

[0160] Comparative Example 2 100 parts by mass of the crude dry product of modified EVOH obtained in Synthesis Example 1, 56 parts by mass of water, and 130 parts by mass of MeOH were charged into an 80 L stirring tank equipped with a jacket, a stirrer, and a reflux condenser, and heated to 80°C to dissolve. This solution was extruded through a cylindrical nozzle with an opening of 4 mm in inner diameter into a mixture of water / MeOH = 90 / 10 (mass ratio) cooled to 5°C to precipitate in the form of strands, and the strands were cut into cylindrical pellets with a length of 4 mm in the extrusion direction and a diameter of 3 mm using a strand cutter to obtain hydrous pellets of modified EVOH. The moisture content of the obtained hydrous pellets of modified EVOH was measured using a Mettler halogen moisture meter "HR73" and was found to be 60% by mass.

[0161] The obtained hydrous pellets of modified EVOH were placed in a 1 g / L aqueous acetic acid solution (bath ratio 20) and washed with stirring for 2 hours. The pellets were deliquinated and then placed in a 1 g / L aqueous acetic acid solution (bath ratio 20) and washed with stirring for 2 hours. After deliquification, the aqueous acetic acid solution was renewed and the same operation was carried out. The hydrous pellets after deliquification were placed in ion-exchanged water (bath ratio 20) and washed with stirring for 2 hours, and then deliquinated. This operation was repeated three times for purification, and hydrous modified EVOH pellets from which catalyst residues from the saponification reaction had been removed were obtained. The moisture content of the obtained pellets containing hydrous modified EVOH was measured using a Mettler halogen moisture meter "HR73" and found to be 55% by mass.

[0162] Next, 1 part by mass of pellets containing hydrous modified EVOH with a water content of 55% by mass was immersed in 18.5 parts by mass (bath ratio 20) of an aqueous solution containing sodium acetate at a concentration of 0.5 g / L, acetic acid at a concentration of 0.4 g / L, and boric acid at a concentration of 0.3 g / L for 4 hours while being periodically stirred. Subsequently, after removing moisture from the pellet surface by centrifugal dehydration, the pellets containing hydrous modified EVOH were arranged on a Teflon sheet so that the pellets did not overlap each other, and were dried at 60°C for 3 hours, 80°C for 3 hours, and 110°C for 20 hours to obtain pellets containing modified EVOH. The moisture content of the obtained pellets containing modified EVOH was measured with a halogen moisture meter "HR73" manufactured by Mettler and was 0.2% by mass. The obtained pellets containing modified EVOH were evaluated in the same manner as in Example 1. The results are shown in Table 2. In addition, (10) for evaluating the blocking resistance of pellets containing hydrous modified EVOH during drying, pellets containing hydrous modified EVOH with a moisture content of 15% by mass after drying at 60°C for 3 hours and at 80°C for 3 hours were used.

[0163] Comparative Example 3 The pellets containing the modified EVOH obtained in Example 1 were melt-kneaded under the following conditions, and the molten material discharged from the twin-screw extruder was extruded into water to obtain a strand-shaped coagulated material. The obtained coagulated material was then cut with a strand cutter to produce cylindrical pellets containing the modified EVOH, which were evaluated in the same manner as in Example 1. The results are shown in Table 2. (Melting and kneading conditions) Extruder: Twin-screw extruder "Labo Plastomill" manufactured by Toyo Seiki Seisakusho Co., Ltd. Screw diameter: 25mmφ Screw rotation speed: 100 rpm Feeder rotation speed: 80 rpm Cylinder and die temperature settings: C1 / C2 / C3 / C4 / C5 / Die=170 / 200 / 200 / 200 / 200 / 200(℃)

[0164] [Table 2]

Claims

1. A method for producing pellets containing a modified ethylene-vinyl alcohol copolymer, comprising: a melt-kneading step of supplying the hydrous modified ethylene-vinyl alcohol copolymer to an extruder and melt-kneading the copolymer to obtain a melt having a water content of 4 to 35% by mass; a coagulation step of extruding the molten material into a coagulation bath to obtain a strand-shaped coagulated material; A cutting step of cutting the coagulated material to obtain cylindrical water-containing pellets; and A drying step of drying the water-containing pellets; and The modified ethylene-vinyl alcohol copolymer is represented by the following formula (I), the contents (mol %) of a, b, and c relative to all monomer units satisfy the following formulas (1) to (3), and the degree of saponification (DS) defined by the following formula (4) is 90 mol % or more. 【Chemistry 1】 [In formula (I), W is a hydrogen atom, a methyl group, or R ２ R represents a group represented by the formula -OY, and X, Y and Z each independently represent a hydrogen atom, a formyl group or an alkanoyl group having 2 to 10 carbon atoms. １ , R ２ each independently represents a single bond, an alkylene group having 1 to 9 carbon atoms, or an alkyleneoxy group having 1 to 9 carbon atoms, and the alkylene group and the alkyleneoxy group may contain a hydroxyl group, an alkoxy group, or a halogen atom. 24≦a≦55 (1) 0.01≦c≦10 (2) [100-(a+c)]×0.9≦b≦[100-(a+c)] (3) DS = [(total number of moles of X, Y, and Z that are hydrogen atoms) / (total number of moles of X, Y, and Z)] × 100 (4)

2. The method for producing pellets containing a modified ethylene-vinyl alcohol copolymer according to claim 1, wherein a water-containing modified ethylene-vinyl alcohol copolymer having a water content of 10 to 60 mass % is supplied to an extruder in the melt-kneading step.

3. The method for producing pellets containing a modified ethylene-vinyl alcohol copolymer according to claim 1 or 2, wherein the melting point of the pellets containing the modified ethylene-vinyl alcohol copolymer is 120 to 163°C.

4. The temperature T of the melt in the extruder ０ is 70 to 180° C., and the cylinder temperature T １ is 65 to 175° C., and T ０ and T １ The method for producing pellets containing the modified ethylene-vinyl alcohol copolymer according to claim 1 or 2, wherein the following formula (5) is satisfied: 5≦T ０ -T １ ≦100 (5)

5. R in formula (I) １ The method for producing pellets containing the modified ethylene-vinyl alcohol copolymer according to claim 1 or 2, wherein is a single bond and W is a hydroxymethyl group.

6. A cylindrical pellet containing a modified ethylene-vinyl alcohol copolymer, The modified ethylene-vinyl alcohol copolymer is represented by the following formula (I), the contents (mol %) of a, b, and c relative to the total monomer units satisfy the following formulas (1) to (3), and the degree of saponification (DS) defined by the following formula (4) is 90 mol % or more, A pellet containing a modified ethylene-vinyl alcohol copolymer that satisfies the following formulas (6) and (7): 【Chemistry 2】 [In formula (I), W is a hydrogen atom, a methyl group, or R ２ R represents a group represented by the formula -OY, and X, Y and Z each independently represent a hydrogen atom, a formyl group or an alkanoyl group having 2 to 10 carbon atoms. １ , R ２ each independently represents a single bond, an alkylene group having 1 to 9 carbon atoms, or an alkyleneoxy group having 1 to 9 carbon atoms, and the alkylene group and the alkyleneoxy group may contain a hydroxyl group, an alkoxy group, or a halogen atom. 24≦a≦55 (1) 0.01≦c≦10 (2) [100-(a+c)]×0.9≦b≦[100-(a+c)] (3) DS = [(total number of moles of X, Y, and Z that are hydrogen atoms) / (total number of moles of X, Y, and Z)] × 100 (4) ΔHma / ΔHmb≦1.05 (6) A-B≧0.3 (7) [In the formula (6), ΔHma (J / g) is the crystalline melting enthalpy of the pellets containing the modified ethylene-vinyl alcohol copolymer, and ΔHmb is the crystalline melting enthalpy (J / g) of a cylindrical comparative pellet having the same diameter and length as the pellets containing the modified ethylene-vinyl alcohol copolymer, which is obtained by extruding the molten material obtained by holding the pellets containing the modified ethylene-vinyl alcohol copolymer at 210° C. for 6 minutes into water and then cutting the molten material. In addition, in the formula (7), A is the water absorption rate (mass%) of the pellets containing the modified ethylene-vinyl alcohol copolymer after holding it at 40° C. and 90% RH for 300 hours, and B is the water absorption rate (mass%) of the comparative pellets after holding it at 40° C. and 90% RH for 300 hours.]

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