Method for manufacturing ethylene-vinyl alcohol copolymer resin composition pellets

Abstract

This method for manufacturing EVOH resin composition pellets comprises: a first drying step (I) for introducing EVOH hydrous pellets having a water content W0 of 25-50 mass% into a dryer to reduce the water content W1 of the pellets to 5-25 mass%; a melting-kneading step (II) for introducing the pellets obtained in the first drying step (I) into an extruder, adding a water dispersion liquid or an aqueous solution containing an additive, and melting and kneading the mixture; a cutting step (III) for cutting the molten resin composition discharged from the extruder to obtain EVOH resin composition hydrous pellets having a water content W2 of 5-20 mass%; and a second drying step (IV) for drying the hydrous pellets obtained in the cutting step (III) to obtain EVOH resin composition pellets having a water content W3 of 0.5 mass% or less. The reduction (W0-W1) of the water content in the first drying step (I) is 10-45 mass%. Accordingly, it is possible to efficiently obtain EVOH resin composition pellets by increasing the production speed when adding an additive to hydrous EVOH in an extruder.

Description

Method for producing ethylene-vinyl alcohol copolymer resin composition pellets

[0001] The present invention relates to a method for producing ethylene-vinyl alcohol copolymer resin composition pellets.

[0002] Ethylene-vinyl alcohol copolymer (hereinafter sometimes referred to as EVOH) is a polymeric material that has excellent gas barrier properties, fuel barrier properties, oil resistance, aroma retention, anti-static properties, etc., and is widely used in the form of films, sheets, containers, etc. There are various methods for molding EVOH into various molded products, but melt molding using an extruder, such as extrusion molding or injection molding, is common. However, because EVOH typically requires a melt temperature of 200°C or higher during molding, additive-free EVOH is prone to degradation during melt molding, which can result in the formation of fisheyes and lumps in the product, reducing its quality.

[0003] To solve this problem, a method of adding trace components such as acidic substances and / or metal salts to EVOH is known. In order to improve long-run properties and suppress appearance defects such as gels and particles, a method of blending at least one additive selected from carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts is known.

[0004] One known method for incorporating such additives into EVOH is to immerse EVOH hydrous pellets in an aqueous solution containing the additives, thereby impregnating the pellets with the additives (see, for example, Patent Document 1). However, this method requires a long time to uniformly impregnate the EVOH pellets with the additives. It also requires a treatment bath and a treatment tower for immersing the EVOH pellets, as well as wastewater treatment and recovery facilities for disposing of the treatment solution after use.

[0005] In order to solve these problems, a method has been proposed in which water-containing EVOH pellets are fed into an extruder and melt-kneaded, and an aqueous solution containing the additives is added to the molten water-containing EVOH and kneaded, thereby blending the additives into the EVOH.

[0006] For example, Example 1 of Patent Document 2 describes that EVOH hydrous pellets having a moisture content of 39% by mass are fed into an extruder, dehydrated through a dehydration slit, and then an aqueous solution containing additives is added, followed by melt-kneading and subsequent pelletization, thereby obtaining hydrous EVOH resin composition pellets containing additives and having a moisture content of 20% by mass.Then, it describes that the obtained hydrous EVOH resin composition pellets are dried in a hot air dryer to obtain EVOH resin composition pellets having a moisture content of 0.2% by mass.

[0007] Furthermore, Example 4 of Patent Document 3 describes that EVOH hydrous pellets with a moisture content of 32% by mass are introduced into a hot air dryer to reduce the moisture content of the pellets to 9.9% by mass, and then the pellets are charged into an extruder, an aqueous solution containing additives is added, and the pellets are melt-kneaded, and then degassed through a vent port using a vacuum pump, and then discharged from the extruder and subsequently pelletized, thereby obtaining EVOH resin composition pellets containing additives and with a moisture content of 0.2% by mass. The pellets thus obtained have a sufficiently low moisture content and can be directly subjected to melt molding.

[0008] Japanese Patent Application Laid-Open No. 64-66262 Japanese Patent Application Laid-Open No. 2002-284811 WO2004 / 009313A1

[0009] However, in the above-mentioned conventional methods, when an attempt is made to increase the production speed by, for example, increasing the amount of water-containing EVOH supplied to the extruder, the EVOH leaks out from the dehydration slit or vent port, making it difficult to increase the production speed. More specifically, when the production speed is increased by increasing the amount of water-containing EVOH supplied to the extruder under the conditions of Patent Document 2, the water-containing EVOH leaks out from the dehydration slit, and when the production speed is increased by increasing the amount of water-containing EVOH supplied to the extruder under the conditions of Patent Document 3, the extruder vents up and the EVOH leaks out from the vent port, making it difficult to efficiently increase the production speed.

[0010] The present invention has been made to solve the above-mentioned problems, and provides a method for efficiently obtaining EVOH resin composition pellets by improving the production speed when adding additives to water-containing EVOH in an extruder.

[0011] The above problem is the moisture content W ０ 25 to 50% by mass of ethylene-vinyl alcohol copolymer water-containing pellets are introduced into a dryer, and the water content W of the pellets is １ a first drying step (I) of reducing the water content W to 5 to 25% by mass; a melt-kneading step (II) of introducing the pellets obtained in the first drying step (I) into an extruder, adding an aqueous solution or aqueous dispersion containing an additive, and melt-kneading the pellets; and a melt-kneading step (III) of cutting the molten resin composition discharged from the extruder to reduce the water content W ２ a cutting step (III) for obtaining water-containing pellets of an ethylene-vinyl alcohol copolymer resin composition having a water content of 5 to 20% by mass; and drying the water-containing pellets obtained in the cutting step (III) to obtain water-containing pellets of an ethylene-vinyl alcohol copolymer resin composition having a water content of 5 to 20% by mass. ３ a second drying step (IV) for obtaining ethylene-vinyl alcohol copolymer resin composition pellets having a water content of 0.5% by mass or less, ０ -W １ The above-mentioned problem is solved by providing a method for producing ethylene-vinyl alcohol copolymer resin composition pellets, wherein the ethylene unit content of the ethylene-vinyl alcohol copolymer is 20 to 60 mol % and the degree of saponification is 95 mol % or more.

[0012] In this case, in the melt-kneading step (II), the average residence time of the ethylene-vinyl alcohol copolymer in the extruder is preferably 300 seconds or less. It is also preferable that the aqueous solution or aqueous dispersion added in the melt-kneading step (II) is an aqueous solution in which at least one additive selected from carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts is dissolved. Furthermore, in the melt-kneading step (II), it is also preferable to discharge liquid water or water vapor from at least one location in the extruder, and in this case, it is more preferable to discharge the liquid water or water vapor from a position downstream of the position where the aqueous solution or aqueous dispersion is added.

[0013] The above-mentioned problems can also be solved by the method for producing ethylene-vinyl alcohol copolymer resin composition pellets, which comprises the steps of: (A) introducing an ethylene-vinyl alcohol copolymer solution containing 50 parts by mass or more of an alcohol having a boiling point of 100°C or less per 100 parts by mass of the ethylene-vinyl alcohol copolymer into a container, contacting the ethylene-vinyl alcohol copolymer with water vapor in the container to discharge the alcohol together with the water vapor, and discharging a hydrous ethylene-vinyl alcohol copolymer from the container; (B) feeding the hydrous ethylene-vinyl alcohol copolymer into an extruder, melt-kneading the copolymer, and then discharging the copolymer from the extruder; and (C) cutting the hydrous ethylene-vinyl alcohol copolymer discharged from the extruder, and then supplying the obtained hydrous ethylene-vinyl alcohol copolymer pellets to the first drying step (I).

[0014] According to the method for producing EVOH resin composition pellets of the present invention, the production speed when adding additives to the water-containing EVOH in the extruder can be improved, and EVOH resin composition pellets can be obtained efficiently. Here, "efficiently" means that even if the production speed is improved (the residence time of the water-containing EVOH in the extruder is reduced), leakage of EVOH from the extruder can be suppressed and foaming of the EVOH discharged from the extruder can be suppressed.

[0015] FIG. 1 is a diagram showing cylinder configuration a and screw configuration X of twin-screw extruders in Examples 1 to 7 and Comparative Examples 1 and 2. FIG. 2 is a diagram showing cylinder configuration b and screw configuration Y of twin-screw extruders in Example 8 and Comparative Examples 3 to 6. FIG. 3 is a diagram showing cylinder configuration c and screw configuration Y of twin-screw extruders in Comparative Examples 7 and 8. FIG. 4 is a diagram showing cylinder configuration d and screw configuration X of twin-screw extruders in Comparative Examples 9 and 10.

[0016] The present invention is based on the moisture content W ０ 25 to 50% by mass of ethylene-vinyl alcohol copolymer water-containing pellets are introduced into a dryer, and the water content W of the pellets is １a first drying step (I) of reducing the water content W to 5 to 25% by mass; a melt-kneading step (II) of introducing the pellets obtained in the first drying step (I) into an extruder, adding an aqueous solution or aqueous dispersion containing an additive, and melt-kneading the pellets; and a melt-kneading step (III) of cutting the molten resin composition discharged from the extruder to reduce the water content W ２ a cutting step (III) for obtaining water-containing pellets of an ethylene-vinyl alcohol copolymer resin composition having a water content of 5 to 20% by mass; and drying the water-containing pellets obtained in the cutting step (III) to obtain water-containing pellets of an ethylene-vinyl alcohol copolymer resin composition having a water content of 5 to 20% by mass. ３ a second drying step (IV) for obtaining ethylene-vinyl alcohol copolymer resin composition pellets having a water content of 0.5% by mass or less, ０ -W １ ) is 10 to 45 mass %, the ethylene unit content of the ethylene-vinyl alcohol copolymer is 20 to 60 mol %, and the saponification degree is 95 mol % or more.

[0017] First, the method for producing the EVOH used in the present invention will be described. EVOH is usually obtained by saponifying an ethylene-vinyl ester copolymer. The copolymerization of ethylene and vinyl ester may be any of solution polymerization, suspension polymerization, emulsion polymerization, and bulk polymerization. Furthermore, it may be either a continuous system or a batch system. An example of the polymerization conditions for solution polymerization is shown below.

[0018] The solvent used is preferably an alcohol having a boiling point of 100°C or less, from the viewpoints of solubility of the ethylene-vinyl ester copolymer and EVOH, ease of handling, and ability to efficiently replace alcohol with water. The boiling point is more preferably 80°C or less, and even more preferably 70°C or less. Examples of alcohols having a boiling point of 100°C or less include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, and t-butyl alcohol, with methanol being particularly preferred.

[0019] Examples of initiators that can be used in the polymerization include azonitrile initiators such as 2,2-azobisisobutyronitrile, 2,2-azobis-(2,4-dimethylvaleronitrile), 2,2-azobis-(4-methoxy-2,4-dimethylvaleronitrile), and 2,2-azobis-(2-cyclopropylpropionitrile), and organic peroxide initiators such as isobutyryl peroxide, cumyl peroxy neodecanoate, diisopropyl peroxycarbonate, di-n-propyl peroxydicarbonate, t-butyl peroxy neodecanoate, lauroyl peroxide, benzoyl peroxide, and t-butyl hydroperoxide.

[0020] Examples of vinyl esters include fatty acid vinyl esters such as vinyl acetate, vinyl propionate, and vinyl pivalate, with vinyl acetate being preferred. In addition to ethylene and vinyl esters, monomers copolymerizable therewith, such as α-olefins such as propylene, butylene, isobutylene, pentene, hexene, α-octene, and α-dodecene; 3-acyloxy-1-propene, 3-acyloxy-1-butene, 4-acyloxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4-acyloxy-1 ... siloxy-2-methyl-1-butene, 4-acyloxy-3-methyl-1-butene, 3,4-diacyloxy-2-methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, 4,5-diacyloxy-1-pentene, 4-acyloxy-1-hexene, 5-acyloxy-1-hexene, 6-acyloxy-1-hexene, 5,6-diacyloxy-1-hexene, It is also possible to carry out polymerization in the presence of small amounts of alkenes having an ester group such as 1,3-diacetoxy-2-methylenepropane; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, and itaconic acid, and their anhydrides, salts, and mono- or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallylsulfonic acid, or salts thereof; vinyl silanes such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxyethoxy)silane, and γ-methacryloxypropylmethoxysilane; alkyl vinyl ethers; vinyl ketones; N-vinylpyrrolidone; vinyl chloride; vinylidene chloride; etc. The content of other monomer units in the EVOH other than ethylene, vinyl ester, and vinyl alcohol is preferably 20 mol% or less, and in some cases, 10 mol% or less, 5 mol% or less, 3 mol% or less, 1 mol% or less, or 0.1 mol% or less is preferred. The EVOH may not contain the other monomer units.

[0021] The polymerization conditions are preferably as follows: (1) Temperature: preferably 20 to 90°C, more preferably 40 to 70°C. (2) Time (average residence time in the case of a continuous polymerization): preferably 2 to 15 hours, more preferably 3 to 11 hours. (3) Conversion rate: preferably 10 to 90%, more preferably 30 to 80%, based on the vinyl ester charged. (4) Resin content in the solution after polymerization: preferably 5 to 85% by mass, more preferably 20 to 70% by mass.

[0022] After polymerization for a predetermined time has reached a predetermined polymerization rate, a polymerization inhibitor is added as necessary, unreacted ethylene gas is evaporated and removed, and then unreacted vinyl ester is purged. For example, a method for purging the unreacted vinyl ester may be employed in which the polymerization solution from which ethylene has been removed is continuously fed at a constant rate from the top of a column packed with Raschig rings, vapor of an organic solvent, preferably an alcohol having a boiling point of 100°C or less, and most preferably methanol, is blown into the bottom of the column, a mixed vapor of the organic solvent and unreacted vinyl ester is distilled from the top of the column, and the copolymer solution from which unreacted vinyl ester has been removed is taken out from the bottom of the column.

[0023] An alkali catalyst is added to the copolymer solution from which the unreacted vinyl ester has been removed, and the vinyl ester component in the copolymer is saponified. The saponification method can be either continuous or batchwise. Examples of alkali catalysts that can be used include sodium hydroxide, potassium hydroxide, and alkali metal alcoholates. 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 the solution: 10 to 50 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 a continuous method): 10 minutes to 6 hours

[0024] In general, continuous saponification allows for more efficient removal of methyl acetate produced by saponification, resulting in a resin with a higher degree of saponification with a smaller amount of catalyst than batch saponification. Furthermore, continuous saponification requires higher temperatures to prevent EVOH from precipitating. Therefore, continuous saponification preferably uses the following reaction temperature and catalyst amount: Reaction temperature: 70 to 150°C. Catalyst amount used: 0.005 to 0.1 equivalents (per vinyl ester component).

[0025] The saponification degree of the EVOH used in the present invention is 95 mol% or more. A saponification degree of less than 95 mol% is undesirable because increasing the production rate may increase the torque applied to the extruder. The saponification degree is preferably 98 mol% or more, more preferably 99 mol% or more, and even more preferably 99.5 mol% or more. The saponification degree can be adjusted as desired depending on the conditions. Since the saponification degree does not substantially change in any of the first drying step (I), the melt-kneading step (II), the cutting step (III), and the second drying step (IV), the saponification degree of EVOH can be considered to be the same in both the hydrous EVOH pellets introduced in the first drying step (I) and the EVOH resin composition pellets after the second drying step (IV). Therefore, the saponification degree of EVOH satisfies the above numerical range in both the hydrous EVOH pellets introduced in the first drying step (I) and the EVOH resin composition pellets after the second drying step (IV).

[0026] The EVOH used in the present invention has an ethylene unit content of 20 to 60 mol%. If the ethylene unit content is less than 20 mol%, the affinity for water is too high, and EVOH is likely to leak from the dehydration slit in the melt-kneading step (II). Note that either water vapor or liquid water may be discharged from the dehydration slit in this specification. To effectively prevent EVOH leakage, the ethylene unit content is more preferably 24 mol% or more, and even more preferably 28 mol% or more. On the other hand, an ethylene unit content of 60 mol% or less improves the gas barrier properties of EVOH. The ethylene unit content is preferably 50 mol% or less, and more preferably 45 mol% or less. Since the ethylene unit content does not substantially change in any of the first drying step (I), the melt-kneading step (II), the cutting step (III), and the second drying step (IV), it may be considered that the ethylene unit content of EVOH is the same in both the aqueous EVOH pellets introduced in the first drying step (I) and the EVOH resin composition pellets after the second drying step (IV). Therefore, the ethylene unit content of EVOH satisfies the above-mentioned numerical range in both the aqueous EVOH pellets introduced in the first drying step (I) and the EVOH resin composition pellets after the second drying step (IV).

[0027] The saponification process yields a solution containing EVOH. Hereinafter, the EVOH-containing solution will be referred to simply as the EVOH solution. Hereinafter, the term "EVOH solution" also includes solutions that are not completely homogeneous but have a phase-separated paste-like structure. A post-treatment method for the EVOH solution after the saponification reaction involves supplying a mixed vapor of solvent and water to a tower vessel from the bottom of the vessel and supplying the EVOH solution from a position above the supply position of the mixed vapor. This replaces a portion of the solvent present in the supplied EVOH solution with water, thereby producing a highly concentrated EVOH solution. The EVOH concentration in the EVOH solution supplied to the tower vessel is preferably 15 to 50% by mass, more preferably 25 to 40% by mass. It is also preferable that the ratio of the supply rate of the EVOH solution to the supply rate of the mixed vapor (solution supply rate / steam supply rate) be 100 / 400 to 100 / 8 by mass. Furthermore, it is preferable that the water content in the mixed vapor be 20 to 70% by mass. The solvent used for the mixed vapor is preferably an alcohol having a boiling point of 130° C. or less, and examples of such alcohol include alcohols such as methanol, ethanol, propanol, butanol, etc. Alcohols having a boiling point of 100° C. or less are more preferred, and among these, methanol is preferred because it is easily available, inexpensive, has a low boiling point, and is easy to handle.

[0028] The high-concentration EVOH solution thus obtained typically contains 50 parts by mass or more of an alcohol having a boiling point of 100°C or less per 100 parts by mass of EVOH. The alcohol content is preferably 1,000 parts by mass or less, and more preferably 500 parts by mass or less. By setting the alcohol content within this range, the fluidity of the EVOH solution is ensured and efficient resin production becomes possible. The alcohol used here is preferably methanol. The EVOH solution may also contain water together with the alcohol, and preferably contains 10 to 500 parts by mass of water.

[0029] A suitable method for obtaining the hydrous EVOH pellets used in the present invention includes, for example, subjecting the high-concentration EVOH aqueous solution obtained as described above to the following steps (A), (B), and (C) in this order. Specifically, the hydrous EVOH pellets used in the present invention are obtained by the following steps: (A) introducing an EVOH solution containing 50 parts by mass or more of an alcohol having a boiling point of 100° C. or less per 100 parts by mass of EVOH into a vessel, contacting the EVOH with steam in the vessel to remove the alcohol together with the steam, and removing the hydrous EVOH from the vessel; (B) feeding the hydrous EVOH into an extruder, melt-kneading the extruder, and then discharging the copolymer from the extruder; and (C) cutting the hydrous EVOH discharged from the extruder. This method not only efficiently replaces the alcohol in the EVOH solution with water, but also facilitates adjustment of the water content and temperature of the EVOH.

[0030] In step (A), the method for contacting the EVOH solution introduced into a vessel with steam within the vessel is not particularly limited, and may be either a continuous or batch method. The vessel shape is also not particularly limited, but a tower-type vessel is preferred for the continuous method, and a tank-type vessel is preferred for the batch method. Considering production efficiency, the continuous method is industrially preferable. Examples of tower-type vessels include plate towers such as perforated plate towers and bubble cap towers, and packed towers containing ring-type packings.

[0031] In a tower-type vessel, steam is supplied from the bottom of the vessel, and the EVOH solution is supplied from a position above the steam supply position, thereby removing the solvent (alcohol) present in the supplied EVOH solution together with the steam, and discharging a hydrous EVOH having a water content of 10 to 90% by mass from the vessel. If the amount of steam introduced is too small, the solvent (alcohol) removal efficiency will be poor, while if it is too large, it will be disadvantageous in terms of cost. Therefore, the amount of steam introduced is preferably 0.3 to 30 times, more preferably 0.5 to 10 times, and even more preferably 0.7 to 5 times, the amount of EVOH solution introduced, expressed by mass ratio. The steam contacted with the EVOH solution may contain up to 10 parts by mass of the solvent (alcohol) per 100 parts by mass of steam. However, to efficiently remove the solvent (alcohol), it is preferable that the steam does not contain the solvent (alcohol).

[0032] The alcohol vapor and water vapor discharged from the top of the column are condensed in a condenser and recovered as an aqueous alcohol solution, which can be purified and reused as necessary. The EVOH solution comes into direct contact with water vapor in the vessel, gradually reducing the solvent (alcohol) content. During this time, the EVOH remains in a swollen, paste-like state, allowing it to be discharged from the vessel while maintaining its fluidity and without gelling. EVOH dissolves in a methanol / water mixed solvent at atmospheric pressure, for example, at temperatures of approximately 60-70°C, but does not dissolve in water alone. However, in the presence of pressurized water vapor at temperatures of, for example, 90°C or higher, EVOH can maintain its fluidity even when it contains essentially only water.

[0033] The temperature inside the container is preferably 100 to 150°C. If the temperature inside the container is less than 100°C, the fluidity of the water-containing EVOH will be insufficient, and gelation or blockage may occur inside the container. A temperature of 110°C or higher is more preferable, and 120°C or higher is even more preferable. On the other hand, if the temperature inside the container exceeds 150°C, the EVOH may deteriorate. A temperature of 140°C or lower is more preferable.

[0034] Furthermore, if the pressure inside the vessel is too low, the efficiency of alcohol removal may decrease. The pressure inside the vessel is preferably 0.1 MPa or more, more preferably 0.15 MPa or more, and even more preferably 0.2 MPa or more. On the other hand, if the pressure inside the vessel is too high, the water content of the water-containing EVOH discharged from the vessel may become too high, which may result in the melt viscosity of the water-containing EVOH introduced into the extruder described below becoming too low. Therefore, the pressure inside the vessel is preferably 0.6 MPa or less, more preferably 0.5 MPa or less, and even more preferably 0.4 MPa or less.

[0035] After the EVOH solution is brought into contact with water vapor as described above, the fluid water-containing EVOH is discharged from the vessel. In step (B), the water-containing EVOH discharged from the vessel is fed to an extruder and melt-kneaded, and the copolymer is then discharged from the extruder.

[0036] In step (B), the water content of the water-containing EVOH introduced into the extruder is 10 to 90% by mass. If the water content is less than 10% by mass, the melt viscosity of the water-containing EVOH becomes too high, making it impossible to extrude the water-containing EVOH from the tip of the extruder, or the melt temperature must be increased to ensure fluidity, resulting in deterioration of the EVOH and a deterioration in its color. The water content is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 45% by mass or more. On the other hand, if the water content exceeds 90% by mass, the melt viscosity of the water-containing EVOH becomes too low, making it prone to leakage along with the discharged water when the water content of the water-containing EVOH is reduced. The water content is preferably 80% by mass or less, more preferably 70% by mass or less, even more preferably 60% by mass or less, and particularly preferably 55% by mass or less. The water content of the water-containing EVOH introduced into the extruder is measured by the method described in the Examples below.

[0037] From the viewpoint of preserving the working environment and the surrounding environment and preventing the resulting hydrous EVOH pellets from sticking together, the content of alcohol having a boiling point of 100°C or less in the hydrous EVOH introduced into the extruder in step (B) is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0.5% by mass or less.

[0038] In step (B), the water-containing EVOH introduced into the extruder may contain, for example, about 0.1 to 5% by mass, calculated as the metal, of an alkali metal salt, which corresponds to the residue of the catalyst used in the saponification step, and may also contain by-product salts, other impurities, etc. The content of components other than EVOH, water, and alcohol having a boiling point of 100°C or less in the water-containing EVOH supplied to the extruder is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and particularly preferably 1% by mass or less.

[0039] The extruder used in step (B) may be a single-screw extruder or a multi-screw extruder, but a twin-screw extruder is preferred. The L / D ratio of the extruder is preferably 8 to 30, more preferably 9 to 25, and even more preferably 10 to 20. The cylinder of the extruder is provided with an inlet for the water-containing EVOH, through which the water-containing EVOH is introduced, and then melt-kneaded by the rotation of a screw disposed in the cylinder, and discharged from a discharge port at the tip of the cylinder. At this time, it is preferred to provide a dewatering slit in the cylinder to remove moisture.

[0040] The water content of the water-containing EVOH discharged from the extruder is preferably 25 to 50% by mass. When the water content is 25% by mass or more, the melt viscosity of the water-containing EVOH decreases, and the water-containing EVOH tends to be easily discharged. The water content is more preferably 30% by mass or more. On the other hand, when the water content is 50% by mass or less, the melt viscosity of the water-containing EVOH increases, and leakage of the EVOH tends to be suppressed. The water content is more preferably 40% by mass or less.

[0041] Following step (B), in step (C), the water-containing EVOH discharged from the extruder is cut to obtain water-containing EVOH pellets. The method for this is not particularly limited, and examples include a method in which the water-containing EVOH (in a molten state) discharged from the extruder is directly cut, or a method in which the water-containing EVOH discharged from the extruder is extruded into a coagulation liquid in the form of a strand, solidified, and then cut. Of these, the method of directly cutting the water-containing EVOH is preferred. Methods for directly cutting the water-containing EVOH discharged from the extruder include a hot-cut method and an underwater-cut method. When the water-containing EVOH is extruded in the form of a strand, solidified, and then cut, cylindrical pellets are obtained, while when the water-containing EVOH is directly cut in the molten state, spherical (or nearly spherical) pellets are obtained. The size of the produced water-containing EVOH pellets can be, for example, 1 mm to 10 mm in diameter if the pellets are spherical (or nearly spherical), or 1 mm to 10 mm in diameter and 1 mm to 10 mm in length if the pellets are cylindrical. As described below, the method of cutting the hydrous EVOH in a molten state is superior in productivity to the method of extruding an EVOH solution into a coagulating liquid, extruding it into the form of strands, coagulating them, and then cutting them, because it is not necessary to consider the take-up speed at which strands can be stably formed. The hydrous EVOH pellets obtained as described above are subjected to the first drying step (I).

[0042] Another method for obtaining the hydrous EVOH pellets used in the present invention is to extrude the high-concentration EVOH aqueous solution from a nozzle into a coagulation liquid in the form of a strand, coagulate it in a water bath, and then cut it. Water is used as the coagulation liquid, but it may contain a small amount of alcohol. The coagulated strand is cut into pellets with a cutter. A strand cutter is preferably used as the cutter. The size of the obtained pellets can be, for example, 1 mm to 10 mm in diameter and 1 mm to 10 mm in length in the case of a cylindrical shape, or 1 mm to 10 mm in diameter in the case of a spherical shape. The hydrous EVOH pellets obtained in this manner can also be subjected to the first drying step (I).

[0043] The hydrous EVOH pellets obtained as described above contain 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. In this case, some catalyst residues such as sodium acetate may remain in the hydrous EVOH pellets.

[0044] In the first drying step (I), the moisture content W obtained as described above is ０ EVOH water-containing pellets having a water content of 25 to 50% by mass are introduced into a dryer, and the water content W of the pellets is １ The EVOH water-containing pellets introduced into the dryer are porous and have a high drying rate, so they can be dried at a low drying temperature in a short time.

[0045] Moisture content W when introduced into the dryer ０ is 25 to 50 mass%. ０ When the water content W is 25% by mass or more, the color of the resulting EVOH resin composition pellets becomes good, and the water content W is preferably 30% by mass or more. ０ When the water content W is less than 25% by mass, the average residence time can be shortened even if the mixture is subjected to the melt-kneading step (II) as is, so there is little point in adopting the first drying step (I). ０ If the moisture content W exceeds 50% by mass, the material may stick together in the dryer and the drying efficiency may decrease. ０ is preferably 45 mass % or less.

[0046] The dryer used in the first drying step (I) is not particularly limited as long as it can dry the pellets while maintaining their shape. A hot air dryer or the like can be used. The drying method may be a fluidized drying method using a fluidized dryer or a static drying method using a static dryer, but fluidized drying is preferred to prevent the pellets from sticking together. A combination of these methods may also be used, or a method may be used in which the pellets are first dried by fluidized drying and then dried by static drying.

[0047] The drying temperature is not particularly limited, but drying at 40 to 150°C for 0.1 to 15 hours is preferred. The EVOH hydrous pellets introduced into the dryer can be dried quickly even at low temperatures, thereby suppressing thermal degradation. The drying temperature is more preferably 50°C or higher, and even more preferably 60°C or higher. The drying temperature is more preferably 120°C or lower, even more preferably 100°C or lower, and optimally 90°C or lower. The drying time varies depending on the drying temperature and the target moisture content, but is more preferably 0.2 hours or longer, even more preferably 0.5 hours or longer. It is also more preferably 5 hours or shorter, and even more preferably 3 hours or shorter. Drying may be performed in air or in an inert gas such as nitrogen. When drying in an inert gas, thermal degradation is less likely to occur even if the drying temperature is set higher.

[0048] The moisture content W of the EVOH hydrous pellets obtained by drying in the first drying step (I) １ is 5 to 25% by mass, and the reduction in water content (W ０ -W １ ) is 10 to 45 mass%. １ If the water content W is less than 5% by mass, the resin temperature in the extruder in the melt-kneading step (II) becomes too high, and the water-containing EVOH discharged from the extruder is likely to foam. １ is preferably 7% by mass or more, and more preferably 10% by mass or more. １ If the water content W exceeds 25% by mass, the water content in the extruder in the melt-kneading step (II) will be too high, causing EVOH to leak from the dewatering slit or foaming of the discharged EVOH composition. １ is preferably 22% by mass or less, more preferably 18% by mass or less. ０ -W １ When the moisture content (W) is less than 10% by mass, there is little point in providing the first drying step (I). ０ -W １ ) is preferably 15% by mass or more, more preferably 20% by mass or more. ０ -W １If the moisture content (W) exceeds 45% by mass, it is difficult to dry the pellets in a short time while maintaining their shape. ０ -W １ ) is preferably 35% by mass or less, more preferably 30% by mass or less.

[0049] In the melt-kneading step (II), the pellets obtained in the first drying step (I) are introduced into an extruder, and an aqueous solution or aqueous dispersion containing additives is added and melt-kneaded. This allows the additives to be uniformly dispersed in the water-containing EVOH molten in the extruder. The additives may be dissolved in water in the form of an aqueous solution or a dispersion in water. Among these, an aqueous solution containing at least one additive selected from carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts is preferred.

[0050] The carboxylic acid contained in the aqueous solution is not particularly limited. Examples include acetic acid, lactic acid, oxalic acid, succinic acid, benzoic acid, and citric acid, with carboxylic acids having four or fewer carbon atoms being preferred. Among these, acetic acid is preferred from the standpoints of cost and availability. The carboxylic acid content in the dried EVOH resin composition pellets of the present invention is preferably 10 to 5,000 ppm, since too little may cause discoloration during melt molding, while too much may result in insufficient interlayer adhesion. The carboxylic acid content is more preferably 30 ppm or more, and even more preferably 50 ppm or more. The carboxylic acid content is more preferably 1,000 ppm or less, and even more preferably 500 ppm or less.

[0051] Examples of boron compounds contained in the aqueous solution include, but are not limited to, boric acids, borate esters, borate salts, and boron hydrides. Specific 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 various boric acids listed above. Among these compounds, orthoboric acid (hereinafter simply referred to as boric acid) is preferred. The content of the boron compound in the dried EVOH resin composition pellets of the present invention is preferably 10 to 2000 ppm, more preferably 50 to 1000 ppm, of boron, since too little improves thermal stability and too much can lead to gelation and poor moldability.

[0052] Examples of the phosphate compound contained in the aqueous solution 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. The cation species is not particularly limited, but alkali metal salts and alkaline earth metal salts are preferred. Among these, the phosphate compound is preferably added in the form of sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, or dipotassium hydrogen phosphate. The content of the phosphate compound in the dried EVOH resin composition pellets of the present invention is preferably 1 to 1,000 ppm, calculated as phosphate radicals. Addition within this range can suppress discoloration and the occurrence of gels and particles in molded products. If the phosphate compound content is less than 1 ppm, discoloration may occur during melt molding. If the content exceeds 1,000 ppm, gels and particles may occur in molded products.

[0053] Examples of alkali metal salts contained in the aqueous solution include aliphatic carboxylates, aromatic carboxylates, and phosphates. Examples include sodium acetate, potassium acetate, sodium phosphate, lithium phosphate, sodium stearate, potassium stearate, and the sodium salt of ethylenediaminetetraacetic acid. Of these, sodium acetate, potassium acetate, and sodium phosphate are preferred. The content of alkali metal salts in the dried EVOH resin composition pellets of the present invention is preferably 5 to 5,000 ppm, calculated as the alkali metal element, more preferably 20 to 1,000 ppm, and even more preferably 30 to 750 ppm.

[0054] Examples of alkaline earth metal salts contained in the aqueous solution include magnesium salts, calcium salts, barium salts, and beryllium salts, with magnesium salts and calcium salts being particularly preferred. The anion species of the alkaline earth metal salt is not particularly limited, but acetate and phosphate are preferred. The content of alkaline earth metal salt in the dried EVOH resin composition pellets of the present invention is preferably 10 to 1,000 ppm, more preferably 20 to 500 ppm, calculated as metal. If the content of alkaline earth metal salt is less than 10 ppm, the effect of improving long-run properties may be insufficient. Furthermore, if the content exceeds 1,000 ppm, the resin may be more likely to discolor when melted.

[0055] On the other hand, the dispersion to be added to the hydrous EVOH may be a colloid of inorganic particles such as colloidal silica, colloidal titania, or colloidal zirconia, or a dispersion of inorganic particles having a larger particle size.

[0056] The extruder used in the melt-kneading step (II) may be a single-screw extruder or a multi-screw extruder, but a twin-screw extruder is preferred. The L / D ratio of the extruder is preferably 10 to 55, more preferably 20 to 47. The cylinder of the extruder is provided with an inlet for EVOH hydrous pellets, through which the EVOH hydrous pellets are introduced, and then melt-kneaded by the rotation of a screw disposed within the cylinder, and discharged from a discharge port at the tip of the cylinder. The screw configuration within the cylinder is not particularly limited, but it is preferable to provide a full-flight screw and a partial reverse-flight screw to thoroughly knead the molten resin.

[0057] The resin temperature inside the extruder is preferably 120 to 210°C. If the resin temperature is too low, the screw torque may become too large, so the resin temperature is more preferably 140°C or higher, and even more preferably 150°C or higher. On the other hand, if the resin temperature is too high, the resulting EVOH resin composition pellets tend to foam, and may become discolored or form gels when melt-kneaded for a long period of time. Therefore, the resin temperature is more preferably 200°C or lower, and even more preferably 190°C or lower.

[0058] The extruder used in the melt-kneading step (II) is provided with an additive introduction section downstream of the pellet introduction port. From the additive introduction section, an aqueous solution or dispersion containing additives is injected into the molten, water-containing EVOH and melt-kneaded. The amount of the aqueous solution or dispersion added is preferably 1 to 30 parts by mass per 100 parts by mass of the dry weight of EVOH. If the amount added is less than 1 part by mass, uniform blending may be difficult; more preferably, it is 2 parts by mass or more, and even more preferably, 5 parts by mass or more. On the other hand, if the amount added exceeds 30 parts by mass, the water content of the water-containing EVOH becomes too high, making it more likely to leak from the dehydration slit and increasing the energy required for drying. Therefore, the amount added is more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less.

[0059] In the melt-kneading step (II), it is preferable to discharge liquid water or water vapor from at least one location in the extruder. This can reduce the water content of the water-containing EVOH in the extruder. The method for discharging liquid water or water vapor is not particularly limited, and a dewatering slit or a vacuum vent can be used. In the melt-kneading step of the present invention, the water content of the water-containing EVOH resin composition discharged from the extruder is not particularly low, so a vacuum vent is often unnecessary, and a dewatering slit is preferably used. Either water vapor or liquid water can be discharged from the dewatering slit, but discharging water vapor is preferred from the viewpoint of removing the latent heat of vaporization and removing heat. Furthermore, in the melt-kneading step (II) of the present invention, it is preferable to discharge liquid water or water vapor from a position downstream of the position where the aqueous solution or aqueous dispersion is added. This can effectively reduce the water content of the discharged water-containing EVOH resin composition and suppress foaming.

[0060] In the melt-kneading step (II), the average residence time of the EVOH in the extruder is preferably 300 seconds or less. The shorter the average residence time of the EVOH in the extruder, the higher the productivity of the extruder can be and the more thermal degradation can be prevented. The average residence time is more preferably 200 seconds or less, even more preferably 100 seconds or less, and particularly preferably 40 seconds or less. The average residence time is usually 5 seconds or more.

[0061] In the cutting step (III), the molten resin composition discharged from the extruder is cut to reduce the water content W ２The resulting hydrous EVOH resin composition pellets have a molecular weight of 5 to 20% by mass. The cutting method is not particularly limited, and examples include a method in which the hydrous EVOH resin composition in a molten state discharged from the extruder is directly cut, or a method in which the hydrous EVOH resin composition discharged from the extruder is extruded into a coagulation liquid in the form of a strand, solidified, and then cut. Of these, the method in which the hydrous EVOH resin composition is directly cut is preferred. Methods for directly cutting the hydrous EVOH resin composition discharged from the extruder include a hot-cut method and an underwater cutting method. When the hydrous EVOH resin composition is extruded in the form of a strand, solidified, and then cut, cylindrical pellets are obtained, while when the hydrous EVOH resin composition is directly cut in the molten state, spherical (or nearly spherical) pellets are obtained. The size of the produced hydrous EVOH resin composition pellets can be, for example, 1 mm to 10 mm in diameter if spherical (or nearly spherical), or 1 mm to 10 mm in diameter and 1 mm to 10 mm in length if cylindrical.

[0062] The water content W of the water-containing pellets of the EVOH resin composition obtained in the cutting step (III) ２ is 5 to 20 mass%. ２ By making the water content W 5% by mass or more, the temperature of the molten resin in the melt-kneading step (II) can be lowered, and therefore, thermal deterioration of the EVOH during melt-kneading can be suppressed. ２ If the moisture content W is 5% by mass or more, it is not necessary to provide a vacuum vent in the extruder to reduce the moisture content, and the equipment can be simplified. ２ By setting the content of EVOH to 20% by mass or less, leakage of EVOH from the dewatering slit can be suppressed even when the extruder is operated at high speed, thereby improving productivity. In addition, foaming of the resulting pellets can be suppressed, and energy consumption in the subsequent second drying step (IV) can also be suppressed.

[0063] The EVOH resin composition hydrous pellets thus obtained in the cutting step (III) are subjected to the second drying step (IV). The dryer used in the second drying step (IV) is not particularly limited as long as it can dry the pellets while maintaining their shape. A hot air dryer or the like can be used. The drying method may be a fluidized drying method using a fluidized dryer or a static drying method using a static dryer, or a combination of these methods may be used. A method in which the pellets are first dried at a relatively low temperature using a fluidized dryer, and then dried at a high temperature using a static dryer is preferably used.

[0064] The drying temperature and drying time are not particularly limited, but the drying temperature is preferably 50 to 150°C, and the drying time is preferably 1 hour to 7 days. When both fluidized drying and static drying are employed, the drying temperatures of both methods are included in the above temperature range, and the sum of the drying times of both methods is included in the above drying time. The drying temperature is more preferably 60°C or higher, even more preferably 70°C or higher, and particularly preferably 80°C or higher. The drying temperature is more preferably 140°C or lower, even more preferably 130°C or lower, and particularly preferably 120°C or lower. The drying time is more preferably 2 hours or longer, even more preferably 5 hours or longer. It is also more preferably 5 days or shorter, and even more preferably 3 days or shorter. When both fluidized drying and static drying are employed, the drying temperature of the latter method is preferably 5°C or higher, and even more preferably 10°C or higher, than the drying temperature of the former method. Drying may be performed in air or in an inert gas such as nitrogen. When drying is performed in an inert gas, thermal degradation is unlikely to occur even if the drying temperature is set high.

[0065] The moisture content W of the EVOH resin composition pellets obtained by drying in the second drying step (IV) ３ The moisture content W is 0.5% by mass or less. ３ When the water content W is 0.5% by mass or less, problems such as foaming do not occur even if the composition is subjected to melt molding without further drying. ３ is preferably 0.4% by mass or less, and more preferably 0.3% by mass or less. ３is usually 0.01% by mass or more, and the water content W ３ Lowering it will only increase energy consumption.

[0066] In this manner, dried pellets of the EVOH resin composition containing additives are obtained. According to the production method of the present invention, the production speed when adding additives to the water-containing EVOH in an extruder can be improved, and EVOH resin composition pellets can be obtained efficiently. The EVOH resin composition pellets thus obtained can be melt-molded into various molded articles such as films, sheets, containers, pipes, and fibers, and can also be used for a variety of other purposes.

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

[0068] (1) Measurement of Moisture Content of Pellets Using a halogen moisture analyzer, the moisture content of the pellets obtained in the examples and comparative examples was measured by a heated dry mass measurement method under the conditions of a drying temperature of 180°C, a drying time of 20 minutes, and a sample weight of 10 g. The moisture content of the pellets was calculated using the following formula: Moisture content (mass%) = [(mass before drying - mass after drying) / mass before drying] x 100

[0069] (2) Determination of Carboxylic Acid 20 g of the dried EVOH resin composition pellets obtained in the Examples and Comparative Examples was added to 100 mL of ion-exchanged water and extracted by heating for 6 hours at 95° C. The obtained extract was subjected to neutralization titration with 0.01 mol / L sodium hydroxide solution using phenolphthalein as an indicator to calculate the carboxylic acid content in the dried EVOH resin composition pellets.

[0070] (3) Quantification of Metal Salts, Boron Compounds, and Phosphate Compounds 0.5 g of EVOH resin composition pellets obtained in the Examples and Comparative Examples 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 capped and further decomposed by heating at 150°C for 10 minutes and then at 180°C for 5 minutes in a wet decomposition apparatus ("MWS-2" manufactured by Actac Corporation). The decomposition solution was then transferred to a 50 mL measuring flask and diluted with ion-exchanged water to prepare a sample solution for measurement. The contents of metal elements, boron elements, and phosphorus elements in the sample solution were measured using an ICP atomic emission spectrometer ("OPTIMA 4300DV" manufactured by PerkinElmer). From the obtained values, the metal salt content (metal ion content) in terms of metal elements, the content of boron compounds in terms of elemental boron, and the content of phosphate compounds in terms of phosphate radicals in the EVOH resin composition pellets were determined.

[0071] (4) Evaluation of EVOH Leakage EVOH resin composition pellets were continuously produced by the methods described in the Examples and Comparative Examples, and the presence of white marks due to EVOH leakage on the dehydration slit, which is an outlet for water or steam provided in the twin-screw extruder, or the presence of resin adhering to the vent port, which is an outlet for steam, was visually confirmed, and evaluated according to the following evaluation criteria. A rating of C was determined to indicate that efficient production was not possible. A: No marks due to EVOH leakage were observed at the outlet port even after continuous operation for 10 days or more. B: Marks due to EVOH leakage were observed at the outlet port after continuous operation for 7 days or more but less than 10 days. C: Marks due to EVOH leakage were observed at the outlet port after continuous operation for less than 7 days, or resin was observed adhering to the vent port.

[0072] (5) Foaming 100 g of EVOH resin composition pellets were obtained by cutting and drying the resin composition after extrusion from the extruder, and the percentage (mass %) of pellets showing defects in shape such as dents, trapped air bubbles, foaming, etc. was determined and evaluated according to the following criteria. When the evaluation was C, it was determined that efficient production was not possible. (Evaluation) A: Less than 1 mass % B: 1 mass % or more but less than 5 mass % C: 5 mass % or more

[0073] Example 1 An EVOH solution containing 100 parts by mass of EVOH having an ethylene unit content of 32 mol% and a saponification degree of 99.8 mol%, 100 parts by mass of methanol, 50 parts by mass of water, and 2 parts by mass of sodium acetate (calculated as sodium) was continuously supplied to the top plate of a 10-plate tower having a tower diameter of 0.6 m at a rate of 521 kg / hr, and steam was blown into the bottom plate of the tower at a rate of 600 kg / hr, so that the EVOH solution and steam were brought into countercurrent contact within the tower. The temperature inside the tower was 130°C, and the pressure inside the tower was 3 kg / cm. ２ Methanol vapor and water vapor were distilled off from the top of the plate column and condensed in a condenser to recover an aqueous methanol solution. A water-containing EVOH composition was continuously extracted from the bottom of the plate column. This water-containing EVOH composition contained 0.05 parts by mass of methanol, 105 parts by mass of water, and 2 parts by mass of sodium acetate, calculated as sodium, per 100 parts by mass of EVOH.

[0074] Next, this aqueous EVOH composition was fed at 430 kg / hr to a kneader with a 50 mm diameter and an L / D ratio of 13.2 and equipped with a liquid outlet. The screw rotation speed was 1,000 rpm. The aqueous EVOH composition obtained from the discharge port contained 0.03 parts by mass of methanol, 68 parts by mass of water (water content: 40% by mass), and 1.2 parts by mass of sodium acetate (calculated as sodium) per 100 parts by mass of EVOH, and had a temperature of 118°C. Subsequently, this aqueous EVOH composition was extruded through a die having six holes with a hole diameter of 3 mm and cut with an eight-blade hot cutter at a distance of 0.05 mm from the die to obtain aqueous EVOH pellets. The cutter blade rotation speed was 2,500 rpm.

[0075] The obtained pellets were fed at 348 kg / hr to the top of a tower-type processor with a diameter of 1.2 m and a height of 4 m. A 0.5 g / L aqueous acetic acid solution (50°C) was charged to the bottom of the processor at a rate of 500 L / hr, and the pellets and the aqueous acetic acid solution were brought into countercurrent contact within the processor. The aqueous acetic acid solution was discharged from the top of the processor, and washed pellets were continuously removed from the bottom of the processor. The water content of the washed EVOH hydrous pellets was 40% by mass, and 0.002% by mass of sodium acetate remained in the pellets, calculated as sodium.

[0076] The moisture content W thus obtained ０ EVOH hydrous pellets (ethylene unit content: 32 mol%, saponification degree: 99.8 mol%) having a water content of 40% by mass were placed in a fluidized bed dryer and dried at 80°C for 60 minutes. １ EVOH hydrous pellets with a hydroxyl group content of 13% by mass were fed into a twin-screw extruder. The cylinder and screw configurations of the twin-screw extruder are shown in Figure 1. The resin temperature measured by temperature sensor 3 was set to 160°C, and an aqueous solution of acetic acid, boric acid, sodium acetate, magnesium acetate, and potassium dihydrogen phosphate was added through additive introduction section 2. The amount of the aqueous solution added per unit time was 20.8 L / hr. The aqueous solution contained 3.5 g / L of acetic acid, 15 g / L of boric acid, 7.7 g / L of sodium acetate trihydrate, 3.1 g / L of magnesium acetate tetrahydrate, and 1.7 g / L of potassium dihydrogen phosphate.

[0077] The specifications of the twin-screw extruder are as follows: The twin-screw extruder cylinder (cylinder configuration a, screw configuration X) shown in Figure 1 is provided with a pellet supply section 1, an additive introduction section 2, and a dewatering slit 4. The screw is a combination of a full-flight screw 6 and a reverse-flight screw 7 as shown in Figure 1. Furthermore, a temperature sensor 3 is provided at the end of the cylinder. Type: Twin-screw extruder L / D: 45.5 Bore: 30 mmφ Screw: Fully intermeshing type in the same direction Rotation speed: 300 rpm Die bore: 3.0 mmφ

[0078] The molten water-containing EVOH resin composition discharged from the twin-screw extruder was cut with a hot cutter to obtain water-containing pellets of the EVOH resin composition. ２The water content of the EVOH resin composition was 10% by mass, the discharge rate of the EVOH from the twin-screw extruder was 208 kg / hour (excluding the amount of water contained), and the residence time was 25 seconds. EVOH resin composition pellets were continuously produced under the above conditions, and the leakage and foaming of EVOH were evaluated according to the methods described in (4) and (5) above. The results are shown in Table 1. The obtained water-containing EVOH resin composition pellets were dried in a fluidized bed dryer at 90°C for 15 hours, and then dried in a static dryer at 105°C for 15 hours, to determine the water content W ３ The EVOH resin composition pellets thus obtained were subjected to quantitative analysis of the carboxylic acid, metal salt, boron compound, and phosphorus compound according to the methods described in (2) and (3) above. The acetic acid content was 260 ppm, the boric acid content was 260 ppm in terms of boron, the phosphoric acid content was 90 ppm in terms of phosphate radical, the sodium ion content was 125 ppm, the potassium ion content was 35 ppm, and the magnesium ion content was 35 ppm.

[0079] [Examples 2, 3, 5 to 7, Comparative Examples 1 and 2] Ethylene unit content and moisture content W of EVOH hydrous pellets ０ EVOH resin composition pellets were prepared in the same manner as in Example 1, except that the drying temperature and drying time in the first drying step, and the resin temperature, amount of aqueous solution added, and EVOH discharge rate and residence time in the melt-kneading step were changed as shown in Table 1. In the examples and comparative examples of the present application, the discharge rate and residence time were adjusted by adjusting the feed rate of the hydrous EVOH pellets to the twin-screw extruder, and the extruder rotation speed was adjusted according to the production rate. The results are shown in Table 1. All dried EVOH resin composition pellets contained trace components at similar levels to those in Example 1, with an acetic acid content of 240 to 300 ppm, a boric acid content of 240 to 270 ppm in terms of boron, a phosphoric acid content of 85 to 95 ppm in terms of phosphate radical, a sodium ion content of 120 to 140 ppm, a potassium ion content of 30 to 40 ppm, and a magnesium ion content of 30 to 40 ppm. It should be noted that even when trace components similar to those in Example 1 were contained in the following Examples and Comparative Examples, the values ​​were within the above range.

[0080] Example 4 EVOH resin composition pellets were prepared in the same manner as in Example 1, except that the drying temperature in the first drying step, and the resin temperature and amount of aqueous solution added in the melt-kneading step were changed as shown in Table 1, and the aqueous solution containing additives was changed to an aqueous solution containing 1.8 g / L of acetic acid, 8 g / L of boric acid, 3.8 g / L of sodium acetate trihydrate, 1.5 g / L of magnesium acetate tetrahydrate, and 0.9 g / L of potassium dihydrogen phosphate. EVOH resin composition pellets were then analyzed and evaluated in the same manner as in Example 1. The results are shown in Table 1. The obtained dried EVOH resin composition pellets contained trace components at the same level as in Example 1.

[0081] Example 8 EVOH resin composition pellets were prepared in the same manner as in Example 1, except that the drying temperature in the first drying step, and the cylinder configuration, resin temperature, and amount of aqueous solution added in the melt-kneading step were changed as shown in Table 1, and the aqueous solution containing additives was changed to an aqueous solution containing 7.0 g / L of acetic acid, 30 g / L of boric acid, 15.4 g / L of sodium acetate trihydrate, 6.2 g / L of magnesium acetate tetrahydrate, and 3.4 g / L of potassium dihydrogen phosphate. These pellets were then analyzed and evaluated in the same manner as in Example 1. Here, as shown in FIG. 2 , when the cylinder configuration is designated as b in this specification, the screw configuration is designated as Y. The results are shown in Table 1. The obtained dried EVOH resin composition pellets contained trace components at the same level as in Example 1.

[0082] [Comparative Examples 3 to 6] Ethylene unit content, saponification degree and moisture content W of EVOH hydrous pellets ０ In Comparative Example 5, the concentration of additives in the aqueous solution added to the extruder was the same as in Example 8. The results are shown in Table 1. All of the dried EVOH resin composition pellets contained trace components at the same level as in Example 1.

[0083] Comparative Example 7 Dried EVOH resin composition pellets were prepared in the same manner as in Example 1, except that the ethylene unit content and degree of saponification of the hydrous EVOH pellets, as well as the cylinder configuration, resin temperature, amount of aqueous solution added, EVOH discharge rate, and residence time in the melt-kneading step were changed as shown in Table 1, and analyzed and evaluated in the same manner as in Example 1. Here, as shown in FIG. 3 , when the cylinder configuration is defined as c in this specification, the screw configuration is Y. The concentrations of additives in the aqueous solution added to the extruder were the same as in Example 8. The results are shown in Table 1. The obtained dried EVOH resin composition pellets contained trace components to the same extent as in Example 1.

[0084] Comparative Example 8 An attempt was made to prepare dried EVOH resin composition pellets in the same manner as in Example 7, except that the amount of aqueous solution added, the amount of EVOH discharged, and the residence time in the melt-kneading step were changed as shown in Table 1. However, the torque applied to the extruder increased, making melt-kneading impossible, and the subsequent steps were discontinued.

[0085] [Comparative Examples 9 and 10] Degree of saponification and moisture content W of EVOH hydrous pellets ０ The cylinder configuration, resin temperature, amount of aqueous solution added, amount of EVOH discharged, and residence time in the melt-kneading step were changed as shown in Table 1. In the first drying step, the pellets were dried at 65°C for 60 minutes using a stationary hot air dryer, and then dried at 80°C for 25 minutes using a stationary hot air dryer to obtain a moisture content W １ Dried EVOH resin composition pellets were prepared in the same manner as in Example 1, except that the amount of the ethylenediamine diol was 9.9% by mass and the second drying step was not performed after the cutting step, and the pellets were analyzed and evaluated in the same manner as in Example 1. Here, as shown in FIG. 4 , when the cylinder configuration is defined as d in this specification, the screw configuration is X. The concentrations of the additives in the aqueous solution added to the extruder were the same as in Example 4. The results are shown in Table 1. All of the dried EVOH resin composition pellets contained trace components at the same level as in Example 1.

[0086] [Comparative Example 11] Degree of saponification and moisture content W of EVOH hydrous pellets ０An attempt was made to prepare dried EVOH resin composition pellets in the same manner as in Example 1, except that the drying time in the first drying step and the drying time in the second drying step were changed as shown in Table 1. However, since the hydrous EVOH pellets stuck together in the first drying step, the subsequent steps were discontinued.

[0087]

[0088] 1 Pellet supply section 2 Additive introduction section 3 Temperature sensor 4 Dewatering slit 5 Vent 6 Full-flight screw 7 Reverse-flight screw

Claims

1. Moisture content W ０ 25 to 50% by mass of ethylene-vinyl alcohol copolymer water-containing pellets are introduced into a dryer, and the water content W of the pellets is １ a first drying step (I) in which the a melt-kneading step (II) of introducing the pellets obtained in the first drying step (I) into an extruder, adding an aqueous solution or aqueous dispersion containing additives, and melt-kneading the pellets; The molten resin composition discharged from the extruder is cut to obtain a water content W ２ a cutting step (III) for obtaining hydrous pellets of an ethylene-vinyl alcohol copolymer resin composition having a content of 5 to 20% by mass; The water-containing pellets obtained in the cutting step (III) are dried to have a water content W ３ a second drying step (IV) for obtaining ethylene-vinyl alcohol copolymer resin composition pellets having a content of 0.5% by mass or less, The reduction in moisture content (W ０ -W １ ) is 10 to 45 mass %, The ethylene-vinyl alcohol copolymer has an ethylene unit content of 20 to 60 mol % and a saponification degree of 95 mol % or more.

2. 2. The method according to claim 1, wherein in the melt-kneading step (II), the average residence time of the ethylene-vinyl alcohol copolymer in the extruder is 300 seconds or less.

3. 3. The production method according to claim 1 or 2, wherein the aqueous solution or aqueous dispersion added in the melt-kneading step (II) is an aqueous solution in which at least one additive selected from a carboxylic acid, a boron compound, a phosphoric acid compound, an alkali metal salt, and an alkaline earth metal salt is dissolved.

4. 3. The production method according to claim 1, wherein in the melt-kneading step (II), liquid water or water vapor is discharged from at least one location of the extruder.

5. The method according to claim 4, wherein in the melt-kneading step (II), liquid water or water vapor is discharged from a position downstream of a position where the aqueous solution or aqueous dispersion is added.

6. a step (A) of introducing an ethylene-vinyl alcohol copolymer solution containing 50 parts by mass or more of an alcohol having a boiling point of 100°C or less per 100 parts by mass of the ethylene-vinyl alcohol copolymer into a container, contacting the ethylene-vinyl alcohol copolymer with water vapor in the container to discharge the alcohol together with the water vapor, and discharging a water-containing ethylene-vinyl alcohol copolymer from the container; a step (B) of supplying the water-containing ethylene-vinyl alcohol copolymer to an extruder, melt-kneading the copolymer, and then discharging the copolymer from the extruder; and a step (C) of cutting the water-containing ethylene-vinyl alcohol copolymer discharged from the extruder.

3. The method according to claim 1, wherein the ethylene-vinyl alcohol copolymer hydrous pellets obtained through the above step (a) are supplied to the first drying step (I).