Method for producing pellets of ethylene-vinyl alcohol copolymer resin composition

Abstract

A method for producing pellets of an EVOH resin composition, the method comprising: a first drying step (I) in which water-containing EVOH pellets having a water content (W0) of 25-50 mass% are introduced into a dryer, and the water content (W1) of the pellets is reduced to 5-25 mass%; a melt-kneading step (II) in which the pellets obtained in the first drying step (I) are introduced into an extruder, an aqueous solution or an aqueous dispersion containing an additive is added, and melt-kneading is performed; a cutting step (III) for obtaining water-containing pellets of the EVOH resin composition having a water content (W2) of 5-20 mass% by cutting the molten resin composition discharged from the extruder; and a second drying step (IV) for drying the water-containing pellets obtained in the cutting step (III) to obtain EVOH resin composition pellets having a water content (W3) of 0.5% by mass or less, the reduction (W0-W1) of the water content in the first drying step (I) being 10-45% by mass, whereby the production speed when adding an additive to the water-containing EVOH in an extruder can be increased and EVOH resin composition pellets can be efficiently obtained.

Description

Technical Field

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

[0002] Ethylene-vinyl alcohol copolymer (hereinafter sometimes referred to as EVOH) is a polymer material with excellent gas barrier properties, fuel barrier properties, oil resistance, aroma retention, and anti-static properties. It is widely used in films, sheets, containers, and other products. There are various methods for forming EVOH into various molded products, but melt molding using extruders, such as extrusion molding or injection molding, is common. However, since EVOH molding typically requires a melt temperature of 200°C or above, additive-free EVOH is susceptible to degradation during melt molding, sometimes causing fisheyes and pitting in the product, reducing quality.

[0003] To solve this problem, methods are known to add trace components such as acidic substances and / or metal salts to EVOH. To improve long-term performance and suppress appearance defects such as gels and pitting, methods are known to incorporate at least one additive selected from carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts.

[0004] As a method for incorporating such additives into EVOH, one known method involves immersing aqueous EVOH pellets in an aqueous solution containing the additive to impregnate the pellets with the additive (e.g., Patent Document 1). However, this method requires a significant amount of time to uniformly impregnate the EVOH pellets with the additive. Furthermore, a treatment bath and treatment tower are required for immersing the EVOH pellets, as well as wastewater treatment and recovery equipment for discarding the treated liquid after use.

[0005] To solve such problems, a method has been proposed in which EVOH hydrous pellets are fed into an extruder for melt kneading, and an aqueous solution containing the additive is added to the molten hydrous EVOH and kneaded, thereby blending the additive into the EVOH.

[0006] For example, Example 1 of Patent Document 2 describes feeding EVOH hydrous pellets having a moisture content of 39% by mass into an extruder, dehydrating them in a dehydration slit, adding an aqueous solution containing an additive, and melt-kneading the mixture. The mixture is then pelletized to produce hydrous pellets of an EVOH resin composition containing the additive and having a moisture content of 20% by mass. Furthermore, the patent document describes drying the resulting hydrous pellets of the EVOH resin composition in a hot air dryer to produce pellets of an EVOH resin composition having a moisture content of 0.2% by mass.

[0007] Furthermore, Example 4 of Patent Document 3 describes introducing EVOH pellets with a moisture content of 32% by mass into a hot air dryer, reducing the moisture content of the pellets to 9.9% by mass, and then feeding them into an extruder. An aqueous solution containing an additive is then added and melt-kneaded. After exhausting the mixture through a vacuum pump through the exhaust port, the mixture is discharged from the extruder and pelletized. This produces pellets of an EVOH resin composition containing an additive and having a moisture content of 0.2% by mass. The pellets thus obtained have a sufficiently low moisture content to be directly used for melt molding.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 64-66262

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 2002-284811

[0012] Patent Document 3: WO2004 / 009313A1 Summary of the Invention

[0013] Problems to be solved by the invention

[0014] However, in the conventional methods described above, increasing the production speed by, for example, increasing the amount of water-containing EVOH supplied to the extruder causes EVOH to leak from the dewatering slits and vents, making it difficult to increase the production speed. More specifically, increasing the amount of water-containing EVOH supplied to the extruder to increase the production speed under the conditions of Patent Document 2 causes water-containing EVOH to leak from the dewatering slits. Furthermore, increasing the amount of water-containing EVOH supplied to the extruder to increase the production speed under the conditions of Patent Document 3 causes excessive venting at the vents, leading to EVOH leakage from the vents. This makes it difficult to efficiently increase the production speed.

[0015] The present invention is made to solve the above-mentioned problems and provides a method for increasing the production speed when adding additives to aqueous EVOH in an extruder to efficiently obtain EVOH resin composition pellets.

[0016] Means used to solve problems

[0017] The above-mentioned problems are solved by providing a method for producing pellets of an ethylene-vinyl alcohol copolymer resin composition, which comprises:

[0018] The first drying step (I): introducing the ethylene-vinyl alcohol copolymer water-containing pellets having a moisture content W0 of 25 to 50% by mass into a dryer to reduce the moisture content W1 of the pellets to 5 to 25% by mass;

[0019] 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 an additive is added and melt-kneaded;

[0020] Cutting step (III): cutting the molten resin composition discharged from the extruder to obtain water-containing pellets of an ethylene-vinyl alcohol copolymer resin composition having a moisture content W2 of 5 to 20% by mass; and

[0021] Second drying step (IV): drying the water-containing pellets obtained in the cutting step (III) to obtain ethylene-vinyl alcohol copolymer resin composition pellets having a moisture content W3 of 0.5% by mass or less,

[0022] The reduction in moisture content (W0-W1) in the first drying step (I) is 10 to 45% by mass.

[0023] The ethylene-vinyl alcohol copolymer has an ethylene unit content of 20 to 60 mol% and a saponification degree of 95 mol% or more.

[0024] 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. Furthermore, in the melt-kneading step (II), the aqueous solution or aqueous dispersion added is preferably 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. Furthermore, in the melt-kneading step (II), liquid water or water vapor is preferably discharged from at least one location in the extruder. In this case, the liquid water or water vapor is preferably discharged from a location downstream of the location where the aqueous solution or aqueous dispersion is added.

[0025] In addition, the above-mentioned problem is also solved by supplying the ethylene-vinyl alcohol copolymer hydrous pellets obtained by the following steps to the above-mentioned first drying step (I) in the above-mentioned method for producing ethylene-vinyl alcohol copolymer resin composition pellets: step (A): introducing an ethylene-vinyl alcohol copolymer solution into a container, allowing it to contact with water vapor in the above-mentioned container, discharging the above-mentioned alcohol together with the water vapor, and discharging the hydrous ethylene-vinyl alcohol copolymer from the above-mentioned container, wherein the ethylene-vinyl alcohol copolymer solution contains 50 parts by mass or more of an alcohol having a boiling point of 100°C or less relative to 100 parts by mass of the ethylene-vinyl alcohol copolymer; step (B): supplying the above-mentioned hydrous ethylene-vinyl alcohol copolymer to an extruder, melt-kneading it, and then discharging the above-mentioned copolymer from the extruder; and step (C): cutting the hydrous ethylene-vinyl alcohol copolymer discharging from the extruder.

[0026] Effects of the Invention

[0027] The method for producing EVOH resin composition pellets according to the present invention increases the production speed when adding additives to aqueous EVOH in an extruder, thereby efficiently producing EVOH resin composition pellets. "Efficient" here means that even when the production speed is increased (by reducing the residence time of the aqueous EVOH in the extruder), leakage of EVOH from the extruder is suppressed, and foaming of the EVOH discharged from the extruder is also suppressed, thereby achieving production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] [ Figure 1 ] A diagram showing the barrel configuration a and the screw configuration X of the twin-screw extruder in Examples 1 to 7 and Comparative Examples 1 and 2.

[0029] [ Figure 2 ] A diagram showing the barrel structure b and screw structure Y of the twin-screw extruder in Example 8 and Comparative Examples 3 to 6.

[0030] [ Figure 3 ] is a diagram showing the barrel composition c and screw composition Y of the twin-screw extruder in Comparative Examples 7 and 8.

[0031] [ Figure 4 ] is a diagram showing the barrel composition d and screw composition X of the twin-screw extruder in Comparative Examples 9 and 10. DETAILED DESCRIPTION

[0032] The present invention is a method for producing ethylene-vinyl alcohol copolymer resin composition pellets, which comprises:

[0033] The first drying step (I): introducing the ethylene-vinyl alcohol copolymer water-containing pellets having a moisture content W0 of 25 to 50% by mass into a dryer to reduce the moisture content W1 of the pellets to 5 to 25% by mass;

[0034] 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 an additive is added and melt-kneaded;

[0035] Cutting step (III): cutting the molten resin composition discharged from the extruder to obtain water-containing pellets of an ethylene-vinyl alcohol copolymer resin composition having a moisture content W2 of 5 to 20% by mass; and

[0036] Second drying step (IV): drying the water-containing pellets obtained in the cutting step (III) to obtain ethylene-vinyl alcohol copolymer resin composition pellets having a moisture content W3 of 0.5% by mass or less,

[0037] The reduction in moisture content (W0-W1) in the first drying step (I) is 10 to 45% by mass.

[0038] The ethylene-vinyl alcohol copolymer has an ethylene unit content of 20 to 60 mol% and a saponification degree of 95 mol% or more.

[0039] First, the production method of EVOH used in the present invention will be described. EVOH is typically obtained by saponifying an ethylene-vinyl ester copolymer. The copolymerization of ethylene and vinyl ester can be performed by any of solution polymerization, suspension polymerization, emulsion polymerization, and bulk polymerization. Furthermore, the copolymerization can be performed by either continuous or batch polymerization. An example of polymerization conditions for solution polymerization is shown below.

[0040] As the solvent used, from the perspectives of solubility of the ethylene-vinyl ester copolymer and EVOH, ease of handling, and efficient replacement of the alcohol with water, an alcohol having a boiling point of 100°C or lower is preferred. The boiling point is more preferably 80°C or lower, and even more preferably 70°C or lower. Examples of the alcohol having a boiling point of 100°C or lower include methanol, ethanol, n-propanol, isopropanol, and tert-butanol, with methanol being particularly preferred.

[0041] As the initiator used in the polymerization, for example, azonitrile-based 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) can be used; as well as organic peroxide-based initiators such as isobutyryl peroxide, cumyl peroxyneodecanoate, diisopropyl peroxycarbonate, di-n-propyl peroxydicarbonate, t-butyl peroxyneodecanoate, lauroyl peroxide, benzoyl peroxide, and t-butyl hydroperoxide can be used.

[0042] Examples of vinyl esters include fatty acid vinyl esters such as vinyl acetate, vinyl propionate, and vinyl pivalate, with vinyl acetate being suitable. In addition to ethylene and vinyl esters, a small amount of monomers copolymerizable with these monomers may coexist, such as α-olefins such as propylene, butene, isobutylene, pentene, hexene, α-octene, and α-dodecene; 3-acyloxy-1-propylene, 3-acyloxy-1-butene, 4-acyloxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4-acyloxy-2-methyl-1-butene, 4-acyloxy-3-methyl-1-butene, 3,4-diacyloxy-2-methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, 4,5-diacyloxy-1-pentene, 4-acyloxy-1-hexene, 5-acyloxy-1-hexene, 6-acyloxy-1-pentene. The present invention can be used to polymerize olefins having an ester group, such as 1-hexene, 5,6-diacyloxy-1-hexene, and 1,3-diacetoxy-2-methylenepropane; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, and itaconic acid, and their anhydrides, salts, monoalkyl esters, or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as ethylenesulfonic acid, allylsulfonic acid, and methallylsulfonic acid, or their salts; vinyl silanes such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxy-ethoxy)silane, and γ-methacryloyloxypropylmethoxysilane; alkyl vinyl ethers; vinyl ketones; N-vinylpyrrolidone; vinyl chloride, vinylidene chloride, etc. The content of monomer units other than ethylene, vinyl ester, and vinyl alcohol in the EVOH is preferably 20 mol% or less, and may be preferably 10 mol% or less, 5 mol% or less, 3 mol% or less, 1 mol% or less, or 0.1 mol% or less. The EVOH may not contain any of the other monomer units.

[0043] The polymerization conditions are preferably as follows.

[0044] (1) Temperature: preferably 20 to 90°C, more preferably 40 to 70°C.

[0045] (2) Time (in the case of a continuous method, average residence time): preferably 2 to 15 hours, more preferably 3 to 11 hours.

[0046] (3) Polymerization rate: preferably 10 to 90%, more preferably 30 to 80%, based on the charged vinyl ester.

[0047] (4) Resin content in the solution after polymerization: preferably 5 to 85% by mass, more preferably 20 to 70% by mass.

[0048] After polymerization for a predetermined time and reaching a predetermined polymerization rate, a polymerization inhibitor is added as needed, and unreacted ethylene gas is evaporated and removed, whereupon the unreacted vinyl ester is discharged. For example, the following method can be used to discharge the unreacted vinyl ester: the polymerization solution from which ethylene has been removed is continuously supplied at a constant rate from the top of a column packed with Raschig rings; vapor of an organic solvent, preferably an alcohol with a boiling point of 100°C or less, and most preferably methanol, is blown into the column from the bottom; 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 the unreacted vinyl ester has been removed is withdrawn from the bottom of the column.

[0049] An alkali catalyst is added to the copolymer solution after unreacted vinyl ester has been removed, and the vinyl ester component in the copolymer is saponified. Both continuous and batch saponification methods are possible. Alkaline catalysts such as sodium hydroxide, potassium hydroxide, and alkali metal alkoxides can be used. Methanol is preferably used as the solvent for saponification. For example, the saponification conditions are as follows.

[0050] (1) Concentration of ethylene-vinyl ester copolymer in solution: 10 to 50% by mass

[0051] (2) Reaction temperature: 30-150°C

[0052] (3) Catalyst dosage: 0.005 to 0.6 equivalents (relative to the vinyl ester component)

[0053] (4) Time (in the case of continuous mode, the average residence time): 10 minutes to 6 hours

[0054] Generally speaking, continuous saponification allows for more efficient removal of methyl acetate generated by saponification, thus enabling the production of a resin with a high degree of saponification with a smaller amount of catalyst compared to batch saponification. Furthermore, in the continuous process, saponification must be performed at a higher temperature to prevent the precipitation of EVOH generated by saponification. Therefore, the reaction temperature and catalyst amount in the continuous process are preferably within the following ranges.

[0055] Reaction temperature: 70~150℃.

[0056] Catalyst dosage: 0.005 to 0.1 equivalents (relative to the vinyl ester component).

[0057] The saponification degree of EVOH used in the present invention is 95 mol% or more. If the saponification degree is less than 95 mol%, the torque applied to the extruder may increase when the production speed is increased, so it is not preferred. The saponification degree is preferably 98 mol% or more, more preferably 99 mol% or more, and further preferably 99.5 mol% or more. The saponification degree can be adjusted arbitrarily according to the conditions. It should be noted that 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), it can be considered that the saponification degree of EVOH in the EVOH aqueous pellets introduced into the first drying step (I) and in the EVOH resin composition pellets after the second drying step (IV) are the same. Therefore, the saponification degree of EVOH in the EVOH aqueous pellets introduced into the first drying step (I) and in the EVOH resin composition pellets after the second drying step (IV) both meet the above-mentioned numerical range.

[0058] Furthermore, 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 the EVOH is likely to leak out of the dehydration slits during the melt-kneading step (II). It should be noted that either water vapor or liquid water can be discharged from the dehydration slits described herein. To effectively prevent leakage of EVOH, the ethylene unit content is more preferably 24 mol% or greater, and further preferably 28 mol% or greater. 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 further preferably 45 mol% or less. It should be noted that 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). Therefore, it can be assumed that the ethylene unit content of EVOH in the EVOH pellets introduced into the first drying step (I) and in the EVOH resin composition pellets after the second drying step (IV) is the same. Therefore, the EVOH ethylene unit content in both the EVOH hydrous pellets introduced into the first drying step (I) and the EVOH resin composition pellets after the second drying step (IV) satisfies the above-mentioned numerical range.

[0059] A solution containing EVOH can be obtained through the saponification process. Hereinafter, the solution containing EVOH will be referred to as EVOH solution, but herein, a paste-like substance that is not completely uniform and has undergone phase separation is also included in the EVOH solution. As a post-treatment method for the EVOH solution after the saponification reaction, a mixed vapor of a solvent and water can be supplied from the lower part of the container in a tower container, and an EVOH solution can be supplied from a position higher than the supply position of the mixed vapor, thereby replacing a part of the solvent in the supplied EVOH solution with water to prepare a high-concentration EVOH solution. The EVOH concentration in the EVOH solution supplied to the tower container is preferably 15 to 50% by mass, more preferably 25 to 40% by mass. In addition, the ratio of the supply amount of the EVOH solution to the supply amount of the mixed vapor (solution supply amount / vapor supply amount) is also preferably 100 / 400 to 100 / 8 in terms of mass ratio. Furthermore, the water content in the mixed vapor is preferably 20 to 70% by mass. The solvent used in the mixed vapor is preferably an alcohol having a boiling point of 130°C or lower. Examples of such alcohols include methanol, ethanol, propanol, butanol, and the like. More preferably, an alcohol having a boiling point of 100°C or lower is used. Among these, methanol is preferred due to its easy availability, low cost, low boiling point, and ease of handling.

[0060] The high-concentration EVOH solution obtained in this manner generally contains 50 parts by mass or more of an alcohol having a boiling point of 100°C or less relative to 100 parts by mass of EVOH. The alcohol content is preferably 1000 parts by mass or less, 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 the resin can be produced efficiently. The alcohol used here is preferably methanol. In addition, the EVOH solution may also contain water in addition to the alcohol, preferably 10 to 500 parts by mass of water.

[0061] A suitable method for obtaining the hydrous EVOH pellets used in the present invention includes, for example, sequentially subjecting the high-concentration EVOH aqueous solution obtained as described above to the following steps (A), (B), and (C). Specifically, the hydrous EVOH pellets used in the present invention are obtained by introducing the EVOH solution into a container, contacting it with water vapor within the container, removing the alcohol along with the water vapor, and removing the hydrous EVOH from the container. The EVOH solution 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 the EVOH; supplying the hydrous EVOH to an extruder, melt-kneading it, and then discharging the copolymer from the extruder; and cutting the hydrous EVOH discharged from the extruder. This method efficiently replaces the alcohol in the EVOH solution with water and also facilitates adjustment of the water content and temperature of the EVOH.

[0062] In step (A), the method for contacting the EVOH solution introduced into the container with water vapor within the container is not particularly limited and can be either continuous or batch. Furthermore, the container configuration is also not particularly limited; for continuous processing, a tower-type container is suitable, while for batch processing, a tank-type container is suitable. Considering production efficiency, a continuous type is industrially preferred. Examples of tower-type containers include perforated plate towers, bubble cap towers, and other tray-type towers, and packed towers equipped with ring-type packings.

[0063] It is suitable to supply water vapor from the bottom of the tower container and supply EVOH solution from a position above the water vapor supply position, thereby extracting the solvent (alcohol) present in the supplied EVOH solution together with the water vapor, and extracting the water-containing EVOH with a water content of 10 to 90% by mass from the container. If the amount of water vapor introduced is too small, the removal efficiency of the solvent (alcohol) is poor. Conversely, if it is too large, it becomes disadvantageous in terms of cost. Therefore, the amount of water vapor introduced relative to the amount of EVOH solution introduced, expressed as a mass ratio, is preferably 0.3 to 30 times, more preferably 0.5 to 10 times, and even more preferably 0.7 to 5 times. The water vapor in contact with the EVOH solution may contain 10 parts by mass or less of the solvent (alcohol) relative to 100 parts by mass of the water vapor. In order to efficiently remove the solvent (alcohol), the water vapor preferably does not contain the solvent (alcohol).

[0064] The alcohol vapor and water vapor extracted from the upper part of the tower are condensed in a condenser and recovered as an alcohol-water solution. It can be purified and reused as needed. The EVOH solution is in direct contact with the water vapor in the container, and the solvent (alcohol) content gradually decreases. However, during this period, the EVOH is in a swollen paste state and can be extracted from the container while maintaining fluidity without gelling. EVOH dissolves in a methanol / water mixture at normal pressure, such as a temperature of about 60-70°C. However, it does not dissolve at normal pressure when the solvent is only water. However, in the presence of pressurized water vapor at a temperature of, for example, 90°C or above, EVOH can maintain fluidity even when it is essentially only water.

[0065] The temperature inside the container is preferably 100-150°C. If the temperature inside the container is lower than 100°C, the fluidity of the hydrous EVOH may be insufficient, causing gelation or clogging inside the container. It is more preferably 110°C or higher, and even more preferably 120°C or higher. On the other hand, if the temperature inside the container exceeds 150°C, the EVOH may deteriorate. It is more preferably 140°C or lower.

[0066] If the pressure within the container is too low, the alcohol removal efficiency may decrease. The pressure within the container is preferably 0.1 MPa or higher, more preferably 0.15 MPa or higher, and even more preferably 0.2 MPa or higher. On the other hand, if the pressure within the container is too high, the water content of the hydrous EVOH discharged from the container becomes too high, which may result in the melt viscosity of the hydrous EVOH introduced into the extruder described later becoming too low. Therefore, the pressure within the container is preferably 0.6 MPa or lower, more preferably 0.5 MPa or lower, and even more preferably 0.4 MPa or lower.

[0067] As described above, after the EVOH solution is brought into contact with water vapor, the fluid hydrous EVOH is withdrawn from the container. In step (B), the hydrous EVOH withdrawn from the container is fed to an extruder, melt-kneaded, and the copolymer is discharged from the extruder.

[0068] In step (B), the water content of the hydrous EVOH introduced into the extruder is 10 to 90% by mass. When the water content is less than 10% by mass, the melt viscosity of the hydrous EVOH becomes too high, and the hydrous EVOH cannot be discharged from the front end of the extruder. In addition, in order to ensure fluidity, the melting temperature becomes high, the EVOH deteriorates, and its color worsens. The water content is preferably 20% by mass or more, more preferably 30% by mass or more, further 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 hydrous EVOH becomes too low, and when the water content of the hydrous EVOH is reduced, the EVOH is likely to leak out together with the discharged water. The water content is preferably 80% by mass or less, more preferably 70% by mass or less, further preferably 60% by mass or less, and particularly preferably 55% by mass or less. The water content of the hydrous EVOH introduced into the extruder is measured by the method described in the examples described below.

[0069] From the viewpoint of protecting the working environment and the surrounding environment and from the viewpoint of preventing the obtained EVOH hydrous pellets from sticking to each other, the content of alcohol with a boiling point below 100°C 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, further preferably 1% by mass or less, and particularly preferably 0.5% by mass or less.

[0070] In step (B), the hydrous EVOH introduced into the extruder may contain, for example, approximately 0.1 to 5% by mass of an alkali metal salt, such as the catalyst residue used in the saponification step, in terms of metal, and may also contain by-product salts and other impurities. The content of components other than EVOH, water, and an alcohol having a boiling point of 100°C or less in the hydrous 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.

[0071] The extruder used in step (B) can be a single-screw extruder or a multi-screw extruder, preferably a twin-screw extruder. The extruder preferably has an L / D ratio of 8 to 30, more preferably 9 to 25, and even more preferably 10 to 20. The extruder barrel is provided with an inlet for introducing the hydrous EVOH. After the hydrous EVOH is introduced, the screw disposed within the barrel rotates, thereby melt-kneading the EVOH, which is then discharged from a discharge port at the front end of the barrel. A dehydration slit is preferably provided in the barrel to remove moisture.

[0072] The water content of the hydrous EVOH extruded from the extruder is preferably 25 to 50% by mass. If the water content is 25% by mass or greater, the melt viscosity of the hydrous EVOH decreases, making it easier to expel the hydrous EVOH. More preferably, the water content is 30% by mass or greater. On the other hand, if the water content is 50% by mass or less, the melt viscosity of the hydrous EVOH increases, preventing EVOH from leaking out. More preferably, the water content is 40% by mass or less.

[0073] Following step (B), in step (C), the hydrous EVOH discharged from the extruder is cut to produce hydrous EVOH pellets. The method for this is not particularly limited, but examples include: directly cutting the hydrous EVOH (in the molten state) discharged from the extruder; and extruding the hydrous EVOH discharged from the extruder into a coagulation liquid to solidify it in a strand-like manner, followed by cutting. Of these, direct cutting of the hydrous EVOH is preferred. Methods for directly cutting the hydrous EVOH discharged from the extruder include heat cutting and underwater cutting. Extruding the hydrous EVOH in a strand-like manner and then cutting it after solidification yields cylindrical pellets, while direct cutting of the molten EVOH yields spherical (or substantially spherical) pellets. The dimensions of the produced hydrous EVOH pellets can be, for example, spherical (or substantially spherical) in diameter from 1 mm to 10 mm, cylindrical in diameter from 1 mm to 10 mm, and cylindrical in length from 1 mm to 10 mm. As described below, this method of cutting the hydrous EVOH in a molten state offers superior productivity, as compared to methods that extrude the EVOH solution into a coagulation solution, extruding it into strands, and then coagulating and cutting it. The hydrous EVOH pellets obtained in this manner can be used in the first drying step (I).

[0074] In addition, as another method for obtaining the EVOH aqueous pellets used in the present invention, there is also a method in which the high-concentration EVOH aqueous solution is extruded from a nozzle into a coagulation liquid in the form of strands, coagulated in a water bath, and then cut. Water is used as the coagulation liquid, but it may contain a small amount of alcohol. The coagulated strands are cut using a cutter to form pellets. As the cutter, a strand cutter is suitable. Regarding the size of the pellets, for example, in the case of a cylindrical shape, the diameter can be set to be greater than 1 mm and less than 10 mm, and the length can be set to be greater than 1 mm and less than 10 mm. In the case of a spherical shape, the diameter can be set to be greater than 1 mm and less than 10 mm. The EVOH aqueous pellets obtained in this way can also be used for the first drying step (I).

[0075] The EVOH pellets obtained by the above operation contain the alkali catalyst, by-product salts such as sodium acetate and potassium acetate, and other impurities. Therefore, these can be removed by neutralization and washing as needed. At this time, some catalyst residues such as sodium acetate may remain in the EVOH pellets.

[0076] In the first drying step (I), the EVOH pellets having a moisture content W0 of 25 to 50% by mass obtained as described above are introduced into a dryer to reduce their moisture content W1 to 5 to 25% by mass. The EVOH pellets introduced into the dryer are porous and dry quickly, allowing them to be dried at a low drying temperature in a short time.

[0077] The moisture content W0 when introduced into the dryer is 25 to 50% by mass. The EVOH resin composition pellets obtained by having a moisture content W0 of 25% by mass or more have a good color tone and are preferably 30% by mass or more. When the moisture content W0 is less than 25% by mass, the average residence time can be shortened even if the melt-kneading step (II) is directly supplied, so the significance of adopting the first drying step (I) is small. On the other hand, when the moisture content W0 exceeds 50% by mass, there is a possibility of sticking in the dryer, and the efficiency of drying is also likely to be reduced. The moisture content W0 is preferably 45% by mass or less.

[0078] The drying machine 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 can be a flow drying method using a flow drying machine or a static drying method using a static drying machine. In order to prevent the pellets from sticking to each other, the flow drying method is preferred. Alternatively, these methods can be used in combination, or a method of first drying the pellets using the flow drying method and then drying the pellets using the static drying method can be used.

[0079] The drying temperature is not particularly limited, but it is preferably dried at 40 to 150°C for 0.1 to 15 hours. The EVOH hydrous pellets introduced into the dryer can be dried quickly even at low temperatures, and thermal degradation can be suppressed. The drying temperature is more preferably 50°C or higher, and further preferably 60°C or higher. In addition, the drying temperature is more preferably 120°C or lower, further preferably 100°C or lower, and most preferably 90°C or lower. The drying time varies depending on the drying temperature and the target moisture content, and is more preferably 0.2 hours or higher, and further preferably 0.5 hours or higher. In addition, it is more preferably 5 hours or lower, and further preferably 3 hours or lower. Drying can be done 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 to a higher level.

[0080] The moisture content W1 of the EVOH hydrous pellets obtained by drying in the first drying step (I) is 5 to 25% by mass, and the reduction in moisture content (W0-W1) in this step is 10 to 45% by mass. When the moisture content W1 is less than 5% by mass, the resin temperature in the extruder in the melt-kneading step (II) is too high, and the hydrous EVOH discharged from the extruder is likely to foam. The moisture content W1 is preferably 7% by mass or more, and more preferably 10% by mass or more. On the other hand, when the moisture content W1 exceeds 25% by mass, the moisture content in the extruder in the melt-kneading step (II) is too high, and the EVOH leaks from the dehydration slit, or the discharged EVOH composition foams. The moisture content W1 is preferably 22% by mass or less, and more preferably 18% by mass or less. In addition, when the reduction in moisture content (W0-W1) is less than 10% by mass, there is little point in setting up the first drying step (I). The reduction in moisture content (W0-W1) is preferably 15% by mass or more, more preferably 20% by mass or more. On the other hand, if the reduction in moisture content (W0-W1) exceeds 45% by mass, it becomes difficult to dry the pellets in a short period of time while maintaining their shape. The reduction in moisture content (W0-W1) is preferably 35% by mass or less, more preferably 30% by mass or less.

[0081] 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 an additive is added and melt-kneaded. This allows the additive to be uniformly dispersed in the aqueous EVOH melted in the extruder. The additive may be an aqueous solution dissolved in water or a dispersion dispersed in water. 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.

[0082] The carboxylic acid contained in the aqueous solution is not particularly limited. Examples thereof include acetic acid, lactic acid, oxalic acid, succinic acid, benzoic acid, and citric acid, and carboxylic acids having 4 or fewer carbon atoms are preferred. Among them, acetic acid is preferred from the perspectives of cost and availability. If the content of carboxylic acid in the dried EVOH resin composition pellets of the present invention is too low, coloring may sometimes occur during melt molding. If it is too high, interlayer adhesion may become insufficient, and therefore, it is preferably 10 to 5000 ppm. The content of carboxylic acid is more preferably 30 ppm or more, and further preferably 50 ppm or more. In addition, the content of carboxylic acid is more preferably 1000 ppm or less, and further preferably 500 ppm or less.

[0083] As the boron compound contained in the above-mentioned aqueous solution, boric acid, boric acid ester, borate, borohydride and the like can be mentioned, but it is not limited thereto. Specifically, as the boric acid, orthoboric acid, metaboric acid, tetraboric acid and the like can be mentioned, as the boric acid ester, triethyl borate, trimethyl borate and the like can be mentioned, as the borate, alkali metal salts, alkaline earth metal salts, borax and the like of the above-mentioned various boric acids can be mentioned. Among these compounds, orthoboric acid (hereinafter referred to as boric acid) is preferred. If the content of the boron compound in the dried EVOH resin composition pellets of the present invention is too little, the effect of improving the thermal stability is small. In addition, if it is too much, gelation sometimes occurs and the moldability becomes poor. Therefore, it is preferably 10 to 2000 ppm in terms of boron conversion, and more preferably 50 to 1000 ppm.

[0084] Examples of the phosphate compound contained in the aqueous solution include various acids such as phosphoric acid and phosphorous acid, and their salts. As phosphates, they may be contained in the form of monophosphates, diphosphates, and triphosphates, and the type of cations is not particularly limited, but alkali metal salts and alkaline earth metal salts are preferred. Among them, it is preferred to add the phosphate compound in the form of sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate. The content of the phosphate compound in the dried EVOH resin composition pellets of the present invention is preferably 1 to 1000 ppm in terms of phosphate radical. By adding within such a range, the coloring of the molded product and the generation of gels and pitting can be suppressed. When the content of the phosphate compound is less than 1 ppm, coloring may be easily generated during melt molding. In addition, when it exceeds 1000 ppm, gels and pitting may be easily generated in the molded product.

[0085] Examples of the alkali metal salt 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. Among them, sodium acetate, potassium acetate, and sodium phosphate are suitable. The content of the alkali metal salt in the dried EVOH resin composition pellets of the present invention, calculated as the alkali metal element, is preferably 5 to 5000 ppm. It is more preferably 20 to 1000 ppm, and even more preferably 30 to 750 ppm.

[0086] As the alkaline earth metal salt contained in the above-mentioned aqueous solution, magnesium salt, calcium salt, barium salt, beryllium salt, etc. can be mentioned, and magnesium salt and calcium salt are particularly preferred. The type of anion of the alkaline earth metal salt is not particularly limited, and acetate and phosphate are preferred. The content of the alkaline earth metal salt in the dried EVOH resin composition pellets of the present invention is preferably 10 to 1000 ppm, more preferably 20 to 500 ppm, calculated as metal. When the content of the alkaline earth metal salt is less than 10 ppm, the long-term improvement effect may become insufficient. In addition, if it exceeds 1000 ppm, the resin may be easily colored when it is melted.

[0087] On the other hand, as the dispersion liquid added to the aqueous EVOH, colloids of inorganic particles such as colloidal silica, colloidal titania, and colloidal zirconia, or dispersions of inorganic particles having a larger particle size than these particles can be added.

[0088] The extruder used in the melt-kneading step (II) may be a single-screw extruder or a multi-screw extruder, preferably a twin-screw extruder. Furthermore, the L / D of the extruder is preferably 10 to 55, more preferably 20 to 47. The barrel of the extruder is provided with an inlet for the EVOH hydrous pellets. After the EVOH hydrous pellets are introduced therefrom, the screw disposed in the barrel rotates, thereby melt-kneading the pellets and discharging them from the discharge port at the front end. The screw structure inside the pellets is not particularly limited. In addition to a full-screw, a partially reverse-screw screw is preferably provided to fully mix the molten resin.

[0089] The resin temperature in the extruder is preferably 120-210°C. If the resin temperature is too low, the screw torque may become excessive. Therefore, it is more preferably 140°C or higher, and 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 there is a risk of coloring or gel formation during prolonged melt kneading. Therefore, the resin temperature is more preferably 200°C or lower, and more preferably 190°C or lower.

[0090] In the extruder used in the melt-kneading step (II), an additive introduction portion is provided at a position downstream of the pellet inlet. An aqueous solution or aqueous dispersion containing an additive is injected into the molten aqueous EVOH from the additive introduction portion to carry out melt kneading. The amount of the aqueous solution or aqueous dispersion added is preferably 1 to 30 parts by mass relative to 100 parts by mass of the dry weight of EVOH. When the amount added is less than 1 part by mass, it is sometimes difficult to mix uniformly, and it is more suitable to be 2 parts by mass or more, and further preferably 5 parts by mass or more. On the other hand, when the amount added exceeds 30 parts by mass, the water content of the aqueous EVOH becomes too high, EVOH easily leaks from the dehydration slit, and the energy required for drying also increases. Therefore, the amount added is more preferably 20 parts by mass or less, and further preferably 15 parts by mass or less.

[0091] In the melt-kneading step (II), liquid water or water vapor is preferably discharged from at least one point of the above-mentioned extruder. In this way, the water content of the hydrous EVOH in the extruder can be reduced. The method of discharging liquid water or water vapor is not particularly limited, and a dehydration slit or a vacuum exhaust hole can be used. In the melt-kneading step of the present invention, the water content of the hydrous EVOH resin composition discharged from the extruder is not so low. Therefore, in many cases, a vacuum exhaust hole can be omitted and a dehydration slit is suitable. From the dehydration slit, water vapor or liquid water can be discharged, but from the viewpoint of being able to remove the latent heat of evaporation for heat removal, it is preferred to discharge water vapor. In addition, in the melt-kneading step (II) of the present invention, liquid water or water vapor is preferably discharged from a position closer to the downstream than the position where the aqueous solution or aqueous dispersion is added. In this way, the water content of the discharged hydrous EVOH resin composition can be effectively reduced, and foaming can be suppressed.

[0092] In the melt-kneading step (II), the average residence time of EVOH in the extruder is preferably 300 seconds or less. A shorter average residence time of EVOH in the extruder can improve the productivity of the extruder and prevent thermal degradation. The average residence time is more preferably 200 seconds or less, further preferably 100 seconds or less, and particularly preferably 40 seconds or less. The average residence time is typically 5 seconds or more.

[0093] In the cutting step (III), the molten resin composition discharged from the extruder is cut to obtain water-containing pellets of the EVOH resin composition having a moisture content W2 of 5 to 20% by mass. The cutting method is not particularly limited, and examples include a method of directly cutting the molten water-containing EVOH resin composition discharged from the extruder, and a method of extruding the water-containing EVOH resin composition discharged from the extruder into strands in a coagulation liquid and then cutting the strands after solidification. Among these, the method of directly cutting the water-containing EVOH resin composition is preferred. As a method of directly cutting the water-containing EVOH resin composition discharged from the extruder, a thermal cutting method or an underwater cutting method is used. When the water-containing EVOH resin composition is extruded into strands and then solidified and then cut, cylindrical pellets can be obtained. When the water-containing EVOH resin composition is directly cut in a molten state, spherical (or approximately spherical) pellets can be obtained. Regarding the size of the obtained EVOH resin composition water-containing pellets, for example, in the case of spherical (or roughly spherical) shape, the diameter can be greater than 1 mm and less than 10 mm, in the case of cylindrical shape, the diameter can be greater than 1 mm and less than 10 mm, and the length can be greater than 1 mm and less than 10 mm.

[0094] The moisture content W2 of the EVOH resin composition water-containing pellets obtained in the cutting process (III) is 5 to 20% by mass. By making the moisture content W2 5% or more, the temperature of the molten resin in the melt-kneading process (II) can be reduced, thereby suppressing the thermal degradation of EVOH during melt-kneading. In addition, if the moisture content W2 is 5% or more, in order to reduce the moisture content, it is also possible not to provide a vacuum exhaust hole on the extruder, which can simplify the equipment. On the other hand, by making the moisture content W2 20% or less, even when the extruder is operated at high speed, it is possible to suppress the leakage of EVOH from the dehydration slit, thereby improving productivity. In addition, the foaming of the obtained pellets can be suppressed, and the energy consumption in the subsequent second drying process (IV) can also be suppressed.

[0095] The EVOH resin composition water-containing pellets obtained in the cutting step (III) are supplied to the second drying step (IV). The dryer used in the second drying step (IV) can be dried while maintaining the pellet form, and is not particularly limited. A hot air dryer or the like can be used. The drying method can be a flow drying method using a flow dryer, or a static drying method using a static dryer, or a combination thereof. It is suitable to first use a flow dryer to dry at a relatively low temperature, and then use a static dryer to dry at a high temperature.

[0096] The drying temperature and drying time are not particularly limited. The drying temperature is preferably 50 to 150°C, and the drying time is preferably 1 hour to 7 days. If both the fluidized drying method and the static drying method are used, the drying temperatures of both methods are within the above-mentioned temperature range, and the total drying time of the two methods is included in the above-mentioned drying time. The drying temperature is more preferably 60°C or higher, further preferably 70°C or higher, and particularly preferably 80°C or higher. In addition, the drying temperature is more preferably 140°C or lower, further preferably 130°C or lower, and particularly preferably 120°C or lower. The drying time is more preferably 2 hours or higher, further preferably 5 hours or higher. In addition, it is more preferably 5 days or lower, and further preferably 3 days or lower. When both the fluidized drying method and the static drying method are used, the drying temperature of the latter is preferably increased by 5°C or higher than the drying temperature of the former, and further preferably by 10°C or higher. During drying, drying can be performed in air or in an inert gas such as nitrogen. When drying in an inert gas, thermal degradation is less likely to occur even if the drying temperature is set high.

[0097] The moisture content W3 of the EVOH resin composition pellets obtained by drying in the second drying step (IV) is 0.5% by mass or less. When the moisture content W3 is 0.5% by mass or less, even if the pellets are directly supplied to melt molding without further drying, problems such as foaming will not occur. The moisture content W3 is preferably 0.4% by mass or less, and more preferably 0.3% by mass or less. On the other hand, the moisture content W3 is generally 0.01% by mass or more, and even if the moisture content W3 is reduced to a level higher than necessary, energy consumption will only increase.

[0098] The above operation produces dry pellets of an additive-containing EVOH resin composition. The production method of the present invention increases the production speed when adding additives to aqueous EVOH in an extruder, allowing efficient production of EVOH resin composition pellets. The EVOH resin composition pellets thus obtained can be melt-molded into various molded articles such as films, sheets, containers, tubes, and fibers, and can be used in a variety of applications.

[0099] Example

[0100] Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples. In the examples and comparative examples described below, analysis and evaluation were performed by the following methods.

[0101] (1) Determination of moisture content of pellets

[0102] The moisture content of the pellets obtained in Examples and Comparative Examples was measured using a halogen moisture content analyzer using a heat-dried mass method at a drying temperature of 180°C, a drying time of 20 minutes, and a sample size of 10 g. The moisture content of the pellets was determined using the following formula.

[0103] Moisture content (mass %) = [(mass before drying - mass after drying) / mass before drying] × 100

[0104] (2) Quantification of carboxylic acid

[0105] 20 g of the dried EVOH resin composition pellets obtained in the Examples and Comparative Examples were added to 100 mL of ion-exchanged water and heated for extraction at 95°C for 6 hours. The resulting extract was neutralized and titrated 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.

[0106] (3) Quantification of metal salts, boron compounds, and phosphate compounds

[0107] 0.5 g of the EVOH resin composition pellets obtained in the examples and comparative examples were placed in a Teflon (registered trademark) pressure vessel, 5 mL of concentrated nitric acid was added thereto, and the mixture was decomposed at room temperature for 30 minutes. After decomposition, the pressure vessel was covered and heated at 150° C. for 10 minutes using a wet decomposition device ("MWS-2" manufactured by Akutake Co., Ltd.), followed by heating at 180° C. for 5 minutes, and further decomposed, and then cooled to room temperature. The treated liquid was transferred to a 50 mL volumetric flask and fixed to volume with ion exchange water to prepare a sample solution for measurement. The contents of metal elements, boron elements, and phosphorus elements in the sample solution were determined by an ICP emission spectrometer ("OPTIMA4300DV" manufactured by Parkin Elmer). Based on the values ​​obtained, the metal salt content (metal ion content) converted to metal elements, the content of boron compounds converted to boron elements, and the content of phosphate compounds converted to phosphate radicals in the EVOH resin composition pellets were determined.

[0108] (4) Evaluation of EVOH leakage

[0109] EVOH resin composition pellets were continuously produced using the methods described in the Examples and Comparative Examples. The presence of white traces of EVOH leaking out of the dewatering slits (which serve as outlets for water or steam) on the twin-screw extruder, or the presence of resin adhering to the exhaust ports (which serve as outlets for water vapor), was visually confirmed. Evaluation was performed according to the following criteria. A rating of C indicated that efficient production was not possible.

[0110] A: Even if it is operated continuously for more than 10 days, no trace of EVOH leakage is observed at the discharge port.

[0111] B: During continuous operation for more than 7 days and less than 10 days, EVOH leakage was observed at the discharge port.

[0112] C: During continuous operation for less than 7 days, EVOH leakage was observed at the outlet, or resin adhered to the outlet.

[0113] (5) Foaming

[0114] 100 g of EVOH resin composition pellets, cut and dried after the resin composition ejected from the extruder, were collected. The proportion (mass %) of pellets with observed shape defects such as dents, trapped bubbles, and foaming was determined and evaluated according to the following criteria. A rating of C indicated that efficient production was not possible.

[0115] (evaluate)

[0116] A: less than 1% by mass

[0117] B: 1% by mass or more and less than 5% by mass

[0118] C: 5% by mass or more

[0119] [Example 1]

[0120] An EVOH solution containing 100 parts by mass of methanol, 50 parts by mass of water, and 2 parts by mass of sodium acetate (in terms of sodium) was continuously fed at 521 kg / hr to the top layer of a 0.6 m diameter, 10-stage tray tower. Water vapor was blown into the bottom layer of the tray tower at 600 kg / hr, allowing countercurrent contact between the EVOH solution and the water vapor. The temperature within the tray tower was 130°C, and the pressure within the tray tower was 3 kg / cm². 2 Methanol vapor and water vapor are distilled off from the top of the tray column, condensed in a condenser, and recovered as a methanol-water solution. An aqueous EVOH composition is continuously withdrawn from the bottom of the tray column. This aqueous EVOH composition contains 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.

[0121] Next, the aqueous EVOH composition was fed at 430 kg / hr to a kneader with a 50 mm diameter liquid discharge port and an L / D ratio of 13.2. The screw speed was 1000 rpm. The aqueous EVOH composition obtained from the discharge port contained 0.03 parts by mass of methanol, 68 parts by mass of water (40% water content), and 1.2 parts by mass of sodium acetate (calculated as sodium) per 100 parts by mass of EVOH, and the temperature was 118°C. Next, the aqueous EVOH composition was extruded through a die with six holes and a 3 mm diameter. The pellets were cut at a distance of 0.05 mm from the die using a thermal cutter with eight blades to produce aqueous EVOH pellets. The cutting blades rotated at 2500 rpm.

[0122] The resulting 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 added to the bottom of the processor at 500 L / hr, allowing countercurrent contact between the pellets and the aqueous acetic acid solution within the processor. The aqueous acetic acid solution was discharged from the top of the processor, and the washed pellets were continuously removed from the bottom of the processor. The washed EVOH pellets had a moisture content of 40% by mass, with residual sodium acetate at 0.002% by mass, calculated as sodium.

[0123] The EVOH pellets (ethylene unit content 32 mol%, saponification degree 99.8 mol%) with a water content W0 of 40% by mass were fed into a fluidized dryer and dried at 80°C for 60 minutes. The dried EVOH pellets with a water content W1 of 13% by mass were fed into a twin-screw extruder. The barrel and screw configurations of the twin-screw extruder are as follows: Figure 1 As shown. 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 / potassium dihydrogen phosphate was added from additive inlet 2. The amount of this aqueous solution added per unit time was 20.8 L / hr. This aqueous solution contained 3.5 g / L acetic acid, 15 g / L boric acid, 7.7 g / L sodium acetate trihydrate, 3.1 g / L magnesium acetate tetrahydrate, and 1.7 g / L potassium dihydrogen phosphate.

[0124] The specifications of the twin-screw extruder are as follows. Figure 1 The twin-screw extruder barrel (barrel structure a, screw structure X) is equipped with a pellet feeding section 1, an additive introduction section 2, and a dewatering slit 4. Figure 1 The shown combination comprises a full-flight screw 6 and a reverse-flight screw 7. Furthermore, a temperature sensor 3 is provided at the end of the barrel.

[0125] Type: Twin-shaft extruder

[0126] L / D:45.5

[0127] Diameter: 30mmφ

[0128] Screw: Fully meshing in the same direction

[0129] Speed: 300rpm

[0130] Mould diameter: 3.0mmφ

[0131] The molten water-containing EVOH resin composition discharged from the above-mentioned twin-screw extruder was cut with a hot cutter to obtain water-containing pellets of the EVOH resin composition. The water content W2 of the water-containing pellets of the EVOH resin composition immediately after being obtained was 10% by mass, the discharge amount of EVOH discharged from the twin-screw extruder was 208 kg / hour (excluding the water content), and the residence time was 25 seconds. EVOH resin composition pellets were continuously manufactured under the above-mentioned conditions, and the leakage and foaming of EVOH were evaluated according to the methods described in (4) to (5) above. The results are shown in Table 1. In addition, the obtained water-containing pellets of the EVOH resin composition were dried at 90°C for 15 hours using a fluidized bed dryer, and then dried at 105°C for 15 hours using a static dryer, thereby obtaining EVOH resin composition pellets with a water content W3 of 0.2% by mass. The obtained EVOH resin composition pellets were quantitatively analyzed for carboxylic acid, metal salt, boron compound, and phosphorus compound according to the methods described in (2) to (3) above. The results showed that the acetic acid content was 260 ppm, the boric acid content was 260 ppm in terms of boron conversion, the phosphoric acid content was 90 ppm in terms of phosphate radical conversion, the sodium ion content was 125 ppm, the potassium ion content was 35 ppm, and the magnesium ion content was 35 ppm.

[0132] [Examples 2, 3, 5 to 7, Comparative Examples 1 and 2]

[0133] EVOH resin composition pellets were prepared and analyzed and evaluated in the same manner as in Example 1, except that the ethylene unit content and moisture content W0 of the EVOH hydrous pellets, the drying temperature and drying time in the first drying step, and the 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. In the Examples and Comparative Examples of this application, the discharge rate and residence time were adjusted by adjusting the feed rate of the EVOH hydrous pellets to the twin-screw extruder, and the extruder rotation speed was adjusted according to the production speed. The results are shown in Table 1. All dried EVOH resin composition pellets contained trace components at levels comparable to those in Example 1, with acetic acid content ranging from 240 to 300 ppm, boric acid content from 240 to 270 ppm (boron equivalent), phosphoric acid content from 85 to 95 ppm (phosphate equivalent), sodium ion content from 120 to 140 ppm, potassium ion content from 30 to 40 ppm, and magnesium ion content from 30 to 40 ppm. It should be noted that even in the following Examples and Comparative Examples, where trace components were present at levels comparable to those in Example 1, these values ​​were also within the aforementioned ranges.

[0134] [Example 4]

[0135] EVOH resin composition pellets were prepared by the same method as in Example 1, except that the drying temperature in the first drying step, the resin temperature in the melt-kneading step, and the amount of aqueous solution added were changed as shown in Table 1. The aqueous solution containing the additives was changed to an aqueous solution containing 1.8 g / L acetic acid, 8 g / L boric acid, 3.8 g / L sodium acetate trihydrate, 1.5 g / L magnesium acetate tetrahydrate, and 0.9 g / L potassium dihydrogen phosphate. EVOH resin composition pellets were analyzed and evaluated in the same manner as in Example 1. The results are shown in Table 1. The resulting dried EVOH resin composition pellets contained trace components at the same level as in Example 1.

[0136] [Example 8]

[0137] EVOH resin composition pellets were prepared in the same manner as in Example 1, except that the drying temperature in the first drying step, the cylinder configuration, the resin temperature, and the amount of aqueous solution added in the melt-kneading step were changed as shown in Table 1, and the aqueous solution containing the 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. EVOH resin composition pellets were analyzed and evaluated in the same manner as in Example 1. Figure 2 As shown, in this specification, when the barrel configuration is defined as b, the screw configuration is defined as Y. The results are shown in Table 1. The obtained dry EVOH resin composition pellets contained trace components in the same amount as in Example 1.

[0138] [Comparative Examples 3 to 6]

[0139] The ethylene unit content, saponification degree, and moisture content W0 of the EVOH aqueous pellets, as well as the barrel configuration, resin temperature, aqueous solution addition amount, EVOH discharge amount, and residence time in the melt kneading process were changed as shown in Table 1. Drying in the first drying process was omitted. Dry EVOH resin composition pellets were prepared by the same method as in Example 1, and analyzed and evaluated in the same manner as in Example 1. The concentration of the additive in the aqueous solution added to the extruder in Comparative Example 5 was the same as in Example 8. The results are shown in Table 1. Each of the dry EVOH resin composition pellets contained trace components to the same extent as in Example 1.

[0140] [Comparative Example 7]

[0141] Except that the ethylene unit content and saponification degree of the EVOH aqueous pellets, the cylinder configuration, resin temperature, amount of aqueous solution added, EVOH discharge amount, and residence time in the melt kneading step were changed as shown in Table 1, dry EVOH resin composition pellets were prepared by the same method as in Example 1, and analyzed and evaluated in the same manner as in Example 1. Figure 3As shown, in this specification, when the barrel configuration is set to C, the screw configuration is Y. The concentration of the additive in the aqueous solution added to the extruder was the same as that in Example 8. The results are shown in Table 1. The obtained dry EVOH resin composition pellets contained trace components to the same extent as in Example 1.

[0142] [Comparative Example 8]

[0143] The amount of aqueous solution added, the EVOH discharge amount and the residence time in the melt kneading process were changed as shown in Table 1. In addition, the intention was to produce dry EVOH resin composition pellets by the same method as Example 7. However, the torque applied to the extruder increased, making melt kneading impossible, so the subsequent steps were abandoned.

[0144] [Comparative Examples 9 and 10]

[0145] The saponification degree and moisture content W0 of the EVOH hydrous pellets, as well as the barrel configuration, resin temperature, amount of aqueous solution added, EVOH discharge amount, 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 static hot air dryer and then dried at 80°C for 25 minutes using a static hot air dryer to set the moisture content W1 of the pellets to 9.9% by mass. Except that the second drying step was not performed after the cutting step, dried EVOH resin composition pellets were prepared by the same method as in Example 1 and analyzed and evaluated in the same manner as in Example 1. Here, as Figure 4 In this specification, the screw configuration is X when the barrel configuration is d. The concentration of the additive in the aqueous solution added to the extruder was the same as that in Example 4. The results are shown in Table 1. All dried EVOH resin composition pellets contained trace components to the same extent as in Example 1.

[0146] [Comparative Example 11]

[0147] The saponification degree and moisture content W0 of the EVOH hydrous pellets and the drying time in the first drying step were changed as shown in Table 1. In addition, the same method as in Example 1 was used to produce dried EVOH resin composition pellets. However, the EVOH hydrous pellets adhered to each other in the first drying step, so the subsequent steps were abandoned.

[0148] [Table 1]

[0149]

[0150] Explanation of symbols

[0151] 1. Pellet supply unit

[0152] 2 Additive introduction part

[0153] 3 Temperature sensor

[0154] 4 Dehydration slits

[0155] 5 exhaust holes

[0156] 6 full-thread screw

[0157] 7 Reverse thread screw

Claims

1. A method for producing ethylene-vinyl alcohol copolymer resin composition pellets, comprising: First drying step (I): introducing the ethylene-vinyl alcohol copolymer water-containing pellets having a moisture content W0 of 25 to 50% by mass into a dryer to reduce the moisture content W1 of the pellets to 5 to 25% by mass; 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 an additive is added and melt-kneaded; Cutting step (III): cutting the molten resin composition discharged from the extruder to obtain water-containing pellets of an ethylene-vinyl alcohol copolymer resin composition having a moisture content W2 of 5 to 20% by mass; and Second drying step (IV): drying the water-containing pellets obtained in the cutting step (III) to obtain ethylene-vinyl alcohol copolymer resin composition pellets having a moisture content W3 of 0.5% by mass or less, The reduction in moisture content (W0-W1) in the first drying step (I) is 10 to 45% by 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. The manufacturing 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. The manufacturing method according to claim 1 or 2, wherein: In the melt-kneading step (II), the aqueous solution or aqueous dispersion added 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.

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

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

6. The production method according to any one of claims 1 to 5, wherein The ethylene-vinyl alcohol copolymer water-containing pellets obtained through the following steps are supplied to the first drying step (I). Step (A): introducing an ethylene-vinyl alcohol copolymer solution into a container, bringing the solution into contact with water vapor in the container, removing the alcohol together with the water vapor, and removing the hydrous ethylene-vinyl alcohol copolymer from the container, wherein the ethylene-vinyl alcohol copolymer solution 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 the ethylene-vinyl alcohol copolymer; step (B): supplying the hydrous ethylene-vinyl alcohol copolymer to an extruder, melt-kneading the copolymer, and then discharging the copolymer from the extruder; and step (C): cutting the hydrous ethylene-vinyl alcohol copolymer discharged from the extruder.

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