Method for producing dry pellet containing ethylene-vinyl alcohol copolymer

Abstract

To provide a method for producing a dry pellet containing EVOH which can obtain high-quality pellets having little coloring or the like, and low levels of volatile and carboxylic acid content.SOLUTION: There is provided a method for producing a dry pellet containing EVOH including: a melt-kneading step of feeding water-containing pellets of EVOH with an ethylene unit content of 20 to 50 mol% and a saponification degree of 99 mol% or more, and an additive containing a carboxylic acid into an extruder and melt-kneading them to obtain a molten composition; a pelletizing step of cutting the extruded molten composition to obtain intermediate pellets; and a drying step of drying the intermediate pellets to obtain dry pellets. In the melt-kneading step, the water-containing pellets having a water content (A1) of 5 to 22 weight % are fed into the extruder, and in the drying step the intermediate pellets having a water content (A2) of 1.5 to 20 weight % are dried in a nitrogen atmosphere to obtain the dry pellets having a water content (A3) of 1 weight % or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing dry pellets comprising ethylene-vinyl alcohol copolymers. [Background technology]

[0002] Ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as "EVOH") is a useful polymeric material with excellent oxygen barrier properties, oil resistance, antistatic properties, mechanical strength, etc., and is widely used as various packaging materials such as films, sheets, containers, etc. The most common method for producing EVOH is to saponify an ethylene-vinyl ester copolymer obtained by copolymerizing ethylene with a vinyl ester such as vinyl acetate in an organic solvent containing alcohol in the presence of a saponification catalyst.

[0003] Known methods for post-treating the alcohol solution of EVOH obtained by saponification include introducing the alcohol solution of EVOH into an apparatus and contacting it with water in the apparatus to replace the alcohol in the solution with water, and then cutting the aqueous EVOH composition discharged from the apparatus to obtain aqueous EVOH pellets.

[0004] On the other hand, there are various methods for molding EVOH pellets into various molded products, but melt molding using an extruder is the most common, such as extrusion molding or injection molding. In this case, the molding process begins by putting the raw EVOH pellets into the hopper of the extruder. However, when molding EVOH, the melt temperature must be 200°C or higher. EVOH that does not contain additives is prone to deterioration during melt molding, and this can cause discoloration of the product, which can lead to a decrease in quality.

[0005] To solve this problem, a method of adding a trace component such as a carboxylic acid or a metal salt to EVOH is known. For example, a method of melt-kneading EVOH hydrous pellets and a trace component in an extruder and then discharging them (Patent Documents 1 and 2) is known to be a useful method that can reduce production costs because the addition of the trace component and dehydration can be performed in the extruder. In addition, Patent Document 3 describes a method in which a paste consisting of a hydrous composition of EVOH obtained by contacting an alcohol solution or a water / alcohol mixed solvent solution of EVOH with water or steam in a washing vessel (de-alcoholization step) and washing water containing an additive such as a carboxylic acid are introduced into a pipe mixer and stirred and mixed to obtain a hydrous EVOH composition with a low alcohol content, and pelletized. It is described that this method reduces impurities in the obtained hydrous EVOH composition, and can improve the quality of the final product EVOH and the molded product using this EVOH. It is also described that the additives can be uniformly dispersed into the inside of the paste. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2022 / 138858 [Patent Document 2] JP 2001-96606 A [Patent Document 3] JP 2011-111473 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the methods described in Patent Documents 1 and 2, a large amount of carboxylic acid volatilizes from the EVOH when the EVOH discharged from the extruder is dried. In addition, in the method described in Patent Document 3, a large amount of carboxylic acid is used in the washing water, and the water-containing EVOH composition obtained by stirring and mixing EVOH and additives such as carboxylic acid has a high water content, so that a large amount of carboxylic acid volatilizes during dehydration and drying.

[0008] The present invention has been made to solve the above-mentioned problems, and aims to provide a method for producing dry pellets containing EVOH, which can produce high-quality pellets with little discoloration, and which uses a small amount of carboxylic acid and volatilizes the same, and also reduces foaming during film formation using the obtained dry pellets. [Means for solving the problem]

[0009] The above-mentioned problem is solved by providing a method for producing dry pellets containing EVOH, the method comprising: a melt-kneading step of feeding hydrous pellets of EVOH having an ethylene unit content of 20 to 50 mol% and a saponification degree of 99 mol% or more and an additive containing a carboxylic acid into an extruder, and then melt-kneading the pellets to obtain a molten composition; a pelletizing step of cutting the molten composition discharged from the extruder to obtain intermediate pellets; and a drying step of drying the intermediate pellets to obtain dry pellets, the method comprising: feeding the hydrous pellets having a moisture content (A1) of 5 to 22% by weight into the extruder in the melt-kneading step; and drying the intermediate pellets having a moisture content (A2) of 1.5 to 20% by weight under a nitrogen atmosphere in the drying step to obtain the dry pellets having a moisture content (A3) of 1 weight% or less.

[0010] In this case, it is preferable that the additive further includes at least one selected from the group consisting of phosphoric acid, boron compounds, alkali metal salts, and alkaline earth metal salts. It is preferable to supply the hydrous pellets, the moisture content of which (A1) has been adjusted to 5 to 22% by weight by carrying out a preliminary drying step, to the extruder. It is also preferable that the moisture content (A2) of the intermediate pellets is 5 to 17% by weight. It is also preferable that in the drying step, the intermediate pellets are dried at 107 to 130°C for 5 to 20 hours. It is also preferable that the ratio (B2 / B1) of the carboxylic acid content B1 (ppm) of the intermediate pellets to the carboxylic acid content B2 (ppm) of the dried pellets is 0.70 or more. It is also preferable that the ratio (B2 / B3) of the carboxylic acid content B2 (ppm) of the dried pellets to the carboxylic acid content B3 (ppm) of the intermediate pellets dried in the same manner as the dried pellets except that the intermediate pellets are dried under air is 1.10 or more. It is also preferable that the content of the alcohol in the hydrous pellets is less than 10 parts by weight based on 100 parts by weight of the EVOH. Effect of the Invention

[0011] According to the production method of the present invention, high-quality pellets with little coloring can be obtained, and the amount of carboxylic acid used and the amount of volatilization are small, so that costs and environmental loads are reduced. In addition, foaming when a film is formed using the obtained pellets can be reduced. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing the cylinder configuration and screw configuration of twin-screw extruders in Examples 1 to 10 and Comparative Examples 1 to 15. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention is a method for producing dry pellets containing EVOH, comprising a melt-kneading step of feeding hydrous pellets of EVOH having an ethylene unit content of 20-50 mol% and a saponification degree of 99 mol% or more and an additive containing a carboxylic acid into an extruder and then melt-kneading them to obtain a molten composition, a pelletizing step of cutting the molten composition discharged from the extruder to obtain intermediate pellets, and a drying step of drying the intermediate pellets to obtain dry pellets, wherein in the melt-kneading step, the hydrous pellets having a moisture content (A1) of 5-22% by weight are fed to the extruder, and in the drying step, the intermediate pellets having a moisture content (A2) of 1.5-20% by weight are dried under a nitrogen atmosphere to obtain the dry pellets having a moisture content (A3) of 1% by weight or less. According to the production method of the present invention, a high-quality molded product with little coloring can be obtained, and the amount of carboxylic acid used and the amount of volatilization are small, thereby reducing costs and environmental load.

[0014] The EVOH hydrous pellets used in the present invention contain EVOH and water. The EVOH constituting the EVOH hydrous pellets used in the present invention (hereinafter, sometimes referred to as "EVOH used in the present invention" or "the EVOH") is usually obtained by saponifying an ethylene-vinyl ester copolymer. The ethylene unit content in the EVOH is 20 to 50 mol%. From the viewpoint of improving melt moldability, the ethylene unit content is preferably 23 mol% or more, more preferably 25 mol% or more, and even more preferably 30 mol% or more.

[0015] The method for producing the EVOH will be specifically described below. As described above, the 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. In addition, the copolymerization may be any of continuous and batch polymerization, and the polymerization conditions in the case of solution polymerization are as follows.

[0016] 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, etc. The boiling point is more preferably 80° C. or less, and even more preferably 70° C. or less.

[0017] 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.

[0018] Examples of initiators 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 peroxy dicarbonate, t-butyl peroxy neodecanoate, lauroyl peroxide, benzoyl peroxide, and t-butyl hydroperoxide.

[0019] Examples of vinyl esters include fatty acid vinyl esters such as vinyl acetate, vinyl propionate, and vinyl pivalate, with vinyl acetate being preferred. EVOH can also contain 0.0002 to 0.2 mol% of a vinyl silane compound as a copolymerization component. Examples of vinyl silane-based compounds include vinyl trimethoxy silane, vinyl triethoxy silane, vinyl tri(β-methoxy-ethoxy) silane, and γ-methacryloxypropyl methoxy silane. Among these, vinyl trimethoxy silane and vinyl triethoxy silane are preferably used.

[0020] The polymerization conditions are preferably as follows: (1) Temperature: preferably 20 to 90°C, more preferably 40 to 80°C. (2) Time (average residence time in the case of a continuous system); preferably 2 to 15 hours, more preferably 3 to 11 hours. (3) Polymerization rate: preferably 10 to 90%, more preferably 30 to 80%, based on the charged vinyl ester. (4) Resin content in the solution after polymerization: preferably 5 to 85% by weight, more preferably 20 to 70% by weight.

[0021] In addition to ethylene and vinyl esters, monomers copolymerizable therewith, for example, α-olefins such as propylene, butylene, isobutylene, pentene, hexene, α-octene, and α-dodecene; 3-acyloxy-1-propene, 3-acyloxy-1-butene, 4-acyloxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4-acyloxy-2-methyl-1-butene, 4-acyloxy-3-methyl-1-butene, 3,4-diacyloxy-2-methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, 4,5-diacyloxy-1-pentene, 4-acyloxy-1-hexene, 5-acyloxy-1-propene, 5-acyloxy-1-hex ... It is also possible to carry out polymerization in the presence of small amounts of alkenes having ester groups such as 1-hexene, 6-acyloxy-1-hexene, 5,6-diacyloxy-1-hexene, and 1,3-diacetoxy-2-methylenepropane; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, and itaconic acid, anhydrides, salts, and mono- or dialkyl esters thereof; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid, or salts thereof; alkyl vinyl ethers, vinyl ketones, N-vinylpyrrolidone, vinyl chloride, and vinylidene chloride. The content of other monomer units 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 does not necessarily need to contain the other monomer units.

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

[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. As the alkali catalyst, sodium hydroxide, potassium hydroxide, alkali metal alcoholate, etc. are used. Moreover, methanol is preferable as the solvent used for saponification. For example, the saponification conditions are as follows. (1) Concentration of ethylene-vinyl ester copolymer in solution: 10 to 50% by weight (2) Reaction temperature: 30 to 150°C (3) Amount of catalyst used: 0.005 to 0.6 equivalents (per vinyl ester component) (4) Time (average residence time in the case of continuous type): 10 minutes to 6 hours

[0024] In general, when saponification is performed in a continuous system, methyl acetate produced by saponification can be removed more efficiently, so a resin with a high degree of saponification can be obtained with a smaller amount of catalyst than in the batch system. In addition, in the case of a continuous system, saponification must be performed at a higher temperature to prevent the precipitation of EVOH produced by saponification. Therefore, in the continuous system, it is preferable to set the reaction temperature and catalyst amount in the following ranges. Reaction temperature: 70~150℃. Amount of catalyst used: 0.005 to 0.1 equivalent (per vinyl ester component).

[0025] The saponification degree of the resulting EVOH is 99 mol % or more, preferably 99.5 mol % or more, and can be adjusted as desired by changing the conditions.

[0026] In particular, when producing dried pellets having excellent melt stability and good long-run properties, the saponification degree of EVOH is preferably 99.7 mol % or more, more preferably 99.8 mol % or more, and even more preferably 99.9 mol % or more. In order to obtain such an EVOH, it is preferable to further adjust the saponification conditions as follows.

[0027] A continuous process is preferred as a method for obtaining EVOH with an extremely high degree of saponification. Examples of methods for obtaining a high degree of saponification in a continuous process include a method for adding a catalyst from multiple locations in a saponification reaction tower, a method for increasing the amount of catalyst used, and a method for increasing the amount of methanol blown into the bottom of a saponification reaction tower. Examples of methods for obtaining EVOH with an extremely high degree of saponification in a batch process include a method for adding a catalyst in multiple batches, a method for increasing the amount of catalyst used, and a method for increasing the amount of methanol vapor or nitrogen gas blown into a saponification reaction tank.

[0028] The saponification step produces a solution or paste containing EVOH. The EVOH after the saponification reaction contains an alkali catalyst, by-product salts such as sodium acetate and potassium acetate, and other impurities, which may be removed by neutralization and washing as necessary. When the EVOH after the saponification reaction is washed with ion-exchanged water or the like that contains almost no metal ions, chloride ions, or the like, some catalyst residues such as sodium acetate and potassium acetate may remain in the EVOH.

[0029] The EVOH solution or paste thus obtained usually contains 50 parts by weight or more of alcohol having a boiling point of 100°C or less per 100 parts by weight of EVOH. The alcohol content is preferably 1000 parts by weight or less. By keeping the alcohol content within this range, the fluidity of the EVOH solution is ensured and efficient resin production is possible. The alcohol is preferably methanol.

[0030] Next, the obtained EVOH solution or paste is hydrous pelletized. The hydrous pelletization method is not particularly limited, and examples thereof include a method in which the EVOH solution or paste is melt-kneaded in an extruder, then discharged and cut. Specific examples of the method for cutting EVOH include a method in which EVOH is extruded into a strand shape and then cut with a pelletizer, and a method in which EVOH is extruded from a die and then cut using a hot cut method or an underwater cut method.

[0031] When the EVOH solution or paste is melt-kneaded in an extruder and then discharged and cut, a post-treatment method for the EVOH solution or paste after the saponification reaction is preferably to supply steam from the bottom of a tower-type vessel and supply the EVOH solution or paste from a position above the steam supply position, thereby drawing out the solvent (alcohol) present in the EVOH solution or paste together with the steam, and drawing out from the vessel a water-containing EVOH containing 0 to 10 parts by weight of the solvent (alcohol) and 10 to 1000 parts by weight of water per 100 parts by weight of EVOH. If the amount of steam introduced is too small, the efficiency of removing the solvent (alcohol) is poor, and conversely, if it is too large, it is disadvantageous in terms of cost, so that 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, in terms of weight ratio, relative to the amount of the EVOH solution or paste introduced. The water vapor to be brought into contact with the EVOH solution or paste may contain 10 parts by weight or less of a solvent (alcohol) per 100 parts by weight of the water vapor. However, in order to efficiently remove the solvent (alcohol), it is preferable that the water vapor does not contain any solvent (alcohol).

[0032] In this case, the EVOH solution or paste comes into direct contact with water vapor in the container, and the content of the solvent (alcohol) gradually decreases, during which the EVOH remains in a swollen paste state and can be removed from the container without gelling while retaining its fluidity. EVOH dissolves in a methanol / water mixed solvent at a temperature of, for example, about 60 to 70°C under normal pressure, but does not dissolve under normal pressure when the solvent is water alone. However, in the presence of pressurized water vapor at a temperature of, for example, 100°C or higher, EVOH can retain its fluidity even when it contains substantially only water.

[0033] The hydrous EVOH discharged from the vessel preferably contains 0 to 10 parts by weight of the solvent (alcohol) and 10 to 1000 parts by weight of water per 100 parts by weight of EVOH, and is discharged from the vessel in a flowing state. The content of the solvent (alcohol) in the hydrous EVOH discharged from the vessel is preferably 0 to 5 parts by weight, more preferably 0 to 1 part by weight, and even more preferably 0 to 0.1 parts by weight. The low content of the solvent (alcohol) can prevent the solvent (alcohol) from volatilizing in the subsequent process, and the working environment and the surrounding environment can be maintained. In addition, when washing the saponification catalyst residue, etc., the pellets are unlikely to stick to each other even if the temperature of the washing liquid is increased, so that the washing temperature can be increased, and as a result, the washing speed can be increased. In addition, from the viewpoint of good fluidity in the vessel, the content of water in the hydrous EVOH discharged from the vessel is preferably 10 parts by weight or more, more preferably 30 parts by weight or more, and even more preferably 50 parts by weight or more. On the other hand, the content of water discharged from the vessel is preferably 1000 parts by weight or less, more preferably 500 parts by weight or less, and even more preferably 200 parts by weight or less. When the content of water is 1000 parts by weight or less, uniform pellets tend to be produced in the pelletizing step described below.

[0034] The hydrous EVOH discharged from the vessel is cut directly in a molten state and the cut pellets are water-cooled, or the hydrous EVOH discharged from the vessel is extruded into a cooling liquid in the form of a strand, solidified, and then cut to produce hydrous EVOH pellets. When the hydrous EVOH discharged from the vessel is made into pellets, it is preferable to feed the hydrous EVOH to an extruder (different from the extruder used for producing intermediate pellets) to cut the hydrous EVOH directly in a molten state and water-cool the extruder to produce hydrous EVOH pellets. When the hydrous EVOH discharged from the vessel is fed to an extruder, the moisture content of the obtained hydrous EVOH can also be adjusted by the conditions of the extruder. As a method for directly cutting the hydrous EVOH in a molten state, the hot cut method or the underwater cut method is exemplified as a suitable method. From the viewpoint of ease of handling of the pellets, the nozzle aperture is preferably 2 to 5 mmφ (φ is diameter, the same applies below). The size of the produced pellets can be, for example, 1 to 10 mm in diameter if spherical (or nearly spherical), and 1 to 10 mm in diameter and 1 to 10 mm in length if cylindrical.

[0035] The cooling liquid used for the water-cooling is water, but may contain a small amount of alcohol. The temperature of the cooling liquid is preferably 0 to 50°C, and the temperature of the molten water-containing EVOH during extrusion is preferably 100 to 150°C. This temperature difference allows the water-containing EVOH to be cooled and solidified in a short time. The temperature of the cooling liquid is more preferably 0 to 30°C. Furthermore, the temperature of the molten water-containing EVOH is more preferably 110 to 140°C.

[0036] The EVOH hydrous pellets thus obtained can be used as the EVOH hydrous pellets to be supplied to the extruder in the melt kneading step. Also, the EVOH hydrous pellets after the washing step and the preliminary drying step described below can be used as the EVOH hydrous pellets to be supplied to the extruder. In the resin constituting the hydrous pellets to be supplied to the extruder, the proportion of EVOH is preferably 90% by weight or more, more preferably 95% by weight or more, even more preferably 99% by weight or more, and it is particularly preferable that the hydrous pellets consist of only EVOH. Also, the proportion of EVOH and water in the EVOH hydrous pellets is preferably 90% by weight or more, more preferably 95% by weight or more, even more preferably 99% by weight or more, and it is particularly preferable that the hydrous pellets consist of only EVOH and water. Furthermore, when the EVOH hydrous pellets contain a saponification catalyst residue, the proportion of EVOH, water, and a saponification catalyst residue in the hydrous pellets is preferably 90% by weight or more, more preferably 95% by weight or more, and even more preferably 99% by weight or more. It is particularly preferable that the EVOH hydrous pellets consist only of EVOH, water, and a saponification catalyst residue.

[0037] The EVOH hydrous pellets obtained after the saponification reaction may contain an alkali metal salt, which is a saponification catalyst residue. However, if the content is large, quality problems such as coloring may occur, so a step of washing and removing the saponification catalyst residue may be performed. The washing method is not particularly limited, but examples include a method of washing by immersing in an aqueous solution of water or an acid such as acetic acid, and a method of washing by supplying water or an aqueous solution of an acid into an extruder in a melt-kneading step. In this case, in the washing method of immersing in water or an aqueous solution, either a batch-type treatment vessel or a continuous treatment vessel can be used. Among them, a method of continuously supplying pellets in a tower-type vessel and treating them is preferable from the viewpoint of productivity. The washing temperature is usually in the range of 10 to 80°C. From the viewpoint of improving the washing efficiency, a higher washing temperature is preferable, but if the temperature is too high, fusion of the hydrous pellets occurs, which is not preferable. The lower limit of the washing temperature is preferably 20°C or higher. The upper limit of the washing temperature is preferably 70°C or lower.

[0038] The content of alkali metal salts in the washed EVOH hydrous pellets is preferably 5% by weight or less, more preferably 1% by weight or less, even more preferably 0.1% by weight or less, even more preferably 0.05% by weight or less, and particularly preferably 0.03% by weight or less, calculated as metal.

[0039] The obtained EVOH hydrous pellets may be subjected to a preliminary drying process to adjust the moisture content (A1) to the range described below. This shortens the time during which the EVOH resin is melt-kneaded at high temperature in the extruder, and the deterioration of the color of the EVOH resin can be suppressed. Furthermore, there is a possibility that the production efficiency can be improved. This method is not particularly limited, but for example, a hot air dryer can be used.

[0040] The method for producing EVOH-containing dry pellets of the present invention includes a melt-kneading step of feeding the EVOH-containing hydrous pellets and an additive containing a carboxylic acid to an extruder, and then melt-kneading the pellets to obtain a molten composition. The temperature of the EVOH-containing hydrous pellets used in this step is preferably 0 to 80°C.

[0041] The temperature of the EVOH water-containing pellets fed to the extruder is preferably 0°C or higher, more preferably 10°C or higher, and even more preferably 25°C or higher. If the temperature of the water-containing pellets fed to the extruder is lower than 0°C, the feedability of the water-containing pellets is likely to be problematic, the EVOH is not completely melted, and the foamed pellets tend to increase and the color tone is deteriorated. The temperature of the water-containing pellets fed to the extruder is preferably 80°C or lower, more preferably 75°C or lower, and even more preferably 65°C or lower. If the temperature of the water-containing pellets fed to the extruder exceeds 80°C, the moisture content (A1) of the water-containing pellets fed to the extruder is not stable, the EVOH is not completely melted in the extruder, and the foamed pellets tend to increase and the color tone is deteriorated. The temperature of the water-containing pellets fed to the extruder can be appropriately adjusted according to the conditions before being fed to the extruder.

[0042] The moisture content (A1) of the EVOH hydrous pellets fed to the extruder must be 5 to 22% by weight. When the moisture content (A1) is 5% by weight or more, dry pellets having a good color can be obtained. The moisture content (A1) is preferably 7% by weight or more, more preferably 10% by weight or more, and even more preferably 15% by weight or more. On the other hand, when the moisture content (A1) is 22% by weight or less, foaming during melt molding of the dry pellets is suppressed. The moisture content (A1) is preferably 21% by weight or less, more preferably 20% by weight or less, and even more preferably 19% by weight or less. The moisture content (A1) of the hydrous pellets can be adjusted by the conditions for pelletizing the hydrous EVOH after the saponification reaction, the washing conditions for the hydrous EVOH pellets, the dehydration conditions for the hydrous EVOH pellets, and the like.

[0043] The EVOH hydrous pellets fed to the extruder may contain alcohol as long as the effects of the present invention are not impaired. Since alcohol is a flammable liquid, from the viewpoint of safety, the alcohol content in the hydrous pellets is preferably 10% by weight or less, more preferably 5% by weight or less, and even more preferably 1% by weight or less.

[0044] The additives fed to the extruder include carboxylic acids, and by including such additives, dry pellets with good color can be obtained.

[0045] Examples of the carboxylic acid include oxalic acid, succinic acid, benzoic acid, citric acid, acetic acid, propionic acid, and lactic acid. Among these, acetic acid, propionic acid, and lactic acid are preferred from the viewpoints of cost and availability. The amount of the carboxylic acid added is preferably 0.001 to 0.5 parts by weight relative to 100 parts by weight of EVOH. The amount of the carboxylic acid added is more preferably 0.01 parts by weight or more, and even more preferably 0.015 parts by weight or more. The amount of the carboxylic acid added is preferably 0.3 parts by weight or less, more preferably 0.1 parts by weight or less, and even more preferably 0.05 parts by weight or less. According to the present invention, even if the amount of the carboxylic acid added is relatively small, a dried pellet containing the necessary amount of carboxylic acid, which is inhibited from discoloring during melt molding and has good thermal stability can be obtained.

[0046] It is preferable that the additive further contains at least one selected from the group consisting of phosphoric acid, boron compounds, alkali metal salts, and alkaline earth metal salts. Examples of boron compounds include, but are not limited to, boric acids, boric acid esters, borate salts, and boron hydrides. Specifically, examples of boric acids include orthoboric acid, metaboric acid, and tetraboric acid, examples of borate esters include triethyl borate and trimethyl borate, and examples of borates include alkali metal salts, alkaline earth metal salts, and borax of the above-mentioned various boric acids. Among these compounds, orthoboric acid (hereinafter simply referred to as boric acid) is preferable. When a boron compound is added, the amount is preferably 0.002 to 0.2 parts by weight relative to 100 parts by weight of EVOH. When the amount of the boron compound added is within the above range, the thermal stability and moldability tend to be good.

[0047] Examples of the phosphoric acid compound include various acids such as phosphoric acid and phosphorous acid and their salts. The phosphate may be contained in the form of any of primary phosphate, secondary phosphate, and tertiary phosphate, and the cationic species is not particularly limited, but is preferably an alkali metal salt or an alkaline earth metal salt. Among them, it is preferable to add the phosphoric acid compound in the form of sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, or dipotassium hydrogen phosphate. When the phosphoric acid compound is added, the amount is preferably 0.0001 to 0.1 parts by weight relative to 100 parts by weight of EVOH. By adding the phosphoric acid compound in such a range, it is possible to suppress coloring of the molded product and the occurrence of gels and bumps.

[0048] Examples of the alkali metal salt include aliphatic carboxylates, aromatic carboxylates, phosphates, and metal complexes of monovalent metals. For example, sodium acetate, potassium acetate, sodium phosphate, lithium phosphate, sodium stearate, potassium stearate, and sodium salt of ethylenediaminetetraacetic acid are listed. Among them, sodium acetate, potassium acetate, and sodium phosphate are preferable. When an alkali metal salt is added, the amount is preferably 0.0005 to 0.5 parts by weight based on 100 parts by weight of EVOH. By adding the alkali metal salt in such a range, it is possible to effectively improve interlayer adhesion and compatibility, and the thermal stability during melt molding is further increased.

[0049] Examples of alkaline earth metal salts 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 acetates and phosphates are preferred. When an alkaline earth metal salt is added, the amount is preferably 0.0001 to 0.1 parts by weight per 100 parts by weight of EVOH. By adding within this range, the long-run properties tend to be improved, and coloring during resin melting tends to be suppressed.

[0050] Both the additives and the EVOH water-containing pellets are fed to an extruder, melt-kneaded, and then the molten composition is obtained. FIG. 1 is a diagram showing the cylinder configuration and screw configuration of a twin-screw extruder in Examples and Comparative Examples. One embodiment of the melt-kneading method of the water-containing pellets and the additives will be specifically described with reference to FIG. 1. As the extruder used for melt-kneading the water-containing pellets and the additives, a twin-screw extruder is preferable, and among them, a twin-screw extruder in which the screws rotate in the same direction is more preferable. In addition, an extruder with an L / D of 15 or more is preferable. As the cylinder, a block cylinder or the like is used. As the screw, a segment type or the like is used.

[0051] The EVOH hydrous pellets are fed from a raw material feed section 1. Meanwhile, the additives are fed from a minor component addition section 3. Thus, in the present invention, the additives are added to the hydrous EVOH in the extruder. This allows the additives to be mixed uniformly with the hydrous EVOH, so that dry pellets with good color can be obtained. The additives can be added individually, or multiple additives can be added simultaneously depending on the embodiment.

[0052] In the present invention, when the additive is added to the water-containing EVOH in the extruder, the additive is preferably added to the extruder at a position where the water-containing EVOH is in a molten state in the extruder in order to fully exert the effects of the present invention. In particular, it is preferable to add the additive to the water-containing EVOH in a water-containing and molten state. It is preferable that the extruder has a kneading section, and it is particularly preferable that the additive is added to the kneading section of the extruder in order to easily mix the additive uniformly with the water-containing EVOH.

[0053] The form of addition of the additive is not particularly limited. Examples of the additive include a method of adding the additive as a dry powder in the extruder, a method of adding the additive as a paste impregnated with a solvent, a method of adding the additive in a suspended state in a liquid, and a method of adding the additive as a solution by dissolving the additive in a solvent. From the viewpoint of controlling the amount of the additive and uniformly dispersing the additive in the water-containing EVOH, the method of adding the additive as a solution by dissolving the additive in a solvent is particularly preferable. The solvent is not particularly limited, but water is preferable from the viewpoints of the solubility of the additive, cost benefits, ease of handling, and safety of the working environment. That is, the additive is preferably an aqueous solution containing a carboxylic acid and, if necessary, at least one selected from the group consisting of a boron compound, a phosphoric acid compound, an alkali metal salt, and an alkaline earth metal salt. In addition, as a method of addition, the additive is preferably added to the extruder from one or more than two places.

[0054] The extruder may be simultaneously fed with EVOH pellets different from the hydrous pellets of EVOH, within the scope of not impairing the effects of the present invention. The hydrous pellets different from the EVOH pellets may be dry-blended in advance with the hydrous pellets and fed into the raw material feed section 1 of the extruder, or may be simultaneously fed into the raw material feed section 1 without being dry-blended with the hydrous pellets, or may be fed separately from a raw material feed section different from the hydrous pellets (using an extruder equipped with two raw material feed sections). Among these, the method of feeding the hydrous pellets and the EVOH pellets different from the hydrous pellets separately from different raw material feed sections is superior in terms of quantitative feeding and reducing quality variation.

[0055] In addition, other components can be added to the extruder to the extent that the effect of the present invention is not impaired. Examples of other components include inorganic substances, plasticizers, lubricants, stabilizers, surfactants, coloring agents, antioxidants, UV absorbers, antistatic agents, drying agents, crosslinking agents, metal salts, fillers, and reinforcing agents such as various fibers. The other components may be introduced into the extruder in a solid state such as powder or as a melt, but it is preferable to mix them as solutes contained in a solution or dispersoids contained in a dispersion from the viewpoint of uniformly dispersing them in the intermediate pellets obtained and suppressing the variation in the amount added. As the solution and dispersion, an aqueous solution and an aqueous dispersion are preferable, respectively. When the other components are in a solid state such as powder, they may be dry-blended in advance with the water-containing pellets and then fed into the raw material feed section 1 of the extruder, or they may be simultaneously fed without dry-blending. When they are mixed as solutes contained in a solution or dispersoids contained in a dispersion, they may be added from the trace component addition section 3 at the same time as the additive of the present invention, or a new addition section may be provided and the other components may be added from a site other than the additive.

[0056] The temperature T0 of the molten composition containing the EVOH, the additives and water in the extruder is preferably 70 to 180°C. If the temperature T0 is less than 70°C, the fluidity of the water-containing EVOH is insufficient, and the water-containing EVOH may gel or block in the container. The temperature T0 is more preferably 80°C or higher, even more preferably 110°C or higher, even more preferably 125°C or higher, and particularly preferably 130°C or higher. On the other hand, if the temperature T0 exceeds 180°C, the color of the dried pellets is significantly deteriorated. The temperature T0 is more preferably 175°C or lower, even more preferably 170°C or lower, and particularly preferably 165°C or lower. Here, the temperature T0 of the molten material refers to the temperature detected by a temperature sensor installed in the cylinder of the extruder in contact with the molten composition, and the detection point is near the discharge port at the tip of the extruder. The temperature T0 can be adjusted by the temperature of the water-containing pellets fed to the extruder, the cylinder temperature of the extruder, the screw rotation speed of the extruder, and the like.

[0057] In the production method of the present invention, the cylinder temperature T1 of the extruder is preferably 65 to 175°C. If the cylinder temperature T1 is less than 65°C, the fluidity of the water-containing EVOH is insufficient, and there is a risk of gelation or blockage in the container. The temperature T1 is more preferably 70°C or higher, even more preferably 75°C or higher, even more preferably 85°C or higher, particularly preferably 90°C or higher, and most preferably 95°C or higher. On the other hand, by setting the temperature T1 to 175°C or lower, dried pellets with a better color can be obtained. The temperature T1 is more preferably 165°C or lower, even more preferably 150°C or lower, even more preferably 135°C or lower, particularly preferably 130°C or lower, and most preferably 125°C or lower. Here, the cylinder temperature T1 means the highest temperature among the temperatures of the cylinder at a position downstream of the portion where the raw material is supplied to the extruder.

[0058] As described above, the saponification catalyst residue can be washed and removed in the extruder, and this process can be carried out in the extruder. Specifically, the water-containing pellets are fed to the extruder, a washing liquid is injected from at least one point in the extruder, the resin is washed, and the washing liquid is discharged from at least one point downstream of the injection part. This method is preferred because it allows efficient washing and requires less space.

[0059] In the present invention, it is preferable to dehydrate EVOH in a water-containing state in the extruder. It is also preferable to degas EVOH. Specifically, it is preferable to discharge water and / or water vapor from at least one location in the extruder. The method of discharging is not particularly limited, but includes a method of discharging from a dehydration slit, a dehydration hole, or a vent port arranged in the cylinder of the extruder. As the dehydration slit, a wedge wire type dehydration slit and a screen mesh type dehydration slit are preferably mentioned. Furthermore, as the vent port, a vacuum vent that removes water vapor under reduced pressure and an open vent that removes water vapor under normal pressure are mentioned.

[0060] Among these, dehydration slits or dehydration holes are preferred. These can discharge both water and water vapor, so they can efficiently remove water from resins with high water content, and in this respect are often more effective than vents, which can generally only discharge water vapor. In addition, when discharging water using a vent, resin is likely to adhere to the vent, and such adhered resin may deteriorate and be mixed into the extruder, so dehydration slits or dehydration holes are also preferred from this point of view. Furthermore, when a dehydration hole is used, the molten material may overflow from the hole, and from this point of view, it is preferred to use a dehydration slit.

[0061] The dehydration means may be used alone, or multiple dehydration means of the same type may be used, or different types may be used in combination. For example, it is possible to remove a certain amount of water from a resin with a high water content by using a dehydration slit, and then remove further water from a vent port downstream.

[0062] The above-mentioned dehydration operation is carried out to adjust the moisture content of the molten composition in the extruder and after extrusion.In order to prevent the moisture content of the molten composition from becoming lower than necessary, water may be supplied to the extruder in addition to the above-mentioned dehydration operation or without the above-mentioned dehydration operation.The method of supplying water to the extruder is not particularly limited, and may include a method of pressing water using a plunger pump or the like.

[0063] In the pelletizing step, the molten composition discharged from the extruder in the melt kneading step is cut to obtain intermediate pellets. The pelletizing method is not particularly limited, but an example is a method in which the molten composition discharged from the extruder is directly cut in a molten state to produce pellets. As a direct cutting method, a hot cut method or an underwater cut method is preferably exemplified, and the nozzle aperture is usually 2 to 5 mmφ (φ is diameter, the same applies below). The size of the intermediate pellets is, for example, preferably 1 to 10 mm in diameter, more preferably 3 to 8 mm, if spherical, and 1 to 10 mm in diameter and 1 to 10 mm in length if cylindrical.

[0064] The intermediate pellets need to have a moisture content (A2) of 1.5 to 20% by weight. When the moisture content (A2) is 20% by weight or less, foaming during melt molding of the dried pellets is suppressed. The moisture content (A2) is preferably 17% by weight or less, more preferably 15% by weight or less, even more preferably 12% by weight or less, and even more preferably 10% by weight or less. On the other hand, when the moisture content (A2) is 1.5% by weight or more, coloring of the obtained dried pellets is reduced. The moisture content (A2) is preferably 3% by weight or more, more preferably 4% by weight or more, and even more preferably 5% by weight or more.

[0065] The carboxylic acid content B1 (ppm) of the intermediate pellets is preferably 30 to 1000 ppm. When the carboxylic acid content B1 is 30 ppm or more, coloration of the resulting dry pellets is further suppressed. The carboxylic acid content B1 is more preferably 50 ppm or more, more preferably 100 ppm or more, even more preferably 150 ppm or more, and particularly preferably 200 ppm or more. On the other hand, when the carboxylic acid content B1 is 1000 ppm or less, the thermal stability of the resulting dry pellets is further suppressed. The carboxylic acid content B1 is more preferably 700 ppm or less, more preferably 500 ppm or less, even more preferably 300 ppm or less, and particularly preferably 250 ppm or less.

[0066] There is a limit to the dehydration of hydrous pellets using an extruder, and the intermediate pellets having a moisture content (A2) in the above range are obtained using the extruder, and then the intermediate pellets are dried in the drying step to efficiently produce the dried pellets. The intermediate pellets are subjected to the drying step. In the present invention, the intermediate pellets having a moisture content (A2) of 1.5 to 20% by weight are dried in a nitrogen atmosphere in the drying step to obtain the dried pellets having a moisture content (A3) of 1% by weight or less.

[0067] Conventionally, a method of incorporating a carboxylic acid into EVOH has been known as a method for suppressing coloration caused by deterioration of EVOH during melt molding. Among them, a method of melt-kneading EVOH water-containing pellets with a carboxylic acid in an extruder and then discharging the mixture is known to be a useful method for reducing production costs because the addition of the carboxylic acid and dehydration can be performed in the extruder. However, a large amount of carboxylic acid is volatilized when the molten composition discharged from the extruder is dried.

[0068] Therefore, the present inventors have conducted extensive research to reduce the amount of carboxylic acid used and the amount of volatilization when producing dried pellets containing EVOH, and as a result, have found that when the moisture content (A2) of the intermediate pellets before drying is within a predetermined range, there is a difference in the amount of carboxylic acid remaining between the case where the drying is performed in air (atmosphere) and the case where the drying is performed in a nitrogen atmosphere. The cause of this is not clear, but the following is considered. It is considered that the size and number of pores contained in the intermediate pellets affect the volatilization of carboxylic acid during drying. The pores contained in intermediate pellets having a moisture content (A2) below the lower limit are small and few in number, so that the carboxylic acid is difficult to volatilize, and it is considered that there is no significant difference in the amount of carboxylic acid remaining between the case where the drying is performed in air and the case where the drying is performed in a nitrogen atmosphere. On the other hand, the pores contained in intermediate pellets having a moisture content (A2) exceeding the upper limit are large and many in number, so that the carboxylic acid is easily volatilized, and in this case, it is considered that there is no significant difference in the amount of carboxylic acid remaining between the case where the drying is performed in air and the case where the drying is performed in a nitrogen atmosphere.

[0069] On the other hand, since nitrogen is less likely to permeate pellets than air, when the moisture content (A2) of the intermediate pellets is within the above range, it is considered that the carboxylic acid is more likely to remain in the pellets by drying under a nitrogen atmosphere, which makes it possible to reduce the amount of acetic acid used and the amount of acetic acid volatilized into the atmosphere.

[0070] The drying method used in the drying step is not particularly limited as long as it is a method carried out under a nitrogen atmosphere. A method using a stationary dryer or a fluidized dryer is preferred, and a multi-stage drying step in which several drying methods are combined can also be adopted. The nitrogen concentration in the dryer is preferably 95% or more by volume, more preferably 99% or more. The drying temperature is preferably 107 to 130°C. The temperature is more preferably 120°C or less. The drying time is preferably 5 to 20 hours. The drying time is more preferably 7 hours or more, and even more preferably 10 hours or more. On the other hand, by setting the drying time to 20 hours or less, coloration of the obtained dried pellets is further reduced. The drying temperature is more preferably 17 hours or less, and even more preferably 14.5 hours or less.

[0071] In the drying step, the intermediate pellets are dried as described above to obtain dried pellets having a moisture content (A3) of 1% by weight or less, preferably 0.5% by weight or less.

[0072] The carboxylic acid content B2 of the dry pellets is preferably 30 to 1000 ppm. When the carboxylic acid content B2 is 30 ppm or more, coloration of the dry pellets is further suppressed. The carboxylic acid content B2 is more preferably 50 ppm or more, further preferably 100 ppm or more, and even more preferably 150 ppm or more. On the other hand, when the carboxylic acid content B2 is 1000 ppm or less, the thermal stability of the dry pellets is further suppressed. The carboxylic acid content B2 is more preferably 500 ppm or less, further preferably 400 ppm or less, even more preferably 300 ppm or less, and particularly preferably 200 ppm or less.

[0073] In the production method of the present invention, it is also preferable that the ratio (B2 / B1) of the carboxylic acid content B1 (ppm) of the intermediate pellet to the carboxylic acid content B2 (ppm) of the dried pellet is 0.70 or more. It is also preferable that the ratio (B2 / B3) of the carboxylic acid content B2 (ppm) of the dried pellet obtained by drying the intermediate pellet under a nitrogen atmosphere to the carboxylic acid content B3 (ppm) of the intermediate pellet dried in the same manner as the dried pellet except that the intermediate pellet was dried under air atmosphere is 1.10 or more, and more preferably 1.12 or more.

[0074] The proportion of EVOH in the dry pellets is preferably 90% by weight or more, more preferably 95% by weight or more, and even more preferably 99% by weight or more. The proportion of EVOH and additives in the dry pellets is preferably 90% by weight or more, more preferably 95% by weight or more, and even more preferably 99% by weight or more, and it is particularly preferred that the dry pellets consist essentially of EVOH and additives.

[0075] The dried pellets thus obtained can be melt-molded into various articles such as films, sheets, containers, pipes, fibers, etc., and can also be used for a variety of other purposes. EXAMPLES

[0076] The present invention will now be described in more detail with reference to examples. In the examples and comparative examples described later, analyses and evaluations were carried out by the methods shown below.

[0077] 1) Measurement of the moisture content of pellets Using a halogen moisture content analyzer, the moisture content of the pellets (EVOH moisture-containing pellets fed to the extruder, intermediate pellets before drying) used in the examples and comparative examples or the obtained dried pellets containing EVOH was measured by a heat-dry weight measurement method under the conditions of a drying temperature of 180°C, a drying time of 18 minutes, and a sample amount of 10 g. The moisture content of the pellets was calculated using the following formula. Moisture content (weight %) = (weight before drying - weight after drying) / weight before drying x 100

[0078] 2) Determination of carboxylic acids In the examples and comparative examples, 20 g of the intermediate pellets before drying or the dried pellets containing the obtained EVOH were added to 100 mL of ion-exchanged water and extracted by heating at 95°C for 6 hours. The obtained extract was neutralized and titrated with 0.01 mol / L sodium hydroxide solution using phenolphthalein as an indicator to calculate the carboxylic acid content relative to the total solid content in the intermediate pellets or the dried pellets containing EVOH. (B2 / B1) indicates the ratio of the carboxylic acid content B1 (ppm) of the intermediate pellets to the carboxylic acid content B2 (ppm) of the dried pellets, and (B3 / B2) indicates the ratio of the acetic acid content B2 of the dried pellets obtained by drying the intermediate pellets in nitrogen to the acetic acid content B3 of the dried pellets obtained by drying the intermediate pellets in air (atmosphere).

[0079] 3) Foaming during melt molding Using the dried pellets obtained in the examples and comparative examples, film formation was carried out under the following conditions to form a single layer film of 20 μm. The occurrence of lumps, bubbles, and holes in the film due to foaming of water in the film was evaluated as follows. The number of lumps in the film was counted per 1.0 m. 2 The number of hits was converted and judged as follows. (Film forming conditions) Extrusion temperature: Feeding section / Compression section / Metering section / Die =170 / 210 / 210 / 210℃ Screw rotation speed: 40 rpm Take-up roll temperature: 80℃ (evaluation) A: Film 1.0m 2 Medium, less than 20 B: Film 1.0m 2 Medium, 20 to less than 60 C: Film 1.0m 2 Medium, 60 pieces or more

[0080] 4) Coloring The YI value of the dry pellets containing EVOH was measured using a color difference meter (Lab Scan), and the coloring of the pellets was evaluated according to the following criteria. (evaluation) A: YI<15 B: 15≦YI<20 C:20≦YI

[0081] Example 1 EVOH hydrous pellets at 60°C, containing 82% by weight of EVOH with a water content (A1) of 18% by weight, an ethylene unit content of 32 mol%, and a saponification degree of 99.9 mol%, were fed into a twin-screw extruder. The cylinder configuration and screw configuration of the twin-screw extruder are shown in Figure 1. The cylinder temperature T1 (the highest temperature at a position downstream of the raw material supply section 1) was set to 100°C, and an additive consisting of an aqueous solution of acetic acid / sodium acetate / phosphoric acid was added from the trace component addition section 3 at the tip of the discharge side shown in Figure 1. The amount of EVOH hydrous pellets fed per unit time was 8.0 kg / hr (including the weight of water contained), and the amount of additives fed per unit time was 0.42 L / hr. The additive was an aqueous solution containing 3.9 g / L of acetic acid, 3.2 g / L of sodium acetate, and 0.15 g / L of phosphoric acid. The specifications of the twin-screw extruder are shown below. Type Twin screw extruder L / D 45.5 Diameter 30mmΦ Screw Same direction full intermeshing type Die diameter 3.0mmΦ

[0082] The twin-screw extruder shown in Figure 1 is composed of a raw material supply section 1, a draining section 2, and a trace component adding section 3, with a draining slit 5 provided in the draining section 2. The screw is a combination of a full-flight screw 6, a reverse-flight screw 7, and a seal ring 8 as shown in Figure 1. Furthermore, a temperature sensor 4 is provided at the end of the cylinder.

[0083] The temperature T0 of the molten composition in the twin-screw extruder was 140°C. The temperature T0 was measured using a temperature sensor 4 arranged at the end of the cylinder in contact with the molten composition. The molten composition discharged from the twin-screw extruder was cut with a hot cutter to obtain spherical intermediate pellets with a diameter of 5 to 6 mm. The moisture content (A2) of the intermediate pellets immediately after the pellets were obtained was measured according to the method described in 1) above, and was 5.1% by weight. The acetic acid content (B1) at this time was measured and was 236 ppm. As a result of drying at 110°C for 12 hours using a nitrogen dryer (nitrogen flow rate: 3.0 L / min, nitrogen concentration: volume ratio 99% or more), the moisture content (A3) of the dried pellets containing EVOH after drying was 0.2% by weight, the acetic acid content (B2) was 185 ppm, the content of the phosphoric acid compound was 6 ppm in terms of phosphoric acid, and the content of the alkali metal salt (sodium acetate) was 202 ppm in terms of metal (sodium). The evaluation results are shown in Table 1.

[0084] Examples 2 to 10, Comparative Examples 1 to 15 Dried pellets were produced and evaluated in the same manner as in Example 1, except that the ethylene unit content and degree of saponification of the EVOH used in the EVOH hydrous pellets, the moisture content (A1), the composition of additives, the amounts of the EVOH hydrous pellets and additives added per unit time, and the drying conditions were as shown in Table 1. The results are shown in Table 1. In Example 6 and Comparative Example 11, EVOH hydrous pellets having a moisture content of 40% by weight and an alcohol content of 1% by weight or less were pre-dried using a hot air dryer at 110°C for 2 hours to adjust the moisture content (A1) to 18% by weight, and then fed to the extruder.

[0085] [Table 1] [Explanation of symbols]

[0086] 1 Raw material supply section 2 Deliquid section 3 Trace component addition section 4 Temperature Sensor 5 Dehydration slit 6 Full Flight Screw 7 Reverse Flight Screw 8 Seal ring

Claims

1. a melt-kneading step of supplying hydrous pellets of an ethylene-vinyl alcohol copolymer having an ethylene unit content of 20 to 50 mol% and a saponification degree of 99 mol% or more and an additive containing a carboxylic acid to an extruder, and then melt-kneading the pellets to obtain a molten composition; A pelletizing step of cutting the molten composition discharged from the extruder to obtain intermediate pellets; and A method for producing dry pellets containing an ethylene-vinyl alcohol copolymer, comprising a drying step of drying the intermediate pellets to obtain dry pellets, In the melt-kneading step, the water-containing pellets having a water content (A1) of 5 to 22% by weight are supplied to the extruder, In the drying step, the intermediate pellets having a moisture content (A2) of 1.5 to 20% by weight are dried under a nitrogen atmosphere to obtain the dried pellets having a moisture content (A3) of 1% by weight or less.

2. The method for producing dry pellets containing an ethylene-vinyl alcohol copolymer according to claim 1, wherein the additive further comprises at least one selected from the group consisting of phosphoric acid, a boron compound, an alkali metal salt, and an alkaline earth metal salt.

3. The method for producing dried pellets containing an ethylene-vinyl alcohol copolymer according to claim 1 or 2, wherein the water-containing pellets having a moisture content (A1) adjusted to 5 to 22% by weight by carrying out a preliminary drying step are supplied to the extruder.

4. The method for producing dry pellets containing an ethylene-vinyl alcohol copolymer according to claim 1 or 2, wherein the moisture content (A2) of the intermediate pellets is 5 to 17% by weight.

5. The method for producing dried pellets containing an ethylene-vinyl alcohol copolymer according to claim 1 or 2, wherein in the drying step, the intermediate pellets are dried at 107 to 130° C. for 5 to 20 hours.

6. The method for producing dry pellets containing an ethylene-vinyl alcohol copolymer according to claim 1 or 2, wherein the ratio (B2 / B1) of the carboxylic acid content B1 (ppm) of the intermediate pellets to the carboxylic acid content B2 (ppm) of the dry pellets is 0.70 or more.

7. 3. The method for producing dried pellets containing an ethylene-vinyl alcohol copolymer according to claim 1 or 2, wherein a ratio (B2 / B3) of a carboxylic acid content B2 (ppm) of the dried pellets to a carboxylic acid content B3 (ppm) of the intermediate pellets dried in the same manner as the dried pellets except that the intermediate pellets are dried under air is 1.10 or more.

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