Method for producing ethylene-vinyl alcohol copolymer resin composition

Abstract

The present invention provides a method for producing an ethylene-vinyl alcohol copolymer resin composition in which an additive and an ethylene-vinyl alcohol copolymer hydrous pellet at 0-80°C are introduced into an extruder (X) and are melt-kneaded, wherein: the additive includes at least one type of additive selected from the group consisting of carboxylic acids, boron compounds, phosphate compounds, alkali metal salts, and alkaline-earth metal salts; the additive is added to the ethylene-vinyl alcohol copolymer inside the extruder (X); the temperature T0 of the molten product in the extruder (X) is 70-180°C; the cylinder temperature T1 of the extruder (X) is 65-175°C; T0 and T1 satisfy formula (1): 5≤T0-T1≤100; the water content of the hydrous pellet that is introduced into the extruder (X) is 20-60 mass%; and the water content of the hydrous resin composition immediately after discharge from the extruder (X) is 10-35 mass%. This production method makes it possible to highly efficiently dehydrate an ethylene-vinyl alcohol copolymer hydrous pellet and to obtain an EVOH resin composition with less foaming and with a good hue, in a method in which the ethylene-vinyl alcohol copolymer hydrous pellet and a minor component are melt-kneaded in an extruder and then discharged.

Description

[Technical Field]

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

[0002] Ethylene-vinyl alcohol copolymer (hereinafter sometimes referred to as EVOH) is a polymeric material with excellent oxygen barrier properties, aroma retention, oil resistance, anti-static properties, mechanical strength, etc., and is widely used after being molded into 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 an alcohol solution of EVOH obtained by saponification include a method in which water is added to a methanol solution of EVOH in an amount such that EVOH does not precipitate, to produce a methanol / water mixed solution of EVOH, and this is extruded into water or a methanol / water mixed solution having a lower methanol concentration than the mixed solution to precipitate in the form of strands, which are then cut to obtain hydrous EVOH pellets (Patent Document 1); and a method in which an alcohol solution of EVOH is introduced into an apparatus, brought into contact with water in the apparatus to replace the alcohol in the solution with water, and the hydrous EVOH composition discharged from the apparatus is cut to obtain hydrous EVOH pellets (Patent Document 2).

[0004] While there are various methods for molding EVOH pellets into various molded products, the most common is melt molding using an extruder, such as extrusion molding or injection molding. The molding process begins by feeding the raw EVOH pellets into the extruder's hopper. However, because EVOH molding typically requires a melt temperature of 200°C or higher, additive-free EVOH is prone to degradation during melt molding, resulting in fisheyes and lumps in the product, reducing its quality.

[0005] To solve this problem, a method of adding trace components such as acidic substances and metal salts to EVOH is known. As an example, Patent Document 2 describes a method in which EVOH water-containing pellets and trace components are melt-kneaded in an extruder and then discharged in order to improve qualities such as thermal stability. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-239316 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-284811 Summary of the Invention [Problem to be solved by the invention]

[0007] The method of melt-kneading EVOH hydrous pellets and minor components in an extruder and then discharging them is a useful method that can reduce production costs because the addition of the minor components and dehydration can be performed in the extruder. However, the hydrous EVOH resin composition pellets discharged by the above-mentioned conventional method may foam, and when the dried EVOH resin composition containing foamed pellets is molded, the discharge of the molten resin may become unstable, making it difficult to perform stable molding.

[0008] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a production method in which hydrous EVOH pellets and minor components are melt-kneaded in an extruder and then discharged, which can dehydrate the hydrous EVOH pellets with high efficiency and produce an EVOH resin composition with little foaming and good color. [Means for solving the problem]

[0009] The above-mentioned problem is solved by a method for producing an EVOH resin composition, which comprises supplying EVOH hydrous pellets at 0 to 80°C and additives to an extruder (X) and melt-kneading them, wherein the additives comprise at least one selected from the group consisting of carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts, and the additives are added to the EVOH in the extruder (X), and the temperature T0 of the melt in the extruder (X) is 70 to 180°C, the cylinder temperature T1 of the extruder (X) is 65 to 175°C, and T0 and T1 satisfy the following formula (1), 5≦T0-T1≦100 (1) The problem is solved by providing a production method in which the water-containing pellets supplied to the extruder (X) have a water content of 20 to 60 mass %, and the water-containing resin composition immediately after being discharged from the extruder (X) has a water content of 10 to 35 mass %.

[0010] In this case, the additive is preferably an aqueous solution containing at least one selected from the group consisting of carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts. [Effects of the Invention]

[0011] According to the production method of the present invention, in which hydrous EVOH pellets and minor components are melt-kneaded in an extruder and then discharged, it is possible to dehydrate the hydrous EVOH pellets with high efficiency, and to obtain an EVOH resin composition with little foaming and good color. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing the cylinder configuration and screw configuration of a twin-screw extruder (extruder (X)) in Examples 1 to 8 and Comparative Examples 1 to 3 and 6. [Figure 2] FIG. 1 is a diagram showing the cylinder configuration and screw configuration of a twin-screw extruder (extruder (X)) in Comparative Example 4. [Figure 3] FIG. 1 is a diagram showing the cylinder configuration and screw configuration of a twin-screw extruder (extruder (X)) in Comparative Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention is a method for producing an EVOH resin composition, which comprises supplying EVOH hydrous pellets at 0 to 80°C and additives to an extruder (X) and melt-kneading them, wherein the additives comprise at least one selected from the group consisting of carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts, and the additives are added to the EVOH in the extruder (X), and the temperature T0 of the melt in the extruder (X) is 70 to 180°C, the cylinder temperature T1 of the extruder (X) is 65 to 175°C, and T0 and T1 satisfy the following formula (1), 5≦T0-T1≦100 (1) In this production method, the moisture content of the hydrous EVOH pellets fed to the extruder (X) is 20 to 60% by mass, and the moisture content of the hydrous resin composition immediately after discharge from the extruder (X) is 10 to 35% by mass. This production method enables highly efficient dehydration of the hydrous EVOH pellets, resulting in an EVOH resin composition with minimal foaming and good color. While the reason for this is unclear, it is presumed that by setting the moisture content of the hydrous EVOH pellets fed to the extruder (X) and T0-T1 within appropriate ranges, the shear and melting state of the hydrous EVOH pellets in the extruder is specific, resulting in uniform and appropriate dispersion of the water contained in the discharged hydrous EVOH, making foaming less likely to occur. This effect of achieving high dehydration efficiency while suppressing foaming is first realized under the production conditions of the present invention and was first discovered through extensive research by the present inventors. Furthermore, the present inventors have found that supplying an additive to the extruder (X) makes the situation more prone to foaming compared to when no additive is supplied. Surprisingly, even under such conditions, the production method of the present invention exhibits the effect of suppressing foaming while realizing high dehydration efficiency.

[0014] Here, the term "water-containing resin composition" or "water-containing EVOH resin composition" as used herein means a resin composition in a water-containing state containing additives that is discharged from the extruder (X), and the term "EVOH resin composition" means a dried resin composition obtained by drying the water-containing EVOH resin composition.

[0015] In the present invention, a method is used in which EVOH hydrous pellets and trace components are melt-kneaded in an extruder (X) and then discharged. However, other known methods for obtaining EVOH resin composition pellets containing added trace components include (1) a method in which EVOH hydrous pellets are immersed in an aqueous solution containing the trace components, followed by dewatering and drying. However, the addition method (1) requires a treatment bath or treatment tower for immersing the EVOH hydrous pellets, and the energy consumption for drying the treated EVOH hydrous resin composition pellets is significant, resulting in high production costs. Therefore, the method of adding trace components in the production method of the present invention can be said to be more efficient than other addition methods.

[0016] The EVOH hydrous pellets used in the present invention are pellets containing EVOH and water. The water content of the hydrous pellets may be 20 to 60% by mass, and the EVOH content may be 40 to 80% by mass. As described below, the EVOH hydrous pellets may contain other components such as alcohols and alkali metal salts.

[0017] 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 content in the EVOH is preferably 20 to 60 mol%. From the viewpoint of improving melt moldability, the ethylene content is preferably 23 mol% or more, more preferably 25 mol% or more, and even more preferably 30 mol% or more. On the other hand, from the viewpoint of improving gas barrier properties, the ethylene content is preferably 55 mol% or less, more preferably 50 mol% or less.

[0018] The method for producing the EVOH will be specifically described below. As mentioned 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. The copolymerization may be either continuous or batchwise, and the polymerization conditions for solution polymerization are as follows:

[0019] 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.

[0020] 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.

[0021] Examples of initiators that can be used in the polymerization include azonitrile initiators such as 2,2-azobisisobutyronitrile, 2,2-azobis-(2,4-dimethylvaleronitrile), 2,2-azobis-(4-methoxy-2,4-dimethylvaleronitrile), and 2,2-azobis-(2-cyclopropylpropionitrile), and organic peroxide initiators such as isobutyryl peroxide, cumyl peroxy neodecanoate, diisopropyl peroxycarbonate, di-n-propyl peroxydicarbonate, t-butyl peroxy neodecanoate, lauroyl peroxide, benzoyl peroxide, and t-butyl hydroperoxide.

[0022] 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 vinylsilane compound as a copolymerization component. Examples of vinylsilane compounds include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxyethoxy)silane, and γ-methacryloxypropylmethoxysilane. Of these, vinyltrimethoxysilane and vinyltriethoxysilane are preferred.

[0023] 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 mass, more preferably 20 to 70% by mass.

[0024] 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-pentene, 5-acyloxy-1-hex ... Polymerization can also be performed in the presence of small amounts of alkenes having an ester group, 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, as well as their anhydrides, salts, and mono- or dialkyl esters; nitriles, such as acrylonitrile and methacrylonitrile; amides, such as acrylamide and methacrylamide; olefin sulfonic acids, such as ethylene sulfonic acid, allyl sulfonic acid, and methallylsulfonic acid, or their salts; alkyl vinyl ethers, vinyl ketone, N-vinylpyrrolidone, vinyl chloride, and vinylidene chloride. The content of other monomer units in the EVOH other than ethylene, vinyl ester, and vinyl alcohol is preferably 20 mol% or less, and in some cases, 10 mol% or less, 5 mol% or less, 3 mol% or less, 1 mol% or less, or 0.1 mol% or less is preferred. The EVOH may not contain the other monomer units.

[0025] After polymerization for a predetermined time has reached a predetermined polymerization rate, a polymerization inhibitor is added as necessary, unreacted ethylene gas is evaporated and removed, and then unreacted vinyl ester is purged. For example, a method for purging the unreacted vinyl ester may be employed in which the polymerization solution from which ethylene has been removed is continuously fed at a constant rate from the top of a column packed with Raschig rings, vapor of an organic solvent, preferably an alcohol having a boiling point of 100°C or less, and most preferably methanol, is blown into the bottom of the column, a mixed vapor of the organic solvent and unreacted vinyl ester is distilled from the top of the column, and the copolymer solution from which unreacted vinyl ester has been removed is taken out from the bottom of the column.

[0026] An alkali catalyst is added to the copolymer solution from which the unreacted vinyl ester has been removed, and the vinyl ester component in the copolymer is saponified. The saponification method can be either continuous or batchwise. Examples of alkali catalysts that can be used include sodium hydroxide, potassium hydroxide, and alkali metal alcoholates. Methanol is preferred as the solvent for saponification. For example, the saponification conditions are as follows: (1) Concentration of ethylene-vinyl ester copolymer in the solution: 10 to 50% by mass (2) Reaction temperature: 30 to 150°C (3) Amount of catalyst used: 0.005 to 0.6 equivalents (per vinyl ester component) (4) Time (average residence time in the case of continuous type): 10 minutes to 6 hours

[0027] Generally, when saponification is carried out in a continuous system, methyl acetate produced by saponification can be removed more efficiently, and therefore a resin with a higher degree of saponification can be obtained with a smaller amount of catalyst than in a batch system. Furthermore, in the case of a continuous system, saponification must be carried out at a higher temperature to prevent the precipitation of EVOH produced by saponification. Therefore, in a continuous system, it is preferable to use a reaction temperature and catalyst amount within the following ranges: Reaction temperature: 70 to 150°C. Amount of catalyst used: 0.005 to 0.1 equivalents (per vinyl ester component).

[0028] The degree of saponification of the resulting EVOH varies depending on the purpose, but is preferably 80 mol % or more of the vinyl ester component, more preferably 95 mol % or more, even more preferably 98 mol % or more, and particularly preferably 99 mol % or more. The degree of saponification can be adjusted as desired depending on the conditions.

[0029] As described above, when producing EVOH pellets that have particularly excellent melt stability and good long-run properties, the saponification degree of the EVOH is preferably 99.7 mol % or more, more preferably 99.8 mol % or more, even more preferably 99.9 mol % or more, and particularly preferably 99.95 mol % or more. To obtain such an EVOH, it is preferable to further adjust the saponification conditions as follows.

[0030] A continuous process is preferred as a method for obtaining EVOH with a high saponification degree of 99.9 mol% or more. Examples of continuous processes for obtaining a high saponification degree include adding a catalyst from multiple locations in the saponification reaction tower, increasing the amount of catalyst used, and increasing the amount of methanol blown into the bottom of the saponification reaction tower. Examples of batch processes for obtaining EVOH with a high saponification degree of 99.9 mol% or more include adding the catalyst in multiple batches, increasing the amount of catalyst used, and increasing the amount of methanol vapor or nitrogen gas blown into the saponification reaction tank.

[0031] The saponification step yields a solution or paste containing EVOH. The saponification reaction EVOH 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 saponification reaction EVOH is washed with ion-exchanged water or the like containing almost no metal ions or chloride ions, some catalyst residues such as sodium acetate and potassium acetate may remain in the EVOH.

[0032] The EVOH solution or paste thus obtained typically contains 50 parts by mass or more of an alcohol having a boiling point of 100°C or less per 100 parts by mass of EVOH. The alcohol content is preferably 70 parts by mass or more, more preferably 80 parts by mass or more. The alcohol content is preferably 1000 parts by mass or less, more preferably 500 parts by mass 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.

[0033] Next, the obtained EVOH solution or paste is hydropelletized. The hydropelletization method is not particularly limited, and examples include a method in which the EVOH solution or paste is cooled and solidified, and then cut, or a method in which the EVOH solution or paste is melt-kneaded in an extruder, then discharged, and then cut. Specific examples of EVOH cutting methods include a method in which EVOH is extruded into strands 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.

[0034] Examples of methods for cooling and solidifying the EVOH solution or paste after the saponification reaction and cutting it include a method in which an alcohol / water mixed solution of EVOH is extruded into the solidifying liquid, precipitated into strands, and then cut. A preferred post-treatment method for the EVOH solution after the saponification reaction involves supplying a mixed vapor of solvent and water from the bottom of a tower vessel and supplying the EVOH solution from a position above the supply position of the mixed vapor, thereby replacing a portion of the solvent present in the supplied EVOH solution with water and producing a high-concentration EVOH solution. The EVOH concentration in the EVOH solution supplied to the tower vessel is preferably 15 to 50% by mass, more preferably 25 to 40% by mass. It is also preferred that the ratio of the supply rate of the EVOH solution to the supply rate of the mixed vapor (solution supply rate / steam supply rate) be 100 / 400 to 100 / 8 by mass. Furthermore, it is preferred that the water content in the mixed vapor be 20 to 70% by mass. The solvent used for the mixed vapor is preferably an alcohol having a boiling point of 130° C. or less, and examples of such alcohol include alcohols such as methanol, ethanol, propanol, butanol, etc. Alcohols having a boiling point of 100° C. or less are more preferred, and among these, methanol is preferred because it is easily available, inexpensive, has a low boiling point, and is easy to handle.

[0035] When an EVOH solution is extruded into strands and pelletized, the coagulation liquid used for precipitation may be water or a water / alcohol mixed solvent, aromatic hydrocarbons such as benzene, ketones such as acetone and methyl ethyl ketone, ethers such as dipropyl ether, or organic acid esters such as methyl acetate, ethyl acetate, and methyl propionate. However, water or a water / alcohol mixed solvent is preferred for ease of handling. Examples of alcohols that can be used include methanol, ethanol, and propanol, with methanol being industrially preferred. The mass ratio of the coagulation liquid to the EVOH strands (coagulation liquid / EVOH strands) is not particularly limited, but is preferably 50 to 10,000. A mass ratio within this range makes it possible to obtain hydrous EVOH pellets with a uniform size distribution.

[0036] The lower limit of the temperature at which the EVOH solution is brought into contact with the coagulation liquid (the bath temperature during pelletizing) is preferably -10°C, more preferably 0°C. Meanwhile, the upper limit is preferably 40°C, more preferably 20°C, even more preferably 15°C, and even more preferably 10°C. The EVOH solution is extruded into the coagulation liquid in the form of strands through a nozzle of any shape. The shape of the nozzle is not particularly limited, but a cylindrical shape is preferred. In this way, the EVOH solution is extruded in the form of strands through the nozzle. In this case, the strand does not necessarily have to be a single strand; any number between several and several hundred strands can be extruded. Next, the extruded EVOH in the form of strands is cut after sufficient coagulation has progressed, to obtain hydrous EVOH pellets. Thereafter, if necessary, washing may be performed as described below. The size of such pellets can be, for example, 1 mm to 10 mm in diameter and 1 mm to 10 mm in length for cylindrical pellets, or 1 mm to 10 mm in diameter for spherical pellets.

[0037] When the EVOH solution or paste is melt-kneaded in an extruder and then discharged and cut, a suitable post-saponification process for the EVOH solution or paste involves supplying steam to a tower vessel from the bottom and supplying the EVOH solution or paste from a position above the steam supply point, thereby removing the solvent (alcohol) present in the supplied EVOH solution or paste together with the steam, and extracting a hydrous EVOH containing 0 to 10 parts by mass of the solvent (alcohol) and 10 to 1,000 parts by mass of water per 100 parts by mass of EVOH from the vessel. If the amount of steam introduced is too small, the solvent (alcohol) removal efficiency will be poor, while if it is too large, it will be cost-effective. Therefore, the amount of steam introduced is preferably 0.3 to 30 times, more preferably 0.5 to 10 times, and even more preferably 0.7 to 5 times the amount of EVOH solution or paste introduced. The water vapor to be brought into contact with the EVOH solution or paste may contain 10 parts by mass or less of a solvent (alcohol) per 100 parts by mass of water vapor. However, in order to efficiently remove the solvent (alcohol), it is preferable that the water vapor does not contain any solvent (alcohol).

[0038] In this case, the EVOH solution or paste comes into direct contact with water vapor in the container, gradually reducing the solvent (alcohol) content. During this time, the EVOH remains in a swollen paste state, allowing it to be removed from the container while maintaining its fluidity and without gelling. EVOH dissolves in a methanol / water mixed solvent at, for example, a temperature of about 60-70°C under normal pressure, but does not dissolve in water alone. However, in the presence of pressurized water vapor at a temperature of, for example, 100°C or higher, EVOH can maintain its fluidity even when it contains essentially only water.

[0039] The hydrous EVOH discharged from the vessel preferably contains 0 to 10 parts by mass of the solvent (alcohol) and 10 to 1,000 parts by mass of water per 100 parts by mass of EVOH, and is discharged from the vessel in a fluidized state. The solvent (alcohol) content of the hydrous EVOH discharged from the vessel is preferably 0 to 5 parts by mass, more preferably 0 to 1 part by mass, and even more preferably 0 to 0.1 part by mass. A low solvent (alcohol) content prevents the solvent (alcohol) from volatilizing in subsequent processes, thereby preserving the working and surrounding environments. Furthermore, when washing saponification catalyst residues, etc., pellets are less likely to stick together even if the temperature of the washing solution is increased, allowing the washing temperature to be increased, thereby increasing the washing speed. The water content of the hydrous EVOH discharged from the vessel is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 50 parts by mass or more. A water content of 10 parts by mass or more tends to improve the fluidity within the vessel. On the other hand, the content of water discharged from the vessel is preferably 1000 parts by mass or less, more preferably 500 parts by mass or less, and even more preferably 200 parts by mass or less. When the content of water is 1000 parts by mass or less, uniform pellets tend to be produced in the pellet production step described below.

[0040] The hydrous EVOH discharged from the vessel can be directly cut in a molten state and the cut pellets can be water-cooled to produce hydrous EVOH pellets, for example, by extruding the hydrous EVOH in a molten state into a cooling liquid to form strands, solidifying the strands, and then cutting them. 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 (X)), directly cut the hydrous EVOH 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 resulting hydrous EVOH can also be adjusted by adjusting the conditions of the extruder. Suitable examples of methods for directly cutting the hydrous EVOH in a molten state include the hot-cut method and the underwater-cut method. From the viewpoint of ease of handling of pellets, the nozzle diameter is preferably 2 to 5 mmφ (φ is diameter; the same applies below). The size of the produced pellets can be, for example, a diameter of 1 mm to 10 mm in the case of spherical (or nearly spherical) pellets, and a diameter of 1 mm to 10 mm in the case of cylindrical pellets and a length of 1 mm to 10 mm. Note that cylindrical pellets are obtained when extruding into a strand, solidifying, and then cutting, whereas spherical (or nearly spherical) pellets are obtained when cutting directly in a molten state. This method of cutting in a molten state is superior to the method of extruding into a solidifying liquid, precipitating into a strand, and then cutting, in that it does not require consideration of the take-up speed required to stably form strands, and therefore is more productive. For example, even in cases where strand formation is difficult, such as with EVOH with a low ethylene content, cutting in a molten state facilitates the production of EVOH hydrous pellets.

[0041] The coolant used for the water cooling is water, but may contain a small amount of alcohol. The temperature of the coolant 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 coolant is more preferably 0 to 30°C. Furthermore, the temperature of the molten water-containing EVOH is more preferably 110 to 140°C.

[0042] The EVOH hydrous pellets thus obtained can be used as the EVOH hydrous pellets to be fed to the extruder (X). Alternatively, the EVOH hydrous pellets after undergoing the washing step described below can also be used as the EVOH hydrous pellets to be fed to the extruder (X). The proportion of EVOH in the resin constituting the EVOH hydrous pellets to be fed to the extruder (X) is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and it is particularly preferred that the EVOH hydrous pellets consist solely of EVOH. The proportion of EVOH and water in the EVOH hydrous pellets is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and it is particularly preferred that the EVOH hydrous pellets consist solely of EVOH and water. Furthermore, when the EVOH hydrous pellets contain saponification catalyst residues, the proportion of EVOH, water, and saponification catalyst residues in the EVOH hydrous pellets is preferably 90 mass% or more, more preferably 95 mass% or more, and even more preferably 99 mass% or more, and it is particularly preferable that the EVOH hydrous pellets consist only of EVOH, water, and saponification catalyst residues.

[0043] The EVOH hydrous pellets obtained after the saponification reaction may contain alkali metal salts, which are saponification catalyst residues. However, if the content is large, quality problems such as discoloration may occur. Therefore, 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 immersion in water or an aqueous solution of an acid such as acetic acid, or a method of washing by supplying water or an aqueous solution of an acid into the extruder (X). In this washing method of immersion in water or an aqueous solution, either a batch-type treatment vessel or a continuous treatment vessel can be used. Among these, a method of continuously supplying pellets to a tower-type vessel and treating them is preferred from the viewpoint of productivity. The washing temperature is usually in the range of 10 to 80°C. A higher washing temperature is preferable from the viewpoint of improving washing efficiency, but an excessively high temperature is undesirable because it causes fusion between the hydrous pellets. 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.

[0044] The content of alkali metal salts in the washed EVOH hydrous pellets is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.1% by mass or less, even more preferably 0.05% by mass or less, and particularly preferably 0.03% by mass or less, calculated as metal.

[0045] The obtained EVOH hydrous pellets may be subjected to a dehydration step or the like to adjust the moisture content. The dehydration method is not particularly limited, but examples thereof include centrifugal dehydration.

[0046] The method for producing EVOH resin composition pellets of the present invention includes a step of supplying the EVOH hydrous pellets obtained by the above-mentioned method or the like and additives to an extruder (X) and melt-kneading them. The EVOH hydrous pellets used in this step have a temperature of 0 to 80°C and a moisture content of 20 to 60% by mass.

[0047] The temperature of the EVOH hydrous pellets fed to the extruder (X) is 0°C or higher, preferably 10°C or higher, and more preferably 25°C or higher. If the temperature of the EVOH hydrous pellets fed to the extruder (X) is lower than 0°C, problems with the feedability of the EVOH hydrous pellets are likely to occur, the EVOH does not completely melt, and the number of foamed pellets tends to increase and the color tends to deteriorate. Furthermore, the temperature of the EVOH hydrous pellets fed to the extruder (X) is 80°C or lower, preferably 75°C or lower, and more preferably 65°C or lower. If the temperature of the EVOH hydrous pellets fed to the extruder (X) exceeds 80°C, the moisture content of the EVOH hydrous pellets fed to the extruder (X) becomes unstable, the EVOH does not completely melt in the extruder (X), and the number of foamed pellets tends to increase and the color tends to deteriorate. The temperature of the EVOH hydrous pellets fed to the extruder (X) can be appropriately adjusted by the conditions before feeding them to the extruder (X).

[0048] The moisture content of the EVOH hydrous pellets fed to the extruder (X) must be 20 to 60% by mass. A moisture content of 20% by mass or more results in an EVOH resin composition with a good color. The moisture content is preferably 25% by mass or more, more preferably 30% by mass or more, and even more preferably 35% by mass or more. On the other hand, a moisture content of less than 60% by mass suppresses foaming of the EVOH resin composition. The moisture content is preferably 55% by mass or less, more preferably 45% by mass or less. The moisture content of the EVOH hydrous pellets can be adjusted by the conditions for pelletizing the hydrous EVOH after the saponification reaction, the conditions for washing the EVOH hydrous pellets, the conditions for dehydrating the EVOH hydrous pellets, etc.

[0049] The EVOH hydrous pellets fed to the extruder (X) may contain alcohol as long as the effects of the present invention are not impaired. The alcohol content in the EVOH hydrous pellets is usually 10% by mass or less, preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.1% by mass or less.

[0050] The additives fed to the extruder (X) include at least one selected from the group consisting of carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts. By incorporating such additives, an EVOH resin composition having a good color can be obtained.

[0051] Examples of carboxylic acids 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 in terms of cost and availability. When the EVOH resin composition contains a carboxylic acid, the content thereof is preferably 1 to 500 ppm based on the total solid content. The lower limit of the carboxylic acid content is more preferably 10 ppm or more, and even more preferably 50 ppm or more. The upper limit of the carboxylic acid content is preferably 400 ppm or less, and more preferably 300 ppm or less. The carboxylic acid content in the EVOH resin composition is measured by the method described in the Examples. A carboxylic acid content of 1 ppm or more tends to suppress discoloration during melt molding. A carboxylic acid content of 500 ppm or less tends to improve thermal stability.

[0052] Examples of boron compounds include, but are not limited to, boric acids, borate esters, borate salts, and boron hydrides. Specifically, examples of boric acids include orthoboric acid, metaboric acid, and tetraboric acid. Examples of borate esters include triethyl borate and trimethyl borate. Examples of borates include alkali metal salts, alkaline earth metal salts, and borax of the various boric acids listed above. Among these compounds, orthoboric acid (hereinafter simply referred to as boric acid) is preferred. When the EVOH resin composition contains a boron compound, its content is preferably 10 to 2000 ppm, more preferably 50 to 1000 ppm, calculated as boron, relative to the total solids content. A boron compound content within the above ranges tends to improve thermal stability and moldability. The contents of the boron compound, phosphate compound, alkali metal salt, or alkaline earth metal salt in the EVOH resin composition are measured by the methods described in the Examples.

[0053] Examples of phosphoric acid compounds 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 cation species is not particularly limited, but alkali metal salts and alkaline earth metal salts are preferred. Among these, 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 EVOH resin composition contains a phosphoric acid compound, its content is preferably 1 to 1,000 ppm, calculated as phosphorus element, relative to the total solids content. Addition within this range can suppress discoloration of molded products and the occurrence of gels and particles.

[0054] Examples of alkali metal salts include monovalent metal aliphatic carboxylates, aromatic carboxylates, phosphates, and metal complexes. Examples include sodium acetate, potassium acetate, sodium phosphate, lithium phosphate, sodium stearate, potassium stearate, and the sodium salt of ethylenediaminetetraacetic acid. Among these, sodium acetate, potassium acetate, and sodium phosphate are preferred. When the EVOH resin composition contains an alkali metal salt, the content thereof, calculated as the alkali metal element, relative to the total solids content is preferably 5 to 5,000 ppm, more preferably 20 to 1,000 ppm, and even more preferably 30 to 750 ppm. By including an alkali metal element at 5 ppm or more, interlayer adhesion and compatibility can be effectively improved, and by including an alkali metal element at 5,000 ppm or less, thermal stability during melt molding can be further enhanced.

[0055] 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 the EVOH resin composition contains an alkaline earth metal salt, its content is preferably 10 to 1,000 ppm, more preferably 20 to 500 ppm, calculated as alkaline earth metal element, relative to the total solids. When the alkaline earth metal content is 10 ppm or more, long-term run properties tend to be good. Furthermore, when it is 1,000 ppm or less, discoloration during resin melting tends to be suppressed.

[0056] The additives and the hydrous EVOH pellets are both fed into an extruder (X) and melt-kneaded to obtain a hydrous EVOH resin composition. FIG. 1 shows the cylinder and screw configurations of the twin-screw extruder used in Examples 1 to 8 and Comparative Examples 1 to 3 and 6. One embodiment of the melt-kneading method for the hydrous EVOH pellets and the additives will be specifically described with reference to FIG. 1. The extruder (X) used to melt-knead the hydrous EVOH pellets and the additives is preferably a twin-screw extruder, and more preferably a twin-screw extruder with the same screw rotation direction. Furthermore, an extruder with an L / D ratio of 15 or greater is preferred. A block cylinder or the like is used as the cylinder. A segmented type screw or the like is used as the screw. The screw rotation speed is preferably 320 to 1,000 rpm. Setting the screw rotation speed within this range facilitates adjustment of the temperature of the melt in the extruder (X). The screw rotation speed is more preferably 400 rpm or greater, even more preferably 500 rpm or greater, and particularly preferably 550 rpm or greater. On the other hand, the screw rotation speed is more preferably 800 rpm or less, further preferably 700 rpm or less, and particularly preferably 650 rpm or less.

[0057] The EVOH hydrous pellets are fed through a raw material feed section 1. Meanwhile, the additives are fed through a trace component feed section 3. In this manner, in the present invention, the additives are added to the hydrous EVOH in the extruder (X). This allows the additives to be uniformly mixed with the hydrous EVOH, resulting in a hydrous EVOH resin composition with a good color. The additives can be added individually, or multiple additives may be added simultaneously depending on the embodiment.

[0058] In the present invention, when the additives are added to the water-containing EVOH in the extruder (X), it is preferable that the additives be added to the extruder (X) at a position where the water-containing EVOH is in a molten state in the extruder (X), in order to fully exert the effects of the present invention. In particular, it is preferable that the additives be added to the water-containing EVOH in a water-containing and molten state. It is preferable that the extruder (X) has a kneading section, and it is particularly preferable that the additives be added to the kneading section of the extruder (X), in order to easily mix the additives uniformly with the water-containing EVOH.

[0059] The additives may be added in any form. Examples include adding the additives to the extruder (X) as a dry powder, as a paste impregnated with a solvent, as a suspension in a liquid, or as a solution dissolved in a solvent. However, from the viewpoints of controlling the amount added and uniformly dispersing the additives in the hydrous EVOH, the method of adding the additives as a solution dissolved in a solvent is particularly preferred. While the solvent is not particularly limited, water is preferred from the viewpoints of the solubility of the additives, cost benefits, ease of handling, and safety of the working environment. In other words, the additive is preferably an aqueous solution containing at least one selected from the group consisting of carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts. Furthermore, the additive is preferably added to the extruder (X) from one or more locations.

[0060] When the additive is added as a solution to the hydrous EVOH, the lower limit of the amount of the solution added is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 4 parts by mass or more, per 100 parts by mass of the dry mass of the EVOH. The upper limit of the amount of the solution added is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of the dry mass of the EVOH. When the amount of the solution added is 1 part by mass or more, the concentration of the solution tends to be easily adjusted, and the dispersibility of the additive in the hydrous EVOH tends to be improved. When the amount is 50 parts by mass or less, the moisture content of the resulting hydrous EVOH resin composition pellets tends to be easily controlled.

[0061] To the extruder (X), EVOH pellets different from the hydrous EVOH pellets may be simultaneously fed, as long as the effects of the present invention are not impaired. The EVOH pellets different from the hydrous EVOH pellets may be dry-blended in advance with the hydrous EVOH pellets and then fed into the raw material feed section 1 of the extruder (X), or may be simultaneously fed into the raw material feed section 1 without being dry-blended with the hydrous EVOH pellets, or may be fed separately from a raw material feed section different from the hydrous EVOH pellets (using an extruder (X) equipped with two raw material feed sections). Among these, the method of separately feeding the hydrous EVOH pellets and the EVOH pellets different from the hydrous EVOH pellets from different raw material feed sections is advantageous in terms of quantitative feeding and reducing quality variations.

[0062] Other components may also be added to the extruder (X) to the extent that the effects of the present invention are not impaired. Examples of other components include inorganic substances, plasticizers, lubricants, stabilizers, surfactants, colorants, antioxidants, UV absorbers, antistatic agents, desiccants, 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. However, from the viewpoints of uniformly dispersing the components in the resulting EVOH hydrous resin composition pellets and suppressing variations in the amount added, it is preferable to incorporate them as solutes in a solution or dispersoids in a dispersion. The solution and dispersion are preferably aqueous solutions and aqueous dispersions, respectively. When the other components are in a solid state, such as powder, they may be dry-blended with the EVOH hydrous pellets before being introduced into the raw material supply section 1 of the extruder (X), or they may be simultaneously introduced without dry-blending. Furthermore, when blending as a solute contained in a solution or a dispersoid contained in a dispersion, the trace component may be added from the trace component addition section 3 simultaneously with the additive of the present invention, or a new addition section may be provided and the other component may be added from a site separate from the additive.

[0063] The temperature T0 of the melt containing the EVOH, the additives, and water in the extruder (X) must be 70 to 180°C. If the temperature T0 is below 70°C, the fluidity of the water-containing EVOH is insufficient, resulting in gelation or blockage in the container. The temperature T0 is preferably 80°C or higher, more preferably 110°C or higher, even more preferably 125°C or higher, even more preferably 140°C or higher, and particularly preferably 155°C or higher. On the other hand, if the temperature T0 exceeds 180°C, the color of the EVOH resin composition deteriorates significantly. The temperature T0 is preferably 175°C or lower, more preferably 170°C or lower, and even more preferably 165°C or lower. Here, the temperature T0 of the melt refers to the temperature detected by a temperature sensor installed in the cylinder of the extruder (X) in contact with the melt, and the detection point is near the discharge port at the tip of the extruder (X). The temperature T0 can be adjusted by the temperature of the EVOH water-containing pellets fed to the extruder (X), the cylinder temperature of the extruder (X), the screw rotation speed of the extruder (X), and the like.

[0064] In the production method of the present invention, the cylinder temperature T1 of the extruder (X) must be 65 to 175°C. If the cylinder temperature T1 is less than 65°C, the fluidity of the hydrous EVOH may be insufficient, which may result in gelation or blockage in the container. The temperature T1 is preferably 70°C or higher, more preferably 75°C or higher, even more preferably 85°C or higher, even more preferably 90°C or higher, and particularly preferably 95°C or higher. On the other hand, if the temperature T1 is 175°C or lower, an EVOH resin composition with a good color tone can be obtained. The temperature T1 is preferably 165°C or lower, more preferably 150°C or lower, even more preferably 135°C or lower, even more preferably 130°C or lower, and particularly preferably 125°C or lower. Here, the cylinder temperature T1 refers to the highest temperature of the cylinder at a position downstream of the point where the raw material is supplied to the extruder (X).

[0065] In the production method of the present invention, the temperature T0 (°C) of the melt in the extruder (X) and the cylinder temperature T1 (°C) of the extruder (X) must satisfy the following formula (1). 5≦T0-T1≦100 (1)

[0066] In the present invention, as shown in the above formula (1), by setting the temperature T0 to be at least 5°C higher than the temperature T1, an EVOH resin composition with surprisingly little foaming can be obtained. T0 - T1 is preferably 15 or more, more preferably 25 or more, even more preferably 35 or more, even more preferably 40 or more, and particularly preferably 45 or more. On the other hand, by setting T0 - T1 to 100 or less, an EVOH resin composition with good color can be obtained. T0 - T1 is preferably 90 or less, more preferably 85 or less, even more preferably 80 or less, even more preferably 75 or less, and particularly preferably 65 or less. The temperature T0 - T1 can be adjusted by changing the screw configuration, cylinder configuration, the temperature of the EVOH pellets to be fed, the cylinder temperature, and the screw rotation speed, etc.

[0067] As described above, the saponification catalyst residue can be washed and removed in the extruder, and this step can also be carried out in the extruder (X). Specifically, the EVOH hydrous pellets are fed to the extruder (X), a washing liquid is injected into at least one location in the extruder (X) to wash the resin, and the washing liquid is discharged from at least one location downstream of the injection point. This method is preferred because it allows efficient cleaning in a space-saving manner. In this case, the saponification catalyst residue contained in the EVOH hydrous pellets fed to the extruder (X) is preferably an alkali metal salt. When washing is carried out in the extruder (X), the content of the alkali metal salt contained in the EVOH hydrous pellets fed to the extruder (X) is preferably in the range of 0.1 to 5 mass% in terms of metal.

[0068] In this case, the alkali metal salt content in the washed hydrous EVOH is preferably 0.05% by mass or less, more preferably 0.04% by mass or less, and even more preferably 0.03% by mass or less, calculated as metal.

[0069] The cleaning solution used is not particularly limited as long as it can remove saponification catalyst residues, but is preferably an aqueous solution of an acid with a pKa of 3.5 or higher at 25°C. If an aqueous solution of an acid with a pKa of less than 3.5 at 25°C is used, the discoloration resistance and interlayer adhesion of the EVOH may be unsatisfactory. As such an acid with a pKa of 3.5 or higher, a carboxylic acid is preferred, and from the standpoint of cost, acetic acid and propionic acid are particularly preferred. When an aqueous solution of an acid is used, the concentration of the acid is preferably 0.01 to 10 g / L, more preferably 0.1 to 2 g / L. The amount of cleaning solution injected is preferably 0.1 to 100 L per kg of resin input mass.

[0070] The method for injecting the cleaning liquid is not particularly limited as long as it is a method that can inject the cleaning liquid into the extruder (X), and examples thereof include a method of pressurizing the cleaning liquid using a plunger pump or the like. The method for discharging the cleaning liquid is not particularly limited as long as it is a method that can discharge the liquid from the extruder (X) using a discharge section arranged downstream of the injection section, and examples of suitable methods include a dewatering slit or a dewatering hole. Note that multiple injection sections or multiple discharge sections may be provided. Furthermore, such washing is preferably carried out upstream of the section of the extruder (X) where the additives are supplied, from the viewpoint of incorporating an appropriate amount of additive into the resulting hydrous EVOH resin composition pellets.

[0071] In the present invention, it is preferable to dehydrate the hydrous EVOH in the extruder (X) after the above-mentioned washing in the extruder (X) or without the above-mentioned washing. It is also preferable to degas the EVOH. Specifically, it is preferable to discharge water and / or water vapor from at least one location in the extruder (X). The method of discharge is not particularly limited, but examples include a method of discharging from a dewatering slit, dewatering hole, or vent port arranged in the cylinder of the extruder (X). Suitable examples of the dewatering slit include a wedge wire type dewatering slit and a screen mesh type dewatering slit. Examples of the vent port include a vacuum vent that removes water vapor under reduced pressure and an open vent that removes water vapor under normal pressure.

[0072] Among these, dewatering slits or dewatering holes are preferred. These can discharge both water and water vapor, making it possible to efficiently remove water from resins with high water content. In this respect, they are often more effective than vents, which can generally only discharge water vapor. Furthermore, when discharging water using a vent, resin tends to adhere to the vent, and the adhered resin may deteriorate and become mixed into the extruder (X). From this point of view, dewatering slits or dewatering holes are also preferred. Furthermore, when a dewatering hole is used, the molten material may overflow from the hole, making the use of a dewatering slit preferred.

[0073] 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 using a dehydration slit, and then remove further water from a vent port downstream.

[0074] The dehydration operation described above is carried out to adjust the water content of the EVOH in the extruder (X) and after extrusion. To prevent the water content of the EVOH from becoming lower than necessary, water may be supplied to the extruder (X) in addition to the dehydration operation described above, or without the dehydration operation described above. There are no particular limitations on the method for supplying water to the extruder (X), and examples include a method in which water is supplied under pressure using a plunger pump or the like.

[0075] In the present invention, the water content of the aqueous EVOH resin composition immediately after being discharged from the extruder (X) must be 10 to 35% by mass. A water content of 35% by mass or less suppresses foaming in the EVOH resin composition. The water content is preferably 32% by mass or less, more preferably 28% by mass or less, even more preferably 26% by mass or less, even more preferably 24% by mass or less, and particularly preferably 22% by mass or less. Alternatively, the water content may be 10% by mass or more, and may be preferably 12% by mass or more, 14% by mass or more, 16% by mass or more, or 18% by mass or more.

[0076] In the present invention, the water removal rate calculated by the following formula using the water content A (parts by mass) per 100 parts by mass of EVOH in the hydrous EVOH pellets fed to the extruder (X) and the water content B (parts by mass) per 100 parts by mass of EVOH in the hydrous EVOH resin composition immediately after being discharged from the extruder (X) is preferably 0.1 or more, more preferably 0.3 or more, even more preferably 0.4 or more, even more preferably 0.45 or more, and particularly preferably 0.5 or more. On the other hand, the water removal rate may be 0.95 or less, 0.9 or less, 0.85 or less, 0.8 or less, or 0.75 or less. Water removal rate=(AB) / A

[0077] When the EVOH aqueous resin composition discharged from the extruder (X) is pelletized, the method is not particularly limited, but an example is a method in which the EVOH aqueous resin composition is fed into the extruder (X) and directly cut in a molten state to produce pellets. Suitable examples of direct cutting methods include a hot cutting method and an underwater cutting method, and the nozzle diameter is preferably 2 to 5 mmφ (φ is diameter; the same applies below). The size of the produced pellets is preferably 1 mm or more and 10 mm or less in diameter, for example, if they are spherical.

[0078] The obtained EVOH hydrous resin composition pellets are usually subjected to a drying step. The moisture content of the EVOH resin composition pellets after drying is preferably 1.0% by mass or less, more preferably 0.5% by mass or less. The drying method is not particularly limited, but suitable methods include static drying and fluidized drying. It is also possible to adopt a multi-stage drying process combining several drying methods. Among these, a method in which drying is first performed by fluidized drying and then by static drying is preferred.

[0079] The proportion of EVOH in the resin constituting the EVOH resin composition pellets is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and it is particularly preferred that the EVOH resin composition pellets consist solely of EVOH. The proportion of EVOH and additives in the EVOH resin composition pellets is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and it is particularly preferred that the EVOH resin composition pellets consist essentially of EVOH and additives.

[0080] The melt flow rate (MFR) (190°C, 2160 g load) of the obtained EVOH resin composition pellets is usually 0.5 to 100 g / 10 min, preferably 1 to 50 g / 10 min, and more preferably 1.5 to 20 g / 10 min. When the MFR is 0.5 g / 10 min or more, moldability tends to be good, and when the MFR is 100 g / 10 min or less, the mechanical properties of the obtained molded article tend to be good.

[0081] The EVOH resin composition pellets thus obtained can be melt-molded into various molded articles such as films, sheets, containers, pipes, fibers, etc., and can also be used for a variety of other purposes. [Example]

[0082] The present invention will be described in more detail below with reference to examples. In the examples and comparative examples described below, analyses and evaluations were carried out by the methods shown below.

[0083] (1) Measurement of the moisture content of pellets The moisture content of the pellets used or obtained in the examples and comparative examples was measured by a heating and drying mass measurement method using a halogen moisture analyzer under the conditions of a drying temperature of 180°C, a drying time of 20 minutes, and a sample weight of 10 g. The moisture content of the pellets was calculated using the following formula. Moisture content (mass%) = (mass before drying - mass after drying) / mass before drying x 100

[0084] (2) Determination of carboxylic acids 20 g of the EVOH resin composition pellets obtained in the Examples and Comparative Examples were placed in 100 mL of ion-exchanged water and extracted by heating at 95° C. for 6 hours. The obtained extract was subjected to neutralization titration with 0.01 mol / L sodium hydroxide solution using phenolphthalein as an indicator, to calculate the carboxylic acid content in the EVOH resin composition pellets.

[0085] (3) Quantitative determination of metal salts, boron compounds, and phosphate compounds 0.5 g of the EVOH resin composition pellets obtained in the Examples and Comparative Examples was placed in a Teflon pressure vessel, and 5 mL of concentrated nitric acid was added and decomposed at room temperature for 30 minutes. After decomposition, the pressure vessel was capped and further decomposed by heating at 150°C for 10 minutes and then at 180°C for 5 minutes in a wet decomposition apparatus (Actac's "MWS-2"), followed by cooling to room temperature. This treated solution was transferred to a 50 mL measuring flask and made up to the desired volume with ion-exchanged water to prepare a measurement sample solution. The metal, boron, and phosphorus contents in the sample solution were measured using an ICP emission spectrometer (PerkinElmer's "OPTIMA4300DV"). From the obtained values, the metal salt content (in terms of metal elements), the boron compound content (in terms of boron elements), and the phosphate compound content (in terms of phosphorus elements) in the EVOH resin composition pellets were calculated.

[0086] (4) Foaming 100 g of the EVOH resin composition pellets obtained in the examples and comparative examples were sampled, and the proportion (mass %) of pellets exhibiting shape defects such as dents or bubbles was determined and evaluated according to the following criteria: Pellets in which the proportion of pellets exhibiting shape defects was less than 5 mass % (evaluated as A or B) were suitable for practical use. (evaluation) A: Less than 1% by mass B: 1% by mass or more and less than 5% by mass C: 5% by mass or more

[0087] (5) Coloring Using the EVOH resin composition pellets obtained in the examples and comparative examples, film formation was carried out under the following conditions to obtain a 20 μm monolayer film. One hour after the start of film formation, the film was wound onto a paper tube, and the coloration of the film edge was evaluated visually according to the following criteria. Pellets rated A or B are suitable for practical use. (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: No coloring was observed B: Slight yellowing was observed C: Yellowing was observed

[0088] (6) Melt flow rate (MFR) The dried resin composition pellets obtained in each Example and Comparative Example were filled into a 9.55 mm inner diameter, 162 mm long cylinder of a Melt Indexer L244 (manufactured by Takara Kogyo Co., Ltd.) and melted at 190°C. A load was then applied uniformly to the molten resin composition using a plunger with a mass of 2,160 g and a diameter of 9.48 mm. The amount of resin composition extruded per unit time (g / 10 min) through a 2.1 mm diameter orifice located in the center of the cylinder was measured and used as the MFR. For Example 3, the MFR was measured after melting at 210°C.

[0089] Example 1 EVOH hydrous pellets (ethylene content 32 mol%, saponification degree 99.99 mol%, alkali metal salt (metal equivalent) 20 ppm) with a moisture content of 40% by mass and a temperature of 60°C were fed into a twin-screw extruder. The cylinder and screw configurations of the twin-screw extruder are shown in Figure 1. The cylinder temperature T1 (the highest temperature downstream of the raw material supply section 1) was set to 100°C, and the screw rotation speed was set to 600 rpm. An additive consisting of an aqueous solution of acetic acid, boric acid, sodium acetate, magnesium acetate, and potassium dihydrogen phosphate was added through the trace component addition section 3 at the tip of the discharge side shown in Figure 1. The hourly input rate of the EVOH hydrous pellets was 34.6 kg / hr (including the mass of water contained), and the input rate of the additives was 1.7 L / hr. The additives were an aqueous solution containing 5.4 g / L of acetic acid, 19 g / L of boric acid, 9.6 g / L of sodium acetate trihydrate, 3.9 g / L of magnesium acetate tetrahydrate, and 2.2 g / L of potassium dihydrogen phosphate. The specifications of the twin-screw extruder are as follows: Type Twin-screw extruder L / D 45.5 Diameter 30mmΦ Screws, same direction, full intermeshing type Die diameter 3.0mmΦ

[0090] The twin-screw extruder shown in Figure 1 is composed of a raw material supply section 1, a liquid removal section 2, and a trace ingredient addition section 3, with a liquid removal slit 5 provided in the liquid removal 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.

[0091] The temperature T0 of the melt in the twin-screw extruder was 160°C. Temperature T0 was measured using a temperature sensor 4 attached to the end of the cylinder and in contact with the melt. The molten EVOH hydrous resin composition discharged from the twin-screw extruder was cut with a hot cutter to obtain EVOH hydrous resin composition pellets. The moisture content of the obtained EVOH hydrous resin composition pellets was measured immediately following the method described in (1) above. The results are shown in Table 1. The obtained EVOH hydrous resin composition pellets were dried using a fluidized bed dryer at 90°C for 15 hours and then at 105°C for 15 hours using a static dryer to obtain EVOH resin composition pellets with a moisture content of 0.2% by mass. The EVOH resin composition pellets were subjected to quantitative analysis of carboxylic acid, metal salts, boron compounds, and phosphorus compounds, evaluation of foaming and coloration, and measurement of MFR according to the methods described in (2) to (6) above. The results are shown in Table 1.

[0092] (Examples 2 to 7, Comparative Examples 1 to 3 and 6) EVOH resin composition pellets were produced and evaluated in the same manner as in Example 1, except that the ethylene unit content of EVOH, the moisture content and temperature of the hydrous EVOH pellets fed to the extruder, the screw rotation speed, the cylinder temperature T1, the temperature T0 of the melt in the twin-screw extruder, and the moisture content of the hydrous EVOH resin composition pellets were changed as shown in Table 1. The results are shown in Table 1.

[0093] Example 8 EVOH resin composition pellets were prepared and evaluated in the same manner as in Example 1, except that an aqueous solution containing 5.4 g / L of acetic acid and 9.6 g / L of sodium acetate trihydrate was used as the additive. The results are shown in Table 1.

[0094] Comparative Example 4 EVOH hydrous pellets (ethylene content 32 mol%, saponification degree 99.98 mol%, alkali metal salt (metal equivalent) 20 ppm) with a moisture content of 39% by mass and a temperature of 50°C were fed into a twin-screw extruder. The cylinder and screw configurations of the twin-screw extruder are shown in Figure 2. The cylinder temperature (T1) was set to 100°C, and the screw rotation speed was set to 300 rpm. An additive consisting of an aqueous solution of acetic acid, boric acid, sodium acetate, magnesium acetate, and potassium dihydrogen phosphate was added through the trace ingredient addition section 3 at the discharge end (shown in Figure 2). The hourly input rate of the EVOH hydrous pellets was 10.7 kg / hr (including the mass of water), and the hourly input rate of the additive was 0.65 L / hr. The additive was an aqueous solution containing 4.3 g / L of acetic acid, 15 g / L of boric acid, 7.6 g / L of sodium acetate trihydrate, 3.9 g / L of magnesium acetate tetrahydrate, and 2.2 g / L of potassium dihydrogen phosphate. The specifications of the twin-screw extruder are shown below. Type Twin-screw extruder L / D 45.5 Diameter 30mmΦ Screws, same direction, full intermeshing type Die diameter 3.0mmΦ

[0095] The twin-screw extruder shown in Figure 2 is composed of a raw material supply section 1, a liquid removal section 2, and a trace ingredient addition section 3, with a liquid removal slit 5 provided in the liquid removal section 2. The screw is a combination of a full-flight screw 6 and a reverse-flight screw 7, as shown in Figure 2. Furthermore, a temperature sensor 4 is provided at the end of the cylinder.

[0096] The temperature T0 of the melt in the twin-screw extruder was 100°C. The temperature T0 was measured using a temperature sensor 4 disposed at the end of the cylinder. The molten EVOH resin discharged from the twin-screw extruder was cut with a hot cutter to obtain EVOH hydrous resin composition pellets. The moisture content of the obtained EVOH hydrous resin composition pellets was measured immediately after the measurement according to the method described in (1) above. The results are shown in Table 1. The obtained EVOH hydrous resin composition pellets were dried using a fluidized bed dryer at 90°C for 15 hours and then at 105°C for 15 hours using a static dryer to obtain EVOH resin composition pellets with a moisture content of 0.2% by mass. The EVOH resin composition pellets were subjected to quantitative analysis of carboxylic acid, metal salt, boron compound, and phosphorus compound, evaluation of foaming and coloration, and measurement of MFR according to the methods described in (2) to (6) above. The results are shown in Table 1.

[0097] (Comparative Example 5) EVOH hydrous pellets (ethylene content: 32 mol%, saponification degree: 99.95 mol%) with a moisture content of 39% by mass were fed at a rate of 33 kg / hr to the top of a tower-type reactor with a diameter of 0.8 m and a height of 4 m. A treatment solution (50°C) consisting of an aqueous solution of acetic acid, sodium acetate, magnesium acetate, and potassium dihydrogen phosphate was added to the bottom of the reactor at a rate of 500 L / hr. The treatment solution contained 1.7 g / L of acetic acid, 0.67 g / L of sodium acetate, 1.84 g / L of magnesium acetate tetrahydrate, and 0.77 g / L of potassium dihydrogen phosphate. Treated pellets were continuously withdrawn from the bottom of the reactor. EVOH resin composition pellets were prepared and evaluated in the same manner as in Comparative Example 4, except that the obtained EVOH hydrous pellets with a moisture content of 39% by mass and a temperature of 50°C were used, the cylinder and screw configurations of the twin-screw extruder were changed as shown in Figure 3, and no additives were added to the twin-screw extruder. The results are shown in Table 1.

[0098] [Table 1]

[0099] (Comparative Example 7) An attempt was made to produce EVOH resin composition pellets in the same manner as in Example 1, except that the water-containing pellet supply temperature was changed to 100°C. However, the pellets stuck together when fed into the twin-screw extruder, and the desired EVOH resin composition pellets could not be obtained. [Explanation of symbols]

[0100] 1 Raw material supply section 2 Deliquid section 3 Trace component addition section 4 Temperature Sensor 5 Dewatering slit 6 Full Flight Screw 7 reverse flight screw 8 Seal ring

Claims

1. A method for producing an ethylene-vinyl alcohol copolymer resin composition, comprising supplying ethylene-vinyl alcohol copolymer hydrous pellets at 0 to 80°C and additives to an extruder (X) and melt-kneading the pellets, the additive comprises at least one selected from the group consisting of a carboxylic acid, a boron compound, a phosphoric acid compound, an alkali metal salt, and an alkaline earth metal salt; adding the additives to the ethylene-vinyl alcohol copolymer in the extruder (X); The temperature T of the melt in the extruder (X) ０ is 70 to 180°C, and the cylinder temperature T １ is 65 to 175°C, T ０ and T １ satisfies the following formula (1), and 5≦T ０ -T １ ≦100 (1) The water-containing pellets to be supplied to the extruder (X) have a water content of 20 to 60 mass %, and the water-containing resin composition immediately after being discharged from the extruder (X) has a water content of 10 to 35 mass %.

2. 2. The method according to claim 1, wherein the additive is an aqueous solution containing at least one selected from the group consisting of carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts.

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