Ethylene-vinyl alcohol copolymer porous pellets and their manufacturing method

Abstract

Provided are: ethylene-vinyl alcohol (EVOH) porous pellets for which not only can cleaning of a saponified residue be performed in a short amount of time, but agglutination of the pellets themselves during cleaning at high temperatures is suppressed; and a method for manufacturing the same. The ethylene-vinyl alcohol copolymer porous pellets of the present invention have pores, and a ratio (V2 / V1×100) of a total value (V2) of the pore volume at a pore diameter of 0.5-100 μm to a total value (V1) of the pore volume at a pore diameter of 0.005-100 μm is 25-40 vol%. Furthermore, the pore surface area at 0.005-100 μm is 25-45 m2 / g.

Description

[Technical Field]

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

[0002] Ethylene-vinyl alcohol copolymer (hereinafter also 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 an alcohol / water mixed solution of EVOH is prepared, extruded into a coagulation bath, precipitated in the form of strands, and then cut to obtain hydrous EVOH pellets having a microporous internal structure with uniformly distributed pores (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with water in the apparatus to replace the alcohol in the solution with water, and then the hydrous EVOH composition withdrawn from the apparatus is cut to obtain hydrous EVOH pellets (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-293077 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-121290 Summary of the Invention [Problem to be solved by the invention]

[0005] However, since the pore size of the EVOH hydrous pellets described in Patent Document 1 is controlled to be uniform, it takes a long time to wash and dry the saponification residue and the pellets may stick together when washed at high temperatures.Furthermore, although porous pellets are obtained from the EVOH hydrous pellets described in Patent Document 2, the pore size is not controlled, so it takes a long time to wash and dry the saponification residue and the pellets may stick together when washed at high temperatures.

[0006] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide EVOH porous pellets that not only enable washing of saponification residues in a short time but also suppress adhesion of pellets to each other during high-temperature washing, and a method for producing the same. [Means for solving the problem]

[0007] According to the present invention, the above object is to [1] A porous ethylene-vinyl alcohol copolymer pellet having pores, wherein the ratio (V2 / V1 × 100) of the total pore volume (V2) of pores having a diameter of 0.5 to 100 μm to the total pore volume (V1) of pores having a diameter of 0.005 to 100 μm is 25 to 40 volume %, and the pore surface area of ​​pores having a diameter of 0.005 to 100 μm is 25 to 45 m 2 / g of ethylene-vinyl alcohol copolymer porous pellets; [2] The ethylene-vinyl alcohol copolymer porous pellet according to [1], wherein the median diameter of the pores in the pore diameter range of 0.005 to 100 μm is 0.05 to 0.13 μm; [3] Porous pellets of the ethylene-vinyl alcohol copolymer of [1] or [2], having an average particle size of 2.5 to 8 mm; [4] Porous pellets of an ethylene-vinyl alcohol copolymer according to any one of [1] to [3] containing water; [5] The ethylene-vinyl alcohol copolymer porous pellet according to [4], having a moisture content of 5 to 50 mass%; [6] A first step of introducing a water-containing ethylene-vinyl alcohol copolymer having a water content W1 of 10 to 90% by mass into an extruder and melt-kneading it, and a second step of obtaining porous pellets of ethylene-vinyl alcohol copolymer containing water by cutting the water-containing ethylene-vinyl alcohol copolymer discharged from the extruder. The temperature of the water-containing ethylene-vinyl alcohol copolymer discharged from the extruder is 80 to 100°C. The ratio (V2 / V1×100) of the total pore volume (V2) at a pore diameter of 0.5 to 100 μm to the total pore volume (V1) at a pore diameter of 0.005 to 100 μm of the porous pellets of ethylene-vinyl alcohol copolymer is 25 to 40% by volume. The pore surface area of the porous pellets of ethylene-vinyl alcohol copolymer is 25 to 45 m 2 / g. A method for producing porous pellets of ethylene-vinyl alcohol copolymer; [7] In the second step, the method for producing porous pellets of ethylene-vinyl alcohol copolymer according to [6], wherein the water-containing ethylene-vinyl alcohol copolymer discharged from the extruder is cut in a molten state; is achieved by providing the following.

Effects of the Invention

[0008] According to the production method of the present invention, it is possible to provide EVOH porous pellets in which saponification residue can be washed in a short time and adhesion between pellets during high-temperature washing is suppressed, and a production method thereof.

Brief Description of the Drawings

[0009] [Figure 1] It is a diagram showing the cylinder configuration and screw configuration of the twin-screw extruder in Examples 1 to 10 and Comparative Example 1. [Figure 2] It is a diagram showing the configuration of the hot cutter in Examples 1 to 10 and Comparative Example 1.

Modes for Carrying Out the Invention

[0010] In this specification, "~" representing a numerical range means a range including each lower limit value and upper limit value. For example, A~B represents that it is A or more and B or less.

[0011] <EVOH porous pellets> The EVOH porous pellets of the present invention have pores, and with respect to the total pore volume (V1) at pore diameters of 0.005 to 100 μm (hereinafter, may be abbreviated as "pore volume (V1)"), the ratio (V2 / V1×100) (hereinafter, may be abbreviated as "pore volume ratio (V2 / V1)") of the total pore volume (V2) at pore diameters of 0.5 to 100 μm (hereinafter, may be abbreviated as "pore volume (V2)") is 25 to 40% by volume, and the pore surface area at 0.005 to 100 μm is 25 to 45 m 2 / g. Here, the pore volume, pore surface area, and the median diameter of the pores described later can be calculated from the pore distribution, and such pore distribution means the one measured by the mercury intrusion method, and specifically, it can be measured according to the method described in the examples. Also, the fact that the pore volume ratio (V2 / V1) is 25 to 40% by volume means that the pore distribution has a certain spread. The EVOH porous pellets of the present invention, particularly by having a specific pore volume ratio and a specific pore surface area, tend to improve the washing efficiency of saponification residues and suppress adhesion between pellets during high-temperature washing. Further, because it has a specific pore volume ratio (V2 / V1) and pore surface area, the drying efficiency is high, and deterioration due to heat of the obtained dried EVOH pellets can also be suppressed. From the viewpoint of maximizing the above-described effects, the EVOH porous pellets of the present invention are preferably EVOH water-containing porous pellets containing water.

[0012] The total pore volume (V1) of the EVOH porous pellets of the present invention for pores with diameters of 0.005 to 100 μm is preferably 0.2 ml / g or more, more preferably 0.22 ml / g or more, and even more preferably 0.25 ml / g or more. Furthermore, the pore volume (V1) is preferably 0.5 ml / g or less, more preferably 0.4 ml / g or less, and even more preferably 0.35 ml / g or less. When the pore volume (V1) is within the above range, adhesion of pellets to each other during high-temperature washing can be suppressed, and drying efficiency tends to be improved.

[0013] The pore volume ratio (V2 / V1) of the EVOH porous pellets of the present invention is 25% by volume or more, preferably 28% by volume or more, more preferably 30% by volume or more, even more preferably 32% by volume or more, and even more preferably 33.5% by volume or more. If the pore volume ratio (V2 / V1) is less than 25% by volume, the efficiency of washing the saponification residue decreases and drying takes a long time, which tends to reduce production efficiency. Furthermore, the pore volume ratio (V2 / V1) is 40% by volume or less, preferably 38.5% by volume or less. If the pore volume ratio (V2 / V1) exceeds 40% by volume, the pellets tend to stick together during high-temperature washing. The pore volume ratio (V2 / V1) can be adjusted by the following conditions in the production method described below: the cylinder temperature of the extruder used in the first step, the temperature of the hydrous EVOH introduced into the extruder, the content of alcohol with a boiling point of 100°C or less in the hydrous EVOH introduced into the extruder, the ethylene unit content, and the temperature of the hydrous EVOH discharged from the extruder.

[0014] The pore surface area of ​​the EVOH porous pellet of the present invention in the range of 0.005 to 100 μm is 25 m 2 / g or more, and 30m 2 / g or more is preferable, and 32.0m 2 / g or more. 2 If the surface area of ​​the pores in the EVOH porous pellets is less than 45 m / g, the efficiency of washing the saponification residue tends to decrease. 2 / g or less, and 41m 2 / g or less is preferable, and 39m 2 / g or less is more preferable, and 37m 2 / g or less is more preferable. 2 When the pore surface area exceeds 1 / g, the pellets tend to stick together during high-temperature washing. The pore surface area can be adjusted by the following conditions in the production method described below: the cylinder temperature of the extruder used in the first step, the temperature of the water-containing EVOH introduced into the extruder, the water content W1 of the water-containing EVOH introduced into the extruder, the content of alcohol having a boiling point of 100°C or less in the water-containing EVOH introduced into the extruder, the temperature of the water-containing EVOH discharged from the extruder, the ethylene unit content, and the water content W2 of the EVOH porous pellets discharged from the extruder and cut.

[0015] The median diameter of the pores of the EVOH porous pellets of the present invention having a diameter of 0.005 to 100 μm is preferably 0.05 μm or more, more preferably 0.06 μm or more, and even more preferably 0.07 μm or more, from the viewpoints of washing efficiency of the saponification residue and drying efficiency. The median diameter may be, for example, 0.3 μm or less or 0.2 μm or less, but is preferably 0.13 μm or less, more preferably 0.12 μm or less, from the viewpoint of suppressing adhesion of the pellets to each other during high-temperature washing.

[0016] The shape of the EVOH porous pellets of the present invention is preferably spherical (or approximately spherical). The average particle size of the EVOH porous pellets of the present invention is preferably 2.5 mm or more and 8 mm or less, more preferably 2.8 mm or more and 5 mm or less, from the viewpoint of suppressing adhesion of pellets to each other during high-temperature washing. The average particle size of the EVOH porous pellets can be measured by the method described in the Examples.

[0017] The EVOH constituting the EVOH porous pellets of the present invention can be obtained by a known method, and is obtained by saponifying an ethylene-vinyl ester copolymer.

[0018] The ethylene unit content of the EVOH constituting the EVOH porous pellets of the present invention is preferably 20 mol% or more, more preferably 24 mol% or more, and even more preferably 26 mol% or more from the viewpoint of melt moldability, while the ethylene unit content is preferably 60 mol% or less, more preferably 48 mol% or less, and even more preferably 46 mol% or less from the viewpoint of gas barrier properties.

[0019] The saponification degree of the EVOH constituting the EVOH porous pellets of the present invention is not particularly limited, but from the viewpoint of maintaining gas barrier properties and improving long-run properties, it is preferably 95 mol% or more, more preferably 98 mol% or more, and even more preferably 99 mol% or more. On the other hand, the saponification degree of the EVOH may be 100 mol% or less, or 99.99 mol% or less. The saponification degree is 1 It can be measured by H-NMR.

[0020] The EVOH constituting the EVOH porous pellets of the present invention may contain units derived from other monomers other than ethylene, vinyl esters, and saponified products thereof. When the EVOH contains units derived from the other monomers, the content of the units derived from the other monomers relative to the total structural units of the EVOH is preferably 30 mol% or less, more preferably 20 mol% or less, even more preferably 10 mol% or less, and particularly preferably 5 mol% or less. When the EVOH contains units derived from the other monomers, the lower limit may be 0.05 mol% or 0.10 mol%. Examples of the other monomers include alkenes such as propylene, butylene, pentene, and hexene; 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, and 4-acyloxy-3-methyl -1-butene, 3,4-diacyloxy-2-methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, 4,5-diacyloxy-1-pentene, 4-acyloxy-1-hexene, 5-acyloxy-1-hexene, 6-acyloxy-1-hexene, 5,6-diacyloxy-1-hexene, 1,3-diacetoxy-2-methyl- Examples of suitable EVOH include alkenes having an ester group such as olefin propane or saponified alkenes; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, and itaconic acid or their anhydrides, salts, or mono- or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, and methallylsulfonic acid or their salts; vinyl silane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxyethoxy)silane, and γ-methacryloxypropylmethoxysilane; alkyl vinyl ethers, vinyl ketones, N-vinylpyrrolidone, vinyl chloride, and vinylidene chloride. EVOH (A) may be post-modified by methods such as urethanization, acetalization, cyanoethylation, and oxyalkylenation.

[0021] The EVOH porous pellets of the present invention are preferably hydrous EVOH porous pellets containing water. The moisture content of the hydrous EVOH porous pellets is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more. The moisture content of the hydrous EVOH porous pellets is preferably 50% by mass or less, more preferably 45% by mass or less. When the moisture content of the hydrous EVOH porous pellets is within the above range, it tends to be easier to adjust the pore surface area and pore volume ratio (V2 / V1) within the ranges of the present invention. When the moisture content of the hydrous EVOH porous pellets is within the above range, fine pores tend to be present stably.

[0022] In order to improve qualities such as thermal stability, the EVOH porous pellets of the present invention preferably contain at least one additive selected from the group consisting of carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts. The addition method is not particularly limited, and known methods can be used. Examples include a method of immersing the EVOH porous pellets in an aqueous solution containing at least one additive selected from the group consisting of carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts to adsorb the additive, and a method of blending and melt-kneading at least one additive selected from carboxylic acids, boron compounds, phosphoric acid compounds, alkali metal salts, and alkaline earth metal salts in an extruder separate from the extruder of the present invention.

[0023] Examples of carboxylic acids include oxalic acid, succinic acid, benzoic acid, citric acid, acetic acid, lactic acid, and propionic acid. From the viewpoints of cost and availability, it is preferable to use acetic acid, lactic acid, or propionic acid. The carboxylic acid content in the EVOH porous pellets of the present invention is preferably 10 to 5,000 ppm from the viewpoints of color and adhesion to other layers. The lower limit of the carboxylic acid content is preferably 30 ppm, more preferably 50 ppm. The upper limit of the carboxylic acid content is preferably 1,000 ppm, more preferably 500 ppm.

[0024] 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 cation species is not particularly limited, but an alkali metal salt or alkaline earth metal salt is 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. The content of the phosphoric acid compound in the EVOH porous pellets of the present invention is preferably 1 to 1,000 ppm in terms of phosphate radical, from the viewpoint of suppressing discoloration of the molded product and the occurrence of gels and particles.

[0025] Examples of boron compounds include, but are not limited to, boric acids, boric acid esters, borate salts, and boron hydrides. Specific examples of boric acids include orthoboric acid, metaboric acid, and tetraboric acid. Examples of borate esters include triethyl borate and trimethyl borate. Examples of borates include alkali metal salts, alkaline earth metal salts, and borax of the above-mentioned various boric acids. Among these compounds, orthoboric acid (simply referred to as boric acid) is preferred. From the viewpoints of thermal stability and moldability, the content of the boron compound in the EVOH porous pellets of the present invention is preferably 10 to 2000 ppm, more preferably 50 to 1000 ppm, calculated as boron.

[0026] The inclusion of an alkali metal salt can effectively improve interlayer adhesion and compatibility. The content of the alkali metal salt in the EVOH porous pellets of the present invention is preferably 5 to 5,000 ppm, more preferably 20 to 1,000 ppm, and even more preferably 30 to 750 ppm, calculated as the alkali metal element. Examples of alkali metals include lithium, sodium, and potassium. Examples of alkali metal salts include aliphatic carboxylates, aromatic carboxylates, phosphates, and metal complexes. Examples of alkali metal salts include sodium acetate, potassium acetate, sodium propionate, sodium phosphate, lithium phosphate, sodium stearate, potassium stearate, and the sodium salt of ethylenediaminetetraacetic acid. Among these, sodium acetate, potassium acetate, sodium propionate, and sodium phosphate are preferred.

[0027] Although the inclusion of an alkaline earth metal salt may slightly deteriorate discoloration resistance, it can reduce the amount of thermally deteriorated resin adhering to the die of the molding machine during melt molding. The alkaline earth metal salt is not particularly limited, and examples 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 also not particularly limited, but aliphatic carboxylate anions and phosphate anions are preferred. Among these, magnesium acetate, calcium acetate, magnesium propionate, calcium propionate, magnesium phosphate, and calcium phosphate are preferred. From the viewpoints of hue and long-run properties, the content of the alkaline earth metal salt in the EVOH porous pellets of the present invention is preferably 10 to 1,000 ppm, more preferably 20 to 500 ppm, calculated as alkaline earth metal elements.

[0028] The EVOH porous pellets of the present invention may contain additives other than EVOH, water, carboxylic acid, boron compound, phosphate compound, alkali metal salt and alkaline earth metal salt, as long as the effects of the present invention are not inhibited. Examples of the other additives include anti-blocking agents, processing aids, stabilizers, antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, surfactants, desiccants, oxygen absorbers, crosslinking agents, reinforcing agents such as various fibers, and the like.

[0029] The EVOH porous pellets may be used alone or in combination of two or more. Further, the EVOH porous pellets may be composed of one type of EVOH or may be composed of two or more types of EVOH.

[0030] Among all the resin components constituting the EVOH porous pellets of the present invention, the proportion occupied by EVOH is, for example, more than 50% by mass, preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, still further preferably 99% by mass or more, and particularly preferably consisting only of EVOH. When all the resin components constituting the EVOH porous pellets are within the above range, the effects of the present invention tend to be remarkably exhibited. Also, the proportion occupied by EVOH and water in the EVOH porous pellets is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and particularly preferably 99% by mass or more. When the proportion occupied by EVOH and water in the EVOH porous pellets of the present invention is within the above range, the effects of the present invention tend to be more remarkably exhibited.

[0031] <Method for producing EVOH porous pellets> The method for producing the porous EVOH pellets of the present invention will be described below. The method for producing the porous EVOH pellets of the present invention comprises a first step of introducing a water-containing EVOH having a water content W1 of 10 to 90% by mass into an extruder and melt-kneading it, and a second step of cutting the water-containing EVOH discharged from the extruder to obtain water-containing porous EVOH pellets. The temperature of the water-containing EVOH discharged from the extruder is 80 to 100°C, and the ratio (V2 / V1 x 100) of the total pore volume (V2) of pores having a diameter of 0.5 to 100 μm to the total pore volume (V1) of pores having a diameter of 0.005 to 100 μm of the EVOH porous pellets is 25 to 40% by volume, and the pore surface area of ​​the porous EVOH pellets is 25 to 45 m 2 / g.

[0032] In this specification, the hydrous EVOH introduced into the extruder may be referred to as the hydrous EVOH used in the present invention, and the hydrous EVOH obtained by being discharged from the extruder may be referred to as the hydrous EVOH obtained in the present invention.

[0033] The hydrous EVOH used in the present invention contains EVOH and water. The hydrous EVOH has a water content W1 of 10 to 90 mass %. As will be described later, the hydrous EVOH may also contain other components such as alcohols and alkali metal salts.

[0034] The EVOH constituting the hydrous EVOH used in the present invention (hereinafter sometimes referred to as "EVOH used in the present invention" or "the EVOH") can suitably be the same as the EVOH constituting the EVOH porous pellets.

[0035] As mentioned above, the EVOH is usually obtained by saponifying an ethylene-vinyl ester copolymer. The copolymerization of ethylene and vinyl ester may be carried out by any of solution polymerization, suspension polymerization, emulsion polymerization, and bulk polymerization. It may also be carried out by any of continuous and batch polymerization. An example of the polymerization conditions for solution polymerization is shown below.

[0036] 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 of the alcohol used is more preferably 80°C or less, and even more preferably 70°C or less.

[0037] 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.

[0038] 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 peroxyneodecanoate, diisopropyl peroxycarbonate, di-n-propyl peroxydicarbonate, t-butyl peroxyneodecanoate, lauroyl peroxide, benzoyl peroxide, and t-butyl hydroperoxide.

[0039] 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.

[0040] The polymerization conditions are preferably as follows: (1) Temperature: preferably 20 to 90°C, more preferably 40 to 70°C. (2) Time (average residence time in the case of a continuous 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. It is also possible to carry out the polymerization in the presence of a monomer copolymerizable with ethylene and vinyl ester.

[0041] After the polymerization is continued for a predetermined time and a predetermined polymerization rate is reached, a polymerization inhibitor is added as necessary, and unreacted ethylene gas is evaporated and removed. The unreacted vinyl ester is then removed. For example, the unreacted vinyl ester can be removed by continuously feeding the polymerization solution from which ethylene has been removed at a constant rate from the top of a tower packed with Raschig rings, blowing vapor of an organic solvent, preferably an alcohol with a boiling point of 100°C or less, and most preferably methanol, into the bottom of the tower, distilling a mixed vapor of the organic solvent and unreacted vinyl ester from the top of the tower, and withdrawing the copolymer solution from which unreacted vinyl ester has been removed from the bottom of the tower.

[0042] 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

[0043] 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).

[0044] 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, and from the viewpoint of further improving the gas barrier property, is 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.

[0045] In particular, when producing EVOH pellets with 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 EVOH, it is preferable to further adjust the saponification conditions as follows.

[0046] 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.

[0047] 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.

[0048] A suitable post-treatment method for the EVOH solution or paste 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 or paste from a position above the supply position of the mixed vapor, thereby replacing a portion of the solvent present in the supplied EVOH solution or paste 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 preferable that the ratio of the supply rate of the EVOH solution to the supply rate of the mixed vapor (solution supply rate / vapor supply rate) is 100 / 400 to 100 / 8 by mass. Furthermore, it is preferable that the water content in the mixed vapor is 20 to 70% by mass. The solvent used in the mixed vapor is preferably an alcohol with a boiling point of 130°C or lower. Examples of such alcohols include methanol, ethanol, propanol, and butanol. Alcohols with a boiling point of 100°C or less are more preferable, and among these, methanol is preferred because it is readily available, inexpensive, has a low boiling point, and is easy to handle.

[0049] 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 1,000 parts by mass or less, and 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 becomes possible. The alcohol is preferably methanol. The EVOH solution after saponification may not only be an alcohol solution, but also a mixed solvent solution to which, if necessary, other solvents such as water are added to the extent that EVOH does not precipitate.

[0050] A preferred method for obtaining the hydrous EVOH used in the present invention is, for example, to introduce the EVOH solution obtained as described above, which contains 100 parts by mass of EVOH and 50 parts by mass or more of an alcohol having a boiling point of 100°C or less, into a vessel, contact the EVOH with water vapor in the vessel to remove the alcohol together with the water vapor, remove the hydrous EVOH from the vessel, and introduce the hydrous EVOH removed from the vessel into an extruder described below. This method not only allows the alcohol in the EVOH solution to be efficiently replaced with water, but also makes it easy to adjust the water content of the EVOH.

[0051] The method for contacting the EVOH solution introduced into the vessel with water vapor within the vessel is not particularly limited, and either a continuous or batch method may be used. The vessel shape is also not particularly limited, but a tower-type vessel is preferred for the continuous method, and a tank-type vessel is preferred for the batch method. Considering production efficiency, the continuous method is industrially preferable. Examples of tower-type vessels include plate towers such as perforated plate towers and bubble cap towers, and packed towers containing ring-type packing.

[0052] In a tower-type vessel, steam is supplied from the bottom of the vessel, and the EVOH solution or paste is supplied from a position above the steam supply point. The solvent (alcohol) present in the supplied EVOH solution or paste is removed together with the steam, and a hydrous EVOH with a water content of 10 to 90% by mass is removed 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-inefficient. 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 steam contacted with the EVOH solution or paste may contain up to 10 parts by mass of the solvent (alcohol) per 100 parts by mass of steam. However, for efficient solvent (alcohol) removal, it is preferable that the steam does not contain any solvent (alcohol). The hydrous EVOH may contain 0 to 10 parts by mass of the solvent (alcohol) per 100 parts by mass of EVOH. Furthermore, the hydrous EVOH may contain saponification catalyst residues and the like.

[0053] The alcohol can be recovered as an aqueous alcohol solution and reused after purification as necessary. 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 atmospheric pressure, for example, at temperatures of approximately 60-70°C, but does not dissolve in water alone. However, in the presence of pressurized water vapor at temperatures of, for example, 90°C or higher, EVOH can maintain its fluidity even when it contains essentially only water.

[0054] The temperature inside the container is preferably 100 to 150°C. If the temperature inside the container is below 100°C, the fluidity of the hydrous EVOH will be insufficient, and gelation or blockage may occur inside the container. A temperature of 110°C or higher is more preferable, and 120°C or higher is even more preferable. On the other hand, if the temperature inside the container exceeds 150°C, the EVOH may deteriorate. A temperature of 140°C or lower is more preferable.

[0055] Furthermore, if the pressure inside the vessel is too low, the efficiency of alcohol removal may decrease. The pressure inside the vessel is preferably 0.1 MPa or higher, more preferably 0.15 MPa or higher, and even more preferably 0.2 MPa or higher. On the other hand, if the pressure inside the vessel is too high, the water content of the water-containing EVOH discharged from the vessel may become too high, which may result in the melt viscosity of the water-containing EVOH introduced into the extruder described below becoming too low. Therefore, the pressure inside the vessel is preferably 0.6 MPa or lower, more preferably 0.5 MPa or lower, and even more preferably 0.4 MPa or lower.

[0056] After the EVOH solution is brought into contact with water vapor as described above, the water-containing EVOH is discharged from the vessel, and is suitably used as the water-containing EVOH to be supplied to the extruder in the first step.

[0057] In the first step, water-containing EVOH having a water content W1 of 10 to 90% by mass is introduced into an extruder and melt-kneaded. The form of the water-containing EVOH introduced into the extruder is not particularly limited, but examples include a paste. As described above, by bringing the EVOH solution into direct contact with water vapor in the vessel, a paste-like water-containing EVOH is obtained. The EVOH is discharged from the vessel while maintaining its fluidity and without gelling.

[0058] The water content W1 of the hydrous EVOH introduced into the extruder is 10 to 90% by mass. When the water content W1 is less than 10% by mass, the hydrous EVOH contains little water, and the pore surface area of ​​the EVOH porous pellets discharged from the extruder and cut is less than 25 m 2 / g, the pore surface area tends to be smaller than 25m 2When the water content W1 is less than 90% by mass, the washing efficiency of the saponification residue decreases, and drying takes a long time, which tends to decrease production efficiency. The water content W1 is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 45% by mass or more. On the other hand, when the water content W1 exceeds 90% by mass, the pore surface area becomes 45m 2 / g. The pore surface area tends to exceed 45 m 2 If the water content exceeds 1 / g, the pellets tend to stick together during high-temperature washing. The water content W1 is preferably 80% by mass or less, more preferably 70% by mass or less, even more preferably 60% by mass or less, and particularly preferably 55% by mass or less. The water content W1 of the water-containing EVOH introduced into the extruder is measured by the method described in the Examples below. The water content W1 can be adjusted, for example, by the conditions for post-treating the EVOH solution or paste, or the conditions for obtaining the water-containing EVOH from the EVOH solution or paste.

[0059] The temperature of the hydrous EVOH fed to the extruder is not particularly limited, but is preferably 80 to 130°C. If the temperature is lower than 80°C, the pore volume ratio (V2 / V1) of the EVOH porous pellets discharged from the extruder and cut tends to be smaller than 25% by volume. If the pore volume ratio (V2 / V1) is smaller than 25% by volume, the efficiency of washing the saponification residue decreases, and drying takes a long time, which tends to decrease production efficiency. The temperature is preferably 90°C or higher, and more preferably 95°C or higher. On the other hand, if the temperature exceeds 130°C, the pore volume ratio (V2 / V1) tends to exceed 40% by volume, and the pore surface area tends to be smaller than 45m. 2 / g. When the pore volume ratio (V2 / V1) exceeds 40% by volume or the pore surface area is less than 45m 2 If the water content exceeds 1 / g, the pellets tend to stick together during high-temperature washing. The temperature is preferably 125°C or lower, more preferably 115°C or lower. The temperature of the hydrous EVOH can be adjusted, for example, by the conditions for obtaining the hydrous EVOH from the EVOH solution or paste.

[0060] From the viewpoint of preventing the resulting EVOH porous pellets from sticking together and influencing the pore volume ratio (V2 / V1) of the pellets, the content of alcohol having a boiling point of 100°C or less in the water-containing EVOH introduced into the extruder is preferably 5% by mass or less, more preferably 1% by mass or less, and particularly preferably 0.5% by mass or less. If the alcohol content is more than 5% by mass, the pore volume ratio (V2 / V1) tends to exceed 40% by volume, and the pore surface area tends to be less than 45 m 2 / g. When the pore volume ratio (V2 / V1) exceeds 40% by volume or the pore surface area is less than 45m 2 If the porosity exceeds 1 / g, the pellets tend to stick together during high-temperature washing.

[0061] The hydrous EVOH introduced into the extruder may contain, for example, about 0.1 to 5% by mass, calculated as the metal, of alkali metal salts, which correspond to residues of the catalyst used in the saponification step, and may also contain by-product salts, other impurities, etc. The content of components other than EVOH, water, and alcohols having a boiling point of 100°C or less in the hydrous EVOH supplied to the extruder is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and particularly preferably 1% by mass or less.

[0062] Fig. 1 is a diagram showing the cylinder configuration (upper side of Fig. 1) and screw configuration (lower side of Fig. 1) of the extruder used in Example 1 etc., which will be described later. The first step will be further described with reference to Fig. 1.

[0063] The extruder used in the first step may be a single-screw or multi-screw extruder, but a twin-screw extruder is preferred. The L / D ratio of the extruder is preferably 8 to 30, more preferably 9 to 25, and even more preferably 10 to 20. A block cylinder or the like is used as the cylinder 1. An inlet 2 for the hydrous EVOH is provided in the cylinder 1 of the extruder. After the hydrous EVOH is introduced into the inlet 2, the rotation of the screw disposed within the cylinder 1 causes the hydrous EVOH to flow along the axis of the cylinder 1 toward the tip side (downstream side 3) of the cylinder 1. At this time, water in the hydrous EVOH is discharged from a liquid outlet (back slit 4) provided in the cylinder 1, thereby reducing the moisture content of the hydrous EVOH.

[0064] When the extruder is viewed from above in a direction perpendicular to the axis of the cylinder 1, the back slit 4 is preferably located upstream 7 of the water-containing EVOH flow 5 relative to the water-containing EVOH inlet 2, and the inlet 2 and the back slit 4 do not overlap. That is, the most downstream portion 3 of the back slit 4 is preferably located upstream of the most upstream portion 7 of the inlet 2. It is also preferable that the extruder does not have a liquid outlet downstream of the water-containing EVOH inlet 2, and more preferably does not have any liquid outlet other than the back slit 4. When the extruder does not have any liquid outlet other than the back slit 4, it tends to be easier to control the moisture content W2 of the EVOH porous pellets discharged from the extruder and cut. The type of back slit 4 used is not particularly limited, and a general dewatering slit may be used. Specifically, a wedge wire dewatering slit, a screen mesh dewatering slit, or the like may be used.

[0065] The cylinder temperature of the extruder is preferably 70 to 100° C. By setting the cylinder temperature in this range, the pore surface area of ​​the EVOH porous pellets discharged from the extruder and cut is 25 to 45 m 2 / g, and the pore volume ratio (V2 / V1) tends to be controlled to 25 to 40% by volume. The temperature is preferably 98°C or lower, and more preferably 95°C or lower. Here, the cylinder temperature refers to the maximum temperature at the portion downstream of the water-containing EVOH inlet 2.

[0066] The extruder may be of a segmented type. The screw rotation speed is preferably 10 to 2000 rpm. By setting the screw rotation speed within this range, elution of EVOH is further suppressed. The screw rotation speed is preferably 50 rpm or higher, more preferably 120 rpm or higher, even more preferably 150 rpm or higher, and particularly preferably 200 rpm or higher. On the other hand, the screw rotation speed is preferably 1500 rpm or lower, even more preferably 1000 rpm or lower, even more preferably 800 rpm or lower, and particularly preferably 500 rpm or lower.

[0067] In the second step, the hydrous EVOH extruded from the extruder is cut to obtain hydrous EVOH porous pellets (hydrous EVOH porous pellets). The obtained EVOH porous pellets preferably have a water content W2 of 5 to 50% by mass. When the water content W2 is less than 5% by mass, the pore surface area of ​​the pellets is 25 m 2 / g. The pore surface area tends to be smaller than 25m 2 When the water content W2 is less than 50% by mass, the washing efficiency of the saponification residue decreases, and drying takes time, which tends to decrease production efficiency. The water content W2 is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. On the other hand, when the water content W2 exceeds 50% by mass, the pore surface area becomes 45 m 2 / g. The pore surface area tends to exceed 45m 2 If the water content exceeds 1 / g, the pellets tend to stick together during high-temperature washing. The water content W2 is preferably 45% by mass or less, and more preferably 40% by mass or less. The water content W2 is measured by the method described in the Examples.

[0068] In the present invention, the ratio (W2 / W1) of the moisture content W2 of the porous EVOH pellets obtained by cutting the discharged hydrous EVOH to the moisture content W1 of the hydrous EVOH introduced into the extruder is preferably 0.2 or more and less than 1. When the ratio (W2 / W1) is within this range, the pore volume ratio (V2 / V1) of the pellets is easily controlled to 25 to 40 volume percent. The ratio (W2 / W1) is preferably 0.3 or more, more preferably 0.4 or more, even more preferably 0.5 or more, particularly preferably 0.55 or more, and most preferably 0.6 or more. On the other hand, the ratio (W2 / W1) is preferably 0.9 or less, more preferably 0.85 or less, even more preferably 0.8 or less, particularly preferably 0.75 or less, and most preferably 0.7 or less. The moisture content W2 can be adjusted, for example, by the moisture content W1, cylinder temperature, screw rotation speed, etc. As described above, the water content W2 can be adjusted by providing a back slit and draining water.

[0069] The temperature of the water-containing EVOH discharged from the extruder is 80 to 100° C. If the temperature is less than 80° C., the pore surface area of ​​the EVOH porous pellets obtained by cutting the discharged water-containing EVOH will be 25 m 2 / g, and the pore volume ratio (V2 / V1) tends to be less than 25% by volume. 2 / g or the pore volume ratio (V2 / V1) is less than 25% by volume, the efficiency of washing the saponification residue decreases, and drying takes time, which tends to decrease production efficiency. The temperature is preferably 85°C or higher. On the other hand, when the temperature exceeds 100°C, the pore surface area becomes 45m 2 / g, and the pore volume ratio (V2 / V1) exceeds 40 vol%. 2 If the pore volume ratio (V2 / V1) exceeds 40% by volume, the pellets tend to stick together during high-temperature washing. The temperature is preferably 98°C or less, more preferably 95°C or less, and particularly preferably 93°C or less. The temperature of the hydrous EVOH discharged from the extruder is measured by the method described in the Examples.

[0070] From the viewpoint of controlling the pore volume ratio (V2 / V1) of the EVOH porous pellets obtained by cutting the discharged water-containing EVOH to 25 to 40% by volume, it is preferable that the temperature of the water-containing EVOH introduced into the extruder is higher than the temperature of the water-containing EVOH discharged from the extruder. The temperature of the water-containing EVOH introduced into the extruder is more preferably 1°C or more higher, even more preferably 5°C or more higher, and particularly preferably 10°C or more higher than the temperature of the water-containing EVOH discharged from the extruder.

[0071] In the second step, the hydrous EVOH discharged from the extruder is cut to obtain porous EVOH pellets. The method for this is not particularly limited, and examples include a method in which the hydrous EVOH (molten state) discharged from the extruder is directly cut, or a method in which the hydrous EVOH discharged from the extruder is extruded into a coagulating liquid in the form of strands, solidified, and then cut. Of these, the method of directly cutting the hydrous EVOH is preferred. Methods for directly cutting the hydrous EVOH discharged from the extruder include hot cutting and underwater cutting. The cutting method for a hydrous EVOH composition described in Patent Document 2 is preferably used. From the viewpoint of ease of handling of the porous EVOH pellets, the nozzle diameter is preferably 2 to 5 mm (φ is the diameter; the same applies below). The size of the produced porous EVOH pellets can be, for example, 1 mm to 10 mm in diameter if they are spherical (or nearly spherical), or 1 mm to 10 mm in diameter and 1 mm to 10 mm in length if they are cylindrical. Note that if the extrusion is performed in the form of strands, solidified, and then cut, cylindrical pellets are obtained, whereas if the extrusion is performed directly in the molten state, spherical (or nearly spherical) pellets are obtained. This method of cutting hydrous EVOH in the molten state is superior to the method of extruding the hydrous EVOH in the form of strands into a solidifying liquid, solidifying it, and then cutting it, in that it is not necessary to consider the take-up speed at which strands can be stably formed, and therefore is more productive. For example, even in cases where strand formation is not easy, such as with EVOH with a low ethylene content, cutting it in the molten state makes it easy to produce porous EVOH pellets.

[0072] The hydrous EVOH extruded from the extruder is cut by a hot cutting method or an underwater cutting method, and the pellets immediately after cutting are cooled with cooling water, which may contain a small amount of alcohol.

[0073] From the viewpoint of controlling the median pore diameter of the EVOH porous pellets obtained by cutting the discharged hydrous EVOH, the cooling water temperature is preferably 0 to 40°C. The cooling water temperature is preferably 0 to 30°C, more preferably 0 to 15°C, and most preferably 0 to 9°C. When the cooling water temperature exceeds 40°C, the median pore diameter tends to be greater than 0.13 μm. When the median pore diameter is 0.13 μm or less, pellets are particularly unlikely to stick together during high-temperature washing, which tends to improve production efficiency. When the cooling water temperature is lower than 0°C, it may freeze and become impossible to circulate.

[0074] The EVOH porous pellets thus obtained contain alkali metal salts, which are residues of the catalyst used in saponification. If a large amount of alkali metal salts is present, quality problems such as discoloration may occur, so it is preferable to wash them away. The washing method is not particularly limited, but examples include a method of immersing the pellets in water or an aqueous solution of an acid such as acetic acid.

[0075] The washing temperature can be in the range of 0 to 95°C. While a higher washing temperature is preferable from the viewpoint of improving washing efficiency, too high a temperature is undesirable because it can cause pellets to stick together. The lower limit of the washing temperature is preferably 20°C or higher, more preferably 30°C or higher, and optimally 40°C or higher. Conventional washing temperatures are generally around 25 to 30°C. The EVOH porous pellets of the present invention can be washed at higher temperatures, thereby further improving washing efficiency. The upper limit of the washing temperature is preferably 80°C or lower, more preferably 70°C or lower. The alkali metal salt content after washing should be 0.05 parts by mass or less, more preferably 0.03 parts by mass or less, calculated as metal elements, per 100 parts by mass of EVOH. The reduction in the alkali metal salt content due to washing can be confirmed by a decrease in the electrical conductivity of the washing solution when washed with ion-exchanged water. It is preferable that the electrical conductivity of the washing solution be 3 μS / cm or less.

[0076] The resulting EVOH porous pellets are typically subjected to a drying process. The moisture content of the EVOH resin composition pellets obtained by drying the EVOH porous pellets is generally 1% by mass or less, preferably 0.5% by mass or less. The EVOH resin composition pellets also include pellets consisting essentially of EVOH. One of the features of the EVOH porous pellets of the present invention is their fast drying rate. Therefore, in this case, it is possible to shorten the drying time compared to conventional methods, which is advantageous in terms of cost. The drying method is not particularly limited, but preferred examples include static drying and fluidized drying. It is also possible to adopt a multi-stage drying process combining several drying methods, such as first drying by fluidized drying and then drying by static drying. When drying the EVOH porous pellets of the present invention, efficient drying may be possible using only one drying method, even when efficient drying previously required a combination of multiple drying methods. This is one of the useful advantages, not only because of the shortened drying time but also because of the greater flexibility in adopting the drying process.

[0077] The melt flow rate (MFR) (190°C, 2160 g load) of the EVOH resin composition pellets obtained from the EVOH porous pellets is preferably 0.5 to 100 g / 10 min, more preferably 1 to 50 g / 10 min, and even 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 resulting molded article tend to be good. The MFR is measured by the method described in the Examples below.

[0078] 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 applications. The production method of the present invention can improve the productivity of such EVOH resin composition pellets. [Example]

[0079] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0080] [Evaluation method] (1) Measurement of pore volume ratio (V2 / V1), pore surface area, and pore median diameter The EVOH porous pellets obtained in the examples and comparative examples were frozen at -80°C, freeze-dried, and returned to room temperature to obtain samples for pore size measurement. Approximately 0.5 g of the sample was placed in a standard 5 cc powder cell (stem volume 0.4 cc), and the pore size distribution was measured using a Micromeritics pore size distribution analyzer (Shimadzu Corporation, Autopore V9620) at an initial pressure of 2.6 kPa. Mercury parameters were set at a mercury contact angle of 130 degrees and a mercury surface tension of 485 dynes / cm. The pore surface area and median pore diameter were calculated for pore sizes between 0.005 and 100 μm. The pore volume ratio (V2 / V1) was calculated from the sum of the pore volumes for pore sizes between 0.005 and 100 μm (V1) and the sum of the pore volumes for pore sizes between 0.5 and 100 μm (V2).

[0081] (2) Measurement of average particle size The average particle size of the 100g pore measurement sample (freeze-dried EVOH porous pellets) prepared in the above evaluation method (1) was measured using Verder Scientific's "CAMSIZER XT." The particle size (Q3 50.0%) at which the cumulative particle size distribution from the small particle size side of the circle equivalent particle size calculated by dynamic image analysis in accordance with ISO 13322-2 (2006) is 50% (volume basis) was defined as the average particle size.

[0082] (3) High-temperature washing test 3 kg of the EVOH porous pellets obtained in the examples and comparative examples were stirred and washed in 50°C ion-exchanged water (bath ratio 20) for 1 hour, and the process of draining the water was repeated twice, and the adhesion of the EVOH porous pellets was evaluated according to the following criteria. A: No adhesion between pellets was observed. B: Loose adhesion was observed between pellets (less than 10% of pellets were stuck together). C: Agglutination was observed between pellets (10% to 50% of pellets were agglutinated). D: Severe adhesion was observed between pellets (more than 50% of pellets were stuck together).

[0083] (4) Washing frequency test The EVOH porous pellets after the high-temperature washing test (Evaluation Method (3)) were placed in a 1 g / L aqueous acetic acid solution (bath ratio: 20), washed with stirring at 25°C for 2 hours, and then drained. This procedure was repeated twice. The EVOH porous pellets after washing with the aqueous acetic acid solution were placed in ion-exchanged water (bath ratio: 20), washed with stirring at 25°C for 2 hours, and then drained. This washing with ion-exchanged water and draining procedure was repeated until the electrical conductivity of the solution after washing with ion-exchanged water was 3 μS / cm or less, and the number of times it was repeated was recorded. Electrical conductivity was measured using a "CM-30ET" manufactured by Toa Denpa Kogyo Co., Ltd.

[0084] (5) Measurement of moisture content Using 3 g each of the hydrous EVOH, EVOH porous pellets, and dried EVOH resin composition pellets used or obtained in the Examples and Comparative Examples, the moisture content of the hydrous EVOH (W1), the moisture content of the EVOH porous pellets (W2), and the moisture content of the dried EVOH resin composition pellets were measured using a METTLER halogen moisture analyzer "HR73" at a drying temperature of 180°C for a drying time of 15 minutes.

[0085] (6) Measurement of alcohol content Five grams of the hydrous EVOH used in the examples and comparative examples was freeze-pulverized in liquid nitrogen, and immediately after pulverization, a sample (approximately 500 mg) was placed in an HSS vial and analyzed for methanol under the following conditions: Each sample was measured twice, and the alcohol content was calculated from the average. Headspace (HSS)-GC / MS Oven temperature: 120°C (MHE method: [120°C x 30 minutes] x 5 times) Loop temperature: 200℃ Transfer temperature: 200°C, with shaking GC / MS Column: DB-WAXetr (30 m - 0.25 mm - 0.5 μm) Oven: 50°C (hold for 5 minutes) → 10°C / min → 200°C (hold for 10 minutes) Injection port: 230°C (split ratio 20:1) Measurement mode: SIM (m / z = 31)

[0086] (7) Melt flow rate (MFR) measurement The MFR of the dried EVOH resin composition pellets obtained in the examples and comparative examples was measured according to the method described in JIS K 7210:2014. Specifically, the pellets were filled into a cylinder of a melt indexer L244 (manufactured by Takara Kogyo Co., Ltd.) with an inner diameter of 9.55 mm and a length of 162 mm, and melted at 210°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.

[0087] (8) Determination of sodium ions, phosphate and boric acid 0.5 g of dried EVOH resin composition pellets obtained in the Examples and Comparative Examples were placed in a Teflon pressure vessel, and 5 mL of concentrated nitric acid was added and decomposed at room temperature for 30 minutes. After 30 minutes, the vessel was capped and heated at 150°C for 10 minutes and then 180°C for 5 minutes using a wet decomposition apparatus (Actac Corporation, "MWS-2"), followed by cooling to room temperature. This treated solution was transferred to a 50 mL volumetric flask (TPX®) and made up to the desired volume with purified water. The metal content of this solution was analyzed using an ICP emission spectrometer (PerkinElmer, "OPTIMA4300DV") to calculate the amount of sodium ion (elemental sodium), the amount of phosphoric acid equivalent to phosphate radical, and the amount of boric acid equivalent to boron. Quantitative analysis was performed using calibration curves prepared using commercially available standard solutions.

[0088] (9) Measurement of acetic acid content 20 g of the dried EVOH resin composition pellets obtained in the Examples and Comparative Examples were added to 100 ml of ion-exchanged water and extracted by heating at 95° C. for 6 hours. Using phenolphthalein as an indicator, the extract was neutralized by titration with 1 / 50 N NaOH to calculate the acetic acid content.

[0089] Example 1 An EVOH solution containing 100 parts by mass of EVOH with an ethylene unit content of 32 mol% and a degree of saponification of 99.98 mol%, 60 parts by mass of methanol, and 40 parts by mass of water was continuously fed into a 10-plate tower with a diameter of 0.3 m and a column diameter of 10. Steam was blown into the bottom tray, resulting in countercurrent contact between the EVOH solution and the steam. The temperature inside the tower was 130°C, and the pressure inside the tower was 0.3 MPa. The hydrous EVOH obtained by countercurrent contact with the steam was withdrawn from the bottom of the tower. The temperature of the hydrous EVOH obtained was 120°C, and the water content (W1) measured according to the above-mentioned evaluation method (5) was 52.4% by mass. The alcohol content measured according to the above-mentioned evaluation method (6) was 0.02% by mass. The results are shown in Table 1.

[0090] The resulting water-containing EVOH, with a moisture content (W1) of 52.4% by mass, was heated to 110°C and fed at 42 kg / hr into a twin-screw extruder (Figure 1) with a backslit 4 located upstream of the water-containing EVOH inlet 2 (Figure 1). The extruder was extruded through a die with eight 30 mm orifices attached to the extruder tip under the following conditions. The resulting melt was cut 0.05 mm from the die using a two-blade hot cutter (Figure 2) to obtain flattened spherical EVOH porous pellets. The flow rate of the circulating water was 300 L / min, the temperature of the circulating water (cooling water) was 5°C, and the cutter blade rotation speed was 3000 rpm. The resin temperature (at the outlet) was 95°C, and the moisture content (W2) measured according to the evaluation method (5) above was 35.5% by mass. The resin temperature (at the outlet) was measured using a temperature sensor in contact with the melt, located near the discharge outlet at the tip of the cylinder. Some of these extrusion conditions and the measurement results are shown in Table 1. The pore volume ratio, pore surface area, pore median diameter, and average particle diameter of the obtained EVOH porous pellets were measured according to the methods described in the above evaluation methods (1) and (2). The results are shown in Table 1. The pore volume (V1) was 0.289 ml / g. <Twin-screw extruder conditions> L / D: 14 Caliber: 30mm Screw: Full flight Rotation speed: 300 rpm Cylinder temperature: 90°C (maximum temperature downstream of the water-containing EVOH inlet 2) Die temperature: 120℃ Number of dice holes: 8

[0091] A high-temperature washing test and a washing frequency test were conducted according to the methods described in the evaluation methods (3) and (4) above, and washed EVOH porous pellets were obtained. The obtained washed EVOH porous pellets were placed in an aqueous solution (bath ratio: 20) containing 0.510 g / L of sodium acetate, 0.8 g / L of acetic acid, and 0.04 g / L of phosphoric acid. The pellets were immersed for 4 hours with periodic stirring for chemical treatment. The pellets were drained and dried at 95°C for 3 hours under a nitrogen stream with an oxygen concentration of 1% by volume or less to obtain dried EVOH resin composition pellets with a moisture content of 0.5% by mass. The obtained dried EVOH resin composition pellets were evaluated for moisture content (moisture content after 3 hours of drying), MFR (MFR after drying), sodium ion content, phosphoric acid content, and acetic acid content according to the methods described in the evaluation methods (5) and (7) to (9) above. The sodium ion content was 100 ppm, the phosphoric acid equivalent of 40 ppm, and the acetic acid content was 200 ppm. Other results are shown in Table 1.

[0092] (Examples 2 to 10, Comparative Example 1) EVOH porous pellets and dried EVOH resin composition pellets were produced and evaluated in the same manner as in Example 1, except that the ethylene unit content, alcohol content, temperature and water content W1 of the resin fed to the extruder, cylinder temperature, temperature of the resin extruded from the extruder, and circulating water (cooling water) temperature were changed to be as shown in Table 1. The results are shown in Table 1. In all of the Examples and Comparative Examples, the sodium ion content was 100 ppm, the amount of phosphoric acid converted to phosphate radical was 40 ppm, and the acetic acid content was 200 ppm. The pore volume (V1) of Comparative Example 1 was 0.418 ml / g.

[0093] Example 11 Dried EVOH resin composition pellets of Example 11 were obtained in the same manner as in Example 9, except that the aqueous solution used in the chemical treatment was an aqueous solution containing sodium acetate at a concentration of 0.510 g / L, acetic acid at a concentration of 0.8 g / L, phosphoric acid at a concentration of 0.04 g / L, and boric acid at a concentration of 0.57 g / L (bath ratio: 20). The moisture content, MFR, sodium ion content, phosphoric acid content, boric acid content, and acetic acid content of the obtained dried EVOH resin composition pellets were evaluated according to the methods described in the above evaluation methods (5) and (7) to (9). The sodium ion content was 100 ppm, the phosphoric acid phosphate radical equivalent content was 40 ppm, the acetic acid content was 200 ppm, and the boron equivalent content was 800 ppm. Other results are shown in Table 1.

[0094] (Comparative Example 2) An EVOH solution containing 100 parts by weight of EVOH with an ethylene unit content of 32 mol% and a saponification degree of 99.98 mol%, 60 parts by weight of methanol, and 40 parts by weight of water was extruded into a water and methanol mixed solution (water / methanol = 9 / 1 mass ratio) maintained at -5°C through a gold plate with a circular opening of 3.5 mm in diameter into strands. The strands precipitated and solidified, and were then cut with a cutter to obtain porous EVOH pellets (cylindrical, 4 mm in diameter and 4 mm in length). The EVOH was then poured into cold water at 10°C and stirred for approximately 4 hours to obtain porous EVOH pellets. The pore volume ratio (V2 / V1), pore surface area, median pore diameter, average particle size, and water content of the resulting porous EVOH pellets were measured according to the methods described in the evaluation methods (1), (2), and (5) above. The results are shown in Table 1. The pore volume (V1) was 0.485 ml / g.

[0095] Next, a high-temperature washing test was conducted according to the method described in the above evaluation method (3). As a result of the high-temperature washing test, D: severe adhesion between pellets was observed. After removing the adhered pellets, a washing cycle test was conducted according to the method described in (4) to obtain washed EVOH porous pellets. The obtained washed EVOH porous pellets were placed in an aqueous solution (bath ratio: 20) containing sodium acetate at a concentration of 0.510 g / L, acetic acid at a concentration of 0.8 g / L, and phosphoric acid at a concentration of 0.04 g / L. The resulting EVOH porous pellets were immersed for 4 hours with periodic stirring for chemical treatment. The pellets were drained and dried at 95°C for 3 hours under a nitrogen stream with an oxygen concentration of 1% by volume or less, yielding pellets with a moisture content of 25% by mass. Because drying was insufficient, the resulting pellets were further dried at 125°C for 18 hours under a nitrogen stream with an oxygen concentration of 1% by volume or less, yielding dried EVOH resin composition pellets with a moisture content of 0.3%. The moisture content, MFR, sodium ion content, phosphoric acid content, and acetic acid content of the dried EVOH resin composition pellets were evaluated according to the methods described in the above evaluation methods (5) and (7) to (9). The sodium ion content was 100 ppm, the phosphoric acid phosphate radical equivalent content was 40 ppm, and the acetic acid content was 200 ppm. Other results are shown in Table 1.

[0096] (Comparative Example 3) An EVOH solution containing 100 parts by weight of EVOH with an ethylene unit content of 32 mol% and a saponification degree of 99.98 mol%, 60 parts by weight of methanol, and 40 parts by weight of water was extruded into a water and methanol mixed solution (water / methanol = 9 / 1 mass ratio) maintained at 5°C through a gold plate with a circular opening of 3.5 mm in diameter into strands. The strands precipitated and solidified, and then cut with a cutter to obtain porous EVOH pellets. The EVOH was then poured into warm water at 30°C and stirred for approximately 4 hours to obtain porous EVOH pellets. The pore volume ratio (V2 / V1), pore surface area, median pore diameter, average particle size, and water content of the resulting porous EVOH pellets were measured according to the methods described in the evaluation methods (1), (2), and (5) above. The results are shown in Table 1.

[0097] Next, a high-temperature washing test was conducted according to the method described in the above evaluation method (3). As a result of the high-temperature washing test, C: adhesion between pellets was observed. After removing the adhered pellets, a washing cycle test was conducted according to the method described in (4) to obtain washed EVOH porous pellets. The obtained washed EVOH porous pellets were placed in an aqueous solution (bath ratio: 20) containing sodium acetate at a concentration of 0.510 g / L, acetic acid at a concentration of 0.8 g / L, and phosphoric acid at a concentration of 0.04 g / L. The resulting EVOH porous pellets were immersed for 4 hours with periodic stirring for chemical treatment. The pellets were drained and dried at 95°C for 3 hours under a nitrogen stream with an oxygen concentration of 1% by volume or less, yielding pellets with a moisture content of 18% by mass. Because drying was insufficient, the resulting pellets were further dried at 125°C for 18 hours under a nitrogen stream with an oxygen concentration of 1% by volume or less, yielding dried EVOH resin composition pellets with a moisture content of 0.3%. The moisture content, MFR, sodium ion content, phosphoric acid content, and acetic acid content of the dried EVOH resin composition pellets were evaluated according to the methods described in the above evaluation methods (5) and (7) to (9). The sodium ion content was 100 ppm, the phosphoric acid phosphate radical equivalent content was 40 ppm, and the acetic acid content was 200 ppm. Other results are shown in Table 1.

[0098] Comparative Example 4 EVOH porous pellets were produced and evaluated in the same manner as in Example 1, except that the conditions were changed so that the ethylene unit content, alcohol content, temperature and water content W1 of the resin fed to the extruder, cylinder temperature, and temperature of the resin extruded from the extruder were as shown in Table 1, and the water-containing EVOH discharged from the twin-screw extruder was extruded through four nozzles (diameter 6 mm) into a coagulating liquid (cooling water) made of water at 10°C, coagulated into strands, and cut into pellets with a strand cutter. The results are shown in Table 1.

[0099] The resulting EVOH porous pellets were subjected to a high-temperature washing test according to the method described in Evaluation Method (3) above. During the first washing cycle of the high-temperature washing test, almost no adhesion between pellets was observed. However, after the second washing cycle following dewatering, adhesion between pellets was observed. After removing the adhered pellets, a washing cycle test was performed according to the method described in Evaluation Method (4) above to obtain washed EVOH porous pellets. The resulting washed EVOH porous pellets were placed in an aqueous solution (bath ratio: 20) containing sodium acetate at a concentration of 0.510 g / L, acetic acid at a concentration of 0.8 g / L, and phosphoric acid at a concentration of 0.04 g / L. The resulting EVOH porous pellets were immersed for 4 hours with periodic stirring for chemical treatment. The pellets were then dewatered and dried at 95°C for 3 hours under a nitrogen stream with an oxygen concentration of 1% by volume or less to obtain dried EVOH resin composition pellets with a moisture content of 0.7% by mass. The moisture content, MFR, sodium ion content, phosphoric acid content, and acetic acid content of the dried EVOH resin composition pellets were evaluated according to the methods described in Evaluation Methods (5) and (7) to (9) above. The sodium ion content was 100 ppm, the amount of phosphoric acid converted to phosphate radical was 40 ppm, and the acetic acid content was 200 ppm. Other results are shown in Table 1.

[0100] [Table 1]

[0101] As shown in Table 1, the EVOH porous pellets of Examples 1 to 11 were evaluated as A or B in the high-temperature washing test and were washed 4 or less times in the number of washings test. This indicates that the saponification residue can be washed off in a short time and that adhesion between pellets during high-temperature washing is suppressed. Among the examples, the pore volume ratio (V2 / V1) is 32% by volume or more and the pore surface area is 32.0 m 2 The EVOH porous pellets of Examples 1, 3, 5 to 7, and 9 to 11, in which the pore volume ratio (V2 / V1) was 38.5 vol% or less and the pore surface area was 32.0 m / g or more, were washed three times or less in the washing frequency test, and washing could be performed in a shorter time. 2 / g or more 41m 2The EVOH porous pellets of Examples 1 and 9 to 11, in which the porosity was 1 / g or less, were washed 3 times or less in the washing frequency test and were evaluated as A in the temperature-lowering washing test, and thus exhibited particularly high effects. [Explanation of symbols]

[0102] 1 cylinder 2. Introduction 3 Downstream 4 Back slit 5. Water-containing EVOH flow 6 Temperature Sensor 7 Upstream 8 Full Flight Screw 30 Hot Cutter 31 Melt supply port 32 Die 33 Rotary Blade 34 Rotation axis 35 Cutter Box 36 Cooling water supply port 37 Cooling water 38 Water film 39 Pellet outlet 40 Cooling water and pellets

Claims

1. A porous ethylene-vinyl alcohol copolymer pellet having pores, wherein the ratio (V2 / V1×100) of the total pore volume (V2) of pores having a diameter of 0.5 to 100 μm to the total pore volume (V1) of pores having a diameter of 0.005 to 100 μm is 25 to 38.5 vol%, and the pore surface area of ​​pores having a diameter of 0.005 to 100 μm is 25 to 37 m. ２ / g of ethylene-vinyl alcohol copolymer porous pellets.

2. 2. The ethylene-vinyl alcohol copolymer porous pellet according to claim 1, wherein the median diameter of pores in the pore diameter range of 0.005 to 100 μm is 0.05 to 0.13 μm.

3. 3. The ethylene-vinyl alcohol copolymer porous pellet according to claim 1, having an average particle size of 2.5 to 8 mm.

4. The ethylene-vinyl alcohol copolymer porous pellet according to any one of claims 1 to 3, which contains water.

5. The ethylene-vinyl alcohol copolymer porous pellet according to claim 4, having a moisture content of 5 to 50% by mass.

6. The method comprises a first step of introducing a paste-like water-containing ethylene-vinyl alcohol copolymer having a water content W1 of 10 to 90% by mass into an extruder and melt-kneading the copolymer, and a second step of cutting the water-containing ethylene-vinyl alcohol copolymer discharged from the extruder to obtain water-containing porous ethylene-vinyl alcohol copolymer pellets, In the second step, the water-containing ethylene-vinyl alcohol copolymer discharged from the extruder is cut in a molten state, and the temperature of the water-containing ethylene-vinyl alcohol copolymer discharged from the extruder is 80 to 100°C; the ratio (V2 / V1×100) of the total pore volume (V2) of pores having a diameter of 0.5 to 100 μm to the total pore volume (V1) of pores having a diameter of 0.005 to 100 μm of the ethylene-vinyl alcohol copolymer porous pellets is 25 to 38.5 vol%, The pore surface area of ​​the ethylene-vinyl alcohol copolymer porous pellets is 25 to 37 m ２ / g, Method for producing porous ethylene-vinyl alcohol copolymer pellets.

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