JP2023101488A - Resin composition, multilayer structure, packaging container and method for producing resin composition - Google Patents

Abstract

To provide a resin composition which is excellent in gas barrier properties and moisture resistance under high temperature and high humidity and can suppress whitening of a multilayer structure after retort processing, a multilayer structure composed of the resin composition and a method for producing the resin composition.SOLUTION: There is provided a resin composition comprising an ethylene-vinyl alcohol copolymer (A) and a metal salt having a hydrophobic group (B) capable of forming a hydrate, wherein the metal salt (B) having a hydrophobic group capable of forming a hydrate contains at least one selected from the group consisting of a phosphate, a phosphonate, a phosphinate, a sulfonate or a sulfinate.SELECTED DRAWING: None

Description

The present invention relates to a resin composition containing an ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as "EVOH") and a metal salt having a hydrophobic group capable of forming a hydrate. A multilayer structure having a layer made of the resin composition is suitably used as a packaging container to be retorted.

Glass, metal and metal foil are still dominant as materials for containers for retorting foods such as vegetables and seafood. Recently, however, plastic containers are commonly used as containers for retorting soups, pet foods, and other foods. Since the container is rigid or semi-rigid, EVOH, which has excellent workability and gas barrier properties, is employed as a barrier resin for the plastic container.

Due to its chemical structure, EVOH is known to have a tendency to deteriorate its gas barrier properties in an environment where the relative humidity exceeds 85%. It is believed that this is because water acts as a plasticizer for EVOH, weakening hydrogen bonding in the amorphous regions of EVOH and increasing the amount of free volume, resulting in increased gas diffusion in the polymer matrix. Therefore, when the package is subjected to a typical steam retort treatment at a temperature of 110 to 132° C. for 15 to 80 minutes, the oxygen permeation rate of EVOH dramatically increases, and the food is oxidatively deteriorated, resulting in a decrease in flavor and a shortened shelf life. On the other hand, for example, a method of adding a desiccant to EVOH is known. For example, Patent Document 1 describes that a multilayer structure composed of a resin composition containing EVOH, a phosphate capable of forming a hydrate, and a dispersing agent, has excellent gas barrier properties and excellent moisture resistance under high temperature and high humidity conditions.

Patent Document 2 describes that a resin composition containing an EVOH resin and a partially dehydrated or completely dehydrated carboxylate hydrate suppresses an increase in viscosity during kneading and is excellent in handleability, and that a multilayer structure having at least one layer containing the resin composition has excellent gas barrier properties after hydrothermal treatment.

Patent Document 3 describes that a resin composition containing an EVOH resin, a hydrate-forming carboxylate having a median diameter of 0.5 to 25 μm, and a basic metal salt suppresses an increase in viscosity during melt-kneading, is excellent in long-run processability, and that a molded product obtained from the resin composition can suppress the generation of a cloudy pattern that occurs when stored for a long time under high humidity.

JP 2008-75084 A JP 2010-59418 A JP 2016-121335 A

However, the multi-layer structures described in Patent Documents 1 to 3 are whitened after retort processing, and the food in the container cannot be seen, resulting in poor visibility of the food. Moreover, when a carboxylate is used, corrosion may be observed in the extruder during melt-kneading.
The present invention has been made to solve the above problems, and an object thereof is to provide a resin composition that has excellent gas barrier properties, excellent moisture resistance under high temperature and high humidity conditions, and that can suppress whitening of a multilayer structure after retort treatment. Another object of the present invention is to provide a multi-layered structure having a layer made of the resin composition, in which deterioration of gas barrier properties is suppressed even during retort treatment. Furthermore, it aims at providing the suitable manufacturing method of this resin composition.

The present inventors have found that a resin composition containing EVOH and a specific metal salt can solve the above problems. Its specific configuration is as follows.

(1) A resin composition comprising an ethylene-vinyl alcohol copolymer (A) and a metal salt (B) having a hydrophobic group capable of forming a hydrate,
A resin composition containing at least one metal salt (B) having a hydrophobic group capable of forming a hydrate selected from the group consisting of phosphates, phosphonates, phosphinates, sulfonates and sulfinates;
(2) The resin composition according to (1) above, which contains 70.0 to 99.0% by mass of the ethylene-vinyl alcohol copolymer (A) and 1.0 to 30.0% by mass of the metal salt (B) having a hydrophobic group capable of forming a hydrate in the resin composition;
(3) The resin composition according to (1) or (2) above, wherein the metal salt (B) having a hydrophobic group capable of forming a hydrate has either an aromatic ring or an alkyl group;
(4) further contains a polyamide (C),
The resin composition according to any one of (1) to (3), wherein the content of the polyamide resin (C) is 0.1 to 20.0 parts by mass with respect to the total 100 parts by mass of the ethylene-vinyl alcohol copolymer (A) and the alkali metal salt (B) having a hydrophobic group capable of forming a hydrate;
(5) The method for producing a resin composition according to any one of (1) to (4) above, comprising a step of precipitating a melt containing an ethylene-vinyl alcohol copolymer (A) and a metal salt (B) having a hydrophobic group capable of forming a hydrate;
(6) The method for producing a resin composition according to any one of (1) to (4) above, comprising a step of immersing hydrous pellets of the ethylene-vinyl alcohol copolymer (A) having a water content of 1 to 200% by mass in an aqueous solution containing an alkali metal salt (B) having a hydrophobic group capable of forming a hydrate;
(7) The method for producing a resin composition according to any one of the above (1) to (4), comprising the step of adding an aqueous solution containing a metal salt (B) having a hydrophobic group capable of forming a hydrate to a melt containing the ethylene-vinyl alcohol copolymer (A) and water; and the step of melt-kneading the melt to which the aqueous solution has been added;
(8) The method for producing a resin composition according to any one of (1) to (4) above, comprising the step of melt-kneading the ethylene-vinyl alcohol copolymer (A) and the metal salt (B) having a hydrophobic group capable of forming a hydrate;
(9) A multilayer structure comprising at least one layer comprising the resin composition layer according to any one of (1) to (4) above;
(10) A multilayer structure having at least one layer made of a resin composition from a recovered multilayer structure having a layer made of the resin composition according to any one of (1) to (4) and a layer made of at least one thermoplastic resin selected from the group consisting of polyolefin, polystyrene, polyester, polyamide, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate and polyacrylonitrile;
(11) A packaging container comprising the multilayer structure according to (9) or (10);
(12) A retort packaging container comprising the packaging container according to (11) filled with contents;
(13) A method of sterilizing the retort packaging container according to (12) above with steam or hot water at a temperature of 70°C or higher and 140°C or lower.

By using the resin composition of the present invention, it is possible to obtain a resin composition that has excellent gas barrier properties, excellent moisture resistance under high temperature and high humidity conditions, and that can suppress whitening of a multilayer structure after retort treatment.

The resin composition of the present invention is a resin composition containing an ethylene-vinyl alcohol copolymer (A) and a metal salt (B) having a hydrophobic group capable of forming a hydrate, wherein the metal salt (B) having a hydrophobic group capable of forming a hydrate contains at least one selected from the group consisting of phosphates, phosphonates, phosphinates, sulfonates and sulfinates. By blending EVOH (A) with a metal salt (B) having a hydrophobic group capable of forming a hydrate, sheet whitening occurring after retort treatment can be improved.

(EVOH (A))
The ethylene content of EVOH (A) used in the resin composition of the present invention is preferably 15 to 65 mol %. If the ethylene content is less than 15 mol %, the moisture resistance may be insufficient, making it unsuitable for use under high-temperature and high-humidity conditions such as retort treatment. The ethylene content is more preferably 20 mol % or more, more preferably 25 mol % or more. If the ethylene content exceeds 65 mol%, gas barrier properties may be insufficient. The ethylene content is more preferably 50 mol % or less, even more preferably 40 mol % or less.

The degree of saponification of EVOH (A) is preferably 95 mol % or more. If the degree of saponification is less than 95 mol %, the crystallinity of the EVOH is low, the gas barrier properties are low, and the thermal stability during melt molding is greatly reduced. The degree of saponification is preferably 98 mol% or more, more preferably 99 mol% or more.

The melt flow rate of EVOH (A) (210° C., under a load of 2160 g) is preferably 0.1 to 50 g/10 minutes. If the melt flow rate is less than 0.1 g/10 minutes, melt molding may become difficult. The melt flow rate is more preferably 0.5 g/10 minutes or more, more preferably 1 g/10 minutes or more. If the melt flow rate exceeds 50 g/10 minutes, extrusion molding of the resin composition may become difficult, and the strength of the resulting layer containing EVOH (A) may decrease. The melt flow rate is more preferably 20 g/10 minutes or less, even more preferably 10 g/10 minutes or less.

EVOH (A) may have units derived from monomers other than ethylene, vinyl esters, and saponified products thereof, as long as the effects of the present invention are not impaired. When EVOH (A) has units derived from other monomers, the content thereof is preferably 10 mol% or less, more preferably 5 mol% or less, and even more preferably 3 mol% or less, relative to the total monomer units in EVOH (A). Also, the content of other monomer units may be 0.05 mol % or more. Examples of other monomers include vinylsilane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxy-ethoxy)silane, and γ-methacryloxypropylmethoxysilane.

EVOH (A) may have at least one of structural unit (I) represented by formula (I) below, structural unit (II) represented by formula (II) below, and structural unit (III) represented by general formula (III) below, as long as the object of the present invention is not impaired. When EVOH (A) has such a structural unit, the thermoformability of the resulting multilayer structure can be enhanced.

In formula (I), R1, R2 and R3 each independently represents a hydrogen atom, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, an alicyclic hydrocarbon group having 3 to 10 carbon atoms, an aromatic hydrocarbon group having 6 to 10 carbon atoms or a hydroxyl group. Also, one pair of R1, R2 and R3 may be bonded. In addition, some or all of the hydrogen atoms of the aliphatic hydrocarbon group having 1 to 10 carbon atoms, the alicyclic hydrocarbon group having 3 to 10 carbon atoms and the aromatic hydrocarbon group having 6 to 10 carbon atoms may be substituted with a hydroxyl group, a carboxyl group or a halogen atom.

In formula (II), R4, R5, R6 and R7 each independently represents a hydrogen atom, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, an alicyclic hydrocarbon group having 3 to 10 carbon atoms, an aromatic hydrocarbon group having 6 to 10 carbon atoms or a hydroxyl group. Also, R4 and R5, or R6 and R7 may be bonded. Further, some or all of the hydrogen atoms of the aliphatic hydrocarbon group having 1 to 10 carbon atoms, the alicyclic hydrocarbon group having 3 to 10 carbon atoms and the aromatic hydrocarbon group having 6 to 10 carbon atoms may be substituted with a hydroxyl group, an alkoxy group, a carboxyl group or a halogen atom.

In formula (III), R8, R9, R10 and R11 each independently represents a hydrogen atom, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, an alicyclic hydrocarbon group having 3 to 10 carbon atoms, an aromatic hydrocarbon group having 6 to 10 carbon atoms or a hydroxyl group. Further, some or all of the hydrogen atoms of the aliphatic hydrocarbon group having 1 to 10 carbon atoms, the alicyclic hydrocarbon group having 3 to 10 carbon atoms and the aromatic hydrocarbon group having 6 to 10 carbon atoms may be substituted with a hydroxyl group, an alkoxy group, a carboxyl group or a halogen atom. R12 and R13 each independently represent a hydrogen atom, a formyl group or an alkanoyl group having 2 to 10 carbon atoms.

When EVOH (A) contains a structural unit represented by the above formula, the lower limit of the content is preferably 0.1 mol%, more preferably 0.5 mol%, and even more preferably 1 mol%. Moreover, the upper limit of the content is preferably 30 mol %, more preferably 15 mol %, and even more preferably 10 mol %. When the content of the structural unit represented by the above formula is within the above range, the flexibility and processability of the resin composition are improved, and the thermoformability of the obtained multilayer structure is improved.

In the structural unit shown in the above formula, examples of aliphatic hydrocarbon groups having 1 to 10 carbon atoms include alkyl groups and alkenyl groups, examples of alicyclic hydrocarbon groups having 3 to 10 carbon atoms include cycloalkyl groups and cycloalkenyl groups, and examples of aromatic hydrocarbon groups having 6 to 10 carbon atoms include phenyl groups and the like.

In the structural unit (I), R1, R2 and R3 are preferably each independently a hydrogen atom, a methyl group, an ethyl group, a hydroxyl group, a hydroxymethyl group and a hydroxyethyl group. Among them, each independently a hydrogen atom, a methyl group, a hydroxyl group and a hydroxymethyl group are preferred from the viewpoint of further improving the thermoformability of the obtained multilayer structure.

In structural unit (II), both R4 and R5 are preferably hydrogen atoms. More preferably, both R4 and R5 are hydrogen atoms, one of R6 and R7 is an aliphatic hydrocarbon group having 1 to 10 carbon atoms, and the other is a hydrogen atom. This aliphatic hydrocarbon group is preferably an alkyl group or an alkenyl group. From the viewpoint of placing particular importance on the gas barrier properties of the resulting multilayer structure, it is particularly preferred that one of R6 and R7 is a methyl group or an ethyl group, and the other is a hydrogen atom. It is also particularly preferred that one of R6 and R7 is a substituent represented by (CH ₂ ) _h OH (where h is an integer of 1 to 8) and the other is a hydrogen atom. In the substituent represented by (CH ₂ ) _h OH, h is preferably an integer of 1 to 4, more preferably 1 or 2, and particularly preferably 1.

In structural unit (III), R8, R9, R10 and R11 are preferably a hydrogen atom or an aliphatic hydrocarbon group having 1 to 5 carbon atoms, and the aliphatic hydrocarbon group is preferably a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group or an n-pentyl group.

EVOH (A) may be used singly or in combination of two or more.

(Metal salt (B) having a hydrophobic group capable of forming a hydrate)
The metal salt (B) having a hydrophobic group capable of forming a hydrate (hereinafter sometimes abbreviated as metal salt (B)) absorbs water by forming a hydrate, and contains at least one selected from the group consisting of phosphates, phosphonates, phosphinates, sulfonates and sulfinates. By adding the metal salt (B) to the EVOH (A), the metal salt (B) takes in moisture that permeates the resin composition during the retort treatment, and a high gas barrier property can be maintained even after the retort treatment. The metal salt (B) is preferably a phosphate, a phosphonate or a phosphinate, and more preferably a phosphate because it forms a hydrate containing a plurality of water molecules as water of crystallization and can absorb a large amount of water per unit weight. Since the number of molecules of water of crystallization that can be formed by phosphate increases stepwise as the humidity rises, the phosphate can gradually absorb water as the humidity environment changes.

In the resin composition of the present invention, since the metal salt (B) has a hydrophobic group, aggregation of the metal salt due to water absorption during retort treatment can be suppressed, and whitening of the obtained multilayer structure can be suppressed. The hydrophobic group of the metal salt (B) includes, for example, an aromatic ring or an alkyl group, specifically a phenyl group such as a phenyl group, a 4-nitrophenyl group and a 2,5-dihydroxybenzyl group; a naphthyl group such as a 1-naphthyl group;

Examples of the metal salt (B) include disodium phenyl phosphate, disodium 4-nitrophenyl phosphate, disodium ethyl phosphate, monosodium 1-naphthyl phosphate, disodium 1-naphthyl phosphate, disodium α-glycerophosphate, disodium β-glycerophosphate, phenyl calcium phosphate, phenyl magnesium phosphate, disodium phenylphosphonate, sodium benzenesulfonate, sodium p-toluenesulfonate, sodium p-toluenesulfinate, calcium bis(2,5-dihydroxybenzenesulfonate), and the like. , disodium phenyl phosphate, disodium phenylphosphonate, and disodium ethyl phosphate are preferred. These may be anhydrides or hydrates.

(Polyamide (C))
The resin composition of the present invention further contains a polyamide (C), and the content of the polyamide (C) is 0.1 to 20.0 parts by mass with respect to a total of 100 parts by mass of the EVOH (A) and the metal salt (B). When the content of the polyamide (C) is within the above range, whitening can be suppressed when the multilayer structure made of the resin composition of the present invention is subjected to retort treatment. The content of the polyamide (C) is more preferably 1.0 to 15.0 parts by mass, more preferably 3.0 to 12.0 parts by mass.

Specific examples of polyamide (C) include polycapramide (nylon 6), poly-ω-aminoheptanoic acid (nylon 7), poly-ω-aminononanoic acid (nylon 9), polyundecaneamide (nylon 11), polylauryllactam (nylon 12), polyethylenediamineadipamide (nylon 26), polytetramethyleneadipamide (nylon 46), polyhexamethyleneadipamide (nylon 66), polyhexamethylenesebacamide (nylon 610), polyhexamethylenedodeca. polyoctamethyleneadipamide (nylon 86), polydecamethyleneadipamide (nylon 106), caprolactam/lauryllactam copolymer (nylon 6/12), caprolactam/ω-aminononanoic acid copolymer (nylon 6/9), caprolactam/hexamethylenediammonium adipate copolymer (nylon 6/66), lauryllactam/hexamethylenediammonium adipate copolymer (nylon 12/66), ethylene Diammonium adipate/hexamethylenediammonium adipate copolymer (nylon 26/66), caprolactam/hexamethylenediammonium adipate/hexamethylenediammonium sebacate copolymer (nylon 6/66/610), ethylenediammonium adipate/hexamethylenediammonium adipate/hexamethylenediammonium sebacate copolymer (nylon 26/66/610), polyhexamethylene isophthalamide (nylon 6I), polyhexamethylene terephthalamide (nylon 6) T), hexamethylene isophthalamide/hexamethylene terephthalamide copolymer (nylon 6I/6T), 11-aminoundecaneamide/hexamethylene terephthalamide copolymer, polynonamethylene terephthalamide (nylon 9T), polydecamethylene terephthalamide (nylon 10T), polyhexamethylenecyclohexylamide, polynonamethylenecyclohexylamide, or those obtained by modifying these polyamides with aromatic amines such as methylenebenzylamine and metaxylenediamine. In addition, meta-xylylene diammonium adipate and the like are also included. Among them, polycapramide (nylon 6) is preferable from the viewpoint of compatibility with EVOH.

The degree of polymerization of the polyamide (C) is preferably 1.7 to 5.0, more preferably 2.0 to 5.0, as measured according to JIS K6810.

As a method for polymerizing the polyamide (C), melt polymerization, interfacial polymerization, solution polymerization, bulk polymerization, solid phase polymerization, or a combination thereof can be employed. In addition, ε-caprolactam is preferable as the raw material for the polyamide because it provides better retort resistance.

(resin composition)
The compounding ratio of EVOH (A) and metal salt (B) in the resin composition of the present invention is preferably 70.0 to 99.0% by mass of (A) and 1.0 to 30.0% by mass of (B) with respect to a total of 100% by mass of (A) and (B). In the resin composition of the present invention, EVOH (A) is the main component and forms a matrix to ensure gas barrier properties. When the content of the metal salt (B) is less than 1.0% by mass, the moisture resistance of the resin composition, especially under high temperature and high humidity conditions, is lowered. The content of the metal salt (B) is more preferably 3.0% by mass or more, and even more preferably 5.0% by mass or more. On the other hand, when the content of the metal salt (B) exceeds 30.0% by mass with respect to the total of 100 parts by weight of (A) and (B), elution of the resin composition layer at the edges of the multilayer structure may occur after the resulting multilayer structure is subjected to retort treatment. The content of the metal salt (B) is more preferably 20.0% by mass or less, even more preferably 15.0% by mass or less.

The resin composition of the present invention may contain other components as long as the effects of the present invention are not impaired. For example, thermoplastic resins other than EVOH (A) may be contained, and polyolefins such as polyethylene (ultra-low density, low density, medium density, high density), ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, polypropylene, ethylene-propylene copolymer, ionomer; graft modified products of the above polyolefins such as maleic anhydride and glycidyl methacrylate; Aliphatic polyesters such as polyethylene succinate and polybutylene succinate; polyethers such as polyethylene glycol and polyphenylene ether;

In addition, other various plasticizers, stabilizers, surfactants, coloring agents, ultraviolet absorbers, antistatic agents, cross-linking agents, metal salts, fillers, reinforcing agents such as various fibers, etc., can also be contained.

Although the method for producing the resin composition of the present invention is not particularly limited, it is usually produced by the following methods (1) to (4).
(1) A method of preparing a mixed paste by mixing EVOH (A) and metal salt (B) in a solvent, precipitating strands, pelletizing and drying.
(2) A method of immersing a hydrous EVOH (A) pellet in a solution containing a metal salt (B).
(3) A method of adding a metal salt (B) to a melt containing EVOH (A) and water in an extruder, followed by melt-kneading.
(4) A method of melt-kneading EVOH (A) and pulverized and dried metal salt (B) in an extruder.

((1) Method of mixing EVOH (A) and metal salt (B) in a solvent to prepare a mixed paste, precipitating strands, pelletizing and drying)
As the solvent, a solvent in which both EVOH (A) and metal salt (B) are dissolved is preferably used. Water, alcohol, and a mixed solvent of water and alcohol are preferably used from the viewpoint that the residual solvent can be easily removed, and among them, a mixed solvent of water and methanol is particularly preferably used.

The blending ratio of water and methanol in the mixed solvent is preferably 20 to 70% by mass of water and 30 to 80% by mass of methanol with respect to 100% by mass of water and methanol in total. When the content of methanol is less than 30% by mass with respect to the total of 100% by mass of water and methanol, the solubility of EVOH in the mixed solvent is lowered. The content of methanol is more preferably 35% by mass or more, still more preferably 40% by mass or more, and particularly preferably 45% by mass or more. If the content of methanol is 80% by mass or more with respect to the total of 100% by mass of water and methanol, the solubility of the metal salt (B) in the mixed solvent decreases. The content of methanol is more preferably 70% by mass or less, still more preferably 60% by mass or less, and particularly preferably 55% by mass or less.

The content of EVOH (A) is preferably 10 to 50% by mass with respect to the total 100% by mass of EVOH (A), metal salt (B) and mixed solvent. When the content of EVOH (A) is less than 10% by mass, solidification of the resin composition is less likely to proceed during strand precipitation in a solvent. The content of EVOH (A) is more preferably 20% by mass or more, still more preferably 30% by mass or more, and particularly preferably 35% by mass or more. When the content of EVOH (A) is 50% by mass or more, the viscosity of the solution is high, and strand precipitation may not be performed. The content of EVOH (A) is more preferably 45% or less, even more preferably 40% or less.

From the viewpoint of promoting dissolution, it is preferable to dissolve EVOH (A) while the mixed solvent is heated. The mixed paste is strand-precipitated in a solvent and pelletized. Since the pellets obtained by this production method contain a solvent, it is preferable to dry them at 60 to 130° C. after pelletizing.

((2) Method of immersing hydrous EVOH (A) pellets in solution containing metal salt (B))
The water content of the hydrous EVOH (A) is preferably 1 to 200% by mass based on the solid content of the EVOH. If the water content of the hydrous EVOH (A) is less than 1% by mass, even if the hydrous EVOH (A) is immersed in an aqueous solution containing the metal salt (B), the metal salt (B) may not be sufficiently incorporated into the hydrous EVOH (A). The water content of the hydrous EVOH is more preferably 20% by mass or more, still more preferably 50% by mass or more, and particularly preferably 80% by mass or more. If the water content of the hydrous EVOH (A) exceeds 200% by mass, the metal salt (B) may not be stably incorporated into the hydrous EVOH (A). The water content of the hydrous EVOH (A) is more preferably 150% by mass or less.

The immersion time of the hydrous EVOH (A) in the aqueous solution containing the metal salt (B) is preferably 10 minutes to 48 hours. If the water-containing EVOH (A) is immersed for less than 10 minutes, the metal salt (B) may not be sufficiently incorporated into the water-containing EVOH (A). The soaking time of the water-containing EVOH (A) is more preferably 30 minutes or longer, more preferably 1 hour or longer, and particularly preferably 2 hours or longer. If the water-containing EVOH (A) is immersed for 48 hours or longer, water may volatilize from the aqueous solution, increasing the concentration of the metal salt (B). The soaking time of the water-containing EVOH (A) is more preferably 24 hours or less, still more preferably 18 hours or less, and particularly preferably 12 hours or less. Since the pellets obtained by this production method contain water, it is preferable to dry them at 60 to 130° C. after pelletizing.

((3) A method of adding a metal salt (B) to a melt containing EVOH (A) and water in an extruder and melt-kneading)
The EVOH (A) to be used may be in a hydrated state or in a dry state. When the EVOH (A) is in a water-containing state, for example, the water content of the water-containing EVOH (A) is preferably less than 200% by mass based on the solid content of the EVOH. If the water content of the hydrous EVOH (A) is 200% by mass or more, water vapor may flow back in the extruder feeding section, causing the resins to adhere to each other. The water content of the hydrous EVOH (A) is more preferably 150% by mass or less, still more preferably 100% by mass or less.

Melt-kneading in the extruder is usually carried out at a temperature of 100-250°C. If the kneading temperature is lower than 100°C, the hydrous EVOH (A) will not melt and will not be sufficiently mixed with the metal salt (B). The kneading temperature is preferably 120°C or higher, more preferably 140°C or higher. If the kneading temperature is 250° C. or higher, the hydrous EVOH (A) may deteriorate due to heat. The kneading temperature is preferably 230°C or lower, more preferably 220°C or lower.

The molten hydrous EVOH (A) is mixed with the metal salt (B). Here, the metal salt (B) may be mixed with the hydrous EVOH (A) and then kneaded, or an aqueous solution of the metal salt (B) may be added to the EVOH (A) previously melted in the extruder and mixed in the extruder. From the viewpoint of suppressing the generation of voids during pelletization, it is preferable to vent the water contained in the aqueous solution of the hydrous EVOH (A) and the metal salt (B).

((4) Method of melt-kneading EVOH (A) and pulverized and dried metal salt (B) in an extruder)
The metal salt (B) should not contain coarse particles, and a powder having a specific particle size distribution or a specific average particle size is preferably used. The method for producing such powder is not particularly limited, but it is preferable to pulverize the metal salt (B) in advance before melt-kneading. Examples of the pulverizing device include jet mills, ball mills, cutting mills, impact pulverizers and the like. Among them, a jet mill, particularly a fluidized bed jet mill is preferably used. In the fluidized bed jet mill, the particles can be pulverized while preventing metal contamination by causing the particles to collide with each other due to the collision of opposed jet air. Moreover, it is preferable that the pulverizer incorporates a classifier. As the built-in classifier, a multi-wheel classifier is preferable, whereby powder with a sharp particle size distribution can be efficiently obtained.

The water content of the metal salt (B) is preferably 2% by mass or less. If the water content of the metal salt (B) exceeds 2% by mass, aggregates tend to form in the resulting resin composition when melt-kneaded with EVOH (A). The water content of the metal salt (B) is more preferably 1% by mass or less, and even more preferably 0.5% by mass or less. As a method for adjusting the water content of the metal salt (B) to the above range, for example, a method of drying the metal salt (B) in advance at 60 to 130° C. before melt-kneading with EVOH (A) can be mentioned.

As for the drying of the metal salt (B), only the metal salt (B) may be dried in advance, or it may be dried at the same time as the pulverization. Examples of the method of performing pulverization and drying at the same time include a method of pulverizing while introducing a dry gas into a pulverizer. When using a jet mill, pulverization and drying can be performed simultaneously by pulverizing using a heated compressed gas.

In the case of melt-kneading in an extruder, a general device used for melt-kneading of resins can be employed, and a continuous kneading device such as a single-screw extruder or a twin-screw extruder may be used, or a batch-type kneading device such as a Banbury mixer may be used. Also, the metal salt (B) may be pre-mixed with the pellets of EVOH (A) using a Henschel mixer or a tumbler before charging into the kneading device.

The temperature during melt-kneading in the extruder is not particularly limited as long as it is a temperature at which EVOH (A) can be melted, but 190 to 260°C is preferable. If the melt-kneading temperature is less than 190°C, the EVOH (A) may not melt sufficiently. The temperature during melt-kneading is more preferably 210° C. or higher. If the melt-kneading temperature exceeds 260° C., the EVOH (A) and/or the metal salt (B) may decompose. The temperature during melt-kneading is more preferably 245° C. or lower.

When the resin composition of the present invention further contains a polyamide (C), the method for mixing the polyamide (C) may be to melt-knead the polyamide (C) into the resin composition containing the EVOH (A) and the metal salt (B) obtained by the above-described methods (1) to (4), or to melt-knead the metal salt (B) in an extruder after previously mixing the EVOH (A) and the polyamide (C).

The resin composition of the present invention shows little decrease in gas barrier properties even after being subjected to treatment such as retort treatment under high temperature and high humidity conditions. Also, in addition to the usual retort treatment that heats and pressurizes at 100 ° C. or higher in an autoclave, steam retort treatment, water cascade retort treatment, microwave retort treatment, hot filling, sterilization treatment, boiling treatment, etc. It is expected that similar effects can be obtained.

The resin composition of the present invention is molded into various moldings such as films, sheets, containers, pipes and fibers by melt molding. Extrusion molding, inflation extrusion, blow molding, melt spinning, injection molding and the like can be used as the melt molding method. The melt-molding temperature varies depending on the melting point of EVOH (A) and the like, but is preferably about 150 to 270°C.

When the resin composition of the present invention is melt-molded, it is preferable to previously adjust the water content of the resin composition to 1% by mass or less before melt-molding. By setting the water content within the above range, foaming during melt molding can be prevented. The water content is more preferably 0.5% by mass or less, and even more preferably 0.25% by mass or less.

(multilayer structure)
A multilayer structure comprising at least one layer comprising the resin composition of the present invention is also a preferred embodiment of the present invention. As for the layer structure of the multilayer structure, X is a thermoplastic resin layer, Y is a layer made of the resin composition of the present invention, and Z is an adhesive resin layer. When a plurality of layers made of other resins are provided, they may be of different types or may be of the same type. Furthermore, a resin composition layer made of scraps such as trim generated when molding a multilayer structure may be provided separately, or a resin composition made of the recovered material may be used by blending it with a layer made of another resin. The thickness of the multilayer structure is not particularly limited, but from the viewpoint of moldability and cost, the ratio of the thickness of the resin composition layer Y of the present invention to the total thickness is preferably 2 to 20%.

The multilayer structure of the present invention preferably has at least one thermoplastic resin layer selected from the group consisting of polyolefin, polystyrene, polyester, polyamide, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate and polyacrylonitrile on both sides of the layer of the resin composition of the present invention. By setting it as the said structure, the multilayer structure of this invention is excellent in moisture resistance. From the viewpoint of moisture resistance, the thermoplastic resin is more preferably polyolefin, polystyrene and polyester, and more preferably polyolefin.

Polyolefins include, for example, low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, polypropylene, polybutene, polymethylpentene, and ionomer.

The multilayer structure of the present invention preferably has a layer made of at least one thermoplastic resin selected from the group consisting of polyolefin, polystyrene, polyester, polyamide, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate and polyacrylonitrile on at least one side of the layer made of the resin composition of the present invention via an adhesive resin layer.

The adhesive resin layer is not particularly limited as long as it can adhere the resin composition layer of the present invention and the thermoplastic resin layer, but preferably contains carboxylic acid-modified polyolefin. Carboxylic acid-modified polyolefin refers to a modified olefin-based polymer containing carboxyl groups obtained by chemically bonding an ethylenically unsaturated carboxylic acid or its anhydride to an olefin-based polymer (for example, by an addition reaction or a graft reaction). Further, the olefinic polymer refers to polyethylene (low pressure, medium pressure, high pressure), linear low density polyethylene, polypropylene, polyolefins such as polybutene, copolymers of olefins and comonomers (vinyl esters, unsaturated carboxylic acid esters, etc.) capable of copolymerizing the olefins, such as ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, and the like. Ethylenically unsaturated carboxylic acids or their anhydrides include ethylenically unsaturated monocarboxylic acids, esters thereof, ethylenically unsaturated dicarboxylic acids, mono- or diesters thereof, and anhydrides thereof, among which ethylenically unsaturated dicarboxylic acid anhydrides are preferred. Specific examples include maleic acid, fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride, maleic acid monomethyl ester, maleic acid monoethyl ester, maleic acid diethyl ester, fumaric acid monomethyl ester, etc. Maleic anhydride is particularly preferred.

The addition amount or graft amount (modification degree) of the ethylenically unsaturated carboxylic acid or its anhydride to the olefinic polymer is 0.01 to 15% by weight, preferably 0.02 to 10% by weight, based on the olefinic polymer.

Various additives can also be added to each layer of the multilayer structure of the present invention. Examples of such additives include antioxidants, plasticizers, heat stabilizers, ultraviolet absorbers, antistatic agents, lubricants, colorants, fillers, and the like, and specifically include those described above as those that can be added to the resin composition of the present invention.

Various molded articles (films, sheets, tubes, bottles, etc.) can be obtained by subjecting the coextruded multilayer structure or coinjection multilayer structure obtained from the resin composition of the present invention to secondary processing. For example:
(1) A multilayer co-stretched sheet or film obtained by stretching a multilayer structure (sheet or film, etc.) uniaxially or biaxially and optionally heat-treated (2) A multilayer rolled sheet or film obtained by rolling a multilayer structure (sheet or film, etc.) (3) A multilayer tray cup-shaped container obtained by subjecting a multilayer structure (sheet or film, etc.) to thermoforming such as vacuum forming, pneumatic forming, vacuum pressure forming, etc. Bottle-shaped container by biaxial stretch blow molding from a structure (parison, etc.)

Applications of the resin composition and multilayer structure of the present invention are not particularly limited, and for example, they are suitably used as materials for packaging containers, packaging films, deep-drawn containers, cup-shaped containers, bottles, and the like. Among others, it is suitable as a container for packaging contents, especially foods, which are susceptible to deterioration due to oxygen. Since the multilayer structure of the present invention has excellent gas barrier properties even under high temperature and high humidity conditions, it is particularly suitable as a container for retort processing. As the retort treatment, steam retort treatment, water cascade retort treatment, microwave retort treatment, etc. are employed in addition to normal retort treatment in which the material is heated to 100° C. or higher and pressurized. Moreover, it is suitable not only for retort treatment but also as a container for hot filling, sterilization treatment, and boiling treatment.

The packaging container of the present invention is obtained by sterilizing the packaging container filled with the content in hot water. The contents to be filled in the container are not particularly limited, and include foods, beverages, pharmaceuticals, and the like.

The hot water sterilization treatment in the present invention is a method of sterilizing a retort packaging container with steam or hot water at a temperature of 70 ° C. or higher and 140 ° C. or lower, and specifically includes retort treatment and boiling treatment, and includes a method of pressure sterilizing a packaging container having an intermediate layer made of a gas barrier resin and filled with food etc. under the conditions of 105 to 140 ° C., 0.15 to 0.3 MPa, and 5 to 120 minutes. The retort processing apparatus includes a steam type using heated steam, a hot water immersion type using pressurized superheated water, and the like, which are appropriately used depending on the sterilization conditions of the contents such as food. Boiling treatment is a method of sterilizing foods with hot water for preserving them, and although it depends on the contents, usually, a container having an intermediate layer made of a gas barrier resin filled with foods, etc. is sterilized at 60 to 100° C. under atmospheric pressure for 10 to 120 minutes. Boiling treatment is usually performed using a hot water bath, and there is a batch type in which the water is immersed in a hot water bath at a constant temperature and taken out after a certain period of time, and a continuous method in which the water is sterilized by passing it through a tunnel.

Since the packaging container sterilized with hot water according to the present invention has excellent gas barrier properties, deterioration in the quality of contents such as foods and medicines can be suppressed for a long period of time.

EXAMPLES The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

(1) Moisture Content of Hydrous EVOH Resin Pellets The moisture content of hydrous EVOH resin pellets was measured using a halogen moisture content analyzer "HR73" manufactured by Mettler Toledo under the conditions of a drying temperature of 180°C, a drying time of 20 minutes, and a sample amount of about 10 g. The water content of the hydrous EVOH is % by mass based on the dry mass of the EVOH.

(2) Haze before retort treatment Using the EVOH resin composition pellets obtained in Examples and Comparative Examples as a raw material, a three-kind five-layer co-extruder was used to form a film having a five-layer configuration of a polypropylene (PP) layer (210 μm) / an adhesive resin layer (20 μm) / an EVOH resin composition layer (40 μm) / an adhesive resin layer (20 μm) / a PP layer (210 μm) to produce a multilayer sheet. As the PP, "Novatec EG7FTB" manufactured by Japan Polypropylene Corporation was used, and as the adhesive resin, "ADMER QF500" manufactured by Mitsui Chemicals was used.
The haze of the obtained multilayer sheet was measured according to ASTM D1003-61 using a haze meter "MURAKAMI HR-100" manufactured by Murakami Color Research Laboratory. Table 1 shows the results. In Comparative Example 6, an EVOH resin (“EVAL L171” manufactured by Kuraray Co., Ltd.) was used as a raw material instead of the EVOH resin composition pellets.

(3) Haze measurement after retort treatment The multilayer sheet obtained in (2) was subjected to retort treatment by immersing it in hot water at 120°C for 30 minutes using “RCS-60” manufactured by HISAKA MFG. Table 1 shows the results.

(4) Oxygen transmission rate (OTR) after retort treatment
The multilayer sheet obtained in (2) was subjected to retort treatment by being immersed in hot water at 120°C for 30 minutes using "RCS-60" manufactured by Hisaka Seisakusho Co., Ltd. The multilayer sheet immediately after being taken out was conditioned for 24 hours under the conditions of 20°C and 65% RH (external)/100% RH (internal), and then the oxygen transmission rate was measured using "OX-TORAN MODEL 2/21" manufactured by Mocon under the same conditions. . Table 1 shows the results.

Example 1
A mixed solvent was prepared by adding 930 g of pure water and 930 g of methanol to a 5 L separable flask. 140 g of phenyl disodium phosphate dihydrate (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) was added to and dissolved in the resulting mixed solvent. 1100 g of EVOH resin (“EVAL L171” manufactured by Kuraray Co., Ltd.) was added to the obtained solution and dissolved with stirring at 90°C. The resulting solution was a pasty, highly viscous liquid. The resulting solution was continuously extruded into a solution of water/methanol=90/10 (mass ratio) at 0° C. to deposit strands, and then the resulting strands were cut to obtain hydrous EVOH resin composition chips (moisture content: 145% by mass). The obtained hydrous EVOH resin composition chips were put in a steam dryer and dried at 80°C for 3 hours, then put in a hot air dryer and dried at 80°C for 3 hours, and then dried at 120°C for 15 hours. After drying, EVOH resin composition chips were used and a 20 mm extruder "D2020" (D (mm) = 20, L/D = 20, compression ratio = 2.0, screw: full flight) manufactured by Toyo Seiki Seisakusho Co., Ltd. was used to obtain EVOH resin composition pellets under the following conditions. No corrosion was observed inside the extruder during melt-kneading.
Cylinder temperature: supply section 180°C, compression section 220°C, metering section 220°C
Die temperature: 220°C
Screw rotation speed: 120 rpm
Discharge rate: 2.1 kg/hour Various physical properties of the obtained EVOH resin composition pellets were evaluated as described above. Table 1 shows the results.

Examples 2 to 7, Comparative Example 2, Comparative Example 5
EVOH resin composition pellets were obtained in the same manner as in Example 1, except that the content of EVOH (A) and the type and content of metal salt (B) were changed as shown in Table 1. Various physical properties of the obtained EVOH resin composition pellets were evaluated as described above. Table 1 shows the results. In Examples 2 to 7 and Comparative Example 2, corrosion was not observed in the extruder during melt-kneading, but in Comparative Example 5, corrosion was observed in the extruder during melt-kneading.

Example 8
Dried EVOH resin composition chips were obtained in the same manner as in Example 1. After mixing 950 g of the obtained EVOH resin composition chips, 50 g of polyamide resin (“Ube Nylon SF1018A” manufactured by Ube Industries, Ltd.) and 2.9 g of magnesium stearate (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.), a 25 mm extruder “D2020” manufactured by Toyo Seiki Seisakusho Co., Ltd. (D (mm) = 25, L / D = 25, compression ratio = 2.0, screw: same direction complete mesh type) was used, EVOH resin composition pellets were obtained under the following conditions. No corrosion was observed inside the extruder during melt-kneading.
Cylinder temperature: supply section 180°C, compression section 230°C, metering section 230°C
Die temperature: 220°C
Feeder rotation speed: 37 rpm
Screw rotation speed: 100 rpm
Discharge rate: 2.5 kg/hour Various physical properties of the obtained EVOH resin composition pellets were evaluated as described above. Table 1 shows the results.

Example 9
A mixed solvent was prepared by adding 930 g of pure water and 930 g of methanol to a 5 L separable flask. 1100 g of EVOH resin (“EVAL L171” manufactured by Kuraray Co., Ltd.) was added to the obtained mixed solvent and dissolved with stirring at 90°C. The resulting solution was continuously extruded into a solution of water/methanol = 90/10 (mass ratio) at 0°C to deposit strands. After cutting the strands, a large amount of water was added to wash the strands.

Next, 6200 g of pure water and 780 g of phenyl disodium phosphate dihydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added to a 10 L plastic bucket to prepare an aqueous solution. 1800 g of the above hydrous EVOH resin chips (water content: 143% by mass) were added to the resulting aqueous solution, and the mixture was stirred at 20°C for 4 hours. Thereafter, the hydrous EVOH resin composition chips were taken out from the aqueous solution, placed in a hot air dryer and dried at 80° C. for 3 hours, and further dried at 120° C. for 15 hours. After drying, EVOH resin composition chips were used and a 20 mm extruder "D2020" (D (mm) = 20, L/D = 20, compression ratio = 2.0, screw: full flight) manufactured by Toyo Seiki Seisakusho Co., Ltd. was used to obtain EVOH resin composition pellets under the following conditions. No corrosion was observed inside the extruder during melt-kneading.
Cylinder temperature: supply section 180°C, compression section 220°C, metering section 220°C
Die temperature: 220°C
Screw rotation speed: 120 rpm
Discharge rate: 2.1 kg/hour Various physical properties of the obtained EVOH resin composition pellets were evaluated as described above. Table 1 shows the results.

Example 10
A mixed solvent was prepared by adding 930 g of pure water and 930 g of methanol to a 5 L separable flask. 1100 g of EVOH resin (“EVAL L171” manufactured by Kuraray Co., Ltd.) was added to the obtained mixed solvent and dissolved with stirring at 90°C. The resulting solution was continuously extruded into a solution of water/methanol = 90/10 (mass ratio) at 0°C to deposit strands. After cutting the strands, a large amount of water was added to wash the strands. The same operation was repeated 10 more times to obtain a total of 11,000 g of hydrous EVOH resin chips (moisture content: 143% by mass). The obtained hydrous EVOH resin chips were placed in a hot air dryer and dried at 80° C. for 4 hours to obtain hydrous EVOH resin chips (water content: 5% by mass).

Next, using the above water-containing EVOH resin chips (water content of 5% by mass), a twin-screw extruder "TEM-35BS" (37 mmφ, L/D = 52.5) manufactured by Toshiba Machine Co., Ltd. was used to obtain EVOH resin composition pellets under the following conditions. A 25% by mass aqueous solution of phenyl disodium phosphate was added from the compression section of the extruder, and water was removed from the vent. Furthermore, a 25% by mass aqueous solution of disodium phenyl phosphate was added from the compression section of the extruder, and water was removed from the vent. No corrosion was observed inside the extruder during melt kneading.
Cylinder temperature: supply section 110°C, compression section 200°C, metering section 200°C
Die temperature: 200°C
Screw rotation speed: 200 rpm
Discharge rate: 10.0 kg/hour Various physical properties of the obtained EVOH resin composition pellets were evaluated as described above. Table 1 shows the results.

Example 11
Phenyl disodium phosphate dihydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was pulverized using a fluidized bed jet mill (“Hosokawa AFG-400” manufactured by Alpine and Hosokawa Micron Powder Systems) while heating and drying in a convection oven at 120°C for 12 hours to obtain anhydrous phenyl disodium phosphate. The resulting disodium phenyl phosphate anhydride and EVOH resin (“EVAL L171” manufactured by Kuraray Co., Ltd.) were melt-kneaded so that the content of disodium phenyl phosphate in the resulting resin composition was 10% by weight. For melt kneading, a 25 mm extruder "D2020" (D (mm) = 25, L/D = 25, compression ratio = 2.0, screw: same direction complete meshing type) manufactured by Toyo Seiki Seisakusho Co., Ltd. was used, and EVOH resin composition pellets were obtained under the following conditions. No corrosion was observed inside the extruder during melt-kneading.
Cylinder temperature: supply section 180°C, compression section 230°C, metering section 230°C
Die temperature: 230°C
Feeder rotation speed: 170 rpm
Screw rotation speed: 100 rpm
Discharge rate: 6.0 kg/hour Various physical property values were evaluated for the obtained EVOH resin composition pellets as described above. Table 1 shows the results.

Comparative example 1
EVOH resin composition pellets were obtained in the same manner as in Example 9, except that the content of EVOH (A) and the type and content of metal salt (B) were changed as shown in Table 1. No corrosion was observed inside the extruder during melt-kneading.
Various physical properties of the obtained EVOH resin composition pellets were evaluated as described above. Table 1 shows the results.

Comparative Examples 3 and 4
EVOH resin composition pellets were obtained in the same manner as in Example 10, except that the content of EVOH (A) and the type and content of metal salt (B) were changed as shown in Table 1. No corrosion was observed inside the extruder during melt-kneading.
Various physical properties of the obtained EVOH resin composition pellets were evaluated as described above. Table 1 shows the results.

SHAPE \* MERGEFORMAT

As can be seen from Table 1, by using the metal salt (B), the obtained multilayer structure including the resin composition layer is excellent in gas barrier properties after retort treatment. Furthermore, since the metal salt (B) has a hydrophobic group, aggregation of the metal salt due to water absorption during retort treatment can be suppressed, and whitening of the obtained multilayer structure can be suppressed. Further, as shown in Comparative Examples 1 to 4, whitening occurs after retort treatment when a metal salt having no hydrophobic group and capable of forming a hydrate is used. Moreover, as shown in Comparative Example 5, when a carboxylate is used as the metal salt, corrosion occurs in the extruder during melt-kneading. Furthermore, as shown in Comparative Example 6, when no metal salt is used, the gas barrier property after retort treatment is lowered. From this, the metal salt (B) forms a hydrate, so that the gas barrier property after retort processing can be maintained, and by having a hydrophobic group, aggregation of the metal salt is suppressed, and whitening can be suppressed.

Claims (13)

A resin composition comprising an ethylene-vinyl alcohol copolymer (A) and a metal salt (B) having a hydrophobic group capable of forming a hydrate,
A resin composition in which the metal salt (B) having a hydrophobic group capable of forming a hydrate contains at least one selected from the group consisting of phosphates, phosphonates, phosphinates, sulfonates and sulfinates. The resin composition according to claim 1, wherein the resin composition contains 70.0 to 99.0% by mass of the ethylene-vinyl alcohol copolymer (A) and 1.0 to 30.0% by mass of the metal salt (B) having a hydrophobic group capable of forming a hydrate. 3. The resin composition according to claim 1, wherein the metal salt (B) having a hydrophobic group capable of forming a hydrate has either an aromatic ring or an alkyl group. Further contains a polyamide (C),
The content of the polyamide resin (C) is 0.1 to 20.0 parts by mass with respect to the total 100 parts by mass of the ethylene-vinyl alcohol copolymer (A) and the alkali metal salt (B) having a hydrophobic group capable of forming a hydrate. The resin composition according to any one of claims 1 to 3. The method for producing the resin composition according to any one of claims 1 to 4, comprising the step of precipitating a melt containing the ethylene-vinyl alcohol copolymer (A) and the metal salt (B) having a hydrophobic group capable of forming a hydrate. The method for producing a resin composition according to any one of claims 1 to 4, comprising the step of immersing water-containing pellets of the ethylene-vinyl alcohol copolymer (A) having a water content of 1 to 200% by mass in an aqueous solution containing an alkali metal salt (B) having a hydrophobic group capable of forming a hydrate. The method for producing a resin composition according to any one of claims 1 to 4, comprising the step of adding an aqueous solution containing a metal salt (B) having a hydrophobic group capable of forming a hydrate to a melt containing the ethylene-vinyl alcohol copolymer (A) and water; and the step of melt-kneading the melt to which the aqueous solution has been added. The method for producing the resin composition according to any one of claims 1 to 4, comprising a step of melt-kneading the ethylene-vinyl alcohol copolymer (A) and the metal salt (B) having a hydrophobic group capable of forming a hydrate. A multilayer structure comprising at least one layer comprising the resin composition layer according to any one of claims 1 to 4. A layer comprising the resin composition according to any one of claims 1 to 4 and at least one selected from the group consisting of polyolefin, polystyrene, polyester, polyamide, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate and polyacrylonitrile. A multilayer structure having at least one layer comprising a resin composition comprising a layer comprising a thermoplastic resin. A packaging container comprising the multilayer structure according to claim 9 or 10. A retort packaging container comprising the packaging container according to claim 11 filled with contents. A method of sterilizing the retort packaging container according to claim 12 with steam or hot water at a temperature of 70°C or higher and 140°C or lower.