JP7337593B2 - Pellets, melt-molded products made from the same, and methods for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to ethylene-vinyl alcohol copolymer pellets with suppressed variation in volatile carboxylic acid content and excellent long-run properties during melt molding, a melt molded product obtained therefrom, and a method for producing the same.

BACKGROUND ART Ethylene-vinyl alcohol copolymers (hereinafter sometimes abbreviated as EVOH) are widely used as various packaging materials such as films, sheets, and containers because of their properties such as excellent gas barrier properties. Since these packaging materials are usually molded by a melt molding method, EVOH should have excellent appearance characteristics, that is, transparency, little coloring such as yellowing, and no generation of gels and pimples. In addition, long-run properties, that is, physical properties such as viscosity do not change significantly even after long-term molding, and no fish eyes, streaks, or the like are required.

In order to improve the above-described properties required of EVOH, Patent Documents 1 to 3 disclose EVOH compositions containing additives such as various carboxylic acids and metal ions to improve appearance properties and long-run properties. It is stated that Further, Patent Document 4 describes that heat treatment under specific conditions improves mechanical strength without impairing appearance properties and long-run properties.

JP-A-64-66262 WO2002/053639 WO2011/118648 JP 2006-282833 A

On the other hand, EVOH is highly hydrophilic and has the property of easily absorbing moisture in the air. If moisture-absorbed EVOH is melt-molded, molding defects such as foaming will occur. Therefore, when manufacturing EVOH pellets, after sufficiently drying to reduce the volatile content, use aluminum foil or a moisture-proof packaging material with a vapor deposition layer. It is commonly packaged. Under such a packaging environment, the moisture absorption rate of EVOH pellets is sufficiently low, and stable quality can be maintained for a relatively long period of time. However, at the site of melt molding, EVOH pellets may be left for a long time with the moisture-proof packaging open, and moisture absorption progresses during this time, causing molding defects such as foaming in the subsequent melt molding. There is Such problems tend to occur particularly in areas with hot and humid climates. In order to subject the moisture-absorbed EVOH pellets to melt molding, it is necessary to reduce the volatile content by sufficiently re-drying in advance, but at this time, some of the carboxylic acid also volatilizes and disappears along with the moisture. In addition, there is a risk that the balance of the additives will be lost, the appearance characteristics and long-run properties will be deteriorated, and the quality of the resulting melt-molded product will be uneven.

An object of the present invention is to provide an ethylene-vinyl alcohol copolymer that is excellent in color resistance and long-run properties during melt molding, and in which fluctuations in the volatile carboxylic acid content are suppressed even when moisture-absorbed EVOH pellets are re-dried. To provide polymer pellets.

As a result of intensive studies on the above problem, the present inventors found that by increasing the heat of fusion of EVOH pellets, fluctuations in the content of volatile carboxylic acids can be suppressed even when moisture-absorbed EVOH pellets are re-dried. I found Further, the present inventors have found that a molded product having excellent long-run properties during melt molding and excellent appearance characteristics can be obtained by containing a specific amount of divalent metal ions, and have completed the present invention. That is, the above problem is
[1] Pellets mainly composed of ethylene-vinyl alcohol copolymer (A),
The ethylene-vinyl alcohol copolymer (A) has an ethylene unit content of 15 to 60 mol%, a saponification degree of 85 mol% or more, an alkali metal ion (B) of 50 to 500 ppm, and a divalent metal ion (C). 10 to 100 ppm, and 20 to 400 ppm of a carboxylic acid (D) having a boiling point of less than 150 ° C., and the heat of fusion ΔHp of the pellet measured by differential scanning calorimetry and the pellet It is measured after melting and resolidifying. Pellets having a heat of fusion difference (ΔHp−ΔHm) from the heat of fusion ΔHm of 5 J/g or more;
[2] The pellet of [1], which has a heat of fusion difference (ΔHp−ΔHm) of 10 J/g or more;
[3] The pellet of [1] or [2], which has a heat of fusion ΔHp of 85 J/g or more;
[4] The pellet of any one of [1] to [3], further containing 5 to 200 ppm of a phosphoric acid compound (E) in terms of phosphate radical;
[5] The pellet of any one of [1] to [4], further containing 50 to 400 ppm of boron compound (F) in terms of boron element;
[6] The pellet of any one of [1] to [5], further containing 5000 to 50000 ppm of a hindered phenolic compound (G) having an ester bond or an amide bond;
[7] The pellet of any one of [1] to [6], which has a yellowness index of less than 30;
[8] The difference between the maximum and minimum values of the heat of fusion ΔHp measured by differential scanning calorimetry for five pellets arbitrarily selected from any one of [1] to [7] is less than 5 J/g. ,pellet;
[9] Contains an ethylene-vinyl alcohol copolymer (A), an alkali metal ion (B), a divalent metal ion (C) and a carboxylic acid (D) having a boiling point of less than 150°C, and a volatile content of 0 [1] to [8], including a step of heat-treating unheated pellets of less than 5 mass% at a temperature 15 to 25 ° C. lower than the melting point of the ethylene-vinyl alcohol copolymer (A) for 1 to 5 hours. ]
A method for producing pellets according to any one of;
[10] The method for producing pellets of [9], wherein the heat treatment is performed in a nitrogen atmosphere with an oxygen concentration of 1000 ppm or less;
[11] The method for producing pellets of [9] or [10], wherein heat treatment is performed while the pellets are fluidized;
[12] A molten compact made of the pellets of any one of [1] to [8];
is resolved by providing

The EVOH pellets of the present invention suppress fluctuations in the volatile carboxylic acid content even when the moisture-absorbed EVOH pellets are re-dried, and are excellent in long-run performance during melt molding. Reusable.

Embodiments of the present invention will be described below. In the following description, specific materials (compounds, etc.) may be exemplified as materials exhibiting specific functions, but the present invention is not limited to embodiments using such materials. In addition, unless otherwise specified, the exemplified materials may be used alone or in combination.

<EVOH (A)>
EVOH (A) is the main component of the pellets of the present invention. EVOH (A) is a copolymer having ethylene units and vinyl alcohol units as main structural units. EVOH (A) is usually obtained by polymerizing ethylene and vinyl ester and saponifying the obtained ethylene-vinyl ester copolymer. The main component means that the content of EVOH (A) in the resin constituting the pellet of the present invention is 70% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and 95% by mass or more. It is particularly preferably at least 99% by mass, and may be at least 99% by mass. By setting the content of EVOH (A) within this range, the melt moldability of the obtained pellets is improved, and the gas barrier properties of the molded product obtained therefrom are also excellent.

The ethylene unit content of EVOH (A), that is, the ratio of the number of ethylene units to the total number of monomer units in EVOH (A) should be in the range of 15 to 60 mol %. The lower limit of the ethylene unit content of EVOH (A) is preferably 20 mol%, more preferably 23 mol%. On the other hand, the upper limit of the ethylene unit content of EVOH (A) is preferably 55 mol%, more preferably 50 mol%. When the ethylene unit content of EVOH (A) is less than 15 mol %, the gas barrier property under high humidity is lowered, and the melt moldability may be deteriorated. If the ethylene unit content of EVOH (A) exceeds 60 mol %, sufficient gas barrier properties may not be obtained.

The degree of saponification of EVOH (A), that is, the ratio of the number of vinyl alcohol units to the total number of vinyl alcohol units and vinyl ester units in EVOH (A) must be 85 mol % or more. The lower limit of the degree of saponification of EVOH (A) is preferably 95 mol%, more preferably 99 mol%. On the other hand, the upper limit of the degree of saponification of EVOH (A) is preferably 100 mol%, more preferably 99.99 mol%. If the degree of saponification of EVOH (A) is less than 85 mol%, sufficient gas barrier properties may not be obtained, and thermal stability may be insufficient.

When EVOH (A) is a mixture of two or more EVOHs with different ethylene unit contents, the average value calculated from the mixture mass ratio is taken as the ethylene unit content. In this case, the difference in ethylene unit content between EVOHs with the most distant ethylene unit contents is preferably 30 mol % or less, more preferably 20 mol % or less, and even more preferably 15 mol % or less. Similarly, when EVOH (A) is a mixture of two or more EVOHs with different saponification degrees, the average value calculated from the mixture mass ratio is taken as the saponification degree of the mixture. In this case, the difference in saponification degree between the most distant EVOHs is preferably 7% or less, more preferably 5% or less. When a resin composition having a higher balance of thermoformability and gas barrier properties is desired, EVOH having an ethylene unit content of 24 mol% or more and less than 34 mol% and a degree of saponification of 99 mol% or more is used. (A-1) and EVOH (A-2) having an ethylene unit content of 34 mol% or more and less than 50 mol% and a degree of saponification of 99 mol% or more, at a blending mass ratio (A-1/A- 2) is preferably mixed so as to be 60/40 to 90/10 and used as EVOH (A). The ethylene unit content and saponification degree of EVOH (A) can be determined by a nuclear magnetic resonance (NMR) method.

The lower limit of the melt flow rate of EVOH (A) conforming to JIS K 7210:2014 (hereinafter sometimes simply referred to as "MFR") (temperature 210 ° C., load 2160 g) is preferably 0.1 g / 10 minutes, 0.5 g/10 min is more preferred, and 1 g/10 min is even more preferred. On the other hand, the upper limit of the MFR of EVOH (A) is preferably 50 g/10 minutes, more preferably 30 g/10 minutes, even more preferably 15 g/10 minutes. By setting the MFR of EVOH (A) to a value within this range, the melt moldability of the resulting resin composition is improved.

EVOH (A) can contain, as copolymer units, monomeric units other than ethylene units, vinyl alcohol units and vinyl ester units as long as the object of the present invention is not hindered. Examples of the monomers include α-olefins such as propylene, 1-butene, isobutene, 4-methyl-1-pentene, 1-hexene, and 1-octene; itaconic acid, methacrylic acid, acrylic acid, maleic acid; Unsaturated carboxylic acids such as, salts thereof, partial or complete esters thereof, nitriles thereof, amides thereof, anhydrides thereof; vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxyethoxy)silane, γ-methacryloxypropyl vinylsilane compounds such as trimethoxysilane; unsaturated sulfonic acids or salts thereof; unsaturated thiols; and vinylpyrrolidones. The content of monomer units other than ethylene units, vinyl alcohol units and vinyl ester units in EVOH (A) is usually 5 mol % or less, preferably 2 mol % or less, more preferably 1 mol % or less.

<Alkali metal ion (B)>
The pellets of the present invention should contain 50 to 500 ppm of alkali metal ions (B). The lower limit of the content of alkali metal ions (B) is preferably 70 ppm, more preferably 90 ppm. On the other hand, the upper limit of the content of alkali metal ions (B) is preferably 400 ppm, more preferably 300 ppm. If the content of the alkali metal ion (B) is less than 50 ppm, the interlayer adhesion of the multilayer structure including the layer obtained by molding the pellets of the present invention may be insufficient. On the other hand, when the content of alkali metal ions (B) exceeds 500 ppm, coloration due to thermal deterioration may become a problem. The reason why the interlayer adhesion is improved by the alkali metal ion (B) is not clear, but when the layer adjacent to the EVOH (A) has a molecule having a functional group capable of reacting with the hydroxyl group of the EVOH (A), , the acceleration of this bond formation reaction by the alkali metal ion (B) is considered to be one factor. Further, by controlling the content ratio of the alkali metal ion (B) and the carboxylic acid (D) described later, the melt moldability and coloration resistance of the obtained pellets can be further improved.

Alkali metal ions (B) include, for example, ions of lithium, sodium, potassium, rubidium, and cesium, with sodium or potassium ions being preferred from the standpoint of industrial availability. In particular, by using potassium ions, the hue of the pellet of the present invention and the interlaminar adhesion of a multilayer structure including a layer obtained by molding the pellet of the present invention may be compatible at a high level. These may be used individually by 1 type, and may use 2 or more types together.

Alkali metal salts that give alkali metal ions (B) include, for example, aliphatic carboxylates, aromatic carboxylates, carbonates, hydrochlorides, nitrates, sulfates, and phosphoric acids of alkali metals such as lithium, sodium, and potassium. Examples include salts and metal complexes. Among them, sodium acetate, potassium acetate, sodium phosphate, and potassium phosphate are more preferable from the viewpoint of easy availability.

<Divalent metal ion (C)>
The pellets of the present invention should contain 10 to 100 ppm of divalent metal ions (C). The lower limit of the content of divalent metal ions (C) is preferably 20 ppm. On the other hand, the upper limit of the content of divalent metal ions (C) is more preferably 50 ppm. By setting the content of the divalent metal ion (C) within this range, the pellets of the present invention can suppress coloration due to thermal deterioration of EVOH (A), and even when melt-molded for a long period of time, the molded product can be Generation of gels and pimples may be suppressed.

Examples of divalent metal ions (C) include ions of beryllium, magnesium, calcium, strontium, barium, iron, copper, and zinc. , calcium or zinc ions are preferred. Magnesium ions are particularly preferred from the viewpoint of effectively suppressing the generation of gels and pimples with a small content, but calcium ions and zinc ions, particularly zinc ions, are preferred from the viewpoint of color balance. These may be used individually by 1 type, and may use 2 or more types together.

Examples of divalent metal salts that give divalent metal ions (C) include aliphatic carboxylates such as magnesium, calcium and zinc, aromatic carboxylates, carbonates, hydrochlorides, nitrates, sulfates and phosphates. , metal complexes. Among them, magnesium acetate, calcium acetate, and zinc acetate are more preferable because they are readily available.

<Carboxylic acid (D)>
The pellets of the present invention should contain 20 to 400 ppm of carboxylic acid (D) having a boiling point of less than 150°C. If the boiling point of the carboxylic acid (D) is less than 150°C, it becomes easier to control the content of the carboxylic acid (D) in the drying step described below. The lower limit of the content of carboxylic acid (D) is preferably 40 ppm, more preferably 60 ppm. On the other hand, the upper limit of the content of carboxylic acid (D) is preferably 350 ppm, more preferably 300 ppm. When the content of the carboxylic acid (D) is less than 20 ppm, the color resistance at high temperatures and the color resistance of the obtained melt-molded product may be insufficient. On the other hand, when the content of the carboxylic acid (D) exceeds 400 ppm, the melt moldability may become insufficient, and odor may become a problem. The content of carboxylic acid (D) is obtained by extracting 10 g of pellets with 50 ml of pure water at 95° C. for 8 hours, and then titrating the obtained extract. As for the content of carboxylic acid (D) in the pellet, the carboxylic acid present as a salt in the extract is not considered. In addition, when the pellets of the present invention contain acidic compounds other than carboxylic acid (D), such as carboxylic acids having a boiling point of 150 ° C. or higher, inorganic acids, etc., the contribution of these acidic compounds is calculated from the measured value by titration. By subtracting, the content of carboxylic acid (D) in the pellet can be obtained.

The pKa of carboxylic acid (D) is preferably 3.5 to 5.5. When the pKa of the carboxylic acid (D) is within the above range, the pH buffering capacity of the resin composition constituting the obtained pellets is increased, the melt moldability is further improved, and the coloring due to acidic substances and basic substances is further improved. can.

Examples of the carboxylic acid (D) include monovalent carboxylic acids, and these may be used singly or in combination of two or more. A monovalent carboxylic acid is a compound having one carboxyl group in the molecule. The monovalent carboxylic acid having a boiling point of less than 150°C and a pKa in the range of 3.5 to 5.5 is not particularly limited, and for example, formic acid (pKa = 3.77), acetic acid (pKa = 4.76), propion acid (pKa=4.85), acrylic acid (pKa=4.25) and the like. These carboxylic acids may further have a substituent such as a hydroxyl group, an amino group, or a halogen atom as long as the boiling point is less than 150°C. Among them, acetic acid is preferred because it is highly safe and easy to obtain and handle.

<Other ingredients>
The pellets of the present invention may contain other ingredients as long as they do not impair the effects of the present invention. Other components include, for example, a phosphoric acid compound (E), a boron compound (F), an acidic compound other than the carboxylic acid (D) (for example, a carboxylic acid having a boiling point of 150° C. or higher, an inorganic acid, etc.), and a Thermoplastic resin, cross-linking agent, desiccant, oxidant accelerator, antioxidant, oxygen absorber, plasticizer, lubricant, heat stabilizer (melt stabilizer), processing aid, surfactant, deodorant, antistatic agent , ultraviolet absorbers, antifog agents, flame retardants, pigments, dyes, fillers, fillers, and reinforcing agents such as various fibers.

<Phosphate compound (E)>
The pellets of the present invention may further contain a phosphate compound (E). When the phosphoric acid compound (E) is contained, the lower limit of the content in the pellet of the present invention is preferably 5 ppm, more preferably 10 ppm in terms of phosphate radical. On the other hand, the upper limit of the content of the phosphate compound (E) in the pellets of the present invention is preferably 200 ppm, more preferably 100 ppm, in terms of phosphate radicals. By containing the phosphoric acid compound (E) within this range, coloration of the obtained pellets and the obtained melt-molded article may be suppressed, and thermal stability may be improved.

As the phosphoric acid compound (E), for example, various acids such as phosphoric acid and phosphorous acid, salts thereof, and the like are used. The phosphate may be a primary phosphate, a secondary phosphate, or a tertiary phosphate. Although the cationic species of the phosphate is not particularly limited, the cationic species is preferably an alkali metal or an alkaline earth metal. Among them, sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate are preferable as the phosphate compound (E).

<Boron compound (F)>
The pellets of the present invention may further contain a boron compound (F). When the boron compound (F) is contained, the lower limit of the content in the pellet of the present invention is preferably 50 ppm, more preferably 100 ppm in terms of boron element. On the other hand, the upper limit of the content of the boron compound (F) in the pellets of the present invention is preferably 400 ppm, more preferably 200 ppm in terms of boron element. By containing the boron compound (F) within this range, the thermal stability of the obtained pellets during melt molding may be improved, and the generation of gels and lumps may be suppressed. In addition, the drawdown resistance and the neck-in resistance when the pellet is formed into a film by melt molding may be improved, and the mechanical properties of the resulting molded product may be improved. These effects are presumed to be due to the occurrence of chelate interaction between EVOH (A) and boron compound (F).

Boron compounds (F) include, for example, boric acid, borate esters, borates, and borohydride. Specifically, boric acids such as orthoboric acid (H ₃ BO ₃ ), metaboric acid and tetraboric acid; borate esters such as trimethyl borate and triethyl borate; alkali metal salts or alkaline earth metals of the above boric acids Examples include salts, borate salts such as borax, and the like. Among them, orthoboric acid is preferred.

<Hindered phenolic compound (G) having an ester bond or an amide bond>
The pellet of the present invention may further contain a hindered phenolic compound (G) having an ester bond or an amide bond. A hindered phenolic compound is an organic compound containing at least one phenolic group, the aromatic moiety of which is located in at least one, preferably both, positions directly adjacent to a carbon having a phenolic hydroxyl group as a substituent. It means an organic compound that is positionally substituted. Substituents adjacent to the hydroxyl group may be suitably selected from alkyl groups having 1 to 10 carbon atoms, preferably a tertiary butyl group.

The hindered phenol compound (G) is preferably solid at around room temperature. For the purpose of suppressing bleeding out, the melting point or softening temperature of the hindered phenolic compound (G) is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 70°C or higher. For the same reason, the molecular weight of the hindered phenolic compound (G) is preferably 200 or more, more preferably 400 or more, even more preferably 600 or more. In order to facilitate mixing with EVOH (A), the melting point or softening temperature of the hindered phenolic compound (G) is preferably 200°C or lower, more preferably 190°C or lower, and even more preferably 180°C or lower. .

The hindered phenolic compound (G) has an ester bond or an amide bond. Since the hindered phenolic compound (G) has an ester bond or an amide bond, it is possible to stabilize the viscosity of the EVOH (A) when subjecting the pellets of the present invention to melt molding, thereby preventing gel formation. be able to. This effect is particularly remarkable when the hindered phenolic compound (G) has an amide bond.

A specific structure of the hindered phenol compound (G) is pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate commercially available as Irganox 1010 from BASF. ], stearyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, commercially available as Irganox 1076, 2,2′-thiodiethylbis[3, commercially available as Irganox 1035 -(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate commercially available as Irganox 1135, Bis(3-tert-butyl-4-hydroxy-5-methylbenzenepropanoic acid) ethylene bis(oxyethylene) commercially available as Irganox 245, 1,6-hexanediol bis[ 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N,N′-hexamethylenebis[3-(3,5-di-tert-butyl) commercially available as Irganox 1098 -4-hydroxyphenyl)propanamide] and the like. Among them, N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanamide] commercially available as Irganox 1098 is particularly preferable because it has an amide bond. .

The content of the hindered phenolic compound (G) in the pellets of the present invention is preferably 5,000 to 50,000 ppm, more preferably 10,000 to 30,000 ppm. By setting the content of the hindered phenolic compound (G) within the above range, it is possible to prevent the EVOH from decomposing or cross-linking during melt-kneading or melt-molding of the pellets, thereby maintaining a stable viscosity over a long period of time. can be maintained. Furthermore, it is possible to prevent the generation of gel when melt-kneading the pellets or during melt-molding, so that a molded article having an excellent appearance can be produced.

<Polyvalent carboxylic acid>
The pellets of the present invention may further contain a polyvalent carboxylic acid other than the carboxylic acid (D). By further containing a polycarboxylic acid, it may be possible to further improve the coloration resistance of pellets at high temperatures and the coloration resistance of the obtained melt-molded product. Also, the polyvalent carboxylic acid compound preferably has 3 or more carboxyl groups. In this case, it may be possible to improve the coloring resistance more effectively.

A polyvalent carboxylic acid is a compound having two or more carboxyl groups in the molecule. In this case, the pKa of at least one carboxyl group is preferably in the range of 3.5 to 5.5. (pKa2 = 4.44), malic acid (pKa2 = 5.13), glutaric acid (pKa1 = 4.30, pKa2 = 5.40), adipic acid (pKa1 = 4.43, pKa2 = 5.41), pimelic acid (pKa1 = 4.71), phthalic acid (pKa2 = 5.41), isophthalic acid (pKa2 = 4.46), terephthalic acid (pKa1 = 3.51, pKa2 = 4.82), citric acid (pKa2 = 4.75), tartaric acid (pKa2 = 4.40), glutamic acid (pKa2 = 4.07), aspartic acid (pKa = 3.90) and the like.

The pellets of the present invention may further contain a thermoplastic resin other than EVOH (A). Examples of thermoplastic resins other than EVOH (A) include various polyolefins (polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, ethylene and α- Copolymers with olefins, copolymers of polyolefins and maleic anhydride, ethylene-vinyl ester copolymers, ethylene-acrylate copolymers, or modifications obtained by grafting these with unsaturated carboxylic acids or derivatives thereof polyolefin, etc.), various polyamides (nylon 6, nylon 6.6, nylon 6/66 copolymer, nylon 11, nylon 12, poly-metaxylylene adipamide, etc.), various polyesters (polyethylene terephthalate, polybutylene terephthalate, polyethylene phthalate, etc.), polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate and modified polyvinyl alcohol resin. The content of the thermoplastic resin in the pellets of the present invention is less than 30% by mass, preferably less than 20% by mass, more preferably less than 10% by mass, even more preferably 5% by mass or less, and 1% by mass or less. may

The pellet of the present invention has a heat of fusion difference (ΔHp-ΔHm) between the heat of fusion ΔHp of the pellet measured by differential scanning calorimetry and the heat of fusion ΔHm measured after melting and re-solidifying the pellet is 5 J/g or more. It is important that The heat of fusion difference (ΔHp−ΔHm) is preferably 10 J/g or more, more preferably 15 J/g or more. When the heat of fusion difference (ΔHp−ΔHm) is within the above range, the moisture absorption rate of the pellets can be reduced, and even when the moisture-absorbed pellets are re-dried, fluctuations in the volatile carboxylic acid content can be suppressed. The heat of fusion ΔHp of the pellet is preferably 85 J/g or more, more preferably 90 J/g or more, and even more preferably 95 J/g or more. The heat of fusion ΔHm after resolidification largely depends on the ethylene unit content and degree of saponification of the composition constituting the pellet, especially EVOH (A), but the difference in heat of fusion (ΔHp−ΔHm) is the same (for example, 10 J/g). Even in the case of , by setting the heat of fusion ΔHp of the pellet within the above range, it may be easier to suppress fluctuations in the volatile carboxylic acid content. The yellowness index of the pellets of the present invention is preferably less than 30, more preferably less than 26, more preferably less than 24, particularly preferably less than 22, and most preferably less than 20.

<Manufacturing method of pellet>
In the method for producing the pellets of the present invention, finally, EVOH (A), alkali metal ions (B), divalent metal ions (C) and carboxylic acid (D) are contained within the above ranges, and the differential As long as the difference (ΔHp−ΔHm) between the heat of fusion ΔHp of the pellet measured by scanning calorimetry and the heat of fusion ΔHm measured after the pellet is melted and re-solidified is 5 J/g or more, there is no limitation, which will be described later. It is preferably manufactured by the manufacturing method of the present invention.

The method of adding alkali metal ions (B), divalent metal ions (C) and carboxylic acid (D) to the pellets of the present invention is not particularly limited. For example, a method of immersing hydrous pellets or unheated pellets containing EVOH (A) in a solution in which the above compound is dissolved, a method of melting EVOH (A) and mixing the above compound, a method of mixing EVOH (A) with an appropriate A method of dissolving in a solvent and mixing the above compounds can be applied.

Among them, a method of immersing a water-containing pellet containing EVOH (A), which will be described later, in a solution of the above compound is preferable in order to exhibit the effects of the present invention more remarkably. This treatment can be carried out in either batch mode or continuous mode operation. In addition, the shape of the EVOH (A) may be any shape such as powder, granules, spheres, and cylindrical pellets. Moreover, the concentration of each compound in the solution is not particularly limited. The solvent for the solution is not particularly limited, but an aqueous solution is preferred from the viewpoint of ease of handling, environmental impact, and the like. The immersion time varies depending on the form of EVOH (A), but in the case of pellets of about 1 to 10 mm, it is preferably 1 hour or more, preferably 2 hours or more. The immersion treatment in the solution of each of the above compounds may be performed by dividing into a plurality of solutions and immersing them in the solutions, or by treating them all at once. When treated by dipping in solution as described above, a final drying step yields untreated EVOH pellets with less than 0.5% volatiles.

As the unheated pellets used in the present invention, it is possible to use a conventionally known general method for producing EVOH pellets.

EVOH is usually synthesized by saponification of an ethylene-vinyl ester copolymer, and vinyl acetate is generally used as the vinyl ester. Other fatty acid vinyl esters (vinyl propionate, vinyl pivalate, etc.) can also be used in combination when ethylene and vinyl acetate are copolymerized.

Polymerization of ethylene and vinyl ester may be solution polymerization, suspension polymerization, emulsion polymerization or bulk polymerization, and may be continuous or batchwise. The polymerization conditions in this case are as follows.

Solvent: Alcohols are preferred, but other organic solvents (such as dimethyl sulfoxide) capable of dissolving ethylene, vinyl ester and ethylene-vinyl ester copolymer can be used. As alcohols, methyl alcohol, ethyl alcohol, propyl alcohol, n-butyl alcohol, t-butyl alcohol and the like can be used, and methyl alcohol is particularly preferred.
Catalyst; 2,2'-azobisisobutyronitrile, 2,2'-azobis-(2,4-dimethylvaleronitrile), 2,2'-azobis-(4-methyl-2,4-dimethylvaleronitrile ), 2,2′-azobis-(4-methoxy-2,4-dimethylvaleronitrile), 2,2′-azobis-(2-cyclopropylpropionitrile) and other azonitrile initiators and isobutyryl peroxide , cumyl peroxyneodecanoate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, t-butyl peroxyneodecanoate, lauroyl peroxide, benzoyl peroxide, t-butyl hydroperoxide, etc. and the like are used.
Temperature; 20 to 90°C, preferably 40 to 70°C.
Time; 2 to 15 hours, preferably 3 to 11 hours.
Polymerization rate: 10 to 90%, preferably 30 to 80%, based on charged vinyl ester.
Resin content in solution after polymerization; 5 to 85%, preferably 20 to 70%.

In addition to ethylene and vinyl ester, it is also possible to coexist a small amount of a monomer that can be copolymerized with them. Examples of copolymerizable monomers include α-olefins such as propylene, isobutylene, α-octene and α-dodecene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid and itaconic acid, or their anhydrides; compounds, salts, mono- or dialkyl esters, etc.; vinylsilanes such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxy-ethoxy)silane, γ-methacryloxypropylmethoxysilane; acrylonitrile, methacrylonitrile, etc. Nitriles; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as ethylenesulfonic acid, allylsulfonic acid and methallylsulfonic acid, or salts thereof; alkyl vinyl ethers, vinyl ketones, N-vinylpyrrolidone, vinyl chloride, vinylidene chloride, etc. is mentioned.

After polymerization for a predetermined time and reaching a predetermined rate of polymerization, a polymerization inhibitor is added as necessary, unreacted ethylene gas is removed by evaporation, and unreacted vinyl acetate is expelled. As a method for expelling unreacted vinyl acetate from the ethylene-vinyl acetate copolymer from which ethylene has been evaporated off, for example, the copolymer solution is continuously supplied at a constant rate from the upper part of a tower packed with Raschig rings, and There is a method in which vapor of an organic solvent such as methanol is blown into the column, a mixed vapor of an organic solvent such as methanol and unreacted vinyl acetate is distilled from the top of the column, and the unreacted vinyl acetate is removed from the bottom of the column to remove the copolymer solution. Adopted.

An alkaline catalyst is added to the copolymer solution from which unreacted vinyl acetate has been removed to saponify the vinyl acetate component in the copolymer. The saponification method can be either continuous or batchwise. Sodium hydroxide, potassium hydroxide, alkali metal alcoholate and the like are used as the alkali catalyst. For example, saponification conditions in the case of a batch system are as follows.
Copolymer solution concentration; 10 to 50%.
Reaction temperature; 30-60°C.
Amount of catalyst used: 0.02 to 0.6 equivalents (per vinyl acetate component).
Time; 1 to 6 hours.
Also, after the saponification step, an acid such as acetic acid is generally added to neutralize the remaining alkali catalyst.

The granulation operation includes, for example, (1) a method of extruding a solution containing EVOH into a low-temperature poor solvent to precipitate it, or a method of solidifying and cutting immediately after or further cooling and solidifying, and (2) a method of EVOH solution. is brought into contact with water vapor to obtain a water-containing resin composition of EVOH in advance, and then the water-containing resin composition is cut. The water content in the EVOH hydrous pellets obtained by these methods is preferably 50 to 200 parts by mass, more preferably 70 to 150 parts by mass, per 100 parts by mass of EVOH.

The unheated pellets are obtained, for example, by drying the water-containing EVOH pellets obtained in the granulation step. The volatile matter in the unheated pellets is preferably less than 0.5% by mass, more preferably less than 0.3% by mass, for the purpose of preventing sticking or the like during heat treatment. Drying methods for the hydrous pellets include, for example, static drying and fluidized drying. These drying methods may be used alone or in combination. The drying treatment may be performed by either a continuous method or a batch method. When a plurality of drying methods are used in combination, a continuous method or a batch method can be freely selected for each drying method. From the viewpoint of reducing deterioration of the pellets due to oxygen during drying, it is also preferable to carry out drying in a low oxygen concentration or in an oxygen-free state. Drying temperatures are typically below 150°C.

The pellets of the present invention can be obtained, for example, by heat-treating the unheated pellets having a volatile content of less than 0.5% by mass obtained above at a temperature 15 to 25° C. lower than the melting point of EVOH (A) for 1 to 5 hours. can get.

As for the equipment for heat treatment, either indirect heating method or direct heating method can be used for the heating method, and either batch method or continuous method can be used, and the atmosphere and temperature in the apparatus can be kept constant. Anything you can do is good. Specific examples include hopper dryers, fluidized bed dryers, static dryers, rotary kilns, tumbler dryers, etc., but are not limited to these. From the viewpoint of homogenizing the environment to which the pellets are exposed during the heat treatment, such as temperature, humidity, and oxygen concentration, and reducing the variation in quality among the pellets obtained, using a fluidized bed dryer, rotary kiln, tumbler dryer, etc. Heat treatment is preferably performed while the pellets are fluidized.

The heat treatment may be performed in the air, but the coloration of the pellets can be reduced by performing the heat treatment in a nitrogen atmosphere with an oxygen concentration of 1000 ppm or less. The atmospheric oxygen concentration is more preferably 500 ppm or less, still more preferably 200 ppm or less, still more preferably 100 ppm or less, and particularly preferably 10 ppm or less.

The method for adjusting the atmospheric oxygen concentration within the above range during heat treatment is not particularly limited. The oxygen concentration can be adjusted by using a mixed gas of nitrogen and air and adjusting the mixture ratio. In the case of a direct heating method such as a rotary kiln or a tumbler dryer, the oxygen concentration can be adjusted by adjusting the oxygen concentration of the blown gas when gas is blown in as in the indirect heating method.
In the present invention, a method of adjusting the oxygen concentration by a method other than those listed here can also be employed.

The temperature at which the unheated pellets are heat treated is preferably 15 to 25° C. lower than the melting point of EVOH (A). If the heat treatment is performed at a temperature lower than this range, it takes a very long time to obtain pellets that fully exhibit the effects of the present invention, which is not economical. On the other hand, if the heat treatment is performed at a temperature higher than the above range, the EVOH (A) may melt or agglutinate between the pellets, which may reduce the subsequent handleability.

The heat treatment time may be determined according to the balance between the heat of fusion ΔHp of the pellet and the degree of coloration, and is preferably 1 to 5 hours, more preferably 2 to 4 hours. If the heat treatment time is less than 1 hour, pellets having the effect of the present invention cannot be obtained. If the heat treatment time exceeds 4 hours, it is not preferable from the viewpoint of productivity, and the hue and thermal stability of the obtained pellets may deteriorate.

<Molded body>
The pellets of the present invention can be processed into various molded bodies by various melt molding methods. The molded article thus obtained is also an aspect of the present invention. Examples of the molded article of the present invention include a molded article having a single-layer structure and a multi-layered structure having a layer made of the molded article of pellets of the present invention and other layers. Molding methods include, for example, extrusion molding, thermoforming, profile molding, blow molding, rotational molding, and injection molding. Suitable uses of the molded article of the present invention include, for example, films, sheets, containers, bottles, tanks, pipes, hoses and the like.

The following methods are exemplified as specific molding methods. Films, sheets, pipes, hoses and the like can be obtained by extrusion molding. A container shape can be obtained by injection molding. Hollow containers such as bottles and tanks are obtained by hollow molding or rotational molding. Examples of blow molding include extrusion blow molding in which a parison is obtained by extrusion molding, followed by blowing and molding, and injection blow molding in which a preform is molded by injection molding and then blown to mold. . As a method for forming a flexible packaging material or a container, a method of obtaining a packaging material such as a multilayer film by extrusion molding, and a method of thermoforming a multilayer sheet obtained by extrusion molding into a container-like packaging material are preferably used. .

<Multilayer structure>
A multi-layer structure comprising a layer of the shaped pellets of the present invention is also a preferred embodiment of the present invention. The multilayer structure is formed by laminating a layer made of the molded pellets of the present invention and other layers. As the layer other than the resin composition layer, a layer made of a resin other than EVOH (A) is preferable. Moreover, the multilayer structure may further have a layer made of an adhesive resin. As the layer structure of the multilayer structure, x layers are layers made of a resin other than EVOH (A), y layers are layers made of the molded product of the pellets of the present invention, and z layers are adhesive resin layers. /y, x/y/x, x/z/y, x/z/y/z/x, x/y/x/y/x, x/z/y/z/x/z/y/z /x and the like. When a plurality of x layers, y layers, and z layers are provided, the types may be the same or different. Further, a layer using a recovered resin made of scraps such as trim generated during molding may be provided separately, or the recovered resin may be blended into any of the layers. The thickness and structure of each layer of the multilayer structure are not particularly limited, but the thickness ratio of the y layer to the total layer thickness is preferably 2 to 20% from the viewpoint of moldability, cost, and the like.

From the viewpoint of workability, etc., a thermoplastic resin is preferable as the resin used for the x layer. Examples of thermoplastic resins include various polyolefins (polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymers, copolymers of ethylene and α-olefins having 4 or more carbon atoms, , copolymers of polyolefin and maleic anhydride, ethylene-vinyl ester copolymers, ethylene-acrylic acid ester copolymers, or modified polyolefins obtained by graft-modifying these with unsaturated carboxylic acids or their derivatives), various polyamides (nylon 6, nylon 6.6, nylon 6/66 copolymer, nylon 11, nylon 12, polymetaxylylene adipamide, etc.), various polyesters (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), polychloride vinyl, polyvinylidene chloride, polystyrene, polyacrylonitrile, polyurethane, polycarbonate, polyacetal, polyacrylate and modified polyvinyl alcohol resins. The thermoplastic resin layer may be unstretched, uniaxially or biaxially stretched or rolled. Among them, polyolefin is preferable from the viewpoint of excellent moisture resistance, mechanical properties, economic efficiency, heat sealability, etc., and polyamide and polyester are preferable from the viewpoint of excellent mechanical properties, heat resistance and the like.

The adhesive resin used in the z layer is not particularly limited as long as it can adhere each layer, and polyurethane-based or polyester-based one-component or two-component curable adhesives, carboxylic acid-modified polyolefins, and the like can be used. It is preferably used. Carboxylic acid-modified polyolefins include, for example, polyolefin copolymers containing unsaturated carboxylic acids or their anhydrides (maleic anhydride, etc.) as copolymer components; or obtained by grafting unsaturated carboxylic acids or their anhydrides onto polyolefins. graft copolymers and the like.

Examples of the method for obtaining a multilayer structure containing a layer made of the pellet molded body of the present invention include co-extrusion molding, co-extrusion hollow molding, coinjection molding, extrusion lamination, co-extrusion lamination, dry lamination, solution coating, and the like. be done. In addition, the multilayer structure obtained by such a method is further subjected to vacuum or compressed air deep drawing molding, blow molding, press molding, etc., after reheating in the range below the melting point of EVOH (A), and then secondary Processing and molding may be performed to obtain a desired molded body. In addition, the multilayer structure is uniaxially or biaxially stretched after reheating in a range below the melting point of EVOH (A) by a method such as a roll stretching method, a pantograph stretching method, an inflation stretching method, etc. You can also get a struct.

Examples Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited by these examples. In addition, each analysis and evaluation in the present Example were performed with the following method.

(1) Heat of fusion ΔHp of pellets and its variation, and heat of fusion ΔHm after melting and re-solidifying pellets
The pellets obtained in each example and comparative example were heated from 20 ° C. to 220 ° C. at a rate of 10 ° C./min using a differential scanning calorimeter ("Q2000" manufactured by TA Instrument Co.). After cooling to 20°C at a rate of °C/min, the endothermic amount was measured when the temperature was again raised from 20°C to 220°C at a rate of 10°C/min. The amount of heat absorbed during the first temperature rise was defined as the heat of fusion ΔHp of the pellet, and the amount of heat absorbed during the second temperature increase was defined as the heat of fusion ΔHm after the pellet was melted and re-solidified. The measurement was performed on any 5 pellets, and the average value was used for the results. In addition, regarding the dispersion of the heat of fusion ΔHp of the pellets, a case where the difference between the maximum value and the minimum value of each measured value of the five pellets was less than 5 J/g was evaluated as A, and a case where it was 5 J/g or more was evaluated as B.

(2) Yellowness of Pellets The yellowness (YI) of the pellets obtained in Examples and Comparative Examples was measured using a spectrophotometer ("LabScan XE Sensor" manufactured by HunterLab). The YI value is an index representing the yellowness of an object, and the higher the YI value, the stronger the yellowness, while the lower the YI value, the weaker the yellowness and less coloring.

(3) Melting point of EVOH (A) The temperature of the maximum value of the endothermic peak during the second temperature rise in (1) was taken as the melting point of EVOH (A) in each example and comparative example.

(4) Ethylene unit content and saponification degree of EVOH (A) Pellets obtained in Examples and Comparative Examples containing tetramethylsilane (TMS) as an internal standard and trifluoroacetic acid (TFA) as an additive It was dissolved in heavy dimethyl sulfoxide (DMSO-d ₆ ) and measured at 80° C. using 500 MHz ¹ H-NMR (manufactured by JEOL Ltd. “GX-500”). The ethylene unit content and saponification degree were obtained from the peak intensity ratio.

(5) Contents of alkali metal ions (B), divalent metal ions (C), phosphate compounds (E) and boron compounds (F) (registered trademark) pressure vessel, 5 mL of concentrated nitric acid was added thereto, and decomposed at room temperature for 30 minutes. After decomposition, the vessel was capped and further decomposed by heating at 150° C. for 10 minutes, then at 180° C. for 5 minutes in a wet decomposition apparatus, and then cooled to room temperature. This treatment liquid was transferred to a 50 mL volumetric flask and diluted with pure water. The content of alkali metal ions, divalent metal ions, phosphate compounds and boron compounds in the pellets was quantified by measuring this solution with an ICP emission spectrometer ("Optima 4300DV" manufactured by Perkin Elmer).

(6) Content of carboxylic acid (D) 10 g of pellets obtained in each example and comparative example and 50 mL of pure water were put into a 100 mL Erlenmeyer flask with a common stopper, attached with a cooling condenser, and stirred at 95 ° C. for 8 hours. . After the obtained extract was cooled to 20° C., the content of carboxylic acid (D) was quantified by titration with a 0.02 mol/L sodium hydroxide aqueous solution using phenolphthalein as an indicator.

(7) Content of carboxylic acid (D) after re-drying 1 kg of pellets obtained in each example and comparative example are stored in a constant temperature and humidity machine at 40 ° C. and 90% RH ("PR-4J" manufactured by Espec Co., Ltd.) Then, the volatile content was measured over time, and the volatile content was adjusted to 5±0.2% by mass. The pellets were dried again using a fluid bed dryer at 100° C. for 12 hours. Next, 10 g of the dried pellets and 50 mL of pure water were put into a 100 mL Erlenmeyer flask with a common stopper, attached with a cooling condenser, and stirred at 95° C. for 8 hours. After cooling the obtained extract to 20° C., the content of the carboxylic acid (D) after redrying was determined by titration with a 0.02 mol/L sodium hydroxide aqueous solution using phenolphthalein as an indicator. did.

(7) Long-run performance during processing (die lip adhesion amount)
Using a single-screw extruder ("D2020" manufactured by Toyo Seiki Seisakusho Co., Ltd., diameter 20 mmφ, L/D20), the pellets obtained in each example and comparative example were subjected to 5 single-layer films with a thickness of 20 μm under the following conditions. After a period of time, the screw speed was increased to 50 rpm, and the inside of the extruder was purged (washed) with 500 g of high-density polyethylene. Next, the die was disassembled, and the heat-degraded resin adhering to the lip portion was sampled and weighed to evaluate the long-run property during processing (die lip adhesion amount). The heat-degraded resin adhering to the lip portion tends to cause defects such as gels and lumps during film formation, and a small accumulated amount means that it is possible to melt and mold stably over a long period of time.
Screw diameter: 20 mmφ (L/D = 20, compression ratio = 3.5, full flight type)
Screw rotation speed: 20 rpm
Extrusion temperature: feeding section/compression section/measuring section/die = 180/220/220/250°C
Die: 300 mm wide coat hanger die Take-up roll temperature: 80°C
Take-up speed: about 1.5 m/min (adjusted for a thickness of 20 μm)

[Example 1]
Hydrous EVOH pellets with an ethylene content of 32 mol%, a degree of saponification of 99.95 mol%, a melting point of 182°C, and a volatile content of 110% by mass were immersed in an aqueous solution containing sodium acetate, magnesium acetate, and acetic acid at 25°C for 6 hours and stirred. did. The concentrations of sodium acetate, magnesium acetate and acetic acid in the aqueous solution in the immersion treatment were such that the contents of sodium, magnesium and acetic acid in the obtained pellets were 160 ppm, 35 ppm and about 250 ppm, respectively. After the immersion treatment, the aqueous solution and the water-containing pellet are separated by centrifugal dehydration and deliquored, and then placed in a hot air dryer and dried at 80 ° C. for 3 hours and then at 110 ° C. for 35 hours. The volatile content is 0.1 mass. % of untreated pellets was obtained. The volatile content of the hydrous EVOH pellets and the unheated pellets was measured using a halogen moisture content analyzer ("HX204" 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 10 g. measured by the method. However, the volatile content in the present specification is mass % based on dry weight. The obtained unheated pellets were heat-treated in the air at 162° C. for 3.5 hours using a fluidized bed dryer to obtain the pellets of the present invention. The obtained pellets were subjected to various evaluations described above. The results are shown in Tables 1 and 2.

[Examples 2 to 4, Comparative Example 9 ]
Pellets were obtained in the same manner as in Example 1, except that the heat treatment time was set as shown in Table 2, and various evaluations were performed. The results are shown in Tables 1 and 2.

[Example 6]
Pellets were produced in the same manner as in Example 1, except that a stationary dryer was used instead of the fluidized bed dryer, and analyzed and evaluated. In the pellets of Example 6, the variation in the heat of fusion ΔHp of the pellets was large. The results are shown in Tables 1 and 2.

[Example 7]
Pellets were obtained in the same manner as in Example 1 except that heat treatment was performed in a nitrogen atmosphere with an oxygen concentration of 500 ppm using a fluidized bed dryer, and various evaluations were performed. The obtained pellets had a low degree of yellowness and a particularly good appearance. The results are shown in Tables 1 and 2.

[Examples 8 and 9]
Pellets were obtained in the same manner as in Example 1 except that the amount of magnesium acetate added was changed as shown in Table 1, and various evaluations were performed. The results are shown in Tables 1 and 2.

[Example 10]
Pellets were obtained in the same manner as in Example 1 except that calcium acetate was used instead of magnesium acetate and the amount added was changed as shown in Table 1, and various evaluations were performed. The results are shown in Tables 1 and 2.

[Example 11]
Pellets were obtained in the same manner as in Example 1 except that zinc acetate was used instead of magnesium acetate and the amount added was changed as shown in Table 1, and various evaluations were performed. The results are shown in Tables 1 and 2.

[Example 12]
Pellets were obtained in the same manner as in Example 1 except that potassium acetate was used instead of sodium acetate and the amount added was changed as shown in Table 1, and various evaluations were performed. The results are shown in Tables 1 and 2.

[Example 13]
Pellets were obtained in the same manner as in Example 1 except that propionic acid was used instead of acetic acid and the amount added was changed as shown in Table 1, and various evaluations were performed. When the obtained pellets were used to form a single layer film, a peculiar odor was felt. The results are shown in Tables 1 and 2.

[Example 14]
Pellets were obtained in the same manner as in Example 1, except that phosphoric acid was further added at the concentration shown in Table 1 during the immersion treatment, and various evaluations were performed. The obtained pellets were slightly better in yellowness than the pellets of Example 1. The results are shown in Tables 1 and 2.

[Example 15]
Further, pellets were obtained in the same manner as in Example 1 except that boric acid was added at the ratio shown in Table 1, and various evaluations were performed. When the obtained pellets were used to form a single layer, neck-in was reduced as compared to the case where the pellets of Example 1 were used to form a single layer. The results are shown in Tables 1 and 2.

[Example 16]
Before heat-treating the unheated pellets obtained in Example 1, a hindered phenolic compound having an amide bond ("Irganox 1098" manufactured by BASF, melting point 160 ° C., molecular weight 637) was extruded to 220 using a twin-screw extruder. Pellets were obtained in the same manner as in Example 1 except that the pellets were obtained by melt-kneading at ° C. and then heat-treated, and various evaluations were performed. When single layer film formation was performed using the obtained pellets, the amount of die lip adhesion was reduced. The results are shown in Tables 1 and 2.

[Example 17]
Pellets were obtained in the same manner as in Example 1 except that hydrous EVOH pellets with an ethylene content of 44 mol%, a degree of saponification of 99.95 mol%, and a melting point of 165 ° C. were used, and the heat treatment temperature was changed to 145 ° C., and various evaluations were performed. did The obtained pellets had a lower yellowness and a better appearance than in Example 1, and were used to form a single layer film. , the amount of die lip adhesion was reduced. The results are shown in Tables 1 and 2.

[Comparative Example 1]
Pellets were obtained in the same manner as in Example 1, except that the heat treatment was not performed, and various evaluations were performed. The results are shown in Tables 1 and 2.

[Comparative Example 2]
Pellets were obtained in the same manner as in Comparative Example 1 except that magnesium acetate was not used, and various evaluations were performed. The results are shown in Tables 1 and 2.

[Comparative Example 3]
Pellets were obtained in the same manner as in Example 1 except that magnesium acetate was not used, and various evaluations were performed. The results are shown in Tables 1 and 2.

[Comparative Examples 4 and 5]
Pellets were obtained in the same manner as in Example 1 except that the amount of magnesium acetate added was changed as shown in Table 1, and various evaluations were performed. The results are shown in Tables 1 and 2.

[Comparative Example 6]
Pellets were obtained in the same manner as in Example 7 except that magnesium acetate was not used, and various evaluations were performed. The results are shown in Tables 1 and 2.

[Comparative Example 7]
Pellets were obtained in the same manner as in Example 1 except that the amount of sodium acetate added was changed as shown in Table 1, and various evaluations were performed. The results are shown in Tables 1 and 2.

[Comparative Example 8]
Pellets were obtained in the same manner as in Example 1 except that the amount of acetic acid added was changed as shown in Table 1, and various evaluations were performed. The results are shown in Tables 1 and 2.

Claims (11)

A pellet mainly composed of an ethylene-vinyl alcohol copolymer (A),
The ethylene-vinyl alcohol copolymer (A) has an ethylene unit content of 15 to 60 mol% and a saponification degree of 85 mol% or more,
50 to 500 ppm of alkali metal ion (B), 10 to 100 ppm of divalent metal ion (C), and 20 to 400 ppm of carboxylic acid (D) having a boiling point of less than 150 ° C.,
The heat of fusion difference (ΔHp−ΔHm) between the heat of fusion ΔHp of the pellet measured by differential scanning calorimetry and the heat of fusion ΔHm measured after melting and re-solidifying the pellet is 5 J/g or more,
Pellets with a yellowness index of less than 30 . 2. The pellet according to claim 1, wherein the heat of fusion difference (ΔHp−ΔHm) is 10 J/g or more. 3. The pellet according to claim 1 or 2, having a heat of fusion ΔHp of 85 J/g or more. The pellet according to any one of claims 1 to 3, further containing 5 to 200 ppm of a phosphoric acid compound (E) in terms of phosphate radical. The pellet according to any one of claims 1 to 4, further containing 50 to 400 ppm of a boron compound (F) in terms of boron element. The pellet according to any one of claims 1 to 5, further comprising 5000 to 50000 ppm of a hindered phenolic compound (G) having an ester bond or an amide bond. A pellet in which the difference between the maximum value and the minimum value of heat of fusion ΔHp measured by differential scanning calorimetry for five pellets arbitrarily selected from the pellets according to any one of claims 1 to 6 is less than 5 J/g. Contains ethylene-vinyl alcohol copolymer (A), alkali metal ion (B), divalent metal ion (C) and carboxylic acid (D) having a boiling point of less than 150°C, and has a volatile content of 0.5 mass % of the unheated pellets, at a temperature 15 to 25 ° C. lower than the melting point of the ethylene-vinyl alcohol copolymer (A), heat treatment for 1 to 5 hours, any one of claims 1 to 7 . A method for producing the described pellets. The method for producing pellets according to claim 8 , wherein the heat treatment is performed in a nitrogen atmosphere with an oxygen concentration of 1000 ppm or less. The method for producing pellets according to claim 8 or 9 , wherein the heat treatment is performed while the pellets are fluidized. A melt-molded product comprising the pellets according to any one of claims 1 to 7 .