JP6704688B2 - Resin composition and multilayer structure - Google Patents

Description

The present invention relates to an ethylene-vinyl alcohol copolymer, a resin composition, and a multilayer structure.

Melt molding using a resin composition is generally used for molding containers, films, sheets and the like. Such a resin composition has few defects such as streaks and fish eyes and can be formed into a molded article having excellent appearance, and long-term operation characteristics (long run property) in which defects are unlikely to occur even if melt molding is performed for a long time. ) Is required. In particular, such defects not only impair the appearance of the molded product but also cause performance deterioration, so it is important to suppress the occurrence of defects.

On the other hand, an ethylene-vinyl alcohol copolymer (hereinafter, also referred to as “EVOH”) is a polymer material excellent in gas barrier properties against oxygen and the like, oil resistance, non-charging property, mechanical strength and the like. Therefore, the EVOH-containing resin composition is widely used as a molding material for molded articles such as containers.

However, EVOH has a relatively active hydroxyl group in the molecule, and therefore, even inside the extruder with almost no oxygen, oxidation and cross-linking reaction may occur in a high-temperature molten state, resulting in a thermally deteriorated product. In particular, when a long-term continuous operation is performed, heat-deteriorated products accumulate inside the molding machine, and gel-like particles that cause fish eyes are likely to occur. Therefore, in melt molding using the EVOH-containing resin composition, long-run property tends to be insufficient.

Various EVOH-containing resin compositions have been developed to improve such inconvenience. For example, by containing a boron compound, sodium acetate, and magnesium acetate, an EVOH-containing resin composition having improved long-run property during melt molding (see JP-A No. 11-60874) and a conjugated polyene compound melted. By incorporating a gel composition, an EVOH-containing resin composition in which generation of lumps is suppressed (see Japanese Patent Application Laid-Open No. 9-71620), a specific carboxylic acid metal salt and a hindered phenolic antioxidant, heat stability is improved. An EVOH-containing resin composition (see Japanese Patent Application Laid-Open No. 4-227744), which is excellent and in which the formation of an oxidizing gel at high temperatures is suppressed, has been developed.

However, in these conventional EVOH-containing resin compositions, not only the long-run property is not sufficiently improved, but also when a large amount of a metal salt is contained in the resin composition, a molded product is yellowed and a defective appearance is likely to occur. Further, from the viewpoint of environmental protection, for example, reduction of the amount of raw materials and waste of molded products such as packaging materials, it is required to make the molded products thinner. When such thinning is realized, film forming defects such as streaks and film forming defects and appearance defects due to coloring are likely to occur, so that further improvement in appearance properties is required.

JP, 11-60874, A JP, 9-71620, A JP-A-4-227744

The present invention has been made based on the above circumstances, the object thereof is excellent in long-run property of melt molding, occurrence of film forming defects such as film forming defects and streaks, and coloration is suppressed, An object of the present invention is to provide an ethylene-vinyl alcohol copolymer, a resin composition, and a multi-layer structure having excellent appearance.

The present invention is an ethylene-vinyl alcohol copolymer obtained by saponifying a copolymer of ethylene and vinyl ester, using a gel permeation chromatograph equipped with a differential refractive index detector and an ultraviolet-visible absorbance detector. The molecular weight measured after heat treatment at 220° C. for 50 hours in a nitrogen atmosphere satisfies the condition represented by the following formula (1).
(Ma-Mb)/Ma<0.45 (1)
Ma: molecular weight converted to polymethylmethacrylate at the maximum value of the peak measured by a differential refractive index detector Mb: converted to polymethylmethacrylate converted at the maximum value of the absorption peak at a wavelength of 220 nm measured by an ultraviolet-visible absorbance detector Molecular weight

The ethylene-vinyl alcohol copolymer is a gel permeation chromatograph equipped with a differential refractive index detector and an ultraviolet-visible absorbance detector, and the molecular weight measured after heat treatment at 220° C. for 50 hours under a nitrogen atmosphere has the following formula ( It is preferable that the condition 2) is further satisfied.
(Ma-Mc)/Ma<0.45 (2)
Mc: Polymethylmethacrylate-equivalent molecular weight at the maximum value of the absorption peak at a wavelength of 280 nm measured by an ultraviolet-visible absorbance detector

The vinyl ester is preferably vinyl acetate. The content of acetaldehyde in this vinyl acetate is preferably less than 100 ppm.

The present invention includes a resin composition containing the ethylene-vinyl alcohol copolymer.

The resin composition may further contain an alkali metal salt of an organic acid. In this case, the content of the alkali metal salt is preferably 0.0001 mass% or more and 0.1 mass% or less in terms of metal.

The present invention includes a multilayer structure having a plurality of layers, at least one of the plurality of layers being formed from the resin composition.

Here, when showing the content of each component by "ppm", this "ppm" means the mass ratio of the content of each component, and 1 ppm is 0.0001 mass %.

INDUSTRIAL APPLICABILITY The ethylene-vinyl alcohol copolymer and the resin composition of the present invention have excellent long-run properties in melt molding, and can suppress the occurrence of film-forming defects such as streaks and film-forming defects, and coloration. Therefore, the ethylene-vinyl alcohol copolymer and the resin composition can provide a molded article such as a multilayer structure having excellent appearance.

The relationship between the molecular weight (logarithmic value) of EVOH, the signal value (RI) measured by the differential refractive index detector, and the absorbance (UV) measured by the absorbance detector (measurement wavelength 220 nm and 280 nm) is schematically shown. It is a graph.

The present invention includes an ethylene-vinyl alcohol copolymer, a resin composition and a multilayer structure. These will be described below. However, the present invention is not limited to the following description. The materials exemplified below may be used alone or in combination of two or more, unless otherwise specified.

<Ethylene-vinyl alcohol copolymer>
The ethylene-vinyl alcohol copolymer (hereinafter, also referred to as “EVOH(A)”) of the present invention is a saponified copolymer of ethylene and vinyl ester.

The method for copolymerizing ethylene and vinyl ester is not particularly limited, and known methods such as solution polymerization, suspension polymerization, emulsion polymerization and bulk polymerization can be used. Further, the copolymerization method may be either continuous type or batch type.

As a lower limit of the ethylene content of EVOH (A), 10 mol% is preferable, 20 mol% is more preferable, and 25 mol% is further preferable. On the other hand, as the upper limit of the ethylene content of EVOH (A), 60 mol% is preferable, 55 mol% is more preferable, 50 mol% is further preferable, and 40 mol% is particularly preferable. When the ethylene content is less than the above lower limit, the thermal stability at the time of melt extrusion is lowered, gelation tends to occur, and film forming defects such as streaks and fish eyes may easily occur. In particular, if the operation is performed for a long time under conditions of high temperature or high speed as compared with the conditions for general melt extrusion, the possibility of gelation increases. On the other hand, when the ethylene content exceeds the above upper limit, the gas barrier property and the like are deteriorated, and the advantageous properties of EVOH may not be sufficiently exhibited.

As the vinyl ester, vinyl acetate is preferably used from the viewpoint of industrial availability. This vinyl acetate usually contains a small amount of acetaldehyde as an unavoidable impurity. The content of acetaldehyde in this vinyl acetate is preferably less than 100 ppm. As the upper limit of the acetaldehyde content of this vinyl acetate, 60 ppm is more preferable, 25 ppm is further preferable, and 15 ppm is particularly preferable. By setting the acetaldehyde content of vinyl acetate within the above range, it becomes easy to prepare EVOH (A) satisfying the formula (1) described later.

EVOH (A) may contain other structural units derived from monomers other than ethylene and vinyl ester. Examples of the monomer that provides such another structural unit include a vinylsilane compound and other polymerizable compounds. The content of the other structural unit is preferably 0.0002 mol% or more and 0.2 mol% or less based on all the structural units of EVOH (A).

[Saponification degree]
The lower limit of the degree of saponification of the structural unit derived from the vinyl ester of EVOH (A) is usually 85 mol%, preferably 90 mol%, more preferably 98 mol%, even more preferably 98.9 mol%. If the saponification degree is less than the above lower limit, the thermal stability may be insufficient.

[Peak top molecular weight (Ma)]
The peak top molecular weight (Ma) was determined by separating EVOH (A) after heat treatment at 220° C. for 50 hours in a nitrogen atmosphere using gel permeation chromatography (hereinafter, also referred to as “GPC”), and then separating it from the column. It is a value corresponding to the maximum value of the main peak of the signal (“RI” in FIG. 1) measured in the differential refractive index detector as schematically shown in FIG. 1 of the eluted EVOH (A). The peak top molecular weight (Ma) in the present invention is a polymethyl methacrylate conversion value (hereinafter, also referred to as “PMMA conversion”) calculated using a calibration curve prepared by the method described below.

The lower limit of the peak top molecular weight (Ma) is preferably 30,000, more preferably 35,000, further preferably 40,000, particularly preferably 50,000. On the other hand, the upper limit of the peak top molecular weight (Ma) is preferably 100,000, more preferably 80,000, further preferably 65,000, particularly preferably 60,000.

[Absorption peak molecular weight (Mb) and (Mc)]
The absorption peak molecular weights (Mb) and (Mc) were measured by a UV-visible absorbance detector after separating EVOH (A) by GPC under the same conditions as the measurement of the peak top molecular weight (Ma) as schematically shown in FIG. It is a value corresponding to the maximum value of the absorption peak of the signal (“UV” in FIG. 1) at the specified wavelength. The absorption peak molecular weights (Mb) and (Mc) are polymethylmethacrylate-equivalent molecular weights. The molecular weight of the absorption peak at a wavelength of 220 nm is expressed as "Mb", and the molecular weight of the absorption peak at a wavelength of 280 nm is expressed as "Mc".

The lower limit of the absorption peak molecular weight (Mb) is preferably 30,000, more preferably 35,000, further preferably 40,000, particularly preferably 50,000. On the other hand, the upper limit of the absorption peak molecular weight (Mb) is preferably 75,000, more preferably 60,000, and even more preferably 55,000.

As a minimum of absorption peak molecular weight (Mc), 35,000 are preferred, 40,000 are more preferred, 45,000 are still more preferred, and 48,000 are especially preferred. On the other hand, the upper limit of the absorption peak molecular weight (Mc) is preferably 75,000, more preferably 55,000, even more preferably 50,000.

(Creation of calibration curve)
The calibration curve is, for example, as a standard, a monodispersed PMMA (peak top molecular weight: 1,944,000, 790,000, 467,400, 271,400, 144,000, 79,250, 35,300 of Agilent Technologies). , 13,300, 7,100, 1,960, 1,020, 690) are measured and prepared for each of the differential refractive index detector and the absorbance detector. It is preferable to use analysis software for creating the calibration curve. In the PMMA measurement of this measurement, for example, a column that can separate the peaks of standard samples having both molecular weights of 1,944,000 and 271,400 is used.

[Molecular weight correlation of EVOH (A)]
EVOH (A) satisfies the condition represented by the following formula (1).

(Ma-Mb)/Ma<0.45 (1)

The left side (Ma-Mb)/Ma of the formula (1) is preferably less than 0.40, more preferably less than 0.30, and even more preferably less than 0.10. Here, as the difference between Ma and Mb (Ma-Mb) becomes smaller, the main peak (P _RI ) obtained from the differential refractive index detector in FIG. 1 and the absorption peak (P _UV ) obtained from the UV-visible absorbance detector. (220 nm)) are close to each other. On the contrary, if the value of the difference in molecular weight (Ma-Mb) is large, it means that both of these peaks ( _PRI , _PUV (220 nm)) are separated. That is, when the value of the difference in molecular weight (Ma-Mb) between both peaks ( _PRI , _PUV (220 nm)) is large, it means that there are many components that absorb ultraviolet rays having a wavelength of 220 nm among components having a relatively low molecular weight. To do. Therefore, when EVOH (A) does not satisfy the above formula (1), it means that there are many components having a relatively low molecular weight that absorb ultraviolet rays having a wavelength of 220 nm. Then, in this case, EVOH (A) is thermally deteriorated during melt molding using the resin composition containing EVOH (A), and stable workability and moldability cannot be obtained for a long time due to thickening due to coloring or gelation. Molding defects tend to become apparent under the molding conditions on the high temperature side.

It is considered that the effect obtained by satisfying the above expression (1) occurs due to the following reasons. That is, EVOH produces a carbon-carbon double bond or a carbonyl group that absorbs ultraviolet rays having a wavelength of 220 nm in the molecule by causing thermal deterioration such as dehydration, and these groups accelerate gelation of the resin composition. .. The above-mentioned gelation promoting action depends on the molecular weight of the heat-deteriorated EVOH. When the molecular weight of the heat-deteriorated EVOH is large, the promoting action is weak, and the smaller the molecular weight is, the stronger the promoting action is. Therefore, it is considered that when EVOH satisfies the above formula (1), that is, when the EVOH can maintain a relatively high molecular weight even when it is thermally deteriorated, molding defects can be suppressed.

EVOH (A) preferably satisfies the condition of the following formula (2).

(Ma-Mc)/Ma<0.45 (2)

As the left side (Ma-Mc)/Ma of the formula (2), less than 0.40 is more preferable, less than 0.30 is further preferable, and less than 0.15 is particularly preferable. Here, when the value of (Ma-Mc)/Ma on the left side of the equation (2) increases, the main peak (P _RI ) obtained from the differential refractive index detector and the absorption peak (P _RI ) obtained from the UV-visible absorbance detector. _UV (280 nm)) is distant from each other, and a relatively low molecular weight component has a large amount of components that absorb an ultraviolet ray having a wavelength of 280 nm. In this case, EVOH may be deteriorated by heat during melt-molding, and it may not be possible to obtain stable workability for a long time due to viscosity increase due to coloring or gelation, and molding failure tends to become apparent under high-temperature molding conditions. It is in.

The effect obtained by satisfying the above equation (2) is considered to occur due to the following reasons. That is, in EVOH, after the carbon-carbon double bond or the carbonyl group is generated in the molecule due to the above-mentioned thermal deterioration, the thermal deterioration further progresses, so that the conjugated double bond that absorbs ultraviolet rays having a wavelength of 280 nm is in the molecule. And the yellowing of the resin composition is promoted by this conjugated double bond. The above-described yellowing promoting action depends on the molecular weight of the heat-deteriorated EVOH, like the above-mentioned gelling promoting action, and when the molecular weight of the heat-deteriorated EVOH is large, the promoting action is weak and the molecular weight is small. The higher the acceleration effect, the stronger. Therefore, it is considered that if EVOH satisfies the above formula (2), that is, if a relatively high molecular weight can be maintained even if thermal deterioration progresses, defective molding can be further suppressed.

As a method for preparing EVOH (A) satisfying the condition represented by the formula (1), a conventional EVOH is prepared by
(A) A method of previously removing a radical polymerization inhibitor contained in a vinyl ester in the preparation of a copolymer of ethylene and a vinyl ester as a raw material,
(B) In the preparation of a copolymer of ethylene and a vinyl ester which is a raw material, a method in which impurities contained in the vinyl ester used for radical polymerization are set to a specific amount,
(C) In the preparation of a copolymer of ethylene and vinyl ester, which are raw materials, a method in which the polymerization temperature is within a specific range,
(D) A method of adding an organic acid in the polymerization step in the preparation of a copolymer of ethylene and a vinyl ester as a raw material, or in the step of recovering and reusing unreacted vinyl ester after the polymerization step,
(E) In the preparation of a copolymer of ethylene and a vinyl ester as a raw material, a method in which impurities of a solvent used for the polymerization are set to specific amounts,
(F) In the preparation of a copolymer of ethylene and a vinyl ester as a raw material, a method of increasing the mass ratio of the solvent used for the polymerization and the vinyl ester (solvent/vinyl ester),
(G) A method of using an azonitrile-based initiator or an organic peroxide-based initiator as a radical polymerization initiator used when radically polymerizing ethylene and a vinyl ester monomer,
(H) In the preparation of a copolymer of ethylene and a vinyl ester as a raw material, the addition amount of the radical polymerization inhibitor after the radical polymerization is set to a specific amount with respect to the remaining undecomposed radical polymerization initiator. Method,
(I) A method of using an alcohol solution of a copolymer of ethylene and a vinyl ester from which the remaining vinyl ester has been removed as much as possible in a saponification reaction,
(J) A method of adding an antioxidant to the copolymer of ethylene and vinyl ester used for saponification may be mentioned, and (A) to (J) may be appropriately combined. Further, EVOH(A) satisfying the condition represented by the formula (2) can be prepared from (A) to (J). The methods (A) to (J) will be described below.

((A) A method of previously removing a radical polymerization inhibitor contained in a vinyl ester in the preparation of a copolymer of ethylene as a raw material and a vinyl ester)
Examples of the radical polymerization inhibitor include the same as those exemplified as the radical polymerization inhibitor added after radical polymerization in (H) described later. Examples of the method for removing the radical polymerization inhibitor include a method using column chromatography, a reprecipitation method, a distillation method and the like, and a distillation method is usually adopted. When the radical polymerization inhibitor is removed by the distillation method, since the boiling point of the vinyl ester is lower than the boiling point of the radical polymerization inhibitor, the vinyl ester from which the polymerization inhibitor has been removed can be obtained from the top of the distillation column.

((B) In the preparation of a copolymer of ethylene and a vinyl ester, which is a raw material, a method in which a specific amount of impurities are contained in the vinyl ester used for radical polymerization)
As a minimum of the total content of impurities contained in the vinyl ester used for radical polymerization, 1 ppm is preferable, 3 ppm is more preferable, and 5 ppm is further preferable. The upper limit of the total content of the impurities is preferably 1,200 ppm, more preferably 1,100 ppm, and even more preferably 1,000 ppm.

The above-mentioned impurities include aldehydes such as acetaldehyde, crotonaldehyde, acrolein; acetals such as acetaldehyde dimethyl acetal, crotonaldehyde dimethyl acetal, acrolein dimethyl acetal obtained by acetalizing this aldehyde with a solvent alcohol; ketones such as acetone; methyl acetate, acetic acid. Examples thereof include esters such as ethyl.

In addition, acetaldehyde among the above impurities is easily generated in the production of vinyl acetate and the like, and is likely to prevent EVOH (A) from satisfying the formula (1). Therefore, in this method, it is particularly preferable to reduce the content of acetaldehyde.

((C) In the preparation of a copolymer of ethylene and a vinyl ester, which are raw materials, a method in which the polymerization temperature is within a specific range)
As a minimum of the polymerization temperature of the copolymer of ethylene and vinyl ester, 20 °C is preferred and 40 °C is more preferred. On the other hand, the upper limit of the polymerization temperature is preferably 90°C, more preferably 70°C.

((D) In the preparation of a copolymer of ethylene and vinyl ester as a raw material, an alcohol solvent is used, and an organic acid is added in the polymerization step or in the step of recovering and reusing unreacted vinyl ester after the polymerization step. Method)
In this method, addition of an organic acid to the polymerization system suppresses alcoholysis of vinyl ester with alcohol and hydrolysis with a trace amount of water, thereby suppressing the production of aldehydes such as acetaldehyde. Examples of the organic acids include hydroxycarboxylic acids such as glycolic acid, glyceric acid, malic acid, citric acid, lactic acid, tartaric acid and salicylic acid; polycarboxylic acids such as malonic acid, succinic acid, maleic acid, phthalic acid, oxalic acid and glutaric acid. Examples thereof include carboxylic acid.

The lower limit of the amount of the organic acid added is preferably 1 ppm, more preferably 3 ppm, even more preferably 5 ppm. The upper limit of the amount of the organic acid added is preferably 500 ppm, more preferably 300 ppm, even more preferably 100 ppm.

((E) In the preparation of a copolymer of ethylene and a vinyl ester which is a raw material, a method in which impurities of a solvent used for polymerization are set to specific amounts)
The lower limit of the total content of impurities in the solvent used for the polymerization is preferably 1 ppm, more preferably 3 ppm, even more preferably 5 ppm. As an upper limit of the total content of the impurities, 1,200 ppm is preferable, 1,100 ppm is more preferable, and 1,000 ppm is further preferable. Examples of the impurities of the solvent used for the polymerization include those exemplified as the impurities contained in the above-mentioned vinyl ester.

((F) In the preparation of a copolymer of ethylene and a vinyl ester which is a raw material, a method of increasing the mass ratio (solvent/vinyl ester) of a solvent and vinyl ester used for polymerization)
The lower limit of the mass ratio of the solvent used for the polymerization to the vinyl ester (solvent/vinyl ester) is preferably 0.03. On the other hand, the upper limit of the mass ratio (solvent/vinyl ester) is, for example, 0.4.

((G) Method of using azonitrile-based initiator or organic peroxide-based initiator as radical polymerization initiator used in radical polymerization of ethylene and vinyl ester monomer)
Examples of the azonitrile-based initiator include 2,2-azobisisobutyronitrile, 2,2-azobis-(2,4-dimethylvaleronitrile) and 2,2-azobis-(4-methoxy-2,4-). Dimethyl valeronitrile), 2,2-azobis-(2-cyclopropylpropionitrile) and the like. Examples of the organic peroxide include acetyl peroxide, isobutyl peroxide, diisopropyl peroxycarbonate, diallyl peroxydicarbonate, di-n-propyl peroxydicarbonate, dimyristyl peroxydicarbonate, di(2-ethoxyethyl). ) Peroxydicarbonate, di(2-ethylhexyl)peroxydicarbonate, di(methoxyisopropyl)peroxydicarbonate, di(4-tert-butylcyclohexyl)peroxydicarbonate and the like can be mentioned.

((H) In the preparation of a copolymer of ethylene and vinyl ester as a raw material, the addition amount of the radical polymerization inhibitor after radical polymerization is set to a specific amount with respect to the remaining undecomposed radical polymerization initiator. how to)
When the radical polymerization inhibitor is added after radical polymerization, the addition amount is preferably 5 molar equivalents or less with respect to the remaining undecomposed radical polymerization initiator. Examples of the radical polymerization inhibitor include compounds having a conjugated double bond and having a molecular weight of 1,000 or less, which stabilize radicals and inhibit the polymerization reaction. Specific examples of the radical polymerization inhibitor include isoprene, 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-t-butyl-1,3-butadiene, 1 ,3-pentadiene, 2,3-dimethyl-1,3-pentadiene, 2,4-dimethyl-1,3-pentadiene, 3,4-dimethyl-1,3-pentadiene, 3-ethyl-1,3-pentadiene , 2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene, 4-methyl-1,3-pentadiene, 1,3-hexadiene, 2,4-hexadiene, 2,5-dimethyl-2 ,4-hexadiene, 1,3-octadiene, 1,3-cyclopentadiene, 1,3-cyclohexadiene, 1-methoxy-1,3-butadiene, 2-methoxy-1,3-butadiene, 1-ethoxy-1 , 3-butadiene, 2-ethoxy-1,3-butadiene, 2-nitro-1,3-butadiene, chloroprene, 1-chloro-1,3-butadiene, 1-bromo-1,3-butadiene, 2-bromo -1,3-Butadiene, fulvene, tropone, ocimene, ferrandrene, myrcene, farnesene, sembrene, sorbic acid, sorbic acid ester, sorbate, abietic acid and other two carbon-carbon double bond conjugated structure Conjugated diene containing; containing three carbon-carbon double bonds such as 1,3,5-hexatriene, 2,4,6-octatriene-1-carboxylic acid, eleostearic acid, tung oil, cholecalciferol Conjugated triene containing a conjugated structure; Conjugated polyene containing a conjugated structure of 4 or more carbon-carbon double bonds such as cyclooctatetraene, 2,4,6,8-decatetraene-1-carboxylic acid, retinol, retinoic acid Such as polyene. Any of those having a plurality of stereoisomers such as 1,3-pentadiene, myrcene, farnesene may be used. As the radical polymerization inhibitor, p-benzoquinone, hydroquinone, hydroquinone monomethyl ether, 2-phenyl-1-propene, 2-phenyl-1-butene, 2,4-diphenyl-4-methyl-1-pentene, 3, 5-diphenyl-5-methyl-2-heptene, 2,4,6-triphenyl-4,6-dimethyl-1-heptene, 3,5,7-triphenyl-5-ethyl-7-methyl-2- Nonene, 1,3-diphenyl-1-butene, 2,4-diphenyl-4-methyl-2-pentene, 3,5-diphenyl-5-methyl-3-heptene, 1,3,5-triphenyl-1. -Hexene, 2,4,6-triphenyl-4,6-dimethyl-2-heptene, 3,5,7-triphenyl-5-ethyl-7-methyl-3-nonene, 1-phenyl-1,3 -Aromatic compounds such as butadiene and 1,4-diphenyl-1,3-butadiene are also included.

((I) Method of using alcohol solution of copolymer of ethylene and vinyl ester in which residual vinyl ester is removed as much as possible in saponification reaction)
The lower limit of the residual monomer removal rate is preferably 99 mol%, more preferably 99.5 mol%, and even more preferably 99.8 mol%. Examples of the method for removing the residual monomer include a method using column chromatography, a reprecipitation method, a distillation method and the like, and a distillation method is preferable. When removing residual monomers by the distillation method, a copolymer solution of ethylene and vinyl ester is continuously supplied at a constant rate from the upper part of the distillation column filled with Raschig rings, and an organic solvent vapor such as methanol is supplied from the lower part of the distillation column. Blow in. As a result, a mixed vapor of the organic solvent and unreacted vinyl ester can be distilled from the top of the distillation column, and a copolymer solution of ethylene and vinyl ester from which the unreacted vinyl ester has been removed from the bottom of the distillation column. Can be taken out. Here, the "removal rate of the residual monomer" is a value calculated by the following formula by measuring the monomer content before and after the removal treatment in the alcohol solution of the copolymer of ethylene and vinyl ester.
Removal rate (mol%) of residual monomer={1-(residual monomer content after removal/remaining monomer content before removal)}×100

((J) Method of adding antioxidant to copolymer of ethylene and vinyl ester used for saponification)
The above-mentioned antioxidant is not particularly limited, but examples thereof include phenol-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants and the like. Of these, the above-mentioned antioxidant is preferably a phenol-based antioxidant, more preferably an alkyl-substituted phenol-based antioxidant.

Examples of the phenolic antioxidant include 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate and 2,4-di-t-amyl-. Acrylate compounds such as 6-(1-(3,5-di-t-amyl-2-hydroxyphenyl)ethyl)phenyl acrylate; 2,6-di-t-butyl-4-methylphenol, 2,6- Di-t-butyl-4-ethylphenol, octadecyl-3-(3,5-)di-t-butyl-4-hydroxyphenyl)propionate, 2,2'-methylene-bis(4-methyl-6-t) -Butylphenol), 4,4'-butylidene-bis(4-methyl-6-t-butylphenol), 4,4'-butylidene-bis(6-t-butyl-m-cresol), 4,4'-thiobis (3-methyl-6-t-butylphenol), bis(3-cyclohexyl-2-hydroxy-5-methylphenyl)methane, 3,9-bis(2-(3-(3-t-butyl-4-hydroxy) -5-Methylphenyl)propionyloxy)-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane, 1,1,3-tris(2-methyl-4-) Hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, tetrakis(methylene-3-). (3',5'-di-t-butyl-4'-hydroxyphenyl)propionate)methane, triethylene glycol bis(3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate), etc. Alkyl-substituted phenol compounds; 6-(4-hydroxy-3,5-di-t-butylanilino)-2,4-bis-octylthio-1,3,5-triazine, 6-(4-hydroxy-3,5 -Dimethylanilino)-2,4-bis-octylthio-1,3,5-triazine, 6-(4-hydroxy-3-methyl-5-t-butylanilino)-2,4-bis-octylthio-1, Examples thereof include triazine group-containing phenolic compounds such as 3,5-triazine and 2-octylthio-4,6-bis-(3,5-di-t-butyl-4-oxyanilino)-1,3,5-triazine. Be done.

Examples of phosphorus-based antioxidants include triphenylphosphite, diphenylisodecylphosphite, phenyldiisodecylphosphite, tris(nonylphenyl)phosphite, tris(dinonylphenyl)phosphite, tris(2-t-butyl- 4-methylphenyl)phosphite, tris(cyclohexylphenyl)phosphite, 2,2-methylenebis(4,6-di-t-butylphenyl)octylphosphite, 9,10-dihydro-9-oxa-10-phosphite Faphenanthrene-10-oxide, 10-(3,5-di-t-butyl-4-hydroxybenzyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-decyloxy- Monophosphite compounds such as 9,10-dihydro-9-oxa-10-phosphaphenanthrene; 4,4′-butylidene-bis(3-methyl-6-t-butylphenyl-ditridecylphosphite), 4 ,4'-isopropylidene-bis(phenyl-dialkyl(C12-15) phosphite), 4,4'-isopropylidene-bis(diphenylmonoalkyl(C12-15)phosphite), 1,1 ,3-tris(2-methyl-4-ditridecylphosphite-5-t-butylphenyl)butane, tetrakis(2,4-di-t-butylphenyl)-4,4'-biphenylenephosphite and other diphosphites System compounds and the like. Of these, monophosphite compounds are preferable as the phosphorus antioxidant.

Examples of the sulfur-based antioxidant include dilauryl 3,3′-thiodipropionate, distearyl 3,3′-thiodipropionate, lauryl stearyl 3,3′-thiodipropionate, pentaerythritol-tetrakis-( β-lauryl-thiopropionate), 3,9-bis(2-dodecylthioethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane and the like.

When the antioxidant is added to the copolymer of ethylene and vinyl ester, the lower limit of the content of the antioxidant is not particularly limited, but 0.001 part by mass relative to 100 parts by mass of the copolymer. Is preferable and 0.01 mass part is more preferable. On the other hand, the upper limit of the content of the antioxidant is not particularly limited, but is preferably 5 parts by mass and more preferably 1 part by mass with respect to 100 parts by mass of the copolymer. If the content of the antioxidant is less than the above lower limit, it may be difficult to prepare EVOH (A) satisfying the formula (1). On the other hand, when the content of the antioxidant exceeds the above upper limit, there is a possibility that the effect commensurate with the cost increase due to the increase of the content cannot be obtained.

When EVOH (A) is prepared by the above methods (A) and (C) to (J), the content of acetaldehyde contained in the vinyl ester (vinyl acetate) does not have to be in the above range. In this case, the lower limit of the content of acetaldehyde is preferably 150 ppm, more preferably 250 ppm, even more preferably 350 ppm. Thus, by setting the content of acetaldehyde within the above range, the step of removing acetaldehyde from vinyl acetate can be omitted, so that the manufacturing cost can be reduced. The upper limit of the content of acetaldehyde in this case is not particularly limited, but is, for example, 1,000 ppm.

[Melt viscosity of EVOH (A) (melt flow rate)]
The lower limit of the melt flow rate of EVOH (A) is preferably 0.5 g/10 min, more preferably 1.0 g/10 min, and even more preferably 1.4 g/10 min. On the other hand, as the upper limit of the melt flow rate of EVOH (A), 30 g/10 min is preferable, 25 g/10 min is more preferable, 20 g/10 min is further preferable, 15 g/10 min is particularly preferable, 10 g/10 min is further particularly preferable, Most preferably 1.6 g/10 min. When the melt flow rate of EVOH (A) is less than the above lower limit or exceeds the above upper limit, moldability and appearance may be deteriorated.

The melt flow rate is a value measured according to JIS-K7210 (1999) at a temperature of 190° C. and a load of 2,160 g.

<Resin composition>
The resin composition of the present invention contains EVOH (A). The resin composition may further contain an alkali metal salt of an organic acid in addition to EVOH (A). Further, the resin composition may contain other optional components and the like. As a minimum of content of EVOH (A) in the resin portion of the resin composition, 70 mass% is preferred, 90 mass% is more preferred, and 95 mass% is still more preferred.

[Alkali metal salts of organic acids]
The alkali metal forming the alkali metal salt of an organic acid may be a single metal species or a plurality of metal species. Examples of the alkali metal include lithium, sodium, potassium, rubidium, cesium and the like, and sodium and potassium are preferable from the viewpoint of industrial availability. When the resin composition contains an alkali metal, the long-run property and the interlayer adhesive strength when forming a multilayer structure are improved.

As the organic acid, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, palmitic acid, stearic acid, succinic acid, linoleic acid, oleic acid. Aliphatic carboxylic acids such as benzoic acid, salicylic acid and phthalic acid; hydroxycarboxylic acids such as lactic acid, tartaric acid, citric acid and malic acid; carboxylic acids such as ethylenediaminetetraacetic acid and p-toluenesulfonic acid Sulfonic acid, etc. Among them, the organic acid is preferably a carboxylic acid, more preferably an aliphatic carboxylic acid, and further preferably acetic acid.

The alkali metal salt of an organic acid is not particularly limited, and examples thereof include aliphatic carboxylic acid salts of lithium, sodium, potassium and the like, aromatic carboxylic acid salts, and the like. Specific examples of the alkali metal salt of an organic acid include sodium acetate, potassium acetate, sodium stearate, potassium stearate, and sodium salt of ethylenediaminetetraacetic acid. Of these, the alkali metal salts of organic acids are preferably sodium acetate and potassium acetate.

When the resin composition contains an alkali metal salt of an organic acid, the lower limit of the content of the alkali metal salt of an organic acid (content in the dry resin composition) is 0.0001 mass% in terms of metal. Preferably, 0.0005 mass% is more preferable, 0.0010 mass% is further preferable, and 0.0080 mass% is particularly preferable. On the other hand, the upper limit of the content of the alkali metal salt of an organic acid is, in terms of metal, preferably 0.1% by mass, more preferably 0.08% by mass, further preferably 0.055% by mass, and 0.025% by mass. % Is particularly preferred, and 0.015% by mass is even more particularly preferred. If the content of the alkali metal salt of an organic acid is less than the above lower limit, the interlayer adhesiveness may decrease. On the other hand, when the content of the alkali metal salt of an organic acid exceeds the above upper limit, it is difficult to reduce the coloring of the resin composition, and the appearance may be deteriorated.

[Other optional ingredients]
Other optional components include, for example, antioxidants, ultraviolet absorbers, plasticizers, antistatic agents, lubricants, colorants, fillers, polyvalent metal salts of higher aliphatic carboxylic acids, hindered phenol compounds and hindered amine compounds. Examples thereof include heat stabilizers such as compounds, other resins such as polyamide and polyolefin, and hydrotalcite compounds. The total content of other optional components of the resin composition is usually 1% by mass or less.

Examples of the filler include glass fiber, ballastonite, calcium silicate, talc, montmorillonite and the like.

Examples of the polyvalent metal salt of higher aliphatic carboxylic acid include calcium stearate, magnesium stearate and the like.

As a measure against gelation, for example, a hindered phenol-based compound and a hindered amine-based compound exemplified as the heat stabilizer, a polyvalent metal salt of the higher aliphatic carboxylic acid, a hydrotalcite compound, or the like is added to the resin composition. May be. When a compound for preventing gelation is added to the resin composition, the addition amount is usually 0.01% by mass or more and 1% by mass or less.

[Melt viscosity of resin composition (melt flow rate)]
The lower limit of the melt flow rate of the resin composition is preferably 0.5 g/10 min, more preferably 1.0 g/10 min, even more preferably 1.4 g/10 min. On the other hand, as the upper limit of the melt flow rate of the resin composition, 30 g/10 min is preferable, 25 g/10 min is more preferable, 20 g/10 min is further preferable, 15 g/10 min is particularly preferable, 10 g/10 min is further particularly preferable, Most preferably 1.6 g/10 min. When the melt flow rate of the resin composition is less than the above lower limit or exceeds the above upper limit, moldability and appearance may be deteriorated.

<Method for producing resin composition>
As a method for producing the resin composition, for example, a method of mixing EVOH (A) pellets with an alkali metal salt, other optional components and the like as necessary and melt-kneading, and EVOH (A) pellets for each component And a method of immersing it in a solution containing. A ribbon blender, a high speed mixer co-kneader, a mixing roll, an extruder, an intensive mixer, or the like can be used to mix the pellets with other components.

<Manufacturing method of multilayer structure>
The resin composition may be a molded product having a single layer structure, or may be a molded product having two or more types of multilayer structures (multilayer structure) together with other various base materials.

When the resin composition has a multilayer structure, a thermoplastic resin layer may be adjacent to a layer made of the resin composition.

As the resin forming the thermoplastic resin layer,
High density, medium density or low density polyethylene;
Polyethylene obtained by copolymerizing vinyl acetate, acrylic ester, or α-olefins such as butene and hexene;
Ionomer resin;
Polypropylene homopolymer;
Polypropylene obtained by copolymerizing α-olefins such as ethylene, butene and hexene;
Polyolefins such as modified polypropylene blended with rubber polymers;
Resins obtained by adding or grafting maleic anhydride to these resins are preferable.

The multilayer structure may further have a thermoplastic resin layer other than the thermoplastic resin layer, as the resin forming the other thermoplastic resin layer in this case, polyamide, polyester, polystyrene, poly Examples thereof include vinyl chloride, acrylic resin, polyurethane, polycarbonate, polyvinyl acetate and the like. Of these, polyester is preferred.

The layers of the multilayer structure may be laminated via an adhesive resin layer. Examples of the adhesive resin used for forming the adhesive resin layer include acid-modified polyolefin. Examples of the acid-modified polyolefin include an olefin polymer in which an unsaturated carboxylic acid or a derivative thereof is introduced by a chemical bond.

The method for obtaining the multilayer structure is not particularly limited, and examples thereof include extrusion laminating method, dry laminating method, extrusion blow molding method, coextrusion laminating method, coextrusion sheet molding method, coextrusion pipe molding method, The coextrusion blow molding method, the coinjection molding method, the solution coating method and the like can be mentioned. The multilayer structure obtained by such a method is further reheated to a temperature below the melting point of EVOH (A) by a method such as vacuum pressure deep drawing and blow molding, and then subjected to secondary processing. May be given.

The scrap generated during extrusion molding, blow molding, thermoforming, etc. may be blended with the thermoplastic resin layer for reuse, or may be used as a separate recovery layer.

The layer structure of the multilayer structure is not particularly limited, but from the viewpoint of moldability, cost, etc., the thermoplastic resin layer/the resin composition layer/thermoplastic resin layer, the resin composition layer/adhesiveness Typical examples are resin layer/thermoplastic resin layer, thermoplastic resin layer/adhesive resin layer/resin composition layer/adhesive resin layer/thermoplastic resin layer. Among these, the layer constitution of thermoplastic resin layer/the resin composition layer/thermoplastic resin layer is preferable, and more specifically, the layer made of the thermoplastic polyester is directly provided on both sides of the layer made of the resin composition. A laminated structure is more preferable. When thermoplastic resin layers are provided on both outer layers of the resin composition layer, the thermoplastic resin layers on both outer layers may be layers made of different resins or may be layers made of the same resin. ..

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.

<Synthesis of EVOH>
[Synthesis Example 1] (Synthesis of EVOH pellets)
(Polymerization of ethylene-vinyl acetate copolymer)
A 250-liter pressure reactor equipped with a jacket, a stirrer, a nitrogen inlet, an ethylene inlet, and an initiator inlet was charged with 83 kg of vinyl acetate and 14.9 kg of methanol (hereinafter referred to as MeOH) and heated to 60°C. Then, the reaction solution was bubbled with nitrogen gas for 30 minutes to replace the inside of the reaction tank with nitrogen. Then, ethylene was introduced so that the reaction tank pressure (ethylene pressure) was 4.0 MPa. After adjusting the temperature in the reaction vessel to 60° C., 12.3 g of 2,2′-azobis(2,4-dimethylvaleronitrile) (“V-65” manufactured by Wako Pure Chemical Industries, Ltd.) was used as an initiator. It was added as a methanol solution to initiate polymerization. During the polymerization, the ethylene pressure was maintained at 4.0 MPa and the polymerization temperature was maintained at 60°C. After 5 hours, the polymerization was stopped by cooling when the polymerization rate of vinyl acetate reached 40%. Ethylene was exhausted from the reaction tank, and nitrogen gas was bubbled through the reaction solution to completely remove ethylene. Then, after removing unreacted vinyl acetate under reduced pressure, an ethylene-vinyl acetate copolymer (hereinafter referred to as "EVAc") was obtained. The vinyl acetate used in the synthesis was one to which the content of acetaldehyde shown in Table 1 was added.

(Saponification)
Methanol was added to the obtained EVAc solution to obtain an EVAc solution having a concentration of 15% by mass. To 253.4 kg of this methanol solution of EVAc (38 kg of EVAc in the solution) was added 76.6 L of a methanol solution containing 10% by mass of sodium hydroxide (a molar ratio of 0.4 to the vinyl acetate unit in EVAc). The EVAc was saponified by stirring at 60° C. for 4 hours. Six hours after the start of the reaction, 9.2 kg of acetic acid and 60 L of water were added to neutralize the above reaction liquid to stop the reaction.

(Washing)
The neutralized reaction solution was transferred from the reactor to a drum and left at room temperature for 16 hours to be cooled and solidified into a cake. Then, the cake-shaped resin was deliquored using a centrifuge (“H-130” manufactured by Domestic Centrifuge Co., Ltd., rotation speed 1200 rpm). Next, the step of washing with ion-exchanged water continuously from above to the center of the centrifuge and washing the resin with water was carried out for 10 hours. The conductivity of the cleaning liquid 10 hours after the start of cleaning was 30 μS/cm (measured by “CM-30ET” manufactured by Toa Denpa Kogyo Co., Ltd.).

(Granulation)
The resin after the washing was dried at 60° C. for 48 hours using a drier to obtain a powdered EVOH. 20 kg of dried powdered EVOH was dissolved in 43 L of a mixed solution of water and methanol (mass ratio: water/methanol=4/6) and stirred at 80° C. for 12 hours. Next, the stirring was stopped, the temperature of the dissolution tank was lowered to 65° C., and the mixture was left for 5 hours to degas the EVOH water and methanol solution. Then, from a metal plate having a circular opening with a diameter of 3.5 mm, it is extruded into a mixed solution of water and methanol (mass ratio: water/methanol=9/1) at 5° C. to deposit in strands and cut. Thus, water-containing EVOH pellets having a diameter of about 4 mm and a length of about 5 mm were obtained.

(Purification)
The water-containing EVOH pellets were deliquored with a centrifuge and further washed by repeating the operation of adding a large amount of water and deliquoring to obtain EVOH pellets. The EVOH obtained had a saponification degree of 99 mol %.

[Synthesis Examples 2 to 4 and Comparative Synthesis Example 1]
EVOH was synthesized in the same manner as in Synthesis Example 1 except that the acetaldehyde content, ethylene content and saponification degree of vinyl acetate were as shown in Table 1.

[Synthesis example 5]
EVOH was synthesized in the same manner as in Synthesis Example 1 except that acetaldehyde content, ethylene content and saponification degree of vinyl acetate were as shown in Table 1 and that tartaric acid (50 ppm) was further added to vinyl acetate.

[Comparative Synthesis Example 2]
(Synthesis of polyvinyl acetate)
A 6 L separable flask equipped with a stirrer, a thermometer, a nitrogen introduction tube, and a reflux tube was previously deoxygenated, 2,555 parts by mass of vinyl acetate monomer containing 500 ppm of acetaldehyde, and 945 parts by mass of methanol containing 50 ppm of acetaldehyde dimethyl acetal. Parts, and a tartaric acid 1% by mass methanol solution (addition amount to vinyl acetate monomer: 20 ppm) were charged, and the temperature was adjusted to 60° C. under a nitrogen stream. An ethylene glycol aqueous solution at -10°C was circulated in the reflux tube. Thereafter, 18.6 mL of a 0.55 mass% methanol solution of di-n-propylperoxydicarbonate was added to initiate polymerization. After the initiation of the polymerization, the same methanol solution of di-n-propylperoxydicarbonate was continuously added at a rate of 20.9 mL/hour until the completion of the polymerization, and the temperature during the polymerization was kept at 60° C. to perform the polymerization. After 4 hours from the start of the polymerization, when the solid content concentration of the polymerization solution reached 25.1% by mass, the amount of di-n-propylperoxydicarbonate remained undecomposed in the polymerization solution at 3 times the molar equivalent. 1,200 parts by mass of methanol containing 0.0141 parts by mass of the corresponding sorbic acid was added, and the polymerization liquid was cooled to terminate the polymerization. The polymerization rate of the vinyl acetate monomer when the polymerization was stopped was 35.0%. After cooling to room temperature, the vinyl acetate monomer and methanol were distilled off under reduced pressure with a water aspirator to precipitate polyvinyl acetate. The operation of adding 3,000 parts by mass of methanol to the precipitated polyvinyl acetate, dissolving the polyvinyl acetate while heating at 30° C., and then distilling it off again under reduced pressure of a water stream aspirator was repeated three times. Methanol was added to the precipitated polyvinyl acetate to obtain a 40 mass% methanol solution of polyvinyl acetate having a vinyl acetate monomer removal rate of 99.8%. Further, a part of the obtained methanol solution was collected, and a 10 mass% methanol solution of sodium hydroxide was added so that the molar ratio of sodium hydroxide to vinyl acetate unit in polyvinyl acetate was 0.1. The gel was crushed when the gelled product was formed, and Soxhlet extraction was performed with methanol for 3 days. The obtained polyvinyl alcohol was dried and the viscosity average degree of polymerization was measured. As a result, the degree of polymerization was 1,700. This was used as an index of the degree of polymerization of polyvinyl acetate.

[Comparative Synthesis Example 3]
(Synthesis of polyvinyl alcohol)
8% by mass methanol solution of sodium hydroxide (methanol and methanol) so that the total solid content concentration (saponification concentration) was 30% by mass with respect to the 40% by mass methanol solution of polyvinyl acetate synthesized in Comparative Synthesis Example 2. A molar ratio of sodium hydroxide to vinyl acetate monomer units in polyvinyl acetate was 0.020) was added with stirring, and the saponification reaction was started at 40°C. The gel was crushed at the time when a gelled product was produced as the saponification reaction proceeded, the crushed gel was transferred to a container at 40° C., and 60 minutes after the start of the saponification reaction, methanol, methyl acetate and water ( It was immersed in a solution having a mass ratio of 25/70/5) and neutralized. The obtained swollen gel is centrifuged, and a mass of twice the mass of the swollen gel is added, immersed and allowed to stand for 30 minutes, and then centrifuged. This operation is repeated 4 times, at 60° C. for 1 hour, 100 times. It dried at 2 degreeC for 2 hours, and obtained polyvinyl alcohol (PVA).

<Preparation of Resin Compositions of Examples 1 to 5 and Comparative Examples 1 and 2>
The EVOH pellets obtained in Synthesis Examples 1 to 5 and Comparative Synthesis Example 1 and 20 kg of PVA obtained in Comparative Synthesis Example 3 were washed with an aqueous acetic acid solution and ion-exchanged water, and then immersed in an aqueous solution containing sodium acetate. went. After the aqueous solution for immersion treatment and the resin composition chip were separated and deliquored, they were placed in a hot air drier and dried at 80° C. for 4 hours, and further dried at 100° C. for 16 hours. 5 and the resin composition of Comparative Example 1 (hereinafter, also referred to as “EVOH resin composition”) were obtained as dry pellets. The PVA synthesized in Comparative Synthesis Example 3 was used as the resin composition of Comparative Example 2. Using the dried pellets, the saponification degree of EVOH, ethylene content, alkali metal content, etc. shown in Table 1 were measured by the method described below. In Table 1, "-" indicates that the resin was not dissolved in the solvent and therefore the molecular weight was not measured.

[Ethylene content of EVOH and degree of saponification]
The dry EVOH pellets were ground by freeze grinding. The obtained pulverized EVOH was sieved with a sieve having a nominal size of 1 mm (standard sieve standard JIS-Z8801 compliant). 5 g of EVOH powder that passed through this sieve was immersed in 100 g of ion-exchanged water, stirred at 85° C. for 4 hours, drained and dried. This operation was performed twice. Using the obtained powder EVOH after washing, ¹ H-NMR measurement was performed under the following measurement conditions, and the ethylene content and the saponification degree were determined by the following analysis method.

(Measurement condition)
Device name: Superconducting nuclear magnetic resonance device ("Lambda500" from JEOL Ltd.)
Observation frequency: 500 MHz
Solvent: _{DMSO-d 6}
Polymer concentration: 4% by mass
Measurement temperature: 40℃ and 95℃
Number of integrations: 600 times Pulse delay time: 3.836 seconds Sample rotation speed: 10 Hz to 12 Hz
Pulse width (90° pulse): 6.75 μsec

(analysis method)
In the measurement at 40° C., a hydrogen peak in the water molecule was observed around 3.3 ppm, and the peak of 3.1 ppm to 3.7 ppm of the methine hydrogen peak of the vinyl alcohol unit of EVOH overlapped. On the other hand, in the measurement at 95° C., although the overlap generated at 40° C. is eliminated, the hydrogen peak of the hydroxyl group of the vinyl alcohol unit of EVOH existing near 4 ppm to 4.5 ppm is the methine of the vinyl alcohol unit of EVOH. It overlapped with the 3.7 ppm to 4 ppm portion of the hydrogen peak. That is, regarding the quantification of methine hydrogen (3.1 ppm to 4 ppm) of the vinyl alcohol unit of EVOH, in order to avoid overlapping with the hydrogen peak of water or a hydroxyl group, the portion of 3.1 ppm to 3.7 ppm was 95%. The measurement data of 40 degreeC was employ|adopted for the part of 3.7 ppm-4 ppm, and the total amount of the said methine hydrogen was quantified as the total value of these. It is known that the hydrogen peak of water or a hydroxyl group shifts to the high magnetic field side by increasing the measurement temperature. Therefore, analysis was performed using the measurement results at both 40° C. and 95° C. as follows. From the above spectrum measured at 40° C., the integral value (I ₁ ) of the peak of the chemical shift of 3.7 ppm to 4 ppm and the integral value (I ₂ ) of the peak of the chemical shift of 0.6 ppm to 1.8 ppm were obtained. ..

On the other hand, from the spectrum measured at 95° C., the integral value (I ₃ ) of the peak of chemical shift of 3.1 ppm to 3.7 ppm, the integral value (I ₄ ) of the peak of chemical shift of 0.6 ppm to 1.8 ppm, and The integrated value (I ₅ ) of the peak of the chemical shift of 1.9 ppm to 2.1 ppm was obtained. Here, the peak of the chemical shift of 0.6 ppm to 1.8 ppm is mainly derived from methylene hydrogen, and the peak of the chemical shift of 1.9 ppm to 2.1 ppm is in the unsaponified vinyl acetate unit. It is derived from methyl hydrogen. From these integrated values, the ethylene content was calculated by the following formula (3), and the saponification degree was calculated by the following formula (4).

[Alkali metal content]
The measurement of the alkali metal content was quantified using a spectroscopic analyzer. Specifically, 0.5 g of dry EVOH pellets was added to a Teflon (registered trademark) pressure resistant container manufactured by ACTAC, and 5 mL of nitric acid (for precision analysis manufactured by Wako Pure Chemical Industries, Ltd.) was added. After leaving it for 30 minutes, the container was covered with a cap lip with a rupture disc, and it was heated at 150° C. for 10 minutes, and then at 180° C. for 10 minutes by a microwave high-speed decomposition system (“Speed Wave MWS-2” manufactured by ACTAC). Treatment was performed to decompose dry EVOH pellets. In addition, when the decomposition of the dry EVOH pellets could not be completed in the above-mentioned treatment, the treatment conditions were appropriately adjusted. The obtained decomposition product was diluted with 10 mL of ion-exchanged water, the whole solution was transferred to a 50 mL volumetric flask, and the volume was deionized with ion-exchanged water to obtain a decomposition solution. The alkali metal content was measured by quantitatively analyzing the decomposed solution at a wavelength of 589.592 nm of Na using an ICP emission spectroscopic analyzer (“Optima 4300 DV” manufactured by Perkin Elmer Japan).

[Melt viscosity (melt flow rate)]
The melt viscosity (melt flow rate) was measured according to JIS-K7210 (1999) at a temperature of 190° C. and a load of 2160 g.

[Measurement of molecular weight of EVOH]
(Preparation of measurement sample)
The measurement sample was produced by heating EVOH at 220° C. for 50 hours in a nitrogen atmosphere.

(GPC measurement)
The GPC measurement was performed using "GPCmax" manufactured by VISCOTECH. The molecular weight was calculated based on the signal intensity detected by the differential refractive index detector and the UV-visible absorbance detector. "TDA305" and "UV Detector2600" manufactured by VISCOTECH were used as the differential refractive index detector and the UV-visible absorbance detector. The detection cell of this absorbance detector used had an optical path length of 10 mm. As the GPC column, "GPC HFIP-806M" manufactured by Showa Denko KK was used. As the analysis software, "OmniSEC (Version 4.7.0.406)" attached to the apparatus was used.

(Measurement condition)
A measurement sample was collected and dissolved in hexafluoroisopropanol (hereinafter referred to as “HFIP”) containing 20 mmol/L of sodium trifluoroacetate to prepare a 0.100 wt/vol% solution. For the measurement, a solution filtered with a 0.45 μm polytetrafluoroethylene filter was used. The measurement sample was dissolved by allowing it to stand overnight at room temperature.

As the mobile phase, HFIP containing 20 mmol/L sodium trifluoroacetate was used. The mobile phase flow rate was 1.0 mL/min. The sample injection amount was 100 μL, and the measurement was performed at a GPC column temperature of 40° C.

In addition, for the sample having a viscosity average degree of polymerization of PVA exceeding 2,400, GPC measurement was performed using an appropriately diluted sample (100 μL). From the measured value, the absorbance at a sample concentration of 1.00 mg/mL was calculated by the following formula (5). α (mg/mL) is the concentration of the diluted sample.
Absorbance=(1.00/α)×measured value of absorbance... (5)

(Creation of calibration curve)
As a standard, polymethylmethacrylate (hereinafter abbreviated as "PMMA") manufactured by Agilent Technologies (peak top molecular weight: 1,944,000, 79,000, 467,400, 271,400, 144,000, 79, 250, 35, 300, 13, 300, 7, 100, 1, 960, 1, 020 or 690) to convert the elution volume into PMMA molecular weight for each of the differential refractive index detector and the absorbance detector. A calibration curve was prepared. The above analysis software was used to create each calibration curve. In this measurement, a column that can separate peaks of standard samples having both molecular weights of 1,944,000 and 271,400 was used in PMMA measurement.

The peak intensity obtained from the differential refractive index detector is represented by "mV", and as a standard sample, an American Polymer Standard Corp. The peak intensity when using a PMMA sample (PMMA85K: weight average molecular weight 85,450, number average molecular weight 74,300, intrinsic viscosity 0.309) of the same company at a concentration of 1.000 mg/mL was 358.31 mV.

In addition, the peak intensity obtained from the UV-visible absorbance detector is represented by the absorbance (absorption unit), and the absorbance of the UV-visible absorbance detector was converted to 1 absorption unit = 1,000 mV in the analysis software.

<Evaluation of EVOH resin compositions of Examples 1 to 5 and Comparative Example 1>
The EVOH resin compositions of Examples 1 to 5 and Comparative Example 1 thus obtained were evaluated for film forming defects and film appearance properties (streaks and coloring of roll ends) as follows. The evaluation results are shown in Table 2. The PVA of Comparative Example 2 was not evaluated for film-forming defects and film appearance because the gelation was severe and film formation was impossible, and the evaluation items of these EVOH resin compositions and PVA were: It is shown in Table 2 as "-".

[(1) Film forming defect evaluation]
Each dry EVOH resin composition pellet using a single-screw extruder ("D2020" manufactured by Toyo Seiki Seisakusho Co., Ltd.; D (mm) = 20, L/D = 20, compression ratio = 2.0, screw: full flight) A monolayer film having an average thickness of 20 μm was produced from. The conditions at this time are as shown below.

Extrusion temperature: 250°C
Screw rotation speed: 40 rpm
Dice width: 30 cm
Take-up roll temperature: 80°C
Take-up roll speed: 3.1 m/min

A single layer film was produced by continuously operating under the above conditions, and the number of defects per film length of 17 cm was counted for each of the films produced 10 hours and 50 hours after the operation started. The number of defects was counted by using a film defect inspection device ("AI-10" manufactured by Frontier System Co., Ltd.). The detection camera in this film defect inspection apparatus was installed so that the lens position was 195 mm from the film surface. Film forming defects are "good (A)" when the number of defects is less than 50, "slightly good (B)" when the number of defects is 50 or more and less than 200, and "bad (C)" when 200 or more are defective. Was judged as.

[(2) Evaluation of film appearance]
The appearance (streak) of the film produced after 10 hours and 50 hours after the start of operation was visually evaluated according to the following evaluation criteria. In addition, a roll in which 100 m of the film was wound around a paper tube was produced, and the coloring due to yellowing of the end portion of the roll was evaluated.

(Streak evaluation criteria)
Good (A): No streak was observed Somewhat good (B): Streak was confirmed Poor (C): Many streaks were confirmed

(Evaluation criteria for coloring the end of roll)
Good (A): Colorless Fair (B): Yellowing Poor (C): Remarkably yellowing

As shown in Table 2, in the EVOH resin compositions of Examples 1 to 5, the film-forming defects of the films formed 10 hours and 50 hours after the start of operation, streaks, and the occurrence of coloration at the end of the roll were suppressed. .. That is, the EVOH resin compositions of Examples 1 to 5 were able to form films having excellent long-run properties during melt molding and excellent appearance.

On the other hand, in the EVOH resin composition of Comparative Example 1, many film-forming defects and streaks were observed in the films formed 10 hours and 50 hours after the start of operation, and the roll ends were significantly yellowed. Was.

[Example 6] (Coextrusion sheet molding method (with extrusion temperature))
A multilayer sheet was prepared using the EVOH resin composition obtained in Example 4, and the appearance was evaluated. Specifically, an EVOH resin composition, an ethylene-α-olefin copolymer, and a carboxylic acid-modified polyolefin are charged into separate extruders, and an ethylene-α-olefin copolymer/carboxylic acid-modified polyolefin/EVOH resin composition is prepared. /Carboxylic acid modified polyolefin/Ethylene-α-olefin copolymer (average film thickness: 200 μm/25 μm/50 μm/25 μm/200 μm) Coextrusion of a multilayer sheet of 3 types and 5 layers having an average thickness of 500 μm Obtained by a sheet forming apparatus. The extrusion was carried out at a temperature of 200° C. to 240° C. with an extruder having a diameter of 65 mm for the ethylene-α-olefin copolymer and L/D=22, and a diameter of 40 mm, L for the carboxylic acid-modified polyolefin. /D=26 extruder with a single screw at a temperature of 160°C-220°C, for EVOH resin composition a diameter of 40 mm, L/D=22 with an extruder with a single screw 160°C-240°C. The feed block die (width 600 mm) was operated at 250° C. The set temperature of the feed block die (width 600 mm) was set to 250° C., which was higher by 10° C. than usual, and the appearance of the sheet after continuous molding for 10 hours was evaluated. As a result, the film surface was good.

INDUSTRIAL APPLICABILITY The ethylene-vinyl alcohol copolymer and the resin composition of the present invention have excellent long-run properties in melt molding, and can suppress the occurrence of film-forming defects such as streaks and film-forming defects, and coloration. Therefore, the ethylene-vinyl alcohol copolymer and the resin composition can provide a molded article such as a multilayer structure having excellent appearance.

Claims (4)

A resin composition containing an ethylene-vinyl alcohol copolymer obtained by saponifying a copolymer of ethylene and a vinyl ester,
The ethylene-vinyl alcohol copolymer,
Using a gel permeation chromatograph equipped with a differential refractive index detector and an ultraviolet-visible absorbance detector, under a nitrogen atmosphere, the molecular weight measured after heat treatment at 220° C. for 50 hours satisfies the condition represented by the following formula (1):
A resin composition further comprising an alkali metal salt of a carboxylic acid, wherein the content of the alkali metal salt is 0.0010 mass% or more and 0.015 mass% or less in terms of metal.
(Ma-Mb)/Ma<0.10 (1)
Ma: molecular weight converted to polymethylmethacrylate at the maximum value of the peak measured by a differential refractive index detector Mb: converted to polymethylmethacrylate converted at the maximum value of the absorption peak at a wavelength of 220 nm measured by an ultraviolet-visible absorbance detector Molecular weight The ethylene-vinyl alcohol copolymer,
Using a gel permeation chromatograph equipped with a differential refractive index detector and an ultraviolet-visible absorbance detector, the molecular weight measured after heat treatment at 220° C. for 50 hours under a nitrogen atmosphere further satisfies the condition represented by the following formula (2). The resin composition according to claim 1.
(Ma-Mc)/Ma<0.45 (2)
Mc: Polymethylmethacrylate-equivalent molecular weight at the maximum value of the absorption peak at a wavelength of 280 nm measured by an ultraviolet-visible absorbance detector The resin composition according to claim 1 or 2, wherein the vinyl ester is vinyl acetate, and the content of acetaldehyde in the vinyl acetate is less than 100 ppm. A multilayer structure having a plurality of layers,
At least one layer of said several layers is formed from the resin composition of Claim 1, Claim 2, or Claim 3, The multilayer structure characterized by the above-mentioned.

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