JP7047379B2 - A method for producing an ethylene-vinyl alcohol-based copolymer pellet and an ethylene-vinyl alcohol-based copolymer pellet containing a conjugated polyene and an alkali metal. - Google Patents

Description

The present invention relates to pellets of an ethylene-vinyl alcohol-based copolymer (hereinafter, may be referred to as "EVOH") capable of providing a film in which fish eyes are extremely low when formed into a film, and more particularly, alkali. The present invention relates to an EVOH pellet containing a metal and having an adjusted content of conjugated polyene present on the surface of the pellet, and a method for producing the same.

In EVOH, the hydroxyl groups contained in the molecular chain are strongly hydrogen-bonded to form a crystal portion, and the crystal portion prevents the invasion of gas such as oxygen from the outside, so that the EVOH has excellent gas barrier properties including oxygen barrier properties. It shows the sex. Taking advantage of these characteristics, EVOH is used by being molded into films and sheets such as food packaging materials, pharmaceutical packaging materials, industrial chemical packaging materials, pesticide packaging materials, and packaging containers such as bottles.

EVOH is usually formed and processed into a film shape, a sheet shape, a bottle shape, a cup shape, a tube shape, a pipe shape, or the like by melt molding, and is put into practical use. Therefore, the formability and processability of EVOH are important.

However, since EVOH has a relatively active hydroxyl group in the molecule, an oxidation / cross-linking reaction may occur due to a high-temperature melting state even inside an extruder in a state where there is almost no oxygen, and a heat-deteriorated product may be produced. It is known that this heat-degraded product has the inconvenience of generating a gel-like mass that causes fish eyes.

In order to improve such inconvenience, Patent Document 1 proposes an EVOH composition in which EVOH contains a conjugated polyene to suppress the generation of fish eyes such as gel-like lumps due to melt molding.

In Patent Document 1, in the method for producing a vinyl acetate-based copolymer, after copolymerizing a monomer such as vinyl acetate, a conjugated polyene having a boiling point of 20 ° C. or higher is added, and further, the obtained vinyl acetate-based copolymer is obtained. It discloses the method of copolymerization. As the EVOH composition produced by this method, 0.00002 to 1% by weight (0.2 ppm to 10000 ppm), preferably 0.0001 to 0.2% by weight (1 ppm to) of conjugated polyene having a boiling point of 20 ° C. or higher is added to EVOH. It is disclosed that the composition contains (2000 ppm) (paragraph 0034).

Patent Document 1 explains that if the polyene compound remains in the final saponified product, it causes odor generation, exudation, etc. Therefore, from the viewpoint of using it in a packaging container or the like, it is not desirable that the residual amount is too large. .. Then, it is described that it is preferable to use a polyene compound that is easily washed and removed by washing with water after saponification (paragraph 0011).
Specifically, after polymerizing vinyl acetate under ethylene pressurization, conjugated polyene is added, ethylene is removed, and then Kenification is performed to produce EVOH, and EVOH particles are washed with a large amount of water for the purpose. EVOH particles are obtained (Example 1).
The film produced by using the EVOH particles thus obtained has little coloring, and it has been shown that the number of gel-like masses of 100 μm or more is 3 to 10 per 100 cm ² (see Table 1).

Further, in Patent Document 2, as a method for producing a vinyl alcohol-based polymer having less fish eyes during molding, suppression of coloring, and suppression of odor, a vinyl acetate-based compound is polymerized and not yet used in a distillation column. It is disclosed that after removing vinyl acetate from the reaction, at least one of N, N-dialkylhydroxylamine, a styrene derivative, a hydroquinone derivative, a quinone derivative, a piperidine derivative, and a conjugated polyene is supplied as a polymerization inhibitor.

Japanese Unexamined Patent Publication No. 9-71620 Japanese Patent Application Laid-Open No. 2003-89706

In recent years, the demands on the appearance and odor of packaging materials have become more and more stringent, and it is desired to suppress the generation of fish eyes while ensuring melt moldability. In particular, there is a demand for EVOH pellets that can sufficiently suppress the generation of minute fish eyes having a diameter of 200 μm or less.

The present invention has been made in view of the above circumstances, and an object thereof is an EVOH pellet capable of suppressing the generation of minute fish eyes having a diameter of 200 μm or less and also suppressing the generation of odor. And its manufacturing method.

We investigated the relationship between EVOH pellets containing conjugated polyenes and the development of fish eyes. As a result of various studies, it was found that the occurrence of fish eyes can be suppressed by allowing the conjugated polyene to be present in the pellet surface layer in an amount of a predetermined amount or more. Although the mechanism is not clear, when EVOH pellets containing conjugated polyene are melted by an extruder, a predetermined amount of conjugated polyene is present on the pellet surface, which is the contact portion between the pellet and a high-temperature metal such as a barrel or screw. As described above, it is considered that the presence thereof can trap the radicals locally generated near the pellet surface and suppress the generation of fish eyes.

However, when conjugated polyenes are added, the pH of EVOH may be biased toward acidity or basicity, resulting in unexpected side reactions such as decomposition and cross-linking. Especially in the vicinity of the pellet surface, it is easily affected by heat from an extruder or the like, and if the pH is not adjusted, a sufficient fish eye suppressing effect cannot be obtained. By containing an alkali metal in EVOH, the pH of the resin composition, particularly the pH near the pellet surface, can be controlled in an appropriate region by the buffering action, so that the fisheye suppressing effect can be further improved. It is presumed that it can be done.

Based on this recognition, the present inventors focused on the content of the conjugated polyene on the surface layer of the pellet and the content of the alkali metal, and determined the content of the conjugated polyene on the surface of the pellet and the content of the alkali metal in EVOH. The present invention has been completed by finding that the fish eye is reduced by setting the temperature within a predetermined range.

That is, the present invention is an EVOH pellet containing a conjugated polyene and an alkali metal (hereinafter, may be simply referred to as "conjugated polyene and an alkali metal-containing EVOH pellet"), and the content of the conjugated polyene in the surface layer portion of the pellet. However, the first gist is an EVOH pellet having an alkali metal content of 1 to 500 ppm per pellet weight, which is 30 ppb or more per pellet weight.

Further, the present invention is a method for producing a conjugated polyene and an alkali metal-containing EVOH pellet according to the first gist, wherein the EVOH pellet and a treatment liquid containing the conjugated polyene are brought into contact with each other, and the EVOH pellet and the alkali metal are brought into contact with each other. The second gist is a method for producing a conjugated polyene and an alkali metal-containing EVOH pellet, which comprises a step of contacting with.

In the conjugated polyene and alkali metal-containing EVOH pellets of the present invention, the content of the conjugated polyene on the surface layer of the pellet is 30 ppb or more per the weight of the pellet, and the alkali metal content is 1 to 500 ppm per the weight of the pellet. Therefore, the melt-molded product using the conjugated polyene and the alkali metal-containing EVOH pellet is excellent in the effect of suppressing the generation of fish eyes.

Further, among the present inventions, in particular, when the total content of the conjugated polyene in the entire conjugated polyene and the alkali metal-containing EVOH pellet is 0.1 to 10000 ppm per the weight of the pellet, the effect of further suppressing the generation of fish eyes is obtained. It will be excellent.

Further, among the present inventions, in particular, the weight ratio of the conjugated polyene content of the pellet surface layer portion to the total conjugated polyene content of the entire conjugated polyene and alkali metal-containing EVOH pellet (surface layer portion conjugated polyene content / total conjugated polyene content). ) Is 1.5 × 10 ^-5 or more, the effect of suppressing the generation of fish eyes is further excellent.

Further, in the present invention, in particular, when the conjugated polyene is at least one selected from the group consisting of sorbic acid, sorbic acid ester, and sorbic acid salt, it is easy to adjust the amount of adhesion to the EVOH pellet surface. Become.

Further, according to the method of the present invention for producing a conjugated polyene and an alkali metal-containing EVOH pellet, which comprises a step of contacting an EVOH pellet with a treatment liquid containing a conjugated polyene and a step of contacting the EVOH pellet with an alkali metal. Conventional manufacturing equipment can be used to produce conjugated polyene and alkali metal-containing EVOH pellets.

Then, in the production method of the present invention, when the above-mentioned EVOH pellet is a solidified and pelletized EVOH alcohol solution or water / alcohol mixed solution, the pellet can be made into a porous EVOH pellet.

Further, in the production method of the present invention, when the above-mentioned EVOH pellet is a porous pellet, the conjugated polyene can be efficiently incorporated into the surface layer portion of the EVOH pellet.

Further, in the production method of the present invention, the conjugated polyene and alkali obtained when the production step of the ethylene-vinyl ester-based copolymer before saponification of the EVOH includes a step of blending a conjugated polyene as a polymerization inhibitor. It is possible to suppress the generation of fish eyes and the like when the metal-containing EVOH pellets are melt-molded.

Hereinafter, the present invention will be described in detail, but these are examples of desirable embodiments and are not specified in their contents.

In the conjugated polyene and alkali metal-containing EVOH pellets of the present invention, the conjugated polyene content of the pellet surface layer portion is 30 ppb or more per the pellet weight, and the alkali metal content is 1 to 500 ppm per the pellet weight.

Here, the "conjugated polyene content of the pellet surface layer portion" refers to the amount of conjugated polyene present near the surface layer of the conjugated polyene and the alkali metal-containing EVOH pellet, specifically, the conjugated polyene and the alkali metal-containing EVOH. The content of conjugated polyene in the solution obtained by stirring 20 g of pellets in 30 mL of a mixed solution of distilled water: methanol = 1: 1 (volume ratio) for 10 minutes was quantified using a liquid chromatograph, and the above EVOH pellets were used. It means the content of conjugated polyene obtained by dividing by weight (20 g).

In the present invention, the "alkali metal content" refers to the amount of alkali metal contained on the surface, inside, or both of the conjugated polyene and the alkali metal-containing EVOH pellets. Specifically, when the alkali metal is contained only on the surface of the conjugated polyene and the alkali metal-containing EVOH pellet, the amount of the alkali metal compound added in terms of alkali metal may be used as the content, and the inside of the conjugated polyene and the alkali metal-containing EVOH pellet may be contained. When alkali metal is contained in, for example, dried conjugated polyene and alkali metal-containing EVOH pellets are incinerated, dissolved in an aqueous solution of hydrochloric acid, and measured by an induction coupling plasma emission analyzer (ICP-AES). It can be obtained by converting the value obtained by a method of quantifying the alkali metal content from the calibration line of the standard solution into the content of the entire pellet.

Hereinafter, prior to the description of the conjugated polyene and the alkali metal-containing EVOH pellet of the present invention, each component and a method for producing the EVOH pellet before containing the conjugated polyene will be described.

<EVOH>
The EVOH constituting the conjugated polyene and the alkali metal-containing EVOH pellet of the present invention is a resin usually obtained by saponifying a copolymer (ethylene-vinyl ester-based copolymer) of ethylene and a vinyl ester monomer. , A water-insoluble thermoplastic resin generally called an ethylene-vinyl alcohol-based copolymer or an ethylene-vinyl ester-based copolymer saken product.

As the vinyl ester monomer, vinyl acetate is typically used because it is easily available on the market and the processing efficiency of impurities during production is good. Examples of other vinyl ester monomers include fats such as vinyl formate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl capricate, vinyl laurate, vinyl steanoate, and vinyl versatic acid. Examples thereof include group vinyl esters and aromatic vinyl esters such as benzoate vinyl, and it is possible to use an aliphatic vinyl ester having 3 to 20 carbon atoms, preferably 4 to 10 carbon atoms, and particularly preferably 4 to 7 carbon atoms. can. These are usually used alone, but if necessary, a plurality of types may be used at the same time.

As the ethylene and vinyl ester monomers, petroleum-derived raw materials such as naphtha are usually used, but natural gas-derived raw materials such as shale gas, sugars and starches contained in sugar cane, tensai, corn, potatoes and the like, etc. Or a monomer from a plant-derived raw material purified from a component such as cellulose contained in rice, wheat, millet, grass and plants may be used.

The EVOH used in the present invention may be copolymerized with the following comonomer (referred to as "other comonomer") to the extent that the effect of the present invention is not impaired (for example, 10 mol% or less).
Examples of other comonomers include olefins such as propylene, 1-butene, and isobutene; 3-butene-1-ol, 3-butene-1,2-diol, 4-penten-1-ol, and 5-hexene-. Hydroxy group-containing α-olefins such as 1,2-diol and derivatives such as esterified products and acylated products; acrylic acid, methacrylic acid, crotonic acid, (anhydrous) phthalic acid, (anhydrous) maleic acid, (anhydrous) itacon Unsaturated acids such as acids or salts thereof or mono or dialkyl esters having 1 to 18 carbon atoms; acrylamide, N-alkylacrylamide with 1 to 18 carbon atoms, N, N-dimethylacrylamide, 2-acrylamide propanesulfonic acid or its like. Acrylamides such as salts, acrylamide propyldimethylamine or esters thereof or quaternary salts thereof; metaacrylamide, N-alkylmetharylamide having 1 to 18 carbon atoms, N, N-dimethylmethargylamide, 2-methacrylate propanesulfonic acid. Alternatively, methacrylamides such as salts thereof, methallylamide propyldimethylamine or salts thereof or quaternary salts thereof; N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide; acrylicnitrile, methacrylicnitrile. Vinyl cyanide such as; vinyl ethers such as alkyl vinyl ether having 1 to 18 carbon atoms, hydroxyalkyl vinyl ether, alkoxyalkyl vinyl ether; vinyl halide such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, vinyl bromide and the like. Compounds; Vinyl silanes such as trimethoxyvinylsilane; Allyl halides such as allyl acetate and allyl chloride; Allyl alcohols such as allyl alcohol and dimethoxyallyl alcohol; trimethyl- (3-acrylamide-3-dimethylpropyl) -ammonium Examples thereof include comonomer such as chloride and acrylamide-2-methylpropanesulfonic acid. These can be used alone or in combination of two or more.

The copolymerization of ethylene and vinyl ester monomer and other comonomer used as needed can be carried out by a known polymerization method, that is, solution polymerization, suspension polymerization, emulsion polymerization, bulk polymerization and the like, from the viewpoint of uniform diffusion. Solution polymerization is preferably used. Further, the polymerization method may be either a continuous method or a batch method.

The above solution polymerization is usually carried out by putting a solution containing a vinyl ester monomer, a solvent and a polymerization catalyst into a polymerization can, and while stirring the solution, press-fitting ethylene and heating to polymerize. The ethylene pressure is usually about 20 to 80 kg / cm ² .

Alcohols are preferable as the solvent, but other organic solvents (dimethyl sulfoxide and the like) capable of dissolving ethylene, vinyl acetate and ethylene-vinyl acetate copolymer can be used. As the alcohols, for example, fatty alcohols having 1 to 10 carbon atoms such as methanol, ethanol, propanol, n-butanol, and t-butanol can be used. These can be used alone or in combination of two or more. Of these, methanol is particularly preferable.

As the catalyst used for solution polymerization, any radical initiator can be used without particular limitation, but 2,2'-azobis- (2,4-dimethylvaleronitrile) and 2,2'-azobis-are preferable. (2,4,4-trimethylvaleronitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobis- (4-methoxy-2,4-dimethylvaleronitrile), 2,2'- Azobis- (2-methylisobutyrate) and other azo compounds; t-butylperoxyneodecanoate, t-butylperpivalate, t-butylperoxy-2-ethylhexinoate and other alkylperesters Peroxy such as bis- (4-t-butylcyclohexyl) peroxy-dicarbonate, dicyclohexylperoxy-dicarbonate, bis (2-ethylhexyl) di-sec-butylperoxy-dicarbonate, diisopropylperoxy-dicarbonate, etc. Dicarbonates; azonitrile-based initiators such as acetyl peroxides, benzoyl peroxides, lauroyl peroxides, dilauroyl peroxides, didecanoyl peroxides, dioctanoyl peroxides, dipropyl peroxides and other peroxides, and organic compounds. An initiator such as an oxide-based initiator can be used. These can be used alone or in combination of two or more. However, in the batch-type polymerization method, when a catalyst having a short half-life is used, the catalysts cannot be charged all at once and must be continuously charged.

The polymerization temperature is usually 20 to 90 ° C, preferably 40 ° C to 70 ° C. The polymerization time is usually 2 to 15 hours, preferably 3 to 11 hours. In the case of continuous polymerization, it is preferable that the average residence time in the polymerization can is about the same.

In the case of solution polymerization, the polymerization is stopped when a predetermined polymerization rate is reached. The polymerization rate is usually 10 to 90 mol%, preferably 30 to 80 mol% with respect to the charged vinyl ester monomer. The resin content in the solution after polymerization is usually 5 to 85% by weight, preferably 20 to 70% by weight.

The termination of the polymerization is usually carried out by adding a polymerization inhibitor. As the polymerization inhibitor, N, N-dialkylhydroxylamine, styrene derivative, hydroquinone derivative, quinone derivative, piperidine derivative, conjugated polyene and the like can be used. These can be used alone or in combination of two or more. Of these, conjugated polyenes are preferably used. This is because the conjugated polyene can contribute to the suppression of the generation of fish eyes and the like even if it remains in relation to the content of the surface layer portion of the pellet to be finally obtained.

As the conjugated polyene used as the polymerization inhibitor, the compounds listed in the conjugated polyene described later can be used.

It is preferable that the conjugated polyene used as the polymerization inhibitor is dissolved in the solvent used for the polymerization and added as a conjugated polyene solution from the viewpoint of uniform diffusion.
When a conjugated polyene is used as a polymerization inhibitor, the amount of the conjugated polyene added is usually 0.0001 to 3 parts by weight, preferably 0.0005 to 1 part by weight, more preferably 0.005 to 1 part by weight, based on 100 parts by weight of the vinyl ester monomer charged. It is 0.001 to 0.5 parts by weight.

After completion of the polymerization, the ethylene-vinyl ester-based copolymer solution removes unreacted ethylene gas and unreacted vinyl ester monomer, and then saponification.
The unreacted ethylene gas can be removed by, for example, evaporation removal or the like. Further, as a method of removing the unreacted vinyl ester monomer from the ethylene-vinyl ester-based copolymer solution, for example, the ethylene-vinyl ester-based copolymer solution is continuously sprayed from the upper part of a column filled with Rasichling at a constant rate. The unreacted vinyl ester monomer was removed from the bottom of the tower by blowing organic solvent vapor such as methanol from the bottom of the tower and flowing out the mixed vapor of the organic solvent such as methanol and the unreacted vinyl ester monomer from the top of the tower. A method of taking out an ethylene-vinyl ester-based copolymer solution can be adopted.

Saponification can be performed by a known method. Usually, the saponification reaction is started by adding an alkali catalyst for saponification to the ethylene-vinyl ester-based copolymer solution from which the unreacted vinyl ester monomer has been removed.
Further, as the saponification method, either a continuous method or a batch method can be used.
As the saponification catalyst, for example, an alkali catalyst such as sodium hydroxide, potassium hydroxide, or alkali metal alcoholate is used.

The saponification conditions differ depending on the saponification catalyst used, the ethylene content of the ethylene-vinyl ester copolymer, the desired saponification degree, etc., but for example, the suitable saponification conditions in the case of a batch type are as follows. It's a street.
The saponification reaction temperature is preferably 30 to 60 ° C., and the amount of the saponification catalyst used is usually preferably 0.001 to 0.6 equivalent (per vinyl ester group). The saponification time depends on the saponification conditions and the target saponification degree, but is usually selected from 1 to 6 hours.

In this way, a solution or slurry of EVOH is obtained. The content of EVOH in the solution or slurry of EVOH is preferably about 10 to 50% by weight. Further, the content of this EVOH solution or slurry can be adjusted by using a solvent, and as the solvent, an alcohol such as methanol or a water / alcohol mixed solution is usually preferably used.

The EVOH used in the present invention may be further subjected to "post-denaturation" such as urethanization, acetalization, cyanoethylation, and oxyalkyleneization.

The EVOH as described above is mainly composed of ethylene-derived structural units and vinyl alcohol structural units, and usually contains a small amount of vinyl ester structural units remaining without saponification as needed. When other comonomer is copolymerized, the structural unit derived from the comonomer is further contained.

The EVOH used in the present invention preferably has the following composition.

The content of ethylene structural unit in EVOH is a value measured based on ISO14663, and is usually 20 to 60 mol%, preferably 25 to 50 mol%. If the content is too low, the gas barrier property and melt moldability under high humidity tend to decrease, and if the content is too high, the gas barrier property tends to decrease.

The degree of saponification of the vinyl ester component in EVOH is a value measured based on JIS K6726 (however, EVOH is used as a solution uniformly dissolved in a water / methanol solvent), and is usually 90 to 100 mol%, preferably 95 to 95. It is 100 mol%. If the degree of saponification is too low, the gas barrier property, thermal stability, moisture resistance and the like tend to deteriorate.

<Conjugated polyene>
The conjugated polyene used in the present invention is a structure in which carbon-carbon double bonds and carbon-carbon single bonds are alternately connected, and the number of carbon-carbon double bonds is two or more, so-called conjugate. It is a compound having a double bond. A conjugated polyene is a conjugated diene having a structure in which two carbon-carbon double bonds and one carbon-carbon single bond are alternately connected. Three carbon-carbon double bonds and two carbon-carbon bonds. It may be a conjugated triene having a structure in which single bonds are alternately connected, or a conjugated polyene having a structure in which a larger number of carbon-carbon double bonds and carbon-carbon single bonds are alternately connected. However, if the number of conjugated carbon-carbon double bonds is 8 or more, there is a concern that the molded product will be colored by the color of the conjugated polyene itself, so the number of conjugated carbon-carbon double bonds is 7 or less. It is preferably polyene. Further, the above-mentioned conjugate double bond composed of two or more carbon-carbon double bonds may be formed in a plurality of pairs in one molecule without conjugating with each other. For example, a compound having three conjugated trienes in the same molecule, such as tung oil, is also included in the conjugated polyene.

Examples of such conjugated polyene include isoprene, 2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-t-butyl-1,3-butadiene, 1, 3-Pentidiene, 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-phenyl-1,3-butadiene, 1,4-diphenyl-1,3-butadiene, 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, fluben, tropon, osimene, piperylene, milsen, farnesene, sembrene, sorbic acid, sorbic acid ester, Conjugated diene consisting of two carbon-carbon double bonds such as sorbate and avietinic acid; 1,3,5-hexatriene, 2,4,6-octatriene-1-carboxylic acid, eleostea Conjugated triene consisting of a conjugated structure of three carbon-carbon double bonds such as acid, tung oil, and cholecalciferol; cyclooctatetraene, 2,4,6,8-decatetraene-1-carboxylic acid, retinol, retinoic acid, etc. Examples thereof include conjugated polyene having a conjugated structure of four or more carbon-carbon double bonds. For those having a plurality of stereoisomers such as 1,3-pentadiene, myrcene and farnesene, any of them may be used. Such conjugated polyenes may be used alone or in combination of two or more.

Of these, sorbic acid, sorbic acid ester, and sorbic acid salt have a carboxyl group and have a high affinity with water, so that the amount of adhesion to the EVOH pellet surface can be easily adjusted, which is particularly preferable. ..

<Alkali metal>
Examples of the alkali metal used in the present invention include lithium, sodium, potassium, rubidium, and cesium. These can be used alone or in combination of two or more. Of these, sodium and potassium are preferred, and sodium is particularly preferred. Further, the content when two or more kinds of alkali metals are used together is the total content of all alkali metals.

Examples of the alkali metal source of the alkali metal used in the present invention include alkali metal compounds such as alkali metal oxides, alkali metal hydroxides, and alkali metal salts. Of these, alkali metal salts are preferable from the viewpoint of dispersibility. Further, the alkali metal compound used in the present invention preferably excludes inorganic layered compounds and double salts from the viewpoint of economy and dispersibility.

The alkali metal compound may exist, for example, as an alkali metal salt, in an ionized state, or in a complex state of a resin or another ligand.
Examples of the alkali metal salt include inorganic salts such as carbonate, hydrogen carbonate, phosphate, borate, sulfate and chloride; acetate, butyrate, propionate, enanthate and capric acid. Monocarboxylates having 2 to 11 carbon atoms such as salts; Dicarboxylates having 2 to 11 carbon atoms such as oxalates, malonates, succinates, adipates, sverates, and sebatates; EVOH Examples thereof include a carboxylate salt and a carboxyl group at the polymerization terminal of the resin. These can be used alone or in combination of two or more. The molecular weight of the alkali metal compound is usually 20 to 10000, preferably 20 to 1000, and particularly preferably 20 to 500.
Among these, a carboxylate is preferable, a carboxylate having 2 to 11 carbon atoms is particularly preferable, and an aliphatic carboxylate having 2 to 11 carbon atoms is more preferable, and carbon is particularly preferable. The number 2 to 6 is an aliphatic monocarboxylic acid salt, most preferably an acetate.

[Other ingredients]
The conjugated polyene and alkali metal-containing EVOH pellets of the present invention contain resins other than EVOH generally used in EVOH compositions within a range that does not impair the effects of the present invention (for example, 20% by weight or less, preferably 10% by weight or less). A resin composition obtained by mixing is also included.

The boron compound and alkali metal-containing EVOH resin pellets of the present invention are generally blended with EVOH as long as the effects of the present invention are not impaired, such as heat stabilizers, antioxidants, antistatic agents, and colorants. UV absorbers, plasticizers, light stabilizers, surfactants, antibacterial agents, desiccants, antiblocking agents, flame retardants, cross-linking agents, curing agents, foaming agents, crystal nucleating agents, anti-fog agents, biodegrading additives , Silane coupling agent, oxygen absorber and the like may be contained. These can be used alone or in combination of two or more. When the alkali metal salt is blended here, the blending amount is included in the content of the alkali metal in the conjugated polyene and the alkali metal-containing EVOH pellet of the present invention.

<Manufacturing of EVOH pellets>
As a method for producing pellets from EVOH, a conventionally known method can be adopted, for example,
a) A hot-cut method in which fluid EVOH is extruded from the discharge port of an extruder, cut in a molten state, and then cooled and solidified to produce pellets.
b) A strand cut method in which fluid EVOH is extruded into a coagulation bath and the EVOH strands obtained by cooling and solidifying are cut.
And so on. Of these, the b) strand cut method is preferable in that porous pellets, which will be described later, can be obtained.

Regardless of the above a) hot-cut method or b) strand-cut method, the EVOH used as the pellet raw material is (α) a solution or slurry of EVOH obtained by saponification in the above-mentioned EVOH production method. , Or an EVOH hydrous composition; or pellets of (β) EVOH (dry EVOH composition) can be melted and EVOH in such a molten state can be used.

The EVOH water-containing composition is obtained by appropriately adjusting the water content of the EVOH solution or slurry using a solvent, and the concentration of EVOH in the EVOH water-containing composition is 20 to 60% by weight.

As the above solvent, alcohol, water / alcohol mixed solvent and the like can be used. Of these, a water / alcohol mixed solvent is preferable. As the alcohol, for example, an aliphatic alcohol having 1 to 10 carbon atoms such as methanol, ethanol, propanol, n-butanol, and t-butanol can be used, and methanol is particularly preferable. The water / alcohol mixed weight ratio is preferably 80/20 to 5/95.

The EVOH water-containing composition preferably contains 0 to 10 parts by weight of alcohol and 10 to 500 parts by weight of water with respect to 100 parts by weight of EVOH.

The method for adjusting the water content of the EVOH solution or slurry water-containing composition is not particularly limited, but in order to increase the water content, a method of spraying the above solvent on the EVOH solution or slurry, the EVOH solution or slurry. A method of mixing the above-mentioned solvent with the above-mentioned solvent, a method of contacting a solution or slurry of EVOH with the vapor of the above-mentioned solvent, and the like can be adopted. In order to reduce the water content, it may be dried as appropriate, and for example, it can be dried using a fluid hot air dryer or a static hot air dryer.

Next, a) a hot cut method and b) a strand cut method will be described.

a) Hot-cut method When the EVOH solution / water-containing composition is put into an extruder as a pellet raw material to be produced by the hot-cut method, the temperature of the EVOH solution / water-containing composition in the extruder is preferably 70 to 170 ° C. The temperature is preferably 80 to 170 ° C, more preferably 90 to 170 ° C. If the temperature of the EVOH solution / water-containing composition is too low, the EVOH tends not to melt completely, and if it is too high, the EVOH tends to be susceptible to thermal deterioration.
When the dried EVOH composition is put into an extruder as a pellet raw material, the temperature of the dried EVOH composition in the extruder is preferably 150 to 300 ° C, more preferably 160 to 280 ° C, still more preferably 170 to 250 ° C. Is.
The temperature of the EVOH solution / water-containing composition and the dried EVOH composition in the extruder means the temperature detected in the vicinity of the ejection port at the tip of the extruder by the temperature sensor installed in the extruder cylinder.

The EVOH solution / water-containing composition or dry EVOH composition extruded from the die of the extruder, that is, the EVOH in a molten state, is cut before cooling and solidifying. The cutting method may be either a hot cutting method of cutting in the atmosphere (air hot cutting method) or an underwater cutting method of extruding into a cutter installation container filled with cooling water and cutting in cooling water.

The temperature of the cooling water in the underwater cutting method is such that the EVOH extruded in the molten state does not instantly solidify (solidify), and the temperature of the cooling water when the EVOH solution / water-containing composition is used as a raw material is -20. The temperature is preferably about 50 ° C, more preferably −5 to 30 ° C.
Further, when the dried EVOH composition is used as a raw material, it is easier to solidify than when the EVOH solution / water-containing composition is used as a raw material. It is usually 0 to 90 ° C, preferably 20 to 70 ° C.

The cooling water is not limited to water, but is a water / alcohol mixed solution; aromatic hydrocarbons such as benzene; ketones such as acetone and methyl ethyl ketone; ethers such as dipropyl ether; methyl acetate, ethyl acetate and propionic acid. Organic esters such as methyl can also be used. Of these, water or a water / alcohol mixed solution is used because it is easy to handle. In the water / alcohol mixed solution, the water / alcohol (weight ratio) is usually 90/10 to 99/1. As the alcohol, lower alcohols such as methanol, ethanol and propanol can be used, and methanol is preferably used industrially.

b) Strand-cut method When the EVOH solution / water-containing composition is put into an extruder as a pellet raw material, the temperature of the EVOH solution extruded into the coagulation bath is usually 10 to 100 ° C., and the temperature of the coagulation bath is extruded. The temperature at which EVOH can be cooled and solidified is usually −10 to 40 ° C., and the residence time is usually about 10 to 400 seconds.
When the dried EVOH composition is put into an extruder as a pellet raw material, the temperature at which EVOH is extruded into the coagulation bath is usually 150 to 300 ° C, the temperature of the coagulation bath is usually 0 to 90 ° C, and the residence time is It takes about 2 to 400 seconds.

As the coagulation liquid used in the coagulation bath, a solution similar to the above-mentioned a) hot-cut type cooling water can be adopted.

In this way, EVOH pellets are obtained.

Among the above-mentioned EVOH pellets, it is preferable to use porous pellets from the viewpoint of the treatment containing conjugated polyene, which will be described later. The porous pellets can be obtained by using EVOH alcohol or a water / alcohol solution (EVOH water-containing composition) as a pellet raw material in the above b) strand cut method. When the pellet of EVOH is porous, by infiltrating the conjugated polyene into the pores, the conjugated polyene can be easily retained in the pellet, and the conjugated polyene can be efficiently incorporated into the surface layer portion of the pellet. The size of the pores of the porous pellet is not particularly limited as long as the conjugated polyene can penetrate into the pores.

The shape of the EVOH pellets usually depends on the method for producing the pellets, and various shapes can be used. The EVOH pellets obtained by each of the above methods and the conjugated polyene and alkali metal-containing EVOH pellets of the present invention can be used. The shape is arbitrary. The shape of the pellet includes, for example, a spherical shape, an oval shape, a cylindrical shape, a cubic shape, a rectangular parallelepiped shape, an amorphous shape, etc., but usually it is an oval shape or a cylindrical shape, and the size thereof is later used as a molding material. From the viewpoint of convenience in the case, the major axis is usually 1 to 10 mm, preferably 2 to 7 mm in the case of the oval type, the minor axis is usually 1 to 6 mm, preferably 2 to 5 mm in the case of the cylindrical type, and the bottom surface in the case of the cylindrical type. The diameter of the cylinder is usually 1 to 10 mm, preferably 2 to 7 mm, and the length is usually 1 to 10 mm, preferably 3 to 8 mm.

The EVOH solution / water-containing composition used as the pellet raw material usually contains an alkali catalyst, by-product salts, other impurities and the like used at the time of saponification. Therefore, EVOH pellets produced by using the EVOH solution / water-containing composition as a raw material for pellets usually contain these impurities and the like. Therefore, the porous pellets thus obtained may be subjected to a washing treatment with water.

Further, in the above-mentioned EVOH manufacturing process, when the pellet of EVOH obtained by using the conjugated polyene as a polymerization inhibitor is washed with water, the conjugated polyene can also be removed, but the ease of removal is the conjugated polyene. A certain amount of conjugated polyene remains in the pellet of EVOH, depending on the polarity and the like.

<Manufacturing of EVO H pellets containing conjugated polyenes and alkali metals>
The conjugated polyene and alkali metal-containing EVOH pellets of the present invention can be obtained through the following steps of producing the conjugated polyene-containing EVOH pellets and the alkali metal-containing EVOH pellets. Either of these steps may be performed first, or may be performed at the same time.

<Manufacturing of EVOH pellets containing conjugated polyene>
The conjugated polyene-containing EVOH pellet can be produced by incorporating the conjugated polyene on the surface of the EVOH pellet.

As a method of containing the conjugated polyene on the surface of the pellet of EVOH, for example, there is a method of contacting the pellet of EVOH prepared in advance with the conjugated polyene, a method of containing the conjugated polyene at the stage of producing the pellet of EVOH, and the like.

As described above, since the conjugated polyene can be used as a polymerization inhibitor, EVOH pellets containing the conjugated polyene can be produced by adding the conjugated polyene as a polymerization inhibitor at the end of the polymerization. However, in the case of EVOH pellets produced by such a method, the content of conjugated polyene in the surface layer portion tends to be low because the conjugated polyene is contained almost evenly in the entire pellet. Further, if the amount of conjugated polyene added as a polymerization inhibitor is increased, it may cause coloring of the pellets, so that washing with water may be required after the pellets are produced. Therefore, it is generally difficult to adjust the amount of conjugated polyene in the surface layer of the pellet to an amount effective for suppressing the generation of fish eyes at the stage of producing the pellet of EVOH.

Therefore, in order to contain the conjugated polyene in the surface layer portion of the EVOH pellet, a method of bringing the pre-prepared EVOH pellet into contact with the conjugated polyene is preferable.

As a method of contacting the EVOH pellet prepared in advance with the conjugated polyene, a method of contacting the EVOH pellet with a treatment liquid containing a conjugated polyene (hereinafter, may be referred to as “conjugated polyene-containing treatment liquid”) is used. Preferably, as another contact method, conjugated polyene may be added directly to the pellet of EVOH and mixed.

As a method of bringing the above-mentioned EVOH pellets into contact with the conjugated polyene-containing treatment liquid, for example, a method of spraying the conjugated polyene-containing treatment liquid on the EVOH pellets; a method of immersing the EVOH pellets in the conjugated polyene-containing treatment liquid; A method of washing the pellets with a conjugated polyene-containing treatment liquid; a method of spraying a conjugated polyene-containing treatment liquid or the like onto EVOH pellets whose surface has been adjusted to a specific high temperature and coating the pellets with a solution can be carried out. Of these, a method of immersing in a conjugated polyene-containing treatment liquid and a method of washing with a conjugated polyene-containing treatment liquid are preferably used.

The method of contacting the EVOH pellet with the conjugated polyene-containing treatment liquid can efficiently increase the conjugated polyene content in the surface layer portion of the EVOH pellet. Further, by adjusting the conjugated polyene concentration of the treatment liquid, there is an advantage that the conjugated polyene content of the pellet surface layer portion can be adjusted with high accuracy.

The concentration of the conjugated polyene in the conjugated polyene-containing treatment liquid is usually 0.01 to 500 ppm, preferably 0.1 to 50 ppm, per weight of the conjugated polyene-containing treatment liquid. If the concentration is too low, it tends to be difficult to contain a predetermined amount of conjugated polyene, and if it is too high, the precipitate of the conjugated polyene adheres to the pellet surface, and agglomerates are formed in the molded film. It may occur.

In the contact treatment with the conjugated polyene-containing treatment liquid, the concentration of the conjugated polyene, the contact treatment time, the contact treatment temperature, the stirring speed at the time of the contact treatment, the water content of the EVOH pellets to be treated, and the like are changed in the surface layer portion. It is possible to control the content of conjugated polyene.

The EVOH pellets after the contact treatment with the conjugated polyene may be subjected to the next step as they are, but it is usually preferable to dry the pellets. A known method can be adopted for such drying, for example, a cylindrical / groove type stirring dryer, a cylindrical dryer, a rotary dryer, a fluidized bed dryer, a vibrating fluidized bed dryer, a conical rotary type dryer and the like. It may be dried by the fluidized bed used, a batch type box type dryer, a band dryer, a tunnel dryer, a static drying using a vertical silo dryer, or the like. Efficient drying can be achieved by passing a gas such as nitrogen gas at 80 to 150 ° C. through the dryer.

As described above, EVOH pellets containing conjugated polyene can be obtained.

<Manufacturing of EVOH pellets containing alkali metal>
The alkali metal-containing EVOH pellet can be produced by incorporating an alkali metal into the EVOH pellet.

The above-mentioned EVOH pellets are generally produced by using an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide as a saponification catalyst. The alkali metal in such a catalyst is inevitably present in the pellet of EVOH as an alkali metal acetate by-product during saponification or by forming a salt with a carboxyl group generated in a trace amount at the end of the EVOH polymer chain. do. Under such circumstances, the amount of alkali metal present in the pellets of EVOH is usually about 3000 ppm per weight of the pellets of EVOH in the unwashed state.

When the alkali metal remains in the EVOH pellets in an amount of a predetermined amount or more, the alkali metal content can be adjusted by washing the EVOH pellets more than usual. Specifically, it is difficult to remove the alkali metal in the pellets of EVOH only by washing with water. Therefore, it is preferable to wash the EVOH pellets with an acid washing solution such as acetic acid and then wash with water. In particular, the alkali metal bonded to the carboxyl group at the end of the polymer chain can be efficiently removed by washing with an acid washing solution.

Examples of the acid used in the acid cleaning solution include water-soluble weak acids such as acetic acid, propionic acid, and butyric acid, and acetic acid is preferably used among these. Further, as the water used for the cleaning liquid, water from which metal ions as impurities such as ion-exchanged water, distilled water, and filtered water have been removed is preferable.

In the present invention, a method of containing an alkali metal in the pellet of EVOH from which the alkali metal salt generated in the saponification step has been removed is preferable because the content of the alkali metal in the pellet of EVOH can be easily adjusted.

Examples of the method of containing the alkali metal in the EVOH pellets include a method of bringing the previously prepared EVOH pellets into contact with the alkali metal, a method of leaving the alkali metal salt generated in the ketonization step of EVOH, and the like. Of these, a method in which the EVOH pellets prepared in advance and the alkali metal are brought into contact with each other is preferable.

As a method of contacting the EVOH pellets prepared in advance with the alkali metal, a method of contacting the EVOH pellets with a treatment liquid containing an alkali metal (hereinafter, may be referred to as "alkali metal-containing treatment liquid"). However, as another contact method, the alkali metal compound may be directly added to the pellets of EVOH and mixed.

As a method of bringing the above-mentioned EVOH pellets into contact with the alkali metal-containing treatment liquid, for example, a method of spraying the alkali metal-containing treatment liquid on the EVOH pellets; a method of immersing the EVOH pellets in the alkali metal-containing treatment liquid; A method of washing the pellets with an alkali metal-containing treatment liquid; a method of spraying an alkali metal-containing treatment liquid onto EVOH pellets whose surface has been adjusted to a specific high temperature and coating the pellets with a solution or the like can be carried out. Of these, a method of washing EVOH pellets with an alkali metal-containing treatment liquid is preferably used because it can efficiently contain alkali metals. By this method, the alkali metal is removed when the excess alkali metal is contained, and is added when the alkali metal is insufficient.

The concentration of the alkali metal in the alkali metal-containing treatment liquid is usually 0.001 to 1% by weight, preferably 0.003 to 0.5% by weight, based on the weight of the alkali metal-containing treatment liquid. If the concentration is too low, it tends to be difficult to contain a predetermined amount of alkali metal, and if it is too high, the appearance of the finally obtained molded product tends to be deteriorated.

As described above, the method of contacting EVOH pellets from which the alkali metal salt generated in the saponification step with the alkali metal is preferable because the content of the alkali metal in EVOH can be easily adjusted.

After the contact treatment with the alkali metal, it may be subjected to the next step as it is, but it is usually preferable to dry the pellets. For such drying, the same method as for producing the conjugated polyene-containing EVOH pellets can be adopted.

By the above steps, alkali metal-containing EVOH pellets can be obtained.

By going through the steps of containing the conjugated polyene and the step of containing an alkali metal, the conjugated polyene and the alkali metal-containing EVOH pellets can be obtained.
In the present invention, from the viewpoint of work efficiency, it is preferable to simultaneously perform the step of containing the conjugated polyene and the step of containing the alkali metal by using the treatment liquid containing the conjugated polyene and the alkali metal.

Furthermore, the step of containing the conjugated polyene and the alkali metal by contacting the pellet of EVOH with the treatment liquid containing the conjugated polyene and the alkali metal is a step of containing other preferable additives, particularly acetic acid and acetate (excluding the alkali metal). ) Can also be used for concentration adjustment processing. Specifically, a treatment liquid containing an additive of acetic acid and an acetate (excluding the alkali metal) may be used together with the conjugated polyene and the alkali metal. By such a method, the content ratio of the other additive component with the conjugated polyene and the alkali metal can be easily adjusted.

<EVOH pellets containing conjugated polyenes and alkali metals>
The conjugated polyene content of the surface layer of the conjugated polyene and the alkali metal-containing EVOH pellet of the present invention is 30 ppb or more, preferably 34 ppb or more, and more preferably 38 ppb or more per the weight of the pellet. By setting the conjugated polyene content of the pellet surface layer portion to 30 ppb or more, preferably 34 ppb or more, more preferably 38 ppb or more per weight of the pellet, it is possible to effectively suppress the generation of minute fish eyes having a diameter of 200 μm or less. .. In addition, when the content of conjugated polyene is low, many fish eyes occur. The upper limit of the content of the conjugated polyene in the surface layer portion is usually 10000 ppb (10 ppm), preferably 8000 ppb (8 ppm), and particularly preferably 5000 ppb (5 ppm).

The content of the conjugated polyene in the surface layer portion is obtained by stirring 20 g of the conjugated polyene and the alkali metal-containing EVOH pellet in 30 mL of a mixture of water / methanol = 1/1 (volume ratio) for 10 minutes as described above. The solution is obtained by quantifying the content of conjugated polyene using a liquid chromatograph and dividing by the weight (20 g) of the above EVOH pellets.

The conjugated polyene and the alkali metal-containing EVOH pellet of the present invention may have at least the abundance of conjugated polyene in the surface layer portion of the pellet measured by the above measuring method as long as it is 30 ppb or more per the weight of the pellet. The conjugated polyene and the alkali metal-containing EVOH pellet may contain almost no conjugated polyene, or the pellet may contain a larger amount of conjugated polyene.

For example, when a pellet raw material (EVOH solution / water-containing composition) is used as in the case where a conjugated polyene is added as a polymerization inhibitor in the EVOH manufacturing process, the content of the conjugated polyene inside the pellet tends to be high. It is in.

When the conjugated polyene and the alkali metal-containing EVOH pellet also contain the conjugated polyene, the total content of the conjugated polyene is usually 0.1 to 10000 ppm, more preferably 0.5 to 8000 ppm, and more preferably 0.5 to 8000 ppm per weight of the pellet. It is preferably 1 to 5000 ppm, and particularly preferably 1 to 2000 ppm. If the total content of the conjugated polyene is too small, the content of the conjugated polyene in the surface layer of the pellet is relatively small, and the fisheye tends to increase. Further, if the content of the conjugated polyene becomes too large, the molded product may be colored by the color of the conjugated polyene itself.

The above-mentioned "total content of conjugated polyene" means the content of conjugated polyene contained in the conjugated polyene and the alkali metal-containing EVOH pellet, specifically, after crushing the conjugated polyene and the alkali metal-containing EVOH pellet. , The amount of conjugated polyene in the extract is converted from the value measured using a liquid chromatograph after solvent extraction.

The weight ratio of the content of the conjugated polyene in the surface layer of the conjugated polyene and the alkali metal-containing EVOH pellet (the content of the conjugated polyene in the surface layer / the total content of the conjugated polyene) to the total content of the conjugated polyene in the entire conjugated polyene and the alkali metal-containing EVOH pellet is , Usually 1.5 × 10 ^-5 or more, preferably 3 × 10 ^-5 or more, and more preferably 5 × 10 ^-5 or more. If the weight ratio of the content of the conjugated polyene in the surface layer portion of the pellet to the total content of the conjugated polyene in the entire pellet is too small, the effect of suppressing the generation of fish eyes tends to be insufficient. The upper limit is usually 1 × 10 ⁻² .

The alkali metal content in the conjugated polyene and the alkali metal-containing EVOH pellet is usually 1 to 500 ppm, preferably 50 to 230 ppm, and more preferably 100 to 180 ppm per weight of the pellet. If the content is too small, the formation of fine fish eyes may be observed in the film, and if the content is too large, the formation of fine fish eyes may be observed in the film.

The above-mentioned "alkali metal content" refers to the amount of alkali metal contained on the surface, inside, or both of the conjugated polyene and the alkali metal-containing EVOH pellets. Specifically, when the surface of the conjugated polyene and the alkali metal-containing EVOH pellet contains an alkali metal, the amount of the alkali metal added to the surface of the EVOH pellet may be the content, and the inside of the conjugated polyene and the alkali metal-containing EVOH pellet may be contained. In the case of containing alkali metal, for example, dried conjugated polyene and alkali metal-containing EVOH pellets are incinerated, dissolved in an aqueous hydrochloric acid solution, and measured by an induction-bonded plasma emission analyzer (ICP-AES) to be standard. It can be obtained by converting the value obtained by a method of quantifying the alkali metal content from the calibration line of the liquid into the content of the entire conjugated polyene and alkali metal-containing EVOH pellets.

The water content of the conjugated polyene and the alkali metal-containing EVOH pellet of the present invention is usually 0.01 to 1% by weight, preferably 0.05 to 0.5% by weight. If the water content is too low, EVOH will not be plasticized by water molecules, and the conjugated polyene and alkali metal-containing EVOH pellets will be difficult to melt during extrusion molding, and fish eyes due to unmelted matter will tend to occur easily. If the amount is too large, a foaming phenomenon occurs during extrusion molding, and the appearance of the molded product tends to be deteriorated.

The melt flow rate (MFR) (210 ° C., load 2160 g) of the conjugated polyene and the alkali metal-containing EVOH pellet is usually 0.5 to 100 g / 10 minutes, preferably 1 to 50 g / 10 minutes, and particularly preferably. 2 to 35 g / 10 minutes. If the MFR is too large, the film forming property tends to be unstable, and if it is too small, the viscosity tends to be too high and melt extrusion tends to be difficult.

<Use>
The conjugated polyene and alkali metal-containing EVOH pellets of the present invention can be molded into, for example, a film, a sheet, a cup, a bottle, or the like by a melt molding method. Examples of such a melt molding method include an extrusion molding method (T-die extrusion, inflation extrusion, blow molding, melt spinning, profile extrusion, etc.), an injection molding method, and the like. The melt molding temperature is usually selected from the range of 150 to 300 ° C. It is also possible to uniaxially or biaxially stretch a film, sheet, fiber or the like.

The conjugated polyene and alkali metal-containing EVOH pellets of the present invention may be subjected to melt molding as they are, or may be subjected to melt molding by appropriately blending other thermoplastic resin pellets. Further, as the conjugated polyene and the alkali metal-containing EVOH pellet, a mixture of two or more kinds of the conjugated polyene and the alkali metal-containing EVOH pellet may be used. The mixture of two or more types of conjugated polyene and alkali metal-containing EVOH pellets refers to a mixture of EVOH pellets having different types of EVOH ethylene content, saponification degree, MFR, and composition.

Other thermoplastic resins include, for example, various polyolefins (eg, polyethylene, polypropylene, poly1-butene, poly4-methyl-1-pentene, ethylene-propylene copolymer, ethylene and α-olefin having 4 or more carbon atoms. Polymers with, polyolefins with maleic anhydride, ethylene-vinyl acetate copolymers, ethylene-acrylic acid ester copolymers, or modified polyolefins graft-modified with unsaturated carboxylic acids or derivatives thereof. Etc.), various nylons (eg, nylon 6, nylon 66, nylon 6/66 copolymer, etc.), polyvinyl chloride, polyvinylidene chloride, polyester, polystyrene, polyacrylonitrile, polyurethane, polyacetal, modified polyvinyl alcohol resin, etc. are used. be able to.

The EVOH film obtained from the conjugated polyene and the alkali metal-containing EVOH pellet of the present invention can be put into practical use as a single-layer film or a multilayer structure having at least one layer of the above-mentioned EVOH film. It is also possible to co-extrude coat or solution coat the conjugated polyene and alkali metal-containing EVOH pellets on a base film such as paper, plastic film and metal leaf.

Hereinafter, the multilayer structure will be described.
In manufacturing the above-mentioned multilayer structure, another base material (thermoplastic resin, etc.) is laminated on one side or both sides of a layer formed by using the conjugated polyene and the alkali metal-containing EVOH pellet of the present invention. As a laminating method, for example, a method of melt-extruding and laminating another base material on a film, a sheet or the like formed by using the conjugated polyene and the alkali metal-containing EVOH pellet of the present invention, and conversely, the book on another base material. The method of melt-extruding and laminating the conjugated polyene and the alkali metal-containing EVOH pellet of the present invention, the method of co-extruding the conjugated polyene and the alkali metal-containing EVOH pellet of the present invention with another substrate, the conjugated polyene and the alkali metal of the present invention. A film, sheet, etc. (layer) made of contained EVOH pellets or the like and another base material (layer) are dry-laminated using a known adhesive such as an organic titanium compound, an isocyanate compound, a polyester compound, or a polyurethane compound. The method etc. can be mentioned. The melt molding temperature at the time of melt extrusion is often selected from the range of 150 to 300 ° C.

As such other base materials, thermoplastic resins are useful, specifically, various polyethylenes such as linear low-density polyethylene, low-density polyethylene, ultra-low-density polyethylene, medium-density polyethylene, and high-density polyethylene, and ethylene-. Vinyl acetate copolymer, ionomer, ethylene-propylene (block or random) copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, polypropylene, propylene-α-olefin (4 to 20 carbon atoms) Α-Olefin) copolymers, olefins such as polybutene and polypentene alone or copolymers, or olefins alone or copolymers of these olefins graft-modified with unsaturated carboxylic acids or esters thereof in a broad sense. Based resin, polyester resin, polyamide resin (including copolymerized polyamide), polyvinyl chloride, polyvinylidene chloride, acrylic resin, polystyrene resin, vinyl ester resin, polyester elastomer, polyurethane elastomer, chlorinated polyethylene, chlorine Examples thereof include copolymerized polypropylene, aromatic or aliphatic polyketones, polyalcohols obtained by reducing them, and EVOH other than EVOH used in the present invention. From the viewpoint of practicality such as physical properties (particularly strength) of the multilayer structure, polypropylene, ethylene-propylene (block or random) copolymer, polyamide resin, polyethylene, ethylene-vinyl acetate copolymer, polystyrene resin, polyethylene Terephthalate (PET) and polyethylene naphthalate (PEN) are preferably used.

Further, another base material may be extruded and coated on a molded product such as a film or a sheet formed by using the conjugated polyene and the alkali metal-containing EVOH pellet of the present invention, or a film, a sheet or the like of another base material may be applied. When laminating with an adhesive, the substrate may be any substrate (paper, metal foil, uniaxial or biaxially stretched plastic film or sheet and its inorganic deposits, in addition to the above-mentioned thermoplastic resin. Woven cloth, non-woven fabric, metal cotton strip, wood, etc.) can also be used.

The layer structure of the multilayer structure of the present invention comprises a (a1, a2, ...) Layer formed by using the conjugated polyene and the alkali metal-containing EVOH pellet of the present invention, and another substrate, for example, a thermoplastic resin. When the layer is b (b1, b2, ...), The structure is such that the a layer is the innermost layer, and not only the two-layer structure of [inside] a / b [outside] (same below) but also, for example, Any combination such as a / b / a, a1 / a2 / b, a / b1 / b2, a1 / b1 / a2 / b2, a1 / b1 / b2 / a2 / b2 / b1 is possible, and at least When the regrind layer composed of a mixture of the conjugated polyene and the alkali metal-containing EVOH composition of the present invention and a thermoplastic resin is R, for example, a / R / b, a / R / a / b, a / b / It is also possible to use R / a / R / b, a / b / a / R / a / b, a / b / R / a / R / a / R / b, and the like.

In the above layer structure, an adhesive resin layer can be provided between the layers as needed. Various adhesive resins can be used, but in terms of obtaining a multilayer structure having excellent stretchability, for example, an unsaturated carboxylic acid or an anhydride thereof is used as an olefin polymer (in the broad sense described above). A modified olefin-based polymer containing a carboxyl group, which is obtained by chemically bonding to the polyolefin-based resin) by an addition reaction, a graft reaction, or the like, can be mentioned.

Specifically, maleic anhydride graft-modified polyethylene, maleic anhydride graft-modified polypropylene, maleic anhydride graft-modified ethylene-propylene (block and random) copolymer, maleic anhydride graft-modified ethylene-ethyl acrylate copolymer, anhydrous. One or a mixture of two or more selected from a maleic anhydride graft-modified ethylene-vinyl acetate copolymer or the like is preferable. At this time, the amount of the unsaturated carboxylic acid or its anhydride contained in the thermoplastic resin is preferably 0.001 to 3% by weight, more preferably 0.01 to 1% by weight, and particularly preferably 0.03. ~ 0.5% by weight. If the amount of modification in the modified product is too small, the adhesiveness tends to decrease, and conversely, if it is too large, a crosslinking reaction occurs and the moldability tends to decrease.

In addition, these adhesive resins include EVOH derived from the conjugated polyene and alkali metal-containing EVOH pellets of the present invention, other rubber / elastomer components such as EVOH, polyisobutylene, ethylene-propylene rubber, and a b-layer resin. Etc. can also be blended. In particular, blending a polyolefin-based resin different from the polyolefin-based resin that is the base of the adhesive resin may improve the adhesiveness, which is useful.

The thickness of each layer of the multilayer structure cannot be unequivocally determined depending on the layer structure, the type of layer b, the application, the form of the molded product, the required physical properties, etc., but usually, the a layer is 5 to 500 μm, preferably 10 to 10. The 200 μm, the b layer is selected from the range of 10 to 5000 μm, preferably 30 to 1000 μm, and the adhesive resin layer is selected from the range of 5 to 400 μm, preferably about 10 to 150 μm.

The multi-layer structure is used as it is for various shapes, but it is also preferable to perform a heat-stretching treatment in order to improve the physical properties of the multi-layer structure. Here, the "heat-stretching treatment" means that a film, a sheet, or a parison-shaped laminate heated uniformly by heat is formed into a cup, a tray, or a tray by a forming means such as a chuck, a plug, a vacuum force, a compressed air force, or a blow. It means the operation of uniformly forming into a tube or film. The stretching may be either uniaxial stretching or biaxial stretching, and it is better to perform stretching at the highest possible magnification in terms of physical characteristics. A stretched molded product having excellent gas barrier properties, which does not cause delamination (delamination) or the like, can be obtained.

As a stretching method for the multilayer structure, a roll stretching method, a tenter stretching method, a tubular stretching method, a stretching blow method, vacuum compressed air forming, or the like, which has a high stretching ratio can also be adopted. In the case of biaxial stretching, either a simultaneous biaxial stretching method or a sequential biaxial stretching method can be adopted. The stretching temperature is selected from the range of 60 to 170 ° C., preferably about 80 to 160 ° C. It is also preferable to perform heat fixing after the stretching is completed. The heat fixing can be carried out by a well-known means, and the heat fixing can be performed by heat-treating the stretched film at 80 to 170 ° C., preferably 100 to 160 ° C. for about 2 to 600 seconds while maintaining a tense state. can.

When used for heat-shrinkable packaging of raw meat, processed meat, cheese, etc., the product film is not fixed by heat after stretching, and the above-mentioned raw meat, processed meat, cheese, etc. are stored in the film. The film is heat-shrinked at 50 to 130 ° C., preferably 70 to 120 ° C. for about 2 to 300 seconds, and then tightly packaged.

The shape of the multilayer structure thus obtained may be any shape, and examples thereof include a film, a sheet, a tape, and a modified cross-section extruded product. In addition, the multi-layer structure can be heat-treated, cooled, rolled, printed, dry-laminated, solution or melt-coated, bag-made, deep-drawn, boxed, tube-processed, and split-processed, if necessary. And so on.

The bags made of films, sheets, stretched films and the containers and lids made of cups, trays, tubes, bottles, etc. thus obtained have excellent appearance with little coloring and almost no fish eyes. Therefore, it can be suitably used as a packaging material that requires gas barrier properties and has strict requirements for appearance. Specifically, in addition to general foods, it is useful as a container for various packaging materials such as mayonnaise, seasonings such as dressings, fermented foods such as miso, oil and fat foods such as salad oil, beverages, cosmetics, and pharmaceuticals.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.
In the example, "part" means a weight standard.

First, a method for measuring and evaluating pellets used in Examples and Comparative Examples will be described.

<Measurement evaluation method>
(1) Total content of conjugated polyene (sorbic acid) in the pellet When the conjugated polyene was added directly to the pellet surface of EVOH, the addition amount was regarded as the content. When the conjugated polyene was present inside the conjugated polyene and the alkali metal-containing EVOH pellet, the content of the conjugated polyene was quantified by the following measuring method.
8 mL of an extraction solvent (distilled water: methanol = 1: 1, volume ratio) was added to 1 g of the freeze-ground powder of the conjugated polyene and the alkali metal-containing EVOH pellets. This solution was subjected to sonication at a temperature of 20 ° C. and allowed to stand for 1 hour to extract sorbic acid in the resin, and after cooling, the volume was adjusted to 10 mL with an extraction solvent. This solution was filtered through a filter having a pore size of 0.45 μm, and then sorbic acid in the extract solution was quantified by a liquid chromatograph-ultraviolet spectrodetector.
[HPLC measurement conditions]
LC system: Agilent 1260/1290 [manufactured by Agilent Technologies]
Detector: Agilent 1260 infinity diode array detector [manufactured by Agilent Technologies]
Column: Cadenza CD-C18 (100 x 3.0 mm, 3 μm) [manufactured by Imtakt]
Column temperature: 40 ° C
Mobile phase A: 0.05% formic acid-containing 5% acetonitrile aqueous solution Mobile phase B: 0.05% formic acid-containing 95% acetonitrile aqueous solution Time program: 0.0 → 5.0 minutes B% = 30%
5.0 → 8.0 minutes B% = 30% → 50%
8.0 → 10.0 minutes B% = 50%
10.0 → 13.0 minutes B% = 50% → 30%
13.0 → 15.0 minutes B% = 30%
Flow rate: 0.2 mL / min UV detection wavelength: 190-400 nm
Quantitative wavelength: 262 nm
In addition, "%" in the said HPLC measurement condition means volume%.

(2) Conjugated polyene (sorbic acid) content in the surface layer of the pellet 20 g of the conjugated polyene and alkali metal-containing EVOH pellets are extracted by stirring in 30 mL of an extraction solvent (distilled water: methanol = 1: 1, volume ratio) for 10 minutes. Was carried out. The obtained extract was concentrated to 2 mL and then filtered through a filter having a pore size of 0.45 μm. The obtained filtrate was used as a test solution, and conjugated polyene was quantified by a liquid chromatograph. The amount of conjugated polyene in the filtrate was measured, and the content of the conjugated polyene in the surface layer of the pellet was determined by dividing by the weight of the conjugated polyene and the alkali metal-containing EVOH pellet (20 g). The measurement conditions of the liquid chromatograph were the same as the measurement of the total content of conjugated polyene in the pellets described above.

(3) Alkali metal content of the pellet Regarding the content of the alkali metal in the conjugated polyene and the alkali metal-containing EVOH pellet, when the alkali metal is directly added to the surface of the conjugated polyene and the alkali metal-containing EVOH pellet. The added amount can be regarded as the content, but when the alkali metal is present inside the conjugated polyene and the alkali metal-containing EVOH pellet, it is calculated by the following method.
2 g of the conjugated polyene and alkali metal-containing EVOH pellets were collected in a platinum dish, several mL of sulfuric acid was added, and the mixture was heated with a gas burner. After confirming that the pellets were carbonized and the white smoke of sulfuric acid disappeared, a few drops of sulfuric acid were added and the mixture was heated again. This operation was repeated until the organic matter was exhausted, and the ash was completely incinerated. The ashed container was allowed to cool, and 1 mL of hydrochloric acid was added to dissolve it. This hydrochloric acid solution was washed with ultrapure water and the volume was adjusted to 50 mL. The alkali metal content in this sample solution was measured by an inductively coupled plasma atomic emission spectrometer (ICP-AES) (Generic Technologies, Inc., 720-ES type). Finally, the alkali metal concentration in the solution was converted into the alkali metal content in the conjugated polyene and the alkali metal-containing EVOH pellets.

(4) A single-layer film having a thickness of 30 μm was obtained by forming a film using a fisheye conjugated polyene and an EVOH pellet containing an alkali metal under the following film forming conditions.
Fisheye was measured for the single-layer film having a thickness of 30 μm using a digital defect inspection device (GX-70LT manufactured by Mamiya-OP Co., Ltd.).
For fisheye measurement, light is applied from the lower surface of the single-layer film, and the part that does not transmit light (diameter 0.1 to 0.2 mm) is regarded as one fisheye, and it is per 100 cm ² (size: 10 cm x 10 cm). This was done by counting the number of fish eyes.
The reading speed at the time of measurement is 3 m / min.
[Film formation conditions]
Extruder: Diameter (D) 40 mm, L / D = 28
Screw: Full flight type compression ratio = 2.5
Screen pack: 60/90/60 mesh die: Width 450 mm, coat hanger type Set temperature: C1 / C2 / C3 / C4 / A / D = 180/200/220/220/210/210 ° C.
Screw rotation speed: 40 rpm
Roll temperature: 80 ° C

<Manufacturing of EVO H pellets containing conjugated polyenes and alkali metals>
[Example 1]
500 parts of vinyl acetate, 100 parts of methanol, 0.0585 parts of acetyl peroxide and 0.015 parts of citric acid are charged in a polymerization can equipped with a cooling coil, and the inside of the polymerization can is once replaced with nitrogen gas and then with ethylene. Substitution was performed and press-fitted until the ethylene pressure reached 40 kg / cm ² . Polymerization was started by raising the temperature to 67 ° C. with stirring under ethylene pressurization. Six hours after the start of the polymerization, when the polymerization rate reached 60%, 0.0525 parts of sorbic acid was added. As a result, an ethylene-vinyl acetate copolymer having an ethylene content of 32.5 mol% was obtained. Then, a reaction solution containing an ethylene-vinyl acetate copolymer was supplied to a distillation column, and unreacted vinyl acetate was removed by introducing methanol vapor from the lower part of the column to obtain a methanol solution of ethylene-vinyl acetate copolymer. rice field. The ethylene-vinyl acetate copolymer was saponified by supplying a methanol solution containing 0.007 equivalents of sodium hydroxide to the residual acetic acid groups in the copolymer to obtain EVOH. A methanol solution (EVOH 30% by weight, methanol 70% by weight) was obtained. The saponification degree of such EVOH was 99.7 mol%.
By blowing steam into the obtained methanol solution of EVOH and removing the generated steam of methanol to the outside of the system, a mixed solution of EVOH 40% by weight of water / methanol = 40/60 (weight ratio) was obtained. This mixed solution of EVOH in water / methanol is extruded into a strand shape in cold water, and the obtained strand-like substance (hydrous porous body) is cut with a cutter to have a diameter of 3.8 mm and a length of 4 mm and an EVOH content of 35. Porous pellets by weight were obtained.

300 parts of treated water for cleaning (treatment liquid) containing 0.1 part of sodium acetate / 0.1 part of acetic acid / 0.003 part of boric acid (boron equivalent) / 0.0008 part of sorbic acid with respect to 100 parts of this porous pellet. The porous pellets were washed for 1 hour with a boric acid concentration of 2.7 ppm and an alkali metal concentration of 89 ppm (corresponding to). The cleaning treatment was performed a total of 5 times. Next, the obtained porous pellets were dried at 110 ° C. for 8 hours under a nitrogen stream having an oxygen concentration of 0.5% by volume or less, and the water content per EVOH was 0.15% by weight / sodium content 0.02% by weight /. EVOH pellets containing 0.015% by weight (boron equivalent) of boric acid were obtained. When the conjugated polyene and alkali metal contents of the obtained EVOH pellets (conjugated polyene and alkali metal-containing EVOH pellets) were measured based on the above evaluation method, the total content of the conjugated polyene was 150 ppm, and the surface layer contained the conjugated polyene. The amount was 39 ppb and the content of the alkali metal was 200 ppm.

The obtained conjugated polyene and alkali metal-containing EVOH pellets were formed into a film using a single-layer T-die extruder at a maximum temperature of 220 ° C. and a screw rotation speed of 40 rpm to produce a single-layer film having a thickness of 30 μm. With respect to this single-layer film, the number of fish eyes generated was evaluated by the above method. The results are shown in Table 1 below.

[Example 2]
In Example 1, the total content of the conjugated polyene, the content of the conjugated polyene on the surface layer, and the content of the alkali metal were adjusted as shown in Table 1 below to prepare a conjugated polyene and an alkali metal-containing EVOH pellet. When the conjugated polyene and alkali metal contents of the obtained conjugated polyene and alkali metal-containing EVOH pellets were measured based on the above evaluation method, the total content of the conjugated polyene was 60 ppm, and the content of the conjugated polyene on the surface layer was 280 ppb. The alkali metal content was 140 ppm.
Next, using these pellets, a single-layer film was prepared in the same manner as in Example 1, and the number of fish eyes generated was evaluated. The results are shown in Table 1 below.

[Comparative Example 1]
With respect to the EVOH pellet obtained in Example 1, an EVOH pellet having a conjugated polyene and an alkali metal content adjusted so that the alkali metal content was 700 ppm was obtained.
Then, using these pellets, a single-layer film was prepared in the same manner as in Example 1, and the number of fish eyes generated was evaluated. The results are shown in Table 1 below.

[Comparative Example 2]
Sodium acetate 0.1 part / acetic acid 0.1 part / boric acid 0.003 part (boron equivalent) for 100 parts of porous pellets so that the content of sorbic acid is as shown in Table 1 below. ), But EVOH pellets were prepared in the same manner as in Example 1.
Then, using these pellets, a single-layer film was prepared in the same manner as in Example 1, and the number of fish eyes generated was evaluated. The results are shown in Table 1 below.

As can be seen from Table 1, examples in which the conjugated polyene content of the surface layer of the EVOH pellet, that is, the sorbic acid content is 30 ppb or more per the pellet weight, and the alkali metal content is 1 to 500 ppm per the pellet weight. In 1 and 2, the occurrence of fish eyes was suppressed.

On the other hand, although the amount of sorbic acid was the same as that of Example 1, Comparative Example 1 containing a larger amount of alkali metal than a predetermined range had insufficient suppression of fish eyes. Further, the total sorbic acid content and the alkali metal content were the same as in Example 1, but the content of Comparative Example 2 in which the sorbic acid content in the surface layer portion was less than 30 ppb was insufficient to suppress fish eyes.

Since the conjugated polyene and the alkali metal-containing EVOH pellet of the present invention can prevent the generation of fish eyes, they can be suitably used as a packaging material having strict requirements for the appearance of the film. Further, according to the production method of the present invention, since it is only necessary to change the composition of the cleaning liquid for the pellets, the conjugated polyene and the alkali metal-containing EVOH pellets of the present invention can be produced by utilizing the existing production equipment. ..

Claims (7)

An ethylene-vinyl alcohol-based copolymer pellet containing a conjugated polyene and an alkali metal, the content of the conjugated polyene on the surface layer of the pellet is 30 ppb or more per the weight of the pellet, and the entire pellet contains the entire conjugated polyene. The weight (surface layer conjugated polyene content / total conjugated polyene content) ratio of the conjugated polyene content of the pellet surface layer to the amount is 2.6 × 10 ^-4 or more, and the alkali metal content is the pellet weight. Ethylene-vinyl alcohol-based copolymer pellets characterized by 1 to 500 ppm per unit. The ethylene-ethylene according to claim 1, wherein the total content of the conjugated polyene in the whole ethylene-vinyl alcohol-based copolymer pellet containing the conjugated polyene and the alkali metal is 0.1 to 10,000 ppm per the weight of the pellet. Vinyl alcohol-based copolymer pellets. The ethylene-vinyl alcohol-based copolymer pellet according to claim 1 or 2 , wherein the conjugated polyene is at least one selected from the group consisting of sorbic acid, sorbic acid ester, and sorbic acid salt. The method for producing an ethylene-vinyl alcohol-based copolymer pellet containing the conjugated polyene and the alkali metal according to any one of claims 1 to 3 , wherein the copolymer is conjugated with the pellet of the ethylene-vinyl alcohol-based copolymer. An ethylene-vinyl alcohol system containing a conjugated polyene and an alkali metal, which comprises a step of contacting with a treatment liquid containing a polyene and a step of contacting a pellet of an ethylene-vinyl alcohol-based copolymer with an alkali metal. Method for producing copolymer pellets. The fourth aspect of claim 4 , wherein the pellet of the ethylene-vinyl alcohol-based copolymer is obtained by solidifying and pelletizing an alcohol solution or a water / alcohol mixed solution of the ethylene-vinyl alcohol-based copolymer. A method for producing an ethylene-vinyl alcohol-based copolymer pellet containing a conjugated polyene and an alkali metal. The method for producing an ethylene-vinyl alcohol copolymer pellet containing a conjugated polyene and an alkali metal according to claim 4 or 5 , wherein the pellet of the ethylene-vinyl alcohol-based copolymer is a porous pellet. .. 4. The present invention is characterized in that, in the step of producing the ethylene-vinyl ester-based copolymer before the ethylene-vinyl alcohol-based copolymer is saponified, a step of blending a conjugated polyene as a polymerization-prohibiting agent is provided. 6. The method for producing an ethylene-vinyl alcohol-based copolymer pellet containing a conjugated polyene and an alkali metal according to any one of 6.