JP2018109169A - Ethylene-vinyl alcohol copolymer pellet and method for producing ethylene-vinyl alcohol copolymer pellet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ethylene-vinyl alcohol copolymer pellet that is capable of suppressing the occurrence of fish eyes even with a single layer film of an ethylene-vinyl alcohol copolymer, the ethylene-vinyl alcohol copolymer pellet containing a boron compound and an alkali metal, and a method for producing the ethylene-vinyl alcohol copolymer pellet.SOLUTION: An ethylene-vinyl alcohol copolymer pellet contains a boron compound and an alkali metal. The boron compound content in the pellet surface layer part is 1.7 ppm or less per weight of the pellet in terms of boron, and the alkali metal content is 500 ppm or less per the pellet weight.SELECTED DRAWING: None

Description

  The present invention relates to a pellet of an ethylene-vinyl alcohol copolymer (hereinafter sometimes referred to as “EVOH”) that can provide a film with little fish eye when formed into a film. In particular, the present invention relates to an EVOH pellet containing an alkali metal and a method for producing the same.

  EVOH is an excellent gas barrier, including oxygen barrier properties, because hydroxyl groups contained in molecular chains are strongly hydrogen bonded to form crystal parts, and these crystal parts prevent the entry of gases such as oxygen from the outside. Can show gender. Taking advantage of such characteristics, EVOH is used after being formed into a film or sheet of food packaging material, pharmaceutical packaging material, industrial chemical packaging material, agricultural chemical packaging material or the like, or a packaging container such as a bottle.

  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 to practical use. Therefore, the formability and workability of EVOH are important.

  Therefore, in improving melt moldability, Patent Document 1 discloses boric acid or a salt thereof from the viewpoint of film moldability of a melt-formable vinyl alcohol copolymer such as EVOH, in particular, prevention of surging during film formation. As a blended composition, it is disclosed that it is effective to melt-mold a composition having an increased melt viscosity.

In Patent Document 2, EVOH treated with a boron compound is coextruded with polyolefin to obtain a laminate having excellent adhesion between the EVOH layer and the polyolefin layer, which is suitable in a field requiring gas barrier performance. It is disclosed that a simple packaging material can be provided.
The boron compound treatment of Patent Document 2 is performed by adding a boron compound to an EVOH solution or dispersion, and EVOH pellets containing a boron component are used as an extrusion molding raw material.

By the way, due to the recent increase in demand for the appearance of EVOH film or multilayer structure as a packaging material, improvement is also required for small fish eyes of less than 0.1 mm.
Patent Document 3 finds that the boron-containing EVOH pellets obtained by performing the treatment of adding a boron compound to EVOH have a relationship with the generation of fish eyes having a moisture content of less than 0.1 mm. It is disclosed that the generation of fish eyes of less than 0.1 mm can be suppressed by contacting with water after drying to 0001 to 2% by weight.

  In the example of Patent Document 3, EVOH pellets subjected to boron compound addition treatment were immersed in water and then dried to adjust the content and water content of the boron compound [water content 0.13 to 0] .4 wt%, boron content 0.015 to 0.039 parts by weight (150 to 390 ppm) with respect to 100 parts by weight of EVOH], and the EVOH pellets are fed to a multilayer extruder to provide a multilayer of 3 types and 5 layers. A laminate is manufactured (Examples 1, 3, and 4). The evaluation of fish eyes of the obtained multilayer structure is performed by counting the number of fish eyes having a diameter of 0.01 to 0.1 mm by visual observation (paragraphs [0038] to [0041]. ]).

Japanese Patent Publication No.62-3866 Japanese Patent Publication No. 3-11270 JP 2000-44756 A

  In recent years, demands on the appearance of packaging materials have become increasingly severe, and further improvement of fish eyes is desired while ensuring melt moldability such as prevention of surging during molding. In particular, when EVOH is formed as a single layer, fish eyes are more likely to be generated and the number of generations tends to be larger than in the case of a multilayer structure. Suppressed EVOH pellets have been demanded, and the techniques disclosed in Patent Documents 1 to 3 have not been satisfactory yet.

  The present invention has been made in view of the circumstances as described above, and an object of the present invention is to provide an EVOH pellet containing a boron compound and an alkali metal that can suppress the generation of fisheye even in an EVOH single-layer film, and its It is to provide a manufacturing method.

  The present inventors investigated the relationship between the generation of fish eyes and EVOH pellets containing a boron compound. As a result of various investigations, it is considered that fish eyes are generated by agglomeration of boron compounds causing local thickening of EVOH. In the case of single layer film formation, the boron compound existing in the pellet surface layer portion that comes into contact with the metal of the molding machine tends to aggregate, and as a result, fish eyes are likely to be generated and considered to be conspicuous.

  Further, when EVOH stays inside the extruder, deterioration and gelation proceed, and when this staying matter is discharged, fish eyes are generated. Since alkali metal has a viscosity reducing effect on EVOH, it was considered that the increase in viscosity due to cross-linking when EVOH stays inside the extruder can be mitigated, and as a result, the generation of fish eyes can be suppressed.

  Furthermore, in view of the above two types of fish eye generation mechanism, the added alkali metal interacts with the boron compound on the EVOH pellet surface, thereby suppressing aggregation of the boron compound that may exist on the EVOH pellet surface. It was considered that the generation of fish eyes derived from boron compounds can be suppressed by containing an alkali metal.

Based on this recognition, the present inventors focused on the boron compound content in the pellet surface layer part, and further on the alkali metal content, making the content of the boron compound in the pellet surface layer part smaller than before, and in EVOH. It was found that the fisheye was reduced by containing an alkali metal, particularly by setting the content to a predetermined amount or less, and the present invention was completed.
Note that the film (including layers and films) obtained using the EVOH pellets containing boron and alkali metal of the present invention is excellent in formability and appearance even if it is a single layer film. Of course, the present invention can also be applied to a multilayer structure in which other resin layers are laminated from the viewpoint of strength and the like.

  That is, the present invention is an EVOH pellet containing a boron compound and an alkali metal (hereinafter sometimes simply referred to as “boron compound and alkali metal-containing EVOH pellet”), and the content of the boron compound in the surface layer of the pellet is First, EVOH pellets having a boron conversion of 1.7 ppm or less per pellet weight and an alkali metal content per pellet weight of 500 ppm or less are set as the first gist.

  The present invention also includes a step of bringing the EVOH pellet into contact with the boron compound and the alkali metal to contain the boron compound and the alkali metal, and washing the pellet obtained by the above-mentioned step, so that the boron compound content in the pellet surface layer portion Is a manufacturing method of EVOH pellets comprising a step of making 1.7 ppm or less per EVOH pellet weight in terms of boron, the step of containing the alkali metal so that the alkali metal is 500 ppm or less per pellet weight The washing in the washing step is to contact the dried pellets with a water / alcohol mixed solution or alcohol having a weight ratio of water to alcohol (water / alcohol) of 80/20 to 0/100 or alcohol. The second essential point is the method of manufacturing EVOH pellets To.

  The boron compound and alkali metal-containing EVOH pellets of the present invention have a boron compound content of the pellet surface layer portion of 1.7 ppm or less per pellet weight in terms of boron, and an alkali metal content per pellet weight. Is 500 ppm or less. Therefore, the boron compound and alkali metal-containing EVOH pellets of the present invention are excellent in the effect of suppressing the generation of fish eyes while ensuring melt moldability.

  In the present invention, in particular, when the total boron compound content of the boron compound and alkali metal-containing EVOH pellets is 10 to 1000 ppm per pellet weight in terms of boron, a viscosity suitable for film formation is obtained. The film performance can be improved, and as a result, the effect of suppressing the generation of fish eyes can be improved.

Furthermore, among the present invention, in particular, the weight ratio of the boron compound content (boron conversion) of the pellet surface layer portion to the boron compound total content (boron conversion) of the entire boron compound and alkali metal-containing EVOH pellets (surface layer boron compound) If the content / total content of boron compound is 1.38 × 10 ⁻² or less, the effect of suppressing the generation of fish eyes can be further improved, and the film appearance can be improved. be able to.

  In the present invention, in particular, when the water content of the boron compound and alkali metal-containing EVOH pellets is 0.01 to 1% by weight, the effect of suppressing the generation of fisheye is further improved. In addition, the film appearance can be improved.

  Also, the step of containing the boron compound and the alkali metal by bringing the EVOH pellet into contact with the boron compound and the alkali metal, and the pellet obtained by the above step are washed, and the boron compound content of the pellet surface layer portion is converted into boron EVOH pellet manufacturing method comprising a step of making 1.7 ppm or less per EVOH pellet weight, wherein the step of containing the alkali metal includes adding the alkali metal to 500 ppm or less per pellet weight. The washing in the washing step is to bring the dried pellets into contact with water / alcohol mixed solution or alcohol having a weight ratio of water to alcohol (water / alcohol) of 80/20 to 0/100. And the EVOH pellet manufacturing method of the present invention, Boron compound and alkali metal-containing EVOH pellets with reduced boron compound content in the layer part can be obtained, and melt molded products using the pellets have good melt moldability and reduced generation of fish eyes It becomes.

  The present invention will be described in detail below, but these show examples of desirable embodiments and are not limited to these contents.

  In the present specification, the content measured as the boron content in the boron compound and alkali metal-containing EVOH pellets is referred to as “boron compound content (in terms of boron)” or simply “boron content”.

  In the boron compound and alkali metal-containing EVOH pellets of the present invention, the boron compound content in the surface layer of the pellets is 1.7 ppm or less per pellet weight in terms of boron, and the alkali metal content per pellet weight Is 500 ppm or less.

Here, the “boron compound content in the pellet surface layer portion” refers to the amount of the boron compound present in the vicinity of the surface among the boron compounds contained in the boron compound and the alkali metal-containing EVOH pellet, specifically, Then, 4 g of EVOH pellets containing boron compound and alkali metal were immersed in 20 mL of methanol at 30 ° C. for 6 hours, and then boron content in the obtained methanol solution was measured using an inductively coupled plasma mass spectrometer (ICP-MS). Measured and divided by the weight (4 g) of the EVOH pellets. The “boron compound in the pellet surface layer portion” includes a boron compound only attached to the pellet surface, a boron compound bleeded on the surface, and the like.
The “boron compound content in the pellet surface layer” is distinguished from the boron compound content (“total boron compound content in the pellet”) contained in the boron compound and alkali metal-containing EVOH pellets. is there.

  The “alkali metal content” of the present invention means the amount of alkali metal contained in the surface of the boron compound and the alkali metal-containing EVOH pellets, or inside, or both. Specifically, when an alkali metal is contained on the surface of a boron compound and an alkali metal-containing EVOH pellet, the amount of the alkali metal added to the EVOH pellet surface can be regarded as the content. In addition, when an alkali metal is contained inside the boron compound and alkali metal-containing EVOH pellets, for example, the dried boron compound and alkali metal-containing EVOH pellets are incinerated and then dissolved in an aqueous hydrochloric acid solution, and inductively coupled plasma emission spectrometry is performed. A value obtained by a method such as measuring with a meter (ICP-AES) and quantifying the content of alkali metal from a calibration curve of a standard solution is converted into the content of the whole pellet.

  Hereinafter, prior to the description of the boron compound and alkali metal-containing EVOH pellets of the present invention, a method for producing EVOH pellets before each component and boron compound and alkali metal are contained will be described.

<EVOH>
The EVOH constituting the boron compound and alkali metal-containing EVOH pellets of the present invention is usually a resin obtained by saponifying a copolymer of ethylene and a vinyl ester monomer (ethylene-vinyl ester copolymer). In general, it is a water-insoluble thermoplastic resin called a saponified ethylene-vinyl alcohol copolymer or ethylene-vinyl ester copolymer. The polymerization method can also be carried out using any known polymerization method such as solution polymerization, suspension polymerization, and emulsion polymerization. Generally, however, solution polymerization using a lower alcohol such as methanol, particularly preferably methanol as a solvent. Is used. Saponification of the obtained ethylene-vinyl ester copolymer can also be performed by a known method.
EVOH produced in this manner mainly comprises ethylene-derived structural units and vinyl alcohol structural units, and usually contains some vinyl ester structural units that remain without being saponified as necessary.

  As the vinyl ester-based monomer, vinyl acetate is typically used because it is easily available from the market and has good treatment efficiency of impurities during production. Examples of other vinyl ester monomers include vinyl formate, vinyl propionate, vinyl valelate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl versatate, etc. Aliphatic vinyl esters; aromatic vinyl esters such as vinyl benzoate and the like can be mentioned. Usually, aliphatic vinyl esters having 3 to 20 carbon atoms, preferably 4 to 10 carbon atoms, particularly preferably 4 to 7 carbon atoms are used. Can do. These are usually used alone, but a plurality of them may be used simultaneously as necessary.

  The ethylene and the vinyl ester monomer are usually petroleum-derived raw materials such as naphtha, but natural gas-derived raw materials such as shale gas, sugars and starches contained in sugar cane, sugar beet, corn, potato, etc. Or a monomer derived from a plant-derived raw material purified from a component such as cellulose contained in rice, wheat, millet, grass plant or the like.

  The content of the ethylene structural unit in EVOH is a value measured based on ISO 14663, and is usually 20 to 60 mol%, preferably 25 to 50 mol%, particularly preferably 27 to 48 mol%. When the content is too low, the gas barrier property and melt moldability under high humidity tend to be lowered, and when it is too high, the gas barrier property tends to be lowered.

  The saponification degree of the vinyl ester component in EVOH is a value measured based on JIS K6726 (however, water / methanol is used as a solvent), and is usually 90 to 100 mol%, preferably 95 to 100 mol%, particularly preferably. 99 to 100 mol%. When the degree of saponification is too low, gas barrier properties, thermal stability, moisture resistance and the like tend to decrease.

  Further, the melt flow rate (MFR) (210 ° C., load 2160 g) of the EVOH is usually 0.5 to 100 g / 10 minutes, preferably 1 to 50 g / 10 minutes, particularly preferably 2 to 35 g / 10 minutes. It is. If the MFR is too large, the film formability tends to be unstable, and if it is too small, the viscosity becomes too high and melt extrusion tends to be difficult.

  The EVOH used in the present invention may further contain structural units derived from the comonomer shown below within a range not inhibiting the effects of the present invention (for example, 10 mol% or less).

  Examples of the comonomer include olefins such as propylene, 1-butene, and isobutene, 3-buten-1-ol, 3-butene-1,2-diol, 4-penten-1-ol, and 5-hexene-1,2. -Hydroxyl vinylidenes such as hydroxyl group-containing α-olefins such as diols and esterified products thereof, 2-methylenepropane-1,3-diol, 3-methylenepentane-1,5-diol; 1,3-diacetoxy-2 -Derivatives such as hydroxyalkylvinylidene diacetates, acylated products such as methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, 1,3-dibutyronyloxy-2-methylenepropane; acrylic acid, methacrylic acid , Crotonic acid, (anhydrous) phthalic acid, (anhydrous) maleic acid, (anhydrous) itaconic acid, etc. Acids or salts thereof or mono- or dialkyl esters having 1 to 18 carbon atoms; acrylamide, N-alkyl acrylamide having 1 to 18 carbon atoms, N, N-dimethylacrylamide, 2-acrylamidopropanesulfonic acid or salts thereof, acrylamidopropyldimethyl Acrylamides such as amines or acid salts thereof or quaternary salts thereof; methacrylamide, N-alkylmethacrylamide having 1 to 18 carbon atoms, N, N-dimethylmethacrylamide, 2-methacrylamideamidopropanesulfonic acid or salts thereof, methacryl Methacrylamides such as amidopropyldimethylamine or its acid salts or quaternary salts; N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide; acrylic nitrile Vinyl cyanides such as methacrylonitrile, vinyl ethers such as alkyl vinyl ethers having 1 to 18 carbon atoms, hydroxyalkyl vinyl ethers, alkoxyalkyl vinyl ethers; vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, vinyl bromide, etc. Vinyl silanes such as trimethoxyvinyl silane; allyl halide compounds such as allyl acetate and allyl chloride; allyl alcohols such as allyl alcohol and dimethoxyallyl alcohol; trimethyl- (3-acrylamido-3-dimethyl) And a comonomer such as propyl) -ammonium chloride and acrylamide-2-methylpropanesulfonic acid. These may be used alone or in combination of two or more.

  In particular, EVOH copolymerized with a hydroxyl group-containing α-olefin is preferable from the viewpoint of good secondary moldability. Among them, EVOH having a primary hydroxyl group in the side chain, particularly a 1,2-diol structure in the side chain. EVOH having is preferable.

  EVOH having such a 1,2-diol structure in the side chain contains a 1,2-diol structural unit in the side chain. The 1,2-diol structural unit is specifically a structural unit represented by the following general formula (1).

In the general formula (1), R ^{1 to} R ⁶ each independently represent a hydrogen atom or an organic group, and X represents a single bond or a bonded chain.

Examples of the organic group in the 1,2-diol structural unit represented by the general formula (1) include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a tert-butyl group. A saturated hydrocarbon group such as a group; an aromatic hydrocarbon group such as a phenyl group and a benzyl group; a halogen atom, a hydroxyl group, an acyloxy group, an alkoxycarbonyl group, a carboxyl group, and a sulfonic acid group.
R ^{1 to} R ³ are preferably a saturated hydrocarbon group or a hydrogen atom having 1 to 30 carbon atoms, particularly 1 to 15 carbon atoms, more preferably 1 to 4 carbon atoms, and most preferably a hydrogen atom. R ^{4 to} R ⁶ are preferably an alkyl group having 1 to 30 carbon atoms, particularly 1 to 15 carbon atoms, more preferably 1 to 4 carbon atoms, or a hydrogen atom, and most preferably a hydrogen atom. In particular, it is most preferable that R ^{1 to} R ⁶ are all hydrogen atoms.

Moreover, X in the structural unit represented by the general formula (1) is typically a single bond. In addition, as long as the effect of this invention is not inhibited, X may be a bond chain. Such a bond chain is not particularly limited, but for example, a hydrocarbon chain such as alkylene, alkenylene, alkynylene, phenylene, naphthylene (these hydrocarbons may be substituted with halogen such as fluorine, chlorine, bromine, etc.) _{other, -O -, - (CH 2} O) m -, - (OCH 2) m -, - (CH 2 O) mCH 2 - structure containing an ether binding site such as; -CO -, - COCO -, - A structure containing a carbonyl group such as CO (CH ₂ ) mCO— or —CO (C ₆ H ₄ ) CO—; a structure containing a sulfur atom such as —S—, —CS—, —SO— or —SO ₂ —; A structure containing a nitrogen atom such as —NR—, —CONR—, —NRCO—, —CSNR—, —NRCS—, —NRNR—, etc .; a structure containing a heteroatom such as a structure containing a phosphorus atom such as —HPO ₄ —; _{-Si (OR) 2 -, -} OSi ( _{R) 2 -, - OSi (} OR) structure containing ₂ O- such as silicon _{atoms; -Ti (OR) 2 -,} - OTi (OR) 2 -, - OTi the (OR) ₂ O- or titanium atoms A structure containing a metal atom such as a structure containing an aluminum atom such as -Al (OR)-, -OAl (OR)-, and -OAl (OR) O-.
M is a natural number, and is usually 1-30, preferably 1-15, and more preferably 1-10. Of these, —CH ₂ OCH ₂ — and a hydrocarbon chain having 1 to 10 carbon atoms are preferable from the viewpoint of stability during production or use, and further a hydrocarbon chain having 1 to 6 carbon atoms, particularly 1 carbon atom. It is preferable that

The most preferable structure in the 1,2-diol structural unit represented by the general formula (1) is one in which R ^{1 to} R ⁶ are all hydrogen atoms and X is a single bond. That is, the structural unit represented by the following general formula (1a) is most preferable.

  When the 1,2-diol structural unit represented by the general formula (1a) is contained, the content thereof is usually 0.1 to 20 mol%, further 0.1 to 15 mol%, particularly 0.1. The thing of 10 mol% is preferable.

  Furthermore, the EVOH used in the present invention may be EVOH that has been “post-modified” such as urethanization, acetalization, cyanoethylation, oxyalkyleneation and the like.

<Boron compound>
Examples of the boron compound used in the present invention include boric acid or a metal salt thereof such as sodium borate (sodium metaborate, sodium diborate, sodium tetraborate, sodium pentaborate, sodium hexaborate, sodium octaborate). Etc.), potassium borate (potassium metaborate, potassium tetraborate, potassium pentaborate, potassium hexaborate, potassium octaborate, etc.), lithium borate (lithium metaborate, lithium tetraborate, lithium pentaborate) Etc.), calcium borate, barium borate (barium orthoborate, barium metaborate, barium diborate, barium tetraborate, etc.), magnesium borate (magnesium orthoborate, magnesium diborate, magnesium metaborate, tetraborate) Trimagnesium acid, pentamagnesium tetraborate, etc.), boric acid Ngan (manganese borate, manganese metaborate, manganese tetraborate, etc.), cobalt borate, zinc borate (zinc tetraborate, zinc metaborate, etc.), cadmium borate (cadmium orthoborate, cadmium tetraborate) ), Silver borate (silver metaborate, silver tetraborate, etc.), copper borate (cupric borate, copper metaborate, copper tetraborate, etc.), nickel borate (nickel orthoborate, diborate) Nickel, nickel tetraborate, nickel octaborate, etc.), aluminum borate, potassium, ammonium borate (ammonium metaborate, ammonium tetraborate, ammonium pentaborate, ammonium octaborate, etc.), lead borate (metaborate) Lead acid, lead hexaborate, etc.), bismuth borate, etc., borax, carnite, inyoite, olivine, suianite, zyberite Borate minerals and the like of, preferably borax, boric acid. These may be used alone or in combination of two or more. Here, when the alkali metal salt of the boron compound is contained, the content is included in the content of the alkali metal in the boron compound and the alkali metal-containing EVOH pellet of the present invention.

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

Examples of the alkali metal source for incorporating the alkali metal into the boron compound and alkali metal-containing EVOH pellets of the present invention include alkali metal compounds such as alkali metal oxides, alkali metal hydroxides, and alkali metal salts. These are preferably water-soluble. Of these, alkali metal salts are preferred from the viewpoint of dispersibility.
Moreover, it is preferable that the alkali metal compound used for this invention remove | excludes an inorganic layered compound and double salt from the point of economical efficiency and a dispersibility.

For example, the alkali metal compound may exist in an ionized state or in the form of a complex having a resin or other ligand, in addition to the case where the alkali metal compound exists as an alkali metal salt.
Examples of the alkali metal salt include inorganic salts such as carbonate, bicarbonate, phosphate, borate, sulfate, chloride; acetate, butyrate, propionate, enanthate, capric acid C2-C11 monocarboxylates such as salts; C2-C11 dicarboxylates such as oxalate, malonate, succinate, adipate, suberate, sebacate; EVOH Examples thereof include a carboxylate with a polymerization terminal carboxyl group 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, particularly preferably 20 to 500.
Among these, a carboxylate is preferable, a carboxylate having 2 to 11 carbon atoms is more preferable, an aliphatic carboxylate having 2 to 11 carbon atoms is more preferable, and a carbon number is more preferable. 2 to 6 aliphatic monocarboxylates, particularly preferably acetate.

<Manufacture of EVOH pellets>
As a method for producing pellets from EVOH, a conventionally known method can be adopted, for example,
a) Hot cut method in which molten EVOH is extruded from the discharge port of the extruder, cut in the molten state, and then cooled and solidified to produce pellets;
b) A strand cutting method in which EVOH in a molten state is extruded into a coagulation bath and EVOH strands obtained by cooling and solidification are cut.

  In both of the above a) hot cut method and b) strand cut method, EVOH used as a raw material for pellets is obtained by saponifying an ethylene-vinyl ester copolymer solution in the production of (α) EVOH. The obtained EVOH solution or slurry, or EVOH water-containing composition (hereinafter sometimes referred to as “EVOH solution / water-containing composition”); or (β) EVOH (dried EVOH) pellets are melted and the molten state EVOH 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. The concentration of EVOH in the EVOH water-containing composition is usually 20 to 60% by weight.

  As said solvent, alcohol, water / alcohol mixed solvent, etc. can be used. Of these, a water / alcohol mixed solvent is preferred. As said alcohol, C1-C10 aliphatic alcohols, such as methanol, ethanol, a propanol, n-butanol, tert-butanol, can be used, for example, Methanol is especially preferable. The water / alcohol mixing weight ratio is preferably 80/20 to 5/95.

  Moreover, as said EVOH hydrous composition, it is preferable to contain normally 0-10 weight part of alcohol and 10-500 weight part of water with respect to 100 weight part of EVOH normally.

  The method of 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 solvent onto the EVOH solution or slurry, a solution or slurry of EVOH And a method of mixing the solvent with the above solvent, a method of bringing an EVOH solution or slurry into contact with the vapor of the solvent, and the like. In order to lower the moisture content, the EVOH solution or slurry may be appropriately dried. For example, the EVOH solution or slurry may be dried using a fluid hot air dryer or a stationary 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 produced by the hot-cut method, the temperature of the EVOH solution / water-containing composition in the extruder is preferably 70 to 170 ° C, more Preferably it is 80-170 degreeC, More preferably, it is 90-170 degreeC. When the temperature of the EVOH solution / water-containing composition is too low, EVOH tends not to melt completely, and when it is too high, EVOH tends to be susceptible to thermal degradation.
Moreover, when using dry EVOH as a pellet raw material, the temperature of EVOH in an extruder has preferable 150-300 degreeC, More preferably, it is 160-280 degreeC, More preferably, it is 170-250 degreeC.
The temperature of the EVOH solution / water-containing composition and dry EVOH refers to a temperature detected in the vicinity of the discharge port at the tip of the extruder by a temperature sensor installed in the extruder cylinder.

  The EVOH solution / water-containing composition extruded from the extruder die, that is, the EVOH in a molten state, is cut before being cooled and solidified. The cutting method may be either a hot cutting method for cutting in the air (air hot cutting method) or an underwater cutting method in which it is extruded into a cutter installation container filled with cooling water and cut in cooling water.

The temperature of the cooling water in the underwater cutting method is such a temperature that EVOH extruded in a molten state does not instantaneously solidify (solidify), and the temperature of the cooling water when the EVOH solution / water-containing composition is used as a raw material is − It is preferable to set it as 20-50 degreeC, More preferably, it is -5-30 degreeC.
In addition, when dry EVOH is used as a raw material, it is easier to solidify than when an EVOH solution / water-containing composition is used as a raw material, so the temperature of the cooling water in the underwater cutting method is when using EVOH solution / water-containing composition as a raw material. Higher, usually 0 to 90 ° C, preferably 20 to 70 ° C.

  The cooling water is not limited to water, but 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, 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. In addition, as said alcohol, lower alcohols, such as methanol, ethanol, propanol, can be used, and methanol is used preferably industrially.

b) Strand cut method When the EVOH solution / water-containing composition is charged into an extruder as a pellet raw material produced by the strand cut method, the temperature of the EVOH solution / water-containing composition extruded into the coagulation bath is usually 10 to 100 ° C. . The temperature of the coagulation bath is a temperature at which the extruded EVOH can be cooled and solidified, and is usually −10 to 40 ° C., and the residence time is usually about 10 to 400 seconds.
In addition, when dry EVOH is fed into the extruder as a raw material for pellets, the temperature at which EVOH is extruded into the coagulation bath is usually 150 to 300 ° C, and the temperature of the coagulation bath is usually 0 to 90 ° C and the residence time Is 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 employed.

  In this way, EVOH pellets are obtained.

  Among the EVOH pellets described above, it is preferable to use a porous pellet having a plurality of pores inside the pellet from the viewpoint of the boron compound containing treatment described later. By permeating the boron compound into the pores, the boron compound can be easily held in the pellet, and the boron compound can be efficiently taken into the pellet. The size of the pores in the porous pellet is not particularly limited as long as the boron compound can penetrate into the pores.

  Such porous pellets usually use the above-mentioned EVOH water-containing composition as a pellet raw material, and the EVOH concentration in the EVOH water-containing composition, the type of solvent, the temperature during extrusion, the temperature of the coagulation bath, the residence time, etc. It can be obtained by adjusting

  The moisture content of the porous pellet is preferably 20 to 80% by weight. The porous pellet having the water content can uniformly and rapidly contain a boron compound in the step of containing a boron compound described later.

  The shape of the EVOH pellets usually depends on the method of producing the pellets, and various shapes can be used. The shapes of the EVOH pellets obtained by the above methods and the boron compound and alkali metal-containing EVOH pellets of the present invention are as follows. Is optional. As the shape of the pellet, for example, there are a spherical shape, an oval shape, a cylindrical shape, a cubic shape, a rectangular parallelepiped shape, an indeterminate shape, etc., but it is usually an oval shape or a cylindrical shape, and its size is used as a molding material later From the viewpoint of convenience in the case, in the case of an oval shape, the major axis is usually 1 to 10 mm, preferably 2 to 7 mm, the minor axis is usually 1 to 6 mm, and preferably 2 to 5 mm. The diameter 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 pellets used in the present invention may be a mixture with different EVOH pellets. As the other EVOH pellets, those having different ethylene structural unit contents, those having different saponification degrees, and melt flow rates. Examples thereof include those having different (MFR) and different copolymerization components, such as those having different contents of the 1,2-diol structural unit represented by the general formula (1).

  The boron compound and alkali metal-containing EVOH pellets of the present invention can be obtained by adding a predetermined amount of boron compound and alkali metal to the EVOH pellets. The method for producing the boron compound and alkali metal-containing EVOH pellet of the present invention is not particularly limited, but a typical production method will be described below.

<Production of boron compound and alkali metal-containing EVOH pellets>
The boron compound and alkali metal-containing EVOH pellets of the present invention comprise a step of containing a boron compound by bringing the EVOH pellets into contact with the boron compound, a step of bringing the alkali metal into contact with the EVOH pellets and an alkali metal, and The EVOH pellets containing the boron compound can be washed to obtain a boron compound content in the pellet surface layer portion of 1.7 ppm or less per pellet weight in terms of boron. Any of these steps may be performed first or at the same time. When performing the said process simultaneously, it can carry out by using the solution which the boron compound and the alkali metal melt | dissolved, for example.

<Step of containing boron compound>
The step of containing the boron compound is performed by bringing the EVOH pellets into contact with the boron compound.

As a method of bringing the EVOH pellets into contact with the boron compound, for example,
i) a method of bringing EVOH into contact with a boron compound in the EVOH pellet manufacturing stage;
ii) a method of bringing a previously prepared EVOH pellet into contact with a boron compound;
Etc.

As a method of contacting EVOH and a boron compound in the EVOH pellet manufacturing stage of i), for example, a boron compound is added to a pellet raw material (EVOH solution / water-containing composition, dry EVOH), or a solution containing a boron compound is used. The method used for the coagulation liquid at the time of pellet manufacture is mention | raise | lifted.
When an EVOH solution / water-containing composition is used as a pellet raw material, a boron compound may be added to the EVOH solution / water-containing composition. Moreover, what is necessary is just to make a dry EVOH contain a boron compound previously, when a dry EVOH pellet is fuse | melted and EVOH of this molten state is used as a raw material.
Preferably, the EVOH water-containing composition to which the boron compound is added is extruded into a coagulating liquid in the form of a strand, and the resulting strand is cut.

  As a method of contacting the EVOH pellet prepared in advance in ii) with the boron compound, a method of spraying a solution containing the boron compound onto the EVOH pellet; a method of immersing the EVOH pellet in a solution containing the boron compound; An example is a method in which EVOH pellets are added while stirring the contained solution. Among these, a method of introducing EVOH pellets while stirring a solution containing a boron compound is preferably used in that the boron compound can be efficiently contained inside the pellet.

  As the solvent of the solution containing the boron compound, for example, water; lower alcohols such as methanol, ethanol, propanol, etc .; water / alcohol mixture solution, and the like can be used. In the water / alcohol mixed solution, the water / alcohol (weight ratio) is usually 90/10 to 10/90.

  Moreover, the density | concentration of the solution of the boron compound used for the contact process of EVOH pellet and a boron compound is 0.001-1 weight% normally, Preferably it is 0.003-0.5 weight%. If the concentration is too low, it tends to be difficult to contain a predetermined amount of boron compound, and if it is too high, the appearance of the finally obtained molded product tends to be lowered.

  The amount of boron compound contained in the pre-cleaning boron compound-containing EVOH pellets obtained by such a boron compound contact treatment (the total content of boron compounds in the pellets) is usually 10 to 10,000 ppm per pellet weight in terms of boron. , Preferably 20 to 5000 ppm, more preferably 30 to 3000 ppm. When the content is too small, the effect of adding the boron compound tends to be insufficient, and when the content is too large, the appearance of the finally obtained molded product tends to deteriorate.

  The amount of boron compound in the EVOH pellet (the total content of boron compound in the EVOH pellet) is the concentration of boron compound in the solution containing the boron compound, the contact treatment time, the contact treatment temperature, the stirring speed and treatment during the contact treatment. It can be controlled by the moisture content of the EVOH pellets to be controlled.

  Among the methods for bringing the EVOH pellets into contact with the boron compound as described above, the method can be applied to various pellets, and is excellent in versatility, so that the previously prepared EVOH pellets and the boron compound are brought into contact with each other. Is preferred. More preferably, the porous EVOH pellet is brought into contact with a boron compound solution.

  EVOH pellets containing a boron compound obtained by such a boron compound contact treatment (the boron compound content in the pellet surface layer is unadjusted; hereinafter, this pellet is referred to as “EVOH pellet before surface layer boron adjustment”) The amount of boron compound contained (the total content of boron compounds in the EVOH pellets) is usually 10 to 10,000 ppm, preferably 20 to 5000 ppm, more preferably 30 to 3000 ppm in terms of boron. If the content is too small, the effect of adding the boron compound tends to decrease, and if it is too large, the appearance of the finally obtained molded product tends to decrease.

  The amount of boron compound contained in the EVOH pellets before the surface layer boron adjustment [total boron compound content (in terms of boron)] is obtained by treating the pellets with concentrated nitric acid by a microwave decomposition method. This is the amount measured with an inductively coupled plasma optical emission spectrometer (ICP-AES) using a solution obtained by adding pure water and making a constant volume.

  The boron compound EVOH pellet before surface layer boron adjustment obtained by the above step may be subjected to the next step as it is, but it is usually preferable to dry the pellet. For such drying, a known method can be employed. 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 dryer, etc. What is necessary is just to dry by the stationary drying etc. which used the fluidized drying used, the batch-type box dryer, the band dryer, the tunnel dryer, the vertical silo dryer, etc. By passing a gas such as nitrogen gas at 80 to 150 ° C. through the dryer, the gas can be efficiently dried without affecting the EVOH pellets before adjusting the surface layer boron.

<Step of cleaning EVOH pellets>
Next, a process of cleaning the EVOH pellet will be described.
The EVOH pellet before the surface layer part boron adjustment is dependent on the total content of the boron compound contained in the pellet and the content of the boron compound in the pellet surface part, but the content of the boron compound in the pellet surface part by the cleaning treatment Can be adjusted.

  The cleaning treatment is performed by bringing the cleaning treatment solution into contact with the EVOH pellets before surface layer boron adjustment. Examples of the contact method include, for example, a method of immersing and stirring the surface layer boron pre-EV adjustment pellets in a cleaning treatment solution, a method of circulating the surface layer boron pre-adjustment EVOH pellets in a cleaning treatment solution, and a surface layer It can be carried out by a method of spraying a cleaning treatment liquid onto EVOH pellets before partial boron adjustment. In the above immersion method, it is also effective to apply vibrations such as ultrasonic waves during immersion. Among the above-mentioned methods, industrially, preferably a method of immersing EVOH pellets before surface layer boron adjustment in a cleaning treatment solution and stirring, a method of circulating EVOH pellets before surface layer boron adjustment in the cleaning treatment solution Is used.

  The washing treatment liquid is preferably a water / alcohol mixed solution or alcohol, more preferably a water / alcohol mixed solution.

  Examples of the alcohol include 1 to 8 carbon atoms such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, and 2-methyl-2-propanol. In particular, it is preferable to use 1 to 5, more preferably 1 to 3, and among these, methanol is particularly preferably used because it is easily available and inexpensive.

  When a water / alcohol mixed solution or alcohol is used as the cleaning treatment liquid, the water / alcohol (weight ratio) is 80/20 to 0/100, preferably 65/35 to 15/85, and particularly preferably 50 / 50-20 / 80. Even if there is too much water or the alcohol concentration becomes too high, the effect of reducing the boron compound content in the surface layer portion tends to decrease, so a water / alcohol mixed solution in the above range is preferred.

  In general, since the solubility of a boron compound is higher in alcohol than in water, alcohol is usually used as a cleaning treatment liquid for adjusting the content of the boron compound. However, in the present invention, surprisingly, by using a water / alcohol mixed solution as a cleaning treatment solution rather than alcohol alone, the boron compound can be more efficiently eluted from the EVOH pellets before surface layer boron adjustment. I found out that I can do it. The solubility of the boron compound in 10 g of water at 23 ° C. is about 0.1 to 10% by weight, and the solubility in 10 g of methanol at 23 ° C. is about 15 to 30% by weight.

  The contact time of the EVOH pellet before surface layer boron adjustment and the cleaning treatment liquid is not particularly limited as long as the boron compound content has a predetermined concentration, but is usually 5 minutes to 48 hours, and more preferably 10 minutes to 24 hours is preferable, and the temperature of the cleaning treatment liquid is preferably 10 to 80 ° C., more preferably 20 to 60 ° C.

  The boron compound-containing EVOH pellets after the washing treatment may be dried as necessary. Specifically, it is preferable to dry to a moisture content of about 0.01 to 1% by weight, preferably about 0.05 to 0.5% by weight. As the drying method, the same method as the method for drying the EVOH pellets before adjusting the surface layer boron can be adopted.

  The content of the boron compound in the pellet surface layer portion can be reduced by the above washing treatment, and the boron compound content in the pellet surface layer portion, which is the first feature of the present invention, is reduced to 1.7 ppm or less in terms of boron. EVOH pellets containing boron compounds are obtained.

  Next, the step of incorporating an alkali metal into the EVOH pellet, which is the second feature of the present invention, will be described.

<Step of containing alkali metal>
An EVOH pellet containing an alkali metal can be produced by adding an alkali metal to the EVOH pellet.

As a method for adding an alkali metal to EVOH, for example,
iii) a method of contacting with an alkali metal in the EVOH pellet manufacturing stage,
iv) A method of contacting EVOH pellets prepared in advance with an alkali metal,
v) A method of leaving the alkali metal salt generated in the EVOH saponification step,
Etc.

Examples of the method of contacting the alkali metal in the pellet production stage of iii) include, for example, a method of adding an alkali metal compound to a pellet raw material (EVOH solution / water-containing composition, dry EVOH); For example, a method used for a coagulation liquid when extrusion molding.
When an EVOH solution / water-containing composition is used as a pellet raw material, an alkali metal compound may be dispersed in the EVOH solution / water-containing composition. Moreover, when using dry EVOH pellets as a raw material, the dry EVOH pellets may be melted and the molten EVOH and the alkali metal compound may be melt-kneaded with an extruder.
Preferably, the alkali metal compound is dispersed in the EVOH solution / water-containing composition.

  As a method of contacting the previously prepared EVOH pellet and alkali metal in iv) above, a method of spraying a solution containing an alkali metal onto the EVOH pellet; a method of immersing the EVOH pellet in a solution containing an alkali metal; There are a method in which EVOH pellets are added while stirring a solution containing alkenyl; a method in which an alkali metal compound powder is directly added to EVOH pellets and mixed. Among these, a method of introducing EVOH pellets while stirring a solution containing an alkali metal is preferably used in that an alkali metal can be efficiently contained.

  The concentration of the alkali metal in the solution containing the alkali metal is usually 0.001 to 1% by weight, preferably 0.01 to 0.1% by weight. 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 deteriorate. In addition, as a solvent of the solution containing an alkali metal, the thing similar to the solution containing the said boron compound is mention | raise | lifted.

  In the contact method using the alkali metal-containing solution, the alkali metal concentration depends on the alkali metal concentration in the solution, the contact treatment time, the contact treatment temperature, the stirring speed during the contact treatment, the moisture content of the EVOH pellets to be treated, and the like. It is possible to control the content.

  Moreover, when adding the powder of an alkali metal compound directly to EVOH pellets, the added amount can be set as the content, and the amount of the alkali metal compound to be added is usually 500 ppm or less per EVOH pellet weight in terms of alkali metal. Preferably, it is 400 ppm or less, More preferably, it is 300 ppm or less. In addition, the minimum of alkali metal content is 10 ppm. If the alkali metal content is too low, there is a tendency that the fish eye reduction effect due to reducing the viscosity of EVOH cannot be obtained. If the alkali metal content is too high, the alkali metal salt which has become insufficiently dispersed in EVOH aggregates to cause fish. When the eye is increased or the decomposition of EVOH proceeds excessively, EVOH tends to be colored or odor tends to be generated.

  The method for leaving the alkali metal salt generated in the EVOH saponification step v) above will be described. EVOH is generally produced using an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide as a saponification catalyst. The alkali metal in such a saponification catalyst is inevitably present in EVOH as an alkali metal acetate formed as a by-product during saponification or by forming a salt with a carboxyl group generated in a small amount at the end of the EVOH polymer chain. To do. Incidentally, under such circumstances, the amount of alkali metal present in EVOH is usually about 3000 ppm per EVOH weight in an unwashed state.

  As described above, when the alkali metal remains in the EVOH pellet in a predetermined amount or more, the content of the alkali metal is adjusted to a specific amount specified in the present invention by further washing the EVOH pellet than usual. . If it demonstrates concretely, it will be difficult to remove an alkali metal to the said specific trace concentration only by water washing. Therefore, when EVOH produced by saponification is used, it is preferable to use EVOH washed with an acid washing solution such as acetic acid and then washed 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. Among these, acetic acid is preferably used. Moreover, as water used for a washing | cleaning liquid, the water from which the metal ion as an impurity was removed, such as ion-exchange water, distilled water, filtered water, is preferable.

  Among the methods for containing an alkali metal in the EVOH pellets, iv) is preferred because it can be applied to various pellets and is excellent in versatility. A method of charging EVOH pellets while stirring an alkali metal solution is particularly preferable.

  And as said EVOH pellet, it is preferable to use the EVOH pellet from which the alkali metal generated in the saponification step is removed according to the method of v) from the viewpoint of easy adjustment of the alkali metal content.

  The EVOH pellets containing the alkali metal may be dried as necessary. Specifically, it is preferable to dry to a moisture content of about 0.01 to 1% by weight, particularly about 0.05 to 0.5% by weight. As the drying method, the same method as the method for drying the EVOH pellets before adjusting the surface layer boron can be adopted.

  The EVOH pellet containing an alkali metal is obtained by the above process.

  The boron compound and the alkali metal-containing EVOH pellet of the present invention can be obtained through the step of containing the boron compound, the step of washing the EVOH pellet containing the boron compound, and the step of containing the alkali metal.

  Among them, from the viewpoint of work efficiency, a step of containing a boron compound, a step of bringing a boron compound into contact with an EVOH pellet, a step of containing a boron compound, and a step of containing an alkali metal are performed at the same time, and then the EVOH pellet is washed. It is preferable to perform the process to do. In particular, the step of containing a boron compound is particularly preferably performed in the step ii), and the step of adding an alkali metal is performed in the step iv). In order to simultaneously perform the step of containing the boron compound by bringing the boron compound into contact with the EVOH pellet and the step of containing the alkali metal, the solution containing the boron compound and the alkali metal can be brought into contact with the EVOH pellet. That's fine.

<Boron compound and alkali metal-containing EVOH pellets>
The total content of the boron compound in the boron compound and alkali metal-containing EVOH pellets is preferably 10 to 1000 ppm, more preferably 20 to 500 ppm, and still more preferably 30 to 200 ppm in terms of boron. In addition, the total content of the boron compound in the boron compound and the alkali metal-containing EVOH pellet can be measured by the same method as the amount of the boron compound contained in the EVOH pellet before adjusting the surface layer boron.

  If the boron compound content contained in the boron compound and alkali metal-containing EVOH pellets is too small, the melt viscosity tends to be low and the film forming performance tends to be lowered, and in particular, inflation film formation tends to be difficult. Therefore, it is preferable to contain the boron compound so that the boron content is at least about 10 ppm.

Further, in the boron compound and alkali metal-containing EVOH pellets, the boron compound content in the pellet surface layer portion is 1.7 ppm or less, preferably 1.6 ppm or less, more preferably 1.5 ppm or less, in terms of boron, per pellet weight. It is. The lower limit is not particularly limited, but when the total content of boron compounds in the boron compound and alkali metal-containing EVOH pellets (in terms of boron) is within the above range, it is usually 1 ppb or more, preferably 50 ppb or more, more preferably 100 ppb or more. It is.
When the boron compound content (in terms of boron) in the pellet surface layer portion is too large, fish eyes and the like are likely to be generated, the film appearance is lowered, and the film formability is also lowered.

  Boron compound content (in terms of boron) in the surface layer of the pellet is derived from boron content in a methanol solution obtained after 4 g of a boron compound and alkali metal-containing EVOH pellets are allowed to stand still in 20 mL of methanol at 30 ° C. for 6 hours. It is measured using a coupled plasma mass spectrometer (ICP-MS) and divided by the weight of the EVOH pellet (4 g).

The boron compound and alkali metal-containing EVOH pellet is a weight ratio of the boron compound content (boron conversion) of the surface layer portion to the total boron compound content (boron conversion) in the boron compound and alkali metal-containing EVOH pellet (boron compound of the surface layer portion) Content / total boron compound content) is preferably 1.38 × 10 ⁻² or less, more preferably 1.35 × 10 ⁻² or less, and further preferably 1.30 × 10 ⁻² or less. . If the ratio is too high, fish eyes are likely to be generated, and the film appearance tends to deteriorate. The lower limit is usually 1 × 10 ⁻⁷ .

  Further, the alkali metal content in the boron compound and alkali metal-containing EVOH pellets is 500 ppm or less, preferably 400 ppm or less, more preferably 300 ppm or less, per weight of the boron compound and alkali metal-containing EVOH pellets. In addition, the minimum of the amount of alkali metals is 10 ppm. If the alkali metal content is too small, the effect of suppressing fish eye by reducing the viscosity of EVOH tends to be reduced. If the content is too large, the alkali metal salt that is insufficiently dispersed in EVOH is aggregated. When the fish eye is increased or the decomposition of EVOH proceeds excessively, EVOH tends to be colored or odors tend to be generated.

  The content of the alkali metal means the amount of the alkali metal contained in the surface of the boron compound and the alkali metal-containing EVOH pellet, or in the inside, or both. Specifically, when an alkali metal is contained on the surface of a boron compound and an alkali metal-containing EVOH pellet, the amount of the alkali metal added to the EVOH pellet surface can be regarded as the content. In addition, when an alkali metal is contained inside a boron compound and alkali metal-containing EVOH pellet, for example, the dried EVOH pellet is incinerated and then dissolved in an aqueous hydrochloric acid solution, and then an inductively coupled plasma emission spectrometer (ICP-AES) The value obtained by a method such as quantifying the content of alkali metal from the calibration curve of the standard solution is converted into the content of the whole pellet.

  The water content of the boron compound and alkali metal-containing EVOH pellets 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 plasticization due to water molecules will not occur, and EVOH pellets will be difficult to melt during extrusion molding, which tends to cause fish eye defects due to unmelted materials. Sometimes a foaming phenomenon occurs, and the appearance of the molded product tends to deteriorate.

[Other ingredients]
The boron compound and alkali metal-containing EVOH pellets of the present invention are those other than EVOH generally used in EVOH compositions, as long as the effects of the present invention are not impaired (for example, 20% by weight or less, preferably 10% by weight or less). A resin composition obtained by mixing a resin can also be included.

  In addition, the boron compound and alkali metal-containing EVOH pellets of the present invention generally contain a compounding agent such as a heat stabilizer, an antioxidant, an antistatic agent, and a colorant, as long as the effects of the present invention are not impaired. , UV absorbers, plasticizers, light stabilizers, surfactants, antibacterial agents, drying agents, antiblocking agents, flame retardants, crosslinking agents, curing agents, foaming agents, crystal nucleating agents, antifogging agents, biodegradable additives An agent, a silane coupling agent, an oxygen absorbent and the like may be contained. These may be used alone or in combination of two or more.

  The heat stabilizer is an organic acid such as acetic acid, propionic acid, butyric acid, lauric acid, stearic acid, oleic acid, behenic acid, or an alkali thereof for the purpose of improving various physical properties such as heat stability during melt molding. Metal salts (sodium, potassium, etc.), alkaline earth metal salts (calcium, magnesium, etc.), zinc salts, etc .; or inorganic acids such as sulfuric acid, sulfurous acid, carbonic acid, phosphoric acid, or alkali metal salts thereof (sodium) , Potassium, etc.), alkaline earth metal salts (calcium, magnesium, etc.), zinc salts and the like; Among these, it is particularly preferable to add acetic acid, acetate, and phosphate. These may be used alone or in combination of two or more. Here, when the alkali metal salt is blended, the blending amount is included in the content of the alkali metal in the boron compound of the present invention and the alkali metal-containing EVOH pellet.

  When these components are blended, the blending may be usually performed at any stage before the contact treatment with the boron compound or alkali metal and the EVOH pellet, together with the contact treatment, or after the contact treatment. It is preferable to carry out with the contact treatment in that the influence on the boron compound or alkali metal content is small.

  The blending method of the other components is not particularly limited, but it can usually be carried out by bringing EVOH pellets into contact with a solution containing these blending agents. Therefore, if it is before the contact treatment with a boron compound or an alkali metal, the above formulation is further added by immersing EVOH pellets in a solution containing the above compounding agent or in a solution containing at least one of a boron compound and an alkali metal. It can mix | blend by using the solution which also contained the agent.

  The melt-formed product of the boron compound and alkali metal-containing EVOH pellets of the present invention is excellent in moldability and appearance even if it is a single layer film, but from the viewpoint of water resistance, strength, etc., if necessary, A multilayer structure in which other resin layers are laminated may be used.

Hereinafter, such a multilayer structure will be described.
In producing the multilayer structure, another base material (thermoplastic resin or the like) is laminated on one or both sides of the layer formed using the boron compound and the alkali metal-containing EVOH pellet of the present invention. However, as a lamination method, for example, a method of melt-extrusion laminating another substrate on a film, sheet or the like formed using the boron compound of the present invention and an alkali metal-containing EVOH pellet, etc. A method of melt extrusion laminating the boron compound and alkali metal-containing EVOH pellets of the present invention, a method of co-extruding the boron compound and alkali metal-containing EVOH pellets of the present invention and other substrates, the boron compound and alkali of the present invention A film, sheet or the like (layer) using a metal-containing EVOH pellet or the like and another base material (layer) are combined with organic titanium. Compound, an isocyanate compound, polyester compound, and a method of dry lamination using a known adhesive such as polyurethane compounds. The melt molding temperature at the time of the melt extrusion is often selected from a range of 150 to 300 ° C.

  As such another base material, a thermoplastic resin is useful. Specifically, various polyethylenes such as linear low density polyethylene, low density polyethylene, ultra-low density polyethylene, medium density polyethylene, and high density polyethylene, 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) Of α-olefin) copolymers, polybutenes, polypentenes and other olefins or copolymers, or polyolefins in a broad sense such as those obtained by graft-modifying these olefins alone or copolymers with unsaturated carboxylic acids or esters thereof Resin, polyester resin, polyamide resin Resin (including copolyamide), polyvinyl chloride, polyvinylidene chloride, acrylic resin, polystyrene resin, vinyl ester resin, polyester elastomer, polyurethane elastomer, chlorinated polyethylene, chlorinated polypropylene, aromatic or aliphatic polyketone Further, polyalcohols obtained by reducing these, and EVOH other than EVOH used in the present invention can be mentioned. Polypropylene, ethylene-propylene (block or random) copolymer, polyamide resin, polyethylene, ethylene-vinyl acetate copolymer, polystyrene resin, polyethylene from the point of practicality such as physical properties (particularly strength) of the multilayer structure Terephthalate (PET) and polyethylene naphthalate (PEN) are preferably used.

  Furthermore, other substrates are extrusion-coated on molded articles such as films and sheets formed using the boron compound and alkali metal-containing EVOH pellets of the present invention, films and sheets of other substrates, In the case of laminating using an adhesive or the like, as the base material, in addition to the above thermoplastic resin, any base material (paper, metal foil, uniaxial or biaxially stretched plastic film or sheet and its inorganic deposit, Woven fabric, non-woven fabric, metal strip, wood, etc.) can also be used.

  The layer structure of the multilayer structure includes a layer formed using the boron compound and alkali metal-containing EVOH pellets of the present invention as a (a1, a2,...), And another substrate such as a thermoplastic resin layer. When b (b1, b2,...) is used, the a layer is the innermost layer, and not only a two-layer structure of [inner side] a / b [outer side] (hereinafter the same), for example, a / Arbitrary combinations such as b / a, a1 / a2 / b, a / b1 / b2, a1 / b1 / a2 / b2, a1 / b1 / b2 / a2 / b2 / b1 are possible, and at least the present invention. When R is a regrind layer composed of a mixture of a boron compound and an EVOH pellet containing alkali metal and a thermoplastic resin, for example, a / R / b, a / R / a / b, a / b / R / a / R / b, a / b / a / R / a / b, a / b / R / / It is also possible to R / a / R / b and the like.

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

  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 acid graft-modified ethylene-vinyl acetate copolymer and the like is preferred. At this time, the amount of the unsaturated carboxylic acid or anhydride thereof contained in the thermoplastic resin is preferably 0.001 to 3% by weight, more preferably 0.01 to 1% by weight, particularly preferably 0.03. ~ 0.5 wt%. If the amount of modification in the modified product is too small, the adhesiveness tends to decrease, and conversely if too large, a crosslinking reaction occurs and the moldability tends to decrease.

  Further, these adhesive resins include EVOH derived from the boron compound and alkali metal-containing EVOH pellets of the present invention, other EVOH, rubber / elastomer components such as polyisobutylene, ethylene-propylene rubber, and further, a b-layer resin. Etc. can be blended. In particular, blending a polyolefin resin different from the base polyolefin resin of the adhesive resin is useful because the adhesiveness may be improved.

  The thickness of each layer of the multilayer structure cannot be generally stated depending on the layer configuration, the type of b layer, the use and form of the molded product, the required physical properties, etc. Usually, the a layer is 5 to 500 μm, preferably 10 to 10 μm. 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 about 5 to 400 μm, preferably about 10 to 150 μm.

  The multilayer structure is used in various shapes as it is, but in order to improve the physical properties of the multilayer structure, it is also preferable to perform a heat stretching treatment. Here, the “heat stretching treatment” means a film, a sheet, and a parison-like laminate that have been heated uniformly and uniformly by a molding means such as a chuck, a plug, a vacuum force, a pneumatic force, a blow, and the like. It means an operation for uniformly forming a tube or film. Such stretching may be either uniaxial stretching or biaxial stretching, and it is better to perform stretching at as high a magnification as possible, and pinholes and cracks, stretching unevenness, uneven thickness, and delamination during stretching. A stretched molded article excellent in gas barrier properties that does not cause (delamination: delamination) or the like is obtained.

  As the stretching method for the multilayer structure, a roll stretching method, a tenter stretching method, a tubular stretching method, a stretching blow method, a vacuum / pressure forming method, or the like having a high stretching ratio can be employed. In the case of biaxial stretching, both a simultaneous biaxial stretching method and a sequential biaxial stretching method can be employed. The stretching temperature is selected from the range of about 60 to 170 ° C, preferably about 80 to 160 ° C. It is also preferable to perform heat setting after the end of stretching. The heat setting can be performed by a well-known means, and heat setting 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 tension state. it can.

  In addition, when used for heat shrink packaging applications such as raw meat, processed meat, cheese, etc., after heat stretching after stretching, it is a product film, and after storing the above raw meat, processed meat, cheese, etc. in the film, The film is heat-shrinked at 50 to 130 ° C., preferably 70 to 120 ° C. for about 2 to 300 seconds, so that the film is heat-shrinked for close-packaging.

  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 extrudate. In addition, the above multi-layered structure may be subjected to heat treatment, cooling treatment, rolling treatment, printing treatment, dry laminating treatment, solution or melt coating treatment, bag making processing, deep drawing processing, box processing, tube processing, split processing as necessary. Etc. can be performed.

  Containers and lids made of bags, cups, trays, tubes, bottles, etc. made of films, sheets, stretched films, and the like obtained as described above are seasonings such as mayonnaise and dressing, miso, etc. It is useful as a container for various packaging materials for fermented foods, fats and oils such as salad oil, beverages, cosmetics, and pharmaceuticals.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the description of the examples unless it exceeds the gist.
In the examples, “parts” and “%” mean weight basis.

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

[Measurement evaluation method]
(1) Total content of boron compounds in pellets (in terms of boron)
A solution obtained by treating 0.1 g of EVOH pellets with concentrated nitric acid by the microwave decomposition method and having a constant volume (0.75 mg / mL) in pure water was used as a test solution, and an inductively coupled plasma emission spectrometer (ICP) was used. -AES) (Agilent Technology, 720-ES type). The measured boron content corresponds to the boron content derived from the boron compound. This measurement evaluation method is applied to the EVOH pellets before adjusting the surface layer boron and the EVOH pellets containing boron compound and alkali metal.

(2) Boron compound content in the pellet surface layer (in terms of boron)
4 g of the boron compound and alkali metal-containing EVOH pellets were immersed in 20 mL of methanol (30 ° C.) for 6 hours, and the obtained methanol solution was used as a measurement sample. About this measurement sample, the boron content was measured using an inductively coupled plasma mass spectrometer (ICP-MS) (ELAN DRCII, manufactured by Perkin Elmer), and divided by the EVOH pellet weight (4 g), the pellet surface layer part The boron content of was determined. The measured boron content corresponds to the boron content derived from the boron compound.

(3) Alkali metal content of pellets 2 g of boron compound and alkali metal-containing EVOH pellets were collected in a platinum dish, and several mL of sulfuric acid was added and heated with a gas burner. After confirming that the pellets were carbonized and free of white sulfuric acid smoke, a few drops of sulfuric acid were added and heated again. This operation was repeated until there was no organic matter, and it was completely incinerated. The container after incineration was allowed to cool, and 1 mL of hydrochloric acid was added and dissolved. This hydrochloric acid solution was washed with ultrapure water and made up to a volume of 50 mL. The alkali metal content in the sample solution was measured by an inductively coupled plasma optical emission spectrometer (ICP-AES) (manufactured by Agilent Technologies, 720-ES type). Finally, it was converted from the alkali metal concentration in the solution as the alkali metal content in the EVOH pellet of the sample. Moreover, when adding an alkali metal compound directly to the EVOH pellet surface, the addition amount in terms of alkali metal was regarded as the content.

(4) Moisture content of pellets (%)
Volatiles were determined from the weight of EVOH pellets before drying and the weight of EVOH pellets after drying at 150 ° C. for 5 hours, and this was used as the moisture content of the EVOH pellets. Specifically, the moisture content is represented by the following formula. This measurement evaluation method is applied to EVOH pellets, EVOH pellets before surface layer boron adjustment, and boron compound and alkali metal-containing EVOH pellets.
Moisture content (%) = (EVOH pellet weight before drying−EVOH pellet weight after drying) / EVOH pellet weight before drying × 100

(5) Fisheye A single-layer film having a thickness of 30 μm was formed under the following conditions using a boron compound and an alkali metal-containing EVOH pellet.
(Deposition 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 Setting temperature: C1 / C2 / C3 / C4 / A / D = 190/200/210/210/210/210 ° C.
Screw rotation speed: 20rpm
Roll temperature: 80 ° C
About the 30 micrometer-thick single layer film, the fish eye was measured using the digital defect inspection apparatus (the Mamiya Opie company make, GX-70LT).
The measurement of fish eye is about 100 cm ² (size: 10 cm × 10 cm) with light from the lower surface of the single-layer film and the part that did not transmit light (diameter 0.1-0.2 mm) as one fish eye. This was done by counting the number of fish eyes.
In addition, the reading speed at the time of measurement is 3 m / min.

[Manufacture of EVOH pellets containing boron compound and alkali metal]
<Example 1>
EVOH [ethylene content: 44 mol%, saponification degree: 99.6 mol%, MFR: 3.8 g / 10 min (210 ° C., load 2160 g)] was mixed with a water / methanol mixed solvent [water / methanol = 20/80. (Weight ratio)] solution (60 ° C., EVOH concentration 40%) was extruded into a strand shape in a water tank containing water maintained at 5 ° C. and solidified, then cut with a cutter, and cylindrical A pellet having a diameter of 4 mm and a length of 4 mm was obtained. Next, this EVOH pellet was put into warm water at 30 ° C. and stirred for about 4 hours to obtain a porous EVOH pellet having a water content of 50%.

100 parts of this EVOH pellet is put into 200 parts of an aqueous solution containing 0.0054% boric acid and 0.0407% sodium acetate, and stirred at 30 ° C. for 5 hours, so that the boron compound and alkali metal-containing EVOH pellets before washing are washed. Was recovered.
The boron compound and alkali metal-containing EVOH pellets before washing were dried to a moisture content of 20% by passing nitrogen gas at 75 ° C. for 3 hours in a batch tower type fluidized bed dryer.
Subsequently, 125 degreeC nitrogen gas was passed through for 18 hours using a batch type box ventilation type dryer, and it was dried to a moisture content of 0.3%.
The EVOH pellet before adjusting the surface layer boron containing the alkali metal obtained as described above was subjected to the following cleaning treatment.

  In a stainless steel container, 5 parts of EVOH pellets before surface layer boron adjustment containing the alkali metal and 10 parts of a water / methanol mixed solvent [water / methanol = 3/7 (weight ratio)] as a treatment liquid for cleaning are placed in a stainless steel container. And stirred at 35 ° C. for 1 hour. Thereafter, the pellets were taken out and dried under a nitrogen stream at 120 ° C. for 16 hours. As described above, a boron compound and an alkali metal content EVOH pellet were obtained.

  With respect to the obtained boron compound and alkali metal content EVOH pellets, the total boron compound content, the boron compound content in the surface layer part, the alkali metal content, and the moisture content were measured by the above-described measurement evaluation method. The total boron compound content (in terms of boron) was 128.8 ppm, the boron compound content (in terms of boron) in the surface layer portion was 1.1 ppm, the alkali metal content was 240 ppm, and the water content was 0.13% by weight.

  The obtained boron compound and alkali metal content EVOH pellets were formed into a film at a maximum temperature of 210 ° C. and a screw rotation speed of 20 rpm using a single-layer T-die extrusion device 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 examined by the above-described measurement evaluation method. The results are shown in Table 1 below.

<Example 2>
Except for changing the composition of the cleaning treatment liquid to water / methanol = 1/1 (weight ratio) and adjusting the alkali metal content to the content shown in Table 1 below, as in Example 1, Boron compounds and alkali metal EVOH pellets were obtained. The total boron compound content of the obtained boron and alkali metal EVOH pellets, the boron compound content of the surface layer part, and the alkali metal content were measured (moisture content 0.10%).
Subsequently, using this pellet, a single layer film was produced in the same manner as in Example 1, and the generation of fish eyes was evaluated. The results are shown in Table 1 below.

<Example 3>
In Example 1, the alkali metal content was adjusted to the content shown in Table 1 to obtain a boron compound and an alkali metal-containing EVOH pellet. Moreover, the boron compound content of the obtained boron compound and alkali metal-containing EVOH pellets, the boron compound content of the surface layer part, and the alkali metal content were measured (water content 0.15%).
Subsequently, using this pellet, a single layer film was produced in the same manner as in Example 1, and the generation of fish eyes was evaluated. The results are shown in Table 1 below.

<Comparative example 1>
A boron compound and an alkali metal-containing EVOH pellet were obtained in the same manner as in Example 1 except that the cleaning treatment solution was changed to water. Further, the total content of boron compounds in the obtained boron compound and alkali metal-containing EVOH pellets, the boron compound content in the surface layer portion, and the alkali metal content were measured (water content 0.13%).
Subsequently, using this pellet, a single layer film was produced in the same manner as in Example 1, and the generation of fish eyes was evaluated. The results are shown in Table 1 below.

<Comparative example 2>
A boron compound and an alkali metal-containing EVOH pellet were obtained in the same manner as in Example 1 except that the cleaning with the cleaning treatment liquid was not performed. Moreover, the boron compound total content in a boron compound and an alkali metal containing EVOH pellet, the boron compound content of a surface layer part, and an alkali metal content were measured (water content 0.09%).
Subsequently, using this pellet, a single layer film was produced in the same manner as in Example 1, and the generation of fish eyes was evaluated. The results are shown in Table 1 below.

<Comparative Example 3>
A boron compound and an alkali metal-containing EVOH pellet were obtained in the same manner as in Example 2 except that the alkali metal content was adjusted to the content shown in Table 1 below. The total boron compound content of the obtained boron compound and alkali metal-containing EVOH pellets, the boron compound content of the surface layer portion, and the alkali metal content were measured (water content 0.09%).
Subsequently, using this pellet, a single layer film was produced in the same manner as in Example 1, and the generation of fish eyes was evaluated. The results are shown in Table 1 below.

  The boron compound and alkali metal-containing EVOH of Examples 1 to 3 in which the boron compound content in the surface layer part is 1.7 ppm or less per pellet weight in terms of boron and the alkali metal content is 500 ppm or less per pellet weight The pellet was able to significantly suppress the generation of fish eyes compared to the comparative example.

  The boron compound and alkali metal-containing EVOH pellets of the present invention reduce the content of the boron compound in the surface layer of the pellet and reduce the alkali metal content to a predetermined amount or less, thereby reducing the appearance without impairing moldability. Since it can improve, it can utilize suitably for the field | area with a severe external appearance request | requirement as a packaging material rather than the conventional EVOH pellet.

Claims (5)

An ethylene-vinyl alcohol copolymer pellet containing a boron compound and an alkali metal,
The content of boron compound in the surface layer of the pellet is 1.7 ppm or less per pellet weight in terms of boron, and the content of alkali metal per pellet weight is 500 ppm or less. Copolymer pellets.   2. The ethylene according to claim 1, wherein the total content of the boron compound in the ethylene-vinyl alcohol copolymer pellets containing the boron compound and the alkali metal is 10 to 1000 ppm per pellet weight in terms of boron. -Vinyl alcohol copolymer pellets. Weight ratio of boron compound content (boron conversion) of the pellet surface layer part to total boron compound content (boron conversion) of the whole ethylene-vinyl alcohol copolymer pellets containing the boron compound and alkali metal (surface layer boron) 3. The ethylene-vinyl alcohol copolymer pellets according to claim 1, wherein the compound content / the total content of boron compounds is 1.38 × 10 ⁻² or less.   4. The ethylene according to claim 1, wherein the water content of the ethylene-vinyl alcohol copolymer pellets containing the boron compound and the alkali metal is 0.01 to 1% by weight. -Vinyl alcohol copolymer pellets. The step of containing a boron compound and an alkali metal by bringing the ethylene-vinyl alcohol copolymer pellets into contact with the boron compound and an alkali metal, and washing the pellet obtained by the above step, containing the boron compound in the surface layer of the pellet A method for producing ethylene-vinyl alcohol copolymer pellets comprising a step of making the amount 1.7 ppm or less per weight of ethylene-vinyl alcohol copolymer pellets in terms of boron,
The step of containing the alkali metal is to contain the alkali metal to 500 ppm or less per the pellet weight,
The washing in the washing step is characterized by bringing the dried pellets into contact with a water / alcohol mixed solution or alcohol having a weight ratio of water to alcohol (water / alcohol) of 80/20 to 0/100 or alcohol. A method for producing ethylene-vinyl alcohol copolymer pellets.