JP7031302B2 - Method for producing ethylene-vinyl alcohol-based copolymer pellets and ethylene-vinyl alcohol-based copolymer pellets - Google Patents

Description

The present invention relates to pellets of an ethylene-vinyl alcohol-based copolymer (hereinafter, may be referred to as "EVOH") that can provide a film that generates less fish eyes when formed into a film, and more particularly, the pellet surface. The present invention relates to an EVOH pellet having an adjusted content of a boron compound present in the above and containing an alkali metal, 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. Can show 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.

Therefore, in order to improve the melt moldability, Patent Document 1 describes boric acid or a salt thereof from the viewpoint of film moldability of a melt moldable vinyl alcohol-based copolymer such as EVOH, particularly from the viewpoint of preventing surging during film formation. It is disclosed that it is effective to melt-mold a composition having an increased melt viscosity as the blended composition.

Further, in Patent Document 2, EVOH treated with a boron compound is co-extruded with a polyolefin to obtain a laminate having excellent adhesiveness between the EVOH layer and the polyolefin layer, which is suitable in a field requiring gas barrier performance. It is disclosed that various packaging materials can be provided.
The boron compound treatment of Patent Document 2 is performed by adding a boron compound to an EVOH solution or a 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 an EVOH film or a multilayer structure as a packaging material, improvement is required even for a small fish eye of less than 0.1 mm.
In Patent Document 3, it has been found that the boron-containing EVOH pellets obtained by treating EVOH with a boron compound are related to the generation of fish eyes having a water content of less than 0.1 mm in the pellets, and the water content is 0. 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 examples of Patent Document 3, EVOH pellets to which a boron compound has been added are immersed in water and then dried to adjust the content and water content of the boron compound [moisture content 0.13 to 0]. .4% by weight, boron content per 100 parts by weight of EVOH 0.015 to 0.039 parts by weight (150 to 390 ppm)], and the EVOH pellets are supplied to a multi-layer extruder to supply 3 types and 5 layers of multi-layers. The laminate is manufactured (Examples 1, 3 and 4). Then, the evaluation of the 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]-[0041]. ]).

Special Publication No. 62-3866 Tokusho No. 3-1270 Gazette Japanese Unexamined Patent Publication No. 2000-44756

In recent years, the demand for the appearance of packaging materials has become more and more strict, and it is desired to further improve the fish eye while ensuring melt moldability such as prevention of surging during molding. In particular, when a single layer of EVOH is formed, larger fisheyes tend to be generated and the number of generated fish eyes tends to be larger than in the case of a multilayer structure. Therefore, even in a single layer film of EVOH, fisheyes are generated. Suppressed EVOH pellets have been demanded, and the disclosed techniques of Patent Documents 1 to 3 are still unsatisfactory.

The present invention has been made in view of the above circumstances, and an object thereof is an EVOH pellet containing a boron compound and an alkali metal capable of suppressing the generation of fisheye even in an EVOH single-layer film, and an EVOH pellet thereof. The purpose 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 studies, it is considered that fish eyes are generated by the aggregation of boron compounds causing the local thickening of EVOH. Then, in the case of a single-layer film formation, the boron compound present in the surface layer portion of the pellet, which comes into contact with the metal of the molding machine, tends to aggregate, and as a result, fish eyes are likely to occur, which may be conspicuous.

Further, when EVOH stays inside the extruder, deterioration and gelation proceed, and when this stay is discharged, it leads to the generation of fish eyes. Since the alkali metal has a slimming effect on EVOH, it is considered that the thickening due to cross-linking when EVOH stays inside the extruder can be alleviated, and as a result, the generation of fish eyes can be suppressed.

Furthermore, in view of the above two types of fisheye generation mechanisms, the added alkali metal interacts with the boron compound on the surface of the EVOH pellet to suppress the aggregation of the boron compound that may exist on the surface of the EVOH pellet, resulting in this. It was considered that the generation of fish eyes derived from boron compounds could be suppressed by containing an alkali metal.

Based on this recognition, the present inventors focused on the content of the boron compound in the surface layer of the pellet and the content of the alkali metal, reduced the content of the boron compound in the surface of the pellet from the conventional one, and in EVOH. The present invention has been completed by finding that the fish eye is reduced by containing an alkali metal in the above, and particularly by reducing the content to a predetermined amount or less.
The film (including the layer and the film) obtained by using the EVOH pellet containing boron and the alkali metal of the present invention has excellent moldability and appearance even if it is a single-layer film, and thus is water resistant. From the viewpoint of strength and the like, it can be naturally applied to a multilayer structure in which other resin layers are laminated.

That is, the present invention is an EVOH pellet containing a boron compound and an alkali metal (hereinafter, may be simply referred to as "boron compound and an alkali metal-containing EVOH pellet"), and the content of the boron compound in the surface layer of the pellet is The first gist is an EVOH pellet having a boron equivalent of 1.7 ppm or less per pellet weight and an alkali metal content of 500 ppm or less per pellet weight.

Further, in the present invention, the EVOH pellet is brought into contact with the boron compound and the alkali metal to contain the boron compound and the alkali metal, and the pellet obtained by the above step is washed to contain the boron compound in the surface layer of the pellet. Is a method for producing an EVOH pellet including a step of reducing the amount of the alkali metal to 1.7 ppm or less per EVOH pellet weight in terms of boron, so that the step of containing the alkali metal is such that the alkali metal is 500 ppm or less per the weight of the pellet. In the washing of the above-mentioned washing step, the pellet is brought into contact with a water / alcohol mixed solution or alcohol having a weight ratio (water / alcohol) of 80/20 to 0/100 to alcohol of water. The second gist is a method for producing EVOH pellets.

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

Further, among the present inventions, in particular, when the total content of the boron compound in the entire EVOH pellet containing the boron compound and the alkali metal is 10 to 1000 ppm per the weight of the pellet in terms of boron, the viscosity becomes suitable for film formation. The film performance can be improved, and the effect of suppressing the generation of fish eyes can be excellent.

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

Further, among the present inventions, in particular, when the water content of the boron compound and the alkali metal-containing EVOH pellets is 0.01 to 1% by weight, the effect of further suppressing the generation of fisheye is enhanced. And can improve the appearance of the film.

Further, 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 step, the boron compound content of the pellet surface layer portion is converted into boron. In the method for producing EVOH pellets, which comprises a step of reducing the weight of the EVOH pellet to 1.7 ppm or less, the step of containing the alkali metal is such that the alkali metal is contained so as to be 500 ppm or less per the weight of the pellet. Yes, the washing in the washing step is to bring the pellets after drying into contact with a water / alcohol mixed solution or alcohol having a weight ratio (water / alcohol) of water to alcohol of 80/20 to 0/100. According to the method for producing EVOH pellets of the present invention, it is possible to obtain EVOH pellets containing a boron compound and an alkali metal in which the content of the boron compound in the surface layer is reduced, and the melt-molded product using the pellets has melt-moldability. Is good, and the occurrence of fish eyes is reduced.

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 present specification, the content measured as the amount of boron in the boron compound and the alkali metal-containing EVOH pellet is referred to as "boron compound content (boron equivalent)" or simply "boron content".

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

Here, the "boron compound content in the surface layer of the pellet" refers to the amount of the boron compound present near the surface among the boron compounds contained in the boron compound and the alkali metal-containing EVOH pellet, specifically. , Boron compound and alkali metal-containing EVOH pellets were soaked in 20 mL of methanol at 30 ° C. for 6 hours, and then the boron content in the obtained methanol solution was measured using an induction-bonded plasma mass analyzer (ICP-MS). It was measured and divided by the weight (4 g) of the above EVOH pellets. The "boron compound on the surface layer of the pellet" includes a boron compound that is only attached to the surface of the pellet, a boron compound that has bleeded on the surface, and the like.
The "boron compound content in the surface layer of the pellet" is distinguished from the boron compound content in the boron compound and the alkali metal-containing EVOH pellet ("total boron compound content in the pellet"). be.

The "alkali metal content" of the present invention means the amount of alkali metal contained on the surface, inside, or both of the boron compound and the alkali metal-containing EVOH pellets. Specifically, when the surface of the EVOH pellet containing the boron compound and the alkali metal contains the alkali metal, the amount of the alkali metal added to the surface of the EVOH pellet can be regarded as the content. When an alkali metal is contained inside the EVOH pellet containing a boron compound and an alkali metal, for example, the dried boron compound and the EVOH pellet containing the alkali metal are incinerated and then dissolved in an aqueous hydrochloric acid solution for induction-bonded plasma emission analysis. The value obtained by measuring with a meter (ICP-AES) and quantifying the content of alkali metal from the calibration line of the standard solution is converted into the content of the entire pellet.

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

<EVOH>
The EVOH constituting the boron compound and the alkali metal-containing EVOH pellet of the present invention is usually a resin obtained by saponifying a copolymer (ethylene-vinyl ester-based copolymer) of ethylene and a vinyl ester-based monomer. It is a water-insoluble thermoplastic resin generally referred to as an ethylene-vinyl alcohol-based copolymer or an ethylene-vinyl ester-based copolymer saken product. The polymerization method can also be carried out by using any known polymerization method, for example, solution polymerization, suspension polymerization or emulsion polymerization, but in general, solution polymerization using a lower alcohol such as methanol, particularly preferably methanol as a solvent. Is used. The obtained ethylene-vinyl ester copolymer can also be saponified by a known method.
The EVOH produced in this manner 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, if necessary.

As the vinyl ester-based 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-based monomers include vinyl formate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl capricate, vinyl laurate, vinyl stearate, vinyl versatic acid and the like. An aliphatic vinyl ester; an aromatic vinyl ester such as vinyl benzoate can be mentioned, and an aliphatic vinyl ester having usually 3 to 20 carbon atoms, preferably 4 to 10 carbon atoms, and particularly preferably 4 to 7 carbon atoms is used. Can be done. These are usually used alone, but if necessary, a plurality of types may be used at the same time.

The ethylene and vinyl ester-based monomers usually use petroleum-derived raw materials such as naphtha, 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 monomers from plant-derived raw materials purified from components such as cellulose contained in rice, wheat, millet, grass plants and the like may be used.

The content of ethylene structural units in EVOH is a value measured based on ISO14663, usually 20 to 60 mol%, preferably 25 to 50 mol%, and particularly preferably 27 to 48 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 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. It is 99 to 100 mol%. If the degree of saponification is too low, the gas barrier property, thermal stability, moisture resistance and the like tend to deteriorate.

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, and particularly preferably 2 to 35 g / 10 minutes. Is. 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.

The EVOH used in the present invention may further contain structural units derived from the commonomers shown below, as long as the effects of the present invention are not impaired (for example, 10 mol% or less).

Examples of the comonomer 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-1,2. -Hydrity-containing α-olefins such as diols and esterified products thereof, hydroxyalkylvinylidenes such as 2-methylenepropane-1,3-diol and 3-methylenepentane-1,5-diol; 1,3-diacetoxy-2. -Hydroxyalkyl vinylidene diacetates such as methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, 1,3-dibutyronyloxy-2-methylenepropane, derivatives such as allylicides; acrylic acid, methacrylic acid. , Crotonic acid, (anhydrous) phthalic acid, (anhydrous) maleic acid, (anhydrous) itaconic acid and other unsaturated acids or salts thereof or mono or dialkyl esters having 1 to 18 carbon atoms; acrylamide, having 1 to 18 carbon atoms. Acrylamides such as N-alkylacrylamide, N, N-dimethylacrylamide, 2-acrylamide propanesulfonic acid or a salt thereof, acrylamidepropyldimethylamine or an ester thereof or a quaternary salt thereof; metaacrylamide, N having 1 to 18 carbon atoms. -Methylamidos such as alkylmethylamide, N, N-dimethylmethacrylate, 2-methallylamide propanesulfonic acid or a salt thereof, methallylamide propyldimethylamine or an ester thereof or a quaternary salt thereof; N-vinylpyrrolidone, N. -N-vinylamides such as vinylformamide and N-vinylacetamide; vinyl cyanide such as acrylic nitrile and methacrylic nitrile; vinyl ethers such as alkyl vinyl ethers having 1 to 18 carbon atoms, hydroxyalkyl vinyl ethers and alkoxyalkyl vinyl ethers; vinyl chloride , Vinyl halide compounds such as vinylidene chloride, vinyl fluoride, vinylidene fluoride, vinyl bromide; vinylsilanes such as trimethoxyvinylsilane; allyl halides such as allyl acetate and allyl chloride; allyl alcohol, dimethoxyallyl alcohol Allyl alcohols such as: trimethyl- (3-acrylamide-3-dimethylpropyl) -ammonium chloride, acrylamide-2-methylpropanesulfonic acid and other commonomers. These can be used alone or in combination of two or more.

In particular, EVOH obtained by copolymerizing a hydroxyl group-containing α-olefin is preferable in that the secondary formability is improved. Among them, EVOH having a primary hydroxyl group in the side chain, particularly 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 1,2-diol structural units in the side chain. The 1,2-diol structural unit is specifically a structural unit represented by the following general formula (1).

In the above general formula (1), R ¹ to R ⁶ 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. Saturated hydrocarbon groups such as groups; aromatic hydrocarbon groups such as phenyl groups and benzyl groups; halogen atoms, hydroxyl groups, acyloxy groups, alkoxycarbonyl groups, carboxyl groups, sulfonic acid groups and the like can be mentioned.
R ¹ to R ³ are usually preferably saturated hydrocarbon groups or hydrogen atoms having 1 to 30 carbon atoms, particularly 1 to 15 carbon atoms, and further preferably 1 to 4 carbon atoms, and hydrogen atoms are most preferable. R ⁴ to R ⁶ are usually preferably an alkyl group or a hydrogen atom having 1 to 30 carbon atoms, particularly 1 to 15 carbon atoms, and further preferably 1 to 4 carbon atoms, and a hydrogen atom is most preferable. In particular, it is most preferable that R ¹ to R ⁶ are all hydrogen atoms.

Further, X in the structural unit represented by the general formula (1) is typically a single bond. In addition, X may be a binding chain as long as it does not hinder the effect of the present invention. The bonded chain is not particularly limited, but for example, a hydrocarbon chain such as alkylene, alkenylene, alkynylene, phenylene, and naphthylene (these hydrocarbons may be substituted with halogens such as fluorine, chlorine, and bromine). Other structures containing ether binding sites such as -O-,-(CH ₂ O) m-,-(OCH ₂ ) m-,-(CH ₂ O) mCH ₂ -;-CO-, -COCO-,- Structure containing carbonyl group such as CO (CH ₂ ) mCO-, -CO (C ₆ H ₄ ) CO-; Structure containing sulfur atom such as -S-, -CS-, -SO-, -SO _2- ; Structures containing nitrogen atoms such as -NR-, -CONR-, -NRCO-, -CSNR-, -NRCS-, -NRNR-; Structures containing heteroatoms such as structures containing phosphorus atoms such as -HPO _4- ; Structures containing silicon atoms such as -Si (OR) _2- , -OSi (OR) _2- , -OSi (OR) ₂ O-; -Ti (OR) _2- , -OTi (OR) _2- , -OTi (OR) ₂ Structure containing titanium atom such as O-; Structure containing metal atom such as structure containing aluminum atom such as -Al (OR)-, -OAl (OR)-, -OAl (OR) O-, etc. Can be given.
Further, m is a natural number, and is usually 1 to 30, preferably 1 to 15, and more preferably 1 to 10. Among them, -CH ₂ OCH _2- and a hydrocarbon chain having 1 to 10 carbon atoms are preferable in terms of stability during production or use, and a hydrocarbon chain having 1 to 6 carbon atoms, particularly 1 carbon number of carbon atoms. Is preferable.

The most preferable structure in the 1,2-diol structural unit represented by the general formula (1) is that 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 above general formula (1a) is contained, the content thereof is usually 0.1 to 20 mol%, further 0.1 to 15 mol%, and particularly 0.1. It is preferably from 10 mol%.

Further, the EVOH used in the present invention may be "post-denatured" EVOH such as urethanization, acetalization, cyanoethylation, and oxyalkyleneization.

<Boron compound>
The boron compound used in the present invention includes boric acid or a metal salt thereof, for example, 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.) Etc.), calcium borate, barium borate (barium orthoborate, barium metaborate, barium diborate, barium tetraborate, etc.), magnesium borate (magnesium orthoborate, magnesium diborate, magnesium metaborate, tetraborate) Trimagnesic acid, pentaborate tetraborate, etc.), manganese borate (primary borate, manganese metaborate, manganese tetraborate, etc.), cobalt borate, zinc borate (zinc tetraborate, zinc metaborate, etc.) ), Cadmium borate (cadmium orthoborate, cadmium tetraborate, etc.), silver borate (silver metaborate, silver tetraborate, etc.), copper borate (second copper borate, copper metaborate, copper tetraborate, etc.) Etc.), Nickel borate (nickel orthoborate, nickel diborate, nickel tetraborate, nickel octaborate, etc.), aluminum borate / potassium borate, ammonium borate (ammonium metaborate, ammonium tetraborate, pentaboric acid, etc.) Ammium, ammonium octaborate, etc.), lead borate (lead metaborate, lead hexaborate, etc.), bismuth borate, etc. Examples thereof include borate minerals, and preferred examples include boric acid and boric acid. These can be used alone or in combination of two or more. Here, when the alkali metal salt of the boron compound is contained, the content thereof is included in the content of the alkali metal in the boron compound of the present invention and the alkali metal-containing EVOH pellets.

<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. The content when two or more kinds are used together is the total content of all alkali metals.

Examples of the alkali metal source for containing the alkali metal in the boron compound and the alkali metal-containing EVOH pellet 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 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 more preferable, an aliphatic carboxylate having 2 to 11 carbon atoms is more preferable, and an aliphatic carboxylate salt having 2 to 11 carbon atoms is more preferable. It is an aliphatic monocarboxylic acid salt of 2 to 6, and particularly preferably an acetate.

<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 EVOH in a molten state is extruded from the discharge port of an extruder, cut in a molten state, and then cooled and solidified to produce pellets.
b) Examples include a strand cut method in which EVOH in a molten state is extruded into a coagulation bath and the EVOH strands obtained by cooling and solidifying are cut.

In both of the above a) hot-cut method and b) strand-cut method, the EVOH used as the pellet raw material is (α) by saponifying the solution of the ethylene-vinyl ester-based copolymer in the production of EVOH. The obtained EVOH solution or slurry, or EVOH hydrated composition (hereinafter, may be referred to as "EVOH solution / hydrated composition"); or (β) EVOH (dried EVOH) pellets are melted, and such a molten state is obtained. 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, and the concentration of EVOH in the EVOH water-containing composition is usually 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 tert-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 usually 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, the EVOH solution or slurry may be appropriately dried, 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 dry EVOH is used as a pellet raw material, the temperature of EVOH in the extruder is preferably 150 to 300 ° C, more preferably 160 to 280 ° C, and even more preferably 170 to 250 ° C.
The temperature of the EVOH solution / water-containing composition and the dried EVOH 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 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 that cuts in the atmosphere (air hot cutting method) or an underwater cutting method that is extruded into a cutter installation container filled with cooling water and cut in cooling water.

The temperature of the cooling water in the above-mentioned 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-. The temperature is preferably 20 to 50 ° C, more preferably −5 to 30 ° C.
Further, 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. Therefore, the temperature of the cooling water in the underwater cutting method is the case where the EVOH solution / water-containing composition is used as a raw material. Higher, usually 0-90 ° C, preferably 20-70 ° 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 to be 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.
When dry EVOH 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 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 a porous pellet having a plurality of pores inside the pellet from the viewpoint of the treatment containing a boron compound described later. By infiltrating the boron compound into the pores, the boron compound can be easily retained in the pellet, and the boron compound can be efficiently taken into the pellet. The size of the pores of the porous pellets is not particularly limited as long as the boron compound can penetrate into the pores.

For such porous pellets, the above EVOH water-containing composition is usually used as a pellet raw material, and the EVOH concentration in the EVOH water-containing composition, the type of solvent, the temperature at the time of extrusion, the temperature of the coagulation bath, the residence time, etc. Can be obtained by adjusting.

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

The shape of the EVOH pellet usually depends on the method for producing the pellet, and various shapes can be used. The shape of the EVOH pellet obtained by each of the above methods and the shape of the boron compound and alkali metal-containing EVOH pellet of the present invention is Optional. 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 pellet used in the present invention may be a mixture with other EVOH pellets different from each other, and the other EVOH pellets mentioned above include those having a different content of ethylene structural units, those having a different degree of saponification, and melt flow rate. Examples thereof include those having different (MFR) and those having different other copolymerization components, for example, those having different contents of 1,2-diol structural unit represented by the general formula (1).

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

<Manufacturing of EVOH pellets containing boron compounds and alkali metals>
The boron compound and alkali metal-containing EVOH pellet of the present invention contains a boron compound by contacting the EVOH pellet with the boron compound, a step of containing the alkali metal by contacting the EVOH pellet with the alkali metal, and a step of containing the alkali metal. It can be obtained by washing EVOH pellets containing a boron compound and reducing the content of the boron compound in the surface layer of the pellet to 1.7 ppm or less per the weight of the pellet in terms of boron. Either of these steps may be performed first, or may be performed at the same time. When the above steps are performed at the same time, for example, a solution in which a boron compound and an alkali metal are dissolved can be used.

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

As a method for bringing the above EVOH pellet into contact with the boron compound, for example,
i) A method of contacting EVOH with a boron compound at the EVOH pellet manufacturing stage,
ii) A method of contacting a previously prepared EVOH pellet with a boron compound,
It can be done by such as.

As a method of contacting EVOH with a boron compound in the EVOH pellet production stage of i), for example, a boron compound is added to a pellet raw material (EVOH solution / water-containing composition, dried EVOH), or a solution containing a boron compound is used. Examples thereof include a method used for a coagulating liquid in the production of pellets.
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. When the dried EVOH pellets are melted and the melted EVOH is used as a raw material, the dried EVOH may contain a boron compound in advance.
A method is preferably used in which an EVOH hydrous composition to which a boron compound is added is extruded into a coagulating liquid in the form of strands, and the obtained strands are cleaved.

As a method of contacting the previously prepared EVOH pellets of ii) with the boron compound, a method of spraying a solution containing a boron compound onto the EVOH pellets; a method of immersing the EVOH pellets in a solution containing a boron compound; Examples thereof include a method of adding EVOH pellets while stirring the contained solution. Of these, a method of charging the EVOH pellet while stirring the solution containing the boron compound is preferably used because the boron compound can be efficiently contained even inside the pellet.

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

The concentration of the solution of the boron compound used for the contact treatment between the EVOH pellet and the boron compound is usually 0.001 to 1% by weight, preferably 0.003 to 0.5% by weight. If the concentration is too low, it tends to be difficult to contain a predetermined amount of the boron compound, and if it is too high, the appearance of the finally obtained molded product tends to be deteriorated.

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

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

Among the methods for contacting the EVOH pellet with the boron compound as described above, the method for contacting the EVOH pellet prepared in advance of ii) with the boron compound in that it can be applied to various pellets and has excellent versatility. Is preferable. More preferably, it is a method of contacting the porous EVOH pellet with a solution of a boron compound.

An EVOH pellet containing a boron compound obtained by such a boron compound contact treatment [the content of the boron compound in the surface layer of the pellet has not been adjusted, and the pellet is hereinafter referred to as "EVOH pellet before adjusting the boron in the surface layer"]. The amount of the boron compound contained (total content of the boron compound in the EVOH pellet) is usually 10 to 10000 ppm, preferably 20 to 5000 ppm, and 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 be deteriorated, and if it is too large, the appearance of the finally obtained molded product tends to be deteriorated.

The amount of boron compound [total boron compound content (boron equivalent)] contained in the above-mentioned surface layer portion boron-adjusted EVOH pellet is determined by adding the pellet to a solution obtained by treating the pellet with concentrated nitrate by a microwave decomposition method. The amount measured by an inductively coupled plasma emission spectrometer (ICP-AES) is a test solution prepared by adding pure water to a constant volume.

The surface layer portion boron-adjusted boron compound EVOH pellets obtained by the above steps may be used as they are in the next step, 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 dryer, or the like. It may be dried by the fluidized bed used or static drying using a batch type box dryer, a band dryer, a tunnel dryer, a vertical silo dryer or the like. By passing a gas such as nitrogen gas at 80 to 150 ° C. through the dryer, the surface layer portion of the EVOH pellet before boron adjustment can be efficiently dried without affecting the EVOH pellets.

<Step of cleaning EVOH pellets>
Next, a step of washing the EVOH pellets will be described.
The above-mentioned EVOH pellet before adjusting the boron in the surface layer portion has the content of the boron compound in the surface layer portion of the pellet by the washing treatment, although it depends on the total content of the boron compound contained in the pellet and the content of the boron compound in the surface layer portion of the pellet. Can be adjusted.

The cleaning treatment is performed by bringing the cleaning treatment liquid into contact with the EVOH pellets before adjusting the surface layer boron. Examples of the contact method include a method of immersing the surface layer boron-adjusted EVOH pellet in a cleaning treatment liquid and stirring it, a method of circulating the surface layer boron-adjusted EVOH pellet in the cleaning treatment liquid, and a surface layer. This can be done by spraying a cleaning treatment liquid onto the EVOH pellets before adjusting the partial boron. Further, in the above dipping method, it is also effective to apply vibration such as ultrasonic waves during the dipping. Among the above methods, industrially, industrially, a method of immersing the surface layer boron-adjusted EVOH pellets in a cleaning treatment liquid and stirring them, and a method of circulating the surface layer boron-adjusted EVOH pellets in the cleaning treatment liquid. Is used.

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

Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl-2-propanol and the like having 1 to 8 carbon atoms. In particular, it is preferable to use 1 to 5 and even 1 to 3 alcohols, and among these, methanol is particularly preferably used in terms of easy availability and low cost.

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 /. It is 50 to 20/80. Even if the amount of water is too large or the alcohol concentration is too high, the effect of reducing the boron compound content in the surface layer tends to decrease, so that the water / alcohol mixed solution in the above range is preferable.

In general, the solubility of a boron compound is higher in alcohol than in water. Therefore, it is usual to use alcohol 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 liquid rather than alcohol alone, it is possible to more efficiently elute the boron compound from the EVOH pellet before adjusting the surface layer boron. I found out what I could do. 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 of the boron compound in 10 g of methanol at 23 ° C. is about 15 to 30% by weight.

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

The boron compound-containing EVOH pellets after the cleaning treatment may be dried if 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.

By the above cleaning treatment, the content of the boron compound in the surface layer of the pellet can be reduced, and the content of the boron compound in the surface layer of the pellet, 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, a 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>
The EVOH pellet containing an alkali metal can be produced by including the alkali metal in the EVOH pellet.

As a method of containing an alkali metal in EVOH, for example,
iii) Method of contacting with alkali metal at the EVOH pellet manufacturing stage,
iv) A method of contacting a prefabricated EVOH pellet with an alkali metal,
v) A method for retaining an alkali metal salt generated in the saponification step of EVOH,
It can be done by such as.

As a method of contacting with an alkali metal at the pellet manufacturing stage of iii), for example, a method of adding an alkali metal compound to a pellet raw material (EVOH solution / water-containing composition, dried EVOH); a solution containing an alkali metal is pelleted. Examples thereof include a method used as a coagulating liquid for extrusion molding.
When an EVOH solution / water-containing composition is used as the pellet raw material, the alkali metal compound may be dispersed in the EVOH solution / water-containing composition. When the dried EVOH pellets are used as a raw material, the dried EVOH pellets may be melted and the melted EVOH and the alkali metal compound may be melt-kneaded by an extruder.
A method of dispersing the alkali metal compound in the EVOH solution / water-containing composition is preferable.

As a method of contacting the EVOH pellet prepared in advance in iv) with the alkali metal, a method of spraying the EVOH pellet with a solution containing the alkali metal; a method of immersing the EVOH pellet in the solution containing the alkali metal; A method of adding the EVOH pellets while stirring the solution containing the above; a method of directly adding the powder of the alkali metal compound to the EVOH pellets and mixing them. Of these, a method of charging EVOH pellets while stirring a solution containing an alkali metal is preferably used because the 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 be deteriorated. As the solvent of the solution containing the alkali metal, the same solvent as the solution containing the boron compound can be mentioned.

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

When the powder of the alkali metal compound is directly added to the EVOH pellet, the added amount can be used 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. It is preferably 400 ppm or less, more preferably 300 ppm or less. The lower limit of the alkali metal content is 10 ppm. If the alkali metal content is too low, the fish eye reduction effect by reducing the viscosity of EVOH tends to be lost, and if it is too high, the alkali metal salts with insufficient dispersion in EVOH aggregate and fish. By increasing the number of eyes or excessively decomposing EVOH, EVOH tends to be colored or odor is generated.

The method for retaining the alkali metal salt generated in the saponification step of EVOH in v) will be described. EVOH is 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 saponification catalyst is inevitably present in EVOH as an alkali metal acetate by-produced 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. Incidentally, under such circumstances, the amount of alkali metal present in EVOH is usually about 3000 ppm per weight of EVOH in an unwashed state.

As described above, when the alkali metal remains in the EVOH pellet in an amount of a predetermined amount or more, the content of the alkali metal is adjusted to a specific trace amount specified in the present invention by washing the EVOH pellet more than usual. .. Specifically, it is difficult to remove the alkali metal to the above-mentioned specific trace concentration only by washing with water. 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, 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.

Among the methods for containing an alkali metal in the EVOH pellets, the method of iv), in which the EVOH pellets prepared in advance and the alkali metal are brought into contact with each other, is preferable because it can be applied to various pellets and has excellent versatility. A method of adding EVOH pellets while stirring the alkali metal solution is particularly preferable.

As the EVOH pellets, it is preferable to use EVOH pellets from which the alkali metal generated in the saponification step has been removed according to the method of v), because the content of the alkali metal can be easily adjusted.

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

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

The boron compound and alkali metal-containing EVOH pellets of the present invention can be obtained by going through the steps of containing the boron compound, washing the EVOH pellets containing the boron compound, and the steps of containing the alkali metal.

Among them, from the viewpoint of work efficiency, a step of containing a boron compound, a step of containing a boron compound by contacting the boron compound with an EVOH pellet, and a step of containing an alkali metal are simultaneously performed, and then the EVOH pellet is washed. It is preferable to carry out the step of performing. Among them, it is particularly preferable that the step of containing the boron compound is carried out in the above step ii) and the step of containing the alkali metal is carried out in the above step iv). In order to simultaneously perform the step of containing the boron compound by contacting the boron compound with the EVOH pellet and the step of containing the alkali metal, a solution containing the boron compound and the alkali metal should be brought into contact with the EVOH pellet. All you have to do is.

<EVOH pellets containing boron compounds and alkali metals>
The total content of the boron compound in the boron compound and the alkali metal-containing EVOH pellet is preferably 10 to 1000 ppm, more preferably 20 to 500 ppm, still more preferably 30 to 200 ppm per weight of the pellet in terms of boron. 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 surface layer portion boron-adjusted EVOH pellet.

If the content of the boron compound contained in the boron compound and the alkali metal-containing EVOH pellet is too small, the melt viscosity tends to be low, the film forming performance tends to be deteriorated, and the inflation film forming tends to be particularly 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 surface layer of the pellet is 1.7 ppm or less, preferably 1.6 ppm or less, and more preferably 1.5 ppm or less per weight of the pellet in terms of boron. Is. The lower limit is not particularly limited, but when the total content of the boron compound (boron equivalent) in the boron compound and the alkali metal-containing EVOH pellet is within the above range, it is usually 1 ppb or more, preferably 50 ppb or more, more preferably 100 ppb or more. Is.
If the content of the boron compound (boron equivalent) in the surface layer of the pellet is too large, fish eyes and the like are likely to occur, the appearance of the film is deteriorated, and the film forming property is also deteriorated.

The boron compound content (boron equivalent) on the surface layer of the pellet induces the boron content in the obtained methanol solution after allowing 4 g of the boron compound and alkali metal-containing EVOH pellets to stand and soak in 20 mL of methanol at 30 ° C. for 6 hours. It was measured using an inductively coupled plasma mass spectrometer (ICP-MS) and divided by the weight (4 g) of the above EVOH pellets.

The boron compound and alkali metal-containing EVOH pellets are the weight ratio of the boron compound content (boron equivalent) in the surface layer to the total boron compound content (boron equivalent) in the boron compound and alkali metal-containing EVOH pellets (boron compound in the surface layer). The content / total boron compound content) is preferably 1.38 × 10 ⁻² or less, more preferably 1.35 × 10 ⁻² or less, still more preferably 1.30 × 10 ⁻² or less. .. If the ratio is too high, fish eyes are likely to occur and the appearance of the film tends to be deteriorated. The lower limit is usually 1 × 10 ^-7 .

The alkali metal content in the boron compound and alkali metal-containing EVOH pellets is 500 ppm or less, preferably 400 ppm or less, and more preferably 300 ppm or less, based on the weight of the boron compound and alkali metal-containing EVOH pellets. The lower limit of the amount of alkali metal is 10 ppm. If the alkali metal content is too small, the effect of suppressing fish eyes by reducing the viscosity of EVOH tends to decrease, and if it is too large, the alkali metal salts having insufficient dispersion in EVOH aggregate. By increasing fish eyes or excessively decomposing EVOH, EVOH tends to be colored or odor is generated.

The alkali metal content means the amount of the alkali metal contained on the surface, the inside, or both of the boron compound and the alkali metal-containing EVOH pellets. Specifically, when the surface of the EVOH pellet containing the boron compound and the alkali metal contains the alkali metal, the amount of the alkali metal added to the surface of the EVOH pellet can be regarded as the content. When an alkali metal is contained inside the EVOH pellet containing a boron compound and an alkali metal, for example, the dried EVOH pellet is incinerated and then dissolved in an aqueous solution of hydrochloric acid to be dissolved in 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 line of the standard solution is converted into the content of the entire 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, the EVOH will not be plasticized by water molecules, and the EVOH pellets will be difficult to melt during extrusion molding, and fisheye defects due to unmelted matter will tend to occur. If it is too high, extrusion molding will occur. Occasionally, 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 used in a range 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 resins can also be included.

In addition, the boron compound and alkali metal-containing EVOH 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 absorber, plasticizer, light stabilizer, surfactant, antibacterial agent, desiccant, antiblocking agent, flame retardant, cross-linking agent, hardening agent, foaming agent, crystal nucleating agent, antistatic agent, biodegradation addition Agents, silane coupling agents, oxygen absorbers and the like may be contained. These can be used alone or in combination of two or more.

The heat stabilizer includes organic acids such as acetic acid, propionic acid, butyric acid, lauric acid, stearic acid, oleic acid, and behenic acid, or alkalis thereof, for the purpose of improving various physical properties such as thermal 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, sulfite, carbonic acid, phosphoric acid, etc., or alkali metal salts (sodium) thereof. , Potassium, etc.), alkaline earth metal salts (calcium, magnesium, etc.), salts such as zinc salts; and the like may be added. Of these, acetic acid, acetate, and phosphate are particularly preferable. 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 boron compound of the present invention and the alkali metal-containing EVOH pellets.

When these components are blended, the blending may be usually carried out at any stage before the contact treatment between the boron compound or the alkali metal and the EVOH pellet, 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 content of the boron compound or the alkali metal is small.

The method of blending the other components is not particularly limited, but it can usually be carried out by contacting the EVOH pellet with the solution containing these blending agents. Therefore, before the contact treatment with the boron compound or the alkali metal, the EVOH pellet may be further blended by immersing the EVOH pellet in a solution containing the above-mentioned compounding agent, or in a solution containing at least one of the boron compound and the alkali metal. It can be blended by using a solution containing an agent.

The melt-molded product of the boron compound and the alkali metal-containing EVOH pellet 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 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 boron compound and alkali metal-containing EVOH pellets of the present invention. However, 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 boron compound and the alkali metal-containing EVOH pellet of the present invention, or conversely, on another base material. A method of melt-extruding and laminating a boron compound and an alkali metal-containing EVOH pellet of the present invention, a method of co-extruding the boron compound and the alkali metal-containing EVOH pellet of the present invention with another substrate, the boron compound and the alkali of the present invention. A film, sheet, etc. (layer) made of metal-containing 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. How to do it. 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 boron compound 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 thermoplastic resin. Woven cloth, non-woven fabric, metal cotton strip, wood, etc.) can also be used.

In the layer structure of the multilayer structure, a layer formed by using the boron compound and the alkali metal-containing EVOH pellet of the present invention is a (a1, a2, ...), And another substrate, for example, a thermoplastic resin layer is used. When b (b1, b2, ...) Is used, 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, a / Any combination such as b / a, a1 / a2 / b, a / b1 / b2, a1 / b1 / a2 / b2, a1 / b1 / b2 / a2 / b2 / b1 is possible, and at least the present invention. When the regrind layer composed of a mixture of a boron compound, an alkali metal-containing EVOH pellet, or the like and a thermoplastic resin is R, for example, a / R / b, a / R / a / b, a / b / R / a. It is also possible to use / 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 boron compound 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 the simultaneous biaxial stretching method or the 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 containers and lids made of films, sheets, stretched films, etc. made of cups, trays, tubes, bottles, etc. obtained as described above are not only general foods, but also seasonings such as mayonnaise and dressings, miso, etc. It is useful as a container for various packaging materials such as fermented foods, 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 description of the examples as long as the gist of the present invention is not exceeded.
In the example, "part" and "%" mean the 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 boron compound in pellets (boron equivalent)
An inductively coupled plasma emission spectrometer (ICP) was obtained by treating 0.1 g of EVOH pellets with concentrated nitric acid by a microwave decomposition method and using pure water for a constant volume (0.75 mg / mL) as a test solution. -AES) (Agilent Technologies, 720-ES type) was used for measurement. The measured boron content corresponds to the amount of boron derived from the boron compound. The measurement and evaluation method is applied to the surface layer portion of the EVOH pellet before boron adjustment and the EVOH pellet containing a boron compound and an alkali metal.

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

(3) Alkali metal content of pellets 2 g of a boron compound and an EVOH pellet containing an alkali metal 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 EVOH pellets of the sample. When the alkali metal compound was directly added to the surface of the EVOH pellet, the addition amount in terms of alkali metal was regarded as the content.

(4) Moisture content of pellets (%)
The volatile content was determined from the weight of the EVOH pellet before drying and the weight of the EVOH pellet after drying at a temperature of 150 ° C. for 5 hours, and this was taken as the water content of the EVOH pellet. Specifically, the water content is expressed by the following formula. The measurement and evaluation method is applied to EVOH pellets, EVOH pellets having a surface layer before boron adjustment, and EVOH pellets containing a boron compound and an alkali metal.
Moisture content (%) = (EVOH pellet weight before drying-EVOH pellet weight after drying) / EVOH pellet weight before drying x 100

(5) Using the fisheye boron compound and the alkali metal-containing EVOH pellets, a single-layer film having a thickness of 30 μm was formed under the following conditions.
(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 = 190/200/210/210/210/210 ° C.
Screw rotation speed: 20 rpm
Roll temperature: 80 ° C
Fisheye was measured for a 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 bottom surface of the single-layer film, and the part that does not transmit light (diameter 0.1 to 0.2 mm) is taken as one fisheye, and is around 100 cm ² (size: 10 cm x 10 cm). It was done by counting the number of fish eyes.
The reading speed at the time of measurement is 3 m / min.

[Manufacturing of EVOH pellets containing boron compounds and alkali metals]
<Example 1>
EVOH [ethylene content: 44 mol%, saponification degree: 99.6 mol%, MFR: 3.8 g / 10 minutes (210 ° C., load 2160 g)] with water / methanol mixed solvent [water / methanol = 20/80] (Weight ratio)] The solution (60 ° C, EVOH concentration 40%) dissolved in] was extruded into a strand shape in a water tank containing water maintained at 5 ° C to solidify it, and then cut with a cutter to form a columnar column. Pellets (diameter 4 mm, length 4 mm) were obtained. Next, the EVOH pellets were put into warm water at 30 ° C. and stirred for about 4 hours to obtain porous EVOH pellets having a water content of 50%.

100 parts of this EVOH pellet was 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 to obtain a pre-cleaning boron compound and an alkali metal-containing EVOH pellet. Was recovered.
The pre-cleaning boron compound and the alkali metal-containing EVOH pellets were dried to a moisture content of 20% by passing nitrogen gas at 75 ° C. for 3 hours in a batch column type fluidized bed dryer.
Then, using a batch box type aeration dryer, nitrogen gas at 125 ° C. was passed for 18 hours to dry to a moisture content of 0.3%.
The surface layer boron-adjusted EVOH pellets containing an alkali metal obtained as described above were subjected to the following cleaning treatment.

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

The obtained boron compound and alkali metal content EVOH pellets were measured for the total boron compound content, the boron compound content on the surface layer, the alkali metal content, and the water content by the above measurement and evaluation method. The total content of the boron compound (boron equivalent) was 128.8 ppm, the boron compound content (boron equivalent) of the surface layer 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 using a single-layer T-die extruder at a maximum temperature of 210 ° C. and a screw rotation speed of 20 rpm to produce a single-layer film having a thickness of 30 μm. For this single-layer film, the number of fish eyes generated was examined by the above measurement and evaluation method. The results are shown in Table 1 below.

<Example 2>
The composition of the cleaning treatment liquid was changed to water / methanol = 1/1 (weight ratio), and the alkali metal content was adjusted to the content shown in Table 1 below. Boron compounds and alkali metal EVOH pellets were obtained. The total boron compound content, the boron compound content of the surface layer portion, and the alkali metal content of the obtained boron and alkali metal EVOH pellets were measured (moisture content 0.10%).
Then, using this pellet, a single-layer film was prepared in the same manner as in Example 1, and the occurrence 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 below to obtain EVOH pellets containing a boron compound and an alkali metal. In addition, the total boron compound content, the boron compound content in the surface layer portion, and the alkali metal content of the obtained boron compound and alkali metal-containing EVOH pellets were measured (moisture content 0.15%).
Then, using this pellet, a single-layer film was prepared in the same manner as in Example 1, and the occurrence of fish eyes was evaluated. The results are shown in Table 1 below.

<Comparative Example 1>
EVOH pellets containing a boron compound and an alkali metal were obtained in the same manner as in Example 1 except that the cleaning treatment liquid was changed to water. In addition, the total content of the boron compound in the obtained boron compound and the alkali metal-containing EVOH pellet, the boron compound content in the surface layer portion, and the alkali metal content were measured (moisture content 0.13%).
Then, using this pellet, a single-layer film was prepared in the same manner as in Example 1, and the occurrence of fish eyes was evaluated. The results are shown in Table 1 below.

<Comparative Example 2>
EVOH pellets containing a boron compound and an alkali metal were obtained in the same manner as in Example 1 except that the cleaning with the cleaning treatment liquid was not performed. In addition, the total content of the boron compound in the boron compound and the alkali metal-containing EVOH pellet, the boron compound content of the surface layer portion, and the alkali metal content were measured (water content 0.09%).
Then, using this pellet, a single-layer film was prepared in the same manner as in Example 1, and the occurrence 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, the boron compound content of the surface layer portion, and the alkali metal content of the obtained boron compound and alkali metal-containing EVOH pellets were measured (moisture content 0.09%).
Then, using this pellet, a single-layer film was prepared in the same manner as in Example 1, and the occurrence of fish eyes was evaluated. The results are shown in Table 1 below.

The boron compound content of Examples 1 to 3 and the alkali metal-containing EVOH having a boron compound content in the surface layer portion of 1.7 ppm or less per pellet weight in terms of boron and an alkali metal content of 500 ppm or less per pellet weight. The pellets were able to significantly suppress the occurrence of fish eyes as compared with 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 content of the alkali metal to a predetermined amount or less, so that the appearance is not impaired in formability. Since it can be improved, it can be suitably used in a field where the appearance requirement as a packaging material is stricter than that of the conventional EVOH pellets.

Claims (4)

Ethylene-vinyl alcohol-based copolymer pellets containing a boron compound and an alkali metal.
The content of the boron compound in the surface layer of the pellet is 1.7 ppm or less per the weight of the pellet in terms of boron, and the content of the alkali metal per the weight of the pellet is 500 ppm or less . Weight ratio of boron compound content (boron equivalent) in the surface layer of the pellet to the total boron compound content (boron equivalent) of the entire ethylene-vinyl alcohol copolymer pellet contained (boron compound content in the surface layer / total boron compound) Content) is 1.38 × 10 ⁻² or less, which is an ethylene-vinyl alcohol-based copolymer pellet. The ethylene according to claim 1, wherein the total content of the boron compound in the ethylene-vinyl alcohol-based copolymer pellet containing the boron compound and the alkali metal is 10 to 1000 ppm per the weight of the pellet in terms of boron. -Vinyl alcohol-based copolymer pellets. The ethylene-vinyl alcohol-based copolymer according to claim 1 or 2 , wherein the ethylene-vinyl alcohol-based copolymer pellet containing the boron compound and the alkali metal has a water content of 0.01 to 1% by weight. Combined pellets. The step of bringing the ethylene-vinyl alcohol-based copolymer pellet into contact with the boron compound and the alkali metal to contain the boron compound and the alkali metal, and the pellet obtained by the above step are washed to contain the boron compound in the surface layer of the pellet. A method for producing an ethylene-vinyl alcohol-based copolymer pellet, which comprises a step of reducing the amount to 1.7 ppm or less per weight of the ethylene-vinyl alcohol-based copolymer pellet in terms of boron.
The step of containing the alkali metal is to contain the alkali metal so as to be 500 ppm or less per the weight of the pellet.
The washing in the washing step is characterized in that the pellet after drying is brought into contact with a water / alcohol mixed solution or alcohol having a weight ratio (water / alcohol) of water to alcohol of 80/20 to 0/100. A method for producing ethylene-vinyl alcohol-based copolymer pellets.