JP2023152997A - Ethylene-vinyl alcohol copolymer composition, multilayer structure, method for producing ethylene-vinyl alcohol copolymer composition, and method for producing multilayer structure - Google Patents

Abstract

To provide an ethylene-vinyl alcohol copolymer composition which is suppressed in thermal deterioration during heating such as melt molding.SOLUTION: An ethylene-vinyl alcohol copolymer composition contains an ethylene-vinyl alcohol copolymer (A), a polyolefin resin (B), and a titanium compound (C). The content of the titanium compound (C) in terms of metal is 0.00005 ppm or more and less than 0.5 ppm per mass of the ethylene-vinyl alcohol copolymer composition.SELECTED DRAWING: None

Description

The present invention relates to an ethylene-vinyl alcohol copolymer (hereinafter sometimes referred to as "EVOH resin") composition, a multilayer structure, a method for producing an EVOH resin composition, and a method for producing a multilayer structure.

EVOH resin has excellent transparency, gas barrier properties against oxygen and other gases, aroma retention, solvent resistance, oil resistance, mechanical strength, etc., and can be molded into films, sheets, bottles, etc., and is used as food packaging materials, pharmaceutical packaging materials, It is widely used as a variety of packaging materials such as industrial drug packaging materials and agricultural chemical packaging materials. Although such sheet-like or film-like packaging materials can be made from the EVOH resin alone, they are usually made using an adhesive layer to provide water resistance, strength, and other functions. Therefore, it is often used as a multilayer structure made by laminating polyolefin resins and the like.

In addition, scraps such as scraps of molded products, unnecessary parts such as edges, and defective products generated after manufacturing molded products such as containers from the multilayer structure, and garbage after using the molded products for various purposes, can be removed. The material may be collected and melt-molded, and the collected material may be reused as a recycled layer (hereinafter sometimes referred to as a "regrind layer") in at least one layer of a multilayer structure. When using such a recovered product, there is a demand for a molded product that prevents discoloration of the molded product, suppresses the generation of eye discharge resulting from decomposed products of the EVOH resin, and has an excellent appearance.
In order to improve such poor appearance, a resin composition has been proposed in which a saponified product of ethylene-vinyl acetate copolymer and a thermoplastic resin, such as a polyolefin resin, are blended with higher fatty acid metal salts, hydrotalcite, etc. (See Patent Document 1).

Japanese Patent Application Publication No. 8-311254

Although the resin composition disclosed in Patent Document 1 has improved appearance defects to some extent, it tends to suffer thermal deterioration during heating during melt-kneading, melt-molding, etc., so improvements in long-run properties are required. ing. There is also a need for further quality improvements in molded products when the molded products are collected and reused.

An object of the present invention is to provide an EVOH resin composition in which thermal deterioration of the EVOH resin during heating during melt molding or the like is suppressed, has excellent long-run properties, and is suitable for reuse.

However, in view of such circumstances, the present inventors have obtained an EVOH resin composition in which thermal deterioration of the EVOH resin during heating during melt molding etc. is suppressed by adding a polyolefin resin and a specific trace amount of a titanium compound to the EVOH resin. I found out that it can be done.

That is, the present invention has the following aspects.
[1] An EVOH resin composition containing an EVOH resin (A), a polyolefin resin (B), and a titanium compound (C),
An EVOH resin composition in which the content of the titanium compound (C) in terms of metal is 0.00005 ppm or more and less than 0.5 ppm per mass of the EVOH resin composition.
[2] The EVOH resin composition according to [1], wherein the mass content ratio (A)/(B) of the EVOH resin (A) to the polyolefin resin (B) is 1/99 to 99/1.
[3] The EVOH resin according to [1] or [2], wherein the content of the titanium compound (C) in terms of metal per total mass of the EVOH resin (A) and the titanium compound (C) is 0.001 to 3 ppm. Composition.
[4] The EVOH resin composition according to any one of [1] to [3], wherein the polyolefin resin (B) is a polyolefin resin having a density of 0.89 g/cm ³ or more.
[5] The EVOH resin composition according to [4], wherein the polyolefin resin (B) is polypropylene.
[6] A multilayer structure comprising at least one layer made of the EVOH resin composition according to any one of [1] to [5].
[7] A method for producing the EVOH resin composition according to any one of [1] to [5], comprising:
A method for producing an EVOH resin composition, comprising a step of melt-mixing composition raw materials containing the EVOH resin and a titanium compound.
[8] A method for manufacturing the multilayer structure according to [6], comprising:
A method for producing a multilayer structure, comprising the step of melt-molding a layer made of the EVOH resin composition.

Since the EVOH resin composition of the present invention has excellent thermal stability, it is possible to suppress thermal deterioration of the EVOH resin during heating during melt-kneading, melt-molding, and the like. In particular, those containing a polyolefin resin (B) having a relatively high density and excellent mechanical strength are particularly suitable since they can yield particularly high quality molded products.

In addition, the multilayer structure including the layer made of the resin composition of the present invention suppresses thermal deterioration of the EVOH resin during heating during melt-kneading and melt-molding, so it can be used for various molded products, such as foods, etc. It can be suitably used as a packaging material for medicines, agricultural chemicals, etc. Further, when obtaining a molded product intended for reuse or a molded product requiring relatively high mechanical strength, it is possible to provide a molded product of higher quality, which is suitable.

Hereinafter, the present invention will be described in more detail based on embodiments of the present invention, but the present invention is not limited to these embodiments.
In addition, in the present invention, when expressed as "X to Y" (X, Y are arbitrary numbers), unless otherwise specified, it means "more than or equal to X and less than or equal to Y", and also means "preferably greater than X" or "preferably It also includes the meaning of "less than Y".
In addition, when expressed as "more than or equal to X" (X is any number) or "less than or equal to Y" (Y is any number), it is also possible to indicate that "it is preferably greater than X" or "it is preferably less than Y". It also includes meaning.
In the present invention, "x and/or y (x, y are arbitrary structures or components)" means three combinations: x only, y only, and x and y.

<EVOH resin composition>
The EVOH resin composition according to one embodiment of the present invention (hereinafter referred to as "this EVOH resin composition") comprises an EVOH resin (A), a specific polyolefin resin (B), and a specific trace amount of a titanium compound ( C).
Each component will be explained below.

[EVOH resin (A)]
The EVOH resin (A) used in the present invention is usually a resin obtained by saponifying an ethylene-vinyl ester copolymer, which is a copolymer of ethylene and a vinyl ester monomer, and is a water-insoluble resin. It is a thermoplastic resin.

As the vinyl ester monomer, vinyl acetate is typically used because of its market availability and good efficiency in treating impurities during production. Examples of vinyl ester monomers other than vinyl acetate include vinyl formate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, and versatic acid. Examples include aliphatic vinyl esters such as vinyl, aromatic vinyl esters such as vinyl benzoate, and aliphatic vinyls having usually 3 to 20 carbon atoms, preferably 4 to 10 carbon atoms, and particularly preferably 4 to 7 carbon atoms. Esters are used. These are usually used alone, but multiple types may be used simultaneously if necessary.

The copolymerization method for copolymerizing ethylene and the vinyl ester monomer can be carried out using any known polymerization method, such as solution polymerization, suspension polymerization, emulsion polymerization, etc., but generally methanol is used. Solution polymerization using a solvent is used. Furthermore, the obtained ethylene-vinyl ester copolymer may be saponified by a known method.
The EVOH resin (A) produced in this way mainly contains structural units derived from ethylene and vinyl alcohol structural units, and contains a small amount of vinyl ester structural units that remain without being saponified.

The content of ethylene structural units in the EVOH resin (A) is usually 20 to 60 mol%, preferably 25 to 50 mol%, particularly preferably 25 to 35 mol%. The content of the ethylene structural unit can be controlled by the pressure of ethylene when copolymerizing the vinyl ester monomer and ethylene, and if this content is too low, the gas barrier property under high humidity, melt molding On the other hand, if it is too high, gas barrier properties tend to decrease.
Note that the content of such ethylene structural units can be measured based on ISO14663.

The saponification degree of the EVOH resin (A) is usually 90 to 100 mol%, preferably 95 to 100 mol%, particularly preferably 99 to 100 mol%. The degree of saponification can be controlled by the amount, temperature, time, etc. of the saponification catalyst (usually an alkaline catalyst such as sodium hydroxide is used) when saponifying the ethylene-vinyl ester copolymer. If the degree of oxidation is too low, gas barrier properties, thermal stability, moisture resistance, etc. tend to deteriorate.
The degree of saponification of the EVOH resin (A) can be measured based on JIS K6726 (however, the EVOH resin is used as a solution uniformly dissolved in a water/methanol solvent).

The melt flow rate (MFR) (210°C, load 2160 g) of the EVOH resin (A) is usually 0.5 to 100 g/10 minutes, preferably 1 to 50 g/10 minutes, particularly preferably 3 to 35 g/10 minutes. It's 10 minutes. If the MFR is too large, stability during film formation tends to be impaired, and if it is too small, the viscosity tends to become too high, making melt extrusion difficult.
The MFR is an index of the degree of polymerization of the EVOH resin (A), and can be adjusted by adjusting the amount of polymerization initiator and the amount of solvent when copolymerizing ethylene and vinyl ester monomer.

Further, the EVOH resin (A) may further contain a structural unit derived from a comonomer shown below within a range that does not impede the effects of the present invention (for example, 10 mol% of the EVOH resin (A)). below).
Examples of the comonomer include olefins such as propylene, 1-butene, and isobutene, 3-buten-1-ol, 3-buten-1,2-diol, 4-penten-1-ol, 5-hexene-1, Hydroxy group-containing α-olefins such as 2-diol, and derivatives thereof such as esters and acylated products; Hydroxyalkylvinylidenes such as 2-methylenepropane-1,3-diol and 3-methylenepentane-1,5-diol ; Hydroxyalkyl vinylidene diacetates such as 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, 1,3-dibutyryloxy-2-methylenepropane; Acrylic acid, methacrylic Acid, unsaturated acids such as crotonic acid, phthalic acid (anhydride), maleic acid (anhydride), and itaconic acid (anhydride), or their salts, or mono- or dialkyl esters with an alkyl group having 1 to 18 carbon atoms; acrylamide, alkyl Acrylamides such as N-alkylacrylamide, N,N-dimethylacrylamide, 2-acrylamidopropanesulfonic acid or its salt, acrylamidepropyldimethylamine, its acid salt, or its quaternary salt; meth Acrylamide, N-alkylmethacrylamide whose alkyl group has 1 to 18 carbon atoms, N,N-dimethylmethacrylamide, 2-methacrylamidopropanesulfonic acid or its salt, methacrylamidepropyldimethylamine or its acid salt, or its quaternary Methacrylamides such as salts; N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, and N-vinylacetamide; vinylcyanides such as acrylonitrile and methacrylnitrile; Vinyl ethers such as alkyl vinyl ether, hydroxyalkyl vinyl ether, and alkoxyalkyl vinyl ether; Vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, and vinyl bromide; Vinyl silanes such as trimethoxyvinylsilane; Allyl acetate , allyl halides such as allyl chloride; allyl alcohols such as allyl alcohol and dimethoxyallyl alcohol; comonomers such as trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride and acrylamide-2-methylpropanesulfonic acid. can be given. These can be used alone or in combination of two or more.

Among these, hydroxy group-containing α-olefins are preferred, with 3-butene-1,2-diol and 5-hexene-1,2-diol being particularly preferred. When the hydroxy group-containing α-olefins are copolymerized, the resulting EVOH resin will have a primary hydroxyl group in the side chain. Such an EVOH resin having a primary hydroxyl group in the side chain, particularly an EVOH resin having a 1,2-diol structure in the side chain, is preferable because it maintains gas barrier properties and has good secondary moldability.

When the EVOH resin (A) used in the present invention has a primary hydroxyl group in the side chain, the content of the structural unit derived from the monomer having the primary hydroxyl group is usually 0.1 to 20 mol of the EVOH resin (A). %, preferably 0.5 to 15 mol %, particularly preferably 1 to 10 mol %.

Further, as the EVOH resin (A), it is also possible to use an EVOH resin that has been "post-modified" such as esterification, urethanization, acetalization, cyanoethylation, or oxyalkylenation.

When using the post-modified EVOH resin, the modification rate is usually 10 mol% or less, preferably 4 mol% or less. If the modification rate of the EVOH resin used is too high, it tends to be easily thermally degraded and its long run properties tend to decrease.

Further, the EVOH resin (A) may be a mixture of EVOH resins having different contents of ethylene structural units, degrees of saponification, degrees of polymerization, copolymerization components, and the like.

[Polyolefin resin (B)]
The polyolefin resin (B) used in the present invention is not particularly limited, and examples thereof include linear low density polyethylene (LLDPE), low density polyethylene (LDPE), very low density polyethylene (VLDPE), and medium density polyethylene. (MDPE), high density polyethylene (HDPE), ionomer, ethylene-propylene (block or random) copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, polypropylene (PP), propylene-α- Copolymers of olefins (α-olefins having 4 to 20 carbon atoms), monopolymers or copolymers of olefins such as polybutene, polypentene, polymethylpentene, or monopolymers or copolymers of these olefins with unsaturated carboxylic acids or their Examples include polyolefin resins in a broad sense, such as those graft-modified with esters. These can be used alone or in combination of two or more, and among them, polypropylene (PP), polyethylene (MDPE, HDPE), and blends thereof are preferred in order to obtain molded products with excellent mechanical strength. . In particular, polypropylene is optimal in terms of effectiveness.

The density of the polyolefin resin (B) used in the present invention is usually 0.89 g/cm ³ or more, preferably 0.90 g/cm 3 ^{or more} and less than 0.98 g/cm ³ . For example, when reusing a molded article obtained using the present EVOH resin composition, it may be used to reinforce the mechanical strength of the EVOH resin composition. In order to obtain a resin composition with excellent density and mechanical strength, it is preferable to use a relatively high-density polyolefin resin (B).

In the present EVOH resin composition, the mass content ratio (A)/(B) of EVOH resin (A) to polyolefin resin (B) is preferably 1/99 to 99/1, more preferably 2/98. ~75/25, more preferably 3/97 ~ 50/50, particularly preferably 4/96 ~ 25/75, particularly preferably 5/95 ~ 10/90. When the mass content ratio of the EVOH resin (A) and the olefin polymer (B) is within the above range, the effect of suppressing thermal deterioration will be more excellent.

Further, the total content of EVOH resin (A) and polyolefin resin (B) in the present EVOH resin composition is usually 70% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass. That's all. Note that the upper limit of the total content of the EVOH resin (A) and the polyolefin resin (B) is the total mass of the resin composition excluding the titanium compound (C).

[Titanium compound (C)]
Examples of the titanium compound (C) used in the present invention include inorganic titanium compounds and organic titanium compounds. Note that the titanium compounds may be used alone or in combination of two or more. Among them, inorganic titanium compounds are preferred.

Examples of the inorganic titanium compound include titanium oxide, titanium hydroxide, titanium chloride, and inorganic salts of titanium.
Examples of the titanium oxide include titanium (II) oxide, titanium (III) oxide, titanium (IV) oxide, and titanium suboxide.
Examples of the titanium hydroxide include titanous titanium hydroxide, titanium dihydroxide, and the like.
Examples of the titanium chloride include titanous titanium chloride and titanium chloride.
Examples of the inorganic salt of titanium include titanium phosphate and titanium sulfate.
Among these, titanium oxide is preferred, titanium (IV) oxide is more preferred, and rutile type titanium (IV) oxide is particularly preferred.

Examples of the organic titanium compound include titanium carboxylates such as titanium acetate, titanium butyrate, and titanium stearate.

In addition, the titanium compound (C) may exist in the EVOH resin composition not only as a titanium compound but also in an ionized state or in a complex state that interacts with the EVOH resin or other ligands. It's okay.

The average particle size of the titanium compound (C) is usually 0.001 to 100 μm, preferably 0.01 to 50 μm, and more preferably 0.015 to 20 μm. When the average particle size of the titanium compound is within the above range, thermal stability tends to be further improved.

The content of the titanium compound (C) in terms of metal is 0.00005 ppm or more and less than 0.5 ppm per mass of the EVOH resin composition. Preferably it is 0.0005 to 0.3 ppm, more preferably 0.0015 to 0.2 ppm, particularly preferably 0.005 to 0.1 ppm. By setting the content of the titanium compound (C) within the above range, thermal deterioration during melt molding can be suppressed, resulting in excellent long-run properties. Moreover, if the content of the titanium compound (C) is too small, the effect of suppressing thermal deterioration will be reduced, and if the content is too large, thermal decomposition of the EVOH resin (A) will easily occur and coloration will occur.

The metal equivalent content of the titanium compound (C) is determined by weighing the present EVOH resin composition into a platinum crucible, sequentially incinerating it with a burner and an electric furnace, and heating and decomposing the ashed product with nitric acid and hydrofluoric acid. Titanium in a fixed volume solution obtained by treatment with a mixed acid of nitric acid and dilute hydrofluoric acid is measured by ICP mass spectrometry using an ICP mass spectrometer (manufactured by Agilent Technologies, Agilent 8800). It can be quantified by

Further, the metal equivalent content of the titanium compound (C) per the total mass of the EVOH resin (A) and the titanium compound (C) is preferably 0.001 to 3 ppm, more preferably 0.03 to 1 ppm. The content is particularly preferably 0.05 to 0.5 ppm.
If the content of the titanium compound (C) is too low, the effect of suppressing thermal deterioration will be reduced, and if the content is too high, thermal decomposition of the EVOH resin (A) will easily occur and coloration will occur.

Here, it is generally known that EVOH resin deteriorates due to heat. Although the mechanism is not clear, the reason why thermal deterioration progresses is that a double bond structure is generated in the main chain of the EVOH resin during the above reaction, and this site becomes a reaction starting point, causing further dehydration reaction. This is thought to be due to the formation of a polyene structure in the main chain of the EVOH resin.

On the other hand, if the EVOH resin composition contains a titanium compound, it is thought that the EVOH resin composition will be colored by titanium ions, so it is common general knowledge for those skilled in the art to avoid the use of titanium compounds.

However, in the present invention, contrary to such common technical knowledge, we have developed an EVOH resin whose thermal deterioration is significantly suppressed when a polyolefin resin (B) and a specific trace amount of a titanium compound (C) are used in combination. They have found that a composition can be obtained.

That is, titanium is stable as a tetravalent ion, and even if it is in a small amount, it coordinates with the double bond in the main chain of EVOH resin and stabilizes it by forming a chelate. It is assumed that this suppresses the formation of In addition, when polyolefin resin coexists with titanium compounds, many double bond sites are distributed within the resin composition, which suppresses the formation of further double bonds and further improves thermal stability. Guessed.
On the other hand, if the content of the titanium compound (C) is too large, it is thought that thermal decomposition of the EVOH resin will occur due to the titanium compound (C), so in the present invention, the content of the titanium compound (C) is reduced to a specific trace amount. Limited.

[Other thermoplastic resins]
In addition to the EVOH resin (A) and the polyolefin resin (B), the present EVOH resin composition may contain other thermoplastic resins as resin components within a range that does not impede the effects of the present invention (for example, the present EVOH resin composition). (usually 30% by mass or less, preferably 20% by mass or less, particularly preferably 10% by mass or less).

As other thermoplastic resins, known thermoplastic resins can be used, such as polyester resins, polystyrene resins, polyvinyl chloride resins, polycarbonate resins, polyvinylidene chloride, polyester elastomers, polyurethane elastomers, and chlorine. Examples include chlorinated polyethylene and chlorinated polypropylene. These can be used alone or in combination of two or more.

[Other combination agents]
Further, the present EVOH resin composition may contain additives that are generally blended into EVOH resins within a range that does not impede the effects of the present invention. Examples of the compounding agents include inorganic double salts (such as hydrotalcite), plasticizers (such as aliphatic polyhydric alcohols such as ethylene glycol, glycerin, and hexanediol), and oxygen absorbers [such as aluminum powder and potassium sulfite]. Inorganic oxygen absorbers such as ascorbic acid, its fatty acid esters and metal salts, gallic acid, polyhydric phenols such as hydroxyl group-containing phenol aldehyde resin, terpene compounds, blends of tertiary hydrogen-containing resins and transition metals. (e.g., a combination of polypropylene and cobalt), blends of carbon-carbon unsaturated bond-containing resins and transition metals (e.g., a combination of polybutadiene and cobalt), photooxidatively degradable resins (e.g., polyketones), anthraquinone polymers (e.g., polyvinyl anthraquinone), etc., and polymeric oxygen absorbers such as those containing photoinitiators (benzophenone, etc.), antioxidants and deodorants (activated carbon, etc.) other than those mentioned above], thermally stable Contains additives, light stabilizers, ultraviolet absorbers, colorants, antistatic agents, surfactants (excluding those used as lubricants), antibacterial agents, anti-blocking agents, fillers (e.g. inorganic fillers, etc.). It's okay. These compounds can be used alone or in combination of two or more.

[Method for manufacturing EVOH resin composition]
The present EVOH resin composition is manufactured using the EVOH resin (A), polyolefin resin (B), and titanium compound (C), which are the essential components, and each of the above-mentioned optional components as necessary. Examples of the method include known methods such as a dry blending method, a melt mixing method, a solution mixing method, and an impregnation method. It is preferable to manufacture by including a step of. Moreover, these manufacturing methods can also be combined arbitrarily.

Examples of the dry blending method include a method of dry blending (I) EVOH resin (A) pellets, polyolefin resin (B), and titanium compound (C) using a tumbler or the like.

As the melt mixing method, for example, (II) a dry blend of EVOH resin (A) pellets, polyolefin resin (B), and titanium compound (C) is melt-kneaded to obtain pellets or other molded products. and (III) a method in which polyolefin resin (B) and titanium compound (C) are added to molten EVOH resin (A) and melt-kneaded to obtain pellets or other molded products.

As the solution mixing method, for example, (IV) a solution is prepared using EVOH resin (A) pellets, a polyolefin resin (B) and/or a titanium compound (C) is blended therein, and the mixture is coagulated and molded. In the method of pelletizing, solid-liquid separation and drying, and the manufacturing process of (V) EVOH resin (A), the ethylene-vinyl ester copolymer solution before saponification and the EVOH resin (A) after saponification are used. Examples include a method in which the polyolefin resin (B) and/or the titanium compound (C) are contained in a homogeneous solution (water/alcohol solution, etc.), then coagulated and formed into pellets, solid-liquid separated, and dried.

As the impregnation method, for example, (VI) EVOH resin (A) pellets are brought into contact with an aqueous solution containing a polyolefin resin (B) and/or a titanium compound (C), and the EVOH resin (A) pellets are Examples include a method of impregnating a polyolefin resin (B) and/or a titanium compound (C) and then drying it.

In addition, in each of the above methods, EVOH resin (A) and/or polyolefin resin (B) and titanium compound (C) are blended in a predetermined ratio in advance, and a composition with a high concentration of titanium compound (C) (master It is also possible to obtain a resin composition with a desired concentration by preparing a batch) and blending this composition (masterbatch) with an EVOH resin (A) or a polyolefin resin (B).

Furthermore, in the present invention, it is possible to combine the different methods described above. Among these, the melt-mixing method is preferred, and the method (II) is particularly preferred, since a resin composition with more remarkable productivity and the effects of the present invention can be obtained.

The pellets of the resin composition obtained by each of the above methods and the pellets containing EVOH resin (A) and/or polyamide resin (B) used in each of the above methods may have any shape, such as spherical, Any shape such as an oval shape, a cylindrical shape, a cubic shape, a rectangular parallelepiped shape, etc. can be adopted. The shape of the pellet is usually oval or cylindrical, and its size is such that the diameter of the bottom is usually 1 to 6 mm, preferably 2 mm, from the viewpoint of convenience when later used as a molding material. 5 mm, and the length is usually 1 to 6 mm, preferably 2 to 5 mm. In the case of an oval shape, the major axis is usually 1.5 to 30 mm, preferably 3 to 20 mm, and more preferably 3.5 to 10 mm. The short axis is usually 1 to 10 mm, preferably 2 to 6 mm, particularly preferably 2.5 to 5.5 mm. The method of measuring the major axis and minor axis is, for example, by picking up the pellet, observing it, measuring the major axis using a measuring device such as a caliper, and then visually observing the position of the cross section that has the maximum area among the cross sections perpendicular to the major axis. Another method is to identify it by touch and similarly measure the short axis assuming such a cross section.

In addition, when the present EVOH resin composition is in the form of pellets, it is preferable to attach a known lubricant to the surface of the pellets in order to stabilize the feedability during melt molding. Types of lubricants include, for example, higher fatty acids having 12 or more carbon atoms (for example, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, etc.), higher fatty acid esters (higher fatty acid methyl esters, isopropyl esters, butyl ester, octyl ester, etc.), higher fatty acid amides (for example, saturated higher fatty acid amides such as lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, etc.); Bis-higher fatty acid amides such as saturated higher fatty acid amide, ethylene bis stearic acid amide, ethylene bis oleic acid amide, ethylene bis erucic acid amide, ethylene bis lauric acid amide, etc.), low molecular weight polyolefins (for example, low molecular weight of about 500 to 10,000) (polyethylene, low molecular weight polypropylene, etc., or acid-modified products thereof), higher alcohols having 6 or more carbon atoms, ester oligomers, fluorinated ethylene resins, etc. These compounds can be used alone or in combination of two or more. Further, the content of such a lubricant is usually 5% by mass or less, preferably 1% by mass or less of the EVOH resin composition. Note that the lower limit is usually 0% by mass.

The present EVOH resin composition obtained in this manner can suppress thermal deterioration during heating, and the weight loss rate of the present EVOH resin composition is usually 1.8% or less, preferably It is 1.6% or less, particularly preferably 1.5% or less. The lower the lower limit of the weight reduction rate, the better.
Note that the difference in weight reduction rate of 0.1% appears as a large difference in yield in actual production, so the difference is very large.

The weight loss rate was determined by measuring 5 mg of pellets of the present EVOH resin composition using a thermogravimeter (Pyris 1 TGA, manufactured by Perkin Elmer) under a nitrogen atmosphere, air flow rate: 20 mL/min, temperature: 230 ° C. The weight is measured under conditions of time: 1 hour, and is determined by the following formula.
<Formula>
Weight reduction rate (%) = [(weight before heating - weight after heating) / weight before heating] x 100

Further, the water content of the EVOH resin composition is usually 0.01 to 0.5% by mass, preferably 0.05 to 0.35% by mass, particularly preferably 0.1 to 0.3% by mass. It is.

The water content of the present EVOH resin composition is measured and calculated by the following method.
Weigh the mass (W ₁ ) of the EVOH resin composition before drying using an electronic balance, dry it in a hot air dryer at 150°C for 5 hours, and weigh the mass (W ₂ ) after leaving it to cool in a desiccator for 30 minutes. It is calculated using the formula below.
<Formula>
Moisture content (mass%) = [(W ₁ - W ₂ )/W ₁ ] x 100

The present EVOH resin composition is prepared in various forms such as pellets, powder, and liquid, and is provided as a molding material for various molded products. In particular, in the present invention, it is preferable to provide the material as a material for melt molding, since the effects of the present invention tend to be more efficiently obtained.
Note that the present EVOH resin composition also includes a resin composition obtained by mixing resins other than the EVOH resin (A) and polyamide resin (B) used in the present EVOH resin composition.

Examples of the molded product include a single layer film molded from the present EVOH resin composition, and a multilayer structure having layers made of the present EVOH resin composition.

[Multilayer structure]
A multilayer structure according to an embodiment of the present invention (hereinafter referred to as "this multilayer structure") includes a layer made of the present EVOH resin composition. A layer made of the present EVOH resin composition (hereinafter simply referred to as "the present EVOH resin composition layer") may be formed by using another base material (hereinafter referred to as a base material) containing a thermoplastic resin as a main component other than the present EVOH resin composition. (sometimes abbreviated as "base material resin"), the EVOH resin composition layer can be further strengthened, protected from the effects of moisture, etc., and provided with other functions. be able to.

Examples of the base resin include linear low density polyethylene, low density polyethylene, very low density polyethylene, medium density polyethylene, high density polyethylene, ethylene-propylene (block and random) copolymers, and ethylene-α-olefin. Polyethylene resins such as (α-olefin having 4 to 20 carbon atoms) copolymers, polypropylene, polypropylene resins such as propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers, polybutene, polypentene , (unmodified) polyolefin resins such as polycyclic olefin resins (polymers with a cyclic olefin structure having at least one of a main chain and a side chain), and graft modification of these polyolefins with unsaturated carboxylic acids or their esters. Broadly defined polyolefin resins including modified olefin resins such as unsaturated carboxylic acid-modified polyolefin resins, ionomers, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylic acid ester copolymers, Polyester resin, polyamide resin (including copolyamide polyamide), polyvinyl chloride, polyvinylidene chloride, acrylic resin, polystyrene resin, vinyl ester resin, polyester elastomer, polyurethane elastomer, polystyrene elastomer, chlorinated Examples include halogenated polyolefins such as polyethylene and chlorinated polypropylene, aromatic or aliphatic polyketones, and the like. These can be used alone or in combination of two or more.

Among these, hydrophobic resins such as polyamide resins, polyolefin resins, polyester resins, and polystyrene resins are preferable, and polyethylene resins, polypropylene resins, polycyclic olefin resins, and unsaturated resins thereof are more preferable. Polyolefin resins such as carboxylic acid-modified polyolefin resins, particularly polycyclic olefin resins, are preferably used as hydrophobic resins.

The layer structure of the present multilayer structure is a/b, where the present EVOH resin composition layer is a (a1, a2, ...) and the base resin layer is b (b1, b2, ...). b/a/b, a/b/a, a1/a2/b, a/b1/b2, b2/b1/a/b1/b2, b2/b1/a/b1/a/b1/b2, etc., arbitrary A combination of these is possible. In addition, recycled products containing a mixture of the present EVOH resin composition and a thermoplastic resin other than the present EVOH resin composition obtained by remelting and molding the edges and defective products generated in the process of manufacturing the multilayer structure When the layer is R, b/R/a, b/R/a/b, b/R/a/R/b, b/a/R/a/b, b/R/a/R/a /R/b etc. is also possible. The total number of layers in the present multilayer structure is usually 2 to 15, preferably 3 to 10. In the above layered structure, an adhesive resin layer containing an adhesive resin may be interposed between each layer, if necessary.

As the adhesive resin, any known adhesive resin can be used, and may be appropriately selected depending on the type of thermoplastic resin used for the base resin layer "b". A typical example is a modified polyolefin polymer containing a carboxyl group obtained by chemically bonding an unsaturated carboxylic acid or its anhydride to a polyolefin resin by an addition reaction, a graft reaction, or the like. Examples of the modified polyolefin polymer containing a carboxyl group include maleic anhydride-grafted modified polyethylene, maleic anhydride-grafted modified polypropylene, maleic anhydride-grafted modified ethylene-propylene (block and random) copolymers, and maleic anhydride. Examples include graft-modified ethylene-ethyl acrylate copolymer, maleic anhydride graft-modified ethylene-vinyl acetate copolymer, maleic anhydride-modified polycyclic olefin resin, maleic anhydride graft-modified polyolefin resin, and the like. These may be used alone or in combination of two or more.

In this multilayer structure, when an adhesive resin layer is used between the present EVOH resin composition layer and the base resin layer, since the adhesive resin layer is located on both sides of the present EVOH resin composition layer, the hydrophobic It is preferable to use an adhesive resin with excellent properties.

The base resin and the adhesive resin may contain a conventionally known plasticizer within a range that does not impede the spirit of the present invention (for example, 30% by mass or less, preferably 10% by mass or less based on the entire resin). , fillers, clays (such as montmorillonite), colorants, antioxidants, antistatic agents, lubricants, core materials, antiblocking agents, waxes, and the like. These can be used alone or in combination of two or more.

Lamination of the present EVOH resin composition layer and the base resin layer (including the case where an adhesive resin layer is interposed) can be performed by a known method. For example, a method of melt extrusion laminating a base resin on a film, sheet, etc. of the present EVOH resin composition, a method of melt extrusion laminating the present EVOH resin composition on a base resin layer, a method of melt extrusion laminating the present EVOH resin composition and a base resin, A method of dry laminating the present EVOH resin composition (layer) and a base resin (layer) using a known adhesive such as an organic titanium compound, an isocyanate compound, a polyester compound, or a polyurethane compound. Examples include a method in which a solution of the present EVOH resin composition is applied onto the base resin and then the solvent is removed. Among these, in consideration from the viewpoint of cost and environment, the present EVOH resin composition layer can be manufactured by including a step of melt molding. Specifically, a coextrusion method is preferred.

This multilayer structure may be subjected to (heating) stretching treatment if necessary. The stretching treatment may be either uniaxial stretching or biaxial stretching, and in the case of biaxial stretching, simultaneous stretching or sequential stretching may be performed. Further, as the stretching method, a method with a high stretching ratio among roll stretching methods, tenter stretching methods, tubular stretching methods, stretch blowing methods, vacuum-pressure forming, etc. can be adopted. The stretching temperature is selected from the range of usually 40 to 170°C, preferably about 60 to 160°C, near the melting point of the multilayer structure. If the stretching temperature is too low, the stretchability will be poor, and if it is too high, it will be difficult to maintain a stable stretched state.

Further, the present multilayer structure after the stretching treatment may be heat-set for the purpose of imparting dimensional stability. Heat fixation can be carried out by well-known means. For example, the stretched multilayer structure is heat-treated at a temperature of usually 80 to 180°C, preferably 100 to 165°C, for about 2 to 600 seconds while maintaining a tensioned state. conduct.

When the stretched multilayer structure is used as a shrink film, in order to impart heat shrinkability, the above heat setting is not performed, and the stretched multilayer structure is, for example, blown with cold air. Processing such as cooling and fixing may be performed.

The thickness of the present multilayer structure (including the stretched one) and the thickness of the present EVOH resin composition layer, base resin layer, and adhesive resin layer that constitute the multilayer structure are determined by the layer structure and the type of base resin. The thickness of the present multilayer structure (including the stretched one) is usually 10 to 5000 μm, preferably 30 to 3000 μm, although it cannot be definitively stated depending on the type of adhesive resin, application, packaging form, required physical properties, etc. Particularly preferred is 50 to 2000 μm. The EVOH resin composition layer is usually 1 to 500 μm, preferably 3 to 300 μm, particularly preferably 5 to 200 μm, and the base resin layer is usually 5 to 3000 μm, preferably 10 to 2000 μm, particularly preferably 20 to 1000 μm. The adhesive resin layer has a thickness of usually 0.5 to 250 μm, preferably 1 to 150 μm, particularly preferably 3 to 100 μm.

Furthermore, in the present multilayer structure, the thickness ratio of the present EVOH resin composition layer to the base resin layer (present EVOH resin composition layer/base material resin layer) is the thickness ratio between the thickest layers when there is a plurality of each layer. The ratio is usually 1/99 to 50/50, preferably 5/95 to 45/55, particularly preferably 10/90 to 40/60. In addition, the thickness ratio of the present EVOH resin composition layer to the adhesive resin layer in the present multilayer structure (present EVOH resin composition layer/adhesive resin layer) is the ratio of the thickest layers when there is a plurality of each layer. The ratio is usually 10/90 to 99/1, preferably 20/80 to 95/5, particularly preferably 50/50 to 90/10.

Moreover, it is also possible to obtain a multilayer container in the form of a cup or a tray using the present multilayer structure. In that case, a draw forming method is usually employed, and specific examples thereof include a vacuum forming method, a pressure forming method, a vacuum pressure forming method, a plug-assisted vacuum pressure forming method, and the like. Furthermore, when obtaining a tube or bottle-shaped multilayer container (laminate structure) from a multilayer parison (a hollow tubular preform before blowing), a blow molding method is employed. Specifically, extrusion blow molding methods (double-head type, moving mold type, parison shift type, rotary type, accumulator type, horizontal parison type, etc.), cold parison blow molding, injection blow molding, biaxial stretching Examples include blow molding methods (extrusion type cold parison biaxial stretch blow molding method, injection type cold parison biaxial stretch blow molding method, injection molding inline type biaxial stretch blow molding method, etc.). The obtained laminate may be subjected to heat treatment, cooling treatment, rolling treatment, printing treatment, dry lamination treatment, solution or melt coating treatment, bag making processing, deep drawing processing, box processing, tube processing, split processing, etc. as necessary. I can do it.

Bags made of films, sheets, and stretched films obtained using this multilayer structure, as well as containers and lids made of cups, trays, tubes, bottles, etc., can be used for general foods, seasonings such as mayonnaise, dressing, etc. It is useful as a variety of packaging material containers for fermented foods such as miso, oil and fat foods such as salad oil, beverages, cosmetics, pharmaceuticals, etc. In particular, the present EVOH resin composition using a polyolefin resin (B) with excellent mechanical strength is a molding resin material that has excellent mechanical strength and is suppressed from discoloration due to thermal deterioration. Therefore, it is particularly useful as a packaging material that requires high mechanical strength and a beautiful appearance. Furthermore, since it has excellent thermal stability even after being subjected to repeated thermal history, it is useful as a packaging material etc. that is intended to be reused.

Hereinafter, the present invention will be specifically explained with reference to Examples. However, the present invention is not limited in any way by the following examples.
In addition, "part" in the examples means a mass standard unless otherwise specified.

<Example 1>
As the EVOH resin (A), pellets of an EVOH resin having an ethylene structural unit content of 29 mol %, a degree of saponification of 99.6 mol %, and an MFR of 4 g/10 minutes (210° C., load 2160 g) were used.
In addition, polypropylene (manufactured by Nippon Polypro Co., Ltd., EA9, density: 0.90 g/cm ³ ) was used as the polyolefin resin (B), and titanium oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as the titanium compound (C). there was.

150 parts of pellets of the EVOH resin (A), 2850 parts of the polyolefin resin (B), and the titanium oxide are dry blended so that the metal equivalent content is 0.01 ppm per mass of the EVOH resin composition, A mixture was obtained. The mixture was then supplied to a twin-screw extruder (20 mmφ) equipped with a two-hole die, extruded under the following extrusion conditions, and the extruded strand was cooled and solidified in a water tank. Next, water droplets on the surface of the strand were removed by blowing air onto the solidified strand, and then cut to obtain pellets of the EVOH resin composition.

[Extrusion conditions]
Extruder setting temperature (℃): C1/C2/C3/C4/C5/C6
=150/200/210/210/210/210

<Example 2>
Pellets of an EVOH resin composition were obtained in the same manner as in Example 1, except that the amount of titanium oxide was changed to 0.083 ppm per mass of the EVOH resin composition in metal terms.

<Comparative example 1>
Pellets of an EVOH resin composition were obtained in the same manner as in Example 1, except that titanium oxide was not used.

<Comparative example 2>
Pellets of an EVOH resin composition were obtained in the same manner as in Example 1, except that the amount of titanium oxide was changed to 0.83 ppm per mass of the EVOH resin composition in metal terms.

The following thermal stability evaluation was performed using the obtained pellets of the EVOH resin compositions of Examples 1 and 2 and Comparative Examples 1 and 2. The results are shown in Table 1 below.

[Thermal stability evaluation]
Using 5 mg of the obtained pellets of the EVOH resin composition, the conditions were measured using a thermogravimetric analyzer (manufactured by PerkinElmer, Pyris 1 TGA) under nitrogen atmosphere, air flow rate: 20 mL/min, temperature: 230°C, time: 1 hour. The weight at the bottom was measured, and the weight loss rate was determined using the following formula. The lower the value, the less the resin composition is decomposed, and the better the thermal stability of the resin composition.
<Formula>
Weight reduction rate (%) = [(weight before heating - weight after heating) / weight before heating] x 100

From Table 1 above, the EVOH resin compositions of Examples 1 and 2 containing a polyolefin resin (B) and a specific trace amount of a titanium compound (C) are different from the EVOH resin of Comparative Example 1 containing no titanium compound (C). It can be seen that the composition shows a small change in weight and has excellent thermal stability compared to the EVOH resin composition of Comparative Example 2 containing titanium compound (C) in an amount larger than the specific range.
Further, the multilayer structure including the layers made of the EVOH resin compositions of Examples 1 and 2 also has excellent thermal stability with suppressed thermal deterioration.

This EVOH resin composition suppresses thermal deterioration during heating during melt molding, etc., so it can be used in various foods, seasonings such as mayonnaise and dressing, fermented foods such as miso, oil and fat foods such as salad oil, water, etc. It is useful as a variety of packaging materials for beverages, cosmetics, pharmaceuticals, etc.

Claims (8)

An ethylene-vinyl alcohol copolymer composition containing an ethylene-vinyl alcohol copolymer (A), a polyolefin resin (B), and a titanium compound (C),
An ethylene-vinyl alcohol copolymer composition in which the content of the titanium compound (C) in terms of metal is 0.00005 ppm or more and less than 0.5 ppm per mass of the ethylene-vinyl alcohol copolymer composition. The ethylene-vinyl alcohol according to claim 1, wherein the mass content ratio (A)/(B) of the ethylene-vinyl alcohol copolymer (A) to the polyolefin resin (B) is 1/99 to 99/1. based copolymer composition. The ethylene according to claim 1 or 2, wherein the content of the titanium compound (C) in terms of metal per total mass of the ethylene-vinyl alcohol copolymer (A) and the titanium compound (C) is 0.001 to 3 ppm. - Vinyl alcohol copolymer composition. The ethylene-vinyl alcohol copolymer composition according to claim 1 or 2, wherein the polyolefin resin (B) is a polyolefin resin having a density of 0.89 g/cm ³ or more. The ethylene-vinyl alcohol copolymer composition according to claim 4, wherein the polyolefin resin (B) is polypropylene. A multilayer structure comprising at least one layer made of the ethylene-vinyl alcohol copolymer composition according to claim 1 or 2. A method for producing the ethylene-vinyl alcohol copolymer composition according to claim 1 or 2, comprising:
A method for producing an ethylene-vinyl alcohol copolymer composition, comprising the step of melt-mixing composition raw materials containing the ethylene-vinyl alcohol copolymer and a titanium compound. A method for manufacturing the multilayer structure according to claim 6, comprising:
A method for producing a multilayer structure, comprising the step of melt-molding a layer made of the ethylene-vinyl alcohol copolymer composition.