阅读说明：本技术 乙烯-乙烯醇系共聚物组合物、粒料组及多层结构体 (Ethylene-vinyl alcohol copolymer composition, pellet group, and multilayer structure ) 是由 碓氷真太郎 西村大知 池下美奈子 于 2018-06-27 设计创作，主要内容包括：本发明提供一种着色被抑制、热稳定性优异的乙烯-乙烯醇系共聚物组合物,其含有：具有乙烯结构单元含量不同的2种以上乙烯-乙烯醇系共聚物的乙烯-乙烯醇系共聚物(A)、及铁化合物(B),所述铁化合物B的含量在单位重量的乙烯-乙烯醇系共聚物组合物中以金属换算计为0.01～5ppm。(The present invention provides an ethylene-vinyl alcohol copolymer composition with suppressed coloration and excellent thermal stability, which comprises: an ethylene-vinyl alcohol copolymer (A) comprising 2 or more ethylene-vinyl alcohol copolymers having different ethylene structural unit contents, and an iron compound (B), wherein the iron compound (B) is contained in an amount of 0.01 to 5ppm in terms of metal in a unit weight of the ethylene-vinyl alcohol copolymer composition.)

1. An ethylene-vinyl alcohol copolymer composition comprising: an ethylene-vinyl alcohol copolymer A comprising 2 or more ethylene-vinyl alcohol copolymers having different ethylene structural unit contents, and an iron compound B, wherein the iron compound B is contained in an amount of 0.01 to 5ppm in terms of metal in a unit weight of the ethylene-vinyl alcohol copolymer composition.

2. The ethylene-vinyl alcohol copolymer composition according to claim 1, wherein the difference in the content of the ethylene structural unit between the ethylene-vinyl alcohol copolymer A having 2 or more types of ethylene-vinyl alcohol copolymers having different ethylene structural unit contents is 2 mol% or more.

3. The ethylene-vinyl alcohol copolymer composition according to claim 1 or 2, wherein the ethylene-vinyl alcohol copolymer a having 2 or more ethylene-vinyl alcohol copolymers having different ethylene structural unit contents has at least: an ethylene-vinyl alcohol copolymer A1 having an ethylene structural unit content of less than 35 mol%, and an ethylene-vinyl alcohol copolymer A2 having an ethylene structural unit content of 35 mol% or more.

4. The ethylene-vinyl alcohol copolymer composition according to claim 3, wherein the weight blending ratio of the ethylene-vinyl alcohol copolymer A1 having an ethylene structural unit content of less than 35 mol% to the ethylene-vinyl alcohol copolymer A2 having an ethylene structural unit content of 35 mol% or more is A1/A2-90/10-10/90.

5. A pellet group comprising the ethylene-vinyl alcohol copolymer composition according to any one of claims 1 to 4.

6. A multilayer structure comprising a layer formed from the ethylene-vinyl alcohol copolymer composition according to any one of claims 1 to 4.

Technical Field

The present invention relates to an EVOH resin composition containing an ethylene-vinyl alcohol copolymer (hereinafter referred to as "EVOH resin") as a main component, a pellet group formed of the EVOH resin composition, and a multilayer structure, and more specifically, to an EVOH resin composition with suppressed coloration and excellent thermal stability, a pellet group formed of the EVOH resin composition, and a multilayer structure having a layer formed of the EVOH resin composition.

Background

EVOH resins, particularly ethylene-vinyl acetate copolymer saponified products, are widely used in various applications such as films, sheets, containers, and fibers because of their excellent properties such as gas barrier properties and mechanical strength.

EVOH resins tend to have more excellent stretchability as the content of ethylene structural units (hereinafter referred to as "ethylene content") is higher. On the other hand, the higher the ethylene content (the lower the content of the vinyl alcohol structural unit (hereinafter referred to as "vinyl alcohol content"), the lower the gas barrier property. In order to achieve both of the gas barrier property and the stretchability, it is proposed to use an EVOH resin having a high vinyl alcohol content (in other words, having a low ethylene content and a high saponification degree) in combination with an EVOH resin having a low vinyl alcohol content (in other words, having a high ethylene content and a low saponification degree).

For example, Japanese patent application laid-open No. Sho 63-230757 (see, for example, patent document 1) proposes a composition using EVOH resins having different ethylene contents and saponification degrees in combination. Patent document 1 describes that a molded article obtained by vacuum-pressure air-molding a laminate laminated with polystyrene layers, in which an EVOH resin composition used in combination has a difference in ethylene content of 4 mol% or more and a difference in saponification degree of 3 mol% or more and a difference in solubility parameter of a predetermined value or more is used as an intermediate layer, is excellent in transparency and appearance, is free from cracks and thickness unevenness, and is also excellent in gas barrier properties.

Japanese patent application laid-open No. 8-311276 (see, for example, patent document 2) discloses: an EVOH resin composition containing 2 kinds of EVOH resins having a difference in ethylene content of 3 to 20 mol% and having a specific boron concentration. It is disclosed that a laminated film obtained by laminating polypropylene layers via an adhesive resin layer with the EVOH resin composition as an intermediate layer is free from uneven stretching such as whitening and streaks even when it is subjected to heat stretching (stretching 4 times in the machine direction and 6 times in the transverse direction).

In order to produce various molded articles by using the above-mentioned technique, melt molding such as extrusion molding or injection molding is performed, but when an EVOH resin composition is melt molded, thermal degradation is likely to occur. In particular, in the method using different EVOH resins, since EVOH resins having different melting points are melt-molded at a single temperature, EVOH resins having a low melting point tend to be thermally deteriorated and easily colored.

As a method for suppressing such coloring that occurs when different EVOH resins are used, for example, the following techniques are known: an EVOH resin having a molecular weight measured after heat treatment at 220 ℃ for 50 hours in a nitrogen atmosphere and satisfying specific conditions was used (see, for example, patent document 3). However, in order to produce EVOH resins satisfying the above-described specific conditions, it is necessary to adjust various production conditions, and an easier improvement method is required.

Disclosure of Invention

Problems to be solved by the invention

Under such a background, an object of the present invention is to provide a resin composition containing 2 or more kinds of EVOH resins having different melting points, which is suppressed in coloring even after heat treatment and is excellent in thermal stability.

Means for solving the problems

However, the present inventors have made extensive studies in view of the above circumstances, and as a result, they have found that an EVOH resin composition in which coloring is suppressed even after heat treatment can be obtained by blending a specific trace amount of an iron compound into a resin composition containing 2 or more EVOH resins having different ethylene contents.

That is, a first aspect of the present invention is an EVOH resin composition comprising: EVOH resin (A) having at least 2 EVOH resins with different ethylene contents, and an iron compound (B), wherein the content of the iron compound (B) is 0.01 to 5ppm in terms of metal in the EVOH resin composition per unit weight. A second aspect of the present invention is a pellet group formed from the EVOH resin composition, and a third aspect of the present invention is a multilayer structure including a layer formed from the EVOH resin composition.

ADVANTAGEOUS EFFECTS OF INVENTION

The EVOH resin composition of the present invention contains an EVOH resin (A) having 2 or more EVOH resins having different ethylene contents and an iron compound (B), and the content of the iron compound (B) is 0.01 to 5ppm in terms of metal in the EVOH resin composition per unit weight, so that coloring is suppressed even after heat treatment and thermal stability is excellent.

In addition, when the difference between the ethylene contents of the EVOH resin (a) having 2 or more kinds of EVOH resins having different ethylene contents, the EVOH resin having the highest ethylene content and the EVOH resin having the lowest ethylene content is 2 mol% or more, the coloring is further suppressed, and the thermal stability is excellent.

If the EVOH resin (a) having 2 or more kinds of EVOH resins having different ethylene contents has at least EVOH resin (a1) having an ethylene content of less than 35 mol% and EVOH resin (a2) having an ethylene content of 35 mol% or more, coloration is further suppressed, and thermal stability is excellent.

Further, when the weight blending ratio of the EVOH resin (a1) having an ethylene content of less than 35 mol% to the EVOH resin (a2) having an ethylene content of 35 mol% or more is (a1)/(a2) — 90/10 to 10/90, coloring is further suppressed, and thermal stability is excellent.

The pellet group formed from the EVOH resin composition of the present invention is suppressed in coloring and excellent in thermal stability, and therefore, can be suitably used as a packaging material for various molded articles, for example, food, medicine, agricultural chemicals, and the like.

The multilayer structure having a layer formed of the EVOH resin composition of the present invention is particularly useful as a packaging material for foods, medicines, agricultural chemicals, and the like, for example, because of its good quality.

Detailed Description

The configuration of the present invention will be described in detail below, but these are examples of preferred embodiments and are not limited to these.

[ EVOH resin (A) ]

The EVOH resin is generally 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 thermoplastic resin. The EVOH resin (a) used in the present invention has 2 or more kinds of EVOH resins having different ethylene contents. The ethylene content of the EVOH resin is a value measured in accordance with ISO 14663.

The difference in ethylene content between the EVOH resin (a) having the highest ethylene content and the EVOH resin having the lowest ethylene content is preferably 2 mol% or more, more preferably 2 to 25 mol%, even more preferably 4 to 20 mol%, and particularly preferably 5 to 18 mol%. When the difference in ethylene content is too small, it tends to be difficult to maintain the balance between moldability and gas barrier properties, and when it is too large, compatibility with each other tends to be lowered.

The difference in ethylene content between 2 or more kinds of EVOH resins contained in the EVOH resin (a) can be determined by measuring the melting peak temperature. That is, since the ethylene content of the EVOH resin generally correlates with the melting point of the EVOH resin, the ethylene content of 2 or more species of EVOH resins contained in the EVOH resin (a) can be calculated by measuring the melting peak temperature of the EVOH resin composition of the present invention. The melting peak temperature is a peak temperature measured by a Differential Scanning Calorimeter (DSC) at 10 ℃ per minute from-50 ℃ to 230 ℃, at 10 ℃ per minute from 230 ℃ to-50 ℃, and at 10 ℃ per minute from-50 ℃ to 230 ℃.

The EVOH resin (A) used in the present invention has a melting peak temperature difference obtained by the above-mentioned measurement method of usually 3 ℃ or more, preferably 3 to 40 ℃, more preferably 10 to 35 ℃, and particularly preferably 20 to 30 ℃. When the temperature difference is too small, it tends to be difficult to maintain the balance between moldability and gas barrier properties, and when it is too large, compatibility with each other tends to be lowered.

The number of types of EVOH resins having different ethylene contents in the EVOH resin (A) is usually 2 to 4, preferably 2 to 3, and particularly preferably 2. The larger the number of the above types, the lower the productivity and the economic efficiency tend to be.

From the viewpoint of suppressing coloration after heat treatment, it is preferable that the EVOH resin (a) used in the present invention has at least an EVOH resin (a1) (hereinafter referred to as "EVOH resin (a 1)") having an ethylene content of less than 35 mol% and an EVOH resin (a2) (hereinafter referred to as "EVOH resin (a 2)") having an ethylene content of 35 mol% or more.

The EVOH resin (A1) has an ethylene content of usually less than 35 mol%, preferably 20 to 34 mol%, more preferably 22 to 34 mol%, and particularly preferably 25 to 33 mol%. When the ethylene content is too low, the decomposition temperature and the melting point tend to be too close to each other, and the resin composition tends to be hardly deformed by melting, whereas when too high, the effect of imparting gas barrier properties by the EVOH resin (a1) tends to be insufficient.

On the other hand, the ethylene content of the EVOH resin (a2) is usually 35 mol% or more, preferably 35 to 60 mol%, more preferably 37 to 56 mol%. When the ethylene content is too low, the effect of improving the stretchability by the EVOH resin (a2) is small, and as a result, the secondary moldability tends to decrease, whereas when too high, only the one having a high ethylene content can be selected as the other EVOH resin (a1) in order to bring the difference in ethylene content within a predetermined range, and as a result, the gas barrier property of the EVOH resin composition layer becomes insufficient.

The ethylene contents of the EVOH resin (a1) and the EVOH resin (a2) were measured according to ISO 14663.

The saponification degree of the vinyl ester component in the EVOH resin (a1) is usually 90 mol% or more, preferably 95 to 100 mol%, and particularly preferably 98 to 100 mol%. When the saponification degree is too low, the gas barrier property-imparting effect by the EVOH resin (a1) tends to be insufficient.

On the other hand, the saponification degree of the vinyl ester component in the EVOH resin (a2) is usually 90 mol% or more, preferably 93 to 100 mol%, and particularly preferably 98 to 100 mol%. When the saponification degree is too low, the gas barrier property-imparting effect by the EVOH resin (a2) tends to be insufficient.

The saponification degree of the vinyl ester component of the EVOH resin (a1) and the EVOH resin (a2) is a value measured according to JIS K6726 (in which EVOH is used as a solution uniformly dissolved in a water/methanol solvent).

The Melt Flow Rate (MFR) (210 ℃ C., load 2160g) of the EVOH resin (A1) is usually 1 to 100g/10 min, preferably 3 to 50g/10 min, and particularly preferably 3 to 10g/10 min. When the MFR is too large, the stability during film formation tends to be impaired, and when it is too small, the extrusion processability tends to be lowered.

The Melt Flow Rate (MFR) (210 ℃ C., load 2160g) of the EVOH resin (A2) is usually 1 to 100g/10 min, preferably 3 to 50g/10 min, and particularly preferably 3 to 30g/10 min. When the MFR is too large, the stability during film formation tends to be impaired, and when it is too small, the extrusion processability tends to be lowered.

In the combination of the EVOH resin (A1) and the EVOH resin (A2), the difference (Δ MFR) between the MFR (210 ℃ C., load 2160g) is preferably 5g/10 min or less, more preferably 1g/10 min or less, in order to achieve the same resin flowability during melt molding. The MFR of the EVOH resin can be usually adjusted by adjusting the saponification degree or the like.

The content ratio of the EVOH resin (a1) and the EVOH resin (a2) in the EVOH resin (a) is usually 50 wt% or more, preferably 70 wt% or more, and particularly preferably 90 wt% or more, based on the total of the EVOH resin (a1) and the EVOH resin (a 2).

The weight ratio of the EVOH resin (A1) to the EVOH resin (A2) (EVOH resin (A1)/EVOH resin (A2)) is usually 90/10 to 10/90, preferably 90/10 to 50/50, more preferably 88/12 to 60/40, and particularly preferably 85/15 to 70/30. When the proportion of the EVOH resin (a1) is too small, the gas barrier property of the EVOH resin composition layer tends to be insufficient, and when the proportion of the EVOH resin (a1) is too large, the stretching improvement effect by the EVOH resin (a2) tends to be reduced.

Such EVOH resins having different ethylene contents can be obtained, for example, in the following manner.

The EVOH resin can be generally obtained by saponifying an ethylene-vinyl ester copolymer, which is a copolymer of ethylene and a vinyl ester monomer. As the vinyl ester monomer, vinyl acetate is generally used from the economical viewpoint.

The polymerization method of ethylene and a vinyl ester monomer may be any known polymerization method, for example, solution polymerization, suspension polymerization, emulsion polymerization, etc., but solution polymerization using methanol as a solvent is generally used. The saponification of the ethylene-vinyl ester copolymer obtained can also be carried out by a known method.

The EVOH resin produced in this way is mainly composed of structural units derived from ethylene and structural units derived from vinyl alcohol, and also contains a small amount of structural units of vinyl ester remaining without being saponified.

Vinyl acetate is typically used as the vinyl ester monomer in view of its high commercial availability and impurity treatment efficiency during production. Examples of the other vinyl ester monomers include: aliphatic vinyl esters such as vinyl formate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, and vinyl versatate, and aromatic vinyl esters such as vinyl benzoate, and aliphatic vinyl esters having usually 3 to 20 carbon atoms, preferably 4 to 10 carbon atoms, and particularly preferably 4 to 7 carbon atoms can be used. These are usually used alone, but a plurality of them may be used simultaneously as required.

The ethylene content in EVOH resin can be controlled by the pressure of ethylene at the time of copolymerizing ethylene with a vinyl ester monomer, thereby producing EVOH resins having different ethylene contents.

The EVOH resin used in the present invention may further contain a structural unit derived from a comonomer shown below within a range not impairing the effects of the present invention (for example, 20 mol% or less of the EVOH resin (a)).

Examples of the comonomer include: olefin-based compounds such as propylene, 1-butene and isobutylene, hydroxyl group-containing α -olefins such as 3-butene-1-ol, 3-butene-1, 2-diol, 4-pentylene-1-ol and 5-hexene-1, 2-diol, and their derivatives such as esters and acylates; hydroxyalkyl ethylenes such as 2-methylenepropane-1, 3-diol and 3-methylenepentane-1, 5-diol; hydroxyalkyl vinylene diacetate esters such as 1, 3-diacetoxy-2-methylene propane, 1, 3-dipropoyloxy-2-methylene propane and 1, 3-dibutyryloxy-2-methylene propane; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, phthalic acid (anhydride), maleic acid (anhydride), itaconic acid (anhydride), and salts thereof, or monoalkyl esters or dialkyl esters of these unsaturated acids having 1 to 18 carbon atoms in the alkyl group; acrylamides such as acrylamide, N-alkylacrylamide in which the number of carbon atoms in the alkyl group is 1 to 18, N-dimethylacrylamide, 2-acrylamidopropanesulfonic acid or a salt thereof, acrylamidopropyldimethylamine or an acid salt thereof or a quaternary salt thereof; methacrylamides such as methacrylamide, N-alkylmethacrylamides having 1 to 18 carbon atoms in the alkyl group, N-dimethylmethacrylamide, 2-methacrylamidopropanesulfonic acid or a salt thereof, methacrylamidopropyldimethylamine or an acid salt thereof or a quaternary salt thereof; n-vinylamides such as N-vinylpyrrolidone, N-vinylformamide and N-vinylacetamide; vinyl cyanides such as acrylonitrile and methacrylic acid nitrile; vinyl ethers having 1 to 18 carbon atoms in the alkyl group such as alkyl vinyl ether, hydroxyalkyl vinyl ether and alkoxyalkyl vinyl ether; halogenated vinyl compounds such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, and vinyl bromide; vinylsilanes such as trimethoxyvinylsilane; allyl acetate; halogenated allyl compounds such as chloropropene; allyl alcohols such as allyl alcohol and dimethoxyallyl alcohol; trimethyl- (3-acrylamide-3-dimethylpropyl) -ammonium chloride, acrylamide-2-methylpropanesulfonic acid and the like. These may be used alone or in combination of 2 or more.

In particular, from the viewpoint of maintaining the gas barrier properties and improving the secondary moldability, EVOH resins having a primary hydroxyl group in the side chain are preferable, EVOH resins having a hydroxyl group-containing α -olefin copolymerized therein are particularly preferable, and EVOH resins having a1, 2-diol structure in the side chain are particularly preferable. In particular, when the resin has a primary hydroxyl group in a side chain, the content thereof is usually 0.1 to 20 mol%, more preferably 0.5 to 15 mol%, and particularly preferably 1 to 10 mol% of the EVOH resin.

The EVOH resin used in the present invention may be one obtained by "post-modification" such as urethanization, acetalization, cyanoethylation, or oxyalkylene.

The EVOH resin (a) used in the present invention has 2 or more species of EVOH resins having different ethylene contents selected from the EVOH resins obtained in the above-described manner.

The content of the ethylene structural unit in the EVOH resin (a) is a value measured in accordance with ISO14663, and is usually 20 to 60 mol%, preferably 25 to 50 mol%, and particularly preferably 25 to 48 mol%. When the content is too small, the gas barrier properties and stretchability tend to be reduced in the case of use in gas barrier properties, and when the content is too large, the gas barrier properties tend to be reduced.

The saponification degree of the vinyl ester component of the EVOH resin (a) is a value measured in accordance with JIS K6726 (wherein EVOH is used as a solution uniformly dissolved in a water/methanol solvent), and is usually 90 to 100 mol%, preferably 95 to 100 mol%, and particularly preferably 98 to 100 mol%. If the saponification degree is too low, gas barrier properties, thermal stability, moisture resistance, and the like tend to be reduced.

Further, the Melt Flow Rate (MFR) (210 ℃ C., load 2160g) of the EVOH resin (A) is usually 0.5 to 100g/10 min, preferably 1 to 50g/10 min, and particularly preferably 2 to 35g/10 min. When the MFR is too large, the film-forming property tends to become unstable, and when it is too small, the viscosity tends to become too high, and melt extrusion tends to be difficult.

[ iron Compound (B) ]

The EVOH resin composition of the present invention is characterized by containing an iron compound (B) in addition to the EVOH resin (A) having 2 or more EVOH resins having different ethylene contents, and by having a specific trace amount of the iron compound (B) blended therein. The EVOH resin composition of the present invention has the above-described structure, and therefore can suppress coloring and has excellent thermal stability.

In general, EVOH resins are colored due to thermal degradation. This is considered to be because hydroxyl groups of the EVOH resin are dehydrated by heat, double bonds are generated in the main chain of the EVOH resin, and the sites become reaction origins to promote dehydration, thereby forming a conjugated polyene structure.

In addition, since the EVOH resin composition containing the iron compound (B) is considered to cause coloring of a product due to iron ions, it is generally avoided if it is a person skilled in the art. However, the present inventors have unexpectedly found that an EVOH resin composition having excellent thermal stability can be obtained with suppressed coloration after heat treatment by containing a small amount of the iron compound (B) in the EVOH resin composition.

The reason why the above-described effects can be obtained is presumed to be: since iron is stable as a 3-valent ion, even a trace amount of iron forms an ionic bond or a chelate with a plurality of functional groups such as a hydroxyl group and a carboxyl group as described above, and is stabilized, the dehydration can be suppressed.

The iron compound (B) may be present in the EVOH resin composition in the form of, for example, an oxide, a hydroxide, a chloride, or an iron salt, in an ionized state, or in the form of a complex that interacts with a resin or another ligand. Examples of the oxide include: ferric oxide, ferroferric oxide, ferrous oxide, and the like. Examples of the chloride include: ferrous chloride, ferric chloride, and the like. Examples of the hydroxide include: ferrous hydroxide, ferric hydroxide, and the like. Examples of the iron salt include: inorganic salts such as iron phosphate and iron sulfate, and organic salts such as iron carboxylate (e.g., acetic acid, butyric acid, and stearic acid). These may be used alone or in combination of 2 or more.

From the viewpoint of dispersibility in the EVOH resin composition, the iron compound (B) is preferably water-soluble. In addition, from the viewpoint of dispersibility and productivity, the molecular weight is usually 100 to 10000, preferably 100 to 1000, and particularly preferably 100 to 500.

The EVOH resin composition of the present invention contains an iron compound (B) in an amount of 0.01 to 5ppm in terms of metal in the EVOH resin composition per unit weight. The content of the iron compound is preferably 0.05 to 3ppm, and particularly preferably 0.3 to 1.5 ppm. When the content of the iron compound (B) is too small, the coloring-suppressing effect becomes insufficient, whereas when too large, the thermal stability deteriorates.

Here, the content of the iron compound (B) can be determined as follows: 0.5g of the EVOH resin composition was subjected to ashing treatment in an infrared heating furnace (650 ℃ C., 1 hour in an oxygen gas stream), and then the remaining ash was dissolved in acid and fixed to a constant volume with pure water, and the solution was measured by ICP-MS (7500 ce model, manufactured by Agilent Technologies Co., Ltd.; Standard addition method).

[ other thermoplastic resins ]

The EVOH resin composition of the present invention may contain a thermoplastic resin other than the EVOH resin (a) within a range not impairing the effects of the present invention (for example, usually 30 wt% or less, preferably 20 wt% or less, and particularly preferably 10 wt% or less of the EVOH resin composition).

As the other thermoplastic resin, a known thermoplastic resin can be used. Specific examples thereof include: polyamide resins, polyolefin resins, polyester resins, polystyrene resins, polyvinyl chloride resins, polycarbonate resins, polyacrylic resins, ionomers, ethylene-acrylate copolymers, ethylene-methacrylate copolymers, polyvinylidene chloride, vinyl ester resins, polyester elastomers, polyurethane elastomers, chlorinated polyethylene, chlorinated polypropylene, and the like. These may be used alone or in combination of 2 or more.

[ other compounding agents ]

The EVOH resin composition of the present invention may contain a compounding agent that is usually compounded with an EVOH resin within a range that does not impair the effects of the present invention. For example, it is possible to compound: inorganic double salts (e.g., hydrotalcite), plasticizers (e.g., aliphatic polyhydric alcohols such as ethylene glycol, glycerin, and hexylene glycol), oxygen absorbers [ e.g., inorganic oxygen absorbers such as aluminum powder, potassium sulfite, and photocatalytic titanium oxide; ascorbic acid, and fatty acid esters and metal salts thereof, polyhydric phenols such as hydroquinone, gallic acid and phenol-containing resins, coordination compounds of nitrogen-containing compounds such as bis-salicylaldehyde-cobalt imide, tetraethylenepentamine cobalt, schiff base cobalt complexes, porphyrins, macrocyclic polyamine complexes and polyethyleneimine-cobalt complexes with transition metals other than iron, terpene compounds, reactants of amino acids and hydroxyl-containing reducing substances, and organic compound-based oxygen absorbents such as triphenylmethyl compounds; a complex compound of a nitrogen-containing resin and a transition metal other than iron (for example, a combination of m-xylylenediamine (MXD) nylon and cobalt), a blend of a tertiary hydrogen-containing resin and a transition metal other than iron (for example, a combination of polypropylene and cobalt), a blend of a resin having a carbon-carbon unsaturated bond and a transition metal other than iron (for example, a combination of polybutadiene and cobalt), a photooxidatively degradable resin (for example, polyketone), an anthraquinone polymer (for example, polyethyleneanthraquinone), and the like, and further a polymer-based oxygen absorber, such as one obtained by adding a photoinitiator (benzophenone, etc.), a peroxide scavenger (commercially available antioxidant, etc.), a deodorant (activated carbon, etc.), a heat stabilizer, a light stabilizer, an ultraviolet absorber, a coloring agent, an antistatic agent, a surfactant (excluding a lubricant user), an antibacterial agent, an antiblocking agent, Filler (e.g., inorganic filler, etc.), and the like. Among them, from the viewpoint of suppressing coloring, an oxygen absorber is preferable, and a terpene compound is particularly preferably used. These compounds may be used alone or in combination of 2 or more.

[ method for producing EVOH resin composition ]

The EVOH resin composition of the present invention can be produced by the following steps: a step for producing an EVOH resin (A) by mixing EVOH resins having different ethylene contents; and (B) adding an iron compound (B) to the EVOH resin or the EVOH resin (a).

Examples of the mixing method in the step of producing the EVOH resin (a) by mixing EVOH resins having different ethylene contents include: known methods such as a dry blending (pellet blending) method, a melt blending (compound) method, and a solution blending method.

Examples of the dry blending (pellet blending) method include: (I) and a method of mixing pellets of EVOH resins having different ethylene contents using a flat-bottomed glass.

Examples of the melt mixing (compounding) method include: (II) a method of melting and kneading EVOH resins having different ethylene contents with a twin-screw extruder or the like to form pellets.

Examples of the solution mixing method include: (III) a method of dissolving and mixing EVOH resins having different ethylene contents in a solvent, molding the resulting solution by a known method such as strand method, thermal cutting method, or underwater cutting method to form pellets, and drying the obtained pellets; (IV) a method comprising dissolving and mixing ethylene-vinyl ester copolymers having different ethylene contents in a solvent, saponifying the solution, molding the resulting solution of the EVOH resin (A) by a known method such as strand method, thermal cutting method, or underwater cutting method to obtain pellets, and drying the obtained pellets.

In the step of incorporating the iron compound (B) into the EVOH resin or EVOH resin (a), examples of the method of incorporating the iron compound (B) into the EVOH resin or EVOH resin (a) include: known methods such as dry blending, melt blending, solution blending, and dipping, and they may be combined arbitrarily.

Examples of the dry blending method include: (i) a method of dry-blending the EVOH resin or the pellets of the EVOH resin (A) and the iron compound (B) using a tumbler or the like.

Examples of the above melt mixing method include: (ii) a method in which an EVOH resin or a dry blend of pellets of an EVOH resin (A) and an iron compound (B) is melt-kneaded to obtain pellets or a molded article; (iii) a method of adding an iron compound (B) to an EVOH resin or an EVOH resin (A) in a molten state and melt-kneading the mixture to obtain pellets or molded articles.

Examples of the solution mixing method include: (iv) a method in which a solution is prepared using pellets of a commercially available EVOH resin, an iron compound (B) is added to the solution, the mixture is coagulated and granulated, and solid-liquid separation and drying are performed; (v) in the production process of the EVOH resin (a), the iron compound (B) is added to a homogeneous solution (water/alcohol solution or the like) of the EVOH resin, followed by coagulation molding to form pellets, solid-liquid separation, and drying.

Examples of the impregnation method include: (vi) a method comprising bringing EVOH resin or pellets of EVOH resin (A) into contact with an aqueous solution containing an iron compound (B) to incorporate the iron compound (B) into the EVOH resin or pellets of EVOH resin (A) and then drying the EVOH resin or pellets.

In the present invention, the EVOH resin composition can be produced by combining the different methods described above. Among these, the method (I) is preferable for the step of producing the EVOH resin (a) by mixing EVOH resins having different ethylene contents, and the method (ii) is preferable for the step of adding the iron compound (B) to the EVOH resin or the EVOH resin (a), from the viewpoint that the resin composition having more remarkable productivity and the effect of the present invention can be obtained.

The shapes of the pellets of the EVOH resin composition of the present invention obtained by the above methods and the EVOH resin or EVOH resin (a) used in the above methods are arbitrary. For example, the shape is a sphere, an oval, a cylinder, a cube, a cuboid, etc., but the shape is generally an oval or a cylinder, and the minor diameter is generally 1 to 10mm, preferably 2 to 6mm, more preferably 2.5 to 5.5mm, and the major diameter is generally 1.5 to 30mm, preferably 3 to 20mm, more preferably 3.5 to 10mm in the oval shape from the viewpoint of convenience in the subsequent use as a molding material. In addition, when the cylindrical shape is adopted, the diameter of the bottom surface is usually 1-6 mm, preferably 2-5 mm, and the length is usually 1-6 mm, preferably 2-5 mm.

As the iron compound (B) used in each of the above methods, as described above, a water-soluble iron compound is preferably used, and examples thereof include: iron salts such as oxides such as iron trioxide, ferroferric oxide, and ferrous oxide, chlorides such as ferrous chloride and ferric chloride, hydroxides such as ferrous hydroxide and ferric hydroxide, inorganic salts such as iron phosphate and ferric sulfate, and organic salts such as iron carboxylate (acetic acid, butyric acid, stearic acid, and the like). As described above, the iron compound (B) may be present in the EVOH resin composition in an ionized state or in a complex state by interaction with a resin or other ligands, in addition to the salt state.

As the aqueous solution containing the iron compound (B) used in the method (vi), an aqueous solution in which iron ions are eluted by immersing an iron-steel material in water containing various chemicals can be used. In this case, the content (in terms of metal) of the iron compound (B) in the EVOH resin composition may be controlled by the concentration of the iron compound (B) in the aqueous solution in which the pellet is immersed, the immersion temperature, the immersion time, and the like. The dipping temperature and the dipping time are usually 0.5 to 48 hours, preferably 1 to 36 hours, and the dipping temperature is usually 10 to 40 ℃, preferably 20 to 35 ℃. The impregnated pellets are subjected to solid-liquid separation by a known method and dried by a known drying method. As the drying method, various drying methods can be used, and either of static drying and fluidized drying can be used. Further, they may be combined.

The water content of the EVOH resin composition pellet is usually 0.01 to 0.5 wt%, preferably 0.05 to 0.35 wt%, and particularly preferably 0.1 to 0.3 wt%.

The water content of the EVOH resin composition pellet in the present invention is measured/calculated by the following method.

The weight of EVOH resin composition pellets before drying (W1) was weighed by an electronic balance, dried in a hot air dryer at 150 ℃ for 5 hours, and the weight of the pellets after leaving the dryer and cooling for 30 minutes (W2) was measured and calculated by the following formula.

Water content (% by weight) of [ (W1-W2)/W1] x 100

The thermal stability of the EVOH resin composition of the present invention can be evaluated by the weight loss ratio, and the weight loss ratio in the EVOH resin composition of the present invention is usually 0.7 to 1.1%, preferably 0.8 to 1.0%, and particularly preferably 0.9%. If the value of the weight loss ratio is too small (too small weight loss), the EVOH resin composition is hardly decomposed, and tends to increase in viscosity with time during melt molding, thereby lowering the moldability during long-term operation, while if the value of the weight loss ratio is too large (too large weight loss), it means that the EVOH resin composition is excessively decomposed, and gas or the like caused by the decomposition of the EVOH resin composition causes foaming, thereby tending to adversely affect the appearance of a molded article or the like.

The weight loss ratio is calculated by the following method: a crushed product of 5mg of an EVOH resin composition crushed to a square of 1 to 5mm was measured by a thermogravimetric analyzer (manufactured by Perkin Elmer Co., Ltd., Pyris 1TGA) under a nitrogen atmosphere at an airflow rate: 20 mL/min, temperature: 230 ℃ and time: the weight of the mixture was measured under 1 hour conditions, and the weight of the mixture before and after heating was calculated from the following equation.

Weight loss ratio (%) [ (Wa-Wb)/Wa ] × 100

In the above formula, Wa represents the weight of the EVOH resin composition before heating, and Wb represents the weight of the EVOH resin composition after heating.

The pellets of the EVOH resin composition obtained in this way can be directly subjected to melt molding, but it is also preferable that a known lubricant is adhered to the surface of the pellets in order to stabilize the feeding property at the time of melt molding. Examples of the type of lubricant include: higher fatty acids having 12 or more carbon atoms (e.g., lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, etc.), higher fatty acid esters (e.g., methyl ester, isopropyl ester, butyl ester, octyl ester, etc. of higher fatty acids), higher fatty acid amides (e.g., saturated higher fatty acid amides such as lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, etc.), unsaturated higher fatty acid amides such as oleic acid amide, erucic acid amide, etc., di-higher fatty acid amides such as 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 (e.g., low molecular weight polyethylene having a molecular weight of about 500 to 10000, low molecular weight polypropylene, etc., or acid-modified products thereof), higher alcohols having 6 or, ester oligomers, fluorinated vinyl resins, and the like. These compounds may be used alone or in combination of 2 or more. The content of the lubricant is usually 5% by weight or less, preferably 1% by weight or less of the EVOH resin composition.

The EVOH resin composition of the present invention is prepared in the form of pellets or EVOH resin compositions in various forms such as powder and liquid, and is provided as a molding material for various molded articles. In particular, in the present invention, it is preferable to provide the thermoplastic resin as a material for melt molding because the effects of the present invention tend to be obtained more efficiently. The EVOH resin composition of the present invention further includes: a resin composition obtained by mixing resins other than the EVOH resin (a) used in the EVOH resin composition of the present invention.

The molded article may be used in practice as a multilayer structure having a layer formed using the EVOH resin composition of the present invention, such as a single-layer film formed using the EVOH resin composition of the present invention.

[ multilayer Structure ]

The multilayer structure of the present invention includes a layer formed of the EVOH resin composition of the present invention. The layer formed of the EVOH resin composition of the present invention (hereinafter referred to as "EVOH resin composition layer") may be laminated with another base material (hereinafter referred to as "base material resin") containing a thermoplastic resin other than the EVOH resin composition of the present invention as a main component, to further impart strength, protect the EVOH resin composition layer from moisture, or impart other functions.

Examples of the base resin include: a polyethylene resin such as a linear low-density polyethylene, a low-density polyethylene, an ultra-low-density polyethylene, a medium-density polyethylene, a high-density polyethylene, an ethylene-propylene (block and random) copolymer, an ethylene- α -olefin (α -olefin having 4 to 20 carbon atoms) copolymer, a polypropylene resin such as a polypropylene, a propylene- α -olefin (α -olefin having 4 to 20 carbon atoms) copolymer, an unmodified polyolefin resin such as a polybutene, a polycycloolefin resin (a polymer having a cyclic olefin structure in at least one of the main chain and the side chain), a modified polyolefin resin such as an unsaturated carboxylic acid-modified polyolefin resin obtained by graft-modifying these polyolefins with an unsaturated carboxylic acid or an ester thereof, an ionomer, an ethylene-vinyl acetate copolymer, a polyolefin resin in a broad sense including a modified olefin resin such as an unsaturated carboxylic acid-modified polyolefin resin, an ionomer, an ethylene-vinyl acetate copolymer, a polyethylene copolymer, Ethylene-acrylic acid copolymers, ethylene-acrylic acid ester copolymers, polyester resins, polyamide resins (including copolyamides), polyvinyl chloride, polyvinylidene chloride, acrylic resins, polystyrene resins, vinyl ester resins, polyester elastomers, polyurethane elastomers, polystyrene elastomers, halogenated polyolefins such as chlorinated polyethylene and chlorinated polypropylene, aromatic or aliphatic polyketones, and the like. These polymers may be used alone or in combination of 2 or more.

Among these, preferred hydrophobic resins include polyamide resins, polyolefin resins, polyester resins, and polystyrene resins, and more preferred are polyolefin resins such as polyethylene resins, polypropylene resins, polycycloolefin resins, and unsaturated carboxylic acid-modified polyolefin resins thereof.

When the EVOH resin composition layer of the present invention is a (a1, a2, …) and the base resin layer is b (b1, b2, …), the layer structure of the multilayer structure may be any combination of a/b, b/a/b, a/b/a, a1/a2/b, a/b1/b2, b2/b1/a/b1/b2, b2/b1/a/b1/a/b1/b2, and the like. When R is a recycled layer of a mixture containing the EVOH resin composition of the present invention and a base resin obtained by remelting end parts, defective parts, and the like produced in the production of the multilayer structure, it may be b/R/a, b/R/a/b, b/R/a/R/b, b/a/R/a/b, b/R/a/R/b, or the like. The number of layers of the multilayer structure is usually 2 to 15, preferably 3 to 10, in total. In the above layer structure, an adhesive resin layer containing an adhesive resin may be interposed between the layers as necessary.

As the adhesive resin, known ones can be used, and the type of the thermoplastic resin used for the base resin layer "b" may be appropriately selected. Typically, the carboxyl group-containing modified polyolefin-based polymer is obtained by chemically bonding an unsaturated carboxylic acid or an anhydride thereof to a polyolefin-based resin by an addition reaction, a graft reaction, or the like. Examples of the carboxyl group-containing modified polyolefin-based polymer include: 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, maleic anhydride graft-modified ethylene-vinyl acetate copolymer, maleic anhydride modified polycycloolefin resin, maleic anhydride graft-modified polyolefin resin, and the like. Further, a mixture of 1 or 2 or more selected from these may be used.

In the multilayer structure, when an adhesive resin layer is used between the EVOH resin composition layer of the present invention and the base resin layer, the adhesive resin layer is located on both sides of the EVOH resin composition layer, and therefore, an adhesive resin having excellent hydrophobicity is preferably used.

The base resin and the adhesive resin may contain conventionally known plasticizers, fillers, clay (montmorillonite and the like), colorants, antioxidants, antistatic agents, lubricants, nucleating agents, antiblocking agents, waxes and the like in a range not to impair the gist of the present invention (for example, 30 wt% or less, preferably 10 wt% or less based on the whole resin). These may be used alone or in combination of 2 or more.

The lamination of the EVOH resin composition of the present invention with the above-mentioned base resin (including the case of interposing an adhesive resin layer) can be performed by a known method. Examples thereof include: a method of melt extrusion-laminating a base resin to a film, a sheet or the like of the EVOH resin composition of the present invention, a method of melt extrusion-laminating the EVOH resin composition of the present invention to a base resin layer, a method of co-extruding the EVOH resin composition and the base resin, a method of dry-laminating the EVOH resin composition layer and the base resin layer using a known adhesive such as an organotitanium compound, an isocyanate compound, a polyester-based compound, a polyurethane compound or the like, a method of coating a solution of the EVOH resin composition on the base resin and then removing the solvent, and the like. Among these, the coextrusion method is preferable from the viewpoint of cost and environment.

The multilayer structure as described above is then subjected to (heat) stretching treatment as 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. As a drawing method, it is also possible to adopt: a method of increasing the draw ratio in a roll stretching method, a tenter stretching method, a tubular stretching method, a stretch blow molding method, a vacuum pressure-air molding method, or the like. The stretching temperature is a temperature near the melting point of the multilayer structure, and is usually 40 to 170 ℃, preferably about 60 to 160 ℃. When the stretching temperature is too low, the stretchability tends to be poor, and when it is too high, it tends to be difficult to maintain a stable stretched state.

The heat fixation may be performed for the purpose of imparting dimensional stability after stretching. The heat-fixing can be carried out by a known method, for example, by performing a heat treatment at a temperature of usually 80 to 180 ℃ and preferably 100 to 165 ℃ for usually about 2 to 600 seconds while keeping the stretched film in a stretched state. When the multilayer stretched film obtained from the EVOH resin composition of the present invention is used as a film for shrinking, for example, a treatment such as blowing cold air to the stretched film and cooling and fixing the film may be performed to impart heat shrinkability without performing the above-described heat fixing.

In some cases, a cup-or tray-shaped multilayer container can be obtained from the multilayer structure of the present invention. In this case, a drawing method is generally employed, and specific examples thereof include: vacuum forming, pressure-air forming, vacuum pressure-air forming, plunger-assisted vacuum pressure-air forming, and the like. In addition, when a tube-or bottle-shaped multilayer container (laminate structure) is obtained from a multilayer parison (hollow tube-shaped preform before blow molding), a blow molding method is employed. Specifically, there may be mentioned: extrusion blow molding (twin-head, die-moving, parison-moving, rotary, accumulation, horizontal parison, etc.), cold parison blow molding, injection blow molding, biaxial stretch blow molding (extrusion cold parison biaxial stretch blow molding, injection in-line biaxial stretch blow molding, etc.), and the like. 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, pipe processing, slitting processing, and the like.

The thickness of the multilayer structure (including drawn ones), and further the thickness of the EVOH resin composition layer, the base resin layer and the adhesive resin layer constituting the multilayer structure, is not always 10 to 5000 μm, preferably 30 to 3000 μm, and particularly preferably 50 to 2000 μm, because the layer structure, the type of the base resin, the type of the adhesive resin, the use, the packaging method, the required physical properties, and the like are different. The EVOH resin composition layer is usually 1 to 500 μm, preferably 3 to 300 μm, and particularly preferably 5 to 200 μm, the base resin layer is usually 5 to 3000 μm, preferably 10 to 2000 μm, and particularly preferably 20 to 1000 μm, and the adhesive resin layer is usually 0.5 to 250 μm, preferably 1 to 150 μm, and particularly preferably 3 to 100 μm.

Further, the thickness ratio of the EVOH resin composition layer to the base resin layer in the multilayer structure (EVOH resin composition layer/base resin layer) is usually 1/99-50/50, preferably 5/95-45/55, and particularly preferably 10/90-40/60, in terms of the ratio between the thickest layers in the case where a plurality of layers are provided. In addition, the thickness ratio of the EVOH resin composition layer to the adhesive resin layer (EVOH resin composition layer/adhesive resin layer) in the multilayer structure is usually 10/90-99/1, preferably 20/80-95/5, and particularly preferably 50/50-90/10, in terms of the ratio between the thickest layers in the case of having a plurality of layers.

The container and lid material including the bag, cup, tray, tube, bottle and the like formed of the film, sheet and stretched film obtained as described above are useful as containers for various packaging materials such as sauces such as mayonnaise and salad dressing, fermented foods such as miso, oil and fat foods such as salad oil, beverages, cosmetics, pharmaceuticals and the like, in addition to usual foods. In particular, the EVOH resin composition of the present invention has a layer in which coloring is suppressed and which is excellent in thermal stability, and therefore, is particularly useful as a packaging material for foods, medicines, agricultural chemicals, and the like.