Resin composition, film and multilayer structure using the same

Abstract

The present invention is a resin composition comprising a biopolyethylene-based resin (A), an ethylene-vinyl alcohol-based copolymer (B), and an alkaline metal salt (C), wherein the alkaline metal salt (C) content is 10 to 1500 ppm in terms of the metal relative to the weight of the ethylene-vinyl alcohol-based copolymer (B). This resin composition suppresses a drop in transparency or the occurrence of a gel during forming, and therefore allows a formed product having an excellent external appearance to be obtained.

Description

[Technical Field]

[0001] The present invention relates to a resin composition, and more specifically to a resin composition that contains a biopolyethylene resin but suppresses gel formation and can be used to form molded articles with excellent transparency, as well as a film and a multilayer structure using the same. [Background technology]

[0002] In recent years, the environmental burden caused by plastic waste has become a major problem, and in order to reduce this burden, various technologies have been proposed to replace petroleum-derived plastics with biomass plastics derived from biomass resources such as plants.

[0003] For example, ethylene-vinyl alcohol copolymers (hereinafter sometimes abbreviated as "EVOH") are widely used as food packaging materials due to their excellent gas barrier properties and transparency. However, in most cases, they are used as multilayer structures in which polyolefin resins or the like are laminated via an adhesive layer to impart water resistance, strength, and other functions.

[0004] Therefore, it has been proposed that in such a multilayer structure, part or all of the polyolefin resin layers be formed from, for example, a polyethylene resin derived from biomass resources (biopolyethylene resin).

[0005] Furthermore, in order to improve the recyclability of resources, it has been proposed to configure at least a part of such a multilayer structure with a recovered layer (see Patent Document 1 below).

[0006] The recovered layer is a layer formed by recovering scraps such as chips, unnecessary parts such as edges, and defective products of the molded product that are generated after the production of a molded product such as a container using the multilayer structure, or waste after the molded product has been used for various purposes, and melting and molding them into pellets or the like. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-30942 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0008] However, since the biopolyethylene resin contains a larger amount of low-molecular-weight components than petroleum-derived polyethylene resins, there is a risk that thermal degradation may occur during molding, resulting in the formation of gels and a decrease in the inherent transparency of the resin. For this reason, in molded products using the above-mentioned recovered layer, and in molded products using the biopolyethylene resin and EVOH for the purpose of combining gas barrier properties and mechanical strength even without using a recovered layer, deterioration in appearance may become a problem, and there is a strong demand for improvement in this regard.

[0009] Therefore, an object of the present invention is to provide an excellent resin composition that can suppress gel formation and loss of transparency during molding even when it contains a biopolyethylene resin. [Means for solving the problem]

[0010] As a result of extensive research into solving the above-mentioned problems, the inventors discovered that the above-mentioned problems can be solved by further incorporating an alkali metal salt in a specific ratio relative to the EVOH in a resin composition combining a biopolyethylene resin and EVOH, and thus arrived at the present invention.

[0011] That is, the present invention provides the following [1] to [9]. [1] A resin composition containing a biopolyethylene resin (A), an EVOH (B), and an alkali metal salt (C), wherein the content of the alkali metal salt (C) is 10 to 1500 ppm in terms of metal relative to the weight of the EVOH (B). [2] The resin composition according to [1], wherein the ratio (A / B) of the biopolyethylene resin (A) to the ethylene-vinyl alcohol copolymer (B) is 100 / 0.01 to 100 / 25 by weight. [3] The resin composition according to [1] or [2], wherein the ethylene content in the ethylene-vinyl alcohol copolymer (B) is 20 to 60 mol %. [4] The resin composition according to any one of [1] to [3], wherein the resin composition contains an adhesive resin (D). [5] The resin composition according to any one of [1] to [4], wherein the adhesive resin (D) is a maleic acid-modified polymer. [6] The resin composition according to any one of [1] to [5], wherein the alkali metal salt (C) is an acetate salt of an alkali metal. [7] The resin composition according to any one of [1] to [5], wherein the alkali metal salt (C) is sodium acetate. [8] A film made of the resin composition according to any one of [1] to [7]. [9] A multilayer structure having a gas barrier layer, a base resin layer, and an intermediate layer provided between the gas barrier layer and the base resin layer, wherein the intermediate layer is a layer containing the resin composition according to any one of [1] to [7]. [Effects of the Invention]

[0012] The resin composition of the present invention is a resin composition that combines a biopolyethylene resin (A) and an EVOH (B), and further contains an alkali metal salt (C) in a specific ratio relative to the EVOH (B). This configuration suppresses gel formation and loss of transparency when the resin composition is melted, heated, and molded, thereby achieving the effect of producing molded articles with excellent appearance. Furthermore, because the appearance of molded articles made from a biopolyethylene resin is comparable to that of articles made from conventional petroleum-derived polyethylene resins, the use of biopolyethylene resins in resin molded articles can be promoted, contributing to reducing environmental impact.

[0013] Furthermore, the film and multilayer structure of the present invention each use the resin composition of the present invention, and therefore, as described above, have an excellent appearance despite using a biopolyethylene resin, and can contribute to reducing the environmental burden. In the present invention, the term "film" includes so-called "sheets" and "tapes."

[0014] Here, the reason why such effects are obtained in the present invention is thought to be that when the resin composition of the present invention is melted and heated while in contact with high-temperature metal such as a barrel or a screw, the alkali metal salt (C) controls the pH of the resin composition that comes into contact with the high-temperature metal within an appropriate range, thereby suppressing thermal degradation of low-molecular-weight components of the biopolyethylene resin and unexpected side reactions of EVOH, and thereby suppressing an increase in viscosity that causes gel formation and a decrease in transparency. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments for carrying out the present invention will be specifically described, but the present invention is not limited to these.

[0016] The resin composition of the present invention contains a biopolyethylene resin (A), an EVOH (B), and an alkali metal salt (C). Each component will be described below.

[0017] [Bio-polyethylene resin (A)] The term "biopolyethylene resin" refers to a polyethylene resin obtained by chemical or biological synthesis using renewable biomass resources as raw materials. Even when incinerated, the biopolyethylene resin has the characteristic of not increasing the carbon dioxide concentration in the atmosphere due to the carbon-neutral nature of biomass.

[0018] The biopolyethylene resin (A) preferably uses plant-derived ethylene derived from bioethanol obtained from plant raw materials, i.e., the biopolyethylene resin (A) is preferably a plant-derived polyethylene resin.

[0019] Plant (biomass resource) derived polyethylene resins and petroleum derived polyethylene resins do not differ in physical properties such as molecular weight, mechanical properties, and thermal properties. Therefore, to distinguish between them, the biomass ratio is generally used. The biomass ratio is defined as the carbon content of petroleum derived polyethylene resins. 14 Since it does not contain C (radioactive carbon 14, half-life 5730 years), 14 The concentration of C is measured by accelerator mass spectrometry and used as an index of the content of plant-derived biopolyethylene resin. Therefore, if a film uses plant-derived polyethylene resin, measuring the biomass degree of that film will result in a biomass degree that corresponds to the content of plant-derived polyethylene resin. The biomass degree can be measured, for example, by the following method.

[0020] [Biomass Degree Measurement] The sample to be measured is burned to generate carbon dioxide, which is then purified in a vacuum line and reduced with hydrogen using iron as a catalyst to generate graphite. This graphite is then analyzed using a tandem accelerator-based 14 Attach it to the C-AMS dedicated device (manufactured by NEC) 14 Counting C, 13 The concentration of C ( 13 C / 12 C). 14 The concentration of C ( 14 C / 12 C) and from these measurements, the carbon content of the sample relative to the standard modern carbon is 14 Calculate the percentage of C concentration.

[0021] The biopolyethylene resin (A) may be not only a polyethylene homopolymer obtained by polymerizing ethylene derived from bioethanol, but also a polyethylene copolymer obtained by copolymerizing such ethylene with a small amount of a comonomer. Examples of the polyethylene copolymer include those composed of ethylene and less than 50% by weight of another α-olefin monomer, or 3% or less by weight of a non-olefin monomer having a functional group.

[0022] Examples of the other α-olefin monomers include α-olefins having 3 to 20 carbon atoms, such as propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, 3-methyl-2-propanediol ... ethyl-1-butene, 4-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 4,4-dimethyl-1-pentene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, 9-methyl-1-decene, 11-methyl-1-dodecene, 12-ethyl-1-tetradecene, etc. These may be used alone or in combination of two or more.

[0023] Examples of the non-olefin monomer include styrene-based monomers, diene-based monomers, cyclic monomers, oxygen atom-containing monomers, etc. These may be used alone or in combination of two or more.

[0024] Examples of the styrene-based monomer include styrene, 4-methylstyrene, and 4-dimethylaminostyrene.

[0025] Examples of the diene monomer include 1,3-butadiene, 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 1,4-octadiene, 1,5-octadiene, 1,6-octadiene, 1,7-octadiene, 2-methyl-1,5-hexadiene, 6-methyl-1,5-heptadiene, 7-methyl-1,6-octadiene, 4-ethylidene-8-methyl-1,7-nonadiene, 4,8-dimethyl-1,4,8-decatriene (DMDT), dicyclopentadiene, cyclohexadiene, and dicyclooctadiene.

[0026] Examples of the cyclic monomer include methylenenorbornene, 5-vinylnorbornene, 5-ethylidene-2-norbornene, 5-methylene-2-norbornene, 5-isopropylidene-2-norbornene, 6-chloromethyl-5-isopropenyl-2-norbornene, 2,3-diisopropylidene-5-norbornene, 2-ethylidene-3-isopropylidene-5-norbornene, 2-propenyl-2,2-norbornadiene, and cyclopentene.

[0027] Examples of the oxygen atom-containing monomer include hexenol, hexenoic acid, and methyl octenoate.

[0028] These other α-olefin monomers and non-olefin monomers may be derived from renewable biomass resources or petroleum. When using those derived from renewable biomass resources, the biomass content of the final product can be further increased. When using those derived from petroleum, a wide variety of them are available, so by using them in combination, the physical properties of the final biopolyethylene resin can be easily adjusted according to the purpose.

[0029] The biopolyethylene resin (A) used in the present invention is obtained by homopolymerization of ethylene or copolymerization of ethylene with the above-mentioned comonomers, and the polymerization or copolymerization can be carried out in accordance with a conventional method using a metallocene catalyst or a Ziegler-Natta catalyst. Of these, the use of a metallocene catalyst is preferred.

[0030] Specific examples of the biopolyethylene resin (A) include high-density polyethylene (HDPE, density 0.940 g / cm 3 or more), medium density polyethylene (MDPE, density 0.925g / cm 3 More than 0.940g / cm 3 less than 0.925g / cm 3 less than 0.910g / cm), linear low-density polyethylene (LLDPE, density 0.910-0.925g / cm 3 These may be used alone or in combination of two or more. Among these, high-density polyethylene and linear low-density polyethylene are preferred.

[0031] The melt flow rate (MFR) (190°C, 2160 g load) of the biopolyethylene resin (A) is usually 0.1 to 50 g / 10 min, preferably 0.5 to 30 g / 10 min, and particularly preferably 2 to 10 g / 10 min. If the MFR is too high, film-forming properties tend to become unstable, while if it is too low, the viscosity tends to become too high, making melt extrusion difficult.

[0032] Commercially available biopolyethylene resins (A) suitable for use in the present invention include Green PE manufactured by Braskem.

[0033] [EVOH(B)] The EVOH (B) used together with the biopolyethylene resin (A) is a water-insoluble thermoplastic resin obtained by saponifying an ethylene-vinyl ester copolymer, which is a copolymer of ethylene and a vinyl ester monomer. For economic reasons, vinyl acetate is generally used as the vinyl ester monomer.

[0034] The polymerization method of the ethylene and the vinyl ester monomer may be any known polymerization method, such as solution polymerization, suspension polymerization, or emulsion polymerization, and solution polymerization using methanol as a solvent is generally used. The saponification of the obtained ethylene-vinyl ester copolymer may also be carried out by a known method.

[0035] The EVOH (B) produced in this manner is mainly composed of structural units derived from ethylene and vinyl alcohol structural units, and usually contains a small amount of vinyl ester structural units that remain unsaponified.

[0036] Vinyl acetate is typically used as the vinyl ester monomer because of its availability on the market and the efficiency of removing impurities during production. Other vinyl ester monomers include, for example, 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. Aliphatic vinyl esters having typically 3 to 20 carbon atoms, preferably 4 to 10 carbon atoms, and particularly preferably 4 to 7 carbon atoms, can be used. These can be used alone or in combination of two or more.

[0037] The ethylene content in the EVOH (B) can be controlled by the ethylene pressure when copolymerizing the vinyl ester monomer with ethylene, and is preferably 20 to 60 mol %, more preferably 25 to 50 mol %, and particularly preferably 25 to 35 mol %. If the content is too low, the gas barrier properties and melt moldability under high humidity conditions tend to decrease, while if the content is too high, the gas barrier properties tend to decrease. The ethylene content can be measured in accordance with ISO14663.

[0038] The degree of saponification of the vinyl ester component in the EVOH (B) can be controlled by the amount, temperature, time, etc. of the saponification catalyst (usually an alkaline catalyst such as sodium hydroxide) used when saponifying the ethylene-vinyl ester copolymer, and is usually 90 to 100 mol%, preferably 95 to 100 mol%, particularly preferably 99 to 100 mol%. If the degree of saponification is low, the gas barrier properties, thermal stability, moisture resistance, etc. tend to decrease. The degree of saponification of the EVOH (B) can be measured in accordance with JIS K6726 (wherein the EVOH is used as a solution uniformly dissolved in a water / methanol solvent).

[0039] The MFR (210°C, load 2160g) of the EVOH (B) is usually 0.5 to 100g / 10min, preferably 1 to 50g / 10min, and particularly preferably 3 to 35g / 10min. If the MFR is too high, moldability tends to be unstable, whereas if it is too low, the viscosity tends to be too high, making melt extrusion difficult. The MFR is an index of the degree of polymerization of EVOH, and can be adjusted by the amount of polymerization initiator and the amount of solvent used when copolymerizing ethylene with a vinyl ester monomer.

[0040] The EVOH (B) may further contain structural units derived from the comonomers shown below within a range that does not impair the effects of the present invention (for example, 10 mol % or less of the EVOH (B)). Examples of the comonomers include olefins such as propylene, 1-butene, and isobutene; hydroxyl group-containing α-olefins such as 3-butene-1-ol, 3-butene-1,2-diol, 4-pentene-1-ol, and 5-hexene-1,2-diol, and derivatives thereof such as esters and acylation products; hydroxyalkylvinylidenes such as 2-methylenepropane-1,3-diol and 3-methylenepentane-1,5-diol; 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-methylenepropane, and 1,3-dibutyryloxy. hydroxyalkylvinylidene diacetates such as 2-methylenepropane; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, (anhydrous) phthalic acid, (anhydrous) maleic acid, (anhydrous) itaconic acid, or their salts or mono- or di-alkyl esters in which the alkyl group has 1 to 18 carbon atoms; acrylamide, N-alkylacrylamide in which the alkyl group has 1 to 18 carbon atoms, N,N-dimethylacrylamide, 2-acrylamidopropanesulfonic acid or its salts, acrylamidopropyldimethylamine or its acid salts or its quaternary salts, etc. Acrylamides; methacrylamide, N-alkylmethacrylamides in which the 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 salt; N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide; vinyl cyanides such as acrylonitrile and methacrylonitrile; alkyl vinyl ethers in which the alkyl group has 1 to 18 carbon atoms, hydrochlorides vinyl ethers such as alkoxyalkyl vinyl ether and alkoxyalkyl vinyl ether; halogenated vinyl compounds such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride and vinyl bromide; vinyl silanes such as trimethoxyvinylsilane; halogenated allyl compounds such as allyl acetate and allyl chloride; allyl alcohols such as allyl alcohol and dimethoxyallyl alcohol; and comonomers such as trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride and acrylamido-2-methylpropanesulfonic acid.These may be used alone or in combination of two or more.

[0041] In particular, it is preferable to use EVOH having a primary hydroxyl group in the side chain as EVOH (B) used in the present invention, as this improves secondary moldability while maintaining gas barrier properties. Among these, EVOH copolymerized with hydroxy group-containing α-olefins is preferred, and EVOH having a 1,2-diol structure in the side chain is particularly preferred. In the case of EVOH having a primary hydroxyl group in the side chain, the content of structural units derived from a monomer having the primary hydroxyl group is usually 0.1 to 20 mol %, preferably 0.5 to 15 mol %, and particularly preferably 1 to 10 mol % of the EVOH.

[0042] The EVOH (B) used in the present invention may be "post-modified" such as urethanized, acetalized, cyanoethylated, or oxyalkylened.

[0043] Furthermore, the EVOH (B) used in the present invention may be a mixture of two or more types of EVOH (B), for example, EVOHs having different ethylene contents, different degrees of saponification, different degrees of polymerization, or different copolymerization components.

[0044] In the resin composition of the present invention, the ratio (A / B) of the biopolyethylene resin (A) to the EVOH (B) is preferably 100 / 0.01 to 100 / 25 by weight, more preferably 100 / 1 to 100 / 20, and particularly preferably 100 / 5 to 100 / 15. If the blending ratio of the biopolyethylene resin (A) is too low, moldability at low temperatures tends to decrease, while if the blending ratio of the biopolyethylene resin (A) is too high, barrier properties tend to decrease.

[0045] [Alkali metal salt (C)] In the present invention, the alkali metal salt (C) used together with the biopolyethylene resin (A) and EVOH (B) includes organic acid salts of alkali metals and inorganic acid salts of alkali metals, which may be used alone or in combination of two or more.

[0046] Examples of alkali metals constituting the alkali metal salt (C) include lithium, sodium, potassium, cesium, etc., and examples of organic acids that form salts with these alkali metals include carboxylic acids such as acetic acid, propionic acid, butyric acid, lauric acid, stearic acid, oleic acid, and behenic acid. Examples of inorganic acids include sulfuric acid, sulfurous acid, carbonic acid, and phosphoric acid. Among these, sodium acetate and potassium acetate are preferably used.

[0047] In the present invention, the content of the alkali metal salt (C) is 10 to 1500 ppm, calculated as the metal, relative to the weight of the EVOH (B). It is preferably 50 to 1000 ppm, and more preferably 70 to 500 ppm. If the content of the alkali metal salt (C) is outside the above range, the pH balance of the resin composition is impaired, and the effect of suppressing gel formation and loss of transparency during melt heating tends to be insufficient.

[0048] [Other ingredients] In addition to the essential components (A) to (C), the resin composition of the present invention may contain optional components other than the essential components (A) to (C) as long as the effects of the present invention are not impaired. For example, in order to suppress the generation of die deposits that may occur when molding using this resin composition, the following adhesive resin (D) may be added.

[0049] [Adhesive resin (D)] Examples of the adhesive resin (D) include modified polyolefin polymers containing carboxy groups obtained by chemically bonding an unsaturated carboxylic acid or its anhydride to a polyolefin resin by addition reaction, graft reaction, etc. Examples of the modified polyolefin polymers containing carboxy groups include maleic anhydride-modified polymers such as maleic anhydride-grafted polyethylene, maleic anhydride-grafted polypropylene, maleic anhydride-grafted ethylene-propylene (block and random) copolymers, maleic anhydride-grafted ethylene-ethyl acrylate copolymers, maleic anhydride-grafted ethylene-vinyl acetate copolymers, maleic anhydride-modified polycyclic olefin resins, and maleic anhydride-grafted polyolefin resins. These may be used alone or as a mixture of two or more kinds.

[0050] As the adhesive resin (D) that can be used in the present invention, maleic anhydride-modified polymers such as maleic anhydride-modified polyethylene and maleic anhydride-modified ethylene-α-olefin copolymer are particularly suitable, since they not only have the effect of suppressing the generation of die-cast during molding, but also contribute to the effect of suppressing the generation of gel during melt heating and the effect of suppressing a decrease in transparency.

[0051] The acid value of the maleic anhydride-modified polymer is usually 50 mgKOH / g or less, preferably 30 mgKOH / g or less, and particularly preferably 20 mgKOH / g or less. If the acid value is too high, the number of reaction sites with the hydroxyl groups in the EVOH (B) increases, resulting in the formation of highly polymerized products during the melt-kneading process, which reduces stability during extrusion processing and makes it difficult to obtain good molded products. The lower limit of the acid value is usually 1 mgKOH / g, preferably 2 mgKOH / g. The acid value is measured according to JIS K0070.

[0052] When maleic anhydride-modified polyethylene is used as the maleic anhydride-modified polymer, the MFR (190°C, load 2160 g) is usually 0.01 to 150 g / 10 min, preferably 0.1 to 50 g / 10 min, more preferably 1 to 25 g / 10 min, and even more preferably 3 to 10 g / 10 min.

[0053] Furthermore, when a maleic anhydride-modified ethylene-α-olefin copolymer is used as the maleic anhydride-modified polymer, the MFR (230°C, load 2160 g) is usually 0.1 to 150 g / 10 min, preferably 0.5 to 100 g / 10 min, more preferably 1 to 50 g / 10 min, and even more preferably 5 to 35 g / 10 min.

[0054] If the MFR is outside the above range, the compatibility with the biopolyethylene resin (A) and the EVOH (B) decreases, and dispersibility during mixing tends to decrease.

[0055] When the resin composition of the present invention contains the maleic anhydride-modified polymer as the adhesive resin (D), the content thereof is preferably 0.01 to 25 parts by weight, more preferably 1 to 20 parts by weight, and particularly preferably 5 to 15 parts by weight, per 100 parts by weight of the total of the biopolyethylene resin (A) and EVOH (B). When the content of the maleic anhydride-modified polymer is within the above range, a synergistic effect with the essential components (A) and (B) can be obtained, which is preferable, as it allows for more excellent effects in suppressing gel formation and transparency reduction.

[0056] The resin composition of the present invention may further contain other thermoplastic resins or additives that are generally added to thermoplastic resins.

[0057] Examples of the additives include plasticizers (e.g., aliphatic polyhydric alcohols such as ethylene glycol, glycerin, and hexanediol), oxygen absorbers, heat stabilizers, light stabilizers, ultraviolet absorbers, colorants, antistatic agents, surfactants (excluding those used as lubricants), antibacterial agents, antiblocking agents, fillers (e.g., inorganic fillers), etc. These additives may be used alone or in combination of two or more.

[0058] [Production of resin composition] The resin composition of the present invention can be produced using the above-mentioned (A) to (C) as essential components, and optionally using the above-mentioned other component (D) and optional additives, etc. The essential components, biopolyethylene resin (A) and EVOH (B), can be raw materials (unrecycled products) that have never been used in molding, but recycled materials from used multilayer structures having layers containing biopolyethylene resin (A) and EVOH (B), or unnecessary parts or defective products removed during the manufacturing process of products using such multilayer structures, can also be used.

[0059] In addition, the recycled multilayer structures generally have a structure in which a reinforcing layer made at least in part of a biopolyethylene resin (A) and a gas barrier layer made of EVOH (B) are bonded together with an adhesive resin (D). Therefore, when this recycled material is used to make the resin composition of the present invention, the resin composition will inevitably contain the adhesive resin (D).

[0060] The method for producing the resin composition of the present invention will be described below in the case where a recycled multilayer structure containing a layer made of a biopolyethylene resin (A) and an EVOH (B) is used.

[0061] The recovered multilayer structure is usually crushed and, if necessary, adjusted in particle size using a sieve or the like, and then used as a raw material for the resin composition of the present invention.

[0062] The recovered material can be pulverized using a known pulverizer. The apparent density of the pulverized product is usually 0.25 to 0.85 g / mL, preferably 0.3 to 0.7 g / mL, and particularly preferably 0.35 to 0.6 g / mL. If the apparent density is too low, the dispersion of the biopolyethylene resin (A) in the resin composition tends to be poor, and the melt moldability and mechanical properties tend to deteriorate during the process of obtaining a molded product. If the apparent density is too high, poor feeding in the extruder tends to cause deterioration in the melt moldability of the regrind layer of the resulting molded product. The apparent density of the pulverized product is a value measured in accordance with the test method "5.3 Apparent Density" of JIS K6891.

[0063] The apparent density can be controlled by adjusting the shape of the grinding blade of the grinding machine, the rotation speed of the grinding blade, the grinding processing speed, the size of the mesh openings used as a sieve, etc. The shape and particle size of the ground product can be adjusted by known methods.

[0064] To obtain the resin composition of the present invention using the pulverized product (hereinafter referred to as "pulverized product") recovered from the multilayer structure, the pulverized product is blended with the alkali metal salt (C) and mixed uniformly. From the viewpoint of productivity, the pulverized product may also be blended with an unrecycled biopolyethylene resin (A) or an unrecycled EVOH (B).

[0065] The above-mentioned two components can be mixed by known methods such as dry blending, melt kneading, solution mixing, and impregnation.

[0066] The dry blending method may, for example, be (i) a method in which the pulverized product and the alkali metal salt (C) are dry blended using a tumbler, etc. When dry blending, the alkali metal salt (C) may be dry blended as is, or pellets of a thermoplastic resin containing the alkali metal salt (C) may be prepared in advance, and the pellets of the thermoplastic resin may be dry blended with the pulverized product.

[0067] Examples of the melt-kneading method include (ii) a method of melt-kneading the dry blend, and (iii) a method of adding an alkali metal salt (C) to the molten ground product and melt-kneading the mixture.

[0068] Furthermore, examples of the solution mixing method include (iv) a method in which a solution is prepared using the pulverized product, an alkali metal salt (C) is added thereto, and the solution is solidified and molded, followed by solid-liquid separation and drying.

[0069] Among these methods, the melt-kneading method is preferred in terms of productivity, and method (ii) is particularly preferred. Furthermore, a combination of two or more of these methods may be used.

[0070] The resin composition of the present invention does not necessarily need to be made from pulverized products obtained by recovering the multilayer structure as described above, and unrecycled products, i.e., biopolyethylene resin (A) and EVOH (B) produced from scratch, may also be used. When using the unrecycled products, the resin composition may be prepared using a known general method, such as a dry blending method, a melt-kneading method, a solution mixing method, etc., so as to have the blending composition of the present invention.

[0071] In the resin composition of the present invention, the alkali metal salt (C), which is an essential component, can be prepared when preparing EVOH (B) so that a predetermined proportion of alkali metal salt (C) is contained in EVOH (B). Of course, EVOH (B) may be prepared without containing alkali metal salt (C), and when mixing the resin composition, the alkali metal salt (C) may be blended and mixed with resin components (A) and (B) in the same manner as described above, thereby obtaining the resin composition of the present invention.

[0072] The resin composition of the present invention is prepared as a resin composition in various forms, such as pellets or powder, after uniformly mixing the components, and is provided as a molding material for various molded products. In particular, in the present invention, when provided as a material for melt molding, although this resin composition contains the biopolyethylene resin (A), the generation of gels and the decrease in transparency are suppressed upon melt heating, and molded products with excellent appearance can be obtained, so providing it as a material for melt molding is particularly preferred.

[0073] Molded articles obtained using the resin composition of the present invention can be put to practical use as single-layer films that make use of the properties of the resin composition of the present invention, as well as multilayer structures having a layer molded using the resin composition of the present invention, and various single-layer or multilayer molded articles that have been given a three-dimensional shape.

[0074] As a molding method for obtaining the above molded product, a melt molding method is suitable. As the melt molding method, mainly used are extrusion molding methods (T-die extrusion, inflation extrusion, blow molding, melt spinning, profile extrusion, etc.) and injection molding. The melt molding temperature is usually in the range of 150 to 300°C, preferably 160 to 250°C, and particularly preferably 170 to 230°C. Within the above melt molding temperature range, the resin composition of the present invention can be molded well, and molded products with excellent appearance can be obtained without the generation of gels or loss of transparency that have conventionally been problems with resin compositions containing biopolyethylene resins.

[0075] [Multilayer structure] As an example of a molded article using the resin composition of the present invention, a multilayer structure will be described. A layer containing the resin composition of the present invention (including both a layer consisting solely of the resin composition of the present invention and a layer consisting of a mixed resin composition with another resin composition) can be laminated with a base resin layer or a gas barrier layer consisting of another base material (hereinafter referred to as a "base resin") whose main component is a thermoplastic resin other than the resin composition of the present invention, thereby imparting further strength or other functions. Among such multilayer structures, a multilayer structure having a gas barrier layer, a base resin layer, and an intermediate layer provided between these layers, in which the intermediate layer is a layer containing the resin composition of the present invention, is particularly preferred. When there are two or more intermediate layers, it is preferable that at least one of the intermediate layers contains the resin composition of the present invention.

[0076] Examples of the base resin include polyethylene-based resins such as 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 (α-olefin having 4 to 20 carbon atoms) copolymers; polypropylene-based resins such as polypropylene and propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers; (unmodified) polyolefin-based resins such as polybutene, polypentene, and polycyclic olefin-based resins (polymers having a cyclic olefin structure in at least one of the main chain and side chain); and polyolefin-based resins obtained by dissolving these polyolefins in an unsaturated carboxylic acid or Examples include polyolefin resins in the broad sense, including modified olefin resins such as unsaturated carboxylic acid-modified polyolefin resins graft-modified with an ester thereof, ionomers, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylic acid ester copolymers, polyester resins, polyamide resins (including copolymerized polyamides), 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, and aromatic or aliphatic polyketones.

[0077] Among these, polyamide-based resins, polyolefin-based resins, polyester-based resins, and polystyrene-based resins are preferred from the viewpoint of economic efficiency and productivity, and polyolefin-based resins such as polyethylene-based resins, polypropylene-based resins, polycyclic olefin-based resins, and unsaturated carboxylic acid-modified polyolefin-based resins thereof are more preferred.

[0078] The gas barrier layer is not particularly limited, and examples thereof include inorganic gas barrier layers and organic gas barrier layers. Examples of inorganic gas barrier layers include metal layers such as aluminum foil and aluminum vapor deposition layers, and metal compound layers such as silicon oxide vapor deposition layers and aluminum oxide vapor deposition layers. Examples of organic gas barrier layers include layers made of polyvinylidene chloride polymers and layers made of vinyl alcohol polymers such as polyvinyl alcohol and EVOH.

[0079] The layer structure of the multilayer structure can be any combination, such as a / b, b / a / b, a / b / a, a1 / a2 / b, a / b1 / b2, b2 / b1 / a / b1 / b2, or b2 / b1 / a / b1 / a / b1 / b2, where a (a1, a2, ...) represents a layer containing the resin composition of the present invention and a base resin layer represents a base resin layer. It is also possible to provide a recycled layer containing a mixture of the resin composition of the present invention and a base resin, obtained by remelting and molding edges or defective products generated during the manufacturing process of the multilayer structure. The total number of layers in the multilayer structure is usually 2 to 15, preferably 3 to 10. In the above layer structure, an adhesive resin layer containing an adhesive resin may be interposed between each layer, if necessary.

[0080] Furthermore, the layer structure of the multilayer structure can be any combination, such as a / c, c / a / c, a / c / a, a1 / a2 / c, a / c1 / c2, c2 / c1 / a / c1 / c2, or c2 / c1 / a / c1 / a / c1 / c2, where a (a1, a2, ...) represents a layer containing the resin composition of the present invention and a gas barrier layer (c1, c2, ...). It is also possible to provide a recycled layer containing a mixture of the resin composition of the present invention and a gas barrier layer-forming material, obtained by remelting and molding end portions or defective products generated during the manufacturing process of the multilayer structure. The total number of layers in the multilayer structure is usually 2 to 15, preferably 3 to 10. In the above layer structure, an adhesive resin layer containing an adhesive resin may be interposed between each layer, if necessary.

[0081] Furthermore, the layer structure of the multilayer structure can be any combination, such as c / a / b, b / a / c / b, c / a / b / a, c / a1 / a2 / b, a / c / b1 / b2, b2 / b1 / a / c / b1 / b2, or b2 / b1 / c / a / b1 / a / c / b1 / b2, where a (a1, a2, ...) represents a layer containing the resin composition of the present invention, b (b1, b2, ...), and c (c1, c2, ...). Furthermore, a recycled layer containing a mixture of the resin composition of the present invention, a base resin, and a gas barrier layer-forming material can be provided by remelting and molding end portions or defective products generated during the manufacturing process of the multilayer structure. The total number of layers in the multilayer structure is typically 2 to 15, preferably 3 to 10. In the above layer structure, an adhesive resin layer containing an adhesive resin may be interposed between each layer, if necessary.

[0082] The adhesive resin may be any known resin, and may be selected appropriately depending on the type of thermoplastic resin used in the base resin layer "b". A typical example is a modified polyolefin polymer containing a carboxy group, which is obtained by chemically bonding an unsaturated carboxylic acid or its anhydride to a polyolefin resin by addition reaction, graft reaction, or the like. The adhesive resin may be the same resin as the adhesive resin (D) that can be used in the present invention, and therefore further explanation is omitted.

[0083] The base resin and adhesive resin may contain conventionally known plasticizers, fillers, clay (montmorillonite, etc.), colorants, antioxidants, antistatic agents, lubricants, core materials, antiblocking agents, waxes, etc., within a range that does not impair the spirit of the present invention (for example, 30% by weight or less, preferably 10% by weight or less, based on the total weight of the resin).

[0084] The lamination of the resin composition of the present invention and the above-mentioned base resin (including the case where an adhesive resin layer is interposed) can be carried out by a known method. For example, a method of melt-extrusion laminating the base resin onto a film or the like made of the resin composition of the present invention, a method of melt-extrusion laminating the resin composition of the present invention onto a base resin layer, a method of co-extruding the resin composition and the base resin, a method of dry-laminating the resin composition layer and the base resin layer using a known adhesive such as an organic titanium compound, an isocyanate compound, a polyester compound, a polyurethane compound, or the like, a method of applying a solution of the resin composition onto the base resin and then removing the solvent, etc. Among these, from the viewpoints of cost and environment, the method of co-extruding the resin composition and the base resin is preferred. When a mixed resin composition of the resin composition of the present invention and another resin composition is laminated on the above-mentioned base resin, the same method as above can be used.

[0085] The multilayer structure can be subjected to a (heat) stretching treatment as needed. The stretching treatment may be either uniaxial stretching or biaxial stretching, and in the case of biaxial stretching, it may be simultaneous stretching or sequential stretching. Furthermore, the stretching method may be a roll stretching method, tenter stretching method, tubular stretching method, stretch-blow method, vacuum pressure forming, or the like, whichever provides a higher stretch ratio. The stretching temperature is a temperature near the melting point of the multilayer structure, and is usually selected from the range of 40 to 170°C, preferably about 60 to 160°C. 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.

[0086] After the stretching treatment, heat setting may be carried out for the purpose of imparting dimensional stability. Heat setting can be carried out by known means, and for example, the multilayer structure after the stretching treatment is heat-treated while maintaining tension, usually at 80 to 180°C, preferably 100 to 165°C, for usually 2 to 600 seconds. When a stretched film made of a multilayer structure obtained using the resin composition of the present invention is used as a shrink film, in order to impart heat shrinkability, the above-mentioned heat setting may not be carried out, but rather a treatment such as cooling and setting the stretched film by applying cold air may be carried out.

[0087] In some cases, the multilayer structure of the present invention can be used to produce cup- or tray-shaped multilayer containers. In such cases, a drawing method is typically employed, specifically vacuum forming, pressure forming, vacuum-pressure forming, plug-assisted vacuum-pressure forming, etc. Furthermore, blow molding is employed to produce tube- or bottle-shaped multilayer containers (laminate structure) from a multilayer parison (a hollow tubular preform before blowing). Specific examples include extrusion blow molding (two-head, mold-moving, parison-shift, rotary, accumulator, horizontal parison, etc.), cold parison blow molding, injection blow molding, and biaxial stretch blow molding (extrusion-type cold parison biaxial stretch blow molding, injection-type cold parison biaxial stretch blow molding, injection-molding in-line biaxial stretch blow molding, etc.). The resulting laminate may be subjected to heat treatment, cooling treatment, rolling treatment, printing treatment, dry lamination treatment, solution or melt coating treatment, bag making, deep drawing, box processing, tube processing, splitting processing, etc. as required.

[0088] The thickness of the multilayer structure (including a stretched structure), as well as the thickness of the resin composition layer, substrate resin layer, and adhesive resin layer that make up the multilayer structure, cannot be generally determined depending on the layer configuration, type of substrate resin, type of adhesive resin, intended use, packaging form, required physical properties, etc., but the thickness of the multilayer structure (including a stretched structure) is usually 10 to 5,000 μm, preferably 30 to 3,000 μm, and particularly preferably 50 to 2,000 μm. The resin composition layer is usually 1 to 500 μm, preferably 3 to 300 μm, and particularly preferably 5 to 200 μm. The substrate resin layer is usually 5 to 3,000 μm, preferably 10 to 2,000 μm, and particularly preferably 20 to 1,000 μm. The adhesive resin layer is usually 0.5 to 250 μm, preferably 1 to 150 μm, and particularly preferably 3 to 100 μm.

[0089] Furthermore, the thickness ratio of the resin composition layer to the base resin layer in the multilayer structure (resin composition layer / base resin layer), when there are multiple layers, is typically 1 / 99 to 50 / 50, preferably 5 / 95 to 45 / 55, and particularly preferably 10 / 90 to 40 / 60, and when there are multiple layers, the thickness ratio of the resin composition layer to the adhesive resin layer (resin composition layer / adhesive resin layer), when there are multiple layers, is typically 10 / 90 to 99 / 1, preferably 20 / 80 to 95 / 5, and particularly preferably 50 / 50 to 90 / 10.

[0090] The films and stretched films obtained from the above multilayer structures are used in bags and containers such as cups, trays, tubes, and bottles. Because they use biopolyethylene resins, they have a smaller environmental impact than conventional containers made from 100% petroleum-derived polyethylene, meeting social demands. Furthermore, despite the use of biopolyethylene resins, gel formation is suppressed in the resin composition layer, and they have excellent transparency, resulting in an excellent appearance. They can be widely used as packaging materials and containers for a variety of items, including general foods, as well as seasonings such as mayonnaise and dressings, fermented foods such as miso, oily foods such as salad oil, beverages, cosmetics, and pharmaceuticals. [Example]

[0091] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. Unless otherwise specified, "parts" and "%" below are by weight.

[0092] Prior to the examples, the following ingredients were prepared:

[0093] [Bio-polyethylene resin (A)] A-1: Plant-derived linear low-density polyethylene [SLH118 (Braskem, Green PE), MFR 1.0 g / 10 min (190°C, load 2160 g)] A-2: Plant-derived linear low-density polyethylene [SEB853 (Braskem, Green PE), MFR 2.7 g / 10 min (190°C, load 2160 g)]

[0094] [Petroleum polyethylene resin (A')] A': Low-density polyethylene [LF448K1 (Nippon Polyethylene Co., Ltd., Novatec LD), MFR 2.0 g / 10 min (190 °C, load 2160 g)]

[0095] [EVOH(B)] B-1: Ethylene-vinyl alcohol copolymer [ethylene content 29 mol%, saponification degree 99.7 mol%, MFR 8 g / 10 min (210 °C, load 2160 g)] B-2: Ethylene-vinyl alcohol copolymer [ethylene content 29 mol%, saponification degree 99.7 mol%, MFR 8 g / 10 min (210 °C, load 2160 g)] B-3: Ethylene-vinyl alcohol copolymer [ethylene content 44 mol%, saponification degree 99.6 mol%, MFR 12 g / 10 min (210 °C, load 2160 g)] B-4: Ethylene-vinyl alcohol copolymer [ethylene content 44 mol%, saponification degree 98.5 mol%, MFR 4 g / 10 min (210 °C, load 2160 g)] B-5: Ethylene-vinyl alcohol copolymer [ethylene content 44 mol%, saponification degree 99.6 mol%, MFR 13 g / 10 min (210 °C, load 2160 g)]

[0096] [Alkali metal salt (C)] Sodium acetate (Na acetate) Potassium acetate (K acetate)

[0097] [Other metal salts (C')] Calcium stearate (StCa) Magnesium stearate (StMg) Zinc stearate (StZn) Calcium acetate (Ca acetate) [Adhesive resin (D)] Maleic anhydride-modified polymer: Maleic anhydride-modified polyethylene [Mitsubishi Chemical Corporation, Modic M533, MFR 2.5 g / 10 min (190°C, load 2160 g)]

[0098] <Explanation of evaluation items (evaluation method, evaluation criteria)> Next, the details of the evaluation items for the example products, comparative example products, and reference example products are shown below.

[0099] (1) Gel amount Using pellets made of the resin compositions used in the Examples, Comparative Examples, and Reference Examples, a film was formed under the following film-forming conditions to obtain a single-layer film having a thickness of 30 μm. <Film formation conditions> Extruder: diameter (H) 40 mm, L / H=28 Screw: Full flight type Compression ratio = 2.5 The amount of gel in this monolayer film was then visually measured. Specifically, light was applied to the bottom of the monolayer film, and the number of gels per unit area (4 cm × 4 cm) was counted, with each non-light-transmitting portion (diameter 0.4 mm or more) counted as one gel, and the evaluation was performed as follows: × (poor): Number of gels is 40 or more, or film formation is not possible △ (good): Number of gels: 15 or more, less than 40 ○ (very good): Number of gels: 4 or more, less than 15 ◎ (Excellent): The number of gels is 3 or less, or no gels are measured.

[0100] (2) Transparency (internal haze) A 30 μm-thick monolayer film was prepared in the same manner as described above using pellets made from the resin compositions used in the Examples, Comparative Examples, and Reference Examples. The transparency of this monolayer film was then measured for total haze (%) in accordance with JIS K7105 using a haze meter (NDH2000, manufactured by Nippon Denshoku Co., Ltd.). The total haze is the diffuse light transmittance of the test piece divided by the total light transmittance, expressed as a percentage. A lower total haze value indicates better film transparency. To evaluate the internal haze of the film, however, a sample was coated with liquid paraffin on both sides of the film during measurement, and the internal haze (%) was measured in a state where the influence of the film surface irregularities was eliminated. The resulting value was used to evaluate the film as follows: ×(poor): 20% or more △(good): 15% or more, less than 20% ○ (very good): 10% or more, less than 15% ◎(excellent): Less than 10%

[0101] [Examples 1 to 9, Comparative Examples 1 to 8, Reference Examples 1 to 3] The components were blended to obtain the compositions shown in Tables 1 to 3 below, introduced into the cylinder through the raw material supply port of a twin-screw kneading extruder (TEX32, manufactured by The Japan Steel Works, Ltd.), transported to a kneading zone set at a temperature of 240°C, melt-blended, and the molten blend was extruded in the form of strands through a die attached to the discharge port. The resulting strand-like extrudate was pelletized using a resin pelletizer to obtain a pellet-like resin composition.

[0102] The above-mentioned evaluation items (gel amount, transparency [internal haze]) were measured and evaluated for the obtained products of Examples 1 to 9, Comparative Examples 1 to 8, and Reference Examples 1 to 3. The results are shown in Tables 1 to 3 below.

[0103] [Table 1]

[0104] [Table 2]

[0105] [Table 3]

[0106] From the above results, it can be seen that all of the products of Examples 1 to 9 were generally good in both evaluation items and had excellent appearance. On the other hand, the products of Comparative Examples 1 to 8 were all inferior to the products of the Examples in at least one of the two evaluation items, and it is clear that they have problems with appearance. Furthermore, according to Reference Examples 1 to 3, when petroleum-derived polyethylene is used, the evaluations for the two evaluation items are equivalent to those of the Example products, regardless of whether or not an alkali metal salt is added, and it can be seen that the addition of an alkali metal salt does not affect the two evaluations. These results show that the appearance problem of the products of Comparative Examples 1 to 8 is a specific issue that occurs only when a biopolyethylene resin is used, and that this issue can be resolved by adding an alkali metal salt.

[0107] Although the above examples show specific embodiments of the present invention, the examples are merely illustrative and should not be construed as limiting. Various modifications that are obvious to those skilled in the art are all intended to fall within the scope of the present invention. [Industrial Applicability]

[0108] The present invention relates to a resin composition containing a biopolyethylene resin (A), EVOH (B), and an alkali metal salt (C). Although the present invention contains the biopolyethylene resin (A), the generation of gels and the decrease in transparency during molding are suppressed, and the resin composition can be widely used as a resin composition that can give molded articles with excellent appearance.

Claims

1. A resin composition containing a biopolyethylene resin (A), an ethylene-vinyl alcohol copolymer (B), and an alkali metal salt (C), wherein the content of the alkali metal salt (C) is 10 to 1500 ppm in terms of metal relative to the weight of the ethylene-vinyl alcohol copolymer (B), A resin composition characterized in that the content ratio (A / B) of the biopolyethylene resin (A) to the ethylene-vinyl alcohol copolymer (B) is 100 / 0.01 to 100 / 25 by weight.

2. 2. The resin composition according to claim 1, wherein the ethylene content in the ethylene-vinyl alcohol copolymer (B) is 20 to 60 mol %.

3. 3. The resin composition according to claim 1, further comprising an adhesive resin (D).

4. 4. The resin composition according to claim 3, wherein the adhesive resin (D) is a maleic acid-modified polymer.

5. A resin composition described in any one of claims 1 to 4, characterized in that the alkali metal salt (C) is an organic acid salt of an alkali metal.

6. 6. The resin composition according to claim 1, wherein the alkali metal salt (C) is an acetate salt of an alkali metal.

7. 6. The resin composition according to claim 1, wherein the alkali metal salt (C) is sodium acetate.

8. A film comprising the resin composition according to any one of claims 1 to 7.

9. A multilayer structure having a gas barrier layer, a base resin layer, and an intermediate layer provided between the gas barrier layer and the base resin layer, wherein the intermediate layer is a layer comprising the resin composition according to any one of claims 1 to 7.

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