Resin composition, molding material, multilayer structure, molded body, food package, and methods for producing resin composition and multilayer structure

Abstract

The present invention provides a resin composition described below, which has excellent thermal stability and is capable of suppressing coloring due to thermal deterioration.　The present invention specifically provides a resin composition which contains a polyvinyl alcohol resin, a nickel compound, and a compound (X). The polyvinyl alcohol resin is an ethylene-modified polyvinyl alcohol resin which contains 1-19 mol% of an ethylene structural unit. The compound (X) is at least one compound that is selected from among an alkaline earth metal compound, and acetic acid other than an alkaline earth metal compound and / or a salt thereof. The content of the nickel compound in terms of elemental metal is 0.0001-2 ppm with respect to the mass of the resin composition.

Description

Resin composition, molding material, multilayer structure, molded article, food packaging material, and method for producing resin composition and multilayer structure

[0001] The present invention relates to a resin composition containing a polyvinyl alcohol resin, a molding material, a multilayer structure, a molded article, a food packaging material, a resin composition, and a method for producing a multilayer structure.

[0002] Polyvinyl alcohol resin (hereinafter, sometimes referred to as "PVA resin") is one of the few crystalline water-soluble polymers that has excellent film-forming properties, transparency, strength properties, and surface activity. Therefore, it is widely used in paper modifiers such as paper coating agents and paper internal additives, adhesives for paper, wood, inorganic materials, etc., stabilizers for emulsion polymerization and suspension polymerization, optical films, etc.

[0003] However, PVA resins generally have problems with thermal stability, such as the melting point and thermal decomposition temperature being very close to each other, making them difficult to process using hot melt molding, and they have been used in the form of an aqueous solution.

[0004] Therefore, in order to improve the thermal stability, for example, Patent Document 1 proposes an ethylene-modified PVA resin composition having a specific degree of polymerization and a specific degree of saponification, having a predetermined amount of carboxy groups and lactone rings, and containing 2 to 19 mol % of ethylene units.

[0005] Furthermore, Patent Document 2 proposes a resin composition containing 0.01 to 3 mmol (586 ppm or more) of a metal salt per 1 g of PVA resin in order to melt-mold the PVA resin.

[0006] Furthermore, Patent Document 3 discloses PVA fibers containing a predetermined amount of transition metal, and states that the PVA polymer may be ethylene-modified.

[0007] Japanese Patent Application Laid-Open No. 2000-309607 Japanese Patent Publication No. 6-47628 Japanese Patent Application Laid-Open No. 2000-336574

[0008] According to the investigations of the present inventors, the technology disclosed in the above Patent Document 1 has a certain effect on thermal stability, but the thermal stability is still insufficient, and there is a problem of coloration due to thermal degradation.

[0009] Furthermore, the techniques disclosed in Patent Documents 2 and 3 both relate to resin compositions containing only a nickel compound as a metal salt, and the addition of a small amount of nickel compound does not improve thermal stability, resulting in the problem of discoloration due to thermal degradation.

[0010] In view of the above, the present invention provides a resin composition that is excellent in thermal stability and can suppress discoloration due to thermal degradation.

[0011] However, in view of the above circumstances, the present inventors have conducted extensive research and found that a resin composition having excellent thermal stability and capable of suppressing discoloration due to thermal degradation can be obtained by incorporating a trace amount of a nickel compound and a specific compound (X) into an ethylene-modified PVA resin.

[0012] That is, the present invention has the following aspects. [1] A resin composition containing a PVA resin, a nickel compound, and compound (X), wherein the PVA resin is an ethylene-modified PVA resin containing 1 to 19 mol% of ethylene structural units, and compound (X) is at least one selected from alkaline earth metal compounds and acetic acid and / or a salt thereof other than alkaline earth metal compounds, and the content of the nickel compound in terms of metal is 0.0001 to 2 ppm relative to the mass of the resin composition. [2] The resin composition according to [1], wherein compound (X) is an alkaline earth metal compound. [3] The resin composition according to [2], wherein the content of the alkaline earth metal compound in terms of metal is 0.0001 to 1 ppm relative to the mass of the resin composition. [4] The resin composition according to [2] or [3], wherein the alkaline earth metal compound is a magnesium compound. [5] The resin composition according to any one of [2] to [4], wherein the mass ratio of the content of the alkaline earth metal compound in terms of metal to the content of the nickel compound in terms of metal is 0.000005 to 10,000. [6] The resin composition according to any one of [1] to [5], wherein the compound (X) contains acetic acid and / or a salt thereof other than an alkaline earth metal compound. [7] The resin composition according to [6], wherein the content of the acetic acid and / or a salt thereof is 10 to 10,000 ppm relative to the mass of the resin composition. [8] The resin composition according to [6] or [7], wherein the mass ratio of the content of the acetic acid and / or a salt thereof to the content of the nickel compound is 5 to 100,000,000. [9] The resin composition according to any one of [1] to [8], wherein the content of the nickel compound in terms of metal is 0.0001 ppm or more and less than 0.5 ppm relative to the mass of the resin composition.

[10] The resin composition according to any one of [1] to [9], wherein the PVA resin is non-crosslinked.

[11] A molding material comprising the resin composition according to any one of [1] to

[10] .

[12] The molding material according to

[11] , wherein the molding material is in pellet form.

[13] A multilayer structure having a layer comprising the resin composition according to any one of [1] to

[10] .

[14] A molded article comprising the multilayer structure according to

[13] .

[15] A food packaging article comprising the multilayer structure according to

[13] .

[16] A method for producing the resin composition according to any one of [1] to

[10] , comprising a step of melt-mixing a raw composition containing the PVA resin and the nickel compound.

[17] A method for producing the multilayer structure according to

[13] , comprising a step of melt-molding a layer containing the resin composition.

[0013] The resin composition of the present invention has excellent thermal stability and can suppress discoloration due to thermal degradation. Furthermore, molding materials, molded articles, and food packaging materials containing the resin composition of the present invention, as well as multilayer structures having a layer containing the resin composition of the present invention, also have excellent thermal stability and can suppress discoloration due to thermal degradation.

[0014] Hereinafter, embodiments for carrying out the present invention will be specifically described, but the present invention is not limited to these.

[0015] In this specification, "x and / or y (x and y are any configuration)" means at least one of x and y, and can mean three things: x only, y only, or x and y. When expressed as "X to Y" (X and Y are any numbers), unless otherwise specified, it also means "X or more and Y or less," as well as "preferably more than X" or "preferably less than Y." When expressed as "X or more" (X is any number) or "Y or less" (Y is any number), it also means "preferably more than X" or "preferably less than Y." With regard to the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of that numerical range can also be replaced with the value shown in the examples. In this specification, the term "layer" refers to not only thick layers but also relatively thin layers such as "films," "tapes," and "sheets."

[0016] A resin composition according to one embodiment of the present invention (hereinafter referred to as "the resin composition") contains a PVA resin, compound (X), and a specific trace amount of a nickel compound, wherein compound (X) contains at least one selected from an alkaline earth metal compound and acetic acid and / or a salt thereof other than the alkaline earth metal compound. That is, the base resin of the resin composition is a PVA resin, and the content of the PVA resin in the resin composition is typically 70% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. The resin composition will be described in order, with the case where compound (X) of the resin composition contains an alkaline earth metal compound being referred to as a "first embodiment" and the case where compound (X) contains acetic acid and / or a salt thereof other than the alkaline earth metal compound being referred to as a "second embodiment."

[0017] <<First Aspect>> The first aspect includes the following aspects <I-1> to <I-13>. <I-1> A resin composition containing a PVA resin, a nickel compound, and an alkaline earth metal compound, wherein the PVA resin is an ethylene-modified PVA resin containing 1 to 19 mol% of ethylene structural units, and the content of the nickel compound, converted into metal, is 0.0001 to 2 ppm relative to the mass of the resin composition. <I-2> The resin composition according to <I-1>, wherein the content of the alkaline earth metal compound, converted into metal, is 0.0001 to 1 ppm relative to the mass of the resin composition. <I-3> The resin composition according to <I-1> or <I-2>, which contains a magnesium compound as the alkaline earth metal compound. <I-4> The resin composition according to any one of <I-1> to <I-3>, wherein the content of the nickel compound, converted into metal, is 0.0001 ppm or more and less than 0.5 ppm relative to the mass of the resin composition. <I-5> The resin composition according to any one of <I-1> to <I-4>, wherein the mass ratio of the alkaline earth metal compound content in terms of metal to the nickel compound content in terms of metal is 0.000005 to 10,000. <I-6> The resin composition according to any one of <I-1> to <I-5>, wherein the PVA resin is non-crosslinked. <I-7> A molding material comprising the resin composition according to any one of <I-1> to <I-6>. <I-8> The molding material according to <I-7>, wherein the molding material is in pellet form. <I-9> A multilayer structure having a layer comprising the resin composition according to any one of <I-1> to <I-6>. <I-10> A molded article comprising the multilayer structure according to <I-9>. <I-11> A food packaging article comprising the multilayer structure according to <I-9>. <I-12> A method for producing the resin composition according to any one of <I-1> to <I-6>, comprising a step of melt-mixing a resin composition raw material containing the PVA resin and the nickel compound. <I-13> A method for producing the multilayer structure according to <I-9>, comprising a step of melt-molding a layer containing the resin composition.

[0018] The present invention will be described below based on an example of a form for carrying out the first aspect. However, the present invention is not limited to the embodiment described below. <Resin Composition> A resin composition according to one embodiment of the present invention (hereinafter referred to as "the present resin composition (1)") contains a PVA resin and also contains an alkaline earth metal compound and a specific trace amount of a nickel compound. That is, the base resin of the present resin composition (1) is a PVA resin, and the content of the PVA resin in the present resin composition (1) is usually 70% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. Each component will be described below.

[0019] [PVA Resin] The PVA resin used in the present embodiment is an ethylene-modified PVA resin having an ethylene structural unit, and is usually obtained by copolymerizing a vinyl ester monomer in the presence of ethylene and a polymerization initiator, and then saponifying the copolymer.

[0020] The content of ethylene structural units in the PVA resin is 1 to 19 mol%, preferably 2 to 15 mol%, and more preferably 3 to 10 mol%. When the content of ethylene structural units is equal to or less than the upper limit, the gas barrier property tends to be excellent. On the other hand, when the content of ethylene structural units is equal to or more than the lower limit, the gas barrier property under high humidity conditions and the melt moldability tend to be excellent.

[0021] The content of ethylene structural units in the PVA resin was determined from proton NMR of polyvinyl ester containing ethylene structural units, which is a precursor of the PVA resin. Specifically, the obtained polyvinyl ester was thoroughly purified by reprecipitation with n-hexane / acetone at least three times, and then dried under reduced pressure at 80°C for three days to prepare a polyvinyl ester for analysis. The polyvinyl ester was dissolved in DMSO-D and measured at 80°C using a 500 MHz proton NMR (JEOL GX-500). The content of ethylene structural units can be calculated using the signal (4.7 to 5.2 ppm) derived from the main chain methine of the vinyl ester and the signal (0.8 to 1.6 ppm) derived from the main chain methylene of ethylene, vinyl ester, and third component.

[0022] The saponification degree of the PVA resin is usually 90 to 99.99 mol%, preferably 95 to 99.5 mol%, and more preferably 97 to 99 mol%. When the saponification degree is equal to or greater than the lower limit, the PVA resin tends to have better gas barrier properties, thermal stability, moisture resistance, etc. On the other hand, when the saponification degree is equal to or less than the upper limit, the PVA resin tends to be less susceptible to thermal degradation. The saponification degree of such a PVA resin can be measured in accordance with JIS K6726.

[0023] The melting point of the PVA resin is usually 100 to 270°C, preferably 120 to 250°C, and more preferably 150 to 230°C. When the melting point is equal to or higher than the lower limit, the PVA resin tends to have excellent heat resistance. When the melting point is equal to or lower than the upper limit, the PVA resin tends to be less susceptible to thermal degradation.

[0024] Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. Among these, vinyl acetate is preferred from the viewpoint of obtaining a PVA resin. These monomers can be used alone or in combination of two or more. Furthermore, the PVA resin may be a copolymer of a vinyl ester monomer, ethylene, and another monomer copolymerizable therewith. Any conventionally known monomer can be used as the other copolymerizable monomer. The content of the structural unit derived from the other copolymerizable monomer is usually preferably 15 mol% or less, more preferably 10 mol% or less, and even more preferably 5 mol% or less, based on the PVA resin. It may be absent.

[0025] The structural unit derived from the other copolymerizable monomer includes a structural unit having a primary hydroxyl group in the side chain, and a preferred structural unit is the structural unit represented by the following general formula (1):

[0026] R 1 ~R 3is not particularly limited as long as it is a hydrogen atom or an organic group. Examples of the organic group include hydrocarbon groups such as alkyl groups, alkenyl groups, alkynyl groups, phenyl groups, and naphthyl groups (these hydrocarbon groups may have a hydroxyl group, fluorine, chlorine, bromine, or the like as a substituent).

[0027] X, which connects the polymer main chain and the primary hydroxyl group structure, represents a single bond or a connecting chain. The connecting chain is not particularly limited, but examples thereof include hydrocarbons such as alkylene, alkenylene, alkynylene, phenylene, and naphthylene (these hydrocarbons may have a hydroxyl group, fluorine, chlorine, bromine, or the like as a substituent), hydrocarbons connected to the polymer main chain by an ether bond such as oxyalkylene, oxyalkenylene, oxyalkynylene, oxyphenylene, and oxynaphthylene (these hydrocarbons may have a hydroxyl group, fluorine, chlorine, bromine, or the like as a substituent), as well as -CO-, -CO(CH2) m CO-, -CO(CH2) m COR 4 -, -NR 5 --, --CONR 5 - and the like (R 4 , R 5 are independently any substituent, preferably a hydrogen atom or an alkyl group, and m is a natural number.

[0028] To obtain the PVA resin having a primary hydroxyl group in the side chain, for example, the following methods can be used: (I) a method in which a monomer having a primary hydroxyl group in the side chain and / or a monomer in which the primary hydroxyl group in the side chain is protected with an ester or the like is copolymerized with ethylene and a vinyl ester monomer, followed by deprotection by saponification or the like; or (II) a method in which a copolymer of ethylene and a vinyl ester monomer is first saponified to obtain a PVA resin, and then the PVA resin is post-modified to generate a primary hydroxyl group in the side chain. Among these, method (I) is preferred from the viewpoint of productivity. The method for producing the PVA resin of the present invention will be described below. First, in the case of method (I), ethylene and a vinyl ester monomer are copolymerized with a monomer having a primary hydroxyl group in the side chain and / or a monomer in which the hydroxyl group is protected with an ester or the like.

[0029] In the above method (I), examples of the monomer having a primary hydroxyl group in the side chain include monohydroxyalkyl group-containing monomers such as allyl alcohol, 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 6-hepten-1-ol, and methallyl alcohol; and dihydroxyalkyl group-containing monomers such as 2-methylene-1,3-propanediol, 3,4-diol-1-butene, 4,5-diol-1-pentene, 4,5-diol-3-methyl-1-pentene, 5,6-diol-1-hexene, and glycerin monoallyl ether. These may be used alone or in combination of two or more.

[0030] Furthermore, in the above method (I), examples of the monomer in which the primary hydroxyl group in the side chain is protected with an ester or the like (hereinafter sometimes referred to as "monomer in which the hydroxyl group is protected with an ester or the like") include, for example, acetate esters of the above monomers having a primary hydroxyl group in the side chain. Specific examples include monoacetoxyalkyl group-containing monomers such as allyl acetate, 3-butenyl acetate, 4-pentenyl acetate, 5-hexenyl acetate, 6-heptenyl acetate, and methallyl acetate; and diacetoxyalkyl group-containing monomers such as 2-methylene-1,3-propanediol diacetate, 3,4-diacetoxy-1-butene, 4,5-diacetoxy-1-pentene, 4,5-diacetoxy-3-methyl-1-pentene, 5,6-diacetoxy-1-hexene, and 3-allyloxy-1,2-propanediol diacetate. These may be used alone or in combination of two or more.

[0031] In the above method (I), a monomer having a primary hydroxyl group in the side chain and a monomer in which the hydroxyl group is protected with an ester or the like can be used in combination and copolymerized with ethylene and a vinyl ester monomer.

[0032] Among these, from the viewpoint of productivity, monomers in which the hydroxyl group is protected with an ester or the like are preferred, diacetoxyalkyl group-containing monomers are more preferred, 3,4-diacetoxy-1-butene and 2-methylene-1,3-propanediol diacetate are even more preferred, and 3,4-diacetoxy-1-butene is particularly preferred. When, for example, the above-mentioned 3,4-diacetoxy-1-butene is used as the copolymerization component in the above method (I), the PVA resin obtained by deprotection by saponification or the like preferably has a primary hydroxyl group represented by the following general formula (2) in the side chain.

[0033] Furthermore, when, for example, the above-mentioned 2-methylene-1,3-propanediol diacetate is used as a copolymerization component in the above-mentioned method (I), the obtained PVA resin preferably has a primary hydroxyl group represented by the following general formula (3) in its side chain.

[0034] In the methods (I) and (II), a copolymerizable ethylenically unsaturated monomer may be copolymerized as a copolymerization component within a range that does not impair the effects of the present invention. Examples of such ethylenically unsaturated monomers include olefins such as propylene, 1-butene, and isobutene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, phthalic acid (anhydride), maleic acid (anhydride), and itaconic acid (anhydride), or their salts or mono- or di-alkyl esters having 1 to 18 carbon atoms; acrylamide, N-alkylmethacrylamide having 1 to 18 carbon atoms, N,N-dimethylacrylamide, 2-acrylamidopropanesulfonic acid or its salts; acrylamidopropyldimethylamine or its acid salts or its quaternary salts; methacrylamide, methyl methacrylamide having 1 to 18 carbon atoms ... Examples of the vinyl silane include methacrylamides such as N-alkylmethacrylamide (N-8), N,N-dimethylmethacrylamide, and 2-methacrylamidopropanesulfonic acid or a salt thereof; N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, and N-vinylacetamide; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl ethers such as alkyl vinyl ethers, hydroxyalkyl vinyl ethers, and alkoxyalkyl vinyl ethers having 1 to 18 carbon atoms; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, and vinyl bromide; and vinylsilanes. These may be used alone or in combination of two or more.

[0035] As a polymerization method for copolymerizing the ethylene and the vinyl ester monomer in the presence of a polymerization initiator, any known polymerization method can be used, for example, bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc., but the method is usually carried out by a bulk polymerization method or a solution polymerization method in which polymerization is carried out without a solvent or in a solvent such as an alcohol.

[0036] The alcohol used as a solvent in the solution polymerization is usually a lower alcohol such as methanol, ethanol, propanol, etc. These may be used alone or in combination of two or more kinds.

[0037] Examples of the polymerization initiator include known initiators such as azo initiators or peroxide initiators, such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethyl-valeronitrile), benzoyl peroxide, and n-propyl peroxydicarbonate. These can be used alone or in combination of two or more. The polymerization reaction temperature is selected from the range of 0 to 150°C.

[0038] The saponification can be carried out by a known method, and is usually carried out by dissolving the obtained copolymer in a saponification solvent in the presence of a saponification catalyst. Examples of the saponification solvent include lower alcohols such as methanol, methyl acetate, dimethyl sulfoxide, and dimethylformamide. These can be used alone or in combination of two or more.

[0039] As the saponification catalyst, for example, alkaline substances such as potassium hydroxide, sodium hydroxide, etc. These may be used alone or in combination of two or more kinds.

[0040] The PVA resin may be a crosslinked PVA resin or a non-crosslinked PVA resin. In the case of a crosslinked PVA resin, OH groups in the PVA resin typically become reaction sites, resulting in a decrease in their amount. However, in the case of a non-crosslinked PVA resin, OH groups are present in sufficient quantities in the resin. As described below, OH groups in the resin are thought to contribute to thermal stability, so a non-crosslinked PVA resin with a greater number of OH groups is preferred. Known methods for crosslinking a PVA resin include, for example, a method of dehydration crosslinking in a dry heat stretching process using an acid or a salt that acts as a dehydration catalyst, and a method of linking and crosslinking with other polymers using an acrylic acid-based polymer, an organic peroxide, an isocyanate compound, a urethane compound, an epoxy compound, a dialdehyde, or the like. It is preferable to use a non-crosslinked PVA resin in this embodiment that has not been subjected to such a crosslinking reaction.

[0041] [Nickel Compound] Examples of the nickel compound used in this embodiment include inorganic nickel compounds and organic nickel compounds. These can be used alone or in combination of two or more. Among these, inorganic nickel compounds are preferred.

[0042] Examples of the inorganic nickel compounds include nickel oxide, nickel hydroxide, and inorganic salts of nickel. Examples of the nickel oxides include nickel(II) oxide, nickel(III) oxide, nickel(IV) oxide, and nickel dioxide. Examples of the nickel hydroxides include nickel(I) hydroxide and nickel(II) hydroxide. Examples of the inorganic salts of nickel include nickel(II) chloride, nickel(II) phosphate, nickel(II) sulfate, and nickel nitrate. Among these, nickel oxides are preferred, and nickel(II) oxide is more preferred, in that the effects of the invention can be more easily achieved.

[0043] Examples of the organic nickel compounds include nickel carboxylates such as nickel acetate, nickel butyrate, and nickel stearate.

[0044] From the viewpoints of dispersibility in the resin composition (1) and productivity, the molecular weight of the nickel compound is usually 50 to 10,000, preferably 60 to 1,000, and more preferably 70 to 800. From the viewpoints of economy and dispersibility, it is preferable that the nickel compound used in this embodiment does not include layered inorganic compounds such as montmorillonite and double salts such as hydrotalcite.

[0045] The nickel compound may be in any form, such as a solid (powder, fine powder, flakes, etc.), a semi-solid, a liquid, a paste, a solution, an emulsion (aqueous dispersion), etc. Among these, a powder form is preferred because of ease of handling.

[0046] The content of the nickel compound in terms of metal is 0.0001 to 2 ppm, preferably 0.0001 ppm or more and 1 ppm or less, more preferably 0.0001 ppm or more and less than 0.5 ppm, even more preferably 0.001 ppm or more and less than 0.5 ppm, and particularly preferably 0.01 ppm or more and less than 0.5 ppm, relative to the mass of the resin composition (1). The content of the nickel compound in terms of metal is the content of elemental nickel. When the content of the nickel compound in terms of metal is equal to or less than the upper limit, the resin composition (1) tends to be less susceptible to thermal decomposition and coloration, while when the content is equal to or more than the lower limit, the effect of suppressing thermal degradation tends to be excellent.

[0047] The content of the nickel compound in terms of metal in the resin composition (1) of the present embodiment can be determined, for example, by heating and ashing the resin composition (1), treating it with an acid such as hydrochloric acid, adding pure water to the resulting solution, and measuring the volume of the test solution with an atomic absorption photometer.

[0048] [Alkaline earth metal compound] Examples of the alkaline earth metal compound include salts, oxides, hydroxides, and hydrates thereof of alkaline earth metals. These may be used alone or in combination of two or more. Among these, alkaline earth metal salts and alkaline earth metal oxides are preferred from the viewpoints of economy and dispersibility, and alkaline earth metal salts are particularly preferred.

[0049] Examples of the alkaline earth metal salt include inorganic salts of alkaline earth metals and carboxylates of alkaline earth metals.

[0050] Examples of the inorganic salts of alkaline earth metals include carbonates, hydrogen carbonates, phosphates, borates, sulfates, and chlorides of alkaline earth metals.

[0051] Examples of the alkaline earth metal carboxylates include saturated or unsaturated carboxylates having 2 to 25 carbon atoms, preferably 2 to 22, and more preferably 6 to 20 carbon atoms, and specific examples include monocarboxylic acid salts such as acetate, butyrate, propionate, enanthate, caprate, laurate, palmitate, stearate, 12-hydroxystearate, behenate, and montanate, and dicarboxylic acid salts such as oxalate, malonate, succinate, adipate, suberate, and sebacate. Of these, linear saturated carboxylates are preferred in terms of commercial availability, and monocarboxylic acid salts are more preferred.

[0052] Examples of the alkaline earth metal species of the alkaline earth metal compound include beryllium, magnesium, calcium, strontium, barium, and radium. Among these, magnesium and calcium are preferred in terms of market availability and economic efficiency, and magnesium is particularly preferred.

[0053] Among these, magnesium chloride is preferred as the alkaline earth metal compound, and magnesium chloride hydrate is more preferred. From the viewpoints of economy and dispersibility, it is preferable that the alkaline earth metal compound does not include layered inorganic compounds such as montmorillonite and double salts such as hydrotalcite.

[0054] The alkaline earth metal compound may be in any form, such as a solid (powder, fine powder, flakes, etc.), a semi-solid, a liquid, a paste, a solution, or an emulsion (aqueous dispersion), with a powder being preferred.

[0055] The alkaline earth metal compounds can be used alone or in combination of two or more kinds. When multiple kinds of alkaline earth metal compounds are used, the content is the total content (mass) of the multiple kinds of alkaline earth metal compounds in terms of metal.

[0056] The content of the alkaline earth metal compound in terms of metal is preferably 0.0001 to 1 ppm, more preferably 0.001 to 0.8 ppm, and even more preferably 0.01 to 0.5 ppm, relative to the mass of the resin composition (1). The content of the alkaline earth metal compound in terms of metal is, in other words, the content of the alkaline earth metal element. When the content of the alkaline earth metal compound in terms of metal is equal to or less than the upper limit, the thermal stability tends to be excellent, and when equal to or more than the lower limit, the moldability of the resin composition (1) tends to be excellent.

[0057] The metal-equivalent content of the alkaline earth metal compound can be measured using an atomic absorption spectrophotometer by adding pure water to a solution obtained by heating and incinerating the resin composition (1) and treating the resultant solution with an acid such as hydrochloric acid, and then adjusting the volume of the solution to a constant volume.

[0058] The mass ratio of the alkaline earth metal compound content in terms of metal to the nickel compound content in terms of metal is preferably 0.000005 to 10000, more preferably 0.0005 to 5000, and even more preferably 0.05 to 1000. When the mass ratio is equal to or less than the upper limit, the thermal stability tends to be excellent, and when the mass ratio is equal to or more than the lower limit, coloration of the molded product tends to be suppressed.

[0059] The reason why the combined use of the alkaline earth metal compound used in this embodiment and the nickel compound provides such excellent effects is not clear, but it is presumed that the combined use of specific amounts of the nickel compound and the alkaline earth metal compound produces an interactant (complex, etc.), which interacts with the oxygen of the OH group in the PVA resin, thereby suppressing the formation of a polyene structure and improving thermal stability.

[0060] [Other Thermoplastic Resins] The resin composition (1) may contain thermoplastic resins other than the ethylene-modified PVA resin within a range that does not impair the effects of the present invention (for example, typically 30% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less of the resin composition (1), the lower limit being typically 0% by mass). Examples of other thermoplastic resins that may be used include known thermoplastic resins, such as polyester resins, polystyrene resins, polyvinyl chloride resins, polycarbonate resins, ionomers, polyvinylidene chloride, polyester elastomers, polyurethane elastomers, chlorinated polyethylene, and chlorinated polypropylene. These may be used alone or in combination of two or more.

[0061] [Other Compounding Agents] The resin composition (1) may also contain compounding agents (excluding nickel compounds and alkaline earth metal compounds) that are generally compounded with ethylene-modified PVA resins, within a range that does not impair the effects of the present invention (for example, typically 30% by mass or less of the resin composition (1), preferably 20% by mass or less, more preferably 10% by mass or less, the lower limit being typically 0% by mass). Examples of the compounding agents include inorganic double salts, plasticizers (e.g., aliphatic polyhydric alcohols such as ethylene glycol, glycerin, and hexanediol), oxygen absorbers (e.g., inorganic oxygen absorbers such as aluminum powder and potassium sulfite; ascorbic acid, its fatty acid esters and metal salts, etc.; gallic acid; polyhydric phenols such as hydroxyl group-containing phenolaldehyde resins; terpene compounds; blends of tertiary hydrogen-containing resins and transition metals other than nickel (e.g., a combination of polypropylene and cobalt); and blends of carbon-carbon unsaturated bond-containing resins and transition metals other than nickel. The polymeric oxygen absorbers may also contain additives such as blends with transition metals (e.g., a combination of polybutadiene and cobalt), photooxidatively degradable resins (e.g., polyketones), anthraquinone polymers (e.g., polyvinyl anthraquinone), and mixtures thereof to which photoinitiators (e.g., benzophenone) or other antioxidants or deodorizers (e.g., activated carbon) have been added, heat stabilizers, light stabilizers, ultraviolet absorbers, colorants, antistatic agents, surfactants (excluding those used as lubricants), antibacterial agents, antiblocking agents, and fillers (e.g., inorganic fillers). These compounds may be used alone or in combination of two or more.

[0062] [Method for Producing Resin Composition (1)] The resin composition (1) can be produced by mixing the ethylene-modified PVA resin, the nickel compound, and the alkaline earth metal compound by a known method, such as a dry blending method, a melt mixing method, a solution mixing method, an impregnation method, etc. Among these, the resin composition (1) is preferably produced by a method including a step of melt mixing the raw materials for the resin composition (1) containing the ethylene-modified PVA resin and the nickel compound. These production methods can also be used in any combination.

[0063] The dry blending method may, for example, be (i) a method in which a pellet-shaped ethylene-modified PVA resin, an alkaline earth metal compound, and a nickel compound are dry-blended using a tumbler or the like.

[0064] Examples of the melt-mixing method include (ii) a method in which a pellet-shaped ethylene-modified PVA resin is dry-blended with an alkaline earth metal compound and a nickel compound, and the dry-blended product is melt-kneaded; and (iii) a method in which an alkaline earth metal compound and a nickel compound are added to a molten ethylene-modified PVA resin, and the resulting mixture is melt-kneaded.

[0065] Examples of the solution mixing method include (iv) a method in which a solution is prepared using a commercially available ethylene-modified PVA resin, an alkaline earth metal compound and a nickel compound are blended therein, the mixture is coagulated and molded, and then the mixture is subjected to solid-liquid separation by known means and dried; and (v) a method in which an alkaline earth metal compound and a nickel compound are added to an ethylene-vinyl ester copolymer solution before saponification or a homogeneous solution of the ethylene-modified PVA resin (such as a water / alcohol solution) during the production process of the ethylene-modified PVA resin, the mixture is coagulated and molded, and then the mixture is subjected to solid-liquid separation by known means and dried.

[0066] The impregnation method includes, for example, (vi) a method in which pellets of ethylene-modified PVA resin are brought into contact with an aqueous solution containing an alkaline earth metal compound and a nickel compound to incorporate the alkaline earth metal compound and the nickel compound into the ethylene-modified PVA resin, and then the resulting mixture is dried.

[0067] The aqueous solution containing the nickel compound may be an aqueous solution of a nickel compound or a solution obtained by immersing a nickel compound in water containing various chemicals to elute nickel ions.

[0068] In the impregnation method, the contents (in terms of metals) of the alkaline earth metal compound and the nickel compound can be controlled by the concentrations of the alkaline earth metal compound and the nickel compound in the aqueous solution in which the ethylene-modified PVA resin is immersed, the immersion temperature, the immersion time, etc. The immersion temperature and the immersion time are usually 0.5 to 48 hours, preferably 1 to 36 hours, and the immersion temperature is usually 10 to 40°C, preferably 20 to 35°C.

[0069] As the drying method in each of the above-mentioned production methods, various drying methods can be used, and either static drying or fluidized drying may be used, or these may be used in combination.

[0070] As described above, in this embodiment, the above-mentioned different methods can be combined. Among them, the melt mixing method is preferred, and method (ii) is particularly preferred, in terms of productivity and the fact that a resin composition can be obtained in which the effects of the present invention are more pronounced. Furthermore, when using the other thermoplastic resins and other compounding agents, they may be compounded by a conventional method according to the above-mentioned manufacturing method.

[0071] The resin composition (1) obtained by each of the above-described production methods may have any shape, but pellets are preferred because they more easily achieve the effects of the present invention. The pellets contain the resin composition (1) and preferably consist solely of the resin composition (1). The pellets may be spherical, oval, cylindrical, cubic, or rectangular, but are typically oval or cylindrical. From the perspective of convenience when subsequently used as a molding material, the pellets typically have a minor axis of 1 to 10 mm, preferably 2 to 6 mm, and more preferably 2.5 to 5.5 mm, and a major axis of 1.5 to 30 mm, preferably 3 to 20 mm, and more preferably 3.5 to 10 mm. Furthermore, the cylindrical pellets typically have a base diameter of 1 to 6 mm, preferably 2 to 5 mm, and a length of 1 to 6 mm, preferably 2 to 5 mm. The pellets also preferably have the same shape and size as the PVA resin pellets used in each of the above-described production methods.

[0072] The water content of the resin composition (1) is usually 0.01 to 0.5% by mass, preferably 0.05 to 0.35% by mass, and more preferably 0.1 to 0.3% by mass.

[0073] The water content of the resin composition (1) is measured and calculated by the following method: The mass (W1) of the resin composition (1) before drying is weighed on an electronic balance, dried in a hot air dryer at 150°C for 5 hours, and then cooled in a desiccator for 30 minutes, after which the mass (W2) is weighed and calculated using the following formula: Water content (mass%) = [(W1 - W2) / W1] x 100

[0074] When the resin composition (1) is in the form of pellets, it is also preferable to adhere a known lubricant to the surface of the pellets in order to stabilize the feedability during melt molding. Examples of lubricants 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 (methyl esters, isopropyl esters, butyl esters, octyl esters of higher fatty acids, etc.), 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.; bis-higher fatty acid amides such as ethylene bisstearic acid amide, ethylene bisoleic acid amide, ethylene biserucic acid amide, ethylene bislauric acid amide, etc.), low-molecular-weight polyolefins (e.g., low-molecular-weight polyethylene or low-molecular-weight polypropylene having a molecular weight of about 500 to 10,000, or acid-modified products thereof), higher alcohols having 6 or more carbon atoms, ester oligomers, and fluorinated ethylene resins. These compounds may be used alone or in combination of two or more. The content of such lubricants is usually 5% by mass or less, preferably 1% by mass or less, of the resin composition (1). The lower limit is usually 0% by mass.

[0075] The resin composition (1) thus obtained, as measured using a visual analyzer IRIS VA400 (manufactured by Alphamos), has a ratio ("1637" + "1638" + "1639") / ("1621") of the sum of color numbers "1637" (R: 104, G: 104, B: 88), "1638" (R: 104, G: 104, B: 104), and "1639" (R: 104, G: 104, B: 120) to color number "1621" (R: 104, G: 88, B: 88), which is typically 0.8 or greater, preferably 0.85 or greater, and more preferably 0.9 or greater. The higher this ratio, the better the thermal stability and the more suppressed discoloration due to thermal degradation. A difference of 0.1 in this ratio results in a significant difference in yield in actual production, so the difference is very significant.

[0076] The yellow index (YI value) of the resin composition (1) is usually 50 or less, preferably 45 or less, and more preferably 40 or less. The smaller the YI value, the more excellent the thermal stability and the more suppressed the coloration due to thermal degradation. The YI value can be measured using a spectrophotometer (manufactured by Nippon Denshoku Industries Co., Ltd.).

[0077] The resin composition (1) thus obtained is prepared in various forms, such as pellets, powder, or liquid, and is provided as a molding material for various molded products. In particular, in this embodiment, when it is provided as a material for melt molding, the effects of the present invention tend to be more efficiently obtained, which is preferable. Note that the resin composition (1) also includes resin compositions obtained by mixing resins other than the PVA resin used in the resin composition (1).

[0078] Examples of the molded product include a single layer film molded from the present resin composition (1), as well as a multilayer structure having at least one layer made of the present resin composition (1).

[0079] <Multilayer structure> A multilayer structure according to one embodiment of the present invention (hereinafter referred to as "the present multilayer structure (1)") has a layer containing the present resin composition (1), and preferably has a layer consisting only of the present resin composition (1). The layer containing the present resin composition (1) (hereinafter simply referred to as "the present resin composition layer (1)") can be laminated with another substrate (hereinafter, the resin used for the substrate may be abbreviated as "substrate resin") containing a thermoplastic resin other than the present resin composition (1) as a main component to impart further strength, protect the present resin composition layer (1) from the effects of moisture, etc., or impart other functions.

[0080] 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 the main chain and / or side chain); and polyolefin-based resins obtained by combining these polyolefins with unsaturated carboxylic acids or esters thereof. Examples of suitable polyethylene include polyolefin resins in the broad sense, including modified olefin resins such as unsaturated carboxylic acid-modified polyolefin resins graft-modified with terephthalates; 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. These may be used alone or in combination of two or more. The terms linear low-density polyethylene, low-density polyethylene, very low-density polyethylene, medium-density polyethylene, and high-density polyethylene are commonly used terms to represent types of polyethylene.

[0081] Among these, hydrophobic resins such as polyamide-based resins, polyolefin-based resins, polyester-based resins, and polystyrene-based resins are preferred, and more preferred are polyolefin-based resins such as polyethylene-based resins, polypropylene-based resins, polycyclic olefin-based resins, and unsaturated carboxylic acid-modified polyolefin-based resins thereof.

[0082] The layer structure of the multilayer structure (1) 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 represents the resin composition layer (1) and b represents the base resin layer (b1, b2, etc.). Furthermore, when R represents a recycled layer containing a mixture of the resin composition (1) and a thermoplastic resin other than the resin composition (1), obtained by remelting and molding edges or defective products generated during the manufacturing process of the multilayer structure (1), b / R / a, b / R / a / b, b / R / a / R / b, b / a / R / a / b, b / R / a / R / a / R / b, or b / R / a / R / a / R / b, etc. The total number of layers in the multilayer structure (1) 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 the respective layers, if necessary.

[0083] Known adhesive resins can be used, and may be selected appropriately depending on the type of thermoplastic resin used in the base resin layer "b." Representative examples include modified polyolefin polymers containing carboxy groups, which are obtained by chemically bonding an unsaturated carboxylic acid or its anhydride to a polyolefin resin via an addition reaction, a graft reaction, or the like. Examples of modified polyolefin polymers containing carboxy groups include 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-grafted polycyclic olefin resins, and maleic anhydride-grafted polyolefin resins. These may be used alone or in combination of two or more.

[0084] In the present multilayer structure (1), when an adhesive resin layer is used between the present resin composition layer (1) and the base resin layer, since the adhesive resin layers are located on both sides of the present resin composition layer (1), it is preferable to use an adhesive resin with excellent hydrophobicity.

[0085] The base resin and adhesive resin may contain conventionally known plasticizers, fillers, clays (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 mass or less, preferably 10% by mass or less, based on the total mass of the resin). These may be used alone or in combination of two or more.

[0086] The lamination of the resin composition layer (1) and the substrate resin layer (including the case where an adhesive resin layer is interposed) can be carried out by a known method. Examples include a method of melt-extrusion laminating the substrate resin onto a film, sheet, etc. of the resin composition (1), a method of melt-extrusion laminating the resin composition (1) onto the substrate resin layer, a method of co-extruding the resin composition (1) and the substrate resin, a method of dry-laminating the resin composition (1) (layer) and the substrate resin (layer) using a known adhesive such as an organic titanium compound, an isocyanate compound, a polyester compound, a polyurethane compound, etc., and a method of applying a solution of the resin composition (1) onto the substrate resin and then removing the solvent. Among these, in consideration of cost and environmental considerations, it is preferable to produce the layer including the resin composition layer (1) by melt-molding it, and specifically, a co-extrusion method is preferred.

[0087] The multilayer structure (1) may be subjected to a (heat) stretching treatment, if necessary. 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, as the stretching method, a method with a high stretch ratio, such as roll stretching, tenter stretching, tubular stretching, stretch-blow method, or vacuum / pressure forming, may also be used. 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. When the stretching temperature is equal to or higher than the lower limit, the stretchability tends to be good, and when it is equal to or lower than the upper limit, a stable stretched state tends to be maintained.

[0088] The stretched multilayer structure (1) may be heat-set for the purpose of imparting dimensional stability. Heat-setting can be performed by known means, for example, by subjecting the stretched multilayer structure (1) to heat treatment while maintaining tension, usually at 80 to 180°C, preferably 100 to 165°C, for usually 2 to 600 seconds.

[0089] When the stretched multilayer structure (1) is used as a shrink film, the above-mentioned heat setting is not carried out, and instead, a treatment such as cooling and setting the stretched multilayer structure (1) by applying cold air thereto may be carried out in order to impart heat shrinkability.

[0090] The thickness of the multilayer structure (1) (including the stretched structure), and further the thickness of the resin composition layer (1), base resin layer, and adhesive resin layer constituting the multilayer structure, cannot be generally determined depending on the layer configuration, type of base resin, type of adhesive resin, intended use, packaging form, required physical properties, etc., but the thickness of the multilayer structure (1) (including the stretched structure) is usually 10 to 5,000 μm, preferably 30 to 3,000 μm, more preferably 50 to 2,000 μm. The resin composition layer (1) is usually 1 to 500 μm, preferably 3 to 300 μm, more preferably 5 to 200 μm, the base resin layer is usually 5 to 3,000 μm, preferably 10 to 2,000 μm, more preferably 20 to 1,000 μm, and the adhesive resin layer is usually 0.5 to 250 μm, preferably 1 to 150 μm, more preferably 3 to 100 μm.

[0091] Furthermore, the thickness ratio of the present resin composition layer (1) to the base resin layer in the present multilayer structure (1) (present resin composition layer (1) / base resin layer), expressed as the ratio between the thickest layers when there are multiple layers of each, is usually 1 / 99 to 50 / 50, preferably 5 / 95 to 45 / 55, and more preferably 10 / 90 to 40 / 60. Furthermore, the thickness ratio of the present resin composition layer (1) to the adhesive resin layer in the present multilayer structure (1) (present resin composition layer (1) / adhesive resin layer), expressed as the ratio between the thickest layers when there are multiple layers of each, is usually 10 / 90 to 99 / 1, preferably 20 / 80 to 95 / 5, and more preferably 50 / 50 to 90 / 10.

[0092] The multilayer structure (1) can also be used to produce cup- or tray-shaped molded articles and food packaging. 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 structures) from multilayer parisons (hollow tubular preforms before blowing). Specific examples include extrusion blow molding (double-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.

[0093] A single layer film formed from the present resin composition (1), and containers and lid materials such as bags, cups, trays, tubes, and bottles made from the present multilayer structure (1) are useful as various packaging materials and containers for general foods, as well as seasonings such as mayonnaise and dressings, fermented foods such as miso, oily foods such as salad oil, beverages, cosmetics, pharmaceuticals, etc.

[0094] <<Second Aspect>> The second aspect includes the following aspects <II-1> to <II-12>. <II-1> A resin composition containing a PVA resin, a nickel compound, and acetic acid and / or a salt thereof other than an alkaline earth metal compound, wherein the PVA resin is an ethylene-modified PVA resin containing 1 to 19 mol% of ethylene structural units, and the content of the nickel compound, converted into metal, is 0.0001 to 2 ppm relative to the mass of the resin composition. <II-2> The resin composition according to <II-1>, wherein the content of the acetic acid and / or a salt thereof is 10 to 10,000 ppm relative to the mass of the resin composition. <II-3> The resin composition according to <II-1> or <II-2>, wherein the content of the nickel compound, converted into metal, is 0.0001 ppm or more and less than 0.5 ppm relative to the mass of the resin composition. <II-4> The resin composition according to any one of <II-1> to <II-3>, wherein the mass ratio of the content of the acetic acid and / or a salt thereof to the content of the nickel compound is 5 to 100,000,000. <II-5> The resin composition according to any one of <II-1> to <II-4>, wherein the PVA resin is non-crosslinked. <II-6> A molding material comprising the resin composition according to any one of <II-1> to <II-5>. <II-7> The molding material according to <II-6>, wherein the molding material is in pellet form. <II-8> A multilayer structure having a layer comprising the resin composition according to any one of <II-1> to <II-5>. <II-9> A molded article comprising the multilayer structure according to <II-8>. <II-10> A food packaging product comprising the multilayer structure according to <II-8>. <II-11> A method for producing the resin composition according to any one of <II-1> to <II-5>, comprising the step of melt-mixing a resin composition raw material containing the PVA resin and the nickel compound. <II-12> A method for producing the multilayer structure according to <II-8>, comprising a step of melt-molding a layer containing the resin composition. The present invention will be described below based on examples of embodiments for carrying out the second aspect. However, the present invention is not limited to the embodiments described below.<Resin Composition> A resin composition according to one embodiment of the present invention (hereinafter referred to as "the present resin composition (2)") contains a PVA resin and also contains acetic acid and / or a salt thereof other than alkaline earth metal compounds, and a specific trace amount of a nickel compound. That is, the base resin of the present resin composition (2) is a PVA resin, and the content of the PVA resin in the present resin composition (2) is usually 70% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. Each component will be described below.

[0095] [PVA Resin] The PVA resin used in this embodiment is an ethylene-modified PVA resin having an ethylene structural unit, and is usually a resin obtained by copolymerizing a vinyl ester monomer in the presence of ethylene and a polymerization initiator and saponifying the copolymer. The same PVA resin as described in the first embodiment can be used.

[0096] [Nickel Compound] The nickel compound used in this embodiment may be the same as the [Nickel Compound] described in the first embodiment. Examples include inorganic nickel compounds and organic nickel compounds. These may be used alone or in combination of two or more. Among these, inorganic nickel compounds are preferred.

[0097] The content of the nickel compound in terms of metal is 0.0001 to 2 ppm, preferably 0.0001 ppm or more and 1 ppm or less, more preferably 0.0001 ppm or more and less than 0.5 ppm, even more preferably 0.001 ppm or more and less than 0.5 ppm, and particularly preferably 0.001 ppm or more and less than 0.5 ppm, relative to the mass of the resin composition (2). The content of the nickel compound in terms of metal is, in other words, the content of elemental nickel. When the content of the nickel compound in terms of metal is equal to or less than the upper limit, the resin composition (2) tends to be less susceptible to thermal decomposition and coloration, whereas when the content is equal to or more than the lower limit, the effect of suppressing thermal degradation tends to be excellent.

[0098] The content of the nickel compound in terms of metal in the resin composition (2) of the present embodiment can be determined, for example, by heating and ashing the resin composition (2), treating it with an acid such as hydrochloric acid, adding pure water to the resulting solution, and measuring the volume of the test solution with an atomic absorption photometer.

[0099] [Acetic acid and / or salts thereof] The acetic acid and / or salts thereof used in this embodiment are other than the [alkaline earth metal compounds] described in the first embodiment, and specific examples thereof include acetic acid, sodium acetate, potassium acetate, manganese acetate, copper acetate, cobalt acetate, zinc acetate, etc. These can be used alone or in combination of two or more. Among these, acetic acid, sodium acetate, and potassium acetate are preferred, acetic acid, sodium acetate, and potassium acetate are more preferred, acetic acid and sodium acetate are even more preferred, and acetic acid is particularly preferred.

[0100] The content of the acetic acid and / or salt thereof is usually 10 to 10,000 ppm, preferably 100 to 999 ppm, more preferably 200 to 700 ppm, and even more preferably 300 to 600 ppm, relative to the mass of the resin composition (2). When the content is equal to or less than the upper limit, the thermal stability tends to be excellent, and when the content is equal to or more than the lower limit, the moldability of the resin composition (2) tends to be excellent.

[0101] The content of acetic acid and / or a salt thereof can be measured by a known analytical method, for example, liquid chromatography mass spectrometry (LC / MS) or gas chromatography mass spectrometry (GC / MS).

[0102] The mass ratio of the content of the acetic acid and / or salt thereof to the content of the nickel compound is usually 5 to 100,000,000, preferably 10 to 1,000,000, and more preferably 100 to 10,000. When the mass ratio is equal to or less than the upper limit, the thermal stability tends to be excellent, and when the mass ratio is equal to or more than the lower limit, the moldability of the resin composition (2) tends to be excellent.

[0103] Although the reason why excellent effects can be obtained by combining appropriate amounts of the nickel compound and acetic acid and / or a salt thereof is not clear, it is presumed that the combined use of a specific amount of the nickel compound and the acetic acid and / or a salt thereof appropriately reduces the pH, strengthening the hydrogen bonds in the hydroxyl groups of the PVA resin, thereby improving thermal stability.

[0104] [Other Thermoplastic Resins] The resin composition (2) may contain thermoplastic resins other than the ethylene-modified PVA resin within a range that does not impair the effects of the present invention (for example, typically 30% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less of the resin composition (2), the lower limit being typically 0% by mass). Examples of other thermoplastic resins that may be used include known thermoplastic resins, such as polyester resins, polystyrene resins, polyvinyl chloride resins, polycarbonate resins, ionomers, polyvinylidene chloride, polyester elastomers, polyurethane elastomers, chlorinated polyethylene, and chlorinated polypropylene. These may be used alone or in combination of two or more.

[0105] [Other Additives] The resin composition (2) may also contain additives (excluding nickel compounds and acetic acid and / or its salts) that are generally added to ethylene-modified PVA resins, within a range that does not impair the effects of the present invention (for example, typically 30% by mass or less of the resin composition (2)), preferably 20% by mass or less, more preferably 10% by mass or less, the lower limit being typically 0% by mass). Examples of the additives include inorganic double salts (e.g., hydrotalcite, etc.), plasticizers (e.g., aliphatic polyhydric alcohols such as ethylene glycol, glycerin, and hexanediol), oxygen absorbers (e.g., inorganic oxygen absorbers such as aluminum powder and potassium sulfite; ascorbic acid, its fatty acid esters and metal salts, etc.; gallic acid; polyhydric phenols such as hydroxyl group-containing phenolaldehyde resins; terpene compounds; blends of tertiary hydrogen-containing resins with transition metals other than nickel (e.g., a combination of polypropylene and cobalt); and carbon-carbon unsaturated bond-containing resins. Polymeric oxygen absorbers such as blends with transition metals other than nickel (e.g., a combination of polybutadiene and cobalt), photooxidatively degradable resins (e.g., polyketones), anthraquinone polymers (e.g., polyvinyl anthraquinone), and combinations thereof with the addition of photoinitiators (e.g., benzophenone), antioxidants other than those mentioned above, and deodorants (e.g., activated carbon), 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. may also be blended. These compounds may be used alone or in combination of two or more.

[0106] [Method for Producing Resin Composition (2)] The resin composition (2) can be produced by mixing the ethylene-modified PVA resin, the nickel compound, and acetic acid and / or a salt thereof by a known method, such as a dry blending method, a melt mixing method, a solution mixing method, an impregnation method, etc. Among these, the resin composition (2) is preferably produced by a method including a step of melt mixing a raw composition containing the ethylene-modified PVA resin and the nickel compound. These production methods can also be used in any combination.

[0107] The dry blending method may, for example, be (i) a method in which a pellet-shaped ethylene-modified PVA resin, a nickel compound, and acetic acid and / or a salt thereof are dry-blended using a tumbler or the like.

[0108] Examples of the melt-mixing method include (ii) a method in which a pellet-shaped ethylene-modified PVA resin is dry-blended with a nickel compound, and acetic acid and / or a salt thereof, and the dry-blended product is melt-kneaded; and (iii) a method in which a nickel compound, and acetic acid and / or a salt thereof are added to a molten ethylene-modified PVA resin, and the mixture is melt-kneaded.

[0109] Examples of the solution mixing method include (iv) a method in which a solution is prepared using a commercially available ethylene-modified PVA resin, a nickel compound and acetic acid and / or a salt thereof are blended therein, the mixture is coagulated and molded, and then the mixture is subjected to solid-liquid separation by known means and dried; and (v) a method in which a nickel compound and acetic acid and / or a salt thereof are added to a solution of an ethylene-vinyl ester copolymer before saponification or a homogeneous solution of an ethylene-modified PVA resin (such as a water / alcohol solution) during the production of a PVA resin, the mixture is coagulated and molded, and then the mixture is subjected to solid-liquid separation by known means and dried.

[0110] Examples of the impregnation method include (vi) a method in which pellets of ethylene-modified PVA resin are brought into contact with an aqueous solution containing a nickel compound and acetic acid and / or a salt thereof to incorporate the nickel compound and acetic acid and / or a salt thereof into the ethylene-modified PVA resin, and then the resulting mixture is dried.

[0111] The aqueous solution containing the nickel compound may be an aqueous solution of a nickel compound or a solution obtained by immersing a nickel compound in water containing various chemicals to elute nickel ions.

[0112] In the impregnation method, the contents of acetic acid and / or its salt and nickel compound (in terms of metal) can be controlled by the concentrations of the nickel compound and acetic acid and / or its salt in the aqueous solution in which the ethylene-modified PVA resin is immersed, as well as the immersion temperature, immersion time, etc. The immersion temperature and immersion time are usually 0.5 to 48 hours, preferably 1 to 36 hours, and the immersion temperature is usually 10 to 40°C, preferably 20 to 35°C.

[0113] As the drying method in each of the above-mentioned production methods, various drying methods can be used, and either static drying or fluidized drying may be used, or these may be used in combination.

[0114] As described above, in this embodiment, the above-mentioned different methods can be combined. Among them, the melt mixing method is preferred, and method (ii) is particularly preferred, in terms of productivity and the ability to obtain a resin composition (2) that exhibits the effects of the present invention more significantly. Furthermore, when using the other thermoplastic resins and other compounding agents, they may be compounded by a conventional method according to the above-mentioned production method.

[0115] The resin composition (2) obtained by each of the above-described production methods may have any shape, but pellets are preferred because they more easily achieve the effects of the present invention. The pellets contain the resin composition (2), and are preferably pellets consisting solely of the resin composition (2). The pellets may be, for example, spherical, oval, cylindrical, cubic, or rectangular. They are typically oval or cylindrical. From the perspective of convenience when subsequently used as a molding material, the size of the pellets is typically 1 to 10 mm, preferably 2 to 6 mm, and more preferably 2.5 to 5.5 mm, for the oval shape, and typically 1.5 to 30 mm, preferably 3 to 20 mm, and more preferably 3.5 to 10 mm, for the cylindrical shape. The diameter of the base is typically 1 to 6 mm, preferably 2 to 5 mm, and the length is typically 1 to 6 mm, preferably 2 to 5 mm. The shape and size of the pelletized PVA resin used in each of the above-described production methods are also preferably similar.

[0116] The water content of the resin composition (2) is usually 0.01 to 0.5% by mass, preferably 0.05 to 0.35% by mass, and more preferably 0.1 to 0.3% by mass.

[0117] The water content of the resin composition (2) is measured and calculated by the following method: The mass (W1) of the resin composition (2) before drying is weighed on an electronic balance, dried in a hot air dryer at 150°C for 5 hours, and then cooled in a desiccator for 30 minutes, after which the mass (W2) is weighed and calculated using the following formula: Water content (mass%) = [(W1 - W2) / W1] x 100

[0118] When the resin composition (2) is in the form of pellets, it is also preferable to adhere a known lubricant to the surface of the pellets in order to stabilize the feedability during melt molding. Examples of lubricants 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 (methyl esters, isopropyl esters, butyl esters, octyl esters of higher fatty acids, etc.), 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.; bis-higher fatty acid amides such as ethylene bisstearic acid amide, ethylene bisoleic acid amide, ethylene biserucic acid amide, ethylene bislauric acid amide, etc.), low-molecular-weight polyolefins (e.g., low-molecular-weight polyethylene or low-molecular-weight polypropylene having a molecular weight of about 500 to 10,000, or acid-modified products thereof), higher alcohols having 6 or more carbon atoms, ester oligomers, and fluorinated ethylene resins. These compounds can be used alone or in combination of two or more. The content of such lubricants is usually 5% by mass or less, preferably 1% by mass or less, of the resin composition (2). The lower limit is usually 0% by mass.

[0119] The resin composition (2) thus obtained was measured using a visual analyzer IRIS VA400 (manufactured by Alphamos) to determine the ratio ("2183" + "2184" + "2185") / ("1604" + "1605") of the sum of color numbers "2183" (R: 136, G: 136, B: 120), "2184" (R: 136, G: 136, B: 136), and "2185" (R: 136, G: 136, B: 152) to the sum of color numbers "1604" (R: 104, G: 72, B: 72) and "1605" (R: 104, G: 72, B: 88). The ratio is usually 5.8 or more, preferably 6 or more, and more preferably 6.2 or more. The higher the ratio, the more excellent the thermal stability and the more likely it is that coloration due to thermal degradation will be suppressed. A difference of 0.1 in the ratio is very significant, as it appears as a large difference in yield in actual production.

[0120] The yellow index (YI value) of the resin composition (2) is usually 50 or less, preferably 45 or less, and more preferably 40 or less. The smaller the YI value, the more excellent the thermal stability and the more suppressed the coloration due to thermal degradation. The YI value can be measured using a spectrophotometer (manufactured by Nippon Denshoku Industries Co., Ltd.).

[0121] The resin composition (2) thus obtained is prepared in various forms, such as pellets, powder, or liquid, and is provided as a molding material for various molded products. In particular, in this embodiment, when it is provided as a material for melt molding, the effects of the present invention tend to be more efficiently obtained, which is preferable. Note that the resin composition (2) also includes resin compositions obtained by mixing resins other than the PVA resin used in the resin composition (2).

[0122] Examples of the molded product include a monolayer film molded from the present resin composition (2), as well as a multilayer structure having at least one layer made of the present resin composition (2).

[0123] <Multilayer structure> A multilayer structure according to one embodiment of the present invention (hereinafter referred to as "the present multilayer structure (2)") has a layer containing the present resin composition (2), and preferably has a layer consisting only of the present resin composition (2). The layer containing the present resin composition (2) (hereinafter simply referred to as "the present resin composition layer (2)") can be laminated with another substrate (hereinafter, the resin used for the substrate may be abbreviated as "substrate resin") containing a thermoplastic resin other than the present resin composition (2) as a main component to impart further strength, protect the present resin composition layer (2) from the effects of moisture, etc., or impart other functions.

[0124] 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 the main chain and / or side chain); and polyolefin-based resins obtained by combining these polyolefins with unsaturated carboxylic acids or esters thereof. Examples of suitable polyethylene include polyolefin resins in the broad sense, including modified olefin resins such as unsaturated carboxylic acid-modified polyolefin resins graft-modified with terephthalates; 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. These may be used alone or in combination of two or more. The terms linear low-density polyethylene, low-density polyethylene, very low-density polyethylene, medium-density polyethylene, and high-density polyethylene are commonly used terms to represent types of polyethylene.

[0125] Among these, hydrophobic resins such as polyamide-based resins, polyolefin-based resins, polyester-based resins, and polystyrene-based resins are preferred, and more preferred are polyolefin-based resins such as polyethylene-based resins, polypropylene-based resins, polycyclic olefin-based resins, and unsaturated carboxylic acid-modified polyolefin-based resins thereof.

[0126] The layer structure of the present multilayer structure (2) 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 represents the present resin composition layer (2) and b represents the base resin layer (b1, b2, etc.). Furthermore, when R represents a recycled layer containing a mixture of the present resin composition (2) and a thermoplastic resin other than the present resin composition (2), obtained by remelting and molding edges or defective products generated during the manufacturing process of the present multilayer structure (2), b / R / a, b / R / a / b, b / R / a / R / b, b / a / R / a / b, b / R / a / R / a / R / b, or b / R / a / R / a / R / b, etc. The total number of layers in the present multilayer structure (2) 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 the respective layers, if necessary.

[0127] Known adhesive resins can be used, and may be selected appropriately depending on the type of thermoplastic resin used in the base resin layer "b." Representative examples include modified polyolefin polymers containing carboxy groups, which are obtained by chemically bonding an unsaturated carboxylic acid or its anhydride to a polyolefin resin via an addition reaction, a graft reaction, or the like. Examples of modified polyolefin polymers containing carboxy groups include 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-grafted polycyclic olefin resins, and maleic anhydride-grafted polyolefin resins. These may be used alone or in combination of two or more.

[0128] In the present multilayer structure (2), when an adhesive resin layer is used between the present resin composition layer (2) and the base resin layer, since the adhesive resin layers are located on both sides of the present resin composition layer (2), it is preferable to use an adhesive resin with excellent hydrophobicity.

[0129] The base resin and adhesive resin may contain conventionally known plasticizers, fillers, clays (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 mass or less, preferably 10% by mass or less, based on the total mass of the resin). These may be used alone or in combination of two or more.

[0130] The lamination of the resin composition layer (2) and the substrate resin layer (including the case where an adhesive resin layer is interposed) can be carried out by a known method. Examples include a method of melt-extrusion laminating the substrate resin onto a film, sheet, etc. of the resin composition (2), a method of melt-extrusion laminating the resin composition (2) onto the substrate resin layer, a method of co-extruding the resin composition (2) and the substrate resin, a method of dry-laminating the resin composition (2) (layer) and the substrate resin (layer) using a known adhesive such as an organic titanium compound, an isocyanate compound, a polyester compound, a polyurethane compound, etc., and a method of applying a solution of the resin composition (2) onto the substrate resin and then removing the solvent. Among these, in consideration of cost and environmental considerations, it is preferable to produce the layer including the resin composition layer (2) by a step of melt-molding the layer, and specifically, a co-extrusion method is preferred.

[0131] The multilayer structure (2) may be subjected to a (heat) stretching treatment, if necessary. 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, as the stretching method, a method with a high stretch ratio, such as roll stretching, tenter stretching, tubular stretching, stretch-blow method, or vacuum / pressure forming, may also be used. 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. When the stretching temperature is equal to or higher than the lower limit, the stretchability tends to be good, and when it is equal to or lower than the upper limit, a stable stretched state tends to be maintained.

[0132] The stretched multilayer structure (2) may be heat-set for the purpose of imparting dimensional stability. Heat-setting can be performed by known means, for example, by subjecting the stretched multilayer structure (2) to heat treatment while maintaining tension, typically at 80 to 180°C, preferably 100 to 165°C, for typically 2 to 600 seconds.

[0133] When the stretched multilayer structure (2) is used as a shrink film, in order to impart heat shrinkability, the above-mentioned heat setting is not carried out, but rather a treatment such as cooling and setting the stretched multilayer structure (2) by applying cold air thereto may be carried out.

[0134] The thickness of the multilayer structure (2) (including the stretched structure), and further the thickness of the resin composition layer (2), base resin layer, and adhesive resin layer constituting the multilayer structure, cannot be generally determined depending on the layer configuration, type of base resin, type of adhesive resin, intended use, packaging form, required physical properties, etc., but the thickness of the multilayer structure (2) (including the stretched structure) is usually 10 to 5,000 μm, preferably 30 to 3,000 μm, more preferably 50 to 2,000 μm. The resin composition layer (2) is usually 1 to 500 μm, preferably 3 to 300 μm, more preferably 5 to 200 μm, the base resin layer is usually 5 to 3,000 μm, preferably 10 to 2,000 μm, more preferably 20 to 1,000 μm, and the adhesive resin layer is usually 0.5 to 250 μm, preferably 1 to 150 μm, more preferably 3 to 100 μm.

[0135] Furthermore, the thickness ratio of the present resin composition layer (2) to the base resin layer in the present multilayer structure (2) (present resin composition layer (2) / base resin layer), expressed as the ratio between the thickest layers when there are multiple layers of each, is usually 1 / 99 to 50 / 50, preferably 5 / 95 to 45 / 55, and more preferably 10 / 90 to 40 / 60. Furthermore, the thickness ratio of the present resin composition layer (2) to the adhesive resin layer in the present multilayer structure (2) (present resin composition layer (2) / adhesive resin layer), expressed as the ratio between the thickest layers when there are multiple layers of each, is usually 10 / 90 to 99 / 1, preferably 20 / 80 to 95 / 5, and more preferably 50 / 50 to 90 / 10.

[0136] The multilayer structure (2) can also be used to produce cup- or tray-shaped molded articles and food packaging. 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 structures) from multilayer parisons (hollow tubular preforms before blowing). Specific examples include extrusion blow molding (double-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.

[0137] A single layer film formed from this resin composition (2), and containers and lid materials such as bags, cups, trays, tubes, and bottles made from this multilayer structure (2) are useful as various packaging materials and containers for general foods, as well as seasonings such as mayonnaise and dressings, fermented foods such as miso, oily foods such as salad oil, beverages, cosmetics, pharmaceuticals, etc.

[0138] 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. In the examples, "parts" and "%" are based on mass.

[0139] <<First Aspect>> Prior to the Examples, the following components were prepared. Ethylene-modified PVA resin: pellets of PVA resin (non-crosslinked) having an ethylene structural unit content of 7.4 mol%, a melting point of 213°C, and a saponification degree of 98 mol%. Unmodified PVA resin: pellets of PVA resin (non-crosslinked) having an ethylene structural unit content of 0 mol%, a melting point of 226°C, and a saponification degree of 99 mol%. Alkaline earth metal compound: magnesium chloride hexahydrate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.). Nickel compound: nickel(II) oxide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.).

[0140] Example I-1: The ethylene-modified PVA resin pellets were dry-blended with the magnesium chloride hexahydrate so that the content, in terms of metal, was 0.1 ppm relative to the mass of the resin composition, and the nickel oxide so that the content, in terms of metal, was 0.001 ppm relative to the mass of the resin composition, to obtain a mixture. The mixture was then fed to a twin-screw extruder (20 mmφ) equipped with a two-hole die, and extruded under the following extrusion conditions. The extruded strands were cooled and solidified by air cooling. The solidified strands were then cut using a pelletizer to obtain pellets of the resin composition.

[0141] [Extrusion conditions] Extruder set temperatures (°C): C1 / C2 / C3 / C4 / C5 / C6 = 200 / 210 / 225 / 225 / 225 / 225

[0142] Example I-2 Pellets of a resin composition were obtained in the same manner as in Example I-1, except that the content of nickel oxide in terms of metal was changed to 0.1 ppm relative to the mass of the resin composition.

[0143] Example I-3 Pellets of a resin composition were obtained in the same manner as in Example I-1, except that the content of nickel oxide in terms of metal was changed to 1.0 ppm relative to the mass of the resin composition.

[0144] Comparative Example I-1 Pellets of a resin composition were obtained in the same manner as in Example I-1, except that nickel oxide was not used.

[0145] Comparative Example I-2 Pellets of a resin composition were obtained in the same manner as in Example I-1, except that the content of nickel oxide, calculated as metal, was changed to 10 ppm relative to the mass of the resin composition.

[0146] Comparative Example I-3 Pellets of a resin composition were obtained in the same manner as in Example I-1, except that the content of nickel oxide in terms of metal was changed to 1.0 ppm relative to the mass of the resin composition and magnesium chloride hexahydrate was not used.

[0147] Comparative Example I-4 Pellets of a resin composition were obtained in the same manner as in Example I-1, except that an unmodified PVA resin was used instead of the ethylene-modified PVA resin in Example I-1, and the content of nickel oxide, calculated as metal, was changed to 0.1 ppm relative to the mass of the resin composition.

[0148] The pellets of the resin compositions of Examples I-1 to I-3 and Comparative Examples I-1 to I-4 were used to evaluate the thermal stability as follows, and the results are shown in Table I-1.

[0149] [Evaluation of coloration due to thermal degradation] Pellets of the resin compositions obtained in Examples I-1 to I-3 and Comparative Examples I-1 to I-4 were used as samples, and a visual analyzer IRIS VA400 (manufactured by Alphamos) was used to measure the color number "1621" (R: 104, G: 88, B: 88) relative to the color number "1637" (R: 104, G: 104, B: 88), "1638" (R: 104, G: 104, B: 104), and "1639" (R: 104, G: 104, B: 120). The ratio of the sum of these numbers ("1637" + "1638" + "1639") / ("1621") was evaluated. Color number "1621" is a color with a deep yellow tint, and color numbers "1637," "1638," and "1639" are colors with a light yellow tint. The greater this ratio, the better the thermal stability and the more suppressed the discoloration of the sample.

[0150] [YI Value] The resulting pellets of the resin compositions of Examples I-1 to I-3 and Comparative Example I-4 were crushed and filled into a cylinder having an inner diameter of 32 mm and a height of 30 mm, and the yellow index (YI value) was measured in this state using a spectrophotometer (manufactured by Nippon Denshoku Industries Co., Ltd.) A larger YI value means that the resin composition is colored yellow after heating, and indicates poorer thermal stability.

[0151]

[0152] As can be seen from Table I-1, the resin compositions of Examples I-1 to I-3, which contain an ethylene-modified PVA resin, an alkaline earth metal compound, and a specific amount of nickel compound, have superior thermal stability and are less susceptible to discoloration due to thermal degradation than the resin composition of Comparative Example I-1, which does not contain a nickel compound; the resin composition of Comparative Example I-2, which contains a nickel compound in excess of a specific range; the resin composition of Comparative Example I-3, which does not contain an alkaline earth metal compound; and the resin composition of Comparative Example I-4, which uses an unmodified PVA resin. Furthermore, the multilayer structures, molded articles, and food packaging articles having layers containing the resin compositions of Examples I-1 to I-3 also have superior thermal stability and are less susceptible to discoloration due to thermal degradation.

[0153] <<Second Aspect>> Prior to the Examples, the following components were prepared. Ethylene-modified PVA resin: pellets of PVA resin (non-crosslinked) having an ethylene structural unit content of 7.4 mol%, a melting point of 213°C, and a saponification degree of 98 mol%. Unmodified PVA resin: pellets of PVA resin (non-crosslinked) having an ethylene structural unit content of 0 mol%, a melting point of 226°C, and a saponification degree of 99 mol%. Acetic acid and / or a salt thereof: acetic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.). Nickel compound: nickel(II) oxide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.).

[0154] Example II-1: The ethylene-modified PVA resin pellets were dry-blended with the acetic acid to a concentration of 500 ppm relative to the mass of the resin composition, and the nickel oxide to a concentration of 0.001 ppm, calculated as a metal, relative to the mass of the PVA resin, to obtain a mixture. The mixture was then fed to a twin-screw extruder (20 mmφ) equipped with a two-hole die, and extruded under the following extrusion conditions. The extruded strands were cooled and solidified by air cooling. The solidified strands were then cut using a pelletizer to obtain pellets of the resin composition.

[0155] [Extrusion conditions] Extruder set temperatures (°C): C1 / C2 / C3 / C4 / C5 / C6 = 200 / 210 / 225 / 225 / 225 / 225

[0156] Example II-2 Pellets of a resin composition were obtained in the same manner as in Example II-1, except that the content of nickel oxide in terms of metal was changed to 0.1 ppm relative to the mass of the resin composition.

[0157] Example II-3 Pellets of a resin composition were obtained in the same manner as in Example II-1, except that the content of nickel oxide in terms of metal was changed to 1.0 ppm relative to the mass of the resin composition.

[0158] Comparative Example II-1 Pellets of a resin composition were obtained in the same manner as in Example II-1, except that nickel oxide was not used.

[0159] Comparative Example II-2 Pellets of a resin composition were obtained in the same manner as in Example II-1, except that the content of nickel oxide in terms of metal was changed to 10 ppm relative to the mass of the resin composition.

[0160] Comparative Example II-3 Pellets of a resin composition were obtained in the same manner as in Example II-1, except that the content of nickel oxide in terms of metal was changed to 1.0 ppm relative to the mass of the resin composition and acetic acid was not used.

[0161] Comparative Example II-4 Pellets of a resin composition were obtained in the same manner as in Example II-1, except that an unmodified PVA resin was used instead of the ethylene-modified PVA resin in Example II-1, and the content of nickel oxide, calculated as metal, was changed to 0.1 ppm relative to the mass of the resin composition.

[0162] The pellets of the resin compositions of Examples II-1 to II-3 and Comparative Examples II-1 to II-4 were used to evaluate the thermal stability as follows, and the results are shown in Table 1 below.

[0163] [Evaluation of coloration due to thermal degradation] Pellets of the resin compositions obtained in Examples II-1 to II-3 and Comparative Examples II-1 to II-4 were used as samples, and a visual analyzer IRIS VA400 (manufactured by Alphamos) was used to evaluate the color number "1604" (R: 104, G: 72, B: 72) and "1605" (R: 104, G: 72, B: 88) relative to the sum of color numbers "2183" (R: 136, G: 136, B: 120), "2184" (R: 136, G: 136, B: 136), and "2185" (R: 136, G: 136, B: 152). The ratio of the sum to the sum ("2183" + "2184" + "2185") / ("1604" + "1605") was evaluated. The results are shown in Table 1 below. Color numbers "1604" and "1605" are colors with a deep yellow tint, while color numbers "2183", "2184" and "2185" are colors with a light yellow tint. The greater this ratio, the better the thermal stability and the more suppressed the discoloration of the sample.

[0164] The resulting pellets of the resin compositions of Examples II-1 to II-3 and Comparative Example II-4 were packed into a cylinder with an inner diameter of 32 mm and a height of 30 mm, and the yellow index (YI value) was measured in this state using a spectrophotometer (manufactured by Nippon Denshoku Industries Co., Ltd.) The larger this value, the more yellow the resin composition became after heating, which means that the thermal stability was poor.

[0165]

[0166] As can be seen from Table 1, the resin compositions of Examples II-1 to II-3, which contain an ethylene-modified PVA resin, acetic acid and / or a salt thereof, and a specific amount of a nickel compound, have excellent thermal stability and are less susceptible to discoloration due to thermal degradation than the resin composition of Comparative Example II-1, which does not contain a nickel compound; the resin composition of Comparative Example II-2, which contains a nickel compound in an amount greater than the specific range; the resin composition of Comparative Example II-3, which does not contain acetic acid and / or a salt thereof; and the resin composition of Comparative Example II-4, which uses an unmodified PVA resin. Furthermore, the multilayer structures, molded articles, and food packages having layers containing the resin compositions of Examples II-1 to II-3 also have excellent thermal stability and are less susceptible to discoloration due to thermal degradation.

[0167] 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 intended to fall within the scope of the present invention.

[0168] The resin composition has excellent thermal stability and can suppress discoloration due to thermal degradation. Therefore, it is useful as a packaging material for various foods, as well as for seasonings such as mayonnaise and dressings, fermented foods such as miso, oily foods such as salad oil, beverages, cosmetics, medical products, etc., and as a material for molded products to be packaged for pesticides, detergents, civil engineering additives, disinfectants, dyes, pigments, etc.

Claims

1. A resin composition containing a polyvinyl alcohol resin, a nickel compound, and compound (X), wherein the polyvinyl alcohol resin is an ethylene-modified polyvinyl alcohol resin containing 1 to 19 mol% of ethylene structural units, and compound (X) is at least one selected from alkaline earth metal compounds, and acetic acid and / or a salt thereof other than alkaline earth metal compounds, and the content of the nickel compound in terms of metal is 0.0001 to 2 ppm relative to the mass of the resin composition.

2. The resin composition according to claim 1, wherein the compound (X) comprises an alkaline earth metal compound.

3. The resin composition according to claim 2, wherein the content of said alkaline earth metal compound in terms of metal is 0.0001 to 1 ppm based on the mass of the resin composition.

4. The resin composition according to claim 2 or 3, wherein the alkaline earth metal compound comprises a magnesium compound.

5. A resin composition according to any one of claims 2 to 4, wherein the mass ratio of the content of the alkaline earth metal compound converted into metal to the content of the nickel compound converted into metal is 0.000005 to 10,000.

6. The resin composition according to any one of claims 1 to 5, wherein the compound (X) contains acetic acid and / or a salt thereof other than an alkaline earth metal compound.

7. The resin composition according to claim 6, wherein the content of said acetic acid and / or a salt thereof is 10 to 10,000 ppm based on the mass of the resin composition.

8. The resin composition according to claim 6 or 7, wherein the mass ratio of the content of said acetic acid and / or a salt thereof to the content of said nickel compound is 5 to 100,000,000.

9. The resin composition according to any one of claims 1 to 8, wherein the content of the nickel compound in terms of metal is 0.0001 ppm or more and less than 0.5 ppm based on the mass of the resin composition.

10. The resin composition according to any one of claims 1 to 9, wherein the polyvinyl alcohol resin is non-crosslinked.

11. A molding material comprising the resin composition according to any one of claims 1 to 10.

12. The molding material according to claim 11, wherein the molding material is in the form of pellets.

13. A multilayer structure having a layer containing the resin composition according to any one of claims 1 to 10.

14. A molded article comprising the multilayer structure of claim 13.

15. A food package comprising the multilayer structure of claim 13.

16. A method for producing a resin composition according to any one of claims 1 to 10, comprising the step of melt-mixing a composition raw material containing the polyvinyl alcohol resin and the nickel compound.

17. A method for producing the multilayer structure according to claim 13, comprising the step of melt-molding a layer containing a resin composition.

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