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

Abstract

To provide a resin composition that exhibits superior thermal stability and is capable of suppressing coloration caused by thermal degradation.SOLUTION: A polyvinyl alcohol resin composition contains a polyvinyl alcohol resin, a nickel compound, and acetic acid and / or a salt thereof, the polyvinyl alcohol resin being an ethylene-modified polyvinyl alcohol resin including 1 to 19 mol% of ethylene structural units, and the nickel compound having a metal-converted content of 0.0001 to 2 ppm with respect to the mass of the resin composition.SELECTED DRAWING: None

Description

[Technical Field]

[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. [Background technology]

[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 internal additives, adhesives for paper, wood, and inorganic materials, stabilizers for emulsion polymerization and suspension polymerization, optical films, etc.

[0003] However, PVA resins generally have problems with thermal stability, such as their 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. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-309607 [Patent Document 2] Special Publication No. 6-47628 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-336574 Summary of the Invention [Problem to be solved by the invention]

[0008] According to the studies of the present inventors, the technology disclosed in 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 technologies disclosed in Patent Documents 2 and 3 both involve resin compositions containing only nickel compounds as metal salts, and the addition of small amounts of nickel compounds does not improve thermal stability, resulting in the problem of discoloration due to thermal degradation.

[0010] Under these circumstances, an object of the present invention is to provide a resin composition that is excellent in thermal stability and can suppress discoloration due to thermal degradation. [Means for solving the problem]

[0011] However, in view of the above circumstances, the present inventors have conducted extensive research and have found that by incorporating a trace amount of a nickel compound and acetic acid and / or a salt thereof into an ethylene-modified PVA resin in a resin composition, a resin composition can be obtained that is excellent in thermal stability and can suppress discoloration due to thermal degradation. Based on this discovery, the present invention has been completed.

[0012] That is, the present invention has the following aspects. [1] A resin composition containing a PVA resin, a nickel compound, and acetic acid and / or a salt thereof, the PVA resin is an ethylene-modified PVA resin containing 1 to 19 mol% of ethylene structural units, A resin composition, wherein 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 the content of the acetic acid and / or a salt thereof is 10 to 10,000 ppm based on the mass of the resin composition. [3] The resin composition according to [1] or [2], 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. [4] The resin composition according to any one of [1] to [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. [5] The resin composition according to any one of [1] to [4], wherein the PVA resin is non-crosslinked. [6] A molding material comprising the resin composition according to any one of [1] to [5]. [7] The molding material according to [6], wherein the molding material is in pellet form. [8] A multilayer structure having a layer containing the resin composition according to any one of [1] to [5]. [9] A molded article comprising the multilayer structure according to [8].

[10] A food packaging product comprising the multilayer structure described in [8].

[11] A method for producing the resin composition according to any one of [1] to [5], A method for producing a resin composition, comprising the step of melt-mixing a resin composition raw material containing the PVA resin and the nickel compound.

[12] A method for producing the multilayer structure according to [8], A method for producing a multilayer structure, comprising a step of melt-molding a layer containing a resin composition. [Effects of the Invention]

[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. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described below based on examples of embodiments for carrying out the present invention, but the present invention is not limited to the embodiments described below.

[0015] In this specification, "x and / or y (x and y are optional configurations)" means at least one of x and y, and can mean three possibilities: x only, y only, or x and y. When expressed as "X to Y" (X and Y are any numbers), unless otherwise specified, it 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." In the present specification, when numerical ranges are described in stages, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. In addition, in the numerical ranges described in this specification, the upper or lower limit of the numerical range can also be replaced with the values shown in the examples. In this specification, the term "layer" includes not only thick layers but also relatively thin layers such as "films," "tapes," and "sheets."

[0016] <Resin composition> A resin composition according to one embodiment of the present invention (hereinafter referred to as "the resin composition") contains a PVA resin, and also contains acetic acid and / or a salt thereof, and a specific trace amount of a nickel compound. That is, the base resin of the present resin composition is a PVA resin, and the content of the PVA resin in the present resin composition 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.

[0017] [PVA resin] The PVA resin used in this 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.

[0018] 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.

[0019] The content of ethylene structural units in the PVA resin was determined by proton NMR of the polyvinyl ester containing ethylene structural units, which is the 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 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.

[0020] 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 higher 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 lower than the upper limit, the PVA resin tends to be less susceptible to thermal degradation. The degree of saponification of such a PVA resin can be measured in accordance with JIS K6726.

[0021] 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.

[0022] 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 for obtaining 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.

[0023] Examples of the structural unit derived from the other copolymerizable monomer include those having a primary hydroxyl group in the side chain, and preferred examples include the structural unit of the following general formula (1): [ka]

[0024] R 1 ~R 3 is 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 hydroxyl groups, fluorine, chlorine, bromine, etc. as substituents).

[0025] 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, etc. 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, etc. as a substituent), as well as -CO-, -CO(CH2) m CO-, -CO(CH2) m COR 4 -, -NR 5 -,-CONR 5 - etc. (R 4 ,R 5 are independently any substituent, preferably a hydrogen atom or an alkyl group, and m is a natural number.

[0026] In order to obtain the PVA resin having a primary hydroxyl group in the side chain, for example, (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; (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 primary hydroxyl groups in the side chains; Among these, the above 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 the above method (I), ethylene and vinyl ester monomers are copolymerized with a monomer having a primary hydroxyl group on the side chain and / or a monomer in which the hydroxyl group is protected with an ester or the like.

[0027] 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.

[0028] 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 acetate esters of the above-mentioned 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.

[0029] 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.

[0030] 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 a copolymerization component in the above-mentioned 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 its side chain. [ka]

[0031] 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. [ka]

[0032] In the above 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, (anhydrous) phthalic acid, (anhydrous) maleic acid, and (anhydrous) itaconic acid, 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; acrylamides such as acrylamidopropyldimethylamine, or its acid salts or its quaternary salts; methacrylamide, Examples of suitable vinyl silanes 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.

[0033] 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.

[0034] The alcohol used as a solvent in 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] The PVA resin may be a crosslinked PVA resin or a non-crosslinked PVA resin. In the case of crosslinked PVA resins, the OH groups in the PVA resin usually become reaction sites, resulting in a decrease in their amount, but in the case of non-crosslinked PVA resins, there are sufficient OH groups in the resin. As will be described later, it is believed that the OH groups in the resin contribute to thermal stability, so non-crosslinked PVA resins with a larger number of OH groups are preferred. Known methods for crosslinking PVA resin include, for example, a method of dehydration crosslinking in a dry heat stretching step 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 polymer, an organic peroxide, an isocyanate compound, a urethane compound, an epoxy compound, a dialdehyde, etc. It is preferable to use a non-crosslinked PVA resin in this embodiment that has not been subjected to such a crosslinking reaction.

[0039] [Nickel compounds] Examples of nickel compounds 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.

[0040] Examples of the inorganic nickel compound include nickel oxide, nickel hydroxide, and inorganic salts of nickel. Examples of the nickel oxide include nickel (II) oxide, nickel (III) oxide, nickel (IV) oxide, and nickel dioxide. Examples of the nickel hydroxide include nickel(I) hydroxide and nickel(II) hydroxide. Examples of the inorganic salt of nickel include nickel(II) chloride, nickel(II) phosphate, nickel(II) sulfate, and nickel nitrate. Among these, nickel oxide is preferred, and nickel (II) oxide is more preferred, in that the effects of the present invention can be easily obtained.

[0041] Examples of the organic nickel compounds include nickel carboxylates such as nickel acetate, nickel butyrate, and nickel stearate.

[0042] 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 dispersibility in the resin composition and productivity. From the viewpoint 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.

[0043] 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 its ease of handling.

[0044] 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. The metal-equivalent content of the nickel compound is the content of elemental nickel. When the metal-equivalent content of such nickel compound is equal to or less than the upper limit, the resin composition tends to be less susceptible to thermal decomposition and coloration, and when it is equal to or more than the lower limit, the resin composition tends to be more effective in suppressing thermal degradation.

[0045] The metal-equivalent content of the nickel compound in the resin composition of this embodiment can be determined, for example, by heating and ashing the resin composition, treating it with an acid such as hydrochloric acid, adding pure water to the resulting solution, and measuring the test solution with an atomic absorption photometer.

[0046] [Acetic acid and / or its salts] Specific examples of acetic acid and / or a salt thereof used in this embodiment include acetic acid, sodium acetate, potassium acetate, calcium acetate, magnesium 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, potassium acetate, calcium acetate, and magnesium 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.

[0047] 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. When the content is equal to or less than the upper limit, the thermal stability of the resin composition tends to be excellent, and when the content is equal to or more than the lower limit, the moldability of the resin composition tends to be excellent.

[0048] 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).

[0049] 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 it is equal to or more than the lower limit, the moldability of the resin composition tends to be excellent.

[0050] Although the reason why excellent effects can be obtained by combining appropriate amounts of the nickel compound and acetic acid and / or its salt is not clear, it is presumed that the combined use of a specific amount of the nickel compound and the acetic acid and / or its salt reduces the pH appropriately, strengthening the hydrogen bonds in the hydroxyl groups of the PVA resin and thereby improving thermal stability.

[0051] [Other thermoplastic resins] The resin composition may contain a thermoplastic resin 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 of the resin composition, preferably 20% by mass or less, more preferably 10% by mass or less, the lower limit being typically 0% by mass). As the other thermoplastic resin, known thermoplastic resins can be used, such as polyester resins, polystyrene resins, polyvinyl chloride resins, polycarbonate resins, ionomers, polyvinylidene chloride, polyester elastomers, polyurethane elastomers, chlorinated polyethylene, chlorinated polypropylene, etc. These can be used alone or in combination of two or more.

[0052] [Other compounding agents] The resin composition may also contain additives (excluding nickel compounds and acetic acid and / or its salts) that are generally incorporated into ethylene-modified PVA resins, provided that the additives do not impair the effects of the present invention (for example, typically 30% by mass or less of the resin composition, preferably 20% by mass or less, more preferably 10% by mass or less, the lower limit being typically 0% by mass). Examples of such additives include inorganic double salts (e.g., hydrotalcite), 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 resins containing carbon-carbon unsaturated bonds. 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 photoinitiators (e.g., benzophenone), antioxidants other than those mentioned above, and deodorants (e.g., activated carbon) may also be added, as well as 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.

[0053] [Method for producing resin composition] The resin composition 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 is preferably produced by a method including a step of melt mixing a composition raw material containing the ethylene-modified PVA resin and the nickel compound. These production methods can also be used in any combination.

[0054] The dry blending method may be, for example, (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.

[0055] 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 resulting mixture is melt-kneaded.

[0056] 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 solution is coagulated and molded, and then the solid-liquid separation is performed by a known means, followed by drying; 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 process of a PVA resin, the solution is coagulated and molded, and then the solid-liquid separation is performed by a known means, followed by drying.

[0057] Examples of the impregnation method include (vi) a method in which pellets of an ethylene-modified PVA resin are brought into contact with an aqueous solution containing a nickel compound and acetic acid and / or a salt thereof, so that the nickel compound and acetic acid and / or a salt thereof are contained in the ethylene-modified PVA resin, and then the resin is dried.

[0058] 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.

[0059] In the impregnation method, the contents (in terms of metal) of acetic acid and / or its salt and nickel compound 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.

[0060] 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.

[0061] 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.

[0062] The resin composition obtained by each of the above-mentioned production methods may be in any shape, but pellets are preferred because the effects of the present invention can be more easily achieved. The pellets contain the resin composition, and preferably consist solely of the resin composition. The pellets may be, for example, spherical, oval, cylindrical, cubic, or rectangular, but are typically oval or cylindrical. From the viewpoint 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. 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. Moreover, it is preferable that the shape and size of the pellet-shaped PVA resin used in each of the above-mentioned production methods are similar.

[0063] The water content of the present resin composition 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.

[0064] The water content of the resin composition is measured and calculated by the following method. The mass (W1) of this resin composition before drying is weighed on an electronic balance, dried in a hot air dryer at 150°C for 5 hours, and then left to cool in a desiccator for 30 minutes, after which the mass (W2) is weighed and calculated using the following formula. Moisture content (mass%)=[(W1-W2) / W1]×100

[0065] When the resin composition is in the form of pellets, it is also preferable to apply a known lubricant to the surface of the pellets 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 with 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 in the resin composition is usually 5% by mass or less, preferably 1% by mass or less. The lower limit is usually 0% by mass.

[0066] The resin composition 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 is suppressed. A difference of 0.1 in the ratio is very significant, since it appears as a large difference in yield in actual production.

[0067] The yellow index (YI value) of the present resin composition 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 likely it is that coloration due to thermal degradation is suppressed. The YI value can be measured using a spectrocolorimeter (manufactured by Nippon Denshoku Industries Co., Ltd.).

[0068] The resin composition thus obtained is prepared into various forms, such as pellets, powder, or liquid, and is provided as a molding material for various molded products. In particular, in the present embodiment, when the resin composition is provided as a material for melt molding, the effects of the present invention tend to be more efficiently obtained, which is preferable. The present resin composition also includes resin compositions obtained by mixing resins other than the PVA resin used in the present resin composition.

[0069] Examples of the molded article include a single layer film molded from the present resin composition, as well as a multilayer structure having at least one layer made of the present resin composition.

[0070] <Multilayer structure> A multilayer structure according to one embodiment of the present invention (hereinafter referred to as "the multilayer structure") has a layer containing the present resin composition, and preferably has a layer consisting solely of the present resin composition. The layer containing the present resin composition (hereinafter simply referred to as "the present resin composition layer") can be laminated with another substrate (hereinafter, the resin used in the substrate may be abbreviated as "substrate resin") whose main component is a thermoplastic resin other than the present resin composition to impart additional strength, protect the present resin composition layer from the effects of moisture, etc., or impart other functions.

[0071] 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 dissolving these polyolefins in an unsaturated carboxylic acid or its ester. Examples of the polyolefin resin include polyolefin resins in the broad sense, including modified olefin resins such as unsaturated carboxylic acid-modified polyolefin resins graft-modified with ter, 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 to represent types of polyethylene.

[0072] 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.

[0073] The layer structure of the present multilayer structure can be any combination, such as a / b, b / a / b, a / b / a, a1 / a2 / b, a / b1 / b2, b2 / b1 / a / b1 / b2, or b2 / b1 / a / b1 / a / b1 / b2, where a (a1, a2, ...) represents the resin composition layer and b (b1, b2, ...) represents the base resin layer. Furthermore, when R represents a recycled layer containing a mixture of the present resin composition and a thermoplastic resin other than the present resin composition, obtained by remelting and molding edges or defective products generated during the manufacturing process of the present multilayer structure, the layer structure can be 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 the like. The total number of layers in the present multilayer structure is usually 2 to 15, preferably 3 to 10. In the above layer structure, an adhesive resin layer containing an adhesive resin may be interposed between the respective layers, if necessary.

[0074] 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 through 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.

[0075] In the present multilayer structure, when an adhesive resin layer is used between the present resin composition layer and the base resin layer, since the adhesive resin layers are located on both sides of the present resin composition layer, it is preferable to use an adhesive resin with excellent hydrophobicity.

[0076] 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 the 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 resin). These may be used alone or in combination of two or more.

[0077] The lamination of the present resin composition layer and the above-mentioned 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 present resin composition, a method of melt-extrusion laminating the present resin composition onto a substrate resin layer, a method of co-extruding the present resin composition and the substrate resin, a method of dry-laminating the present resin composition (layer) and the substrate resin (layer) using a known adhesive such as an organic titanium compound, an isocyanate compound, a polyester compound, or a polyurethane compound, and a method of applying a solution of the present resin composition onto the substrate resin and then removing the solvent. Among these, from the viewpoints of cost and environment, it is preferable to produce the layer including the present resin composition layer by a step of melt-molding the layer, and specifically, a co-extrusion method is preferred.

[0078] The multilayer structure 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, simultaneous stretching or sequential stretching may be used. Furthermore, the stretching method may be a roll stretching method, tenter stretching method, tubular stretching method, stretch-blow method, vacuum pressure forming, or the like, whichever provides a higher stretch ratio. The stretching temperature is a temperature near the melting point of the multilayer structure, and is usually selected from the range of 40 to 170°C, preferably about 60 to 160°C. 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.

[0079] The stretched multilayer structure may be heat-set to provide dimensional stability. Heat setting can be performed by known means, for example, by heat-treating the stretched multilayer structure while maintaining tension at typically 80 to 180°C, preferably 100 to 165°C, for typically 2 to 600 seconds.

[0080] When the stretched multilayer structure is to be used as a shrink film, the heat-shrinkability can be imparted by, for example, applying cold air to the stretched multilayer structure to cool and fix it, without carrying out the heat-setting process described above.

[0081] The thickness of the present multilayer structure (including a stretched one), and further the thickness of the present resin composition layer, substrate resin layer, and adhesive resin layer that constitute the multilayer structure, cannot be generally determined depending on the layer configuration, type of substrate resin, type of adhesive resin, intended use, packaging form, required physical properties, etc., but the thickness of the present multilayer structure (including a stretched one) is usually 10 to 5,000 μm, preferably 30 to 3,000 μm, and more preferably 50 to 2,000 μm. The present resin composition layer is usually 1 to 500 μm, preferably 3 to 300 μm, and more preferably 5 to 200 μm. The substrate resin layer is usually 5 to 3,000 μm, preferably 10 to 2,000 μm, and more preferably 20 to 1,000 μm. The adhesive resin layer is usually 0.5 to 250 μm, preferably 1 to 150 μm, and more preferably 3 to 100 μm.

[0082] Furthermore, the thickness ratio of the present resin composition layer to the base resin layer in the present multilayer structure (present resin composition layer / base resin layer), when there are multiple layers, is typically 1 / 99 to 50 / 50, preferably 5 / 95 to 45 / 55, and more preferably 10 / 90 to 40 / 60, and when there are multiple layers, the thickness ratio of the present resin composition layer to the adhesive resin layer (present resin composition layer / adhesive resin layer), when there are multiple layers, is typically 10 / 90 to 99 / 1, preferably 20 / 80 to 95 / 5, and more preferably 50 / 50 to 90 / 10.

[0083] This multilayer structure can also be used to produce cup- or tray-shaped molded articles and food packaging. In such cases, a drawing method is typically used, specifically vacuum forming, pressure forming, vacuum-pressure forming, plug-assisted vacuum-pressure forming, etc. Furthermore, blow molding is used 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.

[0084] Single-layer films formed from the present resin composition, bags made from the present multilayer structure, and containers and lids made from cups, trays, tubes, bottles, etc. are useful as packaging materials and containers for a variety of items, including general foods, as well as seasonings such as mayonnaise and dressings, fermented foods such as miso, oily foods such as salad oil, beverages, cosmetics, pharmaceuticals, etc. [Example]

[0085] 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 by mass.

[0086] Prior to the examples, the following ingredients were prepared: Ethylene-modified PVA resin: Pellets of PVA resin (non-crosslinked) with 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: PVA resin (non-crosslinked) pellets with 0 mol% ethylene structural unit content, melting point of 226°C, and saponification degree of 99 mol% Acetic acid and / or its salts: acetic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), Nickel compound: Nickel(II) oxide (Fujifilm Wako Pure Chemical Industries, Ltd.)

[0087] Example 1 The ethylene-modified PVA resin pellets were dry-blended with the acetic acid at 500 ppm and the nickel oxide at 0.001 ppm (as metal) relative to the mass of the resin composition to obtain a mixture. The mixture was then fed into 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.

[0088] [Extrusion conditions] Extruder setting temperature (℃): C1 / C2 / C3 / C4 / C5 / C6 =200 / 210 / 225 / 225 / 225 / 225

[0089] <Example 2> Pellets of a resin composition were obtained in the same manner as in Example 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.

[0090] Example 3 Pellets of a resin composition were obtained in the same manner as in Example 1, except that the content of nickel oxide, converted into metal, was changed to 1.0 ppm relative to the mass of the resin composition.

[0091] <Comparative Example 1> Pellets of a resin composition were obtained in the same manner as in Example 1, except that nickel oxide was not used.

[0092] <Comparative Example 2> Pellets of a resin composition were obtained in the same manner as in Example 1, except that the content of nickel oxide, converted into metal, was changed to 10 ppm relative to the mass of the resin composition.

[0093] <Comparative Example 3> Pellets of a resin composition were obtained in the same manner as in Example 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.

[0094] <Comparative Example 4> Pellets of the resin composition were obtained in the same manner as in Example 1, except that an unmodified PVA resin was used instead of the ethylene-modified PVA resin in Example 1, and the content of nickel oxide, calculated as metal, was changed to 0.1 ppm relative to the mass of the resin composition.

[0095] The following thermal stability evaluation was carried out using the obtained pellets of the resin compositions of Examples 1 to 3 and Comparative Examples 1 to 4. The results are shown in Table 1 below.

[0096] [Evaluation of coloration due to thermal degradation] Pellets of the resin compositions obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were used as samples, and the ratio 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) was evaluated using a visual analyzer IRIS VA400 (manufactured by Alphamos). 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.

[0097] The obtained pellets of the resin compositions of Examples 1 to 3 and Comparative Example 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 using a spectrophotometer (manufactured by Nippon Denshoku Industries Co., Ltd.) after being completely worn out. The larger this value, the more yellow the resin composition becomes after heating, which means that the thermal stability is poor.

[0098] [Table 1]

[0099] As can be seen from Table 1, the resin compositions of Examples 1 to 3, which contain an ethylene-modified PVA resin, acetic acid and / or a salt thereof, and a specific amount of a nickel compound, have superior thermal stability and are less susceptible to discoloration due to thermal degradation than the resin composition of Comparative Example 1, which does not contain a nickel compound; the resin composition of Comparative Example 2, which contains a nickel compound in an amount greater than a specific range; the resin composition of Comparative Example 3, which does not contain acetic acid and / or a salt thereof; and the resin composition of Comparative Example 4, which uses an unmodified PVA resin. The multilayer structures, molded articles, and food packaging articles having layers containing the resin compositions of Examples 1 to 3 also have excellent thermal stability, and are inhibited from becoming discolored due to thermal degradation. [Industrial Applicability]

[0100] 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 acetic acid and / or a salt thereof, the polyvinyl alcohol resin is an ethylene-modified polyvinyl alcohol resin containing 1 to 19 mol% of ethylene structural units, A resin composition, wherein 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 content of the acetic acid and / or salt thereof is 10 to 10,000 ppm based on the mass of the resin composition.

3. The resin composition according to claim 1 or 2, 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.

4. 3. The resin composition according to claim 1, wherein the mass ratio of the content of the acetic acid and / or salt thereof to the content of the nickel compound is 5 to 100,000,000.

5. The resin composition according to claim 1 or 2, wherein the polyvinyl alcohol resin is non-crosslinked.

6. A molding material comprising the resin composition according to claim 1 or 2.

7. The molding material according to claim 6, wherein the molding material is in the form of pellets.

8. A multilayer structure having a layer containing the resin composition according to claim 1 or 2.

9. A molded article comprising the multilayer structure of claim 8.

10. A food package comprising the multilayer structure of claim 8.

11. A method for producing the resin composition according to claim 1 or 2, A method for producing a resin composition, comprising the step of melt-mixing a resin composition raw material containing the polyvinyl alcohol resin and the nickel compound.

12. 9. A method for producing the multilayer structure of claim 8, comprising: A method for producing a multilayer structure, comprising a step of melt-molding a layer containing a resin composition.

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