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

Abstract

The following is provided as a resin composition having excellent thermal stability.　This resin composition comprises a polyvinyl alcohol resin, a titanium compound, and a compound (X), wherein: the polyvinyl alcohol resin is an ethylene-modified polyvinyl alcohol resin containing 1-19 mol% of an ethylene structural unit; the compound (X) is at least one selected from the group consisting of an alkaline earth metal compound (A), an alkali metal compound (B), sorbic acid (C), and acetic acid (D); and the content of the titanium compound in terms of 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 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 coating agents, paper modifiers such as 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 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 structural units.

[0005] Furthermore, Patent Document 2 proposes a PVA resin having a viscosity-average degree of polymerization of a specific amount or more and containing a titanium compound in an amount of 5 to 500 ppm relative to the PVA resin in order to improve moist heat resistance.

[0006] Furthermore, Patent Document 3 proposes a PVA polymer film containing at least one metal element selected from the group consisting of transition metals and aluminum, in order to obtain a PVA polymer film that has excellent slip properties, suppresses the occurrence of wrinkles even when wound into a long film roll, is less likely to be discolored, and has excellent transparency.

[0007] Furthermore, in order to improve thermal stability, for example, Patent Document 4 proposes a modified ethylene-vinyl alcohol resin composition containing a modified ethylene-vinyl alcohol resin having 1 to 16.5 mol % of primary hydroxyl group structural units in the side chains and 0.1 to 500 ppm of a conjugated polyene.

[0008] JP 2000-309607 A JP 5-222609 A International Publication No. 2013 / 146533 JP 2023-077420 A

[0009] According to the investigations of the present inventors, although the technology disclosed in Patent Document 1 has a certain effect on thermal stability, the thermal stability is still insufficient and there is room for improvement.

[0010] Furthermore, the technology disclosed in Patent Document 2 improves moist heat resistance by incorporating 5 to 500 ppm of titanium into PVA resin, but if the amount is less than 5 ppm, the crosslinking effect is low and high moist heat resistance cannot be obtained.

[0011] Furthermore, the technology disclosed in Patent Document 3 uses an unmodified PVA resin and further contains a titanium compound, but the thermal stability is still insufficient and there is room for improvement.

[0012] Furthermore, according to the investigations of the present inventors, although the technology disclosed in Patent Document 4 has a certain effect on thermal stability, the thermal stability is still insufficient and there is room for improvement.

[0013] In view of this background, the present invention provides a resin composition having excellent thermal stability.

[0014] However, in view of the above circumstances, the present inventors have conducted extensive research and found that a resin composition having excellent thermal stability can be obtained by incorporating a trace amount of a titanium compound and a specific compound (X) into an ethylene-modified PVA resin.

[0015] That is, the present invention has the following aspects. [1] A resin composition containing a PVA resin, a titanium compound, and compound (X), wherein the PVA resin is an ethylene-modified PVA resin containing 1 to 19 mol% of ethylene structural units, and the compound (X) is at least one selected from the group consisting of alkaline earth metal compound (A), alkali metal compound (B), sorbic acid (C), and acetic acid (D), and the content of the titanium 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 compound (X) is alkaline earth metal compound (A). [3] The resin composition according to [2], wherein the content of the alkaline earth metal compound (A) 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 (A) is a magnesium compound. [5] The resin composition according to any one of [1] to [4], wherein the compound (X) is an alkali metal compound (B). [6] The resin composition according to [5], wherein the content of the alkali metal compound (B) in terms of metal is 0.0001 to 5000 ppm relative to the mass of the resin composition. [7] The resin composition according to [5] or [6], wherein the alkali metal compound (B) is a sodium compound. [8] The resin composition according to any one of [1] to [7], wherein the compound (X) is sorbic acid (C). [9] The resin composition according to [8], wherein the content of the sorbic acid (C) is 0.005 to 100 ppm relative to the mass of the resin composition.

[10] The resin composition according to any one of [1] to [9], wherein the compound (X) is acetic acid (D).

[11] The resin composition according to

[10] , wherein the content of the acetic acid (D) is 10 to 10,000 ppm relative to the mass of the resin composition.

[12] The resin composition according to any one of [1] to

[11] , wherein the content of the titanium compound in terms of metal is 0.0001 ppm or more and less than 1 ppm relative to the mass of the resin composition.

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

[12] .

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

[12] .

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

[14] .

[16] A food packaging product comprising the multilayer structure according to

[14] .

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

[12] , comprising a step of melt-mixing a resin composition raw material containing the PVA resin and the titanium compound.

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

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

[0016] The resin composition of the present invention has excellent thermal stability. 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.

[0017] 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.

[0018] In this specification, "x and / or y (x and y are any constituent or component)" refers to three combinations: x only, y only, and x and y. When "X to Y" (X and Y are any numbers) is used, unless otherwise specified, it encompasses "X or more and Y or less," as well as "preferably more than X" or "preferably less than Y." When "X or more" (X is any number) or "Y or less" (Y is any number) is used, it also encompasses "preferably more than X" or "preferably less than Y." Regarding 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 the numerical range can be replaced with the value shown in the examples. In this specification, the term "layer" refers to a thick layer as well as a relatively thin layer such as a "film," "tape," or "sheet."

[0019] A resin composition according to one embodiment of the present invention (hereinafter, sometimes referred to as "the resin composition") comprises a PVA resin as a main component and a specific trace amount of a titanium compound and compound (X), wherein compound (X) contains at least one selected from the group consisting of alkaline earth metal compound (A), alkali metal compound (B), sorbic acid (C), and acetic acid (D). 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 the following order: when compound (X) of the resin composition contains alkaline earth metal compound (A), it is referred to as a "first aspect," when it contains alkali metal compound (B), it is referred to as a "second aspect," when it contains sorbic acid (C), it is referred to as a "third aspect," and when it contains acetic acid (D), it is referred to as a "fourth aspect."

[0020] <<First Aspect>> The first aspect includes the following aspects <I-1> to <I-10>. <I-1> A resin composition containing a PVA resin, a titanium compound, and an alkaline earth metal compound (A), wherein the PVA resin is an ethylene-modified PVA resin containing 1 to 19 mol% of ethylene structural units, and the content of the titanium 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 (A), 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>, wherein the alkaline earth metal compound (A) is a magnesium compound. <I-4> The resin composition according to any one of <I-1> to <I-3>, wherein the content of the titanium compound in terms of metal is 0.0001 ppm or more and less than 1 ppm, relative to the mass of the resin composition. <I-5> A molding material comprising the resin composition according to any one of <I-1> to <I-4>. <I-6> A multilayer structure having a layer comprising the resin composition according to any one of <I-1> to <I-4>. <I-7> A molded article comprising the multilayer structure according to <I-6>. <I-8> A food packaging article comprising the multilayer structure according to <I-6>. <I-9> A method for producing the resin composition according to any one of <I-1> to <I-4>, comprising a step of melt-mixing a resin composition raw material containing the PVA resin and the titanium compound. <I-10> A method for producing the multilayer structure according to <I-6>, comprising a step of melt-molding a layer comprising the resin composition.

[0021] 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> The resin composition according to the first aspect of the present invention (hereinafter, sometimes referred to as "the present resin composition (1)") contains a PVA resin as a main component and specific trace amounts of a titanium compound and an alkaline earth metal compound (A). 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.

[0022] [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 and ethylene in the presence of a polymerization initiator and saponifying the copolymer.

[0023] 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 one or more vinyl ester monomers with other monomers copolymerizable therewith. Any conventionally known monomer can be used as the other copolymerizable monomer. The content of the structural units derived from the other copolymerizable monomers is typically preferably 15 mol % or less, more preferably 10 mol % or less, and even more preferably 5 mol % or less, based on the PVA resin. The PVA resin may be free of any of these structural units.

[0024] As a polymerization method for copolymerizing the ethylene and the vinyl ester-based 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 copolymerization 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 alcohol.

[0025] 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.

[0026] 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. The polymerization reaction temperature is selected from the range of 0 to 150°C. These initiators can be used alone or in combination of two or more.

[0027] Saponification can be carried out by a known method, and is usually carried out by dissolving the obtained copolymer in alcohol or dimethyl sulfoxide in the presence of a saponification catalyst. Examples of saponification solvents include methanol, methyl acetate, dimethyl sulfoxide, and dimethylformamide. These can be used alone or in combination of two or more.

[0028] As the saponification catalyst, for example, an alkaline substance such as potassium hydroxide or sodium hydroxide can be used, which can be used alone or in combination of two or more kinds.

[0029] 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.

[0030] The content of ethylene structural units in the PVA resin is usually 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 greater than the lower limit, the PVA resin tends to have excellent gas barrier properties and thermal stability. On the other hand, when the content of ethylene structural units is equal to or less than the upper limit, the PVA resin tends to have excellent gas barrier properties under high humidity conditions and excellent melt moldability.

[0031] 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 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.

[0032] 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. On the other hand, when the melting point is equal to or lower than the upper limit, the PVA resin tends to be less susceptible to thermal degradation.

[0033] [Titanium Compound] Examples of the titanium compound used in this embodiment include inorganic titanium compounds and organic titanium compounds. The titanium compounds may be used alone or in combination of two or more. Among these, inorganic titanium compounds are preferred.

[0034] Examples of the inorganic titanium compounds include titanium oxide, titanium hydroxide, titanium chloride, and inorganic salts of titanium. Examples of the titanium oxides include titanium(II) oxide, titanium(III) oxide, titanium(IV) oxide, and titanium suboxide. Examples of the titanium hydroxides include titanium(I) hydroxide and titanium(II) hydroxide. Examples of the titanium chlorides include titanium(I) chloride and titanium(II) chloride. Examples of the inorganic salts of titanium include those other than the titanium chlorides, such as titanium phosphate and titanium sulfate. Among these, titanium oxide is preferred, titanium(IV) oxide is more preferred, and rutile-type titanium(IV) oxide is particularly preferred.

[0035] Examples of the organic titanium compounds include titanium carboxylates such as titanium acetate, titanium butyrate, and titanium stearate.

[0036] In addition to the case where the titanium compound is present in the resin composition as a titanium compound, the titanium compound may be present in an ionized state or in the form of a complex interacting with the PVA resin or other ligands.

[0037] The average particle size of the titanium compound is usually 0.001 to 100 μm, preferably 0.01 to 50 μm, and more preferably 0.015 to 20 μm. When the average particle size of the titanium compound is within the above range, the thermal stability tends to be further improved. The average particle size here refers to the median diameter.

[0038] The content of the titanium compound in terms of metal is 0.0001 to 2 ppm, preferably 0.001 to 1 ppm, more preferably 0.001 ppm or more and less than 1 ppm, and even more preferably 0.01 to 0.5 ppm, based on the mass of the resin composition. When the content of the titanium compound is equal to or more than the lower limit, the effect of suppressing thermal degradation tends to be excellent, while when the content is equal to or less than the upper limit, the PVA resin tends to be less susceptible to thermal decomposition and discoloration.

[0039] The content of the titanium compound in terms of metal can be determined by measuring the titanium in a constant volume solution obtained by weighing the resin composition (1) into a platinum crucible, ashing it with a burner and then an electric furnace, thermally decomposing the ashed material with nitric acid and hydrofluoric acid, treating it with a mixed acid of dilute nitric acid and dilute hydrofluoric acid, and measuring the titanium in the constant volume solution by ICP mass spectrometry using an ICP mass spectrometer (Agilent 8800, manufactured by Agilent Technologies).

[0040] It is speculated that the thermal decomposition of PVA resin is caused by the formation of a polyene structure in the main chain due to a dehydration reaction initiated by an OH group in the PVA resin under alkaline conditions. In the present resin composition (1), titanium in the titanium compound is stabilized as a tetravalent ion. Therefore, when a polyene structure is formed in the main chain of the PVA resin, it is thought that the titanium compound stabilizes the polyene structure by coordinating with the double bond of the polyene structure to form a chelate. It is speculated that even a trace amount of titanium compound inhibits the further formation of a polyene structure.

[0041] [Alkaline earth metal compound (A)] Examples of the alkaline earth metal compound (A) used in this embodiment include salts and oxides 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 standpoints of economy and dispersibility, and alkaline earth metal oxides are particularly preferred.

[0042] Examples of the alkaline earth metal salt include inorganic salts of alkaline earth metals and carboxylates of alkaline earth metals.

[0043] Examples of the inorganic salts of alkaline earth metals include alkaline earth metal carbonates, hydrogencarbonates, phosphates, borates, sulfates, chlorides, etc. Examples of the carboxylates of alkaline earth metals 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. Among these, linear saturated carboxylates are preferred in terms of commercial availability, and monocarboxylic acid salts are more preferred.

[0044] Examples of the alkaline earth metal species of the alkaline earth metal compound (A) 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.

[0045] Among these, magnesium oxide is preferred as the alkaline earth metal compound (A). From the viewpoints of economy and dispersibility, it is preferred that the alkaline earth metal compound (A) does not include layered inorganic compounds such as montmorillonite and double salts such as hydrotalcite.

[0046] The alkaline earth metal compound (A) 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). Of these, a powder form is preferred.

[0047] The alkaline earth metal compound (A) can be used alone or in combination of two or more kinds. When multiple kinds of alkaline earth metal compounds are used, the content thereof is the total content (mass) of the multiple kinds of alkaline earth metal compounds in terms of metal.

[0048] The content of the alkaline earth metal compound (A) in terms of metal, relative to the mass of the resin composition, is usually 0.0001 to 1 ppm, preferably 0.001 to 0.8 ppm, and more preferably 0.01 to 0.5 ppm. The content of alkaline earth metal in terms of metal, that is, the content of alkaline earth metal element, is the content of the alkaline earth metal. When the content of alkaline earth metal compound (A) in terms of metal 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.

[0049] The metal-equivalent content of the alkaline earth metal compound (A) can be measured, for example, by heating and ashing the present resin composition (1), treating the resultant with an acid such as hydrochloric acid, adding pure water to the resulting solution, and measuring the volume of the solution with an atomic absorption spectrophotometer.

[0050] The mass ratio of the content of the alkaline earth metal compound (A) in terms of metal to the content of the titanium compound in terms of metal is usually 0.01 to 5000, preferably 0.05 to 500, and more preferably 0.1 to 10. 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.

[0051] Although the reason why the combined use of the alkaline earth metal compound (A) used in this embodiment and the titanium compound provides such excellent effects is unclear, it is believed that the combined use of a specific amount of titanium compound and alkaline earth metal compound (A) forms an interactant (complex, alloy, etc.), which then interacts with the oxygen of the OH group present in the PVA resin, thereby suppressing the formation of a polyene structure, thereby improving thermal stability.

[0052] [Other Thermoplastic Resins] The resin composition (1) may contain thermoplastic resins other than PVA resins 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.

[0053] [Other Additives] The resin composition (1) may also contain additives (excluding titanium compounds and alkaline earth metal compounds (A)) that are generally added to 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 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 and transition metals (e.g., a combination of polypropylene and cobalt); and carbon-carbon unsaturated bond-containing resins and Polymeric oxygen absorbers 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 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.

[0054] [Method for Producing Resin Composition] The resin composition (1) can be produced by mixing the PVA resin, titanium compound, and alkaline earth metal compound (A) by a known method, such as a dry blending method, a melt mixing method, a solution mixing method, an impregnation method, etc. Among these, it is preferable to produce the resin composition by a method including a step of melt mixing the resin composition raw materials containing the PVA resin and the titanium compound. Furthermore, these production methods can be used in any combination.

[0055] The dry blending method may be, for example, (i) a method in which a pellet-shaped PVA resin, an alkaline earth metal compound (A), and a titanium compound are dry-blended using a tumbler or the like.

[0056] Examples of the melt-mixing method include (ii) a method in which a pellet-shaped PVA resin is dry-blended with the alkaline earth metal compound (A) and the titanium compound, and the dry-blended product is melt-kneaded; and (iii) a method in which the alkaline earth metal compound (A) and the titanium compound are added to a molten PVA resin, and the resulting mixture is melt-kneaded.

[0057] Examples of the solution mixing method include (iv) a method in which a solution is prepared using a commercially available PVA resin, and then the alkaline earth metal compound (A) and the titanium compound are blended therein, followed by coagulation molding, followed by solid-liquid separation by known means, and drying; and (v) a method in which, during the production process of a PVA resin, the alkaline earth metal compound (A) and the titanium compound are added to an ethylene-vinyl ester copolymer solution before saponification or a homogeneous solution of a PVA resin (such as a water / alcohol solution), followed by coagulation molding, followed by solid-liquid separation by known means, and drying.

[0058] The impregnation method includes, for example, (vi) a method in which pellets of PVA resin are brought into contact with an aqueous solution containing the alkaline earth metal compound (A) and the titanium compound, so that the alkaline earth metal compound (A) and the titanium compound are contained in the PVA resin, and then the PVA resin is dried.

[0059] The aqueous solution containing the titanium compound may be an aqueous solution of the titanium compound or a titanium compound immersed in water containing various chemicals to elute titanium ions.

[0060] In the impregnation method, the contents (in terms of metals) of the alkaline earth metal compound (A) and the titanium compound can be controlled by the concentrations of the alkaline earth metal compound (A) and the titanium compound in the aqueous solution in which the 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.

[0061] 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.

[0062] As mentioned above, in the present invention, 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 production method.

[0063] The resin composition (1) obtained by each of the above-described production methods may have any shape, but is preferably in the form of pellets. Examples of the pellets include spherical, oval, cylindrical, cubic, and rectangular parallelepiped shapes. Typically, the pellets are oval or cylindrical. From the viewpoint of convenience when subsequently used as a molding material, the size of the pellets is such that, in the case of an oval shape, the minor axis is typically 1 to 10 mm, preferably 2 to 6 mm, and more preferably 2.5 to 5.5 mm, and the major axis is typically 1.5 to 30 mm, preferably 3 to 20 mm, and more preferably 3.5 to 10 mm. Furthermore, in the case of a 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.

[0064] 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.

[0065] The water content of the resin composition (1) is measured and calculated by the following method. １ ) was weighed on an electronic balance, dried in a hot air dryer at 150°C for 5 hours, and allowed to cool in a desiccator for 30 minutes, after which the mass (W ２ ) is weighed and calculated using the following formula: Water content (mass%) = [(W １ -W ２ ) / W１ ]×100

[0066] 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 in the resin composition (1) is usually 5% by mass or less, preferably 1% by mass or less. The lower limit is usually 0% by mass.

[0067] The resin composition (1) thus obtained can suppress thermal degradation during heating, and the temperature at which the resin composition (1) loses 5% by mass is usually more than 350°C, preferably 351°C or higher. The upper limit of the temperature at which the mass loss is 5% is preferably as high as possible, but is usually 550°C. A difference of 1°C in the temperature at which the mass loss occurs is very large, as it appears as a large difference in yield in actual production.

[0068] The "temperature at which a 5% mass reduction occurs" can be measured using a thermogravimetric analyzer, for example, by the method described in the Examples below.

[0069] 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 articles. In particular, in the present invention, 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).

[0070] Examples of the molding material include a monolayer film formed from the present resin composition (1), as well as a multilayer structure having at least one layer containing the present resin composition (1).

[0071] [Multilayer structure] The multilayer structure according to the first aspect of the present invention (hereinafter referred to as "the present multilayer structure (1)") has a layer containing the present resin composition (1). The layer made of 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.

[0072] Examples of the base resin include polyethylene-based resins such as linear low-density polyethylene, low-density polyethylene, very low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-propylene (block and random) copolymers, and ethylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers; polypropylene-based resins such as polypropylene and propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers; (unmodified) polyolefin-based resins such as polybutene, polypentene, and polycyclic olefin-based resins (polymers having a cyclic olefin structure in at least one of the main chain and side chain); and polyolefins obtained by modifying these polyolefins with unsaturated carboxylic acids or the like. 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 an ester of polyethylene, 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.

[0073] 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.

[0074] 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.

[0075] 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 addition reaction, 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.

[0076] 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.

[0077] The base resin and adhesive resin may contain conventionally known plasticizers, fillers, clay (montmorillonite, etc.), colorants, antioxidants, antistatic agents, lubricants, core materials, antiblocking agents, waxes, etc., within a range that does not impair the spirit of the present invention (for example, 30% by 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 kinds.

[0078] 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 performed by a known method. For example, a method of melt-extrusion laminating a substrate resin onto a film, sheet, etc. of the resin composition (1), a method of melt-extrusion laminating the resin composition (1) onto a 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) (the resin composition layer (1)) and the substrate resin (substrate resin layer) using a known adhesive such as an organic titanium compound, an isocyanate compound, a polyester compound, or a polyurethane compound, a method of applying a solution of the resin composition (1) onto the substrate resin and then removing the solvent, etc. Among these, from the viewpoints of cost and environment, it is preferable to produce the resin composition layer (1) by including a step of melt-molding the resin composition layer (1), and specifically, a co-extrusion method is preferred.

[0079] 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, 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 excellent, and when it is equal to or lower than the upper limit, a stable stretched state tends to be maintained.

[0080] 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.

[0081] When the stretched multilayer structure (1) is used as a shrink film, in order to impart heat shrinkability, the heat setting described above is not carried out, but rather a treatment such as cooling and setting the stretched multilayer structure (1) by applying cold air thereto may be carried out.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] <<Second Aspect>> The second aspect includes the following aspects <II-1> to <II-10>. <II-1> A resin composition containing a PVA resin, a titanium compound, and an alkali metal compound (B), wherein the PVA resin is an ethylene-modified PVA resin containing 1 to 19 mol% of ethylene structural units, and the titanium compound has a metal-equivalent content of 0.0001 to 2 ppm relative to the mass of the resin composition. <II-2> The resin composition according to <II-1>, wherein the alkali metal compound (B) has a metal-equivalent content of 0.0001 to 5000 ppm relative to the mass of the resin composition. <II-3> The resin composition according to <II-1> or <II-2>, wherein the alkali metal compound (B) is a sodium compound. <II-4> The resin composition according to any one of <II-1> to <II-3>, wherein the content of the titanium compound in terms of metal is 0.0001 ppm or more and less than 1 ppm, relative to the mass of the resin composition. <II-5> A molding material comprising the resin composition according to any one of <II-1> to <II-4>. <II-6> A multilayer structure having a layer comprising the resin composition according to any one of <II-1> to <II-4>. <II-7> A molded article comprising the multilayer structure according to <II-6>. <II-8> A food packaging article comprising the multilayer structure according to <II-6>. <II-9> A method for producing the resin composition according to any one of <II-1> to <II-4>, comprising a step of melt-mixing a resin composition raw material containing the PVA resin and the titanium compound. <II-10> A method for producing the multilayer structure according to <II-6>, comprising a step of melt-molding a layer comprising the resin composition.

[0086] The present invention will be described below based on an example of a form for carrying out the second aspect. However, the present invention is not limited to the embodiment described below. <Resin composition> The resin composition according to the second aspect of the present invention (hereinafter sometimes referred to as "present resin composition (2)") contains a PVA resin as the main component and specific trace amounts of a titanium compound and an alkali metal compound (B). That is, the present resin composition (2) has a PVA resin as the base 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.

[0087] [PVA Resin] The PVA resin used in the present embodiment is an ethylene-modified PVA resin having an ethylene structural unit, and is typically a resin obtained by copolymerizing a vinyl ester monomer and ethylene in the presence of a polymerization initiator and saponifying the copolymer. The PVA resin may be the same as the [PVA resin] described in the first embodiment.

[0088] [Titanium Compound] As the titanium compound used in this embodiment, the same titanium compound as described in the first embodiment can be used.

[0089] The content of the titanium compound in terms of metal is 0.0001 to 2 ppm, preferably 0.0001 to 1 ppm, more preferably 0.001 ppm or more and less than 1 ppm, and even more preferably 0.01 to 0.5 ppm, based on the mass of the resin composition. When the content of the titanium compound is equal to or greater than the lower limit, the effect of suppressing thermal degradation tends to be excellent, and when the content is equal to or greater than the upper limit, the resin composition tends to be less susceptible to thermal decomposition and less susceptible to coloration.

[0090] The content of the titanium compound in terms of metal can be determined by measuring the titanium in a constant volume solution obtained by weighing the resin composition (2) into a platinum crucible, ashing it with a burner and an electric furnace, thermally decomposing the ashed material with nitric acid and hydrofluoric acid, treating it with a mixed acid of dilute nitric acid and dilute hydrofluoric acid, and measuring the titanium in the constant volume solution by ICP mass spectrometry using an ICP mass spectrometer (Agilent 8800, manufactured by Agilent Technologies).

[0091] It is speculated that the thermal decomposition of PVA resin is caused by the formation of a polyene structure in the main chain due to a dehydration reaction initiated by an OH group in the PVA resin under alkaline conditions. In the present resin composition (2), titanium in the titanium compound is stabilized as a tetravalent ion. Therefore, when a polyene structure is formed in the main chain of the PVA resin, it is thought that the titanium compound stabilizes the polyene structure by coordinating with the double bond of the polyene structure to form a chelate. It is speculated that even a trace amount of titanium compound inhibits the further formation of a polyene structure.

[0092] [Alkali Metal Compound (B)] Examples of the alkali metal compound (B) include salts and oxides of alkali metals. These may be used alone or in combination of two or more. Among these, the alkali metal compound (B) is preferably water-soluble, and from the viewpoint of dispersibility, alkali metal salts are preferred.

[0093] Examples of the alkali metal salt include inorganic salts of alkali metals and carboxylates of alkali metals, among which carboxylates of alkali metals are preferred.

[0094] Examples of the inorganic salts of alkali metals include alkali metal carbonates, hydrogencarbonates, phosphates, borates, sulfates, chlorides, etc. Examples of the carboxylates of alkali metals include monocarboxylates having 2 to 11 carbon atoms such as acetate, butyrate, propionate, enanthate, and caprate, dicarboxylates having 2 to 11 carbon atoms such as oxalate, malonate, succinate, adipate, suberate, and sebacate, monocarboxylates having 12 or more carbon atoms such as laurate, palmitate, stearate, 12-hydroxystearate, behenate, and montanate, and carboxylates such as carboxylates with the polymerization terminal carboxy group of ethylene-vinyl alcohol resins.

[0095] Examples of the alkali metal species of the alkali metal compound (B) include lithium, sodium, potassium, rubidium, and cesium. Of these, sodium and potassium are preferred, and sodium is particularly preferred.

[0096] For these reasons, the alkali metal compound (B) is preferably a sodium compound, more preferably a sodium carboxylate.

[0097] The molecular weight or formula weight of the alkali metal compound (B) is usually 20 to 10,000, preferably 20 to 1,000, and particularly preferably 20 to 500.

[0098] Among these, sodium acetate is preferred as the alkali metal compound (B). From the viewpoints of economy and dispersibility, it is preferred that the alkali metal compound (B) does not include inorganic layered compounds and double salts.

[0099] The content of the alkali metal compound (B) in terms of metal mass, relative to the mass of the resin composition, is usually 0.0001 to 5000 ppm, preferably 0.1 to 800 ppm, more preferably 5 to 500 ppm, and particularly preferably 8 to 200 ppm. When the content of the alkali metal compound (B) is equal to or less than the upper limit, the thermal stability tends to be improved, and when it is equal to or more than the lower limit, the moldability of the resin composition tends to be improved.

[0100] The metal-equivalent content of the alkali metal compound (B) can be measured using an atomic absorption spectrophotometer, for example, by adding pure water to a solution obtained by heating and incinerating the resin composition (2) and treating the resultant solution with an acid such as hydrochloric acid, and then adjusting the volume of the solution to a constant volume.

[0101] The mass ratio of the metal-equivalent content of the alkali metal compound (B) to the metal-equivalent content of the titanium compound is preferably 0.01 to 50,000, more preferably 0.05 to 2,500, and particularly preferably 10 to 1,000. 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 tends to be excellent.

[0102] Although the reason why the combined use of the alkali metal compound (B) and the titanium compound used in this embodiment provides such excellent effects is unclear, it is believed that the combined use of a specific amount of titanium compound and the alkali metal compound (B) forms an interactant (complex, alloy, etc.), which then interacts with the oxygen of the OH group present in the PVA resin, thereby suppressing the formation of a polyene structure, thereby improving thermal stability.

[0103] [Other Thermoplastic Resins] The resin composition (2) may contain a thermoplastic resin other than the 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 (2), preferably 20% by mass or less, and particularly preferably 10% by mass or less, the lower limit being typically 0% by mass). As the other thermoplastic resin, the same ones as those described in the [Other Thermoplastic Resins] of the first embodiment may be used.

[0104] [Other Additives] The resin composition (2) may contain additives (excluding titanium compounds and alkali metal compounds (B)) that are generally added to PVA-based 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 (2), preferably 20% by mass or less, particularly 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 and transition metals (e.g., a combination of polypropylene and cobalt); carbon-carbon unsaturated bond-containing resins and Polymeric oxygen absorbers 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 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.

[0105] [Method for Producing Resin Composition] The resin composition (2) can be produced by mixing the PVA resin, titanium compound, and alkali metal compound (B) by a known method, such as a dry blending method, a melt mixing method, a solution mixing method, an impregnation method, etc. Among these, it is preferable to produce the resin composition (2) by a method including a step of melt mixing the resin composition raw materials containing the PVA resin and the titanium compound. Furthermore, these production methods can be arbitrarily combined.

[0106] The dry blending method may be, for example, (i) a method in which a pellet-shaped PVA resin, an alkali metal compound (B), and a titanium compound are dry-blended using a tumbler or the like.

[0107] Examples of the melt-mixing method include (ii) a method in which a pellet-shaped PVA resin is dry-blended with an alkali metal compound (B) and a titanium compound, and the dry-blended product is melt-kneaded; and (iii) a method in which an alkali metal compound (B) and a titanium compound are added to a molten PVA resin, and the resulting mixture is melt-kneaded.

[0108] Examples of the solution mixing method include (iv) a method in which a solution is prepared using a commercially available PVA resin, an alkali metal compound (B) and a titanium 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, during the production process of a PVA resin, an alkali metal compound (B) and a titanium compound are added to an ethylene-vinyl ester copolymer solution before saponification or a homogeneous solution of a PVA resin (such as a water / alcohol solution), the mixture is coagulated and molded, and then the mixture is subjected to solid-liquid separation by known means and dried.

[0109] The impregnation method includes, for example, (vi) a method in which pellets of PVA resin are brought into contact with an aqueous solution containing the alkali metal compound (B) and the titanium compound, thereby incorporating the alkali metal compound (B) and the titanium compound into the PVA resin, and then drying the resulting mixture.

[0110] The aqueous solution containing the titanium compound may be an aqueous solution of the titanium compound or a titanium compound immersed in water containing various chemicals to elute titanium ions.

[0111] In the impregnation method, the contents (in terms of metals) of the alkali metal compound (B) and the titanium compound can be controlled by the concentrations of the alkali metal compound (B) and the titanium compound in the aqueous solution in which the 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.

[0112] 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.

[0113] As mentioned above, in the present invention, 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 production method.

[0114] The resin composition (2) obtained by each of the above-described production methods may have any shape, but is preferably in the form of pellets. Examples of the pellets include spherical, oval, cylindrical, cubic, and rectangular parallelepiped shapes. They are typically oval or cylindrical. From the viewpoint of convenience when subsequently used as a molding material, the size of the pellets is such that, in the case of an oval shape, the minor axis is typically 1 to 10 mm, preferably 2 to 6 mm, and more preferably 2.5 to 5.5 mm, and the major axis is typically 1.5 to 30 mm, preferably 3 to 20 mm, and more preferably 3.5 to 10 mm. Furthermore, in the case of a 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.

[0115] 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.

[0116] 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

[0117] 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.

[0118] The present resin composition (2) thus obtained can suppress thermal degradation during heating, and the remaining amount (%) of the present resin composition (2) at 550° C. is usually 6% by mass or more, preferably 7% by mass or more, and more preferably 8% by mass or more. The higher the remaining amount (%) at 550° C., the better, but the upper limit is usually 100% by mass.

[0119] The temperature (°C) at which the resin composition (2) loses 10% by mass is usually more than 350°C, preferably 351°C or higher, and more preferably 356°C or higher. The upper limit of the temperature (°C) at which the resin composition (2) loses 10% by mass is preferably as high as possible, but is usually 550°C. A difference of 1°C in the temperature at which the mass is lost is very large, as it results in a large difference in yield in actual production.

[0120] The "remaining amount (%) at 550°C" and "temperature (°C) at 10% mass loss" can be measured using a thermogravimetric analyzer, for example, by the method described in the Examples below.

[0121] The yellow index (YI) of the resin composition (2) is usually less than 60, preferably not more than 50, more preferably not more than 40, and even more preferably not more than 30. The lower limit is 0%. The increase rate of the YI can be calculated, for example, by the method described in the examples below.

[0122] [Molding material] The resin composition (2) thus obtained is prepared into various forms, such as pellets, powder, or liquid, and is provided as a molding material for various molded articles. In particular, in the present invention, 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).

[0123] Examples of the molding material include a monolayer film formed from the present resin composition (2), as well as a multilayer structure having at least one layer containing the present resin composition (2).

[0124] [Multilayer structure] The multilayer structure according to the second aspect of the present invention (hereinafter referred to as "the present multilayer structure (2)") has a layer containing the present resin composition (2). The layer made of 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.

[0125] Examples of the base resin include polyethylene, such as polyethylene-based resins including 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 including polypropylene and propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers; (unmodified) polyolefin-based resins such as polybutene, polypentene, and polycyclic olefin-based resins (polymers having a cyclic olefin structure in at least one of the main chain and side chain); and unsaturated carboxylic acid copolymers of these polyolefins. 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 carboxylic acid or its ester; 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.

[0126] 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.

[0127] 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.

[0128] 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 addition reaction, 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.

[0129] 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.

[0130] The base resin and adhesive resin may contain conventionally known plasticizers, fillers, clay (montmorillonite, etc.), colorants, antioxidants, antistatic agents, lubricants, core materials, antiblocking agents, waxes, etc., within a range that does not impair the spirit of the present invention (for example, 30% by 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 kinds.

[0131] 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 performed by a known method. For example, a method of melt-extrusion laminating a substrate resin onto a film, sheet, etc. of the resin composition (2), a method of melt-extrusion laminating the resin composition (2) onto a 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) (the resin composition layer (2)) and the substrate resin (substrate resin layer) using a known adhesive such as an organic titanium compound, an isocyanate compound, a polyester compound, or a polyurethane compound, a method of applying a solution of the resin composition (2) onto the substrate resin and then removing the solvent, etc. Among these, from the viewpoints of cost and environment, it is preferable to produce the resin composition layer (2) by including a step of melt-molding the resin composition layer (2), and specifically, a co-extrusion method is preferred.

[0132] 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, 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 excellent, while when it is equal to or lower than the upper limit, a stable stretched state tends to be maintained.

[0133] 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.

[0134] When the stretched multilayer structure (2) is used as a shrink film, in order to impart heat shrinkability, the heat setting described above 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.

[0135] 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, particularly 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.

[0136] 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.

[0137] 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.

[0138] <<Third Aspect>> The third aspect includes the following aspects <III-1> to <III-9>. <III-1> A resin composition containing a PVA resin, a titanium compound, and sorbic acid (C), wherein the PVA resin is an ethylene-modified PVA resin containing 1 to 19 mol% of ethylene structural units, and the titanium compound has a metal-equivalent content of 0.0001 to 2 ppm relative to the mass of the resin composition. <III-2> The resin composition according to <III-1>, wherein the sorbic acid (C) has a metal-equivalent content of 0.005 to 100 ppm relative to the mass of the resin composition. <III-3> The resin composition according to <III-1> or <III-2>, wherein the titanium compound has a metal-equivalent content of 0.0001 ppm or more and less than 1 ppm relative to the mass of the resin composition. <III-4> A molding material comprising the resin composition according to any one of <III-1> to <III-3>. <III-5> A multilayer structure having a layer containing the resin composition according to any one of <III-1> to <III-3>. <III-6> A molded article comprising the multilayer structure according to <III-5>. <III-7> A food packaging article comprising the multilayer structure according to <III-5>. <III-8> A method for producing the resin composition according to any one of <III-1> to <III-3>, comprising a step of melt-mixing a resin composition raw material containing the PVA resin and the titanium compound. <III-9> A method for producing the multilayer structure according to <III-5>, comprising a step of melt-molding a layer containing the resin composition.

[0139] The present invention will be described below based on examples of modes for carrying out the third aspect, although the present invention is not limited to the embodiments described below.

[0140] <Resin Composition> A resin composition according to a third aspect of the present invention (hereinafter sometimes referred to as "the present resin composition (3)") contains a PVA resin as a main component and specific trace amounts of a titanium compound and sorbic acid (C). That is, the base resin of the present resin composition (3) is a PVA resin, and the content of the PVA resin in the present resin composition (3) 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.

[0141] [PVA Resin] The PVA resin used in the present embodiment is an ethylene-modified PVA resin having an ethylene structural unit, and is typically a resin obtained by copolymerizing a vinyl ester monomer and ethylene in the presence of a polymerization initiator and saponifying the copolymer. The PVA resin may be the same as the [PVA resin] described in the first embodiment.

[0142] [Titanium Compound] As the titanium compound used in this embodiment, the same titanium compound as described in the first embodiment can be used.

[0143] The content of the titanium compound in terms of metal is 0.0001 to 2 ppm, preferably 0.0001 to 1 ppm, more preferably 0.001 ppm or more and less than 1 ppm, and even more preferably 0.01 to 0.5 ppm, based on the mass of the resin composition. When the content of the titanium compound is equal to or greater than the lower limit, the effect of suppressing thermal degradation tends to be excellent, and when the content is equal to or greater than the upper limit, the resin composition tends to be less susceptible to thermal decomposition and less susceptible to coloration.

[0144] The content of the titanium compound in terms of metal can be determined by measuring the titanium in a constant volume solution obtained by weighing the resin composition (3) into a platinum crucible, ashing it with a burner and an electric furnace, thermally decomposing the ashed material with nitric acid and hydrofluoric acid, treating it with a mixed acid of dilute nitric acid and dilute hydrofluoric acid, and measuring the titanium in the constant volume solution by ICP mass spectrometry using an ICP mass spectrometer (Agilent 8800, manufactured by Agilent Technologies).

[0145] It is speculated that the thermal decomposition of PVA resin is caused by the formation of a polyene structure in the main chain due to a dehydration reaction initiated by an OH group in the PVA resin under alkaline conditions. In the present resin composition (3), titanium in the titanium compound is stabilized as a tetravalent ion. Therefore, when a polyene structure is formed in the main chain of the PVA resin, it is thought that the titanium compound stabilizes the polyene structure by coordinating with the double bond of the polyene structure to form a chelate. It is speculated that even a trace amount of titanium compound inhibits the further formation of polyene structures.

[0146] [Sorbic Acid (C)] The sorbic acid (C) is preferably one having a carboxy group, since it has a high affinity for water, and more preferably a chain compound having a carboxy group.

[0147] The content of the sorbic acid (C) is usually 0.005 to 100 ppm, preferably 0.01 to 75 ppm, and more preferably 0.1 to 50 ppm, relative to the mass of the resin composition. When the content of the sorbic acid (C) is equal to or less than the upper limit, the resin composition tends to have excellent thermal stability, and when the content is equal to or more than the lower limit, the resin composition tends to have excellent moldability.

[0148] The content of sorbic acid (C) can be measured, for example, using a liquid chromatograph-ultraviolet spectrophotometer, according to the following procedure. [Method for Measuring the Content of Sorbic Acid (C)] (1) 8 mL of extraction solvent (distilled water:methanol = 1:1, by volume) is added to 1 g of powder obtained by freeze-pulverizing the present resin composition (3). (2) This solution is subjected to ultrasonic treatment at a temperature of 20°C while standing for 1 hour to extract the sorbic acid in the resin, and after cooling, the volume is adjusted to 10 mL with the extraction solvent. Furthermore, the solution may be diluted to an arbitrary ratio as necessary. (3) The solution is filtered through a filter with a pore size of 0.45 μm, and the sorbic acid in the extraction solution is measured using a liquid chromatograph-ultraviolet spectrophotometer. (4) A calibration curve is created from a standard solution of sorbic acid prepared using the extraction solvent, and the sorbic acid content is quantified by the absolute calibration curve method. [HPLC measurement conditions] LC system: Agilent 1260 / 1290 [Agilent Technologies] Detector: Agilent 1260 infinity diode array detector [Agilent Technologies] Column: Cadenza CD-C18 (100 x 3.0 mm, 3 μm) [Imtakt] Column temperature: 40°C Mobile phase A: 5% acetonitrile aqueous solution containing 0.05% formic acid Mobile phase B: 95% acetonitrile aqueous solution containing 0.05% formic acid Time program: 0.0 → 5.0 min B% = 30% 5.0 → 8.0 min B% = 30% → 50% 8.0 → 10.0 min B% = 50% 10.0 to 13.0 minutes: B% = 50% to 30% 13.0 to 15.0 minutes: B% = 30% Flow rate: 0.2 mL / min UV detection wavelength: 190 to 400 nm Quantitative wavelength: 262 nm In the HPLC measurement conditions, "%" means volume %.

[0149] The mass ratio of the content of the sorbic acid (C) to the content of the titanium compound in terms of metal is preferably 0.0025 to 1,000,000, more preferably 0.05 to 50,000, and particularly preferably 10 to 1,000. 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 tends to be excellent.

[0150] The reason why excellent effects can be obtained by blending appropriate amounts of the titanium compound and the sorbic acid (C) is not clear, but it is presumed that the combined use of specific amounts of the titanium compound and the sorbic acid (C) appropriately lowers the pH and strengthens the hydrogen bonds in the hydroxyl groups of the PVA resin, thereby improving the thermal stability.

[0151] [Other Thermoplastic Resins] The resin composition (3) may contain thermoplastic resins other than the 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 (3), preferably 20% by mass or less, and particularly preferably 10% by mass or less, the lower limit being typically 0% by mass). As the other thermoplastic resin, the same ones as those described in the [Other Thermoplastic Resins] of the first embodiment may be used.

[0152] [Other Additives] The resin composition (3) may also contain additives generally added to PVA resins (except titanium compounds and sorbic acid (C)) 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, particularly 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, 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 and transition metals (e.g., a combination of polypropylene and cobalt); and carbon-carbon unsaturated bond-containing resins and Polymeric oxygen absorbers 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 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.

[0153] [Method for Producing Resin Composition] The resin composition (3) can be produced by mixing the PVA resin, titanium compound, and sorbic acid (C) by a known method, such as a dry blending method, a melt mixing method, a solution mixing method, an impregnation method, etc. Among these, it is preferable to produce the resin composition by a method including a step of melt mixing a resin composition raw material containing the PVA resin and the titanium compound. Furthermore, these production methods can be arbitrarily combined.

[0154] The dry blending method may be, for example, (i) a method in which a pellet-shaped PVA resin, sorbic acid (C), and a titanium compound are dry-blended using a tumbler or the like.

[0155] Examples of the melt-mixing method include (ii) a method in which pellet-shaped PVA resin, sorbic acid (C), and a titanium compound are dry-blended, and the dry-blended product is melt-kneaded; and (iii) a method in which sorbic acid (C) and a titanium compound are added to a molten PVA resin, and the resulting mixture is melt-kneaded.

[0156] Examples of the solution mixing method include (iv) a method in which a solution is prepared using a commercially available PVA resin, sorbic acid (C) and a titanium compound are blended therein, the resulting mixture is coagulated and molded, and then the resulting mixture is subjected to solid-liquid separation by known means and dried; and (v) a method in which, during the production process of a PVA resin, sorbic acid (C) and a titanium compound are added to an ethylene-vinyl ester copolymer solution before saponification or a homogeneous solution of a PVA resin (such as a water / alcohol solution), the resulting mixture is coagulated and molded, and then the resulting mixture is subjected to solid-liquid separation by known means and dried.

[0157] Examples of the impregnation method include (vi) a method in which pelleted PVA resin is contacted with an aqueous solution containing sorbic acid (C) and a titanium compound to incorporate the sorbic acid (C) and titanium compound into the PVA resin, followed by drying. The aqueous solution containing the titanium compound can be an aqueous solution of a titanium compound or a titanium compound immersed in water containing various chemicals to elute titanium ions. In the impregnation method, the content of sorbic acid (C) and the content of the titanium compound (in terms of metal) can be controlled by the concentrations of the sorbic acid (C) and titanium compound in the aqueous solution in which the PVA resin is immersed, as well as the immersion temperature and immersion time. The immersion temperature and immersion time are typically 0.5 to 48 hours, preferably 1 to 36 hours, and the immersion temperature is typically 10 to 40°C, preferably 20 to 35°C.

[0158] 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.

[0159] As mentioned above, in the present invention, 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 production method.

[0160] The resin composition (3) obtained by each of the above-described production methods may have any shape, but is preferably in the form of pellets. Examples of the pellets include spherical, oval, cylindrical, cubic, and rectangular parallelepiped shapes. Typically, the pellets are oval or cylindrical. From the viewpoint of convenience when subsequently used as a molding material, the size of the pellets is such that, in the case of an oval shape, the minor axis is typically 1 to 10 mm, preferably 2 to 6 mm, and more preferably 2.5 to 5.5 mm, and the major axis is typically 1.5 to 30 mm, preferably 3 to 20 mm, and more preferably 3.5 to 10 mm. Furthermore, in the case of a 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.

[0161] The water content of the resin composition (3) 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.

[0162] The water content of the resin composition (3) is measured and calculated by the following method: The mass (W1) of the resin composition (3) 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

[0163] When the resin composition (3) 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 (3). The lower limit is usually 0% by mass.

[0164] The resin composition (3) thus obtained can suppress thermal degradation during heating, and the temperature (°C) at which the resin composition (3) has undergone a 40% mass reduction is usually 391°C or higher, preferably 393°C or higher, and more preferably 395°C or higher. The higher the temperature (°C) at which the resin composition (3) has undergone a 40% mass reduction, the better, but the upper limit is usually 550°C.

[0165] The temperature (°C) at which the resin composition (3) loses 5% by mass is usually higher than 336°C, and preferably 340°C or higher. The upper limit of the temperature (°C) at which the resin composition (3) loses 5% by mass is preferably as high as possible, but is usually 550°C. A difference of 1°C in the temperature at which the mass is lost is very large, as it results in a large difference in yield in actual production.

[0166] The "temperature (°C) at 40% mass reduction" and "temperature (°C) at 5% mass reduction" can be measured using a thermogravimetric analyzer, for example, by the method described in the Examples below.

[0167] [Molding material] The resin composition (3) thus obtained is prepared into various forms, such as pellets, powder, or liquid, and is provided as a molding material for various molded articles. In particular, in the present invention, 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 (3) also includes resin compositions obtained by mixing resins other than the PVA resin used in the resin composition (3).

[0168] Examples of the molded article include a monolayer film molded from the present resin composition (3), as well as a multilayer structure having at least one layer containing the present resin composition (3).

[0169] [Multilayer structure] The multilayer structure according to the third aspect of the present invention (hereinafter referred to as "the present multilayer structure (3)") has a layer containing the present resin composition (3). The layer made of the present resin composition (3) (hereinafter simply referred to as "the present resin composition layer (3)") 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 (3) as a main component, to impart further strength, protect the present resin composition layer (3) from the effects of moisture, etc., or impart other functions.

[0170] Examples of the base resin include polyethylene-based resins such as linear low-density polyethylene, low-density polyethylene, very low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-propylene (block and random) copolymers, and ethylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers; polypropylene-based resins such as polypropylene and propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers; (unmodified) polyolefin-based resins such as polybutene, polypentene, and polycyclic olefin-based resins (polymers having a cyclic olefin structure in at least one of the main chain and side chain); and polyolefins obtained by dissolving these polyolefins in an unsaturated carboxylic acid or its derivatives. 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 an ester of polyethylene, 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.

[0171] 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.

[0172] The layer structure of the present multilayer structure (3) 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 (3) 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 (3) and a thermoplastic resin other than the present resin composition (3), obtained by remelting and molding edges or defective products generated during the manufacturing process of the present multilayer structure (3), 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 (3) 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.

[0173] 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 addition reaction, 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.

[0174] In the present multilayer structure (3), when an adhesive resin layer is used between the present resin composition layer (3) and the base resin layer, since the adhesive resin layers are located on both sides of the present resin composition layer (3), it is preferable to use an adhesive resin with excellent hydrophobicity.

[0175] The base resin and adhesive resin may contain conventionally known plasticizers, fillers, clay (montmorillonite, etc.), colorants, antioxidants, antistatic agents, lubricants, core materials, antiblocking agents, waxes, etc., within a range that does not impair the spirit of the present invention (for example, 30% by 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 kinds.

[0176] The lamination of the resin composition layer (3) and the substrate resin layer (including the case where an adhesive resin layer is interposed) can be performed by a known method. For example, a method of melt-extrusion laminating a substrate resin onto a film, sheet, etc. of the resin composition (3), a method of melt-extrusion laminating the resin composition (3) onto a substrate resin layer, a method of co-extruding the resin composition (3) and the substrate resin, a method of dry-laminating the resin composition (3) (the resin composition layer (3)) and the substrate resin (substrate resin layer) using a known adhesive such as an organic titanium compound, an isocyanate compound, a polyester compound, or a polyurethane compound, a method of applying a solution of the resin composition (3) onto the substrate resin and then removing the solvent, etc. Among these, from the viewpoints of cost and environment, it is preferable to produce the resin composition layer (3) by including a step of melt-molding the resin composition layer (3), and specifically, a co-extrusion method is preferred.

[0177] The multilayer structure (3) 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, 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 excellent, and when it is equal to or lower than the upper limit, a stable stretched state tends to be maintained.

[0178] The stretched multilayer structure (3) may be heat-set to provide dimensional stability. Heat-setting can be performed by known means, for example, by subjecting the stretched multilayer structure (3) to heat treatment while maintaining tension, typically at 80 to 180°C, preferably 100 to 165°C, for typically 2 to 600 seconds.

[0179] When the stretched multilayer structure (3) is used as a shrink film, in order to impart heat shrinkability, the heat setting described above is not carried out, but rather a treatment such as cooling and setting the stretched multilayer structure (3) by applying cold air thereto may be carried out.

[0180] The thickness of the present multilayer structure (3) (including a stretched structure), and further the thickness of the present resin composition layer (3), 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 present multilayer structure (3) (including a stretched structure) is usually 10 to 5,000 μm, preferably 30 to 3,000 μm, more preferably 50 to 2,000 μm. The present resin composition layer (3) 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, particularly 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.

[0181] Furthermore, the thickness ratio of the present resin composition layer (3) to the base resin layer in the present multilayer structure (3) (present resin composition layer (3) / 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 (3) to the adhesive resin layer in the present multilayer structure (3) (present resin composition layer (3) / 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.

[0182] The multilayer structure (3) 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 (two-head, mold-moving, parison-shift, rotary, accumulator, horizontal parison, etc.), cold parison blow molding, injection blow molding, and biaxial stretch blow molding (extrusion-type cold parison biaxial stretch blow molding, injection-type cold parison biaxial stretch blow molding, injection-molding in-line biaxial stretch blow molding, etc.). The resulting laminate may be subjected to heat treatment, cooling treatment, rolling treatment, printing treatment, dry lamination treatment, solution or melt coating treatment, bag making, deep drawing, box processing, tube processing, splitting processing, etc. as required.

[0183] <<Fourth Aspect>> The fourth aspect includes the following aspects <IV-1> to <IV-9>. <IV-1> A resin composition containing a PVA resin, a titanium compound, and acetic acid (D), wherein the PVA resin is an ethylene-modified PVA resin containing 1 to 19 mol% of ethylene structural units, and the content of the titanium compound in terms of metal is 0.0001 to 2 ppm relative to the mass of the resin composition. <IV-2> The PVA resin composition according to <IV-1>, wherein the content of the acetic acid (D) is 10 to 10,000 ppm relative to the mass of the resin composition. <IV-3> The resin composition according to <IV-1> or <IV-2>, wherein the content of the titanium compound in terms of metal is 0.0001 ppm or more and less than 1 ppm relative to the mass of the resin composition. <IV-4> A molding material comprising the resin composition according to any one of <IV-1> to <IV-3>. <IV-5> A multilayer structure having a layer containing the resin composition according to any one of <IV-1> to <IV-3>. <IV-6> A molded article comprising the multilayer structure according to <IV-5>. <IV-7> A food packaging article comprising the multilayer structure according to <IV-5>. <IV-8> A method for producing the resin composition according to any one of <IV-1> to <IV-3>, comprising a step of melt-mixing a resin composition raw material containing the PVA resin and the titanium compound. <IV-9> A method for producing the multilayer structure according to <IV-5>, comprising a step of melt-molding a layer containing the resin composition.

[0184] The present invention will be described below based on examples of modes for carrying out the fourth aspect, although the present invention is not limited to the embodiments described below.

[0185] <Resin Composition> A resin composition according to a fourth aspect of the present invention (hereinafter sometimes referred to as "the present resin composition (4)") contains a PVA resin as a main component, acetic acid (D), and a specific trace amount of a titanium compound. That is, the base resin of the present resin composition (4) is a PVA resin, and the content of the PVA resin in the present resin composition (4) 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.

[0186] [PVA Resin] The PVA resin used in the present embodiment is an ethylene-modified PVA resin having an ethylene structural unit, and is typically a resin obtained by copolymerizing a vinyl ester monomer and ethylene in the presence of a polymerization initiator and saponifying the copolymer. The PVA resin may be the same as the [PVA resin] described in the first embodiment.

[0187] [Titanium Compound] As the titanium compound used in this embodiment, the same titanium compound as described in the first embodiment can be used.

[0188] The content of the titanium compound in terms of metal is 0.0001 to 2 ppm, preferably 0.0001 to 1 ppm, more preferably 0.001 ppm or more and less than 1 ppm, and even more preferably 0.01 to 0.5 ppm, based on the mass of the resin composition. When the content of the titanium compound is equal to or greater than the lower limit, the effect of suppressing thermal degradation tends to be excellent, while when the content is equal to or less than the upper limit, the resin composition tends to be less susceptible to thermal decomposition and less susceptible to coloration.

[0189] The content of the titanium compound in terms of metal can be determined by measuring the titanium in a constant volume solution obtained by weighing the resin composition (4) into a platinum crucible, ashing it with a burner and an electric furnace, thermally decomposing the ashed material with nitric acid and hydrofluoric acid, treating it with a mixed acid of dilute nitric acid and dilute hydrofluoric acid, and measuring the titanium in the constant volume solution by ICP mass spectrometry using an ICP mass spectrometer (Agilent 8800, manufactured by Agilent Technologies).

[0190] It is speculated that the thermal decomposition of PVA resin is caused by the formation of a polyene structure in the main chain due to a dehydration reaction initiated by an OH group in the PVA resin under alkaline conditions. In the present resin composition (4), titanium in the titanium compound is stabilized as a tetravalent ion. Therefore, when a polyene structure is formed in the main chain of the PVA resin, it is thought that the titanium compound stabilizes the polyene structure by coordinating with the double bond of the polyene structure to form a chelate. It is speculated that even a trace amount of titanium compound inhibits the further formation of a polyene structure.

[0191] [Acetic Acid (D)] The content of the acetic acid (D) is usually 0.01 to 10,000 ppm, preferably 0.1 to 10,000 ppm, more preferably 10 to 10,000 ppm, still more preferably 20 to 800 ppm, and particularly preferably 50 to 500 ppm, relative to the mass of the resin composition. When the content of the acetic acid (D) 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.

[0192] The content of acetic acid (D) can be measured by a known analytical method, for example, liquid chromatography mass spectrometry (LC / MS) or gas chromatography mass spectrometry (GC / MS).

[0193] The ratio of the content of the acetic acid (D) to the content of the titanium compound in terms of metal is preferably 0.01 to 50,000, more preferably 0.05 to 2,500, and particularly preferably 10 to 1,000. 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 tends to be excellent.

[0194] The reason why excellent effects can be obtained by blending appropriate amounts of the titanium compound and acetic acid (D) is not clear, but it is presumed that the combined use of specific amounts of the titanium compound and acetic acid (D) appropriately reduces the pH, strengthening the hydrogen bonds in the hydroxyl groups of the PVA resin and thereby improving the thermal stability.

[0195] [Other Thermoplastic Resins] The resin composition (4) may contain thermoplastic resins other than the 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 (4), preferably 20% by mass or less, and particularly preferably 10% by mass or less, the lower limit being typically 0% by mass). As the other thermoplastic resin, the same ones as those described in the [Other Thermoplastic Resins] of the first embodiment may be used.

[0196] [Other Additives] The resin composition (4) may contain additives generally added to PVA resins (excluding titanium compounds and acetic acid (D)) 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 (4), preferably 20% by mass or less, particularly 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 and transition metals (e.g., a combination of polypropylene and cobalt); and carbon-carbon unsaturated bond-containing resins and Polymeric oxygen absorbers 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 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.

[0197] [Method for Producing Resin Composition] The resin composition (4) can be produced by mixing the PVA resin, the titanium compound, and the acetic acid (D) by a known method, such as a dry blending method, a melt mixing method, a solution mixing method, an impregnation method, etc. Among these, it is preferable to produce the resin composition (4) by a method including a step of melt mixing the resin composition raw materials containing the PVA resin and the titanium compound. Furthermore, these production methods can be arbitrarily combined.

[0198] The dry blending method may be, for example, (i) a method in which a pellet-shaped PVA resin, acetic acid (D), and a titanium compound are dry-blended using a tumbler or the like.

[0199] Examples of the melt-mixing method include (ii) a method in which pellet-shaped PVA resin, acetic acid (D), and a titanium compound are dry-blended, and the dry-blended product is melt-kneaded; and (iii) a method in which acetic acid (D) and a titanium compound are added to a molten PVA resin, and the resulting mixture is melt-kneaded.

[0200] Examples of the solution mixing method include (iv) a method in which a solution is prepared using a commercially available PVA resin, acetic acid (D) and a titanium 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, during the production process of a PVA resin, acetic acid (D) and a titanium compound are added to an ethylene-vinyl ester copolymer solution before saponification or a homogeneous solution of a PVA resin (such as a water / alcohol solution), the mixture is coagulated and molded, and then the mixture is subjected to solid-liquid separation by known means and dried.

[0201] The impregnation method includes, for example, (vi) a method in which pellets of PVA resin are brought into contact with an aqueous solution containing acetic acid (D) and a titanium compound, so that the acetic acid (D) and the titanium compound are contained in the PVA resin, and then the PVA resin is dried.

[0202] The aqueous solution containing the titanium compound may be an aqueous solution of the titanium compound or a titanium compound immersed in water containing various chemicals to elute titanium ions.

[0203] In the impregnation method, the content of acetic acid (D) and the content of the titanium compound (in terms of metal) can be controlled by the concentrations of acetic acid (D) and the titanium compound in the aqueous solution in which the 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.

[0204] 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.

[0205] As mentioned above, in the present invention, 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 production method.

[0206] The resin composition (4) obtained by each of the above-described production methods may have any shape, but is preferably in the form of pellets. Examples of the pellets include spherical, oval, cylindrical, cubic, and rectangular parallelepiped shapes. They are typically oval or cylindrical. From the viewpoint of convenience when subsequently used as a molding material, the size of the pellets is such that, in the case of an oval shape, the minor axis is typically 1 to 10 mm, preferably 2 to 6 mm, and more preferably 2.5 to 5.5 mm, and the major axis is typically 1.5 to 30 mm, preferably 3 to 20 mm, and more preferably 3.5 to 10 mm. Furthermore, in the case of a 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.

[0207] The water content of the resin composition (4) 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.

[0208] The water content of the resin composition (4) is measured and calculated by the following method: The mass (W1) of the resin composition (4) 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

[0209] When the resin composition (4) 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 in the resin composition (4) is usually 5% by mass or less, preferably 1% by mass or less. The lower limit is usually 0% by mass.

[0210] The resin composition (4) thus obtained can suppress thermal degradation during heating, and the temperature (°C) at which the resin composition (4) loses 5% by mass is usually 345°C or higher. The higher the temperature (°C) at which the resin composition loses 5% by mass, the better, but the upper limit is usually 700°C. A difference of 0.1°C in the mass loss temperature is very significant, as it appears as a large difference in yield in actual production.

[0211] The residual amount (%) of the resin composition (4) at 550° C. is usually 2.0% by mass or more, preferably 3% by mass or more, and more preferably 3.5% by mass or more. The higher the residual amount (%) at 550° C., the better, but the upper limit is usually 100% by mass.

[0212] The "temperature (°C) at 5% mass reduction" and "remaining amount (%) at 550°C" can be measured using a thermogravimetric analyzer, for example, by the method described in the Examples below.

[0213] [Molding material] The resin composition (4) thus obtained is prepared into various forms, such as pellets, powder, or liquid, and is provided as a molding material for various molded articles. In particular, in the present invention, 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 (4) also includes resin compositions obtained by mixing resins other than the PVA resin used in the resin composition (4).

[0214] Examples of the molding material include a monolayer film formed from the present resin composition (4), as well as a multilayer structure having at least one layer containing the present resin composition (4).

[0215] [Multilayer structure] The multilayer structure according to the fourth aspect of the present invention (hereinafter referred to as "the present multilayer structure (4)") has a layer containing the present resin composition (4). The layer made of the present resin composition (4) (hereinafter simply referred to as "the present resin composition layer (4)") 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 (4) as a main component, to impart further strength, protect the present resin composition layer (4) from the effects of moisture, etc., or impart other functions.

[0216] Examples of the base resin include polyethylene-based resins such as linear low-density polyethylene, low-density polyethylene, very low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-propylene (block and random) copolymers, and ethylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers; polypropylene-based resins such as polypropylene and propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymers; (unmodified) polyolefin-based resins such as polybutene, polypentene, and polycyclic olefin-based resins (polymers having a cyclic olefin structure in at least one of the main chain and side chain); and polyolefins obtained by dissolving these polyolefins in an unsaturated carboxylic acid or its derivatives. 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 an ester of polyethylene, 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.

[0217] 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.

[0218] The layer structure of the present multilayer structure (4) 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 (4) 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 (4) and a thermoplastic resin other than the present resin composition (4), obtained by remelting and molding edges or defective products generated during the manufacturing process of the present multilayer structure (4), 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 (4) 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.

[0219] 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 addition reaction, 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.

[0220] In the present multilayer structure (4), when an adhesive resin layer is used between the present resin composition layer (4) and the base resin layer, since the adhesive resin layers are located on both sides of the present resin composition layer (4), it is preferable to use an adhesive resin with excellent hydrophobicity.

[0221] The base resin and adhesive resin may contain conventionally known plasticizers, fillers, clay (montmorillonite, etc.), colorants, antioxidants, antistatic agents, lubricants, core materials, antiblocking agents, waxes, etc., within a range that does not impair the spirit of the present invention (for example, 30% by 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 kinds.

[0222] The lamination of the resin composition layer (4) and the substrate resin layer (including the case where an adhesive resin layer is interposed) can be performed by a known method. For example, a method of melt-extrusion laminating a substrate resin onto a film, sheet, etc. of the resin composition (4), a method of melt-extrusion laminating the resin composition (4) onto a substrate resin layer, a method of co-extruding the resin composition (4) and the substrate resin, a method of dry-laminating the resin composition (4) (the resin composition layer (4)) and the substrate resin (substrate resin layer) using a known adhesive such as an organic titanium compound, an isocyanate compound, a polyester compound, or a polyurethane compound, a method of applying a solution of the resin composition (4) onto the substrate resin and then removing the solvent, etc. Among these, from the viewpoints of cost and environment, it is preferable to produce the resin composition layer (4) by including a step of melt-molding the resin composition layer (4), and specifically, a co-extrusion method is preferred.

[0223] The multilayer structure (4) 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, 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 excellent, and when it is equal to or lower than the upper limit, a stable stretched state tends to be maintained.

[0224] The stretched multilayer structure (4) may be heat-set to provide dimensional stability. Heat-setting can be performed by known means, for example, by subjecting the stretched multilayer structure (4) to heat treatment while maintaining tension, typically at 80 to 180°C, preferably 100 to 165°C, for typically 2 to 600 seconds.

[0225] When the stretched multilayer structure (4) is used as a shrink film, in order to impart heat shrinkability, the heat setting may be omitted, and a treatment such as cooling and setting the stretched multilayer structure (4) by applying cold air thereto may be carried out.

[0226] The thickness of the present multilayer structure (4) (including a stretched structure), and further the thickness of the present resin composition layer (4), 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 present multilayer structure (4) (including a stretched structure) is usually 10 to 5,000 μm, preferably 30 to 3,000 μm, more preferably 50 to 2,000 μm. The present resin composition layer (4) 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.

[0227] Furthermore, the thickness ratio of the present resin composition layer (4) to the base resin layer in the present multilayer structure (4) (present resin composition layer (4) / 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 (4) to the adhesive resin layer in the present multilayer structure (4) (present resin composition layer (4) / 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.

[0228] The multilayer structure (4) 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.

[0229] 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.

[0230] <<First Aspect>> Prior to the Examples, the following components were prepared. Ethylene-modified PVA resin: pellets of ethylene-modified PVA resin having an ethylene structural unit content of 4 mol%, a melting point of 213°C, and a saponification degree of 98 mol% Unmodified PVA resin: pellets of PVA resin having an ethylene structural unit content of 0 mol%, a melting point of 227°C, and a saponification degree of 99 mol% Titanium compound: rutile-type titanium(IV) oxide having an average particle size of 5 μm or less (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Alkaline earth metal compound (A): magnesium chloride hexahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0231] Example I-1: The ethylene-modified PVA resin pellets were dry-blended with the magnesium chloride hexahydrate so that the content, calculated as a metal, was 0.1 ppm relative to the mass of the resin composition, and the titanium oxide so that the content, calculated as a metal, was 0.1 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.

[0232] [Extrusion conditions] Extruder set temperatures (°C): C1 / C2 / C3 / C4 / C5 / C6 = 200 / 210 / 225 / 225 / 225 / 225

[0233] Example I-2 Pellets of a resin composition were obtained in the same manner as in Example I-1, except that the titanium oxide content, calculated as metal, was changed to 1.0 ppm relative to the mass of the resin composition.

[0234] Comparative Example I-1 Pellets of a resin composition were obtained in the same manner as in Example I-1, except that titanium oxide was not used.

[0235] Comparative Example I-2 Pellets of a resin composition were obtained in the same manner as in Example I-1, except that the titanium oxide content, calculated as metal, was changed to 3.0 ppm relative to the mass of the resin composition.

[0236] Comparative Example I-3 Pellets of a resin composition were obtained in the same manner as in Example I-2, except that magnesium chloride hexahydrate was not used.

[0237] 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.

[0238] The pellets of the resin compositions of Examples I-1 and I-2 and Comparative Examples I-1 to I-4 were subjected to the following thermal stability evaluation, and the results are shown in Table I-1.

[0239] [Evaluation of Thermal Stability] Using 5 mg of pellets of the obtained resin composition, the temperature (°C) at 5% loss was measured using a thermogravimetric analyzer (Pyris 1 TGA, manufactured by Perki Elmer) under conditions of an air flow rate of 20 mL / min, a heating rate of 10°C / min, and a temperature range of 30 to 550°C in a nitrogen atmosphere. A higher temperature (°C) at 5% loss indicates better thermal stability of the resin composition. Evaluation was also carried out based on the following criteria: A (good): 351°C or higher B (average): 346°C or higher but lower than 351°C C (poor): 341°C or higher but lower than 346°C D (very poor): lower than 341°C

[0240]

[0241] As can be seen from Table I-1, the resin compositions of Examples I-1 and I-2, which contain specific amounts of a titanium compound and an alkaline earth metal compound (A) in an ethylene-modified PVA resin, have superior thermal stability compared to the resin composition of Comparative Example I-1, which does not contain a titanium compound; the resin composition of Comparative Example I-2, which contains a titanium compound in an amount greater than the specific range; the resin composition of Comparative Example I-3, which does not contain an alkaline earth metal compound (A); and the resin composition of Comparative Example I-4, which uses an unmodified PVA resin. Furthermore, multilayer structures, molded articles, and food packages having layers containing the resin compositions of Examples I-1 and I-2 also exhibit suppressed thermal degradation and superior thermal stability.

[0242] <<Second Aspect>> Prior to the Examples, the following components were prepared. Ethylene-modified PVA resin: pellets of ethylene-modified PVA resin having an ethylene structural unit content of 4 mol%, a melting point of 213°C, and a saponification degree of 98 mol% Unmodified PVA resin: pellets of PVA resin having an ethylene structural unit content of 0 mol%, a melting point of 227°C, and a saponification degree of 99 mol% Titanium compound: rutile-type titanium(IV) oxide having an average particle size of 5 μm or less (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Alkali metal compound (B): sodium acetate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0243] Example II-1: The ethylene-modified PVA resin pellets were dry-blended with the sodium acetate and titanium oxide to a metal equivalent content of 10 ppm and 0.1 ppm, respectively, relative to the mass of the resin composition. 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 resulting 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.

[0244] [Extrusion conditions] Extruder set temperatures (°C): C1 / C2 / C3 / C4 / C5 / C6 = 200 / 210 / 225 / 225 / 225 / 225

[0245] Example II-2 Pellets of a resin composition were obtained in the same manner as in Example II-1, except that the titanium oxide content, calculated as metal, was changed to 1 ppm relative to the mass of the resin composition.

[0246] Example II-3 Pellets of a resin composition were obtained in the same manner as in Example II-1, except that the content of sodium acetate in terms of metal was changed to 100 ppm relative to the mass of the resin composition.

[0247] Comparative Example II-1 Pellets of a resin composition were obtained in the same manner as in Example II-3, except that titanium oxide was not used.

[0248] Comparative Example II-2 Pellets of a resin composition were obtained in the same manner as in Example II-3, except that the titanium oxide content, calculated as metal, was changed to 10 ppm relative to the mass of the resin composition.

[0249] Comparative Example II-3 Pellets of a resin composition were obtained in the same manner as in Example II-2, except that sodium acetate was not used.

[0250] Comparative Example II-4 Pellets of a resin composition were obtained in the same manner as in Example II-2, except that an unmodified PVA resin was used instead of the ethylene-modified PVA resin.

[0251] Using the obtained pellets of the resin compositions of Examples II-1 to II-3 and Comparative Examples II-1 to II-3, the remaining amounts at 550° C. were measured as follows. The results are shown in Table II-1 below.

[0252] [Residual Amount at 550°C] Using 5 mg of pellets of the obtained resin composition, the residual amount (%) at 550°C was measured using a thermogravimetric analyzer (Pyris 1 TGA, manufactured by Perki Elmer) under conditions of an airflow rate of 20 mL / min, a heating rate of 10°C / min, and a temperature range of 30 to 550°C in a nitrogen atmosphere. A higher residual amount (%) at 550°C indicates better thermal stability of the resin composition. Evaluation was also carried out based on the following criteria. The results are shown in Table II-1 below. A (good): 6.0% or more B (average): 4.0% or more and less than 6.0% C (poor): 2.0% or more and less than 4.0% D (very poor): less than 2.0

[0253] [Temperature at 10% Decrease] Using 5 mg of pellets of the resin compositions obtained in Examples II-1 and II-2, the temperature (°C) at 10% decrease was measured using a thermogravimetric analyzer (Pyris 1 TGA, manufactured by Perki Elmer) under conditions of an airflow rate of 20 mL / min, a heating rate of 10°C / min, and a temperature range of 30 to 550°C in a nitrogen atmosphere. A higher temperature (°C) at 10% decrease indicates better thermal stability of the resin composition. Evaluation was also carried out based on the following criteria. The results are shown in Table II-2 below. AA (excellent): 356°C or higher A (good): 351°C or higher but lower than 356°C B (average): 347°C or higher but lower than 351°C C (poor): lower than 347°C

[0254] [Yellow Index (YI)] The pellets obtained in Example II-1 and Comparative Example II-4 were filled into a cylinder with an inner diameter of 32 mm and a height of 30 mm, and the resulting pulverized material was used to measure the YI value using a spectrophotometer (manufactured by Nippon Denshoku Industries Co., Ltd.) after the cylinder was completely filled. Evaluation was also carried out based on the following criteria. The results are shown in Table II-3 below. A (good): 0 or more and less than 30 B (average): 30 or more and less than 60 C (poor): 60 or more and less than 90 D (very poor): 90 or more

[0255]

[0256]

[0257]

[0258] As can be seen from Tables II-1 to II-3, the resin compositions of Examples II-1 to II-3, which contain an ethylene-modified PVA resin, an alkali metal compound (B), and a specific amount of a titanium compound, have superior thermal stability compared to the resin composition of Comparative Example II-1, which does not contain a titanium compound; the resin composition of Comparative Example II-2, which contains a titanium compound in an amount greater than the specific range; the resin composition of Comparative Example II-3, which does not contain an alkali metal compound (B); and the resin composition of Comparative Example II-4, which uses an unmodified PVA resin. Furthermore, the multilayer structures comprising layers made of the resin compositions of Examples II-1 to II-3 also have superior thermal stability.

[0259] <<Third Aspect>> Prior to the examples, the following components were prepared. Ethylenic PVA resin: pellets of ethylene-modified PVA resin having an ethylene structural unit content of 4 mol%, a melting point of 213°C, and a saponification degree of 98 mol%. Titanium compound: rutile-type titanium oxide (IV) having an average particle size of 5 μm or less (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). Sorbic acid (C): sorbic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.).

[0260] Example III-1: The ethylene-modified PVA resin pellets were dry-blended with the sorbic acid so that the sorbic acid was 50 ppm relative to the mass of the resin composition, and the titanium oxide was 0.1 ppm relative to the mass of the resin composition in terms of metal, 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.

[0261] [Extrusion conditions] Extruder set temperatures (°C): C1 / C2 / C3 / C4 / C5 / C6 = 200 / 210 / 225 / 225 / 225 / 225

[0262] Example III-2 Pellets of a resin composition were obtained in the same manner as in Example III-1, except that the titanium oxide content, calculated as metal, was changed to 1 ppm relative to the mass of the resin composition.

[0263] Comparative Example III-1 Pellets of a resin composition were obtained in the same manner as in Example III-1, except that titanium oxide was not used.

[0264] Comparative Example III-2 Pellets of a resin composition were obtained in the same manner as in Example III-1, except that the titanium oxide content, calculated as metal, was changed to 10 ppm relative to the mass of the resin composition.

[0265] Comparative Example III-3 Pellets of a resin composition were obtained in the same manner as in Example III-2, except that sorbic acid was not used.

[0266] Using the pellets of the resin compositions of Examples III-1 and III-2 and Comparative Examples III-1 to III-3, the temperatures at which the resin composition was reduced by 40% were measured as follows, and the results are shown in Table III-1.

[0267] [Temperature at 40% reduction] Using 5 mg of pellets of the obtained resin composition, the weight change was measured using a thermogravimetric analyzer (Pyris 1 TGA, manufactured by Perki Elmer) under conditions of an air flow rate of 20 mL / min, a heating rate of 10°C / min, and a temperature range of 30 to 550°C, and the temperatures at 40% reduction were compared. A higher temperature at 40% reduction indicates better thermal stability of the resin composition. Evaluation was also carried out based on the following criteria. A (good): 393°C or higher B (average): 390°C or higher but less than 393°C C (poor): less than 390°C

[0268] [Temperature at 5% Decrease] Using 5 mg of pellets of the resin compositions obtained in Examples III-1 and III-2, the temperature (°C) at 5% decrease was measured using a thermogravimetric analyzer (Pyris 1 TGA, manufactured by Perki Elmer) under conditions of an airflow rate of 20 mL / min, a heating rate of 10°C / min, and a temperature range of 30 to 550°C in a nitrogen atmosphere. A higher temperature (°C) at 5% decrease indicates better thermal stability of the resin composition. Evaluation was also carried out based on the following criteria. The results are shown in Table III-2. AA (excellent): 341°C or higher A (good): 336°C or higher and lower than 341°C B (average): lower than 336°C

[0269]

[0270]

[0271] As can be seen from Tables III-1 and III-2, the resin compositions of Examples III-1 and III-2, which contained an ethylene-modified PVA resin, sorbic acid, and a specific amount of a titanium compound, were superior in thermal stability to the resin composition of Comparative Example III-1, which contained no titanium compound, the resin composition of Comparative Example III-2, which contained a titanium compound in an amount greater than the specific range, and the resin composition of Comparative Example III-3, which did not contain sorbic acid. Furthermore, the multilayer structures comprising layers made of the resin compositions of Examples III-1 and III-2 also exhibited excellent thermal stability.

[0272] <<Fourth Aspect>> Prior to the examples, the following components were prepared. Ethylene-modified PVA resin: pellets of ethylene-modified PVA resin having an ethylene structural unit content of 4 mol%, a melting point of 213°C, and a saponification degree of 98 mol% Unmodified PVA resin: pellets of PVA resin having an ethylene structural unit content of 0 mol%, a melting point of 227°C, and a saponification degree of 99 mol% Titanium compound: rutile-type titanium(IV) oxide having an average particle size of 5 μm or less (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Acetic acid (D): acetic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0273] Example IV-1: The ethylene-modified PVA resin pellets were dry-blended with the acetic acid at 500 ppm relative to the mass of the resin composition and the titanium oxide at 0.1 ppm relative to the mass of the resin composition in terms of metal, 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.

[0274] [Extrusion conditions] Extruder set temperatures (°C): C1 / C2 / C3 / C4 / C5 / C6 = 200 / 210 / 225 / 225 / 225 / 225

[0275] Example IV-2 Pellets of a resin composition were obtained in the same manner as in Example IV-1, except that the titanium oxide content in terms of metal was changed to 1 ppm based on the mass of the resin composition.

[0276] Comparative Example IV-1 Pellets of a resin composition were obtained in the same manner as in Example IV-1, except that titanium oxide was not used.

[0277] Comparative Example IV-2 Pellets of a resin composition were obtained in the same manner as in Example IV-1, except that the titanium oxide content, calculated as metal, was changed to 10 ppm relative to the mass of the resin composition.

[0278] Comparative Example IV-3 Pellets of a resin composition were obtained in the same manner as in Example IV-2, except that acetic acid was not used.

[0279] Comparative Example IV-4 Pellets of a resin composition were obtained in the same manner as in Example IV-1, except that an unmodified PVA resin was used instead of the ethylene-modified PVA resin.

[0280] Using the pellets of the resin compositions of Examples IV-1 and IV-2 and Comparative Examples IV-1 to IV-4, the temperatures at which the resin composition decreased by 5% were measured as follows, and the results are shown in Table IV-1.

[0281] [Temperature at 5% Decrease] Using 5 mg of pellets of the obtained resin composition, the temperature at 5% decrease (°C) was measured using a thermogravimetric analyzer (Pyris 1 TGA, manufactured by Perki Elmer) under the conditions of an air flow rate of 20 mL / min, a heating rate of 10°C / min, and a temperature range of 30 to 550°C in a nitrogen atmosphere. A higher temperature at 5% decrease (°C) indicates better thermal stability. Evaluation was also carried out based on the following criteria. A (good): 345°C or higher B (average): 340°C or higher but lower than 345°C C (poor): 335°C or higher but lower than 340°C D (very poor): lower than 335°C

[0282] [Residual Amount at 550°C] Using 5 mg of pellets of the resin compositions obtained in Examples IV-1 and IV-2, the residual amount (%) at 550°C was measured using a thermogravimetric analyzer (Pyris 1 TGA, manufactured by Perki Elmer) under conditions of an airflow rate of 20 mL / min, a heating rate of 10°C / min, and a temperature range of 30 to 550°C in a nitrogen atmosphere. A higher residual amount (%) at 550°C indicates better thermal stability of the resin composition. Evaluation was also performed based on the following criteria. The evaluation results are shown in Table IV-2. AA (excellent): 4.0% or more A (good): 2.0% or more but less than 4.0% B (average): less than 2.0%

[0283]

[0284]

[0285] As can be seen from Tables IV-1 and IV-2, the resin compositions of Examples IV-1 and IV-2, which contained acetic acid and a specific amount of a titanium compound, had superior thermal stability compared to the resin composition of Comparative Example IV-1, which did not contain a titanium compound; the resin composition of Comparative Example IV-2, which contained a titanium compound in an amount greater than the specific range; the resin composition of Comparative Example IV-3, which did not contain acetic acid; and the resin composition of Comparative Example IV-4, which used an unmodified PVA resin. Furthermore, the multilayer structures comprising layers made of the resin compositions of Examples IV-1 and IV-2 also had excellent thermal stability.

[0286] 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.

[0287] The present resin composition has an improved thermal decomposition temperature during melt molding and excellent thermal stability, making it useful as a packaging material for a variety of 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., and as a material for molded articles used to package pesticides, detergents, civil engineering additives, disinfectants, dyes, pigments, etc.

Claims

1. A resin composition containing a polyvinyl alcohol resin, a titanium compound, and a compound (X), wherein the polyvinyl alcohol resin is an ethylene-modified polyvinyl alcohol resin containing 1 to 19 mol% of ethylene structural units, the compound (X) is at least one selected from the group consisting of an alkaline earth metal compound (A), an alkali metal compound (B), sorbic acid (C), and acetic acid (D), and the metal-equivalent content of the titanium compound 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) is an alkaline earth metal compound (A).

3. The resin composition according to claim 2, wherein the content of the alkaline earth metal compound (A) 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 (A) is a magnesium compound.

5. The resin composition according to any one of claims 1 to 4, wherein the compound (X) is an alkali metal compound (B).

6. The resin composition according to claim 5, wherein the content of the alkali metal compound (B) in terms of metal is 0.0001 to 5000 ppm based on the mass of the resin composition.

7. The resin composition according to claim 5 or 6, wherein the alkali metal compound (B) is a sodium compound.

8. The resin composition according to any one of claims 1 to 7, wherein the compound (X) is sorbic acid (C).

9. The resin composition according to claim 8, wherein the content of the sorbic acid (C) is 0.005 to 100 ppm based on the mass of the resin composition.

10. The resin composition according to any one of claims 1 to 9, wherein the compound (X) is acetic acid (D).

11. The resin composition according to claim 10, wherein the content of the acetic acid (D) is 10 to 10,000 ppm based on the mass of the resin composition.

12. A resin composition according to any one of claims 1 to 11, wherein the content of the titanium compound in terms of metal is equal to or more than 0.0001 ppm and less than 1 ppm based on the mass of the resin composition.

13. A molding material comprising the resin composition according to any one of claims 1 to 12.

14. A multilayer structure having a layer containing the resin composition according to any one of claims 1 to 12.

15. A molded article comprising the multilayer structure according to claim 14.

16. A food package comprising the multi-layer structure of claim 14.

17. A method for producing a resin composition according to any one of claims 1 to 12, comprising the step of melt-mixing a resin composition raw material containing the polyvinyl alcohol resin and the titanium compound.

18. A method for producing the multilayer structure according to claim 14, comprising the step of melt-molding a layer containing the resin composition.

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