Ethylene-vinyl alcohol copolymer composition and method for producing same, particles,

Abstract

Provided is an EVOH resin composition having an increased thermal decomposition temperature during melt molding and excellent thermal stability. An ethylene-vinyl alcohol copolymer composition which contains an ethylene-vinyl alcohol copolymer having a degree of saponification of more than 91 mol% and 99.5 mol% or less, and a titanium compound, the content of the titanium compound in terms of metal is 0.001 ppm or more and less than 5 ppm relative to the mass of the ethylene-vinyl alcohol copolymer composition.

Description

Technical Field

[0001] This invention relates to ethylene-vinyl alcohol copolymer compositions and their preparation methods, particles, and multilayer structures and their preparation methods, as well as various articles obtained from multilayer structures. Background Technology

[0002] Ethylene-vinyl alcohol copolymers (hereinafter sometimes referred to as "EVOH resins") have excellent transparency, gas barrier properties such as oxygen, aroma retention, solvent resistance, oil resistance, and mechanical strength. They are molded into films, sheets, bottles, etc., and are widely used as packaging materials for various products such as food, pharmaceuticals, industrial chemicals, and pesticides.

[0003] In particular, resin compositions formulated with EVOH resin of low saponification degree are widely used in thermoformed containers and other applications due to their good transparency and secondary processing properties.

[0004] Furthermore, the heat-shrinkable multilayer film having at least one layer of EVOH resin composition with low saponification degree exhibits excellent elongation, heat shrinkage, gas barrier properties, and transparency after heat shrinkage.

[0005] However, EVOH resins have relatively active hydroxyl groups in their molecules, which makes them prone to deterioration due to heat. Improvements are needed in terms of thermal stability, such as the decomposition temperature during melt molding.

[0006] To address the aforementioned technical problems, for example, Patent Document 1 discloses an EVOH resin composition containing a specific amount of an alkali metal salt (A), a specific amount of a carboxylic acid or its salt (C), and an EVOH resin with a saponification degree of 80-99 mol%. The EVOH with a low saponification degree exhibits superior softness compared to conventional EVOH with a high saponification degree, and is therefore used in applications where softness is more important than gas barrier properties. In particular, a resin composition made by combining EVOH with a high saponification degree and EVOH with a low saponification degree is disclosed and is widely used in thermoformed containers and the like as a resin composition with good transparency and secondary processing properties.

[0007] Furthermore, Patent Document 2 discloses a heat-shrinkable multilayer film with excellent stretchability, heat shrinkage, gas barrier properties, and transparency after heat shrinkage. The heat-shrinkable multilayer film is characterized by having at least one resin composition layer containing EVOH, wherein the EVOH reduces the saponification degree of vinyl acetate by reacetylation, and the ethylene content is 20-60 mol% and the saponification degree is 98 mol% or less.

[0008] Furthermore, Patent Document 3 discloses a resin composition that can suppress thickness unevenness in the TD (width) direction during film formation such as blow molding. The resin composition is characterized by containing ethylene-vinyl acetate copolymer saponified (A) and organic phthalate (B). In the examples, it is disclosed that 0.003 parts of tetraisopropyl titanate (B) are used (0.0005 parts in titanium equivalent).

[0009] Furthermore, Patent Document 4 discloses that by including unsaturated aldehydes in the EVOH resin, oxidative degradation during melt molding of the EVOH resin can be suppressed, thereby inhibiting coloring.

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 1: Japanese Patent Application Publication No. 2005-068414

[0013] Patent Document 2: Japanese Patent Application Publication No. 2000-211068

[0014] Patent Document 3: Japanese Patent Application Publication No. 2004-24445

[0015] Patent Document 4: International Publication No. 2013 / 146961 Summary of the Invention

[0016] The problem that the invention aims to solve

[0017] However, in Patent Documents 1 and 2, the thermal stability of the low-saponification EVOH resin compositions during melt molding is insufficient, leaving room for further improvement. Furthermore, in Patent Document 3, when the EVOH resin composition contains 5 ppm of titanium, the decomposition reaction of the EVOH resin proceeds rapidly at a specific temperature, thus tending towards low extrusion stability during extrusion molding. Moreover, in Patent Document 4, even trace amounts of aldehyde compounds such as unsaturated aldehydes can sometimes contribute to foul odors, raising concerns about their volatilization during high-temperature molding processes, potentially deteriorating the working environment. Therefore, there is a requirement for an EVOH resin composition that does not use such volatile compounds.

[0018] This invention provides an EVOH resin composition that improves the thermal decomposition temperature of EVOH resin during melt molding and exhibits excellent thermal stability.

[0019] Solution for solving the problem

[0020] However, in view of this situation, the inventors discovered that by adding a specific trace amount of titanium compound to EVOH resin with low saponification degree, an EVOH resin composition in which thermal degradation of EVOH resin during melt molding is suppressed can be obtained.

[0021] That is, the present invention has the following solution. [1]

[0023] An ethylene-vinyl alcohol copolymer composition comprising an ethylene-vinyl alcohol copolymer and a titanium compound, wherein the degree of saponification of the ethylene-vinyl alcohol copolymer is greater than 91 mol% and less than 99.5 mol%, and the metal conversion content of the titanium compound relative to the mass of the ethylene-vinyl alcohol copolymer composition is greater than 0.001 ppm and less than 5 ppm. [2]

[0025] According to the ethylene-vinyl alcohol copolymer composition of [1], the metal conversion content of the titanium compound is 0.001 ppm or more and 0.9 ppm or less relative to the mass of the ethylene-vinyl alcohol copolymer composition. [3]

[0027] A particle formed from the ethylene-vinyl alcohol copolymer composition described in [1] or [2]. [4]

[0029] A multilayer structure having at least one layer formed of the ethylene-vinyl alcohol copolymer composition described in [1] or [2] or the particles described in [3]. [5]

[0031] A thermoformed container formed from the multilayer structure described in [4]. [6]

[0033] A packaging film formed of the multilayer structure described in [4]. [7]

[0035] A multilayer shrink film formed from the multilayer structure described in [4]. [8]

[0037] A deep drawing forming membrane is formed from the multilayer structure described in [4]. [9]

[0039] An agricultural film formed from the multilayer structure described in [4].

[10]

[0041] A method for manufacturing an ethylene-vinyl alcohol copolymer composition, which is a method for manufacturing the ethylene-vinyl alcohol copolymer composition described in [1] or [2], comprising the following steps: melt-mixing a composition raw material containing an ethylene-vinyl alcohol copolymer and a titanium compound.

[11]

[0043] A method for manufacturing a multilayer structure, which is a method for manufacturing the multilayer structure described in [4], comprising the following steps: obtaining a layer formed of the ethylene-vinyl alcohol copolymer composition by melt molding.

[0044] Advantages of the invention

[0045] The EVOH resin composition of the present invention increases the thermal decomposition temperature of the EVOH resin during melt molding and has excellent thermal stability. Detailed description of the specific embodiments

[0046] Hereinafter, the present invention will be described in more detail based on the embodiments of the present invention, but the present invention is not limited to these embodiments.

[0047] It should be noted that in this specification, when expressed as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it includes the meaning of "X or more and Y or less", and includes the meaning of "preferably greater than X" or "preferably less than Y".

[0048] In addition, when expressed as "X or more" (X is an arbitrary number) or "Y or less" (Y is an arbitrary number), it also includes the meaning of "preferably greater than X" or "preferably less than Y".

[0049] Regarding the numerical ranges described step by step in this specification, the upper limit value or lower limit value of a certain step's numerical range can be arbitrarily combined with the upper limit value or lower limit value of other steps' numerical ranges. In addition, in the numerical ranges described in this specification, the upper limit value or lower limit value of this numerical range can also be replaced with the values shown in the examples.

[0050] In addition, in this specification, "film" means that it also includes the meanings of "tape" and "sheet".

[0051] <EVOH resin composition>

[0052] The low-saponification-degree EVOH resin composition of one embodiment of the present invention (hereinafter referred to as "this EVOH resin composition") is mainly composed of a low-saponification-degree EVOH resin and contains a specific trace amount of a titanium compound.

[0053] That is, the base resin of this EVOH resin composition is EVOH resin, and the content of EVOH resin in this EVOH resin composition is usually 70% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0054] The following is a description of each component.

[0055] [EVOH resin]

[0056] The EVOH resin used in this invention is typically a resin obtained by saponifying an ethylene-ethylene ester copolymer, which is a copolymer of ethylene and ethylene ester monomers, and is a non-water-soluble thermoplastic resin.

[0057] Vinyl acetate is representatively used as the vinyl ester monomer, considering its market availability and efficient impurity removal during manufacturing. Other vinyl ester monomers besides vinyl acetate include, for example, aliphatic vinyl esters such as vinyl formate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl neovalerate, vinyl decanoate, vinyl laurate, vinyl stearate, vinyl tert-carbonate, and aromatic vinyl esters such as vinyl benzoate. Aliphatic vinyl esters with 3 to 20 carbon atoms are typically used, preferably 4 to 10, and particularly preferably 4 to 7. They are usually used alone, but multiple types can also be used simultaneously as needed.

[0058] As a polymerization method for copolymerizing ethylene with ethylene ester monomers, any known polymerization method can be used, such as solution polymerization, suspension polymerization, emulsion polymerization, etc., typically using solution polymerization with methanol as a solvent. Furthermore, the saponification of the resulting ethylene-ethylene ester copolymer can also be carried out using known methods.

[0059] The EVOH resin produced in this way is mainly composed of structural units derived from ethylene and vinyl alcohol, and contains a certain amount of unsaponified and residual vinyl ester structural units.

[0060] The content of ethylene structural units in the EVOH resin is typically 20–60 mol%, preferably 25–57 mol%, more preferably 30–55 mol%, and even more preferably 35–53 mol%. The content of ethylene structural units can be controlled by the ethylene pressure during copolymerization of ethylene ester monomers and ethylene. If the content is too low, there is a tendency for reduced secondary processing properties and flexibility; conversely, if the content is too high, there is a tendency for reduced gas barrier properties.

[0061] It should be noted that the content of this ethylene structural unit can be determined based on ISO 14663.

[0062] The degree of saponification in the EVOH resin is greater than 91 mol% and less than 99.5 mol%, preferably 93 to 99.3 mol%, more preferably 95 to 99 mol%. Furthermore, as a lower limit, it is preferably 96 mol% or more, and most preferably 97 mol% or more. The degree of saponification can be controlled by the amount of saponification catalyst (typically an alkaline catalyst such as sodium hydroxide) used during the saponification of the ethylene-vinyl ester copolymer, the temperature, and the time. If the degree of saponification is too low, there is a tendency for a decrease in gas barrier properties, thermal stability, and moisture resistance.

[0063] The degree of saponification of this EVOH resin can be determined by the following method.

[0064] [Degree of saponification]

[0065] Weigh approximately 50 mg of EVOH into a vial, add 1 mL of dimethyl sulfoxide-d6 (DMSO-d6), heat and stir at 50 °C to dissolve, and perform NMR determination under the following conditions.

[0066] <Measurement Conditions>

[0067] • Device name: Bruker superconducting nuclear magnetic resonance device "AVANCEIIIHD 400".

[0068] • Observation frequency: 400MHz.

[0069] Solvent: DMSO-d6.

[0070] • Polymer concentration: 5 w / v%.

[0071] • Measurement temperature: 50℃.

[0072] • Total number of times: 16.

[0073] <Analytical Methods>

[0074] Based on the measured spectrum, the integral values ​​(I1) of the peak with a chemical shift of 4.0–3.3 ppm and the integral value (I2) of the peak with a chemical shift of 2.0 ppm were calculated. Here, the peak with a chemical shift of 4.0–3.3 ppm mainly originates from the methylene hydrogen adjacent to the hydroxyl group, and the peak with a chemical shift of 2.0 ppm originates from the methyl hydrogen in the unsaponified vinyl acetate unit. The degree of saponification was calculated using these integral values ​​using the following formula.

[0075] [Mode]

[0076] (3×I1) / {(3×I1)+I2}×100

[0077] The melt flow rate (MFR) of the EVOH resin (210°C, 2160g load) is typically 0.5–100g / 10min, preferably 1–50g / 10min, and particularly preferably 3–35g / 10min. If the MFR is too high, there is a tendency for the stability during film formation to be compromised; if it is too low, there is a tendency for the viscosity to become too high, making melt extrusion difficult.

[0078] The MFR is an indicator of the degree of polymerization of EVOH resin, which can be adjusted by the amount of polymerization initiator and solvent used in the copolymerization of ethylene and ethylene ester monomers.

[0079] Furthermore, the EVOH resin may also contain structural units derived from the comonomers shown below (e.g., less than 10 mol% of the EVOH resin) to a extent that does not impede the effects of the present invention.

[0080] Examples of comonomers include: olefins such as propylene, 1-butene, and isobutene; hydroxyl-containing α-olefins such as 3-buten-1-ol, 3-buten-1,2-diol, 4-penten-1-ol, and 5-hexen-1,2-diol, and their esterifications, acylates, and other derivatives; hydroxyalkyl vinylides such as 2-methylenepropane-1,3-diol and 3-methylenepentane-1,5-diol; and 1,3-diacetoxy-2-methylenepropane, 1,3-dipropionyloxy-2-... Hydroxyalkyl vinylidene diacetate esters such as methylene propane and 1,3-dibutyryloxy-2-methylene propane; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, phthalic acid (anhydride), maleic acid (anhydride), itaconic acid (anhydride), or their salts, or monoalkyl or dialkyl esters with alkyl groups having 1 to 18 carbon atoms; acrylamide, N-alkylacrylamide, N,N-dimethylacrylamide, 2-acrylamide propanesulfonic acid or their salts, and acrylamide propyl Acrylamides such as dimethylamine or its acid salts or quaternary ammonium salts; methacrylamides, N-alkylmethacrylamides with 1 to 18 carbon atoms in alkyl groups, N,N-dimethylmethacrylamide, 2-methacrylamide propanesulfonic acid or its salts, methacrylamide propyl dimethylamine or its acid salts or quaternary ammonium salts, etc.; N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, etc.; vinyl cyanides such as acrylonitrile and methacrylonitrile; alkyl groups with 1 to 18 carbon atoms. Vinyl ethers, such as alkyl vinyl ethers, hydroxyalkyl vinyl ethers, and alkoxyalkyl vinyl ethers, in the range of 1 to 18; halogenated vinyl compounds, such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, and vinyl bromide; vinyl silanes, such as trimethoxyvinylsilane; halogenated allyl compounds, such as allyl acetate and allyl chloride; allyl alcohols, such as allyl alcohol and dimethoxyallyl alcohol; and comonomers, such as trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride and acrylamide-2-methylpropanesulfonic acid. These can be used alone or in combination of two or more.

[0081] Preferably, α-olefins containing hydroxyl groups are preferred, with 3-buten-1,2-diol and 5-hexen-1,2-diol being particularly preferred. When these α-olefins are copolymerized, the resulting EVOH resin has primary hydroxyl groups in its side chains. Such EVOH resins with primary hydroxyl groups in their side chains, especially those with 1,2-diol structures in their side chains, are preferred in terms of maintaining gas barrier properties and improving secondary molding properties.

[0082] In the case where the EVOH resin has primary hydroxyl groups in its side chains, the content of structural units derived from monomers having said primary hydroxyl groups is typically 0.1 to 20 mol% of the EVOH resin, preferably 0.5 to 15 mol%, and particularly preferably 1 to 10 mol%.

[0083] In addition, EVOH resins that have undergone "post-modification" such as esterification, carbamate esterification, acetalization, cyanoethylation, and oxyalkyleneification can also be used as the EVOH resin.

[0084] When using the post-modified EVOH resin, the modification rate is typically 10 mol% or less, preferably 4 mol% or less. If the modification rate of the EVOH resin is too high, it tends to easily deteriorate thermally and reduce thermal stability.

[0085] Furthermore, the EVOH resin can also be a mixture of EVOH resins with different contents of ethylene structural units, degree of saponification, degree of polymerization, copolymerization components, etc.

[0086] [Titanium compounds]

[0087] Examples of titanium compounds include inorganic titanium compounds and organic titanium compounds. It should be noted that titanium compounds can be used alone or in combination of two or more. Inorganic titanium compounds are preferred.

[0088] Examples of such inorganic titanium compounds include titanium oxides, titanium hydroxides, titanium chlorides, and inorganic salts of titanium.

[0089] Examples of titanium oxides include titanium oxide (II), titanium oxide (III), titanium oxide (IV), and sub-titanium oxide.

[0090] Examples of titanium hydroxides include trivalent titanium hydroxide and tetravalent titanium hydroxide.

[0091] Examples of titanium chlorides include trivalent titanium chloride and tetravalent titanium chloride.

[0092] Inorganic salts of titanium include, for example, titanium phosphate and titanium sulfate.

[0093] Among them, titanium oxide is preferred, titanium oxide (IV) is more preferred, and rutile titanium oxide (IV) is particularly preferred.

[0094] Examples of such organotitanium compounds include titanium acetate, titanium butyrate, titanium stearate, and other carboxylic acid titanium compounds.

[0095] It should be noted that, in addition to existing as titanium compounds in the EVOH resin composition, the titanium compounds may also exist in an ionized state or as complexes formed by interactions with EVOH resin and other ligands.

[0096] The average particle size of the titanium compound is typically 0.001–100 μm, preferably 0.01–50 μm, and more preferably 0.015–20 μm. When the average particle size of the titanium compound is within this range, it tends to exhibit excellent thermal stability.

[0097] The metal equivalent content of the titanium compound relative to the mass of this EVOH resin composition is 0.001 ppm or more and less than 5 ppm. Preferably, it is 0.005 to 4 ppm, more preferably 0.01 to 3 ppm, and particularly preferably 0.05 to 2 ppm. Furthermore, as an upper limit, it is preferably 0.9 ppm or less, and most preferably 0.5 ppm or less. By setting the content of the titanium compound within the aforementioned range, thermal decomposition during melt molding can be suppressed, resulting in excellent thermal stability. However, when the content of the titanium compound is too low, the effect of suppressing thermal decomposition tends to decrease; when the content is too high, decomposition occurs rapidly in high-temperature regions, thus tending to compromise extrusion stability.

[0098] The metal conversion content of the titanium compound can be quantified by the following method: weigh the EVOH resin composition into a platinum crucible, ashing it sequentially in a burner and an electric furnace, decomposing the ashed material by heating with nitric acid and hydrofluoric acid, treating it with a mixed acid of dilute nitric acid and dilute hydrofluoric acid and making up to volume, and determining the titanium in the obtained solution by ICP mass spectrometry (manufactured by Agilent Technologies, Agilent 8800).

[0099] Typically, EVOH resins undergo thermal decomposition and discoloration due to thermal degradation. This is believed to be because the degradation of EVOH resins by heat generates free radicals. The hydroxyl groups of the EVOH resin are dehydrated by these free radicals, forming double bonds in the main chain of the EVOH resin. This site becomes the reaction initiation point, further promoting dehydration and forming a conjugated polyene structure in the main chain of the EVOH resin.

[0100] In response, this EVOH resin composition contains a specific trace amount of titanium compound, which increases the thermal decomposition temperature of the EVOH resin and provides excellent thermal stability.

[0101] That is, it is speculated that titanium, as a tetravalent ion, is stable. Even trace amounts will be stabilized by coordinating with the double bonds of the main chain of the EVOH resin as described above to form chelates, thereby inhibiting the formation of polyene structures.

[0102] [Other thermoplastic resins]

[0103] In this EVOH resin composition, a thermoplastic resin other than EVOH resin may be contained within a range that does not hinder the effects of the present invention (e.g., typically 30% by mass or less, preferably 20% by mass or less, and particularly preferably 10% by mass or less of this EVOH resin composition).

[0104] Other thermoplastic resins that can be used include well-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. They can be used alone or in combination of two or more.

[0105] [Other compounding agents]

[0106] Furthermore, this EVOH resin composition may contain a compounding agent typically compounded with EVOH resin, within a range that does not impair the effects of the present invention. Examples of such compounding agents include inorganic complex salts (e.g., hydrotalcite), plasticizers (e.g., aliphatic polyols such as ethylene glycol, glycerol, and hexanediol), oxygen absorbers (e.g., inorganic oxygen absorbers such as aluminum powder and potassium sulfite); ascorbic acid and its fatty acid esters, metal salts, gallic acid, polyphenols such as hydroxyl-containing phenolic resins, terpene compounds, blends of resins containing tertiary hydrogen and transition metals (e.g., a combination of polypropylene and cobalt), and blends of resins containing carbon-carbon unsaturated bonds and transition metals (e.g., polybutadiene). Polymer oxygen absorbers, including combinations of dienes and cobalt, photo-oxidative degradable resins (e.g., polyketides), anthraquinone polymers (e.g., polyvinyl anthraquinone), and substances formed by adding photoinitiators (e.g., benzophenone), antioxidants (other than those mentioned above), deodorizers (e.g., activated carbon), heat stabilizers, light stabilizers, ultraviolet absorbers, colorants, antistatic agents, surfactants (excluding substances used as lubricants), antibacterial agents, anti-blocking agents, and fillers (e.g., inorganic fillers), etc. These compounds can be used alone or in combination of two or more.

[0107] [Method for manufacturing EVOH resin composition]

[0108] This EVOH resin composition can be manufactured by the following steps: melt-mixing a composition raw material containing the EVOH resin and a titanium compound, for example, by using a dry mixing method, a melt mixing method, a solution mixing method, an impregnation method, etc. Furthermore, these manufacturing methods can be combined arbitrarily.

[0109] Examples of dry mixing methods include: (i) a method of dry mixing granular EVOH resin with titanium compounds using a drum or similar device.

[0110] Examples of the melt mixing method include: (ii) a method of melt mixing a dry mixture obtained by dry mixing granular EVOH resin with a titanium compound; and (iii) a method of melt mixing EVOH resin by adding a titanium compound to molten EVOH resin.

[0111] Examples of the solution mixing method include: (iv) preparing a solution using commercially available EVOH resin, adding a titanium compound thereto, solidifying the solution, and then separating and drying the solution using a known method; (v) during the manufacturing process of EVOH resin, containing a titanium compound in a solution of ethylene-vinyl ester copolymer before saponification or a homogeneous solution of EVOH resin (water / alcohol solution, etc.), solidifying the solution, and then separating and drying the solution using a known method.

[0112] Examples of the impregnation method include: (vi) contacting particulate EVOH resin with an aqueous solution containing a titanium compound, thereby contaminating the EVOH resin with the titanium compound, and then drying it.

[0113] As the aqueous solution containing the titanium compound, an aqueous solution of the titanium compound or an aqueous solution in which titanium ions are dissolved by immersing the titanium compound in water containing various reagents can be used.

[0114] It should be noted that, in the impregnation method, the content of titanium compounds (metal conversion) can be controlled by the concentration of titanium compounds in the aqueous solution of EVOH resin, the impregnation temperature, the impregnation time, etc.

[0115] 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.

[0116] As a drying method in each of the aforementioned manufacturing methods, various drying methods can be used, including any of the following: static drying and flow drying. Furthermore, combinations of these methods can also be employed.

[0117] As described above, different methods can be combined in this invention. From the perspective of productivity and obtaining a resin composition with more significant effects than those described in this invention, melt mixing is preferred, and method (ii) is particularly preferred. Furthermore, when using other thermoplastic resins or other compounding agents, they can be formulated using conventional methods according to the manufacturing method described above.

[0118] The shape of the EVOH resin composition obtained by the aforementioned manufacturing methods is arbitrary, but granules are preferred.

[0119] The particles can be spherical, elliptical, cylindrical, cubic, or cuboid in shape, but are typically elliptical or cylindrical. In terms of size, considering convenience for use as a molding material, in the case of an elliptical particle, the minor axis is typically 1–10 mm, preferably 2–6 mm, more preferably 2.5–5.5 mm, and the major axis is typically 1.5–30 mm, preferably 3–20 mm, more preferably 3.5–10 mm. Furthermore, in the case of a cylindrical particle, the diameter of the base is typically 1–6 mm, preferably 2–5 mm, and the length is typically 1–6 mm, preferably 2–5 mm.

[0120] Furthermore, the shape and size of the granular EVOH resin used in each of the manufacturing methods are preferably the same.

[0121] The water content of this EVOH resin composition is typically 0.01 to 0.5% by mass, preferably 0.05 to 0.35% by mass, and particularly preferably 0.1 to 0.3% by mass.

[0122] It should be noted that the moisture content of this EVOH resin composition was determined / calculated using the following method.

[0123] Weigh the mass (W1) of the EVOH resin composition before drying using an electronic balance. Dry it in a hot air dryer at 150°C for 5 hours. Weigh the mass (W2) after cooling in the dryer for 30 minutes. Calculate the mass using the following formula.

[0124] Moisture content (mass%) = [(W1-W2) / W1] × 100

[0125] Furthermore, when the EVOH resin composition is in the form of granules, it is preferable to attach a known lubricant to the surface of the granules from the perspective of stabilizing the feedability during melt molding. Examples of lubricants include: higher fatty acids with 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, etc. of higher fatty acids); higher fatty acid amides (e.g., saturated higher fatty acid amides such as laurylamide, myristicamide, palmitamide, stearamide, behenamide, etc.; unsaturated higher fatty acid amides such as oleamide, erucamide, etc.; bis-higher fatty acid amides such as ethylene bis-stearamide, ethylene bis-oleamide, ethylene bis-erucamide, ethylene bis-lauramide, etc.); low molecular weight polyolefins (e.g., low molecular weight polyethylene or low molecular weight polypropylene with a molecular weight of approximately 500 to 10,000, or their acid-modified forms); higher alcohols with 6 or more carbon atoms; ester oligomers; fluoroethylene resins, etc. These compounds can be used alone or in combination of two or more. Furthermore, the content of this lubricant is typically 5% by mass or less, preferably 1% by mass or less, of the EVOH resin composition. It should be noted that the lower limit is typically 0% by mass.

[0126] The EVOH resin composition obtained in this way can suppress thermal degradation during heating. The 10% weight reduction temperature of the EVOH resin composition is generally 361°C or higher, preferably 365°C or higher, and more preferably 370°C or higher.

[0127] The higher the upper limit of the temperature for a 10% weight reduction, the better; typically it is 450°C.

[0128] The 1°C difference in temperature resulting in a reduction in weight will manifest as a large difference in yield in actual manufacturing, and therefore the difference is very significant.

[0129] Furthermore, the value obtained by subtracting the 5% weight reduction temperature from the 10% weight reduction temperature of this EVOH resin composition is typically 9 or higher, preferably 10 or higher, and more preferably 15 or higher. A higher value indicates better thermal stability. The higher the upper limit of this value, the better; typically, it is 40.

[0130] The "5% weight loss temperature" and "10% weight loss temperature" can be measured using a thermogravimetric analyzer, for example, by the method described in the embodiments below.

[0131] The EVOH resin composition thus obtained can be prepared into various forms such as granules, powders, or liquids, and provided as molding materials for various molded articles. In particular, in the present invention, it is preferred that the effects of the present invention be obtained more efficiently when it is provided as a material for melt molding.

[0132] It should be noted that this EVOH resin composition also includes resin compositions obtained by mixing resins other than the EVOH resin used in this EVOH resin composition.

[0133] Examples of the molded products include, for instance, a single-layer film molded from the present EVOH resin composition, and a multilayer structure having layers formed from the present EVOH resin composition.

[0134] [Multi-layer structure]

[0135] A multilayer structure (hereinafter referred to as "this multilayer structure") according to one embodiment of the present invention includes a layer formed of the present EVOH resin composition. By laminating the layer formed of the present EVOH resin composition (hereinafter simply referred to as "this EVOH resin composition layer") with other substrates whose main component is a thermoplastic resin other than the present EVOH resin composition (hereinafter, the resin used in the substrate is sometimes simply referred to as "substrate resin"), it is possible to further impart strength, protect the present EVOH resin composition layer from the effects of moisture, and impart other functions.

[0136] Examples of the base resins include: linear low-density polyethylene, low-density polyethylene, ultra-low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-propylene (block and random) copolymers, ethylene-α-olefin (α-olefin with 4 to 20 carbon atoms) copolymers, polypropylene, propylene-α-olefin (α-olefin with 4 to 20 carbon atoms) copolymers, polybutene, polypentene, polycyclic olefin resins (polymers having a cyclic olefin structure in at least one of the main chain and side chain), and other (unmodified) polyolefin resins containing these. Polyolefins, including unsaturated carboxylic acid-modified polyolefin resins (those grafted with unsaturated carboxylic acids or their esters), are a broad category of polyolefin resins, encompassing ionomers, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylate copolymers, polyester resins, polyamide resins (including copolyamides), polyvinyl chloride, polyvinylidene chloride, acrylic resins, polystyrene resins, vinyl ester resins, polyester elastomers, polyurethane elastomers, polystyrene elastomers, halogenated polyolefins such as chlorinated polyethylene and chlorinated polypropylene, and aromatic or aliphatic polyketides. These can be used alone or in combination of two or more.

[0137] Among these, polyamide resins, polyolefin resins, polyester resins, and polystyrene resins are preferred as hydrophobic resins, and polyethylene resins, polypropylene resins, polycyclic olefin resins, and polyolefin resins modified with unsaturated carboxylic acids thereof are more preferred as polyolefin resins.

[0138] When the EVOH resin composition layer is designated as a (a1, a2, ...) and the substrate resin layer is designated as b (b1, b2, ...), the layer configuration of this multilayer structure can be any combination such as a / b, b / a / b, a / b / a, a1 / a2 / b, a / b1 / b2, b2 / b1 / a / b1 / b2, b2 / b1 / a / b1 / a / b1 / b2, etc. Furthermore, when the recycled layer, which is a mixture containing the EVOH resin composition and a thermoplastic resin other than the EVOH resin composition, obtained by remelting and molding the ends, defective products, etc., generated during the manufacturing process of this multilayer structure, is designated as R, it can also be designated as b / R / a, b / R / a / b, b / R / a / R / b, b / a / R / a / b, b / R / a / R / a / R / b, etc. The total number of layers in this multilayer structure is typically 2 to 15, preferably 3 to 10. In the above-mentioned layer structure, an adhesive resin layer containing adhesive resin can be sandwiched between each layer as needed.

[0139] As the adhesive resin, any known adhesive resin can be used, and the appropriate type of thermoplastic resin can be selected based on the type of resin used in the substrate resin layer "b". Representative examples include modified polyolefin polymers containing carboxyl groups, obtained by chemically bonding unsaturated carboxylic acids or their anhydrides to polyolefin resins through addition reactions, grafting reactions, etc. Examples of such modified polyolefin polymers containing carboxyl groups include: maleic anhydride-grafted modified polyethylene, maleic anhydride-grafted modified polypropylene, maleic anhydride-grafted modified ethylene-propylene (block and random) copolymers, maleic anhydride-grafted modified ethylene-ethyl acrylate copolymers, maleic anhydride-grafted modified ethylene-vinyl acetate copolymers, maleic anhydride-modified polycyclic olefin resins, and maleic anhydride-grafted modified polyolefin resins. These can be used alone or in combination of two or more.

[0140] In this multilayer structure, when an adhesive resin layer is used between the EVOH resin composition layer and the substrate resin layer, the adhesive resin layer is located on both sides of the EVOH resin composition layer, so it is preferable to use an adhesive resin with excellent hydrophobicity.

[0141] The base resin and adhesive resin may contain conventionally known plasticizers, fillers, clays (montmorillonite, etc.), colorants, antioxidants, antistatic agents, lubricants, nucleating agents, anti-blocking agents, waxes, etc., within a range that does not hinder the spirit of the present invention (e.g., typically 30% by mass or less, preferably 10% by mass or less relative to the total resin). These may be used alone or in combination of two or more.

[0142] The lamination of the EVOH resin composition layer and the substrate resin layer (including the case where an adhesive resin layer is sandwiched) can be performed by known methods. For example, this multilayer structure can be manufactured by performing a process of melt-forming the EVOH resin composition layer. Specifically, examples include: a method of melt-extruding and laminating a substrate resin onto a film or sheet of the EVOH resin composition; a method of melt-extruding and laminating the EVOH resin composition onto a substrate resin layer; a method of co-extruding the EVOH resin composition and a substrate resin; a method of dry laminating the EVOH resin composition (layer) and a substrate resin (layer) using known adhesives such as organotitanium compounds, isocyanate compounds, polyester compounds, and polyurethane compounds; and a method of applying a solution of the EVOH resin composition onto the substrate resin and then removing the solvent. Among these methods, from the viewpoints of cost and environment, the co-extrusion method is preferred.

[0143] This multi-layer structure can also undergo (heated) stretching treatment as needed. The stretching treatment can be any type of uniaxial stretching or biaxial stretching; in the case of biaxial stretching, it can be simultaneous or sequential stretching. Furthermore, as stretching methods, methods with high stretch ratios such as roller stretching, tenter frame stretching, tubular stretching, stretch blow molding, and vacuum forming can be used. The stretching temperature is near the melting point of the multi-layer structure, typically selected from the range of 40℃ to 170℃, preferably around 60℃ to 160℃. If the stretching temperature is too low, there is a tendency for poor stretchability; if the stretching temperature is too high, there is a tendency for it to be difficult to maintain a stable stretching state.

[0144] Furthermore, for the purpose of imparting dimensional stability, the stretched multilayer structure can also be heat-fixed. Heat fixing can be carried out by well-known methods, such as heat-treating the stretched multilayer structure at a temperature of typically 80–180°C, preferably 100–165°C, for approximately 2–600 seconds while keeping it under tension.

[0145] When the multilayer structure that has undergone the stretching treatment is used as a shrink film (heat shrinkable film), in order to impart heat shrinkability, the above-mentioned heat fixation is not performed. For example, it is sufficient to perform cooling fixation by blowing cold air on the multilayer structure after stretching treatment.

[0146] The thickness of this multilayer structure (including the stretched multilayer structure), as well as the thicknesses of the EVOH resin composition layer, the substrate resin layer, and the adhesive resin layer constituting the multilayer structure, varies depending on the layer composition, the type of substrate resin, the type of adhesive resin, the application, the packaging method, and the required physical properties. The thickness of this multilayer structure (including the stretched multilayer structure) is typically 10–5000 μm, preferably 30–3000 μm, and particularly preferably 50–2000 μm. The thickness of the EVOH resin composition layer is typically 1–500 μm, preferably 3–300 μm, and particularly preferably 5–200 μm. The thickness of the substrate resin layer is typically 5–3000 μm, preferably 10–2000 μm, and particularly preferably 20–1000 μm. The thickness of the adhesive resin layer is typically 0.5–250 μm, preferably 1–150 μm, and particularly preferably 3–100 μm.

[0147] Furthermore, in the case of multiple layers, the thickness ratio of the EVOH resin composition layer to the substrate resin layer (EVOH resin composition layer / substrate resin layer), calculated as the ratio of the thickest layers, is typically 1 / 99 to 50 / 50, preferably 5 / 95 to 45 / 55, and particularly preferably 10 / 90 to 40 / 60. Additionally, in the case of multiple layers, the thickness ratio of the EVOH resin composition layer to the adhesive resin layer (EVOH resin composition layer / adhesive resin layer), calculated as the ratio of the thickest layers, is typically 10 / 90 to 99 / 1, preferably 20 / 80 to 95 / 5, and particularly preferably 50 / 50 to 90 / 10.

[0148] Furthermore, this multi-layer structure can also be used to obtain multi-layer containers in the shape of cups or trays. In this case, deep drawing forming methods are typically used, specifically including: vacuum forming, air-forming, vacuum air-forming, and plunger-assisted vacuum air-forming. Moreover, when obtaining multi-layer containers (laminated structures) in the shape of tubes or bottles from multi-layer preforms (hollow tubular preforms before blow molding), blow molding methods are used. Specifically, examples include: extrusion blow molding (double-head type, mold moving type, preform moving type, rotary type, reservoir type, horizontal preform type, etc.), cold preform blow molding, injection blow molding, and biaxial stretch blow molding (extrusion-type cold preform biaxial stretch blow molding, injection-type cold preform biaxial stretch blow molding, injection-type tandem biaxial stretch blow molding, etc.). The resulting laminate can be subjected to heat treatment, cooling treatment, calendering treatment, printing treatment, dry lamination treatment, solution or melt coating treatment, bag making, deep drawing treatment, box processing, tube processing, separation processing, etc., as needed.

[0149] The single-layer film formed from this EVOH resin composition, the bags formed from this multi-layer structure, and the containers and lids made of cups, trays, tubes, bottles, etc. are useful as various packaging materials and containers for condiments such as mayonnaise and sauces, fermented foods such as bean paste, oily foods such as salad oil, beverages, cosmetics, pharmaceuticals, etc., in addition to general food products.

[0150] Furthermore, when the multilayer structure is in the form of a film, the thermal stability of this EVOH resin composition is excellent. Therefore, this multilayer structure is also useful as a material for thermoforming containers, packaging films, multilayer shrink films, deep drawing films, and agricultural films.

[0151] Examples of agricultural films include silage films and soil covering films.

[0152] Example

[0153] The present invention will now be specifically described through embodiments. However, the present invention is not limited to any of the embodiments described below.

[0154] It should be noted that, unless otherwise specified, "share" in the example refers to the quality standard.

[0155] <Example 1>

[0156] As the EVOH resin, granules of EVOH resin with a content of 38 mol% of ethylene structural units and a degree of saponification of 98.5 mol% are used.

[0157] In addition, titanium dioxide (manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd.) is used as a titanium compound.

[0158] The titanium dioxide was dry-blended with the EVOH resin particles at a mass of 0.1 ppm relative to the mass of the EVOH resin composition in metal equivalent terms to obtain a mixture.

[0159] The mixture is fed into a twin-screw extruder equipped with a dual-die. The extruded and discharged filament under the following extrusion conditions is cooled and solidified in a water bath. Then, the water droplets on the surface of the solidified filament are removed by blowing air through it, and then it is cut to obtain granules of the EVOH resin composition.

[0160] [Extrusion Conditions]

[0161] Extruder set temperature (°C): C1 / C2 / C3 / C4

[0162] =160 / 200 / 200 / 200.

[0163] <Example 2>

[0164] The amount of titanium oxide was changed to 1 ppm relative to the mass of the EVOH resin composition in metal equivalents. Otherwise, EVOH resin composition particles were obtained in the same manner as in Example 1.

[0165] <Example 3>

[0166] Particles of EVOH resin with an ethylene structural unit content of 38 mol% and a saponification degree of 95.2 mol% were used, otherwise, particles of the EVOH resin composition were obtained in the same manner as in Example 1.

[0167] <Example 4>

[0168] Particles of EVOH resin with an ethylene structural unit content of 44 mol% and a saponification degree of 97.6 mol% were used, otherwise, particles of the EVOH resin composition were obtained in the same manner as in Example 1.

[0169] <Example 5>

[0170] Particles of EVOH resin with an ethylene structural unit content of 51 mol% and a saponification degree of 93.7 mol% were used, otherwise, particles of the EVOH resin composition were obtained in the same manner as in Example 1.

[0171] <Comparative Example 1>

[0172] Without using titanium dioxide, particles of the EVOH resin composition were obtained in the same manner as in Example 1.

[0173] <Comparative Example 2>

[0174] The amount of titanium oxide was changed to 5 ppm relative to the mass of the EVOH resin composition in metal equivalents. Otherwise, EVOH resin composition particles were obtained in the same manner as in Example 1.

[0175] <Comparative Example 3>

[0176] Particles of EVOH resin with an ethylene structural unit content of 38 mol% and a saponification degree of 99.97 mol% were used, otherwise, particles of the EVOH resin composition were obtained in the same manner as in Example 1.

[0177] <Comparative Example 4>

[0178] Particles of EVOH resin with an ethylene structural unit content of 38 mol% and a saponification degree of 91 mol% were obtained, otherwise, particles of the EVOH resin composition were obtained in the same manner as in Example 1.

[0179] <Comparative Example 5>

[0180] Particles of EVOH resin with an ethylene structural unit content of 44 mol% and a saponification degree of 91 mol% were obtained, otherwise, particles of the EVOH resin composition were obtained in the same manner as in Example 1.

[0181] The thermal stability of the EVOH resin compositions obtained in Examples 1 to 5 and Comparative Examples 1 to 5 was evaluated as follows. The results are shown in Table 1 below.

[0182] [Evaluation of thermal stability]

[0183] Using 10 mg of the obtained EVOH resin composition particles, a thermogravimetric analyzer (Shimadzu Corporation, TA-60) was used under nitrogen atmosphere, gas flow rate: 20 mL / min, heating rate: 10 °C / min, temperature range: 50–550 °C. The temperatures at which the weight decreased to 95% of the original weight (5% reduction temperature) and at which the weight decreased to 90% of the original weight (10% reduction temperature) were measured. The value obtained by subtracting the 5% reduction temperature from the 10% reduction temperature of the resin composition was calculated. A higher value indicates slower resin composition decomposition, and a higher 10% reduction temperature indicates better thermal stability.

[0184] [Table 1]

[0185]

[0186] As shown in Table 1 above, the EVOH resin compositions of Examples 1 and 2, which contain EVOH resin with low saponification degree and trace amounts of titanium compounds, have higher 10% reduction temperatures compared to the EVOH resin composition of Comparative Example 1, which does not contain titanium compounds. Furthermore, in the EVOH resin composition of Comparative Example 2, which contains titanium compounds exceeding a certain range, the value obtained by subtracting the 5% reduction temperature from the 10% reduction temperature is smaller. This indicates rapid decomposition, suggesting insufficient extrusion stability during extrusion molding.

[0187] Furthermore, it is known that Examples 3 to 5, which fall within the saponification range specified in this invention, exhibit high 10% reduction temperatures and excellent thermal stability. In contrast, Comparative Examples 3 to 5, which fall outside the saponification range specified in this invention, show low 10% reduction temperatures and are prone to heat degradation.

[0188] Furthermore, the multilayer structure having layers formed from the EVOH resin composition of the embodiments also exhibits excellent thermal stability. Because the multilayer structure having layers formed from this EVOH resin composition has excellent thermal stability, it is useful as a material for thermoforming containers, packaging films, multilayer shrink films, deep-drawing films, and agricultural films.

[0189] The above embodiments illustrate specific aspects of the present invention, but these embodiments are merely examples and not intended to be limiting. It is intended that various modifications, which will be apparent to those skilled in the art, are within the scope of the present invention.

[0190] Industrial availability

[0191] This EVOH resin composition exhibits an increased thermal decomposition temperature and excellent thermal stability during melt molding. Therefore, in addition to various foods, it is useful as a packaging material for various products such as mayonnaise, sauces, fermented foods like soybean paste, oils like salad oil, beverages, cosmetics, and pharmaceuticals.

Claims

1. An ethylene-vinyl alcohol copolymer composition, said ethylene-vinyl alcohol copolymer composition comprising an ethylene-vinyl alcohol copolymer and a titanium compound, The degree of saponification of the ethylene-vinyl alcohol copolymer exceeds 91 mol% and is below 99.5 mol%. The metal conversion content of the titanium compound is greater than 0.001 ppm and less than 5 ppm relative to the mass of the ethylene-vinyl alcohol copolymer composition.

2. The ethylene-vinyl alcohol copolymer composition according to claim 1, wherein, The metal conversion content of the titanium compound relative to the mass of the ethylene-vinyl alcohol copolymer composition is more than 0.001 ppm and less than 0.9 ppm.

3. A particle formed from the ethylene-vinyl alcohol copolymer composition of claim 1 or 2.

4. A multilayer structure comprising at least one layer formed of the ethylene-vinyl alcohol copolymer composition of claim 1 or 2 or the particles of claim 3.

5. A thermoformed container, said thermoformed container being formed from the multilayer structure of claim 4.

6. A packaging film, said packaging film being formed from the multilayer structure of claim 4.

7. A multilayer shrink film, said multilayer shrink film being formed from the multilayer structure of claim 4.

8. A film for deep drawing, said film being formed from the multilayer structure of claim 4.

9. An agricultural film, said agricultural film being formed from the multilayer structure of claim 4.

10. A method for manufacturing an ethylene-vinyl alcohol copolymer composition, wherein the method for manufacturing the ethylene-vinyl alcohol copolymer composition according to claim 1 or 2 comprises the following steps: The raw materials containing ethylene-vinyl alcohol copolymers and titanium compounds are melt-mixed.

11. A method for manufacturing a multi-layer structure, the method comprising the steps of manufacturing the multi-layer structure of claim 4: A layer formed from the ethylene-vinyl alcohol copolymer composition is obtained by melt molding.

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