Polyvinyl alcohol resin composition, film or sheet, and multilayer structure

Abstract

The present invention relates to a resin composition comprising a polyvinyl alcohol-based resin, a formate, and an acetate, the content of the formate in the resin composition being 4-500 ppm, and the content ratio of the formate to the acetate (formate / acetate) being 0.001-0.200.

Description

Technical Field

[0001] The present invention relates to a resin composition comprising a polyvinyl alcohol-based resin and exhibiting excellent thermal and molding stability during melt molding, a film or sheet formed from the resin composition, and a multilayer structure comprising a layer formed from the resin composition. Background Technology

[0002] Gas barrier properties are required for containers and packaging films used in a wide range of fields, including agriculture, civil engineering, industry, medical, packaging, leisure, toys, groceries, daily necessities, containers, and parts, from the perspective of preventing the deterioration of the quality of the contents.

[0003] Polyvinyl alcohol (PVA) has high crystallinity due to the hydrogen bonds between its hydroxyl groups. Based on this high crystallinity, it has excellent gas barrier properties. Therefore, PVA-based resins or resin compositions thereof are used as gas barrier layers for the aforementioned containers and packaging films.

[0004] Generally speaking, from a production point of view, molded products such as containers and membranes are manufactured by melt molding.

[0005] On the other hand, it is known that the melting point and decomposition temperature of polyvinyl alcohol (PVA) are close, making it difficult to manufacture molded articles by thermoforming. However, a modified PVA-based resin that can be melt-formed has been proposed. (For example, PVA-based resins with 1,2-diol side chains described in Patent Documents 1, 2, and 3).

[0006] Furthermore, since molded PVA-based resins are known to be rigid, plasticizers must be added to PVA-based resin compositions used for melt molding of packaging films, containers, etc. (for example, Patent Document 4).

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2002-284818

[0010] Patent Document 2: Japanese Patent Application Publication No. 2004-285143

[0011] Patent Document 3: Japanese Patent Application Publication No. 2006-95825

[0012] Patent Document 4: Japanese Patent Application Publication No. 2001-288321 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] However, the excellent gas barrier properties of PVA-based resins are based on the high crystallinity of the PVA molecular chain. Therefore, modified PVA-based resins containing plasticizers or copolymerized with other monomers suffer from crystallinity disorder, leading to a decrease in gas barrier properties. Furthermore, when PVA-based resins are continuously melt-molded for extended periods, the viscosity changes significantly, resulting in increased viscosity and poor molding stability. This also generates heat-induced degradation products, leading to poor thermal stability. Therefore, improvements are needed to address these technical problems.

[0015] The present invention was made in view of the following circumstances, and its object is to provide a resin composition comprising a PVA-based resin and having excellent thermal stability and molding stability during melt molding.

[0016] Solution for solving the problem

[0017] The inventors discovered that by preparing a resin composition in which PVA-based resin contains appropriate amounts of formate and acetate, the thermal stability and molding stability during melt molding are improved compared to the case of PVA-based resin alone, thus completing the present invention.

[0018] That is, the main idea of ​​this invention is as follows.

[0019] Scheme 1 of the present invention is a resin composition comprising a polyvinyl alcohol resin, formate, and acetate, characterized in that the formate content in the resin composition is 4 to 500 ppm, and the formate to acetate content ratio (formate / acetate) is 0.001 to 0.200.

[0020] The resin composition of embodiment 2 of the present invention, in embodiment 1, is characterized in that the content of acetate in the resin composition is less than 10,000 ppm.

[0021] The resin composition of embodiment 3 of the present invention, in embodiment 1 or 2, is characterized in that the polyvinyl alcohol resin comprises structural units having modified groups other than ethylene.

[0022] The resin composition of embodiment 4 of the present invention, in any one of embodiments 1 to 3, is characterized in that the polyvinyl alcohol resin comprises a structural unit having a hydrophilic modified group.

[0023] The resin composition of embodiment 5 of the present invention, in any one of embodiments 1 to 4, is characterized in that the polyvinyl alcohol resin contains structural units having primary hydroxyl groups in the side chains.

[0024] The resin composition of Scheme 6 of the present invention, in any one of Schemes 1 to 5, is characterized in that the formate content is 5 to 100 ppm.

[0025] Aspect 7 of the present invention is a molded body, and the molded body contains the resin composition according to any one of Aspects 1 to 6.

[0026] Aspect 8 of the present invention is a film, and the film contains the resin composition according to any one of Aspects 1 to 6.

[0027] Aspect 9 of the present invention is a sheet, and the sheet contains the resin composition according to any one of Aspects 1 to 6.

[0028] Aspect 10 of the present invention is a multilayer structure, and the multilayer structure contains at least one layer formed from the resin composition according to any one of Aspects 1 to 6.

[0029] Advantages of the Invention

[0030] The resin composition of the present invention contains a PVA-based resin and has excellent thermal stability and molding stability during melt molding. Detailed Embodiments

[0031] [Resin Composition]

[0032] The resin composition of the present invention is a resin composition containing a polyvinyl alcohol-based resin (PVA-based resin), formate, and acetate. Among them, the content of formate in the resin composition is 4 to 500 ppm, and the content ratio of formate to acetate (formate / acetate) is 0.001 to 0.200.

[0033] [PVA-Based Resin]

[0034] The PVA-based resin used in the resin composition of the present invention is a PVA-based resin formed by solution casting method for molding represented by film formation. In addition to unmodified PVA, it also includes copolymer-modified PVA-based resins obtained by saponifying copolymers after copolymerizing modification monomers to impart desired properties (such as water resistance), and post-modified PVA-based resins obtained by post-modifying PVA-based resins.

[0035] In this specification, unless otherwise specified, "PVA-based resin" is a general term for unmodified PVA, copolymer-modified PVA, and post-modified PVA. When copolymer-modified PVA and post-modified PVA are collectively referred to, they are called "modified PVA-based resins".

[0036] 1. Unmodified PVA-Based Resin

[0037] The unmodified PVA-based resin is polyvinyl alcohol obtained by saponifying polyvinyl acetate obtained by polymerizing vinyl ester monomers, and contains vinyl alcohol units represented by the following formula (1) and vinyl ester units as unsaponified parts (the following formula (2)). Vinyl ester units are included when the saponification degree is less than 100%.

[0038] [Chemical Formula 1]

[0039]

[0040] [Chemical Formula 2]

[0041]

[0042] Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl valerate, vinyl decanoate, vinyl laurate, vinyl stearate, vinyl benzoate, and vinyl tert-carbonate, but vinyl acetate is preferred for economic reasons.

[0043] In equation (2), R a Depending on the type of vinyl ester monomer used, in the case of vinyl acetate monomer, it is methyl.

[0044] The number-average degree of polymerization (measured according to JIS K6726:1994) of unmodified PVA-based resins is typically 150–4000, preferably 200–2000, more preferably 250–800, and even more preferably 300–600. When this average degree of polymerization is too low, there is a tendency for it to be difficult to form a stable shape during melt molding; when this average degree of polymerization is too high, there is a tendency for the viscosity of the resin composition to become too high, making it difficult to mold.

[0045] The viscosity of the aqueous solution can be used as an indicator of the average degree of polymerization of the unmodified PVA resin. The viscosity of a 4% by weight aqueous solution at 20°C, as measured according to JIS K6726:1994, is typically 1.5–20 mPa·s, preferably 2–12 mPa·s, and particularly preferably 2.5–8 mPa·s. When this viscosity is too low, there is a tendency to make it difficult to form a stable shape during melt molding; when this viscosity is too high, there is a tendency to make molding difficult.

[0046] The degree of saponification of unmodified PVA-based resins is typically 70–99.9 mol%, preferably 75–99.7 mol%, and particularly preferably 78–99.5 mol%. When the degree of saponification is too low, the softness becomes too high, and there is a tendency for the shape stability during stacking to decrease.

[0047] It should be noted that the degree of saponification was determined according to JIS K6726:1994.

[0048] The melting point of unmodified PVA resin also depends on the degree of polymerization and the degree of saponification, and is preferably around 200-250℃, while the decomposition temperature is preferably around 250-300℃.

[0049] It should be noted that in the case of typical PVA resins, the main chain bonding is mainly 1,3-diol bonds, and the content of 1,2-diol bonds is about 1.5 to 1.7 mol%. However, by using a high polymerization temperature when polymerizing ethylene ester monomers, the content of 1,2-diol bonds can be increased.

[0050] 2. Modified PVA-based resins

[0051] Copolymer-modified PVA resins are obtained by saponifying copolymers obtained by copolymerizing modified monomers.

[0052] Examples of comonomers (modifying monomers) used in the above-mentioned copolymer-modified PVA resins include: olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, and itaconic acid, or their salts or monoalkyl or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methyl allyl sulfonic acid, or their salts; alkyl vinyl ethers, N-acrylamide methyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethyl allyl vinyl ketone, N-vinylpyrrolidone, vinyl chloride, vinylidene chloride, and polyoxyethylene (methylene) Polyoxyalkylene (meth)allyl ethers, polyoxypropylene (meth)allyl ethers, and other polyoxyalkylene (meth)allyl ethers; polyoxyethylene (meth)acrylates, polyoxypropylene (meth)acrylates, and other polyoxyalkylene (meth)acrylates; polyoxyethylene (meth)acrylamides, polyoxypropylene (meth)acrylamides, and other polyoxyalkylene (meth)acrylamides; polyoxyethylene (1-(meth)acrylamide-1,1-dimethylpropyl) esters, polyoxyethylene vinyl ethers, polyoxypropylene vinyl ethers, polyoxyethylene allylamines, polyoxypropylene allylamines, polyoxyethylene vinylamines, polyoxypropylene vinylamines, 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, and other hydroxyl-containing α-olefins and their acylated derivatives, etc.

[0053] Post-modified PVA resins are obtained by post-modifying PVA resins.

[0054] Examples of post-modified PVA resins include: resins having acetyl groups obtained by reacting with diketene; resins having polyepoxyalkyl groups obtained by reacting with ethylene oxide; resins having hydroxyalkyl groups obtained by reacting with epoxy compounds, etc.; and resins obtained by reacting aldehyde compounds having various functional groups with PVA resins.

[0055] The amount of modification in modified PVA resins, that is, the content of structural units derived from various monomers or functional groups introduced through post-reaction in the copolymer, varies greatly depending on the type of modification and cannot be generalized. It is usually in the range of 0.1 to 20 mol%, and is particularly preferred in the range of 0.5 to 15 mol%.

[0056] Among these various modified PVA resins, in this embodiment, from the viewpoint of barrier properties at low humidity, it is preferable to use a PVA resin containing structural units with modified groups other than ethylene.

[0057] Furthermore, among these various modified PVA resins, in this embodiment, from the viewpoint of water solubility, PVA resins containing structural units with hydrophilic modifying groups (hydrophilic modifying groups) are preferred. Examples of hydrophilic modifying groups include hydroxyl groups, carboxyl groups, and amino groups. Furthermore, from the viewpoint of melt processing, PVA resins containing structural units with primary hydroxyl groups in the side chains are preferred. Particularly from the viewpoint of thermal stability, PVA resins containing structural units with 1,2-diol modifying groups are preferred.

[0058] For modified PVA resins containing structural units having 1,2-diol modified groups, in addition to the ethylene alcohol units constituting polyvinyl alcohol as shown in formula (1) below and the ethylene ester units as the unsaponified portion (formula (2) below), structural units having 1,2-diol modified groups on the side chains are also included. The ethylene ester units are included when the degree of saponification is less than 100%.

[0059] [Chemical Formula 3]

[0060]

[0061] [Chemical Formula 4]

[0062]

[0063] In equation (2), R a It depends on the type of vinyl ester monomer used; for example, if vinyl acetate monomer is used, it is methyl.

[0064] As a structural unit having a 1,2-diol modified group in the side chain, it is preferred to have a unit with a 1,2-diol-containing side chain as shown in the following formula (3).

[0065] [Chemical Formula 5]

[0066]

[0067] In equation (3), R 1 ~R 6Each can be independently represented by a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X represents a single bond or a bonded chain.

[0068] In general formula (3), R 1 ~R 6 Each of the following is independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms (methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, etc., optionally having a halogen group, hydroxyl group, ester group, carboxylic acid group, sulfonic acid group, etc.). Hydrogen atoms are more preferred. R 1 ~R 6 The atoms can be all the same or different, but it is preferred that they are all hydrogen atoms. When they are all hydrogen atoms, the ends of the side chains become primary hydroxyl groups, which increases their reactivity with adhesive resins such as acid-modified polyolefin resins and makes it easier to form laminates. This is preferred from the perspective of hydrogen atoms.

[0069] In formula (3), X is a single bond or a bonded chain. For example, the bonded chain (X) can be: alkylene, alkenylene, ynylene, phenylene, naphthylene, etc. (these alkylene groups can be replaced by halogen atoms such as fluorine, chlorine, and bromine atoms), -O-, -(CH2O). m -、-(OCH2) m -、-(CH2O) m CH2-, -CO-, -COCO-, -CO(CH2) m CO-, -CO(C6H4)CO-, -S-, -CS-, -SO-, -SO2-, -NR-, -CONR-, -NRCO-, -CSNR-, -NRCS-, -NRNR-, -HPO4-, -Si(OR)2-, -OSi(OR)2-, -OSi(OR)2O-, -Ti(OR)2-, -OTi(OR)2-, -OTi(OR)2O-, -Al(OR)-, -OAl(OR)-, -OAl(OR)O-, etc. (R is an arbitrary substituent, preferably a hydrogen atom or an alkyl group, and m is an integer from 1 to 5).

[0070] Regarding stability during manufacturing or use, X is preferably a single bond, an alkylene group (especially a methylene group) with 6 or fewer carbon atoms, or -CH2OCH2-, with a single bond being the most preferred in terms of thermal stability, stability at high temperatures, or stability under acidic conditions.

[0071] As the structural unit shown in equation (3) above, R is particularly preferred. 5 and R 6 The structural unit is a hydrogen atom with a primary hydroxyl group in the side chain. The most preferred structural unit is the structural unit shown in formula (3a) below, wherein R 1 ~R 6All are hydrogen atoms, and X is a single bond.

[0072] [Chemical Formula 6]

[0073]

[0074] The degree of modification (content) of the modified PVA-based resin is preferably 0.1 to 20 mol%, more preferably 0.5 to 15 mol%, even more preferably 1 to 10 mol%, and particularly preferably 2 to 8 mol%. When the modification rate is too low, there is a tendency for the reactivity with adhesive resins such as acid-modified polyolefin resins to decrease. When the modification rate is too high, there is a tendency for the crystallization rate to become too slow, and in the case of forming a laminate with other resins, the appearance deteriorates, such as the laminate deforming.

[0075] The number-average degree of polymerization (measured according to JIS K6726:1994) of the modified PVA-based resin is preferably 150 to 4000, more preferably 200 to 2000, further preferably 250 to 800, and particularly preferably 300 to 600. When this average degree of polymerization is too low, there is a tendency for it to be difficult to form a stable shape during melt molding; when this average degree of polymerization is too high, there is a tendency for the viscosity of the resin composition to become too high, making it difficult to mold.

[0076] The viscosity of a 4% by mass aqueous solution of the modified PVA resin at 20°C, as determined according to JIS K6726:1994, is preferably 1.5–20 mPa·s, more preferably 2–12 mPa·s, and particularly preferably 2.5–8 mPa·s. When the viscosity is too low, there is a tendency for it to be difficult to form a stable shape during melt molding; when the viscosity is too high, there is a tendency for molding to become difficult.

[0077] The degree of saponification of the modified PVA resin (average degree of saponification as determined according to JIS K6726:1994) is preferably 70 to 100 mol%, more preferably 80 to 99.9 mol%, and particularly preferably 85 to 99.7 mol%. When the degree of saponification is too low, there is a tendency for the gas barrier properties to decrease.

[0078] The melting point of modified PVA resins also depends on the degree of polymerization and the degree of saponification, but the preferred melting point is 160-230℃, and the preferred decomposition temperature is 250-350℃.

[0079] The PVA-based resin that can be used in the resin composition of the present invention can be one type or a mixture of two or more types. When using two or more mixtures, examples include the unmodified PVA-based resins described above, combinations of unmodified PVA-based resins with various modified PVA-based resins, and combinations of different types of modified PVA-based resins. Furthermore, combinations of modified PVA-based resins of the same type but with different degrees of saponification, degree of polymerization, and modification rate can also be included.

[0080] Furthermore, the content of PVA-based resin in the resin composition is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0081] Formic acid, formate ions

[0082] Formic acid is a carboxylic acid that has a formyl group in addition to a carboxyl group.

[0083] Regarding PVA-based resins, the thermal stability and molding stability can be improved by adjusting the ratio of acid to alkali. Generally, acetic acid and / or acetates are used as the acid. However, the inventors have discovered that by using formic acid and / or formate salts in addition to these, the thermal stability and molding stability of PVA-based resins during melt molding can be improved.

[0084] The reason is not yet clear, but it is speculated that formic acid and formate have reducing properties, thus inhibiting the oxidative decomposition of PVA resins compared to the case where only acetic acid and acetate are used.

[0085] Here, acetic acid and acetate ions are collectively referred to as "acetic acid ion", and formic acid and formic acid ions are collectively referred to as "formate ion".

[0086] Formic acid can usually be produced by the following methods: (i) reacting methanol and carbon monoxide under strong alkaline conditions to produce methyl formate, followed by hydrolysis; (ii) reacting methyl formate with ammonia to produce formaldehyde, followed by hydrolysis with sulfuric acid; (iii) reacting sodium hydroxide with carbon monoxide to produce sodium formate, followed by neutralization with hydrochloric acid, etc.

[0087] It should be noted that formic acid can be commercially available products, such as formic acid manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd.

[0088] Formate ions can be added using formate salts. Examples of formate salts include sodium formate, potassium formate, lithium formate, magnesium formate, calcium formate, barium formate, zinc formate, copper formate, iron formate, nickel formate, manganese formate, lead formate, tin formate, chromium formate, and ammonium formate, with sodium formate being the preferred choice.

[0089] It should be noted that commercially available sodium formate can be used. For example, sodium formate manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd. can be listed as commercially available products.

[0090] Furthermore, the formate content (per unit mass of the resin composition) in the resin composition of the present invention is 4 to 500 ppm, preferably 4 to 450 ppm, and more preferably 5 to 100 ppm. Here, the formate content is preferably 4.3 ppm or more, more preferably 4.5 ppm or more, further preferably 4.8 ppm or more, even more preferably 5 ppm or more, particularly preferably 10 ppm or more, and especially preferably 15 ppm or more. Furthermore, the formate content is preferably 450 ppm or less, more preferably 400 ppm or less, further preferably 300 ppm or less, even more preferably 200 ppm or less, particularly preferably 150 ppm or less, and especially preferably 100 ppm or less. It should be noted that the numerical range of the formate content can be set by any combination of the aforementioned lower and upper limits and the values ​​described in the Example section. The same applies to numerical ranges other than the formate content.

[0091] To achieve the improved thermal and molding stability benefits from formate, the aforementioned content (4–500 ppm) is required. With a formate content of 4 ppm or higher, thermal stability becomes good. Furthermore, with a formate content of 500 ppm or lower, molding stability during melt molding becomes good.

[0092] It should be noted that the formate content in the resin composition can be determined by the determination method described in Example 1.

[0093] It should be noted that the resin composition of the present invention may contain only formic acid, only formic acid ions, or both formic acid and formic acid ions as the formate group.

[0094] <Acetic acid, acetate ion>

[0095] The resin composition of the present invention also contains acetate (acetic acid, acetate ion).

[0096] Acetic acid is a carboxylic acid with a straight-chain saturated hydrocarbon chain. Acetic acid can be synthesized by carbonylation of methanol. Commercially available products include acetic acid manufactured by companies such as Fujifilm and Kojun Pharmaceutical Co., Ltd.

[0097] Acetate salts can be used to add acetate ions. There is no single limitation on the type of acetate used, but sodium acetate is preferred. Commercially available sodium acetate products include those manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd.

[0098] Furthermore, from the viewpoint of molding stability during melt molding, the acetate content (per unit mass of the resin composition as a whole) in the resin composition of the present invention is preferably 1000 ppm or more, more preferably 1500 ppm or more, even more preferably 1800 ppm or more, and particularly preferably 2000 ppm or more. Furthermore, from the viewpoint of thermal stability, the acetate content is preferably 10000 ppm or less, more preferably 9500 ppm or less, even more preferably 9000 ppm or less, and particularly preferably 8500 ppm or less. The acetate content is, for example, 10000 ppm or less, preferably 1000 to 10000 ppm.

[0099] It should be noted that acetate is not limited to being present as an impurity generated during the manufacturing process of PVA-based resins; it can also be present by additional addition.

[0100] In addition, the acetate content in the resin composition can be determined by the determination method described in Example 1.

[0101] Furthermore, from the viewpoint of thermal stability and molding stability, the formate to acetate content ratio (formate / acetate) is 0.001 or more, preferably 0.0015 or more, more preferably 0.0018 or more, and particularly preferably 0.002 or more. Furthermore, from the viewpoint of thermal stability, the formate / acetate content ratio (formate / acetate) is 0.200 or less, more preferably 0.100 or less, and particularly preferably 0.050 or less. That is, the formate to acetate content ratio (formate / acetate) is 0.001 to 0.200. It should be noted that the formate to acetate content ratio (formate / acetate) is based on mass.

[0102] It should be noted that the resin composition of the present invention may contain only acetic acid, only acetate ions, or both acetic acid and acetate ions as the acetate group.

[0103] <Other Ingredients>

[0104] 1. Other plasticizers

[0105] The resin composition of the present invention may contain other plasticizers as long as it does not impair the effects of the present invention (water solubility, gas barrier properties).

[0106] 2. Other resins

[0107] The resin composition of the present invention may contain other polymers (resins) within a range that does not hinder the effects of the present invention (e.g., less than 30% by mass of the resin composition). Examples of polymers (resins) that may be contained include various thermoplastic resins such as polyamide, polyester, polyethylene, polypropylene, and polystyrene.

[0108] 3. Other additives

[0109] Furthermore, in the resin composition of the present invention, within a range that does not hinder the effects of the present invention (e.g., less than 10% by mass of the resin composition), reinforcing agents, fillers, pigments, dyes, lubricants, antioxidants, antistatic agents, ultraviolet absorbers, heat stabilizers, light stabilizers, surfactants, antibacterial agents, antistatic agents, desiccants, antiblocking agents, flame retardants, crosslinking agents, curing agents, foaming agents, crystallizing nucleating agents, etc., may be included as needed.

[0110] The resin composition of the present invention having the composition as described above exhibits good thermal stability and molding stability through the coexistence of formate and acetate groups without impairing the properties of PVA-based resins.

[0111] <Method for manufacturing resin composition>

[0112] Regarding resin compositions having the composition described above, examples include: (i) a method of melt-blending formic acid and / or formate, acetic acid and / or acetate, and other components in a PVA-based resin; and (ii) a method of mixing an aqueous solution of a PVA-based resin, formic acid and / or formate, acetic acid and / or acetate, and other components. Method (i) is preferred, as it yields a resin composition in particulate form.

[0113] It should be noted that acetate ions may be present as impurities generated during the manufacturing process of PVA-based resins. In this case, acetic acid and / or acetate salts may not need to be added in the methods described in (i) or (ii) above.

[0114] When adding acetic acid and / or acetate, the order of addition of formic acid and / or formate to acetic acid and / or acetate can be either one first, or they can be added to the PVA resin as a mixture prepared in advance. Alternatively, formic acid and / or formate can be added to a mixture prepared in advance by mixing PVA resin with acetic acid and / or acetate.

[0115] [Melted Molded Articles of Resin Compositions and Their Manufacturing Methods]

[0116] The resin composition of the present invention can be melt-molded using the melt extrusion molding method commonly used in thermoplastic resins.

[0117] Therefore, the resin composition of the present invention can be suitably used in the manufacture of various molded articles. For example, it can be used for melt-molded articles requiring gas barrier properties, particularly melt-molded films, stretch films, bags formed from sheets, and containers and caps formed from cups, trays, tubes, bottles, etc.

[0118] The film, sheet, or container can be formed solely (single-layer) from the resin composition of the present invention, or it can be used as a multilayer structure formed by laminating two or more layers of other thermoplastic resins, paper, etc. In such a multilayer structure, at least one layer formed from the resin composition of the present invention (resin composition layer) is required.

[0119] Applications of multilayer structures incorporating the resin composition layer of the present invention include, for example: food packaging materials such as coffee capsules and shrink films; pharmaceutical packaging materials; cosmetic packaging materials such as toner and foundation cases; packaging materials for metal parts; packaging materials for electronic parts; packaging materials for articles whose properties are to be suppressed by oxidation and moisture absorption; packaging materials for substances for which there is concern about odor transfer or leakage; and multilayer structures used in various agricultural sheets and agricultural materials such as multilayer sheets, fumigation sheets, seedling trays, and covering sheets.

[0120] Examples of applicable melt forming methods include injection molding and extrusion molding. Extrusion molding is particularly suitable for forming films or sheets, and examples include T-die molding and blow molding (tubular film method). It can be single-layer extrusion or multi-layer extrusion. In the manufacture of multi-layer structures formed by stacking film layers, multi-layer extrusion (co-extrusion molding) is appropriate.

[0121] The resulting film or sheet can undergo secondary processing such as uniaxial or biaxial stretching. The resin composition of the present invention has excellent stretchability; therefore, stretching is preferably performed to improve the film strength and further enhance gas barrier properties.

[0122] Example

[0123] The present invention will be further described below through examples and comparative examples, but the present invention is not limited to the following examples.

[0124] [Measurement and Evaluation Methods]

[0125] 1. Degree of saponification (mol%)

[0126] The determination was carried out in accordance with JIS K6726:1994.

[0127] 2. Number-average degree of aggregation

[0128] The determination was carried out in accordance with JIS K6726:1994.

[0129] 3. Degree of modification (mol%)

[0130] The amount of comonomer used in the synthesis of PVA-based resins is determined based on the amount of comonomers used.

[0131] 4. Formate content determination

[0132] Formate was quantified using the Journal of Pharmaceutical and Biomedical Analysis 41(2006) 738-743 as a reference.

[0133] Dissolve 5.0 g of p-toluenesulfonic acid in ethanol to prepare a 500 ml solution (1% p-toluenesulfonic acid-ethanol solution). Accurately weigh 0.5 g of the sample (cryogenically ground particles) into a 20 ml vial, add 5 ml of the 1% p-toluenesulfonic acid-ethanol solution using a pipette, and seal with a handclipper (for blank samples, use only 5 ml of the 1% p-toluenesulfonic acid-ethanol solution). Place the vial in an ultrasonic cleaner set to 60°C and run for 2 hours to perform ethyl esterification of formic acid. Remove from the ultrasonic cleaner and allow to stand at room temperature for at least 3 hours. Accurately weigh 0.5 g of formic acid into a volumetric flask and dilute to 50 ml with ethanol (10000 mg / L solution). Prepare a standard solution by appropriate serial dilution. Accurately weigh 0.5 g of the standard solution into a 20 ml vial, add 5 ml of the 1% p-toluenesulfonic acid-ethanol solution using a pipette, and seal with a handclipper. Headspace analysis was performed under the conditions shown in Table 1 below.

[0134] [Table 1]

[0135] headspace sampler

[0136] Various projects condition Use equipment Agilent 7697A Oven 60℃ Ring Road 100℃ transmission line 100℃ Small bottle balance 15min Small bottle stirrer 7 stages, 136 stirrings per minute Inflow time 0.05min Fill flow 50 mL / min Filling pressure 23.2psi Fill time 1min Fill mode Fill at a constant flow rate until the specified pressure is reached. Loop size 3mL

[0137] GC

[0138] Various projects condition Use equipment Agilent 7890B Analytical chromatographic columns <![CDATA[DB-1301(60m * 0.32mm * 1.0μm)]]> Oven 60℃ (9 min) → Rate 100℃ / min → 200℃ (2 min) Inlet temperature 170℃ carrier gas Helium (0.8 mL / min) Total flow 55.8 mL / min Purge flow rate 3mL / min Flow split ratio 65:1 Diverting traffic 52 mL / min MSD transmission line 220℃

[0139] MS

[0140] Various projects condition Use equipment Agilent 5977B Ion temperature reduction 230℃ MS quadrupole temperature 150℃ (SIM mode) Detection of ions m / z = 31, 45, 56, 74 (Quantitative: m / z = 74)

[0141] It should be noted that in Table 1, GC refers to gas chromatography. Furthermore, MS refers to mass spectrometry.

[0142] 5. Acetate content determination

[0143] The acetate content was determined using the pH measurement and neutralization titration method described below.

[0144] (1) pH measurement

[0145] Measure 6.00 g of resin composition granules and 138 g of water into a culture medium bottle, cap the bottle, and place it in a constant temperature water bath at 30 ± 1 °C for 2 hours with stirring to dissolve. After 2 hours, open the cap of the culture medium bottle and continue stirring for 10 minutes to dissolve, then stop stirring. Remove the electrode of the pH meter "F-54 (HORIBA)" from the immersion solution, rinse it with pure water, and calibrate the pH meter using buffer solutions of pH = 4.01 and pH = 6.86. After calibration, immerse the sample in the electrode and measure the pH.

[0146] (2) Neutralization titration

[0147] Measure 3.00 g of resin composition granules and 100 g of water into an Erlenmeyer flask. Heat and stir until the resin composition granules dissolve. After dissolution, cool to room temperature and add 5 drops of indicator (methyl orange). Titrate with 0.1 mol / L HCl aqueous solution until the solution turns yellow-red.

[0148] 6. Thermal stability

[0149] Thermal stability was evaluated using the following TGA isothermal method.

[0150] For 5 mg resin composition particles, the weight after heating was determined using a thermogravimetric analyzer (Perkin Elmer, Pyris1TGA) under nitrogen atmosphere, at a rate of 20 mL / min, a temperature of 230 °C, and a heating time of 1 hour, thereby determining the residual rate.

[0151] With a survival rate of over 90%, the thermal stability is rated as good.

[0152] If the survival rate is less than 90%, the thermal stability is rated as poor.

[0153] 7. Molding stability

[0154] The dynamic viscosity behavior is evaluated using the following method.

[0155] 55g of resin composition granules were mixed using a plasticizer (Brabender) at 230°C and 50rpm for 30 minutes. Torque values ​​were measured at 5 minutes and 20 minutes, and evaluated using the torque ratio (torque(20 minutes) / torque(5 minutes)). A higher value indicates a higher viscosity of the PVA-based resin composition. In melt molding, dynamic viscosity behavior with minimal viscosity change is preferred.

[0156] [PVA-based resins]

[0157] As a PVA-based resin containing primary hydroxyl groups in the side chain, a PVA-based resin with 1,2-diol side chain structural units as shown in formula (3a) was used. The degree of modification (content of 1,2-diol side chain structural units) of the PVA-based resin used was 6 mol%, the degree of saponification was 99.2 mol% as determined by JIS K6726, and the number-average degree of polymerization was 450 as determined by JIS K6726.

[0158] [Chemical Formula 7]

[0159]

[0160] (1) Formic acid

[0161] Formic acid manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd. is used.

[0162] (2) Sodium formate

[0163] Sodium formate manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd. is used.

[0164] (3) Acetic acid

[0165] Acetic acid manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd. is used.

[0166] (4) Sodium acetate

[0167] Sodium acetate is used with Fujifilm and Kodenpaku sodium.

[0168] [Preparation and Evaluation of Resin Compositions]

[0169] (Examples 1-6, Comparative Examples 1-4)

[0170] The side-chain 1,2-diol modified PVA resin, formic acid, sodium formate, acetic acid, and sodium acetate were mixed in the proportions shown in Table 2 and melt-blended using a twin-screw extruder TEM-18DS (Shibaura Machinery Co., Ltd.) under the following conditions to produce the resin composition particles of Examples 1 to 6 and Comparative Examples 1 to 4.

[0171] Diameter (D) 20mm

[0172] L / D = 48

[0173] Screw speed: 300 rpm.

[0174] Set temperature:

[0175] C1 / C2 / C3 / C4 / C5 / C6 / D=160 / 200 / 200 / 210 / 210 / 200 / 200℃.

[0176] Screw type: Twin mixing screw.

[0177] Screen mesh size: 90 / 120 / 90 mesh.

[0178] Discharge rate: 5 kg / hr.

[0179] For resin composition particles prepared using the above-described measurement and evaluation methods, thermal stability based on the TGA isothermal method and molding stability based on dynamic viscosity behavior were evaluated. The results are shown in Table 2.

[0180] [Table 2]

[0181]

[0182]

[0183] As shown in Table 2 above, it can be seen that the resin composition of Comparative Example 1, which contains a large amount of formate and has a high formate / acetate ratio, and the resin compositions of Comparative Examples 2 and 3, which have low formate / acetate ratios, exhibited low residue rates in the TGA isothermal method evaluation, indicating poor thermal stability. Furthermore, it can be seen that the resin composition of Comparative Example 4, which has low formate content, showed large viscosity changes in the dynamic viscosity behavior evaluation, indicating poor molding stability. On the other hand, the resin compositions of Examples 1-6 showed high residue rates in the TGA isothermal method evaluation and small viscosity changes in the dynamic viscosity behavior evaluation. These results indicate that the resin compositions of the present invention exhibit good thermal and molding stability.

[0184] (Examples 7-8, Comparative Examples 5-6)

[0185] Unmodified PVA resin was used as the PVA-based resin. The degree of saponification of the PVA-based resin used was 87.6 mol% as determined by JIS K6726, and the number-average degree of polymerization was 500 as determined by JIS K6726.

[0186] Except for mixing the unmodified PVA resin, formic acid, sodium formate, acetic acid, and sodium acetate in the proportions shown in Table 3, the resin composition particles of Examples 7-8 and Comparative Examples 5-6 were prepared in the same manner as in Examples 1-6 and Comparative Examples 1-4.

[0187] For the resin composition particles prepared based on the above-described measurement and evaluation methods, thermal stability based on the TGA isothermal method and molding stability based on dynamic viscosity behavior were evaluated. The results are shown in Table 3.

[0188] [Table 3]

[0189]

[0190]

[0191] As shown in Table 3 above, it can be seen that the resin composition of Comparative Example 6, which has a low formate content, exhibits a large viscosity change in the dynamic viscosity behavior evaluation, resulting in poor molding stability. On the other hand, the resin compositions of Examples 7 and 8 show high residue rates in the TGA isothermal method evaluation, and furthermore, compared to the resin compositions of Comparative Examples 5 and 6, exhibit smaller viscosity changes in the dynamic viscosity behavior evaluation. These results indicate that the resin compositions of the present invention possess good thermal stability and molding stability.

[0192] 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, obvious to those skilled in the art, fall within the scope of the present invention.

[0193] It should be noted that this application is based on Japanese patent application filed on March 31, 2023 (Japanese Patent Application No. 2023-58957), the contents of which are incorporated herein by reference.

[0194] Industrial availability

[0195] The resin composition of the present invention contains PVA-based resin and has sufficient thermal and molding stability during melt molding, and therefore can be appropriately used in a variety of packaging materials, especially food packaging materials such as coffee capsules.

Claims

1. A resin composition comprising a polyvinyl alcohol resin, formate, and acetate, wherein the formate content in the resin composition is 4-500 ppm, and the formate to acetate content ratio, i.e., formate / acetate, is 0.001-0.

200.

2. The resin composition according to claim 1, wherein, The content of acetate in the resin composition is less than 10,000 ppm.

3. The resin composition according to claim 1, wherein, The polyvinyl alcohol-based resin contains structural units with modified groups other than ethylene.

4. The resin composition according to claim 1, wherein, The polyvinyl alcohol-based resin contains structural units with hydrophilic modified groups.

5. The resin composition according to claim 1, wherein, The polyvinyl alcohol-based resin contains structural units with primary hydroxyl groups in the side chains.

6. The resin composition according to claim 1, wherein, The formate content is 5-100 ppm.

7. A molded article comprising a resin composition according to any one of claims 1 to 6.

8. A membrane comprising a resin composition according to any one of claims 1 to 6.

9. A sheet comprising a resin composition according to any one of claims 1 to 6.

10. A multilayer structure comprising at least one layer formed of a resin composition according to any one of claims 1 to 6.

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