Resin composition, film or sheet, and multilayer structure

Abstract

The present invention provides a resin composition containing a polyvinyl alcohol-based resin and having excellent melt viscosity stability during melt molding. A resin composition according to the present invention contains: a polyvinyl alcohol-based resin having a primary hydroxyl group in a side chain; and 1,2-butanediol. A film and sheet according to the present invention comprise the resin composition according to the present invention. A multilayer structure according to the present invention includes at least one film or sheet according to the present invention.

Description

Resin composition, film or sheet, and multilayer structure

[0001] The present invention relates to a resin composition containing a polyvinyl alcohol-based resin, a film or sheet made of the resin composition, and a multilayer structure containing the film or sheet.

[0002] Polyvinyl alcohol-based resins (hereinafter, polyvinyl alcohol may be abbreviated as PVA) are excellent in toughness, heat resistance, transparency, oil resistance, biodegradability, and the like, and further have characteristics such as not generating harmful gases when incinerated. Therefore, they are molded into the shape of films or sheets and used as various packaging materials for clothing, pesticides, detergents, etc., agricultural films for greenhouses, curtains, etc., and the like.

[0003] Generally, molded articles such as containers and films are produced by melt molding from the viewpoint of productivity. On the other hand, it is known that it is difficult to produce molded articles from polyvinyl alcohol (PVA) by hot melt molding because the melting point and decomposition temperature are close to each other. However, modified PVA-based resins that can be melt molded have also been proposed. For example, Patent Documents 1 and 2 each describe PVA-based resins having a 1,2-diol structure in the side chain.

[0004] Japanese Patent Publication No. 2004-75866 Japanese Patent Publication No. 2006-89538

[0005] According to the investigations of the present inventors, when PVA-based resins are melt-molded continuously for a long period of time, the viscosity of the PVA-based resin changes significantly, resulting in an increase in viscosity, leaving room for improvement in molding stability. Furthermore, since thermal degradation products may be generated during melt-molding, there is also room for improvement in thermal stability.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a resin composition which contains a PVA-based resin and has excellent melt viscosity stability during melt molding, i.e., excellent molding stability.

[0007] The present inventors have discovered that a resin composition containing a PVA-based resin and 1,2-butanediol improves the melt viscosity stability during melt molding compared to a PVA-based resin alone, and have completed the present invention.

[0008] That is, the gist of the present invention is as follows.

[0009] A first aspect of the present invention is a resin composition containing a polyvinyl alcohol resin having a primary hydroxyl group in a side chain and 1,2-butanediol.

[0010] A second aspect of the present invention is the resin composition of the first aspect, wherein the content of 1,2-butanediol in the resin composition is 0.1 to 1000 ppm.

[0011] A third aspect of the present invention is the resin composition of the first or second aspect, wherein the content of 1,2-butanediol in the resin composition is 0.5 to 400 ppm.

[0012] A fourth aspect of the present invention is the resin composition according to any one of the first to third aspects, wherein the polyvinyl alcohol resin having a primary hydroxyl group in a side chain has a structural unit represented by the following formula (3):

[0013]

[0014] In formula (3), R １ ~R ６ each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X represents a single bond or a bonding chain.

[0015] A fifth aspect of the present invention is a film or sheet made of the resin composition of any one of the first to fourth aspects.

[0016] A sixth aspect of the present invention is a multilayer structure comprising at least one layer of the film or sheet of the fifth aspect.

[0017] The resin composition of the present invention has excellent melt viscosity stability during melt molding, enabling stable molding. The resin composition of the present invention is suitable for producing various molded products such as resin containers and resin films, and is particularly useful as a packaging material because it contains a polyvinyl alcohol-based resin.

[0018] The resin composition of the present invention and its use will be described in detail below. Regarding the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of the numerical range can also be replaced with the values ​​shown in the examples. Furthermore, when the term "weight" is used in this specification, it can be read as "mass."

[0019] [Resin Composition] The resin composition of the present invention is a resin composition containing a polyvinyl alcohol-based resin having primary hydroxyl groups in the side chains (hereinafter also referred to as a PVA-based resin containing primary hydroxyl groups in the side chains) and 1,2-butanediol.

[0020] <PVA-Based Resin Having Primary Hydroxyl Groups in the Side Chain> In this specification, a PVA-based resin having primary hydroxyl groups in the side chain refers to a modified PVA-based resin containing a structural unit having a primary hydroxyl group in the side chain. Specifically, it refers to a modified PVA-based resin containing a structural unit having a primary hydroxyl group in the side chain in addition to vinyl alcohol units represented by the following formula (1) constituting polyvinyl alcohol and vinyl ester units represented by the following formula (2) as unsaponified portions. The vinyl ester unit is included when the saponification degree is less than 100%. In the resin composition of the present invention, using a PVA-based resin having primary hydroxyl groups in the side chain as the PVA-based resin is preferable because it achieves excellent melt moldability. The number of primary hydroxyl groups in the PVA-based resin having primary hydroxyl groups in the side chain is preferably 1 to 5, more preferably 1 to 2, and particularly preferably 1. In addition to the primary hydroxyl groups, it is also preferable for the PVA-based resin to have a secondary hydroxyl group.

[0021]

[0022]

[0023] In formula (2), R ａ is a group derived from the type of vinyl ester monomer used, and when vinyl acetate monomer is used, for example, it is a methyl group.

[0024] Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, and vinyl versatate, with vinyl acetate being economically preferred.

[0025] As the structural unit having a primary hydroxyl group in the side chain, a structural unit having a 1,2-diol group in the side chain represented by the following formula (3) is preferred.

[0026]

[0027] In formula (3), R １ ~R ６ each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X represents a single bond or a bonding chain.

[0028] Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a tert-butyl group, and may have a substituent such as a halogen group, a hydroxyl group, an ester group, a carboxylic acid group, or a sulfonic acid group. １ ~R ６ is more preferably a hydrogen atom. １ ~R ６ may all be the same or different, but preferably all are hydrogen atoms. １ ~R ６ When all of the groups are hydrogen atoms, the reactivity with adhesive resins such as acid-modified polyolefin resins is improved, and it is therefore preferable to easily form a laminate.

[0029] In formula (3), X represents a single bond or a bonding chain. Examples of the bonding chain include hydrocarbon groups such as alkylene groups, alkenylene groups, alkynylene groups, phenylene groups, and naphthylene groups (these hydrocarbon groups may be substituted with halogen atoms such as fluorine atoms, chlorine atoms, and bromine atoms), -O-, -(CH ２ O) ｍ -, -(OCH ２ ) ｍ -, -(CH ２ O)ｍ CH ２ -, -CO-, -COCO-, -CO(CH ２ ) ｍ CO-, -CO(C ６ H ４ )CO-, -S-, -CS-, -SO-, -SO ２ -, -NR-, -CONR-, -NRCO-, -CSNR-, -NRCS-, -NRNR-, -HPO ４ -, -Si(OR) ２ -, -OSi(OR) ２ -, -OSi(OR) ２ O-, -Ti (OR) ２ -, -OTi(OR) ２ -, -OTi(OR) ２ Examples include O-, -Al(OR)-, -OAl(OR)-, -OAl(OR)O-, etc. (each R is independently an arbitrary substituent, preferably a hydrogen atom or an alkyl group, and m is an integer of 1 to 5). From the viewpoint of stability during production or use, X is preferably a single bond, an alkylene group having 6 or less carbon atoms (particularly a methylene group), or -CH ２ OCH ２ Among them, a single bond is most preferable in terms of thermal stability and stability under high temperature and acidic conditions.

[0030] Therefore, the most preferred structural unit among those represented by formula (3) is a structural unit having 1,2-diol in a side chain represented by formula (3a): A structural unit having 1,2-diol in a side chain is also referred to as a "structural unit having 1,2-diol in a side chain," and a PVA-based resin containing a structural unit having 1,2-diol in a side chain is sometimes referred to as a "PVA-based resin having 1,2-diol in a side chain."

[0031]

[0032] The identification of the 1,2-diol structural unit in the PVA resin and the measurement of its content (molar fraction) were carried out using a PVA resin that was completely saponified. １It can be determined from a H-NMR spectrum (solvent: DMSO-d6, internal standard: tetramethylsilane), and specifically, it can be calculated from the peak areas derived from hydroxyl group protons, methine protons, and methylene protons in the 1,2-diol unit, methylene protons in the main chain, protons of hydroxyl groups linked to the main chain, etc.

[0033] The degree of modification (content) of the PVA-based resin having a primary hydroxyl group in a side chain (preferably a PVA-based resin having a 1,2-diol in a side chain) 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%. If the degree of modification is too low, the reactivity with adhesive resins such as acid-modified polyolefin-based resins tends to decrease, while if the degree of modification is too high, the crystallization rate becomes too slow, and when a laminate is formed with another resin, the laminate tends to deform, resulting in a poor appearance.

[0034] The number average degree of polymerization (measured in accordance with JIS K6726:1994) of the PVA-based resin having primary hydroxyl groups in the side chains (preferably a PVA-based resin having 1,2-diol in the side chains) is preferably 150 or more, more preferably 200 or more, even more preferably 250 or more, and particularly preferably 300 or more, and is preferably 4000 or less, more preferably 2000 or less, even more preferably 800 or less, and particularly preferably 600 or less. When the average degree of polymerization is equal to or more than the above-mentioned lower limit, a stable shape tends to be easily formed during melt molding, whereas when the average degree of polymerization is equal to or less than the above-mentioned upper limit, the viscosity of the resin composition does not become too high, and molding tends to be easier.

[0035] The viscosity of an aqueous solution of a PVA-based resin containing primary hydroxyl groups in a side chain may be used as an index of the average degree of polymerization. The viscosity of a 4 wt % aqueous solution at 20°C, measured in accordance with JIS K6726:1994, is preferably 1.5 mPa·s or more, more preferably 2 mPa·s or more, and particularly preferably 2.5 Pa·s or more, while it is preferably 20 mPa·s or less, more preferably 12 mPa·s or less, and particularly preferably 8 mPa·s or less. If the viscosity is above the lower limit, a stable shape tends to be formed during melt molding, while if it is below the upper limit, molding tends to be easier.

[0036] The PVA resin containing a primary hydroxyl group in a side chain may be obtained by saponifying a copolymer obtained using a copolymerizable monomer. Examples of the copolymerizable monomer (modifying monomer) to be used 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 mono- or di-alkyl 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 methallylsulfonic acid, or their salts; alkyl vinyl ethers, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallyl vinyl ketone, N-vinylpyrrolidone, vinyl chloride, vinylidene chloride, polyoxyethylene (meth)allyl ether, polyoxypropylene (meth)allyl ether, and the like. polyoxyalkylene (meth)allyl ethers such as p) allyl ether; polyoxyalkylene (meth)acrylates such as polyoxyethylene (meth)acrylate and polyoxypropylene (meth)acrylate; polyoxyalkylene (meth)acrylamides such as polyoxyethylene (meth)acrylamide and polyoxypropylene (meth)acrylamide; hydroxy group-containing α-olefins such as polyoxyethylene (1-(meth)acrylamide-1,1-dimethylpropyl) ester, polyoxyethylene vinyl ether, polyoxypropylene vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, polyoxypropylene vinylamine, 3-buten-1-ol, 4-penten-1-ol, and 5-hexen-1-ol, and derivatives thereof, such as acylated products.

[0037] The saponification degree of such a PVA-based resin having a primary hydroxyl group in a side chain is preferably 70 mol% or more, more preferably 80 mol% or more, and particularly preferably 85 mol% or more, and is preferably 100 mol% or less, more preferably 99.9 mol% or less, and particularly preferably 99.7 mol% or less. When the saponification degree is equal to or greater than the lower limit, the gas barrier property tends to be improved. The saponification degree of the PVA-based resin having a primary hydroxyl group in a side chain is measured in accordance with JIS K6726:1994.

[0038] The PVA-based resin that can be used in the resin composition of the present invention may be one type or a mixture of two or more types. When a mixture of two or more types is used, examples of the mixture include a combination of an unmodified PVA-based resin and a PVA-based resin having a side chain primary hydroxyl group, and a combination of a different type of modified PVA-based resin and a PVA-based resin having a side chain primary hydroxyl group. Also included are combinations of PVA-based resins having side chain primary hydroxyl groups that differ in degree of saponification, degree of polymerization, modification rate, etc.

[0039] The PVA-based resin content 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.

[0040] <1,2-Butanediol> By incorporating 1,2-butanediol into a PVA-based resin having a primary hydroxyl group in the side chain, the stability of the melt viscosity can be improved.

[0041] The reason for this is not clear, but it is presumed that by incorporating 1,2-butanediol into a PVA-based resin having primary hydroxyl groups in its side chains, the resin exhibits a plasticizing effect when melted, and also acts as a crystal nucleating agent when solidifying after melting, promoting crystallization.

[0042] The content of 1,2-butanediol in the resin composition of the present invention (per mass of the total resin composition) is preferably 0.1 to 1000 ppm, more preferably 0.3 to 600 ppm, even more preferably 0.5 to 400 ppm, still more preferably 0.7 to 350 ppm, particularly preferably 1.0 to 300 ppm, and most preferably 3.0 to 280 ppm. That is, the lower limit of the 1,2-butanediol content in the resin composition is, in order of preference, 0.1 ppm or more, 0.3 ppm or more, 0.5 ppm or more, 0.7 ppm or more, 1.0 ppm or more, and 3.0 ppm or more, and the upper limit is, in order of preference, 1000 ppm or less, 600 ppm or less, 400 ppm or less, 350 ppm or less, 300 ppm or less, and 280 ppm or less.

[0043] When the content of 1,2-butanediol in the resin composition is equal to or greater than the lower limit, the stability of the melt viscosity is improved. When the content of 1,2-butanediol in the resin composition is equal to or less than the upper limit, the glass transition temperature (Tg) increases due to the interaction with the PVA-based resin, and the heat resistance of the molded product is improved.

[0044] The content of 1,2-butanediol in the resin composition can be measured using a GC / MS device equipped with a dynamic headspace device. The measurement conditions are specifically as follows: <Dynamic headspace conditions> Thermal desorption apparatus: TDS-3 / CIS4 (manufactured by Gestell Corporation) Sample amount: Approximately 5 to 15 mg Heating conditions: 150°C, 30 minutes <GC / MS measurement conditions> GC section apparatus: Agilent 6890GC (manufactured by Agilent Technologies) Column: DB-WAX (cross-linked polyethylene glycol (PEG) capillary column) Column temperature: Hold at 40°C for 5 minutes → Heat to 250°C at 10°C / min → Hold at 250°C for 15 minutes Injection port temperature (CIS4): -150°C (collection) → 250°C Carrier gas: Helium Column flow rate: 1.0 mL / min Split ratio: 1 / 30 MS section apparatus: Agilent 5973MSD (manufactured by Agilent Technologies) Mode: SCAN mode

[0045] <Other Components> 1. Plasticizer The resin composition of the present invention may contain a plasticizer within a range that does not impair the effects of the present invention (melt viscosity stability and thermal stability during melt molding). Examples of plasticizers include aliphatic polyhydric alcohols (e.g., ethylene glycol, hexanediol, glycerin, trimethylolpropane, diglycerin, etc.), compounds in which ethylene oxide is added to a polyhydric alcohol, various alkylene oxides (e.g., ethylene oxide, propylene oxide, mixed adducts of ethylene oxide and propylene oxide, etc.), sugars (e.g., sorbitol, mannitol, pentaerythritol, xylol, arabinose, ribulose, etc.), phenol derivatives such as bisphenol A and bisphenol S, amide compounds such as N-methylpyrrolidone, and glucosides such as α-methyl-D-glucoside.

[0046] 2. Other Resins The resin composition of the present invention may contain other polymers (resins) within a range that does not impair the effects of the present invention (for example, less than 30% by mass of the resin composition). Examples of polymers (resins) that can be contained include various thermoplastic resins such as polyamide, polyester, polyethylene, polypropylene, and polystyrene.

[0047] 3. Other Additives The resin composition of the present invention may further contain, as necessary, a reinforcing agent, a filler, a pigment, a dye, a lubricant, an antioxidant, an antistatic agent, an ultraviolet absorber, a heat stabilizer, a light stabilizer, a surfactant, an antibacterial agent, an antistatic agent, a drying agent, an antiblocking agent, a flame retardant, a crosslinking agent, a curing agent, a foaming agent, a crystal nucleating agent, and the like, within a range that does not impair the effects of the present invention (for example, 10% by mass or less of the resin composition).

[0048] The resin composition of the present invention having the above-mentioned composition does not impair the properties of the PVA-based resin, and has good thermal stability and molding stability due to the coexistence of 1,2-butanediol.

[0049] <Method for Producing Resin Composition> Examples of methods for producing a resin composition having the above-described composition include (i) a method of mixing 1,2-butanediol with a slurry obtained after saponification of a PVA-based resin having primary hydroxyl groups in its side chains, (ii) a method of mixing 1,2-butanediol with particles filtered out after saponification of a PVA-based resin having primary hydroxyl groups in its side chains, and (iii) a method of mixing 1,2-butanediol with a molten PVA-based resin having primary hydroxyl groups in its side chains. Method (i) is preferred, as it allows for the production of a resin composition in which 1,2-butanediol is uniformly dispersed. When the resin composition contains components other than the PVA-based resin having primary hydroxyl groups in its side chains and 1,2-butanediol, the other components may be mixed simultaneously with or subsequent to the 1,2-butanediol.

[0050] [Melt-molded article of resin composition and its manufacturing method] The resin composition of the present invention is melt-moldable, and can be produced by a melt extrusion method generally used for thermoplastic resins. Therefore, the resin composition of the present invention can be used for melt-molded articles that require gas barrier properties, particularly for bags made from melt-molded films, stretched films, and sheets, and for containers and lids made from cups, trays, tubes, bottles, etc.

[0051] The present invention provides a film or sheet made from the resin composition of the present invention described above. A melt-molded product containing the resin composition of the present invention may be a single-layer structure made from the resin composition of the present invention, or may be a multilayer structure composited with other layers. The present invention also provides a multilayer structure containing at least one film or sheet made from the resin composition of the present invention. The multilayer structure is used as a structure having two or more layers laminated together, with a film or sheet made from the resin composition of the present invention laminated with other thermoplastic resins, papers, etc. In the multilayer structure, the layer made from the resin composition of the present invention (resin composition layer) serves as a gas barrier layer.

[0052] Examples of multilayer structures comprising a resin composition layer of the present invention as a gas barrier layer include food packaging materials such as coffee capsules and shrink films, medicine packaging materials, cosmetic packaging materials such as cases for lotion and foundation, packaging materials for metal parts, packaging materials for electronic parts, packaging materials for items in which deterioration of properties due to oxidation or moisture absorption should be suppressed, packaging materials for substances in which odor transfer or odor leakage is a concern, and multilayer structures used in various agricultural sheets and agricultural materials such as mulch sheets, fumigation sheets, seedling trays, and covering sheets.

[0053] Applicable melt molding methods include injection molding and extrusion molding. Extrusion molding is particularly suitable as a molding method for films or sheets, and examples thereof include T-die molding and inflation molding (tubular film method). Not only single-layer extrusion but also multi-layer extrusion may be used. Multi-layer extrusion (co-extrusion molding) is suitable for producing a multi-layer structure in which films are laminated.

[0054] The obtained film or sheet may be subjected to secondary processing such as uniaxial or biaxial stretching. Since the resin composition of the present invention has excellent stretchability, it is preferable to subject the film or sheet to a stretching treatment in order to improve the strength of the film and further improve the gas barrier properties.

[0055] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples. In the following examples and comparative examples, "parts" are based on mass unless otherwise specified.

[0056] [Measurement and Evaluation Methods] 1. Saponification Degree (mol %) The saponification degree was measured in accordance with JIS K6726:1994.

[0057] 2. Number-average degree of polymerization The number-average degree of polymerization was measured in accordance with JIS K6726:1994.

[0058] 3. Degree of modification (mol%) The degree of modification is １ H-NMR (300 MHz proton NMR, d ６ - Calculated from the integrated value measured in DMSO solution (internal standard: tetramethylsilane, 50°C).

[0059] 4. Measurement of 1,2-butanediol Amount The amount of 1,2-butanediol was measured using a GC / MS device equipped with a dynamic headspace device under the conditions shown below. <Dynamic headspace conditions> Thermal desorption apparatus: TDS-3 / CIS4 (manufactured by Gestell Corporation) Sample amount: Approximately 5 to 15 mg Heating conditions: 150°C, 30 minutes <GC / MS measurement conditions> GC section apparatus: Agilent 6890GC (manufactured by Agilent Technologies) Column: DB-WAX (cross-linked polyethylene glycol (PEG) capillary column) Column temperature: Hold at 40°C for 5 minutes → Heat to 250°C at 10°C / min → Hold at 250°C for 15 minutes Injection port temperature (CIS4): -150°C (collection) → 250°C Carrier gas: Helium Column flow rate: 1.0 mL / min Split ratio: 1 / 30 MS section apparatus: Agilent 5973MSD (manufactured by Agilent Technologies) Mode: SCAN mode

[0060] 5. Melt Viscosity Stability The melt viscosity stability was evaluated by the following method. The resin composition was charged in an amount equivalent to 55 g of resin content into a Plastograph (Brabender Plastograph EC) and kneaded at 230°C for 2 hours. The torque values ​​were measured after 5 minutes and 80 minutes, and the increase in torque was calculated.

[0061] 6. Glass Transition Temperature (Tg) The glass transition temperature (Tg) was measured by the following method. A differential scanning calorimeter (TA Instruments "DSC Q2000") was used to measure according to the following 1) to 3). 1) The resin composition was held at -50°C for 5 minutes, heated to 200°C at a heating rate of 10°C / min, and then held at that temperature for 1 minute. 2) The resin composition was cooled to -50°C at a cooling rate of 30°C / min, and held at that temperature for 5 minutes. 3) The resin composition was heated to 200°C at a heating rate of 10°C / min. The glass transition temperature (Tg) was calculated from 3) above.

[0062] As the 1,2-butanediol, 1,2-butanediol manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. was used.

[0063] Preparation and Evaluation of Resin Compositions (Example 1) A reaction vessel equipped with a reflux condenser, a dropping funnel, and a stirrer was charged with 68.0 parts of vinyl acetate, 23.8 parts of methanol, and 8.2 parts of 3,4-diacetoxy-1-butene. 0.3 mol % azobisisobutyronitrile (relative to the vinyl acetate charged) was then added, and the temperature was raised under a nitrogen stream while stirring to initiate polymerization. When the vinyl acetate polymerization rate reached 90%, m-dinitrobenzene was added to terminate the polymerization. Subsequently, unreacted vinyl acetate monomer was removed from the system by blowing in methanol vapor to obtain a methanol solution of the copolymer. The methanol solution was then further diluted with methanol to a concentration of 45% and charged into a kneader. While maintaining the solution temperature at 35°C, a 2% methanol solution of sodium hydroxide was added at a ratio of 10.5 mmol per 1 mole of the total amount of vinyl acetate structural units and 3,4-diacetoxy-1-butene structural units in the copolymer to perform saponification. As the saponification proceeded, the saponified product precipitated and was filtered off at the point where it became particulate. The filtered polyvinyl alcohol was swollen for 1 hour in methanol with a bath ratio of 6 while maintaining the temperature at 30°C, and 1,2-butanediol was added dropwise thereto, followed by stirring for another 1 hour. The polyvinyl alcohol was filtered off again and dried in a vacuum dryer at 60°C for 17 hours to obtain a resin composition.

[0064] The degree of saponification of the polyvinyl alcohol obtained above was analyzed based on the amount of alkali consumed for hydrolysis of the remaining vinyl acetate and 3,4-diacetoxy-1-butene, and was found to be 99.2 mol%. The average degree of polymerization of the PVA-based resin was analyzed in accordance with JIS K 6726-1994 and was found to be 450. The content of 1,2-diol structural units in the polyvinyl alcohol was １ H-NMR (300 MHz proton NMR, d ６ The concentration was calculated from the integrated value measured in a DMSO solution (internal standard: tetramethylsilane, 50° C.) to find that it was 6 mol %.

[0065] The amount of 1,2-butanediol in the resin composition obtained above was measured by the measurement method described above. The glass transition temperature (Tg) of the resin composition was also measured by the measurement method described above. Furthermore, the torque value of the resin composition was measured by the measurement method described above, and the torque increase value was calculated by subtracting the torque value after 5 minutes from the torque value after 80 minutes.

[0066] The glass transition temperature (Tg) and torque increase values ​​were evaluated comprehensively based on the following evaluation criteria. These evaluation criteria were rated in order of superiority as "A," "B," "C," and "D." [Evaluation criteria] A: Torque increase value is 30 Nm or less, and Tg is 60°C or more B: Torque increase value is 30 Nm or less, and Tg is less than 60°C C: Torque increase value is more than 30 Nm, and Tg is 60°C or more D: Torque increase value is more than 30 Nm, and Tg is less than 60°C

[0067] The results are shown in Table 1.

[0068] (Examples 2 to 5, Comparative Example 1) The same procedure as in Example 1 was carried out, except that the amount of 1,2-butanediol added was changed as shown in Table 1. The results are shown in Table 1. In Comparative Example 1, 1,2-butanediol was not added when the resin composition was prepared, and the amount of 1,2-butanediol was below the detection limit (N.D.: 0.1 ppm) even when the above-mentioned "4. Measurement of 1,2-butanediol amount" was carried out, so it is considered that 1,2-butanediol is not contained.

[0069]

[0070] From the viewpoint of processing stability during melt extrusion, the torque increase value is desirably 30 Nm or less. As shown in Table 1 above, Examples 1 to 5, in which 1,2-butanediol was blended into the PVA-based resin composition, exhibited an upper limit of 30 Nm or less. Compared to Comparative Example 1, which did not contain 1,2-butanediol, Examples 1 to 5 exhibited suppressed torque increase and good melt viscosity stability. Furthermore, from the viewpoint of heat resistance during practical use of the laminate, it is desirable that the glass transition temperature (Tg) be 60°C or higher. While there was a tendency for the glass transition temperature (Tg) to decrease as the 1,2-butanediol content increased, the glass transition temperature (Tg) did not decrease significantly compared to Comparative Example 1 in Examples 1 to 5. In particular, the resin compositions of Examples 1 to 4 had glass transition temperatures (Tg) of 60°C or higher, demonstrating excellent melt viscosity stability as well as high thermal stability.

[0071] Although the above examples show specific embodiments of the present invention, the examples are merely illustrative and should not be construed as limiting. Various modifications that are obvious to those skilled in the art are intended to fall within the scope of the present invention.

[0072] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made thereto without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2024-003886) filed on January 15, 2024, the contents of which are incorporated herein by reference.

[0073] The resin composition of the present invention contains a PVA-based resin and has sufficient melt viscosity stability during melt molding, and therefore can be suitably used for various packaging materials, particularly packaging materials for food products such as coffee capsules.

Claims

1. A resin composition comprising a polyvinyl alcohol-based resin having a primary hydroxyl group in a side chain and 1,2-butanediol.

2. The resin composition according to claim 1, wherein the content of the 1,2-butanediol in the resin composition is 0.1 to 1000 ppm.

3. The resin composition according to claim 1, wherein the content of the 1,2-butanediol in the resin composition is 0.5 to 400 ppm.

4. The resin composition according to claim 1, wherein the polyvinyl alcohol-based resin having a primary hydroxyl group in the side chain has a structural unit represented by the following formula (3). In formula (3), R １ ~ R ６ each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and X represents a single bond or a linking chain.

5. A film or sheet comprising the resin composition according to any one of claims 1 to 4.

6. A multilayer structure comprising at least one layer of the film or sheet according to claim 5.

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