Modified polyvinyl alcohol polymer, water-soluble film, water-soluble fiber, and barrier packaging material

Abstract

This modified polyvinyl alcohol polymer has a vinyl alcohol unit and a structural unit represented by formula (1). The distribution of the modification rate of the structural unit represented by (1) with respect to 100 mol% of all structural units in the modified polyvinyl alcohol polymer is 0.5 mol% or less.

Description

Modified polyvinyl alcohol polymer, water-soluble film, water-soluble fiber, and barrier packaging material

[0001] The present invention relates to a modified polyvinyl alcohol polymer, a water-soluble film, a water-soluble fiber, and a barrier packaging material.

[0002] Vinyl alcohol polymers are one of the few crystalline, water-soluble polymers. Taking advantage of their excellent water solubility and film properties (strength, oil resistance, film-forming ability, oxygen gas barrier properties, etc.), vinyl alcohol polymers are widely used in emulsifiers, suspending agents, surfactants, fiber processing agents, various binders, paper processing agents, adhesives, films, etc. Except in special cases, vinyl alcohol polymers are used in the form of an aqueous solution, which can have difficulties in handling. For example, after being prepared as an aqueous solution, the viscosity of the solution increases over time, particularly in winter when the water temperature is low, reducing its fluidity. In extreme cases, the fluidity may be lost due to gelation. Furthermore, foaming may occur during agitation when preparing the aqueous solution, and the resulting foam may be difficult to eliminate, i.e., the foam may not dissipate easily.

[0003] As a method for improving the viscosity stability of a vinyl alcohol polymer aqueous solution, a method of introducing a hydrophobic group or an ionic group into the vinyl alcohol polymer is known. However, the method of introducing a hydrophobic group reduces the solubility of the vinyl alcohol polymer in water, which may require a high temperature for preparing the aqueous solution or lower the cloud point of the prepared aqueous solution. The method of introducing an ionic group may reduce the water resistance of the formed film.

[0004] Patent Document 1 discloses a vinyl alcohol polymer having a hydroxyalkyl group in the side chain that suppresses foaming in an aqueous solution. However, there is a problem that the viscosity stability of the aqueous solution at low temperatures is still not satisfactory. Patent Documents 2 and 3 disclose vinyl alcohol polymers having a 1,2-glycol bond in the side chain that improve the viscosity stability of the aqueous solution. However, there is a problem that the film properties of these polymers deteriorate under high humidity conditions due to their hygroscopicity.

[0005] Furthermore, the polymer described in Patent Document 3 is produced using an unsaturated monomer such as 3,4-diacetoxy-1-butene as a modified species. However, from the viewpoint of copolymerizability ratio, the unsaturated monomer used for modification does not selectively polymerize in the modified species. Therefore, unless the polymerization is driven to a high polymerization rate, the unsaturated monomer used for modification remains even after polymerization, resulting in an increase in waste and a problem in terms of production costs.

[0006] In order to solve the above problems, a hydroxymethyl group-containing vinyl alcohol polymer has been developed which has excellent solubility in water, excellent viscosity stability of an aqueous solution, little foaming of the aqueous solution, and excellent film properties under high humidity (see, for example, Patent Document 4).

[0007] However, no modified polyvinyl alcohol polymer with sufficiently improved solvent resistance has been obtained.

[0008] Japanese Patent Laid-Open No. 8-319318 Japanese Patent Laid-Open No. 2002-284818 Japanese Patent Laid-Open No. 2004-285143 Japanese Patent Laid-Open No. 2013-177576

[0009] An object of the present invention is to provide a modified polyvinyl alcohol-based polymer having improved solvent resistance, a water-soluble film containing the modified polyvinyl alcohol-based polymer, a water-soluble fiber containing the modified polyvinyl alcohol-based polymer, and a barrier packaging material containing the modified polyvinyl alcohol-based polymer.

[0010] As a result of extensive investigations, the present inventors have found that a modified polyvinyl alcohol-based polymer having vinyl alcohol units and structural units represented by the following formula (1) can have a modification rate distribution of 0.50 mol % or less relative to 100 mol % of all structural units in a modified polyvinyl alcohol-based polymer, and have completed the present invention. More specifically, allyl type monomers typically have a reactivity ratio with vinyl acetate (r ＶＡｃ ) and the reactivity ratio of the comonomer (r ＣＯＭ) are roughly the same value, and the feed ratio of vinyl acetate to allyl type monomers is often the same as the composition ratio of vinyl acetate to allyl type monomers in the polymer. However, although 2-methylene-1,3-propanediol diacetate (MPDAc) is an allyl type monomer, the reactivity ratio with vinyl acetate (r ＶＡｃ ) and the reactivity ratio of the comonomer (r ＣＯＭ ), the composition ratio of vinyl acetate to 2-methylene-1,3-propanediol diacetate (MPDAc) in the polymer is significantly different from that of vinyl acetate. Therefore, the present inventors have found that by adding 2-methylene-1,3-propanediol diacetate (MPDAc) using the "dropping polymerization method" rather than the "lump addition method," it is possible to adjust the composition ratio of vinyl acetate to 2-methylene-1,3-propanediol diacetate (MPDAc) in the polymer to a desired value for the first time, and have completed the present invention.

[0011] That is, the present invention includes the following items [1] to [8]: [1] A modified polyvinyl alcohol-based polymer having vinyl alcohol units and structural units represented by the following formula (1), wherein the distribution of the modification rate of the structural units represented by the following formula (1) relative to 100 mol % of all structural units in the modified polyvinyl alcohol-based polymer is 0.5 mol % or less. [2] The modified polyvinyl alcohol-based polymer according to [1] above, wherein the modification rate of the structural unit represented by formula (1) relative to 100 mol% of all structural units in the modified polyvinyl alcohol-based polymer is 0.1 to 40.0 mol%. [3] The modified polyvinyl alcohol-based polymer according to [2] above, wherein the modification rate of the structural unit represented by formula (1) relative to 100 mol% of all structural units in the modified polyvinyl alcohol-based polymer is 0.8 to 10.0 mol%. [4] The modified polyvinyl alcohol-based polymer according to any of [1] to [3] above, wherein the saponification degree is 80.0 to 99.7 mol%. [5] A method for producing the modified polyvinyl alcohol-based polymer according to any of [1] to [4] above, comprising copolymerizing a vinyl ester-based monomer and 2-methylene-1,3-propanediol diacetate by dropwise polymerization and saponifying the resulting vinyl ester-based copolymer to produce the modified polyvinyl alcohol-based polymer. [6] A water-soluble film comprising the modified polyvinyl alcohol-based polymer according to any one of [1] to [4] above. [7] A water-soluble fiber comprising the modified polyvinyl alcohol-based polymer according to any one of [1] to [4] above. [8] A barrier packaging material comprising the modified polyvinyl alcohol-based polymer according to any one of [1] to [4] above.

[0012] According to the present invention, it is possible to provide a modified polyvinyl alcohol-based polymer having improved solvent resistance, a water-soluble film containing the modified polyvinyl alcohol-based polymer, a water-soluble fiber containing the modified polyvinyl alcohol-based polymer, and a barrier packaging material containing the modified polyvinyl alcohol-based polymer.

[0013] The following describes an embodiment of the present invention. However, the embodiment described below is merely an example for embodying the technical concept of the present invention, and the present invention is not limited to the following description. In this specification, preferred embodiments are shown, but a combination of two or more of the individual preferred embodiments is also a preferred embodiment. For matters indicated as numerical ranges, when there are several numerical ranges, the lower and upper limits can be selectively combined to form a preferred embodiment. In this specification, when a numerical range is described as "XX to YY," it means "XX or more and YY or less." In this specification, "structural unit" means "a repeating unit constituting a polymer." In this specification, "room temperature" means 20 to 25°C. In this specification, "degree of polymerization" means the number-average degree of polymerization measured by size exclusion chromatography (SEC).

[0014] [Modified Polyvinyl Alcohol Polymer] The modified polyvinyl alcohol polymer of the present invention has a vinyl alcohol unit and a structural unit represented by the following formula (1), and may further have other structural units, if necessary.

[0015] The arrangement order of the structural unit represented by formula (1), the vinyl alcohol unit, and any other structural unit in the modified polyvinyl alcohol polymer of the present invention is not particularly limited, and may be random, block, alternating, or the like.

[0016] The total of the vinyl alcohol units and the structural units represented by formula (1) relative to 100 mol% of all structural units in the modified polyvinyl alcohol-based polymer is not particularly limited, but is preferably 70 mol% or more, more preferably 80 mol% or more, particularly preferably 90 mol% or more, and may be 100 mol%. The total of the vinyl alcohol units and the structural units represented by formula (1) relative to 100 mol% of all structural units in the modified polyvinyl alcohol-based polymer is １ It can be measured by H-NMR.

[0017] <Structural Unit Represented by Formula (1)> The modified polyvinyl alcohol polymer of the present invention has the structural unit represented by formula (1) (i.e., a structure having a 1,3-diol structure in the main chain of the polymer), which reduces the crystallinity of the modified polyvinyl alcohol polymer and improves handleability such as solubility and viscosity stability. Furthermore, when the modified polyvinyl alcohol polymer of the present invention is processed into a film, the high hydrogen bonding strength of the 1,3-diol structure can reduce a decrease in film strength due to a decrease in crystallinity, and the film can maintain its toughness even under high humidity.

[0018] <<Modification Rate of Structural Unit Represented by Formula (1)>> The modification rate (content) of the structural unit represented by formula (1) relative to 100 mol% of all structural units in the modified polyvinyl alcohol-based polymer is not particularly limited, but from the viewpoint of cold water solubility, it is preferably 0.1 mol% or more, more preferably 0.8 mol% or more, and particularly preferably 2.0 mol% or more, while from the viewpoint of biodegradability, it is preferably 40.0 mol% or less, more preferably 20.0 mol% or less, even more preferably 15.0 mol% or less, even more preferably 10.0 mol% or less, and particularly preferably 9.0 mol% or less. The modification rate of the structural unit represented by formula (1) relative to 100 mol% of all structural units in the modified polyvinyl alcohol-based polymer can be measured by the method used in the examples described later.

[0019] <<Distribution of Modification Rate of Structural Unit Represented by Formula (1)>> The distribution of the modification rate of the structural unit represented by formula (1) relative to 100 mol% of all structural units in the modified polyvinyl alcohol-based polymer is not particularly limited as long as it is 0.5 mol% or less. From the viewpoint of solvent resistance, it is preferably 0.4 mol% or less, more preferably 0.3 mol% or less, even more preferably 0.2 mol% or less, particularly preferably 0.1 mol% or less, and most preferably 0.0 mol%. The distribution of the modification rate of the structural unit represented by formula (1) relative to 100 mol% of all structural units in the modified polyvinyl alcohol-based polymer can be measured by the method used in the examples described below. When the modification rate distribution is 0.5 mol% or less, the amount of components that swell excessively in a solvent is reduced, resulting in a lower overall swelling degree, thereby improving solvent resistance. By adding an "unsaturated monomer that can be converted into a structural unit represented by formula (1)" described below, such as 2-methylene-1,3-propanediol diacetate (MPDAc), using the "dropping polymerization method" rather than the "lump addition method," the distribution of the modification rate can be set to 0.5 mol% or less.

[0020] <Saponification degree of modified polyvinyl alcohol polymer> The saponification degree of the modified polyvinyl alcohol polymer is not particularly limited, but from the viewpoint of biodegradability, it is preferably 80.0 mol% or more, more preferably 82.0 mol% or more, and particularly preferably 85.0 mol% or more, and from the viewpoint of cold water solubility, it is preferably 99.7 mol% or less, more preferably 99.5 mol% or less, and particularly preferably 99.2 mol% or less. The saponification degree of the modified polyvinyl alcohol polymer refers to the degree to which the vinyl alcohol units (-CH ) contained in the modified polyvinyl alcohol polymer have been converted by saponification. ２ The degree of saponification is the ratio (mol %) of the number of moles of vinyl alcohol units to the total number of moles of structural units (typically vinyl ester units) that can be converted to —CH(OH)— and vinyl alcohol units (i.e., the molar fraction of hydroxyl groups to the total of hydroxyl groups and ester bonds in the modified polyvinyl alcohol-based polymer). The degree of saponification is determined by taking into account the amount of the structural unit represented by formula (1) and its derivatives. １It can be measured by H-NMR, more specifically, by the method used in the examples described below.

[0021] The modified polyvinyl alcohol polymer can be obtained by saponifying a vinyl ester copolymer, and the saponification of the vinyl ester copolymer is carried out, for example, in a state where the vinyl ester copolymer is dissolved in alcohol or aqueous alcohol.

[0022] The alcohol used for saponification is not particularly limited, and examples thereof include lower alcohols such as methanol and ethanol. These may be used alone or in combination of two or more. Among these, methanol is preferred from an economical viewpoint.

[0023] The alcohol used for saponification may contain other solvents such as acetone, methyl acetate, ethyl acetate, benzene, etc., as long as the amount of the other solvents is 40% by mass or less of the mass of the alcohol.

[0024] Examples of catalysts used for saponification include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide; alkali catalysts such as sodium methylate; and acid catalysts such as mineral acids. These may be used alone or in combination of two or more. Among these, sodium methoxide is preferred from an economical viewpoint.

[0025] The temperature at which the saponification is carried out is not particularly limited, but is preferably in the range of 20 to 60°C. If a gel-like product precipitates as the saponification proceeds, the product can be pulverized, washed, and dried to obtain a modified polyvinyl alcohol polymer. The saponification method is not limited to the above-mentioned method, and known methods can be used.

[0026] <Degree of polymerization of modified polyvinyl alcohol polymer> The degree of polymerization of the modified polyvinyl alcohol polymer of the present invention is not particularly limited, but from the viewpoint of film strength, it is preferably 100 or more, more preferably 200 or more, and particularly preferably 300 or more, and from the viewpoint of industrial production, it is preferably 7,000 or less, more preferably 5,000 or less, and particularly preferably 4,000 or less. The degree of polymerization of the modified polyvinyl alcohol polymer can be measured by the method used in the examples described later.

[0027] <Other Structural Units> The modified polyvinyl alcohol polymer of the present invention may further contain structural units other than the structural unit represented by formula (1), the vinyl alcohol unit, and the vinyl ester unit, as long as the effects of the present invention are obtained. The other structural units are not particularly limited, and examples thereof include structural units derived from ethylenically unsaturated monomers copolymerizable with vinyl esters. The modified polyvinyl alcohol polymer of the present invention may also contain structural units derived from unsaturated monomers copolymerizable with vinyl ester monomers and convertible into the structural unit represented by formula (1) (structural units that were not converted into the structural unit represented by formula (1) by saponification). The total proportion of the structural unit represented by formula (1), the vinyl alcohol unit, and the vinyl ester unit in the modified polyvinyl alcohol polymer is not particularly limited, but is preferably 80 mol% or more, more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may even be 99 mol% or more, based on 100 mol% of the total number of moles of all structural units constituting the modified polyvinyl alcohol polymer.The ethylenically unsaturated monomer is not particularly limited, and examples thereof include α-olefins such as ethylene, propylene, n-butene, isobutylene, and 1-hexene; acrylic acid and its salts; unsaturated monomers having an acrylic ester group; methacrylic acid and its salts; unsaturated monomers having a methacrylic ester group; acrylamide derivatives such as acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid and its salts; acrylamidopropyldimethylamine and its salts (e.g., quaternary salts); methacrylamide; methacrylamido derivatives such as N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid and its salts; and methacrylamidepropyldimethylamine and its salts (e.g., quaternary salts). vinyl amide derivatives; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, and 2,3-diacetoxy-1-vinyloxypropane; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinyl halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane and allyl chloride; unsaturated dicarboxylic acids and salts or esters thereof such as maleic acid, itaconic acid, and fumaric acid; vinyl silyl compounds such as vinyltrimethoxysilane; isopropenyl acetate; etc. These may be used alone or in combination of two or more.

[0028] <Other Components> The modified polyvinyl alcohol polymer of the present invention can be further blended with additives such as fillers, processing stabilizers such as copper compounds, weathering stabilizers, colorants, ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, plasticizers, other thermoplastic resins, lubricants, fragrances, antifoaming agents, deodorizers, extenders, release agents, mold release agents, reinforcing agents, crosslinking agents, fungicides, preservatives, and crystallization rate retarders, as needed, to prepare a polymer composition containing the modified polyvinyl alcohol polymer of the present invention. These additives may be used alone or in combination of two or more.

[0029] The modified polyvinyl alcohol polymer of the present invention can be used, by utilizing its properties, alone or as a polymer composition with other components added thereto, in various applications in which vinyl alcohol polymers are used, by known methods such as molding, spinning, emulsification, etc. The modified polyvinyl alcohol polymer of the present invention can be used, for example, in the following applications: (1) Adhesives: Adhesives for wood, paper, aluminum foil, plastics, etc., pressure-sensitive adhesives, rewetting agents, binders for nonwoven fabrics, binders for various building materials such as gypsum board and fiberboard, binders for various powder granulations, battery binders, additives for cement and mortar, hot-melt adhesives, pressure-sensitive adhesives, fixing agents for anionic paints, adhesives for polarizing plates, water-based vinyl adhesives, honeymoon adhesives, etc. (2) Molded products: Fibers, long-fiber nonwoven fabrics, composite fibers, films for hollow fibers (especially water-soluble films for packaging agricultural chemicals, detergents, laundry clothes, civil engineering additives, disinfectants, dyes, pigments, etc.), water-soluble fibers, water-soluble materials for composite fibers (hollow fibers), barrier packaging materials (biodegradable barrier materials for coffee capsules, etc., barrier packaging materials, etc.), support materials for 3D printers, masking materials, temporary protective materials, sanitary products such as napkins and disposable diapers, waste disposal products such as ostomy bags, medical products such as blood-absorbing sheets, seedling raising sheets, high-pressure gas transfer hoses, etc. (3) Coating Agents: Paper clear coating agents, paper pigment coating agents, paper sizing agents, textile sizing agents, warp sizing agents, textile processing agents, leather finishing agents, paints, anti-fogging agents, metal corrosion inhibitors, zinc plating brighteners, antistatic agents, conductive agents, temporary paints, etc. (4) Emulsifiers: Emulsifiers for emulsion polymerization of ethylenically unsaturated compounds, butadiene compounds, and various acrylic monomers, post-emulsifiers for hydrophobic resins such as polyolefins and polyester resins, epoxy resins, paraffin, and bitumen, etc. (5) Suspension Agents: Pigment dispersion stabilizers for paints, India ink, water-based colors, and adhesives, dispersion stabilizers for suspension polymerization of various vinyl compounds such as vinyl chloride, vinylidene chloride, styrene, (meth)acrylate, and vinyl acetate, etc. (6) Thickeners: Thickeners for various aqueous solutions and emulsions, etc. (7) Resin Raw Materials: Raw materials for polyvinyl acetal resins, raw materials for photosensitive resins, etc.(8) Others: Flocculants for suspended and dissolved matter in water, drainage aids for pulp and slurry, soil conditioners, ion exchange resins, ion exchange membranes, surfactants, textile processing agents, drilling fluid conditioners, diverting agents, etc.

[0030] The molding method for molding the polyvinyl alcohol polymer of the present invention or a polymer composition containing other components is not particularly limited, and examples thereof include a method of molding from a solution state in which the polymer is dissolved in a solvent such as water or dimethyl sulfoxide (e.g., cast molding), a method of plasticizing the polymer by heating and molding (e.g., extrusion molding, injection molding, inflation molding, press molding, blow molding), etc. By these molding methods, molded articles having any shape such as films, sheets, tubes, bottles, etc. can be obtained.

[0031] The polyvinyl alcohol-based polymer of the present invention has high film strength even under high humidity conditions, and is therefore particularly suitable for use as an internal additive for paper and various water-soluble binders. In addition, since the solubility of the vinyl alcohol-based polymer in water affects the simplification of the process for use in these applications, the high water solubility of the polyvinyl alcohol-based polymer of the present invention is advantageous and useful.

[0032] [Method for Producing Modified Polyvinyl Alcohol-Based Polymer] The method for producing the modified polyvinyl alcohol-based polymer of the present invention is not particularly limited, and examples thereof include a method of copolymerizing a vinyl ester-based monomer with an unsaturated monomer copolymerizable therewith and convertible into a structural unit represented by formula (1), converting the vinyl ester units of the obtained vinyl ester-based copolymer into vinyl alcohol units, and converting the units derived from the unsaturated monomer convertible into a structural unit represented by formula (1) into the structural unit represented by formula (1).

[0033] <Unsaturated Monomers Convertible to Structural Units Represented by Formula (1)> A specific example of an unsaturated monomer convertible to a structural unit represented by formula (1) is represented by the following formula (2).

[0034] In formula (2), R represents an alkyl group having 1 to 10 carbon atoms, preferably an alkyl group having 1 to 5 carbon atoms. Specific examples of the alkyl group having 1 to 5 carbon atoms include linear or branched alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, and pentyl. Substituents that R may have include alkoxy groups, halogen atoms, and hydroxyl groups. Multiple R may be the same or different. The structure of R is not particularly limited, and it may have a branched or cyclic structure in part, or may be substituted in part with another functional group.

[0035] Examples of the unsaturated monomer represented by formula (2) include hydroxymethylvinylidene diacetate, and specific examples include 2-methylene-1,3-propanediol diacetate (1,3-diacetoxy-2-methylenepropane), 1,3-dipropionyloxy-2-methylenepropane, and 1,3-dibutyronyloxy-2-methylenepropane. These may be used alone or in combination of two or more. Among these, 2-methylene-1,3-propanediol diacetate (1,3-diacetoxy-2-methylenepropane) is preferred from the viewpoint of ease of production.

[0036] The unsaturated monomer represented by formula (2) generally undergoes a copolymerization reaction with a vinyl ester monomer more easily than other allylic unsaturated monomers (e.g., allyl glycidyl ether) used in modifying polyvinyl alcohol polymers. Therefore, the modified polyvinyl alcohol polymer of the present invention is less restricted in the modification rate and polymerization degree during polymerization, and can achieve a high modification rate and polymerization degree. Furthermore, since the amount of unreacted unsaturated monomer remaining at the end of polymerization can be reduced, the modified polyvinyl alcohol polymer of the present invention is also excellent in terms of the environment and cost during industrial production.

[0037] The vinyl ester monomer used in producing the modified polyvinyl alcohol polymer of the present invention is not particularly limited, and examples thereof include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, and vinyl benzoate. These may be used alone or in combination of two or more. Among these, vinyl acetate is preferred from an economical viewpoint.

[0038] <Polymerization method> The polymerization method when copolymerizing the unsaturated monomer represented by formula (2) with the vinyl ester-based monomer is not particularly limited, and may be, for example, any of batch polymerization, semi-batch polymerization, continuous polymerization, semi-continuous polymerization, etc., and known methods such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc. can be applied as the polymerization method. Bulk polymerization or solution polymerization, in which polymerization proceeds without a solvent or in a solvent such as alcohol, is usually used. When obtaining a vinyl ester-based copolymer with a high degree of polymerization, emulsion polymerization is preferred.

[0039] The solvent for the solution polymerization method is not particularly limited, and examples thereof include lower alcohols such as methanol, ethanol, and propanol. These may be used alone or in combination of two or more. Among these, methanol is preferred from an economical viewpoint.

[0040] The amount of solvent used in the polymerization system may be selected in consideration of chain transfer of the solvent depending on the polymerization degree of the target modified polyvinyl alcohol-based polymer. For example, when the solvent is methanol, the mass ratio of the solvent to the total monomers contained in the polymerization system {= (solvent) / (total monomers)} is preferably selected within the range of 0.01 to 10, more preferably within the range of 0.02 to 5, and particularly preferably within the range of 0.05 to 3.

[0041] <Polymerization initiator> The polymerization initiator used for copolymerization of the unsaturated monomer represented by formula (2) and the vinyl ester monomer is not particularly limited, and examples thereof include known polymerization initiators selected from azo initiators, peroxide initiators, and redox initiators depending on the polymerization method. These may be used alone or in combination of two or more.

[0042] <<Azo Initiator>> The azo initiator is not particularly limited, and examples thereof include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), etc. These may be used alone or in combination of two or more.

[0043] <<Peroxide Initiator>> The peroxide initiator is not particularly limited, and examples thereof include percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; perester compounds such as t-butyl peroxyneodecanate and α-cumyl peroxyneodecanate; acetylcyclohexylsulfonyl peroxide; 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate; and acetyl peroxide. These may be used alone or in combination with two or more. Potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like may be combined with the above initiators to form a polymerization initiator.

[0044] <<Redox Initiator>> The redox initiator is not particularly limited, and examples thereof include polymerization initiators that combine the above-mentioned peroxide initiators with a reducing agent such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, Rongalit, etc. These may be used alone or in combination of two or more.

[0045] The amount of the polymerization initiator used is not particularly limited, but is appropriately selected depending on the polymerization catalyst and polymerization rate. For example, when 2,2'-azobisisobutyronitrile or acetyl peroxide is used as the polymerization initiator, the amount is preferably 0.01 to 0.20 mol %, more preferably 0.02 to 0.15 mol %, based on the vinyl ester monomer.

[0046] The polymerization temperature is not particularly limited, but is preferably from room temperature to about 150° C., more preferably 40° C. or higher and not higher than the boiling point of the solvent used.

[0047] The copolymerization of the unsaturated monomer represented by formula (2) and the vinyl ester monomer may be carried out in the presence of a chain transfer agent, as long as the effects of the present invention can be obtained.

[0048] The chain transfer agent is not particularly limited, and examples thereof include aldehydes such as acetaldehyde and propionaldehyde, ketones such as acetone and methyl ethyl ketone, mercaptans such as 2-hydroxyethanethiol, phosphinates such as sodium phosphinate hydrate, etc. These may be used alone or in combination of two or more.

[0049] The amount of the chain transfer agent to be added to the polymerization system can be determined depending on the chain transfer coefficient of the chain transfer agent to be added and the degree of polymerization of the desired modified polyvinyl alcohol polymer, and is not particularly limited, but is preferably 0.1 to 10 parts by mass per 100 parts by mass of the vinyl ester monomer.

[0050] The modified polyvinyl alcohol polymer of the present invention can be obtained by saponifying a vinyl ester copolymer obtained by copolymerizing an unsaturated monomer represented by formula (2) with a vinyl ester monomer. By saponifying the vinyl ester copolymer, the vinyl ester units in the vinyl ester copolymer are converted into vinyl alcohol units. Furthermore, the ester bonds of the structural units derived from the unsaturated monomer represented by formula (2) are also saponified, converting them into structural units having a 1,3-diol structure represented by formula (1). Therefore, the modified polyvinyl alcohol polymer of the present invention can be produced without further reactions such as hydrolysis after saponification.

[0051] A preferred example of the method for producing the modified polyvinyl alcohol polymer of the present invention includes a method in which a vinyl ester monomer and 2-methylene-1,3-propanediol diacetate (1,3-diacetoxy-2-methylenepropane) are copolymerized by dropwise polymerization, and the resulting vinyl ester copolymer is saponified to produce the modified polyvinyl alcohol polymer.

[0052] [Water-soluble film] The water-soluble film of the present invention contains the modified polyvinyl alcohol-based polymer of the present invention. Taking advantage of its excellent water solubility, the modified polyvinyl alcohol-based polymer of the present invention can be suitably used for various water-soluble film applications.

[0053] The water-soluble film of the present invention has improved water solubility because the modified polyvinyl alcohol polymer contained therein contains a structural unit having a 1,3-diol structure represented by the above formula (1). Although this does not limit the present invention in any way, it is thought that the reason for the above advantages is that the structural unit represented by formula (1) reduces crystallinity, etc.

[0054] The content of the modified polyvinyl alcohol-based polymer of the present invention in the water-soluble film of the present invention is not particularly limited, but from the viewpoint of the mechanical properties of the film, it is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more, while from the viewpoint of water solubility, it is preferably 100% by mass or less, more preferably 95% by mass or less, and particularly preferably 90% by mass or less.

[0055] The water-soluble film of the present invention can contain a plasticizer in addition to the modified polyvinyl alcohol-based polymer of the present invention. The plasticizer is not particularly limited, and polyhydric alcohols are preferred. Specific examples of the plasticizer are not particularly limited, and include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. These may be used alone or in combination of two or more. Among these, glycerin is preferred from an economical viewpoint.

[0056] The content of the plasticizer in the water-soluble film of the present invention is not particularly limited, but is preferably 50 parts by mass or less, more preferably 45 parts by mass or less, and particularly preferably 40 parts by mass or less, relative to 100 parts by mass of the modified polyvinyl alcohol-based polymer in the water-soluble film. By making the content 50 parts by mass or less, it is possible to prevent the film from becoming too flexible and reducing handleability.

[0057] Furthermore, the water-soluble film of the present invention may contain starch and / or other water-soluble polymers for the purposes of imparting mechanical strength, maintaining moisture resistance when handling the water-soluble film, or adjusting the speed of softening due to water absorption when dissolving the water-soluble film and the time required for diffusion in water.

[0058] The starch is not particularly limited, and examples thereof include natural starches such as corn starch, potato starch, sweet potato starch, wheat starch, rice starch, tapioca starch, and sago starch; processed starches that have been subjected to etherification processing, esterification processing, oxidation processing, etc. These may be used alone or in combination of two or more.

[0059] The starch content in the water-soluble film of the present invention is not particularly limited, but is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, per 100 parts by mass of the modified polyvinyl alcohol-based polymer in the water-soluble film. When the starch content in the water-soluble film of the present invention is 15 parts by mass or less, the impact resistance of the water-soluble film is improved, and processability is also improved.

[0060] The other water-soluble polymers are not particularly limited and include, for example, dextrin, gelatin, glue, casein, shellac, gum arabic, polyacrylic acid amide, sodium polyacrylate, polyvinyl methyl ether, a copolymer of methyl vinyl ether and maleic anhydride, a copolymer of vinyl acetate and itaconic acid, polyvinylpyrrolidone, cellulose, acetyl cellulose, acetyl butyl cellulose, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, sodium alginate, etc. These may be used alone or in combination of two or more.

[0061] The content of the other water-soluble polymer in the water-soluble film of the present invention is not particularly limited, but is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, relative to 100 parts by mass of the modified polyvinyl alcohol-based polymer in the water-soluble film. When the content of the other water-soluble polymer in the water-soluble film of the present invention is 15 parts by mass or less, the water solubility and dispersibility of the film are improved.

[0062] The water-soluble film of the present invention may further contain additives such as fillers, processing stabilizers such as copper compounds, weathering stabilizers, colorants, ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, other thermoplastic resins, lubricants, fragrances, antifoaming agents, deodorizers, extenders, peeling agents, release agents, reinforcing agents, crosslinking agents, mildew inhibitors, preservatives, and crystallization rate retarders, as needed.

[0063] The total proportion of the modified polyvinyl alcohol polymer, plasticizer, starch, and other water-soluble polymer in the water-soluble film of the present invention is not particularly limited, but is preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on the mass of the water-soluble film.

[0064] The thickness of the water-soluble film of the present invention is not particularly limited, but from the viewpoint of achieving both strength and water solubility, it is preferably 1 to 100 μm, more preferably 5 to 75 μm, and particularly preferably 10 to 60 μm.

[0065] The length and width of the water-soluble film of the present invention are not particularly limited, but from the viewpoint of productivity during processing, the length is preferably 1 m or more, more preferably 100 m or more, and particularly preferably 1,000 m or more, and the width is preferably 0.5 m or more, more preferably 0.8 m or more, and particularly preferably 1.0 m or more.

[0066] The method for producing the water-soluble film of the present invention is not particularly limited, and a production method that results in a more uniform thickness and width of the water-soluble film after film formation can be preferably used. For example, the water-soluble film can be produced using a film-forming solution in which a modified polyvinyl alcohol-based polymer constituting the water-soluble film, and optionally at least one of a plasticizer, starch, other water-soluble polymer, additive, and surfactant, is dissolved in a liquid medium; or a film-forming solution in which a modified polyvinyl alcohol-based polymer, and optionally at least one of a plasticizer, starch, other water-soluble polymer, additive, surfactant, and liquid medium, is dissolved, and the modified polyvinyl alcohol-based polymer is dissolved. When the film-forming solution contains at least one of a plasticizer, starch, other water-soluble polymer, additive, and surfactant, it is preferable that these components are uniformly mixed.

[0067] [Water-soluble fiber] The water-soluble fiber of the present invention includes the modified polyvinyl alcohol-based polymer of the present invention. Taking advantage of its excellent water solubility, the modified polyvinyl alcohol-based polymer of the present invention can be suitably used for various water-soluble fiber applications.

[0068] The content of the modified polyvinyl alcohol-based polymer of the present invention in the water-soluble fiber of the present invention is not particularly limited, but from the viewpoint of moldability, it is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more, while from the viewpoint of water solubility, it is preferably 100% by mass or less, more preferably 95% by mass or less, and particularly preferably 90% by mass or less.

[0069] [Barrier Packaging Material] The barrier packaging material of the present invention contains the modified polyvinyl alcohol-based polymer of the present invention. Here, the barrier packaging material preferably has home compostability (i.e., disintegrability and biodegradability), barrier properties, and melt moldability. Taking advantage of its excellent water solubility, the modified polyvinyl alcohol-based polymer of the present invention can be suitably used in various barrier packaging material applications.

[0070] The content of the modified polyvinyl alcohol polymer of the present invention in the barrier packaging material of the present invention is not particularly limited, but from the viewpoint of barrier properties, it is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more, while from the viewpoint of processability, it is preferably 100% by mass or less, more preferably 95% by mass or less, and particularly preferably 90% by mass or less.

[0071] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples and comparative examples, "%" and "parts" represent "% by mass" and "parts by mass", respectively, unless otherwise specified. The measurement methods and evaluation methods employed in the following examples and comparative examples are shown below.

[0072] [Primary structure of modified polyvinyl alcohol polymer (saponification degree, modification rate)] The primary structure of the modified polyvinyl alcohol polymer used in the following examples (saponification degree, modification rate) was １ Analysis was carried out using H-NMR. １ Deuterated DMSO was used as the solvent for H-NMR measurement.

[0073] [Method for measuring the distribution of modification rate] (1) 0.5 g of the modified polyvinyl alcohol polymer obtained in each Example or Comparative Example was dissolved in 5 mL of water, and then added to 20 mL of three types of solutions of ethanol / water with a mass ratio of 65 / 35, 70 / 30, and 77 / 23 to cause precipitation. (2) The precipitate was separated and dried, and then measured using a 270 MHz １ (3) The solution after separating the precipitate was dried to solidify the solution, and the dissolved components were recovered. １The modification rate (B mole %) was measured by H-NMR. (4) From the obtained values, (B-A) mole % was defined as the modification rate distribution, and the largest value among the measured values ​​obtained in the measurements performed with each of the three solvent compositions was adopted.

[0074] [Evaluation of Solvent Resistance] The swelling degree of an ethanol / water film was measured as an index of solvent resistance. A 10% by mass aqueous solution of a modified polyvinyl alcohol polymer was prepared, cast onto a PET film, and dried at 20°C for one week to obtain a 70 μm-thick polyvinyl alcohol resin film. The obtained film was cut into a 30 mm x 30 mm piece, added to 10 mL of an 80 / 20 (mass ratio) ethanol / water mixed solution, and held at 50°C for three hours before being removed. The mass A of the swollen film was measured. The film was then dried at 80°C for 24 hours, and the mass B of the bone-dry film was measured. The swelling degree was calculated according to the following formula. Since the swelling property in the above solvents is largely dependent on the content of unit structures other than vinyl alcohol units, the content of unit structures other than vinyl alcohol units was classified into the following cases and evaluated accordingly. In both cases, a lower swelling degree indicates higher solvent resistance. (1) When the content of unit structures other than vinyl alcohol is less than 10 mol%, A: The swelling degree is less than 150%. C: The swelling degree is 150% or more. (2) When the content of unit structures other than vinyl alcohol is 10 mol% or more but less than 20 mol%, A: The swelling degree is less than 200%. C: The swelling degree is 200% or more. (3) When the content of unit structures other than vinyl alcohol is 20 mol% or more, B: The swelling degree is less than 250%. C: The swelling degree is 250% or more.

[0075] [Evaluation of cold water solubility] A 10% by mass aqueous solution of a modified polyvinyl alcohol polymer was prepared, cast onto a PET film, and dried at 20°C for one week to obtain a 70 μm thick polyvinyl alcohol resin film. The obtained film was cut into 35 mm x 45 mm pieces and added to 500 mL of water at 10°C. The time until complete dissolution was measured and evaluated according to the following criteria: A: Complete dissolution time less than 500 seconds B: Complete dissolution time 500 to 2,000 seconds C: Complete dissolution time more than 2,000 seconds

[0076] [Evaluation of biodegradability] The modified vinyl alcohol polymer powder was crushed and classified (using a sieve with 300 μm openings) to make the particle size uniform, and the biodegradability was evaluated by a biodegradability test method in accordance with OECD 301B. The test conditions are shown below. The biodegradation rate (mass%) was calculated based on the theoretical oxygen demand calculated from the polymer composition. Apparatus: OXI TOP (manufactured by WTW) Sludge used: Return sludge from a general sewage treatment plant Test medium: 200 mL Sample concentration: Approximately 30 ppm (15 mg DOC / L) Sludge concentration: 30 mg / L Temperature: 22°C Duration: 28 days Biodegradation rate (mass%) = {(actual amount of oxygen consumed) / (theoretical oxygen demand)} x 100

[0077] [Evaluation of Barrier Properties] The oxygen transmission rate (OTR) is an index of oxygen gas barrier properties, and it can be said that the lower the OTR value, the higher the oxygen gas barrier properties. The unit of the OTR value is [cc / (m ２ ·day·atm)]. Specific measurements were carried out as follows. A 10% concentration aqueous solution of modified polyvinyl alcohol polymer was prepared, and this was applied to a 12 μm PET film using a variable applicator (manufactured by YOSHIMITSU), and dried at a drying temperature of 60°C for 1 hour to obtain a PET laminated film. The obtained film was cut into a 15 cm x 15 cm piece, and measured under conditions of 20% and 65% RH using an oxygen gas transmission rate measuring device OX-TRAN2 / 21 (manufactured by Mocon), and the oxygen transmission rate (OTR) of the film was calculated as F1 [cc / (m ２ ·day·atm)] was obtained. After the measurement, the film thickness T (μm) of the film was measured using an electromagnetic film thickness meter SAMAC-PRO manufactured by Sanko Electronics Laboratory Co., Ltd. Then, the OTR value A [cc. 20 μm / (m ２ A = F1 × T / 20 (1) When measuring the oxygen gas barrier property of the laminate, the measured OTR value of the entire laminate was calculated as F [cc / (m ２ ·day·atm)], and F1 is calculated from the following formula (2), and then, using formula (1), the value A [cc. 20 μm / (m ２The meaning of each symbol in the following formula (2) is as follows: OTR actual measurement value of the entire multilayer film: F [cc / (m ２ · day · atm)] · OTR of modified vinyl alcohol polymer layer: F1 [cc / (m ２ · day · atm)] · PET film OTR actual measurement value: F2 [cc / (m ２ ・day・atm)] (1 / F)=(1 / F1)+(1 / F2) (2)

[0078] (Example 1) A reaction vessel equipped with a reflux condenser, a stirrer, a nitrogen inlet, an initiator addition port, and a solution feed port was charged with 60 parts by mass of vinyl acetate, 25.5 parts by mass of 2-methylene-1,3-propanediol diacetate, and 0 parts by mass of methanol. The temperature was increased under a nitrogen stream while stirring, and the internal temperature was stabilized at 60 ° C., after which 0.15 parts by mass of 2,2'-azobisisobutyronitrile (0.13 mol% relative to vinyl acetate) was added to initiate polymerization. Thereafter, 18.3 parts by mass of a 50% by mass methanol solution of 2-methylene-1,3-propanediol diacetate was added dropwise at 2.6 parts by mass / h, and the reaction was continued for 7 hours until the conversion rate of vinyl acetate ("polymerization rate" in Table 1) reached 40 mol%. 0.43 parts by mass of sorbic acid was added as a polymerization inhibitor, and the polymerization was terminated. Subsequently, methanol was added and the unreacted vinyl acetate monomer was removed from the system by distillation at 40 ° C. to obtain a methanol solution of the copolymer. Next, the methanol solution was diluted with methanol to a concentration of 20% by mass, and while maintaining the solution temperature at 40 ° C., a 13% by mass methanol solution of sodium hydroxide was added at a ratio of 0.03 moles per mole of the total amount of vinyl acetate structural units and 2-methylene-1,3-propanediol diacetate structural units in the copolymer, and saponification was carried out. As the saponification proceeded, a saponified product precipitated, and a gel was formed about 7 minutes after addition. This was pulverized and left for 60 minutes at 40 ° C. to allow saponification to proceed, after which methyl acetate was added to neutralize the remaining alkali. After confirming the completion of neutralization using a phenolphthalein indicator, the product was filtered to obtain a white solid, to which 25 parts by mass of methanol was added and heated under reflux for 1 hour. The washing procedure was repeated three times, and the resulting white solid was then centrifuged and dried in a vacuum dryer at 40°C for 24 hours to obtain a modified polyvinyl alcohol polymer. The saponification degree and modification rate of the resulting modified polyvinyl alcohol polymer were: １The degree of saponification was calculated by H NMR (solvent: deuterated DMSO) and the modification rate was 99.9 mol % and 30.5 mol %, respectively. The distribution of the modification rate was measured by the above-mentioned measurement method and found to be 0.3 mol %. The degree of polymerization was measured by the following polymerization degree measurement and found to be 500. The physical properties of the obtained modified polyvinyl alcohol polymer are shown in Table 2. (Number-average degree of polymerization) The number-average molecular weight (Mn) of the polymer was measured using a size-exclusion high-performance liquid chromatography apparatus "HLC-8320GPC" manufactured by Tosoh Corporation. The measurement conditions were as follows: Column: Two HFIP columns "GMHHR-H(S)" manufactured by Tosoh Corporation connected in series Standard sample: Polymethyl methacrylate Solvent and mobile phase: Sodium trifluoroacetate-HFIP solution (concentration 20 mM) Flow rate: 0.2 mL / min Temperature: 40°C Sample solution concentration: 0.1 mass% (filtered through a filter with an opening diameter of 0.45 μm) Injection volume: 10 μL Detector: RI The number-average degree of polymerization DPn of the polymer was calculated using the following formula: DPn = Mn × 100 / (44 × a + 88 × b) a: content (mol%) of polyvinyl alcohol unit b: content (mol%) of 2-methylene-1,3-propanediol

[0079] (Examples 2 to 7, Comparative Examples 1 and 2) Modified polyvinyl alcohol polymers were produced in the same manner as in Example 1, except that the polymerization conditions such as the charged amounts of vinyl acetate, methanol, and 2-methylene-1,3-propanediol diacetate, the feed rates, and the saponification conditions such as the concentration of modified PVAc during saponification and the molar ratio of sodium hydroxide to vinyl acetate units shown in Table 1 were changed as shown in Table 1. The physical properties of the obtained modified polyvinyl alcohol polymers are shown in Table 2.

[0080]

[0081]

[0082] As is clear from the above results (comparison between Examples 1 to 7 and Comparative Examples 1 and 2), solvent resistance can be improved by setting the distribution of the modification rate of the structural unit represented by the following formula (1) relative to 100 mol% of all structural units in the modified polyvinyl alcohol-based polymer to 0.5 mol% or less. Furthermore, as is clear from the above results (comparison between Examples 3 to 4 and 6 and Examples 1, 5, and 7), Examples 3 to 4 and 6 can improve biodegradability compared to Examples 1 and 5, which have a high modification rate, and can improve cold water solubility compared to Example 7, which has a low modification rate. Furthermore, as is clear from the above results (comparison between Examples 3 and 6 and Example 2), Examples 3 and 6 can improve cold water solubility compared to Example 2, which has a high degree of saponification.

[0083] According to the present invention, a modified polyvinyl alcohol-based polymer with improved solvent resistance can be provided. The modified polyvinyl alcohol-based polymer of the present invention can be used, for example, as a water-soluble film, a water-soluble fiber, a water-soluble nonwoven fabric, a barrier packaging material (biodegradable barrier materials for coffee capsules, etc., barrier packaging materials, etc.), a support material for 3D printers, a masking material, a temporary protective material, a binder, an adhesive, a dispersion stabilizer, etc. Note that the masking material and the temporary protective material may be used as a masking material by applying an aqueous solution and drying it, and then washed away with water.

Claims

1. A modified polyvinyl alcohol-based polymer having vinyl alcohol units and a structural unit represented by the following formula (1), wherein the distribution of the modification rate of the structural unit represented by the following formula (1) relative to 100 mol % of all structural units in the modified polyvinyl alcohol-based polymer is 0.5 mol % or less.

2. The modified polyvinyl alcohol-based polymer according to claim 1, wherein the modification rate of the structural unit represented by formula (1) is 0.1 to 40.0 mol % relative to 100 mol % of all structural units in the modified polyvinyl alcohol-based polymer.

3. The modified polyvinyl alcohol-based polymer according to claim 2, wherein the modification rate of the structural unit represented by formula (1) is 0.8 to 10.0 mol % relative to 100 mol % of all structural units in the modified polyvinyl alcohol-based polymer.

4. The modified polyvinyl alcohol polymer according to any one of claims 1 to 3, having a degree of saponification of 80.0 to 99.7 mol %.

5. A method for producing a modified polyvinyl alcohol polymer according to any one of claims 1 to 3, comprising copolymerizing a vinyl ester monomer with 2-methylene-1,3-propanediol diacetate by dropwise polymerization, and saponifying the resulting vinyl ester copolymer to produce the modified polyvinyl alcohol polymer.

6. A water-soluble film comprising the modified polyvinyl alcohol polymer according to any one of claims 1 to 3.

7. A water-soluble fiber comprising the modified polyvinyl alcohol polymer according to any one of claims 1 to 3.

8. A barrier packaging material comprising the modified polyvinyl alcohol polymer according to any one of claims 1 to 3.

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