Poly(vinyl alcohol)-based resin film, optical film, water-soluble film, and poly(vinyl alcohol)-based resin composition

Abstract

Provided is a poly(vinyl alcohol)-based resin film which, when produced using a dissolution can, an extruder, a die, a metallic roll, a belt, etc., is less apt to cause corrosional deterioration of these, thereby bringing about excellent production efficiency and maintainability.　This poly(vinyl alcohol)-based resin film includes a poly(vinyl alcohol)-based resin (A), and has a C14 value in terms of pMC, as determined by ASTM D6866 (method B), of 9-50.

Description

Polyvinyl alcohol-based resin film, optical film, water-soluble film, and polyvinyl alcohol-based resin composition

[0001] The present invention relates to a polyvinyl alcohol-based resin film, an optical film, a water-soluble film, and a polyvinyl alcohol-based resin composition.

[0002] Polyvinyl alcohol resins have traditionally been applied in a wide range of fields due to their excellent properties and diverse quality, and are excellent in gas barrier properties, mechanical strength, transparency, gloss, water solubility, etc., and are used in a wide range of fields, such as optical film applications, packaging for food and healthcare applications, medical infusion bags, packaging for various pharmaceuticals such as liquid detergents and pesticides, seed tapes for encapsulating seeds, etc. Films using these polyvinyl alcohol resins are manufactured by dissolving the polyvinyl alcohol resin in a solvent such as water to prepare a stock solution, then forming a film using a casting mold such as a metal roll or belt by a solution casting method (casting method), and drying using a metal heating roll, floating dryer, etc.

[0003] On the other hand, the stock solutions of these polyvinyl alcohol-based resins in water or the like generally exhibit weak acidity. Therefore, in the melt casting of polyvinyl alcohol-based resins, there is a problem that the metal materials used in the melting can, extruder, die, metal rolls, belts, etc. used in the molding process are susceptible to corrosion. Conventionally, in these various devices, the surfaces of the metal materials have been plated or the like to reduce corrosion degradation (see, for example, Patent Documents 1 to 4).

[0004] JP 1-28396 A JP 2012-21174 A JP 2014-46672 A JP 2014-148754 A

[0005] However, the pH of polyvinyl alcohol-based resins tends to decrease further due to long-term residence under high-temperature conditions during molding, and although the above-mentioned plating technology has improved corrosion degradation to some extent, it is not possible to completely prevent corrosion degradation from a long-term perspective, and melting cans, extruders, die molds, metal rolls and belts, etc., require repairs such as re-plating after a certain period of use. The cost and time required for these repairs have a significant impact on production efficiency, so there is a need to extend the period until these repairs are required as much as possible. By suppressing the pH decrease of the polyvinyl alcohol-based resin, which serves as the base resin, during molding, it is possible to extend the period until the above-mentioned various equipment and devices require repair, thereby improving production efficiency and maintainability.

[0006] Therefore, under such circumstances, the present invention provides a polyvinyl alcohol-based resin film and a polyvinyl alcohol-based resin composition that suppress corrosion and deterioration of a melting can, an extruder, a die, a metal roll, a belt, etc., which are used in producing a polyvinyl alcohol-based resin film, and that are excellent in production efficiency and maintainability.

[0007] However, the present inventors have conducted extensive research in light of these circumstances, and have found that, when a polyvinyl alcohol-based resin film is produced, the use of a polyvinyl alcohol-based resin film having a C14 pMC value of 9 to 50 as measured by ASTM D6866 (Method B) can be expected to reduce corrosion and deterioration of a melting can, an extruder, a die, a metal roll, a belt, etc. by suppressing a decrease in pH of the polyvinyl alcohol-based resin composition during the film-forming process.

[0008] That is, the present invention has the following aspects. [1] A polyvinyl alcohol-based resin film containing a polyvinyl alcohol-based resin (A), wherein the C14 pMC value measured by ASTM D6866 (Method B) is 9 to 50. [2] The polyvinyl alcohol-based resin film according to [1], wherein the polyvinyl alcohol-based resin (A) has a degree of saponification of 80 to 99.9 mol%. [3] The polyvinyl alcohol-based resin film according to [1] or [2], wherein the polyvinyl alcohol-based resin (A) has a weight-average molecular weight of 20,000 to 150,000. [4] The polyvinyl alcohol-based resin film according to any one of [1] to [3], which contains a plasticizer (B). [5] The polyvinyl alcohol-based resin film according to [4], wherein the content of the plasticizer (B) is 1 to 45 parts by mass per 100 parts by mass of the polyvinyl alcohol-based resin (A). [6] The polyvinyl alcohol-based resin film according to any one of [1] to [5], having a thickness of 10 to 130 μm. [7] The polyvinyl alcohol-based resin film according to any one of [1] to [6], which is used for producing a polarizing film. [8] An optical film, in which the polyvinyl alcohol-based resin film according to any one of [1] to [7] is used. [9] The optical film according to [8], in which the optical film is a polarizing film.

[10] A water-soluble film, in which the polyvinyl alcohol-based resin film according to any one of [1] to [6] is used.

[11] A polyvinyl alcohol-based resin composition containing at least a polyvinyl alcohol-based resin (A) and having a C14 pMC value of 9 to 50 as measured according to ASTM D6866 (Method B).

[12] The polyvinyl alcohol-based resin composition according to

[11] , which contains a plasticizer (B).

[13] A polyvinyl alcohol-based resin film, in which the polyvinyl alcohol-based resin composition (A) according to

[11] or

[12] is used.

[0009] The polyvinyl alcohol-based resin film of the present invention is excellent in inhibiting corrosion and deterioration of various equipment and devices, such as melting cans, extruders, die molds, metal rolls and belts, during film production, and can extend the period until repairs are required for each equipment and device, thereby improving production efficiency and maintainability.

[0010] The present invention will be described in detail below, but the present invention is not limited to the following examples.

[0011] As used herein, "x and / or y (x and y are any configuration)" refers to at least one of x and y, and can mean three things: x only, y only, or x and y. In this specification, when "X to Y" (X and Y are any numbers) is used, unless otherwise specified, it also means "X or more and Y or less," as well as "preferably greater than X" or "preferably less than Y." In this specification, when "X or more" (X is any number) or "Y or less" (Y is any number) is used, it also means "preferably greater than X" or "preferably less than Y." For 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 herein, the upper or lower limit of the numerical range can also be replaced with the values ​​shown in the examples.

[0012] In this specification, the term "film" also includes "tape" and "sheet." In this specification, the term "main component" refers to a component that has a significant effect on the properties of the target object, and the content of the component is usually 50% by mass or more, preferably 55% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, and may be 100% by mass.

[0013] A polyvinyl alcohol-based resin film according to one embodiment of the present invention (hereinafter, may be referred to as "the present polyvinyl alcohol-based resin film") is a polyvinyl alcohol-based resin film having a C14 pMC value of 9 to 50 as measured according to ASTM D6866 (Method B).

[0014] The C14 pMC value of this polyvinyl alcohol-based resin film, as measured by ASTM D6866 (Method B), has an upper limit of 50 or less, preferably 48 or less, more preferably 46 or less, even more preferably 45 or less, and particularly preferably 44 or less. The lower limit of this value is preferably 9 or more, more preferably 15 or more, even more preferably 20 or more, and particularly preferably 25 or more. By setting the C14 pMC value within the above range, the decrease in pH of the polyvinyl alcohol-based resin composition during the film-forming process can be suppressed, reducing corrosion and deterioration of the melting can, extruder, die, metal roll, belt, etc., thereby allowing the film to be preferably used as a base film that can extend the period until repairs are required for each device and equipment. While the function of suppressing pH decrease is not clearly understood, it is presumed that the pH of the aqueous solution decreases due to the release of acetate groups contained in part of the polyvinyl alcohol-based resin. The pMC (percent modern carbon) of C14 is the relative concentration ratio of C14 in the measurement sample to the modern reference standard (NIST4990C) as specified in the biobased content testing standard ASTM D6866-20.

[0015] The polyvinyl alcohol-based resin film of the present invention is sufficient to contain at least a polyvinyl alcohol-based resin (A), and preferably contains a plasticizer (B) as other components. If necessary, it may contain a surfactant (C), starch (D), a water-soluble polymer (E) other than (A), and the like.

[0016] <Polyvinyl Alcohol Resin (A)> The polyvinyl alcohol resin (A) used in the present embodiment will be described.

[0017] The polyvinyl alcohol-based resin film is required to contain at least one "polyvinyl alcohol-based resin (A1) in which all or part of the carbon constituting the polyvinyl alcohol-based resin is derived from biological ethylene." In other words, the polyvinyl alcohol-based resin (A) used may be a "polyvinyl alcohol-based resin (A1) in which all or part of the carbon constituting the polyvinyl alcohol-based resin is derived from biological ethylene" alone, or a mixture of a "polyvinyl alcohol-based resin (A1) in which all or part of the carbon constituting the polyvinyl alcohol-based resin is derived from biological ethylene" and a "polyvinyl alcohol-based resin (A'1) obtained only from fossil fuel-derived raw materials."

[0018] There are no particular limitations on the method for obtaining such a "polyvinyl alcohol-based resin (A1) in which all or a part of the carbon constituting the polyvinyl alcohol-based resin is derived from biological ethylene." Examples include, for example, (1) a method in which only a biovinyl ester monomer obtained by polymerizing only bioethylene-derived biovinyl ester monomers is polymerized to obtain a polyvinyl ester; (2) a method in which a polyvinyl ester obtained by polymerizing a biovinyl ester monomer obtained by using a mixture of bioethylene and fossil fuel-derived ethylene as a raw material is saponified; (3) a method in which a polyvinyl ester obtained by copolymerizing a biovinyl ester monomer obtained by using bioethylene-derived biovinyl ester monomers and a vinyl ester monomer obtained by using fossil fuel-derived ethylene as a raw material is saponified; (4) a method in which a mixture of a polyvinyl ester obtained by polymerizing only biovinyl ester monomers obtained by using bioethylene-derived biovinyl ester monomers and a polyvinyl ester obtained by polymerizing only fossil fuel-derived vinyl ester monomers is saponified; and (5) a method in which the above methods (2) to (4) are combined. Among these methods, the method (1) or (2) is preferred in that it allows efficient production of a polyvinyl alcohol-based resin (A1) in which all or part of the carbon constituting the polyvinyl alcohol-based resin is derived from biologically-derived ethylene.

[0019] Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate, and among these, vinyl acetate is preferred.

[0020] There are no particular limitations on the method for producing a vinyl ester monomer; for example, it can be obtained by reacting ethylene with a compound having a carboxy group represented by R-COOH. Vinyl acetate can be synthesized as follows. Typically, vinyl acetate can be obtained by subjecting ethylene, acetic acid, and oxygen to a gas-phase reaction in the presence of a catalyst. In this case, vinyl acetate containing a predetermined amount of C14 can be obtained by using ethylene containing a predetermined amount of C14 or acetic acid containing a predetermined amount of C14 as the compound having a carboxy group. An example of ethylene containing a predetermined amount of C14 is bioethylene.

[0021] In the production of vinyl ester monomers, it is preferable to use raw materials other than ethylene, such as carboxylic acids, that are derived from living organisms. However, since the carboxylic acid group is removed from the polymer backbone of the polyvinyl ester during saponification and is usually recovered and reused, even if fossil fuel-derived materials are used, they do not increase the amount of carbon dioxide present in the global environment and do not contribute to global warming.

[0022] The polyvinyl ester is preferably one obtained using one or more vinyl ester monomers, more preferably one obtained using only one vinyl ester monomer, or may be a copolymer of one or more vinyl ester monomers with other monomers copolymerizable therewith.

[0023] Ethylene is preferred as another monomer copolymerizable with the vinyl ester monomer. That is, the polyvinyl alcohol contained in the polyvinyl alcohol-based resin film of the present invention preferably contains ethylene units. The content of ethylene units is preferably 1 mol% or more, more preferably 1.5 mol% or more, based on the number of moles of all structural units constituting the vinyl ester polymer. The content of ethylene units is preferably less than 15 mol%, more preferably less than 10 mol%, based on the number of moles of all structural units constituting the vinyl ester polymer. When the polyvinyl alcohol-based resin film of the present invention is used as a raw film for producing an optical film, the water resistance and other properties of the polyvinyl alcohol-based resin film can be improved without significantly impairing the optical properties of the polyvinyl alcohol-based resin film. The reason for this is not entirely clear, but it is presumed that the introduction of ethylene units into the polymer main chain weakens hydrophilicity, while the volume occupied by the ethylene units in the crystal is not significantly different from the volume of the vinyl alcohol units, so that the crystalline structure of the polyvinyl alcohol is not significantly disrupted.

[0024] Examples of other monomers copolymerizable with vinyl ester monomers include, in addition to ethylene, olefins having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutene; acrylic acid or its salts; acrylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, and octadecyl acrylate; methacrylic acid or its salts; methyl methacrylate, ethyl methacrylate, methacrylic acid, and the like. Methacrylic acid esters such as n-propyl acrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, and octadecyl methacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetone acrylamide, acrylamidopropanesulfonic acid or a salt thereof, acrylamidopropyldimethylamine or a salt thereof, and N-methylolacrylamide or a derivative thereof. methacrylamide derivatives such as methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid or a salt thereof, methacrylamidepropyldimethylamine or a salt thereof, N-methylolmethacrylamide or a derivative thereof; N-vinylamides such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; 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, and stearyl vinyl ether; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or a salt, ester, or acid anhydride thereof; itaconic acid or a salt, ester, or acid anhydride thereof; vinylsilyl compounds such as vinyltrimethoxysilane; and isopropenyl acetate.The vinyl ester polymer may have structural units derived from one or more of these other monomers.

[0025] The proportion of structural units derived from other monomers in the polyvinyl ester is preferably 15 mol % or less, and more preferably 5 mol % or less, based on the number of moles of all structural units constituting the polyvinyl ester, from the viewpoints of the strength of the resulting polyvinyl alcohol-based resin film and the optical performance when the polyvinyl alcohol-based resin film is used as a raw film for producing an optical film.

[0026] The other monomer copolymerizable with the vinyl ester monomer may be a monomer derived from a fossil fuel or a monomer derived from a plant.

[0027] The weight-average molecular weight of the polyvinyl alcohol-based resin (A) is preferably 20,000 to 150,000, particularly preferably 60,000 to 130,000, and even more preferably 70,000 to 120,000. If the weight-average molecular weight is too small, mechanical strength tends to decrease, while if it is too large, productivity tends to decrease. Furthermore, if the weight-average molecular weight is too small, it tends to be difficult to obtain sufficient optical performance when the polyvinyl alcohol-based resin is used to form an optical film, while if it is too large, stretching tends to be difficult when a polarizing film is produced using the polyvinyl alcohol-based resin film. The weight-average molecular weight of the polyvinyl alcohol-based resin is a weight-average molecular weight measured by GPC.

[0028] The polyvinyl alcohol-based resin (A) preferably has a dispersity (weight average molecular weight / number average molecular weight) of 1.95 to 3.50, particularly preferably 1.96 to 2.50, and even more preferably 1.97 to 2.10. If the dispersity is too small, stretching tends to be difficult when a polarizing film is produced using the polyvinyl alcohol-based resin film, while if the dispersity is too large, sufficient optical performance tends to be difficult to obtain when the polyvinyl alcohol-based resin is used as an optical film. The weight average molecular weight and number average molecular weight when measuring the dispersity of the polyvinyl alcohol-based resin are weight average molecular weights and number average molecular weights measured by GPC.

[0029] The average saponification degree of the polyvinyl alcohol-based resin (A) is usually preferably 80 mol% or more, more preferably 87 mol% or more, particularly preferably 99 mol% or more, even more preferably 99.5 mol% or more, and particularly preferably 99.8 mol% or more. If the average saponification degree is too low, sufficient optical performance tends to be difficult to obtain when the polyvinyl alcohol-based resin film is used as a polarizing film. Here, the average saponification degree in this specification is measured in accordance with JIS K 6726.

[0030] The polyvinyl alcohol-based resin (A) has a C14 pMC value measured according to ASTM D6866 (Method B), and the upper limit is preferably 48 or less, more preferably 45 or less, even more preferably 43 or less, and particularly preferably 41 or less. The lower limit is preferably 2 or more, more preferably 5 or more, even more preferably 10 or more, and particularly preferably 15 or more. By setting the pMC value within the above range, a decrease in the pH of the polyvinyl alcohol-based resin composition during the film-forming process can be suppressed, and corrosion deterioration of a melting can, an extruder, a die, a metal roll, a belt, etc. can be reduced, thereby allowing the polyvinyl alcohol-based resin composition to be preferably used as a base film that can extend the period until repairs are required for each device and equipment.

[0031] As the polyvinyl alcohol-based resin (A), one type of polyvinyl alcohol may be used, or two or more types of polyvinyl alcohols having different degrees of polymerization, saponification, or modification may be blended and used.

[0032] <Plasticizer (B)> Examples of the plasticizer (B) include glycerins such as glycerin, diglycerin, and triglycerin, alkylene glycols such as triethylene glycol, polyethylene glycol, polypropylene glycol, dipropylene glycol, and propylene glycol, and sugar alcohols such as trimethylolpropane, sorbitol, xylitol, and maltitol. These can be used alone or in combination of two or more. Among them, glycerin, polyethylene glycol, and diglycerin are preferably used because they are easily available and can obtain a plasticizing effect with a small amount.

[0033] The content of the plasticizer (B) is preferably 1 to 45 parts by mass, particularly 3 to 30 parts by mass, and even more preferably 5 to 25 parts by mass, per 100 parts by mass of the polyvinyl alcohol-based resin (A). If the content of the plasticizer (B) is too low, the stretchability during production of the polarizing film tends to decrease, whereas if the content is too high, the strength of the resulting polyvinyl alcohol-based resin film tends to decrease.

[0034] <Surfactant (C)> The surfactant (C) generally has the function of smoothing the film surface and suppressing adhesion of films to each other when wound into a roll, and for example, nonionic surfactants, anionic surfactants, and cationic surfactants can be used alone or in combination of two or more thereof.

[0035] Examples of the nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene hexyl ether, polyoxyethylene heptyl ether, polyoxyethylene octyl ether, polyoxyethylene nonyl ether, polyoxyethylene decyl ether, polyoxyethylene dodecyl ether, polyoxyethylene tetradecyl ether, polyoxyethylene hexadecyl ether, polyoxyethylene octadecyl ether, polyoxyethylene eicosyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, coconut oil reduced alcohol ethylene oxide adduct, and beef tallow reduced alcohol ethylene oxide adduct; caproic acid mono- or diethanolamide; caprylic acid mono- or diethanolamide; capric acid mono- or diethanolamide; lauric acid mono- or diethanolamide; palmitic acid mono- or diethanolamide; stearic acid mono- or diethanolamide; oleic acid mono- or diethanolamide; coconut oil fatty acid mono- or diethanolamide; and propanoic acid mono- or diethanolamide instead of these ethanolamides. higher fatty acid alkanolamides such as caproic acid amide, caprylic acid amide, capric acid amide, lauric acid amide, palmitic acid amide, stearic acid amide, and oleic acid amide; polyoxyethylene alkylamines such as hydroxyethyl laurylamine, polyoxyethylene hexylamine, polyoxyethylene heptylamine, polyoxyethylene octylamine, polyoxyethylene nonylamine, polyoxyethylene decylamine, polyoxyethylene dodecylamine, polyoxyethylene tetradecylamine, polyoxyethylene hexadecylamine, polyoxyethylene octadecylamine, polyoxyethylene oleylamine, polyoxyethylene laurylamine, and polyoxyethylene eicosylamine; polyoxyethylene higher fatty acid amides such as polyoxyethylene caproic acid amide, polyoxyethylene caprylic acid amide, polyoxyethylene capric acid amide, polyoxyethylene lauric acid amide, polyoxyethylene palmitic acid amide, polyoxyethylene stearic acid amide, and polyoxyethylene oleic acid amide;Examples include amine oxides such as dimethyl lauryl amine oxide, dimethyl stearyl oxide, and dihydroxyethyl lauryl amine oxide, and fluoroalkyl acids such as perfluorooctanoic acid.

[0036] Examples of the anionic surfactants include sulfate salts such as alkyl sulfates, such as sodium hexyl sulfate, sodium heptyl sulfate, sodium octyl sulfate, sodium nonyl sulfate, sodium decyl sulfate, sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, sodium octadecyl sulfate, and sodium eicosyl sulfate, as well as potassium salts, calcium salts, and ammonium salts thereof; polyoxyethylene hexyl ether sodium sulfate, polyoxyethylene heptyl ether sodium sulfate, polyoxyethylene octyl ether sodium sulfate, polyoxyethylene nonyl ether sodium sulfate, polyoxyethylene decyl ether sodium sulfate, polyoxyethylene dodecyl ether sodium sulfate, polyoxyethylene tetradecyl ether sodium sulfate, polyoxyethylene hexadecyl ether sodium sulfate, polyoxyethylene octadecyl ether sodium sulfate, and polyoxyethylene eicosyl ether sodium sulfate, as well as potassium salts and ammonium salts thereof; polyoxyethylene alkyl phenyl ether sulfates such as polyoxyethylene alkyl ether sulfates, polyoxyethylene hexyl phenyl ether sodium sulfate, polyoxyethylene heptyl phenyl ether sodium sulfate, polyoxyethylene octyl phenyl ether sodium sulfate, polyoxyethylene nonyl phenyl ether sodium sulfate, polyoxyethylene decyl phenyl ether sodium sulfate, polyoxyethylene dodecyl phenyl ether sodium sulfate, polyoxyethylene tetradecyl phenyl ether sodium sulfate, polyoxyethylene hexadecyl phenyl ether sodium sulfate, polyoxyethylene octadecyl phenyl ether sodium sulfate, polyoxyethylene eicosyl phenyl ether sodium sulfate, or potassium salts or ammonium salts thereof; caproic acid ethanolamide sodium sulfate, caprylic acid ethanolamide sodium sulfate, capric acid ethanolamide sodium sulfate, lauric acid ethanolamide sodium sulfate, palmitic acid ethanolamide sodium sulfate, stearic acid ethanolamide sodium sulfate;Examples include sodium oleic acid ethanolamide sulfate or potassium salts thereof, and, instead of these ethanolamides, higher fatty acid alkanolamide sulfate salts such as propanolamide and butanolamide, sulfated oils, higher alcohol ethoxy sulfates, monoglycerides, etc. In addition to the sulfate ester salts, examples include carboxylate salts such as fatty acid soaps, N-acylamino acids and their salts, polyoxyethylene alkyl ester carboxylates, and acylated peptides, sulfonate salts such as alkyl sulfonates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, formalin polycondensates of naphthalene sulfonic acid salts, formalin condensates of melamine sulfonic acid salts, dialkyl sulfosuccinate salts, alkyl sulfosuccinate disalts, polyoxyethylene alkyl sulfosuccinate disalts, alkyl sulfoacetates, α-olefin sulfonates, N-acylmethyl taurine salts, and dimethyl-5-sulfoisophthalate sodium salt, and phosphate salts such as polyoxyethylene alkyl ether phosphates, polyoxyethylene alkyl phenyl ether phosphates, and alkyl phosphates.

[0037] Examples of the cationic surfactant include laurylamine hydrochloride, lauryltrimethylammonium chloride, and laurylpyridinium chloride.

[0038] Among these, nonionic surfactants are preferred, and higher fatty acid alkanolamides are particularly preferred, and lauric acid mono- or diethanolamide, palmitic acid mono- or diethanolamide, stearic acid mono- or diethanolamide, and oleic acid mono- or diethanolamide are even more preferred, and lauric acid mono- or diethanolamide is even more preferred, and lauric acid diethanolamide is even more preferred.

[0039] The surfactant (C) may be used alone or in combination of two or more thereof, and it is preferred to use an anionic surfactant and a nonionic surfactant in combination in terms of film transparency.

[0040] The content of the surfactant (C) is preferably 0.01 to 1 part by mass, particularly preferably 0.02 to 0.5 parts by mass, and even more preferably 0.03 to 0.2 parts by mass, per 100 parts by mass of the polyvinyl alcohol-based resin (A). If the content of the surfactant (C) is too low, it tends to be difficult to obtain an anti-blocking effect, and if it is too high, the transparency of the film tends to decrease.

[0041] Furthermore, when an anionic surfactant and a nonionic surfactant are used in combination, the amount of the anionic surfactant is preferably 0.01 to 1 part by mass, particularly 0.02 to 0.2 parts by mass, and even more preferably 0.03 to 0.1 parts by mass, relative to 100 parts by mass of the polyvinyl alcohol-based resin (A), and the amount of the nonionic surfactant is preferably 0.01 to 1 part by mass, particularly 0.02 to 0.2 parts by mass, and even more preferably 0.03 to 0.1 parts by mass. If the amount of the anionic surfactant is too small, the dispersibility of the dye during production of the polarizing film tends to decrease, resulting in increased dye spots. If the amount is too large, the polyvinyl alcohol-based resin tends to foam violently when dissolved, making it easier for air bubbles to become trapped in the film, making it unusable as an optical film. If the amount of the nonionic surfactant is too small, it is difficult to obtain an anti-blocking effect, and if the amount is too large, the transparency and flatness of the film tend to decrease.

[0042] <Starch (D)> Examples of the starch (D) include raw starches (corn starch, potato starch, sweet potato starch, wheat starch, cassava starch, sago starch, tapioca starch, sorghum starch, rice starch, bean starch, kudzu starch, bracken starch, lotus starch, and water chestnut starch), physically modified starches (α-starch, fractionated amylose, and heat-moisture treated starch), enzyme-modified starches (hydrolyzed dextrin, enzymatically decomposed dextrin, and amylose), chemically decomposed and modified starches (acid-treated starch, hypochlorite-oxidized starch, and dialdehyde starch), and chemically modified starch derivatives (esterified starch, etherified starch, cationized starch, and cross-linked starch). Of these, raw starches, particularly corn starch and rice starch, are preferred from the standpoints of availability and economy. These may be used alone or in combination of two or more.

[0043] The content of the starch (D) is preferably 15 parts by mass or less, and more preferably 10 parts by mass or less, relative to 100 parts by mass of the polyvinyl alcohol-based resin (A). If the amount of starch (D) is more than 15 parts by mass, the processability during production of the polyvinyl alcohol-based resin film may be deteriorated.

[0044] <Water-soluble polymer (E) other than (A)> Examples of the water-soluble polymer (E) other than the polyvinyl alcohol-based resin (A) include 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.

[0045] The content of the water-soluble polymer (E) is preferably 15 parts by mass or less, and more preferably 10 parts by mass or less, per 100 parts by mass of the polyvinyl alcohol-based resin (A). If the content of the water-soluble polymer (E) is more than 15 parts by mass, the physical properties of the polyvinyl alcohol-based resin film may be impaired.

[0046] <Other Components> The present polyvinyl alcohol-based resin film may contain components such as water, antioxidants, ultraviolet absorbers, lubricants, crosslinking agents, colorants, fillers, preservatives, antifungal agents, other polymer compounds, etc., in addition to plasticizers, surfactants, starch, and water-soluble polymers other than the polyvinyl alcohol-based resin (A), as long as the effects of the present invention are not impaired. These may be used alone or in combination of two or more.

[0047] The polyvinyl alcohol-based resin film is preferably a film obtained by using a polyvinyl alcohol-based resin composition.

[0048] The upper limit of the C14 pMC value of such a polyvinyl alcohol-based resin composition measured by ASTM D6866 (Method B) must be 50 or less, preferably 48 or less, more preferably 45 or less, even more preferably 40 or less, and particularly preferably 35 or less. The lower limit of this value is preferably 9 or more, more preferably 15 or more, even more preferably 20 or more, and particularly preferably 25 or more. By setting the C14 pMC value within the above range, the polyvinyl alcohol-based resin composition can be used as a base resin that suppresses a decrease in pH of the polyvinyl alcohol-based resin composition during the film-forming process, and by reducing corrosion deterioration of melting cans, extruders, die molds, metal rolls, belts, etc., the period until repair of each device and equipment is required can be extended.

[0049] <Method for Producing Polyvinyl Alcohol-Based Resin Film> The polyvinyl alcohol-based resin film can be produced by any method, including a film-forming stock solution (aqueous solution of a polyvinyl alcohol-based resin composition) obtained by homogenizing a polyvinyl alcohol-based resin (A) with a solvent, additives, etc., a casting film-forming method, a wet film-forming method (discharge into a poor solvent), a dry-wet film-forming method, a gel film-forming method (a method in which the film-forming stock solution is cooled to gel, and then the solvent is extracted and removed to obtain a polyvinyl alcohol-based resin film), or a combination of these methods, or a melt-extrusion film-forming method or inflation film-forming method in which the film-forming stock solution is obtained using an extruder or the like and extruded through a T-die or the like to form a film. Among these, the casting film-forming method and the melt-extrusion film-forming method are preferred because they can produce homogeneous films with good productivity. The casting film-forming method and the melt-extrusion film-forming method for polyvinyl alcohol-based resin films are described below.

[0050] When the polyvinyl alcohol-based resin film is produced by a casting film-forming method or a melt extrusion film-forming method, the film-forming solution is degassed, cast onto a support such as a metal roll or a metal belt, and heated to remove the solvent, thereby solidifying the film. Examples of degassing methods include static degassing and degassing using a multi-screw extruder with a vent. A twin-screw extruder with a vent is usually used as the multi-screw extruder with a vent. The solidified film is peeled from the support, dried using a drying roll, a drying oven, or the like as needed, further heat-treated as needed, and wound up to obtain a roll-shaped, long polyvinyl alcohol-based resin film.

[0051] The resin concentration of the film-forming solution (the concentration of non-volatile components such as polyvinyl alcohol resins that are not removed by volatilization or evaporation during film formation) is preferably 10 to 60% by mass, particularly preferably 12 to 55% by mass, and even more preferably 20 to 50% by mass. If the resin concentration of such an aqueous solution is too low, the drying load increases, which tends to reduce productivity, while if it is too high, the viscosity becomes too high, making it difficult to achieve uniform dissolution.

[0052] Here, the term "resin concentration of the film-forming solution" in this specification refers to the volatile content calculated by the following formula.

[0053] Resin concentration (mass%) of film-forming solution = (Wb / Wa) x 100 (where Wa represents the mass (g) of the film-forming solution, and Wb represents the mass (g) of the film-forming solution Wa (g) after drying it in an electric dryer at 105°C for 16 hours.)

[0054] The method for preparing the film-forming solution is not particularly limited, and examples thereof include a method in which the polyvinyl alcohol resin (A) and additives such as the plasticizer (B) and surfactant (C) are dissolved in a dissolution tank or the like, and a method in which the polyvinyl alcohol in a water-containing state is melt-kneaded together with the plasticizer (B), surfactant (C), etc. using a single-screw extruder or a twin-screw extruder.

[0055] When a polyvinyl alcohol-based resin film is produced by a casting film-forming method or a melt extrusion film-forming method, the film-forming solution is cast in the form of a film onto a support such as a metal roll or a metal belt from a film-forming discharge device, and is heated to remove the solvent, thereby solidifying and forming a film.

[0056] The surface temperature of the support onto which the membrane-forming solution is cast is preferably 50° C. or higher, more preferably 60° C. or higher, and even more preferably 65° C. or higher. The surface temperature of the support onto which the membrane-forming solution is cast is preferably 110° C. or lower, more preferably 100° C. or lower, and even more preferably 95° C. or lower. If the surface temperature is too low, the releasability of the film obtained by film formation when peeled from the casting mold tends to decrease, and if the surface temperature is too high, foaming tends to occur.

[0057] The drying speed may be adjusted by uniformly blowing hot air at a speed of 1 to 10 m / sec onto the entire area of ​​the non-contact side of the polyvinyl alcohol film while heating the polyvinyl alcohol resin film on the support. From the viewpoints of drying efficiency, drying uniformity, etc., the temperature of the hot air blown onto the non-contact side is preferably 50°C or higher, more preferably 70°C or higher. From the viewpoints of drying efficiency, drying uniformity, etc., the temperature of the hot air blown onto the non-contact side is preferably 150°C or lower, more preferably 120°C or lower.

[0058] The polyvinyl alcohol-based resin film peeled from the support is dried on the support, preferably to a volatile content of 5 to 50% by mass, and then peeled off, and further dried as necessary. The drying method is not particularly limited, and examples include contacting the film with a drying oven or drying rolls. When drying is performed with multiple drying rolls, it is preferable to alternately contact one side of the film with the drying rolls to achieve uniformity on both sides. The number of drying rolls is preferably three or more, more preferably four or more, and even more preferably five or more. The number of drying rolls is preferably 30 or less. When drying rolls are used, the contact time between each drying roll and the film is preferably 1 to 60 seconds, particularly preferably 2 to 30 seconds, more preferably 3 to 20 seconds, and especially preferably 4 to 10 seconds. If the contact time is too short, the film tends to be insufficiently dried, while if the contact time is too long, the equipment load tends to increase. In this embodiment, the temperatures of all drying ovens and drying rolls used are preferably 40 to 150° C., particularly preferably 50 to 140° C., further preferably 60 to 130° C., and particularly preferably 70 to 120° C. If the temperatures of the drying ovens and drying rolls are too low, drying tends to be insufficient, whereas if they are too high, crystallization of the polyvinyl alcohol-based resin proceeds, and the film tends to become too hard.

[0059] The dried polyvinyl alcohol-based resin film can be further heat-treated as needed to adjust its physical properties, such as strength and water solubility. The heat treatment in the present invention is preferably performed from both sides of the film, since this allows for uniform drying on both sides of the film. Examples of such heat treatment methods include a method of blowing hot air onto both sides of the film using a floating dryer, and a method of irradiating both sides of the film with near-infrared rays using an infrared lamp. The heat treatment temperature is preferably 50 to 150°C, and particularly preferably 70 to 120°C. The heat treatment time is not particularly limited, but when using a floating dryer, it is preferably 10 to 100 seconds, and particularly preferably 20 to 80 seconds.

[0060] The polyvinyl alcohol-based resin film produced in this manner may be further subjected to humidity conditioning treatment, cutting of both ends (edges) of the film, etc., as necessary, wound into a roll on a cylindrical core, and then moisture-proof packaged to form a product.

[0061] The volatile content of the polyvinyl alcohol-based resin film finally obtained by the above-described series of treatments is not necessarily limited. The volatile content of the polyvinyl alcohol-based resin film is preferably 1% by mass or more, more preferably 2% by mass or more. The volatile content of the polyvinyl alcohol-based resin film is preferably 10% by mass or less, more preferably 5% by mass or less.

[0062] The length of the polyvinyl alcohol-based resin film of the present invention thus obtained is preferably 0.5 km or more from the viewpoint of production efficiency, more preferably 1 km or more, and particularly preferably 5 to 50 km from the viewpoint of transportation weight. If the length is too short, switching of the film tends to be troublesome, while if it is too long, poor appearance due to tight winding and excessive weight tend to occur.

[0063] The width of the polyvinyl alcohol-based resin film is appropriately selected depending on the application, etc., but is preferably 300 to 8000 mm, particularly preferably 500 to 7000 mm, and further preferably 600 to 6000 mm. If the width is too narrow, production efficiency tends to decrease, while if it is too wide, it tends to be difficult to control slack and film thickness.

[0064] The thickness of the polyvinyl alcohol-based resin film is appropriately selected depending on the application, etc., but is preferably 10 to 130 μm, particularly preferably 15 to 110 μm, and further preferably 15 to 60 μm. If the thickness is too thin, the mechanical strength of the film tends to decrease, while if the thickness is too thick, the film-forming efficiency tends to decrease.

[0065] The composition used to prepare the polyvinyl alcohol-based resin film preferably exhibits a pH difference of 0.28 or less, more preferably 0.26 or less, and even more preferably 0.25 or less, when subjected to the pH difference measurement test described below. The lower limit of the pH difference is not particularly specified, but a value closer to zero is preferable, so it is preferably 0 or more. By achieving the above pH difference, it is expected to reduce corrosion and deterioration of the dissolving can, extruder, die, metal roll, belt, etc. used in the production. <Method for Measuring pH Difference> A 19% polyvinyl alcohol-based resin composition (X) containing 12 parts by mass of glycerin per 100 parts by mass of polyvinyl alcohol-based resin was prepared. The polyvinyl alcohol-based resin composition (X) was further diluted to 4% with ion-exchanged water to prepare polyvinyl alcohol-based resin composition (X1), and the polyvinyl alcohol-based resin composition (X) was maintained at 90°C for 1 week and then diluted to 4% with ion-exchanged water to prepare polyvinyl alcohol-based resin composition (X2). The pH of compositions (X1) and (X2) was measured using a pH meter (HORIBA, Castani ACT, D-21) in accordance with JIS Z 8802, and the resulting pH values ​​were designated pH(X1) and pH(X2), respectively. The liquid temperature at this time was 25°C. The difference in pH value was designated pH(X1) - pH(X2).

[0066] The polyvinyl alcohol-based resin film thus obtained can suppress corrosiveness to melting cans, extruders, die molds, metal rolls, belts, and the like used in the production, and enables the production of polyvinyl alcohol-based resin films with excellent maintainability and stable quality. Therefore, the film is useful for polarizing film applications (liquid crystal televisions, smartphones, tablets, personal computers, projectors, in-vehicle panels, and the like) and water-soluble film applications (unit packaging applications for chemicals such as pesticides and detergents, (hydraulic) transfer films, sanitary products such as napkins and disposable diapers, waste disposal products such as ostomy bags, medical products such as blood-absorbing sheets, and temporary substrates such as seedling raising sheets, seed tapes, and embroidery base fabrics, and the like).

[0067] A method for producing a polarizing film according to one embodiment of the present invention (hereinafter, sometimes referred to as "the present polarizing film") will be described below.

[0068] The polarizing film is produced by unwinding the polyvinyl alcohol-based resin film from a roll and transporting it horizontally, followed by processes such as swelling, dyeing, crosslinking, stretching, washing, and drying.

[0069] The swelling step is carried out before the dyeing step. The swelling step not only cleans the surface of the polyvinyl alcohol-based resin film from dirt, but also has the effect of preventing uneven dyeing by swelling the polyvinyl alcohol-based resin film. In the swelling step, water is usually used as the treatment liquid. As long as the treatment liquid is mainly composed of water, it may contain small amounts of additives such as iodide compounds and surfactants, alcohol, etc. The temperature of the swelling bath is usually about 10 to 45°C, and the immersion time in the swelling bath is usually about 0.1 to 10 minutes.

[0070] The dyeing process is carried out by bringing the film into contact with a liquid containing iodine or a dichroic dye. An aqueous solution of iodine and potassium iodide is usually used, with an iodine concentration of usually 0.1 to 2 g / L and a potassium iodide concentration of usually 1 to 100 g / L. A practical dyeing time is usually about 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 50°C. The aqueous solution may contain a small amount of an organic solvent that is compatible with water in addition to the water solvent.

[0071] The crosslinking step is carried out using a boron compound such as boric acid or borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture, usually at a concentration of about 10 to 100 g / L, and it is preferable to have potassium iodide coexist in the solution from the viewpoint of stabilizing the polarizing performance. The treatment temperature is usually about 30 to 70°C, and the treatment time is preferably about 0.1 to 20 minutes. If necessary, a stretching operation may be carried out during the treatment.

[0072] The stretching step is preferably 3 to 10 times in one axial direction, and particularly preferably 3.5 to 6 times. At this time, slight stretching (stretching to the extent that shrinkage in the width direction is prevented, or more) may also be performed in the direction perpendicular to the stretching direction. The temperature during stretching is preferably 30 to 170°C. Furthermore, the final stretching ratio need only be set within the above range, and the stretching operation may be performed not only in one stage but also at any stage in the production process.

[0073] The washing step is carried out, for example, by immersing the polyvinyl alcohol resin film in water or an aqueous iodide solution such as potassium iodide, and can remove precipitates that form on the surface of the film. When using an aqueous potassium iodide solution, the potassium iodide concentration may be approximately 1 to 80 g / L. The temperature during the washing treatment is usually 5 to 50°C, preferably 10 to 45°C. The treatment time is usually 1 to 300 seconds, preferably 10 to 240 seconds. Note that washing with water and washing with an aqueous potassium iodide solution may be performed in combination as appropriate.

[0074] The drying step may be carried out in normal air at 40 to 80° C. for 1 to 10 minutes.

[0075] The degree of polarization of the polarizing film is preferably 99.8% or more, particularly preferably 99.9% or more. If the degree of polarization is too low, it tends to be difficult to ensure contrast in a liquid crystal display. The degree of polarization is generally calculated according to the following formula using the light transmittance (H11) measured at a wavelength λ when two polarizing films are stacked so that their orientation directions are in the same direction, and the light transmittance (H1) measured at a wavelength λ when two polarizing films are stacked so that their orientation directions are perpendicular to each other: [(H11-H1) / (H11+H1)] 1 / 2

[0076] Furthermore, the single transmittance of the polarizing film is preferably 42% or more, particularly preferably 43% or more. If the single transmittance is too low, it tends to be difficult to achieve high brightness in liquid crystal displays. The single transmittance is a value obtained by measuring the light transmittance of the polarizing film alone using a spectrophotometer.

[0077] Thus, the present polarizing film is obtained, which is suitable for producing a polarizing plate with little unevenness in the degree of polarization.

[0078] The obtained polarizing film can also be used as a polarizing plate by laminating and adhering an optically isotropic polymer film or sheet as a protective film on one or both sides thereof. Examples of the protective film include films or sheets of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, crosslinked methacrylate resins, cycloolefin polymers, cycloolefin copolymers, polystyrene, polyethersulfone, polyarylene esters, poly-4-methylpentene, polyphenylene oxide, etc. Furthermore, in order to reduce the thickness of the polarizing film, instead of the above protective film, a curable resin such as a urethane resin, an acrylic resin, or a urea resin can be coated on one or both sides thereof, cured, and laminated.

[0079] A polarizing film obtained from the present polyvinyl alcohol-based resin film is free from color unevenness and has excellent in-plane uniformity of polarization performance, and is preferably used for, for example, liquid crystal display devices such as portable information terminals, personal computers, televisions, projectors, signage, electronic desk calculators, electronic clocks, word processors, electronic paper, game consoles, videos, cameras, photo albums, thermometers, audio equipment, meters for automobiles and machinery, sunglasses, anti-glare glasses, 3D glasses, wearable displays, anti-reflection layers for display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys, etc.

[0080] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded. In the examples, "parts" and "%" are based on mass.

[0081] <Measurement Conditions> <GPC Measurement of Polyvinyl Alcohol Resin> A chromatogram was obtained using gel permeation chromatography (GPC) under the following measurement conditions. Using a calibration curve obtained by measuring standard polyethylene oxide and polyethylene glycol (PEO / PEG), the elution time was converted into molecular weight, and the weight-average molecular weight of the polyvinyl alcohol resin in terms of the standard sample (PEO / PEG) was calculated. [GPC Measurement Conditions] Detector: RI, Shodex RI-501 Column: TSKgel α-M 13 μm 7.8 mm I.D. × 30 cm manufactured by Tosoh Corporation Mobile Phase: 0.2 M NaNO3 aqueous solution Mobile Phase Flow Rate: 0.50 mL / min Column Temperature: 35°C Calibration Curve: A calibration curve was created using 12 PEO / PEG standard samples with different molecular weights.

[0082] <Method for Measuring pH Difference> A 19% polyvinyl alcohol resin composition (X) containing 12 parts by mass of glycerin per 100 parts by mass of polyvinyl alcohol resin was prepared. The polyvinyl alcohol resin composition (X) was further diluted to 4% with ion-exchanged water to prepare polyvinyl alcohol resin composition (X1). The polyvinyl alcohol resin composition (X) was then maintained at 90°C for one week and then diluted to 4% with ion-exchanged water to prepare polyvinyl alcohol resin composition (X2). The pH of compositions (X1) and (X2) was measured using a pH meter (HORIBA, Castany ACT, D-21) in accordance with JIS Z 8802, and the resulting pH values ​​were designated pH(X1) and pH(X2), respectively. The liquid temperature at this time was 25°C. The pH difference was calculated by subtracting pH(X1) from pH(X2). The pH difference was measured three times, and the average value was reported as the pH difference, as shown in Table 1 below.

[0083] Synthesis Example of Polyvinyl Alcohol Resin (A1) (Bio-derived PVA Resin) 650 parts by mass of vinyl acetate (i.e., the carbon in the vinyl group moiety is bio-derived) and 131 parts by mass of methanol were added to a reactor equipped with a reflux condenser, a sample inlet, and a stirring blade, and the reactor was immersed in a water bath and heated. When reflux from the condenser was observed (internal temperature was approximately 60°C), 0.052 parts by mass of 2,2'-azobis(isobutyronitrile) was added as an initiator. During the polymerization, the temperature of the water bath was adjusted appropriately to ensure continuous reflux from the condenser, and sampling was performed to confirm the progress of the polymerization based on the solids concentration. When the vinyl acetate conversion rate reached 55%, 0.013 parts by mass of m-dinitrobenzene and 500 parts by mass of methanol were added as polymerization terminators to terminate the polymerization. It took 6.75 hours from the addition of the initiator to reach the target conversion rate. The resulting post-polymerization solution was distilled under reduced pressure to remove the methanol and vinyl acetate. When the viscosity increased appropriately, methanol was added to remove the remaining vinyl acetate, obtaining a methanol solution of polyvinyl acetate. The thus obtained methanol solution of polyvinyl acetate was diluted with methanol to a concentration of 4% by mass, and 2,500 parts by mass of this polyvinyl acetate methanol solution (100 parts by mass as polyvinyl acetate) was charged into the same reactor as above. The reactor was immersed in a water bath and heated to an internal temperature of 65 ° C. 26.7 parts by mass of a 3.5% by mass solution of sodium hydroxide in methanol was added thereto to initiate the saponification reaction. As the saponification reaction progressed, a saponified product precipitated, but stirring was continued as is. 1.5 hours after the addition of the sodium hydroxide methanol solution, the obtained saponified product was filtered and charged back into the reactor, where 700 parts by mass of methanol was added and heated to 65 ° C. 20 parts by mass of a 3.5% by mass solution of sodium hydroxide in methanol was added thereto and reacted for 2.5 hours to drive the saponification reaction. Thereafter, 1.3 parts by mass of acetic acid and 1,200 parts by mass of methanol were added to neutralize the mixture, and the mixture was suction filtered while washing with methanol to obtain a saponified product. 1,800 parts by mass of methanol was added to the resulting saponified product, which was then washed at 65° C. for 30 minutes and filtered.The washed saponified product was dried in a vacuum dryer at 50°C for 12 hours to obtain a polyvinyl alcohol resin (A1) (bio-derived PVA resin) (weight average molecular weight 81,000; pMC of C14 94.8; degree of saponification 99.8 mol%).

[0084] Synthesis Example of Polyvinyl Alcohol Resin (A'1) (Petroleum-Derived PVA Resin) 650 parts by mass of petroleum-derived vinyl acetate and 131 parts by mass of methanol were added to a reactor equipped with a reflux condenser, a sample inlet, and a stirring blade, and the reactor was immersed in a water bath and heated. When reflux from the condenser was observed (internal temperature was approximately 60°C), 0.052 parts by mass of 2,2'-azobis(isobutyronitrile) was added as an initiator. During the polymerization, the temperature of the water bath was adjusted appropriately to ensure continuous reflux from the condenser, and sampling was conducted to confirm the progress of the polymerization based on the solids concentration. When the vinyl acetate conversion rate reached 50%, 0.013 parts by mass of m-dinitrobenzene and 500 parts by mass of methanol were added as polymerization terminators to terminate the polymerization. It took 5 hours from the addition of the initiator to reach the target conversion rate. The resulting post-polymerization solution was distilled under reduced pressure to remove the methanol and vinyl acetate. When the viscosity increased appropriately, methanol was added to remove the remaining vinyl acetate, obtaining a methanol solution of polyvinyl acetate. The thus obtained methanol solution of polyvinyl acetate was diluted with methanol to a concentration of 6% by mass, and 2000 parts by mass of this polyvinyl acetate methanol solution (120 parts by mass as polyvinyl acetate) was charged into the same reactor as above. The reactor was immersed in a water bath and heated to an internal temperature of 50 ° C. 128 parts by mass of a 3.5% by mass solution of sodium hydroxide in methanol was added thereto to initiate the saponification reaction. As the saponification reaction progressed, a saponified product precipitated, but stirring was continued as is. 2.5 hours after the addition of the sodium hydroxide methanol solution, the obtained saponified product was filtered and charged back into the reactor, where 700 parts by mass of methanol was added and heated to 50 ° C. 96 parts by mass of a 3.5% by mass solution of sodium hydroxide in methanol was added thereto and reacted for 4 hours to drive the saponification reaction. Thereafter, 6.0 parts by mass of acetic acid was added to the mixture to neutralize it, and the mixture was subjected to suction filtration while washing with methanol to obtain a saponified product. The saponified product was then washed with 1,200 parts by mass of methanol at 50° C. for 30 minutes, followed by filtration. This procedure was repeated twice.The washed saponified product was dried in a vacuum dryer at 50°C for 12 hours to obtain polyvinyl alcohol resin (A'1) (petroleum-derived PVA resin) (weight average molecular weight 79,400; pMC detection limit of C14 (0.44) or less; saponification degree 99.8 mol%).

[0085] Example 1: The polyvinyl alcohol-based resin (A1) (bio-derived PVA resin) and polyvinyl alcohol-based resin (A'1) (petroleum-derived PVA resin) obtained in the above Synthesis Example were mixed in a mass ratio of 10:90 to obtain 100 parts by mass of polyvinyl alcohol-based resin (A), and 12 parts by mass of glycerin (special grade reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as plasticizer (B) was added to the resulting composition. Ion-exchanged water was added to the composition so that the concentration of the composition became 19% by mass, and the mixture was dissolved in an autoclave at 130°C for 1 hour to obtain an aqueous polyvinyl alcohol-based resin composition (1). The pH difference test using the resulting aqueous polyvinyl alcohol-based resin composition (1) yielded a result of 0.23. The aqueous solution of the polyvinyl alcohol-based resin composition was applied to a chrome-plated stainless steel plate placed on a hot plate heated to 90°C using an applicator (clearance 450 μm, coating width 150 mm), dried on the hot plate at 90°C for 2.5 minutes, and then peeled off. Thereafter, heat treatment was performed in a dryer at 120°C for 1 minute to obtain a 45 μm-thick polyvinyl alcohol-based resin film (1-1) (pMC of C14 = 16.4).

[0086] Example 2 A polyvinyl alcohol-based resin aqueous solution (2) and a polyvinyl alcohol-based resin film (2-1) (pMC of C14 = 30.5) were obtained in the same manner as in Example 1, except that the polyvinyl alcohol-based resin (A1) (bio-derived PVA resin) and the polyvinyl alcohol-based resin (A'1) (petroleum-derived PVA resin) obtained in the above Synthesis Example were mixed in a mass ratio of 25:75. The pH difference test was also performed using the obtained polyvinyl alcohol-based resin composition aqueous solution (2), and the result was 0.23.

[0087] [Example 3] A polyvinyl alcohol-based resin aqueous solution (3) and a polyvinyl alcohol-based resin film (3-1) (pMC of C14 = 43.5) were obtained in the same manner as in Example 1, except that the polyvinyl alcohol-based resin (A1) (bio-derived PVA resin) and the polyvinyl alcohol-based resin (A'1) (petroleum-derived PVA resin) obtained in the above Synthesis Example were mixed in a mass ratio of 40:60. In addition, the pH difference test was performed using the obtained polyvinyl alcohol-based resin composition aqueous solution (3), and the result was 0.12.

[0088] Comparative Example 1: 100 parts by mass of the polyvinyl alcohol-based resin (A'1) (petroleum-derived PVA resin) obtained in the above synthesis example was blended with 12 parts by mass of glycerin (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) as the plasticizer (B). Ion-exchanged water was added to the composition so that the concentration of the composition was 19% by mass, and the mixture was dissolved at 130 ° C. using an autoclave for 1 hour to obtain an aqueous solution of a polyvinyl alcohol-based resin composition (1'). This aqueous solution of the polyvinyl alcohol-based resin composition was applied to a chrome plate placed on a hot plate heated to 90 ° C. using an applicator with a clearance of 450 μm, dried on the hot plate at 90 ° C. for 2.5 minutes, and then the film was peeled off. This was followed by heat treatment in a dryer at 120 ° C. for 1 minute to obtain a 45 μm-thick polyvinyl alcohol-based resin film (1'-1) (pMC of C14 = 8.1). The result of the pH difference test using the resulting aqueous solution of polyvinyl alcohol-based resin composition (1') was 0.43.

[0089] Comparative Example 2 An aqueous solution of a polyvinyl alcohol-based resin composition (2') and a polyvinyl alcohol-based resin film (2'-1) (pMC of C14 = 61.2) were obtained in the same manner as in Example 1, except that the polyvinyl alcohol-based resin (A1) (bio-derived PVA resin) and polyvinyl alcohol-based resin (A'1) (petroleum-derived PVA resin) obtained in the above Synthesis Example were mixed in a mass ratio of 60:40. The pH difference test using the obtained aqueous solution of polyvinyl alcohol-based resin composition (2') gave a result of 0.31.

[0090] Comparative Example 3 An aqueous solution of a polyvinyl alcohol-based resin composition (3') and a polyvinyl alcohol-based resin film (3'-1) (pMC of C14 = 78.7) were obtained in the same manner as in Example 1, except that the polyvinyl alcohol-based resin (A1) (bio-derived PVA resin) and polyvinyl alcohol-based resin (A'1) (petroleum-derived PVA resin) obtained in the above Synthesis Example were mixed in a mass ratio of 80:20. The pH difference test using the obtained aqueous solution of polyvinyl alcohol-based resin composition (3') gave a result of 0.31.

[0091] Comparative Example 4 An aqueous solution of a polyvinyl alcohol-based resin composition (4') and a polyvinyl alcohol-based resin film (4'-1) (pMC of C14 = 95.6) were obtained in the same manner as in Example 1, except that 100 parts by mass of the polyvinyl alcohol-based resin (A1) (bio-derived PVA resin) obtained in the above Synthesis Example was used. The pH difference test using the obtained aqueous solution of polyvinyl alcohol-based resin composition (4') was carried out, and the result was 0.29.

[0092]

[0093] The polyvinyl alcohol-based resin films of Examples 1 to 3 had pMC values ​​of C14 measured by ASTM D6866 (Method B) within the range specified in the present invention, and polyvinyl alcohol-based resin films in which a decrease in pH value was suppressed were obtained. In contrast, the polyvinyl alcohol-based resin films of Comparative Examples 1 to 4 had pMC values ​​of C14 measured by ASTM D6866 (Method B) outside the range specified in the present invention, and therefore were polyvinyl alcohol-based resin films in which a decrease in pH value was significant.

[0094] 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.

[0095] The polyvinyl alcohol-based resin film of the present invention is a polyvinyl alcohol-based resin composition and polyvinyl alcohol-based resin film that inhibit corrosion and deterioration of dissolving cans, extruders, die molds, metal rolls and belts, etc. used in production, and are excellent in production efficiency and maintainability. For example, the polyvinyl alcohol-based resin film is preferably used in polarizing film applications (liquid crystal televisions, smartphones, tablets, personal computers, projectors, in-vehicle panels, etc.), water-soluble film applications (unit packaging applications for chemicals such as pesticides and detergents, (hydraulic) transfer films, sanitary products such as napkins and disposable diapers, waste disposal products such as ostomy bags, medical products such as blood-absorbing sheets, temporary base materials such as seedling raising sheets, seed tapes, and embroidery base fabrics), etc.

Claims

1. A polyvinyl alcohol-based resin film containing a polyvinyl alcohol-based resin (A), the polyvinyl alcohol-based resin film having a pMC value of C14 measured according to ASTM D6866 (Method B) of 9 to 50.

2. The polyvinyl alcohol resin film according to claim 1, wherein the polyvinyl alcohol resin (A) has a degree of saponification of 80 to 99.9 mol %.

3. The polyvinyl alcohol-based resin film according to claim 1 or 2, wherein the weight-average molecular weight of the polyvinyl alcohol-based resin (A) is 20,000 to 150,000.

4. The polyvinyl alcohol resin film according to any one of claims 1 to 3, which contains a plasticizer (B).

5. The polyvinyl alcohol-based resin film according to claim 4, wherein the content of the plasticizer (B) is 1 to 45 parts by mass per 100 parts by mass of the polyvinyl alcohol-based resin (A).

6. The polyvinyl alcohol resin film according to any one of claims 1 to 5, having a thickness of 10 to 130 µm.

7. The polyvinyl alcohol resin film according to any one of claims 1 to 6, which is used for producing a polarizing film.

8. An optical film, comprising the polyvinyl alcohol-based resin film according to any one of claims 1 to 7.

9. The optical film according to claim 8, wherein said optical film is a polarizing film.

10. A water-soluble film comprising the polyvinyl alcohol-based resin film according to any one of claims 1 to 6.

11. A polyvinyl alcohol resin composition comprising at least a polyvinyl alcohol resin (A) and having a C14 pMC value of 9 to 50 as measured according to ASTM D6866 (Method B).

12. The polyvinyl alcohol resin composition according to claim 11, which contains a plasticizer (B).

13. A polyvinyl alcohol-based resin film comprising the polyvinyl alcohol-based resin composition (A) according to claim 11 or 12.

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