Polyvinyl alcohol-based film

Abstract

Provided is the following as a PVA-based film excellent in transparency, particularly yellowing resistance.　A polyvinyl alcohol-based film containing a polyvinyl alcohol-based resin, wherein the integral ratio of the polyvinyl alcohol-based film as determined by formula (1) below from an 1H-NMR spectrum of the polyvinyl alcohol-based film is 7.0 x 10-3 or less.　(1): Integral ratio = (B / 3) / (b / 3 + a / 2 + B / 3) In formula (1), B is the integral value of methyl groups observed at 2.19 to 2.18 ppm, a is the integral value of methylene groups observed at 2.30 to 2.19 ppm and 2.18 to 1.47 ppm, and b is the integral value of methyl groups observed at 2.49 to 2.30 ppm.

Description

Polyvinyl alcohol-based film

[0001] The present invention relates to a polyvinyl alcohol-based film, and more particularly to a polyvinyl alcohol-based film with excellent resistance to yellowing.

[0002] Polyvinyl alcohol (hereinafter referred to as "PVA") resins are known as water-soluble resins and are used in a variety of applications. Applications as aqueous solutions include adhesives, emulsifiers, suspending agents, and coatings, while applications as molded products (mainly films) include polarizing films, water-soluble films, gas barrier films, seed tapes, and fibers. The fields in which they are used are also diverse, including papermaking, agriculture, electrical engineering, pharmaceuticals, cosmetics, food additives, and food packaging materials.

[0003] In particular, when used in cosmetics and edible products, there is a growing demand from customers for performance and design features, requiring products with more stable properties against changes in physical properties, appearance, and color over time. Strict control is especially required for changes in color tone. PVA-based films have long been known to be prone to yellowing, and as a technology to suppress this yellowing, for example, Patent Document 1 discloses a technology comprising a PVA-based resin and a hydrazine-based compound, wherein the content of the hydrazine-based compound is 0.01 to 20 parts by mass per 100 parts by mass of the PVA-based resin. Furthermore, Patent Document 2 discloses a technology for a water-soluble film comprising a PVA-based resin, at least two types of plasticizers and sulfites, wherein the content of plasticizers is 5 to 50 parts by weight per 100 parts by weight of the PVA-based resin, and the content ratio of sulfites to plasticizers is greater than 0.02 and less than or equal to 0.35.

[0004] Japanese Patent Publication No. 2002-256126 Japanese Patent Publication No. 2005-179390

[0005] However, especially when used in cosmetics or edible applications, it is necessary to suppress discoloration over a longer period of time. While the methods described in Patent Documents 1 and 2 can suppress some degree of yellowing, they are still insufficient for long-term suppression of yellowing, and changes in color have been a problem.

[0006] Therefore, against this background, the present invention provides a PVA-based film that is excellent in transparency, and especially in resistance to yellowing.

[0007] However, in view of these circumstances, the inventors have diligently conducted research and have found that a PVA-based film containing a PVA-based resin is １ H-NMR was measured, １ We found that the aforementioned problem can be solved by ensuring that the signal integral value of a specific methyl group observed in the chemical shift, determined from the H-NMR spectrum, satisfies a specified value.

[0008] In other words, the present invention has the following aspects: [1] A PVA-based film containing a PVA-based resin, wherein the PVA-based film １ The integral ratio obtained from the H-NMR spectrum using the following formula (1) is 7.0 × 10⁻¹⁰. －３ The following PVA-based film: Integral ratio = (B / 3) / (b / 3 + a / 2 + B / 3) ... (1) In formula (1), B is the integral value of methyl groups observed at 2.19 to 2.18 ppm, a is the integral value of methylene groups observed at 2.30 to 2.19 ppm and 2.18 to 1.47 ppm, and b is the integral value of methyl groups observed at 2.49 to 2.30 ppm. [2] The PVA-based film according to [1], wherein the PVA-based resin is an unmodified PVA-based resin and / or a modified PVA-based resin having 1,2-diol structural units. [3] A PVA film according to [1] or [2], wherein the rate of change of YI, which can be determined by the following formula (2) from the YI value (initial YI) measured using a spectrophotometer in accordance with JIS K7373:2006 and the YI value after standing for 28 days in an environment of 23°C and 50% RH (after YI acceleration), is 1.8 or less. Rate of change of YI = after YI acceleration / initial YI ... (2) [4] The integral ratio is 5.0 × 10 －３ A PVA-based film as described in any of [1] to [3] below. [5] A PVA-based film as described in any of [1] to [4] that is for cosmetic use or edible use.

[0009] The PVA-based film of the present invention is excellent in transparency, and in particular in its resistance to yellowing.

[0010] The present invention will be described below based on examples of embodiments for carrying out the present invention. However, the present invention is not limited to the embodiments described below.

[0011] In this specification, "x and / or y (where x and y are any combination)" means at least one of x and y, and can mean x only, y only, or x and y. In this specification, when "X to Y" (where X and Y are any numbers) is used, unless otherwise specified, it means "greater than or equal to X and less than or equal to Y," and also includes the meaning of "preferably greater than X" or "preferably less than Y." In this specification, when "greater than or equal to X" (where X is any number) or "less than or equal to Y" (where Y is any number) is used, it also includes the meaning of "preferably greater than X" or "preferably less than Y." In this specification, for numerical ranges described in stages, the upper or lower limit of a numerical range in one stage can be arbitrarily combined with the upper or lower limit of a numerical range in another stage. Furthermore, in numerical ranges described in this specification, the upper or lower limit of that numerical range can be replaced with the values ​​shown in the examples.

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

[0013] A polyvinyl alcohol-based film according to one embodiment of the present invention (hereinafter referred to as "this PVA-based film") contains a PVA-based resin, １ Obtained by H-NMR measurement １ The integral ratio obtained from the H-NMR spectrum using the following formula (1) is 7.0 × 10⁻¹⁰. －３The following holds. Integration ratio = (B / 3) / (b / 3 + a / 2 + B / 3) ··· (1) The integration ratio obtained by the above formula (1) is 6.0×10 －３ or less, more preferably 5.0×10 －３ or less, and particularly preferably 4.0×10 －３ or less. Here, in the above formula (1), B is the integration value of the methyl group observed at 2.19 to 2.18 ppm, a is the integration value of the methylene group observed at 2.30 to 2.19 ppm and 2.18 to 1.47 ppm, and b is the integration value of the methyl group observed at 2.49 to 2.30 ppm. When the integration ratio is within the above range, yellowing of the film can be suppressed. By satisfying such an integration ratio, the reason for the improvement of the yellowing resistance of the film is presumed to be that the generation of carbonyl groups and double bonds due to thermal decomposition of the PVA-based resin is suppressed by making the integration value of the signal of the specific methyl group defined in the above formula (1) lower than a certain number.

[0014] The PVA-based film satisfying the above integration ratio can be obtained, for example, by a method of washing the PVA-based resin, a method of adjusting the amount of the saponification catalyst, a method of adjusting the film-forming conditions, or a method of combining these.

[0015] The １ measurement conditions and analysis conditions of 1H-NMR are as follows. [Measurement conditions] Apparatus: Ascend 400 AVANCE III manufactured by Bruker Solvent: D ２ O Concentration: 5 w / v% Measurement program: N Proton Number of integrations: 16 Measurement temperature (°C): 50 Repetition time: 10 [Analysis conditions] １ Calculate the integration values of the following parts from the 1H-NMR chart. a: 2.30 to 2.19 ppm, 2.18 to 1.47 ppm b: 2.49 to 2.30 ppm B: 2.19 to 2.18 ppm

[0016] In accordance with JIS K7373:2006 of this PVA-based film, the YI value (YI initial) measured using a spectrophotometer is preferably 2.5 or less, more preferably 2.3 or less, and particularly preferably 2.1 or less from the viewpoint of transparency.

[0017] Furthermore, the YI value (after YI enhancement), measured using a spectrophotometer in accordance with JIS K7373:2006 after the PVA-based film has been left standing for 28 days in an environment of 23°C and 50% RH, is preferably 3.0 or less, more preferably 2.5 or less, and particularly preferably 2.3 or less, from the viewpoint of transparency.

[0018] The PVA-based film preferably has a YI change rate of 1.8 or less, more preferably 1.7 or less, and particularly preferably 1.6 or less, calculated by the following formula (2) from the initial YI stage and after YI acceleration. YI change rate = after YI acceleration / initial YI stage ... (2) The PVA-based film tends to have excellent yellowing resistance when the YI change rate is within the above range. The YI change rate can be set to the above range by, for example, a method of washing the PVA-based resin, a method of adjusting the amount of saponification catalyst, a method of adjusting the film formation conditions, or a method of combining these.

[0019] The following describes each component contained in this PVA-based film.

[0020] <PVA-based resin> First, the PVA-based resin contained in this PVA-based film will be described. Examples of the PVA-based resin include unmodified PVA-based resin and modified PVA-based resin. The PVA-based resin may contain one or more types of unmodified PVA-based resin and modified PVA-based resin.

[0021] [Unmodified PVA-based resin] The unmodified PVA-based resin is a resin mainly composed of vinyl alcohol structural units, obtained by saponifying a polyvinyl ester resin obtained by polymerizing vinyl ester compounds, and consists of vinyl alcohol structural units corresponding to the degree of saponification and vinyl ester structural units that remain unsaponified.

[0022] Examples of such vinyl ester compounds include vinyl formate, vinyl acetate, vinyl trifluoroacetate, vinyl propionate, vinyl butyrate, vinyl caprate, vinyl laurylate, vinyl versaticate, vinyl palmitate, and vinyl stearate, but vinyl acetate is preferred. One or more of the vinyl ester compounds can be used in combination.

[0023] [Modified PVA Resins] Modified PVA resins are resins in which modified groups are introduced through copolymerization or post-reactions to resins that mainly consist of vinyl alcohol structural units obtained by saponifying polyvinyl ester resins, which are obtained by polymerizing vinyl ester compounds.

[0024] Examples of the modified PVA resin include copolymerized modified PVA resins obtained by copolymerizing a vinyl ester compound with an unsaturated monomer, and post-modified PVA resins obtained by introducing a modifying group to an unmodified PVA resin through a post-reaction. The copolymerized modified PVA resin consists of vinyl alcohol structural units corresponding to the degree of saponification, vinyl ester structural units that remain unsaponified, and unsaturated monomer structural units obtained by copolymerization. The post-modified PVA resin also consists of vinyl alcohol structural units corresponding to the degree of saponification, vinyl ester structural units that remain unsaponified, and structural units obtained by a post-reaction. Among these, copolymerized modified PVA resins are preferred due to their excellent resistance to yellowing.

[0025] As the vinyl ester compound, the same compound as in the case of the unmodified PVA resin can be used.

[0026] Unsaturated monomers used in the copolymer-modified PVA resin include, for example, olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, and itaconic acid, or their salts or mono or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid, or their salts; alkyl vinyl ethers such as glycerin monoallyl ether; N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallyl vinyl ketone, N-vinylpyrrolidone, vinyl chloride, vinylidene chloride, polyoxyethylene (meth)allyl ether, polyoxypropylene (meth)allyl ether, and other polyoxyalkylenes. Examples include polyoxyalkylene (meth)acrylates such as meth)allyl ether, polyoxyethylene (meth)acrylate, and polyoxypropylene (meth)acrylate; polyoxyalkylene (meth)acrylamides such as polyoxyethylene (meth)acrylamide and polyoxypropylene (meth)acrylamide; polyoxyethylene (1-(meth)acrylamide-1,1-dimethylpropyl) ester; polyoxyethylene vinyl ether; polyoxypropylene vinyl ether; polyoxyethylene allylamine; polyoxypropylene allylamine; polyoxyethylene vinylamine; polyoxypropylene vinylamine; hydroxyl group-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, and 3,4-diacetoxy-1-butene, and their acylated derivatives; vinylethylene carbonate; and carbonates such as 2,2-dialkyl-4-vinyl-1,3-dioxolane. The aforementioned unsaturated monomers can be used individually or in combination of two or more.

[0027] As the copolymerized modified PVA resin, a modified PVA resin having primary hydroxyl groups in its side chains is preferred due to its excellent resistance to yellowing. The number of primary hydroxyl groups in the modified PVA resin having primary hydroxyl groups in its side chains is usually 1 to 5, preferably 1 to 2, and particularly preferably 1. Furthermore, the modified PVA resin having primary hydroxyl groups in its side chains may also have secondary hydroxyl groups in addition to primary hydroxyl groups.

[0028] Examples of modified PVA resins having primary hydroxyl groups in the side chains include modified PVA resins having hydroxyalkyl groups in the side chains and modified PVA resins having 1,2-diol structural units in the side chains. Among these, modified PVA resins having 1,2-diol structural units in the side chains are preferred due to their excellent resistance to yellowing.

[0029] Examples of the post-modified PVA resins include those having acetoacetyl groups obtained by reaction with diketene, those having polyalkylene oxide groups obtained by reaction with ethylene oxide, those having hydroxyalkyl groups obtained by reaction with epoxy compounds, etc., or those obtained by reacting PVA resins with aldehyde compounds having various functional groups by esterification, acetalization, urethaneization, etherization, grafting, phosphate esterification, oxyalkyleneization, etc.

[0030] The amount of modification of the modified PVA resin is preferably 1 to 20 mol%, more preferably 1.5 to 15 mol%, and particularly preferably 2 to 12 mol%. If the amount of modification is too small, the solubility of the PVA film in water tends to decrease, and if it is too large, the productivity of the PVA resin tends to decrease, the biodegradability tends to decrease, and the PVA film tends to become more prone to blocking.

[0031] Further, when using a modified PVA-based resin having a primary hydroxyl group in the side chain as the modified PVA-based resin, the modification amount is preferably 1 to 10 mol%, more preferably 1.5 to 9 mol%, and particularly preferably 2 to 8 mol%. If such a modification amount is too small, the solubility of the PVA-based film in water tends to decrease. If it is too large, the productivity of the PVA resin tends to decrease and the biodegradability tends to decrease. Also, the PVA-based film tends to cause blocking.

[0032] In this PVA-based film, from the viewpoint of film physical properties such as solubility and mechanical properties, it is preferable that the PVA-based resin is the main component of this PVA-based film. Among them, from the viewpoint of yellowing resistance, an unmodified PVA-based resin and / or a modified PVA-based resin having a primary hydroxyl group in the side chain is preferable, and more preferably an unmodified PVA-based resin and / or a modified PVA-based resin having a 1,2-diol structural unit.

[0033] When the PVA-based resin contains an unmodified PVA-based resin and a modified PVA-based resin having a primary hydroxyl group in the side chain, the mass content ratio (unmodified PVA-based resin / modified PVA-based resin having a primary hydroxyl group in the side chain) is usually 1 / 99 to 99 / 1, preferably 5 / 95 to 95 / 5, and more preferably 10 / 90 to 90 / 10. Also, from the viewpoint of film physical properties such as solubility in water, the mass content ratio (unmodified PVA-based resin / modified PVA-based resin having a primary hydroxyl group in the side chain) is preferably 5 / 95 to 40 / 60, particularly preferably 6 / 94 to 30 / 70, and more preferably 7 / 93 to 20 / 80. If the content ratio of the unmodified PVA-based resin is too small, the yellowing resistance tends to decrease. If the content ratio of the modified PVA-based resin is too small, the solubility tends to decrease.

[0034] [Method for Producing PVA-Based Resin] Next, a method for producing a PVA-based resin will be described. When the PVA-based resin is an unmodified PVA-based resin, it can be obtained by saponifying a polymer obtained by polymerizing a vinyl ester-based compound. When the PVA-based resin is a modified PVA-based resin, it can be obtained by a method of polymerizing an unsaturated monomer copolymerizable with a vinyl ester-based monomer and then saponifying, or a method of introducing a modifying group into an unmodified PVA-based resin by a post-reaction, etc.

[0035] Further, when the PVA-based resin is a modified PVA-based resin having a 1,2-diol structural unit in the side chain, for example, (i) a method of saponifying a polymer of vinyl acetate and 3,4-diacetoxy-1-butene, (ii) a method of saponifying and decarboxylating a polymer of vinyl acetate and vinyl ethylene carbonate, (iii) a method of saponifying and deketalizing a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane, (iv) a method of saponifying a polymer of vinyl acetate and glycerin monoallyl ether, etc. can be used for production.

[0036] As the polymerization method, for example, known polymerization methods such as solution polymerization method, emulsion polymerization method, suspension polymerization method, etc. can be arbitrarily used, but usually, it is carried out by a solution polymerization method using an alcohol such as methanol, ethanol or isopropyl alcohol as a solvent.

[0037] Also, it is preferable to use a polymerization catalyst for the polymerization. The polymerization catalyst can be appropriately selected according to the polymerization method, and examples include known polymerization catalysts such as azo-based catalysts such as azobisisobutyronitrile, and peroxide catalysts such as acetyl peroxide, benzoyl peroxide, lauroyl peroxide, etc.

[0038] Also, the reaction temperature of the polymerization is selected from the range of about 50°C to the boiling point.

[0039] Saponification can be carried out by known methods, and is usually performed by dissolving the resulting polymer in an alcohol in the presence of a saponification catalyst. Examples of alcohols include methanol, ethanol, and butanol. The concentration of the copolymer in the alcohol is selected from a range of 20 to 50% by mass from the viewpoint of solubility.

[0040] As the saponification catalyst, for example, alkali catalysts such as alkali metal hydroxides or alkoxides such as sodium hydroxide, potassium hydroxide, sodium methylate, sodium ethylate, and potassium methylate can be used, and acid catalysts can also be used. From the viewpoint of keeping the integral ratio obtained by formula (1) below a certain number, the amount of saponification catalyst used is usually 1 to 100 mmol equivalents, preferably 1.2 to 50 mmol equivalents, more preferably 1.5 to 20 mmol equivalents, and particularly preferably 1.7 to 10 mmol equivalents per mole of vinyl acetate structural units of the polymer.

[0041] Furthermore, after saponification, it is preferable to wash the obtained PVA-based resin with a washing solution, from the viewpoint of making the integral ratio determined by formula (1) below a certain number. Examples of such washing solutions include alcohols such as methanol, ethanol, isopropyl alcohol, and butanol, with methanol being preferred from the viewpoint of washing efficiency and drying efficiency.

[0042] Furthermore, while a continuous cleaning method is acceptable, a batch method is usually employed. The bath ratio (mass of cleaning solution / mass of PVA resin) is typically 1 to 30, preferably 2 to 20, and more preferably 3 to 10. If the bath ratio is too high, a large cleaning device is required, which tends to increase costs, while if the bath ratio is too low, the cleaning effect decreases, which tends to increase the number of cleaning cycles.

[0043] The washing temperature is typically 10 to 80°C, with 20 to 70°C being particularly preferred. If the temperature is too high, the amount of volatilization of the washing solution increases, and a reflux system tends to be required. If the temperature is too low, the washing efficiency tends to decrease. The washing time is typically 5 minutes to 12 hours. If the washing time is too long, production efficiency tends to decrease, and if the washing time is too short, the washing tends to be insufficient. The number of washing cycles is typically 1 to 10, with 1 to 5 being particularly preferred. If the number of washing cycles is too high, productivity tends to decrease and costs tend to increase.

[0044] The washed PVA resin is dried with hot air or the like in a continuous or batch process. The drying temperature (temperature inside the dryer) is usually preferably 50 to 150°C, more preferably 60 to 130°C, and particularly preferably 70 to 110°C. If the drying temperature is too high, the PVA resin tends to degrade due to heat, and if the drying temperature is too low, drying tends to take a long time. The drying time is usually preferably 1 to 48 hours, and particularly preferably 2 to 36 hours. If the drying time is too long, the PVA resin tends to degrade due to heat, and if the drying time is too short, drying tends to be insufficient or high-temperature drying may be required.

[0045] The solvent content in the PVA resin after drying is typically 0 to 10% by mass, more preferably 0.1 to 5% by mass, and even more preferably 0.1 to 1% by mass.

[0046] The average degree of saponification of the PVA resin is preferably 80 mol% or more, particularly preferably 85 to 99 mol%, and even more preferably 90 to 98 mol%. If the average degree of saponification is too low, the solubility in water tends to decrease. Conversely, if the average degree of saponification is too high, the solubility in water also tends to decrease.

[0047] The average degree of saponification of the unmodified PVA resin is preferably 80 mol% or more, particularly preferably 82 to 99 mol%, and even more preferably 85 to 90 mol%. If the average degree of saponification is too low, the solubility in water tends to decrease. Conversely, if the average degree of saponification is too high, the solubility in water also tends to decrease.

[0048] The average degree of saponification of the modified PVA resin is preferably 80 mol% or more, particularly preferably 85 to 99.9 mol%, and even more preferably 90 to 99.0 mol%. If the average degree of saponification is too low, the solubility in water tends to decrease. If the average degree of saponification is too high, the solubility in water tends to decrease significantly due to the thermal history during film formation.

[0049] Furthermore, when a modified PVA resin having primary hydroxyl groups in its side chains is used as the modified PVA resin, its average degree of saponification is preferably 85 mol% or more, particularly preferably 88 to 99.9 mol%, even more preferably 90 to 99.5 mol%, and especially preferably 90 to 99.0 mol%.

[0050] The viscosity of the 4% by mass aqueous solution of the PVA-based resin at 20°C is preferably 10 to 50 mPa·s, particularly preferably 15 to 45 mPa·s, and even more preferably 20 to 40 mPa·s. If the viscosity is too low, the mechanical strength tends to decrease, and if it is too high, the viscosity of the aqueous solution during film formation tends to be high, which tends to reduce productivity.

[0051] The viscosity of the 4% by mass aqueous solution of the unmodified PVA resin at 20°C is preferably 10 to 50 mPa·s, particularly preferably 15 to 45 mPa·s, and even more preferably 20 to 40 mPa·s. If the viscosity is too low, the mechanical strength tends to decrease, and if it is too high, the viscosity of the aqueous solution during film formation tends to be high, which tends to reduce productivity.

[0052] The viscosity of the 4% by mass aqueous solution of the modified PVA resin at 20°C is preferably 10 to 50 mPa·s, particularly preferably 15 to 45 mPa·s, and even more preferably 20 to 40 mPa·s. If the viscosity is too low, the mechanical strength tends to decrease, and if it is too high, the viscosity of the aqueous solution during film formation tends to be high, which tends to reduce productivity.

[0053] The average degree of saponification was measured in accordance with JIS K 6726 3.5, and the viscosity of the 4% by mass aqueous solution was measured in accordance with JIS K 6726 3.11.2.

[0054] This PVA-based film may also contain plasticizers, fillers, surfactants, and other additives in addition to the PVA-based resin.

[0055] [Plasticizer] This PVA-based film is preferable to contain a plasticizer, as it can impart appropriate flexibility to the film. One type of plasticizer may be used, or two or more types may be used in combination. Using two or more types in combination is preferable from the viewpoint of the film's mechanical properties and moldability.

[0056] Examples of the aforementioned plasticizers include glycerin derivatives such as glycerin, diglycerin, and triglycerin; alkylene glycols such as diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, and dipropylene glycol; and sugar alcohols such as trimethylolpropane, sorbitol, xylitol, and maltitol. Among these, glycerin, diglycerin, and polyethylene glycol are preferred because they are readily available and provide a plasticizing effect in small amounts, and sorbitol is preferred in terms of the long-term stability of PVA-based films. These can be used individually or in combination of two or more.

[0057] When two or more plasticizers are used in combination, it is preferable to use a polyhydric alcohol with a melting point of 80°C or higher and a polyhydric alcohol with a melting point of 50°C or lower. Furthermore, as the plasticizer, a compound that is liquid at room temperature is preferred in terms of productivity and the mechanical properties of the resulting film, and a melting point of 30°C or lower, particularly 20°C or lower, is preferred. The lower limit of the melting point is usually -95°C, preferably -40°C, particularly preferably -15°C, and even more preferably -5°C.

[0058] If the PVA-based film contains a plasticizer, the content is preferably 10 to 60 parts by mass, particularly preferably 15 to 55 parts by mass, and even more preferably 20 to 50 parts by mass, per 100 parts by mass of the PVA-based resin. If the plasticizer content is too low, the plasticizing effect is low and the processability tends to decrease, while if it is too high, the strength of the film tends to decrease and blocking tends to occur.

[0059] [Filler] This PVA-based film may contain a filler as needed. The filler is included for the purpose of preventing blocking, and examples include organic fillers and inorganic fillers, but the inclusion of an organic filler is preferred. One or more types of fillers may be used in combination.

[0060] The average particle diameter of the filler is preferably 0.1 to 50 μm, and particularly preferably 1 to 35 μm. The average particle diameter of the filler is a value measured using a laser diffraction particle size distribution analyzer, and is calculated from the D50 value (particle diameter at 50% cumulative volume) of the obtained cumulative volume distribution.

[0061] The aforementioned organic filler refers to particulate matter (primary particles) composed of organic compounds, having any shape such as needle-shaped, rod-shaped, layered, flake-shaped, or spherical, or aggregates of such particulate matter (secondary particles). The aforementioned organic filler is mainly selected from polymer compounds, and examples include melamine resins, polymethyl (meth)acrylate resins, polystyrene resins, as well as biodegradable resins such as starch and polylactic acid. Among these, biodegradable resins such as polymethyl (meth)acrylate resins, polystyrene resins, and starch are preferred, and starch is particularly preferred in terms of dispersibility in PVA resins.

[0062] Examples of the aforementioned starches include raw starch (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, water chestnut starch, etc.), physically modified starch (α-starch, fractionated amylose, moist heat-treated starch, etc.), enzyme-modified starch (hydrolyzed dextrin, enzymatically decomposed dextrin, amylose, etc.), chemically decomposed modified starch (acid-treated starch, hypochlorite-oxidized starch, dialdehyde starch, etc.), and chemically modified starch derivatives (esterified starch, etherified starch, cationized starch, cross-linked starch, etc.). Among these, raw starch, particularly corn starch and rice starch, is preferred in terms of biodegradability, ease of availability, and economic efficiency.

[0063] The average particle size of the organic filler is preferably 5 to 50 μm, particularly preferably 10 to 40 μm, and even more preferably 15 to 35 μm. If the average particle size is too small, the blocking properties of the film tend to increase, and if it is too large, the fillers tend to aggregate, reducing dispersibility, and pinholes tend to form when the film is stretched during molding.

[0064] As the inorganic filler, oxide-based inorganic compounds and talc are preferred, and in particular titanium oxide, talc, and silica are preferred, and even more preferably silica is used.

[0065] The average particle size of the inorganic filler is preferably 1 to 20 μm, particularly preferably 2 to 15 μm, and even more preferably 3 to 10 μm. If the average particle size is too small, the flexibility and toughness of the film tend to decrease, and blocking properties tend to increase. If it is too large, pinholes tend to form when the film is stretched during molding.

[0066] If this PVA-based film contains filler, the amount is preferably 1 to 30 parts by mass, particularly preferably 1.5 to 25 parts by mass, and even more preferably 2 to 20 parts by mass, per 100 parts by mass of PVA-based resin. If the amount is too low, the blocking properties of the film tend to increase, and if it is too high, the flexibility and toughness of the film tend to decrease.

[0067] [Surfactants] This PVA-based film may contain surfactants as needed. The surfactants are included for the purpose of improving the release properties from the cast surface during film manufacturing, and typically include nonionic surfactants, cationic surfactants, and anionic surfactants. Specifically, examples include polyoxyethylene nonylphenyl ether, polyoxyethylene octyl nonyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene alkyl allyl ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, polyoxyalkylene alkyl ether phosphate monoethanolamine salt, polyoxyethylene laurylamino ether, polyoxyethylene stearylamino ether, and other polyoxyethylene alkylamino ethers, sorbitan monopalmitate, sorbitan monostearate, glyceryl stearate, sucrose fatty acid ester, etc. Among these, polyoxyalkylene alkyl ether phosphate monoethanolamine salt and polyoxyethylene laurylamino ether are preferred in terms of manufacturing stability. The surfactants can be used individually or in combination of two or more types.

[0068] If the PVA-based film contains a surfactant, its content is preferably 0.01 to 3 parts by mass, particularly preferably 0.05 to 2.5 parts by mass, and even more preferably 0.1 to 2 parts by mass, per 100 parts by mass of the PVA-based resin. If the content is too low, the peelability between the casting surface of the film-making apparatus and the manufactured film tends to decrease, reducing productivity. If the content is too high, blocking tends to occur, and the adhesive strength when sealing a package using the film tends to decrease.

[0069] Furthermore, this PVA-based film may also contain, to the extent that it does not hinder the purpose of the invention, antioxidants, fragrances, rust inhibitors, colorants, fillers, defoamers, ultraviolet absorbers, liquid paraffins, fluorescent whitening agents, bittering components (e.g., denatonium benzoate), etc. These can be used individually or in combination of two or more.

[0070] Examples of the aforementioned antioxidants include sulfites such as sodium sulfite, potassium sulfite, calcium sulfite, and ammonium sulfite, as well as tartaric acid, ascorbic acid, sodium thiosulfate, catechol, and rongalit. These can be used individually or in combination of two or more. Among these, sulfites are preferred, and sodium sulfite is more preferred.

[0071] Although this PVA-based film can suppress yellowing even without containing an antioxidant, if an antioxidant is further included, the content is preferably 0.1 to 10 parts by mass, particularly preferably 0.2 to 5 parts by mass, and even more preferably 0.3 to 3 parts by mass, per 100 parts by mass of the PVA-based resin.

[0072] <Manufacturing of PVA-based film> This PVA-based film can be manufactured by preparing an aqueous solution (film-forming raw material) of a PVA-based resin composition containing a PVA-based resin, and then forming a film.

[0073] In detail, a PVA-based film can be manufactured by a manufacturing method comprising, in this order, a preparation step of dissolving or dispersing a PVA-based resin composition containing a PVA-based resin, preferably a plasticizer, filler, surfactant, etc., in water to obtain an aqueous solution of the PVA-based resin composition (film-forming raw material), and a film-forming step of forming a PVA-based film using the film-forming raw material obtained in the above step. Each step will be described in detail below.

[0074] [Preparation Process] The preparation process involves dissolving or dispersing the PVA-based resin composition in water to prepare an aqueous solution of the PVA-based resin composition (film-forming raw material). The preparation process refers to the steps taken to obtain an aqueous solution of the PVA-based resin free of undissolved matter, by dissolving or dispersing the PVA-based resin composition in water.

[0075] Common methods for dissolving the PVA-based resin composition in water include dissolution at room temperature, dissolution at high temperature, and dissolution under pressure. Among these, dissolution at high temperature and dissolution under pressure are preferred because they produce less undissolved material and offer superior productivity.

[0076] The dissolution temperature is typically 80 to 100°C, preferably 90 to 95°C, for high-temperature dissolution, and typically 80 to 130°C, preferably 90 to 120°C, for pressure dissolution. The dissolution time can be adjusted as appropriate depending on the dissolution temperature and pressure, but is typically 1 to 20 hours, preferably 2 to 15 hours, and more preferably 3 to 10 hours. If the dissolution time is too short, undissolved material tends to remain, and if it is too long, productivity tends to decrease.

[0077] Furthermore, examples of stirring blades used in the dissolution process include paddles, full zones, max blends, twin stars, anchors, ribbons, and propellers.

[0078] The solid content concentration of the film-forming raw material is preferably 10 to 50% by mass, particularly preferably 15 to 40% by mass, and even more preferably 20 to 35% by mass. If the concentration is too low, the productivity of the film tends to decrease, and if it is too high, the viscosity becomes too high, which tends to require more time to degas the film-forming raw material or cause die lines to form during film formation.

[0079] Furthermore, after dissolution, the resulting aqueous solution of the PVA-based resin composition is subjected to a defoaming treatment. Examples of such defoaming methods include static defoaming, vacuum defoaming, and twin-screw extrusion defoaming. Among these, static defoaming and twin-screw extrusion defoaming are preferred. The temperature for static defoaming is usually 50 to 100°C, preferably 70 to 95°C, and the defoaming time is usually 2 to 30 hours, preferably 5 to 20 hours.

[0080] [Film Forming Process] In the film forming process, the film-forming raw material prepared in the preparation process is formed into a film, and a drying treatment is performed as necessary to form a PVA-based film. For film forming, methods such as melt extrusion and casting can be used, and casting is preferred in terms of accuracy of film thickness.

[0081] As for the casting method, for example, the PVA-based film can be manufactured by casting the film-forming raw material by (I) passing it through gaps using an applicator, bar coater, etc., and casting it onto a casting surface such as a metal surface, or (II) extruding it from a slit such as a T-type slit die and casting it onto a casting surface such as a metal surface of an endless belt or drum roll, and then drying it. Among these, method (II) is preferred. Method (II) will be described below.

[0082] The temperature at which the film-forming raw material is cast is preferably 60 to 98°C, and particularly preferably 70 to 95°C. If the temperature is too low, the viscosity of the film-forming raw material tends to increase, reducing the productivity of PVA-based films, and if it is too high, foaming and other issues tend to occur.

[0083] After casting, the film-forming raw material is dried on the cast surface. The surface temperature of the cast surface is preferably 50 to 110°C, and particularly preferably 70 to 100°C. If the surface temperature is too low, the film tends to have a high moisture content due to insufficient drying, making it prone to blocking. If it is too high, the film-forming raw material tends to foam, resulting in poor film formation. In addition, drying during film formation can be done in combination with methods such as drying with a hot roll, drying by blowing hot air onto the film using a floating dryer, or drying with a far-infrared device or dielectric heating device.

[0084] After drying the film-forming raw material in the above drying process until the moisture content is 15% by mass or less, the PVA-based film is obtained by peeling it off the cast surface (or peeling it off the drying hot roll if further drying with a hot roll is performed after peeling from the cast surface). The PVA-based film peeled off the cast surface (or drying hot roll) is cooled in an environment of 10 to 35°C.

[0085] Furthermore, while the surface of this PVA-based film may be plain, it is also preferable to apply an embossed pattern, a fine uneven pattern, or a special engraved pattern to one or both sides of the PVA-based film for reasons of blockage resistance, slipperiness during processing, reduced adhesion between products, and appearance.

[0086] The processing temperature during the aforementioned texture processing is usually 60 to 150°C, preferably 80 to 140°C. The processing pressure is usually 2 to 8 MPa, preferably 3 to 7 MPa. The processing time depends on the processing pressure and film formation speed, but is usually 0.01 to 5 seconds, preferably 0.1 to 3 seconds. If necessary, the PVA-based film may be cooled after the texture processing to prevent unintended stretching of the film due to heat.

[0087] Furthermore, the PVA-based film is preferably manufactured in an environment of 10 to 35°C, particularly 15 to 30°C, and the humidity is preferably 70% RH or less. In this way, the PVA-based film can be manufactured.

[0088] The thickness of this PVA-based film is preferably 10 to 120 μm, particularly preferably 30 to 110 μm, and even more preferably 60 to 100 μm. If the thickness is too thin, the mechanical strength of the PVA-based film tends to decrease, and if it is too thick, the film-forming efficiency tends to decrease.

[0089] Furthermore, the moisture content of the PVA-based film is preferably 1 to 12% by mass, and particularly preferably 4 to 10% by mass. If the moisture content of the film is too low, the PVA-based film tends to become too hard, reducing its moldability and impact resistance, while if it is too high, blocking tends to occur.

[0090] The PVA-based film obtained in this way has excellent transparency, and especially resistance to yellowing, making it useful for a variety of applications, including polarizing films requiring high optical properties (LCD TVs, smartphones, tablets, personal computers, projectors, automotive panels, etc.) and water-soluble film applications (unit packaging for chemicals such as pesticides and detergents, cosmetics and edible products, (water pressure) transfer films, sanitary products such as napkins and diapers, waste disposal products such as ostomy bags, medical products such as blood-absorbing sheets, and temporary substrates such as seedling sheets, seed tapes, and embroidery base fabrics). In particular, this PVA-based film can be suitably used for cosmetic and edible applications.

[0091] 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 unless it exceeds the gist of the invention. In the examples, "parts" and "%" refer to mass.

[0092] [Preparation of PVA-based resin (A)] (PVA-based resin 1) In a reaction vessel equipped with a reflux condenser, dropping funnel, and stirrer, 28 parts vinyl acetate, 30 parts methanol, and 0.06 mol% acetyl peroxide (relative to the charged vinyl acetate) were charged, and polymerization was started by raising the temperature while stirring under a nitrogen atmosphere. Furthermore, 0.4 hours after the start of polymerization, 72 parts vinyl acetate was added dropwise at a constant rate over 9.5 hours. When the polymerization rate of vinyl acetate reached 92%, a predetermined amount of hydroquinone monomethyl ether was added to terminate the polymerization, and then unreacted vinyl acetate monomer was removed from the system by distillation while blowing methanol vapor to obtain a methanol solution of vinyl acetate polymer. Subsequently, the methanol solution of vinyl acetate polymer was further diluted with methanol to a solid content concentration of 50%, and charged into a kneader. After that, while maintaining the solution temperature at 35°C, saponification was carried out by adding a 2% methanol solution of sodium hydroxide at a ratio of 6.0 mmol per mole of vinyl acetate structural units in the polymer. As saponification progressed, the saponified product precipitated and became particulate. At this point, it was diluted with methanol, centrifuged, and dried to obtain a PVA-based resin. The PVA-based resin obtained above was placed in methanol (at room temperature) at a bath ratio of 4:1 and washed by stirring for 2 hours, followed by solid-liquid separation. Further, methanol (at room temperature) was gradually added to the PVA-based resin. After the added methanol came into contact with the PVA-based resin, solid-liquid separation was performed using a rotating shaker. Then, fresh methanol was gradually added, and solid-liquid separation was performed by shaking. This process was repeated (a total of 6 times (by mass) of methanol was used). Next, it was vacuum-dried at 90°C until the volatile content was 1% or less. Furthermore, 13 times (by mass) of methanol was added to the vacuum-dried PVA-based resin, and it was heated and stirred at 80°C for 6 hours. The methanol was then removed, and 13 times (by mass) of methanol was added again, and it was heated and stirred at 80°C for 6 hours. Finally, the methanol was removed by suction to obtain a PVA-based resin. The obtained PVA-based resin was vacuum-dried at 98°C and 12 kPa for 4 hours to obtain PVA-based resin 1. The degree of saponification of the obtained PVA-based resin 1 was analyzed by the amount of alkali consumed for hydrolysis of the remaining vinyl acetate, and was found to be 88 mol%, and the viscosity of a 4% aqueous solution was 5 mPa·s.Furthermore, the integral ratio of PVA resin 1, which can be determined by the method described later, is 4.7 × 10. －３ That was the case.

[0093] (PVA-based resin 2) In a reaction vessel equipped with a reflux condenser, dropping funnel, and stirrer, 100 parts vinyl acetate, 14 parts methanol, and 0.05 mol% azobisisobutyronitrile (relative to the charged vinyl acetate) were charged, and polymerization was started by raising the temperature while stirring under a nitrogen atmosphere. Five hours after the start of polymerization, when the polymerization rate of vinyl acetate reached 65%, m-dinitrobenzene was added to terminate the polymerization, and then unreacted vinyl acetate monomer was removed from the system by distillation while blowing methanol vapor to obtain a methanol solution of vinyl acetate polymer. Subsequently, the methanol solution of vinyl acetate polymer was further diluted with methanol to a solid content concentration of 33% and charged into a kneader. Then, while maintaining the solution temperature at 40°C, a 3.5% methanol solution of sodium hydroxide was added at a ratio of 2.0 mmol per mole of vinyl acetate structural units in the polymer to carry out saponification. As saponification progressed, the saponified product precipitated and became particulate, at which point it was diluted with methanol, centrifuged, and dried to obtain a PVA-based resin. The PVA-based resin obtained above was placed in methanol (at room temperature) at a bath ratio of 4:1 and washed by stirring for 2 hours, followed by solid-liquid separation. Further, methanol (at room temperature) was gradually added to the PVA-based resin. The added methanol came into contact with the PVA-based resin and was separated into solid and liquid components using a rotating shaker. Then, fresh methanol was gradually added, and solid-liquid separation was performed by shaking. This process was repeated (a total of 6 times the bath ratio (by mass) of methanol was used). Next, the mixture was vacuum-dried at 90°C until the volatile content was less than 1% to obtain PVA-based resin 2. The degree of saponification of the obtained PVA-based resin 2 was analyzed by the amount of alkali consumed for hydrolysis of the remaining vinyl acetate, and was found to be 88 mol%, with a viscosity of 4% aqueous solution of 42 mPa·s. Furthermore, the integral ratio of PVA-based resin 2, determined by the method described later, was 4.2 × 10⁻⁶. －３ That was the case.

[0094] (PVA-based resin 3) In a reaction vessel equipped with a reflux condenser, dropping funnel, and stirrer, 28 parts vinyl acetate, 30 parts methanol, and 0.06 mol% acetyl peroxide (relative to the charged vinyl acetate) were charged, and polymerization was started by raising the temperature while stirring under a nitrogen atmosphere. Furthermore, 0.4 hours after the start of polymerization, 72 parts vinyl acetate was added dropwise at a constant rate over 9.5 hours. When the polymerization rate of vinyl acetate reached 92%, a predetermined amount of hydroquinone monomethyl ether was added to terminate the polymerization, and then unreacted vinyl acetate monomer was removed from the system by distillation while blowing methanol vapor to obtain a methanol solution of vinyl acetate polymer. Subsequently, the methanol solution of vinyl acetate polymer was further diluted with methanol to a solid content concentration of 50% and charged into a kneader. Then, while maintaining the solution temperature at 35°C, saponification was carried out by adding a 2% methanol solution of sodium hydroxide at a ratio of 6.0 mmol per mole of vinyl acetate structural units in the polymer. As saponification progressed, the saponified product precipitated and became particulate. At this point, it was diluted with methanol, centrifuged, and dried to obtain PVA-based resin 3. The degree of saponification of the obtained PVA-based resin 3 was analyzed by the amount of alkali consumed for hydrolysis of the remaining vinyl acetate, and was found to be 88 mol%. The viscosity of a 4% aqueous solution was 5 mPa·s. Furthermore, the integral ratio of PVA-based resin 3, determined by the method described later, was 11.4 × 10⁻⁶. －３ That was the case.

[0095] (PVA-based resin 4) In a reaction vessel equipped with a reflux condenser, dropping funnel, and stirrer, 100 parts vinyl acetate, 14 parts methanol, and 0.05 mol% azobisisobutyronitrile (relative to the charged vinyl acetate) were charged, and polymerization was started by raising the temperature while stirring under a nitrogen atmosphere. Furthermore, when the polymerization rate of vinyl acetate reached 65% after 5 hours from the start of polymerization, m-dinitrobenzene was added to terminate the polymerization, and then unreacted vinyl acetate monomer was removed from the system by distillation while blowing methanol vapor to obtain a methanol solution of vinyl acetate polymer. Subsequently, the methanol solution of vinyl acetate polymer was further diluted with methanol to a solid content concentration of 33% and charged into a kneader. After that, while maintaining the solution temperature at 40°C, a 3.5% methanol solution of sodium hydroxide was added at a ratio of 2.0 mmol per mole of vinyl acetate structural units in the polymer to carry out saponification. As saponification progressed, the saponified product precipitated and became particulate. At this point, it was diluted with methanol, centrifuged, and dried to obtain PVA-based resin 4. The degree of saponification of the obtained PVA-based resin 4 was analyzed by the amount of alkali consumed for hydrolysis of the remaining vinyl acetate, and was found to be 88 mol%. The viscosity of a 4% aqueous solution was 42 mPa·s. Furthermore, the integral ratio of PVA-based resin 4, determined by the method described later, was 10.2 × 10⁻⁶. －３ That was the case.

[0096] (PVA-based resin 5) In a reaction vessel equipped with a reflux condenser, dropping funnel, and stirrer, 300 parts vinyl acetate, 87 parts methanol, and 0.15 parts monomethyl maleate were charged, and the reaction vessel was immersed in a water bath and heated. With reflux occurring in the reaction vessel, 1.05 parts of 2,2'-azobis(isobutyronitrile) was added as a polymerization catalyst to start polymerization. Simultaneously with the start of polymerization, a 5% monomethyl maleate solution consisting of 5% monomethyl maleate, 5% methanol, and 90% vinyl acetate was added dropwise. After polymerization for 6 hours, 0.12 parts m-dinitrobenzene and 500 parts methanol were added as polymerization termination agents to terminate polymerization. The obtained polymerized solution was distilled off under reduced pressure to remove methanol and vinyl acetate, and when the viscosity increased, methanol was added to expel the remaining vinyl acetate to obtain a methanol solution of vinyl acetate polymer. Subsequently, the obtained methanol solution of vinyl acetate polymer was further diluted with methanol to a solid concentration of 9%. 1500 parts of a methanol solution of this vinyl acetate polymer were placed in a reaction vessel similar to the one described above, and heated to an internal temperature of 50°C. 90.1 parts of a 3.5% methanol solution of sodium hydroxide were added to initiate the saponification reaction. Fifty minutes after adding the 3.5% methanol solution of sodium hydroxide, 1.5 parts of acetic acid and 500 parts of methanol were added to stop the saponification reaction, and the resulting saponified product was crushed and filtered. The obtained saponified product was washed with methanol and then dried in a vacuum dryer at 50°C for 20 hours to obtain a carboxyl group-modified PVA resin (PVA resin 5). The degree of saponification of the obtained carboxyl group-modified PVA resin (PVA resin 5) was analyzed by the amount of alkali consumed for hydrolysis of the remaining vinyl acetate, and was found to be 94 mol%. The viscosity of a 4% aqueous solution was 22 mPa·s, and the maleate monomethyl modification rate was 2.0 mol%. Furthermore, the integral ratio of PVA resin 5, determined by the method described later, was 8.6 × 10⁻⁶. －３ That was the case.

[0097] [Plasticizer (B)] ・Plasticizer (b1): Xylitol ・Plasticizer (b2): Sorbitol ・Plasticizer (b3): ​​Glycerin [Other additives] ・Starch (average particle size 20 μm)

[0098] <Example 1> 100 parts of PVA resin 2, 8 parts of plasticizer (b1), 7 parts of plasticizer (b2), 2.5 parts of plasticizer (b3), 0.8 parts of starch as a filler, and water were mixed and dissolved to obtain an aqueous solution of the PVA resin composition in which starch was dispersed (solid content concentration 25%). The obtained aqueous solution of the PVA resin composition was degassed at 80°C and cooled to 40°C. The aqueous solution of the PVA resin composition was cast onto a polypropylene film and dried by passing it through a 10 m drying chamber (60-80°C) at a speed of 2-4 m / min to obtain a water-soluble film with a thickness of 78 μm and a water content of 7%.

[0099] <Example 2> The conditions were the same as in Example 1, except that the PVA resin used was 30 parts of PVA resin 1 and 70 parts of PVA resin 2, and a water-soluble film with a thickness of 80 μm and a water content of 7% was obtained.

[0100] <Example 3> The conditions were the same as in Example 1, except that the PVA resin used was 70 parts of PVA resin 2 and 30 parts of PVA resin 3, and a water-soluble film with a thickness of 80 μm and a water content of 7% was obtained.

[0101] <Comparative Example 1> 90 parts of PVA resin 5, 10 parts of PVA resin 4, 20 parts of plasticizer (b2), 20 parts of plasticizer (b3), 8 parts of starch as a filler, and water were mixed and dissolved to obtain an aqueous solution of the PVA resin composition in which starch was dispersed (solid content concentration 30%). The obtained aqueous solution of the PVA resin composition was degassed at 80°C and cooled to 40°C. The aqueous solution of the PVA resin composition was cast onto a polypropylene film and dried by passing it through a 10 m drying chamber (60-80°C) at a speed of 2-4 m / min to obtain a water-soluble film with a thickness of 76 μm and a water content of 7%.

[0102] <Comparative Example 2> The conditions were the same as in Example 1, except that the PVA resin used was 30 parts of PVA resin 1 and 70 parts of PVA resin 4, and a water-soluble film with a thickness of 80 μm and a water content of 7% was obtained.

[0103] The following evaluations were performed using the PVA-based films of the above-mentioned examples and comparative examples. The results are shown in Table 1 below.

[0104] [ １[H-NMR Measurement] The PVA-based films of the examples and comparative examples were measured under the following conditions. １ 1H-NMR measurements were performed, and the results were obtained. １ The 1H-NMR spectrum was analyzed under the following conditions. The integral ratio was then calculated using the following equation (1). [Measurement Conditions] Apparatus: Brucker Ascend 400 AVANCE III Solvent: D ２ O concentration: 5 w / v% Measurement program: N Proton Number of cumulative operations: 16 Measurement temperature (°C): 50 Repeat time: 10 [Analysis conditions] １ The integral values ​​for the following regions are calculated from the H-NMR chart: a: 2.30–2.19 ppm, 2.18–1.47 ppm b: 2.49–2.30 ppm B: 2.19–2.18 ppm

[0105] [Integration Ratio] Integration ratio = (B / 3) / (b / 3 + a / 2 + B / 3) ... (1) In equation (1) above, B is the integral value of the methyl group observed between 2.19 and 2.18 ppm, a is the integral value of the methylene group observed between 2.30 and 2.19 ppm and between 2.18 and 1.47 ppm, and b is the integral value of the methyl group observed between 2.49 and 2.30 ppm.

[0106] [Degree of Yellowing (YI Value)] The degree of yellowing (YI value) of the PVA-based films of the examples and comparative examples was measured using a spectrophotometer in accordance with JIS K7373:2006 (initial YI). In addition, the PVA-based films of the examples and comparative examples were left to stand for 28 days in an environment of 23°C and 50% RH, and the degree of yellowing after standing was measured (after YI acceleration), and the YI change rate was calculated from the following formula (2). YI change rate = YI after YI acceleration / YI initial ... (2)

[0107]

[0108] From the results in Table 1 above, the integral ratio is 7.0 × 10 －３ The PVA-based film of the following example had a low YI change rate and excellent yellowing resistance. On the other hand, the integral ratio was 7.0 × 10 －３ The comparative PVA-based films exceeding the specified value showed a larger YI change rate and inferior resistance to yellowing compared to the PVA-based film in the example.

[0109] While the above embodiments illustrate specific forms of the present invention, these embodiments are merely illustrative and should not be interpreted restrictively. Various modifications that are obvious to those skilled in the art are intended to fall within the scope of the present invention.

[0110] This PVA-based film is useful for a variety of applications requiring high design aesthetics due to its excellent transparency and, in particular, its resistance to yellowing. Among these, this PVA-based film is particularly suitable for use in cosmetics and edible products.

Claims

1. A polyvinyl alcohol-based film containing a polyvinyl alcohol-based resin, wherein the polyvinyl alcohol-based film １ The integral ratio obtained from the H-NMR spectrum using the following formula (1) is 7.0 × 10⁻¹⁰. －３ The following is a polyvinyl alcohol-based film. Integral ratio = (B / 3) / (b / 3 + a / 2 + B / 3) ... (1) In equation (1) above, B is the integral value of methyl groups observed at 2.19 to 2.18 ppm, a is the integral value of methylene groups observed at 2.30 to 2.19 ppm and 2.18 to 1.47 ppm, and b is the integral value of methyl groups observed at 2.49 to 2.30 ppm.

2. The polyvinyl alcohol film according to claim 1, wherein the polyvinyl alcohol resin is an unmodified polyvinyl alcohol resin and / or a modified polyvinyl alcohol resin having 1,2-diol structural units.

3. A polyvinyl alcohol-based film according to claim 1 or 2, wherein the rate of change of YI, determined by the following formula (2) from the YI value (initial YI) measured using a spectrophotometer in accordance with JIS K7373:2006 and the YI value after standing for 28 days in an environment of 23°C and 50% RH (after YI enhancement), is 1.8 or less. Rate of change of YI = YI after YI enhancement / YI initial ... (2) 4. The integral ratio is 5.0 × 10 －３ The polyvinyl alcohol-based film according to claim 1 or 2, which is as follows:

5. A polyvinyl alcohol-based film according to claim 1 or 2, which is for cosmetic or edible purposes.

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