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

Abstract

Provided is a polyvinyl alcohol-based resin film which is capable of suppressing the yellowness of the film at a high level and which has excellent yellowing resistance even when used in a high-temperature environment and / or a highly humid and hot environment. A polyvinyl alcohol-based resin film which contains a polyvinyl alcohol-based resin (A) and which has a biomass degree of more than 50% as calculated from a measured value of radioactive carbon C14.

Description

Technical Field

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

[0002] Traditionally, polyvinyl alcohol-based resins have been used in a wide range of applications due to their excellent properties and diverse quality. Due to their excellent gas barrier properties and / or mechanical strength, transparency, gloss, and water solubility, they are used in a wide range of fields, including optical films, packaging for food and / or healthcare applications, medical infusion bags, packaging for various pharmaceuticals such as liquid lotions and / or pesticides, and seed tapes for seed encapsulation.

[0003] Films using these polyvinyl alcohol resins are produced by dissolving the polyvinyl alcohol resin in a solvent such as water to prepare a stock solution, forming a film using a casting mold such as a metal roll and / or belt by a solution casting method (casting method), and drying using a metal heating roll and / or a floating dryer.

[0004] As mentioned above, films using polyvinyl alcohol-based resins are often used as polarizing films for optical applications and / or individual packaging films for food, healthcare, and liquid detergents. However, in recent years, as these applications have demanded higher film performance, for example, in optical applications, with the increasing brightness and high definition of screens such as liquid crystal televisions, there has been a demand for polyvinyl alcohol-based resin films that are more colorless and transparent than conventional products and that do not yellow due to ultraviolet rays and / or heat rays from light sources.

[0005] Furthermore, in liquid detergent applications, there is a problem of yellowing over time due to contact with the liquid detergent. As a result, the packaging is also sensitive to color changes, and a water-soluble polyvinyl alcohol-based resin film with less yellowing over time is required.

[0006] In response to these demands, for example, to the problem of yellowing of white display in liquid crystal displays, a method of adjusting the hue by adding a special adhesive to the adhesive used to bond the polyvinyl alcohol-based resin film to the protective film has been disclosed (see Patent Document 1).

[0007] In addition, as a polyvinyl alcohol resin film with excellent hue and excellent optical properties when made into an optical film, and a method for manufacturing the same, a method has been proposed in which a polyvinyl alcohol resin aqueous solution is prepared by dissolving the polyvinyl alcohol resin in water in a dissolution tank formed of special stainless steel (see Patent Document 2).

[0008] In addition, a technology has been proposed for using a polyvinyl alcohol resin aqueous solution containing an alkyl sulfonate-based surfactant to produce a polyvinyl alcohol resin film useful as a raw material for a polarizing film having excellent transmittance and / or hue and colorless transparency, or as a packaging material for packaging clothing and / or food, etc. (see Patent Document 3).

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-311827

[0012] Patent Document 2: Japanese Patent Application Laid-Open No. 2006-188657

[0013] Patent Document 3: Japanese Patent Application Laid-Open No. 2006-193694 Summary of the Invention

[0014] Problems to be solved by the invention

[0015] However, as the demand level has been further improved in recent years, the expectation for use under high temperature and high humidity and heat environment has also increased. The above-mentioned conventional methods cannot fully exert performance, and it is necessary to improve the yellowing resistance under time change and / or heat resistance.

[0016] Furthermore, in order to meet such demands, the performance of the polyvinyl alcohol-based resin itself as the base resin must be excellent in transparency and / or hue, and further, in resistance to yellowing due to changes over time in the use environment, etc.

[0017] Therefore, against this background, the present invention provides a polyvinyl alcohol-based resin film, an optical film, a water-soluble film, and a polyvinyl alcohol-based resin composition that can suppress the yellowness of the film at a high level and have excellent yellowing resistance even when used in a high-temperature environment and / or a high-humidity and heat environment.

[0018] Solutions for solving problems

[0019] In view of this situation, the present inventors conducted intensive research and found that by controlling the biomass content calculated from the radioactive carbon C14 measurement value when forming a polyvinyl alcohol-based resin film within a specific range, the yellowing of the film can be suppressed to a high level and the yellowing resistance during use in a high-temperature environment can also be improved.

[0020] That is, the present invention has the following aspects.

[0021] [1] A polyvinyl alcohol-based resin film comprising a polyvinyl alcohol-based resin (A), wherein the polyvinyl alcohol-based resin film has a biomass degree calculated from a radioactive carbon C14 measurement value of greater than 50%.

[0022] [2] The polyvinyl alcohol-based resin film according to [1], wherein the polyvinyl alcohol-based resin (A) has a saponification degree of 80 to 99.9 mol%.

[0023] [3] The polyvinyl alcohol-based resin film according to [1] or [2], wherein the weight average molecular weight of the polyvinyl alcohol-based resin (A) is 20,000 to 150,000.

[0024] [4] The polyvinyl alcohol-based resin film according to any one of [1] to [3], further comprising a plasticizer (B).

[0025] [5] The polyvinyl alcohol-based resin film according to [4], wherein the content of the plasticizer (B) is 1 to 45 parts by mass relative to 100 parts by mass of the polyvinyl alcohol-based resin (A).

[0026] [6] The polyvinyl alcohol-based resin film according to any one of [1] to [5], wherein the change in YI value (ΔYI) when subjected to the following heating yellowing test is 0.45 or less.

[0027] <Heating Yellowing Test>

[0028] (i) Cut a piece of polyvinyl alcohol-based resin film into a size of 3 cm x 3 cm and measure its transmittance at wavelengths of 200 to 800 nm using a spectrophotometer. Calculate the yellowness index YI1 of the film before heating from the obtained data. The calculation of the yellowness index YI is based on (JIS K 7373:2006).

[0029] (ii) The film obtained in (i) was placed in a glass container and allowed to stand in a dryer heated to 160° C. for 25 minutes.

[0030] (iii) The heated film was taken out and its transmittance at wavelengths of 200 to 800 nm was measured using a spectrophotometer. The yellowness index YI2 was calculated from the obtained data.

[0031] (iv) The yellowing degree ΔYI upon heating is obtained from the above YI1 and YI2 according to the following formula (1).

[0032] ΔYI=YI2-YI1 (1)

[0033] [7] The polyvinyl alcohol-based resin film according to any one of [1] to [6], wherein the amount of change (Δb) in the b* value when subjected to the following heating yellowing test is 0.30 or less.

[0034] <Heating Yellowing Test>

[0035] (i) Cut a piece of polyvinyl alcohol-based resin film into a size of 3 cm x 3 cm and measure its transmittance at wavelengths of 200 to 800 nm using a spectrophotometer. Calculate the b* value (b1) of the film before heating from the obtained data. The b* value is calculated in accordance with (JIS Z 8729-1994).

[0036] (ii) The film obtained in (i) was placed in a glass container and allowed to stand in a dryer heated to 160° C. for 25 minutes.

[0037] (iii) The heated film is taken out and its transmittance at wavelengths of 200 to 800 nm is measured using a spectrophotometer. The b* value (b2) of the heated film is calculated from the obtained data.

[0038] (iv) The yellowing degree Δb upon heating is obtained from the above b1 and b2 according to the following formula (2).

[0039] Δb=b2-b1 (2)

[0040] [8] The polyvinyl alcohol-based resin film according to any one of [1] to [7], which has a thickness of 10 to 130 μm.

[0041] [9] The polyvinyl alcohol-based resin film according to any one of [1] to [8], which is used for producing a polarizing film.

[0042]

[10] An optical film using the polyvinyl alcohol-based resin film according to any one of [1] to [9].

[0043]

[11] The optical film according to

[10] , wherein the optical film is a polarizing film.

[0044]

[12] A water-soluble film using the polyvinyl alcohol-based resin film according to any one of [1] to [8].

[0045]

[13] A polyvinyl alcohol-based resin composition comprising at least a polyvinyl alcohol-based resin (A), wherein the polyvinyl alcohol-based resin composition has a biomass degree calculated from a radioactive carbon C14 measurement value of greater than 50%.

[0046]

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

[13] , further comprising a plasticizer (B).

[0047]

[15] A polyvinyl alcohol-based resin film comprising the polyvinyl alcohol-based resin composition described in

[13] or

[14] .

[0048] Effects of the Invention

[0049] The polyvinyl alcohol-based resin film of the present invention can suppress yellowing to a high degree and exhibits excellent yellowing resistance even during use in high-temperature environments. As a result, the film exhibits excellent transmittance, excellent hue, and excellent colorless transparency even during long-term use. It is useful as a raw material for polarizing films used in polarized sunglasses and / or liquid crystal displays, or as a packaging material for clothing, food, liquid detergents, and the like.

[0050] Furthermore, the amount of surfactant used can be reduced, and the aggregation of the surfactant and / or the generation of decomposition products derived from the surfactant, as well as the film defects caused by the aggregation of the surfactant and / or its decomposition products, can be suppressed during film formation. Furthermore, even when the film is stretched at a high stretch ratio, the increase in the haze of the film or the breakage of the film can be suppressed, and the productivity is also excellent. DETAILED DESCRIPTION

[0051] The present invention will be described in detail below. However, the present invention is not limited to the following embodiments.

[0052] In this specification, "x and / or y (x, y are arbitrary structures)" means at least one of x and y, and has three meanings: only x, only y, or x and y.

[0053] In this specification, when expressed as "X to Y" (X, Y are arbitrary numbers), unless otherwise specified, it includes the meaning of "X or more and Y or less", and also includes the meaning of "preferably greater than X" or "preferably less than Y".

[0054] In this specification, the expression "X or more" (X is an arbitrary number) or "Y or less" (Y is an arbitrary number) also includes the meaning of "preferably greater than X" or "preferably less than Y".

[0055] In this specification, for the numerical ranges recorded in stages, the upper limit or lower limit of the numerical range of a certain stage can be arbitrarily combined with the upper limit or lower limit of the numerical range of another stage. In addition, in the numerical ranges recorded in this specification, the upper limit or lower limit of the numerical range can also be replaced with the value shown in the examples.

[0056] In addition, in this specification, "film" also includes the meaning of "tape" and / or "sheet".

[0057] In this specification, the "main component" refers to a component that has a significant influence on the properties of the object, and the content of this component is usually 50% by mass or more in the object, preferably 55% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, and may be 100% by mass.

[0058] The polyvinyl alcohol-based resin film according to one embodiment of the present invention (hereinafter sometimes referred to as "the present polyvinyl alcohol-based resin film") has a biomass degree exceeding 50% as calculated from a radioactive carbon C14 measurement value.

[0059] The biomass content of the polyvinyl alcohol-based resin film, as calculated from radioactive carbon C14 measurements, has a lower limit of greater than 50%, preferably 53% or greater, more preferably 55% or greater, even more preferably 60% or greater, and particularly preferably 63% or greater. Furthermore, the upper limit is preferably less than 100%, more preferably 98% or less, even more preferably 95% or less, and particularly preferably 90% or less.

[0060] By setting the biomass content calculated from radioactive carbon C14 measurements within the above range, a base resin with excellent yellowing resistance can be used even in high-temperature, high-humidity, and high-heat conditions. Furthermore, the amount of surfactant used to suppress yellowing can be reduced, suppressing the aggregation of the surfactant during film formation and / or the generation of film defects derived from its decomposition products. Furthermore, it is possible to suppress an increase in haze and breakage of the film when the film is stretched at a high stretch ratio.

[0061] The biomass content calculated from the measured value of radiocarbon C14 is a value measured according to ASTM D6866-20 (Method B) specified by the American Society of Testing and Materials.

[0062] The present polyvinyl alcohol-based resin film may contain at least a polyvinyl alcohol-based resin (A), preferably a plasticizer (B) as another component, and may contain a surfactant (C), starch (D), a water-soluble polymer (E) other than (A), etc. as needed.

[0063] <Polyvinyl alcohol resin (A)>

[0064] The polyvinyl alcohol-based resin (A) used in this embodiment will be described.

[0065] The present polyvinyl alcohol-based resin film must contain at least one type of "polyvinyl alcohol-based resin (A1) in which all or part of the carbon constituting the polyvinyl alcohol-based resin is derived from bio-derived ethylene."

[0066] In other words, as the polyvinyl alcohol-based resin (A) used, "polyvinyl alcohol-based resin (A1) in which all or part of the carbon constituting the polyvinyl alcohol-based resin is derived from bio-sourced ethylene" can be used alone, or a mixture of "polyvinyl alcohol-based resin (A1) in which all or part of the carbon constituting the polyvinyl alcohol-based resin is derived from bio-sourced ethylene" and "polyvinyl alcohol-based resin (A'1) obtained only from raw materials derived from fossil fuels" can be used.

[0067] The method for obtaining the "polyvinyl alcohol-based resin (A1) in which all or part of the carbon constituting the polyvinyl alcohol-based resin is derived from bio-derived ethylene" is not particularly limited, and examples thereof include the following methods.

[0068] (1) A method of saponifying polyvinyl ester obtained by polymerizing bio-vinyl ester monomers using bio-ethylene as a raw material,

[0069] (2) a method of saponifying a polyvinyl ester obtained by polymerizing a bio-vinyl ester monomer using a mixture of bio-ethylene and ethylene derived from fossil fuels as a raw material,

[0070] (3) a method of saponifying a polyvinyl ester obtained by copolymerizing a bio-vinyl ester monomer using bio-ethylene as a raw material with a vinyl ester monomer using fossil fuel-derived ethylene as a raw material,

[0071] (4) A method of mixing polyvinyl ester obtained by polymerizing only bio-vinyl ester monomers using bio-ethylene as a raw material with polyvinyl ester obtained by polymerizing only fossil fuel-derived vinyl ester monomers and then saponifying the mixture;

[0072] (5) A method of combining the above methods (2) to (4).

[0073] Among these methods, method (1) or (2) is preferred from the viewpoint of being able to efficiently produce a polyvinyl alcohol-based resin (A1) in which all or part of the carbon constituting the polyvinyl alcohol-based resin is derived from bio-derived ethylene.

[0074] Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. Among these, vinyl acetate is preferred.

[0075] The method for producing vinyl ester monomers is not particularly limited. For example, vinyl ester monomers can be obtained by reacting ethylene with a compound having a carboxyl group represented by R—COOH. Vinyl acetate can be synthesized as follows. Generally, vinyl acetate can be obtained by reacting ethylene, acetic acid, and oxygen in the presence of a catalyst in a gas phase. 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 carboxyl group. Examples of ethylene containing a predetermined amount of C14 include bio-ethylene.

[0076] It should be noted that in the production of vinyl ester monomers, it is preferred to use raw materials other than ethylene, such as carboxylic acids, that are also of biological origin. However, the carboxylic acid groups are detached from the polymer backbone of the polyvinyl ester during saponification and are generally recovered and reused. Therefore, even if fossil fuel-derived materials are used, this does not increase the amount of carbon dioxide in the global environment and does not contribute to global warming.

[0077] The polyvinyl ester is preferably obtained using one or two or more vinyl ester monomers, and more preferably obtained using only one vinyl ester monomer.

[0078] Furthermore, the polyvinyl ester may be a copolymer of one or more vinyl ester monomers and other monomers copolymerizable therewith.

[0079] As other monomers capable of copolymerizing with vinyl ester monomers, ethylene is preferred. That is, the polyvinyl alcohol contained in the polyvinyl alcohol-based resin film of the present invention preferably contains ethylene units. In addition, the content of ethylene units is preferably 1 mol% or more, more preferably 1.5 mol% or more, based on the molar number of all structural units constituting the vinyl ester polymer. In addition, the content of ethylene units is preferably less than 15 mol%, more preferably less than 10 mol%, based on the molar number of all structural units constituting the vinyl ester polymer. By having the content of ethylene units within the above range, when the polyvinyl alcohol-based resin film of the present invention is used as a raw film for manufacturing optical films, the optical properties of the polyvinyl alcohol-based resin film can be improved without significantly damaging the water resistance. The reason for this is unclear, but it is speculated that although the introduction of ethylene units into the polymer backbone weakens hydrophilicity, the volume occupied by the ethylene units in the crystals is not much different from the volume of the vinyl alcohol units, resulting in a less significant crystalline structure of the polyvinyl alcohol.

[0080] Examples of other monomers copolymerizable with the vinyl ester monomer include, in addition to ethylene, olefins having 3 to 30 carbon atoms, such as propylene, 1-butene, and isobutylene; acrylic acid or its salts; acrylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, and octadecyl acrylate; methacrylic acid or its salts; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, and octadecyl methacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid or its salts, acrylamidopropyldimethylamine or its salts, N-methylacrylamide - Acrylamide derivatives such as hydroxymethyl acrylamide or its derivatives; methacrylamide derivatives such as methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamidopropanesulfonic acid or its salts, methacrylamidopropyl dimethylamine or its salts, N-hydroxymethyl methacrylamide or its derivatives; 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, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-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 its salts, esters, or anhydrides; itaconic acid or its salts, esters, or anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate, etc. The vinyl ester polymer may have structural units derived from one or two or more of these other monomers.

[0081] From the viewpoint of the strength of the obtained polyvinyl alcohol-based resin film and / or the optical properties of the polyvinyl alcohol-based resin film when used as a raw film for the manufacture of optical films, the proportion of structural units derived from other monomers in polyvinyl ester is preferably 15 mol% or less, and more preferably 5 mol% or less, based on the molar number of all structural units constituting the polyvinyl ester.

[0082] Other monomers copolymerizable with the vinyl ester monomer may be monomers derived from fossil fuels or monomers derived from plants.

[0083] The weight average molecular weight of the polyvinyl alcohol resin (A) is preferably 20,000 to 150,000, particularly preferably 60,000 to 130,000, and further preferably 70,000 to 120,000. If the weight average molecular weight is too small, there is a tendency for the mechanical strength to decrease. On the other hand, if it is too large, there is a tendency for the productivity to decrease. In addition, if the weight average molecular weight is too small, when the polyvinyl alcohol resin is made into an optical film, there is a tendency that it is not easy to obtain sufficient optical properties. If it is too large, when the polyvinyl alcohol resin film is used to manufacture a polarizing film, there is a tendency that stretching becomes difficult. It should be noted that the weight average molecular weight of the polyvinyl alcohol resin is a weight average molecular weight measured based on the GPC method.

[0084] The dispersion degree (weight average molecular weight / number average molecular weight) of the polyvinyl alcohol-based resin (A) is preferably 1.95 to 3.50, particularly preferably 1.96 to 2.50, and further preferably 1.97 to 2.10.

[0085] If the dispersion degree is too small, stretching of the polyvinyl alcohol resin film in the production of a polarizing film tends to be difficult, while if it is too large, sufficient optical performance tends to be difficult to obtain when the polyvinyl alcohol resin is formed into an optical film.

[0086] In addition, the weight average molecular weight and number average molecular weight when measuring the dispersion degree of the polyvinyl alcohol-based resin are the weight average molecular weight and number average molecular weight measured by the GPC method.

[0087] The average saponification degree of the polyvinyl alcohol-based resin (A) is generally preferably 80 mol% or more, more preferably 87 mol% or more, particularly preferably 99 mol% or more, further 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 may not be achieved when the polyvinyl alcohol-based resin film is formed into a polarizing film.

[0088] Here, the average saponification degree in this specification is measured based on JIS K 6726.

[0089] The biomass content of the polyvinyl alcohol-based resin (A), as calculated from radioactive carbon C14 measurement, is preferably 45% or higher, more preferably 50% or higher, even more preferably 55% or higher, and particularly preferably 58% or higher. Furthermore, it is preferably less than 100%, more preferably 94% or lower, even more preferably 90% or lower, and particularly preferably 83% or lower.

[0090] By setting the biomass content calculated from the radioactive carbon C14 measurement value within the above range, it is possible to use the resin as a base resin with excellent yellowing resistance even under high-temperature and high-humidity conditions. Furthermore, the amount of surfactant used to inhibit yellowing can be reduced, and the aggregation of the surfactant and / or the generation of surfactant-derived decomposition products during film formation, as well as the generation of film defects caused by the aggregation of the surfactant and / or its decomposition products, can be suppressed. Furthermore, when the film is stretched at a high stretch ratio, an increase in film haze or film breakage can be suppressed.

[0091] As the polyvinyl alcohol-based resin (A), one type of polyvinyl alcohol-based resin may be used, or two or more types of polyvinyl alcohol-based resins having different polymerization degrees and / or saponification degrees, modification degrees, etc. may be blended and used.

[0092] <Plasticizer (B)>

[0093] Examples of the plasticizer (B) include glycerols such as glycerol, diglycerol, and triglycerol; alkylene glycols such as triethylene glycol, polyethylene glycol, polypropylene glycol, dipropylene glycol, and propylene glycol; and / or sugar alcohols such as trimethylolpropane, sorbitol, xylitol, and / or maltitol. These can be used alone or in combination of two or more. Among these, glycerol, polyethylene glycol, and diglycerol are preferably used because they are readily available and can achieve a plasticizing effect even in small amounts.

[0094] The content of the plasticizer (B) is preferably 1 to 45 parts by mass, particularly preferably 3 to 30 parts by mass, and even more preferably 5 to 25 parts by mass, relative to 100 parts by mass of the polyvinyl alcohol-based resin (A). If the content of the plasticizer (B) is too low, the stretchability during polarizing film production tends to decrease, while if it is too high, the strength of the resulting polyvinyl alcohol-based resin film tends to decrease.

[0095] <Surfactant (C)>

[0096] The above-mentioned surfactant (C) usually has the function of smoothing the surface of the film and / or inhibiting the adhesion of the films to each other when they are wound into a roll. For example, nonionic surfactants, anionic surfactants, and cationic surfactants can be used alone or in combination of two or more.

[0097] Examples of the nonionic surfactant include polyoxyethylene hexyl ether, polyoxyethylene heptyl ether, polyoxyethylene octyl ether, polyoxyethylene nonyl ether, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene tetradecyl ether, polyoxyethylene cetyl ether, polyoxyethylene octadecyl ether, polyoxyethylene eicosyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, polyoxyethylene coconut alcohol ethylene oxide adduct, tallow alcohol ethylene oxide adduct and other polyoxyethylene alkyl ethers, caproic acid monoethanolamide or caproic acid diethanolamide, caprylic acid monoethanolamide or caprylic acid diethanolamide, capric acid monoethanolamide or capric acid diethanolamide, lauric acid monoethanolamide or lauric acid diethanolamide, palmitic acid monoethanolamide or palmitic acid diethanolamide, stearic acid monoethanolamide or stearic acid diethanolamide, oleic acid monoethanolamide or oleic acid diethanolamide, coconut fatty acid monoethanolamide or coconut fatty acid diethanolamide, or combinations thereof. Amide can be replaced by higher fatty acid alkanolamides such as propanolamide and butanolamide; higher fatty acid amides such as caproamide, caprylamide, caprylamide, lauramide, palmitamide, stearamide, and oleamide; 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 oleamine, polyoxyethylene laurylamine, and polyoxyethylene eicosylamine; polyoxyethylene higher fatty acid amides such as polyoxyethylene caproamide, polyoxyethylene caprylamide, polyoxyethylene caprylamide, polyoxyethylene lauramide, polyoxyethylene palmitamide, polyoxyethylene stearamide, and polyoxyethylene oleamide; amine oxides such as dimethyl laurylamine oxide, dimethyl stearylamine oxide, and dihydroxyethyl laurylamine oxide; and fluoroalkyl acids such as perfluorooctanoic acid.

[0098] Examples of the anionic surfactant include, for example, sulfate ester salts of the type described above, sodium hexyl sulfate, sodium heptyl sulfate, sodium octyl sulfate, sodium nonyl sulfate, sodium decyl sulfate, sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium cetyl sulfate, sodium octadecyl sulfate, sodium eicosyl sulfate, or alkyl sulfate ester salts such as potassium salts, calcium salts, and ammonium salts thereof, sodium polyoxyethylene hexyl ether sulfate, sodium polyoxyethylene heptyl ether sulfate, sodium polyoxyethylene octyl ether sulfate, sodium polyoxyethylene nonyl ether sulfate, sodium polyoxyethylene decyl ether sulfate, sodium polyoxyethylene lauryl ether sulfate, sodium polyoxyethylene tetradecyl ether sulfate, sodium polyoxyethylene cetyl ether sulfate, sodium polyoxyethylene octadecyl ether sulfate, sodium polyoxyethylene eicosyl ether sulfate, or polyoxyethylene alkyl ether sulfates such as potassium salts and ammonium salts thereof, sodium polyoxyethylene hexylphenyl ether sulfate, sodium polyoxyethylene heptylphenyl ether sulfate, sodium polyoxyethylene polyoxyethylene alkylphenyl ether sulfates such as sodium octylphenyl ether sulfate, sodium polyoxyethylene nonylphenyl ether sulfate, sodium polyoxyethylene decylphenyl ether sulfate, sodium polyoxyethylene dodecylphenyl ether sulfate, sodium polyoxyethylene tetradecylphenyl ether sulfate, sodium polyoxyethylene hexadecylphenyl ether sulfate, sodium polyoxyethylene octadecylphenyl ether sulfate, sodium polyoxyethylene eicosylphenyl ether sulfate, or potassium salts thereof; sodium caproic acid ethanolamide sulfate, sodium capric acid ethanolamide sulfate, sodium lauric acid ethanolamide sulfate, sodium palmitic acid ethanolamide sulfate, sodium stearic acid ethanolamide sulfate, sodium oleic acid ethanolamide sulfate, or potassium salts thereof; higher fatty acid alkanolamide sulfates in which these ethanolamides are replaced with propanolamide, butanolamide, etc.; sulfated oils; higher alcohol ethoxysulfates; monoglyceride sulfates; and the like. In addition to the above-mentioned sulfate ester salt type, there can be mentioned carboxylate salt types such as fatty acid soaps, N-acylamino acids and salts thereof, polyoxyethylene alkyl ester carboxylates, acylated peptides, alkyl sulfonates, alkylbenzenesulfonates, alkylnaphthalenesulfonates, naphthalenesulfonic acid salt formaldehyde condensates, melaminesulfonic acid salt formaldehyde condensates, dialkylsulfosuccinates, alkylsulfosuccinate disalts, polyoxyethylene alkylsulfosuccinate disalts, alkylsulfoacetates, α-olefin sulfonates, N-acylmethyltaurates, dimethyl isophthalate-5-sulfonic acid sodium salt and the like, and phosphate ester salt types such as polyoxyethylene alkyl ether phosphates, polyoxyethylene alkylphenyl ether phosphates, and alkyl phosphates.

[0099] Examples of the cationic surfactant include lauramine hydrochloride, lauryltrimethylammonium chloride, and laurylpyridinium chloride.

[0100] Among these, nonionic surfactants are preferred, higher fatty acid alkanolamides are particularly preferred, lauric acid monoethanolamide or lauric acid diethanolamide, palmitic acid monoethanolamide or palmitic acid diethanolamide, stearic acid monoethanolamide or stearic acid diethanolamide, oleic acid monoethanolamide or oleic acid diethanolamide are further preferred, lauric acid monoethanolamide or lauric acid diethanolamide are particularly preferred, and lauric acid diethanolamide is more preferred.

[0101] The surfactant (C) may be used alone or in combination of two or more. From the viewpoint of film transparency, it is preferred to use an anionic surfactant and a nonionic surfactant in combination.

[0102] 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 further 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, the anti-blocking effect tends to be difficult to obtain, while if it is too high, the transparency of the film tends to decrease.

[0103] 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 preferably 0.02 to 0.2 parts by mass, and further 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 preferably 0.02 to 0.2 parts by mass, and further preferably 0.03 to 0.1 parts by mass. If the amount of the anionic surfactant is too low, the dispersibility of the dye during polarizing film production is reduced, tending to increase uneven dyeing. If the amount is too high, foaming occurs violently during dissolution of the polyvinyl alcohol-based resin, and bubbles are easily incorporated into the film, making it unusable as an optical film. If the amount of the nonionic surfactant is too low, the anti-blocking effect is difficult to achieve. If the amount is too high, the transparency and / or planar smoothness of the film tend to be reduced.

[0104] <Starch (D)>

[0105] Examples of the starch (D) 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 root starch, bracken starch, lotus seed starch, water chestnut starch, etc.), physically modified starch (α-starch, isolated amylose, heat-moisture treated starch, etc.), enzyme-modified starch (hydrolyzed dextrin, enzymatically decomposed dextrin, amylose, etc.), chemically decomposed modified starch (acid-treated starch, hypochlorous acid-oxidized starch, dialdehyde starch, etc.), and chemically modified starch derivatives (esterified starch, etherified starch, cationized starch, cross-linked starch, etc.). Raw starch is preferably used, and corn starch and rice starch are particularly preferably used, from the perspective of availability and / or economic efficiency. These can be used alone or in combination of two or more.

[0106] The content of starch (D) is preferably 15 parts by mass or less, 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) exceeds 15 parts by mass, there is a concern that the process performance during the production of the polyvinyl alcohol-based resin film may be deteriorated.

[0107] <Water-soluble polymer (E) other than (A)>

[0108] Examples of the water-soluble polymer (E) other than the polyvinyl alcohol-based resin (A) include dextrin, gelatin, glue, casein, shellac, gum arabic, polyacrylamide, sodium polyacrylate, polyvinyl methyl ether, copolymers of methyl vinyl ether and maleic anhydride, copolymers of vinyl acetate and itaconic acid, polyvinyl pyrrolidone, cellulose, acetyl cellulose, acetylbutyl cellulose, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, and sodium alginate. These may be used alone or in combination of two or more.

[0109] The content of the water-soluble polymer (E) is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, relative to 100 parts by mass of the polyvinyl alcohol-based resin (A). If the content of the water-soluble polymer (E) exceeds 15 parts by mass, there is a concern that the physical properties of the polyvinyl alcohol-based resin film may be impaired.

[0110] <Other ingredients>

[0111] The polyvinyl alcohol resin film may contain a plasticizer, a surfactant, starch, a water-soluble polymer other than the polyvinyl alcohol resin (A), and may also contain components such as water, an antioxidant, an ultraviolet absorber, a lubricant, a cross-linking agent, a colorant, a filler, a preservative, a mildewproofing agent, and other polymer compounds, as long as the effects of the present invention are not impaired. These components may be used alone or in combination of two or more.

[0112] The polyvinyl alcohol-based resin film is preferably a film obtained using a polyvinyl alcohol-based resin composition.

[0113] It is important that the biomass content of the polyvinyl alcohol-based resin composition, as calculated from the radioactive carbon C14 measurement value, is greater than 50%. It is preferably 53% or greater, more preferably 55% or greater, even more preferably 60% or greater, and particularly preferably 63% or greater. Furthermore, it is preferably less than 100%, more preferably 98% or less, even more preferably 95% or less, and particularly preferably 90% or less.

[0114] By setting the biomass content calculated from radiocarbon C14 measurements within the above range, a base resin can be used that exhibits excellent yellowing resistance even during use at high temperatures and high humidity. Furthermore, the amount of surfactant used to suppress yellowing can be reduced, suppressing the aggregation of surfactants and / or the generation of surfactant-derived decomposition products during film formation, as well as the generation of film defects caused by surfactant aggregation and / or its decomposition products. Furthermore, when the film is stretched at a high stretch ratio, an increase in film haze or film breakage can be suppressed.

[0115] <Method for producing polyvinyl alcohol-based resin film>

[0116] For the manufacture method of this polyvinyl alcohol resin film, the film-making stock solution (aqueous solution of polyvinyl alcohol resin composition) obtained by adding a solvent, an additive, etc. to the polyvinyl alcohol resin (A) and homogenizing it can be prepared by using a casting film-making method, a wet film-making method (discharging into a poor solvent), a dry-wet film-making method, a gel film-making method (the film-making stock solution is temporarily cooled and gelled and then the solvent is extracted and removed to obtain a method for polyvinyl alcohol resin film), or a combination of these methods, and / or by using an extruder etc. to obtain the above-mentioned film-making stock solution and extrude it from a T die etc. to prepare a film by any method such as a melt extrusion film-making method and / or a blow molding method. Among these, the casting film-making method and the melt extrusion film-making method can obtain a homogeneous film with good productivity, so they are preferred. The casting film-making method or the melt extrusion film-making method of the polyvinyl alcohol resin film are described below.

[0117] When the polyvinyl alcohol resin film is made into a film by a casting film method or a melt extrusion film method, the above-mentioned film-making stock solution is deaerated and cast into a film on supports such as metal rollers and / or metal belts, heated and solvent removed, thereby making it solidified, filmized. As a deaeration method, methods such as standing deaeration and / or utilizing a multi-screw extruder with an air vent can be enumerated. As the multi-screw extruder with an air vent, a twin-screw extruder with an air vent is usually used. The film of solidification is peeled off from the support, dried with a drying roller, a drying oven, etc. as needed, and then heat-treated as needed, coiled, and thus the strip-shaped polyvinyl alcohol resin film of roll can be obtained.

[0118] The resin concentration of the film-forming stock solution (the concentration of non-volatile components such as the polyvinyl alcohol-based resin that are not removed by volatilization and / 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 the aqueous solution is too low, the drying load increases, thereby tending to reduce productivity. If it is too high, the viscosity becomes too high, tending to make uniform dissolution difficult.

[0119] Here, in this specification, "resin concentration of the membrane-forming stock solution" refers to the volatile content calculated by the following formula.

[0120] Resin concentration of film-forming stock solution (mass %) = (Wb / Wa) × 100

[0121] (Wa represents the mass (g) of the film-forming stock solution, and Wb represents the mass (g) of the film-forming stock solution after Wa (g) is dried in an electric drying machine at 105°C for 16 hours.)

[0122] The method for preparing the film-forming stock solution is not particularly limited. For example, there can be mentioned a method in which the polyvinyl alcohol-based resin (A) and additives such as a plasticizer (B) and a surfactant (C) are dissolved in a dissolution tank, and / or a method in which the plasticizer (B), a surfactant (C), etc. are melt-kneaded together with the water-containing polyvinyl alcohol-based resin (A) using a single-screw extruder or a twin-screw extruder.

[0123] When the polyvinyl alcohol resin film is produced by the cast film method or the melt extrusion film method, the film-forming stock solution is cast from a film-forming device onto a support such as a metal roll and / or a metal belt into a film shape, and then heated to remove the solvent, thereby solidifying and forming a film.

[0124] The surface temperature of the support for the cast film stock solution 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 for the cast film stock solution 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 peelability of the film obtained by film production from the casting die tends to decrease, while if it is too high, foaming tends to occur.

[0125] While heating the polyvinyl alcohol-based resin film on the support, hot air at a speed of 1 to 10 m / s can be evenly blown across the entire non-contact surface of the polyvinyl alcohol film to adjust the drying rate. From the perspectives of drying efficiency and / or drying uniformity, the temperature of the hot air blown toward the non-contact surface is preferably 50°C or higher, more preferably 70°C or higher. From the perspectives of drying efficiency and / or drying uniformity, the temperature of the hot air blown toward the non-contact surface is preferably 150°C or lower, more preferably 120°C or lower.

[0126] The polyvinyl alcohol resin film peeled from the support is preferably dried on the support to a volatile content of 5 to 50% by mass before peeling, and may be further dried as needed. The drying method is not particularly limited, and examples include contact with a drying oven and / or drying rolls.

[0127] When drying with multiple drying rollers, alternating contact between one side and the other side of the film is preferred because this allows for uniform drying of both sides. The number of drying rollers is preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more. The number of drying rollers is preferably 30 or less. When using drying rollers, the contact time between each drying roller and the film is preferably 1 to 60 seconds, particularly preferably 2 to 30 seconds, even more preferably 3 to 20 seconds, and even more preferably 4 to 10 seconds. If this contact time is too short, drying tends to be insufficient, while if it is too long, the load on the equipment tends to increase.

[0128] In this embodiment, the temperature of all drying furnaces and drying rollers used is preferably 40 to 150°C, particularly preferably 50 to 140°C, further preferably 60 to 130°C, and particularly preferably 70 to 120°C.

[0129] If the temperature of the drying furnace or the drying roller is too low, drying tends to be insufficient, while if it is too high, crystallization of the polyvinyl alcohol-based resin (A) proceeds, and the film tends to become too hard.

[0130] In order to adjust the physical properties such as strength and water solubility of the dried polyvinyl alcohol-based resin film, a heat treatment may be further performed as needed. From the perspective of being able to make the dry state of both sides of the film uniform, the heat treatment in this embodiment is preferably performed on both sides of the film. Examples of such heat treatment methods include a method of using a floating dryer to blow hot air onto both sides of the film, and a method of using an infrared lamp to irradiate both sides of the film with near-infrared rays.

[0131] The heat treatment temperature is preferably 50 to 150° C., particularly preferably 70 to 120° C. The heat treatment time is not particularly limited, but when a floating dryer is used, it is preferably 10 to 100 seconds, particularly preferably 20 to 80 seconds.

[0132] The polyvinyl alcohol-based resin film thus produced is further subjected to humidity conditioning treatment and cutting of both ends (ear parts) of the film as needed, and is wound into a roll on a cylindrical core and moisture-proof packaged to obtain a product.

[0133] The volatile content of the polyvinyl alcohol-based resin film finally obtained through the above series of treatments is not necessarily limited. The volatile content of the polyvinyl alcohol-based resin film is preferably 1% by mass or greater, more preferably 2% by mass or greater. The volatile content of the polyvinyl alcohol-based resin film is preferably 10% by mass or less, more preferably 5% by mass or less.

[0134] From the perspective of production efficiency, the length of the polyvinyl alcohol-based resin film obtained in this manner is preferably 0.5 km or longer, more preferably 1 km or longer, and particularly preferably 5 to 50 km from the perspective of transport weight. If the length is too short, film replacement tends to be laborious, while if it is too long, tight winding tends to result in poor appearance and / or excessive weight.

[0135] The width of the polyvinyl alcohol-based resin film can be appropriately selected depending on the intended use, but is preferably 300 to 8000 mm, particularly preferably 500 to 7000 mm, and even more preferably 600 to 6000 mm. If the width is too narrow, production efficiency tends to decrease, while if it is too wide, control of sag and / or film thickness tends to become difficult.

[0136] The thickness of the polyvinyl alcohol-based resin film can be appropriately selected depending on the intended use, but is preferably 10 to 130 μm, particularly preferably 15 to 110 μm, and even more preferably 15 to 60 μm. If the thickness is too thin, the mechanical strength of the film tends to decrease, while if it is too thick, the film production efficiency tends to decrease.

[0137] The amount of change (ΔYI) in the YI value of the polyvinyl alcohol-based resin film when subjected to the following heating yellowing test is preferably 0.45 or less.

[0138] The amount of change in the YI value (ΔYI) is particularly preferably 0.40 or less, and more preferably 0.35 or less. The smaller the amount of change in the YI value (ΔYI), the better, and it is preferably 0 or more.

[0139] If this value is too high, the colorless transparency of the film tends to be lost during long-term use in a high-temperature, high-humidity environment.

[0140] The amount of change (Δb) in the b* value of the polyvinyl alcohol-based resin film when subjected to the following heating yellowing test is preferably 0.30 or less.

[0141] The amount of change in the b* value (Δb) is particularly preferably 0.28 or less, more preferably 0.26 or less, and particularly preferably 0.25 or less. The smaller the amount of change in the b* value (Δb), the better, and it is preferably 0 or greater.

[0142] If this value is too high, the colorless transparency of the film tends to be lost during long-term use in a high-temperature, high-humidity environment.

[0143] <Heating Yellowing Test>

[0144] (i) A piece of polyvinyl alcohol-based resin film was cut into a size of 3 cm x 3 cm, and the transmittance at wavelengths of 200 to 800 nm was measured using a spectrophotometer (UV-3600 Plus, manufactured by Shimadzu Corporation). The b* value (b1) and yellowness index YI1 of the film before heating were calculated from the obtained data. The b* value was calculated in accordance with (JIS Z 8729-1994), and the yellowness index YI was calculated in accordance with (JIS K 7373:2006).

[0145] (ii) The film obtained in (i) was placed in a glass container and allowed to stand in a dryer (manufactured by Sanyo Electric Co., Ltd., Constant Temperature Dryer MOV-212F) heated to 160°C for 25 minutes.

[0146] (iii) The heated film was taken out and its transmittance at wavelengths of 200 to 800 nm was measured using a spectrophotometer (UV-3600 Plus, manufactured by Shimadzu Corporation). The b* value (b2) and yellowness index YI2 of the heated film were calculated from the obtained data.

[0147] (iv) The yellowing degree Δb and ΔYI on heating are obtained from the above b1, b2, YI1 and YI2 according to the following formulas (1) and (2).

[0148] ΔYI=YI2-YI1 (1)

[0149] Δb=b2-b1 (2)

[0150] The polyvinyl alcohol-based resin film thus obtained has high transparency and excellent antistatic properties, and is therefore useful for applications requiring high optical properties such as polarizing films (LCD TVs, smartphones, tablets, personal computers, projectors, and automotive panels) and / or water-soluble film applications (unit packaging for pesticides and / or lotions, for (hydraulic) transfer films, sanitary napkins / diapers and other sanitary products, waste disposal products such as ostomy bags, medical products such as blood-absorbing sheets, seedling sheets, seed tapes, and temporary substrates such as embroidery base fabrics).

[0151] Hereinafter, 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.

[0152] The polarizing film is produced by rolling the polyvinyl alcohol resin film from a roll, conveying it horizontally, and then undergoing the following steps: swelling, dyeing, cross-linking, stretching, washing, and drying.

[0153] The swelling process is performed before the dyeing process. This process can clean stains from the surface of the polyvinyl alcohol resin film. Swelling the polyvinyl alcohol resin film also prevents uneven dyeing. Water is typically used as the treatment liquid in the swelling process. If the treatment liquid is primarily water, small amounts of additives such as iodine compounds, surfactants, and alcohol may be added. The temperature of the swelling bath is typically approximately 10 to 45°C, and the immersion time in the swelling bath is typically approximately 0.1 to 10 minutes.

[0154] The dyeing step is performed by contacting the film with a liquid containing iodine or a dichroic dye. An aqueous iodine-potassium iodide solution is typically used, with the iodine concentration typically being 0.1 to 2 g / L and the potassium iodide concentration typically being 1 to 100 g / L. A dyeing time of approximately 30 to 500 seconds is generally practical. The treatment bath temperature is preferably 5 to 50°C. The aqueous solution may also contain a small amount of a water-compatible organic solvent other than water.

[0155] The crosslinking step is carried out using a boron compound such as boric acid and / or borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture, typically at a concentration of about 10 to 100 g / L. From the perspective of stabilizing polarization performance, potassium iodide is preferably present in the liquid.

[0156] The preferred treatment temperature is generally about 30 to 70° C., and the treatment time is about 0.1 to 20 minutes. If necessary, stretching may be performed during the treatment.

[0157] The stretching step is preferably performed uniaxially to a ratio of 3 to 10, particularly preferably 3.5 to 6. In this case, some stretching (to a degree sufficient to prevent shrinkage in the width direction, or to a degree greater than this) in a direction perpendicular to the stretching direction is also acceptable. The temperature during stretching is preferably 30 to 170°C. Furthermore, the final stretching ratio may be set within the aforementioned range, and the stretching operation may be performed at any stage in the manufacturing process, not just in one stage.

[0158] The cleaning process is carried out by immersing the polyvinyl alcohol resin film in an aqueous solution of an iodide such as water and / or potassium iodide, so that the precipitate produced on the surface of the film can be removed. The concentration of potassium iodide when using an aqueous solution of potassium iodide can be about 1 to 80 g / L. The temperature during the cleaning process 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. It should be noted that water cleaning and cleaning with an aqueous solution of potassium iodide can also be appropriately combined.

[0159] The drying step may be performed usually in the air at 40 to 80° C. for 1 to 10 minutes.

[0160] The polarization degree of the polarizing film is preferably 99.8% or higher, particularly preferably 99.9% or higher. If the polarization degree is too low, the contrast of the liquid crystal display tends to be unable to be ensured.

[0161] It should be noted that the degree of polarization is usually calculated using the transmittance (H11) measured at a wavelength λ when two polarizing films are overlapped so that their orientation directions are in the same direction, and the transmittance (H1) measured at a wavelength λ when two polarizing films are overlapped so that their orientation directions are orthogonal to each other.

[0162] [(H11-H1) / (H11+H1)] 1 / 2

[0163] Furthermore, the single-element transmittance of the present polarizing film is preferably 42% or higher, particularly preferably 43% or higher. If the single-element transmittance is too low, it tends to be difficult to achieve high brightness of a liquid crystal display.

[0164] The single-piece transmittance is a value obtained by measuring the transmittance of the polarizing film alone using a spectrophotometer.

[0165] The polarizing film is thus obtained, and the polarizing film is suitable for manufacturing polarizing plates with small polarization degree unevenness.

[0166] The resulting polarizing film can also be used as a polarizing plate by laminating an optically isotropic polymer film or sheet on one or both sides as a protective film. Examples of protective films include films or sheets made of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cross-linked methacrylate resins, cycloolefin polymers, cycloolefin copolymers, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, and polyphenylene oxide.

[0167] Furthermore, for the purpose of thinning, a curable resin such as urethane resin, acrylic resin, or urea resin may be coated on one or both sides of the polarizing film, cured, and laminated instead of the protective film.

[0168] The polarizing film obtained from the present polyvinyl alcohol-based resin film has no color unevenness and excellent in-plane uniformity of polarization performance. It can be preferably used in, for example, liquid crystal display devices such as portable information terminals, computers, televisions, projectors, signs, desktop electronic calculators, electronic clocks, word processors, electronic paper, game consoles, video recorders, cameras, photo albums, thermometers, audio equipment, automotive and / or mechanical measuring instruments, sunglasses, anti-glare glasses, stereo 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.

[0169] Example

[0170] Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist of the present invention.

[0171] In addition, "part" and "%" in the examples are based on mass.

[0172] <Measurement Conditions>

[0173] <GPC Measurement of Polyvinyl Alcohol Resin>

[0174] Gel permeation chromatography (GPC) was used to measure the chromatogram under the following measurement conditions. A calibration curve obtained by measuring standard polyethylene oxide and polyethylene glycol (PEO / PEG) was used, and the elution time was converted to a molecular weight to calculate the weight-average molecular weight of the standard sample (PEO / PEG) of the polyvinyl alcohol-based resin.

[0175] [GPC measurement conditions]

[0176] Detector: RI, Shodex RI-501

[0177] Column: TSKgel α-M 13 μm 7.8 mm ID×30 cm manufactured by Tosoh Corporation was used.

[0178] Mobile phase: 0.2M NaNO3 aqueous solution

[0179] Mobile phase flow rate: 0.50 mL / min

[0180] Column temperature: 35°C

[0181] Standard curve: 12 PEO / PEG standard samples with different molecular weights were used to create a standard curve.

[0182] <Heating Yellowing Test>

[0183] (i) A piece of the obtained polyvinyl alcohol-based resin film was cut into a size of 3 cm x 3 cm, and the transmittance at wavelengths of 200 to 800 nm was measured using a spectrophotometer (UV-3600 Plus, manufactured by Shimadzu Corporation). The b* value (b1) and yellowness index YI1 of the film before heating were calculated from the obtained data. The b* value was calculated in accordance with (JIS Z 8729-1994), and the yellowness index YI was calculated in accordance with (JIS K 7373:2006).

[0184] (ii) The film obtained in (i) was placed in a glass container and allowed to stand in a dryer (manufactured by Sanyo Electric Co., Ltd., Constant Temperature Dryer MOV-212F) heated to 160°C for 25 minutes.

[0185] (iii) The heated film was taken out and its transmittance at wavelengths of 200 to 800 nm was measured using a spectrophotometer (UV-3600 Plus, manufactured by Shimadzu Corporation). The b* value (b2) and yellowness index YI2 of the heated film were calculated from the obtained data.

[0186] (iv) The yellowing degree Δb and ΔYI on heating are obtained from the above b1, b2, YI1 and YI2 according to the following formulas (1) and (2).

[0187] ΔYI=YI2-YI1 (1)

[0188] Δb=b2-b1 (2)

[0189] <Synthesis Example of Polyvinyl Alcohol-Based Resin (A1) (Biogenic PVA Resin)>

[0190] In a reactor equipped with a reflux condenser, a sample inlet, and a stirring blade, 650 parts by mass of vinyl acetate, a biomass-derived carbon with vinyl moieties, and 131 parts by mass of methanol were added. The reactor was then immersed in a water bath and heated. When reflux from the condenser was observed (internal temperature approximately 60°C), 0.052 parts by mass of 2,2'-azobisisobutyronitrile was added as an initiator. During polymerization, the water bath temperature was appropriately adjusted to maintain reflux from the condenser, and samples were taken. The progress of polymerization was confirmed by the solid content concentration. When the vinyl acetate conversion 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. The time from the addition of the initiator to reaching the target conversion was 6.75 hours.

[0191] The obtained post-polymerization solution was subjected to distillation under reduced pressure to remove methanol and vinyl acetate. When the viscosity increased, methanol was appropriately added to discharge the remaining vinyl acetate, thereby obtaining a methanol solution of polyvinyl acetate.

[0192] The methanol solution of polyvinyl acetate obtained in this manner was diluted with methanol to a concentration of 4% by mass. 2500 parts by mass of this methanol solution of polyvinyl acetate (100 parts by mass of polyvinyl acetate) was placed in 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 sodium hydroxide solution in methanol was added to initiate a saponification reaction. Saponified products precipitated during the saponification reaction, but stirring was continued. 1.5 hours after the addition of the methanol solution of sodium hydroxide, the resulting saponified products were filtered out and placed back into the reactor. 700 parts by mass of methanol were added and heated to 65°C. 20 parts by mass of a 3.5% by mass sodium hydroxide solution in methanol were added and allowed to react for 2.5 hours to complete the saponification reaction. Subsequently, 1.3 parts by mass of acetic acid and 1200 parts by mass of methanol were added for neutralization. The saponified products were filtered off while being washed with methanol to obtain saponified products. The obtained saponified product was subjected to the following procedures: 1800 parts by mass of methanol was added, 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-based resin (A1) (bio-derived PVA resin) (weight-average molecular weight 81,000; biomass content 95%; saponification degree 99.8 mol%).

[0193] <Synthesis Example of Polyvinyl Alcohol Resin (A'1) (Petroleum-derived PVA Resin)>

[0194] In a reactor equipped with a reflux condenser, a sample inlet, and a stirring blade, 650 parts by mass of petroleum-derived vinyl acetate and 131 parts by mass of methanol were added. The reactor was immersed in a water bath and heated. When reflux from the condenser was observed (internal temperature approximately 60°C), 0.052 parts by mass of 2,2'-azobisisobutyronitrile was added as an initiator. During polymerization, the water bath temperature was appropriately adjusted to maintain reflux from the condenser, and samples were taken to confirm the progress of polymerization by measuring the solids concentration. When the vinyl acetate conversion 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.

[0195] It took 5 hours from the addition of the initiator to reach the target conversion.

[0196] The obtained post-polymerization solution was subjected to distillation under reduced pressure to remove methanol and vinyl acetate. When the viscosity increased, methanol was appropriately added to discharge the remaining vinyl acetate, thereby obtaining a methanol solution of polyvinyl acetate.

[0197] The methanol solution of polyvinyl acetate obtained in this manner was diluted with methanol to a concentration of 6% by mass, and 2000 parts by mass of this methanol solution of polyvinyl acetate (120 parts by mass of polyvinyl acetate) was placed in 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 sodium hydroxide solution in methanol was added to initiate a saponification reaction. During the saponification reaction, saponified products precipitated, but the mixture was stirred while maintaining this state. 2.5 hours after the addition of the methanol solution of sodium hydroxide, the saponified products were filtered out and placed back into the reactor. 700 parts by mass of methanol were added to the mixture and heated to 50°C. 96 parts by mass of a 3.5% by mass sodium hydroxide solution in methanol were added to the mixture and allowed to react for 4 hours to complete the saponification reaction. Thereafter, 6.0 parts by mass of acetic acid was added for neutralization, and the saponified products were obtained by suction filtration while being washed with methanol. The obtained saponified product was subjected to the following procedures twice: 1200 parts by mass of methanol was added, the product was washed at 50°C for 30 minutes, and then filtered. The washed saponified product was dried in a vacuum dryer at 50°C for 12 hours to obtain a polyvinyl alcohol-based resin (A'1) (petroleum-derived PVA resin) (weight-average molecular weight 79,400; biomass content 0%; saponification degree 99.8 mol%).

[0198] [Example 1]

[0199] To a composition prepared by mixing 12 parts by mass of glycerin (special grade reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a plasticizer (B) with respect to 100 parts by mass of the polyvinyl alcohol-based resin (A) obtained in the above-mentioned synthesis example, which was obtained by mixing the polyvinyl alcohol-based resin (A1) (bio-derived PVA resin) and the polyvinyl alcohol-based resin (A'1) (petroleum-derived PVA resin) at a mass ratio of 60:40, ion-exchanged water was added 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 solution of the polyvinyl alcohol-based resin composition.

[0200] The aqueous solution of the polyvinyl alcohol resin composition was applied to a chrome-plated stainless steel plate placed on a hot plate heated to 90°C using an applicator (coating width 150 mm) so that the film thickness after drying was 45 μm. After drying on the hot plate at 90°C for 2.5 minutes, the film was peeled off. Subsequently, the film was heat-treated in a dryer at 120°C for 1 minute to obtain a polyvinyl alcohol resin film (1) having a thickness of 45 μm (biomass degree = 61%). The obtained polyvinyl alcohol resin film (1) was subjected to the above-mentioned heat yellowing test, and the results are shown in Table 1 below.

[0201] [Example 2]

[0202] A polyvinyl alcohol resin film (2) (biomass content = 79%) was obtained in the same manner as in Example 1, except that the polyvinyl alcohol resin (A1) (bio-derived PVA resin) obtained in the above synthesis example was mixed with the polyvinyl alcohol resin (A'1) (petroleum-derived PVA resin) at a mass ratio of 80:20. The above-mentioned heat yellowing test was conducted using the obtained polyvinyl alcohol resin film (2). The results are shown in Table 1 below.

[0203] [Comparative Example 1]

[0204] A composition was prepared by adding 12 parts by mass of glycerin (special grade reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a plasticizer (B) to 100 parts by mass of the polyvinyl alcohol-based resin (A'1) obtained in the above synthesis example (a petroleum-derived PVA resin). 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 solution of the polyvinyl alcohol-based resin composition.

[0205] The aqueous solution of the polyvinyl alcohol resin composition was applied to a chrome plate placed on a hot plate heated to 90°C using an applicator (coating width 150 mm) so that the film thickness after drying was 45 μm. After drying on the hot plate at 90°C for 2.5 minutes, the film was peeled off. Subsequently, the film was heat-treated in a dryer at 120°C for 1 minute to obtain a polyvinyl alcohol resin film (1') having a thickness of 45 μm (biomass content = 8%). The obtained polyvinyl alcohol resin film (1') was subjected to the above-mentioned heat yellowing test, and the results are shown in Table 1 below.

[0206] [Comparative Example 2]

[0207] A polyvinyl alcohol resin film (2') (biomass content = 16%) was obtained in the same manner as in Example 1, except that the polyvinyl alcohol resin (A1) (bio-derived PVA resin) obtained in the above synthesis example was mixed with the polyvinyl alcohol resin (A'1) (petroleum-derived PVA resin) at a mass ratio of 10:90. The above-described heat yellowing test was conducted using the obtained polyvinyl alcohol resin film (2'). The results are shown in Table 1 below.

[0208] [Comparative Example 3]

[0209] A polyvinyl alcohol resin film (3') (biomass content = 30%) was obtained in the same manner as in Example 1, except that the polyvinyl alcohol resin (A1) (bio-derived PVA resin) obtained in the above synthesis example was mixed with the polyvinyl alcohol resin (A'1) (petroleum-derived PVA resin) at a mass ratio of 25:75. The above-described heat yellowing test was conducted using the obtained polyvinyl alcohol resin film (3'). The results are shown in Table 1 below.

[0210] [Table 1]

[0211]

[0212] It is found that the polyvinyl alcohol-based resin films of Examples 1 and 2 have a biomass degree of more than 50% as calculated from the measured value of radioactive carbon C14, and therefore have a small rate of change in yellowing due to heating and are excellent in yellowing resistance even when used in a high-temperature environment.

[0213] In contrast, the polyvinyl alcohol-based resin films of Comparative Examples 1 to 3 had a biomass degree calculated from the radioactive carbon C14 measurement value of 50% or less, and therefore were found to have poor yellowing resistance during use in a high-temperature environment.

[0214] The above embodiments illustrate specific aspects of the present invention, but the above embodiments are merely illustrative and are not to be construed as limiting. Various modifications obvious to those skilled in the art should be considered to be within the scope of the present invention.

[0215] Industrial applicability

[0216] The polyvinyl alcohol-based resin film of the present invention is useful in optical applications such as optical films and / or independent packaging applications, and water-soluble film applications. In particular, the polarizing film obtained from the polyvinyl alcohol-based resin film has no color unevenness and excellent in-plane uniformity of polarization performance. It can be preferably used in, for example: liquid crystal display devices such as portable information terminals, computers, televisions, projectors, signs, desktop electronic calculators, electronic clocks, word processors, electronic paper, game consoles, video recorders, cameras, photo albums, thermometers, audio equipment, automobile and / or mechanical measuring instruments, sunglasses, anti-glare glasses, stereo 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.

Claims

A polyvinyl alcohol-based resin film comprising a polyvinyl alcohol-based resin A, wherein the polyvinyl alcohol-based resin film has a biomass degree calculated from a radioactive carbon C14 measurement value exceeding 50%.

2. The polyvinyl alcohol-based resin film according to claim 1, wherein The polyvinyl alcohol-based resin A has a saponification degree 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. The polyvinyl alcohol-based resin film according to any one of claims 1 to 3, further comprising 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 relative to 100 parts by mass of the polyvinyl alcohol-based resin A.

6. The polyvinyl alcohol-based resin film according to any one of claims 1 to 5, wherein The change in YI value ΔYI during the following heating yellowing test is 0.45 or less. Heating yellowing test: (i) A piece of polyvinyl alcohol-based resin film was cut into a size of 3 cm × 3 cm, and the transmittance at wavelengths of 200 to 800 nm was measured using a spectrophotometer. The yellowness index YI1 of the film before heating was calculated from the obtained data. The calculation of the yellowness index YI was based on JIS K 7373:2006. (ii) The film of (i) was placed in a glass container and allowed to stand in a dryer heated to 160°C for 25 minutes. (iii) The heated film was taken out and the transmittance at wavelengths of 200 to 800 nm was measured using a spectrophotometer. The yellowness YI2 was calculated from the obtained data. (iv) The yellowing degree ΔYI on heating is obtained from the YI1 and YI2 according to the following formula (1): ΔYI=YI2-YI1 (1).

7. The polyvinyl alcohol-based resin film according to any one of claims 1 to 6, wherein The change in b* value Δb during the following heating yellowing test is 0.30 or less. Heating yellowing test: (i) A piece of polyvinyl alcohol-based resin film was cut into a size of 3 cm × 3 cm, and the transmittance at wavelengths of 200 to 800 nm was measured using a spectrophotometer. The b* value b1 of the film before heating was calculated from the obtained data. The b* value was calculated in accordance with JIS Z8729-1994. (ii) The film of (i) was placed in a glass container and allowed to stand in a dryer heated to 160°C for 25 minutes. (iii) The heated film is taken out and the transmittance at wavelengths of 200 to 800 nm is measured using a spectrophotometer. The b* value b2 of the heated film is calculated from the obtained data. (iv) The yellowing degree Δb upon heating is obtained from b1 and b2 according to the following formula (2): Δb=b2-b1 (2). 8 . The polyvinyl alcohol-based resin film according to claim 1 , which has a thickness of 10 to 130 μm. 9 . The polyvinyl alcohol-based resin film according to claim 1 , which is used for producing a polarizing film. 10 . An optical film comprising the polyvinyl alcohol-based resin film according to claim 1 .

11. The optical film according to claim 10, wherein The optical film is a polarizing film. 12 . A water-soluble film comprising the polyvinyl alcohol-based resin film according to claim 1 .

13. A polyvinyl alcohol-based resin composition comprising at least a polyvinyl alcohol-based resin A, wherein the polyvinyl alcohol-based resin composition has a biomass degree calculated from a radioactive carbon C14 measurement value exceeding 50%. The polyvinyl alcohol-based resin composition according to claim 13 , further comprising a plasticizer B. 15 . A polyvinyl alcohol-based resin film comprising the polyvinyl alcohol-based resin composition according to claim 13 .

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