Polyvinyl alcohol-based film, polarizing film, and polarizing plate

Abstract

Provided is a polyvinyl alcohol-based film that suppresses defects such as an optical streak of the film, has uniform optical performance, and has good optical performance.　In this polyvinyl alcohol-based film containing a polyvinyl alcohol-based resin and a surfactant, the surfactant contains a nonionic surfactant (A) and an anionic surfactant (B), the nonionic surfactant (A) includes a nitrogen-containing nonionic surfactant (A1) and an ether-type nonionic surfactant (A2), the total amount (X) of the nonionic surfactant (A) and the anionic surfactant (B) with respect to 100 parts by mass of the polyvinyl alcohol-based resin is 0.2 parts by mass or less, and the percentage content of the nitrogen-containing nonionic surfactant (A1) with respect to the total amount (X) is 50 mass% or less.

Description

Polyvinyl alcohol-based film, polarizing film, and polarizing plate

[0001] The present invention relates to a polyvinyl alcohol-based film. More specifically, it relates to a polyvinyl alcohol-based film with uniform optical performance that suppresses defects such as optical streaks in the film and reduces voids present inside the film that cause degradation of optical performance, as well as a polarizing film and a polarizing plate using the same.

[0002] Conventionally, polyvinyl alcohol-based films have been produced by dissolving a polyvinyl alcohol-based resin in a solvent, defoaming to prepare a stock solution, and then drying the film formed by the solution casting method using a metal heating roll or the like. The polyvinyl alcohol-based film thus obtained has excellent shape stability and is used in many applications as a film. One of its useful applications is an optical film, particularly a polarizing film.

[0003] Such a polarizing film is mainly a film obtained by uniaxially stretching the polyvinyl alcohol-based film and dyeing it with iodine, which is a dichroic dye, and is used as a basic component of a liquid crystal display. In recent years, with the increasing high definition, high brightness, and large size of liquid crystal display screens, there is a need for a polarizing film that is even more excellent in polarization than conventional products and has excellent optical characteristics without color unevenness.

[0004] Among these, improvements are also required for the polyvinyl alcohol-based film that serves as the raw material. Such improvement methods include suppressing the generation of optical streaks, suppressing the generation of voids, making the film thickness uniform, making the in-plane retardation (Rd) value uniform, suppressing the blocking of wound films from damaging their appearance, and various other measures.

[0005] In particular, as a countermeasure to improve the occurrence of optical streaks and blocking resistance of polyvinyl alcohol-based films, for example, Patent Document 1 proposes a polyvinyl alcohol-based film containing a polyvinyl alcohol-based resin, a sulfate ester salt type anionic surfactant (a), an ether type nonionic surfactant (b), and a nitrogen-containing type nonionic surfactant (c).

[0006] Japanese Patent Publication No. 2005-206809

[0007] However, when a relatively large amount of nitrogen-containing nonionic surfactant, such as lauric acid diethanolamide, as described in Patent Document 1, was used in a polyvinyl alcohol-based film, optical streaks could be suppressed, but numerous voids were generated, resulting in a decrease in optical performance.

[0008] The present invention was made to solve the aforementioned problems, and the objective of the present invention is to provide a polyvinyl alcohol-based film, a polarizing film, and a polarizing plate that have uniform optical performance with suppressed defects such as optical streaks in the film, and that reduce voids present inside the film that cause a decrease in optical performance.

[0009] As a result of diligent research to solve the aforementioned problems, the inventors have found that by using a combination of nonionic and anionic surfactants as surfactants in a polyvinyl alcohol-based film, and by including at least one of each of nitrogen-containing nonionic surfactants and ether-type nonionic surfactants in a predetermined proportion, a polyvinyl alcohol-based film suitable for producing a polarizing film that can suppress the occurrence of voids and optical streaks can be obtained.

[0010] In other words, the present invention has the following embodiments: [1] A polyvinyl alcohol film containing a polyvinyl alcohol resin and a surfactant, wherein the surfactant contains a nonionic surfactant (A) and an anionic surfactant (B), the nonionic surfactant (A) comprises a nitrogen-containing nonionic surfactant (A1) and an ether-type nonionic surfactant (A2), the total amount (X) of the nonionic surfactant (A) and the anionic surfactant (B) per 100 parts by mass of the polyvinyl alcohol resin is 0.2 parts by mass or less, and the content of the nitrogen-containing nonionic surfactant (A1) in relation to the total amount (X) is 50% by mass or less, a polyvinyl alcohol film. [2] The polyvinyl alcohol film according to [1], wherein the nitrogen-containing nonionic surfactant (A1) is a higher fatty acid alkanolamide. [3] The polyvinyl alcohol film according to [1] or [2], wherein the ether-type nonionic surfactant (A2) is a polyoxyethylene alkyl ether. [4] A polyvinyl alcohol-based film according to any one of [1] to [3], wherein the anionic surfactant (B) is a sulfur-containing anionic surfactant (B1) and / or a phosphate ester salt type anionic surfactant (B2). [5] A polyvinyl alcohol-based film according to any one of [1] to [4], wherein the film thickness is 15 to 60 μm. [6] A polyvinyl alcohol-based film according to any one of [1] to [5], wherein the surface roughness (Sa) is 10 nm or less. [7] A polyvinyl alcohol-based film according to any one of [1] to [6], used as a base film for a polarizing film. [8] A polarizing film made using a polyvinyl alcohol-based film according to any one of [1] to [7]. [9] A polarizing plate comprising the polarizing film according to [8] and a protective film provided on at least one side of the polarizing film.

[0011] The polyvinyl alcohol-based film of the present invention contains a polyvinyl alcohol-based resin, a nitrogen-containing nonionic surfactant (A1), an ether-type nonionic surfactant (A2), and an anionic surfactant (B) in specific amounts and ratios. As a result, it exhibits a low incidence of optical streaks and optical color unevenness, and can suppress the generation of voids within the film that cause a decrease in optical performance. Therefore, the polyvinyl alcohol-based film of the present invention is useful as a base film for polarizing films.

[0012] Furthermore, the polarizing films and polarizing plates of the present invention have excellent optical performance because they are obtained from polyvinyl alcohol-based films that have fewer optical streaks and optical color unevenness, and in which the generation of voids present inside the film is suppressed.

[0013] 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.

[0014] 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 includes the meaning of "greater than or equal to X and less than or equal to Y," as well as "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. Also, 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. 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.

[0015] The present invention will be described in detail below. A polyvinyl alcohol-based film according to one embodiment of the present invention (hereinafter referred to as "the polyvinyl alcohol-based film") is a polyvinyl alcohol-based film containing a polyvinyl alcohol-based resin and a nonionic surfactant (A) and an anionic surfactant (B) as surfactants, and is manufactured by forming a film from an aqueous solution of polyvinyl alcohol-based resin (film-forming stock solution) containing the polyvinyl alcohol-based resin, nonionic surfactant (A) and anionic surfactant (B) as raw materials.

[0016] The polyvinyl alcohol-based resin used is typically an unmodified polyvinyl alcohol-based resin, i.e., a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate. Alternatively, the polyvinyl alcohol-based resin may be obtained by saponifying a copolymer of vinyl acetate and a small amount (usually 10 mol% or less, preferably 5 mol% or less) of a component copolymerizable with vinyl acetate. Examples of components copolymerizable with vinyl acetate include unsaturated carboxylic acids (e.g., salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (e.g., ethylene, propylene, n-butene, isobutene, etc.), vinyl ethers, and unsaturated sulfonates. Modified polyvinyl alcohol-based resins obtained by chemically modifying the hydroxyl groups after saponification can also be used.

[0017] Furthermore, a polyvinyl alcohol-based resin having a 1,2-diol structure in its side chain can also be used. Such a polyvinyl alcohol-based resin having a 1,2-diol structure in its side chain can be obtained, for example, by (i) saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, (ii) saponifying and decarboxylating a copolymer of vinyl acetate and vinyl ethylene carbonate, (iii) saponifying and deketalizing a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane, or (iv) saponifying a copolymer of vinyl acetate and glycerol monoallyl ether.

[0018] The weight-average molecular weight of the polyvinyl alcohol-based resin is 70,000 or more, preferably 110,000 or more, and more preferably 120,000 or more. The upper limit of the weight-average molecular weight is usually 300,000 or less, preferably 280,000 or less, and more preferably 260,000 or less, with a range of, for example, 70,000 to 300,000. If the weight-average molecular weight is too low, it tends to be difficult to obtain sufficient optical performance when using the polyvinyl alcohol-based resin as an optical film, and if it is too high, it tends to be difficult to stretch when manufacturing a polarizing film using the polyvinyl alcohol-based film. The weight-average molecular weight of the polyvinyl alcohol-based resin is the weight-average molecular weight measured by the GPC-MALS method.

[0019] The average degree of saponification of the polyvinyl alcohol-based resin is preferably 98 mol% or higher, particularly preferably 99 mol% or higher, even more preferably 99.5 mol% or higher, and especially preferably 99.8 mol% or higher. If the average degree of saponification is too low, sufficient optical performance tends not to be obtained when the polyvinyl alcohol-based film is used as a polarizing film. Here, the average degree of saponification in this specification is measured in accordance with JIS K 6726.

[0020] Two or more types of polyvinyl alcohol-based resins with different characteristics such as modified species, degree of modification, weight-average molecular weight, and average degree of saponification may be used in combination.

[0021] The polyvinyl alcohol-based film can be continuously manufactured by preparing an aqueous solution of polyvinyl alcohol-based resin using the polyvinyl alcohol-based resin, extruding and casting the aqueous solution of polyvinyl alcohol-based resin onto a rotating cast mold, and forming and drying the film by a casting method. For example, it can be manufactured by the following steps: (I) a step of preparing an aqueous solution of polyvinyl alcohol-based resin; (II) a step of forming a film of the aqueous solution of polyvinyl alcohol-based resin by a casting method; (III) a step of heating and drying the formed film, and heat-treating it as necessary; (IV) a step of slitting both ends of the dried film and then winding it onto a roll.

[0022] Examples of the casting mold include a cast drum (drum-type roll) and an endless belt, but it is preferable to use a cast drum due to its advantages in terms of width, length, and uniformity of film thickness. The following explanation will use the case where the casting mold is a cast drum as an example.

[0023] <Step (I)> First, Step (I) will be explained. The preparation of the polyvinyl alcohol resin aqueous solution is carried out by dissolving the polyvinyl alcohol resin, a surfactant (described later), and a plasticizer, if necessary, in a solvent such as warm water or hot water. The polyvinyl alcohol resin may be used as is, but it is also preferable to wash the polyvinyl alcohol resin with a solvent such as water, dehydrate it using a centrifuge or the like to obtain a polyvinyl alcohol resin wet cake with a water content of 50% by mass or less, and then use this polyvinyl alcohol resin wet cake for preparation. If the water content of the polyvinyl alcohol resin wet cake is too high, it tends to become difficult to obtain the desired aqueous solution concentration.

[0024] The method for preparing an aqueous solution of polyvinyl alcohol-based resin is not particularly limited. For example, it may be prepared by putting the polyvinyl alcohol-based resin and a solvent into a heated multi-screw extruder and extruding it, or by putting the polyvinyl alcohol-based resin into a dissolution tank equipped with an upward and downward circulating flow generating agitator blade, blowing steam into the tank to dissolve and adjust the concentration.

[0025] In addition to the polyvinyl alcohol resin, the aqueous solution of the polyvinyl alcohol resin must also contain the following surfactants: a nonionic surfactant (A) consisting of a nitrogen-containing nonionic surfactant (A1) and an ether-type nonionic surfactant (A2), and an anionic surfactant (B).

[0026] The total amount (X) of nonionic surfactant (A) and anionic surfactant (B) in the aqueous solution of polyvinyl alcohol resin (the polyvinyl alcohol film) is 0.2 parts by mass or less, preferably 0.19 parts by mass or less, more preferably 0.18 parts by mass or less, even more preferably 0.12 parts by mass, particularly preferably 0.1 parts by mass or less, and especially preferably 0.08 parts by mass or less, per 100 parts by mass of polyvinyl alcohol resin. The lower limit of the total amount (X) is preferably 0.005 parts by mass or more, more preferably 0.01 parts by mass or more, and even more preferably 0.02 parts by mass or more, and the range is, for example, 0.005 to 0.2 parts by mass. If the content is too high, the number of voids in the film tends to increase, and if it is too low, the optical streaks in the film tend to increase, and the peelability from the cast drum, as described later, tends to decrease.

[0027] In this specification, "void" refers to a bubble smaller than 1 μm, which can be measured by the method described later. It is presumed that voids contained in polyvinyl alcohol-based films can be reduced by the effective defoaming effect achieved by combining them with specific surfactants.

[0028] [Nonionic surfactant (A)] The nonionic surfactant (A) comprises a nitrogen-containing nonionic surfactant (A1) and an ether-type nonionic surfactant (A2). It may also contain nonionic surfactants other than the nitrogen-containing nonionic surfactant (A1) and the ether-type nonionic surfactant (A2). However, it is preferable that it consists only of the nitrogen-containing nonionic surfactant (A1) and the ether-type nonionic surfactant (A2) in order to more easily exhibit the effects of the present invention.

[0029] [Nitrogen-containing nonionic surfactant (A1)] As the nitrogen-containing nonionic surfactant (A1), typically, higher fatty acid alkanolamides such as higher fatty acid monoalkanolamides or higher fatty acid dialkanolamides represented by the following general formula (1), higher fatty acid amides represented by the following general formula (2), polyoxyethylene alkylamines represented by the following general formula (3), etc. are included. These can be used alone or in combination of two or more. R ｘ , ２ , １ , ４ , １ CONH-R'-OH or R １ CON-(R'-OH) ２ ...(1) R １ CONH ２ ...(2) R １ NH(C ２ H ４ O) ｘ H or H(C ２ H ４ O) ｙ N(R １ )(C ２ H ４ O) ｘ H...(3) Here, R in general formulas (1) to (3) １ is an alkyl group or an alkenyl group, and the number of carbon atoms thereof is preferably 6 to 22, more preferably 8 to 18. The alkyl group may be a single alkyl group or a mixed alkyl group. That is, the alkyl group may be an alkyl group having an alkyl distribution obtained from coconut oil, palm oil, palm kernel oil, beef tallow, etc. R' in general formula (1) is -C ２ H ４ -, -C ３ H ６ -, -C ４ H ８ - any one of them. x and y in general formula (3) are each an integer of 1 to 20.

[0030] Examples of the nitrogen-containing nonionic surfactant (A1) include caproic acid mono or diethanolamide, caprylic acid mono or diethanolamide, capric acid mono or diethanolamide, lauric acid mono or diethanolamide, palmitic acid mono or diethanolamide, stearic acid mono or diethanolamide, oleic acid mono or diethanolamide, coconut oil fatty acid mono or diethanolamide, or higher fatty acid alkanolamides such as those in which these ethanolamides are replaced with propanolamide or butanolamide; caproic acid amide, caprylic acid amide, capric acid Examples include higher fatty acid amides such as mid, lauric acid amide, palmitic acid amide, stearic acid amide, and oleic acid amide; and polyoxyethylene alkylamines such as polyoxyethylene hexylamine, polyoxyethylene heptylamine, polyoxyethylene octylamine, polyoxyethylene nonylamine, polyoxyethylene decylamine, polyoxyethylene dodecylamine, polyoxyethylene tetradecylamine, polyoxyethylene hexadecylamine, polyoxyethylene octadecylamine, polyoxyethylene oleylamine, and polyoxyethylene eicosylamine. These can be used individually or in combination of two or more.

[0031] Among these, higher fatty acid alkanolamides are preferred, more preferably lauric acid mono or diethanolamide, palmitic acid mono or diethanolamide, stearic acid mono or diethanolamide, oleic acid mono or diethanolamide, coconut oil fatty acid mono or diethanolamide, even more preferably lauric acid mono or diethanolamide, coconut oil fatty acid mono or diethanolamide, and particularly preferably lauric acid diethanolamide.

[0032] The content of nitrogen-containing nonionic surfactant (A1) relative to the total amount (X) [(A1) × 100 / (X); mass%] is 50% by mass or less, preferably 48% by mass or less, more preferably 45% by mass or less, and particularly preferably 44% by mass or less. The lower limit of the content is usually 3% by mass or more, preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more, and the range is, for example, 3 to 50% by mass. If the content of nitrogen-containing nonionic surfactant (A1) is too high, the number of voids in the film tends to increase, and if the content is too low, the number of optical streaks tends to increase.

[0033] The content of the nitrogen-containing nonionic surfactant (A1) is preferably 0.1 parts by mass or less, more preferably 0.07 parts by mass or less, even more preferably 0.04 parts by mass or less, and particularly preferably 0.03 parts by mass or less, per 100 parts by mass of the polyvinyl alcohol resin. The lower limit of the content is usually 0.005 parts by mass or more, preferably 0.01 parts by mass or more, and the range is, for example, 0.005 to 0.1 parts by mass. If the content of the nitrogen-containing nonionic surfactant (A1) is too high, the number of voids in the film tends to increase, and if the content is too low, the number of optical streaks tends to increase.

[0034] [Ether-type nonionic surfactant (A2)] Typical examples of the ether-type nonionic surfactant (A2) include polyoxyethylene alkyl ether represented by the following general formula (4), polyoxyethylene alkylphenyl ether represented by the following general formula (5), and polyoxyethylene sorbitan fatty acid ester represented by the following general formula (6). ２ -O(C) ２ H ４ O) ｎ H ... (4) R ２ -Ph-O(C) ２ H ４ O) ｎ H...(5) (C ６ H ８ O) (OC ２ H ４ )ｗ＋ｘ＋ｙ＋ｚ (OCOR ２ ) (OH) ３ ... (6) Here, R in general formulas (4), (5), and (6) ２ is an alkyl group or alkenyl group, and its carbon number is usually 6 to 30, preferably 8 to 26. The alkyl group may be a single alkyl group or a mixed alkyl group. That is, the alkyl group may be an alkyl group having an alkyl distribution obtained from coconut oil, palm oil, palm kernel oil, beef tallow, etc. In general formulas (4) and (5), n (degree of condensation of polyoxyethylene units) is usually an integer from 1 to 70, preferably 4 to 30. In general formula (6), w, x, y, z (degree of condensation of polyoxyethylene units) are usually integers from 1 to 20, preferably 1 to 10. In general formula (5), Ph is a phenylene group.

[0035] Examples of the ether-type nonionic surfactant (A2) include polyoxyethylene alkyl ethers such as polyoxyethylene hexyl ether, polyoxyethylene heptyl ether, polyoxyethylene octyl ether, polyoxyethylene nonyl ether, polyoxyethylene decyl ether, polyoxyethylene dodecyl ether, polyoxyethylene tetradecyl ether, polyoxyethylene hexadecyl ether, polyoxyethylene octadecyl ether, polyoxyethylene eicosyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, coconut oil reduced alcohol ethylene oxide adduct, beef tallow reduced alcohol ethylene oxide adduct; polyoxyethylene hexylphenyl ether, polyoxyethylene Examples include polyoxyethylene heptylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene decylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene tetradecylphenyl ether, polyoxyethylene hexadecylphenyl ether, polyoxyethylene octadecylphenyl ether, polyoxyethylene eicosylphenyl ether; polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, and polyoxyethylene sorbitan monocoquette. These can be used individually or in combination of two or more.

[0036] Among these, polyoxyethylene alkyl ethers and polyoxyethylene sorbitan fatty acid esters are preferred, more preferably polyoxyethylene dodecyl ethers, polyoxyethylene octadecyl ethers, coconut oil reduced alcohol ethylene oxide adducts, beef tallow reduced alcohol ethylene oxide adducts, and polyoxyethylene sorbitan monooleate are preferred, even more preferably polyoxyethylene dodecyl ethers, polyoxyethylene octadecyl ethers, and polyoxyethylene sorbitan monooleate are preferred, and polyoxyethylene dodecyl ether is particularly preferred.

[0037] The content of the ether-type nonionic surfactant (A2) relative to the total amount (X) [(A2) × 100 / (X); mass%] is usually 45% by mass or less, preferably 43% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less. The lower limit of the content is usually 3% by mass or more, preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, and the range is, for example, 3 to 45% by mass. If the content of the ether-type nonionic surfactant (A2) is too high, the number of voids in the film tends to increase, and if the content is too low, the number of optical streaks tends to increase.

[0038] Furthermore, the mass content ratio [(A1):(A2)] of the nitrogen-containing nonionic surfactant (A1) and the ether-type nonionic surfactant (A2) is usually 85 / 15 to 15 / 85, preferably 75 / 25 to 25 / 75, and more preferably 70 / 30 to 30 / 70. If the mass content ratio of the nitrogen-containing nonionic surfactant (A1) is too high, the number of voids in the film tends to increase, and if the mass content ratio of the nitrogen-containing nonionic surfactant (A1) is too low, the number of optical streaks tends to increase.

[0039] [Anionic surfactant (B)] The anionic surfactant (B) is not particularly limited as long as it satisfies the relationship with the nonionic surfactant (A) defined in the present invention, but from the viewpoint of more easily achieving the effects of the present invention, it is preferable that it be a sulfur-containing anionic surfactant (B1) and / or a phosphate ester salt type anionic surfactant (B2).

[0040] [Sulfur-containing anionic surfactant (B1)] Typical examples of the sulfur-containing anionic surfactant (B1) include alkyl sulfonates represented by the following general formula (7), alkyl sulfates represented by the following general formula (8), polyoxyethylene alkyl ether sulfates represented by the following general formula (9), and alkylbenzene sulfonates represented by the following general formula (10). R ３ SO ３ － ... (7) R ３ OSO ３ － ... (8) R ３ -O(C) ２ H ４ O) ｎ SO ３ － ... (9) R ３ -Ph-SO ３ － ... (10) Here, R in general formulas (7) to (10) ３ R is an alkyl group or an alkenyl group. In particular, R in general formula (7) ３ The number of carbon atoms is usually 6 to 30, preferably 8 to 20. Also, R in general formulas (8) to (10) ３ The number of carbon atoms is usually 6 to 22, preferably 8 to 18. ３ The alkyl group may be a single alkyl group or a mixed alkyl group. That is, the alkyl group may be an alkyl group having an alkyl distribution obtained from coconut oil, palm oil, palm kernel oil, beef tallow, etc. In general formula (9), n (degree of condensation of polyoxyethylene units) is usually an integer from 1 to 20, preferably from 1 to 10.

[0041] Examples of the sulfur-containing anionic surfactant (B1) include sodium hexylsulfonate, sodium heptylsulfonate, sodium octylsulfonate, sodium nonylsulfonate, sodium decylsulfonate, sodium dodecylsulfonate, sodium tetradecylsulfonate, sodium hexadecylsulfonate, sodium octadecylsulfonate, or alkyl sulfonates such as alkali metal salts such as potassium salts of these, alkaline earth metal salts such as calcium salts, or organic amine salts such as ammonium salts; sodium hexyl sulfate, sodium heptyl sulfate, sodium octyl sulfate, sodium nonyl sulfate, sodium decyl sulfate, sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, sodium octadecyl sulfate, sodium eicosyl sulfate, or alkalis such as potassium salts of these. Alkyl sulfate ester salts such as metal salts, alkaline earth metal salts such as calcium salts, and organic amine salts such as ammonium salts; polyoxyethylene alkyl sulfates such as 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 dodecyl ether sulfate, sodium polyoxyethylene tetradecyl ether sulfate, sodium polyoxyethylene hexadecyl ether sulfate, sodium polyoxyethylene octadecyl ether sulfate, sodium polyoxyethylene eicosyl ether sulfate, or alkali metal salts such as potassium salts, alkaline earth metal salts such as calcium salts, and organic amine salts such as ammonium salts;Examples include sodium hexylbenzenesulfonate, sodium heptylbenzenesulfonate, sodium octylbenzenesulfonate, sodium nonylbenzenesulfonate, sodium decylbenzenesulfonate, sodium tetradecylbenzenesulfonate, sodium hexadecylbenzenesulfonate, sodium octadecylbenzenesulfonate, sodium eicosylbenzenesulfonate, or alkylbenzenesulfonates such as alkali metal salts (potassium salts, etc.), alkaline earth metal salts (calcium salts, etc.), and organic amine salts (ammonium salts, etc.) of these. These can be used individually or in combination of two or more.

[0042] [Phosphate ester type anionic surfactant (B2)] Typical examples of the phosphate ester type anionic surfactant (B2) include phosphate monoester salts or phosphate diester salts represented by the following general formula (11), polyoxyethylene alkyl ether phosphate monoester salts or polyoxyethylene alkyl ether phosphate diester salts represented by the following general formula (12), etc. R ４ O-PO ３ ２－ or (R ４ O) ２ -PO ２ － ... (11) R ４ O-(C) ２ H ４ O) ｎ -PO ３ ２－ or [R ４ O-(C) ２ H ４ O) ｎ ] ２ -PO ２ － ... (12) Here, R in general formulas (11) and (12) ４The group is an alkyl group or an alkenyl group, and its carbon number is usually 8 to 22, preferably 8 to 20. The alkyl group may be a single alkyl group or a mixed alkyl group. That is, the alkyl group may be an alkyl group having an alkyl distribution obtained from coconut oil, palm oil, palm kernel oil, beef tallow, etc. In general formulas (11) and (12), n (degree of condensation of polyoxyethylene units) is usually an integer from 1 to 70, preferably 4 to 30.

[0043] Examples of the phosphate ester type anionic surfactant (B2) include phosphate ester salts such as octyl phosphate mono or diester potassium, decyl phosphate mono or diester potassium, dodecyl phosphate mono or diester potassium, tetradecyl phosphate mono or diester potassium, hexadecyl phosphate mono or diester potassium, octadecyl phosphate mono or diester potassium, eicosyl phosphate mono or diester potassium, or alkali metal salts, ammonium salts, and other organic amine salts of the sodium salts thereof; polyoxyethylene octyl phosphate mono or diester potassium, polyoxyethylene decyl phosphate mono or diester potassium, polyoxyethylene dodecyl phosphate mono or diester potassium, polyoxyethylene tetradecyl phosphate mono or diester potassium, polyoxyethylene hexadecyl phosphate mono or diester potassium, polyoxyethylene octadecyl phosphate mono or diester potassium, polyoxyethylene eicosyl phosphate mono or diester potassium, or alkali metal salts, ammonium salts, and other organic amine salts of the sodium salts thereof, such as polyoxyethylene alkyl ether phosphate ester salts. These can be used individually or in combination of two or more.

[0044] Among these anionic surfactants (B), sulfur-containing anionic surfactants (B1) are preferred from the viewpoint of suppressing optical streaks. Among these, alkyl sulfonates are preferred, more preferably alkali metal salts of alkyl sulfonic acids, even more preferably sodium salts of alkyl sulfonic acids, particularly preferably a mixture of sodium dodecylsulfonate, sodium tetradecylsulfonate, sodium hexadecylsulfonate, and secondary alkylsulfonates having 8 to 18 carbon atoms, especially preferably a mixture of sodium dodecylsulfonate and secondary alkylsulfonates having 8 to 18 carbon atoms, and most preferably sodium dodecylsulfonate.

[0045] The content of the anionic surfactant (B) relative to the total amount (X) [(B1 and B2) × 100 / (X); mass%] is usually 5% by mass or more, preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. The upper limit of the content is usually 94% by mass or less, preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 55% by mass or less, and the range is, for example, 5 to 94% by mass. If the content of the anionic surfactant (B) is too high, optical streaks tend to increase, and if the content is too low, voids in the film tend to increase.

[0046] When the anionic surfactant (B) consists of a sulfur-containing anionic surfactant (B1) and a phosphate ester salt type anionic surfactant (B2), the mass content ratio [(B1):(B2)] is preferably 95 / 5 to 10 / 90, more preferably 90 / 10 to 20 / 80, and even more preferably 85 / 15 to 30 / 70. When these mass content ratios are within the above range, the generation of voids in the film tends to be suppressed.

[0047] Furthermore, the mass content ratio of the nonionic surfactant (A) to the anionic surfactant (B) [(A):(B)] is preferably 10 / 90 to 99 / 1, more preferably 15 / 85 to 95 / 5, and even more preferably 30 / 70 to 75 / 25. When these mass content ratios are within the above range, the occurrence of optical streaks and voids tends to be suppressed.

[0048] The aforementioned aqueous solution of polyvinyl alcohol-based resin may, if necessary, contain commonly used plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, or trimethylolpropane, which is more preferable in terms of film-forming properties. These can be used individually or in combination of two or more.

[0049] If the aforementioned aqueous solution of polyvinyl alcohol-based resin (the polyvinyl alcohol-based film) contains a plasticizer, its content is usually 1 part by mass or more, preferably 3 parts by mass or more, and more preferably 5 parts by mass or more, per 100 parts by mass of the polyvinyl alcohol-based resin. The upper limit of the content is usually 35 parts by mass or less, preferably 30 parts by mass or less, and more preferably 25 parts by mass or less, and the range is, for example, 1 to 35 parts by mass. If the plasticizer content is too low, the stretchability during the production of the polarizing film tends to decrease, and if it is too high, the strength of the resulting polyvinyl alcohol-based film tends to decrease.

[0050] The resin concentration of the polyvinyl alcohol-based resin aqueous solution obtained in this manner is preferably 15 to 60% by mass, particularly preferably 17 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, which tends to reduce production capacity, and if it is too high, the viscosity becomes too high, making it difficult to obtain a uniform aqueous solution.

[0051] Next, the obtained polyvinyl alcohol-based resin aqueous solution is subjected to degassing treatment. Degassing methods include static degassing and degassing using a multi-screw extruder. The multi-screw extruder is not particularly limited as long as it has a vent, but a twin-screw extruder with a vent is usually used.

[0052] <Process (II)> Process (II) is a process for forming a film of polyvinyl alcohol-based resin aqueous solution by casting. The polyvinyl alcohol-based resin aqueous solution is introduced into a T-type slit die in fixed amounts, discharged and cast onto a rotating casting drum, and formed into a film by casting.

[0053] The temperature of the polyvinyl alcohol-based resin aqueous solution at the outlet of the T-type slit die is preferably 80 to 100°C, and more preferably 85 to 98°C. If the temperature of the polyvinyl alcohol-based resin aqueous solution is too low, it tends to flow poorly, and if it is too high, it tends to foam.

[0054] The viscosity of the aforementioned polyvinyl alcohol-based resin aqueous solution is preferably 50 to 200 Pa·s, and more preferably 70 to 150 Pa·s, at the time of discharge. If the viscosity of the aqueous solution is too low, it tends to flow poorly, and if it is too high, it tends to become difficult to spit out.

[0055] The discharge rate of the polyvinyl alcohol-based resin aqueous solution discharged from the T-type slit die to the casting drum is preferably 0.2 to 5 m / min, more preferably 0.4 to 4 m / min, and even more preferably 0.6 to 3 m / min. If the discharge rate is too slow, productivity tends to decrease, and if it is too fast, it tends to become difficult to achieve proper flow.

[0056] The diameter of the cast drum is preferably 2 to 5 m, more preferably 2.4 to 4.5 m, and even more preferably 2.8 to 4 m. If the diameter is too small, the drying length tends to be insufficient and it is difficult to achieve a high speed, and if it is too large, transportability tends to decrease.

[0057] The width of the casting drum is preferably 4 m or more, more preferably 4.5 m or more, even more preferably 5 m or more, and particularly preferably 5 to 6 m. If the width of the casting drum is too small, productivity tends to decrease.

[0058] The rotational speed of the casting drum is preferably 3 to 50 m / min, more preferably 4 to 40 m / min, and even more preferably 5 to 35 m / min. If the rotational speed is too slow, productivity tends to decrease, and if it is too fast, drying tends to be insufficient.

[0059] The surface temperature of the cast drum is preferably 40 to 99°C, and more preferably 50 to 95°C. If the surface temperature is too low, drying tends to be inadequate, and if it is too high, foaming tends to occur.

[0060] <Process (III)> Process (III) is a process in which the formed film is heated and dried, and heat-treated as necessary.

[0061] The drying of the film formed in the cast drum is carried out by alternately bringing the front and back surfaces of the film into contact with multiple heat rolls. The surface temperature of the heat rolls is usually 40 to 150°C, preferably 50 to 130°C, and more preferably 60 to 110°C. If the surface temperature is too low, drying tends to be insufficient, and if it is too high, it tends to dry too much, leading to defects in appearance such as waviness. The heat rolls are, for example, rolls with a diameter of 0.2 to 2 m whose surfaces are hard chrome plated or mirror-finished, and it is preferable to use 2 to 30 rolls, preferably 10 to 25 rolls, for drying.

[0062] After drying with a hot roll, it is preferable to heat-treat the film. Examples of heat-treating methods include contacting the film with a high-temperature hot roll or using a floating dryer. The heat-treating temperature is preferably 60 to 150°C, and more preferably 70 to 140°C. If the heat-treating temperature is too low, the polyvinyl alcohol-based film tends to have insufficient water resistance or cause phase difference deviation, while if it is too high, the stretchability during polarizing film production tends to decrease.

[0063] <Process (IV)> Process (IV) is the process of slitting both ends of the dried film and then winding it onto a roll. After drying, the film, which has been heat-treated as needed, becomes the product (this polyvinyl alcohol-based film) through the above process (IV).

[0064] Up to this point, we have described a method for producing the polyvinyl alcohol-based film by preparing an aqueous solution of polyvinyl alcohol-based resin, casting this solution onto a rotating casting drum (drum-type roll), forming a film by casting, and drying it. However, the polyvinyl alcohol-based film can also be produced by casting the aqueous solution of polyvinyl alcohol-based resin onto a resin film or a metal belt, forming a film, and drying it.

[0065] The film thickness of this polyvinyl alcohol-based film is preferably 15 to 60 μm, more preferably 15 to 55 μm, even more preferably 20 to 50 μm, and particularly preferably 25 to 45 μm, considering the thinning and durability of the polarizing film.

[0066] The width of this polyvinyl alcohol-based film is preferably 2 m or more, more preferably 3 m or more, and even more preferably 4 to 6 m, from the viewpoint of large-area application.

[0067] The length of this polyvinyl alcohol-based film is preferably 4 km or more, more preferably 4.5 km or more from the viewpoint of large-area production, and even more preferably 4.5 to 50 km from the viewpoint of transport weight.

[0068] Furthermore, the surface roughness (Sa) of this polyvinyl alcohol-based film is preferably 10 nm or less, more preferably 9 nm or less, even more preferably 7 nm or less, and particularly preferably 5 nm or less. There is no particular lower limit to the surface roughness (Sa) of the film, but it is preferably 0.01 nm or more, more preferably 0.05 nm or more, even more preferably 0.1 nm or more, and particularly preferably 0.5 nm or more, with a range of, for example, 0.01 to 10 nm. If the surface roughness (Sa) of the film is within the above range, the occurrence of optical streaks tends to be suppressed. The surface roughness (Sa) of the film can be measured on both the surface on the cast side and the surface opposite to the cast side, or on each of them, and it is preferable that the surface roughness (Sa) of the film surface (Air surface) opposite to the surface in contact with the cast side is within the above range.

[0069] This polyvinyl alcohol-based film is useful for optical applications because it exhibits fewer optical streaks and color unevenness, and suppresses the generation of voids within the film. In particular, it is extremely useful as a base film for polarizing films. The following describes a method for manufacturing polarizing films and polarizing plates made from this polyvinyl alcohol-based film.

[0070] A polarizing film according to one embodiment of the present invention is manufactured by unwinding the polyvinyl alcohol-based film from a roll and transporting it horizontally, followed by processes such as swelling, dyeing, boric acid crosslinking, stretching, washing, and drying.

[0071] The swelling process is performed before the dyeing process, for example, by immersing the film in a swelling solution (swelling bath). The swelling process not only cleans dirt from the surface of the polyvinyl alcohol-based film, but also prevents uneven dyeing by swelling the film. In the swelling process, water is usually used as the swelling solution. The swelling solution may contain small amounts of additives such as iodide compounds, surfactants, and alcohol, as long as the main component is water. The temperature of the swelling bath is usually around 10 to 45°C, and the immersion time in the swelling bath is usually around 0.1 to 10 minutes. In addition, a stretching operation may be performed during the process as needed.

[0072] The aforementioned dyeing process is carried out by contacting the film with a liquid (dyeing solution) containing iodine or a dichroic dye, for example, by immersing the film in the dyeing solution. Typically, an aqueous solution of iodine-potassium iodide is used as the dyeing solution, with a suitable iodine concentration of 0.1 to 2 g / L and a potassium iodide concentration of 1 to 100 g / L. The aqueous solution may also contain a small amount of an organic solvent that is compatible with water. A practical dyeing time is approximately 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 50°C. Furthermore, stretching may be performed during the treatment process as needed.

[0073] The boric acid crosslinking process is carried out using boric acid or a boron compound such as borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 10 to 100 g / L, and it is preferable to include potassium iodide in the solution for stabilizing the polarization performance. The processing temperature is preferably about 30 to 70°C, and the processing time is preferably about 0.1 to 20 minutes. If necessary, a stretching operation may be performed during the process.

[0074] The stretching step preferably involves stretching the film 3 to 10 times, more preferably 3.5 to 6 times, in the axial direction. At this time, some stretching in the direction perpendicular to the stretching direction (to the extent that shrinkage in the width direction is prevented, or more) is also acceptable. The stretching temperature is preferably 30 to 170°C. Furthermore, the stretching ratio only needs to be set to the above range in the end, and the stretching operation may be performed not only in one stage, but at any stage within the manufacturing process.

[0075] The aforementioned washing step is performed, for example, by immersing the film in an iodide aqueous solution such as water or potassium iodide, which can remove precipitates that form on the surface of the film. When using a potassium iodide aqueous solution, the potassium iodide concentration can be about 1 to 80 g / L. The temperature during the washing process is usually 5 to 50°C, preferably 10 to 45°C. The processing time is usually 1 to 300 seconds, preferably 10 to 240 seconds. Note that washing with water and washing with a potassium iodide aqueous solution may be performed in combination as appropriate.

[0076] The drying process can be carried out, for example, by using a dryer and drying in the air at 40 to 80°C for 1 to 10 minutes.

[0077] The polarization degree of the polarizing film obtained in this way is preferably 99.5% or higher, more preferably 99.8% or higher. If the polarization degree is too low, it tends to become impossible to ensure contrast in liquid crystal displays. The polarization degree is generally measured by the light transmittance (H) measured at wavelength λ with two polarizing films superimposed so that their orientation directions are in the same direction. １１ ) and the light transmittance (H) measured at wavelength λ with two polarizing films superimposed so that their orientation directions are perpendicular to each other. １ From ), it is calculated according to the following formula: Polarization degree (%) = [(H １１ -H １ ) / (H １１ +H １ ) １／２

[0078] Furthermore, the transmittance of the polarizing film itself is preferably 42% or higher. If the transmittance of the polarizing film itself is too low, it tends not to be possible to achieve high brightness in the liquid crystal display. The transmittance of the polarizing film itself is a value obtained by measuring the light transmittance of the polarizing film itself using a spectrophotometer.

[0079] The polarizing film obtained in this manner according to one embodiment of the present invention is suitable for manufacturing polarizing plates with minimal polarization unevenness. The method for manufacturing a polarizing plate according to the present invention will be described below.

[0080] A polarizing plate according to one embodiment of the present invention is manufactured by laminating an optically isotropic resin film as a protective film to one or both sides of the polarizing film via an adhesive.

[0081] Examples of protective films include films or sheets made of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, and polyphenylene oxide.

[0082] The bonding method is carried out by known techniques, for example, by uniformly applying a liquid adhesive composition to the polarizing film, the protective film, or both, then bonding the two together, pressing them together, and irradiating them with heat or active energy rays.

[0083] Furthermore, a curable resin such as urethane resin, acrylic resin, or urea resin can be applied to one or both sides of the polarizing film, and cured to form a cured layer, thereby creating a polarizing plate. In this way, the cured layer acts as a protective film, allowing for a thinner film. One or more of these can be used in combination.

[0084] Polarizing films and polarizing plates obtained using this polyvinyl alcohol-based film are preferably used in portable information terminals, personal computers, televisions, projectors, signage, electronic desktop calculators, electronic clocks, word processors, electronic paper, game consoles, video players, cameras, photo albums, thermometers, audio equipment, liquid crystal display devices such as instruments in automobiles and machinery, sunglasses, anti-glare glasses, 3D glasses, wearable displays, anti-reflective layers for display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys, and the like.

[0085] 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 and comparative examples, "parts" and "%" refer to mass.

[0086] Prior to the examples, the following were prepared. [Polyvinyl alcohol-based resins] ・Polyvinyl alcohol-based resin 1 (PVA1): Unmodified polyvinyl alcohol resin with a weight-average molecular weight of 142,000 and an average saponification degree of 99.8 mol% ・Polyvinyl alcohol-based resin 2 (PVA2): Unmodified polyvinyl alcohol resin with a weight-average molecular weight of 120,000 and an average saponification degree of 99.8 mol% [Nitrogen-containing nonionic surfactants (A1)] ・(A1-1): Lauric acid diethanolamide (1:1 molar type) ・(A1-2): Coconut oil fatty acid diethanolamide (1:2 molar type) ・(A1-3): Coconut oil fatty acid diethanolamide (1:1 molar type) [Ether-type nonionic surfactants (A2)] ・(A2-1): Polyoxyethylene dodecyl ether (10-30, centered around polyoxyethylene condensation degree of 21) ・(A2-2): Polyoxyethylene dodecyl ether (1-10, centered around polyoxyethylene condensation degree of 4) • (A2-3): Polyoxyethylene dodecyl ether (condensation degree of polyoxyethylene 1 to 20, centered around 12) • (A2-4): Polyoxyethylene hexadecyl ether (condensation degree of polyoxyethylene 10 to 30, centered around 21) [Sulfur-containing anionic surfactants (B1)] • (B1-1): Sodium dodecyl sulfonate • (B1-2): Sodium polyoxyethylene dodecyl ether sulfate • (B1-3): Diethanolamine dodecyl sulfonate • (B1-4): Sodium dodecylbenzene sulfonate [Phosphate salt type anionic surfactants (B2)] • (B2-1): Potassium polyoxyethylene phosphate (condensation degree of polyoxyethylene 4 to 30)

[0087] <Example 1> (Production of polyvinyl alcohol-based film) 100 parts of PVA1 as a polyvinyl alcohol-based resin, 12 parts of glycerin as a plasticizer, 0.02 parts of lauric acid diethanolamide (1:1 molar type) (A1-1) as a nitrogen-containing nonionic surfactant (A1), 0.02 parts of polyoxyethylene dodecyl ether (A2-1) as an ether-type nonionic surfactant (A2), 0.1 parts of sodium dodecyl sulfonate (B1-1) as a sulfur-containing anionic surfactant (B1), and 300 parts of water were mixed and heated to 130°C, and dissolved under pressure to obtain a polyvinyl alcohol-based resin aqueous solution with a resin concentration of 26% in which each component was uniformly dissolved. The obtained polyvinyl alcohol-based resin aqueous solution was degassed using a twin-screw extruder. Subsequently, the polyvinyl alcohol-based resin aqueous solution was continuously discharged and cast through a T-type slit die into a cast drum heated to 70°C to form a film. Subsequently, the obtained film was peeled from the cast drum, dried using a hot roll, and then heat-treated using a floating dryer. Finally, both ends of the film were cut off with slits and wound up to obtain the polyvinyl alcohol-based film (film thickness 30 μm) of Example 1.

[0088] <Examples 2, 3, 6-8, 10, Comparative Examples 1, 4, 6-8> Polyvinyl alcohol-based films (film thickness 30 μm) of Examples 2, 3, 6-8, 10, and Comparative Examples 1, 4, 6-8 were obtained in the same manner as in Example 1, except that the polyvinyl alcohol-based resin and the surfactant were changed to the formulations described in Tables 1 and 2 below.

[0089] <Example 4> A polyvinyl alcohol-based film (film thickness 45 μm) of Example 4 was obtained in the same manner as in Example 1, except that the polyvinyl alcohol-based resin and the surfactant were changed to the formulations shown in Table 1 below, and the temperature of the casting drum was changed to 80°C.

[0090] <Examples 5, 9, 11, 12, Comparative Example 5> Polyvinyl alcohol-based films (film thickness 45 μm) of Examples 5, 9, 11, 12, and Comparative Example 5 were obtained in the same manner as in Example 4, except that the polyvinyl alcohol-based resin and the surfactant were changed to the formulations described in Tables 1 and 2 below.

[0091] <Comparative Examples 2 and 3> Polyvinyl alcohol-based films (film thickness 60 μm) of Comparative Examples 2 and 3 were obtained in the same manner as in Example 4, except that the polyvinyl alcohol-based resin and the surfactant were changed to the formulations shown in Table 2 below, and the temperature of the casting drum was changed to 90°C.

[0092] The void number and surface roughness (Sa) were measured using the polyvinyl alcohol-based films obtained for each example and comparative example. The results are shown in Tables 1 and 2 below.

[0093] <Measurement of Void Number> The void number was measured 10 μm inside the surface of the polyvinyl alcohol-based film, both on the side facing the cast surface and on the side opposite to the cast surface, using a laser microscope VK-9710 (manufactured by Keyence Corporation) under the following measurement conditions: 0.061 mm ２ The area was photographed, and the captured images were analyzed using ImageJ (luminance threshold: 65) to measure the number of voids (total number on the cast surface side and the opposite side of the cast surface side), and evaluated according to the following criteria. [Measurement conditions] Objective lens: 50x Filter: 100% Brightness setting: 10500 [Evaluation criteria] ○ (very good): Number of voids is 20 or less △ (good): Number of voids is 21 to 30 × (poor): Number of voids is 31 or more

[0094] <Measurement of surface roughness (Sa)> For the film surface (Air surface) opposite to the surface in contact with the cast surface of the polyvinyl alcohol-based film, a scanning white light interferometer VertScan (manufactured by Ryoka Systems Co., Ltd.) was used to measure 0.16 mm. ２ Surface roughness (Sa) was measured within the specified range and evaluated according to the following criteria: [Evaluation Criteria] ○ (very good): Surface roughness (Sa) of 7 nm or less △ (good): Surface roughness (Sa) greater than 7 nm and 10 nm or less × (poor): Surface roughness (Sa) greater than 10 nm

[0095] (Manufacturing of polarizing film) The polyvinyl alcohol-based films obtained in Examples 1 to 12 and Comparative Examples 1 to 8 were unwound from the roll and transported horizontally while being immersed in a water bath at 25°C to swell, and stretched to 1.6 times the original roll size in the flow direction (MD direction). Next, while adjusting the amount of iodine so that the single-layer transmittance of the final polarizing film obtained was 43.6%, the film was immersed in a 28°C aqueous solution containing 30 g / L potassium iodide to stain it, and stretched to 2.2 times the original roll size in the flow direction (MD direction). Then, while immersed in a 50°C aqueous solution containing 40 g / L boric acid and 24 g / L potassium iodide, the film was stretched to 5.4 times the original roll size in the flow direction (MD direction). Finally, the film was washed with potassium iodide aqueous solution and dried at 80°C for 40 seconds to obtain a polarizing film.

[0096]

[0097]

[0098] Tables 1 and 2 show that the polyvinyl alcohol-based films of Examples 1 to 12 had a low void count and good transparency. Furthermore, the polyvinyl alcohol-based films of Examples 1 to 12 had low surface roughness (Sa), and no streaks, which are an indicator of optical performance, were observed. In contrast, the polyvinyl alcohol-based film of Comparative Example 1 had a relatively low void count, but its surface roughness (Sa) was insufficient, resulting in the presence of streaks. The polyvinyl alcohol-based films of Comparative Examples 2 to 5 had a high void count and high surface roughness (Sa), resulting in noticeable streaks. Furthermore, the polyvinyl alcohol-based films of Comparative Examples 6 to 8 had relatively low surface roughness (Sa), but a high void count. Therefore, it can be seen that the polarizing films using the polyvinyl alcohol-based films of Examples 1 to 12 exhibit no color unevenness, excellent transparency, and a superior appearance.

[0099] While the above embodiments illustrate specific forms of the present invention, these embodiments are merely illustrative and should not be interpreted restrictively. Furthermore, various modifications that are obvious to those skilled in the art are intended to fall within the scope of the present invention.

[0100] Polarizing films and polarizing plates obtained using this polyvinyl alcohol-based film are preferably used in portable information terminals, personal computers, televisions, projectors, signage, electronic desktop calculators, electronic clocks, word processors, electronic paper, game consoles, video players, cameras, photo albums, thermometers, audio equipment, liquid crystal display devices such as instruments in automobiles and machinery, sunglasses, anti-glare glasses, 3D glasses, wearable displays, anti-reflective layers for display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys, and the like.

Claims

1. A polyvinyl alcohol-based film comprising a polyvinyl alcohol-based resin and a surfactant, wherein the surfactant comprises a nonionic surfactant (A) and an anionic surfactant (B), the nonionic surfactant (A) comprises a nitrogen-containing nonionic surfactant (A1) and an ether-type nonionic surfactant (A2), the total amount (X) of the nonionic surfactant (A) and anionic surfactant (B) per 100 parts by mass of the polyvinyl alcohol-based resin is 0.2 parts by mass or less, and the content of the nitrogen-containing nonionic surfactant (A1) relative to the total amount (X) is 50% by mass or less.

2. The polyvinyl alcohol-based film according to claim 1, wherein the nitrogen-containing nonionic surfactant (A1) is a higher fatty acid alkanolamide.

3. The polyvinyl alcohol-based film according to claim 1 or 2, wherein the ether-type nonionic surfactant (A2) is a polyoxyethylene alkyl ether.

4. The polyvinyl alcohol-based film according to claim 1 or 2, wherein the anionic surfactant (B) is a sulfur-containing anionic surfactant (B1) and / or a phosphate ester salt type anionic surfactant (B2).

5. The polyvinyl alcohol-based film according to claim 1 or 2, wherein the film thickness is 15 to 60 μm.

6. The polyvinyl alcohol-based film according to claim 1 or 2, wherein the surface roughness (Sa) is 10 nm or less.

7. A polyvinyl alcohol-based film according to claim 1 or 2, used as a base film for a polarizing film.

8. A polarizing film made using the polyvinyl alcohol-based film described in claim 1 or 2.

9. A polarizing plate comprising a polarizing film according to claim 8 and a protective film provided on at least one side of the polarizing film.

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