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

Abstract

The present invention provides a polyvinyl alcohol-based film which has few defects as a master film for a polarizing film, and with which it is possible to produce a polarizing film with high productivity.　This polyvinyl alcohol-based film contains a polyvinyl alcohol-based resin (A), a nitrogen-containing nonionic surfactant (B), and a higher fatty acid salt (C1) or a higher fatty acid analogue (C) (a higher fatty acid salt (C1) and / or a higher fatty acid (C2)), wherein the mass content ratio (((C1) or (C)) / (B)) of the higher fatty acid salt (C1) or the higher fatty acid analogue (C) to the nitrogen-containing nonionic surfactant (B) in the film is 0.3 or less.

Description

Polyvinyl alcohol film, polarizing film, and polarizing plate

[0001] The present invention relates to a polyvinyl alcohol-based film that has few defects, particularly defects, when used as a raw sheet for a polarizing film and that can be used to produce a polarizing film with high productivity, and to a polarizing film and a polarizing plate using such a polyvinyl alcohol-based film.

[0002] Conventionally, polyvinyl alcohol-based films have been produced by dissolving a polyvinyl alcohol-based resin in a solvent such as water, blending it with additives such as a plasticizer such as glycerin and a surfactant to prepare a film-forming solution, forming the film by a solution casting method (casting method), and drying it using a metal heating roll, etc. The polyvinyl alcohol-based films produced in this manner are used in many applications as films with excellent transparency and dyeability, and one of their useful applications is a polarizing film.

[0003] Such polarizing films are used as key components of liquid crystal display devices such as mobile information terminals and televisions. In recent years, with the trend toward higher brightness and higher definition of liquid crystal displays, there has been a demand for polarizing films with high light transmittance and a high degree of polarization. Furthermore, with the trend toward larger screen sizes and thinner screens for liquid crystal televisions and the like, there has been a demand for polarizing films that are wider, longer, and thinner than conventional products.

[0004] To meet the above demands, a wide, long, thin polyvinyl alcohol-based film with better dyeability than ever before is required, and polyvinyl alcohol-based films containing specific surfactants have been proposed (see, for example, Patent Documents 1 to 3).

[0005] Japanese Patent Application Laid-Open No. 2005-206809 Japanese Patent Application Laid-Open No. 2005-206810 Japanese Patent Application Laid-Open No. 2006-188656

[0006] However, in the techniques disclosed in Patent Documents 1 to 3, the surfactants and other additives added may not be sufficiently dissolved in the film-forming solution, resulting in defects such as remaining in the film, or may bleed out onto the film surface, preventing sufficient dyeability. In this respect, there is room for improvement.

[0007] Under these circumstances, the present invention provides a polyvinyl alcohol-based film that has few defects as a raw sheet for polarizing films and can be used to produce polarizing films with high productivity, as well as a polarizing film and a polarizing plate that use this polyvinyl alcohol-based film.

[0008] In view of the above circumstances, the present inventors have conducted extensive research and, as a result, have focused on the contents of nitrogen-containing nonionic surfactant and higher fatty acid and / or higher fatty acid salt in a polyvinyl alcohol film, and have found that the above-mentioned problem can be solved when the content ratio of higher fatty acid and / or higher fatty acid salt to nitrogen-containing nonionic surfactant is a specific value or less.

[0009] That is, the gist of the present invention is as follows. [1] A polyvinyl alcohol-based film containing a polyvinyl alcohol-based resin (A), a nitrogen-containing nonionic surfactant (B), and a higher fatty acid salt (C1), wherein the mass content ratio of the nitrogen-containing nonionic surfactant (B) to the higher fatty acid salt (C1) in the film ((C1) / (B)) is 0.3 or less. [2] A polyvinyl alcohol-based film containing a polyvinyl alcohol-based resin (A), a nitrogen-containing nonionic surfactant (B), and a higher fatty acid (C), wherein the higher fatty acid (C) comprises a higher fatty acid salt (C1) and / or a higher fatty acid (C2), and the mass content ratio of the nitrogen-containing nonionic surfactant (B) to the higher fatty acid (C) ((C) / (B)) in the film is 0.3 or less. [3] The polyvinyl alcohol-based film according to [1], wherein the higher fatty acid salt (C1) is a higher fatty acid salt having 8 to 20 carbon atoms. [4] The polyvinyl alcohol film according to [2], wherein the higher fatty acid salt (C1) and the higher fatty acid (C2) are higher fatty acid salt and higher fatty acid having 8 to 20 carbon atoms. [5] The polyvinyl alcohol film according to any one of [1] to [4], which has a film thickness of 10 to 65 μm. [6] The polyvinyl alcohol film according to any one of [1] to [5], which is used for producing a polarizing film. [7] A polarizing film obtained by using the polyvinyl alcohol film according to any one of [1] to [6]. [8] A polarizing plate comprising the polarizing film according to [7] and a protective film provided on at least one surface of the polarizing film.

[0010] The polyvinyl alcohol-based film of the present invention has few defects as a raw sheet of polarizing film, and polarizing films can be produced with high productivity. The defect is that, although small in size, nuclei are present inside the film, and these nuclei appear on the film surface during the stretching process in polarizing plate production, causing poor appearance. The polyvinyl alcohol-based film of the present invention is a raw sheet film with few defects that are difficult to manage due to its small size, and polarizing films can be produced with high productivity.

[0011] Embodiments of the present invention are described in detail below. However, the present invention is not limited to these embodiments. In this specification, "x and / or y (x and y are optional)" means at least one of x and y, and can mean x only, y only, or both x and y. In this specification, when "X to Y" (X and Y are optional numbers) is used, it also means "X or more and Y or less" unless otherwise specified, and also includes "preferably more than X" or "preferably less than Y." In this specification, when "X or more" (X is optional number) or "Y or less" (Y is optional number) is used, it also includes "preferably more than X" or "preferably less than Y." With regard to numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of the numerical range can also be replaced with the values ​​shown in the examples.

[0012] A polyvinyl alcohol film according to one embodiment of the present invention (hereinafter referred to as "Polyvinyl Alcohol Film 1") is a polyvinyl alcohol film containing a polyvinyl alcohol resin (A), a nitrogen-containing nonionic surfactant (B), and a higher fatty acid salt (C1), and is characterized in that the mass content ratio of the nitrogen-containing nonionic surfactant (B) to the higher fatty acid salt (C1) in the film [(C1) / (B)] is 0.3 or less. Another polyvinyl alcohol film according to another embodiment of the present invention (hereinafter referred to as "Polyvinyl Alcohol Film 2") is a polyvinyl alcohol film containing a polyvinyl alcohol resin (A), a nitrogen-containing nonionic surfactant (B), and a higher fatty acid (C), and is characterized in that the higher fatty acid (C) comprises a higher fatty acid salt (C1) and / or a higher fatty acid (C2), and the mass content ratio of the nitrogen-containing nonionic surfactant (B) to the higher fatty acid (C) [(C) / (B)] is 0.3 or less. The present polyvinyl alcohol film 1 and the present polyvinyl alcohol film 2 are sometimes collectively referred to as the "present polyvinyl alcohol film." In the present invention, "higher fatty acid salt (C1) and / or higher fatty acid (C2)" means any of those present in the present polyvinyl alcohol film as higher fatty acid salt (C1), those present as higher fatty acid (C2), and those present as both higher fatty acid salt (C1) and higher fatty acid (C2). The present polyvinyl alcohol film contains a salt. Therefore, by incorporating a higher fatty acid (C2) into the polyvinyl alcohol film, the salt in the film reacts with the higher fatty acid (C2) to form the higher fatty acid salt (C1), which is often present in the film. The effects of the present invention are influenced by the contents of both the higher fatty acid salt (C1) and the higher fatty acid (C2) present in the film.

[0013] In the present polyvinyl alcohol-based film 1, by setting the content ratio [(C1) / (B)] to the specified value or less, a polyvinyl alcohol-based film with few defects can be obtained. The content ratio [(C1) / (B)] is preferably 0.25 or less, more preferably 0.20 or less, even more preferably 0.15 or less, and particularly preferably 0.10 or less. The lower limit of the content ratio [(C1) / (B)] is not particularly limited, but is preferably 0.001 or more, more preferably 0.005 or more, even more preferably 0.010 or more, and particularly preferably 0.015 or more.

[0014] Furthermore, in the present polyvinyl alcohol-based film 2, by setting the content ratio [(C) / (B)] to the specified value or less of the present invention, a polyvinyl alcohol-based film with few defects can be obtained. The content ratio [(C) / (B)] is preferably 0.25 or less, more preferably 0.20 or less, even more preferably 0.15 or less, and particularly preferably 0.10 or less. The lower limit of the content ratio [(C) / (B)] is not particularly limited, but is preferably 0.001 or more, more preferably 0.005 or more, even more preferably 0.010 or more, and particularly preferably 0.015 or more.

[0015] The method for producing the present polyvinyl alcohol-based film will be described in more detail in the order of steps, but the present polyvinyl alcohol-based film is not limited to these embodiments.

[0016] The polyvinyl alcohol-based film is preferably produced through the following steps (I) to (III), and preferably also through step (IV) as necessary. Step (I): A step of preparing an aqueous solution of polyvinyl alcohol-based resin (A). Step (II): A step of casting the aqueous solution of polyvinyl alcohol-based resin (A) into a cast mold to form a film. Step (III): A step of drying the formed film. Step (IV): A step of heat-treating the obtained film.

[0017] <Step (I)> Step (I) is a step of preparing an aqueous solution of polyvinyl alcohol resin (A). First, the polyvinyl alcohol resin (A) and the aqueous solution of polyvinyl alcohol resin (A), which are the materials for the present polyvinyl alcohol film, will be described. In the present invention, the polyvinyl alcohol resin (A) constituting the polyvinyl alcohol film is typically an unmodified polyvinyl alcohol resin, i.e., a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate. If necessary, a resin 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 can also be used. 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 resins obtained by chemically modifying hydroxyl groups after saponification can also be used. These may be used alone or in combination of two or more.

[0018] Furthermore, a polyvinyl alcohol resin having a 1,2-diol structure in a side chain can also be used as the polyvinyl alcohol resin (A). Such a polyvinyl alcohol resin having a 1,2-diol structure in a side chain can be obtained, for example, by (i) a method of saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, (ii) a method of saponifying and decarboxylating a copolymer of vinyl acetate and vinyl ethylene carbonate, (iii) a method of saponifying and deketalizing a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane, or (iv) a method of saponifying a copolymer of vinyl acetate and glycerin monoallyl ether.

[0019] The weight-average molecular weight of the polyvinyl alcohol-based resin (A) is 100,000 or more, preferably 110,000 or more, and more preferably 120,000 or more, with an upper limit of 300,000 or less, preferably 280,000 or less, and more preferably 260,000 or less. The weight-average molecular weight ranges, for example, from 100,000 to 300,000. If the weight-average molecular weight is too small, sufficient optical performance tends to be difficult to obtain when the polyvinyl alcohol-based resin (A) is used to form an optical film. If the weight-average molecular weight is too large, stretching of the polyvinyl alcohol-based film tends to be difficult when a polarizing film is produced using the polyvinyl alcohol-based resin (A). The weight-average molecular weight of the polyvinyl alcohol-based resin (A) is a weight-average molecular weight measured by GPC-MALS.

[0020] The average saponification degree of the polyvinyl alcohol resin (A) used in the present invention is usually preferably 98 mol% or more, more preferably 99 mol% or more, even more preferably 99.5 mol% or more, and particularly preferably 99.8 mol% or more. If the average saponification degree is too low, sufficient optical performance tends to be difficult to obtain when the polyvinyl alcohol film is used as a polarizing film. Here, the average saponification degree in the present invention is measured in accordance with JIS K 6726.

[0021] As the polyvinyl alcohol-based resin (A) used in the present invention, two or more kinds of resins differing in the modified species, the degree of modification, the weight-average molecular weight, the average degree of saponification, etc. may be used in combination.

[0022] In the present invention, an aqueous solution of polyvinyl alcohol-based resin (A) is prepared using the polyvinyl alcohol-based resin (A). In the present polyvinyl alcohol-based film 1, the aqueous solution of polyvinyl alcohol-based resin (A) contains, in addition to the polyvinyl alcohol-based resin (A), essential components of a nitrogen-containing nonionic surfactant (B) and a higher fatty acid salt (C1). In the present polyvinyl alcohol-based film 2, the aqueous solution of polyvinyl alcohol-based resin (A) contains, in addition to the polyvinyl alcohol-based resin (A), essential components of a nitrogen-containing nonionic surfactant (B) and a higher fatty acid (C).

[0023] Examples of the nitrogen-containing nonionic surfactant (B) used in the present invention include polyoxyethylene alkylamines such as hydroxyethyl laurylamine, polyoxyethylene hexylamine, polyoxyethylene heptylamine, polyoxyethylene octylamine, polyoxyethylene nonylamine, polyoxyethylene decylamine, polyoxyethylene dodecylamine, polyoxyethylene tetradecylamine, polyoxyethylene hexadecylamine, polyoxyethylene octadecylamine, polyoxyethylene oleylamine, and polyoxyethylene eicosylamine; higher fatty acid amides such as caproic acid amide, enanthic acid amide, caprylic acid amide, pelargonic acid amide, capric acid amide, undecylic acid amide, lauric acid amide, tridecylic acid amide, myristic acid amide, pentadecylic acid amide, palmitic acid amide, margaric acid amide, stearic acid amide, nonadecylic acid amide, arachidic acid amide, henicosyl acid amide, behenic acid amide, tricosyl acid amide, lignoceric acid amide, cerotic acid amide, montanic acid amide, melissic acid amide, and oleic acid amide; polyoxyethylene higher fatty acid amides such as polyoxyethylene caproic acid amide, polyoxyethylene enanthic acid amide, polyoxyethylene caprylic acid amide, polyoxyethylene pelargonic acid amide, polyoxyethylene capric acid amide, polyoxyethylene undecylic acid amide, polyoxyethylene lauric acid amide, polyoxyethylene tridecylic acid amide, polyoxyethylene myristic acid amide, polyoxyethylene pentadecylic acid amide, polyoxyethylene palmitic acid amide, polyoxyethylene margaric acid amide, polyoxyethylene stearic acid amide, polyoxyethylene nonadecylic acid amide, polyoxyethylene arachidic acid amide, polyoxyethylene henicosyl acid amide, polyoxyethylene behenic acid amide, polyoxyethylene tricosyl acid amide, polyoxyethylene lignoceric acid amide, polyoxyethylene cerotic acid amide, polyoxyethylene montanic acid amide, polyoxyethylene melissic acid amide, and polyoxyethylene oleic acid amide;N-alkanol higher fatty acid amides such as N-ethanol undecylic acid amide, N-ethanol lauric acid amide, N-ethanol tridecylic acid amide, N-ethanol myristic acid amide, N-ethanol pentadecylic acid amide, N-ethanol palmitic acid amide, N-diethanol margaric acid amide, N-ethanol stearic acid amide, N-ethanol nonadecylic acid amide, N-ethanol arachidic acid amide, N-ethanol heneicosyl acid amide, N-ethanol behenic acid amide, N-ethanol tricosyl acid amide, N-ethanol lignoceric acid amide, N-ethanol cerotic acid amide, N-ethanol montanic acid amide, N-ethanol melissic acid amide, and N-ethanol oleic acid amide; N,N-dialkanol higher fatty acid amides such as N,N-diethanol undecylic acid amide, N,N-diethanol lauric acid amide, N,N-diethanol tridecylic acid amide, N,N-diethanol myristic acid amide, N,N-diethanol pentadecylic acid amide, N,N-diethanol palmitic acid amide, N,N-diethanol margaric acid amide, N,N-diethanol stearic acid amide, N,N-diethanol nonadecylic acid amide, N,N-diethanol arachidic acid amide, N,N-diethanol heneicosyl acid amide, N,N-diethanol behenic acid amide, N,N-diethanol tricosyl acid amide, N,N-diethanol lignoceric acid amide, N,N-diethanol cerotic acid amide, N,N-diethanol montanic acid amide, N,N-diethanol melissic acid amide, and N,N-diethanol oleic acid amide; Amine oxides such as dimethyl lauryl amine oxide, dimethyl stearyl oxide, and dihydroxyethyl lauryl amine oxide;

[0024] Among these, higher fatty acid amides, polyoxyethylene alkylamines, and N,N-dialkanol higher fatty acid amides are preferred in that they can provide polyvinyl alcohol-based films with excellent optical performance and no defects such as optical streaks. It is also preferred to use two or more nitrogen-containing nonionic surfactants (B), and among these, it is particularly preferred to use polyoxyethylene alkylamines as an essential surfactant in terms of improving optical color unevenness caused by defects and suppressing optical streaks, and it is particularly preferred to use polyoxyethylene alkylamines in combination with higher fatty acid amides or N,N-dialkanol higher fatty acid amides in terms of suppressing blocking defects.

[0025] The content of the nitrogen-containing nonionic surfactant (B) is usually 0.001 to 1 part by mass, preferably 0.005 to 0.9 parts by mass, more preferably 0.01 to 0.8 parts by mass, and particularly preferably 0.02 to 0.7 parts by mass, relative to 100 parts by mass of the polyvinyl alcohol resin (A). When the content of the nitrogen-containing nonionic surfactant (B) is within the above range, optical color unevenness due to defects tends to be improved and the occurrence of optical streaks tends to be suppressed.

[0026] In the present invention, if necessary, other surfactants than the nitrogen-containing nonionic surfactant (B) may be used in combination, such as nonionic surfactants other than the nitrogen-containing nonionic surfactant (B), anionic surfactants other than the higher fatty acids (C), and cationic surfactants.

[0027] The higher fatty acid salt (C1) used in the present polyvinyl alcohol film 1 is preferably a higher fatty acid salt having 8 to 20 carbon atoms, more preferably a higher fatty acid salt having 10 to 18 carbon atoms, and even more preferably a higher fatty acid salt having 12 to 18 carbon atoms. Specific examples of such higher fatty acid salt (C1) include salts of lauric acid (C12) and stearic acid (C18).

[0028] Examples of salts constituting the higher fatty acid salt (C1) include metal salts and amine salts. Examples of metal salts include sodium salts, potassium salts, magnesium salts, calcium salts, zinc salts, aluminum salts, lead salts, chromium salts, molybdenum salts, manganese salts, iron salts, and cobalt salts. The higher fatty acid salt (C1) can be used alone or in combination of two or more.

[0029] The content of the higher fatty acid salt (C1) is usually 0.0001 to 0.8 parts by mass, preferably 0.0005 to 0.5 parts by mass, more preferably 0.0007 to 0.4 parts by mass, and even more preferably 0.001 to 0.3 parts by mass, relative to 100 parts by mass of the polyvinyl alcohol-based resin (A). When the content of the higher fatty acid salt (C1) is within the above range, optical color unevenness due to defects tends to be improved and the occurrence of optical streaks tends to be suppressed.

[0030] The higher fatty acids (C) used in the polyvinyl alcohol-based film 2 are higher fatty acid salts (C1) and / or higher fatty acids (C2). Examples of the higher fatty acid salts (C1) include the higher fatty acid salts (C1) described in the polyvinyl alcohol-based film 1. The higher fatty acid (C2) is preferably a higher fatty acid having 8 to 20 carbon atoms, more preferably a higher fatty acid having 10 to 18 carbon atoms, and even more preferably a higher fatty acid having 12 to 18 carbon atoms. Specific examples of such higher fatty acids (C2) include lauric acid (C12) and stearic acid (C18). The higher fatty acid salts (C1) and higher fatty acids (C2) can be used alone or in combination of two or more.

[0031] The content of the higher fatty acid (C) is usually 0.0001 to 0.8 parts by mass, preferably 0.0005 to 0.5 parts by mass, more preferably 0.0007 to 0.4 parts by mass, and even more preferably 0.001 to 0.3 parts by mass, relative to 100 parts by mass of the polyvinyl alcohol-based resin (A). When the content of the higher fatty acid (C) is within the above range, optical color unevenness due to defects tends to be improved and the occurrence of optical streaks tends to be suppressed.

[0032] In the step (I), the timing at which the nitrogen-containing nonionic surfactant (B) and the higher fatty acid salt (C1) or the higher fatty acids (C) are blended into the aqueous solution of polyvinyl alcohol-based resin (A) is not particularly limited. For example, when the aqueous solution of polyvinyl alcohol-based resin (A) is prepared in a dissolver, the nitrogen-containing nonionic surfactant (B) and the higher fatty acid salt (C1) or the higher fatty acids (C) may be blended into the aqueous solution of polyvinyl alcohol-based resin (A) in the dissolver, or when the aqueous solution of polyvinyl alcohol-based resin (A) is prepared in a twin-screw extruder, the nitrogen-containing nonionic surfactant (B) and the higher fatty acid salt (C1) or the higher fatty acids (C) may be blended into the aqueous solution of polyvinyl alcohol-based resin (A) in the dissolver.

[0033] When the aqueous solution of polyvinyl alcohol-based resin (A) is prepared in a dissolver, after blending the nitrogen-containing nonionic surfactant (B), the higher fatty acid salt (C1), or the higher fatty acids (C) into the aqueous solution of polyvinyl alcohol-based resin (A) in the dissolver, the preparation temperature of the aqueous solution is preferably 120° C. or higher, more preferably 130° C. or higher, and even more preferably 135° C. or higher, and the upper limit is usually 150° C. or lower, preferably 145° C. The preparation temperature is particularly preferably 120 to 150° C., more preferably 130 to 150° C., and even more preferably 135 to 145° C.

[0034] The preparation time of the aqueous solution is preferably 12 to 48 hours, with the upper limit being 48 hours or less, more preferably 36 hours or less, and even more preferably 24 hours or less. The preparation time is particularly preferably 12 to 48 hours, more preferably 12 to 36 hours, and even more preferably 12 to 24 hours. The preparation temperature means the temperature inside the dissolver, and the preparation time means the residence time in the dissolver.

[0035] In addition, when the aqueous solution of polyvinyl alcohol resin (A) is prepared using a twin-screw extruder, the nitrogen-containing nonionic surfactant (B), the higher fatty acid salt (C1), or the higher fatty acid (C) is preferably blended within 80% of the effective screw length (L) of the twin-screw extruder from the downstream side, more preferably within 70% of the effective screw length (L), and even more preferably within 60% of the effective screw length (L) of the twin-screw extruder from the downstream side, when the total length of the effective screw length (L) of the twin-screw extruder is taken as 100%. By blending within the above-mentioned range, the surfactant in the aqueous solution of polyvinyl alcohol resin (A) can be efficiently dispersed, and thermal decomposition of the surfactant can also be suppressed.

[0036] When the nitrogen-containing nonionic surfactant (B), the higher fatty acid salt (C1), or the higher fatty acids (C) are compounded in a twin-screw extruder, the preparation temperature during compounding is 80° C. or higher, preferably 85° C. or higher, more preferably 90° C. or higher, with the upper limit being preferably 100° C. or lower. The preparation temperature is preferably 80 to 100° C., more preferably 85 to 100° C., and even more preferably 90 to 100° C.

[0037] Furthermore, when the nitrogen-containing nonionic surfactant (B), the higher fatty acid salt (C1), or the higher fatty acids (C) are blended in a twin-screw extruder, the preparation time during blending is preferably 0.001 hour or more, more preferably 0.003 hour or more, even more preferably 0.01 hour or more, and particularly preferably 0.05 hour or more, with the upper limit being 2 hours or less, preferably 1.5 hours or less, even more preferably 1 hour, and particularly preferably 0.8 hours. The preparation time is preferably 0.001 to 2 hours, more preferably 0.003 to 1.5 hours, even more preferably 0.01 to 1 hour, and particularly preferably 0.05 to 0.8 hours. The preparation temperature refers to the temperature of the twin-screw extruder, and the preparation time refers to the time it takes for the mixture to pass through the twin-screw extruder and the T-slit die.

[0038] In addition to the polyvinyl alcohol-based resin (A), the aqueous solution of the polyvinyl alcohol-based resin (A) may contain, as necessary, commonly used plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, trimethylolpropane, and surfactants other than the nitrogen-containing nonionic surfactant (B), and it is preferable to contain these from the viewpoint of film-forming properties. One selected from these can be used alone, or two or more can be used in combination.

[0039] When the aqueous solution of polyvinyl alcohol-based resin (A) contains a plasticizer, the content thereof is usually 1 part by mass or more, preferably 3 parts by mass or more, and more preferably 5 parts by mass or more, relative to 100 parts by mass of polyvinyl alcohol-based resin (A). 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 content ranges, for example, from 1 to 35 parts by mass. If the content of the plasticizer is too low, the stretchability during production of the polarizing film tends to decrease, while if the content is too high, the strength of the resulting polyvinyl alcohol-based film tends to decrease.

[0040] When the aqueous solution of polyvinyl alcohol-based resin (A) contains a surfactant other than the nitrogen-containing nonionic surfactant (B), the content thereof is preferably 0.15 parts by mass or less, more preferably 0.1 parts by mass or less, and even more preferably 0.07 parts by mass or less, per 100 parts by mass of polyvinyl alcohol-based resin (A). The lower limit is usually 0.001 parts by mass, and the content ranges, for example, from 0.001 to 0.15 parts by mass.

[0041] The resin concentration of the aqueous solution of polyvinyl alcohol resin (A) thus obtained is preferably 15% by mass or more, more preferably 17% by mass or more, and even more preferably 20% by mass or more, with the upper limit being preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. If the resin concentration of such an aqueous solution is too low, the drying load will increase, and production capacity will tend to decrease, while if it is too high, the viscosity will be too high, making it difficult to achieve uniform dissolution.

[0042] Next, the obtained aqueous solution of polyvinyl alcohol-based resin (A) is subjected to a degassing treatment. Examples of the degassing method include static degassing and degassing using a multi-screw extruder. The multi-screw extruder may be any multi-screw extruder equipped with a vent, and typically a twin-screw extruder equipped with a vent is used.

[0043] <Step (II)> In step (II), the aqueous solution of the polyvinyl alcohol-based resin (A) is cast into a casting mold to form a film. After the degassing treatment, the aqueous solution of the polyvinyl alcohol-based resin (A) is introduced into a T-shaped slit die in fixed amounts, and then extruded and cast onto a rotating casting drum to form a film by a continuous casting method.

[0044] The resin temperature of the aqueous solution of polyvinyl alcohol-based resin (A) at the outlet of the T-shaped slit die is preferably 70 to 100° C., more preferably 80 to 98° C. If the resin temperature of the aqueous solution of polyvinyl alcohol-based resin (A) is too low, the flow tends to be poor, and if it is too high, the solution tends to foam.

[0045] The viscosity of the aqueous solution of polyvinyl alcohol resin (A) at the time of extrusion is preferably 50 Pa s or more, more preferably 70 Pa s or more, and the upper limit is preferably 200 Pa s or less, more preferably 150 Pa s or less. If the viscosity of the aqueous solution is too high, the flow tends to be poor, and if the viscosity is too low, casting film formation tends to be difficult.

[0046] The discharge speed of the aqueous solution of polyvinyl alcohol-based resin (A) discharged from the T-shaped slit die onto 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 speed is too slow, productivity tends to decrease, while if the discharge speed is too fast, casting tends to become difficult.

[0047] The diameter of the casting drum is preferably 2 m or more, more preferably 2.4 m or more, and even more preferably 2.8 m or more, with the upper limit being preferably 5 m or less, more preferably 4.5 m or less, and even more preferably 4 m or less. The diameter of the casting 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 zone on the casting drum becomes short, and the speed tends to be difficult to increase, while if the diameter is too large, transportability tends to decrease.

[0048] The width of the casting drum is preferably 3 m or more, more preferably 3.5 m or more, even more preferably 4 m or more, particularly preferably 4.5 m or more, and particularly preferably 5 to 8 m. If the width of the casting drum is too small, productivity tends to decrease.

[0049] The rotation speed of the cast drum is preferably 3 m / min or more, more preferably 7 m / min, and even more preferably 10 m / min, with the upper limit being preferably 50 m / min or less, more preferably 40 m / min, and even more preferably 35 m / min. The rotation speed of the cast drum is also preferably 3 to 50 m / min, more preferably 7 to 40 m / min, and even more preferably 10 to 35 m / min. If the rotation speed is too slow, productivity tends to decrease, and if it is too fast, drying tends to be insufficient.

[0050] The upper limit of the surface temperature of the cast drum is preferably 100° C. or less, since foaming during drying can be suppressed and a film with excellent appearance can be obtained, more preferably 97° C. or less, even more preferably 95° C. or less, and particularly preferably 92° C. or less. The lower limit is preferably 60° C. or more, since excellent releasability can be obtained when the formed film is peeled from the casting mold, more preferably 65° C. or more, even more preferably 70° C. or more, particularly preferably 75° C. or more, and especially preferably 80° C. or more.

[0051] <Step (III)> Step (III) is a step of heating and drying the formed film. The film (the formed film) peeled from the casting drum is transported in the machine direction (MD) using nip rolls or the like, and the front and back surfaces of the film are dried by alternately contacting them with multiple heated rolls. The heated rolls are, for example, rolls with a diameter of 0.2 to 2 m and whose surfaces have been hard chrome plated or mirror-finished, and drying is preferably carried out using typically 2 to 30 rolls, preferably 10 to 25 rolls.

[0052] The surface temperature of the heated roll is not particularly limited, but is usually 30° C. or higher, preferably 40° C. or higher, with the upper limit usually being 150° C. or lower, preferably 140° C. or lower. The surface temperature of the heated roll is usually 30 to 150° C., preferably 40 to 140° C. If the surface temperature is too low, drying tends to be insufficient, whereas if the surface temperature is too high, drying tends to be excessive, which tends to result in poor appearance such as waviness.

[0053] <Step (IV)> Step (IV) is a step of heat-treating the obtained film using hot air. The film that has undergone step (III) may be heat-treated, for example, using a floating dryer. The upper limit of the heat treatment temperature is preferably 150°C or lower, more preferably 140°C or lower, even more preferably 135°C or lower, and particularly preferably 130°C or lower. The lower limit is preferably 100°C or higher, more preferably 103°C or higher, even more preferably 105°C or higher, and particularly preferably 110°C or higher. The heat treatment temperature range is, for example, 100 to 150°C. If the heat treatment temperature is too high, the dyeability during production of the polarizing film tends to decrease. If the heat treatment temperature is too low, the film is likely to wrinkle or fold during the swelling step during production of the polarizing film, which tends to deteriorate the appearance of the polarizing film. The heat treatment time is preferably 20 to 100 seconds, and particularly preferably 40 to 70 seconds.

[0054] Up to this point, a method for producing a polyvinyl alcohol film has been described in which an aqueous solution of a polyvinyl alcohol resin (A) is prepared, the aqueous solution is cast onto a rotating cast drum (drum-shaped roll), a film is formed by a casting method, and the film is dried. However, it is also possible to cast an aqueous solution of a polyvinyl alcohol resin (A) onto a resin film or a metal belt, a film is formed, and the film is dried.

[0055] [Polyvinyl Alcohol Film] Thus, a polyvinyl alcohol film is obtained through the above steps (I) to (III) and, if necessary, step (IV), and is finally wound up on a roll to become a finished product.

[0056] The upper limit of the thickness of the present polyvinyl alcohol-based film is preferably 65 μm or less, more preferably 50 μm or less, even more preferably 45 μm or less, particularly preferably 45 μm or less, and especially preferably 40 μm or less. From the viewpoint of production stability of the polarizing film, the lower limit of the film thickness is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 15 μm or more, and particularly preferably 20 μm or more. The range of the film thickness is, for example, 5 to 65 μm.

[0057] The length of the present polyvinyl alcohol film is preferably 4 km or more from the viewpoint of increasing the area of ​​the polarizing film, and more preferably 5 to 50 km from the viewpoint of transport mass.

[0058] The width of the polyvinyl alcohol film is preferably 1 m or more, more preferably 2 m or more, even more preferably 3 m or more, and particularly preferably 3.5 m or more. The upper limit of the film width is usually 7 m or less, and the film width ranges from 1 to 7 m, for example.

[0059] The polyvinyl alcohol-based film has excellent thickness accuracy and is therefore useful for optical applications. In particular, it is extremely useful as a raw film for polarizing films. Hereinafter, methods for producing polarizing films and polarizing plates made from the polyvinyl alcohol-based film will be described.

[0060] [Method for Producing Polarizing Film] The polarizing film of the present invention is produced by unwinding the polyvinyl alcohol film from a roll and transporting it horizontally, followed by processes such as swelling, dyeing, boric acid crosslinking, stretching, washing, and drying.

[0061] The swelling step is carried out before the dyeing step. The swelling step not only cleans the surface of the polyvinyl alcohol-based film from dirt, but also has the effect of preventing uneven dyeing by swelling the polyvinyl alcohol-based film. In the swelling step, water is usually used as the treatment liquid. As long as the treatment liquid is mainly composed of water, it may contain additives such as iodide compounds and surfactants, alcohol, etc. The temperature of the swelling bath is usually about 10 to 45°C, and the immersion time in the swelling bath is usually about 0.1 to 10 minutes.

[0062] The dyeing process is carried out by bringing the film into contact with a liquid containing iodine or a dichroic dye. An aqueous solution of iodine and potassium iodide is usually used, with an iodine concentration of 0.1 to 2 g / L and a potassium iodide concentration of 1 to 100 g / L being appropriate. A practical dyeing time is approximately 30 to 500 seconds. The treatment bath temperature is preferably 5 to 50°C. The aqueous solution may contain a small amount of a water-compatible organic solvent in addition to the aqueous solvent.

[0063] The boric acid crosslinking step is carried out using a boron compound such as boric acid or borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 10 to 100 g / L, and it is preferable to have potassium iodide coexist in the solution from the viewpoint of stabilizing the polarization performance. The treatment temperature is preferably about 30 to 70°C, and the treatment time is preferably about 0.1 to 20 minutes. If necessary, a stretching operation may be carried out during the treatment.

[0064] In the stretching step, the film is preferably stretched uniaxially by 3 to 10 times, preferably 3.5 to 7 times. At this time, slight stretching (stretching to a degree sufficient to prevent shrinkage in the width direction, or more) may also be performed in the direction perpendicular to the stretching direction. The temperature during stretching is preferably 40 to 170°C. Furthermore, the final stretching ratio need only be set within the above range, and the stretching operation may be performed not only in one step but also multiple times during the production process.

[0065] The washing step is carried out, for example, by immersing the film in water or an aqueous iodide solution such as potassium iodide, and can remove precipitates that form on the surface of the film. When using an aqueous potassium iodide solution, the potassium iodide concentration may be approximately 10 to 1,000 g / L. The temperature during the washing treatment is usually 5 to 50°C, preferably 10 to 45°C. The treatment time is usually 1 to 300 seconds, preferably 10 to 240 seconds. Note that washing with water and washing with an aqueous potassium iodide solution may be performed in combination as appropriate.

[0066] The drying step is carried out, for example, using a dryer at 40 to 100° C. for 0.1 to 10 minutes.

[0067] A polarizing film is thus obtained, and the polarization degree of the polarizing film is preferably 99.90% or more, more preferably 99.99% or more. If the polarization degree is too low, the contrast of the liquid crystal display tends to decrease. The polarization degree is generally determined by the light transmittance (H 11 The degree of polarization is calculated according to the following formula (1) from the light transmittance (H1) measured at a wavelength λ in a state where the two polarizing films are superimposed so that the orientation directions are perpendicular to each other. 11 −H1) / (H 11 + H1) 1 / 2 ...(1)

[0068] Furthermore, the single transmittance of the polarizing film of the present invention is preferably 41% or more, more preferably 43% or more. If the single transmittance is too low, it tends to be difficult to achieve high brightness in liquid crystal displays. The single transmittance is a value obtained by measuring the light transmittance of the polarizing film alone using a spectrophotometer.

[0069] Next, a method for producing a polarizing plate of the present invention using the polarizing film of the present invention will be described. The polarizing film of the present invention is suitable for producing a polarizing plate with little color unevenness and excellent polarizing performance.

[0070] [Method for manufacturing polarizing plate] The polarizing plate of the present invention is produced by laminating an optically isotropic resin film as a protective film to one or both sides of the polarizing film of the present invention via an adhesive. Examples of the protective film include a film made of an acetyl cellulose-based resin such as triacetyl cellulose or diacetyl cellulose, a film made of a polyester-based resin such as polyethylene terephthalate, polyethylene naphthalate, or polybutylene terephthalate, a polycarbonate-based resin film, a cycloolefin-based resin film, an acrylic-based resin film, and a film made of a chain olefin-based resin such as a polypropylene-based resin.

[0071] The lamination method is carried out by a known method, for example, by uniformly applying a liquid adhesive composition to the polarizing film, the protective film, or both, and then laminating and pressing the two together, followed by heating or irradiating with active energy rays.

[0072] Alternatively, a polarizing plate can be fabricated by applying a curable resin such as a urethane resin, an acrylic resin, or a urea resin to one or both sides of the polarizing film and curing the resin to form a cured layer. In this way, the cured layer serves as a substitute for the protective film, thereby enabling a thinner polarizing plate to be fabricated.

[0073] The polarizing films and polarizing plates obtained using the present polyvinyl alcohol-based film have excellent polarization performance, and are preferably used in liquid crystal display devices such as portable information terminals, personal computers, televisions, projectors, signage, electronic desk calculators, electronic clocks, word processors, electronic paper, game consoles, videos, cameras, photo albums, thermometers, audio equipment, meters for automobiles and machinery, sunglasses, anti-glare glasses, 3D glasses, wearable displays, foldable displays, anti-reflection layers for display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys, etc.

[0074] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded. In the examples, "parts" refers to parts by mass.

[0075] <Measurement conditions> [Number of defects (pieces / m 2 The obtained polyvinyl alcohol film was unwound from the roll to a length of 30,000 m. 2 Defects (bright and dark defects) with a diameter of 50 μm to 100 μm were detected by an automatic foreign matter inspection device, and the total number of detected bright and dark defects was counted at 30,000 m. 2 The value divided by the number of defects (number / m 2 ) In this specification, "bright and dark defects" refer to defects that are detected as bright and dark spots in the texture area (normal area of ​​the film) when the defective area is detected by a camera in the automatic foreign body inspection device. The setting conditions for the automatic foreign body inspection device are as follows:

[0076] Illumination: Transmitted light, angle 90° (perpendicular to the film), distance 300 mm, light source halogen lamp 150 W Detection: 20 CCD cameras, position 483 mm, 5000 pixels / camera, resolution 48 μm / pixel, 50 mm lens (F2.8) (Evaluation criteria) ◯ (very good): 5 × 10 -3 (pcs / m 2 ) Less than △ (good): 5 x 10 -3 ~15 x 10 -3 (pcs / m 2 ) ×(poor) :15×10 -3 (pcs / m 2 ) more

[0077] [Method for measuring nitrogen-containing nonionic surfactant (B), higher fatty acid salt (C1) and / or higher fatty acid (C2) in film] The contents of nitrogen-containing nonionic surfactant (B) and higher fatty acid salt (C1) and / or higher fatty acid (C2) in the film are measured by the following method. - Pretreatment Pretreatment was performed using a high-speed solvent extraction apparatus under the following conditions: Apparatus: Dionex ASE-200 (11 mL cell) Extraction solvent: methanol / water = 90 / 10 (volume ratio) Heat-up time: 5 min Extraction pressure / resting time: 150 psi / 10 min Flush volume: 80% Purge time: 60 sec Cycles: 2 cycles Number of extractions: 2 - Quantification of higher fatty acid salt (C1) and / or higher fatty acid (C2) Measured using a liquid chromatograph-mass spectrometer (LC-MS) under the following conditions. Instrument LC: Agilent Technologies 1260 Infinity Instrument MS: Thermoscientific Q Exactive Focus Column: YMC YMC-Pack ODS-A 3.0 x 150 mm 5 μm Column temperature: 30°C Mobile phase A: 10 mM ammonium acetate aqueous solution Mobile phase B: Methanol Gradient: A / B = 25 / 75 (0 to 15 min) → 5 / 95 (15 to 30 min) Flow rate: 0.45 mL / min UV / Vis wavelength: 190 to 900 nm Mass detector Measurement condition 1 (ion mode): Positive ion mode Tune File: HES1_400 nLmin MSI: Full scan (m / z 150 to 2000) Measurement condition 2 (ion mode): Negative ion mode Tune File: HES1_40011 min MSI : Full scan (m / z 150-2000)

[0078] Example 1 (Production of Polyvinyl Alcohol Film) 2,500 kg of polyvinyl alcohol resin with a weight-average molecular weight of 142,000 and a degree of saponification of 99.9 mol%, 6,520 kg of water, and 300 kg of glycerin as a plasticizer were added, and water vapor was blown in while stirring to dissolve under pressure, to prepare a polyvinyl alcohol resin aqueous solution with a resin concentration of 29% by mass. The preparation temperature was 140°C, and the preparation time was 20 hours. Next, the polyvinyl alcohol resin aqueous solution was fed into a twin-screw extruder, and an aqueous solution containing 1.4 kg of a nitrogen-containing nonionic surfactant (lauric acid diethanolamide) (0.055 parts per 100 parts of polyvinyl alcohol resin) and 0.045 kg of a higher fatty acid (lauric acid (C12)) dissolved in water was continuously added from a position 50% upstream of the effective screw length (L) of the twin-screw extruder. The preparation time from the twin-screw extruder was 0.1 hours. The temperature of the polyvinyl alcohol-based resin aqueous solution was raised to 80 ° C., and the solution was extruded (rotation speed 16 m / min) and cast onto a rotating cast drum from a T-type slit die outlet to form a film. The film thus formed was peeled off from the cast drum, and the front and back surfaces of the film were dried while alternately contacting a total of 10 heated rolls. Next, the peeled film was heat-treated by blowing hot air at 90 ° C. from both sides, and then both ends in the width direction (TD direction) were slit to obtain a polyvinyl alcohol-based film (thickness 30 μm, width 5 m, length 5 km). The mass content ratio of the nitrogen-containing nonionic surfactant (B) to the higher fatty acid salt (C1) or higher fatty acid (C) [(C1) or (C) / (B)] and the number of defects in the obtained polyvinyl alcohol-based film were measured and listed in Table 1 below.

[0079] Example 2 A polyvinyl alcohol film having a thickness of 60 μm, a width of 5 m, and a length of 5 km was produced in the same manner as in Example 1, except that the rotation speed of the cast drum during film formation was changed to 10 m / min and the amount of higher fatty acid (lauric acid (C12):stearic acid (C18) = 1:1) was changed to 0.078 kg. The mass content ratio [(C1) or (C) / (B)] of the nitrogen-containing nonionic surfactant (B) to the higher fatty acid salt (C1) or higher fatty acid (C) in the obtained polyvinyl alcohol film and the number of defects were measured and are shown in Table 1 below.

[0080] Example 3 A polyvinyl alcohol film (thickness 30 μm, width 5 m, length 5 km) was obtained in the same manner as in Example 1, except that the blending amount of the nitrogen-containing nonionic surfactant (polyoxyethylene laurylamine) was 0.825 kg (blended amount 0.033 part per 100 parts of polyvinyl alcohol resin), the blending amount of the higher fatty acid (stearic acid (C18)) was 0.075 kg, and the preparation time from the twin-screw extruder was 0.7 hours. The mass content ratio [(C1) or (C) / (B)] of the nitrogen-containing nonionic surfactant (B) to the higher fatty acid salt (C1) or higher fatty acid (C) in the obtained polyvinyl alcohol film and the number of defects were measured and are shown in Table 1 below.

[0081] Example 4 A polyvinyl alcohol film (thickness 30 μm, width 5 m, length 5 km) was obtained in the same manner as in Example 1, except that the blending amount of the nitrogen-containing nonionic surfactant (polyoxyethylene laurylamine) was 0.725 kg (blended amount 0.029 part per 100 parts of polyvinyl alcohol resin) and the blending amount of the higher fatty acid (stearic acid (C18)) were 0.0725 kg. The mass content ratio [(C1) or (C) / (B)] of the nitrogen-containing nonionic surfactant (B) to the higher fatty acid salt (C1) or higher fatty acid (C) in the obtained polyvinyl alcohol film and the number of defects were measured and are shown in Table 1 below.

[0082] Comparative Example 1 (Production of Polyvinyl Alcohol-Based Film) 2,500 kg of polyvinyl alcohol-based resin with a weight average molecular weight of 142,000 and a degree of saponification of 99.9 mol%, 6,520 kg of water, 335 kg of glycerin as a plasticizer, 1.4 kg of a nitrogen-containing nonionic surfactant (polyoxyethylene laurylamine) (amount of blending 0.055 parts per 100 parts of polyvinyl alcohol-based resin), and a surfactant containing 0.79 kg of higher fatty acid (stearic acid (C18)) were added, and water vapor was blown in while stirring to dissolve under pressure, to prepare a polyvinyl alcohol-based resin aqueous solution with a resin concentration of 29% by mass. The preparation temperature was 140 ° C. and the preparation time was 20 hours. Next, the polyvinyl alcohol-based resin aqueous solution was fed into a twin-screw extruder and degassed, and then the aqueous solution temperature was raised to 80 ° C., and the solution was discharged from a T-slit die outlet onto a rotating cast drum (rotation speed 16 m / min) and cast to form a film. The formed film was peeled off from the casting drum, and the front and back sides of the film were dried while alternately contacting a total of 10 heated rolls. Next, the peeled film was heat-treated by blowing hot air at 90°C onto both sides, and then both ends in the width direction (TD direction) were slit to obtain a polyvinyl alcohol film (thickness 30 μm, width 5 m, length 5 km). The properties of the obtained polyvinyl alcohol film were as shown in Table 1 below. The mass content ratio of the nitrogen-containing nonionic surfactant (B) to the higher fatty acid salt (C1) or higher fatty acid (C) [(C1) or (C) / (B)] and the number of defects in the obtained polyvinyl alcohol film were measured and are listed in Table 1 below.

[0083] Comparative Example 2: A polyvinyl alcohol film having a thickness of 60 μm, a width of 5 m, and a length of 5 km was produced in the same manner as in Comparative Example 1, except that the rotation speed of the cast drum during film formation was changed to 10 m / min and 0.48 kg of higher fatty acid (lauric acid (C12)) was used. The mass content ratio of the nitrogen-containing nonionic surfactant (B) to the higher fatty acid salt (C1) or higher fatty acids (C) [(C1) or (C) / (B)] and the number of defects in the obtained polyvinyl alcohol film were measured and are shown in Table 1 below.

[0084]

[0085] The polyvinyl alcohol films of Examples 1 to 4 have a mass content ratio (C1) or (C) / (B) of the nitrogen-containing nonionic surfactant (B) to the higher fatty acid salt (C1) or higher fatty acids (C) within the range specified in the present application, and therefore have few defects. On the other hand, the polyvinyl alcohol films of Comparative Examples 1 and 2 have a large mass content ratio (C1) or (C) / (B) of the nitrogen-containing nonionic surfactant (B) to the higher fatty acid salt (C1) or higher fatty acids (C), and therefore have many defects in the film.

[0086] Polarizing films and polarizing plates made of the present polyvinyl alcohol-based film have no polarization unevenness and excellent in-plane uniformity of polarization performance, and are preferably used in liquid crystal display devices such as portable information terminals, personal computers, televisions, projectors, signage, electronic desk calculators, electronic clocks, word processors, electronic paper, game consoles, videos, cameras, photo albums, thermometers, audio equipment, meters for automobiles and machinery, sunglasses, anti-glare glasses, 3D glasses, wearable displays, anti-reflection layers for display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys, etc.

Claims

1. A polyvinyl alcohol film containing a polyvinyl alcohol resin (A), a nitrogen-containing nonionic surfactant (B), and a higher fatty acid salt (C1), wherein the mass content ratio of the nitrogen-containing nonionic surfactant (B) to the higher fatty acid salt (C1) in the film [(C1) / (B)] is 0.3 or less.

2. A polyvinyl alcohol film containing a polyvinyl alcohol resin (A), a nitrogen-containing nonionic surfactant (B), and higher fatty acids (C), wherein the higher fatty acids (C) consist of higher fatty acid salts (C1) and / or higher fatty acids (C2), and the mass content ratio of the nitrogen-containing nonionic surfactant (B) to the higher fatty acids (C) in the film [(C) / (B)] is 0.3 or less.

3. The polyvinyl alcohol film according to claim 1, wherein the higher fatty acid salt (C1) is a higher fatty acid salt having 8 to 20 carbon atoms.

4. The polyvinyl alcohol film according to claim 2, wherein the higher fatty acid salt (C1) and the higher fatty acid (C2) are higher fatty acid salts and higher fatty acids having 8 to 20 carbon atoms.

5. The polyvinyl alcohol film according to claim 1 or 2, wherein the thickness of the film is 10 to 65 μm.

6. The polyvinyl alcohol film according to claim 1 or 2, which is used for producing a polarizing film.

7. A polarizing film obtained by using the polyvinyl alcohol film according to claim 1 or 2.

8. A polarizing plate comprising the polarizing film according to claim 7 and a protective film provided on at least one surface of the polarizing film.

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