Polyvinyl alcohol film and method for producing polarizing film using the same

Abstract

A PVA film, which is a polyvinyl alcohol film containing polyvinyl alcohol (A), anionic surfactant (B) and fatty acid salt (C), characterized in that the anionic surfactant (B) is a sulfate type or sulfonate type, and the content of the anionic surfactant (B) is 0.01 to 0.20 parts by mass relative to 100 parts by mass of polyvinyl alcohol (A), the fatty acid salt (C) is an alkali metal salt or an amine salt, and the content of the fatty acid salt (C) is 0.02 to 0.20 parts by mass relative to 100 parts by mass of polyvinyl alcohol (A), and the content of the nonionic surfactant is less than 0.01 parts by mass relative to 100 parts by mass of polyvinyl alcohol (A). Thus, a PVA film and a method for manufacturing a polarizing film using the PVA film are provided, wherein the PVA film has a small number of optical defects and active agent aggregates, a low haze value, good peelability, and excellent polarization performance when processed into a polarizing film.

Description

Technical Field

[0001] The present invention relates to a polyvinyl alcohol film and a method for producing a polarizing film using the polyvinyl alcohol film. The polyvinyl alcohol film contains polyvinyl alcohol (A), an anionic surfactant (B) and a fatty acid salt (C). Background Art

[0002] Polyvinyl alcohol (hereinafter, sometimes referred to as PVA) films are used for various purposes by utilizing unique properties related to transparency, optical properties, mechanical strength, water solubility, etc. In particular, by utilizing its excellent optical properties, PVA films are used as raw materials (raw films) for manufacturing polarizing films that constitute polarizing plates, which are basic components of liquid crystal displays (LCDs), and their use is expanding. Polarizing plates for LCDs require high optical performance, and polarizing films, which are their components, also require high optical performance.

[0003] Polarizers are usually made by dyeing, uniaxially stretching, and fixing with boron compounds etc. to produce a polarizing film, and then laminating a protective film such as a triacetyl cellulose (TAC) film to the surface of the polarizing film. The original PVA film is usually made by drying a film-making stock solution containing PVA by a casting method or the like.

[0004] To date, a variety of technologies related to PVA films or methods for manufacturing them are known. Patent document 1 describes a method for manufacturing a polyvinyl alcohol film, which is characterized in that it includes the following steps: using a polyvinyl alcohol resin aqueous solution containing an alkyl sulfonate surfactant, the polyvinyl alcohol film is manufactured by a casting method. According to this, a method for manufacturing a polyvinyl alcohol film that is excellent in colorlessness and transparency in addition to optical properties can be provided. However, in polyvinyl alcohol films using an alkyl sulfonate surfactant alone, there are sometimes problems with the peelability when manufacturing the film. Moreover, in the case of further using a nonionic surfactant in the alkyl sulfonate surfactant in order to improve the peelability, sometimes the number of surfactant aggregates is large, the haze value is high, and the polarization performance when processed into a polarizing film deteriorates, which is desired to be improved.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2006-193694. Summary of the invention

[0008] Problems to be solved by the invention

[0009] The present invention is made to solve the above-mentioned problems, and its purpose is to provide a PVA film and a method for manufacturing a polarizing film using the PVA film, wherein the PVA film has a small number of optical defects and active agent aggregates, a low haze value, good peelability, and excellent polarization performance when processed into a polarizing film.

[0010] Means for solving problems

[0011] The above-mentioned problems are solved by providing a polyvinyl alcohol film, which contains polyvinyl alcohol (A), anionic surfactant (B) and fatty acid salt (C), wherein the anionic surfactant (B) is a sulfate ester type or a sulfonate type, and the content of the anionic surfactant (B) is 0.01 to 0.20 parts by mass relative to 100 parts by mass of the polyvinyl alcohol (A), the fatty acid salt (C) is an alkali metal salt or an amine salt, and the content of the fatty acid salt (C) is 0.02 to 0.20 parts by mass relative to 100 parts by mass of the polyvinyl alcohol (A), and the content of the nonionic surfactant is less than 0.01 parts by mass relative to 100 parts by mass of the polyvinyl alcohol (A).

[0012] In this case, the content ratio (B:C) of the anionic surfactant (B) and the fatty acid salt (C) is preferably 25:75 to 75:25. The fatty acid salt (C) is preferably an alkali metal salt or amine salt of a fatty acid having 12 to 16 carbon atoms.

[0013] In addition, the film width is preferably 1.5 m or more. The film length is preferably 3000 m or more. The film thickness is preferably 10 to 70 m m.

[0014] The above-mentioned problems are also solved by providing a method for producing a polarizing film, the method comprising: a step of dyeing the above-mentioned polyvinyl alcohol film and a step of stretching the film.

[0015] Effects of the Invention

[0016] The PVA film of the present invention has a small number of optical defects and active agent aggregates, a low haze value, and good peelability, so it has excellent process acceptance. Therefore, by using the PVA film as a raw roll, a polarizing film with good polarization performance can be obtained. DETAILED DESCRIPTION

[0017] The PVA film of the present invention contains PVA (A), anionic surfactant (B) and fatty acid salt (C). At this time, the content of nonionic surfactant is less than a certain amount.

[0018] The inventors have found that a PVA film containing a certain amount of PVA (A), anionic surfactant (B) and fatty acid salt (C), respectively, and the content of nonionic surfactant is less than a certain amount, has few optical defects and active agent aggregates, low haze value and good peelability. Subsequently, it was clarified that by using such a PVA film, a polarizing film with excellent polarization performance can be obtained. The inventors have confirmed that when the content of PVA (A), anionic surfactant (B) and fatty acid salt (C) is not within a certain range, a PVA film with good film quality and peelability cannot be obtained. In addition, the inventors have also confirmed that when the content of nonionic surfactant exceeds a certain amount, the number of active agent aggregates is large and the haze value increases.

[0019] Therefore, it is important to have a PVA film containing a certain amount of PVA (A), anionic surfactant (B) and fatty acid salt (C), respectively, and the content of nonionic surfactant is less than a certain amount, as in the present invention. By satisfying such a structure, a PVA film with few optical defects and active agent aggregates, low haze value, good peelability, and excellent polarization performance when processed into a polarizing film can be obtained.

[0020] [PVA (A)]

[0021] As PVA (A), PVA manufactured by saponifying the vinyl ester polymer obtained by polymerizing vinyl ester can be used. As vinyl ester, for example, vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, versatic acid (Versatic Acid) vinyl ester, etc. can be listed. These can be used alone or in combination of two or more, but the former is preferred. From the viewpoints of availability, cost, the yield of PVA (A), as vinyl ester, vinyl acetate is preferred.

[0022] Examples of other monomers copolymerizable with the vinyl ester include: ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutylene; acrylic acid or its salts; acrylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, and octadecyl acrylate; methacrylic acid or its salts; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, and octadecyl methacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid or its salts, acrylamidopropyldimethylamine or its salts, N-hydroxymethylacrylamide acrylamide derivatives such as amine or its derivatives; methacrylamide derivatives such as methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamide propanesulfonic acid or its salts, methacrylamide propyl dimethylamine or its salts, N-hydroxymethyl methacrylamide or its derivatives; N-vinylamides such as N-vinyl formamide, N-vinylacetamide, N-vinyl pyrrolidone; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or its salts, esters or anhydrides; itaconic acid or its salts, esters or anhydrides; vinyl silyl compounds such as vinyl trimethoxysilane; isopropenyl acetate, etc. These other monomers may be used alone or in combination of two or more. Among them, as the other monomer, ethylene and olefins having 3 to 30 carbon atoms are preferred, and ethylene is more preferred.

[0023] The proportion of the structural units derived from the other monomers in the vinyl ester polymer is not particularly limited, but is preferably 15 mol % or less, more preferably 5 mol % or less, based on the number of moles of the total structural units constituting the vinyl ester polymer.

[0024] There is no restriction on the degree of polymerization of PVA (A), but as the degree of polymerization decreases, the film strength tends to decrease, so it is preferably 200 or more, more preferably 300 or more, further preferably 400 or more, and particularly preferably 500 or more. In addition, if the degree of polymerization is too high, the viscosity of the aqueous solution of PVA (A) or the molten PVA (A) increases, and there is a tendency to be difficult to form a film, so it is preferably 10,000 or less, more preferably 9,000 or less, further preferably 8,000 or less, and particularly preferably 7,000 or less. Here, the degree of polymerization of PVA (A) refers to the average degree of polymerization measured according to the description of JIS K6726-1994, which is measured in water at 30°C after re-saponification and purification of PVA (A), and the limiting viscosity [η] (unit: deciliter / g) is measured by the following formula.

[0025] Degree of polymerization = ([η] × 10 4 / 8.29) (1 / 0.62)

[0026] There is no particular limitation on the saponification degree of PVA (A). For example, PVA (A) of 60 mol% or more can be used. From the perspective of being used as an original roll film for the manufacture of optical films such as polarizing films, the saponification degree of PVA (A) is preferably 95 mol% or more, more preferably 98 mol% or more, and further preferably 99 mol% or more. Here, the saponification degree of PVA (A) refers to the ratio (mol%) of the molar number of the vinyl alcohol unit possessed by PVA (A) relative to the total molar number of the structural unit (typically a vinyl ester monomer unit) converted into a vinyl alcohol unit by saponification and the vinyl alcohol unit. The saponification degree of PVA (A) can be measured according to the description of JIS K6726-1994.

[0027] PVA (A) can use one type of PVA alone, or can use two or more types of PVA with different polymerization degree, saponification degree, modification degree, etc. in combination. However, if the PVA film contains: PVA with acidic functional groups such as carboxyl and sulfonic acid groups, PVA with acid anhydride groups, PVA with basic functional groups such as amino groups, and their neutralization products, etc., which have functional groups that promote cross-linking reactions, the secondary processability of the PVA film sometimes decreases due to the cross-linking reaction between PVA molecules. Therefore, as shown in the original roll film for optical film manufacturing, when excellent secondary processability is required, it is preferred that the content of PVA with acidic functional groups, PVA with acid anhydride groups, PVA with basic functional groups, and their neutralization products in PVA (A) is less than 0.1% by mass, and more preferably none of them are contained.

[0028] The content of PVA (A) in the above-mentioned PVA film is preferably 50% by mass or more, more preferably 70% by mass or more, and further preferably 85% by mass or more. The content of PVA (A) is usually 90% by mass or less.

[0029] [Anionic surfactant (B)]

[0030] The anionic surfactant (B) used in the present invention is a sulfate type or a sulfonate type. The number of carbon atoms in the anionic surfactant (B) is not particularly limited, but is preferably 9 or more, more preferably 10 or more, and further preferably 12 or more. On the other hand, the number of carbon atoms is preferably 30 or less, more preferably 26 or less, further preferably 20 or less, and particularly preferably 16 or less.

[0031] Examples of the sulfuric acid ester salt type include sodium alkyl sulfate, potassium alkyl sulfate, ammonium alkyl sulfate, triethanolamine alkyl sulfate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxypropylene alkyl ether sulfate, sodium polyoxyethylene alkylphenyl ether sulfate, etc. As the alkyl group, an alkyl group having 8 to 20 carbon atoms is preferred, and an alkyl group having 10 to 16 carbon atoms is more preferred.

[0032] Examples of the sulfonate type include sodium alkyl sulfonate, potassium alkyl sulfonate, ammonium alkyl sulfonate, triethanolamine alkyl sulfonate, sodium alkylbenzene sulfonate, disodium dodecyl diphenyl ether disulfonate, sodium alkyl naphthalene sulfonate, disodium alkyl sulfosuccinate, disodium polyoxyethylene alkyl sulfosuccinate, etc. The alkyl group is preferably an alkyl group having 8 to 20 carbon atoms, and more preferably an alkyl group having 10 to 16 carbon atoms.

[0033] The above-mentioned surfactants may be used alone or in combination of two or more. Among them, the anionic surfactant (B) is preferably a sulfonate type from the viewpoint of reducing the number of aggregates of the active agent and lowering the haze value.

[0034] In the PVA film of the present invention, the content of the anionic surfactant (B) is 0.01 to 0.20 parts by mass relative to 100 parts by mass of PVA (A). When the content of the anionic surfactant (B) is less than 0.01 parts by mass, the following problems will arise: many optical defects will be generated in the PVA film, the haze value will increase, and the number of active agent aggregates in the PVA film will increase. The content of the anionic surfactant (B) is preferably 0.015 parts by mass or more. On the other hand, when the content of the anionic surfactant (B) exceeds 0.20 parts by mass, many optical defects will be generated in the PVA film. The content of the anionic surfactant (B) is preferably 0.18 parts by mass or less, more preferably 0.13 parts by mass or less, and further preferably 0.11 parts by mass or less.

[0035] [Fatty acid salt (C)]

[0036] The fatty acid salt (C) is not particularly limited, but an alkali metal salt or amine salt of a fatty acid having 8 to 18 carbon atoms is preferred. Here, the number of carbon atoms refers to the number of carbon atoms of the fatty acid forming the salt in the fatty acid salt (C). When the number of carbon atoms is less than 8, optical defects may occur in the PVA film, and the peeling property may deteriorate. The number of carbon atoms is more preferably 10 or more, and further preferably 12 or more. On the other hand, when the number of carbon atoms exceeds 18, the haze value may increase and the number of active agent aggregates in the PVA film may increase. The number of carbon atoms is more preferably 16 or less. A saturated fatty acid or an unsaturated fatty acid can be used as the fatty acid, but from the viewpoint of thermal stability, a saturated fatty acid is suitable. As the saturated fatty acid, suitable are saturated fatty acids such as capric acid, lauric acid, myristic acid, and palmitic acid.

[0037] The fatty acid salt (C) used in the present invention is an alkali metal salt or an amine salt. Examples of alkali metal ions in the alkali metal salt include ions of lithium, sodium, potassium, rubidium, and cesium. Examples of amines in the amine salt include alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine. Among them, the fatty acid salt (C) is preferably an amine salt. In addition, as the amine in the amine salt, diethanolamine is preferred from the viewpoint of solubility.

[0038] In the PVA film of the present invention, the content of the fatty acid salt (C) is 0.02 to 0.20 parts by mass relative to 100 parts by mass of PVA (A). When the content of the fatty acid salt (C) is less than 0.02 parts by mass, many optical defects are generated in the PVA film, and the peelability is deteriorated. The content of the fatty acid salt (C) is preferably 0.03 parts by mass or more. On the other hand, when the content of the fatty acid salt (C) exceeds 0.20 parts by mass, the following problems will arise: the number of active agent aggregates in the PVA film increases and the haze value increases. The content of the fatty acid salt (C) is preferably 0.18 parts by mass or less, more preferably 0.15 parts by mass or less, and further preferably 0.10 parts by mass or less.

[0039] In the present invention, the content of the nonionic surfactant is less than 0.01 parts by mass relative to 100 parts by mass of PVA (A). When the content of the nonionic surfactant is 0.01 parts by mass or more, the following problems may occur: the number of active agent aggregates increases and the haze value increases. The content of the nonionic surfactant is preferably 0.008 parts by mass or less, more preferably 0.006 parts by mass or less, further preferably 0.004 parts by mass or less, and particularly preferably substantially free of the nonionic surfactant.

[0040] Examples of the nonionic surfactant include alkyl ether types such as polyoxyethylene oleyl ether; alkyl phenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; alkyl amine types such as polyoxyethylene lauryl amino ether; alkyl amide types such as polyoxyethylene lauric acid amide; polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether; aliphatic alkanolamide types such as lauric acid diethanolamide and oleic acid diethanolamide; allyl phenyl ether types such as polyoxyalkylene allyl phenyl ether, and the like.

[0041] In the present invention, the content ratio (B:C) of the anionic surfactant (B) and the fatty acid salt (C) is preferably 25:75 to 75:25. When the content ratio (B:C) is less than 25:75, the following problems may occur: many optical defects are generated in the PVA film, and the number of active agent aggregates in the PVA film increases. The content mass ratio (B:C) is more preferably 30:70 or more. On the other hand, when the content ratio (B:C) exceeds 75:25, the peelability may deteriorate. The content ratio (B:C) is more preferably 60:40 or less.

[0042] [PVA film]

[0043] From the viewpoint of imparting flexibility to the PVA film, the PVA film of the present invention preferably contains a plasticizer. Preferred plasticizers include polyols, specifically, ethylene glycol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, etc. These may use only one plasticizer, or may use two or more plasticizers in combination. Among them, from the viewpoint of compatibility with PVA (A) or availability, ethylene glycol or glycerol is preferred.

[0044] The content of the plasticizer is preferably in the range of 1 to 30 parts by mass relative to 100 parts by mass of PVA (A). If the content of the plasticizer is 1 part by mass or more, problems are less likely to occur in mechanical properties such as impact strength or process qualification during secondary processing. On the other hand, if the content of the plasticizer is 30 parts by mass or less, the film becomes appropriately soft and the workability is improved.

[0045] The PVA film of the present invention may further contain other components except PVA (A), anionic surfactant (B), fatty acid salt (C) and plasticizer as required. As such other components, for example, water, antioxidant, ultraviolet light absorber, lubricant, coloring agent, filler (inorganic particles / starch, etc.), preservative, mildewproofing agent, other macromolecular compounds except the above components, etc. can be listed. The content of other components in the PVA film is preferably below 10% by mass.

[0046] The width of the PVA film of the present invention is not particularly limited. Considering the wide polarizing film required in recent years, the width is preferably 1.5 m or more. In addition, if the width of the PVA film is too wide, the manufacturing cost of the film-making device used to manufacture the PVA film increases, and when using a practical manufacturing device to manufacture an optical film, it is sometimes difficult to stretch it uniformly, so the width of the PVA film is usually 7.5 m or less.

[0047] The shape of the PVA film of the present invention is not particularly limited. From the perspective of being able to continuously and smoothly manufacture a more uniform PVA film, or being continuously used when manufacturing an optical film, etc., a long film is preferably used. The length of the long film (length in the flow direction) is not particularly limited and can be appropriately set. The length of the film is preferably 3,000 m or more. On the other hand, the length of the film is preferably 30,000 m or less. The long film is preferably wound around a core to form a film roll.

[0048] The thickness of the PVA film of the present invention is not particularly limited and can be appropriately set. From the viewpoint of using it as a raw film for producing an optical film such as a polarizing film, the thickness of the film is preferably 10 to 70 mm. m In addition, the thickness of a PVA film can be calculated|required as the average value of the value measured at arbitrary 10 places.

[0049] The haze and number of active agent aggregates of the PVA film of the present invention are measured by the method described in the following examples. The haze value is preferably 0.3 or less, more preferably 0.2 or less, and further preferably 0.15 or less. In addition, the number of active agent aggregates is preferably 240 or less, more preferably 180 or less, and further preferably 75 or less.

[0050] The method for producing the PVA film of the present invention is not particularly limited, and is preferably a method for producing the PVA film as follows: a method for producing a PVA film containing PVA (A), anionic surfactant (B) and fatty acid salt (C), comprising the following steps: a step of blending PVA (A), anionic surfactant (B) and fatty acid salt (C) to prepare a film-forming stock solution; and a step of using the film-forming stock solution to form a film. At this time, as described above, the content of the nonionic surfactant is preferably less than a certain amount.

[0051] In the process of preparing the membrane-forming stock solution, a liquid medium may be further mixed. Examples of the liquid medium at this time include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc., and one or more of these can be used. Among them, water is preferred in terms of low environmental load and recyclability.

[0052] In the method for producing the PVA film of the present invention, for example, a film-making stock solution containing PVA (A), anionic surfactant (B), fatty acid salt (C), liquid medium, and further containing the above-mentioned plasticizer or other components as required can be used, using known methods such as cast film-making method or melt extrusion film-making method. It should be noted that the film-making stock solution can be a stock solution formed by dissolving PVA (A) in a liquid medium, or a stock solution obtained by melting PVA (A).

[0053] The volatility of the film-forming stock solution (the proportion of volatile components such as the liquid medium removed by volatilization or evaporation during film formation in the film-forming stock solution) also varies depending on the film-forming method, film-forming conditions, etc., and is preferably in the range of 50 to 90% by mass, and more preferably in the range of 55 to 80% by mass. By making the volatility of the film-forming stock solution 50% or more by mass, the viscosity of the film-forming stock solution will not be too high and film formation will be easy. On the other hand, by making the volatility of the film-forming stock solution 90% or less by mass, the viscosity of the film-forming stock solution will not be too low, and the thickness uniformity of the resulting PVA film will be improved.

[0054] The above-mentioned film-making stock solution is used, and the PVA film of the present invention is suitable for manufacturing by a casting film-making method or a melt extrusion film-making method. There is no particular limitation on the specific manufacturing method at this time. For example, the film-making stock solution can be cast or sprayed onto a support such as a drum or a belt to form a film, and then dried on the support to obtain it. For the obtained film, a drying roller or a hot air drying device can be further dried, or a heat treatment device can be used to perform heat treatment, or a humidity conditioning device can be used to perform humidity conditioning as needed. The manufactured PVA film is preferably wound on a core, etc. to form a film roll. In addition, the two ends of the width direction of the manufactured PVA film can be cut off.

[0055] The PVA film of the present invention can be suitably used as a raw film for manufacturing polarizing films, phase difference films, special light-concentrating films, etc. According to the present invention, a PVA film with excellent optical properties and high quality can be obtained. Therefore, a suitable embodiment of the present invention is an optical PVA film.

[0056] A suitable embodiment of the present invention is: a method for manufacturing a polarizing film having a step of dyeing the above-mentioned PVA film and a step of stretching. The manufacturing method may further have a fixing treatment step, a drying treatment step, a heat treatment step, etc. There is no particular limitation on the order of dyeing and stretching, and the dyeing treatment may be performed before the stretching treatment, at the same time as the stretching treatment, or after the stretching treatment. In addition, the steps of stretching, dyeing, etc. may be repeated multiple times. In particular, if the stretching is divided into two or more stages, it is easy to perform uniform stretching, so it is preferred.

[0057] As dyes for dyeing the PVA film, iodine or dichroic organic dyes (for example, direct black 17, 19, 154; direct brown 44, 106, 195, 210, 223; direct red 2, 23, 28, 31, 37, 39, 79, 81, 240, 242, 247; direct blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; direct violet 9, 12, 51, 98; direct green 1, 85; direct yellow 8, 12, 44, 86, 87; direct orange 26, 39, 106, 107 and other dichroic dyes) can be used. These dyes can be used alone or in combination of two or more. Dyeing can usually be performed by immersing the PVA film in a solution containing the above-mentioned dyes, but there is no particular limitation on the treatment conditions or treatment methods.

[0058] As methods for stretching the PVA film, there are: uniaxial stretching method and biaxial stretching method, and the former is preferred. The uniaxial stretching of stretching the PVA film along the flow direction (MD) or the like can be performed by any method of a wet stretching method or a dry heat stretching method, but from the perspective of the stability of the performance and quality of the resulting polarizing film, the wet stretching method is preferred. As wet stretching methods, there are: methods of stretching the PVA film in pure water, aqueous solutions containing various components such as additives or water-soluble organic solvents, or aqueous dispersions in which various components are dispersed. Specific examples of uniaxial stretching methods based on the wet stretching method include: methods of uniaxial stretching in warm water containing boric acid, methods of uniaxial stretching in a solution containing the above-mentioned dye or in a fixing treatment bath described later, and the like. In addition, the PVA film after absorbing water can be uniaxially stretched in the air, or uniaxially stretched by other methods.

[0059] The stretching temperature during uniaxial stretching is not particularly limited. In the case of wet stretching, a temperature in the range of preferably 20 to 90°C, more preferably 25 to 70°C, and further preferably 30 to 65°C is used. In the case of dry heat stretching, a temperature in the range of preferably 50 to 180°C is used.

[0060] Regarding the stretching ratio of the uniaxial stretching treatment (the total stretching ratio in the case of uniaxial stretching in multiple stages), from the perspective of polarization performance, it is preferred to stretch the film as much as possible before it is about to break, specifically, preferably 4 times or more, more preferably 5 times or more, and further preferably 5.5 times or more. There is no particular upper limit to the stretching ratio, as long as the film does not break, and in order to perform uniform stretching, it is preferably 8.0 times or less.

[0061] When manufacturing a polarizing film, in order to make the adsorption of the dye on the uniaxially stretched PVA film firm, it is preferably fixed. As a fixing treatment, the PVA film can be immersed in a treatment bath added with common boric acid and / or a boron compound. At this time, an iodine compound can be added to the treatment bath as needed.

[0062] It is preferred that the PVA film subjected to uniaxial stretching, or uniaxial stretching and fixing, is then dried or heat treated. The temperature of the drying or heat treatment is preferably 30 to 150° C., particularly preferably 50 to 140° C. If the temperature is too low, the dimensional stability of the resulting polarizing film is likely to decrease. On the other hand, if the temperature is too high, the polarization performance is likely to decrease due to the decomposition of the dye, etc.

[0063] A polarizing plate can be prepared by laminating an optically transparent protective film having mechanical strength to both sides or one side of the polarizing film obtained by the above operation. As the protective film in this case, triacetyl cellulose (TAC) film, cellulose acetate / butyrate (CAB) film, acrylic film, polyester film, etc. are used. In addition, as an adhesive for laminating the protective film, a PVA adhesive or an urethane adhesive is generally used, among which a PVA adhesive is preferably used.

[0064] The polarizing plate obtained as described above can be used as a component of a liquid crystal display device by being bonded to a glass substrate after being coated with an acrylic adhesive or the like. When bonding the polarizing plate to a glass substrate, a retardation film, a viewing angle enhancement film, a brightness enhancement film, etc. can be bonded simultaneously. Example

[0065] Hereinafter, the present invention will be specifically described by way of examples etc., but the present invention is not limited to these examples at all.

[0066] [Qualification of PVA film manufacturing process]

[0067] (Peelability)

[0068] In the film production of long films of more than 4000 m, when the film was peeled off from the casting drum, a film that could be peeled off without any problem was evaluated as A, a film that was easily peeled off although partially adhered to the drum and had no problem with the yield was evaluated as B, and a film that adhered to the drum and could not be peeled off was evaluated as C.

[0069] [Quality of PVA film]

[0070] (Evaluation method of optical defects)

[0071] The streak defects and shark skin defects on the PVA film that are parallel to the flow direction (MD direction) during film formation were visually observed and evaluated. Specifically, the sample pieces cut from the PVA film obtained in the following examples and comparative examples were hung vertically in the MD direction, a 30W straight tube fluorescent lamp was placed vertically behind it and lit, and the optical defects were evaluated according to the following criteria.

[0072] A: There are absolutely no stripe or shark skin defects, which is the most suitable level for the product;

[0073] B: Although there are some stripe-like or shark skin-like defects, the product is acceptable.

[0074] C: There are many streaky or sharkskin-like defects, which is not suitable for the product level.

[0075] (Measurement method of haze)

[0076] A 10-meter area was cut from the surface side of the PVA film roll to be measured, and three square pieces (60 mm thick) with a size of MD50 mm×TD50 mm were collected from any position. m m) Sample piece: The haze of the central portion of the PVA film was measured three times for each sample collected using a haze meter "HZ-2" manufactured by Suga Test Instruments Co., Ltd. in accordance with JIS K7136, and the average value was determined.

[0077] (Method for determining the number of active agent aggregates)

[0078] A 10-meter area was cut from the surface side of the PVA film roll to be measured, and a 50-mm × 50-mm (60-mm thick) MD was collected from an arbitrary position. m The sample was taken by using a microscope VHX6000 (magnification 1000 times) manufactured by KEYENCE Co., Ltd., and the sample was observed in the film thickness direction by about 1 m Images were taken at intervals of m, and the number of active agent aggregates reflected in the taken images was counted.

[0079] [Production of polarizing film]

[0080] A long PVA film with a width of 650 mm cut from the PVA film roll obtained in the examples and comparative examples was continuously rolled up, and subjected to swelling treatment, dyeing treatment, crosslinking treatment, stretching treatment, fixing treatment and drying treatment in sequence to produce a polarizing film, and a sample with MD30 cm×TD20 cm was collected.

[0081] The conditions of each of the above treatments are as follows. As a swelling treatment, the PVA film was immersed in distilled water (temperature: 30°C) for 1 minute, during which it was uniaxially stretched to 2.0 times its original length in the longitudinal direction (MD). As a dyeing treatment, it was immersed in an aqueous solution containing an iodine-based pigment (iodine concentration: 0.02-0.05% by mass, potassium iodide concentration: 1.0% by mass, temperature: 32°C) for 1 minute, during which it was uniaxially stretched to 2.5 times its original length in the longitudinal direction (MD). As a cross-linking treatment, it was immersed in a boric acid aqueous solution (boric acid concentration: 2.6% by mass, temperature: 32°C) for 2 minutes, during which it was uniaxially stretched to 3.6 times its original length in the longitudinal direction (MD). As a stretching treatment, it was uniaxially stretched to 6.0 times its original length in the longitudinal direction (MD) during immersion in a boric acid aqueous solution (boric acid concentration: 2.8% by mass, potassium iodide concentration: 5.0% by mass, temperature: 57°C). As a fixing treatment, the film was immersed in a boric acid aqueous solution (boric acid concentration: 1.5 mass %, potassium iodide concentration: 5.0 mass %, temperature: 22° C.) for 10 seconds. Then, as a drying treatment, the stretched PVA film was dried at 60° C. for 1 minute to prepare a polarizing film.

[0082] [Polarization performance of polarizing film]

[0083] (a) Determination of transmittance Ts

[0084] Two square samples of MD20mm×TD20mm were collected from the polarizing film made by using the PVA film obtained in the embodiment or the comparative example, and a spectrophotometer with an integrating sphere ("V7100" manufactured by JASCO Corporation) was used to perform visual acuity correction in the visible light region of C light source and 2° field of view according to JISZ8722:2009 (Method for Determining Object Color). For one sample, the transmittance of light when tilted 45° relative to the longitudinal direction and the transmittance of light when tilted -45° were measured, and their average value Ts1 (%) was obtained. The same operation was performed on another sample, and the transmittance of light when tilted 45° and the transmittance of light when tilted -45° were measured, and their average value Ts2 (%) was obtained. Ts1 and Ts2 were averaged by the following formula (1) to obtain the transmittance Ts (%) of the polarizing film.

[0085] Ts=(Ts1+Ts2) / 2 (1)

[0086] (b) Determination of polarization degree V

[0087] For the two samples collected in the measurement of the transmittance Ts mentioned above, the same operation as in the above "(a) Measurement of transmittance Ts" is performed to measure the transmittance T∥(%) of the light when overlapping in a manner parallel to their length directions and the transmittance T⊥(%) of the light when overlapping in a manner perpendicular to their length directions, and the polarization degree V(%) is calculated using the following formula (2).

[0088] V = {(T∥-T⊥) / (T∥+T⊥)} 1 / 2 ×100 (2)

[0089] (c) Light transmittance

[0090] For a polarizer having a transmittance Ts of 43.0% to 44.0% produced by adjusting the iodine concentration of the dye bath, the transmittance Ts when the polarization degree V was 99.995% was calculated based on the relationship between the transmittance Ts and the polarization degree V as an index of light transmittance.

[0091] Example 1

[0092] As PVA (A), a small chip of PVA (saponified product of homopolymer of vinyl acetate) having a polymerization degree of 2400 and a saponification degree of 99.9 mol % was used. 100 parts by mass of the small chip of PVA was immersed in 2500 parts by mass of distilled water at 35° C. and then centrifuged to obtain a PVA water-containing small chip having a volatility of 60% by mass.

[0093] 250 parts by mass of the PVA water-containing flakes (100 parts by mass of dry PVA) were mixed with 25 parts by mass of distilled water, 12 parts by mass of glycerol, 0.02 parts by mass of anionic surfactant (B), and 0.04 parts by mass of fatty acid salt (C), and the resulting mixture was heated and melted using a twin-screw extruder (maximum temperature 130° C.) to prepare a film-forming stock solution. The anionic surfactant (B) used at this time was sodium alkyl sulfonate (the number of carbon atoms in the alkyl group was 15), and the fatty acid salt (C) was diethanolamine salt of lauric acid.

[0094] The film-forming stock solution was cooled to 100°C by a heat exchanger, and then extruded from a coathanger die with a width of 180 cm onto a drum with a surface temperature of 90°C to form a film. The film was then dried using a hot air drying device. The two ends of the film thickened by shrinkage during film formation were cut off, thereby continuously producing a film with a thickness of 60 cm. mm, 165 cm wide PVA film. Then, a 4,000 m portion of the manufactured PVA film was wound around a cylindrical core to make a film roll. The optical defects, haze, and number of active agent aggregates of the obtained PVA film were evaluated using the above method. In addition, the obtained PVA film was used to manufacture a polarizing film, and the light transmittance as a polarization performance was evaluated. The results are shown in Table 1.

[0095] Examples 2 to 10, Comparative Examples 1 to 5

[0096] The same operation as in Example 1 was performed to produce and evaluate PVA films except that the types and amounts of anionic surfactants (B) and fatty acid salts (C) were changed as shown in Table 1. It should be noted that the anionic surfactant (B) used in Example 6 and Comparative Example 5 was polyoxyethylene lauryl ether sodium sulfate of sulfate ester type (the number of carbon atoms of the alkyl group was 12 and the number of ethylene oxide additions was 3), the fatty acid salt (C) used in Example 7 was potassium salt of lauric acid, the fatty acid salt (C) used in Example 8 was diethanolamine salt of capric acid, the fatty acid salt (C) used in Example 9 was diethanolamine salt of myristic acid, and the nonionic surfactant used in Example 10, Comparative Example 4 and Comparative Example 5 was tertiary amide type lauric acid diethanolamide.

[0097] As shown in Table 1, the PVA films of Examples 1 to 10 have excellent peelability, few optical defects and active agent aggregates, low haze values, and good quality. In addition, the light transmittance of the polarizing film is also excellent, and the light transmittance of Examples 1 to 4, Examples 6 to 8, and Example 10 is particularly excellent. On the other hand, the PVA film of Comparative Example 1 with a large amount of fatty acid salt (C) has a large number of active agent aggregates and a high haze value. In addition, the light transmittance of the polarizing film is not good. The PVA film of Comparative Example 2 that does not contain fatty acid salt (C) has poor peelability and produces many optical defects. The PVA film of Comparative Example 3 that does not contain anionic surfactant (B) produces many optical defects, a large number of active agent aggregates, and a high haze value. Compared with Example 2 containing anionic surfactant (B) and fatty acid salt (C), the PVA film of Comparative Example 4 that further contains a certain amount of nonionic surfactant has a large number of active agent aggregates and a high haze value. In Comparative Example 5, which did not contain the fatty acid salt (C) but contained a nonionic surfactant and an anionic surfactant, the number of surfactant aggregates was large and the haze value was high. In addition, the light transmittance of the polarizing film was not good.

[0098]

Claims

1. A polyvinyl alcohol film comprising polyvinyl alcohol (A), an anionic surfactant (B) and a fatty acid salt (C), in, The anionic surfactant (B) is a sulfate ester type or sulfonate type of an alkyl group having 10 to 16 carbon atoms. The content of the anionic surfactant (B) is 0.01 to 0.20 parts by mass relative to 100 parts by mass of the polyvinyl alcohol (A). The fatty acid salt (C) is an alkali metal salt or amine salt of a fatty acid having 8 to 18 carbon atoms. The content of the fatty acid salt (C) is 0.02 to 0.20 parts by mass based on 100 parts by mass of the polyvinyl alcohol (A), and the content of the nonionic surfactant is less than 0.01 parts by mass based on 100 parts by mass of the polyvinyl alcohol (A).

2. The polyvinyl alcohol film according to claim 1, wherein The content ratio (B:C) of the anionic surfactant (B) and the fatty acid salt (C) is 25:75 to 75:

25.

3. The polyvinyl alcohol film according to claim 1 or 2, which has a width of 1.5 m or more.

4. The polyvinyl alcohol film according to claim 1 or 2, which has a length of 3000 m or more.

5. The polyvinyl alcohol film according to claim 1 or 2, which has a thickness of 10 to 70 μm. 6 . A method for producing a polarizing film, comprising: a step of dyeing the polyvinyl alcohol film according to claim 1 or 2 and a step of stretching the film.

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