WO2021132207A1

WO2021132207A1 - Polyvinyl alcohol film, and method for producing polarizing film using same

Info

Publication number: WO2021132207A1
Application number: PCT/JP2020/047834
Authority: WO
Inventors: 洋平鷹取; 功浜島; 慎二中井
Original assignee: 株式会社クラレ
Priority date: 2019-12-24
Filing date: 2020-12-22
Publication date: 2021-07-01
Also published as: CN114829489A; KR20220121802A; TW202134324A; JPWO2021132207A1

Abstract

This polyvinyl alcohol film is characterized by containing a polyvinyl alcohol (A), an anionic surfactant (B), and a fatty acid salt (C), wherein: the anionic surfactant (B) is a sulfate ester salt-type or a sulfonate-type surfactant; the content of the anionic surfactant (B) is 0.01-0.20 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol (A); the fatty acid salt (C) is an alkali metal salt or an amine salt; the content of the fatty acid salt (C) is 0.02-0.20 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol (A); and the content of a nonionic surfactant is less than 0.01 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol (A). Therefore, provided are: a PVA film having a small number of optical defects and activator aggregates, a low haze value, good peelability, and excellent polarization performance when processed into a polarizing film; and a method for producing a polarizing film using the PVA film.

Description

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

The present invention relates to a polyvinyl alcohol film containing polyvinyl alcohol (A), an anionic surfactant (B), and a fatty acid salt (C), and a method for producing a polarizing film using the same.

Polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) film is used for various purposes by utilizing its unique properties related to transparency, optical properties, mechanical strength, water solubility, and the like. In particular, PVA film is used as a raw material (raw film) for producing a polarizing film that constitutes a polarizing plate, which is a basic component of a liquid crystal display (LCD), by utilizing its excellent optical characteristics. Applications are expanding. High optical performance is required for LCD polarizing plates, and high optical performance is also required for the polarizing film, which is a component of the polarizing plate.

Generally, a polarizing plate is produced by subjecting a PVA film of raw fabric to dyeing, uniaxial stretching, and if necessary, fixing treatment with a boron compound or the like to produce a polarizing film, and then cellulose triacetate is formed on the surface of the polarizing film. (TAC) Manufactured by laminating a protective film such as a film. Then, the PVA film of the raw material is generally produced by a method of drying a film-forming stock solution containing PVA, such as a cast film-forming method.

Many technologies related to PVA film and its manufacturing method are known so far. Patent Document 1 comprises a step of forming a polyvinyl alcohol-based film by a casting method using a polyvinyl alcohol-based resin aqueous solution containing an alkyl sulfonate-based surfactant. The manufacturing method is described. According to this, it is said that it is possible to provide a method for producing a polyvinyl alcohol-based film having excellent colorless transparency in addition to optical characteristics. However, in the polyvinyl alcohol-based film in which the alkyl sulfonate-based surfactant is used alone, there is a case that there is a problem in the peelability at the time of forming the film. When a nonionic surfactant is further used as the alkyl sulfonate-based surfactant in order to improve the peelability, the number of activator aggregates is large, the haze value is high, and the polarizing film is formed. The polarization performance when processed into the above may be inferior, and improvement has been desired.

Japanese Unexamined Patent Publication No. 2006-193694

The present invention has been made to solve the above problems, has a small number of optical defects and activator aggregates, a low haze value, good peelability, and polarization performance when processed into a polarizing film. It is an object of the present invention to provide an excellent PVA film and a method for producing a polarizing film using the same.

The above-mentioned problem is a polyvinyl alcohol film containing a polyvinyl alcohol (A), an anionic surfactant (B), and a fatty acid salt (C), wherein the anionic surfactant (B) is a sulfate ester salt type or a sulfone. It is an acid salt type, and the content of the anionic surfactant (B) is 0.01 to 0.20 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A), and the fatty acid salt (C) is an alkali metal. It is a salt or amine salt, the content of the fatty acid salt (C) is 0.02 to 0.20 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol (A), and the content of the nonionic surfactant is , Polyvinyl alcohol (A) is solved by providing a polyvinyl alcohol film which is less than 0.01 parts by mass with respect to 100 parts by mass.

At this time, the content ratio (B: C) of the anionic surfactant (B) and the fatty acid salt (C) is preferably 25:75 to 75:25. It is also preferable that the fatty acid salt (C) is an alkali metal salt or an amine salt of a fatty acid having 12 to 16 carbon atoms.

It is also preferable that the film width is 1.5 m or more. The length of the film is preferably 3000 m or more. It is also preferable that the film thickness is 10 to 70 μm.

The above problem is also solved by providing a method for producing a polarizing film, which comprises a step of dyeing the above polyvinyl alcohol film and a step of stretching the polyvinyl alcohol film.

The PVA film of the present invention has a small number of optical defects and activator aggregates, a low haze value, and good peelability, so that it has excellent process passability. Therefore, by using the PVA film as the raw material, a polarizing film having good polarization performance can be obtained.

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

The present inventors have a PVA film containing a certain amount of PVA (A), an anionic surfactant (B) and a fatty acid salt (C), respectively, and the content of a nonionic surfactant is less than a certain amount. It was found that the number of optical defects and activator aggregates was small, the haze value was low, and the peelability was good. Then, it was clarified that a polarizing film having excellent polarization performance can be obtained by using such a PVA film. The present inventors could not obtain a PVA film having good film quality and peelability when the contents of PVA (A), anionic surfactant (B) and fatty acid salt (C) were not within a certain range. I have confirmed that. The present inventors have also confirmed that when the content of the nonionic surfactant exceeds a certain amount, the number of activator aggregates is large and the haze value is high.

Therefore, as in the present invention, PVA contains a certain amount of PVA (A), an anionic surfactant (B) and a fatty acid salt (C), and the content of the nonionic surfactant is less than a certain amount. It is important that it is a film. By satisfying such a configuration, a PVA film having a small number of optical defects and activator aggregates, a low haze value, good peelability, and excellent polarization performance when processed into a polarizing film can be obtained. be able to.

[PVA (A)]
As PVA (A), one produced by saponifying a vinyl ester-based polymer obtained by polymerizing vinyl ester can be used. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatic acid and the like. One of these may be used alone, or two or more thereof may be used in combination, but the former is preferable. Vinyl acetate is preferable as the vinyl ester from the viewpoints of availability, cost, productivity of PVA (A) and the like.

Other monomers copolymerizable with vinyl ester include, for example, ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutene; acrylic acid or a salt thereof; methyl acrylate, ethyl acrylate, acrylic acid. Acrylic acid esters such as n-propyl, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacryl Acid or salt thereof; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate , Methacrylate esters such as dodecyl methacrylate, octadecyl methacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid or salts thereof, acrylamidepropyldimethylamine or An acrylamide derivative such as its salt, N-methylolacrylamide or a derivative thereof; methacrylamide, N-methylmethacrylate, N-ethylmethacrylate, methacrylamide propanesulfonic acid or a salt thereof, methacrylicamidepropyldimethylamine or a salt thereof, N- Methylamide derivatives such as methylolmethacrylamide or derivatives thereof; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methylvinyl ether, ethylvinyl ether, n-propylvinyl ether, i-propylvinyl ether, n- Vinyl ethers such as butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; vinyl cyanide such as acrylonitrile and methacrylonitrile; halogenation of vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride and the like. Vinyl; allyl compounds such as allyl acetate and allyl chloride; maleic acid or salts thereof, esters or acid anhydrides; itaconic acid or salts thereof, esters or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate and the like. Can be mentioned. One type of these other monomers may be used alone, or two or more types may be used in combination. Among them, as the other monomer, ethylene and an olefin having 3 to 30 carbon atoms are preferable, and ethylene is more preferable.

The ratio of the structural units derived from the other monomers to the vinyl ester-based polymer is not particularly limited, but is 15 mol% or less based on the number of moles of all the structural units constituting the vinyl ester-based polymer. It is preferably 5 mol% or less, and more preferably 5 mol% or less.

The degree of polymerization of PVA (A) is not necessarily limited, but it is preferably 200 or more, more preferably 300 or more, and further preferably 400 or more because the film strength tends to decrease as the degree of polymerization decreases. , Especially preferably 500 or more. Further, if the degree of polymerization is too high, the viscosity of the aqueous solution of PVA (A) or the melted PVA (A) tends to be high, and film formation tends to be difficult. Therefore, the degree of polymerization is preferably 10,000 or less, which is more preferable. Is 9,000 or less, more preferably 8,000 or less, and particularly preferably 7,000 or less. Here, the degree of polymerization of PVA (A) means the average degree of polymerization measured according to the description of JIS K6726-1994, and the PVA (A) is re-saponified, purified, and then measured in water at 30 ° C. It is calculated by the following formula from the obtained ultimate viscosity [η] (unit: deciliter / g).
Degree of polymerization = ([η] × 10 ⁴ / 8.29) ^{(1 / 0.62)}

The degree of saponification of PVA (A) is not particularly limited, and for example, 60 mol% or more of PVA (A) can be used, but from the viewpoint of using it as a raw film for producing an optical film such as a polarizing film, PVA The saponification degree of (A) is preferably 95 mol% or more, more preferably 98 mol% or more, and further preferably 99 mol% or more. Here, the degree of saponification of PVA (A) is the total number of moles of the structural unit (typically a vinyl ester-based monomer unit) and the vinyl alcohol unit of PVA (A) that can be converted into vinyl alcohol units by saponification. It means the ratio (mol%) of the number of moles of the vinyl alcohol unit to the vinyl alcohol unit. The degree of saponification of PVA (A) can be measured according to the description of JIS K6726-1994.

As PVA (A), one type of PVA may be used alone, or two or more types of PVA having different degrees of polymerization, saponification, modification, etc. may be used in combination. However, the PVA film has a PVA having an acidic functional group such as a carboxyl group or a sulfonic acid group; a PVA having an acid anhydride group; a PVA having a basic functional group such as an amino group; If a PVA having a functional group that promotes the above is contained, the secondary processability of the PVA film may be lowered due to the cross-linking reaction between the PVA molecules. Therefore, in the case where excellent secondary processability is required, such as a raw film for producing an optical film, PVA having an acidic functional group, PVA having an acid anhydride group, and basicity in PVA (A). The contents of PVA having a functional group and neutralized products thereof are preferably 0.1% by mass or less, and more preferably none of them.

The content of PVA (A) in the 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.

[Anionic surfactant (B)]
The anionic surfactant (B) used in the present invention is a sulfate ester salt type or a sulfonate type. The carbon number of 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.

Examples of the sulfate 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 alkyl phenyl ether sulfate, and the like. Can be mentioned. As the alkyl, an alkyl having 8 to 20 carbon atoms is preferable, and an alkyl having 10 to 16 carbon atoms is more preferable.

Examples of the sulfonate type include sodium alkylsulfonate, potassium alkylsulfonate, ammonium alkylsulfonate, triethanolamine alkylsulfonate, sodium alkylbenzene sulfonate, disodium dodecyldiphenyl ether disulfonate, sodium alkylnaphthalene sulfonate, and alkyl sulfosuccinate. Examples thereof include disodium acid and disodium polyoxyethylene alkyl sulfosuccinate. As the alkyl, an alkyl having 8 to 20 carbon atoms is preferable, and an alkyl having 10 to 16 carbon atoms is more preferable.

The above-mentioned surfactant may be used alone or in combination of two or more. Above all, the anionic surfactant (B) is preferably a sulfonate type from the viewpoint that the number of activator aggregates is small and the haze value is low.

In the PVA film of the present invention, the content of the anionic surfactant (B) is 0.01 to 0.20 parts by mass with respect to 100 parts by mass of PVA (A). When the content of the anionic surfactant (B) is less than 0.01 parts by mass, many optical defects are generated in the PVA film, the haze value is high, and the number of activator aggregates in the PVA film is large. , The problem occurs. 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, a large number of optical defects occur 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. ..

[Fatty acid salt (C)]
The fatty acid salt (C) is not particularly limited, but is preferably an alkali metal salt or an amine salt of a fatty acid having 8 to 18 carbon atoms. The carbon number referred to here means the carbon number of the fatty acid forming the salt in the fatty acid salt (C). If the number of carbon atoms is less than 8, optical defects may occur in the PVA film and the peelability may deteriorate. The number of carbon atoms is more preferably 10 or more, and even more preferably 12 or more. On the other hand, when the number of carbon atoms exceeds 18, the haze value becomes high, and the number of activator aggregates in the PVA film may increase. More preferably, the number of carbon atoms is 16 or less. Saturated fatty acids or unsaturated fatty acids can be used as the fatty acids, but saturated fatty acids are preferable from the viewpoint of thermal stability. As the saturated fatty acid, saturated fatty acids such as capric acid, lauric acid, myristic acid, and palmitic acid are suitable.

The fatty acid salt (C) used in the present invention is an alkali metal salt or an amine salt. Examples of the alkali metal ion in the alkali metal salt include ions of lithium, sodium, potassium, rubidium, and cesium. Examples of amines in amine salts include alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine. Above all, the fatty acid salt (C) is preferably an amine salt. Further, as the amine in the amine salt, diethanolamine is preferable from the viewpoint of solubility.

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 with respect 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, a large number of optical defects occur in the PVA film and the peelability deteriorates. 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, there arises a problem that the number of activator 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.

In the present invention, the content of the nonionic surfactant is less than 0.01 part by mass with respect to 100 parts by mass of PVA (A). When the content of the nonionic surfactant is 0.01 parts by mass or more, problems such as a large number of activator aggregates and a high haze value occur. 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 substantially. It is particularly preferable that it is not contained.

Examples of the nonionic surfactant include an alkyl ether type such as polyoxyethylene oleyl ether; an alkylphenyl ether type such as polyoxyethylene octylphenyl ether; an alkyl ester type such as polyoxyethylene laurate; and polyoxyethylene laurylamino. Alkylamine type such as ether; Alkylamide type such as polyoxyethylene lauric acid amide; Polyethylene glycol ether type such as polyoxyethylene polyoxypropylene ether; aliphatic alkanolamide type such as lauric acid diethanolamide and oleate diethanolamide; Examples thereof include an allylphenyl ether type such as polyoxyalkylene allylphenyl ether.

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. If the content ratio (B: C) is less than 25:75, problems such as a large number of optical defects occurring in the PVA film and an increase in the number of activator aggregates in the PVA film may occur. The content mass ratio (B: C) is more preferably 30:70 or more. On the other hand, if the content ratio (B: C) exceeds 75:25, the peelability may deteriorate. The content ratio (B: C) is more preferably 60:40 or less.

[PVA film]
From the viewpoint of imparting flexibility to the PVA film, the PVA film of the present invention preferably contains a plasticizer. Preferred plasticizers include polyhydric alcohols, and specific examples thereof include ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane. For these, only one kind of plasticizer may be used, or two or more kinds of plasticizers may be used in combination. Of these, ethylene glycol or glycerin is preferable from the viewpoint of compatibility with PVA (A) and availability.

The content of the plasticizer is preferably in the range of 1 to 30 parts by mass with respect to 100 parts by mass of PVA (A). When the content of the plasticizer is 1 part by mass or more, problems are unlikely to occur in mechanical properties such as impact strength and process passability during secondary processing. On the other hand, when the content of the plasticizer is 30 parts by mass or less, the film becomes appropriately flexible and the handleability is improved.

The PVA film of the present invention may further contain components other than PVA (A), anionic surfactant (B), fatty acid salt (C) and a plasticizer, if necessary. Examples of such other components include water, antioxidants, ultraviolet absorbers, lubricants, colorants, fillers (inorganic particles, starch, etc.), preservatives, fungicides, and other components other than those described above. Examples include polymer compounds. The content of other components in the PVA film is preferably 10% by mass or less.

The width of the PVA film of the present invention is not particularly limited. Since a wide polarizing film has been demanded in recent years, the width is preferably 1.5 m or more. Further, if the width of the PVA film is too wide, the manufacturing cost of the film-forming device for forming the PVA film increases, and further, it is uniform when the optical film is manufactured by the practical manufacturing device. The width of the PVA film is usually 7.5 m or less because it may be difficult to stretch the film.

The shape of the PVA film of the present invention is not particularly limited, but it is long because it can continuously and smoothly produce a more uniform PVA film and it is continuously used when producing an optical film or the like. It is preferably a long film. The length of the long film (length in the flow direction) is not particularly limited and can be set as appropriate. 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. It is preferable that a long film is wound around a core to form a film roll.

The thickness of the PVA film of the present invention is not particularly limited and can be set as appropriate. From the viewpoint of being used as a raw film for producing an optical film such as a polarizing film, the thickness of the film is preferably 10 to 70 μm. The thickness of the PVA film can be obtained as an average value of values measured at any 10 locations.

The haze of the PVA film of the present invention and the number of activator aggregates are measured by the method described in the examples below. The haze value is preferably 0.3 or less, more preferably 0.2 or less, and even more preferably 0.15 or less. The number of such activator aggregates is preferably 240 or less, more preferably 180 or less, and even more preferably 75 or less.

The method for producing a PVA film of the present invention is not particularly limited, but is a method for producing a PVA film containing PVA (A), an anionic surfactant (B) and a fatty acid salt (C). A method for producing a PVA film, which comprises a step of preparing a film-forming stock solution by blending an anionic surfactant (B) and a fatty acid salt (C), and a step of forming a film using the film-forming stock solution. preferable. At this time, as described above, the content of the nonionic surfactant is preferably less than a certain amount.

A liquid medium can be further added in the process of preparing the film-forming stock solution. Examples of the liquid medium at this time include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, and the like. Diethylenetriamine and the like can be mentioned, and one or more of these can be used. Of these, water is preferable because it has a small impact on the environment and is recoverable.

In the method for producing a PVA film of the present invention, for example, PVA (A), anionic surfactant (B), fatty acid salt (C), a liquid medium, and, if necessary, the above-mentioned plasticizer and other components are further added. A known method such as a casting film forming method or a melt extrusion film forming method can be adopted by using the contained film-forming stock solution. The film-forming stock solution may be one in which PVA (A) is dissolved in a liquid medium, or one in which PVA (A) is melted.

The volatile content of the membrane-forming stock solution (the content ratio of volatile components such as liquid media removed by volatilization or evaporation during membrane-forming in the membrane-forming stock solution) varies depending on the membrane-forming method, membrane-forming conditions, etc., but is 50 to It is preferably in the range of 90% by mass, and more preferably in the range of 55 to 80% by mass. When the volatile fraction of the film-forming stock solution is 50% by mass or more, the viscosity of the film-forming stock solution does not become too high and the film-forming becomes easy. On the other hand, when the volatile content of the film-forming stock solution is 90% by mass or less, the viscosity of the film-forming stock solution does not become too low, and the thickness uniformity of the obtained PVA film is improved.

The PVA film of the present invention is suitably produced by the casting film forming method or the melt extrusion film forming method using the above-mentioned film forming stock solution. The specific manufacturing method at this time is not particularly limited, and for example, the film-forming stock solution can be obtained by casting or discharging the film-forming stock solution in a film form on a support such as a drum or a belt and drying it on the support. Can be done. If necessary, the obtained film may be further dried by a drying roll or a hot air drying device, heat-treated by a heat treatment device, or humidity-controlled by a humidity control device. The produced PVA film is preferably made into a film roll by winding it around a core. Further, both ends of the manufactured PVA film in the width direction may be cut off.

The PVA film of the present invention can be suitably used as a raw film for producing a polarizing film, a retardation film, a special condensing film and the like. According to the present invention, a PVA film having excellent optical performance and high quality can be obtained. Therefore, an optical PVA film is a preferred embodiment of the present invention.

A method for producing a polarizing film having a step of dyeing the PVA film and a step of stretching the PVA film is a preferred embodiment of the present invention. The manufacturing method may further include a fixing treatment step, a drying treatment step, a heat treatment step, and the like. The order of dyeing and stretching is not particularly limited, and the dyeing treatment may be performed before the stretching treatment, the dyeing treatment may be performed at the same time as the stretching treatment, or the dyeing treatment may be performed after the stretching treatment. .. Further, steps such as stretching and dyeing may be repeated a plurality of times. In particular, it is preferable to divide the stretching into two or more stages because uniform stretching can be easily performed.

Dyes used for dyeing PVA films include iodine or dichroic organic dyes (eg, DirectBlack 17, 19, 154; DirectBrown 44, 106, 195, 210, 223; DirectRed 2, 23, 28, 31, 37, 39. , 79, 81, 240, 242, 247; DirectBlue 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; dichroic dyes such as Direct Orange 26, 39, 106, 107) and the like 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 dye, but the treatment conditions and treatment method are not particularly limited.

Examples of the method for stretching the PVA film include a uniaxial stretching method and a biaxial stretching method, and the former is preferable. The uniaxial stretching method for stretching the PVA film in the flow direction (MD) or the like may be performed by either a wet stretching method or a dry heat stretching method, but the wet stretching method is used from the viewpoint of the performance and quality stability of the obtained polarizing film. Is preferable. Examples of the wet stretching method include a method of stretching a PVA film in an aqueous solution containing various components such as pure water, additives and a water-soluble organic solvent, or an aqueous dispersion in which various components are dispersed. Specific examples of the uniaxial stretching method by the wet stretching method include a method of uniaxial stretching in warm water containing boric acid, a method of uniaxial stretching in a solution containing the dye, and a method of uniaxial stretching described later. Further, the PVA film after water absorption may be used for uniaxial stretching in the air, or uniaxial stretching may be performed by other methods.

The stretching temperature during uniaxial stretching is not particularly limited, but in the case of wet stretching, a temperature in the range of preferably 20 to 90 ° C, more preferably 25 to 70 ° C, still more preferably 30 to 65 ° C is adopted, and drying is performed. In the case of heat stretching, a temperature in the range of 50 to 180 ° C. is preferably adopted.

The stretch ratio of the uniaxial stretching treatment (the total stretching ratio in the case of uniaxial stretching in multiple stages) is preferably stretched as much as possible until just before the film is cut from the viewpoint of polarization performance, and specifically, it is 4 times or more. Is preferable, 5 times or more is more preferable, and 5.5 times or more is further preferable. The upper limit of the draw ratio is not particularly limited as long as the film is not broken, but it is preferably 8.0 times or less in order to perform uniform stretching.

In the production of the polarizing film, it is preferable to carry out a fixing treatment in order to strengthen the adsorption of the dye on the uniaxially stretched PVA film. As the fixing treatment, a method of immersing the PVA film in a treatment bath to which a general boric acid and / or boron compound is added can be adopted. At that time, an iodine compound may be added to the treatment bath if necessary.

It is preferable that the PVA film that has undergone the uniaxial stretching treatment or the uniaxial stretching treatment and the fixing treatment is then subjected to a drying treatment or a heat treatment. The temperature of the drying treatment 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 obtained polarizing film tends to decrease. On the other hand, if the temperature is too high, the polarization performance tends to deteriorate due to the decomposition of the dye.

A protective film that is optically transparent and has mechanical strength can be attached to both sides or one side of the polarizing film obtained as described above to form a polarizing plate. As the protective film in that case, a cellulose triacetate (TAC) film, a cellulose acetate / butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Further, as the adhesive for adhering the protective film, a PVA-based adhesive, a urethane-based adhesive, or the like is generally used, and among them, the PVA-based adhesive is preferably used.

The polarizing plate obtained as described above can be used as a component of a liquid crystal display device by coating it with an adhesive such as an acrylic material and then attaching it to a glass substrate. When the polarizing plate is attached to the glass substrate, a retardation film, a viewing angle improving film, a brightness improving film, or the like may be attached at the same time.

Hereinafter, the present invention will be specifically described with reference to Examples and the like, but the present invention is not limited to these Examples.

[Process passability for PVA film manufacturing]
(Removability)
In the film formation of a long film of 4000 m or more, when the film is peeled off from the cast drum, the one that can be peeled off without any problem is A, and the one that partially adheres to the drum but easily peels off and there is no problem in productivity. Was evaluated as B, and those that could not be peeled off due to adhesion to the drum were evaluated as C.

[Quality of PVA film]
(Evaluation method of optical defects)
The streak-like defects and the shark-skin-like defects existing parallel to the flow direction (MD direction) during film formation on the PVA film were visually observed and evaluated. Specifically, a sample piece cut out from the PVA film obtained in the following Examples and Comparative Examples is hung so that the MD direction is vertical, and a 30 W straight tubular fluorescent lamp is vertically placed behind the sample piece to light it. , Optical defects were evaluated according to the following criteria.
A: The most suitable level for the product without any streaky or shark-skin-like defects.
B: There are some streaky or shark-skin-like defects, but it is a level that can be used as a product.
C: A level that is not suitable for products due to many streaky or shark-skin-like defects.

(Measuring method of haze)
A region of 10 m from the surface layer side of the PVA film roll to be measured was cut out, and three square sample pieces of MD50 mm × TD50 mm (thickness 60 μm) were collected from arbitrary positions. The collected sample was measured for haze at the center of the PVA film three times each using a haze meter "HZ-2" manufactured by Suga Test Instruments Co., Ltd. according to JIS K7136, and the average value was calculated.

(Method of measuring the number of activator aggregates)
A region of 10 m from the surface layer side of the PVA film roll to be measured was cut out, and a sample piece of MD50 mm × TD50 mm (thickness 60 μm) was collected from an arbitrary position. Images of the collected samples were taken at intervals of about 1 μm in the film thickness direction using a microscope VHX6000 (magnification: 1000 times) manufactured by KEYENCE CORPORATION, and the number of activator aggregates reflected in the taken images was counted. ..

[Preparation of polarizing film]
A long PVA film having a width of 650 mm cut out from the PVA film rolls obtained in Examples and Comparative Examples is continuously unwound, and swelling treatment, dyeing treatment, cross-linking treatment, stretching treatment, fixing treatment and drying treatment are performed in this order. A polarizing film was produced, and a sample of MD30 cm × TD20 cm was taken.

The conditions for each of the above processes are as follows. As a swelling treatment, the PVA film was immersed in distilled water (temperature: 30 ° C.) for 1 minute, during which time it was uniaxially stretched 2.0 times the original length in the length direction (MD). As a dyeing treatment, the mixture was immersed in an aqueous solution containing an iodine-based dye (iodine concentration: 0.02 to 0.05% by mass, potassium iodide concentration: 1.0% by mass, temperature: 32 ° C.) for 1 minute. In the meantime, it was uniaxially stretched in the length direction (MD) up to 2.5 times the original length. As a cross-linking treatment, it is immersed in an aqueous boric acid solution (boric acid concentration: 2.6% by mass, temperature: 32 ° C.) for 2 minutes, during which time it is uniaxial in the length direction (MD) up to 3.6 times the original length. It was stretched. As a stretching treatment, while immersed in an aqueous boric acid solution (boric acid concentration: 2.8% by mass, potassium iodide concentration: 5.0% by mass, temperature: 57 ° C.), the original length was 6.0 times. It was uniaxially stretched in the length direction (MD). As a fixing treatment, the mixture was immersed in an aqueous boric acid solution (boric acid concentration: 1.5% by mass, potassium iodide concentration: 5.0% by 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 obtain a polarizing film.

[Polarization performance of polarizing film]
(A) Measurement of Transmittance Ts Two square samples of MD20 mm × TD20 mm were collected from a polarizing film produced using the PVA film obtained in the Example or Comparative Example, and a spectrophotometer with an integrating sphere (JASCO Corporation). Using "V7100" manufactured by Co., Ltd.), the visibility of the visible light region of the C light source and 2 ° field is corrected in accordance with JIS Z8722: 2009 (measurement method of object color), and the length of one sample is long. The light transmittance when tilted by 45 ° with respect to the vertical direction and the light transmittance when tilted by −45 ° were measured, and their average value Ts1 (%) was obtained. In the same manner for the other sample, the light transmittance when tilted by 45 ° and the light transmittance when tilted by −45 ° were measured, and their average value Ts2 (%) was obtained. Ts1 and Ts2 were averaged according to the following formula (1) to obtain the transmittance Ts (%) of the polarizing film.
Ts = (Ts1 + Ts2) / 2 (1)
(B) Measurement of degree of polarization V Light transmittance T∥ (%) and length when two samples collected in the above-mentioned measurement of transmittance Ts are stacked so that their length directions are parallel to each other. The light transmittance T⊥ (%) when the light is stacked so that the vertical directions are orthogonal to each other is measured in the same manner as in the case of “(a) Measurement of transmittance Ts” above, and the degree of polarization is calculated by the following equation (2). V (%) was calculated.
V = {(T∥-T⊥) / (T∥ + T⊥)} ^1/2 × 100 (2)
(C) Light transmittance For a polarizer prepared by adjusting the iodine concentration of the dyeing bath and having a transmittance Ts of 43.0% to 44.0%, the degree of polarization V is determined from the relationship between the transmittance Ts and the degree of polarization V. The transmittance Ts at 99.995% was calculated and used as an index of light transmittance.

Example 1
As PVA (A), a chip of PVA (saponified product of a homopolymer of vinyl acetate) having a degree of polymerization of 2400 and a degree of saponification of 99.9 mol% was used. After immersing 100 parts by mass of the PVA chip in 2500 parts by mass of distilled water at 35 ° C., centrifugal dehydration was performed to obtain a PVA water-containing chip having a volatile content of 60% by mass.

25 parts by mass of distilled water, 12 parts by mass of glycerin, 0.02 parts by mass of anionic surfactant (B), 0 parts of fatty acid salt (C) with respect to 250 parts by mass of the PVA-containing chip (100 parts by mass of dried PVA). After mixing .04 parts by mass, the obtained mixture was heated and melted (maximum temperature 130 ° C.) with a twin-screw extruder to obtain a film-forming stock solution. The anionic surfactant (B) used at this time was sodium alkylsulfonate (the alkyl group has 15 carbon atoms), and the fatty acid salt (C) was a diethanolamine salt of lauric acid.

This undiluted film-forming solution is cooled to 100 ° C. with a heat exchanger, then extruded from a 180 cm wide coat hanger die onto a drum having a surface temperature of 90 ° C., and further dried using a hot air drying device, and then dried. By cutting off both ends of the film thickened by the neck-in during film formation, a PVA film having a film thickness of 60 μm and a width of 165 cm was continuously produced. Next, a length of 4,000 m of the produced PVA film was wound around a cylindrical core to form a film roll. The obtained PVA film was evaluated for the number of optical defects, haze, and activator aggregates by the above method. Further, a polarizing film was produced using the obtained PVA film, and the light transmittance was evaluated as the polarization performance. The results are shown in Table 1.

Examples 2 to 10, Comparative Examples 1 to 5
A PVA film was produced and evaluated in the same manner as in Example 1 except that the types and amounts of the anionic surfactant (B) and the fatty acid salt (C) were changed as shown in Table 1. The anionic surfactant (B) used in Example 6 and Comparative Example 5 was a sulfate ester salt type polyoxyethylene lauryl ether sodium sulfate (alkyl group having 12 carbon atoms and ethylene oxide addition number of 3). ), The fatty acid salt (C) used in Example 7 was a potassium salt of lauric acid, and the fatty acid salt (C) used in Example 8 was a diethanolamine salt of capric acid, which was used in Example 9. The fatty acid salt (C) is a diethanolamine salt of myristic acid, and the nonionic surfactant used in Example 10, Comparative Example 4, and Comparative Example 5 is a tertiary amide type lauric acid diethanolamide.

As shown in Table 1, the PVA films of Examples 1 to 10 had excellent peelability, a small number of optical defects and activator aggregates, a low haze value, and good quality. Further, the light transmittance of the polarizing film was also excellent, and the light transmission of Examples 1 to 4, 6 to 8 and 10 was particularly excellent. On the other hand, the PVA film of Comparative Example 1 having a large amount of fatty acid salt (C) had a large number of activator aggregates and a high haze value. In addition, the light transmittance of the polarizing film was not good. The PVA film of Comparative Example 2 containing no fatty acid salt (C) did not have good peelability and had many optical defects. The PVA film of Comparative Example 3 containing no anionic surfactant (B) had many optical defects, a large number of activator aggregates, and a high haze value. Compared to Example 2 containing the anionic surfactant (B) and the fatty acid salt (C), the PVA film of Comparative Example 4 containing a certain amount or more of the nonionic surfactant is the number of activator aggregates. The haze value was high. In Comparative Example 5 which did not contain the fatty acid salt (C) and contained the nonionic surfactant and the anionic surfactant, the number of activator aggregates was large and the haze value was high. In addition, the light transmittance of the polarizing film was not good.

Claims

A polyvinyl alcohol film containing a polyvinyl alcohol (A), an anionic surfactant (B), and a fatty acid salt (C).
The anionic surfactant (B) is a sulfate ester salt type or a sulfonate type,
The content of the anionic surfactant (B) is 0.01 to 0.20 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A).
The fatty acid salt (C) is an alkali metal salt or an amine salt,
The content of the fatty acid salt (C) is 0.02 to 0.20 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A), and the content of the nonionic surfactant is 100 parts by mass of polyvinyl alcohol (A). A polyvinyl alcohol film that is less than 0.01 parts by mass with respect to parts by mass.
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.
The polyvinyl alcohol film according to claim 1 or 2, wherein the fatty acid salt (C) is an alkali metal salt or an amine salt of a fatty acid having 8 to 18 carbon atoms.
The polyvinyl alcohol film according to any one of claims 1 to 3, wherein the film width is 1.5 m or more.
The polyvinyl alcohol film according to any one of claims 1 to 4, wherein the length of the film is 3000 m or more.
The polyvinyl alcohol film according to any one of claims 1 to 5, wherein the film thickness is 10 to 70 μm.
A method for producing a polarizing film, comprising a step of dyeing and stretching the polyvinyl alcohol film according to any one of claims 1 to 6.