CN114829489A

CN114829489A - Polyvinyl alcohol film and method for producing polarizing film using same

Info

Publication number: CN114829489A
Application number: CN202080089934.0A
Authority: CN
Inventors: 鹰取洋平; 浜岛功; 中井慎二
Original assignee: Kuraray Co Ltd
Current assignee: Kuraray Co Ltd
Priority date: 2019-12-24
Filing date: 2020-12-22
Publication date: 2022-07-29
Also published as: WO2021132207A1; TWI837448B; KR20220121802A; JPWO2021132207A1; TW202134324A; JP7512309B2

Abstract

A PVA film comprising a polyvinyl alcohol (A), an anionic surfactant (B) and a fatty acid salt (C), wherein the anionic surfactant (B) is a sulfate ester type or a sulfonate ester type, the content of the anionic surfactant (B) is 0.01 to 0.20 parts by mass per 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 to 0.20 parts by mass per 100 parts by mass of the polyvinyl alcohol (A), and the content of the nonionic surfactant is less than 0.01 parts by mass per 100 parts by mass of the polyvinyl alcohol (A). Thus, a PVA film having a small number of optical defects and active agent aggregates, a low haze value, good releasability, and excellent polarizing performance when processed into a polarizing film, and a method for producing a polarizing film using the PVA film are provided.

Description

Polyvinyl alcohol film and method for producing polarizing film using same

Technical Field

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.

Background

Polyvinyl alcohol (hereinafter, abbreviated as PVA) films are used for various applications by utilizing unique properties related to transparency, optical characteristics, mechanical strength, water solubility, and the like. In particular, due to its excellent optical properties, PVA films are used as a raw material (raw roll film) for producing polarizing films constituting polarizers, which are basic components of Liquid Crystal Displays (LCDs), and their applications are expanding. The polarizing plate for LCD requires high optical performance, and also the polarizing film as a constituent thereof requires high optical performance.

A polarizing plate is generally manufactured by producing a polarizing film by dyeing and uniaxially stretching a PVA film in a raw roll, fixing the PVA film with a boron compound or the like as necessary, and then attaching a protective film such as a triacetyl cellulose (TAC) film to the surface of the polarizing film. The PVA film in a roll is usually produced by a method of drying a film-forming dope containing PVA by a casting film-forming method or the like.

Heretofore, various techniques have been known for PVA films or methods for producing the same. Patent document 1 describes a method for producing a polyvinyl alcohol film, which is characterized by comprising the steps of: a polyvinyl alcohol film is produced by a casting method using an aqueous polyvinyl alcohol resin solution containing an alkyl sulfonate surfactant. Thus, a method for producing a polyvinyl alcohol film having excellent colorless transparency in addition to optical characteristics can be provided. However, in a polyvinyl alcohol film using an alkylsulfonate surfactant alone, there is a problem in peelability in the production of the film. Further, when a nonionic surfactant is further used as the alkyl sulfonate surfactant for improving the releasability, the number of active agent aggregates is large, the haze value is high, and the polarization performance when the polarizing film is processed is sometimes deteriorated, and it is desired to improve the releasability.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2006 and 193694.

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above problems, and an object of the present invention is to provide: provided are a PVA film which 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, and a method for producing a polarizing film using the PVA film.

Means for solving the problems

The above object is achieved by providing a polyvinyl alcohol film comprising a polyvinyl alcohol (A), an anionic surfactant (B) and a fatty acid salt (C), wherein the anionic surfactant (B) is a sulfate ester type or a sulfonate ester type, the content of the anionic surfactant (B) is 0.01 to 0.20 parts by mass and the fatty acid salt (C) is an alkali metal salt or an amine salt based on 100 parts by mass of the polyvinyl alcohol (A), 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).

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

In addition, theFurther, the film width is preferably 1.5m or more. The film length is preferably 3000m or more. Further, the film thickness is preferably 10 to 70μm。

The above object is also achieved by providing a method for producing a polarizing film, comprising: a step of dyeing the polyvinyl alcohol film and a step of stretching the polyvinyl alcohol film.

Effects of the invention

The PVA film of the present invention has excellent process acceptability because of a small number of optical defects and active agent aggregates, a low haze value, and good peelability. Therefore, by using this PVA film as a raw roll, a polarizing film having good polarizing performance can be obtained.

Detailed Description

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

The inventor finds that: a PVA film which contains a certain amount of PVA (A), a certain amount of an anionic surfactant (B) and a certain amount of a fatty acid salt (C) and contains a nonionic surfactant in an amount smaller than the certain amount has a small number of optical defects and active agent aggregates, a low haze value and good peelability. Subsequently, it is clear that: by using such a PVA film, a polarizing film having excellent polarizing 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 having good film quality and good peelability cannot be obtained. In addition, the present inventors have confirmed that: when the content of the nonionic surfactant exceeds a certain amount, the number of the active agent aggregates increases, and the haze value increases.

Therefore, as in the present invention, a PVA film containing a certain amount of each of PVA (a), anionic surfactant (B), and fatty acid salt (C) and a non-ionic surfactant less than a certain amount is important. By satisfying such a constitution, a PVA film having a small number of optical defects and active agent aggregates, a low haze value, good releasability, and excellent polarizing performance when processed into a polarizing film can be obtained.

[PVA (A)]

As the PVA (a), PVA produced by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester can be used. Examples of vinyl esters include: vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate (Versatic Acid), and the like. These can be used alone, also can be used in combination with 2 or more, but preferably the former. Vinyl acetate is preferred as the vinyl ester from the viewpoints of availability, cost, yield of pva (a), and the like.

Examples of other monomers copolymerizable with vinyl esters include: ethylene; olefins having 3 to 30 carbon atoms such as propylene, 1-butene, and isobutylene; acrylic acid or a salt thereof; acrylates 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 a salt thereof; methacrylates 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 derivatives such as acrylamide, N-methylacrylamide, N-ethylacrylamide, N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid or a salt thereof, acrylamidopropyldimethylamine or a salt thereof, and N-methylolacrylamide or a derivative thereof; methacrylamide derivatives such as methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid or a salt thereof, methacrylamidopropyldimethylamine or a salt thereof, and N-methylolmethacrylamide or a derivative thereof; n-vinylamides such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or a salt, ester or anhydride thereof; itaconic acid or a salt, ester or anhydride thereof; vinyl silyl compounds such as vinyltrimethoxysilane; isopropenyl acetate, and the like. These other monomers may be used alone in 1 kind, or 2 or more kinds may be used in combination. Among these, ethylene and an olefin having 3 to 30 carbon atoms are preferable as the other monomer, and ethylene is more preferable.

The proportion of the structural unit derived from the other monomer in the vinyl ester polymer is not particularly limited, and 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.

The polymerization degree of PVA (A) is not necessarily limited, but the film strength tends to decrease with a decrease in the polymerization degree, and therefore, it is preferably 200 or more, more preferably 300 or more, still more preferably 400 or more, and particularly preferably 500 or more. Further, when the polymerization degree is too high, the viscosity of the aqueous solution of pva (a) or the molten pva (a) tends to be high, and film formation tends to be difficult, and therefore, it is preferably 10,000 or less, more preferably 9,000 or less, still more preferably 8,000 or less, and particularly preferably 7,000 or less. The polymerization degree of PVA (A) is an average polymerization degree measured according to JIS K6726-1994, and the polymerization degree of PVA (A) is determined by the following formula, after further saponification and purification, measurement in water at 30 ℃ and the ultimate viscosity [ eta ] (unit: deciliter/g) measured.

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

The saponification degree of pva (a) is not particularly limited, and for example, 60 mol% or more of pva (a) may be used, and from the viewpoint of use as a raw roll film for producing an optical film such as a polarizing film, the saponification degree of pva (a) is preferably 95 mol% or more, more preferably 98 mol% or more, and still more preferably 99 mol% or more. The saponification degree of pva (a) is a ratio (mol%) of the number of moles of the vinyl alcohol unit to the total number of moles of the structural unit (typically, vinyl ester monomer unit) converted into the vinyl alcohol unit by saponification and the vinyl alcohol unit possessed by pva (a). The degree of saponification of PVA (A) can be measured according to JIS K6726-1994.

PVA (A) may be used alone in 1 type, or 2 or more types of PVA differing in polymerization degree, saponification degree, modification degree, etc. may be used in combination. However, if the PVA film contains: when PVA having an acidic functional group such as a carboxyl group or a sulfonic acid group, PVA having an acid anhydride group, PVA having a basic functional group such as an amino group, neutralized products thereof, or the like has a functional group which promotes a crosslinking reaction, the secondary processability of the PVA film may be lowered due to the crosslinking reaction between the PVA molecules. Therefore, as shown in the raw film for producing an optical film, when excellent secondary processability is required, the contents of the PVA having an acidic functional group, the PVA having an acid anhydride group, the PVA having a basic functional group and the neutralized product thereof in PVA (a) 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 still more 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 type or a sulfonate type. The number of carbon atoms 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 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, and the like. The alkyl group is preferably an alkyl group having 8 to 20 carbon atoms, more preferably an alkyl group having 10 to 16 carbon atoms.

Examples of the sulfonate type include: sodium alkylsulfonate, potassium alkylsulfonate, ammonium alkylsulfonate, triethanolamine alkylsulfonate, sodium alkylbenzenesulfonate, disodium dodecyldiphenylether disulfonate, sodium alkylnaphthalenesulfonate, disodium alkylsulfosuccinate, disodium polyoxyethylene alkylsulfosuccinate, and the like. The alkyl group is preferably an alkyl group having 8 to 20 carbon atoms, more preferably an alkyl group having 10 to 16 carbon atoms.

The surfactant may be used alone in 1 kind, or may be used in combination of 2 or more kinds. Among them, from the viewpoint of reducing the number of active agent aggregates and reducing the haze value, the anionic surfactant (B) is preferably a sulfonate type.

The PVA film of the present invention contains 0.01 to 0.20 parts by mass of an anionic surfactant (B) per 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 occur: many optical defects are generated in the PVA film, the haze value is increased, and the number of active agent aggregates in the PVA film is increased. 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 are 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.

[ 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. Here, the number of carbon atoms means 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 peelability may be deteriorated. The number of carbon atoms is more preferably 10 or more, and still more 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. As the fatty acid, a saturated fatty acid or an unsaturated fatty acid may be used, but from the viewpoint of thermal stability, a saturated fatty acid is suitable. As the saturated fatty acid, saturated fatty acids such as capric acid, lauric acid, myristic acid, palmitic acid and the like 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, cesium. As amines in the amine salts, there may be mentioned: 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 preferable from the viewpoint of solubility.

The PVA film of the present invention contains 0.02 to 0.20 part by mass of a fatty acid salt (C) per 100 parts by mass of the PVA (A). In the case where 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 at the same time, 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 occur: the PVA film had an increased number of active agent aggregates and an increased haze value. 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, the following problems 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 none.

Examples of the nonionic surfactant include: alkyl ether types such as polyoxyethylene oleyl ether; alkylphenyl ether type such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; alkylamine type such as polyoxyethylene lauryl amino ether; alkylamide types such as polyoxyethylene laurylamide; polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; aliphatic alkanolamide types such as lauric acid diethanolamide and oleic acid diethanolamide; and an allylphenyl ether type such as polyoxyalkylene allylphenyl ether.

In the present invention, the content ratio (B: C) of the anionic surfactant (B) to the fatty acid salt (C) is preferably 25: 75-75: 25. in a content ratio (B: C) of 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 of the PVA film increases. The content mass ratio (B: C) is more preferably 30: more than 70. On the other hand, when the content ratio (B: C) exceeds 75: in case of 25, the peelability may be deteriorated. The content ratio (B: C) is more preferably 60: 40 or less.

[ PVA film ]

The PVA film of the present invention preferably contains a plasticizer from the viewpoint of imparting flexibility to the PVA film. Preferred plasticizers include: specific examples of the polyhydric alcohol include: ethylene glycol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. These may be used alone in 1 kind of plasticizer, or 2 or more kinds of plasticizers may be used in combination. Among them, ethylene glycol or glycerin is preferable from the viewpoint of compatibility with pva (a), acquisition property, and the like.

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 less likely to occur in mechanical properties such as impact strength and in process acceptability at secondary processing. On the other hand, when the content of the plasticizer is 30 parts by mass or less, the film becomes moderately soft, and the handling property is improved.

The PVA film of the present invention may further contain, if necessary, other components other than PVA (a), anionic surfactant (B), fatty acid salt (C), and plasticizer. Examples of such other components include: moisture, an antioxidant, an ultraviolet absorber, a lubricant, a colorant, a filler (inorganic particles/starch, etc.), a preservative, a fungicide, a polymer compound other than the above components, and the like. The content of other components in the PVA film is preferably 10 mass% or less.

The width of the PVA film of the present invention is not particularly limited. In recent years, the width is preferably 1.5m or more in terms of a polarizing film required to have a wide width. Further, if the width of the PVA film is too wide, the manufacturing cost of the film forming apparatus for manufacturing the PVA film increases, and in the case of manufacturing an optical film using a manufacturing apparatus already put into practical use, uniform stretching may be difficult, and therefore the width of the PVA film is usually 7.5m or less.

The shape of the PVA film of the present invention is not particularly limited, and a long film is preferable in terms of enabling continuous and smooth production of a more uniform PVA film, continuous use in the production of an optical film, or the like. The length of the longitudinal film (length in the flow direction) is not particularly limited and can be set as appropriate. The length of the film is preferably 3,000m or more. On the other hand, the length of the film is preferably 30,000m or less. The long film is preferably wound around a core or the like to form a film roll.

The thickness of the PVA film of the present invention is not particularly limited, and may be appropriately set. From the viewpoint of use as a raw film for producing an optical film such as a polarizing film, the film preferably has a thickness of 10 to 70μAnd m is selected. The thickness of the PVA film can be determined as an average value of values measured at arbitrary 10 points.

The haze and the number of active agent aggregates of the PVA film of the present invention were measured by the methods 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. The number of the active agent aggregates is preferably 240 or less, more preferably 180 or less, and still more preferably 75 or less.

The method for producing the PVA film of the present invention is not particularly limited, and the following methods are preferred: a method for producing a PVA film containing PVA (A), an anionic surfactant (B) and a fatty acid salt (C), comprising the steps of: blending PVA (A), an anionic surfactant (B) and a fatty acid salt (C) to prepare a film-forming stock solution; and a step of forming a film using the film-forming dope. In this case, as described above, the content of the nonionic surfactant is preferably less than a certain amount.

In the step of preparing a film-forming dope, a liquid medium may be further blended. Examples of the liquid medium in this case include: water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc., and 1 or 2 or more of these can be used. Among them, water is preferable in terms of a small load on the environment and recyclability.

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

The evaporation fraction of the film-forming stock solution (the content of volatile components such as a liquid medium removed by evaporation or evaporation during film formation in the film-forming stock solution) varies depending on the film-forming method, film-forming conditions, and the like, and is preferably within a range of 50 to 90 mass%, and more preferably within a range of 55 to 80 mass%. By setting the volatile fraction of the film-forming dope to 50 mass% or more, the film can be easily formed without excessively increasing the viscosity of the film-forming dope. On the other hand, when the volatile fraction of the film-forming dope is 90 mass% or less, the viscosity of the film-forming dope is not excessively low, and the thickness uniformity of the PVA film obtained is improved.

The PVA film of the present invention can be suitably produced by a casting film forming method or a melt extrusion film forming method using the film forming dope. The specific production method in this case is not particularly limited, and for example, the film-forming dope can be obtained by casting or discharging the dope onto a support such as a drum or a belt to form a film, and drying the film on the support. 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-adjusted by a humidity-adjusting device, as required. The PVA film produced is preferably wound on a core or the like to make a film roll. In addition, both ends of the manufactured PVA film in the width direction may be cut.

The PVA film of the present invention can be suitably used as a raw film for producing a polarizing film, a phase difference film, a special condensing film, and the like. The present invention can provide a PVA film having excellent optical properties and high quality. Accordingly, a suitable embodiment of the present invention is a PVA film for optical use.

Suitable embodiments of the invention are: a method for producing a polarizing film, which comprises a step of dyeing the PVA film and a step of stretching the PVA film. 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, simultaneously with the stretching treatment, or after the stretching treatment. In addition, the processes of stretching, dyeing and the like can be repeated for a plurality of times. In particular, it is preferable to divide the stretching into 2 or more stages because uniform stretching is easily performed.

As dyes for dyeing of PVA film, there may be used: iodine or dichroic organic dyes (e.g., dichroic dyes such as 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), etc.), and the like. These dyes may be used alone in 1 kind or in combination of 2 or more kinds. The dyeing can be usually carried out by immersing the PVA film in a solution containing the above dye, but the treatment conditions and the treatment method are not particularly limited.

As a method of stretching the PVA film, there may be mentioned: the former is preferable as the uniaxial stretching method and the biaxial stretching method. The uniaxial stretching in which the PVA film is stretched 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 preferable from the viewpoint of stability of the performance and quality of the obtained polarizing film. Examples of the wet stretching method include: a method of stretching a PVA film in pure water, an aqueous solution containing various components such as an additive 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 uniaxially stretching in warm water containing boric acid, a method of uniaxially stretching in a solution containing the above dye or in a fixing treatment bath described later, or the like. The PVA film after water absorption may be uniaxially stretched in air, or may be uniaxially stretched by other methods.

The stretching temperature in the uniaxial stretching is not particularly limited, and in the case of wet stretching, a temperature in the range of preferably 20 to 90 ℃, more preferably 25 to 70 ℃, and further preferably 30 to 65 ℃ is used, and in the case of dry stretching, a temperature in the range of preferably 50 to 180 ℃.

The stretching ratio of the uniaxial stretching treatment (total stretching ratio in the case of uniaxial stretching in multiple stages) is preferably as much as possible immediately before the film is stretch-broken from the viewpoint of polarization performance, and specifically, is preferably 4 times or more, more preferably 5 times or more, and further preferably 5.5 times or more. The upper limit of the draw ratio is not particularly limited as long as the film is not broken, and is preferably 8.0 times or less for uniform drawing.

In the production of a polarizing film, it is preferable to perform a fixing treatment in order to secure the adsorption of the dye to the uniaxially stretched PVA film. As the fixing treatment, a method of immersing the PVA film in a treatment bath to which ordinary boric acid and/or a boron compound is added, or the like can be employed. In this case, an iodine compound may be added to the treatment bath as needed.

The PVA film subjected to the uniaxial stretching treatment, or the uniaxial stretching treatment and the fixing treatment is preferably subjected to a subsequent drying treatment or a heat treatment. The temperature of the drying treatment or the heat treatment is preferably 30 to 150 ℃, and particularly preferably 50 to 140 ℃. If the temperature is too low, the dimensional stability of the obtained polarizing film tends to be lowered. On the other hand, if the temperature is too high, the polarization performance tends to be lowered by decomposition of the dye.

The polarizing film obtained in the above manner can be laminated on both sides or one side with an optically transparent protective film having mechanical strength to prepare a polarizing plate. As the protective film in this case, a cellulose Triacetate (TAC) film, a cellulose acetate/butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. As the adhesive for attaching the protective film, a PVA adhesive, a Urethane (Urethane) adhesive, or the like is generally used, and among them, a PVA adhesive is preferably used.

The polarizing plate obtained in the above manner is coated with an adhesive such as acrylic and then bonded to a glass substrate, and is used as a member of a liquid crystal display device. When the polarizing plate is bonded to a glass substrate, a retardation film, a viewing angle improving film, a brightness improving film, and the like can be simultaneously bonded.

Examples

The present invention will be described specifically with reference to examples and the like, but the present invention is not limited to these examples at all.

[ Process acceptability for PVA film production ]

(releasability)

In the production of a long film of 4000m or more, a film which could be peeled without any problem when the film was peeled from a casting drum was evaluated as a, a film which could be easily peeled though a part of the film was adhered to the drum and had no problem in productivity was evaluated as B, and a film which could not be peeled by adhering to the drum was evaluated as C.

[ quality of PVA film ]

(method of evaluating optical Defect)

The PVA film was evaluated by visually observing streak-like defects and shark-skin-like defects existing parallel to the flow direction (MD direction) during film formation. Specifically, sample pieces obtained by cutting out the PVA films obtained in the following examples and comparative examples were hung so as to be perpendicular to the MD direction, and a 30W straight tube-shaped fluorescent lamp was placed perpendicularly behind the sample pieces and lighted up, and optical defects were evaluated according to the following criteria.

A: the product has no defects of stripe shape and shark skin shape, and is the most suitable level for the product;

b: although there are some streaky or sharkskin-like defects, this is a level that can be used as a product;

c: there are many streaky or sharkskin-like defects that are not suitable levels for the product.

(method of measuring haze)

A10 m region was cut from the surface layer side of the PVA film roll to be measured, and 3 pieces of squares (60 mm in thickness) of MD50mm × TD50mm were sampled from arbitrary positionsμm) sample pieces. The haze value of the central portion of the PVA film was measured 3 times each using a haze meter "HZ-2" manufactured by Suga test Co., Ltd in accordance with JIS K7136, and the average value was determined.

(method of measuring the number of active agent aggregates)

A10 m region was cut from the surface layer side of the PVA film roll to be measured, and MD50mm XTD 50mm (thickness 60) was sampled from an arbitrary positionμm) of the sample piece. The collected sample was examined with a microscope VHX6000 (magnification: 1000 times) manufactured by KEYENCE corporation, and the film thickness direction was about 1μImages were taken at m-spaced locations, and the number of active agent aggregates on the images taken was counted.

[ production of polarizing film ]

A long PVA film having a width of 650mm, which was obtained by winding and cutting the PVA films obtained in examples and comparative examples, was continuously wound up, and subjected to swelling treatment, dyeing treatment, crosslinking treatment, stretching treatment, fixing treatment and drying treatment in this order to produce a polarizing film, and a sample of MD30cm XTD 20cm was collected.

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

[ polarizing Properties of polarizing film ]

(a) Measurement of transmittance Ts

2 pieces of a square sample of MD20mm × TD20mm were collected from a polarizing film prepared using the PVA film obtained in example or comparative example, and the sample was analyzed by using an integrating sphere spectrophotometer ("V7100" manufactured by japan spectrographic corporation) in accordance with JIS Z8722: 2009 (method for measuring object color) was performed to correct the visual acuity of the C light source and the visible light region of the 2 ° field, and the light transmittance at a 45 ° tilt from the longitudinal direction and the light transmittance at a 45 ° tilt were measured for 1 sample, and the average value Ts1 (%) thereof was obtained. The same operation was performed for the other 1 sample, and the light transmittance was measured for the case of tilt 45 and the light transmittance was measured for the case of tilt-45, and the average value Ts2 (%) thereof was obtained. Ts1 and Ts2 were averaged by the following formula (1) to obtain a transmittance Ts (%) of the polarizing film.

Ts=(Ts1+Ts2)/2　(1)

(b) Measurement of degree of polarization V

The same operation as in the case of the above-described "(a) measurement of the transmittance Ts" was performed on 2 samples collected in the measurement of the transmittance Ts, and the transmittance T/(%) of light in the case where the samples were overlapped so as to be parallel to the longitudinal direction thereof and the transmittance T ≠ (%) of light in the case where the samples were overlapped so as to be perpendicular to the longitudinal direction thereof were measured, and the degree of polarization V (%) was obtained by the following formula (2).

V={(T∥-T⊥)/(T∥+T⊥)} ^1/2 ×100　(2)

(c) Light transmittance

With respect to a polarizer having a transmittance Ts of 43.0% to 44.0% prepared by adjusting the iodine concentration in the dyeing bath, the transmittance Ts at the time when the degree of polarization V was 99.995% was calculated from the relationship between the transmittance Ts and the degree of polarization V as an index of light transmittance.

Example 1

PVA (saponified homopolymer of vinyl acetate) chips (chips) having a polymerization degree of 2400 and a saponification degree of 99.9 mol% were used as PVA (A). 100 parts by mass of the PVA flakes were immersed in 2500 parts by mass of distilled water at 35 ℃ and then subjected to centrifugal dehydration to obtain PVA water-containing flakes having a volatile fraction of 60 mass%.

To 250 parts by mass of the PVA-containing pellets (100 parts by mass of dry PVA), 25 parts by mass of distilled water, 12 parts by mass of glycerin, 0.02 part by mass of an anionic surfactant (B), and 0.04 part by mass of a fatty acid salt (C) were mixed, and the resulting mixture was heated and melted by a twin-screw extruder (maximum temperature 130 ℃ C.) to prepare a film-forming stock solution. The anionic surfactant (B) used in this case was sodium alkylsulfonate (the number of carbon atoms in the alkyl group was 15), and the fatty acid salt (C) was a diethanolamine salt of lauric acid.

The film-forming dope was cooled to 100 ℃ by a heat exchanger, extruded through a coat hanger die (coat hanger die) having a width of 180cm onto a drum having a surface temperature of 90 ℃ to form a film, dried by a hot air drying apparatus, and then both ends of the film thickened by neck-in at the time of film-forming were cut off, thereby continuously producing a film having a film thickness of 60 mmμm, width 165 cm. Then, a part of the manufactured PVA film having a length of 4,000m was wound on a cylindrical core to make a film roll. The obtained PVA film was evaluated for optical defects, haze, and the number of active agent aggregates by the methods described above. Further, a polarizing film was produced using the obtained PVA film, and light transmittance as a polarizing property was evaluated. The results are shown in Table 1.

Examples 2 to 10 and comparative examples 1 to 5

PVA films were produced and evaluated in the same manner as in example 1, except that the kind and the amount 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 type sodium polyoxyethylene lauryl ether sulfate (the number of carbon atoms in the alkyl group was 12, and the number of ethylene oxide additions was 3), the fatty acid salt (C) used in example 7 was a potassium salt of lauric acid, the fatty acid salt (C) used in example 8 was a diethanolamine salt of capric acid, the fatty acid salt (C) used in example 9 was a diethanolamine salt of myristic acid, and the nonionic surfactant used in example 10, comparative example 4, and comparative example 5 was a tertiary amide type lauric acid diethanolamide.

As shown in Table 1, the PVA films of examples 1 to 10 were excellent in releasability, small in the number of optical defects and active agent aggregates, low in haze value, and good in quality. The polarizing film also had excellent light transmittance, and examples 1 to 4, 6 to 8 and 10 had particularly excellent light transmittance. 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 active agent aggregates and a high haze value. Further, the light transmittance of the polarizing film is also poor. The PVA film of comparative example 2 containing no fatty acid salt (C) had poor peelability and many optical defects were generated. The PVA film of comparative example 3 containing no anionic surfactant (B) had many optical defects, a large number of active agent aggregates, and a high haze value. The PVA film of comparative example 4, which further contained a certain amount or more of a nonionic surfactant, had a high number of active agent aggregates and a high haze value, compared to example 2, which contained an anionic surfactant (B) and a fatty acid salt (C). In comparative example 5, which contained no fatty acid salt (C) and contained a nonionic surfactant and an anionic surfactant, the number of active agent aggregates was large, and the haze value was high. Further, the polarizing film is also inferior in light transmittance.

Claims

1. A polyvinyl alcohol film comprising polyvinyl alcohol (A), an anionic surfactant (B) and a fatty acid salt (C),

wherein the anionic surfactant (B) is a sulfate type or a sulfonate type,

the content of the anionic surfactant (B) is 0.01-0.20 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,

the content of the fatty acid salt (C) is 0.02-0.20 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 part by mass per 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) to the fatty acid salt (C) is 25: 75-75: 25.

3. 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.

4. The polyvinyl alcohol film according to any one of claims 1 to 3, which has a width of 1.5m or more.

5. The polyvinyl alcohol film according to any one of claims 1 to 4, which has a length of 3000m or more.

6. The polyvinyl alcohol film according to any one of claims 1 to 5, which has a thickness of 10 to 70μm。

7. A method for producing a polarizing film, comprising: a process for dyeing the polyvinyl alcohol film according to any one of claims 1 to 6, and a process for stretching the film.