JPWO2020138287A1 - Polyvinyl alcohol film and a method for producing a polarizing film using the same - Google Patents

Abstract

A polyvinyl alcohol film containing a polyvinyl alcohol (A), a nonionic surfactant (B), an anionic surfactant (C) having no carboxyl group, and a surfactant (D) having a carboxyl group. , The content of the nonionic surfactant (B) is 0.01 to 0.12 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol (A), and the content of the anionic surfactant (C) is It is 0.01 to 0.24 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A), the surfactant (D) is an alkali metal salt or an amine salt, and the content of the surfactant (D). However, it is characterized in that it is 0.005 to 0.06 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A). As a result, a PVA film having a small number of optical defects, optical spots and activator aggregates, a low haze value, and excellent in-plane uniformity and light transmission when processed into a polarizing film was used. A method for producing a polarizing film is provided.

Description

The present invention is a polyvinyl alcohol containing polyvinyl alcohol (A), a nonionic surfactant (B), an anionic surfactant (C) having no carboxyl group, and a surfactant (D) having a carboxyl group. The present invention relates to a film and a method for producing a polarizing film using the film.

Polyvinyl alcohol (hereinafter, may be abbreviated as PVA) film is used in various applications 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 manufacturing 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.

So far, many techniques related to PVA film and its manufacturing method are known. Patent Document 1 describes that the correlation length derived from the result of light scattering measurement using a He-Ne laser having a wavelength of 633 nm as a light source is 200 nm or less, and the content of fatty acids having 10 or more carbon atoms present in the film is Polyvinyl alcohol-based films having a pH of 1 to 100 ppm have been described. According to this, since the light scatterer in the film has little influence on the light in the visible light region, it is possible to obtain a polarizing film having excellent light transmittance by using the polyvinyl alcohol-based film. ing.

Further, in Patent Document 2, when the film surface is subjected to negative ion mass spectrometry with a time-of-flight secondary ion mass spectrometer and the total detection intensity of all negative ions is set to 1, a fat having 10 to 30 carbon atoms Polyvinyl in which the total detection intensity of group carboxylic acid fragment ions a, the total detection intensity of sulfur-containing fragment ions b, and the total detection intensity of nitrogen-containing fragment ions c are all in the range of 0.0001 to 0.01. Alcohol-based films are described. According to this, it is said that there is no optical unevenness and an excellent blocking resistance effect can be exhibited even during storage and transportation in a rolled state.

Japanese Unexamined Patent Publication No. 2006-206880 Japanese Unexamined Patent Publication No. 2006-219637

However, in the PVA films obtained in Patent Documents 1 and 2, activator aggregates are formed, the haze value is high, and the light transmittance of the polarizing film may not be good, and improvement is required. rice field. The present invention has been made to solve the above problems, and has a small number of optical defects, optical spots and activator aggregates, a low haze value, in-plane uniformity and light when processed into a polarizing film. It is an object of the present invention to provide a PVA film having excellent transparency and a method for producing a polarizing film using the same.

The above-mentioned problem is polyvinyl alcohol containing polyvinyl alcohol (A), a nonionic surfactant (B), an anionic surfactant (C) having no carboxyl group, and a surfactant (D) having a carboxyl group. It ’s a film,
The content of the nonionic surfactant (B) is 0.01 to 0.12 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A).
The content of the anionic surfactant (C) is 0.01 to 0.24 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A).
The surfactant (D) is an alkali metal salt or an amine salt, and the content of the surfactant (D) is 0.005 to 0.06 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol (A). It is solved by providing a certain polyvinyl alcohol film.

［式（Ｉ）中、Ｒは炭素数８〜１８のアルキル基であり、ポリオキシエチレン鎖数（ｎ）は２〜１０であり、Ｍはアルカリ金属またはアミンである。］At this time, it is preferable that the content ratio (B: C) of the nonionic surfactant (B) and the anionic surfactant (C) is 20:80 to 49:51. Further, it is preferable that the anionic surfactant (C) is a sulfonate type surfactant, and the surfactant (D) is a polyoxyethylene alkyl ether carboxylic acid represented by the following formula (I). It is preferably an acid salt.

[In the formula (I), R is an alkyl group having 8 to 18 carbon atoms, the polyoxyethylene chain number (n) is 2 to 10, and M is an alkali metal or an amine. ]

［式（II）及び式（III）中、Ｒは炭素数８〜１８のアルキル基であり、ｎは１〜３であり、Ｍはアルカリ金属またはアミンである。］It is preferable that the surfactant (D) is an alkylaminocarboxylic acid salt represented by the following formula (II) or an alkylimide dicarboxylic acid salt represented by the following formula (III).

[In formulas (II) and (III), R is an alkyl group having 8 to 18 carbon atoms, n is 1 to 3, and M is an alkali metal or amine. ]

［式（IV）中、Ｒは炭素数８〜１８のアルキル基である。］It is preferable that the surfactant (D) is an alkyldimethylbetaine represented by the following formula (IV).

[In formula (IV), R is an alkyl group having 8 to 18 carbon atoms. ]

It is preferable that the surfactant (D) is an alkali metal salt or an amine salt of a fatty acid having 12 or more carbon atoms.

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

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

According to the present invention, a high quality PVA film having a small number of optical defects, optical spots and activator aggregates and a low haze value can be obtained. Therefore, by using the PVA film as the raw material, a polarizing film having excellent in-plane uniformity and light transmission can be obtained.

The PVA film of the present invention contains PVA (A), a nonionic surfactant (B), an anionic surfactant (C) having no carboxyl group, and a surfactant (D) having a carboxyl group. ..

The present inventors are PVA films containing a certain amount of each of PVA (A), a nonionic surfactant (B), an anionic surfactant (C), and a surfactant having a carboxyl group (D). Moreover, since the surfactant (D) is an alkali metal salt or an amine salt, a high-quality PVA film having a small number of optical defects, optical spots and activator aggregates and a low haze value can be obtained. I found that it was possible. Then, it was clarified that by using such a PVA film, a polarizing film having excellent in-plane uniformity and light transmission can be obtained. The present inventors have good quality PVA when the contents of PVA (A), nonionic surfactant (B), anionic surfactant (C) and surfactant (D) are not within a certain range. It has been confirmed that no film can be obtained and that the in-plane uniformity and light transmission are inferior when processed into a polarizing film. Further, when the surfactant (D) having a carboxyl group is not an alkali metal salt or an amine salt but an aliphatic carboxylic acid, the present inventors have a large number of activator aggregates and a haze value. It has been confirmed that the light transmittance is high and the light transmittance when processed into a polarizing film is inferior.

Therefore, as in the present invention, PVA (A), a nonionic surfactant (B), an anionic surfactant (C), and a surfactant having a carboxyl group (D) are contained in a certain amount, respectively, and It is important that the surfactant (D) is a PVA film that is an alkali metal salt or an amine salt. By satisfying such a configuration, the number of optical defects, optical spots and activator aggregates is small, the haze value is low, and the PVA film is excellent in in-plane uniformity and light transmission when processed into a polarizing film. Can be obtained.

[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-methylmethacrylamide, 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 kind of PVA may be used alone, or two or more kinds of PVA having different degrees of polymerization, saponification, degree of modification and the like 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 manufacturing 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.

[Nonion-based surfactant (B)]
The nonionic surfactant (B) used in the present invention is not particularly limited, but is an alkyl ether type such as polyoxyethylene oleyl ether; an alkylphenyl ether type such as polyoxyethylene octylphenyl ether; polyoxyethylene laurate and the like. Alkyl ester type; Alkylamine type such as polyoxyethylene laurylamino ether; Alkylamide type such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Diethanolamide lauric acid, oleic acid An aliphatic alkanolamide type such as diethanolamide; an allylphenyl ether type such as polyoxyalkylene allylphenyl ether is preferable. Among these, the aliphatic alkanolamide type is more preferably used as the nonionic surfactant (B). As the aliphatic alkanolamide type, a tertiary amide type aliphatic alkanolamide and a secondary amide type aliphatic alkanolamide can be used. From the viewpoint that the number of activator aggregates is small and the haze value is low, a secondary amide type aliphatic alkanolamide represented by the following formula (V) is more preferably used.

［式（Ｖ）中、Ｒは炭素数８〜１８のアルキル基であり、ポリオキシエチレン鎖数（ｎ）が２〜１０である。］

[In the formula (V), R is an alkyl group having 8 to 18 carbon atoms, and the polyoxyethylene chain number (n) is 2 to 10. ]

In the above formula (V), R is an alkyl group having 8 to 18 carbon atoms. The alkyl group may be a straight chain or a branched chain, but is preferably a straight chain. If the carbon number (alkyl chain length) of R is less than 8, a large number of optical defects may occur in the PVA film. The carbon number (alkyl chain length) of R is preferably 9 or more, and more preferably 10 or more. On the other hand, when the number of carbon atoms (alkyl chain length) of R exceeds 18, there is a possibility that problems such as a large number of activator aggregates and a high haze value may occur in the PVA film. The carbon number (alkyl chain length) of R is preferably 15 or less, and more preferably 13 or less.

In the above formula (V), the number of polyoxyethylene chains (n) is 2 to 10. When the number of polyoxyethylene chains (n) is less than 2, problems such as a large number of activator aggregates in the PVA film and a high haze value may occur. The number of polyoxyethylene chains (n) is preferably 4 or more. On the other hand, when the number of polyoxyethylene chains (n) exceeds 10, a large number of optical defects may occur in the PVA film. The number of polyoxyethylene chains (n) is preferably 8 or less.

In the PVA film of the present invention, the content of the nonionic surfactant (B) is 0.01 to 0.12 parts by mass with respect to 100 parts by mass of PVA (A). If the content of the nonionic surfactant (B) is less than 0.01 parts by mass, a large number of optical defects occur in the PVA film, which makes it unsuitable for products. The content of the nonionic surfactant (B) is preferably 0.02 or more, and more preferably 0.03 or more. On the other hand, when the content of the nonionic surfactant (B) exceeds 0.12 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 nonionic surfactant (B) is preferably 0.1 part by mass or less, more preferably 0.08 part by mass or less, and further preferably 0.06 part by mass or less. .. The nonionic surfactant (B) used in the present invention may be used alone or in combination of two or more.

[Anionic surfactant (C) having no carboxyl group]
The anionic surfactant (C) used in the present invention does not have a carboxyl group, and is preferably at least one selected from the group consisting of a sulfate ester salt type and a sulfonate type.

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 alkylbenzenesulfonate, disodium dodecyldiphenyl ether disulfonate, sodium alkylnaphthalene sulfonate, and alkylsulfosuccinate. Examples thereof include disodium acid, disodium polyoxyethylene alkyl sulfosuccinate and the like. 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 (C) 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 (C) is 0.01 to 0.24 parts by mass with respect to 100 parts by mass of PVA (A). When the content of the anionic surfactant (C) is less than 0.01 parts by mass, problems such as an increase in the number of activator aggregates and an increase in haze value occur. In addition, the light transmittance when processed into a polarizing film is inferior. The content of the anionic surfactant (C) is preferably 0.02 parts by mass or more, and more preferably 0.03 parts by mass or more. On the other hand, when the content of the anionic surfactant (C) exceeds 0.24 parts by mass, a large number of optical defects occur in the PVA film, which makes it unsuitable for products. The content of the anionic surfactant (C) is preferably 0.18 parts or less, more preferably 0.16 parts by mass or less, further preferably 0.14 parts by mass or less, and 0. It is particularly preferable that the amount is 12 parts by mass or less.

In the present invention, the content ratio (B: C) of the nonionic surfactant (B) and the anionic surfactant (C) is preferably 20:80 to 49:51. As described above, by increasing the content of the anionic surfactant (C) more than the nonionic surfactant (B), there is an advantage that the number of activator aggregates can be reduced and the haze value can be lowered. If the content ratio (B: C) is less than 20:80, many optical defects may occur in the PVA film. The content mass ratio (B: C) is more preferably 25:75 or more, and further preferably 30:70 or more. On the other hand, when the content ratio (B: C) exceeds 49:51, problems such as an increase in the number of activator aggregates in the PVA film and an increase in the haze value may occur. The content ratio (B: C) is more preferably 47:53 or less, and further preferably 45:55 or less.

[Surfactant having a carboxyl group (D)]
The surfactant (D) used in the present invention has a carboxyl group and is composed of an alkali metal salt or an amine salt. When an aliphatic carboxylic acid is used instead of an alkali metal salt or an amine salt, the present inventors have a large number of activator aggregates, a high haze value, and light transmission when processed into a polarizing film. It has been confirmed that the sex is inferior. Therefore, it is important that the surfactant (D) has a carboxyl group and is an alkali metal salt or an amine salt. The alkali metal is preferably at least one selected from the group consisting of lithium, sodium, potassium and cesium, and more preferably at least one selected from the group consisting of sodium and potassium. The amine is preferably at least one selected from the group consisting of ammonia, monoethanolamine, monoethanolamine, diethanolamine and triethanolamine, and more preferably diethanolamine.

Examples of the surfactant (D) used in the present invention include a polyoxyethylene alkyl ether carboxylate represented by the following formula (I), an alkylamino carboxylate represented by the following formula (II), and the following formula ( At least one selected from the group consisting of an alkylimide dicarboxylate represented by III), an alkyldimethylbetaine represented by the following formula (IV), and an alkali metal salt or an amine salt of a fatty acid having 12 or more carbon atoms. It is preferable to have.

［式（Ｉ）中、Ｒは炭素数８〜１８のアルキル基であり、ポリオキシエチレン鎖数（ｎ）は２〜１０であり、Ｍはアルカリ金属またはアミンである。］

[In the formula (I), R is an alkyl group having 8 to 18 carbon atoms, the polyoxyethylene chain number (n) is 2 to 10, and M is an alkali metal or an amine. ]

［式（II）及び式（III）中、Ｒは炭素数８〜１８のアルキル基であり、ｎは１〜３であり、Ｍはアルカリ金属またはアミンである。］

[In formulas (II) and (III), R is an alkyl group having 8 to 18 carbon atoms, n is 1 to 3, and M is an alkali metal or amine. ]

［式（IV）中、Ｒは炭素数８〜１８のアルキル基である。］

[In formula (IV), R is an alkyl group having 8 to 18 carbon atoms. ]

In the above formulas (I), (II), (III) and (IV), R is an alkyl group having 8 to 18 carbon atoms. The alkyl group may be a straight chain or a branched chain, but is preferably a straight chain. When the carbon number (alkyl chain length) of R is less than 8, the amount of segregation on the film surface is small and the optical spots may become large. The carbon number (alkyl chain length) of R is preferably 9 or more, and more preferably 10 or more. On the other hand, when the number of carbon atoms (alkyl chain length) of R exceeds 18, there is a possibility that the film will aggregate and the haze of the film will increase. The carbon number (alkyl chain length) of R is preferably 15 or less, and more preferably 13 or less. Further, in the above formulas (I), (II) and (III), M is an alkali metal or an amine. As the specific alkali metal or amine, the above-mentioned ones can be preferably used.

In the above formula (I), the number of polyoxyethylene chains (n) is 2 to 10. When the number of polyoxyethylene chains (n) is less than 2, there is a possibility that the film will aggregate and the haze of the film will increase. The number of polyoxyethylene chains (n) is preferably 4 or more. On the other hand, when the number of polyoxyethylene chains (n) exceeds 10, the amount of segregation on the film surface is small and the optical spots may become large. The number of polyoxyethylene chains (n) is preferably 8 or less. Further, in the above formulas (II) and (III), n is 1 to 3. From the viewpoint of compatibility with PVA (A), availability, and the like, n in the above formulas (II) and (III) is preferably 2 to 3.

As described above, alkali metal salts or amine salts of fatty acids having 12 or more carbon atoms are also preferably used as the surfactant (D). The carbon chain of the fatty acid may be a straight chain or a branched chain, but a straight chain is preferable. The number of carbon atoms of the fatty acid is preferably 18 or less, and more preferably 16 or less. The fatty acid may be a saturated fatty acid or an unsaturated fatty acid, but is preferably a saturated fatty acid. Specific examples of alkali metal salts or amine salts of fatty acids having 12 or more carbon atoms include alkali metal salts or amine salts such as lauric acid, myristic acid, pentadecylic acid, palmitic acid, and stearic acid. Among them, an alkali metal salt or an amine salt of at least one fatty acid selected from the group consisting of lauric acid, myristic acid, pentadecic acid and palmitic acid is more preferably used as the surfactant (D). As the specific alkali metal or amine, the above-mentioned ones can be preferably used.

In the PVA film of the present invention, the content of the surfactant (D) is 0.005 to 0.06 parts by mass with respect to 100 parts by mass of PVA (A). When the content of the surfactant (D) is less than 0.005 parts by mass, a large number of optical spots are generated, and the in-plane uniformity when processed into a polarizing film is deteriorated. The content of the surfactant (D) is preferably 0.008 part by mass or more, and more preferably 0.01 part by mass or more. On the other hand, when the content of the surfactant (D) exceeds 0.06 parts by mass, there arises a problem that the number of activator aggregates increases and the haze value increases. In addition, the light transmittance when processed into a polarizing film is inferior. The content of the surfactant (D) is preferably 0.05 parts by mass or less, more preferably 0.04 parts by mass or less, and further preferably 0.03 parts by mass 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 contains components other than PVA (A), nonionic surfactant (B), anionic surfactant (C), surfactant (D) and a plasticizer, if necessary. It may be further contained. Examples of such other components include moisture, antioxidants, ultraviolet absorbers, lubricants, colorants, fillers (inorganic particles, starch, etc.), preservatives, fungicides, and other components other than those described above. Examples include high molecular 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 3000 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 methods described in the examples below. The haze value is preferably 0.4 or less, more preferably 0.3 or less, and even more preferably 0.2 or less. The number of such activator aggregates is preferably 140 or less, more preferably 120 or less, and even more preferably 110 or less.

The method for producing the PVA film of the present invention is not particularly limited, but the PVA film containing PVA (A), a nonionic surfactant (B), an anionic surfactant (C), and a surfactant (D). A production method for preparing a film-forming stock solution by blending PVA (A), a nonionic surfactant (B), an anionic surfactant (C), and a surfactant (D). It is preferable that the method for producing a PVA film includes a step of forming a film using a film-forming stock solution.

In the step of preparing the film-forming stock solution, a liquid medium can be further added. 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), a nonionic surfactant (B), an anionic surfactant (C), a surfactant (D), a liquid medium, and if necessary, Further, a known method such as a casting film forming method or a melt extrusion film forming method can be adopted by using a film forming stock solution containing the above-mentioned plasticizer and other components. 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 50. 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 a casting film forming method or a 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, it 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 in-plane uniformity and light transmission 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 should be 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 and the 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.

[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.

(Evaluation method of optical spots)
Optical spots were evaluated by measuring the retardation (Re) of the PVA film. Specifically, a sample piece of MD100 cm × TD30 cm (thickness 60 μm) was cut out from the central portion of the PVA film roll obtained in the following Examples and Comparative Examples in the TD direction, and further divided into four in the MD direction, and manufactured by Photonic Lattice. The retardation (Re) was measured using a birefringence evaluation device. The maximum and minimum values of retardation (Re) in the region of MD 100 cm × TD 30 cm were used as indexes of optical spots and evaluated according to the following criteria.
A: The difference between the maximum and minimum values of Re is small and the level is suitable for the product.
B: A level that is not suitable for products because the difference between the maximum and minimum values of Re is large.

(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 haze at the center of the PVA film was measured three times for each of the collected samples 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 is 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) In-plane uniformity An observation polarizing plate is placed on a surface light source (backlight) in a dark room, and the absorption axis of the observation polarizing plate and the absorption axis of the produced polarizing film are placed on the observation polarizing plate. The polarizing film was placed so that the angle between the two was 90 degrees. Next, the polarizing film is irradiated with light from the backlight through the polarizing plate for observation (brightness 15000 cd), and the polarizing film is visually observed from a position 1 m above the polarizing film, thereby causing color spots on the polarizing film. Was inspected for the presence of The in-plane uniformity was evaluated according to the following criteria.
A: A level where the color spots are thin and do not pose a problem in practical use.
B: A level at which color spots that are practically defective can be confirmed.
(B) Measurement of Transmittance Ts Two square samples of MD 20 mm × TD 20 mm were taken from a polarizing film produced using the PVA film obtained in the Example or Comparative Example, and a spectrophotometer with an integrating sphere (Nippon Spectroscopy). 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. Similarly 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)
(C) 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 directions are orthogonal to each other is measured in the same manner as in the case of “(b) Measurement of transmittance Ts” above, and the degree of polarization is measured by the following formula (2). V (%) was calculated.
V = {(T‖-T⊥) / (T‖ + T⊥)} ^1/2 x 100 (2)
(D) 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 PVA (saponified product of a homopolymer of vinyl acetate) chip 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-containing chip having a volatile content of 60% by mass.

25 parts by mass of distilled water, 12 parts by mass of glycerin, 0.05 parts by mass of nonionic surfactant (B), and anionic surfactant (100 parts by mass of dry PVA) with respect to 250 parts by mass of the PVA-containing chip (dry PVA is 100 parts by mass). C) 0.08 parts by mass and 0.02 parts by mass of a surfactant having a carboxyl group (D) After mixing, the obtained mixture is heated and melted by a twin-screw extruder (maximum temperature 130 ° C.) to form a film-forming stock solution. And said. The nonionic surfactant (B) used at this time was a polyoxyethylene fatty acid monoalkanolamide (alkyl group has 12 carbon atoms and ethylene oxide addition number (n) is 6), and is an anionic surfactant (anionic surfactant (n). C) was sodium alkylsulfonate (alkyl group having 15 carbon atoms), and the surfactant having a carboxyl group (D) was sodium imide dicarboxylic acid (R has 12 carbon atoms and n is 2). ..

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 4000 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, optical spots, haze, and activator aggregates by the above method. Further, a polarizing film was produced using the obtained PVA film, and in-plane uniformity and light transmission were evaluated as polarization performance. The results are shown in Table 1.

Examples 2-10, Comparative Examples 1-8
Example 1 and Example 1 except that the types and amounts of the nonionic surfactant (B), the anionic surfactant (C), and the surfactant (D) having a carboxyl group were changed as shown in Table 1. A PVA film was produced in the same manner and evaluated. The nonionic surfactant used in Example 3 was a tertiary amide type lauric acid diethanolamide, and the anionic surfactant (C) used in Example 4 was a sulfate ester type polyoxyethylene. The surfactant (D) having a carboxyl group, which is sodium lauryl ether sulfate (the number of carbon atoms of the alkyl group is 12 and the number of additions of ethylene oxide is 3), is sodium polyoxyethylene alkyl ether carboxylate. (R has 12 carbon atoms and n is 6), and the carboxyl group-containing surfactant (D) used in Example 6 is alkyldimethylbetaine (R has 12 carbon atoms).

As shown in Table 1, the PVA films of Examples 1 to 10 had a small number of optical defects, optical spots, and activator aggregates, a low haze value, and good quality. In addition, the PVA films of Examples 1 to 10 were also excellent in in-plane uniformity and light transmission of the polarizing film.
On the other hand, the PVA films of Comparative Example 1 in which the amount of the nonionic surfactant (B) was small and Comparative Example 4 in which the amount of the anionic surfactant (C) was large had many optical defects.
Comparative Example 2 in which the amount of nonionic surfactant (B) is large, Comparative Example 3 in which the amount of anionic surfactant (C) is small, Comparative Example 6 in which the amount of the surfactant (D) having a carboxyl group is large, and Surface activity having a carboxyl group. PVA film of Comparative Example 7 in which lauric acid was used as the agent (D) and Comparative Example 8 in which lauric acid was used as the surfactant (D) having a carboxyl group without using the anionic surfactant (C). 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.
The PVA film of Comparative Example 5 in which the amount of the surfactant (D) having a carboxyl group was small had large optical spots, and the in-plane uniformity of the polarizing film was not good.

Claims (11)

A polyvinyl alcohol film containing a polyvinyl alcohol (A), a nonionic surfactant (B), an anionic surfactant (C) having no carboxyl group, and a surfactant (D) having a carboxyl group. ,
The content of the nonionic surfactant (B) is 0.01 to 0.12 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A).
The content of the anionic surfactant (C) is 0.01 to 0.24 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A).
The surfactant (D) is an alkali metal salt or an amine salt, and the content of the surfactant (D) is 0.005 to 0.06 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol (A). A polyvinyl alcohol film. The polyvinyl alcohol film according to claim 1, wherein the content ratio (B: C) of the nonionic surfactant (B) and the anionic surfactant (C) is 20:80 to 49:51. The polyvinyl alcohol film according to claim 1 or 2, wherein the anionic surfactant (C) is a sulfonate-type surfactant. The polyvinyl alcohol film according to any one of claims 1 to 3, wherein the surfactant (D) is a polyoxyethylene alkyl ether carboxylate represented by the following formula (I).

[In the formula (I), R is an alkyl group having 8 to 18 carbon atoms, the polyoxyethylene chain number (n) is 2 to 10, and M is an alkali metal or an amine. ] The invention according to any one of claims 1 to 3, wherein the surfactant (D) is an alkylaminocarboxylic acid salt represented by the following formula (II) or an alkylimide dicarboxylic acid salt represented by the following formula (III). Polyvinyl alcohol film.

[In formulas (II) and (III), R is an alkyl group having 8 to 18 carbon atoms, n is 1 to 3, and M is an alkali metal or amine. ] The polyvinyl alcohol film according to any one of claims 1 to 3, wherein the surfactant (D) is an alkyldimethylbetaine represented by the following formula (IV).

[In formula (IV), R is an alkyl group having 8 to 18 carbon atoms. ] The polyvinyl alcohol film according to any one of claims 1 to 3, wherein the surfactant (D) is an alkali metal salt or an amine salt of a fatty acid having 12 or more carbon atoms. The polyvinyl alcohol film according to any one of claims 1 to 7, wherein the film width is 1.5 m or more. The polyvinyl alcohol film according to any one of claims 1 to 8, wherein the length of the film is 3000 m or more. The polyvinyl alcohol film according to any one of claims 1 to 9, wherein the film thickness is 10 to 70 μm. A method for producing a polarizing film, comprising a step of dyeing the polyvinyl alcohol film according to any one of claims 1 to 10 and a step of stretching the polyvinyl alcohol film.