JP7284716B2 - Polarizing film and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polarizing film having small shrinkage force at high temperatures and excellent optical performance, and a method for producing the same.

A polarizer, which has the function of transmitting and shielding light, is a basic component of a liquid crystal display (LCD) along with a liquid crystal that changes the polarization state of light. Many polarizing plates have a structure in which a protective film such as a cellulose triacetate (TAC) film is attached to the surface of the polarizing film in order to prevent the polarizing film from fading or shrinking. As the polarizing film constituting the polarizing plate, an iodine-based dye (I ₃ ^- , I ₅ ^- ) is adsorbed is the mainstream.

LCDs are widely used in small devices such as calculators and wristwatches, smart phones, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, car navigation systems, and measuring instruments used indoors and outdoors. devices are required to be thin and high-definition. Along with this, in recent years, glass used for LCDs has been made thinner and polarizing films have been made to have a higher draw ratio, and as a result, the occurrence of warping of LCD panels has become a problem. It is said that the main cause of warping of LCD panels is the shrinkage of polarizing films at high temperatures, and there is a demand for polarizing films that have high optical performance and low shrinkage force at high temperatures.

As a means for improving the optical performance of a polarizing film, a method using PVA with a high degree of polymerization is known (for example, Patent Document 1). However, although the use of PVA with a high degree of polymerization improves the optical performance of the polarizing film, it also increases the shrinkage force, making it difficult to achieve both.

In Patent Document 2, by reducing the amount of boric acid in the PVA film and providing a step of drying the PVA film between the boric acid treatment step and the water washing step, the shrinkage force at high temperatures is small and the color tone is good. It is described that a good polarizing film can be obtained. However, even if the amount of boric acid in the polarizing film is reduced, it has been difficult to sufficiently reduce the shrinkage force while maintaining high optical performance.

JP-A-01-084203 JP 2013-148806 A

The present invention has been made to solve the above problems, and an object of the present invention is to provide a polarizing film having a small shrinkage force at high temperatures and excellent optical performance.

The above problem is to solve the above-mentioned problems by using PVA (A), at least one boron-containing compound (B ), wherein the boron element content derived from the boron-containing compound (B) in the polarizing film is 0.1 to 3.0 parts by mass with respect to 100 parts by mass of PVA (A) It is solved by providing a polarizing film.

[In formula (I), R ¹ is a monovalent aliphatic group having 1 to 20 carbon atoms, and R ¹ and a boronic acid group are linked via a boron-carbon bond. ]

At this time, R ¹ is preferably a saturated aliphatic group. It is also preferred that R ¹ is an aliphatic hydrocarbon group. It is also preferred that R ¹ has 2 to 5 carbon atoms.

The above problem is a process of immersing the film in an aqueous solution of a boron-containing compound (B) in a method for producing a polarizing film including a dyeing treatment of dyeing a PVA film with a dichroic dye and a stretching treatment of uniaxially stretching the film. It is also solved by providing a method for producing the polarizing film.

The polarizing film of the present invention has a small shrinkage force at high temperatures and is excellent in optical performance. Therefore, by using the polarizing film of the present invention, it is possible to obtain an LCD panel that is resistant to warping at high temperatures and has high image quality. Moreover, according to the manufacturing method of this invention, such a polarizing film can be manufactured.

1 is a ¹ H-NMR chart of the polarizing film obtained in Example 1. FIG. FIG. 2 is a graph plotting the shrinkage force on the horizontal axis and the degree of polarization on the vertical axis for the polarizing films of Examples 1 to 7 and Comparative Examples 1 and 3 to 9. FIG.

The polarizing film of the present invention contains PVA (A) and at least one boron-containing compound selected from the group consisting of monoboronic acids represented by the following formula (I) and compounds convertible to the monoboronic acids in the presence of water. A polarizing film containing a compound (B), wherein the boron element content derived from the boron-containing compound (B) in the polarizing film is 0.1 to 3.0 mass parts per 100 mass parts of PVA (A) It is a polarizing film that is a part. By cross-linking the PVA (A) with the boron-containing compound (B), the optical performance can be improved while reducing the shrinkage force at high temperatures. Here, in formula (I), R ¹ is a monovalent aliphatic group having 1 to 20 carbon atoms, and R ¹ and a boronic acid group are linked via a boron-carbon bond.

A monoboronic acid is a compound represented by the above formula (I) and has one boronic acid group [-B(OH) ₂ ] in one molecule. The boronic acid group has a structure in which a boron atom to which two hydroxyl groups are bonded is bonded to a carbon atom. In the compound represented by formula (I), R ¹ and the boronic acid group are boron- connected by carbon bonds. In boric acid [B(OH) ₃ ], a boron atom is bonded to three hydroxyl groups, whereas a boronic acid group is different in that it has a boron-carbon bond. Boron-containing groups that can be converted into boronic acid groups in the presence of water include, but are not limited to, the following boronate ester groups.

A hydroxyl group in a boronic acid group contained in monoboronic acid can form an ester with an alcohol, like a hydroxyl group in boric acid. The following structural formula (II) is a monoboronic acid monoester in which one molecule of alcohol (R ² —OH) reacts with boronic acid. Here, when the boronic acid group is bonded to the hydroxyl group of PVA (A), R ² in structural formula (II) is a PVA chain, and the carbon-containing group is bonded to the PVA chain via a boron atom. become.

Structural formula (III) below is an example of a monoboronic acid diester in which two molecules of alcohol (R ² —OH) are reacted with monoboronic acid. Here, when the boronic acid group is bonded to the hydroxyl group of PVA, both of the two ^R2 's in structural formula (III) are PVA chains.

Monoboronic acid has two hydroxyl groups that can react with the hydroxyl groups of PVA to form esters, resulting in moderate cross-linking of PVA chains. Since this cross-linking is stable to heat, the shrinkage force of the polarizing film at high temperatures is reduced. This suppresses the warping of the LCD panel using the polarizing film at high temperatures. In addition, it is believed that moderate cross-linking of the PVA chains improves the alignment state of the PVA chains and improves the optical performance of the polarizing film.

In formula (I) above, R ¹ is a monovalent aliphatic group having 1 to 20 carbon atoms. The solubility of the boron-containing compound (B) in water and the reactivity with hydroxyl groups of PVA can be controlled by setting R ¹ to an appropriate length. The number of carbon atoms in R ¹ is preferably 10 or less, more preferably 6 or less, even more preferably 5 or less. On the other hand, the number of carbon atoms in R ¹ is preferably 2 or more, more preferably 3 or more, from the viewpoint of particularly excellent balance between optical performance and shrinkage force of the polarizing film.

In formula (I) above, R ¹ is a monovalent aliphatic group, and R ¹ and a boronic acid group may be linked via a boron-carbon bond. R ¹ may be a saturated aliphatic group or an unsaturated aliphatic group, the former being preferred. When R ¹ is a saturated aliphatic group, coloration of the obtained polarizing film is suppressed and durability is improved. In addition, since R ¹ is a saturated aliphatic group, the orientation of the dichroic dye is improved and the optical performance is further improved. The unsaturated aliphatic group includes a carbon-carbon double bond, a carbon-carbon triple bond, a carbon-oxygen double bond, a carbon-nitrogen double bond, a nitrogen-nitrogen double bond, a carbon-sulfur double bond, and the like. is an aliphatic group having a structure containing a multiple bond with a bond order of 2 or more, and a saturated aliphatic group is an aliphatic group having only a single bond structure. Monoboronic acids in which R ¹ is a saturated aliphatic group include methylboronic acid, ethylboronic acid, propylboronic acid, butylboronic acid, pentylboronic acid, hexylboronic acid, heptylboronic acid, octylboronic acid, nonylboronic acid, decanylboronic acid, un decanylboronic acid, dodecanylboronic acid, tridecanylboronic acid, tetradecanylboronic acid, pentadecanylboronic acid, hexadecanylboronic acid, heptadecanylboronic acid, octadecanylboronic acid, nonadecanylboron acids, icosanylboronic acid and their isomers, cyclopropylboronic acid, cyclobutylboronic acid, cyclopentylboronic acid, cyclohexylboronic acid, cycloheptylboronic acid, cyclooctylboronic acid, cyclononylboronic acid, cyclodecanylboronic acid, cyclo Undecanyl boronic acid, cyclododecanyl boronic acid, cyclotridecanyl boronic acid, cyclotetradecanyl boronic acid, cyclopentadecanyl boronic acid, cyclohexadecanyl boronic acid, cycloheptadecanyl boronic acid, cyclooctadeca nylboronic acid, cyclononadecanylboronic acid, cycloicosanylboronic acid and their isomers, 2-oxa-propylboronic acid, 2-oxa-butylboronic acid, 2-oxa-hexylboronic acid, 2-oxa- Heptylboronic acid, 2-oxa-octylboronic acid, 2-oxa-nonylboronic acid, 2-oxa-decanylboronic acid, 2-oxa-undecanylboronic acid, 2-oxa-dodecanylboronic acid, 2-oxa-tri decanylboronic acid, 2-oxa-tetradecanylboronic acid, 2-oxa-pentadecanylboronic acid, 2-oxa-hexadecanylboronic acid, 2-oxa-heptadecanylboronic acid, 2-oxa-octa decanylboronic acid, 2-oxa-nonadecanylboronic acid, 2-oxa-icosanylboronic acid and their isomers, 2-aza-propylboronic acid, 2-aza-butylboronic acid, 2-aza-hexylboronic acid, 2-aza-heptylboronic acid, 2-aza-octylboronic acid, 2-aza-nonylboronic acid, 2-aza-decanylboronic acid, 2-aza-undecanylboronic acid, 2-aza-dodecanylboronic acid, 2 - aza-tridecanylboronic acid, 2-aza-tetradecanylboronic acid, 2-aza-pentadecanylboronic acid, 2-aza-hexadecanylboronic acid, 2-aza-heptadecanylboronic acid, 2 -aza-octadecanylboronic acid, 2-aza-nonadecanylboronic acid, 2-aza-icosanylboronic acid and their isomers, 2-phospha-propylboronic acid, 2-phospha-butylboronic acid, 2-phospha-hexyl Boronic acid, 2-phospha-heptylboronic acid, 2-phospha-octylboronic acid, 2-phospha-nonylboronic acid, 2-phospha-decanylboronic acid, 2-phospha-undecanylboronic acid, 2-phospha-dodecanylboron acid, 2-phospha-tridecanylboronic acid, 2-phospha-tetradecanylboronic acid, 2-phospha-pentadecanylboronic acid, 2-phospha-hexadecanylboronic acid, 2-phospha-heptadecanylboron acids, 2-phospha-octadecanylboronic acid, 2-phospha-nonadecanylboronic acid, 2-phospha-icosanylboronic acid and their isomers, 2-thia-propylboronic acid, 2-thia-butylboronic acid, 2- thia-hexylboronic acid, 2-thia-heptylboronic acid, 2-thia-octylboronic acid, 2-thia-nonylboronic acid, 2-thia-decanylboronic acid, 2-thia-undecanylboronic acid, 2-thia- dodecanylboronic acid, 2-thia-tridecanylboronic acid, 2-thia-tetradecanylboronic acid, 2-thia-pentadecanylboronic acid, 2-thia-hexadecanylboronic acid, 2-thia-hepta Examples include decanylboronic acid, 2-thia-octadecanylboronic acid, 2-thia-nonadecanylboronic acid, 2-thia-icosanylboronic acid and isomers thereof. In addition, examples of compounds that can be converted into monoboronic acids in the presence of water include salts of the monoboronic acids.

R ¹ may be an aliphatic hydrocarbon group or may contain a heteroatom such as oxygen, nitrogen, sulfur or halogen. In consideration of availability and the like, R ¹ is preferably an aliphatic hydrocarbon group containing no heteroatoms. The aliphatic hydrocarbon group is preferably an unbranched linear aliphatic hydrocarbon group. This improves the adsorptivity to the polarizing film and enhances the effect of improving the optical performance. Specific examples of boronic acids in which R ¹ is an aliphatic hydrocarbon group include methylboronic acid, ethylboronic acid, propylboronic acid, butylboronic acid, pentylboronic acid, hexylboronic acid, heptylboronic acid, octylboronic acid, and nonylboronic acid. Acid, decanylboronic acid, undecanylboronic acid, dodecanylboronic acid, tridecanylboronic acid, tetradecanylboronic acid, pentadecanylboronic acid, hexadecanylboronic acid, heptadecanylboronic acid, octadecanylboron acids, nonadecanylboronic acid, icosanylboronic acid and their isomers, cyclopropylboronic acid, cyclobutylboronic acid, cyclopentylboronic acid, cyclohexylboronic acid, cycloheptylboronic acid, cyclooctylboronic acid, cyclononylboronic acid, cyclo decanylboronic acid, cycloundecanylboronic acid, cyclododecanylboronic acid, cyclotridecanylboronic acid, cyclotradecanylboronic acid, cyclopentadecanylboronic acid, cyclohexadecanylboronic acid, cycloheptadecanyl Examples include boronic acid, cyclooctadecanylboronic acid, cyclononadecanylboronic acid, cycloicosanylboronic acid and isomers thereof. In addition, examples of compounds that can be converted into monoboronic acids in the presence of water include salts of the monoboronic acids.

Specifically, R ¹ is preferably an alkyl group, more preferably an alkyl group represented by the following formula (IV).

In the above formula (IV), n is 1-20. n is preferably 10 or less, more preferably 6 or less, and even more preferably 5 or less. On the other hand, n is preferably 2 or more, more preferably 3 or more.

R ¹ is particularly preferably a saturated aliphatic hydrocarbon group having 2 to 5 carbon atoms from the viewpoint of obtaining a polarizing film having extremely low shrinkage force at high temperatures and excellent optical performance.

Specific examples of monoboronic acids represented by formula (I) include methylboronic acid, ethylboronic acid, propylboronic acid, butylboronic acid, pentylboronic acid, hexylboronic acid, heptylboronic acid, octylboronic acid, nonylboronic acid, decanylboronic acid, undecanylboronic acid, dodecanylboronic acid, tridecanylboronic acid, tetradecanylboronic acid, pentadecanylboronic acid, hexadecanylboronic acid, heptadecanylboronic acid, octadecanylboronic acid, Nonadecanylboronic acid, icosanylboronic acid, and isomers thereof are preferred, and propylboronic acid, butylboronic acid, and pentylboronic acid are preferred because of their good adsorptivity to the polarizing film and high effect of improving optical performance. Especially preferred. Further, examples of the compound that can be converted to the monoboronic acid represented by the above formula (I) in the presence of water include salts of the monoboronic acid.

The boron element content derived from the boron-containing compound (B) in the polarizing film of the present invention should be 0.1 to 3.0 parts by mass with respect to 100 parts by mass of PVA (A). If the elemental boron content derived from the boron-containing compound (B) is less than 0.1 parts by mass, the effect of improving optical performance becomes insufficient. The boron element content is preferably 0.2 parts by mass or more, more preferably 0.4 parts by mass or more. On the other hand, if the content of elemental boron derived from the boron-containing compound (B) exceeds 3.0 parts by mass, there is a possibility that the productivity may be lowered, such as requiring a long treatment time. Also, although the reason is not clear, if the elemental boron content exceeds 3.0 parts by mass, the iodine complex that absorbs short-wavelength light may be poorly formed and optical performance may deteriorate, which is not preferable. The boron element content is particularly preferably 2.0 parts by mass or less. The boron element content derived from the boron-containing compound (B) in the polarizing film can be obtained by ¹ H-NMR measurement.

The polarizing film of the invention may further contain boric acid. This may further improve the optical performance. At this time, the total boron element content in the polarizing film is preferably 0.2% by mass or more. Here, the total boron element content refers to the boron element derived from the boron-containing compound (B), the boron element derived from boric acid, and the boron-containing compound (B) and boron-containing compounds other than boric acid contained in the polarizing film. It is the total amount of the originating boron elements. On the other hand, if the total boron element content in the polarizing film is too high, the shrinkage force of the polarizing film may increase. The total boron element content in the polarizing film is usually 5.5% by mass or less, preferably 5.0% by mass or less, more preferably 4.5% by mass or less, and even more preferably It is 4.0% by mass or less. The total boron element content in the polarizing film can be determined by ICP emission analysis or the like.

The degree of polymerization of PVA (A) contained in the polarizing film of the present invention is preferably within the range of 1,500 to 6,000, more preferably within the range of 1,800 to 5,000, More preferably, it is in the range of 2,000 to 4,000. When the degree of polymerization is 1,500 or more, the durability of the polarizing film obtained by uniaxially stretching the film can be improved. On the other hand, when the degree of polymerization is 6,000 or less, it is possible to suppress an increase in production cost, poor processability during film formation, and the like. The degree of polymerization of PVA (A) in this specification means the average degree of polymerization measured according to the description of JIS K6726-1994.

The degree of saponification of the PVA (A) contained in the polarizing film of the present invention is preferably 95 mol% or more, more preferably 96 mol% or more, from the viewpoint of the water resistance of the polarizing film obtained by uniaxially stretching the film. is more preferable, and 98 mol % or more is even more preferable. In _this specification, the degree of saponification of PVA refers to structural units (typically vinyl ester units) and vinyl It refers to the ratio (mol%) of the number of moles of the vinyl alcohol unit to the total number of moles of the vinyl alcohol unit. The degree of saponification can be measured according to the description of JIS K6726-1994.

The method for producing PVA (A) used in the present invention is not particularly limited. For example, a method of converting a vinyl ester unit of a polyvinyl ester obtained by polymerizing a vinyl ester monomer into a vinyl alcohol unit can be mentioned. Vinyl ester monomers used in the production of PVA (A) are not particularly limited, but examples include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, and vinyl caproate. , vinyl caprylate, vinyl caprate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, vinyl benzoate, and the like. Vinyl acetate is preferred from an economic point of view.

Further, the PVA (A) used in the present invention is a vinyl ester unit of a vinyl ester copolymer obtained by copolymerizing a vinyl ester monomer and another monomer copolymerizable therewith, and a vinyl alcohol unit. may be converted to Other monomers copolymerizable with vinyl ester monomers include, for example, ethylene, propylene, 1-butene, α-olefins having 2 to 30 carbon atoms such as isobutene; (meth)acrylic acid or salts thereof; (meth)methyl acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, (meth)acrylic acid esters such as t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate; (meth)acrylamide, N-methyl (Meth)acrylamide, N-ethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, diacetone (meth)acrylamide, (meth)acrylamidopropanesulfonic acid or its salts, (meth)acrylamidopropyldimethylamine or its salts , N-methylol (meth)acrylamide or derivatives thereof; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, Vinyl ethers such as i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; vinyl cyanides such as (meth)acrylonitrile; vinyl chloride, vinylidene chloride, vinyl fluoride, fluorine vinyl halides such as vinylidene chloride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or its salts, esters or acid anhydrides; itaconic acid or its salts, esters or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane and unsaturated sulfonic acid. The above vinyl ester copolymer can have structural units derived from one or more of the above-described other monomers. The other monomer may be preliminarily present in the reaction vessel when the vinyl ester monomer is subjected to the polymerization reaction, or may be added to the reaction vessel during the progress of the polymerization reaction. You can use it by doing something like From the viewpoint of optical performance, the content of units derived from other monomers is preferably 10 mol% or less relative to the number of moles of all structural units constituting PVA (A), and is preferably 5 mol. % or less, more preferably 2 mol % or less.

Among the monomers that can be copolymerized with the above vinyl ester monomers, stretchability is improved and stretching can be performed at a higher temperature, which reduces the occurrence of troubles such as stretch breaks during the production of polarizing films. Ethylene is preferred because it further improves the productivity of the film. When PVA (A) contains ethylene units, the content of ethylene units is, from the viewpoint of stretchability and stretchable temperature as described above, with respect to the number of moles of all structural units constituting PVA (A), 1 to 10 mol % is preferred, and 2 to 6 mol % is more preferred.

The PVA film used for producing the polarizing film of the present invention can contain a plasticizer in addition to the PVA (A) described above. Preferred plasticizers include polyhydric alcohols, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like. Furthermore, one or more of these plasticizers can be included. Among these, glycerin is preferable from the viewpoint of the effect of improving stretchability.

The content of the plasticizer in the PVA film used for producing the polarizing film of the present invention is preferably in the range of 1 to 20 parts by mass, and 3 to 17 parts by mass, relative to 100 parts by mass of PVA (A). is more preferably within the range of , more preferably within the range of 5 to 15 parts by mass. When the content is 1 part by mass or more, the stretchability of the film is improved. On the other hand, when the content is 20 parts by mass or less, it is possible to prevent the film from becoming too soft and the handleability from deteriorating.

The PVA film used in the production of the polarizing film of the present invention may further contain fillers, processing stabilizers such as copper compounds, weather stabilizers, colorants, ultraviolet absorbers, light stabilizers, antioxidants, and antistatic agents. agents, flame retardants, other thermoplastic resins, lubricants, fragrances, antifoaming agents, deodorants, bulking agents, release agents, release agents, reinforcing agents, cross-linking agents, antifungal agents, preservatives, crystallization rate Additives other than the PVA (A) and the plasticizer, such as a retarder, can be appropriately blended as needed. The content of other additives in the PVA film is usually 10% by mass or less, preferably 5% by mass or less.

The degree of swelling of the PVA film used for producing the polarizing film of the present invention is preferably in the range of 160 to 240%, more preferably in the range of 170 to 230%, and more preferably in the range of 180 to 220%. It is particularly preferred to be within When the degree of swelling is 160% or more, extreme progress of crystallization can be suppressed, and the film can be stably stretched up to a high draw ratio. On the other hand, when the degree of swelling is 240% or less, dissolution during stretching is suppressed, and stretching can be performed even at higher temperatures.

The thickness of the PVA film used for producing the polarizing film of the present invention is not particularly limited, but is generally 1 to 100 μm, preferably 5 to 60 μm, particularly preferably 10 to 45 μm. If the PVA film is too thin, stretch breakage tends to occur during the uniaxial stretching process for producing the polarizing film. Further, if the PVA film is too thick, there is a tendency that stretching unevenness is likely to occur during the uniaxial stretching treatment for producing the polarizing film, and that the shrinkage force of the produced polarizing film is likely to be large.

The width of the PVA film used for producing the polarizing film of the present invention is not particularly limited, and can be determined depending on the intended use of the produced polarizing film. In recent years, the screen size of liquid crystal televisions and liquid crystal monitors has been increasing. Therefore, if the width of the PVA film used for manufacturing the polarizing film is set to 3 m or more, it is suitable for these uses. On the other hand, if the width of the PVA film used for the production of the polarizing film is too large, it tends to be difficult to carry out uniform uniaxial stretching when producing the polarizing film using a practical apparatus. The width of the PVA film used for is preferably 10 m or less.

The production method of the PVA film used for producing the polarizing film of the present invention is not particularly limited, and a production method that makes the thickness and width of the film after film formation uniform is preferably employed. For example, PVA (A), and, if necessary, one or more of the plasticizer, the other additives, and the surfactant described below are dissolved in a liquid medium. , PVA (A), and, if necessary, one or more of plasticizers, other additives, surfactants, liquid media, etc., and when PVA (A) is melted It can be produced using a membrane-forming stock solution. When the membrane-forming stock solution contains at least one of a plasticizer, other additives, and a surfactant, it is preferable that these components are uniformly mixed.

Examples of the liquid medium used for preparing the membrane-forming stock solution include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol. , trimethylolpropane, ethylenediamine, diethylenetriamine, etc., and one or more of these can be used. Among them, water is preferable from the viewpoint of load on the environment and recoverability.

The volatile content of the film-forming solution (the content of volatile components such as liquid media removed by volatilization or evaporation during film-forming in the film-forming solution) varies depending on the film-forming method, film-forming conditions, etc., but generally Specifically, it is preferably in the range of 50 to 95% by mass, more preferably in the range of 55 to 90% by mass. When the volatile content of the membrane-forming stock solution is 50% by mass or more, the viscosity of the membrane-forming stock solution does not become too high, and filtration and defoaming are performed smoothly during the preparation of the membrane-forming stock solution, resulting in a film with few foreign substances and defects. facilitating the manufacture of On the other hand, when the volatile content of the membrane-forming stock solution is 95% by mass or less, the concentration of the membrane-forming stock solution does not become too low, thereby facilitating industrial film production.

The membrane-forming stock solution preferably contains a surfactant. Inclusion of a surfactant improves the film formability, suppresses the occurrence of uneven thickness of the film, and facilitates the peeling of the film from the metal roll or belt used for film formation. When a PVA film is produced from a film-forming stock solution containing a surfactant, the film may contain the surfactant. Although the type of the surfactant is not particularly limited, an anionic surfactant or a nonionic surfactant is preferable from the viewpoint of releasability from a metal roll or belt.

Examples of suitable anionic surfactants include carboxylic acid type surfactants such as potassium laurate; sulfuric acid type surfactants such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and sulfonic acid type surfactants such as dodecylbenzene sulfonate.

Examples of nonionic surfactants include alkyl ether types such as polyoxyethylene oleyl ether; alkylphenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; alkylamine type such as ether; alkylamide type such as polyoxyethylene lauric acid amide; polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; Allyl phenyl ether types such as alkylene allyl phenyl ether are preferred.

These surfactants can be used singly or in combination of two or more.

When the membrane-forming stock solution contains a surfactant, the content thereof is preferably in the range of 0.01 to 0.5 parts by weight with respect to 100 parts by weight of PVA (A) contained in the membrane-forming stock solution. , more preferably in the range of 0.02 to 0.3 parts by mass, and particularly preferably in the range of 0.05 to 0.2 parts by mass. When the content is 0.01 parts by mass or more, film formability and peelability are further improved. On the other hand, when the content is 0.5 parts by mass or less, it is possible to prevent the surfactant from bleeding out to the surface of the PVA film, causing blocking, and lowering the handleability.

Examples of the film-forming method for forming a PVA film using the film-forming stock solution include a cast film-forming method, an extrusion film-forming method, a wet film-forming method, and a gel film-forming method. These film-forming methods may employ only one type or a combination of two or more types. Among these film-forming methods, the cast film-forming method and the extrusion film-forming method are preferable because a PVA film used for the production of a polarizing film having uniform thickness and width and good physical properties can be obtained. The formed PVA film can be dried or heat-treated as necessary.

Specific examples of the method for producing the PVA film used for producing the polarizing film of the present invention include, for example, using a T-shaped slit die, a hopper plate, an I-die, a lip coater die, etc., to prepare the above film-forming stock solution. A film that is uniformly discharged or cast on the circumferential surface of a rotating heated first roll (or belt) located on the most upstream side and discharged or cast on the circumferential surface of this first roll (or belt) drying by evaporating volatile components from one side of the, followed by further drying on the peripheral surface of one or more rotating heated rolls arranged downstream thereof, or in a hot air dryer It is possible to industrially preferably employ a method of passing through and further drying and then winding up with a winding device. Drying with heated rolls and drying with a hot air dryer may be combined as appropriate. Alternatively, a multilayer PVA film may be formed by forming a layer of PVA (A) on one side of a substrate film composed of a single resin layer.

The method for producing the polarizing film of the present invention is not particularly limited. A suitable manufacturing method is a method for manufacturing a polarizing film comprising a dyeing treatment of dyeing a PVA film with a dichroic dye and a stretching treatment of uniaxially stretching the film, wherein the film is immersed in an aqueous solution of a boron-containing compound (B). It is a method for producing a polarizing film having a treatment to do. The PVA film may be subjected to dyeing treatment, uniaxial stretching treatment, and, if necessary, swelling treatment, boric acid cross-linking treatment, fixing treatment, washing treatment, drying treatment, heat treatment, and the like. In this case, the order of each treatment such as swelling treatment, dyeing treatment, boric acid cross-linking treatment, uniaxial stretching treatment, and fixing treatment is not particularly limited, and one or more treatments can be performed simultaneously. Also, one or more of each treatment may be performed two or more times.

The swelling treatment can be performed by immersing the PVA film in water. The temperature of the water in which the film is immersed is preferably in the range of 20 to 40°C, more preferably in the range of 22 to 38°C, even more preferably in the range of 25 to 35°C. . The time for immersion in water is, for example, preferably within the range of 0.1 to 5 minutes, more preferably within the range of 0.2 to 3 minutes. The water in which the film is immersed is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or a mixture of water and a hydrophilic medium.

The dyeing treatment can be performed by bringing a dichroic dye into contact with the PVA film. As dichroic dyes, iodine-based dyes and dichroic dyes are generally used. The timing of the dyeing treatment may be any stage before the uniaxial stretching treatment, during the uniaxial stretching treatment, or after the uniaxial stretching treatment. The dyeing treatment is generally carried out by immersing the PVA film in a solution (especially an aqueous solution) containing iodine-potassium iodide as a dyeing bath, or in a solution (especially an aqueous solution) containing a plurality of dichroic dyes. be. The concentration of iodine in the dyeing bath is preferably in the range of 0.01 to 0.5% by mass, and the concentration of potassium iodide is preferably in the range of 0.01 to 10% by mass. The temperature of the dyeing bath is preferably 20-50°C, more preferably 25-40°C. A suitable staining time is 0.2 to 5 minutes. When a dichroic dye is used, the dichroic dye is preferably an aqueous dye. Further, the dye concentration in the dyeing bath is preferably 0.001 to 10% by mass. In addition, if necessary, a dyeing assistant may be used, and an inorganic salt such as sodium sulfate, a surfactant, or the like may be used. When using sodium sulfate, it is preferably 0.1 to 10% by mass. The dyeing temperature is preferably 30-80°C. Specific dichroic dyes include C.I. i. Direct Yellow 28, C.I. i. Direct Orange 39, C.I. i. Direct Yellow 12, C.I. i. Direct Yellow 44, C.I. i. Direct Orange 26, C.I. i. Direct Orange 71, C.I. i. direct. Orange 107, C.I. i. Direct Red 2, C.I. i. Direct Red 31, C.I. i. direct. Red 79, C.I. i. Direct Red 81, C.I. i. Direct Red 247, C.I. i. Direct Green 80, C.I. i. Dichroic dyes developed for manufacturing polarizing plates are preferred, although Direct Green 59 and the like can be mentioned.

A boric acid cross-linking treatment can also be applied to the PVA film. In this case, it is possible to more effectively prevent the PVA (A) from eluting into water during wet stretching at a high temperature. From this point of view, the boric acid cross-linking treatment is preferably performed before the uniaxial stretching treatment. The boric acid cross-linking treatment can be performed by immersing the PVA film in an aqueous solution containing a boric acid cross-linking agent. As the boric acid cross-linking agent, one or more of boron-containing inorganic compounds such as boric acid and borates such as borax can be used. The concentration of the boric acid cross-linking agent in the aqueous solution containing the boric acid cross-linking agent is preferably within the range of 0.1 to 6.0% by mass. More preferably, the concentration of the boric acid cross-linking agent is 0.2% by mass or more. Moreover, it is more preferable that it is 4.0 mass % or less. When the concentration of the boric acid cross-linking agent is within the above range, stretchability may be improved in some cases. If the concentration of the boric acid cross-linking agent is too high, it may become difficult to include the boron-containing compound (B) in the subsequent steps, so the concentration should not be too high. The aqueous solution containing the boric acid cross-linking agent may contain an auxiliary agent such as potassium iodide. The temperature of the aqueous solution containing the boric acid cross-linking agent is preferably within the range of 20-50°C, particularly within the range of 25-40°C.

Apart from the uniaxial stretching treatment described later, the PVA film may be stretched (pre-stretched) during or between the above-described treatments. Thus, the total draw ratio of the pre-stretching performed before the uniaxial stretching treatment (the ratio obtained by multiplying the draw ratios in each treatment) depends on the raw material before stretching from the viewpoint of the optical performance of the resulting polarizing film. Based on the original length of the PVA film, it is preferably 1.5 times or more, more preferably 2.0 times or more, and even more preferably 2.5 times or more. On the other hand, the total draw ratio is preferably 4.0 times or less, more preferably 3.5 times or less. The draw ratio in the swelling treatment is preferably 1.05 to 2.5 times. The draw ratio in the dyeing treatment is preferably 1.1 to 2.5 times. The draw ratio in the boron cross-linking treatment is preferably 1.1 to 2.5.

The uniaxial stretching treatment may be performed by either a wet stretching method or a dry stretching method. In the wet drawing method, the film is drawn in an aqueous solution. It can also be stretched in the above dyeing bath or in an aqueous solution of boric acid. In the case of the dry stretching method, the uniaxial stretching treatment may be performed at room temperature, the uniaxial stretching treatment may be performed while heating, or the uniaxial stretching treatment may be performed in the air using the PVA film after absorbing water. can also Among these, the wet stretching method is preferred, and the uniaxial stretching treatment in an aqueous solution containing boric acid is more preferred. The concentration of boric acid in the boric acid aqueous solution is preferably in the range of 0.5 to 6% by mass, more preferably in the range of 1 to 5% by mass. Further, the boric acid aqueous solution may contain potassium iodide, and its concentration is preferably in the range of 0.01 to 10% by mass. The stretching temperature in the uniaxial stretching treatment is preferably 30° C. or higher, more preferably 40° C. or higher, and even more preferably 50° C. or higher. On the other hand, the stretching temperature is preferably 90° C. or lower, more preferably 80° C. or lower, and even more preferably 70° C. or lower. Moreover, the draw ratio in the uniaxial drawing treatment is preferably 2.0 to 4.0 times. From the viewpoint of the optical performance of the obtained polarizing film, the draw ratio is more preferably 2.2 times or more. On the other hand, the draw ratio is more preferably 3.5 times or less. In addition, the total draw ratio before fixing treatment, which will be described later, is preferably 5 times or more based on the original length of the raw material PVA film before drawing, from the viewpoint of the optical performance of the resulting polarizing film. It is more preferably 5 times or more. Although the upper limit of the draw ratio is not particularly limited, the draw ratio is preferably 8 times or less.

When a long PVA film is uniaxially stretched, the direction of uniaxial stretching is not particularly limited, and uniaxial stretching in the longitudinal direction, horizontal uniaxial stretching, or so-called oblique stretching can be employed. A uniaxial stretching treatment in the longitudinal direction is preferable because a polarizing film having excellent optical performance can be obtained. The uniaxial stretching treatment in the longitudinal direction can be performed by using a stretching device having a plurality of rolls parallel to each other and changing the peripheral speed between the rolls. On the other hand, transverse uniaxial stretching can be performed using a tenter type stretching machine.

In the production of the polarizing film, it is preferable to carry out a fixing treatment after the uniaxial stretching treatment in order to strengthen the adsorption of the dichroic dye (such as an iodine dye) to the PVA film. An aqueous solution containing the boron-containing compound (B) is preferably used as the fixation treatment bath used for the fixation treatment. Moreover, boric acid, an iodine compound, a metal compound, or the like may be further added to the fixing treatment bath, if necessary. The temperature of the fixing treatment bath is preferably 10-80°C. The draw ratio in the fixing treatment is preferably 1.3 times or less, more preferably 1.2 times or less, and still more preferably less than 1.1 times.

The boron-containing compound (B) may be adsorbed to the polarizing film in any of the steps of dyeing treatment, boric acid cross-linking treatment, uniaxial stretching treatment, and fixing treatment. It is particularly preferable from the viewpoint that the PVA film is prevented from being cut during the stretching process. Moreover, the boron-containing compound (B) may be used not only by one type but also by mixing two or more types. The concentration of the boron-containing compound (B) in the aqueous solution is preferably 0.05 to 15% by mass. When the concentration of the boron-containing compound (B) in the aqueous solution is lower than 0.05% by mass, the adsorption may be slowed down. It is even more preferable to have On the other hand, when the concentration of the boron-containing compound (B) in the aqueous solution is higher than 15% by mass, the boron-containing compound (B) may be unevenly distributed near the surface of the polarizing film. Optical performance may deteriorate. Moreover, there is also a possibility that a deposit of the boron-containing compound (B) may occur on the surface of the polarizing film. The concentration of the boron-containing compound (B) is more preferably 10% by mass or less, even more preferably 5.0% by mass or less, and particularly preferably 3.5% by mass or less. Further, the aqueous solution containing the boron-containing compound (B) preferably contains an iodide aid such as potassium iodide from the viewpoint of improving optical performance, and the concentration of the iodide is 0.5 to 15% by mass. is preferred. Moreover, the temperature of the aqueous solution is preferably 10 to 80°C. If the temperature is too low, the boron compound (B) may precipitate in the treatment bath. The temperature of the aqueous solution is more preferably 15° C. or higher, more preferably 20° C. or higher. On the other hand, if the temperature is too high, it will be difficult to manufacture easily industrially under relatively mild conditions. The temperature of the aqueous solution is more preferably 70° C. or lower, still more preferably 60° C. or lower, and particularly preferably 45° C. or lower. The immersion time in the aqueous solution is preferably 5 to 400 seconds.

A suitable manufacturing method for adsorbing the boron-containing compound (B) to the polarizing film during the fixation treatment is to perform swelling treatment, uniaxial stretching treatment, and fixing treatment in this order, swelling treatment, boric acid cross-linking treatment, and uniaxial stretching treatment. , fixing treatment in this order, or swelling treatment, uniaxial stretching treatment, fixing treatment, and boric acid cross-linking treatment in this order. After this, one or more treatments selected from washing treatment, drying treatment and heat treatment may be further performed as necessary.

The washing treatment is generally carried out by immersing the film in distilled water, pure water, an aqueous solution, or the like. At this time, from the viewpoint of improving optical performance, it is preferable to use an aqueous solution containing an iodide such as potassium iodide as an auxiliary agent, and the concentration of the iodide is preferably 0.5 to 10% by mass. The temperature of the aqueous solution in the cleaning treatment is generally 5 to 50°C, preferably 10 to 45°C, more preferably 15 to 40°C. From an economical point of view, it is not preferable that the temperature of the aqueous solution is too low, and if the temperature of the aqueous solution is too high, the optical performance may deteriorate.

The conditions for the drying treatment are not particularly limited, but drying is preferably carried out at a temperature within the range of 30 to 150°C, particularly within the range of 50 to 130°C. By drying at a temperature within the range of 30 to 150° C., it is easy to obtain a polarizing film with excellent dimensional stability.

By performing a heat treatment after the drying treatment, it is possible to obtain a polarizing film with even better dimensional stability. Here, the heat treatment means a treatment for further heating a polarizing film having a moisture content of 5% or less after drying to improve the dimensional stability of the polarizing film. The heat treatment conditions are not particularly limited, but the heat treatment is preferably performed within the range of 60°C to 150°C, particularly within the range of 70°C to 150°C. If the heat treatment is performed at a temperature lower than 60° C., the dimensional stabilization effect of the heat treatment is insufficient, and if the heat treatment is performed at a temperature higher than 150° C., the polarizing film may undergo severe red discoloration.

It is preferable that the polarizing film of the present invention thus obtained has a transmittance of 42.0% or more and a degree of polarization of 99.9% or more. If the transmittance of the polarizing film is less than 42.0%, the resulting LCD may have insufficient brightness. The transmittance is more preferably 43.0% or higher, and even more preferably 43.5% or higher. On the other hand, the transmittance is usually 45% or less. In addition, since the degree of polarization of the polarizing film is 99.9% or more, an LCD panel with high image quality can be obtained. The transmittance and degree of polarization of the polarizing film are measured by the methods described in the examples below.

The polarizing film of the present invention is usually used as a polarizing plate by laminating an optically transparent protective film having mechanical strength on one or both sides thereof. As the protective film, a cellulose triacetate (TAC) film, a cellulose acetate-butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Further, examples of adhesives for bonding include PVA-based adhesives and UV curing adhesives.

The polarizing plate obtained as described above may be attached to a retardation film, a viewing angle improving film, a brightness improving film, or the like. Also, after coating the polarizing plate with an acrylic adhesive or the like, the polarizing plate can be bonded to a glass substrate and used as an LCD component.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples. In addition, each measurement or evaluation method adopted in the following examples and comparative examples is shown below.

[Measurement of boron element content derived from boron-containing compound (B) with respect to 100 parts by mass of PVA (A)]
After dissolving the polarizing film in heavy water to a concentration of 0.003% by mass, the solution was concentrated by a rotary evaporator to a concentration of 0.15% by mass and used as a sample for ¹ H-NMR measurement. ¹ H-NMR (JNM-AL400 manufactured by JEOL Ltd.: 400 MHz) was measured at 80° C., and the number of times of integration was set to 256 times. Analysis was performed by the following method using ALICE2 (manufactured by JEOL Ltd.). For the ¹ H-NMR chart obtained by the measurement, after adjusting the phase so that the baseline becomes smooth, the average point was set to 20 and the baseline was automatically corrected. Next, the reference was automatically set so that the peak of heavy water, which is the solvent for measurement, was at the position of 4.65 ppm. Thereafter, as shown in FIG. 1, the hydrogen peak of the hydrocarbon group contained in the boron-containing compound (B) was integrated to obtain the peak area (area A). At this time, the sum of the hydrogen peak areas of the hydrocarbon groups contained in the boron-containing compound (B) that does not overlap with the hydrogen peak derived from PVA (area B) is used as a reference for the peak area, and the boron-containing compound (B) It was set so that the number of hydrogen atoms and the area B of the corresponding hydrocarbon group of were the same. Next, the hydrogen peaks in the range of 1.6 ppm to 2.4 ppm are overlapped with the hydrogen peaks derived from the methylene groups of PVA and the hydrogen peaks derived from the methylene groups of PVA. Hydrocarbon groups contained in the boron-containing compound (B) The peak area (Area C) was determined by considering the sum of the hydrogen peaks of . Thereafter, the area D was calculated by subtracting from the area C the number of hydrogen atoms in the hydrocarbon groups of the boron-containing compound (B) overlapping the hydrogen peaks of the methylene groups derived from PVA. The values obtained by these methods were substituted into the following formula (1) to calculate the elemental boron content (parts by mass) derived from the boron-containing compound (B) with respect to 100 parts by mass of PVA (A). In the following formula (1), X is the number of hydrogen atoms in the hydrocarbon group contained in the boron-containing compound (B) that does not overlap with the PVA peak, and Y is the number of boron atoms per molecule of the boron-containing compound (B). . Formula (1) is a formula used when non-modified PVA is used, and when using modified PVA as a raw material, it is necessary to modify formula (1) as appropriate.
Boron element content (parts by mass) derived from the boron-containing compound (B) relative to 100 parts by mass of PVA (A)
= {(Area B/X)/(Area D/2)} x (10.811 x Y/44.0526)
×100 (1)
10.811 is the atomic weight of boron, and 44.0526 is the molecular weight per mole of repeating units of unmodified PVA. ^{The 1} H-NMR chart in FIG. 1 is obtained by measuring the polarizing film of Example 1.

[Calculation of total boron element content (mass%) in polarizing film]
The mass [E (g)] of the polarizing film was measured and dissolved in 20 mL of distilled water so that the polarizing film became 0.005% by mass. An aqueous solution in which the polarizing film was dissolved was used as a measurement sample, and its mass [F (g)] was measured. After that, the boron concentration [G (ppm)] of the measurement sample was measured using a multi-type ICP emission spectrometer (ICP) manufactured by Shimadzu Corporation. After that, the value calculated by substituting the value into the following formula (2) was taken as the total boron element content (% by mass) in the polarizing film.
Total boron element content in polarizing film (% by mass)
= [(G × 10 ^-6 × F) / E] × 100 (2)

[Optical Performance of Polarizing Film]
(1) Measurement of transmittance Ts Two samples of 4 cm in the stretching direction of the polarizing film and 2 cm in the width direction were taken from the center of the polarizing film obtained in the following examples or comparative examples, and spectroscopy with an integrating sphere was performed. Using a photometer ("V7100" manufactured by JASCO Corporation), in accordance with JIS Z 8722 (method for measuring object color), C light source, visibility correction in the visible light region of 2 ° field of view, one sheet For the sample, the light transmittance when tilted +45° and the light transmittance when tilted −45° with respect to the length direction were measured, and the average value Ts1 (%) was obtained. For the other sample, the light transmittance when tilted at +45° and the light transmittance when tilted at -45° were similarly measured, and the average value Ts2 (%) was obtained. Ts1 and Ts2 were averaged according to the following formula (3) to obtain the transmittance Ts (%) of the polarizing film.
Ts=(Ts1+Ts2)/2 (3)

(2) Measurement of the degree of polarization V The light transmittance T⊥ (%) when the two samples used in the measurement of the transmittance Ts are superimposed so that the stretching directions are orthogonal to each other, and the stretching The light transmittance T // (%) when the light is superimposed so that the directions are parallel is measured using a spectrophotometer with an integrating sphere ("V7100" manufactured by JASCO Corporation) according to JIS Z 8722 (object color Measurement method), C light source, luminosity correction in the visible light region of 2° field of view. The degree of polarization V (%) was obtained by substituting the measured T//(%) and T⊥ (%) into the following formula (4).
V={(T∥−T⊥)/(T∥+T⊥)} ^1/2 ×100 (4)

(3) Dichroism ratio (DC) at 650 nm
The dichroic ratio at each wavelength of the polarizing film was measured using a spectrophotometer with an integrating sphere equipped with a Glan-Taylor polarizer ("V7100" manufactured by JASCO Corporation). From the central part of the obtained polarizing film, a sample of 4 cm in the stretching direction of the polarizing film and 2 cm in the width direction is taken, and the MD transmittance and TD transmittance are obtained in the wavelength range of 380 nm to 780 nm, and the following formula ( 5), the dichroism ratio at each wavelength was calculated. Here, "MD transmittance" indicates the transmittance when the direction of polarized light emitted from the Glan-Taylor polarizer and the transmission axis of the polarizing plate sample are made parallel. Further, "TD transmittance" indicates the transmittance when the direction of polarized light emitted from the Glan-Taylor polarizer and the transmission axis of the polarizing plate sample are perpendicular to each other. In this example, the dichroism ratio at 650 nm was used as an index of optical performance.
DC={log ₁₀ (TD transmittance/100)}/{log ₁₀ (MD transmittance/100)} (5)

[Shrinkage force of polarizing film]
The shrinkage force was measured using an autograph with a constant temperature bath "AG-X" manufactured by Shimadzu Corporation and a video extensometer "TR ViewX120S". A polarizing film conditioned at 20° C./20% RH for 18 hours was used for the measurement. After setting the constant temperature bath of the autograph "AG-X" to 20 ° C, attach the polarizing film (15 cm in the length direction, 1.5 cm in the width direction) to the chuck (chuck interval 5 cm), and at the same time as starting pulling, heat the temperature to 80 ° C. Heating of the tank was started. The polarizing film was pulled at a speed of 1 mm/min, and when the tension reached 2 N, the pulling was stopped, and the tension was measured for 4 hours after that state. At this time, since the distance between the chucks changes due to thermal expansion, a marker line sticker is attached to the chuck, and the distance between the chucks is the amount of movement of the marker line sticker attached to the chuck using the video extensometer "TR View X120S". The measurement was performed while correcting so that . In addition, when the minimum value of tension occurs in the initial stage of measurement (within 10 minutes from the start of measurement), the minimum value of tension was subtracted from the measured value of tension after 4 hours, and the difference was taken as the shrinkage force of the polarizing film.

[Swelling degree of PVA film]
A PVA film was cut into 5 cm×10 cm and immersed in 1000 mL of distilled water at 30° C. for 30 minutes. After that, the PVA film was taken out, the moisture on the surface of the PVA film was wiped off with filter paper, and the PVA film mass (mass H) after immersion was measured. After that, the PVA film was placed in a drier at 105° C. and dried for 16 hours, and then the PVA film mass (mass I) after drying was measured. The degree of swelling of the PVA film was calculated by substituting the values of mass H and mass I into the following formula (6).
Degree of swelling (%) = (mass H / mass I) x 100 (6)

[Example 1]
Contains 100 parts by mass of PVA (degree of saponification 99.9 mol%, degree of polymerization 2400), 10 parts by mass of glycerin as a plasticizer, and 0.1 parts by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant, PVA content is 10% by mass as the film-forming stock solution, dried on a metal roll at 80°C, and the resulting film is heat treated in a hot air dryer at 120°C for 10 minutes to swell. The degree was adjusted to 200% to produce a PVA film with a thickness of 30 μm.

A sample of 5 cm wide by 9 cm long was cut from the central portion of the PVA film thus obtained in the width direction so that a range of 5 cm wide by 5 cm long could be uniaxially stretched. This sample was immersed in pure water at 30° C. for 30 seconds and uniaxially stretched 1.1 times in the length direction for swelling treatment. Subsequently, while immersing in an aqueous solution (dyeing treatment bath) (temperature 30 ° C.) containing 0.04% by mass of iodine and 4.0% by mass of potassium iodide (KI) for 60 seconds, the times) and uniaxially stretched in the length direction to adsorb iodine. Furthermore, while being immersed in an aqueous solution (crosslinking treatment bath) containing 3.0% by mass of boric acid and 3% by mass of potassium iodide (temperature: 30°C) for 45 seconds, it was lengthened 1.2 times (total 2.7 times). The film was uniaxially stretched in the longitudinal direction to adsorb boric acid. Then, while being immersed in an aqueous solution (stretching treatment bath) containing 4.0% by mass of boric acid and 6.0% by mass of potassium iodide (temperature of 60° C.), it was elongated 2.2 times (6.0 times in total). It was oriented by uniaxial stretching in the longitudinal direction. After that, it was immersed for 100 seconds in an aqueous solution (fixing treatment bath) containing 1.0% by mass of n-propylboronic acid and 4.0% by mass of potassium iodide (temperature: 30°C). In the fixing process, the PVA film was not stretched (stretch ratio of 1.0). Finally, it was dried at 60°C for 4 minutes to produce a polarizing film.

When ¹ H-NMR of the obtained polarizing film was measured and analyzed, a hydrogen peak of n-propylboronic acid that did not overlap with the hydrogen peak derived from PVA appeared at 1.1 to 1.3 ppm, so this peak area (Area B) was set to 5. Next, the peak area (Area C) of the hydrogen of the methylene group of PVA, in which the peak appeared in the range of 1.6 to 2.4 ppm, was calculated. Since the hydrogen peak of the methylene group of PVA and the hydrogen peak of the hydrocarbon group at C2 of n-propylboronic acid overlapped, the number of hydrogen atoms of the hydrocarbon group at C2 of n-propylboronic acid was subtracted from area C to obtain area D. asked for Substituting these values into the formula (1), the content of elemental boron derived from the boron-containing compound (B) was 1.5 parts by mass with respect to 100 parts by mass of PVA (A). Moreover, when the total boron element content in the polarizing film was measured, it was 3.4% by mass.

The optical properties of the obtained polarizing film were measured, and the transmittance was 44.14%, the degree of polarization was 99.96%, and the dichroic ratio was 83.88. Moreover, when the shrinkage force of the obtained polarizing film was measured, it was 4.8N. These results are also shown in Table 1. FIG. 2 shows a graph in which the degree of polarization is plotted against the shrinkage force of the polarizing film.

[Example 2]
A polarizing film was produced in the same manner as in Example 1, except that the time for immersion in the fixing treatment bath was changed to 300 seconds, and each measurement and each evaluation were performed by the above methods. The results are shown in Table 1 and FIG.

[Example 3]
A polarizing film was produced in the same manner as in Example 1 except that an aqueous solution containing 1.0% by mass of n-butylboronic acid and 3.0% by mass of potassium iodide (temperature: 30°C) was used as the fixing treatment bath. Then, each measurement and each evaluation were performed by the above method. The results are shown in Table 1 and FIG.

[Example 4]
A polarizing film was prepared in the same manner as in Example 1, except that an aqueous solution (temperature: 30°C) containing 0.5% by mass of n-butylboronic acid and 3.5% by mass of potassium iodide was used as the fixing treatment bath. Each measurement and each evaluation were performed by the above method. The results are shown in Table 1 and FIG.

[Example 5]
A polarizing film was prepared in the same manner as in Example 1 except that an aqueous solution containing 0.5% by mass of n-pentylboronic acid and 3.0% by mass of potassium iodide (treatment temperature: 30° C.) was used as the fixing treatment bath. was prepared, and each measurement and each evaluation were performed by the above method. The results are shown in Table 1 and FIG.

[Example 6]
An aqueous solution containing 1.0% by mass of methylboronic acid and 2.0% by mass of potassium iodide was used as the fixation treatment bath (treatment temperature: 30°C), and the immersion time in the fixation treatment bath was changed to 10 seconds. A polarizing film was produced in the same manner as in Example 1 except that the above was performed, and each measurement and each evaluation were performed by the above methods. The results are shown in Table 1 and FIG.

[Example 7]
An aqueous solution (temperature 62° C.) containing 0.5% by mass of n-propylboronic acid, 4.0% by mass of boric acid and 5.2% by mass of potassium iodide was used as a stretching treatment bath; A polarizing film in the same manner as in Example 1 except that an aqueous solution (temperature 30 ° C.) containing 3.0% by mass of potassium iodide was used as the was prepared, and each measurement and each evaluation were performed by the above method. The results are shown in Table 1 and FIG.

[Comparative Example 1]
The same as in Example 1 except that an aqueous solution containing 1.0% by mass of n-butylboronic acid (temperature: 10°C) was used as the fixation treatment bath, and that the time for immersion in the fixation treatment bath was set to 20 seconds. Then, a polarizing film was produced, and each measurement and each evaluation were performed by the above methods. At this time, regarding the measurement of the boron element content derived from the boron-containing compound (B) with respect to 100 parts by mass of PVA (A), the boron-containing compound (B) could not be detected when the number of times of integration was 256 times, so the number of times of integration was 4096 times. , the boron element content derived from the boron-containing compound (B) relative to 100 parts by mass of PVA (A) was measured. The results are shown in Table 1 and FIG.

[Comparative Example 2]
A polarizing film was produced in the same manner as in Example 1, except that an aqueous solution (temperature: 30°C) containing 1.0% by mass of phenylboronic acid and 1.0% by mass of potassium iodide was used as the fixing treatment bath. , Each measurement and each evaluation were performed by the above method. The results are shown in Table 1 and FIG.

[Comparative Example 3]
A polarizing film was produced in the same manner as in Example 1, except that an aqueous solution (temperature: 30°C) containing 2.0% by mass of boric acid and 2.5% by mass of potassium iodide was used as the fixing treatment bath. , Each measurement and each evaluation were performed by the above method. The results are shown in Table 1 and FIG.

[Comparative Example 4]
A polarizing film was produced in the same manner as in Example 1, except that an aqueous solution (temperature: 30°C) containing 1.0% by mass of boric acid and 2.0% by mass of potassium iodide was used as the fixing treatment bath. , Each measurement and each evaluation were performed by the above method. The results are shown in Table 1 and FIG.

[Comparative Example 5]
A polarizing film was produced in the same manner as in Example 1, except that an aqueous solution (temperature: 30°C) containing 0.5% by mass of boric acid and 2.0% by mass of potassium iodide was used as the fixing treatment bath. , Each measurement and each evaluation were performed by the above method. The results are shown in Table 1 and FIG.

[Comparative Example 6]
A polarizing film was produced in the same manner as in Example 1 except that the fixing treatment was not performed, and each measurement and each evaluation were performed by the above methods. The results are shown in Table 1 and FIG.

[Comparative Example 7]
The same as in Example 1 except that an aqueous solution containing 2.0% by mass of potassium iodide (temperature: 30°C) was used as the fixation treatment bath, and that the time for immersion in the fixation treatment bath was set to 5 seconds. Then, a polarizing film was produced, and each measurement and each evaluation were performed by the above methods. The results are shown in Table 1 and FIG.

[Comparative Example 8]
A polarizing film was prepared in the same manner as in Comparative Example 7 except that the time for immersion in the fixing treatment bath was set to 10 seconds, and each measurement and each evaluation were performed by the above methods. The results are shown in Table 1 and FIG.

[Comparative Example 9]
A polarizing film was produced in the same manner as in Comparative Example 7 except that the time for immersion in the fixing treatment bath was set to 20 seconds, and each measurement and each evaluation were performed by the above methods. The results are shown in Table 1 and FIG.

In Examples 2 to 7 and Comparative Examples 1 to 9, an aqueous solution (temperature: 30° C.) containing iodine and potassium iodide at a mass ratio of 1:100 was used as the dyeing treatment bath. At this time, the concentration of iodine and potassium iodide in the dyeing treatment bath was adjusted so that the transmittance of the polarizing film after drying was 43.8% to 44.2%.

FIG. 2 is a graph plotting the shrinkage force on the horizontal axis and the degree of polarization on the vertical axis for the polarizing films of Examples 1 to 7 and Comparative Examples 1 and 3 to 9. As shown in FIG. 2, the polarizing films of Examples 1 to 7, which satisfy the stipulations of the present invention, had small shrinkage force at high temperatures and excellent optical performance. On the other hand, the polarizing film (Comparative Example 1) in which the elemental boron content derived from the boron-containing compound (B) was less than 0.1 parts by mass had high shrinkage force. The polarizing film containing phenylboronic acid as the boron element compound (Comparative Example 2) has high shrinkage force and insufficient optical performance, and falls outside the range of the graph. When an aqueous solution containing boric acid and potassium iodide was used as the fixing treatment bath (Comparative Examples 3 to 5), the concentration of boric acid in the aqueous solution was lowered to reduce the total elemental boron content in the polarizing film. Although the shrinkage force decreased, the optical performance decreased, and it was difficult to achieve both. When the fixing treatment was not performed (Comparative Example 6), the shrinkage force of the polarizing film was significantly high. Further, when an aqueous solution containing potassium iodide was used as the fixing treatment bath (Comparative Examples 7 to 9), the optical performance of the polarizing film was insufficient. As described above, in the cases where the provisions of the present invention were not satisfied (Comparative Examples 1 to 9), it was difficult to achieve both shrinkage characteristics and optical performance.

1 Hydrogen peak derived from heavy water as a measurement solvent 2 Hydrogen peak derived from methine group of PVA 3 Hydrogen peak derived from methylene group of PVA 4 Hydrocarbon group contained in boron-containing compound (B) overlapping with hydrogen peak derived from PVA A hydrogen peak derived from a hydrocarbon group contained in the boron-containing compound (B) that does not overlap with a hydrogen peak derived from 5 PVA

Claims (4)

Polyvinyl alcohol (A) and at least one boron-containing compound (B) selected from the group consisting of monoboronic acids represented by the following formula (I) and compounds that can be converted to the monoboronic acids in the presence of water A polarizing film comprising, the boron element content derived from the boron-containing compound (B) in the polarizing film is 0.1 to 3.0 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A), The polarizing film, wherein the compound convertible to the monoboronic acid in the presence of water is an ester formed by reacting the monoboronic acid with polyvinyl alcohol (A).

[In formula (I), R ¹ is a monovalent heteroatom-free saturated aliphatic hydrocarbon group having 1 to 20 carbon atoms , and R ¹ and a boronic acid group are linked via a boron-carbon bond. . ] The polarizing film according to claim 1 , wherein R ¹ has 2 to 5 carbon atoms. 3. The polarizing film according to claim 1 , which has a transmittance of 42.0% or more and a degree of polarization of 99.9% or more. In a method for producing a polarizing film comprising a dyeing treatment of dyeing a polyvinyl alcohol film with a dichroic dye and a stretching treatment of uniaxially stretching the film, the film is immersed in an aqueous solution of the boron-containing compound (B). A method for producing a polarizing film according to any one of claims 1 to 3 , characterized by:

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