KR102682994B1 - Polarizing film and its manufacturing method - Google Patents

Abstract

At least one boron-containing compound (B) selected from the group consisting of polyvinyl alcohol (A), diboronic acid represented by the following formula (I), and compounds capable of being converted to diboronic acid in the presence of water, and boric acid (C) A polarizing film containing a boron element concentration (α) derived from the boron-containing compound (B) of 1 to 7 atomic% in a range from the surface of the polarizing film to 1 μm inward, and from the center outward. In the range up to 1 μm, the boron element concentration (β) derived from the boron-containing compound (B) is 0.1 to 2 at%, and the ratio (α/β) of the concentration (α) to the concentration (β) is Use a polarizing film with a rating of 1.5 or higher. The polarizing film has good polarization performance and color, and has low shrinkage force.
[In formula (I), R ¹ is a divalent organic group having 1 to 20 carbon atoms, and R ¹ and two boronic acid groups are connected by a boron-carbon bond.]

Description

Polarizing film and its manufacturing method

The present invention relates to a polarizing film with good polarization performance and color and low shrinkage force, and a method for producing the same.

A polarizer, which has the function of transmitting and blocking 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 cellulose triacetate (TAC) film is bonded to the surface of the polarizing film in order to prevent the polarizing film from fading or shrinking. The constituting polarizing film contains an iodine-based dye (I ₃ ^- , I ₅ ^-, etc.) in a matrix formed by uniaxially stretching a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be referred to as "PVA"). What is adsorbed has become the mainstream.

LCDs are widely used in small devices such as electronic desk calculators and wristwatches, smart phones, laptop computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, and measuring instruments. Recently, these devices are required to be thinner and lighter, and the glass used in LCDs is becoming thinner. However, as the glass becomes thinner, bending of the LCD panel occurs, which is a problem. It is said that the main cause of LCD panel warpage is shrinkage of the polarizing film that occurs at high temperatures, and a polarizing film with low shrinkage force is required. In addition, improvements in the contrast of LCDs are required, and improvements in polarization performance and color of polarizing films are also required.

In Patent Document 1, after performing the dyeing process, crosslinking process, and stretching process, a first drying process of drying the PVA film at 25 ° C. or higher and less than 65 ° C. and a second drying process of drying the PVA film at 65 ° C. or higher and 115 ° C. or lower are performed. A method for producing a polarizing film is described. Patent Document 1 describes that, according to the method, shrinkage of the polarizing film under high temperature can be reduced and dimensional stability can be improved. However, since drying was performed at a high temperature, there was a problem that the polarization performance of the obtained polarizing film was lowered or the color became worse.

Patent Document 2 describes a method of preventing shrinkage of the polarizing film and improving heat resistance by treating the PVA film with diboronic acid in the swelling process, dyeing process, or stretching process. However, the polarizing film had the problem of low polarization performance and poor color.

Patent Document 3 describes that by reducing the amount of boric acid in the PVA film and providing a process for drying the PVA film between the boric acid treatment process and the water washing process, a polarizing film with small shrinkage force under high temperature and good color can be obtained. . However, if the amount of boric acid in the polarizing film is reduced, the shrinkage force decreases, but it is difficult to maintain high polarization performance.

Japanese Patent Publication No. 2015-028634 KR10-2014-0075154 Japanese Patent Publication No. 2013-148806

The purpose of the present invention is to provide a polarizing film with good polarization performance and color and low shrinkage force, and a simple manufacturing method thereof.

The above problem includes at least one boron-containing compound (B) selected from the group consisting of PVA (A), diboronic acid represented by the following formula (I), and a compound capable of being converted to diboronic acid in the presence of water, and boric acid ( A polarizing film containing C), wherein the boron element concentration (α) derived from the boron-containing compound (B) in the range from the surface of the polarizing film to 1 μm inward is 1 to 7 atomic%, and from the center The boron element concentration (β) derived from the boron-containing compound (B) in the range outward to 1 μm is 0.1 to 2 atomic%, and the ratio of concentration (α) to concentration (β) (α/β) ) is solved by providing a polarizing film characterized in that it is 1.5 or more.

[Formula 1]

[In formula (I), R ¹ is a divalent organic group having 1 to 20 carbon atoms, and R ¹ and two boronic acid groups are connected by a boron-carbon bond.]

It is preferable that 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 also preferable that R ¹ is an aliphatic group. It is also preferable that the total boron element content in the polarizing film is 1.0 to 5.0 mass%.

The above problem is 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 in an aqueous solution of boric acid, wherein the boron element content derived from boric acid is 0.5 to 5.0. This problem can also be solved by providing a method for producing the above-described polarizing film, in which the PVA film after stretching treatment is immersed in an aqueous solution with a boron-containing compound (B) concentration of 0.1 to 5.0 mass%, and then the film is dried at 95° C. or lower. do.

The polarizing film of the present invention has good polarization performance and color, and has low shrinkage force. According to the manufacturing method of the present invention, such a polarizing film can be easily manufactured.

1 is a ¹ H-NMR chart of the polarizing film obtained in Example 1.

The polarizing film of the present invention contains at least one boron-containing compound (B) selected from the group consisting of PVA (A), diboronic acid represented by the following formula (I), and a compound that can be converted to diboronic acid in the presence of water. and boric acid (C), wherein the boron element concentration (α) derived from the boron-containing compound (B) in the range from the surface of the polarizing film to 1 μm inward is 1 to 7 atomic%. , the boron element concentration (β) derived from the boron-containing compound (B) in the range from the center to the outside is 0.1 to 2 atomic%, and the ratio of the concentration (α) to the concentration (β) is ( α/β) is 1.5 or more.

[Formula 2]

[In formula (I), R ¹ is a divalent organic group having 1 to 20 carbon atoms, and R ¹ and two boronic acid groups are connected by a boron-carbon bond.]

The boron element concentration (α) derived from the boron-containing compound (B) in the range from the surface of the polarizing film to 1 μm inward must be 1 to 7 atomic%. When the boron element concentration (α) is less than 1 atomic%, the amount of crosslinking near the surface of the polarizing film is too small, and polarization performance becomes insufficient. The boron element concentration (α) is preferably 2 atomic% or more. On the other hand, when the boron element concentration (α) exceeds 7 atomic%, the surface becomes too hard and the polarizing film becomes prone to tearing. The boron element concentration (α) is preferably 6 atomic% or less.

Moreover, the boron element concentration (β) derived from the boron-containing compound (B) in a range from the center of the polarizing film to the outside of 1 μm must be 0.1 to 2 atomic%. When the boron element concentration (β) exceeds 2 atomic%, polarization performance decreases or color worsens. Although the reason for this is not clear, it is thought that the cause is that the boron-containing compound (B) inhibits the formation of an iodine complex that absorbs short-wavelength light. The boron element concentration (β) is preferably 1 atomic% or less. On the other hand, when the boron element concentration (β) is less than 0.1 atomic%, the shrinkage force of the polarizing film increases. The boron element concentration (α) and boron element concentration (β) in the polarizing film can be determined using an X-ray photoelectron spectrometer (GCIB XPS) equipped with a gas cluster ion beam gun. Specifically, it can be obtained by the method described in the Examples described later.

The thickness of the polarizing film is preferably 5 to 30 μm. If the thickness is less than 5 μm, stretching breaks are likely to occur during manufacturing, and there is a risk that productivity may decrease. The thickness is preferably 10 μm or more. On the other hand, if the thickness exceeds 30 μm, there is a risk that the performance required for the polarizing plate, such as thinning or lightening, may not be met.

In the polarizing film, the ratio (α/β) of the boron element concentration (α) to the boron element concentration (β) needs to be 1.5 or more. When the ratio (α/β) is less than 1.5, polarization performance may become insufficient or color may deteriorate. The ratio (α/β) is preferably 2 or more, and more preferably 3 or more. On the other hand, the above ratio (α/β) is usually 50 or less.

As mentioned above, a major feature of the polarizing film is that the boron element derived from the boron-containing compound (B) has a predetermined concentration distribution in the thickness direction. When the boron-containing compound (B) is adsorbed on a PVA film by a general method, there is no substantial difference in concentration near the surface and the center of the film, and the effect of reducing the shrinkage force is obtained, but there are cases where polarization performance and color deteriorate, which becomes a problem. there was. As a result of repeated studies to achieve both polarization performance and color and shrinkage, the present inventors found that reducing the content of the boron-containing compound (B) in the center of the polarizing film compared to that near the surface reduced the polarization performance and color. It was discovered that the contractile force can be reduced while suppressing the effect. The reason for this is not clear, but by reducing the content of the boron-containing compound (B) in the center of the polarizing film, the formation of an iodine complex that absorbs short-wavelength light is promoted in that portion, thereby improving polarization performance and color. It is thought that the decline can be prevented.

It is preferable that 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). When the content exceeds 3.0 parts by mass, the amount of crosslinking increases too much, and there is a risk that the polarizing film may become brittle and easily crack. The content is more preferably 2.0 parts by mass or less. On the other hand, when the content is less than 0.1 part by mass, the amount of crosslinking is too small, and there is a risk that the shrinkage force of the polarizing film may increase. The content is more preferably 0.3 parts by mass or more. The boron element content derived from the boron-containing compound (B) can be determined by ¹ H-NMR measurement. Specifically, it can be obtained by the method described in the Examples described later.

It is preferable that the total boron element content in the polarizing film is 1.0 to 5.0 mass%. When the content exceeds 5.0 mass%, there is a risk that the shrinkage force of the polarizing film may increase. The content is more preferably 4.0 mass% or less, and even more preferably 3.0 mass% or less. On the other hand, when the content is less than 1.0 mass%, there is a risk that polarization performance may become insufficient. The content is more preferably 2.0 mass% or more, and even more preferably 2.2 mass% or more. The total boron element content in the polarizing film can be determined by ICP emission analysis. Specifically, it can be obtained by the method described in the Examples described later.

The boron-containing compound (B) used in the present invention is at least one member selected from the group consisting of diboronic acid represented by the following formula (I) and compounds that can be converted to diboronic acid in the presence of water. Diboronic acid is a boron-containing compound having two boronic acid groups [-B(OH) ₂ ] in one molecule. In formula (I), R ¹ is a divalent organic group having 1 to 20 carbon atoms, and R ¹ and two boronic acid groups are linked by a boron-carbon bond. The boronic acid group has a structure in which a boron atom is bonded to two hydroxyl groups and a carbon atom. Therefore, in boric acid [B(OH) ₃ ], the boron atom is bonded to three hydroxyl groups, whereas boronic acid is different in that it has a boron-carbon bond. And, since the boron-carbon bond of the boronic acid group is not hydrolyzed, it is stable even in an environment where water is present.

[Formula 3]

In addition, the hydroxyl group in the boronic acid group can form an ester with alcohol in the same way as the hydroxyl group in boric acid, so the boron-containing compound (B) used in the present invention is capable of forming an ester by reacting with the hydroxyl group of PVA. It has four hydroxyl groups, and boronic acid groups exist at positions separated from each other via R ¹ . For these reasons, it is thought that the boron-containing compound (B) used in the present invention can effectively crosslink PVA.

Boron-containing groups that can be converted to boronic acid groups in the presence of water include, but are not limited to, boronic acid ester groups described below. The following structural formula (II) is a diboronic acid monoester obtained by reacting one molecule of alcohol (R ² -OH) with diboronic acid. Here, when the boronic acid group is bonded to the hydroxyl group of PVA, R ² in structural formula (II) is PVA, and an organic group is bonded to PVA through a boron atom.

[Formula 4]

The following structural formula (III) is an example of a diboronic acid diester in which two molecules of alcohol (R ² -OH) react with diboronic acid. Here, when the boronic acid group is bonded to the hydroxyl group of PVA, both R ² in structural formula (III) are PVA chains.

[Formula 5]

In the formula (I), R ¹ is a divalent organic group having 1 to 20 carbon atoms. When R ¹ is an appropriate length, the PVA chain can be efficiently crosslinked. The number of carbon atoms of R ¹ is preferably 10 or less, more preferably 6 or less, and still more preferably 4 or less. Moreover, it is preferable that the number of carbon atoms of R ¹ is 2 or more. R ¹ is a divalent organic group, and R ¹ and two boronic acid groups may be linked by a boron-carbon bond. R ¹ may be a hydrocarbon group or may contain hetero atoms such as oxygen, nitrogen, sulfur, or halogen. Considering ease of availability, etc., it is preferable that R ¹ does not contain a hetero atom, and it is more preferable that R ¹ is a hydrocarbon group.

Since it is easy to keep the boron element concentration (α) and boron element concentration (β) in the above range, it is preferable that R ¹ is an aliphatic compound. When R ¹ is an aromatic group, adsorption to the PVA film and diffusion in the PVA film become slow, and it may be difficult to set the boron element concentration (α) or boron element concentration (β) in the above range.

The boron-containing compound (B) specifically includes methanediboronic acid, 1,2-ethanediboronic acid, 1,3-propanediboronic acid, 1,4-butanediboronic acid, 1,5-pentanediboronic acid, and 1,6. -hexanediboronic acid, 1,7-heptanediboronic acid, 1,8-octanediboronic acid, 1,9-nonanediboronic acid, 1,10-decanediboronic acid, 1,11-undecanediboronic acid, 1,12- Dodecanediboronic acid, 1,13-tridecanediboronic acid, 1,14-tetradecanediboronic acid, 1,15-pentadecanediboronic acid, 1,16-hexadecanediboronic acid, 1,17-heptadecanediboronic acid, Boron-containing compounds where R ¹ is a hydrocarbon group such as 1,18-octadecanediboronic acid, 1,19-nonadecanediboronic acid, 1,20-icosanediboronic acid and their isomers, 2-oxa-1,3-propanedibo Boron-containing compounds containing a hetero atom at R ¹ such as ronic acid, 3-oxa-1,5-pentanediboronic acid, 4-oxa-1,7-heptanediboronic acid and their isomers, 1,4-phenylenediboronic acid, and Boron-containing compounds where R ¹ is an aromatic group, such as their isomers, can be mentioned. Among them, 1,2-ethanediboronic acid, 1,3-propanediboronic acid, and 1,4-butanediboronic acid are preferable.

The degree of polymerization of PVA (A) is preferably in the range of 1,500 to 6,000, more preferably in the range of 1,800 to 5,000, and even more preferably in the range of 2,000 to 4,000. When the degree of polymerization is 1,500 or more, the optical properties of a 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 increases in manufacturing costs and defects in process passability during film forming. In addition, the degree of polymerization of PVA (A) in the present invention means the average degree of polymerization measured according to the description of JIS K6726-1994.

The saponification degree of PVA (A) is preferably 95% or more, more preferably 96% or more, and still more preferably 98% or more from the viewpoint of water resistance of a polarizing film obtained by uniaxially stretching a PVA film. In addition, the degree of saponification of PVA (A) refers to the structural unit (typically a vinyl ester unit) that PVA (A) has, which can be converted into a vinyl alcohol unit (-CH ₂ -CH(OH)-) by saponification. It refers to the ratio (%) 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 manufacturing method of PVA (A) is not particularly limited. For example, there is a method of converting the vinyl ester unit of polyvinyl ester, obtained by polymerizing vinyl ester monomers, into vinyl alcohol units. The vinyl ester monomer used in the production of PVA is not particularly limited, but examples include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, and caprylic acid. Examples include vinyl, vinyl caprate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, and vinyl benzoate. Vinyl acetate is preferred from an economic standpoint.

PVA (A) may be a polyvinyl ester copolymer obtained by copolymerizing a vinyl ester monomer and another monomer copolymerizable with it, wherein the vinyl ester units are converted into vinyl alcohol units. Other monomers copolymerizable with the vinyl ester monomer include, for example, α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutene; (meth)acrylic acid or its salt; Methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t- (meth)acrylic acid. (meth)acrylic acid esters such as butyl, 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)acrylamide propanesulfonic acid or its salt, (meth) ) (meth)acrylamide derivatives such as acrylamide propyldimethylamine or its salt, N-methylol (meth)acrylamide or its derivative; N-vinylamides such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; Vinyl such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether. ether; Vinyl cyanide such as (meth)acrylonitrile; Vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; Allyl compounds such as allyl acetate and allyl chloride; Maleic acid or its salt, ester or acid anhydride; Itaconic acid or its salt, ester, or acid anhydride; Vinyl silyl compounds such as vinyl trimethoxysilane; Unsaturated sulfonic acids, etc. can be mentioned. The vinyl ester copolymer may have structural units derived from one or two or more of the other monomers described above. The other monomer can be used by pre-existing it in the reaction vessel when providing the vinyl ester monomer to the polymerization reaction, or by adding it into the reaction vessel while the polymerization reaction is in progress. From the viewpoint of polarization performance, the content of units derived from other monomers is preferably 10 mol% or less, more preferably 5 mol% or less, and even more preferably 2 mol% or less.

Among the monomers that can be copolymerized with the vinyl ester monomer, stretchability is improved and can be stretched at a higher temperature, which reduces the occurrence of problems such as stretching breakage during optical film production, further improving the productivity of the optical film. In, ethylene is preferred. When PVA contains an ethylene unit, the content of the ethylene unit is preferably 1 to 4 mol% relative to the number of moles of all structural units constituting the PVA from the viewpoint of stretchability and stretchability temperature as described above. 2 to 3 mol% is more preferable.

When polymerizing vinyl ester monomer, the polymerization method may be any of batch polymerization, semi-batch polymerization, continuous polymerization, and semi-continuous polymerization, and polymerization methods include bulk polymerization, solution polymerization, suspension polymerization, and emulsion. Known methods such as polymerization can be applied. A bulk polymerization method or a solution polymerization method in which polymerization proceeds without a solvent or in a solvent such as alcohol is usually employed. When obtaining polyvinyl ester with a high degree of polymerization, an emulsion polymerization method is also preferable. The solvent for the solution polymerization method is not particularly limited, but is, for example, alcohol. The alcohol used as a solvent in the solution polymerization method is, for example, a lower alcohol such as methanol, ethanol, or propanol. The amount of solvent used in the polymerization solution may be selected in consideration of chain transfer of the solvent depending on the degree of polymerization of the desired PVA. For example, when the solvent is methanol, the mass ratio of the solvent and all monomers (solvent/all monomers) As, it is preferably selected within the range of 0.01 to 10, more preferably within the range of 0.05 to 3.

The polymerization initiator used in the polymerization of vinyl ester monomer may be selected according to the polymerization method from known polymerization initiators, such as azo-based initiators, peroxide-based initiators, and redox-based initiators. Azo-based initiators include, for example, 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy -2,4-dimethylvaleronitrile). Peroxide-based initiators include, for example, percarbonate-based compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; Perester-based compounds such as t-butylperoxyneodecanate and α-cumylperoxyneodecanate; Acetylcyclohexylsulfonyl peroxide; 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate; It is acetyl peroxide. Potassium persulfate, ammonium persulfate, hydrogen peroxide, etc. may be combined with the above initiator to serve as a polymerization initiator. The redox-based initiator is, for example, a polymerization initiator that combines the above-mentioned peroxide-based initiator with a reducing agent such as sodium bisulfite, sodium bicarbonate, tartaric acid, L-ascorbic acid, and rongalite. The amount of polymerization initiator used is not uniformly determined because it varies depending on the type of polymerization initiator, but may be selected depending on the polymerization rate. For example, when using 2,2'-azobisisobutyronitrile or acetyl peroxide as a polymerization initiator, the amount is preferably 0.01 to 0.2%, and more preferably 0.02 to 0.15% relative to the vinyl ester monomer. The polymerization temperature is not particularly limited, but is suitably between room temperature and 150°C, and is preferably 40°C or higher and below the boiling point of the solvent used.

The polymerization of vinyl ester monomer may be carried out in the presence of a chain transfer agent. Chain transfer agents include, for example, aldehydes such as acetaldehyde and propionaldehyde; Ketones such as acetone and methyl ethyl ketone; Mercaptans such as 2-hydroxyethanethiol; These include phosphinate salts such as sodium phosphinate monohydrate. Among them, aldehydes and ketones are preferably used. The amount of the chain transfer agent used can be determined depending on the chain transfer coefficient of the chain transfer agent used and the degree of polymerization of the target PVA, but is generally preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the vinyl ester monomer.

Saponification of polyvinyl ester can be performed, for example, with the polyvinyl ester dissolved in alcohol or hydrous alcohol. The alcohol used for saponification includes, for example, lower alcohols such as methanol and ethanol, and methanol is preferable. The alcohol used for saponification may contain other solvents, such as acetone, methyl acetate, ethyl acetate, and benzene, for example, at a ratio of 40 mass% or less of the mass. Catalysts used for saponification are, for example, hydroxides of alkali metals such as potassium hydroxide and sodium hydroxide, alkaline catalysts such as sodium methylate, and acid catalysts such as mineral acids. The temperature at which saponification is performed is not limited, but is preferably within the range of 20 to 60°C. If a gel-like product precipitates as saponification progresses, PVA can be obtained by pulverizing the product, then washing and drying. The saponification method is not limited to the above-described method and any known method can be applied.

The PVA film may contain a plasticizer in addition to the PVA (A). Preferred plasticizers include polyhydric alcohols, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane. Additionally, it may contain one or two or more types of these plasticizers. Among these, glycerin is preferable from the viewpoint of the effect of improving stretchability.

The content of the plasticizer in the PVA film is preferably within the range of 1 to 20 parts by mass, more preferably within the range of 3 to 17 parts by mass, and within the range of 5 to 15 parts by mass with respect to 100 parts by mass of PVA (A). It is more desirable. When the content is 1 part by mass or more, the stretchability of the film is further 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.

PVA film further contains fillers, processing stabilizers such as copper compounds, weathering stabilizers, colorants, ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, other thermoplastic resins, lubricants, fragrances, anti-foaming agents, deodorants, extenders, and release agents. Additives such as mold release agents, reinforcing agents, crosslinking agents, mold inhibitors, preservatives, and crystallization rate retardants can be appropriately mixed as needed.

The proportion of the total of PVA (A) and plasticizer in the PVA film is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the mass of the PVA film. do.

The swelling degree of the PVA film is preferably within the range of 160 to 240%, more preferably within the range of 170 to 230%, and particularly preferably within the range of 180 to 220%. When the swelling degree is 160% or more, extreme crystallization can be suppressed, and stretching can be carried out stably at a high magnification. On the other hand, when the swelling degree is 240% or less, dissolution during stretching is suppressed, and stretching becomes possible even under higher temperature conditions. The swelling degree of the PVA film can be determined by the method described in the Examples described later.

The thickness of the PVA film is preferably about 5 to 100 μm, more preferably about 5 to 60 μm, and especially about 10 to 45 μm. If the thickness is too thin, stretching breaks tend to occur easily during stretching processing such as uniaxial stretching for producing a polarizing film. Moreover, if the thickness is too thick, the shrinkage force of the polarizing film may become too large.

The width of the PVA film is not particularly limited and can be determined depending on the purpose of the polarizing film being manufactured. In recent years, liquid crystal televisions and liquid crystal monitors are becoming larger screens, so it is preferable for these applications if the width of the PVA film used in the production of the polarizing film is 3 m or more. On the other hand, if the width of the PVA film used in the production of the polarizing film is too large, it is likely to be difficult to uniformly perform uniaxial stretching when producing the polarizing film with a commercially available device, so it is used in the production of the polarizing film. The width of the PVA film is preferably 7 m or less.

The production method of the PVA film is not particularly limited, and a production method that allows the thickness and width of the film after film formation to be more uniform can be preferably adopted. For example, the above-described method that constitutes the PVA film used in the production of the polarizing film is not particularly limited. PVA (A) and, if necessary, one or more of the above-mentioned plasticizers, additives, and surfactants described later, a film forming stock solution or PVA (A) dissolved in a liquid medium, and, if necessary, Accordingly, it can be manufactured using a film forming stock solution in which PVA (A) is molten and contains one or two or more of plasticizers, additives, surfactants, and liquid media. When the film forming stock solution contains at least one of a plasticizer, an additive, and a surfactant, it is preferable that these components are uniformly mixed.

The liquid medium used for preparing the film forming stock solution includes, for example, water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, Triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc. may be used, and one or two or more of these may be used. Among them, water is preferable in terms of environmental load and recoverability.

The volatile content of the raw film forming solution (the percentage content in the raw film forming solution of volatile components such as liquid media that are removed by volatilization or evaporation during film forming) varies depending on the film forming method, film forming conditions, etc., but is generally 50 to 50%. It is preferable that it exists in the range of 95 mass %, and it is more preferable that it exists in the range of 55-90 mass %. When the volatile content of the film forming solution is 50% by mass or more, the viscosity of the film forming solution does not become too high, filtration and degassing during preparation of the film forming solution are performed smoothly, and it becomes easy to produce a PVA film with few foreign substances and defects. On the other hand, when the volatile matter ratio of the film forming solution is 95% by mass or less, the concentration of the film forming solution does not become too low, making it easy to manufacture industrial PVA films.

It is preferable that the film forming stock solution contains a surfactant. By including a surfactant, film forming properties are improved, occurrence of thickness unevenness of the PVA film is suppressed, and peeling of the PVA film from the metal roll or belt used for film forming becomes easy. When a PVA film is manufactured from a film forming stock solution containing a surfactant, the PVA film may contain a surfactant. The type of the surfactant is not particularly limited, but anionic surfactants or nonionic surfactants are preferable from the viewpoint of peelability from metal rolls or belts.

Examples of anionic surfactants include carboxylic acid types such as potassium laurate; Sulfuric acid ester types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; Sulfonic acid types such as dodecylbenzenesulfonate are preferable.

Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether; Alkylphenyl ether types such as polyoxyethylene octylphenyl ether; Alkyl ester types such as polyoxyethylene laurate; Alkylamine types such as polyoxyethylene laurylamino ether; Alkyl amide types such as polyoxyethylene lauric acid amide; Polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether; Alkanolamide types such as lauric acid diethanolamide and oleic acid diethanolamide; Allyl phenyl ether types such as polyoxyalkylene allyl phenyl ether are preferable.

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

When the film forming stock solution contains a surfactant, the content is preferably within the range of 0.01 to 0.5 parts by mass, and more preferably within the range of 0.02 to 0.3 parts by mass, based on 100 parts by mass of PVA (A) contained in the film forming stock solution. And it is particularly preferable that it is within the range of 0.05 to 0.2 parts by mass. When the content is 0.01 part by mass or more, film forming properties 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 deteriorating handling properties.

Examples of the film forming method for forming the PVA film used in the production of the polarizing film using the above-mentioned film forming solution include cast film forming method, extrusion film forming method, wet film forming method, and gel film forming method. . These film forming methods may be used alone or in 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 they provide a PVA film used in the production of a polarizing film with uniform thickness and width and good physical properties. The formed PVA film can be subjected to drying or heat treatment as needed.

Examples of specific manufacturing methods of PVA films include, for example, using a T-type slit die, hopper plate, I-die, lip coater die, etc., to roll the film forming stock solution into a rotating heated first roll located on the most upstream side. The film is uniformly discharged or stretched on the main surface of the first roll (or belt), the volatile component is evaporated from one side of the film discharged or stretched on the main surface of the first roll (or belt), and dried, and so on. An industrially preferred method is to dry the product further on the main surface of one or more rotating heated rolls placed downstream, or to further dry it by passing it through a hot air dryer and then winding it up with a winding device. can do. Drying using heated rolls and drying using a hot air drying device may be performed in appropriate combination. Additionally, a multilayer PVA film may be formed by forming a layer made of PVA (A) on one side of the base film composed of a single resin layer.

The method for producing the polarizing film of the present invention is not particularly limited. A preferred production method is a polarizing film production method including a dyeing treatment of dyeing a PVA film with a dichroic dye and a stretching treatment of uniaxially stretching the film, wherein the boron element content derived from boric acid is 0.5 to 5.0 mass%. This is a method for producing a polarizing film in which the PVA film after phosphorus stretching treatment is immersed in an aqueous solution with a concentration of a boron-containing compound (B) of 0.1 to 5.0% by mass, and then the film is dried at 95°C or lower. For the PVA film used in the production of the polarizing film of the present invention, a method of performing dyeing treatment, stretching treatment, and, if necessary, additionally swelling treatment, boric acid crosslinking treatment, fixing treatment, washing treatment, heat treatment, etc. there is. In this case, the order of each treatment is not particularly limited, but it is preferable to perform the swelling treatment, boric acid crosslinking treatment, stretching treatment, and fixing treatment in this order. In addition, it is preferable that the dyeing treatment is performed before the boric acid crosslinking treatment. Additionally, one or two or more treatments may be performed simultaneously, and one or two 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 water when immersed in water is preferably 20 to 40°C, more preferably 22 to 38°C, and even more preferably 25 to 35°C. Moreover, the time for immersion in water is preferably 0.1 to 5 minutes, and more preferably 0.2 to 3 minutes. In addition, the water used for immersion is not limited to pure water, but includes iodide and salt components such as potassium iodide, calcium iodide, zinc chloride, and sodium sulfate, and carboxylic acid types such as potassium laurate; Sulfuric acid ester types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; Sulfonic acid type anionic surfactants such as dodecylbenzene sulfonate and alkyl ether type such as polyoxyethylene oleyl ether; Alkylphenyl ether types such as polyoxyethylene octylphenyl ether; Alkyl ester types such as polyoxyethylene laurate; Alkylamine types such as polyoxyethylene laurylamino ether; Alkyl amide types such as polyoxyethylene lauric acid amide; Polypropylene glycol ether types such as polyoxyethylene polyoxypropylene ether; Alkanolamide types such as lauric acid diethanolamide and oleic acid diethanolamide; It may be an aqueous solution in which surfactant components such as allyl phenyl ether type nonionic surfactant such as polyoxyalkylene allyl phenyl ether are dissolved, dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, N-methyl pyrrolidone, It may be a mixture with an aqueous medium such as ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane or structural isomers thereof.

Dyeing treatment can be performed by bringing a dichroic dye into contact with the PVA film. It is common to use iodine-based dyes or dichroic dyes as dichroic dyes. It is possible to perform dyeing treatment at any stage before, during, or after the stretching treatment, but from the viewpoint of efficiently adsorbing the dichroic dye to the PVA film and efficiently orienting the dichroic dye adsorbed to the PVA film. , it is preferable to perform dyeing treatment after swelling treatment and before stretching treatment. The dyeing treatment is generally performed by immersing the PVA film in a solution (particularly an aqueous solution) containing iodine-potassium iodide as a dyeing bath, or a solution (particularly an aqueous solution) containing a plurality of dichroic dyes. In the case of a solution containing iodine-potassium iodide, the concentration of iodine in the dyeing bath is preferably 0.01 to 0.5 mass%, and the concentration of potassium iodide is preferably 0.01 to 10 mass%. Moreover, the temperature of the dyeing bath is preferably 20 to 50°C, especially 25 to 40°C. The preferred dyeing time is 0.2 to 5 minutes. When using a dichroic dye, the dichroic dye is preferably an aqueous dye. Moreover, it is preferable that the dye concentration in the dyeing bath is 0.001 to 10 mass%. Additionally, a dyeing aid may be used as needed, and an inorganic salt such as sodium sulfate or a surfactant may be used. When using sodium sulfate, 0.1 to 10 mass% is preferable. The dyeing temperature is preferably 30 to 80°C. Specific dichroic dyes include: kid. Direct Yellow 28, p. kid. Direct Orange 39, p. kid. Direct Yellow 12, p. kid. Direct Yellow 44, p. kid. Direct Orange 26, Si. kid. Direct Orange 71, p. kid. Direct Orange 107, p. kid. Direct Red 2, p. kid. Direct Red 31, Poetry. kid. Direct Red 79, p. kid. Direct Red 81, Poetry. kid. Direct Red 247, p. kid. Direct Green 80, p. kid. Direct Green 59, etc. may be mentioned, and dichroic dyes developed for manufacturing polarizing plates are preferred.

By subjecting the PVA film to boric acid crosslinking treatment, it is possible to effectively prevent PVA (A) or the dichroic dye adsorbed on the PVA film from dissolving into water during wet stretching at high temperature. From this viewpoint, it is more preferable to carry out the boric acid crosslinking treatment after the dyeing treatment and before the stretching treatment. The boric acid crosslinking treatment can be performed by immersing the PVA film in an aqueous solution containing a boric acid crosslinking agent. As the boric acid crosslinking agent, one or two or more types of boron-containing inorganic compounds such as boric acid and borates such as borax can be used. From the viewpoint of ease of handling, the boric acid crosslinking agent is preferably boric acid. The concentration of the boric acid crosslinking agent in the aqueous solution containing the boric acid crosslinking agent is preferably 1 to 10% by mass, and more preferably 2 to 7% by mass. When the concentration of the boric acid crosslinking agent is 1 to 10% by mass, sufficient stretchability can be maintained. If the concentration of the boric acid crosslinking agent exceeds 10% by mass, excessive crosslinking may occur and stretchability may decrease, which is not preferable. In addition, if the concentration of the boric acid crosslinking agent is less than 1% by mass, the effect of preventing the dichroic dye adsorbed on PVA (A) or PVA film from dissolving into water when stretching at high temperature may be insufficient, so it is not preferable. not. The aqueous solution containing the boric acid crosslinking agent may contain an auxiliary such as potassium iodide. The temperature of the aqueous solution containing the boric acid crosslinking agent is preferably 20 to 50°C, and particularly preferably 25 to 40°C. Boric acid crosslinking can be carried out efficiently by setting the temperature to 20 to 50°C.

Apart from the stretching treatment described later, the PVA film may be stretched (pre-stretched) during or between the treatments described above. In this way, the total draw ratio of the pre-stretching performed before the stretching treatment (multiplying the stretching ratio in each treatment) is based on the original length of the raw PVA film before stretching from the viewpoint of polarization performance of the obtained polarizing film, etc. Therefore, 1.5 times or more is preferable, 2.0 times or more is more preferable, and 2.5 times or more is still more preferable. On the other hand, the overall draw ratio is preferably 4.0 times or less, and more preferably 3.5 times or less. The stretching ratio in the swelling treatment is preferably 1.05 to 2.5 times. The stretching ratio in dyeing treatment is preferably 1.1 to 2.5 times. The stretching ratio in the boron crosslinking treatment is preferably 1.1 to 2.5.

The stretching treatment may be either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it may be carried out in an aqueous solution containing a boric acid crosslinking agent, or in the dyeing treatment bath described above. In addition, 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 air using the PVA film after water absorption. Among these, the wet stretching method is preferable, and the uniaxial stretching treatment in an aqueous solution containing a boric acid crosslinking agent is particularly preferable. From ease of handling, it is preferable that the boric acid crosslinking agent is boric acid. The concentration of boric acid in the aqueous solution is preferably 0.5 to 5% by mass, and more preferably 2 to 5% by mass. When the concentration of boric acid is less than 0.5 mass%, the boric acid content in the PVA film becomes too low, and when the PVA film after stretching treatment is immersed in an aqueous solution of the boron-containing compound (B), the boron-containing compound (B) is excessively adsorbed. Therefore, the polarizing film may become vulnerable. On the other hand, when the boric acid concentration exceeds 5% by mass, the boric acid content in the PVA film becomes too large, and when the PVA film after stretching treatment is immersed in an aqueous solution of the boron-containing compound (B), boric acid is converted into the boron-containing compound (B). ) may excessively inhibit the adsorption of . The boric acid aqueous solution may contain potassium iodide, and the concentration of potassium iodide is preferably 0.01 to 10 mass%. The stretching temperature in the stretching treatment is preferably 30 to 90°C. The temperature is more preferably 40°C or higher, and even more preferably 50°C or higher. Meanwhile, the temperature is more preferably 80°C or lower, and even more preferably 70°C or lower. Moreover, the stretching ratio (total stretching ratio from the raw PVA film) in the stretching treatment is preferably 2.0 to 4.0 times. From the viewpoint of polarization performance of the obtained polarizing film, etc., 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 stretch ratio before the fixing treatment described later is preferably 5 times or more, and more preferably 5.5 times or more from the viewpoint of polarization performance. The upper limit of the draw ratio is not particularly limited, but the draw ratio is preferably 8 times or less.

When stretching a long PVA film, there are no particular restrictions on the direction of the uniaxial stretching process, and uniaxial stretching in the long direction, transverse uniaxial stretching, or so-called oblique stretching can be adopted. However, since a polarizing film with excellent polarization performance can be obtained, uniaxial stretching treatment in the long direction is preferable. The uniaxial stretching process in the long direction can be performed by using a stretching device equipped with a plurality of rolls parallel to each other and changing the peripheral speed between each roll. On the other hand, transverse uniaxial stretching treatment can be performed using a tenter-type stretching machine.

When producing a polarizing film, it is preferable to perform a fixing treatment after the stretching treatment in order to strengthen the adsorption of the dichroic dye (iodine-based dye, dichroic dye, etc.) to the PVA film. As a fixing treatment bath used for fixing treatment, an aqueous solution containing a boron-containing compound (B) is preferable. Additionally, if necessary, boric acid, iodine, iodide, metal compounds, etc. may be added to the fixing treatment bath, and it is preferable to add iodide such as potassium iodide. The temperature of the fixing treatment bath is preferably 10 to 70°C, and more preferably 20 to 40°C. It is preferable to add 0.5 to 10% by mass of iodide. The draw ratio in the fixing treatment is preferably 1.3 times or less, more preferably 1.2 times or less, and even more preferably less than 1.1 times.

A boron-containing compound (B) is adsorbed to the PVA film after stretching treatment. If the boron-containing compound (B) is adsorbed before or during the stretching treatment, a large amount of the boron-containing compound (B) will be adsorbed to the center of the polarizing film, and there is a risk that the color may worsen. In addition, there is a risk that the stretchability may decrease due to too many crosslinks between molecules. The boron-containing compound (B) may be adsorbed to the PVA film in any of the dyeing, boric acid crosslinking, and fixing processes as long as it is a step after the stretching treatment. However, adsorbing the boron-containing compound (B) in the fixing treatment does not worsen the color, and the stretching process It is preferable from the viewpoint of performance, and specifically, it is preferable to adsorb the boron-containing compound (B) to the PVA film by immersing the PVA film in an aqueous solution with a boron-containing compound (B) concentration of 0.1 to 5.0 mass%.

If the concentration of the boron-containing compound (B) in the aqueous solution is less than 0.1% by mass, there is a risk that the color may deteriorate and the effect of reducing the shrinkage force may be insufficient. The concentration is more preferably 0.2 mass% or more, and even more preferably 0.3 mass% or more. On the other hand, when the concentration exceeds 5.0% by mass, the boron-containing compound (B) is excessively adsorbed, which may make the surface of the polarizing film brittle or cause precipitates of the boron-containing compound (B) to form on the surface. The concentration is more preferably 4% by mass or less. Additionally, the temperature of the aqueous solution is preferably 10 to 70°C. If the temperature is less than 10°C, there is a risk that the boron-containing compound (B) may precipitate in the treatment bath. The temperature is more preferably 20°C or higher. On the other hand, when the temperature exceeds 70°C, there is a risk that wrinkles may easily occur in the polarizing film. The temperature is more preferably 60°C or lower, more preferably 50°C or lower, and particularly preferably 40°C or lower. The time for immersion in the aqueous solution is preferably 5 to 400 seconds. From the viewpoint of improving polarization performance, the aqueous solution preferably contains iodide such as potassium iodide as an auxiliary agent, and the content is preferably 0.5 to 10% by mass.

The content of boron element derived from boric acid in the PVA film used for adsorption of the boron-containing compound (B) needs to be 0.5 to 5.0 mass%. This makes it possible to adjust the concentration of the boron-containing compound (B) in the thickness direction of the polarizing film, and set the boron element concentration (α) and boron element concentration (β) derived from the boron-containing compound (B) to the above range. You can. It is thought that the boric acid in the PVA film moderately inhibits the adsorption of the boron-containing compound (B), making it easier for the boron-containing compound (B) to adsorb near the surface of the polarizing film and making it difficult to adsorb in the center. If the boron element content derived from boric acid in the PVA film is less than 0.5% by mass, when the PVA film is immersed in an aqueous solution of the boron-containing compound (B), the boron-containing compound (B) is excessively adsorbed and the color deteriorates. , the surface of the polarizing film may become too hard and easily tear. The content is preferably 1% by mass or more. On the other hand, if the content exceeds 5.0 mass%, there is a risk that adsorption of the boron-containing compound (B) may be excessively inhibited when the PVA film is immersed in an aqueous solution of the boron-containing compound (B). In addition, the boron element content derived from boric acid in the PVA film can be adjusted by the temperature of the treatment bath, boric acid concentration, immersion time, etc. in the stretching treatment or boric acid crosslinking treatment.

The content of the boron-containing compound (B) in the polarizing film can be controlled by adjusting the concentration of the boron-containing compound (B) in the aqueous solution, the temperature of the aqueous solution, or the immersion time in the aqueous solution in the fixing treatment, but the temperature or When the immersion time is adjusted, there is a risk that wrinkles may occur in the polarizing film, so it is preferable to adjust it according to the concentration of the boron-containing compound (B).

A washing treatment may be performed before the drying treatment. Cleaning treatment is generally performed by immersing the PVA film in water, distilled water, pure water, etc. At this time, from the viewpoint of improving polarization performance, the aqueous solution used in the washing treatment preferably contains iodide such as potassium iodide, and the concentration of iodide is preferably 0.5 to 10 mass%. Moreover, the temperature of the aqueous solution in a washing process is generally 5-50 degreeC, 10-45 degreeC is preferable, and 10-40 degreeC is especially preferable. From an economic standpoint, it is undesirable that the temperature of the aqueous solution is too low, and if the temperature of the aqueous solution is too high, polarization performance may deteriorate.

The PVA film is immersed in an aqueous solution of the boron-containing compound (B), and then subjected to a drying treatment in which the film is dried at 95°C or lower. If the drying temperature exceeds 95°C, there is a risk that the color may deteriorate. The temperature is preferably 90°C or lower, and more preferably 80°C or lower. On the other hand, if the drying temperature is less than 40°C, it is not preferable because the shrinkage force tends to increase. The temperature is preferably 50°C or higher. The drying time is preferably 10 to 600 seconds.

By performing heat treatment after drying treatment, a polarizing film with further excellent dimensional stability can be obtained. Here, heat treatment is a treatment that improves the dimensional stability of the polarizing film by further heating the polarizing film after drying treatment with a moisture content of 5% or less. The conditions for heat treatment are not particularly limited, but the heat treatment temperature is preferably 60°C to 95°C, and particularly preferably 70°C to 90°C. If heat treatment is performed at a temperature lower than 60 ℃, it is not desirable because the effect of improving dimensional stability by heat treatment may be insufficient, and if heat treatment is performed at a temperature higher than 95 ℃, intense redness may occur in the polarizing film. It is not desirable because there are

The polarizing film obtained as described above is usually used as a polarizing plate by bonding a protective film that is optically transparent and has mechanical strength to both sides or one side. As the protective film, cellulose triacetate (TAC) film, cellulose acetate/butyrate (CAB) film, acrylic film, polyester film, etc. are used. In addition, adhesives for bonding include PVA-based adhesives and ultraviolet curing-based adhesives, but among them, PVA-based adhesives are preferable.

The polarizing plate obtained as described above can be used as a component of an LCD by coating it with an adhesive such as an acrylic adhesive and then bonding it to a glass substrate. At the same time, it may be bonded with a retardation film, a viewing angle improvement film, a brightness improvement film, etc.

Example

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is in no way limited by these examples. In addition, each measurement or evaluation method employed in the following examples and comparative examples is shown below.

[Optical properties of polarizing film]

A rectangular sample measuring 4 cm in the longitudinal direction and 2 cm in the width direction of the polarizing film was taken from the central portion in the width and longitudinal directions of the polarizing film, and a spectrophotometer V-7100 (manufactured by Nippon Spectrophotography Co., Ltd.) equipped with an integrating sphere was analyzed with Glan. The parallel transmittance and cross-Nicol transmittance of the polarizing film were measured using an automatic polarizing film measuring device VAP-7070S (manufactured by Nippon Spectroscope Co., Ltd.) equipped with a Taylor polarizer. In addition, the measurement wavelength range is set to 380 nm to 780 nm, and the transmittance when the vibration direction of polarized light incident on the polarizing film through the Glan Taylor polarizer is parallel to the transmission axis of the polarizing film is called parallel transmittance, and the transmission of the polarizing film The case perpendicular to the axis was taken as Cross-Nicol transmittance. Afterwards, using the “Polarizing Film Evaluation Program” (manufactured by Nippon Spectroscope Co., Ltd.), visibility correction was performed in the visible light region with a C light source and a 2° field of view in accordance with JIS Z 8722 (Method for measuring object color), and the polarizing film was evaluated. The single transmittance, degree of polarization, and single b value (hue) were calculated, and these three values were obtained as optical properties of the polarizing film.

[contraction force]

Contraction force was measured using an Autograph "AG-X" equipped with a thermostat manufactured by Shimadzu Corporation and a video extensometer "TR ViewX120S". For the measurement, a polarizing film whose humidity was controlled at approximately 20°C/20%RH for 18 hours was used. After setting the thermostat of the Autograph "AG-X" to 20°C, attach the polarizing film (15 cm in the longitudinal direction, 1.5 cm in the width direction) to the chuck (chuck spacing 5 cm), and immediately upon starting the tension, pull it out at 10°C/min. The temperature increase in the thermostat was started to 80°C at a temperature increase rate of . The polarizing film was stretched at a speed of 1 mm/min, the stretching was stopped when the tension reached 2 N, and the tension was measured until 4 hours later. At this time, since the distance between the chucks changes due to thermal expansion, mark seals are attached to each of the upper and lower chucks, and measurement is performed by correcting the movement of the mark seals so that the distance between chucks is constant using the video extensometer "TR ViewX120S". It was carried out. In addition, when a minimum value occurred in the tension at the beginning of the measurement (within 10 minutes from the start of the measurement), the minimum value was subtracted from the tension measurement value 4 hours later, and that value was used as the shrinkage force of the polarizing film.

[Boron element concentration derived from boron-containing compound (B)]

The boron element concentration derived from the boron-containing compound (B) in the polarizing film was measured using an For the measurement, a polarizing film whose humidity was controlled at approximately 23°C/50%RH for 16 hours was used. Sputtering ^was performed in a 2 mm ) was carried out. XPS measurements were performed using monochromated Al as the The species was selected. In addition, when using a dichroic dye as a dichroic dye, it is necessary to appropriately select elements such as nitrogen and sulfur contained in the dichroic dye as detection elements. Next, using the analysis software "MultiPack" (manufactured by Ulvak Pi Co., Ltd.), the boron element concentration (a, atomic %) at each depth of the polarizing film was determined based on 284.8 eV, which is the binding energy of the CC and CH bonds. was calculated. Afterwards, for the The resulting binding energy was appropriately set, and peak separation was performed using the least square method using the pseudo Voigt function. Additionally, a linear function calculated from the average value of the intensity of the XPS spectrum from 187 to 189 eV and the average value of the XPS spectrum from 195 to 197 eV was used as a baseline. In this way, the peak area ratio (b, %) of the boron derived from the boron-containing compound (B) relative to the sum of the boron derived from boric acid and the boron of the boron-containing compound (B) is calculated, and substituted into the following calculation formula (1) By doing this, the boron element concentration derived from the boron-containing compound (B) at each depth was calculated.

Boron element concentration (atomic %) derived from boron-containing compound (B)

= a × b × 10 ^-2 (1)

Additionally, the binding energy resulting from boron in the boron-containing compound (B) changes depending on the structure of the compound. Therefore, it is necessary to set the above binding energy appropriately depending on the type of boron-containing compound (B). For example, when the boron-containing compound (B) is 1,4-butanediboronic acid, it is 191.3 eV. Additionally, when peak separation was performed using the least squares method using the pseudo Voigt function, the Laurent water content ratio of boric acid was set to 0.115, and 2 ^1/2 × σ was set to 0.809. Additionally, the Lorentz water content and half width of the boron-containing compound (B) also change depending on the structure of the compound. Therefore, it is necessary to appropriately set the Laurent water content ratio and 2 ^1/2 × σ depending on the type of the compound. When the boron-containing compound (B) was 1,4-butanediboronic acid, the Laurent water content ratio was set to 0.263 and 2 ^1/2 × σ was set to 0.797.

By this method, the boron element concentration derived from the boron-containing compound (B) is determined every 50 nm from the surface to 1 μm inward on both sides of the polarizing film, and the average value is calculated at 1 μm inward from the surface of the polarizing film. The boron element concentration (α, atomic %) derived from the boron-containing compound (B) was in the range of . In addition, the boron element concentration derived from the boron-containing compound (B) is determined every 50 nm from the center of the polarizing film to 1 μm outward, and the average value is calculated as the boron-containing compound in the range from the center of the polarizing film to 1 μm outward. (B) derived boron element concentration (β, atomic%).

[Boron element content derived from boron-containing compound (B) relative to 100 parts by mass of PVA (A)]

The polarizing film whose humidity was controlled at 23°C/50%RH for 16 hours was dissolved in heavy water to approximately 0.003% by mass, and then concentrated with a rotary evaporator to approximately 0.15% by mass. The solution was used as a measurement sample for ¹ H-NMR. ¹ H-NMR (JNM-AL400, manufactured by Nippon Electronics Co., Ltd.: 400 MHz) measurement was conducted at 80°C and analyzed using ALICE2 (manufactured by Nippon Electronics Co., Ltd.) using the following method. For the ^1H -NMR chart obtained by measurement, the phase was adjusted so that the baseline was smooth, and then the average point was set to 20 to automatically correct the baseline. Next, the peak of heavy water, which is the measurement solvent, was automatically set at the position of 4.65 ppm as a reference. Thereafter, as shown in FIG. 1, the hydrogen peak of the hydrocarbon group contained in the boron-containing compound (B) was integrated, and the peak area was determined. At this time, the hydrogen peak area derived from PVA (A) plus the hydrogen peak area of the hydrocarbon group contained in the boron-containing compound (B) that does not overlap (area c) is used as the standard for the peak area, and the peak area of the boron-containing compound (B) is taken as the standard. The number of hydrogens and the area c of the corresponding hydrocarbon were set to be the same. Next, the hydrogen peak in the range of 1.7 ppm to 2.4 ppm is included in the boron-containing compound (B) that overlaps with the hydrogen peak derived from the methylene group of PVA (A) and the hydrogen peak derived from the methylene group of PVA (A). The peak area (area d) was determined by considering it as the sum of the hydrogen peaks of the hydrocarbon group. After that, the area e was calculated by subtracting the hydrogen peak of the methylene group derived from PVA (A) and the hydrogen number of the hydrocarbon of the boron-containing compound (B) overlapping from the area d. The values obtained by these methods were substituted into the formula below to calculate the boron element content derived from the boron-containing compound (B) relative to 100 parts by mass of PVA (A). In addition, in the following formula (2), In addition, Formula (2) is a formula used when unmodified PVA is used, and when modified PVA is used as a raw material, Formula (2) needs to be modified appropriately.

Boron element content (parts by mass) derived from boron-containing compound (B)

= {(Area c/X)/(Area e/2)} × {(10.811 × Y)/44.0526} × 100 (2)

In formula (2), 10.811 is the atomic weight of boron, and 44.0526 is the molecular weight per mole of the repeating unit of unmodified PVA. For example, ^{the 1} H-NMR chart in FIG. 1 is a measurement of the polarizing film of Example 1, and the boron element content derived from the boron-containing compound (B) relative to 100 parts by mass of PVA is 0.5 mass by raising the second decimal place. It became wealth.

[Total boron element content in polarizing film]

The mass f (g) of the polarizing film whose humidity was controlled at approximately 23°C/50%RH for 16 hours was measured, and the polarizing film was dissolved in approximately 20 mL of distilled water so that it would be approximately 0.005% by mass. The aqueous solution in which the polarizing film was dissolved was used as a measurement sample, and its mass g (g) was measured. Thereafter, the boron concentration h (ppm) of the measurement sample was measured using a multi-type ICP emission spectrometer manufactured by Shimadzu Corporation. After that, the value was substituted into the following formula (3) and the calculated value was used as the total boron element content (% by mass) in the polarizing film.

Total boron element content in polarizing film (mass%)

= [(h × 10 ^-6 × g)/f] × 100 (3)

[Content of boron element derived from boric acid in PVA film after stretching treatment]

After the stretching treatment and before the fixing treatment, the PVA film was taken and dried, and the humidity was controlled at 23°C/50%RH for 16 hours, then the mass i (g) was measured, and the PVA film was diluted with distilled water so that the content was about 0.005% by mass. Dissolved in about 20 mL. The obtained aqueous solution was used as a measurement sample, and its mass j (g) was measured. Thereafter, the boron concentration k (ppm) of the measurement sample was measured using a multi-type ICP emission spectrometer manufactured by Shimadzu Corporation. Thereafter, the value was substituted into the following formula (4) and the calculated value was used as the boron element content (% by mass) derived from boric acid in the PVA film after the stretching treatment and before the fixing treatment.

Boron element content derived from boric acid in PVA film (mass%)

= [(k × 10 ^-6 × j)/i] × 100 (4)

[Swelling degree of PVA film]

The PVA film was cut into 5 cm x 10 cm and immersed in 1000 mL of distilled water at 30°C for 30 minutes. After that, the PVA film was taken out, moisture on the surface of the PVA film was wiped off with a filter paper, and the mass (mass l) of the PVA film after immersion was measured. After that, the PVA film was placed in a dryer at 105°C and dried for 16 hours, and then the mass (mass m) of the PVA film after drying was measured. The swelling degree of the PVA film was calculated by substituting the values of mass l and mass m into the following equation (5).

Swelling degree (%) = (mass l/mass m) × 100 (5)

[Example 1]

Prepare a PVA aqueous solution containing 100 parts by mass of PVA (degree of saponification 99.9%, degree of polymerization 2400), 10 parts by mass of glycerin as a plasticizer, and 0.1 part by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant, with a PVA content of 10 mass%. did. The film obtained by drying the PVA aqueous solution on a metal roll at 80°C was heat-treated in a hot air dryer (120°C) for 10 minutes to obtain a PVA film with a thickness of 30 μm and a swelling degree of 200%.

From the center portion in the width direction of the obtained PVA film, a sample of 5 cm in width x 9 cm in length was cut so that a range of 5 cm in width x 5 cm in length could be uniaxially stretched. This sample was uniaxially stretched 1.1 times in the longitudinal direction while immersed in pure water at 30°C for 30 seconds, and subjected to swelling treatment. Subsequently, iodine is adsorbed by uniaxially stretching it 2.2 times (total 2.4 times) in the longitudinal direction while immersing it in an aqueous solution (dyeing bath) (temperature 30°C) containing 0.035 mass% of iodine and 3.5 mass% of potassium iodide (temperature 30°C) for 60 seconds. I ordered it. Next, it was uniaxially stretched in the longitudinal direction 1.2 times (2.7 times in total) while immersed in an aqueous solution (boric acid crosslinking treatment bath) (temperature 30°C) containing 3.0% by mass of boric acid and 3% by mass of potassium iodide. . Additionally, it was uniaxially stretched in the longitudinal direction up to 6.0 times overall while immersed in a 60°C aqueous solution (stretching treatment bath) containing 4.0% by mass of boric acid and 6% by mass of potassium iodide. After the uniaxial stretching treatment, the aqueous solution (fixation treatment bath) (temperature 30°C) containing 0.5% by mass of 1,4-butanediboronic acid and 2.5% by mass of potassium iodide as the boron-containing compound (B) for 100 seconds. It was immersed. In the fixing process, the PVA film was not stretched (stretch ratio 1.0 times). Finally, it was dried at 60°C for 240 seconds to produce a polarizing film (thickness 13 ㎛).

After the stretching treatment, ICP measurement was performed on a uniaxially stretched film produced by only drying without performing a fixing treatment, and the content of boron element derived from boric acid in the film was found to be 4.5% by mass.

As a result of measuring and analyzing the The boron element concentration (β) derived from the boron-containing compound (B) in the range was 0.7 atomic%.

As a result of ¹ H-NMR measurement and analysis of the polarizing film, the boron element content derived from the boron-containing compound (B) with respect to 100 parts by mass of the PVA was 0.5 parts by mass.

When the ICP measurement of the polarizing film was performed, the total boron element content in the polarizing film was 2.5 mass%.

Using the polarizing film, the optical properties and shrinkage force of the polarizing film were evaluated by the above-mentioned method, and the single transmittance was 43.96%, the polarization degree was 99.93%, the single b value (color) was 2.1, and the shrinkage force was 6.1 N. The above results are shown in Table 1.

[Example 2]

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 1,2-ethanediboronic acid and 4% by mass of potassium iodide was used in the fixation treatment bath. , each measurement and evaluation was performed. The results are shown in Table 1.

[Example 3]

A polarizing film was produced in the same manner as in Example 1, except that an aqueous solution (temperature 30°C) containing 0.3% by mass of 1,4-butanediboronic acid and 4% by mass of potassium iodide was used in the fixation treatment bath. , each measurement and evaluation was performed. The results are shown in Table 1.

[Example 4]

A polarizing film was produced in the same manner as in Example 1 except that the immersion time in the fixing treatment bath was changed to 10 seconds, and each measurement and evaluation was performed. The results are shown in Table 1.

[Example 5]

A polarizing film was produced in the same manner as in Example 1 except that the boric acid concentration in the stretching bath was changed to 2.0% by mass, the stretching bath temperature was changed to 58°C, and the immersion time in the fixing bath was changed to 10 seconds, and each measurement and evaluation was performed. was carried out. The results are shown in Table 1.

[Comparative Example 1]

Referring to KR10-2014-0075154, it was immersed in pure water at 30°C for 120 seconds and uniaxially stretched in the longitudinal direction so that the total size was 1.3 times the swelling treatment. Subsequently, uniaxially stretched in the longitudinal direction by 1.1 times (1.4 times in total) while immersed in an aqueous solution (dyeing treatment bath) (temperature 30°C) containing 10 parts by mass of potassium iodide to 1 part by mass of iodine for 240 seconds. It was dyed while doing so. Subsequently, while immersed in an aqueous solution (stretching bath) at 50°C containing 0.5% by mass of 1,4-butanediboronic acid and 5% by mass of potassium iodide for 120 seconds, the strips were stretched 4.3 times (6.0 times in total) in the longitudinal direction. The axis was stretched. After that, it was immersed in pure water (washing treatment bath) at 30°C for 10 seconds. Finally, it was dried at 60°C for 4 minutes to produce a polarizing film. Each measurement and evaluation were performed on the obtained polarizing film. The results are shown in Table 1.

[Comparative Example 2]

A polarizing film was produced in the same manner as in Comparative Example 1 except that the 1,4-butanediboronic acid concentration in the stretching treatment bath was changed to 0.2% by mass, and then each measurement and evaluation were performed. The results are shown in Table 1.

[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 3% by mass of potassium iodide was used as a fixation treatment bath, and each measurement and evaluation was performed. was carried out. The results are shown in Table 1.

[Comparative Example 4]

Examples except that an aqueous solution (temperature 30°C) containing 2.0% by mass of boric acid and 3% by mass of potassium iodide was used as the fixing treatment bath, and that the immersion time in the fixing treatment bath was changed to 10 seconds. A polarizing film was produced in the same manner as in 1, and each measurement and evaluation was performed. The results are shown in Table 1.

[Comparative Example 5]

Example 2, except that an aqueous solution (temperature 30°C) containing 1.0% by mass of boric acid and 3% by mass of potassium iodide was used as the fixing treatment bath, and the immersion time in the fixing treatment bath was changed to 10 seconds. A polarizing film was produced in the same manner as above, and each measurement and evaluation was performed. The results are shown in Table 1.

[Comparative Example 6]

Example 1, except that an aqueous solution (temperature 30°C) containing 0.5% by mass of boric acid and 3% by mass of potassium iodide was used as the fixing treatment bath, and the immersion time in the fixing treatment bath was changed to 10 seconds. A polarizing film was produced in the same manner as above, and each measurement or evaluation was performed. The results are shown in Table 1.

[Comparative Example 7]

A polarizing film was prepared in the same manner as in Example 1, except that an aqueous solution (temperature 30°C) containing potassium iodide at a rate of 2% by mass was used as the fixing treatment bath, and the immersion time in the fixing treatment bath was changed to 20 seconds. was manufactured and each measurement and evaluation was performed. The results are shown in Table 1.

[Comparative Example 8]

As a fixing treatment bath, an aqueous solution containing 2.0% by mass of boric acid and 3% by mass of potassium iodide (temperature: 30°C) was used, and the drying temperature was changed to 100°C, in the same manner as in Example 1. A polarizing film was produced, and each measurement and evaluation was performed. The results are shown in Table 1.

Additionally, in Examples 2 to 5 and Comparative Examples 3 to 8, as in Example 1, an aqueous solution (dyeing treatment bath) (temperature of 30°C) containing 100 parts by mass of potassium iodide to 1 part by mass of iodine was added at 60 °C. Iodine was adsorbed by uniaxially stretching in the longitudinal direction 2.2 times (total 2.4 times) while immersed for a second. At this time, the iodine and potassium iodide concentration of the dyeing treatment bath was adjusted so that the transmittance of the polarizing film after drying was 43.8% to 44.2%. In Comparative Examples 1 to 2, while immersed in an aqueous solution (dyeing treatment bath) (temperature 30°C) containing 10 parts by mass of potassium iodide to 1 part by mass of iodine for 240 seconds, the length was increased by 1.1 times (1.4 times in total). Iodine was adsorbed by stretching uniaxially in one direction. At this time, the iodine and potassium iodide concentration of the dyeing treatment bath was adjusted so that the transmittance of the polarizing film after drying was 43.8% to 44.2%.

As is clear from the above results, the polarizing films of Examples 1 to 5 that satisfy the provisions of the present invention have excellent optical properties, with a polarization degree of 99.8% or more and a single b value of 0 to 3, and a shrinkage force of 12. It can be seen that the contractile force is low below N. On the other hand, in Comparative Examples 1 to 2 in which the boron element concentration (β) derived from the boron-containing compound (B) in the range from the center of the polarizing film to 1 μm outward exceeds 2%, the shrinkage force is not low. However, the optical properties were poor. In addition, the polarizing films of Comparative Examples 3 to 8 produced without using the boron-containing compound (B) also had high shrinkage force (Comparative Examples 3 to 6) or insufficient optical properties (Comparative Examples 7 and 8). could not be reconciled.

1: Peak derived from heavy water, the measurement solvent
2: Peak derived from the methine group of PVA
3: Peak derived from methylene group of PVA
4: Peak derived from hydrocarbon group contained in boron-containing compound, overlapping with peak derived from PVA
5: Peak derived from a hydrocarbon group contained in a boron-containing compound that does not overlap with the peak derived from PVA

Claims (5)

At least one boron-containing compound (B) selected from the group consisting of polyvinyl alcohol (A), diboronic acid represented by the following formula (I), and compounds capable of being converted to diboronic acid in the presence of water, and boric acid (C) As a polarizing film containing,
The boron element concentration (α) derived from the boron-containing compound (B) in the range from the surface of the polarizing film to 1 µm inward is 1 to 7 atomic%, and in the range from the center to 1 µm outward. The boron element concentration (β) derived from the boron-containing compound (B) is 0.1 to 2 atomic%, and
A polarizing film characterized in that the ratio (α/β) of concentration (α) to concentration (β) is 1.5 or more.

[In formula (I), R ¹ is a divalent organic group having 1 to 20 carbon atoms, and R ¹ and two boronic acid groups are connected by a boron-carbon bond.] According to claim 1,
A polarizing film in which 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). According to claim 1,
A polarizing film in which R ¹ is an aliphatic group. According to claim 1,
A polarizing film wherein the total boron element content in the polarizing film is 1.0 to 5.0 mass%. 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 in an aqueous boric acid solution,
A stretched polyvinyl alcohol film having a boron element content derived from boric acid of 0.5 to 5.0 mass% is immersed in an aqueous solution having a boron-containing compound (B) concentration of 0.1 to 5.0 mass%, and then the film is dried at 95°C or lower. The method for producing the polarizing film according to any one of claims 1 to 4, characterized in that: