JP7282042B2 - Polarizing film and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polarizing film having good polarizing performance and hue and low shrinkage force, 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, smartphones, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, car navigation systems, measuring instruments, and the like. In recent years, these devices have been required to be thinner and lighter, and the glass used in LCDs has been made thinner. there is It is said that the main cause of warpage of LCD panels is the shrinkage of polarizing films that occurs at high temperatures, and there is a demand for polarizing films with low shrinkage force. In addition, improvement in the contrast of LCDs is required, and improvement in polarization performance and hue of polarizing films is also required.

Patent Document 1 describes a first drying step of drying the PVA film at 25° C. or higher and lower than 65° C. and a second drying step of drying the PVA film at 65° C. or higher and 115° C. or lower after performing the dyeing step, the cross-linking step and the stretching step. A method for producing a polarizing film is described. Patent Literature 1 describes that according to the method, the shrinkage of the polarizing film at high temperatures can be reduced to improve the dimensional stability. However, since the drying is performed at a high temperature, there is a problem that the polarizing performance of the obtained polarizing film is lowered and the hue is deteriorated.

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

In Patent Document 3, 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 hue is good. It is described that a good polarizing film can be obtained. However, when the amount of boric acid in the polarizing film is reduced, the shrinkage force decreases, but it is difficult to maintain high polarizing performance.

JP 2015-028634 A KR10-2014-0075154 JP 2013-148806 A

An object of the present invention is to provide a polarizing film having good polarizing performance and hue, and low shrinkage force, and a simple production method thereof.

At least one boron-containing compound (B) selected from the group consisting of PVA (A), a diboronic acid represented by the following formula (I), and a compound that can be converted to the diboronic acid in the presence of water, and A polarizing film containing 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 1 μm outward is 0.1 to 2 atomic %, and the ratio of the concentration (α) to the concentration (β) (α / The problem is solved by providing a polarizing film characterized by β) being 1.5 or more.

[In the 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 via a boron-carbon bond. ]

The boron element content derived from the boron-containing compound (B) in the polarizing film is preferably 0.1 to 3.0 parts by mass with respect to 100 parts by mass of PVA (A). It is also preferred 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% by mass.

The above problem is a method for producing a polarizing film, which includes a dyeing treatment of dyeing a PVA film with a dichroic dye and a stretching treatment of uniaxially stretching the film in an aqueous boric acid solution, in which the boron element content derived from boric acid is 0. A stretched PVA film of 5 to 5.0% by mass is immersed in an aqueous solution having a boron-containing compound (B) concentration of 0.1 to 5.0% by mass, and then the film is heated to 95 ° C. or less. It is also solved by providing a method for manufacturing the polarizing film, which is dried at.

The polarizing film of the present invention has good polarizing performance and hue, and low shrinkage force. According to the production method of the present invention, such a polarizing film can be produced easily.

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

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

[In the 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 via a boron-carbon bond. ]

The boron element concentration (α) derived from the boron-containing compound (B) must be 1 to 7 atomic % in the range of 1 μm inward from the surface of the polarizing film. If the boron element concentration (α) is less than 1 atomic %, the amount of cross-linking in the vicinity of the surface of the polarizing film is too small, resulting in insufficient polarizing performance. 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 tends to tear. The boron element concentration (α) is preferably 6 atomic % or less.

Further, the boron element concentration (β) derived from the boron-containing compound (B) in the range of 1 μm outward from the center of the polarizing film should be 0.1 to 2 atomic %. If the boron element concentration (β) exceeds 2 atomic %, the polarizing performance is lowered and the hue is deteriorated. Although the reason for this is not clear, it is believed 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 the boron element concentration (β) in the polarizing film can be determined using an X-ray photoelectron spectrometer with a gas cluster ion beam gun (GCIB XPS). Specifically, it can be determined by the method described in the examples below.

The thickness of the polarizing film is preferably 5 to 30 μm. If the thickness is less than 5 μm, stretching breakage is likely to occur during production, which may reduce productivity. The thickness is preferably 10 μm or more. On the other hand, if the thickness exceeds 30 μm, there is a risk that performance required for the polarizing plate, such as thinning and weight reduction, may not be satisfied.

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

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 as described above. When the boron-containing compound (B) is adsorbed to the PVA film by a general method, there is no substantial difference in concentration between the surface and the center of the film, and the effect of reducing the shrinkage force is obtained, but the polarization performance In some cases, a problem arises due to a decrease in color tone and hue. The present inventors, as a result of repeated studies in order to achieve both polarizing performance and hue, and shrinkability, by reducing the content of the boron-containing compound (B) in the center of the polarizing film than near the surface, It was found that shrinkage force can be reduced while suppressing deterioration of polarization performance and hue. Although the reason for this is not clear, by reducing the content of the boron-containing compound (B) in the central portion of the polarizing film, the formation of an iodine complex that absorbs short-wavelength light is promoted in that portion. It is thought that the deterioration of polarization performance and hue can be prevented.

The boron element content derived from the boron-containing compound (B) in the polarizing film is preferably 0.1 to 3.0 parts by mass with respect to 100 parts by mass of PVA (A). If the content exceeds 3.0 parts by mass, the amount of cross-linking may become too large and the polarizing film may become fragile and easily cracked. The content is more preferably 2.0 parts by mass or less. On the other hand, when the content is less than 0.1 parts by mass, the amount of cross-linking is too small, and 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 determined by the method described in the examples below.

The total boron element content in the polarizing film is preferably 1.0 to 5.0% by mass. If the content exceeds 5.0% by mass, the shrinkage force of the polarizing film may increase. The content is more preferably 4.0% by mass or less, and even more preferably 3.0% by mass or less. On the other hand, if the content is less than 1.0% by mass, the polarizing performance may be insufficient. The content is more preferably 2.0% by mass or more, and even more preferably 2.2% by mass or more. The total boron element content in the polarizing film can be determined by ICP emission spectrometry. Specifically, it can be determined by the method described in the examples below.

The boron-containing compound (B) used in the present invention is at least one selected from the group consisting of diboronic acids represented by the following formula (I) and compounds convertible to diboronic acids in the presence of water. A 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 via boron-carbon bonds. A boronic acid group has a structure in which a boron atom is bonded to two hydroxyl groups and a carbon atom. Therefore, while boric acid [B(OH) ₃ ] has a boron atom bonded to three hydroxyl groups, boronic acid differs in that it has a boron-carbon bond. Since the boron-carbon bond of the boronic acid group is not hydrolyzed, it is stable even in the presence of water.

In addition, since the hydroxyl group in the boronic acid group can form an ester with an alcohol in the same manner as the hydroxyl group in boric acid, the boron-containing compound (B) used in the present invention reacts with the hydroxyl group of PVA to form an ester. and the boronic acid groups are separated from each other via R ¹ . For these reasons, it is believed that the boron-containing compound (B) used in the present invention can effectively crosslink PVA.

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. 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, ^R2 in structural formula (II) is PVA, and the organic group is bonded to PVA via the boron atom.

The following structural formula (III) is an example of a diboronic acid diester in which two molecules of alcohol (R ² —OH) are reacted with diboronic 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.

In formula (I) above, R ¹ is a divalent organic group having 1 to 20 carbon atoms. An appropriate length of R ¹ enables efficient cross-linking of PVA chains. The number of carbon atoms in R ¹ is preferably 10 or less, more preferably 6 or less, even more preferably 4 or less. Moreover, the number of carbon atoms in R ¹ is preferably 2 or more. R ¹ is a divalent organic group as long as R ¹ and two boronic acid groups are linked via a boron-carbon bond. R ¹ may be a hydrocarbon group or may contain a heteroatom such as oxygen, nitrogen, sulfur or halogen. Considering availability, etc., R ¹ preferably does not contain a heteroatom, and more preferably R ¹ is a hydrocarbon group.

R ¹ is preferably an aliphatic compound because it is easy to set the elemental boron concentration (α) and the elemental boron concentration (β) within the above ranges. When R ¹ is an aromatic group, adsorption to the PVA film and diffusion in the PVA film are slowed down, and it may be difficult to set the boron element concentration (α) and the boron element concentration (β) within the above ranges. .

Specific examples of the boron-containing compound (B) include methanediboronic acid, 1,2-ethanediboronic acid, 1,3-propanediboronic acid, 1,4-butanediboronic acid, 1,5-pentanediboronic acid, 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-heptadecanediborone Boron-containing compounds in which R ¹ is a hydrocarbon group, such as acids, 1,18-octadecanediboronic acid, 1,19-nonadecanediboronic acid, 1,20-icosanediboronic acid and isomers thereof, 2- ^heteroatom -containing compounds such as oxa-1,3-propanediboronic acid, 3-oxa-1,5-pentanediboronic acid, 4-oxa-1,7-heptanediboronic acid and their isomers. and boron-containing compounds in which R ¹ is an aromatic group, such as 1,4-phenylenediboronic acid and isomers thereof. Among them, 1,2-ethanediboronic acid, 1,3-propanediboronic acid and 1,4-butanediboronic acid are preferred.

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 2,000 to 4,000. It is more preferable to be within the range. When the degree of polymerization is 1,500 or more, the optical properties 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 the present invention means the average degree of polymerization measured according to the description of JIS K6726-1994.

The degree of saponification of PVA (A) is preferably 95% or more, more preferably 96% or more, more preferably 98% or more, from the viewpoint of the water resistance of the polarizing film obtained by uniaxially stretching the PVA film. It is even more preferable to have The degree of saponification of PVA (A) refers to a structural unit (typically a vinyl ester unit) of PVA (A) that can be converted into a vinyl alcohol unit (—CH ₂ —CH(OH)—) by saponification. The ratio (%) of the number of moles of the vinyl alcohol unit to the total number of moles of the vinyl alcohol unit and 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) 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 are 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. Vinyl, 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.

PVA (A) is obtained by converting the vinyl ester units of a polyvinyl ester copolymer obtained by copolymerizing a vinyl ester monomer and another monomer copolymerizable therewith into vinyl alcohol units. good too. 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 polarizing performance, the content of units derived from other monomers is preferably 10 mol% or less, more preferably 5 mol% or less, and 2 mol% or less. More preferred.

Among the monomers that can be copolymerized with the vinyl ester monomer, stretchability is improved and stretching can be performed at a higher temperature, thereby reducing the occurrence of troubles such as stretch breakage during the production of optical films. Ethylene is preferred because it further improves the productivity of the optical film. When PVA contains ethylene units, the content of ethylene units is 1 to 4 mol% with respect to the number of moles of all structural units constituting PVA, from the viewpoint of stretchability and stretchable temperature as described above. Preferably, 2 to 3 mol % is more preferable.

The polymerization system for polymerizing the vinyl ester monomer may be any system such as batch polymerization, semi-batch polymerization, continuous polymerization, and semi-continuous polymerization. A known method such as a polymerization method or an emulsion polymerization method can be applied. A bulk polymerization method or a solution polymerization method, in which the polymerization proceeds without solvent or in a solvent such as alcohol, is usually employed. Emulsion polymerization is also preferred for obtaining a polyvinyl ester with a high degree of polymerization. A solvent for the solution polymerization method is not particularly limited, and is, for example, alcohol. Alcohols used as solvents in the solution polymerization method are lower alcohols such as methanol, ethanol and propanol. The amount of solvent used in the polymerization solution may be selected in consideration of the chain transfer of the solvent according to the desired degree of polymerization of PVA. For example, when the solvent is methanol, the mass ratio of the solvent to the total monomers ( (solvent/total monomer) is preferably in the range of 0.01 to 10, more preferably in the range of 0.05 to 3.

The polymerization initiator used for the polymerization of the vinyl ester monomer may be selected from known polymerization initiators such as azo initiators, peroxide initiators and redox initiators according to the polymerization method. Azo 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, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, diethoxyethyl peroxydicarbonate and other peroxydicarbonate compounds; t-butyl peroxyneodecanate, α- acetylcyclohexylsulfonyl peroxide; 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate; and acetyl peroxide. Potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like may be used in combination with the above initiator as the polymerization initiator. The redox initiator is, for example, a polymerization initiator obtained by combining the above peroxide initiator with a reducing agent such as sodium hydrogensulfite, sodium hydrogencarbonate, tartaric acid, L-ascorbic acid, or Rongalite. The amount of the polymerization initiator to be used varies depending on the type of the polymerization initiator and cannot be generally determined, but may be selected according to the polymerization rate. For example, when 2,2'-azobisisobutyronitrile or acetyl peroxide is used as the polymerization initiator, it is preferably 0.01 to 0.2%, more preferably 0.02 to 0.15, relative to the vinyl ester monomer. % is more preferred. The polymerization temperature is not particularly limited, but room temperature to about 150° C. is suitable, preferably 40° C. or more and the boiling point of the solvent used or less.

Polymerization of vinyl ester monomers may be carried out in the presence of a chain transfer agent. Examples of chain transfer agents include aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethanethiol; phosphinates such as sodium phosphinate monohydrate. Among them, aldehydes and ketones are preferably used. The amount of chain transfer agent to be used can be determined according to the chain transfer coefficient of the chain transfer agent to be used and the desired degree of polymerization of PVA. ~10 parts by mass is preferred.

Saponification of the polyvinyl ester can be performed, for example, in a state in which the polyvinyl ester is dissolved in alcohol or water-containing alcohol. Alcohols used for saponification include, for example, lower alcohols such as methanol and ethanol, preferably methanol. The alcohol used for saponification may contain other solvents such as acetone, methyl acetate, ethyl acetate, benzene, etc., for example in proportions of up to 40% by weight of its weight. Catalysts used for saponification are, for example, alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, alkali catalysts such as sodium methylate, and acid catalysts such as mineral acids. Although the temperature for saponification is not limited, it is preferably within the range of 20 to 60°C. When a gel-like product precipitates as the saponification progresses, the product can be pulverized, washed and dried to obtain PVA. The saponification method is not limited to the methods described above, and known methods can be applied.

The PVA film can contain a plasticizer in addition to the above PVA (A). 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 is preferably in the range of 1 to 20 parts by mass, more preferably in the range of 3 to 17 parts by mass, relative to 100 parts by mass of PVA (A). More preferably, it falls 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 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 films may also contain fillers, processing stabilizers such as copper compounds, weather stabilizers, colorants, UV absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, and other thermoplastic resins. Additives such as lubricants, fragrances, defoamers, deodorants, extenders, release agents, release agents, reinforcing agents, cross-linking agents, anti-mold agents, preservatives, crystallization rate retarders, etc. It can be blended as appropriate.

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

The degree of swelling of the PVA film is preferably in the range of 160-240%, more preferably in the range of 170-230%, and particularly preferably in the range of 180-220%. 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 degree of swelling of the PVA film can be determined by the method described in Examples below.

The thickness of the PVA film is preferably about 5-100 μm, more preferably about 5-60 μm, especially about 10-45 μm. If the thickness is too thin, there is a tendency that stretch breakage tends to occur during stretching such as uniaxial stretching for producing a polarizing film. On the other hand, if the thickness is too large, 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 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, uniform uniaxial stretching tends to be difficult when the polarizing film is produced by a practical apparatus. The width of the PVA film used is preferably 7 m or less.

The production method of the PVA film is not particularly limited, and a production method that makes the thickness and width of the film after film formation more uniform can be preferably adopted. PVA (A), and, if necessary, one or more of the plasticizers, additives, and surfactants described later are dissolved in a liquid medium for film-forming undiluted solutions, and PVA ( A) and, if necessary, a membrane-forming stock solution containing one or more of plasticizers, additives, surfactants, liquid media, etc., in which PVA (A) is melted can be manufactured by When the membrane-forming stock solution contains at least one of a plasticizer, an additive, 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, filtration and defoaming are performed smoothly during preparation of the membrane-forming stock solution, and the PVA has few foreign substances and defects. Film production is facilitated. 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 the industrial production of PVA films.

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 PVA film, and facilitates the peeling of the PVA 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 PVA 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 the PVA film used for the production of the polarizing film using the film forming stock solution described above include cast film forming method, extrusion film forming method, wet film forming method, gel film forming method, and the like. is mentioned. 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.

As a specific example of a method for producing a PVA film, for example, using a T-shaped slit die, a hopper plate, an I-die, a lip coater die, etc., the above-mentioned film-forming stock solution is subjected to rotating heating located on the most upstream side. It is uniformly discharged or cast on the peripheral surface of the first roll (or belt), and the volatile components are removed from one surface of the film discharged or cast on the peripheral surface of the first roll (or belt). After drying by evaporation followed by further drying on the circumferential surface of one or more rotating heated rolls arranged downstream therefrom or by passage through a hot air dryer, A method of winding with a winding device can be industrially preferably employed. 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 polarizing film manufacturing 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 A stretched PVA film of 5.0% by mass is immersed in an aqueous solution having a boron-containing compound (B) concentration of 0.1 to 5.0% by mass, and then the film is dried at 95 ° C. or less. A method for producing a polarizing film. The PVA film used for producing the polarizing film of the present invention may be subjected to dyeing treatment, stretching treatment, and, if necessary, swelling treatment, boric acid cross-linking treatment, fixing treatment, washing treatment, heat treatment, or the like. . In this case, the order of each treatment is not particularly limited, but it is preferable to perform the swelling treatment, the boric acid cross-linking treatment, the stretching treatment, and the fixing treatment in this order. Further, the dyeing treatment is preferably performed before the boric acid cross-linking treatment. It should be noted that one or more treatments may be performed simultaneously, and one or more of each treatment may be performed twice or more.

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. Also, the time for immersion in water is preferably, for example, 0.1 to 5 minutes, more preferably 0.2 to 3 minutes. The water used for immersion in water is not limited to pure water. Sulfuric acid ester type such as ethylene lauryl ether sulfate and octyl sulfate; sulfonic acid type anionic surfactant such as dodecylbenzene sulfonate, alkyl ether type such as polyoxyethylene oleyl ether; alkyl such as polyoxyethylene octylphenyl ether Phenyl ether type; Alkyl ester type such as polyoxyethylene laurate; Alkyl amine type such as polyoxyethylene lauryl amino ether; Alkyl amide type such as polyoxyethylene lauric acid amide; Polypropylene glycol such as polyoxyethylene polyoxypropylene ether Ether type; alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; allylphenyl ether type nonionic surfactant such as polyoxyalkylene allylphenyl ether, etc. Even if it is an aqueous solution in which surfactant components are dissolved, or mixtures with aqueous media such as dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane and structural isomers thereof may be

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. Dyeing can be performed at any stage before stretching, during stretching, or after stretching. From the viewpoint of orientation, dyeing treatment is preferably performed after the swelling treatment and before the 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. 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% by mass, and the concentration of potassium iodide is 0.01 to 10% by mass. is preferred. 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 aid 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.

By subjecting the PVA film to a cross-linking treatment with boric acid, it is possible to effectively prevent the PVA (A) or the dichroic dye adsorbed to the PVA film from eluting into water during wet stretching at high temperature. . From this point of view, the boric acid cross-linking treatment is more preferably performed after the dyeing treatment and before the 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 borate salts such as boric acid and borax can be used. Boric acid is preferred. The concentration of the boric acid cross-linking agent in the aqueous solution containing the boric acid cross-linking agent is preferably 1 to 10% by mass, more preferably 2 to 7% by mass. Sufficient stretchability can be maintained by setting the concentration of the boric acid cross-linking agent to 1 to 10% by mass. If the concentration of the boric acid cross-linking agent exceeds 10% by mass, cross-linking may proceed excessively and stretchability may decrease, which is not preferable. In addition, when the concentration of the boric acid cross-linking agent is less than 1% by mass, the effect of preventing the dichroic dye adsorbed to PVA (A) or the PVA film from eluting into water during stretching at high temperature becomes insufficient. I don't like it because there is something. 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 20-50°C, particularly preferably 25-40°C. By setting the temperature to 20 to 50° C., efficient boric acid cross-linking can be achieved.

Apart from the stretching treatment described later, the PVA film may be stretched (pre-stretched) during or between the above-described treatments. In this way, the total draw ratio of the pre-stretching performed before the stretching treatment (the ratio obtained by multiplying the draw ratios in each treatment) is determined from the viewpoint of the polarizing performance of the resulting polarizing film. Based on the original length of the 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 stretching treatment may be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution containing a boric acid cross-linking agent, or in the dyeing treatment bath described above. 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 preferable, and it is particularly preferable to perform the uniaxial stretching treatment in an aqueous solution containing a boric acid cross-linking agent. For ease of handling, the boric acid cross-linking agent is preferably boric acid. The concentration of boric acid in the aqueous solution is preferably 0.5 to 5% by mass, more preferably 2 to 5% by mass. If the concentration of boric acid is less than 0.5% by mass, the content of boric acid in the PVA film becomes too small, and when the stretched PVA film is immersed in an aqueous solution of the boron-containing compound (B), In addition, the boron-containing compound (B) may be excessively adsorbed and the polarizing film may become brittle. 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 stretched PVA film is immersed in an aqueous solution of the boron-containing compound (B), Boric acid may excessively inhibit the adsorption of the boron-containing compound (B). The boric acid aqueous solution may contain potassium iodide, and the concentration of potassium iodide is preferably 0.01 to 10% by mass. The drawing temperature in the drawing treatment is preferably 30 to 90°C. The temperature is more preferably 40° C. or higher, and even more preferably 50° C. or higher. On the other hand, the temperature is more preferably 80° C. or lower, more preferably 70° C. or lower. Further, the draw ratio in the drawing process (total draw ratio from the raw material PVA film) is preferably 2.0 to 4.0 times. From the viewpoint of the polarizing 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, more preferably 5.5 times or more, from the viewpoint of polarization performance. 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 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 polarizing 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 stretching treatment in order to strengthen the adsorption of the dichroic dye (iodine dye, dichroic dye, etc.) to the PVA film. An aqueous solution containing the boron-containing compound (B) is preferable as the fixation treatment bath used for the fixation treatment. In addition, if necessary, boric acid, iodine, iodides, metal compounds, etc. may be added to the fixing treatment bath, and it is preferable to add iodides such as potassium iodide. The temperature of the fixing treatment bath is preferably 10 to 70°C, 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 still more preferably less than 1.1 times.

A boron-containing compound (B) is adsorbed on the PVA film after the 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) is adsorbed to the center of the polarizing film, which may deteriorate the hue. In addition, there is a possibility that intermolecular cross-linking may become excessive and stretchability may be lowered. The boron-containing compound (B) may be adsorbed to the PVA film in any of the dyeing treatment, the boric acid cross-linking treatment, and the fixing treatment as long as it is a step after the stretching treatment. It is preferable from the viewpoint of not deteriorating the hue and stretchability. Specifically, the PVA film is obtained by immersing the PVA film in an aqueous solution having a concentration of the boron-containing compound (B) of 0.1 to 5.0% by mass. It is preferable to allow the boron-containing compound (B) to be adsorbed on.

If the concentration of the boron-containing compound (B) in the aqueous solution is less than 0.1% by mass, the hue may deteriorate and the effect of reducing shrinkage force may become insufficient. The concentration is more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more. On the other hand, when the concentration exceeds 5.0% by mass, the boron-containing compound (B) is excessively adsorbed, and the surface of the polarizing film becomes brittle, and a precipitate of the boron-containing compound (B) is formed on the surface. be. More preferably, the concentration is 4% by mass or less. Also, the temperature of the aqueous solution is preferably 10 to 70°C. If the temperature is lower than 10°C, the boron-containing compound (B) may precipitate in the treatment bath. As for the said temperature, 20 degreeC or more is more preferable. On the other hand, if the temperature exceeds 70° C., the polarizing film may be easily wrinkled. The temperature is more preferably 60° C. or lower, still more preferably 50° C. or lower, and particularly preferably 40° C. or lower. The immersion time in the aqueous solution is preferably 5 to 400 seconds. The aqueous solution preferably contains an iodide such as potassium iodide as an auxiliary agent from the viewpoint of improving polarizing performance, and the content thereof is preferably 0.5 to 10% by mass.

The boron element content derived from boric acid in the PVA film used for adsorption of the boron-containing compound (B) should be 0.5 to 5.0% by mass. This makes it possible to adjust the concentration of the boron-containing compound (B) in the thickness direction of the polarizing film, and the boron element concentration (α) and the boron element concentration (β) derived from the boron-containing compound (B) are set within the above ranges. can be done. 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 be adsorbed near the surface of the polarizing film and less likely to be adsorbed in the center. it is conceivable that. When the boron element content derived from boric acid in the PVA film is less than 0.5% by mass, the boron-containing compound (B) is excessively adsorbed when the PVA film is immersed in an aqueous solution of the boron-containing compound (B). , the hue may be deteriorated, and the surface of the polarizing film may become too hard to be easily torn. The content is preferably 1% by mass or more. On the other hand, if the content exceeds 5.0% by mass, 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). The boron element content derived from boric acid in the PVA film can be adjusted by adjusting the temperature of the treatment bath, boric acid concentration, immersion time, etc. in the stretching treatment and the boric acid cross-linking 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. However, when the temperature and the immersion time are adjusted, wrinkles may occur in the polarizing film, so it is preferable to adjust the concentration of the boron-containing compound (B).

A washing treatment may be performed before the drying treatment. The washing treatment is generally carried out by immersing the PVA film in water, distilled water, pure water, or the like. At this time, the aqueous solution used for the cleaning treatment preferably contains an iodide such as potassium iodide from the viewpoint of improving the polarization performance, and the concentration of the iodide is preferably 0.5 to 10% by mass. Also, the temperature of the aqueous solution in the cleaning treatment is generally 5 to 50°C, preferably 10 to 45°C, particularly preferably 10 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 polarizing performance may deteriorate, which is not preferable.

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

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 the dried polarizing film having a moisture content of 5% or less to improve the dimensional stability of the polarizing film. The heat treatment conditions are not particularly limited, but the heat treatment temperature is preferably 60°C to 95°C, particularly preferably 70°C to 90°C. If the heat treatment is performed at a temperature lower than 60°C, the effect of improving the dimensional stability due to the heat treatment may be insufficient. I don't like it because

The polarizing film obtained as described above 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 the adhesive for bonding include PVA-based adhesives and UV-curing adhesives, among which PVA-based adhesives are preferred.

The polarizing plate obtained as described above can be used as an LCD component by being coated with an acrylic pressure-sensitive adhesive and then pasted onto a glass substrate. At the same time, it may be attached to a retardation film, a viewing angle improving film, a brightness improving film, or the like.

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.

[Optical properties of polarizing film]
A rectangular sample of 4 cm in the length direction × 2 cm in the width direction of the polarizing film was collected from the center of the polarizing film in the width direction and the length direction, and a spectrophotometer V-7100 with an integrating sphere (manufactured by JASCO Corporation) was used. The parallel transmittance and crossed Nicols transmittance of the polarizing film were measured using an automatic polarizing film measurement device VAP-7070S (manufactured by JASCO Corporation) equipped with a Glan-Taylor polarizer. The measurement wavelength range is set to 380 nm to 780 nm, and the transmittance when the vibration direction of the polarized light incident on the polarizing film through the Glan-Taylor polarizer is parallel to the transmission axis of the polarizing film is defined as the parallel transmittance, and the transmittance of the polarizing film. The crossed Nicols transmittance was defined as the case perpendicular to the axis. After that, using a "polarizing film evaluation program" (manufactured by JASCO Corporation), C light source, visibility correction in the visible light region of 2 ° visual field so as to comply with JIS Z 8722 (object color measurement method). Then, the transmittance of the polarizing film, the degree of polarization, and the b value (hue) of the polarizing film were calculated, and these three values were obtained as the optical properties of the polarizing film.

[Contraction force]
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 about 20° C./20% RH for 18 hours was used for the measurement. After setting the thermostat of the autograph "AG-X" to 20 ° C., the polarizing film (15 cm in the length direction, 1.5 cm in the width direction) was attached to the chuck (chuck interval 5 cm), and at the same time as the start of pulling, 10 ° C./min. The temperature of the constant temperature bath was started to rise to 80°C at a rate of temperature rise of . 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, mark-line stickers are attached to the upper and lower chucks, respectively. The measurement was performed while correcting only the amount of movement. In the initial stage of measurement (within 10 minutes from the start of measurement), when a minimum value of tension occurred, the minimum value was subtracted from the measured value of tension after 4 hours, and the resulting value was taken 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 X-ray photoelectron spectrometer (manufactured by ULVAC-Phi, Inc.: PHI5000 VersaProbe II) (GCIB-XPS) equipped with a gas cluster ion beam gun. A polarizing film conditioned at about 23° C./50% RH for 16 hours was used for the measurement. Sputtering is performed in a range of 2 mm × 2 mm while neutralizing under the conditions of a sputtering ion source of Ar2500 ⁺ , an acceleration voltage of 20 keV, and a current value of 30 nA. rice field. XPS measurement is performed using monochromatic Al as an X-ray source, with an X-ray spot diameter of 100 μm, an X-ray output of 15 kV, and 25 W, and five elements of carbon, boron, oxygen, iodine, and potassium are detected. Selected. When a dichroic dye is used as the 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 ULVAC-Phi, Inc.), the boron element concentration at each depth of the polarizing film ( a, atomic %) was calculated. After that, for the XPS spectrum at each depth, using the spreadsheet software "Microsoft 2010" (manufactured by Microsoft Corporation), the binding energy caused by boron in boric acid was 192.3 eV, and boron in the boron-containing compound (B) The resulting binding energy was appropriately set, and peak separation was performed by the least-squares method using the pseudo-Voigt function. A linear function calculated from the average 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 boron derived from the boron-containing compound (B) is calculated with respect to the sum of boron derived from boric acid and boron in the boron-containing compound (B), and the following calculation formula (1) to calculate the boron element concentration derived from the boron-containing compound (B) at each depth.
Boron element concentration (atomic %) derived from the boron-containing compound (B)
= a x b x 10 ^-2 (1)

The binding energy of the boron-containing compound (B) due to boron changes depending on the structure of the compound. Therefore, it is necessary to appropriately set the binding energy depending on the type of boron-containing compound (B). For example, it is 191.3 eV when the boron-containing compound (B) is 1,4-butanediboronic acid. Further, when performing peak separation by the method of least squares using the pseudo Voigt function, the Lorentz function ratio of boric acid was set to 0.115, and 2 ^1/2 ×σ was set to 0.809. The Lorentzian function ratio and half-value width of the boron-containing compound (B) also change depending on the structure of the compound. Therefore, it is necessary to appropriately set the Lorenz function 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 Lorenz function ratio was set to 0.263 and 2 ^1/2 ×σ was set to 0.797.

By such a method, on both sides of the polarizing film, the boron element concentration derived from the boron-containing compound (B) is obtained every 50 nm from the surface to 1 μm inward, and the average value is 1 μm inward from the surface of the polarizing film. The boron element concentration (α, atomic %) derived from the boron-containing compound (B) within the range was used. Further, 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 on both sides, and the average value is the boron-containing compound in the range of 1 μm to the outside from the center of the polarizing film. It was taken as the boron element concentration (β, atomic %) derived from (B).

[Boron element content derived from boron-containing compound (B) relative to 100 parts by mass of PVA (A)]
After dissolving the polarizing film conditioned at 23° C./50% RH for 16 hours with heavy water to a concentration of approximately 0.003% by mass, the solution was ^concentrated by a rotary evaporator to approximately 0.15% by mass. This was used as a measurement sample for H-NMR. ¹ H-NMR (JNM-AL400: 400 MHz, manufactured by JEOL Ltd.) was measured at 80° C. and analyzed 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. After that, 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. 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 (A) (area c) is used as a reference for the peak area, and the boron-containing compound It was set so that the number of hydrogen atoms of the corresponding hydrocarbon in (B) and the value of the area c were the same. Next, the hydrogen peak in the range of 1.7 ppm to 2.4 ppm is overlapped with the hydrogen peak derived from the methylene group of PVA (A) and the hydrogen peak derived from the methylene group of PVA (A) Boron-containing compound (B) The peak area (area d) was determined by considering the sum of the hydrogen peaks of the hydrocarbon groups contained in . After that, the area e was calculated by subtracting the hydrogen number of the hydrocarbon of the boron-containing compound (B) overlapping the hydrogen peak of the methylene group derived from the PVA (A) from the area d. The values obtained by these methods were substituted into the following formula to calculate the elemental boron content derived from the boron-containing compound (B) with respect to 100 parts by mass of PVA (A). In addition, X and Y in the following formula (2) are respectively the number of hydrogen atoms in the hydrocarbon group contained in the boron-containing compound (B) that does not overlap with the peak of PVA, and the number of boron atoms per molecule of the boron-containing compound (B). is. Formula (2) is a formula used when non-modified PVA is used, and when using modified PVA as a raw material, formula (2) must be modified as appropriate.
Boron element content (parts by mass) derived from the 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 repeating units of unmodified PVA. For example, ^{the 1} H-NMR chart in FIG. 1 is obtained by measuring the polarizing film of Example 1, and the boron element content derived from the boron-containing compound (B) with respect to 100 parts by mass of PVA is rounded to the second decimal place and is 0.00. 5 parts by mass.

[Total boron element content in polarizing film]
The mass f (g) of the polarizing film that had been conditioned at approximately 23° C./50% RH for 16 hours was measured, and dissolved in approximately 20 mL of distilled water so that the polarizing film would be approximately 0.005% by mass. An aqueous solution in which the polarizing film was dissolved was used as a measurement sample, and its mass g (g) was measured. After that, 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 calculated by substituting the value into the following formula (3) was taken as the total boron element content (% by mass) in the polarizing film.
Total boron element content in polarizing film (% by mass)
= [(h×10 ⁻⁶ ×g)/f]×100 (3)

[Boric element content derived from boric acid in PVA film after stretching]
After the stretching treatment, the PVA film before the fixing treatment was sampled, dried and then conditioned at 23° C./50% RH for 16 hours, and then the mass i (g) was measured. It was dissolved in approximately 20 mL of distilled water to a concentration of 0.005% by mass. The resulting aqueous solution was used as a measurement sample, and its mass j (g) was measured. After that, the boron concentration k (ppm) of the measurement sample was measured using a multi-type ICP emission spectrometer manufactured by Shimadzu Corporation. After that, the value calculated by substituting the value into the following formula (4) was defined 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 (% by mass) derived from boric acid in PVA film
= [(k x ^10-6 x j)/i] x 100 (4)

[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 l) 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 m) after drying was measured. The degree of swelling of the PVA film was calculated by substituting the values of mass l and mass m into the following formula (5).
Degree of swelling (%) = (mass l/mass m) x 100 (5)

[Example 1]
Contains 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 parts by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant, and the content of PVA is A PVA aqueous solution of 10% by mass was prepared. A 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 having a thickness of 30 μm and a degree of swelling of 200%.

A sample of 5 cm wide by 9 cm long was cut from the central portion of the obtained PVA film 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, it is immersed in an aqueous solution (dyeing treatment bath) containing 0.035% by mass of iodine and 3.5% by mass of potassium iodide (temperature: 30 ° C.) for 60 seconds while increasing 2.2 times (total 2.4 times). The film was uniaxially stretched in the length direction to adsorb iodine. Next, while being immersed in an aqueous solution containing 3.0% by mass of boric acid and 3% by mass of potassium iodide (boric acid cross-linking treatment bath) (temperature 30 ° C.), 1.2 times (2.7 in total) times) was uniaxially stretched in the length direction. Furthermore, while being immersed in an aqueous solution (stretching treatment bath) at 60°C containing 4.0% by mass of boric acid and 6% by mass of potassium iodide, the film was uniaxially stretched in the length direction up to a total of 6.0 times. . After the uniaxial stretching treatment, an aqueous solution (fixing treatment bath) containing 0.5% by mass of 1,4-butanediboronic acid and 2.5% by mass of potassium iodide as the boron-containing compound (B) (temperature 30 ° C. ) for 100 seconds. In the fixing process, the PVA film was not stretched (stretch ratio of 1.0). Finally, it was dried at 60° C. for 240 seconds to produce a polarizing film (thickness: 13 μm).

After the stretching treatment, the uniaxially stretched film prepared only by drying without performing the fixing treatment was subjected to ICP measurement, and the boron element content derived from boric acid in the film was 4.5% by mass. .

When the XPS spectrum of the polarizing film was measured and analyzed, the boron element concentration (α) derived from the boron-containing compound (B) in the range of 1 μm inside from the surface of the polarizing film was 5.0 atomic%, and the center of the polarizing film The boron element concentration (β) derived from the boron-containing compound (B) in the range from 1 μm to 1 μm was 0.7 atomic %.

When the ¹ H-NMR of the polarizing film was measured and analyzed, the elemental boron content derived from the boron-containing compound (B) was 0.5 parts by mass with respect to 100 parts by mass of the PVA.

ICP measurement of the polarizing film revealed that the total boron element content in the polarizing film was 2.5% by mass.

Using a polarizing film, the optical properties and shrinkage force of the polarizing film were evaluated by the methods described above. It was 6.1N. Table 1 shows the above results.

[Example 2]
Polarization was performed 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 as the fixation treatment bath. A film was produced and each measurement and evaluation were performed. Table 1 shows the results.

[Example 3]
Polarized light was obtained 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 as the fixation treatment bath. A film was produced and each measurement and evaluation were performed. Table 1 shows the results.

[Example 4]
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 10 seconds, and each measurement and evaluation were performed. Table 1 shows the results.

[Example 5]
A polarizing film was produced in the same manner as in Example 1, except that the concentration of boric acid in the stretching bath was changed to 2.0% by mass, the temperature of the stretching bath was changed to 58°C, and the time of immersion in the fixing bath was changed to 10 seconds. Then, each measurement and evaluation were performed. Table 1 shows the results.

[Comparative Example 1]
With reference to KR10-2014-0075154, the film was immersed in pure water at 30° C. for 120 seconds and stretched uniaxially in the length direction so as to be 1.3 times the total length for swelling treatment. Subsequently, while immersing in an aqueous solution (dyeing treatment bath) (temperature 30 ° C.) containing 10 parts by mass of potassium iodide at a ratio of 1 part by mass of iodine for 240 seconds, 1.1 times (total 1.4 times ) while being uniaxially stretched in the length direction. Subsequently, while immersing for 120 seconds in an aqueous solution (stretching treatment bath) containing 0.5% by mass of 1,4-butanediboronic acid and 5% by mass of potassium iodide at 50° C., it was stretched 4.3 times (total 6.0 times) was uniaxially stretched in the length direction. After that, it was immersed in pure water (cleaning treatment bath) at 30° C. for 10 seconds. Finally, it was dried at 60°C for 4 minutes to prepare a polarizing film. Each measurement and evaluation were performed on the obtained polarizing film. Table 1 shows the results.

[Comparative Example 2]
A polarizing film was prepared in the same manner as in Comparative Example 1, except that the concentration of 1,4-butanediboronic acid in the stretching treatment bath was changed to 0.2% by mass, and then each measurement and evaluation were performed. Table 1 shows the results.

[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 the fixing treatment bath. Then, each measurement and evaluation were performed. Table 1 shows the results.

[Comparative Example 4]
An aqueous solution containing 2.0% by mass of boric acid and 3% by mass of potassium iodide was used as the fixing treatment bath (temperature: 30°C), and the time for immersion in the fixing treatment bath was changed to 10 seconds. A polarizing film was produced in the same manner as in Example 1 except that the measurement and evaluation were performed. Table 1 shows the results.

[Comparative Example 5]
An aqueous solution containing 1.0% by mass of boric acid and 3% by mass of potassium iodide (temperature: 30° C.) was used as the fixing treatment bath, and the time for immersion in the fixing treatment bath was changed to 10 seconds. Except for that, a polarizing film was produced in the same manner as in Example 2, and each measurement and evaluation were performed. Table 1 shows the results.

[Comparative Example 6]
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 time for immersion in the fixing treatment bath was changed to 10 seconds. Except for that, a polarizing film was produced in the same manner as in Example 1, and each measurement or evaluation was performed. Table 1 shows the results.

[Comparative Example 7]
As the fixation treatment bath, an aqueous solution (temperature: 30°C) containing 2% by mass of potassium iodide was used, and the procedure was the same as in Example 1, except that the time for immersion in the fixation treatment bath was changed to 20 seconds. Then, a polarizing film was produced, and each measurement and evaluation were performed. Table 1 shows the results.

[Comparative Example 8]
Except for using an aqueous solution (temperature of 30°C) containing 2.0% by mass of boric acid and 3% by mass of potassium iodide as the fixing treatment bath, and changing the drying temperature to 100°C, A polarizing film was produced in the same manner as in Example 1, and each measurement and evaluation were performed. Table 1 shows the results.

In Examples 2 to 5 and Comparative Examples 3 to 8, as in Example 1, an aqueous solution (dyeing treatment bath) containing 100 parts by mass of potassium iodide with respect to 1 part by mass of iodine (temperature: 30 ° C. ) for 60 seconds, the film was uniaxially stretched 2.2 times (total 2.4 times) in the length direction to adsorb iodine. 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%. In Comparative Examples 1 and 2, while immersing 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, 1.1 times (total 1.4 times at 1.4 times) and uniaxially stretched in the length direction to adsorb iodine. 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%.

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

1 Peak derived from heavy water, which is a measurement solvent 2 Peak derived from 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 PVA A peak derived from a hydrocarbon group contained in a boron-containing compound that does not overlap with

Claims (5)

Polyvinyl alcohol (A), at least one boron-containing compound (B) selected from the group consisting of diboronic acid represented by the following formula (I) and a compound that can be converted to the diboronic acid in the presence of water, and boric acid ( C) a polarizing film comprising
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 the boron-containing compound in the range from the center to 1 μm. The boron element concentration (β) derived from (B) is 0.1 to 2 atomic % ,
The ratio (α/β) of the concentration (α) to the concentration (β) is 1.5 or more, and
The polarizing film, wherein the compound convertible to the diboronic acid in the presence of water is an ester formed by reacting the diboronic acid with polyvinyl alcohol (A).

[In the formula (I), R ¹ is a divalent hydrocarbon group containing no heteroatom and having 1 to 20 carbon atoms , and R ¹ and two boronic acid groups are linked via a boron-carbon bond. . ]
The polarizing film according to claim 1, 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 polyvinyl alcohol (A). . 3. The polarizing film according to claim 1 or 2, wherein ^R1 is an aliphatic group. The polarizing film according to any one of claims 1 to 3, wherein the total boron element content in the polarizing film is 1.0 to 5.0% by mass. In a method for producing a polarizing film including 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% by mass is treated with an aqueous solution having a boron-containing compound (B) concentration of 0.1 to 5.0% by mass. The method for producing a polarizing film according to any one of claims 1 to 4, characterized in that the film is dried at 95°C or less after being immersed in.

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