KR20190024989A - Polarizing film and manufacturing method thereof - Google Patents

Abstract

(B) having at least one functional group selected from the group consisting of a polyvinyl alcohol (A), a boronic acid group and a boron-containing group which can be converted to a boronic acid group in the presence of water, Wherein the content of the boron element derived from the boron-containing compound (B) in the film is 0.1 to 3 parts by mass relative to 100 parts by mass of the polyvinyl alcohol (A). And further contains boric acid, and the content of the total boron element in the polarizing film is preferably 0.2 to 5% by mass. Thereby, a polarizing film excellent in anti-wet heat performance is provided.

Description

Polarizing film and manufacturing method thereof

The present invention relates to a polarizing film having excellent heat and humidity resistance and a method for producing the polarizing film.

A polarizing plate having light transmission and shielding functions is a fundamental component of a liquid crystal display (LCD) together with a liquid crystal that changes the polarization state of light. Most polarizing plates have a structure in which a protective film such as a cellulose acylate (TAC) film is bonded to the surface of a polarizing film in order to prevent discoloration of the polarizing film or prevent shrinkage of the polarizing film, (I ₃ ^- , I ₅ ^-, and the like) are added to a matrix obtained by uniaxially stretching a polyvinyl alcohol film (hereinafter sometimes referred to as " PVA " Is adsorbed by the adsorbent.

LCDs are used in a wide range of small-sized devices such as electronic desk calculators and wrist watches, mobile phones, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, vehicle navigation systems, and measuring instruments used indoors and outdoors. It is required to be thin and lightweight. Therefore, each member of the LCD is also required to be thin. However, if the protective film of the polarizing plate, which is one of the members of the LCD, is made thinner, there is a concern that the function of preventing discoloration of the iodine polarizing film is lowered. Therefore, there is a demand for an iodine-based polarizing film excellent in resistance to humidity and humidity, which has a low discoloration under high temperature and high humidity.

As a method for improving the heat and humidity resistance of the iodine-based polarizing film, there have been proposed a method of crosslinking the polarizing film with polyaldehyde (Patent Document 1) and a method of crosslinking with a polyvalent carboxylic acid compound (Patent Document 2) Is known.

Japanese Patent Application Laid-Open No. 6-235815 Japanese Laid-Open Patent Publication No. 2011-257756

However, in the case of using polyhydric aldehyde, since aldehyde is easily volatilized and concentration control is difficult, industrial implementation is difficult. In addition, since the polyvalent carboxylic acid compound has low reactivity and requires use of an acid catalyst or treatment at a high temperature, there is a problem that the polarizing film is colored.

Therefore, an object of the present invention is to provide a polarizing film excellent in resistance to moisture and heat, which can be produced industrially easily, without using an acid catalyst, requiring no treatment at a high temperature.

As a result of diligent studies to achieve the above object, the present inventors have found that the above problems can be solved by a polarizing film containing polyvinyl alcohol and a specific boron-containing organic compound, thereby completing the present invention.

The above problem is solved by a polarizing plate comprising a polyvinyl alcohol (A), a polarizing plate containing a boron-containing compound (B) having at least one functional group selected from the group consisting of a boronic acid group and a boron- Wherein the content of the boron element derived from the boron-containing compound (B) in the polarizing film is 0.1 to 3 parts by mass relative to 100 parts by mass of the polyvinyl alcohol (A).

At this time, it is preferable that boric acid is further contained and the content of the total boron element in the polarizing film is 0.2 to 5% by mass. It is also preferable that the boron-containing compound (B) has a plurality of the above functional groups.

The above object is also achieved by a method for producing a polarizing film comprising a dyeing treatment for dyeing a polyvinyl alcohol film with a dichroic dye and a stretching treatment for uniaxially stretching the film, By mass of the polarizing film in an aqueous solution of the polarizing film.

According to the present invention, a polarizing film having excellent heat and humidity resistance is provided. According to the production method of the present invention, such a polarizing film can be industrially easily produced.

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

The polarizing film of the present invention comprises a polyvinyl alcohol (A), a boron-containing compound (B) having at least one functional group selected from the group consisting of a boronic acid group and a boron-containing group capable of being converted into a boronic acid group in the presence of water . By crosslinking the polyvinyl alcohol with the boron-containing compound (B), the heat and humidity resistance of the polarizing film is improved.

The boron-containing compound (B) used in the present invention is an organic compound having at least one functional group selected from the group consisting of a boronic acid group and a boron-containing group which can be converted into a boronic acid group in the presence of water. The boronic acid group is a monovalent substituent represented by the following structural formula (1) and has a structure in which a boron atom is bonded to two hydroxyl groups and carbon atoms (not shown). In boric acid [B (OH) ₃ ], a boron atom is bonded to three hydroxyl groups, whereas boronic acid differs in that it has a boron-carbon bond. Since the boron-carbon bond of the boronate group is not hydrolyzed, it is stable even in an environment in which water exists. As the boron-containing group which can be converted into a boronic acid group in the presence of water, the boronic acid ester group described below can be exemplified, but is not limited thereto.

[Chemical Formula 1]

The hydroxyl group of the boronic acid group can form an ester with an alcohol in the same manner as the hydroxyl group of boric acid. The following structural formula (2) is a boronic acid monoester group in which one molecule of alcohol (R-OH) is reacted with a boronic acid group. Here, when the boronic acid group is bonded to the hydroxyl group of the PVA, R in the structural formula (2) is a PVA chain, and the carbon-containing group is bonded to the PVA chain via a boron atom, so that the humidity resistance of the polarizing film is improved.

(2)

The following structural formula (3) is a boronic acid diester group in which two molecules of alcohol (R-OH) have reacted with respect to the boronic acid group. Here, when the boronic acid group is bonded to the hydroxyl group of PVA, the two R's in the structural formula (3) are all PVA chains, and a plurality of PVA chains are cross-linked to each other, effectively improving the moisture and heat resistance of the obtained polarizing film.

(3)

Examples of the boron-containing compound (B) used in the present invention include methylboronic acid, ethylboronic acid, propylboronic acid, butylboronic acid, pentylboronic acid, hexylboronic acid, isomers thereof and phenylboronic acid . These have at least one functional group selected from the group consisting of a boronic acid group in the molecule and a boron-containing group capable of being converted into a boronic acid group in the presence of water.

When the boron-containing compound (B) is an aromatic compound, the moisture resistance of the polarizing film may be improved. Although the reason is not clear, it is presumed that the water permeation becomes difficult due to the π-π stacking of the aromatic rings, and the effect of improving the heat and humidity resistance of the polarizing film is increased. Examples of the boron-containing compound (B) include phenylboronic acid, 1,4-benzene diboronic acid, 1,3-benzene diboronic acid, and 1,3,5-benzenetric boronic acid.

The boron-containing compound (B) has a plurality of functional groups selected from the group consisting of a boronic acid group in the molecule and a boron-containing group capable of being converted into a boronic acid group in the presence of water, . The boron-containing compound (B) having two boronic acid groups in the molecule is shown in the following structural formula (4). Here, X is a divalent organic group and is an alkylene group or an arylene group. In this case, there are four points of reacting with the hydroxyl group of PVA to form an ester, so that the PVA chain is more effectively crosslinked.

[Chemical Formula 4]

Examples of the boron-containing compound (B) having a plurality of the functional groups include methane diboronic acid, ethane diboronic acid, propane diboronic acid, butane diboronic acid, pentane diboronic acid, hexane diboronic acid and isomers thereof, Lonic acid, 1,3-benzene diboronic acid, and 1,3,5-benzenetric boronic acid.

The content of the boron element derived from the boron-containing compound (B) in the polarizing film of the present invention is required to be 0.1 to 3 parts by mass relative to 100 parts by mass of the polyvinyl alcohol (A). When the content of the boron element derived from the boron-containing compound (B) is less than 0.1 part by mass, the crosslinking amount of the polyvinyl alcohol (A) is small and the effect of improving the resistance to humidity and humidity is insufficient. The boron element content derived from the boron-containing compound (B) is preferably 0.2 parts by mass or more, and more preferably 0.3 parts by mass or more. On the other hand, if the content of the boron element derived from the boron-containing compound (B) is more than 3 parts by mass, the film becomes too hard and the handling property is lowered. The content of the boron element derived from the boron-containing compound (B) is preferably 2 parts by mass or less, particularly preferably 1 part by mass or less. The boron element content derived from the boron-containing compound (B) can be obtained by ¹ H-NMR measurement.

It is preferable that the polarizing film of the present invention further contains boric acid. As a result, it is possible to more effectively prevent the PVA from being eluted into water when subjected to wet stretching at a high temperature. At this time, the content of the total boron element in the polarizing film is preferably 0.2 to 5% by mass. Here, the total boron element content is the sum of the contents of all the boron elements including the content of the boron element derived from the boron-containing compound (B) and the content of the boron element derived from the boric acid. When the content of the total boron element in the polarizing film is less than 0.2 mass%, the effect of improving the heat and humidity resistance deteriorates. The content of the total boron element in the polarizing film is more preferably 1% by mass or more. On the other hand, when the content of the total boron element in the polarizing film is more than 5 mass%, the dimensional change of the polarizing film at high temperature may be increased. It is more preferable that the content of the total boron element in the polarizing film is 4.5 mass% or less. The content of the entire boron element in the polarizing film can be obtained by ICP emission analysis or the like.

The degree of polymerization of PVA contained in the polarizing film of the present invention is preferably in the range of 1,500 to 6,000, more preferably in the range of 1,800 to 5,000, and still more preferably in the range of 2,000 to 4,000. When the degree of polymerization is 1,500 or more, the durability of the polarizing film obtained by uniaxially stretching the film can be improved. On the other hand, when the degree of polymerization is 6,000 or less, it is possible to suppress the increase in the production cost and the defective processability at the time of film formation. In the present specification, the degree of polymerization of PVA means the average degree of polymerization measured according to the description of JIS K 6726-1994.

The degree of saponification of the PVA contained in the polarizing film of the present invention is preferably 95 mol% or more, more preferably 96 mol% or more, and more preferably 98 mol% or more in view of the water resistance of the polarizing film obtained by uniaxially stretching the film Is more preferable. The saponification degree of PVA in the present specification means that the PVA has a structural unit (typically, a vinyl ester unit) which can be converted into a vinyl alcohol unit (-CH ₂ -CH (OH) -) Refers to the ratio (mol%) of the number of moles of the vinyl alcohol unit to the total number of moles of alcohol units. The degree of saponification can be measured in accordance with the description of JIS K 6726-1994.

The production method of the PVA used in the present invention is not particularly limited. For example, there can be mentioned a method of converting a vinyl ester unit of a polyvinyl ester into a vinyl alcohol unit, which is obtained by polymerizing a vinyl ester monomer. The vinyl ester monomer used in the production of PVA is not particularly limited, and examples thereof include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caprate, Vinyl, caprylic acid, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate and vinyl benzoate. From an economic standpoint, vinyl acetate is preferred.

The PVA used in the present invention may be obtained by converting a vinyl ester unit of a polyvinyl ester copolymer obtained by copolymerizing a vinyl ester monomer and another monomer copolymerizable therewith into a vinyl alcohol unit. Other monomers copolymerizable with the vinyl ester monomer include, for example,? -Olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; (Meth) acrylic acid or a salt thereof; (Meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t- (Meth) acrylic acid esters such as butyl, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate and octadecyl (meth) acrylate; (Meth) acrylamide; (Meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylamide propanesulfonic acid or a salt thereof, ) Acrylamidopropyldimethylamine or a salt thereof, (meth) acrylamide derivatives such as N-methylol (meth) acrylamide or derivatives thereof; N-vinyl amides such as N-vinyl formamide, N-vinylacetamide and N-vinyl pyrrolidone; Vinyl ethers 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; Vinylsilyl compounds such as vinyltrimethoxysilane; Unsaturated sulfonic acid, and the like. The vinyl ester copolymer may have a structural unit derived from one or more of the above-mentioned other monomers. The other monomer may be used when the vinyl ester monomer is present in the reaction vessel when the polymerization reaction is carried out, or may be added to the reaction vessel during the course of the polymerization reaction. From the viewpoint of the polarization performance, the content of the unit derived from the other monomer is preferably 10 mol% or less, more preferably 5 mol% or less, and still more preferably 2 mol% or less.

Among the monomers copolymerizable with the vinyl ester monomer, the stretching property can be improved and the stretching can be carried out at a higher temperature, the occurrence of troubles such as breakage of stretching during production of the optical film is reduced, and the productivity of the optical film is further improved , Ethylene is preferred. When the PVA contains an ethylene unit, the content of the ethylene unit is preferably 1 to 4 mol% with respect to the number of moles of all the structural units constituting the PVA from the viewpoint of the stretching property and the stretchable temperature as described above, And more preferably 2 to 3 mol%.

The polymerization method for polymerizing the vinyl ester monomer may be any of batch polymerization, semi-batch polymerization, continuous polymerization and semi-continuous polymerization. Examples of the polymerization method include bulk polymerization, solution polymerization, suspension polymerization, A known method such as a polymerization method can be applied. A bulk polymerization method or a solution polymerization method in which polymerization is allowed to proceed in a solvent such as a solvent or alcohol is usually employed. In the case of obtaining a polyvinyl ester of high polymerization degree, an emulsion polymerization method is also preferable. The solvent of the solution polymerization method is not particularly limited, but is, for example, an alcohol. Alcohols used in the solvent of the solution polymerization method are, for example, lower alcohols such as methanol, ethanol and propanol. The amount of the solvent used in the polymerization solution may be selected in consideration of the 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 solvent to total monomer (solvent / , Preferably in the range of 0.01 to 10, more preferably in the range of 0.05 to 3.

The polymerization initiator used in the polymerization of the vinyl ester monomer may be selected according to the polymerization method in known polymerization initiators such as an azo-based initiator, a peroxide-based initiator, and a redox-based initiator. Examples of azo-based initiators include azo initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis -2,4-dimethylvaleronitrile). The peroxide-based initiator includes, for example, percarbonate-based compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; per-tertiary compounds such as t-butyl peroxyneodecanate and? -cumyl peroxyneodecanate; Acetylcyclohexylsulfonylperoxide; 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate; Acetyl peroxide. Potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like may be combined with the initiator to form a polymerization initiator. The redox-type initiator is, for example, a polymerization initiator in which the peroxide-based initiator is combined with a reducing agent such as sodium hydrogensulfite, sodium hydrogencarbonate, tartaric acid, L-ascorbic acid, and ronic acid. The amount of the polymerization initiator to be used can not be uniformly determined because it varies depending on the kind of the polymerization initiator, but may be selected depending on the polymerization rate. For example, when 2,2'-azobisisobutyronitrile or acetyl peroxide is used as the polymerization initiator, the amount is preferably 0.01 to 0.2 mol%, more preferably 0.02 to 0.15 mol% based on the vinyl ester monomer. The polymerization temperature is not particularly limited, but is suitably from room temperature to 150 ° C, preferably 40 ° C or more, and is not more than the boiling point of the solvent used.

The polymerization of the vinyl ester monomer may be carried out in the presence of a chain transfer agent. The chain transfer agent includes, for example, aldehydes such as acetaldehyde and propionaldehyde; Ketones such as acetone and methyl ethyl ketone; Mercaptans such as 2-hydroxyethanethiol; And phosphinic acid salts such as sodium phosphinate sodium monohydrate. Among them, aldehydes and ketones are preferably used. The amount of the 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 polymerization degree of the desired PVA, but is generally 0.1 to 10 parts by mass per 100 parts by mass of the vinyl ester monomer.

The saponification of the polyvinyl ester can be carried out, for example, in a state in which the polyvinyl ester is dissolved in an alcohol or a hydrated alcohol. Alcohols used for saponification include, for example, lower alcohols such as methanol and ethanol, and preferably methanol. The alcohol used for saponification may contain other solvents such as acetone, methyl acetate, ethyl acetate and benzene in a proportion of 40 mass% or less of the mass thereof. The catalyst used for the saponification is, for example, a hydroxide of an alkali metal such as potassium hydroxide or sodium hydroxide, an alkali catalyst such as sodium methylate, or an acid catalyst such as a mineral acid. The temperature at which the saponification is carried out is not limited, but is preferably in the range of 20 to 60 占 폚. When a gel-like product precipitates in accordance with progress of saponification, the product is pulverized, washed and dried to obtain PVA. The saponification method is not limited to the above-mentioned method, but a known method can be applied.

The PVA film used for producing the polarizing film of the present invention may contain a plasticizer in addition to the PVA. Examples of suitable plasticizers include polyhydric alcohols. Specific examples thereof include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane. In addition, these plasticizers may contain one or more of these plasticizers. Of these, glycerin is preferable in terms of improving the stretchability.

The content of the plasticizer in the PVA film used in the production of the polarizing film of the present invention is preferably in the range of 1 to 20 parts by mass, more preferably in the range of 3 to 17 parts by mass with respect to 100 parts by mass of PVA, And more preferably in the range of 5 to 15 parts by mass. Since the content is 1 part by mass or more, the stretching property of the film is further improved. On the other hand, when the content is 20 parts by mass or less, the film is excessively softened and deterioration in handling properties can be suppressed.

The PVA film used in the production of the polarizing film of the present invention may further contain additives such as processing stabilizers such as fillers and copper compounds, weather stabilizers, colorants, ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, other thermoplastic resins, , An antifoaming agent, a deodorant, an extender, a stripping agent, a releasing agent, a reinforcing agent, a crosslinking agent, a fungicide, a preservative, and a crystallization rate retarder.

The proportion of the total of PVA and plasticizer in the PVA film used for producing the polarizing film of the present invention is preferably 80% by mass or more, more preferably 90% by mass or more based on the mass of the PVA film, And more preferably 95 mass% or more.

The degree of swelling of the PVA film used in the production of the polarizing film of the present invention is preferably in the range of 160 to 240%, more preferably in the range of 170 to 230%, and particularly preferably in the range of 180 to 220% . When the swelling degree is 160% or more, the progress of crystallization can be suppressed to an extreme, and the stretching can be performed stably at a high magnification. On the other hand, when the degree of swelling is 240% or less, dissolution at the time of stretching is suppressed, and stretching can be performed even at a higher temperature.

The thickness of the PVA film to be used in the production of the polarizing film of the present invention is not particularly limited, but is preferably 1 to 100 탆, more preferably 5 to 60 탆, particularly preferably 10 to 45 탆. If the thickness is too small, stretching tends to occur easily in the uniaxial stretching process for producing a polarizing film. In addition, if the thickness is excessively large, unevenness in stretching tends to occur in the uniaxial stretching process for producing a polarizing film.

The width of the PVA film used in the production of the polarizing film of the present invention is not particularly limited and can be determined depending on the use of the polarizing film to be produced and the like. In recent years, when the width of the PVA film used in the production of the polarizing film is set to 3 m or more in view of the ongoing enlargement of the liquid crystal television or the liquid crystal monitor, it is preferable for these applications. On the other hand, when the width of the PVA film used for producing the polarizing film is too large, it is difficult to uniformly conduct the uniaxial stretching in the case of producing a polarizing film by a device that is put into practical use. The width of the PVA film is preferably 7 m or less.

The production method of the PVA film to be used in the production of the polarizing film of the present invention is not particularly limited and a production method in which the thickness and width of the film after film formation become more uniform can be preferably employed. For example, PVA, PVA, and PVA which constitute the PVA film used in the present invention and, if necessary, the aforementioned plasticizer, additive, and surfactant described later, dissolved in a liquid medium, If necessary, further containing one or more kinds of plasticizer, additive, surfactant, liquid medium and the like, and PVA is melted. When the stock solution for film formation contains at least one of a plasticizer, an additive and a surfactant, it is preferable that the components are uniformly mixed.

Examples of the liquid medium used for the preparation of the film-forming stock solution include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, Triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, and the like, and one or more of these may be used. Among them, water is preferred from the standpoint of environmental load and recoverability.

The volatile matter content of the stock film-forming solution (the content ratio of volatile components such as a liquid medium, which is removed by volatilization or evaporation at the time of film formation in the film-forming stock solution) varies depending on the film-forming method, By mass to 95% by mass, and more preferably within the range of 55 to 90% by mass. By virtue of the volatile matter content of the stock film-forming solution being 50 mass% or more, the viscosity of the stock film-forming solution does not become excessively high, and filtration and defoaming at the time of preparation of the film-forming solution are smoothly carried out. On the other hand, when the volatile fraction of the film-forming raw liquid is 95 mass% or less, the concentration of the film-forming stock solution is not excessively low and production of an industrial film is facilitated.

It is preferable that the stock solution contains a surfactant. By containing the surfactant, the film-forming property is improved, the occurrence of the thickness irregularity of the film is suppressed, and the film from the metal roll or the belt used for the film formation is easily peeled off. When a PVA film is produced from a film forming stock solution containing a surfactant, the film may contain a surfactant. The kind of the surfactant is not particularly limited, but an anionic surfactant or a nonionic surfactant is preferable from the viewpoint of peelability from a metal roll or a belt.

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

Examples of the nonionic surfactant include alkyl ether types such as polyoxyethylene oleyl ether and the like; Alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether; Alkyl ester types such as polyoxyethylene laurate; Alkylamine type such as polyoxyethylene lauryl amino ether; Alkyl amide types such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Alkanolamide types such as diethanolamide laurate, and diethanolamide oleic acid; And allyl phenyl ether type such as polyoxyalkylene allyl phenyl ether.

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

When the stock solution contains a surfactant, the content thereof is preferably within a range of 0.01 to 0.5 part by mass, more preferably within a range of 0.02 to 0.3 part by mass, more preferably within a range of 0.02 to 0.3 part by mass with respect to 100 parts by mass of PVA contained in the stock solution To 0.2 parts by mass. When the content is 0.01 part by mass or more, the film forming property and the peeling property are further improved. On the other hand, when the content is 0.5 parts by mass or less, it is possible to inhibit the surfactant from bleeding out on the surface of the PVA film to cause blocking and deterioration in handling properties.

Examples of a film forming method for forming a PVA film to be used in the production of a polarizing film using the above-mentioned film forming stock solution include a cast film forming method, an extrusion film forming method, a wet film forming method, and a gel film forming method . These film-forming methods may be used alone or in combination of two or more. Among these film forming methods, the cast film forming method and the extrusion film forming method are preferable from the viewpoint of obtaining a PVA film to be used for producing a polarizing film having uniform thickness and width and good physical properties. The PVA film thus formed can be dried or heat-treated as required.

Examples of a specific method for producing the PVA film to be used in the production of the polarizing film of the present invention include a method of producing the PVA film by using the T-shaped slit die, hopper plate, I-die, lip coater die, (Or belt) on the circumferential surface of the first roll (or belt), and the volatile component And then further dried on the circumferential surface of one or a plurality of rotating heated rolls arranged on the downstream side thereof or further dried in a hot air dryer to be dried, It is industrially preferable to employ a method of winding by the above method. The drying by the heated roll and the drying by the hot air drying apparatus may be carried out in appropriate combination.

The method for producing the polarizing film of the present invention is not particularly limited. A preferred production method is a production method of a polarizing film comprising a dyeing treatment for staining a polyvinyl alcohol film with a dichroic dye and a stretching treatment for uniaxially stretching the film, And then immersing the film in an aqueous solution. The PVA film used for producing the polarizing film of the present invention is subjected to a dyeing treatment, a uniaxial stretching treatment and, if necessary, further swelling treatment, boric acid crosslinking treatment, fixing treatment, cleaning treatment, drying treatment, Method. In this case, the order of each treatment such as swelling treatment, dyeing treatment, boric acid crosslinking treatment, uniaxial stretching treatment and fixing treatment is not particularly limited, and one or two or more treatments may be simultaneously carried out. In addition, one or two or more of the treatments may be performed twice or more.

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

The dyeing treatment can be carried out by bringing a dichroic dye into contact with the PVA film. As the dichroic dye, an iodine dye is generally used. The dyeing treatment may be performed at any stage before uniaxial stretching, uniaxial stretching, or uniaxial stretching. The dyeing treatment is generally carried out by immersing the PVA film in a solution (particularly an aqueous solution) containing iodine-potassium iodide as a dyeing bath. The concentration of iodine in the dyeing bath is preferably in the range of 0.01 to 0.5 mass%, and the concentration of potassium iodide is preferably in the range of 0.01 to 10 mass%. The temperature of the dyeing bath is preferably 20 to 50 캜, particularly 25 to 40 캜. The preferred dyeing time is 0.2 to 5 minutes.

By carrying out a boric acid crosslinking treatment on the PVA film, it is possible to more effectively prevent the PVA from being eluted into water upon wet stretching at a high temperature. From this point of view, the boric acid cross-linking treatment is preferably carried out before the uniaxial stretching treatment. The boric acid crosslinking treatment can be carried out by immersing the PVA film in an aqueous solution containing a boric acid crosslinking agent. As the boric acid crosslinking agent, boron-containing inorganic compounds such as boric acid, borax, and other boron-containing inorganic compounds may be used. The concentration of the boric acid crosslinking agent in the aqueous solution containing the boric acid crosslinking agent is preferably in the range of 1 to 15 mass%, more preferably in the range of 2 to 7 mass%. The concentration of the boric acid crosslinking agent is in the range of 1 to 15 mass%, so that sufficient stretchability can be maintained. An aqueous solution containing a boric acid crosslinking agent may contain an auxiliary agent such as potassium iodide. The temperature of the aqueous solution containing the boric acid crosslinking agent is preferably in the range of 20 to 50 캜, particularly in the range of 25 to 40 캜. By setting the temperature within the range of 20 to 50 占 폚, boric acid crosslinking can be efficiently carried out.

The uniaxial stretching treatment may be carried out by 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 boric acid, or in a fixed bath described later or in a dyeing bath described later. In the case of the dry stretching method, the film may be subjected to a uniaxial stretching treatment at room temperature, a uniaxial stretching treatment while heating, or a monoaxial stretching treatment in air using the absorbed PVA film. Of these, the wet stretching method is preferable, and it is more preferable to perform the uniaxial stretching treatment in an aqueous solution containing boric acid. The concentration of boric acid in the aqueous solution of boric acid is preferably within a range of 0.5 to 6 mass%, more preferably within a range of 1 to 5 mass%. The boric acid aqueous solution may contain potassium iodide, and the concentration thereof is preferably within a range of 0.01 to 10 mass%. The stretching temperature in the uniaxial stretching treatment is preferably in the range of 30 to 90 占 폚, more preferably in the range of 40 to 80 占 폚, and particularly preferably in the range of 50 to 70 占 폚. The stretching magnification factor (the total stretching magnification factor from the raw PVA film) in the uniaxial stretching treatment is preferably 5 times or more, more preferably 5.5 times or more from the viewpoint of the polarizing performance of the resulting polarizing film. The upper limit of the draw ratio is not particularly limited, but the draw ratio is preferably 8 times or less.

There is no particular limitation on the direction of the uniaxial stretching treatment in the case of performing the uniaxial stretching treatment on the elongated PVA film. The uniaxial stretching treatment and the transverse uniaxial stretching treatment in the longitudinal direction or the so-called oblique stretching treatment are employed However, uniaxial stretching in the longitudinal direction is preferable in that a polarizing film excellent in polarization performance can be obtained. The uniaxial stretching process in the longitudinal direction can be carried out by changing the peripheral velocity between rolls by using a stretching device having a plurality of rolls parallel to each other. On the other hand, the transverse uniaxial stretching treatment can be carried out using a tenter type stretching machine.

In the production of the polarizing film, it is preferable to perform the fixing treatment after the uniaxial stretching treatment in order to strengthen the adsorption of the dichroic dye (iodine-based dye, etc.) on the PVA film. An aqueous solution containing the boron-containing compound (B) can be preferably used as the fixed treatment bath used for the fixing treatment. If necessary, boric acid, an iodine compound, a metal compound, and the like may be added to the fixed treatment bath. The temperature of the fixed treatment bath is preferably 15 to 60 ° C, particularly 25 to 40 ° C.

The boron-containing compound (B) may be adsorbed to the polarizing film in any of the dyeing treatment, the boric acid crosslinking treatment, the uniaxial stretching treatment, and the fixing treatment. The adsorption during the fixing treatment affects the cutting in the uniaxial stretching treatment And is particularly preferable in that it does not give. The boron-containing compound (B) may be used alone or in combination of two or more. The concentration of the aqueous solution of the boron-containing compound (B) is preferably from 0.05 to 15 mass%, particularly preferably from 0.1 to 10 mass%. When the aqueous solution concentration of the boron-containing compound (B) is lower than 0.05 mass%, adsorption may be slowed. When the aqueous solution concentration is higher than 15 mass%, precipitates of the boron-containing compound (B) There is a case. It is preferable that the aqueous solution containing the boron-containing compound (B) contains an auxiliary agent such as potassium iodide in terms of improving the polarization performance. The temperature of the treatment bath is preferably 10 to 70 캜, more preferably 20 to 60 캜, and particularly preferably 20 to 50 캜. If the temperature is too low, the boron-containing compound (B) may precipitate in the treatment bath. On the other hand, if the temperature is too high, it becomes difficult to industrially easily produce under relatively mild conditions.

A preferable production method when the boron-containing compound (B) is adsorbed to the polarizing film at the time of fixing treatment is to carry out the swelling treatment, the boric acid crosslinking treatment, the uniaxial stretching treatment and the fixing treatment in this order. Thereafter, one or more treatments selected from the cleaning treatment, the drying treatment and the heat treatment may be carried out in this order, if necessary.

The cleaning treatment is generally performed by immersing the film in water, distilled water, or pure water. At this time, it is preferable that the aqueous solution used for the washing treatment in the aspect of the improvement of the polarization performance contains iodide such as potassium iodide as an auxiliary agent, and the concentration of the iodide is preferably 0.5 to 10% by mass. The temperature of the aqueous solution in the cleaning treatment is generally 5 to 50 캜, preferably 10 to 45 캜, and more preferably 15 to 40 캜. From an economical point of view, it is not preferable that the temperature of the aqueous solution is excessively low, and if the temperature of the aqueous solution is excessively high, the polarization performance may be deteriorated.

The conditions for the drying treatment are not particularly limited, but it is preferable to carry out the drying at a temperature in the range of 30 to 150 ° C, particularly in the range of 50 to 130 ° C. It is easy to obtain a polarizing film having excellent dimensional stability by drying at a temperature within the range of 30 to 150 ° C.

By performing the heat treatment after the drying treatment, a polarizing film having further excellent dimensional stability can be obtained. Here, the heat treatment refers to a treatment for further increasing the dimensional stability of the polarizing film by further heating the polarizing film after the drying treatment in which the water content is 5% or less. The conditions of the heat treatment are not particularly limited, but it is preferable that the heat treatment is performed within the range of 60 占 폚 to 150 占 폚, particularly 70 占 폚 to 150 占 폚. When heat treatment is performed at a temperature lower than 60 deg. C, the effect of stabilizing the dimension due to heat treatment is insufficient. When the heat treatment is performed at a temperature higher than 150 deg.

The anti-moisture heat performance of the polarizing film obtained as described above can be evaluated with the discoloration of the color derived from the PVA-iodine complex under high temperature and high humidity as an index. Concretely, it can be evaluated by the percentage (absorbance remaining ratio) of the absorbance D (610 nm) after fading to the absorbance C (610 nm) before the two polarizing films are superimposed on Cross Nicol. The absorbance remaining ratio after fading at 60 DEG C / 90% RH for 8 hours is preferably 22% or more, and more preferably 25% or more.

The polarizing film is usually used as a polarizing plate by adhering a protective film optically transparent and having mechanical strength on both sides or one side thereof. As the protective film, a cellulose triacetate (TAC) film, an acetic acid-butyric acid cellulose (CAB) film, an acrylic film, a polyester film and the like are used. As the adhesive for bonding, PVA adhesive, urethane adhesive and the like can be mentioned, and among them, PVA adhesive is preferable.

The polarizing plate obtained as described above can be used as a component of an LCD after being coated with a pressure-sensitive adhesive such as an acryl-based adhesive and then adhered to a glass substrate. At the same time, it may be laminated with a retardation film, a viewing angle improving film, a luminance improving film or the like.

Example

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples at all. Each measurement or evaluation method employed in the following examples and comparative examples is shown below.

[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. Thereafter, the PVA film was taken out, the water on the surface of the PVA film was wiped off with a filter paper, and the mass of the PVA film after the immersion (mass E) was measured. Thereafter, the PVA film was put in a drier at 105 DEG C and dried for 16 hours, and then the mass (F) of the PVA film after drying was measured. The degree of swelling of the PVA film was calculated by substituting the values of mass E and mass F into the following equation (5).

Swelling degree (%) = (mass E / mass F) x 100 (5)

[Optical properties of polarizing film]

(1) Measurement of transmittance Ts

Two samples of 4 cm in the stretching direction of the polarizing film and 2 cm in the width direction were collected from the central portion of the polarizing film obtained in the following Examples and Comparative Examples, and a spectrophotometer (manufactured by Nippon Spectroscope, V7100 "), the visual sensitivity of the C light source and the visible region of the 2 ° field of view was corrected in accordance with JIS Z 8722 (measurement of the object color), and the sample was tilted by + 45 ° with respect to the longitudinal direction And the transmittance of light when the light was inclined at -45 [deg.] Were measured, and their average value Ts1 (%) was determined. In the same manner for the other one sample, the transmittance of light when tilted by + 45 ° and the transmittance of light when tilted by -45 ° were measured, and their average value Ts2 (%) was determined. Ts1 and Ts2 were averaged by the following equation (6) to obtain the transmittance Ts (%) of the polarizing film.

Ts = (Ts1 + Ts2) / 2 (6)

(2) Measurement of polarization degree V

The two samples used in the measurement of the transmittance Ts were measured for transmittance T // (%) of light in the case where the stretching directions were orthogonal to each other and transmittance of light in the case of superimposing the stretching directions T // %) Was measured using a spectrophotometer ("V7100" manufactured by Nihon Spectroscope KK) equipped with an integrating sphere, according to JIS Z 8722 (measurement of object color), and the visual sensitivity of the C light source and the visible region of 2 ° field And measured. The polarization degree V (%) was obtained by substituting the measured T // (%) and T ⊥ (%) into the following equation (7).

[Wet heat performance]

Two polarizing films were each fixed to a metal frame, superimposed on Cross-Nicol, and absorbance C (610 nm) at the initial (0 hour) was measured with a spectrophotometer. Further, the polarizing film fixed to the metal frame was allowed to stand for 8 hours under an atmosphere of 60 deg. C / 90% RH, then superposed on Cross-Nicol, and the absorbance D (610 nm) after 8 hours was measured with a spectrophotometer . The value of the absorbance D / absorbance C x 100 was taken as the residual rate (%), which was used as an indicator of the color fading resulting from the PVA-iodine complex.

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

A polarizing film conditioned at 23 ° C / 50% RH for 16 hours was dissolved in 0.005% by mass of water and concentrated to 0.15% by mass using a rotary evaporator. The solution was analyzed by ¹ H-NMR And a measurement sample. ¹ H-NMR (JNM-AL400: 400 MHz, manufactured by NOF Corporation) was carried out at 80 占 폚 and analyzed by ALICE2 (manufactured by Nihon Electronics Co., Ltd.) by the following method. For the ¹ H-NMR chart obtained by measurement, the phase was adjusted so that the baseline became smooth, and then the baseline was automatically corrected by setting the average point to 20. Next, the reference was set automatically so that the peak of the heavy water as the measuring solvent would be at a position of 4.65 ppm. Thereafter, as shown in Fig. 1, the hydrogen peak of the hydrocarbon group contained in the boron-containing compound (B) was integrated to determine the peak area thereof. At this time, the peak area of the peak of the boron-containing compound (B) was determined by adding the hydrogen peak area derived from the PVA plus the hydrogen peak area of the hydrocarbon group contained in the boron-containing compound (B) Is set so that the value of the area G and the number of the hydrogen atoms of the corresponding hydrocarbon groups are the same. Next, the hydrogen peak in the range of 1.7 ppm to 2.4 ppm is converted to the hydrogen peak of the hydrocarbon group contained in the boron-containing compound (B) superimposed on the hydrogen peak derived from the methylene group of PVA and the hydrogen peak derived from the methylene group of PVA And the peak area (area H) was obtained. Thereafter, an area I obtained by subtracting the hydrogen number of the hydrocarbon group of the boron-containing compound (B) superimposed on the hydrogen peak of the methylene group derived from PVA from the area H was calculated. The values obtained by these methods were substituted into the following equation (8) to calculate the boron element content from the boron-containing compound (B) relative to 100 parts by mass of the polyvinyl alcohol (A). X and Y in the following formula (8) are the number of hydrocarbons in the hydrocarbon group contained in the boron-containing compound (B) not overlapping with the peak of the PVA and the number of boron per molecule in the boron-containing compound (B) . The equation (8) is a formula used when unmodified PVA is used, and it is necessary to appropriately modify the equation (8) when using the modified PVA as a raw material.

(Parts by mass) = (area G / X) / (area I / 2)} (10.811 x Y) / (amount of boron contained in boron-containing compound (B)) relative to 100 parts by mass of polyvinyl alcohol 44.0526} x 100 (8)

10.811 is the atomic weight of boron, and 44.0526 is the molecular weight per mole of repeating unit of PVA without denaturation. The ¹ H-NMR chart of FIG. 1 is obtained by measuring the polarizing film of Example 1. The content of boron element derived from the boron-containing compound (B) relative to 100 parts by mass of the polyvinyl alcohol (A) And then 0.5 mass part was added.

[Calculation of the total boron element content (mass%) in the polarizing film]

The mass (J (g)) of the polarizing film that was humidified at 23 ° C / 50% RH for 16 hours was measured and dissolved in 20 ml of distilled water to make the polarizing film 0.005% by mass. An aqueous solution in which a polarizing film was dissolved was used as a measurement sample, and its mass (K (g)) was measured. Thereafter, the boron concentration (L (ppm)) of the measurement sample was measured using a multi-type ICP emission spectrometer (ICP) manufactured by Shimadzu Corporation. Thereafter, the value calculated by substituting the value in the following equation (9) was used as the content (mass%) of the total boron element in the polarizing film.

The content (% by mass) of the total boron element in the polarizing film

= [(L x 10 ^-6 K) / J] x 100 (9)

[Example 1]

100 parts by mass of PVA (saponification degree: 99.9 mol%, degree of polymerization: 2400), 10 parts by mass of glycerin as a plasticizer, and 0.1 part by mass of polyoxyethylene lauryl ether sodium sulfate as a surfactant, and a PVA content of 10% The resultant film was dried on a metal roll at 80 캜, and the resulting film was heat-treated at 120 캜 for 10 minutes in a hot-air dryer to adjust the degree of swelling to 200% to prepare a PVA film having a thickness of 30 탆.

A sample having a width of 5 cm and a length of 9 cm was cut from the central portion in the width direction of the PVA film thus obtained so as to be uniaxially stretched in the range of 5 cm in width x 5 cm in length. This sample was uniaxially stretched in the longitudinal direction by a factor of 1.1 times while being immersed in pure water at 30 DEG C for 30 seconds, and swelled. Subsequently, while being immersed in an aqueous solution (dyeing treatment bath) (temperature 30 ° C) containing 0.04% by mass of iodine and 4.0% by mass of iodine for 60 seconds, the film was uniaxially stretched in the longitudinal direction at 2.2 times . Subsequently, while being immersed in an aqueous solution (boric acid crosslinking treatment bath) (temperature 30 ° C) containing 3 mass% of boric acid and 3 mass% of potassium iodide, the composition was uniaxially stretched in the longitudinal direction to 1.2 times (2.7 times as a whole) . And then uniaxially stretched in the longitudinal direction up to 6.0 times as a whole while immersing it in an aqueous solution (uniaxial stretching treatment bath) at 58 DEG C containing 4 mass% of boric acid and 6 mass% of potassium iodide. Thereafter, the substrate was immersed in an aqueous solution (fixed treatment bath) (temperature: 30 ° C) containing 1% by weight of 1,4-butane diboronic acid and 4% by weight of potassium iodide for 100 seconds. Finally, the film was dried at 60 DEG C for 4 minutes to prepare a polarizing film. Two polarizing films after drying were each fixed on a metal frame, and the absorbance (610 nm) when they were superimposed on Cross-Nicol was 3.9.

As a result of ¹ H-NMR analysis of the obtained polarizing film, hydrogen peaks of 1,4-butane diboronic acid not overlapping with hydrogen peaks derived from PVA appeared at 1.0 to 1.3 ppm, Was set to four. Next, the peak area (area H) of hydrogen of the methylene group of PVA in which the peak appears in the range of 1.7 to 2.4 ppm was calculated. Since there was a hydrogen peak of 1,4-butane diboronic acid overlapping with the hydrogen peak of the methylene group of PVA, the hydrogen number of 1,4-butane diboronic acid, which corresponds to the hydrogen peak overlapping with the methylene group of PVA, H and the area I was calculated. These values were substituted into the calculation formula (8). As a result, the boron content derived from the boron-containing compound (B) relative to 100 parts by mass of the polyvinyl alcohol (A) was 0.5 parts by mass.

Further, 0.00099 g (mass J) of the polarizing film prepared by the same method was dissolved in 20 ml of distilled water to prepare a measurement sample for ICP measurement. The mass of the sample for measurement was measured and found to be 20.03 g (mass K). Thereafter, as a result of ICP measurement, the boron concentration of the measurement sample was 1.24 ppm (boron concentration L). As a result of substituting these values into the equation (9), the content of the total boron element in the polarizing film was 2.5 mass%. Using the obtained polarizing film, the optical characteristics and anti-wet heat performance of the polarizing film were evaluated by the above-described method. Table 1 summarizes the above results.

In Examples 2 to 4 and Comparative Examples 1 to 3, while immersing for 60 seconds in an aqueous solution (dyeing treatment bath) (temperature 30 ° C) containing potassium iodide in an amount of 100 parts by mass relative to 1 part by mass of iodine, 2.4 times as a whole) to uniaxially stretch in the longitudinal direction to adsorb iodine. At this time, the concentrations of iodine and potassium iodide in the dyeing treatment bath were adjusted so that the two polarizing films after drying were each fixed to the metal frame and the absorbance (610 nm) when they were superimposed on Cross-Nicol was 3.6 to 4.2.

[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 1,3-propanediboronic acid and 3% by mass of potassium iodide was used in the fixed treatment bath , Each measurement or evaluation was carried out. 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 1.0% by mass of phenylboronic acid and 2.0% by mass of potassium iodide was used in the fixed treatment bath, . The results are shown in Table 1.

[Example 4]

A polarizing film was produced in the same manner as in Example 1 except that an aqueous solution (temperature: 30 ° C) containing 4.0% by mass of n-propyl boronic acid and 3.0% by mass of potassium iodide was used in the fixed treatment bath, Measurement or evaluation. The results are shown in Table 1.

[Comparative Example 1]

A polarizing film was produced in the same manner as in Example 1 except that an aqueous solution (temperature: 30 占 폚) containing boric acid at 2 mass% and potassium iodide at a ratio of 3 mass% Respectively. The results are shown in Table 1.

[Comparative Example 2]

A polarizing film was produced in the same manner as in Example 1 except that an aqueous solution (temperature: 30 ° C) containing 1.0% by mass of boric acid and 3% by mass of potassium iodide was used in the fixed treatment bath, Respectively. 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 占 폚) containing boric acid at 0.5 mass% and potassium iodide at a ratio of 3 mass% Respectively. The results are shown in Table 1.

Comparing Examples 1 and 2 and Comparative Example 2, it can be seen that the absorbance remaining ratio in Examples 1 and 2 is higher than that in Comparative Example 2, although the content of all boron elements in the polarizing film is equal or less. Comparing Examples 3 and 4 with Comparative Example 1, it can be seen that the absorbance remaining ratio of Examples 3 and 4 is higher than that of Comparative Example 1, although the content of all boron elements in the polarizing film is equal or less. From the above, it can be seen that the polarizing films of Examples 1 to 4 satisfying the requirements of the present invention are excellent in anti-wet heat performance.

1: Hydrogen peak derived from heavy water as a measurement solvent
2: Hydrogen peak derived from methylene group of PVA
3: Hydrogen peak derived from methylene group of PVA
4: Hydrogen peak derived from a hydrocarbon group contained in the boron-containing compound (B) superimposed on the hydrogen peak derived from PVA
5: Hydrogen peak derived from a hydrocarbon group contained in the boron-containing compound (B) not overlapping with the hydrogen peak derived from PVA

Claims (4)

(B) having at least one functional group selected from the group consisting of polyvinyl alcohol (A), a boronic acid group and a boron-containing group which can be converted into a boronic acid group in the presence of water, Wherein the content of the boron element derived from the boron-containing compound (B) in the film is 0.1 to 3 parts by mass relative to 100 parts by mass of the polyvinyl alcohol (A). The method according to claim 1,
Further comprising boric acid, wherein the content of the total boron element in the polarizing film is 0.2 to 5 mass%. 3. The method according to claim 1 or 2,
Wherein the boron-containing compound (B) has a plurality of the functional groups. A process for producing a polarizing film comprising a dyeing process for dyeing a polyvinyl alcohol film with a dichroic dye and a stretching process for uniaxially stretching the film, wherein the film is immersed in an aqueous solution of the boron-containing compound (B) The method of manufacturing a polarizing film according to any one of claims 1 to 3,

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