TWI733862B - Polarizing film and method for producing same - Google Patents

Abstract

The present invention provides a polarizing film, which is a polarizing film comprising polyvinyl alcohol (A) and a boron-containing compound (B), wherein the boron-containing compound (B) is selected from the group consisting of a boronate group and the presence in water At least one functional group in the boron-containing group that can be converted into a boronate group is characterized by the content of boron element derived from the boron-containing compound (B) in the polarizing film relative to 100 parts by mass The polyvinyl alcohol (A) is 0.1 to 3 parts by mass. Preferably, it further contains boric acid and the content of all boron elements in the polarizing film is 0.2-5 mass%. Thereby, it is possible to provide a polarizing film with excellent moisture and heat resistance.

Description

Polarizing film and manufacturing method thereof

The present invention relates to a polarizing film excellent in moisture and heat resistance and a method of manufacturing the same.

The polarizing plate with the function of light penetration and shielding and the liquid crystal that changes the polarization state of light are the basic components of liquid crystal displays (LCD). It has a structure in which a protective film such as cellulose triacetate (TAC) film is attached to the surface of the polarizing film. As the polarizing film constituting the polarizing plate, a uniaxially stretched polyvinyl alcohol film (hereinafter sometimes referred to as "polyvinyl alcohol") The matrix made of "PVA") adsorbs iodine-based pigments (I ₃ ^- or I ₅ ^-, etc.) as the mainstream.

LCD series are used in a wide range of small devices such as computers and watches, mobile phones, notebook computers, liquid crystal displays, liquid crystal color projectors, liquid crystal televisions, car navigation systems, indoor and outdoor measuring instruments, etc. In recent years, these The equipment is required to be thin/lightweight. Therefore, each member of the LCD is also required to be thinner, but if the protective film of the polarizing plate, which is one of the LCD members, is thinned, there is a concern that the function of preventing the discoloration of the iodine-based polarizing film may be reduced. Therefore, there is a demand for an iodine-based polarizing film that has little fading under high temperature and high humidity, that is, so-called excellent heat and humidity resistance.

In addition, as for the method of improving the heat and humidity resistance of the iodine-based polarizing film, a method of cross-linking the polarizing film with a polyhydric aldehyde (Patent Document 1) or a method of cross-linking the polarizing film with a polycarboxylic acid compound is known. Treatment method (Patent Document 2).

Prior art literature Patent literature

Patent Document 1 Japanese Patent Application Laid-Open No. 6-235815

Patent Document 2 JP 2011-257756 A

However, in the case of using polyhydric aldehydes, the aldehydes are easily volatilized and it is difficult to manage the concentration, so it is quite difficult to implement industrially. In addition, the polycarboxylic acid compound has low reactivity and requires the use of an acid catalyst or treatment at high temperature. Therefore, there is a problem of coloring of the polarizing film.

Therefore, the object of the present invention is to provide a polarizing film that does not use an acid catalyst, does not require high-temperature processing, and can be easily manufactured industrially with excellent moisture and heat resistance.

The inventors of the present invention devoted themselves to research in order to achieve the above-mentioned object. As a result, they found that the above-mentioned problem can be solved by a polarizing film containing polyvinyl alcohol and a specific boron-containing organic compound, thus completing the present invention.

The above problem is solved by providing a polarizing film, the polarizing film is a polarizing film comprising polyvinyl alcohol (A) and a boron-containing compound (B), wherein the boron-containing compound (B) is selected from the group consisting of boronate group) and in the water At least one functional group in the boron-containing group that can be converted into a boronate group in the presence of the polarizing film is characterized by the content of boron element derived from the boron-containing compound (B) in the polarizing film relative to 100 mass Parts of polyvinyl alcohol (A) are 0.1 to 3 parts by mass.

At this time, the polarizing film preferably further contains boric acid and the content of all boron elements in the polarizing film is 0.2-5 mass %. In addition, it is also preferable that the boron-containing compound (B) has a plurality of the aforementioned functional groups.

In addition, the above-mentioned problems are also solved by providing a method for manufacturing the aforementioned polarizing film. The method for manufacturing the polarizing film is characterized by including a dyeing process of dyeing a polyvinyl alcohol film with a dichroic dye and uniaxial stretching of the film. In the method of manufacturing a polarizing film of the stretching treatment, the film is immersed in an aqueous solution of the boron-containing compound (B).

According to the present invention, it is possible to provide a polarizing film having excellent moisture and heat resistance. Moreover, according to the manufacturing method of the present invention, such a polarizing film can be easily manufactured industrially.

1‧‧‧The hydrogen peak derived from heavy water used as a solvent for determination

2‧‧‧The hydrogen peak of methine derived from PVA

3‧‧‧Methylene hydrogen peak derived from PVA

4‧‧‧The hydrogen peak derived from the hydrocarbon group contained in the boron-containing compound (B) overlapping with the hydrogen peak derived from PVA

5‧‧‧The hydrogen peak derived from the hydrocarbon group contained in the boron-containing compound (B) that does not overlap with the hydrogen peak derived from PVA

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

The polarizing film of the present invention is a polarizing film, which is a polarizing film containing polyvinyl alcohol (A) and a boron-containing compound (B), wherein the boron-containing compound (B) is selected from the group consisting of boronate group and At least one functional group in the boron-containing group that can be converted into a boronate group in the presence of water. By cross-linking polyvinyl alcohol with the boron-containing compound (B), the moisture and heat resistance of the polarizing film is improved.

The boron-containing compound (B) used in the present invention has at least one function selected from the group consisting of a boronate group and a boron-containing group that can be converted into a boronate group in the presence of water Based organic compounds. The boronate 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 a carbon atom (not shown). Compared with the boron atom of boric acid [B(OH) ₃ ] which is bonded with three hydroxyl groups, the two are different in that boronic acid has a boron-carbon bond. In addition, the boron-carbon bond of the boronate group does not hydrolyze, so it is quite stable in the presence of water. As for the boron-containing group that can be converted into a boronate group in the presence of water, the boronic ester group described below can be cited as a representative, but it is not limited thereto.

The hydroxyl group of the boronate group can form an alcohol and an ester like the hydroxyl group of a boric acid. The following structural formula (2) is a boronic monoester group obtained by reacting one molecule of alcohol (R-OH) with a boronate group. Here, when the boronate group is bonded to the hydroxyl group of the PVA, R in the structural formula (2) is the PVA chain, and the carbon-containing group is bonded to the PVA chain through the boron atom. The polarizing film is resistant to humidity and heat Sex will improve.

The following structural formula (3) is a boronic diester group obtained by reacting two molecules of alcohol (R-OH) with a boronate group. Here, when the boronate group is bonded to the hydroxyl group of the PVA, the two Rs in the structural formula (3) are both PVA Chains, multiple PVA chains will cross-link each other, and the resulting polarizing film will effectively improve the humidity and heat resistance.

The boron-containing compound (B) used in the present invention can be exemplified by methyl boronate, ethyl boronate, propyl boronate, butyl boronate, Pentyl boronate, hexyl boronate, and their isomers, phenyl boronate, etc. These have at least one functional group in the molecule selected from the group consisting of a boronate group and a boron-containing group that can be converted into a boronate group in the presence of water.

Since the boron-containing compound (B) is an aromatic compound, the humidity and heat resistance of the polarizing film may be improved. The reason for this is not clear, but it is speculated that the π-π accumulation effect of the aromatic ring makes it difficult for moisture to penetrate, and the effect of improving the moisture and heat resistance of the polarizing film becomes higher. Such boron-containing compounds (B) include: phenyl boronate, 1,4-benzene diboronic acid, 1,3-benzene diboronic acid (1 ,3-benzene diboronic acid), 1,3,5-benzene triboronic acid (1,3,5-benzene triboronic acid), etc.

In addition, the boron-containing compound (B) has a plurality of at least selected from the group consisting of a boronic acid group (boronate group) and a boron-containing group that can be converted into a boronic acid group (boronate group) in the molecule. One kind of functional group, the humidity and heat resistance of the polarizing film will be effectively improved. The following structural formula (4) shows a boron-containing compound (B) when it has two boronate groups in the molecule. Here, X is a divalent organic group, and it is an alkylene group, an arylene group, or the like. In this case, there are 4 points that react with the hydroxyl groups of the PVA to form esters, and the PVA chains will be more effectively cross-linked.

The boron-containing compound (B) having a plurality of the aforementioned functional groups includes: methane diboronic acid, ethane diboronic acid, propane diboronic acid, butane Butane diboronic acid, pentane diboronic acid, hexane diboronic acid, and their isomers, and 1,4-benzene diboronic acid (1,4-benzene diboronic acid) diboronic acid), 1,3-benzene diboronic acid (1,3-benzene diboronic acid), 1,3,5-benzene triboronic acid (1,3,5-benzene triboronic acid), etc.

The content of the boron element derived from the boron-containing compound (B) in the polarizing film of the present invention must 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 parts by mass, the amount of crosslinking of the polyvinyl alcohol (A) is small, and the effect of improving the moisture and heat resistance is insufficient. The content of the boron element derived from the boron-containing compound (B) is preferably 0.2 parts by mass or more, 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 workability is lowered, and there is a possibility that the productivity may be lowered, such as requiring a long processing time. . 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.

The polarizing film of the present invention preferably further contains boric acid, so that it can more effectively prevent PVA from eluting into water during wet stretching at high temperature. At this time, the content of all boron elements in the polarizing film is preferably 0.2 to 5% by mass. Here, the content of all boron elements means the sum of the content of all boron elements including the content of boron elements derived from the boron-containing compound (B) and the content of boron elements derived from boric acid. In the case where the content of all boron elements in the polarizing film is less than 0.2% by mass, the effect of improving the humidity and heat resistance may decrease. The content of all boron elements in the polarizing film is more preferably 1% by mass or more. On the other hand, when the content of all boron elements in the polarizing film is more than 5% by mass, the dimensional change of the polarizing film at high temperatures may increase. The content of all boron elements in the polarizing film is more preferably 4.5% by mass or less. The content of all boron elements in the polarizing film is obtained by ICP emission spectroscopy.

The degree of polymerization of the 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 the uniaxially stretched 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 manufacturing costs, poor process progress during film formation, and the like. In addition, the degree of polymerization of PVA in this specification means the average degree of polymerization measured in accordance with the description of JIS K6726-1994.

From the viewpoint of the water resistance of the polarizing film obtained by uniaxially stretching the film, the degree of saponification of 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, it is 98 mol% or more. In addition, the degree of saponification of PVA in this specification refers to a structural unit (usually a vinyl ester unit) _{that can be converted into a vinyl alcohol unit (-CH 2 -CH(OH)-) by saponification.} ) And the total number of moles of vinyl alcohol units, the ratio (mole%) of the number of moles of the vinyl alcohol unit. The degree of saponification can be measured in accordance with the description of JIS K6726-1994.

The manufacturing method of the PVA used in the present invention is not particularly limited. For example, a method of converting a vinyl ester unit of a polyvinyl ester into a vinyl alcohol unit obtained by polymerizing a vinyl ester monomer can be mentioned. The vinyl ester monomer used in the manufacture of PVA is not particularly limited, but examples include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, and trimethyl vinyl acetate. (vinyl pivalate), vinyl versatate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate Esters, vinyl benzoate, etc. From the viewpoint of economic efficiency, vinyl acetate is preferred.

In addition, the PVA used in the present invention may be obtained by converting the vinyl ester unit of the polyvinyl ester copolymer obtained by copolymerizing a vinyl ester monomer and another monomer copolymerizable with the vinyl ester monomer into a vinyl alcohol unit. As for other monomers that can be copolymerized with vinyl ester monomers, for example, ethylene, propylene, 1-butene, isobutylene, and other α-olefins with 2 to 30 carbon atoms; (meth)acrylic acid or its salts; Methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate Ester, tertiary butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, etc. (meth)acrylic acid Ester; (meth)acrylamide; N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, two Acetone (meth)acrylamide, (meth)acrylamide propane sulfonic acid or its salt, (meth)acrylamide propyldimethylamine or its salt, N-methylol (meth)propylene (Meth)acrylamide derivatives such as amide or its derivatives; N-vinylamide such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; methyl Vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tertiary butyl vinyl ether, dodecyl Vinyl ethers such as vinyl ether and stearyl vinyl ether; vinyl cyanides such as (meth)acrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; acetic acid Allyl compounds such as allyl ester and chloropropylene; maleic acid or its salt, ester or anhydride; itaconic acid or its salt, ester or anhydride; vinyl trimethoxysilane and other vinyl silyl compounds ; Unsaturated sulfonic acid and so on. The above-mentioned vinyl ester copolymer may have one type or two or more types of structural units derived from the aforementioned other monomers. This other single system is used when supplying the vinyl ester monomer to the polymerization reaction, pre-existing in the reaction vessel, or adding it to the reaction vessel during the progress of the polymerization reaction. From the viewpoint of polarization performance, the content of the units derived from other monomers is preferably 10 mol% or less, more preferably 5 mol% or less, and still more preferably 2 mol% or less.

Among the above-mentioned monomers that can be copolymerized with vinyl ester monomers, they can be stretched at a higher temperature while improving the stretchability, and reduce the occurrence of defects such as tensile breakage during the manufacture of optical films. From the viewpoint of improving the productivity of the optical film, ethylene is preferred. In the case where PVA contains ethylene units, from the viewpoints of stretchability or stretchable temperature as described above, the content of ethylene units relative to the number of moles of all the structural units constituting the PVA is preferably It is 1~4 mole%, more preferably 2~3 mole%.

The polymerization method when polymerizing vinyl ester monomers can be batch polymerization, semi-batch polymerization, continuous polymerization, semi-continuous polymerization, etc. As for the polymerization method, block polymerization method, solution polymerization method, and suspension polymerization method are applicable. Well-known methods such as emulsification polymerization method, generally use the block polymerization method or the solution polymerization method in which polymerization is carried out without a solvent or in a solvent such as alcohol. In the case of obtaining a polyvinyl ester with a high degree of polymerization, the emulsion polymerization method is also preferred. The solvent of the solution polymerization method is not particularly limited, and is, for example, alcohol. The alcohol used in the solvent of the solution polymerization method is, for example, a lower alcohol such as methanol, ethanol, and propanol. The amount of solvent used in the polymerization solution can be selected in accordance with the degree of polymerization of the target PVA in consideration of the chain transfer of the solvent. For example, when the solvent is methanol, it is preferable to select the quality of the solvent and all monomers from the range of 0.01 to 10 The ratio (solvent/all monomers) is more preferably to select the mass ratio of the solvent to all monomers (solvent/all monomers) from the range of 0.05 to 3.

The polymerization initiator used for the polymerization of vinyl ester monomers may be selected from well-known polymerization initiators, for example, azo-based initiators, peroxide-based initiators, and redox-based initiators according to the polymerization method. The azo-based initiator is, for example, 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4 -Methoxy-2,4-dimethylvaleronitrile). The peroxide-based initiator is, for example, peroxycarbonate-based compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, diethoxyethyl peroxydicarbonate; Perester compounds such as tertiary butyl oxyneodecanoate and peroxyneodecanoic acid-α-cumyl; acetyl cyclohexyl sulfonyl peroxide; 2-peroxybenzene 2,4,4-Trimethylpentyl oxyacetic acid; Acetyl peroxide. It is also possible to combine potassium persulfate, ammonium persulfate, hydrogen peroxide, etc. with the above-mentioned initiator to prepare a polymerization initiator. The redox-based initiator is, for example, a polymerization initiator in which the above-mentioned peroxide-based initiator is combined with a reducing agent such as sodium bisulfite, sodium bicarbonate, tartaric acid, L-ascorbic acid, and rongalite. The amount of the polymerization initiator used varies with the type of polymerization initiator, so it cannot be determined uniformly, but only needs to be selected according to the polymerization speed. For example, when 2,2'-azobisisobutyronitrile or acetyl peroxide is used as the polymerization initiator, it is preferably 0.01 to 0.2 mol% relative to the vinyl ester monomer. Preferably, it is 0.02~0.15 mol%. The polymerization temperature is not particularly limited, but room temperature to about 150°C is appropriate, preferably 40°C or higher and below the boiling point of the solvent used.

The polymerization of vinyl ester monomers can be carried out in the presence of a chain transfer agent. Chain transfer agents are, for example, aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethane mercaptan; phosphinates such as sodium phosphinate monohydrate Among them, aldehydes and ketones are preferably used. The amount of the chain transfer agent used can be determined according to the chain transfer coefficient of the chain transfer agent used and the degree of polymerization of the target PVA, but it is generally preferably 0.1-10 parts by mass relative to 100 parts by mass of the vinyl ester monomer.

The saponification system of the polyvinyl ester can be performed in a state where the polyvinyl ester is dissolved in, for example, alcohol or hydrous alcohol. Examples of alcohols used for saponification include lower alcohols such as methanol and ethanol, and methanol is preferred. The alcohol used for saponification may also contain other solvents such as acetone, methyl acetate, ethyl acetate, benzene, etc., in a proportion of 40% by mass or less of its mass. The catalyst used for saponification is, for example, hydroxides of alkali metals such as potassium hydroxide and sodium hydroxide, alkali catalysts such as sodium methoxide, and acid catalysts such as mineral acid. The temperature for performing saponification is not limited, but it is preferably in the range of 20 to 60°C. When a gel-like product precipitates due to the progress of the saponification, the product can be crushed, washed and dried to obtain PVA. The saponification method is not limited to the aforementioned method, and a well-known method can be used.

In addition to the above-mentioned PVA, the PVA film used to manufacture the polarizing film of the present invention can also contain a plasticizer. As far as preferable plasticizers are concerned, polyhydric alcohols can be cited, and specific examples include: ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, tetraethylene glycol, Trimethylolpropane and the like can further include one or two or more of these plasticizers. Among these, from the viewpoint of the effect of improving stretchability, glycerin is preferred.

The content of the plasticizer in the PVA film used to manufacture the polarizing film of the present invention is preferably in the range of 1-20 parts by mass, more preferably in the range of 3-17 parts by mass relative to 100 parts by mass of PVA Within, more preferably within the range of 5 to 15 parts by mass. With the content of 1 part by mass or more, the stretchability of the film will be further improved. On the other hand, when the content is 20 parts by mass or less, it is possible to suppress the decrease in workability caused by the film becoming too soft.

The PVA film used to manufacture the polarizing film of the present invention can be further appropriately blended with processing stabilizers such as fillers and copper compounds, weather resistance stabilizers, colorants, ultraviolet absorbers, light stabilizers, and antioxidants as appropriate. , Antistatic agents, flame retardants, other thermoplastic resins, lubricants, fragrances, defoamers, deodorants, extenders, stripping agents, mold release agents, reinforcing agents, crosslinking agents, antifungal agents, antiseptics Additives such as agents, crystallization rate retarders, etc.

The total proportion of PVA and plasticizer in the PVA film used to manufacture the polarizing film of the present invention is based on the quality of the PVA film, and is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95 Above mass%.

The degree of swelling of the PVA film used to manufacture the polarizing film of the present invention is preferably in the range of 160-240%, more preferably in the range of 170-230%, particularly preferably in the range of 180-220%. With a swelling degree of 160% or more, the extreme development of crystals can be suppressed, and it can be stretched to a high magnification stably. On the other hand, when the degree of swelling is 240% or less, dissolution during stretching can be suppressed, and stretching can be performed even under higher temperature conditions.

The thickness of the PVA film used in the production of the polarizing film of the present invention is not particularly limited, but generally it is preferably 1-100 μm, more preferably 5-60 μm, and particularly preferably 10 to 45 μm. If the thickness is too thin, it tends to be easily broken during the uniaxial stretching process for producing a polarizing film. In addition, if the thickness is too thick, uneven stretching is likely to occur during the uniaxial stretching process used to manufacture the 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 according to the use of the produced polarizing film and the like. In recent years, from the point of view that liquid crystal televisions or liquid crystal displays are moving towards large screens, if the width of the PVA film used to make the polarizing film is 3m or more, it is suitable for these applications. On the other hand, if the width of the PVA film used to manufacture the polarizing film is too wide, it is easy to be difficult to uniformly uniaxially stretch the polarizing film in a practical device. The width of the PVA film is preferably 7 m or less.

The manufacturing method of the PVA film used to manufacture the polarizing film of the present invention is not particularly limited. A manufacturing method that makes the thickness and width of the film more uniform can be preferably used. For example, the structure can be used A film-forming stock solution prepared by dissolving one or more of the above-mentioned PVA of the above-mentioned PVA film, and the above-mentioned plasticizer, additives, and the following surfactant, etc., which are added as necessary, in the PVA film of the polarizing film in a liquid medium It can be produced, or it can be produced using a film-forming stock solution containing PVA and, if necessary, further containing one or two or more of plasticizers, additives, surfactants, and liquid media, and molten PVA. When the film-forming stock solution contains at least one of a plasticizer, an additive, and a surfactant, it is preferable to uniformly mix these components.

Regarding the above-mentioned liquid medium used to prepare the film-forming stock solution, for example, water, dimethyl sulfide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and ethylene two Alcohol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc., one or more of these can be used . Among them, from the viewpoint of load on the environment and recyclability, water is preferred.

The volatile fraction of the film-forming stock solution (the content ratio of the volatile components such as the liquid medium removed by volatilization or evaporation during film-forming in the film-forming stock solution) varies depending on the film forming method, film forming conditions, etc., but Generally, it is preferably in the range of 50 to 95% by mass, and more preferably in the range of 55 to 90% by mass. With the volatile content of the film-forming stock solution being 50% by mass or more, the viscosity of the film-forming stock solution will not become too high, the filtration or defoaming when preparing the film-forming stock solution can be smoothly performed, and it is easy to produce foreign objects or defects. film. On the other hand, when the volatile fraction of the film-forming stock solution is 95% by mass or less, the concentration of the film-forming stock solution does not become too low, and it is easy to manufacture a thin film industrially.

The film-forming stock solution preferably contains a surfactant. By containing the surfactant, the film-forming properties are improved and the unevenness of the film thickness is suppressed, and the film can be peeled from the metal roll or tape used for film-forming. Easy. When a PVA film is produced from a film-forming stock solution containing a surfactant, the film may contain a surfactant. The type of the surfactant is not particularly limited, but from the viewpoint of the peelability of a metal roll or belt, etc., an anionic surfactant or a nonionic surfactant is preferred.

As for anionic surfactants, suitable are, for example, carboxylic acid types such as potassium laurate; sulfate ester types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; sulfonic acid types such as dodecylbenzene sulfonate, etc. .

As for the nonionic surfactant, suitable are, for example, alkyl ether type such as polyoxyethylene oleyl ether; alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether; and alkyl group such as polyoxyethylene laurate. Ester type; Alkylamine type such as polyoxyethylene lauryl amino ether; Alkyl amine type such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Diethanolamide laurate , Alkanol amide type such as diethanolamide oleic acid; Allyl phenyl ether type such as polyoxy allyl phenyl ether etc.

These surfactant systems can be used individually by 1 type or in combination of 2 or more types.

When the film-forming stock solution contains a surfactant, its content is preferably in the range of 0.01 to 0.5 parts by mass, and more preferably 0.02 to 0.3 parts by mass relative to the PVA contained in 100 parts by mass of the film-forming stock solution It is 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-forming properties and releasability 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 oozing out to the surface of the PVA film to cause adhesion and decrease in workability.

The film forming method when manufacturing the PVA film used to manufacture the polarizing film using the above-mentioned film forming stock solution includes, for example, a cast film method, an extrusion film method, a wet film method, a gel film method, etc. . Only one type of these film forming methods may be used, or a combination of two or more types may be used. Among these film forming methods, the cast film forming method and the extrusion film forming method are preferable because they can obtain a PVA film for producing a polarizing film with uniform thickness and width and good physical properties. The PVA film obtained by film formation can be dried or heat-treated as necessary.

As for the specific manufacturing method of the PVA film used to manufacture the polarizing film of the present invention, for example, the following methods can be preferably adopted in industry: using a T-shaped slit mold, a hopper plate, and an I-shaped mold , Lip coater die, etc., uniformly spit out or cast the above-mentioned film-forming stock solution on the surrounding surface of the heated first roller (or belt) that is located on the most upstream side to make it volatile The components evaporate and dry from one side of the film discharged or cast on the peripheral surface of the first roll (or belt), and then around one or more rotating heated rolls arranged on the downstream side After the surface is further dried or passed through a hot-air drying device for further drying, it is wound by a winding device. Drying by a heated roll or a drying system by a hot-air drying device can be suitably combined and implemented.

The method for manufacturing the polarizing film of the present invention is not particularly limited. A suitable manufacturing method is a method of manufacturing a polarizing film including a dyeing process of dyeing a polyvinyl alcohol film with a dichroic dye and a stretching process of uniaxially stretching the film, including immersing the film in a boron-containing compound (B) A manufacturing method of polarizing film processed by aqueous solution. For the PVA film used to manufacture the polarizing film of the present invention, it can be enumerated: applying dyeing treatment, uniaxial stretching treatment, and further applying swelling treatment, boric acid crosslinking treatment, fixing treatment, washing treatment, drying treatment, Methods such as heat treatment. In this case, the order of each treatment such as swelling treatment, dyeing treatment, boric acid cross-linking treatment, uniaxial stretching treatment, and fixing treatment is not particularly limited, and one or two or more treatments can be carried out at the same time. In addition, it is also possible to perform one or two or more treatments twice or more.

The swelling treatment can be performed 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°C, more preferably in the range of 22 to 38°C, and still more preferably in the range of 25 to 35°C. In addition, the time for immersion in water is, for example, preferably in the range of 0.1 to 5 minutes, and more preferably in the range of 0.2 to 3 minutes. In addition, the water when immersed in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or may be a mixture of water and an aqueous medium.

The dyeing process can be performed by bringing the dichroic dye into contact with the PVA film. For dichroic dyes, iodine-based dyes are usually used. The timing of the dyeing treatment may be any stage before the uniaxial stretching treatment, during the uniaxial stretching treatment, and after the uniaxial stretching treatment. The dyeing treatment is usually performed by immersing the PVA film in a solution (especially an aqueous solution) containing iodine-potassium iodide as a dyeing bath. The concentration of iodine in the dye bath is preferably in the range of 0.01 to 0.5% by mass, and the concentration of potassium iodide is preferably in the range of 0.01 to 10% by mass. In addition, the temperature of the dyeing bath is preferably 20 to 50°C, particularly preferably 25 to 40°C. The suitable dyeing time is 0.2 minutes to 5 minutes.

By applying the boric acid crosslinking treatment to the PVA film, it is possible to more effectively prevent the PVA from dissolving into water during wet stretching at high temperatures. From this point of view, the boric acid crosslinking treatment is preferably performed before the uniaxial stretching treatment. The boric acid crosslinking treatment can be performed by immersing the PVA film in an aqueous solution containing a boric acid crosslinking agent. As the boric acid crosslinking agent, one or two or more types of boron-containing inorganic compounds such as boric acid and borax salts can 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 1-15% by mass, more preferably in the range of 2-7% by mass. When the concentration of the boric acid crosslinking agent is in the range of 1 to 15% by mass, sufficient stretchability can be maintained. The aqueous solution containing the boric acid crosslinking agent may also contain auxiliary agents 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°C, particularly preferably in the range of 25 to 40°C. By setting the temperature in the range of 20 to 50°C, boric acid crosslinking can be effectively performed.

The uniaxial stretching treatment system can 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 a boric acid-containing aqueous solution, or can also be carried out in the above-mentioned dyeing bath or the fixed treatment bath described later. Moreover, in the case of the dry stretching method, the uniaxial stretching process can be performed directly at room temperature, or the uniaxial stretching process can also be performed while heating, or the PVA film can be used after water absorption. Perform uniaxial stretching in air. Among these, the wet stretching method is preferred, and the uniaxial stretching treatment in an aqueous solution containing boric acid is more preferred. The concentration of boric acid in the boric acid aqueous solution is preferably in the range of 0.5 to 6% by mass, more preferably in the range of 1 to 5% by mass. In addition, the boric acid aqueous solution may contain potassium iodide, and its concentration is preferably in the range of 0.01 to 10% by mass. The stretching temperature of the uniaxial stretching treatment is preferably in the range of 30 to 90°C, more preferably in the range of 40 to 80°C, and particularly preferably in the range of 50 to 70°C. In addition, from the viewpoint of the polarization performance of the obtained polarizing film, the stretching ratio of the uniaxial stretching treatment (total stretching ratio from the raw material PVA film) is preferably 5 times or more, more preferably 5.5 times above. The upper limit of the stretching ratio is not particularly limited, but the stretching ratio is preferably 8 times or less.

There are no special restrictions on the direction of the uniaxial stretching treatment when the long PVA film is uniaxially stretched. The uniaxial stretching treatment in the longitudinal direction or the transverse uniaxial stretching treatment, or the so-called However, from the viewpoint of obtaining a polarizing film with excellent polarizing properties, uniaxial stretching in the longitudinal direction is preferred. The uniaxial stretching process in the longitudinal direction can be performed by using a stretching device provided with a plurality of rolls parallel to each other and changing the peripheral speed between the rolls. On the other hand, the transverse uniaxial stretching treatment system can be performed using a tenter type stretching machine.

When manufacturing a polarizing film, in order to strengthen the adsorption of the dichroic dye (iodine-based dye, etc.) to the PVA film, it is better to perform a fixing treatment after the uniaxial stretching treatment. As for the fixing treatment bath used for the fixing treatment, an aqueous solution containing the boron-containing compound (B) can be preferably used. In addition, boric acid, iodine compounds, metal compounds, etc. may be added to the fixed treatment bath as needed. The temperature of the fixed treatment bath is preferably 15-60°C, particularly preferably 25-40°C.

The boron-containing compound (B) can be adsorbed on the polarizing film in any step of dyeing treatment, boric acid cross-linking treatment, uniaxial stretching treatment, and fixing treatment, but it never affects the breakage during uniaxial stretching treatment. It is particularly preferred to perform adsorption during the fixation process. In addition, not only one type of boron-containing compound (B) may be used, but two or more types may be mixed and used. The concentration of the aqueous solution of the boron-containing compound (B) is preferably 0.05 to 15% by mass, particularly preferably 0.1% to 10% by mass. When the concentration of the boron-containing compound (B) in the aqueous solution is less than 0.05% by mass, the adsorption sometimes becomes slow, and when the concentration of the aqueous solution is higher than 15% by mass, the boron-containing compound (B) may precipitate on the surface of the polarizing film. . In addition, from the viewpoint of improving the polarization performance, the aqueous solution containing the boron-containing compound (B) preferably contains an auxiliary agent such as potassium iodide. In addition, the temperature of the treatment bath is preferably 10 to 70°C, more preferably 20 to 60°C, and particularly preferably 20 to 50°C. If the temperature is too low, the boron-containing compound (B) may precipitate in the treatment bath. In addition, if the temperature is too high, it will be difficult to manufacture easily industrially under relatively mild conditions.

A suitable manufacturing method in the case where the boron-containing compound (B) is adsorbed on the polarizing film during the fixing treatment is to sequentially apply the swelling treatment, the boric acid cross-linking treatment, the uniaxial stretching treatment, and the fixing treatment. If necessary, one or more treatments selected from washing treatment, drying treatment, and heat treatment are sequentially applied.

The washing treatment is usually performed by immersing the film in water, distilled water, pure water, or the like. At this time, from the viewpoint of improving the polarization performance, the aqueous solution used for the cleaning treatment preferably contains an iodide such as potassium iodide as an auxiliary agent, and the concentration of the iodide is preferably 0.5 to 10% by mass. In addition, the temperature of the aqueous solution in the washing treatment is usually 5 to 50°C, preferably 10 to 45°C, and more preferably 15 to 40°C. From an economic point of view, the lower the temperature of the aqueous solution, the worse, and if the temperature of the aqueous solution is too high, the polarization performance may decrease.

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

By performing the heat treatment after the drying treatment, a polarizing film with more excellent dimensional stability can be obtained. Here, the heat treatment refers to a process of further heating the dried polarizing film with a moisture content of 5% or less to improve the dimensional stability of the polarizing film. The conditions of the heat treatment are not particularly limited, but the heat treatment is preferably performed in the range of 60°C to 150°C, and particularly preferably the heat treatment is performed in the range of 70°C to 150°C. If the heat treatment is performed at a temperature lower than 60°C, the dimensional stabilization effect caused by the heat treatment will not be sufficient; if the heat treatment is performed at a temperature higher than 150°C, the polarizing film may be intensely reddened.

The humidity and heat resistance of the polarizing film obtained as described above can be evaluated using the color fading derived from the PVA-iodine complex under high temperature and high humidity as an index. Specifically, it can be evaluated as the percentage (absorbance residual ratio) of the absorbance D (610 nm) after fading to the absorbance C (610 nm) before fading when the two polarizing films are laminated into crossed nicol. The residual rate of absorbance after fading for 8 hours at 60°C/90%RH is preferably 22% or more, more preferably 25% or more.

The polarizing film is usually used as a polarizing plate by bonding an optically transparent and mechanically strong protective film on both sides or one side. As the protective film, cellulose triacetate (TAC) film, cellulose acetate-butyrate (CAB) film, acrylic film, polyester film, etc. can be used. In addition, the adhesive for bonding includes a PVA-based adhesive, a urethane-based adhesive, and the like, but among them, a PVA-based adhesive is preferred.

The polarizing plate system obtained as described above can be used as a member of LCD after applying an adhesive such as acrylic, and then bonding it to a glass substrate. It can also be laminated with retardation film, viewing angle enhancement film, brightness enhancement film, etc. at the same time.

[Example]

Hereinafter, the present invention will be explained in more detail through examples, but the present invention is not limited in any way by these examples. In addition, each measurement or evaluation method used in the following Examples and Comparative Examples is shown below.

[Swelling degree of PVA film]

The 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 with filter paper, and the quality of the PVA film after immersion (mass E) was measured. After that, the PVA film was placed in a dryer at 105° C. and dried for 16 hours, and then the quality of the dried PVA film (mass F) was measured. The values of mass E and mass F are substituted into the following calculation formula (5) to calculate the swelling degree of the PVA film.

Swelling degree (%)=(quality E/quality F)×100 (5)

[Optical properties of polarizing film]

(1) Determination of transmittance Ts

From the central part of the polarizing film obtained in the following examples or comparative examples, two samples were taken 4 cm along the stretching direction of the polarizing film and 2 cm along the width direction, and a spectrophotometer with an integrating sphere (Japan "V7100" manufactured by Seiko Co., Ltd.), in accordance with JIS Z 8722 (Method for Measuring Object Color), the visibility of C light source and 2° field of view in the visible light region is corrected. For one sample, the measurement is inclined +45° with respect to the longitudinal direction. Obtain the average value Ts1(%) of the light transmittance at time and the light transmittance at -45°. For another piece of sample, proceed in the same way, measure the light transmittance when tilted +45° and the light transmittance when tilted -45°, and obtain the average value Ts2 (%) of these. The Ts1 and Ts2 are averaged by the following calculation formula (6), and used as the transmittance Ts (%) of the polarizing film.

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

(2) Measurement of polarization degree V

For the two samples used in the above-mentioned measurement of transmittance Ts, use a spectrophotometer with an integrating sphere ("V7100" manufactured by JASCO Corporation), and perform C in accordance with JIS Z 8722 (Method for Measuring Object Color) Visibility correction of the visible light area of the light source and 2° field of view is used to measure the light transmittance T⊥(%) when overlapped so that the stretching directions are orthogonal to each other, and when overlapped so that the stretching directions are parallel to each other. Light transmittance T//(%). Substitute the measured T//(%) and T⊥(%) into the following calculation formula (7) to obtain the degree of polarization V(%).

V={(T//-T⊥)/(T//+T⊥)} ^1/2 ×100 (7)

[Damp and heat resistance]

Two polarizing films were respectively fixed to a metal frame and stacked to form a cross-polarized light, and the initial (0 hour) absorbance C (610 nm) was measured with a spectrophotometer. Then the polarized film fixed on the metal frame was placed in a 60°C/90%RH environment for 8 hours, then superimposed into a cross-polarized light, and the absorbance D (610nm) after 8 hours was measured by a spectrophotometer. The value of absorbance D/absorbance C×100 was defined as a residual rate (%) as an index of the color fading derived from the PVA-iodine complex compound.

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

The polarizing film whose humidity was controlled at 23° C./50% RH for 16 hours was dissolved in heavy water to make 0.005% by mass, and a solution concentrated to 0.15% by mass by a rotary evaporator was used as a ¹ H-NMR measurement sample. ^{The 1} H-NMR (JNM-AL400: 400MHz, manufactured by JEOL Ltd.) measurement system was performed at 80°C, and analysis was performed by the following method using ALICE2 (manufactured by JEOL Ltd.). ^{For the 1} H-NMR chart obtained by the measurement, after adjusting the phase so that the baseline becomes flat, the average point is set to 20 and the baseline is automatically corrected. Next, it is automatically set as a reference so that the peak of heavy water as a measurement solvent is located at 4.65 ppm. Thereafter, as in FIG. 1, the hydrogen peaks of the hydrocarbon groups contained in the boron-containing compound (B) are integrated to obtain the peak area. At this time, the sum (area G) of the hydrogen peak area of the hydrocarbon group contained in the boron-containing compound (B) that does not overlap with the hydrogen peak derived from PVA is used as the peak area standard, and the boron-containing compound (B) The number of hydrogen of the hydrocarbon group and the value of the area G are set so that the value becomes the same. Next, let the hydrogen peak in the range of 1.7 ppm to 2.4 ppm be the hydrogen peak of the hydrocarbon group contained in the boron-containing compound (B) that overlaps the hydrogen peak derived from the methylene group derived from PVA and the hydrogen peak derived from the methylene group derived from PVA. The total of the peaks, and the peak area (area H) is obtained. Then, the area I obtained by subtracting the hydrogen number of the hydrocarbon group of the boron-containing compound (B) that overlaps with the hydrogen peak of the methylene group derived from PVA from the area H was calculated. The value obtained by such a method is substituted into the following calculation formula (8), and the content of the boron element derived from the boron-containing compound (B) relative to 100 parts by mass of the polyvinyl alcohol (A) is calculated. In addition, X and Y of the following calculation formula (8) are the number of hydrogen in the hydrocarbon group contained in the boron-containing compound (B) that does not overlap the peak of PVA, and the number of boron per molecule of the boron-containing compound (B) . In addition, the calculation formula (8) is used when unmodified PVA is used, and when the modified PVA is used as a raw material, the calculation formula (8) must be changed appropriately.

The boron element content (parts by mass) derived from the boron-containing compound (B) relative to 100 parts by mass of polyvinyl alcohol (A) = {(area G/X)/(area I/2))×{(10.811×Y )/44.0526)×100 (8)

10.811 is the atomic weight of boron, and 44.0526 is the molecular weight per 1 mol of repeated units of unmodified PVA. ^{In addition, the 1} H-NMR chart in FIG. 1 is a chart for measuring the polarizing film of Example 1. The boron element content derived from the boron-containing compound (B) of 100 parts by mass of polyvinyl alcohol (A) is a decimal point The second place is unconditionally carried and becomes 0.5 parts by mass.

[Calculation of all boron content (mass%) in polarizing film]

The mass (J(g)) of the polarizing film whose humidity was controlled at 23° C./50% RH for 16 hours was measured, and the polarizing film was dissolved in 20 mL of distilled water to make it 0.005 mass%. The aqueous solution in which the polarizing film is dissolved is used as a measurement sample, and its mass (K(g)) is measured. After that, a Multi-Type ICP emission spectrometer (ICP) manufactured by Shimadzu Corporation was used to measure the boron concentration (L (ppm)) of the measurement sample. After that, the value obtained by substituting this value into the following calculation formula (9) is used as the total boron element content (mass %) in the polarizing film.

The content of all boron in the polarizing film (mass%) =[(L×10 ^-6 ×K)/J]×100 (9)

[Example 1]

Contains 100 parts by mass of PVA (degree of saponification: 99.9 mol%, degree of polymerization: 2400), 10 parts by mass of glycerin as a plasticizer, and 0.1 parts by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant, using PVA to contain An aqueous solution with a rate of 10% by mass was used as the film-forming stock solution, which was dried on a metal roll at 80°C, and the resulting film was heat-treated in a hot air dryer at 120°C for 10 minutes to adjust the degree of swelling to 200 % To produce a PVA film with a thickness of 30μm.

From the center part in the width direction of the PVA film obtained as described above, a sample having a width of 5 cm × a length of 9 cm was cut out so as to be uniaxially stretched in a range of 5 cm in width × 5 cm in length. This sample was immersed in pure water at 30°C for 30 seconds, while being uniaxially stretched 1.1 times in the longitudinal direction, and subjected to swelling treatment. Next, immersed in an aqueous solution (dyeing bath) (temperature 30°C) containing 0.04% by mass of iodine and 4.0% by mass of potassium iodide for 60 seconds, while uniaxially stretching 2.2 times (2.4 times as a whole) in the longitudinal direction, and making It adsorbs iodine. Next, it was immersed in an aqueous solution (boric acid cross-linking treatment bath) containing 3% by mass of boric acid and 3% by mass of potassium iodide (at a temperature of 30°C), and at the same time uniaxially stretched 1.2 times in the longitudinal direction (2.7 times as a whole) ). It was immersed in a 58°C aqueous solution (uniaxial stretching treatment bath) containing 4% by mass of boric acid and 6% by mass of potassium iodide, and uniaxially stretched to 6.0 times the entire length in the longitudinal direction. Then, immerse in an aqueous solution (fixed treatment bath) (temperature 30°C) containing 0.5% by mass of 1,4-butane diboronic acid and 4% by mass of potassium iodide for 100 seconds Bell. Finally, it was dried at 60°C for 4 minutes to produce a polarizing film. The two polarized films after drying were respectively fixed to a metal frame, and the absorbance (610 nm) when the cross-polarized light was superimposed was 3.9.

^{After measuring and analyzing the 1} H-NMR of the obtained polarizing film, 1,4-butane diboronic acid (1,4-butane diboronic acid), which did not overlap with the hydrogen peak derived from PVA, appeared at 1.0 to 1.3 ppm. Therefore, the peak area (area G) is set to 4, and then the peak area (area H) of hydrogen of the methylene group of PVA whose peak appears in the range of 1.7 to 2.4 ppm is calculated. Since the hydrogen peak of 1,4-butane diboronic acid (1,4-butane diboronic acid) overlaps with the hydrogen peak of the methylene group of PVA, the hydrogen corresponding to the methylene group of PVA is subtracted from the area H The peak 1,4-butane diboronic acid (1,4-butane diboronic acid) has a hydrogen number of 4 and the area I is calculated. After substituting these values into the calculation formula (8), it is obtained that the boron content derived from the boron-containing compound (B) is 0.5 parts by mass relative to 100 parts by mass of the polyvinyl alcohol (A).

Furthermore, 0.00099 g (mass J) of the polarizing film produced in the same manner was dissolved in 20 mL of distilled water to produce a measurement sample for ICP measurement. After measuring the mass of the prepared sample for measurement, the mass was 20.03 g (mass K). After that, after the ICP measurement, the boron concentration of the measurement sample was 1.24 ppm (boron concentration L). After substituting these values into the calculation formula (9), it is obtained that the content of all boron elements relative to the polarizing film is 2.5% by mass. In addition, the obtained polarizing film was used to evaluate the optical properties and moisture and heat resistance of the polarizing film by the above-mentioned method. The above results are summarized in Table 1.

In addition, in Examples 2 to 4 and Comparative Examples 1 to 3, one side was immersed in an aqueous solution containing potassium iodide in a ratio of 100 parts by mass to 1 part by mass of iodine (dyeing treatment bath) (temperature 30°C) 60 Seconds, one The surface is uniaxially stretched 2.2 times in the length direction (2.4 times as a whole) and adsorbs iodine. At this time, the concentration of iodine or potassium iodide in the dyeing bath was adjusted so that the absorbance (610 nm) of the two polarized films after drying was fixed to a metal frame and stacked to form a cross-polarized light from 3.6 to 4.2.

[Example 2]

Except that the fixed treatment bath uses 0.5% by mass of 1,3-propane diboronic acid (1,3-propane diboronic acid) and 3% by mass of potassium iodide in an aqueous solution (temperature 30°C), the same as in Example 1. The polarizing film was produced in the same manner, and various measurements or evaluations were performed. The results are shown in Table 1.

[Example 3]

A polarizing film was produced in the same manner as in Example 1, except that an aqueous solution (temperature 30°C) containing phenyl boronate at a ratio of 1.0% by mass and potassium iodide at a ratio of 2.0% by mass was used in the fixed treatment bath, and various measurements were performed. Or evaluation. The results are shown in Table 1. Example 3 is a reference example.

[Example 4]

A polarizing film was produced in the same manner as in Example 1, except that an aqueous solution (temperature 30°C) containing n-propyl boronate at a ratio of 4.0% by mass and potassium iodide at a ratio of 3.0% by mass was used for the fixed treatment bath. Perform various measurements or evaluations. The results are shown in Table 1. Example 4 is a reference example.

[Comparative Example 1]

A polarizing film was produced in the same manner as in Example 1, except that an aqueous solution (temperature 30°C) containing boric acid at a ratio of 2% by mass and potassium iodide at a ratio of 3% by mass was used in the fixed treatment bath, and various measurements and evaluations were performed. 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 boric acid at a ratio of 1.0% by mass and potassium iodide at a ratio of 3% by mass was used for the fixed treatment bath, and various measurements and evaluations were performed. The results are shown in Table 1.

[Comparative Example 3]

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

Comparing Examples 1 and 2 with Comparative Example 2, it can be seen that even if the content of all boron elements in the polarizing film is the same or less, the residual absorbance ratio of Examples 1 and 2 is higher than that of Comparative Example 2. In addition, comparing Examples 3 and 4 with Comparative Example 1, it can be seen that even if the content of all boron elements in the polarizing film is the same or less, the residual absorbance ratios of Examples 3 and 4 are higher than those of Comparative Example 1. From the above, it can be seen that the polarizing films of Examples 1 to 4 that meet the requirements of the present invention have excellent moisture and heat resistance.

Claims (2)

A polarizing film comprising polyvinyl alcohol (A) and a boron-containing compound (B) represented by the following formula (4), characterized in that the polarizing film is derived from the boron-containing compound (B) The content of boron element is 0.1 to 3 parts by mass relative to 100 parts by mass of polyvinyl alcohol (A), which further contains boric acid, and the content of all boron elements in the polarizing film is 0.2 to 5% by mass,

In the above formula (4), X is a divalent organic group. A method for manufacturing a polarizing film, which is the method for manufacturing a polarizing film as claimed in claim 1, characterized in that it includes a dyeing process of dyeing a polyvinyl alcohol film with a dichroic pigment and a stretching process of uniaxially stretching the film The manufacturing method of the treated polarizing film includes a process of immersing the film in an aqueous solution of the boron-containing compound (B).

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