JP6788673B2 - Polarizing film and its manufacturing method - Google Patents

Description

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

A polarizing plate having a function of transmitting and shielding light is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes the polarization state of light. Many polarizing plates have a structure in which a protective film such as a cellulose triacetate (TAC) film is bonded to the surface of the polarizing film in order to prevent fading of the polarizing film and to prevent shrinkage of the polarizing film. , polyvinyl alcohol film as a polarizing film constituting the polarizing plate (hereinafter, "polyvinyl alcohol" and may be referred to as "PVA") was uniaxially stretched to become matrix iodine dye (I ₃ ^- and I ₅ ^-, etc. ) Is adsorbed in the mainstream.

LCDs are widely used in small devices such as calculators and wristwatches, mobile phones, laptop computers, LCD monitors, LCD color projectors, LCD TVs, in-vehicle navigation systems, and measuring devices used indoors and outdoors. These devices are required to be thin and lightweight. Therefore, each member of the LCD is also required to be thin, but if the protective film of the polarizing plate, which is one of the members of the LCD, is thinned, there is a concern that the function of preventing the fading of the iodine-based polarizing film may be reduced. ing. Therefore, there is a demand for an iodine-based polarizing film having excellent so-called moisture heat resistance, which causes less fading under high temperature and high humidity.

By the way, as a method for improving the moist heat resistance of an iodine-based polarizing film, a method for cross-linking a polarizing film with a polyvalent aldehyde (Patent Document 1) and a method for cross-linking with a polyvalent carboxylic acid compound (Patent Document 2). ) Is known.

Japanese Unexamined Patent Publication No. 6-235815 Japanese Unexamined Patent Publication No. 2011-257756

However, when a multivalent aldehyde is used, it is difficult to carry out industrially because the aldehyde easily volatilizes and it is difficult to control the concentration. Further, since the polyvalent carboxylic acid compound has low reactivity and requires the 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 having excellent moisture and heat resistance, which does not use an acid catalyst, does not require treatment at a high temperature, and can be easily manufactured industrially.

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

The above-mentioned problem is a boron-containing compound (B) having at least one functional group selected from the group consisting of polyvinyl alcohol (A) and a boron-containing group that can be converted into a boronic acid group in the presence of a boronic acid group and water. A polarizing film containing the above, 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 with respect to 100 parts by mass of the polyvinyl alcohol (A). This is solved by providing a polarizing film.

At this time, it is preferable that boric acid is further contained and the total boron element content 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 functional groups.

Further, the above problem is to make the film into an aqueous solution of the boron-containing compound (B) in a method for producing a polarizing film including a dyeing treatment for dyeing a polyvinyl alcohol film with a dichroic dye and a stretching treatment for uniaxially stretching the film. It is also solved by providing a method for producing the polarizing film, which comprises a process of immersing.

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

^{1 1} H-NMR chart of the polarizing film obtained in Example 1

The polarizing film of the present invention is a boron-containing compound having at least one functional group selected from the group consisting of polyvinyl alcohol (A) and a boron-containing group that can be converted to a boronic acid group in the presence of water. It is a polarizing film containing (B) and. 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 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 that can be converted to 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 a carbon atom (not shown). In boric acid [B (OH) ₃ ], the boron atom is bonded to three hydroxyl groups, whereas boronic acid is different in that it has a boron-carbon bond. Since the boron-carbon bond of the boronic acid group is not hydrolyzed, it is stable even in an environment where water is present. Typical examples of the boron-containing group that can be converted into a boronic acid group in the presence of water include, but are not limited to, the boronic acid ester group described below.

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 PVA, R in the structural formula (2) is a PVA chain, and a carbon-containing group is bonded to the PVA chain via a boron atom. The moisture and heat resistance of the film is improved.

The following structural formula (3) is a boronic acid diester group in which two molecules of alcohol (R-OH) are reacted with a boronic acid group. Here, when the boronic acid group is bonded to the hydroxyl group of PVA, the two Rs in the structural formula (3) are both PVA chains, and a plurality of PVA chains are crosslinked with each other, which is obtained. The moisture and heat resistance of the polarizing film is effectively improved.

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 and a boron-containing group that can be converted to a boronic acid group in the presence of water in the molecule.

When the boron-containing compound (B) is an aromatic compound, the moisture and heat resistance of the polarizing film may be improved. Although the reason is not clear, it is presumed that the π-π stacking of aromatic rings makes it difficult for moisture to permeate, and the effect of improving the moisture resistance and heat resistance of the polarizing film is enhanced. Examples of such a boron-containing compound (B) include phenylboronic acid, 1,4-benzenediboronic acid, 1,3-benzenediboronic acid, and 1,3,5-benzenetriboronic acid.

Further, the boron-containing compound (B) has a plurality of at least one functional group selected from the group consisting of a boronic acid group and a boron-containing group that can be converted into a boronic acid group in the presence of water in the molecule. The moisture and heat resistance of the polarizing film is effectively improved. The following structural formula (4) shows the boron-containing compound (B) when the molecule has two boronic acid groups. Here, X is a divalent organic group, such as an alkylene group or an arylene group. In this case, there are four points that react with the hydroxyl group of PVA to form an ester, and the PVA chain is crosslinked more effectively.

Examples of the boron-containing compound (B) having the plurality of functional groups include methanediboronic acid, ethanediboronic acid, propanediboronic acid, butandiboronic acid, pentandiboronic acid, hexanediboronic acid, and isomers thereof, and 1,4. −benzenediboronic acid, 1,3-benzenediboronic acid, 1,3,5-benzenetriboronic acid and the like can be mentioned.

The content of the boron element derived from the boron-containing compound (B) in the polarizing film of the present invention needs to be 0.1 to 3 parts by mass with respect to 100 parts by mass of 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 crosslinked polyvinyl alcohol (A) is small, and the effect of improving the moist 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, 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 increased to more than 3 parts by mass, the film becomes too hard and the handleability is lowered, and the productivity is lowered because a long treatment time is required. There is also a risk of doing so. The content of the boron element derived from the boron-containing compound (B) is preferably 2 parts by mass or less, and particularly preferably 1 part by mass or less. The boron element content derived from the boron-containing compound (B) can be obtained by ^{1 1} H-NMR measurement.

It is preferable that the polarizing film of the present invention further contains boric acid. This makes it possible to more effectively prevent PVA from elution into water during wet stretching at a high temperature. At this time, the total boron element content in the polarizing film is preferably 0.2 to 5% by mass. Here, the total boron element content is the total amount of all boron elements including the boron element content derived from the boron-containing compound (B) and the boron element content derived from boric acid. When the total boron element content in the polarizing film is less than 0.2% by mass, the effect of improving the moist heat resistance is reduced. It is more preferable that the total boron element content in the polarizing film is 1% by mass or more. On the other hand, when the total boron element content in the polarizing film is more than 5% by mass, the dimensional change of the polarizing film at high temperature may be large. It is more preferable that the total boron element content in the polarizing film is 4.5% by mass or less. The total boron element content in the polarizing film can be determined by ICP emission spectrometry 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 more preferably 2,000. It is more preferably in the range of ~ 4,000. When the degree of polymerization is 1,500 or more, the durability of the polarizing film obtained by uniaxially stretching the film can be improved. On the other hand, when the degree of polymerization is 6,000 or less, it is possible to suppress an increase in manufacturing cost and a defect in process passability during film formation. The degree of polymerization of PVA in the present specification means the average degree of polymerization measured according to the description of JIS K6726-1994.

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, from the viewpoint of water resistance of the polarizing film obtained by uniaxially stretching the film. It is preferably 98 mol% or more, and more preferably 98 mol% or more. The degree of saponification of PVA in the present specification refers to structural units (typically vinyl ester units) and vinyl possessed by PVA that can be converted into vinyl alcohol units (-CH _2- CH (OH)-) by saponification. The ratio (mol%) of the number of moles of the vinyl alcohol unit to the total number of moles with the alcohol unit. The saponification degree can be measured according to the description of JIS K6726-1994.

The method for producing PVA used in the present invention is not particularly limited. For example, a method of converting the vinyl ester unit of the polyvinyl ester obtained by polymerizing the vinyl ester monomer into the vinyl alcohol unit can be mentioned. The vinyl ester monomer used in the production of PVA is not particularly limited, and for example, vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatic acid, vinyl caproate, caprylic acid. Examples thereof include vinyl, vinyl caproate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, vinyl benzoate and the like. Vinyl acetate is preferable from an economic point of view.

Further, in the PVA used in the present invention, the vinyl ester unit of the polyvinyl ester copolymer obtained by copolymerizing the vinyl ester monomer and another monomer copolymerizable therewith is converted into a vinyl alcohol unit. It may be a thing. Other monomers copolymerizable with the vinyl ester monomer include, for example, α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutene; (meth) acrylic acid or a salt thereof; Methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, (Meta) acrylates such as t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate; (meth) acrylamide; N-methyl (Meta) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylamide propanesulfonic acid or a salt thereof, (meth) acrylamidepropyldimethylamine or a salt thereof (Meta) acrylamide derivatives such as N-methylol (meth) acrylamide or derivatives thereof; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methylvinyl ether, ethylvinyl ether, n-propylvinyl ether, Vinyl ethers such as i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; vinyl cyanide such as (meth) acryliconitrile; vinyl chloride, vinylidene chloride, vinyl fluoride, foot Vinyl halides such as vinylidene, allyl compounds such as allyl acetate and allyl chloride; maleic acid or salts thereof, esters or acid anhydrides; itaconic acid or salts thereof, esters or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane ; Unsaturated sulfonic acid and the like can be mentioned. The vinyl ester copolymer described above can have a structural unit derived from one or more of the other monomers described above. The other monomer may be present in the reaction vessel in advance when the vinyl ester monomer is subjected to the polymerization reaction, or it may be added to the reaction vessel during the polymerization reaction. It can be used by doing so. From the viewpoint of polarization performance, the content of units derived from other monomers is preferably 10 mol% or less, more preferably 5 mol% or less, and preferably 2 mol% or less. More preferred.

Among the monomers copolymerizable with the above vinyl ester monomer, the stretchability is improved and the film can be stretched at a higher temperature, so that troubles such as stretch breakage are reduced during the production of the optical film, and the optical film is used. Ethylene is preferable because the productivity of the film is further improved. When PVA contains ethylene units, the content of ethylene units is 1 to 4 mol% with respect to the number of moles of all structural units constituting PVA from the viewpoint of stretchability and stretchable temperature as described above. Preferably, 2-3 mol% is more preferable.

The polymerization method for polymerizing the vinyl ester monomer may be any of batch polymerization, semi-batch polymerization, continuous polymerization, semi-continuous polymerization and the like, and the polymerization method includes a massive polymerization method, a solution polymerization method and a suspension. Known methods such as a polymerization method and an emulsion polymerization method can be applied. A massive polymerization method or a solution polymerization method in which the polymerization proceeds in a solvent such as solvent-free or alcohol is usually adopted. When obtaining a polyvinyl ester having a high degree of polymerization, an emulsion polymerization method is also preferable. The solvent of the solution polymerization method is not particularly limited, but is, for example, alcohol. The alcohol used as the solvent in the solution polymerization method is a lower alcohol such as methanol, ethanol or propanol. The amount of the solvent used in the polymerization solution may be selected in consideration of the chain transfer of the solvent according to the degree of polymerization of the target PVA. For example, when the solvent is methanol, the mass ratio of the solvent to all the monomers ( The solvent / total monomer) is preferably selected from the range of 0.01 to 10, more preferably from the range of 0.05 to 3.

The polymerization initiator used for the polymerization of the vinyl ester monomer may be selected from known polymerization initiators such as azo-based initiators, peroxide-based initiators, and redox-based initiators according to the polymerization method. Examples of the azo-based initiator include 2,2'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), and 2,2'-azobis (4-methoxy-2,4-). Dimethylvaleronitrile). Peroxide-based initiators are percarbonate-based compounds such as diisopropylperoxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethylperoxydicarbonate; t-butylperoxyneodecanate, α-. Perester compounds such as cumyl peroxyneodecanate; acetylcyclohexylsulfonyl peroxide; 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate; acetyl peroxide. Potassium persulfate, ammonium persulfate, hydrogen peroxide and the like may be combined with the above-mentioned initiator to obtain a polymerization initiator. The redox-based initiator is, for example, a polymerization initiator that is a combination of the above-mentioned peroxide-based initiator and a reducing agent such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, and longalit. The amount of the polymerization initiator used varies depending on the type of the polymerization initiator and cannot be unconditionally determined, but it may be selected according to the polymerization rate. For example, when 2,2'-azobisisobutyronitrile or acetyl peroxide is used as the polymerization initiator, 0.01 to 0.2 mol% is preferable with respect to the vinyl ester monomer, and 0.02 to 0. 15 mol% is more preferable. The polymerization temperature is not particularly limited, but is appropriately about room temperature to 150 ° C., preferably 40 ° C. or higher and lower 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 is, for example, aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethanethiol; and phosphinates such as sodium phosphite monohydrate. Of these, 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 is generally 0.1 with respect to 100 parts by mass of the vinyl ester monomer. It is preferably 10 parts by mass.

The saponification of the polyvinyl ester can be carried out, for example, in a state where the polyvinyl ester is dissolved in an alcohol or a hydrous alcohol. Examples of the alcohol used for saponification include lower alcohols such as methanol and ethanol, and methanol is preferable. The alcohol used for saponification may contain other solvents such as acetone, methyl acetate, ethyl acetate and benzene in a proportion of 40% by mass or less based on the mass thereof. The catalyst used for saponification is, for example, an alkali metal hydroxide such as potassium hydroxide or sodium hydroxide, an alkali catalyst such as sodium methylate, or an acid catalyst such as mineral acid. The temperature at which saponification is carried out is not limited, but is preferably in the range of 20 to 60 ° C. When a gel-like product is precipitated as the saponification progresses, the product can be pulverized, washed and dried to obtain PVA. The saponification method is not limited to the method described above, and 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 above-mentioned PVA. Preferred plasticizers include polyhydric alcohols, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like. Furthermore, one or more of these plasticizers can be included. Among these, glycerin is preferable from the viewpoint of improving stretchability.

The content of the plasticizer in the PVA film used for producing the polarizing film of the present invention is preferably in the range of 1 to 20 parts by mass with respect to 100 parts by mass of PVA, and is in the range of 3 to 17 parts by mass. It is more preferable, and it is further preferable that it is in the range of 5 to 15 parts by mass. When the content is 1 part by mass or more, the stretchability of the film is further improved. On the other hand, when the content is 20 parts by mass or less, it is possible to prevent the film from becoming too flexible and the handleability from being lowered.

The PVA film used in the production of the polarizing film of the present invention further includes a filler, a processing stabilizer such as a copper compound, a weather resistance stabilizer, a colorant, an ultraviolet absorber, a light stabilizer, an antioxidant, and an antioxidant. , Flame retardant, other thermoplastics, lubricants, fragrances, defoaming agents, deodorants, bulking agents, release agents, mold release agents, reinforcing agents, cross-linking agents, fungicides, preservatives, delayed crystallization Additives such as agents can be appropriately added as needed.

The ratio of the total of PVA and the 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. It is preferably 95% by mass or more, and more preferably 95% by 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 in the range of 180 to 220%. Is particularly preferable. When the degree of swelling is 160% or more, it is possible to suppress the extremely progress of crystallization, and it is possible to stably stretch to a high magnification. On the other hand, when the degree of swelling is 240% or less, dissolution during stretching is suppressed, and stretching can be performed even under higher temperature conditions.

The thickness of the PVA film used for producing the polarizing film of the present invention is not particularly limited, but is generally 1 to 100 μm, more preferably 5 to 60 μm, and particularly preferably about 10 to 45 μm. If the thickness is too thin, stretch breakage tends to occur easily during the uniaxial stretching process for producing a polarizing film. On the other hand, if the thickness is too thick, stretching spots are likely to occur during the uniaxial stretching treatment for producing a polarizing film.

The width of the PVA film used for producing the polarizing film of the present invention is not particularly limited, and can be determined according to the intended use of the polarizing film to be produced. In recent years, since the screen size of liquid crystal televisions and liquid crystal monitors has been increasing, it is suitable for these applications if the width of the PVA film used for manufacturing the polarizing film is 3 m or more. On the other hand, if the width of the PVA film used for producing the polarizing film is too large, it tends to be difficult to uniformly perform uniaxial stretching when producing the polarizing film with a practical device. The width of the PVA film used is preferably 7 m or less.

The method for producing a PVA film used for producing 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 adopted. For example, production of a polarizing film can be adopted. One or more of the above-mentioned PVA constituting the PVA film used in the above, and if necessary, the above-mentioned plasticizers, additives, and the surfactant described below are dissolved in a liquid medium. Use a film-forming stock solution containing one or more of a film stock solution, PVA, and, if necessary, a plastic agent, an additive, a surfactant, a liquid medium, and the like, in which PVA is melted. Can be manufactured. When the film-forming stock solution 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 preparing the membrane-forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol. , Trimethylolpropane, ethylenediamine, diethylenetriamine and the like, and one or more of these can be used. Of these, water is preferable from the viewpoint of environmental load and recoverability.

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

The film-forming stock solution preferably contains a surfactant. By containing the surfactant, the film-forming property is improved, the occurrence of thickness unevenness of the film is suppressed, and the film can be easily peeled off from the metal roll or belt used for the film-forming. 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 above-mentioned 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.

As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate; a sulfate ester type such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and a sulfonic acid type such as dodecylbenzene sulfonate are suitable.

Examples of the nonionic surfactant include an alkyl ether type such as polyoxyethylene oleyl ether; an alkylphenyl ether type such as polyoxyethylene octylphenyl ether; an alkyl ester type such as polyoxyethylene laurate; and polyoxyethylene laurylamino. Alkylamine type such as ether; Alkylamide type such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; Polyoxy An allylphenyl ether type such as alkylene allylphenyl ether is suitable.

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

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

Examples of the film-forming method for forming a PVA film used for producing 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. Can be mentioned. These film forming methods may adopt only one kind or a combination of two or more kinds. Among these film-forming methods, the cast film-forming method and the extrusion film-forming method are preferable because a PVA film used for producing a polarizing film having a uniform thickness and width and good physical properties can be obtained. The formed PVA film can be dried or heat-treated as needed.

As an example of a specific method for producing a PVA film used for producing the polarizing film of the present invention, for example, a T-type slit die, a hopper plate, an I-die, a lip coater die, or the like is used to prepare the above-mentioned film-forming stock solution. A film that is uniformly discharged or spread on the peripheral surface of a rotating heated first roll (or belt) located on the most upstream side, and discharged or spread on the peripheral surface of the first roll (or belt). The volatile components are evaporated from one surface to dry and then further dried on the peripheral surface of one or more rotating heated rolls placed downstream thereof, or in a hot air drying device. An industrially preferable method can be adopted in which the film is further dried and then wound by a winding device. Drying with a heated roll and drying with a hot air drying device may be carried out in an appropriate combination.

The method for producing the polarizing film of the present invention is not particularly limited. A suitable production method is a method for producing a polarizing film including a dyeing treatment for dyeing a polyvinyl alcohol film with a dichroic dye and a stretching treatment for uniaxially stretching the film, in which the film is made into an aqueous solution of a boron-containing compound (B). This is a method for producing a polarizing film having a dipping process. The PVA film used for producing the polarizing film of the present invention is subjected to dyeing treatment, uniaxial stretching treatment, and if necessary, further swelling treatment, boric acid cross-linking treatment, fixing treatment, washing treatment, drying treatment, heat treatment and the like. The method can be mentioned. In this case, the order of each treatment such as swelling treatment, dyeing treatment, boric acid cross-linking treatment, uniaxial stretching treatment, and fixing treatment is not particularly limited, and one or more treatments can be performed at the same time. It is also possible to perform one or more of each process 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 preferably in the range of 25 to 35 ° C. More preferred. 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. 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 a mixture of water and an aqueous medium.

The dyeing treatment can be performed by contacting the PVA film with a dichroic dye. Iodine-based dyes are generally used as the dichroic dyes. 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 generally carried out by immersing the PVA film in a solution containing iodine-potassium iodide (particularly an aqueous solution) as a dyeing bath. The concentration of iodine in the dyeing bath is preferably in the range of 0.01 to 0.5% by mass, and the concentration of potassium iodide is preferably in the range of 0.01 to 10% by mass. The temperature of the dyeing bath is preferably 20 to 50 ° C, particularly preferably 25 to 40 ° C. A suitable staining time is 0.2 to 5 minutes.

By subjecting the PVA film to a boric acid cross-linking treatment, it is possible to more effectively prevent PVA from elution into water during wet stretching at a high temperature. From this point of view, the boric acid cross-linking treatment is preferably performed before the uniaxial stretching treatment. The boric acid cross-linking treatment can be performed by immersing the PVA film in an aqueous solution containing a boric acid cross-linking agent. As the boric acid cross-linking agent, one or more kinds of boron-containing inorganic compounds such as borate such as boric acid and borax can be used. The concentration of the boric acid cross-linking agent in the aqueous solution containing the boric acid cross-linking agent is preferably in the range of 1 to 15% by mass, more preferably in the range of 2 to 7% by mass. Sufficient stretchability can be maintained when the concentration of the boric acid cross-linking agent is in the range of 1 to 15% by mass. The aqueous solution containing the boric acid cross-linking agent may contain an auxiliary agent such as potassium iodide. The temperature of the aqueous solution containing the boric acid cross-linking agent is preferably in the range of 20 to 50 ° C., particularly preferably in the range of 25 to 40 ° C. By setting the temperature within the range of 20 to 50 ° C., boric acid cross-linking can be performed efficiently.

The uniaxial stretching treatment may be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution containing boric acid, in the above-mentioned dyeing bath or in the fixing treatment bath described later. In the case of the dry stretching method, the uniaxial stretching treatment may be performed at room temperature, the uniaxial stretching treatment may be performed while heating, or the uniaxial stretching treatment may be performed in the air using a PVA film after water absorption. You can also do it. Among these, the wet stretching method is preferable, and the uniaxial stretching treatment is more preferable in an aqueous solution containing boric acid. The concentration of boric acid in the boric acid aqueous solution is preferably in the range of 0.5 to 6% by mass, more preferably in the range of 1 to 5% by mass. Further, the boric acid aqueous solution may contain potassium iodide, and the concentration thereof is preferably in the range of 0.01 to 10% by mass. The stretching temperature in 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. Further, the draw ratio (total draw ratio from the raw material PVA film) in the uniaxial stretching treatment is preferably 5 times or more, and more preferably 5.5 times or more, from the viewpoint of the polarization performance of the obtained polarizing film. preferable. 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 when the long PVA film is subjected to the uniaxial stretching treatment, and the uniaxial stretching treatment in the long direction, the lateral uniaxial stretching treatment, or the so-called diagonal stretching treatment can be adopted. Since a polarizing film having excellent polarization performance can be obtained, uniaxial stretching treatment in the long direction is preferable. The uniaxial stretching process in the long direction can be performed by using a stretching device including a plurality of rolls parallel to each other and changing the peripheral speed between the rolls. On the other hand, the horizontal uniaxial stretching treatment can be performed using a tenter type stretching machine.

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

The boron-containing compound (B) may be adsorbed on the polarizing film in any of the steps of dyeing treatment, boric acid cross-linking treatment, uniaxial stretching treatment, and fixing treatment, but adsorbing during the fixing treatment is the cutting during the uniaxial stretching treatment. It is particularly preferable because it does not affect the above. Further, the boron-containing compound (B) is not limited to one type, and 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, and particularly preferably 0.1% by mass to 10% by mass. If the aqueous solution concentration of the boron-containing compound (B) is lower than 0.05% by mass, adsorption may be delayed, and if the aqueous solution concentration is higher than 15% by mass, the boron-containing compound (B) may appear on the surface of the polarizing film. Precipitates may occur. Further, the aqueous solution containing the boron-containing compound (B) preferably contains an auxiliary agent such as potassium iodide from the viewpoint of improving the polarization performance. 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. Further, if the temperature is too high, it becomes difficult to manufacture easily industrially under relatively mild conditions.

When the boron-containing compound (B) is adsorbed on the polarizing film during the fixing treatment, a suitable production method is to perform a swelling treatment, a boric acid cross-linking treatment, a uniaxial stretching treatment, and a fixing treatment in this order. After that, if necessary, one or more treatments selected from a cleaning treatment, a drying treatment, and a heat treatment may be performed in this order.

The cleaning treatment is generally 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 iodide such as potassium iodide as an auxiliary agent, and the concentration of the iodide is preferably 0.5 to 10% by mass. .. The temperature of the aqueous solution in the cleaning treatment is generally 5 to 50 ° C, preferably 10 to 45 ° C, and more preferably 15 to 40 ° C. From an economical point of view, it is not preferable that the temperature of the aqueous solution is too low, and if the temperature of the aqueous solution is too high, the polarization performance may deteriorate.

The conditions of the drying treatment are not particularly limited, but it is preferable to perform drying at a temperature in the range of 30 to 150 ° C., particularly in the range of 50 to 130 ° C. By drying at a temperature in the range of 30 to 150 ° C., a polarizing film having excellent dimensional stability can be easily obtained.

By performing heat treatment after the drying treatment, a polarizing film having further excellent dimensional stability can be obtained. Here, the heat treatment is a process of further heating the polarizing film after the drying treatment having 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., particularly 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 of the heat treatment is insufficient, and if the heat treatment is performed at a temperature higher than 150 ° C., the polarizing film may be severely reddish.

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

The polarizing film is usually used as a polarizing plate by laminating a protective film that is optically transparent and has mechanical strength on both sides or one side thereof. As the protective film, a cellulose triacetate (TAC) film, a cellulose acetate / butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Further, examples of the adhesive for bonding include PVA-based adhesives and urethane-based adhesives, and among them, PVA-based adhesives are preferable.

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

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. The measurement or evaluation methods adopted in the following examples and comparative examples are shown below.

[PVA film swelling degree]
The PVA film was cut into 5 cm × 10 cm and immersed in 1000 mL of distilled water at 30 ° C. for 30 minutes. Then, 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 (mass E) of the PVA film after immersion was measured. Then, the PVA film was put in a dryer at 105 ° C., dried for 16 hours, and then the mass (mass F) of the dried PVA film 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 formula (5).
Swelling degree (%) = (mass E / mass F) x 100 (5)

[Optical characteristics of polarizing film]
(1) Measurement of Transmittance Ts Two samples of 4 cm in the stretching direction and 2 cm in the width direction of the polarizing film were collected from the central portion of the polarizing film obtained in the following Example or Comparative Example, and spectroscopic with an integrating sphere. Using a photometer (“V7100” manufactured by Nippon Spectroscopy Co., Ltd.), the visibility of the visible light region of the C light source and 2 ° field is corrected in accordance with JIS Z 8722 (measurement method of object color), and one sheet is used. For the sample, the light transmittance when tilted by + 45 ° with respect to the length direction and the light transmittance when tilted by −45 ° were measured, and the average value Ts1 (%) of them was obtained. Similarly for the other sample, the light transmittance when tilted by + 45 ° and the light transmittance when tilted by −45 ° were measured, and their average value Ts2 (%) was obtained. Ts1 and Ts2 were averaged by the following calculation formula (6) to obtain the transmittance Ts (%) of the polarizing film.
Ts = (Ts1 + Ts2) / 2 (6)

(2) Measurement of degree of polarization V With respect to the two samples used in the measurement of the above-mentioned transmittance Ts, the light transmittance T⊥ (%) when the stretching directions are overlapped so as to be orthogonal to each other, and the stretching thereof. Using a spectrophotometer with an integrating sphere (“V7100” manufactured by JASCO Corporation), the transmittance T // (%) of light when stacked so that the directions are parallel is measured by JIS Z 8722 (object color). According to the measurement method), the C light source and the visual sensitivity of the visible light region of the 2 ° field were corrected for measurement. The measured T // (%) and T⊥ (%) were substituted into the following formula (7) to obtain the degree of polarization V (%).
V = {(T‖-T⊥) / (T‖ + T⊥)} ^1/2 x 100 (7)

[Moisture and heat resistance]
The two polarizing films were fixed to a metal frame and superposed on Cross Nicol, and the initial (0 hour) absorbance C (610 nm) was measured with a spectrophotometer. Further, the polarizing film fixed to the metal frame was allowed to stand in an atmosphere of 60 ° C./90% RH for 8 hours, then superposed on Cross Nicol, and the absorbance D (610 nm) after 8 hours was measured with a spectrophotometer. The value of absorbance D / absorbance C × 100 was defined as the residual rate (%) and used as an index of color fading derived from the PVA-iodine complex.

[Measurement of Boron Element Content Derived from Boron-Containing Compound (B) with respect to 100 Parts by Mass of Polyvinyl Alcohol (A)]
A polarizing film adjusted to a humidity of 23 ° C./50% RH for 16 hours was dissolved in heavy water to a concentration of 0.005% by mass, and a solution concentrated to 0.15% by mass using a rotary evaporator was prepared by ¹ H-NMR. It was used as a measurement sample. ^{1 1} H-NMR (JNM-AL400 manufactured by JEOL Ltd.) was measured at 80 ° C. and analyzed by the following method using ALICE2 (manufactured by JEOL Ltd.). The phase of the ¹ H-NMR chart obtained by the measurement was adjusted so that the baseline became smooth, and then the average point was set to 20 to automatically correct the baseline. Next, the peak of heavy water, which is the measurement solvent, was automatically set as a reference so as to be at the position of 4.65 ppm. Then, as shown in FIG. 1, the hydrogen peaks of the hydrocarbon groups contained in the boron-containing compound (B) were integrated to determine the peak area. At this time, the sum of the hydrogen peak areas of the hydrocarbon groups contained in the boron-containing compound (B) that does not overlap with the hydrogen peak derived from PVA (area G) is used as the reference for the peak area, and the boron-containing compound (B) is used. It was set so that the number of hydrogens of the corresponding hydrocarbon group and the value of the area G were the same. Next, the hydrocarbon group contained in the boron-containing compound (B) in which the hydrogen peak in the range of 1.7 ppm to 2.4 ppm overlaps with the hydrogen peak derived from the methylene group of PVA and the hydrogen peak derived from the methylene group of PVA. The peak area (area H) was calculated by regarding the total number of hydrogen peaks in the above. Then, the area I obtained by subtracting the number of hydrogens of the hydrocarbon group of the boron-containing compound (B) overlapping with 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 formula (8) to calculate the boron element content derived from the boron-containing compound (B) with respect to 100 parts by mass of polyvinyl alcohol (A). In addition, X and Y of the following formula (8) are the number of hydrogens of the hydrocarbon group contained in the boron-containing compound (B) which does not overlap with the peak of PVA, respectively, and the boron per molecule of the boron-containing compound (B). It is a number. The calculation formula (8) is a formula used when unmodified PVA is used, and when the modified PVA is used as a raw material, the calculation formula (8) needs to be appropriately modified.
Boron element content (parts by mass) derived from boron-containing compound (B) with respect to 100 parts by mass of polyvinyl alcohol (A) = {(area G / X) / (area I / 2)} × {(10.811 × Y) /44.0526} x 100 (8)
10.811 is the atomic weight of boron and 44.0526 is the molecular weight per mole of unmodified PVA repeating unit. The ¹ H-NMR chart in FIG. 1 is a measurement of the polarizing film of Example 1, and the content of the boron element derived from the boron-containing compound (B) with respect to 100 parts by mass of polyvinyl alcohol (A) is in the second decimal place. Was carried up to 0.5 parts by mass.

[Calculation of total boron element content (mass%) in polarizing film]
The mass (J (g)) of the polarizing film adjusted for 16 hours at 23 ° C./50% RH was measured, and the polarizing film was dissolved in 20 mL of distilled water so as to be 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. Then, the boron concentration (L (ppm)) of the measurement sample was measured using a multi-type ICP emission spectrometer (ICP) manufactured by Shimadzu Corporation. Then, the value calculated by substituting the value into the following calculation formula (9) was used as the total boron element content (mass%) in the polarizing film.
Total boron element content (mass%) in polarizing film
= [(L × ^10-6 × K) / J] × 100 (9)

[Example 1]
Contains 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 parts by mass of polyoxyethylene lauryl ether sodium sulfate as a surfactant, and contains PVA. An aqueous solution containing 10% by mass of alcohol is used as a film-forming stock solution, which is dried on a metal roll at 80 ° C., and the obtained film is swelled by heat treatment at a temperature of 120 ° C. for 10 minutes in a hot air dryer. The degree was adjusted to 200% to produce a PVA film having a thickness of 30 μm.

A sample having a width of 5 cm and a length of 9 cm was cut from the central portion of the PVA film thus obtained in the width direction so that a range of 5 cm in width × 5 cm in length could be uniaxially stretched. This sample was uniaxially stretched 1.1 times in the length direction while being immersed in pure water at 30 ° C. for 30 seconds for swelling treatment. Then, while immersing in an aqueous solution (dyeing treatment bath) (temperature 30 ° C.) containing 0.04% by mass of iodine and 4.0% by mass of potassium iodide for 60 seconds, the concentration was increased 2.2 times (2.4 times in total). Iodine was adsorbed by uniaxial stretching in the length direction. Next, while immersed in an aqueous solution (boric acid cross-linking treatment bath) (temperature 30 ° C.) containing 3% by mass of boric acid and 3% by mass of potassium iodide, 1.2 times (2.7 times in total). It was uniaxially stretched in the length direction. Further, while immersing in an aqueous solution (uniaxial stretching treatment bath) at 58 ° C. containing boric acid in a proportion of 4% by mass and potassium iodide in a proportion of 6% by mass, the whole was uniaxially stretched up to 6.0 times in the length direction. Then, it was immersed in an aqueous solution (fixing treatment bath) (temperature 30 ° C.) containing 0.5% by mass of 1,4-butaniboronic acid and 4% by mass of potassium iodide for 100 seconds. Finally, it was dried at 60 ° C. for 4 minutes to produce a polarizing film. The absorbance (610 nm) when the two dried polarizing films were fixed to a metal frame and superposed on Cross Nicol was 3.9.

When ¹ H-NMR of the obtained polarizing film was measured and analyzed, a hydrogen peak of 1,4-butandiboronic acid that did not overlap with the hydrogen peak derived from PVA appeared at 1.0 to 1.3 ppm. The area (area G) was set to 4. Next, the peak area (area H) of hydrogen of the methylene group of PVA in which a peak appears in the range of 1.7 to 2.4 ppm was calculated. Since there was a hydrogen peak of 1,4-butandiboronic acid that overlaps with the hydrogen peak of the methylene group of PVA, the hydrogen number 4 of 1,4-butandiboronic acid, which corresponds to the hydrogen peak of the methylene group of PVA, is subtracted from the area H. Area I was calculated. When these values were substituted into the calculation formula (8), the boron content derived from the boron-containing compound (B) was 0.5 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol (A).

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. When the mass of the prepared measurement sample was measured, the mass was 20.03 g (mass K). After that, when ICP measurement was performed, the boron concentration of the measurement sample was 1.24 ppm (boron concentration L). When these values were substituted into the calculation formula (9), the total boron element content with respect to the polarizing film was 2.5% by mass. Further, using the obtained polarizing film, the optical characteristics and moisture heat resistance performance of the polarizing film were evaluated by the above-mentioned method. The above results are summarized in Table 1.

In Examples 2 to 4 and Comparative Examples 1 to 3, the mixture was immersed in an aqueous solution (dyeing treatment bath) (temperature 30 ° C.) containing 100 parts by mass of potassium iodide with respect to 1 part by mass of iodine for 60 seconds. While uniaxially stretching in the length direction 2.2 times (2.4 times as a whole), iodine was adsorbed. At this time, the concentration of iodine and potassium iodide in the dyeing bath has an absorbance (610 nm) of 3.6 to 4 when the two dried polarizing films are fixed to a metal frame and superposed on cross Nicol. Adjusted to 0.2.

[Example 2]
The same as in Example 1 except that an aqueous solution (temperature 30 ° C.) containing 1,3-propanediboronic acid in an amount of 0.5% by mass and potassium iodide in an amount of 3% by mass was used in the fixing treatment bath. A polarizing film was prepared and each measurement or evaluation was performed. The results are shown in Table 1.

[Example 3]
Polarizing film 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 fixing treatment bath. Was prepared and each measurement or evaluation was performed. The results are shown in Table 1.

[Example 4]
The same as in Example 1 except that an aqueous solution (temperature 30 ° C.) containing n-propylboronic acid in an amount of 4.0% by mass and potassium iodide in an amount of 3.0% by mass was used in the fixing treatment bath. A polarizing film was prepared and each measurement or evaluation was performed. The results are shown in Table 1.

[Comparative Example 1]
A polarizing film was prepared in the same manner as in Example 1 except that an aqueous solution (temperature 30 ° C.) containing 2% by mass of boric acid and 3% by mass of potassium iodide was used in the fixing treatment bath. Each measurement or evaluation was performed. The results are shown in Table 1.

[Comparative Example 2]
A polarizing film was prepared 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 fixing treatment bath. Each measurement or evaluation was performed. The results are shown in Table 1.

[Comparative Example 3]
A polarizing film was prepared in the same manner as in Example 1 except that an aqueous solution (temperature 30 ° C.) containing 0.5% by mass of boric acid and 3% by mass of potassium iodide was used in the fixing treatment bath. Each measurement or evaluation was performed. The results are shown in Table 1.

Comparing Examples 1 and 2 with Comparative Example 2, the residual absorbance of Examples 1 and 2 is higher than that of Comparative Example 2 even though the total boron element content in the polarizing film is equal to or less than that of Comparative Example 2. I understand. Further, when Examples 3 and 4 are compared with Comparative Example 1, the residual absorbance of Examples 3 and 4 is higher than that of Comparative Example 1 even though the total boron element content in the polarizing film is equal to or less than that of Comparative Example 1. It turns out to be expensive. From the above, it can be seen that the polarizing films of Examples 1 to 4 satisfying the provisions of the present invention have excellent moisture and heat resistance.

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

Claims (2)

A polarizing film containing polyvinyl alcohol (A), a boron-containing compound (B) represented by the following formula (4), and boric acid, which contains a boron element derived from the boron-containing compound (B) in the polarizing film. amount Ri 0.1-3 parts by der against polyvinyl alcohol (a) 100 parts by mass of the polarization of the total boron element content in the polarizing film and wherein 0.2 to 5% by mass Rukoto the film.

[In the above formula (4), X is a divalent organic group. ] A dyeing treatment for dyeing a polyvinyl alcohol film with a bicolor dye, a borate cross-linking treatment for immersing the film in an aqueous solution containing 1 to 15% by mass of a borate cross-linking agent, a stretching treatment for uniaxially stretching the film, and the film. Is a method for producing a polarizing film including a fixing treatment in which the film is immersed in an aqueous solution containing 0.05 to 15% by mass of a boron-containing compound (B) , wherein the fixing treatment is performed after the boric acid cross-linking treatment. The method for producing a polarizing film according to claim 1 .

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