WO2020226153A1

WO2020226153A1 - Polarising film and method for producing same

Info

Publication number: WO2020226153A1
Application number: PCT/JP2020/018525
Authority: WO
Inventors: 亘大橋; 辻　嘉久
Original assignee: 株式会社クラレ
Priority date: 2019-05-09
Filing date: 2020-05-07
Publication date: 2020-11-12
Also published as: CN114096899A; JP7451508B2; KR20220007091A; TW202104418A; JPWO2020226153A1

Abstract

Provided is a polarising film including: a polyvinyl alcohol (A); at least one boron-containing compound (B) selected from the group comprising compounds which, in the presence of water and monoboronic acid represented by formula (I), can be converted into said monoboronic acid; and at least one boron-containing compound (C) selected from the group comprising compounds which, in the presence of water and diboronic acid represented by formula (II), can be converted into said diboronic acid, wherein the mass ratio (B/C) of the element boron derived from the boron-containing compound (B) to the element boron derived from the boron-containing compound (C) is 0.8-3.0, and the content of the element boron derived from the boron-containing compound (B) is 0.15-3.0 parts by mass in relation to 100 parts by mass of the polyvinyl alcohol (A). Said polarising film has a low contractile force at high temperature, as well as excellent optical performance and moisture/heat resistance. [In formula (I), R¹ is a C1-20 monovalent aliphatic group, and R¹ and the boronic acid group are linked by a boron-carbon bond.] [In formula (II), R² is a C1-20 divalent aliphatic group, and R² and the boronic acid groups are linked by a boron-carbon bond.]

Description

Polarizing film and its manufacturing method

The present invention relates to a polarizing film having a small shrinkage force at high temperature and excellent optical performance and moisture 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 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. ) And dichromatic dyes such as dichroic dyes are adsorbed on the mainstream.

LCDs are widely used in small devices such as calculators and wristwatches, smartphones, laptop computers, LCD monitors, LCD color projectors, LCD TVs, in-vehicle navigation systems, and measuring devices used indoors and outdoors. Equipment is required to be thin and have high definition. Along with this, in recent years, the thinning of glass used for LCDs, the thinning of protective films used for polarizing plates, and the increase in draw ratio of polarizing films have progressed, and as a result, the occurrence of warpage of LCD panels has become a problem. It has become. It is said that the main cause of warpage of an LCD panel is that the polarizing film shrinks at a high temperature, and there is a demand for a polarizing film having high optical performance and a small shrinking force at a high temperature. Further, since the effect of preventing the color fading of the polarizing film of the protective film is reduced by thinning the protective film, there is a concern that the iodine-based polarizing film will fade at high temperature and high humidity. Therefore, there is also 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 means for improving the optical performance of a polarizing film, a method using PVA having a high degree of polymerization is known (for example, Patent Document 1). However, although the optical performance of the polarizing film is improved by using PVA having a high degree of polymerization, the shrinkage force is increased, and it is difficult to achieve both.

In Patent Document 2, the amount of boric acid in the PVA film is reduced, and a step of drying the PVA film is provided between the boric acid treatment step and the washing step, so that the shrinkage force at high temperature is small and the color tone is good. It is described that a flexible polarizing film can be obtained. However, it has been difficult to sufficiently reduce the shrinkage force while maintaining high optical performance by reducing the amount of boric acid in the polarizing film.

Patent Document 3 describes that a polarizing film having high optical performance and moisture heat resistance can be obtained by using PVA having high syndiotacticity. However, when PVA having high syndiotacticity is used, stretching at a high temperature is required due to the high crystallinity of PVA, which is difficult to carry out industrially.

On the other hand, as a method for improving the moist heat resistance of the iodine-based polarizing film, a method of cross-linking the PVA film with a polyvalent aldehyde (Patent Document 4) or a polyvalent carboxylic acid compound (Patent Document 5), or a method of cross-linking the PVA film with boronic acid A method for treating (Patent Document 6) and a method for stretching a PVA film in an aqueous solution in which diboronic acid is dissolved (Patent Document 7) are known.

However, the method described in Patent Document 4 is difficult to carry out industrially because polyvalent aldehyde is easily volatilized and concentration control is difficult.

The method described in Patent Document 5 has a problem that the polarizing film is colored because the reactivity between the polyvalent carboxylic acid compound and PVA is low and it is necessary to use an acid catalyst or treat at a high temperature.

Although the polarizing film obtained by the method of treating with boronic acid described in Patent Document 6 has excellent moisture and heat resistance, the optical performance may still be insufficient. The polarizing film obtained by stretching in an aqueous solution in which diboronic acid is dissolved described in Patent Document 7 is excellent in moisture and heat resistance, but may still have insufficient optical performance.

Further, the method of treating with diboronic acid described in Patent Document 8 is difficult to control the concentration because diboronic acid is unstable in water and decomposes, and it is difficult to carry out industrially.

Japanese Unexamined Patent Publication No. 1-084203 Japanese Unexamined Patent Publication No. 2013-148806 Japanese Unexamined Patent Publication No. 6-265727 Japanese Unexamined Patent Publication No. 6-235815 Japanese Unexamined Patent Publication No. 2011-257756 WO2018 / 021274 KR10-2014-0075154 JP-A-2018-180022

The present invention has been made to solve the above problems, and an object of the present invention is to provide a polarizing film having a small shrinkage force at high temperature and excellent optical performance and moisture heat resistance.

The above-mentioned problem is at least one boron-containing compound (B) selected from the group consisting of PVA (A), a monoboronic acid represented by the following formula (I), and a compound capable of converting to the monoboronic acid in the presence of water. ), And a polarizing film containing at least one boron-containing compound (C) selected from the group consisting of a diboronic acid represented by the following formula (II) and a compound capable of converting to the diboronic acid in the presence of water. The mass ratio (B / C) of the boron element derived from the boron-containing compound (B) to the boron element derived from the boron-containing compound (C) is 0.8 to 3.0, and is derived from the boron-containing compound (B). The boron element content of the above is solved by providing a polarizing film having a boron element content of 0.15 to 3.0 parts by mass with respect to 100 parts by mass of PVA (A).

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

[In formula (II), R ² is a divalent aliphatic group having 1 to 20 carbon atoms, and R ² and a boronic acid group are connected by a boron-carbon bond. ]

At this time, it is preferable that R ¹ and R ² are saturated aliphatic groups. It is also preferable that R ¹ and R ² are aliphatic hydrocarbon groups. It is also preferable that R ¹ has 2 to 5 carbon atoms and R ² has 3 to 5 carbon atoms.

The above-mentioned problem is in a method for producing a polarizing film including a dyeing treatment for dyeing a PVA film with a dichroic dye and a stretching treatment for uniaxially stretching the film, the film is subjected to a boron-containing compound (B) and a boron-containing compound (C). ) Is also solved by providing a method for producing the polarizing film, which comprises a treatment of immersing in an aqueous solution containing.

At this time, it is preferable to immerse the stretched PVA film in the aqueous solution. Further, the concentration ratio (B / C) of the boron-containing compound (B) to the boron-containing compound (C) in the aqueous solution is less than 1, and the concentration of the boron-containing compound (B) exceeds 0.1% by mass. Is also preferable.

The polarizing film of the present invention has a small shrinkage force at high temperatures, and is also excellent in optical performance and moisture heat resistance. Therefore, by using the polarizing film of the present invention, it is possible to obtain an LCD panel that does not easily warp at high temperatures, has high image quality, and has excellent moisture and heat resistance. Further, according to the production method of the present invention, such a polarizing film can be produced.

6 is a ¹ H-NMR chart of the polarizing film obtained in Example 1. It is a figure which plotted the contraction force on the horizontal axis, and the luminosity factor correction degree of polarization on the vertical axis about the polarizing film of Examples 1-6 and Comparative Examples 1-13. For the polarizing films of Examples 1 to 6 and Comparative Examples 1 to 3, 5, 6, 9 to 13, the attenuation coefficient of the PVA-iodine complex is plotted on the horizontal axis, and the luminosity factor correction polarization degree is plotted on the vertical axis. ..

The polarizing film of the present invention contains at least one boron selected from the group consisting of PVA (A), a monoboronic acid represented by the following formula (I), and a compound capable of converting to the monoboronic acid in the presence of water. Polarization containing at least one boron-containing compound (C) selected from the group consisting of compound (B), diboronic acid represented by the following formula (II), and a compound capable of converting to diboronic acid in the presence of water. In the film, the mass ratio (B / C) of the boron element derived from the boron-containing compound (B) to the boron element derived from the boron-containing compound (C) is 0.8 to 3.0, and the boron-containing compound ( A polarizing film having a boron element content derived from B) of 0.15 to 3.0 parts by mass with respect to 100 parts by mass of PVA (A). The boron-containing compound (B) necessary for improving the optical performance is adsorbed on the PVA (A), and the PVA (A) is crosslinked with the boron-containing compound (B) and the boron-containing compound (C) in an appropriate ratio. As a result, the optical performance and the heat resistance to moisture and heat can be improved while reducing the shrinkage force of the polarizing film under high temperature.

Monoboronic acid is a compound represented by the above formula (I) and has one boronic acid group [-B (OH) ₂ ] in one molecule. In formula (I), R ¹ is a monovalent aliphatic group having 1 to 20 carbon atoms. The boronic acid group, the boron atom to which two hydroxyl groups are bonded, have a structure bonded to a carbon atom in the compound represented by the formula (I), R ¹ and boronic acid group and boron - It is connected by a carbon bond. In boric acid [B (OH) ₃ ], the boron atom is bonded to three hydroxyl groups, whereas the boronic acid group 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. 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, a boronic acid ester group described later.

Diboronic acid is a compound represented by the above formula (II) and has two boronic acid groups [-B (OH) ₂ ] in one molecule. R ² in the formula (II) is a divalent aliphatic group having 1 to 20 carbon atoms, and R ² and a boronic acid group are connected by a boron-carbon bond.

The hydroxyl groups in the boronic acid group contained in monoboronic acid and diboronic acid can form an ester with alcohol in the same manner as the hydroxyl groups in boric acid. The following formula (III) is a boronic acid monoester group obtained by reacting one molecule of alcohol (R-OH) with boronic acid. Here, when the boronic acid group is bonded to the hydroxyl group of PVA (A), R in the following formula (III) is a PVA chain, and a carbon-containing group is bonded to the PVA chain via a boron atom. Become.

The following structural formula (IV) is a boronic acid diester group in which two molecules of alcohol (R-OH) have reacted with a boronic acid group. Here, when the boronic acid group is bonded to the hydroxyl group of PVA, both of the two Rs in the structural formula (IV) are PVA chains.

Monoboronic acid has two hydroxyl groups that can react with the hydroxyl groups of PVA to form an ester, and the PVA chain is appropriately crosslinked. Since this cross-linking is heat-stable, the shrinkage force of the polarizing film at high temperature is reduced. As a result, the warpage of the LCD panel using the polarizing film under high temperature is suppressed. Further, it is considered that the linearity of the PVA chain is improved by introducing the ring structure into the PVA chain by performing the intramolecular cross-linking, and the optical performance of the polarizing film is improved.

Diboronic acid has four hydroxyl groups capable of reacting with the hydroxyl groups of PVA to form an ester, and the PVA chain is strongly crosslinked. Since this cross-linking is heat-stable, the shrinkage force of the polarizing film at high temperature is reduced. As a result, the warpage of the LCD panel using the polarizing film under high temperature is suppressed. Further, it is considered that the strong cross-linking of the PVA chain reduces the motility of the PVA chain under high temperature and high humidity, so that the moisture and heat resistance of the polarizing film is improved.

In the above formula (I), R ¹ is a monovalent aliphatic group having 1 to 20 carbon atoms. When R ¹ has an appropriate length, the solubility of the boron-containing compound (B) in water and the reactivity of PVA (A) with the hydroxyl group can be controlled. The carbon number of R ¹ is preferably 10 or less, more preferably 6 or less, and further preferably 5 or less. On the other hand, from the viewpoint of particularly excellent balance between the optical performance and the shrinkage force of the polarizing film, the carbon number of R ¹ is preferably 2 or more, and more preferably 3 or more.

In the above formula (I), R ¹ is a monovalent aliphatic group, and R ¹ and a boronic acid group may be connected by a boron-carbon bond. R ¹ may be a saturated aliphatic group or an unsaturated aliphatic group, but the former is preferable. Since R ¹ is a saturated aliphatic group, coloring of the obtained polarizing film is suppressed and durability is improved. Further, since R ¹ is a saturated aliphatic group, the orientation of the dichroic dye is improved and the optical performance is further improved.

R ¹ may be an aliphatic hydrocarbon group or may contain heteroatoms such as oxygen, nitrogen, sulfur and halogen. Considering the availability, it is preferable that R ¹ is an aliphatic hydrocarbon group. The aliphatic hydrocarbon group is preferably a straight chain aliphatic hydrocarbon group having no branch. As a result, it is considered that the adsorptivity of the boron-containing compound (B) to the PVA film is improved, and the effect of improving the optical performance and the effect of reducing the shrinkage force are further enhanced.

Specifically, R ¹ is preferably an alkyl group, and more preferably an alkyl group represented by the following formula (V).

In the above formula (V), n is 1 to 20. n is preferably 10 or less, more preferably 6 or less, and even more preferably 5 or less. On the other hand, n is preferably 2 or more, and more preferably 3 or more.

It is particularly preferable that R ¹ is a saturated aliphatic hydrocarbon group having 2 to 5 carbon atoms from the viewpoint of obtaining a polarizing film having a smaller shrinkage force at a high temperature and further excellent optical performance. If the number of carbon atoms is less than 2, the stability of the bond between PVA (A) and the boron-containing compound (B) is lowered, so that the effect of lowering the shrinkage force and the effect of improving the optical performance may be insufficient. is there. If the number of carbon atoms is larger than 5, the boron-containing compound (B) is unevenly distributed on the surface of the polarizing film, so that the effect of reducing the shrinkage force and the effect of improving the optical performance may be insufficient.

Specific examples of the monoboronic acid represented by the above formula (I) include methylboronic acid, ethylboronic acid, propylboronic acid, butylboronic acid, pentylboronic acid, hexylboronic acid, heptylboronic acid, octylboronic acid, and nonylboronic acid. Decanylboronic acid, undecanylboronic acid, dodecanylboronic acid, tridecanylboronic acid, tetradecanylboronic acid, pentadecanylboronic acid, hexadecanylboronic acid, heptadecanylboronic acid, octadecanylboronic acid, Examples thereof include nonadecanylboronic acid, icosanylboronic acid and isomers thereof. Propylboronic acid, butylboronic acid and pentylboronic acid are particularly preferable because they have good adsorptivity to the polarizing film and have a higher effect of improving optical performance. In addition, examples of the compound that can be converted into monoboronic acid represented by the above formula (I) in the presence of water include salts of the monoboronic acid, monoboronic acid esters, and the like.

In the above formula (II), R ² is a divalent aliphatic group having 1 to 20 carbon atoms. When R ² has an appropriate length, the solubility of the boron-containing compound (C) in water and the reactivity of PVA (A) with the hydroxyl group can be controlled. The number of carbon atoms in R ² is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 5 or less. On the other hand, from the viewpoint of further improving the moisture and heat resistance of the polarizing film, the carbon number of R ² is preferably 3 or more, and more preferably 4 or more.

In the above formula (II), R ² is a divalent aliphatic group, and it is sufficient that R ² and a boronic acid group are connected by a boron-carbon bond. R ² may be a saturated aliphatic group or an unsaturated aliphatic group, but the former is preferable. Since R ² is a saturated aliphatic group, coloring of the obtained polarizing film is suppressed. Further, it is considered that since R ² is a saturated aliphatic group, the diffusibility of the boron-containing compound (C) into the polarizing film is improved, and the effect of improving the moist heat resistance and the effect of reducing the shrinkage force are further enhanced. Be done.

R ² may be an aliphatic hydrocarbon group or may contain heteroatoms such as oxygen, nitrogen, sulfur and halogen. Considering the availability, it is preferable that R ² is an aliphatic hydrocarbon group. The aliphatic hydrocarbon group is preferably a straight chain aliphatic hydrocarbon group having no branch. As a result, it is considered that the adsorptivity of the boron-containing compound (C) to PVA (A) is improved, and the effect of improving the moist heat resistance and the effect of reducing the shrinkage force are further enhanced.

Specifically, R ² is preferably an alkylene group, and more preferably an alkylene group represented by the following formula (VI).

In the above formula (VI), n is 1 to 20. n is preferably 10 or less, more preferably 8 or less, further preferably 6 or less, and particularly preferably 5 or less. On the other hand, n is preferably 3 or more, and more preferably 4 or more.

From the viewpoint of obtaining a polarizing film having further excellent moisture and heat resistance, it is particularly preferable that R ² is a saturated aliphatic hydrocarbon group having 3 to 5 carbon atoms. When the number of carbon atoms is less than 3, the cross-linking efficiency between the PVA chains by the boron-containing compound (C) is lowered, so that the effect of improving the moist heat resistance may be insufficient. When the number of carbon atoms is larger than 5, the effect of improving the moist heat resistance may be insufficient because the boron-containing compound (C) is unevenly distributed on the surface of the polarizing film. Further, since the water solubility of the boron-containing compound (C) is also lowered, the boron-containing compound (C) is likely to be precipitated on the surface of the polarizing film.

Specific examples of the diboronic acid represented by the above formula (II) include methanediboronic acid, ethanediboronic acid, propandiboronic acid, butanediboronic acid, pentandiboronic acid, hexanediboronic acid, heptandiboronic acid, and octanediboronic acid. , Nonandiboronic acid, Decandiboronic acid, Undecandiboronic acid, Dodecandiboronic acid, Tridecandiboronic acid, Tetradecandiboronic acid, Pentadecandiboronic acid, Hexadecandiboronic acid, Heptadecandiboronic acid, Octadecandiboronic acid, Nonade Examples thereof include candiboronic acid, icosandiboronic acid and isomers thereof. Propaneboronic acid, butandiboronic acid, and pentaneboronic acid are particularly preferable because they have good adsorptivity to the polarizing film and are highly effective in improving moist heat resistance. In addition, examples of the compound that can be converted to diboronic acid represented by the above formula (II) in the presence of water include salts of the diboronic acid and diboronic acid esters.

The mass ratio (B / C) of the boron element derived from the boron-containing compound (B) to the boron element derived from the boron-containing compound (C) in the polarizing film of the present invention needs to be 0.8 to 3.0. .. This makes it possible to obtain a polarizing film having particularly excellent optical performance, shrinkage force and moisture heat resistance. On the other hand, when the mass ratio (B / C) is out of the above range and one of the boron-containing compound (B) and the boron-containing compound (C) is excessively adsorbed on the polarizing film, the excessively adsorbed boron-containing compound is the other boron. Since the effect of the contained compound is inhibited, any one of optical performance, shrinkage force, and moisture heat resistance becomes insufficient. The mass ratio (B / C) is preferably 1.0 or more, more preferably 1.2 or more, and even more preferably 1.4 or more. On the other hand, the mass ratio (B / C) is preferably 2.8 or less, more preferably 2.6 or less, and even more preferably 2.4 or less.

The content of the boron element derived from the boron-containing compound (B) in the polarizing film of the present invention needs to be 0.15 to 3.0 parts by mass with respect to 100 parts by mass of PVA (A). If the content is less than 0.15 parts by mass, the optical performance of the polarizing film becomes insufficient. The boron element content is preferably 0.16 parts by mass or more, more preferably 0.20 parts by mass or more, and further preferably 0.25 parts by mass or more. On the other hand, when the content of the boron element derived from the boron-containing compound (B) exceeds 3.0 parts by mass, the reason is not clear, but the cross-linking of PVA (A) by the boron-containing compound (C) is inhibited, so that it is moisture resistant. It is not preferable because the thermal property may be insufficient or the formation of an iodine complex that absorbs light of a short wavelength may be poorly formed, resulting in deterioration of optical performance. In addition, productivity may decrease due to the need for long processing time and high temperature processing. The boron element content is preferably 2.5 parts by mass or less, more preferably 2.0 parts by mass or less, further preferably 1.0 part by mass or less, and particularly preferably 0.5 parts by mass or less. The boron element content derived from the boron-containing compound (B) and the boron element content derived from the boron-containing compound (C) in the polarizing film can be obtained by ¹ H-NMR measurement.

The boron element content derived from the boron-containing compound (C) in the polarizing film of the present invention is appropriately determined by the boron element content derived from the boron-containing compound (B) and the mass ratio (B / C), and is not particularly limited. However, it is preferably 0.10 to 2.0 parts by mass with respect to 100 parts by mass of PVA (A). Thereby, PVA (A) can be sufficiently crosslinked, and the moisture and heat resistance can be further improved. On the other hand, although the reason is not clear, when the boron element content derived from the boron-containing compound (C) exceeds 2.0, the action of the boron-containing compound (B) to reduce the shrinkage force is inhibited, and the shrinkage force is increased. It may not be sufficiently lowered. Therefore, the content of the boron element derived from the boron-containing compound (C) in the polarizing film is more preferably 0.12 to 1.0 parts by mass with respect to 100 parts by mass of PVA (A). It is more preferably 14 to 0.6 parts by mass.

The polarizing film of the present invention may further contain boric acid. This may further improve the optical performance. At this time, the total boron element content in the polarizing film is preferably 0.2% by mass or more. Here, the total boron element content refers to the boron element derived from the boron-containing compound (B) and the boron-containing compound (C), the boron element derived from boric acid, and the boron-containing compound (B) contained in the polarizing film. It is the total amount of the boron element derived from the boron-containing compound (C) and the boron-containing compound other than boric acid. On the other hand, if the total boron element content in the polarizing film is too large, the shrinkage force of the polarizing film may increase. The total boron element content in the polarizing film is usually 5.5% by mass or less, preferably 5.0% by mass or less, more preferably 4.5% by mass or less, and even more preferably. It is 4.0% 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 (A) 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. It is more preferably in the range of 2,000 to 4,000. When the degree of polymerization is 1,500 or more, the durability of the polarizing film obtained by uniaxially stretching the film can be improved. On the other hand, when the degree of polymerization is 6,000 or less, it is possible to suppress an increase in manufacturing cost and a defect in process passability during film formation. The degree of polymerization of PVA (A) in the present specification means the average degree of polymerization measured according to the description of JIS K6726-1994.

The saponification degree of PVA (A) contained in the polarizing film of the present invention is preferably 95 mol% or more, preferably 96 mol% or more, from the viewpoint of water resistance of the polarizing film obtained by uniaxially stretching the film. More preferably, it is more preferably 98 mol% or more. Incidentally, a degree of saponification of PVA herein, PVA having a vinyl alcohol unit by saponification _(-CH 2 -CH (OH) -) vinyl the converted may structural units (typically vinyl ester units) and 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 (A) 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 (A) is not particularly limited, and for example, vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatic acid, vinyl caproate, etc. , Vinyl caprylate, 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 PVA (A) used in the present invention, the vinyl ester unit of the vinyl ester copolymer obtained by copolymerizing the vinyl ester monomer and another monomer copolymerizable therewith is a vinyl alcohol unit. It may be converted to. 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, preferably 5 mol% or less, based on the number of moles of all structural units constituting PVA (A). It is more preferably% or less, and further preferably 2 mol% or less.

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 polarizing film, and polarized light is obtained. Ethylene is preferred because it further improves film productivity. When PVA (A) contains ethylene units, the content of ethylene units is based on the number of moles of all structural units constituting PVA (A) from the viewpoint of stretchability and stretchable temperature as described above. 1 to 10 mol% is preferable, and 2 to 6 mol% is more preferable.

The PVA film used for producing the polarizing film of the present invention may contain a plasticizer in addition to the above PVA (A). Preferred plasticizers include polyhydric alcohols, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like. Furthermore, one or more of these plasticizers can be included. Among these, glycerin is preferable from the viewpoint of 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 (A), and is preferably 3 to 17 parts by mass. It is more preferably in the range of 5 to 15 parts by mass, and further preferably 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 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 antistatic agent. Agents, flame retardants, other thermoplastics, lubricants, fragrances, defoaming agents, deodorants, bulking agents, release agents, mold release agents, reinforcing agents, cross-linking agents, fungicides, preservatives, crystallization rate Additives other than PVA (A) and the plasticizer, such as a retarder, can be added as needed. The content of the other additive in the PVA film is usually 10% by mass or less, preferably 5% by mass or less.

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%. It is particularly preferable to be inside. 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, preferably 5 to 60 μm, and particularly preferably 10 to 45 μm. If the PVA film is too thin, stretch breakage tends to occur easily during the uniaxial stretching process for producing a polarizing film. Further, if the PVA film is too thick, stretching spots tend to occur during the uniaxial stretching process for producing the polarizing film, and the shrinkage force of the produced polarizing film tends to increase.

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 when 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 wide, it tends to be difficult to uniformly perform uniaxial stretching when producing the polarizing film with a practical device, so that the polarizing film is produced. The width of the PVA film used in the above is preferably 10 m or less.

The production method of the 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 are uniform is preferably adopted. For example, a film-forming stock solution in which one or more of PVA (A) and, if necessary, the plasticizer, the other additive, and a surfactant described later are dissolved in a liquid medium. PVA (A), and if necessary, one or more of plasticizers, other additives, surfactants, liquid media, etc., and PVA (A) melts. It can be manufactured using the existing film-forming stock solution. When the film-forming stock solution contains at least one of a plasticizer, other additives, and a surfactant, it is preferable that these components are uniformly mixed.

Examples of the liquid medium used for preparing the film-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 membrane-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.

Examples of the anionic surfactant include carboxylic acid types such as potassium laurate; polyoxyethylene lauryl ether sulfate, sodium alkyl sulfate, potassium alkyl sulfate, ammonium alkyl sulfate, triethanolamine alkyl sulfate, and polyoxyethylene alkyl ether sulfate. Sulfate type such as sodium, polyoxypropylene alkyl ether sulfate sodium, polyoxyethylene alkylphenyl ether sulfate sodium, octyl sulfate, etc .; sodium alkyl sulfonate, potassium alkyl sulfonate, ammonium alkyl sulfonate, triethanolamine alkyl sulfonate, alkyl benzene Sulfonic acid types such as sodium sulfonate, disodium dodecyldiphenyl ether disulfonate, sodium alkylnaphthalene sulfonate, disodium alkylsulfosuccinate, disodium polyoxyethylene alkylsulfosuccinate, dodecylbenzenesulfonate, etc .; sodium alkylphosphate, alkylphosphorus Acid ester potassium, alkyl phosphate ammonium ester, alkyl phosphate ester triethanolamine, polyoxyethylene alkyl ether phosphate sodium, polyoxypropylene alkyl ether phosphate sodium, polyoxyethylene alkylphenyl ether phosphate sodium, etc. A phosphoric acid ester type or the like is 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 film-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 (A) contained in the film-forming stock solution. It is more preferably in the range of 0.02 to 0.3 parts by mass, and particularly preferably in the range of 0.05 to 0.2 parts by mass. When the content is 0.01 parts by mass or more, 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 method for forming a PVA film using the above-mentioned undiluted film-forming solution include a cast film-forming method, an extrusion film-forming method, a wet film-forming method, and a gel film-forming method. These film forming methods may 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 from the viewpoint that 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. Further, a multilayer PVA film may be formed by forming a layer made of PVA (A) on one surface of a base film made of a single resin layer.

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 PVA film with a dichroic dye and a stretching treatment for uniaxially stretching the film, wherein the film is subjected to a boron-containing compound (B) and a boron-containing compound. This is a method for producing a polarizing film, which comprises a treatment of immersing in an aqueous solution containing (C). Examples thereof include a method of subjecting the PVA film to a dyeing treatment, a uniaxial stretching treatment, and, if necessary, a swelling treatment, a boric acid cross-linking treatment, a fixing treatment, a washing treatment, a drying treatment, a heat treatment, and the like. 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 for immersing the film is preferably in the range of 20 to 40 ° C, more preferably in the range of 22 to 38 ° C, and further preferably in the range of 25 to 35 ° C. .. 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 in which the film is immersed is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or a mixture of water and a hydrophilic medium.

The dyeing process can be performed by bringing the dichroic dye into contact with the PVA film. As the dichroic dye, an iodine dye or a dichroic dye is generally 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 generally performed by immersing the PVA film in a solution containing iodine-potassium iodide (particularly an aqueous solution) or a solution containing a plurality of bicolor dyes (particularly an aqueous solution) using a PVA film as a dyeing bath. is there. 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 0.2-5 minutes. When a dichroic dye is used, the dichroic dye is preferably an aqueous dye. The dye concentration in the dyeing bath is preferably 0.001 to 10% by mass. Further, if necessary, a dyeing aid may be used, or an inorganic salt such as sodium sulfate or a surfactant may be used. When sodium sulfate is used, it is preferably 0.1 to 10% by mass. The dyeing temperature is preferably 30 to 80 ° C. Specific dichroic dyes include C.I. Ai. Direct Yellow 28, Sea. Ai. Direct Orange 39, Sea. Ai. Direct Yellow 12, Sea. Ai. Direct Yellow 44, Sea. Ai. Direct Orange 26, Sea. Ai. Direct Orange 71, Sea. Ai. direct. Orange 107, Sea. Ai. Direct Red 2, Sea. Ai. Direct Red 31, Sea. Ai. direct. Red 79, Sea. Ai. Direct Red 81, Sea. Ai. Direct Red 247, Sea. Ai. Direct Green 80, Sea. Ai. Examples thereof include Direct Green 59, but a dichroic dye developed for manufacturing a polarizing plate is preferable.

The PVA film can also be subjected to boric acid cross-linking treatment. In this case, it is possible to more effectively prevent PVA (A) from eluting 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 0.1 to 6.0% by mass. The concentration of the boric acid cross-linking agent is more preferably 0.2% by mass or more. Further, it is more preferably 4.0% by mass or less. When the concentration of the boric acid cross-linking agent is within the above range, the stretchability may be improved. If the concentration of the boric acid cross-linking agent is too high, it may be difficult to contain the boron-containing compound (B) or the boron-containing compound (C) in a later step, so the concentration should not be too high. Is good. 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.

Apart from the uniaxial stretching treatment described later, the PVA film may be stretched (pre-stretched) during or between the above-mentioned treatments. As described above, the total stretching ratio of the pre-stretching performed before the uniaxial stretching treatment (the magnification obtained by multiplying the stretching ratio in each treatment) is the raw material before stretching from the viewpoint of the optical performance of the obtained polarizing film. Based on the original length of the PVA film, 1.5 times or more is preferable, 2.0 times or more is more preferable, and 2.5 times or more is further preferable. On the other hand, the total draw ratio is preferably 4.0 times or less, more preferably 3.5 times or less. The draw ratio in the swelling treatment is preferably 1.05 to 2.5 times. The draw ratio in the dyeing treatment is preferably 1.1 to 2.5 times. The draw ratio in the boric acid cross-linking treatment is preferably 1.1 to 2.5 times.

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, stretching is performed in an aqueous solution. It can also be stretched in the above-mentioned dyeing bath or in an aqueous boric acid solution. 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 boric acid concentration in the boric acid aqueous solution is preferably in the range of 0.5 to 6% by mass, and 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 30 ° C. or higher, more preferably 40 ° C. or higher, and even more preferably 50 ° C. or higher. On the other hand, the stretching temperature is preferably 90 ° C. or lower, more preferably 80 ° C. or lower, and even more preferably 70 ° C. or lower. The stretching ratio in the uniaxial stretching treatment is preferably 2.0 to 4.0 times. From the viewpoint of the optical performance of the obtained polarizing film, the draw ratio is more preferably 2.2 times or more. On the other hand, the draw ratio is more preferably 3.5 times or less. Further, the total draw ratio up to the fixing treatment described later is preferably 5 times or more based on the original length of the raw material PVA film before stretching from the viewpoint of the optical performance of the obtained polarizing film. More preferably, it is 5 times or more. 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, the so-called diagonal stretching treatment can be adopted. Since a polarizing film having excellent optical 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, etc.) on the PVA film. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing a boron-containing compound (B) and a boron-containing compound (C) can be preferably used. Further, if necessary, boric acid, an iodine compound, a metal compound and the like may be further added to the fixing treatment bath. The temperature of the fixing treatment bath is preferably 10 to 80 ° C. The draw ratio in the fixing treatment is preferably 1.3 times or less, more preferably 1.2 times or less, and further preferably less than 1.1 times.

The boron-containing compound (B) and the boron-containing compound (C) may be adsorbed on the PVA film in any of the steps of dyeing treatment, boric acid cross-linking treatment, uniaxial stretching treatment, and fixing treatment, but PVA during the uniaxial stretching treatment. It is particularly preferable to adsorb it during the fixing treatment after the uniaxial stretching treatment from the viewpoint of suppressing the cutting of the film and obtaining a polarizing film having particularly excellent optical performance. The boron-containing compound (B) and the boron-containing compound (C) are not limited to one type, and two or more types may be mixed and used. Further, although the reason is not clear, since the effect of improving the optical performance is enhanced, the PVA film is immersed in an aqueous solution containing a boron-containing compound (B) and a boron-containing compound (C) to obtain these compounds. It is preferable to adsorb to.

At this time, it is preferable that the concentration ratio (B / C) of the boron-containing compound (B) (mass%) to the boron-containing compound (C) (mass%) in the aqueous solution is less than 1. The boron-containing compound (B) has a higher adsorption rate to the polarizing film than the boron-containing compound (C). Therefore, when the concentration ratio (B / C) exceeds 1, the boron-containing compound (B) inhibits the adsorption of the boron-containing compound (C), and the effect of improving the moist heat resistance may be insufficient. On the other hand, the boron-containing compound (C) has a higher binding force to the polarizing film than the boron-containing compound (B). Therefore, if the concentration of the boron-containing compound (C) is excessively high, the boron-containing compound (B) cannot be adsorbed inside the PVA film, and the effect of improving the optical performance may be insufficient. Therefore, the concentration ratio (B / C) is preferably 0.05 or more, more preferably 0.35 or more, and particularly preferably 0.5 or more.

It is also preferable that the concentration of the boron-containing compound (B) in the aqueous solution exceeds 0.1% by mass. When the concentration of the boron-containing compound (B) is 0.1% by mass or less, the adsorption rate of the boron-containing compound (B) is slow, and the effect of improving the optical performance may be insufficient, which is not preferable. The concentration of the boron-containing compound (B) is more preferably 0.15% by mass or more, and further preferably 0.17% by mass or more. On the other hand, the upper limit of the concentration of the boron-containing compound (B) is not particularly limited, but if it is higher than 15% by mass, the boron-containing compound (B) may be unevenly distributed near the surface of the polarizing film, and as a result, the result is obtained. The optical performance of the polarizing film is deteriorated. In addition, a precipitate of the boron-containing compound (B) may be formed on the surface of the polarizing film. The concentration of the aqueous solution of the boron-containing compound (B) is more preferably 10% by mass or less, further preferably 5.0% by mass or less, particularly preferably 3.5% by mass or less, and 1.5% by mass. Most preferably, it is by mass or less. The concentration of the aqueous solution of the boron-containing compound (B) is preferably 0.5% by mass or less from the viewpoint that a polarizing film having extremely high optical performance and extremely little precipitation of the boron-containing compound (B) can be obtained.

From the viewpoint of further improving the optical performance, the aqueous solution containing the boron-containing compound (B) and the boron-containing compound (C) preferably contains an iodide auxiliary such as potassium iodide, and the concentration of the iodide is 0. It is preferably .5 to 15% by mass. The temperature of the aqueous solution is preferably 10 to 80 ° C. If the temperature is too low, the boron-containing compound (B) and the boron-containing compound (C) may precipitate in the treatment bath. The temperature of the aqueous solution is more preferably 15 ° C. or higher, and even more preferably 20 ° C. or higher. On the other hand, if the temperature is too high, it may be difficult to manufacture it industrially. The temperature of the aqueous solution is more preferably 70 ° C. or lower, and even more preferably 60 ° C. or lower. The time of immersion in the aqueous solution is preferably 5 to 400 seconds.

When the boron-containing compound (B) and the boron-containing compound (C) are adsorbed on the PVA film during the fixing treatment, suitable production methods include swelling treatment, uniaxial stretching treatment, and fixing treatment in this order, swelling treatment, and boric acid. The acid cross-linking treatment, the uniaxial stretching treatment, and the fixing treatment are performed in this order, and the swelling treatment, the uniaxial stretching treatment, the fixing treatment, and the boric acid cross-linking treatment are performed in this order. After performing these treatments, one or more treatments selected from a cleaning treatment, a drying treatment, and a heat treatment may be further performed, if necessary.

The cleaning treatment is generally performed by immersing the film in distilled water, pure water, an aqueous solution, or the like. At this time, from the viewpoint of optical performance, it is preferable to use an aqueous solution containing an 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 even more preferably 15 to 40 ° C. From an economic 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 optical performance may deteriorate.

The conditions of the drying treatment are not particularly limited, but it is preferable to perform drying at a temperature within the range of 30 to 150 ° C., particularly within 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 process, dimensional stability may be further improved. Here, the heat treatment is a treatment for further heating a polarizing film having a moisture content of 5% or less after the drying treatment. 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 temperature is less than 60 ° C., the dimensional stabilization effect may be insufficient, and if it exceeds 150 ° C., the polarizing film may be severely reddish.

The polarizing film of the present invention thus obtained has a small shrinkage force at high temperatures, and is also excellent in optical performance and moisture heat resistance. It is preferable that the luminosity factor correction polarization degree of the polarizing film at a luminosity factor correction single transmittance 43.8 to 44.2% is 99.94% or more. The shrinkage force of the polarizing film is preferably less than 10N, more preferably 8N or less. Further, the attenuation coefficient of the PVA-iodine complex in the polarizing film is preferably −0.5 or more, and more preferably −0.3 or more. The luminosity factor correction single transmittance, the luminosity factor correction polarization degree, the shrinkage force, and the attenuation coefficient of the PVA-iodine complex of the polarizing film are measured by the methods described in Examples described later.

The polarizing film of the present invention 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. In addition, examples of the adhesive for bonding include a PVA-based adhesive and a UV-curable adhesive.

The polarizing plate obtained as described above may be bonded to a retardation film, a viewing angle improving film, a brightness improving film, or the like. Further, after coating a polarizing plate with an adhesive such as acrylic, it can be bonded to a glass substrate and used as an LCD component.

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.

[Measurement of Boron Element Content from Boron-Containing Compound (B) or Boron-Containing Compound (C) in Polarizing Film Containing Boron-Containing Compound (B) and Boron-Containing Compound (C)]
A polarizing film was dissolved in heavy water so that its content was 0.003% by mass, and then a solution concentrated by a rotary evaporator so that the content was 0.15% by mass was used as a ¹ H-NMR measurement sample. And said. ^{1 1} H-NMR (JNM-AL400: 400 MHz manufactured by JEOL Ltd.) was measured at 80 ° C., and the number of integrations was set to 256. Analysis was performed 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 1 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 peak 6 of the methyl group derived from the boron-containing compound (B) appearing in the range of 1.2 to 1.3 ppm was integrated to obtain the peak area (area A). Next, the hydrogen peaks 5 of the hydrocarbon groups derived from the boron-containing compound (B) and the boron-containing compound (C), which overlap in the range of 1.0 to 1.2 ppm, are integrated, and the peak area (area B) thereof is integrated. ) Was asked. Further, a boron-containing compound (B) and a boron-containing compound in which a hydrogen peak in the range of 1.6 to 2.3 ppm overlaps with the hydrogen peak 3 derived from the methylene group of PVA and the hydrogen peak 3 derived from the methylene group of PVA. The total area (area C) of hydrogen peaks in the range of 1.6 to 2.3 ppm was determined by regarding it as the total of hydrogen peaks 4 of the hydrocarbon group derived from (C). At this time, the area (area A) of the hydrogen peak 6 of the methyl group derived from the boron-containing compound (B), which does not overlap with the hydrogen peak derived from PVA or the hydrogen peak derived from the boron-containing compound (C), is used as the reference for the peak area. , The number of hydrogens in the methyl group was set to 3, which is the same as the number of hydrogens. Then, the area D obtained by subtracting the area B of the hydrogen peak 5 of the boron-containing compound (B) and the hydrocarbon group derived from the boron-containing compound (C) overlapping the hydrogen peak of the methylene group derived from PVA from the area C was calculated. .. By substituting the values obtained by these methods into the following formula (1), the boron element content (parts by mass) derived from the boron-containing compound (B) with respect to 100 parts by mass of PVA (A) was calculated. W in the following formula (1) is the number of borons per molecule of the boron-containing compound (B). Further, the following formula (1) is a formula used when unmodified PVA is used, and when the modified PVA is used as a raw material, the following formula (1) 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 PVA (A)
= {(Area A / 3) / (Area D / 2)} × (10.811 × W / 44.0526) × 100 (1)

Next, the value obtained in the following formula (2) was substituted to calculate the boron element content derived from the boron-containing compound (C) per 100 parts by mass of PVA (A). In addition, X of the following formula (2) overlaps with the hydrogen peak of the hydrocarbon group derived from the boron-containing compound (C) in the range of 1.0 to 1.2 ppm, and hydrogen of the hydrocarbon group derived from the boron-containing compound (B). It is a number, and Y is the number of hydrogens per molecule of the hydrocarbon group derived from the boron-containing compound (C) in the range of 1.0 ppm to 1.2 ppm. Further, Z is the number of borons per molecule of the boron-containing compound (C). The following formula (2) is a formula used when unmodified PVA is used, and when the modified PVA is used as a raw material, the following formula (2) needs to be appropriately modified.

Boron element content (parts by mass) derived from boron-containing compound (C) with respect to 100 parts by mass of PVA (A)
= {(Area A / 3) / (Area D / 2)} × {(Area B) -X} / Y ×
(10.81 × Z / 44.0526) × 100 (2)
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.

[Measurement of Boron Element Content Derived from Boron-Containing Compound (B) or Boron-Containing Compound (C) in a Polarizing Film Containing Only One of Boron-Containing Compound (B) and Boron-Containing Compound (C)]
The measurement was carried out by the following procedure with reference to the method of Patent Document 3. A polarizing film was dissolved in heavy water so that its content was 0.003% by mass, and then a solution concentrated by a rotary evaporator so that the content was 0.15% by mass was used as a ¹ H-NMR measurement sample. And said. ^{1 1} H-NMR (JNM-AL400: 400 MHz manufactured by JEOL Ltd.) was measured at 80 ° C., and the number of integrations was set to 256. Analysis was performed 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, the hydrogen peaks of the boron-containing compound (B) or the hydrocarbon group derived from the boron-containing compound (C) were integrated to determine the peak area (area E). At this time, the sum of the hydrogen peak areas of the boron-containing compound (B) that does not overlap with the hydrogen peak derived from PVA or the hydrogen peak area of the hydrocarbon group derived from the boron-containing compound (C) (area F) is used as the reference for the peak area. , The value of the hydrogen number and the area F of the corresponding hydrocarbon group of the boron-containing compound (B) or the boron-containing compound (C) were set to be the same. Next, the hydrogen peak in the range of 1.6 ppm to 2.3 ppm is overlapped with the hydrogen peak derived from the methylene group of PVA and the hydrogen peak derived from the methylene group of PVA. The boron-containing compound (B) or the boron-containing compound ( The peak area (area G) was determined by regarding it as the total hydrogen peaks of the hydrocarbon groups contained in C). Then, the area H was calculated by subtracting the number of hydrogens of the boron-containing compound (B) or the hydrocarbon group derived from the boron-containing compound (C) overlapping with the hydrogen peak of the methylene group derived from PVA from the area G. Substituting the values obtained by these methods into the following formula (3), the boron element content (parts by mass) derived from the boron-containing compound (B) or the boron-containing compound (C) with respect to 100 parts by mass of PVA (A) can be obtained. Calculated. In the following formula (3), S is the number of hydrogens of the hydrocarbon group contained in the boron-containing compound (B) or the boron-containing compound (C) that does not overlap with the peak of PVA, and T is the boron-containing compound (B). Alternatively, it is the number of borons per molecule of the boron-containing compound (C). The formula (3) is a formula used when unmodified PVA is used, and when the modified PVA is used as a raw material, it is necessary to appropriately modify the formula (3).

Boron element content (parts by mass) derived from boron-containing compound (B) or boron-containing compound (C) with respect to 100 parts by mass of PVA (A)
= {(Area F / S) / (Area H / 2)} × (10.811 × T / 44.0526) × 100 (3)

10.811 is the atomic weight of boron and 44.0526 is the molecular weight per mole of unmodified PVA repeating unit.

[Calculation of total boron element content (mass%) in polarizing film]
The mass [I (g)] of the polarizing film was measured and dissolved in 20 mL of distilled water so that the content of the polarizing film was 0.005% by mass. An aqueous solution in which a polarizing film was dissolved was used as a measurement sample, and its mass [J (g)] was measured. Then, the boron concentration [K (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 formula (4) was taken as the total boron element content (mass%) in the polarizing film.

Total boron element content (mass%) in polarizing film
= [(K × ^10-6 × J) / I] × 100 (4)

[Optical performance of polarizing film]
(1) Measurement of Visibility-Corrected Single Transmittance Ts The visual sensitivity-corrected single-transmittance Ts of the polarizing film obtained in the following Example or Comparative Example (hereinafter, “visual sensitivity-corrected single-transmittance Ts” is referred to as “transmission Ts” (Sometimes referred to as) uses an automatic polarizing film measuring device VAP-7070S (manufactured by JASCO Corporation) equipped with a spectrophotometer with an integrating sphere (“V7100” manufactured by JASCO Corporation) and a Grantera polarizer. It was measured. From the central portion of the obtained polarizing film, one sample of 4 cm in the stretching direction and 2 cm in the width direction of the polarizing film was collected. The MD transmittance (%) and TD transmittance (%) of the collected polarizing film in the range of 380 nm to 780 nm were measured, and the transmittance Ts (%) was measured using the "polarizing film evaluation program" (manufactured by JASCO Corporation). ) Was calculated. Here, the "MD transmittance" indicates the transmittance (%) when the direction of polarized light emitted from the Grantera polarizer and the transmission axis of the polarizing film sample are parallel to each other. Further, the "TD transmittance" indicates the transmittance (%) when the direction of polarized light emitted from the Grantera polarizer and the transmission axis of the polarizing film sample are orthogonal to each other. The transmittance Ts is calculated from the MD transmittance and the TD transmittance by applying a sensitivity correction called luminosity factor correction.

(2) Measurement of visual sensitivity correction polarization degree V For the polarizing film sample used in the above measurement of transmittance Ts (%), a spectrophotometer with an integrating sphere (“V7100” manufactured by JASCO Corporation) and a Grantera polarizer were used. The measurement was performed using the automatic polarizing film measuring device VAP-7070S (manufactured by JASCO Corporation) provided. Measure the MD transmittance (%) and TD transmittance (%) of the sample in the range of 380 nm to 780 nm, and use the "polarizing film evaluation program" (manufactured by JASCO Corporation) to correct the luminosity factor V (%). (Hereinafter, "luminosity factor correction polarization degree V" may be referred to as "polarization degree V").

[Shrinking force of polarizing film]
The contraction force was measured using an autograph "AG-X" with a constant temperature bath manufactured by Shimadzu Corporation and a video type extensometer "TR ViewX120S". A polarizing film whose humidity was controlled at 20 ° C./20% RH for 18 hours was used for the measurement. After the constant temperature bath of the autograph "AG-X" was set to 20 ° C, a rectangular polarizing film [length direction (stretching direction) 15 cm, width direction 1.5 cm] was attached to the chuck (chuck interval 5 cm), and tension was started. At the same time, the temperature of the constant temperature bath was started to rise to 80 ° C. The polarizing film was pulled at a speed of 1 mm / min, the tension was stopped when the tension reached 2N, and the tension was measured up to 4 hours later in that state. At this time, since the distance between the chucks changes due to thermal expansion, a marked line sticker is attached to the chuck, and the distance between the chucks is increased by the amount of movement of the marked line sticker attached to the chuck using the video type extensometer "TR ViewX120S". The measurement was performed while correcting so that was constant. When the minimum value of tension occurs at the initial stage of measurement (within 10 minutes from the start of measurement), the minimum value of tension is subtracted from the measured value of tension after 4 hours, and the difference is taken as the shrinkage force of the polarizing film. When the minimum value did not occur, the value obtained by subtracting 2N, which is the tension when the tension was stopped, from the measured value of the tension after 4 hours was taken as the shrinkage force of the polarizing film.

[Moisture and heat resistance]
The moisture and heat resistance of the polarizing film was evaluated using a spectrophotometer with an integrating sphere (“V7100” manufactured by JASCO Corporation) and an automatic polarizing film measuring device VAP-7070S (manufactured by JASCO Corporation) equipped with a Grantera polarizer. .. The collected polarizing film was fixed to a metal frame and used as an evaluation sample. Next, using a spectrophotometer with an integrating sphere (“V7100” manufactured by JASCO Corporation) and an automatic polarizing film measuring device VAP-7070S (manufactured by JASCO Corporation) equipped with a Grantera polarizer, the initial stage of the evaluation sample (0). The orthogonal transmittance (%) at 610 nm in time) was measured. The orthogonal transmittance (%) is a value calculated from the following formula (5). Then, by substituting the calculated orthogonal transmittance of 610 nm into the following formula (6), the orthogonal absorbance A ₀ of 610 nm at the initial stage (0 hours) was calculated. Then, using a small thermo-hygrostat (“IW223” manufactured by Yamato Scientific Co., Ltd.), the evaluation sample was allowed to stand for 1 hour in an atmosphere of 60 ° C./90% RH, left for 2 hours, and then for 4 hours. By measuring the orthogonal transmittance (%) at 610 nm at each standing time after standing for 6 hours, standing for 8 hours, and then substituting into the following formula (6), each standing is performed. Orthogonal absorbance A over time was calculated. The orthogonal transmittance was measured using the same evaluation sample until 8 hours later. Next, the relationship between the test time and Ln (A / A ₀ ) was illustrated using Microsoft Excel, and the slope was obtained by approximating it as a linear equation. This slope was used as the attenuation coefficient of the PVA-iodine complex, and was used as an index of fading (an index of moisture resistance) in the present invention. The smaller the attenuation coefficient, the faster the fading of the iodine-based polarizing film progresses. Therefore, the smaller the attenuation coefficient, the lower the moist heat resistance.

Orthogonal transmittance (%) of 610 nm at each standing time
= (MD transmittance at 610 nm at each standing time × TD transmittance at 610 nm at each standing time) / 100 (5)

Absorbance A at each standing time
= 2-Log (Orthogonal transmittance at 610 nm at each standing time) (6)

[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 L) 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 M) of the dried PVA film was measured. The degree of swelling of the PVA film was calculated by substituting the values of mass L and mass M into the following formula (7).

Swelling degree (%) = (mass L / mass M) x 100 (7)

[Example 1]
Contains 100 parts by mass of PVA (saponification degree 99.9 mol%, polymerization degree 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 the content of PVA. Using an aqueous solution containing 9% by mass as a film-forming stock solution, this was dried on a metal roll at 80 ° C., and the obtained film was heat-treated at a temperature of 120 ° C. for 10 minutes in a hot air dryer. A PVA film having a thickness of 30 μm was produced so that the swelling degree of the PVA film was adjusted to 200%.

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. Subsequently, it was immersed in an aqueous solution (dyeing treatment bath) (temperature 30 ° C.) containing 0.043% by mass of iodine and 4.3% by mass of potassium iodide (KI) for 60 seconds while being immersed 2.2 times (2.4 in total). Iodine was adsorbed by uniaxially stretching in the length direction. Further, it is 1.2 times longer (2.7 times as a whole) while being immersed in an aqueous solution (crosslinking bath) (temperature 30 ° C.) containing 3.0% by mass of boric acid and 3% by mass of potassium iodide for 45 seconds. Boric acid was adsorbed by uniaxial stretching in the longitudinal direction. Then, while immersing in an aqueous solution (stretching treatment bath) (temperature 60 ° C.) containing 4.0% by mass of boric acid and 6.0% by mass of potassium iodide, the length is 2.2 times (6.0 times as a whole). It was uniaxially stretched and oriented in the longitudinal direction. Then, in an aqueous solution (fixation treatment bath) (temperature 50 ° C.) containing 0.2% by mass of n-propylboronic acid, 0.3% by mass of 1,4-butandiboronic acid and 5.0% by mass of potassium iodide. Soaked for 100 seconds. In the fixing treatment, the PVA film was not stretched (stretching ratio 1.0 times). Finally, it was dried at 60 ° C. for 4 minutes to produce a polarizing film.

When ¹ H-NMR of the obtained polarizing film was measured and analyzed, a hydrogen peak of a hydrocarbon group derived from PVA and hydrogen of a hydrocarbon group derived from 1,4-butandiboronic acid were found at 1.2 to 1.3 ppm. Since a hydrogen peak 6 of a methyl group derived from n-propylboronic acid that does not overlap with the peak appeared, this peak area (area A) was set to 3. Next, the peak area (area B) of the hydrogen peak 5 in which the hydrogen of the hydrocarbon group derived from n-propylboronic acid and 1,4-butandiboronic acid, which appears in the range of 1.0 ppm to 1.2 ppm, overlaps was calculated. .. After that, the hydrogen peak 3 of the methylene group of PVA overlapped with the hydrogen peak 4 of the hydrocarbon group derived from n-propylboronic acid and 1,4-butandiboronic acid, so that the hydrogen peak in the range of 1.6 to 2.3 ppm was generated. Considering the sum of the hydrogen peak 3 derived from the methylene group of PVA and the hydrogen peak 4 of the hydrocarbon group derived from n-propylboronic acid and 1,4-butaniboronic acid, the hydrogen peak in the range of 1.6 to 2.3 ppm The total area (area C) of Area D was obtained by subtracting the area of the hydrogen peak (corresponding to area B) of the hydrocarbon group derived from n-propylboronic acid and 1,4-butandiboronic acid from the area C. When these values were substituted into the above formula (1), the content of the boron element derived from the boron-containing compound (B) was 0.34 parts by mass with respect to 100 parts by mass of PVA (A). Further, when these values were substituted into the above formula (2), the content of the boron element derived from the boron-containing compound (C) was 0.15 parts by mass with respect to 100 parts by mass of PVA (A). The total boron element content in the polarizing film was measured and found to be 2.6% by mass.

When the optical performance of the obtained polarizing film was measured, the transmittance Ts was 43.98% and the degree of polarization V was 99.96%. Moreover, when the shrinkage force of the obtained polarizing film was measured, it was 5.8N. The attenuation coefficient of the PVA-iodine complex was −0.23. These results are shown in Table 1, FIGS. 2 and 3.

[Examples 2 to 6, Comparative Example 1]
Except that the concentrations and temperatures of n-propylboronic acid, 1,4-butandiboronic acid and potassium iodide in the aqueous solution used as the fixation treatment bath and the time of immersion in the fixation treatment bath were changed as shown in Table 1. A polarizing film was prepared in the same manner as in Example 1, and each measurement and each evaluation were performed by the above method. The results are shown in Table 1, FIGS. 2 and 3.

[Comparative Examples 2 to 4]
The fact that 1,4-butaniboronic acid was not added to the aqueous solution used as the fixed treatment bath, the concentration of n-propylboronic acid and potassium iodide in the aqueous solution, the temperature of the aqueous solution, and the time of immersion in the fixed treatment bath were determined. A polarizing film was prepared in the same manner as in Example 1 except that the changes were made as shown in Table 1, and each measurement and each evaluation were carried out by the above method. The results are shown in Table 1, FIGS. 2 and 3. However, although the polarizing film of Comparative Example 4 used the boron-containing compound (B), its optical performance was remarkably low, so that the evaluation of wet heat resistance was not performed.

[Comparative Example 5]
The same as in Example 1 except that an aqueous solution (temperature 10 ° C.) containing 1.0% by mass of n-butylboronic acid was used as the fixing treatment bath and the time of immersion in the fixing treatment bath was set to 20 seconds. A polarizing film was prepared, and each measurement and each evaluation were performed by the above method. At this time, regarding the measurement of the boron element content derived from n-butylboronic acid, the number of integrations was changed to 4096 because the boron-containing compound (B) could not be detected when the number of integrations was 256. The results are shown in Table 1, FIGS. 2 and 3.

[Comparative Examples 6 to 8]
Except that n-propylboronic acid was not added to the aqueous solution used as the fixing treatment bath, and the concentrations and temperatures of 1,4-butandiboronic acid and potassium iodide in the aqueous solution were changed as shown in Table 1. A polarizing film was produced in the same manner as in Example 1, and each measurement and each evaluation were performed by the above method. The results are shown in Table 1, FIGS. 2 and 3. However, since the optical performance of the polarizing films of Comparative Examples 7 and 8 was lower than that of Comparative Example 6, the evaluation of moisture and heat resistance was not performed.

[Comparative Example 9]
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 2.0% by mass of potassium iodide was used in the fixing treatment bath. Each measurement and each evaluation were performed by the method. The results are shown in Table 1, FIGS. 2 and 3.

[Comparative Example 10]
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 2.0% by mass of potassium iodide was used in the fixing treatment bath. , Each measurement and each evaluation were performed by the above method. The results are shown in Table 1, FIGS. 2 and 3.

[Comparative Example 11]
A polarizing film was produced in the same manner as in Example 1 except that the fixing treatment was not performed, and each measurement and each evaluation were performed by the above method. The results are shown in Table 1, FIGS. 2 and 3.

[Comparative Example 12]
Polarization in the same manner as in Example 1 except that an aqueous solution (temperature 30 ° C.) containing 2.0% by mass of potassium iodide was used as the fixing treatment bath and the time of immersion in the fixing treatment bath was set to 5 seconds. A film was prepared, and each measurement and each evaluation were performed by the above method. The results are shown in Table 1, FIGS. 2 and 3.

[Comparative Example 13]
A polarizing film was prepared in the same manner as in Comparative Example 12 except that the time of immersion in the fixing treatment bath was 20 seconds, and each measurement and each evaluation were carried out by the above method. The results are shown in Table 1, FIGS. 2 and 3.

In Examples 2 to 6 and Comparative Examples 1 to 13, an aqueous solution (temperature 30 ° C.) containing iodine and potassium iodide at a mass ratio of 1: 100 was used for the dyeing treatment bath. At this time, the iodine and potassium iodide concentrations in the dyeing bath were adjusted so that the transmittance of the polarizing film after drying was 43.8% to 44.2%.

FIG. 2 is a diagram in which the contraction force is plotted on the horizontal axis and the luminosity factor correction polarization degree V is plotted on the vertical axis for the polarizing films of Examples 1 to 6 and Comparative Examples 1 to 13. FIG. 3 is a diagram in which the attenuation coefficient of the PVA-iodine complex is plotted on the horizontal axis and the degree of polarization V is plotted on the vertical axis for the polarizing films of Examples 1 to 6 and Comparative Examples 1 to 3, 5, 6 and 9 to 13. Is. As shown in FIGS. 2 and 3, the polarizing films of Examples 1 to 6 satisfying the provisions of the present invention have a degree of polarization V of 99.94% or more, a shrinkage force of less than 10N, and an attenuation coefficient of the PVA-iodine complex of −0. It was .5 or more, had a small shrinkage force, and was excellent in optical performance and moisture heat resistance. As shown in FIGS. 2 and 3, the polarizing film of Comparative Example 1 having a boron element content derived from the boron-containing compound (B) of 0.14 parts by mass has a degree of polarization V of less than 99.94%. The effect of improving the optical performance of the boron-containing compound (B) was insufficient. As shown in FIG. 2, the polarizing film of Comparative Example 2 fixed using only the high-concentration boron-containing compound (B) as the boron-containing compound has a low shrinkage force and is excellent in optical performance. As shown in FIG. 3, the attenuation coefficient of the PVA-iodine complex was less than −0.5, and the moisture and heat resistance was insufficient. As shown in FIG. 2, the polarizing films of Comparative Examples 3 and 4 which were fixed using only the low-concentration boron-containing compound (B) as the boron-containing compound had a degree of polarization V of less than 99.94%. The optical performance was insufficient. As shown in FIG. 2, the polarizing film of Comparative Example 5 in which a high-concentration boron-containing compound (B) was used as the boron-containing compound and fixed treatment was performed without using potassium iodide in the fixing treatment bath had a large shrinkage force. The degree of polarization V was less than 99.94%, and the optical performance was also insufficient.

As shown in FIGS. 2 and 3, the polarizing film of Comparative Example 6 which was fixed using only the boron-containing compound (C) having a relatively high concentration as the boron-containing compound had a low shrinkage force and became moist heat resistant. Although it was excellent, the degree of polarization V was less than 99.94%, and the optical performance was insufficient. As shown in FIG. 2, the polarizing films of Comparative Examples 7 and 8 which were fixed using only the low-concentration boron-containing compound (C) as the boron-containing compound were compared with the polarizing film of Comparative Example 6. Furthermore, the optical performance was low. As shown in FIG. 2, the polarizing films of Comparative Examples 9 and 10 which were fixed with boric acid without using the boron-containing compound (B) and the boron-containing compound (C) had a degree of polarization V of 99.94%. Less than, the shrinkage force was 10 N or more, the optical performance was insufficient, and the shrinkage force was also high. As shown in FIG. 2, the polarizing film of Comparative Example 11 which was not fixed had a degree of polarization V of less than 99.94%, a shrinkage force of 10 N or more, insufficient optical performance, and shrinkage. The power was also high. As shown in FIG. 2, the polarizing film of Comparative Example 12 which was fixed with an aqueous solution of KI for 5 seconds had a degree of polarization V of less than 99.94%, a shrinkage force of 10 N or more, and insufficient optical performance. Besides, the contraction force was also high. As shown in FIG. 3, the polarizing film of Comparative Example 13 which had been fixed in the KI aqueous solution for 20 seconds had a degree of polarization V of less than 99.94% and an attenuation coefficient of the PVA-iodine complex of less than −0.5. , Optical performance and moisture heat resistance were insufficient. As described above, it has been difficult for the polarizing films (Comparative Examples 1 to 13) that do not satisfy the provisions of the present invention to satisfy all of the shrinkage force, the optical performance, and the heat resistance to moisture.

1 Hydrogen peak derived from heavy water as a measurement solvent 2 Hydrogen peak derived from the methine group of PVA 3 Hydrogen peak derived from the methylene group of PVA 4 Hydrogen-containing compound (B) and boron-containing compound (C) that overlap with the hydrogen peak derived from PVA Hydrogen peak derived from hydrocarbon group contained in 5 Hydrogen peak derived from hydrocarbon group that does not overlap with hydrogen peak derived from PVA but overlaps with boron-containing compound (B) and boron-containing compound (C) 6 Hydrogen peak derived from PVA And the hydrogen peak derived from the methyl group of the boron-containing compound (B) that does not overlap with the hydrogen peak derived from the boron-containing compound (C).

Claims

At least one boron-containing compound (B) selected from the group consisting of polyvinyl alcohol (A), monoboronic acid represented by the following formula (I), and a compound capable of converting to monoboronic acid in the presence of water. A polarizing film containing at least one boron-containing compound (C) selected from the group consisting of diboronic acid represented by the following formula (II) and a compound capable of converting to diboronic acid in the presence of water. The mass ratio (B / C) of the boron element derived from the boron-containing compound (B) to the boron element derived from the boron-containing compound (C) is 0.8 to 3.0, and the boron derived from the boron-containing compound (B). A polarizing film having an element content of 0.15 to 3.0 parts by mass with respect to 100 parts by mass of polyvinyl alcohol (A).

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

[In formula (II), R 2 is a divalent aliphatic group having 1 to 20 carbon atoms, and R 2 and a boronic acid group are connected by a boron-carbon bond. ]
The polarizing film according to claim 1, wherein R 1 and R 2 are saturated aliphatic groups.
The polarizing film according to claim 1 or 2, wherein R 1 and R 2 are aliphatic hydrocarbon groups.
The polarizing film according to any one of claims 1 to 3, wherein R 1 has 2 to 5 carbon atoms and R 2 has 3 to 5 carbon atoms.
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, the film contains a boron-containing compound (B) and a boron-containing compound (C). The method for producing a polarizing film according to any one of claims 1 to 4, which comprises a treatment of immersing in an aqueous solution.
The method for producing a polarizing film according to claim 5, further comprising a process of immersing the film after the stretching treatment in the aqueous solution.
The claim that the concentration ratio (B / C) of the boron-containing compound (B) to the boron-containing compound (C) in the aqueous solution is less than 1, and the concentration of the boron-containing compound (B) exceeds 0.1% by mass. The method for producing a polarizing film according to 5 or 6.