WO2021020349A1

WO2021020349A1 - Polarizing film and method for producing same

Info

Publication number: WO2021020349A1
Application number: PCT/JP2020/028729
Authority: WO
Inventors: 璃生岡田; 亘大橋; 孝徳磯崎
Original assignee: 株式会社クラレ
Priority date: 2019-07-29
Filing date: 2020-07-27
Publication date: 2021-02-04
Also published as: TW202110987A; KR20220041093A; CN114174875B; JPWO2021020349A1; CN114174875A

Abstract

A polarizing film which contains a polyvinyl alcohol (A), at least one boron-containing compound (B) that is selected from the group consisting of a specific monoboronic acid and a compound that is able to be converted into the monoboronic acid in the presence of water, and boric acid (C), wherein: the concentration (α) of elemental boron derived from the boron-containing compound (B) in a range of 1 µm from the center toward the outside in the thickness direction is from 0.1% by atom to 3% by atom; the concentration (β) of elemental boron derived from boric acid (C) in a range of 1 µm from the center toward the outside in the thickness direction is from 0.1% by atom to 8% by atom; and the ratio of the concentration (α) to the concentration (β), namely, α/β is 0.1 or more. This polarizing film has a low contractile force at high temperatures, while having excellent optical performance.

Description

Polarizing film and its manufacturing method

The present invention relates to a polarizing film and a method for producing the same.

A polarizing plate having a function of transmitting and shielding light is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes the polarization state of light. Many polarizing plates have a structure in which a protective film such as a cellulose triacetate (TAC) film is bonded to the surface of the polarizing film in order to prevent fading of the polarizing film and to prevent shrinkage of the polarizing film. As the polarizing film constituting the polarizing plate, an iodine-based dye (I ^3- , I ^5-, etc.) is formed on a matrix formed by uniaxially stretching a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be referred to as "PVA"). ) Is adsorbed in 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. Electronic devices are required to be thin and have high definition. Along with this, in recent years, the thickness of the glass used for the LCD has been reduced and the magnification of the polarizing film has been increased, and as a result, the occurrence of warpage of the LCD panel has become a problem. 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.

By the way, in a recent method for producing a polarizing film, it is known to use an aqueous solution of boronic acid in order to crosslink the PVA molecular chains in the polarizing film. Specifically, Patent Document 1 describes polarized light having excellent moisture and heat resistance by immersing the uniaxially stretched polarizing film in an aqueous solution (fixing treatment bath) containing 1,4-butaniboronic acid and potassium iodide. It is stated that the film was obtained. Further, Patent Document 2 describes that a polarizing film having excellent water resistance and adhesive strength was obtained by adding a boronic acid inducing group to the washing step. Further, Patent Document 3 describes that a polarizing film having excellent heat resistance and moist heat resistance was obtained by using a cross-linking solution containing a hydrocarbon compound having an aldehyde group.

WO2018 / 021274 KR10-2016-0054229 KR10-2015-0001276 Publication

However, the polarizing films described in Patent Documents 1 to 3 have a large shrinkage force at high temperatures or have insufficient optical performance. Therefore, it has not been possible to meet the recent demand for thinner and higher definition electronic devices.

Therefore, an object of the present invention is to provide a polarizing film having a small shrinkage force at a high temperature and excellent optical performance, and a method for producing the same.

As a result of diligent studies by the present inventors, in order to reduce the shrinkage force while maintaining the excellent optical performance of the polarizing film, the boric acid crossing the PVA molecular chain in the polarizing film is replaced with boronic acid. It has been found that it is important to allow the substitution reaction to proceed not only to the surface portion of the polarizing film but also to the central portion in the thickness direction of the polarizing film. Further, the more the substitution reaction proceeds to the central portion in the thickness direction of the polarizing film, that is, the more the boric acid in the central portion in the thickness direction of the polarizing film is replaced with boronic acid, the more the shrinkage force of the polarizing film becomes stronger. It was found to be reduced. Therefore, the present inventors have completed the present invention by setting the ratio of the concentration of boron elements derived from boronic acid (boron-containing compound) and boric acid at the center in the thickness direction of the polarizing film within a specific range. ..

Further, in order to allow the substitution reaction of substituting boric acid in the polarizing film with boronic acid to proceed to the center in the thickness direction of the polarizing film, the boric acid-crosslinked polarizing film is immersed in a relatively low concentration boronic acid aqueous solution. It is important to process. Normally, when a boric acid-crosslinked polarizing film is immersed in an aqueous solution of boronic acid, a substitution reaction in which boric acid in the polarizing film is replaced with boronic acid proceeds from the surface portion of the polarizing film. Here, when the concentration of the boronic acid aqueous solution is relatively high, as a result of excessive adsorption of boronic acid on the surface portion of the polarizing film, it is difficult for the substitution reaction to proceed to the central portion in the thickness direction of the polarizing film. Become. Further, in such a case, a precipitate of boronic acid may be formed on the surface portion of the polarizing film. On the other hand, in the present invention, the substitution reaction can be allowed to proceed to the central portion in the thickness direction of the polarizing film by immersing the boric acid-crosslinked polarizing film in a relatively low-concentration boronic acid aqueous solution.

The present invention is as described in [1] to [7] below.
[1] At least one boron-containing compound (B) selected from the group consisting of polyvinyl alcohol (A), monoboric acid represented by the following formula (I), and a compound capable of converting to monoboric acid in the presence of water. A polarizing film containing boric acid (C) and a boron element concentration (α) derived from the boron-containing compound (B) in the range from the center to the outside in the thickness direction of 0.1 to 3 atomic%. The boron element concentration (β) derived from boric acid (C) is 0.1 to 8 atomic% in the range from the center to the outside in the thickness direction to 1 μm, and the concentration (α) with respect to the concentration (β). ) Ratio (α / β) is 0.1 or more;

[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. ]
[2] The polarizing film according to [1], wherein R ¹ is a saturated aliphatic group;
[3] The polarizing film according to [1] or [2], wherein R ¹ is a linear aliphatic hydrocarbon group;
[4] The polarizing film according to any one of [1] to [3], wherein R ¹ has 2 to 5 carbon atoms; [5] the transmittance is 42.0% or more, and the degree of polarization is 99. The polarizing film according to any one of [1] to [4], which is 85% or more;
[6] The polarizing film according to any one of [1] to [5], wherein the shrinkage force in the absorption axis direction per 1.5 cm in width and 13 μm in thickness when held at 80 ° C. for 4 hours is less than 12 N;
[7] 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 concentration of the boron-containing compound (B) is 0.2. The method for producing a polarizing film according to any one of [1] to [6], which comprises a treatment of immersing in an aqueous solution of about 5% by mass and a temperature of 20 to 70 ° C.

According to the present invention, it is possible to provide a polarizing film having a small shrinkage force at a high temperature and excellent optical performance, and a method for producing the same.

It is sectional drawing when the polarizing film of this invention is cut in the vertical direction.

<Polarizing film>
The polarizing film of the present invention contains at least one boron selected from the group consisting of polyvinyl alcohol (A), monoboric acid represented by the following formula (I), and a compound capable of converting to monoboric acid in the presence of water. A polarizing film containing compound (B) and boric acid (C), wherein the boron element concentration (α) derived from the boron-containing compound (B) is 0.1 in the range from the center in the thickness direction to 1 μm outward. Boric acid (C) -derived boron element concentration (β) is 0.1 to 8 atomic% and the concentration (β) is in the range of up to 1 μm from the center in the thickness direction to 3 atomic%. The ratio (α / β) of the concentration (α) to to is 0.1 or more.

[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. ]

FIG. 1 is a cross-sectional view of the polarizing film of the present invention cut in the vertical direction. The central portion 3 in the thickness direction of the polarizing film is a range from the center 1 in the thickness direction of the polarizing film to 1 μm in both directions on the surface portion 2 side of the polarizing film, and is in the range shown by diagonal lines in FIG. is there. In the polarizing film of the present invention, the boron element concentration (α) derived from the boron-containing compound (B) in the range of 1 μm outward from the center in the thickness direction of the polarizing film, and from the center in the thickness direction of the polarizing film to the outside. The ratio (α / β) of the boron element concentration (β) derived from boric acid (C) and the concentration (α) to the concentration (β) in the range up to 1 μm is in a specific range. When the polarizing film crosslinked with boric acid (C) is immersed in an aqueous solution of the boron-containing compound (B), the substitution reaction between the boron-containing compound (B) and boric acid (C) proceeds from the surface portion of the polarizing film. The fact that the above α, β and their ratio α / β are within a specific range means that the substitution reaction between the boron-containing compound (B) and boric acid (C) has proceeded to the center in the thickness direction of the polarizing film. As a result, a polarizing film having a small shrinkage force at a high temperature and excellent optical performance can be obtained.

The boron element concentration (α) derived from the boron-containing compound (B) in the range from the center in the thickness direction of the polarizing film to the outside of 1 μm needs to be 0.1 to 3 atomic%. When the boron element concentration (α) is less than 0.1 atomic%, a sufficient amount of the boron-containing compound (B) does not exist up to the center in the thickness direction of the polarizing film, and the effect of reducing the shrinkage force is low. Become. On the other hand, when the boron element concentration (α) exceeds 3 atomic%, it is considered that the optical performance and shrinkage force of the polarizing film are not affected, but the fixing treatment of immersing in an aqueous solution of the boron-containing compound (B) described later The time may increase and the productivity of the polarizing film may decrease.

The concentration of boric acid (C) -derived boron element (β) in the range from the center of the polarizing film in the thickness direction to the outside of 1 μm needs to be 0.1 to 8 atomic%. When the boron element concentration (β) is less than 0.1 atomic%, the amount of boric acid (C) at the center in the thickness direction of the polarizing film is not sufficient, and the orientation state of the PVA molecular chain in the polarizing film is changed. Disturbance and reduced optical performance. On the other hand, when the boron element concentration (β) exceeds 8 atomic%, the PVA molecular chain oriented by boric acid cross-linking is excessively present at the center in the thickness direction of the polarizing film, so that the shrinkage force is reduced. It may not be enough.

The ratio (α /) of the boron element concentration (α) derived from the boron-containing compound (B) to the boron element concentration (β) derived from boric acid (C) in the range from the center in the thickness direction of the polarizing film to 1 μm outward. β) needs to be 0.1 or more. When the ratio of boron element concentration (α / β) is less than 0.1, the amount of boric acid (C) in the central portion in the thickness direction of the polarizing film is large and the amount of the boron-containing compound (B) is small. Presumed. In this case, since the PVA molecular chains oriented by boric acid cross-linking are excessively present in the central portion in the thickness direction of the polarizing film, the shrinkage force may not decrease. On the other hand, even if the ratio of boron element concentration (α / β) exceeds 3, it is considered that the optical performance and shrinkage force of the polarizing film are not affected, but in an aqueous solution of the boron-containing compound (B) described later. The ratio of the boron element concentration (α / β) is preferably 3 or less because the time for the fixing treatment for immersion becomes long and the productivity of the polarizing film may decrease.

The boron element concentration (α) and the boron element concentration (β) in the polarizing film can be determined by using an X-ray photoelectron spectrometer (GCIB XPS) equipped with a gas cluster ion beam gun. Specifically, it can be obtained by the method described in Examples described later.

The thickness of the polarizing film is preferably 5 to 30 μm. If the thickness is too thin, stretch breakage tends to occur easily during the uniaxial stretching process for producing a polarizing film. The thickness is preferably 10 μm or more. On the other hand, if the thickness 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 boron-containing compound (B) in the present invention is at least one selected from the group consisting of monoboronic acid represented by the following formula (I) and a compound capable of converting to monoboronic acid in the presence of water. Here, in the 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.

Monoboronic acid is a compound represented by the above formula (I) and has one boronic acid group [-B (OH) ₂ ] in one molecule. 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. Typical examples of the boron-containing group that can be converted into a boronic acid group in the presence of water include, but are not limited to, the boronic acid ester group described below.

The hydroxyl group in the boronic acid group contained in monoboronic acid can form an ester with alcohol in the same manner as the hydroxyl group in boric acid. Formula (II) is an alcohol of 1 molecule with respect to boronic acid (R 2 ^-OH) is reacted Monoboron acid monoester. Here, when the phenylboronic acid group is bonded to the hydroxyl group of PVA (A), R ² in the formula (II) is a PVA chain, and a carbon-containing group is bonded to the PVA chain via a boron atom. Become.

Formula (III) is, two molecules alcohol (R 2 ^-OH) are examples of Monoboron acid diester react to Monoboron acid. Here, if the boronic acid group is bound to the hydroxyl group of PVA, any two R ² in formula (III) is a PVA chain.

Monobolonic acid has two hydroxyl groups capable of reacting 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 PVA chain is appropriately crosslinked to improve the orientation state of the PVA chain and improve the optical performance of the polarizing film.

In 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 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 formula (I), R ¹ is a monovalent aliphatic group, and it is sufficient that R ¹ and a boronic acid group are 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. The unsaturated aliphatic group is a carbon-carbon double bond, a carbon-carbon triple bond, a carbon-oxygen double bond, a carbon-nitrogen double bond, a nitrogen-nitrogen double bond, a carbon-sulfur double bond, etc. It is an aliphatic group having a structure including a double bond having a bond order of 2 or more, and a saturated aliphatic group is an aliphatic group having only a single bond structure. The Monoboron acid R ¹ is a saturated aliphatic group, methyl boronic acid, ethylboronic acid, propyl acid, butyl boronic acid, Penchiruboron acid, hexyl acid, to Puchiruboron acid, octyl boronic acid, Noniruboron acid, Dekaniruboron acid, undecyl Decanylboronic acid, dodecanylboronic acid, tridecanylboronic acid, tetradecanylboronic acid, pentadecanylboronic acid, hexadecanylboronic acid, heptadecanylboronic acid, octadecanylboronic acid, nonadecanylboronic acid Acids, icosanylboronic acid and their isomers, cyclopropylboronic acid, cyclobutylboronic acid, cyclopentylboronic acid, cyclohexylboronic acid, cycloheptylboronic acid, cyclooctylboronic acid, cyclononylboronic acid, cyclodecanylboronic acid, cyclo Undecanylboronic acid, cyclododecanylboronic acid, cyclotridecanylboronic acid, cyclotetradecanylboronic acid, cyclopentadecanylboronic acid, cyclohexadecanylboronic acid, cycloheptadecanylboronic acid, cyclooctadeca Nylboronic acid, cyclononadecanylboronic acid, cycloicosanylboronic acid and their isomers, 2-oxa-propylboronic acid, 2-oxa-butylboronic acid, 2-oxa-hexylboronic acid, 2-oxa- Heptylboronic acid, 2-oxa-octylboronic acid, 2-oxa-nonylboronic acid, 2-oxa-decanylboronic acid, 2-oxa-undecanylboronic acid, 2-oxadodecanylboronic acid, 2-oxatri Decanylboronic acid, 2-oxa-tetradecanylboronic acid, 2-oxa-pentadecanylboronic acid, 2-oxa-hexadecanylboronic acid, 2-oxa-heptadecanylboronic acid, 2-oxa-octa Decanylboronic acid, 2-oxa-nonadecanylboronic acid, 2-oxa-icosanylboronic acid and their isomers, 2-aza-propylboronic acid, 2-aza-butylboronic acid, 2-aza-hexylboronic acid, 2-aza-heptylboronic acid, 2-aza-octylboronic acid, 2-aza-nonylboronic acid, 2-aza-decanylboronic acid, 2-aza-undecanylboronic acid, 2-azaddecanylboronic acid, 2 -Aza-tridecanylboronic acid, 2-aza-tetradecanylboronic acid, 2-aza-pentadecanylboronic acid, 2-aza-hexadecanylboronic acid, 2-aza-heptadecanylboronic acid, 2 -Aza-octadecanylboronic acid, 2-aza-nonadeca Nylboronic acid, 2-aza-icosanylboronic acid and their isomers, 2-phospha-propylboronic acid, 2-phospha-butylboronic acid, 2-phospha-hexylboronic acid, 2-phosphat-heptylboronic acid, 2-phosphar- Octylboronic acid, 2-phospha-nonylboronic acid, 2-phospha-decanylboronic acid, 2-phospha-undecanylboronic acid, 2-phosparddecanylboronic acid, 2-phosphatridecanylboronic acid, 2-phospha -Tetradecanylboronic acid, 2-phosphat-pentadecanylboronic acid, 2-phosphat-hexadecanylboronic acid, 2-phosphat-heptadecanylboronic acid, 2-phosphat-octadecanylboronic acid, 2-phosphata -Nonadecanylboronic acid, 2-phospha-icosanylboronic acid and their isomers, 2-thia-propylboronic acid, 2-thia-butylboronic acid, 2-thia-hexylboronic acid, 2-thia-heptylboronic acid, 2-Thia-octylboronic acid, 2-thia-nonylboronic acid, 2-thia-decanylboronic acid, 2-thia-undecanylboronic acid, 2-thia-dodecanylboronic acid, 2-thia-tridecanylboronic acid , 2-Thia-tetradecanylboronic acid, 2-thia-pentadecanylboronic acid, 2-thia-hexadecanylboronic acid, 2-thia-heptadecanylboronic acid, 2-thia-octadecanylboronic acid , 2-Thia-nonadecanylboronic acid, 2-thia-icosanylboronic acid and isomers thereof, and the like are exemplified. Moreover, as a compound which can be converted into the monobolonic acid exemplified in the presence of water, the salt of the monobolonic acid and the like can be mentioned.

R ¹ may be an aliphatic hydrocarbon group or may contain heteroatoms such as oxygen, nitrogen, sulfur and halogen. Considering availability, it is preferable that R ¹ is an aliphatic hydrocarbon group containing no heteroatom. The aliphatic hydrocarbon group is preferably a straight chain aliphatic hydrocarbon group having no branch. As a result, the adsorptivity to the polarizing film is improved, and the effect of improving the optical performance is enhanced. Specific examples of the boronic acid in which R ¹ is a linear aliphatic hydrocarbon group include methylboronic acid, ethylboronic acid, n-propylboronic acid, n-butylboronic acid, n-pentylboronic acid, and n-hexylboronic acid. , N-heptylboronic acid, n-octylboronic acid, n-nonylboronic acid, n-decanylboronic acid, n-undecanylboronic acid, n-dodecanylboronic acid, n-tridecanylboronic acid, n-tetradeca Nylboronic acid, n-pentadecanylboronic acid, n-hexadecanylboronic acid, n-heptadecanylboronic acid, n-octadecanylboronic acid, n-nonadecanylboronic acid, n-icosanylboronic acid, etc. Illustrated. Moreover, as a compound which can be converted into the boronic acid exemplified in the presence of water, the salt of the boronic acid and the like can be mentioned.

Specifically, as the monoboronic acid represented by the above formula (I), ethylboronic acid, n-propylboronic acid, n-butylboronic acid, and n-pentylboronic acid are particularly preferable. In addition, examples of the compound that can be converted into these exemplified boronic acids in the presence of water include salts of the boronic acid.

<PVA (A)>
PVA (A) in the present invention is a polymer having a vinyl alcohol unit (-CH _2- CH (OH)-) as a main structural unit.

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 is, for example, vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatic acid, vinyl caproate. , 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-butyl, 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) acrylic acid esters 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) acrylamide propyldimethylamine 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) acrylonitrile; vinyl chloride, vinylidene chloride, vinyl fluoride, foot Vinyl halides such as vinylidene hydride; 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 optical 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 the polarized light is polarized. 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 viewpoints 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, antifungal agents, 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 degree of swelling of the PVA film is measured by the method described in the examples.

<Manufacturing method of polarizing film>
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 if the width of the PVA film used for manufacturing the polarizing film is 3 m or more. On the other hand, if the width of the PVA film used for producing the polarizing film is too large, it tends to be difficult to uniformly perform uniaxial stretching when producing the polarizing film with a practical device, 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 membrane-forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol. , Trimethylolpropane, ethylenediamine, diethylenetriamine and the like, and one or more of these can be used. Of these, water is preferable from the viewpoint of environmental load and recoverability.

The volatile content of the film-forming stock solution (the content ratio of volatile components such as liquid media removed by volatilization or evaporation during film-forming in the film-forming stock solution) varies depending on the film-forming method, film-forming conditions, etc., but is generally used. 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.

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

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

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

When the membrane-forming stock solution contains a surfactant, the content thereof is preferably in the range of 0.01 to 0.5 parts by mass with respect to 100 parts by mass of PVA (A) contained in the membrane-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 film-forming method for forming a PVA film using the above-mentioned film-forming stock solution include a cast film-forming method, an extrusion film-forming method, a wet film-forming method, and a gel film-forming method. These film forming methods may adopt only one kind or a combination of two or more kinds. Among these film-forming methods, the cast film-forming method and the extrusion film-forming method are preferable because a PVA film used for producing a polarizing film having a uniform thickness and width and good physical characteristics 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, in which the film is immersed in an aqueous solution of a boron-containing compound (B). It is a method of manufacturing a polarizing film having a process of processing. At this time, in addition to the dyeing treatment and the uniaxial stretching treatment, a method of further subjecting the PVA film to a swelling treatment, a boric acid cross-linking treatment, a fixing treatment, a washing treatment, a drying treatment, a heat treatment, or the like can be mentioned. .. In this case, the order of each treatment such as swelling treatment, dyeing treatment, boric acid cross-linking treatment, uniaxial stretching treatment, and fixing treatment is not particularly limited, and two or more treatments can be performed at the same time. Moreover, each process can be performed 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. 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, and a dichroic dye developed for manufacturing a polarizing plate is preferable.

By subjecting the PVA film to a boric acid cross-linking treatment, the PVA molecular chains in the PVA film are cross-linked and the orientation of the PVA molecular chains is improved. As a result, the orientation of the dichroic dye adsorbed on the PVA film is improved, so that the optical performance of the obtained polarizing film is improved. From this viewpoint, it is more preferable that the boric acid cross-linking treatment is carried out after the dyeing treatment and before the stretching treatment. The boric acid cross-linking treatment can be performed by immersing the PVA film in an aqueous solution containing a boric acid cross-linking agent. As the boric acid cross-linking agent, one or more boron-containing inorganic compounds such as borate such as boric acid and borax can be used, and the boric acid cross-linking agent is easy to handle. It is preferably boric acid. The concentration of the boric acid cross-linking agent in the aqueous solution containing the boric acid cross-linking agent is preferably 1 to 10% by mass, more preferably 2 to 7% by mass. When the concentration of the boric acid cross-linking agent is 1 to 10% by mass, sufficient stretchability can be maintained. If the concentration of the boric acid cross-linking agent exceeds 10% by mass, the cross-linking may proceed excessively and the stretchability may decrease, or the PVA molecular chains may be excessively oriented and the contractile force may increase, which is not preferable. Further, when the concentration of the boric acid cross-linking agent is less than 1% by mass, the orientation of the dichroic dye adsorbed on the PVA film may not be sufficiently improved, and the optical performance of the obtained polarizing film may not be sufficiently improved. Therefore, it is not preferable. The aqueous solution containing the boric acid cross-linking agent may contain an auxiliary agent such as potassium iodide. The temperature of the aqueous solution containing the boric acid cross-linking agent is preferably 20 to 50 ° C, particularly preferably 25 to 40 ° C. Boric acid cross-linking can be performed efficiently by setting the temperature to 20 to 50 ° 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 (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.

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, the PVA film is stretched in an aqueous solution. The PVA film can also be stretched in the above-mentioned dyeing bath or boric acid aqueous 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 concentration of boric acid 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 perform 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 the boron-containing compound (B) is 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. From the viewpoint of accelerating the substitution reaction between the boron-containing compound (B) and boric acid (C) in the central portion of the polarizing film in the thickness direction, it is preferable that the fixing treatment bath is substantially free of boric acid. 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 even more preferably less than 1.1 times.

The boron-containing compound (B) may be adsorbed on the polarizing film in any of the steps of dyeing treatment, boric acid cross-linking treatment, uniaxial stretching treatment, and fixing treatment, but it is uniaxially adsorbed during the fixing treatment after the uniaxial stretching treatment. It is particularly preferable because the cutting of the PVA film during the stretching treatment is suppressed. Further, the boron-containing compound (B) is not limited to one type, and two or more types may be mixed and used. From the viewpoint of allowing the substitution reaction between the boron-containing compound (B) and boric acid (C) to proceed to the center in the thickness direction of the polarizing film, the concentration of the aqueous solution of the boron-containing compound (B) is 0.2 to 5% by mass. Must be. When the concentration of the boron-containing compound (B) in the aqueous solution is lower than 0.2% by mass, the adsorption of the boron-containing compound (B) on the surface of the polarizing film is delayed, which is 0.4% by mass or more. More preferably, it is more preferably 0.6% by mass or more. On the other hand, when the concentration of the boron-containing compound (B) in the aqueous solution is higher than 5.0% by mass, the boron-containing compound (B) is excessively adsorbed on the surface of the polarizing film, and the boron-containing compound (B) The substitution reaction between boron and boric acid (C) becomes difficult to proceed. In addition, a precipitate of the boron-containing compound (B) may be formed on the surface of the polarizing film. The concentration of the boron-containing compound (B) is more preferably 4.0% by mass or less, further preferably 2.0% by mass or less, and particularly preferably 1.0% by mass or less.

Further, the aqueous solution containing the boron-containing compound (B) preferably contains an iodide auxiliary such as potassium iodide from the viewpoint of improving optical performance, and the concentration of iodide is 0.5 to 15% by mass. Is preferable. Further, the temperature of the aqueous solution containing the boron-containing compound (B) needs to be 20 to 70 ° C. If the temperature of the aqueous solution containing the boron-containing compound (B) is less than 20 ° C., it becomes difficult to proceed the substitution reaction for replacing boric acid in the polarizing film with boronic acid to the central portion in the thickness direction of the polarizing film. In addition, the boron-containing compound (B) may precipitate in an aqueous solution containing the boron-containing compound (B). The temperature of the aqueous solution containing the boron-containing compound (B) is preferably 23 ° C. or higher, more preferably 25 ° C. or higher. On the other hand, if the temperature of the aqueous solution containing the boron-containing compound (B) is too high, it becomes difficult to easily industrially produce a polarizing film under relatively mild conditions. The temperature of the aqueous solution containing the boron-containing compound (B) is preferably 60 ° C. or lower, more preferably 40 ° C. or lower. The time for immersing in the aqueous solution containing the boron-containing compound (B) is preferably 5 to 400 seconds.

Examples of a method for producing a polarizing film by adsorbing a boron-containing compound (B) on a polarizing film during the fixing treatment include swelling treatment, uniaxial stretching treatment, and fixing treatment in this order, swelling treatment, and boric acid cross-linking treatment. It is preferable that 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 PVA film in distilled water, pure water, an aqueous solution, or the like. At this time, from the viewpoint of improving optical performance, it is preferable to use an aqueous solution containing 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, a polarizing film with even better dimensional stability can be obtained. Here, the heat treatment is a process of further heating a polarizing film having a moisture content of 5% or less after the drying treatment to improve the dimensional stability of the polarizing film. The conditions of the heat treatment are not particularly limited, but the heat treatment is preferably performed in the range of 60 ° C. to 150 ° C., particularly in the range of 70 ° C. to 150 ° C. If the temperature is lower than 60 ° C., the dimensional stabilization effect of the heat treatment is insufficient, and if the temperature is higher than 150 ° C., the polarizing film may be severely reddish.

It is preferable that the transmittance of the polarizing film of the present invention thus obtained is 42.0% or more and the degree of polarization is 99.85% or more. If the transmittance of the polarizing film is less than 42.0%, the brightness of the obtained LCD may be insufficient. The transmittance is more preferably 43.0% or more, further preferably 43.5% or more. On the other hand, the transmittance is usually 45% or less. Further, when the degree of polarization of the polarizing film is 99.85% or more, an LCD panel having high image quality can be obtained. The transmittance and the degree of polarization of the polarizing film are measured by the methods described in Examples described later.

It is preferable that the polarizing film of the present invention thus obtained has a shrinkage force of less than 12 N in the absorption axis direction per width of 1.5 cm and thickness of 13 μm when held at 80 ° C. for 4 hours. If the shrinkage force of the polarizing film is 12 N or more, when the LCD is enlarged, the LCD tends to warp due to heat generated by the screen, and light leakage may occur from the end portion. The shrinkage force of the polarizing film is measured by the method described in the examples.

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.

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

<Optical performance of polarizing film>
A rectangular sample of 4 cm in length x 2 cm in width was taken from the center of the polarizing film in the width and length directions, and a spectrophotometer with an integrating sphere V-7100 (manufactured by JASCO Corporation) was used. The parallel transmittance and the cross Nicol transmittance of the polarizing film were measured using an automatic polarizing film measuring device VAP-7070S (manufactured by JASCO Corporation) equipped with a Grantera polarizer. Here, the measurement wavelength range is set to 380 nm to 780 nm, and the transmittance when the vibration direction of the polarized light incident on the polarizing film through the Grantera polarizer is parallel to the transmission axis of the polarizing film is the parallel transmittance, and the transmittance of the polarizing film. The case perpendicular to the transmission axis was defined as the cross Nicol transmittance. After that, using the "Polarizing Film Evaluation Program" (manufactured by Nippon Spectral Co., Ltd.), using the above-mentioned parallel transmittance and cross Nicol transmittance so as to comply with JIS Z 8722 (object color measurement method), C Luminosity correction was performed for the visible light region of the light source and the 2 ° field, and the single transmittance and the degree of polarization of the polarizing film were calculated, and these two values were obtained as the optical characteristics of the polarizing film.

<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 "TRViewX120S". Since the absorption axis direction and the length direction (stretch axis direction) of the polarizing film are substantially the same, the contraction force in the absorption axis direction of the polarizing film is measured by measuring the tension in the length direction (stretch axis direction). Asked. For the measurement, a polarizing film (length direction (stretching axis direction) 15 cm, width direction 1.5 cm) adjusted at 20 ° C./20% RH for 18 hours was attached to the chuck (chuck interval 5 cm), and at the same time as the tension was started, 80 The temperature rise of the constant temperature bath to ℃ was started. 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 ViewWX120S". The measurement was performed while correcting so that was constant. If the minimum tension value occurs at the initial stage of measurement (within 10 minutes from the start of measurement), the minimum tension value is subtracted from the measured value of tension after 4 hours, and the difference is the contraction force in the stretching axial direction of the polarizing film. And said.

<Swelling degree of PVA film>
The PVA film was cut into 5 cm × 10 cm and immersed in 1000 mL of distilled water at 30 ° C. for 30 minutes. 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 H) 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 I) of the dried PVA film was measured. The degree of swelling of the PVA film was calculated by substituting the values of mass H and mass I into the following formula (1).
Swelling degree (%) = (mass H / mass I) x 100 (1)

<Boron element concentration (α) and boron element concentration (β)>
The concentration of boron element derived from the boron-containing compound (B) in the polarizing film was measured using an X-ray photoelectron spectrometer with a gas cluster ion beam gun (manufactured by ULVAC PHI Co., Ltd .: PHI5000 VersaProbe II) (GCIB-XPS). For the measurement, a polarizing film adjusted at about 23 ° C./40% RH for 16 hours or more was used. Under the conditions of a sputter ion source Ar2500 +, an acceleration voltage of 10 keV, and a current value of 30 nA, sputtering was performed in a range of 1 mm × 1 mm while neutralizing, and X-ray photoelectron spectroscopy measurement (XPS measurement) was performed. XPS measurement is performed using monochromatic Al as the X-ray source, the X-ray spot diameter is set to 200 μm, the X-ray output is set to 15 kV, and 50 W, and the detection elements are carbon, boron, oxygen, iodine, and potassium. Selected. When a dichroic dye is used as the dichroic dye, it is necessary to appropriately select elements such as nitrogen and sulfur contained in the dichroic dye as detection elements. Next, using the analysis software "MultiPak" (manufactured by ULVAC PHI Co., Ltd.), at each depth in the thickness direction of the polarizing film, based on 284.8 eV, which is the binding energy of the CC and CH bonds. The boron element concentration (a, atomic%) was calculated. After that, for the XPS spectrum at each depth, the binding energy caused by boron of boric acid (C) and the binding energy caused by boron of the boron-containing compound (B) are appropriately set, and the spreadsheet software "Microsoft Excel 2010" ( Peak separation was performed by the minimum square method using a pseudo-Bort function using (manufactured by Microsoft Corporation). A linear function calculated from the average value of the intensity of the XPS spectrum of 187 to 189 eV and the average value of the XPS spectrum of 195 to 197 was used as the baseline. In this way, the peak area (b,%) of boron derived from the boron-containing compound (B) is calculated with respect to the total of boron derived from boric acid (C) and boron derived from the boron-containing compound (B), and the following formula is used. By substituting into (2), the concentration of boron element derived from the boron-containing compound (B) at each depth was calculated.
Boron element concentration (atomic%) derived from boron-containing compound (B)
= A × b × 10 ^-2 (2)

The binding energy of the boron-containing compound (B) due to boron changes depending on the structure of the compound. Therefore, it is necessary to appropriately set the binding energy according to the type of the boron-containing compound (B). For example, when the boron-containing compound (B) is n-propylboronic acid, it is around 191.5 eV. Further, when peak separation was performed by the least squares method using the pseudo Voigt function, the Lorentz function ratio of boric acid was set to 0.241, and 2 ^1/2 × σ was set to 0.916. The Lorentz function ratio and full width at half maximum of the boron-containing compound (B) also change depending on the structure of the compound. Therefore, it is necessary to appropriately set the Lorentz function ratio and 2 ^1/2 × σ depending on the type of the compound. When the boron-containing compound (B) was n-propylboronic acid, the Lorentz function ratio was set to 0.000, and ^{2 1/2} × σ was set to 0.769.

By such a method, the boron element concentration (α, atomic%) derived from the boron-containing compound (B) from the center in the thickness direction of the polarizing film to the outside 1 μm was determined. In addition, the concentration of boric acid-derived boron element (β, atomic%) from the center of the polarizing film in the thickness direction to 1 μm outside was determined.

<Example 1>
It contains 100 parts by mass of PVA (saponification degree 99.9%, degree of polymerization 2400), 10 parts by mass of glycerin as a plasticizer, and 0.1 parts by mass of polyoxyethylene lauryl ether sodium sulfate as a surfactant, and has a PVA content. A 10% by mass PVA aqueous solution was prepared. The film obtained by drying the PVA aqueous solution on a metal roll at 80 ° C. was heat-treated in a hot air dryer (120 ° C.) for 10 minutes to obtain a PVA film having a thickness of 30 μm and a swelling degree of 200%.

A sample having a width of 5 cm and a length of 9 cm was cut so that a range of 5 cm in width × 5 cm in length could be uniaxially stretched from the central portion in the width direction of the obtained PVA film. 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, the length was 2.2 times (2.4 times in total) while being immersed in an aqueous solution (dyeing treatment bath) at 30 ° C. containing 0.035% by mass of iodine and 3.5% by mass of potassium iodide for 60 seconds. Iodine was adsorbed by uniaxially stretching in the direction. Next, while immersing in an aqueous solution (boric acid cross-linking treatment bath) at 30 ° C. containing 3.0% by mass of boric acid and 3% by mass of potassium iodide, 1.1 times (2.7 times in total). It was uniaxially stretched in the length direction. Further, while immersing in an aqueous solution (stretching treatment bath) at 60 ° C. containing boric acid in a proportion of 4.0% by mass and potassium iodide in a proportion of 6% by mass, the whole was uniaxially stretched up to 6.0 times in the length direction. .. After the uniaxial stretching treatment, 100 in an aqueous solution (fixed treatment bath) at 30 ° C. containing 0.7% by mass of n-propylboronic acid and 2 to 5% by mass of potassium iodide as the boron-containing compound (B). Soaked for seconds. In the fixing treatment, the PVA film was not stretched (stretching ratio 1.0 times). Finally, it was dried at 60 ° C. for 240 seconds to prepare a polarizing film (thickness 13 μm).

When the XPS spectrum of the polarizing film was measured and analyzed, the boron element concentration (α) derived from the boron-containing compound (B) in the range of 1 μm from the center in the thickness direction of the polarizing film was 1.4 atomic%, and the polarized light was polarized. The boron element concentration (β) derived from boric acid in the range of 1 μm from the center in the thickness direction of the film was 1.5 atomic%. When the optical characteristics and shrinkage force of the polarizing film were evaluated by the above method, the transmittance was 44.18%, the degree of polarization was 99.89%, and the shrinkage force was 0.6N.

<Examples 2 to 4>
A polarizing film was prepared in the same manner as in Example 1 except that the time of immersion in the fixing treatment bath and the concentration of the aqueous solution were changed as shown in Table 1, and each measurement and evaluation was performed.

<Comparative example 1>
This is an example of a polarizing film that does not contain the boron-containing compound (B). Same as Example 1 except that an aqueous solution (temperature 30 ° C.) containing potassium iodide in a proportion of 2% by mass was used as the fixing treatment bath and the time of immersion in the fixing treatment bath was changed to 20 seconds. To prepare a polarizing film, each measurement and evaluation was performed. The concentration of boron element (β) derived from boric acid (C) was low, and the shrinkage force of the polarizing film was as low as 6.4 N, but the degree of polarization was less than 99.85%, which was insufficient.

<Comparative example 2>
This is an example of a polarizing film that does not contain the boron-containing compound (B). Same as Example 1 except that an aqueous solution (temperature 30 ° C.) containing potassium iodide at a ratio of 2% by mass was used as the fixing treatment bath and the time of immersion in the fixing treatment bath was changed to 5 seconds. To prepare a polarizing film, each measurement and evaluation was performed. At this time, the shrinkage force of the polarizing film exceeded 12N, and the shrinkage force was not sufficiently reduced.

In Examples 2 to 4 and Comparative Example 1, as in Example 1, an aqueous solution (dyeing treatment bath) (temperature 30 ° C.) containing 100 parts by mass of potassium iodide with respect to 1 part by mass of iodine was prepared. Iodine was adsorbed by uniaxially stretching in the length direction 2.2 times (2.4 times in total) while immersing for 60 seconds. 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%.

As shown in Table 1, it can be seen that the polarizing films of Examples 1 to 4 have a small shrinkage force at high temperatures and are excellent in optical performance.

As shown in the examples, the polarizing film of the present invention has high optical performance but low shrinkage force. Therefore, it is possible to meet the recent demand for thinner and higher definition electronic devices.

1 Center in the thickness direction of the polarizing film 2 Surface part of the polarizing film 3 Center in the thickness direction of the polarizing film

Claims

At least one boron-containing compound (B) and boric acid 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 (C), wherein the boron element concentration (α) derived from the boron-containing compound (B) is 0.1 to 3 atomic% in the range from the center in the thickness direction to 1 μm outward. The boron element concentration (β) derived from boric acid (C) is 0.1 to 8 atomic% in the range from the center to the outside in the thickness direction to 1 μm, and the ratio of the concentration (α) to the concentration (β). A polarizing film having (α / β) of 0.1 or more.

[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. ]
The polarizing film according to claim 1, wherein R 1 is a saturated aliphatic group.
The polarizing film according to claim 1 or 2, wherein R 1 is a linear aliphatic hydrocarbon group.
The polarizing film according to any one of claims 1 to 3, wherein R 1 has 2 to 5 carbon atoms.
The polarizing film according to any one of claims 1 to 4, which has a transmittance of 42.0% or more and a degree of polarization of 99.85% or more.
The polarizing film according to any one of claims 1 to 5, wherein the shrinkage force in the absorption axis direction per width of 1.5 cm and thickness of 13 μm when held at 80 ° C. for 4 hours is less than 12 N.
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 concentration of the boron-containing compound (B) is 0.2 to 5 mass by mass. The method for producing a polarizing film according to any one of claims 1 to 6, which comprises a treatment of immersing in an aqueous solution having a temperature of 20 to 70 ° C. in%.