CN111615654A

CN111615654A - Polarizing film and method for producing same

Info

Publication number: CN111615654A
Application number: CN201980010049.6A
Authority: CN
Inventors: 大桥亘; 矶崎孝德
Original assignee: Kuraray Co Ltd
Current assignee: Kuraray Co Ltd
Priority date: 2018-01-25
Filing date: 2019-01-24
Publication date: 2020-09-01
Anticipated expiration: 2039-01-24
Also published as: TW201937215A; CN111615654B; TWI795515B; KR20200110372A; JP7284716B2; WO2019146677A1; JPWO2019146677A1

Abstract

A polarizing film comprising polyvinyl alcohol (A) and at least 1 boron-containing compound (B) selected from a group consisting of a boronic acid represented by the following formula (I) and a compound capable of converting into the boronic acid in the presence of water, wherein the content of a boron element derived from the boron-containing compound (B) in the polarizing film is 0.1 to 3.0 parts by mass relative to 100 parts by mass of the polyvinyl alcohol (A). The polarizing film has a small shrinkage force at high temperature and excellent optical properties.

[ in the formula (I), R¹Is a carbon atom number of1 to 20 valent aliphatic group, R¹And the organoboronate group is connected by a boron-carbon bond.]。

Description

Polarizing film and method for producing same

Technical Field

The present invention relates to a polarizing film having a small shrinkage force at high temperature and excellent optical properties, and a method for producing the same.

Background

A polarizing plate having a function of transmitting and shielding light is an essential constituent of a Liquid Crystal Display (LCD) together with a liquid crystal that changes the polarization state of light. Most polarizing plates have a structure in which a protective film such as a Triacetylcellulose (TAC) film is attached to the surface of a polarizing film in order to prevent discoloration of the polarizing film or to prevent shrinkage of the polarizing film, and as a polarizing film constituting the polarizing plate, a polarizing plate in which an iodine-based dye (I) is adsorbed onto a substrate obtained by uniaxially stretching a polyvinyl alcohol film (hereinafter, polyvinyl alcohol may be referred to as "PVA") has been mainly used₃ ^-、I₅ ^-Etc.) are prepared.

LCDs are widely used in small devices such as calculators and watches, smart phones, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, car navigation systems, measuring instruments used indoors and outdoors, and the like, and in recent years, these devices are required to be thin and high-definition. Along with this, in recent years, thinning of glass used for LCDs and high stretching magnification of polarizing films have been advanced, and as a result, warping of LCD panels has occurred, which has become a problem. The main cause of the warping of the LCD panel is said to be that the polarizing film sometimes shrinks at high temperature, and a polarizing film having high optical performance and small shrinking force at high temperature is required.

As a means for improving the optical performance of a polarizing film, a method using PVA having a high polymerization degree is known (for example, patent document 1). However, when a PVA having a high polymerization degree is used, the optical performance of the polarizing film is improved, but the shrinkage force is increased, and it is difficult to achieve both of them.

Patent document 2 describes that a polarizing film having a small shrinkage force at high temperature and a good color tone is obtained by providing a step of drying a PVA film between a boric acid treatment step and a water washing step while reducing the amount of boric acid in the PVA film. However, even if the amount of boric acid in the polarizing film is reduced, it is difficult to sufficiently reduce the shrinking force while maintaining high optical performance.

Documents of the prior art

Patent document

[ patent document 1] Japanese patent application laid-open No. H01-084203

[ patent document 2] Japanese patent laid-open No. 2013-148806.

Disclosure of Invention

Problems to be solved by the invention

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 properties.

Means for solving the problems

The polarizing film comprises PVA (A) and at least 1 boron-containing compound (B) selected from a group consisting of a boronic acid represented by the following formula (I) and a compound capable of converting into the boronic acid in the presence of water, wherein the content of a boron element derived from the boron-containing compound (B) in the polarizing film is 0.1 to 3.0 parts by mass relative to 100 parts by mass of PVA (A).

[ solution 1]

[ in the formula (I), R¹Is a 1-valent aliphatic group having 1 to 20 carbon atoms, R¹And the organoboronate group is connected by a boron-carbon bond.]。

In this case, R is preferably¹Is a saturated aliphatic group. Also preferred is R¹Is an aliphatic hydrocarbon group. Also preferred is R¹The number of carbon atoms of (A) is 2 to 5.

The above problems are solved by providing a method for producing a polarizing film comprising a dyeing process for dyeing a PVA film with a dichroic dye and a stretching process for uniaxially stretching the film, wherein the method comprises a process for immersing the film in an aqueous solution of a boron-containing compound (B).

Effects of the invention

The polarizing film of the present invention has a small shrinkage force at high temperature and is excellent in optical properties. Therefore, by using the polarizing film of the present invention, an LCD panel with high image quality and less warping at high temperature can be obtained. Further, according to the manufacturing method of the present invention, such a polarizing film can be manufactured.

Drawings

[ FIG. 1]

FIG. 1: of the polarizing film obtained in example 1¹H-NMR chart.

FIG. 2: the polarizing films of examples 1 to 7 and comparative examples 1 and 3 to 9 were plotted with the horizontal axis as the shrinkage force and the vertical axis as the degree of polarization.

Detailed Description

The polarizing film of the present invention is a polarizing film comprising PVA (A) and at least 1 boron-containing compound (B) selected from a group consisting of a boronic acid represented by the following formula (I) and a compound capable of converting into the boronic acid in the presence of water, and the content of a boron element derived from the boron-containing compound (B) in the polarizing film is 0.1 to 3.0 parts by mass relative to 100 parts by mass of PVA (A). By crosslinking PVA (A) with the boron-containing compound (B), the shrinkage force at high temperatures can be reduced and the optical properties can be improved. In the formula (I), R¹Is a 1-valent aliphatic group having 1 to 20 carbon atoms, R¹And the organoboronate group is connected by a boron-carbon bond.

[ solution 2]

The monoboronic acid is a compound represented by the above formula (I) having 1 organoboronic acid group [ -B (OH) ] in 1 molecule₂]. The organoboronic acid group has a structure in which a boron atom to which 2 hydroxyl groups are bonded is bonded to a carbon atom, and R in the compound represented by the formula (I)¹And the organoboronate group is connected by a boron-carbon bond. Boric acid [ B (OH) ]₃]In which the boron atom is bonded to 3 hydroxyl groups, as opposed to organoboronic acid groups in which the boron-carbon bond is locatedThe facets are different. Examples of the boron-containing group which can be converted into an organic boronic acid group in the presence of water include, but are not limited to, the following borate group as a representative group.

The hydroxyl group in the organic boronic acid group contained in the monoboronic acid can form an alcohol and an ester in the same manner as the hydroxyl group in the boronic acid. The following structural formula (II) is an alcohol (R) having reacted 1 molecule with respect to a boric acid²-OH) mono-borate. Here, R in the formula (II) is represented by the case where the organic boronic acid group is bonded to the hydroxyl group of PVA (A)²Is a PVA chain, to which a carbon-containing group is bonded via a boron atom.

[ solution 3]

The following structural formula (III) is an alcohol (R) having reacted 2 molecules with respect to a monoboronic acid²Examples of diesters of monoboronic acid with-OH). Here, in the case where an organoboronic acid group is bonded to the hydroxyl group of PVA, 2 Rs in the structural formula (III)²Are PVA chains.

[ solution 4]

Monoboronic acid has 2 hydroxyl groups that can react with the hydroxyl groups of PVA to form esters, resulting in moderate crosslinking of the PVA chains. Since the crosslinking is thermally stable, the shrinkage force of the polarizing film at high temperature becomes small. Thus, the LCD panel using the polarizing film is suppressed from warping at high temperatures. Further, it is considered that the PVA chains are appropriately crosslinked, whereby the alignment state of the PVA chains becomes good, and the optical performance of the polarizing film is improved.

In the above formula (I), R¹Is a 1-valent aliphatic group having 1 to 20 carbon atoms. By reacting R¹The boron-containing compound (B) can be controlled in its solubility in water and reactivity with the hydroxyl group of PVA to an appropriate length. R¹The number of carbon atoms of (b) is preferably 10 or less, more preferably 6 or less, and still more preferably 5 or less. On the other hand, the balance between the optical properties and the shrinkage force of the polarizing film is particularly excellentFrom a different viewpoint, R¹The number of carbon atoms of (b) is preferably 2 or more, more preferably 3 or more.

In the above formula (I), R¹Is a 1-valent aliphatic radical, R¹And the organic boronic acid group may be linked through a boron-carbon bond. R¹The aliphatic group may be a saturated aliphatic group or an unsaturated aliphatic group, and the former is preferable. By R¹The saturated aliphatic group suppresses coloring of the obtained polarizing film and improves durability. Furthermore, by R¹The saturated aliphatic group improves the alignment property of the dichroic dye, and further improves the optical performance. The unsaturated aliphatic group is an aliphatic group having a multiple bonding structure in which the number of bonding times is 2 or more, such as 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, and a carbon-sulfur double bond, and the saturated aliphatic group is an aliphatic group having only a single bond structure. As R¹Examples of the monoboronic acid having a saturated aliphatic group include methylboronic acid, ethylboronic acid, propylboronic acid, butylboronic acid, pentylboronic acid, hexylboronic acid, heptylboronic acid, octylboronic acid, nonylboronic acid, decylboronic acid, undecylboronic acid, dodecylboronic acid, tridecylboronic acid, tetradecylboronic acid, pentadecylboronic acid, hexadecylboronic acid, heptadecylboronic acid, octadecylboronic acid, nonadecylboronic acid, eicosylboronic acid and isomers thereof, cyclopropylboronic acid, cyclobutylboronic acid, cyclopentylboronic acid, cyclohexylboronic acid, cycloheptylboronic acid, cyclooctylboronic acid, cyclononylboronic acid, cyclodecylboronic acid, cycloundecylboronic acid, cyclododecylboronic acid, cyclotridecylboronic acid, cyclotetradecylboronic acid, cyclopentadeylboronic acid, cycloheptadeylboronic acid, cyclooctadecylboronic acid, cyclononadecylboronic acid, Cycloeicosylboronic acid and isomers thereof, 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-decylboric acid, 2-oxa-undecylboronic acid, 2-oxa-dodecylboronic acid, 2-oxa-tridecylboronic acid, 2-oxa-tetradecylboronic acid, 2-oxa-pentadecylboronic acid, 2-oxa-hexadecylboronic acid, 2-oxa-decadecafluoroboric acidHeptaalkylboronic acids, 2-oxa-octadecylboronic acids, 2-oxa-nonadecylboric acids, 2-oxa-eicosylboronic acids 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-decylboronic acid, 2-aza-undecylboronic acid, 2-aza-dodecylboronic acid, 2-aza-tridecylboronic acid, 2-aza-tetradecylboronic acid, 2-aza-pentadecylboronic acid, 2-aza-hexadecylboronic acid, 2-aza-heptadecylboric acid, 2-aza-nonadecylboronic acid, 2-oxa-eicosylboronic acid, 2-aza-octadecylboronic acid, 2-aza-nonadecylboronic acid, 2-aza-eicosylboronic acid and their isomers, 2-phospha-propylboronic acid, 2-phospha-butylboronic acid, 2-phospha-hexylboronic acid, 2-phospha-heptylboronic acid, 2-phospha-octylboronic acid, 2-phospha-nonylboronic acid, 2-phospha-decylboronic acid, 2-phospha-undecylboronic acid, 2-phospha-dodecylboronic acid, 2-phospha-tridecylboronic acid, 2-phospha-tetradecylboronic acid, 2-phospha-pentadecylboronic acid, 2-phospha-hexadecylboronic acid, 2-phospha-heptadecylboronic acid, 2-phospha-decylboronic acid, 2-phospha, 2-phospha-octadecylboronic acid, 2-phospha-nonadecylboronic acid, 2-phospha-eicosylboronic 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-decylboronic acid, 2-thia-undecylboronic acid, 2-thia-dodecylboronic acid, 2-thia-tridecylboronic acid, 2-thia-tetradecylboronic acid, 2-thia-pentadecylboronic acid, 2-thia-hexadecylboronic acid, 2-thia-heptadecylboronic acid, 2-thia-octadecylboronic acid, 2-thia-nonadecylboronic acid, 2-thia-eicosylboronic acid, isomers thereof and the like. Examples of the compound which can be converted into the exemplified monoboronic acid in the presence of water include salts of the monoboronic acid.

R¹May be an aliphatic hydrocarbon group, and may contain a hetero atom such as oxygen, nitrogen, sulfur, halogen, or the like. Considering the ease of acquisition, etc., R¹Aliphatic hydrocarbon groups containing no hetero atoms are preferred. The aliphatic hydrocarbon group is preferably a straight-chain aliphatic hydrocarbon group having no branch. Thereby, the adhesiveness to the polarizing film becomesGood, the effect of improving the optical performance becomes high. R is defined as¹Specific examples of the aliphatic hydrocarbon group-containing boric acid include methylboronic acid, ethylboronic acid, propylboronic acid, butylboronic acid, pentylboronic acid, hexylboronic acid, heptylboronic acid, octylboronic acid, nonylboronic acid, decylboronic acid, undecylboronic acid, dodecylboronic acid, tridecylboronic acid, tetradecylboronic acid, pentadecylboronic acid, hexadecylboronic acid, heptadecylboronic acid, octadecylboronic acid, nonadecylboronic acid, eicosylboronic acid and isomers thereof, cyclopropylboronic acid, cyclobutylboronic acid, cyclopentylboronic acid, cyclohexylboronic acid, cycloheptylboronic acid, cyclooctylboronic acid, cyclononylboronic acid, cyclodecylboronic acid, cyclododecylboronic acid, cyclotridecylboronic acid, cyclotetradecylboronic acid, cyclopentadeylboronic acid, cyclohexadecylboronic acid, cyclooctadecylboronic acid, cyclononadecylboronic acid, cycloeicosylboronic acid, isomers thereof, and the like. Examples of the compound which can be converted into the exemplified monoboronic acid in the presence of water include salts of the monoboronic acid.

In particular, R¹The alkyl group is preferred, and the alkyl group represented by the following formula (IV) is more preferred.

[ solution 5]

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

From the viewpoint of obtaining a polarizing film having extremely low shrinkage force at high temperature and extremely excellent optical properties, R¹Particularly preferably a saturated aliphatic hydrocarbon group having 2 to 5 carbon atoms.

Specifically, the monoboronic acid represented by the formula (I) is preferably methylboronic acid, ethylboronic acid, propylboronic acid, butylboronic acid, pentylboronic acid, hexylboronic acid, heptylboronic acid, octylboronic acid, nonylboronic acid, decylboronic acid, undecylboronic acid, dodecylboronic acid, tridecylboronic acid, tetradecylboronic acid, pentadecylboronic acid, hexadecylboronic acid, heptadecylboronic acid, octadecylboronic acid, nonadecylboronic acid, eicosylboronic acid, or isomers thereof, and particularly preferably propylboronic acid, butylboronic acid, pentylboronic acid because these compounds have good adsorptivity to the polarizing film and a high effect of improving optical properties. In addition, examples of the compound which can be converted into the monoboronic acid represented by the above formula (I) in the presence of water include salts of the monoboronic acid.

The content of boron element derived from the boron-containing compound (B) in the polarizing film of the present invention is required to be 0.1 to 3.0 parts by mass based on 100 parts by mass of the PVA (A). When the content of the boron element derived from the boron-containing compound (B) is less than 0.1 part by mass, the effect of improving the optical properties becomes insufficient. The boron element content is preferably 0.2 parts by mass or more, and more preferably 0.4 parts by mass or more. On the other hand, if the content of boron element derived from the boron-containing compound (B) exceeds 3.0 parts by mass, a long treatment time is required, and the productivity may be lowered. The reason is not clearly understood, and when the content of boron element exceeds 3.0 parts by mass, poor formation of iodine complex which absorbs short-wavelength light may be caused to degrade optical performance, which is not preferable. The boron element content is particularly preferably 2.0 parts by mass or less. The content of boron element derived from the boron-containing compound (B) in the polarizing film may be controlled by¹H-NMR measurement.

The polarizing film of the present invention may further contain boric acid. This may further improve the optical performance. In this case, the total boron element content in the polarizing film is preferably 0.2 mass% or more. Here, the total boron content refers to the amount of boron elements derived from the boron-containing compound (B), boron elements derived from boric acid, and boron elements derived from boron-containing compounds other than the boron-containing compound (B) and boric acid, which are contained in the polarizing film, in total. On the other hand, when the total boron element content in the polarizing film is too high, the shrinkage force of the polarizing film may become large. The total boron 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 still more preferably 4.0% by mass or less. The total boron element content in the polarizing film can be determined by ICP emission analysis or the like.

The polymerization degree of the 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, and still more preferably in the range of 2,000 to 4,000. When the polymerization degree 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 polymerization degree is 6,000 or less, an increase in production cost, a poor step-through property during film formation, and the like can be suppressed. The polymerization degree of PVA (A) in the present specification means an average polymerization degree measured according to JIS K6726-1994.

The saponification degree of pva (a) contained in the polarizing film of the present invention is preferably 95 mol% or more, more preferably 96 mol% or more, and even more preferably 98 mol% or more, from the viewpoint of water resistance of the polarizing film obtained by uniaxially stretching the film. The saponification degree of PVA in the present specification means that PVA has a saponification degree that can be converted into a vinyl alcohol unit (-CH) by saponification₂The total mole number of the structural unit of-CH (OH) -, typically a vinyl ester unit, and a vinyl alcohol unit, and the proportion (mol%) of the mole number of the vinyl alcohol unit. The degree of saponification can be measured according to JIS K6726-1994.

The method for producing the PVA (A) used in the present invention is not particularly limited. For example, a method of converting a vinyl ester unit of polyvinyl ester obtained by polymerizing a vinyl ester monomer into a vinyl alcohol unit can be mentioned. The vinyl ester monomer used for producing pva (a) is not particularly limited, and examples thereof include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, and vinyl benzoate. From the economical viewpoint, vinyl acetate is preferred.

The pva (a) used in the present invention may be obtained by converting a vinyl ester unit of a vinyl ester copolymer obtained by copolymerizing a vinyl ester monomer and another monomer copolymerizable therewith into a vinyl alcohol unit. Examples of the other monomer copolymerizable with the vinyl ester monomer include α -olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutylene; (meth) acrylic acid or a salt thereof; (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, and octadecyl (meth) acrylate; (meth) acrylamide derivatives such as (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylamidopropanesulfonic acid or a salt thereof, (meth) acrylamidopropyldimethylamine or a salt thereof, and N-methylol (meth) acrylamide or a derivative thereof; n-vinylamides such as N-vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; cyanoethenyl groups such as (meth) acrylonitrile; halogenated vinyl groups such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid or a salt, ester or anhydride thereof; itaconic acid or a salt, ester or anhydride thereof; vinyl silyl compounds such as vinyltrimethoxysilane; unsaturated sulfonic acids, and the like. The vinyl ester copolymer may have 1 or 2 or more structural units derived from the other monomers. The other monomer may be present in the reaction vessel in advance when the vinyl ester monomer is supplied to the polymerization reaction, or may be added to the reaction vessel during the progress of the polymerization reaction. From the viewpoint of optical properties, the content of the unit derived from another monomer is preferably 10 mol% or less, more preferably 5 mol% or less, and still more preferably 2 mol% or less, relative to the number of moles of the total constituent units constituting pva (a).

Among the monomers copolymerizable with the vinyl ester monomer, ethylene is preferable from the viewpoint of improving the stretchability and stretching at a higher temperature, reducing the occurrence of troubles such as stretch breaking during the production of the polarizing film, and further improving the productivity of the polarizing film. When the pva (a) contains an ethylene unit, the content of the ethylene unit is preferably 1 to 10 mol%, more preferably 2 to 6 mol%, based on the number of moles of the total structural units constituting the pva (a), from the viewpoints of stretchability, stretchability temperature, and the like as described above.

The PVA film used in the production of the polarizing film of the present invention may further contain a plasticizer in addition to the PVA (a) described above. Examples of the preferable plasticizer include polyhydric alcohols, and specific examples thereof include ethylene glycol, glycerol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. Further, 1 or 2 or more of these plasticizers may be contained. Among these, glycerin is preferable from the viewpoint of the effect 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, more preferably in the range of 3 to 17 parts by mass, and still more preferably in the range of 5 to 15 parts by mass, based on 100 parts by mass of PVA (a). 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, the film can be prevented from being excessively soft and the handling property can be prevented from being lowered.

The PVA film used for producing the polarizing film of the present invention may further contain, as necessary, PVA (a) such as a filler, a processing stabilizer such as a copper compound, a weather resistance stabilizer, a coloring agent, an ultraviolet absorber, a light stabilizer, an antioxidant, an antistatic agent, a flame retardant, another thermoplastic resin, a lubricant, a fragrance, an antifoaming agent, a deodorizing agent, an extender, a releasing agent, a release agent, a reinforcing agent, a crosslinking agent, a rust preventive, a preservative, a crystallization rate retarder, and other additives besides a plasticizer. The content of the other additives in the PVA film is usually 10 mass% or less, and preferably 5 mass% or less.

The PVA film used for producing the polarizing film of the present invention preferably has a swelling degree within a range of 160 to 240%, more preferably within a range of 170 to 230%, and particularly preferably within a range of 180 to 220%. By setting the swelling degree to 160% or more, the progress of crystallization can be suppressed extremely, and the fiber can be stretched stably to a high magnification. On the other hand, when the swelling degree 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. mu.m, preferably 5 to 60 μm, and particularly preferably 10 to 45 μm. If the PVA film is too thin, it tends to be easily broken by stretching in a uniaxial stretching process for producing a polarizing film. Further, when the PVA film is too thick, there is a tendency that stretching unevenness is likely to occur during uniaxial stretching treatment for producing a polarizing film, and the shrinkage force of the produced polarizing film tends to be large.

The width of the PVA film used in the production of the polarizing film of the present invention is not particularly limited, and may be determined according to the use of the polarizing film to be produced, and the like. In recent years, from the viewpoint of the development of large screens for liquid crystal televisions and liquid crystal monitors, a PVA film used for producing a polarizing film is suitable for these applications if the width of the PVA film is 3m or more. On the other hand, if the width of the PVA film used for the production of the polarizing film is too large, it is likely to be difficult to uniformly perform uniaxial stretching when the polarizing film is produced by a practical apparatus, and therefore the width of the PVA film used for the production of the polarizing film is preferably 10m or less.

The method for producing 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 employed, and for example, a film-forming stock solution obtained by dissolving 1 or 2 or more of PVA (a), and, if necessary, the plasticizer, the other additive, the surfactant described later, and the like in a liquid medium; a film-forming dope comprising 1 or 2 or more of PVA (A) and, if necessary, a plasticizer, other additives, a surfactant, a liquid medium, and the like, and PVA (A) melted. When the film-forming dope contains at least 1 of the plasticizer, other additives, and the surfactant, it is preferable to uniformly mix these components.

Examples of the liquid medium used for the preparation of the film-forming solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, and diethylenetriamine, and 1 or 2 or more of these can be used. Among them, water is preferable from the viewpoint of the burden on the environment and the recyclability.

The evaporation fraction of the film-forming stock solution (the content of volatile components such as a liquid medium that are removed by evaporation or evaporation during film formation) also varies depending on the film-forming method, film-forming conditions, and the like, and is generally preferably within a range of 50 to 95 mass%, and more preferably within a range of 55 to 90 mass%. By setting the volatile fraction of the film-forming dope to 50 mass% or more, the viscosity of the film-forming dope is not excessively high, filtration and deaeration in the preparation of the film-forming dope are smoothly performed, and a film with few foreign matters and defects can be easily produced. On the other hand, when the volatile fraction of the film-forming dope is 95 mass% or less, the concentration of the film-forming dope is not too low, and the industrial film production becomes easy.

The film-forming dope preferably contains a surfactant. By including the surfactant, the film forming property is improved, occurrence of thickness unevenness of the film is suppressed, and the film is easily peeled from a metal roll or a belt used for film formation. In the case of producing a PVA film from a film-forming stock solution containing a surfactant, the film may contain a surfactant. The type of the surfactant is not particularly limited, but an anionic surfactant or a nonionic surfactant is preferable from the viewpoint of releasability from a metal roll or a belt.

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

As the nonionic surfactant, for example, alkyl ether type such as polyoxyethylene oleyl ether; alkylphenyl ether type such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; alkylamine type such as polyoxyethylene lauryl amino ether; alkylamide types such as polyoxyethylene laurylamide; polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; alkanolamide types such as lauric acid diethanolamide and oleic acid diethanolamide; and an allylphenyl ether type such as polyoxyalkylene allylphenyl ether.

These surfactants may be used alone in 1 kind or in combination of 2 or more kinds.

When the film-forming stock solution contains the surfactant, the content thereof is preferably in the range of 0.01 to 0.5 parts by mass, 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, based on 100 parts by mass of pva (a) contained in the film-forming stock solution. When the content is 0.01 parts by mass or more, film forming properties and peeling properties are further improved. On the other hand, when the content is 0.5 parts by mass or less, blocking due to bleeding of the surfactant on the surface of the PVA film and deterioration in handling property can be suppressed.

Examples of the film forming method in the case of forming a PVA film using the film forming dope include a casting film forming method, an extrusion film forming method, a wet film forming method, a gel film forming method, and the like. These film-forming methods may be used alone in 1 kind, or 2 or more kinds may be used in combination. Among these film forming methods, a casting film forming method and an extrusion film forming method are preferable from the viewpoint of obtaining a PVA film used for producing a polarizing film having uniform thickness and width and good physical properties. The PVA film obtained by the film formation may be dried and heat-treated as necessary.

As an example of a specific method for producing the PVA film used for producing the polarizing film of the present invention, the following method may be industrially preferably employed: for example, a method in which the above-mentioned film-forming raw solution is uniformly discharged or cast on the circumferential surface of a 1 st rotating and heated roll (or belt) located on the most upstream side using a T-slot die, a hopper plate, an I-die, a lip coater die, or the like, volatile components are evaporated from one surface of the film discharged or cast on the circumferential surface of the 1 st roll (or belt) to dry the film, and then the film is further dried on the circumferential surfaces of 1 or more rotating and heated rolls disposed on the downstream side thereof, or further dried in a hot air drying apparatus, and then wound up by a winding apparatus. Drying with the heated roller and drying with the hot air drying device may be carried out in an appropriate combination. Further, a multilayer PVA film can be formed by forming a layer containing PVA (a) on one surface of a base film composed of a single resin layer.

The method for manufacturing the polarizing film of the present invention is not particularly limited. A suitable production method is a method for producing a polarizing film, which comprises a dyeing treatment for dyeing a PVA film with a dichroic dye and a stretching treatment for uniaxially stretching the film, wherein the method comprises a treatment for immersing the film in an aqueous solution of a boron-containing compound (B). Examples thereof include a method of subjecting the PVA film to dyeing treatment, uniaxial stretching treatment, and if necessary, further subjecting the PVA film to swelling treatment, boric acid crosslinking treatment, fixing treatment, washing treatment, drying treatment, heat treatment, and the like. In this case, the order of performing the respective treatments such as swelling treatment, dyeing treatment, boric acid crosslinking treatment, uniaxial stretching treatment, and fixing treatment in order is not particularly limited, and 1 or 2 or more treatments may be performed simultaneously, or 1 or 2 or more treatments may be performed 2 times or more.

The swelling treatment may be performed by immersing the PVA film in water. The temperature of the water for the dipping film is preferably within a range of 20 to 40 ℃, more preferably within a range of 22 to 38 ℃, and further preferably within a range of 25 to 35 ℃. The time for immersing 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 used for impregnating the membrane is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or may be a mixture of water and a hydrophilic medium.

The dyeing treatment may be performed by contacting the PVA film with a dichroic dye. As the dichroic dye, an iodine-based dye or a dichroic dye is generally used. The dyeing treatment may be performed at any stage of before the uniaxial stretching treatment, during the uniaxial stretching treatment, or after the uniaxial stretching treatment. The dyeing treatment is generally performed by immersing the PVA film in a solution (particularly, an aqueous solution) containing iodine-potassium iodide as a dyeing bath or a solution (particularly, an aqueous solution) containing a plurality of dichroic dyes. The concentration of iodine in the dyeing bath is preferably in the range of 0.01 to 0.5 mass%, and the concentration of potassium iodide is preferably in the range of 0.01 to 10 mass%. The temperature of the dyeing bath is preferably 20 to 50 ℃, particularly 25 to 40 ℃. The dyeing time is suitably 0.2 to 5 minutes. In the case of using a dichroic dye, the dichroic dye is preferably an aqueous dye. The concentration of the dye in the dyeing bath is preferably 0.001 to 10% by mass. Further, a dyeing assistant may be used as necessary, and inorganic salts such as sodium sulfate, surfactants, and the like may be used. When sodium sulfate is used, the amount is preferably 0.1 to 10% by mass. The dyeing temperature is preferably 30-80 ℃. Specific examples of the dichroic dye include c.i. direct yellow 28, c.i. direct orange 39, c.i. direct yellow 12, c.i. direct yellow 44, c.i. direct orange 26, c.i. direct orange 71, c.i. direct orange 107, c.i. direct red 2, c.i. direct red 31, c.i. direct red 79, c.i. direct red 81, c.i. direct red 247, c.i. direct green 80, and c.i. direct green 59, and preferably dichroic dyes developed for polarizing plate production.

The PVA film may be subjected to boric acid crosslinking treatment. In this case, the dissolution of pva (a) into water during wet stretching at high temperature can be more effectively prevented. From this viewpoint, the boric acid crosslinking treatment is preferably performed before the uniaxial stretching treatment. The boric acid crosslinking treatment may be performed by impregnating the PVA film in an aqueous solution containing a boric acid crosslinking agent. As the boric acid crosslinking agent, 1 or 2 or more kinds of boron-containing inorganic compounds such as boric acid and boric acid salts such as borax can be used. The concentration of the boric acid crosslinking agent in the aqueous solution containing the boric acid crosslinking agent is preferably in the range of 0.1 to 6.0 mass%. The concentration of the boric acid crosslinking agent is more preferably 0.2% by mass or more. Further, it is more preferably 4.0 mass% or less. By setting the concentration of the boric acid crosslinking agent within the above range, stretchability may be improved in some cases. When the concentration of the boric acid crosslinking agent is too high, it is sometimes difficult to contain the boron-containing compound (B) in the subsequent step, and therefore the concentration may not be too high. The aqueous solution containing the boric acid crosslinking agent may also contain an auxiliary agent such as potassium iodide. The temperature of the aqueous solution containing the boric acid crosslinking agent is within a range of 20 to 50 ℃, particularly preferably within a range of 25 to 40 ℃.

In addition to the uniaxial stretching treatment described later, the PVA film may be stretched (pre-stretched) during the above-described treatments. As described above, the total stretching ratio of the pre-stretching performed before the uniaxial stretching treatment (ratio obtained by multiplying the stretching ratios in the respective treatments) is preferably 1.5 times or more, more preferably 2.0 times or more, and further preferably 2.5 times or more the original length of the PVA film based on the raw material before stretching, from the viewpoint of the optical performance of the obtained polarizing film and the like. On the other hand, the total draw ratio is preferably 4.0 times or less, more preferably 3.5 times or less. The stretch ratio in the swelling treatment is preferably 1.05 to 2.5 times. The stretch ratio in the dyeing treatment is preferably 1.1 to 2.5 times. The stretch ratio in the boron crosslinking 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, stretching may be performed in an aqueous solution. Stretching may be performed 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 absorbing water. Among these, wet stretching is preferable, and uniaxial stretching treatment in an aqueous solution containing boric acid is more preferable. The concentration of boric acid in the aqueous solution of boric acid is preferably in the range of 0.5 to 6 mass%, more preferably in the range of 1 to 5 mass%. The aqueous boric acid solution may contain potassium iodide, and the concentration thereof is preferably in the range of 0.01 to 10 mass%. The stretching temperature in the uniaxial stretching treatment is preferably 30 ℃ or higher, and more preferably 40 ℃ or higher, and still more preferably 50 ℃ or higher. On the other hand, the stretching temperature is preferably 90 ℃ or lower, more preferably 80 ℃ or lower, and further preferably 70 ℃ or lower. The stretching ratio in the uniaxial stretching treatment is preferably 2.0 to 4.0 times. The stretching ratio is more preferably 2.2 times or more from the viewpoint of optical properties of the obtained polarizing film and the like. On the other hand, the stretch ratio is more preferably 3.5 times or less. Further, the total stretching magnification before the fixing treatment described later is preferably 5 times or more, more preferably 5.5 times or more, based on the original length of the PVA film before stretching, from the viewpoint of the optical properties of the obtained polarizing film. The upper limit of the stretching magnification is not particularly limited, and the stretching magnification is preferably 8 times or less.

The direction of the uniaxial stretching treatment in the case of subjecting a long PVA film to the uniaxial stretching treatment is not particularly limited, and a uniaxial stretching treatment in the long direction, a transverse uniaxial stretching treatment, a so-called oblique stretching treatment may be employed, and from the viewpoint of obtaining a polarizing film excellent in optical properties, a uniaxial stretching treatment in the long direction is preferred. The uniaxial stretching treatment in the longitudinal direction can be performed by changing the peripheral speed between the rollers using a stretching apparatus having a plurality of rollers parallel to each other. On the other hand, the transverse uniaxial stretching treatment can be performed using a tenter type stretching machine.

In order to enhance the adsorption of the dichroic dye (iodine-based dye) on the PVA film during the production of the polarizing film, it is also preferable to perform a fixing treatment after the uniaxial stretching treatment. As the fixing treatment bath used for the fixing treatment, an aqueous solution containing the boron-containing compound (B) is suitably used. Further, boric acid, an iodine compound, a metal compound, or the like may be further added to the fixing treatment bath as necessary. The temperature of the fixing treatment bath is preferably 10-80 ℃. The stretch 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) may be adsorbed to the polarizing film in any of the dyeing treatment, boric acid crosslinking treatment, uniaxial stretching treatment, and fixing treatment, and is particularly preferably adsorbed at the time of fixing treatment after the uniaxial stretching treatment from the viewpoint of suppressing cutting of the PVA film at the time of the uniaxial stretching treatment. The boron-containing compound (B) may be used alone or in combination of two or more. The concentration of the aqueous solution of the boron-containing compound (B) is preferably 0.05 to 15 mass%. When the concentration of the boron-containing compound (B) in the aqueous solution is less than 0.05 mass%, adsorption may be slow, and is more preferably 0.1 mass% or more, and still more preferably 0.2 mass% or more. On the other hand, if the concentration of the boron-containing compound (B) in the aqueous solution is higher than 15 mass%, the boron-containing compound (B) may not be uniformly present in the vicinity of the surface of the polarizing film, and as a result, the optical performance of the polarizing film obtained may be lowered. In addition, there is a possibility that precipitates of the boron-containing compound (B) may be generated on the surface of the polarizing film. The concentration of the boron-containing compound (B) is more preferably 10% by mass or less, still more preferably 5.0% by mass or less, and particularly preferably 3.5% by mass or less. In addition, from the viewpoint of improving the optical performance of the aqueous solution containing the boron-containing compound (B), it is preferable that an auxiliary agent containing an iodide such as potassium iodide is contained, and the concentration of the iodide is preferably 0.5 to 15% by mass. In addition, the temperature of the aqueous solution is preferably 10 to 80 ℃. If the temperature is too low, the boron compound (B) may be deposited in the treatment bath. The temperature of the aqueous solution is more preferably 15 ℃ or higher, still more preferably 20 ℃ or higher. On the other hand, if the temperature is too high, it is difficult to industrially easily produce the resin under relatively mild conditions. The temperature of the aqueous solution is more preferably 70 ℃ or lower, still more preferably 60 ℃ or lower, particularly preferably 45 ℃ or lower. The time for immersing in the aqueous solution is preferably 5 to 400 seconds.

A suitable production method for the case where the boron-containing compound (B) is adsorbed on the polarizing film at the time of the fixing treatment is: a method of sequentially performing swelling treatment, uniaxial stretching treatment, and fixing treatment; a method of sequentially performing swelling treatment, boric acid crosslinking treatment, uniaxial stretching treatment, and fixing treatment; or a method of sequentially performing swelling treatment, uniaxial stretching treatment, fixing treatment, and boric acid crosslinking treatment. Then, 1 or more treatments selected from washing treatment, drying treatment and heat treatment may be further performed as necessary.

The washing treatment is generally performed by immersing the membrane in distilled water, pure water, an aqueous solution, or the like. In this case, from the viewpoint of improving 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 washing treatment is generally 5 to 50 ℃, preferably 10 to 45 ℃, and more preferably 15 to 40 ℃. From the economical point of view, it is not preferable that the temperature of the aqueous solution is too low, and if the temperature of the aqueous solution is too high, the optical properties may be deteriorated.

The conditions for the drying treatment are not particularly limited, but the drying is preferably carried out at a temperature within a range of 30 to 150 ℃, particularly within a range of 50 to 130 ℃. By drying at a temperature in the range of 30 to 150 ℃, a polarizing film having excellent dimensional stability is easily obtained.

By performing the heat treatment after the drying treatment, a polarizing film further excellent in dimensional stability can be obtained. Here, the heat treatment is a treatment of further heating the polarizing film having a water content of 5% or less after the drying treatment to improve the dimensional stability of the polarizing film. The heat treatment conditions are not particularly limited, and the heat treatment is preferably performed at a temperature in the range of 60 ℃ to 150 ℃, particularly preferably at a temperature in the range of 70 ℃ to 150 ℃. If the heat treatment is performed at a lower temperature than 60 ℃, the dimensional stability effect by the heat treatment is not sufficient, and therefore, it is not preferable, and if the heat treatment is performed at a higher temperature than 150 ℃, a drastic red change may occur in the polarizing film.

The polarizing film of the present invention thus obtained has a transmittance of 42.0% or more and a degree of polarization of preferably 99.9% or more. If the transmittance of the polarizing film is less than 42.0%, the brightness of the LCD obtained may be insufficient. The transmittance is more preferably 43.0% or more, and still more preferably 43.5% or more. On the other hand, the transmittance is usually 45% or less. Further, by setting the polarization degree of the polarizing film to 99.9% or more, an LCD panel with high image quality can be obtained. The transmittance and degree of polarization of the polarizing film can be measured by the methods described in the examples below.

The polarizing film of the present invention is generally used as a polarizing plate by laminating optically transparent and mechanically strong protective films on both or one side thereof. As the protective film, a cellulose Triacetate (TAC) film, a Cellulose Acetate Butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Further, examples of the adhesive used for bonding include a PVA adhesive, a UV curable adhesive, and the like.

The polarizing plate obtained as described above may be attached to a retardation film, a viewing angle improving film, a brightness improving film, or the like. Further, the polarizing plate may be used as a member of an LCD by applying an adhesive such as acrylic to the polarizing plate and then bonding the polarizing plate to a glass substrate.

Examples

The present invention will be described in further detail with reference to examples below, but the present invention is not limited to these examples at all. The following examples and comparative examples show the respective measurement or evaluation methods used in the following examples and comparative examples.

[ measurement of the content of boron derived from the boron-containing Compound (B) based on 100 parts by mass of PVA (A) ]

After the polarizing film was dissolved in heavy water to 0.003 mass%, a solution concentrated by a rotary evaporator was prepared to 0.15 mass%¹H-NMR measurement sample.¹H-NMR (JNM-AL 400: 400MHz, manufactured by Nippon electronics Co., Ltd.) measurement was carried out at 80 ℃ and the number of integration times was set to 256. Using ALICE2 (manufactured by japan electronics corporation), analysis was performed by the following method. Obtained by measurement¹In the H-NMR chart, after the phase was adjusted so that the baseline became smooth, the number of average points was set to 20, and the baseline was automatically corrected. Then, the peak of heavy water as a measurement solvent was automatically set as a reference so as to reach a position of 4.65 ppm. Then, as shown in fig. 1, the peak area (area a) of the hydrogen peak of the hydrocarbon group contained in the boron-containing compound (B) is determined by integrating the peak areas. In this case, the number of hydrogens in the corresponding hydrocarbon group of the boron-containing compound (B) is set to be the same as the value of the area B, based on the area (area B) obtained by adding the hydrogen peak areas of the hydrocarbon groups contained in the boron-containing compound (B) that do not overlap with the PVA-derived hydrogen peak. Then, the peak area (area C) was determined by considering the hydrogen peak in the range of 1.6 to 2.4ppm as the sum of the hydrogen peak of the methylene group derived from PVA and the hydrogen peak of the hydrocarbon group contained in the boron-containing compound (B) overlapping with the hydrogen peak of the methylene group derived from PVA. Then, the number of hydrogens of the hydrocarbon group of the boron-containing compound (B) overlapping with the hydrogen peak derived from the methylene group of PVA is subtracted from the area C to calculate the area D. The values obtained by these methods were substituted into the following formula (1), and the content (parts by mass) of boron element derived from the boron-containing compound (B) relative to 100 parts by mass of pva (a) was calculated. X in the following formula (1) is hydrogen of a hydrocarbon group contained in the boron-containing compound (B) which does not overlap with the peak of PVAAnd Y is the number of boron atoms in 1 molecule of the boron-containing compound (B) on average. The formula (1) is a formula used when an unmodified PVA is used, and when a modified PVA is used as a raw material, the formula (1) needs to be appropriately modified.

Content (parts by mass) of boron element derived from the boron-containing compound (B) relative to 100 parts by mass of PVA (A)

= (area B/X)/(area D/2) } × (10.811 × Y/44.0526)

×100 (1)。

10.811 is the atomic weight of boron and 44.0526 is the average molecular weight of 1 mole of the repeating units of unmodified PVA. Note that, FIG. 1 shows¹The H-NMR chart was obtained by measuring the polarizing film of example 1.

[ calculation of the Total boron element content (mass%) in the polarizing film ]

The mass of the polarizing film [ E (g) ] was measured, and the polarizing film was dissolved in 20mL of distilled water to 0.005 mass%. The aqueous solution in which the polarizing film was dissolved was used as a measurement sample, and the mass thereof was measured [ F (g) ]. Thereafter, the boron concentration [ G (ppm) ] of the measurement sample was measured using a multichannel ICP emission spectrometer (ICP) manufactured by Shimadzu corporation. Then, the value calculated by substituting the value into the following formula (2) is referred to as the total boron element content (mass%) in the polarizing film.

Total boron element content (mass%) in polarizing film

=[(G×10^-6×F)/E]×100 (2)。

[ optical Properties of polarizing film ]

(1) Measurement of transmittance Ts

From the central portions of the polarizing films obtained in the following examples or comparative examples, 2 samples of the polarizing films having a stretching direction of 4cm and a width direction of 2cm were collected, and a C light source and a visual sensitivity correction in a visible light region of a 2 ° field of view were performed in accordance with JIS Z8722 (measuring method of body color) using an integrating sphere-equipped spectrophotometer ("V7100" manufactured by japan society of mass spectrometry), and the transmittance of light inclined at + 45 ° and the transmittance of light inclined at-45 ° with respect to the longitudinal direction were measured for 1 sample, and the average value Ts1(%) thereof was obtained. The transmittance of light at an inclination of + 45 ° and the transmittance of light at an inclination of-45 ° were measured in the same manner for 1 sample, and the average value Ts2(%) was obtained. Ts1 and Ts2 were averaged by the following formula (3) to obtain a transmittance Ts (%) of the polarizing film.

Ts=(Ts1＋Ts2)/2 (3)。

(2) Measurement of degree of polarization V

For 2 samples used for the measurement of the transmittance Ts, a spectrophotometer with an integrating sphere (product of japan spectrographic association, inc. "V7100") was used to correct the visual sensitivity of the C light source and the visible light region of the 2 ° field of view in accordance with JIS Z8722 (method for measuring the body color), and the transmittance T ≠ of light when the two samples were overlapped so that the stretching directions thereof were perpendicular to each other and the transmittance T// (%) of light when the two samples were overlapped so that the stretching directions thereof were parallel to each other were measured. The measured T// (%) and T ≠ are substituted into the following formula (4), and the degree of polarization V (%) is obtained.

V={(T∥-T⊥)/(T∥＋T⊥)}^1/2×100 (4)。

(3) Dichroic ratio (DC) in 650nm

The dichroic ratio of each wavelength of the polarizing film was measured using a spectrophotometer with an integrating sphere (manufactured by japan spectro corporation, "V7100") equipped with a Glan-Taylor polarizer. 1 piece of the polarizing film was sampled from the center thereof in a direction of 4cm in the stretching direction and 2cm in the width direction, and the MD transmittance and TD transmittance were determined in the wavelength range of 380nm to 780nm, and the dichroic ratio in each wavelength was calculated from the following formula (5). Here, "MD transmittance" represents transmittance when the polarization direction emitted by the Glan-Taylor polarizer and the transmission axis of the polarizing plate sample are parallel. In addition, "TD transmittance" represents transmittance when the polarization direction emitted by the Glan-Taylor polarizer is perpendicular to the transmission axis of the polarizing plate sample. The dichroic ratio of 650nm in this example was used as an index of optical performance.

DC={log₁₀(TD transmittance/100) }/{ log₁₀(MD transmittance/100) } (5).

[ shrinkage force of polarizing film ]

The shrinkage force was measured using an Autograph "AG-X" with a thermostatic bath manufactured by Shimadzu and a camera type extensometer "TRViewX 120S". For the measurement, a polarizing film conditioned at about 20 ℃/20% RH for 18 hours was used. After the temperature in the thermostatic bath of Autograph "AG-X" was set to 20 ℃, the polarizing film (15 cm in the longitudinal direction and 1.5cm in the width direction) was mounted on a jig (jig interval: 5cm), and temperature rise in the thermostatic bath to 80 ℃ was started simultaneously with the start of stretching. The polarizing film was stretched at a rate of 1mm/min, and the stretching was stopped at a time when the tension reached 2N, and the tension in this state was measured up to 4 hours later. At this time, since the distance between the jigs changes due to the thermal expansion, the reticle label is attached to the jigs, and the measurement is performed while correcting the reticle label attached to the jigs by a moving amount so that the distance between the jigs becomes constant, using a camera type extensometer "TRViewX 120S". When a minimum value is generated in the tension at the initial stage of measurement (within 10 minutes from the start of measurement), the minimum value of the tension is subtracted from the measured value of the tension after 4 hours, and the difference is referred to as the shrinkage force of the polarizing film.

[ degree of swelling of PVA film ]

The PVA film was cut into 5 cm. times.10 cm and immersed in 1000mL of distilled water at 30 ℃ for 30 minutes. Thereafter, the PVA film was taken out, and the water content on the surface of the PVA film was wiped with filter paper, and the mass (mass H) of the PVA film after immersion was measured. Thereafter, the PVA film was charged into a drier at 105 ℃ and dried for 16 hours, and then the mass (mass I) of the PVA film after drying 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 (6).

Degree of swelling (%) = (mass H/mass I) × 100 (6).

[ example 1]

An aqueous solution containing 100 parts by mass of PVA (degree of saponification: 99.9 mol%, degree of polymerization: 2400), 10 parts by mass of glycerol as a plasticizer, and 0.1 part by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant and having a PVA content of 10% by mass was used as a film-forming stock solution, and the film was dried on a metal roll at 80 ℃ to obtain a film, and the obtained film was heat-treated in a hot air dryer at 120 ℃ for 10 minutes to produce a PVA film having a swelling degree adjusted to 200% and a thickness of 30 μm.

From the widthwise central portion of the thus-obtained PVA film, a sample having a width of 5cm × length of 9cm was cut so as to be uniaxially stretchable in a range of 5cm × length of 5 cm. The sample was immersed in pure water at 30 ℃ for 30 seconds while uniaxially stretched 1.1 times in the longitudinal direction, and subjected to a swelling treatment. Subsequently, the resultant was immersed in an aqueous solution (dyeing bath) (temperature 30 ℃) containing 0.04 mass% of iodine and 4.0 mass% of potassium iodide (KI) for 60 seconds while uniaxially stretched 2.2 times in the longitudinal direction (2.4 times in total), and iodine was adsorbed. Further, the sheet was immersed in an aqueous solution (crosslinking treatment bath) containing 3.0 mass% of boric acid and 3 mass% of potassium iodide (temperature 30 ℃) for 45 seconds, and uniaxially stretched in the longitudinal direction by 1.2 times (2.7 times as much as the whole), thereby adsorbing boric acid. Then, the film was immersed in an aqueous solution (stretching bath) (temperature 60 ℃) containing 4.0 mass% of boric acid and 6 mass% of potassium iodide, and uniaxially stretched 2.2 times (6.0 times as much as the whole) in the longitudinal direction to be oriented. Then, the substrate was immersed in an aqueous solution (fixed treatment bath) (temperature 30 ℃) containing 1.0 mass% of n-propylboronic acid and 4.0 mass% of potassium iodide for 100 seconds. In the fixing treatment, the PVA film was not stretched (stretching ratio 1.0 times). Finally, the polarizing film was dried at 60 ℃ for 4 minutes.

Measuring the polarizing film obtained¹As a result of analysis by H-NMR, a PVA-derived hydrogen peak and a non-overlapping hydrogen peak of n-propylboronic acid appeared at 1.1 to 1.3ppm, and the peak area (area B) was set to 5. Then, the area (area C) of the hydrogen peak of the methylene group of PVA having a peak in the range of 1.6 to 2.4ppm was calculated. Since the hydrogen peak of the methylene group of PVA and the hydrogen peak of the C2 hydrocarbon group of n-propylboronic acid overlap, the area D was determined by subtracting the number of hydrogen atoms of the C2 hydrocarbon group of n-propylboronic acid, 2, from the area C. These values are substituted into the above formula (1), and as a result, the content of the boron element derived from the boron-containing compound (B) is 1.5 parts by mass with respect to 100 parts by mass of the pva (a). Further, the total boron element content in the polarizing film was measured, and as a result, it was 3.4 mass%.

The optical properties of the obtained polarizing film were measured, and as a result, the transmittance was 44.14%, the degree of polarization was 99.96%, and the dichroic ratio was 83.88. The shrinkage force of the obtained polarizing film was measured, and found to be 4.8N. These results are shown in Table 1. Fig. 2 shows a graph in which the degree of polarization is plotted against the shrinkage force of the polarizing film.

[ example 2]

A polarizing film was produced in the same manner as in example 1 except that the immersion time in the fixing treatment bath was changed to 300 seconds, and each measurement and each evaluation were performed by the above-described method. The results are shown in table 1 and fig. 2.

[ example 3]

A polarizing film was produced in the same manner as in example 1 except that an aqueous solution containing n-butyl boronic acid in a proportion of 1.0 mass% and potassium iodide in a proportion of 3.0 mass% was used as the fixing treatment bath (temperature 30 ℃), and each measurement and each evaluation were performed by the above-described method. The results are shown in table 1 and fig. 2.

[ example 4]

A polarizing film was produced in the same manner as in example 1 except that an aqueous solution containing n-butyl boronic acid in a proportion of 0.5 mass% and potassium iodide in a proportion of 3.5 mass% was used as the fixing treatment bath (temperature 30 ℃), and each measurement and each evaluation were performed by the above-described method. The results are shown in table 1 and fig. 2.

[ example 5]

A polarizing film was produced in the same manner as in example 1 except that an aqueous solution containing n-pentylboronic acid in an amount of 0.5 mass% and potassium iodide in an amount of 3.0 mass% was used as the fixing treatment bath (treatment temperature 30 ℃), and the measurements and the evaluations were performed by the methods described above. The results are shown in table 1 and fig. 2.

[ example 6]

A polarizing film was produced in the same manner as in example 1 except that an aqueous solution containing methylboronic acid in an amount of 1.0 mass% and potassium iodide in an amount of 2.0 mass% was used as the fixing treatment bath (treatment temperature 30 ℃), and the immersion time in the fixing treatment bath was changed to 10 seconds, and the measurements and the evaluations were performed by the methods described above. The results are shown in table 1 and fig. 2.

[ example 7]

A polarizing film was produced in the same manner as in example 1 except that an aqueous solution containing n-propylboronic acid in a proportion of 0.5 mass%, boric acid in a proportion of 4.0 mass%, and potassium iodide in a proportion of 5.2 mass% was used as the stretching treatment bath (temperature 62 ℃), and an aqueous solution containing potassium iodide in a proportion of 3.0 mass% (temperature 30 ℃) was used as the fixing treatment bath, and the time for immersion in the fixing treatment bath was 5 seconds, and the measurements and evaluations were performed by the methods described above. The results are shown in table 1 and fig. 2.

Comparative example 1

A polarizing film was produced in the same manner as in example 1 except that an aqueous solution containing n-butyl boronic acid at a ratio of 1.0 mass% (temperature 10 ℃) was used as the fixing treatment bath, and the immersion time in the fixing treatment bath was 20 seconds, and each measurement and each evaluation were performed by the above-described method. In this case, since the boron-containing compound (B) cannot be detected when the number of accumulations is 256, the number of accumulations is changed to 4096, and the content of the boron element derived from the boron-containing compound (B) is measured with respect to 100 parts by mass of pva (a). The results are shown in table 1 and fig. 2.

Comparative example 2

A polarizing film was produced in the same manner as in example 1 except that an aqueous solution containing phenylboronic acid at a ratio of 1.0 mass% and potassium iodide at a ratio of 1.0 mass% was used as the fixing treatment bath (temperature 30 ℃), and each measurement and each evaluation were performed by the above-described method. The results are shown in table 1 and fig. 2.

Comparative example 3

A polarizing film was produced in the same manner as in example 1 except that an aqueous solution containing boric acid at a ratio of 2.0 mass% and potassium iodide at a ratio of 2.5 mass% was used as the fixing treatment bath (temperature 30 ℃), and each measurement and each evaluation were performed by the above-described method. The results are shown in table 1 and fig. 2.

Comparative example 4

A polarizing film was produced in the same manner as in example 1 except that an aqueous solution containing boric acid at a ratio of 1.0 mass% and potassium iodide at a ratio of 2.0 mass% was used as the fixing treatment bath (temperature 30 ℃), and each measurement and each evaluation were performed by the above-described method. The results are shown in table 1 and fig. 2.

Comparative example 5

A polarizing film was produced in the same manner as in example 1 except that an aqueous solution containing boric acid in a proportion of 0.5 mass% and potassium iodide in a proportion of 2.0 mass% was used as the fixing treatment bath (temperature 30 ℃), and each measurement and each evaluation were performed by the above-described method. The results are shown in table 1 and fig. 2.

Comparative example 6

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-described method. The results are shown in table 1 and fig. 2.

Comparative example 7

A polarizing film was produced in the same manner as in example 1 except that an aqueous solution containing potassium iodide in a proportion of 2.0 mass% (temperature 30 ℃) was used as the fixing treatment bath and the immersion time in the fixing treatment bath was changed to 5 seconds, and the measurements and the evaluations were performed by the methods described above. The results are shown in table 1 and fig. 2.

Comparative example 8

A polarizing film was produced in the same manner as in comparative example 7 except that the immersion time in the fixing treatment bath was 10 seconds, and each measurement and each evaluation were performed by the above-described method. The results are shown in table 1 and fig. 2.

Comparative example 9

A polarizing film was produced in the same manner as in comparative example 7 except that the immersion time in the fixing treatment bath was 20 seconds, and each measurement and each evaluation were performed by the above-described method. The results are shown in table 1 and fig. 2.

In examples 2 to 7 and comparative examples 1 to 9, the mass ratio of 1: 100 aqueous solution (temperature 30 ℃) containing iodine and potassium iodide was used for the dyeing treatment bath. At this time, the concentrations of iodine and potassium iodide in the dyeing bath were adjusted so that the transmittance of the dried polarizing film became 43.8% to 44.2%.

[ Table 1]

FIG. 2 is a graph in which the horizontal axis represents the shrinkage force and the vertical axis represents the degree of polarization of the polarizing films of examples 1 to 7 and comparative examples 1 and 3 to 9. As shown in FIG. 2, the polarizing films of examples 1 to 7 satisfying the requirements of the present invention have a small shrinkage force at high temperature and excellent optical properties. On the other hand, the polarizing film (comparative example 1) having a boron element content derived from the boron-containing compound (B) of less than 0.1 parts by mass has a high shrinkage. The polarizing film (comparative example 2) containing phenylboronic acid as a boron compound had high shrinkage and insufficient optical properties, and deviated downward from the range of the graph. When an aqueous solution containing boric acid and potassium iodide was used as the fixing treatment bath (comparative examples 3 to 5), the boric acid concentration in the aqueous solution was decreased and the total boron content in the polarizing film was decreased, so that the shrinkage force was decreased, but the optical performance was decreased, and it was difficult to achieve both of them. When the fixing treatment was not performed (comparative example 6), the shrinkage force of the polarizing film was significantly increased. In addition, when an aqueous solution containing potassium iodide was used as the fixing treatment bath (comparative examples 7 to 9), the optical performance of the polarizing film was insufficient. As can be seen from the above, when the specifications of the present invention are not satisfied (comparative examples 1 to 9), it is difficult to achieve both the shrinkage characteristics and the optical performance.

Description of the reference numerals

1 hydrogen peak from heavy water as solvent for determination

2 hydrogen peak of methine group derived from PVA

3 Hydrogen Peak derived from methylene group of PVA

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

5 Hydrogen Peak derived from Hydrocarbon group contained in boron-containing Compound (B) which does not overlap with the PVA-derived Hydrogen Peak

Claims

1. A polarizing film comprising a polyvinyl alcohol (A) and a boron-containing compound (B) selected from at least 1 of a boronic acid represented by the following formula (I) and a compound capable of converting into the boronic acid in the presence of water, the polarizing film having a boron element content derived from the boron-containing compound (B) of 0.1 to 3.0 parts by mass per 100 parts by mass of the polyvinyl alcohol (A),

[ solution 1]

In the formula (I), R¹Is a 1-valent aliphatic group having 1 to 20 carbon atoms, R¹And the organoboronate group is connected by a boron-carbon bond.

2. The polarizing film of claim 1, wherein R¹Is a saturated aliphatic group.

3. The polarizing film of claim 1 or 2, wherein R¹Is an aliphatic hydrocarbon group.

4. The polarizing film of any one of claims 1 to 3, wherein R¹The number of carbon atoms of (A) is 2 to 5.

5. The polarizing film according to any one of claims 1 to 4, wherein the transmittance is 42.0% or more and the degree of polarization is 99.9% or more.

6. The method for producing a polarizing film according to any one of claims 1 to 5, which comprises a dyeing process for dyeing a polyvinyl alcohol film with a dichroic dye and a stretching process for uniaxially stretching the film, wherein the method comprises a process for immersing the film in an aqueous solution containing a boron compound (B).