TW201937215A - Polarizing film and method for producing same - Google Patents

Abstract

A polarizing film including polyvinyl alcohol (A), and at least one species of boron-containing compound (B) selected from the group consisting of monoboronic acids represented by formula (I) and compounds that can be transformed to such a monoboronic acid in the presence of water, wherein the content of elemental boron originating from the boron-containing compound (B) in the polarizing film is 0.1-3.0 parts by mass with respect to 100 parts by mass of the polyvinyl alcohol (A). The polarizing film has low contractile force at high temperature, as well as excellent optical performance. [In formula (I), R1 is a C1-20 monovalent aliphatic group, and R1 and the boronic acid groups are linked by a boron-carbon bond.].

Description

Polarizing film and manufacturing method thereof

The invention relates to a polarizing film with small shrinkage force at high temperature and excellent optical performance, and a method for manufacturing the same.

A polarizing plate having the function of transmitting and shielding light is the same basic constituent element of a liquid crystal display (LCD) as a liquid crystal that changes the polarization state of light. Most polarizing plates have a structure in which a protective film such as a cellulose triacetate (TAC) film is laminated on the surface of the polarizing film in order to prevent discoloration of the polarizing film and shrinkage of the polarizing film. As a polarizing film constituting a polarizing plate, the mainstream In order to adsorb an iodine-based pigment (I ₃ ^- or I _5- ^, etc.) to a substrate obtained by uniaxially stretching a polyvinyl alcohol film (hereinafter sometimes referred to as "polyvinyl alcohol" as "PVA").

LCDs are widely used in small devices such as computers and watches, smartphones, laptops, LCD monitors, LCD color projectors, LCD TVs, car navigation systems, and measurement equipment used indoors and outdoors. These machines are required to be thin and high-definition. In accordance with the foregoing, in recent years, the thickness of glass used in LCDs or the high stretching ratio of polarizing films has progressed. As a result, the generation of warpage of LCD panels has become a problem. It is said that the owner of the warpage of the LCD panel The main reason is that the polarizing film shrinks at high temperature, so it is necessary to have a polarizing film with high optical properties and a small shrinkage force at high temperature.

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, by using PVA with a high degree of polymerization, although the optical properties of the polarizing film are improved, the shrinkage force is increased, making it difficult to achieve both.

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

[Prior technical literature] [Patent Literature]

Patent Document 1: Japanese Unexamined Patent Publication No. 01-084203

Patent Document 2: Japanese Patent Application Publication No. 2013-148806

The present invention has been made in order to solve the above-mentioned problems, and an object thereof is to provide a polarizing film that has a small shrinkage force at high temperatures and is also excellent in optical properties.

The above-mentioned problem is solved by providing a polarizing film including PVA (A) and a compound selected from the group consisting of a monoboric acid represented by the following formula (I) and a compound that can be converted into the monoboric acid in the presence of water Group of at least A polarizing film containing a boron-containing compound (B). The content of the boron element derived from the boron-containing compound (B) in the polarizing film is 0.1 to 3.0 parts by mass based on 100 parts by mass of PVA (A).

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

In this case, R ¹ is preferably a saturated aliphatic group. Preferably, R ¹ is an aliphatic hydrocarbon group. The carbon number of R ¹ is preferably 2 to 5.

The above-mentioned problem is solved by providing a method for manufacturing the above-mentioned polarizing film, which is a method for manufacturing a polarizing film including a dyeing process of dyeing a PVA film with a dichroic dye and a uniaxially-stretching stretching process of the film. There is a treatment in which the film is immersed in an aqueous solution of a boron-containing compound (B).

The polarizing film of the present invention has a small shrinkage force at high temperatures and is also excellent in optical performance. Therefore, by using the polarizing film of the present invention, it is possible to obtain an LCD panel that is not easily warped at high temperatures and has high image quality. Moreover, according to the manufacturing method of this invention, such a polarizing film can be manufactured.

1‧‧‧Hydrogen peak from heavy water used to determine the solvent

2‧‧‧Hydrogen peak derived from PVA

3‧‧‧ Peak of hydrogen derived from methylene of PVA

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

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

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

FIG. 2 shows deviations from Examples 1 to 7 and Comparative Examples 1 and 3 to 9. For light films, plot the shrinkage force on the horizontal axis and the degree of polarization on the vertical axis.

[Form of Implementing Invention]

The polarizing film of the present invention is a polarizing film comprising PVA (A) and a member selected from the group consisting of a monoboric acid represented by the following formula (I) and a compound capable of being converted into the monoboric acid in the presence of water The polarizing film of at least one type of boron-containing compound (B), and the content of boron element derived from the boron-containing compound (B) in the polarizing film is 0.1 to 3.0 parts by mass based on 100 parts by mass of PVA (A). By cross-linking PVA (A) with a boron-containing compound (B), the shrinkage force at high temperatures can be reduced, and optical performance can be improved at the same time. Here, in formula (I), R ¹ is a monovalent aliphatic group having 1 to 20 carbon atoms, and R ¹ and a boric acid group are connected by a boron-carbon bond.

Monoboric acid is a compound represented by the above formula (I), and has one boronic acid group [-B (OH) ₂ ] in one molecule. This boric acid group has a structure in which a boron atom having two hydroxyl groups bonded to a carbon atom is bonded. In the compound represented by formula (I), R ¹ and a boric acid group are connected by a boron-carbon bond. The boric acid group differs from the point having a boron-carbon bond in that the boron atom system is bonded to three hydroxyl groups in boric acid [B (OH) ₃ ]. Examples of the boron-containing group that can be converted into a boric acid group in the presence of water include boric acid ester groups described below as a representative, but the invention is not limited thereto.

The hydroxyl group in the boric acid group contained in the monoboric acid can form an ester with an alcohol in the same manner as the hydroxyl group in the boric acid. The following structural formula (II) is a monoboric acid monoester obtained by reacting one molecule of alcohol (R ² -OH) with boric acid. Here, when a boric acid group is bonded to a hydroxyl group of PVA (A), R ² in the structural formula (II) is a PVA chain, and a carbon-containing group is bonded to the PVA chain via a boron atom.

The following structural formula (III) is an example of a monoboronic acid diester obtained by reacting two molecules of an alcohol (R ² -OH) with monoboric acid. Here, when the boric acid group is bonded to the hydroxyl group of PVA, both R ² in the structural formula (III) are PVA chains.

Monoboric acid has two hydroxyl groups that can react with the hydroxyl group of PVA to form an ester, and the PVA chain is appropriately crosslinked. Since this cross-linking is stable to heat, the shrinking force of the polarizing film at a high temperature becomes small. Thereby, the LCD panel using a polarizing film can be suppressed from warping at a high temperature. In addition, it is considered that by properly crosslinking the PVA chain, the alignment state of the PVA chain becomes good, and the optical properties of the polarizing film are improved.

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

In the above formula (I), R ¹ is a monovalent aliphatic group, and R ¹ and the boric acid group may be connected by a boron-carbon bond. R ¹ may be a saturated aliphatic group or an unsaturated aliphatic group, but the former is preferred. When R ¹ is a saturated aliphatic group, the coloration of the obtained polarizing film can be suppressed and durability can be improved. In addition, since R ¹ is a saturated aliphatic group, the alignment of the dichroic pigment can be improved, and the optical performance can be further improved. In addition, the unsaturated aliphatic group has carbon-carbon double bonds or carbon-carbon triple bonds, carbon-oxygen double bonds, carbon-nitrogen double bonds, nitrogen-nitrogen double bonds, carbon-sulfur double bonds and the like, and includes the number of bondings. An aliphatic group having a structure of multiple bonds of 2 or more, and a saturated aliphatic group is an aliphatic group having a structure of only a single bond. Examples of the monoboric acid in which R ¹ is a saturated aliphatic group include methylboronic acid, ethylboronic acid, propylboronic acid, butylboronic acid, pentylboronic acid, hexylboronic acid, heptylboronic acid, octylboronic acid, nonylboronic acid, and decane Boronic acid, undecyl boronic acid, dodecyl boronic acid, tridecyl boronic acid, tetradecyl boronic acid, pentadecyl boronic acid, hexadecyl boronic acid, heptadecyl boronic acid, octadecyl boronic acid, undecyl boronic acid, twentieth Boronic acid and its isomers, cyclopropylboronic acid, cyclobutylboronic acid, cyclopentylboronic acid, cyclohexylboronic acid, cycloheptylboronic acid, cyclooctylboronic acid, cyclononylboronic acid, cyclodecylboronic acid, ring Undecylboronic acid, cyclododecylboronic acid, cyclotridecylboronic acid, cyclotetradecylboronic acid, cyclopentadecylboronic acid, cyclohexadecylboronic acid, cyclohexadecylboronic acid, cyclooctadecylboronic acid, cyclo19 Boronic acid, cycloicosylboronic 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-decylboronic 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-hexadecylboronic acid, 2-oxa-octadecylboronic acid, 2-oxa-nonadecylboronic acid, 2-oxa-icosylboronic 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-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-hexadecylboronic acid, 2-aza-octadecylboronic acid, 2-aza-nonadecylboronic acid, 2-aza-icosylboronic acid and the like Isomers, 2-phospho-propylboronic acid, 2-phospho-butylboric acid, 2-phospho-hexylboronic acid, 2-phospho-heptylboronic acid, 2-phospho-octylboronic acid, 2 -Phosphino-nonylboronic acid, 2-Phosphate-decylboronic acid, 2-Phosphate-undecylboronic acid, 2-Phosphate-dodecylboronic acid, 2-Phosphlo-tridecylboronic acid, 2-Phosphorus Hetero-tetradecylboronic acid, 2-phospho hetero-pentadecylboronic acid, 2 -Phosphate-hexadecylboronic acid, 2-Phosphate-heptadecylboronic acid, 2-Phosphate-octadecylboronic acid, 2-Phosphate-nonadecylboronic acid, 2-Phosphate-icosylboronic acid and the like 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-thio-dodecylboronic acid, 2-thio-tridecylboronic acid, 2-sulfur Hetero-tetradecylboronic acid, 2-thia-pentadecylboronic acid, 2-thia-hexadecylboronic acid, 2-thia-heptadecylboronic acid, 2-thia-octadecylboronic acid, 2-sulfur Hetero-nonadecylboronic acid, 2-thia-eicosylboronic acid and these isomers. Examples of the compound that can be converted into the exemplified monoboric acid in the presence of water include salts of the monoboric acid.

R ¹ may be an aliphatic hydrocarbon group or may include a hetero atom such as oxygen, nitrogen, sulfur, or halogen. Considering the ease of acquisition and the like, it is preferable that R ¹ is an aliphatic hydrocarbon group not containing a hetero atom. The aliphatic hydrocarbon group is preferably a linear aliphatic hydrocarbon group having no branch. Thereby, the adsorptivity to a polarizing film becomes favorable, and the effect of improving optical performance becomes high. Moreover, as boric acid in which R ¹ is an aliphatic hydrocarbon group, specifically, methyl boric acid, ethyl boric acid, propyl boric acid, butyl boric acid, pentyl boric acid, hexyl boric acid, heptyl boric acid, octyl boric acid, Nonylboronic acid, decylboronic acid, undecylboronic acid, dodecylboronic acid, tridecylboronic acid, tetradecylboronic acid, pentadecylboronic acid, hexadecylboronic acid, heptylboronic acid, octadecylboronic acid, nineteen Boronic acid, eicosylboronic acid and its isomers, cyclopropylboronic acid, cyclobutylboronic acid, cyclopentylboronic acid, cyclohexylboronic acid, cycloheptylboronic acid, cyclooctylboronic acid, cyclononylboronic acid, cyclic Decylboronic acid, cycloundecylboronic acid, cyclododecylboronic acid, cyclotridecylboronic acid, cyclotetradecylboronic acid, cyclopentadecylboronic acid, cyclohexadecylboronic acid, cyclohexadecylboronic acid, cyclooctadecyl Boric acid, cyclononadecylboronic acid, cycloicosylboronic acid and the isomers thereof. Examples of the compound that can be converted into the exemplified monoboric acid in the presence of water include salts of the monoboric acid.

Specifically, R ^{1 is} preferably an alkyl group, and more preferably an alkyl group represented by the following formula (IV).

-C _n H _{2n + 1} (IV)

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

From the viewpoint of obtaining a polarizing film having extremely small shrinkage force at high temperatures and excellent optical properties, R ^{1 is} particularly preferably a saturated aliphatic hydrocarbon group having 2 to 5 carbon atoms.

As the monoboric acid represented by the formula (I), specifically, methylboronic acid, ethylboronic acid, propylboronic acid, butylboronic acid, pentylboronic acid, hexylboronic acid, heptylboronic acid, octylboronic acid, etc. Nonylboronic acid, decylboronic acid, undecylboronic acid, dodecylboronic acid, tridecylboronic acid, tetradecylboronic acid, pentadecylboronic acid, hexadecylboronic acid, heptylboronic acid, octadecylboronic acid, nineteen Boric acid, eicosylboronic acid, and these isomers are particularly preferred from the viewpoints of good adsorption of the aforementioned polarizing film and high effect of improving optical performance, propylboronic acid, butylboronic acid, pentyl Based boric acid. Examples of the compound that can be converted into the monoboric acid represented by the formula (I) in the presence of water include salts of the monoboric acid and the like.

The content of the boron element derived from the boron-containing compound (B) in the polarizing film of the present invention must be 0.1 to 3.0 parts by mass based on 100 parts by mass of 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 optical performance becomes insufficient. The content of the boron element is preferably 0.2 parts by mass or more, and more preferably 0.4 parts by mass or more. On the other hand, when the content of the boron element derived from the boron-containing compound (B) exceeds 3.0 parts by mass, productivity may be reduced, such as requiring a long processing time. In addition, although the reason is not clear, when the content of the boron element exceeds 3.0 parts by mass, poor formation of an iodine complex that absorbs short-wavelength light may occur, and the optical performance may be lowered, which is not preferable. The boron content is particularly preferably 2.0 parts by mass or less. The content of the boron element derived from the boron-containing compound (B) in the polarizing film can be obtained by ¹ H-NMR measurement.

The polarizing film of the present invention may further contain boric acid. As a result, the optical performance may be further improved. At this time, the total boron content in the polarizing film is preferably 0.2% by mass or more. Here, total boron The element content is a total amount of the boron element derived from the boron-containing compound (B), the boron element derived from the boric acid, and the boron element derived from the boron-containing compound (B) and the boron-containing compound other than the boric acid contained in the polarizing film. . On the other hand, when the total boron content in the polarizing film is too large, the shrinkage force of the polarizing film may increase. The total boron content in the polarizing film is generally 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 content in the polarizing film can be determined by ICP emission analysis or the like.

The degree of polymerization of PVA (A) contained in the polarizing film of the present invention is preferably in the range of 1,500 to 6,000, more preferably in the range of 1,800 to 5,000, and even more preferably in the range of 2,000 to 4,000. When the degree of polymerization is 1,500 or more, the durability of a 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 or a defect in process passability during film formation. In addition, the polymerization degree of PVA (A) in this specification means the average polymerization degree measured according to JIS K6726-1994.

From the viewpoint of the water resistance of the polarizing film obtained by uniaxially stretching the film, the saponification degree of the PVA (A) contained in the polarizing film of the present invention is preferably 95 mol% or more, and more preferably 96 mol. % Or more, more preferably 98 mol% or more. In addition, the degree of saponification of PVA in this specification refers to a structural unit (typically a vinyl ester unit) and a vinyl alcohol with respect to a structural unit (-CH ₂ -CH (OH)-) which can be converted into a vinyl alcohol unit (-CH ₂ -CH (OH)-) by saponification. The total number of moles of the unit is the ratio (mole%) of the moles of the vinyl alcohol unit in the PVA. This saponification degree can be measured according to the description of JIS K 6726-1994.

The manufacturing method of PVA (A) used by this invention is not specifically limited. Examples thereof include a method of converting a vinyl ester unit of a polyvinyl ester obtained by polymerizing a vinyl ester monomer into a vinyl alcohol unit. The vinyl ester monomer used in the production of PVA (A) is not particularly limited, and examples thereof include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, and trimethyl acetate Vinyl ester, vinyl neodecanoate, vinyl hexanoate, vinyl octoate, vinyl tallowate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, vinyl benzoate, etc. . From the viewpoint of economy, vinyl acetate is preferred.

The PVA (A) used in the present invention may be one in which a vinyl ester unit of a vinyl ester copolymer obtained by copolymerizing a vinyl ester monomer and other monomers copolymerizable therewith is converted into a vinyl alcohol unit. . Examples of other monomers copolymerizable with vinyl ester monomers include, for example, α-olefins having 2 to 30 carbon atoms, such as ethylene, propylene, 1-butene, and isobutylene; (meth) acrylic acid or a salt thereof; Methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate (Meth) acrylates such as tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, and octadecyl (meth) acrylate; (meth) Acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (methyl ) Acrylamide, (meth) acrylamide propanesulfonic acid or a salt thereof, (meth) acrylamide propyldimethylamine or a salt thereof, N-methylol (meth) acrylamide or a derivative thereof (Meth) acrylamide derivatives; N-vinylmethylamine, N-vinylacetamide, N-vinylpyrrolidone, etc .; methyl vinyl ether, ethyl vinyl ether, n- C Vinyl ethers such as vinyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, secondary butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; (meth) acrylonitrile Ethylene cyanide; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, difluoroethylene; allyl compounds such as allyl acetate, allyl chloride; maleic acid or its salts, esters or anhydrides; clothing Conic acid or its salt, ester or anhydride; ethylene silane compounds such as ethylene trimethoxysilane; unsaturated sulfonic acids and the like. The vinyl ester copolymer may have a structural unit derived from one or two or more of the other monomers. This other monomer can be used in advance when a vinyl ester monomer is supplied to a polymerization reaction, or it can be added to a reaction container during the polymerization reaction. From the viewpoint of optical performance, the content of units derived from other monomers is preferably 10 mol% or less, and more preferably 5 mol%, relative to the number of moles of the total structural unit constituting PVA (A). Hereinafter, it is more preferably 2 mol% or less.

From the viewpoint of improving the stretchability, it can also be stretched at a higher temperature, and can reduce the troubles such as elongation breakage during the production of polarizing films to further improve the productivity of polarizing films. Among the monomers to be polymerized, ethylene is preferred. When the PVA (A) contains an ethylene unit, the content ratio of the ethylene unit is preferably from the viewpoint of the elongation or elongation temperature described above to the mole number of the total structural unit constituting the PVA (A). 1 to 10 mole%, more preferably 2 to 6 mole%.

The PVA film used for producing the polarizing film of the present invention may contain a plasticizer in addition to the PVA (A) described above. Examples of preferred plasticizers include polyhydric alcohols. Specific examples include ethylene glycol, Glycerol, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like. Furthermore, one or two or more of these plasticizers may be contained. From the viewpoint of improving the elongation effect, glycerin is preferred among these.

The content of the plasticizer in the PVA film used for producing the polarizing film of the present invention is preferably within a range of 1 to 20 parts by mass, and more preferably 3 to 17 parts by mass, relative to 100 parts by mass of PVA (A). Within the range, it is more preferably within a range of 5 to 15 parts by mass. When the content is 1 part by mass or more, the stretchability of the film can be improved. On the other hand, when the content is 20 parts by mass or less, it is possible to suppress a decrease in handleability due to the film becoming too soft.

The PVA film used in the production of the polarizing film of the present invention may be appropriately blended with processing stabilizers such as fillers, copper compounds, weather-resistant stabilizers, colorants, ultraviolet absorbers, light stabilizers, antioxidants, and antistatics as needed Agents, flame retardants, other thermoplastic resins, lubricants, fragrances, defoamers, deodorants, extenders, release agents, mold release agents, reinforcing agents, cross-linking agents, mold inhibitors, preservatives, crystallization Additives other than PVA (A) such as speed retarder and plasticizer. The content of the other additives in the PVA film is usually 10% by mass or less, and preferably 5% by mass or less.

The swelling degree of the PVA film used for manufacturing 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 particularly preferably in the range of 180 to 220%. When the degree of swelling is 160% or more, the progress of crystallization can be extremely suppressed, and it can be stably extended to a high magnification. On the other hand, when the degree of swelling is 240% or less, It can dissolve during elongation, and can be extended even under higher temperature conditions.

The thickness of the PVA film used to manufacture 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, it tends to be prone to elongation breakage during uniaxial stretching processing for producing a polarizing film. When the PVA film is too thick, the uniaxial stretching process for producing a polarizing film tends to cause uneven stretching or the shrinking 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 depending on the purpose of the produced polarizing film and the like. In recent years, from the viewpoint of increasing the screen size of liquid crystal televisions and liquid crystal monitors, if the width of a PVA film used for producing a polarizing film is set to 3 m or more, it is suitable for these applications. On the other hand, if the width of a PVA film used for manufacturing a polarizing film becomes too large, it becomes difficult to uniformly uniaxially stretch it when manufacturing a polarizing film using a practical device. Therefore, PVA used for manufacturing a polarizing film The width of the film is preferably 10 m or less.

The manufacturing method of the PVA film used for manufacturing the polarizing film of the present invention is not particularly limited, and it is preferred to use a manufacturing method in which the thickness and width of the film after film formation are uniform. For example, a film-forming stock solution obtained by dissolving PVA (A) in a liquid medium and further dissolving one or more of the aforementioned plasticizer, the aforementioned other additives, and the below-mentioned surfactants can be used. , Or contain PVA (A), and further include plasticizers, other additives, surfactants, and liquid media as needed One or two or more of them are produced by melting PVA (A) into a film forming stock solution. When the film-forming dope contains at least one of a plasticizer, other additives, and a surfactant, it is preferred that these components be uniformly mixed.

Examples of the liquid medium used for the preparation of the film-forming dope include water, dimethylmethylene, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and ethylenediamine. Alcohol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, ethylenediamine, etc., and one of these or 2 or more. Among them, water is preferred from the viewpoint of environmental load or recyclability.

The volatile content of the film-forming stock solution (the content of the film-forming stock solution of the volatile components such as the liquid medium that is removed by volatilization or evaporation during film formation) varies depending on the film-forming method and film-forming conditions, but In general, it is preferably within a range of 50 to 95% by mass, and more preferably within a range of 55 to 90% by mass. Since the volatile content of the film-forming dope is 50% by mass or more, the viscosity of the film-forming dope will not become too high, and it can smoothly filter or defoam when preparing the film-forming dope. Easy. On the other hand, since the volatile content of the film-forming dope is 95% by mass or less, the concentration of the film-forming dope does not become excessively low, and industrial film manufacturing becomes easy.

The film-forming dope preferably contains a surfactant. By including a surfactant, the film-forming property can be improved and the occurrence of non-uniform thickness of the film can be suppressed. At the same time, the film can be easily peeled from the metal roller or belt used for film-making. When a PVA film is produced from a film-forming dope containing a surfactant, the film may contain a surfactant. Types of the aforementioned surfactants Although it does not specifically limit, From the viewpoint of peelability from a metal roll or a belt, an anionic surfactant or a nonionic surfactant is preferable.

Examples of the anionic surfactant include carboxylic acid types such as potassium laurate; sulfate types such as polyoxyethylene lauryl ether sulfate and octyl sulfate; and sulfonic acid types such as dodecylbenzenesulfonate.

Examples of nonionic surfactants are: alkyl ether types such as polyoxyethylene oleyl ether; alkylphenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; polyoxyethylene lauryl Alkylamines, such as amine ethers; Alkylamines, such as polyoxyethylene laurate; Polypropylene glycol ethers, such as polyoxyethylene polyoxypropylene ethers; Alkanols, such as diethanolammonium laurate and diethanolammonium oleate Phenamine type; allylphenyl ether type such as polyoxyallyl allyl phenyl ether and the like are suitable.

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

When the film-forming dope contains a surfactant, its content is preferably in the range of 0.01 to 0.5 parts by mass, and more preferably in the range of 0.02 to 0.3 parts by mass relative to 100 parts by mass of PVA (A) contained in the film-forming dope. Within the range, particularly preferred is in the range of 0.05 to 0.2 parts by mass. When the content is 0.01 parts by mass or more, film forming properties and peelability are further improved. On the other hand, when the content is 0.5 parts by mass or less, the surfactant overflows on the surface of the PVA film to cause adhesion, and it is possible to suppress a decrease in handleability.

Examples of the film forming method in the case of forming a PVA film using the above-mentioned film forming stock solution include a casting film forming method, an extrusion film forming method, a wet film forming method, and a gel film forming method. Film making party Only one method may be used, or two or more methods may be used in combination. Among these film forming methods, a cast film forming method and an extrusion film forming method are preferred from the viewpoint that a PVA film that can be used to produce a polarizing film having a uniform thickness and width and good physical properties can be obtained. The formed PVA film can be dried or heat-treated if necessary.

As an example of a specific manufacturing method of the PVA film used for manufacturing the polarizing film of the present invention, it is industrially preferable to use, for example, a T-slot die, a hopper plate, an I-die, a lip coater die, etc. The film-forming dope is uniformly discharged or cast on the peripheral surface of the heated first roller (or belt) in the rotation on the uppermost side, and is discharged or cast on the first roller (or belt). On one side of the film on the peripheral surface, the volatile components are evaporated and dried, and then the peripheral surface of one or more rotating heated rollers disposed on the downstream side is further dried or passed through. A method for further drying in a hot-air drying device, and then winding up by a winding device. The drying using a heated roller and the drying using a hot-air drying device may be appropriately combined and implemented. In addition, a layer including PVA (A) may be formed on one surface of a base film composed of a single resin layer, thereby forming a multilayer PVA film.

The method for producing the polarizing film of the present invention is not particularly limited. A suitable manufacturing method is a method for manufacturing a polarizing film, which is a method for manufacturing a polarizing film including a dyeing process of dyeing a PVA film with a dichroic pigment and a uniaxially stretching process for the film, including This film is immersed in an aqueous solution containing a boron compound (B). Examples include PVA films that are dyed and uniaxially stretched. Stretching treatment, and further methods such as swelling treatment, boric acid crosslinking treatment, fixing treatment, cleaning treatment, drying treatment, heat treatment, etc. if necessary. At this time, the order of each treatment such as a swelling treatment, a dyeing treatment, a boric acid crosslinking treatment, a uniaxial stretching treatment, and a fixing treatment is not particularly limited, and one or two or more treatments may be performed simultaneously. In addition, one or two or more treatments may be performed twice or more.

The swelling treatment can be performed by immersing a PVA film in water. The temperature of the water as the impregnated film is preferably in the range of 20 to 40 ° C, more preferably in the range of 22 to 38 ° C, and even more preferably in the range of 25 to 35 ° C. The time for immersion in water is, for example, preferably within a range of 0.1 to 5 minutes, and more preferably within a range of 0.2 to 3 minutes. The water used to impregnate the film 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 contacting a dichroic dye with a PVA film. As the dichroic dye, an iodine-based dye or a dichroic dye is generally used. The period of the dyeing process may be any stage before the uniaxial stretching process, during the uniaxial stretching process, or after the uniaxial stretching process. The dyeing treatment is generally performed by immersing a 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 within a range of 0.01 to 0.5% by mass, and the concentration of potassium iodide is preferably within a range of 0.01 to 10% by mass. The temperature of the dyeing bath is preferably 20 to 50 ° C, and particularly preferably 25 to 40 ° C. Suitable dyeing 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. ~ 10% by mass. If necessary, a dyeing aid may be used, and an inorganic salt such as sodium sulfate or a surfactant may be used. When sodium sulfate is used, it is preferably 0.1 to 10% by mass. The dyeing temperature is preferably 30 to 80 ° C. Specific dichroic dyes include CI Direct Yellow 28, CI Direct Orange 39, CI Direct Yellow 12, CI Direct Yellow 44, CI Direct Orange 26, CI Direct Orange 71, CI Direct Orange 107, and CI Direct Red 2 , CI Direct Red 31, CI Direct Red 79, CI Direct Red 81, CI Direct Red 247, CI Direct Green 80, CI Direct Green 59, etc., but it is preferably a dichroic dye developed for the manufacture of polarizing plates.

The PVA film may be subjected to a boric acid crosslinking treatment. In this case, it is possible to more effectively prevent the PVA (A) from eluting to water during wet stretching at a high temperature. From this viewpoint, the boric acid crosslinking treatment is preferably performed before the uniaxial stretching treatment. The boric acid crosslinking treatment can be performed by immersing a PVA film in an aqueous solution containing a boric acid crosslinking agent. As the boric acid crosslinking agent, one or two or more kinds of boron-containing inorganic compounds such as boric acid such as boric acid and 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% by mass. The concentration of the boric acid crosslinking agent is more preferably 0.2% by mass or more. The content is more preferably 4.0% by mass or less. When the concentration of the boric acid crosslinking agent is within the above range, elongation may be improved. When the concentration of the boric acid crosslinking agent is too high, it becomes difficult to contain the boron-containing compound (B) in the subsequent steps. Therefore, it is preferable that the concentration is not too high. The aqueous solution containing a boric acid crosslinking agent may also contain adjuvants, such as potassium iodide. The temperature of the aqueous solution containing a boric acid crosslinking agent is preferably in the range of 20 to 50 ° C, and particularly preferably in the range of 25 to 40 ° C.

Different from the uniaxial extension processing described below, During each treatment or between treatments, the PVA film is stretched (front stretched). As mentioned above, the total stretching magnification (the magnification obtained by multiplying the stretching magnifications in each processing) of the front stretching performed before the uniaxial stretching process is based on the optical performance of the obtained polarizing film, etc. The original length of the raw material PVA film before stretching is used as a reference, preferably 1.5 times or more, more preferably 2.0 times or more, and even more preferably 2.5 times or more. On the other hand, the total stretching ratio is preferably 4.0 times or less, and more preferably 3.5 times or less. The stretching ratio in the swelling treatment is preferably 1.05 to 2.5 times. The stretching ratio in the dyeing process is preferably 1.1 to 2.5 times. The stretching ratio in the boron crosslinking treatment is preferably 1.1 to 2.5.

The uniaxial stretching process can be performed by either a wet stretching method or a dry stretching method. In the case of a wet stretching method, stretching is performed in an aqueous solution. Stretching can also be performed in the above-mentioned dyeing bath or an aqueous boric acid solution. In the case of the dry stretching method, the uniaxial stretching process may be performed while maintaining room temperature, or the uniaxial stretching process may be performed while heating, or the uniaxial stretching process may be performed in the air using a water-absorbent PVA film. Among these, a wet stretching method is preferred, and a uniaxial stretching treatment is more preferably performed in an aqueous solution containing boric acid. The concentration of the boric acid in the boric acid aqueous solution is preferably in a range of 0.5 to 6 mass%, and more preferably in a range of 1 to 5 mass%. The boric acid aqueous solution may contain potassium iodide, and its concentration is preferably set in a 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 elongation 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 process is preferably 2.0 to 4.0 times. Derived from From the viewpoint of the optical performance of the optical film, the stretch ratio is more preferably 2.2 times or more. On the other hand, the stretching ratio is more preferably 3.5 times or less. From the viewpoint of the optical performance of the obtained polarizing film, the total stretching ratio up to the later-mentioned fixing process is based on the original length of the PVA film of the raw material before stretching, and is preferably 5 times or more, more preferably 5.5 times or more. The upper limit of the stretching magnification is not particularly limited, but the stretching magnification is preferably 8 times or less.

In the case of uniaxially stretching a long PVA film, the direction of uniaxially stretching is not particularly limited. Uniaxially stretching in a long direction, transverse uniaxially stretching, or so-called oblique stretching processing may be used, but From the viewpoint of obtaining a polarizing film having excellent optical properties, uniaxial stretching treatment in a long direction is preferred. The uniaxial stretching treatment in the long direction can be performed by using a stretching device having a plurality of rollers parallel to each other and changing the peripheral speed between the rollers. On the other hand, the horizontal uniaxial stretching process can be performed using a tenter type stretching machine.

When manufacturing a polarizing film, in order to strengthen the adsorption of a dichroic pigment (iodine-based pigment, etc.) on a PVA film, it is preferable to perform a fixing process after a uniaxial stretching process. As the fixed processing bath used for the fixed processing, an aqueous solution containing a boron-containing compound (B) is preferably used. Moreover, if necessary, boric acid, an iodine compound, a metal compound, etc. may be further added to a fixed processing bath. The temperature of the fixed treatment bath is preferably 10 to 80 ° C. The stretching magnification in the fixing process 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) can be adsorbed on a polarizing film in any one of a dyeing process, a boric acid crosslinking process, a uniaxial stretching process, and a fixing process. It is particularly preferable that the film is adsorbed during the fixing process after the uniaxial stretching process from the viewpoint of suppressing the breakage of the PVA film during the uniaxial stretching process. 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 from 0.05 to 15% by mass. When the concentration of the boron-containing compound (B) in the aqueous solution is lower than 0.05% by mass, the adsorption may be slowed, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more. On the other hand, when the concentration of the boron-containing compound (B) in the aqueous solution is higher than 15% by mass, the boron-containing compound (B) may be concentrated near the surface of the polarizing film. As a result, the optical properties of the obtained polarizing film may be increased. Risk of reduced performance. In addition, there is a possibility that precipitates of the boron-containing compound (B) are generated on the surface of the polarizing film. The concentration of the boron-containing compound (B) is more preferably 10% by mass or less, even more preferably 5.0% by mass or less, and particularly preferably 3.5% by mass or less. From the viewpoint of improving optical performance, the aqueous solution containing the boron-containing compound (B) is preferably an auxiliary agent containing iodide such as potassium iodide, and the concentration of the iodide is preferably 0.5 to 15% by mass. The temperature of the aqueous solution is preferably 10 to 80 ° C. If the temperature is too low, the boron compound (B) may be precipitated in the processing bath. The temperature of the aqueous solution is more preferably 15 ° C or higher, and still more preferably 20 ° C or higher. On the other hand, if the temperature is too high, it becomes difficult to easily manufacture it industrially under relatively mild conditions. The temperature of the aqueous solution is more preferably 70 ° C or lower, still more preferably 60 ° C or lower, and particularly preferably 45 ° C or lower. The time for immersion in an aqueous solution is preferably 5 to 400 seconds.

A suitable manufacturing method for the case where the boron-containing compound (B) is adsorbed to the polarizing film during the fixing treatment is: implementation in the order of swelling treatment, uniaxial stretching treatment, and fixing treatment; swelling treatment, boric acid treatment Performed in the order of joint treatment, uniaxial extension treatment, fixed treatment; or implemented in the order of swelling treatment, uniaxial extension treatment, fixed treatment, boric acid crosslinking treatment. After that, one or more treatments selected from the group consisting of a washing treatment, a drying treatment, and a heat treatment may be performed as necessary.

The cleaning treatment is generally performed by immersing the film in distilled water, pure water, an aqueous solution, or the like. At this time, from the viewpoint of 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 the viewpoint of economic efficiency, the temperature of the aqueous solution is too low to be unfavorable, and when the temperature of the aqueous solution is too high, the optical performance is reduced.

The conditions of the drying treatment are not particularly limited, and drying is preferably performed at a temperature in a range of 30 to 150 ° C, particularly in a 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 is easily obtained.

By performing the heat treatment after the drying treatment, a polarizing film having more excellent dimensional stability can be obtained. Here, the heat treatment is a process for further heating the 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, and the heat treatment is preferably performed in a range of 60 ° C to 150 ° C, and particularly in a range of 70 ° C to 150 ° C. If the heat treatment is performed at a temperature lower than 60 ° C, the dimensional stabilization effect due to the heat treatment is insufficient. If the heat treatment is performed at a temperature higher than 150 ° C, the polarizing film may have a strong red discoloration.

It is preferable that the polarizing film of the present invention obtained as described above has a transmittance of 42.0% or more and a polarization degree of 99.9% or more. When the transmittance of the polarizing film is less than 42.0%, the brightness of the obtained LCD may become insufficient. The transmittance is more preferably 43.0% or more, and even more preferably 43.5% or more. On the other hand, this transmittance is usually 45% or less. In addition, when the polarization degree of the polarizing film is 99.9% or more, an LCD panel with high image quality can be obtained. The transmittance and degree of polarization of the polarizing film were measured by a method described in Examples described later.

The polarizing film of the present invention is usually used as a polarizing plate by bonding a protective film that is optically transparent and has mechanical strength on both sides or one side. As the protective film, cellulose triacetate (TAC) film, acetic acid. Cellulose butyrate (CAB) film, acrylic film, polyester film, and the like are used. Examples of the adhesive for bonding include PVA-based adhesives and UV curing adhesives.

The polarizing plate obtained as described above may be bonded to a retardation film, a viewing angle enhancement film, a brightness enhancement film, or the like. In addition, the polarizing plate can be used as a part of an LCD after being adhered to a glass substrate after applying an adhesive such as acrylic.

[Example]

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

[Measurement of content of boron element derived from boron-containing compound (B) with respect to 100 parts by mass of PVA (A)]

The polarizing film was dissolved in heavy water to 0.003% by mass, and then concentrated to a 0.15% by mass solution using a rotary evaporator, and this was used as a ¹ H-NMR measurement sample. ¹ H-NMR (JNM-AL400: 400 MHz, manufactured by Japan Electronics Co., Ltd.) was measured at 80 ° C., and the number of accumulations was set to 256 times. The analysis was performed using the following method using ALICE2 (manufactured by Japan Electronics Co., Ltd.). Regarding the ¹ H-NMR spectrum obtained by the measurement, after adjusting the phase to smooth the baseline, the average point was set to 20 to automatically correct the baseline. Next, as a reference, the position where the peak value of the heavy water in the measurement solvent was 4.65 ppm was automatically set. Thereafter, as shown in FIG. 1, the hydrogen peak of the hydrocarbon group contained in the boron-containing compound (B) is integrated, and its peak area (area A) is obtained. At this time, the area of the hydrogen peaks of the hydrocarbon groups contained in the boron-containing compound (B) which does not overlap with the hydrogen peak derived from PVA (area B) is set as a reference for the peak area, and is set to the boron-containing compound ( B) The appropriate number of hydrogens in the hydrocarbon group and the value of the area B are the same. Next, a hydrogen peak in the range of 1.6 ppm to 2.4 ppm is considered to be contained in a boron-containing compound (B) which is a hydrogen peak of a methylene group derived from PVA and a hydrogen peak of a methylene group derived from PVA. The total of the hydrogen peaks of the hydrocarbyl groups was used to determine the peak area (area C). Thereafter, the area D is calculated by subtracting the hydrogen number of the hydrocarbon group of the boron-containing compound (B) that overlaps the hydrogen peak of the methylene derived from PVA from the area C. The numerical values obtained by these methods are substituted into the following formula (1) to calculate the boron element content (parts by mass) derived from the boron-containing compound (B) with respect to 100 parts by mass of the PVA (A). In addition, X in the following formula (1) is the number of hydrogens in the hydrocarbon group contained in the boron-containing compound (B) which does not overlap with the peak of PVA, and Y is the number of boron per molecule of the boron-containing compound (B). In addition, the formula (1) is a formula used when an unmodified PVA is used, and when the modified PVA is used as a raw material, the formula (1) must be appropriately deformed.

Content (parts by mass) of boron element derived from boron-containing compound (B) with respect 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 molecular weight per mole of repeating units of unmodified PVA. In addition, the ¹ H-NMR spectrum of FIG. 1 is a measurement of the polarizing film of Example 1.

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

The mass [E (g)] of the polarizing film was measured, and the polarizing film was dissolved in 20 mL of distilled water at 0.005% by mass. An aqueous solution in which the polarizing film was dissolved was used as a measurement sample, and its mass [F (g)] was measured. Thereafter, a polymorphic ICP emission analysis device (ICP) manufactured by Shimadzu Corporation was used to measure the boron concentration [G (ppm)] of the measurement sample. Thereafter, the value calculated by substituting the value into the following formula (2) is taken as the total boron content (mass%) in the polarizing film.

Total boron content in the polarizing film (% by mass) = [(G × 10 ^-6 × F) / E] × 100 (2)

[Optical properties of polarizing film]

(1) Measurement of transmittance Ts

From the central portion of the polarizing films obtained in the following examples or comparative examples, samples of two polarizing films with an extension direction of 4 cm and a width direction of 2 cm were taken, and a spectrophotometer with an integrating sphere ("V7100", manufactured by JASCO Corporation) was used. "), According to JIS Z 8722 (method for measuring the color of an object), The visibility of the C light source and the visible light region with a 2 ° field of view is corrected. For one sample, the transmittance of the light in the case of + 45 ° tilt in the longitudinal direction and the light transmittance of -45 ° in the longitudinal direction are measured. The average value Ts1 (%). The same was done for the other sample, and the transmittance of light in the case of + 45 ° inclination and the transmittance of light in the case of -45 ° inclination were measured, and the average Ts2 (%) of these was obtained. Ts1 and Ts2 are averaged by the following formula (3), and the transmittance Ts (%) of the polarizing film is used.

Ts = (Ts1 + Ts2) / 2 (3)

(2) Measurement of polarization degree V

Using a spectrophotometer with an integrating sphere ("V7100" manufactured by Japan Spectroscopy Co., Ltd.) in accordance with JIS Z 8722 (measurement method of object color), the visibility correction of the C light source and the visible light region with a 2 ° field of view was corrected. For two samples used for the measurement of the transmittance Ts, the transmittance T⊥ (%) of the light in the case where the extending directions are orthogonal to each other and overlapping, and the transmittance T of the light in the case where the extending directions are parallel and overlapping are measured. // (%). The measured T // (%) and T⊥ (%) were substituted into the following formula (4), and the polarization degree V (%) was calculated.

V = ((T //-T⊥) / (T // + T⊥)) ^1/2 × 100 (4)

(3) dichroism ratio (DC) in 650nm

The dichroism ratio at each wavelength of the polarizing film was measured using a spectrophotometer ("V7100" manufactured by JASCO Corporation) with a integrating sphere equipped with a Glan-Taylor polarizer. From the central portion of the obtained polarizing film, one piece of polarizing film was taken in an extension direction of 4 cm and a width direction of 2 cm. In the range of wavelengths from 380nm to 780nm, the samples were measured for MD transmittance and TD transmittance, and based on the following formula (5), the dichroic ratio at each wavelength was calculated. Here, "MD transmittance" means the transmittance when the direction of the polarized light generated from the Glan-Taylor polarizer is made parallel to the transmission axis of the polarizer sample. The "TD transmittance" indicates the transmittance when the direction of the polarized light generated from the Glan-Taylor polarizer is orthogonal to the transmission axis of the polarizer sample. In this embodiment, a dichroic ratio of 650 nm is used as an index of optical performance.

DC = (log ₁₀ (TD transmittance / 100)) / (log ₁₀ (MD transmittance / 100)) (5)

[Shrink force of polarizing film]

The shrinkage force was measured using an autograph "AG-X" with a thermostatic bath made by Shimadzu Corporation and an image type extensometer "TR ViewX120S". The measurement system used a polarizing film that was humidity-controlled at 20 ° C / 20% RH for 18 hours. After setting the thermostat of the Autograph "AG-X" to 20 ° C, install a polarizing film (15 cm in the length direction and 1.5 cm in the width direction) in a jig (clamp interval of 5 cm), and start the temperature increase of the thermostat while starting stretching To 80 ° C. The polarizing film was stretched at a speed of 1 mm / minute, and the stretching was stopped when the tension reached 2N, and the tension was measured in this state until 4 hours later. At this time, the thermal expansion will change the distance between the fixtures. Therefore, attach a line sticker to the fixture, and use the video type extensometer "TR ViewX120S" to make the distance between the fixtures a certain distance to the line sticker attached to the fixture. The amount of movement is corrected while measuring. Furthermore, the tension pole is generated at the beginning of the measurement (within 10 minutes from the start of the measurement). When the value is small, the minimum value of the tension is subtracted from the measured value of the tension after 4 hours, and the difference is taken as the shrinkage force of the polarizing film.

[Swelling degree of PVA film]

The PVA film was cut into 5 cm × 10 cm and immersed in 1000 mL of distilled water at 30 ° C. for 30 minutes. After that, the PVA film was taken out, and the water on the surface of the PVA film was wiped with filter paper, and the mass (mass H) of the PVA film after the immersion was measured. Then, the PVA film was put into a dryer at 105 ° C., and after drying for 16 hours, the mass (mass I) of the PVA film after drying was measured. The degree of swelling of a PVA film is calculated by substituting the values of mass H and mass I in the following formula (6).

Swelling (%) = (mass H / mass I) × 100 (6)

[Example 1]

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

From the central portion in the width direction of the PVA film obtained as described above, a sample having a width of 5 cm × a length of 9 cm was cut so that a range of 5 cm × 5 cm in length could be uniaxially stretched. The sample was immersed in pure water at 30 ° C for 30 seconds, and uniaxially extended 1.1 times in the length direction. Instead, a swelling treatment is performed. Next, it was immersed in an aqueous solution (dyeing treatment bath) (temperature: 30 ° C.) containing 0.04% by mass of iodine and 4.0% by mass of potassium iodide (KI) for 60 seconds, and uniaxially extended 2.2 times in the lengthwise direction (2.4 times overall). Allow iodine to adsorb. Furthermore, it was immersed in an aqueous solution (crosslinking treatment bath) containing 3.0% by mass of boric acid and 3% by mass of potassium iodide (temperature: 30 ° C.) for 45 seconds, and uniaxially extended 1.2 times in the longitudinal direction (total 2.7 times) so Boric acid adsorption. Then, it was immersed in an aqueous solution (elongation treatment bath) (temperature 60 ° C.) containing 4.0% by mass of boric acid and 6.0% by mass of potassium iodide, and uniaxially stretched 2.2 times (6.0 times as a whole) in the longitudinal direction and aligned. Thereafter, it was immersed in an aqueous solution (fixed treatment bath) (temperature: 30 ° C.) containing 1.0% by mass of n-propylborate and 4.0% by mass of potassium iodide for 100 seconds. During the fixing process, the PVA film was not stretched (elongation ratio 1.0 times). Finally, it was dried at 60 ° C for 4 minutes to produce a polarizing film.

The ¹ H-NMR of the obtained polarizing film was measured and analyzed. As a result, a hydrogen peak of n-propylboronic acid that did not overlap with a hydrogen peak derived from PVA appeared at 1.1 to 1.3 ppm. Therefore, the peak area (area B) Set to 5. Next, the peak area (area C) of the hydrogen of the methylene group of the PVA which has a peak in the range of 1.6 to 2.4 ppm was calculated. The hydrogen peak of the methylene group of PVA overlaps with the hydrogen peak of the C2 hydrocarbon group of n-propylboronic acid, so the area D is obtained by subtracting the hydrogen number 2 of the C2 hydrocarbon group of n-propylboronic acid from the area C. When these values were substituted into the aforementioned formula (1), the content of the boron element derived from the boron-containing compound (B) was 1.5 parts by mass based on 100 parts by mass of the PVA (A). The total boron content in the polarizing film was measured and found to be 3.4% by mass.

The optical properties of the obtained polarizing film were measured. As a result, The emissivity is 44.14%, the polarization is 99.96%, and the dichroism ratio is 83.88. Moreover, when the shrinkage force of the obtained polarizing film was measured, it was 4.8N. These results are also shown in Table 1. A graph obtained by plotting the degree of polarization with respect to the shrinkage force of the polarizing film is shown in FIG. 2.

[Example 2]

Except that the time for immersion in the fixed treatment bath was changed to 300 seconds, a polarizing film was produced in the same manner as in Example 1, and each measurement and each evaluation were performed by the above-mentioned method. The results are shown in Table 1 and FIG. 2.

[Example 3]

For the fixed treatment bath, an aqueous solution (temperature: 30 ° C.) containing 1.0% by mass of n-butylboric acid and 3.0% by mass of potassium iodide was used, and a polarizing film was produced in the same manner as in Example 1 except for the above method Each measurement and each evaluation. The results are shown in Table 1 and FIG. 2.

[Example 4]

For the fixed treatment bath, an aqueous solution (temperature: 30 ° C.) containing 0.5% by mass of n-butylboric acid and 3.5% by mass of potassium iodide was used, and a polarizing film was produced in the same manner as in Example 1 except for the above method. Each measurement and each evaluation. The results are shown in Table 1 and FIG. 2.

[Example 5]

For the fixed treatment bath, an aqueous solution (processing temperature 30 ° C) containing a ratio of 0.5% by mass of n-pentylboric acid and 3.0% by mass of potassium iodide was used. Other than that, it carried out similarly to Example 1, produced the polarizing film, and performed each measurement and each evaluation by the method mentioned above. The results are shown in Table 1 and FIG. 2.

[Example 6]

For the fixed treatment bath, an aqueous solution containing 1.0% by mass of methyl boric acid and 2.0% by mass of potassium iodide (treatment temperature 30 ° C) was used, and the time for immersion in the fixed treatment bath was changed to 10 seconds. Example 1 was performed in the same manner, a polarizing film was produced, and each measurement and each evaluation were performed by the methods described above. The results are shown in Table 1 and FIG. 2.

[Example 7]

For the extension treatment bath, an aqueous solution (temperature: 62 ° C.) containing 0.5% by mass of n-propyl boric acid, 4.0% by mass of boric acid, and 5.2% by mass of potassium iodide was used. For the fixed treatment bath, an aqueous solution containing 3.0% by mass of potassium iodide was used ( The temperature was 30 ° C) and the time for immersion in the fixed treatment bath was changed to 5 seconds. A polarizing film was produced in the same manner as in Example 1, and each measurement and evaluation were performed by the above-mentioned method. The results are shown in Table 1 and FIG. 2.

[Comparative Example 1]

The fixed treatment bath was produced in the same manner as in Example 1 except that an aqueous solution (temperature: 10 ° C.) containing 1.0% by mass of n-butylboric acid was used, and the time for immersion in the fixed treatment bath was 20 seconds. The polarizing film was subjected to each measurement and evaluation by the above method. this In the measurement of the content of boron derived from the boron-containing compound (B) with respect to 100 parts by mass of PVA (A), the number of accumulations cannot be detected because the number of accumulations was 256 times, so the number of accumulations was changed to 4096 times, the content of the boron element derived from the boron-containing compound (B) was measured with respect to 100 parts by mass of the PVA (A). The results are shown in Table 1 and FIG. 2.

[Comparative Example 2]

As for the fixed treatment bath, an aqueous solution (temperature: 30 ° C.) containing 1.0% by mass of phenylboric acid and 1.0% by mass of potassium iodide was used, and a polarizing film was produced in the same manner as in Example 1 except for the above methods. Measurement and evaluation. The results are shown in Table 1 and FIG. 2.

[Comparative Example 3]

For the fixed treatment bath, an aqueous solution (temperature: 30 ° C.) containing 2.0% by mass of boric acid and 2.5% by mass of potassium iodide was used, except that a polarizing film was produced, and each measurement and Each evaluation. The results are shown in Table 1 and FIG. 2.

[Comparative Example 4]

For the fixed treatment bath, an aqueous solution (temperature: 30 ° C.) containing 1.0% by mass of boric acid and 2.0% by mass of potassium iodide was used, except that a polarizing film was produced, and each measurement and Each evaluation. The results are shown in Table 1 and FIG. 2.

[Comparative Example 5]

For the fixed treatment bath, an aqueous solution (temperature: 30 ° C.) containing 0.5% by mass of boric acid and 2.0% by mass of potassium iodide was used, and a polarizing film was produced in the same manner as in Example 1, and each measurement and Each evaluation. 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 process was not performed, and each measurement and each evaluation were performed by the above method. The results are shown in Table 1 and FIG. 2.

[Comparative Example 7]

For the fixed treatment bath, a polarizing film was produced in the same manner as in Example 1 except that an aqueous solution (temperature: 30 ° C.) containing potassium iodide in a proportion of 2.0% by mass was used, and the time for immersion in the fixed treatment bath was 5 seconds. Each measurement and each evaluation were performed by the method mentioned 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 time for immersion in the fixed treatment bath was 10 seconds, and each measurement and evaluation were performed by the methods described above. 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 time for immersion in the fixed treatment bath was 20 seconds. Each measurement and each evaluation were performed by the method. The results are shown in Table 1 and FIG. 2.

In addition, Examples 2 to 7 and Comparative Examples 1 to 9 used an aqueous solution (temperature: 30 ° C.) containing iodine and potassium iodide in a mass ratio of 1: 100 as a dyeing treatment bath. At this time, the concentration of iodine or potassium iodide in the dyeing treatment bath is adjusted so that the transmittance of the polarized film after drying becomes 43.8% to 44.2%.

FIG. 2 is a graph obtained by plotting the contraction force on the horizontal axis and the polarization degree on the vertical axis of the polarizing films of Examples 1 to 7 and Comparative Examples 1 and 3 to 9. FIG. As shown in FIG. 2, the polarizing films of Examples 1 to 7 that meet the requirements of the present invention have small shrinkage force at high temperatures and excellent optical properties. On the other hand, a polarizing film (Comparative Example 1) having a boron element content of less than 0.1 parts by mass derived from the boron-containing compound (B) has a high shrinkage force. A polarizing film (Comparative Example 2) containing phenylboric acid as a boron element compound has high shrinkage force and insufficient optical performance, and it goes beyond the range of the graph downward. In the fixed treatment bath, when an aqueous solution containing boric acid and potassium iodide is used (Comparative Examples 3 to 5), the reduction of the boric acid concentration in the aqueous solution causes the total boron content in the polarizing film to be reduced, thereby reducing the shrinkage force, but the optical performance Reduce, it is difficult to have both. When the fixing process is not performed (Comparative Example 6), the shrinking force of the polarizing film is significantly high. Moreover, when the aqueous solution containing potassium iodide was used for the fixed processing bath (Comparative Examples 7 to 9), the optical performance of the polarizing film was insufficient. As described above, when the requirements of the present invention are not satisfied (Comparative Examples 1 to 9), it is difficult to have both shrinkage characteristics and optical performance.

Claims (6)

A polarizing film comprising polyvinyl alcohol (A) and at least one selected from the group consisting of a monoboric acid represented by the following formula (I) and a compound capable of being converted into the monoboric acid in the presence of water Of the boron-containing compound (B) polarizing film, and the content of 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 polyvinyl alcohol (A); [In the formula (I), R ¹ is a monovalent aliphatic group having 1 to 20 carbon atoms, and R ¹ and a boric acid group are connected by a boron-carbon bond]. The polarizing film of claim 1, wherein R ¹ is a saturated aliphatic group. The polarizing film according to claim 1 or 2, wherein R ¹ is an aliphatic hydrocarbon group. For example, the polarizing film of claim 1 or 2, wherein the carbon number of R ¹ is 2 to 5. For example, the polarizing film of claim 1 or 2 has a transmittance of 42.0% or more and a polarization degree of 99.9% or more. A method for producing a polarizing film according to any one of claims 1 to 5, which is a polarizing film including a dyeing treatment in which a polyvinyl alcohol film is dyed with a dichroic dye, and a stretching treatment in which the film is uniaxially stretched. The manufacturing method of a thin film has the process of immersing this thin film in the aqueous solution of a boron compound (B).