TWI795515B - Polarizing film and method for producing same - Google Patents

Abstract

The present invention is a polarizing film comprising polyvinyl alcohol (A) and one selected from the group comprising monoboric acid represented by the following formula (I) and a compound that can be converted into the monoboric acid in the presence of water A polarizing film of at least one boron-containing compound (B), wherein 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). The polarizing film has small shrinkage force at high temperature and excellent optical properties.

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

Description

Polarizing film and manufacturing method thereof

The invention relates to a polarizing film with low shrinkage force at high temperature and excellent optical performance and its manufacturing method.

Polarizing plates with light transmission and shielding functions, and liquid crystals that change the polarization state of light are the basic components of liquid crystal displays (LCDs). In order to prevent the fading of the polarizing film and the shrinkage of the polarizing film, most polarizing plates have a structure in which a protective film such as triacetate cellulose (TAC) film is attached to the surface of the polarizing film, and as the polarizing film constituting the polarizing plate, the mainstream A substrate obtained by uniaxially stretching a polyvinyl alcohol film (hereinafter, "polyvinyl alcohol" may be referred to as "PVA") to adsorb iodine dyes (I ₃ ^- or I ₅ ^-, etc.).

LCD is widely used in small devices such as computers and watches, smart phones, notebook computers, LCD monitors, liquid crystal color projectors, LCD TVs, car navigation systems, and measuring equipment used indoors and outdoors. These machines are required to be thin and high-definition. Along with the above, in recent years, the thinning of glass used in LCDs and the high stretching ratio of polarizing films have progressed, and as a result, generation of warping of LCD panels has become a problem. It is said that the warping master of LCD panels The main reason is that the polarizing film shrinks at high temperature, so it is necessary to have a polarizing film with high optical performance and small shrinkage force at high temperature.

As a means of improving the optical performance of a polarizing film, a method of using PVA with a high degree of polymerization is known (for example, Patent Document 1). However, by using PVA with a high degree of polymerization, although the optical performance of the polarizing film is improved, the shrinkage force is increased, and it is difficult to have both.

Patent Document 2 describes that by reducing the amount of boric acid in the PVA film and setting a step of drying the PVA film between the boric acid treatment step and the water washing step, a polarizing film with low shrinkage force at high temperature and good color tone can be 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 Art Literature] [Patent Document]

Patent Document 1: Japanese Patent Application Laid-Open No. 01-084203

Patent Document 2: Japanese Patent Laid-Open No. 2013-148806

The present invention was made in order to solve the above-mentioned problems, and an object of the present invention is to provide a polarizing film having a small shrinkage force at high temperature and having excellent optical properties.

The above problems are solved by providing a polarizing film comprising PVA (A), and a compound selected from 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 of a boron-containing compound (B), wherein 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 PVA (A).

[式(I)中，R¹係碳數為1~20之1價脂肪族基，且R¹與硼酸基以硼-碳鍵連接。]

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

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

The above-mentioned problems are solved by providing a method of manufacturing the aforementioned polarizing film, which is a method of manufacturing a polarizing film including dyeing a PVA film with a dichroic dye and stretching the film in a uniaxial stretching process. , which has a treatment of immersing the thin film in an aqueous solution of a boron-containing compound (B).

The polarizing film of the present invention has small shrinkage force at high temperature and excellent optical properties. Therefore, by using the polarizing film of the present invention, it is possible to obtain a high-quality LCD panel that does not easily warp at high temperatures. Also, according to the production method of the present invention, such a polarizing film can be produced.

1‧‧‧Hydrogen peak derived from deuterium water as the determination solvent

2‧‧‧Hydrogen peak derived from the methine of PVA

3‧‧‧Hydrogen peak derived from the methylene group of PVA

4‧‧‧The hydrogen peak derived from the hydrocarbon group contained in the boron-containing compound (B) overlapped with the hydrogen peak derived from PVA

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

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

Fig. 2 is for embodiment 1～7 and comparative example 1 and 3～9 bias A graph obtained by plotting shrinkage force on the abscissa and polarization degree on the ordinate for the optical film.

[Mode of Implementing the Invention]

The polarizing film of the present invention is a polarizing film comprising PVA (A) and selected from the group comprising monoboric acid represented by the following formula (I) and a compound that can be converted into the monoboric acid in the presence of water A polarizing film of at least one boron-containing compound (B), wherein 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 PVA (A). By cross-linking PVA (A) with boron-containing compound (B), the shrinkage force at high temperature can be reduced, and the optical performance can be improved at the same time. Here, in the formula (I), R ¹ is a monovalent aliphatic group with 1 to 20 carbon atoms, and R ¹ is connected to a boronic acid group by a boron-carbon bond.

Monoboronic acid is a compound represented by the above formula (I), and has one boronic acid group [-B(OH) ₂ ] in one molecule. The boronic acid group has a structure in which a boron atom bonded to two hydroxyl groups is bonded to a carbon atom. In the compound shown in formula (I), ^R1 and the boronic acid group are connected by a boron-carbon bond. Compared with the boron atom in boric acid [B(OH) ₃ ], which is bonded to three hydroxyl groups, the boric acid group is different in the point of having a boron-carbon bond. As a boron-containing group which can be converted into a boronic acid group in the presence of water, the following borate ester group is mentioned as a representative thing, but it is not limited to this.

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

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

Monoboronic acid has 2 hydroxyl groups that can react with the hydroxyl groups of PVA to form an ester, and the PVA chains are properly cross-linked. This crosslinking is stable to heat, so the shrinkage force of the polarizing film becomes smaller at high temperature. Thereby, the LCD panel using a polarizing film can be suppressed from warping at high temperature. In addition, it is considered that the alignment state of the PVA chains becomes better through proper cross-linking of the PVA chains, and the optical performance of the polarizing film is improved.

In the above formula (I), R ¹ is a monovalent aliphatic group with 1 to 20 carbon atoms. By making R ¹ 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 at most 10, more preferably at most 6, even more preferably at most 5. On the other hand, the carbon number of R ¹ is preferably 2 or more, and more preferably 3 or more, from the viewpoint of a particularly excellent balance between the optical performance and shrinkage force of the polarizing film.

In the above formula (I), as long as R ¹ is a monovalent aliphatic group, and R ¹ and the boronic acid group are connected by a boron-carbon bond. R ¹ may be a saturated aliphatic group or an unsaturated aliphatic group, but is preferably the former. When R ¹ is a saturated aliphatic group, coloring of the obtained polarizing film can be suppressed and durability can be improved. In addition, when R ¹ is a saturated aliphatic group, the alignment of the dichroic dye can be improved, and the optical performance can be further improved. In addition, the unsaturated aliphatic group has carbon-carbon double bond or carbon-carbon triple bond, carbon-oxygen double bond, carbon-nitrogen double bond, nitrogen-nitrogen double bond, carbon-sulfur double bond, etc. An aliphatic group having a structure of two or more multiple bonds, and a saturated aliphatic group are aliphatic groups having a structure of only a single bond. Examples of monoboronic acid in which R ^is 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, Base 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, ninedecyl boronic acid, twenty Boronic acid and its isomers, cyclopropylboronic acid, cyclobutylboronic acid, cyclopentylboronic acid, cyclohexylboronic acid, cycloheptylboronic acid, cyclooctylboronic acid, cyclononylboronic acid, cyclodecylboronic acid, cyclodecylboronic acid, Undecylboronic acid, cyclododecylboronic acid, cyclotridecylboronic acid, cyclotetradecylboronic acid, cyclopentadecylboronic acid, cyclohexadecylboronic acid, cycloheptadecylboronic acid, cyclooctadecylboronic acid, cycloninedecylboronic acid Boronic acid, cycloeicosylboronic acid and their isomers, 2-oxa-propylboronic acid, 2-oxa-butylboronic acid, 2-oxa-hexylboronic acid, 2-oxa-heptylboronic acid , 2-oxa-octylboronic acid, 2-oxa-nonylboronic acid, 2-oxa-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-heptadecylboronic acid, 2- Oxa-octadecylboronic acid, 2-oxa-nonadecylboronic acid, 2-oxa-eicosylboronic acid and their isomers, 2-aza-propylboronic acid, 2-aza-butane Boronic acid, 2-aza-hexylboronic acid, 2-aza-heptylboronic acid, 2-aza-octylboronic acid, 2-aza-nonylboronic acid, 2-aza-decylboronic acid, 2-aza-octylboronic acid Hetero-undecylboronic acid, 2-aza-dodecylboronic acid, 2-aza-tridecylboronic acid, 2-aza-tetradecylboronic acid, 2-aza-pentadecylboronic acid, 2-aza Hexadecylboronic acid, 2-aza-heptadecylboronic acid, 2-aza-octadecylboronic acid, 2-aza-nonadecylboronic acid, 2-aza-eicosylboronic acid and other iso- Constructs, 2-phospha-propylboronic acid, 2-phospha-butylboronic acid, 2-phospha-hexylboronic acid, 2-phospha-heptylboronic acid, 2-phospha-octylboronic acid, 2-phosphorus Hetero-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-octadecylboronic acid, 2-phospha- Nonadecylboronic acid, 2-phospha-eicosylboronic acid and its 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 Boronic acid, 2-thia-tridecylboronic acid, 2-thia-tetradecylboronic acid, 2-thia-pentadecylboronic acid, 2-thia-hexadecylboronic acid, 2-thia-heptadecylboronic acid Boronic acid, 2-thia-octadecylboronic acid, 2-thia-nonadecylboronic acid, 2-thia-eicosylboronic acid and these isomers, etc. Moreover, the salt etc. of the said monoboric acid are mentioned as a compound convertible into the monoboric acid shown in the presence of water.

R ¹ can be an aliphatic hydrocarbon group, and can also contain heteroatoms such as oxygen, nitrogen, sulfur, and halogen. In consideration of ease of acquisition, etc., R ¹ is preferably an aliphatic hydrocarbon group not containing a heteroatom. As the aliphatic hydrocarbon group, an unbranched straight-chain aliphatic hydrocarbon group is preferable. Thereby, the adsorption property to the polarizing film becomes good, and the effect of improving optical performance becomes high. Furthermore, as the boronic acid in ^which R is an aliphatic hydrocarbon group, specifically, 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, Ninedecylboronic Acid Boronic acid, eicosylboronic acid and their isomers, cyclopropylboronic acid, cyclobutylboronic acid, cyclopentylboronic acid, cyclohexylboronic acid, cycloheptylboronic acid, cyclooctylboronic acid, cyclononylboronic acid, cyclo Decylboronic acid, cycloundecylboronic acid, cyclododecylboronic acid, cyclotricylboronic acid, cyclotetradecylboronic acid, cyclopentadecylboronic acid, cyclohexadecylboronic acid, cycloheptadecylboronic acid, cyclooctadecylboronic acid Boronic acid, cyclononadecanylboronic acid, cycloeicosylboronic acid and their isomers, etc. Moreover, the salt etc. of the said monoboric acid are mentioned as a compound convertible into the monoboric acid shown in the presence of water.

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

-C _n H _2n+1 (IV)

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

^R1 is particularly preferably a saturated aliphatic hydrocarbon group having 2 to 5 carbons from the viewpoint of obtaining a polarizing film with extremely small shrinkage force at high temperature and excellent optical properties.

As the monoboronic acid represented by the above formula (I), specifically, 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, Ninedecylboronic Acid Boronic acid, eicosylboronic acid, and their isomers are particularly preferred to be propylboronic acid, butylboronic acid, pentylboronic acid, and pentylboronic acid from the viewpoint of good adsorption to the aforementioned polarizing film and a high effect of improving optical properties. Boronic acid. Moreover, as a compound which can be converted into the monoboric acid represented by said formula (I) in presence of water, the salt of this monoboric acid etc. are mentioned.

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 relative to 100 parts by mass of PVA (A). When content of the boron element originating in a boron-containing compound (B) is less than 0.1 part by mass, the effect of improving optical performance will become insufficient. The content of the boron element is preferably at least 0.2 parts by mass, more preferably at least 0.4 parts by mass. On the other hand, when the content of the boron element derived from the boron-containing compound (B) exceeds 3.0 parts by mass, there is a possibility that productivity such as long processing time may be reduced. Also, although the reason is not clear, when the content of the boron element exceeds 3.0 parts by mass, poor formation of iodine complexes that absorb short-wavelength light may occur, and optical performance may decrease, which is not preferable. The content of the boron element 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 measured by ¹ H-NMR.

The polarizing film of the present invention may further contain boric acid. Thereby, optical performance may be further improved. At this time, the total boron element content in the polarizing film is preferably at least 0.2% by mass. Here, total boron The element content is the total amount of the boron element derived from the boron-containing compound (B), the boron element derived from boric acid, and the boron element derived from the boron-containing compound (B) and boron-containing compounds other than boric acid contained in the polarizing film . 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 element content in the polarizing film is usually 5.5% by mass or less, preferably 5.0% by mass or less, more preferably 4.5% by mass or less, and more preferably 4.0% by mass or less. The total boron element content in the polarizing film can be obtained by ICP emission analysis or the like.

The degree of polymerization of the PVA(A) contained in the polarizing film of the present invention is preferably in the range of 1,500-6,000, more preferably in the range of 1,800-5,000, and even more preferably in the range of 2,000-4,000. When the degree of polymerization is 1,500 or more, the durability of a polarizing film obtained by uniaxially stretching a 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 production cost, a defect in process passability at the time of film formation, and the like. In addition, the polymerization degree of PVA (A) in this specification means the average polymerization degree measured based on the description of JISK6726-1994.

From the viewpoint of the water resistance of the polarizing film obtained by uniaxially stretching the film, the degree of saponification of the PVA (A) contained in the polarizing film of the present invention is preferably at least 95 mol%, more preferably 96 mol. More than %, more preferably more than 98 mol%. Furthermore, the degree of saponification of PVA in this specification refers to the ratio of structural units (typically vinyl ester units) that can be converted to vinyl alcohol units (-CH ₂ -CH(OH)-) by saponification and vinyl alcohol units. The total number of moles of units, and the proportion of the moles of vinyl alcohol units in PVA (mole %). The degree of saponification can be measured according to the description of JIS K 6726-1994.

The method for producing PVA (A) used in the present invention is not particularly limited. For example, the method of converting the vinyl ester unit of the polyvinyl ester obtained by polymerizing a vinyl ester monomer into a vinyl alcohol unit is mentioned. 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 trimethylacetic acid Vinyl, vinyl neodecanoate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, vinyl benzoate, etc. . From the viewpoint of economic efficiency, vinyl acetate is preferred.

In addition, the PVA (A) used in the present invention may be obtained by converting vinyl ester units of vinyl ester copolymers obtained by copolymerizing vinyl ester monomers and other monomers that can be copolymerized with them into vinyl alcohol units. . As other monomers that can be copolymerized with vinyl ester monomers, for example: α-olefins with 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutylene; (meth)acrylic acid or its salts; Methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate , tertiary butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, octadecyl (meth)acrylate and other (meth)acrylates; base) acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, diacetone (methyl) ) acrylamide, (meth)acrylamidopropanesulfonic acid or its salts, (meth)acrylamidopropyldimethylamine or its salts, N-methylol (meth)acrylamide or its derivatives (meth)acrylamide derivatives such as substances; C Vinyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, secondary butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether and other vinyl ethers; (meth)acrylonitrile Vinyl cyanide, etc.; vinyl chloride, vinylidene chloride, vinylidene fluoride, vinylidene difluoride and other vinyl halides; allyl compounds such as allyl acetate and allyl chloride; maleic acid or its salt, ester or anhydride; Conic acid or its salt, ester or anhydride; vinyl silane compounds such as ethylene trimethoxysilane; unsaturated sulfonic acid, etc. The above-mentioned vinyl ester copolymer may have structural units derived from one or two or more of the aforementioned other monomers. This other monomer can be used by allowing the vinyl ester monomer to exist in the reaction container beforehand when it is subjected to the polymerization reaction, or by adding it to the reaction container during the polymerization reaction. From the viewpoint of optical properties, the content of units derived from other monomers is preferably 10 mol% or less, more preferably 5 mol% relative to the molar number of the total structural units constituting PVA (A). or less, preferably less than 2 mol%.

From the point of view of improving the extensibility and extending at a higher temperature, and reducing the troubles such as stretching and breaking during the production of the polarizing film, and further improving the productivity of the polarizing film, the above-mentioned vinyl ester monomer can be used together. Among monomers to be polymerized, ethylene is preferred. When PVA (A) contains ethylene units, from the viewpoint of elongation or elongation temperature as described above, the content rate of ethylene units is preferably 1-10 mol%, more preferably 2-6 mol%.

The PVA film used for producing the polarizing film of the present invention may contain a plasticizer in addition to the above-mentioned PVA (A). As preferred plasticizers, polyhydric alcohols can be mentioned, and as specific examples, ethylene glycol, Glycerin, propylene glycol, diethylene glycol, diglycerol, triethylene glycol, tetraethylene glycol, trimethylolpropane, etc. In addition, these plasticizers may contain 1 type or 2 or more types. Among these, glycerin is preferred from the viewpoint of the elongation-enhancing effect.

The content of the plasticizer used in the PVA film used to manufacture the polarizing film of the present invention is preferably in the range of 1 to 20 parts by mass, more preferably 3 to 17 parts by mass, relative to 100 parts by mass of PVA (A). within the range, more preferably within the range of 5 to 15 parts by mass. When this content is 1 mass part or more, the extensibility of a film can be improved. On the other hand, when this content is 20 mass parts or less, it can suppress that a film becomes too soft and the handling property falls.

The PVA film used in the manufacture of the polarizing film of the present invention may be suitably blended with processing stabilizers such as fillers, copper compounds, weather resistance stabilizers, colorants, ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, etc. additives, flame retardants, other thermoplastic resins, lubricants, fragrances, defoamers, deodorants, extenders, stripping agents, release agents, reinforcing agents, crosslinking agents, antifungal agents, preservatives, crystallization Other additives other than PVA(A) and plasticizer such as speed retarder. The content of other additives in the aforementioned PVA film is usually 10% by mass or less, preferably 5% by mass or less.

The swelling degree of the PVA film used to manufacture the polarizing film of the present invention is preferably in the range of 160-240%, more preferably in the range of 170-230%, and particularly preferably in the range of 180-220%. With a swelling degree of 160% or more, crystallization can be extremely inhibited, and stable extension to high magnification can be achieved. On the other hand, by having a swelling degree of 240% or less, it is possible to suppress Dissolution during stretching can be stretched even at higher temperatures.

The thickness of the PVA film used to manufacture the polarizing film of the present invention is not particularly limited, and is generally 1-100 μm, ideally 5-60 μm, particularly preferably 10-45 μm. When the PVA film is too thin, it tends to be prone to stretch fracture during the uniaxial stretching process for producing a polarizing film. Also, if the PVA film is too thick, uneven stretching tends to occur during the uniaxial stretching process for producing a polarizing film, or the shrinkage force of the produced polarizing film tends to increase.

The width of the PVA film used to manufacture the polarizing film of the present invention is not particularly limited, and can be determined according to the application of the polarizing film to be manufactured. From the viewpoint of increasing the size of liquid crystal televisions and liquid crystal monitors in recent years, if the width of the PVA film used to manufacture the polarizing film is 3 m or more, it is suitable for these applications. On the other hand, if the width of the PVA film used to make the polarizing film becomes too large, it is easy to become difficult to uniformly uniaxially stretch the polarizing film when the polarizing film is made by a practical device. Therefore, the PVA film used to make the polarizing film The width of the film is preferably 10 m or less.

The manufacturing method of the PVA film used to manufacture the polarizing film of the present invention is not particularly limited, and it is preferable to adopt 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 above-mentioned plasticizer, the above-mentioned other additives, and the surfactant described later can be used. , or include PVA (A), and further include plasticizers, other additives, surfactants, and liquid media, etc. One or more of them and PVA (A) is produced by melting the film-forming stock solution. When the film-forming stock solution contains at least one of a plasticizer, other additives, and a surfactant, it is preferable that these components are uniformly mixed.

As the above-mentioned liquid medium used in the preparation of the membrane-forming stock solution, for example, water, dimethylsulfide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, Alcohol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, etc., and one or more of these can be used 2 or more. Of these, water is preferred from the viewpoint of environmental load and recyclability.

The volatile content of the film-forming stock solution (the proportion of volatile components in the film-forming stock solution that are removed by volatilization or evaporation during film forming) varies depending on the film-forming method, film-forming conditions, etc., but Generally, it is preferably in the range of 50 to 95% by mass, more preferably in the range of 55 to 90% by mass. Since the volatile content of the membrane-forming stock solution is more than 50% by mass, the viscosity of the film-forming stock solution will not become too high, and the filtration or defoaming during the preparation of the film-forming stock solution can be smoothly performed, and the production of a film with less foreign matter or defects easier. On the other hand, since the volatile content of the film-forming stock solution is 95% by mass or less, the concentration of the film-forming stock solution does not become too low, and industrial production of thin films becomes easy.

The membrane-forming stock solution preferably contains a surfactant. By including the surfactant, the film-forming properties are improved, and the occurrence of uneven film thickness can be suppressed, and the film can be easily peeled off from the metal roll or belt used for film-forming. When producing a PVA film from a film-forming stock solution containing a surfactant, the film may contain a surfactant. Types of the above surfactants Although it does not specifically limit, An anionic surfactant or a nonionic surfactant is preferable from the viewpoint of peelability from a metal roll or a belt.

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

As nonionic surfactants, for example: alkyl ether type such as polyoxyethylene oleyl ether; alkyl phenyl ether type such as polyoxyethylene octylphenyl ether; alkyl ester type such as polyoxyethylene laurate; polyoxyethylene lauryl Alkylamine type such as amine ether; Alkylamide type such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Alkanol such as lauric acid diethanolamide and oleic acid diethanolamide Amide type; allyl phenyl ether type such as polyoxyallyl phenyl ether, etc. are suitable.

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

When the film-forming stock solution contains a surfactant, its content 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, relative to 100 parts by mass of PVA (A) contained in the film-forming stock solution within, particularly preferably within the range of 0.05 to 0.2 parts by mass. When this content is 0.01 mass part or more, film-forming property and peelability are improved more. On the other hand, when the content is 0.5 parts by mass or less, the surface active agent overflows on the surface of the PVA film to cause sticking, and a decrease in handling properties can be suppressed.

Examples of film forming methods for forming a PVA film using the above-mentioned film forming stock solution include casting film forming, extrusion film forming, wet film forming, and gel film forming. The film maker For the method, only one type may be used, or two or more types may be used in combination. Among these film forming methods, the casting film forming method and the 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 formed PVA film can be dried or heat-treated as needed.

As an example of the specific manufacturing method of the PVA film that is used to manufacture the polarizing film of the present invention, it is preferable to adopt in the industry, for example: use a T-shaped slot die, a hopper plate, an I-type die, a lip-shaped coating machine die, etc., the above-mentioned The film-making stock solution is uniformly spouted or cast on the circumferential surface of the heated first roller (or belt) in the rotation at the uppermost side, and from the spout or cast on the first roller (or belt) One side of the film on the peripheral surface of the film is dried by evaporating volatile components, and then further dried on the peripheral surface of one or more rotating heated rollers arranged on the downstream side, or passed through After further drying in the hot air drying device, the coiling method is carried out by the coiling device. Drying with a heated roll and drying with a hot air drying device can also be implemented in combination as appropriate. In addition, a layer containing 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 manufacturing method of a polarizing film, which is a method of manufacturing a polarizing film including a dyeing process of dyeing a PVA film with a dichroic pigment, and a stretching process of uniaxially stretching the film. A treatment in which the film is dipped in an aqueous solution of a boron-containing compound (B). For PVA films, dyeing treatment, uniaxial stretching, etc. Stretching treatment, and further methods such as swelling treatment, boric acid cross-linking treatment, fixing treatment, cleaning treatment, drying treatment, heat treatment, etc. if necessary. At this time, the order of swelling treatment, dyeing treatment, boric acid crosslinking treatment, uniaxial stretching treatment, fixation treatment, etc. is not particularly limited, and one or more treatments may be performed simultaneously. Moreover, one or two or more of each treatment may be performed twice or more.

The swelling treatment can be performed by immersing the PVA film in water. The temperature of the water for dipping the film is preferably in the range of 20-40°C, more preferably in the range of 22-38°C, and still more preferably in the range of 25-35°C. Moreover, as time of immersion in water, for example, it is preferable to exist in the range of 0.1-5 minutes, and it is more preferable to exist in the range of 0.2-3 minutes. Furthermore, the water for impregnating 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 bringing a dichroic dye into contact with the PVA film. As a dichroic dye, an iodine-based dye or a dichroic dye is generally used. The timing of the dyeing treatment may be any stage before the uniaxial stretching treatment, during the uniaxial stretching treatment, and after the uniaxial stretching treatment. The dyeing process is generally carried out by immersing the PVA film in a solution (especially an aqueous solution) containing iodine-potassium iodide as a dyeing bath, or a solution (especially 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. Moreover, it is preferable to set the temperature of a dyeing bath as 20-50 degreeC, and it is especially preferable to set it as 25-40 degreeC. The suitable dyeing time is 0.2~5 minutes. When a dichroic dye is used, the dichroic dye is preferably an aqueous dye. Also, the dye concentration in the dyeing bath is preferably 0.001 ~10% by mass. Moreover, dyeing auxiliaries can be used as needed, and inorganic salts, such as sodium sulfate, surfactant, etc. can also be used. When sodium sulfate is used, it is preferably 0.1 to 10% by mass. The dyeing temperature is preferably 30~80°C. Specific dichroic dyes 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, and 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, C.I. Direct Green 59, etc., but dichroic dyes developed for the manufacture of polarizing plates are preferred.

It is also possible to perform boric acid cross-linking treatment on PVA film. In this case, it is possible to more effectively prevent PVA (A) from being eluted into water when performing wet stretching at high temperature. From this point of view, the boric acid crosslinking treatment is preferably performed before the uniaxial stretching treatment. The boric acid crosslinking treatment can be performed by immersing the PVA film in an aqueous solution containing a boric acid crosslinking agent. As the boric acid crosslinking agent, one or two or more boron-containing inorganic compounds such as boric acid and borates 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% by mass. The concentration of the boric acid crosslinking agent is more preferably at least 0.2% by mass. Moreover, more preferably, it is 4.0 mass % or less. When the concentration of the boric acid crosslinking agent is within the above range, the 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 step, so it is preferable that the concentration is not too high. The aqueous solution containing boric acid crosslinking agent may also contain additives such as potassium iodide. The temperature of the aqueous solution containing the 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 stretching treatment described later, it can also be used in the above During each process or between processes, the PVA film is stretched (front stretching). As mentioned above, the total stretching ratio of the pre-stretching performed before the uniaxial stretching treatment (the ratio obtained by multiplying the stretching ratios in each treatment) is determined by the optical performance of the obtained polarizing film. Based on the original length of the raw material PVA film before stretching, it is preferably at least 1.5 times, more preferably at least 2.0 times, and even more preferably at least 2.5 times. On the other hand, the total elongation ratio is preferably at most 4.0 times, more preferably at most 3.5 times. The elongation ratio in the swelling treatment is preferably 1.05 to 2.5 times. The elongation ratio in the dyeing process is preferably 1.1 to 2.5 times. The elongation ratio in the boron crosslinking treatment is preferably 1.1 to 2.5.

The uniaxial stretching treatment 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 carried out in the above-mentioned dyeing bath or boric acid aqueous solution. In addition, 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 air using a water-absorbed PVA film. Among them, the wet stretching method is preferable, and the uniaxial stretching treatment in an aqueous solution containing boric acid is more preferable. The concentration of boric acid in the boric acid aqueous solution is preferably within a range of 0.5 to 6% by mass, more preferably within a range of 1 to 5% by mass. In addition, the boric acid aqueous solution may contain potassium iodide, and its concentration is preferably within a range of 0.01 to 10% by mass. The stretching temperature in the uniaxial stretching process is preferably at least 30°C, more preferably at least 40°C, and still more preferably at least 50°C. On the other hand, the stretching temperature is preferably 90°C or lower, more preferably 80°C or lower, even more preferably 70°C or lower. Also, the stretching ratio in the uniaxial stretching process is preferably 2.0 to 4.0 times. partial from From the viewpoint of the optical properties of the optical film, etc., the elongation ratio is more preferably 2.2 times or more. On the other hand, the elongation ratio is more preferably 3.5 times or less. Also, from the viewpoint of the optical properties of the obtained polarizing film, the total stretching ratio until the fixing treatment described later is preferably 5 times or more based on the original length of the PVA film of the raw material before stretching, more preferably It is more than 5.5 times. The upper limit of the elongation ratio is not particularly limited, but the elongation ratio is preferably 8 times or less.

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

When producing a polarizing film, in order to strengthen the adsorption of dichroic dyes (iodine-based dyes, etc.) to the PVA film, it is preferable to perform a fixation treatment after the uniaxial stretching treatment. It is desirable to use an aqueous solution containing a boron-containing compound (B) as the fixing treatment bath used for the fixing treatment. Moreover, boric acid, an iodine compound, a metal compound, etc. may be further added to a fixed processing bath as needed. The temperature of the fixed treatment bath is preferably 10-80°C. The elongation ratio in the fixing process is preferably at most 1.3 times, more preferably at most 1.2 times, and still more preferably at most 1.1 times.

The boron-containing compound (B) can be adsorbed on the polarizing film in any step of dyeing treatment, boric acid cross-linking treatment, uniaxial extension treatment, and fixation treatment. However, from the viewpoint of suppressing breakage of the PVA film during the uniaxial stretching treatment, it is particularly preferable to perform adsorption during the fixing treatment after the uniaxial stretching treatment. Moreover, the boron-containing compound (B) may be used not only in 1 type but in mixture of 2 or more types. The aqueous solution concentration of the boron-containing compound (B) is preferably 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 down, and it is more preferably at least 0.1% by mass, and even more preferably at least 0.2% by mass. 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 concentrate near the surface of the polarizing film. risk of performance degradation. Also, there is a possibility that a precipitate 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 at most 10% by mass, even more preferably at most 5.0% by mass, and most preferably at most 3.5% by mass. In addition, from the viewpoint of improving optical performance, the aqueous solution containing the boron-containing compound (B) preferably contains an auxiliary agent of iodide such as potassium iodide, 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°C. If the temperature is too low, the boron compound (B) may be precipitated in the treatment bath. The temperature of the aqueous solution is more preferably 15°C or higher, still more preferably 20°C or higher. On the other hand, when the temperature is too high, it will be difficult to easily manufacture 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, particularly preferably 45°C or lower. The time for immersion in the aqueous solution is preferably 5 to 400 seconds.

The appropriate production method for the case where the boron-containing compound (B) is adsorbed on the polarizing film during the fixation treatment is: the one performed in the order of swelling treatment, uniaxial stretching treatment, and fixation treatment; The sequence of joint treatment, uniaxial stretching treatment, and fixation treatment; or the sequence of swelling treatment, uniaxial stretching treatment, fixation treatment, and boric acid crosslinking treatment. Thereafter, one or more treatments selected from washing treatment, drying treatment, and heat treatment may be performed as needed.

The cleaning treatment is generally carried out by immersing the film in distilled water, pure water, aqueous solution, or the like. At this time, 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. Also, the temperature of the aqueous solution in the cleaning treatment is generally 5-50°C, preferably 10-45°C, and more preferably 15-40°C. From an economic point of view, it is not preferable if the temperature of the aqueous solution is too low, and if the temperature of the aqueous solution is too high, the optical performance will decrease.

The conditions of the drying treatment are not particularly limited, but drying is preferably carried out at a temperature within a range of 30 to 150°C, particularly at a temperature within a range of 50 to 130°C. By drying at a temperature in the range of 30 to 150° C., it is easy to obtain a polarizing film excellent in dimensional stability.

By performing heat treatment after drying treatment, a polarizing film having more excellent dimensional stability can be obtained. Here, the heat treatment is a treatment of further heating the polarizing film having a moisture content of 5% or less after drying to improve the dimensional stability of the polarizing film. The conditions of the heat treatment are not particularly limited, but the heat treatment is preferably performed within the range of 60°C to 150°C, especially within the range of 70°C to 150°C. If the heat treatment is performed at a lower temperature than 60°C, the dimensional stabilization effect due to the heat treatment will not be sufficient, and if the heat treatment is performed at a higher temperature than 150°C, the polarizing film may be strongly reddened.

Preferably, the transmittance of the polarizing film of the present invention obtained as described above is 42.0% or higher, and the degree of polarization is 99.9% or higher. 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 at least 43.0%, and even more preferably at least 43.5%. On the other hand, the transmittance is usually 45% or less. Moreover, since the degree of polarization 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 the methods described in Examples described later.

The polarizing film of the present invention is usually used as a polarizing plate by laminating an optically transparent and mechanically strong protective film on both sides or one side thereof. As the protective film, a cellulose triacetate (TAC) film, a cellulose acetate butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Moreover, as an adhesive agent for bonding, a PVA type adhesive agent, a UV hardening adhesive agent, etc. are mentioned.

The polarizing plate obtained as above may be bonded to a phase difference film, a viewing angle improvement film, a brightness improvement film, or the like. Also, after applying an adhesive such as acrylic to the polarizing plate, it can be bonded to a glass substrate and used as a component of an LCD.

[Example]

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

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

After dissolving the polarizing film in heavy water to 0.003% by mass, it was concentrated with a rotary evaporator to a solution of 0.15% by mass, which was used as a measurement sample for ¹ H-NMR. ¹ H-NMR (JNM-AL400 manufactured by JEOL Ltd.: 400 MHz) measurement was performed at 80° C., and the number of times of accumulation was set to 256 times. Analysis was performed by the following method using ALICE2 (manufactured by JEOL Ltd.). For the ¹ H-NMR spectrum obtained by the measurement, the phase was adjusted to smooth the baseline, and the average point was set to 20 to automatically correct the baseline. Next, as a reference, it is automatically set to a position where the peak value of heavy water, which is the measurement medium, becomes 4.65 ppm. Then, as shown in Fig. 1, the hydrogen peaks of the hydrocarbon groups contained in the boron-containing compound (B) are integrated, and the peak area (area A) is obtained. At this time, the sum of the hydrogen peak areas (area B) of the hydrocarbon groups contained in the boron-containing compound (B) that does not overlap with the hydrogen peak derived from PVA is used as the basis of the peak area, and the boron-containing compound ( The hydrogen number of the hydrocarbon group in B) is the same as the value of the area B. Next, the hydrogen peak in the range of 1.6ppm to 2.4ppm is regarded as the hydrogen peak derived from the methylene group of PVA and contained in the boron-containing compound (B) overlapping with the hydrogen peak derived from the methylene group of PVA. The hydrogen peaks of the hydrocarbon groups are summed up, and the peak area (area C) is calculated. Then, the area D was calculated by subtracting the hydrogen number of the hydrocarbon group of the boron-containing compound (B) overlapping with the hydrogen peak of the methylene group derived from PVA from the area C. The numerical values obtained by these methods were substituted into the following formula (1), and the boron element content (parts by mass) derived from the boron-containing compound (B) was calculated with respect to 100 parts by mass of PVA (A). In addition, X in the following formula (1) is the hydrogen number of the hydrocarbon group contained in the boron-containing compound (B) that 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, formula (1) is a formula used when unmodified PVA is used, but when modified PVA is used as a raw material, formula (1) must be modified suitably.

Content of boron element derived from boron-containing compound (B) relative to 100 parts by mass of PVA (A) (parts by mass) ={(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 1 mole of repeating units of unmodified PVA. Furthermore, the ¹ H-NMR spectrum in FIG. 1 is measured for 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. The aqueous solution in which the polarizing film was dissolved was used as a measurement sample, and its mass [F(g)] was measured. Thereafter, the boron concentration [G (ppm)] of the measurement sample was measured using a polymorphic ICP emission analyzer (ICP) manufactured by Shimadzu Corporation. Then, the numerical value calculated by substituting the numerical value into following formula (2) was made into the total boron element content (mass %) in a polarizing film.

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

[Optical properties of polarizing film]

(1) Determination of transmittance Ts

From the central part of the polarizing film obtained in the following examples or comparative examples, two samples of the polarizing film with an extension direction of 4 cm and a width direction of 2 cm were collected, and a spectrophotometer with an integrating sphere (manufactured by JASCO Co., Ltd. "V7100") was used. ”), according to JIS Z 8722 (method of measuring object color), Perform C light source, visibility correction in the visible light region of 2° field of view, and measure the transmittance of light in the case of +45° inclination in the longitudinal direction and the light transmittance in the case of -45° inclination for one sample, and obtain this Equal average value Ts1(%). The same was done for another sample, and the light transmittance in the case of +45° inclination and the light transmittance in the case of -45° inclination were measured, and their average value Ts2 (%) was obtained. Ts1 and Ts2 were averaged according to the following formula (3), and it was defined as the transmittance Ts (%) of the polarizing film.

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

(2) Determination of polarization degree V

Using a spectrophotometer with an integrating sphere (manufactured by JASCO Co., Ltd. "V7100"), according to JIS Z 8722 (measurement method of object color), the C light source, the visibility correction of the visible light region with a 2° field of view, for the above The transmittance T⊥(%) of the two samples used for the measurement of the transmittance Ts is measured when the extending directions are perpendicular to each other and overlapped, and the light transmittance T when the extending directions are parallel and overlapped //(%). The measured T//(%) and T⊥(%) were substituted into the following formula (4) to obtain the degree of polarization V(%).

V={(T//-T⊥)/(T//+T⊥)} ^1/2 ×100 (4)

(3) Dichroic ratio (DC) at 650nm

The dichroic ratio at each wavelength of the polarizing film was measured using a spectrophotometer with an integrating sphere (manufactured by JASCO Corporation "V7100") equipped with a Glan-Taylor polarizer. From the central part of the obtained polarizing film, take a piece of polarizing film with an extension direction of 4 cm and a width direction of 2 cm In the wavelength range of 380nm to 780nm, the MD transmittance and TD transmittance were obtained, and the dichroic ratio at each wavelength was calculated based on the following formula (5). 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 polarizing plate sample. In addition, "TD transmittance" represents the transmittance when the direction of the polarized light generated from the Glan-Taylor polarizer is perpendicular to the transmission axis of the polarizing plate sample. In this embodiment, the dichroic ratio at 650 nm is used as an indicator of optical performance.

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

[Shrinkage force of polarizing film]

Contraction force was measured using Autograph "AG-X" with constant temperature bath and video extensometer "TR ViewX120S" manufactured by Shimadzu Corporation. The measurement system used a polarizing film that was conditioned at 20°C/20%RH for 18 hours. After setting the constant temperature bath of Autograph "AG-X" at 20°C, install the polarizing film (15 cm in the longitudinal direction and 1.5 cm in the width direction) on the clamps (5 cm apart between the clamps), and start to raise the temperature of the constant temperature bath at the same time as stretching to 80°C. The polarizing film was stretched at a rate of 1 mm/min, and the stretching was stopped when the tension reached 2N, and the tension was measured until 4 hours later in this state. At this time, the distance between the jigs will be changed due to thermal expansion, so stick a marking sticker on the jig, and use the video extensometer "TR ViewX120S" to make the distance between the jigs constant according to the marking sticker attached to the jig. The amount of movement is corrected while measuring. Furthermore, in the initial stage of the measurement (within 10 minutes after the start of the measurement), the extreme tension is generated 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 regarded 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. Thereafter, the PVA film was taken out, and the moisture on the surface of the PVA film was wiped with filter paper to measure the mass (mass H) of the PVA film after immersion. Thereafter, the PVA film was placed in a dryer at 105° C. and dried for 16 hours, and then the mass of the dried PVA film (mass I) was measured. The degree of swelling of the PVA film was calculated by substituting the numerical values of mass H and mass I in the following formula (6).

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

[Example 1]

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

A sample of width 5 cm x length 9 cm was cut out from the central part of the width direction of the PVA film obtained as described above, so that the range of width 5 cm x length 5 cm could be uniaxially stretched. The sample was dipped in pure water at 30°C for 30 seconds, while being uniaxially stretched 1.1 times in the longitudinal direction, And carry out swelling treatment. Next, while dipping 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, uniaxially stretched 2.2 times in the longitudinal direction (2.4 times as a whole), Adsorb iodine. Furthermore, while immersed in an aqueous solution containing 3.0% by mass of boric acid and 3% by mass of potassium iodide (crosslinking treatment bath) (temperature 30° C.) for 45 seconds, uniaxially stretched 1.2 times in the longitudinal direction (2.7 times as a whole), so that Boric acid adsorption. Then, while dipping in an aqueous solution containing 4.0% by mass of boric acid and 6.0% by mass of potassium iodide (stretching treatment bath) (temperature 60°C), uniaxially stretched 2.2 times (total 6.0 times) in the longitudinal direction and aligned. Thereafter, it was immersed in an aqueous solution (fixed treatment bath) (temperature 30° C.) containing 1.0 mass % of n-propylboric acid and 4.0 mass % of potassium iodide for 100 seconds. In the fixing process, the PVA film was not stretched (stretching ratio 1.0 times). Finally, it was dried at 60° C. for 4 minutes to manufacture a polarizing film.

The ¹ H-NMR of the obtained polarizing film was measured and analyzed. As a result, the hydrogen peak of n-propyl boric acid that did not overlap with the hydrogen peak derived from PVA appeared at 1.1 to 1.3 ppm, so the peak area (area B) Set to 5. Next, the peak area (area C) of the hydrogen of the methylene group of PVA that peaks 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 above formula (1), the boron element content derived from the boron-containing compound (B) was 1.5 parts by mass relative to 100 parts by mass of PVA (A). Also, the total boron element 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 transmittance The reflectivity is 44.14%, the degree of polarization is 99.96%, and the dichroic ratio is 83.88. Moreover, the shrinkage force of the obtained polarizing film was measured and found to be 4.8N. These results are also shown in Table 1. Moreover, the graph which plotted the degree of polarization with respect to the shrinkage force of a polarizing film is shown in FIG. 2.

[Example 2]

A polarizing film was produced in the same manner as in Example 1 except that the time of immersion in the fixing treatment bath was changed to 300 seconds, 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]

In terms of the fixed treatment bath, an aqueous solution (at a temperature of 30° C.) containing 1.0% by mass of n-butylboric acid and 3.0% by mass of potassium iodide was used, except that it was performed in the same manner as in Example 1 to prepare a polarizing film, and carried out by the above method. Each measurement and each evaluation. The results are shown in Table 1 and FIG. 2 .

[Example 4]

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

[Example 5]

As for the fixed treatment bath, an aqueous solution containing 0.5% by mass of n-pentylboronic acid and 3.0% by mass of potassium iodide (treatment temperature: 30°C) was used, except Except for this, it carried out similarly to Example 1, produced the polarizing film, and performed each measurement and each evaluation by the said method. The results are shown in Table 1 and FIG. 2 .

[Example 6]

As 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 of immersion in the fixed treatment bath was changed to 10 seconds. In the same manner as in Example 1, a polarizing film was produced, and various measurements and evaluations were performed by the above-mentioned methods. The results are shown in Table 1 and FIG. 2 .

[Example 7]

For the elongation treatment bath, an aqueous solution (at a temperature of 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, and for the fixed treatment bath, an aqueous solution containing 3.0% by mass of potassium iodide ( temperature 30° C.) and the time of immersion in the fixed treatment bath was set to 5 seconds, the same procedure as in Example 1 was performed to prepare a polarizing film, and each measurement and evaluation was performed by the above-mentioned method. The results are shown in Table 1 and FIG. 2 .

[Comparative example 1]

In the fixed treatment bath, 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, except that it was performed in the same manner as in Example 1 to produce Polarizing film, and each measurement and each evaluation were carried out by the above-mentioned method. this , regarding the determination of the boron content derived from the boron-containing compound (B) relative to 100 parts by mass of PVA (A), since the boron-containing compound (B) cannot be detected due to the cumulative number of times 256, the cumulative number of times was changed to 4096 times, the measurement of the boron element content derived from the boron-containing compound (B) with respect to 100 mass parts of PVA (A) was performed. The results are shown in Table 1 and FIG. 2 .

[Comparative example 2]

As for the fixed treatment bath, an aqueous solution (at a temperature of 30° C.) containing 1.0% by mass of phenylboronic acid and 1.0% by mass of potassium iodide was used, except that it was carried out in the same manner as in Example 1 to prepare a polarizing film, and each method was carried out by the above method. measurement and evaluation. The results are shown in Table 1 and FIG. 2 .

[Comparative example 3]

As for the fixed treatment bath, an aqueous solution (at a temperature of 30° C.) containing 2.0% by mass of boric acid and 2.5% by mass of potassium iodide was used, except that it was carried out in the same manner as in Example 1 to prepare a polarizing film, and each measurement and Each evaluation. The results are shown in Table 1 and FIG. 2 .

[Comparative example 4]

As for the fixed treatment bath, an aqueous solution (at a temperature of 30° C.) containing 1.0% by mass of boric acid and 2.0% by mass of potassium iodide was used, except that it was carried out in the same manner as in Example 1 to prepare a polarizing film, and each measurement and Each evaluation. The results are shown in Table 1 and FIG. 2 .

[Comparative Example 5]

As for the fixed treatment bath, an aqueous solution (at a temperature of 30° C.) containing 0.5% by mass of boric acid and 2.0% by mass of potassium iodide was used, except that it was carried out in the same manner as in Example 1 to prepare a polarizing film, and each measurement and Each evaluation. The results are shown in Table 1 and FIG. 2 .

[Comparative Example 6]

Except not performing the fixation process, it carried out similarly to Example 1, the polarizing film was produced, and each measurement and each evaluation were performed by the said method. The results are shown in Table 1 and FIG. 2 .

[Comparative Example 7]

In the fixed treatment bath, use an aqueous solution (30° C. of temperature) containing a ratio of potassium iodide 2.0 mass %, and make the time for immersion in the fixed treatment bath to be 5 seconds, except that it is carried out in the same manner as in Example 1 to make a polarizing film. And each measurement and each evaluation were performed by the said method. 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 of immersion in the fixing treatment bath was 10 seconds, and each measurement and each evaluation were performed by the above-mentioned method. The results are shown in Table 1 and FIG. 2 .

[Comparative Example 9]

The time of immersion in the fixed treatment bath was 20 seconds, except that it was carried out in the same manner as in Comparative Example 7 to make a polarizing film, and by the above method method for each measurement and each evaluation. The results are shown in Table 1 and FIG. 2 .

In addition, Examples 2-7 and Comparative Examples 1-9 used an aqueous solution (temperature 30° C.) containing iodine and potassium iodide at 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 dried polarizing film becomes 43.8% to 44.2%.

2 is a graph obtained by plotting the shrinkage force on the horizontal axis and plotting the degree of polarization on the vertical axis for the polarizing films of Examples 1-7 and Comparative Examples 1 and 3-9. As shown in FIG. 2 , the polarizing films of Examples 1 to 7 satisfying the requirements of the present invention have small shrinkage force at high temperature and excellent optical properties. On the other hand, the polarizing film (Comparative Example 1) in which the boron content derived from the boron-containing compound (B) was less than 0.1 parts by mass had high shrinkage force. The polarizing film (Comparative Example 2) containing phenylboronic acid as the boron element compound had high shrinkage force and insufficient optical performance, and was out of the range of the graph downward. In terms of the fixed treatment bath, when using an aqueous solution containing boric acid and potassium iodide (Comparative Examples 3-5), due to the reduction of the concentration of boric acid in the aqueous solution, the total boron content in the polarizing film is reduced, so the shrinkage force is reduced, but the optical properties are reduced. Lower, it is difficult to have both. When no fixation treatment was performed (Comparative Example 6), the shrinkage force of the polarizing film was remarkably high. Also, when using an aqueous solution containing potassium iodide in the fixing treatment 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 achieve 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 monoboric acid represented by the following formula (I) and a compound that can be converted into the monoboric acid in the presence of water The polarizing film of the boron-containing compound (B), wherein 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 with 1 to 20 carbon atoms, and R ¹ is connected to a boronic acid group by a boron-carbon bond]. The polarizing film as claimed in item 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. The polarizing film as claimed in item 1 or 2, wherein the carbon number of R ¹ is 2~5. The polarizing film as claimed in claim 1 or 2 has a transmittance of 42.0% or more and a degree of polarization of 99.9% or more. A method for manufacturing a polarizing film according to any one of Claims 1 to 5, which includes dyeing a polyvinyl alcohol film with a dichroic pigment, and polarizing the film by uniaxially stretching it A method for producing a thin film, comprising a step of immersing the thin film in an aqueous solution of a boron-containing compound (B).

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