JP4017656B1 - Manufacturing method of polarizing film and liquid crystal display device - Google Patents

Abstract

An object of the present invention is to provide a method for producing a polarizing film having a high dichroic ratio.
A method for producing a polarizing film, comprising the following steps (1) to (3):
(1) a step of preparing a solution having an electric conductivity of 50 μS / cm or less (in terms of 0.05% by weight), containing a dichroic dye and a solvent, and exhibiting lyotropic liquid crystallinity;
(2) a step of preparing a base material on which at least one surface is hydrophilized,
(3) A step in which the solution prepared in step (1) is applied to the surface of the base material prepared in step (2) subjected to the hydrophilic treatment at a coating speed of 100 mm / s or more and dried.
[Selection figure] None

Description

  The present invention relates to a method for manufacturing a polarizing film having a high dichroic ratio, and a liquid crystal display device including the polarizing film.

As a polarizing film used for a liquid crystal display device or the like, a film obtained by stretching a polymer film mainly composed of a polyvinyl alcohol resin dyed with iodine is used. However, since the above polarizing film is produced by a stretching method, it is easy to tear in the stretching direction. In addition, when used in a liquid crystal display device or the like, a large dimensional change occurs in the polarizing film with changes in temperature and humidity, thereby causing various adverse effects such as a reduction in contrast ratio and display unevenness.
Therefore, a method for producing a polarizing film by applying a lyotropic liquid crystal-containing solution containing a dichroic dye to a substrate and orienting the dichroic dye is disclosed (for example, see Patent Document 1). .
However, such a polarizing film has a problem that a high dichroic ratio cannot be obtained. Conventionally, a method for improving the dichroic ratio has not been known.
JP 2005-154746 A

An object of the present invention is to provide a method for producing a polarizing film having a high dichroic ratio. Moreover, the objective of this invention is providing a liquid crystal display device provided with the polarizing film obtained by this manufacturing method.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above object can be achieved by the following method for producing a polarizing film, and have completed the present invention.

The manufacturing method of the polarizing film of the present invention includes the following steps (1) to (3):
(1) a step of preparing a solution having an electric conductivity of 50 μS / cm or less (in terms of 0.05% by weight), containing a dichroic dye and a solvent, and exhibiting lyotropic liquid crystallinity;
(2) a step of preparing a base material on which at least one surface is hydrophilized,
(3) A step in which the solution prepared in the step (1) is applied to the surface of the base material prepared in the step (2) subjected to the hydrophilic treatment at a coating speed of 100 mm / second or more and dried.

  In a preferred embodiment, the step (1) includes a treatment for reducing sulfate ions from the solution.

  In a preferred embodiment, the dichroic dye is any one of an organic compound containing a sulfone group, a carboxyl group, or an amino group, or a salt thereof.

  In a preferred embodiment, the solvent is water.

  In preferable embodiment, the electrical conductivity of the said water is 20 microsiemens / cm or less.

  In a preferred embodiment, the concentration of the solution is 5% to 40% by weight.

  In a preferred embodiment, the hydrophilization treatment is a treatment for reducing the contact angle of water at 23 ° C. of the base material by 10% or more compared to before the treatment.

  In a preferred embodiment, the hydrophilization treatment is a treatment wherein the contact angle of water at 23 ° C. of the substrate is 5 ° to 60 °.

  In a preferred embodiment, the hydrophilic treatment is a corona treatment, a plasma treatment, an alkali treatment, or an anchor coat treatment.

  In a preferred embodiment, the substrate is a glass substrate or a polymer film.

  In preferable embodiment, the said polymer film contains a cellulose resin.

  In addition, the liquid crystal display device of the present invention includes a polarizing film obtained by any one of the above manufacturing methods.

  According to the method for manufacturing a polarizing film of the present invention, a polarizing film having a remarkably high dichroic ratio can be obtained by a synergistic action resulting from the combination of the steps as compared with the conventional method for manufacturing a polarizing film.

[A. Outline of the present invention]
The manufacturing method of the polarizing film of the present invention includes the following steps (1) to (3).
(1) a step of preparing a solution having an electric conductivity of 50 μS / cm or less (in terms of 0.05% by weight), containing a dichroic dye and a solvent, and exhibiting lyotropic liquid crystallinity;
(2) a step of preparing a base material on which at least one surface is hydrophilized,
(3) A step in which the solution prepared in the step (1) is applied to the surface of the base material prepared in the step (2) subjected to the hydrophilic treatment at a coating speed of 100 mm / second or more and dried.

  A polarizing film that can be obtained by such a production method has a dichroic ratio that is significantly higher than that of a polarizing film produced by a conventional production method, and can provide excellent polarizing characteristics. In the production method of the present invention, the dichroic ratio of the polarizing film at a wavelength of 600 nm is preferably 25 or more, more preferably 28 or more, and particularly preferably 30 or more. A polarizing film having a dichroic ratio in the above range can provide a high contrast ratio when used in, for example, a liquid crystal display device. Furthermore, since it is not necessary to use a stretching operation during the manufacturing process, a dimensional change is unlikely to occur in the polarizing film, and as a result, a liquid crystal display device that is unlikely to cause a decrease in contrast ratio or display unevenness can be obtained.

[B. Step (1)]
Step (1) of the present invention is a step of preparing a solution exhibiting lyotropic liquid crystallinity having an electric conductivity of 50 μS / cm or less (in terms of 0.05% by weight) and containing a dichroic dye and a solvent. .

In this specification, “electrical conductivity” represents the ease of electricity passing through a substance, and refers to the conductivity of a substance between opposing electrodes having a cross-sectional area of 1 cm ² and a distance of 1 cm. The smaller this value, the less likely the liquid will conduct electricity. “0.05 wt% conversion” represents electrical conductivity when the concentration of the solution used in the present invention is 0.05 wt%. The electrical conductivity in terms of 0.05% by weight is, for example, a value that is 1/20 of the electrical conductivity of a liquid having a concentration of 1% by weight, and is 1/20 of the electrical conductivity of a solution that is 0.5% by weight. The value is 10.

  The electric conductivity (in terms of 0.05% by weight) of the solution used in the present invention is 50 μS / cm or less, preferably 40 μS / cm or less, particularly preferably 30 μS / cm or less, and most preferably 20 μS. / Cm or less. The lower limit value of the electrical conductivity is 0.1 μS / cm as a realizable value. By using a solution having an electric conductivity in the above range, a polarizing film having a high dichroic ratio can be produced when the steps (2) and (3) are combined.

Examples of the method for reducing the electrical conductivity of the solution include a method using a reverse osmosis membrane. The reverse osmosis membrane separates a stock solution (solution) into a concentrated solution containing a dichroic dye and a permeated solution containing monovalent or divalent ions. The average pore size of the reverse osmosis membrane is preferably ^{2 × 10 -8 cm~20 × 10 -8} cm, more preferably ^{5 × 10 -8 cm~10 × 10 -8} cm. Examples of the material for forming the reverse osmosis membrane include polyamide resins, polyester amide resins, polypiperazine amide resins, and cross-linked water-soluble vinyl polymers.

  The structure of the reverse osmosis membrane is, for example, an asymmetric membrane having a dense layer on at least one surface of the membrane, and having fine pores with gradually increasing pore diameters from the dense layer toward the inside of the membrane or the other surface, or an asymmetric membrane Examples include a composite membrane having a thin separation functional layer formed of another material on the dense layer of the membrane. The reverse osmosis membrane can be used in any form such as a hollow fiber membrane form or a flat membrane form.

  The step (1) preferably includes a treatment for reducing sulfate ions from the solution. The treatment for reducing sulfate ions from the solution is preferably performed using a reverse osmosis membrane. Specifically, an aqueous solution in which sulfate ions are reduced can be obtained by allowing an aqueous solution containing sulfate ions to pass through the reverse osmosis membrane at a pressure equal to or higher than the osmotic pressure.

  The solution used in the present invention contains a dichroic dye and a solvent and exhibits lyotropic liquid crystallinity. In this specification, “lyotropic liquid crystallinity” refers to a property of causing a phase transition between an isotropic phase and a liquid crystal phase by changing the temperature and the concentration of a dichroic dye (solute). The liquid crystal phase is not particularly limited, and examples thereof include a nematic liquid crystal phase, a smectic liquid crystal phase, and a cholesteric liquid crystal phase. In addition, these liquid crystal phases can be confirmed and identified by the optical pattern of the liquid crystal phase observed with a polarizing microscope. The solution can orient dichroic dyes by exhibiting lyotropic liquid crystallinity.

  The dichroic dye used in the present invention is an organic compound that absorbs light having a wavelength of 400 nm to 780 nm. In the present specification, the term “dichroic dye” means a dye having a large transition moment in the major axis direction of the dye molecule compared to the minor axis direction or a larger transition moment in the minor axis direction than the major axis direction. Say. Any appropriate dichroic dye may be selected depending on the purpose, but an organic compound exhibiting lyotropic liquid crystallinity in a solution state (that is, lyotropic liquid crystal) is preferable. As the dichroic dye, those showing a nematic liquid crystal phase in a solution state at room temperature are particularly preferable because of excellent alignment.

  Examples of the dichroic dyes include, for example, azo dyes, anthraquinone dyes, perylene dyes, indanthrone dyes, imidazole dyes, indigoid dyes, oxazine dyes, and phthalocyanine dyes according to the classification by chemical structure. Dye, triphenylmethane dye, pyrazolone dye, stilbene dye, diphenylmethane dye, naphthoquinone dye, methocyanine dye, quinophthalone dye, xanthene dye, alizarin dye, acridine dye, quinoneimine dye, thiazole dye Examples thereof include dyes, methine dyes, nitro dyes, and nitroso dyes. Among these, azo dyes, anthraquinone dyes, perylene dyes, indanthrone dyes, and imidazole dyes are preferable. These dichroic dyes can be used alone or in admixture of two or more. In the present invention, in order to obtain a black polarizing film, it is preferable to use a mixture of a plurality of dichroic dyes having different absorption spectra.

The dichroic dye is preferably an organic compound containing a sulfone group (—SO ₃ H), a carboxyl group (—COOH), or an amino group (—NH ₂ , —NHR, —NR ₂ ), or a salt thereof. (Wherein R represents an optional substituent), particularly preferably an organic compound containing a sulfone group or a salt thereof. Introduction of a sulfone group into a dichroic dye is effective for improving the solubility in water. As the number of sulfone groups introduced into the dichroic dye increases, the solubility in water increases. The number of the sulfone groups is appropriately selected so that the solubility in a solvent and the water resistance after forming the polarizing film are compatible.

As the dichroic dye, for example, a lyotropic liquid crystalline dichroic dye represented by the following general formula (1) is preferably used.
Formula (1): (chromogen) (SO ₃ M) _n (where M represents a cation).
As M in the formula (1), hydrogen ions, ions of Group 1 metals such as Li, Na, K and Cs, ammonium ions and the like are preferable.
Moreover, as a chromogen part, what contains an azo derivative unit, an anthraquinone derivative unit, a perylene derivative unit, an indanthrone derivative unit, and / or an imidazole derivative unit is preferable.

  In the dichroic dye represented by the general formula (1), chromogen such as an azo compound or a polycyclic compound structure becomes a hydrophobic site in a solution, and a sulfonic acid and a salt thereof become a hydrophilic site, Hydrophobic sites and hydrophilic sites gather together due to the balance between the two, and the lyotropic liquid crystal phase is expressed as a whole.

  Specific examples of the dichroic dye represented by the general formula (1) include compounds represented by the following general formulas (2) to (8).

式（２）中、Ｒ^１は水素又は塩素であり、Ｒ^２は水素、アルキル基、ＡｒＮＨ又はＡｒＣＯＮＨである。このアルキル基としては炭素数が１〜４のアルキル基が好ましく、中でもメチル基やエチル基がより好ましい。アリール基（Ａｒ）としては置換又は無置換のフェニル基が好ましく、中でも無置換又は４位を塩素で置換したフェニル基がより好ましい。また、Ｍは上記一般式（１）と同様である。

In formula (2), R ¹ is hydrogen or chlorine, and R ² is hydrogen, an alkyl group, ArNH or ArCONH. The alkyl group is preferably an alkyl group having 1 to 4 carbon atoms, and more preferably a methyl group or an ethyl group. As the aryl group (Ar), a substituted or unsubstituted phenyl group is preferable, and among them, a phenyl group which is unsubstituted or substituted with chlorine at the 4-position is more preferable. M is the same as in the general formula (1).

式（３）〜（５）において、Ａは、式（Ａ）又は（Ｂ）で表されるものであり、ｎは２又は３である。ＡのＲ^３は水素、アルキル基、ハロゲン又はアルコキシ基、Ａｒは置換又は無置換のアリール基を示す。アルキル基としては炭素数が１〜４のアルキル基が好ましく、中でもメチル基やエチル基がより好ましい。ハロゲンは臭素又は塩素が好ましい。また、アルコキシ基は炭素数が１又は２個のアルコキシ基が好ましく、中でもメトキシ基がより好ましい。アリール基としては置換又は無置換のフェニル基が好ましく、中でも無置換あるいは４位をメトキシ基、エトキシ基、塩素若しくはブチル基で、又は３位をメチル基で置換したフェニル基が好ましい。Ｍは、上記一般式（１）と同様である。

In the formulas (3) to (5), A is represented by the formula (A) or (B), and n is 2 or 3. R ^{3 in} A represents hydrogen, an alkyl group, a halogen or an alkoxy group, and Ar represents a substituted or unsubstituted aryl group. The alkyl group is preferably an alkyl group having 1 to 4 carbon atoms, and more preferably a methyl group or an ethyl group. The halogen is preferably bromine or chlorine. The alkoxy group is preferably an alkoxy group having 1 or 2 carbon atoms, and more preferably a methoxy group. As the aryl group, a substituted or unsubstituted phenyl group is preferable, and among them, a phenyl group which is unsubstituted or substituted at the 4-position with a methoxy group, ethoxy group, chlorine or butyl group or at the 3-position with a methyl group is preferable. M is the same as that in the general formula (1).

式（６）において、ｎは３〜５であり、Ｍは上記一般式（１）と同様である。

In Formula (6), n is 3-5, M is the same as that of the said General formula (1).

式（７）において、Ｍは上記一般式（１）と同様である。

In the formula (7), M is the same as the general formula (1).

式（８）において、Ｍは上記一般式（１）と同様である。

In the formula (8), M is the same as the general formula (1).

  Examples of the method for introducing a sulfone group into the organic compound (sulfonation) include a method in which sulfuric acid, chlorosulfonic acid, or fuming sulfuric acid is allowed to act on the organic compound to replace the hydrogen in the nucleus with the sulfone group. The salt of the organic compound is obtained by replacing a hydrogen atom capable of dissociating an acid with a monovalent cation such as lithium ion, sodium ion, potassium ion, cesium ion, or ammonium ion.

In addition to these, the above-mentioned dichroic dyes include, for example, JP-A-2006-047966, JP-A-2005-255846, JP-A-2005-154746, JP-A-2002-090526, JP-T-8. -511109 gazette, Japanese translations of PCT publication No. 2004-528603 gazette, etc. can be used.
A commercially available dichroic dye can also be used. Commercially available dichroic dyes include C.I. I. DirectB67, DSCG (INTAL), RU31.156, Metyl orange, AH6556, Sirius Supra Brown RLL, Benzopurpurin, Copper-tetracarboxyphthalocyanine, Acid Red 266, Cyanine Dye, Violet 20, Perylenebiscarboximides, Benzopurpurin 4B, Methyleneblue (Basic Blue 9), Brilliant Yellow, Acid Red 18, Acid Red 27, and the like.

  The solvent used in the present invention is used for dissolving the dichroic dye to develop lyotropic liquid crystal properties. Any appropriate solvent can be selected. The solvent may be, for example, an inorganic solvent such as water, alcohols, ketones, ethers, esters, aliphatic and aromatic hydrocarbons, halogenated hydrocarbons, amides, cellosolves. Organic solvents such as Examples of the solvent include n-butanol, 2-butanol, cyclohexanol, isopropyl alcohol, t-butyl alcohol, glycerin, ethylene glycol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, 2-pentanone, 2 -Hexanone, diethyl ether, tetrahydrofuran, dioxane, anisole, ethyl acetate, butyl acetate, methyl lactate, n-hexane, benzene, toluene, xylene, chloroform, dichloromethane, dichloroformamide, dimethylacetamide, methyl cellosolve, ethyl cellosolve, etc. Can be mentioned. These solvents can be used alone or in admixture of two or more.

  Particularly preferably, the solvent is water. The electric conductivity of the water is preferably 20 μS / cm or less, more preferably 0.001 μS / cm to 10 μS / cm, and particularly preferably 0.001 μS / cm to 5 μS / cm. The lower limit of the electrical conductivity of the water is 0 μS / cm. By setting the electric conductivity of water within the above range, a polarizing film having a high dichroic ratio can be obtained.

  The concentration of the solution can be appropriately adjusted within a range showing lyotropic liquid crystallinity depending on the type of dichroic dye used. The concentration of the dichroic dye in the solution is preferably 5% by weight to 40% by weight, more preferably 5% by weight to 35% by weight, and particularly preferably 5% by weight to 30% by weight. By setting the concentration of the solution in the above range, the solution can exhibit a stable liquid crystal state.

  The solution may further contain any suitable additive. Examples of the additive include a surfactant, a plasticizer, a heat stabilizer, a light stabilizer, a lubricant, an antioxidant, an ultraviolet absorber, a flame retardant, a colorant, an antistatic agent, a compatibilizing agent, a crosslinking agent, And thickeners. The amount of the additive is preferably more than 0 and 10 parts by weight or less with respect to 100 parts by weight of the solution.

  The solution may further contain a surfactant. The surfactant is used for improving the wettability and coating property of the dichroic dye to the substrate surface. The surfactant is preferably a nonionic surfactant. The addition amount of the surfactant is preferably more than 0 and 5 parts by weight or less with respect to 100 parts by weight of the solution.

[C. Step (2)]
Step (2) of the present invention is a step of preparing a base material having at least one surface subjected to a hydrophilic treatment. In the present specification, “hydrophilization treatment” refers to a treatment for reducing the contact angle of water on a substrate. The hydrophilization treatment is used to improve the wettability and coatability of the substrate surface on which the dichroic dye is applied.

  The hydrophilization treatment is a treatment for reducing the contact angle of water at 23 ° C. of the base material by preferably 10% or more, more preferably a treatment for reducing the contact angle of water by 15% to 80%. The treatment is preferably reduced by 20% to 70%. In addition, the ratio (%) to reduce is calculated | required by Formula; {(Contact angle before processing-Contact angle after processing) / Contact angle before processing} × 100.

  Further, the hydrophilization treatment is a treatment for reducing the contact angle of water at 23 ° C. of the substrate, preferably by 5 ° or more, and more preferably a treatment for reducing the contact angle by 10 ° to 65 °. Yes, and particularly preferably a treatment for lowering by 20 ° to 60 °.

  Further, the hydrophilization treatment is a treatment in which the contact angle of water at 23 ° C. of the substrate is preferably 5 ° to 60 °, more preferably 5 ° to 50 °, and particularly preferably. This is a treatment of 5 ° to 45 °. By setting the water contact angle of the substrate within the above range, a polarizing film having a high dichroic ratio and a small thickness variation can be obtained.

  Arbitrary appropriate methods may be employ | adopted for the said hydrophilic treatment. The hydrophilic treatment may be, for example, a dry process or a wet process. Examples of the dry treatment include discharge treatment such as corona treatment, plasma treatment, and glow discharge treatment, flame treatment, ozone treatment, UV ozone treatment, ionizing active ray treatment such as ultraviolet ray treatment, and electron beam treatment. Examples of the wet treatment include ultrasonic treatment using a solvent such as water and acetone, alkali treatment, anchor coat treatment, and the like. These treatments may be used alone or in combination of two or more.

  Preferably, the hydrophilization treatment is a corona treatment, a plasma treatment, an alkali treatment, or an anchor coat treatment. With the above hydrophilization treatment, a polarizing film having a high dichroic ratio and a small thickness variation can be obtained. The conditions for the hydrophilization treatment, such as the treatment time and strength, can be appropriately adjusted as appropriate so that the water contact angle of the substrate falls within the above range.

  The corona treatment is typically a treatment for modifying the substrate surface by passing the substrate through corona discharge. The corona discharge is generated by applying a high frequency and a high voltage between a grounded dielectric roll and an insulated electrode, thereby causing the air between the electrodes to break down and ionize. The plasma treatment is typically a treatment for modifying the substrate surface by passing the substrate through low-temperature plasma. When the glow discharge occurs in an inorganic gas such as a low-pressure inert gas, oxygen, or halogen gas, the low-temperature plasma is generated by ionizing a part of gas molecules. The above ultrasonic cleaning treatment is typically a treatment that removes contaminants on the surface of the substrate and improves the wettability of the substrate by immersing the substrate in water or an organic solvent and applying ultrasonic waves. It is. The alkali treatment is typically a treatment for modifying the substrate surface by immersing the substrate in an alkali treatment solution in which a basic substance is dissolved in water or an organic solvent. The anchor coating treatment is typically a treatment for applying an anchor coating agent to the surface of the substrate.

  The base material used for this invention is used in order to apply | coat uniformly the solution containing the said dichroic dye and a solvent. Any appropriate substrate can be selected. Examples of the substrate include a glass substrate, a quartz substrate, a polymer film, a plastics substrate, a metal plate such as aluminum or iron, a ceramic substrate, a silicon wafer, and the like. The substrate is preferably a glass substrate or a polymer film.

  Any appropriate substrate can be selected as the glass substrate. The glass substrate is preferably used for a liquid crystal cell, and is, for example, soda lime (blue plate) glass containing an alkali component or low alkali borosilicate glass. A commercially available glass substrate may be used as it is. Examples of commercially available glass substrates include Corning Corporation glass cord: 1737, Asahi Glass Co., Ltd. glass cord: AN635, NH Techno Glass Co., Ltd. glass cord: NA-35, and the like.

  Any appropriate resin can be selected as the resin for forming the polymer film. Preferably, the polymer film contains a thermoplastic resin. Examples of the thermoplastic resin include polyolefin resin, cycloolefin resin, polyvinyl chloride resin, cellulose resin, styrene resin, polymethyl methacrylate, polyvinyl acetate, polyvinylidene chloride resin, polyamide resin, and polyacetal resin. Resins, polycarbonate resins, polybutylene terephthalate resins, polyethylene terephthalate resins, polysulfone resins, polyether sulfone resins, polyether ether ketone resins, polyarylate resins, polyamideimide resins, polyimide resins, etc. It is done. Said thermoplastic resin can be used individually or in combination of 2 or more types. The thermoplastic resin can be used after any appropriate polymer modification. Examples of the polymer modification include modifications such as copolymerization, crosslinking, molecular terminals, and stereoregularity.

When a polymer film is used as the substrate, it is preferable to use a polymer film that is excellent in visible light transmittance and excellent in transparency. The light transmittance of visible light in this polymer film is preferably 80% or more, more preferably 90% or more. However, the light transmittance means a Y value obtained by correcting the visibility based on spectrum data measured with a spectrophotometer (product name: U-4100 type, manufactured by Hitachi, Ltd.) with a film thickness of 100 μm. The haze value of the polymer film is preferably 3% or less, more preferably 1% or less. However, in the present invention, the haze value is a value measured according to JIS-K7105.
When a polymer film is used as the substrate, the substrate can be used as a protective film for the polarizing film after the polarizing film is formed.

  The substrate used in the present invention is preferably a polymer film containing a cellulose resin. This is because a polarizing film having excellent dichroic dye wettability, high dichroic ratio, and small thickness variation can be obtained.

  Arbitrary appropriate things can be employ | adopted for the said cellulose resin. The cellulose resin is preferably a cellulose organic acid ester or a cellulose mixed organic acid ester in which part or all of the hydroxyl groups of cellulose are substituted with acetyl groups, propionyl groups, and / or butyl groups. Examples of the cellulose organic acid ester include cellulose acetate, cellulose propionate, and cellulose butyrate. Examples of the cellulose mixed organic acid ester include cellulose acetate propionate and cellulose acetate butyrate. The cellulose resin can be obtained, for example, by the method described in JP-A-2001-188128 [0040] to [0041].

  As the base material used in the present invention, a commercially available polymer film can be used as it is. Alternatively, a commercially available polymer film that has been subjected to secondary processing such as stretching and / or shrinking can be used. As a polymer film containing a commercially available cellulose resin, for example, Fuji Photo Film Co., Ltd. Fujitac series (trade name: ZRF80S, TD80UF, TDY-80UL), Konica Minolta Opto Co., Ltd. trade name “KC8UX2M” Or the like.

  The thickness of the substrate is preferably 20 μm to 100 μm. By setting the thickness of the base material within the above range, the handling property and coating property of the base material are excellent.

  In addition, the order which implements a process (1) and a process (2) is not specifically limited, After performing a process (1) previously, you may perform a process (2) or a process (2). After performing step (1), step (1) may be performed, or step (1) and step (2) may be performed concurrently.

[D. Step (3)]
In the step (3) of the present invention, the solution prepared in the step (1) is applied to the surface of the base material prepared in the step (2) that has been subjected to the hydrophilic treatment at a coating speed of 100 mm / second or more. And drying. The coating speed is 100 mm / second or more, more preferably 500 mm / second to 8000 mm / second, particularly preferably 800 mm / second to 6000 mm / second, and most preferably 1000 mm / second to 4000 mm / second. . In general, in the production of an optical film by the solvent casting method, the coating speed for improving the uniformity of the coating film is preferably slow. It is an unexpectedly excellent effect that a polarizing film having a high dichroic ratio and a small thickness variation can be obtained by using the coating speed defined in the present invention. According to the estimation of the present inventors, the reason why a polarizing film having a high dichroic ratio and a small thickness variation is obtained is that a shearing force suitable for orienting the dichroic dye in the solution is applied. This is probably because of this.

  As a method for applying the solution to the surface of the substrate, a coating method using an appropriate coater may be employed as appropriate. Examples of the coater include a reverse roll coater, a forward rotation roll coater, a gravure coater, a knife coater, a rod coater, a slot die coater, a slot orifice coater, a curtain coater, a fountain coater, an air doctor coater, a kiss coater, a dip coater, a bead coater, and a blade coater. Cast coater, spray coater, spin coater, extrusion coater, hot melt coater and the like. The coater is preferably a reverse roll coater, a forward rotation roll coater, a gravure coater, a rod coater, a slot die coater, a slot orifice coater, a curtain coater, and a fountain coater. If it is the coating system using said coater, a polarizing film with small thickness variation can be obtained.

  As a method for drying the solution, an appropriate method can be adopted as appropriate. Examples of the drying method include drying means such as an air circulation type constant temperature oven in which hot air or cold air circulates, a heater using microwaves or far infrared rays, a roll heated for temperature control, a heat pipe roll, or a metal belt. It is done.

  The temperature at which the solution is dried is not higher than the isotropic phase transition temperature of the solution, and it is preferable that the temperature is gradually raised from a low temperature to a high temperature to be dried. The drying temperature is preferably 10 ° C to 80 ° C, more preferably 20 ° C to 60 ° C. If it is said temperature range, a polarizing film with small thickness variation can be obtained.

  The time for drying the solution can be appropriately selected depending on the drying temperature and the type of the solvent, but in order to obtain a polarizing film with small thickness variation, for example, it is 1 minute to 60 minutes, preferably 5 minutes to 40 minutes. Minutes.

[E. Other processes]
The method for producing a polarizing film of the present invention preferably further includes a step (4) after the above steps (1) to (3):
(4) The film obtained in the above step (3) is selected from the group consisting of aluminum salts, barium salts, lead salts, chromium salts, strontium salts, and compound salts having two or more amino groups in the molecule. Contacting with a solution comprising at least one compound salt.

  In this invention, the said process (4) is used in order to make the polarizing film obtained insoluble or hardly soluble with respect to water. Examples of the compound salt include aluminum chloride, barium chloride, lead chloride, chromium chloride, strontium chloride, 4,4′-tetramethyldiaminodiphenylmethane hydrochloride, 2,2′-dipyridyl hydrochloride, 4,4′-dipyridyl. Examples include hydrochloride, melamine hydrochloride, and tetraaminopyrimidine hydrochloride. With such a compound salt, a polarizing film having excellent water resistance can be obtained.

  The compound salt concentration of the solution containing the above compound salt is preferably 3% by weight to 40% by weight, and particularly preferably 5% by weight to 30% by weight. By bringing the polarizing film into contact with a solution containing a compound salt having a concentration in the above range, a film having excellent durability can be obtained.

  Examples of the method of bringing the membrane obtained in the step (3) into contact with the solution containing the compound salt include, for example, a method of applying a solution containing the compound salt to the surface of the membrane, and the membrane to the compound salt. Arbitrary methods, such as the method of immersing in the solution containing, can be adopted. When these methods are employed, the obtained film is preferably washed with water or an arbitrary solvent, and further dried to obtain a polarizing element having excellent adhesion at the interface between the substrate and the polarizing film. Can be obtained.

[G. Form and application of polarizing film)
The polarizing film obtained by the production method of the present invention can be used for any appropriate application. Preferably, the application of the polarizing film is incorporated as an optical member of a liquid crystal display device. The polarizing film can be used in any form. The form of the polarizing film may be, for example, a single polarizing film or a laminate including a base material and a polarizing film. Alternatively, the polarizing film may be sandwiched between two base materials via an arbitrary adhesive layer. Or the form of the polarizing plate which laminated | stacked retardation film on the laminated body of a polarizing film or a base material and a polarizing film may be sufficient. Further, the polarizing film may include an adhesive layer on at least one side.

  In the present specification, the “adhesive layer” refers to a layer that joins surfaces of adjacent objects and integrates them with practically sufficient adhesive force and adhesion time. Examples of the material for forming the adhesive layer include an adhesive and an anchor coat agent. The adhesive layer may have a multilayer structure in which an anchor coat layer is formed on the surface of an adherend and an adhesive layer is formed thereon. Further, it may be a thin layer (also referred to as a hairline) that cannot be visually recognized.

  As the material for forming the adhesive layer, an appropriate adhesive or anchor coating agent can be appropriately selected according to the type and purpose of the adherend. Specific examples of adhesives include solvent-based adhesives, emulsion-type adhesives, pressure-sensitive adhesives, rehumidifying adhesives, polycondensation-type adhesives, solventless adhesives, and film-like adhesives according to the classification by shape. Agents, hot melt adhesives and the like. According to the classification by chemical structure, synthetic resin adhesives, rubber adhesives, and natural product adhesives can be mentioned. The adhesive includes a viscoelastic substance (also referred to as an adhesive) that exhibits an adhesive force that can be sensed by pressure contact at room temperature.

  Applications of the liquid crystal display device including the polarizing film of the present invention include, for example, OA equipment such as a personal computer monitor, a notebook personal computer, a copy machine, a mobile phone, a clock, a digital camera, a personal digital assistant (PDA), and a portable game machine. Security equipment such as equipment, home electrical equipment such as video cameras, televisions, microwave ovens, back monitors, car navigation system monitors, car audio equipment such as car audio equipment, commercial display information monitors, surveillance monitors, etc. These include nursing care / medical equipment such as equipment, nursing monitors, and medical monitors.

The present invention will be further described using the above examples and comparative examples. In addition, this invention is not limited only to these Examples. In addition, each analysis method used in the Example is as follows.
(1) Method of measuring electrical conductivity:
The electrode of the solution conductivity meter [product name “CM-117” manufactured by Kyoto Electronics Industry Co., Ltd.] was washed with an aqueous solution prepared with a dichroic dye concentration of 0.05% by weight and then connected to the electrode. A sample was filled in a 1 cm ³ container, and the displayed electric conductivity showed a constant value as a measured value.
(2) Measuring method of dichroic ratio (DR):
Using a spectrophotometer with an integrating sphere [product name “U-4100” manufactured by Hitachi, Ltd.], the transmittance with respect to each linearly polarized light is defined as 100% of the completely polarized light obtained through the Glan-Thompson prism polarizer; k ₁ and to determine the _{k 2.} The single transmittance (Ts) was calculated from the formula: Ts = (k ₁ + k ₂ ) / 2. The dichroic ratio (DR) was calculated by the formula: DR = log (1 / k ₂ ) / log (1 / k ₁ ). Here, k ₁ represents a transmittance of the maximum transmittance direction of linearly polarized light, k ₂ represents a transmittance of a linearly polarized light in a direction perpendicular to the maximum transmittance direction.
(3) Measuring method of water contact angle:
Using a solid-liquid interface analyzer [product name “Drop Master 300” manufactured by Kyowa Interface Science Co., Ltd.], the contact angle after 5 seconds had elapsed after the liquid was dropped onto the substrate. The measurement condition is static contact angle measurement. As the water, ultrapure water was used, and the droplets were 0.5 μl. About each base material, the average value of 10 repetitions was made into the measured value.
(4) Evaluation method for variation in single transmittance:
The dispersion of the single transmittance is determined by using a birefringence phase difference measuring apparatus [product name “RETS-1200RF” manufactured by Otsuka Electronics Co., Ltd.] at any 10 positions of k ₁ , k of the sample (size: 5 cm × 5 cm). ₂ was measured and the standard deviation of the single transmittance (Ts) was determined. The single transmittance (Ts) was calculated from the formula: Ts = (k ₁ + k ₂ ) / 2. Here, k ₁ represents a transmittance of the maximum transmittance direction of linearly polarized light, k ₂ represents a transmittance of a linearly polarized light in a direction perpendicular to the maximum transmittance direction.
(5) Measuring method of coating speed:
Using a high-speed camera [Phototron model “FASTCAM-APX RS 250K”], the time required for the bar coater to pass a predetermined distance was analyzed and determined.

[Example 1]
A dichroic dye of lyotropic liquid crystal (organic compound) containing a sulfone group (trade name “LC Polarizer NO15” manufactured by OPTIVA) and pure water (electric conductivity: 1.7 μS / cm); The aqueous solution adjusted to a pigment concentration of 0.25% by weight was purified using a triple flat membrane evaluation apparatus equipped with a reverse osmosis membrane filter trade name “NTR-7430” manufactured by Nitto Denko Corporation. The electric conductivity was adjusted to 20.1 μS / cm (in terms of 0.05% by weight). Next, an aqueous solution containing the dichroic dye of the lyotropic liquid crystal was adjusted using a rotary evaporator so that the concentration of the dichroic dye was 12.2% by weight. When the aqueous solution obtained here was observed with a polarizing microscope, it exhibited a nematic liquid crystal phase at 23 ° C.

  Next, a polymer film (trade name “ZRF80S”, manufactured by Fuji Photo Film Co., Ltd.) having a thickness of 80 μm as a main component is immersed in an aqueous solution in which sodium hydroxide is dissolved, and the surface thereof is alkali-treated. (Also referred to as saponification treatment). The contact angle of water at 23 ° C. of the polymer film was 64.6 ° before the treatment and 42.2 ° after the treatment. Next, an aqueous solution containing the above-mentioned lyotropic liquid crystal dichroic dye is applied to the surface of the polymer film subjected to alkali treatment using a bar coater at a coating speed of 1600 mm / second (wet thickness: 1 μm). Then, it was naturally dried to produce a laminate A of a polarizing film having a single transmittance of 42.12% and a polymer film. The evaluation results of the obtained laminate A are shown in Table 1.

[Example 2]
In the same manner as in Example 1, the dichroic dye of the lyotropic liquid crystal is contained, the electric conductivity is 20.1 μS / cm (converted to 0.05% by weight), and the concentration of the dichroic dye is 12.5. An aqueous solution having a weight percent was prepared. Next, the surface of a 0.7 μm thick glass substrate [Corning Glass Code “1737”] was cleaned by ultrasonic treatment with acetone for 3 minutes and ion-exchanged water for 5 minutes. The contact angle of water at 23 ° C. of the glass substrate at this time was 43.9 ° before the treatment and 30.1 ° after the treatment. Subsequently, a corona treatment (strength: 0.14 kW) was further applied to the surface of the glass substrate subjected to the ultrasonic treatment. The contact angle of water at 23 ° C. of the glass substrate was 30.1 ° before the treatment and 14.2 ° after the treatment. Next, on the corona-treated surface of the glass substrate, an aqueous solution containing the dichroic dye of the lyotropic liquid crystal is applied using a bar coater at a coating speed of 1600 mm / second (wet thickness; 1 μm), It was naturally dried to produce a laminate B of a polarizing film having a single transmittance of 50.20% and a glass substrate. The evaluation results of the obtained laminate B are shown in Table 1.

[Example 3]
In the same manner as in Example 1, the dichroic dye of the lyotropic liquid crystal is contained, the electric conductivity is 20.1 μS / cm (converted to 0.05% by weight), and the concentration of the dichroic dye is 13.0. An aqueous solution having a weight percent was prepared. Next, a polymer film [trade name “ZRF80S” manufactured by Fuji Photo Film Co., Ltd.] having a thickness of 80 μm as a main component and triacetylcellulose as a main component was subjected to alkali treatment in the same manner as in Example 1. Next, an aqueous solution containing the above-mentioned lyotropic liquid crystal dichroic dye is applied to the surface of the polymer film subjected to alkali treatment at a coating speed of 1200 mm / second (wet thickness: 1 μm) using a bar coater. Then, it was naturally dried to produce a laminate C of a polarizing film having a single transmittance of 41.95% and a polymer film. The evaluation results of the obtained laminate C are shown in Table 1.

[Comparative Example 1]
Except that the aqueous solution containing the dichroic dye of the lyotropic liquid crystal was not purified and prepared so that the concentration of the dichroic dye was 13.0% by weight, the same method as in Example 1, A layered product H was produced. The electrical conductivity of the aqueous solution was 159.2 μS / cm (converted to 0.05% by weight). Table 1 shows the evaluation results of the obtained laminate H.

[Comparative Example 2]
A laminate I was produced in the same manner as in Example 1 except that the polymer film containing triacetyl cellulose as a main component was not subjected to alkali treatment. The water contact angle of the polymer film was 64.6 °. The evaluation results of the obtained laminate I are shown in Table 1.

[Comparative Example 3]
A laminate J was produced in the same manner as in Example 1 except that the coating speed was 50 mm / sec. The evaluation results of the obtained laminate J are shown in Table 1.

[Evaluation]
Table 1 shows the dichroic ratio and thickness variation of the laminates including the polarizing films obtained in Examples 1 to 3 and Comparative Examples 1 to 3. As can be seen from Table 1, the laminate including the polarizing films obtained in Examples 1 to 3 had a high dichroic ratio and a small standard deviation of the single transmittance. The standard deviation of the single transmittance has a correlation with the thickness variation, and the smaller the value, the smaller the thickness variation of the polarizing film. On the other hand, the dichroic ratio of the laminate including the polarizing film obtained in Comparative Examples 1 and 2 was small. The polarizing film obtained in Comparative Example 3 had a small dichroic ratio and a large standard deviation of single transmittance.

  As described above, according to the manufacturing method of the present invention, since a polarizing film having a high dichroic ratio can be manufactured, it is extremely useful for improving display characteristics of a liquid crystal display device, for example.

Claims (12)

The manufacturing method of a polarizing film including the process of following (1)-(3):
(1) a step of preparing a solution having an electric conductivity of 50 μS / cm or less (in terms of 0.05% by weight), containing a dichroic dye and a solvent, and exhibiting lyotropic liquid crystallinity;
(2) a step of preparing a base material on which at least one surface is hydrophilized,
(3) A step in which the solution prepared in the step (1) is applied to the surface of the base material prepared in the step (2) subjected to the hydrophilic treatment at a coating speed of 100 mm / second or more and dried.   The method for producing a polarizing film according to claim 1, wherein the step (1) includes a process of reducing sulfate ions from the solution.   The manufacturing method of the polarizing film of Claim 1 or 2 whose said dichroic dye is either the organic compound containing a sulfone group, a carboxyl group, or an amino group, or those salts.   The manufacturing method of the polarizing film in any one of Claim 1 to 3 whose said solvent is water.   The manufacturing method of the polarizing film of Claim 4 whose electrical conductivity of the said water is 20 microsiemens / cm or less.   The manufacturing method of the polarizing film in any one of Claim 1 to 5 whose density | concentration of the said solution is 5 to 40 weight%.   The method for producing a polarizing film according to claim 1, wherein the hydrophilization treatment is a treatment for reducing a contact angle of water at 23 ° C. of the base material by 10% or more as compared to before the treatment.   The manufacturing method of the polarizing film in any one of Claim 1 to 7 whose said hydrophilization process is a process which makes the contact angle of the water in 23 degreeC of the said base material 5 degrees-60 degrees.   The method for producing a polarizing film according to claim 1, wherein the hydrophilization treatment is corona treatment, plasma treatment, alkali treatment, or anchor coat treatment.   The manufacturing method of the polarizing film in any one of Claim 1 to 9 whose said base material is a glass substrate or a polymer film.   The method for producing a polarizing film according to claim 10, wherein the polymer film contains a cellulose-based resin.   A liquid crystal display device provided with the polarizing film obtained by the manufacturing method of the polarizing film in any one of Claims 1-11.