JP2009104113A - Coating liquid and polarizing film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating liquid that gives a polarizing film of a lyotropic liquid crystal compound having high single transmittance and polarization degree, and to provide a polarizing film. <P>SOLUTION: The coating liquid contains a solvent and a lyotropic liquid crystal compound separated by salting out, and has a chloride ion concentration of at most 3×10[4] ppm. The polarizing film is obtained by flow casting the above coating liquid into a thin film and aligning the lyotropic liquid crystal compound. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a coating liquid and a polarizing film using the same.

  In a liquid crystal display, a polarizing plate or a retardation plate is used to control the optical rotation and birefringence of light passing through the liquid crystal. In the organic EL display, a circularly polarizing plate is used to prevent reflection of external light. Conventionally, polarizers obtained by orienting molecules such as dyes by dyeing a resin film such as polyvinyl alcohol with iodine or a dichroic organic dye and stretching the film in one direction (stretching method) are used for these polarizing plates. Has been widely used. However, a polarizer produced by a stretching method has a problem that heat resistance and light resistance are not sufficient depending on a dye or a polymer material to be used. In addition, since a wide film needs to be stretched with an increase in the size of the display panel, it has been a problem that the film forming apparatus is increased in size.

On the other hand, a coating film containing a lyotropic liquid crystal compound and water is applied to a substrate made of a glass plate or a resin film to form a coating film, and a polarizing film is formed by aligning the lyotropic liquid crystal compound in the coating film. A method is known (Patent Document 1). In the present specification, this type of polarizing film is referred to as a “polarizing film of a lyotropic liquid crystal compound”. The polarizing film of the lyotropic liquid crystal compound does not need to be stretched, and since there is no contraction in the width direction due to stretching, it is easy to obtain a polarizing film that is wide in the width direction. However, the conventional polarizing film of a lyotropic liquid crystal compound has a problem in that the polarization characteristics (single transmittance and degree of polarization) are inferior to those of a polarizer produced by a stretching method.
JP 2007-179933 A

  An object of the present invention is to provide a coating liquid and a polarizing film for realizing a polarizing film of a lyotropic liquid crystal compound having a single transmittance and a high degree of polarization.

As a result of investigating the cause of the low polarization degree of the polarizing film of the conventional lyotropic liquid crystal compound, the present inventors have found that impurities in the synthesis reaction of the lyotropic liquid crystal compound are contained in the coating liquid. The lyotropic liquid crystal compound is isolated from the crude product by salting out with an inorganic salt. Therefore, focusing on chloride ions, which are impurities generated during salting out, and reducing the concentration, the polarization characteristics (single transmittance and degree of polarization) were significantly better than the conventional polarizing films of lyotropic liquid crystal compounds. A polarizing film could be obtained. The chloride ion concentration is expressed in ppm by weight ratio of chloride ion / lyotropic liquid crystal compound. In addition, 10 ⁿ is ^expressed as 10 [n] in order to prevent misreading of the index.

式中、Ｑ_１はフェニル基またはナフチル基（これらの基は置換基を有していてもよい）を表わし、Ｑ_２およびＱ_３はそれぞれ独立してフェニレン基またはナフチレン基（これらの基は置換基を有していてもよい）を表わし、Ｒは水素原子、炭素数１〜３のアルキル基、アセチル基、ベンゾイル基またはフェニル基（これらの基は置換基を有していてもよい）を表わし、ｋは０〜４の整数、ｌは０〜４の整数（ただしｋ＋ｌ≦４）、ｍは０〜２の整数、ｎは０〜２の整数を表わし、Ｍは前記の陽イオンを表わす。
（５）本発明のコーティング液は、前記リオトロピック液晶化合物の溶媒に対する溶解度が、溶媒１００ｇに対して１．５ミリモル〜０．１５モルであることを特徴とする。
（６）本発明のコーティング液は、前記コーティング液の全固形分濃度が１重量％〜５０重量％であることを特徴とする。
（７）本発明のコーティング液は、前記コーティング液が２３℃において全固形分濃度が１重量％〜３０重量％の範囲の少なくとも一部で液晶性を示すことを特徴とする。
（８）本発明の偏光膜は、上記のコーティング液を薄膜状に流延し、前記リオトロピック液晶化合物を配向させて得られることを特徴とする。 The gist of the present invention is as follows.
(1) The coating liquid of the present invention is a coating liquid containing a lyotropic liquid crystal compound isolated by salting out and a solvent, and the chloride ion concentration of the coating liquid is 3 × 10 [4] ppm or less. It is characterized by that.
(2) In the coating liquid of the present invention, the lyotropic liquid crystal compound contains at least one hydrophilic group selected from the group consisting of —COOM, —SO ₃ M, —PO ₃ M, —OH, and —NH _2. It is characterized by. M represents a cation, and specifically, a hydrogen ion, a group I metal ion such as Li, Na, K, and Cs, an ammonium ion, and the like are preferable.
(3) The coating liquid of the present invention is characterized in that the lyotropic liquid crystal compound is an azo compound.
(4) The coating liquid of the present invention is characterized in that the azo compound is a compound represented by the following general formula (I).

In the formula, Q ₁ represents a phenyl group or a naphthyl group (these groups may have a substituent), and Q ₂ and Q ₃ each independently represents a phenylene group or a naphthylene group (these groups are substituted) R represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an acetyl group, a benzoyl group, or a phenyl group (these groups may have a substituent). K represents an integer of 0 to 4, l represents an integer of 0 to 4 (where k + 1 ≦ 4), m represents an integer of 0 to 2, n represents an integer of 0 to 2, and M represents the above cation. .
(5) The coating liquid of the present invention is characterized in that the lyotropic liquid crystal compound has a solubility in a solvent of 1.5 to 0.15 mol with respect to 100 g of the solvent.
(6) The coating liquid of the present invention is characterized in that the total solid concentration of the coating liquid is 1% by weight to 50% by weight.
(7) The coating liquid of the present invention is characterized in that the coating liquid exhibits liquid crystallinity in at least a part of the total solid concentration in the range of 1% by weight to 30% by weight at 23 ° C.
(8) The polarizing film of the present invention is obtained by casting the above coating liquid in a thin film and orienting the lyotropic liquid crystal compound.

  According to the present invention, a coating liquid for obtaining a polarizing film of a lyotropic liquid crystal compound having a single transmittance and a high degree of polarization, and a polarizing film could be obtained.

[Coating solution]
The coating liquid of the present invention contains a lyotropic liquid crystal compound isolated by salting out and a solvent. The coating liquid of the present invention may contain any other one. For example, it may contain a lyotropic liquid crystal compound that has not been isolated by salting out. Moreover, you may contain arbitrary additives, such as an alkaline agent, surfactant, and antioxidant.

The total solid concentration of the coating liquid of the present invention is preferably 1% by weight to 50% by weight.
When the total solid content concentration is in the above range, a polarizing film having a target thickness (for example, about 0.4 μm) can be obtained.

  Preferably, the coating liquid of the present invention exhibits liquid crystallinity at 23 ° C. and at least a part of the total solid content concentration in the range of 1 wt% to 30 wt%. By exhibiting liquid crystallinity in at least a part of the total solid concentration in the range of 1% by weight to 30% by weight, the lyotropic liquid crystal compound is oriented well, so that a polarizing film having a high degree of polarization can be obtained.

  The chloride ion concentration of the coating liquid of the present invention is 3 × 10 [4] ppm or less. The degree of polarization of the coating liquid can be increased by reducing the chloride ion concentration. The chloride ion concentration is preferably 2 × 10 [4] ppm or less, more preferably 1.5 × 10 [4] ppm or less, and further preferably 1 × 10 [4] ppm or less. The smaller the chloride ion concentration, the better, and it may be substantially zero. “Substantially zero” includes that whose value measured using an ion chromatograph (for example, DX-320 manufactured by DIONEX) is 0.01 × 10 [4] ppm or less.

[Lyotropic liquid crystal compound]
The lyotropic liquid crystal compound used in the present invention is isolated from the reaction crude product in the synthesis reaction of the lyotropic liquid crystal compound by salting out. In this specification, “salting out” means that when a large amount of salt (usually sodium chloride or lithium chloride) is added to a solution containing a hydrophilic compound, water molecules that are hydrated are deprived and the hydrophilic compound is converted into a salt. It means agglomeration and precipitation.

  In this specification, the “lyotropic liquid crystal compound” refers to a liquid crystal compound having a property of causing a phase transition between an isotropic phase and a liquid crystal phase by changing the concentration of the lyotropic liquid crystal compound in a solution state. There is no limitation on the liquid crystal phase to be expressed, and examples thereof include a nematic liquid crystal phase, a smectic liquid crystal phase, and a cholesteric liquid crystal phase. These liquid crystal phases are confirmed and identified by an optical pattern observed with a polarizing microscope.

  In the lyotropic liquid crystal compound, preferably, the transition moment in the major axis direction of the molecule is larger than that in the minor axis direction, or the transition moment in the minor axis direction is larger than that in the major axis direction. Thus, when the magnitude of the transition moment is different between the major axis and the minor axis, absorption dichroism is exhibited. The lyotropic liquid crystal compound preferably exhibits maximum absorption somewhere in the visible light region (wavelength 380 nm to 780 nm).

The solubility of the lyotropic liquid crystal compound in the solvent is preferably 1.5 mmol to 0.15 mol, more preferably 5 mmol to 50 mmol, with respect to 100 g of the solvent. When the solubility is in the above range, a coating liquid exhibiting a stable liquid crystal phase can be obtained. The lyotropic liquid crystal compound is preferably water-soluble. The lyotropic liquid crystal compound preferably has a hydrophilic group in order to impart water solubility. The hydrophilic group is preferably at least one substituent selected from the group consisting of —COOM, —SO ₃ M, —PO ₃ M, —OH, and —NH ₂ . M represents a cation, preferably a hydrogen ion, a group 1 metal ion such as Li, Na, K, or Cs, or an ammonium ion.

  The lyotropic liquid crystal compound used in the present invention is preferably an azo compound, an anthraquinone compound, a perylene compound, a quinophthalone compound, a naphthoquinone compound or a merocyanine compound. Such a compound exhibits lyotropic liquid crystallinity in a solution state and can exhibit absorption dichroism. Of these, azo compounds are particularly preferred.

式中、Ｑ_１はフェニル基またはナフチル基（これらの基は置換基を有していてもよい）を表わし、Ｑ_２およびＱ_３はそれぞれ独立してフェニレン基またはナフチレン基（これらの基は置換基を有していてもよい）を表わし、Ｒは水素原子、炭素数１〜３のアルキル基、アセチル基、ベンゾイル基またはフェニル基（これらの基は置換基を有していてもよい）を表わし、ｋは０〜４の整数、ｌは０〜４の整数（ただしｋ＋ｌ≦４）、ｍは０〜２の整数、ｎは０〜２の整数を表わし、Ｍは前記の陽イオンを表わす。 The azo compound is preferably a compound represented by the following general formula (I).

In the formula, Q ₁ represents a phenyl group or a naphthyl group (these groups may have a substituent), and Q ₂ and Q ₃ each independently represents a phenylene group or a naphthylene group (these groups are substituted) R represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an acetyl group, a benzoyl group, or a phenyl group (these groups may have a substituent). K represents an integer of 0 to 4, l represents an integer of 0 to 4 (where k + 1 ≦ 4), m represents an integer of 0 to 2, n represents an integer of 0 to 2, and M represents the above cation. .

Q ₁ is preferably a substituent selected from the group consisting of a nitro group, a cyano group, a hydroxyl group, an amino group, a halogen group, a halogenated alkyl group having 1 to 3 carbon atoms, and an alkoxy group having 1 to 3 carbon atoms. Is a phenyl group having one or two. Q ₃ is preferably a naphthylene group having one or two substituents selected from the group consisting of an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a hydroxyl group, and a sulfonic acid group. is there.

The azo compounds represented by the general formula (I) can be obtained, for example, according to Yutaka Hosoda “Theoretical Manufacturing Dye Chemistry” (issued July 15, 1968, Technique Hall, 5th edition, pages 135 to 152). Two kinds of compounds having an amino group can be obtained by diazotization and coupling reaction. Note that the number of substituents Q ₂ linked by an azo bond can be increased by repeating diazotization and coupling reactions.

[solvent]
The solvent used in the present invention preferably dissolves the lyotropic liquid crystal compound and does not contain chloride ions or has a low chloride ion concentration. The solvent is preferably a hydrophilic solvent. Examples of the hydrophilic solvent include water, alcohols, and cellosolves. Water-soluble solvents such as alcohols, ethers, cellosolves, dimethylsulfoxide, dimethylformamide may be added to water. Water-soluble compounds such as glycerin and ethylene glycol may be added. These additives can be used to adjust the solubility of the water-soluble liquid crystal compound and the drying speed of the aqueous solution. The amount of these solvents added is preferably 100 parts by weight or less with respect to 100 parts by weight of water in the aqueous solution.

[Production of coating liquid]
The coating liquid of this invention can be obtained with the manufacturing method containing the following process (1) and process (2), for example.
Step (1): The lyotropic liquid crystal compound is isolated by salting out from the reaction solution obtained by synthesizing the lyotropic liquid crystal compound.
Step (2): The lyotropic liquid crystal compound isolated in Step (1) and a solvent are mixed to obtain a mixed solution, and this mixed solution is ion-exchanged resin and the concentration of chloride ions is 3 × 10 [4 It is processed so as to be equal to or lower than ppm to obtain a coating solution.

  The concentration of chloride ions in the coating solution can be reduced by a membrane membrane in addition to the ion exchange resin. A plurality of these methods for reducing the concentration of chloride ions can be used in combination.

[Polarizing film]
The polarizing film of the present invention is obtained by casting the above coating liquid into a thin film and orienting the lyotropic liquid crystal compound. The polarizing film of the present invention preferably exhibits absorption dichroism in at least a part of a wavelength range of 380 nm to 780 nm, particularly at a wavelength of 550 nm. The dichroic ratio of the polarizing film of the present invention is preferably 20 or more, more preferably 30 or more, at a wavelength of 550 nm. The single transmittance of the polarizing film of the present invention is preferably 30% to 50% at a wavelength of 550 nm. The polarization degree of the polarizing film of the present invention is preferably 90% or more, more preferably 95% or more at a wavelength of 550 nm.

[Casting]
The coating liquid of the present invention can be made into a thin film by, for example, casting on a substrate. The casting method is not particularly limited as long as the coating liquid is uniformly cast, and a casting method using an appropriate coater is employed. Examples of the casting apparatus include a slide coater, a slot die coater, a bar coater, a rod coater, a roll coater, a flexographic printing machine, a screen printing machine, a curtain coater, a spray coater, and a spin coater.

[substrate]
There is no restriction | limiting in a board | substrate, The thing of a single layer may be sufficient and the laminated body of multiple layers (for example, alignment film is included) may be sufficient. Specific examples of the substrate include a glass plate and a resin film. When the substrate includes an alignment film, the alignment film is preferably subjected to an alignment treatment. Examples of the substrate including the alignment film include a substrate in which a glass film is coated with a polyimide film. This polyimide film is provided with orientation by a known method, for example, mechanical orientation treatment such as rubbing in a certain direction, or chemical orientation treatment such as photo-alignment treatment. The alignment treatment of the substrate can be carried out by a known method described in “Liquid Crystal Handbook” (Maruzen Co., Ltd., issued on October 30, 2000), pages 226 to 239.

  The glass plate of the substrate is preferably used for a liquid crystal cell, and examples thereof include alkali-free glass. In the case of using a resin film as the substrate, the substrate can be provided with flexibility, which is suitable for applications that require flexibility. The surface of the resin film may be subjected to orientation treatment by rubbing or the like. Alternatively, an alignment film made of another material may be formed on the surface of the resin film. The material of the resin film used for the substrate is not particularly limited as long as it is a film-forming resin, but a styrene resin, a (meth) acrylic acid resin, a polyester resin, a polyolefin resin, a norbornene resin, a polyimide resin Examples include resins, cellulose resins, polyvinyl alcohol resins, and polycarbonate resins. The thickness of the substrate is not particularly limited except for the application, but is generally in the range of 1 μm to 1000 μm.

[Orientation]
The lyotropic liquid crystal compound used in the present invention can be aligned by flow when a shear stress is applied in a liquid crystal state. The lyotropic liquid crystal compound forms supramolecular aggregates in a liquid crystal state, and when a coating liquid containing the supramolecular aggregates is flowed by applying a shear stress, the major axis direction of the supramolecular aggregates is aligned in the flow direction. The orientation means may be used in combination with shearing stress, orientation treatment such as rubbing treatment or photo-alignment treatment, or orientation by a magnetic field or electric field.

[Dry]
The coating liquid of the present invention may be dried after being cast into a thin film. There is no restriction | limiting in a drying means, For example, natural drying, reduced pressure drying, heating drying, reduced pressure heating drying, etc. are used. As the heating and drying means, a drying method using an arbitrary drying apparatus such as an air circulation type drying oven or a hot roll is used. The drying temperature in the case of heat drying is preferably 50 ° C to 120 ° C, more preferably 80 ° C to 100 ° C.

[Application of polarizing film]
The polarizing film of the present invention is used for various optical elements by taking advantage of optical anisotropy, and can be particularly suitably used as a polarizing plate and a retardation plate. Applications of polarizing films are, for example, OA equipment such as personal computer monitors, notebook personal computers, and copiers, mobile phones, watches, digital cameras, personal digital assistants (PDAs), portable devices such as portable game equipment, video cameras, televisions, and electronic devices. Liquid crystal display devices such as household equipment such as range, in-car equipment such as back monitor, car navigation and car audio, display equipment such as store monitor, security equipment such as monitoring monitor, nursing monitor, medical monitor, etc. Can be mentioned. The polarizing film may be used after being peeled from the substrate, or may be used while being laminated with the substrate. When used for optical purposes with being laminated, the substrate is preferably transparent in the visible light wavelength region. When peeled from the substrate, it is preferably used by being laminated on another support or optical element.

構造式（II）で表わされるアゾ系化合物と水を含む水溶液は塩化物イオンが４２×１０［４］ｐｐｍ程度であったので、イオン交換樹脂（日本錬水株式会社製ＤＩＡＩＯＮ ＡＭＰ０１）を通して塩化物イオン濃度が０．１×１０［４］ｐｐｍとなるように精製した。精製した水溶液は全固形分濃度が０．９重量％程度であったので、ロータリーエバポレーターを用いて全固形分濃度が１８重量％となるように濃縮してコーティング液を作製した。 [Example]
An azo compound represented by the structural formula (II) was synthesized by the following (a) to (c).
(A) A monoazo compound was obtained from p-anisidine and lithium 8-amino-2-naphthalenesulfonate through a diazotization and coupling step by a conventional method.
(B) The obtained monoazo compound was diazotized by a conventional method and subjected to a coupling reaction with lithium 7-amino-1-naphthol-3,6-disulfonate.
(C) Lithium chloride was added to the reaction solution containing the obtained crude product for salting out, and the azo compound represented by the structural formula (II) was isolated.

Since the aqueous solution containing the azo compound represented by the structural formula (II) and water had a chloride ion of about 42 × 10 [4] ppm, the chloride was passed through an ion exchange resin (DIAION AMP01 manufactured by Nippon Nensui Co., Ltd.). It refine | purified so that ion concentration might be set to 0.1x10 [4] ppm. The purified aqueous solution had a total solid content concentration of about 0.9% by weight, and thus was concentrated using a rotary evaporator so that the total solid content concentration was 18% by weight.

Next, the rubbing treatment and corona treatment of the cycloolefin resin film (ZEONOR manufactured by Nippon Zeon Co., Ltd.) is coated with a thin film using a wire bar (count # 1.5) on the surface subjected to rubbing treatment and corona treatment. The film was naturally dried for about 1 minute to produce a polarizing film having a thickness of 0.4 μm. As shown in Table 1, the polarizing film of the example has a high single transmittance of 39.2% and a very high degree of polarization of 98.2%, so it has a good balance and excellent polarization characteristics.

[Comparative Example 1]
A coating solution and a polarizing film were prepared in the same manner as in the Examples except that the treatment time with the ion exchange resin was shortened and the chloride ion concentration was purified to 5 × 10 [4] ppm. As shown in Table 1, the polarizing film of Comparative Example 1 has a very high single transmittance of 46.4%, but a very low degree of polarization of 57.3%.

[Comparative Example 2]
A coating solution and a polarizing film were prepared in the same manner as in the examples except that the treatment time with the ion exchange resin was shortened and purification was performed so that the chloride ion concentration was 10 × 10 [4] ppm. As shown in Table 1, the polarizing film of Comparative Example 2 has a single transmittance as high as 38.4%, but a polarization degree as low as 86.4%.

[Comparative Example 3]
A coating solution and a polarizing film were prepared in the same manner as in the examples except that the treatment time with the ion exchange resin was shortened and purification was performed so that the chloride ion concentration was 20 × 10 [4] ppm. As shown in Table 1, the polarizing film of Comparative Example 3 has a single transmittance of as low as 17.4% and a polarization degree as low as 78.1%.

[Evaluation]
As shown in Table 1, the polarizing films of Examples have high single transmittance and degree of polarization and are excellent in polarization characteristics. On the other hand, the polarizing films of Comparative Example 1 and Comparative Example 2 have low either single transmittance or degree of polarization, and both of the polarizing films of Comparative Example 3 have low polarization characteristics. It is considered that the polarization characteristics of the polarizing film of the example are good because the chloride ion concentration was reduced.

[Measuring method]
The method for quantifying chloride ions is as follows. About 20 mg of a sample (coating solution or polarizing film) is weighed, wrapped in Sn foil, burned using an automatic sample combustion device, and the generated gas is absorbed liquid (30% hydrogen peroxide added to pure water) 10 ml To collect. The absorption solution is made up to 15 ml and measured using an ion chromatograph (for example, DX-320 manufactured by DIONEX).

The dichroic ratio, the single transmittance, and the degree of polarization were measured using a spectrophotometer (JASCO Corp. V-7100) equipped with a Glan-Thompson polarizer, and linearly polarized measuring light with a measuring wavelength was incident, and the following k ₁ And k ₂ are calculated from the following equation.
Dichroic ratio: log (1 / k ₂ ) / log (1 / k ₁ )
Single transmittance: (k ₁ + k ₂ ) / 2
Polarization degree: (k ₁ −k ₂ ) / (k ₁ + k ₂ )
Wherein 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.

Claims (8)

  A coating liquid comprising a lyotropic liquid crystal compound isolated by salting out and a solvent, wherein the coating liquid has a chloride ion concentration of 3 × 10 [4] ppm or less. The lyotropic liquid crystal compound containing at least one hydrophilic group selected from the group consisting of —COOM, —SO ₃ M, —PO ₃ M, —OH, and —NH ₂ , wherein M is a cation. The coating liquid according to claim 1.   The coating liquid according to claim 1, wherein the lyotropic liquid crystal compound is an azo compound. The coating liquid according to claim 1, wherein the azo compound is a compound represented by the following general formula (I).

(Wherein Q ₁ represents a phenyl group or a naphthyl group (these groups may have a substituent), and Q ₂ and Q ₃ each independently represent a phenylene group or a naphthylene group (these groups are And R represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an acetyl group, a benzoyl group or a phenyl group (these groups may have a substituent). K represents an integer of 0 to 4, l represents an integer of 0 to 4 (where k + 1 ≦ 4), m represents an integer of 0 to 2, n represents an integer of 0 to 2, and M represents a cation. )   The coating liquid according to any one of claims 1 to 4, wherein the solubility of the lyotropic liquid crystal compound in a solvent is 1.5 mmol to 0.15 mol with respect to 100 g of the solvent.   6. The coating liquid according to claim 1, wherein the total solid concentration of the coating liquid is 1% by weight to 50% by weight.   The coating liquid according to any one of claims 1 to 6, wherein the coating liquid exhibits liquid crystallinity at a part of the total solid concentration in the range of 1 wt% to 30 wt% at 23 ° C. .   A polarizing film obtained by casting the coating liquid according to any one of claims 1 to 7 in a thin film and aligning the lyotropic liquid crystal compound.