JP2009115866A - Coating liquid, polarizing film and method for producing polarizing film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating liquid having liquid crystal property in a wide temperature range in order to solve the problem that a polarizing film cannot be formed when the conventional azo compound has no liquid crystal property in a solution state or it is required to strictly manage the temperature in spreading the coating liquid when the compound has the liquid crystal property only within a narrow temperature range, so that it is difficult to stably manufacture the polarizing film. <P>SOLUTION: This coating liquid at least contains an azo compound represented by general formula (I) and a solvent. The azo compound shows liquid crystal property in a wide temperature range by forming a strongly bonded supermolecular aggregate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a coating liquid, a polarizing film produced therefrom, and a method for producing the polarizing film.

  In the liquid crystal display, a polarizing plate is used to control the optical rotation of light passing through the liquid crystal. Conventionally, a polarizer obtained by dyeing a resin film such as polyvinyl alcohol with iodine or a dichroic dye and stretching it in one direction has been widely used for these polarizing plates. However, the polarizer described above has problems that heat resistance and light resistance are not sufficient depending on the type of the pigment or the resin film, and that the film stretching apparatus becomes larger as the liquid crystal display becomes larger.

  On the other hand, a method of forming a polarizing film by applying a coating liquid containing a lyotropic liquid crystal compound on a substrate such as a glass plate or a resin film and orienting the lyotropic liquid crystal compound is known. A lyotropic liquid crystal compound forms a supramolecular aggregate exhibiting liquid crystallinity in a solution, and when a coating liquid containing this is subjected to shear stress to flow, the major axis direction of the supramolecular aggregate is aligned in the flow direction. . One such lyotropic liquid crystal compound is an azo compound (Patent Document 1). 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 having a wide width.

However, conventional azo compounds may not exhibit liquid crystallinity in a solution state or may exhibit liquid crystallinity only in a narrow temperature range. If the liquid crystal is not shown, the polarizing film cannot be produced because the azo compound is not aligned. If the temperature range is narrow, the polarizing film is stable because strict temperature control is required when casting the coating liquid. Difficult to manufacture. Therefore, a coating liquid that exhibits liquid crystallinity over a wide temperature range is demanded.
JP 2006-323377 A

  An object of the present invention is to provide a coating liquid exhibiting liquid crystallinity over a wide temperature range, a polarizing film produced therefrom, and a method for producing the polarizing film.

  As a result of studying the chemical structure in order to expand the temperature range in which the azo compound exhibits liquid crystal properties, the present inventors have found that the azo compound represented by the general formula (I) exhibits liquid crystal properties in a wide temperature range. . The reason why this azo compound exhibits liquid crystallinity in a wide temperature range is not clear in detail, but it is considered that a strongly bonded supramolecular aggregate is formed. When water is used as the solvent, the coating solution does not freeze even when the temperature is 0 ° C. or less due to the freezing point depression.

式中、Ｘはニトロ基または炭素数１〜４のアルコキシ基を表わし、Ｑ_１およびＱ_２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（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、Ｍは対イオンを表わす。
（２）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。
（３）本発明のコーティング液は、前記コーティング液のｐＨが４〜９であることを特徴とする。
（４）本発明のコーティング液は、前記アゾ系化合物の濃度が５重量％〜３０重量％であることを特徴とする。
（５）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、乾燥させて得られることを特徴とする。
（６）本発明の偏光膜の製造方法は、上記のコーティング液を薄膜状に流延し、乾燥させる工程を含むことを特徴とする。 The gist of the present invention is as follows.
(1) The coating liquid of the present invention includes at least an azo compound represented by the following general formula (I) and a solvent.

In the formula, X represents a nitro group or an alkoxy group having 1 to 4 carbon atoms, and Q ₁ and Q ₂ each independently represents a phenylene group or a naphthylene group (these groups may have a substituent). R represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an acetyl group, a benzoyl group or a phenyl group (which may have a substituent), k is an integer of 0 to 4, and l is 0 to 0. An integer of 4 (where k + 1 ≦ 4), m is an integer of 0 to 2, n is an integer of 0 to 2, and M represents a counter ion.
(2) 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.
(3) The coating liquid of the present invention is characterized in that the coating liquid has a pH of 4 to 9.
(4) The coating liquid of the present invention is characterized in that the concentration of the azo compound is 5% by weight to 30% by weight.
(5) The polarizing film of the present invention is characterized by being obtained by casting the above coating liquid into a thin film and drying it.
(6) The manufacturing method of the polarizing film of this invention is characterized by including the process of casting said coating liquid in the shape of a thin film, and making it dry.

  A coating solution exhibiting liquid crystallinity in a wide temperature range, for example, −18 ° C. to + 40 ° C., was obtained by the above azo compound. Since the coating liquid of the present invention does not require strict temperature control during casting, the polarizing film can be produced stably. In particular, when water is used as a solvent, the coating liquid of the present invention has the characteristic of exhibiting liquid crystallinity without freezing even at 0 ° C. or lower.

[Coating solution]
The coating liquid of the present invention contains a specific azo compound and a solvent described later. The total solid concentration of the coating liquid of the present invention is preferably 1% by weight to 50% by weight, more preferably 5% by weight to 30% by weight. When the total solid concentration is in the above range, a polarizing film having a target thickness (for example, 0.4 μm) can be easily obtained. The pH of the coating solution of the present invention is preferably 4-9. When the pH is within the above range, a polarizing film having a high degree of orientation can be obtained.

The coating liquid of the present invention may contain any other liquid as long as it contains the specific azo compound and a solvent, for example, other liquid crystal compounds and additives. Examples of the additive include a surfactant, an antioxidant, and an antistatic agent. The concentration of the additive is usually less than 10% by weight. The liquid crystallinity exhibited by the coating liquid of the present invention is not particularly limited, but is preferably a nematic liquid crystal phase. The liquid crystal phase is observed in a certain temperature range (liquid crystal temperature range; ΔT = liquid crystal phase transition temperature T _H on the high temperature side−liquid crystal phase transition temperature T _C on the low temperature side). Liquid crystal phase transition temperature T _C on the low temperature side of the above coating liquid is preferably not 0 ℃ or less, more preferably -20 ℃ ~-5 ℃. Liquid crystal phase transition temperature T _H of the high-temperature side of the coating liquid is preferably at 30 ° C. or higher, more preferably 30 ° C. to 70 ° C.. As described above, it is one of the features of the present invention that the coating liquid does not freeze even at 0 ° C. or lower and exhibits liquid crystallinity over a wide temperature range. In addition, said liquid crystal phase is confirmed and identified by the optical pattern observed with a polarization microscope.

式中、Ｘはニトロ基または炭素数１〜４のアルコキシ基を表わし、Ｑ_１およびＱ_２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（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、Ｍは対イオンを表わす。上記の一般式（Ｉ）で表わされるアゾ系化合物は、細田豊著「理論製造 染料化学 第５版」（昭和４３年７月１５日技法堂発行、１３５ページ〜１５２ページ参照）に従って、例えば、それぞれアミノ基を有する二種類の化合物を、ジアゾ化およびカップリング反応させて得ることができる。なお、アゾ結合で連結された置換基Ｑ１の数は、ジアゾ化およびカップリング反応を繰り返すことにより増加させることができる。 [Azo compounds]
The azo compound used in the coating liquid of the present invention is a compound represented by the following general formula (I). This azo compound exhibits liquid crystallinity over a wide temperature range. Furthermore, since it exhibits absorption dichroism at least at a part of wavelengths of 380 nm to 780 nm, it is suitably used as a polarizing film.

In the formula, X represents a nitro group or an alkoxy group having 1 to 4 carbon atoms, and Q ₁ and Q ₂ each independently represents a phenylene group or a naphthylene group (these groups may have a substituent). R represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an acetyl group, a benzoyl group or a phenyl group (which may have a substituent), k is an integer of 0 to 4, and l is 0 to 0. An integer of 4 (where k + 1 ≦ 4), m is an integer of 0 to 2, n is an integer of 0 to 2, and M represents a counter ion. The azo compound represented by the above general formula (I) is, for example, according to Yutaka Hosoda “Theoretical Manufacturing Dye Chemistry 5th Edition” (published July 15, 1968, Technique Hall, pages 135 to 152). Two kinds of compounds each having an amino group can be obtained by diazotization and coupling reaction. The number of substituents Q1 linked by an azo bond can be increased by repeating diazotization and coupling reactions.

上記のコーティング液中、上記一般式（Ｉ）または（II）で表わされるアゾ系化合物の濃度は、好ましくは５重量％〜３０重量％である。この濃度範囲であれば上記のコーティング液は広い温度範囲で液晶性を示すことができる。上記の一般式（II）で表わされるアゾ系化合物は、アニリン誘導体とアミノナフタレン誘導体とを、ジアゾ化およびアゾカップリングし、得られた化合物をさらにアミノナフトール誘導体とジアゾ化およびアゾカップリングして得ることができる。 The azo compound is preferably a compound represented by the following formula (II). This azo compound exhibits liquid crystallinity over a wide temperature range. When the solvent is mainly water or water, the azo compound has a characteristic that it does not freeze even at 0 ° C. or lower and exhibits liquid crystallinity. In formula (II), R, k, l, m, and M are the same as in formula (I), and o represents an integer of 0 to 4.

The concentration of the azo compound represented by the general formula (I) or (II) in the coating solution is preferably 5% by weight to 30% by weight. If it is this concentration range, said coating liquid can show liquid crystallinity in a wide temperature range. The azo compound represented by the general formula (II) is obtained by diazotizing and azocoupling an aniline derivative and an aminonaphthalene derivative, and further diazotizing and azocoupling the resulting compound with an aminonaphthol derivative. Obtainable.

[solvent]
The solvent used in the present invention is not particularly limited as long as it dissolves the above azo compound, but is preferably an aqueous solvent or a hydrophilic solvent. Examples of the aqueous solvent include water and water added with a water-soluble solvent such as alcohols, ethers, cellosolves, dimethylsulfoxide, and dimethylformamide. Examples of the hydrophilic solvent include alcohols and cellosolves. A water-soluble compound such as glycerin or ethylene glycol may be added to the solvent. These additives can be used to adjust the solubility of the azo compound and the drying rate of the coating liquid.

[Polarizing film]
The polarizing film of the present invention is obtained by casting or coating the above coating liquid in a thin film, orienting the azo compound and drying. The polarizing film exhibits absorption dichroism in at least a part of the wavelength range of 380 nm to 780 nm when the azo compound represented by the general formula (I) is oriented. The thickness of the polarizing film is preferably 0.05 μm to 5 μm, more preferably 0.1 μm to 1 μm. The polarization degree of the polarizing film is preferably 98% or more, more preferably 99% or more.

[Casting (application)]
The method for producing a polarizing film of the present invention includes a step of casting or coating a coating solution in a thin film and drying it. The above step is preferably carried out by casting or applying the above coating solution on a substrate and drying it. The casting (coating) means is not particularly limited as long as the coating liquid is uniformly cast, and a casting means using an appropriate coater is employed. Examples of the casting apparatus that can be used 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, and a spray coater.

[Base material]
There is no restriction | limiting in particular in the base material for apply | coating a coating liquid, The thing of a single layer may be sufficient and the laminated body (for example, alignment film is included) of a multilayer 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 base material including the alignment film include a base material in which a polyimide film is coated on a glass plate. This polyimide film is provided with orientation by a known method, for example, mechanical orientation treatment such as rubbing or photo-alignment treatment. As the glass of the substrate, alkali-free glass used for a liquid crystal cell is preferable. If a resin film is used as the base material, flexibility can be imparted, 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 thereof 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 azo compound used in the present invention forms a supramolecular aggregate exhibiting liquid crystallinity in a solution. When a coating solution containing this is subjected to shear stress to flow, the major axis direction of the supramolecular aggregate is changed. Oriented 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]
There is no particular limitation on the means for drying the cast coating liquid, and natural drying, vacuum drying, heat drying, heat drying under reduced pressure, and the like 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.

[Application of polarizing film]
The polarizing film of the present invention is suitably used as a polarizing element. Polarizing elements are OA equipment such as personal computer monitors, notebook personal computers, copy machines, mobile phones, watches, digital cameras, personal digital assistants, portable devices such as portable game machines, household equipment such as video cameras, TVs, and microwave ovens, backs. Used in liquid crystal display devices for in-vehicle devices such as monitors, car navigation, car audio, display devices such as store monitors, security devices such as monitoring monitors, medical devices such as nursing monitors and medical monitors. The polarizing film of the present invention may be used after being peeled off from the substrate, or may be used while being laminated with the substrate. When used for optical purposes while being laminated with a substrate, the substrate is preferably transparent to visible light. When peeled from the base material, it is preferably used by being laminated on another support or optical element.

[Example]
[Example 1]
[Synthesis of Azo Compound A]
From 4-nitroaniline and 8-amino-2-naphthalenesulfonic acid according to a conventional method (Toyo Hosoda, “Theoretical Production, Dye Chemistry, 5th Edition”, issued July 15, 1968, Technique Hall, pages 135-152) A monoazo compound was prepared through diazotization and a coupling reaction. The obtained monoazo compound was similarly diazotized by a conventional method, subjected to a coupling reaction with 7-amino-1-naphthol-3,6-disulfonic acid lithium salt, and salted out with lithium chloride to give the following general formula (III The azo compound A in which the substituent X is a nitro group was synthesized.

[Preparation of coating liquid A]
The above azo compound A and water were mixed to prepare a coating liquid A having a concentration of azo compound A of 20% by weight. The pH of this coating liquid A was 6.7. As shown in Table 1, the liquid crystallinity of the coating liquid A was a nematic phase, and the temperature range ΔT exhibiting liquid crystallinity was −18 ° C. to + 40 ° C.

[Preparation of Polarizing Film A]
Using a bar coater (mayrrot HS4 manufactured by BUSCHMAN), the above coating liquid A was cast in a thin film on the surface of a cycloolefin resin film (ZEONOR manufactured by Nippon Zeon Co., Ltd., thickness: 100 μm) subjected to rubbing treatment and corona treatment. Then, it was naturally dried in a constant temperature room at 23 ° C. to produce a polarizing film A. As shown in Table 1, the polarization degree of the polarizing film A was 99.1%.

[Example 2]
[Synthesis of Azo Compound B]
An azo compound B in which the substituent X of the general formula (III) is a methoxy group in the same manner as in “Synthesis of azo compound A” in Example 1 except that p-anisidine was used instead of 4-nitroaniline. Was synthesized.

[Preparation of coating liquid B]
The above azo compound B and water were mixed to prepare a coating liquid B having a concentration of 18% by weight of the azo compound B. The pH of this coating liquid B was 6.0. As shown in Table 1, the liquid crystallinity of the coating liquid B was a nematic phase, and the temperature range ΔT exhibiting liquid crystallinity was −8 ° C. to + 40 ° C.

[Preparation of Polarizing Film B]
Using the coating liquid B, a polarizing film B was prepared in the same manner as in “Preparation of polarizing film A” in Example 1. As shown in Table 1, the polarization degree of the polarizing film B was 98.6%.

[Comparative example]
[Synthesis of Azo Compound C]
An azo compound C in which the substituent X of the general formula (III) is a sulfonic acid group in the same manner as in “Synthesis of azo compound A” in Example 1 except that a sulfanyl group was used instead of 4-nitroaniline. Was synthesized.

[Preparation of coating liquid C]
The above azo compound C and water were mixed to prepare a coating liquid C having a concentration of 15% by weight of the azo compound C. The pH of this coating liquid C was 9.8. As shown in Table 1, the coating liquid C did not exhibit liquid crystallinity.

[Preparation of Polarizing Film C]
Using the above coating liquid C, a polarizing film C was produced in the same manner as in “Preparation of polarizing film A” in Example 1. The polarizing film C showed no polarizing action because the azo compound C was not oriented (Table 1).

[Measuring method]
[Method for confirming liquid crystal properties and liquid crystal temperature range ΔT]
The coating solution is collected with a poly dropper and sandwiched between two slide glasses (Matsunami SLIDE GLASS manufactured by Matsunami Glass Co., Ltd.). This is placed on a large sample cooling and heating stage (10013L manufactured by Japan High Tech Co.) for a microscope. After heating to 90 ° C. at 10 ° C./min, the sample was observed with a polarizing microscope (OLYMPUS OPTIPHOT-POL) while cooling to −30 ° C. at −10 ° C./min.

[Measurement method of pH]
The pH of each coating solution was measured using a pH meter (Ultra BASIC manufactured by DENVER INSTRUMENT).

[Measurement method of polarization degree]
A polarized light transmission spectrum in the wavelength range of 380 nm to 780 nm was measured using a spectrophotometer (V-7100 manufactured by JASCO Corporation) equipped with a Glan-Thompson polarizer. From this spectrum, the transmittance Y ₁ of linearly polarized light in the direction of maximum transmittance subjected to visibility correction and the transmittance Y ₂ of linearly polarized light in the direction orthogonal to the maximum transmittance direction were obtained, and the degree of polarization was calculated by the following equation.
Polarization degree = (Y ₁ −Y ₂ ) / (Y ₁ + Y ₂ )

Claims (6)

A coating liquid comprising at least an azo compound represented by the following general formula (I) and a solvent.

(In the formula, X represents a nitro group or an alkoxy group having 1 to 4 carbon atoms, and Q ₁ and Q ₂ are each independently a phenylene group or a naphthylene group (these groups may have a substituent)) R represents a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an acetyl group, a benzoyl group or a phenyl group (which may have a substituent), k is an integer of 0 to 4, and l is 0. An integer of ˜4 (where k + 1 ≦ 4), m is an integer of 0 to 2, n is an integer of 0 to 2, and M represents a counter ion.)   The coating liquid according to claim 1, wherein the total solid concentration of the coating liquid is 1 wt% to 50 wt%.   The coating liquid according to claim 1 or 2, wherein the pH of the coating liquid is 4-9.   The coating solution according to any one of claims 1 to 3, wherein the concentration of the azo compound is 5 to 30% by weight.   A polarizing film obtained by casting the coating liquid according to claim 1 into a thin film and drying it.   A method for producing a polarizing film, comprising a step of casting the coating liquid according to claim 1 into a thin film and drying it.