JP2011128294A - Method for producing polarizing film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a polarizing film, by which an optically uniform polarizing film is produced by effectively suppressing the occurrence of deposit in an evaporation process of a solvent by adjusting the flow casting conditions of a coating liquid when the polarizing film is formed by flow casting a coating liquid containing a bisazo-based lyotropic liquid crystal compound having a naphthalene ring and a solvent. <P>SOLUTION: The method for producing a polarizing film containing a bisazo-based lyotropic liquid crystal compound having a naphthalene ring includes: a process A for obtaining a mixed liquid by mixing the bisazo-based lyotropic liquid crystal compound having a naphthalene ring and a solvent; a process B for obtaining a coating liquid by heating the mixed liquid to dissolve the undissolved bisazo-based lyotropic liquid crystal compound having a naphthalene ring in the solvent; and a process C for obtaining the polarizing film by flow casting the coating liquid into a thin film while maintaining the temperature of the coating liquid at a temperature of ≥40°C or flow casting the coating liquid into a thin film within 12 h after the temperature of the coating liquid has become lower than 40°C. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a process for evaporating a solvent by adjusting a casting condition of the coating solution when casting a coating solution containing a bisazo lyotropic liquid crystal compound having a naphthalene ring and a solvent to produce a polarizing film. The present invention relates to a method for manufacturing a polarizing film, which effectively suppresses the generation of precipitates and produces an optically uniform polarizing film.

  Conventionally, a polarizing film obtained by casting a coating solution containing a bisazo-based lyotropic liquid crystal compound having a naphthalene ring into a thin film is known (Japanese Patent Laid-Open No. 2009-173849). In the liquid crystalline coating solution for producing such a polarizing film, fine crystals are precipitated by introducing a sulfonic acid group into an aminonaphthol skeleton having poor solubility in the azo compound structure contained therein to improve the solubility. Thus, a polarizing film having a low haze (light scattering) can be obtained. Further, such a polarizing film is expected in the future because the thickness can be remarkably reduced as compared with a general-purpose polarizing film obtained by stretching and staining a polyvinyl alcohol film.

JP 2009-173849 A

However, the polarizing film obtained from the liquid crystalline coating solution of Patent Document 1 may produce precipitates in the course of evaporation of the solvent depending on the casting conditions of the liquid crystalline coating solution during the film formation. There is a problem that optical uniformity is reduced.
Therefore, when casting a coating solution containing a bisazo-based lyotropic liquid crystal compound having a naphthalene ring and a solvent to produce a polarizing film, coating is applied to effectively suppress the generation of precipitates during the evaporation of the solvent. There is a need to establish liquid casting conditions.

  The present invention was made in order to solve the above-mentioned conventional problems, and when a polarizing film is produced by casting a coating liquid containing a bisazo-based lyotropic liquid crystal compound part having a naphthalene ring and a solvent, To provide a method for producing a polarizing film capable of producing an optically uniform polarizing film by effectively suppressing the generation of precipitates during the evaporation process of the solvent by adjusting the casting conditions of the coating liquid. Objective.

In order to achieve the above object, a method for producing a polarizing film according to claim 1 is a method for producing a polarizing film containing a bisazo-based lyotropic liquid crystal compound having a naphthalene ring,
A step A in which a bisazo lyotropic liquid crystal compound having a naphthalene ring and a solvent are mixed to obtain a mixed solution;
Heat treating the mixed solution to dissolve a bisazo-based lyotropic liquid crystal compound having an undissolved naphthalene ring in a solvent to obtain a coating solution; and
A step of casting the coating solution into a thin film while maintaining the liquid temperature at 40 ° C. or higher, or casting into a thin film within 12 hours after the liquid temperature falls below 40 ° C. to obtain a polarizing film And C.

化１中、Ｍは、対イオンであり、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、フェニル基、又はそれらの誘導体基であり、Ｘは、水素原子、ハロゲン原子、ニト口基、シアノ基、炭素数１〜３のアルキル基、又は炭素数１〜４のアルコキシ基である。 The method for producing a polarizing film according to claim 2 is characterized in that, in the method for producing a polarizing film according to claim 1, the bisazo lyotropic liquid crystal compound having a naphthalene ring is a compound represented by the following chemical formula (1).

In Formula 1, M is a counter ion, R is a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an acetyl group, a benzoyl group, a phenyl group, or a derivative group thereof, and X is a hydrogen atom, a halogen atom, An atom, a nitrite group, a cyano group, an alkyl group having 1 to 3 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms.

  The method for producing a polarizing film according to claim 3 is the method for producing a polarizing film according to claim 1 or 2, wherein the solvent is a hydrophilic solvent comprising water, alcohols, cellosolves, or a mixed solvent thereof. It is characterized by that.

  The method for producing a polarizing film according to claim 4 is the method for producing a polarizing film according to any one of claims 1 to 3, wherein the temperature of the heat treatment performed in the step B is 85 ° C or higher and lower than 100 ° C. It is characterized by being.

  The method for producing a polarizing film according to claim 5 is the method for producing a polarizing film according to any one of claims 1 to 4, wherein the concentration of the bisazo lyotropic liquid crystal compound in the coating liquid obtained in the step B is 2 wt. % To 40% by weight.

  The method for producing a polarizing film according to claim 6 is the method for producing a polarizing film according to any one of claims 1 to 5, wherein the liquid temperature of the coating liquid maintained in the step C is 40 ° C to 90 ° C. It is characterized by being in the range of

  The method for producing a polarizing film according to claim 7 is the method for producing a polarizing film according to any one of claims 1 to 6, wherein the coating liquid in step C has a liquid temperature lower than 40 ° C. It is characterized by being cast within 6 hours.

  The method for producing a polarizing film according to claim 8 is the method for producing a polarizing film according to any one of claims 1 to 7, wherein the casting liquid is cast after the liquid temperature of the coating liquid falls below 40 ° C in the step C. The holding temperature at which the coating solution is held before being applied is 10 ° C. or higher and lower than 40 ° C.

  A polarizing film manufacturing method according to a ninth aspect is the polarizing film manufacturing method according to the eighth aspect, wherein the holding temperature is 20 ° C. or higher.

  In the method for producing a polarizing film according to the present invention, a mixed liquid of a bisazo-based lyotropic liquid crystal compound having a naphthalene ring and a solvent is obtained in Step A, and the mixed liquid is heat-treated in Step B to undissolved naphthalene ring. A coating solution is obtained by dissolving a bisazo-based lyotropic liquid crystal compound having a solvent in a solvent, and the casting temperature when the coating solution is cast into a thin film to form a polarizing film, the coating solution temperature is 40 ° C. The film is cast into a thin film while maintaining the above, or the film is formed into a thin film after casting by setting the conditions such that the coating liquid is cast into a thin film within 12 hours after the temperature of the coating solution falls below 40 ° C. In the evaporation process of the solvent contained in the coating liquid, the generation of precipitates can be effectively suppressed to produce an optically uniform polarizing film.

Here, by generating a polarizing film by casting the coating liquid into a thin film according to the casting conditions of the coating liquid, the mechanism that can effectively suppress the generation of precipitates in the polarizing film, It is as follows.
First, the deposit that impairs the optical uniformity that appears in the polarizing film is presumed to be caused by crystallization of a bisazo-type lyotropic liquid crystal compound having a naphthalene ring, and casting of a coating solution for suppressing such crystallization is performed. I came to realize that it was necessary to find the conditions.
Since a bisazo lyotropic liquid crystal compound having a naphthalene ring has high crystallinity, it is considered that when its concentration in the coating solution is increased, it may be crystallized due to the influence of impurities contained slightly. Crystal growth increases as the supersaturated state of the coating solution (solution) increases, and crystallization is accelerated when the temperature of the coating solution decreases.

Therefore, as a result of various experiments focusing on the temperature of the coating solution, in a coating solution in which a bisazo lyotropic liquid crystal compound having a naphthalene ring is dissolved in a solvent, the temperature of the coating solution is maintained at 40 ° C. or higher. Crystallization of a bisazo lyotropic liquid crystal compound having a naphthalene ring can be effectively suppressed, and bisazo lyotropic liquid crystal compound can be similarly crystallized within 12 hours even when the temperature of the coating solution falls below 40 ° C. It was found that it can be suppressed.
As a result, the casting conditions of the coating liquid are cast in a thin film state while the liquid temperature of the coating liquid is maintained at 40 ° C. or higher, or within 12 hours after the liquid temperature of the coating liquid falls below 40 ° C. By setting the conditions for casting into a thin film, it is possible to produce an optically uniform polarizing film by effectively suppressing the generation of precipitates during the evaporation process of the solvent contained in the thin film coating liquid after casting. It has become possible to do.
The reason why the precipitate does not occur even when the temperature of the coating solution becomes 40 ° C. or less after casting the coating solution is that the evaporation of the solvent is completed in an extremely short time compared to the crystal growth.

Hereinafter, a manufacturing method of a polarizing film concerning the present invention is explained based on an embodiment which materialized the present invention.
[Production method of polarizing film]
The manufacturing method of the polarizing film which concerns on this embodiment is a manufacturing method of the polarizing film containing the bisazo type | system | group lyotropic liquid crystal compound which has a naphthalene ring, Comprising: The process A-the process C mentioned later are included in this order. Such a production method may include an optional step as long as the effects of the present invention are exhibited.

[Step A]
Step A used in the production method of the present embodiment is a step of obtaining a mixed liquid by mixing a bisazo lyotropic liquid crystal compound having a naphthalene ring and a solvent.
In the present specification, the “bisazo lyotropic liquid crystal compound” refers to a compound having two azo groups (—N═N—) and exhibiting a liquid crystal phase in a state dissolved in a solvent. The bisazo lyotropic liquid crystal compound used in the present embodiment has a naphthalene ring. Such a compound has excellent orientation and exhibits absorption dichroism in a wide range of visible light.

前記化１中、Ｍは、対イオンであり、好ましくは水素原子又はアルカリ金属原子である。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、フェニル基、又はそれらの誘導体基であり、Ｘは、水素原子、ハロゲン原子、ニト口基、シアノ基、炭素数１〜３のアルキル基、又は炭素数１〜４のアルコキシ基である。 The bisazo-based lyotropic liquid crystal compound is preferably represented by the following general formula 1.

In the chemical formula 1, M is a counter ion, preferably a hydrogen atom or an alkali metal atom. R is a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an acetyl group, a benzoyl group, a phenyl group, or a derivative group thereof; X is a hydrogen atom, a halogen atom, a nitrile group, a cyano group, or a carbon number of 1; Or an alkyl group having 3 or 3 or an alkoxy group having 1 to 4 carbon atoms.

The liquid mixture is typically obtained by mixing a powdered or granular bisazo lyotropic liquid crystal compound in a solvent. In such a mixed solution, usually, a bisazo lyotropic liquid crystal compound is partially dissolved in a solvent and the rest is dispersed or precipitated.
The solvent dissolves the bisazo-based lyotropic liquid crystal compound, and is preferably a hydrophilic solvent. Such a hydrophilic solvent is preferably water, alcohols, cellosolves or a mixed solvent thereof.

[Step B]
Step B used in the manufacturing method of the present embodiment is a step of obtaining a coating solution by heat-treating the mixed solution to dissolve a bisazo-based lyotropic liquid crystal compound having an undissolved naphthalene ring in a solvent.

Here, the “heat treatment” is a treatment in which the liquid temperature of the liquid mixture is preferably 85 ° C. or higher and lower than 100 ° C. in order to dissolve the bisazo lyotropic liquid crystal compound in the liquid mixture obtained in step A. By such heat treatment, the bisazo lyotropic liquid crystal compound can be dissolved in a solvent. If the heat treatment is less than 85 ° C., the bisazo lyotropic liquid crystal compound remains undissolved and may cause foreign matters. Moreover, arbitrary means, such as a heater, are used as the heating means.
The concentration of the bisazo lyotropic liquid crystal compound in the coating solution is preferably 2% by weight to 40% by weight.

[Step C]
In Step C used in the manufacturing method of the present embodiment, the coating liquid is cast into a thin film while maintaining the liquid temperature at 40 ° C. or higher, or within 12 hours after the liquid temperature falls below 40 ° C. This is a step of casting a thin film to obtain a polarizing film. According to such a method, a polarizing film having excellent optical uniformity can be obtained.
When the coating liquid is cast into a thin film while maintaining the liquid temperature at 40 ° C. or higher, the liquid temperature of the coating liquid is preferably 40 ° C. to 90 ° C. As long as the liquid temperature is kept at 40 ° C. or higher, the coating liquid can be cast after being stored for a long time (for example, 24 hours or longer).

When the coating liquid is cast after the liquid temperature falls below 40 ° C., the time from the temperature lower than 40 ° C. to casting needs to be within 12 hours, preferably within 6 hours. When the time is significantly longer than 12 hours (for example, 24 hours), precipitates are generated in the coating solution, and a polarizing film having excellent optical uniformity cannot be obtained. In addition, it is preferable that the liquid temperature of the coating liquid is maintained at 10 ° C. or higher and lower than 40 ° C. while 12 hours elapse after the liquid temperature of the coating liquid falls below 40 ° C. until casting. Further, it is preferable to be maintained at 20 ° C. or higher.
As the means for casting the coating solution, a slide coater, a bar coater, a slot die coater or the like is used.

[Polarizing film]
The polarizing film obtained by the manufacturing method according to the present embodiment contains a bisazo lyotropic liquid crystal compound having a naphthalene ring.
The polarizing film exhibits absorption dichroism in the visible light region, and the thickness thereof is preferably 0.1 to 10 micrometers.

[Usage]
The polarizing film obtained by the manufacturing method of this embodiment is preferably used for liquid crystal displays such as televisions and mobile phones.

[Example 1]
4-Nitroaniline and 8-amino-2-naphthalenesulfonic acid can be prepared by a conventional method (Toyo Hosoda, “Theoretical Manufacturing, Dye Chemistry (5th Edition), July 15, 1968, published by Technique Hall, pages 135-152). Then, diazotization and coupling reaction were performed to obtain a monoazo compound. Similarly, this monoazo compound is diazotized by a conventional method, and is further subjected to a coupling reaction with 1-amino-8-naphthol-2,4-disulfonic acid lithium salt to give a bisazo-based lyotropic liquid crystal having the chemical structural formula shown below. A compound was obtained. This bisazo-based lyotropic liquid crystal compound exhibits a nematic liquid crystal phase in an aqueous solution having a concentration of 20% by weight.

  The bisazo lyotropic liquid crystal compound thus obtained and ion-exchanged water were mixed to obtain a mixed solution. While stirring this mixed liquid, a heat treatment is performed using a heater until the liquid temperature reaches 90 ° C. to dissolve the undissolved bisazo lyotropic liquid crystal compound, and the concentration of the bisazo lyotropic liquid crystal compound is 8% by weight. A liquid was obtained.

  The coating solution is allowed to cool in a thermostatic chamber at 23 ° C., and when 1 hour has elapsed since the liquid temperature dropped below 40 ° C., a cycloolefin polymer film that has been subjected to rubbing treatment and corona treatment (product of Nippon Zeon Co., Ltd.) The film was applied using a bar coater (trade name “Mayer rot HS5” manufactured by BUSHMAN) on the name “ZEONOR”) and allowed to dry naturally to produce a polarizing film having a thickness of 0.3 μm.

  When the obtained polarizing film was observed with a polarizing microscope (manufactured by Olympus, product name “OPTIPHOT-POL”), precipitates having a diameter of 5 μm or more were not observed. Table 1 shows a polarizing microscope photograph of the polarizing film.

[Example 2]
The coating solution obtained in the same manner as in Example 1 was transferred to a sealed container and placed in a constant temperature room at 40 ° C. After 24 hours, the coating liquid was taken out from the constant temperature room and immediately used in Example 1. It apply | coated on the same cycloolefin type polymer film. A polarizing film was produced in the same manner as in Example 1 except for this. No precipitate having a diameter of 5 micrometers or more was observed on this polarizing film. Table 1 shows a polarizing microscope photograph of the polarizing film.

[Example 3]
The coating solution obtained in the same manner as in Example 1 was transferred to a sealed container and placed in a constant temperature room at 40 ° C. After 48 hours, the coating liquid was taken out from the constant temperature room and immediately used in Example 1. It apply | coated on the same cycloolefin type polymer film. Other than this, a polarizing film was produced in the same manner as in Example 1. No precipitate having a diameter of 5 micrometers or more was observed on this polarizing film. Table 1 shows a polarizing microscope photograph of the polarizing film.

[Example 4]
The coating solution obtained in the same manner as in Example 1 was allowed to cool in a thermostatic chamber at 23 ° C., and when 5 hours had passed since the liquid temperature dropped below 40 ° C., the same cyclohexane as that used in Example 1 was used. It apply | coated on the olefin type polymer film. Other than this, a polarizing film was produced in the same manner as in Example 1. No precipitate having a diameter of 5 micrometers or more was observed on this polarizing film. Table 1 shows a polarizing microscope photograph of the polarizing film.

[Example 5]
The coating solution obtained in the same manner as in Example 1 was allowed to cool in a thermostatic chamber at 23 ° C., and when 12 hours had passed after the liquid temperature dropped below 40 ° C., the same cyclohexane as that used in Example 1 was used. It apply | coated on the olefin type polymer film. Other than this, a polarizing film was produced in the same manner as in Example 1. No precipitate having a diameter of 5 micrometers or more was observed on this polarizing film. Table 1 shows a polarizing microscope photograph of the polarizing film.

[Comparative Example 1]
The coating solution obtained in the same manner as in Example 1 was transferred to a sealed container and allowed to cool in a thermostatic chamber at 23 ° C. When 24 hours had passed after the liquid temperature dropped below 40 ° C., it was used in Example 1. It was coated on the same cycloolefin polymer film as that used. Other than this, a polarizing film was produced in the same manner as in Example 1. A large number of precipitates having a diameter of 5 micrometers or more were observed on this polarizing film. Table 1 shows a polarizing microscope photograph of the polarizing film.

[Comparative Example 2]
The coating solution obtained in the same manner as in Example 1 was transferred to a sealed container and allowed to cool in a thermostatic chamber at 23 ° C. When 48 hours had passed after the liquid temperature dropped below 40 ° C., the coating solution used in Example 1 was used. It was coated on the same cycloolefin polymer film as that used. Other than this, a polarizing film was produced in the same manner as in Example 1. A large number of precipitates having a diameter of 5 micrometers or more were observed on this polarizing film. Table 1 shows a polarizing microscope photograph of the polarizing film.

[Evaluation]
As shown in Examples 1 to 5, is a coating solution in which a bisazo-type lyotropic liquid crystal compound having a naphthalene ring dissolved is cast into a thin film while maintaining the liquid temperature at 40 ° C. or higher (Examples 2 and 3)? Or when cast in a thin film form within 12 hours after the liquid temperature falls below 40 ° C. (Examples 1, 4, and 5), no precipitate is generated, and as a result, the optical uniformity is excellent. A polarizing film can be obtained.
On the other hand, as shown in Comparative Examples 1 and 2, when the coating solution is cast in a thin film over a period of 12 hours after the temperature of the coating solution falls below 40 ° C., precipitates are generated and excellent in optical uniformity. A polarizing film cannot be obtained.

Claims (9)

A method for producing a polarizing film containing a bisazo-based lyotropic liquid crystal compound having a naphthalene ring,
A step A in which a bisazo lyotropic liquid crystal compound having a naphthalene ring and a solvent are mixed to obtain a mixed solution;
Heat treating the mixed solution to dissolve a bisazo-based lyotropic liquid crystal compound having an undissolved naphthalene ring in a solvent to obtain a coating solution; and
A step of casting the coating solution into a thin film while maintaining the liquid temperature at 40 ° C. or higher, or casting into a thin film within 12 hours after the liquid temperature falls below 40 ° C. to obtain a polarizing film C. The manufacturing method of the polarizing film characterized by including C. The method for producing a polarizing film according to claim 1, wherein the bisazo-based lyotropic liquid crystal compound having a naphthalene ring is a compound represented by the following chemical formula (1):

In Formula 1, M is a counter ion, R is a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an acetyl group, a benzoyl group, a phenyl group, or a derivative group thereof, and X is a hydrogen atom, a halogen atom, An atom, a nitrite group, a cyano group, an alkyl group having 1 to 3 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms.   The method for producing a polarizing film according to claim 1 or 2, wherein the solvent is a hydrophilic solvent composed of water, alcohols, cellosolves, or a mixed solvent thereof.   The method of manufacturing a polarizing film according to any one of claims 1 to 3, wherein the temperature of the heat treatment performed in the step B is 85 ° C or higher and lower than 100 ° C.   5. The polarizing film according to claim 1, wherein the concentration of the bisazo lyotropic liquid crystal compound in the coating liquid obtained in the step B is in the range of 2 wt% to 40 wt%. Production method.   The method for producing a polarizing film according to claim 1, wherein the liquid temperature of the coating liquid maintained in the step C is in a range of 40 ° C. to 90 ° C. 6.   The said coating liquid in the said process C is cast within 6 hours after the liquid temperature falls below 40 degreeC, The manufacturing of the polarizing film in any one of Claim 1 thru | or 6 characterized by the above-mentioned. Method.   The holding temperature at which the coating liquid is held from the time when the temperature of the coating liquid falls below 40 ° C in the step C to the time when it is cast is 10 ° C or higher and lower than 40 ° C. The manufacturing method of the polarizing film in any one of Claim 1 thru | or 7.   The method for producing a polarizing film according to claim 8, wherein the holding temperature is 20 ° C. or higher.