JP2009192577A - Polarizing film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problem: a conventional polarizing film obtained from a liquid crystalline coating liquid containing an azo compound, turns to red because its absorbance in the long wavelength side of the visible ray region (the red region) is less than that in the short wavelength side thereof (the blue region), and to provide a neutral gray polarizing film without such coloring, in the polarizing film obtained from the liquid crystalline coating liquid containing the azo compound. <P>SOLUTION: The absorbance in the long wavelength side of the visible ray region (the red region) is increased so as to be nearly equal to that in the short wavelength side thereof (the blue region) by making the polarizing film which is obtained from the liquid crystalline coating liquid containing the azo compound contain glycerine of a predetermined amount (of 2-50 pts.wt. based on the azo compound of 100 pts.wt.). Accordingly, the absorbance gets nearly flat in the visible ray region, and the polarizing film gets close to neutral gray with only slightest coloring. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polarizing film formed from a liquid crystalline coating solution containing an azo compound.

  In the liquid crystal panel, a polarizing plate is used to control the optical rotation of light passing through the liquid crystal. Conventionally, polarizing plates in which a polymer film such as polyvinyl alcohol is dyed with iodine or a dichroic dye and stretched in one direction are widely used as these polarizing plates. However, the above-mentioned polarizing plate has a problem that heat resistance and light resistance are not sufficient depending on the type of the dye or polymer film, and the film thickness is relatively thick.

  On the other hand, a method of forming a polarizing film by applying a liquid crystal coating liquid containing an azo compound on a substrate such as a glass plate or a polymer film in a thin film and orienting the azo compound is known (Patent Literature). 1). The azo compound forms supramolecular aggregates exhibiting lyotropic liquid crystallinity in the solution, and when the liquid crystalline coating liquid containing the azo compound is flowed by applying a shear stress, the major axis direction of the supramolecular aggregate is changed to the flow direction. Orient. Since this type of polarizing film does not need to be stretched, it is easy to obtain a wide polarizing film, and the film thickness can be remarkably reduced.

In general, a polarizing film is required to exhibit an average polarization performance in the visible light region (wavelength: 380 nm to 780 nm). At this time, since the polarizing film becomes achromatic, such a color tone of the polarizing film is referred to as neutral gray. However, the conventional polarizing film obtained from a liquid crystalline coating solution containing an azo compound has a problem that the absorbance on the long wavelength side (red region) in the visible light region is smaller than that on the short wavelength side (blue region), so that it is colored red. there were. Therefore, there has been a demand for a neutral gray polarizing film having no coloration in a polarizing film obtained from a liquid crystalline coating solution containing an azo compound.
JP 2006-323377 A

  A conventional polarizing film obtained from a liquid crystalline coating solution containing an azo compound has a problem that it is colored red because the absorbance on the long wavelength side in the visible light region is relatively small. An object of the present invention is to provide a polarizing film close to neutral gray having such a small coloration.

  Inclusion of a specific amount of glycerin in a polarizing film obtained from a liquid crystalline coating solution containing an azo compound increases the absorbance on the long wavelength side (red region) in the visible light region and is almost the same as the short wavelength side (blue region). Can be equivalent. As a result, the absorbance is almost flat in the visible light region, and the polarizing film is close to neutral gray with little coloration.

式（I）中、Ｘは独立して水素原子、ハロゲン原子、ニトロ基、炭素数１〜４のアルキル基、炭素数１〜４のアルコキシ基、−ＳＯ_３Ｍ基を表わし、Ｍは対イオンを表わす。 The gist of the present invention is as follows.
(1) The polarizing film of this invention is a polarizing film formed from the liquid crystalline coating liquid containing an azo compound, Comprising: Glycerin in the said polarizing film is 2-50 weight part with respect to 100 weight part of said azo compounds. A part by weight is included.
(2) The polarizing film of the present invention is characterized in that the azo compound is an azo compound represented by the following general formula (I).

In formula (I), X independently represents a hydrogen atom, a halogen atom, a nitro group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a —SO ₃ M group, and M represents a counter ion. Represents.

  Since the absorbance of the polarizing film of the present invention is approximately the same on the long wavelength side (red region) and the short wavelength side (blue region) of the visible light region, a polarizing film close to neutral gray with little coloring can be obtained.

  The present inventors have intensively investigated the cause of red coloration of a conventional polarizing film using a lyotropic liquid crystalline azo compound. The reason is that the azo compound in the polarizing film forms an H-aggregate. It was found that the band was shifted to the shorter wavelength side than the absorption band of one azo compound molecule (absorption band observed in the solution state). Furthermore, it has been found that by containing a specific amount of glycerin in the polarizing film, the absorbance on the long wavelength side (red region) in the visible light region can be increased, and a polarizing film close to neutral gray can be obtained. According to the inventor's estimation, the mechanism by which this effect is obtained is that glycerin, which is likely to interact by hydrogen bonding, forms a supramolecular aggregate together with the azo compound, thereby preventing liquid crystallinity from being impaired. This is because the interaction of the aggregate could be weakened.

[Polarizing film]
The polarizing film of the present invention is a polarizing film formed from a liquid crystalline coating solution containing an azo compound, and glycerin is contained in the polarizing film in an amount of 2 to 50 parts by weight, preferably 5 parts per 100 parts by weight of the azo compound. Parts by weight to 50 parts by weight, more preferably 10 to 40 parts by weight. The polarizing film of the present invention can increase the absorbance on the long wavelength side (red region) of the visible light region by including the above amount of glycerin, and as a result, a polarizing film closer to neutral gray can be obtained. Such polarizing films obtained in the size of the coloration obtained by ^{(a 2 + b 2) 1/2} , preferably 1.3 or less, and more preferably, to 1.2 or less. Said a and b are a value and b value of Hunter Lab color system, respectively.

  The polarizing film of the present invention exhibits absorption dichroism in at least one wavelength in the visible light region (wavelength 380 nm to 780 nm). This characteristic is obtained by aligning and aligning the azo compound in the solution state with lyotropic liquid crystallinity. 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 when the temperature and concentration are changed in a solution state dissolved in a solvent.

  The azo compound can be aligned by flow when a shear stress is applied in a liquid crystal state. The azo compound forms supramolecular aggregates in the liquid crystalline coating solution, and when the liquid crystalline coating solution containing the azo compound is flowed by applying a shear stress, the major axis direction of the supramolecular aggregate is aligned in the flow direction. In addition to the shearing stress, the orientation means may combine orientation treatment such as rubbing treatment or photo-alignment, or orientation by a magnetic field or electric field.

  The thickness of the polarizing film of the present invention is preferably 0.1 μm to 5 μm. The dichroic ratio of the polarizing film of the present invention is preferably 10 or more.

[Liquid crystal coating liquid]
In this specification, the liquid crystalline coating liquid refers to a liquid that exhibits a liquid crystal phase in a specific temperature range or concentration range. The liquid crystalline coating liquid used in the present invention contains an azo compound and a solvent that dissolves the azo compound. The liquid crystal phase exhibited by the liquid crystalline coating liquid is not particularly limited, and examples thereof include a nematic liquid crystal phase, a smectic liquid crystal phase, and a hexagonal liquid crystal phase. The liquid crystal phase is confirmed and identified by an optical pattern observed with a polarizing microscope.

  The concentration of the azo compound in the liquid crystalline coating liquid used in the present invention is preferably 8% by weight to 30% by weight. The liquid crystalline coating liquid preferably exhibits a liquid crystal phase in at least a part of the azo compound concentration in the range of 15 wt% to 25 wt%. The pH of the liquid crystalline coating solution used in the present invention is preferably 4-10.

  The solvent used in the present invention is not particularly limited as long as it dissolves the above azo compound, but a hydrophilic solvent is preferable. Examples of the hydrophilic solvent include water, alcohols, cellosolves, and mixed solvents thereof.

  The liquid crystalline coating liquid used in the present invention may contain other compounds and additives as long as it contains the above azo compound and the above solvent. Examples of the additive include a surfactant, an antioxidant, and an antistatic agent. The concentration of the additive is usually less than 10 parts by weight per 100 parts by weight of the azo compound.

[Azo compound]
There is no restriction | limiting in particular in the azo compound used for this invention, Arbitrary things are used. As the azo compound, for example, those described in JP-A-2005-255846 and JP-A-2006-323377 can be used.

The azo compound used in the present invention is preferably one represented by the following general formula (I). When the azo compound represented by the general formula (I) is used, since glycerin easily forms a hydrogen bond with the hydroxyl group or amino group of the azo compound, a polarizing film closer to neutral gray can be obtained.

The above general formula (I), X is a hydrogen atom and independently represents a halogen atom, a nitro group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a -SO ₃ M group, M Represents a counter ion. The counter ion M is preferably a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a metal ion, or a substituted or unsubstituted ammonium ion. Examples of the metal ions include Li ⁺ , Ni ²⁺ , Fe ³⁺ , Cu ²⁺ , Ag ⁺ , Zn ²⁺ , Al ³⁺ , Pd ²⁺ , Cd ²⁺ , Sn ²⁺ , Co ²⁺ , Mn ²⁺ , and Ce ³⁺ . When the counter ion M is a multivalent ion, a plurality of azo compounds share one multivalent ion (counter ion).

  The azo compound represented by the general formula (I) is prepared according to Yutaka Hosoda, “Theoretical Manufacturing, Dye Chemistry, 5th Edition” issued on July 15, 1943, Technique Hall, pages 135 to 152, for example, aniline derivatives and 8-amino- It can be obtained by diazotization and coupling reaction with 2-naphthalenesulfonic acid to obtain a monoazo compound, further diazotization, and coupling reaction with a 7-amino-1-naphtholsulfonic acid derivative.

[Production method of polarizing film]
If the polarizing film of this invention is formed from the liquid crystalline coating liquid containing an azo compound, there will be no restriction | limiting in particular. One embodiment of the polarizing film of the present invention can be obtained by applying a liquid crystalline coating solution containing an azo compound to a substrate surface in one direction while applying a shearing stress and drying the coating.

  The application method is not particularly limited as long as the liquid crystalline coating solution can be uniformly applied, and an appropriate coater such as a slide coater, a slot die coater, a bar coater, a rod coater, a roll coater, a curtain coater, a spray coater, or the like is used. Moreover, there is no restriction | limiting in particular in a drying method, Natural drying, reduced pressure drying, heat drying, reduced pressure heating drying, etc. are used. As the heating and drying means, an arbitrary drying device such as an air circulation drying oven or a hot roll is used. The drying temperature in the case of heat drying is preferably 50 ° C to 120 ° C.

  There is no restriction | limiting in particular in the base material for apply | coating the liquid crystalline coating liquid used for this invention, The thing of a single layer may be sufficient, and the laminated body with an alignment film, for example, may be sufficient. Specifically, there are a glass plate and a polymer film. When the substrate is a laminate with an alignment film, the alignment film is preferably subjected to an alignment treatment. As a base material of a laminated body with an alignment film, for example, there is a glass plate coated with a polyimide film. This polyimide film is provided with orientation by a known method, for example, mechanical orientation treatment such as rubbing or photo-alignment treatment. As a glass base material, the alkali free glass used for a liquid crystal cell is preferable. Polymer film substrates are suitable for applications that require flexibility. The surface of the polymer film may be aligned by rubbing or the like, or an alignment film may be laminated on the surface of the polymer film. The material of the polymer film is not particularly limited as long as it is a film-forming polymer, but a styrene polymer, a (meth) acrylic acid polymer, an ester polymer, an olefin polymer, a norbornene polymer, an imide polymer, a cellulose polymer There are polymers, vinyl alcohol polymers, carbonate polymers, and the like. The thickness of the substrate is not particularly limited except for the application, but is generally 1 μm to 1000 μm.

[Application of polarizing film]
The polarizing film of the present invention is suitably used as a polarizing element. Polarizing elements are various liquid crystal panels, such as computers, photocopiers, mobile phones, watches, digital cameras, personal digital assistants, portable game machines, video cameras, LCD TVs, microwave ovens, car navigation systems, car audio systems, monitor monitors, and surveillance. Used in LCD panels for medical 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 1]
o-Sulphonic acid aniline and 8-amino-2-naphthalene sulphonic acid according to conventional methods (Toyo Hosoda "Theoretical Manufacturing Dye Chemistry 5th Edition" issued July 15, 1968, Technique Hall, pages 135-152) 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 7-amino-1-naphthol-3,6-disulfonic acid lithium salt to contain a crude product containing an azo compound of the following structural formula (II) Got. This was salted out with lithium chloride to obtain an azo compound of the following structural formula (II). This azo compound exhibits lyotropic liquid crystallinity.

  10 parts by weight of glycerin is mixed with 100 parts by weight of the azo compound of the above structural formula (II), water is further added thereto, and the liquid crystalline coating solution is prepared so that the concentration of the azo compound becomes 19.2% by weight. Prepared. A bar coater (trade name “Mayerrot HS1.5” manufactured by BUSCHMAN) is used on the surface of a norbornene-based polymer film (trade name “ZEONOR” manufactured by Nippon Zeon Co., Ltd., thickness 100 μm) subjected to corona treatment. The film was applied in one direction while applying a shear stress at room temperature (23 ° C.) and naturally dried at room temperature to produce a polarizing film having a thickness of 0.47 μm. The weight ratio of the azo compound and glycerin in the polarizing film is equal to the weight ratio in the liquid crystal coating liquid.

[Example 2]
A liquid crystalline coating solution was prepared in the same manner as in Example 1 except that the content of glycerin was 30 parts by weight with respect to 100 parts by weight of the azo compound, and a polarizing film was prepared.

[Example 3]
A liquid crystalline coating solution was prepared in the same manner as in Example 1 except that the content of glycerin was 50 parts by weight with respect to 100 parts by weight of the azo compound, and a polarizing film was prepared.

[Comparative Example 1]
A liquid-crystalline coating solution was prepared in the same manner as in Example 1 except that glycerin was not mixed to prepare a polarizing film.

[Comparative Example 2]
A liquid crystalline coating solution was prepared in the same manner as in Example 1 except that the content of glycerin was 1 part by weight with respect to 100 parts by weight of the azo compound, and a polarizing film was prepared.

[Comparative Example 3]
A liquid crystalline coating solution was prepared in the same manner as in Example 1 except that the content of glycerin was 100 parts by weight with respect to 100 parts by weight of the azo compound, and a polarizing film was prepared.

[Evaluation]
FIG. 1 shows orthogonal absorption spectra of the polarizing films of Example 1 and Comparative Example 1. As shown in FIG. 1, the polarizing film of Example 1 in which 10 parts by weight of glycerin is mixed with 100 parts by weight of the azo compound has a wavelength of 550 nm to 680 nm as compared with the polarizing film of Comparative Example 1 in which glycerin is not mixed. It can be seen that the absorbance in the vicinity increases, and the red coloration, which has been a problem with conventional polarizing films (not mixed with glycerin), has decreased.

Table 1 and FIG. 2 show the relationship between the glycerin content and the coloring size of the polarizing films of Examples 1 to 3 and Comparative Examples 1 to 3. As shown in Table 1 and FIG. 2, when the glycerin content is 5 to 50 parts by weight with respect to 100 parts by weight of the azo compound, the color of the polarizing film is small (1.0 to 1.2). On the other hand, when the glycerin content is less than 5 parts by weight, the polarizing film is highly colored (exceeds 1.2). When the glycerin content was 100 parts by weight, the coating liquid was repelled on the surface of the substrate, and a polarizing film could not be formed.

[Measuring method]
[Measurement of thickness of polarizing film]
A part of the polarizing film was peeled off, and a step was measured using a three-dimensional non-contact surface shape measurement system (product name “Micromap MM5200” manufactured by Ryoka System Co., Ltd.) to determine the thickness.

[Measurement of orthogonal absorption spectrum]
Using a spectrophotometer equipped with a Glan-Thompson polarizer (product name “polarizing film automatic evaluation system V-7100” manufactured by JASCO Corporation), linearly polarized measuring light is incident and a straight line in a direction perpendicular to the maximum transmittance direction. The polarized light transmittance k ₂ was measured.

[Measurement of coloring size]
Using a product name “polarizing film automatic evaluation system V-7100” manufactured by JASCO Corporation, linearly polarized measuring light is incident to determine the a and b values of the Hunter Lab color system, and the formula: (a ² + b ² ) Calculated by ^1/2 .

The graph which shows the orthogonal absorption spectrum of a polarizing film. The graph which shows the relationship between glycerin content and the magnitude | size of coloring.

Claims (2)

  A polarizing film formed from a liquid crystalline coating liquid containing an azo compound, wherein the polarizing film contains 2 to 50 parts by weight of glycerin with respect to 100 parts by weight of the azo compound. film. The polarizing film according to claim 1, wherein the azo compound is an azo compound represented by the following general formula (I).

(In the formula (I), X independently represents a hydrogen atom, a halogen atom, a nitro group, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a —SO ₃ M group, Represents ions.)

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