JP5695298B2 - Liquid crystalline coating liquid and polarizing film - Google Patents

Description

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

  For the liquid crystal panel, a polarizing plate is used to control the optical rotation of light passing through the liquid crystal. Conventionally, as these polarizing plates, polarizing plates obtained by dyeing a resin film such as polyvinyl alcohol with iodine or a dichroic dye and stretching in one direction are widely used. However, the polarizing plate 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 size of the liquid crystal panel increases, and the size of the film manufacturing apparatus increases.

  On the other hand, a method of forming a polarizing film by casting a liquid crystalline coating solution containing a lyotropic liquid crystal compound on a substrate such as a glass plate or a resin film and aligning the lyotropic liquid crystal compound is known. A lyotropic liquid crystal compound forms a supramolecular aggregate exhibiting liquid crystallinity in a solution. When a liquid crystal coating liquid containing the lyotropic liquid crystal compound is cast by applying a shear stress, the major axis direction of the supramolecular aggregate flows. Oriented in the extending direction. One of such lyotropic liquid crystal compounds 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. Further, since the film thickness can be remarkably reduced, the future is expected.

  However, a polarizing film obtained by casting a liquid crystalline coating solution containing a conventional azo compound causes fine crystals to precipitate in the film during the drying process, resulting in increased haze (light scattering) of the polarizing film and transparency. There was a problem of getting worse. Therefore, a liquid crystalline coating solution containing a novel azo compound that solves the haze problem has been demanded.

JP 2006-323377 A

  An object of the present invention is that in a polarizing film obtained from a liquid crystalline coating solution containing an azo compound, fine crystals are deposited in the film during the drying process, and the haze (light scattering) of the polarizing film is increased, and the transparency is deteriorated. It is an object of the present invention to provide a liquid crystalline coating solution containing a novel azo compound that solves the problem.

  As a result of intensive studies on the precipitation of fine crystals of a liquid crystalline coating liquid containing an azo compound, the present inventors have found that by using an azo compound having an aminonaphthol skeleton in which a substituent such as a sulfonic acid group is substituted at a specific position. It was found that precipitation can be suppressed and a polarizing film having a small haze can be obtained.

一般式（１）中、Ｑは置換基を有していてもよいアリール基が結合したアゾ基を表わす。Ｒは水素原子を表わす。Ｍはリチウムイオンを表わす。
（２）本発明の液晶性コーティング液は、アゾ化合物の濃度が、０．５重量％〜５０重量％であることを特徴とする。
（３）本発明の液晶性コーティング液は、液晶性コーティング液のｐＨが、５〜９であることを特徴とする。
（４）本発明の偏光膜は、上記に記載の液晶性コーティング液を薄膜状に流延し、乾燥して得られることを特徴とする。 The gist of the present invention is as follows.
(1) The liquid crystalline coating liquid of the present invention comprises an azo compound represented by the following general formula (1) and a solvent for dissolving the azo compound.

In general formula (1), Q represents an azo group to which an aryl group which may have a substituent is bonded. R represents a hydrogen atom. M represents a lithium ion .
( 2 ) The liquid crystalline coating liquid of the present invention is characterized in that the concentration of the azo compound is 0.5 wt% to 50 wt%.
( 3 ) The liquid crystalline coating liquid of the present invention is characterized in that the liquid crystalline coating liquid has a pH of 5 to 9.
( 4 ) The polarizing film of the present invention is characterized by being obtained by casting the liquid crystalline coating solution described above into a thin film and drying it.

  The polarizing film obtained by casting and drying the liquid crystalline coating liquid containing the novel azo compound of the present invention has a small haze because it suppresses the precipitation of fine crystals in the film during the drying process.

  The liquid crystalline coating liquid of the present invention containing the above azo compound suppresses the precipitation of fine crystals when the liquid crystalline coating liquid is cast and dried, and as a result, the fine crystals that cause haze are much more difficult than conventional ones. The haze is considered to decrease. The liquid crystalline coating solution of the present invention has an aminonaphthol skeleton that has a high possibility of becoming a poorly soluble site due to its high planarity in the structure of the azo compound contained, and a sulfonic acid group is introduced at a specific position. Easy to dissolve. Thereby, it is considered that precipitation of fine crystals could be suppressed.

式（１）中、Ｑは置換基を有していてもよいアリール基が結合したアゾ基を表わす。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を表わす（これらの基は置換基を有していてもよい）。Ｍは対イオンを表わす。
[Liquid crystal coating liquid]
The liquid crystalline coating liquid of the present invention contains an azo compound represented by the following general formula (1) and a solvent for dissolving the azo compound.

In formula (1), Q represents an azo group to which an aryl group which may have a substituent is bonded . 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). M represents a counter ion.

  In the liquid crystalline coating liquid of the present invention, the azo compound forms a supramolecular aggregate in the liquid and exhibits a liquid crystal phase. The liquid crystal phase is not particularly limited, and examples thereof include a nematic liquid crystal phase and a hexagonal liquid crystal phase. These liquid crystal phases can be identified and confirmed by observing the optical pattern with a polarizing microscope.

  The concentration of the azo compound in the liquid crystalline coating solution of the present invention is preferably 0.5% by weight to 50% by weight. A liquid crystalline coating solution exhibiting a stable liquid crystal phase at at least part of the concentration in the above range can be obtained, and a polarizing film having a desired thickness (eg, 0.4 μm) can be easily obtained.

  The pH of the liquid crystalline coating solution of the present invention is preferably 5-9. When the pH is in the above range, a polarizing film having a high degree of orientation can be obtained. In addition, since the coater made of metal such as stainless steel is not corroded, the productivity is excellent.

  As long as the liquid crystalline coating liquid of the present invention contains the above-mentioned azo compound and a solvent, the liquid crystalline coating liquid may contain other arbitrary liquid crystal compounds, for example, other liquid crystal compounds and additives. Examples of the additive include a surfactant, an antioxidant, and an antistatic agent. The concentration of these additives is usually less than 10% by weight.

  There is no restriction | limiting in particular in the preparation method of the liquid crystalline coating liquid of this invention, For example, said azo compound may be added to a solvent, and a solvent may be added conversely to said azo compound.

[Azo compound]
The azo compound used in the liquid crystalline coating liquid of the present invention is a compound represented by the above general formula (1). When the temperature and concentration are changed in a solution state dissolved in a solvent, the isotropic phase-liquid crystal phase It has the property of causing phase transition (lyotropic liquid crystal). The azo compound represented by the general formula (1) exhibits absorption dichroism in the visible light region (wavelength 380 nm to 780 nm), and has a substituent such as a sulfonic acid group at a specific position, so that fine crystals are precipitated. Is suppressed, and a polarizing film having a small haze can be obtained.

In the above formula (1), Q represents an azo group to which an aryl group which may have a substituent is bonded, and a substituent suitable for adjusting the width of the absorption wavelength is used.

  In said formula (1), R represents a hydrogen atom, a C1-C3 alkyl group, an acetyl group, a benzoyl group, or a phenyl group (these groups may have a substituent).

In the above formula (1), M represents a counter ion, preferably a hydrogen atom, an alkali metal atom, an alkaline earth metal atom, a metal ion of the above metal, 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).

[solvent]
The solvent used in the present invention dissolves the above azo compound, and a hydrophilic solvent is preferably used. The hydrophilic solvent is preferably water, alcohols, cellosolves or a mixed solvent thereof. 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 liquid crystalline coating solution.

[Polarizing film]
The polarizing film of the present invention can be obtained by casting the liquid crystalline coating liquid of the present invention on the surface of a substrate or a metal drum and drying it. The casting means is not particularly limited as long as the liquid crystalline coating liquid can be cast uniformly, and suitable coaters such as a slide coater, a slot die coater, a bar coater, a rod coater, a roll coater, a curtain coater, a spray coater, etc. Used.

  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, any drying apparatus 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. The polarizing film of the present invention is preferably dried so that the residual solvent amount is 5% by weight or less based on the total weight of the film.

  The polarizing film of the present invention preferably exhibits absorption dichroism in the visible light region (wavelength 380 nm to 780 nm). Such characteristics can be obtained by orienting the azo compound in the polarizing film. The above-mentioned azo compound forms supramolecular aggregates in the liquid crystalline coating solution, and when the liquid crystalline coating solution is cast while applying a shear stress, the major axis direction of the supramolecular aggregate is aligned in the casting direction. To do. The orientation means may combine an orientation treatment such as a rubbing treatment or a photo orientation, an orientation by a magnetic field or an electric field, in addition to the shear stress.

  The thickness of the polarizing film of the present invention is preferably 0.1 μm to 3 μm. The polarization degree of the polarizing film of the present invention is preferably 90% or more, more preferably 95% or more. According to the present invention, the haze value of the polarizing film can be preferably 10% or less, more preferably 5% or less, and even more preferably 2% or less.

[Base material]
There is no restriction | limiting in particular in the base material for casting the liquid crystalline coating liquid of this invention, The thing of a single layer may be sufficient and the laminated body (for example, including alignment film) 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 base material, alkali-free glass used for a liquid crystal cell is preferable. For applications requiring flexibility, a resin film base material is suitable. The surface of the resin film may be aligned by rubbing or the like, or 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, (meth) acrylic acid resin, polyester resin, polyolefin resin, norbornene resin, polyimide Resin, cellulose resin, polyvinyl alcohol resin, and polycarbonate resin. 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.

[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, for example, OA equipment such as computers and copiers, portable equipment such as mobile phones, watches, digital cameras, personal digital assistants, portable game machines, household equipment such as video cameras, televisions, and microwave ovens Used in LCD panels for medical equipment such as in-vehicle equipment such as back monitors, car navigation, car audio, display equipment such as store monitors, security equipment such as monitoring monitors, 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 1]
3-Amino-2-naphthol and 8-amino-2-naphthalenesulfonic acid were prepared by a conventional method (Toyo Hosoda, “Theoretical Manufacturing, Dye Chemistry 5th Edition”, July 15, 1968, published by Gihodo, pages 135-152. To obtain a monoazo compound by diazotization and coupling reaction. The obtained monoazo compound was similarly diazotized by a conventional method, and further subjected to a coupling reaction with 1-amino-8-naphthol-2,4-disulfonic acid lithium salt to obtain a crude compound containing an azo compound of the following structural formula (2). A product was obtained and salted out with lithium chloride to obtain an azo compound of the following structural formula (2).

  The azo compound of the structural formula (2) was dissolved in ion-exchanged water to prepare a 20% by weight liquid crystalline coating solution. The liquid crystalline coating solution had a pH of 7.7. This liquid crystalline coating solution was collected with a poly dropper, sandwiched between two slide glasses, and observed with a polarizing microscope at room temperature (23 ° C.). As a result, a nematic liquid crystal phase was observed.

  The liquid crystalline coating solution is cast on the surface of a norbornene polymer film (Zeonor manufactured by Nippon Zeon Co., Ltd.) subjected to rubbing treatment and corona treatment using a bar coater (Mayer rot HS4 manufactured by BUSCHMAN). The film was naturally dried in a thermostatic chamber at 23 ° C. to produce a polarizing film having a thickness of 0.4 μm. Table 1 shows the optical characteristics of the obtained polarizing film.

[Example 2]
An azo compound of the following structural formula (3) was obtained in the same manner as in Example 1 except that 3-amino-2-naphthol was changed to 4′-aminoacetanilide.

  The coating liquid (20 wt%) obtained by dissolving the azo compound of the structural formula (3) in ion exchange water had a pH of 7.2 and exhibited a nematic liquid crystal phase at room temperature (23 ° C.). . The liquid crystalline coating solution was further diluted with ion-exchanged water to prepare 10% by weight. Using this liquid crystalline coating solution, a polarizing film having a thickness of 0.6 μm was produced in the same manner as in Example 1. Table 1 shows the optical characteristics of the obtained polarizing film.

[Example 3]
The following structure was obtained in the same manner as in Example 1 except that 3-amino-2-naphthol was changed to 4-nitroaniline and 8-amino-2-naphthalenesulfonic acid was changed to 5-amino-2-naphthalenesulfonic acid. A compound of formula (4) was obtained.

  The coating liquid (concentration 20% by weight) obtained by dissolving the azo compound of the structural formula (4) in ion-exchanged water had a pH of 7.2 and exhibited a nematic liquid crystal phase at room temperature (23 ° C.). . Using this liquid crystalline coating solution, a polarizing film having a thickness of 0.6 μm was produced in the same manner as in Example 1. Table 1 shows the optical characteristics of the obtained polarizing film.

[Comparative Example 1]
Change 3-amino-2-naphthol to 4-nitroaniline and 1-amino-8-naphthol-2,4-disulfonic acid lithium salt to 7-amino-1-naphthol-3,6-disulfonic acid lithium salt An azo compound of the following structural formula (5) was obtained in the same manner as in Example 1 except that.

The coating liquid (concentration 20% by weight) obtained by dissolving the azo compound of the structural formula (5) in ion-exchanged water had a pH of 6.7 and exhibited a nematic liquid crystal phase at room temperature (23 ° C.). . Using this liquid crystalline coating solution, a polarizing film having a thickness of 0.8 μm was produced in the same manner as in Example 1. Table 1 shows the optical characteristics of the obtained polarizing film.

[Measuring method]
[Observation of liquid crystal phase]
A small amount of the liquid crystalline coating solution was collected with a poly dropper, sandwiched between two slide glasses (MATUNAMI SLIDE GLASS manufactured by Matsunami Glass Co., Ltd.), and observed using a polarizing microscope (OPTIPHOT-POL manufactured by Olympus Corporation).

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

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

[Measurement of degree of polarization]
Using a spectrophotometer (V-7100 manufactured by JASCO Corporation), a polarized light transmission spectrum in a wavelength range of 380 nm to 780 nm was measured. From this spectrum, the transmittance Y1 of the linearly polarized light in the direction of maximum transmittance subjected to the visibility correction and the transmittance Y2 in the direction orthogonal thereto are obtained, and the degree of polarization is obtained by the degree of polarization = (Y1-Y2) / (Y1 + Y2). .

[Measurement of haze]
The haze was measured at room temperature (23 ° C.) using a haze measuring apparatus (HR-100, manufactured by Murakami Color Research Laboratory). The average value of 3 repetitions was taken as the measured value.

Claims (4)

A liquid crystalline coating liquid comprising an azo compound represented by the following general formula (1) and a solvent for dissolving the azo compound.

(In the general formula (1), Q represents an azo group is an aryl group which may have a substituent bonded, R represents a hydrogen atom, M represents a lithium ion.) The liquid crystalline coating liquid according to claim 1, wherein the concentration of the azo compound is 0.5 wt% to 50 wt%. The liquid crystalline coating solution according to claim 1 or 2 , wherein the liquid crystalline coating solution has a pH of 5 to 9. Cast on liquid crystalline coating solution according to any one of claims 1 to 3 into a thin film, polarizing film, characterized in that it is obtained by drying.