JP2005208416A - Reverse wavelength dispersion retardation film, polarizing plate and display apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reverse wavelength dispersion retardation film which can be easily manufactured and shows satisfactory reverse wavelength dispersion characteristics for its thickness. <P>SOLUTION: Liquid crystal monomer having a fluorene skeleton of a cardo-structure part and principal chain mesogene combining with the cardo-structure part and having a polymerizable group at the terminal is immobilized while maintaining such an orientation that the optical axis of the principal chain mesogene is made parallel to the alignment direction of an alignment film and the cardo-structure part is aligned orthogonal to the alignment direction of the principal chain mesogene, thereby obtaining the reverse wavelength dispersion retardation film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a reverse wavelength dispersion retardation film, a polarizing plate using the reverse wavelength dispersion retardation film, and the like.

  Conventionally, as a method for obtaining a reverse wavelength dispersion retardation film, a quarter wavelength plate in which the phase difference of birefringent light is ¼ wavelength and a half wavelength in which the phase difference of birefringent light is ½ wavelength. A method of laminating plates with crossed optical axes (Patent Document 1), a method of laminating optical axes of retardation films having different wavelength dispersions (Patent Document 2), and having positive refractive index anisotropy A method of stretching a polymer film composed of a polymer monomer unit and a polymer monomer unit having negative refractive index anisotropy (Patent Document 3) is known.

In the methods of Patent Documents 1 and 2, a step of laminating a retardation film or the like is necessary, and there is a problem in that the production is complicated, such as mixing foreign substances or shifting the optical axis when laminating. Yes.
In the method of Patent Document 3, a lamination step is not required, and a reverse wavelength dispersion retardation film can be obtained in one layer, but sufficient reverse wavelength dispersion characteristics cannot be obtained unless the film thickness is increased to several tens of μm. Have a problem.

On the other hand, it is known that a retardation film produced by fixing a liquid crystal monomer by ultraviolet irradiation or the like in an aligned state is as thin as several μm (Patent Document 4).
However, the phase difference film produced by fixing the liquid crystal monomer in an aligned state and showing reverse wavelength dispersion characteristics is not yet known.

JP-A-10-68816 JP-A-5-27118 Japanese Patent No. 3325560 JP-A-7-294735

  This invention makes it a subject to provide the reverse wavelength dispersion phase-difference film which can be manufactured simply and shows the reverse wavelength dispersion characteristic sufficient for the film thickness.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have determined that a liquid crystal monomer having a fluorene skeleton having a cardo structure in the molecule and a main chain mesogen bonded to the cardo structure portion is used as the light of the main chain mesogen. By fixing the axis parallel to the orientation direction and the cardo structure oriented so as to be orthogonal to the orientation direction of the main chain mesogen, the reverse wavelength exhibiting a thin reverse wavelength dispersion characteristic. The inventors have found that a dispersion retardation film can be obtained, and have completed the present invention.

That is, the present invention provides a liquid crystal monomer comprising a fluorene skeleton having a cardo structure portion in the molecule and a main chain mesogen bonded to the cardo structure portion and having a polymerizable group at the terminal, as the optical axis of the main chain mesogen. The chromatic dispersion portion is oriented in parallel with the orientation direction of the orientation film and the cardo structure is perpendicular to the orientation direction of the main chain mesogen, and is fixed while maintaining the orientation. A phase difference film is provided.
Here, the cardo structure means that the 9-position carbon atom of the fluorene skeleton has two aromatic rings, and the fluorene skeleton and the aromatic rings are in a twisted positional relationship due to steric hindrance.
The mesogen is also called an intermediate phase (= liquid crystal phase) -forming molecule and has almost the same meaning as the liquid crystal molecular structure.

The reverse wavelength dispersion retardation film of the present invention can be easily produced, and can exhibit reverse wavelength dispersion characteristics sufficient for the film thickness.
Furthermore, the reverse wavelength dispersion retardation film of the present invention can exhibit wavelength dispersion characteristics that generate a substantially uniform retardation across the entire visible wavelength region to be used.

Hereinafter, embodiments of the reverse wavelength dispersion retardation film of the present invention will be described.
The reverse wavelength dispersion retardation film of the present embodiment comprises a liquid crystal monomer comprising a fluorene skeleton having a cardo structure part in the molecule and a main chain mesogen having a polymerizable group at the end bonded to the cardo structure part. The main chain mesogen is fixed so that the optical axis of the main chain mesogen is parallel to the alignment direction of the alignment film and the cardo structure is orthogonal to the alignment direction of the main chain mesogen, and the alignment is maintained. .

The liquid crystal monomer is composed of a fluorene skeleton having a cardo structure in the molecule and a main chain mesogen bonded to the cardo structure and having a polymerizable group at the terminal.
The fluorene skeleton having a cardo structure part is represented by the chemical formula (A-1).

(In the chemical formula, Ar represents an aromatic ring.)

  As the fluorene skeleton having a cardo structure, one having two benzene rings bonded to the 9-position carbon atom of the fluorene skeleton is preferable.

A substituent may be bonded to the aromatic ring part of the fluorene skeleton directly or via a bonding group. As the substituent, an aromatic ring (for example, phenyl group, biphenyl group, etc.) or various functional groups (for example, cyano group, halogen group, alkyl group, etc.) may be substituted on the aromatic ring.
Examples of the linking group include those shown in (B-1) to (B-12).

  In addition to the polymerizable group, the main chain mesogen also has a rigid unit essential for the rod-like compound to exhibit liquid crystallinity. Examples of the rigid unit include those in which two or more ring structures represented by (C-1) to (C-11) are connected directly or via a bonding group. In addition, as said coupling group, the thing similar to said (B-1)-(B-12) is mentioned.

  Examples of the rigid unit include biphenyl, phenyloxycarbonylphenyl, phenylcarbonyloxyphenyl, phenylcarbonyloxycarbonylphenyl, phenyloxycarbonylphenylcarbonyloxyphenyl, phenyloxycarbonylphenyloxycarbonylphenyl, phenylcarbonyloxyphenyloxycarbonylphenyl, And phenyloxycarbonylphenyloxycarbonylphenyl

Examples of the polymerizable group include a methacryloyloxy group, an acryloyloxy group, an epoxy group, and a vinyl ether group. Among these, an acryloyloxy group is preferable.
There is preferably a flexible bonding group called a spacer between the polymerizable group and the rigid unit. A methylene chain is preferably used for the spacer. 2-10 are preferable and, as for the carbon atom number of this methylene chain, 2-6 are more preferable.

  In the liquid crystal monomer of this embodiment, the rigid unit is bonded directly or via the bonding group to an aromatic ring (cardo structure portion) bonded to the 9th carbon atom of the fluorene skeleton.

Specific examples of the liquid crystal monomer of this embodiment are shown in (D-1) to (D-3).
In addition, the liquid crystal monomer of this embodiment shows a nematic phase and / or a smectic phase.

Next, production of the reverse wavelength dispersion retardation film of this embodiment will be described.
The reverse wavelength dispersion retardation film of this embodiment can be produced by coating the liquid crystal monomer on a substrate, and aligning and fixing them.

  As the substrate, a polymer film such as polyethylene terephthalate, triacetyl cellulose, norbornene resin, polyvinyl alcohol, polyimide, polyacrylate, polycarbonate, polysulfone, polyethersulfone, or a glass plate is generally used.

A liquid crystal monomer comprising a fluorene skeleton having a cardo structure part in the molecule and a main chain mesogen bonded to the cardo structure part and having a polymerizable group at a terminal is generally provided on a substrate. Alignment is performed using an alignment film.
As the alignment film, a conventionally known film can be used. For example, a thin film made of polyimide, polyvinyl alcohol or the like on a substrate, a polymer having a photopolymerizable group such as cinnamate or azobenzene, or a photo-alignment film obtained by irradiating polarized ultraviolet rays on a polyimide film, an oblique deposition film, or a stretched film is used.
Typical examples of the alignment film include a polyimide alignment film and a polyvinyl alcohol alignment film.
The alignment film is preliminarily rubbed before the liquid crystal monomer is applied onto the alignment film. The rubbing treatment is performed by rubbing the surface of the alignment film several times in a certain direction with paper or cloth. The rubbing treatment determines the direction in which the liquid crystal is aligned.

Application of the liquid crystal monomer onto the alignment film includes a heat melting method or a method in which the liquid crystal monomer is dissolved in an organic solvent and applied as a solution onto the alignment film. Usually, a method in which a liquid crystal monomer is dissolved in an organic solvent and applied as a solution is used. When dissolved in an organic solvent and applied as a solution, it can be performed using an appropriate coating machine such as a bar coater, a spin coater, or a roll coater.
As the organic solvent, those capable of dissolving the liquid crystal monomer can be used without particular limitation. For example, methyl ethyl ketone, cyclohexanone, tetrahydrofuran and the like are preferable. A high boiling point organic solvent is not preferable from the viewpoint of productivity.

  As a method of aligning the optical axis of the main chain mesogen in parallel with the alignment direction of the alignment film and aligning the cardo structure part orthogonal to the alignment direction of the main chain mesogen, a method of aligning by heating is used. be able to. In general, the temperature of the heating alignment is not less than the Cr (crystal phase) / N (nematic phase) phase transition temperature and not more than the N (nematic phase) / I (isotropic phase) phase transition temperature of the liquid crystalline material. When the temperature is high, the thermal polymerization reaction may proceed and the orientation may be hindered. Therefore, the Cr / N phase transition temperature is preferably + 50 ° C. or lower. The heating time is not particularly limited but is preferably in the range of about 10 seconds to 10 minutes.

The immobilization can be performed by reacting and curing the polymerizable group.
As the immobilization method when the polymerizable group is an acryloyloxy group / methacryloyloxy group, it is preferably performed by irradiation with active energy rays.
As the active energy rays, ultraviolet rays, electron beams, and the like are used, and ultraviolet rays are particularly preferable. In the case of irradiation with ultraviolet rays, the curing reaction can be rapidly advanced by adding a photopolymerization initiator to the liquid crystal monomer.
The photopolymerization initiator is not particularly limited, and examples thereof include benzoin ethers, benzophenones, acetophenones, and benzyl ketals.
The addition amount of the photopolymerization initiator is preferably 0.1 to 10% by weight, more preferably 0.3 to 5% by weight with respect to the liquid crystal monomer.
Depending on the liquid crystal monomer, there are those in which the crystal does not precipitate and maintains the alignment state even when the temperature falls below the Cr / N phase transition temperature after heating alignment. Can do. In the case where crystallization is likely to occur when the temperature is lowered, the active energy rays are irradiated at a temperature equal to or higher than the Cr / N phase transition temperature.

When the polymerizable group is a vinyl ether group or an epoxy group, the curing reaction can be promptly accelerated by irradiation with ultraviolet rays by adding a photoacid generator to the liquid crystal monomer. The addition amount of the photoacid generator is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the liquid crystal monomer.
As the photoacid generator, for example, triazines, aromatic sulfonium salts, aromatic diazonium salts, cyanate esters, aromatic sulfonate esters, nitrobenzyl esters, aromatic sulfamides, and the like can be used. Among these, triazines and aromatic sulfonium salts are particularly preferable from the viewpoints of the addition effect and the lack of influence on the orientation.

The reverse wavelength dispersion retardation film formed on the substrate is used as an optical film.
The reverse wavelength dispersion retardation film can be used as an optical film as it is as an integral body with the substrate, or can be peeled off from the substrate and laminated with another optical film.
The thickness of the reverse wavelength dispersion retardation film of the present embodiment is usually about 0.1 to 20 μm.

In the reverse wavelength dispersion retardation film of this embodiment, by using the alignment film, the main chain mesogen is in the direction parallel to the rubbing direction of the alignment film, and the cardio structure portion of the fluorene skeleton is connected to the main chain mesogen. They are arranged in a direction perpendicular to the orientation direction. At this time, when the wavelength dispersion of the main chain mesogen is larger than the wavelength dispersion of the cardo structure part of the fluorene skeleton, and the phase difference value by the main chain mesogen is smaller than the phase difference value by the cardo structure part of the fluorene skeleton, nd (450 nm) / Δnd (650 nm) is smaller than 1, indicating a so-called reverse wavelength dispersion characteristic.
The degree of the reverse wavelength dispersion characteristic can be changed by selecting the main chain mesogen or the fluorene skeleton.

In the reverse wavelength dispersion phase difference film of the present embodiment, the phase difference given to the polarized light is substantially constant depending on the wavelength, and therefore the state of the polarized light emitted from the reverse wavelength dispersion phase difference film is substantially equal.
A polarizing plate in which an inverse wavelength dispersion retardation film having such characteristics is bonded to a polarizing film, that is, an elliptical polarizing plate, is particularly effective when the retardation is λ / 2 or λ / 4.
When the phase difference is λ / 2, the polarized light emitted from the elliptically polarizing plate is a polarized light whose plane of polarization is rotated by 90 degrees from the polarized light before passing through the elliptically polarizing plate.
When the phase difference is λ / 4, the polarized light emitted from the elliptically polarizing plate is circularly polarized light. The elliptically polarizing plate at this time is particularly called a circularly polarizing plate.
In the reverse wavelength dispersion retardation film of this embodiment, a circularly polarizing plate obtained by laminating a film having a retardation of λ / 4 with a polarizing film is a broadband circularly polarizing plate.
Here, the phase difference (Δnd) is expressed by the following equation. In the following formula, nx and ny indicate the refractive indexes in the X-axis and Y-axis directions in the film, respectively, and d indicates the thickness of the film.
Δnd = (nx−ny) × d
The X-axis direction means an axial direction showing the maximum refractive index in the plane of the film, and the Y-axis direction means an axial direction perpendicular to the X-axis in the plane. The phase difference (Δnd) was measured using an automatic birefringence meter KOBRA-21ADH.
In addition, as the polarizing film, iodine-polyvinyl alcohol (PVA) system, dye-polyvinyl alcohol (PVA) system, or the like is used.

  The broadband polarizing plate is used as an antireflection film for a circularly polarized liquid crystal display device and various display devices. In particular, in an organic EL display device, a broadband polarizing plate is used as an antireflection film that suppresses reflection of a metal electrode, and remarkably improves a bright place contrast ratio.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.

<Measurement of wavelength dispersion (phase difference)>
Oji Scientific Instruments Co., Ltd .: Measured using an automatic birefringence meter KOBRA-21ADH.

(Synthesis of Compound 1)
4-hydroxybenzoic acid (276 g (2 mol)) and a catalytic amount of potassium iodide were added to a potassium hydroxide solution (KOH 300 g, ethanol 700 ml, water 300 ml) and dissolved. Ethylene chlorohydrin (177 g (2.2 mol)) was slowly added while warming, and refluxed for about 15 hours. Potassium chloride precipitated with the reaction. After completion of the reaction, ethanol was distilled off and the reaction solution was put in 2 liters of water. The aqueous solution was washed twice with diethyl ether, and the aqueous layer was acidified with 4 mol / liter hydrochloric acid.
The resulting precipitate was filtered, dried and then recrystallized with ethanol to obtain Compound 1 (298 g).

(Synthesis of Compound 2)
Compound 1 (18.2 g (0.1 mol)) was dissolved in tetrahydrofuran (300 ml). Next, vinyl acrylate (19.5 g (0.2 mol)), lipase PS (Amano Pharmaceutical Co., Ltd.) (18 g) and a trace amount of polymerization inhibitor MEHQ (p-methoxyphenol) were added, and the reaction solution was stirred at 40 ° C. did. The disappearance of the raw materials was confirmed by thin layer chromatography (TLC), the reaction solution was filtered, and the filtrate was distilled off under reduced pressure. The obtained solid was recrystallized from 180 ml of (2-butanone / hexane = 2/1) to obtain Compound 2 (17.5 g).

(Synthesis of Compound 3)
Compound 3 (17.5 g (74 mmol)), 4- (4′-hydroxyphenyl) tetrahydropyranyl ether (14.3 g (74 mmol)), dimethylaminopyridine (950 mg (7.8 mmol)), and a small amount of butylhydroxytoluene in 400 ml of methylene chloride The mixture was stirred at room temperature and suspended, and dichlorocyclohexyldiimide (15.2 g (74 mmol)) dissolved in methylene chloride (10 ml) was added in small portions. After stirring overnight, the precipitated DC urea was filtered off, and the filtrate was washed with 0.5N hydrochloric acid, saturated aqueous sodium hydrogen carbonate solution and saturated brine twice (200 ml each), and the organic layer was dried over anhydrous magnesium sulfate. The solvent was distilled off. The obtained solid was recrystallized from 2-butanone (210 ml) to obtain Compound 3 (23.7 g).

(Synthesis of Compound 4)
Compound 3 (23 g (71 mmol)) and a small amount of butylhydroxytoluene were dissolved in THF (250 ml) and stirred on a water bath at about 60 ° C. 12N-HCl (10 ml) was added thereto, and the mixture was stirred for 30 minutes. Then, THF was removed from the reaction solution by about 3/4, methylene chloride (250 ml) was added, and the mixture was washed twice with saturated brine (250 ml). The organic layer was dried over anhydrous magnesium sulfate. Thereafter, the solvent was distilled off to obtain Compound 4 (15.3 g).

(Synthesis of Compound 5)
Compound 4 (15 g (63 mmol)), terephthalic acid (10.5 g (63 mmol)), dimethylaminopyridine (0.769 g (6.3 mmol)) and a small amount of butylhydroxytoluene were stirred and suspended in methylene chloride (300 ml) at room temperature. Whereupon didichlorocyclohexylcarbodiimide (13.0 g (63 mmol)) dissolved in methylene chloride (10 ml) was added in small portions. After stirring overnight, the precipitated DC urea was filtered off, and the filtrate was washed with 0.5N hydrochloric acid, saturated aqueous sodium hydrogen carbonate solution and saturated brine twice (each 300 ml), and the organic layer was dried over anhydrous magnesium sulfate. The solvent was distilled off. Recrystallization from 2-butanone (330 ml) gave Compound 5 (17.6 g).

(Synthesis of Compound 6)
Compound 5 (3.96 g (16.4 mmol)), 9,9-bis (4-hydroxyphenyl) fluorene (2.80 g (8 mmol)), dimethylaminopyridine (0.098 g (0.8 mmol)), methylene chloride (BHT catalyst amount) 40 ml) was added to form a suspension. The mixture was cooled in a water bath and dicyclohexylcarbodiimide (3.64 g (16.8 mmol)) was added while stirring. After the addition, the water bath was removed and the mixture was stirred at room temperature for 23 hours. The precipitated solid was removed by filtration, and the solvent was distilled off under reduced pressure to obtain a white solid. After recrystallization from methanol, purification was performed with a silica gel column using (hexane / ethyl acetate = 1/1) as a developing solvent to obtain Compound 6 (2.10 g).
It confirmed that the obtained compound 6 showed liquid crystallinity with the polarization microscope.
Cr 130 N 145 I

<Production of retardation film>
(Example 1)
The obtained compound 6 was dissolved in tetrachloroethane to form a 30 wt% solution, and 3 wt% of Irgacure 907 (manufactured by Ciba Specialty Chemicals: photopolymerization initiator) was added to the compound 6. After spin coating on a polyvinyl alcohol rubbing alignment film formed on a glass plate, the film was aligned by heating to 140 ° C. Thereafter, the orientation was fixed by irradiating ultraviolet rays at 100 mJ / cm ² with a high-pressure mercury lamp. The obtained oriented film was 3 μm, and the phase difference determined by the Senarmon method using a He—Ne laser was 300 nm.
When the wavelength dispersion was measured using a phase difference measuring apparatus, Δnd (450 nm) / Δnd (650 nm) = 0.92, which was smaller than 1, confirming that the film was a reverse wavelength dispersion retardation film. When this reverse wavelength dispersion phase difference film was observed between two polarizing plates having transmission axes orthogonal to each other, there was almost no coloring.

(Example 2)
An oriented film was produced in the same manner as in Example 1 except that the concentration of Compound 6 in the tetrachloroethane solution was changed to 17% by weight. The phase difference of the obtained oriented film was 143 nm. The alignment film and the polarizing plate were bonded to each other so that the alignment direction of the alignment film and the stretching axis of the polarizing plate were 45 degrees to prepare a circularly polarizing plate. When the produced circularly polarizing plate was placed on a mirror, it became black and it was confirmed that it functions as a broadband circularly polarizing plate.

(Comparative Example 1)
An alignment film having a retardation was produced in the same manner as in Example 1 except that the liquid crystal monomer shown in (E-1) was used instead of the compound 6.
When this oriented film was observed between two polarizing plates having transmission axes orthogonal to each other, it was colored blue.

  An alignment film having a retardation was produced in the same manner as in Example 2 except that the liquid crystal monomer of Comparative Example 1 was used instead of Compound 6. When a circularly polarizing plate was produced in the same manner as in Example 2 and the produced circularly polarizing plate was placed on a mirror, it was purple and was not a broadband circularly polarizing plate.

From Example 1, a retardation film showing reverse wavelength dispersion characteristics could be obtained.
From Example 2, it was found that a circularly polarizing plate obtained by laminating a retardation film showing reverse wavelength dispersion characteristics and a polarizing plate functions as a broadband circularly polarizing plate.

Claims (5)

A liquid crystal monomer comprising a fluorene skeleton having a cardo structure part in the molecule and a main chain mesogen bonded to the cardo structure part and having a polymerizable group at a terminal;
The optical axis of the main chain mesogen is aligned parallel to the alignment direction of the alignment film, and the cardo structure portion is aligned so as to be orthogonal to the alignment direction of the main chain mesogen, and is fixed while maintaining the alignment. An inverse wavelength dispersion retardation film characterized by the above. A phase difference Δnd (450 nm) measured at a wavelength of 450 nm;
The phase difference Δnd (650 nm) measured at a wavelength of 650 nm is
The reverse wavelength dispersion phase difference film of Claim 1 which satisfy | fills following formula (1).
Δnd (450 nm) / Δnd (650 nm) <1 (1)   A polarizing plate, wherein the reverse wavelength dispersion retardation film according to claim 1 or 2 and a polarizing film are laminated.   The polarizing plate according to claim 3, wherein the retardation of the reverse wavelength dispersion retardation film is λ / 4.   A display device using the reverse wavelength dispersion retardation film according to claim 1 or 2 or the polarizing plate according to claim 3 or 4.