JPH0933908A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device which is greatly improved in angle of visibility characteristic and retains this characteristic without changing over a long period of time at a high temp. SOLUTION: This liquid crystal display device is a liquid crystal display element which has a liquid crystal cell formed by holding twisted nematic liquid crystals between two sheets of electrode substrates, has two sheets of polarizing elements arranged at both ends thereof and has an optical anisotropic element (A) having negative uniaxiality and having the optical axis in a direction normal to the plane, an optical anisotropic element (B) consisting of a layer contg. a disk-shaped compd. or optical anisotropic element (C) having the negative uniaxiality and having the optical axis inclined at 5 to 50 deg. with the direction normal to the plane or the optical anisotropic element (D) having a continuously changing optical tilt angle. The optical anisotropic element (A) is aliphat. cellulose ester having an acetic acid group and propionic acid group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having improved viewing angle characteristics of display contrast and display color of a TN-LCD and having a small change with time.

Display devices for OA equipment such as Japanese word processors and desktop personal computers are being converted from mainstream CRTs to liquid crystal display elements (hereinafter LCDs) which have the great advantages of thinness, light weight and low power consumption. Many of the currently widespread LCDs use twisted nematic liquid crystals. Display methods using such a liquid crystal can be roughly classified into two methods, a birefringence mode and an optical rotation mode.

A display element using a birefringence mode (STN type LCD) has a twist angle of a liquid crystal molecule arrangement of 90 ° or more and has a steep electro-optical characteristic, so that there is no active element (thin film transistor or diode). However, a large-capacity display can be obtained by time-division driving with a simple matrix electrode structure. However, it has a drawback that response speed is slow (several hundred milliseconds) and gradation display is difficult, and it does not exceed the display performance of a liquid crystal display element (TFT-LCD or MIM-LCD) using active elements. .

For the TFT-LCD and the MIM-LCD, an optical rotation mode display mode (TN type LCD) in which the alignment state of liquid crystal molecules is twisted by 90 ° is used. This display method is the most influential method as compared with other types of LCDs because it has a fast response speed (several tens of milliseconds), can easily obtain a black-and-white display, and has a high display contrast. But,
Since the twisted nematic liquid crystal is used, there is a problem in the viewing angle characteristics that the display color and the display contrast change depending on the viewing direction due to the principle of the display system.
The display performance of is not reached.

JP-A-4-229828, JP-A-4-4-2
As disclosed in Japanese Patent No. 58923, a method has been proposed in which a viewing angle is increased by disposing a retardation film between a pair of polarizing plates and a TN type liquid crystal cell. The phase difference film proposed in the above patent publication is
With respect to the liquid crystal cell, the phase difference in the direction perpendicular to the liquid crystal cell is almost zero, and has no optical effect from the front.
It is intended to compensate for the phase difference that appears in the liquid crystal cell when the phase difference appears when observed from the tilted direction. However, even by these methods, the viewing angle of the LCD, specifically, the phenomenon of coloring (coloring phenomenon) or black and white inversion of the display image when tilted from the screen normal direction to the normal viewing angle direction or the left-right direction (reversal phenomenon) ) Is remarkable, and in particular, when it is considered as a vehicle-mounted type or a CRT alternative, the current situation is that it cannot be dealt with at all.

Further, in JP-A-4-366808 and JP-A-4-366809, a viewing angle is improved by using a liquid crystal cell containing a chiral nematic liquid crystal having an inclined optical axis as a retardation film. It is a layered liquid crystal system, which is expensive and very heavy. Further, JP-A-4-113301, JP-A-5-80323,
Japanese Patent Laid-Open No. 5-157913 discloses that a liquid crystal cell is
Although a method using a retardation film in which a polymer chain, an optical axis or an optical elastic axis is inclined is proposed, a uniaxial polycarbonate is used by obliquely slicing it, and a large area retardation film is used. There was a problem that it was difficult to obtain at low cost. Further, although the improvement of the viewing angle with respect to the STN-LCD is mentioned, no concrete effect is shown with respect to the improvement of the viewing angle of the TN-LCD. Further, Japanese Patent Laid-Open No. 215921/1993 proposes a method of optically compensating an LCD by a birefringent plate in which a rod-shaped compound exhibiting a liquid crystal property is sandwiched between a pair of substrates subjected to alignment treatment. In this plan, there is no difference from the so-called double cell type compensator that has been conventionally proposed,
The cost is so high that it is virtually unsuitable for mass production. Further, the effect has not been shown for improving the omnidirectional viewing angle of the TN type LCD. In addition, JP-A-3-932
No. 6, JP-A-3-291601 discloses a plan to use as an optical compensator for LCD by coating a polymer substrate on a film-shaped substrate on which an alignment film is installed. Since it is impossible to orient the light obliquely, improvement in the omnidirectional viewing angle of the TN type LCD cannot be expected.

Further, EP0576304A1 describes a method of improving viewing angle characteristics by using a retardation plate having a negative uniaxial refractive index characteristic and an inclined optical axis thereof. This method surely improves the viewing angle significantly compared to the conventional one, but it is still CR
It was impossible to improve the viewing angle to the extent that T substitution was considered. Therefore, the inventors of the present invention, as shown in EP0646829A1, have an optically anisotropic element whose optical axis is optically negative and whose optical axis is inclined from the normal direction of the film, and an optically anisotropic element whose optical axis is optically negative. It has been found that the viewing angle of the TN type LCD is remarkably improved by the retardation plate having the optical anisotropic element whose axis is in the normal direction of the film. The optical anisotropic element whose optical axis is in the normal direction of the film uses the conventional film forming method, but the optical anisotropic element used in the liquid crystal display device displays birefringence and uneven thickness. In practice, methods other than solution film formation, such as melt film formation, are unsuitable because they greatly affect the characteristics. However, in solution casting, it is impossible to reduce the residual solvent to zero at the time of production, and the solvent inevitably remains at a ratio of several percent with respect to the raw material. However, this residual solvent is gradually volatilized over time, and the plane orientation of the molecules is promoted, so that the refractive index in the thickness direction decreases and the RTH
Occurs over time. Here, RTH is the in-plane refractive index of the film nx, ny the thickness direction refractive index nz,
When the thickness is d, {(nx + ny) / 2-nz}
* D, which will be described in detail later. Also,
The RTH is optimized according to the optical characteristics of the liquid crystal used, and a change with time of the RTH will cause deterioration of the display performance immediately with time.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a TN
(EN) Provided is an LCD using an optical anisotropic element, in which the viewing angle characteristics of a type LCD are remarkably improved and the viewing angle characteristics do not change even after storage at high temperature for a long time.

[0009]

The above-mentioned problems include (1) a liquid crystal cell in which twisted nematic liquid crystal is sandwiched between two electrode substrates, and two polarizing elements arranged at both ends thereof. Between the liquid crystal cell and the polarizing element, at least one optically anisotropic element (A) having an optically negative uniaxial property and an optical axis in a direction normal to the surface, and at least A liquid crystal display device comprising an optical anisotropic element (B) formed from one layer containing a discotic compound, wherein the optical anisotropic element (A) has an acetic acid group and a propionic acid group. And a liquid crystal display device. (2) A liquid crystal cell in which a twisted nematic liquid crystal is sandwiched between two electrode substrates, and two polarizing elements arranged at both ends of the liquid crystal cell, and between the liquid crystal cell and the polarizing element,
One or two or more optically anisotropic elements (A) having an optically negative uniaxial property and whose optical axis is in the direction normal to the surface.
And a liquid crystal display element comprising at least one optically anisotropic element (C) which is optically negative uniaxial and whose optical axis is inclined 5 ° to 50 ° from the direction normal to the surface, A liquid crystal display device, wherein the optically anisotropic element (A) is a fatty acid cellulose ester having an acetic acid group and a propionic acid group. (3) The liquid crystal display device according to (2), wherein the optical anisotropic element (C) is an optical anisotropic element containing a discotic compound. (4) The liquid crystal display device according to (2), wherein the optically anisotropic element (C) is obtained through a step of applying a shearing force to at least both surfaces of the transparent film to give a strain. (5) The liquid crystal display device according to (2) above, wherein the optically anisotropic element (C) contains at least one photoisomerizable substance. (6) The optical anisotropic element (C) is formed of at least two layers, one layer (α) of which has positive uniaxiality, and its optical axis is inclined from the normal direction of the surface. The other layer (β) has the smallest refractive index in the thickness direction and the in-plane direction of the maximum main refractive index, and the direction of the optical axis of (α) and the maximum direction of (β) are The liquid crystal display device according to the above (2), characterized in that the direction of the main refractive index is orthogonal. (7) A liquid crystal cell in which a twisted nematic liquid crystal is sandwiched between two electrode substrates, and two polarizing elements arranged at both ends of the liquid crystal cell, and between the liquid crystal cell and the polarizing element,
One or two or more optically anisotropic elements (A) having an optically negative uniaxial property and whose optical axis is in the direction normal to the surface.
And at least one optical anisotropic element (D) whose optical tilt angle continuously changes, wherein at least one of the optical anisotropic elements (A) is an acetic acid group and a propionic acid. A liquid crystal display device comprising a mixed fatty acid cellulose ester having a group. (8) The liquid crystal display device according to (7), wherein the optical anisotropic element (D) is an optical anisotropic element containing a discotic compound. (9) The liquid crystal display device according to (7), wherein the optically anisotropic element (D) is a liquid crystalline polymer that is in a glass state at a liquid crystal transition temperature or lower. (10) The mixed fatty acid cellulose ester having an acetic acid group and a propionic acid group has an acetic acid substitution degree of 2.0 to 2.7.
The liquid crystal display device according to any one of (1) to (9) above, which is a mixed fatty acid cellulose ester having a propionic acid substitution degree of 0.1 to 0.9. (11) When the principal refractive indices in the plane of the optically anisotropic element formed from the mixed fatty acid cellulose ester having the acetic acid group and the propionic acid group are nx and ny, and the principal refractive index in the thickness direction is nz, The retardation value RTH represented by {(nx + ny) / 2-nz} .d is 20 to 150 nm, and the polarizing film and the liquid crystal cell side have a protective film, and the protective film is optically negative uniaxial. And the optical axis is in the normal direction, and the total value of RTH of the optical anisotropic element and the protective film is 50 nm to 400 nm, The liquid crystal display device according to (1) to (9) above. (12) The front retardation value Re represented by (nx-ny) · d of the mixed fatty acid cellulose ester having an acetic acid group and a propionic acid group is 0 to 40 nm, and the above (1) to (9) ).

The operation of the present invention will be described below with reference to the drawings, taking a TN type liquid crystal display element as an example. 1 and 2 show polarization states of light propagating in a liquid crystal cell when a sufficient voltage equal to or higher than a threshold voltage is applied to the liquid crystal cell. Since the transmittance characteristic of light particularly when a voltage is applied greatly contributes to the viewing angle characteristic of contrast, the case of an applied voltage will be described as an example. FIG. 1 is a diagram showing a polarization state of light when light is vertically incident on a liquid crystal cell. When natural light L0 is vertically incident on a polarizing plate A having a polarization axis PA, the polarizing plate PA
The light transmitted through becomes the linearly polarized light L1.

When the arrangement state of the liquid crystal molecules when a sufficient voltage is applied to the TN type liquid crystal cell is schematically represented by one liquid crystal molecule, LC in the schematic diagram is obtained. When modeled by liquid crystal molecules in a liquid crystal cell, if the molecular long axis of LC in the schematic diagram is parallel to the path of light, a difference in refractive index occurs on the incident surface (in a plane perpendicular to the path of light). Therefore, even when the light passes through the liquid crystal cell, it propagates as linearly polarized light. Polarization axis P of polarizing plate B
When B is set perpendicular to the polarization axis PA of the polarizing plate A, the linearly polarized light L2 that has passed through the liquid crystal cell cannot pass through the polarizing plate B and is in a dark state.

FIG. 2 is a diagram showing the polarization state of light when the light is obliquely incident on the liquid crystal cell. When the natural light L0 is obliquely incident, the polarized light L1 transmitted through the polarizing plate A becomes substantially linearly polarized light. (In the actual case, it becomes elliptically polarized light due to the characteristics of the polarizing plate.) In this case, the refractive index anisotropy of the liquid crystal causes a difference in the refractive index on the incident surface of the liquid crystal cell, and the light L2 transmitted through the liquid crystal cell is elliptically polarized light. And is not completely blocked by the polarizing plate B. As described above, in the case of oblique incidence, blocking of light in a dark state becomes insufficient, which causes a large reduction in contrast, which is not preferable.

It is an object of the present invention to prevent such a decrease in contrast at oblique incidence and improve the viewing angle characteristics. In the present invention, at least one
An optically negative uniaxial optically anisotropic element whose optical axis is normal to the surface and an optically negative uniaxial optically anisotropic element whose optical axis is inclined from the direction normal to the surface, or It is used in combination with any of the optical anisotropic elements whose optical axis tilt angle continuously changes. These optically anisotropic elements may be arranged on one side of the liquid crystal cell or may be separately arranged on both sides.

It is estimated as follows that the viewing angle of the liquid crystal display device can be greatly expanded by the present invention. Most TN-LCDs adopt a normally white mode. In this mode, the transmittance of light from the black display portion remarkably increases as the viewing angle increases, resulting in a sharp decrease in contrast. Black display is the state when voltage is applied,
At this time, the liquid crystal molecules in the TN type liquid crystal cell are lined up as in the model of FIG. 3A, and if the liquid crystal molecules in the liquid crystal cell can be regarded as a positive uniaxial optically anisotropic body, then the birefringence caused by them In order to compensate for the above, an optically anisotropic element in which the tilt angle of the molecule with respect to the substrate surface continuously changes may be used.

Further, when the arrangement of the liquid crystal molecules is approximated by an optically positive uniaxial refractive index ellipsoid, it becomes as shown in FIG. 3 (b). In the TN type liquid crystal cell, the optical axis is normal to the surface of the cell. Considered as a laminated body of four positive uniaxial optical anisotropic bodies slightly tilted from the direction and two positive uniaxial optical anisotropic bodies whose optical axes are in the same direction as the normal direction. You can If the liquid crystal cell can be regarded as a laminated body of four positive uniaxial optical anisotropic bodies, in order to compensate for it, a negative uniaxial optical anisotropic body composed of the same combination of optical axis tilt angles as the laminated body is used. ,
That is, at least one optically anisotropic uniaxial element (A) having at least one optically negative uniaxial property and an optical axis in the normal direction to the surface, and at least one optically negative uniaxial property. In addition, the optical anisotropic element (B) whose optical axis is inclined by 5 ° to 50 ° from the direction normal to the surface may be used. For these reasons, it is presumed that the optical compensation film of the present invention significantly improves the viewing angle characteristics.

The optical anisotropic element (A) used in the present invention is required to have a good light transmittance and to be slightly plane-oriented. The plane orientation referred to in the present invention is
The film has a triaxial refractive index relationship of nx = ny> nz. Here, nx and ny are main refractive indices in the film plane, and nz is a main refractive index in the film thickness direction. Also, the values of nx and ny do not have to be exactly the same, and it is sufficient if they are almost equal. Specifically, if | nx-ny | / | nx-nz | ≤0.3, there is no practical problem, but when the thickness of the base film is d, 20≤RTH <150 (nm) It is preferable to satisfy the conditions. Where RTH =
It is more preferable that {(nx + ny) / 2-nz} * d and that the condition of 20≤RTH <50 (nm) is satisfied. The thickness of the optically anisotropic element (A) is preferably 30 μm ≦ d ≦ 200 μm.

The polarizing element usually has a protective film. The protective film is preferably optically isotropic, but generally has a slight optical anisotropy. If this protective film is outside the liquid crystal cell, it does not affect the viewing angle characteristics of the liquid crystal display device, but since protective films are usually used on both sides of the polarizing element, the protective film on the liquid crystal cell side is different from the optical film of the present invention. It has the same action as the rectangular element (A). Therefore, it is important that the total value of the retardation values RTH of the protective film on the liquid crystal cell side of the polarizing element and the optically anisotropic element (A) is 50 nm to 400 nm, and more preferably 50 nm to 250 nm.

Next, the advantage that fatty acid cellulose ester having an acetic acid group and a propionic acid group is excellent as an optically anisotropic element (A) having an optically negative uniaxial property and an optical axis normal to the normal direction explain. In order to be used as the optical anisotropic element (A), as described above, preferably 20 ≦ RTH <
Assuming 150 nm and d = 100 μm, Δ
n = (nx + ny) / 2-nz is 0.0002-0.
In general, it is necessary that the birefringence be so small as to be isotropic. In order to form such a low birefringence anisotropic element, it is necessary that the material has a small intrinsic birefringence value, and in general, ZEONEX (Nippon Zeon), ARTON (Nippon Synthetic Rubber), Fujitac (Fujitaku) Those sold under the trade names such as photographic film) are preferable. Further, in order to use the above materials as the optical anisotropic element (A), in order to minimize birefringence and unevenness of thickness, as described above, the film must be formed into a film by solution casting. I have to. However, at the time of solution film formation, the residual solvent inevitably remains by a few percent, and in the process of removing the solvent over a long period of time, the surface orientation due to the thickness shrinkage is promoted, and the refractive index in the thickness direction gradually decreases, and thus RTH With an increase. by the way,
Previously known Fujitac, ZEONEX, and ARTON had 1% at 85 ° C even if the initial residual volatile content was suppressed to 2%.
It was found that RTH increased from 10% to 20% under the forced condition of 000 hours, and the viewing angle of LCD was significantly reduced. However, in the fatty acid cellulose having an acetic acid group and a propionic acid group according to the present invention, the increase in RTH could be suppressed to 5% or less under the same conditions. The cause of this has not been fully clarified yet, but it is considered that the intrinsic birefringence value of this material is smaller than those of ZEONEX, ARTON, and FUJITAC.

Next, the substitution degree of the mixed fatty acid cellulose ester of the present invention, that is, the substitution degree of acetic acid (DSAC) and the substitution degree of propionic acid (DSpr) will be described. The mixed fatty acid cellulose ester of the present invention has an acetic acid substitution degree (D
SAC is 2.0 to 2.7, and propionic acid substitution degree (DSp)
r) is 0.1 to 0.9. Here, the substitution degree is
This is the so-called bound fatty acid amount, which is the percentage of the bound fatty acid weight per unit weight of cellulose, ASTM: D-8
It is measured and calculated according to the measurement and calculation of the degree of acetylation in 17-91 (testing method for cellulose acetate and the like). Total degree of substitution of the mixed fatty acid cellulose ester of the present invention, that is, degree of acetic acid substitution (DSAC)
And the sum of propionic acid substitution degree (DSpr) is 2.0 to
Any value between 3.0 can be selected.

Next, the mixed fatty acid cellulose ester used in the present invention is preferably acetyl cellulose having a degree of polymerization of 270 to 400 calculated from the intrinsic viscosity. The degree of polymerization is
It is a factor that controls the viscosity of the polymer solution during solution casting, in order to optimize the economics of the film forming process and the surface condition of the formed film, or to increase the mechanical strength of the formed film to a certain level or higher. In order to retain, it is essential to be within the scope of the invention. Here, the polymerization degree calculated by the intrinsic viscosity means the method of Uda et al. (Kazuo Uda, Hideo Saito, Journal of the Textile Society, Vol. 18, No. 1, pp. 105-120).
Page, 1962). That is,
Intrinsic viscosity (hereinafter referred to as "η") and degree of polymerization (hereinafter referred to as "D") measured in a solution (unit: g / liter) obtained using a mixed solvent of methylene chloride / methanol: 9/1 (w / w).
P)) is shown in the following formula as described on page 25 above. [Η] = (Km × DP) ^a Here, since a = 1 can be approximated, the value of the constant Km is set to 5.2 to 5.4 × 10 ⁻⁴ when the degree of substitution is 2.8 or more, and the degree of polymerization is Is represented by the following formula. DP = [η] ÷ Km

The mixed fatty acid cellulose ester of the present invention may be one synthesized from cotton linter, one synthesized from wood pulp, or a mixture of both. By changing the mixing ratio, the load at the time of stripping after casting can be reduced and the surface condition of the film can be improved.

The optically anisotropic element (B) used in the present invention, which has an optically negative uniaxial property and its optical axis is inclined 5 ° to 50 ° from the normal direction of the film, has a light transmittance of 80. % And at the same time, the principal refractive index of the optically anisotropic element is nx ′,
Assuming that ny ′, nz ′ and thickness are d ′, the relationship of triaxial principal refractive indices satisfies nx ′ = ny ′> nz ′, and RTH is {(nx ′ +
ny ′) / 2−nz ′} · d ′, 30 nm ≦ RTH ≦ 400 nm, preferably 50 nm ≦ RTH ≦ 200 nm. However, the values of nx 'and ny' do not have to be exactly equal, and it is sufficient if they are almost equal. Specifically, there is no practical problem as long as the following. | Nx'-ny '| / | nx'-nz' | ≤0.2 Further, regarding the angle formed by the optical axis and the normal direction of the film,
It is more preferably 10 ° to 50 °. The method for producing the optically anisotropic element (B) of the present invention includes a method in which a discotic compound is oriented obliquely, a method in which a shear force is applied to both sides of the film to impart strain, and isomerization is performed by light such as azobenzene. There is a method of irradiating a compound with polarized light, which will be described below.

First, a method of orienting a discotic compound as an optical anisotropic element (B) will be described. The discotic compound of the present invention is, for example, C.I. Destrade
Et al., Mol. Cryst. 71, 111 pages (1981), benzene derivatives,
B. Kohne et al., Angew. Chem.
Vol. 96, p. 70 (1984) and cyclohexane derivatives described in J. Am. M. J. Lehn et al. C
hem. Commun. Pp. 1794 (1985),
J. Research report by Zhang et al. Am. Chem. S
oc. 116, pp. 2655 (1994), such as azacrown-type and phenylacetylene-type macrocycles. Generally, these are used as the mother nucleus of the molecular center, and straight-chain alkyl groups, alkoxy groups, and substituted benzoyloxy groups are used. It has a structure in which a group or the like is linearly substituted as its straight chain, exhibits liquid crystallinity, and includes what is generally called discotic liquid crystal. However, the molecule is not limited to the above description as long as the molecule itself has negative uniaxiality and can give a certain orientation. In the present invention,
The layer formed from a discotic compound does not require that the finally formed layer be the compound, and for example, the low molecular weight discotic liquid crystal has a group that reacts with heat, light, etc. Polymerize or crosslink by reaction with heat, light, etc.,
Those that have a high molecular weight and lose the liquid crystallinity are also included.

The discotic compound in the present invention means, in addition to the discotic liquid crystals listed below, liquid crystals due to the reaction between the discotic liquid crystals and the reaction between the discotic liquid crystals and other low molecular weight compounds or polymers. It also includes a reaction product of discotic liquid crystal that has stopped exhibiting properties, and basically any compound whose molecule itself has optically negative uniaxiality may be used.

[0025]

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[0026]

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[0027]

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[0028]

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The discotic liquid crystal typified by the above discotic compound is applied after rubbing an organic alignment film provided on a transparent support or after coating it on an inorganic alignment film.
It is possible to orientate obliquely by heating once in the isotropic phase and maintaining it in the liquid crystal phase for a certain period of time.

Examples of the organic alignment film material include polyimide, polystyrene derivatives, gelatin, polyvinyl alcohol and the like. By subjecting all of them to rubbing treatment, the discotic liquid crystal can be oriented obliquely. Of these, alkyl-modified polyvinyl alcohol is particularly preferable, and is excellent in the ability to uniformly align the discotic liquid crystal. It is speculated that this is due to the strong interaction between the alkyl chains on the alignment film surface and the alkyl side chains of the discotic liquid crystal. The alkyl-modified polyvinyl alcohol has an alkyl group at the terminal as listed below, and preferably has a saponification degree of 80% or more and a polymerization degree of 200 or more. In addition, as a commercially available product, MP10
3, MP203, R1130 (Kuraray), etc. are available.

A polyimide film, which is widely used as a liquid crystal alignment film for LCDs, is also preferable as the organic alignment film,
This is obtained by applying a polyamic acid (for example, LQ / LX series (Hitachi Chemical Co., Ltd.), SE series (Nissan Chemical Co., Ltd.)) to the substrate surface, baking at 100 to 300 ° C. for 0.5 to 1 hour, and then rubbing. .

[0032]

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The rubbing treatment is the same method widely used as a liquid crystal alignment treatment process for LCDs, and the surface of the alignment film is made of paper, gauze, felt, rubber, nylon, polyester fiber or the like. It is a method of obtaining alignment by rubbing in a fixed direction. Generally, rubbing is performed several times using a cloth or the like in which fibers of uniform length and thickness are evenly flocked.

As a vapor deposition material for the inorganic oblique vapor deposition film, metal oxides such as TiO ₂ , MgF ₂ and ZnO ₂ and fluorides, and metals such as Au and Al can be cited as a representative of SiO. The metal oxide can be used as the orthorhombic vapor deposition material as long as it has a high dielectric constant, and is not limited to the above. Both the fixed substrate method and the continuous vapor deposition method on the film can be used to form the vapor deposition film. For example, when SiO is used as the vapor deposition material, the discotic liquid crystal has a vapor deposition angle α of about 65 ° to 88 °. Its optical axis is uniformly oriented in a direction approximately orthogonal to the direction of the vapor deposition particle column.

The alignment film has a function of determining the alignment direction of the discotic liquid crystal molecules coated thereon. However, since the orientation of the discotic liquid crystal depends on the orientation film, it is necessary to optimize the combination. next,
The uniformly aligned discotic liquid crystal molecules are aligned at an angle with the normal line of the film, but the tilt angle does not change much depending on the type of the alignment film and often takes a value specific to the discotic liquid crystal molecules. Further, when two or more kinds of discotic liquid crystals are mixed or a compound similar to the discotic liquid crystal is mixed, the tilt angle can be adjusted within a certain range by the mixing ratio. Therefore, for controlling the tilt angle of the oblique alignment, it is more effective to select or mix the discotic liquid crystal.

The optical anisotropic element (B) in the present invention requires a process for obtaining a uniform oblique orientation in the manufacturing process. Specifically, a discotic liquid crystal is applied to a substrate on which a rubbing-treated organic alignment film or an inorganic alignment film is formed, and then the temperature is raised to a liquid crystal phase, more preferably a discotic nematic phase formation temperature. As a result, the liquid crystal is obliquely aligned, and remains in the solid state at room temperature while maintaining the alignment by subsequent cooling. Further, the discotic nematic liquid crystal phase forming temperature is unique to the discotic liquid crystal, but can be arbitrarily adjusted by mixing two or more different substances. The discotic liquid crystal used in the present invention has a discotic nematic liquid crystal phase / solid phase transition temperature of preferably 70 ° C to 300 ° C, particularly preferably 70 ° C to 150 ° C.

Magnetic field orientation and electric field orientation are available as methods other than the above in which the discotic compound coated on the substrate is oriented obliquely. In this method, after the discotic compound is coated on the support, the discotic compound can be oriented obliquely by utilizing a magnetic field, an electric field or the like at a desired angle.

In order to maintain the oblique orientation of the discotic compound thus obtained even under high temperature and high humidity conditions, a polymerizable unsaturated group, an epoxy group, a hydroxyl group, an amino group or a carboxyl group is previously added to the discotic compound. Have functional groups such as
Radical polymerization of polymerizable unsaturated groups by heat or photoinitiator, or ring-opening polymerization of epoxy groups by photoacid generation,
It is preferable to crosslink the discotic compound itself by a crosslinking reaction with a polyvalent isocyanate or a polyvalent epoxy compound. In this case, another compound having the same functional group may be contained.

Further, the optical anisotropic element (B) in the present invention
Can be obtained by applying a shearing force to at least both sides of the transparent film with a device as shown in FIG. Specifically, it is efficiently obtained by sandwiching a film made of a thermoplastic resin and having a light transmitting property between two rolls having different peripheral speeds and applying a shearing force to the film. As the thermoplastic resin used here,
If the light transmittance is 70%, more preferably 85%, there is no problem and there are no other restrictions. Specifically, polycarbonate, polyarylate, polysulfone, polyethylene terephthalate, polyethylene naphthalate, polyether sulfone, polyphenylene sulfide, polyphenylene oxide, polyallyl sulfone, polyvinyl alcohol, polyamide, polyimide, polyolefin, binary or ternary various Polymers, graft copolymers, blends and the like are preferably used.

The photoisomerizable substance in the present invention is one which causes stereoisomerization or structural isomerization by light, and preferably one which causes reverse isomerization by light or heat of another wavelength. These compounds include:
Generally, it is accompanied by a structural change and a change in color tone in the visible region, and many are well known as photochromic compounds. Specifically, azobenzene compounds, benzaldoxime compounds, azomethine compounds, fulgide compounds,
Examples thereof include diarylethene compounds, cinnamic acid compounds, retinal compounds, hemithioindigo compounds and the like. Representative compounds are shown in Chemical formulas 6 and 7.

[0041]

[Chemical 6]

[0042]

[Chemical 7]

[0043]

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Further, it is formed from at least two layers,
One layer (α) has positive uniaxiality, its optical axis is tilted from the normal direction of the surface, and the other layer (β) has the minimum refractive index in the thickness direction. In addition, the direction of the maximum principal refractive index is in the plane, and the direction of the optical axis of (α) and the direction of the maximum principal refractive index of (β) are orthogonal to each other. Can be specifically realized by the following modes. For example, the layer (α) is obtained by coating a transparent film (support) with an alignment film and rubbing it and then coating a nematic liquid crystal thereon, and the other layer (β) has a positive intrinsic birefringence. It is obtained by a uniaxially stretched film or the like. Therefore, it can also be obtained by using a uniaxially stretched film as the layer (β) and forming the layer (A) thereon.

Optically anisotropic element (C) defined in the present invention
Is such that the optical characteristics cannot be defined by the three principal refractive indices, but when the optical anisotropic element is regarded as a laminate of a large number of thin layers, the thin layers are approximately optically It has a uniaxial property, and is preferably negative uniaxial for the purpose of the present invention. The optical tilt angle defined in the present invention means the angle formed by the optical axis of the thin layer, which is approximately regarded as uniaxial, and the normal to the substrate surface of the liquid crystal cell.

Further, it can be realized by using the above discotic compound as the optical anisotropic element (C) whose optical tilt angle continuously changes. However, in order to continuously change the optical tilt angle of the discotic compound in the thickness direction, the following processing is required. Generally, in the case of a liquid crystal cell using a nematic liquid crystal, when the both sides of the liquid crystal are sandwiched by rubbing-treated alignment films, the optical axes of liquid crystal molecules are aligned in a certain direction. That is, the liquid crystal molecules are uniformly aligned in the thickness direction by the alignment regulating force of the alignment films on both sides of the liquid crystal layer. Therefore, by unbalancing the alignment regulating force of the alignment film on both sides, it is possible to continuously change the alignment of molecules in the thickness direction. This idea can also be applied to discotic liquid crystals. Specifically, a discotic liquid crystal is applied to a substrate on which a rubbing-processed organic alignment film or inorganic alignment film is formed, and one side of the liquid crystal layer remains in an open system (air layer) in a liquid crystal phase, more preferably a discotic liquid crystal phase. To raise the temperature to the phase formation temperature.

As a result, the liquid crystal phase has an oblique orientation that continuously changes in the thickness direction, and remains in the solid state at room temperature while maintaining the orientation by cooling thereafter. In this case, the tilt angle near the alignment film can be controlled by a discotic liquid crystal material, alignment film material, rubbing, etc., and the tilt angle is preferably 0 ° to 85 °, more preferably 0 ° to 50 °. Is. Also, the tilt angle near the air layer is
The degree of orientation change in the thickness direction can be controlled with a discotic liquid crystal material, a plasticizer, a binder, a surfactant and the like.

The plasticizer is not particularly limited as long as it is compatible with the discotic liquid crystal used. However, it is preferable to have a reactive substituent from the viewpoint of imparting heat resistance. The amount added to the discotic liquid crystal is
The weight ratio is preferably 0.1 wt% to 50 wt%. The binder is not particularly limited as long as it does not significantly disturb the orientation of the discotic liquid crystal used, but a cellulose-based polymer derivative such as cellulose acetate butyrate is preferable.

Although the discotic nematic liquid crystal phase forming temperature is unique to the discotic liquid crystal, it can be arbitrarily adjusted by mixing two or more different substances or by mixing the plasticizer. The discotic liquid crystal phase / solid phase transition temperature of the discotic liquid crystal according to the present invention is preferably 70 ° C to 300 ° C, more preferably 70 ° C to 170 ° C.

Further, the optically anisotropic element (C) of the present invention in which the optical tilt angle continuously changes is a liquid crystalline polymer composition comprising at least a homeotropically oriented liquid crystalline polymer and a homogeneously oriented polymer. Therefore, by using a liquid crystalline polymer that is in a glass state below the liquid crystal transition temperature, that is, a liquid crystal polymer having a nematic phase or a chiral nematic phase at a temperature above the liquid crystal transition and a glass state at a temperature below the liquid crystal transition temperature, realizable. The liquid crystal polymer composition is temporarily aligned at the liquid crystal temperature and then cooled to fix the liquid crystal state. The glass state is preferably taken at a temperature equal to or lower than the liquid crystal transition temperature because the use of the liquid crystal polymer composition having a crystal phase may destroy the orientation state once obtained.

When the liquid crystalline polymer composition thus obtained is oriented on a substrate, it is not a conventional homeotropic orientation or a homogeneous orientation, but can realize an intermediate orientation. That is, the major axis of the polymer constituting the composition can be oriented so that the major axis is different from the substrate surface and the substrate normal direction. Furthermore, by introducing an optically active unit into the polymer or by allowing an optically active substance to coexist in the composition, a structure having a twisted structure (helical structure) while being tilted can be realized. Further, since the composition of the present invention has a glass phase at a temperature lower than the liquid crystal phase, it can be a transparent material in which the liquid crystal state is fixed to glass. The tilt angle is preferably 0 ° to 85 °, more preferably 0 ° to 50 °.

The liquid crystal polymer of the present invention will be specifically described. First, the features common to homeotropically oriented polymers and homogeneously oriented polymers will be described. The type of liquid crystal polymer used is not particularly limited, and examples thereof include main chain liquid crystal polymers such as polyester, polyamide, polycarbonate, and polyesterimide, or side chain liquid crystal polymers such as polyarylate, polymethacrylate, polymalonate, and polysiloxane. can do. Among them, polyester is preferable from the viewpoint of ease of synthesis, orientation, glass transition and the like. The constitutional unit of the polyester is not particularly limited, but preferable examples include:
(A) a unit derived from a dicarboxylic acid (hereinafter referred to as a dicarboxylic acid unit), (b) a unit derived from a diol (hereinafter referred to as a diol unit), (c) a carboxyl group in one unit. Examples thereof include units derived from oxycarboxylic acids having hydroxyl groups at the same time (hereinafter referred to as oxycarboxylic acid units). Compounds with asymmetric carbon atoms as structural units (optically active compounds or racemates)
Units derived from can also be used, and most of the polymers containing optically active units are chiral nematic phases (twisted nematic phase, cholesteric phase) as the liquid crystal phase.
Will be shown. On the other hand, those containing no optically active unit show a nematic phase as a liquid crystal phase. As the polyester structure, (a) + (b) type, (a) + (b) + (c)
Type and (c) single type.

Examples of the dicarboxylic acid unit (a) include, for example:

[0054]

Embedded image

(X is a halogen such as hydrogen, chlorine or bromine, an alkyl group having 1 to 4 carbon atoms (eg, methyl group, ethyl group, propyl group, isopropyl group, butyl group, t-butyl group, etc.)) Or an alkoxy group (for example,
Methoxy group, ethoxy group, propoxy group, butoxy group and the like) or phenyl group. k is 0 to 2, the same applies hereinafter),

[0056]

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[0057]

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(* Indicates optically active carbon. The same applies hereinafter.)

[0059]

[Chemical 12]

And the like.

Examples of the diol unit (b) include, for example,

[0062]

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[0063]

Embedded image

And the like.

As the oxycarboxylic acid unit of (c),
For example

[0066]

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And the like.

Typical examples of the homeotropically oriented polymer and the homogeneously oriented polymer are shown below.

As the polymer having homeotropic orientation and the polymer having homogeneous orientation other than the above, typically, in the above polyester-based polymer, a part of the constitutional unit is substituted as a constitutional unit or an additional constitutional unit is substituted. Examples of the polyester include an aromatic unit having an alkyl group having 3 or more carbon atoms, preferably 3 to 12 carbon atoms as part of the group or the substituent.

Among the constitutional units, examples of the aromatic unit having a substituent or an alkyl group having 3 or more carbon atoms as a part of the substituent include, for example,

[0071]

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(R is an alkyl group having 3 to 12 carbon atoms) and the like. Further, as the aromatic unit having a fluorine or fluorine-containing substituent,

[0073]

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And the like.

Further, in order to fix the alignment structure of the liquid crystalline polymer composition of the present invention, it is preferable to use one which takes a glass state without causing crystallization at a temperature lower than the liquid crystal phase.
When fixing the liquid crystal structure of the composition, the polymer molecules are once aligned at the liquid crystal temperature and then cooled for fixing, but when a composition having a crystalline phase is used, the once obtained alignment state is destroyed. This is because there is a risk of doing so. For example, in the case of the polyester-based polymer shown in the above example, an ortho-substituted aromatic unit is preferably used as a constituent unit that suppresses crystallization, and a polyester-based polymer having such a unit is suitable. The ortho-substituted aromatic unit here means a structural unit in which the bonds forming the main chain are mutually ortho units. In order for the composition to take a glass state without causing crystallization in the low temperature part due to the liquid crystal phase, at least one of the homeotropic alignment polymer and the homogeneous alignment polymer forming the composition contains these structural units. Preferably. Specific examples of these ortho-substituted aromatic units include catechol units, salicylic acid units, phthalic acid units and those having a substituent on the benzene ring of these groups as shown below.

[0076]

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With respect to the homeotropic alignment polymer and the homogeneous alignment polymer which compose the liquid crystal composition of the present invention, the following polymers can be specifically exemplified as suitable polyesters.

First, as the homeotropically oriented polymer,

[0079]

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A polymer composed of the structural unit of (wherein k, l, and m are compositional ratios (mole) in units, and k = 1 + m, 1 / m = 100/0 to 20/80,
(Preferably 95/5 to 30/70)

[0081]

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A polymer composed of the structural unit of (wherein k, l, and m are compositional ratios (mole) in units, and k = l + m, l / m = 98/2 to 20/80, (Preferably 95/5 to 30/70)

[0083]

[Chemical 21]

A polymer composed of the structural unit (wherein k, l, m, and n are compositional ratios (mole) in units, and k = 1 + m, 1 / m = 98/2 to 20 /). 8
0, preferably 95/5 to 30/70, 1 / n = 98 /
2 to 20/80, preferably 95/5 to 30/70)

[0085]

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A polymer composed of the structural unit (wherein k, l, and m are compositional ratios (mole) in the unit, and k = l + m, l / m = 98/2 to 20/80, (Preferably 95/5 to 30/70)

[0087]

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A polymer composed of the structural unit of (wherein k, l and m are compositional ratios (mole) in the unit, k = 1 + m, 1 / m = 98/2 to 20/80, It is preferably 95/5 to 30/70, and n is an integer of 2 to 12).

[0089]

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A polymer composed of the structural unit of (wherein k, l, and m are compositional ratios (mole) in units, and k = l + m, l / m = 98/2 to 20/80, (Preferably 95/5 to 30/70)

[0091]

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A polymer composed of the structural unit of (wherein k, l, m and n are compositional ratios (mole) in units, and k + 1 = l + m, k / l = 100/0 to 0 /
100, preferably 95/5 to 5/95, m / n = 98
/ 2 to 20/80, preferably 95/5 to 30/70)

[0093]

[Chemical formula 26]

A polymer composed of the structural unit (wherein k, l, and m are compositional ratios (mole) in the unit, and k = 1 + m, 1 / m = 100/0 to 0/100,
It is preferably 98/2 to 2/98, n is an integer of 2 to 12)

And the like. Of course, in these formulas, the composition ratios of the respective structural units k, l, m, etc. merely indicate a molar ratio, not a block-like unit.

Examples of the homogeneously oriented polymer include, for example,

[0097]

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A polymer composed of the structural unit of (wherein k, l, and m are compositional ratios (mole) in units, and k = 1 + m, 1 / m = 80/20 to 20/80,
(Preferably 75/25 to 25/75)

[0099]

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A polymer composed of the structural unit of (wherein k, l and m are compositional ratios (mole) in units, and k = 1 + m, 1 / m = 80/20 to 20/80,
(Preferably 75/25 to 25/75)

[0101]

[Chemical 29]

A polymer composed of the structural unit (wherein k, l, and m are compositional ratios (mole) in the formula, and k = 1 + m, 1 / m = 80/20 to 20/80,
(Preferably 75/25 to 25/75)

[0103]

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A polymer composed of the structural unit of (wherein k, l, m and n are compositional ratios (mole) in units, and k = 1 + m, 1 / m = 80/20 to 20 /). 8
0, preferably 75/25 to 25/75, 1 / n = 80
/ 20 to 20/80, preferably 75/25 to 25/7
5)

[0105]

[Chemical 31]

A polymer composed of the structural unit (wherein k, l, m, and n are compositional ratios (mole) in units, and k = 1 + m, 1 / m = 80/20 to 20 / 8
0, preferably 75/25 to 25/75, 1 / n = 80
/ 20 to 20/80, preferably 75/25 to 25/7
5)

[0107]

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A polymer composed of the structural unit (wherein k, l and m are compositional ratios (mole) in the unit, and k = 1 + m, 1 / m = 80/20 to 20/80,
(Preferably 75/25 to 25/75)

[0109]

[Chemical 33]

A polymer composed of the structural unit of (wherein k, l, and m are compositional ratios (mole) in units, and k = 1 + m, 1 / m = 80/20 to 20/80,
(Preferably 75/25 to 25/75)

[0111]

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A polymer composed of the structural unit (wherein k, l, and m are compositional ratios (mole), and k + l = m + n, k / l = 80/20 to 20/8).
0, preferably 75/25 to 25/75, m / n = 80
/ 20 to 20/80, preferably 75/25 to 25/7
5 and p is 2 to 12)

[0113]

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A polymer composed of the structural unit (wherein k, l, and m are compositional ratios (mole) in the unit, and k + l = m, k / l = 80/20 to 20/80,
It is preferably 75/25 to 25/75 and p is 2 to 12.)

And the like.

The molecular weight of these polymers can be determined in various solvents such as phenol / tetrachloroethane (60/4).
0 (weight ratio)) In a mixed solvent, the logarithmic viscosity measured at 30 ° C. is usually preferably 0.05 to 3.0, and more preferably 0.07 to 2.0. When the logarithmic viscosity is less than 0.05, the strength of the obtained polymer liquid crystal becomes weak, which is not preferable. On the other hand, if it is more than 3.0, the viscosity at the time of forming the liquid crystal is too high, which causes problems such as a decrease in the orientation and an increase in the time required for the orientation.

The method for synthesizing these polymers is not particularly limited, and they are synthesized by a polymerization method known in the art, for example, a melt polymerization method or an acid chloride method using a corresponding acid chloride of dicarboxylic acid. In the case of synthesizing by a melt polymerization method, for example, it can be produced by polymerizing an acetylated product of a corresponding dicarboxylic acid and a corresponding diol under high temperature and high vacuum, and the molecular weight can be easily controlled by controlling the polymerization time. In order to accelerate the polymerization reaction, a conventionally known metal salt such as sodium acetate can also be used. When the solution polymerization method is used, a desired polyester can be easily obtained by dissolving a predetermined amount of dicarboxylic acid chloride and diol in a solvent and heating in the presence of an acid acceptor such as pyridine.

As described above, the liquid crystalline polymer composition of the present invention is characterized in that it contains at least the above-mentioned homeotropically oriented polymer and homogeneously oriented polymer. Further optically active substances can be added to give a twist. In this case, as described above, also when the skeleton of the homeotropically-oriented polymer and / or the homogeneously-oriented polymer contains an optically active unit, similarly, the composition usually takes a chiral nematic phase as a liquid crystal phase.

As such an additive, an optically active substance may be either a low molecular weight compound or a high molecular weight compound as long as it is a compound having optical activity. From the viewpoint of compatibility with a liquid crystalline polymer as a base, an optically active liquid crystal is used. It is preferable that the compound is a volatile compound, and specifically, the following compounds can be exemplified.

[0120]

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[0121]

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Cholesterol derivatives and the like.

Further, as such an optically active substance, other optically active polymers can be mentioned. Any polymer can be used as long as it has an optically active group in the molecule, but a liquid crystalline polymer is preferable from the viewpoint of compatibility with the base polymer. For example, optically active polyarylate, polymalonate, polysiloxane, polyester, polyamide, polypeptide, polycarbonate, or polypeptide, cellulose and the like can be mentioned. Among them, an optically active polyester mainly containing an aromatic compound is preferable from the viewpoint of compatibility with the nematic liquid crystal polymer as the base. Specifically, the following polymers can be exemplified.

[0124]

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[0125]

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A polymer composed of the structural unit of

[0127]

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A polymer composed of structural units (n = 2 to 12),

[0129]

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A polymer composed of the structural unit of

[0131]

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A polymer composed of the structural unit of

[0133]

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A polymer composed of the structural unit of

[0135]

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A polymer composed of the structural unit of

[0137]

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A polymer composed of the structural unit of

[0139]

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A polymer composed of the structural unit of

[0141]

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A polymer composed of the structural unit of

[0143]

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Polymers composed of the structural unit of, and the proportion of the optically active group in these polymers is usually 0.5 mol% to 80 mol%, preferably 5 mol%.
-60 mol% is desirable.

The molecular weight of these polymers is, for example, preferably in the range of 0.55 to 5.0 in logarithmic viscosity measured at 30 ° C. in phenol / tetrachloroethane. If the logarithmic viscosity exceeds 5.0, the viscosity may be too high, resulting in a decrease in orientation, which is not preferable in some cases.
If it is less than 05, the composition may be difficult to control, which is not preferable.

The composition of the present invention can be obtained by mixing the essential components, the homeotropic alignment polymer and the homogeneous alignment polymer, or by mixing the essential component with an optional component such as an optically active compound. . The conditions at this time are not particularly limited and are appropriately selected by a known method.

The mixing ratio of the homeotropic orienting polymer and the homogeneous orienting polymer varies depending on the polymer and the purpose, and cannot be said unconditionally, but usually it is 99: 1 to 0.5: 99.5 by weight. More preferably 98:
2 to 1:99, and more preferably 95: 5 to 2:98. 0.5% by weight of homeotropic oriented polymer
When the amount is less than 1, the properties of the composition are almost the same as when the homogeneously oriented polymer is used alone, and the desired novel oriented structure may not be obtained, and when the amount of the homogeneously oriented polymer is less than 1% by weight, Similarly, the properties may be almost the same as when the homeotropically oriented polymer is used alone.

When an optically active substance is added, its proportion in the composition is usually 50% by weight or less, preferably 40% by weight or less, more preferably 0.1 to 35%.
% By weight is desirable.

The composition of the present invention does not contain an optically active substance, and when neither the homeotropically oriented polymer nor the homogeneously oriented polymer which is an essential component contains an optically active unit, a nematic phase is formed. When it exceeds 0% by weight, it has a twisted nematic phase or a chiral nematic phase, but it is a chiral nematic phase for the embodiment of the present invention in which the optical tilt angle is negative due to negative uniaxiality. preferable. However, when the amount of the optically active substance exceeds 50% by weight, phase separation tends to occur in the composition.

[0150]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments.

Example 1 <Production of Optically Anisotropic Element with Negative Uniaxiality and Optical Axis in Normal Direction> Acetic acid substitution degree is 2.2 and propionic acid substitution degree is 0.7.
Cellulose ester (CAP), ARTONG,
Zeonex and 12.7 parts by weight of cellulostriacetate (CTA) each having a degree of acetic acid substitution of 2.81 were dissolved in 87.3 parts by weight of methylene chloride, cast on a metal band and dried. In addition, tenter stretching and longitudinal uniaxial stretching were carried out as needed to prepare various optical anisotropic elements (A) having a residual volatile content of 2.5% and an equal RTH. <Measurement of RTH> First, an acrylic pressure-sensitive adhesive was transferred to the optical anisotropic element and attached to an optically isotropic quartz plate having a thickness of 1 mm, and an ellipsometer (manufactured by Shimadzu Corporation, AEP
-100), the three main refractive indices of the index ellipsoid are calculated from the retardation value and the average refractive index when tilted by 40 ° from the front and the normal, and RTH is calculated from the calculated values.
Was calculated. Further, after keeping the quartz plate on which the optical anisotropic element (A) was stuck under the condition of 85 ° C. for 1000 hours, RTH was measured in the same manner as above. The results are shown in Table 1.

[0152]

[Table 1]

<Production of Optically Anisotropic Element> A 0.1 μm gelatin thin film is coated on the CAP film as the above-mentioned optical anisotropic element (A), and a long-chain alkyl-modified polyvinyl alcohol ( MP203: trade name, manufactured by Kuraray Co., Ltd.) was applied, dried with hot air at 40 ° C., and then subjected to rubbing treatment to form an alignment film. On this alignment film, 1 wt.% As a photopolymerization initiator was added to m = 6 of the discotic liquid crystal TE-8.
% Michler-ketone + benzophenone (weight ratio, 1:
1) was added, and they were dissolved in methyl ethyl ketone to make a 30 wt% solution as a whole, and bar coating was performed 145
The temperature was raised to ℃, kept for 3 minutes, and irradiated with ultraviolet rays for 1 second at an illuminance of 600 mW / cm ² to form a discotic compound layer (optical anisotropic element (B)). , (B) were produced. On the CTA film, a layer of the compound on the disc was formed in the same manner to prepare an optical anisotropic element composed of the optical anisotropic elements (A) and (B). In addition, in order to estimate the optical properties of the discotic compound alone, a discotic liquid crystal compound was applied onto an optically isotropic quartz plate under the same conditions and irradiated with ultraviolet rays, and then, as in Example 1. Assuming a refractive index ellipsoid, the ellipsometer
Measure the front retardation and the retardation at 40 ° and -40 °, and measure the optical axis inclination angle and RTH.
Was determined by calculation. Since the optical properties of the discotic compound are the same on the quartz plate, CAP, and CTA, the properties on the quartz plate were also used for CAP and CTA. <Built-in liquid crystal display> RTH is 6 on both sides of the polarizer
Nematic liquid crystal with 90 ° twist angle and 4.5μ between two polarizing elements protected by 5nm film
A liquid crystal display element was prepared which had a liquid crystal cell sandwiched so as to have a gap size of m, and two optical anisotropic elements were incorporated between the polarizing element and the liquid crystal cell in the configuration of FIG. . However, the rubbing direction on the lower side of the liquid crystal cell, the projection direction on the film surface of the upper optical anisotropic element nZ ′, and the rubbing direction on the upper side of the liquid crystal cell and the nZ ′ film of the lower optical anisotropic element. The projection direction on the plane is matched. Further, the polarization axes of the polarizing elements were made orthogonal to each other to obtain a normally white mode TN type liquid crystal display device. A rectangular wave voltage of 55 Hz was applied to this TN type liquid crystal display device, and the contrast from the front direction and the direction inclined to the up / down and left / right directions was measured using LCD-5000 manufactured by Otsuka Electronics, and the front contrast was measured. And contrast is 1
Top / bottom and left / right viewing angles of 0 or more were obtained. Also,
After holding the TN type liquid crystal display element in an environment of 85 ° C. for 1000 hours, the same viewing angle characteristics were measured. Table 2 shows the results
Shown in

[0154]

[Table 2]

Example 2 <Production of Optically Anisotropic Element> A non-oriented polycarbonate film having a width of 30 cm and a thickness of 50 μm was sandwiched between two rolls shown in FIG. 4 and molded under the following conditions. Peripheral speed of rolls R1 and R2: 1.003 m / min,
1.00 m / min Temperature of rolls R1 and R2: 138 ° C. Force applied between rolls: 3000 Kg Diameter of rolls R1 and R2: 15 cm Further, the molding film is 3 at a temperature of 160 ° C. in the width direction. ．
It was stretched by 5% to prepare an optically anisotropic element (B). The optical anisotropy element (B) and the CAP film and the Zeonex film of Example 1 were attached to each other with a pressure-sensitive adhesive to form an optical anisotropy element (A), (B). Two types of devices were produced. <Incorporation into Liquid Crystal Display Device> As in Example 2, an optical anisotropic element was incorporated into the liquid crystal display element, and the viewing angle characteristics were measured. Table 2 shows the results.

Example 3 On the CAP film of Example 1, 1.6 g of discotic liquid crystal TE-8 (m = 4), phenol EO-modified (n = 1) acrylate (M101 Toagosei). Four
g, cellulose acetate butyrate (CAB531-
1-Eastman Chemical) 0.05 g and Irgacure-907 0.01 g dissolved in 3.65 g of methyl ethyl ketone are applied with a wire bar (# 4 bar used), and the resulting solution is attached to a metal frame. 3 in a constant temperature bath at ℃
After heating for a minute to align the discotic liquid crystal, 6
Irradiation was performed at an illuminance of 00 mw / cm ² for 1 second to form a layer containing a discotic compound, to prepare an optically anisotropic element composed of optically anisotropic elements (A) and (C). A discotic compound layer was similarly formed on the ARTONG film to prepare an optical anisotropic element composed of the optical anisotropic elements (A) and (C). In addition, in order to estimate the optical properties of the discotic compound alone, a discotic liquid crystal compound was applied onto an optically isotropic quartz plate under the same conditions, and ultraviolet irradiation was performed. The retardation of the optical anisotropic element (B) thus obtained was set to 5 ° from 40 ° to 140 ° from the rubbing axis on a plane perpendicular to the retardation plate surface including the rubbing axis. In increments, Shimadzu Ellipsometer (AEP-10
When measured using 0), there was no direction in which the retardation was 0. Further, the direction in which the retardation is minimum is neither the film normal direction nor the surface direction. Further, assuming that the optical anisotropic element (C) is a stack of thin layers, it is assumed that one thin layer has optically negative uniaxiality, and the inclination angle of the optical axis changes in the thickness direction. As a result of simulation, it was found that the optical tilt angle of the discotic compound layer continuously changed from 20 ° to 50 °, and the integrated value of RTH of the thin layer was 70 nm.
Since the characteristics of the discotic compound are the same on CAP and ARTONG, the characteristics on the quartz plate are the same as those of CAP and ARTON.
Also used for G. <Incorporation into liquid crystal display device> The above-mentioned optically anisotropic element was incorporated into a liquid crystal display element under the same conditions as in Example 2 and the viewing angle characteristics were measured. Table 2 shows the results.

[0157]

According to the present invention, it is possible to provide a TN type liquid crystal display device in which the viewing angle characteristics are remarkably improved and the viewing angle characteristics do not change even after storage at high temperature for a long time. Needless to say, the present invention can be applied to an active matrix liquid crystal display device using not only a TFT but also a three-terminal device such as MIM and a two-terminal device such as TFD.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a polarization state of light when natural light is vertically incident on a liquid crystal cell.

FIG. 2 is a diagram illustrating a polarization state of light when natural light is obliquely incident on a liquid crystal cell.

FIG. 3 is a diagram showing an alignment state and an approximated alignment state of liquid crystal molecules when a voltage is applied to the liquid crystal cell.

FIG. 4 is a diagram of a process of applying a shearing force to both surfaces of the film with a different peripheral speed roller.

FIG. 5 is a diagram showing the polarization axis of the polarizing plate, the rubbing direction of the liquid crystal cell, and the position of the optically anisotropic element when the viewing angle characteristics were measured in Examples.

[Explanation of symbols]

TNC: TN type liquid crystal cell A, B: Polarizing plate PA, PB: Polarization axis LO: Natural light L1: Linearly polarized light L2: Modulated light after passing through the liquid crystal cell LC: When sufficient voltage is applied to the TN type liquid crystal cell State of liquid crystal molecules of RF1 and RF2: Optical anisotropic element BL: Backlight

Claims (12)

[Claims] 1. A liquid crystal cell in which a twisted nematic liquid crystal is sandwiched between two electrode substrates, and two polarizing elements arranged at both ends of the liquid crystal cell, and between the liquid crystal cell and the polarizing element, Formed from at least one layer containing at least one discotic compound and an optically anisotropic element (A) which is optically negative uniaxial and whose optical axis is in the direction normal to the plane. A liquid crystal display device including the optically anisotropic element (B), wherein the optically anisotropic element (A) is a fatty acid cellulose ester having an acetic acid group and a propionic acid group. 2. A liquid crystal cell having a twisted nematic liquid crystal sandwiched between two electrode substrates, and two polarizing elements arranged at both ends of the liquid crystal cell. Between the liquid crystal cell and the polarizing element, At least one optically anisotropic uniaxial element (A) having an optically negative uniaxial property and an optical axis in the normal direction to the surface, and at least one optically negative uniaxial property. A liquid crystal display device comprising an optical anisotropic element (C) whose optical axis is tilted by 5 ° to 50 ° from the normal to the plane, wherein the optical anisotropic element (A) is an acetic acid group and a propionic acid group. A liquid crystal display device comprising a fatty acid cellulose ester having 3. The liquid crystal display device according to claim 2, wherein the optical anisotropic element (C) is an optical anisotropic element containing a discotic compound. 4. The liquid crystal display device according to claim 2, wherein the optically anisotropic element (C) is obtained through a step of applying a shearing force to at least both surfaces of the transparent film to give a strain. . 5. The liquid crystal display device according to claim 2, wherein the optically anisotropic element (C) contains at least one photoisomerizable substance. 6. An optical anisotropic element (C) is formed from at least two layers, one layer (α) of which has positive uniaxiality, and its optical axis is inclined from the normal direction of the surface. The other layer (β) has a minimum refractive index in the thickness direction and a direction of the maximum main refractive index in the plane, and (α)
3. The liquid crystal display device according to claim 2, wherein the direction of the optical axis of (2) and the direction of the maximum principal refractive index of (β) are orthogonal to each other. 7. A liquid crystal cell in which a twisted nematic liquid crystal is sandwiched between two electrode substrates, and two polarizing elements arranged at both ends of the liquid crystal cell, and between the liquid crystal cell and the polarizing element, The optical tilt angle of at least one of the optically anisotropic element (A), which has one or more optically negative uniaxial properties and whose optical axis is in the direction normal to the surface, continuously changes. In the liquid crystal display device including the optically anisotropic element (D), at least one of the optically anisotropic elements (A) is a mixed fatty acid cellulose ester having an acetic acid group and a propionic acid group. Liquid crystal display device. 8. The liquid crystal display device according to claim 7, wherein the optical anisotropic element (D) is an optical anisotropic element containing a discotic compound. 9. The liquid crystal display device according to claim 7, wherein the optically anisotropic element (D) is a liquid crystalline polymer that is in a glass state at a liquid crystal transition temperature or lower. 10. The mixed fatty acid cellulose ester having an acetic acid group and a propionic acid group has an acetic acid substitution degree of 2.0.
~ 2.7, and the degree of propionic acid substitution is 0.1 to 0.9.
10. The liquid crystal display device according to claim 1, which is a mixed fatty acid cellulose ester. 11. An in-plane principal refractive index of the optically anisotropic element formed from the mixed fatty acid cellulose ester having an acetic acid group and a propionic acid group is nx and ny, and a principal refractive index in the thickness direction is nz. When {(nx + ny) / 2-n
The retardation value RTH represented by z} · d is 20 to 1
It has a protective film on the liquid crystal cell side of the polarizing element, the protective film is optically negative uniaxial and the optical axis is in the normal direction, and the total of RTH of the optical anisotropic element and the protective film is 50 nm. The liquid crystal display device according to claim 1, wherein the value is 50 nm to 400 nm. 12. A mixed fatty acid cellulose ester having an acetic acid group and a propionic acid group (nx-ny) .d.
The front retardation value Re shown by is 0 to 40 nm.
10. The liquid crystal display device according to claim 1, wherein: