JP2767382B2 - Optical compensation sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical compensatory sheet, and more particularly to an optical compensatory sheet useful for improving display contrast and viewing angle characteristics of display colors.

[0002]

2. Description of the Related Art A CRT which is a mainstream display device of OA equipment such as a Japanese word processor and a desktop personal computer.
Has been converted to a liquid crystal display element having great advantages such as thin and light weight and low power consumption. Most of the liquid crystal display elements (hereinafter, referred to as LCDs) that are currently widely used 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.

An LCD using a birefringence mode has a liquid crystal molecule arrangement in which the twist angle is twisted by 90 ° or more and has a steep electro-optical characteristic. Therefore, a simple matrix without an active element (thin film transistor or diode) is used. A large-capacity display can be obtained by time-sharing driving with a rectangular electrode structure. But,
LCDs using this birefringence mode have the disadvantage that response speed is slow (several hundred milliseconds) and that gray scale display is difficult. Therefore, liquid crystal display devices using active elements (TFT-LCD, MIM-LCD, etc.) It does not reach the point where the display performance of ()) is exceeded.

In the TFT-LCD and the MIM-LCD, an optical rotation mode display mode (TN type liquid crystal display element) in which the alignment state of liquid crystal molecules is twisted by 90 ° is used. This display method has a fast response speed (several tens of milliseconds), can easily obtain a white display, and has a high display contrast. Therefore, this display method is the most effective method for improving the image quality as compared with LCDs of other methods. is there. However, since the twisted nematic liquid crystal is used, there is a problem in viewing angle characteristics such that a display color and a display contrast change depending on a viewing direction due to a principle of a display method, and the display performance of a CRT cannot be exceeded.

JP-A-4-229828, JP-A-4-2-2
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 retardation film proposed in the above patent gazette has a phase difference of almost zero in a direction perpendicular to the liquid crystal cell, and has no optical effect from directly in front of the liquid crystal cell.
A phase difference is developed when tilted, and the phase difference developed in the liquid crystal cell is to be compensated. However, even with these methods, the viewing angle of the LCD is still insufficient, and further improvement is desired. In particular, when it is considered as an in-vehicle type or as a substitute for a CRT, the current viewing angle cannot be used at all.

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. This is a two-layer liquid crystal system, which is expensive and very heavy. Further, JP-A-4-113301 and JP-A-5-80323 disclose
For liquid crystal cells, a method of using a retardation film whose optical axis is inclined has been proposed, but since uniaxial polycarbonate is sliced obliquely, a large-area retardation film can be used at low cost. There was a problem that it was difficult to obtain. JP-A-5-157913, EP 057630
4A1 proposes a method of using a retardation film whose optical axis is inclined by performing special stretching on polycarbonate, but it is still difficult to obtain a large-area retardation film at low cost. . Furthermore, Japanese Patent Application No. 5
No. 5823 describes a method using a retardation film whose optical axis is inclined using a photoisomerizable substance. According to this method, a lightweight, low-cost liquid crystal display device having a wide viewing angle characteristic can be realized. However, a disadvantage of this method is that the stability of the retardation film against heat and light is not sufficient.

Japanese Patent Application Laid-Open No. Hei 5-215921 proposes a method of optically compensating an LCD by using a birefringent plate in which a pair of alignment-treated substrates is sandwiched with a rod-like compound exhibiting liquid crystallinity when cured. However, this proposal is no different from the so-called double-cell type compensator proposed in the past, which greatly increases the cost and is not suitable for mass production. Further, as long as the rod-shaped compound is used, the birefringent plate has TN for the optical reason described later.
It is impossible to improve the omnidirectional viewing angle of the LCD. Also, JP-A-3-9326 and JP-A-3-291601 describe a method of applying an optical compensator for an LCD by applying a polymer liquid crystal to a film-like substrate provided with an alignment film. However, since it is impossible to align molecules obliquely with this method, TN-type LCDs
It is impossible to improve the omnidirectional viewing angle.

Therefore, the present inventor has filed Japanese Patent Application No. Hei 5-23653.
No. 9 invented an optical compensatory sheet in which a discotic liquid crystal was oriented by an orientation film. The optical properties of the base film used in the production of this sheet were initially isotropic, but if a base film having a slight anisotropy was used, the isotropic It has been found that the viewing angle of a TN-type LCD equipped with the optical compensation sheet becomes wider or narrower than when a base film is used.

[0009]

Accordingly, an object of the present invention is to significantly improve the viewing angle of a TN type LCD by optimizing the optical characteristics of a base film used in an optical compensation sheet having a layer containing a discotic liquid crystal. An object of the present invention is to provide an optical compensatory sheet that can be expanded.

[0010]

The present invention resides in an optical compensation sheet comprising a layer containing a discotic liquid crystal whose optical axis is obliquely aligned on a plane-oriented transparent film. The present invention also relates to a disc with an optical axis obliquely oriented on a rubbed surface-oriented film, on a plane-oriented transparent film on which an orientation film is formed, or on a surface-oriented transparent film on which an orientation film is formed. There is also an optical compensation sheet in which a layer containing a tick liquid crystal is laminated. The present invention further provides an optical compensation sheet in which a layer containing a discotic liquid crystal whose optical axis is obliquely aligned is laminated on a plane alignment transparent film provided with a rubbed organic polymer film. In the optical compensation sheet of the present invention, it is preferable that the layer containing the discotic liquid crystal comprises a discotic liquid crystal phase. Further, it is preferable that the organic polymer film is a polyimide or alkyl chain-modified poval film.

Hereinafter, the usefulness of the present invention will be described. First,
The optical utility will be described using a TN type LCD as an example with reference to the drawings. 1 and 2 show the polarization state of light propagating through the liquid crystal cell when a sufficient voltage equal to or higher than the threshold voltage is applied to the liquid crystal cell. Since the transmittance characteristic of light when a voltage is applied particularly greatly contributes to the viewing angle characteristics of the contrast, the description will be made by taking a voltage application as an example. FIG. 1 is a diagram illustrating a polarization state of light when the light is vertically incident on the liquid crystal cell. When the natural light L0 is perpendicularly incident on the polarizing plate A having the polarizing axis PA, the light transmitted through the polarizing plate PA becomes 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. Natural light L of incident light
When 0 is obliquely incident, the polarized light L1 transmitted through the polarizing plate A becomes substantially linearly polarized light. (In practice, 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 and is not completely blocked by the polarizing plate B. As described above, in the oblique incidence, the blocking of light in the dark state becomes insufficient, and the contrast is greatly reduced, which is not preferable.

An object of the present invention is to provide an optical compensator capable of preventing such a decrease in contrast at oblique incidence and improving viewing angle characteristics. FIG. 3 shows a usage example of the optical compensation sheet manufactured according to the present invention. An optically anisotropic element RF1 having an optical axis inclined from the normal direction of the liquid crystal cell is disposed between the polarizing plate A and the liquid crystal cell TNC.
The optically anisotropic element RF1 is a birefringent body whose phase difference increases as the angle of incidence of light with respect to the optical axis increases.
Further, between the polarizing plate B and the liquid crystal cell TNC, an optically anisotropic element RF2 having an optical axis inclined from the normal direction of the liquid crystal cell is disposed. This optically anisotropic element RF2 is a birefringent body having the same optical characteristics as RF1. When the natural light L0 is obliquely incident on the liquid crystal display device having such a configuration as in the case of FIG. 2, the optical modulation described below occurs. First, the light is converted into linearly polarized light L1 by the polarizing plate A, and is modulated into elliptically polarized light L3 by a phase delay effect when transmitted through the optically anisotropic element RF1. Next, when passing through the liquid crystal cell TNC, the elliptically polarized light L having the opposite phase is obtained.
4 and further passes through the optically anisotropic element RF2, and is returned to the original linearly polarized light L5 by the phase delay effect. By such an operation, the same transmittance of the natural light L0 can be obtained even at various oblique incidences, and a liquid crystal display device capable of high-quality display without dependence on viewing angle can be obtained.

It is estimated that the viewing angle of the liquid crystal display device can be greatly improved by the optical compensatory sheet manufactured according to the present invention as follows. Many TN-LCDs employ a normally white mode.
In this mode, as the viewing angle is increased, the transmittance of light from the black display section is significantly increased, resulting in a sharp decrease in contrast. The black display is a state when a voltage is applied. At this time, the liquid crystal molecules in the TN liquid crystal cell are arranged as shown in the model of FIG. When the arrangement of the liquid crystal molecules is approximated by a plurality of refractive index ellipsoids having substantially the same triaxial refractive index, the result is as shown in FIG. 4B. In the TN liquid crystal cell, the optical axis is slightly inclined from the direction normal to the cell surface. It can be considered as a laminate of four positive uniaxial optically anisotropic bodies and two positive uniaxial optically anisotropic bodies whose normal axis and the optical axis are in the same direction.

If the liquid crystal cell can be regarded as a laminated body of four positive uniaxial optically anisotropic bodies, in order to compensate for it, a negative uniaxial optical element having the same combination of the optical axis inclination angles as that of the laminated body is used. It is preferable to use four anisotropic bodies. In the case of the present invention,
The discotic liquid crystal layer acts as a negative uniaxial optical anisotropic body whose optical axis is slightly inclined from the normal direction to the cell surface, and the negative optical axis is oriented in the same direction as the normal direction to the cell surface. The plane-oriented base film acts as a uniaxial optically anisotropic body. For these reasons, it is presumed that the viewing angle characteristics were significantly improved by the negative uniaxial optically anisotropic laminate in the present invention.

In a specific discotic liquid crystal, if the discotic liquid crystal phase is solidified in an aligned state, its structure is maintained below the discotic liquid crystal phase / solid phase transition temperature. It is thermally stable.

The discotic liquid crystal in the present invention is as listed below, but the molecules themselves have negative uniaxiality and the optical axis is oriented obliquely to the substrate surface by the oblique orientation film. If so, it is not particularly limited to the following substances.

[0019]

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[0020]

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[0021]

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The negative uniaxiality of the discotic liquid crystal layer in the present invention means that n ₁ <n when n ₁ , n ₂ , and n ₃ are arranged in the order of smaller refractive index in the three-axis direction of the liquid crystal layer. ₂ = n ₃
It has the following relationship. Therefore, it has the characteristic that the refractive index in the optical axis direction is the smallest. However,
The values of n ₂ and n ₃ need not be exactly equal, but need only be approximately equal. Specifically, there is no practical problem if | n ₂ −n ₃ | / | n ₂ −n ₁ | ≦ 0.2. Further, as conditions for greatly improving the viewing angle characteristics of the TFT and TN type liquid crystal cells, it is preferable that the optical axis of the liquid crystal layer has an inclination β from the normal direction of the sheet surface of 5 to 50 degrees, 10 degrees to 40 degrees is more preferable. Further, when the thickness of the liquid crystal layer is a, it is preferable to satisfy the following condition: 50 ≦ Δn ′ · a ≦ 300 (nm). Where Δn ′ = (n
₂ + n ₃₎ is / 2-n _1.

There are various methods for the alignment treatment of the discotic liquid crystal which can be used in the present invention. There are discotic liquid crystal / substrate combinations in which effective alignment can be obtained simply by rubbing the surface of the substrate and coating the substrate, but the most versatile method is to use an alignment film. As the alignment film, an inorganic oblique deposition film or an alignment film obtained by rubbing a specific organic polymer film corresponds to this.
Further, a thin film in which molecules are isomerized by light, such as an LB film made of an azobenzene derivative, and in which molecules are arranged with directionality and uniformity is also applicable.

A typical example of the organic alignment film is a polyimide film. This is done by applying a polyamic acid (for example, SE-7210 manufactured by Nissan Chemical Co., Ltd.)
By rubbing after baking at 0 ° C. to 300 ° C., the discotic liquid crystal can be aligned. Also,
Alkyl chain-modified poval (for example, Kuraray Co., Ltd. M
P203, R1130, etc.) does not require baking, and the orientation ability can be imparted only by rubbing. In addition, most organic polymer films that form a hydrophobic surface, such as polyvinyl butyral and polymethyl methacrylate, can impart discotic liquid crystal alignment ability by rubbing the surface. A typical example of the inorganic oblique deposition film is a SiO oblique deposition film. In this method, SiO evaporation particles are applied obliquely to a base film surface in a vacuum chamber, and an obliquely deposited film having a thickness of about 20 to 200 nm is formed to form an alignment film. When the discotic liquid crystal is oriented by the deposited film, the optical axis of the liquid crystal layer is directed to a specific direction on a plane perpendicular to the base film surface, including the trajectory of the deposited SiO particles.

The above-mentioned alignment film has the function of determining the alignment direction of the discotic liquid crystal molecules provided thereon.
However, since the alignment of the discotic liquid crystal depends on the alignment film, it is necessary to optimize the combination. next,
Once aligned, the discotic liquid crystal molecules are aligned with the substrate surface at a certain angle θ, but in a one-component system, the angle of oblique alignment does not change much depending on the type of alignment film, and may take a value specific to the discotic liquid crystal molecules. Many. When two or more discotic liquid crystal molecules are 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 effective to select a discotic liquid crystal type, or to mix two or more types of discotic liquid crystal molecules.

The base film material used for the optical compensatory sheet of the present invention needs to have good light transmittance and plane orientation. The plane orientation referred to in the present invention is a state in which the relation of the triaxial refractive index of the base film satisfies nx = ny> nz. Here, nx and ny are the refractive indexes in the optical axis direction orthogonal to each other in the film plane, and nz is the refractive index in the thickness direction of the film. Also, the values of nx and ny need not be strictly equal, but it is sufficient if they are approximately equal. Specifically, there is no practical problem if | nx-ny | / | nx-nz | ≦ 0.2. Further, when the thickness of the base film is d, it is preferable to satisfy the following condition: 20 ≦ Δnd ≦ 300 (nm). However, Δn = (nx
+ Ny) / 2-nz. Specifically, a film formed of a material having a small intrinsic birefringence value sold under the trade name such as ZEONEX (ZEON CORPORATION), ARTON (Japan Synthetic Rubber), and FUJITAC (Fuji Photo Film) is preferable. However, polycarbonate, polyarylate,
Even a material having a large intrinsic birefringence value, such as polysulfone and polyethersulfone, can form a plane-oriented film of Δnd = 20 to 300 nm by controlling the molecular orientation during film formation. Can also be suitably used.

Other than the above methods for obliquely aligning the discotic liquid crystal applied on the substrate, there are magnetic field alignment and electric field alignment. In this method, after applying a discotic liquid crystal to a substrate, a zone for applying a magnetic field or an electric field at a desired angle is required, but the zone itself needs to be adjusted to a temperature at which a discotic nematic phase is formed. is there.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. Example 1 Triacetyl cellulose 80 μm thick film (Fujitac, manufactured by Fuji Photo Film Co., Ltd., size 250 mm × 25)
0 mm) as a substrate, and an alkyl chain-modified poval (MP203 manufactured by Kuraray Co., Ltd.) is applied thereon as an alignment film to a thickness of 1 μm. This poval film is rubbed with a rubbing machine to impart orientation ability. A discotic liquid crystal material obtained by mixing the above discotic liquid crystal TE-8 and TE-8 at a blend ratio of 4: 1 was dissolved in methyl ethyl ketone solution to make a 10 wt% solution, and the solution was applied at 3000 rpm by a spin coater. Thus, a film having a 1 μm thick discotic liquid crystal non-alignment layer was prepared. After placing this film in a constant temperature bath set at 145 ° C. for 5 minutes, the discotic liquid crystal layer is oriented by contact with a metal surface set at 10 to 20 ° C. and quenching, thereby obtaining an optical compensation sheet sample. I got

Example 2 A 100 μm-thick polycarbonate film (Iupilon, manufactured by Mitsubishi Gas Chemical Co., Ltd.) was heated at 165 ° C. in a lengthwise and widthwise direction of 4 mm each.
% Was drawn to obtain a substrate. Alkyl-modified poval (MP203 manufactured by Kuraray Co., Ltd.) as an alignment film on this substrate
Is applied to a thickness of 1 μm. This poval film is rubbed with a rubbing machine to impart orientation ability. A discotic liquid crystal material obtained by mixing the above discotic liquid crystal TE-8 and TE-8 at a blend ratio of 4: 1 was dissolved in methyl ethyl ketone solution to make a 10 wt% solution, and the solution was applied at 3000 rpm by a spin coater. Thus, a film having a 1 μm thick discotic liquid crystal non-alignment layer was prepared. After placing this film in a thermostat set at 145 ° C. for 5 minutes, the discotic liquid crystal layer was oriented by contacting with a metal surface set at 10 to 20 ° C. and quenching to obtain an optical compensation sheet sample. I got

Comparative Example 1 A glass plate having a thickness of 1 mm was used as a substrate, and an alkyl-modified poval (MP203 manufactured by Kuraray Co., Ltd.) was applied thereon as an alignment film to a thickness of 1 μm. This poval film is rubbed with a rubbing machine to impart orientation ability. On top of that, the discotic liquid crystals TE-8 and TE-8 described above are 4:
A discotic liquid crystal material mixed at a blend ratio of 1 was dissolved in a methyl ethyl ketone solution to make a 10 wt% solution, and the solution was applied at 3000 rpm using a spin coater.
A plate having a μ-thick discotic liquid crystal non-alignment layer was prepared. After placing this plate in a thermostat set at 145 ° C. for 5 minutes, the discotic liquid crystal layer was oriented by contacting the metal surface set at 10 to 20 ° C. and quenching to obtain an optical compensator sample. I got

Comparative Example 2 A 100 μm-thick polycarbonate film (Iupilon, manufactured by Mitsubishi Gas Chemical Co., Ltd.) was prepared at 165 ° C. in each of vertical and horizontal directions.
The substrate was stretched by 3% to obtain a substrate. An alkyl-modified poval (MP20 manufactured by Kuraray Co., Ltd.) was formed on this substrate as an alignment film.
3) is applied to a thickness of 1 μm. This poval film is rubbed with a rubbing machine to impart orientation ability. in addition,
Discotic liquid crystals TE-8 and TE-8 described above
Of a discotic liquid crystal material obtained by dissolving the compound in a blend ratio of 4: 1 in methyl ethyl ketone solution and applying a solution of 10 wt% at 3000 rpm by a spin coater to form a film having a 1 μ thick discotic liquid crystal non-alignment layer. Created things. After placing this film in a constant temperature bath set at 145 ° C. for 5 minutes, the discotic liquid crystal layer is oriented by contact with a metal surface set at 10 to 20 ° C. and quenching, thereby obtaining an optical compensation sheet sample. I got

The Δ of the substrate used in each example and comparative example was
nd is an ellipsometer manufactured by Shimadzu (AEP-10)
0) was set to the transmission mode to determine the angle dependence of the retardation, and the optimum refractive index in the three axial directions was calculated from the value.

The product of the difference between the refractive indexes of the extraordinary light and ordinary light of the liquid crystal and the gap size of the liquid crystal cell is 480 nm and the twist angle is 90.
The optical compensatory sheets obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were attached to the TN type liquid crystal cell of 図 as shown in FIG. 5, and the transmittance (T at 40 V rectangular wave of 0 V to 5 V to the liquid crystal cell (T ) Was measured by Otsuka Electronics LCD-5000. The angle from the direction normal to the surface of the liquid crystal cell to the position at which the contrast ratio (T _1V / T _5V ) shows 10 was defined as the viewing angle, and the vertical, horizontal, and horizontal viewing angles were determined. Here, the measurement of only the TN type liquid crystal cell without any optical compensation sheet was taken as Comparative Example 3. Table 1 shows the results. FIG.
In the arrow, the rubbing direction in the optical compensation sheet,
Also, it indicates the rubbing direction in the liquid crystal cell. FIG.
In the discotic liquid crystal layer of the optical compensation sheet
Both sheets exist on the liquid crystal cell side.

[0034]

[Table 1]

[0035]

As is clear from Table 1, the optical compensation sheet of the present invention can greatly widen the viewing angle of a TN type liquid crystal cell. On the other hand, when the substrate is completely isotropic as in Comparative Example 1, the effect of improving the viewing angle is recognized as compared with Comparative Example 3 in which nothing is mounted.
It does not reach 0 ° and is insufficient. Further, when the surface orientation of the base film exceeds the range of the present invention as in Comparative Example 2, the effect of improving the viewing angle is also reduced. Therefore, by using the optical compensation sheet of the present invention, it is possible to widen the viewing angle of the TN type liquid crystal cell to a very high quality.

[Brief description of the drawings]

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

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

FIG. 3 is a diagram illustrating an example of use of an optical compensation sheet.

FIG. 4 is a diagram showing a liquid crystal molecule arrangement model when a voltage is applied to a TN liquid crystal cell, and a diagram in which the optical characteristics thereof are approximated.

FIG. 5 is a diagram showing a relationship between a polarization axis of a polarizing plate, a rubbing direction of a liquid crystal cell, and a rubbing direction of an optical compensation sheet alignment film when viewing angle characteristics are measured in Examples and Comparative Examples.

[Explanation of symbols]

TNC: TN type liquid crystal cell A, B: polarizing plate PA, PB: polarization axis L0: natural light L1, L5: linearly polarized light L2: modulated light after passing through the liquid crystal cell L3, L4: elliptically polarized light LC: TN type liquid crystal cell State of liquid crystal molecules when voltage is sufficiently applied to RF1, RF2: optical compensation sheet BL: backlight R1, R2: rubbing direction of optical compensation sheet

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-56-90878 (JP, A) JP-A-2-304526 (JP, A) Patent 2640083 (JP, B2) Patent 2556564 (JP, B2) Patent 2641086 (JP, B2) International Patent Publication No. 4-500284 (JP, A) International Publication No. 95/14652 (WO, A) West German Patent Application Publication No. 3911620 (DE, A) (58) Fields investigated (Int. Cl. ⁶ , (DB name) G02B 5/30 G02F 1/1335

Claims (5)

(57) [Claims] An optical axis is formed on a plane-oriented transparent film.
An optical compensatory sheet formed by laminating layers containing discotic liquid crystals in an obliquely oriented state . 2. A rubbed surface distribution MukaiToru bright film on, or the surface alignment layer is formed distribution MukaiToru bright film on a layer containing a discotic liquid crystal optical axis is oriented obliquely are laminated Optical compensation sheet. Wherein rubbed organic polymer membrane provided al
In the surface distribution MukaiToru bright film on the optical compensation sheet layer including a de <br/> Isukotikku liquid crystal optical axis is oriented obliquely are laminated. 4. The optical compensation sheet according to claim 3, wherein the organic polymer film is a polyimide or alkyl chain-modified poval film. 5. The optical compensation sheet according to claim 1, wherein the layer containing a discotic liquid crystal comprises a discotic liquid crystal phase.