JPH0895032A - Elliptically polarizing plate and color liquid crystal display device - Google Patents

Abstract

PURPOSE: To provide a full color liquid crystal display device, in which an angle of visibility, brightness, contrast, and durability are improved and twisted nematic liquid crystal is used, by specifying a visible light transmittance of a polarizing plate and arranging a layer containing a discotic compound on a supporting body in a phase difference plate. CONSTITUTION: In an elliptically polarizing plate in which at least one phase difference plate is laminated on one side of the polarizing plate, a visible light transmittance T of the polarizing plate is 39.5% or more, and at least one layer containing a discotic compound is provided on a supporting body of the phase difference plate. A degree of polarization P of this polarizing plate satisfies the expression P=√ (TP+TC)}>=0.950. In the expression, TP represents a parallel transmittance, while TC represents a straight transmittance. At least one phase difference plate is layered on one side of the polarizing plate, while on the surface of the opposite side, a reflection preventing layer (such as an evaporation film made of silicon oxide group compounds SiOx, x=1.7-2, or magnesium fluoride group compounds MgFx, x=1.7-2) is arranged in the elliptically polarizing plate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color liquid crystal display device having excellent viewing angle, contrast, brightness and resistance to humidity and heat, and / or a viewing angle, transmittance, polarization degree and resistance to humidity and heat used for the same. It relates to an excellent elliptically polarizing plate.

[0002]

2. Description of the Related Art In a liquid crystal display device, a plurality of opposed stripe-shaped electrodes are arranged so as to cross each other through a liquid crystal having a twist angle of 90 ° or more in a molecular arrangement, and at the intersecting portions thereof. This is a simple matrix type pixel forming pixel, a pixel electrode having a three-terminal type or two-terminal type non-linear active element using a thin-layer transistor or diode with a twist angle of 90 ° in the arrangement of liquid crystal molecules, and this pixel electrode There has been proposed an active matrix type in which pixels are formed by a counter electrode and a counter electrode. Of these liquid crystal display devices, word processors, personal computers, or T
A display device such as a V monitor is being changed from a mainstream CRT to an active matrix type, which has high image quality and a high response speed, among liquid crystal display devices having the great advantages of thinness, light weight, and low power consumption.

The active matrix type is basically a twisted nematic type (hereinafter, referred to as TN) liquid crystal cell using a nematic liquid crystal having a twist angle of 90 °, and a non-linear element of a three-terminal type is used. Currently, TFT-LCDs that use thin-layer transistors and MIM-LCDs that use two-terminal type MIM elements are in the mainstream.

The TFT-LCD and MIM-LCD are at least a driving TFT or a MIN for each pixel.
A TN liquid crystal cell having an element, a polarizer arranged so that its transmission axis is orthogonal or parallel to the rubbing direction of the light incident side substrate of the liquid crystal cell, and the rubbing of the light emitting side substrate of the liquid crystal cell. It is composed of an analyzer arranged parallel or orthogonal to the direction, and has a fast response speed (tens of milliseconds) and high display contrast. It is a method. However, since these liquid crystal display devices use a nematic liquid crystal having a twist angle of 90 °, there is a big problem that the contrast is lowered depending on the viewing angle due to the principle of the display system.

On the other hand, JP-A-4-229828,
As seen in JP-A-4-258923,
A method has been proposed in which a retardation plate is arranged between a pair of polarizing plates and a TN type liquid crystal cell to increase the viewing angle. The retardation plate proposed in the above patent publication has almost no retardation in the direction perpendicular to the liquid crystal cell, and does not exert any optical effect from the front, but when tilted, A phase difference is developed and the phase difference developed in the liquid crystal cell is compensated. However, this method cannot improve the viewing angle, particularly the deterioration of the contrast when tilted vertically or horizontally from the screen normal direction.
At present, it is not possible to deal with RT as an alternative.

JP-A-4-366808, JP-A-4-3
In Japanese Patent No. 66809, a liquid crystal cell containing a chiral nematic liquid crystal having an inclined optical axis is used as a retardation plate to improve the viewing angle, but the two-layer liquid crystal system is expensive and very heavy. .

Further, in Japanese Unexamined Patent Publication No. 6-75116 and Japanese Unexamined Patent Publication No. 6-214116 by the present inventors, a retardation plate which optically exhibits negative uniaxiality and whose optical axis is inclined is used. Therefore, a method for improving the viewing angle characteristics of the TN LCD has been proposed. According to this method, the viewing angle is improved as compared with the conventional one, but it is still difficult to realize a wide viewing angle enough to consider CRT substitution.

Therefore, the present inventors have filed a patent application No. 6-1265.
21. An optical anisotropic element having an optically negative uniaxial property, the optical axis of which is inclined from the normal direction of the film,
It was also found that a viewing angle characteristic of a TN type LCD is remarkably improved by a retardation plate having an optically negative uniaxial property and an optical anisotropic element whose optical axis is in the normal direction of the film.

However, these methods only confirm the effect of improving the viewing angle in terms of the contrast in black and white display, and the overall display quality, that is, the viewing angle, brightness, and contrast,
No mention was made of improvement of durability.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to improve viewing angle, brightness, contrast and durability,
A full-color liquid crystal display device using twisted nematic liquid crystal and / or an elliptically polarizing plate used therefor.

[0011]

[Means for Solving the Problems] These aims are (1)
 Laminating at least one retardation plate on one side of the polarizing plate
The elliptically polarizing plate formed by
T is 39.5% or more, and the retardation plate is small on the support.
Characterized by having at least one layer containing a discotic compound
An elliptically polarizing plate. (2) At least one retardation plate on one side of the polarizing plate
In an elliptically polarizing plate formed by stacking
P satisfies the formula, and the phase difference plate is small on the support.
Both are characterized by having a layer containing a discotic compound.
Elliptically polarizing plate. Formula: P = √ {(TP−TC) / (TP + TC)} ≧ 0.950 (where, TP is parallel transmittance and TC is orthogonal transmittance) (3) At least one unit on one side of the polarizing plate Phase difference plate
On the opposite surface (silicon oxide type (SiO 2_X，_X=
1.7-2) or magnesium fluoride system (MgF _X，_X=
Ellipse provided with an antireflection layer (such as the vapor deposition film of 1.7 to 2)
A circularly polarizing plate, wherein the retardation plate is at least on a support.
An ellipse characterized by having one layer containing a discotic compound
Circular polarizing plate. (4) At least one retardation plate on one side of the polarizing plate
An elliptically polarizing plate formed by stacking
Visible when left in an environment of 90 ° C and 90% RH for 500 hours
The change in light transmittance and the change in polarization degree is 2% or less, and the phase
The differential plate contains at least one layer of a discotic compound on a support.
An elliptically polarizing plate having a layer. (5) The polarizing plate contains a dichroic dye.
The ellipse described in (1), (2), (3), or (4)
Polarizer. (6) On both sides of the twisted nematic liquid crystal cell
The two polarizing plates arranged, and the liquid crystal cell and the polarizing plate
A cover having at least one retardation plate disposed therebetween.
In a liquid crystal display device, the visible light transmittance T of the polarizing plate is
Is 39.5% or more, and the retardation plate is small on the support.
Characterized by having at least one layer containing a discotic compound
Color liquid crystal display device. (7) On both sides of the twisted nematic liquid crystal cell
The two polarizing plates arranged, and the liquid crystal cell and the polarizing plate
A cover having at least one retardation plate disposed therebetween.
In a liquid crystal liquid crystal display device, the polarization degree P of the polarizing plate is
And the retardation plate is at least one layer on the support.
Having a layer containing a discotic compound capable of forming liquid crystals
A color liquid crystal display device characterized by. Formula: P = √ {(TP-TC) / (TP + TC)} ≧ 0.950 (where TP is parallel transmittance and TC is orthogonal transmittance) (8) On both sides of the twisted nematic liquid crystal cell
The two polarizing plates arranged, and the liquid crystal cell and the polarizing plate
A cover having at least one retardation plate disposed therebetween.
Of at least one polarizing plate
On the surface (silicon oxide type (SiO_X，_X= 1.7-2) or
Magnesium fluoride (MgF_X，_X= 1.7-2) vapor deposition
An antireflection layer (such as a film) is provided, and the retardation plate is a support.
Having at least one layer containing a discotic compound on top
A color liquid crystal display device characterized by. (9) On both sides of the twisted nematic liquid crystal cell
The two polarizing plates arranged, and the liquid crystal cell and the polarizing plate
A cover having at least one retardation plate disposed therebetween.
Liquid crystal display device, the polarizing plate is placed at 60 ° C. and 90%
Visible light transmittance change when left for 500 hours in RH environment
Change and polarization degree change is less than 2%, and the retarder supports
Having at least one layer containing a discotic compound on the body
A color liquid crystal display device that is characterized. (10) The polarizing plate contains a dichroic dye
(6), (7), (8), or (9)
Liquid crystal display device. (11) At least the optical retardation plate is provided on the support.
Is negative uniaxial and its optical axis is 5 ° from the normal direction of the film.
Characterized by having an optically anisotropic layer inclined by ~ 50 °
The elliptically polarizing plate as described in (1) to (5) above. (12) The retardation film is at least optical on the support.
Is negative uniaxial and its optical axis is 5 ° from the normal direction of the film.
Characterized by having an optically anisotropic layer inclined by ~ 50 °
The color liquid crystal display device according to (6) to (10)
Place In addition to the present invention, the following modes are also possible. (13) Both sides of twisted nematic liquid crystal cell
Of the two polarizing plates arranged in, and the liquid crystal cell and the polarizing plate.
At least one retardation plate disposed between
In a color liquid crystal display device, the visible light transmittance of the polarizing plate
Is 39.5% or more, and the retardation plate is at least one layer
Is optically negative uniaxial and its optical axis is normal to the film.
Having an optically anisotropic layer inclined 5 ° to 50 ° from the direction
A color liquid crystal display device that is characterized. (14) Both sides of twisted nematic liquid crystal cell
Of the two polarizing plates arranged in, and the liquid crystal cell and the polarizing plate.
At least one retardation plate disposed between
In a color liquid crystal display device, the polarization degree P of the polarizing plate is expressed by
And the phase difference plate is at least one layer,
Is negative uniaxial and its optical axis is 5 from the normal direction of the film.
Characterized by having an optically anisotropic layer tilted by 50 °
And color liquid crystal display device. Formula: P = √ {(TP-TC) / (TP + TC)} ≧ 0.950 (where TP is parallel transmittance and TC is orthogonal transmittance) (15) Both sides of twisted nematic liquid crystal cell
Of the two polarizing plates arranged in, and the liquid crystal cell and the polarizing plate.
At least one retardation plate disposed between
In a color liquid crystal display device, at least one polarizing plate
On the surface of silicon oxide type (SiO_X，_X= 1.7-2) or
Magnesium fluoride (MgF_X，_X= 1.7-2) vapor deposition
An antireflection layer such as a film is provided, and the phase difference plate is reduced.
Even more, it is optically negative uniaxial and its optical axis is the film
Optically anisotropic layer tilted 5 ° to 50 ° from the normal direction
A color liquid crystal display device characterized by having. (16) Both sides of twisted nematic liquid crystal cell
Of the two polarizing plates arranged in, and the liquid crystal cell and the polarizing plate.
At least one retardation plate disposed between
In a color liquid crystal display device, the polarizing plate is placed at 60 ° C. 90%
Visible light transmittance change when left for 500 hours in RH environment
Change and polarization degree change is less than 2%, and the phase difference plate is small
At least one layer, the optical axis of which is optically negative and uniaxial
Optical anisotropy tilted 5 ° to 50 ° from the normal line
A color liquid crystal display device having a layer. By
Was achieved.

The fact that the viewing angle is improved in the color liquid crystal display device of the present invention is estimated as follows.
For example, in the color liquid crystal display device of the present invention, in the normally white mode in which the transmission axes of the polarizer and the analyzer are substantially orthogonal to each other, the black display portion is in a state where voltage is applied to the liquid crystal and Along with the increase, the transmittance of light from the black display portion remarkably increases, causing a sharp decrease in contrast. At this time, the arrangement of the liquid crystal molecules inside the TN liquid crystal cell can be regarded as a mixture of the one in which the optical axis is approximately tilted from the normal direction of the cell and the one in which the optical axis is oriented in the normal direction.

If the liquid crystal molecules inside the liquid crystal cell can be regarded as a positive uniaxial optical anisotropic body, in order to compensate the birefringence caused by the liquid crystal molecule, a negative liquid crystal tilted from the normal line direction of the cell is similarly formed. It is necessary to use a uniaxial optical anisotropic body and a negative uniaxial optical anisotropic body oriented in the normal direction. The retardation plate in the present invention is an optically anisotropic uniaxial element whose optical axis is inclined at 5 ° to 50 ° from the normal direction of the film and an optically anisotropic uniaxial element. This is a combination with an optical anisotropic element whose optical axis is in the normal direction of the film. This solves the essential problem that the image quality deteriorates depending on the viewing angle, due to the principle of the display system using a nematic liquid crystal with a twist angle of 90 °. Furthermore, the problems such as color change were improved.

The fact that the brightness and the contrast are improved in the color liquid crystal display device of the present invention is estimated as follows. In the case of a transmissive liquid crystal display device, the visible light emitted by the backlight, and in the case of a reflective liquid crystal display device, the visible light reflected by the reflector is attenuated by absorption in the black matrix and the polarizing plate, respectively. The brightness has decreased. Further, if the polarization degree of the polarizing plate is low or the reflectance of the surface is high, the contrast is lowered. The present inventors cannot actually obtain the wide viewing angle, high brightness, and high contrast that should be originally possessed when the retardation plate of the present invention is used in a full-color liquid crystal display device using a twisted nematic liquid crystal such as TFT. As a result of investigating the cause, it was found that the brightness and contrast of the liquid crystal display device can be dramatically improved by improving the transmittance and polarization degree of the polarizing plate and preventing the reflection on the surface.

It is presumed as follows that the durability of the color liquid crystal display device of the present invention is improved. According to the results of the moisture and heat resistance durability test of the single phase difference plate of the present invention, the durability of the liquid crystal display device was not sufficient although the optical characteristics hardly changed when the crosslinking of the discotic compound was sufficient. , Problems such as brightness and contrast, reduction of viewing angle, and coloring occur. By improving the durability of the polarizing plate, we have found that the moisture and heat resistance of liquid crystal display devices can be dramatically improved.

The polarizing plate of the present invention will be described in detail below. There is no particular limitation on the material of the polarizing plate. Generally, a hydrophilic polymer film such as polyvinyl alcohol type, partially formalized polyvinyl alcohol type, ethylene-vinyl acetate copolymer partially saponified film, etc.
Alternatively, a polarizing plate made of a film obtained by adsorbing a water-soluble or water-insoluble dichroic dye and stretching it, a polyene oriented film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride is used. Further, it is not limited to the one utilizing the above-mentioned absorption dichroism, and for example, Japanese Patent Laid-Open No. 4-21121
A material utilizing a birefringence phenomenon in which light is split into two polarized lights in an optically anisotropic medium as disclosed in JP-A-04-04 is also preferably used.

The transmittance is preferably 39.5% or more, more preferably 43% or more. The degree of polarization is preferably 0.95 or more, more preferably 0.95.
It is 9 or more. However, the transmittance (T) is JIS Z870
Based on 1, T = K∫S (λ) y (λ) τ (λ) dλ
, Where K = 100 / ∫S (λ) y
(Λ) τ (λ) dλ, S (λ): Spectral distribution of standard light used for color display, y (λ): Color matching function in XYZ system, τ (λ): Spectral transmittance. There is no particular limitation on the specific method for improving the transmittance, but generally, when the amount of iodine or dichroic dye is increased, the polarization degree becomes higher but the transmittance becomes lower. A means for making the transmittance and the polarization degree compatible with each other is described in, for example, Japanese Patent Application Laid-Open No. 2-204907. The specific method for improving the degree of polarization is not particularly limited, but is disclosed in, for example, JP-A-64-842.
No. 03, JP-A-2-204907, etc., a method using a polyvinyl alcohol film formed by using an organic solvent instead of water, and JP-A-5-23.
There is a method of increasing the uniaxial stretching temperature of a polyvinyl alcohol-based film described in Japanese Patent No. 2316, etc. to uniformly stretch the film. The specific method for providing the antireflection film of the present invention is not particularly limited, but is disclosed in, for example, JP-A 5-2
It is described in Japanese Patent No. 95519.

Considering the use of a liquid crystal display device in a vehicle or outdoors, it is necessary to have resistance to humidity and heat.
It is preferable that the visible light transmittance change and the polarization degree change when left for 500 hours in an environment of 0% RH are 2% or less.
As a material, dichroic dyes are preferable to iodine-based ones,
As a means for improving durability with iodine, for example, Japanese Patent Laid-Open No.
There is a method of containing cobalt ion or zirconium ion described in JP-A-2-180303 and JP-A-4-351640. Further, for example, Japanese Patent Laid-Open No. 4-3
The use of the dichroic dyes described in Japanese Patent No. 51640, etc. generally gives excellent durability, but further, for example, Japanese Patent Application Laid-Open No. 4-3
There is a method using a water-insoluble dichroic dye and an ultraviolet absorber described in Japanese Patent No. 51640.

The retardation plate in the present invention will be described in detail below. The optically anisotropic element having the optically negative uniaxiality and having the optical axis inclined from 5 ° to 50 ° from the normal direction of the film, which constitutes the retardation plate of the present invention, has a light transmittance. When the main refractive index in the film plane is nx ′, ny ′, the refractive index in the thickness direction is nz ′, and the thickness is d ′, the relationship of the triaxial main refractive index is nz ′. <N
y ′ = nx ′ is satisfied, and the expression {(nx ′ + ny ′) /
The retardation represented by 2-nz ′} × d ′ is 50.
It is preferably from nm to 400 nm. However, n
The values of x ′ and ny ′ do not have to be exactly equal, but they need to be approximately equal. Specifically, there is no problem within the following range. | Nx'-ny '| / | nx'-nz' | ≤0.2 The angle formed by the optical axis and the normal direction of the film is 5
More preferably, the angle is from 50 ° to 50 °. As a method for producing this optical anisotropic element, Japanese Patent Application No. 6-126521 is used.
As described in the specification, the discotic compound is oriented obliquely, a shearing force is applied to both sides of the film to impart strain, or a photoisomerizable compound such as azobenzene is irradiated with polarized light. To be The creation method will be described below.

The discotic compound of the present invention is, for example, C.I.
Report of Destrade et al., Mol. Cryst.
71, page 111 (1981), benzene derivatives and B.I. Report of Kohne et al., Ang
ew. Chem. Vol. 96, p. 70 (1984) and cyclohexane derivatives described in J. Am. M. Lehn et al., J. Chem. Commun. , Pp. 1794 (1985), J. Research report by Zhang et al. A
m. Chem. Soc. 116, 2655 (199
4 years), such as azacrown-type and phenylacetylene-type macrocycles, and these are generally used as the mother nucleus of the molecular center, and straight-chain alkyl groups, alkoxy groups, substituted benzoyloxy groups, etc. It has a structure in which a straight chain is radially substituted, 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.
Further, in the present invention, the term "formed from a discotic compound" does not mean that the final product is the above compound,
For example, those in which the low molecular weight discotic liquid crystal has a group that reacts with heat, light, etc., and consequently polymerizes or crosslinks by reaction with heat, light, etc., and has a high molecular weight and loses liquid crystallinity are also included. I shall.

Next, the discotic compound in the present invention means the reaction of discotic liquid crystals as listed below, and the reaction of discotic liquid crystals which no longer show liquid crystallinity due to reaction with other low molecular weight compounds and polymers. It means all compounds, such as products, in which the molecule itself has optically negative uniaxiality.

[0022]

[Chemical 1]

[0023]

[Chemical 2]

[0024]

[Chemical 3]

[0025]

[Chemical 4]

In the case where the discotic compound in the present invention is a discotic liquid crystal, the layer containing them is oriented so as to have an optically negative uniaxial axis and an optical axis inclined by 5 ° to 50 ° from the normal direction of the film. The following processing is required for this. Specifically, a discotic liquid crystal is applied to a substrate on which a rubbing-treated organic alignment film or inorganic alignment film is formed, and then the temperature is raised to a liquid crystal phase, more preferably a disconematic 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 types. The discotic nematic liquid crystal phase-solid phase transition temperature of the discotic liquid crystal used in the present invention is preferably 70 ° C. or higher and 300 ° C. or lower, and particularly preferably 70 ° C. or higher and 170 ° C. or lower.

The polymer used as the organic alignment film may be polyimide, polystyrene derivative or the like, and the water-soluble polymer may be gelatin, polyvinyl alcohol, carboxymethyl cellulose or 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,
The present inventors have discovered that the discotic liquid crystal has an excellent ability to be uniformly aligned. It is speculated that this is due to the strong interaction between the alkyl chain on the surface of the alignment film and the alkyl side chain of the discotic liquid crystal. The alkyl-modified polyvinyl alcohol has an alkyl group at the terminal as listed below, and has a saponification degree of 80% or more,
The degree of polymerization is preferably 200 or more. Further, polyvinyl alcohol having an alkyl group in a side chain can also be used effectively. As commercial products, MP103, MP20 manufactured by Kuraray
3, R1130 and the like are available.

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

The rubbing treatment is the same as the widely used 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 orientation by rubbing in a certain direction. In general, rubbing is performed several times using a cloth or the like in which fibers of uniform length and thickness are evenly flocked.

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

The above-mentioned alignment film has a function of determining the alignment direction of the discotic liquid crystal molecules coated thereon, but since the alignment property of the discotic liquid crystal depends on the alignment film, its combination is optimized. There is a need. Further, 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 alignment film and often takes a value specific to the discotic liquid crystal molecules. When two or more discotic liquid crystals are mixed or a compound similar to the discotic liquid crystal is mixed, the tilt angle can be adjusted by the mixing ratio. Therefore, a method of selecting or mixing discotic liquid crystals is more effective for controlling the tilt angle of the oblique alignment.

Another method for orienting the discotic liquid crystal obliquely is magnetic field orientation or electric field orientation. In this case, it is necessary to apply a magnetic field or an electric field at a desired angle while heating the substrate coated with the discotic liquid crystal. Diagonal orientation of the discotic compound thus obtained can be maintained at high temperature and high humidity, in advance, the discotic compound, a polymerizable unsaturated group, an epoxy group, a hydroxyl group, an amino group, a carboxyl group. Having a functional group such as a group, heat or a photopolymerization initiator, radical polymerization of a polymerizable unsaturated group, or a ring-opening polymerization of an epoxy group by a photoacid generator, a polyvalent isocyanate,
It is preferable to crosslink the discotic compound itself by a crosslinking reaction with a polyvalent epoxy compound. At this time, another compound having the same functional group may be contained.

In the present invention, the optically anisotropic element is
It can also be obtained by subjecting at least a step of applying a shearing force to both sides of the transparent film. Specifically, it can be 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. The thermoplastic resin used here has no problem as long as it has a light transmittance of 70%, more preferably 85%, and is not particularly limited. Specifically, polycarbonate, polyarylate,
Polysulfone, polyethylene terephthalate, polyethylene naphthalate, polyethylene ether sulfone, polyphenylene sulfide, polyphenylene oxide, polyallyl sulfone, polyvinyl alcohol, polyamide, polyimide, polyolefin, polyvinyl chloride, cellulose polymer, Polyacrylonitrile, polystyrene, various binary and ternary polymers, graft copolymers, blends and the like are preferably used.

Further, the optically anisotropic element of the present invention can be obtained by irradiating a photoisomerizable substance with polarized light. Here, the photoisomerizable substance is one that causes stereoisomerization or structural isomerization by light, and preferably,
The reverse isomerization is caused by light or heat of another wavelength. Generally, as these compounds, those accompanied by structural change and color tone change in the visible region are often well known as photochromic compounds,
Examples thereof include azobenzene compounds, benzaldoxime compounds, azomethine compounds, fulgide compounds, diarylethene compounds, cinnamic acid compounds, retinal compounds and hemithioindigo compounds.

The support constituting the retardation film of the present invention is preferably optically uniaxial and has its optical axis in the normal direction of the film, and has a light transmittance of 80% or more. At the same time, when the main refractive index in the film plane is nx, ny, the main refractive index in the thickness direction is nz, and the film thickness is d,
It is preferable that the triaxial principal refractive index relationship satisfies nz <ny = nx, and the retardation represented by the formula {(nx + ny) / 2−nz} × d is 20 nm to 400 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, | nx
If -ny | / | nx-nz | ≤0.2, there is no practical problem. The front retardation represented by | nx-ny | xd is preferably 50 nm or less, and 20
It is more preferable that the thickness is not more than nm.

The optically anisotropic element is made of a material having a small intrinsic birefringence such as ZEONEX (Nippon Zeon), ARTON (Nippon Synthetic Rubber) and triacetyl cellulose (Daicel), or polycarbonate, polyarylate, polysulfone, polysulfone. It can be prepared by forming a material having a large intrinsic birefringence such as ether sulfone by solution casting, melt extrusion, or the like, and further stretching it in the longitudinal and transverse directions.

The twisted nematic liquid crystal cell of the present invention will be described below. The material of the liquid crystal is not particularly limited, but Δnd is preferably 300 nm or more and 900 nm or less. The twist angle is generally 90 degrees, but it is preferably used in the range of 70 degrees or more and 100 degrees or less. The pretilt is preferably 5 degrees or less, and the cell gap is preferably 3 μm or more and 6 μm.

[0038]

EXAMPLES The present invention will be described in detail below based on examples. Example 1 A dope was dissolved in a mixed solvent of methylene chloride and methanol in a weight ratio of 9: 1 such that triacetyl cellulose was 17.4 wt% and triphenyl phosphate was 2.6 wt% on a stainless band having an effective length of 6 m. 2m
It was cast at a rate of / min so that the dry film thickness was 127 μm, peeled off, and dried with hot air at 60 ° C. to 120 ° C. A gelatin layer (0.1 μm) is applied on one side, then a long-chain alkyl-modified Poval (MP-203 manufactured by Kuraray Co., Ltd.) is applied on the applied gelatin layer, and hot air at 60 ° C. is applied. After being dried for 90 seconds, a rubbing treatment was performed to form an alignment film. When the in-plane main refractive index is nx ', ny', the thickness direction refractive index is nz ', and the thickness is d', the triacetyl cellulose film has a value of | nx'-ny '| xd' = 5n.
m, {(nx '+ ny') / 2-nz '} * d' = 70n
m, which was almost negative uniaxial, and the optical axis was almost in the film normal direction.

On the orientation film, the discotic compound TE-
8 (m = 4) is 25.3 wt%, SARTOMER-
8.5 wt% of 306 (manufactured by Somar Co., Ltd.) and 0.3 wt of Irgacure 907 (manufactured by Ciba-Geigy Co., Ltd.)
%, CAB531 (manufactured by Eastman Chemical Co., Ltd.) at a concentration of 0.1 wt% was applied in a liquid coater at 7 cc / m ² with a bar coater,
A film having a layer containing a disc-like compound having a thickness of 2.5 μm was prepared. The main refractive index of this layer is n1, n2,
In the case of n3, there is a relationship of n1 <n2 = n3, which is negative uniaxial. Further, the optical axis was inclined by 30 ° from the film normal direction. When the layer thickness is d,
(N2-n1) * d = 125 nm. This film was placed in a constant temperature bath set at 120 ° C. for 2 minutes to form a discotic liquid crystal, and after aging, 12
A retardation plate was obtained by irradiating a mercury lamp (400 watts) for 30 seconds under the condition of 0 ° C. and allowing to cool to room temperature.

The Δn · d of the retardation plate of the present invention thus obtained from all directions was measured by an ellipsometer (AEP-100) manufactured by Shimadzu Corporation. The absolute value of Δn · d was the minimum when measured from, and the minimum value was 17 nm. Further, the direction in which the direction in which the absolute value of Δn · d was the minimum was orthographically projected on the film surface was the same as the direction in which the optical axis of the discotic liquid crystal layer was orthographically projected on the film surface.

A pressure sensitive adhesive was applied to the side of the triacetyl cellulose support of the retardation plate of the present invention obtained as described above, and then the discotic liquid crystal layer on the opposite side was made into a polarizing plate NPF-manufactured by Nitto Denko Corporation. F1225DU (T = 44.
5%, TP = 38.5%, TC = 1.4%, P = 0.96
5) was laminated so that its polarization axis would form an angle of 45 ° with the direction in which the optical axis of the discotic liquid crystal layer was orthographically projected on the film surface to obtain an elliptically polarizing plate a.

Example 2 Polarizing plate NPF-G1225DU (T = 44.5%, TP
= 38.5%, TC = 0.4%, P = 0.995), and an elliptical polarizing plate b was obtained in the same manner as in Example 1.

Example 3 NPF-G1225DUAG25 having an antireflection layer
(T = 38.5%, TP = 38.5%, TC = 0.2%,
Elliptic polarizing plate c was obtained in the same manner as in Example 1 except that P = 0.995, haze 9%) was used.

Example 4 Polarizing plate NPF-Q-10 (T = 43.0%, TP = 3)
An elliptically polarizing plate d was obtained in the same manner as in Example 1 except that 1.5%, TC = 5%, P = 0.850, dichroic dye type) was used.

Example 5 TFT type liquid crystal color television 6E-C3 manufactured by Sharp Corporation
Of the elliptic polarizing plate a obtained in Example 1 were attached so as to be orthogonal to each other so that the polarizing axes of the polarizing plates would not change from each other, and the color liquid crystal of the present invention was obtained. A display device A was created.

Example 6 A color liquid crystal display B of the present invention was prepared in the same manner as in Example 5 except that the two elliptically polarizing plates b obtained in Example 2 were used.

Example 7 Except that one elliptically polarizing plate b obtained in Example 2 was used for the back side, that is, the backlight side, and one elliptically polarizing plate c obtained in Example 3 was used for the front side, that is, the outermost layer of the display device. A color liquid crystal display device C of the present invention was prepared in the same manner as in Example 5.

Example 8 A color liquid crystal display device D of the present invention was prepared in the same manner as in Example 5 except that the two elliptically polarizing plates d obtained in Example 4 were used.

With respect to these liquid crystal display devices A, B, C and D, after visual evaluation, white display and black display were performed, and the contrast ratio was measured in all directions. Also 60 ℃ 90% RH
The same evaluation was performed after leaving it for 500 hours in the environment.
The results are shown in Table 1.

[0050]

[Table 1]

Comparative Example 1 Polarizing Plate NPF-Q-10-39 (T = 39.0%, P =
Elliptical polarizing plate e was obtained in the same manner as in Example 1 except that 0.930, dichroic dye type) was used.

Comparative Example 2 A color liquid crystal display device E of the present invention was prepared in the same manner as in Example 5 except that the two elliptically polarizing plates e obtained in Comparative Example 1 were used.

Comparative Example 3 TFT type liquid crystal color television 6E-C3 manufactured by Sharp Corporation
Peel off the polarizing plate and replace it with NPF-F1225DU
Two sheets (T = 44.5%, P = 0.965) were attached so as to be orthogonal to each other so that the polarization axes of the polarizing plates were not changed from each other, and thereby a color liquid crystal display device F was prepared.

For these liquid crystal display devices E and F, after visual evaluation, white display and black display were performed, and the contrast ratio was measured in all directions. Further, the same evaluation was performed after leaving it in an environment of 60 ° C. and 90% RH for 500 hours. The results are shown in Table 1.

As is apparent from Table 1, the liquid crystal display devices A, B, C, and D of the embodiment are different from the liquid crystal display devices E and F of the comparative example in front contrast in black-and-white display and the viewing angle viewed from the contrast. It can be seen that is greatly improved. When a video signal is input to the liquid crystal display device F of the comparative example and a full-color image is output, the image is whitish when viewed from above and is yellowish overall, and the black display portion is immediately inverted when viewed from below. . When viewed from the left and right, there is no inversion in the black display portion, but the contrast is reduced as a whole and it is yellowish, and the image quality is significantly degraded by the viewing angle. In the liquid crystal display devices A, B, C, and D of the example, when viewed from below, inversion was observed in the black display portion when the viewing angle was increased, but above,
When viewed from the left and right, no inversion on the black display part is seen, and the yellowing of the image is slight, and the deterioration of the image quality due to the viewing angle is
There were few. In the liquid crystal display device E of the comparative example, the deterioration of the image quality due to the viewing angle was small, but the front contrast was low and the image was blurred. Further, in the liquid crystal display device D of the example, no deterioration in image quality was observed even after the durability test.

[0056]

According to the present invention, the contrast, brightness, viewing angle characteristics and / or durability of a color liquid crystal display device having a TN type liquid crystal cell, particularly a liquid crystal display device having a non-linear active element such as a TFT are improved. Therefore, it is possible to industrially provide a high-quality liquid crystal display device having excellent visibility. Needless to say, even if the present invention is applied to an active matrix liquid crystal display device using a three-terminal element such as MIM and a two-terminal element such as TFD, excellent effects can be obtained.

Claims (12)

[Claims] 1. An elliptically polarizing plate in which at least one retardation plate is laminated on one side of a polarizing plate, the visible light transmittance T of the polarizing plate is 39.5% or more, and An elliptically polarizing plate, characterized in that the plate has at least one layer containing a discotic compound on a support. 2. An elliptically polarizing plate in which at least one retardation plate is laminated on one side of a polarizing plate, the polarization degree P of the polarizing plate satisfies an expression, and the retardation plate is a support. An elliptically polarizing plate having at least one layer containing a discotic compound thereon. Formula: P = √ {(TP-TC) / (TP + TC)} ≧ 0.950 (where TP is parallel transmittance and TC is orthogonal transmittance) 3. An elliptically polarizing plate in which at least one retardation plate is laminated on one side of a polarizing plate and an antireflection layer is provided on the opposite side, wherein the retardation plate is at least on a support. An elliptically polarizing plate having one layer containing a discotic compound. 4. An elliptically polarizing plate comprising at least one retardation plate laminated on one side of a polarizing plate, which is visible when the polarizing plate is left in an environment of 60 ° C. and 90% RH for 500 hours. An elliptically polarizing plate having a light transmittance change and a polarization degree change of 2% or less, and the retardation plate having at least one layer containing a discotic compound on a support. 5. The elliptically polarizing plate according to claim 1, 2, 3, or 4, wherein the polarizing plate contains a dichroic dye. 6. A color liquid crystal display device comprising two polarizing plates arranged on both sides of a twisted nematic liquid crystal cell, and at least one retardation plate arranged between the liquid crystal cell and the polarizing plate. A color liquid crystal display device in which the visible light transmittance T of the polarizing plate is 39.5% or more, and the retardation plate has at least one layer containing a discotic compound on a support. 7. A color liquid crystal display device having two polarizing plates arranged on both sides of a twisted nematic liquid crystal cell, and at least one retardation plate arranged between the liquid crystal cell and the polarizing plate. , The polarization degree P of the polarizing plate
Satisfies the formula, and the retardation plate has at least one layer containing a discotic compound on a support, a color liquid crystal display device. Formula: P = √ {(TP-TC) / (TP + TC)} ≧ 0.950 (where TP is parallel transmittance and TC is orthogonal transmittance) 8. A color liquid crystal display device having two polarizing plates arranged on both sides of a twisted nematic liquid crystal cell, and at least one retardation plate arranged between the liquid crystal cell and the polarizing plate. A color liquid crystal display device, wherein an antireflection layer is provided on at least one polarizing plate, and the retardation plate has at least one layer containing a discotic compound on a support. 9. A color liquid crystal display device having two polarizing plates arranged on both sides of a twisted nematic liquid crystal cell and at least one retardation plate arranged between the liquid crystal cell and the polarizing plate. , The polarizing plate at 60 ° C.,
Visible light transmittance change and polarization degree change when left for 500 hours in an environment of 90% RH is 2% or less, and the retardation plate has at least one layer containing a discotic compound on a support. A color liquid crystal display device characterized by. 10. The color liquid crystal display device according to claim 6, 7, 8 or 9, wherein the polarizing plate contains a dichroic dye. 11. The retardation plate has, on a support, an optically anisotropic layer which is at least optically uniaxial and whose optical axis is inclined at 5 ° to 50 ° from the normal direction of the film. The elliptically polarizing plate according to claim 1, which is characterized in that 12. The retardation plate has, on a support, an optically anisotropic layer which is at least optically negative uniaxial and whose optical axis is inclined at 5 ° to 50 ° from the normal direction of the film. The color liquid crystal display device according to claim 6, which is characterized in that.