JP3206743B2 - Liquid crystal display - Google Patents

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 specifically, to improve the viewing angle dependency of a display screen by combining a liquid crystal display device with a phase difference compensating layer for compensating an interference color of transmitted light. Liquid crystal display device.

[0002]

2. Description of the Related Art Liquid crystal display devices (liquid crystal display devices)
y; LCD) is widely used for information display devices and the like. As a liquid crystal mode used in these information display devices, twisted nematic (TN) and super twisted nematic (STN) are widely used.

[0003] The performance required for the future liquid crystal display device includes a wide viewing angle and a high-speed response. That is, one problem of the liquid crystal display device is that, when gradation display is performed, display defects such as inversion, blackout, and white spots occur depending on the viewing angle. In the case of displaying a moving image such as a TV image, the responsiveness of the liquid crystal display device becomes a problem. That is, if the response is poor, the display characteristics are deteriorated, such as a blurred outline.

One means for improving the viewing angle is to use a conventional TN type liquid crystal and arrange a phase difference compensation layer between a glass substrate and a polarizing plate. For example, Japanese Patent Application Laid-Open No. Hei 5-313159 discloses that in a TN type liquid crystal display device, only one of the refractive indices of the x, y, and z axes of the optical retardation compensation layer is large, and the other two are the same. A point is disclosed. These are related to the TN type liquid crystal display device and are different from the present invention.

On the other hand, as a means for improving the viewing angle, a liquid crystal display element having a bend alignment (optically compatible) has been proposed.
Attempts have been made to use sated birefringence (OCB). The bend orientation has the advantage that phase difference compensation is simple because there is no twist. This OCB
Using the mode, a retardation compensation layer is disposed between the glass substrate and the polarizing plate. For example, Japanese Patent Application Laid-Open No. 10-104612 discloses that in a liquid crystal layer having a bend alignment, two phase difference compensating layers compensate for modulation received by light passing through approximately half the thickness of the liquid crystal layer. ing. The present invention
It relates to a liquid crystal display device having a bend alignment,
Different from the present invention.

[0006]

However, the response speed of the TN type liquid crystal display device is several tens of ms or more. When displaying a halftone image in a moving image display such as a TV image, the response speed is not high. May be enough. It is desirable that the response speed for obtaining a good moving image display be equal to or less than the frame period (1/60 s) even during gradation display.

On the other hand, an OCB mode liquid crystal display device having a bend alignment is a multistable mode. FIG.
(A), (b), and (c) show schematic configuration diagrams of an OCB mode liquid crystal display device. The OCB mode liquid crystal display element shows a splay alignment state 21 as shown in FIG. 7A in an initial state (V = 0) before application of a drive voltage, and FIG. Bend orientation state 2 as shown in b)
2 is shown. When the voltage is turned off, the alignment state does not return directly from the bend alignment state 22 to the splay alignment state 21;
The state returns to the splay alignment state 21 via the twist state 23 as shown in FIG. Since the OCB mode is a multi-stable mode, it lacks stability, and this also affects the display screen.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to use a homogeneously oriented LCD as a twist-free nematic liquid crystal layer that can easily compensate for a phase difference, and to improve the viewing angle characteristics. To provide a liquid crystal display device having high contrast and high response speed.

[0009]

According to the present invention, there is provided a liquid crystal display device as described in (1) below, in order to achieve the above object. (1) A driving liquid crystal display cell having a nematic liquid crystal layer arranged homogeneously is sandwiched between two polarizing plates, and two phase difference compensation layers are provided between the driving liquid crystal display cell and the polarizing plate. Each of the retardation compensation layers compensates for modulation applied to light passing through the upper and lower portions of the driving liquid crystal display cell, and both retardation compensation layers have a liquid crystal having a negative refractive index anisotropy.
Crystal molecules, arranged at a constant inclination from the normal direction of the optical axis.
The liquid crystal display device characterized by being.

That is, there are two causes for slowing down the response of the liquid crystal display element. The first is twist orientation. Therefore, the TN liquid crystal display device cannot obtain a fast response. Second is the threshold voltage.
Near this threshold voltage, the response speed of the liquid crystal is extremely slow. For this reason, it is desirable to drive in a voltage region deviating from the threshold voltage. In the OCB mode, a threshold voltage is required when changing from the splay alignment to the bend alignment. Although the operation is relatively fast for use in the bend alignment region, the OCB mode is a multistable mode, which affects the display screen.

Therefore, the liquid crystal display element of the present invention employs a driving liquid crystal display cell having a nematic liquid crystal layer in which no twist is present and is homogeneously arranged in a monostable mode. Compensate. Compared with the OCB mode, the multi-stable mode is not set at the time of voltage driving, so that the display screen is not affected.

Further, by adjusting the birefringence of the phase difference compensating layer and the nematic liquid crystal layer, it is possible to display in black and white without the threshold voltage. Therefore, a fast operation can be realized without being affected by a low response speed near the threshold voltage. FIG. 8 shows a voltage-transmittance characteristic of a homogeneous alignment cell using a phase difference compensation layer. V1 as the drive voltage
By using V2, the threshold voltage Vt having a slow response speed
h can be removed. Therefore, a high-speed response can be obtained.

As shown in FIG. 1, the liquid crystal display device according to the present invention comprises a liquid crystal cell 40 having a homogeneous alignment comprising a first substrate 10 and a second substrate 11 and a liquid crystal layer 20 sandwiched therebetween. , A first phase compensation layer 30, a second phase compensation layer 31, a first polarizing plate 12, and a second polarizing plate 13, and the homogeneous alignment cell 40 includes the first phase compensation layer 30. And the second phase difference compensating layer 31, and further, the first phase compensating layer 31 blocks / transmits specific polarized light.
And the second polarizing plate 13. The first and second phase difference compensating layers 30 and 31 have a function of compensating for the modulation received by light passing through the upper part A and the lower part B of the liquid crystal layer 20, respectively.

[0014]

Embodiments of the present invention will be described below in detail with reference to embodiments and the accompanying drawings. FIG. 2 is a schematic configuration diagram showing the relationship between the liquid crystal cell of homogeneous alignment and the phase difference compensation layer according to the first invention of the present invention. When driven, the liquid crystal layer 20 has positive uniaxial optical anisotropy. Discotic LCD 50
By using the phase difference compensating layers 30 and 31 in which the liquid crystal layer 20 is oriented at a constant inclination, the regions A and B of the liquid crystal layer 20 are compensated by the phase difference compensating layers 30 and 31, thereby improving the viewing angle. .

FIGS. 3 and 4 are schematic structural views showing the relationship between a homogeneously aligned liquid crystal cell and a retardation compensation layer according to the second invention of the present invention. When the liquid crystal layer 20 is driven,
It has a positive uniaxial optical anisotropy. In FIG. 3, 3
Reference numerals 0a and 31a are phase difference compensation layers. The angle formed by the discotic liquid crystal molecules 50 and the liquid crystal cell surface is approximately 0 ° in the surface region on the interface side with the liquid crystal layer, and gradually increases to approximately 90 ° in the surface region on the opposite side. Accordingly, the phase difference compensation layer 30a compensates for the upper portion A of the liquid crystal layer 20, and the phase difference compensation layer 31a compensates for the lower portion B of the liquid crystal layer 20.

On the other hand, in FIG. 4, 30b and 31b are phase difference compensation layers. The angle formed by the discotic liquid crystal molecules 50 and the liquid crystal cell surface is approximately 90 ° in the surface region on the interface side with the liquid crystal layer 20, and approximately 0 ° in the surface region on the opposite side.
The phase difference compensation layer 30b compensates for the upper part A of the liquid crystal layer 20 and the phase difference compensation layer 31b compensates for the lower part B of the liquid crystal layer.

It is an object of the present invention to divide the liquid crystal layer 20 and to compensate each of the divided portions by the phase difference compensation layers 30 and 31 located above and below the liquid crystal layer 20. Discotic liquid crystal 5 of retardation compensation layers 30 and 31
The alignment structure of 0 is the upper part A and the lower part B
Cancels out the optical action of the nematic liquid crystal, and becomes optically isotropic over a wide field of view as a whole, and as a result, the viewing angle can be improved.

FIG. 5 is a schematic diagram showing the relationship between the liquid crystal cell of homogeneous alignment and the retardation compensation layer according to the third aspect of the present invention. Two phase difference compensation layers 30, 31
In addition, there is at least one retardation compensation layer 35 in which discotic liquid crystals are aligned in parallel with the liquid crystal cell plane. In this case, the liquid crystal layer 20 is divided, the upper part A and the lower part B of the liquid crystal layer 20 are compensated by the phase difference compensating layers 30 and 31 located above and below the liquid crystal cell 40, and the central part C is newly compensated for phase difference. This is compensated by the layer 35.

As described above, it is an object of the present invention to divide the liquid crystal layer 20 and to use the phase difference compensation layers 30, 31, and 35 for compensating the liquid crystal layer 20, thereby performing a precise phase difference compensation. Each of the retardation compensation layers cancels out the optical action of the nematic liquid crystal, and can improve the viewing angle.

The object of the phase difference compensation is the orientation structure of the liquid crystal layer when the driving voltage is applied, and the product Δnd of Δn of the discotic liquid crystal and the thickness d of the phase difference compensation layer is Δn of the nematic liquid crystal when the voltage is applied and the product thereof. It is necessary that the product of the cell thickness d and the absolute value of Δnd be substantially equal to each other.

In the method for producing a film having a discotic liquid crystal layer, for example, a discotic liquid crystal layer is provided on a transparent film and rubbed, and a discotic liquid crystal layer is provided thereon. There is a method of curing and forming while applying an electric or magnetic field. JP-A-8-5837 ("Optical compensation sheet, method for producing the same and liquid crystal display device using the same": Fuji Photo Film Co., Ltd.) discloses a method for producing a discotic liquid crystal film used in a twisted nematic liquid crystal display device. It is shown.

FIG. 6 shows an example of the relationship between the polarizing plates 12 and 13 and the rubbing direction of the liquid crystal layer 20. Where A
1, P1 indicates the direction of the transmission axis of each polarizing plate by 10
R and 11R indicate the rubbing directions in the homogeneously aligned liquid crystal cell. In a preferred embodiment, the directions A1 and P1 of the transmission axes of the two polarizing plates are orthogonal to each other and form an angle of 45 ° with the rubbing direction of the liquid crystal cell of the homogeneous alignment.
The rubbing direction of the retardation compensation layers 30 and 31 is the same as or opposite to the rubbing direction of the homogeneous alignment cell.

[0023]

The liquid crystal display device of the present invention prevents deterioration such as inversion of the screen in the horizontal and vertical viewing angles, has a high transmittance, and can be driven at a low voltage. That is, the liquid crystal display element of the present invention has a wide viewing angle characteristic and completely compensates for the optical action of the nematic liquid crystal.
(Retardation), phase difference compensation can be performed, a large transmittance can be obtained by selecting a large Δnd, and at the same time, the maximum voltage can be lowered. It is easy to operate without affecting the screen.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a liquid crystal display device according to the present invention.

FIG. 2 is a diagram illustrating a schematic configuration of an example of an optical phase compensation layer included in a liquid crystal display device according to the present invention.

FIG. 3 is a diagram illustrating a schematic configuration of an example of an optical phase compensation layer included in the liquid crystal display device according to the present invention.

FIG. 4 is a diagram illustrating a schematic configuration of an example of an optical phase compensation layer included in the liquid crystal display device according to the present invention.

FIG. 5 is a diagram illustrating a schematic configuration of an example of an optical phase compensation layer included in the liquid crystal display device according to the present invention.

FIG. 6 shows the transmission axis of each layer of the liquid crystal display device according to the present invention.
It is a figure showing the correlation of the rubbing direction.

FIG. 7 is a diagram schematically illustrating a multistable mode of the OCB mode.

FIG. 8 is a diagram showing voltage-transmittance characteristics in the liquid crystal display device according to the present invention.

[Explanation of symbols]

 Reference Signs List 10 upper substrate 11 lower substrate 12 polarizing plate 13 polarizing plate 20 liquid crystal layer 21 splay alignment state 22 bend alignment state 23 twist alignment state 30 phase difference compensation layer 31 phase difference compensation layer 35 phase difference compensation layer 50 discotic liquid crystal molecules 40 liquid crystal cell

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-9-146086 (JP, A) JP-A-9-197397 (JP, A) JP-A 8-327822 (JP, A) JP-A 2000-111914 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/13363 G02F 1/1335 G02F 1/137

Claims (1)

(57) [Claims] 1. A driving liquid crystal display cell having a homogeneously arranged nematic liquid crystal layer is sandwiched between two polarizing plates, and two phase difference compensation layers interposed between the driving liquid crystal display cell and the polarizing plate are provided. Each of the retardation compensation layers compensates for modulation received by light passing through the upper and lower portions of the driving liquid crystal display cell, and both retardation compensation layers have a refractive index anisotropy.
Has negative liquid crystal molecules and has a constant tilt from the normal direction of the optical axis.
A liquid crystal display device characterized by being arranged in the following manner .