JPH0572552A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To excellently display a moving picture and to make display quality excellent. CONSTITUTION:A coloring compensation liquid crystal layer 26 is arranged on one side of a liquid crystal display cell 25, and the twist angle of the liquid crystal 12 of the layer 26 is made the same as that of the liquid crystal 7 of the cell 25. The direction of the twist of the liquid crystal 12 of the layer 26 is made reverse to that of the liquid crystal 7 of the cell 25, and the retardation value of the cell 25 is set to >=1mum and the retardation value of the layer 26 is set to 40-60% of the retardation value of the cell 25, then an angle formed by the absorbing axes of polarizing plates 13 and 14 is set to <=10 deg..

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention has a liquid crystal twist angle of 1
The present invention relates to an STN (Super Twisted Nematic) type liquid crystal display device having an angle of 80 degrees or more.

[0002]

2. Description of the Related Art A STN type liquid crystal display device has a particularly excellent time-division driving characteristic because the transmittance-voltage characteristic has a steep threshold voltage value. Since the transmittance differs depending on the type, the transmitted light is colored.

In order to prevent such coloring, in a conventional liquid crystal display device, a color compensating liquid crystal layer is overlaid on a liquid crystal display cell as disclosed in Japanese Patent Laid-Open No. 130532/1990, and Japanese Patent Laid-Open Publication No. Sho. As shown in Japanese Patent Publication No. 61-89521, a liquid crystal display cell is overlaid with a phase plate.

However, in such a liquid crystal display element, since the driving voltage is low, the response speed is slow, and the total of the rise response time and the fall response time is several hundred ms.
Therefore, when the pointer is moved at a high speed by the mouse operation, the pointer disappears, and the moving image cannot be displayed well.

Therefore, as disclosed in Japanese Patent Laid-Open No. 64-49021, the retardation value Δnd of the color compensation liquid crystal layer, that is, the product of the refractive index anisotropy Δn and the layer thickness d is the retardation value Δnd of the liquid crystal display cell. From 40 to 300n
It has been proposed that the response speed be increased by reducing m.

[0006]

However, in such a liquid crystal display element, since the transmittance is lowered and the display is dark, the display quality is not good.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a liquid crystal display device which can display a moving image in a good condition and has a good display quality.

[0008]

In order to achieve this object, in the present invention, an optical anisotropic body is arranged on at least one side of a liquid crystal display cell, and both sides of the liquid crystal display cell and the optical anisotropic body are sandwiched. ST with polarizing plates
In the N-type liquid crystal display device, the retardation value of the liquid crystal display cell is 1 μm or more, the retardation value of the optically anisotropic body is 40 to 60% of the retardation value of the liquid crystal display cell, and the retardation value of the two polarizing plates is The angle formed by the absorption axis is 10 degrees or less.

[0009]

In this liquid crystal display device, since the retardation value of the optically anisotropic substance is 40 to 60% of the retardation value of the liquid crystal display cell, the driving voltage can be increased and the amount of alignment deformation of liquid crystal molecules can be increased. Since the liquid crystal display cell has a retardation value of 1 μm or more, the transmittance change is large even if the alignment deformation is small.

[0010]

1 is a diagram showing a liquid crystal display device according to the present invention. In the figure, 1 and 2 are glass substrates, 3 and 4 are transparent electrodes formed on the glass substrates 1 and 2, 5 and 6 are alignment films formed on the transparent electrodes 3 and 4, and 7 is glass substrates 1 and 2.
With the liquid crystal enclosed between them, the liquid crystal display cell 25 is composed of the glass substrates 1 and 2, the liquid crystal 7, etc., and the refractive index anisotropy Δn of the liquid crystal 7 of the liquid crystal display cell 25 is 0.165 and the layer thickness d.
Is 6.2 μm, and the retardation value Δnd is 1.023 μm.
m. 8 and 9 are glass substrates, 10 and 11 are alignment films formed on the glass substrates 8 and 9, and 12 is the glass substrates 8 and 9.
Liquid crystals 7 and 12 are the same kind of liquid crystal enclosed between them, and the color compensating liquid crystal layer 26 is constituted by the glass substrates 8, 9 and the liquid crystal 12 and the like. The refractive index anisotropy Δn of the liquid crystal 12 is 0.165, the layer thickness d is 3.1 μm, and the retardation value Δnd is 0.511.
It is 5 μm. Reference numerals 13 and 14 denote polarizing plates provided outside the liquid crystal display cell 25 and the color compensating liquid crystal layer 26.

FIG. 2 is a diagram showing the relationship of axes of the components of the liquid crystal display device shown in FIG. In the figure, 15 is a rubbing axis of the alignment film 5, 16 is a rubbing axis of the alignment film 6, and 17 is a rubbing axis.
Is the rubbing axis of the alignment film 10, 18 is the rubbing axis of the alignment film 11, 19 is the absorption axis of the polarizing plate 14, 20 is the absorption axis of the polarizing plate 13, the liquid crystal 7 has a twist angle of 240 degrees, and the liquid crystal 12 has a twist angle. Is 240 degrees in the opposite direction, rubbing shafts 15 and 17
Forms an angle of 90 degrees, the rubbing shaft 16 and the absorption axis 20 form an angle of 45 degrees, and the rubbing axis 18 and the absorption axis 19 form an angle of 45 degrees.

FIG. 3 is a graph showing the voltage-transmittance characteristic when a voltage is applied to the transparent electrodes 3 and 4 of the liquid crystal display element shown in FIG. 1 at a duty of 1/200. FIG. The liquid crystal layers 7 and 12 of the compensation liquid crystal layer 26 have a refractive index anisotropy Δn of 0.137, a layer thickness d of 6.2 μm, and a retardation value Δnd of 0.8494 μm. 6 is a graph showing voltage-transmittance characteristics when a comparative liquid crystal display element having the same structure is driven at 1/200 duty. As is clear from these figures, the contrast ratio of the liquid crystal display device shown in FIG.
5 and the contrast ratio of the liquid crystal display device for comparison is 16
Therefore, the liquid crystal display element shown in FIG. 1 has a good contrast ratio. In addition, the liquid crystal display element shown in FIG. 1 has a transmittance of 23% in the selected portion and the liquid crystal display element for comparison has a transmittance of 15% in the selected portion. 53% brighter than the display element. Further, the sum of the rise response time and the fall response time of the liquid crystal display element shown in FIG. 1 is 365 ms, and the sum of the rise response time and the fall response time of the comparative liquid crystal display element is 487 ms. The liquid crystal display element shown in FIG. 1 has a 33% faster response speed than the comparative liquid crystal display element. As described above, since the response speed is high, the moving image can be displayed well, and the display at the time of scrolling operation of the word processor and the personal computer and the display at the time of operating the mouse can be performed well. Further, since the contrast ratio and the brightness are improved, the display quality is good.

FIG. 5 is a diagram showing another liquid crystal display element according to the present invention. In the figure, reference numerals 21 and 22 denote retardation films made of polycarbonate.
22 is arranged between the liquid crystal display cell 25 and the polarizing plates 13 and 14. The refractive index anisotropy Δn of the liquid crystal 7 of the liquid crystal display cell 25 is 0.210, the layer thickness d is 6.2 μm, the retardation value Δnd is 1.302 μm, and the retardation values Δnd of the retardation films 21 and 22 are 0.3
It is 38 μm.

FIG. 6 is a diagram showing the relationship of axes of the components of the liquid crystal display device shown in FIG. In the figure, 23, 24
Is the optical axis of the retardation films 21 and 22, the optical axis 23 and the rubbing axis 15 are orthogonal to each other, and the optical axis 24 and the rubbing axis 1 are
6 is orthogonal.

In the liquid crystal display element shown in FIG. 5, as is apparent from FIG. 7 showing the voltage-transmittance characteristic, the driving voltage can be increased, so that the response time is fast and the rising response time and the falling response time are low. Total with response time is 372ms
Therefore, the moving image can be displayed well, the contrast ratio can be 35, and the transmittance of the selected portion can be 32%. Therefore, the display quality is good. Further, since the transmittance when no voltage is applied is as high as 25%, it can be used in a reflective liquid crystal display device, a liquid crystal display device having a low-brightness backlight such as an electrofluorescent luminescent material (EL),
Moreover, since the ratio of the selection voltage to the non-selection voltage is small, the bias voltage can be increased and the drive voltage can be decreased, so that the liquid crystal display element can be made thin and lightweight and the battery can be lightened. Therefore, it is possible to reduce the weight of the liquid crystal display device.

In the above embodiment, the color compensating liquid crystal layer 26 and the retardation films 21 and 22 are optically anisotropic bodies.
However, other optically anisotropic bodies may be used. Further, in the above-mentioned examples, the retardation films 21 and 22 are arranged on both sides of the liquid crystal display cell 25, but the retardation film is arranged on one side of the liquid crystal display cell 25, and the optical axis of the retardation film and the retardation film are arranged. The angle formed by the rubbing axis of the adjacent alignment film may be 90 degrees. Further, in the above-mentioned examples, the retardation films 21 and 2 made of polycarbonate are used.
Although 2 was used, a retardation film made of polyvinyl alcohol, polyvinyl chloride or the like may be used. Further, in the above-mentioned embodiment, the same type of liquid crystal is used as the liquid crystal of the liquid crystal display cell 25 and the color compensation liquid crystal layer 26, but different types of liquid crystal may be used.

[0017]

As described above, in the liquid crystal display device according to the present invention, the driving voltage can be increased and the amount of alignment deformation of the liquid crystal molecules can be reduced, so that the response speed can be increased and the alignment can be achieved. Even if the deformation is small, the change in transmittance is large, so that the contrast ratio and the brightness are improved, so that the display quality is good. As described above, the effect of the present invention is remarkable.

[Brief description of drawings]

FIG. 1 is a diagram showing a liquid crystal display element according to the present invention.

FIG. 2 is a diagram showing a relationship between axes of components of the liquid crystal display device shown in FIG.

3 is a graph showing voltage-transmittance characteristics of the liquid crystal display element shown in FIG.

FIG. 4 is a graph showing voltage-transmittance characteristics of a comparative liquid crystal display element.

FIG. 5 is a diagram showing another liquid crystal display element according to the present invention.

6 is a diagram showing the relationship of axes of the constituent elements of the liquid crystal display element shown in FIG.

7 is a graph showing voltage-transmittance characteristics of the liquid crystal display device shown in FIG.

[Explanation of symbols]

 13, 14 ... Polarizing plates 21, 22 ... Retardation film 25 ... Liquid crystal display cell 26 ... Color compensation liquid crystal layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsumi Kondo 4026 Kuji Town, Tsuchiura City, Ibaraki Prefecture, Hitachi Research Institute Co., Ltd. Hitachi Research Laboratory

Claims (1)

[Claims] 1. An STN type liquid crystal display device in which an optical anisotropic body is arranged on at least one surface of a liquid crystal display cell, and polarizing plates are arranged on both sides of the liquid crystal display cell and the optical anisotropic body, respectively. The retardation value of the liquid crystal display cell is 1 μm or more, and the retardation value of the optically anisotropic body is 40 to 60% of the retardation value of the liquid crystal display cell.
The liquid crystal display element is characterized in that the angle formed by the absorption axes of the two polarizing plates is 10 degrees or less.