JPS622229A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain good visibility even if the number of scanning lines is >=100 by using a liquid crystal having the spiral structure in which the liquid crystal molecules are twisted in a 180-360 deg. range in the thickness direction thereof for the liquid crystal between upper and lower substrates and setting the ratio between the spacing of the panel and the pitch of a liquid crystal mixture at 0.20-1.0. CONSTITUTION:The angle at which the rubbing directions of both upper and lower substrates intersect with each other is set at 270 deg. right-hand helix and the spacing of the panel is set at 6.5mum in the stage of assembly. A proper amt. of the right-hand chiral nematic liquid crystal is added to the liquid crystal compsn. to be injected to the panel to constitute the panel having the structure in which the liquid crystal molecules in the liquid crystal panel are twisted 270 deg. and the ratio d/p between the spacing (d) of the panel and the pitch (p) of the liquid crystal mixture is 0.47. An upper polarizing plate is so disposed that the axis of polarization thereof coincides with the direction deviated by 30 deg. in the counterclockwise direction when viewed from above the panel with respect to the axis of the adjacent liquid crystal molecules (coinciding with the rubbing direction. The lower polarizing plate is disposed in the direction where the axis of polarization is deviated by 60 deg. in the counterclockwise direction with the axis of the liquid crystal molecules adjacent thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to liquid crystal display devices, particularly cholesteric display devices.
The present invention relates to a dot matrix type liquid crystal display element for time division driving using a twisted or chiral nematic twist type liquid crystal panel.

2. Description of the Related Art In recent years, as the number of devices incorporating microcomputers and LSIs has increased, there has been an increasing need for dot matrix displays as simple display devices. In addition, in order to respond to the highly information-oriented society, it is desired that a simple display with a high level of display capability befitting the society will emerge. That is, a liquid crystal panel with high visibility and a large display capacity is desired.

In the case of a dot matrix type liquid crystal panel, having a large display capacity means that the number of scanning lines of the panel increases. This means that the ratio between the ON voltage value applied to the panel and the voltage value at 077 can only take a very small value. That is, this is the voltage averaging method used to drive a normal dot matrix panel, and is the reason why the number of scanning lines cannot be increased.

As long as the IJ type liquid crystal display panel (with a large number of scanning lines) is driven using the voltage averaging method,
In order to obtain high visibility even when the voltage ratio with respect to 7 o'clock is small, the electro-optical characteristics of the liquid crystal panel, that is, the voltage-luminance characteristics must be sharp.

9, which is the mainstream of conventional dot matrix type liquid crystal display devices.
In response to these demands, efforts have been made to improve the characteristics of twisted nematic (TN) type liquid crystal panels having a twist angle of 0 degrees by improving the physical properties of nematic liquid crystal materials and devising panel configurations.

In other words, from the perspective of nematic liquid crystal materials, efforts were made to reduce the ratio of the bending elastic constant of 33 and the spreading elastic constant of 11, as well as dielectric constant anisotropy Δε and dielectric constant ε in the direction perpendicular to the liquid crystal molecular axis (perpendicular). Efforts have been made to reduce the ratio of Since such liquid crystal panels have not yet achieved sufficient characteristics for display quality higher than that of a book, improvements are desired.

The electro-optical characteristics of a conventional twisted nematic liquid crystal panel will be explained below with reference to the drawings.

Figure 2 shows the electro-optical characteristics of a conventional twisted nematic liquid crystal panel, where the horizontal axis is the applied voltage and the vertical axis is the relative brightness.7 Here, the parameter used to evaluate the sharpness of the threshold characteristic If we define γ as
%, the applied voltage that gives % is Vso%, and the ratio Vso%
/V1o% is defined as γ. In order to sharpen the threshold characteristics, that is, the voltage-luminance characteristics, of conventional twisted-nematic (TN) type liquid crystal panels, we have improved the physical properties of the liquid crystal material and devised the liquid crystal panel configuration, such as polarizing the polarizing plate. Even in a panel in which measures were taken to optimize the intersection angle of the axes, γ was 1.132. (Refer to Figure 2) γ is 1.132, which means that as long as the voltage averaging method mentioned above is used, the number of scanning lines can only be 100 or less as calculated using the following formula (1). This means that it cannot be driven.

Problems to be Solved by the Invention As stated in the previous section, is the conventional twisted-nematic (TN) type liquid crystal panel with a twist angle of 90 degrees? In order to sharpen the threshold characteristics, that is, the voltage-luminance characteristics, we are working on improving the physical properties of the liquid crystal material and devising the structure of the liquid crystal panel, such as optimizing the crossing angle of the polarization axes of the polarizing plates. Efforts have been made for a long time to make the system more accessible. However, with conventional panel configurations, even with such improvements and optimizations, the visibility at a display capacity of around 64 scanning lines is the limit for LCD displays, and increasing the number of scanning lines beyond that level significantly reduces visibility. The display becomes difficult to view, and improvements are desired.

In view of the above-mentioned problems, the present invention has the number of scanning electrodes io.

The object of the present invention is to provide a liquid crystal display element that can realize good visibility even during high-time division driving of more than 100 kHz.

As a solution to the problem, the present inventors propose a liquid crystal panel having a structure different from the conventional nematic (TN) type in which the twist angle of liquid crystal molecules is 90 degrees. In other words, the liquid crystal molecules sandwiched between the two upper and lower substrates rotate from 180 degrees to 36 degrees in the thickness direction.
A cholesteric-twist type or chiral nematic twist type liquid crystal panel with a helical structure twisted in the 0 degree range, a pretilt angle of 5 degrees or less, and an optimized lamination angle of two linear polarizing plates. By doing so, it is possible to obtain a liquid crystal panel with sharp voltage-luminance characteristics, and to embody a liquid crystal display element that exhibits good display quality even during time-division driving with 100 or more scanning lines.

By specifying the panel configuration of cholesteric-twist or chiral nematic-twist type liquid crystal panels, the present inventors have obtained sharp voltage-luminance characteristics and achieved a structure with a scanning line count of 1.
We were able to materialize a liquid crystal display device that exhibits good display quality even when time-divisionally driving 00 or more lines. This is of great significance for liquid crystal display elements that utilize electro-optic effects, particularly for dot matrix type liquid crystal display elements that are driven in a time-division manner. Examples for making the present invention more clear will be described below.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings.

Embodiment 1 FIG. 1 shows the relationship between the alignment direction of liquid crystal molecules and the axis of a polarizing plate in a liquid crystal display element to explain an embodiment of the present invention. Here, as a means for aligning liquid crystal molecules, T
A method of rubbing the alignment film, which is commonly used in the case of N-type liquid crystal panels, was used. At this time, the angle between the substrate surface and the axis of the liquid crystal molecules in contact with the substrate surface (pretilt angle) is 5 degrees or less. In Fig. 1, 1 is the rubbing direction of the upper electrode substrate, 2 is the rubbing direction of the lower electrode substrate, 3 is the polarization axis (or absorption axis) of the upper polarizer, and 4 is the polarization axis (or absorption axis) of the lower polarizer. absorption axis).

Furthermore, assembly is performed using the same method as the panel manufacturing method for conventional TN-type liquid crystal panels, but at that time, the intersection angle of the rubbing direction of both the upper and lower substrates is twisted to the right (counterclockwise when viewed from the top of the panel). ) is 270 degrees (5 indicates the twisting direction of the liquid crystal molecules), and the gap between the panels is 6.6 μm. By adding an appropriate amount of CB-15, a right-handed chiral nematic liquid crystal manufactured by B, D, and H companies, to the liquid crystal composition injected into the panel, the liquid crystal molecules in the liquid crystal panel are 2.
The panel has a structure with a twist of 70 degrees and a d/p of 0.47.

As shown in Figure 1, the polarization axis of the upper polarizing plate coincides with the direction shifted by 30 degrees counterclockwise when viewed from the top of the panel with respect to the axis of the adjacent liquid crystal molecules (coinciding with the rubbing direction). The lower polarizing plate was arranged so that its polarization axis was shifted by 60 degrees counterclockwise with respect to the liquid crystal molecule axis adjacent to it.

FIG. 3 shows the electro-optical characteristics of the chiral nematic twist type liquid crystal panel having the above-described structure, where the horizontal axis is the applied voltage and the vertical axis is the relative brightness. At this time,
γ as a parameter for evaluating the steepness of threshold characteristics
The value is 1.035, and according to equation (1) shown above, time division driving is sufficiently possible even when the number of scanning lines is 100 or more.

Embodiment 2 FIG. 4 shows a rubbing direction 11.12 of a liquid crystal display element and an axis 13.1 of a polarizing plate for explaining a second embodiment of the present invention.
This shows the relationship with 4.

The intersection angle in the rubbing direction is 240 degrees with right twist, and
The panel gap is 7.07trn. The liquid crystal composition injected into the panel includes B, which is a right-handed optically active substance,
By adding an appropriate amount of 0B-15 manufactured by D and H companies, the liquid crystal molecules can be twisted at 240 degrees and have a d/p of 0.
The panel has a structure of 55. The polarizing plate is installed in such a way that the polarizing axis of the upper polarizing plate is offset by 35 degrees counterclockwise when viewed from the top of the panel with respect to the liquid crystal molecule axis adjacent to it, while the polarizing axis of the lower polarizing plate is The liquid crystal molecular axes adjacent thereto are offset by 45 degrees counterclockwise.

The parameter γ value expressing the steepness of the electro-optical characteristics for this panel was 1.040. Therefore, it is possible to time-divisionally drive this liquid crystal display element even when the number of scanning electrodes is 100 or more.

Embodiment 3 FIG. 5 shows the rubbing directions 21, 22 of a liquid crystal display element and the axes 23, 23 of a polarizing plate for explaining a third embodiment of the present invention.
This shows the relationship with 24.

The intersection angle in the rubbing direction is 30 degrees with right twist, and
The panel gap is 6.8 μm. Furthermore, d/p is 0.
The optically active substance was added to the liquid crystal composition to be injected so as to have a molecular weight of 60%. Regarding the polarizing plate, the upper polarizing plate is rotated 86° clockwise relative to the liquid crystal molecular axis adjacent to it when viewed from the top of the panel.
The polarization axis of the lower polarizing plate is shifted by 15 degrees clockwise with respect to the adjacent liquid crystal molecule axis.
I pasted it so that it was off-centered.

The parameter γ value expressing the steepness of the electro-optical characteristics for this panel was 1.051. This means that time division driving is possible even when the number of scanning electrodes is 100 or more.

By the way, when d/p is 0.20 or less, it is difficult to set the twist angle of the liquid crystal molecules in the range of 180 degrees to 360 degrees. Further, when d/p is 1.0 or more, hysteresis occurs in the electro-optical characteristics, which deteriorates time-division driveability and makes it impossible to obtain good visibility.

As is clear from the above description, the present invention sets the twist angle of liquid crystal molecules between 180 degrees and 360 degrees, and d/
By setting p to 0.20 or more and 1.0 or less, a liquid crystal panel with steep threshold characteristics can be obtained, and good visibility can be obtained even in high time division driving.

In the above example, the rubbing method was used as a method for setting the pretilt angle to 5 degrees or less, but this can also be achieved by forming an alignment film by oblique vapor deposition. Further, in the above embodiments, the case where the liquid crystal molecules are twisted to the right is shown, but the same effects can be achieved in the case where the liquid crystal molecules are twisted to the left. Further, regarding the polarizing plate, the same effect can be obtained even if the polarization axis is replaced with the absorption axis.

Effects of the Invention As is clear from the above explanation, the present invention makes the twist angle of the liquid crystal molecules between 180 degrees and 360 degrees, and d/
By setting p to 0.20 or more and 1.0 or less, we were able to create a liquid crystal panel with sharp threshold characteristics, which makes it possible to create a liquid crystal panel with sharp threshold characteristics, even during high time division driving, that is, when the number of scanning lines is 100 or more. The excellent effect of obtaining good visibility was obtained.

Due to this effect, a high-quality liquid crystal display device could be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the orientation direction of liquid crystal molecules and the polarization axis of the polarizing plate in the liquid crystal display element of the first embodiment according to the present invention, and FIG. FIG. 3 is a diagram showing threshold characteristics of the liquid crystal display element of the first embodiment of the present invention, and FIGS. 4 and 5 are diagrams of the second and third embodiments of the present invention. FIG. 3 is a diagram showing the relationship between the orientation direction of liquid crystal molecules and the polarization axis of a polarizing plate in the liquid crystal display element of FIG. 1.11.21...Liquid crystal molecule alignment direction on the upper electrode substrate, 2,12,22......Liquid crystal molecule alignment direction on the lower electrode substrate, 3,13.23... ...Polarization axis direction of the upper polarizing plate, 4,14.24...Polarization axis direction of the lower polarizing plate, 5,15.25...Twisting direction of liquid crystal molecules. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 4
Figure-c″3 Annual income overlap 3 @ Sono Shiosu, ki method

Claims (2)

[Claims] (1) Regarding a twist type display panel using a nematic liquid crystal composition having positive dielectric anisotropy and added with an optically active substance, the liquid crystal molecules between the upper and lower substrates are arranged at 180 degrees in the thickness direction.
It has a helical structure twisted in a range of 360 degrees to 360 degrees, and the ratio d/p of the panel gap d to the pitch p of the liquid crystal mixture is set to 0.20 or more and 1.0 or less. Characteristic liquid crystal display element. (2) The liquid crystal display element according to claim 1, wherein the pretilt angle is 5 degrees or less.