JPS61209420A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To improve the steepness of voltage response by orienting liquid crystal molecules to the twist structure of 270 deg. twist angle between upper and lower electrode substrates. CONSTITUTION:This liquid crystal display element is constituted by disposing a liquid crystal cell having the twist structure of 270 deg. twist angle between a pair of polarizing plates and subjecting the same to multiplex driving. The liquid crystal molecules 1 rise while maintaining the 270 deg. twist structure when the voltage above the threshold voltage Vx is impressed between the upper and lower electrode substrates 2 and 3. The angle of the rise is nearly perpendicular in the intermediate part of the liquid crystal layer and the angle theta of inclination is maintained near the electrode substrate surface. On the other hand, the angle of inclination of the liquid crystal molecules is considered to be nearly 0 deg. in the intermediate part of the 270 deg. twist structure while no voltage is impressed. The molecules 1 are twisted 270 deg. clockwise from the upper substrate 2 toward the lower substrate 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid crystal display element, and more particularly to a liquid crystal display element that has rapid voltage response and is suitable for multiplex driving.

Liquid crystal display elements, especially field effect type liquid crystal display elements represented by 90° twist mode, have the advantages of low power consumption and thinness, and are therefore widely used as small display panels for watches, calculators, etc. Recently, large displays such as computer terminal display gray, etc.
Attempts have been made to use a liquid crystal display element instead of a CRT 7'' (striped screen).

In such a large display/mother panel, the number of pixels, which are the minimum unit of display, is extremely large, so it is impossible from a circuit technology point of view to directly drive each of these pixels with a dedicated electrode. Therefore, it is necessary to form a matrix by crossing common electrodes and drive these in a time-divisional manner.

Such a driving method is called multiplex driving (time division multiplex driving).

In multiplex driving, if the number of time divisions is increased sequentially, non-selected pixels begin to be driven, so the contrast with selected pixels is lost, and the purpose of display is no longer fulfilled. This phenomenon is called crosstalk, and it defines the limit on the number of time divisions.

Therefore, in order to suppress crosstalk and increase the number of time divisions, there is a strong demand for a voltage-responsive immune liquid crystal display element that responds rapidly in an extremely narrow voltage range.

Therefore, an object of the present invention is to provide a liquid crystal display element with immune voltage responsiveness and suitable for multiplex driving.
For the above purpose, in the present invention, a liquid crystal cell having a twist structure with a twist angle of 2700 is disposed between a pair of polarizing plates, and is driven in a multiplex manner.

This will be explained below with reference to the drawings.

FIG. 1 is a diagram schematically showing the orientation state of liquid crystal molecules in a conventional 90° twisted liquid crystal cell, with FIG. 1(a) being a side view and FIG. 1(b) being a plan view.

When a pair of electrode substrates (2) and (3) that have been subjected to alignment treatment are arranged facing each other so that the directions of the alignment treatment are perpendicular to each other, and a nematic liquid crystal having positive dielectric anisotropy is interposed between them, liquid crystal molecules (1) is oriented in a twisted structure twisted by 90° between the side substrates as shown in FIG. 1(a). As shown in FIG. 1(b), the liquid crystal molecules (1) are turning 9o0 to the left from the upper substrate (2) toward the lower substrate (3).

The tilt angle θ of the liquid crystal molecules with respect to the substrate surface varies depending on the alignment process. If SiO is obliquely evaporated at an angle of approximately 60° from the perpendicular direction to the electrode substrate, θ = 00, and when SiO is obliquely evaporated at an angle of 80° or more. Then, θ=15° to 40°. On the other hand, when the electrode substrate surface is rubbed, θ=1°
It is known that the angle is ~5°.

When a driving voltage is applied between the side substrates, liquid crystal molecules (1) having positive dielectric anisotropy rise in a direction perpendicular to the substrates, as shown in FIG.

As the orientation structure changes, the polarization plane rotation effect or birefringence effect of the twisted structure changes.
By arranging a pair of polarizing plates on both sides of a liquid crystal cell, the change in the amount of transmitted light caused by the application of a driving voltage creates a visual contrast.

In such a 90' twisted liquid crystal cell, the rise characteristics of the liquid crystal molecules with respect to the driving voltage, that is, the voltage responsiveness, depends on the tilt angle θ. In this figure, the horizontal axis shows the driving voltage, and the vertical axis shows the dielectric constant measured in the thickness direction of the liquid crystal cell.

When the tilt angle θ is 15° or more, the liquid crystal molecules rise continuously as the voltage increases, as shown by curve (4).
Does not exhibit a clear threshold voltage. On the other hand, when θ is 0°, a clear threshold voltage is shown as shown by curve (6), and the response is relatively fast. However, in this case, since the rising direction of the liquid crystal molecules is not defined in one direction, opposite rising directions coexist, causing a reverse tilt domain and interfering with display.

Therefore, a rubbing alignment process that exhibits a response as shown in curve (5) is generally adopted for liquid crystal cells for multiplex driving. However, such voltage responsiveness does not provide sufficient dispatchability, and the number of time divisions cannot be increased.

With the aim of improving the voltage responsiveness of twisted liquid crystal cells, the present inventor investigated the relationship between the twist angle and the responsiveness, and found that as the twist angle increases, the responsiveness gradually increases.
It has been found that the most immunoresponsiveness is obtained when the twist angle is 27o0.

It has been previously reported that the viewing angle characteristics are improved when the twist angle is set to 2700 (Japanese Patent Laid-Open No. 52-10883).
8).

The present invention has discovered that this 27o0 twisted liquid crystal cell exhibits extremely unique voltage responsiveness, and utilizes this characteristic as a liquid crystal display element for multiplex driving.

Hereinafter, embodiments will be described with reference to the drawings.

A pair of electrode substrates that have been oriented by oblique evaporation of SiO so that the tilt angle θ is approximately 20' are placed facing each other so that the orientation directions are perpendicular to each other, and a positive electrode substrate to which an optically active substance is added is placed between them. When a nematic liquid crystal having a dielectric anisotropy of 2 is interposed, the liquid crystal molecules are oriented in a 90' twist or a 270° twist structure depending on the amount of the optically active substance added.

A nematic liquid crystal doped with an optically active substance has a characteristic pitch (P) that is almost inversely proportional to the amount added, but if the ratio d/P to the thickness d) of the liquid crystal layer is less than 0.5, a 90' twisted structure is formed. Prioritize.

On the other hand, when d/P becomes 0.5 or more, a 270° twisted structure appears.

FIG. 4 is a diagram schematically showing the orientation of liquid crystal molecules in the 270° twisted structure constructed in this manner.

A threshold voltage (Vx
), the liquid crystal molecule (1) rotates at 270°.
Stand up while maintaining the twisted structure. In this case, as shown in FIG. 4(a), it is considered that the rising angle is close to vertical in the middle part of the liquid crystal layer, and the tilt angle θ is maintained near the electrode substrate surface.

On the other hand, when no voltage is applied, the tilt angle of the liquid crystal molecules is considered to be close to Oo in the middle part of the 270° twisted structure.

FIG. 4(b) is a plan view showing a 270° twisted structure, in which the liquid crystal molecules (1) are rotated 270° clockwise from the upper substrate (2) toward the lower substrate (3).

Figure 5 is a diagram showing the voltage response curve (force) of the 2700 twisted liquid crystal cell of the present invention in comparison with the characteristics of a 90° twisted liquid crystal cell.Curves (4) and (6) are shown in Figure 3. curve (4) is 9 with an inclination angle of 15° or more.
The curve (6) shows the characteristics of a 90° twisted liquid crystal cell with a tilt angle of O0.

The 2700 twisted liquid crystal cell exhibits a very unique response as seen in curve (7) in FIG. That is, in the low voltage region, it shows a behavior similar to curve (6), reaches a clear threshold voltage and rises to a courier, and further changes in the high voltage region similar to curve (4).

In this example, as mentioned earlier, the inclination angle θ is approximately 20°, but as shown in Fig. 5, the dielectric constant is extremely low when no voltage is applied. Close to curve (6).

From this, it seems that in the 270° twisted liquid crystal cell, the liquid crystal molecules in the intermediate layer, which constitutes the majority of the liquid crystal layer, are oriented almost parallel to the substrate when no voltage is applied.
This is thought to be the cause of the poor voltage response.

In addition, in the example, the tilt angle θ of the liquid crystal molecules was set to about 20°.
However, if the tilt angle is in the range of 15° to 40°, excellent voltage responsiveness can be obtained.

When multiplex driving a conventional 90° twisted liquid crystal cell, the limit was around 32 divisions due to crosstalk, but when driving a 270° twisted liquid crystal cell, which has extremely responsive response, in multiplex. for,
High-division multiplexing driving of 64 divisions or even 100 divisions or more is possible.

Incidentally, the rise of liquid crystal molecules when a voltage is applied in a 270° twisted liquid crystal cell is accompanied by a rotation effect of the plane of polarization and a change in the birefringence effect, as in the 90° twisted liquid crystal cell. Therefore, only by placing this between a pair of polarizing plates can visual contrast be produced by the effects of each.

Although polarizing plates are not particularly shown in the embodiments, it goes without saying that the pair of polarizing plates are essential members as a display element.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams showing the orientation of liquid crystal molecules in a conventional 90° twisted liquid crystal cell, and Figure 3 is a diagram showing the orientation of liquid crystal molecules in a conventional 90° twisted liquid crystal cell.
Figure 4 shows the voltage response of the twisted liquid crystal cell. Figure 4 shows the orientation of liquid crystal molecules when voltage is applied in the 270° twisted liquid crystal cell of the present invention. Figure 5 shows the voltage response of the 270° twisted liquid crystal cell of the present invention. FIG. 3 is a diagram illustrating responsiveness in comparison with voltage responsiveness of a conventional 90° twisted liquid crystal cell. Applicant Citizen Watch Co., Ltd. Figure 1 Figure 2 (CI) Figure 3 Figure 4 (a) (b) Figure 5

Claims (1)

[Claims] A pair of upper and lower electrode substrates, which are aligned so that the tilt angle of the liquid crystal molecules with respect to the substrates is 15° to 40°, are placed facing each other so that the directions of the alignment treatment are orthogonal to each other, and a positive electrode substrate containing an optically active substance is placed between them. A twist angle of 270° is created between the upper and lower electrode substrates by injecting nematic liquid crystal with a dielectric anisotropy of
1. A liquid crystal display element characterized in that a liquid crystal cell, which has a liquid crystal cell oriented in a twisted structure of 100 degrees centigrade to enhance rapid voltage response, is arranged between a pair of polarizing plates and driven in a multiplex manner.