JPS59181321A - Guest-host type liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain low voltage drivability and contrast with high responsiveness by sealing a (p) type nematic liquid crystal contg. a chiral agent and a dichromatic dye in a cell of a hybrid type and specifying the ratio between the thickness of the cell and the twist orienting pitch of the liquid crystal at a specific value. CONSTITUTION:A (p) type nematic liquid crystal contg. a chiral agent and a dichromatic dye is sealed in a cell of a hybrid type formed by subjecting one electrode substrate to a vertical orienting treatment and the other electrode substrate to a horizontal orienting treatment and the ratio d/p between the thickness (d) of the cell of the hybrid type and the twist orienting pitch (p) of the liquid crystal is set at >=1.5, <=2.5. Such liquid crystal exhibits a twist orientation and a color display is made by the dichromatic dye on turning off. The liquid crystal orients perpendicularly to the substrate and is made transparent on turning on. The cell is usable with a low voltage without generating a focal conic state and the liquid crystal having good contrast is obtainable. Low voltage drivability and contrast with high responsiveness are thus obtd. and the device is usable for various kinds of display such as the time display of a watch.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a guest-host type liquid crystal display device using a nematic-cholesteric phase transition type liquid crystal (fvtVc). A nematic-cholesteric phase transition type guest-host display device in which a chiral agent and a dichroic dye are mixed into liquid crystal is known.
There are two types.

One is both facing each other! This is a camellia substrate subjected to vertical alignment treatment. We will call this type A here. The other one is one in which both [1i substrates are subjected to horizontal alignment treatment. This is herein referred to as type B. In both types A and B, in the OFF state, the liquid crystal exhibits a twisted orientation of the cholesteric phase as shown in Figure 1, and color display is performed using dichroic dyes.

In the ON state when a driving voltage is applied, as shown in the second figure, the vertical Vc resistance to the substrate is 1 and the transparency is 2. Using this color display and transparency, a color display device is fabricated.

The thickness of the helical pitch of the liquid crystal is determined by the amount of chiral agent added, but the ratio between this twisted orientation and the driving voltage V of the liquid crystal is as follows: It is known that there is a certain relationship.

Now, when using a certain B-type nematic liquid crystal, d/
The relationship between p and V is indicated by line A for A-type cells and line B for B-type cells in the graph of FIG. The voltage value differs slightly depending on the liquid crystal used, but A and B
The relationship is almost the same.

Everywhere on lines A and B on these graphs, A
However, there are limitations to the practical use of Tr1B type, Tr1B type, and Tr1B type display devices.

A type display fi! ! j if d/p <;-3, the response is poor and it cannot be used for watches, etc. That is, d/p≦3
In this case, a kind of scattering state called focal conic curvature remains when the light falls, and it takes a very long time for the dichroic dye to become a clear color due to the initial twisted orientation of the liquid crystal. Therefore, it is necessary to set the dlp value to be greater than 3, but there is a restriction that the driving voltage of Vc must be set to be higher than 6V.

Regarding the B-type display device, there are no restrictions on the fall time as there are for the A-type display device, but when looking at the same dlp value, as you can see from the graph, it is about 3 times lower than the A-type display device.
■The drive voltage increases. Therefore, if you try to drive with a voltage lower than 6V, the value of d/7) will become smaller than about 1.5. However, as the dlp value becomes smaller, another problem arises. In other words, there is a certain relationship between the dlp value and the contrast and spacing of the display, and as the dlp value decreases, the contrast becomes worse, and when d/p <1', 5, the underlying coloring is no longer clear and the color becomes muddy. The contrast is also low. To obtain a certain contrast,
5≦d/p is required, but then the corresponding voltage must be about 6V or more, and there is a constraint that the branch drive voltage must not be too low.

Furthermore, in the case of B4+, there is a delicate balance between the wake angle and the chiral agent. Ta.

This invention attempts to solve the drawbacks of the conventional VC.

As a feature of the present invention, vertical images in the vertical direction I11. Cells that have a so-called hybrid orientation, in which a horizontal direction is applied to the M-type substrate by applying the same process, will be referred to here as a hybrid type. Using this hybrid cell, the above-mentioned t
This hybrid type display uses the same B-type nematic liquid crystal as used in the B-type and B-type display devices, mixes a chiral agent and dichroic dye, and encapsulates the liquid crystal to form a display cell. How to display cells @1, 2 A shown in the diagram
This is the same as in the case of type B and type B, and when it is OFF, the liquid crystal is twisted and oriented, and when it is ON, it is aligned perpendicular to the substrate and becomes transparent. Manufacturing is easy because there is no need to strictly control the mixing ratio, and even slight variations do not affect performance.

The relationship between the cell thickness d of this hybrid type cell, the ratio d/p of the twisted orientation bi-notch p of the liquid crystal, and the drive force and pressure is shown by line C in Figure 3.

In this hybrid type, the focal conic state does not occur when falling at K d/7t < 3, as in the A-type display cell W, and even at a driving voltage of 6 V or less (lf Can be used.Compared with fCB type (in case of 2 types, the dir value is larger at the same drive normal pressure)
(obtained).The contrast across I is better than that of type B.The d of this hybrid type cell
The upper limit is set to 25 since the driving voltage is 6 V when ir>value is 6 V or less, and the lower limit is set to 1.5 on the condition that there is no practical problem with the contrast. In other words, the ratio dAy of the liquid crystal cell thickness d and the liquid crystal screw h alignment pitchle is 1.5 <
VC1pt is formed so that d, /T≦25. If the cell thickness of the liquid crystal cell is constant, the size of the twisted orientation of the liquid crystal is determined by the mixing ratio of the chiral agent mixed into the liquid crystal, so controlling the dir value is effective.

According to the guest-honuto type liquid crystal display device of the present invention, which is constructed of buried soil, it is possible to meet the requirements of low snow pressure driving performance, high responsiveness, and high contrast, and it can be used for various displays such as the time display on a clock.

[Brief explanation of the drawing]

Figure 1.2 shows the conventional example, the 19th diagram showing the display effect, and the 3rd diagram.
Figure 1-1' shows the relationship between display cell "W dir" and drive voltage. Applicant Seikosha Co., Ltd.

Claims (1)

[Claims] A p-type nematic liquid crystal mixed with a chiral agent and a dichroic dye is sealed in a cell in which one electrode substrate is vertically aligned and the other electrode substrate is horizontally aligned. A guest-host type liquid crystal display device, characterized in that the ratio d/p of the cell thickness d and the twisted orientation/direction I chip p of the liquid crystal is 15 or more and 2.5 or less.