JPS6289027A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the display quality even when the number of time divisions is increased by incorporating a liq. crystal composition obtained by adding and mixing a P-type dichroic dye into a nematic liq. crystal into a TN type cell and aligning the absorption axis of a polarizer with the orientation of liq. crystal molecules. CONSTITUTION:Striped electrodes 13 and 15 are respectively formed on electrode substrates 12 and 14. The oriented film of a polyimide resin is furnished on the substrates 12 and 14 and the surface of the film is lapped by a cotton roller to form TN oriented layers 16 and 18. Then an adhesive 19 is coated on the bonding parts of the substrates 12 and 14 and the two substrates are matched with each other so that the respective rubbing directions are vertically crossed and bonded to form a dot matrix type liq. crystal cell. The liq. crystal composition 20 obtained by adding and mixing a specified amt. of the P-type dichroic dye into a liq. crystal material is injected into the liq. crystal cell which is hermetically sealed. then the polarizers 22 and 24 are stuck on the outside of the substrates 12 and 14 so that the respective absorption axes are aligned with the orientation of the long molecules of the liq. crystal on the respective substrate sides and a twist nematic type liq. crystal display element is obtained. Consequently, a display having excellent visibility is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention particularly relates to a liquid crystal display element suitably driven with a time division number of 32 or more.

[Technical background of the invention and its problems] Liquid crystal display elements utilize optical changes in liquid crystal that occur when a voltage is applied to liquid crystal sandwiched between two substrates equipped with electrodes. The unique orientation of the liquid crystal when no voltage is applied (
This method utilizes the phenomenon that the initial orientation (initial orientation) changes with voltage application.
.

For example, in a twisted nematic (TN) liquid crystal display element, the molecular axes of the nematic liquid crystal are horizontal to the substrate surface and have directionality, and as they move away from one Jk board surface, they are continuously twisted little by little until they face each other. The substrate surface is aligned so that it is twisted approximately 90 degrees near the other substrate surface.

By the way, the number of time divisions is 3 using the above TN type liquid crystal display element.
If two or more drives are performed, a problem arises in that display contrast and viewing angle decrease.

In order to solve these problems, improvements are being made in terms of liquid crystal compositions and cell configurations. For example, the number of time divisions is 3
With the aim of providing a display element with a high contrast ratio and a wide viewing angle, the liquid crystal material is designed to be a blend of n-type pyrimidine liquid crystal and demus ester liquid crystal. Constant ratio (K, , /3.
), but sufficient display performance has not yet been achieved.

Furthermore, it is known that characteristics suitable for time-division driving can be obtained by optimizing the birefringence (Δn) and cell thickness (d) of a liquid crystal composition. Shows sufficient multiplex characteristics under optimal conditions. However, a new problem arises in that the viewing angle becomes narrower, so a display element with excellent visibility cannot be obtained.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problems, and provides a liquid crystal display element whose display quality does not deteriorate even when the number of time divisions increases.

[Summary of the invention]

In the present invention, a liquid crystal composition prepared by adding and mixing a p-type dichroic dye to a nematic liquid crystal is injected into a TN cell, and the absorption axis of the polarizer is aligned with the alignment direction of the liquid crystal molecules.

The operating principle of the present invention will be explained with reference to FIG.

Polarizers 4 and 6 are arranged on both sides of a liquid crystal layer 2 made of liquid crystal containing a P-type dichroic dye and having a molecular arrangement twisted by 90 degrees. The absorption axes 5 and 7 of the polarizers 4 and 6 are arranged to coincide with the long axis direction of the liquid crystal molecules arranged on each side. When no voltage is applied to the liquid crystal display element, Figure 1a
As shown in , the transmitted light 8 becomes colored. On the other hand, when a voltage is applied, the liquid crystal molecules and the dichroic dye orient in the direction of the electric field, and the optical rotation ability of the liquid crystal layer 2 disappears, resulting in an uncolored (light-blocking) state, as shown in the figure. . As a result, a black display can be obtained against a lightly colored background, the range of good viewing angles for display can be widened, and a liquid crystal display element with excellent visibility can be obtained.

Note that adding and mixing a dichroic dye to a liquid crystal composition
For example, it is known as Special Publication No. 47-3778.

However, this material exhibits a colored state due to dye absorption when no voltage is applied, and exhibits an uncolored (transparent) state by changing the molecular arrangement of the liquid crystal when a voltage is applied. Since the orientation is parallel, time-division driving is difficult.

Further, the use of a liquid crystal composition to which a dichroic dye is added in a TN type liquid crystal display element is described in JP-A-52-8843. However, in this case, since the absorption axis of the polarizer is perpendicular to the alignment direction of the liquid crystal molecules, absorption occurs in the long axis direction of the dye when no voltage is applied.

In addition, when voltage is applied, the dye exhibits absorption in the short axis direction.
There is a problem that the background color is dark and the contrast is reduced.

In the present invention, the amount of p-type dichroic dye added to the liquid crystal material is preferably 0.1 wt% to 0.5 tit%,
If the amount is less than 0.1%+1%, the effect of adding the dichroic dye will not be obtained and the display quality will not be improved. Moreover, if it exceeds 0.511 t%, the multiplex performance will deteriorate and at the same time the display quality will deteriorate. In addition, as the p-type dichroic dye, for example, there are those shown in the table, but among them, 350-500 nm
A yellowish color having absorption in is preferable in order to improve visibility. Furthermore, all of the p-type dichroic dyes shown in the table are manufactured by Nippon Kanko Shiki.

(Margin below) [Embodiments of the invention] FIG. 2 shows a cross-sectional view of one embodiment of the invention.

Striped electrodes 13.15 are formed on each of the pair of electrode substrates 12.14. Electrode substrate 12.14
An alignment film of polyimide resin (manufactured by Hitachi Chemical, trade name HL-1100) is provided on the top using a spinner, and this film is rubbed with a cotton cloth roller] ゛N alignment layer 1
6.18 was formed. After that, an adhesive 19 is applied to the bonded portions of the peripheral substrates 12 and 14, and the two substrates are stacked and sealed so that their rubbing directions are perpendicular to each other.
It is a dot matrix type liquid crystal cell. In this liquid crystal cell, 0.25νt of p-type dichroic dye G-232 (manufactured by Nippon Kanko Shiki) was added to the liquid crystal material ZLI-2459 (manufactured by Merck & Co., Ltd.).
% liquid crystal composition 20 was injected and sealed. Thereafter, polarizers 22.24 are pasted on the outside of the electrode substrates 12.14 so that their respective absorption axes substantially coincide with the long molecular alignment direction of the liquid crystal on the respective substrate sides.
This is a nematic type liquid crystal display element.

A waveform voltage of 1732 duty was supplied from an external drive circuit to the liquid crystal display element thus prepared to turn it on. As a result, a black display was made on a pale f1 background color, and a display with excellent visibility was obtained.

〔Effect of the invention〕

According to this invention, even if the product (Δn-d) of the birefringence index (Δn) of the liquid crystal material and the cell thickness (d) is optimized to improve multiplex characteristics, the problem of narrow viewing angle can be solved. This problem is solved, and a liquid crystal display element with excellent visibility is realized.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the operation of the liquid crystal display element of the present invention, and FIG. 2 is a cross-sectional view of the liquid crystal display element of one embodiment of the present invention. 12, 14... Electrode substrate 13, 15... Electrode 16, 18... Alignment layer 20... Liquid crystal composition 22, 24... Polarizer... 2 Color/+4 dye fabricated island, mark cuff (V=D) 1750-F/force, (J='1) (b) Figure 1 Figure 2

Claims (3)

[Claims] (1) A twisted nematic liquid crystal layer between a pair of electrodes,
Further, in a TN type liquid crystal display element in which a pair of polarizers are arranged on both sides of the liquid crystal layer, a liquid crystal composition containing a p-type dichroic dye is used as the liquid crystal layer, and the absorption axes of the pair of polarizers are A liquid crystal display element characterized by aligning the liquid crystal molecules in the same direction. (2) The liquid crystal display element according to claim 1, which is driven in a time division number of 32 or more. (3) The liquid crystal display element according to claim 1, wherein the p-type dichroic dye is a yellow dye.