JPH0440411A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain a bright display, to eliminate its coloring, and to prevent the display from being seen double by using a liquid crystal and the orientation distribution which obtain nearly linear polarized light when light made incident on a liquid crystal cell reaches a reflecting plate. CONSTITUTION:A polyimide orienting film 13 is applied on a glass substrate 11 where an ITO transparent electrode 12 is formed and a pair of substrates which are rubbed is adhered together across a sealant 15. Then the liquid crystal cell formed by heating and charging the liquid crystal 14 in the substrate gap is held between a polarizing plate 16 and the reflecting plate 17 and a lighting device 18 which makes light incident from the flanks of the glass substrates 11 is provided to obtain the element. Then the liquid crystal and orientation distribution which obtain the nearly linear polarized light when the light made incident on the liquid crystal cell reaches the reflecting plate 17 are employed. Consequently, the display is bright, colored only little, and not seen double.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a reflective liquid crystal display element.

[Prior Art] Reflective TN mode and STN mode liquid crystal display elements have low power consumption and are therefore widely used in display devices such as portable personal computers and word processors. A conventional reflective liquid crystal display element consists of a liquid crystal cell, two polarizing plates placed on both sides of the liquid crystal cell, and a reflecting plate provided outside the polarizing plates.

[Problems to be Solved by the Invention] However, conventional liquid crystal display devices using reflective TN mode or STN mode have problems such as dark display and double images depending on the angle.

Particularly in the reflective STN mode, coloring of the display was also a problem.

The present invention has been made to solve the above-mentioned problems, and its purpose is to introduce a new reflective liquid crystal mode and add an illumination device to produce a reflective liquid crystal display that is bright, non-colored, and does not display double images. The purpose is to provide display elements.

[Means for Solving the Problems] In order to solve the above problems, the liquid crystal display element of the present invention has the following features: (1) a liquid crystal cell formed by sandwiching twisted oriented nematic liquid crystal between two substrates having electrodes; In a liquid crystal display element equipped with two polarizing plates, one reflective plate, and a means for inputting light from the side surface of the substrate constituting the liquid crystal cell, a state in which the light incident on the liquid crystal cell reaches the reflective plate. It is characterized by the use of a liquid crystal and orientation distribution that produces almost linearly polarized light.

(2) In the liquid crystal cell, the twist angle of the liquid crystal molecules is 0.
degree or more and 70 degrees or less, the absolute value of the product of the birefringence index of the liquid crystal and the cell gap is 0.2 μm or more and 0.7 μm or less, and the direction of the polarization axis (absorption axis or transmission axis) of the polarizing plate is similar to that of the polarizing plate. It is characterized in that the angle formed between the substrate interface on the side in contact with the polarizing plate and the long axis direction of the liquid crystal molecules is 35 degrees or more and 115 degrees or less, with the twist direction of the liquid crystal molecules being positive.

(3) In the liquid crystal cell, the twist angle of the liquid crystal molecules is 1
The angle is 70 degrees or more and 270 degrees or less, and the absolute value of the product of the birefringence index of the liquid crystal and the cell gap is 0.4 μm or more and 1.0 μm or less.

(4) At least one of the two substrates constituting the liquid crystal cell has a step difference of 0° or more than 1 μm on the liquid crystal side surface.
It is characterized by providing unevenness of μm or less.

(5) The reflective plate is provided on the liquid crystal side surface of the liquid crystal cell substrate.

[Example] (Example 1) FIG. 1 is a sectional view of a liquid crystal display element of the present invention.

■A liquid crystal cell in which a pair of substrates in which a polyimide alignment film 13 is coated and rubbed on a glass substrate 11 on which transparent electrodes 12 are formed are bonded together via a sealant 15, and a liquid crystal 14 is heated and sealed in the gap between the substrates. The polarizing plate 16 and the reflecting plate 17
A device was obtained by providing an illumination device 18 which was sandwiched between the glass substrates 11 and irradiated light from the side surface of the glass substrate 11. ZLI4472 manufactured by Merck & Co. (birefringence Δn=0.0871) was used as the liquid crystal, and the cell gap d was set to 5.3 μm. The product of birefringence and cell gap (Δnd, hereinafter referred to as retardation) is 0.46 μm.

FIG. 3 is a diagram showing the relationship between the axes of the liquid crystal display element of the present invention as viewed from the viewing direction. 33 is the polarization axis direction of the polarizing plate, 34
is the rubbing direction of the upper substrate, and 35 is the rubbing direction of the lower substrate. Further, 31 indicates the angle θ (the twist direction of the liquid crystal is a positive value) formed by 33 and 34, and 32 indicates the twist angle of the liquid crystal. Here, the angle θ was set to 4 degrees, and the twist angle was set to 60 degrees to the left. When we applied an alternating current electric field to the device fabricated using the above method and measured its voltage reflectance characteristics, we found that normal TN
The same level of steepness as the mode was obtained. The maximum possible contrast ratio is 1:42, and the duty ratio is 1/42.
Multiplex driving of 2 to 1/16 is also possible.

(Example 2) The device of this example also has the configuration shown in FIG. The liquid crystal used was Merck ZLI-4427 (△n=0.1127),
The cell gap d was set to 6.6 μm. Retardation Δnd=0.74 μm. Here, polyimide RN-721 manufactured by Nissan Chemical Industries, Ltd. was used as the alignment film, and a pretilt angle of about 10 degrees was given to the liquid crystal molecules at the interface by rotational rubbing of a rayon flocked cloth. Also, in Fig. 3, the angle 31
(θ) was set to 14 degrees, and the twist angle 32 was set to 255 degrees to the left. The device thus obtained had a very good voltage reflectance characteristic steepness, and therefore exhibited a high contrast ratio of 1:23 even when multiplex driving was performed at a duty ratio of 1/480.

Since the lighting device is provided on the side of the substrate, good display performance can be obtained even in dark surroundings.

(Example 3) FIG. 2 is a cross-sectional view of the liquid crystal display element of this example. A reflective film 21 which also served as a pixel electrode was provided on the liquid crystal layer side of the lower substrate.

This reflective film 21 is a thin aluminum film formed by sputtering on the surface of ground glass having a surface unevenness of about 0.5 μm, and has a reflection characteristic with little directivity. As in Example 1, ZLI-4472 was used as the liquid crystal, the average Δnd was set to 0.46 μm, the twist angle was set to 60 degrees, and the angle θ was set to 4 degrees. By arranging the reflector in the liquid crystal cell in this manner, it is possible to solve the problem of double images peculiar to conventional reflective liquid crystal display elements. Furthermore, there is also the secondary effect that minute variations in the thickness of the liquid crystal layer average out the displayed colors and reduce coloration.

The material for the electrode/reflection film may be any silvery white material such as nickel or chromium in addition to aluminum, and the surface irregularities may be formed by polishing or chemical treatment.

When patterning this electrode/reflection film, there are two methods: one is to directly form a metal thin film, and the other is to provide a transparent electrode on the metal thin film via an insulator and pattern the transparent electrode. The latter is because the insulating layer has the effect of alleviating surface irregularities.
This is particularly effective when the twist angle is large and the d/p margin (p: spontaneous pitch of the liquid crystal) is narrow.

[Effect of the invention J As described above, according to the present invention, by introducing a new reflective liquid crystal mode and adding an illumination means, a liquid crystal display element that is bright, has little color change, and does not display double images can be obtained. can be provided.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a liquid crystal display element in Examples 1 and 2 of the present invention. FIG. 2 is a cross-sectional view of a liquid crystal display element in Example 3 of the present invention. FIG. 3 is a diagram showing the positional relationship of the axes of each element in the liquid crystal display element of the present invention. Substrate Transparent electrode alignment film Liquid crystal layer sealing member Polarizing plate Reflecting plate Lighting device Reflective film that also serves as pixel electrode Angle θ between the polarizing axis direction of the polarizing plate and the rubbing direction of the upper substrate Twist angle of liquid crystal Polarizing axis direction of the polarizing plate Upper substrate Rubbing direction Lower board rubbing direction or higher Applicant Seiko Epson Co., Ltd. Agent Patent attorney Kizobe Suzuki (1 person) = 72 = Figure

Claims (5)

[Claims] (1) A liquid crystal cell consisting of a twisted nematic liquid crystal sandwiched between two substrates having electrodes, one polarizing plate, one reflecting plate, and light incident from the side of the substrates constituting the liquid crystal cell. What is claimed is: 1. A liquid crystal display element equipped with a means for controlling the liquid crystal cell, characterized in that the liquid crystal and orientation distribution are used such that light incident on the liquid crystal cell becomes substantially linearly polarized light when it reaches a reflecting plate. (2) In the liquid crystal cell, the twist angle of the liquid crystal molecules is 0.
degree or more and 70 degrees or less, the absolute value of the product of the birefringence index of the liquid crystal and the cell gap is 0.2 μm or more and 0.7 μm or less, and the direction of the polarization axis (absorption axis or transmission axis) of the polarizing plate is similar to that of the polarizing plate. 2. The liquid crystal display according to claim 1, wherein the angle formed between the substrate interface on the side in contact with the polarizing plate and the long axis direction of the liquid crystal molecules is 35 degrees or more and 115 degrees or less, with the twist direction of the liquid crystal molecules being positive. element. (3) In the liquid crystal cell, the twist angle of the liquid crystal molecules is 1
2. The liquid crystal display element according to claim 1, wherein the angle is 70 degrees or more and 270 degrees or less, and the absolute value of the product of the birefringence index of the liquid crystal and the cell gap is 0.4 μm or more and 1.0 μm or less. (4) There is a step difference of 0.1 μm or more on the liquid crystal side surface of at least one of the two substrates constituting the liquid crystal cell.
2. The liquid crystal display element according to claim 1, wherein the liquid crystal display element is provided with irregularities of .mu.m or less. (5) The liquid crystal display element according to claim 1, wherein the reflective plate is provided on the liquid crystal side surface of the liquid crystal cell substrate.