JPH04338714A - Liquid crystal electrooptic element - Google Patents

Abstract

PURPOSE:To offer a color liquid crystal display element which is used suitably as a light valve for, specially, a single plate type liquid crystal projector. CONSTITUTION:The liquid crystal electrooptic element consists of a liquid crystal cell, formed by sandwiching nematic liquid crystal between two opposite arranged electrodes, and a couple of polarizing plates, and the twist angle of the liquid crystal is 80-100 deg.; and the couple of polarizing plates are so arranged that the axes of transmission or absorption cross each other at right angles and the axis of transmission or absorption of one polarizing plate deviates from the liquid crystal molecule orienting direction of an adjacent electrode substrate by 40-50 deg.. Then the retardation nd of a liquid crystal layer is at least >=0.9mum.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal electro-optical device, and more particularly to a liquid crystal electro-optic device suitable for use as a light valve for a liquid crystal projector.

0002

2. Description of the Related Art A liquid crystal electro-optical element used as a light valve for a conventional liquid crystal projector uses a TN mode in which the display is less colored. In order to perform a color display, a high definition and bright display is generally possible by using three light valves for each of red, green, and blue in combination with a color filter.

However, such a projector using three light valves requires a complicated optical system and tends to be expensive, which is hindering its widespread use. For this reason, so-called single-panel projectors have been proposed that provide color display using only one light bulb, but in principle they merely project an enlarged image of an LCD TV;
Since one pixel is composed of three blue pixels, the resolution is reduced and the light usage efficiency is poor, resulting in a dark display.

[0004] Therefore, a homogeneous type E that changes color by controlling the birefringence of liquid crystal without using a color filter has been developed.
CB mode light valves have been proposed. Although ECB mode light bulbs cannot display full color, they can display multicolors such as white, reddish-purple, green, blue-cyan, and yellow, because they change the spectral transmittance of the pixel itself without using a color filter. , high-definition and bright display is possible. Furthermore, the poor viewing angle characteristics, which has been considered a problem in the conventional homogeneous ECB mode, will not be a problem as long as it is used as a light valve for a projector.

[0005]

However, in the conventional homogeneous ECB mode, a high contrast ratio could not be obtained because the transmittance does not decrease over the entire visible light range. Figure 5 shows retardation △nd
The color change of transmitted light when a voltage is applied to an ECB mode liquid crystal cell with 1.00 μm is shown on the chromaticity coordinates. FIG. 6 shows changes in transmittance with visibility correction. In the conventional ECB mode, the displayed color can be changed by changing the applied voltage, but since the transmittance does not decrease, black cannot be expressed. Therefore, it was not possible to obtain a display with a high contrast ratio.

Therefore, the present invention optimizes the cell conditions such as the twist angle of the liquid crystal layer, the retardation △nd, and the polarizing plate arrangement angle, and applies a voltage to the liquid crystal layer so that the displayed color is the same as that of the conventional ECB mode. The object of the present invention is to propose a liquid crystal display mode in which the display can be changed to a state where the transmittance is small, that is, the display can be made black, and realize a display with a high contrast ratio.

[0007]

[Means for Solving the Problems] The liquid crystal electro-optical element of the present invention includes a liquid crystal cell formed by sandwiching a nematic liquid crystal between two electrode plates arranged oppositely, and a liquid crystal cell arranged on both sides with the liquid crystal cell sandwiched therebetween. the nematic liquid crystal has a helical structure with a twist angle in the range of 80 degrees to 120 degrees, and the pair of polarizing plates have transmission axes or absorption axes orthogonal to each other; The transmission axis or absorption axis of one of the polarizing plates is 40 degrees parallel to the liquid crystal molecule orientation direction of the adjacent electrode substrate.
The product Δnd of the refractive index anisotropy Δn of the nematic liquid crystal and the thickness d of the liquid crystal layer is at least 0.9 μm. Further, it is characterized in that at least one of the two electrode substrates arranged facing each other has an active element such as a TFT or MIM.

[0008]

[Example] An example of the present invention is shown below in Figs. 1, 2, and 3.
This is explained by:

As an embodiment of the present invention, the number of pixels is 640×
We created a light valve for a 2-inch diagonal LCD projector with 400 TFT elements. FIG. 1 shows the rubbing direction of the upper and lower electrode substrates and the arrangement of the polarizing plates of the liquid crystal electro-optic device produced in this example. 102 is the rubbing direction of the upper electrode substrate. 103 is the rubbing direction of the lower electrode substrate. 105 is the twist angle direction of the liquid crystal in the liquid crystal cell. This time, the twist angle was set to 90 degrees. This liquid crystal cell has 640 x 400 poly-Si layers on the lower substrate.
It includes a TFT element, and a black mask on the upper substrate that blocks light leaking between pixels. Furthermore, polyimide is formed as an alignment film to a thickness of 500 Å on both the upper and lower substrates. The liquid crystal cell is a liquid crystal manufactured by Chisso (△n=0.15
) was used to achieve twisted orientation between two electrode substrates. Further, the liquid crystal layer d was set to 10.0 μm so that Δnd was 1.50 μm. In this liquid crystal cell, the transmission axis direction 101 of the upper polarizing plate was shifted by 45 degrees from the rubbing direction 102 of the upper electrode substrate. Further, the transmission axis direction 104 of the lower polarizing plate was arranged to be perpendicular to the transmission axis direction 101 of the upper polarizing plate. FIG. 2 shows the color change of the light valve manufactured in this example with respect to the applied voltage on the chromaticity coordinates. FIG. 3 shows the change in transmittance of the light valve manufactured in this example with respect to the applied voltage. The light valve of the present invention is white at an applied voltage of 1.5V, green at 2.3V, cyan at 2.4V, blue at 2.6V, magenta at 3.0V, red at 3.3V, and yellow at 3.5V. By setting the voltage to black at 4.0 V or higher and driving it, it was possible to display an eight-color multicolor display compatible with the CRT screen of a personal computer. Further, the ratio of brightness between white and black, that is, the contrast ratio, was obtained to be 1:100 or more.

Although the embodiments have been described above, the present invention can be applied not only to the above embodiments but also to a wide variety of liquid crystal display elements as active matrix liquid crystal display modes.

[0011]

As described above, according to the present invention, there is an effect that a multi-color liquid crystal display element with high brightness and high contrast ratio can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the rubbing direction and polarizing plate arrangement of a liquid crystal cell of a liquid crystal electro-optic device manufactured in an example of the present invention.

FIG. 2 is a diagram showing a color change of transmitted light with respect to an applied voltage of a liquid crystal electro-optical element manufactured in an example of the present invention.

FIG. 3 is a diagram showing changes in the amount of transmitted light with respect to applied voltage of a liquid crystal electro-optical element manufactured in an example of the present invention.

FIG. 4 is a diagram showing the rubbing direction and polarizing plate arrangement of a liquid crystal cell of a conventional homogeneous ECB mode liquid crystal electro-optical element.

FIG. 5 is a diagram showing a color change of transmitted light with respect to an applied voltage of a conventional homogeneous ECB mode liquid crystal electro-optical element.

FIG. 6 is a diagram showing changes in the amount of transmitted light with respect to applied voltage of a conventional homogeneous ECB mode liquid crystal electro-optical element.

[Explanation of symbols]

101 Transmission axis direction of upper polarizing plate 102 Rubbing direction of upper electrode substrate 103 Rubbing direction of lower electrode substrate 104 Transmission axis direction of lower polarizing plate 105 Twist angle direction of liquid crystal in liquid crystal cell 301
Transmission axis direction 302 of upper polarizing plate Rubbing direction 303 of upper electrode substrate Rubbing direction 304 of lower electrode substrate Transmission axis direction of lower polarizing plate

Claims (2)

[Claims] 1. A liquid crystal cell comprising a nematic liquid crystal sandwiched between two electrode plates disposed facing each other, and a pair of polarizing plates disposed on both sides of the liquid crystal cell, wherein the nematic liquid crystal is The pair of polarizing plates have a helical structure with a twist angle in the range of 80 degrees to 100 degrees, and the transmission or absorption axes of the pair of polarizing plates are perpendicular to each other, and the transmission or absorption axis of either polarizing plate is opposite to the adjacent electrode. The liquid crystal molecule alignment direction of the substrate and 40
A liquid crystal electro-optical element, which is arranged 50 degrees from the nematic liquid crystal, and has a product Δnd of the refractive index anisotropy Δn of the nematic liquid crystal and the thickness d of the liquid crystal layer of at least 0.9 μm. 2. The liquid crystal electro-optical device according to claim 1, wherein at least one of the two electrode substrates arranged facing each other has an active element such as a TFT or an MIM.