JPS61114291A - Liquid crystal display unit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

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

(Conventional structure and its problems) In general, a reflective liquid crystal display device has a liquid crystal sandwiched between a pair of transparent substrates on which transparent electrodes have been formed and which have been subjected to alignment treatment.
A structure is known in which a linear polarizing plate and a reflecting plate are attached to the outside of one substrate, and only a linear polarizing plate is attached to the outside of the other substrate, each of which is adhered with an adhesive or the like.

A liquid crystal display device must have good contrast, provide a bright display, and have good visibility. Therefore, in order to obtain a bright display with high contrast, it is desirable that the linear polarizing plate used has a good degree of polarization and good transmittance.

However, the characteristics of polarizing plates are that those with a good degree of polarization generally have poor transmittance, and those with good transmittance generally have a poor degree of polarization.

For this reason, the visibility of conventional liquid crystal display devices has been forced to sacrifice either contrast or brightness, which are contradictory, or to produce displays with poor visibility that compromise both of these characteristics. This is the actual situation. in this regard,
Attenuation of the amount of light in a liquid crystal display device having a conventional structure as shown in FIG. 1 will be explained in detail. In the figure, natural light 12 is polarized by a polarizing plate 9, passes through a polarizing plate 10 on the other side of the liquid crystal cell, and is reflected by a reflecting plate 11.

Thereafter, the light returns through the polarizing plate 1o and the liquid crystal cell once again, passes through the polarizing plate 9, and is observed as an image with shading.

Here, to simplify the explanation, it is assumed that there is no attenuation by the reflector [1], and the transmittance of the polarizing plate for natural light is T
, if the transmittance of the polarizing plate (when the axes are parallel) to polarized light is 'I'll, and the transmittance of the liquid crystal cell and output side polarizing plate to polarized light is TΔ, the natural light 12 first passes through the polarizing plate. 9, and further attenuates to TXTΔ when passing through the liquid crystal cell and the other polarizing plate 10. After that, the light returning from the reflecting plate 11 is attenuated to TXTΔXT by the polarizing plate 1o, and then once again transmitted by the liquid crystal cell and the polarizing plate 9 to TXTΔXT.
, IXTΔ and obtained as output light 12'.

That is, when a sufficient voltage is applied to the liquid crystal cell and the liquid crystal molecules are completely erected, the incident light 12 is 'rx'r,
, is returned as output light 12', but when the liquid crystal molecules are not completely busy, it decreases to TXTΔxTu. This relationship is shown in curve a in Figure 3. Here, an example is shown in which a polarizing plate with a transmittance of 40% is used. As is clear from the figure, when the applied voltage is low, the amount of output light 12' cannot be less than 2 inches of the amount of incident light 12, and for this reason, the negative display liquid crystal display device is When displaying images by time-division driving, there is a drawback that images are very dark and have poor visibility under normal room light.

(Object of the Invention) The present invention aims to eliminate such conventional drawbacks and to provide a liquid crystal display device that can provide a bright display with good contrast.

(Structure of the Invention) In order to achieve the above object, the liquid crystal display device of the present invention has transparent electrodes formed between a pair of transparent substrates subjected to alignment treatment.
A reflective liquid crystal display device comprising a pair of linearly polarizing plates and a reflecting plate sandwiching a liquid crystal cell sandwiching a liquid crystal, wherein a gap is provided between one substrate of the liquid crystal cell and the adjacent polarizing plate. The structure is such that light is allowed to enter through this gap.

(Explanation of Examples) Embodiments of the present invention will be described based on the drawings.

First, as shown in FIG. 2, an electrode 3 is formed by etching a transparent conductive film of indium oxide doped with tin provided on a transparent glass substrate 1. Next, an alignment film 5 is provided on the electrode side surface of the substrate 1, and the surface is rubbed in a certain direction with a cloth. Thereafter, a transparent electrode 4 and an alignment film 6 are formed in the same manner as on this substrate 1, and the other rubbed substrate 2 is placed facing each other so that the rubbing directions are perpendicular to each other, maintaining a predetermined gap, and the outer periphery. The cell is assembled by applying sealant 7 to the parts and pasting them together. Thereafter, a nematic liquid crystal having positive dielectric anisotropy or a mixed liquid crystal 8 obtained by adding an optically active material to the nematic liquid crystal is sealed in the cell to complete the liquid crystal cell. After that, a linear polarizing plate 10 is placed on the outside of one of the substrates 2 so that its polarization axis or absorption axis is parallel to the rubbing direction of the substrate 2, and the plate is closely attached to the substrate.
Further, a reflective plate 11 is attached to the outside thereof in close contact.

Next, a linear polarizing plate 9 is placed on the outside of the other substrate 1, and a polarizing plate 10 whose polarization axis or absorption axis is provided on the substrate 1 is placed on the outside of the other substrate 1.
facing parallel to the polarization axis or absorption axis of
In addition, it is arranged with a gap maintained between it and the substrate 1 so that light can be let in from between it and the substrate 1.

The reflective negative display liquid crystal display device completed in this way is configured to let in light from the gap between the polarizing plate 9 and the substrate 1, so that the natural light of the incident light 13 is absorbed by the polarizing plate 10 by T%. However, when the returned light T% passes through the polarizing plate 9, it is observed as an image with shading.

Here, if a sufficient voltage is applied to the liquid crystal cell and the liquid crystal molecules are completely erected, the output light 13' will have a brightness of 'rx'r,, 2, and even when it is not completely erected, 'l'XT ,
Only IXTΔ comes out. FIG. 3 shows the ratio of output light and incident light to the applied voltage of the liquid crystal display device. In the figure, a shows the characteristics of a conventional configuration, and b shows the characteristics of an embodiment of the configuration of the present invention. As is clear from the figure, the characteristics of the configuration of the present invention are 10 to 25 times brighter than the conventional configuration, especially in the low voltage range.
An image with good visibility was obtained.

(Effects of the Invention) As explained above, the present invention makes it possible to dramatically brighten the display in a reflective negative liquid crystal display device and significantly improve the display quality by simply improving the construction method of the polarizing plate. .

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a conventional reflective liquid crystal display device, FIG. 2 is a structural cross-sectional view showing an embodiment of the reflective liquid crystal display device of the present invention, and FIG. 3 is a voltage applied to the liquid crystal display device. FIG. 3 is a characteristic diagram showing the relationship between the output image and the output scene, where a shows the characteristics of a conventional liquid crystal display device, and b shows the characteristics of the liquid crystal display device of the present invention. 1.2...Transparent substrate, 3,4...Transparent electrode, 5,6...
・Liquid crystal alignment film, 7...Sealing agent, 8...Liquid crystal, 9,1
゜... linear polarizing plate, 11... reflecting plate, 12.13.
-Incoming light, 12', 13'...output light. Figure 1 Figure 2

Claims (1)

[Claims] A reflective liquid crystal display device comprising a pair of linearly polarizing plates and a reflector, which sandwich a liquid crystal cell in which a liquid crystal is sandwiched between a pair of transparent substrates on which transparent electrodes are formed and which have been subjected to alignment treatment, the liquid crystal cell being A liquid crystal display device characterized in that a gap is provided between one of the substrates and the linear polarizing plate adjacent thereto, and light is let in through the gap.