JP2543682B2 - Liquid crystal electro-optical device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a scattering type liquid crystal display device using liquid crystal.

[Conventional technology]

As a conventional scattering type liquid crystal display using a liquid crystal, a film-like display device in which DSM (dynamic scattering effect mode) or liquid crystal encapsulated as disclosed in JP-A-59-178429 is known.

[Problems to be solved by the invention]

However, in the above-mentioned conventional technology, the current flows in the cell, the reliability of the liquid crystal display device is low (DSM type), the driving voltage is as high as 50 V or more, and the manufacturing method is also special, and the conventional process is not used. (Liquid crystal capsule type) There was a problem.

Therefore, the present invention solves such a problem,
An object of the invention is to provide a field effect liquid crystal display device which has a high light transmission characteristic in one switching state and can be driven at a low voltage. Another object of the present invention is to provide a liquid crystal display device which can utilize the conventional manufacturing process as it is.

[Means for solving problems]

The liquid crystal electro-optical device of the present invention is a liquid crystal electro-optical device in which a liquid crystal layer is sandwiched between a pair of substrates having electrodes on the inner surfaces of the opposing substrates, wherein a plurality of transparent substances are dispersed in the liquid crystal layer, The surface of the transparent material is subjected to an alignment treatment, and incident light is scattered by the transparent material dispersed in the liquid crystal layer.

The second liquid crystal electro-optical device according to the present invention is characterized in that the substrate surface is subjected to a treatment for aligning liquid crystal molecules of the liquid crystal layer substantially in parallel.

A third liquid crystal electro-optical device according to the present invention is characterized in that a refractive index of liquid crystal molecules of the liquid crystal layer with respect to normal light is substantially equal to a refractive index of the transparent material.

A fourth liquid crystal electro-optical device according to the present invention is characterized in that the liquid crystal layer contains a cholesterol derivative.

A fifth liquid crystal electro-optical device according to the present invention is characterized in that the liquid crystal layer contains a dichroic dye.

[Work]

According to the above configuration of the present invention, light scattering that occurs between liquid crystal materials that are sealed between opposed substrates and transparent particles that are dispersed between the liquid crystal materials, and light scattering that occurs due to minute alignment defects in the liquid crystal materials. The phenomenon can be controlled by a voltage applied from the outside to display.

The maximum diameter of the dispersed transparent particles was set to be equal to or smaller than the substrate gap, whereby minute light scattering centers were obtained. Further, by giving a vertical alignment treatment to the transparent particles, uniform alignment defects are generated on the entire display device, and light scattering at the interface between the particles and the liquid crystal can be controlled. When the same alignment control is performed also on the substrate side, a more uniform display is obtained, and the most effective alignment processing is parallel alignment.

In the present invention, since the birefringence of the liquid crystal material and the refractive index change in the minute region of the transparent particles are used as a scattering phenomenon, in the transparent state where a voltage is applied, the refractive index of the liquid crystal to normal light is Since it is almost equal to the refractive index, an ON state with excellent transparency can be obtained. This is to obtain high optical switching characteristics. Further, in the light-scattering state, high light-scattering ability was also obtained by containing a cholesterol derivative in the liquid crystal. Further, the scattered light is absorbed by the dichroic dye, and more excellent optical switch characteristics can be obtained.

〔Example〕

Embodiment 1. FIG. 1 is a sectional view of a liquid crystal display device according to the present invention.
Transparent particles 102 are dispersed in a liquid crystal composed of liquid crystal molecules 101,
It is enclosed between the substrates 105. The electrode 103 is a voltage applying means, and thereby a pixel is formed. 104 represents a power supply. 106 is incident light, 107 is outgoing light, and 108 is scattered light.

 Specifically, it has the configuration shown in Table 1.

The refractive index of this liquid crystal is different for normal light and extraordinary light.
They are 1.68 and 1.50. The refractive index of the transparent particles is 1.46, which is close to the normal light refractive index of the liquid crystal. As will be described later, this can suppress light scattering in the transmission state and obtain high contrast.

In FIG. 1, a voltage application state (hereinafter referred to as an ON state, the left side in FIG. 1) and a voltage non-application state (hereinafter referred to as an OFF state) are shown.
The right side of FIG. 1) is depicted. In the OFF state on the right side, the substrate is subjected to parallel alignment treatment and the transparent particles are subjected to vertical alignment treatment. Thus, the liquid crystal molecules tend to be oriented parallel at the substrate interface and vertically at the transparent particle interface. For this reason, many discontinuous points of orientation called disclinations occur. This gives an apparent cloudy light scattering. Furthermore, liquid crystal has a higher isotropic refractive index than transparent particles.
Since it has a large extraordinary refractive index of 0.2 or more, the optical path is largely refracted or reflected depending on the direction of incident light.
This also causes light scattering. Since these light scattering factors exist uniformly and randomly between the substrates, the OFF state becomes a cloudy light scattering state, and the incident light 106 diffuses the light as shown by 108.

On the other hand, in the ON state shown on the left side of FIG. 1, an external electric field is applied and a torque according to the dielectric anisotropy of the liquid crystal acts on the liquid crystal molecules. Therefore, when a torque stronger than the alignment force acts, the liquid crystal molecules are rearranged perpendicularly to the substrate as shown in the figure. In this state, the refractive index of the incident light 106 received from the liquid crystal is the normal light refractive index, which is 1.50 in this case. By the way, since the refractive index of transparent particles is 1.46, which is a close value, the refracting power received by incident light is small. Further, the alignment defects of the liquid crystal disappear by rearrangement due to an external electric field. From these, a transparent ON state is obtained. 107 is the outgoing light transmitted in this way.

The solid line in FIG. 2 represents the applied voltage-transmittance characteristic of the liquid crystal display device thus obtained.

The characteristics shown by the broken line in FIG. 2 are those of the liquid crystal display device manufactured without performing the alignment treatment. Although the display characteristics are degraded, it indicates that operation is possible.

Example 2 Example 2 is a liquid crystal display device in which a small amount of a cholesterol derivative is mixed with liquid crystal to enhance the scattering ability. The basic structure is the same as in the first embodiment. Table 2 shows a specific configuration.

Table 2 Liquid crystal Nematic liquid crystal ZLI-1691 CB-15 (cholesterol derivative) 1.5 wt% added (Merck Japan Ltd.) Transparent particles AEROSIL (maximum particle size 10 μm) No alignment treatment Substrate Pyrex glass electrode ITO transparent electrode The applied voltage-transmittance characteristic of the liquid crystal display device obtained by the constitution is shown by the solid line in FIG. A cholesterol derivative-free product is indicated by a broken line. As can be seen from this, the driving voltage increased, but the transmittance in the OFF state decreased. In addition, the uniformity of the entire display is improved, and an effect that alignment processing is not required is brought about.

Example 3 Example 3 is a liquid crystal display device in which a dichroic dye is added to liquid crystal to improve display characteristics. The basic structure is the same as in the first embodiment. Table 3 shows the specific configuration.

FIG. 4 shows the applied voltage-transmittance characteristics of the liquid crystal display device having such a structure. Thus, a high-contrast liquid crystal display device was obtained. The reason why the contrast is improved is that in addition to the decrease in transmittance due to light scattering when OFF,
This is because of the absorption of light by the dichroic dye. On the contrary, when ON, the dichroic dye is rearranged together with the liquid crystal molecules, light absorption is reduced, and a higher light transmittance can be obtained as compared with a dye that isotropically absorbs light.

〔The invention's effect〕

With the above configuration, the following effects can be obtained.

That is, a liquid crystal electro-optical device that can be driven at a low voltage can be realized by using a structure in which a plurality of transparent substances are dispersed in the liquid crystal layer.

[Brief description of drawings]

FIG. 1 is a sectional view of a part of the liquid crystal display device of the present invention. FIG. 2 is a diagram showing applied voltage-transmittance characteristics. FIG. 3 is a diagram showing applied voltage-transmittance characteristics when a liquid crystal added with a cholesterol derivative is used. FIG. 4 is a diagram showing applied voltage-transmittance characteristics when a dichroic dye is added. 101 ... Liquid crystal molecule 102 ... Transparent particle 103 ... Electrode 104 ... Power supply 105 ... Substrate

Claims (5)

(57) [Claims] 1. A liquid crystal electro-optical device in which a liquid crystal layer is sandwiched between a pair of substrates having electrodes on the inner surfaces of opposing substrates, wherein a plurality of transparent substances are dispersed in the liquid crystal layer. A liquid crystal electro-optical device characterized in that an incident light is scattered by the transparent substance dispersed in the liquid crystal layer, the surface of which is subjected to an alignment treatment. 2. The liquid crystal electro-optical device according to claim 1, wherein the surface of the substrate is subjected to a treatment for aligning liquid crystal molecules of the liquid crystal layer substantially in parallel. 3. The liquid crystal electro-optical device according to claim 1, wherein a refractive index of liquid crystal molecules of the liquid crystal layer with respect to normal light is substantially equal to a refractive index of the transparent material. 4. The liquid crystal electro-optical device according to claim 1, wherein the liquid crystal layer contains a cholesterol derivative. 5. The liquid crystal electro-optical device according to claim 1, wherein the liquid crystal layer contains a dichroic dye.