JP2001201735A - Liquid crystal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device necessitating no backlight and having an advantage of a thinner size. SOLUTION: Parallel rays of light are produced from the light emitted by a light source 13 and are made to irradiate a cholesteric liquid crystal layer 7 held between transparent electrodes 5 and 6 from the lateral direction. When no voltage is applied between the transparent electrodes 5 and 6, a focal conic polydomain texture is formed in the liquid crystal layer 7. Thereby the light irradiating the liquid crystal layer 7 is scattered and emitted from the transparent electrode 5 to the outside of the liquid crystal cell 8 (a light emitting state). When a voltage is applied between the transparent electrodes 5 and 6, the liquid crystal layer 7 gets into a homeotropic alignment state and the light irradiating the liquid crystal layer 7 goes straight on hardly being scattered. Thereby there is almost no light emitted from the transparent electrode 5 to the outside of the liquid crystal cell 8 (a dark state).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for modulating light intensity and displaying information by utilizing a state change of a liquid crystal in response to an electric field. Such a device is referred to herein as a liquid crystal device.

[0002]

2. Description of the Related Art Today, various liquid crystal devices such as an optical modulator, an optical shutter, and a liquid crystal display are generally used. Most of these liquid crystal devices include a liquid crystal cell in which a twisted liquid crystal (twisted liquid crystal) is sandwiched between a pair of plate-shaped or film-shaped transparent electrodes, and a pair of liquid crystal cells mounted on outer surfaces of the pair of transparent electrodes, respectively. It has a polarizing plate, and transmits / blocks light using a change in optical rotation caused by a change in the alignment state of liquid crystal in response to an electric field. Such a liquid crystal device is hereinafter referred to as a polarization type liquid crystal device.

[0003]

The polarization type liquid crystal device includes:
When the illumination light passes through two polarizing plates, there is a problem that most of the energy of the light is lost. For this reason, for example, in a liquid crystal display, a backlight that is strong enough to ensure a sufficient light emission amount of the liquid crystal cell even after loss of light energy must be used, which hinders reduction in power consumption. Further, in general, a backlight is configured to obtain uniform surface illumination by combining a light source such as a fluorescent lamp and a reflector or a light guide, but when the backlight having such a configuration is to be made thinner, Problems such as a decrease in luminance and noticeable spots occur. That is, the use of a backlight having a high light intensity hinders further reduction in the thickness of the liquid crystal display.

[0004]

A liquid crystal device according to the present invention, which has been made to solve the above-mentioned problems, comprises a pair of plate-like or film-like electrodes including a transparent electrode disposed on a light-emitting surface side, and the pair of electrodes. A liquid crystal cell including a chiral liquid crystal layer sandwiched between the electrodes, and an illuminating means for irradiating the chiral liquid crystal layer with light emitted from a light source from the side.

In the specification of the present application, cholesteric liquid crystal (chiral nematic liquid crystal) or a mixture of cholesteric liquid crystal and chiral smectic C liquid crystal is used.
A liquid crystal material in which the texture (texture) of the liquid crystal changes between a polydomain texture and a homeotropic texture in response to a change in the electric field is collectively referred to as a chiral liquid crystal.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid crystal device using a chiral liquid crystal has been known (for example, see Japanese Patent Application Laid-Open No. 4-1193).
Japanese Patent Application Laid-Open No. 5-8815
No. 0 publication). This type of liquid crystal device includes a liquid crystal cell including a pair of plate-shaped or film-shaped transparent electrodes and a chiral liquid crystal layer sandwiched between the pair of transparent electrodes. In such a liquid crystal device, when no voltage is applied between the transparent electrodes, the chiral liquid crystal forms a focal conic polydomain structure and scatters light. Cannot pass (dark state). On the other hand, when a voltage is applied between the transparent electrodes, the chiral liquid crystal is in a homeotropic alignment state, and light that has entered the liquid crystal cell substantially perpendicularly to one transparent electrode (light receiving surface side) passes through the liquid crystal while the other liquid crystal transmits the liquid crystal. Light is emitted from the transparent electrode (light emitting surface side) (light emitting state). In such a liquid crystal device (hereinafter referred to as a scattering type liquid crystal device), there is no loss of light energy as described above due to the use of a polarizing plate.

The liquid crystal device according to the present invention utilizes a liquid crystal cell including a chiral liquid crystal layer having the above-described characteristics, and transmits light emitted from a light source to the chiral liquid crystal layer from the side (in a direction substantially parallel to the electrodes). ) Illumination means for irradiation is provided. In the liquid crystal device according to the present invention, the relationship between the presence or absence of application of a voltage between the electrodes and the state of the liquid crystal cell (dark / light emission) is opposite to that of the above-mentioned conventional scattering type liquid crystal device. First, when a voltage is applied between the electrodes, the chiral liquid crystal is in a homeotropic alignment state, and the light applied to the chiral liquid crystal layer from the side travels straight without being scattered, so that the light is emitted from the transparent electrode to the outside of the liquid crystal cell. There is almost no light (dark state). On the other hand, when no voltage is applied between the electrodes, the chiral liquid crystal forms a focal conic polydomain structure and scatters light. The light is emitted to the outside (light emission state).

In the liquid crystal device according to the present invention, a transparent electrode may be used only for the electrode disposed on the light emitting surface side, and the other electrode does not need to be a transparent electrode. Can be mirror-finished. If both electrodes are transparent, a double-sided light emitting liquid crystal device can be obtained.

In the liquid crystal device according to the present invention, the chiral liquid crystal layer has a structure in which a large number of grains (vesicles) are formed by wrapping a small volume of chiral liquid crystal exhibiting a focal conic polydomain structure with a transparent polymer thin film. You may have it. In this way, in addition to the light scattering by the focal conic polydomain structure, light scattering is also caused by the grain interface, so that the light scattering effect as a whole is further enhanced.

[0010]

In the liquid crystal device according to the present invention, no light energy loss is caused by the use of the polarizing plate, so that the output of the light source can be sufficiently reduced. Further, the present invention does not use a conventional backlight, which is advantageous in reducing the thickness of the liquid crystal device.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid crystal light emitting device as an embodiment of the liquid crystal device according to the present invention will be described with reference to FIG. The liquid crystal light emitting device 1 of the present embodiment has a pair of glass plates 3 and 4 opposed to each other at a fixed interval defined by a spacer (not shown), and a film-like transparent film formed inside the glass plates 3 and 4. Electrodes 5 and 6 (for example, an indium oxide (Indium Tin Oxide) film doped with tin oxide) and a transparent electrode 5
And a liquid crystal cell 8 composed of a cholesteric liquid crystal layer 7 sandwiched between. The cholesteric liquid crystal layer 7 is a layer having a structure in which a large number of grains (having a diameter of 1 to 2 μm) formed by wrapping a small volume of cholesteric liquid crystal exhibiting a focal conic polydomain structure with a transparent polymer thin film 9 are stacked. Such a structure can be obtained, for example, by mixing a photopolymerizable polymer and a liquid crystal, and depositing the liquid crystal by photopolymerization phase separation while wrapping a small volume of the liquid crystal with a polymer thin film. The thickness of the cholesteric liquid crystal layer 7 may be appropriately determined in the range of, for example, 5 to 60 μm according to the use (application form) of the liquid crystal light emitting device 1, such as improvement in contrast, reduction in driving voltage, improvement in response speed, and the like. In order to satisfy the requirement in a well-balanced manner, the thickness is preferably about 7 to 15 μm (in the figure, the size of the grains is exaggerated compared to the thickness of the cholesteric liquid crystal layer 7). The transparent electrodes 5 and 6 are connected to a power source 10 and a switch 1
When 1 is turned on, a voltage is applied between the transparent electrodes 5 and 6. The lens 1 is located near one end of the liquid crystal cell 8.
2 are arranged. The lens 12 serves to generate parallel light from the light emitted from the light source 13 and to irradiate the cholesteric liquid crystal layer 7 sandwiched between the transparent electrodes 5 and 6. Also,
The inner surface 4a of the lower glass plate 4 is mirror-finished by aluminum evaporation.

In the liquid crystal light emitting device 1 of this embodiment, when the switch 11 is turned off, a focal conic polydomain structure is formed in the cholesteric liquid crystal layer 7 as shown in FIG. When this happens, the lens 12
Of the cholesteric liquid crystal layer 7 is scattered by the focal conic polydomain structure of the cholesteric liquid crystal layer 7 and scattered at the interface 9 of the grains, and is emitted from the transparent electrode 5 to the outside of the liquid crystal cell 8 (light emitting state). ). On the other hand, when the switch 11 is turned on, a voltage is applied between the transparent electrodes 5 and 6, and the cholesteric liquid crystal layer 7 is in a homeotropic alignment state as shown in FIG. In this case, since the light emitted from the lens 12 to the cholesteric liquid crystal layer 7 travels straight without being scattered, there is almost no light emitted from the transparent electrode 5 to the outside of the liquid crystal cell 8 (dark state).

In the liquid crystal light emitting device 1, if a reflecting mirror is arranged at a position indicated by reference numeral 14 in FIG.
Since the amount of light introduced into the cell 8 from the outside decreases, the amount of light emission in the light emitting state (FIG. 1A) increases.

A method of displaying a pattern using the liquid crystal light emitting device 1 of FIG. 1 will be described with reference to FIG.
2A and 2B are plan views showing the transparent electrode 5 of the liquid crystal light emitting device 1 of FIG. 1, wherein FIG. 2A shows a state where no voltage is applied between the electrodes, and FIG. 2B shows a state where a voltage is applied between the electrodes. It shows the state that it was. The transparent electrode 5 has an opening 5a in a pattern to be displayed. When no voltage is applied between the transparent electrodes 5 and 6, light scattering by the focal conic polydomain structure occurs on the entire surface of the transparent electrode 5, so that the entire surface of the transparent electrode 5 emits light. On the other hand, when a voltage is applied between the transparent electrodes 5 and 6, the cholesteric liquid crystal layer 7 is in a homeotropic alignment state in a region outside the opening 5a, so that the light goes straight without being scattered (dark state). However, the electric field does not change in the opening 5a (the region without the electrode), and the polydomain structure remains.
The light scattering state (light emitting state) is maintained. As a result, as shown in FIG. 2B, a circular light-emitting pattern appears on the transparent electrode 5 on a rectangular background.

Note that the liquid crystal light emitting element 1
In the case of performing the pattern display according to the above, instead of mirror-finish the inner surface 4a of the glass plate 4 as described above, the color of the background at the time of applying a voltage can be changed by coloring the inner surface 4a. Further, for example, a filter can be provided between the light source 13 and the liquid crystal cell 8 and light of a specific color can be introduced into the liquid crystal cell 8 to change the emission color. In this manner, by appropriately selecting and combining the background color and the emission color, a pattern can be displayed with high contrast.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams showing a liquid crystal light emitting device according to an embodiment of the present invention, wherein FIG. 1A shows a state where no voltage is applied between electrodes, and FIG. 1B shows a state where a voltage is applied between electrodes.

2A and 2B are diagrams showing an example of a method of displaying a pattern using the liquid crystal light emitting device of FIG. 1, wherein FIG. 2A shows a state in which no voltage is applied between electrodes, and FIG. Is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Liquid crystal light emitting element 3, 4 ... Glass plate 5, 6 ... Transparent electrode 7 ... Cholesteric liquid crystal layer 8 ... Liquid crystal cell 9 ... Polymer thin film 10 ... Power supply 11 ... Switch 12 ... Lens 13 ... Light source

Claims (2)

[Claims] 1. A liquid crystal cell comprising a pair of plate-like or film-like electrodes including a transparent electrode disposed on a light-emitting surface side and a chiral liquid crystal layer sandwiched between the pair of electrodes, and a light source for emitting light emitted from a light source. A liquid crystal device, comprising: illumination means for irradiating the liquid crystal layer from the side. 2. The chiral liquid crystal layer according to claim 1, wherein the chiral liquid crystal layer has a structure in which a large number of grains are formed by wrapping a small volume of chiral liquid crystal exhibiting a focal conic polydomain structure with a transparent polymer thin film. 3. The liquid crystal device according to claim 1.