JPS62159115A - Thermal writing type liquid crystal display element - Google Patents

Abstract

PURPOSE:To prevent colors except an intended color tone from being observed even if visual angles vary by providing a colored layer which makes selective reflection or transmission of light of a specific wavelength region to the back of a liquid crystal layer. CONSTITUTION:The colored layer 31 is provided behind the liquid crystal element. The central wavelength of scattered light is assumed to be lambda0 and the central wavelength lambda' of the light to be cut by the colored layer to be, for example, R. The light (R light) having the central wavelength lambda0 is reflected from the liquid crystal layer 17 but the light (G and B light) of the wavelengths except said wavelength region is reflected by an absorptive layer 31 without being absorbed therein and therefore the coloration is hardly observed when lambda0approx.=lambda'. On the other hand, the light (for example, G light) of lambda0 as the central wavelength is selectively reflected from the liquid crystal layer 17 when lambda0>>lambda' or lambda0>>lambda' is attained by heating of a cholesteric liquid crystal. The light (B light) which is the light of the wavelength except said wavelength region and is not cut by the colored layer 31 is also reflected from the colored layer 31 and therefore, the color (G+B) of the colored layer is observed. This relation does not change and the color of the colored layer is observed even if the value lambda0 is changed by the visual angle.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal writing type liquid crystal display device that utilizes the thermo-optic effect of a thermochromic liquid crystal.

It is known that images are displayed using thermochromic liquid crystals whose spectral reflectance changes with changes in temperature, and cholesteric liquid crystals are a typical example of this. Cholesteric liquid crystals have a helical structure, and the pitch and/or phase of the helical structure changes with temperature changes, changing the wavelength range in which light is selectively scattered, and is used in liquid crystal thermometers and the like. In addition, by providing a heating means such as a laser or a resistive heating element corresponding to each pixel and selectively heating the cholesteric liquid crystal layer, it is possible to display images by changing the color tone of the heated portion. It is expected to be used in various display devices such as color liquid crystal display devices.

The center wavelength of selective scattering of cholesteric liquid crystal is given by the following equation.

λo=n-pmcos4 (sin-1(jsinψi
) + 5in-1 (isin ψS)) λ0: Center wavelength of selective scattering n: Average refractive index and anisotropy of refractive index in the plane perpendicular to the helical axis p: Helical pitch ψj: Incident angle of light ψS: Light Therefore, when a cholesteric liquid crystal cell is placed on a black background, the scattering angle of black →
Coloration or tone changes occur.

However, as can be seen from the above equation, since the color tone largely depends on the viewing angle, colors other than the intended color tone may be observed depending on the viewing angle of one display.

In addition, if you try to switch from uncolored (black) to colored when the background is black, it is necessary to change λ0 significantly between outside and inside the visible wave mottling range, which causes a large temperature change. required.

Summary of the Invention The present invention provides a thermal writing type liquid crystal display device that prevents colors other than the intended color tone from being observed even when viewing angles are different.

Another object of the present invention is to provide a thermal writing type liquid crystal display device that can perform coloring/non-coloring switching with less thermal energy.

The thermal writing type liquid crystal display device of the present invention has a thermochromic liquid crystal layer, is provided with a heating means corresponding to each pixel, selectively heats the adjacent thermochromic liquid crystal by the heating means, In a thermal writing type liquid crystal display device that performs display using spectral reflectance changes due to temperature of a thermochromic liquid crystal, a colored layer that selectively reflects or transmits light in a specific wavelength range is provided behind the liquid crystal layer. It is characterized by

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

FIG. 1 is a sectional view showing an embodiment of the present invention.

A lead electrode 13.23 is formed on the opposite surface side of the transparent substrate 11.21 made of a plastic film, and a resistance heating element 15 is connected to this lead electrode.
A cholesteric liquid crystal 17 is sealed in between. 19
is a sealant for sealing the outer periphery.

A colored layer 31 is provided on the back side of this liquid crystal element.

Now, assume that the center wavelength of scattered light (reflected light) when the resistance heating element 15 is turned on is λ0, and the center wavelength of light cut by one colored layer is λ' (for example, R). When λ0αλ', light with a center wavelength of λ0 (R light) is transmitted to the liquid crystal layer 17.
However, since light outside this wavelength range (G and B light) is reflected without being absorbed by the absorption layer 31 (R light is absorbed and cut by the absorption layer 31), it ends up being colored. is hardly noticed.

On the other hand, if λ0>>λ' or λ0<<λ' occurs due to heating of the cholesteric liquid crystal, light centered around λ0 (for example, G light) is selectively reflected from the liquid crystal layer 17, and light outside this wavelength range Light that is not cut by the colored layer 31 (B
Light) is also reflected from the colored layer 31, so in the end, 1 colored 2
The color (G+B) is detected. Even if the value of 10 changes depending on the viewing angle, this relationship remains the same and the color of the colored layer is 11!
Colors other than the desired tone are ml! It will go unnoticed. The case where the spectral reflection characteristic of the colored layer is used has been described above, but the same applies to the case where the 1-spectral transmission characteristic is used, and in this case, a reflecting plate is provided on the back side of the colored layer to reflect the transmitted light.

Further, by changing the value of λ0 within the visible wavelength range (RAG in the above example), switching from non-colored to colored can be performed. As described above, the selective scattering spectrum of the cholesteric liquid crystal and the reflection spectrum of the colored layer are set to complement each other, and adjusted so that almost no coloring is observed when λ0=λ'.

The colored layer is made of a high refractive index material such as ZnS and MgF2. N
A multilayer reflective plate made of a low refractive index material such as a5AIF; a dispersion type filter such as a dye pigment is used, and an absorbing plate or a reflecting plate may be provided on the back side if necessary.

A colored substrate may be used as the substrate 21 and used as a colored layer, or the electrode 23 may also have the function of a colored layer.

Furthermore, the formation mode and cell structure of the cholesteric liquid crystal layer are not particularly limited; for example, a resistance heating element may be provided on one side of the substrate or outside the substrate, or liquid crystal ink may be applied without a sandwich structure. A liquid crystal layer may also be formed.

Mizumugi trouble According to the present invention, a specific wavelength range is cut.

By providing a colored layer that reflects or transmits other wavelengths, even if the center wavelength λ0 of scattered light changes depending on the viewing angle,
Light other than the desired color tone is not observed. In addition, switching between coloring and non-coloring can be performed by changing λ0 within the range of visible light by selective heating, so that thermal writing can be performed with a small amount of thermal energy, and an energy-saving type liquid crystal display can be realized.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of a thermal writing type liquid crystal display device of the present invention.

Claims (1)

[Claims] 1. It has a thermochromic liquid crystal layer, a heating means is provided corresponding to each pixel, the heating means selectively heats the nearby thermochromic liquid crystal, and the spectral reflectance change due to the temperature of the thermochromic liquid crystal is utilized. What is claimed is: 1. A thermal writing type liquid crystal display device for displaying images, characterized in that a colored layer that selectively reflects or transmits light in a specific wavelength range is provided behind the liquid crystal layer.