JPS5823615B2 - liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid crystal display device that displays colors by adding a dye.

BACKGROUND ART Conventionally, as liquid crystal display devices that perform color display using added dyes, there are known those that utilize the White Tiller effect and those that utilize the guest-host effect.

Liquid crystal display devices, which generally display symbols such as letters and numbers using colors, are used as reflective display devices because it is easier to see when the letters and numbers themselves are displayed in color than when the background is displayed in color. It is desirable that colors be displayed depending on the application.

However, the above-mentioned white tiller type liquid crystal display device changes from a state exhibiting a dye color to a transparent state upon application of a voltage equal to or higher than a threshold value, and is therefore not suitable for the above-mentioned color display.

On the other hand, some guest-host type dyes exhibit a dye color upon application of a voltage higher than a threshold value, but they generally have the drawback of long response times, particularly long fall times.

An object of the present invention is to provide a liquid crystal display device that exhibits the color of a dye by applying an electric field using a mechanism different from the guest-host type.

In order to achieve the above-mentioned object, the present invention applies cholesteric liquid crystal to nematic liquid crystal with negative dielectric anisotropy such that the concentration C is O<C508po/d (1) o: the intrinsic helical pitch of cholesteric liquid crystal (however, this Pitch is the physical pitch), d is the thickness of the liquid crystal layer], and when a voltage below the threshold is applied, including when no voltage is applied, the mixed liquid crystal with such a ratio is almost homeotropically aligned, and the long axes of the molecules of the mixed liquid crystal are aligned in a direction perpendicular to the direction of the electric field, that is, in a direction parallel to the vertically aligned substrate, due to a voltage above the threshold value. This is utilized as follows. are doing.

That is, the dye has a first absorption spectrum in a direction parallel to the long axis direction of the dye molecule and a second absorption spectrum different from the first absorption spectrum in a direction perpendicular to the long axis direction.
A minute amount of a chromatic dye is added to the mixed liquid crystal, and the long axis of the dichroic dye is aligned parallel to the electric field direction by the homeotropic alignment described above. 2. Display the color determined by the absorption spectrum, and apply the voltage above the threshold value to display the 2.
By arranging the long axes of the chromatic dyes perpendicular to the direction of the electric field, the mixed liquid crystal containing the dichroic dyes displays a color determined by the first absorption spectrum.

Next, the present invention will be explained in detail based on examples.

In FIG. 1, two transparent substrates 1, 1' such as glass
Transparent electrodes 2 and 2' made of indium oxide, tin oxide, etc. are coated on the inner surfaces of the electrodes, respectively.

These substrates and transparent electrodes are vertically aligned using lecithin or a chromium myristate complex.

Between these two transparent substrates 1 and 1', a nematic liquid crystal with negative induced anisotropy is made of 1.4 weight or less (this 1.4
The number is p.

= 0.125μ and d = 9μ) with mixed liquid crystal 3 containing cholesteric liquid crystal.
□Azo-based or azoxy-based dichroic dye 4 is enclosed.

This dichroic pigment has a first absorption spectrum that absorbs specific wavelengths in the visible light range in a direction parallel to the long axis direction of the molecule, and a second absorption spectrum that absorbs almost all visible light in a direction perpendicular to the first absorption spectrum. has.

Therefore, the mixed liquid crystal 3 exhibits a color determined by the specific absorbed wavelength when the long axis of this dichroic pigment is parallel to the substrate, and transparent when the long axis is perpendicular to the substrate. Become.

Moreover, as the above-mentioned nematic liquid crystal with negative dielectric anisotropy, for example, MBBA (-methoxy-benzyli
-dene -cyanoaniI 1ne) and EBB
A (ethoxy-benzyl 1dene-c
yanoan if ine) in a weight ratio of 4:1, and p as the cholesteric liquid crystal.

It is preferable to use cholesteryl nonanoate having a particle diameter of 0.125μ.

5 is a spacer made of 9μ Mylar film.

Here, the operation of the liquid crystal display device of the present invention will be explained based on such a structure.

As shown in FIG.
, 1'.

Therefore, since the long axis of the dichroic dye 4 is also aligned perpendicular to the substrate, almost no light is absorbed.

Therefore, this liquid crystal display device becomes transparent when no voltage is applied or when a voltage below the threshold value is applied.

Next, when a voltage higher than the threshold is applied, the long axes of the liquid crystal molecules are aligned parallel to the substrate, and as shown in Figure 2, the long axes of the dichroic dye are also aligned in the same direction, resulting in the first absorption of the dye. It exhibits a color determined by its spectrum.

In this way, this liquid crystal display device can display the colors of the added dye by applying an electric field.

Since cholesteric liquid crystal is mixed, the fall time and rise time are shortened.

In contrast to the rise and fall times of 400 m5 and 600 ms, respectively, in the case of not mixing cholesteric liquid crystal, that is, in the case of guest-host type, 0.5 to 0.8 weight of the above cholesteric liquid crystal of the present invention is mixed. In this example, the rise and fall times were 300 m5 and 200 m5, respectively, when the applied voltage was IOV.

When the concentration C of the mixed cholesteric liquid crystal is close to the upper limit of 0〈C〉D, there is a risk that the mixed liquid crystal will take on a focal conic structure due to changes in conditions such as temperature and will not be homeotropically aligned. , the above-mentioned situation can be avoided by selecting the concentration C in the range O<C≦Q, 8xJln.

Note that the vertical alignment treatment applied to the substrate is not limited to aligning the liquid crystal molecules completely perpendicular to the substrate, but may also align the liquid crystal molecules at an inclination angle of approximately 80°.

In addition to the cholesterol derivatives shown in the examples, the cholesteric liquid crystal according to the present invention also includes so-called chiral nematic liquid crystal, and C15 manufactured by BDH Chemical Co., Ltd., which is not essentially a liquid crystal but exhibits optical rotation when mixed with nematic liquid crystal. It shall include substances such as.

As described above, according to the present invention, a liquid crystal display device that exhibits the color of a dye by applying an electric field with excellent responsiveness has been realized.

[Brief Description of the Drawings] Fig. 1 is a cross-sectional view of the liquid crystal display device of the present invention in a transparent state, and Fig. 2 is a cross-sectional view similar to Fig. 1 in a state exhibiting a color determined by the first absorption spectrum of the dye. It is a diagram. [Explanation of symbols of main parts], Mixed liquid crystal...3.
Dichroic dye...4, Substrate...1,1'
, Electrode...2゜2', Spacer...5
゜

Claims (1)

[Claims] 1. A first absorption spectrum in a direction parallel to the long axis direction of dye molecules in a mixed liquid crystal of a nematic liquid crystal and a cholesteric liquid crystal having negative dielectric anisotropy, and a first absorption spectrum in a direction perpendicular thereto. A small amount of dichroic dye having a second absorption spectrum different from the absorption spectrum is added, and the concentration C of the cholesteric liquid crystal is adjusted to O<C≦08xpo/d (po: intrinsic helical pitch of cholesteric liquid crystal, d: liquid crystal The dichroic dyes are aligned so that their long axes are approximately perpendicular to the direction of the electric field by applying a vertical alignment treatment to the substrate and applying an electric field above a threshold value. to display a color according to the first absorption spectrum, and by applying an electric field less than the threshold value, arrange the dichroic dyes so that their long axes are substantially horizontal to the direction of the electric field, so that the color corresponds to the second absorption spectrum. A liquid crystal display device characterized by displaying a corresponding color. 2. A liquid crystal display device according to claim 1, wherein the dichroic dye is a transparent color that corresponds to its second absorption spectrum.