JPS5991422A - Colored liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the contrast in display by using a dye of which the long axis of the dye molecule deviates by an angle theta from the absorption axis of light and performing an orientation treatment in two directions + or -theta relatively with the polarization axis direction of a polarization plate. CONSTITUTION:An orientation treatment for orienting horizontally liquid crystal molecules 5 in two directions + or -theta is applied on a glass substrate 1 provided with a transparent electrode 2, and a biphenyl-contg. liquid crystal dissolved therein with an anthraquinone dye as a dichromatic dye 4 having positive absorption anisotropy is injected between the substrates. A polarization plate 6 is disposed on the front surface of the substrate 1. The long axis direction L of the dye 4 deviates by an angle theta from the absorption axis direction K of light and the polarization axis direction H of the plate 6 is deviated by theta from the orientation direction R and therefore the absorption axis direction K of the dye coincides with the polarization axis direction H. The full line shows the characteristics of the color liquid crystal display device wherein the orientation is made on two directions of + or -15 deg. and the broken line indicates the characteristics of said device wherein the orientation is made only in one direction. The full line is evidently better in contrast.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD OF THE INVENTION The present invention relates to improvements in guest-host type color liquid crystal display devices using dichroic dyes.

[Technical background of the invention and its problems]

A guest-host type is known as one type of color liquid crystal display device. Figure 1 explains a conventional device, in which a display material made of a mixture of liquid crystal molecules (5) and dye molecules (4) is placed between two glass substrates (1) having transparent electrodes (2). It has been placed. Two glass substrates (1) have liquid crystal molecules (5
) is subjected to alignment treatment to horizontally align the liquid crystal molecules (
5) are held at predetermined intervals through spacers (3) so that their orientation directions are parallel to each other. Further, a polarizing plate (6) is provided in front of the display side of the substrate. Although such color liquid crystal display devices are highly reliable and have been put into practical use in many cases, their contrast is currently somewhat poor, and improvements are desired.

[Purpose of the invention]

SUMMARY OF THE INVENTION The present invention has been made to satisfy the conventional desires, and it is an object of the present invention to provide a color liquid crystal display device with improved contrast.

[Summary of the invention]

The inventor, Mon, completed the present invention after conducting various experiments and studies for the purpose of improving the contrast of the display. That is, the present invention includes a plurality of horizontally aligned substrates, a liquid crystal material and a dichroic dye having positive dielectric anisotropy sandwiched between the substrates, and a polarized light disposed in front of the display side of the substrates. In the liquid crystal display device equipped with a plate, the dichroic dye is such that the long axis of one molecule of the dye is shifted from the light absorption axis by an angle θ, and the alignment treatment is performed in the direction of the polarization axis of the polarizing plate. In contrast, a color liquid crystal display device is provided which is characterized in that orientation is performed in two force directions, 4=0 and 10. Since the color liquid crystal display device of the present invention uses a device in which the long axis direction of the dye molecules and the light absorption axis direction are shifted, the display color is stable and the display color does not change even when used outdoors for a long time. There is no point. Furthermore, since the orientation treatment is performed in two directions, 10 and 10, with respect to the polarization axis direction of the polarizing plate, the display contrast is very good.

[Embodiments of the invention]

The cross-sectional view of the color liquid crystal display device of the present invention is the same as that in FIG. The present invention will be explained with reference to FIGS. 1 to 3.

On the glass substrate (1) provided with the transparent electrode (2), an alignment treatment is applied to horizontally align the liquid crystal molecules (5) at +15° and -15°.
Two glass substrates (1) are placed in two directions at an angle of 15 degrees so that the alignment directions of liquid crystal molecules (5) are parallel to each other so that they are in contact with the glass substrates (1), respectively, with spacers (3) interposed therebetween.
are placed opposite each other, and an anthraquinone dye (D-5) (B
D) Biphenyl liquid crystal E containing 2% by weight of I company type name)
-8 (Merck model name) is injected. A polarizing plate (6) is placed on the front surface of the substrate (1), and a reflecting plate (not shown) is placed on the ridge of the glass substrate (1).

The yg2 diagram shows the liquid crystal molecules (5) and dichroic dye (4) in the long direction L1 dye (
4) is a diagram showing the relationship between the absorption axis direction of the polarizing plate (6) and the polarization axis direction H of the polarizing plate (6). As described above, in the color liquid crystal display device of the present invention, the long axis direction of the dichroic dye (4) and the light absorption axis direction are shifted by an angle θ. Since the polarization axis direction II of the polarizing plate (6) is shifted by θ with respect to the orientation direction R, the absorption axis direction of the dichroic dye coincides with the polarization axis direction 1).

Figure 3 shows the deviation angle between the horizontal axis and the long axis direction of the liquid crystal molecules (the long axis direction of the dye molecules) when the polarization axis direction is taken as a reference, and the vertical axis represents the absorbance in the liquid crystal cell of light transmitted through the polarizing plate. In the characteristic diagram expressed as , the solid line indicates the alignment direction according to the present invention in two directions of +15°, and the broken line indicates the characteristic of a conventional color liquid crystal display device having only one alignment direction. As is clear from FIG. 3, the color liquid crystal display device of the present invention has better contrast.

Furthermore, in order to examine the stability of displayed colors, an ultraviolet irradiation test was conducted on the liquid crystal display device using D-5 as a dichroic dye according to the present invention, and no change in displayed color was observed even after 1000 hours ( (zero absorbance decrease). In contrast, when an azo dye was used as the dichroic dye, discoloration was already observed after 200 hours (30% decrease in absorption capacity).

In the examples of the present invention, I)-5 was exemplified as the dichroic dye, but indigo dyes, quinophthalone dyes, thioindico dyes, etc. may also be used.

[Brief explanation of drawings]

Figure 1 is a schematic cross-section of a color liquid crystal display device... Figure 2 shows the liquid crystal molecules, the long axis direction of the dichroic dye, the absorption axis direction of the dye, and the polarizing plate according to the color liquid crystal display device of the present invention. FIG. 3 is a diagram showing the absorbance characteristics of the color liquid crystal display device of the present invention and the conventional color liquid crystal display device. 1...Substrate 2...Transparent electrode 4...Dichroic dye 5...Liquid crystal molecule L...Long axis direction of liquid crystal molecule, long axis direction of dichroic dye molecule R alignment direction K... Light absorption axis direction of dichroic dye) 1... Polarization axis direction of polarizing plate

Claims (1)

[Claims] (1) A plurality of horizontally aligned substrates, a liquid crystal material having positive dielectric anisotropy and a dichromatic p+=dye sandwiched between the substrates, and a display panel placed in front of the substrates. In the liquid crystal display device equipped with a polarizing plate, the dichroic dye has a long axis of the dye molecule and a light absorption axis shifted by an angle θ, and the alignment treatment is performed in the direction of the polarization axis of the polarizing plate. On the other hand, a color liquid crystal display device is characterized in that it is oriented in two directions: 10 and 10.