JPS593727B2 - Color liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color liquid crystal display device that utilizes the guest-host effect.

More specifically, the present invention relates to a guest-host effect type color liquid crystal display device that utilizes phase transition from a cholesteric phase to a nematic phase. Various liquid crystal color display elements have been devised, but a guest-host effect type display element that utilizes phase transition is cited as one that is highly practical and has a simple device.

This is a color liquid crystal composition in which an optically active substance and a pleochroic dye are added to a nematic liquid crystal with positive dielectric anisotropy, which is inserted between two parallel electrode substrates and aligned parallel to the substrates. In this state, the color liquid crystal composition has a helical structure (cholesteric phase) due to the optically active substance and exhibits a specific color, but by applying a voltage between the electrode substrates, the liquid crystal molecules are vertically aligned (nematic phase). Phase), as the dye molecules rotate and align in the same direction, the color tone changes due to the pleochroism of the dye, and it is generally colorless. Therefore, it is possible to display a colorless display on a colored background by applying a voltage, and it is significantly superior in terms of brightness and viewing angle characteristics compared to the currently widely used twisted alignment type liquid crystal display elements that use polarizing plates. ing. However, this display element has the disadvantage that the color tone changes gradually as the thickness of the liquid crystal layer changes, so if the liquid crystal is inserted between substrates with an uneven gap, the color tone will change between dark and thin areas. This results in the formation of lumps, which poses a serious problem in mass production. Therefore, an object of the present invention is to provide a display device that is extremely suitable for mass production and does not cause streaks even when the gap is not uniform. . The principle of the present invention is as follows.

The cause of the unevenness is due to the orientation treatment applied to the substrate surface.

For example, if a wedge-shaped panel is constructed with different gaps as shown in FIG. 1, and the color liquid crystal composition 3 described above is inserted, the color tone will vary between points A and B in the figure.
Regions b and c are generated. This is because the alignment treatment applied to the substrate surface has a strong alignment force that tries to align the liquid crystal molecules in the same direction, and the liquid crystal molecules that try to form a helical structure at a certain pitch cannot maintain the original pitch. . That is, since the orientation direction of the surface is determined, even if the gap changes, the helical pitch changes accordingly within a certain range, and there is a region where the rotational speed of the liquid crystal molecules does not change. For example, in Figure 1, the rotation speed of the liquid crystal molecules is 1.5 in region a,
is changed in steps of 2 in the region and 2.5 in the c region, in steps of half a rotation. Therefore, the color tone, which largely depends on the number of rotations of the liquid crystal molecules, changes stepwise due to changes in the gap, resulting in unevenness. Therefore, as shown in FIG. 1, if a parallel alignment process is applied to only the substrate 2 to align the liquid crystal molecules in the same direction, and the liquid crystal molecules are allowed to align in any direction on the other substrate 2, the liquid crystal molecules will be aligned in the same direction. Since only the edges are oriented in the same direction, it is possible to rotate at the original pitch, and therefore, the color tone only changes continuously due to the change in the gap, and the blurring that occurs in the conventional method can be prevented.

The present invention will be explained below with reference to Examples.

Example 1 One side of the substrate was coated with silane agent KBM6O2 (Shin-Etsu Silicone)
After coating, parallel processing is performed by lapping in one direction, and the other board is only cleaned to give a gap of 10.
A panel was created in which the difference between the maximum gap and the minimum gap was approximately 2μ.

In addition, the color liquid crystal composition inserted into the panel contains a pleochroic dye NKI232 (manufactured by Nippon Kanko Shiki Co., Ltd.) 0.5 wt%, an optically active substance ChOlestericNOnanOate,
3. Owt% of P-type nematic liquid crystal composition E7 (BDH
(manufactured by Seishin Corporation). As a result, a display device was obtained that was completely free of streaks, and the color shading was almost inconspicuous. In addition, when a conventional display device in which both substrates were subjected to parallel alignment treatment was similarly prepared with a gap difference of about 2 μm, three regions with different color tones were produced, which was unfavorable in terms of appearance. Example 2 After applying the silane agent KBM6O2 to both substrates, wrapping was performed on only one substrate to create a panel similar to that of Example 1.

As a result, since the liquid crystal molecules could be oriented in any direction on the substrate that had not been wrapped, a display device without spots was obtained as in Example 1. As described above, the present invention
In guest-host type liquid crystal display devices doped with optically active substances, this effectively prevents the unevenness that occurs in conventional panels with uneven gaps. Therefore, it is very effective in mass production, where it is difficult to create panels with uniform gaps. It has great advantages.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional example, and FIG. 2 is a sectional view of the present invention. 1, 2... Substrate, 3... Color liquid crystal composition.

Claims (1)

[Claims] 1. In a guest-host type liquid crystal display device using the electro-optical effect of a nematic liquid crystal composition with positive dielectric anisotropy containing an optically active substance and a pleochroic dye, liquid crystal molecules are placed only on one side of the transparent substrates that sandwich the liquid crystal. 1. A color liquid crystal display device, characterized in that one side is subjected to parallel alignment treatment to align them in the same direction, and the other side allows liquid crystal molecules to be aligned in any direction.