JPH0321890B2 - - Google Patents

Description

[Detailed description of the invention]

Conventionally, various color display modes using liquid crystals have been known. For example, the so-called
The White-Taylor type liquid crystal is constructed by interposing a nematic liquid crystal with positive dielectric anisotropy containing an optically active substance and a dichroic dye between horizontally or vertically aligned substrates. . The display mode of this liquid crystal is colored when the voltage is OFF, and when the voltage is ON, the molecules are aligned perpendicular to the substrate surface, resulting in a blank negative display. This display mode has the advantage of not needing a polarizing plate and can display bright colors, and has a wide viewing angle, but because it is a negative display, the display is somewhat difficult to see, and it has some disadvantages in terms of display quality. There are drawbacks such as: Another display mode is one in which a nematic liquid crystal containing a dichroic dye and having negative dielectric anisotropy is aligned obliquely to the substrate surface, and a polarizing plate is placed in front of one substrate surface. In this case, when the voltage is turned off, the molecules are arranged slightly tilted with respect to the substrate surface, resulting in a slightly colored white spot. When the voltage is turned on, the molecules become horizontal to the substrate surface, so they become colored due to the polarizing action of the polarizing plate. This display mode has the advantage that the display is easy to see because it is a positive display, but it requires a polarizing plate, which increases the cost, and the reliability of the display element is affected by the durability of the polarizing plate under high temperature and high humidity. However, when the voltage is turned off, the molecules are arranged at an angle with respect to the substrate surface, resulting in a slightly colored state, resulting in poor display contrast as a whole. Alternatively, there is a mode that is an inversion of the White-Taylor type display mode described above, that is, a positive type in which a nematic liquid crystal containing dichroic dye and having negative dielectric anisotropy is interposed between vertically aligned substrates. Display modes are also known. However, as long as a regular reflective sheet with a flat surface made of vinyl chloride or the like is used, in order to keep the coloring low when the voltage is OFF, the dye concentration must be extremely low, and the display contrast when the voltage is ON is too low. I can't get it big. This is thought to be correlated with the inability to increase the cholesteric pitch induced when the voltage is turned on. The present invention has been made in view of the above points, and its purpose is to provide a liquid crystal display element that reduces coloring when the voltage is turned off in a color liquid crystal display element that performs positive display, and has high display quality. In order to achieve this object, the present invention provides a device in which a liquid crystal is interposed between two transparent insulating substrates each having an alignment film formed on the inner surface, and a liquid crystal is provided on the outer surface side of one of the insulating substrates. A reflective plate with a roughened reflective surface is arranged, and the distance between the reflective surface of the reflective plate and the outer surface of the insulating substrate is 0.3 to 2.0 mm. Suitable reflector bases used in the present invention include, for example, various metal plates, polyester bases,
Synthetic resins such as acrylic, polyvinyl alcohol, and vinyl chloride are used to make the resin white or have a metallic luster, and the surface is roughened by forming numerous irregularities of approximately 30 to 90 μm in size. This is a reflective plate. Methods for forming this roughened, diffusely reflective surface include a processing method using an irradiation beam, etc., a wet etching method, a sandblasting method, and a method of applying fine powder such as glass beads or alumina beads having a predetermined average particle size together with a binder. and so on.
Alternatively, a combination of both concave portions and convex portions may be used. Figures 1A and 1B are partially enlarged cross-sectional views of the reflector plate. Figure 1A shows a state in which the surface of the reflector plate 8 has numerous convex portions, and Figure 1B shows a roughened surface with countless concave portions formed thereon. It shows. Visually, in order to keep the coloring state low when the voltage is OFF, the larger of the height A and diameter B of the convex part in Figure 1 A, or the depth C and diameter D of the recess part in Figure 1 B. Based on various experimental results, it is preferable that the average value of
m is preferred. In other cases, for example 30 μm
If it is less than 90 μm, the colored state cannot be reduced, and if it is more than 90 μm, the display quality will be significantly degraded. 2 and 3 are cross-sectional views of the liquid crystal display element according to the present invention, in which 1 is an alignment film, 2 is a transparent electrode, 3 is a transparent insulating substrate made of a glass plate,
4 is a liquid crystal, 5 is a dye, 6 is a sealant, 7 is a transparent film made of polyacrylic film, etc., 8 is a reflective plate whose surface has been roughened as described above, 9
is a spacer, and 10 is a void. As shown in FIG. 2, a transparent film 7 is interposed between the lower insulating substrate 3 and the reflecting plate 8, or as shown in FIG. By interposing the spacer 9 on the outer periphery of the insulating substrate 3, the outer surface of the insulating substrate 3 and the reflecting surface of the reflecting plate 8 can be separated by a predetermined distance. Next, examples of the present invention will be described. Example 1 A diazo dichroic dye was added in an amount of 0.7 wt % to a nematic liquid crystal with negative dielectric anisotropy (a liquid crystal composition mainly composed of a cyclohexanecarboxylic acid ester compound) containing a small amount of cholesteric liquid crystal. This composition is vertically aligned using a silane coupling agent and sealed between insulating substrates on which transparent electrodes having a predetermined pattern are formed, thereby forming a cell. On the other hand, on the vinyl chloride sheet, the average particle size is about 60μ
A paste made by distributing glass beads of m in size into a binder is applied and dried to create a reflector plate with numerous fine irregularities on its surface. The roughened side of the reflector is placed toward the back side of the cell, and a spacer of 0.5 mm is formed between the substrate and the reflector by a spacer inserted on the outer periphery ( (See Figure 3). The following table summarizes the evaluation of the coloring state and display quality when the voltage is OFF when the distance between the cell rear substrate and the reflector plate is changed.

[Table] In addition, ◎ mark in the table is particularly good, 〇 mark is good, △
The mark indicates inferiority. The configuration of each display cell is the same as in the first embodiment. As is clear from this table, if the distance between the cell rear substrate and the reflector is maintained at approximately 0.3 mm or more, the voltage will increase.
The coloring is hardly noticeable when turned off. on the other hand,
If the distance between the cell back substrate and the reflector exceeds 2mm,
This is not preferable because the display quality (visibility) of the panel deteriorates. Example 2 A vinyl chloride reflector having a white flat surface was used instead of the reflector, and the other configurations were the same as in Example 1. Example 3 Nematic liquid crystal with negative dielectric anisotropy (mainly cyclohexane carboxylic acid ester) containing trace amounts of ionic substances (tetrabutylammonium bromite, cholesteric liquid crystal, and diazo red dichroic dye (0.25 wt%)) component) was sealed between the substrates with a cell gap of 20 μm.When a display element was made by combining it with the same reflector as in Example 1, almost no coloring was observed when the voltage was turned off.Also, the quality of the panel was As described above, the present invention provides a liquid crystal display element that reduces coloring when the voltage is turned off and has high display quality by slightly separating the cell rear substrate and the reflector. be able to.

[Brief explanation of the drawing]

1A and 1B are partially enlarged cross-sectional views of a reflector according to an embodiment of the present invention, and FIGS. 2 and 3 are cross-sectional views of a liquid crystal display element according to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Alignment treatment film, 2... Transparent electrode, 3... Insulating substrate, 4... Liquid crystal, 7... Transparent film, 8...
...Reflector, 9...Spacer, 10...Void.

Claims (1)

[Claims] 1. A liquid crystal containing a dichroic dye and having negative dielectric anisotropy is interposed between two transparent insulating substrates each having an alignment film formed on the inner surface, and one of the insulating substrates is In a positive display type liquid crystal display element in which a reflective plate is arranged on the outer surface side, main reflection is achieved by attaching glass beads with an average particle size of 30 to 90 μm to the outer surface side of one of the insulating substrates. A liquid crystal display element characterized in that a reflective plate with a roughened surface is arranged, and the distance between the reflective surface of the reflective plate and the outer surface of an insulating substrate is 0.7 to 2.0 mm.