JPS6136879B2 - - 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-TayIor 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 (no electric field), and when the voltage is ON (when there is an electric field)
When the molecules are oriented perpendicular to the substrate surface, a blank negative display is produced. This display mode does not require a polarizing plate and can display bright colors.
It has advantages such as wide viewing angle, but
Since it is a negative display, it has drawbacks such as being somewhat difficult to see and being somewhat disadvantageous in terms of display quality. 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, a mode in which the above-mentioned White-Taylor type display mode is also reversed, 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 flat-surfaced reflective sheet made of vinyl chloride or the like is used, in order to keep the coloration low when the voltage is OFF, the dye concentration must be extremely low, and the display contrast when the voltage is ON is reduced. It can't be too big. This is considered 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 use a display mode that utilizes changes in the molecular arrangement of dichroic dyes induced by dynamic scattering mode (DSM). The hour display stiffness can be made sufficiently high, and
An object of the present invention is to provide a color liquid crystal display element that has a steep threshold value when voltage is applied. To explain the display mode of the DSM of the present invention, as shown in FIG. 1, glass substrates 1 and 2 face each other with a predetermined gap, and transparent electrodes 3 and 4 are formed on the opposing surfaces. . Further, a liquid crystal 5 is sealed within the gap between the substrates 1 and 2. The liquid crystal 5 is a mother liquid crystal having negative dielectric anisotropy, to which a charging active substance is added, and furthermore, a dichroic dye and an ionic substance are added. In addition, the opposing surfaces of both substrates 1 and 2 are subjected to vertical alignment treatment, so that when no electricity is applied, the long axes of liquid crystal molecules and dichroic dyes are aligned with substrates 1 and 2, as shown in Figure a. oriented vertically. For this reason, the light transmittance is high, and the base becomes bright and clean. In this state, the colors of the two-color dye do not appear. Therefore, when a voltage is applied between the electrodes 3 and 4 by the power supply 6, the state of the liquid crystal 5 in the gap between the electrodes changes as the dipole moment of the liquid crystal molecules tries to rotate in the direction of the electric field, as shown in Figure b. An ionic additive added to the liquid crystal causes an ion flow, causing the molecules to rotate, resulting in a disordered state. Since the dichroic dye is also in a disordered state together with the liquid crystal molecules, the incident light is absorbed by the dichroic dye to produce a colored display. Since the dichroic dye is tilted at various angles in the above state, the colored display is easy to see from any direction, resulting in a positive display with high contrast. Hereinafter, the present invention will be explained in more detail based on Examples. [Example] An indium oxide-based transparent electrode is formed in a predetermined shape on a glass substrate, and then a silane coupling agent is applied and a vertical alignment process is performed. Next, two glass substrates are pressed against each other with a gap of 10 μm maintained, thereby producing a liquid crystal cell. Next, a liquid crystal substance having the composition shown below was injected into the liquid crystal cell and sealed to produce a color liquid crystal display element. Mother liquid crystal 97.3ωt% A mixture of cyclohexanecarboxylic acid ester derivatives represented by the following structural formula Optically active substance 1.9ωt% A derivative of biphenyl ester with an alkyl group having an inactive carbon at the end, represented by the following structural formula As a 1,4-naphthylene derivative As a 1,4-phenyline derivative FIG. 2 shows the optical changes in the color liquid crystal display device obtained using tetrabutylammonium bromide. In the figure, the horizontal axis shows the voltage applied to the electrodes of the liquid crystal display element, and the vertical axis shows the brightness of the liquid crystal display element, and the graph (a) shows the voltage applied to the electrodes of the liquid crystal display element, and the graph (a) shows the voltage applied to the electrodes of the liquid crystal display element.
Graph (b) represents the sample in which the above-mentioned optically active substance was not added to the above-mentioned example. Note that the brightness was detected by the voltage generated in the phototransistor. As is clear from the figure, by adding an optically active substance, the threshold value can be made steeper at a lower voltage. Therefore, the concentration of the optically active substance added is determined by the ratio between the cholesteric pitch (P) (levorotation) of the liquid crystal cell due to the addition of the optically active substance and the gap d between the two substrates of the liquid crystal cell, and is determined as follows. As shown in the table, good results were obtained by setting the additive concentration within the range of 0.6d/p0.8. If d/P<0.6, the desired liquid crystal screw cannot be obtained, and if d/P>0.8, the liquid crystal will twist more and the driving voltage will increase. In addition, in the table, the addition concentration is ωt% with respect to the mother liquid crystal to which dichroic dye and ionic substance are added.
It is expressed as

[Table] As described above, according to the present invention, by using the DSAM display mode, a positive display with high display contrast can be obtained, and the remarkable effect of lowering and steepening the threshold voltage can be obtained. play.

[Brief explanation of the drawing]

FIG. 1 relates to a color liquid crystal display element of the present invention,
Figure a is a cross-sectional side view of the main part when no voltage is applied, Figure b is a cross-sectional side view of the main part when voltage is applied, and Figure 2 is a color liquid crystal display with and without the addition of an optically active substance. FIG. 3 is an explanatory diagram illustrating optical changes in an element. 1, 2... Glass substrate, 3, 4... Transparent electrode,
5...Liquid crystal substance.

Claims (1)

[Scope of Claims] 1. A color liquid crystal display element in which at least one of two substrates is subjected to vertical alignment treatment and a liquid crystal substance is sealed in a gap between the substrates, wherein the liquid crystal substance is
A dichroic dye and an ionic substance are added to a mother liquid crystal having negative dielectric anisotropy, and an optically active substance having the following structural formula is added. 0.6d/P0.8 (however, d: gap between substrates,
P: A color liquid crystal display element characterized in that it is made of a material added at a concentration of cholesteric pitch.