JPH01137231A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To make natural display by using color polarizing plates and negative dichromatic dyes having the color tones of the complementary color relation therewith so that the background color and the color of a display part are made colorless. CONSTITUTION:This liquid crystal display element is constituted of the liquid crystal cell formed by disposing substrates 2, 2' on which oriented films 4, 4' are formed and which have transparent electrodes 3, 3' subjected to an orientation treatment so as to face each other and sealing a liquid crystal 6 between the substrates and two sheets of the polarizing plates 1, 1' which are so disposed as to sandwich the above-mentioned cell. The twist angle of the liquid crystal 6 is within a 90-270 deg. range. At least one of the polarizing plates 1, 1' is formed as the color polarizing plate and the dichromatic dye which has the color tone of the complementary color relation with the color of said color polarizing plate and absorbs more strongly the light deflected in the molecular minor axis direction than the light deflected in the molecular major axis direction is added to the liquid crystal 6. The background color and the color of the display part are thereby made colorless simultaneously and the natural display is enabled.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to a so-called STN ( This invention relates to super twisted nematic (super twisted nematic) liquid crystal display elements.

[Prior art]

The liquid crystal display system that has been mainly used in the past is called the TN (twisted nematic) type, in which a liquid crystal layer made of nematic liquid crystal or a mixture of nematic liquid crystal and cholesteric liquid crystal is arranged between a pair of substrates having display electrodes. In this case, the liquid crystal molecules have a structure twisted by about 90 degrees. In this method, polarizing plates are arranged on the outside of each of the upper and lower substrates so that their polarization axes are perpendicular or parallel to each other, and the alignment direction of liquid crystal molecules on the substrate and the polarization axis of the polarizer are perpendicular or parallel to each other. , and utilizes the decorative change in polarization caused by the electric field. This display method has the disadvantage that when high time division driving is performed to increase the display capacity, the contrast deteriorates and the viewing angle becomes narrow. This is because with high time division driving, the ratio of the voltages applied to selected points and non-selected points approaches 1, so in order to obtain a display element with high contrast and a wide viewing angle, the relative transmittance of the element must change by 50%. Voltage V. and the voltage changes by 10%. The ratio (V, o/
V engineering. ) It is necessary to make the steepness γ as small as possible. In the case of TN type, this γ value is about 1.13.

In recent years, in order to reduce this value, a display method called super twisted nematic (STN) mode has been proposed. In this method, the twist angle of the liquid crystal molecules is set to 90° or more, and the orientation direction of the liquid crystal on the substrate is shifted from the polarization axis of the polarizer, thereby utilizing a change in color tone due to a change in birefringence. With such a structure, the γ value can be reduced to 1.1 or less, and high time division parking of about 1/400 duty is possible, but in this case, since birefringence is used, the Due to the refraction effect, both the background and the display area are colored, resulting in an extremely unnatural display.

〔the purpose〕

An object of the present invention is to provide a liquid crystal display element capable of displaying black on a white background by significantly reducing the coloring observed in conventional STN type liquid crystal display elements.

〔composition〕

According to the present invention, a liquid crystal is sandwiched between a pair of alignment-treated substrates having display electrodes, and when no electric field is applied, the long axis of the molecules of the liquid crystal is aligned approximately horizontally with respect to the substrates, and the liquid crystal molecules A liquid crystal cell having a long axis of Mg, a twist angle in the range of more than 90° and less than 270° between the substrates, and the liquid crystal containing a dichroic dye, and a dichroic cell arranged to sandwich the liquid crystal. In a liquid crystal display element consisting of two polarizing plates, at least one of the polarizing plates is a color polarizing plate, and the dichroic dye has a color tone complementary to that of the color polarizing plate. , there is provided a liquid crystal display element characterized in that the extinction coefficient of the dichroic dye is larger for light polarized in the direction of the short axis of the molecules than for light polarized in the direction of the long axis of the molecules.

FIG. 1 shows an example of the structure of a liquid crystal display element of the present invention.

In the figure, L and 1' are polarizing plates, 2 and 2' are substrates, 3 and 3' are display electrodes, 4 and 4' are alignment films, 5 is a sealing material, and 6 is a liquid crystal, respectively.

In the liquid crystal display element of the present invention, alignment films 4, 4' are formed,
a substrate 2 having transparent electrodes 3, 3' subjected to alignment treatment;
2' are arranged facing each other, and a liquid crystal cell is formed by sealing a liquid crystal 6 between them, and two polarizing plates 1 and 1' are arranged to sandwich this cell.

The twist angle of the liquid crystal 6 is in the range of 90° to 270°,
This is the same as the so-called conventional STN type. LCD 6,
If we use colorless polarizing plates 1 and 1' as before,
When the direction of the transmission axis of the polarizing plate is adjusted so that the cell becomes the brightest, the color of the cell becomes yellow to yellow-green. If the cell is removed in this state, a blue display will appear on a yellow to yellow-green background, giving an extremely unnatural feeling (see Figure 2). One of the sheets is a color polarizing plate, and the color tone is complementary to the color of this color polarizing plate.

Moreover, by adding a dichroic dye to the liquid crystal 6 that absorbs light polarized in the direction of the short axis of the molecule more strongly than light polarized in the direction of the long axis of the molecule (having so-called negative dichroism), the background color can be changed. At the same time, the color of the display section is made achromatic, allowing for a natural display.

The color tone of the color polarizing plate used in the present invention is preferably blue. By doing this, the background color becomes close to white. However, if this continues, the color of the display section will become a brighter blue than when a neutral gray polarizing plate is used, and the contrast will decrease. In order to avoid this, by adding a red to red-orange dichroic dye with negative dichroism to the liquid crystal 6, the blue light that has passed through the display area will be absorbed by the dichroic dye. , the display becomes darker and the color approaches an achromatic color.

In a typical configuration of a conventional STN type liquid crystal display element, the direction of the long axis of liquid crystal molecules near the alignment films 4, 4' and the direction of the transmission axis of the polarizing plate on the side closer to the alignment film are about 45 degrees. , in the present invention, in order to avoid a decrease in the contrast of the dichroic dye, 45
It is desirable to set the value smaller than 25°, preferably in the range of 25″ to 45°.In addition, as a dichroic dye with negative dichroism,
Tetrazine dyes are widely known, but in the present invention,
It is not limited to this.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Example An STN type liquid crystal display element having the configuration shown in FIG. 1 was manufactured.

In this case, the liquid crystal used is a nematic liquid crystal (manufactured by A-LUC, 5811) to which a tetrazine-based dichroic dye is added, and the polarizing plates are one neutral play type polarizing plate and one blue color polarizing plate. was used.

FIG. 3 shows a light transmission spectrum diagram of the liquid crystal display element constructed in this manner. As you can see from this figure, with this liquid crystal display element, the background is a little darker, but in the conventional case (
(See Figure 2), the color was significantly closer to white. In addition, the display area became considerably dark and almost achromatic.

〔effect〕

As described above, in the STN type liquid crystal display element of the present invention, by using a color polarizing plate and a negative dichroic dye having a complementary color tone, the background color and the color of the display area are significantly reduced. It can be colored and displayed naturally.

[Brief explanation of the drawing]

FIG. 1 shows a sectional view showing an example of the structure of a liquid crystal display element of the present invention. Figures 2 and 3 show light transmission spectra of liquid crystal display elements, and Figure 2 shows the conventional liquid crystal display element and Figure 3.
The figure shows the results for the liquid crystal display element of the present invention. ■, 1'...Polarizing plate, 2, 2'...Substrate. 3.3'...display electrode, 4,4'...alignment film,
5... Seal material, 6... Liquid crystal.

Claims (1)

[Claims] (1) A liquid crystal is sandwiched between a pair of alignment-treated substrates having display electrodes, and when no electric field is applied, the long axis of the molecules of the liquid crystal is aligned approximately horizontally with respect to the substrates, and the long axis of the liquid crystal molecules is A liquid crystal cell having a twist angle in a range of more than 90° and less than 270° between the substrates, and in which the liquid crystal contains a dichroic dye, and two polarizing plates arranged to sandwich the liquid crystal. a liquid crystal display element comprising: at least one of the polarizing plates is a color polarizing plate; the dichroic dye has a color tone complementary to that of the color polarizing plate; A liquid crystal display element characterized in that the extinction coefficient of the dye is larger for light polarized in the direction of the short axis of the molecules than for light polarized in the direction of the long axis of the molecules.