JP2559215B2 - Liquid crystal display element - Google Patents

Description

The present invention relates to a liquid crystal display device.

[Prior Art] Conventionally, a method of arranging electrodes of a TN type liquid crystal display element in an XY matrix and dynamically driving them to realize a high density display capacitance has been used as an inexpensive method. However, the number of scannable lines is dominated by the steepness of the voltage-transmittance change of this element, and the improvement of such characteristics has almost reached the limit. On the other hand, the twist angle of liquid crystal molecules is 180-360
If the pretilt angle of the liquid crystal molecules at the electrode interface is increased to several degrees or more, the alignment change of the liquid crystal molecules with respect to the voltage becomes sharp. If this element is sandwiched between two polarizing plates and the interference change of light is used as contrast,
It is known that the transmittance changes sharply with respect to the voltage, and even if the number of scanning lines is increased, it is possible to display with a wide viewing angle and high contrast (for example, TJ Scheffe an
d J.Nehring, App.Phys, Lett., 45 (10), 1021 ('84) or TJSchefferet.al.'85 SID Digest paper, 120
('85)) In this display mode, two polarizing plates with neutral absorption are used, and the relative positions of the polarizing plates are changed to change the color from yellow to green and blue to blue-violet, or light It was possible to display mainly two display colors of purple and purple to bluish purple, and good display was impossible with other color tones.

[Problems to be Solved by the Invention] In a conventional display element, two polarizing plates having neutral absorption (almost uniform polarization characteristics in a visible light portion) are used, so that only a display in a specific color tone is effective. However, there were few variations in the display color, and there was a limit in applying it to various purposes.

[Means for Solving the Problem] The present invention has been made to solve the above-mentioned problems, and the liquid crystal molecular axes are relative to the electrode surface on the inner surfaces of a pair of transparent electrodes arranged substantially in parallel. Nematic or cholesteric liquid crystal with positive dielectric anisotropy with a twist angle of 180 ° to 360 ° is enclosed in a cell that is processed with a slight tilt and arranged in parallel, and the periphery is sealed with a sealing material. A polarizing plate is installed outside the cell, and means for applying a voltage is provided between the electrodes facing each other. The optical state is changed by changing the interference state of light passing through the cell according to the magnitude of the applied voltage. In the liquid crystal display device that causes a change, as at least one of the polarizing plates, a polarizing plate having two polarization directions and having polarization degrees in different wavelength regions of visible light is used. Liquid crystal display device Is.

In the present invention, a polarizing plate having two polarization directions and having polarization degrees in different wavelength regions of visible light in the two polarization directions is different from each other when rotated by being overlapped with a medium-sized polarizing plate. What is necessary is that the light of different colors is transmitted to the corners. Specifically, it may be an ordinary color polarizing plate in which polarizing plates having different colors are laminated by shifting the polarization direction or a combination of both in advance. Further, it is desirable that the polarization directions of the respective polarizations are substantially orthogonal to each other so that the hue separation in the ON and OFF states is good. The polarizing plate installed on the other side of the display element may be a neutral polarizing plate, the above-mentioned laminated polarizing plate, or a color polarizing plate, but in order to produce a strong interference color and increase the contrast. For this purpose, it is desirable to use a neutral polarizing plate that can obtain a high degree of polarization.

FIG. 1 is a schematic sectional view showing the basic structure of the present invention.

In FIG. 1, 1 and 2 are polarizing plates, 4A and 4B are transparent substrates such as glass and plastic, 3A and 3B are transparent electrodes such as indium oxide-tin oxide and tin oxide, and 5A and 5B are polyimide, polyamide and SiO. ₂ , alignment film such as Al ₂ O ₃ , 6A and 6B are power supplies, 7A and 7
B is a switch, and 8 is a sealing material.

On the left side of the figure, the switch 7A is turned off, and the liquid crystal molecules are in the twisted state 9. On the right side, the switch 7B is turned on, and the liquid crystal molecules are in the raised state 10.

In the liquid crystal display element of the present invention, the liquid crystal is twisted by about 180 to 360 ° when no voltage is applied in order to display by changing the interference state of light passing through the cell by applying a voltage and causing an optical change. For this purpose, the orientation direction of both substrates is 180
While setting to ~ 360 °, liquid crystal d / p is set to 0.25 to 1.25,
Moreover, the tilt angle of the liquid crystal molecules at the point where the alignment film and the liquid crystal molecules contact each other is set to about 4 to 10 °.

Also, unlike the conventional liquid crystal display element, the polarizing plate is arranged such that its polarization axis is displaced from the alignment direction of the liquid crystal molecules by about 20 to 70 °, and is used in a region where interference color is generated.

Although the power supply, the switch, and the like are shown separately for convenience of description, they may normally be formed by one to a plurality of ICs.

In the present invention, at least one of the polarizing plates 1 and 2 has two polarization directions, and the two polarization directions have polarization degrees in different wavelength ranges of visible light. As a result, the degree of selection of the display color is increased, and the display can be made to suit the user's preference. In this example, a red color polarizing plate and a green color polarizing plate are laminated and bonded so that the polarization directions are shifted by 90 °. Of course, this color may be variously changed, and the crossing angle of the polarization directions can be shifted from 90 °. Further, three or more color polarizing plates may be combined, or color filters may be laminated.

If one of the polarizing plates 1 and 2 is a neutral black-and-white polarizing plate, the degree of polarization can be high and the contrast can be improved.
In addition, this also uses a single color polarizing film,
It is also possible to use a polarizing plate having two polarization directions and having polarization degrees in different visible light wavelength regions in the two polarization directions.

As an example of this preferred embodiment, the polarizing plate 1 has two polarization directions in which two color polarization plates are laminated so that the polarization directions thereof are orthogonal to each other, and the visible light different in the two polarization directions is used. A polarizing plate having a degree of polarization in the wavelength range is used, and the polarizing plate 2 is a neutral polarizing plate.

[Operation] Next, the operation of the device according to the present invention will be described with reference to FIG.

The left half of the figure schematically shows the alignment state of liquid crystal molecules when no voltage is applied. The liquid crystal molecules are twisted between the electrodes such that their molecular axes are substantially parallel to the electrode interface. At this time, the polarized light passing through the polarizing plate 2 is separated into an ordinary light component and an extraordinary light component due to the birefringence of liquid crystal molecules. The two components have different propagation speeds in the liquid crystal layer, and have a phase shift after passing through the liquid crystal layer, that is, an optical phase difference, and when they pass through the polarizing plate, they exhibit coloring due to interference.

The right half of the figure shows the case where a voltage above the threshold value is applied, and the orientation of the liquid crystal molecules changes continuously from the electrode interface to the central part of the liquid crystal layer, and in the central part of the liquid crystal layer, it is almost perpendicular to the electrode surface. Arrange. When light passes through the liquid crystal layer in this state, interference-induced coloring occurs due to the same action as in the off state. When the density of coloring generated at on and off is different, or when the hue changes, it is possible to display, which includes twist angle of liquid crystal molecules, anisotropy of refractive index, thickness of liquid crystal layer,
It depends on the applied voltage.

In the present invention, by using a polarizing plate having two polarization directions in at least one of the polarizing plates and having polarization degrees in different visible light wavelength regions in the two polarization directions, the hue due to the birefringence is obtained. It is possible to widen the range of change of the display and widen the selection range of the display color.

[Example] Example 1 After forming a polyimide resin film on an electrode, the surface was rubbed to form an alignment film of liquid crystal, and a cell having a cell gap of 7.0 µm illustrated in Fig. 1 was produced. A small amount of an optically active substance was added to nematic liquid crystal ZLI-2293 manufactured by Merck Ltd. in this cell, and liquid crystal molecules were controlled so as to be twisted by 200 degrees between both electrodes at the time of off. A neutral polarizing plate having a substantially uniform degree of polarization in the visible light portion was placed on one side of this cell so that its polarization axis was inclined by 35 degrees with respect to the direction of molecules on the adjacent electrodes. On the other side, 2 independent polarizations for red and green
The polarizing plates are integrated so that their polarization axes are substantially orthogonal,
The polarization axes of the green polarizing plate and the red polarizing plate are 40 ° and 50 ° respectively for the liquid crystal molecules on the adjacent electrodes.
Aligned so that it tilts. The background color of this device was green. When a dynamic waveform of 1/100 Duty, 1/11 Bias was applied to this device and it was displayed, red letters could be displayed on a green background. At this time, even if the polarization axes on both sides of the cell were shifted by ± 20 ° with respect to the above-mentioned angle, a normal contrast was obtained although the color tone was slightly changed.

Moreover, when the relative positions of the polarization axes of the laminated polarizing plates were exchanged, it was possible to display green from the red background.

Example 2 In the same manner as in Example 1, the twist angle of liquid crystal molecules was 240.
Created a degree cell. As a laminated polarizing plate, the one having the polarized light separately for orange and blue was similarly used and driven,
It was possible to change the color between pink and black.

Example 3 The twist angle of the liquid crystal molecules was 260 in the same manner as in Example 1.
Created a degree cell. Similarly, when driving was performed using a red and blue laminated polarizing plate, displays of reddish purple and blue green were obtained.

[Advantages of the Invention] As described above, according to the present invention, at least one of the two polarizing plates having polarizations in different wavelength regions is laminated and installed so that their polarization axes are substantially orthogonal to each other. This is an excellent feature that enables changes and widens the range of hue selection.

In the above examples, only the polarizing plate was used, but it is also highly useful to combine it with a color filter to change both the background and the display color and adjust the hue.

[Brief description of drawings]

 FIG. 1 is a sectional explanatory view showing the basic structure of the present invention. 1,2: polarizing plate, 3A, 3B: transparent electrode 4A, 4B: transparent substrate, 5A, 5B: alignment film 6A, 6B: power supply, 7A, 7B: switch 8: seal material, 9: liquid crystal molecule when off Alignment 10: Alignment of liquid crystal molecules when turned on

Continuation of the front page (72) Kazutoshi Sawada 18-33 Higashiterao-Higashidai, Tsurumi-ku, Yokohama-shi (72) Masahito Nakayama 2-59-1 Tsurugamine, Asahi-ku, Yokohama-shi (56) Reference JP-A-54-38150 (JP, A) JP-A-60-107020 (JP, A)

Claims (3)

(57) [Claims] 1. An inner surface of a pair of electrodes arranged substantially parallel to each other is treated so that liquid crystal molecular axes are slightly inclined with respect to the electrode surfaces and arranged substantially parallel to each other, and the periphery thereof is sealed with a sealing material. A nematic or cholesteric liquid crystal with a positive dielectric anisotropy with a twist angle of 180 ° to 360 ° is enclosed in the cell, a polarizing plate is installed outside the cell, and a voltage is applied between the opposing electrodes. In the liquid crystal display element, which has means, changes the interference state of light passing through the cell to cause an optical change in accordance with the magnitude of the applied voltage, at least one polarizing plate has two polarization directions, A liquid crystal display device comprising a polarizing plate having a degree of polarization in visible light wavelength regions which are different in the two polarization directions. 2. A liquid crystal display according to claim 1, wherein the polarizing plate having two polarization directions has a structure in which two polarizing plates each having a polarization degree in a different wavelength region of visible light are bonded to each other. element. 3. A liquid crystal display device according to claim 1, wherein the two polarization directions are orthogonal to each other.