JPH0534657A - Liquid crystal display element - Google Patents

Abstract

(57) [Summary] [Structure] For driving in which a driving voltage is applied between the two polarizing plates 1 and 4 in a twisted arrangement with a spiral axis substantially parallel to the substrate normal line. The present invention relates to a liquid crystal display element in which a liquid crystal cell 3 and a compensating liquid crystal layer 2 having a twisted arrangement in a spiral axis substantially parallel to a substrate normal line of a driving liquid crystal cell are arranged. The two polarizing plates are arranged so that a dark state can be obtained when no voltage is applied, and the twisting angle of the compensating liquid crystal layer is 360 ° or more, and the twisting arrangement is opposite to the twisting direction of the driving liquid crystal layer. Therefore, the long axes of the liquid crystal molecules closest to each other in the driving liquid crystal cell and the compensating liquid crystal layer are substantially parallel to each other. [Effect] It is possible to provide a high-quality display liquid crystal display device having improved viewing angle characteristics of the liquid crystal display device and excellent visibility.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having controlled contrast ratio and viewing angle characteristics of display color.

[0002]

2. Description of the Related Art In recent years, liquid crystal display elements, which have the great advantages of thinness, light weight and low power consumption, have been actively used as display devices for personal OA equipment such as Japanese word processors and desktop personal computers. Most of liquid crystal display elements (hereinafter abbreviated as LCD) use twisted nematic liquid crystal, and the display system can be roughly classified into two systems of a birefringence mode and an optical rotation mode.

The LCD of the birefringence mode display system generally has a molecular arrangement twisted by 90 ° or more (called the ST system) and has steep electro-optical characteristics, so that a switching element (thin film transistor or diode) is provided for each pixel. Even without a simple structure, a large-capacity display can be easily obtained by time-division driving even with a simple matrix electrode structure. However, in this ST method, since the birefringence effect is used, the display colors are so-called yellow mode display of yellow and dark blue or so-called blue mode display of white and blue due to light interference,
Black and white display was impossible. Japanese Patent Publication No. 63-53528 discloses that a black and white display can be realized by disposing a second twisted liquid crystal cell between the polarizing plate and the liquid crystal cell as a means for eliminating such coloring of the display. Has been done. The principle of black and white is that the light of the ordinary light component and the extraordinary light component, which are elliptically polarized in the display liquid crystal cell in which the liquid crystal molecules are arranged in a twisted arrangement, are exchanged with each other by the second liquid crystal cell which is the optical compensation plate. Elliptically polarized light is converted into linearly polarized light. As a result, coloring due to light interference is eliminated, and black and white display can be realized.

On the other hand, the LCD of the optical rotation mode has a molecular arrangement twisted by 90 ° (TN method), has a fast response speed (tens of milliseconds) and shows a high contrast ratio and a good gradation display property. A full-color display LCD TV (TFT-LCD or MI
It is applied to M-LCD).

Regarding color display, a cholesteric liquid crystal cell showing a certain hue utilizing selective scattering when no voltage is applied is arranged between a polarizing plate and a liquid crystal cell, and a combination of the presence or absence of voltage application to the cholesteric liquid crystal cell and the liquid crystal cell is used. It is possible to switch to a two-color display of a specific hue and its complementary color or a monochrome display mode. Mol.Cryst.Liq.Cryst., 1
It is reported in 977, VOL.39, PP.127-138.

However, a liquid crystal display device utilizing these birefringence mode, optical rotation mode and selective scattering has a viewing angle dependency that a display color and a contrast ratio change depending on a viewing angle and an azimuth, and a cold cathode ray tube (CRT). The display performance of is completely exceeded.

[0007]

It is generally known that liquid crystal molecules have different refractive indexes in the major axis direction and the minor axis direction of the liquid crystal molecules. When light of a certain polarization state enters a liquid crystal molecule exhibiting such anisotropy of refractive index, the light changes its polarization state depending on the angle of the liquid crystal molecule. Therefore, the polarization state of the light propagating in the liquid crystal cell is different depending on whether the light enters the liquid crystal cell perpendicularly or obliquely, and as a result, the display state depends on the azimuth and angle when the liquid crystal display element is viewed. The pattern appears in reverse, the display pattern disappears at all, or the display becomes colored, which is not preferable in practice.

The present invention solves the above inconvenience.

[0009]

DISCLOSURE OF THE INVENTION The present invention provides a driving liquid crystal in which a driving voltage is applied between two polarizing plates in a twisted arrangement with a helical axis substantially parallel to the substrate normal. In a liquid crystal display element in which a cell and a compensating liquid crystal layer twisted in a spiral axis substantially parallel to a substrate normal line of the driving liquid crystal cell are arranged, the two polarizing plates are dark when no voltage is applied. The compensating liquid crystal layer has a twist angle of 360 ° or more, and is arranged in a twisted direction opposite to the twist direction of the driving liquid crystal layer. The long axes of the liquid crystal molecules closest to the compensating liquid crystal layer are substantially parallel to each other.

[0010]

In general, there are roughly two types of arrangements of polarizing plates used in liquid crystal display devices. Light is not transmitted when a voltage is not applied to the liquid crystal cell, and a light transmission state is obtained when a voltage is applied ( There are a normally closed system and a system in which light is transmitted when a voltage is not applied to the liquid crystal cell and light is blocked when a voltage is applied (normally open). The TN method will be described below. FIG. 3 shows the contrast ratio dependency of the normally closed and normally open conventional TN methods when the display surface is tilted from 0 ° to 60 ° in the left and right directions from the normal. It is a figure. It is indicated by (13.0) in the case of normally closed and (14.0) in the case of normally open. Comparing these, it can be seen that normally closed has less viewing angle dependence of contrast ratio than normally open. The contrast ratio is a value obtained by dividing the brightness in a state where light is transmitted (bright state) by the brightness in a state where light is blocked (dark state), and the contrast ratio greatly affects the brightness in a dark state. Then, when the viewing angle dependence of the brightness in the left-right direction in the dark state of both the normally open type and the normally closed type is measured, the characteristics as shown in FIG. 4 are obtained. In case of normally closed (13.1), in case of normally open (14.
Shown in 1). As is clear from the figure, normally closed has less viewing angle dependency in the dark state than normally open, and as a result, normally closed has better viewing angle characteristics of contrast ratio than normally open. Therefore, the viewing angle characteristic of the contrast ratio is better when the polarizers are normally closed. However, in the normally closed method, dark coloring is significantly caused by optical rotation dispersion, and the display color in the dark state greatly changes depending on the cell thickness.

As a method of compensating for such a display color in the dark state, the second twisted liquid crystal cell, which is twisted in the opposite direction, is arranged between the polarizing plate and the liquid crystal cell (two-layer cell system) so that the dark state is colored. It has been reported in JP-A-57-96315 (applicant: Sharp) that this can be solved. This principle is exactly the same as the principle of compensating the display color of the ST method described above. According to this method, coloring in a dark state due to light interference is eliminated, and high contrast can be realized. Figure 5 shows this two-layer cell system (8.1) and the conventional example (8.2).
It is a diagram showing the viewing angle dependency of the luminance in the dark state in the left and right direction in FIG. 2. However, as is clear from the figure, this method has the drawback that the viewing angle dependency of the transmittance in the dark state is large and the viewing angle is narrow. As described above, the normally closed liquid crystal cell display color and the wide viewing angle tend to show a trade-off relationship.

As a result of various investigations by the inventors, the liquid crystal cell having a device for applying a voltage to the liquid crystal layer in the twist direction of the second liquid crystal cell has a twist angle of 360 ° or more, that is, a driving liquid crystal cell. By arranging the liquid crystal cell for driving and the second liquid crystal cell in the opposite direction to each other so that the major axis directions of the liquid crystal molecules closest to each other are substantially parallel to each other, the viewing angle of the display color is expanded and the darkness is increased. It has been found that the display color of the state can also be improved. In FIG. 6, the second liquid crystal cell is placed between the polarizing plate and the driving liquid crystal cell so that the long axis direction of the liquid crystal molecules closest to the driving liquid crystal cell and the second liquid crystal cell, which is an optical compensator, are parallel to each other. The transmission spectrum diagram in the dark state in the case of being arranged so as to be orthogonal to that in the case of (9.1) is also shown in the conventional example (9.3). As can be seen from the figure, when the driving liquid crystal cell and the second liquid crystal cell are arranged such that the longest axis of the liquid crystal molecules closest to each other is parallel, the transmission spectrum becomes substantially constant with respect to the wavelength, and as a result, the coloring of the display can be eliminated. ..

Although the TN method has been described above, it is needless to say that the same effect can be obtained also in the ST type liquid crystal display element having a twist angle of 90 ° or more.

It is needless to say that, as the above-mentioned compensation liquid crystal layer, not only cholesteric liquid crystal but also a polymer liquid crystal layer having a twisting property can obtain the same function, and when polymer liquid crystal is used, for example, driving liquid crystal. It can also be obtained by coating such a polymer liquid crystal layer on at least one of the substrates of the cell, which facilitates the production and more desirably provides a liquid crystal display device. In this case, it is possible to use, for example, a high molecular copolymer liquid crystal having a polysiloxane main chain and having biphenylbenzoate and cholesteryl groups in the side chains at an appropriate ratio.

[0015]

EXAMPLES Examples of the liquid crystal display device of the present invention will be described in detail below.

(Embodiment 1) FIGS. 1 and 2 show the cell structure in this embodiment. The liquid crystal display element consists of two polarizing plates 1,
4 and the compensating liquid crystal cell 2 and the driving liquid crystal cell 3 are sandwiched between them. The polarizing plate 1 is a transparent substrate 1a
The polarizing film 1b is attached to the inside of the polarizing plate 4, and the polarizing plate 4 is also formed by attaching the polarizing film 4b to the transparent substrate 4a. The light transmission axes (1.1) and (4.1) of the polarizing plates 1 and 4 are arranged so as to be parallel to each other.

The compensating liquid crystal cell 2 comprises these polarizing plates 1, 4
The liquid crystal cell structure has a liquid crystal layer 2c interposed between the transparent substrates 2a and 2b.

The driving liquid crystal cell 3 is arranged between the compensating liquid crystal cell 2 and the polarizing plate 4. The upper substrate 3a and the lower substrate 3b form transparent electrodes 3c and 3d, respectively, and are connected to a driving power supply 3f. The twisted nematic liquid crystal layer 3e is introduced between the substrates 3a and 3b at a twist angle of 90 °, and the state changes according to the applied voltage from the driving power source 3f.

The optical axis of the liquid crystal of the driving liquid crystal cell 3 is twisted counterclockwise from the lower substrate 3b to the upper substrate 3a (left twist). (3.1) and (3.2) are rubbing axes of the upper and lower substrates, respectively, which are orthogonal to each other. The thickness of the liquid crystal layer of the driving liquid crystal cell 3 is 6.0 μm.

The compensating liquid crystal cell 2 is a liquid crystal cell having a liquid crystal layer 2c with a twist angle of 450 ° and a thickness of 6.0 μm (2.1),
(2.2) are rubbing axes of the upper and lower substrates 2a and 2b, respectively, which are orthogonal to each other.

The transmission axes (1.1) and (4.1) of the polarizing plates 1 and 4, the rubbing axis (2.2) of the lower substrate of the compensating liquid crystal cell 2 and the rubbing axis (3.1) of the upper substrate of the driving liquid crystal cell 3 are In parallel, the rubbing axis (2.2) of the lower substrate of the compensating liquid crystal cell 2 and the rubbing axis (3.2) of the upper substrate of the driving liquid crystal cell 3 are parallel. That is, the liquid crystal molecules closest to the compensating liquid crystal cell 2 and the driving liquid crystal cell 3 are arranged so that their major axis directions are parallel to each other.

An example of the viewing angle dependence of the Y-axis azimuth in FIG. 2 in the dark state (when no voltage is applied) of the liquid crystal display device of this structure is shown in FIG. FIG. 7 shows the liquid crystal cell of FIG.
FIG. 7 is a diagram showing the transmittance of the liquid crystal cell in the dark state when the measurement point is tilted from 0 ° to 60 ° from the z axis in the y and −y directions. (10.1) in the figure shows the viewing angle characteristics in the present embodiment,
(10.2) is a diagram showing viewing angle characteristics in a conventional example. Ideally, it is desirable that the transmittance is small and the change is constant regardless of the angle at which the liquid crystal cell is viewed. Compared to the conventional example, the change of the inclination angle of the transmittance is smaller in this example, and the display panel is a TFT having a diagonal size of 10 inches.
-When an LCD is created with this configuration and 16 gradations are displayed,
We have realized a high-contrast LCD that can distinguish between 16 gradations even if the viewpoint is changed. When the viewing angle characteristics of the contrast ratio were measured, the contrast ratio was 1 for a 60 ° cone.
A value of 0: 1 or more was obtained, and a good display without inversion of display image or change of display color was obtained even when the incident angle was 60 ° or more.

(Comparative Example) In Example 1, the viewing angle characteristics of the liquid crystal display device in the case where the compensating liquid crystal cell 2 was not disposed between the driving liquid crystal cell 3 and the upper polarizing plate 1 were measured. The measurement result is shown in (10.2) of FIG. The dark state changes depending on the viewing angle,
With a 60 ° cone, the maximum contrast ratio was only 5: 1, and when the incident angle was 60 ° or more, the display image was inverted or completely invisible depending on the viewing direction.

Example 2 In Example 1, a polymer liquid crystal film was used as the compensating liquid crystal cell 2, and Example 1 was used.
Arranged in the same way. When the electro-optical characteristics were measured, the same characteristics as in Example 1 were obtained, and 10 inch TFT-
When an LCD was created with this configuration and displayed in 16 gradations, a high contrast LCD capable of distinguishing between 16 gradations even when the viewpoint was changed was realized. When the viewing angle characteristics were measured, a contrast ratio of 15: 1 or more was obtained with a 60 ° cone, and a good display without reversal of display image or change of display color was obtained even when the incident angle was 60 ° or more.

(Example 3) In Example 1, an ST cell twisted by 240 ° was used as the driving liquid crystal cell 3, and the liquid crystal cell 3 was arranged in the same axial configuration as in Example 1 as in Example 1. The angles (1.1), (2.1), (2.2), (3.1), (3.2) and (4.1) in Fig. 8 are the axes (1.1), (2.1), (2.2), (3.1), () in Fig. 2. 3.2), (4.1)
It corresponds to the angle of. (1.1) is 0 °, (2.2) is 120
, (3.1) was 120 °, and (4.1) was 0 °. When the electro-optical characteristics were measured with this configuration, the same compensation effect as in Example 1 was obtained. When the viewing angle characteristics were measured, a contrast ratio of 13: 1 or more was obtained at a 30 ° cone, and an incident angle of 30
Good display was obtained without inversion of the display image or change of the display color even at a temperature of ≥ °.

[0026]

According to the present invention, it is possible to provide a liquid crystal display device of high quality display in which the viewing angle characteristics of the liquid crystal display device are improved and which is excellent in visibility. Needless to say, even if the present invention is applied to an active matrix liquid crystal display element using a 3-terminal or 2-terminal element such as TFT or MIM, excellent effects can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a liquid crystal display element of Example 1 of the present invention.

FIG. 2 is an exploded perspective view showing the configuration of the liquid crystal display element according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a viewing angle characteristic of a contrast ratio of a normally open and normally closed type in a left-right direction of a conventional TN type liquid crystal display device.

FIG. 4 is a diagram for explaining a viewing angle characteristic of luminance in a normally open and normally closed dark state of a conventional TN type liquid crystal display device.

FIG. 5 is a diagram illustrating viewing angle characteristics in a known example and a conventional example having a two-layer cell structure.

FIG. 6 is a diagram for explaining a transmission spectrum of a conventional example, together with the case where the major axis directions of the liquid crystal molecules that are closest to each other in the compensating liquid crystal cell and the driving liquid crystal cell are parallel and orthogonal.

FIG. 7 is a diagram illustrating a viewing angle characteristic in a dark state according to an embodiment of the present invention and a conventional example.

FIG. 8 is a diagram showing an axial configuration of a liquid crystal display element of Example 3 of the present invention.

[Explanation of symbols]

 1, 4 ... Polarizing plate 2 ... Compensation liquid crystal cell 3 ... Driving liquid crystal cell

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[Procedure amendment]

[Submission date] July 2, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

[0010]

In general, there are roughly two types of arrangements of polarizing plates used in liquid crystal display devices. Light is not transmitted when a voltage is not applied to the liquid crystal cell, and a light transmission state is obtained when a voltage is applied ( There are a normally closed system and a system in which light is transmitted when a voltage is not applied to the liquid crystal cell and light is blocked when a voltage is applied (normally open). The TN method will be described below. FIG. 3 shows the contrast ratio dependency of the normally closed and normally open conventional TN methods when the display surface is tilted from 0 ° to 60 ° in the left and right directions from the normal. It is a figure. It is indicated by (13.0) in the case of normally closed and (14.0) in the case of normally open. Comparing these, it can be seen that normally closed has less viewing angle dependence of contrast ratio than normally open. The contrast ratio is a value obtained by dividing the brightness in a state where light is transmitted (bright state) by the brightness in a state where light is blocked (dark state), and the contrast ratio greatly affects the brightness in a dark state. Then, when the viewing angle dependence of the brightness in the left-right direction in the dark state of both the normally open type and the normally closed type is measured, the characteristics as shown in FIG. 4 are obtained. In case of normally closed (14.1) , in case of normally open (13.
Shown in 1) . As is clear from the figure, normally closed has less viewing angle dependency in the dark state than normally open, and as a result, normally closed has better viewing angle characteristics of contrast ratio than normally open. Therefore, the viewing angle characteristic of the contrast ratio is better when the polarizers are normally closed. However, in the normally closed method, dark coloring is significantly caused by optical rotation dispersion, and the display color in the dark state greatly changes depending on the cell thickness.

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Hato 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock company, Toshiba Yokohama Works (72) Inventor Yuzo Kutake 8 Shinsita-cho, Isogo-ku, Yokohama, Kanagawa Ceremony Company Toshiba Yokohama Office

Claims (1)

Claim: What is claimed is: 1. A driving liquid crystal cell in which a driving voltage is applied between two polarizing plates in a twisted arrangement with a helical axis substantially parallel to a substrate normal line. A liquid crystal display element in which a compensating liquid crystal layer twisted in a spiral axis substantially parallel to the substrate normal line of the driving liquid crystal cell is arranged.
The polarizing plates are arranged so that a dark state can be obtained when no voltage is applied, the twisting angle of the compensating liquid crystal layer is 360 ° or more, and the twisting direction is opposite to the twisting direction of the driving liquid crystal layer. Therefore, the liquid crystal display element is characterized in that the driving liquid crystal cell and the liquid crystal molecules closest to the compensating liquid crystal layer have their major axes substantially parallel to each other.