JPH07218933A - Liquid crystal display - Google Patents

Abstract

(57) [Summary] [Object] To provide a liquid crystal display device having a high efficiency of light utilization, especially in a reflection type, which is compatible with a high-definition display having a large number of scanning lines and a large screen by a simple matrix system. [Structure] The angle of the rubbing directions applied to the two substrates and the twist angle (φr) of the liquid crystal molecules in the initial state are made to substantially match, and the interface pretilt angles of each have a relationship of opposite sign. To obtain a liquid crystal display device having two metastable states. By adding a dichroic dye to the liquid crystal layer, it becomes possible to optically distinguish between the two states with a single polarizing plate, and it functions as a display device with a simple structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device using liquid crystal, and more particularly to a liquid crystal display device which is driven by a simple matrix using bistable switching.

[0002]

2. Description of the Related Art Liquid crystal display devices that are currently in practical use as display devices for OA equipment use twisted nematic (TN) type liquid crystals or super twisted nematic (STN) type liquid crystals. For example, M. Schadt and
W. Helfrich: Appl. Phys. Lett. 18 (1971) 127, or TJScheffer and J. Nehring: Appl. Phys. Lett. 45
Since these display methods shown in (1984) 1021. do not have a memory effect, they are driven by a simple matrix driving method by a voltage averaging method or an active matrix driving method in which an active element such as a transistor is provided in each pixel. It

Besides this, although it has not been put to practical use yet,
Various methods have been studied. For example, JP-A-59-21972
0, Japanese Patent Laid-Open No. 60-196728 discloses a technology for speeding up the voltage averaging method, which is disclosed in Japanese Patent Publication 1-51818 and USP 4,239,345.
Japanese Examined Patent Publication No. 3-26368 and Japanese Patent Laid-Open No. 59-58420 disclose a method using bistable switching.

Regarding an operation mode having bistability or a plurality of stable states, it is suitable for high-definition display with a large number of scanning lines when it is possible to selectively switch between these states with an appropriate voltage waveform. Each has its own problems.

For example, Japanese Patent Publication 1-51818 and USP 4,239,34
Since the technology disclosed in 5 has bistability,
Information that has been written can be retained for a long time without using an active element. However, since switching between the two stable states is basically performed by abrupt cutoff of the applied voltage and a slow drop for about 1 second, it is not suitable for simple matrix drive and the writing speed is very slow. In fact, Japanese Patent Publication No. 1-51818 only describes the switching principle, and does not disclose a simple matrix driving method.

The technique disclosed in Japanese Patent Publication No. 3-26368 is
By controlling the applied voltage, relatively fast bistable switching is performed. However, since a high pretilt angle of 35 ° is required, the liquid crystal alignment film must be formed by oblique vapor deposition or the like, which is not practical.

The technique disclosed in Japanese Patent Laid-Open No. 59-58420 is
Whether to write or not can be selected by controlling the applied voltage, but in order to erase the display, the liquid crystal layer must be heated to the isotropic phase. Also, a very high voltage is required for writing.

[0008]

In the operation mode having the above-mentioned bistability or a plurality of stable states,
Generally, since each stable state is optically identified by utilizing the birefringence of liquid crystal, the number of optical elements such as polarizing plates is large and the arrangement is complicated. As a result, there is a problem in that the light utilization efficiency is low and the display surface is dark especially in a reflection type device.

The present invention is intended to solve the above problems, and an object of the present invention is to provide a high-definition liquid crystal display device which can realize a high-quality, particularly reflective type, bright display which can be realized by a simple matrix system. It is in the place of providing.

[0010]

In order to solve the above problems, a liquid crystal display device and a driving method according to the present invention are as follows: (1) A group of scanning electrodes and a group of signal electrodes are arranged in a matrix form, and pixels are arranged at the opposite portions thereof. Liquid crystal display panel constituted by sandwiching liquid crystal having memory effect between substrates to be formed, liquid crystal display comprising at least one polarizer, at least one reflection layer and means for applying a drive voltage signal to the electrode group In the device, the liquid crystal layer constituting the liquid crystal display panel contains a dichroic dye, and the absorption axis distribution of the dichroic dye changes according to the alignment state of the liquid crystal. At least 2 of stable or metastable states
It is characterized in that the polarizer is set in such an arrangement that the two states are optically identified.

(2) The liquid crystal having the memory effect forms a twist angle of φr in an initial state before applying a voltage, and the twist angle is approximately (φr + 180 °) in a relaxed state after applying a pulse voltage group. ) And abbreviation (φr-180
The liquid crystal is characterized by having two metastable states that are (°).

(3) The angle between the long axis direction of the liquid crystal molecule or the main absorption axis direction of the dichroic dye molecule and the transmission axis direction of the polarizer at the interface subjected to the alignment treatment is 45 ° to 135 °.
It is characterized by being °.

[0013]

EXAMPLES The present invention will be described in detail below with reference to specific examples.

An optically active additive (S811 manufactured by E. Merck) was added to a liquid crystal composition (ZLI-3329 manufactured by E. Merck) that exhibits a nematic phase at room temperature to adjust the helical pitch p to 3.5 μm. . To the liquid crystal composition, a black dichroic dye (Mitsui Toatsu: S344) was added in an amount of 3.0% by weight. In the cell, a scanning electrode group and a signal electrode group made of ITO were arranged in a matrix, and a polyimide alignment film was provided, and rubbing treatment was performed on the upper and lower substrates in the antiparallel direction (180 degrees) to obtain a gap d = 1.8 μm. I used one. When the above liquid crystal composition is enclosed, the interface pretilt angle becomes about 5 ° with the opposite sign near the upper and lower substrates, and p / 4 <
Since d <3p / 4, the orientation of the liquid crystal molecules is in a 180 ° twist state having a helical axis in the substrate normal direction. A schematic structure of the liquid crystal display device is shown in FIG. The element of this structure produces two metastable states, that is, a substantially 0 ° twist (uniform) state and a substantially 360 ° twist state depending on the applied drive voltage waveform. In this case, 2 added to the liquid crystal
It was confirmed that the absorption axis distribution of the chromatic dye also changes following the change in the alignment state of the liquid crystal. The memory type liquid crystal panel thus obtained was set to the optical arrangement described below, and a liquid crystal display device having a circuit configuration shown in FIG. 5 was formed to confirm the effects of the present invention.

(Embodiment 1) FIG. 2A shows a first embodiment of the present invention.
The schematic sectional drawing of is shown. Liquid crystal panel (2
1), a polarizing plate (22) and a reflecting plate (23) were arranged.
FIG. 2C shows the relationship between the alignment treatment (rubbing) direction (24) applied to the interface and the transmission axis (25) of the polarizing plate in the display surface (xy plane). In this embodiment, 24 and 2 in FIG.
The angle φ _A formed by 5 was set to about 90 °.

A liquid crystal display device of the present invention is formed by connecting the above-mentioned element (liquid crystal panel) to a drive circuit in a structure as shown in FIG. 5 and applying a drive voltage waveform, an example of which is shown in FIG. 3, to the electrodes. Can work.

In FIG. 3, reference numeral 301 denotes a voltage waveform applied to the scanning electrodes, 302 denotes a voltage waveform applied to the signal electrodes, and 303 denotes a drive voltage waveform applied to the liquid crystal layer as a difference between 301 and 302. Each of t ₀ and t ₁ corresponds to the time for scanning one screen. absolute value during the selection period t ₀₁ in _{t 0 | V 2 -V 3 |} ≦ Vc becomes voltage pulse is applied rise to metastable states of approximately 360 ° twist, the absolute value in the selection period t ₁₁ in t ₁ | A voltage pulse of V ₂ + V ₃ | ≧ Vc is applied to generate a metastable state of approximately 0 ° twist (uniform). Vc is a critical value for switching between two metastable states. FIG. 4 is a schematic diagram showing changes in the alignment state of the liquid crystal and the added dichroic dye caused by the application of the drive voltage waveform. In the initial state where no electric field is applied, the liquid crystal molecules (1) and the dye molecules (11) are twisted by about 180 ° as indicated by A in the figure. Crest value V ₁ shown at 301 in FIG.
4D state occurs due to the Freedericksz transition occurring at the timing when the pulse is applied. Next, the metastable state of C or D is selected according to the crest value of the pulse applied during the above selection period.

In this embodiment, by setting φ _A in FIG. 2 (c) to 90 °, the main absorption axis of the dye molecule and the transmission axis of the polarizing plate are made orthogonal to each other in the state C of FIG. , D
In this state, since the absorption axis is distributed in all directions, the polarized reflected light is absorbed and the light is shielded. Φ _A according to visual observation
It was found that both of them have a function as a display because contrast is generated in the range of 45 to 135 °. The contrast ratio was maximized at φ _A = 90 °.

(Embodiment 2) FIG. 2B shows a second embodiment of the present invention.
The schematic sectional drawing of is shown. The polarizing plate (2
2), the liquid crystal panel (21) and the reflection plate (23) were arranged. FIG. 2C shows the relationship between the alignment treatment (rubbing) direction (24) applied to the interface and the transmission axis (25) of the polarizing plate in the display surface (xy plane). In this embodiment, 24 in FIG.
The angle φ _A formed by and 25 is approximately 90 °.

A liquid crystal display device of the present invention is formed by connecting the above-mentioned element (liquid crystal panel) to a drive circuit in a structure as shown in FIG. 5 and applying a drive voltage waveform, an example of which is shown in FIG. 3, to the electrodes. Can work. The drive voltage waveform used and the operation display principle are the same as those described in the first embodiment.
By visual observation, it was found that both had contrast in the range of φ _A = 45 to 135 ° and that they had a function as a display. The contrast ratio was maximized at φ _A = 90 °.

[0021]

As described above, according to the liquid crystal display device of the present invention, switching between two metastable states which can be arbitrarily selected by the applied waveform is used as a display mode with high light utilization efficiency. A liquid crystal display device with high quality and good visibility can be realized. Further, since the selected state is held for a practically sufficient time as a memory type display device in the same device, it is possible to support a high-definition display having a large number of scanning lines by simple matrix drive. The present invention can be applied not only to the direct-view type liquid crystal display device but also to various light valves, spatial light modulators, and the like.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a liquid crystal display element according to an embodiment of the present invention.

FIG. 2 is a diagram showing a structure and an element arrangement of a liquid crystal display element according to an embodiment of the present invention.

FIG. 3 is a diagram showing a drive voltage waveform used in an embodiment of the present invention.

FIG. 4 is a diagram for explaining the display principle of the embodiment of the present invention.

FIG. 5 is a diagram schematically showing the structure of a liquid crystal display device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Liquid crystal molecule 2 Alignment film 3 Insulating layer 4 Transparent electrode 5 Glass substrate 9 Director vector 11 Dye molecule 21 Liquid crystal panel 22 Polarizing plate 23 Reflecting plate 24 Orientation treatment direction applied to the interface 25 Transmission axis θ ₁ , θ of polarizing plate Pretilt angle of liquid crystal molecules at ₂ interfaces 301 Scanning electrode waveform 302 Signal electrode waveform 303 Composite waveform

Claims (3)

[Claims] 1. A liquid crystal display panel comprising a scanning electrode group and a signal electrode group arranged in a matrix form and sandwiching a liquid crystal having a memory effect between substrates facing each other to form pixels, at least one sheet. A liquid crystal display device comprising a polarizer, at least one reflective layer and means for applying a driving voltage signal to the electrode group, wherein the liquid crystal layer constituting the liquid crystal display panel contains a dichroic dye, Accordingly, the absorption axis distribution of the dichroic dye is changed, and the polarizer is arranged so as to optically identify at least two states among a plurality of stable states or metastable states exhibited by the liquid crystal layer. A liquid crystal display device characterized by being set. 2. The liquid crystal having a memory effect forms a twist angle of φr in an initial state before a voltage is applied,
2. A liquid crystal having a property of having two metastable states in which a twist angle is approximately (φr + 180 °) and approximately (φr−180 °) as a relaxation state after applying a pulse voltage group. The described liquid crystal display device. 3. A major axis direction of liquid crystal molecules or a main absorption axis direction of dichroic dye molecules at an interface subjected to alignment treatment,
The liquid crystal display device according to claim 1, wherein the angle formed by the transmission axis directions of the polarizer is 45 ° to 135 °.