JPH0862640A - Liquid crystal device - Google Patents

Abstract

PURPOSE: To provide a liquid crystal display device capable of dealing with high-fineness display of a large number of scanning lines with a simple matrix system and a large screen by expanding an operation margin relating to a cell gap of a liquid crystal display having a metastable storage effect. CONSTITUTION: The liquid crystal display element having the two metastable states dependently upon applied voltage waveforms is obtd. by the constitution in which the pretilt angles of respective boundaries have a relation of reverse codes by making the angle formed by the rubbing directions applied to two sheets of the substrates 5 and the twist angle (ϕr) of liquid crystal molecules 1 in an initial state to nearly coincide. The liquid crystal display element described above is so formed as to satisfy the conditions 0.5<=K33 /K11 <=3.0, 0.5<=K22 /K11 <=0.8, K22 <=9×10<-12> N relating to the three elastic constants (the respective elastic constants K11 , K22 , K33 of spray deformation, twist deformation and bend deformation) of liquid crystals.

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 a liquid crystal, and more particularly to a liquid crystal device 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 liquid crystal display device of the present invention, a twist angle of φr is formed in the initial state before applying a voltage, and the twist angle is approximately as a relaxed state after applying a pulse voltage group. (Φr + 180 °) and abbreviation (φr-1
It has two metastable states that are 80 °). Conventional T
It is possible in principle to apply the liquid crystal composition developed for use in N, STN, etc. to the liquid crystal device of the present invention, but the operation margin is small with respect to the fluctuation of the cell gap, and slight gap unevenness, etc. When the above occurs, there is a problem that switching between the two metastable states is not performed in a well-balanced manner.

[0009]

The inventor has found that the above-mentioned operation margin depends on the elastic constant of the liquid crystal, and has concluded from the experimental data that the desired characteristics can be obtained under the following conditions. did. Therefore, the liquid crystal device of the present invention is: (1) A liquid crystal display in which a liquid crystal having a memory effect is sandwiched between substrates on which scanning electrode groups and signal electrode groups are arranged in a matrix and pixels are formed in opposed portions thereof. In a liquid crystal device comprising a panel, means for applying a drive voltage signal to the electrode group and means for controlling the drive voltage signal, the liquid crystal enclosed in the liquid crystal display panel exhibits a nematic phase, and an elastic constant K _{11 of} splay deformation, Elastic constant of twist deformation K ₂₂
And the elastic constant K _{33 of} bend deformation satisfies the condition of 0.5 ≤ K ₃₃ / K ₁₁ ≤ 3.0 0.5 ≤ K ₂₂ / K ₁₁ ≤ 0.8 K ₂₂ ≤ ^{9x10 -12} N Is characterized by.

(2) The liquid crystal having the memory effect has 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 (°).

[0011]

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

FIG. 1 is a schematic sectional view of a liquid crystal panel portion of the liquid crystal display device of the present invention. A striped ITO transparent electrode (4), an insulating layer (3), and an alignment film (2) were laminated on a glass substrate (5), and the surfaces were subjected to a rubbing treatment to be opposed to each other. In the figure, 8 is an inter-pixel light shielding layer, and 6 is a leveling layer, but these (6, 8) are not always necessary. When the liquid crystal (1) is enclosed between the substrates, the director vector (9) is arranged with a constant pretilt angle (θ ₁ , θ ₂ ) at the interface of the alignment film due to the effect of the alignment treatment.
By adding an optically active substance to the liquid crystal, the liquid crystal molecules inside have a helical structure.

When the cell gap is d and the liquid crystal helical pitch is p, the liquid crystal molecules are aligned between the upper and lower substrates with a twist angle of 180 ° as an initial state by satisfying the condition of p / 4 <d <3p / 4. To do. In this example, an optically active additive (EM) was added to the liquid crystal composition.
erck: S811) is added to add helical pitch p =
The thickness is adjusted to 2.7 μm, a polyimide alignment film is provided on the substrate interface of the cell, and the upper and lower substrates are rubbed in the antiparallel direction (180 degrees) to have a gap d = 1.5 to 2.0 μm. I was there. The device of this configuration has a twisted (uniform) state of approximately 0 ° depending on the waveform of the driving voltage applied, and approximately 3 °.
It produces two metastable states, a 60 ° twist state. The memory type liquid crystal panel thus obtained was sandwiched between two polarizing plates (7 in FIG. 1) to form a liquid crystal display device having a circuit configuration shown in FIG. 3, and the effects of the present invention were confirmed. .

FIG. 2 shows the basic structure of the drive voltage waveform applied to the present invention. In the figure, 201 and 204 represent voltage waveforms applied to the scan electrodes, and Ts represents a selection period. 202,2
Reference numeral 05 denotes a voltage waveform applied to the signal electrode at Ts, which corresponds to the case of selecting two metastable states in which the twist angles are approximately (φr + 180 °) and approximately (φr−180 °), respectively. 203 and 206 are 201 and 2 respectively
This is a composite waveform applied to the liquid crystal layer as the difference between 02, 204 and 205. Let V _{th be} the voltage threshold value for causing the Freedericksz transition in the liquid crystal and V _c be the voltage threshold value for selecting the two metastable states. | V ₁ ± V ₃ | ≧ V _th | V ₂ − By satisfying the relationship of V ₃ | ≦ V _c | V ₂ + V ₃ | ≧ V _c | V ₃ | ≦ V _th, when the voltage waveform of 203 is applied during the selection period Ts after the Fredericks transition, the twist angle is substantially The metastable state of φr + 180 ° = 360 ° is selected, and when 206 is applied, the metastable state of φr−180 ° = 0 ° uniform is selected.

If two polarizing plates are made to be substantially crossed nicols and arranged so that the angle formed by the average molecular axis direction (rubbing direction) of the 0 ° uniform state and the polarizing plate transmission axis is approximately 45 °, the same 0 ° is obtained. In the uniform state, incident light is transmitted (hereinafter referred to as an ON state), and the 360 ° twist state is in a light shielding state (hereinafter referred to as an OFF state), and has a function as a display body.

Example 1 A liquid crystal composition having a nematic phase at room temperature was obtained with the following mol% composition.

[0017]

Embedded image

40 in the compound represented by (hereinafter referred to as "compound 1").

[0019]

Embedded image

The compound represented by the formula (hereinafter referred to as "compound 2") 30.

[0021]

[Chemical 3]

The compound represented by (hereinafter referred to as "compound 3") 30.

The elastic constant of the above composition is K ₁₁ = 12.4 × 10 ^-12 N K ₂₂ = 8.1 × 10 ^-12 N K ₃₃ = 19.2 × 10 ^-12 N at 30 ° C. .5 ≤ K ₃₃ / K ₁₁ ≤ 3.0 0.5 ≤ K ₂₂ / K ₁₁ ≤ 0.8 K ₂₂ ≤ 9 × 10 ^-12 N.

The helical pitch of the above composition was adjusted by the above-mentioned method to prepare a display panel having the structure shown in FIG. In the circuit configuration of FIG. 3, the drive voltage waveform of FIG. 2 is applied, and the temperature of the display panel and the voltage setting of the waveform applied to the electrodes are fixed to constant values to operate normally (0 ° uniform and 360 ° twist). 2 Metastable states can be selectively switched)
The cell gap range was measured. At 30 ° C
V ₁ = 25v, V ₂ = 3.5v, V ₃ = 1.2v, Ts =
100 μs. The cell gap d = 1.
Normal operation was confirmed in the range of 60 to 1.88 μm (0.28 μm width).

Comparative Example A liquid crystal composition having a nematic phase at room temperature was obtained with the following mol% composition.

[0026]

[Chemical 4]

The compound represented by (hereinafter referred to as "compound 4") 30.

[0028]

[Chemical 5]

The compound represented by (hereinafter referred to as "compound 5") 20.

[0030]

[Chemical 6]

50 for the compound represented by (hereinafter referred to as "compound 3").

The elastic constant of the above composition is K ₁₁ = 14.3 × 10 ^-12 N K ₂₂ = 10.4 × 10 ^-12 NK ₃₃ = 26.3 × 10 ^-12 N at 30 ° C. ₂₂ > 9 × 10 ⁻¹² N.

When the helical pitch of the above composition was adjusted by the above-mentioned method and evaluated by the same method as in Example 1, cell gap d = 1.79 to 1.85 μm (0.06 μm)
Normal operation was confirmed only in the range of (width).

[0034]

As described above, according to the liquid crystal device of the present invention, in the switching between two metastable states which can be arbitrarily selected by the applied waveform, the physical property value of the liquid crystal, particularly the ratio and absolute value of the elastic constants can be determined. By adjusting to a certain range, it is possible to greatly expand the operation margin regarding the cell gap. The liquid crystal device of the present invention can support a high-definition display with a large number of scanning lines by simple matrix driving. It 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.

[0035]

[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 drive voltage waveform used in an embodiment of the present invention.

FIG. 3 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 6 Flattening layer 7 Polarizing plate 8 Light-shielding layer 9 Director vector θ ₁ , θ ₂ Pretilt angle of liquid crystal molecule at the interface 201, 204 Scan electrode waveform 202, 205 Signal electrode waveform 203, 206 Composite (difference) waveform

Claims (2)

[Claims] 1. A liquid crystal display panel comprising a scanning electrode group and a signal electrode group arranged in a matrix and sandwiching a liquid crystal having a memory effect between substrates facing each other to form a pixel. In a liquid crystal device comprising means for applying a drive voltage signal and means for controlling the drive voltage signal, a liquid crystal enclosed in a liquid crystal display panel exhibits a nematic phase, and an elastic constant K _{11 for} spray deformation and an elastic constant K for twist deformation are provided. ₂₂ and the elastic constant K _{33 of} bend deformation satisfy the condition of 0.5 ≤ K ₃₃ / K ₁₁ ≤ 3.0 0.5 ≤ K ₂₂ / K ₁₁ ≤ 0.8 K ₂₂ ≤ 9 × 10 ^-12 N Liquid crystal device that is characterized. 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 application of a pulse voltage group. The liquid crystal device described.