JPH0869017A - Liquid crystal electro-optical device - Google Patents

Abstract

PURPOSE: To provide a liquid crystal display device which can be used for a high definition display or large-size display of a simple matrix system with lots of scanning wires by expanding the operational margin relating to the pretilt angle in a liquid crystal display device having a metastable memory effect. CONSTITUTION: This liquid crystal display element has such a structure that the angle between directions of rubbing applied on two substrates 11, 12 is made almost to match the twisted angle ϕr of the liquid crystal molecule in the initial state and that the pretilt angle on each interface shows opposite direction to each other. The element has two metastable states depending on the waveforms of voltage applied. The three elastic consts. of the liquid crystal 17 satisfy 0.5<=K33 /K11 <=3.0, 0.5<=K22 /K11 <=0.8 and K22 >=8×10<-12> N.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal electro-optical device having a memory property using a chiral nematic liquid crystal.

[0002]

2. Description of the Related Art As one of liquid crystal elements having a memory property, there is a method disclosed in Japanese Patent Publication No. 1-51818. It is equipped with a chiral nematic liquid crystal in which the ratio (d / p) of the liquid crystal layer thickness d and the twist pitch p is adjusted so as to take a 180 ° twist structure in the initial state, and a Fredericks transition is caused once by applying a voltage. As the relaxed state after the heating, it has two arbitrarily selectable orientation states different from the initial state.

FIG. 1 shows a schematic sectional view of the liquid crystal element. The twist angle in the initial state does not necessarily have to be 180 °, but here, the case where the twist angle is 180 ° will be described. A transparent electrode 13, an insulating layer 14, and a liquid crystal alignment film 15 are laminated on the two transparent substrates 11 and 12 (however, the insulating layer is optional) and further subjected to rubbing treatment. Further, d / p of the chiral nematic liquid crystal is adjusted so as to have a 180 ° twist structure in the initial state. By making the directions of the rubbing treatment applied to the upper and lower substrates anti-parallel to each other, the rising direction of the director vector 19 (the liquid crystal molecule long axis direction) of the liquid crystal molecules in contact with the upper and lower substrates has the illustrated relationship. To

After applying a voltage large enough to cause the Freedericksz transition to the liquid crystal layer having such an alignment state, and then rapidly decreasing the voltage, the alignment state is relaxed to a 360 ° twist state and gradually decreased. By doing so, the twist angle is relaxed to a uniform state of 0 °. The two alignment states are metastable and they remain for several seconds. That is, it is not permanent but has bistability. It is not necessary to apply a voltage to maintain the metastable state. After a certain period of time, those metastable states naturally return to the initial state. By appropriately setting the installation angle of the polarizing plate, the two metastable states can be optically distinguished from each other, and thus the optical switching can be performed using the two metastable states.

When the liquid crystal element is applied as a display device, simple matrix drive can be performed by utilizing the bistability, for example, by the drive method shown in FIG. In the figure, 201 and 204 are voltage waveforms applied to the scan electrodes, and T _s is a selection period. Reference numerals 202 and 205 denote voltage waveforms applied to the signal electrode at T _s , respectively, where the twist angles are approximately (φ _r + 180 °) and approximately (φ _r −180).
Corresponds to selecting two metastable states that are 203 and 206 are 201 and 202 and 204, respectively.
And 205 is the combined waveform applied to the liquid crystal layer at T _s as the difference. When V _{th is} a voltage threshold value for causing the Freedericksz transition in the liquid crystal and V _c is a voltage threshold value for selecting two metastable states, a voltage pulse having a peak value V ₁ causes the Freedericksz transition. Sufficiently large and further satisfying the relationship of | V ₂ −V ₃ | ≦ V _c | V ₂ + V ₃ | ≧ V _c | V ₃ | ≦ V _th, so that 203 in the selection period T _s after the Fredericks transition twist angle when a voltage waveform is applied is selected metastable state of approximately _{φ r + 180 ° = 360 °} , at the time 206 is applied is selected metastable state of φ _r -180 ° = 0 ° uniform. Since the cycle of one frame is about several tens of msec, the selected state is maintained until the next selection. Therefore, the selected state (360
By selecting again before the twisted state or uniform state) naturally returns to the initial state, it is possible to display a high contrast ratio.

[0006]

However, it is not so easy to uniformly display the entire display area. One of the reasons is that the alignment of liquid crystal molecules at the liquid crystal-liquid crystal alignment film interface is not uniform.

In the xyz coordinate system shown in FIG. 1, the xy plane is parallel to the macroscopic spreading plane of the liquid crystal layer, and the x axis is parallel to the rubbing direction of the lower substrate. The αβγ coordinate system is a local coordinate system set so that the γ axis is parallel to the surface normal at each point on the surface of the liquid crystal alignment film on each substrate and the α axis is in the xz plane. It is a coordinate system. The director vector in contact with the liquid crystal alignment film at each point on the substrate and the liquid crystal alignment film surface (αβ
The angle formed by the plane) is represented by Ω, and the angle formed by the director vector and the xy plane is represented by θ _p . The general term pretilt angle is used to mean θ _p . Only the average θ _p over a certain area can be measured. Even if the anchoring energy of the liquid crystal alignment film and the liquid crystal layer thickness are uniform in the xy plane, V _c becomes non-uniform if θ _p is non-uniform, and uniform display cannot be performed over the entire display area. The causes of θ _p being non-uniform in the xy plane are (1) Ω (θ _p ) varies depending on the location because the rubbing strength is not uniform even if the liquid crystal alignment film surface is flat. Even if the surface of the alignment film is flat, Ω (θ _p ) varies depending on the location because the film quality of the liquid crystal alignment film is not uniform. (3) If the surface of the liquid crystal alignment film has undulations or irregularities, Ω Even if it is uniform, θ _p varies depending on the location,
That can be mentioned. However, it is very difficult to completely suppress these factors.

It is possible in principle to apply the liquid crystal composition developed for the purpose of use in conventional TN, STN, etc. to the liquid crystal electro-optical device of the present invention, but the operation margin with respect to the fluctuation of θ _p is If it is narrow and θ _p fluctuates, the above 2
There was a problem that switching between two metastable states was not performed in a well-balanced manner. Therefore, at present, a large area and uniform display cannot be realized.

The present invention is intended to solve the above problems, and an object of the present invention is to provide a liquid crystal electro-optical device having uniform characteristics over a large area.

[0010]

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.

The liquid crystal electro-optical device of the present invention is constituted by (1) a scanning electrode group and a signal electrode group are arranged in a matrix, and a liquid crystal having a memory effect is sandwiched between substrates facing each other to form pixels. A liquid crystal element, a liquid crystal electro-optical device comprising means for applying a drive voltage signal to the electrode group and means for controlling the drive voltage signal, wherein the liquid crystal enclosed in the liquid crystal element exhibits a chiral nematic phase and splay deformation Elastic constants K ₁₁ , K _{22 of} twist deformation and K _{33 of} bend deformation are 0.5 <K ₃₃ / K ₁₁ <3.0 0.5 <K ₂₂ / K ₁₁ <0.8 K ₂₂ ≧ 8 × 10 ^-12 N (2) The liquid crystal having the above memory effect,
In the initial state before the voltage is applied, a twist angle of φ _r is formed, and after the pulse voltage group is applied, the twist angle is approximately (φ _r + 180 °) and approximately (φ _r −180 °).
The liquid crystal is characterized by having two metastable states that are (°).

[0012]

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

FIG. 1 is a schematic sectional view of the liquid crystal element used in the embodiment.
Shown in The transparent substrate 11, 12, ITO, polyimide as S _i O _2, a liquid crystal alignment film 15 as an insulating layer 14 is laminated as a strip-shaped transparent electrodes 13. However, it is optional whether or not an insulating layer is provided. Two transparent substrates were superposed via a spacer 16 so that the rubbing directions applied to the liquid crystal alignment film were antiparallel to each other in the upper substrate 13 and the lower substrate 12. However, although not shown, a spherical gap maintaining material was also used, and the accuracy of the liquid crystal layer thickness was set to ± 0.02 μm. This is to suppress the influence of the liquid crystal layer thickness on V _c as much as possible. Then, d / p was adjusted so that the twisted state was 180 ° in the initial state (0.25 <d /
p <0.75) A chiral nematic liquid crystal was enclosed. In addition, the angle should be set to 2 to obtain a sufficiently high contrast ratio.
A sheet of polarizing plate was installed. In the figure, there are five stripe-shaped transparent electrodes provided on the lower substrate, but in reality, 640 and 480 transparent electrodes are provided on the upper and lower substrates, respectively.
A 9-inch diagonal liquid crystal element having 640 × 480 pixels was used. Then, a liquid crystal display device was prepared with a circuit configuration as shown in FIG.

Example 1 In this example, the following mol% of a liquid crystal composition was used as a chiral dopant in E. Me
A liquid crystal composition having a chiral nematic phase of p = 3.0 μm at 30 ° C. was used by adding an appropriate amount of S811 manufactured by Rck.

[0015]

Embedded image

A compound represented by the formula (hereinafter referred to as "compound 1") 20.

[0017]

Embedded image

25, a compound represented by (hereinafter referred to as "compound 2").

[0019]

[Chemical 3]

55 as a compound represented by the following (hereinafter referred to as "compound 3").

The elastic constants of this liquid crystal composition at 30 ° C. are as shown in Table 1, and 0.5 <K ₃₃ / K ₁₁ <3.0 0.5 <K ₂₂ / K ₁₁ <0.8 K ₂₂ ≧ 8 × 10 ⁻¹² The condition N is satisfied. When d = 1.8 μm, the above-mentioned bistable switching was confirmed.

[0022]

[Table 1]

The dependence of V _c of this liquid crystal composition on θ _p is θ _p
6 types of test liquid crystal elements (measurement area is 9 mm
² ) and the test drive waveforms shown in FIG.
Table 2 shows the liquid crystal alignment film used in each test liquid crystal element, its thickness, and θ _p .

[0024]

[Table 2]

To measure V _c , in the drive waveform shown in FIG. 4, T _s = 100 μsec, T _ns = 30 msec, V _r = 25 V, V
It was measured by changing the write voltage V _w with _b = 1 V. The result is shown by the curve (a) in FIG.

This liquid crystal composition is enclosed in the liquid crystal device shown in FIG. 1 and the drive voltage waveform of FIG. 2 is applied in the circuit configuration of FIG. 3 to obtain V ₁ = 25V, V ₂ = 2.5V, V ₃ = 1.1V, T _s = 100μs
When driven as ec, it was possible to display uniformly over the entire display area.

Example 2 In this example, the following mol% of the liquid crystal composition was used as the chiral dopant in E. Me
A liquid crystal composition having a chiral nematic phase of p = 3.0 μm at 30 ° C. was used by adding an appropriate amount of S811 manufactured by Rck.

[0028]

[Chemical 4]

35, a compound represented by the following (hereinafter referred to as "compound 4").

[0030]

[Chemical 5]

35, a compound represented by the following (hereinafter referred to as "compound 5").

[0032]

[Chemical 6]

A compound represented by (hereinafter referred to as "compound 6") 30.

The elastic constants of this liquid crystal composition at 30 ° C. are as shown in Table 1, and 0.5 <K ₃₃ / K ₁₁ <3.0 0.5 <K ₂₂ / K ₁₁ <0.8 K ₂₂ ≧ 8 × 10 ⁻¹² The condition N is satisfied. When d = 1.9 μm, the above-mentioned bistable switching was confirmed. Example 1
The curve (b) of FIG. 5 shows the dependence of V _c on θ _p obtained in the same manner as
Indicate. This liquid crystal composition is enclosed in the liquid crystal device shown in FIG. 1 and V ₁ = 25 V, V ₂ = V ₂ = 25 V in the drive waveform shown in FIG.
When driven at 4.0 V, V ₃ = 0.9 V, and T _s = 100 μsec, uniform display was possible over the entire display area.

Comparative Example In the comparative example, the mol% shown below is used.
As a chiral dopant in the liquid crystal composition of E. Merc
k company: Add S811 in appropriate amount and p at 30 ° C.
A liquid crystal composition exhibiting a chiral nematic phase of 3.0 μm was used.

[0036]

[Chemical 7]

25, a compound represented by the following (hereinafter referred to as "compound 7").

[0038]

Embedded image

15. A compound represented by (hereinafter referred to as "compound 8").

[0040]

[Chemical 9]

40 in the following compound (hereinafter referred to as "compound 9").

[0042]

[Chemical 10]

Compound 20 represented by (hereinafter referred to as "compound 10") 20.

The elastic constant of this liquid crystal composition at 30 ° C. is as shown in Table 1 and does not satisfy the condition of K ₂₂ ≧ 8 × 10 ^-12 N, but when d = 1.8 μm, Bistable switching was confirmed. Example 1
FIG. 6 shows the θ _p dependence of V _c obtained in the same manner as in. Compared to liquid crystal compositions used in Examples 1 and 2, the V _c theta _p
It can be seen that the dependence is quite large. This liquid crystal composition was enclosed in the liquid crystal device shown in FIG. 1 and an attempt was made to display uniformly on the entire display area. In the drive waveform shown in FIG. 2, V ₁ = 25V, V ₃ = 1.3V, T _s = 100 μsec, and V ₂
The display state was observed while changing the value, but it was not possible to drive the display area uniformly.

[0045]

As described above, according to the present invention, the dependence of the switching characteristics on the pretilt angle (θ _p ) can be reduced, so that substantially uniform switching characteristics can be obtained even if θ _p varies depending on the location. be able to. Therefore, there is an effect that a large-area liquid crystal display device without display unevenness can be realized. 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.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a liquid crystal 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.

FIG. 4 is a diagram showing a test drive waveform used to measure the θ _p dependence of V _c .

FIG. 5 is a diagram showing θ _p dependence of V _c of the liquid crystal composition used in Examples.

FIG. 6 is a diagram showing the θ _p dependence of V _c of the liquid crystal composition used in Comparative Example.

[Explanation of symbols]

 11: upper transparent substrate 12: lower transparent substrate 13: transparent electrode 14: ... Insulating layer 15 Liquid crystal alignment film 16 Spacer 17 Liquid crystal layer 18・ ・ ・ ・ ・ Polarizer 19 ・ ・ ・ ・ ・ Director vector 201, 204 ・ ・ ・ ・ ・ Scan electrode waveform 202, 205 ・ ・ ・ ・ ・ Signal electrode waveform 203, 206 ・ ・ ・・ Composite (difference) waveform

Claims (2)

[Claims] 1. A liquid crystal element 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 drive the electrode group. In a liquid crystal electro-optical device comprising a means for applying a voltage signal and a means for controlling the drive voltage signal,
The liquid crystal enclosed in the liquid crystal element exhibits a chiral nematic phase, and an elastic constant K _{11 of} splay deformation, an elastic constant K _{22 of} twist deformation, and an elastic constant K _{33 of} bend deformation are 0.5 <K ₃₃ / K ₁₁ <3.0 0.5. <K ₂₂ / K ₁₁ <0.8 K ₂₂ ≧ 8 × 10 ⁻¹² N A liquid crystal electro-optical device characterized by satisfying the condition. 2. The liquid crystal having a memory effect forms a twist angle of φ _{r in} an initial state before a voltage is applied,
The liquid crystal is characterized by having two metastable states with a twist angle of approximately (φ _r + 180 °) and approximately (φ _r −180 °) as a relaxation state after applying a pulse voltage group. The liquid crystal electro-optical device according to claim 1.