JPH02293718A - Liquid crystal electrooptical element - Google Patents

Abstract

PURPOSE:To obtain the excellent liquid crystal electrooptical element which has a good memory effect by a bistable uniform orientation and is less degraded in contrast by an orientation defect by using the ferroelectric liquid crystal expressed by specific formula by the reforming of substrate surfaces and the orientation control by an electric field treatment. CONSTITUTION:Films 9, 10 consisting of a silane-coupling agent are formed on a pair of glass substrates 1, 2 provided with transparent electrodes 4, 5 consisting of ITO and insulating films 7, 8 consisting of SiO2 and the surfaces thereof are subjected to a rubbing treatment. The silane-coupling agent is a coupling agent having at least one of an amino group, methyl amino group, epoxy group, and mercapto group as a functional group or the mixture composed thereof. A ferroelectric liquid crystal 6 contg. at least one component of the compd. expressed by formula is sealed between a pair of the substrates 1 ad 2 formed in such a manner and thereafter, an electric field is impressed between the electrodes 4 and 5, by which the uniform state having the dense stripe-shaped structure in the direction nearly perpendicularly in the layer direction is exhibited in the orientation state of the liquid crystal 6 and the zigzag defects are removed.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an electro-optical element using ferroelectric liquid crystal.

[Background Art 1] In recent years, computerization of information processing has progressed, and as a result, there has been a strong desire for computers to be made smaller. In particular, CRT displays, which have held a strong position as man-machine interfaces, are heavy and large, so they are being replaced by lighter and thinner liquid crystal displays and plasma displays. Twisted nematic type liquid crystal displays are generally used. However, as a high-definition display, ferroelectric liquid crystals, which have faster response times and memory properties than nematic liquid crystals, which have a slower response, are being researched. (e.g. Clark et al., Ap
pl. Phys. Lett. ,36,899 (1
980)) Conventional methods for controlling the orientation of electro-optical elements using ferroelectric liquid crystals include a method in which an organic polymer layer such as polyimide is provided on the substrate surface and a rubbing treatment, a method in which SiO is evaporated from an oblique direction, and a method in which magnetic field alignment is used. There are methods such as slow cooling while applying a direct current electric field, etc.

[Problem to be solved by the invention 1: The response characteristics of ferroelectric liquid crystals due to electric fields, especially the memory effect,
It is thought that this is largely influenced by chemical or physicochemical interactions between liquid crystal molecules and the substrate surface. According to the switching principle of chiral smectic C phase (hereinafter abbreviated as SmC wood phase), in order to obtain a good memory effect, it is desirable that liquid crystal molecules be aligned parallel to the substrate surface and in one direction.

However, when conventional alignment control methods such as rubbing the surface of a polymer film are used, the molecular alignment in the SmC* phase is in a twisted state, that is, the liquid crystal molecular director rotates on the side surface of a cone from one substrate surface to the opposite substrate surface. Therefore, the spontaneous polarization tends to point inward or outward at both the upper and lower interfaces, and it is therefore difficult to obtain a good memory effect.

In addition, the liquid crystal electro-optical device produced by the above alignment method is “F”
erroelectrics 1984, Vol. 5
9, pp. 69-116'', so-called zigzag defects are likely to occur. When this defect occurs in the device, a significant drop in contrast ratio occurs due to light leakage.

The present invention solves the above problems by modifying the substrate surface and controlling the orientation by electric field treatment.The purpose of the present invention is to have a good memory effect due to bistable uniform orientation, and to reduce contrast due to orientation defects. It is an object of the present invention to provide an excellent liquid crystal electro-optical element with less.

It is characterized by being made by a wrapping method on a ring agent.

(3) The coupling agent is characterized in that it is a coupling agent having at least one of an amino group, a methylamino group, an epoxy group, and a mercapto group as a functional group, or a mixture thereof.

(4) The ferroelectric liquid crystal has the general formula Rl4-o-R21) R3-o-OCO-o-R4*2) [Means for Solving the Problems 1] The liquid crystal electro-optical element of the present invention satisfies the above problems. In order to solve the problem, (1) In a liquid crystal electro-optical element consisting of a ferroelectric liquid crystal sandwiched between a pair of substrates having transparent electrodes, at least one substrate is subjected to alignment treatment, and the ferroelectric liquid crystal is After being encapsulated, an electric field is applied to regulate the orientation state.

(2) The alignment treatment is characterized by using a composition containing at least one component of each of the compounds of each group 1), 2) and 3) represented by a cup applied on the substrate.

1 Embodiment 1) FIG. 1 is a main sectional view of an electro-optical element in an embodiment of the present invention. A film of a silane coupling agent was formed on a glass substrate provided with an ITO transparent electrode and an SiO2 insulating layer, and the surface thereof was subjected to a rubbing treatment. The silane coupling agent used here is γ-aminopropyltriethoxysilane (C2H50)3SiC3H6NH2, which is a compound having an amino group. A 0.2% by weight ethanol solution of the above compound was spin-coated onto the substrate and baked at 80°C for about 60 minutes.

The thus obtained substrates were assembled so that the rubbing direction was 180° at the top and bottom. The cell thickness was approximately 2 μm. Although insulating layers are provided on both the upper and lower substrates in FIG. 1, they may be provided on only one of them. Furthermore, the rubbing treatment may be performed only on one side of the substrate.

Table 1 shows specific examples of liquid crystal compounds used in Examples of the present invention. Examples of compound 1) are shown in 1 to 5, examples of compound 2) are shown in 6, and examples of compound 3) are shown in 7. Next, Table 2 shows examples of liquid crystal compositions in which these compounds 1) to 3) are mixed.

The ferroelectric liquid crystal composition shown in Table 2 was heat-sealed between the substrates and slowly cooled to room temperature. The phase series of this liquid crystal is as follows.

I (59) N tree (54) S m A (46) S m
C * (<0) KO transition temperature/'C Next, when an alternating waveform of ±25 V and 15 Hz was applied between the electrodes of this device for about 10 seconds, the alignment state of the liquid crystal was as follows.
It exhibited a uniform state with dense striations in a direction almost perpendicular to the layer direction. By this electric field treatment, zigzag defects formed during cooling of the encapsulation were removed. The liquid crystal electro-optical element obtained by the above method was sandwiched between polarizing plates whose polarization axes were orthogonal to each other, and the driving waveform shown in FIG. 2(a) was applied to the device as shown in FIG. The optical response was evaluated. The quality of the memory effect is determined by the amount of transmitted light when an electric field is applied (Figure 2 (
■+) in b) and the amount of transmitted light after removing the electric field (Fig. 2(b)
) I2) It is considered that the larger the ratio I2/work1, the better. In this example, at 25°C, I2/I+=
0.93, and the contrast ratio was good, 1:36.

[Example 21] Using an element having the same configuration as in FIG. 1, a film of a silane coupling agent was formed on a glass substrate provided with an ITO transparent electrode and a SiO2 insulating layer, and the surface thereof was subjected to a rubbing treatment. The silane coupling agent used here is N-methyl-3aminopropyltrimethoxysilane (CH30)3SiC3H6NHCH3, which is a compound having a methylamino group. A 0.2% by weight ethanol solution of the above compound was spin-coated onto the substrate and baked at 100°C for about 60 minutes. The thus obtained substrates were assembled so that the rubbing direction was 180° at the top and bottom. The cell thickness was approximately 1.8 μm.

The ferroelectric liquid crystal composition shown in Table 2 was heat-sealed between the substrates and slowly cooled to room temperature. Next, between the electrodes of this element ±25
When an alternating waveform of 15 Hz was applied for about 15 seconds, the alignment state of the liquid crystal exhibited a uniform state with a dense striated structure in a direction substantially perpendicular to the layer direction. This electric field treatment removed the zigzag defects formed during cooling.

The liquid crystal electro-optical element obtained by the above method was sandwiched between polarizing plates whose polarization axes were orthogonal to each other, and the driving waveform shown in FIG. 2(a) was applied to the device as shown in FIG. The optical response was evaluated. In this example, I2/min+ at 25°C
= 0.96, and the contrast ratio was good, 1:45.

[Effects of the Invention] With the above configuration, the present invention uses modification of the substrate surface and orientation control through electric field treatment, solves the drawbacks of the prior art described above, has a good memory effect due to bistable uniform orientation, and improves orientation. We were able to provide an excellent liquid crystal electro-optical element with little contrast reduction due to defects.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a liquid crystal electro-optical element according to an embodiment of the present invention. FIG. 2 is a diagram showing driving waveforms used in evaluating the liquid crystal electro-optical device of the present invention. 1.2',. ．． 4,5. ．． ．． 7,8. ．． ．． 9,10. ．． , 11, 12. ．． 21. ．． ．． 22. ．． ．． Upper and lower glass substrates Spacer Transparent electrode Liquid crystal layer Insulating layer Alignment film Polarizing plate Drive waveform Optical response More than one example of corresponding optical response Applicant Seiko Epson Corporation Agent Patent attorney Kisaburo Suzuki (and one other person) Figure 2 ■

Claims (4)

[Claims] (1) In a liquid crystal electro-optical element consisting of a ferroelectric liquid crystal sandwiched between a pair of substrates having transparent electrodes, at least one substrate is subjected to alignment treatment, and after the ferroelectric liquid crystal is sealed, an electric field is applied. A liquid crystal electro-optical element characterized in that the alignment state is regulated by (2) The liquid crystal electro-optical element according to claim 1, wherein the alignment treatment is performed by a rubbing method on a coupling agent applied on the substrate. (3) The liquid crystal electro-optical element according to claim 2, wherein the coupling agent is a coupling agent having at least one of an amino group, a methylamino group, an epoxy group, and a mercapto group as a functional group, or a mixture thereof. . (4) The above ferroelectric liquid crystal is expressed by the general formula ▲There are mathematical formulas, chemical formulas, tables, etc.▼1) ▲There are mathematical formulas, chemical formulas, tables, etc.▼2) ▲There are mathematical formulas, chemical formulas, tables, etc.▼3) 2. The liquid crystal electro-optical device according to claim 1, wherein the composition contains at least one component of each of the compounds of groups 1), 2) and 3). However, R_1, R_3, R_5 and R_6 have 2 to 2 carbon atoms.
20 alkyl groups. R_2 is an alkoxy group having 2 to 20 carbon atoms. R_4^* is represented by ▲There are mathematical formulas, chemical formulas, tables, etc.▼ or ▲There are mathematical formulas, chemical formulas, tables, etc.▼, where m is an integer from 0 to 8 and n is an integer from 1 to 15. Assume that X and Y are each CH_3 or Cl.