JPH02257120A - Liquid crystal electrooptical element - Google Patents

Abstract

PURPOSE:To obtain the element which has a good memory effect by a bistable uniform orientation and is less degraded in contrast by an orientation defect by subjecting at least one of substrates to an orientation treatment and impressing an electric field to a ferroelectric liquid crystal to regulate the orientation state thereof after the sealing thereof. CONSTITUTION:At least one substrate 1 or 2 is subjected to the orientation treatment and the orientation state of the ferroelectric liquid crystal is regulated by impressing the electric field after the sealing thereof. Namely, the ferroelectric liquid crystal compsn. of Table 2 is sealed under heating between the substrates 1 and 2 and is gradually cooled down to a room temp. and the alternating waveforms of a measuring voltage are impressed for a prescribed period of time between electrodes 4 and 5 of this element, by which the orientation state of the liquid crystal is made into the uniform state having the dense striped structure in the direction nearly perpendicular to the layer direction. The zigzag defects formed at the time of the sealing and cooling are removed by this electric field treatment. The liquid crystal electrooptical element which is provided with a good memory effect by a bistable uniform orientation and is less degraded in contract by the orientation defect is obtd. in this way.

Description

[Detailed description of the invention] [Industrial application field 1 The present invention relates to an electro-optical element using ferroelectric liquid crystal.

[Background Art 1] In recent years, information processing has become increasingly computerized, and along with this, 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, for high-definition displays, ferroelectric liquid crystals, which have faster response times and memory properties, are being researched than nematic liquid crystals, which have slower responses. (e.g. C1ark et al., App
l, Phys, Lett, 36,899 (19
8(1)) Conventional methods for controlling the orientation of electro-optical elements using ferroelectric liquid crystals include forming an organic polymer layer such as polyimide on the substrate surface and performing a rubbing treatment, and depositing SiO from an oblique direction. , a magnetic field orientation method, and a method of slow cooling while applying a direct current electric field.

[Question to be solved by the invention N1: 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 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, spontaneous polarization tends to point inward or outward at both the upper and lower interfaces and exhibit a force state, making it 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. As shown in pp. 69-116'', so-called zigzag defects are likely to occur. When these defects occur 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.

1 Means for Solving the Problems 1 In order to solve the above problems, the liquid crystal electro-optic device of the present invention has the following features: (1) A liquid crystal electro-optic device comprising a ferroelectric liquid crystal sandwiched between a pair of substrates having transparent electrodes In the device, at least one substrate is subjected to alignment treatment, and after the ferroelectric liquid crystal is sealed, an electric field is applied to regulate the alignment state. (3) The coupling agent is a coupling agent having at least one of an amine group, a methylamino group, an epoxy group, and a mercapto group as a functional group, or a mixture thereof. (4) The ferroelectric liquid crystal is a composition containing at least one component of each of the compounds of groups 1), 2), and 3) represented by the general formula %. do.

Embodiment 11 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 cup song agent used here is γ-aminopropyltriethoxysilane (C2Hs○)38iC3HeNH2, which is a compound having an amino group. A 0.2% by weight ethanol solution of the above compound was applied onto the substrate in a spin coater 1 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. Cell thickness is approximately 2μm
And so. In FIG. 1, an insulating layer is provided on both the upper and lower substrates, but it 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 911) are shown in 1 to 3, and examples of compound 2) are shown in 4.
In addition, an example of compound 3) is shown in 5. Next, these 1) to 3)
Table 2 shows examples of liquid crystal compositions containing the following compounds.

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

I (65) N trees (60) SmA (46) SmC books (<
0) KO transition temperature/'C Next, when an alternating waveform of ±25V and 15Hz was applied between the electrodes of this device for about 10 seconds, the alignment state of the liquid crystal was found to be dense streaks in a direction almost perpendicular to the layer direction. It exhibited a uniform condition with a similar structure. 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 (b)
) of I+) and the amount of transmitted light after removing the electric field (I of Fig. 2(b)
It is considered that the larger the ratio I2/II of 2), the better. In this example, I2/1. =0.99,
The contrast ratio was good at 1:35.

[Example 2] 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 an SiO2 insulating layer, and the surface 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-coded 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 15Hz 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. 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. The optical response exhibited was evaluated. In this example, I2/
I+=0. 97, and the contrast ratio was good, 1:40.

[Effect of the Invention 1] With the above configuration, the present invention uses modification of the substrate surface and orientation control by electric field treatment to solve the drawbacks of the prior art, has a good memory effect due to bistable uniform orientation, and improves the 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 Kizobe Meiki (and 1 other person) Figure 2 T

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 coated 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, and R_5 are alkyl groups having 2 to 20 carbon atoms. R_2 is an alkoxy group having 2 to 20 carbon atoms. R_4* and R_6* are represented by ▲There are mathematical formulas, chemical formulas, tables, etc.▼ or ▲There are mathematical formulas, chemical formulas, tables, etc.▼, and m is an integer from 0 to 8 and n is an integer from 1 to 15.