JPH0348817A - Liquid crystal electro-optical element - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal electro-optical element which has good memory effect by bistable uniform orientation and is less degraded in contrast by orientation defect by devising the material quality of a liquid crystal oriented film and a method for forming this film, thereby controlling surface properties. CONSTITUTION:The high-polymer thin film which is approximately oriented to regulate the arrangement of liquid crystal molecules is formed by a Langmuir-Blodgett's technique on at least one substrate of the liquid crystal electrooptical element constituted by crimping a ferroelectric liquid crystal between a pair of the substrates having a scanning electrode group and signal electrode having a scanning electrode group and signal electrode group. The material to constitute the high-polymer thin film is an amphiphatic high-polymer compd. having a hydrophilic group and hydrophobic group in the monomer unit. A thermotropic liquid crystal material is used for this high-polymer compd. The liquid crystal electro-optical element which is provided with good memory effect by the bistable uniform orientation and is less degraded in contrast by orientation defect is obtd. in such a manner.

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 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, for high-definition displays, ferroelectric liquid crystals, which have faster response times and memory properties, are being researched than nematic liquid crystals, which have a slow response. (e.g. C1ark 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 forming an organic polymer layer such as polyimide on the substrate surface and performing a rubbing process, diagonally evaporating SiO, and using a magnetic field. There are an orientation method, a method of slow cooling while applying a DC electric field, etc.

1 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° 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 a conventional orientation control method such as rubbing the surface of a polymer film is used, the molecular orientation in the SmC' phase becomes 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. The Langmuir-Prodgett method (hereinafter abbreviated as LB method) has been proposed as one of the methods for forming an alignment film without performing a rubbing process (for example, Ikeno et al.: IEICE Technical Report Vol. 1.88 No. 26
7 (1988)). However, in the case of conventional polyimide LB films, since polyimide cannot be directly accumulated on the substrate, an imidization reaction is performed on the substrate after stacking polyamic acid as a precursor.

This method involves a complicated process, and since the chemical reaction is carried out in the state of an accumulated film, the resulting polyimide lacks structural uniformity, making it difficult to obtain satisfactory properties as a liquid crystal aligning film.

The present invention solves the above problems by improving the material and forming method of the liquid crystal alignment film and controlling the surface properties.
The purpose is to provide an excellent liquid crystal electro-optical element that has a good memory effect due to bistable uniform alignment and has less contrast deterioration due to alignment defects.

[Means for Solving the Problems 1] In order to solve the above problems, the liquid crystal electro-optical element of the present invention has the following features: (1) scanning "rJ, ferroelectric liquid crystal between a pair of substrates having a pole group and a signal electrode group; The liquid crystal electro-optical device sandwiching the liquid crystal molecules is characterized in that at least one of the substrates has a substantially oriented polymer thin film for regulating the alignment of the liquid crystal molecules.

(2) The polymer fiIII is formed by the Langmuir-Prodgett method.

(3) The material constituting the polymer thin film is characterized in that it is an amphiphilic polymer compound having a hydrophilic group and a hydrophobic group in the 1,000-mer unit.

(4) The polymer compound is a thermotropic liquid crystalline substance.

Embodiment 11 FIG. 1 is a main sectional view of an electro-optical element in an embodiment of the present invention. LBJIQ was formed on a glass substrate provided with an ITO transparent electrode and a SiO2 insulating layer.

As the membrane material, a side chain type polymeric liquid crystal compound shown in structural formula (1) was used.

The compound of (1) above was spread on the water surface to form an L (Langmuir) film, and the surface pressure was maintained at 40 mN/m for 5 av.
A three-layer LB film was formed by moving the substrate up and down at a speed of /sin. The thus obtained substrates were assembled so that the pulling direction was 180° at the top and bottom. Cell thickness is approximately 2
It was set as μm. 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.

A ferroelectric liquid crystal composition was heated and sealed between the substrates, and slowly cooled to room temperature. Here, the liquid crystal is Merck 1zLI-377.
4 was used. 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
) was applied, and the optical response shown in FIG. 6(b) was evaluated. The better the memory effect is, the larger the ratio I2/It of the amount of transmitted light when an electric field is applied (I+ in Figure 2(b)) to the transmitted light 1 after the electric field is removed (12 in Figure 2(b)). it is conceivable that. In this example, at 25°C, I2/I+=0.70 and the contrast ratio was 1:15, which was good.

[Example 21] When an alternating waveform of ±25 V and 15 Hz was applied for about 10 seconds between the electrodes of the device shown in Example 1, the alignment state of the liquid crystal showed a dense striated structure in a direction almost perpendicular to the layer direction. He appeared in a uniform condition.

By this electric field treatment, zigzag defects formed during cooling of the encapsulation were removed. The element was held between polarizing plates whose polarization axes were orthogonal to each other, and the driving waveform shown in FIG. 2(a) was applied to evaluate the optical response shown in FIG. 2(b). In this example, I2/II=0.96 at 25°C,
The contrast ratio was good at 1:35.

1 Effects of the Invention 1 The present invention solves the drawbacks of the prior art by improving the material and forming method of the liquid crystal alignment film and controlling the surface properties, and achieves good results through bistable uniform alignment. It was possible to provide an excellent liquid crystal electro-optical element that has a memory effect and exhibits little reduction in contrast due to alignment 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 an example of a driving waveform used in evaluating the liquid crystal electro-optical element of the present invention and a corresponding optical response. 1.2. ,,upper and lower glass substrates 3 89. Spacer 4.5. ,,transparent electrode 6. 6. Liquid crystal layer 7.8. ,, insulating layer 9, 10. ,,LB alignment film 11.12. , polarizing plate 21 , , drive waveform 22 , , more than optical response

Claims (4)

[Claims] (1) In a liquid crystal electro-optical element comprising a ferroelectric liquid crystal sandwiched between a pair of substrates having a scanning electrode group and a signal electrode group,
1. A liquid crystal electro-optical element comprising, on at least one substrate, a substantially oriented thin polymer film for controlling the alignment of liquid crystal molecules. (2) The liquid crystal electro-optical device according to claim 1, wherein the polymer thin film is formed by a Langmuir-Prodgett method. (3) The liquid crystal electro-optical device according to claim 1, wherein the material constituting the polymer thin film is an amphipathic polymer compound having a hydrophilic group and a hydrophobic group in the monomer unit. (4) The liquid crystal electro-optical element according to claim 3, wherein the polymer compound is a thermotropic liquid crystal substance.