JPH03137620A - Ferroelectric liquid crystal device - Google Patents

Abstract

PURPOSE:To keep the gap between substrates sufficiently narrow and uniform and to enable satisfactory display free from an afterimage and flicker by specifying the diameter and distribution density of spacers. CONSTITUTION:A ferroelectric liq. crystal 104, granular spacers 105 such as alumina or silica beads and adhering bodies 106 are arranged between a pair of substrates 102, 103 to obtain a ferroelectric liq. crystal cell 101. The diameter of the spacers 105 is regulated to 1-10 mum, preferably 1-2 mum and the spreading density to 100-500/mm<2>, preferably 200-400/mm<2>. The spacers 105 are previously spread on one of the substrates 102, 103 and the substrates are superposed. The gap between the substrates can be kept sufficiently narrow and uniform, flickering of an image due to delay of inversion around the spacers is prevented and an afterimage remaining after inversion without vanishing does not remain.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal element used in a liquid crystal display element, a liquid crystal-optical shutter, etc., and particularly to a liquid crystal element using ferroelectric liquid crystal.

[Prior Art] C1ark and Lage are display devices that utilize the refractive index anisotropy of ferroelectric liquid crystal molecules to control transmitted light in combination with a polarizing element.
rwal 1) (Japanese Unexamined Patent Publication No. 1986-1
07216, US Pat. No. 4,367,924, etc.). The ferroelectric liquid crystal used in this display element is
Generally, in a specific temperature range, chiral smectic C
phase (SmC") or H phase (SmH"), and in this state, it takes either the first optically stable state or the second optically stable state in response to an applied electric field, and It has the property of maintaining its state when no voltage is applied, that is, it has bistability, and it also responds quickly to changes in electric field, so it is expected to be widely used for high-speed and memory-type display elements.

In such display elements, it is necessary to maintain a sufficiently small and uniform distance between the two substrates on which electrodes for applying an electric field are formed, and this is generally achieved using silica beads or alumina beads. A method has been adopted in which a hard material (spacer agent) such as the following is dispersed into the element. Also,
In order to suppress disturbances in the alignment state caused by external stresses such as impacts and loads, it has been proposed to spread adhesive particles within the device to suppress misalignment between the substrates.

[Problems to be Solved by the Invention] However, when considering the alignment of liquid crystal displays, the presence of granular spacer agents, granular adhesives, etc. within the element tends to cause alignment defects to occur around them. arise.

When the liquid crystal element is driven in such a state and reversed from the first optically stable state to the second optically stable state, the reversal occurs around the granular spacer agent or granular adhesive. A delay occurs, which manifests itself in the phenomenon of flickering in image quality. Furthermore, if this delay becomes large, a state (afterimage) will occur in which the state of the screen before inversion remains visible even after inversion. This phenomenon becomes more noticeable as the number of granular spacer agents and granular adhesives increases. Such a phenomenon has become a problem as it significantly reduces the image quality of the liquid crystal element.

Therefore, an object of the present invention is to reduce the dispersion density of the granular spacer agent within a range that can maintain a uniform distance between two electrode substrates, which is the original purpose of use, and to reduce the orientation disorder caused by the spacer agent. It is an object of the present invention to provide a ferroelectric liquid crystal element having a high display quality and good alignment with little influence of flickering and afterimage.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a pair of substrates on which an electrode group is formed and arranged at a distance, and a voltage is applied by the electrode group arranged between the pair of substrates. In a ferroelectric liquid crystal element having a ferroelectric liquid crystal driven by voltage and a granular spacer agent for maintaining a uniform distance between a pair of substrates, the diameter of the spacer agent is 1 to 10 μm and the distribution thereof is The density is set to 100 to 500 pieces/mm''.

A pair of substrates is usually bonded by an adhesive between the substrates, and the distance between the substrates is set to a sufficiently small distance to suppress the helical alignment structure of the ferroelectric liquid crystal.
An alignment control film is disposed on at least one of the substrates.

[Example] FIG. 1(A) is a cross-sectional view illustrating a ferroelectric liquid crystal element (cell) of the present invention. A ferroelectric liquid crystal cell 101 includes a ferroelectric liquid crystal 104, a granular spacer 105 (alumina beads, silica beads), and an adhesive for bonding the substrates 102 and 103 between a pair of substrates 102 and 103 (glass, plastic). 106 are arranged.

Transparent electrodes 10 are provided on the inner surfaces of the substrates 102 and 103, respectively.
7 and 108, transparent 8 electrolyte films 109 and 110, and alignment control films 111 and 112 are provided. This orientation control film 1
It is also possible to omit either one of 11 and 112.

As the ferroelectric liquid crystal 104, for example, US Pat. No. 456
Publication No. 1726, Publication No. 4589996, Publication No. 45
Liquid crystals disclosed in U.S. Pat. No. 92858 and U.S. Pat. No. 4,614,609 can be used, and the orientation state thereof is as disclosed in U.S. Pat. No. 4,563,059 and U.S. Pat.
The suppressed or eliminated helical arrangement structure disclosed in Publication No. 3 can be used.

FIG. 2 shows the bistable alignment state of chiral smectic liquid crystal when the helical alignment structure inherent in the bulk state disappears.

This bistable alignment state is achieved by keeping the distance between the pair of substrates 201 and 202 sufficiently small (10 μm or less) to eliminate the spiral alignment structure, and the liquid crystal molecules are , are held as liquid crystal molecules 203A and 203B oriented in one of the stable states. Furthermore, in the present invention, in the absence of an electric field, the liquid crystal molecules 203
It is also possible to use an orientation state in which the substrates 201 and 202 are oriented at a pretilt angle. 204 in FIG. 2 represents a vertical molecular layer organized by a plurality of liquid crystal molecules, and the arrow in the figure represents the direction of the dipole component.

The diameter of the granular spacers used in the present invention is 1 to 10 μm, preferably 1 to 2 μm, and the scattering density is 100 to 500 pieces/mm”%, preferably 200 to 400 pieces/m
m 2 and can be obtained by dispersing it on one of the substrates in advance and then stacking the two substrates together.

It is preferable that the adhesive material 106 be spread on the substrate in advance like the granular spacers 105.

Such a ferroelectric liquid crystal cell 101 includes a pair of polarizers 113.
and 114, the change in the orientation state is optically identified.

FIG. 1(B) is a plan view of the ferroelectric liquid crystal cell 101.
A sealing member 115 that seals the pair of substrates 102 and 103 is arranged except for the injection port 116, and the inside of the sealing member 115 is used as a display section 117.

The alignment control films 111 and 112 include polyvinyl alcohol, polyimide, polyamideimide, polyesterimide, polyparaxylerin, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyamide, polystyrene, cellulose resin, melamine resin, area resin, and acrylic. A film made of an organic insulating material such as a resin that has been subjected to a uniaxial alignment treatment (for example, a rubbing treatment) can be used. Transparent dielectric films 109 and 110
As the material, a film of an inorganic insulating material such as silicon oxide, silicon dioxide, aluminum oxide, zirconia, magnesium fluoride, cerium oxide, cerium fluoride, silicon nitride, silicon carbide, or borate nitride can be used. The alignment control films 111 and 112 generally have 50 to 1,000
The transparent dielectric films 109 and 1 can have a film thickness of 0.
10 can generally range from 100 to 3,000 people.

Hereinafter, the present invention will be explained by giving specific examples and comparative examples.

Two 1.1 mm thick glass plates were prepared for a pair of substrates, transparent stripe electrodes of ITO (indium tin oxide) were formed on each glass plate, and transparent dielectric stripes were formed on each glass plate. A film of 5i02 was formed as a body film by a 500-meter-thickness sputtering method.

On this 5i02 film, LP64, which is a polyimide forming solution, is applied.
(manufactured by Toshisha Co., Ltd.) solution was applied by a printing method and baked at 270° C. to form a 100-layer polyimide orientation control film. The fired coating was subjected to a rubbing treatment using an acetate flocked cloth. After that, one substrate was coated with particles having an average diameter of 5.5 μm using the Nordson electrostatic spraying method.
Epoxy resin adhesive particles (trade name: Trepearl; manufactured by Toshisha Co., Ltd.) were dispersed at a distribution density of 30 particles/mm. On the other substrate, silica microbeads with an average particle size of 1.5 μm were sprayed. was sprayed using the Nordson electrostatic spraying method at a distribution density of 300 particles/mm2.Next, a liquid adhesive (trade name: Nistruct Bond; manufactured by Mitsui Toatsu Co., Ltd.) was applied by printing to a film thickness of 6 μm as the sealing member 115. .

Next, the two glass plates were glued together and compressed by applying a pressure of 2.8 kg/Cm2 at a temperature of 70°C for 5 minutes, and then a pressure of 0.63 kg/Cm2 was applied at a temperature of 150°C.
While applying a pressure of cm', 2 fl of the adhesive was cured over 4 hours to prepare a cell.

Thereafter, the pressure inside this liquid crystal cell was reduced to 10<-4>, and pyrimidine liquid crystal, which is a ferroelectric liquid crystal, was injected at a constant rate. The phase change of this liquid crystal material is shown below.

-15℃ 60.5℃ 73.5℃ 90
,4℃Cryst 4--5 m G"-
-* S m^ □-* Ch --* I s.

SmA; smectic A phase Ch, cholesteric phase 15oH showing isotropic phase. After that, it was cooled to 25° C. to form chiral smectic C phase through the cholesteric phase and smectic A phase.

FIG. 3 shows a schematic sketch of the state of occurrence of alignment defects in the liquid crystal element thus produced, observed under a microscope. As shown in the figure, a hairpin defect 302 and a lightning defect 303 that occur within a pixel 301 occur in pairs, and these are caused by the granular spacers scattered within the element. It is. Therefore, the number of hairpin defects and lightning defects that form a pair is correlated with the number of granular spacers dispersed. These two defects generally differ in optical state from the surrounding domains and can be distinguished using a microscope.

The above-mentioned hairpin defect and lightning defect were clarified in the October 1988 Liquid Crystal Symposium Proceedings P114-115 "Study on the structure of 5SFLC state by microspectroscopy".

Writing was performed on such a liquid crystal element using the multiplexing method using the applied voltage shown in the timing chart of FIG. 4, and the pixels were observed under a microscope. It was confirmed that there was a delay in the reversal around the defect when reversing the state. Further, as a result of visual observation of the above-mentioned state, as shown in Table 1, no flickering or afterimage was observed, and it was confirmed that the image quality was good.

A liquid crystal element was prepared in the same manner as in Example 1, except that the scattering density of granular spacers was 200 pieces/mm' and 400 pieces/mm2, and the same observation was performed. . The results are shown in Table 1 together with the results of Example 1.

An element was produced in the same manner as in Example 1 except that the scattering density of 311 granular spacers was 60 pieces/mm'.

In the case of this element, the spacing between the substrates 102 and 103 shown in Figure N1 (A) could not be obtained uniformly, and an image could not be displayed on the entire surface of the liquid crystal element.

When this liquid crystal element was disassembled and the granular spacers were observed using a scanning electron microscope, it was confirmed that some of the particles had cracks.

A device was prepared in the same manner as in Example 1, except that the density of the granular spacers was set at SOO spacers/mm2, and the same observations as in Example 1 were made. As a result, it was found that the distribution of granular spacers within a pixel showed areas where so-called agglomeration occurred, where multiple spacers existed adjacent to each other, and when driven, the state changed from a first optically stable state to a second optically stable state. It was confirmed that the region around the spacer where the reversal is delayed when the state is reversed is several times larger than the region when the spacer exists alone. Furthermore, as a result of visual observation in the same manner as in Example 1, it was observed that flickering and afterimages, which were not observed in Examples 1 to 3, occurred, and good image quality could not be obtained.

[Effects of the Invention] According to the present invention, the diameter of the spacer agent is 1 to 10 μm, and the distribution density is 100 to 500 particles/mm.
Therefore, it is possible to create a liquid crystal element that can maintain a sufficiently small and uniform substrate spacing and can perform good display without causing deterioration in image quality such as flickering or afterimages during driving.

[Brief explanation of the drawing]

1(A) and (B) are a cross-sectional view and a plan view illustrating the strong charge liquid crystal element of the present invention, and FIG. 2 is a schematic diagram showing the alignment state of liquid crystal molecules in the liquid crystal element of FIG. 1. Figure 3 is a schematic diagram sketching the results of microscopic observation of the liquid crystal element prepared in the example, and Figures 4 (A) to (
C) is a timing chart showing drive waveforms used to study the elements created in Examples. 101: Strongly charged liquid crystal cell, 102, 103: Substrate, 1
04: Strongly conductive liquid crystal, 105: Granular spacer, 107.
108: Transparent electrode, 110° 111: Orientation control film.

Claims (4)

[Claims] (1) A pair of substrates on which electrode groups are formed and spaced apart, a ferroelectric liquid crystal placed between the pair of substrates and driven by a voltage applied by the electrode group, and a gap between the pair of substrates. In a ferroelectric liquid crystal element having a granular spacer agent for uniformly holding the spacer, the spacer agent has a diameter of 1 to 10 μm and a distribution density of 100 to 50 μm.
A ferroelectric liquid crystal element characterized in that the number of ferroelectric liquid crystal elements is 0 pieces/mm^2. (2) The ferroelectric liquid crystal element according to claim 1, further comprising an adhesive between the pair of substrates for bonding the substrates together. (3) The ferroelectric liquid crystal device according to claim 1, wherein the distance between the pair of substrates is set to a distance sufficiently small to suppress a helical alignment structure of the ferroelectric liquid crystal. (4) The ferroelectric liquid crystal device according to claim 1, wherein an alignment control film is disposed on at least one of the pair of substrates.