JPH02103018A - Ferroelectric liquid crystal element - Google Patents

Abstract

PURPOSE:To obtain a ferroelectric liquid crystal element contg. no orientation defect, having fast response characteristic, and high bistability by constituting the element of an orientation film having a two-layered structure consisting of first and second oriented films, and orienting each orientation film to different direction. CONSTITUTION:Each orientation film of the title ferroelectric liquid crystal element is constituted of a two-layered structure comprising a first oriented film 4, 4' and a second oriented film 5, 5'. The oriented film 4, 4' is prepd. by rubbing a thin film consisting of an org. high molecular compd., and the oriented film 5, 5' is constituted of a thermotropic liquid crystalline high molecular compd. having a mesogen group in the principal chain or side chain, wherein the direction of orientation is changed from the orientation direction of the oriented film 4, 4'. In this case, liquid crystal molecules having extremely high bistability are obtd. by the exertion of a regulating power effecting to retain the liquid crystal molecules at an original position even if a driving potential field impressed to a liquid crystal layer is eliminated if each orientation direction coincides almost to each switching direction of the liquid crystal molecules at each driving stage. Thus, a ferroelectric liquid crystal element contg. no orientation defect and having extremely fast response characteristic and high bistability, is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ferroelectric liquid crystal device that has uses such as display devices, light valves, optical shutters, and optical memories.

[Prior art] Liquid crystal display elements using ferroelectric liquid crystals, liquid crystal shutters,
In liquid crystal elements such as liquid crystal light valves, switching elements for optical information processing, and optical memories, it is necessary to preferentially align liquid crystal in one direction. Since this alignment treatment has a great influence on the quality of these liquid crystal elements, much research has been conducted on it.

The alignment state of liquid crystal on the substrate surface can be broadly classified into homogeneous alignment, which is aligned parallel to the substrate surface, and homeotropic alignment, which is aligned perpendicular to the substrate surface.

In actual liquid crystals, by applying an electric field etc. to the ferroelectric liquid crystals oriented in this way, the alignment state of the liquid crystals is changed, and by using birefringence, dichroism, etc., light is turned on and off. conduct.

Conventional methods for aligning liquid crystals include oblique vapor deposition of inorganic materials, rubbing of silane coupling agent coatings, and rubbing of organic polymer coatings, but none of these methods are satisfactory. Oblique deposition of inorganic materials is a batch process, which takes time.
The productivity is poor, and the method of rubbing a silane coupling agent coating has poor reliability.Furthermore, the method of rubbing an organic polymer coating to form an alignment film generally has poor heat resistance. In the case of polyimide, which has good heat resistance and is widely used, it is difficult to obtain homogeneous monodomains, the contrast ratio during driving is low, and furthermore, it has poor bistability and high-speed response. The problem is that it decreases.

In order to eliminate such drawbacks, the present inventors first provided an obliquely vapor-deposited film of an inorganic oxide or a rubbed film of an organic polymer compound as a base layer, and then formed a layer made of a liquid crystalline polymer on the base layer. He proposed a liquid crystal element provided with an alignment layer (Japanese Patent Application No. 79172/1983).

Although these liquid crystal elements have smaller alignment defects and better driving characteristics than conventional ones, subsequent research by the inventors revealed that their bistability was still insufficient. .

[Problem to be solved by the invention]

The present invention has been made in view of the above-mentioned state of the prior art, and its purpose is to provide a liquid crystal element that exhibits good alignment, excellent high-speed response, and excellent bistability. .

[Means to solve the problem]

According to the present invention, the transparent electrodes (3), (3'), the first alignment film (4), (4'), and the second alignment film (5)
, (5') are formed in this order on the transparent substrate (2
), (2') are stacked on top of each other with a small gap in between, and a ferroelectric liquid crystal (7) is sealed in the cell, and a polarizing plate (1) is placed on the outside.
), (1') in a liquid crystal element configured by bonding together the first alignment film (4).

(4') is a rubbed organic polymer film, and the second alignment films (5) and (5'') are liquid crystal polymer films having mesogen groups in the main chain or side chain; 1
A ferroelectric liquid crystal element is provided, characterized in that the alignment films (4) and (4') are rubbed in a different direction.

Generally, liquid crystal molecules are aligned in a specific direction by the alignment regulating force of an alignment film, and are switched left and right around this direction. For this reason, a force constantly acts on the liquid crystal molecules to pull them back toward the center of the regulated alignment, which inhibits their bistability.

As a result of careful consideration of these points, the present inventors have determined that the alignment film has a two-layer structure consisting of a first and second alignment film, and that the alignment directions of the first alignment film and the second alignment film are different. ,
Preferably, these two alignment directions are made to substantially match the two switching directions of the liquid crystal molecules during driving, so that the liquid crystal molecules are kept in the same position even when the driving electric field applied to the liquid crystal layer disappears. The present invention was completed based on the discovery that liquid crystal molecules with extremely good bistability can be obtained through the action of force.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

In Fig. 1, 1.1' is a polarizing plate, 2, 2' are transparent substrates, 3.3' is a transparent electrode, 4.4' is a first alignment film,
5.5' is a second alignment film, 6.6' is a sealant, 7 is a ferroelectric liquid crystal, and 8 is a spacer.

Polarizing plates 1 and 1' are perpendicular to the direction of light propagation and have the function of transmitting only light that vibrates strongly in a specific direction and absorbing other components. Those held between the two are used.

As the transparent substrate 2.2', conventionally known materials are used, such as glass, polyesters such as polystyrene terephthalate and polybutylene terephthalate, plastics such as epoxy resins, phenolic resins, and polyimides. The transparent electrode 3.3' is formed of a transparent electrode material such as ITO (indium tin oxide), SnO, (tin oxide), etc., and is connected to a folding circuit (not shown) to which a signal voltage is applied. In this case, if necessary, a blocking layer of SiO□ or the like may be provided between the transparent substrate and the transparent electrode in order to prevent alkali ions from entering from the transparent substrate.

Furthermore, the electrodes thus provided can be shaped into a desired shape by etching.

4.4' is a first alignment film, which is a thin film made of an organic polymer compound and subjected to a rubbing treatment. As the organic polymer compound, polyimide, polyamide, polyvinyl alcohol, polyetherimide, polysulfone, polyurethane, polybutyral, polycarbonate, etc. are used. To form the first alignment film, these resins are dissolved in a suitable solvent and applied by conventionally known methods such as vapor deposition, spin cord, roller coating, spray coating, dipping, etc., and then heat treated and dried to a film thickness of 100~ After forming the first alignment film of 5,000 people, preferably 500 to 100 people, rubbing treatment may be performed in one direction using cotton cloth, nylon flocked fabric, polyester flocked fabric, or the like.

5.5' is a second alignment film, which is composed of a thermotropic liquid crystal polymer compound having a mesogen group in the main chain or side chain.

As a thermotropic liquid crystalline polymer compound having a mesogen group in the main chain.

Rigid mesogen groups such as esters, ethers, amides, etc.
Examples include those bonded with a bonding group such as carbonate, with bent silver such as polymethylene, polysiloxane, chiral alkyl, etc. inserted as appropriate between them.

As a thermotropic liquid crystal polymer compound having a mesogen group in the side chain.

Examples include those in which a mesogen group such as -(NCN (R is an alkyl group)) is bonded to the main chain of polyacrylic, polymethacrylic, polysiloxane, etc. via a flexible spacer group such as polymethylene.

In order to form the second alignment film, these liquid crystalline polymer compounds are dissolved in a suitable solvent and made into a thin film by the same means as for the first alignment film. Next, the compound used in the second alignment film is heated to a temperature at which it exhibits a liquid crystal phase to align the mesogen groups in the rubbing direction of the first alignment film, and then rapidly cooled to room temperature to freeze the alignment state.

Furthermore, the surface of the second alignment film is rubbed in a direction that forms a certain angle with respect to the rubbing direction of the first alignment film. Almost match the direction in which the molecules switch. That is, as shown in FIG. 2, it is preferable that the switching position of the liquid crystal molecules when positive and negative driving electric fields are applied and the rubbing directions of the first and second alignment films roughly coincide with each other.

Further, as the ferroelectric liquid crystal 7, any conventionally known single-system or multi-component ferroelectric liquid crystal material may be used. Specific examples of single-type liquid crystal materials are shown below.

[Schiff base-based ferroelectric liquid crystal with amyl alcohol as an asymmetric source] [Ferroelectric liquid crystal with a hydroxyl group at the ortho position of the Schip base] [Schiff base-based ferroelectric liquid crystal with a halogen or cyano group at the asymmetric carbon ] [Azo and azoxy ferroelectric liquid crystals] [Other Schiff base compounds] C,, H2n,, 0-C>N=N-C>0-CH, -4
nc, l(.

n: 16 [Bicyclic ferroelectric liquid crystal] 01゜-C11-(C11, juice<II(C113)2 [ferroelectric liquid crystal with ring substituents such as halogen and cyano group introduced] [amyl alcohol, etc. Polycyclic ferroelectric liquid crystal as an asymmetric source]
Ferroelectric liquid crystal using amino acids as an asymmetric source] [Ferroelectric liquid crystal having a pyrimidine ring] Examples of multi-component ferroelectric liquid crystals include C5-101 manufactured by Chisso FTI.
1, C51013, C51014, and TKF-8616 and TKF-8617 manufactured by Teikoku Kagaku Sangyo ■.

In the liquid crystal element of the present invention, these liquid crystals are injected into a cell, and then the cell is sealed with a sealant 6, 6', and then polarizing plates 1, 1 are attached to transparent substrates 2, 2', which are the upper and lower surfaces of the cell. ′ is made by pasting them together.

〔effect〕

The ferroelectric liquid crystal element according to the present invention has a first alignment film made of an organic polymer rubbed on the substrate surface, and a liquid crystal having a mesogen group in the main chain or side chain rubbed in a direction different from the first alignment film. Since the second alignment film made of a synthetic polymer is provided, it has no alignment defects and has excellent high-speed response and bistability.

In particular, in an embodiment in which the rubbing direction of the first alignment film and the second alignment film is made substantially coincident with the switching direction of the ferroelectric liquid crystal molecules, stable bistability is exhibited over an extremely long period of time.

Furthermore, when the transition temperature of the liquid crystalline polymer compound used for the second alignment film to the liquid crystal phase is set higher than the upper limit of the operating temperature of the liquid crystal element, the alignment film is prevented from being eluted into the ferroelectric liquid crystal. Because of this, there is almost no deterioration in liquid crystal characteristics, making it of high practical value.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Polyimide (Optomer AL-1051 manufactured by Nippon Synthetic Rubber Co., Ltd.) was applied as a first alignment film to a glass substrate with a transparent electrode by spin coating to a thickness of about 800 mm.
A thin film obtained by heat treatment at 50° C. for 60 minutes was provided and rubbed with a rayon flocked cloth. On top of this, a monochrome benzene solution of liquid crystalline polysiloxane represented by the following formula as a side chain type liquid crystal polymer was applied by spin coating.
A second alignment film was formed for 00 people. The substrate was then placed in an oven, heated at about 170° C. for 5 minutes, and then rapidly cooled to room temperature.

Thereafter, the surface of the second alignment film was rubbed in a direction of 42 degrees with respect to the rubbing direction of the first alignment film using a rayon flocked cloth. Next, two substrates were bonded together with spacer particles having an average particle size of 2 μm interposed therebetween, with the alignment film surfaces facing inward to form a cell. After injecting Chisso's C5-1014 as a ferroelectric liquid crystal into the cell, it was sealed.
A liquid crystal element was fabricated by attaching a polarizing plate to the outer surface of the cell. The polarization axis of one polarizing plate was set to match the rubbing direction of the first or second alignment film, and the polarization axis of the other polarizing plate was set to be orthogonal thereto. When a driving voltage as shown in FIG. 3(a) is applied to the transparent electrode of the liquid crystal device thus prepared, what is the light transmittance of the device at that time? As a result, it was found that this element exhibited extremely high speed and excellent bistability response characteristics, as shown by the solid line in FIG. 3(b), and was also found to have excellent orientation.

Example 2 A liquid crystal element was produced under the same conditions as in Example 1 except that the following compound was used as the second alignment film material.

CH.

■ The orientation and response characteristics of the obtained liquid crystal element were examined in the same manner as in Example 1, and as in Example 1, it showed excellent orientation with no defects, as well as high-speed response and excellent bistability. Comparative Example 1 Same as Example 1 except that the second blended film was removed.
A liquid crystal element was prepared in the same manner as above, and its response characteristics were examined, and it showed a curve like the broken line in FIG. 3(b). This result shows that the bistability is significantly lower than that of the present invention.

[Brief explanation of drawings]

FIG. 1 is an explanatory cross-sectional view of the liquid crystal element of the present invention, and FIG.
The figure shows the switching position of liquid crystal molecules, the first alignment film, and the second alignment film.
3(a) is a drawing showing the relationship between the rubbing directions of the alignment film; FIG. 3(a) is a drawing showing the waveform diagram of the applied driving voltage; FIG.
FIG. 3(b) is a graph showing the light transmittance of the liquid crystal elements of the present invention and the comparative example when the driving voltage shown in FIG. 3(a) is applied.

Claims (3)

[Claims] (1) Transparent electrodes (3), (3'), first alignment film (4),
(4') and the second alignment film (5), (5') are formed by overlapping the transparent substrates (2), (2') formed in this order with a minute gap in between to strengthen the cell. In a liquid crystal element configured by enclosing a dielectric liquid crystal (7) and pasting polarizing plates (1), (1') on the outside, the first alignment films (4), (
4') is a rubbed organic polymer film, the second alignment films (5) and (5') are liquid crystal polymer films having a mesogen group in the main chain or side chain, and the first A ferroelectric liquid crystal element characterized by being rubbed in a direction different from that of alignment films (4) and (4'). (2) The rubbing direction of the first alignment films (4), (4') and the rubbing direction of the second alignment films (5), (5') are 2 when driving the ferroelectric liquid crystal (7). 2. A ferroelectric liquid crystal device according to claim 1, wherein the ferroelectric liquid crystal device has two switching directions that substantially coincide with each other. (3) The ferroelectric material according to claim 1, wherein the liquid crystal polymer used in the second alignment film (5), (5') has a transition temperature to a liquid crystal phase that is higher than the upper limit of the operating temperature of the liquid crystal element. liquid crystal element.