JPH04243228A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To improve the memory characteristic and orientability of a ferroelectric liquid crystal of the liquid crystal element formed by using the ferroelectric liquid crystal. CONSTITUTION:An oriented film 11 provided on a liquid crystal display substrate 12 is formed by using a liquid crystalline high polymer which exhibits an antiferroelectric characteristic at the temp. higher than room temp. The molecular axis direction within the smectic layer of the antiferroelectric liquid crystal phase exists in two directions and, therefore, this orientation is fixed and is used for the oriented film, by which the uniform orientation is executed without impairing the bistability of the ferroelectric liquid crystal and the memory characteristic is improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal element using ferroelectric liquid crystal, which has uses such as display elements, light valves, optical shutters, and optical memories.

0002

[Prior Art and Problems to be Solved by the Invention] In liquid crystal elements such as liquid crystal display elements, liquid crystal shutters, liquid crystal light valves, switching elements for optical information processing, and optical memories that use ferroelectric liquid crystal, the liquid crystal is unidirectionally It is necessary to preferentially orient it. 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 or the like to the ferroelectric liquid crystals oriented in this way, the alignment state of the liquid crystals is changed, and by using birefringence, dichroism, etc., the O
Perform N-OFF.

Conventional orientation methods 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 vapor deposition of inorganic materials is a batch process, which takes time and has poor productivity. Moreover, the method of rubbing the coating film of the silane coupling agent is poor in reliability. Furthermore, many methods of rubbing organic polymer coatings to form alignment films have poor heat resistance, and in the case of polyimide, which has good heat resistance and is widely used, it is difficult to obtain homogeneous monodomains. It is.

[0005] Therefore, the inventors of the present invention have proposed
In Japanese Patent No. 024, a method using a ferroelectric material for an alignment film was proposed, thereby improving the alignment of ferroelectric liquid crystals. However, although it is relatively easy to obtain uniform orientation using this method, there is still room for improvement in terms of developing sufficient memory properties.

[0006] It is difficult to develop sufficient memory properties with almost all conventional orientation methods. The reason for this is that conventional alignment methods use an action that aligns ferroelectric liquid crystal molecules only in one direction, such as the rubbing direction. A typical example is shown in Figure 1. When an organic polymer thin film such as polyimide is formed on the substrate 1 and its surface is rubbed with a flocked cloth, the long axis direction of the liquid crystal molecules tends to be parallel to the rubbing direction 2. For nematic liquid crystals and smectic A liquid crystals, the long axes of liquid crystal molecules can be aligned in the rubbing direction 2 by this method without any problems. However, among ferroelectric liquid crystal devices (hereinafter also referred to as FLCDs), surface-stabilized FLCDs (SSS) are currently the most studied.
When FLCD) is made using this alignment method, it is difficult to obtain a monodomain, and the film is divided into two domains whose apparent long axis direction is shifted by a certain angle with respect to the rubbing direction 2 (
In this case, the long axis direction of the molecule corresponds to 3 and 3' in Fig. 1). Moreover, since there is a force acting to align the long axes of the molecules in the rubbing direction 2, the memory property becomes weak. By applying different alignment treatments to the upper and lower substrates or using ferroelectric materials as alignment films, the dipole moment directions 4 and 4' when the molecular long axis directions of the ferroelectric liquid crystal are 3 and 3', respectively, can be changed. Although it is possible to control and align only one of the two domains, in this case, it is difficult to provide bistability, so in most cases the memory performance is significantly reduced.

The present invention was made in view of the problems of the prior art, and improves the memory properties and orientation of ferroelectric liquid crystal by using a specific alignment control film.
The object of the present invention is to provide a liquid crystal element having high density, large capacity, and high-speed response.

[0008]

[Means for Solving the Problems] In order to achieve the above object, according to the present invention, a ferroelectric liquid crystal layer and ferroelectric liquid crystal molecules are provided between a pair of substrates, at least one of which is transparent. In a liquid crystal element in which an alignment film is interposed for substantially horizontal alignment, the alignment film is formed by depositing a liquid crystalline polymer that exhibits antiferroelectricity at a temperature higher than room temperature. A liquid crystal element is provided.

The configuration of the present invention will be explained in detail below. The liquid crystalline polymer used as the alignment film in the present invention exhibits an antiferroelectric phase at a temperature higher than room temperature. The alignment state of the antiferroelectric liquid crystal phase is extremely characteristic as shown in FIG. FIG. 2 is a view of a structure in which an alignment film is coated and rubbed on the substrate surface, and an ordinary low-molecular antiferroelectric phase is oriented on the alignment film, as viewed from a direction perpendicular to the substrate surface. Since the long axis directions 7, 7 of liquid crystal molecules in the adjacent smectic layers 5, 5 are inclined in the opposite direction to the rubbing direction 6, the tendency for domain division is significantly weaker than in the ferroelectric phase, resulting in a uniform alignment state. is easy to obtain. The direction of inclination of the long axis of the molecule with respect to the rubbing direction may not be reversed for each smectic layer, but may be reversed for every two layers as illustrated in FIG. Although three or more layers may be parallel or a combination of one layer and two layers may be considered, any orientation specific to the antiferroelectric phase can be utilized in the present invention.

As mentioned above, in the antiferroelectric liquid crystal phase, there are two long axis directions of the molecules in the smectic layer, and if this orientation is fixed and used as an alignment film for the ferroelectric liquid crystal,
It is possible to align the ferroelectric liquid crystal without impairing its bistability, and therefore it is possible to produce a FLCD with excellent memory properties.

[0011] Fixing the orientation in the antiferroelectric liquid crystal phase is achieved by forming a film of a liquid crystal polymer material having an antiferroelectric phase on a substrate, and
This is achieved by heating this polymer to a temperature at which it exhibits an antiferroelectric phase, allowing the desired alignment state to be achieved by the action of an alignment treatment film previously applied to the substrate, and then rapidly cooling it to a temperature at which it does not form a liquid crystal phase. can do. FIG. 4 shows an example of the structure of a liquid crystalline polymer whose orientation is fixed on a substrate. In the figure, 10 is a liquid crystal polymer layer, 11 is an alignment treatment layer, and 12 is a substrate. As the substrate 12, glass or a plastic film can be used. Among plastic films, polyethylene terephthalate, polyether sulfone, polyarylate, and the like are preferred from the viewpoint of heat resistance. As the alignment treatment layer 11, an alignment film formed by a conventional alignment treatment method, such as a rubbed polyimide resin coating or an obliquely vapor-deposited SiO film, is sufficient. When a film such as uniaxially stretched polyethylene terephthalate is used as the substrate 12, the main chain of the polyethylene terephthalate is oriented in the direction of stretching, so the orientation treatment layer 11 may be omitted; When it is desired to have a regulating force in a different direction, the surface of the substrate may be directly rubbed. The latter method is also effective when the substrate is a plastic film that is not uniaxially stretched. An example of a liquid crystalline polymer having an antiferroelectric phase as used in the present invention is a side chain type liquid crystalline polymer having a structure such that it takes an antiferroelectric phase as a mesogen. Examples of such mesogens include those shown in Table 1.

0012

[Table 1]

Although liquid crystal materials having an antiferroelectric phase are not well known, it is thought that many types of antiferroelectric liquid crystal materials will be discovered in the future, and as a result, mesogens that can be used in the present invention will be developed. can be expected to increase as well. The spacer part has 2 to 2 carbon atoms like general liquid crystal polymers.
When it is a methylene chain of 10 or a linear alkoxy group, the liquid crystal phase is stabilized. The main chain skeleton is preferably a vinyl polymer, polysiloxane, or the like.

Although no examples of main chain type liquid crystalline polymers having an antiferroelectric phase are known to date, there are examples of main chain type liquid crystal polymers having a smetic phase and an asymmetric carbon, which are represented by the following formula 1. Materials with an antiferroelectric phase can be expected.

[Formula 1] In Formula 1, copolymers of units with different n can also be used.

Methods for forming a film of a liquid crystalline polymer on a substrate or a substrate with an alignment treatment layer include a method in which the liquid crystalline polymer is directly coated at a temperature equal to or higher than the glass transition point at which the liquid crystalline polymer exhibits fluidity;
Alternatively, there is a method in which the liquid crystalline polymer is dissolved in a solvent, the solution is applied or printed, and then the solvent is evaporated. Chloroform,
Halogenated hydrocarbon solvents such as dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, orthodichlorobenzene, phenolic solvents such as phenol, O-chlorophenol, and cresol;
Aprotic polar solvents such as dimethylformamide and dimethyl sulfoxide, ether solvents such as tetrahydrofuran and dioxane, and mixed solvents thereof can be used. In particular, when a polymer coating film is used as the alignment layer 11, it is necessary to select a solvent so that the alignment force of the alignment layer is not reduced by the solvent for the liquid crystalline polymer.

After providing the liquid crystal polymer layer on the substrate, the liquid crystal polymer is heated to a temperature at which it exhibits an antiferroelectric phase for several minutes to 1 hour.
After the alignment is completed as shown in FIGS. 2 and 3 for a certain period of time, it is rapidly cooled to a temperature at which no liquid crystal phase is formed. This results in
The orientation of the antiferroelectric phase can be fixed. FIG. 5 shows an example of a liquid crystal cell prepared by bonding another substrate prepared in the same manner as above with a sealing material and sealing ferroelectric liquid crystal therein. 16 and 16' are liquid crystalline polymer layers with fixed orientation, which act as alignment films for the ferroelectric liquid crystal 17.

[0017]

[Example] Next, an example of the present invention will be described. Example 1 A polyimide alignment agent was printed on a glass substrate patterned with transparent electrodes, and after drying at 100°C for 30 minutes,
The imidization was completed by baking at 50° C. for 1 hour, and the surface of the alignment film was rubbed. On this alignment film, a solution in which a side-chain polysiloxane liquid crystalline polymer having a mesogen structure represented by the following formula 2 was dissolved in a solvent containing tetrachloroethane as a main ingredient was applied using a spinner.

embedded image After coating, the coating was dried at 100° C. for 1 hour, heated to a temperature at which the liquid crystalline polymer exhibits an antiferroelectric phase, left to stand for 30 minutes, and then rapidly cooled to room temperature. When this substrate was observed with a polarizing microscope, it was found to be a monodomain with an extinction position in the rubbing direction.

[0018] This was laminated to another substrate prepared in the same manner so that the rubbing direction was parallel to it to form a liquid crystal cell. The cell gap was controlled to about 1.7 microns by scattering plastic beads with an average diameter of 1.8 microns. Ferroelectric liquid crystal ZLI-4237-000 manufactured by Merck was sealed in this liquid crystal cell,
When the temperature was raised to 85° C. to obtain an isotropic phase and then slowly cooled at a rate of about 1° C./min, uniform orientation was obtained. When the memory property was evaluated by applying pulsed positive and negative potentials to the electrodes, it was confirmed that the memory property was much more stable than when only a general polyimide alignment agent was used. FIG. 6(a) shows the memory performance of this embodiment, and FIG. 6(b) shows a comparison of the memory performance of the conventional example. It was found that the change in light intensity during the period when no voltage was applied was smaller in (a), indicating that it had stable memory properties.

[0019]

[Effects of the Invention] In the liquid crystal element of the present invention, the liquid crystalline polymer layer in which the orientation of the antiferroelectric phase is fixed is used as an alignment film for aligning the ferroelectric liquid crystal. It is possible to provide a liquid crystal element that can sufficiently exhibit memory properties and can be used as a liquid crystal element capable of displaying a large capacity or as a stable recording medium.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of problems in the prior art.

FIG. 2 is an explanatory diagram of the alignment state of an antiferroelectric liquid crystal phase.

FIG. 3 is an explanatory diagram of another orientation state of an antiferroelectric liquid crystal phase.

FIG. 4 is a cross-sectional view showing an example of the structure of a liquid crystalline polymer with fixed orientation.

FIG. 5 is a cross-sectional view showing a configuration example of a liquid crystal cell according to the present invention.

FIG. 6(a) is a diagram showing memory performance in an embodiment, and FIG. 6(b) is a diagram showing memory performance in a conventional example.

[Explanation of symbols]

10,16,16' liquid crystalline polymer layer 11,
15, 15' alignment treatment layer 12, 13, 13' substrate
14,14' Transparent electrode 17 Ferroelectric liquid crystal

Claims (1)

[Claims] 1. A ferroelectric liquid crystal layer and an alignment film for aligning the ferroelectric liquid crystal molecules substantially horizontally with respect to the substrates are interposed between a pair of substrates, at least one of which is transparent. 1. A liquid crystal element, wherein the alignment film is formed by depositing a liquid crystalline polymer exhibiting antiferroelectricity at a temperature higher than room temperature.