JPH01231022A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal element having superior characteristics for displaying memories as well as obtg. perfect memories by using a ferroelectric liquid crystal and constituting an orientation film of a monomolecular film comprising an org. high molecular compd. formed by the Langmuir- Blodgett's technique or a cumulative film of the monomolecular film. CONSTITUTION:A ferroelectric liquid crystal is used and its orientation film is constituted of a monomolecular film of an org. high molecular compd. formed by the Langmuir-Blodgett's technique or a cumulative film of the monomolecular film. 'Ferroelectric' means that permanent dipoles are aligned to a fixed and same direction of the moment, and that spontaneous polarization is present in the liquid crystal. Preferred polyamide compd. is a polyamideimide compd. and preferred orientation is horizontal orientation. Thus, sufficiently good display of memories and perfect memory characteristic are realized. Moreover, since a bias voltage during a nonselective period is unnecessary, a simple driving wave-shape is obtd., so both electric voltage and consumption of electric power are low.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a liquid crystal element using ferroelectric liquid crystal.

[Conventional technology]

The effective optical properties of liquid crystals can be changed by an electric field, and non-emissive devices that utilize the electro-optic effect of liquid crystals are currently widely used.

Among these, ferroelectric liquid crystals, such as those that exhibit ferroelectricity in a smectic C'' layer, are attracting attention because of their high-speed response and memory properties.

The memory property of this ferroelectric liquid crystal appears due to the bistability of liquid crystal molecular orientation. This bistability means that there are 6
The higher the barrier of free energy of orientation deformation during
It is also said that the lower the free energy barrier in the -axis orientation, the more stable it is.

As a method to develop this memory property, first, the sharing layout method (N, A, C1ark, S, T) is used.

Lagerwall, Appl, Phys, Le
tt,, 36.899 (1980), Japanese Patent Publication No. 56-10
No. 7216, US Pat. No. 110.45M, etc.).

This sharing arrangement method is a method in which a ferroelectric liquid crystal is sandwiched between clean substrates with untreated surfaces, and then the side substrates are slightly shifted to align liquid crystal molecules in one direction.

Further, a method applying the rubbing method, which is applied as a productive alignment method to ordinary liquid crystal elements such as TN type, has been attempted.

In this rubbing method, an organic polymer film such as polyimide is formed on the surface of a substrate by a spin cord method, a dip method, etc., and the surface is rubbed with a nylon or acrylic cloth to apply a -axis orientation regulating force.

Furthermore, an AC stabilization method may be mentioned. This A
The C stabilization method uses a ferroelectric liquid crystal with negative anisotropy and applies a high-frequency AC voltage as a bias voltage to which the response of liquid crystal molecules does not follow during the non-selection period (J, P,
Le Pe5antet al,, Parts L
iquid Crystal Conf,, 1984
゜p217. J.M. Geary, SID'85
Digest, p128).

(Problem to be solved by the invention) However, in the above-mentioned sharing distribution method, it is necessary to make the cell thickness of the device extremely thin, about 1 μm, and although this method is effective for devices with a very small area, it is not practical. Difficult to apply in small areas.

In addition, even in the method applying the rubbing method, as with the shearing arrangement method described above, the cell thickness needs to be approximately 1 μm in this case, and it is difficult to form large-area devices with such a thin cell thickness. The process is extremely difficult. Moreover, the contrast during memory when the electric field is turned off is lower than the contrast when the spiritual world is applied, and the memory performance when the cell thickness is increased further deteriorates.

Although good memory performance can be obtained with the AC stabilization method, since the liquid crystal element is isometrically represented as a parallel circuit of a capacitor C and a resistor R, a large amount of power is required in this case, and low voltage drive and low consumption are required. The advantage of liquid crystal elements, which is power, is lost.

Furthermore, the driving voltage range may exceed the range of a normal liquid crystal element driving IC, and a new dedicated IC must be developed, resulting in high costs.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal element that exhibits good memory performance and provides perfect memory.

[Means to solve the problem]

In order to achieve the above object, the liquid crystal element of the present invention has electrodes on opposing surfaces of a pair of substrates disposed facing each other, a liquid crystal is sealed between the substrates, and the opposing surface of at least one substrate. It has an alignment film that aligns liquid crystal molecules,
The liquid crystal is a ferroelectric liquid crystal, and the alignment film is a monomolecular film or a cumulative film of an organic polymer compound formed by the Langmuir-Prodgett method.

In the above, the organic polymer compound is a polyimide compound,
It is preferably a polyamide compound or a polyamideimide compound, and the orientation is preferably horizontal.

For example, JP-A No. 62-27721 discloses a ferroelectric liquid crystal composition that undergoes a phase change in the order of isotonic phase, cholesteric phase, and smectic C1 phase from the high temperature side, or in the order of isotonic phase and smectic C phase. A memory-imparting liquid crystal light modulation element using the present invention is disclosed.

This is consistent with the present invention in that it uses ferroelectric liquid crystal, but the phase series of the ferroelectric liquid crystal is limited, and it is clearly different from the present invention in which memory properties are imparted by an alignment film. are different from each other.

Further, JP-A-62-209415 discloses a liquid crystal cell in which an alignment film is a monomolecular layer or a cumulative monomolecular layer of polyimide formed using the Langmuir-Prodgett method, and a method for manufacturing the same. There is.

This device is characterized by the lack of selectivity in the liquid crystal used. There is no mention of ferroelectric liquid crystals, and no suggestion of memory functions.

In contrast, the present invention is characterized in that the liquid crystal is a ferroelectric liquid crystal, and its purpose and effects are clearly different.

Hereinafter, the configuration of the present invention will be explained in detail.

A ferroelectric liquid crystal is used as the liquid crystal in the liquid crystal element of the present invention.

Here, ferroelectricity means that permanent dipole moments are aligned in the same direction and that spontaneous polarization exists.

As the ferroelectric liquid crystal, one having a chiral smectic phase is used.

Specific examples of this ferroelectric liquid crystal having a chiral smectic phase are shown below.

(FLC-1) (FLC-2) (FLC-3) (FLC-4) (FLC-5) (FLC-6) (FLC-7) (FLC-8) (FLC-9) (ELC-10) (FLC-11) (FLC-13) (FLC-14) (FLC-15) (FLC-16) In the above, n is preferably 4 to 20, and m is preferably 1 to 6.

Such strong-talking liquid crystals have product names ZLI-3488, ZLI-3489, ZLI-365.
4 (all manufactured by E-Merck), product name C5-1
011, C5-1013, C5-1014, C5-10
15 (all manufactured by Chisso ■).

In addition, in the present invention, a chiral dopant having 03 is added to a liquid crystal having a wide temperature range and low viscosity that exhibits a smectic phase, preferably a smectic C phase, to induce a chiral smectic phase. It may also be used as a liquid crystal.

The liquid crystals exhibiting the above-mentioned smectic phase and having a wide temperature range and low viscosity include the following.

(L-1) (L-2) (L-3) (L-4) (L-5) (L-6) (L-7) (L-8) (L-9) ≧ (L-10 ) Further, specific examples of chiral dopants include the following.

(D-1) (D-2) (D-3) (D-4) (D-6) (D-7) (, D-8) (D-9) (D-10) (D-11 ) (D-12) Including the above specific examples, examples of the dopant include compounds having optically active groups as shown below.

(1=1.2.3.4.5.6) (It=o, 1.2.3.4.5.6) (1=O11,
2, 3, 4, 5, 6) (j2=o, 1.2.3.4.5.6) (λ=051.
2.3.4.5.6) (l=3.4.5) " - O-CHC-H2--1 In the above, m is 1 to 6 as above.

In the present invention, the alignment film for horizontally aligning liquid crystal molecules is a monomolecular film or a cumulative film of an organic polymer compound formed by the Langmuir-Prodgett (LB) method.

The above LB method follows the steps shown below.

An organic polymer compound is dissolved in a water-soluble or volatile solvent (e.g., N-methyl-2-pyrrolidone, N,N-dimethylacetamide, benzene, toluene, ethylene glycol, etc.), and this is slowly dropped onto the water surface. . When the partition plate is then moved to reduce the area of the divided water surface, the area occupied by each molecule decreases and the surface pressure increases, and eventually a regularly arranged condensation film is formed, forming a stable monolayer. Exists as a molecular membrane.

This monomolecular film can be removed layer by layer from above the water surface by moving the substrate of the liquid crystal element up and down while maintaining a constant pressure of usually 10 to 40 dyn/cm.

In this case, depending on the organic polymer compound used, surface pressure, etc., the monomolecular film or cumulative film can be an
Preferably, it is a Z film.

As mentioned above, in addition to the vertical immersion method in which the substrate is placed on the water surface, the horizontal adhesion method in which the monomolecular film is adsorbed with the substrate held horizontally may also be used in the present invention, but the vertical immersion method is preferable and However, it is better to use the pull-up method.

Further, the substrate may be used after being pretreated.

In the present invention, the monomolecular film may be a single layer, or several layers may be transferred to form a cumulative film. In the case of forming a cumulative film, the cumulative number may be 2 to 200 layers, preferably 3 to 10 layers.

In this way, the organic polymer compound film formed by the LB method has uniaxial orientation in which the main chain is oriented with respect to the moving direction of the substrate, and the liquid crystal molecules can be horizontally (homogeneously) oriented without any alignment treatment. ) can be oriented.

Such orientation can be confirmed using polarized FT-IR, a high-sensitivity birefringence measurement device, or the like.

The thickness of the alignment film varies depending on the type of compound used, but it is preferably 4 to 4,000 people, preferably 12 to 200 people.

With such a thickness, good orientation can be obtained. If the thickness exceeds 4000 people,
This is because problems such as coloring become noticeable.

The organic polymer compound used in the present invention is not particularly limited as long as it is an amphipathic compound, but it is preferably a polyimide compound, a polyamide compound, or a polyamideimide compound.

Polyimide compounds are synthesized using tetracarboxylic dianhydride and diamine as starting materials and polyamic acid as a precursor.

As polyamic acid, the product name is Sunever RN-71.
0, Sunever RN-305 (manufactured by Nissan Chemical Industries, Ltd.).

When applying the LB method, the polyamic acid is an alkylamine salt.

For example, an alkyl polyamic acid prepared by reacting 0.5 to 2 equivalents of the long-chain alkyl amine shown below to a polyamic acid synthesized according to the scheme of 2.3.5-tricarboxy 4,4'-diaminodiphenylmethanecyclobentylacetic acid. Examples include amine salts.

Preferred examples of the long-chain alkylamine include N,N-dimedecylamine (H2N-C1oH2S), tetradecylamine (H2N CI4829), and the like.

In addition, polyamic acids are generally synthesized from tetracarboxylic dianhydride and diamine, but as the tetracarboxylic dianhydride that can be used in the present invention, preferably pyromellitic dianhydride, 3,4 .3', 4'
-Biphenyltetracarboxylic dianhydride, bis(3,
4-dicarboxyphenyl)ether dianhydride, 3.4
．． Examples include 3',4'-benzophenonetetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, and the like.

Further, as the diamine, preferably p-phinidine diamine, 4.4'-diaminobiphenyl, 4.4'-
Oxydianiline, 4,4'-methylenedianiline, 4
．． Examples include 4'-sulfonyl dianiline.

The polyimide compound is preferably one obtained by converting the polyamic acid alkylamine salt, which is the above polyamide compound, using heat or an acid anhydride according to a known method.

When using heat, the temperature is 170 to 400°C, preferably 170 to 400°C.
The temperature may be 250°C.

In addition, in the case of using an acid anhydride, acetic anhydride or the like may be used as the acid anhydride.

This polyimide compound is converted by transferring a monomolecular film of polyamic acid alkylamine salt onto a substrate and then immersing the substrate in an acid anhydride or heating it. is preferred.

The polyamide-imide compound used in the present invention is, for example, a polyamide amic acid synthesized according to the scheme of 4-(chloroformyl) 4.4'-oxydianiline phthalic anhydride polyamide amic acid, and an alkyl amine as in the case of a polyimide compound. It is made into a salt and then converted by heat or an acid anhydride. Specifically, it is the one shown below.

In the above, for the synthesis of polyamide amic acid, 4.
In addition to 4'-oxydianiline, the above-mentioned aromatic diamine used in synthesizing polyamic acid can also be used.

The memory properties of the liquid crystal element of the present invention will be considered.

The memory property of strong electrostatic liquid crystals appears due to the bistability of liquid crystal molecular orientation. This bistability is more stable as the free energy barrier for orientation deformation during transition between bistable states is higher, and as the free energy barrier for -axis orientation is lower.

These barriers are higher as the deformation strain during transition between states is larger, that is, as the cell thickness is thinner, and lower as the uniaxial orientation regulating force that forces the cell to take an intermediate state between the bistable states is weaker.
Therefore, if the -axis alignment regulating force can be weakened to the minimum necessary alignment regulating force, the cell thickness can be increased accordingly.

In the rubbing method, a film of an organic polymer compound formed by a spin code method or the like has no orientation ability, so a uniaxial orientation regulating force is applied by rubbing the surface of the film. The uniaxial alignment regulating force in this case is a very strong alignment regulating force associated with van der Waals force and excluded volume effect. This is supported by the fact that the memory property is expressed at a relatively high voltage and the contrast at the time of memory is low.

In other words, since the uniaxial alignment regulating force in the rubbing direction is strong, a correspondingly large amount of energy (high voltage) is required to switch the molecules oriented in the rubbing direction on average, and the external field or removal When the voltage is turned off (voltage off), the liquid crystal molecules return to the stable average rubbing orientation,
Since the effective cone angle becomes smaller, contrast decreases and memory performance also deteriorates.

On the other hand, organic polymer films formed by the LB method have uniaxial orientation in which the main chains are oriented with respect to the direction in which the substrate is pulled up, so liquid crystal molecules can be aligned horizontally (homogeneously) without any alignment treatment. It can be oriented to In this case, the uniaxial alignment regulating force restrains the liquid crystal molecules in a very low energy state compared to the case of alignment treatment such as rubbing, and the liquid crystal molecules are stable even at low energy due to affinity. This is supported by the fact that memory performance is achieved at a lower voltage than before, complete memory performance is achieved, and perfect memory performance is achieved even with a cell thickness of 4 μm. C Example] Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 Various alignment films as shown in Table 1 were formed on the substrate.

The substrate used was one in which a transparent electrode was formed by electron beam evaporation or sputtering and then patterned.

In Table 1, the compounds shown as polyamide and polyimide are as follows.

° Bogemid polyamic acid [Product name Sunever RN-710%RN
-305 was used to prepare an alkylamine salt and convert it into LB.

Polyimide This polyamide is obtained by converting the above polyamide as described below.

The alignment film was formed as follows by the LB method.

The above polyamic acid was dissolved using a mixed solvent of N,N-dimethylacetamide-benzene (1:1), and 1 m
A solution of approximately m o IL/ft was prepared, and an alkylamine was added to the solution to prepare a solution of a polyamic acid alkylamine salt.

This solution was added dropwise to water at 25°C for development.

The water used was purified twice using an ion exchange resin.

Next, the surface pressure was increased to 25 dyne/cm when increasing and 10 or 1 when decreasing using a partition plate.
A monomolecular film or a cumulative film was formed on the substrate as shown in Table 1 by raising and lowering the substrate perpendicular to the water surface at a constant rate of 9 dyne/cm. The speed of the substrate in this case is 5-10 +
The speed was approximately ++m/min.

Thereafter, it was dried in vacuum and used as an alignment film for polyamide.

In the case of polyimide, the above-mentioned polyamide alignment film was immersed in an acid anhydride to obtain an alignment film.

In addition, a film of a high molecular compound such as a polyimide compound was formed on the same substrate as above by a spin cord method, and an alignment film was prepared by performing an alignment treatment by a rubbing method.

Using the above various substrates and various alumina spacers,
Laminate parallel or anti-parallel to the pulling direction or rubbing direction of the substrate,
Product name ZLI-348 as a strong-conductivity liquid crystal in the gap between substrates
8 (manufactured by E-MercK) was sealed, and the cells shown in Table 1 were prepared by slowly cooling from the isoI-ropic phase.

Note that a cell was also fabricated in which the alignment film formed by the LB method was applied to only one substrate (Cell 5.6).

The memory properties of these cells were evaluated.

Note that the contrast ratio is MCR(O
Ratio of MCR (OFF) at off time to N> MCR(
OFF) / MCR(ON).

Further, FIG. 1 shows the relationship between contrast ratio and cell thickness.

From the results shown in Table 1, it is clear that the cell of the present invention exhibits memory at a lower voltage than conventional cells, has perfect memory properties, and even exhibits perfect memory properties even with a cell thickness of 4 μm. I know that there is.

On the other hand, it can be seen that the alignment film produced by the rubbing method exhibits memory properties at a relatively high voltage, has low contrast during memory, and further deteriorates memory properties when the cell thickness is increased.

This is also supported by the results shown in FIG.

Furthermore, in the cell of the present invention, the applied pulse width is 100 μsec.
It has been confirmed that perfect memory properties can be achieved even with the rubbing method, and the applied pulse width at which good memory properties can be obtained can be reduced to 1/10 compared to the rubbing method. Therefore, since the number of scanning lines can be increased, a large-screen, high-definition liquid crystal display becomes possible.

〔Effect of the invention〕

The liquid crystal molecules of the present invention exhibit good memory and can provide perfect memory properties. This perfect memory property can be obtained even with a practical cell thickness of 4 μm or more. Furthermore, since a bias voltage during the non-selection period is not required, the drive waveform is simplified and the advantages of low voltage and low power consumption can be utilized. Furthermore, since the memory property is exhibited at a low voltage, a normal liquid crystal driving IC can be used even if the cell thickness is increased.

The cell thickness can be increased and cell thickness control becomes easy.

In addition, perfect memory properties can be obtained even with a short applied pulse width, so the number of scanning lines can be increased, and as a result, a large-screen, high-definition liquid crystal display becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between contrast ratio and cell thickness in a liquid crystal cell according to the present invention and a conventional liquid crystal cell.

Claims (2)

[Claims] (1) A liquid crystal element having electrodes on opposing surfaces of a pair of substrates disposed opposite to each other, liquid crystal sealed between the substrates, and an alignment film for aligning liquid crystal molecules on the opposing surface of at least one of the substrates. 2. A liquid crystal device according to claim 1, wherein the liquid crystal is a ferroelectric liquid crystal, and the alignment film is a monomolecular film or a cumulative film of an organic polymer compound formed by a Langmuir-Prodgett method. (2) Claim in which the organic polymer compound is a polyimide compound, a polyamide compound, or a polyamideimide compound (
1) The liquid crystal element according to item 1).