JP2877396B2 - Liquid crystal display - Google Patents

Description

The present invention relates to a liquid crystal display device using a ferroelectric liquid crystal.

(B) Conventional technology Among liquid crystals, chiral smectic C phase liquid crystal (hereinafter abbreviated as SmC ^* liquid crystal) has a helical structure and exhibits ferroelectricity.

When this SmC ^* liquid crystal is injected into a cell with a reduced gap, the helical structure of the SmC ^* liquid crystal is loosened under the influence of the interface, and a region where the liquid crystal molecules are tilted by a tilt angle θ with respect to the normal of the smectic layer to become stable. , The liquid crystal molecules move in the opposite direction -θ
The region that is only tilted and stabilized is mixed. By applying a voltage to the SmC ^* liquid crystal in this cell, the orientation of the liquid crystal molecules and their spontaneous polarization can be made uniform, and by switching the polarity of the applied voltage, the orientation of the liquid crystal molecules is maintained at a certain level. The switching drive for switching from the state described above to another state becomes possible. With this switching drive, the birefringent light changes in the SmC ^* liquid crystal in the cell, so that the transmitted light can be controlled by sandwiching the cell between two polarizers. Furthermore, even if the application of the voltage is stopped, the alignment of the liquid crystal molecules is maintained in the state before the stop of the application of the voltage by the alignment regulating force at the interface, so that a memory effect can be obtained.

Therefore, it has been attempted to construct a high-duty liquid crystal display device using a multiplex driving method by utilizing the memory effect of the SmC ^* liquid crystal.

This liquid crystal display device has two
A plurality of transparent electrodes are formed on the mutually facing surfaces of the two glass substrates in a striped arrangement in parallel with each other, and the transparent electrode of one glass substrate and the transparent electrode of the other glass substrate are The arrays are orthogonal to each other. An alignment film is further formed on the transparent electrode forming side surface of each glass substrate via an insulating film, and an SmC ^* liquid crystal layer is interposed between the two glass substrates.

(C) Problems to be Solved by the Invention In the liquid crystal display device as described above, the bias of the polarization charge due to the spontaneous polarization of the liquid crystal molecules generates an electric field (polarization electric field) inside the device, and the orientation angle of the molecules is + in the memory state.
There is a problem that a good memory effect (a memory effect in a bistable state) is lost in the state where θ and the state where −θ are satisfied.

That is, as shown in FIG. 2B, a polarization electric field generated by polarization charges of liquid crystal molecules ubiquitous in the memory state (when no voltage is applied) exists in the cell as shown in FIG. The liquid crystal molecules respond to the polarization electric field and change the orientation so that the energy inside the cell is minimized. As a result, it is considered that a bistable memory state cannot be obtained. In FIG. 2, reference numeral 6 denotes a C-director of liquid crystal molecules. Numeral 7 indicates the spontaneous polarization of the liquid crystal molecules. The tip of the arrow indicates a positive pole, and the opposite of the arrow indicates the negative pole. 8 and 9 represent the ubiquity of positive and negative polarization charges, respectively, and 10 represents the presence of a polarization electric field in the direction of the arrow.

An object of the present invention is to provide a liquid crystal display device having a bistable memory effect while preventing a decrease in memory properties due to a polarization electric field.

(D) Means for Solving the Problems According to the present invention, at least a pair of substrates provided with a transparent electrode and an alignment film are arranged to face each other, and an insulating film is provided between the electrode and the alignment film. In a liquid crystal display device comprising a ferroelectric liquid crystal interposed between the alignment films, the alignment film is made of a synthetic resin containing a conjugated cyano compound or a conjugated halogen compound as an electron acceptor. A liquid crystal display device is provided.

In the present invention, the alignment film is a synthetic resin containing a conjugated cyano compound or a conjugated halogen compound as an electron acceptor, and has uneven lines on the inner surfaces of a pair of substrates sandwiching the ferroelectric control liquid crystal. It is a synthetic resin configured to have root marks.

This alignment film is for aligning the liquid crystal and relaxing or neutralizing the polarization electric field generated inside the device due to the polarization charge bias due to the spontaneous polarization of the liquid crystal molecules.
In other words, the electron acceptor contained in the alignment film reacts with the charge (polarized charge) localized at the liquid crystal / alignment film interface due to spontaneous polarization aligned in one direction as shown in FIG. 2 (a).
By taking in and neutralizing the charge on one side, the electric field on one substrate side can be canceled. Also, although + charges remain at the liquid crystal / alignment film interface on the other substrate side,
Since an electric charge exists at the point at infinity, the polarization electric field generated due to the polarization electric charge existing in the liquid crystal layer is relaxed or neutralized, and the electric field substantially exists at the liquid crystal / alignment film interface. It has the effect of disappearing.

The ferroelectric liquid crystal exhibits a predetermined orientation with a high response speed to the application of a voltage, and transmits or blocks light for a display device. The molecules are chiral and the system is a racemic liquid crystal. A liquid crystal substance having a permanent dipole moment perpendicular to the long axis of the molecule but not in the body and exhibiting the Sc ^* phase can be used. For example, (S) -4'-n-octyloxy-biphenyl-4-carboxylic acid -1-trifluoromethyl-
Heptyl ester, (S) -4'-n-octyloxy-biphenyl-4-carboxylic acid-1-trifluoromethyl-3-phenyl- (trans) -2-propenyl ester, DOBAMBC (p-decyloxybenzylidene-p'-amino-2-methylbutylcinnamate), MORA-8 (S
-4- (6-methyl) octyl-resorcylidene-4 '
-Octylaniline), DOBA-1-MBC (p-decyloxybenzylidene-p'-amino-1-methylbutylcinnamate), CS-1014 (hereinafter Chisso), CS-1013, CS
-1017, CS-1020 or the like can be used alone or in combination with other substances.

As the substrate, a transparent insulating substrate having a transparent electrode formed on its surface is suitable. For example, a glass substrate having a transparent electrode of ITO formed thereon can be used.

The synthetic resin film is formed by coating a synthetic resin containing a conjugated cyano compound or a conjugated halogen compound as an electron acceptor on the substrate by, for example, vapor deposition, coating, and performing a rubbing treatment as necessary. It can be manufactured by forming uneven linear marks on the surface.

The conjugated cyano compound or the conjugated halogen compound as the electron acceptor is for giving a bistable memory effect to the ferroelectric liquid crystal or its composition, and the polarization is caused by spontaneous polarization of the ferroelectric liquid crystal molecule. A material capable of relaxing or neutralizing the polarization electric field generated by the bias of the charge inside the element can be used. This conjugated cyano compound is a compound having a cyano group and having a carbon double bond that can be conjugated to a triple bond of the cyano group. Among them, dichlorodicyanoparabenzoquinone (DDQ), tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCE) and tetrafluorotetracyanoquinodimethane (TFTCNQ)
Is particularly preferable because the liquid crystal having a spontaneous polarization of 20 (nc / cm ² ) or less acts to exhibit a remarkably bistable memory effect. As the conjugated halogen compound, for example, dichlorodifluoroquinone, dichloroanthraquinone, or the like can be used. The content of the conjugated cyano compound or the conjugated halogen compound as the electron acceptor is usually 100 to 10,000 ppm suitable for the synthetic resin (composition), and among these, 200 to 1000 ppm is more preferable. Preferred because it presents memory.

The synthetic resin can be blended using, for example, a polyamide resin, a polyimide resin, or the like.

Specifically, the liquid crystal display device of the present invention comprises a transparent resin having a transparent electrode on its surface, and a synthetic resin containing a conjugated cyano compound or a conjugated halogen compound as an electron acceptor coated thereon. A film is formed, and if necessary, a rubbing treatment is performed on the surface of the film to form an alignment film having uneven linear marks, and a pair of substrates having the alignment film is formed so that the alignment films face each other. , Usually 1-4
The ferroelectric liquid crystal can be prepared by injecting a ferroelectric liquid crystal between the substrates and selectively driving the ferroelectric liquid crystal layer by selectively applying a voltage to the transparent electrode. Can be displayed and used.

(E) Action A conjugated cyano compound or a conjugated halogen compound as an electron acceptor contained in a synthetic resin and constituting an alignment film relaxes a polarization electric field created inside a device due to polarization of polarization charge caused by spontaneous polarization of liquid crystal molecules. Or neutralize.

(F) Example Hereinafter, the present invention will be described more specifically based on examples shown in the drawings.

Example 1 As shown in FIG. 1, transparent electrodes 2a and 2b were formed on glass substrates 1a and 1b using ITO, and O2
An insulating film 3 of SiO ₂ is formed by applying and baking CD TYPE-II using a spinner. Next, a coating solution in which 0.0001 wt% of dichlorocyano parabenzoquinone (DDQ) was mixed in a 1% meta-cresol solution of nylon 6 (manufactured by Toray Industries, Inc.) was applied thereon by a spinner, and baked. Is added to form an alignment film. The two substrates thus formed were subjected to a rubbing treatment to form a cell having a cell thickness of 2.0 μm, and a ferroelectric liquid crystal (CS-1014, manufactured by Chisso Corporation) was injected to form a device. .

It was observed that a liquid crystal display device manufactured by sandwiching this element between two polarizers exhibited good bistable memory at the picture element portion of the matrix electrode.

Example 2 In Example 1, instead of changing the amount of DDQ added to 100 ppm, the conditions were changed to six conditions of 200, 300, 500, 1000, 5000 and 10000 ppm. Six types of liquid crystal display devices corresponding to the conditions were produced.

As a result, all exhibited good bistable memory in the picture element portion of the matrix electrode. Further, among these, the liquid crystal display device constituted by the alignment film formed with the addition amount of DDQ being 200 ppm to 500 ppm exhibited better bistability memory.

Example 3 In Example 1, instead of using DDQ, tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TC
E), tetrafluorotetracyanoquinodimethane (TFTCN)
Q), the conditions were changed to 5 using dichlorodifluoroquinone and dichloroanthraquinone.
In the same manner as in the above, five types of liquid crystal display devices corresponding to the respective conditions were produced.

Each of these liquid crystal display devices exhibited good bistability memory.

Example 4 Instead of using CS-1014 (manufactured by Chisso, spontaneous polarization 5.4) as a liquid crystal in Example 1, CS-1013 (manufactured by Chisso, spontaneous polarization 16 nC / cm ² ) and CS-1017 (manufactured by Chisso) ,
The two conditions of spontaneous polarization 7.1 nC / cm ² ) were changed, and the other conditions were the same as in Example 1 to produce two types of liquid crystal display devices corresponding to the respective conditions.

Each of these liquid crystal display devices exhibited good bistability memory.

(G) Effects of the Invention According to the present invention, it is possible to provide a liquid crystal display device having a bistable memory effect without a decrease in memory properties due to a polarization electric field.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a liquid crystal display device of the present invention, and FIG. 2 is an explanatory view showing instability of a memory caused by a polarization electric field of a ferroelectric liquid crystal element. 1a, 1b: glass substrate, 2a, 2b: transparent electrode, 3: insulating film, 4a, 4b: alignment film, 5: ferroelectric liquid crystal layer, 6:
Director of liquid crystal molecules, 7: spontaneous polarization, 8: positive polarization charge, 9: negative polarization charge, 10: polarization electric field.

Claims (1)

(57) [Claims] 1. A pair of substrates provided with at least a transparent electrode and an alignment film are disposed so as to face each other, an insulating film is provided between the electrode and the alignment film, and a ferroelectric is provided between the alignment films. In a liquid crystal display device configured with an intervening liquid crystal,
A liquid crystal display device, wherein the alignment film is made of a synthetic resin containing a conjugated cyano compound or a conjugated halogen compound as an electron acceptor.