JPH11352525A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid crystal display device which is improved in visual field angle characteristic and does not induce inversion of a contrast ratio in any direction by providing a device with a nematic discotic material held between a pair of transparent substrates. SOLUTION: A pair of transparent substrates have coatings of an electrically conductive transparent material, in which the respective substrates have on one of their surfaces and which act as electrodes and the nematic discotic material which is held between the coated surfaces of the substrates. The substrates are made of glass, plastic or another transparent materials. Electrically conductive materials, such as indium tin oxide and tin oxide, are usable for coating the substrates. The nematic discotic material is preferably hexa-kis [(4-nonylphenyl)ethynyl]benzene of formula I and undecenylbenta-kis[(4- bentiphenyl)ethynyl]phenylether of formula II, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION This invention relates to photoconductive devices, ferroelectrics, light emitting diodes, (photovoltaic) solar cells, optical data storage devices, and many others such as hybrid computer chips for molecular electronics. The present invention relates to an improved liquid crystal display (LCD) device used in the electrical device.

[0002]

2. Description of the Related Art The liquid crystal device industry is currently a billion dollar industry. In this industry, products range from simple wristwatch displays to flat panel color TV screens.
The device described in the present invention has advantages over conventional LCD devices in that it has a wide symmetric viewing angle, no contrast ratio inversion in any direction, and simplifies the manufacturing process. Therefore, the device of the present invention is very useful for various applications in the liquid crystal industry.

When molecular crystals are heated to their melting point,
It usually changes to the liquid phase. Not only the periodic structure of the lattice but also the directional arrangement of the molecules is destroyed. However, if the constituent molecules have a pronounced anisotropy in the form of a rod or disc,
Melting of the lattice occurs before the directional alignment disappears. At that time,
An intermediate phase consisting of molecules is obtained, which molecules are more or less parallel to each other, but at the same time exhibit some fluidity. The molecules can slide with each other while maintaining their parallelism. Thus, the fluid is anisotropic and turbid, but exhibits optical birefringence and dielectric anisotropy like crystals. At higher temperatures, directional melting occurs and the anisotropic fluid changes to a normal isotropic transparent liquid. Such an intermediate phase that occurs as a result of heating or cooling is called a thermotropic liquid crystal.

[0004] Thermotropic liquid crystals can be broadly classified into two classes: (i) rod-shaped molecules known since the end of the 19th century and now accounting for the majority of known liquid crystals ["calamitic" (Referred to as "discotic" liquid crystals), and (ii) recently developed liquid crystals composed of discotic molecules (referred to as "discotic" liquid crystals).

[0005] Discotic liquid crystals, recently discovered by us around 1977, are an example of a new class of thermotropic liquid crystals. In this connection, S.M. Chandrasekhar, B.C. K. Sadasiba
(Sadashiva) and K.S. A. Reference may be made to the book by Suresh, Pranana, 9, 471-480 (1977). In this case, the disks are stacked on each other to form a cylinder,
Different cylinders make up a two-dimensional grid. The basic cylindrical structure is shown in FIG. 1 of the drawings attached hereto.
A number of variations of the basic structure described above have been identified. Certain discotic compounds are similarly nematic (N
_D ) Indicates phase. It is a fluid phase consisting of a directional array of disks, but a translational array over long distances.
rder) and somewhat resembles a stack of coins as shown in FIG. 2 of the drawings attached hereto. But,
Unlike normal nematic calamitics, this nematic discotic is optically negative. The preferred orientation of the axis of the disc is referred to as the director, as shown in FIG. 2 of the drawings.

The advent of discotic liquid crystals has caused a torrent of activity in this field, and well over a thousand discotic compounds have been reported to date. Some discotic compounds are exemplified below: hexaalkonoyloxybenzene, hexaalkoxytriphenylene,
Bis (4-n-decylbenzoyl) methanato copper (II),
Hexa-n-alkanoates and octa-substituted phthalocyanines of truxene.

[0007] Potential applications of such materials include quasi-one-dimensional conductors, photoconductive devices, ferroelectrics, light emitting diodes,
(Photovoltaic) There are such things as solar cells, optical data storage, hybrid computer chips for molecular electronics.

[0008] Display devices based on calamitic liquid crystals are well known. A widely used device is twist
ed) A nematic (TN) display device. In a twisted nematic display, two transparent glass plates are
Their inner surfaces are coated with a thin layer of a transparent electrically conductive material such as tin oxide, and further coated with a thin layer of polyimide. In order to achieve macroscopic alignment of the liquid crystal director, a method of rubbing the substrate in one direction with cotton, rayon, or nylon fabric is widely used. Two glass plates are about 6-10μ
m with a spacer to form a cell,
The rubbing directions of the polyimide layers are perpendicular to each other. The gaps between the cell substrates are filled with calamitic and nematic liquid crystals. The boundary conditions cause the nematic liquid crystal to be oriented parallel to the rubbing direction of each glass plate, so that the director has 90 ° over the distance of the nematic layer.
Torsion. A polarizing plate is attached to the outer surface of the glass plate, and the vibration axis (polarization axis) of each polarizing plate is parallel to the rubbing direction of the glass plate to which it is attached. Unpolarized light is converted to linearly polarized light by a polarizer fixed on the entrance side of the cell and exits with a polarization axis rotated 90 °. The emitted light is transmitted by the second polarizer. Therefore, in this structure, that is, a structure of a so-called normal white system, the display looks bright in a state where it is not activated. A white mode with a wide viewing angle can be achieved by setting the polarizers so that their polarization axes are perpendicular to the rubbing direction. When an electric field is applied perpendicular to the layer, the liquid crystal molecules (those having positive dielectric anisotropy, Δε> 0) are oriented, and their major axes are perpendicular to the layer. In this activated state, the polarization axis of the light is not rotated by the liquid crystal medium and the display looks black. The orientation of one polarizer parallel to the rubbing direction and the second polarizer perpendicular to the rubbing direction results in a dark (black) appearance in the deactivated state and a bright appearance in the activated state. This so-called black system is used for dashboards of automobiles.

A major disadvantage of devices of the above type is that, when viewed obliquely, the viewing angle characteristics are poor, resulting in a loss of contrast and even at certain azimuthal angles the contrast is reversed. Idiomatic T
Y shows a typical polar plot of the contrast ratio (CR) for an N.N device. Toko,
T. Sugiyama, K .; Katoh, Y .; Imura and S.M. J. by Kobayashi
See FIG. 3 of the drawings taken from Appl. Phys., 74, 2071-75 (1993).

[0010] Another device that is widely used is the super twisted nematic (STN) device. The structure of such a device is similar to the structure of a TN device as described above. However, the torsion angle of the director is not 90 °, but 180 ° ~
270 °. Large torsion angles are achieved by incorporating a suitable amount of a chiral compound, such as a dopant, therein prior to filling the cell with the nematic material. However, this device is of no use in improving the viewing angle characteristics.

[0011] For both TN and STN devices, there is a large difference in pixel capacitance between the ON and OFF states for multiplexed displays, which causes crosstalk problems between pixels. It has a shortcoming.

[0012] ON state and OFF state of any display device
The viewing angle profile, symmetry and angle dependence of the intensity contrast ratio with the state are important conditions for determining the performance quality of the device. Several attempts have been made to improve the performance of such devices. These attempts mainly split each pixel into sub-pixels,
It is directed to improving viewing angle characteristics using various techniques, such as adding retardation films, applying an electric field parallel to the substrate surface, and the like. The salient point of all these attempts is that the liquid crystal material used is of the nematic-calamitic type. No attempt has been made to date to use nematic discotic materials to make displays.

For example, with respect to modifications based on applying an electric field parallel to the plane of the substrate, see Baur, R.A. Kiefer, H.E. Klausmann, and F.K. Windscheid, Liquid Crystal
Today, 5, 13-14 (1995); Oh-e, M.E. Yoneya and K.M. Kondo, J. Appl. Phy
s., 82, 528-535 (1997); H. Lee, H.C.
Y. Kim, I.C. C. Park, B. G. FIG. Low
(Rho), J. et al. S. Park, H.E. S. Park
k), and C.I. H. Lee, Appl. Phys. Lett., 71,
2851-2853, (1997).
In this way, the author has improved the viewing angle characteristics of the liquid crystal device by using in-plane electrodes on only one of the substrates to avoid asymmetry of the director profile.

H. Mori, Jpn. J. Appl. Phys., 3
6, 1068-1072 (1997); Mori, Yoj Ito
i Itoh), Yosuke Nishiura, Taku Nakamura, Yuk Shinagawa
io Shinagawa), Jpn. J. Appl. Phys., 36, 143-147
(1997); introduces an optical compensator with negative birefringence to reduce the amount of light leakage in the dark.

K. H. Young, Jpn. J. Appl. Ph
ys., 31, L1603-1605 (1992); Chen,
P. J. Boss, D. R. Bryant,
D. L. Johnson, S.M. H. Jamal
al), J. et al. R. Kelly, SID 95 Digest, 865-8
In the 68 (1995) publication, the authors use multiple domains of liquid crystals, in which case the director orientation is different in each of those domains (pixels).

The device manufactured as described above does not sufficiently improve the viewing angle characteristics of the device. Furthermore, they also include additional steps in the manufacturing method.

Y. Toko, T. Sugiyam
a), K. Katoh, Y .; Limura and S.M. Kobayashi, SID 93 Digest, 622-625
(1993); J. Appl. Phys., 74, 2071-75 (1993) describes a simpler method of making LCDs with improved viewing angle characteristics. In this method, a polymer film is coated on a transparent conductive substrate, but is not rubbed. The unrubbed polymer film is optically and structurally isotropic, and the director is parallel to the surface of the substrate, but is randomly oriented in the plane of the substrate in the OFF state. In the ON state, the director is perpendicular to the plane of the substrate. This device, a so-called amorphous TN device, provides improved viewing angle characteristics without contrast inversion. See FIG. 4 of the drawings. This is taken from the Toco et al. Publication mentioned above. Note that the liquid crystal material used in this device is again of the nematic-calamitic type and not of the nematic-discotic type.

Recognizing the importance of improving the viewing angle characteristics of a liquid crystal device, we have conducted intensive research in this direction. Our long research has led to the discovery that if nematic discotic materials are used in liquid crystal devices, the viewing angle characteristics of such devices can be further improved.

[0019]

SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide a liquid crystal device using a nematic discotic material and having improved viewing angle characteristics.

Another object of the present invention is to provide a liquid crystal device that does not cause the contrast ratio to be inverted in any direction.

Still another object of the present invention is to provide an ON state and an OF state.
Reducing the difference in pixel capacitance between the F state and
It is an object of the present invention to provide a liquid crystal device having substantially reduced crosstalk in the case of a multiplex display device.

Yet another object of the present invention is to provide a liquid crystal device using a simple manufacturing method.

[0023]

In order to achieve the above object, the present invention provides, for the first time, a liquid crystal device using a nematic discotic substance. That is, the present invention provides: (a) a pair of transparent substrates, (b) a coating of an electrically conductive (conductive) transparent material, each substrate having on one of its surfaces, acting as an electrode, (c) Nematic discotic material (nemat) sandwiched between coated surfaces
a liquid crystal display comprising a pair of crossed polarizers, wherein the cells are formed therebetween, and (d) the cells are disposed therebetween.

[0024]

DETAILED DESCRIPTION OF THE INVENTION The present invention differs from any of the conventional LCDs in that a nematic discotic material is used and no calamitic material is used. To date, no nematic discotic materials have been used to manufacture liquid crystal displays.
The substance used has a negative dielectric anisotropy (Δε <0).

The substrate used in this device is made of glass, plastic, or other such transparent material. An electrically conductive material such as indium tin oxide, tin oxide, or the like can be used to coat these substrates. The resulting substrate is preferably coated with an additional layer of polymer to ensure uniform contact between the nematic discotic material and the substrate. If a polymer is used, it may be selected from a class of polymers such as polyimides, polyamides, polyvinyl alcohol, or similar types of polymers. The gap between the cell substrates is defined by spacers, which may be selected from polyethylene terephthalate film, polyimide film, glass microspheres and the like. The use of a polarizer can be avoided by incorporating an appropriate amount of a discotic polychromatic dye known as a dopant into the nematic discotic material before filling into the cell. For this purpose, dyes such as derivatives such as anthraquinone, phthalocyanine and porphyrin can be used.

The nematic discotic material is sandwiched between the substrates. The discotic molecules adhere flatly to the coated surface of the substrate. As a result, the nematic discotic material is uniformly oriented and the director is perpendicular to the surface (ie, along the z-direction in FIG. 5 of the drawings). When an electric field is applied along the z-direction, the director in the material rearranges parallel to the surface of the substrate and the director becomes xy
Orient randomly in the plane (FIG. 6 of the drawing). Thus, between the crossed polarizers, when the electric field is switched on,
A change from dark to light occurs.

This device can also be used in a reflection mode. In such an application, an optical reflector may be incorporated into the lower surface of the display.

The nematic discotic substance used in the apparatus of the present invention includes hexakis [(4-nonylphenyl) ethynyl] benzene of the formula shown in FIG. 7 of the drawings, and undecenylpentane of the formula shown in FIG. 8 of the drawings. Kis [(4-pentylphenyl) ethynyl] phenyl ether, and the α, ω-bis [penta (4-pentylphenylethynyl) phenoxy] phenoxy] alkane of the formula shown in FIG. 9 of the drawings, and FIG. ) And (b) can be selected from substances having negative dielectric anisotropy, such as triphenylene derivatives of the formulas shown in (b).

The compound of the formula shown in FIG. 7 exhibits the following series of transitions [B. Kohne and K.K. Praehu (Pra
efcke), Chimia, 41, 196-198 (1987); Hepke
pke), A. Ranft, and B. Sabchas
aschus), Mol. Cryst. Liq. Cryst. Lett., 8, 17-25
(1991)].

[0030]

Embedded image

The compound of the formula shown in FIG. 8 exhibits the following series of transitions [K. Praefcke, B.A. Kohne
ne); Gundogan, D.C. Singer (S
inger); Demus, S.M. Diele,
G. FIG. Pelzl, and U.S.A. Bakowsk
y), Mol. Cryst. Liq. Cryst., 198, 393-405 (1991)
)].

[0032]

Embedded image

The compounds of the formula shown in FIG. 9 exhibit the following series of transitions [K. Praevke, B. Corne, B.S. Gundogan, D. Singer, D.S. Demus, S.M. Diele,
G. FIG. Perzul, and U.S.A. Bakowski, Mol. Cryst. Li
q. Cryst., 198, 393-405 (1991)].

[0034]

Embedded image

The compounds of the formula shown in FIG. 10 exhibit the following series of transitions [T. J. Phillips, J.M.
C. Jones, and D.C. C. McDonnell (Mc
Donnell), Liquid Crystals. 15, 203-215 (1993)].

[0036]

Embedded image

The device of the present invention can be manufactured according to the following details. Select an appropriate transparent substrate in the visible region of the spectrum. A coating of a transparent electrically conductive material is applied on these substrates. If necessary, an additional coating of polymer may be applied to promote uniform deposition of the nematic discotic material on the substrate. A spacer material is used on the non-electroactive regions of the substrate to fix the spacing between the substrates. The gap between the two substrates is filled with the required amount of nematic discotic material to form a cell. This is done by heating to a temperature above the nematic isotropic point during the filling process and then cooling it to transform the material into a nematic phase. The nematic discotic then spontaneously aligns with the disk-like molecules attached flat to the surface, ie, as if the director were perpendicular to the surface (FIG. 5). Since an ND material has a negative dielectric anisotropy, when a sufficiently strong electric field larger than a threshold value is applied, the director is arranged parallel to the surface of the substrate, and is randomly arranged in the xy plane. (FIG. 6). Thus, between crossed polarizers, switching the electric field ON causes a transition from dark to bright state. Since the molecules are fixed in the boundary layer, the substance returns to the original form in the OFF state.

In one embodiment, an optical reflector is placed on the bottom of the device and used in a reflective manner.

Using hexakis [(4-nonylphenyl) ethynyl] benzene (negative dielectric anisotropy Δε = −0.18), a liquid crystal display device was manufactured as described above.
The cell gap measured by the interference system was 2.6 μm.
10Vrms 1kHz with repetition rate 0.1s ^-1 and duration 5 seconds
A sine wave pulse voltage of z was applied. When the device is switched on by applying an electric field, the time required for the transmitted light intensity to rise from 10% of the maximum intensity to 90% is ~
100 ms, and the time it takes to rise from 10% to 80% of the maximum intensity is ５０50 ms. A typical electro-optical response curve obtained using the above apparatus is shown in FIG.
It is shown in FIG.

A pole plot of the intensity contrast ratio in the ON / OFF state is given in FIG. This number is
The device of the present invention shows a good contrast ratio, and the contour of the same contrast ratio becomes almost concentric, indicating that no contrast inversion occurs.

[0041]

Advantages of the Invention The present invention uses a nematic discotic material in the manufacture of a liquid crystal display device for the first time. 2. The device of the present invention overcomes the disadvantages of conventional TN and STN devices using nematic calamitic materials. 3. Viewing angle chara of the device of the present invention (viewing angle chara
The cteristic is broad and symmetric, thereby improving the performance of the device. 4. ON and OF for nematic discotic
The difference in pixel capacitance during the F state is smaller than that obtained with conventional TN and STN devices using calamitic liquid crystals, thus reducing crosstalk problems in multiplexed displays. 5. The manufacture of the device of the present invention is simplified because no steps involving polymer rubbing are performed. 6. The need to coat a substrate with a polymer can be eliminated by using a substrate having an optically flat surface, thereby further simplifying the device manufacturing process. 7. The incorporation of a discotic multicolor dye in a nematic discotic material can also avoid the use of polarizers, thereby making the device economical to manufacture.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating a basic columnar structure of a discotic liquid crystal.

FIG. 2 is a perspective view illustrating a director in the axial direction of a disk of a fluid-phase nematic discotic liquid crystal.

FIG. 3 shows a contrast ratio (C) for a conventional TN device.
FIG. 2 is a diagram showing a typical polarplot of R).

FIG. FIG. 4 is a polar plot showing improved viewing angle characteristics of a nematic calamitic TN device by Toko et al.

FIG. 5 is a diagram illustrating a state in which a director of a nematic discotic substance is perpendicular to the substrate surface (z direction) between substrates.

FIG. 6 shows the nematic
FIG. 3 is a diagram illustrating a state where directors of discotic materials are randomly oriented parallel to a substrate surface.

FIG. 7 is a diagram showing a structural formula of an example of a nematic discotic substance used in the present invention.

FIG. 8 is a diagram showing a structural formula of another example of a nematic discotic substance used in the present invention.

FIG. 9 is a view showing a structural formula of still another example of a nematic discotic substance used in the present invention.

FIG. 10 is a view showing a structural formula of still another example of a nematic discotic substance used in the present invention.

FIG. 11 is a diagram showing an electro-optical response curve of an example of the liquid crystal display device according to the present invention.

FIG. 12 shows ON / O of an example of a liquid crystal display device according to the present invention.
FIG. 7 is a diagram illustrating a pole plot of a contrast ratio in an FF state.

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[Procedure amendment]

[Submission date] December 29, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

[Correction contents]

[0001]

FIELD OF THE INVENTION The present invention relates to improved liquid crystal display (LCD) devices used in many electrical devices.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Subarao Krishna Prasad Bangalore-560 013, Karnataka, India; Oh. Box 1329 Center for Liquid Crystal Research (72) Inventor Gesa Gopinasun Nail Karnataka, India Bangalore-560 013, Jaraharuri, P.K. Oh. Box 1329 Center for Liquid Crystal Research (72) Inventor Doddane Mane Sleini Basamurshii Shankar Lao Karnataka, India Bangalore-560 013, Jaraharuri, P.K. Oh. Box 1329 Center for Liquid Crystal Research (72) Inventor Sundeep Kumar Bangalore-560 013, Karnataka, India; Jaraharuri; Oh. Box 1329 Center for Liquid Crystal Research (72) Inventor Mayandi Sebal Manikkum Bangalore-560 013, Karnataka, India; Oh. Box 1329 Center for Liquid Crystal Research

Claims (10)

[Claims] 1. A pair of transparent substrates, (b) a coating of a transparent electrically conductive material acting as an electrode, each substrate having on one of its surfaces, (c) between the coated surfaces of said substrates A liquid crystal display comprising a pair of crossed polarizers having a nematic discotic material sandwiched between the cells, forming a cell therebetween, and (d) the cell disposed therebetween. . 2. The apparatus according to claim 1, wherein the substrate is made of a material such as glass, plastic, or other such transparent material. 3. As an electrically conductive material for coating a substrate,
The device according to claim 1, wherein a material such as indium tin oxide or tin oxide is used. 4. The apparatus of claim 1 wherein the resulting substrate is further coated with a layer of a polymer such that contact between the substrate and the material is uniform. 5. The apparatus according to claim 4, wherein the polymer is selected from the group such as polyimide, polyamide, polyvinyl alcohol, or a similar type of polymer. 6. The substrate is spaced apart by using a spacer such as a polyethylene terephthalate film, a polyimide film, or a glass microsphere,
The device according to claim 1. 7. The device according to claim 1, wherein the device uses a nematic discotic material having a negative dielectric anisotropy, such as a compound of the formula shown in FIG. 7, FIG. 8, or FIG. 8. The nematic discotic substance used is hexakis [(4-nonylphenyl) ethynyl] benzene of the formula shown in FIG. 7 of the drawing, and undecenyl pentakis of the formula shown in FIG. 8 of the drawing. (4-pentylphenyl)
Ethynyl] phenyl ether, α, ω-bis [penta (4-pentylphenylethynyl) phenoxy] phenoxy] alkane of the formula shown in FIG. 9 of the drawings, and FIGS. 10A and 10B of the drawings. The device according to claim 1, wherein the device is selected from a material having a negative dielectric anisotropy, such as a triphenylene derivative of the formula: 9. The device of claim 1, wherein the optical reflector is located on a lower surface of the device and is used in a reflective manner. 10. A discotic multicolor dye such as a derivative of anthraquinone, phthalocyanine or porphyrin,
2. The device of claim 1, wherein the device is disposed in a nematic discotic material prior to loading it into a cell.