Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
1999-10-06
2001-04-17
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S299640, C252S299650, C252S299660, C252S299670
Reexamination Certificate
active
06217954
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel phenyl triester compound and an anti-ferroelectric liquid crystal composition containing it and controlled layer rotation.
2. Prior Art
A liquid crystal display device has been so far used mainly for various small-sized display devices owing to its operability at low voltage, low power consumption and display performance with a thin screen. However, with recent increases in the application and use of liquid crystal display devices to/in the fields of information and office automation-related machines and equipment and the field of television sets, there are rapidly increasing demands for large-sized and high-performance liquid crystal display devices having larger display capacity and higher display quality than those of existing CRT display devices.
However, so long as a nematic liquid crystal available at present is used in a display device, even an active matrix liquid crystal display device (TFT) used in a liquid crystal television set finds it not easy to increase its size and decrease its production cost due to its complicated production process and a low yield. In a simple matrix STN liquid crystal display device (STN), the driving of a large-capacity display device is not necessarily easy and its response time is limited as well, so that video frame rate display is difficult to obtain. At present, therefore, it cannot at all be said that the nematic liquid crystal display device can satisfy demands toward the above high-performance large-sized liquid crystal display device.
As for display quality, further, both TFT and STN display devices using a nematic liquid crystal have a serious problem that the viewing angle is narrow. Although various improvement measures have been proposed, it is difficult to find out a drastic improvement measure so long as a nematic liquid crystal is used.
Under the circumstances, a liquid crystal display device for which a ferroelectric liquid crystal is used is attracting attention as a liquid crystal display device with a fast response speed and a wide viewing angel. A surface-stabilized ferroelectric liquid crystal (SSFLC) device disclosed by Clark and Lagerwall comes to notice in that it has a fast response speed and a wide viewing angle which have not been achieved in the past. Its switching characteristics have been studied in detail, and a number of ferroelectric liquid crystal compounds have been synthesized for optimizing various physical property constants.
When a ferroelectric liquid crystal is used as a liquid crystal display device, however, a special devising with regard to the alignment of the liquid crystal is required for achieving a contrast free of a problem in practical use, since it has an insufficient threshold characteristic and has a layer structure formed of a chevron structure. Further, since the alignment of its liquid crystal molecules is extremely difficult to control, it is not easy to attain the bistability, which is one of the most important characteristics of SSFLC, with good reproducibility. Further, there is another problem that when the alignment of the liquid crystal molecules is damaged by a mechanical shock, it is difficult to restore its alignment. It is therefore essentially required to overcome these problems in order to put the display device to practical use.
PROBLEMS TO BE SOLVED BY THE INVENTION
As described above, efforts including efforts to develop novel modes have been made in various ways for increasing the size of a liquid crystal display device and achieving a liquid crystal display with finer definition. Under the circumstances, development of display devices having switching mechanisms completely different from the prior devices is also under way simultaneously.
Switching among tristable states of a liquid crystal compound having an anti-ferroelectric phase (to be referred to as “anti-ferroelectric liquid crystal” hereinafter) is one of these new switching mechanisms (Japanese Journal of Applied Physics, Vol. 27, pp. L729, 1988).
The anti-ferroelectric liquid crystal device has three stable states, i.e., two uniform states (Ur, Ul) observed in a ferroelectric liquid crystal device and a third state. Chandani et al. report that the above third state is an anti-ferroelectric phase (Japanese Journal of Applied Physics, vol. 28, pp. L1261, 1989; ditto, pp. L1265). The above switching among three stable states is the first characteristic of an anti-ferroelectric liquid crystal device.
The second characteristic of the anti-ferroelectric liquid crystal device is that a sharp threshold value exists in respect to an applied voltage.
Further, the anti-ferroelectric liquid crystal device has a memory effect, and this is the third characteristic of the anti-ferroelectric liquid crystal device.
By utilizing the above excellent characteristic features, a liquid crystal display device having a fast response speed and a high contrast can be achieved.
The anti-ferroelectric liquid crystal device has another important characteristic that its layer structure easily performs switching when an electric field is applied (Japanese Journal of Applied Physics, Vol. 28, pp. L119, 1989; ditto, vol. 29, pp. L111, 1990).
On the basis of the above characteristics, there can be produced a liquid crystal display device having very few defect and the capability to self-restoring a molecule alignment, and a liquid crystal display device having an excellent contrast can be achieved.
However, when an anti-ferroelectric liquid crystal device is left in a driven state for a long period of time, there is sometimes observed a phenomenon that it shows a decrease in a display contrast.
One reason therefor is presumably that a smectic liquid crystal layer undergoes a layer rotation so that an extinction position shifts from an initial position (Japanese Journal of Phys. Vol. 33, pp. L1620, 1994).
The above layer rotation is a very important problem from the viewpoint of reliability in driving.
The expedient that is adopted against the layer rotation is presumably to increase the thickness of an alignment film to make it as large as possible, so that the alignment film is intensified in controlling force. However, the voltage which is generally effectively applied to a liquid crystal is expressed by the following equation.
Veff=Vex−P(d/&egr;)
wherein Veff is a voltage actually applied to a liquid crystal, Vex is a driving voltage, P is a polarization of the liquid crystal, d is a thickness of an alignment film, and E is a dielectric constant of the alignment film.
As is clear from the above equation, the voltage actually applied to a liquid crystal decreases in proportion to a thickness of an alignment film, so that the voltage applied to the liquid crystal comes to be inadequate as the thickness of the alignment film increases, which results in a failure in obtaining a good display quality. There is therefore a limit to increasing the thickness of the alignment film for controlling a layer rotation.
Generally, further, the degree of the layer rotation increases with an increase in temperature. An attempt is made to maintain a panel temperature at a constant temperature for controlling the layer rotation to the extent that the display quality is not downgraded (Japanese Laid-open Patent Publication No. JP-A-9-297311). However, the above attempt requires addition of a temperature sensor, a temperature controller and a cooling system to a panel, and it undesirably results in an increase in the cost of the panel as a whole. It is therefore the most advantageous to improve liquid crystal materials for solution.
Means to Solve the Problems
The present inventors have therefore made diligent studies for developing a compound which functions to control the layer rotation when contained into an anti-ferroelectric liquid crystal compound. As a result, the present invention has been arrived at.
According to the present invention, therefore, there is provided a novel phenyl triester compound of the formula (1),
wherein R
1
Johno Masahiro
Matsumoto Takahiro
Motoyama Yuki
Yui Tomoyuki
Mitsubishi Gas Chemical Co Inc
Wu Shean C.
LandOfFree
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