Compositions – Liquid crystal compositions – Containing nonsteryl liquid crystalline compound of...
Reexamination Certificate
1999-09-28
2001-03-06
Kelly, C. H. (Department: 1756)
Compositions
Liquid crystal compositions
Containing nonsteryl liquid crystalline compound of...
C252S299650, C428S001100, C349S143000, C560S077000, C560S065000
Reexamination Certificate
active
06197216
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel ferrielectric liquid crystal compound suitable for use in an active matrix-type liquid crystal display device in which a liquid crystal is driven for each pixel independently, and to its use.
2. Prior Art of the Invention
A liquid crystal display device (LCD) has been being widely used as a flat panel display as a substitute for a conventional Braun tube (CRT) display, mainly in portable machines and equipment. Along with the recent expansion of the functions of personal computers and word processors and with the recent increase in the capacity of data processing, LCD is also required to have higher functions, that is, to have functions such as a large display capacity, a full-color display, a wide viewing angle, a high-speed response and a high contrast.
As a liquid crystal display method (liquid crystal driving method) to comply with such requirements, there has been proposed and, in some areas, is practically used an active matrix (AM) display device which works by a method in which thin film transistors (TFT) or diodes (MIM) are formed such that one transistor or diode corresponds to one pixel on a display screen and a liquid crystal is driven for one pixel independently of another.
Although the above display method has problems that it is difficult to decrease a cost due to a low production yield and that it is difficult to form a large-sized display screen, the above display method is about to surpass an STN display method which has been so far a mainstream and to overtake CRT due to its high display quality.
Problems to be Solved by the Invention
However, the above AM display device has the following problems due to the use of a TN (twisted nematic) liquid crystal as a liquid crystal material.
(1) A TN liquid crystal is a nematic liquid crystal, and the response speed is generally low (several tens ms), so that no good image quality can be obtained in the display of video rate.
(2) A twisted state (twist alignment) of liquid crystal molecules is used for displaying, and the viewing angle is therefore narrow. In displaying with a gray scale in particular, the viewing angle becomes sharply narrowed. That is, the contrast ratio, the color or the like changes depending upon viewing angles to a display screen.
For overcoming the above problems, there have been, in recent years, proposed AM panels which use a ferroelectric liquid crystal or an anti-ferroelectric liquid crystal in place of the TN liquid crystal (Japanese Laid-open Patent Publications Nos. JP-A-5-249502, JP-A-5-150257 and JP-A-6-95080). At present, however, the following problems remain to solve for the practical use of these liquid crystals.
(3) A ferroelectric liquid crystal has spontaneous polarization. An image sticking is liable to occur due to constant presence of the spontaneous polarization, and the driving is hence made difficult. In displaying with a ferroelectric liquid crystal, it is very difficult to perform a gray-scale display since only a binary display of black and white is possible in principle.
For the gray-scale display, a special devising is required (for example, use of a ferroelectric liquid crystal device using monostability; Keiichi NITO et al., SID '94, Preprint, p. 48), and it is required to develop a high technique for practical use.
(4) An anti-ferroelectric liquid crystal is free from the image sticking problem described in the above (3) since it has no spontaneous polarization.
In the AM driving, however, there is needed a liquid crystal material which can be at least driven at 10 V or lower. However, the anti-ferroelectric liquid crystal generally shows a high threshold voltage, and its driving at a low voltage is therefore difficult. Further, it has another problem that the gray-scale display is difficult to perform since its optical response involves a hysteresis.
It is an object of the present invention to provide a novel material which can overcome the above problems and is suitable for use in AM driving, and a ferrielectric liquid crystal is thinkable as the above novel material.
In 1989, a ferrielectric phase (Sc&ggr;* phase) was found for the first time in 4-(1-methylheptyloxy-carbonyl)phenyl-4-(4′-octyloxybiphenyl)carboxylate (called “MHPOBC” for short) that is an anti-ferroelectric liquid crystal compound (Japanese Journal of Applied Physics, Vol. 29, No. 1, pp. L131-137 (1990)).
The chemical structural formula and phase transition temperatures (° C.) of the MHPOBC are as follows.
Structural formula
C
8
H
17
—O—Ph—Ph—COO—Ph—COO—C*H(CH
3
)—C
6
H
13
wherein Ph is a 1,4-phenylne group and C* is an asymmetric carbon atom.
Phase Sequence
Cr(30)SIA*(65)SCA*(118)SC&ggr;*(119)SC*(121)SC&agr;*(122)SA(147)I
wherein Cr is a crystal phase, SIA* is a chiral smectic IA phase, SCA* is a chiral smectic CA phase (anti-ferroelectric phase), SC&ggr;* is a chiral smectic C&ggr; phase (ferrielectric phase), SC* is a chiral smectic C phase (ferroelectric phase), SC&agr;* is a chiral smectic C&agr; phase, SA is a smectic A phase, and I is an isotropic phase.
Molecular arrangement states of a ferrielectric liquid crystal and an optical response of a ferrielectric phase to a triangular wave will be explained with reference to drawings hereinafter.
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Johno Masahiro
Mine Takakiyo
Yui Tomoyuki
Kelly C. H.
Mitsubishi Gas Chemical Co Inc
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