Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
2000-07-07
2004-02-03
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S299610, C252S299630, C252S299640, C252S299670, C544S298000, C544S303000, C549S369000, C560S064000, C560S065000, C560S128000, C570S126000, C570S128000, C570S131000
Reexamination Certificate
active
06685995
ABSTRACT:
TECHNICAL FIELD
The present invention relates to liquid crystalline compounds and liquid crystal compositions. More specifically, the invention relates to liquid crystalline ester compounds preferable as component of liquid crystal compositions particularly for TN mode, STN mode, or TFT mode, to liquid crystal compositions comprising the compounds, and to liquid crystal display devices fabricated by using the liquid crystal composition as a material to be incorporated therein. In this specification, the term “liquid crystalline compounds” is used as a generic name both for the compounds which exhibit a liquid crystal phase and the compounds which do not exhibit a liquid crystal phase but are useful as component of liquid crystal compositions.
BACKGROUND ART
Liquid crystal display devices employ optical anisotropy and dielectric anisotropy of liquid crystal substances; the devices are classified by their displaying method into various modes such as twisted nematic (TN) mode, dynamic scattering (DS) mode, guest-host (GH) mode, deformation of aligned phases (DAP) mode, super-twisted nematic (STN) mode, electrically controlled birefringence (VCB, ECB, or TB) mode, and vertical alignment (VA) mode; and properties of liquid crystal substances suitable for each of the modes are different. It is necessary to the liquid crystal substances used for any mode of display devices that the liquid crystal substances are stable against moisture, air, heat, and light. For liquid crystal materials employed in display devices particularly using active matrix driving, especially high voltage holding ratio is required.
In recent years, investigations for lowering driving voltage of liquid crystal display devices have been conducted and thus liquid crystal materials having large absolute value of dielectric anisotropy &Dgr;&egr; have been sought. For instance, in TN mode, liquid crystal materials having positive and large &Dgr;&egr; value make driving of the devices at a low voltage possible, and in VA mode, liquid crystal materials having negative and large &Dgr;&egr; make the low voltage driving possible. Besides, in the case of in-plane switching (IPS) mode employing the change in birefringence of liquid crystal materials by on-off switching of transverse electric field (electric field directed parallel to the plane of the substrates), liquid crystal materials having large &Dgr;&egr; or −&Dgr;&egr; have been sought.
In order to increase response speed of liquid crystal display devices, low viscosity is required of liquid crystal materials. In order to make display in a practically wide temperature range possible, excellent miscibility at low temperatures and high clearing point are required of liquid crystal materials.
Further, it is also required that liquid crystal materials used for STN mode have steep threshold characteristics.
Since most favorable optical anisotropy value &Dgr;n of liquid crystal compositions is different depending on display mode and cell thickness, &Dgr;n value required of liquid crystal compounds is in a wide range.
It is known that when the benzene ring at the core part of liquid crystal compounds is replaced by cyclohexane ring, &Dgr;n value of the liquid crystal compounds becomes small (KIKAN KAGAKU SOSETSU (Seasonal publication, General Remarks in Chemistry) No. 22, 1994, Chemistry of Liquid Crystals, page 43). In connection with the structure of the core part, knowledge in the past on the characteristics of liquid crystalline compounds classified by the presence or absence of an aromatic ring such as benzene ring and pyrimidine ring at the core part is described below.
Liquid crystalline compounds having no aromatic ring at the core part generally have small &Dgr;n value. For instance, 4-(4-pentylcyclohexyl)cyclohexanecarbonitrile (Compound (10)) is described on page 44 of the Chemistry of Liquid Crystals described above. Extrapolated &Dgr;n value of this compound is 0.06 (according to the determination by the present inventors, the value is 0.068).
As shown in Example 31 (Comparative Example 1) described below, extrapolated &Dgr;&egr; value of the compound (10) is as small as 3.7 and extrapolated value of viscosity is as high as 55.0 mPa·s according to the determinations by the present inventors. Thus, whereas the compound (10) has small &Dgr;n value, it is difficult to actualize low voltage driving of liquid crystal display devices due to its small &Dgr;&egr; value, and it is also difficult to actualize high speed response due to its high viscosity. Besides, its voltage holding ratio is low, and therefore the compound cannot be used for liquid crystal display devices for TFT mode.
In Mol. Cryst. Liq. Cryst., 1991, Vol. 204, pages 86 and 84, 4-(4-propylcyclohexyl)cyclohexyl trifluoromethyl ketone (Compound (11)) and 4-(4-propylcyclohexyl)cyclohexanecarboxylic acid 2,2,2-trifluoroethyl ester (Compound (12)) are described, respectively. Whereas these compounds also have small &Dgr;n value, their &Dgr;&egr; value are as small as 5.1 and 2.0, respectively, and thus it is difficult to actualize low voltage driving.
At present, exploitation of compounds having large absolute value of &Dgr;&egr; and low viscosity while having small &Dgr;n value are required.
As the compounds having an aromatic ring at the core part and having large &Dgr;&egr; value, following compounds in which cyano group or halogen atoms are bonded to the benzene ring at a terminal of molecule are known.
Whereas all these compounds have medium or large &Dgr;n value since they have an aromatic ring, the compound (13) has low voltage holding ratio and thus can not stand in the use for TFT. Whereas Compounds (14) and (15) have good voltage holding ratio, they have disadvantages that clearing point is low and viscosity is high. As shown in Example 32 (Comparative Example 2) described below, clearing point of the compound (14) is as low as 95.7° C. and its viscosity is as high as 46.3 mPa·s. Accordingly, exploitation of compounds having high clearing point, low viscosity, and high voltage holding ratio while having medium or large &Dgr;n value are currently required.
DISCLOSURE OF THE INVENTION
An object of the present invention is to solve the defects in conventional technology. Another object of them present invention is to provide liquid crystalline compounds having large &Dgr;&egr; value and low viscosity while having small &Dgr;n value, or liquid crystalline compounds having high voltage holding ratio, high clearing point, and low viscosity while having medium or large &Dgr;n value; to provide liquid crystal compositions comprising one side or both sides of the compounds described above thereby low voltage driving, high speed response, and driving at a wide temperature range of liquid crystal display devices become possible; and to provide liquid crystal display devices fabricated by using the liquid crystal composition as material to be incorporated in the devices.
As a result of the investigations by the present inventors to achieve the objects described above, it has been found that compounds having an ester group in which a halogen atom or halogenated alkyl group is bonded to the carbon atom of carbonyl, and having no aromatic ring at the core part have small &Dgr;n value, large &Dgr;&egr; value, low viscosity, and high voltage holding ratio, that such compounds as described above but having an aromatic ring at the core part have medium or large &Dgr;n value, high voltage holding ratio, high clearing point, and low viscosity, and that liquid crystal compositions comprising the former compound or the latter compound are the most suitable materials for low voltage driving, driving at a wide temperature range to be used, and high speed response of diversified liquid crystal display devices, leading to the accomplishment of the present invention.
That is, the present invention is summarized as follows:
(1) An ester compound expressed by the general formula (1)
wherein R
1
represents hydrogen atom, cyano group, nitro group, amino group, a halogen atom, a straight chain or branched alkyl
Haseba Yasuhiro
Matsui Shuichi
Nakagawa Etsuo
Takeshita Fusayuki
Takeuchi Hiroyuki
Chisso Corporation
Wenderoth Lind & Ponack LLP
Wu Shean C.
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