Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
2001-08-10
2003-04-08
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S299610, C252S299630, C252S299660, C252S299670, C544S335000, C549S011000, C549S369000, C560S065000, C570S127000, C570S144000, C570S129000
Reexamination Certificate
active
06544604
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a liquid crystalline compound and a liquid crystal composition, more specifically, to a liquid crystalline compound having a difluoropropyleneoxy group as a bonding group, which shows physical properties particularly suited as a component of a liquid crystal composition for a TN mode, an STN mode, a TFT mode and an OCB mode, a liquid crystal composition comprising the same and a liquid crystal display element containing this liquid crystal composition. A liquid crystalline compound herein means a compound showing a liquid crystal phase and also a compound which does not show a liquid crystal phase but is useful as a component of a liquid crystal composition.
BACKGROUND OF THE INVENTION
A liquid crystal display element makes use of optical anisotropy and dielectric anisotropy of a liquid crystal substance and is classified into various modes such as a twisted nematic (TN) mode, a dynamic scattering (DS) mode, a guest-host (GH) mode, a “deformation of aligned phases (DAP)” mode, a super twisted nematic (STN) mode, a voltage controlling birefringence (VCB, ECB or TB) mode, a vertical alignment (VA) mode, a multidomain vertical alignment (MVA) mode and an OCB mode according to a display mode thereof. Liquid crystal substances suited to the respective modes have different properties.
All liquid crystal substances, regardless of the modes, are required to have the following properties:
1) stability to external environmental factors such as moisture, air, heat and light;
2) a liquid crystal phase in a wide temperature range around room temperature;
3) a low viscosity;
4) a reduced driving voltage when driving a display element;
5) a suitable dielectric anisotropy (&Dgr;&egr;); and
6) a suitable refractive anisotropy (&egr;n).
Under the present circumstances, however, any single compound satisfying all the above characteristics is not available, and several to twenty or more kinds of liquid crystalline compounds are mixed to prepare a liquid crystal composition, which is used for a liquid crystal display element.
Accordingly, liquid crystalline compounds used as components of a composition have to show good compatibility with each other. Recently, they have been required to be used under various environments, and therefore, to have a good compatibility particularly at a very low temperature.
In recent years, a liquid crystal display element has been required to show higher display performances in a contrast, a display volume, a response time, and the like. In order to meet the requirement, there has been a demand for a display element of an active matrix mode represented by a TFT (thin film transistor) mode mainly in the fields of televisions and viewfinders.
A display element of an STN mode is produced in a simple process at a low cost while having a large display volume, so that it is generally used in the display fields of portable telephones, personal computers and the like.
A recent development in these fields has mainly been in miniaturization and portability of liquid crystal display elements as seen in TV and note type personal computers. Accordingly, liquid crystalline compounds having a low driving voltage, i.e., those which can reduce a threshold voltage, and liquid crystal compositions having a low threshold voltage which comprise the above compounds have been required as liquid crystal materials used in this case.
As known well, a threshold voltage (Vth) is shown by the following equation (H. J. Deuling, et al., Mol.
Cryst. Liq. Cryst., 27 (1975) 81):
Vth=&pgr;
(
K/&egr;
0&Dgr;&egr;)
½
wherein K is an elastic constant of a liquid crystal material, and &egr;0 is a dielectric constant in vacuo.
As seen from the above equation, increasing &Dgr;&egr; or decreasing K can be considered as a method for reducing Vth. However, it is still difficult to actually control an elastic constant K of a liquid crystal material by conventional techniques, and a liquid crystal material having large &Dgr;&egr; has generally been used to meet the requirement. Under such circumstances, liquid crystalline compounds having large As have actively been developed.
As a well-known method for increasing &Dgr;&egr; in a liquid crystalline compound, a substituent having a large hi dipole moment such as a cyano group and a trifluoromethyl group may be introduced as a terminal group of the molecule. Also effective is a method of substituting a 1,4-phenylene group constituting the compound with fluorine so that the dipole moment turns toward the same molecular axis direction as a dipole moment in a terminal group. In general, however, the number of fluorine substituted on a 1,4-phenylene group is relative to the viscosity, and a clearing point of the compound is reduced as the number of substituted fluorine increases. Accordingly, it has so far been considered difficult to elevate only &Dgr;&egr; while preventing both rise in the viscosity and reduction in the clearing point.
In recent years, liquid crystal display elements have become widely used in information terminals and portable games. These display elements are driven by batteries, and therefore, it is requested that the threshold voltage is low and the power consumption is low from a viewpoint of use for long time. Particularly in order to reduce a power consumption of an element itself, a reflective display element not requiring backlight has actively been developed recently, and increase in use thereof for portable telephones is anticipated. Liquid crystal compositions used for these reflective display elements are required to have a small refractive anisotropy (&Dgr;n) as well as a low threshold voltage. Accordingly, it is important in this field to develop a liquid crystalline compound having a-large dielectric anisotropy and a small refractive anisotropy as a liquid crystal material constituting the composition. The following compounds (13) and (14) (JP-A 2-233626) can be shown as a representative liquid crystal material for driving a display element at a low voltage, which is used for a liquid crystal display element of a TFT mode:
wherein R represents an alkyl group.
Both the compounds (13) and (14) have a 3,4,5-trifluorophenyl group at a terminal of a molecule and are expected as a liquid crystal material for driving a display element at a low voltage. However, the compound (13) has a small dielectric anisotropy (&Dgr;&egr;=about 10) for use in the reflective display element described above, and the compound (14) has a satisfactory dielectric anisotropy (&Dgr;&egr;=about 12) but has a large refractive anisotropy of about 0.12, so that it is considered difficult to prepare a liquid crystal composition which can sufficiently satisfy the above requirements by using these compounds.
In recent years, novel modes such as an in-plain switching (IPS) mode, a vertical alignment (VA) mode, a multidomain vertical alignment (MVA) mode and an OCB mode have been developed as a mode for overcoming a narrow view angle which is the largest problem of a liquid crystal display element. Among these modes, the VA mode and the MVA mode are particularly excellent in response and have a wide view angle, and further, a high contrast, so that they have been actively developed by respective display makers. Liquid crystal compositions used for the liquid crystal display elements of these modes are characterized in that they have a relatively small refractive anisotropy and a negative dielectric anisotropy. For example, the following compound (15) is reported as a compound showing a large negative dielectric anisotropy (V. Reiffenrath et al., Liq. Cryst., 5 (1), 159 (1989)).
It can be found from the above literature that the compound (15) shows a large negative dielectric anisotropy (&Dgr;&egr;=−4.1), but it has a large refractive anisotropy (&Dgr;n=0.18). Accordingly, it is anticipated that the above compound hardly satisfies the requirements of the VA mode or the MVA mode described above.
As explained above, a liquid crystalline compound having a large positive
Furuya Mayumi
Kawano Katsuyuki
Kubo Yasuhiro
Matsui Shuichi
Miyazawa Kazutoshi
Chisso Corporation
Wenderoth , Lind & Ponack, L.L.P.
Wu Shean C.
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