Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
2001-03-15
2002-05-28
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S299630, C252S299670
Reexamination Certificate
active
06395353
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a nematic liquid crystal composition having a negative dielectric anisotropy and to a liquid crystal display element containing the composition. More particularly, it relates to a liquid crystal composition having a negative dielectric anisotropy which is used for an active matrix liquid crystal display element, and to a liquid crystal display element containing the composition.
BACKGROUND OF THE INVENTION
A liquid crystal display (LCD) element consumes less electric power, and can be downsized and save weight as compared with a cathode ray tube (CRT) display. Therefore, several kinds of liquid crystal display systems such as twist nematic (TN), super twist nematic (STN) and thin film transistor (TFT) modes have been put to practical use. Among them, an active matrix liquid crystal display element (AM-LCD) has been the focus of interest as the most expected system because of its advanced colorization and minuteness.
A liquid crystal composition used in AM-LCD is required to have the following properties:
1) high voltage holding ratio to maintain high contrast of the liquid crystal display element,
2) broad nematic phase range to cope with various environments,
3) suitable refractive anisotropy (&Dgr;n) in accordance with cell thickness, and
4) suitable threshold voltage in accordance with drive circuit.
A drive system of AM-LCD has mainly been TN mode in which twist angle of alignment of liquid crystal molecules between upper and lower electrode substrates is 90 degrees. However, it has a difficulty in applying for wide view displays because of the narrow view angle. Some modes for improving view angle have been proposed as follows:
a) IPS display mode in which a liquid crystal display element shows homogeneous alignment of liquid crystal molecules when voltage is unimpressed and the molecules rotate at an angle of 45 to 90 degrees within the same plane when voltage is impressed (R. Kiefer, B. Weber, F. Windscheid and G. Baur, In-Plane Switching of Nematic Liquid Crystals, JAPAN DISPLAY '92, p. 547; and
b) VA display mode in which a liquid crystal display element shows homeotropic alignment when voltage is unimpressed and then shows horizontal alignment in one direction when voltage is impressed (K. Ohmuro, S. Kataoka, T. Sasaki and Y. Koike, Development of Super-High-Image-Quality Vertical-Alignment-Mode LCD, SID 97 Digest, p. 845).
These display systems have characteristics of quick response and high contrast in addition to the wide view angle. Further, they have a remarkable characteristic that they can comprise a liquid crystal composition having a negative dielectric anisotropy (&Dgr;&egr;).
These drive systems utilize an electrically controlled birefringence mode. A product (&Dgr;n.d) of refractive anisotropy (&Dgr;n) and cell thickness (d) should be, for example, &Dgr;n.d=approx. 0.275 &mgr;m so as to provide a suitable contrast. Accordingly, a &Dgr;n value should be 0.05 to 0.13 so as to obtain a cell thickness of 2 to 6 &mgr;m. Since response time is proportioned to viscosity of a liquid crystal composition (hereinafter referred to as &eegr;), a liquid crystal composition is required to have a small &eegr;. Further, threshold voltage decreases as an absolute value of dielectric anisotropy (hereinafter referred to as &Dgr;&egr;) increases, and therefore, a liquid crystal composition is required to have a largely negative &Dgr;&egr;.
Such a liquid crystal composition has been studied for various purposes, but is always required to be much more improved.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a liquid crystal composition applicable for the display systems of the above a) and b), which can realize a wide view angle, a suitable &Dgr;n, and particularly a largely negative dielectric anisotropy, a broad range of nematic liquid crystal phase, a high voltage holding ratio and a low viscosity while satisfying various properties required for a liquid crystal composition for the AM-LCD.
The present inventors have studied liquid crystal compositions comprising various kinds of liquid crystalline compounds to solve the above problems, and found that the object can be achieved by a liquid crystal composition comprising several compounds as Components I to III, thus attaining the present invention.
The first liquid crystal composition of the present invention is described below in the items (1) and (2).
(1) A liquid crystal composition comprising Component I selected from the group consisting of the compounds represented by formula (I), Component II selected from the group consisting of the compounds represented by formula (II) and Component III selected from the group consisting of the compounds represented by formulas (III-1) and (III-2)
wherein each R
1
independently represents an alkyl group having 1-10 carbon atoms or an alkenyl group having 2-10 carbon atoms; each R
2
independently represents an alkyl or alkoxy group having 1-10 carbon atoms, or an alkenyl group having 2-10 carbon atoms; Z
1
and Z
2
represent —CH
2
SiH
2
—, a single bond or —CH
2
CH
2
—, with the proviso that one of Z
1
and Z
2
represents —CH
2
SiH
2
— and the other represents a single bond or —CH
2
CH
2
—; ring A
1
represents a trans-1,4-cyclohexylene group, or a 1,4-phenylene group in which one or more hydrogen atoms may be substituted with fluorine atoms; m is 0 or 1, with the proviso that when m is 0, Z
2
represents —CH
2
SiH
2
—; Z
3
and Z
4
each independently represent a single bond, —CH
2
CH
2
—, —CF
2
O— or —OCF
2
—; rings A
2
and A
3
represent a tetrahydropyran-2,5-diyl group, a trans-1,4-cyclohexylene group, a cyclohexa-1-ene-1,4-diyl group, or a 1,4-phenylene group in which one or more hydrogen atoms may be substituted with fluorine atoms; n is 0 or 1; with the proviso that when n=0 and Z
4
represents a single bond or —CH
2
CH
2
—, then ring A
3
represents a tetrahydropyran-2,5-diyl group; when n=0 and Z
4
represents —CF
2
O— or —OCF
2
—, then ring A
3
represents a trans-1,4-cyclohexylene group or a cyclohexa-1-ene-1,4-diyl group; when n=1 and Z
3
and Z
4
each independently represent a single bond or —CH
2
CH
2
—, then one of rings A
2
and A
3
represents a tetrahydropyran-2,5-diyl group; when n=1 and Z
3
and/or Z
4
represent —CF
2
O— or —OCF
2
—, then rings A
2
and A
3
represent a trans-1,4-cyclohexylene group, a cyclohexa-1-ene-1,4-diyl group, or a 1,4-phenylene group in which one or more hydrogen atoms may be substituted with fluorine atoms; each R
3
independently represents an alkyl group having 1-10 carbon atoms or an alkenyl group having 2-10 carbon atoms, in which one —CH
2
— may be substituted with —O—; ring A
4
represents a 1,4-phenylene group or a trans-1,4-cyclohexylene group; ring A
5
represents a trans-1,4-cyclohexylene group, or a 1,4-phenylene group in which one or more hydrogen atoms may be substituted with fluorine atoms; p, q and s are each independently 0 or 1 with the proviso that (p+q) is 0 or 1.
(2) A liquid crystal composition as described in the above item (1), which comprises 3-80% by weight of Component I, 3-80% by weight of Component II and 1-80% by weight of Component III.
The second liquid crystal composition of the present invention is described below in the item (3).
(3) A liquid crystal composition as described in the above item (1) or (2), which further comprises Component IV selected from the group consisting of the compounds represented by formula (IV)
wherein R
4
represents an alkyl group having 1-10 carbon atoms or an alkenyl group having 2-10 carbon atoms, R
5
represents an alkyl or alkoxy group having 1-10 carbon atoms or an alkenyl group having 2-10 carbon atoms, Z
5
and Z
6
each independently represent a single bond or —CH
2
CH
2
—, ring A
6
represents a 1,4-phenylene group or a trans-1,4-cyclohexylene group, and t is 0 or 1.
The third liquid crystal composition of the present invention is described below in the item (4).
(4) A liquid crystal composition as described in any one of the items (1
Kubo Yasuhiro
Nakagawa Etsuo
Yanai Motoki
Chisso Corporation
Wu Shean C.
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