Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
2001-02-02
2003-06-03
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S299610, C252S299630, C252S299660, C252S299670
Reexamination Certificate
active
06572938
ABSTRACT:
FIELD OF INDUSTRIAL APPLICATION
The present invention relates to a nematic liquid crystal composition. More specifically, the present invention relates to a liquid crystal composition for an active matrix liquid crystal display (AM-LCD) and a liquid crystal display using this liquid crystal composition.
RELATED ART
At present, a transmissive AM-LCD using a back light has been put to practical use as a matrix liquid crystal display capable of displaying full color in various fields such as computer terminals, car navigation systems and the like. However, it has the defect that this back light consumes a large electricity, and brought about is the inconvenience that digital still cameras and digital video cameras which are loaded with the transmissive AM-LCD can not be used for long time.
In order to solve this problem, a reflective AM-LCD using no back light has been developed. As reported in SID97 Digest, p. 643 by S. -T. Wu, C. -S. Wu and C. -L. Kuo, light passes twice through a liquid crystal layer in the reflective AM-LCD, and therefore a product (&Dgr;n·d) of a thickness (d) of the liquid crystal layer and a birefringence (&Dgr;n) of the liquid crystal has to be set to a lower level. To be specific, a &Dgr;n required to a liquid crystal used for an AM-LCD of a conventional transmissive TN type has been roughly 0.075 to 0.120 but in the case of an AM-LCD of a reflective TN type, a &Dgr;n required to a liquid crystal is 0.075 or less.
Characteristics other than a &Dgr;n required to a liquid crystal composition for a reflective AM-LCD include the following items (1) to (4):
(1) In order to improve a contrast of the LCD, the composition has a high resistivity and a high voltage-holding ratio (VHR).
(2) In order to make it possible to use the LCD outdoors, the temperature range showing a nematic phase is wide (the upper limit temperature showing a nematic phase is high, and the lower limit temperature showing a nematic phase is low).
(3) In order to reduce an electricity consumed by the LCD, the threshold voltage (Vth) is low.
(4) In order to shorten the response time, the viscosity (&eegr;) is low.
Literatures disclosing liquid crystalline compounds or liquid crystal compositions which are considered to be usable for an AM-LCD include, for example, Japanese Patent Application Laid-Open No. 29771/1999, Japanese Patent Application Laid-Open No. 245559/1998, Japanese Patent Application Laid-Open No. 255956/1997 and Japanese Patent Application Laid-Open No. 249881/1997. However, these disclosed liquid crystal compositions have the defects that the &Dgr;n is large or the &Dgr;n is relatively small but the lower limit temperature showing a nematic phase is high and the voltage-holding ratio is low, and therefore it has been unsatisfactory for use in an AM-LCD of a reflective TN type.
As described above, the liquid crystal compositions for an AM-LCD have intensively been investigated according to various purposes, but the existing state is that they are always. requested to be newly improved.
PROBLEMS TO BE SOLVED BY THE INVENTION
An object of the present invention is to provide a liquid crystal composition which has particularly a high upper limit temperature of a nematic phase, a low lower limit temperature of the nematic phase and a small birefringence while satisfying general characteristics required to the liquid crystal composition for an AM-LCD described above.
MEANS FOR SOLVING THE PROBLEMS
Intensive investigations repeated by the present inventors in order to solve these problems have resulted in finding that the expected object can be achieved by a liquid crystal composition comprising a component I comprising at least one compound selected from the group of compounds represented by Formula (I-1) or (I-2), a component II comprising at least one compound selected from the group of compounds represented by Formulas (II-1) to (II-8) and a component III comprising at least one compound selected from the group of compounds represented by Formulas (III-1) to (III-5). Thus, they have come to complete the present invention.
The liquid crystal composition of the present invention is shown by the following items (1), (2) and (3):
(1) A liquid crystal composition comprising a component I comprising at least one compound selected from the group of compounds represented by Formula (I-1) or (I-2), a component II comprising at least one compound selected from the group of compounds represented by Formulas (II-1) to (II-8) and a component III comprising at least one compound selected from the group of compounds represented by Formulas (III-1) to (III-5):
wherein R
1
and R
2
each represent independently an alkyl group, an alkoxy group, an alkoxymethyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms; R
3
represents an alkyl group, an alkoxy group, an alkoxymethyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms or —COO—R
6
; R
6
represents an alkyl group having 1 to 10 carbon atoms; R
4
represents an alkyl group, an alkoxy group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms; R
5
represents an alkyl group, an alkoxy group, an alkoxymethyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms; Z
1
and Z
4
each represent independently a single bond or —CH
2
CH
2
—; Z
2
and Z
3
each represent independently a single bond, —CH
2
CH
2
— or —CH═CH—; X
1
represents F, Cl, OCHF
2
or OCF
3
; X
2
represents F, OCHF
2
or OCF
3
; Y
1
and Y
2
each represent independently H or F; and Q represents H or F.
(2) The liquid crystal composition as described in the above item (1), wherein the component I has a content of 3 to 30% by weight; the component II has a content of 5 to 80% by weight; and the component III has a content of 3 to 70% by weight each based on the whole weight of the liquid crystal composition.
(3) The liquid crystal composition as described in the above item (1) or (2), wherein a nematic phase has an upper limit temperature of 70° C. or higher, a lower limit temperature of −20° C. or lower and a birefringence of 0.075 or less.
The liquid crystal display of the present invention is shown by the following item (4):
(4) A liquid crystal display comprising the liquid crystal composition as described in any of the above items (1) to (3).
EMBODIMENT OF THE INVENTION
The component I in the liquid crystal composition of the present invention comprises at least one compound selected from the group of the compounds represented by Formula (I-1) or (I-2). The compound represented by Formula (I-1) has a birefringence (&Dgr;n) of almost 0, a clearing point (Tc) falling in a range of 10 to 30° C. and a dielectric anisotropy (&Dgr;∈) of almost 0 and is excellent in a heat stability, a chemical stability and a compatibility. The compound represented by Formula (I-2) has a &Dgr;n falling in a range of about 0.06 to 0.07, a Tc falling in a range of 140 to 160° C. and a &Dgr;∈ of almost 0 and is excellent in a heat stability, a chemical stability and a compatibility. This allows the component I to assume a role to reduce a &Dgr;n while maintaining particularly a high Tc in a liquid crystal composition for a TFT to which a high reliability is required. However, a composition prepared only from these compounds not only has a too narrow temperature range showing a nematic phase of the composition but also is increased too much in a threshold voltage and therefore is not preferred.
The component II in the liquid crystal composition of the present invention comprises at least one compound selected from the group of the compounds represented by Formulas (II-1) to (II-8). The compounds represented by Formulas (II-1) to (II-8) have a Tc falling in a range of roughly −50 to 160° C., a &Dgr;∈ falling in a range of roughly 5 to 20 and a &Dgr;n falling in a range of roughly 0.03 to 0.12 and is excellent in a heat stability, a chemical stability and a compatibility. This allows the component II to assume a role to reduce particularly a threshold vol
Kubo Yasuhiro
Nakagawa Etsuo
Yanai Motoki
Chisso Corporation
Wenderoth , Lind & Ponack, L.L.P.
Wu Shean C.
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