Liquid crystal compositions and liquid crystal display devices

Details Liquid crystal compositions and liquid crystal display devices Liquid crystal compositions and liquid crystal display devices

2002-04-26

2004-07-06

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C428S001300, C252S299630, C252S299640, C252S299660

Reexamination Certificate

active

06759102

ABSTRACT:

TECHNICAL FIELD
This invention relates to liquid crystal compositions, liquid crystal display devices comprising said liquid crystal compositions and those of an OCB mode. For convenience, the liquid crystal composition of the present invention is sometimes expressed herein merely as the composition. Further, the compound represented by the formula (I) is sometimes expressed as Compound (I), and the compounds represented by other formulas are each sometimes expressed in this manner.
BACKGROUND ART
Practical application of a liquid crystal display device using an OCB (optically compensated bend) mode has been studied, because of its broad viewing angle and reduced response time. Recently, a liquid crystal composition having more reduced response time and being suitable for the OCB mode has been demanded so as to cope with an animation.
For conventional liquid crystal display devices of TFT (thin film transistor) drive, speeding up has been attempted using a TN (twisted nematic) mode, an IPS (in-plain switching) mode or a VA (vertical alignment) mode. However, displaying an animation as in CRT (cathode-ray tube) requires more reduced response time. Thus a liquid crystal composition and a liquid crystal display device with more reduced response time have been desired. The same applies to a liquid crystal display device of an OCB mode, for which a liquid crystal composition with a reduced response time is needed. Further, low power consumption in liquid crystal display devices has been attempted. To drive the liquid crystal display device at low voltage, a liquid crystal composition having low threshold voltage has been also desired.
The liquid crystal display devices of an OCB mode are disclosed in JP-A 7-84254 and Society for Information Display International Symposium (SID '93), 277 (1993). The liquid crystal compositions used in the liquid crystal display device of an OCB mode are disclosed in JP-A 9-176645 and JP-A 11-302653. The liquid crystal display devices of a reflection type R-OCB mode are disclosed, for example, in Society for Information Display International Symposium (SID '96), 618 (1996).
DISCLOSURE OF THE INVENTION
An object of the invention is to provide a liquid crystal composition having reduced response time and low threshold voltage and a liquid crystal display device using said composition, especially that of an OCB mode.
We have found that the liquid crystal composition of the present invention as described below has more reduced response time and lower threshold voltage as compared with conventional ones, the present composition can be suitably used in a liquid crystal display device, and that in particular a liquid crystal display device of an OCB mode. We have completed the present invention based on these findings.
The present invention resides in the following items 1 to 8.
(1) A liquid crystal composition which comprises as a first component at least one compound selected from the group of compounds represented by the formula (I) and as a second component at least one compound selected from the group of compounds represented by the formula (II), wherein the content of the first component is 30 to 95% by weight and the content of the second component is 5 to 70% by weight, based on the total weight of the composition
wherein R
1
and R
3
are independently an alkyl of 1 to 10 carbon atoms and any —CH
2
— in the alkyl may be replaced by —O— or —CH═CH—; R
2
is an alkyl of 1 to 10 carbon atoms, —F or —Cl; X
1
, X
2
, X
3
, X
4
, X
5
, X
6
, X
7
, X
8
and X
10
are independently —F or —H; X
9
is —F, —Cl, —CF
3
, —OCF
3
or —OCF
2
H; A
1
and A
2
are independently 1,4-cyclohexylene, pyrimidine-2,5-diyl or 1,4-phenylene in which any —H may be replaced by —F; Z
1
and Z
3
are independently a single bond, —(CH
2
)
2
— or —(CH
2
)
4
—; Z
2
is a single bond or —CF
2
O—; and Z
4
is a single bond, —COO— or —CF
2
O—.
The meaning of the expression “any —CH
2
— in the alkyl may be replaced by —O— or —CH═CH—” as defined herein is illustrated by the following examples, to which the present invention is not limited. For the case of the alkyl being C
4
H
9
—, examples of the alkyl in which —CH
2
— is replaced by —O— or —CH═CH— include C
3
H
7
O—, CH
3
—CH
2
—O—CH
2
—, CH
3
—O—CH
H
2
C═CH—(CH
2
)
3
—, CH
3
—CH═CH—(CH
2
)
2
— and H
2
C═CH—(CH
2
)
2
shown in these examples, the term “any” denotes “at least one”. In view of the stability of the compound, CH
3
—O—CH
2
—O— wherein oxygens are not adjacent each other is more preferable than CH
3
—O—O—CH
2
— wherein oxygens are adjacent each other.
(2) The liquid crystal composition according to item 1, which further comprises as a third component at least one compound selected from the group of compounds of the formulas (III-1) and (III-2)
wherein R
4
, R
5
and R
6
are independently an alkyl of 1 to 10 carbon atoms and any —CH
2
— in the alkyl may be replaced by —O— or —CH═CH—; R
7
is an alkyl of 1 to 10 carbon atoms, an alkoxy of 1 to 10 carbon atoms, —F, —Cl or —OCF
3
; A
3
is 1,4-cyclohexylene or 1,4-phenylene in which any —H may be replaced by —F; Z
5
is a single bond, —(CH
2
)
2
—, —COO— or —CF
2
O—, and X
11
and X
12
are independently —F or —H.
(3) The liquid crystal composition according to item 1 wherein the first component is at least one compound selected from the group of compounds of the formulas (I-1) and (I-2)
wherein R
1
, A
1
, Z
2
, R
2
, X
4
and X
5
each have the same meanings as defined in item 1.
(4) The liquid crystal composition according to item 1, wherein the second component is at least one compound selected from the group of compounds of the formulas (II-1), (II-2) and (II-3)
wherein R
3
, X
6
, X
8
, X
9
, X
10
, A
2
and Z
3
each have the same meanings as defined in item 1.
(5) The liquid crystal composition according to item 2, wherein the content of the third component is 2 to 30% by weight based on the total weight of the composition.
(6) An application of the liquid crystal compositions according to any one of items 1 to 5, to a liquid crystal display device of an OCB mode.
(7) A liquid crystal display device containing a liquid crystal composition according to any one of items 1 to 5.
(8) A liquid crystal display device of an OCB mode containing a liquid crystal composition according to any one of items 1 to 5.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
The effects achieved by each component in the present composition are explained below.
Compound (I) has relatively large optical anisotropy and high clearing point. This compound contributes to an increase in optical anisotropy and an elevation in a phase transition temperature of a nematic-isotropic liquid (clearing point: T
NI
). Preferred examples of Compound (I) are shown below.
In the above compounds, R
1
has the same meaning as defined in item 1. Preferable R
1
includes an alkyl of 1 to 10 carbon atoms, an alkenyl of 2 to 11 carbon atoms or an alkoxy of 1 to 9 carbon atoms. Especially preferable R
1
is an alkyl of 2 to 7 carbon atoms.
Compound (II) has large dielectric anisotropy, and middle or large optical anisotropy. This compound increases the dielectric anisotropy of the composition without appreciable reduction in the optical anisotropy. Preferable examples of Compound (II) are shown below.
In the above compounds, R
3
has the same meaning as defined in item 1. Preferable R
3
includes an alkyl of 1 to 10 carbon atoms, an alkenyl of 2 to 11 carbon atoms or an alkoxy of 1 to 9 carbon atoms. Especially preferable R
3
is an alkyl of 2 to 7 carbon atoms.
Compound (III-1) and Compound (III-2) have low viscosity and low clearing point. These compounds are used for adjusting the clearing point of the composition, lowering the viscosity of the composition and improving the compatibility at low temperatures in the composition. Preferable examples of Compound (III-1) and Compound (III-2) are shown below.
In the above formulas, R′ is an alkyl of 1 to 10 carbon atoms or an alkoxy of 1 to 10 carbon atoms; R
4
, R
5
and R
6
have the same meanings as defined in item 2

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