Liquid crystal composition and liquid crystal displays

Details Liquid crystal composition and liquid crystal displays Liquid crystal composition and liquid crystal displays

2000-07-05

2002-06-04

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299610, C252S299630, C252S299670

Reexamination Certificate

active

06399163

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a nematic liquid crystal composition. More specifically, the invention relates to a liquid crystal composition for an active matrix liquid crystal display device and to a liquid crystal display device using the liquid crystal composition.
BACKGROUND ART
To date, a transmission-type active matrix liquid crystal display device (AM-LCD) using a backlighting as a light source has been used practically as a device enabling full color display. As this backlighting has a weak point to consume considerable electric power, a digital still camera and a digital video camera equipped with such AM-LCD have an inconvenience that they cannot be used for a long time.
To solve the problem of the electric power consumed, a reflection-type AM-LCD has been developed. In the reflection-type AM-LCD, as reported by S.-T. Wu, C.-S. Wu, C.-L. Kuo et al. in SID 97 Digest/643, light passes twice through a liquid crystal layer so that the product (&Dgr;n·d) of thickness of the liquid crystal layer (d) and optical anisotropy (&Dgr;n) should be set smaller. For this reason, &Dgr;n required for the liquid crystals of the reflection TN-type AM-LCD is 0.07 and less compared to 0.075~0.120 of &Dgr;n required for the liquid crystals of a conventional transmission TN-type AM-LCD.
Besides &Dgr;n, characteristics of the liquid crystal composition required for the reflection-type AM-LCD are as follows, just like for the conventional transmission-type AM-LCD:
(1) to have high specific resistance and a large voltage holding ratio in order to keep high contrast of the LCD;
(2) to have a broad temperature range exhibiting a nematic phase in order to make outdoor use of the LCD possible, namely, to have a higher upper-limit of temperature exhibiting a nematic phase and a lowere lower-limit of temperature exhibiting a nematic phase;
(3) to have low threshold voltage in order to reduce electric power consumed in the LCD; and
(4) to have low viscosity in order to accelerate display speed of the LCD.
Literature disclosing liquid crystal compounds or liquid crystal compositions which is thought to be applicable to the AM-LCD can be illustrated as follows: WO 96/23851, Japanese Patent Kokai Hei 9-71779 (1997), Japanese Patent Kokai Hei 9-110981 (1997), DE 19629812 A1 and WO 98/17664. However, the liquid crystal compositions disclosed in these literatures, as shown in the comparative examples of the present application, have deficiencies such as large &Dgr;n, a high lower-limit of temperature exhibiting a nematic phase in spite of &Dgr;n being relatively small, or a small voltage holding ratio so that they are insufficient to use for the reflection-type AM-LCD.
Thus the liquid crystal compositions are always requested improvement though they have been keenly investigated depending on various purposes.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide a liquid crystal composition which has, in particular, a high upper-limit of temperature exhibiting a nematic phase, a low lower-limit of temperature exhibiting a nematic phase, and small optical anisotropy while satisfying general properties required for an AM-LCD.
The inventors of the present invention, after enthusiastic investigation of the liquid crystal composition using various liquid crystal compounds to solve these subjects, have found that the liquid crystal composition described in the present invention as shown later can be used for the reflection TN-type AM-LCD with possibility of displaying full color so that the object intended can be achieved. Followings are detailed explanation of the present invention.
The first of the present invention is a liquid crystal composition characterized in that it comprises at least one compound expressed by formula (1) as the first component, at least one compound expressed by formula (2) as the second component, and at least one compound expressed by either formula (3-1) or (3-2) as the third component.
wherein R
1
, R
3
, R
4
and R
5
each independently represent alkyl having 1 to 10 carbon; R
2
represents alkyl or alkoxy having 1 to 10 carbon, or —COO—R
6
; Z
1
represents a single bond or —C
2
H
4
—; and R
6
represents alkyl having 1 to 10 carbon.
The second of the present invention is a liquid crystal composition characterized in that it comprises as the first component at least one compound expressed by formula (1) in 5 to 95% by weight based on the total weight of the composition; it comprises as the second component at least one compound expressed by formula (2) in 5 to 25% by weight based on the total weight of the composition; and it comprises as the third component at least one compound expressed by either formula (3-1) or (3-2) in 5 to 70% by weight based on the total weight of the composition.
The third of the present invention is a liquid crystal composition characterized in that it comprises, as the fourth component in addition to the first, the second, and the third components, at least one compound selected from the group of compounds expressed by formulae (4-1) to (4-3) in 85% and less by weight based on the total weight of the composition.
wherein R
7
, R
8
and R
9
each independently represent alkyl having 1 to 10 carbon; X
1
, X
3
, X
4
, and X
5
each independently represent H or F; X
2
represents Cl, F, or alkoxy having 1 to 10 carbon; Z
2
represents —COO—, —C
2
H
4
— or a single bond; Z
3
and Z
4
each independently represent —C
2
H
4
— or a single bond; with the proviso that Z
2
is always —COO— when X
1
and X
3
are H simultaneously.
The fourth of the present invention is a liquid crystal composition characterized in that an upper-limit of temperature exhibiting a nematic phase is 70° C. or more, a lower-limit of temperature exhibiting a nematic phase is −20° C. and less, and optical anisotropy is 0.07 and less.
The fifth of the present invention relates to a liquid crystal display device using any liquid crystal composition described in the first to the fourth of the present invention.
BEST EMBODIMENT TO PRACTICE THE PRESENT INVENTION
Now, we explain the preferable embodiment of compounds constituting the liquid crystal composition of the present invention. The compounds expressed by following formulae (1-1) to (1-3) are preferably used among those expressed by formula (1).
wherein R and R′ each independently represent linear alkyl having 1 to 10 carbon.
The compounds expressed by following formula (2-1) are preferably used among those expressed by formula (2).
wherein R represents linear alkyl having 1 to 10 carbon.
The compounds expressed by following formula (3-1-1) or (3-1-2) are preferably used among those expressed by formula (3-1).
wherein R represents linear alkyl having 1 to 10 carbon.
The compounds expressed by the following formula (3-2-1) are preferably used among those expressed by formula (3-2).
wherein R represents linear alkyl having 1 to 10 carbon.
The compounds expressed by the following formulae (4-1-1) to (4-1-7) are preferably used among those expressed by formula (4-1).
wherein R and R′ each independently represent linear alkyl having 1 to 10 carbon.
The compounds expressed by following formulae (4-2-1) to (4-2-5) are preferably used among those expressed by formula (4-2)
wherein R represents linear alkyl having 1 to 10 carbon.
The compounds expressed by the following formula (4-3-1) are preferably used among those expressed by formula (4-3).
wherein R represents linear alkyl having 1 to 10 carbon.
Next, we explain a roll of each compound constituting the liquid crystal composition of the present invention.
The compound expressed by formula (1) has features that dielectric anisotropy is nearly zero, a value of specific resistance is large, the upper-limit of temperature exhibiting a nematic phase is relatively low, viscosity is low, and optical anisotropy is considerably small. For this reason, the compound expressed by formula (1) is specifically used for the object to reduce viscosity and to minimize optical anisotropy while maintaining a high voltage holding rate of the l

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