Electro-optical liquid-crystal display

Details Electro-optical liquid-crystal display Electro-optical liquid-crystal display

2000-04-28

2003-08-05

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299630, C252S299660, C252S299670

Reexamination Certificate

active

06602562

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to electro-optical liquid-crystal displays, and more particularly, mediums for such displays.
BACKGROUND OF THE INVENTION
In conventional liquid-crystal displays (TN, STN, OMI AMD-TN), the electric fields for the re-alignment are generated essentially perpendicular to the liquid-crystal layer.
International Patent Application WO 91/10936 discloses a liquid-crystal display in which the electric fields have a significant component parallel to the liquid-crystal layer (IPS, in-plane switching). The principles of operation of a display of this type are described, for example, by R. A. Soref in Journal of Applied Physics, Vol. 45, No. 12, pp. 5466-5468 (1974).
For example, EP 0 588 568 discloses various possibilities for designing the electrodes and for addressing a display of this type.
Compounds of the formula
in which R=alkyl are disclosed in EP 0 019 665 and U.S. Pat. No. 4,455,261.
However, there is no indication therein that the properties of IPS displays can be improved with the aid of these substances.
IPS displays containing liquid-crystal media including a compound of the formula
and compounds of the formula
have already been mentioned in DE 198 48 181. However, the liquid-crystal media achieved therein have only inadequate dielectric anisotropy values and excessively low clearing point values.
These IPS displays can be operated with liquid-crystalline materials of either positive or negative dielectric anisotropy (&Dgr;&egr;≠0). However, the materials disclosed hitherto generally give not only poor low-temperature storage stabilities and long response times in IPS displays, but in addition the liquid-crystalline materials have excessively high birefringence values, inadequate voltage holding ratios and, in particular, excessively low clearing point values and very particularly excessively low dielectric anisotropy values.
In particular the combination of high dielectric anisotropy, for achieving a relatively low threshold, with a high clearing point was desirably needed without severe impact on the voltage holding ratio, the low-temperature stability and the response time.
SUMMARY OF THE INVENTION
As used herein, the terms “include” or “have” mean to take in, enfold, or comprise as a discrete or subordinate part or item of a larger aggregate, group or principle.
Surprisingly, this feature has been achieved by using liquid-crystalline materials which can include at least two compounds of the formula I, at least one compound of the formula II and/or at least one compound of the formula III and/or IV.
The IPS mixtures according to the invention can improve over the prior art by their relatively high clearing points and low rotational viscosity values and their increased stability to crystallization at low temperatures.
The invention thus generally relates to an electro-optical liquid-crystal display having a re-alignment layer, for re-aligning the liquid crystals, including a field having a significant component parallel to the liquid-crystal layer, including a liquid-crystalline medium of positive dielectric anisotropy, where the medium includes one or more compounds of the formula I and one or more compounds selected from the group of compounds of the formulae II and III
in which
R
1
, R
2
and R
3
are each, independent of one another,
alkyl or alkoxy having 1 to 7 carbon atoms or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 7 carbon atoms,
Y
11
, Y
12
, Y
21
Y
22
,
Y
31
and Y
32
are each, independent of one another, H or F,
are each, independent of one another,
 and
Q—X is F, Cl, —OCF
2
H or —OCF
3
.
R
1
is particularly preferably ethyl, n-propyl and/or n-butyl.
The liquid-crystalline medium preferably includes two or more, particularly preferably three, four or more, most preferably three, compounds of the formula Ia
which R
1
is as defined under the formula I and is preferably ethyl, n-propyl, n-butyl or n-pentyl, particularly preferably ethyl, n-propyl or n-pentyl.
In addition to the compounds of the formula Ia, the medium preferably includes one or more compounds selected from the group of compounds of the formulae IIa to IIc
particularly preferably one or more compounds of the formula Ia, very particularly preferably one or more compounds of the formula IIc,
in which R
2
is as defined above under the formula II, and
particularly preferably in each case one or more compounds of the formulae Ia and IIc and/or
one or more compounds from the group of the formulae IIIa to IIII
in which R
3
is as defined above for R
1
under the formula I and is preferably ethyl, n-propyl, n-butyl or n-pentyl, particularly preferably ethyl, n-propyl or n-pentyl.
Preference is given to liquid-crystal displays having liquid-crystalline media including one or more compounds of the formula IV
in which
R
4
is H, an alkyl or alkenyl radical having 1 to 15 carbon atoms which is monosubstituted by CN or CF
3
or at least monosubstituted by halogen, preferably by F, where, in addition, one or more CH
2
groups in these radicals may each, independently of one another, be replaced by —O—, —S—,
 —CO—, —CO—, —O—CO—, —O—CO—O— or —C≡C— in such a way that O atoms are not linked directly to one another,
A
41
, A
42
and A
43
are each, independent of one another,
(a) a trans-1,4-cyclohexylene radical, in which, in addition, one or more non-adjacent CH
2
groups may be replaced by —O— and/or —S—,
(b) a 1,4-phenylene radical, in which, in addition, one or two CH groups may be replaced by N,
(c) a radical from the group consisting of 1,4-cyclohexenylene, 1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and 1,2,3,4-tetrahydronaphthalene-2,6-diyl,
where the radicals (a) and (b) may be substituted by one or two fluorine atoms,
Z
41
, Z
42
and Z
43
are each, independent of one another, —CO—O—, —O—CO—, —CH
2
O—, —OCH
2
—, —CH
2
CH
2
—, —CH═CH—, —C≡C— or a single bond, or one of the radicals Z
41
and Z
42
is alternatively —(CH
2
)
4
— or —CH═CH—CH
2
CH
2
—,
X
4
is F, —OCF
2
H or —OCF
3
, preferably F or —OCF
3
,
Y
41
and Y
42
are each, independent of one another, H or F, and
n
1
and n
2
are each, independent of one another, 0 or 1.
In a preferred embodiment, the liquid-crystal displays contain liquid-crystalline media comprising three or more compounds of the formula I, particularly preferably in which R
1
is ethyl, n-propyl or n-butyl, and one or more compounds of the formula IVa and one or more, preferably two or more, compounds of the formula IIId
in which R
4
is in each case as defined above under the formulae IVa and IIId, but is preferably ethyl, n-propyl, n-butyl or n-pentyl, particularly preferably ethyl or n-propyl.
In another preferred embodiment, the liquid-crystal display can include a liquid-crystal medium which predominantly, virtually exclusively or exclusively includes, as dielectrically positive compounds, i.e. as compounds having a &Dgr;&egr; of greater than about +1.5, determined by extrapolation from the data of a mixture of about 15% of the substance in the mixture ZLI-4792 from Merck KGaA, compounds of the formulae I, II and III. In this application, “predominantly” means that the proportion of corresponding other compounds (here, for example, other compounds having &Dgr;&egr;> about +1.5) in the mixture as a whole is less than about 10%, “virtually exclusively” means that this proportion is less than about 5%, and “exclusively” means that this proportion is less than about 1%. The liquid-crystal displays very particularly preferably can include absolutely no compounds having &Dgr;&egr;> about 1.5 other than those of the formulae I, II and III.
In this embodiment, the liquid-crystal mixtures can include
preferably two, three or four, particularly preferably three, compounds of the formula I, particularly preferably of the formula Ia, and
two, three or four, particularly preferably two or three, compounds of the formula II, preferably one or more compounds of the formula Ia and one or more compoun

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