Electro-optical liquid-crystal display

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

2001-03-29

2004-06-15

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

06749907

ABSTRACT:

The invention relates to an electro-optical liquid-crystal display having a realignment layer for realignment of the liquid crystals whose field has a component, which is crucial for the realignment, parallel to the liquid-crystal layer, containing a liquid-crystalline medium of positive dielectric anisotropy, where the medium comprises at least one mesogenic compound of the formula I
in which
R
1
is alkyl or alkoxy having 1 to 7 carbon atoms or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 7 carbon atoms, and
Y
11
and Y
12
are each, independently of one another, H or F.
In conventional liquid-crystal displays (TN, STN, OMI or AMD-TN), the electric fields for realignment are generated essentially perpendicular to the liquid-crystal layer.
International Patent Application WO 91/10936 discloses a liquid-crystal display in which the electric signals are generated in such a way that the electric fields have a significant component parallel to the liquid-crystal layer (IPS, in-plane switching). The principles of operating 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).
EP 0 588 568, for example, discloses various possibilities for the design of the electrodes and for addressing a display of this type. DE 198 24 137 likewise describes various embodiments of IPS displays of this type.
Liquid-crystalline materials for IPS displays of this type are described, for example, in DE 198 48 181.
The IPS displays containing the known liquid-crystalline media are characterized by inadequate, long response times and often excessively high operating voltages. There is thus a demand for IPS displays which do not have these disadvantages or only do so to a reduced extent. To this end, in particular liquid-crystalline materials are required which, besides an adequate phase range, low tendency towards crystallization at low temperatures, low birefringence and adequate electrical resistance, have, in particular, low threshold voltages (V
10
) and low rotational viscosities (&ggr;
1
), which are crucial for the response times.
This object has, surprisingly, been achieved by the use of liquid-crystalline materials which comprise at least one compound of the formula I.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
The IPS mixtures according to the invention are distinguished by their relatively high clearing points and their low rotational viscosity values and their low threshold values.
The invention thus relates to an electro-optical liquid-crystal display having a realignment layer for realignment of the liquid crystals whose field has a significant component parallel to the liquid-crystal layer, containing a liquid-crystalline medium of positive dielectric anisotropy, where the medium comprises at least one compound of the formula I
in which
R
1
is alkyl or alkoxy having 1 to 7 carbon atoms or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 7 carbon atoms,
and
Y
11
and Y
12
are each, independently of one another, H or F.
Particular preference is given to compounds of the formula I in which at least one of the radicals Y
12
and Y
11
is F. Very particular preference is given to compounds of the formula I in which one of the radicals Y
11
and Y
12
is H and the other is F.
Preference is furthermore given to liquid-crystal displays containing liquid-crystalline media which further comprise one or more compounds of the formula II
in which
R
2
is alkyl or alkoxy having 1 to 7 carbon atoms or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 7 carbon atoms,
A
21
and A
22
are each, independently of one another,
 at least one of A
21
and A
22
is
X
2
is F, Cl or CN, and
Z
2
is CH
2
CH
2
, COO, CF
2
O or a single bond.
Particular preference is given to compounds of the formula II in which
Preference is furthermore given to compounds of the formula II in which
Preference is furthermore given to compounds of the formula II in which X
2
is CN.
Preference is furthermore given to liquid-crystal displays in which the liquid-crystalline medium further comprises one or more compounds of the formula III
in which
R
31
and R
32
are each, independently of one another, alkyl or alkoxy having 1 to 7 carbon atoms or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 7 carbon atoms,
are each, independently of one another,
and
Z
31
is CH═CH, COO, CH
2
CH
2
or a single bond.
Particular preference is given to compounds of the formula III in which at least one of the radicals R
31
and R
32
is alkenyl having 2 to 7 carbon atoms, preferably having 2 or 3 carbon atoms.
Preference is furthermore given to compounds of the formula III in which Z
31
is CH═CH or a single bond.
Preference is furthermore given to compounds of the formula III in which at least one of
particularly preferably both are
Preference is furthermore given to liquid-crystal displays in which the liquid-crystalline medium further comprises one or more compounds of the formula IV
in which
R
4
is alkyl or alkoxy having 1 to 7 carbon atoms or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 7 carbon atoms,
are each, independently of one another,
Z
41
and Z
42
are each, independently of one another, CF
2
O, COO, CH
2
CH
2
or a single bond,
n is 0 or 1,
X is OCF
3
, OCF
2
H or F,
and
Y
41
and Y
42
are each, independently of one another, H or F.
Particular preference is given to compounds of the formula IV in which at least one of
Preference is furthermore given to compounds of the formula IV in which Z
41
and Z
42
are each, independently of one another, CH
2
CH
2
or a single bond.
Preference is furthermore given to compounds of the formula IV in which X is OCF
3
, and Y
41
and Y
42
are H, and to compounds of the formula IV in which X is F, and Y
41
and Y
42
are F.
Particular preference is given to media which comprise at least one compound of the formula I and at least one compound of the formula II.
Particular preference is given to liquid-crystal displays in which the liquid-crystalline medium comprises one or more compounds of the formula II selected from the group consisting of the formulae IIa to Iii:
in which R
2
is as defined in the formula II.
The liquid-crystal display particularly preferably contains a liquid-crystalline medium comprising one or more compounds selected from the group consisting of the compounds of the formulae IIa, IIf, IIg, IIh and IIi, in particular IIh and IIi.
Preference is furthermore given to liquid-crystal displays in which the liquid-crystalline medium comprises one or more compounds of the formula III selected from the group consisting of the formulae IIIa to IIIc:
in which
k is 1, 2, 3,4 or 5,
m and n are each, independently of one another, 0, 1, 2 or 3, and m+n ≦5, and
o is 0 or 1.
Preference is furthermore given to liquid-crystal displays in which the liquid-crystalline medium comprises one or more compounds of the formula IV selected from the group consisting of the formulae IVa to IV:
in which R
4
is as defined in the formula IV.
In a further preferred embodiment, the liquid-crystal display cells contain liquid-crystalline media which comprise one or more compounds of the formula IIh, where the concentration of each individual one of these compounds is in the range from 0.1 to 20%, preferably from 1 to 16%, particularly preferably from 2 to 15% and very particularly preferably from 12 to 15%.
In a preferred embodiment of the invention, the liquid-crystal display cells contain liquid-crystalline media which comprise one or more compounds of the formula IIi, where the concentration of each individual one of these compounds is from 0.1 to 10%, preferably from 1 to 7% and particularly preferably from 1 to 5%.
Preferred embodiments are the following liquid-crystal displays:
the medium additionally comprises one or more compounds selected from the group consisting of the formulae Va and Vb
in which R
51
and R
52
are each, independently of one another, alkyl or alkox

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