Electro-optical liquid crystal display

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

2001-04-06

2003-06-24

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299610, C252S299630, C252S299640, C252S299660, C252S299670

Reexamination Certificate

active

06582782

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 aids 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
L is 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 195 28 104.
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, 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 feature has, surprisingly, been achieved by the use of liquid-crystalline materials which comprise at least one compound of the formula I.
The IPS mixtures according to the invention are distinguished by their relatively low rotational viscosity values and their low threshold voltage and response time values.
The invention thus relates to an electro-optical liquid-crystal display having a realignment layer for realignment of the liquid crystals whose field, desirably, 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
L is H or F.
Particular preference is given to compounds of the formula I in which L is F, and to compounds of the formula I in which R
1
is alkyl or alkoxy having 1 to 7 carbon atoms.
The compounds of the formula I have high dielectric anisotropy values and relatively high birefringence and clearing point values. Their use in liquid-crystal mixtures for IPS displays according to the invention facilitates high dielectric anisotropies and low rotational viscosities with retention of high clearing points and favourable birefringence values and produces low threshold voltages and short response times.
It has been found, in particular, that mixtures according to the invention comprising compounds of the formula I have significantly higher clearing point and dielectric anisotropy values, lower rotational viscosity and threshold voltage values, and shorter response times than, for example, analogous mixtures which, instead of the compounds of the formula I, comprise 3,5-difluoro-4-cyanophenylcyclohexanes of the formula:
The compounds of the formula I are disclosed in DE 44 10 606. However, this specification does not describe IPS displays.
Preferred embodiments are IPS displays in which
a) the liquid-crystalline medium comprises one or more compounds of the formula II containing a cyano group:
in which
R
2
is H, an alkyl or alkenyl radical having 1 to 15 carbon atoms which is unsubstituted, monosubstituted by CN or CF
3
or at least monosubstituted by halogen, where one or more CH
2
groups in these radicals may also each, independently of one another, be replaced by —O—, —S—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are not linked directly to one another,
A
1
and A
2
are each, independently of one another,
(a) a trans-1,4-cyclohexylene radical or 1,4-cyclohexenylene 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-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
1
and Z
2
are each, independently of one another, —CO—O—, —O—CO—, —CH
2
O—, —OCH
2
—, —CH
2
CH
2
—, —CH═CH—, —C≡C—, —CHF—CHF—, —CF═CF—, —CF
2
O—, —OCF
2
—, —CF
2
CF
2
— or a single bond, and one of the radicals Z
1
and Z
2
may alternatively be —(CH
2
)
4
— or —CH═CH—CH
2
CH
2
—,
L
1
and L
2
are each, independently of one another, H or F; and
m is 0, 1 or 2;
b) the liquid-crystalline medium comprises one or more compounds of the formula III containing a 3,4,5-trifluorophenyl group:
in which
R
3
has one of the meanings indicated for R
2
in the formula II,
A
3
and A
4
each, independently of one another, have one of the meanings indicated for A
1
and A
2
in the formula II,
Z
3
and Z
4
each, independently of one another, have one of the meanings indicated for Z
1
and Z
2
in the formula II, and
n is 0, 1 or 2;
c) the liquid-crystalline medium comprises one or more compounds of the formula IV:
R
4
—(A
5
—Z
5
)
o
—A
6
—R
5
  IV
in which
R
4
and R
5
each, independently of one another, have one of the meanings indicated for R
2
in the formula II,
A
5
and A
6
each, independently of one another, have one of the meanings indicated for A
1
and A
2
in the formula II,
each Z
5
, independently of the others, has one of the meanings indicated for Z
1
and Z
2
in the formula II, and
o is 1, 2 or 3;
d) the liquid-crystalline medium comprises one or more compounds of the formula V:
in which
R
6
has one of the meanings indicated for R
2
in the formula II,
A
7
and A
8
each, independently of one another, have one of the meanings indicated for A
1
and A
2
in the formula II,
Z
7
and Z
8
each, independently of one another, have one of the meanings indicated for Z
1
and Z
2
in the formula II,
L
1
and L
2
are each, independently of one another, H or F,
Q is a polyfluoroalkylene radical of the formula
—(O)
q
—(CH
2
)
r
—(CF
2
)
s
—, in which
q is 0 or 1,
r is 0, 1, 2, 3, 4, 5 or 6,and
s is 1, 2, 3, 4, 5 or 6,
X is H, F or Cl, and
p is 0, 1 or 2.
The compounds of the formula II are preferably selected from the group comprising the formulae IIa to IIp:
in which R
2
is as defined in the formula II, and L
2
is H or F.
In the compounds of the formulae IIb, IIe, IIk, IIn and IIp, L
2
is particularly preferably F. In the compounds of the formulae IId, IIg, IIh and IIi, L
2
is particularly preferably H.
The liquid-crystalline medium particularly preferably comprises one or more compounds selected from the group consisting of the compounds of the formulae IIa, IIb, IIc, IId, IIh and IIk.
In a further preferred embodiment, the liquid-crystalline medium comprises at least one heterocyclic compound selected from the group comprising the formulae IIm, IIn, IIo and IIp.
The compounds of the formula III are preferably selected from the group comprising the formulae IIIa to IIIi:
in which R
3
is as defined in the formula III.
The liquid-crystal display particularly preferably c

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