Electro-optical liquid-crystal

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

1996-10-10

2002-01-29

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

06342279

ABSTRACT:

SUMMARY OF THE INVENTION
The invention relates to an electro-optical liquid-crystal display having a realignment layer for realigning the liquid crystals, where the field thereof has a significant component parallel to the liquid-crystal layer, containing a liquid-crystalline medium having positive dielectric anisotropy, where the medium comprises at least one mesogenic compound which contains a group of the formula I*
in which
L
1
is H or F.
In conventional liquid-crystal displays (TN, STN, OMI and AMD-TN), the electric fields for realignment are produced essentially perpendicular to the liquid-crystal layer.
International Patent Application WO 91/10936 discloses a liquid-crystal display in which the electric signals are produced in such a way that the electric fields have a component, suitably a significant parallel component, to the liquid-crystal layer (IPS, in-plane switching). The principles of operating such a display 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 discloses various ways of addressing such a display.
These IPS displays can be operated with liquid-crystalline materials either having a positive or a negative dielectric anisotropy (&Dgr;&egr;≠0). However, with the materials known hitherto, IPS displays have relatively high threshold voltages and long response times. The object was therefore to indicate liquid-crystalline materials which are suitable for achieving relatively low threshold voltages and short response times in IPS displays.
Surprisingly, this object has been achieved by using liquid-crystalline materials which comprise at least one compound which contains a laterally fluorinated 4-(cyclohexylcarbonyloxy)benzonitrile group.
Such compounds are disclosed, for example, in JP 58-210 057 and JP 4-279 560.
However, these specifications give no indication that these substances can be used to improve the threshold voltages and the response times of IPS displays.
The invention thus relates to an electro-optical liquid-crystal display having a realignment layer for realigning the liquid crystals, where the field thereof has a significant component parallel to the liquid-crystal layer, comprising a liquid-crystalline medium having positive dielectric anisotropy, where the medium comprises at least one mesogenic compound which contains a group of the formula I*
in which
L
1
is H or F.
Suitable mesogenic compounds typically include (but are not limited to) those having 2-4 ring groups connected in series by bridge groups, single bonds or combinations thereof, wherein terminal ring groups exhibit wing groups. Suitable ring groups include a 1,4-cyclohexenylene or trans-1,4-cyclohexylene radicals in which, in addition, one or more non-adjacent CH
2
groups may be replaced by —O— and/or —S—; 1,4-phenylene radicals in which,in addition, one or two CH groups may be replaced by N; or radicals 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. Ring groups, preferably 1,4-cyclohexylene or 1,4-phenylene, may be substituted, e.g., by one or more fluorine atoms.
Suitable bridge groups include, but are not limited to,:
—CO—O—, —O—CO—, —CH
2
O—, —OCH
2
—, —CH
2
CH
2
—, —CH═CH—, —C≡C —, a single bond, —(CH
2
)
4
— or —CH═CH—CH
2
CH
2
—.
Suitable wing groups include:
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, up to perhalo, wherein addition one or more CH
2
groups in these radicals may each, independently of one another be replaced by —O—, —S—,
—CO—, —CO—O— —O—CO— or —O—CO—C— in such a way that O atoms are not linked directly to one another.
The compound containing the group I* is suitably present in an amount of, e.g., 5-30%, preferably 7-20% by weight, although suitable amounts beyond these ranges are possible and routinely determinable.
Preferred embodiments are IPS displays in which
a) the medium comprises at least one compound of the formula II
in which
R
1
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, up to perhalo, 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—, —O—CO— or —O—CO—O— in such a way that O atoms are not linked directly to one another,
Q is a radical of the formula
—(O)
q
—(CH
2
)
r
—(CF
2
)
s
—
in which
q is 0 or 1,
r is 0 or an integer between 1 and 6, and
s is an integer between 0 and 6,
X is F or Cl, and, in the case where s≠0, is alternatively H, and
 A
1
and A
2
are each, independently of one another,
(a) a 1,4-cyclohexenylene or trans-1,4-cyclo-hexylene 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,
 L
2
and L
3
are each, independently of one another, H or F.
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— or a single bond, or one of the radicals Z
1
and Z
2
is alternatively —(CH
2
)
4
— or —CH═CH—CH
2
CH
2
—, and
m is 0, 1 or 2;
b) the medium comprises at least one compound of the formula I
 in which
L
1
is H or F, and
R
2
is as defined for R
1
;
c) the medium has a dielectric anisotropy &Dgr;&egr; of >8.5, preferably between 8.6 and 14, in particular between 8.7 and 13.5;
d) the medium comprises at least one compound of the formula III
R
3
—(A
3
—Z
3
)
0
—A
4
—R
4
  III
 in which
R
3
and R
4
are each, independently of one another, as defined for R
1
,
A
3
and A
4
are each, independently of one another, as defined for A
1
and A
2
,
Z
3
, is in each case independently of the others, as defined for Z
1
and Z
2
and,
O is 1, 2 or 3; or
e) the medium comprises at least one compound of the formula IV
 in which
R
5
is as defined for R
1
,
Z is a single bond or —COO—, and
L
4
and L
5
are each F or H,
but not of the formula I.
Particular preference is given to an IPS display in which the pixels are addressed by means of an active matrix.
The invention furthermore relates to a liquid-crystalline medium having positive dielectric anisotropy which comprises at least one compound of the formula II and at least one compound containing a group of the formula I*, e.g., a compound of formula I, in particular which preferably comprises, e.g.,
from about 60 to 95% by weight, more preferably from 70 to 90% by weight, of at least one compound of the formula II,
from about 5 to 30% by weight, more preferably from 7 to 20% by weight, of at least one compound of the formula I,
from about 5 to 20% by weight, more preferably from 7 to 15% by weight, of at least one compound of the formula III,
from about 1 to 10% by weight, more preferably from 2 to 8% by weight, of at least one compound of the formula IV.
The medium preferably comprises at least one compound selected from the formulae IIa, IIb and IIc:
 at least one compound selected from the formulae Ia and Ib:
 if desired at: least one compound selected from the formulae IIIa, IIIb and IIIc:
 and
 at least one compound selected from the formulae IVa to IVe:
 and
 Z
2
is —COO—, —CH
2
CH
2
— or a single bond, and R
1
, R
2
, R
3
, R
4
, R
5
, L
1
to L
5
are as defined in each case.
The novel liquid-crystalline media generally have a birefringence (&Dgr;n) of <0.12, preferably between 0.07 and 0.1, in particular between 0.075 and 0.09.
The flow viscosity (at 20° C.

Affiliated with

Also associated with

Rating

Electro-optical liquid-crystal does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Electro-optical liquid-crystal, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electro-optical liquid-crystal will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2856031