Liquid crystalline medium and liquid crystal display

Details Liquid crystalline medium and liquid crystal display Liquid crystalline medium and liquid crystal display

2002-09-30

2004-09-21

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

06793985

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to liquid crystalline media and to liquid crystal displays comprising these media, especially to displays addressed by an active matrix and in particular to displays of the In Plane Switching (IPS) type.
PROBLEM TO BE SOLVED AND STATE OF THE ART
Liquid Crystal Displays (LCDs) are widely used to display information. Electro-optical modes employed are, e.g., the twisted nematic (TN)-, the super twisted nematic (STN)-, the optically compensated bend (OCB)- and the electrically controlled birefringence (ECB)-mode with their various modifications, as well as others. Besides these modes, which all do use an electrical field, which is substantially perpendicular to the substrates, respectively to the liquid crystal layer, there are also electro-optical modes employing an electrical field substantially parallel to the substrates, respectively the liquid crystal layer, like, e.g., the In-Plane Switching mode (as disclosed, e.g., in DE 40 00 451 and EP 0 588 568). Especially this electrooptical mode is used for LCDs for modern desk top monitors and is envisaged to be applied for displays for multi media applications. The liquid crystals according to the present invention are preferably used in this type of displays.
For these displays new liquid crystalline media with improved properties are required. Especially the dielectric anisotropy (&Dgr;∈) should be high enough to allow a reasonably low operation voltage. Preferably &Dgr;∈ should be higher than 7 and very preferably be higher than 10, preferably, however, not higher than 25 and in particular not higher than 20. Otherwise the resistivity of the mixtures tends to become unacceptably low even for IPS displays, which do have slightly less stringent requirements in this respect than TN-AMDs. Besides this parameter, the media have to exhibit a suitably wide range of the nematic phase, a rather small birefingence (&Dgr;n), a rather small rotational viscosity and, as mentioned above, an at least a moderately high specific resistivity.
The displays according to the present invention are preferably addressed by an active matrix (active matrix LCDs, short AMDs), preferably by a matrix of thin film transistors (TFTs). However, the inventive liquid crystals can also beneficially be used in displays with other known addressing means.
There are various different display modes using composite systems of liquid crystal materials of low molecular weight together with polymeric materials such as, e.g., polymer dispersed liquid crystal (PDLC)-, nematic curvilinearily aligned phase (NCAP)- and polymer network (PN)-systems, as disclosed, for example, in WO 91/05 029 or axially symmetric microdomain (ASM) systems and others. In contrast to these, the modes especially preferred according to the instant invention are using the liquid crystal medium as such, oriented on surfaces. These surfaces typically are pretreated to achieve uniform alignment of the liquid crystal material. The display modes according to the instant invention preferably use an electrical field substantially parallel to the composite layer.
LCDs are used for direct view displays, as well as for projection type displays.
Liquid crystal compositions suitable for LCDs and especially for IPS displays are known, e.g., from JP 07-181 439 (A), EP 0 667 555, EP 0 673 986, DE 195 09 410, DE 195 28 106, DE 195 28 107, WO 96/23 851 and WO 96/28 521. These compositions, however, do have significant drawbacks. Most of them have, amongst other deficiencies, too low values of the resistivity and/or require operation voltages which are too high. Many of them also lead to unfavourably long response times.
Thus, there is a significant need for liquid crystalline media with suitable properties for practical applications such as a wide nematic phase range, low viscosities, appropriate optical anisotropy &Dgr;n, according to the display mode used, and especially a high &Dgr;∈.
PRESENT INVENTION
Surprisingly, it now has been found that liquid crystalline media with a suitably high &Dgr;∈, a suitable phase range, and a suitable &Dgr;n can be realized, which do not exhibit the drawbacks of the materials of the prior art or at least do exhibit them to a significantly lesser degree.
These improved liquid crystalline media according to the instant application are comprising at least the following components:
a dielectrically positive component, component A, comprising one or more dielectrically positive compounds selected from formula I and preferably further comprising one or more dielectrically positive compounds selected from the group of formulae II and III
wherein
R
1
, R
2
and R
3
independently of each other, are alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy with 1 to 7 C-atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7 C-atoms,
X
1
, X
2
and X
3
independently of each other, are F or fluorinated alkyl or fluorinated alkoxy, each with 1 to 4 C-atoms,
L
11
, L
12
, L
13
, L
31
, L
32
and L
33
are, independently of each other, H or F.
optionally a dielectrically neutral component, component B, and
also optionally a dielectrically negative component, component C.
Preferably, the dielectrically positive component, component A comprises one or more compounds each of formulae I, II and III.
Preferably, the compounds of formula II are selected from formula IIa
wherein R
2
has the meaning given in formula II.
Preferably the compounds of formula III are selected from the group of compounds of formulae IIIa to IIIc.
wherein R
3
and X
3
have the meanings given in formula III and X
3
is preferably F.
Preferably, the liquid crystal mixtures according to the present invention comprise a component A which, in addition to the compounds of formula I, and, optionally, compounds of formulae II and/or III, comprise one or more compounds of formula IV
wherein
independently of each other, and in case
 is present twice, also these, independently of each other, are
preferably at least one of
 is
 and preferably
Z
41
and Z
42
are, independently of each other, and in case Z
41
is present twice, also these independently of each other, —CH
2
CH
2
—, —COO—, trans- CH═CH—, trans- CF═CF—, —CH
2
O—, —CF
2
O— or a single bond, preferably at least one of them is a single bond and most preferably, if present, at least two of them are a single bond,
X
4
is F, Cl, halogenated alkyl, halogenated alkoxy, halogenated alkenyl or halogenated alkenyloxy, wherein halogenated preferably is fluorinated and/or chlorinated, preferably fluorinated and preferably X
4
is F, OCF
3
or OCF
2
H,
R
4
has one of the meanings given for R
1
in formula I, and
n is 0, 1 or 2, preferably 0 or 1.
Especially preferred component A comprises, preferably predominantly consists of, and most preferably entirely consists of compounds selected from the group of compounds of formulae I to IV.
Preferably, the liquid crystal mixtures according to the present invention do contain at least one further component besides component A. This second component may be component B or component C, preferably the second component present is component B.
Obviously, the mixtures according to the present invention also can contain the third one of these components, component C or B, as the case may be.
Preferably, the liquid crystal mixtures according to the present invention comprise a dielectrically neutral component (component B). This component has a dielectric anisotropy in the range from −1.5 to +3 and consists of compounds which have values in this range. Preferably it comprises, preferably predominantly consists of and most preferably entirely consists of compounds of formula V
wherein
R
51
and R
52
, independently of each other, have the meaning given for R
1
under formula I above,
 independently of each other, and in case
 is present twice, also these, independently of each other, are
 preferably at least one of
 is
Z
51
and Z
52
are, independently of each other, and in case Z
51
is p

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