Supertwist liquid crystal display

Details Supertwist liquid crystal display Supertwist liquid crystal display

1998-12-08

2001-04-03

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299610, C252S299630, C252S299660, C252S299670, C349S186000

Reexamination Certificate

active

06210760

ABSTRACT:

The invention relates to supertwist liquid crystal displays (SLCD) having very short switching times and good gradients and angular dependencies and the new nematic liquid crystal mixtures used in these.
SLCD according to the precharacterizing clause are known, for example, from EP 0,131,216 B1; DE 34 23 993 A1; EP 0,098,070 A2; M. Schadt and F. Leenhouts, 17. Freiburger Arbeitstagung Flussigkristalle (17th Freiburg Conference on Liquid Crystals) (8.-10.04.87); K. Kawasaki et al., SID 87 Digest 391 (20.6); M. Schadt and F. Leenhouts, SID 87 Digest 372 (20.1); K. Katoh et al., Japanese Journal of Applied Physics, Vol. 26, No. 11, L 1784-L 1786 (1987); F. Leenhouts et al., Appl. Phys. Lett. 50 (21), 1468 (1967); H. A. van Sprang and H. G. Koopman, J. Appl. Phys. 62 (5), 1734 (1987); T. J. Scheffer and J. Nehring, Appl. Phys. Lett. 45 (10), 1021 (1984), M. Schadt and F. Leenhouts, Appl. Phys. Lett. 50 (5), 236 (1987) and E. P. Raynes, Mol. Cryst. Liq. Cryst. Letters Volume 4 (1), pages 1-8 (1986). The term SLCD here includes any highly twisted display element having a twisting angle, according to the content, of between 160° and 360°, such as, for example, the display elements according to Waters et al. (C. M. Waters et al., Proc. Soc. Inf. Disp. (New York) (1985) (3rd Intern. Display Conference, Kobe, Japan), and the STN-LCDs (DE OS 35 03 259), SBE-LCDs (T. J. Scheffer and J. Nehring, Appl. Phys. Lett. 45 (1984) 1021), OMI-LCDs (M. Schadt and F. Leenhouts, Appl. Phys. Lett. 50 (1987), 236), DST-LCDs (EP OS 0 246 842) or BW-STN-LCDs (K. Kawasaki et al., SID 87 Digest 391 (20.6)).
In contrast to standard TN displays, such SLCD are distinguished by considerably better gradients of the electrooptical characteristic line and associated better contrast values, as well as by a considerably lower angular dependency of contrast. SLCD having short switching times, especially also at lower temperatures, are of particular interest. To achieve short switching times, the viscosities of the liquid crystal mixtures in particular have hitherto been optimized using usually monotropic additives of relatively high vapor pressure. However, the switching times achieved were not adequate for every use.
There is thus still a great demand for SLCD having very short switching times with a simultaneously high working temperature range, high characteristic line gradient, good angular dependency of the contrast and low threshold voltage.
The invention is based on the object of providing SLCD which have the abovementioned disadvantages to only a minor degree, if at all, and at the same time have very short switching times.
It has now been found that this object can be achieved if nematic liquid crystal mixtures containing the following components:
a) at least one component chosen from group A, consisting of compounds of the formulae AI to AVI:
wherein R
1
and R
2
each independently of one another are each R and
R is alkyl having 1-12 C atoms, wherein one or two non-adjacent CH
2
groups can also be replaced by —O—, —CH═CH—, —CO—, —O—CO— or —CO—O—,
b) at least one component chosen from group B1, consisting of the compounds of the formulae BI to BIV:
wherein R
1
and R
2
each independently of one another have the meaning given for R, Z
2
is —CH
2
CH
2
, —CO—O—, —O—CO— or a single bond and
and/or at least one component chosen from group B2, consisting of the compounds of the formulae BV to BVII:
wherein R
1
has the meaning given for R,
Z
0
is —CH
2
CH
2
— or a single bond and
wherein n is 1 to 9, X is CN or F and Y is H or F, and/or at least one component chosen from group B3, consisting of the compounds of the formulae BVIII and BIX:
wherein R
1
and R
2
each independently of one another have the meaning given for R and
c) 10-80% by weight of a liquid crystal component C, consisting of one or more compounds having a dielectric anisotropy of more than +1.5,
d) 0-20% by weight of a liquid crystal component D, consisting of one or more compounds having a dielectric anisotropy of less than −1.5 and
e) an optically active component E, in an amount such that the ratio between the layer thickness (separation of the plane-parallel carrier plates) and the natural pitch of the nematic liquid crystal mixture is about 0.2 to 1.3,
are used.
The invention thus relates to an SLCD having
two plane-parallel carrier plates which, with an edging, form a cell,
a nematic liquid crystal mixture of positive dielectric anisotropy in the cell,
electrode layers with superimposed orientation layers on the insides of the carrier plates,
an angle of incidence between the longitudinal axis of the molecules on the surface of the carrier plates and the carrier plates of about 1 degree to 30 degrees and
a twisting angle of the liquid crystal mixture in the cell from orientation layer to orientation layer, according to the amount, of between 160 and 360°, characterized in that the nematic liquid crystal mixture contains
a) at least one component chosen from group A, consisting of compounds of the formulae AI to AVI:
wherein R
1
and R
2
each independently of one another are each R and
R is alkyl having 1-12 C atoms, wherein one or two non-adjacent CH
2
groups can also be replaced by —O—, —CH═CH—, —CO—, —O—CO— or —CO—O—,
b) at least one component chosen from croup B1, consisting of the compounds of the formulae BI to BIV:
wherein R
1
and R
2
each independently of one another have the meaning given for R, Z
2
is —CH
2
CH
2
, —CO—O—, —O—CO— or a single bond and
and/or at least one component chosen from group B2, consisting of the compounds of the formulae BV to BVII:
wherein
R
1
has the meaning given for R,
Z
0
is —CH
2
CH
2
— or a single bond and
wherein n is 1 to 9, X is CN or F and Y is H or F, and/or at least one component chosen from group B3, consisting of the compounds of the formulae BVIII and BIX:
wherein R
1
and R
2
each independently of one another have the meaning given for R and
c) 10-80% by weight of a liquid crystal component C, consisting of one or more compounds having a dielectric anisotropy of more than +1.5,
d) 0-20% by weight of a liquid crystal component D, consisting of one or more compounds having a dielectric anisotropy of less than −1.5 and
e) an optically active component E, in an amount such that the ratio between the layer thickness (separation of the plane-parallel carrier plates) and the natural pitch of the nematic liquid crystal mixture is about 0.2 to 1.3, and
in that the nematic liquid crystal mixture has a nematic phase range of at least 60° C., a viscosity of not more than 30 mpa.s and a dielectric anisotropy of at least +5, the dielectric anisotropies of the compounds and the parameters relating to the nematic liquid crystal mixture being based on a temperature of 20° C.
The invention also relates to corresponding liquid crystal mixtures for use in SLCD.
The individual compounds of the formulae AI to AVI, BI to BIV and CI to CIII or other compounds which can be used in the SLCD according to the invention are either known or can be prepared analogously to the known compounds.
Preferred liquid crystal mixtures which can be used according to the invention contain one or more compounds from group A in an amount of 4% to 40%, preferably 10% to 32%. Compounds of the formula AIII to AVI are preferred. In a particularly preferred embodiment, the mixtures simultaneously contain (a) compounds of the formula AV and/or AVI and (b) compounds of the formula AIII and/or AIV. R
1
and R
2
preferably in each case independently of one another are n-alkyl having 1 to 7 C an atoms or (trans)-n-alkenyl having 3 to 7 C atoms.
The content of component(s) from group B1 is preferably 5% to 45%, particularly preferably about 10% to 40%. Components of the formulae BIII and BIV are preferred. Particularly preferred compounds of the formula BIII are those of the following part formulae:
wherein
R
1
is CH
3
—(CH
2
)
n
—O—, CH
3
—(CH
2
)
t
—, trans-H-(CH
2
)
r
—CH═CH—(CH
2
CH
2
)
n
—CH
2
O— or trans-H-(CH
2
)
r
)—CH═CH—(CH
2
CH
2
)
S
—,
R
2
is CH
3
—(CH
2
)
t

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