TN and HTN liquid-crystal display

Details TN and HTN liquid-crystal display TN and HTN liquid-crystal display

1999-11-29

2002-06-11

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

06403171

ABSTRACT:

The invention relates to TN (twisted nematic) and HTN (high performance twisted nematic) liquid-crystal displays having very short response times and good steepness values and angle dependencies, and to the nematic liquid-crystal mixtures used therein.
TN displays in accordance with the preamble are known, for example from M. Schadt and W. Helfrich, Appl. Phys. Lett., 18, 127 (1971). Owing to the limited steepness of their electro-optical characteristic line, TN displays are usually operated at low multiplex rates of, for example, from 1:2 to 1:4. For higher multiplex rates of, for example, 1:16 or more, STN (supertwisted nematic) displays are usually used; these have greater steepness values, but are more expensive and of more complex construction compared with TN displays.
A display type that has been developed recently is the so-called HTN display. This has a higher twisting angle, typically in the range from about 100 to 120°, compared with conventional TN displays. HTN displays allow better electro-optical properties to be achieved, such as, for example, a lower threshold voltage with lower temperature dependence, lower viewing-angle dependence of the contrast and in particular higher steepness values and thus higher multiplex rates, than in conventional TN displays for approximately the same costs. Compared with STN displays, HTN displays have the advantage of a simpler construction. They are therefore particularly suitable for applications in the region of low and moderate multiplex rates, such as, for example, 1:4, 1:8 or 1:16.
In order to achieve a steep electro-optical characteristic line in the liquid-crystal displays according to the invention, the liquid-crystal mixtures should have relatively small values for K
33
/K
11
and relatively small values for &Dgr;&egr;/&egr;
⊥
.
In addition to optimization of the contrast and response times, other important requirements are made of such mixtures:
1. Broad d/p window
2. High long-term chemical stability
3. High electrical resistance
4. Low frequency dependence of the threshold voltage.
The parameter combinations achieved are nowhere near sufficient, in particular for highly twisted displays (HTN). This is in part attributable to the fact that the various requirements are influenced in opposite directions by material parameters.
There thus continues to be a great demand for TN and HTN liquid-crystal displays having a large working-temperature range, high characteristic-line steepness, good angle dependence of the contrast, low threshold voltage and high low-temperature stability which satisfy the abovementioned requirements.
The invention has the object of providing liquid-crystal displays which do not have the abovementioned disadvantages, or only do so to a lesser extent, and at the same time have short response times and very good steepness values.
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.
It has now been found that these objects can be achieved if use. is made of nematic liquid-crystal mixtures which comprise compounds of the formula IA in combination with compounds of the formula IC:
in which
R
1
to R
3
are each, independently of one another, an alkyl group having 1 to 12 carbon atoms, in which, in addition, one or two non-adjacent CH
2
groups may be replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO—,
L
1
is H or F ,
z is —COO—, —CH
2
CH
2
— or a single bond,
 are each, independently of one another,
 and
c is 0 or 1.
The liquid-crystal media according to the invention have a low viscosity with low temperature dependence, long storage times in the display at low temperatures and low S-N transitions.
In particular, the combination of the compounds of the formulae IA and IC effect a significant reduction in the threshold voltage in TN and HTN displays at the same time as increasing the steepness and increasing the low-temperature stability.
The invention thus relates to a liquid-crystal display having
two outer plates which, with a frame, form a cell,
a nematic liquid-crystal mixture of positive dielectric anisotropy in the cell,
electrode layers with alignment layers on the insides of the outer plates,
a tilt angle between the longitudinal axis of the molecules at the surface of the outer plates and the outer plates of from 0 degrees to 15 degrees, and
a twist angle of the liquid-crystal mixture in the cell from alignment layer to alignment layer with a value of between 22.5° and 160°,
a nematic liquid-crystal mixture containing:
a) 10-80% by weight of a liquid-crystalline Component A consisting of one or more compounds having a dielectric anisotropy of greater than +1.5;
b) 15-70% by weight of a liquid-crystalline Component B consisting of one or more compounds having a dielectric anisotropy of between −1.5 and +1.5;
c) 2-50% by weight of a liquid-crystalline Component C consisting of one or more compounds having a dielectric anisotropy of below −1.5, and
d) if desired, an optically active Component D in such an amount that the ratio between the layer thickness (separation of the outer plates) and the natural pitch of the chiral nematic liquid-crystal mixture is from about 0.2 to 1.3,
characterized in that Component A comprises at least one compound of the formula IA
and Component C comprises at least one compound of the formula IC
 in which
R
1
to R
3
are each, independently of one another, an alkyl group having 1 to 12 carbon atoms, in which, in addition, one or two non-adjacent CH
2
groups may be replaced by —CO—, —CH═CH—, —CO—, —OCO— or —COO—,
L
1
is H or F,
Z is —COO—, —CH
2
CH
2
— or a single bond,
 are each, independently of one another,
 and
c is 0 or 1.
The invention also relates to corresponding liquid-crystal mixtures for use in TN and HTN displays.
Preferred compounds of the formula IA are, in particular, compounds of the sub-formulae IA-1 and IA-2
in which alkyl is straight-chain alkyl having 1 to 5 carbon atoms.
Preferred compounds of the formula IC are, in particular, compounds of the following sub-formulae:
in which alkyl is straight-chain alkyl having 1 to 5 carbon atoms, and d is 0 or 1, in particular 1.
In a preferred embodiment, the liquid-crystal mixtures according to the invention additionally comprise one or more compounds of the formula IB
in which R
3
is as defined under the formula IC, k is 0 or 1, and R* is alkenyl having 2 to 12, preferably 2 to 8 carbon atoms.
In particular, the use of compounds of the formula IC results in TN and HTN displays having a high steepness the electro-optical characteristic line and good low-temperature stability.
Component A, besides the compounds of the formula IA, preferably comprises one or more compounds of the formulae II and III
in which
R is as defined for R
1
under the formula IA,
 are each, independently of one another,
L
1
to L
6
are each, independently of one another, H or F
Z
1
is —COO—, —CH
2
CH
2
— or a single bond,
Z
2
is —CH
2
CH
2
—, —COO—, —C≡C— or a single bond,
Q is —CF
2
—, —CHF—, OCF
2
—, —OCHF— or a single bond,
Y is F or Cl,
a is 1 or 2, and
b is 0 or 1.
Preferred compounds of the formulae II and III conform to the following sub-formulae:
in which R, L
3
, and L
4
are as defined above, and Alkyl′ is H or straight-chain alkyl having 1 to 4 carbon atoms.
In addition to one or more compounds of the formulae IA and IC, preferred mixtures comprise two or more compounds of the formula IIa, IIb, IIc, IId, IIf, IIIb, IIId or IIIi, preferably one or more compounds of the formula IIa, IIb or IIc.
Preferred liquid-crystalline mixtures according to the invention comprise from 10% to 80%, in particular from 20% to 60%, of one or more compounds from Component A.
The compounds of Component A preferably have a dielectric anisotropy of greater than +3 (in particular greater than +8, particularly preferably greater than +12).
The mixtures according to the invention preferably comprise one or more compounds of the formula

Affiliated with

Also associated with

Rating

TN and HTN liquid-crystal display does not yet have a rating. At this time, there are no reviews or comments for this patent.

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

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2891517