Stock material or miscellaneous articles – Liquid crystal optical display having layer of specified...
Reexamination Certificate
1999-09-13
2002-04-23
Wu, Shean C. (Department: 1756)
Stock material or miscellaneous articles
Liquid crystal optical display having layer of specified...
C252S299010, C252S299610, C252S299630, C252S299640, C252S299650, C252S299660, C252S299670
Reexamination Certificate
active
06376030
ABSTRACT:
The invention relates to nematic liquid-crystal compositions of negative dielectric anisotropy (&Dgr;∈) based on substituted 2,3-difluorophenylene, in particular based on substituted 4-(trans-1,4-cyclo-hexylene)-2,3-difluorophenylene, and substituted trans-4-(trans-1,4-cyclohexylene) cyclohexylenecarboxylic esters. These compositions are particularly suitable for plasma-addressed display devices.
Plasma-addressed displays (PADs) are of great utility for economically interesting high-information displays. Such PADs are used, for example, in TV applications and, for example in displays for computer screens, automobiles and aircraft.
PADs have electrical switching elements and a plasma cell with a plurality of addressing channels which is connected to the display cell. Such PADs are disclosed, for example, in WO 96/00925, EP 0 628 944, EP 0 545 569, U.S. Pat. No. 4,896,149 and U.S. Pat. No. 5,077,553.
In a PAD, the switching elements are addressed by means of a time multiplexing scheme. This charges the electrodes of a pixel in the limited time during which they are active. They subsequently become and remain inactive until they are addressed again in the next cycle. Consequently, the change in voltage at a plasma-addressed pixel in this inactive time is a not undesired, but very crucial characteristic of such a display. Discharge of the electrodes of the pixel is determined by two factors, namely the capacitance of the pixel (C) and the specific resistance of the liquid-crystal material between the electrodes (R), i.e. of the liquid crystal. The time constant for the experimental drop in voltage is proportional to RC and is known as the RC time.
PADs make particular demands of the dielectric properties of the liquid-crystal compositions. Both &Dgr;∈, as in conventional TFT-AMDs, and ∈
∥
and ∈
⊥
are of crucial importance here. This applies both to PADs in TN mode and in particular to those in ASM mode. Since PADs can be produced in considerably larger screen diagonals compared with conventional active matrix displays (AMDs) with, for example, thin-film transistors (TFTs) as active switching elements, they are suitable, as the first liquid-crystal displays ever, for achieving the long-held target of a wall-hung TV set (Buzak, Information Display 4 & 5 (1998, pp. 22 ff.). TV sets with PADS having a 25 inch diagonal are commercially available and prototypes of displays with a 42 inch screen diagonal have already been produced (Burgmans, Kakizaki and Uede, Information Display 4 & 5 (1998), pp. 14 ff.). With these large screen diagonals, the problem of the relatively high dependence of the contrast and the hue on the viewing angle, often abbreviated to the viewing angle dependence, of the conventionally utilized effect of the twisted nematic (TN) cell becomes predominant. At least with these screen diagonals, but generally already for screen diagonals in the range from 17 to 20 inches, the viewing-angle dependence of TN displays is prohibitive for market success. For this reason, work has been in progress for some time on various solutions for improving the viewing-angle dependence. For PADs, the use of the so-called axially symmetrically aligned microcell (ASM), which allows a viewing-angle range of 140° both horizontally and vertically, is particularly suitable (Burgmans et al.). In particular for ASM-PADs, dielectrically negative liquid-crystal media are suitable. It is now been found that liquid-crystal materials of negative dielectric anisotropy are suitable for ASM-PADs.
It has been found that liquid crystals of negative &Dgr;∈ are particularly suitable for PADs in ASM mode.
There is thus a great demand for liquid-crystal compositions having high specific resistance and other material properties suitable for use in PADs, in particular in. ASM-PADs, such as, for example, a broad nematic mesophase range with an extremely low smectic-nematic transition temperature and no crystallization at low-temperature, and negative dielectric anisotropy.
A further requirement in such compositions is for a low steepness of the characteristic lines (large difference between V
90
and V
10
) for addressing grey shades, where a greater addressing voltage, for example compared with TN-AMDs, can be accepted.
An object of the invention is to provide liquid-crystal compositions of very high specific resistance which also satisfy the other requirements.
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.
An additional requirement is for compositions of low An values of ≦0.1, preferably ≦0.09, particularly preferably ≦0.08, and rotational viscosities of ≦150 mpa·s at 20° C., preferably ≦120 mPa·s, in particular ≦100 mPa·s.
It has now been found that nematic liquid-crystal compositions for plasma-addressed liquid-crystal displays (PALCDs) comprising at least one compound of the formula I
in which
R
11
and R
12
, independently of one another, are alkyl or alkoxy having 1 to 8, preferably 1 to 5, carbon atoms or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 8, preferably 2 to 5, carbon atoms,
Z
11
and Z
12
, independently of one another, and if more than one Z
11
are present, these too independently of one another, are a single bond, —(CH
2
)
2
—, trans—CH═CH— or —CH
2
O—,
A
11
and A
12
, independently of one another, and if more than one A
11
are present, these too independently of one another, are
trans-1,4-cyclohexylene, 1,4-cyclohexenylene, in which, in addition, 1 or 2 non-adjacent —CH
2
—groups may be replaced by oxygen atoms, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,3 difluoro-1,4-phenylene, 3,5-difluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene or 1,5-pyridyl or 1,5-pyrimidyl, in which one or two H atoms may be replaced by F,
where preferably at least one of the rings A
11
and A
12
is a trans-1,4-cyclohexylene ring and particularly preferably two of the rings A
11
and A
12
are trans-1,4-cyclohexylene, and
n is 0, 1 or 2, preferably 0 or 1,
are particularly suitable for PAD applications.
In PADs, very high values for the RC time, i.e. the time constant for discharge of the pixel electrodes, can be achieved. The high values for the RC time, or the voltage holding ratio, which corresponds to this quantity, are achieved on one hand by a thin installation sheet, but on the other hand are also determined essentially by the type and composition of the liquid-crystal material used. These compositions likewise have reduced viscosity and exhibit no crystallization and no smectic phases at temperatures down to −20° C., preferably at temperatures down to −30° C., particularly preferably at temperatures down to −40° C., when stored in test TN-cells with a layer thickness corresponding to an optical retardation of about 0.5 &mgr;m format least 100 hours. They can preferably be stored for at least 500 hours, very particularly preferably for at least 1000 hours.
Preference is furthermore given to liquid-crystal mixtures comprising at least one compound of the formula II
in which
R
21
and R
22
, independently of one another, are alkyl or alkyloxy having 1 to 8, preferably 1 to 5, carbon atoms or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 8, preferably 2 to 5, carbon atoms, and
A
21
is trans-1,4-cyclohexylene, 1,4-phenylene, 3-fluoro-1,4-phenylene, 2-fluoro-1,4-phenylene or 2,3-difluoro-1,4-phenylene.
Particular preference is given to nematic liquid-crystal compositions which comprise at least one compound of the formula III
in which
R
31
and R
32
, independently of one another, are alkyl or alkyloxy having 1 to 8, preferably 1 to 5, carbon atoms or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 8, particularly preferably 2 to 5, carbon atoms,
are each, independently of one another,
and, if more than one
is present, these too independently of one another, are trans-1,4-cyclohexylene, 1,4-phenylene, 3-fluoro-1,4-phenylene or 2-fluoro-1,4-phenylene, and
Z
31
, Z
32
and Z
33
, ea
Heckmeier Michael
Reuter Marcus
Merck Patent Gesellschaft mit beschrankter Haftung
Wu Shean C.
LandOfFree
Nematic liquid-crystal composition, and 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 Nematic liquid-crystal composition, and liquid-crystal..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nematic liquid-crystal composition, and liquid-crystal... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2867708