Compositions – Liquid crystal compositions – Containing nonsteryl liquid crystalline compound of...
Reexamination Certificate
2000-07-24
2002-12-24
Wu, Shean C. (Department: 1756)
Compositions
Liquid crystal compositions
Containing nonsteryl liquid crystalline compound of...
C252S299660, C252S299670, C252S299610
Reexamination Certificate
active
06497828
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to nematic liquid-crystal compositions based on bisalkenyl compounds and terminally fluorinated compounds. These compositions are particulary suitable for plasma-addressed display devices.
Plasma-addressed displays (PADs) are of great utility for high-information displays, which are of commercial interest. Such PADs are used in TV applications and in high-information 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 via a 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 voltage change at a plasma-addressed pixel is an unwanted, but very crucial characteristic of such a display. Discharge of the electrodes of the pixel is determined by two factors, the capacity of the pixel and the specific resistance of the liquid-crystal material, i.e., the liquid crystal, between the electrodes.
Conventional liquid-crystalline materials for active matrix displays (AMDs) are unsuitable for PADs since they have excessively high values for the dielectric anisotropy.
There therefore continues to be a great demand for liquid-crystal compositions having high specific resistance and having other material properties which are suitable for use in PADs, such as, for example, a broad nematic mesophase range with an extremely low smectic-nematic transition temperature and the absence of crystallization at low temperature.
A further requirement in such compositions is for high steepness of the characteristic lines (small difference between V
90
and V
10
).
SUMMARY OF THE INVENTION
An object of the invention is to provide liquid-crystal compositions which have very high specific resistance and which also satisfy the other requirements.
An additional requirement is for compositions having low &Dgr;n values of <0.1 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
1
and R
2
, independently of one another, are alkenyl or alkenyloxy having 1 to 8 carbon atoms,
each Z
1
and Z
2
, independently of one another, and if Z
1
is present a number of times, these radicals also independently of one another, are a single bond, —(CH
2
)
2
— —COO—, —OCO—, trans-CH═CH—, —CH
2
O— or —OCH
2
—, where Z
2
is preferably a single bond,
each A
1
, A
2
and A
3
, independently of one another, and if A
1
is present a number of times, these radicals also independently of one another, are trans-1,4-cyclohexylene, 1,4-cyclohexenylene, in which also one or two nonadjacent CH
2
groups may be replaced by oxygen, 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 are optionally replaced by F,
where at least one of the rings A
2
is preferably a trans-1,4-cyclohexylene rings, and particularly preferably both rings A
2
and A
3
are trans-1,4-cyclohexylene, and
n is 0, 1 or 2,
are particularly suitable for PAD applications. Z
2
is preferably a single bond, and at least one of the rings A
2
and A
3
is preferably a trans-1,4-cyclohexylene ring. Particularly preferably, both rings A
2
and A
3
are trans-1,4-cyclohexylene. In PADs, very high values for the RC time (i.e., the time constant for the discharge of the pixel electrodes) can be achieved. These compositions likewise have reduced viscosity and enable AMDs to be operated at the first transmission minium, and exhibit no crystallization and no occurrence of smectic phases when stored in test cells of appropriate cell gap for times of at least 100 hours preferably 500 hours and most preferably 1000 hours at a temperature of −20° C., preferably at −30° C. and most preferably of −40° C.
Preference is furthermore given to liquid-crystal mixtures which comprise at least one compound of the formula II
in which
R
3
is alkyl, alkenyl, alkyloxy or alkenyloxy having 1-8 carbon atoms,
Z
3
and Z
4
, independently of one another, are a single bond, (CH
2
)
2
, OCH
2
, CH
2
O, COO, CN, F, CF
2
H or CF
3
X is OCF
2
H, OCF
3
, OCH
2
CF
3
, OCHFCF
3
, OCF
2
CF
2
H or F
L is H or F and
A
4
is trans-1,4-cyclohexylene, 1,4-phenylene, 3-fluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene.
Particular preference is given to nematic liquid-crystal compositions which comprise at least one compound of the formula Ia
in which
R
1
and R
2
, independently of one another, are alkenyl or alkenyloxy having 1 to 8 carbon atoms,
and
Z
2
is a single bond, —(CH
2
)
2
— or trans-CH═CH—.
Z
2
is particularly preferably a single bond.
Nematic liquid-crystal compositions of the present invention furthermore preferably comprise at least one compound of the formula III
in which
R
4
and R
5
1
independently of one another,
are alkyl, alkoxy, alkenyl or alkenyloxy having 1 to 10 carbon atoms, in which 1 or a maximum of 2 non-adjacent CH
2
groups may be replaced by O,
each Z
5
if it is present a number of times independently of one another, is a single bond, COO, OCO, (CH
2
)
2
, OCH
2
, CH
2
O or trans-CH═CH,
each A
5
and A
6
independently of one another, and if A
5
is present a number of times these radicals also independently of one another,
are trans-1,4-cyclohexylene, 1,4-cyclohexenylene, in which also one or two nonadjacent CH
2
groups may be replaced by oxygen, 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-pyrimidinediyl, in which one or two H atoms are optionally replaced by F, and
n is 1, 2 or 3.
Very particular preference is given to nematic liquid-crystal compositions which comprise at least one compound of the formula Iaa
in which
R
1
and R
2
, are each, independently of one another, CH═CH
2
, CH═CH—CH
2
—CH
3
and/or CH═CH—CH
3
and
Z
2
is (CH
2
)
2
or a single bond.
Z
2
is preferably a single bond and R
1
and R
2
are preferably identical to each other.
Preference is furthermore given to nematic liquid-crystal compositions which, besides compounds of the formula Iaa, comprise at least one further compound of the formula I
and/or of the formula II
In a preferred embodiment, the compositions according to the invention comprise from 10 to 34% of two or more compounds of the formula I.
The nematic compositions particularly preferably comprise at least two compounds of the formula Iaa from the group consisting of the formulae Ia1 to 1a9:
The symmetrically substituted compounds of the formula Iaa, i.e., the compounds Ia1, Ia3, Ia5 and Ia8, are preferred, and of these, very particular preference is given to the 1-alkenyl compounds Ia1, Ia3 and Ia5. The best response times are achieved when using Ia1, Ia2 and Ia3. The most preferred compounds are those of the formulae Ia1 and Ia5.
The LC compositions according to the invention have a dielectric anisotropy, measured at 20° C. and 1 kHz, of less than 4.0, preferably between 1.0 and 3.0, in particular from 1.5 to 2.5. The LC compositions according to the instant invention have a birefringence at 20° C. and 589 nm of not more than 0.1, preferably not more than 0.08, especially preferred of not more than 0.075 and most preferred of below 0.07. The voltage holding ratio HR after 5 minutes at 100° C. and IV using a commercial equipment of Antronic-Melchers, Germany, is at least 98%, preferably higher than 98.5%, especially preferred higher than 99.0% and most preferr
Hirschmann Harald
Reuter Marcus
Schüpfer Sven
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