Compositions – Liquid crystal compositions
Patent
1997-12-22
1999-05-18
Wu, Shean C.
Compositions
Liquid crystal compositions
25229963, 25229967, C09K19/52;19/30;19/20
Patent
active
059048760
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a nematic liquid-crystal composition based on terminally and laterally fluorinated compounds and dielectrically neutral compounds. This composition is especially useful for plasma-addressed display devices.
Plasma-addressed displays (PAD) are highly favored for commercially interesting displays with a high information content. Such PADs are used for TV application and also for displays with high information content for computer terminals, automobiles and aeroplanes.
PADs have electrical switching elements, a plasma cell associated with the display cell with a plurality of addressing channels.
Such PADs are disclosed for example in EP 0 628 944, EP 0 545 569, U.S. Pat No. 4,896,149 and U.S. Pat. No. 5,077,553.
In PADs the switching elements are addressed in a multiplex scheme. So they charge the electrodes of a pixel in the limited time they are active. Then they become inactive until they are addressed again in the next cycle. Consequently the change of the voltage on a plasma addressed pixel is a nondesired but a very decisive feature of such a display. The discharge of the electrodes of the pixel and resistivity of the dielectric material between the electrodes, namely the liquid crystal.
Conventional liquid crystalline materials for active matrix displays are not suitable for PADs, since they have to high values of birefringence and dielectric anisotropy.
There is thus still a great need for liquid-crystal composition having a high resistivity and other suitable material properties for use in PADs such as a broad nematic mesophase range with an extremely low transition temperature smectic-nematic and no crystallization at low temperature.
The invention has for its object to provide a liquid-crystal composition with a very high resistivity which meets also the other demands.
In addition, most of the conventional liquid-crystalline compositions for AMD applications have a birefringence An .DELTA.n>0.08. There is a demand for compositions with low values of .DELTA.n, preferably with .DELTA.n<0.07 and viscosities of <20 mm s.sup.-1 at 20.degree. C.
It has now been found that a nematic liquid-crystal composition comprising: consisting of ##STR1## in which R.sup.1 is a straight-chain alkyl group of 1 to 5 carbon atoms, ##STR2## in which R.sup.2 and R.sup.3 are each independently a straight-chain alkyl or alkoxy group of 1 to 5 carbon atoms, ##STR3## n is 0 or 1. is highly suited for PAD application. Very high RC time values can be obtained in PADs. These compositions also show a reduced viscosity, allow operation in AMDs in the first minimum of transmission and do not exhibit any crystallization at -30.degree. C.
The inventive LC compositions exhibit a dielectric anisotropy of less than 4.0, preferably between 1.0 and 3.0 in particular 1.5 to 2.5. The clearing point of the compositions according to the invention is higher than 85.degree. C. in particular higher than 90.degree. C.
Such compositions preferably contain two, three or four compounds from group 1. Preferred compositions comprise more than 20% by weight of one or more compounds from group 1.
The compounds from group 1 are known from the European Patent Applns. 0 387 032 and 0 280 902, the European Patents 0 051 738 and 0 125 653, the International Patent Applications WO 89/02884 and WO 85/048874 and U.S. Pat. No. 4,302,352, U.S. Pat. No. 4,710,315 and U.S. Pat. No. 4,419,264 or can be prepared in analogy to known compounds.
The compounds from group 2 are known for example from DE 33 21 373, DE 28 00 553 and DE 32 06 269.
Preferred compositions also comprise one or more compounds from group 0 having two rings: ##STR4## where R.sup.0 denotes a straight-chain alkyl group of 2 to 7 carbon atoms, E.sup.0 is --(CH.sub.2).sub.4-, --(CH.sub.2).sub.2-, --CO--O--or a single bond an L and Q are as defined in group 3. Preferably E.sup.0 is --(CH.sub.2).sub.2 or a single bond, Q is a single bond and one of L is H and the other L is H or F.
The compositions according to this invention preferably comprise 20 to 30% by weight and e
REFERENCES:
patent: 5414440 (1995-05-01), Ilcisin et al.
Ichinose Hideo
Yano Tomoya
Merck Patent Gesellschaft mit beschrankter Haftung
Sony Corporation
Wu Shean C.
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