NEMATIC LIQUID-CRYSTAL COMPOSITION

Abstract: The invention relates to a nematic liquid-crystal composition based on terminally and laterally fluorinated compounds and dielectrically neutral compounds. This composition is highly useful for plasma-addressed display devices.

Description: Nematic liquid-crystal composition 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 0628 944, EP 0545 569, USP 4,896,149 and USP 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 tempera¬ ture 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 Δn > 0.08. There is a demand for compositions with low values of Δn, preferably with Δn < 0.07 and viscosities of < 20 mm s-ι at 20 °C. It has now been found that a nematic liquid-crystal composition comprising: 15 to 35 % by weight of two or more compounds selected from group i consisting of in which Ri is a straight-chain alkyl group of 1 to 5 carbon atoms, L.1 and l_2 are H or F, is F, OCF 2 H oder OCF 3 , and m is 0 or 1 , 65 to 85 % by weight of at least three compound from group 2 selected from: in which R2 and R3 are each independently a straight-chain alkyl or alkoxy group of 1 to 5 carbon atoms, 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 °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 °C in particular higher than 90 °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 0280 902, the European Patents 0051 738 and 0 125653, the Intemational Patent Applications WO 89/02884 and WO 85/048874 and USP 4,302,352, USP 4,710,315 and USP 4,419,264 or can be prepared in analogy to known compounds. The compounds from group 2 are known for example from DE 3321 373, DE 28 00 553 and DE 32 06269. Preferred compositions also comprise one or more compounds from group 0 having two rings: group 0: where Ro denotes a straight-chain alkyl group of 2 to 7 carbon atoms, Eo is -(CH 2 ) 4 -, -(CH 2 ) 2 -, -CO-O- or a single bond an L and Q are as defined in group 3. Preferably Eo is -(CH 2 ) 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 especially 25 to 30 % by weight of components from group 1. The preferred weight percent ranges for the other groups (if pre¬ sent) are as follows: group 0: 5 to 15 %, especially 5 to 10 % group 2: 65 to 85 %, especially 70 to 80 % Preferably the components from groups 0, 1 and 2 from the basis of the claimed compositions and constitute at least 70 % (preferably at least 80 %) by weight of the compositions. It is, however, also possible to use besides components from groups 0 to 3 also other LC components in smaller percentages for fine-tuning the claimed compositions. As a rule the composition consists of 8 to 20, in particular 10 to 17 meso¬ genic compounds selected from the groups 0, 1 and 2. The preparation of the compositions according to the invention is effected in the conventional manner. In general, the desired amount of the compo¬ nents which is used in the smaller amount is dissolved in the components which constitutes the main constituent, preferably at elevated temperature. If this temperature is chosen to be above the clearing point of the main constituent, the completeness of the process of dissolving can be obser- ved particularly easily. However, it is also possible to mix solutions of the components in a suitable organic solvent, for example acetone, chloroform or methanol, and to remove the solvent after thorough mixing, for example by distillation under reduced pressure. It is self-evident that with this method it must be ensured that the solvent does not introduce any contaminants or unde¬ sirable dopants. By means of suitable additives the liquid crystal phases according to the invention can be modified in such a way that they can be used in any hitherto disclosed kind of PAD. The examples below serve to illustrate the invention without limiting it. In the examples, the melting point and clear point of a liquid crystal sub- stance are given in degrees Celsius. The percentages are by weight. Example 1 A liquid-crystal composition consisting of 14 % of trans, trans-4-propyl-4'-methoxy bicyclohexane 13 % of trans, trans-4-propyl-4'-propoxy bicyclohexane 13 % of trans, trans-4-pentyl-4'-methoxy bicyclohexane 5 % of 1-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl]-2-(3,4- difluorophenyl)-ethane 5 % of 1-[trans-4-(trans-4-pentylcyclohexyl)-cyclohexyl]-2-(3,4- difluorophenyl)-ethane 7 % of 4-(trans-4-propylcyclohexyl)-methoxybenzene 3 % of 4-(trans-4-propylcyclohexyl)-ethoxybenzene 5 % of (4-propylphenyl) 4'-propylbicyclohexyl-4-ylcarboxylate 5 % of (4-propylphenyl) 4'-butylbicyclohexyl-4-ylcarboxylate 4 % of [4-(trans-4-propylcyclohexyl)-phenyl] 4'-propylbicyclohexyl-4- ylcarboxylate 4 % of [4-(trans-4-butylcyclohexyl)-phenyl] 4'-propylbicyclohexyl-4- ylcarboxylate 4 % of [4-(trans-4-pentylcyclohexyl)-phenyl] 4'-propylbicyclohexyl-4- ylcarboxylate 6 % of 5-[trans-4-(trans-4-ethylcyclohexyl)-cyclohexyl]-1 ,2,3-trifluoro- benzene 6 % of 5-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl]-1 ,2, 3-trif luoro- benzene 6 % of 5-[trans-4-(trans-4-pentylcyclohexyl)-cyclohexyl]-1,2,3-trifluoro- benzene This composition exhibits the following properties: S → N < -30 °C N → l + 93 °C Δn 0.0668 Δε + 1.9

Claims: Claims 1. A nematic liquid-crystal composition comprising: 15 to 35 % by weight of two or more compounds selected from group 1 consisting of in which Ri is a straight-chain alkyl group of 1 to 5 carbon atoms, Li and L are each independently H or F, is F, OCF 2 H or OCF 3 and m is 0 or 1 Li and L2 are each independently H or F, 65 to 85 % by weight of at least three compounds from group 2 selected from: in which R2 and R3 are each independently a straight-chain alkyl or alkoxy group of 1 to 5 carbon atoms, 0 n is O or 2. A nematic liquid-crystal composition according to claim 1 comprising: at least one compound of formula 1 a, 5 - at least one compound of formula 1 b, in which U is H and X is F at least one compound of formula 2a, in which 0 at least one compound of formula 2a, in which 5 at least one compound of formula 2b, in which n is 0, and at least one compound of formula 2b, in which n is 1. 3. Plasma-addressed display device comprising a nematic liquid-crystal Q composition according to claim 1 or 2. 5

Inventors: ICHINOSE HIDEO, YANO TOMOYA, ICHINOSE, HIDEO, YANO, TOMOYA
Applicants: ICHINOSE HIDEO, MERCK PATENT GMBH, SONY CORP, YANO TOMOYA, ICHINOSE, HIDEO, SONY CORPORATION, YANO, TOMOYA
Application year: 1996
Main classification: C09K19
IPC codes: C09K19, G02F1