LIQUID CRYSTALLINE MEDIUM

Abstract: The invention relates to a liquid-crystalline medium based on a mixture of polar compounds having positive dielectric anisotropy, characterized in that it contains one or more compounds of general formula (I), in which r is 0 or 1, Q<1> is -CH2CH2- or a single bond, A is 1,4-phenylene or trans-1,4-cyclohexylene, L is H or F, R is alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, in each case having up to 7 carbon atoms and X is F, CF3, or OCF2H.

Description: Liquid crystalline medium The present invention relates to a liquid-crystalline medium, to the use thereof for electrooptical purposes, and to dis- plays containing this medium. Liquid crystals are used, in particular, as dielectrics in display devices since the optical properties of such sub¬ stances can be affected by an applied voltage. Electrooptical devices based on liquid crystals are extremely well known to those skilled in the art and may be based on various effects. Devices of this type are, for example, cells having dynamic scattering, DAP (deformation of aligned phases) cells, guest/host cells, TN cells having a twisted nematic struc- ture, STN (super-twisted nematic cells, SBE (super-birefrin¬ gence effect) cells and OMI (optical mode interference) cells. The most common display devices are based on the Schadt-Helfrich effect and have a twisted nematic structure. The liquid-crystal materials must have good chemical and thermal stability and good stability toward electrical fields and electromagnetic radiation. Furthermore, the liquid-crys¬ tal materials should have low viscosity and give short addressing times, low threshold voltages and high contrast in the cells. Furthermore, they should have a suitable mesophase, for example, for the abovementioned cells, a nematic or cholesteric mesophase, at customary operating temperatures, i.e. in the broadest possible range above and below room temperature. Since liquid crystals are generally used as mixtures of a plurality of components, it is impor¬ tant that the components are readily miscible with one another. Further properties, such as electrical conductivity, dielectric anisotropy and optical anisotropy, must meet various requirements depending on the cell type and the area of application. For example, materials for cells having a twisted nematic structure should have positive dielectric anisotropy and low electrical conductivity. For example, the media desired for matrix liquid-crystal displays containing integrated nonlinear elements for switch¬ ing individual image points (MLC displays) are those having high positive dielectric anisotropy, broad nematic phases, relatively low birefringence, very high specific resistance, good UV and temperature stability of the resistance and low vapor pressure. Matrix liquid-crystal displays of this type are known. Exam¬ ples of nonlinear elements which can be used to individually switch the individual image points are active elements (i.e. transistors) . This is then referred to as an "active matrix", and a differentiation can be made between two types: 1. MOS (Metal Oxide Semiconductor) transistors on a silicon wafer as substrate. 2. Thin-film transistors (TFTs) on a glass plate as sub¬ strate. The use of monocrystalline silicon as the substrate material limits the display size since even the modular assembly of various part displays results in problems at the joints. In the case of the more promising type 2, which is preferred, the electrooptical effect used is usually the TN effect. A differentiation is made between two technologies: TFTs com¬ prising compound semiconductors, such as, for example, CdSe, or TFTs based on polycrystalline or amorphous silicon. Inten- sive research efforts are being made worldwide in the latter technology. The TFT matrix is applied to the inside of one glass plate of the display, while the inside of the other glass plate car- ries the transparent counterelectrode. Compared with the size of the image point electrode, the TFT is very small and hardly affects the image at all. This technology can also be extended to fully color-compatible image displays, where a mosaic of red, green and blue filters is arranged in such a manner that each filter element is located opposite a switch- able image element. The TFT displays usually operate as TN cells with crossed polarizers in transmission and are illuminated from the back. The term MLC displays here covers any matrix display contain¬ ing integrated nonlinear elements, i.e. in addition to the active matrix, also displays containing passive elements such as varistors or diodes (MIM = metal-insulator-metal) . MLC displays of this type are particularly suitable for TV application (for example pocket TV sets) or for high-informa¬ tion displays for computer applications (laptops) and in automobile or aircraft construction. In addition to problems with respect to the angle dependency of the contrast and the switching times, problems result in MLC displays due to inadequate specific resistance of the liquid-crystal mixtures TOGASHI, S., SEKIGUCHI, K., TANABE, H., YAMAMOTO, E., SORIMA- CHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H., Proc. Euro- display 84, Sept. 1984: A 210-288, Matrix LCD Controlled by Double Stage Diode Rings, p. 141 ff., Paris; STROMER, M:, Proc. Eurodisplay 84, Sept. 1984: Design of Thin Film Tran¬ sistors for Matrix Adressing of Television Liquid Crystal Displays, p. 145 ff., Paris. As the resistance decreases, the contrast of an MLC display worsens and the problem of "after image elimination" may occur. Since the specific resistance of the liquid-crystal mixture generally decreases over the life of an MLC display due to interaction with the internal surfaces of the display, a high (initial) resistance is very important to give acceptable service lives. In particular, in the case of low-voltage mixtures, it was hitherto not possi¬ ble to achieve very high specific resistances. It is further¬ more important that the specific resistance increases as little as possible with increasing temperature and after heating and/or exposure to UV radiation. The MLC displays of the prior art do not satisfy current demands. Thus, there continues to be a great demand for MLC displays of very high specific resistance and at the same time a broad operating temperature range, short switching times and low threshold voltage which do not have these disadvantages or only do so to a lesser extent. For TN (Schadt-Helfrich) cells, media are desired which facilitate the following advantages in the cells: - broadened nematic phase range (in particular down to low temperatures) , - switchability at extremely low temperatures (outdoor use, automobiles, avionics) , increased stability to UV radiation (longer life) . The media available from the prior art do not make it possi¬ ble to achieve these advantages whilst simultaneously retain¬ ing the other parameters. For supertwisted (STN) cells, media are desired which facili¬ tate a greater multiplexing ability and/or lower threshold voltages and/or broader nematic phase ranges (in particular at low temperatures) . To this end, a further extension of the parameter latitude available (clearing point, smectic-nematic transition or melting point, viscosity, dielectric values, elastic values) is urgently desired. The invention has the object or providing media, in particu¬ lar for MLC, TN or STN displays of this type, which do not have the abovementioned disadvantages or only do so to a lesser extent, and preferably at the same time have very high specific resistance and low threshold voltages. It has now been found that this object can be achieved if media according to the invention are used in displays. The invention thus relates to a liquid-crystalline medium based on a mixture of polar compounds having positive dielec- trie anisotropy, characterized in that it contains one or more compounds of the general formula I R-[- H QI-] in which r is 0 or 1, Q 1 is -CH 2 CH 2 - or a single bond, A is 1,4-phenylene or trans-l,4-cyclohexylene, L is H or F, R is alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, in each case having up to 7 carbon atoms and X is F, CF 3 , OCF 3 or 0CF 2 H. The invention also relates to electrooptical displays (in particular STN or MLC displays having two plane-parallel outer plates which, together with a frame, form a cell, integrated nonlinear elements for switching individual image points on the outer plates, and a nematic liquid-crystal mixture of positive dielectric anisotropy and high specific resistance located in the cell) which contain media of this type, and to the use of these media for electroptical pur¬ poses. In particular the invention relates to a nematic liquid-crys¬ tal composition based on terminally and laterally fluorinated compounds, characterized in that it contains about 10 to 25 % by weight of one or more compounds from group 1: IP- group 1: Ri- H V(CH 2 CH 2 ) n - O V» wherein R 1 denotes a straight-chain alkyl group of 1 to 12 carbon atoms, L 1 is H or F and X 1 is F, CF 3 , 0CF 3 or 0CF 2 H and n is 0 or 1, preferably 0, about 10 to 70 % by weight of one or more compounds from group 2: group 2: wherein R 2 denotes a straight-chain alkyl group of 1 to 12 carbon atoms L 2 is H or F, Q is -THVCH 2 CH 2 - or -CH 2 CH 2 YHV, preferably -(H or and X 2 is F, CF 3 , 0CF 3 or 0CF 2 H, about 5 to 40 %, in particular 5 to 25 % by weight of one or more compounds of the formula la. wherein L3 is F or H, X3 is F, CF 3/ OCF 3 or OCF 2 H, n is 0 or 1, preferably 0, and - y- is about 0 to 15 % by weight of one or more compounds from group 4: group 4 : wherein L« is H or F, about 0 to 25 % by weight of one or more compounds from group 5 : group 5 : wherein R 3 to R 7 each independently denotes a straight-chain alkyl group of 1 to 12 carbon atoms, L 5 is H or F and X 5 is F, CF 3/ OCF 3 or OCF 2 H, and about 0 to 20 % by weight of one or more compounds from group 6: group 6: R* --d( H -( A V- ■ R9 wherein has the meaning given for formula la, and R 8 and R 9 are each independently alkyl or alkoxy groups with one to 12 C atoms, which is highly suited for AMD application. Very high RC time values can be obtained in such AMDs. These compositions also show a reduced viscosity, allow operation in AMDs in the first minimum of transmission and do not exhibit any crystal¬ lization over 1000 hrs at -30 °C. Such compositions preferably contain at least two compounds of group 1 wherein Ri is n-pently, n-hexyl and n-heptyl. In a preferred embodiment the inventive nematic composition contains about 15 to 20 % by weight of two or more compounds from group 1, wherein L 1 is H and X 1 is F, CF 3 or OCF 3 , about 10 to 40 % by weight of two or more compounds from group 2, wherein L 2 is H, X 2 is OCF 3 and m is 0 and about 10 to 40 % by weight of two or more compounds from group 2 wherein L 2 is H or F, X 2 is F or OCF 3 and m is 1, about 5 to 15 % by weight of two or more compounds of formula la wherein L 3 is H and X 3 is F and/or about 5 to 15 % by weight of two or more compounds of formula la wherein L 3 is H and X 3 is OCF 3 additionally the group 6 may contain 0-25 % by weight of one or more compounds of the formula in which RS and R 9 have the meaning given for group 6. The compounds from groups 1 to 6 are known from the German Patents 26 36 684 and 31 02 017, the European Patent 0 051 738 and 0 125 653, the International Patent Application WO 89/02884 and USP 4,302,352, USP 4,710,315 and USP 4,419,264 or can be prepared in analogy to known compounds. The preparation of the compositions according to the inven¬ tion is effected in the conventional manner. In general, the desired amount of the components 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 clear point of the main constituent, the completeness of the process of dissolving can be observed particularly easily. The liquid-crystal mixtures according to the invention facil¬ itate a significant broadening of the parameter latitude available. The achievable combinations of clearing point, viscosity at low temperature, thermal and UV stability and dielectric anisotropy are far superior to previous materials from the prior art. The requirement for a high clearing point, a nematic phase at -40 °C and a high Δε was previously only achievable to an unsatisfactory extent. Although systems such as, for example, ZLI-3119 have a comparable clearing point and comparatively favorable viscosities, they have, however, a Δε of only +3. Other mixture systems have comparable viscosities and values of Δε, but only have clearing points in the region of 60 °C. The liquid-crystal mixtures according to the invention make it possible to achieve, at low viscosities at low tempera¬ tures (at -30 °C < 600, preferably < 550 mPa-s; at -40 °C < 1800, preferably < 1700mPa-s) , simultaneously dielectric anisotropy values Δε > 3.5, preferably > 4.0, clearing points above 65°, preferably above 70°, and a high value for the specific resistance, which means that excellent STN and MLC displays can be achieved. - ¬ lt goes without saying that a suitable choice of the compo¬ nents of the mixtures according to the invention also allows higher clearing points (for example above 90°) to be achieved at higher threshold voltages or lower clearing points to be achieved at lower threshold voltages while retaining the other advantageous properties. The MLC displays according to the invention preferably operate in the first transmission minimum of Gooch and Tarry [C.H. Gooch and H.A. Tarry, Elec¬ tron. Lett. 10, 2-4, 1974; C.H. Gooch and H.A. Tarry, Appl. Phys., Vol. 8, 1575-1584, 1975], in this case, a lower dielectric anisotropy in the second minimum is sufficient in addition to particularly favorable electrooptical properties, such as, for example, high gradient of the characteristic line and low angle dependency of the contrast (German Patent 3022 818) at the same threshold voltage as in an analogous display. This allows significantly higher specific resis¬ tances to be achieved in the first minimum using the mixtures according to the invention than using mixtures containing cyano compounds. A person skilled in the art can use simple routine methods to produce the birefringence necessary for a prespecified cell thickness of the MLC display by a suitable choice of the individual components and their proportions by weight. The viscosity at 20 °C is preferably < 25mPa'S. The nematic phase range is preferably at least 70°, in particular at least 80°. This range preferably extends at least from -30° to +70° more preferred from -30° to 120°. Measurements of the "voltage holding ratio" (HR) [S. Matsumoto et al.. Liquid Crystals .5, 1320 (1989), K. Niwa et al., Proc. SID Conference, San Francisco, June 1984, p. 304 (1984); G. Weber et al.. Liquid Crystals , 1381 (1989)] have shown that mixtures according to the invention containing compounds of the formula I exhibit a considerably smaller decrease in the HR with increasing temperature than do analo¬ gous mixtures in which the compounds of the formula I are replaced by cyanophenylcyclohexanes of the formula The UV stability of the mixtures according to the invention is also considerably better, i.e. they exhibit a signifi¬ cantly smaller decrease in the HR on exposure to UV radiation and/or high temperatures of e.g. 100°. The media according to the invention are distinguished by favorable viscosity values in addition to an unusually broad nematic phase range, resulting, in particular when used in STN displays, in significant advantages over prior-art media. The media according to the invention are preferably based on a plurality (preferably two or more) of compounds of the formula I, i.e. the proportion of these compounds is ≥ 25 %, preferably > 40 %. The individual compounds of the formulae I to XIV and their sub-formulae which can be used in the media according to the invention are either known or can be prepared analogously to the known compounds. Preferred embodiments are indicated below: a medium additionally contains one or more compounds selected from the group comprising the general formulae II, III and IV: Yi / R I--({--{ HHV>-)) r -.--( HH V>-cC 2? HH 4 _--{ 00 >-xX β6 III γ2 in which the individual radicals are as defined below: R: alkyl, oxaalkyl, fluoroalkyl or alkenyl, in each case having up to 7 carbon atoms X 6 : F, Cl, CF 3 , OCF 3 or OCHF 2 Y 1 and Y 2 : in each case, independently of one another, H or F r: 0 or 1. a medium additionally contains one or more compounds selected from the group comprising the general formulae V to VIII. Yi R .-- 0 >--( 0 >--χe VII in which R, X6 and Y 1 and Y 2 are each, independently of one another, as defined in Claim 2. a medium additionally contains one or more compounds selected from the group comprising the general formulae IV to XV: - 1 / R ,-_ H Wy Hy00 H00) )--Xχβ 6 XI γ2 in which R, X 6 and Y 1 and Y 2 are each, independently of one another, as defined in Claim 2. The proportion of compounds of the formulae I to IV together is at least 50 % by weight in the total mixture the proportion of compounds of the formula I is from 10 to 50 % by weight in the total mixture the proportion of compounds of the formulae II to IV is from 30 to 70 % by weight in the total mixture - 0 VcF 3 , - 0 VθCHF 2/ the medium contains compounds of the formulae II and III or IV - R is straight-chain alkyl or alkenyl having 2 to 7 carbon atoms - the medium essentially comprises compounds of the formu¬ lae I to IV - the medium contains further compounds, preferably selected from the following group: The I: (11+ III+ IV) weight ratio is preferably from 1:4 to 1:1. The medium essentially comprises compounds selected from the group comprising the general formulae I to XIV. It has been found that even a relatively small proportion of compounds of the formula I mixed with conventional liquid- crystal materials, but in particular containing one or more compounds of the formula II, III and/or IV, results in a significant improvement in the addressing times, in signifi¬ cantly lower values for the birefringence, and in low thresh- old voltages, and at the same time broad nematic phases with low smectic-nematic transition temperatures are observed. The compounds of the formulae I to IV are colorless, stable and readily miscible with one another and with other liquid-crys¬ tal materials. The term "alkyl" covers straight-chain and branched alkyl groups having 1-7 carbon atoms, in particular the straight- chain groups methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups having 2-5 carbon atoms are generally pre¬ ferred. The term "alkenyl" covers straight-chain and branched alkenyl groups having 2-7 carbon atoms, in particular the straight- chain groups. Preferred alkenyl groups are C 2 -C 7 -lE-alkenyl, C 5 -C 7 - -alkenyl, C 6 -C 7 -5-alkenyl and C 7 -6-alkenyl, in particu¬ lar C 2 -C 7 -lE-alkenyl, C-C 7 -3E-alkenyl and C 5 -C-4-alkenyl. Examples of preferred alkenyl groups are vinyl, lE-propenyl, lE-butenyl, IE-pentenyl, lE-hexenyl, lE-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having up to 5 carbon atoms are generally preferred. The term "fluoroalkyl" preferably covers straight-chain groups containing terminal fluorine, i.e. fluoromethy1, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. However, other positions of the fluorine are not excluded. The term alkoxy preferably covers straight-chain radicals of the formula C n H 2n+1 -0-, in which n is 1 to 6. The term "oxaalkyl" preferably covers straight-chain radicals of the formula C n H 2n+1 -0-(CH 2 ) m , in which n and m are each, independently of one another, from 1 to 6. n is preferably 1 and m is preferably from 1 to 6. Through a suitable choice of the meanings of R, X and Y, the addressing times, the threshold voltage, the gradient of the transmission characteristic lines, etc., can be modified as desired. For example, lE-alkenyl radicals, 3E-alkenyl radi¬ cals, 2E-alkenyloxy radicals and the like generally give shorter addressing times, improved nematic tendencies and a higher ratio between the elastic constants K 33 (bend) and k n (splay) compared with alkyl and alkoxy radicals. 4-Alkenyl radicals, 3-alkenyl radicals and the like generally give lower threshold voltages and lover values of k 33 /k compared with alkyl and alkoxy radicals. A -CH 2 CH 2 - group in Z* or Z 2 generally results in higher values of k 33 /k 1:L compared with a simple covalent bond. Higher values of k 33 /k facilitate, for example, flatter transmission characteristic lines in TN cells with a 90° twist (for achieving gray tones) and steeper transmission characteristic lines in STN, SBE and OMI cells (greater multiplexing ability) , and vice versa. The optimum mixing ratios of the compounds of the formulae I and II + III + IV depends substantially on the desired prop¬ erties, on the choice of the components of the formulae I, II, III and/or IV and on the choice of any other components which may be present. Suitable mixing ratios within the abovementioned range can easily be determined from case to case. The total amount of compounds of the formulae I to XII in the mixtures according to the invention is not crucial. The mixtures may therefore contain one or more further components in order to optimize various properties. However, the effect observed on the addressing times and the threshold voltage is generally greater the higher the total concentration of compounds of the formulae I to XIV. In a particularly preferred embodiment, the media according to the invention contain compounds of the formula II, III, V and/or VII (preferably II and/or III) in which X6 is CF 3 , OCF 3 or 0CHF 2 . A favorable synergistic effect with the compounds of the formula I results in particularly advantageous proper¬ ties. For STN applications, the media preferably contain compounds selected from the group comprising the formulae V to VIII in which X 6 is preferably 0CHF 2 . The media according to the invention may furthermore contain a component A comprising one or more compounds of the general formula I' having a dielectric anisotropy of from -1.5 to +1.5. -R 2 I' in which Ri and R 2 are each, independently of one another, n-alkyl, n-alkoxy, o-fluoroalkyl or n-alkenyl having up to 9 carbon atoms. the rings A 1 , A 2 and A 3 are each, independently of one another, 1,4-phe- nylene, 2- or 3-fluoro-l,4-phenylene, trans-1,4- cyclohexylene or 1,4-cyclohexenylene, Z 1 and Z 2 are each, independently of one another, -CH 2 CH 2 -, -C≡C-, -C0-0-, -O-CO- or a single bond, and m is 0, 1 or 2. Component A preferably contains one or more compounds selected from the group comprising III to 117: Ri-( H >-< >-R2 114 Ri- H VcH 2 CH 2 - H Y-R 2 117 in which Ri and R 2 are as defined under formula I' . Component A preferably additionally contains one or more compounds selected from the group comprising 118 to 1120: Ri- H Y 0 cH 2 CH 2 Y 0 R 2 1113 in which R 1 and R 2 are as defined under formula I', and the 1,4-phenylene groups in 118 to 1117 may each, independently of one another, also be monosubstituted or polysubstistituted by fluorine. Furthermore, component A preferably additionally contains one or more compounds selected from the group comprising 1121 to 1125 in which RI and R2 are as defined under formula I', and the 1,4-phenylene groups in 1121 ro 1125 may also each, indepen¬ dently of one another, be monosubstituted or polysubstituted by fluorine. Finally, preferred mixtures of this type are those in which component A contains one or more compounds selected from the group comprising 1126 and 1127: C r H 2r+1 - H Y/ H YcH 2 -F 1126 C r H 2r+ ι- H Y/ HYcH 2 CH 2 -F 1127 in which C r H 2r+1 is a straight-chain alkyl group having up to 7 carbon atoms. In some cases, the addition of compounds of the formula in which Ri and R2 are as defined under formula I' and Z° is a single bond, -CH 2 CH 2 -, -< Hv- or proves advantageous for suppressing smectic phases and improves the tilt angle, although this may reduce the spe¬ cific resistance. In order to achieve parameter combinations which are ideal for the application, a person skilled in the art can easily determine whether and, if yes, in what amount these compounds may be added. Normally, less than 15 %, in particular 5-10 %, are used. Preference is also given to liquid-crystal mixtures which contain one ore more compounds selected from the group com- prising III' and VI' : R ι- HH Y HH Y >-cCHH 2 ,OORR 22 IV in which Ri and R 2 are as defined under formula I' . The type and amount of the polar compounds having positive dielectric anisotropy is not crucial per se. A person skilled in the art can use simple routine experiments to select suitable materials from a wide range of known and, in many cases, also commercially available components and base mix¬ tures. The media according to the invention preferably con¬ tain one or more compounds of the formula I" in which Z 1 , Z 2 and m are as defined under the formula I', Q 1 and Q 2 are each, independently of one another, 1,4-phenylene, trans-1,4-cyclohexylene or 3-fluoro-l,4-phenylene-, and one of the radicals Q 1 and Q 2 is alternatively trans-l,3-diox- ane-2,5-diyl, pyrimidine-2,5-diyl, pyrimidine-2,5-diyl or 1,4-cyclohexenylene, R° is n-alkyl, n-alkenyl, n-alkoxy or n-oxaalkyl, in each case having up to 9 carbon atoms, Y is H or F and X' is CN, halo¬ gen, CF 3 , OCF 3 or 0CHF 2 . In a preferred embodiment, the media according to the inven¬ tion for STN or TN applications are based on compounds of the formula I" in which X' is CN. It goes without saying that smaller or larger proportions of other compounds of the formula I" (X' ≠ CN) are also possible. For MLC applications, the media according to the invention preferably contain only up to about 10 % of nitriles of the formula I" (but prefera¬ bly no nitriles of the formula I", but instead compounds of the formula I' where X' = halogen, CF 3 , 0CF 3 or 0CHF 2 ) . These media are preferably based on the compounds of the formulae II to XII. The construction of the STN and MLC displays according to the invention from polarizers, electrode base plates and elec¬ trodes with surface treatment corresponds to the construction which is conventional for displays of this type. The term conventional construction here is widely drawn and also covers all derivatives and modifications of the MLC display, in particular also matrix display elements based on poly-Si TFTs or MIMs. An essential difference between the displays according to the invention and those customary hitherto based on the twisted nematic cell is, however, the choice of liquid-crystal param¬ eters in the liquid-crystal layer. The liquid-crystal mixtures which can be used according to the invention are prepared in a manner which is conventional per se. In general, the desired amount of the components used in the lesser amount is dissolved in the components making up the principal constituent, expediently at elevated tempera¬ ture. It is also possible to mix solutions of the components in an organic solvent, for example in acetone, chloroform or methanol, and, after thorough mixing, to remove the solvent again, for example by distillation. The dielectrics may also contain other additives known to those skilled in the art and described in the literature. For example, 0-15 % of pleochroic dyes or chiral dopes can be added. C denotes a crystalline phase, S a smectic phase, S B a smectic B phase, N a nematic phase and I the isotropic phase. V 10 denotes the voltage for 10 % transmission (view angle perpendicular to the plate surface) . t on denotes the switch-on time and t off the switch-off time at an operating voltage corresponding to 2.5 times the value of V 10 • Δn denotes the optical anisotropy and n Q the refractive index. Δε denotes the dielectric anisotropy (Δε = ε|| - ε , where ε|| is the dielec¬ tric constant parallel to the longitudinal molecular axes and εj. is the dielectric constant perpendicular thereto. The electro-optical data were measured in a TN cell at the 1st minimum (i.e. at a d n value of 0.5) at 20 °C, unless expressly stated otherwise. The optical data were measured at 20 °C, unless expressly stated otherwise. The examples below are intended to illustrate the invention without representing a limitation. Above and below all tem- peratures are given in °C. The percentages are percent by weight. In the present application and in the examples below, the structures of the liquid-crystal compounds are indicated by 29 acronyms, with the transformation into chemical formulae taking place in accordance with Tables A and B below. All radicals C n H 2n+1 are straight-chain alkyl radicals containing or m carbon atoms. The coding in Table B is self-evident. In Table A, only the acronym for the base structure is given. In individual cases, the acronym for the base structure is followed, separated by a hyphen, by a code for the substitu- ents Ri, R2, Li, L2 and L 3 : Code for Ri R 2 V- L 2 L3 R 1 , R 2 . Li, L 2 , L3 nF.F.F C n H 2n+1 F H F F nF.F.F.F. C n H 2n+1 F F F F TableA: PYP PYRP CBC CCP CPTP CEPTP ECCP cεcp IA L 2 IA L 2 R-^H -C 2 H 4 -^-R 2 RI- H - O)-COO-(O -R 2 EPCH HP Ri PDX PTP F CH P H CPC CCEB _ CCB CCB-n.FX PCH EHP FET IA L 2 IA L2 R1 "® _ ^ C2H4 \ £ / R2 Ri - θ V( θ ^- R CFET BEP FET CEUP CUEP Table B: C 5 H u -(θ)-(θ)-(OYcN C n H 2n+1 -(θ)- θ)-CN T15 K3n F C n H 2n+1 -0-(θ)-(0)-CN C n H 2n+1 -(H (θ -(θ)-X M3n BCH-n.Fm C n H 2n+1 - H (H)»-OOC-C m H 2m+1 In C-n CH 3 CH 3 C 2 H 5 -CH-CH 2 -0- θ}-(0}-CN C 2 H 5 -CH-CH 2 -(θ)- θ)-CN * * C15 CB15 H -C m H 2m+1 CBC-nmF CC -nm CCPC-n CH-nm HD-nm HH-nm NCB-nm c n H 2n+1 -( -X)-<H) p -c m H 2m+1 C 2 H 5 -(HYCOO-(O>- O>--_. OS-nm CHE C n H 2n+1 -^^C 2 H 4 -(θ)-{θ)-{H C m H 2m+1 ECBC-iim ECCH-nm CCH-nlE C n H 2n+1 -(θ) θ)-{θ)-CN F T-nFn CP-nOCF 3 C n H 2n+1 -(H -(θ)-COO-{θ)-OCF 3 C n H 2n+ ι-(H -COO-(θ)-OCF 3 HP-nOCF 3 D-nOCF 3 C n H 2n+1 -(θ)-COO- θ)-OCF 3 ME-nOCF 3 Examole 1 PCH-6F 13.0 PCH-7F 7.0 CCP-20CF3 10.0 CCP-30CF3 11.0 CCP-40CF3 10.0 CCP-50CF3 12.0 BCH-3F.F 12.0 BCH-5F.F 12.0 CP-30CF3 6.0 CP-50CF3 7.0 Example 2 PCH-βF 13.0 PCH-7F 7.0 CCP-20CF3 10.0 CCP-30CF3 11.0 CCP-40CF3 10.0 CCP-50CF3 12.0 BCH-3F.F 12.0 BCH-5F.F 12.0 HP-30CF3 6.0 HP-50CF3 7.0 Example 3 ME30CF3 5.0 PCH-6F 8.0 PCH-7F 7.0 CCP-20CF3 10.0 CCP-30CF3 11.0 CCP-40CF3 10.0 CCP-50CF3 12.0 BCH-3F.F 12.0 BCH-5F.F 12.0 CP-30CF3 6.0 CP-50CF3 7.0 Example 4 PCH-5F 5.0 PCH-6F 13.0 PCH-7F 7.0 CCP-20CF3 10.0 CCP-30CF3 11.0 CCP-40CF3 10.0 CCP-50CF3 12.0 BCH-3F.F 12.0 BCH-5F.F 12.0 HP-30CF3 .0 HP-50CF3 4.0 Example 5 PCH-5F 13.0 PCH-7F 7.0 CCP-20CF3 8.0 CCP-30CF3 10.0 CCP-40CF3 8.0 CCP-50CF3 10.0 BCH-3F.F 12.0 BCH-5F.F 12.0 HP-30CF3 5.0 HP-50CF3 5.0 CP-30CF3 5.0 CP-50CF3 5.0 Example 6 PCH-5F 5.0 PCH-6F 13.0 PCH-7F 7.0 CCP-20CF3 10.0 CCP-30CF3 11.0 CCP-40CF3 10.0 CCP-50CF3 12.0 BCH-3F.F 12.0 BCH-5F.F 12.0 CP-30CF3 4.0 CP-50CF3 4.0 Example 7 D-30CF3 5.0 PCH-6F 8 .0 PCH-7F 7.0 CCP-20CF3 10.0 CCP-30CF3 11.0 CCP-40CF3 10.0 CCP-50CF3 12.0 BCH-3F.F 12.0 BCH-5F .F 12.0 CP-30CF3 6.0 CP-50CF3 7.0 Example 8 PCH-5F 7.0 PCH-6F 7.0 PCH-7F 6.0 CP-30CF3 10.0 CP-50CF3 10.0 CCP-20CF3 10.0 CCP-30CF3 10.0 CCP-40CF3 9.0 CCP-50CF3 10.0 ECCP-3F .F 11.0 ECCP-5F .F 10.0 Example 9 PCH-5F 10.0 PCH-6F 8.0 PCH-7F 6.0 CCP-20CF3 8.0 CCP-30CF3 12.0 CCP-40CF3 7.0 CCP-50CF3 11.0 BCH-3F.F 12.0 BCH-5F.F 10.0 CP-30CF3 5.0 CP-50CF3 5.0 CBC-33F 2.0 CBC-53F 2.0 CBC-55F 2.0 Example 10 PCH-5F 3.0 PCH-6F 3.0 PCH-7F 3.0 CCP-20CF3 7.0 CCP-30CF3 8.0 CCP-40CF3 7.0 CCP-50CF3 8.0 CP-30CF3 6.0 CP-50CF3 6.0 ECCP-30CF3 6.0 ECCP-50CF3 6.0 ECCP-3F.F 8.0 ECCP-5F.F 8.0 CCH-301 11.0 CCH-303 10.0 Exa ple 11 PCH-5F 7.0 PCH-6F 7.0 PCH-7F 6.0 CP-3F 10.0 CP-5F 10.0 CCP-20CF3 10.0 CCP-30CF3 10.0 CCP-40CF3 9.0 CCP-50CF3 10.0 CP-30CF3 11.0 CP-50CF3 10.0 Example 12 PCH-5F 4.0 PCH-6F 4.0 CCH-301 10.0 CCH-303 10.0 CP-30CF3 10.0 CP-50CF3 10.0 CCP-20CF3 11.0 CCP-30CF3 11.0 CCP-40CF3 9.0 CCP-50CF3 10.0 EHP-3F.F 6.0 EHP-3F.F 6.0 Example 13 PCH-6F 9.0 PCH-6F 7 . 0 PCH-7F 6.0 CP-3F 7 .0 CP-5F 7 .0 CCP-20CF3 9.0 CCP-30CF3 9.0 CCP-40CF3 8 .0 CCP-50CF3 9.0 CP-30CF3 10 .0 CP-50CP3 9.0 CCH-301 10 .0 The properties of the Examples 1-13 are given in the follow¬ ing table: Example 10 11 12 13 S — > N [° C] <-20 <+20 <-20 <0 <-20 Clearing point [° C] +95 +92 +98 +81 +96 +83 99 101 79 76 118 101 95 Viscosity [mm 2 S -1 ] 20° C 15 16 14 16 14 15 14 13 Viscosity [mm 2 S-l] 0° C 41 cryst. 37 42 37 42 Viscosity [_m 2 S _ l] -20° C 180 147 0.5< r<lh 153 Viscosity [i_n 2 S-l] -30° C cryst. smekt. cryst. cryst. Δn (589nm,20°C) +0.0940 +0.0986 +0.0991 +0.0943 +0.0911 0.0911 0.0968 0.0768 0.097 0.078 0.0786 0.0773 0.0732 ne (589nm,20° C) 1.5706 1.5775 1.5749 1.5734 1.5768 1.5687 1.5483 - - 1.5504 1.5468 1.5449 no (589nm,20° C) 1.4765 1.4789 1.4758 1.4791 1.4777 1.4776 1.4715 - HR (100° C)/% HR (20° C)/% HR (20° C)/% Example 14 A liquid-crystal composition consisting of PCH-5F 8.0 % PCH-6F 8.0 % CP-3F 5.0 % CP-5F 5.0 % BCH-3F.F 7.0 % BCH-5F.F 7.0 % CCP-2OCF 3 8.0 % CCP-3OCF 3 7.0 % CCP-4OCF 3 7.0 % CCP-5OCF 3 7.0 % ECCP-3F.F 9.0 % ECCP-5F.F 8.0 % ECCP-3OCF 3 7.0 % ECCP-5OCF 3 7.0 % shows the following properties: Clearing point +102 °C Viscosity (+20 °C) 16 mm 2 s- i Optical anisotropy Δn +0.0876 (20 °C, 589 nm) V(10,0,20) 2.10 (1st) V Example 15 PCH-5F 7.6 S < -10 N 82 I PCH-6F 7.6 V 10 2.25 Volt PCH-7F 7.6 Δn 0.1210 FET-3F 5.7 FET-5F 3.8 CFET-3F.F 7.6 CFET-5F 8.5 BCH-3F.F.F 13.3 BCH-5F.F.F 12.3 BCH-52F 7.6 ECCP-30CF3 6.7 CBC-33F 1.9 CBC-53F 2.9 CBC-55F 1.9 CP-4F 5.0 Example 16 PCH-5F 17.0 S < -30 N 111 I CCP-20CF3 15.0 Δn 0.0894 CCP-30CF3 12.0 Viscosity (20 °C) : 15 mm 2 s- CCP-40CF3 12.0 V 10 2.26 Volt CCP-50CF3 12.0 CP-3F 10.0 CP-5F 10.0 PCH-301 7.0 CPTP-301 5.0 Example 17 A liquid crystalline composition consisting of PCH-5F 9.0 PCH-6F 6.0 PCH-7F 6.0 CCP-20CF3 12.0 CCP-30CF3 12.0 CCP-40CF3 10.0 CCP-50CF3 12.0 BCH-3F.F 12.0 BCH-3F.F 10.0 CP-3F 6.0 CP-5F 5.0 exhibits a broad nematic phase range. Example 18 A liquid crystalline composition consisting of PCH-5F 7.0 PCH-7F 7.0 CCP-20CF3 6.0 CCP-30CF3 6.0 CCP-40CF3 6.0 CCP-50CF3 6.0 CP-20CF3 5.0 CP-30CF3 5.0 CP-40CF3 5.0 CP-50CF3 5.0 ECCP-3F.F 9.0 ECCP-5F.F 9.0 CCH-303 12.0 CCH-501 12.0 shows the following properties: Clearing point: +86 °C Optical anisotropy: Δn +0.0666 (20 °C, 589 nm) V 10 ,o.20 2.10 (1st) V All compositions (Examples 1 to 18) shown above show HR 20 /HRo > 98 % and are thus highly valuable as mixtures for active matrix displays. HR 20 : Voltage eholding ratio after 20 hours exposure to UV-light (280-400 nm, 12 mW cm- 2 ) HRo: Voltage holding ratio before exposure to UV-light Example 19 A liquid crystalline composition consisting of PCH-3 8.0 PCH-4 9.0 PCH-5 5.0 PCH-302 19.0 PCH-304 13.0 CP-30CF3 5.0 CP-50CF3 5.0 ECCP-3F 6.0 CP-33 7.0 CP-35 8.0 CP-43 8.0 CP-45 7.0 shows the following properties: Clearing point: + 92 °C Optical anisotropy: Δn 0.0951 V 10 , 0 , 20 : 2.22 V Example 22 A liquid crystal medi um is prepared consisting of: K6 6.0 K9 7.0 K15 8.0 PCH-3 23.0 PCH-302 7.0 CP-30CF 3 6.0 CP-50C. 3 6.0 PTP-102 5.0 PTP-201 5.0 ECCP-3 6.0 ECCP-31 6.0 ECCP-32 5.0 ECCP-33 5.0 BCH-32 5.0 and exhi bits a broad nematic phase range and a short switching time in a STN display.

Claims: Patent Claims 1. Liquid-crystalline medium based on a mixture of polar compounds having positive dielectric anisotropy, charac- terized in that it contains one or more compounds of the general formula I / --[- H V-Q1-] r -/A VcOoY 0 V. in which r is o or 1, Qi is -CH 2 CH 2 - or a single bond, A is 1, -phenylene or trans-1,4-cyclohexylene, L is H or F, R is alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, in each case having up to 7 carbon atoms and X is F, CF 3 , or 0CF 2 H. Medium according to Claim 1, characterized in that it additionally contains one or more compounds selected from the group comprising the general formulae II, III and IV: ^ in which the individual radicals are as defined below: R: alkyl, oxaalkyl, fluoroalkyl or alkenyl, in each case having up to 7 carbon atoms X 6 : F, Cl, CF 3 , 0CF 3 or 0CHF 2 Y 1 and Y 2 : in each case, independently of one another, H or F r: 0 or 1. 3. Medium according to Claim 1 or 2, characterized in that it additionally contains one or more compounds selected from the group comprising the general formulae V to VIII: in which R, X 6 , Y 1 and Y 2 are each, independently of one another, as defined in Claim 2. 4. Medium according to at least one of Claims 1 to 3, char¬ acterized in that it additionally contains one or more compounds selected from the group comprising the general formulae IX to XIV: in which R, X 6 , Yi and Y 2 are each, independently of one another, as defined in Claim 2. 5. Medium according to Claim 2, characterized in that the proportion of compounds of the formulae I to IV together is at least 50 % by weight in the total mixture. 6. Medium according to Claim 1 or 2, characterized in that the proportion of compounds of formula I is from 10 to 50 % by weight in the total mixture. Medium according to at least one of Claims 2 to 4, char¬ acterized in that the proportion of compounds of the formulae II to IV is from 30 to 70 % by weight in the total mixture. 8. Medium according to at least one of Claims 1 to 4, char¬ acterized in that it essentially comprises compounds selected from the group comprising the general formulae I to XIV. 9. Medium according to at least one of Claims 1 to 8 based on terminally and laterally fluorinated compounds, char¬ acterized in that it contains about 10 to 25 % by weight of one or more compounds from group 1: IA / group 1: Ri-/ H V(CH 2 CH 2 ) n -/ 0 x 1 wherein R denotes a straight-chain alkyl group of 5 or more carbon atoms, L 1 is H or F, χι is F, CF 3 , OCF 3 or 0CF 2 H and n is 0 or 1, preferably 0, about 10 to 70 %, preferably 15 to 25 %, by weight of one or more compounds from group 2: group 2: wherein R 2 denotes a straight-chain alkyl group of 3 to 5 carbon atoms, L 2 is H or F, X 2 is F, CF 3 , 0CF 3 or OCF 2 H, Q is -*(H)*- . -(HVCH 2 CH 2 or CH 2 CH 2 -^H)r-, preferably -(H^T- or - HV-CH 2 CH 2 -, about 5 to 40 %, in particular 5 to 25 % by weight of one or more compounds of the formula la: B?- H la wherein __. is H or F, X 3 is F, CF 3 , OCF 3 or OCF 2 H, n is 0 or 1, preferably 0, and - AV- is -θj or about 0 to 15 % by weight of one or more compounds from group 4. group 4: wherein L^ is H or F about 0 to 25 %, preferably 1 to 5 %, by weight of one or more compounds from group 5: group 5: wherein R 3 to R 7 each independently denotes a straight- chain alkyl group of 1 to 12 carbon atoms, L 5 is H or F, L 5 is H or F, X5 is F, CF 3 , OCF 3 or OCF 2 H, and about 0 to 20 % by weight of one or more compounds from group 6: group 6: Rβ H-(0H-0A -R.9 wherein has the meaning given for formula la, and R 8 and R 9 are each independently alkyl or alkoxy groups with one to 12 carbon atoms. 10. Use of the liquid-crystalline medium according to Claim 1 for electrooptical purposes. 11. Electrooptical liquid-crystal display containing a liquid-crystalline medium according to Claim 1.

Inventors: FINKENZELLER ULRICH, JACOB THOMAS, KURMEIER HANS-ADOLF, PLACH HERBERT, RIEGER BERNHARD, YOSHITAKE HIROKI, FINKENZELLER, ULRICH, JACOB, THOMAS, KURMEIER, HANS-ADOLF, PLACH, HERBERT, RIEGER, BERNHARD, YOSHITAKE, HIROKI
Applicants: MERCK PATENT GMBH, MERCK PATENT GESELLSCHAFT MIT BESCHRAENKTER HAFTUNG
Application year: 1991
Main classification: C09K19
IPC codes: C09K19, G02F1