NL1005373C2 - Liquid crystalline medium. - Google Patents

Description

Nw 1024

Title: Liquid crystalline medium

The invention relates to a liquid crystalline medium based on a mixture of polar compounds with negative dielectric anisotropy, which contains at least one compound of formula I and at least one compound of formula II, wherein R1, R2, R3 and R4 each independently H, an unsubstituted alkyl or alkenyl group of up to 18 carbon atoms, in which one or more non-adjacent CH2 groups may be replaced by a group selected from the group -O-, -S-, and -C * C-; o 1 or 2, and

L1 and L2 H or F

15 proposals.

The principle of the electrically regulated birefringence, the ECB effect (electrically controlled birefringence) or also DAP effect (Deformation aufgerichteter Phasen) was first described in 20 1971 (MF Schieckel and K. Fahrenschon, "Deformation of nematic liquid crystals with vertical orientation in electrical fields ", Appl. Phys. Lett. 19 (1971), 3912). Publications of J.F. Kahn (Appl * Phys.

Lett. 20 (1972), 1193) and G. Labrunie and J. Robert (J.

25 Appl. Phys. 44 (1973), 4869).

The publications of J. Robert and F. Clerc (SID 80 Digest Techn. Papers (1980), 30), J. Duchene (Displays 7 (1986), 3) and H. Schad (SID 82 Digest Techn. Papers (1982) , 244) have shown that liquid crystalline 30 phases must have high values for the ratio of the elastic constants K3 / K1, high values for the optical anisotropy Δη and for the dielectric anisotropy Δε values of -0.5 10n5373 2 and -5 for highly informative indicator elements that are based on the ECB effect. Electro-optical indicator elements based on the ECB effect display a homotropic edge-5 orientation.

For the technical application of this effect in electro-optical indicator elements, FK phases are required which must meet a multitude of requirements. Particularly important here are the chemical resistance to moisture, air and physical influences such as heat, radiation in the infrared, visible and ultraviolet region and electric direct and alternating current fields. Furthermore, liquid crystalline mesophase in a suitable temperature range and low viscosity is required from technically useful FK phases.

None of the hitherto known rows of liquid crystalline mesophase compounds exist to satisfy all of these requirements. Therefore, as a rule, mixtures of 2 to 25, preferably 3 to 18, compounds are prepared to obtain substances useful as FK phases. Optimal phases, however, could not be easily prepared in this way, since hitherto no liquid crystal materials with clearly negative dielectric anisotropy and sufficient long-term stability were available.

Matrix liquid crystal indicators (MFF indicators) are known. Active elements (i.e., transistors) can be used as non-linear elements for individual switching of the individual pixels.

One speaks then of an "active matrix", in which two types can be distinguished from 1. MOS (Metal Oxide Semiconductor) transistors on a silicon wafer as substrate.

2. Thin film transistors (TFT) on a glass plate as a substrate.

In type 1, the electro-optical effect usually uses the dynamic scattering or the guest-host effect. The use of single crystalline silicon as 1005373 3 substrate material limits the display size, because the module-like composition of various partial displays on the sides also leads to problems.

In the more promising type 2, which is preferred, the TN effect is usually used as the electro-optical effect. Two technologies are distinguished: TFTs from semiconductor compounds, such as CdSe, or TFTs based on polycrystalline or amorphous silicon. The latter technology is being worked on very intensively worldwide.

The TFT matrix is arranged on the inside of one glass plate of the indicator while the other glass plate on the inside carries the transparent counter electrode, in relation to the size of the pixel electrode, the TFT is very small and practically does not interfere with the image. This technology can also be extended to full-color image displays, in which a mosaic of red, green and blue filters is arranged such that a filter-20 element is located opposite a switchable pixel.

The TFT indicators known to date usually act as TN cells with crossed polarizers in transmission and are illuminated from behind.

The term MFF indicators here encompasses any matrix-25 display with integrated non-linear elements, i.e. in addition to the active matrix also indicators with passive elements, such as varistors or diodes (MIM = metal insulator-metal).

Such MFF indicators are particularly suitable for TV applications (eg, pocket televisions) or for highly informative displays in automotive or aircraft manufacturing. In addition to problems of angular dependence of contrast and switching times, MFF indicators present difficulties due to the insufficiently high resistivity of the liquid crystal mixtures [TOGASHI, S., SEKIGUCHI, K., TANABE, H ., YAMAMOTO, E., SORIMACHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H., Proc. Eurodisplay 84, Sept. 1984: A210-288 1005373 4

Matrix LCD Controlled by Double Stage Diode Rings, biz.

141 et seq., Paris; STROMER, M., Proc. Eurodisplay 84, Sept. 1984: Design of Thin Film Transistors for Matrix Adressing of Television Liquid Crystal Displays, biz. 145 et seq., Paris 5]. With decreasing resistance, the contrast of an MFF indicator deteriorates. Because the resistivity of the liquid crystal mixture generally decreases over the life of an MFF indicator due to interaction with the internal surfaces of the indicator, 10 a high (initial) resistance is very important for indicators that have acceptable resistance values over a long operating time. must own.

The disadvantage of the MFK-TN indicators known to date lies in their comparatively low contrast, the relatively high angle of view dependence and the difficulty of producing shades of gray in these indicators.

MFP indicators based on the ECB effect are known from EP 0 474 062. The FK blends described therein are based on 2,3-difluorophenyl derivatives which have an ester, ether or ethyl bridge, and exhibit low values of the voltage holding ratio (HR) after UV loading.

Therefore, there is still a great need for 25 MFF indicators with very high resistivity at the same time, large operating temperature range, short switching times and low threshold voltage, by means of which different shades of gray can be produced.

The object of the invention is to provide MFF indicators based on the ECB effect, which do not or only slightly have the above-mentioned drawbacks and at the same time have very high resistances.

It has now been found that this aim can be achieved when nematic liquid crystal mixtures are used in these indicator elements which contain at least one compound of formula I and at least one compound of formula II, in which R1-4, L1, L2 and o the claim 1 have the meaning indicated.

1005373 5

The object of the invention is therefore a liquid crystalline medium based on a mixture of polar compounds with negative dielectric anisotropy according to claim 1.

Particular preference is given to liquid crystalline mixtures containing one or more compounds of the formula la and one or more compounds of the formula Ib.

Preference is given to mixtures containing one or more compounds of the formula Ha and one or more compounds of the formula Ilb.

In a preferred embodiment, the mixture according to the invention essentially consists of the compounds Ia, ib, Ila and Ilb.

Preferably, R 1, R 2, R 3 and R 4 in the compounds of formulas I and II represent straight chain alkyl or alkoxy of 1 to 6 carbon atoms.

Preferred embodiments are further: a) Medium additionally containing one or more compounds of formula III, wherein R5 and R6 are each independently H, an unsubstituted alkyl or alkenyl group having up to 18 carbon atoms, wherein one or more non-adjacent CH2 groups can be replaced by a group selected from the group -O-, -S-, and -CC-.

Preferably R5 and R6 represent straight chain alkyl or alkoxy of 1 to 6 carbon atoms.

b) Medium consisting essentially of four or more compounds selected from formulas I and II and two or more compounds of formula III.

c) Medium containing at least four compounds of formula I.

d) Medium in which the content of compounds of formula I in the total mixture is at least 30% by weight.

1005373 6 e) Medium in which the content of compounds of formula II in the total mixture is at least 15% by weight.

f) Medium in which the content of compounds of formula III in the total mixture is 10-50% by weight.

g) Medium additionally containing one or more compounds of formula IV, wherein R7 and R8 are each independently H, a non-10 substituted alkyl or alkenyl group having up to 18 carbon atoms, wherein one or more non-adjacent CH2 groups are group selected from the group -0-, -S-, and -C * C- may be replaced, 15 proposals.

h) Liquid crystalline medium containing at least two compounds selected from formulas IVa and IVb, wherein Alkyl stands for C 1-6 alkyl.

Especially preferred is a medium containing a compound of formula IVa and at least one compound of formula IVb.

i) Liquid crystalline medium consisting essentially of 30-60 wt% of one or more compounds of formula I, 15-40 wt% of one or more compounds of formula II, and 10-50 wt% of one or more multiple compounds of formula III.

Another object of the invention is an electro-optical indicator with an active matrix addressing based on the ECB effect, characterized in that it contains as a dielectric a liquid crystalline medium according to any one of claims 1-11.

The mixtures according to the invention are particularly suitable for a VAN display (vertically aligned nematic display).

1005373 7

Preferably, the liquid crystal mixture has a nematic phase range of at least 60 K and a viscosity of at most 30 mm 2 / s at 20 ° C.

The liquid crystal mixture according to the invention has a Δε of about -0.5 to -5, in particular of about -2.0 to -4.5, wherein Δε represents the dielectric anisotropy.

The birefringence Δη in the liquid crystal mixture is usually between 0.04 and 0.12, preferably between 0.08 and 0.12. The dielectric constant ε || is preferably greater than or equal to 3, especially 3.2 to 8.5.

In a further embodiment, the media of the invention may additionally contain one or more compounds of formulas V to VIII, wherein r9-16 h, is an unsubstituted alkyl or alkenyl group having up to 18 carbon atoms, wherein one or more non-neighboring CH2 groups may be replaced by a group selected from the group -O-, -S-, and -C »C-20, and represent m 0 or 1.

Media containing one or more compounds of the formulas I, II, III and, optionally, one or more compounds of the formulas IV to VIII, generally exhibit birefringences between 0.10 and 0.20, preferably between 0.10 and 0.16.

The dielectrics may also contain further additives known to those skilled in the art and described in the literature. E.g. 0-15% pleochroic dyes can be added, as well as conductive salts, preferably ethyl dimethyldodecylammonium 4-hexoxybenzoate, tetrabutyl ammonium tetraphenyl boranate or complex salts of crown ethers (cf. eg Haller et al. Mol. Cryst. Liq. Cryst. Vol. 24, pp. 249-258 (1973)) to improve conductivity, or substances for altering the dielectric anisotropy, the viscosity and / or the orientation of the nematic phases. Such materials 1005373 8 are described, for example, in German Patent Applications Laid-Open Nos. 22 09 127, 22 40 864, 23 21 632, 23 38 281, 24 50 088, 26 37 430 and 28 53 728.

The individual components of formulas I to III 5 of the liquid crystal phases of the invention are either known or can be readily deduced from the prior art by those skilled in the art since they rely on standard methods described in the literature.

Corresponding compounds of formula I are described, for example, in WO 89/08633. The compounds of formula II are known from EP 0 022 183 and EP 0 051 738.

Corresponding compounds of formula III are described, for example, in DE 26 36 684. The compounds of formula IV are known from EP 0 132 553.

Corresponding compounds of formula V are described in WO 88/07514.

The nematic liquid crystal mixtures of the indicators of the invention preferably contain at least 30% of compounds of formula I, especially most preferably 30 to 60% of compounds of formula I.

The nematic liquid crystal mixtures in the indicators according to the invention generally contain two components A and B, which in turn consist of one or more individual compounds.

Component A has a clearly negative dielectric anisotropy and gives the nematic phase a dielectric anisotropy of s -0.3. It preferably contains compounds of formulas Ia and / or Ib.

Preferably, one (or more) individual compound (s) are selected for component A and have a value Δε s -0.8. This value should be more negative the smaller the proportion of A in the total mixture.

The component B has a pronounced nematogenicity 35 and a flow viscosity of no more than 30mm2.s -1, preferably no more than 25mm2.s -1 at 20 ° C.

Particularly preferred individual compounds of component B are extremely low viscosity nematic liquid crystals with a viscosity of no more than 18, preferably no more than 12 mm 2 s -1 at 20 ° C. Component B is monotropic or enantiotropic nematic, shows no smectic phases and can prevent the occurrence of smectic phases to very low temperatures in liquid crystal mixtures. For example, if a smectic liquid crystal mixture is mixed with other materials of high nematogenicity, the nematogenicity of these materials can be compared due to the degree of suppression of smectic phases realized.

A variety of suitable materials is known to the person skilled in the art from the literature. Especially preferred are compounds of formula IV.

In addition, these liquid crystal phases can also contain more than 18 components, preferably 18 to 25 components.

Preferably phases 4 to 15, in particular 5 to 12, contain compounds of formulas I, II and III and, optionally, compounds of formulas IV, V, VI, VII and VIII.

In addition to compounds of formulas I to VIII, other components may also be present, e.g. in an amount of up to 45% of the total mixture, but preferably up to 34%, in particular up to 10%.

The other ingredients are preferably selected from the nematic or nematogenic substances, in particular the known substances, from the classes of azoxybenzenes, benzylidene anilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, cyclohexanecarboxylic acid phenyl or 30-cyclohexyl esters, phenylcyclohexes cyclohexylbiphenyls, cyclohexylcyclohexanes, cyclohexylnaphthalenes, 1,4-bis-cyclohexylbiphenyls or cyclohexylpyrimidines, phenyl or cyclohexyl dioxanes, optionally halogenated stilbenes, benzylphenyl ethers, substituted cinnamic acids.

The main compounds which are suitable as constituents of such liquid crystal phases can be characterized by formula IX, wherein 1005373 L1 and E each comprise a carbo or heterocyclic ring system from the 1,4-di-substituted benzene and cyclohexane rings, 4 4'-di-substituted biphenyl, phenylcyclohexane and cyclohexylcyclohexane-5 systems, 2,5-di-substituted pyrimidine and 1,3-dioxane rings, 2,6-di-substituted naphthalene, di- and tetrahydronaphthalene, quinazoline and tetrahydroquinazoline formed group, G -CH = CH- -N (0) = N- 10 -CH-CQ- -CH = N (0) - -CC- -CH2-CH2- -CO-O- -CH2- O - CO-S- -CH2-S - CH = N- -COO-Phe-COO- 15 or a single CC bond, Q halogen, preferably chlorine, or -CN, and R17 and R18 each alkyl, alkoxy, alkanoyloxy or alkoxycarbonylloxy with up to 18, preferably up to 8 carbon atoms, or one of these groups also represent CN, NC, NO2, 20 CF3, F, Cl or Br.

Most of these compounds have R17 and R18 different from each other, with one of these radicals usually being an alkyl or alkoxy group. Other variants of the provided substituents are also usual. Many such substances or also mixtures thereof are commercially available. All these substances can be prepared according to methods known from the literature.

The media of the invention may further contain one or more dyes.

The structure of the liquid crystal indicators according to the invention corresponds to the usual geometry as described, for example, in published European patent application no. 0 240 379.

The following examples are illustrative of the invention without limiting it. Before and after percentages indicate percent by weight; all temperatures are given in degrees Celsius.

1005373 11

Mixtures according to the invention contain, in addition to the compounds of formulas I and II, in particular one or more compounds of the compounds mentioned below (n, m: 1-18): 5 PCH-nOmFF CCP-nOmFF CCP-nmFF BCH-nm BCH- nmF 10 D-nOmFF CBC-nmF CCH-nOm CCH-nm CP-nOmFF 15 CH-nm BCN-nm PTP-nOmFF CPTP-nOmFF PCH-nOm 20 PCH-nm

The indicated threshold voltage values V (10, 20) were measured in a conventional homotropic cell with a layer thickness of 30 μπι at 20 ° C.

The indicator used for the measurement of the threshold voltage has two plane-parallel support plates, at a distance of 5 µm, and electrode layers with lecithin orientation layers on the inner sides of the support plates, which achieve a homotropic orientation of the liquid crystals.

* 005373 12

Examples

Example 1

5 PCH-302FF 10.0% clearance point: + 82 ° C

PCH-502FF 10.0% Δη [589 nm, 20 ° C]: +0.1106 CCP-302FF 9.0% Δε [1 kHz, 20 ° C]: -2.6 CCP-502FF 7.0% ε | j [1 kHz, 20 ° C]: 3.5 CCP-21FF 8.0% c_l [1 kHz, 20 ° C]: 6.1 10 CCP-31FF 8.0% Δε / εχ [1 kHz, 20 ° C]: -0.43 BCH-32 6.0% V (io, o.20): 2.65V (capacitive) BCH-52 5.0% K3 / K1: 1.20 BCH-32F 7.0% BCH-52F 7.0% 15 PCH-301 8.0% PCH-302 15.0% 1005373

Claims (14)

Liquid crystalline medium based on a mixture of polar compounds with negative dielectric anisotropy, characterized in that it contains at least one compound of formula I and at least one compound of formula Ha, wherein R1, R2, R3 and R4 each independently of one another H, a unsubstituted alkyl or alkenyl group having up to 18 carbon atoms, in which one or more non-adjacent CH 2 groups may be replaced by a group selected from the group -0-, -S-, -C = C-; and 0 1 or 2, suggest. 2. Medium according to claim 1, characterized in that it additionally contains one or more compounds of formula III, wherein R5 and R6 each independently H, an unsubstituted alkyl or alkenyl group with up to 18 carbon atoms, in which a or suggest multiple non-neighboring CH2 groups may be replaced by a group selected from the group -O-, -S-, and -C = C-. 3. Medium according to claim 1 or 2, characterized in that it additionally contains one or more compounds of formula IV, wherein R7 and R8 each independently H, an unsubstituted alkyl or alkenyl group with up to 18 carbon atoms, wherein one or more multiple non-adjacent CH2 groups may be replaced by a group selected from the group -O-, -S-, and -C = c-. 100 5373 Medium according to at least one of claims 1 to 3, characterized in that it consists essentially of four or more compounds selected from formulas I and II and two or more compounds of formula III. Medium according to at least one of claims 1 to 4, characterized in that it contains at least four compounds of the formula I. Medium according to any one of claims 1 to 5, characterized in that the content of compounds of the formula I in the total mixture is at least 30% by weight. Medium according to any one of claims 1 to 6, characterized in that the content of compounds of formula II in the total mixture is at least 15% by weight. Medium according to any one of claims 1-7, characterized in that it contains at least one or more compounds of formula Ilb. Medium according to any one of claims 1-8, characterized in that the content of compounds of formula III in the total mixture is 10-50% by weight. Liquid crystalline medium according to claim 3, characterized in that it contains at least two compounds selected from formulas IVa and IVb, wherein Alkyl stands for C 1-6 alkyl. Liquid crystalline medium according to any one of claims 1 to 10, characterized in that it consists essentially of 30-60% by weight of one or more compounds of the formula I, 15-40% by weight of one or more compounds of formula II, and 10-50% by weight of one or more compounds of formula III. Liquid crystalline medium according to claim 1 or 2, characterized in that it additionally contains one or more compounds selected from formulas V to VIII, wherein 1005373 R9 "16 H, an unsubstituted alkyl or alkenyl group having up to to 18 carbon atoms, in which one or more non-neighboring O¾ groups may be replaced by a group selected from the group -O-, -S-, and -CsC-, and m represents 0 or 1. 13. An electro-optical indicator with an active matrix addressing based on the ECB effect, characterized in that it contains as a dielectric a liquid crystalline medium according to any one of claims 1-12. Electro-optical indicator according to claim 13, characterized in that it is a VAN display. 1005373