DE4034590A1 - Electro-optical LC system - Google Patents

Abstract

(+1.11.89(2), 9.12.89, 10.1.90(2), 12.1.90, 16.1.90, 19.1.90(3), 22.1.90, 23.1.90, 25.1.90-DE-936307/8, 940788, 000470/1, 000723, 001023, 001539, 001540/1, 001683, 001843, 002146) Electro-optical LC system comprises a dielectrically positive LC mixt. (LCM) and another optically transparent medium (M2) between 2 electrodes which may be mounted on substrate plates; the LC mols. have an irregular orientation in the "off" state one of the refractive indices of LCM matches that of the matrix (nM) and/or the ratio of the masses (LCM):(M2) is 1.5 or above, and the system shows reduced transmission in one of the switching states w.r.t. the other state, irrespective of the polarisation of the incident light; the novelty is that LCM contains cpd(s). of formula (I). In (I), Q1 = A1-Z1-(Z2-Z2)m- (with A1, A2 = trans-1,4-cyclohexylene (Cyc), 1,4-phenylene (Phe), 2-fluoro-Phe or 3-fluoro-Phe; one of the gps. A1 and (if present) A2 can also = pyridine-, pyrimidine-, 1,3-dioxan- or tetrahydropyran-2,5-diyl, or naphthalene-2,6-diyl; Z1, Z2 = single bond, CH2CH2, COO, OCO, -CC-, and/or CH2O; m = 0, 1 or 2); Y, X = H or F; one gp. X or Y can also = Cl; W = CN, Cl, F, CF3, OCF3, OCHF2, NCS or R2 (with R2 = as for R1 below); R1 = 1-12C alkyl, opt. with 1 or 2 non-adjacent CH2 gps. replaced by O or CH=CH.

Description

The invention relates to an electrically switchable liquid crystal system, containing nematic microdroplets with positive dielectric anisotropy in a clear Matrix.

Examples of such systems are NCAP and PDLD films (NCAP = nematic curvilinear aligned phases, PDLC = polymer dispersed liquid crystal). NCAP films become common obtained by encapsulating the polymer Material such as B. polyvinyl alcohol, the liquid crystal mixture and a carrier material such as e.g. B. water, in be mixed intimately in a colloid mill. Subsequently the carrier material z. B. removed by drying. A corresponding method is described in US 44 35 047. In contrast, the z. B. in EP 02 72 582 and US 46 88 900 described production of PDLC films the liquid crystal mixture first with monomers or Oligomers of the matrix-forming material mixed homogeneously. The mixture is then polymerized and the phase separation induced, whereby between TIPS (temperature-induced phase separation), SIPS (solvent-induced phase separation) and PIPS (polymerization-induced phase separation) is distinguished (Mol. Cryst. Liq. Cryst. Inc. Nonlin. Opt. 157 (1988) 427).  

The liquid crystal mixture generally has a positive dielectric anisotropy Δε and a relatively high optical anisotropy Δn and the ordinary refractive index n _o is usually chosen so that it more or less coincides with the refractive index n _{M of} the polymer matrix.

An electrically switchable light scattering effect is observed on these electro-optical systems. If no voltage is applied to the electrodes, between which the matrix is usually sandwiched, incident light is strongly scattered on the microdroplets, which have a statistical distribution of their texture, and the system is opaque. When a voltage is applied, the liquid crystal molecules are aligned parallel to the field and perpendicular to the E-vector of the light passing through. Due to the adjustment of n _M and n _o , vertically incident light now sees a more or less optically isotropic medium and the system appears transparent. Another embodiment is described in EP 02 72 585, in which the refractive index n _x , which the liquid crystal has with a completely statistical orientation, is matched to the refractive index of the matrix n _M. In this case, the system is transparent in the field-free state, and it is converted to the opaque state by applying a voltage.

Such systems are primarily for large-area display systems, for architectural applications (windows, room dividers, Sunroofs etc.) and for motor vehicles (windows, Canopies, etc.) have been proposed, these Systems also for temperature regulation by controlled Shield the solar radiation. You can by Applying a DC or AC voltage switched will.  

Because these systems are particularly suitable for "outdoor" applications Liquid crystal mixtures are provided needed by a high clearing point, high Δε, a wide nematic range and high UV and temperature stability Marked are.

Other applications include:

• - GH display systems, the spectrum being simple Segment displays up to displays on which with any electrode pattern using conventional printing techniques can be applied. Applications: automotive, Large advertisements, advertising space, clocks;
• - Matrix displays with high information content;
• - projection systems;
• - Counter.

Here too, liquid crystal mixtures are used in particular high Δε and high electrical resistance needed.

In conventional electro-optic liquid crystal systems LC mixtures are usually used, which consist of alkyl or alkoxycyanobiphenylene and terphenylene. So z. B. in US 46 88 900 and EP 02 72 585 the use the liquid crystal mixture E8 (manufactured by BDH, Poole, Great Britain). This liquid crystal mixture is characterized by a high value for the optical anisotropy Δn of 0.247 and a relatively high Flow viscosity value η (20 ° C) of 54 mm² / s, however has a relatively low clearing point at the same time of only 72 ° C. Polynuclear polyphenyl compounds are added to the mixture  to increase the clearing point too, this results in a higher value for the flow viscosity η and an unchanged high or higher value for the optical anisotropy Δn. On the one hand, high Δn values ensure for strong light scattering in the opaque state, on the other hand, however, they cloud the system in the switched state ("haze") and thus one significant deterioration in the electro-optical properties. In systems that are relative low-frequency AC voltage can be controlled, a high flow viscosity η is desirable in order to avoid flicker Get ad; on the other hand, however, in Matrix displays with high information content for implementation faster switching times with liquid crystal mixtures relatively low viscosity needed. E8 has a relative high dielectric anisotropy of Δε = 15.6. To Achieve the lowest possible threshold voltage, however even higher values for Δε advantageous.

The liquid crystal mixture E7 used in US Pat. No. 4,671,618 (manufactured by BDH, Poole, Great Britain), which also consists of alkyl and alkoxycyanobiphenylene and terphenylene, has a low flow viscosity with η = 39 mm² / s and a with Δn = 0.225 somewhat smaller optical anisotropy Δn than E8, but at the same time the clearing point T _C = 60.5 ° C is considerably lower. The dielectric anisotropy is Δε = 13.8.

The liquid crystals used so far meet the Demands for a wide nematic area, one high clearing point, very high stability, high Nematogenicity, one with regard to the respective application Optimizable optical anisotropy Δn and flow viscosity η and a high Δε are insufficient.  

In addition, the previous liquid crystals often have but also insufficient miscibility with the monomers and / or oligomers of the used to form the matrix Polymers on what in particular the application of the PIPS technology significantly restricted. Furthermore the liquid crystals are often too high Solubility marked in the polymer. Another There is often a disadvantage of the previous liquid crystals in that the liquid crystal is one for each Application of unfavorable temperature dependence of the electro-optical Parameters such as B. shows the threshold voltage.

There is therefore still a great need for electro-optical Liquid crystal systems that match the corresponding Better meet requirements and the described Do not have disadvantages or only to a lesser extent.

The invention was based on the object of electro-optical To provide liquid crystal systems that the listed Proportion of conventional systems not or only to a small extent.

Surprisingly, it has now been found that this task can be solved if one uses liquid crystal mixtures for these systems used one or more connections of formula I included

wherein
one of Q¹ and Q² 3-fluoro-4-cyanophenyl or 3,5-difluoro-4-cyanophenyl and the other group

taking at least one of the rings

and the other ring

or trans-1,4-cyclohexylene,
R is alkyl with up to 12 carbon atoms, in which one or two non-adjacent CH₂ groups can be replaced by -O- and / or -CH = CH-, and
n = 1 or in the case

and Q² = R n = 0 mean.

The invention thus relates to an electrically switchable Liquid crystal system containing nematic microdroplets with positive dielectric anisotropy in a matrix, the microdroplets being one or more Contain compounds of formula I. Subject of the invention are also corresponding liquid crystal mixtures and the use of these liquid crystal mixtures in electro-optical systems.

The structure of the electro-optical liquid crystal systems according to the invention corresponds to that for such systems usual design: the transparent matrix in which the Liquid crystal mixture microdispersed or microencapsulated is sandwiched between the conductive ones Electrodes with appropriate leads and at least one of which is transparent. The term conventional construction is broad and encompasses all modifications and modifications.  

The matrix is based in particular on isotropic thermoplastics, Thermosets and elastomers. The received Systems can be flexible depending on the intended use, be elastic or rigid.

A matrix based on a thermoplastic polymer can at temperatures greater than the glass temperature the matrix, easily by the action of a mechanical Tension can be deformed. The caused by it The droplet shape can be changed by cooling the matrix frozen to temperatures below the glass temperature will.

While flexible and / or elastic systems are preferred based on thermoplastics and / or elastomers preferably thermosetting for the production of rigid systems Polymers used. This can occur during curing be mechanically deformed, and the shape and arrangement the microdroplet is in the cured matrix fixed.

Polymers particularly preferred for producing the matrix are z. B. in US 39 35 337, US 46 88 900, US 46 71 618, US 46 73 255, US 44 35 047, EP 03 13 053 and EP 02 72 585 disclosed.

In addition, other transparent materials can also be used such as B. inorganic oxide glass monoliths (US 48 14 211), other inorganic materials (see. e.g. B. Japanese Patent Application 3 03 325/1988) or other materials can also be used.

Preferred embodiment of the electro-optical according to the invention Liquid crystal systems are NCAP films, PDLC films and manufactured according to modified processes  Plastic films. Processes for making these films are z. B. in US 39 35 337, US 46 88 900, US 46 73 255, US 46 71 618, US 44 35 047, EP 02 72 595, EP 03 13 053, J.L. West, Mol. Cryst. Liq. Cryst. 157 (1988) 428, P. S. Drzaic, Liq. Cryst. 3/11 (1988) 1546 and J.W. Doane et al., Appl. Phys. Lett. 48/4 (1986) 269. But there are other embodiments of the invention includes.

The film thickness d is usually chosen to be small in order to achieve the lowest possible threshold voltage V _th . So z. B. reported in US 44 35 047 film thicknesses of 0.8 and 1.6 mm, while in US 46 88 900 layer thicknesses between 10 microns and 300 microns are specified. The electro-optical systems according to the invention only have layer thicknesses d that are significantly larger than a few mm in exceptional cases; layer thicknesses d ≦ 2 mm are preferred.

The threshold voltage is also affected by the size of the microdroplets. In general, smaller microdroplets result in a higher threshold voltage V _th , but shorter switching times t _on and t _off (US Pat. No. 4,673,255). Experimental methods for influencing the mean droplet size are e.g. B. in US 46 73 255 and in JL West, Mol. Cryst. Liq. Cryst. Inc. Nonlin. Opt., 157 (1988) 427. In US 46 73 255 mean drop diameters between 0.1 microns and 8 microns are given, while z. B. a matrix based on a glass monolith has pores with a diameter between 15 and 2000 Å.

A major difference between the electro-optical according to the invention Liquid crystal systems to the usual ones however, consists in the liquid crystal mixture used.

The liquid crystal media according to the invention contain at least one compound of formula I.  

The compounds of formula I include dinuclear compounds of the formula Ia-Id, which are preferred:

R is preferably alkyl, alkenyl or alkoxy 1-10, but especially with 1-8 carbon atoms. More preferred are n-alkoxyalkyl compounds and in particular n-alkoxymethyl and n-alkoxyethyl compounds. Liquid crystal media, the compounds of the formulas Ib and Id contain, have particularly advantageous values for the dielectric anisotropy.

The compounds of formula I further comprise trinuclear Compounds of the formulas Ib1-Ib8

In the compounds of the sub-formulas Ib1-Ib8, R means preferably with n-alkyl, n-alkenyl or n-alkoxy 1-10 carbon atoms, also n-alkoxymethyl or n-alkoxyethyl with 1-8 C atoms.

Such compounds are very particularly preferred Formulas Ib1-Ib8, where R is methyl, ethyl, propyl, Butyl, pentyl, hexyl, heptyl, octyl, methoxy, ethoxy, Propoxy, butoxy, pentoxy, hexoxy, methoxymethyl, ethoxymethyl, Propoxymethyl, butoxymethyl, pentoxymethyl, Methoxyethyl, ethoxyethyl, propoxyethyl, butoxyethyl or pentoxyethyl means.  

The radical R in the compounds of the formula I can be straight-chain or be branched. R is preferably straight-chain, however, compounds of formula I with branched alkyl or alkoxy radicals occasionally because of a better solubility in the usual liquid crystalline Base materials may be important, especially but as chiral dopants if they are optically active. Electro-optical systems according to the The preamble of claim 1, the liquid crystal of which or contains several chiral components are in DE 39 11 255.1.

Branched groups of this type usually contain no more than a chain branch. Preferred branched Radicals R are isopropyl, 2-butyl (= 1-methylpropyl), Isobutyl (= 2-methylpropyl), 2-methylbutyl, isopentyl (= 3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, 2-octyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy, 2-octyloxy, 2-oxa-methylbutyl, 3-oxa-4-methylpentyl, 4-methylhexyl, 2-nonyl, 6-methyloctoxy, 2-methyl-3-oxapentyl, 2-methyl-3-oxahexyl.

The compounds of formula I are known per se Methods as described in the literature (e.g. in standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg-Thieme-Verlag, Stuttgart Bd IX, P. 867 ff.) Are described, namely under reaction conditions, known for the above-mentioned implementations and are suitable. You can also use known, Variants not mentioned here do.  

Most of the compounds of the formula I are known (DE 32 09 178, JP 62-1 03 057, DE 39 29 418, JP 63-2 16 858, DE 34 01 320, EP 01 19 756, DE 36 32 411, EP 02 05 998). All compounds of formula I can according to the there described methods are produced.

The liquid crystal mixtures according to the invention are based in addition to compounds of formula I preferably on compounds of formulas II-IV

wherein
R¹ are each independently an alkyl group with 1-15 C atoms, in which one or two non-adjacent CH₂ groups can also be replaced by -O-, -CO- and / or -CH = CH,
Y is a single bond, -COO- or -OOC-, and

mean.

The liquid crystal mixtures according to the invention can contain other ingredients, preferably selected are made from nematic or nematogenic (monotropic or isotropic) substances, especially substances made of  the classes of azoxybenzenes, benzylidene anilines, biphenyls, Terphenyls, phenyl or cyclohexyl benzoates, cyclohexane carboxylic acid phenyl or cyclohexyl ester, phenyl or Cyclohexyl ester of cyclohexylbenzoic acid, phenyl or Cyclohexyl ester of cyclohexylcyclohexane carboxylic acid, Cyclohexylphenyl ester of benzoic acid, cyclohexane carboxylic acid, or the cyclohexylcyclohexane carboxylic acid, Phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, Cyclohexylcyclohexanes, cyclohexylcyclohexenes, Cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl or Cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, Phenyl- or cyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithiane, 1,2-diphenylethane, 1,2-dicyclohexylethane, 1-phenyl-2-cyclohexylethane, 1-cyclohexyl-2- (4-phenylcyclohexyl) ethane, 1-cyclohexyl-2-biphenylylethane, 1-phenyl-2-cyclohexylphenylethane, optionally halogenated Stilbene, benzylphenyl ether, tolanes and substituted Cinnamic acids. The 1,4-phenylene groups in these Compounds can also be fluorinated.

The most important as further components of the in the electro-optical systems according to the invention used Leave liquid crystals in question are characterized by the formulas 1, 2, 3, 4 and 5:

R′-L-E-R ′ ′ (1)

R′-L-COO-E-R ′ ′ (2)

R′-L-OOC-E-R ′ ′ (3)

R′-L-CH₂CH₂-E-R ′ ′ (4)

R′-L-C≡C-E-R ′ ′ (5)

In formulas 1, 2, 3, 4 and 5, L and E denote that can be the same or different, each independently one bivalent residue from the other from -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-,  -G-Phe- and -G-Cyc- and their mirror images formed Groups where Phe is unsubstituted or through Fluorine substituted 1,4-phenylene, Cyc trans-1,4-cyclohexylene or 1,4-cyclohexenylene, pyr pyrimidine-2,5-diyl or pyridine-2,5-diyl, dio 1,3-dioxane-2,5-diyl and G 2- (trans-1,4-cyclohexyl) ethyl, pyrimidine-2,5-diyl, Pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl mean.

Preferably one of the residues L and E is Cyc, Phe or Pyr. E is preferably Cyc, Phe or Phe-Cyc. Preferably the media according to the invention contain one or several components selected from the compounds of Formulas 1, 2, 3, 4 and 5, where L and E are selected from the group Cyc, Phe and Pyr and at the same time one or several components selected from the compounds of the formulas 1, 2, 3, 4 and 5, wherein one of the radicals L and E is selected from the group consisting of Cyc, Phe and Pyr and the other residue is selected from the group -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-, and optionally one or more components selected from the Compounds of formulas 1, 2, 3, 4 and 5, wherein the Residues L and E are selected from the group -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-.

R 'and R' 'in the compounds of the sub-formulas 1a, 2a, 3a, 4a and 5a each independently Alkyl, alkenyl, alkoxy, alkenyloxy or alkanoyloxy with up to 8 carbon atoms. Most of these connections R 'and R' 'are different from each other, whereby one of these residues is mostly alkyl or alkenyl. In the Connections of sub-formulas 1b, 2b, 3b, 4b and 5b means R '' -CN, -CF₃, -OCF₃, -OCHF₂, F, Cl or -NCS; R¹ has the same for the compounds of the sub-formulas 1a to 5a meaning given and is preferred Alkyl or alkenyl. But also other variants of the provided substituents in the compounds of the  Formulas 1, 2, 3, 4 and 5 are used. Many such Substances or mixtures thereof are commercially available. All of these substances are known from the literature Methods or available in analogy.

The in the electro-optical systems according to the invention Liquid crystals used preferably contain in addition Components from the group of compounds 1a, 2a, 3a, 4a and 5a (group 1) also components from the group of Compounds 1b, 2b, 3b, 4b and 5b (Group 2), their Shares are preferably as follows:

Group 1:
0 to 60%, in particular 5 to 50%,
Group 2:
0 to 60%, especially 5 to 40%.

The in the electro-optical systems according to the invention liquid crystals used preferably contain 1-40%, in particular 5-30%, of compounds of the formula I. The liquid crystals preferably contain 1-5, in particular however 1-3 compounds of the formula I.

The proportion of those consisting of compounds of formulas I-IV Base mixture on the in the electro-optical according to the invention Systems used liquid crystals preferably 15% -100%, but in particular 25% -100%. The basic mixture is based on compounds of the formula I particularly preferred on the following smaller group of compounds, wherein R¹ has the meaning given above Has:

The following mixtures 1-6 are very particularly preferred, the at least one component each of the listed Formulas in the specified mass percentage range included, the sum of the mass percentages in the mixtures contained and listed below Formulas falling connections between 10% and 90% and in particular is between 15% and 85%.  

The electro-optical liquid crystal systems according to the invention are preferably characterized in that none or only one during the manufacture of the system little interaction of the components of the liquid crystal mixture with the polymeric carrier material polar groups comes about.

The electro-optical liquid crystal systems according to the invention can by applying a DC or AC voltage be switched. However, one is preferred  AC voltage is used, which has an effective value of AC amplitude between 1 and 240 volts and an AC voltage frequency between 10 and 10 kHz having. Amplitudes between are particularly preferred 2 and 220 volts and frequencies between 20 and 120 Hz. The amplitude of the is very particularly preferably AC voltage between 2 and 130 V.

The dielectric anisotropy of the liquid crystal mixture used is positive Δε <0 and preferably Δε <3. For smaller values of the dielectric anisotropy Δε very high threshold voltages are observed. Values Δε <5 are particularly preferred, in particular Δε <10 and very particularly Δε <15.

The preparation of the liquid crystal mixtures which can be used according to the invention takes place in a conventional manner. As a rule, the desired amount is less Amount of components used in the main ingredient constituent components solved, useful at elevated temperature. It is also possible to find solutions to the Components in an organic solvent, e.g. B. in Mix acetone, chloroform or methanol and that Remove solvent after thorough mixing, for example by distillation.

The liquid crystal mixtures described can be added by suitable additives be modified so that they are in all electro-optical systems according to the generic term of claim 1 can be used.

Such additives are known to the expert and in the Literature described in detail. So z. B. pleochroic Dyes for the production of colored electro-optical Systems or substances to change the dielectric anisotropy, the optical anisotropy,  the viscosity and / or the temperature dependence of electro-optical Parameters of the media can be added. Such Substances are e.g. B. in H. Kelker, R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980 and in DE-OS 22 09 127, 22 40 864, 23 21 632, 23 38 281, 24 50 088, 26 37 430, 28 53 728 and 29 02 177.

Electro-optical liquid crystal systems in which the Liquid crystal mixture pleochroic dyes in a weight percentage range of 0-25%, in particular 0-20% and especially 0-15% are added prefers.

The person skilled in the art can further select additives from the large pool of nematic or nematogenic substances to the liquid crystal mixtures described in such a way that the birefringence Δn and / or the ordinary refractive index n _o and / or other refractive indices and / or the viscosity and / or the dielectric anisotropy and / or further parameters of the liquid crystal can be specifically optimized with regard to the respective application.

To increase the clearing point, the person skilled in the art Systems used according to the invention liquid crystal mixtures e.g. B. add clarifying substances such. B

where R² and R³ each independently represent alkyl, methoxy, alkoxycarbonyl or alkanoyloxy with 1-15 C atoms. The person skilled in the art will preferably choose the concentration of such additives such that, in particular, Δn and / or n _o and / or another refractive index and / or Δε to be adapted to the particular configuration of the electro-optical system according to the invention is only acceptable and / or small and / or in particular negligible extent is affected.

If the system according to the invention with an AC voltage controlled, is the use of a highly viscous liquid crystal mixture required, otherwise otherwise in particular low to medium frequencies a flickering display with unsatisfactory transmission in the switched state results. A person skilled in the art can increase the viscosity the liquid crystal mixture highly viscous liquid crystal compounds or in particular one or more Side chain polymers, as described in DE 39 19 942 is to clog. Will the electro-optical system oppose it e.g. B. used as a matrix display with high information content, are especially low-viscosity liquid crystal mixtures preferred to achieve short switching times. The professional can be nematic or out of the large pool nematogenic compounds of low viscosity select how B.

where R² and R³ have the meaning given above. The person skilled in the art will choose the substances used for modifying the viscosity and their concentration so that other decisive parameters of the liquid crystal mixture, such as, for. B. Δn, Δε and when using viscosity depressants in particular T _{c is} only influenced to an acceptable and / or small and / or insignificant extent.

If necessary, highly nematogenic substances such. B.

can be added, the expert taking into account that through such additions other parameters and in particular the solubility of the liquid crystal mixture in the for the polymer used did not change too much will.

The person skilled in the art can modify the birefringence e.g. B. in liquid crystal mixtures, the compounds of Formulas II-IV contain the relative proportion of these compounds vary on the mix; for mixtures with very high Δn can e.g. B. in particular 4-alkyl or alkoxy-4 'or 4' '- cyano-biphenyls or -terphenyls used will.

The person skilled in the art will choose the concentration of such additives in such a way that the liquid crystal mixture is optimally matched to the particular design of the electro-optical system; in particular, he will take care that Δn and / or n _o and / or one or more further refractive indices of the liquid crystal are influenced only to an acceptable and / or small and / or negligible extent.

Due to the additives described, the liquid crystal modified with regard to the respective application and be optimized. It is crucial, however, that liquid crystal mixtures, containing compounds of formula I. and in particular those additionally containing one or several compounds of formulas II-IV, for use in electro-optical systems according to the invention in particular are suitable. However, the are particularly suitable  Liquid crystal mixtures 1-6, in addition to compounds of formula I one or more compounds of the formula II-IV in defined mass percentage ranges contain.

Liquid crystal mixtures containing these compounds of the formula I. places for use in electro-optical Systems also particularly suitable "stable Framework mixtures ", which are generally described by the Additives optimized with regard to special requirements can be without other parameters of the mixture at the same time too drastic and usability the mixture in the electro-optical systems considerably experienced adverse change.

Draw the liquid crystals that can be used according to the invention advantageous birefringence values Δn and the flow viscosity η, high stability, poor miscibility with that used for the matrix Polymer and especially by a wide mesogenic Area, a relatively high clearing point and beneficial Values for the dielectric anisotropy and the temperature dependence the electro-optical parameters. The liquid crystals correspond to those described at the beginning Requirements when used in a electro-optical system according to the preamble of Claim 1 are made, in a particularly high degree and much better than before in these systems liquid crystals used.

Draw the electro-optical systems according to the invention through a wide range of working temperatures, favorable values of the electro-optical parameters and their Temperature dependency and in particular through low threshold voltage.  

The following examples are intended to illustrate the invention, without limiting it.

It means:
K: crystalline solid state, S: smectic phase (the index indicates the phase type),
N: nematic phase,
Ch: cholesteric phase,
I: Isotropic phase.

The number between two symbols indicates the transition temperature in degrees Celsius.

The percentages given are percentages by mass.

example 1

• a) An electro-optical system containing a liquid crystal mixture consisting of the following compounds: 20% 1- (trans-4- (trans-4-propylcyclohexyl) cyclohexyl) -2- (3-fluoro-4-cyanophenyl) - ethane
  14.4% p-trans-4-propylcyclohexyl benzonitrile
  11.2% p-trans-4-butylcyclohexyl benzonitrile
  20% p-trans-4-pentylcyclohexyl benzonitrile
  12% p-trans-4-heptylcyclohexyl benzonitrile
  5.6% 4- (trans-4-pentylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl
  4.8% 4-pentyl-4 ′ ′ - cyanoterphenyl
  6.4% 4- (trans-4-propylcyclohexyl) -phenyl-trans-4-butylcyclohexyl-carboxylate
  5.6% 4- (trans-4-pentylcyclohexyl) -4'-cyanobiphenyl.
• b) The electro-optical system is made according to different procedures 1.-3. produced.
  • 1. The liquid crystal mixture from a) is the UV-curable adhesive NOA 65 (Nordland Products) in a ratio of 1.6: 1 stirred at room temperature until a clear solution is obtained, which together with spacers between 2 transparent, provided with electrode layers Glass substrates is brought. The glass substrates are pressed together, whereby a uniform film with a thickness of 20 μm is obtained, which is cured by UV radiation for 1 minute.
  • 2. The liquid crystal mixture from a) is stirred with Epikote 828 and Capcure 3-800 (Miller Stephenson Company) in a ratio of 1: 1: 1 at room temperature until a clear solution is obtained; the stirring time is kept as short as possible since the solution has already hardened after about 1/2 hour at room temperature. The solution is placed together with spacers between 2 transparent glass substrates provided with electrode layers, which are pressed together, whereby a uniform film with a thickness of 20 μm is obtained. To accelerate the curing process, the films can be heated to temperatures up to 100 ° C.
  • 3. 5 g of the liquid crystal mixture from a) are stirred with 15 g of 20% aqueous PVA solution at room temperature for 2 minutes at 2000 rpm. The solution obtained is degassed for 24 hours and applied together with spacers in a thin layer to a glass substrate provided with an electrode layer. The assembly is dried at 85 ° C. for 1 hour before a second glass substrate provided with an electrode layer is pressed on, whereby a uniform film with a thickness of 20 μm is obtained. The system obtained in this way is dried at 85 ° C. for a further 24 h.

According to the procedure b) 1.-3. manufactured electro-optical Systems are characterized by a wide working temperature range, favorable values for the electro-optical Parameters and their temperature dependence and in particular characterized by a low threshold voltage.

Claims (12)

1. Electrically switchable liquid crystal system containing nematic microdroplets with positive dielectric anisotropy in a transparent matrix, the microdroplets containing one or more compounds of the formula I. wherein
one of Q¹ and Q² 3-fluoro-4-cyanophenyl or 3,5-difluoro-4-cyanophenyl and the other group taking at least one of the rings and the other ring or trans-1,4-cyclohexylene,
R alkyl having up to 12 carbon atoms, in which one or two non-adjacent CH₂ groups and can be replaced by -O- and / or -CH = CH-, and
n = 1 or in the case and Q² = R n = 0 mean. 2. System according to claim 1, characterized in that the liquid crystal contains one or more compounds selected from the compounds of the formulas II-IV, wherein
R¹ are each independently an alkyl group with 1-15 C atoms, in which one or two non-adjacent CH₂ groups can also be replaced by -O-, -CO- and / or -CH = CH-,
Y is a single bond, -COO- or -OOC-, and mean. 3. System according to claim 2, characterized in that the proportion of those consisting of compounds I-IV Base mixture on the liquid crystal 15-100% is.   4. Electro-optical system according to at least one of the Claims 1-3, characterized in that the liquid crystal contains more connections that from the classes of azoxybenzenes, benzylidene anilines, Biphenyls, terphenyls, phenyl- or cyclohexylbenzoates, Cyclohexane-carboxylic acid phenyl or cyclohexyl ester, Phenyl or cyclohexyl ester of cyclohexylbenzoic acid, Phenyl or cyclohexyl ester of Cyclohexylcyclohexane carboxylic acid, cyclohexylphenyl ester benzoic acid, cyclohexane carboxylic acid, or the cyclohexylcyclohexane carboxylic acid, phenylcyclohexane, Cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, Cyclohexylcyclohexanes, cyclohexylcyclohexenes, Cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 4,4′-bis-cyclohexylbiphenyls, Phenyl or cyclohexyl pyrimidines, phenyl or Cyclohexylpyridines, phenyl- or cyclohexyldioxanes, Phenyl- or cyclohexyl-1,3-dithiane, 1,2-diphenylethane, 1,2-dicyclohexylethane, 1-phenyl-2-cyclohexylethane, 1-cyclohexyl-2- (4-phenyl-cyclohexyl) ethane, 1-cyclohexyl-2-biphenylylethane, 1-phenyl-2-cyclohexylphenylethane, halogenated stilbene, Benzylphenyl ether, tolanes and substituted cinnamic acids are selected, the 1,4-phenylene groups also be fluorinated in these compounds can. 5. Electro-optical system according to at least one of claims 1-4, characterized in that the liquid crystal contains further compounds of the formulas 1-5 R'-LER '' (1) R'-L-COO-ER '' (2) R '-L-OOC-ER''(3)R'-L-CH₂CH₂-ER''(4)R'-LC≡CER''(5) where
L and E each independently form a divalent radical from -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe - and -G-Cyc- and their mirror images formed group, where Phe unsubstituted or substituted by fluorine-substituted 1,4-phenylene, Cyc trans-1,4-cyclohexylene or 1,4-cyclohexenylene, pyr pyrimidine-2,5-diyl or Pyridine-2,5-diyl, dio 1,3-dioxane-2,5-diyl and G 2- (trans-1,4-cyclohexyl) ethyl, pyrimidine-2,5-diyl, pyridine-2,5- are diyl or 1,3-dioxane-2,5-diyl, and
R 'and R''each independently represent alkyl, alkenyl, alkoxy, alkenyloxy or alkanoyloxy each with 1-8 C atoms or CN, CF₃, F, Cl or NCS. 6. Electro-optical system according to at least one of claims 1-5, characterized in that the liquid crystal is based on one of the mixtures 1-6, where the sum of the mass percentages in the Mixtures contained and listed below Formulas falling connections between 10% and 90% lies. 7. System according to at least one of claims 1-6, characterized in that the liquid crystal has dielectric anisotropy Δε <3. 8. System according to at least one of claims 1-7, characterized in that the liquid crystal at least contains a pleochroic dye.   9. liquid crystal, characterized in that it with the liquid crystal in an electro-optical system is identical according to at least one of claims 2-8. 10. Use of a liquid crystal containing at least a compound of formula I, in an electrical switchable liquid crystal system, which Microdroplets of the liquid crystal embedded in contains a transparent matrix. 11. Use of a liquid crystal according to claim 9 in an electrically switchable liquid crystal system, which microdroplet of the liquid crystal is embedded contained in a transparent matrix.