DE4001541A1 - 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 electro-optical liquid crystal systems according to the preamble of claim 1.

The optically transparent medium can differ from one another contain limited liquid crystal microdroplets or form a spongy, 3-dimensional network, in whose pores, to a greater or lesser extent merge into each other, the liquid crystal is. By the expression liquid crystal microdroplets small, separate liquid crystal compartments elements marked, which are by no means a ball must have a shape, but irregular can be shaped and / or deformed.

Contains the optically transparent medium liquid crystal Microdroplets, it is referred to below as the matrix net, on the other hand, lies a spongy, 3-dimensional networked structure before, the medium is through the expression Network characterized.

NCAP and PDLC films (NCAP = nematic curcilinear aligned phases, PDLC = polymer dispersed liquid crystal) Examples of electro-optic liquid crystal systems, where the liquid crystal is in the form of microdroplets is embedded in the matrix. NCAP films get used to Lich obtained in that the encapsulating polymer  Material such as B. polyvinyl alcohol, the liquid crystal mixture and a carrier material, such as. B. water, in be mixed intimately in a colloid mill. Subsequently the carrier material z. B. removed by drying. A corresponding method is in US 44 35 047 wrote. 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 homogeneously ver mixes. The mixture is then polymerized and induced phase separation, with 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 PN system described in EP 03 13 053 (PN = polymer Network) has a spongy network structure optically transparent medium. The proportion of the liquid crystal on the mass of the light-modulating layer generally greater than 60% and in particular lies between 70-90%. To manufacture the PN systems usually a mixture of the liquid crystal, Monomers or oligomers of the 3-dimensional network forming material and a polymerization initiator, especially a photoinitiator, between 2 with elec brought troden provided substrate plates and then z. B. polymerized by exposure to light.

The liquid crystal generally has a positive dielectric anisotropy Δε and a relatively high optical anisotropy. In microdroplet matrix systems, one of the refractive indices of the liquid crystal, usually the ordinary refractive index n₀, is chosen so that it more or less coincides with the refractive index n _{M of} the polymer matrix. In network systems, it is not absolutely necessary to adjust the refractive indices because of the usually much higher proportion of liquid crystal in the light-modulating layer, but it can be done to increase the light throughput and the contrast.

One observes on these electro-optic liquid crystal Systems an electrically switchable light scattering effect. There is no voltage on the electrodes between which the matrix or the network usually sand arranged wich-like, laid out, becomes striking Light on the statistically aligned liquid crystal Molecules are very scattered, the system is opaque. When a voltage is applied, the liquid crystal molecules parallel to the field and perpendicular to the E-vector of the light passing through.

In microdroplet matrix systems, an optically isotropic medium sees perpendicularly to incident light due to the adaptation of n _o and N _M, and the system appears transparent. Adjustment is required to avoid light scattering at the matrix / liquid crystal droplet phase boundary. 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.

In network systems there is an adjustment of the refraction indices not absolutely necessary because of the high Liquid crystal portion of the mass of the light modulators the layer the scatter at the phase boundary network Liquid crystal is obviously less strong. The System appears without when switched on Transparent refractive index adjustment. With network  werk systems is to achieve the lowest possible Transmission in the non-switched state use of liquid crystals with high optical anisotropy prefers.

Electro-optical liquid crystal systems according to the Ober Concept of claim 1 are especially for large areas Display systems, for architectural applications (windows, Room dividers, sun roofs etc.) and for motor vehicles (Windows, sun roofs, etc.) have been proposed, whereby these systems are also used for temperature regulation controlled shielding of solar radiation are suitable. they can by applying a DC or AC voltage be switched.

Because these systems are especially suitable for "outdoor" users liquid crystals are required, which has a wide nematic due to a high clearing point Range and high UV and temperature stability are drawn. Next is a high value for the dielek trical anisotropy Δε preferred to a low To obtain threshold voltage.

Other applications include:

• - GH display systems, the spectrum being simple Segment displays up to displays on which with conventional printing techniques any electrodes patterns can be applied. Applications: Motor vehicle, 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 required.

So far, microdroplet matrix systems have become more common as LC mixtures used, which consist of alkyl or alkoxy cyanobiphenylene and terphenylene exist. So z. B. in US 46 88 900 and in EP 02 72 585 the use of the liquid crystal mixture E8 (manufactured by BDH, Poole, Great Britain). This liquid crystal mixture draws by a high value for the optical anisotropy Δn of 0.247 and a relatively high value for the flow viscosity η (20 ° C) from 54 mm² / s, but has the same a relatively low clearing point of only 72 ° C. Polynuclear polyphenyl compounds are added to the mixture to increase the clearing point results in a higher one Value for the flow viscosity η and an unchanged high or higher value for the optical anisotropy Δn. Height On the one hand, Δn values ensure strong light scattering in the opaque state, but on the other hand, they can Turbidity of the system in the switched state ("haze") and thus a significant deterioration in the electro-optical Effect properties. In systems developed by a relatively low frequency AC voltage a high flow viscosity η is desired to achieve a get flicker-free display; on the other hand, ever but in matrix displays with high information content Realization of fast switching times liquid crystal mixtures with relatively low viscosity required.

The liquid crystal mixture E7 used in US 46 71 618 (manufactured by BDH, Poole, Great Britain), which also consists of alkyl and alkoxycyanobiphenylene and terphenylene, has a lower flow viscosity with η = 39 mm² / s and with Δn = 0.225 a slightly smaller optical anisotropy Δn than E8, but at the same time the clearing point T _C = 60.5 ° C is considerably lower.

In EP 03 13 053, liquid crystal mixtures based on 2- (4-cyanophenyl) pyridines are proposed for network systems. Such liquid crystals do have relatively high values for the dielectric anisotropy Δε and thus relatively low threshold voltages and high to very high values for the optical anisotropy Δn. At the same time, however, these liquid crystals are characterized by a relatively high viscosity η and a relatively low clearing point T _c . Furthermore, cyanophenyl pyridine compounds generally have a lower temperature and UV stability than cyanooligophenyls.

The liquid crystals used so far meet the Demands for a wide nematic area, one high clearing point, very high stability, one Absence of smectic phases down to low temperatures, one with regard to the respective applications baren optical anisotropy Δn and flow viscosity η and a high Δε is insufficient.

In addition, the previous liquid crystals often have one insufficient miscibility with the monomers and / or oligo mer of the ver to form the matrix or network spent polymers on what the manufacture of PN systems significantly impaired and with microdroplet matrix Systems especially the application of PIPS technology significantly restricted. In addition, the liquid crystals often due to excessive solubility in the matrix or network-forming polymer. Another There is often a disadvantage of the previous liquid crystals in that the liquid crystal for each application unfavorable values of the electro-optical parameters such. B. the steepness of the electro-optical characteristic and / or the Temperature dependence of the electro-optical parameters such as e.g. B. shows the threshold voltage.

There is therefore still a great need for electro optical liquid crystal systems, 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 ange did not or only led to disadvantages of conventional systems to a small extent.

Surprisingly, it has now been found that this task can be solved if you use liquid for these systems crystal mixtures used, one or more ver contain bonds of formula I,

wherein
one of Q¹ and Q² is p-cyanophenyl and the other Q¹ or Q²

being at least one of the ring

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 can be replaced by -O-, and
n = 1 or in the case

and Q² = R n = 0

mean.  

The invention thus relates to an electro-optical Liquid crystal system,

• - Which between 2 electrodes, if necessary are applied to substrate plates, one dielectric positive liquid crystal and a contains another optically transparent medium,
• - Its liquid crystal molecules when switched off Irregular orientation,
• - in which one of the refractive indices of the liquid crystal essentially corresponds to the refractive index of the matrix n _M and / or in which the quotient of the mass of the liquid crystal and the mass of the optically transparent medium is 1.5 or more,
• - Which is independent in one of the two switching states of the polarization of the incident light reduced transmission compared to the other state has, wherein the liquid crystal one or more Contains compounds of formula I.

The structure of the electro-optical liquid according to the invention crystal systems corresponds to that for such systems usual design. The term common design is here at broad and encompasses all variations and modes fications.

So z. B. in PDLC or NCAP films by the Visible medium formed matrix in which the liquid crystal mixture microdispersed or microencapsulated is sandwiched between conductive electrodes arranges.  

The electrodes are i. a. on substrate plates from z. B. Glass, plastic or similar applied; if necessary, the matrix but can also be provided directly with electrodes, so that the use of substrates can be dispensed with can.

The liquid crystal is in network systems in the pores of the spongy, 3-dimensional network. The network is usually between electrodes provided substrates arranged to escape the To prevent liquid crystal.

Both PN systems and microdroplet matrix systems can be operated reflectively or transmissively, so that at least one electrode and, if available, the associated substrate are transparent. Both systems usually do not contain polarizers, which means a significantly higher light throughput results. Farther no orientation layers are required, which is a considerable technological simplification in the manufacture development of these systems compared to conventional liquids crystal systems such as B. TN or STN cells.

The matrix or the 3-dimensional network are based on especially on isotropic thermoplastics, thermosets and Elastomers. The systems obtained can depend on Visible use be flexible, elastic or rigid.

A system 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. This can e.g. B. with micro droplet matrix systems are used to make one deliberately deformed shape of the droplets by cooling the matrix to temperatures below the glass temperature freeze.  

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, being in the cured Matrix z. B. the shape and arrangement of the microdroplets is fixed.

Especially for the production of the matrix or the network preferred polymers are e.g. 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 discloses.

In addition, other transparent materials can also be used lien such. B. inorganic oxidized glass monoliths (US 48 14 211), further inorganic materials (s. e.g. B. Japanese Patent Application 303325/1988) or other materials can also be used.

Preferred embodiment of the electro according to the invention optical liquid crystal systems are NCAP films, PDLC Films and produced by modified processes Micro droplet matrix systems. Manufacturing process these films are e.g. B. in US 39 35 337, US 46 88 900, US 46 73 255, US 46 71 618, US 44 35 047 and EP 02 72 595 described.

Another preferred embodiment of the Invention modern electro-optical systems are the network systems, their manufacture z. B. is described in EP 03 13 053.

However, such embodiments of FIG Invention comprises, in which the transparent medium Structure that is between the network structure one side and the microdroplet matrix configuration tion is on the other side.  

The electro-optical systems according to the invention include also "inverse microdroplet matrix configurations", where the transparent medium in the form of individual e.g. B. spherical particles in the liquid crystal dis is perforated. Such an arrangement is e.g. B. in GB 14 42 360 described.

There are also others that are not explicitly mentioned here Embodiments of the invention include.

The thickness d of the electro-optical systems 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 layer thicknesses of 0.8 and 1.6 mm, while for the layer thickness in US 46 88 900 values between 10 microns and 300 microns and in EP 03 13 053 between 5 microns and 30 microns are given . 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 micro droplets or the mesh size of the network. 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. For the mesh size of the network of PN systems, a preferred range between 0.5 and 2 µm is specified in EP 03 13 053. A significant difference between the electro-optic liquid crystal systems according to the invention and the ones used hitherto, however, is the liquid crystal used.

The liquid crystals according to the invention contain at least least a compound of formula I.

The compounds of the formula I comprise binuclear compounds of formulas Ia 1 and Ia 2, which are preferred:

In the compounds of the formula Ia 1 and Ia 2, R is preferred as n-alkyl or n-alkoxy with 1-10 C atoms, in particular but with 1-8 carbon atoms. Further preferred are Alkoxyalkyl compounds and especially n-alkoxymethyl and n-alkoxyethyl compounds.

The compounds of formula I further comprise trinuclear Compounds of the sub-formulas Ib 1 and Ib 2:

The compounds of the sub-formulas Ib 11-Ib 12 and Ib 21-Ib 22 are preferred:  

In the compounds of the sub-formulas Ib 11-Ib 12 and Ib 21-Ib 22 R preferably denotes n-alkyl- or n-alkoxy with 1-10 C atoms, also n-alkoxymethyl or n-alkoxyethyl, where n-alkoxy contains 1-6 C atoms.

The radical R in the compounds of the formula I can be straight be chain or branched. R is preferably straight chain, however, compounds of formula I with branched alkyl or alkoxy radicals occasionally because of better solubility in the usual liquid crystalline base materials are of importance, ins special 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 ver branched radicals R are isopropyl, 2-butyl (= 1-methyl propyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, Isopentyl (= 3-methylbutyl), 2-methylpentyl, 3-methyl pentyl, 2-ethylhexyl, 2-propylpentyl, 2-octyl, isopro  poxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methyl hexoxy, 2-octyloxy, 2-oxa-3-methylbutyl, 3-oxa-4-methyl pentyl, 4-methylhexyl, 2-nonyl, 6-methyloctoxy, 2-methyl 3-oxapentyl, 2-methyl-3-oxahexyl.

The compounds of formula I are either known and / or are displayed according to known methods, as described in the literature (e.g. in the standard works such as Houben-Weyl, Methods or Organic Chemistry, Georg- Thieme-Verlag, Stuttgart Vol IX, pp. 867 ff.) are, and under reaction conditions that for the mentioned implementations are known and suitable. Here one can also of well-known, not closer here use mentioned variants.

The compounds of formula I are preferably after those in DE 26 36 684, DE 29 22 236, EP 01 02 047, EP 01 29 177, DE 30 40 362 and DE 33 17 597 methods.

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

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-,

mean.

The liquid crystals according to the invention can be further Contain ingredients, preferably selected are made from nematic or nematogenic (monotropic or isotropic) substances, especially substances from 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 cyclohexylcyclohexane carboxylic acid, Phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexyl cyclohexane, cyclohexylcyclohexane, cyclohexylcyclohexene, Cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexyl benzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl or Cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, Phenyl- or cyclohexyldioxane, 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, optionally halo embarrassed stilbenes, benzylphenyl ether, tolanes and sub 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 Group, where Phe unsubstituted or fluorine sub 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- mean diyl or 1,3-dioxane-2,5-diyl.

Preferably one of the residues L and E is Cyc, Phe or Pyr. E is preferably Cyc, Phe or Phe-Cyc. Preferential the liquid crystals according to the invention contain one or more components selected from the ver  bonds of formulas 1, 2, 3, 4 and 5, wherein L and E are selected from the group Cyc, Phe and Pyr and one or more components selected at the same time from the compounds of the formulas 1, 2, 3, 4 and 5, in which one of the residues L and E is selected from the group Cyc, Phe and Pyr and the other residue is selected from -G-Cyc-, and optionally one or more components selected from the compounds of the 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 ver Bonds 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 be indicates R '' -CN, -CF₃, F, Cl or -NCS; R has the specified for the compounds of the sub-formulas 1a to 5a Meaning and is preferably alkyl or alkenyl. But other variants of the proposed substituents in the compounds of formulas 1, 2, 3, 4 and 5 in use. Many such substances or mixtures of which are commercially available. All of these substances are by methods known from the literature or by analogy available for this.

The liquid crystals used in the electro-optical liquid crystal systems according to the invention preferably contain, in addition to components from the group of compounds 1a, 2a, 3a, 4a and 5a (group 1), components from the group of compounds 1b, 2b, 3b, 4b, and 5b (Group 2), the proportions of which 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 liquid according to the invention contain liquid crystal used in crystal systems preferably 1-40%, especially 5-30% of compounds of formula I. The liquid crystals preferably contain 1-5, but especially 1-3 compounds of formula I.

The proportion of which consist of compounds of the formulas I-V the base mixture to the electro in the invention liquid crystal optical systems used liquid crystals is preferably 15% -100%, especially however 25% -100%. The basic mix is based on Ver Compounds of formula I particularly preferably on fol smaller group of compounds, wherein R¹ is the has the meaning given above.

Liquid crystals based on based on the mixtures 1-12 described below, the mass fraction of mixtures 1-12 in the liquid crystal between 10% and 98% and especially between 15% and 95%. Mixtures 1-12 consist of 2 or more compounds listed under 2, 3, 4 or 5 formulas fall from the group of formulas I, II, III, IV and V can be selected. Mixtures 1-12 contain preferably 2-40, but especially 2-38 and very special or 2-35 connections. The mass fraction of this verb Mixtures 1-12 can be added within the range  limits for optimal adaptation to the respective Display type can be varied, the sum of these masses shares in mixtures 1-12 of course 100% is.

The electro-optical liquid crystal according to the invention systems 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-optic liquid crystal Systems can be created by creating an equal or alternate voltage can be switched. However, one is preferred AC voltage is used, which is an effective alternation voltage amplitude between 1 and 240 volts and a Has alternating voltage frequency between 10 and 10 kHz.  

Amplitudes between 2 and 220 volts and frequencies between 20 and 120 Hz. Quite the amplitude of the changes is particularly preferred voltage between 2 and 130 V.

The dielectric anisotropy of the liquid used crystal mixture is positive Δε <0 and preferably Δε <3. For smaller values of dielectric anisotrop 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 which can be used according to the invention crystal mixtures are carried out in a conventional manner. As a rule, the desired amount is less Quantity of components used in the main inventory partially constituent components solved, useful for 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 described can be added by suitable additives crystal mixtures are modified so that they 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. pleo chroitic dyes for the production of colored electro optical systems or substances to change the dielectric anisotropy, optical anisotropy, the viscosity and / or the temperature dependence elec Trooptic parameters of the liquid crystals added  will. 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 pleochroic dyes in one Weight percentage range from 0-25%, especially 0-20% and especially 0-15% are preferred.

The expert can further select from the large pool of nematic or nematogenic substances additives to the liquid crystal mixtures described so that the double refraction 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 optimized with regard to the respective application.

To increase the clearing point, the person skilled in the art Systems used liquid crystal according to the invention mixtures z. 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 the additives in such a way that in particular Δn and / or n _o another refractive index and / or Δε to be adapted to the particular design 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 results. A person skilled in the art can increase the viscosity the liquid crystal mixture highly viscous liquid crystal connections 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. ver as a matrix display with high information content uses, in particular, 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 select the substances used to modify the viscosity and their concentration so that other decisive parameters of the liquid crystal mixture, such as, for. B. Δn, Δε and when using viscous lowers especially T _{c is influenced} only 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 that for the The polymer used in the matrix should not be changed too much.

The expert will choose the concentration of such additives so 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 only influenced to an acceptable and / or small and / or negligible extent.

To modify the birefringence, the expert can, for. B. in liquid crystal mixtures, the compounds of the 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 can be used.

Due to the additives described, the liquid crystal modified with regard to the respective application and op be timed. It is crucial, however, that liquid crystals, containing compounds of formula I and in particular those additionally containing one or more compounds gene of formulas II-V, for use in the invention particularly suitable for electro-optic liquid crystal systems are not. However, the liquids are very particularly suitable crystal mixtures based on mixtures 1-12.

Liquid containing these compounds of formula I. crystal mixtures make 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.

The liquid crystals usable according to the invention advantageous values for the dielectric Anisotropy Δε, high stability, low miscibility speed with the polymer used for the matrix and ins special due to a wide mesogenic range, a relatively high clearing point and a high double refraction. The liquid crystals correspond to the ones described at the beginning The requirements that apply 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 previously used in these systems Liquid crystals.

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 transformation temperature in degrees Celsisus.
The percentages given are percentages by mass.

Example 1

a) An electro-optical liquid crystal system, included tend a liquid crystal mixture resulting from the following Connections exist

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
6.5% 4- (trans-4-propylcyclohexyl) phenyl trans-4-butylcyclohexyl carboxylate
5.6% 4- (trans-4-pentylcyclohexyl) -4'-cyano-biphenyl
20% 1- (trans-4-pentylcyclohexyl) -2- (4-cyano phenyl) ethane

and has the following physical parameters:

Clear point T _C = 80 ° C
Viscosity η = 29 mm² S ^-1 (20 ° C)
Optical anisotropy Δn = 0.14 (20 ° C, 589 nm)
Dielectric anisotropy Δε = 11.8 (20 ° C, 1 kHz)

b) The electro-optic liquid crystal system is after different procedures 1.1-1.3 and 2 are produced.

1. microdroplet matrix systems

1.1 The liquid crystal mixture from a) is with the UV radiation curable adhesive NOA 65 (Norland Products) in a ratio of 1.6: 1 at room temperature  stirred until a clear solution is obtained which together with spacers (20 µm) between 2 through Visible glass sub with electrode layers strate is brought. The glass substrates are squeezed, creating a smooth film with a thickness of 20 microns is obtained by a 1-minute UV radiation is cured.

1.2 The liquid crystal mixture from a) is epikote 828 and Capurce 3-800 (Miller Stephenson Company) at Ratio 1: 1: 1 stirred at room temperature until a clear solution is obtained; the scramble will kept as short as possible since the solution is at room temperature has already hardened after about ½ h. The solution is put together in spacers (20 µm) between 2 transparent, with electrode layers provided glass substrates brought together be pressed, creating a smooth film with a thickness of 20 microns is obtained. For acceleration The curing process can be applied to the films Temperature can be heated up to 100 ° C.

1.3 5 g of the liquid crystal mixture from a) are with 15 g of 20% aqueous PVA solution at room temperature Stirred at 2000 rpm for 2 minutes. The received Solution is degassed for 24 h and together with Spacers (20 µm) in a thin layer on one glass substrate provided with an electrode layer upset. The arrangement is 1 h at 85 ° C dried before a second one with electrodes layered glass substrate is pressed on, creating a uniform film with a thickness of 20 microns is obtained. The system thus obtained is dried at 85 ° C. for a further 24 h.  

2. Network system

The liquid crystal mixture from a) is tri methylpropane triacrylate as a polymerizable Compound and 2-hydroxy-2-methyl-1-phenylpropane 1-on (Darocure 1173, commercial product from E. Merck, Darmstadt) as a photoinitiator in the ratio 80: 19.8: 0.2 stirred and with the addition of Spacers with a thickness of 20 µm between 2 glass plates with electrode layers brought. This was obtained to cure the polymer system with a defined speed (3 / min) through the radiation field of a halogen lamp (70 W / cm) driven.

The manufactured according to the method b) 1.1-1.3 and 2 electro-optical systems are characterized by good Manufacturability, a wide working temperature range, favorable values for the electro-optical parameters and their temperature dependence, through a low smoldering lens tension and a high contrast.

Claims (14)

1. electro-optic liquid crystal system,

• which contains a dielectric positive liquid crystal and another optically transparent medium between two electrodes, which are optionally applied to substrate plates,
• - whose liquid crystal molecules have an irregular orientation when switched off,
• in which one of the refractive indices of the liquid crystal essentially corresponds to the refractive index of the matrix n _M and / or in which the quotient of the mass of the liquid crystal and the mass of the optically transparent medium is 1.5 or more,
• which in one of the two switching states, regardless of the polarization of the incident light, has a reduced transmission compared to the other state,

characterized in that the liquid crystal contains one or more compounds of the formula I. wherein
one of Q¹ and Q² is p-cyanophenyl and the other Q¹ or Q² 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 can be replaced by -O-, and
n = 1 or in the case 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-V, 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-, mean. 3. System according to claim 2, characterized in that the proportion of those consisting of compounds I-V Base mixtures on the liquid crystal 15-100% is. 4. System according to at least one of claims 1-3, characterized in that the liquid crystal contains further connections from the classes of azoxybenzenes, benzylidene anilines, biphenyls, Terphenyls, phenyl or cyclohexyl benzoates, cyclo hexane-carboxylic acid phenyl or cyclohexyl ester, Phenyl or cyclohexyl ester of cyclohexylbenzoe acid, phenyl or cyclohexyl ester of cyclohexyl  cyclohexane carboxylic acid, cyclohexylphenyl ester of Benzoic acid, the cyclohexane carboxylic acid, or the Cyclohexylcyclohexane carboxylic acid, phenylcyclohexane, Cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, Cyclohexylcyclohexanes, cyclohexylcyclohexenes, Cyclohexylcyclohexylcyclohexenes, 1,4-biscyclohexyl benzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl or Cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, Phenyl- or cyclohexyldioxane, phenyl- or cyclo hexyl-1,3-dithiane, 1,2-diphenylethane, 1,2-dicyclo hexylethane, 1-phenyl-2-cyclohexylethane, 1-cyclo hexyl-2- (4-phenyl-cyclohexyl) ethane, 1-cyclohexyl- 2-biphenylylethane, 1-phenyl-2-cyclohexylphenyl ethane, halogenated stilbene, benzylphenyl ether, Tolanes and substituted cinnamic acids selected be, the 1,4-phenylene groups in these Compounds can also be fluorinated. 5. 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 ''1R'-L-COO-ER''2R'-L-OOC-ER''3R'-L-CH₂CH₂-ER''4R'-LC≡CER'' 5worin
L and E each independently form a bivalent radical from the group consisting of -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -G- Phe- and -G-Cyc- and their mirror images formed group, wherein 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-diyl or 1,3-dioxane-2,5-diyl, and
R 'and R''each independently of one another alkyl, alkenyl, alkoxy, alkenyloxy or alkanoyloxy each with 1-8 C atoms or CN, CF₃, F, Cl or NCS
mean. 6. System according to at least one of claims 1-5, characterized in that the liquid crystal is based on one of the mixtures 1-12. the mass fraction of mixtures 1-12 in the liquid crystal is between 10% and 98%. 7. System according to at least one of claims 1-6, characterized in that the liquid crystal has a dielectric anisotropy Δε <3. 8. System according to at least one of claims 1-7, characterized in that the liquid crystal min contains a pleochroic dye. 9. System according to at least one of claims 1-8, characterized in that the liquid crystal in Form of microdroplets in the optically transparent Medium is embedded. 10. System according to at least one of claims 1-9, characterized in that the optically transparent Medium forms a 3-dimensional network in which The liquid crystal is located in the pores. 11. Liquid crystal, characterized in that it has the liquid crystal in an electro-optical system is identical according to at least one of claims 2-8. 12. Use of a liquid crystal containing at least least one compound of formula I, in one system according to claim 9 or 10. 13. Use of a liquid crystal according to claim 11 in a system according to claim 9 or 10.