DE4038767A1 - 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 be abge from each other bordered liquid crystal microdroplets or contain form a spongy, 3-dimensional network, in whose pores, to a greater or lesser extent merge into each other, the liquid crystal is located. By the term liquid crystal microdroplets are small, separated liquid crystal comparti marked, but by no means a bullet must have a shaped shape, but irregular can be shaped and / or deformed.

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

NCAP and PDLC films (NCAP = nematic curvilinear aligned phases, PDLC = polymer dispersed liquid crystal) Examples of electro-optical liquid crystal systems, where the liquid crystal in the form of micro-wells embedded in the matrix. NCAP movies will get used to Lich obtained by the fact that the encapsulating polymeric  Material, such. As polyvinyl alcohol, the liquid crystal mixture and a carrier material, such as. As water, in a colloid mill are intimately mixed. Subsequently is the carrier material z. B. removed by drying. A corresponding method is in US 44 35 047 be wrote. In contrast, at the e.g. 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 mixed. Subsequently, the mixture is polymerized and the phase separation induced, with between TIPS (temperature-induced phase separation), SIPS (solvent- induced phase separation) and PIPS (polymerization-induced phase separation) (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 of optically transparent medium. The proportion of liquid crystal at the mass of the light-modulating layer generally greater than 60% and in particular between 70-90%. For the production of PN systems is usually a mixture of the liquid crystal, Monomers or oligomers of the 3-dimensional network forming material and a polymerization initiator, in particular a photoinitiator, between 2 with Elek placed on the substrate and then coated e.g. polymerized by light irradiation.

The liquid crystal generally has a positive dielectric anisotropy Δε and a relatively high optical anisotropy. In microdroplet matrix systems, one of the calculation indices of the liquid crystal, usually the ordinary refractive index n _o, is chosen to more or less coincide with the refractive index n _{M of} the polymeric matrix. In network systems, an adjustment of the refractive indices because of the usually much higher proportion of liquid crystal at the light modulating layer is not essential, but can be made to increase the light throughput and the contrast.

It is observed at these electro-optical liquid crystal Systems an electrically switchable light scattering effect. There is no voltage to the electrodes, between which the matrix or the network usually sand is disposed, applied, impinged Light on the randomly aligned liquid crystal molecules are strongly scattered, the system is opaque. When a voltage is applied, the liquid crystal molecules parallel to the field and perpendicular to the E vector aligned by the passing light.

In microdroplet matrix systems, due to the matching of n _o and n _M, an optically isotropic medium looks perpendicular to the incident light and the system appears through vision. An adaptation is required to avoid scattering of the light at the phase boundary matrix / liquid crystal droplets. Another embodiment is described in EP 02 72 585, in which the refractive index n _x , which the liquid crystal has in completely random orientation, is adapted to the refractive index of the matrix n _M. In this case, the system is transparent in the field free state, and it is transferred to the opaque state by applying a voltage.

In network systems is an adjustment of refraction Indices are not absolutely necessary, because of the high Liquid crystal content of the mass of light modulate the layer the scatter at the phase boundary network Liquid crystal is obviously less strong. The System also appears without power when switched on Adjustment of refractive indices transparent.  

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

As these systems are especially suitable for "outdoor" applications are provided, are liquid crystal mixtures required by a high clearing point, high Δε, a wide nematic range and a high UV and Temperature stability are characterized.

Other applications include:

• - GH display systems, the spectrum ranges from simple segment displays to displays on which with conventional printing techniques any electrode pattern can be applied. applications:
  Motor vehicle, large displays, advertising space, watches
• - Matrix displays with high information content
• - projection systems
• - Counter.

Again, liquid crystal mixtures are in particular with high Δε and high electrical resistance required.  

In microdroplet matrix systems are so far more common wise LC mixtures used, consisting of alkyl or alkoxy Cyanobiphenylen and -terphenylen exist. For example, 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 drew is characterized by a high value for the optical anisotropy Δn of 0.247 and a relatively high value for the flow Viscosity η (20 ° C) of 54 mm² / s, but has the same early a relatively low clearing point of only 72 ° C. If the mixture is polynuclear polyphenyl compounds to increase the clearing point, results in a higher 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, on the other hand, however, they cause a Turbidity of the system in the switched state ("haze") and thus a significant deterioration of the electro-optical Properties. Although, in systems that are of a relative Low-frequency AC voltage can be controlled, a high flow viscosity η desired to achieve a flicker-free To receive advertisement; on the other hand, however, in matrix Displays with high information content for realization fast switching times liquid crystal mixtures with relatively low viscosity needed.

The liquid crystal mixture E7 (manufactured by BDH, Poole, Great Britain) used in US Pat. No. 4,671,618, which also comprises alkyl- and alkoxycyanobiphenyls and -terphenyls, has a lower flow viscosity with .eta. = 39 mm.sup.2 / s and with .DELTA.n = 0.225 slightly 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 of the mixture E7 is Δε 13.8 and is thus slightly smaller than that of E8 with Δε = 15.6. To achieve the lowest possible threshold voltages, high values for Δε are advantageous.

In EP 03 13 053 liquid crystal mixtures are proposed for network systems based on 2- (4-cyanophenyl) - pyridines. Although such liquid crystals have relatively high values for the dielectric anisotropy Δε and thus relatively small threshold voltages. At the same time, however, these liquid crystals are characterized by a high to very high optical anisotropy Δn, a relatively high viscosity η and a relatively low clearing point T _C.

The liquid crystals used so far meet the Demands for a broad nematic range, one high clearing point, very high stability, one Absence of smectic phases down to low temperatures, one optimized with regard to the respective application Baren optical anisotropy Δn and flow viscosity η and a high Δε only insufficient.

In addition, the previous liquid crystals often have one too low miscibility with the monomers and / or oligo mers of the formation of the matrix or the network ver used polymers, resulting in the production of PN systems significantly impaired and in microdroplet matrix In particular, the application of PIPS technology considerably limited. In addition, the liquid often due to too high solubility in the matrix or network-forming polymer. Another Disadvantage of the previous liquid crystals is often in that the liquid crystal for the particular application unfavorable values of the electro-optical parameters such. B. the steepness of the electro-optical characteristic and / or the Temperature dependence of electro-optical parameters such as z. B. the threshold voltage shows.  

There is thus still a great need for electro optical liquid crystal systems containing the corresponding Requirements better and the described Disadvantages not or only to a lesser extent.

The invention was based on the object, electro-optical Liquid crystal systems provide the ange Disadvantages of conventional systems did not or only to a small extent.

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

R-Q¹-CH₂CH₂-Q²-CN (I)

wherein
R is alkyl having up to 12 carbon atoms, wherein one or two non-adjacent CH₂ groups may be replaced by -O-, and one of the radicals Q¹ and Q² 4,4'-biphenylyl and the other radical 1,4-phenylene mean.

The invention is thus an electro-optical Liquid crystal system,

• - Which between 2 electrodes, if necessary are applied to substrate plates, a dielectrically positive liquid crystal and a contains another optically transparent medium,  
• - Its liquid crystal molecules in the off Condition have an irregular orientation,
• in which one of the refractive indices of the liquid crystal substantially coincides with 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 relation to the other state reduced transmission, wherein the liquid crystal one or more compounds of formula I contains R-Q¹-CH₂CH₂-Q²-CN (I) wherein
  R alkyl having up to 12 carbon atoms, wherein one or two non-adjacent CH₂ groups may be replaced by -O-, and one of the radicals Q¹ and Q² 4,4'-biphenylyl and the other radical 1,4-phenylene

mean.

The structure of the electro-optical liquid according to the invention Crystal systems corresponds to that for such systems usual construction. The term common construction is here in a broad sense, encompassing all modifications and modes fications.  

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

The electrodes are i.a. on substrate plates of e.g. Glass, plastic or similar applied; if necessary, the matrix However, also be provided directly with electrodes, so that dispenses with the use of substrates can.

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

Both PN systems and microdroplet matrix systems can be operated reflective or transmissive, so that at least one electrode and, if available, the associated substrate are transparent. Both systems usually contain no polarizers, causing a significantly higher light throughput results. Farther no orientation layers are required, which is a Significant technological simplification in the manufacture These systems compared with conventional liquid crystal systems such. B. TN or STN cells means.

The matrix or the 3-dimensional network are based on special on isotropic thermoplastics, thermosets and Elastomers. The resulting systems may vary depending on the visible use flexible, elastic or rigid.  

A system based on a thermoplastic polymer can be at temperatures greater than the glass transition temperature of the matrix, easily by the action of a mechanical Tension will be deformed. This can e.g. at micro droplet-matrix systems are used to create a deliberately deformed shape of the droplets by cooling the matrix to temperatures below the glass transition temperature freeze.

While flexible and / or elastic systems are preferred based on thermoplastics and / or elastomers for the production of rigid systems preferred thermosetting Polymers used. These can be during curing be mechanically deformed, being cured in the Matrix z. B. the shape and arrangement of the microdroplets is fixed.

For the production of the matrix or the network especially preferred polymers are, for. 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, however, other transparent Materia such as e.g. inorganic oxide glass monoliths (US 48 14 211), other inorganic materials (s. z. Japanese laid-open specification 3 03 325/1988) or also other materials are used.

Preferred embodiment of the invention optical liquid crystal systems are NCAP films, PDLC Films and produced by modified methods Microdroplets matrix systems. Process for the preparation of these films are e.g. 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 proper electro-optical systems are the network systems, their preparation is described in EP 03 13 053.

Next are also such embodiments of the Invention, in which the transparent medium a Structure that is between the network structure one side and the microdroplet matrix configuration tion on the other side.

The electro-optical systems of the invention include also "inverse microdroplet matrix configurations", in which the transparent medium in the form of individual z. B. spherical particles in the liquid crystal dis is pergiert. Such an arrangement is z. In GB 14 42 360.

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

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 . For example, in US 44 35 047 layer thicknesses of 0.8 and 1.6 mm are reported, while for the layer thickness in US 46 88 900 values between 10 .mu.m and 300 .mu.m and in EP 03 13 053 between 5 .mu.m and 30 .mu.m be become. The electro-optical systems of the invention have only in exceptional cases layer thicknesses d, which are significantly larger than a few mm; preferred are layer thicknesses d ≦ 2 mm.

The threshold voltage is also influenced by the size of the micro droplets or the mesh size of the network. In general, smaller microdroplets cause a higher threshold voltage V _th , but shorter switching times t _on and t _off (US 46 73 255). Experimental methods for influencing the mean droplet size are described, for example, in US Pat. No. 4,673,255 and in JL West, Mol. Cryst. Liq. Cryst. Inc. Nonlin. Opt., 157 (1988) 427. In US 46 73 255 average droplet diameter between 0.1 microns and 8 microns are given, while, for example, a matrix based on a glass monolith having pores with a diameter between 15 and 2000 Å. For the mesh size of the network of PN systems, EP 03 13 053 specifies a preferred range between 0.5 and 2 μm.

A significant difference of the invention elek trooptic liquid crystal systems to the usual however, exists in the liquid crystal used.

The liquid crystals of the invention contain Minde at least one compound of formula I. In the compounds of formula I, R is preferably alkyl or alkoxy with 1-10, but especially with 1-8 C atoms. Continue preferred are n-alkoxy compounds and in particular n-alkoxymethyl and n-alkoxyethyl compounds.

The compounds of formula I include 3-nuclear compounds of the formulas II and III, which are preferred:

In the compounds of the formulas II and III, R is preferably methyl, ethyl, propyl, butyl, pentyl, hexyl, Heptyl, octyl, nonyl, decyl, methoxy, ethoxy, propoxy, Butoxy, pentoxy, hexoxy, heptoxy, octoxy, methoxymethyl, Ethoxymethyl, propoxymethyl, butoxymethyl, methoxyethyl, Ethoxyethyl or propoxyethyl.

In the compounds of the formula I, the radical R can be straight be chained or branched. R is preferably straight kettig, however, compounds of formula I can with branched alkyl or alkoxy radicals occasionally because of a better solubility in the usual flüssigkri stallinen base materials of importance, esp but special as chiral dopants, if they are optical are active. Electro-optical systems according to the preamble of claim 1, the liquid crystal of which is one or more contains chiral components are described in DE 39 11 255.1 described.

Branched groups of this type usually do not contain more than one 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-ethyl hexyl, 2-propylpentyl, 2-octyl, isopropoxy, 2-methyl propoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy, 2-octyl oxy, 2-oxa-3-methylbutyl, 3-oxa-4-methylpentyl, 4-methyl hexyl, 2-nonyl, 6-methyloctoxy, 2-methyl-3-oxapentyl, 2-methyl-3-oxahexyl.

The compounds of the formula I are known per se methods described in the literature (eg in the standard works such as Houben-Weyl, methods of Organic Chemistry, Georg-Thieme-Verlag, Stuttgart Bd IX,  P. 867 ff.), Under reaction conditions known for the said reactions and are suitable. It can also be known by itself, here unspecified variants make use.

The compounds of the formula I are preferably after represented by the method described in US 40 35 056.

The liquid crystals of the invention are based next Compounds of formula I preferably compounds of formulas II-IV

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

The liquid crystals according to the invention can further Contain ingredients that are preferably selected are made of nematic or nematogenic (monotropic or isotropic) substances, in particular substances from the Classes of azoxybenzenes, benzylideneanilines, biphenyls, Terphenyls, phenyl or cyclohexyl benzoates, cyclohexane carboxylic acid phenyl or cyclohexyl esters, phenyl or Cyclohexyl esters of cyclohexylbenzoic acid, phenyl or Cyclohexyl ester of cyclohexylcyclohexanecarboxylic acid, Cyclohexylphenylester of benzoic acid, cyclohexane carboxylic acid, or cyclohexylcyclohexanecarboxylic acid, Phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexyl cyclohexanes, cyclohexylcyclohexanes, cyclohexylcyclohexenes, Cyclohexylcyclohexylcyclohexenes, 1,4-biscyclohexyl benzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl or Cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, Phenyl or cyclohexyl dioxanes, phenyl or cyclohexyl 1,3-dithiane, 1,2-diphenylethane, 1,2-dicyclohexylethane, 1-phenyl-2-cyclohexylethane, 1-cyclohexyl-2- (4-phenyl cyclohexyl) ethanes, 1-cyclohexyl-2-biphenylyethanes, 1-phenyl-2-cyclohexylphenylethane, optionally halo genated stilbenes, benzylphenyl ethers, tolans and sub cinnamic acids. The 1,4-phenylene groups in these Compounds may also be fluorinated.

The most important as further constituents in the used electro-optical systems according to the invention Liquid crystals in candidate compounds leave 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 the formulas 1, 2, 3, 4 and 5, L and E, denote may be the same or different, each independently from each other a bivalent radical from the -Phe-, -Cyc, -Phe-Phe, -Phe-Cyc, -Cyc-Cyc, -Pyr-, -Dio, G-Phe and -G-Cyc- and their mirror images formed Group, wherein Phe is unsubstituted or subfluorinated 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.

Preferably one of the radicals L and E is cyc, phe or Pyr. E is preferably Cyc, Phe or Phe-Cyc. virtue Wise contain the liquid crystals of the invention one or more components selected from the Ver compounds of the 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 formulas 1, 2, 3, 4 and 5, wherein one of the radicals L and E is selected from the group Cyc, Phe and Pyr and the other rest 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 the formulas 1, 2, 3, 4 and 5, wherein the radicals 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. For most of these ver Bonds are R 'and R' 'different from each other, where one of these radicals is usually alkyl or alkenyl. In the  Compounds of sub-formulas 1b, 2b, 3b, 4b and 5b be R 'denotes -CN, -CF₃, F, Cl or -NCS; R has the in the case of the compounds of sub-formulas 1a to 5a Meaning and is preferably alkyl or alkenyl. But also other variants of the proposed substituents in the compounds of formulas 1, 2, 3, 4 and 5 common. Many such substances or mixtures of which are commercially available. All these substances are by literature methods or in analogy available.

The in the electro-optical liquid according to the invention crystal systems used contain liquid crystals preferably in addition to components from the group of Ver compounds 1a, 2a, 3a, 4a and 5a (group 1) also Kompo from the group of compounds 1b, 2b, 3b, 4b, and 5b (Group 2), the proportions of which are preferably as follows are:

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 crystal systems used contain liquid crystals preferably 1-40%, in particular 5-30% of compounds of the formula I. The liquid crystals preferably contain 1-5, but especially 1-3 compounds of formula I.

The proportion consisting of compounds of formulas I-IV the base mixture to the electro in the invention liquid crystal systems used liquid Crystalline is preferably 15% -100%, in particular however 25% -100%. The basic mixture is based on Ver compounds of the formula I particularly preferably on the fol lower group of compounds, wherein R¹ is the has the meaning given above.  

Very particular preference is given to the following mixtures 1-6, the at least one component of each listed Contain formulas in the specified mass percentage range, where the sum of the mass percentages in the mixtures contained and covered by the listed formulas Connections between 10% and 90% and in particular between 15% and 85%.  

The electro-optical liquid crystal according to the invention Systems are preferably characterized by the fact that during the production of the system no or only one low interaction of the components of the liquid crystal mixture with the polymeric carrier over polar groups come about.  

The electrooptical liquid crystal according to the invention Systems can be created by applying a DC or AC be switched voltage. However, a preferred AC voltage used, which is an effective change voltage amplitude between 1 and 240 volts and a AC frequency between 10 and 10 kHz. Particularly preferred are amplitudes between 2 and 220 volts and frequencies between 20 and 120 Hz particularly preferably the amplitude is the change voltage between 2 and 130 V.

The dielectric anisotropy of the liquid used crystal mixture is positive Δε <0 and preferably Δε <3rd For smaller values of dielectric anisotropy pie Δε very high threshold voltages are observed. Particular preference is given to values Δε <5, in particular Δε <10 and especially Δε <15.

The preparation of the liquid used in the invention crystal mixtures is carried out in a conventional manner. Usually, the desired amount is in lesser Quantity of used components in the main stock partially solved components, useful in elevated temperature. It is also possible solutions of Components in an organic solvent, eg. In Acetone, chloroform or methanol, and mix Remove solvent after thorough mixing, for example by distillation.

By suitable additives, the described liquid crystal mixtures are modified so that they are in all electro-optical systems according to the preamble of claim 1 can be used.  

Such additives are known in the art and in the Literature described in detail. So z. B. pleo chroitic dyes for the production of colored electro optical systems or substances for modifying the dielectric anisotropy, the optical anisotropy, the viscosity and / or the temperature dependence elek trooptic parameters of the liquid crystals are added to the like substances are z. In H. Kelker, R. Hatz, Hand book 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 described.

Electro-optical liquid crystal systems in which the Liquid crystal pleochroic dyes in one Weight percent range of 0-25%, especially 0-20% and especially 0-15% are added are preferred.

The skilled person can further select from the large pool of nematic or nematogenic substances additives to the liquid crystal mixtures described so 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 other 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 in the systems according to the invention used liquid crystal mixtures z. B. add high-clarifying substances such. B.

wherein R² and R³ each independently represent alkyl, methoxy, alkoxycarbonyl or alkanoyloxy having 1-15 C atoms. In this case, the expert will preferably choose the concentration of such additives that in particular Δn and / or n _o and / or another, to be adapted in the respective embodiment of the electro-optical system refractive index and / or Δε only in an acceptable and / or small and / or in particular negligible extent is affected.

Is the system according to the invention with an AC voltage controlled, is the use of a high-viscosity liquid crystal mixture required, otherwise in particular at low to medium frequencies a flickering display results. To increase the viscosity of the expert 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, enforce. Is the electro-optical system against it z. B. ver as a matrix display with high information content In particular, low-viscosity liquid crystal are used mixtures are preferred for achieving short switching times. The expert can choose from the large pool nematic or nematogenic compounds such low viscosity select, such as B.

wherein R² and R³ have the meaning given above. The skilled artisan will choose the ver used for modifying the viscosity of used substances and their concentration so that other crucial parameters of the liquid crystal mixture such. B. Δn, Δε and when using Viskosi tätserniedrigern in particular T _c only in an acceptable and / or small and / or negligible extent is influ- impressed.

Optionally, highly nontogenic substances such. B.

be added, the expert considers that by such additives other parameters and in particular the solubility of the liquid crystal mixture in the for The matrix used polymer did not change too much become.

For the modification of the birefringence, the person skilled in the art can z. B. in liquid crystal mixtures, the compounds of Formulas II-IV, the relative proportion of these Ver compounds in the mixture vary; for mixtures with very high Δn can e.g. in particular 4-alkyl or alkoxy-4 'or 4 "-cyano-biphenyls or -terphenyls ver be used.

To achieve low threshold voltages, i. a. Liquid crystal mixtures with very high dielectric Anisotropy Δε needed. The skilled person can increase of Δε compounds such. B.

enforce. These compounds are extremely strong dielectrically positive; the propyl homologue (alkyl = C₃H₇) has z. B. a value Δε = 50. The person skilled in the art will select the concentration of such additives so that the liquid-crystal mixture is optimally matched to the respective design of the electro-optical system; in particular, he will take care that Δn and / or n _o and / or one or more other refractive indices of the liquid crystal are affected only to an acceptable and / or small and / or negligible extent.

By the described additives, the liquid crystal modified with respect to the particular application and be optimized. But the decisive factor is that liquid Crystals containing compounds of the formula I and in especially those additionally containing one or more Compounds of formula II-IV, for use in the invention According to the invention electro-optical liquid crystal systems are particularly suitable. Especially suitable However, the liquid crystal mixtures 1-6, in addition to compounds of the formula I one or more compounds of formula II-IV in defined mass percentage ranges contain.

These compounds of formula I contain liquid crystal mixtures pose for use in electro optical systems also particularly suitable "stable Framework mixtures ", which i.a. by the described Additives optimized for 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 experiencing impairing change.

The liquid crystals which can be used according to the invention are shown NEN through advantageous values for the dielectric Anisotropy Δε, high stability, low miscibility with the polymer used for the matrix and ins special by a wide mesogenic area, one relatively high clearing point and favorable values for the double refraction. The liquid crystals correspond to the one gangs described in a Verwen tion in an electro-optical system according to the Ober Concept of claim 1 are made, in particularly high Dimensions and much better than before in these systems used 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 2 symbols indicates the conversion temperature in degrees Celsius.

The percentages given are by mass.

Example 1

• a) An electro-optical liquid crystal system, containing tend a liquid crystal mixture consisting of the following compounds: 20% 1- (4- (4-pentylphenyl) phenyl) -2- (4-cyanophenyl) -ethane 14.4% p-trans-4-propylcyclohexyl-benzonitrile 11.2% p-trans-4-butylcyclohexyl-benzonitrile 20% p-trans-4-Pentycyclohexyl-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-carboxyl-at 5.6% 4- (trans-4-pentylcyclohexyl) -4'-cyanobiphenyl
• b) The electro-optical liquid crystal system is after various methods 1.1-1.3 and 2 produced.

1. microdroplet matrix systems

• 1.1 The liquid-crystal mixture from a) is mixed with the UV irradiation curable adhesive NOA 65 (Norland Products) in the ratio 1.6: 1 at room temperature stirred until a clear solution is obtained together with spacers between 2 through active, provided with electrode layers glass substrates is brought. The glass substrates become together pressed, creating a uniform film with a Thickness of 20 microns is obtained by a Cured for 1 minute UV irradiation.  
• 1.2 The liquid-crystal mixture from a) is mixed with Epikote 828 and Capcure 3-800 (Miller Stephenson Company) in the ratio 1: 1: 1 stirred at room temperature until a clear solution is obtained; the stirring time is kept as short as possible, as the solution to Room temperature already cured after about 1/2 h is. The solution will work together with spacers between 2 transparent, with electrode layers provided glass substrates, the zusammenge presses, creating a uniform film with a thickness of 20 microns is obtained. To accelerate When the curing process is finished, the films can open Temperature can be heated 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 for 2 minutes at 2000 rpm. The obtained Solution is degassed for 24 h and along with Spacers in a thin layer on a with a Electrode layer provided glass substrate applied. The assembly is dried at 85 ° C for 1 h before a second provided with an electrode layer Glass substrate is pressed, creating an equal moderate film is obtained with a thickness of 20 microns. The system thus obtained is maintained at 85 ° C. for a further 24 h dried.

2. network system

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

Those produced by the methods b) 1.1-1.3 and 2 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 by a low threshold voltage.

example 2

According to Example 1, according to the methods 1.1-1.3 and 2 various electro-optical liquid crystal systems using the following liquid crystal mixture manufactured:

34.65% 4-pentyl-4'-cyanobiphenyl, 13.5% 4-propoxy-4'-cyanobiphenyl, 10.35% 4-pentoxy-4'-cyanobiphenyl, 13.5% 4-octoxy-4'-cyanobiphenyl, 10.0% 4- (trans-4-pentylcyclohexyl) -4'-cyanobiphenyl, 9.0% 4- [2- (p-Propylphenyl) ethyl] -4'-cyanobiphenyl and 9.0% 4- [2- (p-pentylphenyl) ethyl] -4'-cyanobiphenyl

NI 84 °
Δn 0.247

These systems are characterized by a particularly high UV stability out.  

example 3

• a) An electro-optical liquid crystal system comprising a liquid-crystal mixture consisting of the following compounds: 17.5% 2- (4-cyanophenyl) -5-propylpyridine 17.5% 2- (4-cyanophenyl) -5-butylpyridine 17.5% 2- (4-cyanophenyl) -5-pentylyridin 17.5% 2- (4-cyanophenyl) -5- (4-pentylphenyl) -pyridine 15.0% 1- [4- (4-propylphenyl) phenyl -] - 2- (4-cyanophenyl) -ethane 15.0% 1- [4- (4-pentylphenyl) phenyl -] - 2- (4-cyanophenyl) -ethane and having the following physical properties: clearing point T _c = 94 ° C
  optical anisotropy Δn = 0.2722 (20 ° C, 589 nm)
  dielectric anisotropy Δ∈ = 25.6 (20 ° C, 1 kHz)
• b) The electro-optical system, which after the in Example 1b) is described draws through a wide working temperature range, a good manufacturability, favorable values for the electro-optical parameters and in particular by a low threshold voltage off.

Claims (17)

1. Electro-optical liquid crystal system,

• which contains between 2 electrodes, which are given if appropriate on substrate plates, a dielectrically positive liquid crystal and another optically transparent medium,
• whose liquid crystal molecules have an irregular orientation when switched off
• - Wherein one of the refractive indices of the liquid crystal substantially coincides with 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 inde pendent of the polarization of the incident light has a relation to the other state ver-reduced transmission,

characterized
in that the liquid crystal contains one or more compounds of the formula I R-Q¹-CH₂CH₂-Q²-CN (I) wherein
R is alkyl having up to 12 carbon atoms, in which also one or two non-adjacent CH₂ groups may be replaced by -O-, and one of the radicals Q¹ and Q² 4,4'-biphenyl and the other radical 1,4-phenylene mean. 2. System according to claim 1, characterized in that the liquid crystal contains one or more compounds selected from the compounds of formulas II-IV, wherein
R¹ are each independently an alkyl group having 1-15 C atoms, in which also one or two non-adjacent CH₂ groups may 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 the compounds I-IV Base mixture to which liquid crystal is 15-100%. 4. System according to at least one of claims 1-3, characterized in that the liquid crystal contains additional compounds that are from the classes the azoxybenzenes, benzylideneanilines, biphenyls, Terphenyls, phenyl or cyclohexyl benzoates, cyclo hexane-carboxylic acid phenyl or cyclohexyl ester, Phenyl or cyclohexyl ester of cyclohexylbenzoic acid acid, phenyl or cyclohexyl esters of cyclohexyl cyclohexanecarboxylic acid, cyclohexylphenyl ester of Benzoic acid, the cyclohexane carboxylic acid, or the Cyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes, Cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, Cyclohexylcyclohexanes, cyclohexylcyclohexenes, Cyclohexylcyclohexylcyclohexenes, 1,4-biscyclohexyl benzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl or Cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, Phenyl or cyclohexyl dioxanes, phenyl or cyclo hexyl-1,3-dithiane, 1,2-diphenylethane, 1,2-dicyclo hexylethanes, 1-phenyl-2-cyclohexylethane, 1-cyclo hexyl 2- (4-phenylcyclohexyl) ethanes, 1-cyclohexyl 2-biphenylylethane, 1-phenyl-2-cyclohexylphenyl ethane, halogenated stilbenes, benzyl phenyl ether, Tolane and substituted cinnamic acids selected be with the 1,4-phenylene groups in these Compounds may also be fluorinated.   5. System according to any 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) wherein
L and E are each independently a bivalent residue 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 is 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 represent alkyl, alkenyl, alkoxy, alkenyloxy or alkanoyloxy each having 1-8 carbon atoms or CN, CF₃, F, Cl or NCS. 6. System according to at least one of claims 1-5, characterized in that the liquid crystal is based on one of the mixtures 1-6, where the sum of the mass percentages in the Mixtures included and listed below Formulas falling links between 10% and 90% lies. 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 at least one 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 Pores the liquid crystal is located. 11. Liquid crystal, characterized in that it is with the liquid crystal in an electro-optical system according to at least one of claims 2-8 is identical. 12. Use of a liquid crystal containing minde at least one compound of formula I, in a system according to claim 9. 13. Use of a liquid crystal containing minde at least one compound of formula I, in a system according to claim 10. 14. Use of a liquid crystal according to claim 11 in A system according to claim 9. 15. Use of a liquid crystal according to claim 11 in A system according to claim 10.