DE4002146A1 - 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 separated from one another Liquid crystal microdroplets contain or 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 compartments characterized, but by no means a spherical Must have shape but irregular can be shaped and / or deformed.

Does the optically transparent medium contain liquid crystal Microdroplets, it is referred to in the following as a matrix; 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, in which the liquid crystal in the form of microdroplets embedded in the matrix. NCAP films are becoming commonplace obtained by the encapsulating polymeric  Material, such. For example, 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 described in US 44 35 047. In contrast, in 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 Homogenously mixed oligomers of the matrix-forming material. 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 the 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 electrodes provided substrate plates and then z. B. 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 refractive 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 liquid crystal content of the light modulated layer is not necessarily required, but can be made to increase the light throughput and the contrast.

It is observed on these electro-optical liquid crystal systems an electrically switchable light scattering effect. There is no voltage to the electrodes, between the matrix or the network usually sandwiched is arranged, created, becomes incident Light on the randomly aligned liquid crystal molecules strongly scattered, the system is opaque. When a voltage is applied, the liquid crystal molecules become parallel to the field and perpendicular to the E vector aligned by the passing light.

In microdroplet matrix systems, perpendicularly incident light, due to the matching of n _o and n _M, sees an optically isotropic medium and the system appears transparent. 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 by applying a voltage in the opaque state.

In network systems, there is an adjustment of refractive indices not necessarily because of the high Liquid crystal content of the mass of light modulating 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. At network Systems is to achieve the lowest possible Transmission in the non-switched state the use of liquid crystals with high optical anisotropy prefers.

Electro-optical liquid crystal systems according to the preamble of claim 1 are especially for large area 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, liquid crystals are needed, which by a high clearing point a wide nematic Range and high UV and temperature stability are. Next is a high value for the dielectric Anisotropy Δε preferred to a low To get threshold voltage.

Other applications include:

• - GH display systems, ranging from simple segment displays to displays that can be used to apply any pattern of electrodes using conventional printing techniques. applications:
  Motor vehicle, large displays, advertising space, watches
• - Matrix displays with high information content
• - projection systems  
• - Counter.

Again, liquid crystal mixtures with particular high Δε and high electrical resistance needed.

In microdroplet matrix systems are so far commonly LC mixtures used consisting of alkyl or alkoxycyanobiphenylen and -terphenyls exist. So z. 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 flow viscosity η (20 ° C) of 54 mm² / s, but has at the same time 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 can Turbidity of the system in the switched state ("haze") and thus a significant deterioration of the electro-optical Effect properties. Although in systems that by a relatively low-frequency AC voltage is driven be a high flow viscosity η desired to a to get flicker-free display; on the other hand, however in matrix displays with high information content to Realization of fast switching times Liquid crystal mixtures needed with relatively low viscosity.

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. EP 03 13 053 proposes liquid crystal mixtures based on 2- (4-cyanophenyl) pyridines for network systems. Although such liquid crystals have relatively high values for the dielectric anisotropy Δε and thus relatively small 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, cyanophenylpyridine compounds generally have lower temperature and UV stability than cyanooligophenyls.

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 which can be optimized with regard to the respective application 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 oligomers of the matrix used to form the matrix or the network Polymers on what the production of PN systems significantly impaired and in microdroplet matrix In particular, the application of PIPS technology considerably limited. In addition, the liquid crystals 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, 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 to provide the cited Disadvantages of conventional systems not or only to a small extent.

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

R¹-Q¹-CH₂CH₂-Q²-R² (I)

wherein

R¹ and R² are each independently alkyl having up to 12 C atoms, wherein also one or two non-adjacent CH₂ groups may be replaced by -O-, and
the radicals Q.sup.1 and Q.sup.2 are each independently of one another 1,4-cyclohexylene, 1,4-phenylene, 4,4'-biphenylyl, 4,4'-phenylcyclohexyl, 4,4'-cyclohexylphenyl, where one of the 1,4-present in the molecule -Phenylenreste may also be substituted by fluorine or chlorine,
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 is independent in one of the two switching states from the polarization of the incoming light one compared to the other state reduced transmission wherein the liquid crystal has one or more Compounds of formula I contains.

The structure of the electro-optical liquid crystal systems according to the invention corresponds to that for such systems usual construction. The term usual construction is hereby broad and encompasses all modifications and modifications.

So z. B. in PDLC or NCAP films that of the transparent Medium formed matrix in which the liquid crystal mixture microdispersed or microencapsulated is sandwiched between conductive electrodes.  

The electrodes are i. a. on substrate plates of z. B. 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 considerable technological simplification in the production of these systems compared to conventional liquid crystal systems such as B. TN or STN cells, means.

The matrix or the 3-dimensional network are based in particular on isotropic thermoplastics, thermosets and Elastomers. The obtained systems may vary depending on the intended 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 be z. In microdroplets 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 materials such as As 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 embodiments of the electro-optical Liquid crystal systems are NCAP films, PDLC Films and produced by modified methods Microdroplets matrix systems. Process for the preparation these films are z. In US 39 35 337, US 46 88 900, US 46 73 255, US 46 71 619, US 44 35 047 and EP 02 72 595 described.

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

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 on the other side.  

To the electro-optical system according to the invention include also "inverse microdroplet matrix configurations", in which the transparent medium in the form of individual z. B. spherical particles dispersed in the liquid crystal is. 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 . So z. B. in US 44 35 047 layer thicknesses of 0.8 and 1.6 mm reported, while 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 are given. 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 affected by the size of the microdroplets 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 average droplet size are e.g. In US 46 73 255 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 z. For example, 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, EP 03 13 053 specifies a preferred range between 0.5 and 2 μm.

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

The compounds of the formula I include 2-nuclear compounds of the formulas Ia and Ib, which are preferred:

R¹ and R² are independently preferably Alkyl or alkoxy with 1-10, but especially with 1-8 C atoms. More preferred are n-alkoxyalkyl and in particular n-alkoxymethyl and n-alkoxyethyl compounds. One of the two 1,4-phenylene groups can be in the 2- or 3-position by Cl or F, in particular however, be substituted by F and / or in the 3-position.

Particularly preferred are the compounds of the formula Ia1 and Ia2

The compounds of formula I further include 3-ring Compounds of sub-formulas Ib1-Ib4, which are preferred are:  

In the compounds of the formulas Ib1-Ib4 R¹ and R² are preferably independently of one another n-alkyl or n-alkoxy having 1-10 C atoms, besides also n-alkoxymethyl or n-alkoxyethyl having 1-8 C atoms. The connections of the formula Ib1-Ib3 can be attached to one of the 1,4-phenylene groups laterally monosubstituted by X = F or Cl his. Particularly preferred are the monosubstituted Compounds of the formulas Ib11, Ib12, Ib21 and Ib31:

The laterally monosubstituted compounds of the formulas Ib1-Ib4 are usually characterized by lower flow viscosity out as the corresponding unsubstituted Links.

The compounds of formula I further include 4-ring Compounds in which Q¹ and Q² are each independently

mean:

R¹ and R² in the compounds of the formulas Ic1-Ic5 preferably independently of one another 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. The connections of the formulas Ic1-Ic5 can be attached to one of the 1,4-phenylene groups be laterally monosubstituted by F or Cl, where substitution in the 3-position is preferred. These drawing monosubstituted tetranuclear compounds characterized by a high clearing point and a comparatively low flow viscosity η.

In the compounds of the formula I, the radicals R¹ and / or R² be straight-chain or branched. Preferably R¹ and R² are straight-chain, but compounds of the formula I with branched alkyl or alkoxy radicals occasionally because of a better solubility in the customary liquid-crystalline base materials of Be important, but especially as chiral dopants, if they are optically active. electro-optical Systems according to the preamble of claim 1, whose Liquid crystal one or more chiral components contains are described in DE 39 11 255.1.

Branched groups of this kind usually contain no more than a chain branch. Preferred branched Radicals 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-3-methylbutyl, 3-oxa-4-methylpentyl, 4-methylhexyl, 2-nonyl, 6-methyloctoxy, 2-methyl-3 oxapentyl, 2-methyl-3-oxahexyl.  

The compounds of the formula I are known per se Methods presented in the literature (eg. in the standard works such as Houben-Weyl, Methods of the Organic Chemistry, Georg-Thieme-Verlag, Stuttgart, Vol. IX, P. 867 ff.), Under reaction conditions, known for the reactions mentioned and are suitable. It can also be known by itself, Uses not mentioned in detail here do.

The compounds of the formula I are preferably after in EP 00 84 194, JP 61-087 777, GB 22 01 415 and DE 32 37 367 described methods.

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

wherein

R each independently of one another 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-,

mean.

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, cyclohexanecarboxylic acid phenyl or cyclohexyl esters, phenyl or Cyclohexyl esters of cyclohexylbenzoic acid, phenyl or Cyclohexyl ester of cyclohexylcyclohexanecarboxylic acid, Cyclohexylphenyl ester of benzoic acid, cyclohexanecarboxylic acid, or cyclohexylcyclohexanecarboxylic acid, Phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, Cyclohexylcyclohexanes, cyclohexylcyclohexenes, Cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 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-phenylcyclohexyl) - ethane, 1-cyclohexyl-2-biphenylylethane, 1-phenyl-2-cyclohexylphenylethane, optionally halogenated Stilbenes, benzylphenyl ethers, tolans and substituted ones 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'-LER '' (1)
R'-L-COO-ER '' (2)
R'-L-OOC-ER "(3)
R'-L-CH₂CH₂-ER "(4)
R'-LC≡CER '' (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 substituted by fluorine 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. Preferably contain the liquid crystals according to the invention one or more components selected from the compounds 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 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 compounds R 'and R' 'are 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 means R "-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 crystal systems according to the invention used liquid crystals preferably in addition to 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), 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 crystal systems according to the invention used 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 of those consisting of compounds of formulas I-V Base mixture of the electro-optical in the invention Liquid crystal systems used liquid crystals is preferably 15% -100%, in particular however 25% -100%. The base mix is based on compounds of the formula I particularly preferred on the following smaller group of compounds, where R is the has the meaning given above.

Very particular preference is liquid crystals on based on mixtures 1-12 described below, wherein the mass fraction of the mixtures 1-12 on the liquid crystal between 10% and 98% and in particular between 15% and 95%. The mixtures 1-12 consist of 2 or more compounds selected from 2, 3, 4 or 5 formulas fall, from the group of formulas I, II, III, IV and V are selected. The mixtures 1-12 preferably contain 2-40, but especially 2-38 and especially 2-35 connections. The mass fraction of these compounds on the mixtures 1-12 can be within the specified Limits for optimal adaptation to the respective Display type can be varied, the sum of these mass fractions 100% of the mixtures 1-12, of course is.

The electrooptical liquid crystal systems according to the invention 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 substrate over polar groups come about.  

The electrooptical liquid crystal systems according to the invention can by applying a DC or AC voltage be switched. However, a preferred AC voltage uses an effective AC voltage amplitude between 1 and 240 volts and one AC frequency between 10 and 10 kHZ has. Particularly preferred are amplitudes between 2 and 220 volts and frequencies between 10 and 120 Hz Particularly preferred is the amplitude of the AC voltage between 2 and 130 V.

The dielectric anisotropy of the liquid crystal mixture used is positive Δε <0 and preferably Δε <3rd For smaller values of dielectric anisotropy 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 crystal mixtures which can be used according to the invention takes place in a conventional manner. Usually, the desired amount is in lesser Quantity of used components in the main component 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 be 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. pleochroic 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 electro-optical Added parameters of the liquid crystals become. Such substances are z. 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 percent range of 0-25%, especially 0-20% and especially 0-15% are added are preferred.

The person skilled in the art can further select from the large pool of nematic or nematic substances additives to the described liquid-crystal mixtures such 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 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 R⁴ and R³ each independently represent alkyl, methoxy, alkoxycarbonyl or alkanoyloxy having 1-15 carbon atoms. In this case, the skilled person will preferably select 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 in the respective embodiment of the electro-optical system according to the invention only in an acceptable and / or small and / or 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, especially at low to medium frequencies a flickering display results. To increase the viscosity of the expert 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, enforce. Is the electro-optical system against it z. B. used as a matrix display with high information content, are in particular low-viscosity liquid-crystal mixtures 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.  

where R⁴ and R³ have the meaning given above. The skilled person will choose the substances used to modify the viscosity and their concentration so that other crucial parameters of the liquid crystal mixtures such. B. Δn, Δε and when using viscosity reducers in particular T _{c is influenced} only in an acceptable and / or small and / or insignificant extent.

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 contain the relative proportion of these compounds vary in the mixture; for mixtures with very high Δn can z. B. in particular 4-alkyl or alkoxy-4 'or 4' '- cyano-biphenyls or -terphenyls used become.  

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 what matters is that liquid crystals, containing compounds of formula I and in particular those additionally containing one or more Compounds of formulas II-V, for use in the invention electro-optical liquid crystal systems are particularly suitable. Especially suitable However, the liquid crystal mixtures 1-12, in addition to compounds of the formula I one or more compounds of formula II-V in defined mass percent ranges contain.  

These compounds of formula I containing liquid crystal mixtures provide for application 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 characterized characterized by a high stability, low miscibility with the polymer used for the matrix and in particular through a broad mesogenic area, one relatively high clearing point and favorable values for the optical anisotropy Δn and the flow viscosity η. The liquid crystals correspond to those described above 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 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 2 symbols indicates the transformation temperature in degrees Celsius.

The percentages given are by mass.

Example 1

• a) An electro-optical liquid crystal system containing a liquid crystal mixture consisting of the following compounds 18% 4-cyano-4 '- (trans-4-pentylcyclohexyl) -biphenyl
  35% 4-cyano-4'-hexylbiphenyl
  22% 4-cyano-4'-pentylbiphenyl
  9% 4-cyano-4'-pentylterphenyl
  5% 4-cyano-4'-ylbiphenyl-4-heptyl-4'-ylbiphenylcarboxylate
  5% 4-cyano-4'-nonoxybiphenyl
  6% of 1- (trans-4-propylcyclohexyl) -2- (4-pentyl-2-fluoro-4'-yl-biphenyl) -ethane and having the following physical parameters: clearing point T _C = 100 ° C viscosity η = 55 mm² / s ^-1 (20 ° C) dielectric anisotropy Δε = 14.1 (20 ° C, 589 nm) optical anisotropy Δn = 0.24 (20 ° C, 1 kHz)
• b) The electro-optical liquid crystal system is prepared by various methods 1.1-1.3 and 2.
  • 1. microdroplet matrix systems
    • 1.1. The liquid-crystal mixture from a) is stirred at room temperature with UV radiation-curable adhesive NOA 65 (Norland Products) in a ratio of 1.6: 1 until a clear solution is obtained which, together with spacers (20 μm) between 2 transparent , is brought to glass substrates provided with electrode layers. The glass substrates are compressed to obtain a uniform film having a thickness of 20 μm, which is cured by a 1 minute UV irradiation.
    • 1.2 The liquid-crystal mixture from a) is stirred at room temperature with Epikote 828 and Capcure 3-800 (Miller Stephenson Company) in a ratio of 1: 1: 1 until a clear solution is obtained; the stirring time is kept as short as possible, since the solution is already cured at room temperature after about ½ h. The solution, together with spacers (20 μm), is placed between 2 transparent electrode-coated glass substrates, which are pressed together to obtain a uniform film having a thickness of 20 μm. To accelerate the curing process, the films can be heated to a temperature of up to 100 ° C.
    • 1.3 5 g of the liquid-crystal mixture from a) are stirred at room temperature for 2 minutes at 2000 rpm with 15 g of 20% aqueous PVA solution at room temperature. The resulting solution is degassed for 24 hours and applied together with spacers (20 μm) 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, thereby obtaining a uniform film having a thickness of 20 μm. The system thus obtained is dried at 85 ° C for a further 24 h.
  • 2. network system
    The liquid-crystal mixture from a) is reacted with trimethylpropane triacrylate as the polymerizable compound and 2-hydroxy-2-methyl-1-phenylpropan-1-one (Darocure 1173, commercial product of E. Merck, Darmstadt) as a photoinitiator in the ratio 80: 19.8 0.2 was stirred and placed, with the addition of spacers having a thickness of 20 μm, between 2 glass plates provided with electrode layers. To cure the polymer, the resulting system was run at a defined speed (3 m / min) through the radiation field of a halogen lamp (70 W / cm).

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, a low threshold voltage, good manufacturability and a high contrast.

Claims (14)

1. Electro-optical liquid crystal system,

• which contains between 2 electrodes, which are optionally applied to substrate plates, a dielectrically positive liquid crystal and another optically transparent medium,
• whose liquid crystal molecules have an irregular orientation when switched off,
• 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,

characterized,
in that the liquid crystal contains one or more compounds of formula I R¹-Q¹-CH₂CH₂-Q²-R² (I) wherein
R¹ and R² are each independently alkyl having up to 12 C atoms, wherein also one or two non-adjacent CH₂ groups may be replaced by -O-, and
the radicals Q¹ and Q² are each independently 1,4-cyclohexylene, 1,4-phenylene, 4,4'-biphenylyl, 4,4'-cyclohexylphenyl or 4,4'-phenylcyclohexyl, wherein one of the 1,4-present in the molecule -Phenylenreste may also be substituted by fluorine or chlorine,
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, each R independently of one another may be replaced by 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 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 additional compounds that are from the classes the azoxybenzenes, benzylideneanilines, biphenyls,  Terphenyls, phenyl or cyclohexyl benzoates, cyclohexane carboxylic acid phenyl or cyclohexyl esters, Phenyl or cyclohexyl ester of cyclohexylbenzoic acid, Phenyl or cyclohexyl ester of cyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl benzoic acid, cyclohexanecarboxylic acid, or cyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes, Cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, Cyclohexylcyclohexanes, cyclohexylcyclohexenes, Cyclohexylcyclohexylcyclohexenes, 1,4-bis- cyclohexylbenzenes, 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) - ethane, 1-cyclohexyl-2-biphenylylethane, 1-phenyl-2- cyclohexylphenylethanes, halogenated stilbenes, Benzylphenyl ethers, tolans and substituted cinnamic acids be selected, wherein the 1,4-phenylene groups also be fluorinated in these compounds can. 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 '' (1)
R'-L-COO-ER '' (2)
R'-L-OCC-ER '' (3)
R'-L-CH₂CH₂-ER "(4)
R'-LC≡CER '' (5) wherein
L and E are each independently a bivalent radical of the group consisting of -Phe, -Cyc, -Phe-Phe, -Phe-Cyc, -Cyc-Cyc, -Pyr-, -Dio, -G-Phe wherein Phe is unsubstituted or 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 "are each independently alkyl, alkenyl, alkoxy, alkenyloxy or alkanoyloxy each having 1-8 carbon atoms or CN, CF₃, F, Cl or NCS
mean. 6. System according to any one of claims 1-5, characterized in that the liquid crystal is based on one of the mixtures 1-12, wherein the sum of the mass percentages of the compounds contained in the mixtures and falling under the listed formulas is between 10% and 98%. 7. System according to at least one of claims 1-6, characterized in that the liquid crystal is a 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. 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 at least a compound of formula I, in a 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.