EP0429607A1

EP0429607A1 - Electro-optical liquid crystal system

Info

Publication number: EP0429607A1
Application number: EP90908939A
Authority: EP
Inventors: Ulrich Finkenzeller; Dieter Dorsch
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 1989-06-19
Filing date: 1990-06-06
Publication date: 1991-06-05
Also published as: DE3919942A1; US5242616A; WO1990015854A1; JPH04500380A

Abstract

Système électro-optique à cristaux liquides, contenant des microgouttelettes nématiques enrobées dans une matrice transparente et constituées par un mélange de cristaux liquides, caractérisé en ce que le mélange de cristaux liquides renferme, en vue d'accroître la viscosité d'écoulement pour la porter à des valeurs supérieures à 40 mm2 à 20°C, un ou plusieurs polymères à chaînes latérales contenant des motifs monomères de formule (I), dans laquelle P désigne un motif de chaîne principale polymère, Sp désigne un groupe alkylène de 1 à 20 atomes de C, dans lequel un ou plusieurs groupes CH2- non voisins peuvent être remplacés par -O-, -S- et/ou -NR2-, et B désigne un reste organique dit "rod-like" ("en bâtonnets"), ces produits pouvant être utilisés pour la fabrication de systèmes d'affichage de grande surface, fonctionnant notamment sous tension alternative.Electro-optical liquid crystal system, containing nematic microdroplets coated in a transparent matrix and constituted by a mixture of liquid crystals, characterized in that the mixture of liquid crystals contains, with a view to increasing the flow viscosity in order to bring it at values greater than 40 mm2 at 20°C, one or more side chain polymers containing monomer units of formula (I), in which P denotes a polymer main chain unit, Sp denotes an alkylene group of 1 to 20 atoms of C, in which one or more non-neighboring CH2- groups may be replaced by -O-, -S- and/or -NR2-, and B denotes a so-called "rod-like" organic residue, these products can be used for the manufacture of large-area display systems, operating in particular under alternating voltage.

Description

Electro-optical liquid crystal system

The invention relates to an electro-optic liquid crystal system containing nematic microdroplets which are embedded in a transparent matrix and which consist of a liquid crystal mixture, characterized in that the liquid crystal mixture has a value of> 40 mm ² / s at 20 ° C. to increase the flow viscosity or more side chain polymers containing monomer units of the formula I,

- (- P -) - I

I Sp-B

wherein

P is a polymer main chain unit,

Sp is an alkylene group with 1-20 C atoms, in which one or more non-adjacent CH _? - Groups can be replaced by -O-, -S- and / or -NR 2-, and

B means an organic "rod-like" residue,

contains. Such electro-optical liquid crystal systems contain nematic microdroplets which are embedded in a transparent matrix. The matrix is sandwiched between conductive electrodes. Examples of these systems are NCAP and PDLC films (NCAP = nematic curvilinear aligned phases, PDLC = polymer dispersed liquid crystal). NCAP films are usually obtained by intimately mixing the encapsulating polymeric material, such as polyvinyl alcohol, the liquid crystal mixture and a carrier material, such as water, in a colloid mill. The carrier material is then removed, for example by drying. A corresponding method is described in US 4,435,047. In contrast, in the production of PDLC films described, for example, in EP 0,272,582 and US Pat. No. 4,688,900, the liquid crystal mixture is first homogeneously mixed with monomers or oligomers of the matrix-forming material. Then the mixture is polymerized and induces the phase separation, between TIPS (te per- ature-induced phase separation), SIPS (solvent-induced phase ^"separation) and PIPS (polymerization-induced phase separation) a distinction is made (Mol. Cryst. Liq Cryst. Inc. Nonlin. Opt. 157 (1988) 427).

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

An electrically switchable light scattering effect is observed on these electro-optical liquid crystal systems. If there is no voltage applied to the electrodes, incident light is applied to the statistically aligned liquid crystal molecules strongly scattered, the system is opaque. When a voltage is applied, the liquid crystal molecules are aligned parallel to the field and perpendicular to the E-vector of the light passing through. Because of the adaptation of n. ^ To n _Q , the incident light now sees an optically isotropic medium and the system appears transparent. Another embodiment is described in EP 0 272 585, in which the refractive index n, which the liquid crystal has with a completely statistical orientation, is matched to the refractive index of the matrix ^. In this case, the system is transparent in the field-free state, and it is converted to the opaque state by applying a voltage.

Systems of this type have been proposed above all for large-area display systems, for architectural applications (windows, room dividers, sunroofs, etc.) and for motor vehicles (windows, sunroofs, etc.). They can be switched by applying a DC or AC voltage.

Since these systems are also intended in particular for “outdoor” applications, liquid-crystal mixtures are required which are characterized by a high clearing point, a wide nematic range and high UV and temperature stability.

In conventional electro-optic liquid crystal systems, LC mixtures are usually used, which consist of alkyl or alkoxycyanobiphenylene and terphenylene. For example, US 4,688,900 and EP 0272 585 describe the use of the liquid crystal mixture E8 (produced by BDH, Poole, Great Britain). This liquid crystal mixture is distinguished by a relatively high value for the flow viscosity of 54 mm ² / s and a very high value for the optical anisotropy Δn of 0.247, but at the same time has a relatively low clearing point of only 72 ° C. If multinuclear polyphenyl compounds are added to the mixture to recover the clearing point, the result is an unchanged high or even higher value for the optical anisotropy Δn. High Δn values on the one hand ensure strong light scattering in the opaque state, but on the other hand they cause the system to become cloudy in the switched state ("haze") and thus a significant deterioration in the electro-optical properties.

The liquid crystal mixture E7 used in US Pat. No. 4,671,618 (manufactured by BDH, Poole, Great Britain), which also consists of alkyl and alkoxycyanobiphenylene and terphenylene, has a slightly smaller optical anisotropy than Δ8 = Δ25 than E8, but is simultaneous the clearing point T _c = 60.5 ° C and the flow viscosity η = 39 mm ² / s at 20 ° C considerably lower. If the system is controlled with an AC voltage, however, the use of a highly viscous liquid crystal mixture is essential, since otherwise a flickering display will result, especially at low to medium frequencies.

There is therefore still a great need for electro-optical liquid crystal systems which can be switched to flicker-free when an AC voltage is applied and at the same time have a relatively high optical anisotropy Δn and a high clearing point T _c .

The object of the invention was to provide electro-optical liquid crystal systems which do not have the disadvantages of conventional systems mentioned above or only to a small extent. Surprisingly, it has now been found that this object can be achieved if liquid-crystal mixtures which contain one or more side-chain polymers are used for these systems.

The invention thus relates to an electro-optic liquid crystal system containing nematic microdroplets which are embedded in a transparent matrix and which consist of a liquid crystal mixture, characterized in that the liquid crystal mixture to increase the flow viscosity to values> 40 mm ² / s at 20 ° C one or more side chain polymers containing monomer units of the formula I,

- (- P -) - I

I Sp-B

wherein

P is a polymer main chain unit,

Sp is an alkylene group with 1-20 C atoms, in which one or more non-adjacent CH ₉ groups can also be replaced by -O-, -S- and / or -NR 2-, and

B means an organic "rod-like" residue,

contains.

In particular, such electro-optical liquid crystal systems are the subject of the invention, in which B represents a radical of formula II,

R ¹ - (A ¹ -Z ¹ ) _n -A ² -Z ² -A ³ - II wherein

RF, CN or an unsubstituted or substituted by CN or by at least one halogen atom alkyl or alkenyl radical, each with 1-15 carbon atoms, wherein one or more non-adjacent CH ₂ groups by O and / or S atoms and / or can be replaced by -CO-, -O-CO-, -CO-O-, -O-CO-O-, -S-CO- and / or -CO-S- groups,

Z 1 and Z2 each independently of one another -CO-O-,

-0-CO-, -CH ₂ CH ₂ -, -CH ₂ 0-, -OCH--, -C≡C- or a single bond,

A ¹ , A ² 3 and A each independently of one another an a) 1,4-cyclohexylene radical, in which one or two are not adjacent

CH ₂ groups can be replaced by O atoms, b) 1,4-phenylene radical, in which one or more CH groups by

N can be replaced, c) radical from the group 1,4-cyclohexenylene, piperidine-1,4-diyl, bicyclo (2,2,2) octylene, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl , 1,2,3,4-tetrahydronaphthalene,

1,3-cyclobutylene and thiadiazole-2,5-diyl, where the radical b) can be ε-substituted once or twice by F, Cl, CN and / or -CH-, and

n is 0, 1, 2 or 3. The invention furthermore relates to such electro-optical liquid crystal systems which apply an alternating voltage to the electrodes in order to generate an electrical field.

In particular, the invention relates to an electro-optical system in which the liquid crystal mixture contains at least one component selected from the group comprising III and IV,

wherein

R each independently of one another is an alkyl group with 1-15 C atoms, in which one or two non-adjacent CH ₂ groups are also replaced by -O-, -CO-, -COO-, -OOC- and / or -CH = CH- can be, and

W or mean.

Systems which are switched between the transparent and opaque state by applying an alternating voltage are preferred. The dielectric anisotropy of the electro-optical PDLC systems according to the invention is positive and is preferably Δε> 3. In a preferred embodiment of the invention, the liquid crystal mixture can contain a pleochroic dye.

The invention further relates to corresponding liquid crystal mixtures and the use of these liquid crystal mixtures in electro-optical liquid crystal systems

The structure of the electro-optic liquid crystal systems according to the invention corresponds to the construction customary for such systems: the matrix in which the liquid crystal mixture is microdispersed or microencapsulated is arranged in a sandwich-like manner between the conductive electrodes, which are provided with corresponding supply lines. At least one of the electrodes is attached to a transparent substrate made of plastic, glass or a similar material, so that the system can be operated in transmissive or reflective mode. The term customary construction is broad here and encompasses all modifications and modifications.

Preferred embodiments of the electro-optical liquid crystal systems according to the invention are NCAP films, PDLC films and plastic films produced by modified processes. Processes for producing these films are e.g. in US 3,935,337, US 4,688,900, US 4,673,255, US 4,671,618 and US 4,435,047. But other forms of execution of the invention are included.

An essential difference between the electro-optic liquid crystal systems according to the invention and the hitherto customary ones is the liquid crystal mixture used. Liquid-crystalline media which have a viscosity η> 40 mm ² / s at 20 ° C. are used in the electro-optical liquid crystal systems according to the invention. Liquid crystal mixtures with a viscosity η> 50 mm ² / s at 20 ° C are particularly preferred, but very particularly those with η> 55 mm ² / s at 20 ° C. Such high viscosities are necessary in order to be able to switch these systems safely in flicker-free mode in AC operation.

Furthermore, the liquid crystalline media used in these systems show a relatively high optical anisotropy between 0.05 and 0.22. Since a very high optical anisotropy Δn on the one hand causes strong light scattering in the field-free state, but on the other hand also causes haze of the film in the switched state, a range between 0.05 and 0.20 is preferred for Δn . Δn is particularly preferably between 0.05 and 0.17, but the interval between 0.06 and 0.15 is very particularly favorable.

In addition, the liquid crystalline media used in these systems have a high clearing point of

T _c > 75 ° C. This is especially for architectural. "outdoor" applications important. Clear points T _c > 85 ° C. are particularly preferred.

The individual compounds of the formulas A-D or also other compounds which can be used in the electro-optical liquid crystal systems according to the invention are either known or they can be prepared analogously to known compounds.

Preferred liquid crystal solutions which can be used according to the invention contain a total of side chain polymers, in particular of formula I. They contain a total of preferred example 5-30, in particular 9-22 components. Liquid crystal mixtures which each contain at least one component of the formulas III and IV are particularly preferred. Those mixtures which contain at least one 4-alkyl- or 4-alkoxy-4 * -cyanobiphenyl are also preferred.

Above and below, R ¹ , R ² , A ¹ , A ² , A ³ , Z ¹ , Z ² , P, Sp, B and n have the meaning given, unless expressly stated otherwise.

In the mesogenic radicals of the formula II, R preferably denotes an alkyl or alkenyl radical which is unsubstituted or substituted by at least one halogen atom, in which one or two non-adjacent CH ₂ groups of these radicals are represented by O atoms and / or by -O-CO- , -CO-O and or -O-CO-O groups can be replaced.

Halogen is preferably F or Cl.

Furthermore, the mesogenic radicals of the formula II are preferred, in which R denotes CN or F.

If R is an alkyl radical or alkoxy radical, this can be straight-chain or branched. It is preferably straight-chain, has 2, 3, 4, 5, 6, 7 or 8 carbon atoms and accordingly preferably means ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy, Heptoxy or octoxy, and also methyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, nonoxy, decoxy, undexocy, dodecoxy, tridecoxy or tetradecoxy.

Oxaalkyl preferably means straight-chain 2-oxapropyl (= methoxymethyl), 2- (= ethoxymethyl) or 3-oxabutyl (= 2-methoxyethyl), 2-, 3- or 4-0xapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5 -, 6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

If R is an alkenyl radical, this can be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. Accordingly, it means especially vinyl, prop-1 or prop-2-enyl, but-1-, 2- or but-3-enyl, pent-1-, 2-, 3- or pent-4-enyl, hex- 1-, 2-, 3-, 4- or hex-5-enyl, hept-1-, 2-, 3-, 4-, 5- or hept-6-enyl, oct-1-, 2-, 3 -, 4-, 5-, 6- or oct-7-enyl, non-1-, 2-, 3-, 4-, 5-, 6-, 7- or non-8-enyl, dec-1- , 2-, 3-, 4-, 5-, 6-, 7-, 8- or Dec-9-enyl.

Branched groups of this type usually contain no 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-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, 2-decyl, 2-dodecyl, 6-methyloctoxy, 6-methyloctanoyloxy, 5-methylheptyloxycarbonyl, 2-methylbutyryloxy, 3 -Methylvaleryloxy, 4-methylhexanoyl-oxy, 2-chloropropionyloxy, 2-chloro-3-methylbutyryloxy,

2-chloro-4-methylvaleryloxy, 2-chloro-3-methylvaleryloxy, 2-methyl-3-oxapentyl, 2-methyl-3-oxahexyl.

Formula II includes both the racemates of these compounds and the pure enantiomers and mixtures thereof. In the mesogenic radicals of the formula II, the groups A 1, A2 and A3 each independently mean, preferably a 1,4-cyclohexylene radical, a 1,4-phenylene radical, a 2- or 3-fluoro-1,4-radical. phenylenreεt or a 2,3-difluoro-1,4-phenylene radical.

The groups Z 1 and Z2 are preferably -CO-O-,

-O-CO-, -CH ₂ CH ₂ - or a single bond. The mesogenic radicals of the formula II preferably have only one group Z 1 or Z 2, which is different from a single bond.

Among the mesogenic radicals of the formula II and all of its sub-formulas, preference is given to those in which at least one of the radicals contained therein has one of the preferred meanings indicated.

A smaller group of mesogenic residues of the formula II are the following mesogenic residues of the formulas III to 114:

1 2 2 3 R -A -Z -A - III

1 1 1 2 2 3 R -A -Z -A -Z -A - 112

1 1 1 1 1 2 2 3 R -A -Z -A -Z -A -Z -A - 113

_R 1- _A 1- ₂ 1_ _A 1- _Z 1- _A 1_ _Z 1_ _A 2_ _Z _ _A 3_ _{I I4}

Among them, those of the formula III are particularly preferred, in particular those in which A 2 and A3

1,4-phenylene and / or 1,4-cyclohexylene and Z means -COO-, -OCO-, CH ₂ -CH_- or a single bond.

Side chain polymers of the formula I are particularly preferred in which, in the mesogenic radical of the formulas II,

II 1, II 2, II 3 and II 4 means at least one of the groups A 1, A and A3 is a 1,4-cyclohexylene group. In principle, all polymers whose chains have a certain flexibility can be used as the polymer backbone - (-P-). These can be linear, branched or cyclic polymer chains. The degree of polymerization is normally at least 10, preferably 20-300. However, oligomers with 3 to 15, in particular with 4 to 7, monomer units are also suitable.

Polymers with C-C main chains, in particular polyacrylates, methacrylates, α-halogen acrylates, α-cyanoacrylates, acrylamides, acrylonitriles or methylene malonates, are preferably used. Polymers with heteroatoms in the main chain, for example polyethers, esters, amides, imides or urethanes or in particular polysiloxanes, are also preferred.

In the case of the polymers of the formula I according to the invention, alkylene groups with 2 to 20 C atoms, which are linear or branched and in which one or more CH ₂ groups are -O-, -S- and / or -NR, are particularly suitable as spacers - can be replaced.

For example, the following can be considered as spacers:

Ethylene, propylene, butylene, pentylene, hexylene, octylene, decylene, undecylene, dodecylene, octadecylene, ethyleneoxyethylene, methyleneoxybutylene, ethylene thioethylene, ethylene-N-methyliminoethylene or 1-methylalkylene.

Also preferred are those liquid crystal systems in which the side chain polymers of the formula I are copolymers with different “rod-like” residues of the formula II, in particular those copolymers in which the one comonomer is a “rod-like” residue of the formula Ila in which RF or CN is (Co a), and the other comonomer is a radical of the formula IIb which has a radical R ¹ other than F or CN (Co).

The ratio of the comonomers to one another is not critical, preferably between 10 parts and 1 part of comonomer (Co b) with 1 part of comonomer (Co a) are copolymerized with one another.

The side chain polymers to be used according to the invention are known or can be prepared by methods known per se (e.g. DE 27 22 589, DE 38 17 088).

The liquid crystal mixtures which can be used according to the invention are prepared in a manner which is conventional per se. As a rule, the desired amount of the components used in a smaller amount is dissolved in the components which make up the main constituent, expediently at elevated temperature. It is also possible to use solutions of the components in an organic solvent, e.g. in acetone, chloroform or methanol, and to remove the solvent after mixing, for example by distillation.

The dielectrics can also contain further additives known to the person skilled in the art and described in the literature. Electro-optical liquid crystal systems in which pleochroic dyes are added to the liquid crystal mixture in a weight percent range of 0-15% are preferred. The following examples are intended to illustrate the invention without restricting it.

It means:

Glassy state, crystalline solid state, smectic phase (the index characterizes the phase type),

N: nematic phase,

Ch: cholesteric phase,

I: Isotropic phase. Viscosity in mm ² / s at 20 ° C

3,4-PCH-MA poly- [4- (4- (trans-4-propylcyclohexyl) phenyloxy) butyl methacrylate 3,6-PCH-MA poly- [6- (4- (trans-4-propylcyclohexyl ) - phenyloxy) hexyl] methacrylate 5, 4-PCH-MA poly- [4- (4- (trans-4-pentylcyclohexyl) - phenyloxy) butyl] methacrylate 3, 1, 4-CCH-MA poly- [4- (trans, trans-4'-propylbicyclo-hexyl-4-ylmethyl) butyl] methacrylate

(3, 4-PCH / N-4K) -MA poly- [4- (4- (trans-4-propylcyclohexyl) phenyloxy) butyl] -CO- [4- (4'-cyanobiphenyl-4- yl) butyl] methacrylate

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

The percentages given are percentages by weight, example 1

A mixture (A) consisting of

18% p- (trans-4-propylcyclohexyl) benzonitrile

14% p- (trans-4-butylcyclohexyl) benzonitrile 25% p- (trans-4-pentylcyclohexyl) benzonitrile

15% p- (trans-4-heptylcyclohexyl) benzonitrile

7% 4-cyano-4 '- (trans-4-pentylcyclohexyl) biphenyl 6% 4-cyano-4' 'pentyl-p-terphenyl

8% p- (trans-4-propylcyclohexyl) phenyl- (trans-4-butylcyclohexane) carboxylic acid ester

and a mixture (B) consisting of

5% p- (trans-4-ethylcyclohexyl) benzonitrile 15% p- (trans-4-propylcyclohexyl) benzonitrile 11% p- (trans-4-butylcyclohexyl) benzonitrile 21% p- (trans-4-pentylcyclohexyl) -benzonitrile

11% p- (trans-4-heptylcyclohexyl) benzonitrile

5% trans-l-p-ethylphenyl-4-propylcyclohexane

12% 4-ethyl-4 '- (trans-4-propylcyclohexyl) biphenyl 10% 4-ethyl-4' - (trans-4-pentylcyclohexyl) biphenyl 4% 4- (trans-4-propylcyclohexyl) -4 ' - (trans-4-propylcyclohexyl) biphenyl

6% 4- (trans-4-pentylcyclohexyl) -4 '- (trans-4-propylcyclohexyl) biphenyl

are mixed with different amounts of a side chain polymer. As can be seen from Table I, the viscosity is greatly increased, while the other physical parameters hardly change. Table I

Example mixture side chain Δn viscosity clearing point (%) polymer (20 ° C) (° C) Δε 3,4-PCH-MA (%) mm / sec ² la 100 (A) 0 0, 1426 30 92 + 11, lb 99.5 (A) 0.5 0.1442 34 85 + 11, lc 99.0 (A) 1.0 0, 1439 40 85 + 11, ld 98.0 (A) 2.0 0.1436 73 84 + 11, le 95.0 (A) 5.0 0.1417 320 83 + 11, lf 90.0 (A) 10.0 0.1388 - 81 + 11, lg 100 (B) 0 0.1322 21 85 + 10, lh 99.5 (B) 0.5 0.133 31 78.5 + 9, li 99.0 (B) 1.0 0.133 40 78.6 + 9, ij 98.0 (B) 2.0 0.132 67 73.4 + 9, lk 95.0 (B) 5.0 0.131 186 73.0 + 9,

11 90.0 (B) 10.0 0.128 944 74.4 + 8.

Example 2

A mixture (C) consisting of

12% p- (trans-4-propylcyclohexyl) benzonitrile

18% p- (trans-4-pentylcyclohexyl) benzonitrile

12% p- (trans-4-heptylcyclohexyl) benzonitrile

11% trans, trans-4'-propyl-4-cyanobicyclohexyl

13% trans, trans-4'-butyl-4-cyanobicyclohexyl

10% trans, trans-4 * pentyl-4-cyanobicyclohexyl

6% trans, trans-4'-heptyl-4-cyanobicyclohexyl

6% trans, trans-4'-propylbicyclohexyl-4-carboxylic acid (p- (trans-4-propylcyclohexyl) phenyl) ester

6% trans, trans-4'-propylbicyclohexyl-4-carboxylic acid (p- (trans-4-butylcyclohexyl) phenyl) ester

6% trans, trans-4 * propylbicyclohexyl-4-carboxylic acid (p- (trans-4-pentylcyclohexyl) phenyl) ester 5% of different side chain polymers are added. As can be seen from Table II, the viscosity is greatly increased, while the other physical parameters hardly change.

Table II

Example of side chain plastic viscosity at clearing point Δε (10 ° C) (° C) mm / sec ²

2a - 42 0.0937 96 7,

2b 3,6-PCH-MA 529 0.0930 82.1 7.

2c 3,4-PCH-MA 257 0.0932 82.0 7.

2d (3,4-PCH / N-4K- •) MA * 374 0.0939 82.9 7.

The ratio of the two comonomers [4- (4- (trans-4-propylcyclohexyl) phenyloxy) butyl] methacrylate (3,4-PCH-MA) and [4- (4'-cyanobiphenyl- 4-yl) butyl] methacrylate (N-4K-MA) at 4 to 1.

Example 3

A TN cell with a layer thickness of 7.41 μm, filled with a mixture A (example 1), has the following threshold voltages at 20 ° C. and 60 Hz.

V _5Q 2.11 VV _go 2.65 V. The mixtures doped with 2.0% of the side chain polymer 3,4-PCH-MA according to Example 1d lead to the following threshold voltages:

V _1Q 1.83 VV ₅₀ 2.13 VV _9Q 2.59 V.

Thus, the doping hardly affects the threshold voltage.

Example 4

An electro-optic liquid crystal system according to

Example Id (98% mixture A, 2% side chain polymer 3,4-PCH-MA), produced by the process described in EP-0 272 582, is arranged in a matrix-like manner between conductive electrodes and can be switched to flicker-free by applying an AC voltage become.

The electro-optical liquid crystal systems according to the invention are characterized in that during the manufacture of the system there is no or only a slight interaction of the components of the liquid crystal mixture with the polymeric carrier material via polar groups.

The electro-optical liquid crystal systems according to the invention can be switched by applying a direct or alternating voltage. However, an alternating voltage is preferably used which has an alternating voltage amplitude between 1 and 240 volts and an alternating voltage frequency between 10 Hz and 10 kHz. Amplitudes between 2 and 220 volts and frequencies between 20 and 120 Hz are particularly preferred. The amplitude of the alternating voltage is very particularly preferably between 2 and 130 V. The dielectric anisotropy of the liquid crystal mixture used is preferably positive Δε> 0 and in particular Δε> 3. Very high response voltages are observed for smaller values of the dielectric anisotropy Δε. Values Δε> 5 are particularly preferred.

Claims

1. Elektrooptis hes liquid crystal system, containing nematic microdroplets, which are embedded in a transparent matrix and which consist of a liquid crystal mixture, characterized in that the liquid crystal mixture to increase the flow viscosity to values> 40 mm ² / s at 20 ° C. one or several side chain polymers containing monomer units of the formula I,

- (-. p -) - I

I Sp-B

wherein

P is a polymer main chain unit,

Sp An alkylene group with 1-20 C atoms, in which one or more non-adjacent CH «groups can also be replaced by -O-, -S- and / or -NR 2-, and

B means an organic "rod-like" residue,

contains. 2. Electro-optical liquid crystal system according to claim 1, characterized in that B represents a radical of the formula II,

1 1 1 7 7 ~ R - (A -Z ^x ) _n -A -Z -A - II

wherein

RF, CN or an alkyl or alkenyl radical which is unsubstituted or substituted by CN or by at least one halogen atom, each having 1-15 C atoms, in which one or more non-adjacent CH ₂ groups are formed by

O and / or S atoms and / or by -CO-, -O-CO-, -CO-O-, -O-CO-O-, -S-CO and / or -CO-S groups can be replaced

Z and _ "each independently of one another -CO-O-, -O-CO-, -CH ₂ CH ₂ -, -OE O-, -OCH ₂ -, -C≡C- or a single bond,

A ¹ , A ² 3 and A each independently a) 1,4-cyclohexylene radical, in which one or two are not adjacent

CH ₂ groups can be replaced by O atoms, b) 1,4-phenylene radical, in which one or more CH groups can be replaced by N, c) radical from the group 1,4-cyclohexenylene, piperidine-1, diyl, bicyclo (2,2,2) octylene, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene, 1,3-cyclobutylene and thiadiazole-2,5- diyl, where the radical b) can be mono- or disubstituted by F, Cl, CN and / or -CH_, and

n is 0, 1, 2 or 3.

3. Electro-optical liquid crystal system, according to one of claims 1 or 2, characterized in that the side chain polymer contains monomer units with various "rod-like" residues of the formula II ent.

4. Electro-optical liquid crystal system according to claim 3, characterized in that the side chain polymer has at least one “rod-like” radical of the formula II,

wherein

R ¹ F or CN

means

and at least one "rod-like" residue of Formula II,

wherein

R is an alkyl or alkenyl radical which is unsubstituted or substituted by CN or at least one halogen atom, each having 1-15 C atoms, in which one or more CH ₂ groups are represented by O or S atoms or by -O-CO- or - CO-O- can be replaced means

contains. Electro-optical liquid crystal system according to one of Claims 1 to 4, characterized in that an alternating voltage is applied to the electrodes in order to generate an electrical field.

Electro-optical system according to at least one of Claims 1 to 5, characterized in that the liquid crystal mixture contains at least one component selected from the group comprising III and IV,

wherein

R each independently of one another is an alkyl group with 1-15 C atoms, in which one or two non-adjacent CH ₂ groups are also represented by -O-, -CO-,

-COO-, -OOC- and / or -CH = CH- can be replaced, and

W - H \ - or - O \ - mean.

7. Electro-optical liquid crystal system according to at least one of claims 1 to 6, characterized in that the liquid crystal mixture has a dielectric anisotropy Δε> 3. 8. Electro-optical liquid crystal system according to at least one of claims 1 to 7, characterized gekenn¬ characterized in that the liquid crystal mixture contains a pleochroic dye.

9. Liquid crystal mixture according to at least one of claims 1 to 4 and 6 to 8.

10. Use of a liquid crystal mixture according to at least one of claims 1 to 4 and 6 to 6 in an electro-optical liquid crystal system.