DE4011530A1 - Two-layer liq. crystal cell - has compensating layer contg. liq. crystal linked 1,4-phenylene and trans-1,4-cyclohexylene rings - Google Patents

Abstract

A liq. crystal (LC) cell contains 2 twisted nematic LC layers (A) and (B), in which at least one layer (A) is triggered, and in which the optical path differences in the 2 layers are essentially balanced. The LC used in the opt. un-triggered layer (B) is based on a dielectrically neutral component of formula: R-Phe-V-R (IA), R-Cyc-Phe-W-R (IB) or R-Phe-CC-Phe-Z3-(A)m-R (IC), and a dielectrically positive component of formula: R-X-Phe-CN (IIA), R-X-Cyc-CN (IIB) or R-X-Phe-COO-Phe-CN (IIC). Phe = 1,4-phenylene; Cyc = trans-1,4-cyclohexylene; R = 1-15C alkyl, oot. with 1 or 2 non-adjacent CH2 gps. replaced by O, CO, CH=CH and/or C(Hal)2; V = Z1-(A)n- (with Z1 = OCO or single bond); A = Phe or Cyc; W = Z1-Phe-Phe-, -Z1-Phe-Cyc-, -Z2-Cyc-Cyc- or -Z1-Phe-C2H4-Cyc- (with Z2 = CH2CH2, COO, OCO or single bond); X = -(A)-Z2-, -(2,5-pyridyl)-Z2- or -(2,5-(1,3-dioxolanyl))-Z3-(with Z3 = CH2CH2 or single bond); n = 1 or 2; m = 0 or 1. USE/ADVANTAGE - The LC components are useful in LC cells. The LC mixts. used for the compensating layer (B) have good values for dispersion, temp.-dependence of dispersion and birefringence (which can be optimised for partic. applications), together with high thermal and UV stability; the use of such LC layers (B) enables economical optimisation of the optical path difference ratio, and gives LC cells with optimum electro-optical properties. (13pp Dwg.No.0/0)

Description

The invention relates to liquid crystal cells according to the Preamble of claim 1 and for use therein Suitable liquid crystal mixtures for liquid crystal cells.

With TN liquid crystal cells (Twisted Nematic), which in so-called Maugin area are operated where the product from the layer thickness d and the birefringence Δn d · Δn »λ is large compared to the wavelength of light, follows the polarization vector of the incident light in visible spectral range essentially independent of λ the twisted structure of the undeformed cell, so that no interference colors occur in the off state. The cells operated under this condition show however, extremely unsatisfactory electro-optical properties and especially a strong viewing angle dependency of the contrast. DE 30 22 818 states that at values of the product d · Δn between 0.15 µm and 0.60 µm steeper characteristic curves and in particular an essential one Extended viewing angle range reached will. It is disadvantageous, however, that in particular with very smaller values of d · Δn one of the wavelength λ dependent transmission can occur, as is the case in C.H. Gooch, H.A. Tarry, Electronic Letters, 10 (1974), P. 2 is described.

It was proposed for the first time in US 44 43 065 that the TN Cell to compensate for the optical path difference d · Δn and thus to avoid interference colors to combine with another liquid crystal cell.  

A well-known physical principle is used, which, for. B. is also implemented in the Babinet-Soleil compensator and is based on the combination of 2 optically uniaxial media, which have essentially the same optical path difference d · Δn, but with the optical axes of both media being perpendicular to each other. Linearly polarized light, whose direction of polarization does not point in the direction of the optical axis, is split into an ordinary and an extraordinary beam in the 1st medium. Since the optical axes of both media are perpendicular to each other, the ordinary beam of the 1st medium runs in the 2nd medium as an extraordinary beam and vice versa. The optical path difference in the first medium is d · (n _e -n _o ), in the second medium d · (n _o -n _e ), so that the total path difference is zero and the system consisting of the two optically uniaxial media is none Has birefringence.

This principle known as delay compensation can can also be used in particular with STN displays, such as this z. In K. Katoh et al., Jap. J. Appl. Phys. 26 (1987) L 1784, SID Digest Vol. 20, 1989, papers 22.3, 22.4, 22.5. and 22.6. and EP 03 19 351 is described.

In the embodiments described in the literature compensated twisted cells is that in the compensation cell used little liquid crystal so far Attention has been paid. So z. B. in US 44 43 065 the use of the liquid crystal mixture ZLI-1646 (commercial product from E. Merck, Darmstadt) suggested. This mixture mainly consists of Carbonitrile compounds, but generally by an unsatisfactory and at least not all requirements sufficient UV stability are marked. Farther contain the compensation layer and the  Information display used liquid crystal layer same in the cell proposed in US 44 43 065 Liquid crystal. This has the disadvantage of being an improvement of the electro-optical properties required Optimization of the ratio of the optical path differences of the two liquid crystal layers by one Varying the cell thickness must be done, which is at least in the large-scale production because of the then to be observed Layer thickness tolerances is problematic. In the cell described by way of example in EP 03 19 351 the two layers are made with different liquid crystal mixtures filled. The one for the compensation layer used liquid crystal mixture ZLI-3021-000 (Commercial product from E. Merck, Darmstadt) however also on carbonitrile compounds. Farther is this liquid crystal mixture by a relatively low optical anisotropy Δn characterized so that the Compensation layer, if necessary, a high layer thickness has, which leads to a reduction in the transmitted Light intensity leads. In that described in EP 03 19 351 For example, the compensation layer has a thickness from 15 µm.

So far in the compensation layer of liquid crystal cells used according to the preamble of claim 1 Liquid crystal mixtures meet the requirements after a very high UV and temperature stability, one with regard to the thickness and the path difference of the compensation layer optimizable optical anisotropy, a favorable dispersion dΔn / dλ and an advantageous one Temperature dependence of birefringence and dispersion insufficient.

There is therefore still a great need for liquid crystal cells according to the preamble of claim 1, whose compensation layers meet the corresponding requirements do better justice.

The invention was based on the object, liquid crystal cells to provide the disadvantages listed conventional cells not or only to a small extent exhibit.

Surprisingly, it was only found that this task can be solved if you go for the compensation layer of liquid crystal cells according to the preamble of Claim 1 uses liquid crystal mixtures based on dielectric neutral compounds selected from the I, II and III comprehensive groups

and also a dielectric positive component, selected from the compounds of the formulas IV-VI can

wherein

R is an alkyl group with 1-15 C atoms, in which also one or 2 non-adjacent CH₂ groups through -O-, -CO-, -HC = CH-, CHHal and / or CHal₂ replaced could be,

Z¹ -OCO- or a single bond,

n 1 or 2
m 0 or 1

Z² -CH₂CH₂-, -COO-, -OCO- or a single bond, and
Z³ -CH₂CH₂- or a single bond

mean.

The invention thus relates to a liquid crystal cell which contains 2 twisted nematic liquid crystal layers A and B, of which at least one layer A is driven, whose optical path differences (Δn · d) _A and (Δn · d) _B essentially compensate, whereby the liquid crystal is based on dielectric neutral compounds of the formulas I, II and / or III and can additionally contain one or more dielectric positive compounds of the formulas IV, V and / or VI. The invention further relates to the liquid crystals used in the liquid crystal cells according to the invention and their use for the compensation layer of twisted liquid crystal cells.

The structure of the liquid crystal cells according to the invention is based on the usual for such systems Construction. The term conventional construction is broad here summarizes and embraces all modifications and modifications.

The liquid crystal cell consists of 2 arranged one above the other Liquid crystal layers A and B, the Liquid crystals of both layers between plane-parallel, transparent substrates are arranged, the inner sides in the case of controllable liquid crystal layers with electrode layers and overlying orientation layers are provided, while in the case of non-controllable Liquid crystal layers are the electrode layers i. a. are omitted. Preferably, the Increase the transmission of two liquid crystal layers common middle substrate used the two sides of which are then covered with corresponding electrode and / or orientation layers are provided. It can however, 2 separate medium substrates are also used will. Typically, the Cell a polarizing filter. The cell can be transmissive or operated reflectively or transflectively; with reflective or transflective systems is behind the reflector facing away from the polarizer or a reflector and an additional lighting device  appropriate. The liquid crystal in the in each Case controllable and serving to present information Liquid crystal layer A has a twisted one Structure, the twist angle between 0 ° and 360 °, but preferably between 80 ° and 100 ° or is between 180 ° and 360 °. Twist angle ϕ ≦ 90 ° are usually by appropriate alignment of the orientation layers reached while for induction Larger twist angle chiral dopants added will. Also the liquid crystal if necessary controllable compensation layer B lies in a twisted Structure before, with the twist angle in the two liquid crystal layers A and B in opposite directions are. The absolute amounts of the twist angles are preferably chosen essentially the same size; Indeed larger deviations are also possible. The angle between the directions of orientation of the liquid crystal molecules on both sides of the layers A and B common middle substrate or on the under substrate the upper liquid crystal layer and the upper one The substrate of the lower liquid crystal layer is between 30 ° and 150 °, but preferably between 50 ° and 130 ° and in particular essentially 90 °.

An essential difference between the liquid crystal cells according to the invention to the usual ones, however in the liquid crystal used for the compensation layer B, the at least one dielectric neutral Compound of formulas I, II and / or III and optionally a dielectric positive component is selected from the compounds of the formulas IV, V and / or VI.

The dielectrically neutral compounds of the formulas I, II and III comprise 2- and 3-ring compounds of the formulas I1-I12, 4-ring compounds of the formulas II1-II10 and dielectrically neutral tolanes of the formulas III1-III5.

Compounds of the formulas I1-I8, I10 and are preferred I11, II1-II3, II6-II9 and III1-III3, but especially the compounds of the formulas I1-I6, II1-II3, II7-II9 and III1-III3. Draw the compounds of formulas I-III is characterized by high UV and temperature stability. The person skilled in the art can easily do inventive steps a selection of the compounds of the formulas I-III so that the liquid crystal mixture used in layer B with regard to the respective application is optimized. Should z. B. liquid crystals with very high Stability and relatively high or high birefringence Δn are provided for the dielectric neutral Component in particular compounds of the formulas I1, I6, I7, I8, I10, II1, II4, III1, III2 and III3 are used. Clarifying liquid crystals with very high stability However, compounds of the formulas I4, I5 and / or II1-II10 included.

The liquid crystal may optionally be a contain dielectric positive component that from the compounds of the formulas IV-VI is selected. Here is the following smaller group of connections particularly preferred:

Compounds of the formulas IV-VI can be found in layer B liquid crystal used to be added, for. B. the birefringence Δn, the dispersion dΔn / dλ and / or the  Temperature dependence of Δn and / or the dispersion optimize. Furthermore, one or more is added Compounds of formula IV, V and / or VI i. a. required, when the liquid crystal layer B is driven becomes. However, since carbonitrile compounds are usually one UV and temperature stability does not meet all requirements have, are liquid crystal mixtures preferred, the less than 30%, but especially less have than 20% of compounds of the formulas IV-VI. Compounds which have a particular preference are very particularly preferred Share of carbonitrile compounds of less than 10% exhibit.

The liquid crystal used in layer B is i. a. a doping component containing at least one chiral dopant added. The one in the Layer B set twist angle ϕ is in particular the amounts are essentially the same, but of opposite direction of rotation as the twist angle in the Layer A.

The compounds of the formulas I-VI are known per se Methods presented as in the literature (e.g. in the standard works such as Houben-Weyl, methods of organic chemistry, Georg-Thieme-Verlag, Stuttgart, Vol. IX, p. 867 ff.) Are described under Reaction conditions for the reactions mentioned are known and suitable. You can also start from well-known variants not mentioned here Make use.

The person skilled in the art can also readily use suitable dopants take from the literature. Such substances are z. B. in H. Kelker, R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980.  

The liquid crystal layer B can be controlled electrically or not be controllable. However, preferably also operated controllable cells according to the invention, that the liquid crystal layer B is not driven. Cells whose liquid crystal layer B has no electrode layers have and are therefore not controllable, are particularly preferred.

The liquid crystal layers A and B are in the invention Cells arranged one above the other. The chronological order the two layers are preferably so chosen that the layer B z. B. with reflective operated Displays on the light incidence side or for displays, which are operated with an additional light source, is arranged in front of this light source. This has the advantage that through a particularly high UV and temperature stability marked layer B the maximum Exposed to light intensity while layer A, which is controlled and therefore dielectric positive connection of possibly less high stability contains, weakened by the absorption in layer B. Light intensity sees. Are particularly preferred Cells in which the liquid crystal layer B used Crystal blend components with high UV absorption coefficient are clogged. The additional components are preferably selected so that their Dispersion of the absorption coefficient in the UV range to that used in liquid crystal layer A. Liquid crystal mixture approximately or even largely is adjusted. Because it is crucial in these arrangements the stability of the liquid crystal layer B is important, have the liquid crystals used for layer B. especially no carbonitrile compounds.  

The liquid crystal used in layer B can Optimization of birefringence in particular, the clearing point, of the mesogenic range, the dispersion and the temperature dependence of dispersion and birefringence further components, preferably with a percentage by mass ≦ 25% and in particular ≦ 20%, contain the are preferably selected from nematic or nematogenic (monotropic or isotropic) substances, in particular Substances from the classes of azoxybenzenes, benzylidene anilines, Biphenyls, terphenyls, phenyl- or cyclohexylbenzoates, Cyclohexane carboxylic acid phenyl or cyclohexyl esters, phenyl or cyclohexyl esters of cyclohexylbenzoic acid, Phenyl or cyclohexyl ester of cyclohexylcyclohexane carboxylic acid, Cyclohexylphenyl ester of benzoic acid, cyclohexane carboxylic acid or cyclohexylcyclohexane carboxylic acid, Phenylcyclohexanes, cyclohexylbiphenyls, Phenylcyclohexylcyclohexane, cyclohexylcyclohexane, Cyclohexylcyclohexenes, cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes, 4,4'-bis-cyclohexylbiphenyls, Phenyl or cyclohexyl pyrimidines, phenyl or cyclohexylpyridines, phenyl- or cyclohexyldioxanes, Phenyl- or cyclohexyl-1,3-dithiane, 1,2-diphenylethane, 1,2-dicyclohexylethane, 1-phenyl-2-cyclohexylethane, 1-cyclohexyl-2- (4-phenyl-cyclohexyl) ethane, 1-cyclohexyl- 2-biphenylethane, 1-phenyl-2-cyclohexylphenylethane, optionally halogenated stilbenes, benzylphenyl ether, Tolanes and substituted cinnamic acids. The 1,4-phenylene groups in these compounds can also be fluorinated.

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

R′-L-E-R ′ ′ (1)

R′-L-COO-E-R ′ ′ (2)

R′-L-OOC-E-R ′ ′ (3)

R′-L-CH₂CH₂-E-R ′ ′ (4)

R′-L-C≡C-E-R ′ ′ (5)

In formulas 1, 2, 3, 4 and 5, L and E represent the can be the same or different, each independently one bivalent residue from the other from -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe- and -G-Cyc- and their mirror images formed Group, where Phe 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- mean diyl or 1,3-dioxane-2,5-diyl.

Preferably one of the residues L and E is Cyc, Phe or Pyr. E is preferably Cyc, Phe or Phe-Cyc. 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 the formulas 1, 2, 3, 4 and 5, in which one of the residues L and E is selected from the group Cyc, Phe and Pyr and the other residue is selected from 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 residues L and E are selected from the Group -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-.  

R 'and R' 'in the compounds of the sub-formulas 1a, 2a, 3a, 4a and 5a each independently Alkyl, alkenyl, alkoxy, alkenyloxy or alkanoyloxy with up to 8 carbon atoms. Most of these connections R 'and R' 'are different from each other, whereby one of these residues is mostly alkyl or alkenyl. In the Connections of sub-formulas 1b, 2b, 3b, 4b and 5b means R '' - CN, -CF₃, F, Cl or -NCS; R has the specified for the compounds of the sub-formulas 1a to 5a Meaning and is preferably alkyl or alkenyl. But other variants of the proposed substituents in the compounds of formulas 1, 2, 3, 4 and 5 in use. Many such substances or mixtures of which are commercially available. All of these substances are by methods known from the literature or by analogy available for this.

The in the electro-optical liquid crystal according to the invention Systems used contain 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 according to the invention Systems used contain liquid crystals preferably more than 60%, in particular more than 75% and especially more than 85% of compounds of the Formula I, II and / or III. The liquid crystals contain preferably 2-35, but especially 3-20 compounds of the formulas I, II and / or III.  

The proportion of compounds of the formulas IV, V and / or VI is preferably not too high. Liquid crystals are preferred, where the proportion of compounds of the formulas IV, V and / or VI is less than 15%, in particular however, is between 0 and 5% and is particularly 0.

Liquid crystals are particularly preferred in layer B. used that

• (i) at least 40% of compounds of the formulas I2 and / or I3 and
• (ii) at least 15% of compounds of formula VII wherein
  r and s are each independently 0, 1 or 2 and
  r + s 1 or 2
  mean and and R have the meaning given above,

contain; those skilled in the art can use these liquid crystal mixtures without further inventive step in particular Liquid crystal compounds to optimize the optical Add anisotropy.  

Liquid crystals are further particularly preferred in layer B. used that

• (i) at least 35% of compounds of the formulas I1, I2, I3, I4, I5, I6 and / or III1 and
• (ii) at least 3%, but in particular 5% -25%, of compounds of the formula II7

contain.

Liquid crystals are very particularly preferred in layer B. used on the following Base mixes 1-9 are based; the specified Percentages indicate the mass percentage range, in which the respective compounds in the liquid crystal are available. The sum of the mass percentages in the base mixtures contained compounds, is preferred greater than 25% and is in particular between 30% and 100% and especially between 40% and 100%.

The additives described can be used in layer B. Liquid crystal with regard to each Application modified and optimized. Crucial but is that liquid crystals containing one or several compounds of formula I, II and / or III and optionally one or more connections of the formulas IV, V and / or VI, for use in the Layer B of liquid crystal cells according to the invention in particular are suitable. However, are particularly suitable the liquid crystal mixtures 1-9, the compounds of Formulas I, II and / or III in defined mass percentage ranges contain.

The liquid crystal mixtures used in layer B. are characterized by favorable values for the dispersion, the temperature dependence of the dispersion and birefringence, further through one with regard to the birefringence that can be optimized for each application and especially due to high UV and temperature stability on. The liquid crystal cells according to the invention is therefore of considerable economic importance.

The following examples are intended to illustrate the invention, without limiting it. The percentages given are Mass percent.

It means:

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

Example 1

A liquid crystal containing

20% trans-4-propylcyclohexyl-1-ethylbenzene
10% trans-4-propylcyclohexyl-1-methoxybenzene
6% 4-methoxyphenyl trans-4-propylcyclohexyl carboxylate
6% 4-ethoxyphenyl trans-4-propylcyclohexyl carboxylate
6% 4-ethoxyphenyl trans-4-butylcyclohexyl carboxylate
6% 4-methoxyphenyl trans-4-pentylcyclohexyl carboxylate
6% 4-methoxyphenyl trans-4-butylcyclohexyl carboxylate
6% 4-ethoxyphenyl trans-4-pentylcyclohexyl carboxylate
4% 4- (trans-4-propylcyclohexyl) -4'-ethylbiphenyl
4% 4- (trans-4-pentylcyclohexyl) -4'-ethylbiphenyl
4% 4- (trans-4-propylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl
4% 4- (trans-4-pentylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl
6% 4- (trans-4-propylcyclohexyl) phenyl-trans-4- (trans-4-propylcyclohexyl) cyclohexyl carboxylate
6% 4- (trans-4-pentylcyclohexyl) phenyl-trans-4- (trans-4-propylcyclohexyl) cyclohexyl carboxylate
6% 4- (trans-4-butylcyclohexyl) phenyl-trans-4- (trans-4-propylcyclohexyl) cyclohexyl carboxylate

has a high UV and temperature stability and a favorable dispersion and is in the liquid crystal layer B one consisting of 2 liquid crystal layers Cell used.  

Example 2

A liquid crystal containing

20% trans-4-propylcyclohexyl-1-ethylbenzene
10% trans-4-propylcyclohexyl-1-methoxybenzene
4% 4-methoxyphenyl trans-4-propylcyclohexyl carboxylate
4% 4-ethoxyphenyl trans-4-propylcyclohexyl carboxylate
4% 4-methoxyphenyl trans-4-butylcyclohexyl carboxylate
4% 4-methoxyphenyl trans-4-pentylcyclohexyl carboxylate
14% 4- (trans-4-propylcyclohexyl) -4'-ethylbiphenyl
12% 4- (trans-4-pentylcyclohexyl) -4'-ethylbiphenyl
5% 4- (trans-4-propylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl
5% 4- (trans-4-pentylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl
6% 4-propylphenyl-trans-4- (trans-4-propylcyclohexyl) carboxylate
6% 4-pentylphenyl-trans-4- (trans-4-propylcyclohexyl) carboxylate
6% 4-propylphenyl-trans-4- (trans-4-butylcyclohexyl) carboxylate

has a high UV and temperature stability and a favorable dispersion and is in the liquid crystal layer B one consisting of 2 liquid crystal layers Cell used.  

Example 3

A liquid crystal containing:

20% trans-4-propylcyclohexyl-1-ethylbenzene
10% trans-4-propylcyclohexyl-1-methoxybenzene
4% 4-methoxyphenyl trans-4-propylcyclohexyl carboxylate
4% 4-ethoxyphenyl trans-4-propylcyclohexyl carboxylate
4% 4-methoxyphenyl trans-4-butylcyclohexyl carboxylate
3% 4-ethoxyphenyl trans-4-butylcyclohexyl carboxylate
4% 4-methoxyphenyl trans-4-pentylcyclohexyl carboxylate
14% 4- (trans-4-propylcyclohexyl) -4'-ethylbiphenyl
12% 4- (trans-4-pentylcyclohexyl) -4'-ethylbiphenyl
5% 4- (trans-4-propylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl
5% 4- (trans-4-pentylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl
5% 4- (trans-4-propylcyclohexyl) phenyl-trans-4- (trans-4-propylcyclohexyl) cyclohexyl carboxylate
5% 4- (trans-4-pentylcyclohexyl) phenyl-trans-4- (trans-4-propylcyclohexyl) cyclohexyl carboxylate
5% 4- (trans-4-butylcyclohexyl) phenyl-trans-4- (trans-4-propylcyclohexyl) cyclohexyl carboxylate

has a high UV and temperature stability and a favorable dispersion and is in the liquid crystal layer B a 2 liquid crystal layers Cell used.  

Example 4

A liquid crystal containing:

20% trans-4-propylcyclohexyl-1-ethylbenzene
15% trans-4-propylcyclohexyl-1-methoxybenzene
4% 4-ethoxyphenyl trans-4-propylcyclohexyl carboxylate
4% 4-methoxyphenyl trans-4-butylcyclohexyl carboxylate
4% 4-ethoxyphenyl trans-4-butylcyclohexyl carboxylate
4% 4-methoxyphenyl trans-4-pentylcyclohexyl carboxylate
17% 4- (trans-4-propylcyclohexyl) -4'-ethylbiphenyl
14% 4- (trans-4-pentylcyclohexyl) -4'-ethylbiphenyl
4% 4- (trans-4-propylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl
4% 4- (trans-4-pentylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl
5% 4- (trans-4-propylcyclohexyl) phenyl-trans-4- (trans-4-propylcyclohexyl) cyclohexyl carboxylate
5% 4- (trans-4-propylcyclohexyl) -4'-methoxytolane
5% 4- (trans-4-propylcyclohexyl) -4'-ethoxytolane

has a high UV and temperature stability and a favorable dispersion and is in the liquid crystal layer B a 2 liquid crystal layers Cell used.  

Example 5

A liquid crystal containing:

24% trans-4-propylcyclohexyl-1-ethylbenzene
15% p-trans-4-propylcyclohexyl benzonitrile
6% 4-ethyl-4'-cyanobiphenyl
4% 4-propyl-4'-cyanobiphenyl
17% 4- (trans-4-propylcyclohexyl) -4'-ethylbiphenyl
14% 4- (trans-4-pentylcyclohexyl) -4'-ethylbiphenyl
5% 4- (trans-4-propylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl
5% 4- (trans-4-pentylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl
5% 4-propylphenyl-trans-4- (trans-4-propylcyclohexyl) cyclohexyl carboxylate
5% 4-pentylphenyl-trans-4- (trans-4-propylcyclohexyl) cyclohexyl carboxylate

has a high UV and temperature stability and a favorable dispersion and is in the liquid crystal layer B a 2 liquid crystal layers Cell used.  

Example 6

A liquid crystal containing

24% trans-4-propylcyclohexyl-1-ethylbenzene
17% p-trans-4-propylcyclohexyl benzonitrile
6% 4-ethyl-4'-cyanobiphenyl
4% 4-propyl-4'-cyanobiphenyl
17% 4- (trans-4-propylcyclohexyl) -4'-ethylbiphenyl
14% 4- (trans-4-pentylcyclohexyl) -4'-ethylbiphenyl
5% 4- (trans-4-propylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl
5% 4- (trans-4-pentylcyclohexyl) -4 ′ - (trans-4-propylcyclohexyl) biphenyl
4% 4- (trans-4-propylcyclohexyl) -4'-methoxytolane
4% 4- (trans-4-propylcyclohexyl) -4'-ethoxytolane

has a high UV and temperature stability and a favorable dispersion and is in the liquid crystal layer B one consisting of 2 liquid crystal layers Cell used.

Claims (7)

1. liquid crystal cell containing 2 twisted nematic liquid crystal layers A and B, of which at least one layer A is driven, the optical path differences of the two layers (Δn · d) _A and (Δn · d) _B essentially compensating each other, characterized in that that the liquid crystal used in the optionally uncontrolled layer B is based on a dielectrically neutral component selected from the compounds of the formulas I, II and III and can additionally contain a dielectric positive component selected from the compounds of the formulas IV, V and VI wherein
R is an alkyl group with 1-15 C atoms, in which one or two non-adjacent CH₂ groups can also be replaced by -O-, -CO-, -HC = CH-, CHHal and / or CHal₂, Z¹ -OCO or a single bond, n 1 or 2,
m 0 or 1, Z² -CH₂CH₂-, -COO-, OCO or a single bond, and
Z³ -CH₂CH₂- or a single bond
mean. 2. Cell according to claim 1, characterized in that the proportion of the dielectric neutral component more on the liquid crystal used in layer B. than 60%. 3. Cell according to at least one of claims 1-2, characterized in that the liquid crystal used in layer B is based on compounds of the formulas I1-I6, II1-II3, II7-II9 and III1-III3 4. Cell according to at least one of claims 1-3, characterized in that the quotient of the optical path difference of the optionally non-activated layer B (Δn · d) _B and the activated layer A (d · Δn) _A between 0.8 and 1.35. 5. Cell according to at least one of claims 1-5, characterized in that the layer B is not is controlled.   6. Liquid crystal for a liquid crystal cell after at least one of claims 1-5 based on Compounds of formulas I-III and optionally additionally containing at least one compound of the formulas IV, V and / or VI. 7. Use of a liquid crystal according to claim 6 in a liquid crystal cell after at least one of claims 1-5.