WO1992017813A1

WO1992017813A1 - Electro-optical system

Info

Publication number: WO1992017813A1
Application number: PCT/EP1991/000636
Authority: WO
Inventors: Bernhard Scheuble; Günter BAUR; Waltraud Fehrenbach; Barbara Weber
Original assignee: MERCK Patent Gesellschaft mit beschränkter Haftung
Priority date: 1991-04-03
Filing date: 1991-04-03
Publication date: 1992-10-15
Also published as: JP3288697B2; JP2000516728A

Abstract

An electro-optical system according to the preamble of claim 1 is described in which the angle psi formed by the polarization device on the inlet side with the liquid cristal molecule directors on the first substrate surface is optimized to achieve high contrast and/or high brightness and/or contrast and chromaticity which are highly independent of viewing angle.

Description

Electro-optical system

The invention relates to an electro-optical system according to the preamble of claim 1. Important values for assessing the optical properties of electro-optical systems are the values obtained for

- contrast

- brightness

- Viewpoint dependence of the contrast

- Viewpoint dependence of the color values.

Initially, TN displays (twisted nematic) were operated in the so-called Maugin range (d · Δn >> λ), as indicated, for example, in IEEE-Transaction and Electron Devices, 2b (1978), 1125-1137. In this area, the polarization vector of the incident light in the visible spectral range follows the screw structure of the uncontrolled cell, regardless of thickness fluctuations in the cell. However, displays of this type have an extremely high dependence on the viewing angle of the contrast and thus a greatly restricted viewing angle range. A decisive improvement in the viewing angle dependency of the contrast is observed if the system for the

Product of birefringence Δn and layer thickness d des

Liquid crystal has a value from the interval specified in DE 30 22 218 0.150 μm ≤ d · Δn≤ 0.600 μm. It is disadvantageous that in the sub-Maugin range according to Electronics Letters, 10 (1974), 2-4, a blocking behavior which depends on cell thickness and wavelength results, which can result in a certain brightening of the voltage-free state.

A double-cell arrangement has been proposed in US Pat. No. 4,443,065, one cell being electrically controlled and used for displaying information, while the other is used to compensate for the optical path difference d · Δn of the switched cell. However, due to the additional liquid crystal layer, such arrangements often have insufficient values for the contrast and the brightness.

In electro-optical systems based on the ECB (Electrically Controlled Birefrigence) or DAP (Distortion of

Aligned Phases), the liquid crystal molecules have a negative dielectric anisotropy Δε, a homeotropic edge orientation and an untwisted structure, e.g. in Displays 2 (1986), 3. To enlarge the observation angle range, compensation layers have been proposed which are based on polymer films

(EP 0,239,433 and EP 0,240,379) or liquid crystal layers (DE 39,11,620) with negative optical anisotropy. The electro-optical properties of such compensated ECB systems are often impaired by insufficient values for contrast and brightness. The object of the present invention was therefore to provide electro-optical systems based on the TN or ECB effect and containing one or more compensation layers, which are characterized by improved electro-optical properties and in particular high values for contrast and / or brightness and / or viewing angle dependency of contrast and / or the color values.

It has been found that this object can be achieved by providing the electro-optical systems according to the invention.

The invention thus relates to electro-optical systems containing

a twisted nematic liquid crystal layer between two substrates, the inner sides of which are provided with electrode layers and overlying orientation layers, the liquid crystal having a parallel edge orientation and a twist angle 0 ≤ β ≤ 100 ° and in particular 0 <β <90 ° or a homeotropic edge orientation,

- One or more layers to compensate for the optical path difference of the liquid crystal layer d · Δn, and

- At least one device for linear polarization of the light in such an arrangement that the light before entering the liquid crystal layer and after exiting a polarization device passes from this at least once, characterized in that, in order to achieve a high contrast and / or a high brightness and / or a high viewing angle independence of the contrast and / or the color values, the angle ψ that the polarization device has on the input side with the preferred direction which forms liquid crystal molecules on the first substrate surface, satisfies conditions (1) or (2) if there is a polarization device on the input and output side, ψ = (ß + 90 °) / 2 ± 10 ° (1)

ψ = ß / 2 ± 10 ° (2) where the polarizer on the output side is rotated by 90 ° ± 10 ° compared to the polarizer on the input side and the orientation of the polarizers on the input side and the output side can also be reversed, or the conditions (3) or (4) is sufficient if only one

Polymerization device is present on the input side

30 ° ≤ ψ ≤ 70 ° for 0 ≤ ß ≤ 45 ° (3)

35 ° ≤ ψ ≤ 90 ° for 45 ° ≤ ß ≤ 100 ° (4)

The notation used in equations (1) and (2) is intended to indicate that deviations of up to ± 10 ° from that caused by equations ψ = (ß + 90 °) 12

ψ = ß / 2 given angles ψ are possible. The deviations from the optimal angles ψ = (ß + 90 °) / 2 resp. ψ = ß / 2, however, are preferably not larger than ± 7.5 ° and in particular smaller than ± 5 °.

In the case of arrangements with one polarization device each on the input and on the output side, the polarizer on the output side is rotated by 90 ° ± 10 ° with respect to the polarizer on the input side, this notation again expressing that of the optimum

Angles of 90 ° deviations of up to ± 10 ° are possible. However, the deviations from the optimal rotation of the rear polarizer are preferably not greater than ± 7.5 ° and in particular less than ± 5 °.

The orientations of the front and rear polarizers can also be interchanged; i.e. in other words, if ψ gives the orientation of the polarizer on the input side and ψ 'the orientation of the polarizer on the output side, in another arrangement the orientation of the polarizer on the input side can be given by ψ' and that of the polarizer on the output side be given by ψ. Both the arrangements described by equations (1) and (2) and the arrangements given by interchanging the polarizer orientations are preferred.

The electro-optical systems according to the invention contain a controllable liquid crystal layer, which is arranged between plane-parallel, transparent substrates, the inside of which sides are provided with electrode layers and overlying orientation layers. The electrodes consist, for example, of thin, flat and transparent indium tin oxide (ITO) or indium oxide layers. For the edge orientation of the liquid crystals, polymer layers are generally used, for example

Polyimide or polyvinyl alcohol layers are used, which are given a uniform alignment by rubbing, if appropriate with simultaneous application of pressure. In addition, orientation layers can also be formed by vapor deposition with inorganic materials such as Silicon oxide or magnesium fluoride can be obtained. An overview of the different alignment techniques can be found e.g. in Thermotropic Liquid Crystals, G.W. Gray (ed.), Pp. 75-77. If the

If the liquid crystal layer is operated according to the TN principle, the liquid crystals have a parallel edge orientation, usually with a small pretilt angle in the

Order of magnitude e.g. 1 ° to 10 °. On the other hand, if the liquid crystal layer is based on the ECB principle, there is a homeotropic edge orientation of the liquid crystal molecules, the molecules usually having a small pretilt angle of e.g. Are tilted 0.5-5 ° against the vertical. In TN liquid crystal layers, the twist angle is between 0 ° and 100 ° and in particular between 0 ° and 90 °

is usually defined by the orientation of the orientation layers. But it is also possible that the twist angle ß by a cholesteric pitch of the

Liquid crystal is given. Even if the twist angle is not set via the pitch of the liquid crystal, a chiral dopant is generally added in small concentrations to avoid reverse twist and reverse tilt, as described, for example, in DE 25 07 524. In conventional ECB liquid crystal layers, the liquid crystal molecules are essentially untwisted.

In contrast, in the electro-optical systems according to the invention, the ECB liquid crystal plate can have a twist of 0 ° <β 90 90 °, the twist angle β being able to be defined by the orientation of the orientation layers and / or by the cholesteric pitch of the liquid crystal. ECB liquid crystal layers with a twisted structure, like electro-optical systems containing such an ECB liquid crystal layer, are new and preferred and they are the subject of this invention.

In addition to this liquid crystal layer, the electro-optical systems according to the invention can contain one or more, preferably not more than 2, and in particular a compensation layer. The compensation layers can be based on low molecular weight liquid crystals, liquid crystalline polymers or thermoplastic polymers, e.g. stretched two-dimensionally and thus made optically uniaxial.

The use of compensation layers is based on a well known physical principle, e.g. is also implemented in the Babinet-Soleil compensator. You combine e.g. two 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, the direction of polarization of which does not point in the direction of the optical axis, is split into an ordinary and an extraordinary beam in the first medium. Because the optical

If the axes of the two media are perpendicular to each other, the more orderly jet of the first medium runs in the second medium as an extraordinary jet 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 difference is 0 and that the system consisting of the two optical uniaxial media has no birefringence. These considerations can accordingly be transferred to systems with several compensation layers or other, for example, optically biaxial media.

Electro-optical systems with TN liquid crystal layer according to the invention can e.g. contain one or more, but in particular a compensation layer, which is based on low molecular weight nematic liquid crystal layers. The indicatrix of nematic liquid crystal molecules is a three-axis ellipsoid, the refractive index belonging to the long axis of the molecule being large compared to the other two.

Compensation layers based on nematic liquid crystals have already been proposed for TN cells and in particular also STN cells; further information can be found e.g. US 4,435,065, EP 0,139,351, K. Katoh et al., Jap. J. Appl. Phys. 2S. (1987), L 1784 and SID Digest Vol. 20, 1989, papers 22.3-22.6.

The liquid-crystalline compensation layer, like the liquid-crystal layer used to display information, is arranged between plane-parallel substrates provided with orientation layers. Since control of the compensation layer is generally dispensed with, there are usually no electrode layers; However, configurations with electrode layers are also possible. Preferably, one of the is to increase the transmission Liquid crystal layer and the liquid crystalline compensation layer common middle substrate used. However, two separate medium substrates can also be used. The liquid crystal in the compensation layer is preferably in a twisted structure, the twist angle given by the orientation of the orientation layers and / or by the cholesteric pitch of the liquid crystal being in particular opposite to the twist angle β of the liquid crystal layer. The absolute amounts of the twist angles are preferably chosen to be essentially the same size; however, larger deviations are also possible. The angle between the orientations of the orientation layers of the liquid crystal molecules on the two sides of the middle substrate common to the liquid crystalline compensation layer and the liquid crystal layer or on the lower substrate of the upper and the upper substrate of the lower layer is between 30 ° and 150 °, but preferably between 50 ° and 130 ° and in particular essentially 90 °.

Electro-optical systems according to the invention with a TN liquid crystal layer can also have one or more, in particular, however, a compensation layer which is based on a liquid crystalline polymer. Such compensation layers are described in detail in DE 39 19 397.

Electro-optical systems according to the invention with a TN liquid crystal layer may further preferably also have one or more, but in particular a compensation layer, which are based on an optically negative medium with 3 optical refractive indices. In a preferred embodiment of the systems according to the invention, the optical axis corresponding to the smallest refractive index can be oriented essentially parallel to the electrode surfaces, the angle between the optical axis corresponding to the smallest refractive index and the electrode surface being 0 τ 2 2 °. In another preferred embodiment of the systems according to the invention, the electro-optical axis corresponding to the smallest refractive index forms an angle with the electrode surface of 2 ° <τ ≤ 60 °, so that the angle between the optical axes of the controllable liquid crystal layer and the compensation layer during application and startup a voltage across the controllable liquid crystal layer passes through a minimum. The range 5 ° τ 45 45 ° and particularly the range 5 ° ganz τ 25 25 ° is particularly preferred for τ. The plane spanned by the other two refractive indices of the compensation medium forms with the directors of the liquid crystal molecules of the TN layer on both sides of the middle substrate common to the compensation layer and the TN liquid crystal layer or on the lower substrate of the upper and the upper substrate of the lower layer in the substrate plane an angle which is between 30 ° and 150 °, but preferably between 50 ° and 130 ° and in particular essentially 90 °.

In a particularly preferred embodiment, a uniaxial, optically negative compensation medium is used which has an axis of symmetry which is essentially parallel to the extraordinary axis and forms an angle between 0 ° τ 60 60 ° with the substrate plates, with τ in the range 2 ° ≤ τ ≤ 60 ° oriented as stated above. Such compensation layers are new and preferred and they are the subject of this invention. The biaxial or

Uniaxial, optically negative compensation layers are preferably based on low-molecular discotic and / or cholesteric molecules, which can be oriented essentially homeotropically or can also be arranged tilted. For the orientation of these molecules, which are more or less flat, two-dimensional, e.g.

have a disk-like shape, the substrate surface can e.g. with lecitin, quaternary ammonium compounds such as HTAB (US 3,694,053), silane compounds (Appl. Phys.

Lett. 22 (1973), 368), chromium complexes (Appl. Phys. Lett. 27 (1975), 268) or also with orientation layers consisting of other materials. An essentially homeotropic orientation means that the surface normal of the plane spanned by the two larger refractive indices runs essentially parallel to the electrode surface or forms a small angle with it, e.g. forms less than 2 ° ("upright disks"), while this surface normal with a tilted arrangement of the

Molecules with the electrode surfaces at an angle of e.g. Forms 2 ° -60 ° ("coupled discs"), the orientation of this angle being such that the angle between the optical axes of the compensation layer (corresponds to the axis corresponding to the smallest refractive index or the surface norm just mentioned) and the controllable one

Liquid crystal layer initially decreases when a voltage is applied to the controllable liquid crystal layer, passes through a minimum (zero crossing) and then rises again. A series of discotic liquid-crystalline compounds may be mentioned by way of example

Enumeration is only intended to explain the invention, but without limiting it: (1) hexasubstituted benzene

(2) 2, 3, 6, 7, 10, 11-hexasubstituted triphenyls

(3) 2, 3, 7, 8, 12, 13-hexasubstituted truxenes or their oxidized homologs

(4) 1, 2, 3, 5, 6, 7-hexasubstituted anthraquinones

(5) substituted Cu complexes

(6) Tetraarylbipyranylidum

(7) Porphyrin derivatives

in which R in each case independently of one another is an alkyl group with up to 30 C atoms, in which also one or more CH ₂ groups are formed by -O-, -CO-, -O-CO-, -CO-O-, -C≡C- , -CH = CH-,)

can be replaced, whereby 2 O atoms are not

are directly linked.

Compounds (1), (2), (3) and (4) are preferred; in particular, however, compounds (1), (2) and (3). Also particularly preferred are discotic liquid crystal compounds in which at least one —CH ₂ -

Group is replaced by a 1,4-phenylene group. Discotic liquid crystals which have a nematic discotic phase ND are preferred. In contrast to the columnar discotic phase, in which the molecules are packed into columns, the arrangement of the molecules in the nematic discotic phase is less rigid. The molecules can rotate freely and can orient themselves more or less freely, but their planes are arranged parallel to one another on average. Cholestrically nematic discotic phases N _D * can also be used.

An optically negative compensation layer can also be approximated by a sequence of optically positive layers, their orientation changing from layer to layer. By way of example, an arrangement according to the invention is shown schematically in FIG

Liquid crystal with homogeneous orientation (α = 1 °) and a twist angle ß = 0 ° based, combined with a sequence of 8 optically positive compensation layers. These compensation layers consist alternately of parallel (= homogeneous or planar) oriented (α = 1 °) nematic

Liquid crystal layers (ß = 0 °) and homeotropically oriented liquid crystal layers (ß = 0 °), the directors of the liquid crystal molecules on the lower substrate of the controllable layer (or on the corresponding common substrate) with the directors of the liquid crystal molecules on the upper substrate (or on the corresponding common

Substrate) of the adjacent compensation layer 1 of II

(see Fig. 17) forms an angle of approximately 90 °. The thickness of the controllable liquid crystal layer in FIG. 17 is d = 8 μm. The total layer thickness of the compensation layer and the nematic liquid crystals used in the controlled layer and in the compensation layer are chosen so that the optical thickness of the compensation layer is 2 d · Δn twice that of the controlled one

Liquid crystal layer with d · Δn. If, for example, the same liquid crystal is used in the driven liquid crystal layer and in the compensation layer, the total layer thickness of the compensation layer is chosen to be 2 d = 16 μm; however, they are also any other combinations of the layer thickness and the birefringence of the compensation layer

possible. The use of the same liquid crystal has the advantage that the driven liquid crystal layer and the compensation layer have the same dispersion and the same temperature dependence of birefringence and dispersion. The arrangement of FIG. 17 is between 2

Polarizers, the angle ψ, which the front polarizer forms with the direction of orientation of the directors of the nematic liquid crystal molecules on the uppermost substrate plate, is 45 °. The rear polarizer is rotated by 90 ° compared to the front. For this system according to the invention, FIG. 18 shows the transmission as a function of the birefringence Δn of the driven liquid crystal layer at an angle (azimuth angle) ɸ = 135 ° measured in the plane when the system is not activated. It can be seen that the system exhibits ideal blocking behavior in the Δn range shown up to an observation angle θ of approximately 30 °, while a transmission at higher Δn values of more than approximately 0.0735 is found at observation angles θ of more than 45 °.

It was also found that the transmission in the uncontrolled state in the visible spectral range practically does not depend on the wavelength of the light. This transmission behavior corresponds to that of a system according to the invention with an optically negative compensation layer composed of, for example, discotic molecules, which are oriented such that the axis corresponding to the smallest refractive index is essentially parallel to the electrode surfaces or forms an angle τ as defined above.

The compensation layer shown in FIG. 17 consists of 8 cells with a thickness of 2 μm, which are the same

Liquid crystal as the controllable liquid crystal layer are filled. However, such an arrangement is generally not preferred in practice due to the high number of substrates and orientation layers required, etc. on the one hand because of the high structural effort involved in the production of the

Systems and on the other hand because of the many glass substrates and orientation layers significantly reduced

Total transmission. 17 is only intended to illustrate the principle of such a compensation layer, and it is

diverse deviations possible. For example, instead of the layers of monomeric nematic liquid crystals or in combination with them, films of liquid-crystalline polymers, the mesogenic groups of which are oriented accordingly, and / or films of isotropic polymer material which are correspondingly axially stretched, can be stacked on top of one another. Liquid crystalline polymeric compensation films and compensation layers obtained by stretching thermoplastic polymers are briefly described below. When approximating an optically negative compensation layer, it is important that the compensation layer consists of a sequence of optically positive layers, the optical axis of two successive layers forming an angle between 60 ° and 120 ° and in particular 80 ° and 100 ° and in particular essentially are perpendicular to each other. The compensation layer preferably consists of at least 2 and in particular not less than 4 layers; compensation layers of at least 8 successive layers are very particularly preferred. The

Compensation layers preferably have an even number of successive layers.

The liquid crystal molecules or mesogenic groups in liquid crystalline polymers contained in the individual layers of the compensation layer can be untwisted or twisted, the twisting preferably being selected in accordance with that of the controllable liquid crystal layer.

The optical thickness of the compensation layer is preferably at least 1.5 times and in particular at least 1.8 times the optical thickness of the controllable liquid crystal layer.

The orientation of the first layer of the compensation layer following the controllable liquid crystal layer is not very critical. For example, instead of the configuration shown in Fig. 17, e.g. a compensation layer can also be used, the first layer of which is oriented homeotropically or essentially homeotropically. The angle that the liquid crystal molecules of the controllable liquid crystal layer and the adjacent layer of the compensation layer form in the substrate plane in arrangements analogous to FIG. 17 is preferably between 30 ° and 150 °, in particular between 50 ° and 130 ° and very particularly essentially 90 ° (Fig. 17); in other arrangements, the person skilled in the art can select suitable orientations of the parallel-oriented nematic molecules in a controllable manner

Specify the liquid crystal layer and compensation layer slightly.

It has been shown that optically negative compensation layers can be excellently approximated by such a stack of successive, optically positive layers with differently oriented optical axes. With a sequence of at least 8 optically positive layers, the properties of an optically negative compensation layer are practically achieved and, if more layers are used, an improvement can sometimes even be achieved in comparison with an optically negative compensation layer. Such altogether optically negative compensation layers consisting of a stack of optically positive layers are new and the subject of this invention. Also particularly preferred as an optically negative compensation layer are liquid-crystalline side-chain polymers which have cholesteric and / or discotic groups as the mesogenic residue (cf., for example, also DE-PS 34 30 482), for example those of the just mentioned discotic, but also other cholesteric or discotic Connections can be derived. Also preferred are liquid-crystalline side chain polymers with board-like mesogenic groups. An essentially homeotropic orientation of the mesogenic groups is usually achieved by exposing the polymer to an electrical and / or magnetic field and / or a mechanical stress above the glass transition temperature. The orientation induced in this way can be frozen by cooling the polymer below the glass temperature while the field is switched on or while maintaining the mechanical tension. Such liquid-crystalline polymers and methods for their orientation are described in detail in DE 39 19 397. 1a and 1b, the transmission I as a function of the angle 0 measured in the display plane is compared with the observation angle θ measured from the normal of the display plane as a parameter for 2 electro-optical systems according to the invention. The compensation layer of the system from FIG. La is based on a nematic liquid crystal layer and an optically negative compensation layer with homeotropic orientation is used for the system from FIG. 1b, the smallest refractive index being nmin = 1.5000 and the other two being the same size and have a value of 1.5356. The liquid crystal layer has in both arrangements a twist angle of ß = 22.5 and a layer thickness of 8 μm and the pretilt angle is 1 °. A linear polarizer is used on the input and output side of the arrangement with ψ = 56.25 °; the rear polarizer is rotated by 90 ° in relation to the front. The voltage applied to the TN liquid crystal layer is chosen for both arrangements with U = 1.15 V so that when viewed perpendicularly (θ = 0 °), a transmission of 0.23 is observed for all viewing angles. 1a and 1b show the transmissions as a function of 0 for both systems at observation angles of θ = 10 °, 20 °, 30 °, 45 °, 60 ° and 80 °. Deviations from the transmission determined for θ = 0 °, which is represented in this diagram by a circle around the origin with a radius of 0.23, are observed, the magnitude of these deviations being a measure of the viewing angle dependence of the contrast.

By comparing Fig. 1a and 1b it follows that the

System with the new compensation layer according to the invention shows a good viewing angle dependence of the contrast. The transmission profiles are deformed somewhat more elliptically than that in FIG. 1a, but on the other hand they often have a smaller extent than that in FIG. 1a. In the arrangement described in FIG. 1b, the axis corresponding to the smallest refractive index is aligned essentially parallel to the electrode surface. With this compensation method, in addition to the good viewing angle dependence of the transmission shown in FIG. 1b, an optimal blocking behavior is obtained in the non-activated state. It has surprisingly been found that the viewing angle dependency of the contrast can be improved if the optically negative compensation layer has a tilted orientation, ie if the axis corresponding to the smallest refractive index forms an angle τ with the electrode surface. The angle τ is preferably between 2 and 60 °, in particular between 5 and 45 ° and very particularly between 5 ° and 25 ° and is preferably oriented so that the angle between the nematic director of the

Liquid crystal molecules of the controllable liquid crystal layer, i.e. the optical axis of the controllable

Liquid crystal layer, and the axis corresponding to the smallest refraction on the axis initially reduced with increasing voltage, and then increased again after passing through a minimum (zero crossing).

With such an arrangement of the compensation layer, an optimal blocking behavior is not observed in the de-energized state, but when the voltage is raised below the threshold voltage if the angle between the optical axes of the controllable liquid crystal layer and the compensation layer is minimal (zero crossing). This hardly affects the electro-optical properties of such systems. 19 shows the transmission I for a system according to the invention with a tilted, optically negative compensation layer for a wavelength λ =

550 nm and at a voltage corresponding to 1.1 times the threshold voltage (U / U _o = 1.1) as a function of that in the

Display level measured viewing angle with the viewing angle 1 measured from the normal of the display level as a parameter. The controllable liquid crystal layer of this system has a twist angle ß = 0 ° and a pretilt of α = 1 ° and the layer thickness is 8 μm. The compensation layer, whose smallest refractive index is 1,500 while the other two are 1.5527, consists of 8 optically positive layers of 1 μm with alternating homogeneous (α = 1 °) and homeotropic (α = 89 °) orientation. The optical axis corresponding to the smallest refractive index forms an angle with the electrode surface of approximately 15 ° so that the angle between the preferred direction of the nematic directors and the axis corresponding to the smallest refractive index initially decreases with increasing voltage, and then after passing through a minimum ( Zero crossing) to become larger again. It can be seen in FIGS. 19 and 20, which shows a diagram corresponding to FIG. 19 for U / Uo = 1.3, that the transmission for observation angles up to approximately 30 ° differs only slightly from the transmission at θ = 0 °, which is shown in FIG this diagram as a circle around the origin with a radius of about 0.68. A comparison with FIG. 1b shows that the viewing angle dependence of the contrast is significantly improved by the tilted orientation of the optically negative compensation layer. FIG. 21 shows the electro-optical characteristic curve for the system described in FIG. 19; one recognizes that the electro-optical characteristic is practically not impaired by the fact that the optimal blocking state does not coincide with the de-energized state.

Electro-optical systems, which have a controllable nematic liquid crystal layer with 0 ° ß 100 100 ° and in particular 0 ß 90 90 ° and an optically negative, tilt-oriented component layer are new. Systems are preferred in which the polarizer orientations are additionally given by equations (1) or (2) or (3) or (4).

These systems are characterized by excellent properties and are the subject of the present invention. The particular system described in Fig. 19 is only intended to illustrate this invention without, however, limiting it. Corresponding results have also been obtained for systems with a twisted nematic drivable liquid crystal layer. The compensation layer can be on disc-shaped molecules such as e.g. Discotes are based or on other biaxial or uniaxial, optically negative compensation layers. Furthermore, it is also possible, in particular, for the compensation layer to be approximated by one of the stacks of optically positive layers described above with different orientations. Furthermore, electro-optical systems according to the invention with a TN liquid crystal layer can also have one or more, but in particular a compensation layer, which is based on a thermoplastic polymer material, e.g. based on polycarbonate, polyvinyl alcohol or polyethylene terephthalate and aligned axially with the desired orientation; such films are e.g. in EP 0,315,484.

If the twist angle of the TN liquid crystal layer is small and in particular β <60 °, the compensation layer can also be omitted in the electro-optical systems according to the invention. Particularly favorable electro-optical properties show electro-optical systems without compensation layer if the twist angle of the TN liquid crystal layer is ß ≤ 45 °, in particular 15 ° ≤ ß ≤ 30 ° and very particularly ß = 22.5 °. Systems of this type, which are referred to as uncompensated LTN systems (low twisted nematic), are new, preferred and the subject of the present invention.

Electro-optical systems according to the invention with an ECB liquid crystal layer have one or more compensation layers, in particular, however, a compensation layer which is based on thermoplastic polymers, low molecular weight liquid crystals and / or liquid crystalline polymers. Such compensation layers are described in detail in the literature (e.g. DE 39 11 620, DE 39 19 397, EP 0.240.379 and EP 0.239.433).

The electro-optical systems according to the invention further have at least one device for linear polarization of the light in such an arrangement that the light passes through a linear polarizer at least once before it enters the liquid crystal layer and after it exits it. There is often a linear polarizer on both sides of the display; these usually consist of foils that are glued to the substrate plates. Such an arrangement can be operated transmissively or also reflectively or transflectively; in reflective or transflective systems is behind the polarizer facing away from the light source a reflector or a reflector and an additional one

Lighting device attached (see e.g. E. Kaneko, Liquid Crystal TV Display, KTK Scientific Publishers, Tokyo, 1987, p. 25 and p. 30). In other preferred configurations of the electro-optical systems according to the invention, however, only one device for linear polarization of the light is used. An example is the reflective device shown in FIG. 2, in which the light entering or leaving the cell sees the McNeil prism used as the polarizer as a combination of two polarizers rotated by 90 ° with respect to one another. Such a reflective arrangement is e.g. particularly interesting for projection displays.

The structure of the electro-optical systems according to the invention described so far is essentially based on the design customary for such systems. The term customary construction is broadly encompassed and includes all modifications and modifications not explicitly mentioned here. Where new and inventive elements or significant design deviations are mentioned in the structure of the electro-optical systems according to the invention described so far, these are explicitly identified as belonging to the subject matter of the invention. A very significant difference of the electro-optical systems according to the invention is, however, that in order to achieve a high contrast and / or a high brightness and / or a high viewing angle independence of the contrast and / or the color values, the angle ψ that the polarization device on the side facing the light source with the preferred direction of the liquid crystal molecules on the substrate surface is optimized. The following applies to ψ if there is a polarization device on the input and output side ψ = (ß + 90 °) / 2 ± 10 ° (1)

ψ = ß / 2 ± 10 ° (2) where the polarizer on the output side is rotated by 90 ° ± 10 ° compared to the polarizer on the input side and the orientations of the polarizers on the input side and the output side can also be interchanged, or if there is only one polarization device on the input side

30 ° ≤ ψ ≤ 70 ° for 0 ≤ ß 45 ° (3)

35 ° ≤ ψ ≤ 90 ° for 45 ° ≤ ß ≤ 100 ° (4) In Fig. 3 is for a non-compensated electro-optical system with a TN liquid crystal layer, the twist angle ß - 22.5 ° and a layer thickness of 8 microns has the transmission or the brightness in the uncontrolled state for a wavelength of λ = 550 nm and for Θ = 0 ° and 0 = 0 ° as a function of the birefringence Δn of the nematic liquid crystal layer with ψ as a parameter. A non-compensated TN cell is considered, since the transmission for a TN cell with a compensation layer is minimal with crossed polarizers in the non-activated state regardless of the optical anisotropy Δn and the transmission of a compensated system is essentially different from the transmission of the non-activated ones Compensation layer depends. The system has two polarization devices, the rear polarizer being rotated by 90 ° with respect to the front. The transmission or the brightness depends very much on the polarizer position and is for

Ψ _opt. = (ß + 90 °) / 2 = (22.5 ° + 90 °) / 2 = 56.25 ° optimal. Less deviation of the actually set angle ψ from the optimal value can be tolerated. For example, one observes for ψ = 52.5 ° compared to the optimal value ψ _opt. transmission reduced by approximately 2%.

In contrast, a transmission is found for ψ = 45 °, which is more than 13% smaller than the optimal one. The deviation of the actually set angle ψ from the optimal value given by the above equation should generally Do not exceed ± 10 ° and preferably 10% and in particular <7.5% and very particularly <5%.

If there is only one polarization device, the optimal polarization configuration is given by conditions (3) and (4). These electro-optical systems preferably contain liquid crystals with a birefringence 0.035 Δ Δn 0,0 0.010 and the layer thickness of the liquid crystal layer and the compensation layer is preferably 3 μm d d 7 7 μm. Electro-optical systems with the following parameter combinations are very particularly preferred:

Parameter ß d / μm Δn ψ

combination

1 15 ≤ ß ≤ 30 3.5 ≤ d ≤ 5 0.035 ≤ Δn ≤ 0.065 40 ≤ ψ≤ 65

2 40 ≤ ß ≤ 45 3.5 ≤ d≤ 5 0.035 ≤ Δn ≤ 0.065 45 ≤ ψ≤ 65

3 80 ≤ ß ≤ 90 3.5 ≤ d ≤ 5 0.035 ≤ Δn ≤ 0.065 55 ≤ ψ≤ 90 The liquid crystal layer and the compensation layer preferably have essentially the same values for the birefringence and the layer thickness. Electro-optical systems with d = 4 μm, 0.045 ≤ Δn ≤ 0.055 and ß = 22.5 °, 45 ° ≤ ψ≤ 60 ° or ß = 45 °, 50 ° ≤ ψ≤ 60 or ß = 80 ° are very particularly preferred. 60 ° ≤ ψ≤ 85 °.

Systems according to the invention with 2 polarization devices for which ψ is given by equations (1) and (2) are described in detail below.

4a shows the transmission I for a wavelength λ = 550 nm as a function of the viewing angle 0 measured in the display plane with the observation angle 1 gemess measured from the normal of the display plane as a parameter for a conventional TN display and an electro-optical system according to the present Invention with optically positive compensation layer shown in comparison. The conventional TN system has a twist angle of 90 ° and is operated at the 1st transmission minimum; the layer thickness of the TN liquid crystal layer is 8 μm and the pretilt angle is 1 °.

Two polarizing foils arranged in parallel are used so that the display is transparent when not activated. The configuration of the electro-optical system according to the present invention is shown in FIG. 5. The twist angle of the TN liquid crystal layer used for information display is β = 22.5 °. Another TN layer with a twist angle is used as the compensation layer of ß '= -22.5 ° used. The angle ψ, which the front polarizer forms with the direction of orientation of the directors of the liquid crystal molecules on the uppermost substrate plate (-Y axis), is 56.25 °. The rear polarizer is rotated by 90 ° compared to the front. The thickness of the

Information display used TN layer is 8 μm and the pretilt angle is 1 °.

The voltages applied to the conventional TN cell or the system according to the invention are U / U _o = 1.1 and U / U _o =

1.15 chosen so that when viewed vertically (Θ = 0), a transmission of 0.23 is observed for all viewing angles 0. 4a shows the transmissions as a function of 0 for both cells, which were determined at observation angles of Θ = 10 ° or 45 °. Deviations from the transmission determined for Θ = 0, which is represented in this diagram by a circle around the origin with a radius of 0.23, are observed. Since the magnitude of these deviations is a measure of the viewing angle dependence of the contrast, it can be seen from FIG. 4a that the electro-optical systems according to the invention have an improved angular dependence of the contrast compared to conventional TN cells. FIG. 4b shows the dependence of the transmission on the viewing angle 0 for the cells described in FIG. 4a for 2 different observation angles Θ = 10 ° and 45 ° as parameters, with that of the conventional TN cell or of the electro-optical system according to the invention applied voltages with U / Uo = 1.18 or 1.3 are selected so that with vertical observation (θ = 0 °) for all observation angles ∅ a transmission of 0.45 results. Here, too, shows that the electro-optical systems according to the invention have a lower viewing angle dependence of the contrast than conventional TN cells.

6 and 7 show the transmission as a function of the viewing angle 0 with Θ as a parameter for the cells described in FIG. 4a for 2 different wavelengths λ = 450 nm and λ = 650 nm, the voltages applied to the two cells also being shown in FIG U / U0 = 1.18 1.3 are selected so that with vertical observation (Θ = 0 °), a transmission of 0.45 results for all observation angles 0 for light of λ = 550 nm. A comparison of the transmission lines obtained for the two cells shows that the arrangement according to the invention for λ = 650 nm shows a significantly lower viewing angle dependence of the contrast, while for λ = 450 nm for Θ = 10 ° a poorer and for Θ = 45 ° a better transmission line is observed. Overall, the electro-optical systems according to the invention are therefore also characterized by a better viewing angle dependence of the color values.

The dependence of the transmission I and / or the dependence of the contrast on the wavelength of the light can be reduced or even largely compensated for by using a lamp with a suitable spectral distribution for illuminating the system. The spectral distribution of the light emitted by the lamp can be influenced, for example, by a suitable choice of the phosphors and adapted to the wavelength dependence of the transmission, the. Intensity of the lamp light, for example, in wavelength ranges in which the system shows a high transmission. is weakened and vice versa. Electro-optical systems according to the invention, for which the lamp has such a spectral distribution that the dependence of the transmission and / or the viewing angle dependence of the contrast is as small as possible, are preferred and the subject of this invention.

8a and 8b show the viewing angle dependence of the transmission at a wavelength λ = 550 nm for 2 different cells, which essentially correspond to the cells described in FIG. 4a; however, the conventional cell is additionally with one on a nematic

Provide liquid crystal based compensation layer with ß '= -90 °. In Fig. 8a the voltages applied to the conventional cell or the cell according to the invention with U / U _o = 1.1 and 1.15 are selected such that a transmission of 0.23 for all 0 results for Θ = 0 ° ; in Fig. 8b the voltages are U / U _o =

1,2 and 1,3 are chosen, whereby a transmission of 0,45 is obtained for Θ = 0 °. A comparison of the transmission lines in FIGS. 8a and 8b shows that the systems according to the invention also have a significantly better viewing angle dependency of the contrast compared to compensated conventional systems.

9 shows the dependence of the transmission at a wavelength of λ = 589 nm on the polarizer position for an electro-optical system according to the invention with a

ECB liquid crystal is shown. The ECB liquid crystal layer faces the light source and has one Twist angle of 22.5 ° and an optical path difference of d · Δn = 1.0 μm. For example, a uniaxial, optically negative polymer film produced by the process described in EP 0,240,379 is used as the compensation layer. The examined polarizer positions are shown in FIG. 10 and labeled a1-a4. Conventional, untwisted ECB displays usually have the polarizer configuration al or a3, while the configurations a2 or a4 are given by equation (2) and are used in the systems according to the invention. FIG. 9 shows the transmission as a function of the voltage for the different polarizer configurations. It follows from this that the electro-optical systems according to the invention with an optimized polarizer configuration have a significantly higher transmission than systems with conventional orientation of the polarizers. In contrast, the confusion of the orientation of the analyzer and polarizer hardly plays a role, as a comparison of the electro-optical characteristics a1 and a3 or a2 and a4 shows.

An even more significant difference in the transmission is observed when an electro-optical system with an ECB liquid crystal layer with a twist angle of 90 ° and a compensation layer is operated on the one hand with a conventional and on the other hand with an improved polarizer configuration (FIG. 11). The polarizer arrangement used is shown in a matching manner in FIG. 12 and is designated b1-b4; bl and b3 are the conventional and b2 and b4 are the polarizer configurations optimized according to the present invention, wherein the arrangement of polarizer and analyzer is interchanged. While a dark display results from a conventional arrangement, favorable values for the transmission can be found with an optimized polarizer configuration.

The ECB systems according to the invention are further characterized by favorable values for the viewing angle dependence of the contrast, i.a. the viewing angle dependency of the contrast is only slightly influenced by the polarizer position.

The viewing angle dependency of the contrast can, however, be improved substantially both for conventional and for ECB systems according to the invention if the optical path difference is used both for the information display

Liquid crystal layer and the compensation layer d · Δn ≤ 0.4 μm and in particular d · Δn ≤ 0.3 μm is selected. Conventional and inventive ECB systems with such optical path differences are preferred and the subject of this invention.

Figure 13 shows isocontrast curves for a conventional compensated ECB system. The liquid crystal layer used for information display is untwisted and, like the compensation layer, has an optical path difference of d · Δn = 0.28 μm. The layer thickness of the liquid crystal layer used for information display is 5 μm and the refractive index is Δn = 0.056. For example, a uniaxial, optically negative polymer film produced by the process described in EP 0,240,379 can be used as the compensation layer. There is a polarizer on the input and output side, where ψ = 45 ° and the rear polarizer is rotated by 90 ° compared to the front one. Isocontrast lines for contrast values of 5, 10, 20, 30 and 40 are shown. It can be seen from Fig. 13 that the viewing angle dependence of the contrast is excellent for the described conventional system with d · Δn = 0.28. The viewing angle dependency is significantly better than that of conventional systems with a higher path difference of e.g. 0.6 μm ≤ d · Δn ≤ 1.0 μm. 14 shows electro-optical characteristic curves for an ECB system according to the invention, in which the ECB liquid crystal layer has a twist angle of 22.5 ° and an optical path difference of d · Δn = 0.28 μm. For example, a uniaxial, optically negative polymer film is used as the compensation layer. The electro-optical characteristic curve designated a2 in FIG. 14 is obtained with an optimized polarizer position with ψ = 56.25 °, while the curve al corresponds to the conventional polarizer arrangement. The isocontrast lines for the optimized system are shown in FIG. 15. A comparison with those shown in FIG. 16

Isocontrast lines for the system described in FIG. 9 with the polarisaotr configuration a2 shows that the viewing angle dependence of the contrast can be significantly improved by reducing the optical path difference d · Δn.

If one looks at the electro-optical characteristic curves from FIGS. 9 and 14, it becomes clear that systems with a smaller d · Δn have a lower slope of the electro-optical characteristic curve, but this is particularly advantageous in the case of an active matrix control, since the displayability of

Shades of gray is relieved. Even in the case of the ECB systems according to the invention with a higher twist angle of, for example, β = 90 °, a marked improvement in the viewing angle dependence of the contrast is observed if the optical path difference of the ECB layer is small.

The electro-optical systems according to the invention are distinguished from conventional ones by improved electro-optical properties and in particular high contrast and / or high transmission and / or high viewing angle independence of the contrast and / or the color values, so that they are of considerable economic importance.

To Figure 1

a) Twist angle ß = 22.5

Pretilt angle -4 = 1 °

Thickness of the liquid crystal layer and compensation layer each 8 μm

Observation angle θ

o 10 degrees x 45 degrees

Δ 20 degrees ◊ 60 degrees

+ 30 degrees ∇ 80 degrees b) Twist angle ß = 22.5

Pretilt angle α _o = 1 °

Thickness of the liquid crystal layer and compensation layer each 8 pm

Observation angle θ

o 10 degrees x 45 degrees

Δ 20 degrees ♢ 60 degrees

+ 30 degrees ∇ 80 degrees

To Figure 2

1 light source

2 mirrors

3 McNeil prism

4 liquid crystal cell 5 projection lenses

Regarding Figure 3

Twist angle ß = 22.5

Pretilt angle α = 1 °

θ = 0º0 = 0 °

Wavelength λ = 550 nm

angle

+ 15.0 degrees

X 22.5 degrees

♢ 30.0 degrees

∇ 37.5 degrees

⊠ 45.0 degrees

X 52.5 degrees

♦ 56.5 degrees (internal marking: 04.10.89; STAT 157 DAT; TOKI 01.PL)

Regarding Figure 4

TRANSMISSION = f (θ, ɸ)

Twist-90 °, α _o = 1 °, d / p = 0.25

Twist-22.5 °, α _o = 1 °, d / p = 0.0625 a) 1 conventional TN display

Layer thickness 8 μm

Twist angle ß = 90 °

Angle Ψ = 0 °, polarizer and analyzer are parallel liquid crystal layer: U / U _o = 1.1

Wavelength λ = 550 nm

2 display according to the invention

Layer thickness 8 µm

Twist angle ß = 22.5 °

Angle Ψ = 56.25 °

Liquid crystal layer: U / U _o = 1.15

Compensation layer U / U _o = 0

Wavelength λ = 550 nm

Observation angle θ

o = 10 degrees

x = 45 degrees

b) 1 conventional TN display

Layer thickness 8 μm

Twist angle ß = 90 °

Angle Ψ = 0 °, polarizer and analyzer are parallel liquid crystal layer: U / U _o = 1.18

Wavelength λ = 550 nm

2 display according to the invention

Layer thickness 8 μm

Twist angle ß = 22.5 °

Angle Υ = 56.25 °

Liquid crystal layer: U / U _o = 1.3

Compensation layer U / U _o = 0

Wavelength λ = 550 nm

Observation angle θ

o = 10 degrees

x = 45 degrees Regarding FIG. 5 preferred direction of the liquid crystal molecules on the lower substrate plate of the TN liquid crystal layer upper polarization device

Preferred direction of the liquid crystal molecules on the lower substrate plate of the TN liquid crystal layer adjacent substrate plate of the compensation layer

Lower polarizer

6 a) 1 conventional TN display

Layer thickness 8 µm

Twist angle ß = 90

Angle Ψ = 0, polarizer and analyzer are parallel

Liquid crystal layer: U / U _o = 1.18

Wavelength λ = 450 nm

2 display according to the invention

Layer thickness 8 µm

Twist angle ß = 22.5

Angle Ψ = 56.25

Liquid crystal layer: U / U _o = 1.3

Compensation layer: U / U _o = 0

Wavelength λ = 450 nm

To figure 7

1 conventional TN display

Layer thickness 8 μm

Twist angle ß = 90 °

Wavelength λ = 650 nm

2 display according to the invention

Layer thickness 8 μm

Twist angle ß = 22.5 °

AngleΨ = 56.25 °

Liquid crystal layer: U / U _o = 1.3

Compensation layer: U / U _o = 0

Wavelength λ = 650 nm observation angle θ

o = 10 degrees

Δ = 45 degrees

a) 1 conventional TN display

Layer thickness 8 μm

Twist angle ß = 90 °

Angle ψ = 0 °, polarizer and analyzer are crossed

Liquid crystal layer: U / U _o = 1.1

Compensation layer: U / U _o = 0

Wavelength λ = 550 nm

2 display according to the invention

Layer thickness 8 µm

Twist angle ß = 22.5 °

Angle = 56.25 °

Liquid crystal layer: U / U _o = 1.15

Compensation layer U / U _o = 0

Wavelength λ = 550 nm

Observation angle θ

o = 10 degrees

Δ = 45 degrees

b) 1 conventional TN display

Layer thickness 8 μm

Twist angle ß = 90 °

Angle Ψ = 0 °, polarizer and analyzer are crossed

Liquid crystal layer: U / U _o = 1.2

Compensation layer: U / U _o = 0

Wavelength λ = 550 nm

2 display according to the invention

Layer thickness 8 μm

Twist angle ß = 22.5 °

Angle = 56.25 °

Liquid crystal layer: U / U _o = 1.3

Compensation layer U / U _o = 0

Wavelength λ = 550 nm

Observation angle θ

o = 10 degrees

Δ = 45 degrees Regarding Figure 10

Above: Preferred direction of the liquid crystal molecules on the

Substrate plates of the ECB layer

1 Preferred direction of the liquid crystal molecules on the lower substrate plate of the ECB liquid crystal

2 Preferred direction of the liquid crystal molecules on the upper one

ECB liquid crystal substrate plate

a1, a2, a3, a4: polarizer configuration angle Ψ

To figure 12

Above: Preferred direction of the liquid crystal molecules on the

Substrate plates of the ECB layer

2 Preferred direction of the liquid crystal molecules on the upper substrate plate of the ECB liquid crystal

b1, b2, b3, b4: polarizer configuration angle ψ

To Fig. 13

Contrast (589 nm)

5,000

10,000

20,000

30,000

40,000

To Fig. 15

Contrast (589 nm)

5,000

10,000

20,000

30,000

40,000 min (o) = 0.04690

Max. (X) = 2603.25561

To Fig. 16

Contrast (589 nm)

5,000

10,000

20,000

30,000

40,000 To Fig. 17

Approximation of an optically negative compensation layer by a stack of optically positive, differently oriented liquid crystal layers I controllable liquid crystal layer

Twist angle ß = 0 °

homogeneous orientation (α = 1º)

Thickness α = 8 μm

II compensation layer

1,3,5,7: Twist angle ß = 0º

homogeneous orientation (= 1º) thickness α = 2 μm

2,4,6,8: homeotropic orientation (α = 89º)

Twist angle ß = 0º

Thickness α = 2 μm

To Fig. 18

Transmission I as a function of the birefringence n of the activated layer for a system according to the invention with an optically negative compensation layer according to FIG. 17

controllable liquid crystal layer: twist angle ß = 0º

Pretilt angle α = 1º thickness α = 8 μm

Compensation layer: construction as in FIG. 17

Thickness of the individual layers α = 1 μm angle Ψ = 45º

Angle ɸ = 135º

Wavelength λ = 550 nm

Observation angle θ

0 = 0 degrees

▲ = 10 degrees

+ = 20 degrees

X = 30 degrees

♢ = 45 degrees

∇ = 60 degrees

■ = 80 degrees

To Fig. 19

System according to the invention with a tilted, optically negative compensation layer

controllable liquid crystal layer: twist angle ß = 0º homogeneous orientation (α = 1º) (α = 8 μm

U / Uo = 1.1 Compensation layer: angle γ = 15º

Thickness α = 8 μm

Twist angle ß = 180º

η _min = 1.5000, the other two refractive indices each 1.5527

Angle Ψ = 45º

Wavelength λ = 550 nm

Viewing angle 6

O = 10 degrees

Δ = 20 degrees

+ = 30 degrees

X = 45 degrees

♢ = 60 degrees

∇ = 80 degrees

20 as in FIG. 19, however U / Uo = 1.3 is selected for the controllable liquid crystal layer.

Viewing angle 9

O = 10 degrees

Δ = 20 degrees

+ = 30 degrees

X = 45 degrees

♢ = 60 degrees

∇ = 80 degrees

To Fig. 21

Electro-optical characteristic curve for the electro-optical system described in FIG. 19.

Claims

1. containing electro-optical system,

a twisted nematic liquid crystal layer between 2 substrates, the inner sides of which are provided with electrode layers and overlying orientation layers, the liquid crystal having a parallel edge orientation and a twist angle 0 ° ≤ 100 100 ° or a homeotropic edge orientation,

- One or more layers to compensate for the optical path difference of the liquid crystal layer d. Δ n, and

- At least one device for linear polarization of the light in such an arrangement that the light passes through a polarization device at least once before entering and after leaving the liquid crystal layer, characterized in that in order to achieve high contrast and / or high brightness and / or a high viewing angle independence of the contrast and / or the color values of the angles Ψ which the polarization device forms on the input side with the preferred direction of the liquid crystal molecules on the first substrate surface, Conditions (1) or (2) are sufficient if there is a polarizing device on the input and one on the output side

Ψ = (ß + 90 °) / 2 ± 10º (1)

Ψ = ß / 2 + 10º (2) where the polarizer on the output side is rotated by 90º + 10 ° with respect to the polarizer on the input side and the orientations of the polarizers on the input side can also be interchanged, or conditions (3) and ( 4) is sufficient if there is only one polarization device on the input side

30 ° ≤ Ψ≤ 70 ° for 0 N≤ ß≤ 45 ° (3)

35 ° ≤ Ψ≤ 90 ° for 45 <ß ≤ 100 ° (4)

2. System according to claim 1, characterized in that the compensation layer is based on a thermoplastic polymer, a low molecular weight liquid crystal and / or a liquid crystalline polymer.

3. System according to at least one of claims 1 or 2 with a liquid crystal layer having a parallel edge orientation and a twist angle 0 <ß <100 °, characterized in that the compensation layer is based on a twisted nematic liquid crystal, wherein the twist angle ß 'of the compensation layer essentially the same absolute amount, but has the opposite direction of rotation as ß and the preferred directions of the liquid crystal molecules of the liquid crystal layer and compensation layer form an angle between 30 ° and 150 ° on the facing surfaces.

4. System according to at least one of claims 1 or 2 with a liquid crystal layer having a parallel edge orientation and a twist angle 0 ° ≤≤100 °, characterized in that the compensation layer is based on a material having 3 optical refractive indices, one of which is smaller than the other two is, the axis corresponding to this refractive index being essentially parallel to the electrode surfaces or forming an angle 2 ° ζ ζ≤ 60 ° with the electrode surface such that the angle between the optical axes of the

Compensation layer and the controllable liquid crystal layer passes through a minimum when a voltage is applied, and that the plane spanned by the other two refractive indices forms an angle between 30 ° and 150 ° with the directors of the liquid crystal layer on the mutually facing surfaces.

5. System according to at least one of claims 1 or 2 with a liquid crystal layer which has a homeotropic edge orientation, characterized in that the compensation layer is based on a 3 optical refractive index material, one of which is smaller than the other two, the smaller this Refractive index corresponding axis is substantially perpendicular to the electrode surfaces.

6. System according to claim 5, characterized in that the

Liquid crystal layer has a twist angle 0 <ß≤ 90 °.

7. System according to at least one of claims 1-4 or 6, characterized in that the twist angle is 5 ° ≤ ß≤ 60 °.

8. System according to at least one of claims 1-7, characterized in that the system contains only 1 polarization device and at least one reflector.

9. Electro-optical system, comprising - a liquid crystal layer with negative dielectric anisotropy between 2 substrates, the inner sides of which are provided with electrode layers and overlying orientation layers, the liquid crystal having a homeotropic edge orientation, and - at least one device for linear polarization of the light in such an arrangement, that the light passes through a polarizing device at least once before entering and after leaving the liquid crystal layer, characterized in that the liquid crystal has a twist angle of 0 <ß≤ 90 °.

10. Electro-optical system according to claim 9 and at least one of claims 1, 2 or 5-8.

11.Electro-optical system containing - a twisted nematic liquid crystal layer between 2 substrates, the inner sides of which are provided with electrode layers and overlying orientation layers, the liquid crystal having a homeotropic edge orientation - optionally one or more layers to compensate for the optical path difference of the liquid crystal layer, and - At least one device for linear polarization of the light in such an arrangement that the light before entering the liquid crystal layer and after exiting from it at least once passes a polarization device, characterized in that the liquid crystal has a twist angle 0 ° N≤ ß≤ 100 ° and Improving the viewing angle independence of the contrast an optical path difference d. Δn≤ 0.40 μm.

12. Electro-optical system according to claim 12 and at least one of claims 1, 2, 5, 6, 7 or 8.

13. Projection device comprising a system according to at least one of claims 1-12.

14. compensation layer for compensating the optical path difference of an electro-optical system, which

- A twisted nematic liquid crystal layer between 2 substrates, the inside of which are provided with electrode layers and overlying orientation layers, the liquid crystal having a parallel edge orientation and a twist angle 0 ° ≤ ß≤

600 °, and at least one device for linearly polarizing the light in such an arrangement that the light passes through a polarizing device at least once before entering and after leaving the liquid crystal layer, characterized in that the compensation layer on a material having 3 optical refractive indices ba Sized, one of which is smaller than the other two, the axis corresponding to the smaller refractive index being substantially parallel to the electrode surfaces or forming an angle 2 ° oberfläche ≤ ≤ 60 ° with the electrode surface such that the angle between the optical axes of the compensation layer and the controllable liquid crystal layer passes through a minimum when a voltage is applied, and that the plane spanned by the two other refractive indices forms an angle between 30 ° and 150 ° with the directors of the liquid crystal molecules of the liquid crystal layer on the mutually facing surfaces.