WO1995034843A1 - Electro-optical system - Google Patents

Electro-optical system Download PDF

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Publication number
WO1995034843A1
WO1995034843A1 PCT/EP1995/002096 EP9502096W WO9534843A1 WO 1995034843 A1 WO1995034843 A1 WO 1995034843A1 EP 9502096 W EP9502096 W EP 9502096W WO 9534843 A1 WO9534843 A1 WO 9534843A1
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WO
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Prior art keywords
orientation
liquid crystal
layer
layers
electro
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PCT/EP1995/002096
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German (de)
French (fr)
Inventor
Ulrich Finkenzeller
Edgar Böhm
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Merck Patent Gmbh
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Application filed by Merck Patent Gmbh filed Critical Merck Patent Gmbh
Priority to EP95921812A priority Critical patent/EP0765492A1/en
Publication of WO1995034843A1 publication Critical patent/WO1995034843A1/en

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    • GPHYSICS
    • G02OPTICS
    • G02FOPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333Constructional arrangements; Manufacturing methods
    • G02F1/1337Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
    • G02F1/13378Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by treatment of the surface, e.g. embossing, rubbing or light irradiation
    • G02F1/133788Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by treatment of the surface, e.g. embossing, rubbing or light irradiation by light irradiation, e.g. linearly polarised light photo-polymerisation
    • GPHYSICS
    • G02OPTICS
    • G02FOPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333Constructional arrangements; Manufacturing methods
    • G02F1/1337Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
    • G02F1/133711Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by organic films, e.g. polymeric films
    • GPHYSICS
    • G02OPTICS
    • G02FOPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333Constructional arrangements; Manufacturing methods
    • G02F1/1337Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
    • G02F1/133753Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers with different alignment orientations or pretilt angles on a same surface, e.g. for grey scale or improved viewing angle
    • G02F1/133757Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers with different alignment orientations or pretilt angles on a same surface, e.g. for grey scale or improved viewing angle with different alignment orientations
    • GPHYSICS
    • G02OPTICS
    • G02FOPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333Constructional arrangements; Manufacturing methods
    • G02F1/1337Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
    • G02F1/133765Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers without a surface treatment
    • GPHYSICS
    • G02OPTICS
    • G02FOPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/137Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
    • G02F1/139Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent
    • G02F1/141Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent using ferroelectric liquid crystals

Definitions

  • the invention relates to an electro-optical system containing one
  • Liquid crystal layer between two substrates which are provided with electrode layers and orientation layers arranged above them.
  • Electro-optic liquid crystal systems usually require an edge orientation of the molecules.
  • the electrode layers and possibly other layers such as Color filter layers, insulating layers, compensating layers, etc. provided substrates with an orientation layer which is in direct contact with the liquid crystal layer and forces the liquid crystal molecules on their molecular orientation as a preferred direction.
  • planar also referred to as homogeneous
  • homeotropic orientation whereby the preferred direction can be tilted by an angle of attack or tilt against the substrate plane or against the normal of the substrate plane; in the former case one speaks of tilted-planar orientation, while the latter case is referred to as killed-homeotropic.
  • a further distinction is made between low-tilt and high-tilt orientation.
  • a planar orientation is obtained when the evaporation source forms an angle of approximately 30 ° with the substrate plane; on the other hand, if the SiO evaporation source is arranged at a grazing angle with respect to the substrate plane, a high-tilt orientation layer is formed.
  • the most common method currently used in the industrial production of electro-optic liquid crystal displays is that a thin polymer layer is applied to the substrate, which is then rubbed under pressure using, for example, a cloth or similar materials stretched on a roller, thereby determining the preferred direction and a tilt Angle is induced.
  • Various polymer materials such as polyvinyl alcohol (PVA) or polyimides can be used, the latter being very common due to their good chemical and thermal stability.
  • a polyimide film is applied to the substrate provided with electrode layers and possibly further layers, e.g. by spin coating in a thin layer of e.g. 30-100 nm applied and hardened at 150-250 ° C. Then the layer is
  • Tilted-planar orientation films are obtained with polyimide orientation films, the tilt angle typically being 1-8 ° or more.
  • Homeotropic surface orientations can e.g. can be obtained by coating with polyimides, lecithin or quaternary ammonium compounds; chromium complexes or silane compounds have also been proposed.
  • a tied-homeotropic orientation can e.g. are obtained by rubbing a homeotropic orientation layer or by applying surface-active substances to a planar-poised orientation layer.
  • oriented photopolymer coatings as orientation layers, these generally inducing a planar or Iow-tilt orientation.
  • photopolymers such as poly (vinyl-4-methoxycinnamate) are applied to a substrate provided with an electrode and then irradiated with linearly polarized light.
  • oriented photopolymer coatings Schadt et al.
  • a hybrid liquid crystal display which has pixels with different twist values of the liquid crystal.
  • the object of the present invention was therefore to specify new orientation layers and thus to enlarge the range of orientation layers available to the person skilled in the art.
  • the present invention was also based on the object of specifying new electro-optical liquid crystal systems which contain such orientation layers. Other objects of the present invention will be apparent to those skilled in the art from the detailed description below.
  • the invention relates to a method for producing multidirectional, ie two or more preferred orientation layers, which is characterized in that a photocurable precursor of the orientation layer is applied to a substrate and subsequently subjected to linearly polarized light at 2 or more different azimuth angles ⁇ . The exposure can take place alternately at the corresponding azimuth angles or at the same time when light is irradiated with two or more preferred directions of linear polarization.
  • the invention further relates multidirectional orientation layers and electro-optic liquid crystal systems, containing a liquid crystal layer between 2 substrates, which are provided with electrodes and orientation layers arranged above them, at least one of the orientation layers being multidirectionally oriented.
  • the precursor of the photocurable orientation layer is applied to a substrate.
  • the substrate preferably has a flat surface and can be made of various materials such as e.g. Metal, glass, quartz glass or plastic exist, with transparent substrates being preferred. Substrates coated with electrodes are particularly preferred, the
  • Electrode coatings can consist, for example, of structured or unstructured tin oxide or indium tin oxide (ITO) and, in particular, can also have active switching elements such as TFTs (thin film transistors) or MIMs (metal insulator metal).
  • the substrates coated with electrodes and subsequently provided with multidirectional orientation layers can be used for the production of electro-optical liquid crystal elements which can be controlled statically, passively, actively or also according to the so-called in-plane switching method (DE 40 00451).
  • the substrates can also have further coatings, such as, for example, color filter coatings, separator layers which act as diffusion barriers, the order of these coatings being largely free to choose.
  • the precursor of the photocurable orientation layer contains one or more photopolymers or oligomers which are essentially linear and whose degree of polymerization is preferably at least 5, in particular at least 10 and very particularly at least 20.
  • photopolymers or oligomers denotes photoreactive
  • crosslinking reaction can be carried out in various ways. So it is e.g. possible that the precursor of the orientation layer in addition to substantially linear photo oligomers and / or
  • -polymeric, bifunctional, photoreactive additives such as Contains bisazide.
  • An example is the reaction of polydienes with 4-alkyl-2,5-bis (p-azidobenzal) cyclohexanone, which has a maximum absorption at 365 nm.
  • the crosslinking reaction can further be based on the linking of photopolymerizable groups which are contained in the essentially linear photooligomers and / or polymers of the precursor of the orientation layer.
  • the photopolymerizable groups can be used both in the essentially linear photo-oligomers or polymers of the precursor of the orientation layer (main chain connections) or also in side groups which are attached laterally to the essentially linear photo oligomers or polymers (side chain connections).
  • photopolymerizable compounds which contain photopolymerizable groups in the main and side chain linkage.
  • the polymer backbone of the photopolymerizable side chain compounds is preferably based on C-C main chains, it being possible in particular to use poly or oligovinyls and poly- or oligoacrylates and their derivatives. Also preferred are polymers or oligomers with heteroatoms in the main chain, for example poly- or oligoethers, esters, amides, imides, urethanes and siloxanes. Photopolymerizable groups PPG are attached to the polymer backbone - (P) - directly or via a spacer Sp.
  • the spacer groups Sp and the photopolymerizable groups PPG can influence the distance between adjacent preferred lines in the hardened orientation layer.
  • the distance between adjacent preferred lines can be influenced by the structure of the crosslinker molecule.
  • the photooligomer and / or polymer of the precursor of the orientation layer are preferably in a solvent such as e.g. Dissolved methylene chloride, chlorobenzene, toluene or other solvents, optionally a crosslinker component and / or also others
  • a solvent such as e.g. Dissolved methylene chloride, chlorobenzene, toluene or other solvents, optionally a crosslinker component and / or also others
  • Additives such as Adhesion promoter can be added. It is also possible to mix the components of the precursor with one another without the addition of a solvent, if appropriate with gentle heating.
  • the precursor is then applied to the optionally precoated substrate e.g. applied by knife coating and in particular by spin coating. Then the solvent component is preferably heated by heating to temperatures e.g. 50-100 ° C removed.
  • the thickness of the precursor layer is between 20 and 300 and preferably between 40 and 100 nm.
  • the precursor layer is then irradiated with linearly polarized light, preferably using monochromatic light which is matched to the maximum absorption wavelength of the photopolymerizable group or compound.
  • the precursor is irradiated with linearly polarized light at different azimuth angles ⁇ .
  • the angle crest of a second irradiation direction in relation to a first irradiation direction is the angle in the substrate plane which results when the radiation sources are each connected to the mean normal of the substrate. Irradiation with linearly polarized light at different angles ⁇ can take place both simultaneously and in succession, but preferably simultaneously.
  • a plurality of continuous lines of preference are produced, which extend over the entire display without further structuring, while that of Schadt et al. in Jpn. J. Appl. Phys. 31 (1992) 2155 proposed masking technique for generating pixels with different twist.
  • the radiation power assigned to the individual radiation directions can be selected both simultaneously and differently, as a result of which the relative proportion of the different preferred directions in the orientation layer can be varied.
  • the irradiation power is typically between 5 and 50 mW / cm 2 , although deviations from these values are also possible.
  • the irradiation time is generally between 1 min or less and 60 min, in particular between 1-5 min, although deviations from these values are also possible here.
  • the arrangement of the linearly polarized light sources with respect to the substrate plane which is indicated by the height angle ⁇ (angle between the substrate plane and the light source connecting line and the intersection of the normal to the substrate plane), is not very critical and in a further range, for example between 10 and 90 ° (0 ° corresponds to grazing light).
  • the pretilt angle of the orientation layers according to the invention which is typically between 0 ° and 5 °, can only be influenced insignificantly by the variation in the height angle ⁇ .
  • the stability of the hardened orientation layers can generally be improved if the precursor of the orientation layer applied to the substrate before exposure to linearly polarized light and / or after exposure to linearly polarized light, with unpolarized light (power e.g. 500-5000 mW / cm 2 ) is irradiated.
  • a final heat treatment of the orientation layer at temperatures between 50 and 120 ° C. and a treatment time between 15 and a few hours is generally advantageous.
  • the multidirectional orientation layers according to the invention preferably have 2-15, in particular 2-8, particularly preferably at least 2 and very particularly at least 3 preferred directions.
  • orientation layers according to the invention are preferably used for the production of liquid crystal displays. However, applications are also possible in micro-optics, integrated optics, in connection with optical sensors and elsewhere.
  • the orientation layers according to the invention can be used particularly preferably for the production of ferroelectric liquid crystal displays according to the SSFLC principle specified by Lagerwall.
  • the liquid crystal layer has an SmC * phase, as a result of which the liquid crystal molecules have a tilt angle of + ⁇ or - ⁇ on the substrate surfaces.
  • This surface-induced orientation of the liquid crystal molecules continues due to the very small thickness of the liquid crystal layer of typically less than 3 ⁇ m through the entire liquid crystal layer, and the liquid crystal can be switched between 2 bistable states with + ⁇ and - ⁇ ("bookshelf geometry"). It has been found that the stability of the two switching states can be increased if the substrates have bidirectional orientation layers, the two preferred directions of which have been obtained by irradiation with 2 linearly polarized light sources which are mutually opposite
  • liquid crystal displays with orientation layers according to the invention which contain nematic or cholesteric liquid crystals.
  • a twisted nematic cell which contains a doped liquid crystal is particularly preferred, the pitch length of the liquid crystal being highly temperature-dependent.
  • the substrate plates have a multidirectional orientation and force the liquid crystal at a certain temperature as a function of the doping to a certain twist value. If the temperature changes, the pitch length of the liquid crystal changes and the twist jumps discretely if an energetically preferred twist state is defined for the changed pitch length p (T) by the orientation layers.
  • the change in the twist causes a change in transmission, so that the arrangement works as a discrete thermometer. It represents one without the inventive for the expert
  • Routine task to be solved is to adapt the preferred directions of the multidirectional orientation layers, the total concentration of the dopant and its temperature dependency so that a desired temperature display, e.g. the display of 10 K jumps results.
  • the orientation layers according to the invention are preferably used for the production of liquid crystal displays, whereby they enable the improvement of conventional displays and also the realization of completely new displays.
  • the orientation layers according to the invention are therefore of considerable economic importance.

Abstract

A process is disclosed for producing multidirectional orientation layers. A photo-curable precursor of the orientation layer that contains one or several substantially linear photopolymers and/or photo-oligomers is applied on a substrate then exposed to linearly polarised light under 2 or more different azimuth angles Ø. Also disclosed are multidirectional orientation layers produced by this process.

Description

Elektrooptisches System  Electro-optical system
Die Erfindung betrifft ein elektrooptisches System, enthaltend eine The invention relates to an electro-optical system containing one
Flüssigkristallschicht zwischen zwei Substraten, welche mit Elektroden- und darüber angeordneten Orientierungsschichten versehen sind. Liquid crystal layer between two substrates, which are provided with electrode layers and orientation layers arranged above them.
Elektrooptische Flü ss ig kri stallsysteme erfordern üblicherweise eine Randorientierung der Moleküle. Hierzu wird auf die mit Elektrodenschichten und ggf. weiteren Schichten wie z.B. Farbfilterschichten, Isolierschichten, Ausgleichsschichten usw. versehenen Substrate eine Orientierungsschicht aufgebracht, die direkt mit der Flüssigkristallschicht in Kontakt steht und den Flüssigkristallmolekülen ihre molekulare Orientierung als Vorzugsrichtung aufzwingt. Man kann unterscheiden zwischen planarer (auch als homogen bezeichneter) und homeotroper Orientierung, wobei die Vorzugsrichtung um einen Anstell- oder Tiltwinkel gegen die Substratebene bzw. gegen die Normale der Substratebene verkippt (getutet) sein kann; im ersteren Fall spricht man von getiltet-planarer Orientierung, während man den letzteren Fall als getiitet-homeotrop bezeichnet. Je nach Größe des Verkippungswinkels unterscheidet man weiter zwischen low-tilt- und high-tilt-Orientierung. Electro-optic liquid crystal systems usually require an edge orientation of the molecules. For this purpose, the electrode layers and possibly other layers such as Color filter layers, insulating layers, compensating layers, etc. provided substrates with an orientation layer which is in direct contact with the liquid crystal layer and forces the liquid crystal molecules on their molecular orientation as a preferred direction. One can differentiate between planar (also referred to as homogeneous) and homeotropic orientation, whereby the preferred direction can be tilted by an angle of attack or tilt against the substrate plane or against the normal of the substrate plane; in the former case one speaks of tilted-planar orientation, while the latter case is referred to as killed-homeotropic. Depending on the size of the tilt angle, a further distinction is made between low-tilt and high-tilt orientation.
Zur Erzeugung der Orientierungsschichten sind sowohl anorganische als auch organische Materialien vorgeschlagen worden. Both inorganic and organic materials have been proposed for producing the orientation layers.
So ist es z.B. möglich, getiltet-planare Orientierungsschichten durch Bedampfen des Substrates mit SiO in einer Vakuumkammer zu erzeugen. Dabei wird eine planare Orientierung erhalten, wenn die Verdampfungs- quelle einen Winkel von etwa 30° mit der Substratebene bildet; wenn die SiO-Verdampfungsquelle hingegen unter einem streifenden Winkel bezüglich der Substratebene angeordnet ist, kommt es dagegen zur Ausbildung einer high-tilt-Orientierungsschicht. Die bei der industriellen Fertigung von elektrooptischen Flüssigkristalldisplays z.Z. gebräuchlichste Methode besteht darin, daß auf das Substrat eine dünne Polymerschicht aufgebracht wird, die anschließend unter Druckanwendung z.B. mit einem auf einer Walze aufgespannten Tuch oder ähnlichen Materialien gerieben wird, wodurch die Vorzugsrichtung festgelegt und ein Tilt-Winkel induziert wird. Es können verschiedene Polymermaterialien wie z.B. Polyvinylalkohol (PVA) oder Polyimide verwendet werden, wobei letztere wegen ihrer guten chemischen und thermischen Stabilität sehr gebräuchlich sind. For example, it is possible to produce tilted-planar orientation layers by vapor-depositing the substrate with SiO in a vacuum chamber. A planar orientation is obtained when the evaporation source forms an angle of approximately 30 ° with the substrate plane; on the other hand, if the SiO evaporation source is arranged at a grazing angle with respect to the substrate plane, a high-tilt orientation layer is formed. The most common method currently used in the industrial production of electro-optic liquid crystal displays is that a thin polymer layer is applied to the substrate, which is then rubbed under pressure using, for example, a cloth or similar materials stretched on a roller, thereby determining the preferred direction and a tilt Angle is induced. Various polymer materials such as polyvinyl alcohol (PVA) or polyimides can be used, the latter being very common due to their good chemical and thermal stability.
Bei einem typischen Verfahren wird ein Polyimidfilm auf das mit Elektrodenschichten und ggf. weiteren Schichten versehene Substrat z.B. durch Spin-Coating in einer dünnen Schicht von z.B. 30-100 nm aufgebracht und bei 150-250 °C gehärtet. Dann wird die Schicht ggf. In a typical process, a polyimide film is applied to the substrate provided with electrode layers and possibly further layers, e.g. by spin coating in a thin layer of e.g. 30-100 nm applied and hardened at 150-250 ° C. Then the layer is
wiederholt in dieselbe Richtung mit einem Baumwolltuch o.a. bei einem Andruck von z.B. 5-25 kg/cm2 gerieben. repeatedly rubbed in the same direction with a cotton cloth or similar with a pressure of 5-25 kg / cm 2 .
Mit Polyimid-Orientierungsfilmen werden getiltet-planare Orientierungsfilme erhalten, wobei der Tiltwinkel typischerweise 1-8° oder mehr beträgt. Tilted-planar orientation films are obtained with polyimide orientation films, the tilt angle typically being 1-8 ° or more.
Homeotrope Oberflächenorientierungen können z.B. durch Beschichten mit Polyimiden, Lecithin oder quarternären Ammoniumverbindungen erhalten werden; weiterhin sind auch Chrom-Komplexe oder Silanverbindungen vorgeschlagen worden. Eine getittet-homeotrope Orientierung kann z.B. erhalten werden durch Reiben einer homeotropen Orientierungsschicht oder durch Aufbringen oberflächenaktiver Substanzen auf eine planar-getiftete Orientierungsschicht. Homeotropic surface orientations can e.g. can be obtained by coating with polyimides, lecithin or quaternary ammonium compounds; chromium complexes or silane compounds have also been proposed. A tied-homeotropic orientation can e.g. are obtained by rubbing a homeotropic orientation layer or by applying surface-active substances to a planar-poised orientation layer.
Schadt et al. schlagen in Jpn. J. Appl. Phys, 31 (1992) 2155 vor, orientierte Photopolymerbeschichtungen als Orientierungsschichten zu verwenden, wobei diese i.a. eine planare oder Iow-tilt-Orientierung induzieren. Zur Herstellung der orientierten Photopolymerbeschichtungen werden Photopolymere wie z.B. Poly(vinyl-4-methoxycinnamat) auf ein mit einer Elektrode versehenes Substrat aufgebracht und anschließend mit linear polarisiertem Licht bestrahlt. Als Anwendung orientierter Photopolymerbeschichtungen wird von Schadt et al. u.a. ein Hybridflüssigkristalldisplay vorgeschlagen, welches Pixel mit unterschiedlichen Twist-Werten des Flüssigkristalls aufweist. Diese Hybriddisplays werden durch Anwendung einer Maskentechnik unter Änderung der Polarisationsrichtung des zur Härtung des photopolymerisierbaren Materials verwendeten linear-polarisierten Lichts erhalten. Schadt et al. beat in Jpn. J. Appl. Phys, 31 (1992) 2155 propose to use oriented photopolymer coatings as orientation layers, these generally inducing a planar or Iow-tilt orientation. To produce the oriented photopolymer coatings, photopolymers such as poly (vinyl-4-methoxycinnamate) are applied to a substrate provided with an electrode and then irradiated with linearly polarized light. As an application of oriented photopolymer coatings, Schadt et al. Among other things, a hybrid liquid crystal display is proposed which has pixels with different twist values of the liquid crystal. These hybrid displays are obtained by using a mask technique changing the direction of polarization of the linearly polarized light used to cure the photopolymerizable material.
Die bisher in der Literatur beschriebenen Orientierungsschichten erfüllen die sehr unterschiedlichen Anforderungen, die bei deren Verwendung in elektrooptischen Flüssigkristalldisplays gestellt werden, nicht immer in befriedigendem Umfang. The orientation layers described so far in the literature do not always meet the very different requirements that are placed on their use in electro-optical liquid crystal displays to a satisfactory extent.
Der vorliegenden Erfindung lag daher die Aufgabe zugrunde, neue Orientierungsschichten anzugeben und damit die Palette der dem Fachmann verfügbaren Orientierungsschichten zu vergrößern. Weiterhin lag der vorliegenden Erfindung die Aufgabe zugrunde, neue elektrooptische Flüssigkristallsysteme anzugeben, welche derartige Orientierungsschichten entharten. Weitere Aufgaben der vorliegenden Erfindung entnimmt der Fachmann der nachfolgenden detaillierten Beschreibung. The object of the present invention was therefore to specify new orientation layers and thus to enlarge the range of orientation layers available to the person skilled in the art. The present invention was also based on the object of specifying new electro-optical liquid crystal systems which contain such orientation layers. Other objects of the present invention will be apparent to those skilled in the art from the detailed description below.
Es wurde gefunden, daß diese Aufgaben durch die Bereitstellung der erfindungsgemäßen Orientierungsschichten sowie der erfindungsgemäßen elektrooptischen Flüssigkristallsysteme, welche derartige Orientierungsschichten enthalten, gelöst werden. It has been found that these objects are achieved by providing the orientation layers according to the invention and the electro-optic liquid crystal systems according to the invention which contain such orientation layers.
Gegenstand der Erfindung ist ein Verfahren zur Herstellung multidirektionaler, d.h. zwei oder mehr Vorzugsrichtungen aufweisender Orientierungsschichten, welches dadurch gekennzeichnet ist, daß ein photohärtbarer Precursor der Orientierungsschicht auf ein Substrat aufgebracht und nachfolgend mit linear polarisiertem Licht unter 2 oder mehr verschiedenen Azimutwinkeln Φ beaufschlagt wird. Dabei kann die Belichtung alternierend bei den entsprechenden Azimutwinkeln oder auch zeitgleich bei Einstrahlung von Licht mit zwei oder mehr Vorzugsrichtungen der linearen Polarisation erfolgen. Gegenstand der Erfindung sind weiter multidirektionale Orientierungsschichten sowie elektrooptische Flüssigkristallsysteme, enthaltend eine Flüssigkristallschicht zwischen 2 Substraten, welche mit Elektroden- und darüber angeordneten Orientierungsschichten versehen sind, wobei zumindest eine der Orientierungsschichten multidirektional orientiert ist. The invention relates to a method for producing multidirectional, ie two or more preferred orientation layers, which is characterized in that a photocurable precursor of the orientation layer is applied to a substrate and subsequently subjected to linearly polarized light at 2 or more different azimuth angles Φ. The exposure can take place alternately at the corresponding azimuth angles or at the same time when light is irradiated with two or more preferred directions of linear polarization. The invention further relates multidirectional orientation layers and electro-optic liquid crystal systems, containing a liquid crystal layer between 2 substrates, which are provided with electrodes and orientation layers arranged above them, at least one of the orientation layers being multidirectionally oriented.
Zur Erzeugung der multidirektionalen Orientierungsschicht wird der Precursor der photohärtbaren Orientierungsschicht auf ein Substrat aufgebracht. To produce the multidirectional orientation layer, the precursor of the photocurable orientation layer is applied to a substrate.
Das Substrat hat vorzugsweise eine ebene Oberfläche und kann aus verschiedenen Materialien wie z.B. Metall, Glas, Quarzglas oder Kunststoff bestehen, wobei transparente Substrate bevorzugt sind. Besonders bevorzugt sind mit Elektroden beschichtete Substrate, wobei die The substrate preferably has a flat surface and can be made of various materials such as e.g. Metal, glass, quartz glass or plastic exist, with transparent substrates being preferred. Substrates coated with electrodes are particularly preferred, the
Elektrodenbeschichtungen z.B. aus strukturiertem oder unstrukturiertem Zinnoxid oder Indium-Zinnoxid (ITO) bestehen können und insbesondere auch aktive Schaltelemente wie z.B. TFTs (thin film transistor) oder MIM's (metal-insulator-metal) aufweisen können. Die mit Elektroden beschichteten und nachfolgend mit multidirektionalen Orientierungsschichten versehenen Substrate können zur Herstellung elektrooptischer Flüssigkristallelemente verwendet werden, welche statisch, passiv, aktiv oder auch nach dem sogenannten In-plane switching-Verfahren (DE 40 00451 ) angesteuert werden können. Die Substrate können neben der multidirektionalen Orientierungsschicht und der Elektrodenschicht auch noch weitere Beschichtungen wie z.B. Farbfilterbeschichtungen, als Diffusionsbarrieren wirkende Separatorschichten etc. aufweisen, wobei die Reihenfolge dieser Beschichtungen weitgehend frei gewählt werden kann. Lediglich die multidirektionale Orientierungsschicht bildet in aller Regel die äußerste Schicht, die dann in dem elektrooptischen Flüssigkristalldisplay direkt mit dem zu orientierenden Flüssigkristall in Kontakt steht. Der Precursor der photohärtbaren Orientierungsschicht enthält eine oder mehrere Photopolymere oder -oligomere, welche im wesentlichen linear sind und deren Polymerisationsgrad vorzugsweise mindestens 5, insbesondere mindestens 10 und ganz besonders mindestens 20 beträgt. Der Begriff Photopolymere oder -oligomere bezeichnet photoreaktiveElectrode coatings can consist, for example, of structured or unstructured tin oxide or indium tin oxide (ITO) and, in particular, can also have active switching elements such as TFTs (thin film transistors) or MIMs (metal insulator metal). The substrates coated with electrodes and subsequently provided with multidirectional orientation layers can be used for the production of electro-optical liquid crystal elements which can be controlled statically, passively, actively or also according to the so-called in-plane switching method (DE 40 00451). In addition to the multidirectional orientation layer and the electrode layer, the substrates can also have further coatings, such as, for example, color filter coatings, separator layers which act as diffusion barriers, the order of these coatings being largely free to choose. Only the multidirectional orientation layer generally forms the outermost layer, which is then in direct contact with the liquid crystal to be oriented in the electro-optical liquid crystal display. The precursor of the photocurable orientation layer contains one or more photopolymers or oligomers which are essentially linear and whose degree of polymerization is preferably at least 5, in particular at least 10 and very particularly at least 20. The term photopolymers or oligomers denotes photoreactive
Verbindungen, wobei diese die photoreaktive Gruppe entweder selbst enthalten oder aber mit photoreaktiven Zusätzen wie z. B. photoreaktiven Vernetzern reagieren. Die Forderung, daß die photopolyrnerisierbaren Oligomere oder Polymere eine im wesentlichen lineare Struktur aufweisen sollen, rührt daher, daß die multidirektionalen Orientierungsschichten 2 oder mehr eindimensionale Vorzugsrichtungen aufweisen, die den stäbchenförmigen Flüssigkristallmolekülen eine Vorzugsrichtung aufzwingen. Bei Verwendung von im wesentlichen linearen Photooligomeren oder -polymeren ist die spätere Struktur der multidirektionalen Orientierungsschicht im Precursor schon vorgebildet. Durch die Bestrahlung mit linear polarisiertem Licht wird eine gerichtete Crosslinking-Reaktion induziert, wodurch die Photooligomere oder -polymere unter einer im wesentlichen parallelen Orientierung miteinander verknüpft werden. Dadurch wird ein mikroskopisches Array von eindimensionalen, parallelen Vorzugsrichtungen erzeugt, welches zur Randorientierung der Flüssigkristallmoleküle dient. Compounds, which either contain the photoreactive group itself or with photoreactive additives such. B. react photoreactive crosslinkers. The requirement that the photopolymerizable oligomers or polymers should have an essentially linear structure arises from the fact that the multidirectional orientation layers have 2 or more one-dimensional preferred directions which impose a preferred direction on the rod-shaped liquid crystal molecules. When using essentially linear photooligomers or polymers, the later structure of the multidirectional orientation layer is already pre-formed in the precursor. Irradiation with linearly polarized light induces a directional crosslinking reaction, as a result of which the photooligomers or polymers are linked to one another with an essentially parallel orientation. This creates a microscopic array of one-dimensional, parallel preferred directions, which is used for the edge orientation of the liquid crystal molecules.
Die Crosslinking-Reaktion kann auf verschiedene Weise durchgeführt werden. So ist es z.B. möglich, daß der Precursor der Orientierungsschicht neben im wesentlichen linearen Photooligomeren und/oder The crosslinking reaction can be carried out in various ways. So it is e.g. possible that the precursor of the orientation layer in addition to substantially linear photo oligomers and / or
-polymeren bifunktionelle, photoreaktive Zusätze wie z.B. Bisazide enthält. Als Beispiel sei die Umsetzung von Polydienen mit 4-alkyl-2,5-bis(p-azidobenzal)cyclohexanon genannt, welches eine maximale Absorption bei 365 nm aufweist. -polymeric, bifunctional, photoreactive additives such as Contains bisazide. An example is the reaction of polydienes with 4-alkyl-2,5-bis (p-azidobenzal) cyclohexanone, which has a maximum absorption at 365 nm.
Die Crosslinking-Reaktion kann weiter auf der Verknüpfung photopolymerisierbarer Gruppen beruhen, welche in den im wesentlichen linearen Photooligomeren und/oder -polymeren des Precursors der Orientierungsschicht enthalten sind. Dabei können die photopolyrnerisierbaren Gruppen sowohl in den im wesentlichen linearen Photooligomeren oder -polymeren des Precursors der Qrientierungsschicht angeordnet sein (Hauptkettenverbindungen) oder sich aber auch in Seitengruppen befinden, welche seitlich an die im wesentlichen linearen Photooligomere oder -polymere angeheftet sind (Seitenkettenverbindungen). Daneben können natürlich auch photopolymerisierbare Verbindungen verwendet werden, welche photopolymerisierbare Gruppen in Haupt- und Seitenkettenverknüpfung enthalten. The crosslinking reaction can further be based on the linking of photopolymerizable groups which are contained in the essentially linear photooligomers and / or polymers of the precursor of the orientation layer. The photopolymerizable groups can be used both in the essentially linear photo-oligomers or polymers of the precursor of the orientation layer (main chain connections) or also in side groups which are attached laterally to the essentially linear photo oligomers or polymers (side chain connections). In addition, it is of course also possible to use photopolymerizable compounds which contain photopolymerizable groups in the main and side chain linkage.
Besonders bevorzugt sind Seitenkettenverbindungen, bei denen benachbarte Photopolymere und/oder -oligomere über in den Seitengruppen befindliche photopolymerisierbare Gruppen verknüpft werden. Side chain compounds in which adjacent photopolymers and / or oligomers are linked via photopolymerizable groups located in the side groups are particularly preferred.
Das Polymerrückgrat der photopolyrnerisierbaren Seitenkettenverbindungen basiert vorzugsweise auf C-C-Hauptketten, wobei insbesondere Polyoder Oligovinyle und Poly- oder Oligoacrylate sowie deren Derivate eingesetzt werden können. Weiterhin bevorzugt sind auch Polymere bzw. Oligomere mit Heteroatomen in der Hauptkette, beispielsweise Poly- oder Oligoether, -ester, -amide, -imide, -urethane sowie -siloxane. An das Polymerrückgrat -(P)- sind photopolymerisierbare Gruppen PPG direkt oder über einen Spacer Sp angehängt. Schematisch: The polymer backbone of the photopolymerizable side chain compounds is preferably based on C-C main chains, it being possible in particular to use poly or oligovinyls and poly- or oligoacrylates and their derivatives. Also preferred are polymers or oligomers with heteroatoms in the main chain, for example poly- or oligoethers, esters, amides, imides, urethanes and siloxanes. Photopolymerizable groups PPG are attached to the polymer backbone - (P) - directly or via a spacer Sp. Schematic:
Figure imgf000008_0001
Figure imgf000008_0001
Beispiele für bevorzugte PPG's sind in der folgenden Übersicht 1 aufgeführt.
Figure imgf000009_0001
Figure imgf000010_0001
Examples of preferred PPGs are listed in the following overview 1.
Figure imgf000009_0001
Figure imgf000010_0001
In der folgenden Übersicht 2 sind bevorzugte Beispiele für Polymer- rückgrate -(P)- bzw. Gruppierungen -(P)-Sp- angegeben, wobei für PPG insbesondere die oben angegebenen Strukturen einzusetzen sind.
Figure imgf000011_0001
Vorstehender Übersicht 2 sind auch einige Beispiele für geeignete
The following overview 2 shows preferred examples of polymer backbones - (P) - or groupings - (P) -Sp-, the structures specified above being used in particular for PPG.
Figure imgf000011_0001
Overview 2 above is also a few examples of suitable ones
Spacer-Gruppen Sp zu entnehmen. To take spacer groups Sp.
Durch die Spacer-Gruppen Sp und die photopolyrnerisierbaren Gruppen PPG kann der Abstand zwischen benachbarten Vorzugslinien in der gehärteten Orientierungsschicht beeinflußt werden. Bei der oben angegebenen Verknüpfung benachbarter Oligomer- bzw. Polymerverbindungen durch den Zusatz bifunktioneller Agentien (Vernetzer) kann der Abstand benachbarter Vorzugslinien durch die Struktur des Vernetzermoleküls beeinflußt werden. The spacer groups Sp and the photopolymerizable groups PPG can influence the distance between adjacent preferred lines in the hardened orientation layer. When linking adjacent oligomer or polymer compounds by adding bifunctional agents (crosslinkers), the distance between adjacent preferred lines can be influenced by the structure of the crosslinker molecule.
Die angegebenen Strukturen sind nur beispielhaft zu verstehen und sollen die Erfindung lediglich erläutern, ohne sie zu begrenzen. Der Fachmann kann leicht weitere zur Erzeugung linearer, in einem günstigen Abstand angeordneter Vorzugsrichtungen geeignete Verbindungen angeben. The structures given are only to be understood as examples and are only intended to explain the invention without limiting it. The person skilled in the art can easily specify further connections suitable for generating linear preferred directions arranged at a favorable distance.
Die Photooligomer- und/oder polymere des Precursors der Orientierungsschicht werden vorzugsweise in einem Lösungsmittel wie z.B. Methylenchlorid, Chlorbenzol, Toluol oder anderen Lösungsmitteln gelöst, wobei gegebenenfalls eine Vernetzerkomponente und/oder auch weitere The photooligomer and / or polymer of the precursor of the orientation layer are preferably in a solvent such as e.g. Dissolved methylene chloride, chlorobenzene, toluene or other solvents, optionally a crosslinker component and / or also others
Zusätze wie z.B. Haftvermittler beigegeben werden können. Es ist auch möglich, die Komponenten des Precursors ohne Zusatz eines Lösungsmittels, gegebenenfalls unter leichter Erwärmung miteinander zu mischen. Der Precursor wird anschließend auf das gegebenenfalls vorbeschichtete Substrat z.B. durch Rakeln und insbesondere durch Spin-Coating aufgebracht. Anschließend wird die Lösungsmittelkomponente vorzugsweise durch Erwärmen auf Temperaturen von z.B. 50-100 °C entfernt. Die Dicke der Precursor-Schicht beträgt zwischen 20 und 300 und vorzugsweise zwischen 40 und 100 nm.  Additives such as Adhesion promoter can be added. It is also possible to mix the components of the precursor with one another without the addition of a solvent, if appropriate with gentle heating. The precursor is then applied to the optionally precoated substrate e.g. applied by knife coating and in particular by spin coating. Then the solvent component is preferably heated by heating to temperatures e.g. 50-100 ° C removed. The thickness of the precursor layer is between 20 and 300 and preferably between 40 and 100 nm.
Danach wird die Precursor-Schicht mit linear polarisiertem Licht bestrahlt, wobei vorzugsweise monochromatisches Licht verwendet wird, welches an die maximale Absorptionswellenlänge der photopolyrnerisierbaren Gruppe bzw. Verbindung angepaßt ist. Zur Erzeugung der multidirektionalen Struktur der Orientierungsschicht wird der Precursor mit linear polarisiertem Licht unter verschiedenen Azimutwinkeln Φ bestrahlt. Dabei ist der Winkel Φ einer zweiten Beslrahlungsrichtung bezogen auf eine erste Bestrahlungsrichtung der Winkel in der Substratebene, der sich ergibt, wenn die Bestrahlungsquellen jeweils mit der Mittelnormale des Substrates verbunden werden. Die Bestrahlung mit linear polarisiertem Licht unter verschiedenen Winkeln Φ kann sowohl gleichzeitig als auch nacheinander, vorzugsweise jedoch gleichzeitig erfolgen. Durch das erfindungsgemäße Verfahren werden mehrere kontinuierliehe Vorzugslinien erzeugt, die sich ohne weitere Strukturierung über das ganze Display erstrecken, während die von Schadt et al. in Jpn. J. Appl. Phys. 31 (1992) 2155 vorgeschlagene Maskentechnik zur Erzeugung von Pixeln mit verschiedenem Twist führte. Die den einzelnen Bestrahlungsrichtungen zugeordnete Bestrahlungsleistung kann sowohl gleichzeitig als auch verschieden gewählt werden, wodurch der relative Anteil der verschiedenen Vorzugsrichtungen an der Orientierungsschicht variiert werden kann. Die Bestrahlungsleistung beträgt typischerweise zwischen 5 und 50 mW/cm2, wobei jedoch auch Abweichungen von diesen Werten möglich sind. Die Bestrahlungsdauer beträgt in der Regel zwischen 1 min oder weniger und 60 min, insbesondere zwischen 1-5 min, wobei jedoch auch hier Abweichungen von diesen Werten möglich sind. Es wurde gefunden, daß die Anordnung der linear polarisierten Lichtquellen bezüglich der Substratebene, welche durch den Höhenwinkel Θ angegeben wird (Winkel zwischen Substratebene und Verbindungslinie Lichtquelle und Schnittpunkt der Mittelnormalen mit der Substratebene), nicht sehr kritisch ist und in einem weiteren Bereich z.B. zwischen 10 und 90° (0° entspricht streifendem Lichteinfall) variiert werden kann. Auch der Pretiltwinkel der erfindungsgemäßen Orientierungsschichten, der typischerweise zwischen 0° und 5° liegt, kann durch die Variation des Höhenwinkels Θ nur unwesentlich beeinflußt werden. Es wurde weiter gefunden, daß die Stabilität der gehärteten Orientierungsschichten in der Regel verbessert werden kann, wenn der auf das Substrat aufgebrachte Precursor der Orientierungsschicht vor der Beaufschlagung mit linear polarisiertem Licht und/oder nach der Beaufschlagung mit linear polarisiertem Licht, mit unpolarisiertem Licht (Leistung z.B. 500-5000 mW/ cm2) bestrahlt wird. Auch eine abschließende Wärmebehandlung der Orientierungsschicht bei Temperaturen zwischen 50 und 120 °C und einer Behandlungsdauer zwischen 15 und einigen h ist i.a. vorteilhaft. Die erfindungsgemäßen multidirektionalen Orientierungsschichten weisen vorzugsweise 2-15, insbesondere 2-8, besonders bevorzugt mindestens 2 und ganz besonders mindestens 3 Vorzugsrichtungen auf. The precursor layer is then irradiated with linearly polarized light, preferably using monochromatic light which is matched to the maximum absorption wavelength of the photopolymerizable group or compound. To generate the multidirectional structure of the orientation layer, the precursor is irradiated with linearly polarized light at different azimuth angles Φ. In this case, the angle zweiten of a second irradiation direction in relation to a first irradiation direction is the angle in the substrate plane which results when the radiation sources are each connected to the mean normal of the substrate. Irradiation with linearly polarized light at different angles Φ can take place both simultaneously and in succession, but preferably simultaneously. By means of the method according to the invention, a plurality of continuous lines of preference are produced, which extend over the entire display without further structuring, while that of Schadt et al. in Jpn. J. Appl. Phys. 31 (1992) 2155 proposed masking technique for generating pixels with different twist. The radiation power assigned to the individual radiation directions can be selected both simultaneously and differently, as a result of which the relative proportion of the different preferred directions in the orientation layer can be varied. The irradiation power is typically between 5 and 50 mW / cm 2 , although deviations from these values are also possible. The irradiation time is generally between 1 min or less and 60 min, in particular between 1-5 min, although deviations from these values are also possible here. It was found that the arrangement of the linearly polarized light sources with respect to the substrate plane, which is indicated by the height angle Θ (angle between the substrate plane and the light source connecting line and the intersection of the normal to the substrate plane), is not very critical and in a further range, for example between 10 and 90 ° (0 ° corresponds to grazing light). The pretilt angle of the orientation layers according to the invention, which is typically between 0 ° and 5 °, can only be influenced insignificantly by the variation in the height angle Θ. It has also been found that the stability of the hardened orientation layers can generally be improved if the precursor of the orientation layer applied to the substrate before exposure to linearly polarized light and / or after exposure to linearly polarized light, with unpolarized light (power e.g. 500-5000 mW / cm 2 ) is irradiated. A final heat treatment of the orientation layer at temperatures between 50 and 120 ° C. and a treatment time between 15 and a few hours is generally advantageous. The multidirectional orientation layers according to the invention preferably have 2-15, in particular 2-8, particularly preferably at least 2 and very particularly at least 3 preferred directions.
Die erfindungsgemäßen Orientierungsschichten werden bevorzugt zur Herstellung von Flüssigkristalldisplays verwendet. Anwendungen sind jedoch auch in der Mikrooptik, integrierten Optik, im Zusammenhang mit optischen Sensoren und an anderer Stelle möglich. The orientation layers according to the invention are preferably used for the production of liquid crystal displays. However, applications are also possible in micro-optics, integrated optics, in connection with optical sensors and elsewhere.
Besonders bevorzugt können die erfindungsgemäßen Orientierungs- schichten zur Herstellung ferroelektrischer Flüssigkristalldisplays nach dem von Lagerwall angegebenen SSFLC-Prinzip verwendet werden. Die Flüssigkristallschicht weist eine SmC*-Phase auf, wodurch die Flüssigkristallmoleküle an den Substratoberflächen einen Tiltwinkel von +Θ oder -Θ aufweisen. Diese oberflächeninduzierte Orientierung der Flüssigkristallmoleküle setzt sich wegen der sehr geringen Dicke der Flüssigkristallschicht von typischerweise weniger als 3 μm durch die gesamte Flüssigkristallschicht fort, und man kann den Flüssigkristall zwischen 2 bistabilen Zuständen mit +Θ und -Θ schalten ("bookshelf geometry"). Es wurde gefunden, daß die Stabilität der beiden Schaltzustände erhöht werden kann, wenn die Substrate bidirektionale Orientierungsschichten aufweisen, deren beide Vorzugsrichtungen durch Bestrahlung mit 2 linear polarisierten Lichtquellen erhalten wurden, welche gegeneinander um einen The orientation layers according to the invention can be used particularly preferably for the production of ferroelectric liquid crystal displays according to the SSFLC principle specified by Lagerwall. The liquid crystal layer has an SmC * phase, as a result of which the liquid crystal molecules have a tilt angle of + Θ or -Θ on the substrate surfaces. This surface-induced orientation of the liquid crystal molecules continues due to the very small thickness of the liquid crystal layer of typically less than 3 μm through the entire liquid crystal layer, and the liquid crystal can be switched between 2 bistable states with + Θ and -Θ ("bookshelf geometry"). It has been found that the stability of the two switching states can be increased if the substrates have bidirectional orientation layers, the two preferred directions of which have been obtained by irradiation with 2 linearly polarized light sources which are mutually opposite
Azimutwinkel von Φ=20 verdreht sind. Es wurde gefunden, daß derartige ferroelektrische Displays eine deutlich erhöhte Stabilität gegenüber mechanischen Belastungen (Stoßfestigkeit) aufweisen als entsprechende Displays ohne bidirektionale Orientierungsschichten, wobei lediglich eine geringe und in jedem Fall akzeptable Erhöhung der Schaltspannung beobachtet wurde. Azimuth angles of Φ = 20 are rotated. It has been found that such ferroelectric displays have a significantly increased stability show mechanical loads (shock resistance) as corresponding displays without bidirectional orientation layers, whereby only a small and in any case acceptable increase in the switching voltage was observed.
Bevorzugt sind weiter auch Flüssigkristalldisplays mit erfindungsgemäßen Orientierungsschichten, welche nematische oder cholesterische Flüssigkristalle enthatten. Besonders bevorzugt ist etwa eine verdrillte nematische Zelle, die einen dotierten Flüssigkristall enthält, wobei die Pitchlänge des Flüssigkristalls stark temperaturabhängig sein kann. Die Substratplatten weisen eine multidirektionale Orientierung auf und zwingen dem Flüssigkristall bei einer bestimmten Temperatur in Abhängigkeit von der Dotierung einen bestimmten Twistwert auf. Bei einer Temperaturänderurig ändert sich die Pitchlänge des Flüssigkristalls und der Twist springt diskret, wenn für die geänderte Pitchlänge p(T) durch die Orientierungsschichten ein energetisch bevorzugter Twistzustand definiert wird. Die Änderung des Twistes bewirkt eine Transmissionsänderung, so daß die Anordnung als diskretes Thermometer arbeitet. Es stellt für den Fachmann eine ohne erfinderischeAlso preferred are liquid crystal displays with orientation layers according to the invention which contain nematic or cholesteric liquid crystals. For example, a twisted nematic cell which contains a doped liquid crystal is particularly preferred, the pitch length of the liquid crystal being highly temperature-dependent. The substrate plates have a multidirectional orientation and force the liquid crystal at a certain temperature as a function of the doping to a certain twist value. If the temperature changes, the pitch length of the liquid crystal changes and the twist jumps discretely if an energetically preferred twist state is defined for the changed pitch length p (T) by the orientation layers. The change in the twist causes a change in transmission, so that the arrangement works as a discrete thermometer. It represents one without the inventive for the expert
Tätigkeit zu lösende Routineaufgabe dar, die Vorzugsrichtungen der multidirektionalen Orientierungsschichten, die Gesamtkonzentration des Dotierstoffes und seine Temperaturabhängigkeit so aneinander anzupassen, daß eine gewünschte Temperaturanzeige wie z.B. die Anzeige von 10 K-Sprüngen resultiert. Routine task to be solved is to adapt the preferred directions of the multidirectional orientation layers, the total concentration of the dopant and its temperature dependency so that a desired temperature display, e.g. the display of 10 K jumps results.
Die erfindungsgemäßen Orientierungsschichten werden vorzugsweise zur Herstellung von Flüssigkristalldisplays verwendet, wobei sie die Verbesserung herkömmlicher Displays und auch die Realisierung vollständig neuer Displays ermöglichen. Den erfindungsgemäßen Orientierungsschichten kommt daher eine erhebliche wirtschaftliche Bedeutung zu. The orientation layers according to the invention are preferably used for the production of liquid crystal displays, whereby they enable the improvement of conventional displays and also the realization of completely new displays. The orientation layers according to the invention are therefore of considerable economic importance.

Claims

Patentansprüche Claims
1. Verfahren zur Herstellung multidirektionaler Orientierungsschichten, dadurch gekennzeichnet, daß ein photohärtbarer Precursor der Orientierungsschicht, welcher eine oder mehrere, im wesentlichen lineare Photopolymere und/oder -oligomere enthält, auf ein Substrat aufgebracht und nachfolgend mit linear polarisiertem Licht unter 2 oder mehr verschiedenen Azmutwinkeln Φ beaufschlagt wird. 1. A method for producing multidirectional orientation layers, characterized in that a photocurable precursor of the orientation layer, which contains one or more, essentially linear photopolymers and / or oligomers, is applied to a substrate and subsequently with linearly polarized light at 2 or more different azimuth angles Φ is applied.
2. Multidirektionale Orientierungsschicht, erhältlich gemäß dem 2. Multi-directional orientation layer, available according to the
Verfahren nach Anspruch 1.  The method of claim 1.
3. Verwendung der multidirektionalen Orientierungsschicht nach 3. Using the multidirectional orientation layer after
Anspruch 2 zur Herstellung von elektrooptischen Flüssigkristallsystemen.  Claim 2 for the production of electro-optical liquid crystal systems.
4. Elektrooptisches Flüssigkristallsystem, enthaltend eine Flüssigkristallschicht zwischen Substraten, welche mit Elektroden- und darüber angeordneten Orientierungsschichten versehen sind, wobei zumindestens eine der Orientierungsschichten multidirektional orientiert ist. 4. Electro-optical liquid crystal system, comprising a liquid crystal layer between substrates which are provided with electrodes and orientation layers arranged above them, at least one of the orientation layers being multidirectionally oriented.
PCT/EP1995/002096 1994-06-13 1995-06-02 Electro-optical system WO1995034843A1 (en)

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