EP0491901A1 - Systeme electro-optique - Google Patents

Systeme electro-optique

Info

Publication number
EP0491901A1
EP0491901A1 EP91911851A EP91911851A EP0491901A1 EP 0491901 A1 EP0491901 A1 EP 0491901A1 EP 91911851 A EP91911851 A EP 91911851A EP 91911851 A EP91911851 A EP 91911851A EP 0491901 A1 EP0491901 A1 EP 0491901A1
Authority
EP
European Patent Office
Prior art keywords
orientation
liquid crystal
layers
electro
substrates
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP91911851A
Other languages
German (de)
English (en)
Inventor
Stefan Brosig
Jürgen Waldmann
Herbert Plach
Rainer Neeff
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Merck Patent GmbH
Original Assignee
Merck Patent GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Merck Patent GmbH filed Critical Merck Patent GmbH
Publication of EP0491901A1 publication Critical patent/EP0491901A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL 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
    • G02F1/00—Devices 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
    • G02F1/01—Devices 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 
    • G02F1/13—Devices 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
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
    • G02F1/133711—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by organic films, e.g. polymeric films
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL 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
    • G02F1/00—Devices 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
    • G02F1/01—Devices 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 
    • G02F1/13—Devices 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
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers

Definitions

  • the invention relates to electro-optical systems according to the preamble of claim 1 with reduced operating voltage and a method for lowering the operating voltage of electro-optical systems.
  • transmission-voltage diagrams are usually used, from which the important parameters threshold voltage V.,, saturation voltage V, and slope of the electro-optical characteristic curve y can be found.
  • the threshold and saturation voltage can e.g. B. be defined as follows
  • V _ _ ⁇ V 2 _ i.e. H. a system is considered that is switched State with higher transmission. This is the case, for example, in the case of a TN cell which is located between parallel polarizers.
  • V 10 ⁇ 2Q > V go 0 20 which is observed, for example, in the case of TN cells between crossed polarizers, the following is expediently used:
  • An essential requirement for improving electro-optical systems according to the preamble of claim 1 is the reduction of the respective operating voltage, i.e. the threshold and / or saturation voltage. This can significantly simplify and reduce the cost
  • the dielectric anisotropy ⁇ can be increased by using highly polar 4-substituted benzonitriles and the threshold voltage can thus be reduced.
  • the achievable dielectric anisotrope ⁇ is limited by the formation of dimers with an antiparallel correlation of the molecular dipoles.
  • the temperature and UV stability of benzonitrile-containing liquid crystal mixtures meet extremely high requirements, such as those which are placed on systems controlled with an active matrix, often not (see e.g.
  • the invention was based on the object of providing electro-optical systems according to the preamble of claim 1 which, in comparison with conventional systems, are distinguished in particular by low operating voltages.
  • At least one of the orientation layers of the electro-optical system consists of a transparent, highly fluorinated polymer.
  • the invention relates to electro-optical systems which
  • orientation layers characterized in that at least one of the orientation layers consists of a transparent, highly fluorinated polymer.
  • the invention further relates to a method for reducing the operating voltage of electro-optical systems, comprising
  • At least one orientation layer is produced from a thin, transparent and highly fluorinated polymer.
  • the electro-optical systems according to the invention contain at least one electrically controllable, dielectrically positive, twisted nematic liquid crystal layer with a twist angle 0 ⁇ ⁇ 600 ° C, which is located between 2 substrates or carrier plates, which form a cell with a border.
  • nematic is broad here and also includes nematic-cholesteric liquid crystals.
  • Liquid crystal cells with twist angles ⁇ between approximately 80 ° and 100 ° are usually referred to as TN cells (twisted nematic); the construction of such cells is e.g. in Thermotropic Liquid Crystals, G.W. Gray [ed.J, p. 77 ff. Liquid crystal cells with ⁇ > 100 ° are generally called STN cells (supertwisted nematic), while the term LTN cell (low-twisted nematic) has been proposed for cells with ⁇ i ⁇ ⁇ 80 ° in P 40 10 503.
  • STN cells supertwisted nematic
  • LTN cell low-twisted nematic
  • electrode layers On the inside of the substrates there are electrode layers, which e.g. consist of thin, flat and transparent indium tin oxide (ITO) or indium oxide layers (In "0"). If it is a color rendering system, at least one of the two substrates has a further layer between its surface facing the liquid crystal and the electrode layer, which layer contains the organic color materials. Additional layers, such as e.g. Compensating and insulating layers can be arranged.
  • Orientation layers are located on the inner sides of the substrates, which are in direct contact with the liquid crystal and bring about an essentially planar orientation of the liquid crystal molecules.
  • the liquid crystal molecules have a certain angle of attack or pretilt ⁇ , the size of the required Pretilt are generally determined by the twist angle ⁇ of the liquid crystal layer.
  • LTN and TN cells usually have relatively low tilt angles of, for example, 0 ° et et 10 10 ° and in particular 0.5 ° a a 5 5 ° (low-tilt alignment)
  • STN cells are generally characterized by higher angles of attack, for example 2 ° ⁇ ⁇ ⁇ 90 ° and in particular of more than 5 ° and less than 45 ° marked (high-tilt alignment).
  • planar orientation layer with a small pretilt
  • polymer layers e.g. Polyimide or polyvinyl alcohol layers are used, which are given a uniform orientation by rubbing, if appropriate with simultaneous application of pressure.
  • cleaning up these orientation layers is often difficult and contamination of the liquid crystal and thus a reduction in the electrical resistance of the liquid crystal can occur, which is particularly problematic in electro-optical systems controlled by an active matrix (see, for example, HJ Plach et al., loc. cit.).
  • Planar orientation layers with higher angles of attack can be formed by oblique evaporation with inorganic materials such as Silicon oxide or magnesium fluoride can be obtained.
  • P 40 15 869 proposes the use of transparent, highly fluorinated, preferably perfluorinated, amorphous, aliphatic or alicyclic polymers as an orientation layer for passively controlled, high-resolution liquid crystal displays, since pianar orientation layers with a high pretilt can be obtained with these materials , which require significantly lower tempering temperatures than conventional orientation layers. It has now been found that the operating voltage of electro-optical systems can be considerably reduced if at least one orientation layer is made from a thin, transparent and highly fluorinated polymer. This method for lowering the operating voltage is new and the subject of the invention.
  • Example la shows a TN cell according to the invention whose orientation layers have been annealed at 100 ° C., and in FIG. 1 the transmission measured for static control as a function of the voltage is plotted for this system.
  • the cell has an excellent contrast of 600: 1.
  • the conventional TN cell described in Example 1c is considered with a twist angle of 90 °, which has low-tilt polyimide orientation layers.
  • the following values are obtained for the threshold and saturation voltage with static control:
  • the value for the threshold voltage u is approximately 22% and for the saturation voltage is approximately 4% smaller than in the conventional system.
  • V 90.0.20 ° ' 4 V
  • V 10.0.20 1 ' 8 V
  • the values for the threshold and saturation voltages observed in the systems according to the invention are also influenced by the concentration of the chiral dopant (s) used.
  • concentration of the chiral dopant (s) used is also influenced by the concentration of the chiral dopant (s) used.
  • V 90.0.20 1 ' 6 V
  • V 10.0.20 2 ' 8 V
  • the operating voltages, the contrast, the switching times and the pretilt of the systems according to the invention can be influenced by varying the production conditions of the system and by parameters of the liquid crystal mixture used and can be optimized, for example, with regard to the respective application and the driver electronics used.
  • the manufacturing conditions of the orientation layer such as e.g. the fluorinated polymer and / or solvent used, the mechanical treatment used and in particular the annealing temperature.
  • orientation layers can be produced from highly fluorinated polymers and in particular highly fluorinated, amorphous, aliphatic or alicyclic polymers. These are usually in a solvent such as e.g. fluorinated and in particular perfluorinated hydrocarbons, dissolved and applied to the substrate plate. By spinning off the solution from the surface and evaporating the remaining solvent, a thin transparent layer is obtained which is subjected to a heat treatment.
  • the annealing temperature is usually greater than 50 ° C and preferably greater than 100 ° C.
  • Electro-optical systems according to the invention the orientation layers of which are annealed at a temperature between 50 ° C ⁇ T 350 350 ° C and in particular between 70 ° C T T 325 325 ° C, have particularly favorable properties. It should be noted that the optimal tempering temperature in each case also depends on the glass transition temperature of the polymer used. Following the heat treatment, the orientation layers are given a uniform alignment by rubbing or similar mechanical processes, possibly with simultaneous application of pressure.
  • both systems according to the invention in which both substrate plates have an orientation layer made of a highly fluorinated polymer
  • systems according to the invention in which only one orientation layer noses on a highly fluorinated polymer, while the other is, for example, conventionally formed advantageous properties and in particular by cheap Values for the operating voltage are marked.
  • Systems according to the invention are also preferred which contain two orientation layers consisting of highly fluorinated polymer, the two orientation layers, however, being characterized by different manufacturing conditions, such as, for example, annealing temperatures.
  • symmetrical systems which have two orientation layers consisting of highly fluorinated polymer, which have been subjected to the same manufacturing conditions.
  • orientation layers By varying the production conditions of the orientation layers based on highly fluorinated polymers and by combining suitable combinations of these orientation layers with one another or also by combinations of these orientation layers with conventional ones
  • Dielectric positive, nematic or nematic-cholesteric liquid-crystalline media are used in the systems according to the invention. These contain 2-45 and in particular 3-39 components, which are preferably selected from nematic or nematogenic (Monotropic or isotropic) substances, in particular substances from the classes of biphenyls, terphenyls, phenyl- or cyclohexylbenzoates, cyclohexane-carboxylic acid phenyl- or cyclohexyl-esters, phenyl- or cyclohexyl-esters of cyclohexylbenzoic acid, phenyl- or cyclohexyl-esters of cyclohexyl-cyclo-hexano-cyclo-hexo-cyclo-hexo-cyclohexyl , Cyclohexylphenyl ester of benzoic acid, cyclohexane carboxylic acid or cyclohexy
  • the 1,4-phenylene groups in these compounds can also be fluorinated.
  • L and E which may be the same or different, each independently represent a bivalent radical from the group consisting of -Phe-, -Cyc-, -Phe-Phe-, -Phe- Cyc-, -Cyc-Cyc-, -pyr-, -Dio-, -G-Phe- and -G-Cyc- as well as their Speigel pictures group formed, with Phe unsubstituted or substituted by fluorine-1,4-phenylene, Cyc trans-l, 4-cyclohexylene or 1,4-cyclohexenylene, pyr pyrimidine 2,5-diyl or pyridine-2,5-diyl, dio 1,3-dioxane-2,5-diyl and G 2- (trans-1,4-cyclohexyl) ethyl, pyrimidine-2,5-diyl, Pyridine-2,5-diyl
  • one of the radicals L and E is Cyc, Phe or Pyr.
  • E is preferably Cyc, Phe or Phe-Cyc.
  • the media according to the invention preferably contain one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, in which L and E are selected from the group Cyc, Phe and Pyr and at the same time one or more components are selected from the compounds of the formulas 1, 2, 3, 4 and 5, in which one of the radicals L and E is selected from the group Cyc, Phe and Pyr and the other radical is selected from the group -Phe-Phe-, -Phe- Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-, and optionally one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, in which the
  • Residues L and E are selected from the group -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-.
  • R 'and R''in the compounds of the sub-formulas la, 2, a, 3a, 4a and 5a each independently of one another denote alkyl, alkenyl, akoxy, alkenyloxy or alkanoyloxy having up to 8 carbon atoms. In the mesites of these compounds, R 'and R''are different from one another, one of these radicals being alkyl or alkenyl.
  • R '1 is -CN, -CF 3, -OCF 3, F, Cl or NCS; R has the meaning given for the compounds of the formulas Ia to 5a and is preferably alkyl or alkenyl.
  • R 1 ' is particularly preferably selected from the group consisting of -F, Cl, CF 3 and -OCF 3 .
  • R 1 ' is particularly preferably selected from the group consisting of -F, Cl, CF 3 and -OCF 3 .
  • other variants of the intended substances in compounds of the formulas 1, 2, 3, 4 and 5 are also common. Many such substances or mixtures thereof are commercially available. All of these substances can be obtained by methods known from the literature or by analogy.
  • the liquid crystal media used in the systems according to the invention preferably contain, in addition to components from the group of the compounds Ia, 2a, 3a, 4a and 5a (group 1), also components from the group of the compounds Ib, 2b, 3b, 4b and 5b (Group 2), the shares of which are preferably as follows:
  • Group 1 20 to 90%, in particular 30 to 90%
  • group 2 10 to 80%, in particular 10 to 50%
  • the systems according to the invention are preferably controlled by an active matrix, ie the individual pixels are switched by active non-linear elements such as transistors (thin film transistor TFT, metal oxide semiconductor MOS transistors), diodes (metal-insulator-metal MIM diodes) or varistors tet; an overview of active control methods can be found, for example, in E. Kaneko, Liquid Crystal TV Displays, KTK Scientfic Publishers, Tokyo, 1978, chap. 6 and 7. Actively controlled systems according to the invention are based in particular on TN cells, but it is also possible to use cells with other twist angles ⁇ between 0 ° and 600 °. Such systems are new and preferred and are the subject of this invention.
  • active non-linear elements such as transistors (thin film transistor TFT, metal oxide semiconductor MOS transistors), diodes (metal-insulator-metal MIM diodes) or varistors tet; an overview of active control methods can be found, for example, in E. Kaneko, Liquid
  • Systems according to the invention with orientation layers made from fluorinated polymers are often characterized by a very high resistance; they are therefore particularly suitable for actively controlled systems, where a reduction in the resistance z. B. by contamination of the liquid crystal through the orientation layers or as a result of a reaction of the liquid crystal with the orientation layers in order to achieve a high holding ratio must be avoided as far as possible.
  • the systems according to the invention are further preferably operated with a passive multiplex control; an overview of passively controlled systems can be found e.g. in E. Kaneko, loc. cit. , Chap. 4.
  • Systems according to the invention which are passively controlled with low to relatively high multiplex rates from 1: 2 to about 1: 300 are preferred. Multiplex rates that are less than
  • the electro-optical systems according to the invention are characterized by advantageous properties and in particular by advantageous values for the operating voltage. This often leads to a considerable simplification and thus cheaper driver electronics, since, for example, voltage doublers can be dispensed with. The electro-optical systems according to the invention are therefore of considerable economic importance.
  • trans-4-propylcyclohexylcyclohexane carboxylic acid p-pentylphenyl ester 5% trans-, trans-4-butylcyclohexylcyclohexanecarboxylic acid p-propylphenyl ester 5% trans-, rans-4-butylcyclohexylcyclohexanecarboxylic acid p-pentylphenyl ester 3% 4, '-Bis- (trans-4-propylcyclohexyl) biphenyl
  • V 10.0.20 2 ' 8 V b)
  • a conventional TN cell with a twist angle of -90 ° is considered, which has low-tilt polymid orientation layers.

Landscapes

  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Mathematical Physics (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Liquid Crystal (AREA)
  • Liquid Crystal Substances (AREA)

Abstract

Un système électro-optique contient une couche de cristaux liquides nématique torsadée, diélectriquement positive, à commande électrique, agencée entre deux substrats qui, avec une bordure, forment une cellule; et des couches d'électrodes sur lesquelles sont agencées des couches d'orientation, sur les faces internes des substrats, les couches d'orientation assurant une orientation des molécules des cristaux liquides essentiellement parallèle aux bords. Le système électro-optique est commandé statiquement ou par une matrice active ou par une matrice passive, à des taux de multiplexage réduits ou relativement élevés. Au moins une des couches d'orientation est constituée d'un polymère transparent fortement fluoré.
EP91911851A 1990-07-06 1991-06-25 Systeme electro-optique Withdrawn EP0491901A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE4021414A DE4021414A1 (de) 1990-07-06 1990-07-06 Elektrooptisches system
DE4021414 1990-07-06

Publications (1)

Publication Number Publication Date
EP0491901A1 true EP0491901A1 (fr) 1992-07-01

Family

ID=6409709

Family Applications (1)

Application Number Title Priority Date Filing Date
EP91911851A Withdrawn EP0491901A1 (fr) 1990-07-06 1991-06-25 Systeme electro-optique

Country Status (5)

Country Link
EP (1) EP0491901A1 (fr)
JP (1) JPH05501316A (fr)
KR (1) KR920702504A (fr)
DE (1) DE4021414A1 (fr)
WO (1) WO1992001240A1 (fr)

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1408852A (en) * 1972-03-08 1975-10-08 Seiko Instr & Electronics Liquid crystal display device and a method of making the same
DE3150830A1 (de) * 1980-12-25 1982-07-08 Canon K.K., Tokyo Verfahren zur orientierung von fluessigkristallen und fluessigkristallanzeigevorrichtung
JPS6262332A (ja) * 1985-09-13 1987-03-19 Sumitomo Bakelite Co Ltd 液晶表示配向基板

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9201240A1 *

Also Published As

Publication number Publication date
KR920702504A (ko) 1992-09-04
WO1992001240A1 (fr) 1992-01-23
DE4021414A1 (de) 1992-01-09
JPH05501316A (ja) 1993-03-11

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