WO2018172232A1 - Élément de modulation de lumière - Google Patents

Élément de modulation de lumière Download PDF

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Publication number
WO2018172232A1
WO2018172232A1 PCT/EP2018/056785 EP2018056785W WO2018172232A1 WO 2018172232 A1 WO2018172232 A1 WO 2018172232A1 EP 2018056785 W EP2018056785 W EP 2018056785W WO 2018172232 A1 WO2018172232 A1 WO 2018172232A1
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Prior art keywords
light modulation
modulation element
element according
μιτι
cell
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PCT/EP2018/056785
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English (en)
Inventor
Phil Baker
Alex HOLT
Joseph SARGENT
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Merck Patent Gmbh
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Priority to GB1915019.2A priority Critical patent/GB2575579B/en
Publication of WO2018172232A1 publication Critical patent/WO2018172232A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K19/00—Liquid crystal materials
    • C09K19/02—Liquid crystal materials characterised by optical, electrical or physical properties of the components, in general
    • C09K19/0225—Ferroelectric
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K19/00—Liquid crystal materials
    • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
    • C09K19/06—Non-steroidal liquid crystal compounds
    • C09K19/34—Non-steroidal liquid crystal compounds containing at least one heterocyclic ring
    • C09K19/3441—Non-steroidal liquid crystal compounds containing at least one heterocyclic ring having nitrogen as hetero atom
    • C09K19/3444—Non-steroidal liquid crystal compounds containing at least one heterocyclic ring having nitrogen as hetero atom the heterocyclic ring being a six-membered aromatic ring containing one nitrogen atom, e.g. pyridine
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K19/00—Liquid crystal materials
    • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
    • C09K19/06—Non-steroidal liquid crystal compounds
    • C09K19/34—Non-steroidal liquid crystal compounds containing at least one heterocyclic ring
    • C09K19/3441—Non-steroidal liquid crystal compounds containing at least one heterocyclic ring having nitrogen as hetero atom
    • C09K19/345—Non-steroidal liquid crystal compounds containing at least one heterocyclic ring having nitrogen as hetero atom the heterocyclic ring being a six-membered aromatic ring containing two nitrogen atoms
    • C09K19/3458—Uncondensed pyrimidines
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K19/00—Liquid crystal materials
    • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
    • C09K19/06—Non-steroidal liquid crystal compounds
    • C09K19/34—Non-steroidal liquid crystal compounds containing at least one heterocyclic ring
    • C09K19/3491—Non-steroidal liquid crystal compounds containing at least one heterocyclic ring having sulfur as hetero atom
    • C09K19/3497—Non-steroidal liquid crystal compounds containing at least one heterocyclic ring having sulfur as hetero atom the heterocyclic ring containing sulfur and nitrogen atoms

Definitions

  • the invention provides a light modulation element utilizing the vertically aligned deformed helix ferroelectric liquid crystal (VADH FLC) mode.
  • VADH FLC vertically aligned deformed helix ferroelectric liquid crystal
  • the present invention relates to a method of production of such light modulation element, to the use of such light modulation element in an electro-optical device, i.e. in a LC display device, and to electro-optical devices comprising the light modulation element according to the present invention.
  • LCDs are widely used to display information. LCDs are used for direct view displays, as well as for projection type displays.
  • the electro-optical mode which is employed for most displays, is still the twisted nematic (TN)-mode with its various modifications. Besides this mode, the super twisted nematic (STN)-mode, more recently the optically compensated bend (OCB)-mode, the electrically controlled birefringence (ECB)-mode with their various modifications, as e. g.
  • VAN vertically aligned nematic
  • PVA patterned ITO vertically aligned nematic
  • PSVA polymer stabilized vertically aligned nematic
  • MVA multi domain vertically aligned nematic
  • ferroelectric liquid crystal (FLC) mode is known for example from US 2016/0017226 A1 .
  • chiral, tilted smectic phases such as smectic C phases
  • smectic C phases are required [R. B. Meyer, L. Liebert, L. Strzelecki and P. Keller, J. Physique 36, L-69 (1975)]
  • This aim can be achieved by means of compounds which themselves form such phases, for example smectic C phases, or by doping compounds, which do not form chiral, tilted smectic phases, with optically active compounds [M. Brunei, C. Williams, Ann. Phys. , 3, 237 (1978) ].
  • VADH FLC vertically aligned deformed helix ferroelectric helix liquid crystal
  • the cell can be switched by applying an electric field perpendicular to the helix axis.
  • the electric field couples with the spontaneous polarization (Ps) of the helix mode causing the helix to distort, producing a birefringence and hence transmission of light between crossed polarisers.
  • the transmission varies with the applied field strength meaning that grey scales can be realized.
  • VADH FLC mode in comparison with nematic modes is that it is very fast, where the switching time is of the order of tens of microseconds, which allows e.g. field sequential colouring or switching and eliminates the need for colour filters in displays thereby improving transmission efficiency.
  • Kim et al. Journal of SID 16/9 (2008) disclose microsecond switching utilizing the VADH FLC mode with driving fields of 3 V/ ⁇ .
  • Lee et al. suggest in Optical Express 13 7732 (2005) a working cell in the VADH FLC mode with in-plane electrodes. However, a non-uniform transmission and edge defects are observed.
  • VADH FLC modes utilizing IPS electrodes show alignment defects along the electrodes after switching above a certain threshold voltage, like e.g. described by Wu et al. in Opt. Express 13, 7732 (1005) or by Lee et al. in Mol. Cryst. Liq. Cryst. 453, 343 (2006). These alignment defects spoil the dark state and hence the contrast ratio for display applications.
  • the electrode edge defects are a consequence of the nonuniform electric field profile of in-plane electrodes, which contain a large vertical electric field component near the electrode edge. This couples to the spontaneous polarisation of the vertical helix mode creating a torque, which forces the helix to turn over into the horizontal plane.
  • US 2008/0204608 A1 discloses the use of electrodes that extend through a liquid crystal cell in the standing vertical helix chiral mode.
  • this application uses very thick cells (> 50 ⁇ ) with a long chiral pitch to deflect light by switching the chiral pitch. Consequently, through cell electrodes are required because of the large thickness of the cell, as IPS electrodes would suffer from electric field deterioration.
  • US 2008/0204608 A1 does not refer to field induced defects forming when switching and the use of the extended electrodes as means to prevent such defects.
  • the disclosed devices require an extremely large cell gap of 50 ⁇ or more in order to realize a device that has sufficient beam deflection because they are operated in a refractive mode rather than by altering the polarisation state of the light.
  • a general object of the present invention is to alleviate the above problems and to provide an alternative to the known light modulation elements of the prior art, or preferably, to provide an improved light modulation element.
  • an object of the invention is to provide a light modulation element operated in the VADH FLC mode having the capability of generating high contrast and wide viewing angle images, favourable dark states, and exhibiting fast switching, more particularly to reduce the total switching time enabling a satisfactory display of moving images.
  • Further objects of the present invention are to increase the optical aperture ratio and to increase the transmittance of the light modulation element.
  • the invention relates to a light modulation element comprising a pair of transparent substrates, a pair of polarizers, a liquid crystal medium capable of forming a chiral smectic C phase in homeotropic orientation that is located in between the pair of substrates, and an electrode structure which generates an electric field (parallel electric field) in directions parallel to the substrates main plane, characterized in that the electrode structure is formed by at least two electrodes protruding toward the interior of the formed cell.
  • the term "light modulation element” relates to devices capable of altering the phase or polarisation state of the light. Devices that are operated in refractive modes are excluded.
  • the term “liquid crystal (LC)” relates to materials having liquid-crystalline mesophases in some temperature ranges (thermotropic LCs) or in some concentration ranges in solutions (lyotropic LCs). They obligatorily contain mesogenic compounds.
  • mesogenic compound or “liquid crystal compound” are taken to mean a compound comprising one or more uniaxial calamitic (rod-, brick-, or board/lath-shaped) or uniaxial discotic (disk-shaped) mesogenic group.
  • mesogenic group means a group with the ability to induce liquid-crystalline phase (or mesophase) behaviour.
  • the compounds comprising mesogenic groups do not necessarily have to exhibit a liquid- crystalline mesophase themselves. It is also possible that they show liquid- crystalline mesophases only in mixtures with other compounds.
  • a calamitic mesogenic group usually comprises a mesogenic core.
  • the mesogenic core consists of one or more aromatic or non-aromatic cyclic groups, which are connected to each other directly or via linkage groups and optionally comprising terminal groups attached to the ends of the mesogenic core.
  • the mesogenic group comprises one or more groups that are laterally attached to the long side of the mesogenic core, wherein these terminal and lateral groups are usually selected e.g. from carbyl or hydrocarbyl groups, polar groups like halogen, nitro, hydroxy, etc..
  • liquid-crystalline medium or “liquid crystal material” is taken to mean a material, which exhibits liquid-crystalline properties under certain conditions.
  • the term is taken to mean a material, which forms a liquid-crystalline phase under certain conditions.
  • a liquid-crystalline medium may comprise one or more liquid-crystalline compounds and in addition further substances.
  • the term “alignment” or “orientation” relates to the alignment (orientational ordering) of anisotropic units of material such as small molecules or fragments of big molecules in a common direction named “alignment direction”. In an aligned layer of liquid-crystalline material or medium, the liquid-crystalline director coincides with the alignment direction so that the alignment direction corresponds to the direction of the anisotropy axis of the material.
  • VADHF mode refers to the chiral smectic C helix axis being normal to the substrate.
  • director is known in prior art and means the preferred
  • the director is the axis of anisotropy.
  • in-plane electric field is taken to mean employing an AC or DC electrical field substantially parallel to the substrates, respectively the liquid crystal layer.
  • through cell electrodes refers to electrodes protruding toward the interior of the formed cell.
  • electrodes which preferably extend over the over the entire thickness and entire length of the control layer or the formed cell.
  • Suitable electrode structures are disclosed, for example, in WO 2004/029697 A1 .
  • the electrodes are preferably arranged substantially parallel to each other.
  • the electrodes can have a circular cross- section, in the form of a solid wire or a cylinder, or the electrodes can have a rectangular or almost rectangular cross section. Especially preferred is a rectangular or almost rectangular cross section of the electrodes.
  • chiral in general is used to describe an object that is non- superimposable on its mirror image.
  • Achiral (non- chiral) objects are objects that are identical to their mirror image.
  • the birefringence ⁇ herein is defined as,
  • n e the extraordinary refractive index and n 0 is the ordinary refractive index
  • the extraordinary refractive index n e and the ordinary refractive index n 0 can be measured using an Abbe refractometer. The birefringence ( ⁇ ) can then be calculated.
  • clearing point means the temperature at which the transition between the mesophase with the highest temperature range and the isotropic phase occurs.
  • alkyl groups are, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, 2-methyl butyl, n-pentyl, s-pentyl, cyclo- pentyl, n-hexyl, cyclohexyl, 2 ethylhexyl, n-heptyl, cycloheptyl, n-octyl, cyclooctyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, dodecanyl, trifluoro- methyl, perfluoro-n-butyl, 2,2,2-trifluoroethyl, perfluorooctyl, perfluoro- hexyl, dodecanyl, trifluoro-
  • Preferred alkoxy groups are, for example, methoxy, ethoxy, 2-methoxy- ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, t-butoxy, 2- methylbutoxy, n-pentoxy, n-hexoxy, n-heptoxy, n-octoxy, n-nonoxy, n- decoxy, n-undecoxy, and n-dodecoxy.
  • Preferred alkenyl groups are, for example, ethenyl, propenyl, butenyl, pentenyl, cyclopentenyl, hexenyl, cyclohexenyl, heptenyl, cycloheptenyl, octenyl , cyclooctenyl .
  • Preferred alkynyl groups are, for example, ethynyl, propynyl, butynyl, pen- tynyl, hexynyl, octynyl.
  • the ranges of the parameters that are indicated in this application all include the limit values, unless expressly stated otherwise.
  • FIG. 1 is cross-section diagram showing the structure of a light modulation element according to the present invention.
  • FIGS. 2A, 2B, 2C and 2D are schematic diagrams showing the direction of an electric field and the direction of tilt of liquid crystal molecules in a liquid crystal element according to FIG. 1 .
  • FIGS. 3A, 3B and 3C are diagrams modelling the arrangement of liquid crystal molecules in the chiral smectic C phase thereof.
  • FIG.4A, FIG. 4B and FIG.4C show the microscope images through crossed polarisers of a through electrode cell containing the VADH FLC mixture in the original off state before switching, switched state with 0.7 V/ ⁇ and the final off state after switching, respectively.
  • FIG.5A and FIG.5B show exemplarily the optical transmission
  • the light modulation element according to the present invention is described based on FIG. 1 .
  • numeral references 1 , 2, 3, 4, and 5 refer to a light modulation element, substrate, homeotropic alignment layer, electrodes, and a layer of liquid crystal in a smectic C phase, respectively.
  • the polarizers on the outer side of the opposing substrates are omitted.
  • the substrate material is preferably a transparent material with no birefringence. The thickness of the substrate material may be several dozen ⁇ to several hundred ⁇ .
  • the substrate material is selected each and independently from another, from polymeric materials, glass or quartz plates.
  • Suitable and preferred polymeric substrate materials are, for example, films of cyclo olefin polymer (COP), cyclic olefin copolymer (COC), polyester such as polyethyleneterephthalate (PET) or polyethylene-naphthalate (PEN), polyvinylalcohol (PVA), polycarbonate (PC) or triacetylcellulose (TAC), very preferably PET or TAC films.
  • PET films are commercially available for example from DuPont Teijin Films under the trade name Melinex ®.
  • COP films are commercially available for example from ZEON Chemicals L.P. under the trade name Zeonor ® or Zeonex ®.
  • COC films are commercially available for example from TOPAS Advanced Polymers Inc. under the trade name Topas ®.
  • both substrates are glass plates.
  • the space between both substrates is substantially regulated by the electrodes, preferably only by the height of the electrodes.
  • the layer of the liquid-crystalline medium is thereby located in the interspace.
  • a metal or metal oxide electrode having a thickness or height similar to the thickness of the liquid crystal layer in order to apply a uniform, as possible, horizontal electric field to the liquid crystal layer. More preferably, a metal or metal oxide electrode is commonly used as a spacer and the thickness of the liquid crystal layer is regulated by the thickness or height of the metal or metal oxide electrode.
  • the substrates are arranged with a separation from 1 ⁇ or more to approximately 20 ⁇ or less from another, preferably in the range from approximately 1 ⁇ or more to approximately 15 m or less from another, and more preferably in the range from approximately 2 ⁇ or more to approximately 8 ⁇ or less from another. The layer of the liquid-crystalline medium is thereby located in the interspace.
  • each electrode can be up to approximately 20 ⁇ or less, preferably in the range from approximately 1 ⁇ or more to approximately 15 ⁇ or less, and more preferably in the range from approximately 2 ⁇ or more to approximately 8 ⁇ or less.
  • the gap between to electrodes is in a range of approximately 500 nm or more to approximately 150 ⁇ or less, preferably in a range of approximately 1 ⁇ or more to approximately 100 ⁇ or less, more preferably in a range of approximately 1 ⁇ or more to approximately 50 ⁇ or less.
  • the width of each electrode is in a range of approximately 500 nm or more to approximately 3 mm or less, preferably in a range of approximately 1 ⁇ or more to approximately 2 mm or less, more preferably in a range of approximately 1 ⁇ or more to approximately 100 ⁇ or less.
  • Suitable electrode materials are commonly known to the expert, as for example electrodes made of metal, such as for example, tin, copper , aluminium or metal oxides, such as, for example transparent indium tin oxide (ITO).
  • metal such as for example, tin, copper , aluminium or metal oxides, such as, for example transparent indium tin oxide (ITO).
  • ITO transparent indium tin oxide
  • the electrode structure generates a
  • the electrodes of the light modulation element are associated with a switching element, such as a thin film transistor (TFT) or thin film diode (TFD).
  • TFT thin film transistor
  • TFD thin film diode
  • the light modulation element in accordance with the present invention comprises two or more polarisers, at least one of which is arranged on one side of the layer of the liquid-crystalline medium and at least one of which is arranged on the opposite side of the layer of the liquid-crystalline medium.
  • the layer of the liquid-crystalline medium and the polarisers here are preferably arranged parallel to one another.
  • the polarisers are located on the outer side of the substrates.
  • the polarisers can be linear polarisers.
  • precisely two polarisers are present in the light modulation element.
  • the polarisers can be reflective or absorptive polarisers.
  • a reflective polariser in the sense of the present application reflects light having one polarisation direction or one type of circular-polarised light, while being transparent to light having the other polarisation direction or the other type of circular-polarised light.
  • an absorptive polariser absorbs light having one polarisation direction or one type of circular-polarised light, while being transparent to light having the other polarisation direction or the other type of circular-polarised light.
  • the reflection or absorption is usually not quantitative; meaning that complete polarisation of the light passing through the polariser does not take place.
  • both absorptive and reflective polarisers can be employed.
  • polarisers which are in the form of thin optical films.
  • reflective polarisers which can be used in the light modulation element according to the invention are DRPF (diffusive reflective polariser film, 3M), DBEF (dual brightness enhanced film, 3M), DBR (layered-polymer distributed Bragg reflectors, as described in US 7,038,745 and US 6,099,758) and APF (advanced polariser film, 3M).
  • absorptive polarisers which can be employed in the light modulation elements according to the invention, are the Itos XP38 polariser film and the Nitto Denko GU-1220DUN polariser film.
  • An example of a circular polariser which can be used in accordance with the invention, is the APNCP37-035-STD polariser (American Polarizers).
  • a further example is the CP42 polariser (ITOS).
  • the light modulation element according to the present invention comprises one or more alignment layers, which are provided on the inner side (adjacent to the liquid crystalline medium) of at least one substrate. In another preferred at least two alignment layers are provided, each of them provided on the inner side of each of the opposing substrates.
  • the alignment layer are capable of inducing a homeotropic alignment, tilted homeotropic alignment, or pseudo
  • Typical alignment layer materials capable of inducing a homeotropic alignment, tilted homeotropic alignment, or pseudo homeotropic alignment are commonly known to the expert, such as, for example, layers made of alkoxysilanes, alkyltrichlorosilanes, CTAB, lecithin or polyimides, preferably polyimides, such as, for example JALS-2096-R1 .
  • the alignment layer materials can be applied onto the substrate by conventional coating techniques like spin coating, roll-coating, dip coating or blade coating. It can also be applied by vapour deposition or conventional printing techniques, which are known to the expert, like for example screen printing, offset printing, reel-to-reel printing, letter press printing, gravure printing, rotogravure printing, flexographic printing, intaglio printing, pad printing, heat-seal printing, ink-jet printing or printing by means of a stamp or printing plate.
  • conventional coating techniques like spin coating, roll-coating, dip coating or blade coating. It can also be applied by vapour deposition or conventional printing techniques, which are known to the expert, like for example screen printing, offset printing, reel-to-reel printing, letter press printing, gravure printing, rotogravure printing, flexographic printing, intaglio printing, pad printing, heat-seal printing, ink-jet printing or printing by means of a stamp or printing plate.
  • the light modulation element may furthermore comprise filters, which block light of certain wavelengths, for example, UV filters.
  • filters which block light of certain wavelengths, for example, UV filters.
  • further functional layers commonly known to the expert may also be present, such as, for example, protective films and/or compensation films.
  • a chiral smectic liquid crystal material can be utilized as the liquid crystal medium capable of forming a chiral smectic C phase in homeotropic orientation in the light modulation element in accordance to the present invention, which can be provided by adding a chiral compound into a base liquid crystal material with a phase sequence of an isotropic liquid phase, a nematic phase, a smectic A phase and a smectic C phase from the side of higher temperature.
  • the expert commonly knows such materials.
  • a “smectic liquid crystal material” is a liquid crystal material, which can be provided by aligning the directions of the major axis of a liquid crystal molecule such that a layer (as a smectic layer) is formed.
  • a liquid crystal in which the directions of normal of the layer (layer normal direction) correspond to the directions of the major axis of a liquid crystal molecule is referred to as a "smectic A phase”
  • liquid crystal in which the directions of the major axis of a liquid crystal molecule do not correspond to the directions of normal of the layer is referred to as a "smectic C phase”.
  • a ferroelectric liquid crystal material in a smectic C phase thereof has a so-called spiral structure in which the directions of liquid crystal directors are spirally twisted for each smectic liquid crystal material when no external electric field is applied and is referred to as a "chiral smectic C phase".
  • the liquid crystal directors oppose to each other between adjacent layers.
  • These liquid crystals materials in a chiral smectic C phase contain a chiral compound having an asymmetric carbon in its molecular structure, which causes spontaneous polarization.
  • the optical characteristics thereof may be controlled by means of reorientation of the liquid crystal molecules in the directions determined by the spontaneous polarization Ps and the external electric field E.
  • Preferred liquid crystalline media exhibit a spontaneous polarization (Ps) of 1 nC/cm 2 or more, preferably of 10 nC/cm 2 or more, more preferably of 100 nC/cm 2 or more.
  • Preferred liquid crystalline media are selected from liquid crystalline media wherein the following equation is fulfilled: where n ave is the effective average refractive index of the liquid crystalline media and P is the chiral smectic pitch of the liquid crystalline media.
  • the liquid-crystal media in accordance with the present invention preferably have a clearing point of approximately 65°C or more, more preferably approximately 70°C or more, still more preferably 80°C or more, particularly preferably approximately 85°C or more and very particularly preferably approximately 90°C or more.
  • the ⁇ of the liquid-crystal media in accordance with the present invention is preferably in the range from approximately 0.020 or more to approximately 0.35 or more, more preferably in the range from approximately 0.10 or more to approximately 0.35 or more, even more preferably in the range from approximately 0.15 or more to approximately 0.35 or more and very particularly preferably in the range from approximately 0.17 or more to approximately 0.35 or more.
  • a suitable liquid-crystalline medium in accordance with the present invention comprises 3 or more, preferably 5 or more, particularly preferably 8 or more and very particularly preferably 10 or more, different liquid- crystalline compounds exhibiting a smectic C phase.
  • liquid crystalline media for the light modulation element according to the present invention comprise one or more compounds selected from formulae I, II or III,
  • a 1 denotes
  • a 11 denotes X
  • a 11 denotes
  • X denotes S or O, preferably S,
  • Z 11 to Z 32 are each independently selected from - COO-, -OCO-, or a single bond.
  • a 11 to A 32 are each independently in each occurrence 1 ,4-phenylene, or 1 ,4-cyclo-hexylene, whereby for both groups it being possible to be unsubstituted, mono-, di-, tri- or tetrasubstituted with F, CI, CN or alkyi, alkoxy, alkylcarbonyl or alkoxycarbonyl groups with 1 to 7 C atoms, wherein one or more H atoms may be substituted by F or CI, more preferably unsubstituted trans-1 ,4-cyclo-hexylene or 1 ,4-phenylene, which might be unsubstituted, mono-, disubstituted with F, CI, CN or alkyi, alkoxy, alkylcarbonyl or alkoxycarbonyl groups with 1 to 7 C atoms, wherein one or more H atoms may be substituted by F or CI,
  • a is 0 and b or c is 0 or 1 , whereby (b + c) > 1 .
  • Preferred compounds of formula I are selected from compounds of the following formulae:
  • R 11 and R 12 have each and independently from another one of the meanings as given above under formula I.
  • Preferred compounds of formula II are selected from compound of the following formula:
  • R 21 and R 22 have each and independently from another, one of the meanings as given above under formula II.
  • Preferred compounds of formula III are selected from compound of the following formula:
  • R 31 and R 32 have each and independently from another one of the meanings as given above under formula III.
  • the liquid crystalline media for the light modulation element according to the present invention comprises one or more compounds of formula I and one or more compounds of formula II.
  • the liquid crystalline media for the light modulation element according to the present invention comprises one or more compounds of formula I and one or more compounds of formula III. In a preferred embodiment, the liquid crystalline media for the light modulation element according to the present invention comprises one or more compounds of formula II and one or more compounds of formula III. In a preferred embodiment, the liquid crystalline media for the light modulation element according to the present invention comprises one or more compounds of formula I, one or more compounds of formula II, and one or more compounds of formula III.
  • the amount of compounds of formulae I and/or II and /or III in the liquid- crystalline medium is preferably from 10 % or more to 80 % or less, more preferably from 12 % or more to 75 % or less, even more preferably 15 % or more to 70 % or less, by weight of the total mixture.
  • Suitable liquid-crystalline media comprise one or more chiral compounds with a suitable helical twisting power (HTP), which are commonly known to the expert.
  • the chiral compounds are selected from the group of compounds of formulae IV: denote each and independently a chiral alkyl or alkoxy chain having 3 to 12 C-atoms and wherein one or more -CH2- groups are replaced by -CHF-.
  • a suitable the chiral compound is selected from the group of compounds of formulae IVa:
  • R 41 and R 42 denote each and independently a straight alkyl chain having 1 to 10 C-atoms.
  • the amount of chiral compounds in the liquid-crystalline medium is preferably from 10 % or more to 45 % or less, more preferably from 12 % or more to 30 % or less, even more preferably 15 % or more to 35 % or less, by weight of the total mixture.
  • liquid crystalline component formed by all utilized liquid crystalline compounds of the liquid crystalline medium consists of compounds of formula I and/or formula II and/or formula III and formula IV.
  • the liquid-crystalline medium in accordance with the present invention optionally comprises further compounds, for example stabilisers and/or antioxidants, such as for example compounds selected from HALS- stabilizers or compounds selected from the Irganox® series, which are commercially available from CIBA, Switzerland. They are preferably employed in a concentration of 0.01 % or more to approximately 5 % or less, particularly preferably 0.01 or more % to approximately 3 % or less, and very particularly preferably 0.01 % or more to approximately 1 % or less.
  • the liquid-crystal media utilized in the light modulation element according to the present invention are prepared in a manner conventional per se. In general, the desired amount of the components used in lesser amount is dissolved in the components making up the principal constituent, preferably at elevated temperature.
  • FIGS. 2A-2D are schematic diagrams illustrating the direction of an electric field and the direction of tilt of a liquid crystal molecule in the configuration shown in FIG. 1 .
  • the illustrated liquid crystal molecule 5a tilts such that a broad end thereof is above the paper plane and a narrow end thereof is the below the paper plane.
  • the spontaneous polarization (Ps) of the liquid crystal is shown by an arrow.
  • FIGS. 2A and 2C the relationship between the direction of an applied electric field and the tilt direction of the liquid crystal molecule is illustrated in the case where the spontaneous polarization is positive.
  • the liquid crystal molecule undergoes a rotational motion within an ideal conical plane as illustrated in the perspective views of FIGS.
  • FIGS. 3A, 3B and 3C models of various orientations of liquid crystal molecules in a chiral smectic C phase are shown.
  • a layer having a spiral structure is formed on an oriented surface in which the liquid crystal molecules 5a having a tilt angle ⁇ are stacked and twisted around an axes.
  • the liquid crystal directors are spatially averaged by a bilaterally symmetric spiral structure, as shown in FIG. 3A.
  • the average optical axis of the liquid crystal layer 5 in a device according to FIG.1 is oriented in the normal direction of the layer and the configuration is optically isotropic with respect to incident light, which is parallel to the average optic axis.
  • the distortion can be increased with the increase of the strength of the electric field and in turn, the tilt angle of the average optical axis can be also increased. This effect can be confirmed by the movement of the image of cross in the conoscopic image.
  • the strength of the electric field is further increased to be equal to or greater than a certain threshold electric field Es, the spiral structure disappears, as shown in FIG. 3C, and a uniform orientation is provided.
  • the tilt angle of the optical axis is equal to the tilt angle ⁇ of the liquid crystal director. Even when the electric field is further increased, the tilt angle ⁇ cannot be changed and the tilt angle of the optical axis stays constant.
  • the light modulation element according to the present invention can preferably be operated with a bipolar or biphasic square wave with a driving frequency of 1 Hz or more to 1000 Hz or less, more preferably 50 Hz or more to 100 Hz or less, most preferably 100 Hz, and an amplitude (Vamp) from 0.05 V or more to 750 V or less, more preferably 0.5 V or more to 100 V or less and most preferably 0.6 V or more to 40 V or less.
  • a driving frequency 1 Hz or more to 1000 Hz or less, more preferably 50 Hz or more to 100 Hz or less, most preferably 100 Hz
  • Vamp amplitude
  • the applied bipolar or biphasic square wave has a period comprising a positive pulse with the application of positive voltage, followed by the application of 0 voltage, followed by a negative pulse with the application of negative voltage and followed by the application of 0 voltage.
  • the amplitudes (V am p) of the applied pulses, negative and positive, are preferably identical.
  • the applied electric field strength is in the range of 0.1 V/ ⁇ or more to 5 V/ ⁇ or less, preferably 0.5 V/ ⁇ or more to 1 V/ ⁇ or less, and most preferably 0.6 V/ ⁇ or more to 0.8 V/ ⁇ or less.
  • a typical process for the production of a light modulation element according to the invention comprises the following steps:
  • the light modulation element of the present invention can be used in various types of optical and electro-optical devices.
  • Said optical and electro optical devices include, without limitation electro optical displays, liquid crystal displays (LCDs), non-linear optic (NLO) devices, and optical information storage devices.
  • LCDs liquid crystal displays
  • NLO non-linear optic
  • Table A indicates possible stabilizers, which can be added to the LC media according to the invention.
  • the LC media preferably comprise one or more dopants selected from the group consisting of compounds from Table A.
  • the measured phases of a resulting mixture comprising 30 % of compound IVa is: SmC 101.5°C SmA 111.4°C I.
  • a test cell consisting of two glass substrates with a thickness of 2.5 mm, each provided with a homeotropic alignment layer (JALS 2096-R1 from JSR, Japan), and two through cell electrodes made from tin foil and having a height of 15 ⁇ , an electrode width of approximately 2mm and an electrode spacing of 150 ⁇ , ⁇ ⁇ - please refer to table 1 ), is assembled.
  • the cell is filled with a mixture M comprising 30 % of the chiral compound IVa in its isotropic phase via capillary filling.
  • the voltage used to switch the LC mode is an AC bipolar square wave source with driving frequency of 100 Hz and amplitude from 0 to 1 10 V.
  • FIG. 4A to 4C show microscope images through crossed polarisers of a through electrode cell containing the VADH-FLC mixture (M) comprising 30 % w/w of chiral compound IVa in the original off state before switching, switched state with 0.7 V/ ⁇ and the final off state after switching, respectively.
  • M VADH-FLC mixture
  • FIG. 5 A and FIG. 5B show the optical transmission measurements and switching times as a function of electric field across a through cell electrode containing the VADH-FLC mixture comprising 30 % w/w of chiral compound IVa taken between crossed polarisers, respectively.
  • a test cell consisting of two glass substrates with a thickness of 2.5 mm, each provided with a homeotropic alignment layer (JALS 2096-R1 from JSR, Japan), and two through cell electrodes made from tin foil and having a height of 12 ⁇ , an electrode width of approximately 2mm and an electrode spacing of ⁇ ⁇ is assembled.
  • the cell is filled with a mixture M comprising 30 % of the chiral compound IVa in its isotropic phase via capillary filling.
  • the voltage used to switch the LC mode is an AC bipolar square wave source with driving frequency of 100 Hz and amplitude from 0 to 1 10 V and the optical performance is measured.
  • test cell consisting of two glass substrates with a thickness of 2.5 mm, each provided with a homeotropic alignment layer (JALS 2096-R1 from JSR, Japan), and two through cell electrodes made from tin foil and having a height of 7.5 ⁇ , an electrode width of approximately 2mm and an electrode spacing of ⁇ ⁇ is assembled.
  • JALS 2096-R1 homeotropic alignment layer
  • the cell is filled with a mixture M comprising 30 % of the chiral compound IVa in its isotropic phase via capillary filling.
  • the voltage used to switch the LC mode is an AC bipolar square wave source with driving frequency of 100 Hz and amplitude from 0 to 1 10 V and the optical performance is measured.
  • test cell consisting of two glass substrates with a thickness of 2.5 mm, each provided with a homeotropic alignment layer (JALS 2096-R1 from JSR, Japan), and two through cell electrodes made from tin foil and having a height of 12 ⁇ , an electrode width of approximately 2mm and an electrode spacing of ⁇ ⁇ is assembled.
  • JALS 2096-R1 homeotropic alignment layer
  • the cell is filled with a mixture M comprising 19.9 % of the chiral compound IVa in its isotropic phase via capillary filling.
  • the voltage used to switch the LC mode is an AC bipolar square wave source with driving frequency of 100 Hz and amplitude from 0 to 1 10 V and the optical performance is measured.
  • COMPARATIVE EXAMPLE 1 COMPARATIVE EXAMPLE 1 :
  • test cell consisting of two glass substrates with a thickness of 2.5 mm, each provided with a homeotropic alignment layer (JALS 2096-R1 from JSR, Japan), having a cell gap of 5.0 ⁇ and an IPS-electrode structure (electrode spacing 8 ⁇ ) instead of through cell electrodes is prepared.
  • the cell is filled with mixture M comprising 30 % of the chiral compound IVa.
  • the optical performance is measured in analogy to example 1 .
  • test cell consisting of two glass substrates with a thickness of 2.5 mm, each provided with a homeotropic alignment layer (JALS 2096-R1 from JSR, Japan), having a cell gap of 9.0 ⁇ and an IPS-electrode structure (electrode spacing 20 ⁇ ) instead of through cell electrodes is prepared.
  • the cell is filled with mixture M comprising 30 % of the chiral compound IVa.
  • the optical performance is measured in analogy to example 1 .
  • test cell consisting of two glass substrates with a thickness of 2.5 mm, each provided with a homeotropic alignment layer (JALS 2096-R1 from JSR, Japan), having a cell gap of 1 1 .9 ⁇ and an IPS-electrode structure (electrode spacing 50 ⁇ ) instead of through cell electrodes is prepared.
  • the cell is filled with mixture M comprising 30 % of the chiral compound IVa.
  • the optical performance is measured in analogy to example 1 .
  • test cell consisting of two glass substrates with a thickness of 2.5 mm, each provided with a homeotropic alignment layer (JALS 2096-R1 from JSR, Japan), having a cell gap of 13.9 ⁇ and an IPS-electrode structure (electrode spacing 100 ⁇ ) instead of through cell electrodes is prepared.
  • the cell is filled with mixture M comprising 30 % of the chiral compound IVa.
  • the optical performance is measured in analogy to example 1 .
  • test cell consisting of two glass substrates with a thickness of 2.5 mm, each provided with a homeotropic alignment layer (JALS 2096-R1 from JSR, Japan), having a cell gap of 5.0 ⁇ and an IPS-electrode structure (electrode spacing 8 ⁇ ) instead of through cell electrodes is prepared.
  • the cell is filled with mixture M comprising 19.6 % of the chiral compound IVa.
  • the optical performance is measured in analogy to example 1 .
  • test cell consisting of two glass substrates with a thickness of 2.5 mm, each provided with a homeotropic alignment layer (JALS 2096-R1 from JSR, Japan), having a cell gap of 7.2 ⁇ and an IPS-electrode structure (electrode spacing 20 ⁇ ) instead of through cell electrodes is prepared.
  • the cell is filled with mixture M comprising 19.6 % of the chiral compound IVa.
  • the optical performance is measured in analogy to example 1 .
  • test cell consisting of two glass substrates with a thickness of 2.5 mm, each provided with a homeotropic alignment layer (JALS 2096-R1 from JSR, Japan), having a cell gap of 8.6 ⁇ and an IPS-electrode structure (electrode spacing 50 ⁇ ) instead of through cell electrodes is prepared.
  • the cell is filled with mixture M comprising 19.6 % of the chiral compound IVa.
  • the optical performance is measured in analogy to example 1 .
  • Table 1 gives a summary of the cell types tested with the different electrode spacing, cell gaps and chiral dopant concentrations and whether defects were observed and if so above what threshold electric field (Es).

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  • Engineering & Computer Science (AREA)
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  • Organic Chemistry (AREA)
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Abstract

L'invention concerne un élément de modulation de lumière sans défaut utilisant le mode cristal liquide ferroélectrique à hélice déformée aligné verticalement (VADHFLC). En outre, la présente invention concerne un procédé de production d'un tel élément de modulation de lumière, l'utilisation d'un tel élément de modulation de lumière dans un dispositif électro-optique, c'est-à-dire dans un dispositif d'affichage à cristaux liquides et un dispositif électro-optique comprenant l'élément de modulation de lumière selon la présente invention.
PCT/EP2018/056785 2017-03-21 2018-03-19 Élément de modulation de lumière WO2018172232A1 (fr)

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