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
  • G02F1/1334—Constructional arrangements; Manufacturing methods based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
• • 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
  • G02F1/1343—Electrodes
  • G02F1/13439—Electrodes characterised by their electrical, optical, physical properties; materials therefor; method of making
• • 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
  • G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
  • G02F2201/50—Protective arrangements

Definitions

• This invention is concerned with liquid crystal displays .
• a liquid crystal shutter comprising a liquid crystal layer sandwiched between a pair of transparent electrodes, is placed in front of a backlight, such as an electroluminescent backlight, such that the backlight is rearward of the rear electrode of the LC shutter and illuminates the LC shutter.
• a voltage to the electrodes causes switching of the liquid crystal layer between a transmissive state, in which light from the backlight can pass through the LC layer to the viewer, and an absorbing or scattering state, in which the LC layer blocks light emitted by the backlight from reaching the viewer.
• the LC layer is in the form of a physically stabilised liquid crystal layer, such as a polymer dispersed liquid crystal (PDLC) in which droplets of liquid crystal, typically nematic or cholesteric in nature, are dispersed in a polymer matrix (binder) .
• PDLC polymer dispersed liquid crystal
• PDLC shutters are manufactured by forming a transparent conductive layer, usually a layer of ITO material, on a substrate to form a front electrode for the PDLC shutter, coating a PDLC layer on the transparent electrode and then laminating a further substrate also having a conductive layer, usually of ITO material, to the PDLC layer to form a rear electrode.
• a transparent conductive layer usually a layer of ITO material
• front means the side of the display from which the display is to be viewed.
• a method of manufacturing a display comprising providing a substrate having a first electrode formed thereon and coated with a physically stabilised liquid crystal layer and printing a transparent second electrode over the physically stabilised layer.
• a display comprising a physically stabilised liquid crystal layer between a first electrode and a printed, transparent second electrode.
• the second electrode may be formed from a polymer mixture of a sulphonated polystyrene and a polythiophene based polymer.
• a polymer mixture of a sulphonated polystyrene and a polythiophene based polymer produces a second electrode that is transparent and printable and can match the performance of non-printed electrodes, such as ITO.
• the sulphonated polystyrene carries a negative charge, generally arrived at by deprotonation of part of the sulphonyl groups and, in one embodiment, is sodium polystyrene sulphonate.
• the polythiophene based polymer is a conjugated polymer and more preferably, carries a positive charge.
• the polythiophene based polymer may be a polyethylenedioxythiophene and most preferably, 3,4- ethylenedioxythiophene .
• the polymer mixture may be a macromolecular salt where both components are charged.
• the material of the second electrode may have a transparency above 70% and haze below 20%, preferably below 11%.
• the polymer mixture may be PEDOT: PSS.
• the method may comprise forming a barrier layer between the physically stabilised layer and the second electrode, the barrier layer arranged to restrict migration of liquid crystal from the physically stabilised liquid crystal layer to layers rearward of the barrier layer.
• the display may comprise an LC shutter, the LC shutter comprising the physically stabilised liquid crystal layer, the first electrode, the second electrode and the barrier layer.
• the display may comprise a backlight rearward of the second electrode for illuminating the LC shutter.
• An LC shutter does not comprise an EL layer that is driven by the first and second electrodes (common electrodes) that are used for switching the LC layer.
• the display may comprise a hybrid display arrangement comprising an EL layer behind the LC layer that is driven together with the LC layer by the first and second electrodes.
• Liquid crystal vesicles of the physically stabilised layer may include a dye and the barrier layer may be arranged to limit the migration of liquid crystal together with the dye from the LC layer to layers behind the LC layer such that no significant fading of the display occurs due to migration of the liquid crystal together with the dye under pre-determined criteria.
• the term "significant fading" is used herein to mean changes in contrast of the display that are noticeable to the naked eye
• the barrier layer may be arranged to limit the migration of liquid crystal from the LC layer to layers behind the LC layer such that, when the display is heated to 85 degrees over 18hrs, there is virtually no change, and preferably no change whatsoever, in contrast between illuminated and non-illuminated areas of the display.
• the barrier layer may comprise a material in which the liquid crystal has low solubility. As liquid crystal in the LC layer cannot dissolve in the barrier layer, migration of liquid crystal through the barrier layer to layers behind the LC layer is reduced or even eliminated.
• the barrier layer may comprise a material in which the liquid crystal has solubility lower than the solubility of liquid crystal in the polymer resin used in layers behind the barrier layer, such as the phosphor, dielectric, insulator and/or second electrode layers .
• the barrier layer may comprise material in which the liquid crystal has a low enough solubility such that no significant fading of layers behind the LC layer occurs due to migration of the liquid crystal under pre-determined criteria, for example, no significant fading of the layers behind the LC layer occurs due to migration of the liquid crystal when the display is heated at a set temperature for a set time, for example 85 0 C for approximately 18 hrs.
• Solubility can be measured as the maximum amount of solute that can dissolve per amount of solvent under specified conditions.
• the barrier layer may comprise a material in which the liquid crystal has substantially zero, and preferably zero, solubility at room temperature and atmospheric pressure.
• the barrier layer may comprise a hydrophilic layer, in particular a hydrophilic polymer.
• the polymer may be a water soluble polymer, such as polyvinyl alcohol, polyvinyl butyral, polyethylene glycol, polypropylene glycol, gelatine and its derivatives, cellulose derivatives polyacrylics and derived polymers and polyacrylic acids and derived polymers .
• the polymer may be a non- water soluble polymer that can be carried in an emulsion and/or dispersion, such as polyurethanes, polyethylene-acylic acid copolymer and derived copolymers, polymethacrylics and derived copolymers and polymethacrylic acids and derived copolymers.
• the polymer is a polyvinyl alcohol (PVA) .
• the barrier layer may comprise an adhesion promoter to improve the adhesion of the barrier layer with the LC layer.
• the barrier layer may further comprise a surfactant.
• a hydrophilic barrier layer When a hydrophilic barrier layer absorbs water it increases its electrical conductivity (reduces its resistivity) such that the electrical characteristics of the display may be similar to such a display without the barrier layer.
• a completely dry hydrophilic polymer layer may have a resistance of about 10 10 ⁇ cm, whereas, after absorbing water from the environment, its resistivity may reduce to 10 6 or even 10 5 ⁇ cm. In this way, the introduction of a hydrophilic barrier layer has little, or even no, impact on the electrical characteristics of the display, but acts to prevent migration of the liquid crystal.
• the method may comprise forming a dielectric layer over the physically stabilised LC layer and printing a second electrode over the physically stabilised liquid crystal layer and the dielectric layer. This will produce a display comprising a dielectric layer between the physically stabilised liquid crystal layer and the second electrode.
• the display may be an LC shutter and the method may comprise forming a dielectric layer over the physically stabilised LC layer and printing the second electrode over the physically stabilised liquid crystal layer and the dielectric layer.
• the dielectric layer may have a dielectric strength of more than 2V/ ⁇ m, and preferably 20V/ ⁇ m,
• the dielectric layer acts as a barrier to prevent the ink of the second electrode from entering the pin-holes in the physically stabilised layer during manufacture and therefore, reduces the chance of a defective display being manufactured.
• the dielectric layer may be transparent so that the LC shutter can be used with a backlight. Accordingly, in one embodiment, the display comprises a backlight rearward of the second electrode.
• the dielectric layer is reflective.
• Such an LC shutter works by reflecting the ambient light in regions of the LC layer that have been switched into a transparent state.
• a method of manufacturing a display comprises providing a substrate having a first electrode formed thereon and coated with a physically stabilised liquid crystal layer, forming a dielectric layer and printing a second electrode such that the dielectric layer is between the physically stabilised liquid crystal layer and the second electrode, the dielectric layer having a dielectric strength of at least 2V/ ⁇ m,
• a display comprising a physically stabilised liquid crystal layer between a first electrode and a printed, second electrode and a dielectric layer between the physically stabilised liquid crystal layer and the second electrode, the dielectric layer having a dielectric strength of at least 2V/ ⁇ m.
• the dielectric layer may be printed directly onto the physically stabilised liquid crystal layer.
• the dielectric layer is relatively thin having a thickness of less than 25 ⁇ m and preferably around 5 ⁇ m.
• a thin dielectric layer ensures that, in use, the dielectric layer does not significantly reduce the electric field applied across the LC layer.
• the dielectric layer has a high dielectric strength of greater than 2V/ ⁇ m, preferably 20 V/ ⁇ m to be able to withstand in excess of 100V across 5 ⁇ m in the region of pin-holes.
• the material of the dielectric layer should have a high dielectric constant, for example greater than 3 and preferably, above 5. Typical values would be 8 to 15.
• Appropriate materials for the dielectric layer include polyvinylidene fluoride (PVDF) , polyvinylidene fluoride/hexafluoropropylene
• PVDF/HFP polyester, vinyl, epoxy or polyvinylidene fluoride copolymers, such as Kynar 9301 , a proprietary terpolymer sold by Atofina, and cyano-resins, a range of proprietary polymers sold by Shin- Etsu Chemical Company.
• Cyano resins are produced by the reaction of acrylonitrile with a polymer having hydroxyl functionality.
• the first substrate may be a transparent substrate and the first electrode comprising a transparent conductive layer, for example such as an indium tin oxide layer (ITO) .
• ITO indium tin oxide layer
• PEDOT PSS
• BAYER BAYTRON
• AGFA GEVAERT ink by AGFA GEVAERT as ORGACON
• PSS polystyrene sulphonate
• the PSS component is acidic and, in use, the second electrode can pass through the pin-holes and attack the material, such as ITO, of the first electrode. This attack on the ITO layer can result in large and extended regions of non- operation.
• BAYTRON and ORGACON formulations contain an excess of PSS in order to improve dispersion stability and therefore, this problem is particular pronounced with these materials.
• the method may comprise performing a wash, preferably an aqueous wash, of the second electrode.
• the washing fluid is water, although the fluid may include small quantities of additives such as surfactants and detergents to improve the efficiency of the washing process. It has been found that the wash removes corrosive materials left over from printing of the second electrode, such as excess PSS, reducing or even preventing acidic erosion of the first electrode through pin-holes in the PDLC layer.
• the aqueous wash may be carried out in by washing the second electrode in a static bath two or more times or by allowing water to continuously flow over the second electrode for a predetermined length of time.
• the important feature of the wash is that it removes sufficient amounts of corrosive materials left over from printing of the second electrode in order to achieve a level of reliability in the manufacturing process. Accordingly, the approach taken to the wash will depend on how much of the corrosive materials it is deemed appropriate to remove, which itself will depend on the quality of the display to be produced and the level of reliability required in the manufacturing process. It has been found that soaking the film in water for an hour may remove substantially all of the excess PSS when printing an electrode made of PEDOT: PSS.
• the liquid crystal layer is in a physically stabilised form rather than its normal liquid mobile form, for example the liquid crystal may be liquid crystal vesicles encapsulated in a polymer matrix, such as a polymer- dispersed liquid crystal (PDLC) , or a polymer stabilised liquid crystal (PSLC) .
• PDLC polymer- dispersed liquid crystal
• PSLC polymer stabilised liquid crystal
• the method may comprise forming an electroluminescent (EL) layer such that the liquid crystal layer is mounted in front of the EL layer and printing the second electrode over the EL layer such that the first and second electrodes are arranged to generate, in use, an electric field across both the EL layer and the LC layer. Accordingly, the method may be used to form a Hybrid Display in which the LC layer and EL layer are driven by a common set of electrodes.
• the barrier layer may be formed between the LC layer and the EL layer to restrict migration of liquid crystal from the liquid crystal layer to the EL layer.
• the display may comprise an electroluminescent (EL) layer, the layer of physically stabilised liquid crystal switchable to define the information to the displayed mounted in front of the EL layer, at least one pair of electrodes arranged to generate, in use, an electric field across both the EL layer and the LC layer.
• EL electroluminescent
• the polymer matrix of the liquid crystal layer may be any one of water based, monomer free radiation curable urethane oligomer dispersions; acrylic functional polyurethane dispersions and acrylic urethane emulsions .
• the polymer matrix is a UV curable polymer matrix, for example a UV curable aliphatic polyurethane resin, such as those supplied by DSM Neoresin under the trade name NeoRez®.
• the matrix may comprise other film forming UV curable polymers, for example, UV curable polyurethane dispersions (known in the art as UV-PUD) , acrylic dispersions, silicones and mixtures therefore.
• the matrix resin can be formed from an aqueous solution or emulsion that contains very low levels, and preferably no, co-solvent.
• the polymer matrix comprises substantially no PVA.
• substantially no PVA means the polymer matrix comprises less than 5% PVA, preferably less than 1% PVA and most preferably, no PVA.
• a number of different component materials could be used to form a shell of the vesicles.
• One example of a pair of component materials that may be used for the shell is a multifunctional iscocyanate (e.g. the Desmodur range - sold by Bayer) and a diamine, such as ethylene diamine.
• the reaction may be catalysed by a tertiary amine, such as DABCO.
• the liquid crystal may be any one of the main types such material - such as nematic and cholesteric or chiral nematic - the requirement is , generally, for a liquid crystal based material that allows polariserless high contrast electro-optical shuttering operation between a field "on” state that is optically transmissive and a base field “off” state that us less transmissive than the "on” state.
• the liquid crystal contains a dye.
• the liquid crystal includes up to 6% by weight of a dye, preferably a dichroic dye.
• levels of dye in the liquid crystal are 3- 5% by weight.
• the dye attaches to the liquid crystal molecules and acts to obscure light when no field is applied across the liquid crystal but when a field is applied, the dye molecules are aligned for allowing the transmission of light.
• the barrier layer limits the migration of both the liquid crystal and dye to layers behind the liquid crystal layer.
• a display may comprise: an electrically-insulating transparent front layer known as the substrate, usually made of glass or plastic, such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) ; a first electrically-conductive film, for example, made from a material such as indium tin oxide (ITO) , forming one electrode - the front electrode - of the backlight; a polymer dispersed liquid crystal (LC) layer, the liquid crystal vesicles including a dye; a barrier layer of polyvinyl alcohol; a dielectric layer having a dielectric strength of more than 2V/ ⁇ m; and disposed over the rear face of the electrically-insulating layer or
• the substrate usually made of glass or plastic, such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN)
• PET polyethylene terephthalate
• PEN polyethylene naphthalate
• LC polymer dispersed liquid crystal
• the second electrode formed from a polymer mixture of a sulphonated polystyrene and a polythiophene based polymer.
• the display of the invention may incorporate disposed over the entire rear face of the substrate a single (front) electrode, and disposed over the rear face of the reflective electrically-insulating layer a patterned (rear) electrode defining areas of the liquid crystal layer that can be selected to be switched "on” or “off” .
• a patterned (rear) electrode defining areas of the liquid crystal layer that can be selected to be switched "on” or "off” .
• both electrodes to be patterned - as will need be the case if the display is going to be a matrix device where a multitude of very small areas can be illuminated at will so as to enable almost any shape and size of displayed image simply by selecting which areas are lit and which are dark.
• the display may further comprise an electroluminescent (EL) layer (usually a particulate phosphor within a binder matrix) between the barrier layer and the dielectric layer.
• EL electroluminescent
• a dielectric layer in a display comprising a physically stabilised liquid crystal layer between a first electrode and a printed, second electrode, the dielectric layer located between the physically stabilised liquid crystal layer and the second electrode, to prevent the ink used to form the second electrode from entering pin-holes in the physically stabilised liquid crystal layer during manufacture of the display.
• a method of reducing fading of a display comprising a mask defining the information to be displayed, the mask comprising a layer of physically-stabilised liquid crystal comprising liquid crystal vesicles including a dye and a first electrode and a printed, transparent second electrode arranged to generate, in use, an electric field across the LC layer, the method comprising providing a barrier layer between the LC layer and the second electrode that restricts migration of liquid crystal together with the dye from the LC layer to layers rearward of the LC layer.
• the method may comprise identifying a material that, when used as a barrier layer, limits the migration of liquid crystal from the LC layer to layers behind the LC layer such that no significant fading of the display occurs due to migration of the liquid crystal and using the identified material for the barrier layer.
• a method of determining a material suitable for use as a barrier layer in a display comprising :- forming a display comprising a mask defining the information to be displayed, the mask comprising a layer of physically-stabilised liquid crystal and a first electrode and a printed, transparent second electrode arranged to generate, in use, an electric field across the LC layer and a layer of material between the LC layer and the second electrode that has potential as the material of the barrier layer, heating the display to a predetermined temperature for a predetermined length of time, and examining the display for visible signs of liquid crystal migration to layers behind the LC layer.
• a method of manufacturing a display comprising forming a first electrode on a substrate, forming a mask defining the information to be displayed, the mask comprising a layer of physically stabilised liquid, forming a barrier layer, forming a transparent second electrode such that a voltage can be applied to the first and second electrodes to generate an electric field across the LC layer, wherein the barrier layer is made of material identified as suitable for use as a barrier layer in accordance with the tenth aspect of the invention.
• a display comprising a mask defining the information to be displayed, the mask comprising a layer of physically-stabilised liquid crystal switchable to define the information to the displayed, a first electrode and a printed, transparent second electrode arranged to generate, in use, an electric field across the LC layer and a barrier layer between the mask and the second electrode, wherein the barrier layer is made of material identified as suitable for use as a barrier layer in accordance with the tenth aspect of the invention.
• Figure 1 shows a section through a display according to an embodiment of the invention
• Figure 2 shows the display of Figure 1 in plan view
• Figure 3 is a table illustrating the suitability of different materials as a barrier layer; and Figure 4 shows a section through a display comprising an LC shutter and separate backlight.
• FIG. 1 of the accompanying drawings The structure of the embodiment of the display of the invention depicted in Figure 1 of the accompanying drawings can be seen to be, from front to back: a relatively thick protective electrically-insulating transparent front layer (11 ; the substrate) ; over the rear face of the substrate 11 , a very thin transparent electrically-conductive film (12) forming a front (first) electrode of the display; covering the rear face of the front electrode 12, a relatively thin layer 13 of LC material 14 physically-stabilised by being dispersed within a supporting polymer matrix 15 (PDLC layer) ; formed directly on, and covering the rear face of the liquid crystal layer 13, a relatively thin barrier layer 10 of PVA that restricts migration of liquid crystal from the PDLC layer 13 to layers 16 , 19,20 to the rear of the LC layer; a relatively thin layer of electroluminescent/phosphor material 17 dispersed within a supporting matrix 18; over the rear face of the phosphor layer 16, a 5 ⁇ m thick optically- transparent electrically-insulating dielectric layer 19 (in
• the front and rear electrodes together define discrete areas of both the liquid crystal layer and the electroluminescent layer that can be selected to be switched "on” or “off” .
• the LC layer defines a mask defining the information to be displayed and the EL layer providing a source of light to illuminate the areas defined by the mask.
• the back electrode layer may be covered with a protective film (not shown here) .
• the dielectric constant of the electrically insulating layer is around 8 to 15 and the dielectric strength is around 20V/ ⁇ m.
• the PDLC layer 13 of the display is formed in the manner described in GB 0625114.4 with liquid crystal vesicles encapsulated in a UV cured polyurethane matrix.
• the liquid crystal vesicles include up to 6% by weight of a dye, preferably a dichroic dye, such that the PDLC layer 13 is switchable between a transmissive state and absorbing state (in which the PDLC layer 13 is predominately absorbing) .
• the term “relatively thick” means thicknesses in the range of 30 to 300 micrometres. Furthermore, it will be understood that the term “relatively thin” means thicknesses of 50 micrometres or less. In a preferred embodiment, the relatively thick layers are around 100 micrometres and the relatively thin layers are 25 micrometres or less.
• Figure 2 is an example of the types of information that may appear on the display.
• the display may be manufactured substantially as is described in WO 2005/0121878, International patent application No: WO2008075001 and UK patent application No:0865751.5.
• the second electrode 16 may be formed by screen-printing PEDOT: PSS material onto the phosphor layer 19. After printing of the second electrode, an aqueous wash of the resultant film may be performed to remove any excess PSS from the film.
• the aqueous wash comprises soaking of the film in water for an hour.
• a number of materials were evaluated as barrier layers by coating a layer of diluted polymer solution onto a sample of PDLC prepared as described in GB 0625114.4. After drying the layer an EL lamp construction was printed onto the rear side of the layer of diluted polymer solution. Each display was then aged by placing the display in an oven held at 85 0 C for approximately 18 to 24 hrs, at which point it was examined for visible signs of liquid crystal/dye migration. A second display having a barrier layer of each material was characterised electro-optically before and after a similar aging process.
• Figure 3 illustrates the results of these tests.
• PVA has been identified as particularly suitable for use as the barrier layer and a mixture of this polymer and an adhesion promoting polymer has also been identified as suitable depending on the required electro-optical performance of the display.
• test displays prepared using an alternative PVA as a barrier layer were prepared and subjected to a hot-humid aging test at 65°C/90%RH while being driven. It was found that the displays functioned after this test with a small degradation in performance. This was surprising, as it has been found previously that use of a hydrophilic polymer, such as PVA, as the polymer matrix of the PDLC layer can result in poor environmental stability.
• a hydrophilic polymer such as PVA
• barrier layer may be suitable for use as a barrier layer. It is believed these suitable materials can be determined by testing the material in the manner described above. The suitability of the material for the barrier layer will depend on the required performance for the display. Therefore, the temperature to which the display is heated and the time for which the display is heated during the test may be varied depending on the required performance. Materials identified as suitable for a barrier layer then can be used to manufacture a display in accordance with the invention.
• suitable materials will be those in which liquid crystal has low solubility.
• barrier layers it may also be advantageous to include a polymer to improve the adhesion of the barrier layer with the LC layer and/or the EL layer.
• the structure of the embodiment of the LC shutter 101 from front to back comprises: a relatively thick protective electrically-insulating transparent front layer (111 ; the substrate) ; over the rear face of the substrate 111 , a very thin transparent electrically-conductive film 112, of for example ITO, forming the front (first) electrode of the display; covering the rear face of the front electrode 112, a relatively thin layer 113 of LC material 114 physically-stabilised by being dispersed within a supporting polymer matrix 115 (PDLC layer) ; formed directly on, and covering the rear face of the liquid crystal layer 113, a relatively thin barrier layer 110 of PVA that restricts migration of liquid crystal from the PDLC layer 113 to layers 116, 119, 120 to the rear of the LC layer; over the rear face of the barrier layer 110, an optically-transparent electrically-insulating dielectric layer 119, having a dielectric constant of around 8 to 15 and
• This embodiment of the display further comprises a backlight 121 rearward of the rear electrode 120 providing means to illuminate the LC shutter 101.
• the backlight 121 may be an electroluminescent, LED, incandescent or other suitable backlight.
• the backlight 121 may comprise a waveguide to direct light from the light source to illuminate the LC shutter 101.
• the dielectric layer 119 may be a reflective dielectric material, such as a barium titanate loaded polymer resin, to form a reflective LC shutter and no backlight is required.
• the PDLC layer 113 of the display is formed in the manner described in GB 0625114.4 with liquid crystal vesicles encapsulated in a UV cured polyurethane matrix.
• the liquid crystal vesicles include up to 6% by weight of a dye, preferably a dichroic dye, such that the PDLC layer 113 is switchable between a transmissive state and absorbing state (in which the PDLC layer 113 is predominately absorbing) .
• the LC shutter 101 may be manufactured in a similar manner to the hybrid display described with reference to Figures 1 and 2.
• the second rear electrode 120 may be formed by screen-printing PEDOT:PSS material onto the phosphor layer 119.
• the dielectric layer 119 blocks the ink used to form the second electrode 120 from the second rear electrode 120 from entering pin-holes in the LC layer 113.
• the dielectric layer 119 is made of transparent materials rather than reflective materials as light from the backlight 121 has to pass through the LC shutter 101.
• an aqueous wash of the resultant film may be performed to remove any excess PSS from the film.

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• 2008
  • 2008-07-31 GB GB0813970A patent/GB0813970D0/en not_active Ceased
• 2009
  • 2009-07-28 EP EP09785406A patent/EP2307925A1/de not_active Withdrawn
  • 2009-07-28 CN CN200980130588XA patent/CN102112908A/zh active Pending
  • 2009-07-28 WO PCT/GB2009/050932 patent/WO2010013041A1/en active Application Filing

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