Process and structures for selective deposition of liquid-crystal emulsion

FIELD OF THE INVENTION

The present invention relates to a display system having a selectively deposited bistable material, such as polymer-dispersed cholesteric-liquid-crystal material, that can change optical states, and a method of forming a display.

BACKGROUND OF THE INVENTION

Electronic displays are used for many applications, including shelf labels, pricing displays, instrument panels, and signage. The displays can include a range of materials, including bistable materials such as liquid crystal, which can change from one optical state to another in response to applied electrical and/or thermal fields. Materials comprising cholesteric liquid crystals, also referred to as “chiral nematic” liquid crystals, are capable of maintaining a plurality of different optical states in the absence of an electrical field. Additionally, the optical state of the cholesteric liquid-crystal material can be changed from one state to another in response to applied electrical and/or thermal fields. These properties make these materials useful in the development of field-stable, rewritable displays.

In particular, cholesteric liquid-crystal materials are capable of being electrically driven, at ambient temperatures, between a reflective planar state (reflecting a specific visible wavelength of light) and a light-scattering focal-conic state. Cholesteric liquid-crystal materials have the capacity of maintaining these two optical states, planar or focal-conic, in the absence of an electric field. For example, U.S. Pat. No. 5,437,811 issued Aug. 1, 1995 to Doane et al. discloses a light-modulating cell having a polymer-stabilized chiral-nematic liquid-crystal material that is capable of switching between a planar state, reflecting a specific visible wavelength of light, and a weakly light-scattering focal-conic state.

U.S. Pat. No. 5,636,044 discloses a bistable cholesteric display. Two patterned substrates, made of glass or plastic, face each other. Cholesteric material is disposed between the two substrates or plates. The cholesteric material can contain a polymer gel or dye. Electrodes are exposed by offsetting the substrates to expose connection areas on the substrates. The display is built by bonding the two substrates together and then filling the cell with liquid-crystal material, after which radiation is applied to create polymer threads in the display that stabilize the cholesteric material. Cholesteric material processed in such a manner is known as a polymer stabilized cholesteric (PSC). Such displays require two substrates.

U.S. Pat. No. 4,140,016 discloses a plurality of selectively deposited cholesteric materials disposed on a substrate to create a temperature sensing paddle. The cholesteric materials are encapsulated using closed-core microencapsulation. The materials can be deposited by a variety of processes such as gravure printing, silk screen printing, and the like. There are no electrodes in the structure that permit an electric field to be applied across the cholesteric material. Such materials change state only in the presence of a specific temperature, and cease to maintain the second state in the absence of a specific temperature.

Bistable displays can be costly to manufacture and bulky when the associated electrical components are formed on a separate substrate and attached to the display material. The general practice of deploying separate substrates for the display plane and the electronic components is due to heat sensitivity of the display material and manufacturing difficulty in forming multiple components on a single substrate. For example, U.S. Pat. No. 6,118,426 discloses an electrophoretic display printed on a single flexible substrate. It describes printing the various layers comprising the display element by various means of printing and coating. There is no indication of how electrical components could be integrated on the single substrate display element.

Fabrication of flexible, electronically written display sheets is disclosed in U.S. Pat. No. 4,435,047 issued Mar. 6, 1984 to Fergason. An emulsion of nematic liquid crystal in water is coated over a plastic sheet having a low-resistance ITO coating. A doctor blade is used to cast the emulsion over the sheet at a specific thickness. The liquid crystal material is a nematic liquid crystal with a dye that can be electrically switched between a transparent and light-blocking state. The display ceases to present an image when de-energized. The coated electrode is unpatterned, and contacted by a single electrical lead. No mention is made as to how the first electrode is kept free of coated materials that are coated over the first conductor.

U.S. Pat. No. 5,289,300 discloses a liquid-crystal material formed over a semiconductor array. The material is a UV-cured polymer-dispersed cholesteric liquid-crystal material. Coating methods disclosed include solvent coating of the polymer, including water and hydrocarbon solvents, using methods including doctor blades or roll coating. No methods are disclosed that describe how the inner electrodes are clear of the polymer-dispersed overcoat.

Manufacturing of displays with electrical components can include the use of permanent masks, or masks requiring removal by etching. For example, in U.S. Pat. No. 4,665,342, a screen printable electroluminescent display on a single flexible substrate is disclosed, wherein the first conductive layer is covered with a permanent dielectric material. Use of permanent dielectric masks during the manufacture of bistable displays is one way to integrate the associated electronic components on the flexible substrate. However, permanent dielectric masks have several disadvantages. Because the dielectric mask is permanent, the area covered by the mask is permanently unavailable for population by electrical components that require contact with circuitry in close proximity to the display plane, causing the display plane to be larger in size. Further, the permanent dielectric mask can be damaged during subsequent operations needed to create a functioning display plane, resulting in failed operation of the display.

In recent years, attempts to incorporate some electrical components on the display substrate have been made. For example, U.S. Pat. No. 6,369,793 B1 discloses an electrophoretic, electrochromic, thermochromic, or electroluminescent display, together with a printed battery on a flexible substrate. U.S. Pat. No. 6,503,831 B2 discloses using ink jet printing to form an active matrix switching array, a display pixel, or both. Such jetting methods require that the material to be printed conform to the requirements of a printable substance so as to be successfully processed through small diameter nozzles, and still provide the required functionality in the layers formed. U.S. Pat. No. 6,480,182 discloses a printable method for creating a patterned electrophoretic, rotating-ball, or electrostatic display. The above methods are not suitable for continuous manufacture, such as roll-to-roll manufacture of a display.

Other shortcomings of known displays include the difficulty in formulating necessary electrical contacts to conductive layers in the display. U.S. Pat. No. 6,262,697 discloses a coated polymer-dispersed liquid-crystal layer. An inner electrode is buried under the polymer-dispersed material, a piercing pin is used to form connection to the inner electrodes. U.S. Pat. No. 6,236,442 discloses another means for connecting to an inner conductor coated with polymer-dispersed liquid-crystal material. Overcoated layers are removed to expose a power area that permits connection to an inner transparent, electrically conductive layer.

It would be useful to have a process and structure to improve the manufacture of a display in which a polymer-dispersed cholesteric material is built-up on a substrate. It would be advantageous for the process not to require the removal of previously coated layers.

SUMMARY OF THE INVENTION

The need is met according to the present invention by a method of forming a display comprising the steps of (a) providing a substrate; (b) forming a plurality of first conductors over the substrate; (c) depositing a layer of cholesteric liquid-crystal material, in the form of droplets of liquid crystal in a liquid carrier, over a preselected area of each of said first conductors so that a preselected portion of each of said first conductors is uncoated; (d) drying the liquid carrier to form a layer of polymer-dispersed cholesteric liquid-crystal domains in a continuous matrix; and (e) forming a plurality of second conductors, electrically isolated from the first conductors, over the layer of polymer-dispersed liquid-crystal domains so that an electric field between the second conductors and the uncoated portions of the first conductors is capable of changing the optical state of the polymer-dispersed cholesteric liquid-crystal material. Additional steps can include one or more of formation of a circuit layer before or after formation of the first conductors separated therefrom by a mask, providing a mask between the first conductors or circuit layer and a layer of bistable material, and removal of one or more masks after formation of the bistable material layer.

ADVANTAGES

The method of forming an integral electronic display on a single substrate as disclosed herein provides for consistent registration of electrical circuits within the display, better and more reliable connections between electronic components and conductive layers of the display, a thinner display device, and easier formation of electrical connections to the display; reduces risk of damage to the display while forming electrical connections thereto; and alleviates the necessity for a separate circuit board. Further, formation of an integral electronic display can utilize multiple methods of forming circuits and electrical connections, including continuous coating or printing methods, without harm to the display materials. This enables the use of common coating machines for manufacture of the display, and a wider choice of materials, reducing manufacturing costs.

The present invention has the further advantage that minimal amounts of bistable material, for example, polymer-dispersed cholesteric material, are deposited. The absence of a coating over the second conductors permits connection to the first conductors without additional processing steps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a prior-art display element;

FIG. 2 is an isometric view of a display element in accordance with the present invention;

FIG. 3 is a sectional view showing a display element with cholesteric material in two stable optical states;

FIG. 4 is a top view of an array of display elements on a flexible substrate in accordance with prior art;

FIG. 5 is a top view of a continuous substrate having a plurality of display elements, in accordance with the present invention;

FIG. 6 is a side view of a sheet having patterned transparent first conductors;

FIG. 7 is a top view of the sheet of FIG. 6 having patterned transparent first conductors;

FIG. 8 is a side view of a sheet prepared for selective deposition of a liquid-crystal emulsion;

FIG. 9 is a top view of the sheet of FIG. 8 prepared for selective deposition of a liquid-crystal emulsion;

FIG. 10 is a side view of a sheet after selective deposition of a liquid-crystal emulsion on the sheet;

FIG. 11 is a top view of the sheet of FIG. 10 in which the liquid-crystal material has been selectively deposited;

FIG. 12 is a side view of a sheet after selective deposition of a liquid-crystal emulsion on the sheet and showing the removal from the sheet of the apparatus used for selective deposition;

FIG. 13 is a side view of a sheet after a selectively deposited liquid-crystal emulsion has been dried;

FIG. 14 is a top view of the sheet of FIG. 13 showing the dried selectively deposited liquid-crystal emulsion;

FIG. 15 is a top view of one embodiment of a display element after printing of the conductors is completed;

FIG. 16 is a side view of one embodiment of a display element with printed second conductors having electrically addressable pixels;

FIG. 17 is a top view of the display element of FIG. 16;

FIG. 18 is a side view of a second structural embodiment of a display element comprising a selectively deposited liquid-crystal material;

FIG. 19 is a side view of a third structural embodiment of a display element for a selectively deposited liquid-crystal material;

FIG. 20A, FIG. 20B, and FIG. 20C are side views illustrating the process steps for sequentially depositing two different selectively deposited coatings over a sheet comprising first conductors;

FIG. 21 is a view of a substrate with fiducial marks and circuits;

FIG. 22 is the substrate of FIG. 21 further having a mask;

FIG. 23 is the substrate of FIG. 22, further having first conductors;

FIG. 24 is the substrate of FIG. 23, wherein the first conductors are electrically isolated;

FIG. 25 is the substrate of FIG. 24, further having bistable material;

FIG. 26 is the substrate of FIG. 25, wherein the mask is removed; and

FIG. 27 depicts a completed display element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A process of forming electronic displays can include a combination of masking and coating of layers on a substrate. Once a mask is applied to a first conductive layer or circuit layer, additional layers of the display can be formed by coating or printing techniques known in the art, including panel and roll-to-roll processes. Use of a roll-to-roll process can reduce manufacturing costs.

“Coating” as used herein includes coating and printing techniques. Coating methods suitable for use with the display element layers described herein include for example, sheet coating, patch coating, die coating, slot coating, extrusion coating, slide coating, cascade coating, curtain coating, roll coating, forward and reverse roll coating, gravure coating, dip coating, meniscus coating, spin coating, brush coating, air knife coating, and spray coating. As an alternative to coating, various printing methods including, but not limited to, screen printing, electrostatic printing, thermal printing, ink jet printing, gravure printing, and lithography can be used to form the layers of the display element. One or more layers can be formed in a pattern such that the layer covers only those areas requiring the layer material, providing cost and material savings.

An electronic, rewritable display can be used in a signage system. The display can have one or more display element, for example, two, three, or more display elements. Each display element can be flexible. The display element can be made in any shape, for example round, rectangular, parallelogram, square, or irregular. According to certain embodiments, the display can be flexible. The display, when flexible, can follow the shape of a surface to which it is attached, for example, turning a corner of a wall. The display can be double-sided, having at least one display element on each side. Each viewing surface of the display, regardless of display shape, can include one or more display elements. If multiple display elements are used, they can be arranged in a pattern, form a grid covering at least a portion of the surface of the display, or each display element can abut at least one other display element.

The display element can be a rewritable, electronic display element. Display elements can include one or more electrically imageable material. The electrically imageable material can be light emitting or light modulating. Light emitting materials can be inorganic or organic in nature. Exemplary light emitting materials can include organic light emitting diodes (OLED) and polymeric light emitting diodes (PLED). The light modulating material can be reflective or transmissive. Light modulating materials can be electrochemical, electrophoretic, such as Gyricon particles, electrochromic, or liquid crystals. The liquid crystalline material can be twisted nematic (TN), super-twisted nematic (STN), ferroelectric, magnetic, or chiral nematic liquid crystals. Especially preferred are chiral nematic liquid crystals. The chiral nematic liquid crystals can be polymer dispersed liquid crystals (PDLC).

According to certain embodiments, the electrically imageable material can be addressed with an electric field and then retain its image after the electric field is removed, a property typically referred to as “bistable.” Particularly suitable electrically imageable materials that exhibit “bistability” are electrochemical, electrophoretic, such as Gyricon particles, electrochromic, magnetic, or chiral nematic liquid crystals. According to certain embodiments, the bistable material can be chiral nematic liquid crystals. The chiral nematic liquid crystals can be polymer dispersed liquid crystals (PDLC).

The substrate of the display element can be any suitable material, for example, glass or plastic. When the substrate is plastic, it can be flexible, for example, a flexible self-supporting plastic film. “Plastic” means a polymer, usually made from polymeric synthetic resins, which can optionally be combined with other ingredients, such as curatives, fillers, reinforcing agents, colorants, and plasticizers. Plastic includes thermoplastic materials and thermosetting materials. The substrate can be transparent or opaque. The substrate can be coated at least partially with a colored or opaque material to prevent viewing of the electronic components on the substrate in the formed display element. Suitable materials for a flexible substrate can include, but are not limited to, polyethylene terephthalate, polyethylene naphthalate, and polyimide. The substrate can withstand temperatures required for attaching electronic components by solder reflow. The substrate can provide dimensional stability during manufacture of the display element. The substrate can have a thickness of between 12 and 300 microns. Where a flexible plastic substrate is used, it can be reinforced with a hard coating, for example, an acrylic coating. The coating can have a thickness of from 1 to 30 microns, for example, from 2 to 4 microns. Various suitable hard coatings can be used, dependent upon the substrate material. Such coatings can include a mixture of UV-cured polyester acrylate and colloidal silica, known as “Lintec” by Lintec Corporation of Tokyo, Japan, and an acrylic coating sold as Terrapin® by Tekra Corporation, New Berlin, Wis.

A first conductive layer can be formed on the substrate or adjacent the bistable material. The first conductive layer can include one or more metal oxide. A primary metal oxide can be indium oxide, titanium dioxide, cadmium oxide, gallium indium oxide, niobium pentoxide, or tin dioxide, for example. A secondary metal oxide can also be in the conductive layer, and can be, for example, an oxide of cerium, titanium, zirconium, hafnium and/or tantalum. See U.S. Pat. No. 5,667,853 to Fukuyoshi et al. Transparent conductive oxides that can be used include, but are not limited to, ZnO₂, Zn₂SnO₄, Cd₂SnO₄, Zn₂In₂O₅, MgIn₂O₄, Ga₂O₃—In₂O₃, or TaO₃. According to various embodiments, the first conductive layer can be tin-oxide, indium-tin-oxide (ITO), or polythiophene. The first conductive layer can be an opaque electrical conductor formed of metal such as copper, aluminum or nickel. If the conductive layer is an opaque metal, the metal can be a metal oxide to create a light absorbing conductive layer. The first conductive layer can be formed by any known method, including low temperature sputtering techniques and direct current sputtering techniques, such as DC-sputtering or RF-DC sputtering, or printing, depending upon the material or materials of the underlying layer. The first conductive layer can be patterned, for example, into a plurality of electrodes.

A circuit layer can be formed on the substrate or adjacent the bistable material. The circuit layer can be formed by printing or coating. Alternately, the circuits can be preformed and applied to a layer. Optionally, an adhesive can be used to apply the circuit layer. The circuit layer can be adhered to the substrate or first conductive layer by heat, for example, using heat-activated adhesive or by melting or fusing of the materials of the adjacent layers. The circuits can be formed of any conductive material, including those listed for the first conductive layer. For example, the circuits can be any conductive metal, metal oxide, or conductive ink.

The first conductive layer or circuit layer can be coated with a bistable material, or a pre-formed layer of bistable material can be placed over the first conductive layer or circuit layer. The bistable materials can be those described elsewhere herein.

A second conductive layer can be formed over the bistable material. The second conductive layer can be formed by printing or coating techniques on the bistable material, or a preformed layer applied to the bistable material layer. The second conductive layer can be selected from any conductive material as described for the first conductive layer. According to certain embodiments, one or more of the first or second conductive layer can be formed of a transparent material, for example, indium tin oxide (ITO) or polythiophene.

Application of electric fields of various intensity and duration to the bistable material between the first and second conductive layers can cause the bistable material to change its state from a reflective state to a transmissive state, or vice versa. The bistable material can maintain a given state indefinitely after the electric field is removed without further power being applied to the conductive layers.

The second conductive layer can be patterned non-parallel to patterning of the first conductive layer. The intersection of the patterns of the first conductive layer and the second conductive layer forms a pixel. The bistable material in the pixel changes state when an electric field is applied between the first and second conductive layers.

The second conductive layer can be formed as electrically conductive character segments over the bistable material by thick film printing, sputter coating, or other printing or coating techniques. The conductive character segments can be formed by etching, ablation, or other removal techniques if the second conductive layer is formed as a contiguous layer. The conductive character segments can be any known conductive material, for example, carbon, graphite, or silver. An exemplary material is Electrodag 423SS screen printable, electrically conductive material from Acheson Colloids Company, Port Huron, Mich. The conductive character segments can be arranged to form numbers 0-9, a slash, a decimal point, a dollar sign, a cent sign, or any other alphanumeric character or symbol.

Wherein the bistable material is a liquid crystal material, a dielectric layer such as deionized gelatin can be formed over the conductive character segments by standard printing or coating techniques. Via holes can be formed over each conductive character segment by the absence of the dielectric layer over at least a portion of each conductive character segment, or by removing a portion of the dielectric layer over each conductive character segment, for example, by ablation or chemical etching.

Electrically conductive traces can be formed over the dielectric layer by printing or coating techniques. One or more electrically conductive trace can flow through a via hole on formation, making electrical contact with the conductive character segment. The conductive traces can extend from the character segment to an exposed area along a side of the display element, where the conductive trace forms a contact pad in the exposed area. The exposed area is an area of the substrate coated with the first conductive layer or circuit layer.

Contact pads can be any conductive material, for example, silver or carbon. Contact pads can be formed with conductive traces, or separately therefrom. Contact pads that are not formed with conductive traces can be coated or printed on the dielectric layer. A via hole can extend from the conductive pad through the dielectric layer to the first conductive layer or circuit layer. The exposed area and the contact pads thereon can be formed along one side of the display element, along multiple sides of the display element, or in one or more locations on the display element not including a conductive character segment. According to various embodiments, the contact pads can be formed in the exposed area along one edge of the display element. The contact pads can be placed linearly or grouped, such as in a pattern, for example, a square or rectangle, in the exposed area.

The optical state of the bistable material between the conductive character segment and the first conductive layer can be changed by selectively applying drive voltages to the corresponding contact pad that is electrically connected to the conductive character segment through a conductive trace, and to the first conductive layer. Once the optical state of the bistable material has been changed, it can remain in that state indefinitely without further power being applied to the conductive layers. Methods of forming the display element are known to practitioners in the art, and are described, for example, in U.S. Ser. No. 10/134,185, filed Apr. 29, 2002 by Stephenson et al., and in U.S. Ser. No. 10/851,440, filed May 21, 2004, to Burberry et al.

The display element can be formed by inserting one or more masking layer between electrically sensitive layers. For example, a masking layer can be inserted between a first conductive layer and a circuit layer, between a circuit layer and a bistable material layer, or between a first conductive layer and a bistable material layer. The masking layer can be removed in whole or in part at any point in the manufacture of the display element after the formation of the bistable material layer. Alternately, all or a portion of a masking layer can be permanent in the display element structure.

The masking layer can be formed from any material capable of protecting electrically sensitive material from making electrical contact with other electrically sensitive material during formation of subsequent layers of the display element, or an electrically conductive material, depending on the intended purpose of the masking material. For example, the masking layer can be a polymeric film, a metallic foil, or a dielectric material as described elsewhere herein. The masking layer can be coated or printed on portions of the circuit layer, the first conductive layer, or both. The masking layer can be preformed and applied to the circuit layer, first conductive layer, substrate, or combinations thereof. The masking layer can be attached to portions of the circuit layer, first conductive layer, or substrate with an adhesive, heat bonding, chemical bonding, or mechanical retainer, such as but not limited to a clip, pin, or clamp. The masking layer can be formed with openings therein suitable for receiving the remaining layers of the display, or can be formed as a continuous layer and openings formed in the masking layer by etching, chemical or laser ablation, cutting, scratching, or any other method suitable to remove portions of the masking layer without affecting the circuit layer or first conductive layer.

The masking layer can be removably or permanently formed on a portion of the circuit layer, first conductive layer, substrate, or a combination thereof. The masking layer can include a permanent and a removable portion. For example, the masking layer can be formed such that areas of the masking layer covering the circuits are removable where the circuits are desirably connected to other circuits or electrical components, and the remaining portions of the masking layer over the circuits and optionally the substrate are permanent. Similarly, a masking layer formed over a first conductive layer can be removable, permanent, or have both removable and permanent portions. The masking layer can include discrete mask portions, can be continuous over all or a portion of a layer, or can be patterned with no isolated mask portions.

Exemplary methods of forming the display element using a mask are described with reference to the Figures.

Referring to FIG. 1, a display element 10 according to prior art is shown, and includes two substrates 15, made of either glass or plastic. As used herein, the term “display element” will refer to a display and manufacturing intermediates thereof. A display element can be viewed as complete when comprising all components used in the final product which may be either connectably separate from, or integral with, other components such as a drive mechanism and a source of power. In the display element of FIG. 1, conductors are formed in each of the two substrates, and an extended face portion of one substrate 15 provides exposed first conductors 20 for interconnection with an electric field source. A polymer-dispersed cholesteric layer 30 is present between the two substrates 15 and, when the display element is operated on by an electrical field (via appropriate connections), can provide an image on the display element 10. According to the prior art, a seal is provided around the perimeter of the two substrates 15 prior to filling the “cell” in order to retain liquid polymer-dispersed cholesteric layer 30. Cholesteric liquid is then wicked between the two substrates 15. In certain cases, radiation is applied through the substrate 15 to form polymer networks within the cholesteric liquid-crystal material.

FIG. 2 is an isometric view of a display element 10 in accordance with one embodiment of the present invention. Flexible substrate 15 can be a thin transparent polymeric material such as Kodak Estar® film base formed of polyester plastic that has a thickness of between 20 and 200 micrometers. In an exemplary embodiment, substrate 15 can be a 125-micrometer-thick sheet of polyester film base. Other polymers, such as transparent polycarbonate, can also be used. In contrast to FIG. 1, display element 10 only requires a single substrate, for reasons that will become obvious below.

In FIGS. 1 and 2, first conductors 20 are formed over substrate 15. First conductors 20 can be, for example, tin-oxide or indium-tin-oxide (ITO), with ITO being the preferred material. Typically, the material of first conductors 20 is sputtered as a layer over substrate 15 having a resistance of less than 500 ohms per square. The layer is then patterned to form first conductors 20 in any well-known manner. Transparent first conductors 20 can also be formed by printing a transparent organic conductor such as PEDT/PSS, PEDOT/PSS polymer, which materials are sold as Baytron® P by Bayer AG Electronic Chemicals.

Alternatively, first conductors 20 can be an opaque electrical conductor material such as copper, aluminum or nickel. If first conductors 20 are an opaque metal, the metal can have an oxidized surface to provide a light-absorbing surface. First conductors 20 can be formed in a conductive coating by conventional lithographic or laser etching means.

A polymer-dispersed cholesteric layer 30 can cover portions of first conductors 20, leaving uncoated exposed first conductors 22. Polymer-dispersed cholesteric layer 30 includes a polymeric-dispersed cholesteric liquid-crystal material, such as those disclosed in U.S. Pat. No. 5,695,682, the disclosure of which is incorporated by reference. Application of electrical fields of various intensity and duration can drive a chiral-nematic (cholesteric) material into a reflective state, a transmissive state, or an intermediate state. These materials have the advantage of maintaining a given state indefinitely, after the field is removed. Cholesteric liquid crystal materials can be, for example, Merck BL112, BL118, or BL126, available from E.M. Industries of Hawthorne, N.Y.

In a preferred embodiment, polymer-dispersed cholesteric layer 30 is E.M. Industries' cholesteric material BL-118 that is dispersed in deionized photographic gelatin to form an emulsion. The liquid-crystal material can be dispersed, for example, at 8% concentration in a 5% deionized gelatin aqueous solution. The mixture is dispersed to provide 10 micron diameter domains of the liquid crystal in aqueous suspension. The material can be coated over patterned ITO first conductors 20 to provide a 9-micron-thick polymer-dispersed cholesteric coating. Other organic binders such as polyvinyl alcohol (PVA) or polyethylene oxide (PEO) can be used. Such compounds are machine coatable on various equipment, including but not limited to equipment associated with the making of photographic films. A conventional surfactant can be added to the emulsion to improve adhesion to first conductors 20. Conventionally known surfactants can be employed and provided at a concentration that corresponds to the critical micelle concentration (CMC) of the solution. A gel sub layer can be applied over the first conductors 20, prior to applying the polymer-dispersed cholesteric layer 30. Such coatings are disclosed in U.S. Pat. No. 6,690,447 to Stephenson et al.

Second conductors 40 overlay polymer-dispersed cholesteric layer 30. Second conductors 40 can have sufficient conductivity to carry a field across the polymer-dispersed cholesteric layer 30. Second conductors 40 can be formed in a vacuum environment using materials such as aluminum, tin, silver, platinum, carbon, tungsten, molybdenum, indium, or combinations thereof. The metal material can be excited by energy, for example, from resistance heating, cathodic arc, electron beam, sputtering, or magnetron excitation. Oxides of said metals can be used to darken second conductors 40. Tin-oxide or indium-tin oxide coatings can permit second conductors 40 to be transparent to operate in conjunction with opaque first conductors 20. Vacuum deposited second conductors 40 can be areas delimited by etched areas in a conductive coating.

In a preferred embodiment, second conductors 40 are printed using a conductive ink such as Electrodag® 423SS screen-printable electrical conductive material from Acheson Corporation. Such printable materials are finely divided graphite particles in a thermoplastic resin. The second conductors 40 can be formed using printed inks to reduce the cost of display manufacture. The use of a flexible support for substrate 15, laser etched first conductors 20, machine coated polymer-dispersed cholesteric layer 30, and printed second conductors 40 permit the fabrication of very low cost memory displays.

FIG. 3 is a sectional view showing a portion of the display with cholesteric material in two stable optical states in adjacent areas of the display. On the left, a higher voltage field has been applied and quickly switched to zero potential, which causes the liquid crystal molecules in domains to become planar liquid crystals 72. On the right, application of a lower voltage field has caused molecules of the cholesteric liquid crystal in the domains to break into transparent tilted cells that are known as focal-conic liquid crystals 74. Varying electrical field pulses can progressively change the molecular orientation from planar state 72 to a fully evolved and transparent focal conic state 74.

Light-absorbing second conductors 40 can be positioned on the side of the liquid crystal layer opposing the incident light 60. A thin layer of light-absorbing submicron carbon in a gel binder can be disposed between second conductors 40 and polymer-dispersed cholesteric layer 30, as disclosed in U.S. Pat. No. 6,639,637 to Stephenson. Focal-conic liquid crystals 74 are transparent, passing incident light 60, which is absorbed by second conductors 40 to provide a black image. Progressive evolution from planar to focal-conic state causes a viewer to see an initial bright reflected light 62 that transitions to black as the cholesteric material changes from planar state 72 to a fully evolved focal-conic state 74. The transition of the liquid crystal layer to the light-transmitting state is progressive, and varying the low-voltage time permits variable levels of reflection. These variable levels can be mapped out to corresponding gray levels, and when the field is removed, polymer dispersed cholesteric layer 30 maintains a given optical state indefinitely. The states are more fully discussed in U.S. Pat. No. 5,437,811.

FIG. 4 is an array of display elements 10 having a flexible common substrate 16 in accordance with the prior art. U.S. Pat. No. 6,236,442 discloses coating an emulsion of polymer-dispersed cholesteric liquid-crystal material over common substrate 16 using photographic equipment. Such equipment creates a uniform coating over multiple display elements 10 and covers first conductors on common substrate 16. The coated material must be removed or penetrated to form an electrical connection to first conductors. Material deposited outside areas defining display elements 10 is wasted.

FIG. 5 is top view of a continuous common substrate 16 having a plurality of display elements 10 in accordance with the present invention. Sets of first conductors (outlined by the bounded area 20) on common substrate 16 are formed for each individual display element 10 on the common substrate 16. In accordance with one embodiment of the invention, polymer-dispersed cholesteric layer 30 is selectively deposited over each set of first conductors 20 in a manner that leaves portions of each of the first conductors 20 in the set of first conductors exposed for each display element 10. The method permits roll-to-roll manufacture of display elements on a common substrate 16 with minimal waste of deposited polymer-dispersed cholesteric layer 30.

Separate quantities of polymer dispersed cholesteric material 30 can be selectively deposited simultaneously and/or sequentially on all or a portion of a plurality of display elements 10 in an array. For example, a common mask can be used to simultaneously cover 2, 3, 4 or any number of display elements 10 in an array. The display elements 10 can be arrayed as shown if FIG. 5 or there can be any number of columns and rows on a moving web. Alternatively, a non-continuous common substrate 16 in the form of a separate sheet having an array, or plurality, of display elements 10 can be transported, for example by means of a conveyer belt.

FIG. 6 is a side view of a substrate 15 (as a portion of the common substrate 16) of FIG. 5 in which a set of patterned transparent first conductors 20 on substrate 15 is shown. FIG. 7 is an extended top view of the individual display element of FIG. 6, having patterned transparent first conductors 20 on a common substrate. First conductors 20 can be formed by laser etching electrically separated areas on an ITO coating. First conductors can also be printed organic conductors such as PEDOT using conventional coating or printing techniques. In this particular embodiment, optional isolation pads 24 are provided as in certain configurations of the invention. Isolation pads 24 represent etched areas in a conductive coating in the case when substrate 15 is covered continuously with conductive material such as ITO and etched. Isolation pads 24 can be formed by other methods, for example, printing, or masking and coating.

FIG. 8 is a side view of a substrate 15 as a portion of the common substrate 16 of FIG. 5, in which a set of patterned first conductors 20 is shown prepared for selective deposition. FIG. 9 is an extended top view of the display element of FIG. 8 prepared for selective deposition. Referring to FIGS. 8 and 9 together, a mask 50 is provided with an opening 56 exposes a portion of first conductors 20 on sheet or substrate 15. Masked portions of first conductors 20 will form exposed first conductors 22. Mask 50 can be a sheet of thin stainless steel having a thickness of between 12 and 150 micrometers. In the exemplified embodiment, mask 50 is 50 micron thick stainless steel. A liquid crystal emulsion 54 according to the previously described formulation is placed on mask 50. The viscosity of liquid crystal emulsion 54 can be controlled by selecting a temperature that permits wetting of first conductors 20 with a uniform depth of material. The viscosity of liquid crystal emulsion 54 can also be controlled by the concentration of liquid carrier, in this case water, in liquid crystal emulsion 54. Blade 52 is used to move liquid crystal emulsion 54 across opening 56. Blade 52 has an edge that is flush with the surface of mask 50.

FIG. 10 is a side view of a display element after accomplishing selective deposition of the liquid crystal emulsion 54 on the substrate 15 is a portion of the common substrate 16. FIG. 11 is an extended top view of the display element of FIG. 10 after the selective deposition. Liquid crystal emulsion 54 has been deposited as a wet polymer-dispersed cholesteric layer 30 through the mask opening over first conductors. The deposited emulsion thickness is set by the thickness of mask 50, the viscosity of liquid crystal emulsion 54, and the speed of blade 52. In one embodiment, the parameters are selected to provide a 75-micron thick wet coating of liquid crystal emulsion 54.

FIG. 12 is a side view showing a substrate 15, as a portion of common substrate 16, having selectively deposited liquid crystal material over first conductors 20 and isolation pads 24, further showing the removal of apparatus for selective deposition of the material. In the exemplary embodiment, the solid content of the liquid-crystal material or emulsion is 13 percent by weight of the coating material. The carrier liquid, in this case water, comprises 87 percent of the volume. Removal of the carrier liquid through evaporation, significantly reduces the thickness of the deposited material. FIG. 13 is a side view of a sheet after a selectively deposited liquid-crystal emulsion has been dried. Dried polymer-dispersed cholesteric layer 30 coats first conductors 20 and isolation pads 24. In this example, the selectively deposited material, preferably in the form of a wet emulsion, can be deposited at 50 microns of thickness and dried to a thickness of approximately 9.7 microns.

FIG. 14 is an extended top view of a display element in which dried cholesteric material has been selectively deposited over first conductors 20 and isolation pads 24, leaving uncovered areas of first conductors 22. Mask 50 has provided a selectively deposited area of polymer-dispersed cholesteric layer 30, leaving exposed first conductors 22 and portions of isolation pads 24 uncovered. Material has been deposited only in areas needed for image display.

Other means for selectively depositing cholesteric material can be used. For example, instead of employing a mask, the polymer-dispersed cholesteric material can be deposited by gravure printing, screen printing, transfer printing, spray printing, inkjet printing, or other conventional printing means known to the skilled artisan.

Subsequent to the selective deposition of cholesteric material according to the present invention, second conductors 40 can be applied to the display elements, for example, on the same moving web shown in FIG. 5 after selective deposition of the polymer dispersed cholesteric layer 30. Alternatively, second conductors 40 can be applied to display elements 10 after the array of display elements 10 have been divided or cut into discrete sheets containing a selected subset of display elements 10 or singulated into an individual display element 10.

FIG. 15 is a top view of one embodiment of a completed display element 10 with printed second conductors 40. Second conductors 40 can be printed over dried polymer dispersed cholesteric layer 30. In the case where an ITO coating covers substrate 15 and first conductors 20 have been etched into the ITO coating, isolation pads 24 can be used to electrically isolate each second conductor 40 printed outside polymer-dispersed cholesteric layer 30.

FIG. 16 is a bounded side view of a display element with printed second conductors having electrically addressable pixels, which side view is taken through section 16-16 of FIG. 17. FIG. 17 is an extended rear (bottom) view of the display element of FIG. 16. Referring to FIGS. 16 and 17 together, contacts 80 are applied to each first conductor 20 and each second conductor 40. Appropriate electrical signals applied to first conductors 20 and second conductors 40 permit writing of image data onto display element 10.

FIG. 18 is a side view of a second structural embodiment for a display element having selectively deposited cholesteric material over substrate 15. In this case, second conductors 40 are printed only over dried polymer-dispersed cholesteric layer 30. Isolation pads 24 are not needed, and contacts 80 are isolated by means of the polymer-dispersed cholesteric layer 30.

FIG. 19 is a side view of a third structural embodiment for a selectively deposited material on a display element. Conductive material does not exist on substrate 15 outside the areas defined by first conductors 20. Again, in this case, isolation pads 24 are not needed. Second conductors 40 can be printed outside dried polymer dispersed cholesteric layer 30 without being shorted together by extraneous conductive material.

FIGS. 20A-C are side views of one embodiment of sequentially depositing two coatings, a second selectively deposited coating over a first selectively deposited coating. Referring to FIGS. 20A, 20B, and 20C together, a second layer 32 can be a pigmented or dyed layer to improve the contrast of display element 10. Second layer 32 can also be an emulsion containing cholesteric liquid crystal different in properties than a first polymer-dispersed cholesteric layer 30, which second layer 32 can be applied after the first layer 30 is dried. FIG. 20A is a side view of a display element 10 having a selectively deposited and dried polymer dispersed cholesteric layer 30 over first conductors 20 and substrate 15. FIG. 20B is a side view of the display element of FIG. 20A positioned to receive a selectively deposited second layer over polymer dispersed cholesteric layer 30. Mask 50 is provided with an opening 56 exposes a portion of first conductors 20. Mask 50 can be a sheet of thin stainless steel having a thickness of between 12 and 150 microns. In this embodiment, the mask 50 is 50 micron thick stainless steel. An emulsion 54 containing pigment and a binder is placed on mask 50. The viscosity of emulsion 54 is controlled by selecting a temperature that permits wetting of first conductor 20 with a uniform depth of material. Blade 52 is used to move emulsion 54 across opening 56. Blade 52 has an edge that is flush with the surface of mask 50. FIG. 20C is a side view after selective deposition of second layer 32. Second layer 32 contains a solvent which is then dried to provide a dried second layer 32 over dried polymer-dispersed cholesteric second layer 30.

The additional layer can also comprise a background nanopigment layer. The additional layer can comprise a differently colored cholesteric liquid-crystal material. The differently colored cholesteric liquid-crystal material can reflect a different wavelength of light in the planar state, in order to provide multicolor displays. More than one additional layer can be present, wherein each additional layer can be the same or different from each other additional layer.

Another aspect of the present invention relates to a display element in which the mask used for selective deposition is not removed prior to forming a plurality of second conductors, but is maintained as integral to the completed display element. Such a display element comprises (a) a substrate; (b) a plurality of first conductors formed over said substrate; (c) a layer comprising polymer-dispersed liquid-crystal in the form of domains of liquid crystal in a continuous matrix, which layer is formed over said first conductors so as to leave a portion of each of said first conductors uncoated; (d) between the first conductors and the substrate, a spacer element that has openings that are aligned with the areas covered by the layer of polymer-dispersed liquid-crystal, which spacer element had been used as a mask for selective deposition, and (e) a plurality of second conductors, electrically isolated from the first conductors, over said layer of polymer-dispersed liquid-crystal so that an electric field to the second conductors and said uncoated portions of the first conductors is capable of changing the optical state of the polymer dispersed liquid crystal. Such an integral spacer element or mask preferably is made from a low cost material such as a thermoplastic polymer, for example, a polyolefin or polyester material.

Another aspect of the present invention relates to an array of display elements, typically an intermediate in the manufacture of individual display elements, each display element comprising (a) a common substrate; (b) two or more sets of first conductors, each set comprising a plurality of first conductors forming a single display element, formed over said substrate; (c) over each set of first conductors, a layer of polymer-dispersed liquid-crystal material deposited in a manner that leaves a portion of the first conductors in each set uncoated; (d) a corresponding number of sets of second conductors, each set of second conductors comprising a plurality of second conductors forming a single display element with a corresponding set of first conductors, which sets of second conductors are each formed over each layer of polymer-dispersed liquid-crystal material, such that, for each set, an electric field applied to said second conductors and said uncoated portions of said first conductors is capable of changing the optical state of the polymer-dispersed cholesteric-liquid crystal material in a preselected portion of the layer of polymer-dispersed cholesteric liquid-crystal material. The array of display elements can be positioned on a common substrate that is a continuous web as in FIG. 5. Alternatively, the array of display elements can be on a substrate in the form of a non-continuous sheet. The array of display elements can be arrayed in a plurality of columns and rows, the number of which may depend on the size of the manufacturing facility. As exemplified in the embodiment of FIG. 5, each individual display element in the array comprises a separate layer of polymer-dispersed cholesteric liquid-crystal material that is non-contiguous (not in contact) with the layer of polymer-dispersed cholesteric liquid-crystal material in every other display element on the common substrate in the array.

Alternate embodiments including a circuit layer in addition to a first conductive layer and a second conductive layer are described with reference to FIGS. 21-27.

Referring to FIG. 21, the substrate 115 can be formed as an individual substrate for a single display element, or a web wherein many display elements will be formed then separated from each other after manufacture. The substrate 115 can include one or more fiducial mark 105 to aid in aligning subsequent layers on the substrate 115, to track the substrate 115 orientation through manufacturing; for alignment of the finished display element with a housing, circuit board, or other interactive element; or a combination thereof. The fiducial marks 105 can also be used in other ways, as known in the art.

The substrate 115 can be printed with one or more circuit 125. The placement of the circuits can correspond to anticipated connections to external circuits or electrical components outside the display area. One or more circuits 125 can extend to a portion of the substrate 115 on which the first conductive layer will be coated in order to make direct contact with the first conductive layer. The circuits 125 can be created on the substrate 115 by any known methods, including but not limited to electrolytic deposition of metals, vapor deposition, soldering, coating or printing of conductive polymer films, and printing of conductive inks. The circuits 125 can include terminals for electrical connections to the first or second conductive layers, drive circuits, power supplies, or other electrical circuits within the finished display. As used herein, the terms “circuit” and “circuits” are used interchangeably to indicate one or more circuit.

As shown in FIG. 22, a mask 150 can cover at least a portion of the circuits 125. The mask 150 can also cover a portion of the substrate 115. The mask 150 can include one or more opening 156 or window, exposing at least a portion of the circuits 125, at least a portion of the substrate 115, or an area of the substrate 115 including a portion of the circuits 125 in an area where a display is to be formed. The mask 150 can be removable, permanent, or have areas that are removable and areas that are permanent. If the mask 150 has removable and permanent areas, the mask 150 can be made of one or more materials. Multiple masks 150 can be used to provide permanent and/or removable masked areas, or masks 150 over multiple, non-touching areas of the substrate 115, for example, over individual circuits 125. As used herein, “mask” can include one or more masks.

The mask 150 can be formed by printing or pattern coating on the substrate 115 and/or the circuits 125. The mask 150 can be attached to the substrate 115, circuits 125, or both, as a preformed layer by adhesive, heat lamination, chemical bonding, electrostatic attraction, or other means of attachment. The mask 150 can be aligned with the substrate 115, circuits 125, or both, and attached by mechanisms such as pins, clips, staples, or other retaining materials. Any of the above methods of attachment can be permanent or reversible. Wherein the mask includes more than one mask, each mask can be aligned and attached separately from or together with each at least one other mask. Attachment of each mask can be by the same or a different method as attachment of any other mask. Each mask independently can be removable or permanent. The mask 150 can be formed or laid over the entire substrate 115, and one or more mask opening 156 formed by etching, ablation, or other methods of material removal. Such methods can include use of chemicals, lasers, knives, or blades.

The mask 150 can be up to 500 microns thick, for example, less then 10 microns, 10-400 microns, 20-150 microns, or 30-70 microns thick. Other thicknesses can be appropriate depending on masking material and manufacturing methods and equipment. If the mask 150 is too thick, it may be difficult to handle, too thick for manufacturing equipment, unable to flex to accommodate manufacturing equipment requirements, such as wrapping around rollers, or easily separable from the substrate 115. If the mask 150 is too thin, it can tear during manufacturing, or be difficult to apply to or remove from the substrate 115 and/or circuits 125.

Once the mask 150 is formed over the substrate 115, a first conductive layer 120 can be coated over the masked substrate, as shown in FIG. 23. The first conductive layer 120 can cover the mask 150, the portion of the circuits 125 extending into the mask opening 156, a portion of substrate 115, or a combination thereof. The first conductive layer 120 can be printed, sputter coated, deposited by vapor deposition techniques, extruded, or coated, for example. Techniques that only deposit the first conductive layer 120 within the mask opening 156 can be used, for example, printing or coating. As shown in FIG. 24, if a segmented or pixilated display is desired, the first conductive layer 120 can be patterned to create electrically isolated regions 126. The patterning can be achieved by laser or chemical etching, cutting, peeling, or other suitable techniques.

According to various embodiments, the first conductive layer and the circuit layer can be reversed, such that the first conductors are adjacent the substrate, and the circuits are adjacent the bistable material. According to various embodiments, a mask can be positioned between one or more first conductor and one or more circuit. A second mask can be positioned between either the first conductive layer or the circuit layer and the bistable material. The second mask can be removable, permanent, or a combination thereof. The second mask can function to protect the first conductors, circuits, substrate, or a combination thereof, from application of the bistable material. The second mask, like the first mask, can be removed as a whole or in part to expose one or more first conductors, one or more circuits, or a combination thereof, for electrical connection.

After the first conductive layer 120 is applied to the masked substrate, a display material, for example a bistable material 130 such as a cholesteric liquid crystal containing material, can be coated on the first conductive layer 120, as shown in FIG. 25. The bistable material 130 can be coated, printed, or otherwise applied to all or a portion of the first conductive layer 120 and the masked substrate. A suitable method for forming a liquid crystal layer is set forth, for example, in U.S. Patent Application Publication U.S. 2003/0174264 A1. The bistable material 130 optionally can be coated with a dark or colored layer to enhance viewability of the display when the liquid crystal is in a focal conic state. If no dark or colored layer is used, in the focal conic state the viewer will observe the color of the first conductive layer 120.

Other optional layers can include an insulating layer coated directly on the first conductive layer 120 or circuit layer to eliminate shorts through contamination or voids in the adjacent bistable liquid crystal layer 130. If desired, the display material can be coated or printed in such a manner that it does not completely cover the adjacent first conductive layer 120 or circuit layer, thereby providing areas of the first conductive layer 120 or circuit layer available for direct electrical connection.

Once the layer containing the bistable material 130 has been formed, the mask 150 can be removed from the substrate 115, including all materials coated on the mask 150, as shown in FIG. 26. Removal of the mask 150 from the substrate 115 leaves a display layer of bistable material 130 on a first conductive layer 120 that is in electrical contact with at least one circuit 125 on the substrate 115, providing an exposed electrical pathway from the first conductive layer 120 through the circuit 125 to the display driver components. The mask 150 can optionally be removed at a later stage of manufacture. If any portion of the mask 150 is to be removed, preferably it is removed before connection of the circuits 125 to external circuits or electrical components. According to certain embodiments, at least a portion of the mask 150 is permanent and is not removed.

The second conductive layer 140 can be formed on display layer 130, as shown in FIG. 27. The second conductive layer 140 can be formed by printing, pattern deposition, stripe coating, or other suitable techniques depending on the desired placement of the second conductive layer 140 over the display layer 130. The second conductive layer 140 can contact one or more circuit 125 not in contact with the first conductive layer 120. The second conductive layer 140 can be patterned such that, in conjunction with the first conductive layer 120, application of voltages between the conductive layers forms pixels or segmented images in the display. The application of the second conductive layer 140 creates a display element 110 capable of forming images when electrically driven.

The display element 110 can be connected to a drive source, power supply, or other electrical components as desired. The electrical components can be directly attached to the circuits 125, or can be remote form the display element 110 and attached to the circuits 125 by wires or other interconnects, forming a functioning display. The display element 110, alone or with one or more electrical components, can be encapsulated to protect the display element 110 from environmental damage, including damage from exposure to temperature, humidity, electrical shock, or physical forces.

The displays described above can be combined with conventional components to obtain an integral self-contained system. For example, matrix driving of such cholesteric displays are well known in the art, as for example, described in U.S. Ser. No. 10/085,851, filed Feb. 28, 2002, by Stephenson.

As described herein and shown in the Figures, a mask allows use of continuous manufacturing methods in forming the display element. The use of the mask achieves a selective layer application effect because portions of each layer outside the display area can be removed with the mask. The ability to use continuous manufacturing techniques can enable lower costs, faster manufacture, or higher productivity. The use of the mask protects materials in one or more layers from contacting the material in other layers, enabling greater freedom in material choice and handling during manufacture.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

PARTS LIST

10 display element

15 display substrate

16 common substrate

20 first conductors

22 exposed first conductor

24 isolation pads

30 polymer-dispersed cholesteric layer

32 second layer

40 second conductors

50 mask

52 blade

54 emulsion material

56 opening in mask

60 incident light

62 reflected light

72 planar liquid crystal

74 focal-conic liquid crystal

80 contacts

110 display element

115 display substrate

120 first conductors

125 circuits

126 electrically isolated regions

130 bistable material

140 second conductors

150 mask

156 mask opening

	Number	Date	Country
Parent	10365819	Feb 2003	US
Child	11132578	May 2005	US

Process and structures for selective deposition of liquid-crystal emulsion

Information

Publication Number

Date Filed

Date Published

Inventors

Original Assignees

CPC

US Classifications

International Classifications

Abstract

Description

Claims

CROSS-REFERENCE TO RELATED APPLICATIONS

Continuation in Parts (1)