HK1051408A - An improved transflective electrophoretic display - Google Patents

Description

Improved back-transmissive electrophoretic display

The technical field to which the invention belongs

The invention relates to a back-transmissive electrophoretic display comprising isolated cells of well-defined shape, size and aspect ratio, said cells being filled with charged particles dispersed in a dielectric solvent, and having a backlight.

The present invention may have a conventional up/down switching mode, an in-plane switching mode, or a dual switching mode.

Background of the invention

Electrophoretic displays (EPDs) are non-emissive devices fabricated based on electrophoretic phenomena that affect charged pigment particles suspended in a colored dielectric solvent. Such an electrophoretic display was first proposed in 1969. Such displays typically include opposing, spaced apart plate electrodes. Typically, at least one of the electrode plates is transparent from the viewing end. Such passive electrophoretic displays require row and column electrodes at the top (viewing end) and bottom, respectively, to drive the display. In contrast, for an active type electrophoretic display device, a thin film transistor array on a backplane and a common and unpatterned transparent conductor plate on a top viewing substrate are required. The electrophoretic fluid consists of a pigmented dielectric solvent and dispersed charged pigment particles, sealed between two electrode plates.

When a voltage difference is applied between the two electrodes, the pigment particles migrate toward the plate due to attraction by the plate of opposite polarity. Thus, the color displayed on the transparent plate (determined by the selective charging of the plates) may be the color of the solvent or the color of the pigment particles. Reversing the polarity of the plate causes the particles to migrate in the opposite direction, thereby also reversing the color. The different transition colors (grey levels) are determined by the transition pigment density of the transparent plate and can be obtained by controlling the voltage and charging time.

Us patent No.6,184,856 discloses a transmissive electrophoretic display in which a backlight, a color filter, and a substrate with two transparent electrodes are used. The electrophoretic cell functions as a light valve. In the condensed state, the particle arrangement serves to minimize the horizontal area coverage of the cassette, as well as to pass background light through the cassette. In the distributed state, the grain arrangement is used to cover the horizontal area of the pixel, as well as to disperse or absorb the background light. However, the backlight and filter used in such devices consume a lot of energy, which is not suitable for portable devices such as PDAs (personal digital assistants) and e-books.

Electrophoretic displays having different pixel or cell structures are described in the prior art, for example, segmented electrophoretic displays (m.a. hopper and v.novotny, IEEE trans.electric.dev., vol.ed 26, No.8, pp.1148-11529)) and electrophoretic displays prepared by a microcapsule method (U.S. Pat. nos. 5,961,804 and 5,930,026), and each of these prior arts has problems as described below.

In a partition-type electrophoretic display, there are several partitions between the two electrodes to divide its space into small cells to avoid unwanted particle migration (e.g., settling). However, problems are encountered in the following cases: forming partitions, filling the display with a fluid, sealing the fluid in the display, and maintaining different color suspensions separate from each other.

The microencapsulated electrophoretic display has a substantially two-dimensional arrangement of microcapsules, wherein each microcapsule contains an electrophoretic composition consisting of a dielectric fluid and a suspension of charged pigment particles (visually contrasted with the dielectric solvent). The microcapsules are typically prepared in aqueous solution and have a relatively large average particle size (50-150 microns) in order to obtain useful contrast. Large particle sizes can result in poor scratch resistance and slow response times for a given voltage, since the macrocapsule requires a large gap between the two opposing electrodes. Furthermore, the hydrophilic shell of the microcapsules prepared in aqueous solution is sensitive to high humidity and temperature conditions. If the microcapsules are embedded in a large number of polymer matrices to obviate these disadvantages, the use of such matrices can result in longer response times and/or reduced contrast. In order to improve their switching rate, charge control agents are often required in such electrophoretic displays. However, the microencapsulation process in aqueous solution limits the types of charge control agents that can be used. Other disadvantages associated with microcapsule systems include lower resolution, and poor color rendering capabilities.

More recently, improved electrophoretic display technology has been disclosed in the same series of U.S. patent application No.09/518,488 filed on 3/2000, U.S. patent No.09/759,212 filed on 11/1/2001, U.S. patent No.09/606,654 filed on 28/6/2000, and U.S. patent No.09/784,972 filed on 15/2/2001, which are incorporated herein by reference. The improved electrophoretic display comprises isolated cells having well-defined shape, size, and aspect ratio, and the cells are filled with charged pigment particles dispersed in a solvent. The electrophoretic fluid is isolated and sealed within each microcup.

In fact, the micro-cup structure can make the preparation form of the electrophoretic display more flexible, and realize an efficient roll-to-roll continuous manufacturing process. The display can be fabricated on a continuous web conductive film such as ITO/PET, for example, (1) applying a radiation curable composition to the ITO/PET film, (2) fabricating a microcup structure using a microembossing or photo etching process, (3) filling and sealing the microcups with an electrophoretic liquid, (4) laminating other conductive films on the microcups to be sealed, and (5) cutting the display device to a desired size or form for assembly.

One advantage of this electrophoretic display design is that the microcup wall is effectively a built-in spacer that keeps the top and bottom substrates at a fixed distance. The mechanical performance and structural integrity of the microcup display is significantly superior to any prior art display, including those made using spacer particles. In addition, displays made with microcups all have desirable mechanical properties, including reliable display performance when the display is bent, rolled, or subjected to pressure from, for example, a touch screen application. The use of microcup technology also eliminates the need for edge seal adhesives that can limit and predefine the display panel size and restrict the display fluid within a predetermined area. Display fluids in conventional display devices prepared using edge seal adhesive methods may leak completely when the display device is cut, or drilled, in any manner. The damaged display device will no longer have any function. In contrast, the display fluid in a display device prepared with microcup technology is sealed and isolated in each cell. The microcup display can be cut to almost any size without risking that the performance of the display device is compromised by loss of display fluid in the active area. In other words, the microcup structure allows flexibility in the manufacturing process for display devices, wherein the process allows continuous output production of display devices in very large sheet format that can be cut to any desired format. This isolated microcup or cassette structure is particularly important when filling an electrophoresis cassette with fluids of different characteristics, e.g., different colors, switching rates. Without the microcup structure, it is difficult to prevent fluids from mixing in adjacent areas or from cross effects during operation.

Brief description of the invention

Viewing a reflective electrophoretic display requires an external light source. For surface and light management reasons, a backlit electrophoretic display equipped with a backlight system is generally superior to a reflective electrophoretic display with a front-lit system for dark viewing applications. However, the presence of light scattering particles in electrophoretic display cells greatly reduces the effectiveness of the backlight system. It is difficult to obtain high contrast in both bright and dark environments for conventional electrophoretic displays.

The invention relates to a back-transmissive electrophoretic display using microcup technology. The electrophoretic display comprises isolated cells of well-defined shape, size, and aspect ratio prepared with microcups and having a backlight. The cell is filled with charged particles dispersed in a dielectric solvent.

For viewing applications in dark environments, the microcup structure is effective to pass the backlight through the microcup walls to the viewer. Thus, even a low intensity backlight is sufficient for a user viewing a back-transmissive electrophoretic display. Photocell sensors that adjust the intensity of the backlight may be used to further reduce the power consumption of such electrophoretic displays.

The electrophoretic display may have a conventional up/down switching mode, an in-plane switching mode, or a dual switching mode.

In a display having a conventional up/down switching mode, or a dual switching mode, there is a top transparent electrode plate, a bottom electrode plate, and a plurality of isolated cells enclosed between the two electrode plates. In a display with an in-plane switching mode, the cell is sandwiched between a top transparent insulator layer and a bottom electrode plate.

Such isolated cells are isolated by light-transmissive cell walls. The backlight is below the bottom electrode plate. The display may also have a background layer over the backlight system to control the light passing through the display. The background layer is preferably grey in use. A background layer under the backlight system may also be used to improve contrast.

Scatterers may also be added on top of the back-transmissive electrophoretic display to enhance the visual effect.

Brief description of the drawings

Fig. 1A is a side view of an electrophoretic display of the present invention;

fig. 1B is a top view of an electrophoretic display of the present invention;

fig. 1C is a side view of an electrophoretic display with an in-plane switching mode according to the present invention;

fig. 1D is a side view of an electrophoretic display with dual switching modes according to the present invention;

FIG. 2 shows the microcup preparation of a conductive film coated with a UV curable composition exposed to a UV radiation pattern;

fig. 3 shows a flow chart for manufacturing a black/white electrophoretic display or other monochrome electrophoretic display;

fig. 4a-4h are flow diagrams of manufacturing a full color electrophoretic display;

5A-5F illustrate a display having an in-plane switching mode; and

fig. 6A-6C illustrate a display with dual switching modes.

Detailed DescriptionDefinition of

Unless defined otherwise herein, all technical terms used herein are used in accordance with their customary definitions commonly used and understood by those skilled in the art.

The term "microcups" refers to cup-like recesses made by microembossing and pattern exposure followed by solvent development.

In this specification, the term "cartridge" refers to a discrete unit formed from a sealed microcup. The cell is filled with charged pigment particles dispersed in a solvent, or solvent mixture.

When describing the microcups or cassettes, the term "having a well-defined" means that the microcups or cassettes have a well-defined shape, size, and aspect ratio that are predetermined according to the particular parameters of the process.

The term "aspect ratio" is a term commonly known in electrophoretic displays. In this specification, the depth to width, or depth to diameter ratio of the microcups is referred to.

The term "isolated" refers to electrophoretic cells individually sealed with a sealing layer such that electrophoretic fluid in one cell cannot be transferred to other cells.Description of The Preferred Embodiment

As shown in fig. 1A, an electrophoretic display 100 of the present invention includes a top transparent layer 101, a bottom electrode plate 102, and an isolation box layer 103 enclosed between the two electrode plates. The top transparent layer 101 is a transparent conductive film such as ITO on PET for conventional up/down switching mode or dual switching mode, or a transparent insulator layer for in-plane switching mode.

Cells 103a, 103b, and 103c having well-defined shapes, sizes, and aspect ratios are filled with charged particles 104 dispersed in a dielectric solvent 105. The isolated cassette is sealed with a sealing layer 106. A top transparent layer, typically comprising an adhesive layer, is overlaid on the sealed cartridge. A backlight 107 is positioned below the bottom electrode plate layer 102. The backlight may illuminate the display panel through a diffusing light pipe on an edge of the display. The display may optionally have a background layer 108 under the bottom electrode plate layer 102 or the backlight system 107.

FIG. 1B is a top schematic view of the cassette. As shown, the edges of each box are defined by divider vertical side walls 109. The side walls extend between the top transparent layer 101 and the bottom electrode plate 102. The side walls are shown in fig. 1A as being perpendicular to the top transparent layer and the bottom electrode plate, it being understood that the side walls may be angled to facilitate the preparation of the cartridge (e.g., the demolding process described in section i (a) below). In the present invention, the side wall is made of a light-transmitting material.

In a display with a conventional up/down switching mode, the top transparent layer 101 is an electrode plate or film.

In a display with an in-plane switching mode (fig. 1C), the top transparent layer 101 is an insulator substrate, while the bottom electrode plate comprises in-plane electrodes 110a, 110b, and a bottom electrode 111 located between the two and separated by a trench 112. Alternatively, the bottom layer may have only one in-plane switching electrode and one bottom electrode with a trench in between.

In a display with dual switching mode (fig. 1D), the top layer 101 contains a transparent top electrode 116 (not shown). The bottom electrode plate has one in-plane electrode 113a on the left and one bottom electrode 114 and one in-plane electrode 113b on the right. The trench 115 separates the bottom electrode from the in-plane electrode. Alternatively, the bottom electrode plate may have only one in-plane electrode and one bottom electrode with a trench therebetween (not shown).I. Preparation of the microcups

The microcups can generally be prepared by a micro-molding or photo-etching process as described in U.S. patent application No.09/518,488 filed 3/2000 and U.S. patent application No.09/784,972 filed 2/15/2001.I. (a) preparation of microcup arrays using a Micromolding process

Preparation of the Male die

The male mold may be prepared by any suitable method, such as by a diamond cutting process or a photoresist treatment followed by etching or plating. An exemplary embodiment of the male mold is shown in fig. 2. The master template of the male mold may be manufactured by any suitable method, such as electroplating. With electroplating, a thin seed metal layer, typically 3000 angstroms, such as inconel, is deposited on a glass substrate. A photoresist layer is then applied and exposed to radiation, such as Ultraviolet (UV) light. A mask is disposed between the ultraviolet light and the photoresist layer. The exposed areas of the photoresist material harden. The unexposed areas are then removed by washing with a suitable solvent. The remaining cured photoresist is dried and a thin layer of seed metal is sputtered again. The master mold is ready for electroforming. A typical material for electroforming is nickel-cobalt. Furthermore, the master mold may be made of nickel, as described in journal of the society of photographic optics engineers 1663, pp.324(1992) continuous fabrication of thin-coated optical media ("continuous plating of thin-coated optical media", SPIE Proc.), using electroforming or electroless nickel deposition. The bottom plate of the mold is typically between about 50 and 400 microns. The master mold may also be fabricated using other micro-engineering techniques, including e-beam writing, dry etching, chemical etching, laser writing, or laser interference, as described in the Fine optical reproduction for micro-optics, SPIE Proc, volume 3099, pp.76-82(1997), published by the society of photographic optics Engineers. In addition, the mold can be made of plastics, ceramics and metals by photo processing.

The punches thus prepared generally have a projection of about 3 to 500 microns, preferably between about 5 and 100 microns, preferably about 10 to 50 microns. The male mold may be in the form of a belt, a roller, a sheet. For continuous production, a belt-like or roll-like mold is preferred. Before the application of the uv curable resin composition, the mold may be treated with a release agent to aid the release process.

Formation of microcups

The microcups may be made in a batch process or a continuous roll-to-roll process. As disclosed in pending U.S. patent application 09/784,972 filed on 15/2/2001, which provides a continuous, low cost, high throughput manufacturing technique for manufacturing compartments for use in electrophoretic or Liquid Crystal Displays (LCDs). The mold may be treated with a release agent to aid in the release process prior to application of the uv curable resin. To further improve the release process, a substrate coating or adhesion promoting layer may be pre-applied to the conductive film to improve the adhesion between the body and the microcups.

The uv curable resin may be degassed prior to dispensing and may optionally include a solvent. Such solvents, if any, can be easily evaporated. The uv curable resin may be dispensed onto the male mold in any suitable manner, such as coating, dripping, pouring, and the like. The dispenser may be mobile or stationary. To manufacture a display having a conventional up/down switching mode or a dual switching mode, an ultraviolet curable resin is coated on the conductive film. Suitable conductive film embodiments include transparent conductors (ITO) on plastic substrates, such as polyethylene terephthalate (pet), polyethylene naphthalate (pe), aramid (polyaramid), polyimide, polycycloolefin, polysulfone (polysulfonone), and polycarbonate. Pressure may be applied if necessary to ensure proper bonding between the resin and the plastic and to control the thickness of the base plate of the microcups. The pressure may be applied using a laminating roller, vacuum molding, a press or any other similar mechanism. If the male mold is metallic and opaque, the plastic substrate is typically transparent to actinic radiation used to cure the resin. Conversely, the male mold may be transparent while the plastic substrate is opaque to actinic radiation. In order to transfer the molded features well to the transfer sheet, the conductive film must have good adhesion to the uv curable resin, which should have good release properties with respect to the mold surface.

To manufacture a display having an in-plane switching mode, a transparent insulator substrate may be used in a molding step. Suitable transparent insulator substrates include polyethylene terephthalate (PET), polyethylene napthalate (PET), aramid (polyaramid), polyimide, polycycloolefin, polysulfone (polysulfonone), and polycarbonate.

The UV curable component used to prepare the microcups may include multivalent acrylates, or methacrylates, multivalent vinyls including vinylbenzene, vinylsilanes, vinylethers, multivalent epoxides, multivalent propenes, and oligomers or polymers containing crosslinking functionality, among others. Multifunctional acrylates and oligomers thereof are preferred. Combinations of multifunctional epoxides with multifunctional acrylates are also useful to achieve the desired physical and mechanical properties. Crosslinkable oligomers imparting bending resistance, such as urethane acrylates or polyester acrylates, are also typically added to improve the bending resistance of the molded microcups. The composition may comprise polymers, oligomers, monomers, and additives, or only oligomers, monomers, and additives. The glass transition temperature (Tg) of such materials typically ranges from about-70 deg.C to about 150 deg.C, and preferably from about-20 deg.C to about 50 deg.C. The process of micro-molding is typically carried out above the glass transition temperature. A heated stamp or heated indwelling substrate against which the stamp is pressed may be used to control the temperature and pressure of the microembossing. The male mold can be detached from the formed microcups during or after the uv curable resin is uv cured.I. (b) preparation of microcups by photolithography

Alternatively, the microcups of the display may be prepared by photolithography. FIG. 2 shows the preparation of microcups by a pattern exposure process.

As shown in fig. 2A and 2B, a radiation curable material 21a may be applied by any known method to a conductive film 22 of a predetermined pattern on a plastic substrate 23, and exposed to ultraviolet light (or alternatively, other forms of radiation, electron beams, etc.) using a mask 26 to form wall surfaces 21B in accordance with the projected pattern of the mask, thereby preparing an array of microcups.

In the photomask 26 shown in FIG. 2A, the dark squares 24 represent areas that are opaque to the radiation used, and the spaces 25 between the dark squares represent areas that are radiation transparent. The ultraviolet light is radiated on the radiation curable material 21a through the open region 25.

As shown in fig. 2B, the exposed areas 21B are hardened, and then unexposed areas (masked by the opaque areas 24 of the mask 26) are removed with a suitable solvent or developer to form the microcups 27. The solvent or developer is selected from the group of agents commonly used to dissolve or disperse radiation curable materials such as butanone, toluene, acetone, isopropyl alcohol, and the like. Although the microcup pattern 24 of the photomask 26 is precisely registered with the conductive film 22 of the predetermined pattern in fig. a2, it is not necessary for general low resolution applications.

Alternatively, exposure may be accomplished by placing a photomask under the conductive film/substrate. In this case, the conductive film/substrate must be transparent to the wavelength of radiation used for exposure.

To manufacture a display having an in-plane switching mode, a transparent insulator substrate may be used instead of the conductive film. Suitable transparent insulator substrates include polyethylene terephthalate, polyethylene naphthalate, aramid, polyimide, polycycloolefin, polysulfone, polycarbonate, and the like.

In general, the microcups may be of any shape and may vary in size and shape. In one system, the microcups may have approximately the same size and shape. However, in order to maximize the optical effect, mixing microcups of different shapes and sizes may be fabricated. For example, microcups filled with a red dispersion may have a different shape or size than green microcups or blue microcups. In addition, one pixel may be composed of a different number of microcups of different colors. For example, a pixel may be composed of a plurality of small green microcups, a plurality of large red microcups, and a plurality of small blue microcups. The three colors do not have to have the same shape and number.

The openings of the microcups may be circular, square, rectangular, hexagonal, or any other shape. The spacing between the openings is preferably small to achieve high color saturation and contrast while maintaining desirable mechanical properties. Thus, honeycomb openings are preferred over other shaped (e.g., circular) openings.

The size of each microcup may be about 10²To about 1X 10⁶Between square microns, preferably about 10³To about 1X 10⁵Square micron. The depth of the microcups is about 5 to about 200 microns, preferably about 10 to about 100 microns. The ratio of the openings to the total area is from about 0.05 to about 0.95, preferably from about 0.4 to about 0.9.II preparation of suspensions/dispersions

The suspension filled in the microcups includes a dielectric solvent having charged pigment particles dispersed therein, and particles that migrate under the influence of an electric field. The suspension optionally contains added colorants, which may or may not migrate in the electric field. The dispersions can be prepared according to methods well known in the art, for example, U.S. Pat. Nos. 6,017,584, 5,914,806, 5,573,711, 5,403,518, 5,380,362, 4,680,103, 4,285,801, 4,093,534, 4,071,430, 3,668,106, and as described in IEEE trans. Electron devices, ED-24, 827(1977), and J.Appl.Phys.49(9), 4820 (1978).

The suspending fluid medium preferably has a low viscosity and a dielectric constant of from about 2 to about 30, preferably from about 2 to about 15 for high particle mobility. Examples of suitable dielectric solvents include hydrocarbons such as DECALIN (DECALIN), 5-ethylidene-2-norbornene, fatty oils, and undersea oils; aromatic hydrocarbons such as toluene, xylene, phenylxylylethane, dodecylbenzene and alkylnaphthalene; halogenated solvents such as perfluorodecalin, perfluorotoluene, perfluoroxylene, trifluorotoluene dichloride (dichlorobenzotrifluoride), 3, 4, 5-trichlorobenzotrifluoride (3, 4, 5-trichlorobenzotrifluoride), chloropentafluorobenzene (chlorotetrafluorobenzene), dichlorononane, pentachlorobenzene, etc.; perfluorinated solvents from 3M company of St.Paul, Minn., such as FC-43, FC-70 and FC-5060; low molecular weight halogen-containing polymers from TCI America of Portland, Oreg.polyperfluoropropylene oxide (Poly) polychlorotrifluoroethylene poly (chlorotrifluoroethylene) from Halocarban Product of River Edge, N.J., such as halohydrocarbon Oils (Halocarban oil), perfluorinated polyalkyl ethers (Perfluoropolyalkylethere) such as Galden from Ausimont or Krytox Oils and grease K-fluid series from DuPont, Delaware.

The contrasting colorant can be a dye or a pigment. Nonionic azo and anthraquinone dyes are particularly useful. Examples of useful dyes include, but are not limited to: oil-soluble Red EGN (Oil Red EGN), Sudan Red (SudanRed), Sudan Blue (Sudan Blue), Oil-soluble Blue (Oil Blue), Macrolex Blue, Solvent Blue 35(Solvent Blue 35), Pymampirit Black and Fast Spirit Black from Pymap Products, Arizona, Sudan Black B (Sudan Black B) from Aldrich, Thermoplastic Black X-70 from BASF, and anthraquinone Blue, anthraquinone yellow 114, anthraquinone Red 111, 135, anthraquinone Green 28 from Aldrich. In the case of insoluble pigments, pigment particles for coloring the media may also be dispersed in the dielectric media. These coloured particles are preferably uncharged. If the pigment particles used to produce color in the media are charged, they are preferably oppositely charged from the charged pigment particles. If the two pigment particles carry the same charge, they should have different charge densities or different electrophoretic mobility rates. In any case, the dye or pigment used to create the color of the medium must be chemically stable and compatible with the other components in the suspension.

The charged first color pigment particles are preferably white in color and the pigment particles may be organic or inorganic pigments such as titanium dioxide.

If colored pigment particles are used, phthalocyanine blue (phthalocyanine blue), phthalocyanine green (phthalocyanine green), diarylide Yellow (diarylide Yellow), diarylide AAOT Yellow (diarylide AAOT Yellow), quinacridone (quinacridone), azo (azo), rhodamine (rhodamine), perylene pigments (perylene pigment series) from Sun chemical company; hansa yellow G (Hansa yellow G) particles from Kanto Chemicals, Inc., and carbon black (carbon Lampback) from Fisher, Inc. Sub-particle sizes are preferred. The particles should have acceptable optical properties, should not be swollen or softened by the dielectric solvent, and should be chemically stable. Under normal operating conditions, the resulting suspension must also be stable and resistant to settling, emulsification or coagulation.

The pigment particles may themselves be charged, or may be significantly charged using charge control agents, or acquire a charge when suspended in a dielectric solvent. Suitable charge control agents are well known in the art; they may be of polymeric or non-polymeric nature, and may be ionized or non-ionized, including ionic surfactants such as Aerosol ortho-toluidine (Aerosol OT), sodium dodecyl benzene sulfonate, metal soaps, polybutylene succinimide, maleic anhydride copolymers, vinyl pyridine copolymers, vinyl pyrrolidone copolymers (such as Ganex from International specialty Products), copolymers of (meth) acrylic acid, and N, N-dimethylaminoethyl (meth) acrylate copolymers. Fluorinated surfactants are particularly useful as charge control agents in perfluorocarbon solvents. These include FC fluorinated surfactants such as FC-170C, FC-171, FC-176, FC430, FC431 and FC-740 from 3M company, and Zonyl fluorinated surfactants such as Zonyl FSA, FSE, FSN-100, FSO-100, FSD and UR from Dupont company.

Suitable charged pigment dispersions can be made by any known method, including milling, grinding, ball milling, air flow milling (microfluidizing), and ultrasonic techniques. For example, pigment particles in the form of a fine powder are added to the suspending solvent, and the resulting mixture is ball milled or ground for several hours to break down the highly agglomerated dry pigment powder into primary particles. Although not a preferred method, dyes or pigments for imparting color to the suspension medium may be added to the suspension during ball milling.

The particles can be microencapsulated by using a suitable polymer to eliminate precipitation or emulsification of the pigment particles to match the specific gravity of the dielectric solvent. Microencapsulation of the pigment particles can be accomplished by chemical or physical means. Typical microencapsulation processes include interfacial polymerization, in situ polymerization, phase separation, coacervation, electrostatic coating, spray drying, fluidized bed coating, and solvent evaporation.III filling and sealing of microcups

This process of filling and sealing is described in the aforementioned co-pending U.S. patent nos. 09/518,488 and 09/784,972, the disclosures of which are incorporated herein by reference.

The sealing of the microcups may be accomplished in a variety of ways. One preferred method is to disperse a uv curable component comprising a multifunctional acrylate, an acrylic oligomer, and a photoinitiator in an electrophoretic fluid comprising charged pigment particles and a dyed dielectric solvent. The uv curable component is immiscible with the dielectric solvent and has a specific gravity lower than the dielectric solvent and the pigment particles. The two components (uv curable component and electrophoretic fluid) are thoroughly mixed in a radial mixer and immediately applied to the microcups using precision coating machinery such as a Myrad bar, gravure plate, doctor blade, slot coating, or slot coating. Excess fluid is scraped off with a scraper or similar device. A small amount of a weak solvent or solvent mixture, such as isopropyl alcohol, methanol, or other aqueous solvent, may be used to wash the electrophoretic fluid remaining on the top surfaces of the partition walls of the microcups. Volatile organic solvents may be used to control the viscosity and coverage of the electrophoretic fluid. The filled microcups are then dried and the uv curable composition floats to the top of the electrophoretic fluid. The microcups are sealed by curing the UV curable layer floating to the surface during or after it floats to the top. Ultraviolet light, or other forms of radiation such as visible light, infrared, and electron beam may be used to cure and seal the microcups. In addition, heat or moisture may also be used to cure and seal the microcups, if appropriate, heat or moisture curable components may be used.

Preferred dielectric solvent groups (having desirable densities and desirable solubility differences for acrylate monomers and oligomers) are halocarbons and derivatives thereof. Surfactants may be used to improve the viscosity and wettability of the interface between the electrophoretic fluid and the encapsulant. Useful surfactants include FC surfactants from 3M, Zonyl fluorinated surfactants from DuPont, fluorinated acrylates, fluorinated methacrylates, fluoro-substituted long chain alcohols, perfluoro-substituted long chain carboxylic acids and derivatives thereof.

Furthermore, if such a sealing precursor is at least partially compatible with the dielectric solvent, the electrophoretic fluid and the sealing precursor may be applied sequentially to the microcups. Thus, the sealing process can be accomplished by applying a thin layer of a thermosetting precursor that is radiation, heat, moisture, or interfacial reaction curable, and curing it to the surface of the filled microcups.

Volatile organic solvents may be used to adjust the viscosity and thickness of the protective layer. When a volatile solvent is used for the protective layer, a volatile solvent that is immiscible with the dielectric solvent is preferred. In co-pending U.S. patent application No.09/874,391 filed on 4.6.2001, a thermoplastic elastomer is disclosed as a preferred sealing material. Additives such as silica particles and surfactants can be used to improve film integrity and coating quality.

The ultraviolet light curing is carried out after the interfacial polymerization, which is very beneficial to the sealing process. Forming a film by interfacial polymerizationThe separator of (3) so that intermixing between the electrophoretic layer and the overcoat layer is significantly suppressed. Sealing is then accomplished by a post-curing step, preferably with ultraviolet or other light radiation. To further reduce the degree of intermixing, it is preferred that the specific gravity of the overcoat layer be significantly lower than the specific gravity of the electrophoretic fluid. Volatile organic solvents can be used to adjust the viscosity and thickness of the coating. When a volatile solvent is used for the overcoat layer, a volatile solvent that is immiscible with the dielectric solvent is preferred. This two-step coating process is particularly useful where the dye used is at least partially soluble in the thermoset precursor.Preparation of monochrome electrophoretic displays

This process is illustrated by the flow chart shown in fig. 3. All microcups were filled with a suspension of the same color component. The process may be a continuous roll-to-roll process comprising the steps of:

1. a layer of uv curable composition 30 is applied to a continuous web 31 (optionally using a solvent). If a solvent is used, the solvent evaporates very quickly. The continuous web 31 may be a plastic substrate with or without a conductive film of a predetermined pattern on the plastic substrate, depending on the particular application and the switching mode of the display.

2. The uv curable composition 30 is molded at a temperature above the glass transition temperature using a preformed male mold 32.

3. The mold is released from the uv curable layer 30, preferably during or after curing the composition by exposure to uv light.

4. The resulting array of microcups 33 is filled with a charged pigment dispersion 34 in a colored dielectric solvent.

5. The microcups are sealed by the methods described in the same series of U.S. patent application No.09/518,488 filed on 3/2000, U.S. patent application No.09/759,212 filed on 11/1/2001, U.S. patent application No.09/606,654 filed on 28/6/2000, U.S. patent application No.09/784,972 filed on 15/2/2001, and U.S. patent application No.09/874,391 filed on 4/6/2001.

The sealing process involves adding at least one thermoset precursor to a dielectric solvent, the thermoset precursor being immiscible with the solvent and having a lower specific gravity than the solvent and pigment particles, followed by curing the thermoset precursor during or after separation of the thermoset precursor, optionally using, for example, ultraviolet radiation, or heat, or moisture. Alternatively, microcups may be sealed by coating and curing a sealing composition directly on the surface of the electrophoretic fluid.

In U.S. patent application No.09/874,391, thermoplastic elastomers are disclosed as preferred sealing materials. Examples of useful thermoplastic elastomers include diblock, triblock, and multiblock copolymers of the ABA, and (AB) n types, where A is styrene, alpha-methylstyrene, propylene, or norbornene; b is butadiene, isoprene, ethylene, propylene, butylene, dimethylsiloxane, or propylene sulfide; a and B cannot be in the same formula. The number n.gtoreq.1, preferably 1 to 10. Particularly useful are diblock, triblock, and multiblock copolymers of styrene or alpha-methylstyrene, such as SB (poly (styrene-b-butadiene)), SBS (poly (styrene-b-butadiene-b-styrene)), SIS (poly (styrene-b-isoprene-b-styrene)), SEBS (poly (styrene-b-ethylene/butylene-b-styrene)), poly (styrene-b-dimethylsiloxane-b-styrene), poly (alpha-methylstyrene-b-isoprene-b-methylstyrene), poly (alpha-methylstyrene-b-propylene sulfide-b-alpha-methylstyrene), Poly (alpha-methylstyrene-b-dimethylsiloxane-b-alpha-methylstyrene). Additives such as silica particles and surfactants may be used to improve film integrity and coating quality.

6. The array of sealed electrophoretic cells is overlaid with another continuous web 36 comprising electrode or conductor zones pre-coated with an adhesive layer 37, which may be a pressure sensitive adhesive, a hot melt adhesive, or a radiation curable adhesive.

The covering adhesive may be post-cured, with heat or ultraviolet light 38 for example, through either side of the web. The covering step may be followed by cutting 39 of the finished product. Alternatively, the sealed microcups may be cut to size prior to the covering step.

The microcup manufacturing process described above may also be conveniently replaced by a process of pattern exposure of the conductive film coated with a thermosetting precursor and removal of the unexposed areas with a suitable solvent.

For the manufacture of displays with in-plane switching mode, a thermoplastic or thermoset precursor may be applied to the transparent insulator substrate prior to micro-molding or pattern exposure, instead of being applied to the conductive film.Preparation of V. multicolor electrophoretic display

The method of preparing sealed microcups containing electrophoretic fluids of different colors can be used in the common family of U.S. patent application No.09/518,488 filed on 3/2000 and U.S. patent application No.09/879,408 filed on 11/6/2001, which method comprises (1) laminating a positive-working dry film photoresist onto the fabricated microcups, wherein the photoresist contains at least one removable carrier, such as a mixture of Saint-Gobain (workplace, MA) PET-4851, novolac positive photoresist Microposit S1818 from Shipley, and Nacor72-8685 from National Starch and Carboset 515 from BF Goodrich, an alkaline developer layer; (2) selectively opening a number of the microcups by pattern exposing the photoresist, removing the removable carrier film, and developing the positive photoresist with, for example, a diluted Microposit 351 developer from Shipley corporation; (3) filling the opened microcups with an electrophoretic fluid containing charged white pigment (titanium dioxide) particles and a dye or pigment of the first primary color; and (4) sealing the filled microcups as in making a monochrome display. These additional steps may be repeated to fabricate microcups filled with electrophoretic fluid of the second and third primary colors.

More particularly, a multicolor electrophoretic display is prepared according to the steps shown in fig. 4:

1. the thermosetting precursor layer 40 is coated on the conductive film 41.

2. The thermoplastic or thermoset precursor layer is embossed with a preformed male mold (not shown) at a temperature above the glass transition temperature of the thermoplastic or thermoset precursor layer.

3. The mold is demolded from the thermoplastic or thermoset precursor layer, preferably during or after curing by cooling, or cross-linking by radiation, heat, or moisture.

4. A positive dry film photoresist material is applied over the formed array of microcups 42, wherein the photoresist material comprises an adhesive layer 43, a positive photoresist material 44, and a removable plastic protective sheet (not shown).

5. The positive photoresist material is pattern exposed to ultraviolet, visible or other radiation (fig. 4c), the protective sheet is removed, developed in the exposed areas and the microcups are opened. The purpose of steps 4 and 5 is to open the microcups in a predetermined area (FIG. 4 d).

6. The opened microcups are filled with a charged white pigment 45 dispersed in a dielectric solvent, wherein the dielectric solvent comprises at least the dye or pigment of the first primary color, and a thermoset precursor 46 that is immiscible with the solvent and has a lower specific gravity than the solvent and pigment particles.

7. During or after the separation of the thermosetting precursor and the formation of a surface layer floating on top of the liquid phase, the microcups are sealed by curing the thermosetting precursor (preferably by uv irradiation, by thermal or moisture means) to form a sealed electrophoresis cassette containing the electrophoretic fluid of the first primary color (figure 4 e).

8. Steps 5 to 7 can be repeated to produce well-defined cassettes containing electrophoretic fluids of different colors in different areas (fig. 4e, 4f and 4 g).

9. A second transparent conductive film 47 pre-coated with a predetermined pattern of an adhesive layer 48, wherein the adhesive layer 48 may be a pressure sensitive adhesive, a hot melt adhesive, a heat, moisture, or radiation curable adhesive, is registered over the array of sealed electrophoresis cartridges.

10. The adhesive is hardened.

In step 4, the positive photoresist can be directly coated on the microcups instead of covering the microcups with the dry film positive photoresist material. The microcups may be filled with a removable fill material before the microcups are coated or covered with a photoresist material. In which case no cover sheet is required. This is disclosed in co-pending U.S. patent application No.09/879,408 filed on 11.6.2001.

Suitable materials for use as filler materials include inorganic, organic, organometallic, and polymeric materials, or particulate materials thereof. Preferred filler materials are non-film forming particles (non-film forming particles) such as latexes of PMMA, polystyrene, polyethylene and its carboxy copolymers and corresponding salts, wax emulsions, colloidal silica, titanium oxide, calcium carbonate dispersions, and mixtures thereof. Particularly preferred filler materials include dispersions of ionomers of ethylene copolymers, such as Acqua220, Acqua240, and Acqua250 (Honeywell, new jersey).

A multicolor display having an in-plane switching mode can be prepared in a similar manner except that the thermosetting precursor layer in step 1 can be coated on a transparent insulator substrate instead of a conductive film.

Another method can be easily substituted for the microcup preparation described in the above method: the conductive film coated with the thermoset precursor is subjected to a pattern exposure followed by removal of the unexposed regions with a suitable solvent.

Alternatively, the microcups may be sealed by applying a thermosetting precursor material directly to the surface of the liquid phase.

Alternatively, the color electrophoretic display of the present invention may be obtained using color filters on the top of the display, as described in serial U.S. patent application 60/308,437 filed on 7/27 of 2001, or using a colored background on the bottom of the display, as in another serial U.S. patent application 60/306,312 filed on 7/17 of 2001.

The display manufactured by the method can reach the thickness of only one piece of paper. The width of the display may be the width of the coated support screen (typically 3 to 90 inches). The length of the display may be several inches to thousands of feet, depending on the size of the roll.

An optional background layer may be applied to the bottom of the display device by spraying, printing, coating, or otherwise overlaying a color layer. For increasing the contrast, a black or gray background layer is preferably used.

Active matrix electrophoretic displays can be prepared using Thin Film Transistors (TFTs) on the bottom electrode plate of the display. The backlight system may be positioned to the side of the display device and below the background color layer or between the display and the background layer. A light scattering component, such as one filled with polymethylmethacrylate, may be used to enhance the effectiveness of the backlight.VI, the display of the invention

Three types of switching modes will be described in this section. Viewing a reflective electrophoretic display, only one external light source is needed in various situations. For viewing applications in the dark, either a backlight system or a front-lit system may be used. Due to appearance and light management reasons, a back-transmissive electrophoretic display with a backlight system is preferred to a reflective electrophoretic display with front-night light. However, in electrophoretic display cells, the presence of stray light particles greatly reduces the efficiency of the backlight system. It is difficult to achieve high contrast in both bright and dark environments for conventional electrophoretic displays.

In contrast, the display of the present invention based on microcup technology effectively allows the backlight to reach the viewer through the side walls of the microcups.Thus, even a low intensity backlight is sufficient for a user to view the back-transmissive electrophoretic display. Photocell sensors, which are used to adjust the intensity of the backlight, can be used to further reduce the power consumption of electrophoretic displays.VI (a) display with up-down switching mode

When there is a voltage difference between the top and bottom electrode plates, then the charged particles migrate to the top or bottom of the cell. When the particles migrate to and remain on the top of the cell, the color of the particles can be seen through the top transparent layer. The color of the dielectric solvent is visible through the top transparent layer as the particles migrate and remain at the bottom of the cell.VI (b) display with in-plane switching mode

For a monochrome display, the white particles are dispersed in a clear, colorless dielectric solvent in the cell of fig. 5A. All the box backgrounds are the same color (black, blue, cyan, red, magenta, etc.). When there is a voltage difference between the bottom electrode (not shown) and the two in-plane switching electrodes (not shown), the white particles then migrate to the sides of the cell, resulting in the background color being visible through the top transparent opening. When there is no voltage difference between the bottom electrode and the two in-plane switching electrode, the white particles are distributed in the dielectric solvent, and thus the color of the particles (i.e., white) can be seen through the top transparent insulating layer.

Alternatively, as shown in fig. 5B, the same color particles are dispersed in clear colorless dielectric solvent of all the boxes, and the background of the boxes is white. When there is a voltage difference between the bottom electrode (not shown) and the two in-plane switching electrodes (not shown), the colored particles migrate to the sides of the cell, resulting in the background color (i.e., white) being visible through the top transparent opening. When there is no voltage difference between the two in-plane switching electrodes and the bottom electrode, the colored particles are distributed in the dielectric solvent, and thus the color of the particles (i.e., white) can be seen through the top transparent insulator layer.

Fig. 5C-5F show a multi-color display with an in-plane switching mode.

In fig. 5C, the cell is filled with a colorless dielectric solvent having white charged particles dispersed therein, and has a different background color (i.e., red, green, or blue). When a voltage difference is present between the in-plane and bottom electrodes (not shown), the white particles migrate to the sides of the cell, resulting in the background color (i.e., red, green, or blue) being visible through the top transparent opening. When there is no voltage difference between the in-plane electrode and the bottom electrode, the particles are distributed in the dielectric solvent, resulting in a white color (i.e., the color of the particles) being visible through the top transparent opening.

In fig. 5D, the cell is filled with a colorless dielectric solvent having black particles dispersed therein, and has a different background color (i.e., red, green, or blue). When a voltage difference is present between the in-plane and bottom electrodes (not shown), the particles migrate to the sides of the cell, resulting in the background color (i.e., red, green, or blue) being visible through the top transparent opening. When there is no voltage difference between the in-plane electrode and the bottom electrode, the particles are distributed in the dielectric solvent, resulting in a black color (i.e., the color of the particles) being visible through the top transparent opening.

In fig. 5E, the cell is filled with a colorless dielectric solvent having different colored particles (i.e., red, green, or blue) dispersed therein. The box background is black. When a voltage difference is present between the in-plane and bottom electrodes (not shown), the colored charged particles migrate to the sides of the cell, resulting in the background color (i.e., black) being visible through the top transparent opening. When there is no voltage difference between the in-plane electrode and the bottom electrode, the colored particles are distributed in the dielectric solvent, resulting in the color of the particles (i.e., red, green, or blue) being visible through the top transparent opening. In this design, the black state is of high quality.

In fig. 5F the cell is filled with a colorless dielectric solvent having different colored particles (i.e., red, green, or blue) dispersed therein. The box background is white. When a point difference in pressure is present between the in-plane electrode (not shown) and the bottom electrode, the particles migrate to the sides of the cell and the background color (i.e., white) can be seen through the top transparent opening, resulting in a high quality white state. When there is no voltage difference between the in-plane electrode and the bottom electrode, the particles are distributed in the dielectric solvent, resulting in the color of the particles (i.e., red, green, or blue) being visible through the top transparent opening.

As shown in these figures, the in-plane switching mode may cause the particles to move in the in-plane direction (left/right), and the combination of different colors of particles, background and fluid (which are white, black, red, green, or blue, respectively) may result in different multi-color electrophoretic displays.

Furthermore, the particles in the dielectric solvent may be of mixed colors, and the boxes have the same background color.

The top transparent viewing layer of the display may be tinted or a color filter may be added. In this case, the cell is filled with an electrophoretic composition comprising white charged particles in a clear colorless or colored dielectric solvent, and the background of the cell is black. In a monochrome display, the transparent viewing layer on each pixel is the same color (e.g., black, red, green, blue, yellow, cyan, magenta, etc.). In a multi-color display, the transparent viewing layers may be different colors.VI (c) display with double switching modes

For ease of explanation, it is assumed that the application described herein uses positively charged white particles. As shown in fig. 6A-6C, the dual switching mode allows the particles to move vertically (up/down) or in a planar direction (left/right). For example, in FIG. 6A, the voltage of the top electrode is set low, while the bottom electrode and in-plane electrode voltages are set high. The white particles migrate and collect on the top transparent conductive film and the viewer sees a white color (i.e., the color of the particles).

In fig. 6B, the in-plane electrode voltage is set to a low value, while the top and bottom electrode voltages are set to a high value. In this case, the white particles migrate to the side of the cell, and therefore, the color visible through the top transparent conductive film is the color of the background (i.e., black).

In fig. 6C, the top electrode voltage is set to a high value, the bottom electrode voltage is set to a low value, the in-plane electrode voltage is set to a low value, and the white particles migrate to the bottom of the cell. In this case, the fluid color (i.e., red, green, or blue) is visible to the viewer through the top transparent conductive film, as shown by the red box in fig. 6C. In a full color display, the white particles in the green and blue boxes can be attracted to the sides (as shown in fig. 6C), or the top (not shown), if it is desired to render a red pixel. The former is preferred because this approach generally has more desirable color saturation than the latter. Thus, the dual switching mode technique provides a full color electrophoretic display in which all colors, including high quality red, green, blue, and white, are available in the same device.

In addition, the background color may be any color (e.g., cyan, yellow, or magenta) instead of the commonly used black. For example, the cartridge may be filled with a red clear dielectric solvent having white positively charged particles dispersed therein, and the background color of the cartridge is yellow. In this case, the viewer can see the white color (i.e., the color of the particles) when the particles migrate to the top, and the color of the medium (i.e., the red color) through the transparent conductor when the particles migrate to cover the bottom of the cell. However, when the white particles migrate to the sides of the cell, the color seen through the top transparent conductive film will be an orange hue.

Other hues or colors may be obtained by using a combination of different particle/medium/background colors, e.g. white/red/cyan, white/red/magenta, white/blue/yellow, white/blue/cyan, white/blue/magenta, white/green/yellow, white/green/cyan, white/blue/magenta, etc.

The preferred combination to obtain a full color display is a white particle, a black background, and a fluid dyed separately with an additive primary color (i.e., red, green, or blue).

Another aspect of the invention is a monochrome display with highlighting. In this embodiment, all cells in the display device have the same background color and are filled with the same electrophoretic fluid (i.e., have the same particle/solvent color combination). For example, the display device may have white particles, the solvent is one of the primary colors (i.e., red, green, or blue), and the background color is a contrasting color to the color of the solvent. This combination is useful for relatively simple two color devices with color highlighting options. For example, an electrophoretic display with white particles, yellow dielectric solvent, black background, can display at least three different colors in each pixel. When all the white particles are attracted to the top viewing row electrode, the pixel is seen as white. When all the white particles are attracted uniformly to the bottom column electrode, the pixel is seen as yellow. When the white particles are all attracted to the electrodes in either side of the cell, the pixel is seen as black. If the particles are driven to an intermediate state, an intermediate color can be obtained.

While the invention has been described with reference to specific examples thereof, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the purpose, spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, composition, process step or steps, to the objective, spirit and scope of the present invention. All such modifications are considered to be within the scope of the appended claims.

Description of the reference symbols

(UV) ultraviolet light

21a radiation curable material

21b wall surface

22 conductive film

23 Plastic substrate

24 opaque region

25 open area

26 photo mask

27 miniature cup

30 ultraviolet light curing component

31 web

32 preformed male die

33 micro-cup array

34 charged pigment dispersion

37 adhesive layer

38 ultraviolet light

39 cutting

40 thermosetting precursor layer

41 conductive film

42 micro-cup array

43 adhesive layer

44-type photoresist material

45 charged white pigment

46 thermosetting precursor

47 second transparent conductive film

48 adhesive layer

100 electrophoretic display

101 top transparent layer

102 bottom electrode plate

103 isolating cassette layers 103a, 103b and 103c cassettes

104 charged particles

105 dielectric solvent

106 sealing layer

107 backlight

108 background layer

109 vertical side wall

110a in-plane electrode

110b in-plane electrode

111 bottom electrode

112 groove

113a in-plane electrode

113b in-plane electrode

114 bottom electrode

115 groove

116 transparent top electrode

Claims (60)

1. An electrophoretic display comprising:

(a) a top transparent layer;

(b) a plurality of particles having well-defined sizes, shapes, and aspect ratios, and dispersed in

Charged pigment particle filled insulation in dielectric solvents or solvent mixtures

A box separated by light transmissive side walls;

(c) a bottom electrode plate; and

(d) a backlight below the bottom electrode plate.

2. The electrophoretic display of claim 1 further comprising a background layer.

3. An electrophoretic display according to claim 1 wherein the top transparent layer is a conductive film and the display has an up/down switching mode.

4. An electrophoretic display according to claim 1 wherein the top transparent layer is an insulator substrate and the display has an in-plane switching mode.

5. An electrophoretic display according to claim 1 wherein the top transparent layer is one conductive film and the display has an up/down switching mode and an in-plane switching mode.

6. The electrophoretic display of claim 1, wherein the plurality of cells comprise cells of different sizes and shapes.

7. An electrophoretic display according to claim 1 wherein the cells are non-spherical.

8. The electrophoretic display of claim 1 wherein the cell is formed of a material having a thickness of 10²To 1X 10⁶Microcups with square micron open area.

9. The electrophoretic display of claim 1 wherein the cells are of the type having 10³To 1X 10⁵Microcups with square micron open area.

10. The electrophoretic display of claim 1 wherein the cells are comprised of microcups having circular, polygonal, hexagonal, rectangular, or square shaped open areas.

11. An electrophoretic display according to claim 1 wherein the cells have a depth in the range of 5 to 200 microns.

12. An electrophoretic display according to claim 1 wherein the cells have a depth in the range of 10 to 100 microns.

13. The electrophoretic display of claim 1 wherein the ratio of the cell openings to the total area is from 0.05 to 0.95.

14. An electrophoretic display according to claim 1 wherein the ratio of the cell openings to the total area is from 0.4 to 0.9.

15. An electrophoretic display according to claim 3 wherein the cells are filled with a colored dielectric solvent having white charged pigment particles dispersed therein.

16. An electrophoretic display according to claim 15 wherein all of the cells have the same color of the dielectric solvent.

17. An electrophoretic display according to claim 15 wherein the individual cells have different colors of dielectric solvents.

18. An electrophoretic display according to claim 4 wherein the top transparent layer is colorless.

19. The electrophoretic display of claim 18, wherein the display is a monochrome display.

20. The electrophoretic display of claim 19 wherein said dielectric solvent is clear and colorless.

21. An electrophoretic display according to claim 20 wherein all of the cells have white particles and the same background color.

22. The electrophoretic display of claim 21 wherein the background color is black, red, green, blue, yellow, cyan, or magenta.

23. An electrophoretic display according to claim 20 wherein all of the cells have the same color of particles and a white background color.

24. The electrophoretic display of claim 23 wherein said cells are black, red, green, blue, yellow, cyan, or magenta.

25. An electrophoretic display according to claim 24 wherein the individual cells have particles of mixed colors and the same background color.

26. The electrophoretic display of claim 25 wherein said mixed color is comprised of two or more colors selected from the group consisting of black, white, red, green, blue, yellow, cyan, and magenta.

27. The electrophoretic display of claim 26 wherein said background color is selected from the group consisting of black, white, red, green, blue, yellow, cyan, and magenta.

28. An electrophoretic display according to claim 4 wherein said display is a multicolor display.

29. An electrophoretic display according to claim 28 wherein the cells have white particles and a different background color.

30. An electrophoretic display according to claim 28 wherein the cells have black particles and a different background color.

31. An electrophoretic display according to claim 28 wherein the cells have differently colored particles and a white background.

32. An electrophoretic display according to claim 28 wherein the cells have differently colored particles and a black background.

33. An electrophoretic display according to claim 4 wherein the top transparent layer is colored.

34. The electrophoretic display of claim 33 wherein said top transparent layer has a color filter.

35. An electrophoretic display according to claim 33 wherein all of the cells have a white background of particles and a black background.

36. An electrophoretic display according to claim 35 wherein all of the cells have a transparent viewing layer of the same color.

37. An electrophoretic display according to claim 35 wherein the cells have transparent viewing layers of different colors.

38. An electrophoretic display according to claim 4 wherein the substrate containing the array of thin film transistors is used as an in-plane electrode layer as well as a bottom electrode layer.

39. An electrophoretic display according to claim 5 wherein the charged particles are white.

40. The electrophoretic display of claim 39 wherein said charged particles are selected from the group consisting of red, green, blue, yellow, cyan, and magenta.

41. The electrophoretic display of claim 39 wherein the solvent is a color selected from the group consisting of red, green, blue, yellow, cyan, and magenta.

42. An electrophoretic display according to claim 1 or 2 wherein the color of said bottom electrode plate or said background layer is selected from the group consisting of black, red, green, blue, yellow, cyan, and magenta.

43. An electrophoretic display according to claim 5 wherein the electrophoretic display is a monochrome display.

44. An electrophoretic display according to claim 43 wherein all of said cells have white particles.

45. The electrophoretic display of claim 43 wherein all of said cells have particles of the same color selected from the group consisting of red, green, blue, yellow, cyan, and magenta.

46. The electrophoretic display of claim 43 wherein all of said cells have the same color of the dielectric solvent, said color being selected from the group consisting of red, green, blue, yellow, cyan, and magenta.

47. An electrophoretic display according to claim 43 wherein all of said cells have a black background.

48. The electrophoretic display of claim 43 wherein all of said cells have the same background color, said color being selected from the group consisting of red, green, blue, yellow, magenta, and mixtures thereof.

49. An electrophoretic display according to claim 5 wherein the electrophoretic display is a multicolor display.

50. An electrophoretic display according to claim 49 wherein the cells are filled with white particles dispersed in a different color of a dielectric solvent.

51. The electrophoretic display of claim 50 wherein said color is selected from the group consisting of red, green, blue, yellow, cyan, and magenta.

52. The electrophoretic display of claim 51 wherein said color is red, green, or blue.

53. The electrophoretic display of claim 49, wherein said background is black.

54. An electrophoretic display according to claim 49 wherein the individual cells have particles of mixed colors and the same background color.

55. The electrophoretic display of claim 54 wherein said color is two or more colors selected from the group consisting of white, red, green, blue, yellow, cyan, and magenta.

56. The electrophoretic display of claim 54 wherein said background color is selected from the group consisting of black, red, green, blue, yellow, cyan, and magenta.

57. An electrophoretic display according to claim 5 wherein the top layer is colored or has a color filter.

58. An electrophoretic display according to claim 57 wherein the cells have white particles dispersed in a colorless dielectric solvent.

59. An electrophoretic display according to claim 5 wherein the bottom electrode plate comprises a thin film transistor.

60. The electrophoretic display of claim 1, further comprising a diffuser applied on top of the electrophoretic display.