HK1050929A - An improved electrophoretic display with color filters - Google Patents

Description

Improved electrophoretic display with color filter

Technical Field

The invention relates to an electrophoretic display comprising isolated cells of well-defined shape, size and aspect ratio, filled with charged pigment particles dispersed in a solvent, and having a color filter disposed on a top transparent conductive film.

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 comprise two plates with electrodes, the two plates being placed opposite each other and separated by a spacer. At least one of the electrode plates is transparent. Such passive electrophoretic displays require driving the display with row and column electrodes at the top (viewing end) and bottom, respectively. 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 selectively charging 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 (gray levels) are determined by the transition pigment density of the transparent plate and can be obtained by controlling the voltage and charging time. This type of reflective electrophoretic display does not require a backlight.

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 collected state, the microparticle 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 particle arrangement is used to cover the horizontal area of the pixel and to disperse or absorb the background light. However, the backlight and color filters used in such devices consume a large amount of energy, which is not suitable for portable devices such as personal digital processing devices and electronic books.

Electrophoretic displays of different pixel or cell configurations 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.1148-1152(1979)) and microencapsulated electrophoretic displays (U.S. Pat. nos. 5,961,804 and 5,930,026), each of which has problems as described below.

In a partition-type electrophoretic display, there is a number of partitions between the two electrodes to cut the space into smaller cells, preventing unwanted particle movement, such as 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 suspended colorants separate from each other.

Microencapsulated electrophoretic displays have a substantially two-dimensional arrangement of microcapsules, each microcapsule having an electrophoretic composition consisting of a dielectric fluid and a suspension of charged pigment particles (visually contrasting 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 achieve a useful contrast ratio. Large particle sizes result in poor scratch resistance and slow response times for a given voltage, since large capsules require a large gap between the two counter 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 co-pending U.S. patent 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 better than 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 a form such as a touch screen application. The use of microcup technology also eliminates the need for edge seal adhesives, which can limit and predefine the display panel size and restrict the display fluid within a predetermined area. When a conventional display device prepared by cutting, drilling, or using an edge sealing adhesive method is manufactured in any manner, display fluid in the display device may completely leak. The damaged display device will no longer have any function. In contrast, in display devices prepared with microcup technology, the display fluid is sealed and isolated in each cell. The microcup display device can be cut to almost any size without risking that the display performance is compromised by loss of display fluid in the active area. In other words, the microcup structure allows for flexibility in the manufacturing process for the display device, wherein the process allows for continuous output production of the display device in very large sheet form factors, and the sheet form display device can be cut to any desired form factor. This isolated microcup or cassette structure is particularly important when filling an electrophoresis cassette with fluids of different characteristics, such as 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

A first aspect of the invention relates to an electrophoretic display comprising isolated cells of well-defined shape, size and aspect ratio and a color filter arranged on a top transparent conductive film. The cell is filled with charged pigment particles dispersed in a dielectric solvent.

More specifically, the electrophoretic display comprises a top transparent electrode plate, a bottom electrode plate and an isolation box enclosed between the two electrode plates. The display has a color filter with a transparent conductive film on top of the device to make a multicolor electrophoretic display. More particularly, the color filter may be disposed below the conductive film, between the conductive film and a substrate layer on which the conductive film is coated, or on top of the substrate layer.

Brief description of the drawings

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

FIGS. 2A and 2B illustrate the method steps involved in the fabrication of a microcup for a pattern exposure process; and

fig. 3 is a flowchart for manufacturing an electrophoretic display device of the present invention.

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 "cassette" is intended to mean a unit formed by a sealed microcup. The cell is filled with charged pigment particles dispersed in a solvent or solvent mixture.

The term "well-defined," when referring to the microcups or cassettes, 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 display technology. In this patent specification, it refers to the ratio of the depth to the width, or the depth to the length, of the microcups.

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

The term "conductive film" is understood to mean a thin film of conductor applied to a plastic substrate.

Description of The Preferred Embodiment

As shown in fig. 1, the electrophoretic display of the present invention comprises two electrode plates 10, 11, and a sealed, isolated cell layer 12 located between the two electrodes. The top electrode plate 10 is transparent, preferably colorless, and includes a conductive film 13 on a plastic substrate 14. The cartridge has a well-defined shape and size and is filled with charged pigment particles 15 dispersed in a dielectric solvent 16. The capsule is also individually sealed with a sealing layer 17. When a voltage difference is applied between the two electrodes, the charged particles will migrate to one side so that the color of the pigment or the color of the solvent is visible through the top transparent viewing layer.

As shown, the color filter 18 may be placed on top of the plastic substrate, or between the conductive film 13 and the plastic substrate 14 (not shown), or between the conductive film 13 and the sealing layer 17 (not shown).

The charged pigment particles 15 are preferably white and the dielectric solvent 16 is clear and colorless or colored.

Alternatively, each individual cartridge may be filled with positively and negatively charged particles, and the two particles may be of different colors.I. Preparation of the microcups I (a) preparation of the microcups by means of compression molding

The male mold may be prepared by any suitable method, such as a diamond cutting process or treatment with a photoresist followed by etching or plating. The master template for the male mold may then be manufactured by any suitable method, such as electroplating. When electroplating is used, a thin seed metal layer, typically 3000  a, such as inconel, is deposited on a glass substrate. A photoresist layer is then applied and exposed to uv light. A mask is placed between the uv light and the photoresist layer. The exposed areas of the photoresist 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 society of photographic optics engineers, journal 1663, pp.324(1992), Continuous fabrication of thin-coated optical media ("Continuous manufacturing of thin coated optical media", SPIE Proc.), using electroforming or electroless nickel deposition. The bottom plate of the mold is typically about 50 to 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 precision optical Replication technology ("Replication technologies for micro-optics", SPIE Proc.) Vol.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 between about 1 and 500 microns, preferably between about 2 and 100 microns, preferably between about 4 and 50 microns. The male mold may be in the form of a belt, a roller, a sheet. For continuous production, a band former is preferred. Prior to application of the uv curable resin component, the mold may be treated with a release agent to aid in the release process. To further improve the release process, a primer or adhesion promoter layer may be pre-applied to the conductive film to improve the adhesion between the conductor and the microcups.Formation of microcups

As disclosed in U.S. patent application No.09/784,972, filed on 15/2/2001, microcups can be made using either a batch or continuous roll-to-roll process. The latter provides a continuous, low cost, high throughput manufacturing technique for manufacturing compartments for use in electrophoretic or liquid crystal display devices (LCDs). This process is illustrated in fig. 3. The mold may be treated with a release agent before coating with the uv curable resin component to facilitate the release process. The uv curable resin may be degassed prior to dispensing and may optionally include a solvent. The solvent, if any, should be readily evaporated. The uv curable resin is dispensed onto the male mold in any suitable manner, such as coating, dripping, pouring, and the like. The dispenser may be mobile or stationary. The conductive film is covered on the ultraviolet light curing resin. Suitable conductive film embodiments include transparent conductors (ITO) on plastic substrates such as polyethylene terephthalate (pet), polyethylene naphthalate (pet), aramid (polyaramid), polyimide, polycycloolefin, polysulfone (polysulfonone), and polycarbonate. Pressure can be applied if necessary to ensure proper bonding between the resin and the plastic and to control the thickness of the microcup base plate. The pressure may be applied using a laminating roller, vacuum molding, a press or any other similar mechanism. Alternatively, the uv curable resin may be coated on the conductive film and molded using a mold. If the male mold is metallic and opaque, the plastic substrate is typically transparent to the actinic radiation used to cure the resin. Conversely, the male mold may be transparent and the plastic substrate opaque to actinic radiation. In order to transfer the molded features well to the conductive film, the latter must have good adhesion to the uv curable resin, which should have good mold release properties to the mold surface. To improve the adhesion between the conductor and the microcups, the conductive film may be pre-coated with a primer layer or adhesion promoting layer.

The thermoplastic or thermoset precursor used to prepare the microcups may be a multivalent acrylate or methacrylate, multivalent vinyl groups including vinylbenzene, vinylsilane, vinylether, multivalent epoxide, multivalent propylene, and oligomers, polymers, or the like containing crosslinking functional groups. Multifunctional acrylates and oligomers thereof are preferred. Combinations of multifunctional epoxides with multifunctional acrylates are also very useful to achieve the desired physical and mechanical properties. Crosslinkable oligomers which enhance flexibility, such as urethane acrylates or polyester acrylates, are also typically added to enhance the flexural strength of the molded microcups. The component may comprise polymers, oligomers, monomers, and additives, or oligomers, monomers, and additives alone. The glass transition temperature (Tg) of such materials is generally in the range of about-70 deg.C to 150 deg.C, preferably about-20 deg.C to 50 deg.C. The micromolding is typically carried out at a temperature above the glass transition temperature. A heated punch or a heated shoe against which the mold is pressed can be used to control the temperature and pressure of the microembossing.

During or after curing of the thermosetting precursor layer, it is demolded to expose an array of microcups. Hardening of the precursor layer can be accomplished by cooling, and crosslinking by radiation, heat or moisture. If the curing of the thermoset precursor is accomplished using UV radiation, UV light can be applied to the transparent conductive film from the bottom or top of the web, as shown in the two figures. In addition, an ultraviolet lamp may be disposed in the mold. In this case, the mold must be transparent to allow the ultraviolet light to irradiate on the thermosetting precursor layer through the preform male mold.I (b) preparation of microcups by means of pattern exposure

In addition, the microcups may be prepared by pattern-wise exposing a radiation-curable material 21 coated on a conductive film 22 through a mask 20 using ultraviolet light or other forms of radiation (as shown in fig. 2). The conductive film 22 is located on a plastic substrate 23.

For roll-to-roll methods, the photomask may be synchronized with the web and moved at the same speed as the web. In photomask 20 of FIG. 2, dark squares 24 represent opaque regions and spaces 25 between the dark squares represent open regions. The ultraviolet light is irradiated on the radiation curable material through the open region 25. The exposed areas will harden and the unexposed areas (protected by the opaque areas of the mask) are removed using a suitable solvent or developer to form microcups 26. The solvent or developer is selected from materials commonly used to dissolve, disperse, or reduce the viscosity of radiation-curable materials. Typical examples include butanone, ethyl acetate, toluene, acetone, isopropanol, methanol, ethanol, and the like.

Alternatively, the microcup can be prepared by placing a photomask under a conductive film/substrate support screen, in which case ultraviolet light is radiated from the bottom through the photomask, requiring the substrate to be transparent to the radiation.

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 10⁵In the square micron range, preferably about 10³To about 1X 10⁵Micron square. The depth of the microcups is generally from about 5 to about 100 microns, preferably from about 10 to about 50 microns. The ratio of the opening to the total area is from about 0.05 to about 0.95, preferably from about 0.4 to about 0.90.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 may optionally contain 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, such as those described in 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 also in the institute of Electrical and electronics Engineers, electronic devices, ED-24, 827(1977), and J.Appl.Phys.49(9), 4820 (1978).

The suspending fluid medium is preferably a dielectric solvent having a low viscosity and a dielectric constant of about 2 to about 30 (preferably 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, paraffin oils, and the like; aromatic hydrocarbons such as toluene, xylene, phenylxylylethane, decadiphenyl and alkylnaphthalene; halogenated solvents such as dichlorobenzotrifluoride, 3, 4, 5-trichlorobenzotrifluoride, chloropentafluorobenzene, dichlorononene, pentachlorobenzene, and the like; perfluorinated solvents such as perfluorinated decahydronaphthalene, perfluorotoluene, perfluoroxylene, FC-43, FC-70 and FC-5050 from 3M company of St.Paul, Minnesota; low molecular weight fluoropolymer such as polyperfluoropropylene oxide from TCI America of portland, orlon; such as polychlorotrifluoroethylene from Halocarbon products, Inc. of River Edge, N.J.; such as Galden, HT200 and Fluorolink from Ausimont or the perfluorinated polyalkyl ethers from Krytoxoils and great K-Fluid Series from DuPont, Delava. In a preferred embodiment, polychlorotrifluoroethylene is used as the dielectric solvent. In another preferred embodiment, polyperfluoropropylene oxide is used as the dielectric solvent.

The contrasting colorant may be a pigment 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 medium are charged, they are preferably of opposite charge to 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 particles are preferably white, and the first color pigment particles may be organic or inorganic pigments, such as titanium dioxide.

If colored pigment particles are used, the following raw materials may be selected: phthalocyanine blue (phthalocyanine blue), phthalocyanine green (phthalocyanine green), diarylide yellow (diarylide yellow), diarylide AAOT yellow (diarylide AAOTYellow), quinacridone (quinacridone), azo (azo), rhodamine (rhodamine), perylene pigments (perylene pigment series), hansa yellow g (hansa yellow g) by Kanto Chemical. The particle size is preferably in the range of 0.01 to 5 microns, more preferably in the range of 0.05 to 2 microns. 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 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.

For the present invention, the charged particles are typically white and the dielectric solvent is clear and may be colorless or colored.Filling and sealing of microcups

The filling of the microcups can be accomplished using conventional means. However, the sealing of the filled 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 that of 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 component 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, can be used to cure and seal the microcups. In addition, if a heat or moisture curing component is used, heat or moisture may be applied to cure and seal the microcups.

A preferred family of dielectric solvents having the desired density and solubility differential for acrylate monomers and oligomers are halohydrocarbons such as low molecular weight poly (perfluoro-propylene oxide) perfluorosolvents, Ausimont from italy, or perfluoroethyl ether from Du Pont, terawa, and derivatives thereof. Surfactants may be used to improve the adhesion and wetting of the interface between the electrophoretic fluid and the encapsulant. Useful surfactants include FC surfactants from 3M, Zonyl fluorinated surfactants from Du Pont, fluorinated acrylates, fluorinated methacrylates, fluoro-substituted long chain alcohols, perfluoro-substituted long chain carboxylic acids and derivatives thereof.

In addition, the electrophoretic fluid and the sealing precursor may be sequentially coated into the microcups, particularly when the sealing precursor is at least partially compatible with the dielectric solvent. The electrophoretic fluid and the sealing precursor may be sequentially coated into the microcups. Thus, a thin layer of sealing material may be applied to the surface of the filled microcups and cured using radiation, heat, moisture, or interfacial reaction to complete the microcup seal. Thermoplastic rubber is a preferred sealing material. Additives such as silica and surfactants can be used to improve film integrity and coating quality. Interfacial polymerization followed by uv curing is highly beneficial for this sealing process. By forming a thin barrier at the interface by interfacial polymerization, intermixing between the electrophoretic layer and the barrier is significantly inhibited. This sealing is then accomplished by a post-curing step, preferably with ultraviolet radiation. To further reducePreferably, the specific gravity of the overcoating is 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.IV, preparation of the electrophoretic display of the invention

This method will be described with reference to a flowchart shown in fig. 3. All microcups were filled with electrophoretic dispersion. The treatment can be carried out using a continuous roll-to-roll process comprising the steps of:

1. a layer of thermoplastic or thermoset precursor 30, optionally with a solvent, is coated over the conductive film 31. If a solvent is present, it evaporates very quickly.

2. The thermoplastic or thermoset precursor layer is molded using a preformed male mold 32 at a temperature above the glass transition temperature of the thermoplastic or thermoset precursor layer.

3. The mould is demolded from the thermoplastic or thermoset precursor layer in a suitable manner, preferably during or after hardening.

4. The array of microcups 33 made by this method is filled with a charged pigment dispersion 34 in a clear dielectric solvent.

5. The microcups are sealed to form a closed electrophoresis cassette containing an electrophoretic fluid by the methods described in commonly-filed patent applications, namely, U.S. patent 09/518,488 filed on 3/2000, U.S. patent application 09/759,212 filed on 11/1/2001, U.S. patent application 09/606,654 filed on 28/6/2000, U.S. patent application 09/784,972 filed on 15/2/2001, and U.S. patent application 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 with radiation such as ultraviolet light or with heat or moisture. Alternatively, a sealing component may be applied and cured directly on the electrophoretic fluid surface to complete the sealing of the microcups.

6. An ITO/PET second conductive film 36 pre-coated with an adhesive layer 37, wherein the adhesive 37 may be a pressure sensitive adhesive, a hot melt adhesive, a heat, moisture, or radiation curable adhesive, is overlaid on the sealed array of electrophoresis cells. At least one of the conductive films used in step 1 and step 6 is transparent. In the case of an active matrix type electrophoretic display, Thin Film Transistors (TFTs) may be used for this step.

7. A color filter 38 is added to the top transparent ITO/PET layer.

Alternatively, the colour filter may be placed between the top viewing conductor layer (ITO) and the sealing layer, or between the top viewing conductor layer (ITO) and the PET plastic substrate layer.

After covering the adhesive in step 6, if the conductive film is transparent to radiation, it can be cured through the top conductive film using radiation such as ultraviolet light. The finished product may be cut 39 after this covering step.

It is noted that in the above method, the orientation of the ITO liner can be changed. In addition, a color filter may be added after the cut 39.

Alternatively, the microcup preparation process described above can be conveniently replaced by a pattern exposure step using a conductive film coated with a thermoset precursor followed by removal of the unexposed areas with an appropriate solvent.

A color filter of the same color can also be applied to the top transparent conductive film of all cells to obtain a monochrome display of the invention. The top transparent conductive film layer is preferably colorless. The charged particles are typically white and the clear dielectric solvent can be black or other colors. For example, the cell may have a red color filter and charged white particles dispersed in a clear black dielectric solvent. In this case, when the particles migrate and remain on the top of the cell, the red color is visible through the top conductive film. When the particles migrate and remain at the bottom of the cell, the black color is visible through the top conductive film as light that has passed through the color filter is absorbed by the black color of the solvent.

Color filters of different colors (i.e., red, green, blue, yellow, cyan, magenta, etc.) can be placed at the viewing ends of the individual cells to achieve the multi-color display of the present invention. Preferably additive colors (red, green and blue). The color filter may comprise stripes of red, green, or blue color. The charged particles may be white or coloured, preferably white. The dielectric solvents in each cartridge may be of different colors or may be the same color, preferably black. The color filter may optionally include a black matrix (matrix).

Alternatively, the cartridge may be filled with positively as well as negatively charged particles. The two different particles are of different colors. For example, the positively charged particles may be white and the negatively charged particles may be colored. When the white positively charged particles migrate and remain on top of the cell, the color of the color filter can be seen through the top conductive film. The combination of the color filter color and the color of the negatively charged particles can be seen as the colored negatively charged particles migrate to and remain on top of the cell.

The display of the present invention can be manufactured at low cost. Furthermore, color filter displays have certain advantages as they offer the possibility of using colorless dielectric fluids. It is possible to avoid the difficulty of selecting dyes and the complicated pigment dispersion process.

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.

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.

Reference number 10 electrode plate 11 electrode plate 12 box layer 13 conductive film 14 plastic substrate 15 charged pigment particles 16 dielectric solvent 17 sealing layer 18 photo mask 20 photo mask 21 radiation cured material 22 conductive film 23 plastic substrate 24 dark squares 25 spacing 26 micro cups 30 thermoplastic or thermoset precursors 31 conductive film 32 male 33 micro cup array 34 charged pigment dispersion 36 second conductive film 37 adhesive 38 color filter 39 cutting UV light

Claims (26)

1. An electrophoretic display comprising:

(a) a transparent top viewing electrode;

(b) a bottom electrode;

(c) a plurality of isolated cells having a well-defined shape, size, and aspect ratio, and the plurality of cells are filled with charged pigment particles dispersed in a solvent or solvent mixture; and

(d) a color filter layer.

2. The electrophoretic display of claim 1 wherein said transparent top viewing electrode is a transparent conductive film on a transparent plastic substrate.

3. The electrophoretic display of claim 1, wherein the bottom electrode is a conductive film or a substrate comprising thin film transistors.

4. An electrophoretic display according to claim 2 wherein the color filter layer is on top of the transparent plastic substrate layer.

5. The electrophoretic display of claim 2 wherein said color filter layer is between said top conductive film and said plastic substrate layer.

6. The electrophoretic display of claim 2 wherein said color filter layer is under said top conductive film.

7. The electrophoretic display of claim 1 wherein the cells are substantially the same size and shape.

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

9. An electrophoretic display according to claim 1 wherein said cells are non-spherical.

10. The electrophoretic display of claim 1 wherein said cells are comprised of a material having a volume of about 10²To about 1X 10⁶A microcup with square micron opening area.

11. The electrophoretic display of claim 1 wherein said cells are comprised of a material having a volume of about 10³To about 1X 10⁵Square micron openingA region of microcups.

12. The electrophoretic display of claim 1 wherein said cells are formed by microcups having openings that can be circular, polygonal, hexagonal, rectangular, or square.

13. The electrophoretic display of claim 1 wherein said cells have a depth of from about 5 to about 100 microns.

14. The electrophoretic display of claim 1 wherein said cells have a depth of from about 10 to about 50 microns.

15. The electrophoretic display of claim 1 wherein said cells have a ratio of about 0.05 to about 0.95 openings to total area.

16. The electrophoretic display of claim 1 wherein said cells have a ratio of openings to total area of from about 0.4 to about 0.9.

17. An electrophoretic display according to claim 1 being a monochrome display.

18. An electrophoretic display according to claim 1 being a multicolor display.

19. An electrophoretic display according to claim 1 wherein said color filter has the same color or a different color for each of said cells.

20. The electrophoretic display of claim 1 wherein said color filter comprises stripes of red, green, and blue colors.

21. An electrophoretic display according to claim 1 wherein said color filter further comprises a black matrix.

22. An electrophoretic display according to claim 1 wherein said particles are white or colored.

23. An electrophoretic display according to claim 1 wherein said solvent is black or another color.

24. An electrophoretic display according to claim 1 wherein said particles are oppositely charged.

25. An electrophoretic display according to claim 24 wherein said positively charged particles are white and said negatively charged particles are colored.

26. An electrophoretic display according to claim 24 wherein said positively charged particles are colored and said negatively charged particles are white.