EP1118038A1 - Affichages par electrophorese encapsules pourvus d'une monocouche de capsules - Google Patents

Affichages par electrophorese encapsules pourvus d'une monocouche de capsules

Info

Publication number
EP1118038A1
EP1118038A1 EP99950233A EP99950233A EP1118038A1 EP 1118038 A1 EP1118038 A1 EP 1118038A1 EP 99950233 A EP99950233 A EP 99950233A EP 99950233 A EP99950233 A EP 99950233A EP 1118038 A1 EP1118038 A1 EP 1118038A1
Authority
EP
European Patent Office
Prior art keywords
layer
capsules
binder
film
substrate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP99950233A
Other languages
German (de)
English (en)
Inventor
Paul Drzaic
Andrew Loxley
Jonathan D. Albert
Barrett Comiskey
Peter J. Valianatos
Glen Crossley
Katharine Geramita
Karl R. Amundson
Michael L. Steiner
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
E Ink Corp
Original Assignee
E Ink Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by E Ink Corp filed Critical E Ink Corp
Publication of EP1118038A1 publication Critical patent/EP1118038A1/fr
Ceased legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
    • G02F1/1675—Constructional details
    • G02F1/16757—Microcapsules
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
    • G02F1/166—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect
    • G02F1/167—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect by electrophoresis
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/02—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the intensity of light
    • G02B26/026—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the intensity of light based on the rotation of particles under the influence of an external field, e.g. gyricons, twisting ball displays
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
    • G02F1/1675—Constructional details
    • G02F2001/1678—Constructional details characterised by the composition or particle type

Definitions

  • the present invention generally relates to materials and methods for forming a monolayer of capsules for an encapsulated electrophoretic display.
  • the present invention is directed to a bright, high-contrast encapsulated electrophoretic display.
  • a display can be achieved with various materials and methods that allow the display to be constructed such that a monolayer of capsules on a substrate is formed.
  • the capsules contain at least an electrophoretically mobile particle and a suspending fluid.
  • materials and methods of the present invention allow the capsules in the monolayer to pack together and/or deform in certain, useful configurations.
  • capsules can be non-spherical.
  • a display is one example of the broader concept of an element.
  • One or more elements can be ordered into a display or other articles of manufacture.
  • Elements can include any of the features described for a display.
  • particles move within the capsule under the influence of a voltage.
  • various visual states are available.
  • reflecting particles located at the front of the capsule (towards a viewer) in a colored dye, will reflect light and appear “white.”
  • the reflecting particles move towards the rear of the capsule (opposite the viewer) upon application of an electric, the particles will be obscured by the dyed fluid and will appear "dark" to a viewer.
  • Materials such as a polymeric binder, a capsule membrane, and electrophoretic particles and fluid must all be chemically compatible.
  • the capsule membranes may engage in useful surface interactions with the electrophoretic particles, or may act as an inert physical boundary between the fluid and the binder.
  • Polymer binders may set as adhesives between capsule membranes and electrode surfaces.
  • the electrophoretic fluid may be directly dispersed or emulsified into the binder (or a precursor to the binder material) to form what may be called a "polymer-dispersed electrophoretic display.”
  • the individual electrophoretic phases may be referred to as capsules or microcapsules even though no capsule membrane is present.
  • Such polymer-dispersed electrophoretic displays are considered to be subsets of encapsulated electrophoretic displays.
  • the binder material surrounds the capsules and separates the two electrodes.
  • This binder material should be compatible with the capsule and electrodes and should possess properties that allow for facile printing or coating. It may also possess barrier properties for water, oxygen, ultraviolet light, the electrophoretic fluid, or other materials. Further, it may contain surfactants and cross-linking agents, which could aid in coating or durability.
  • the polymer-dispersed electrophoretic display may be of the emulsion or phase separation type.
  • an encapsulated electrophoretic element has a plurality of non-spherical capsules disposed substantially in a single layer on a substrate.
  • an encapsulated electrophoretic element has a plurality of capsules disposed substantially in a single layer on a substrate and in association with a binder, thereby to form a film.
  • the binder can include a binder solid, and a ratio of a mass of the binder solid to a mass of the capsules of at least a portion of the element can be from about 1 :2 to about 1 :20.
  • an encapsulated electrophoretic element has a plurality of capsules disposed substantially in a single layer on a substrate and associated with a binder, thereby to form a film. At least a portion of the element has an optically active fraction of at least 70%.
  • a plurality of capsules can be disposed on the substrate and can be in association with a binder, thereby to form a film.
  • the film can have a binder that includes a binder solid and a ratio of a mass of the binder solid to a mass of the capsules, of at least a portion of the element, can be from about 1 :2 to about 1 :20.
  • At least a portion of the element can have an optically active fraction of at least 70%.
  • the capsules can be non-spherical and/or substantially planar on at least one side proximate the substrate.
  • the film can include closely-packed capsules.
  • At least one of the capsules can include a suspending fluid and at least one species of particle, or at least one of the capsules can include at least two species of particles such that an optical property of at least two of the particle species is different.
  • the capsules can be a polymer matrix having fluid-containing (such as oil) cavities.
  • a capsule wall defines the capsule and can have a thickness from about 0.2 ⁇ m to
  • the substrate can include a polymeric material, a polyester film, and/or at least
  • the substrate can be from about 25 ⁇ m to about 500 ⁇ m thick.
  • An element also can have a layer of material that substantially fills interstices formed within the film that also can be substantially planar or a side opposite the film.
  • a rear substrate can be disposed adjacent the layer of material.
  • the layer of material can be initially associated with the film or with the rear substrate.
  • the capsules, binder, and layer of material can form a stratum having a substantially uniform thickness and/or a stratum that is substantially free from voids.
  • the stratum can be from about 10 ⁇ m to about 500 ⁇ m thick, preferably about 50 ⁇ m to about 300 ⁇ m thick.
  • the capsules can be of substantially uniform size.
  • the layer of material can be the binder.
  • the layer of material can include an insulator, conductor, or semiconductor.
  • the layer of material can be tacky or liquid prior to, during, and/or after substantially filling the interstices within the film.
  • the layer of material can have a thickness of less than or equal to about 50 ⁇ m.
  • the layer of material can include an adhesive containing, for example, carbon particles, gold particles, aluminum particles, platinum particles, silver particles, plated polymer spheres, plated glass spheres, indium tin oxide particles, polyacetylene, polyaniline, polypyrrole, polyethylene dioxythiophene (“P-DOT”), and/or polythiophene.
  • the rear substrate can include at least one electrode, at least one transistor, and/or at least one diode.
  • the transistor can be at least organic material or silicon-based.
  • the rear substrate can include a polymeric material, a glass, or a metal.
  • an encapsulated electrophoretic element in another aspect of the invention, includes a plurality of non-spherical capsules disposed substantially in a single layer on a substrate, thereby to form a film.
  • the element of this embodiment contains substantially no binder.
  • This aspect can have any of the features described above. Additionally, this aspect can have any of the following features.
  • the capsules and layer of material can form a stratum that has a substantially uniform thickness and/or that is substantially free from voids. Additionally, one or more of the elements of this aspect of the invention can be combined with other elements of this aspect or the other aspects of the present invention to form a display.
  • a process for creating an encapsulated electrophoretic element that is capable of having a plurality of capsules disposed on a substrate in substantially a single layer includes the steps of (a) providing the capsules; (b) mixing at least one of the capsules with a binder to create a capsule/binder mixture; (c) coating the capsule/binder mixture onto an at least partially conductive substrate, thereby to create a film; and (d) curing the capsule/binder mixture.
  • the binder can be selected from the group consisting of acrylic, urethane, and poly(vinyl alcohol).
  • the binder can include a polymer latex.
  • the binder can have a fraction that is capable of evaporating.
  • the conductive substrate can include an indium tin oxide sputtered polyester film.
  • At least one of the capsules can contain a plurality of particles (such as titanium dioxide particles) dispersed in a suspending fluid.
  • the suspending fluid can include a halogenated hydrocarbon and/or an aliphatic hydrocarbon.
  • the coating step can include applying pressurized gas to the capsule/binder mixture, thereby to cause deposition of the capsule/binder mixture onto the substrate such that the capsules are disposed on the substrate in substantially a single layer.
  • the coating step can further include heating, cooling, and/or adding a liquid to the pressurized gas prior to or during application of the pressurized gas to the capsule/binder mixture.
  • the liquid can be in droplet form and/or can be an organic solvent.
  • the organic solvent can include, for example, butyl acetate, methylene chloride, and/or chlorobenzene.
  • the organic solvent can include an alcohol, for example, isopropyl alcohol, methanol, and/or ethanol.
  • the coating step can include applying the pressurized gas with an air knife at a distance of about 1 cm to about 15 cm from the surface of the capsule/binder mixture and/or at an angle of from about 0 degrees to about 90 degrees from the surface of the conductive substrate.
  • the pressurized gas can include air.
  • the coating step can include coating at least some of the capsules onto a film through a coating head, for example with a pump that, typically, provides pumping pressure with a low shear force. At least some of the capsules can be disposed in and form a single layer.
  • the coating head can be a slot die coating head. Typically, a width of a slot of the slot die coating head is between about 1 and about 2.5 times the mean diameter of the capsules
  • the process can further include laminating the film to a rear substrate.
  • a layer of material can be disposed between the film and the rear substrate.
  • the layer of material can be associated with the rear substrate and/or with the film prior to laminating. Heating, pressurizing, and/or evacuating of a gas can occur during the step of laminating.
  • the layer of material can be insulating, conductive, or semiconductive.
  • the layer of material can be tacky or in a liquid state during at least a portion of the laminating step.
  • the layer of material can include the binder.
  • the step of laminating can produce a stratum comprising the capsules, binder, and layer of material.
  • the stratum can have at least one substantially planar side proximate the rear substrate, can be substantially free from voids, and/or have a substantially uniform thickness.
  • the layer of material can substantially fill interstices within the film.
  • the layer of material can have a thickness of less than or equal to about 50 ⁇ m.
  • the layer of material can include an adhesive containing, for example, carbon particles, gold particles, aluminum particles, platinum particles, silver particles, plated polymer spheres, plated glass spheres, indium tin oxide particles, polyacetylene, polyaniline, polypyrrole, P-DOT, and/or polythiophene.
  • the binder can include a binder solid and a ratio of the mass of the binder solid to the mass of the capsules of at least a portion of the element can be from about 1 :2 to about 1 :20.
  • the process can further include the step of removing water from association with at least some of the capsules.
  • the step of removing water can include a process selected from the group consisting of centrifuging, absorbing, evaporating, mesh filtrating and osmotic separating.
  • FIG. 1 A is a schematic representation of a cross-section of a monolayer of capsules
  • FIG. IB is a schematic representation of a cross-section of a monolayer of deformable, non-spherical capsules
  • FIG. 2 schematically illustrates a coating process using a slot die coater according to one embodiment of the invention
  • FIG. 3 schematically illustrates a slot die coater depositing a monolayer of capsules according to one embodiment of the invention
  • FIG. 4 schematically illustrates a coating process using an air knife coater according to one embodiment of the invention
  • FIG. 5 A is a schematic illustration of a film prior to contact with a layer of material to fill the interstices within the film
  • FIG. 5B is a schematic illustration of the film of FIG. 5 A after the layer of material has been applied and laminated to a rear substrate;
  • FIG. 6A is a schematic top view of a display illustrating calculation of optically active fraction
  • FIG. 6B is a schematic side view of a display illustrating calculation of optically active fraction
  • FIG. 7 A is a schematic illustration of an apparatus for performing emulsion-based encapsulation
  • FIG. 7B is a schematic illustration of an oil drop of suspending fluid having white and black particles dispersed within it;
  • FIG. 7C is a schematic illustration of an oil drop of darkly dyed suspending fluid having white microparticles and charge control agents dispersed within it;
  • FIG. 8 schematically depicts removing water from association with capsules
  • FIG. 9A is a schematic illustration of a film without binder prior to contact with a layer of material to fill the interstices within the film
  • FIG. 9B is a schematic illustration of the film of FIG. 9A after the layer of material has been applied and after lamination to a rear substrate; and
  • FIG. 10 is a schematic illustration of capsules that are fluid-filled cavities in a matrix.
  • the present invention provides materials and methods that improve performance of encapsulated electrophoretic display devices.
  • a closely packed structure of capsules which typically contain electrophoretic particles
  • capsules in a closely packed structure include those in a high-density, closely-spaced configuration.
  • deformable capsules that allow the walls of the capsules to fit together closely, with little binding material between them, are desirable.
  • these capsules may take on a non-spherical shape.
  • an encapsulated electrophoretic display includes one or more species of particle that either absorb or scatter light.
  • the capsules contain one or more species of electrophoretically mobile particles dispersed in a dyed suspending fluid.
  • Another example is a system in which the capsules contain two separate species of particles suspended in a clear suspending fluid, in which one species of particle absorbs light (dark), while the other species of particle scatters light (white).
  • the particles are commonly solid pigments, dyed particles, or pigment/polymer composites.
  • a single layer of capsules is desirable as the optically active portion of the device.
  • the capsules typically contain an opaque pigment, and transmit little or no light in any state of the device. Thus, light impinging on the first layer of close- packed capsules is either scattered or absorbed. Little light passes through the capsules. If individual capsules (or a second layer of capsules) are positioned underneath the first layer of capsules, little or no light reaches these capsules. As such, the second layer does not contribute significantly to the optical effect. Additionally, because additional layers of capsules add thickness to the film, the voltage required to operate the film is raised without providing any optical benefit.
  • capsules 2 are substantially uniform in size.
  • the capsules 2 can be deformable such that a monolayer 4 can form a flat (or nearly flat) surface 6 as shown in FIG. IB.
  • the flat surface 6 allows the capsules 2 to pack together more closely, thus allowing the particles 8 within the capsules 2 to more uniformly spread across the face of the display (compare the distribution of particles 8 in FIG. 1 A with the distribution in FIG. IB).
  • a flat surface on the other side of the capsules allows for laminating a second substrate (or second conductive substrate) that makes good contact with the capsule layer.
  • This flat top surface can form spontaneously, or can be formed by coating or laminating another material to the capsules.
  • capsules typically have a wall thickness of about 0.2 ⁇ m to about 10 ⁇ m, more preferably about
  • one way to measure the state of the display involves a variable called the "optically active fraction.”
  • This variable refers to an area of a display that is capable of having its appearance changed as compared with the total area of a display.
  • the variable can be expressed as a ratio, namely, (changeable surface area of display) / (total surface area of display).
  • total surface area of display When calculating total area, one can easily calculate a surface area of the display using common geometric formulae.
  • optically active areas of capsules i.e., visible portions of the capsule that change appearance
  • the plane upon which a total surface area usually is calculated.
  • the location of optically active areas must be extrapolated to the plane upon which total surface area is calculated in order to estimate the optically active fraction.
  • FIGS. 6A and 6B illustrate extrapolation of the optically active areas for estimating the optically active fraction.
  • FIG. 6A is a top view and FIG. 6B is a side view of the same structure, both views are aligned.
  • Four capsules 100, 102, 104, 106 are shown in a schematic plane 110 of a display. This rectangular plane 110 represents the total surface area of the display. Due to the shape of the capsules 100, 102, 104, 106, the optically active area of the capsules 100, 102, 104,
  • FIG. 6B shows how a portion of the capsules 100, 102, 104, 106 is close to, but not coincident with, the plane 110 of the display, explaining why the solid lines and dashed lines in FIG. 6A are not coincident.
  • useful optically active fractions are equal to or greater than about 70% and more preferably equal to or greater than about 90%.
  • Non-spherical microcapsules can be formed during the encapsulation phase, by, for example, using a non-uniform shear field or a compressive pressure. Such non- spherical capsules can also be formed during the processing of the display when the binder is drying or curing. In such a system, as the binder shrinks, it pulls capsules close to one another and pulls the capsules down toward the substrate on which they have been coated. For example, an aqueous evaporative binder, such as a waterbourne acrylic, urethane, or poly (vinylalcohol), tends to exhibit such shrinking properties. Typically, a fraction of the binder, such as water, evaporates.
  • non-spherical capsules can be formed, for example, by applying a force to the film as it is drying or curing to permanently deform the capsules. Such a force can be applied by a pair of rollers, by a vacuum lamination press, by a mechanical press, or by any other suitable means. Such non-spherical capsules can also be formed by stretching the cured film in one or both of the planar axes of the film. After completion of the curing process, the capsule can protrude above the surface of the cured film, resulting in a lens effect that enhances the optical properties of the capsule.
  • the capsule also can be formed of a material which softens in the binder, thus allowing the capsules to deform to form a flat surface when the capsules and binder are laid down and the binder is cured.
  • a polymer-dispersed electrophoretic display is constructed in a manner similar to a polymer-dispersed liquid crystal display.
  • a fluid is mixed with a binder.
  • the fluid can be an oil.
  • the binder is dried or is cured, the fluid is pulled into non- spherical cavities.
  • These fluid-containing cavities can be elastomeric capsules. These cavities typically lack capsule walls.
  • FIG. 10 shows a cavity 60 filled with an oil 64. The cavity is situated in a matrix 62.
  • the matrix 62 is adjacent a substrate 66.
  • the matrix 62 is formed from a polymer which can be a binder.
  • the aspect ratio (i.e., ratio of width, w, to height, h) of these cavities is preferably greater than about 1.2.
  • the aspect ratio is more preferably greater than about 1.5, and, in a particularly preferred embodiment, the aspect ratio is greater than about 1.75.
  • a display having non-spherical capsules has a volume fraction (i.e., fraction of total volume) of binder between about 0 to about 0.9. More preferably, the volume fraction is between about 0.05 and about 0.2.
  • An electrophoretic display is constructed as either an encapsulated electrophoretic display or a polymer-dispersed electrophoretic display (similar in construction to a polymer dispersed liquid crystal display), and the non-spherical capsules or liquid droplets are formed by flattening, by shrinkage of the binder, or by mechanical force. In each case, the capsules should be capable of deforming, or they may rupture.
  • the encapsulated phases change shape as the polymer shrinks.
  • the encapsulated phases may be deformed asymmetrically by stretching the substrate.
  • Another technique which may be employed is to first dry the binder in such a way that a tough top skin is formed. The rest of the binder may then be dried slowly with no fear of the top surface breaking or becoming too uneven.
  • Section I generally describes some of the components of electrophoretic displays according to the invention. More detail is provided in United States
  • Section II describes components of displays and processes for constructing displays in a monolayer.
  • a particle is any component that is charged or capable of acquiring a charge (i.e., has or is capable of acquiring electrophoretic mobility), and, in some cases, this mobility may be zero or close to zero (i.e., the particles will not move).
  • the particles may be neat pigments, dyed (laked) pigments or pigment/polymer composites, or any other component that is charged or capable of acquiring a charge.
  • Typical considerations for the electrophoretic particle are its optical properties, electrical properties, and surface chemistry.
  • the particles may be organic or inorganic compounds, and they may either absorb light or scatter light.
  • the particles for use in the invention may further include scattering pigments, absorbing pigments and luminescent particles.
  • the particles may be retroreflective, such as corner cubes, or they may be electroluminescent, such as zinc sulfide particles, which emit light when excited by an AC field, or they may be photoluminescent.
  • the particles may be surface treated so as to improve charging or interaction with a charging agent, or to improve dispersibility.
  • titania One particle for use in electrophoretic displays of the invention is titania.
  • the titania particles may be coated with a metal oxide, such as aluminum oxide or silicon oxide, for example.
  • the titania particles may have one, two, or more layers of metal-oxide coating.
  • a titania particle for use in electrophoretic displays of the invention may have a coating of aluminum oxide and a coating of silicon oxide. The coatings may be added to the particle in any order.
  • the electrophoretic particle is usually a pigment, a polymer, a laked pigment, or some combination of the above.
  • a neat pigment can be any pigment, and, usually for a light colored particle, pigments such as rutile (titania), anatase (titania), barium sulfate, kaolin, or zinc oxide are useful. Some typical particles have high refractive indices, high scattering coefficients, and low absorption coefficients. Other particles are absorptive, such as carbon black or colored pigments used in paints and inks. The pigment should also be insoluble in the suspending fluid. Yellow pigments such as diarylide yellow, hansa yellow, and benzidin yellow have also found use in similar displays. Any other reflective material can be employed for a light colored particle, including non-pigment materials, such as metallic particles.
  • Useful neat pigments include, but are not limited to, PbCrO , Cyan blue GT 55-3295 (American Cyanamid Company, Wayne, NJ), Cibacron Black BG (Ciba Company, Inc., Newport, DE), Cibacron Turquoise Blue G (Ciba), Cibalon Black BGL (Ciba), Orasol Black BRG (Ciba), Orasol Black RBL (Ciba), Acetamine Blac, CBS (E. I. du Pont de Nemours and Company, Inc., Wilmington, DE), Crocein Scarlet N Ex (du Pont) (27290), Fiber Black VF (duPont) (30235), Luxol Fast Black L (duPont) (Solv. Black 17), Nirosine Base No. 424
  • Cyper Black IA (Basic Blk. 3), Diamine Black CAP Ex Cone (GAF) (30235), Diamond Black EAN Hi Con. CF (GAF) (15710), Diamond Black PBBA Ex (GAF) (16505); Direct Deep Black EA Ex CF (GAF) (30235), Hansa Yellow G (GAF) (11680); Indanthrene Black BBK Powd. (GAF) (59850), Indocarbon CLGS Cone. CF (GAF) (53295), Katigen Deep Black NND Hi Cone. CF (GAF) (1571 1), Rapidogen Black 3 G (GAF) (Azoic Blk.
  • Particles may also include laked, or dyed, pigments.
  • Laked pigments are particles that have a dye precipitated on them or which are stained.
  • Lakes are metal salts of readily soluble anionic dyes. These are dyes of azo, triphenylmethane or anthraquinone structure containing one or more sulphonic or carboxylic acid groupings. They are usually precipitated by a calcium, barium or aluminum salt onto a substrate. Typical examples are peacock blue lake (CI Pigment Blue 24) and Persian orange (lake of CI Acid Orange 7), Black M Toner (GAF) (a mixture of carbon black and black dye precipitated on a lake).
  • CI Pigment Blue 24 and Persian orange (lake of CI Acid Orange 7)
  • GAF Black M Toner
  • a dark particle of the dyed type may be constructed from any light absorbing material, such as carbon black, or inorganic black materials.
  • the dark material may also be selectively absorbing.
  • a dark green pigment may be used.
  • Black particles may also be formed by staining latices with metal oxides, such latex copolymers consisting of any of butadiene, styrene, isoprene, methacrylic acid, methyl methacrylate, acrylonitrile, vinyl chloride, acrylic acid, sodium styrene sulfonate, vinyl acetate, chlorostyrene, dimethylaminopropylmethacrylamide, isocyanoethyl methacrylate and N- (isobutoxyme hacrylamide), and optionally including conjugated diene compounds such as diacrylate, triacrylate, dimethylacrylate and trimethacrylate.
  • Black particles may also be formed by a dispersion polymerization technique.
  • the pigments and polymers may form multiple domains within the electrophoretic particle, or be aggregates of smaller pigment/polymer combined particles.
  • a central pigment core may be surrounded by a polymer shell.
  • the pigment, polymer, or both can contain a dye.
  • the optical purpose of the particle may be to scatter light, absorb light, or both. Useful sizes may range from 1 nm up to
  • electrophoretic particle may be substantially matched to that of the suspending (i.e., electrophoretic) fluid.
  • a suspending fluid has a density that is "substantially matched" to the density of the particle if the difference in their respective densities is between about zero and about two grams/milliliter (“g/ml"). This difference is preferably between about zero and about 0.5 g/ml.
  • Useful polymers for the particles include, but are not limited to: polystyrene, polyethylene, polypropylene, phenolic resins, Du Pont Elvax resins (ethylene-vinyl acetate copolymers), polyesters, polyacrylates, polymethacrylates, ethylene acrylic acid or methacrylic acid copolymers (Nucrel Resins - Dupont, Primacor Resins- Dow Chemical), acrylic copolymers and terpolymers (Elvacite Resins, DuPont) and PMMA.
  • Useful materials for homopolymer / pigment phase separation in high shear melt include, but are not limited to, polyethylene, polypropylene, polymethylmethacrylate, polyisobutylmethacrylate, polystyrene, polybutadiene, polyisoprene, polyisobutylene, polylauryl methacrylate, polystearyl methacrylate, polyisobornyl methacrylate, poly-t-butyl methacrylate, polyethyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylonitrile, and copolymers of two or more of these materials.
  • Some useful pigment/polymer complexes that are commercially available include, but are not limited to,
  • VM6223 Magnetic Color Company, Inc., Elizabeth, NJ
  • Naphthol FGR RF6257 Magnetic Color Company, Inc., Elizabeth, NJ
  • the pigment-polymer composite may be formed by a physical process, (e.g., attrition or ball milling), a chemical process (e.g., microencapsulation or dispersion polymerization), or any other process known in the art of particle production.
  • a physical process e.g., attrition or ball milling
  • a chemical process e.g., microencapsulation or dispersion polymerization
  • any other process known in the art of particle production e.g., the processes and materials for both the fabrication of liquid toner particles and the charging of those particles may be relevant.
  • liquid toners and encapsulated electrophoretic inks are similar, in that the pigment or dye must be easily incorporated therein, either by a physical, chemical, or physicochemical process, may aid in the colloidal stability, and may contain charging sites or may be able to incorporate materials which contain charging sites.
  • One general requirement from the liquid toner industry that is not shared by encapsulated electrophoretic inks is that the toner must be capable of "fixing" the image, i.e., heat fusing together to create a uniform film after the deposition of the toner particles.
  • Typical manufacturing techniques for particles may be drawn from the liquid toner and other arts and include ball milling, attrition, jet milling, etc. The process will be illustrated for the case of a pigmented polymeric particle.
  • the pigment is compounded in the polymer, usually in some kind of high shear mechanism such as a screw extruder.
  • composite material is then (wet or dry) ground to a starting size of around 10 ⁇ m. It is then dispersed in a carrier liquid, for example ISOPAR ® (Exxon, Houston, TX), optionally with some charge control agent(s), and milled under high shear for several hours down to a final particle size and/or size distribution.
  • a carrier liquid for example ISOPAR ® (Exxon, Houston, TX), optionally with some charge control agent(s), and milled under high shear for several hours down to a final particle size and/or size distribution.
  • Another manufacturing technique for particles is to add the polymer, pigment, and suspending fluid to a media mill.
  • the mill is started and simultaneously heated to temperature at which the polymer swells substantially with the solvent. This temperature is typically near
  • the pigment is easily encapsulated into the swollen polymer.
  • the mill is gradually cooled back to ambient temperature while stirring. The milling may be continued for some time to achieve a small enough particle size, typically a few microns in diameter.
  • the charging agents may be added at this time.
  • more suspending fluid may be added.
  • Chemical processes such as dispersion polymerization, mini- or micro-emulsion polymerization, suspension polymerization precipitation, phase separation, solvent evaporation, in situ polymerization, seeded emulsion polymerization, or any process which falls under the general category of microencapsulation may be used.
  • a typical process of this type is a phase separation process wherein a dissolved polymeric material is precipitated out of solution onto a dispersed pigment surface through solvent dilution, evaporation, or a thermal change.
  • Other processes include chemical means for staining polymeric latices, for example with metal oxides or dyes.
  • the suspending fluid containing the particles can be chosen based on properties such as density, refractive index, and solubility.
  • a preferred suspending fluid has a low dielectric constant (about 2), high volume resistivity (about 10 15 ohm-cm), low viscosity (less than 5 centistokes (“cst”)), low toxicity and environmental impact, low water solubility (less than 10 parts per million (“ppm”)), high specific gravity (greater than 1.5), a high boiling point (greater
  • suspending fluid may be based on concerns of chemical inertness, density matching to the electrophoretic particle, or chemical compatibility with both the electrophoretic particle and bounding capsule.
  • the viscosity of the fluid should be low when movement of the particles is desired.
  • the refractive index of the suspending fluid may also be substantially matched to that of the particles.
  • the refractive index of a suspending fluid "is substantially matched" to that of a particle if the difference between their respective refractive indices is between about zero and about 0.3, and is preferably between about 0.05 and about 0.2.
  • the fluid may be chosen to be a poor solvent for some polymers, which is advantageous for use in the fabrication of microparticles, because it increases the range of polymeric materials useful in fabricating particles of polymers and pigments.
  • Organic solvents such as halogenated organic solvents, saturated linear or branched hydrocarbons, silicone oils, and low molecular weight halogen-containing polymers are some useful suspending fluids.
  • the suspending fluid may comprise a single fluid.
  • the fluid will, however, often be a blend of more than one fluid in order to tune its chemical and physical properties.
  • the fluid may contain surface modifiers to modify the surface energy or charge of the electrophoretic particle or bounding capsule. Reactants or solvents for the microencapsulation process (oil soluble monomers, for example) can also be contained in the suspending fluid. Charge control agents can also be added to the suspending fluid.
  • Useful organic solvents include, but are not limited to, epoxides, such as decane epoxide and dodecane epoxide; vinyl ethers, such as cyclohexyl vinyl ether and Decave ® (International Flavors & Fragrances, Inc., New York, NY); and aromatic hydrocarbons, such as toluene and naphthalene.
  • Useful halogenated organic solvents include, but are not limited to, tetrafluorodibromoethylene, tetrachloroethylene, trifluorochloroethylene, 1 ,2,4-trichlorobenzene, carbon tetrachloride. These materials have high densities.
  • Useful hydrocarbons include, but are not limited to, dodecane, tetradecane, the aliphatic hydrocarbons in the Isopar ® series (Exxon, Houston, TX), Norpar ® ( series of normal paraffinic liquids), Shell-Sol ® (Shell, Houston, TX), and Sol-Trol ® (Shell), naphtha, and other petroleum solvents. These materials usually have low densities.
  • Useful examples of silicone oils include, but are not limited to, octamethyl cyclosiloxane and higher molecular weight cyclic siloxanes, poly (methyl phenyl siloxane), hexamethyldisiloxane, and polydimethylsiloxane. These materials usually have low densities.
  • Useful low molecular weight halogen-containing polymers include, but are not limited to, poly(chlorotrifluoroethylene) polymer (Halogenated hydrocarbon Inc., River Edge, NJ), Galden
  • the suspending fluid is a poly(chlorotrifluoroethylene) polymer.
  • this polymer has a degree of polymerization from about 2 to about 10. Many of the above materials are available in a range of viscosities, densities, and boiling points.
  • the fluid must be capable of being formed into small droplets prior to a capsule being formed.
  • Processes for forming small droplets include flow-through jets, membranes, nozzles, or orifices, as well as shear-based emulsifying schemes.
  • the formation of small drops may be assisted by electrical or sonic fields.
  • Surfactants and polymers can be used to aid in the stabilization and emulsification of the droplets in the case of an emulsion type encapsulation.
  • One surfactant for use in displays of the invention is sodium dodecylsulfate.
  • the suspending fluid can contain an optically absorbing dye.
  • This dye must be soluble in the fluid, but will generally be insoluble in the other components of the capsule.
  • the dye can be a pure compound, or blends of dyes to achieve a particular color, including black.
  • the dyes can be fluorescent, which would produce a display in which the fluorescence properties depend on the position of the particles.
  • the dyes can be photoactive, changing to another color or becoming colorless upon irradiation with either visible or ultraviolet light, providing another means for obtaining an optical response. Dyes could also be polymerizable, forming a solid absorbing polymer inside the bounding shell.
  • dyes that can be chosen for use in encapsulated electrophoretic display. Properties important here include light fastness, solubility in the suspending liquid, color, and cost. These are generally from the class of azo, anthraquinone, and triphenylmethane type dyes and may be chemically modified so as to increase the solubility in the oil phase and reduce the adsorption by the particle surface.
  • Useful azo dyes include, but are not limited to: the Oil Red dyes, and the Sudan Red and Sudan Black series of dyes.
  • Useful anthraquinone dyes include, but are not limited to: the Oil Blue dyes, and the Macrolex Blue series of dyes.
  • Useful triphenylmethane dyes include, but are not limited to, Michler's hydrol, Malachite Green, Crystal Violet, and Auramine O.
  • C. Charge Control Agents and Particle Stabilizers Charge control agents are used to provide good electrophoretic mobility to the electrophoretic particles. Stabilizers are used to prevent agglomeration of the electrophoretic particles, as well as prevent the electrophoretic particles from irreversibly depositing onto the capsule wall. Either component can be constructed from materials across a wide range of molecular weights (low molecular weight, oligomeric, or polymeric), and may be pure or a mixture.
  • the charge control agent used to modify and/or stabilize the particle surface charge is applied as generally known in the arts of liquid toners, electrophoretic displays, non-aqueous paint dispersions, and engine-oil additives.
  • charging species may be added to non-aqueous media in order to increase electrophoretic mobility or increase electrostatic stabilization.
  • the materials can improve steric stabilization as well.
  • Different theories of charging are postulated, including selective ion adsorption, proton transfer, and contact electrification.
  • An optional charge control agent or charge director may be used. These constituents typically consist of low molecular weight surfactants, polymeric agents, or blends of one or more components and serve to stabilize or otherwise modify the sign and/or magnitude of the charge on the electrophoretic particles.
  • the charging properties of the pigment itself may be accounted for by taking into account the acidic or basic surface properties of the pigment, or the charging sites may take place on the carrier resin surface (if present), or a combination of the two. Additional pigment properties which may be relevant are the particle size distribution, the chemical composition, and the lightfastness.
  • the charge control agent used to modify and/or stabilize the particle surface charge may be applied as generally known in the arts of liquid toners, electrophoretic displays, non-aqueous paint dispersions, and engine-oil additives.
  • charging species may be added to non-aqueous media in order to increase electrophoretic mobility or increase electrostatic stabilization.
  • the materials can improve steric stabilization as well.
  • Different theories of charging are postulated, including selective ion adsorption, proton transfer, and contact electrification.
  • Charge adjuvents may also be added. These materials increase the effectiveness of the charge control agents or charge directors.
  • the charge adjuvent may be a polyhydroxy compound or an aminoalcohol compound, which are preferably soluble in the suspending fluid in an amount of at least 2% by weight.
  • polyhydroxy compounds which contain at least two hydroxyl groups include, but are not limited to, ethylene glycol, 2,4,7, 9-tetramethyl-decyn-4,7- diol, poly (propylene glycol), pentaethylene glycol, tripropylene glycol, triethylene glycol, glycerol, pentaerythritol, glycerol-tri-12 hydroxystearate, propylene glycerol monohydroxystearate, and ethylene glycol monohydroxystrearate.
  • the charge adjuvent is preferably present in the suspending fluid in an amount of about 1 to about 100 milligrams per gram ("mg/g") of the particle mass, and more preferably about 50 to about 200 mg/g.
  • the surface of the particle may also be chemically modified to aid dispersion, to improve surface charge, and to improve the stability of the dispersion, for example.
  • Surface modifiers include organic siloxanes, organohalogen silanes and other functional silane coupling agents (Dow Corning ® Z-6070, Z-6124, and 3 additive, Midland, MI); organic titanates and zirconates (Tyzor ® TOT, TBT, and TE Series, Dupont, Wilmington, DE); hydrophobing agents, such as long chain (C12 to C50) alkyl and alkyl benzene sulphonic acids, fatty amines or diamines and their salts or quaternary derivatives; and amphipathic polymers which can be covalently bonded to the particle surface.
  • charging results as an acid-base reaction between some moiety present in the continuous phase and the particle surface.
  • useful materials are those which are capable of participating in such a reaction, or any other charging reaction as known in the art.
  • charge control agents which are useful include organic sulfates or sulfonates, metal soaps, block or comb copolymers, organic amides, organic zwitterions, and organic phosphates and phosphonates.
  • Useful organic sulfates and sulfonates include, but are not limited to, bis(2-ethyl hexyl) sodium sulfosuccinate, calcium dodecyl benzene sulfonate, calcium petroleum sulfonate, neutral or basic barium dinonylnaphthalene sulfonate, neutral or basic calcium dinonylnaphthalene sulfonate, dodecylbenzenesulfonic acid sodium salt, and ammonium lauryl sulphate.
  • Useful metal soaps include, but are not limited to, basic or neutral barium petronate, calcium petronate, Co-, Ca-, Cu-, Mn-, Ni-, Zn-, and Fe- salts of naphthenic acid, Ba-, A1-, Zn-, Cu-, Pb-, and Fe- salts of stearic acid, divalent and trivalent metal carboxylates, such as aluminum tristearate, aluminum octoate, lithium heptanoate, iron stearate, iron distearate, barium stearate, chromium stearate, magnesium octoate, calcium stearate, iron naphthenate, and zinc naphthenate, Mn- and Zn- heptanoate, and Ba-, A1-, Co-, Mn-, and Zn- Octoate.
  • Useful block or comb copolymers include, but are not limited to, AB diblock copolymers of (A) polymers of 2-(N,N) dimethylaminoethyl methacrylate quaternized with methyl-p-toluenesulfonate and (B) poly-2-ethylhexyl methacrylate, and comb graft copolymers with oil soluble tails of poly (12-hydroxystearic acid) and having a molecular weight of about 1800, pendant on an oil-soluble anchor group of poly (methyl methacrylate-methacrylic acid).
  • Useful organic amides include, but are not limited to, polyisobutylene succinimides such as OLOA 1200, and N-vinyl pyrrolidone polymers.
  • Useful organic zwitterions include, but are not limited to, lecithin.
  • Useful organic phosphates and phosphonates include, but are not limited to, the sodium salts of phosphated mono- and di-glycerides with saturated and unsaturated acid substituents.
  • Particle dispersion stabilizers may be added to prevent particle flocculation or attachment to the capsule walls.
  • nonaqueous surfactants include, but are not limited to, glycol ethers, acetylenic glycols, alkanolamides, sorbitol derivatives, alkyl amines, quaternary amines, imidazolines, dialkyl oxides, and sulfosuccinates.
  • Encapsulation of the internal phase may be accomplished in a number of different ways. Numerous suitable procedures for microencapsulation are detailed in both Microencapsulation, Processes and Applications, (I. E. Vandegaer, ed.), Plenum Press, New York, NY (1974) and Gutcho, Microcapsules and Microencapsulation Techniques, Nuyes Data Corp., Park Ridge, NJ. (1976). The processes fall into several general categories, all of which can be applied to the present invention: interfacial polymerization, in situ polymerization, physical processes, such as coextrusion and other phase separation processes, in-liquid curing, and simple/complex coacervation.
  • Useful materials for simple coacervation processes to form the capsule include, but are not limited to, gelatin, polyvinyl alcohol, polyvinyl acetate, and cellulosic derivatives, such as, for example, carboxymethylcellulose.
  • Useful materials for complex coacervation processes include, but are not limited to, gelatin, acacia, carageenan, carboxymethylcellulose, hydrolyzed styrene anhydride copolymers, agar, alginate, casein, albumin, methyl vinyl ether co-maleic anhydride, and cellulose phthalate.
  • Useful materials for phase separation processes include, but are not limited to, polystyrene, PMMA, polyethyl methacrylate, polybutyl methacrylate, ethyl cellulose, polyvinyl pyridine, and poly acrylonitrile.
  • Useful materials for in situ polymerization processes include, but are not limited to, polyhydroxyamides, with aldehydes, melamine, or urea and formaldehyde; water-soluble oligomers of the condensate of melamine, or urea and formaldehyde; and vinyl monomers, such as, for example, styrene, MMA and acrylonitrile.
  • useful materials for interfacial polymerization processes include, but are not limited to, diacyl chlorides, such as, for example, sebacoyl, adipoyl, and di- or poly- amines or alcohols, and isocyanates.
  • Useful emulsion polymerization materials may include, but are not limited to, styrene, vinyl acetate, acrylic acid, butyl acrylate, t-butyl acrylate, methyl methacrylate, and butyl methacrylate.
  • Capsules produced may be dispersed into a curable carrier, resulting in an ink which may be printed or coated on large and arbitrarily shaped or curved surfaces using conventional printing and coating techniques.
  • capsule properties include the distribution of capsule radii; electrical, mechanical, diffusion, and optical properties of the capsule wall; and chemical compatibility with the internal phase of the capsule.
  • the capsule wall generally has a high electrical resistivity. Although it is possible to use walls with relatively low resistivities, this may limit performance in requiring relatively higher addressing voltages.
  • the capsule wall should also be mechanically strong (although if the finished capsule powder is to be dispersed in a curable polymeric binder for coating, mechanical strength is not as critical).
  • the capsule wall should generally not be porous. If, however, it is desired to use an encapsulation procedure that produces porous capsules, these can be overcoated in a post-processing step (i.e., a second encapsulation). Moreover, if the capsules are to be dispersed in a curable binder, the binder will serve to close the pores.
  • the capsule walls should be optically clear.
  • the wall material may, however, be chosen to match the refractive index of the internal phase of the capsule (i.e., the suspending fluid) or a binder in which the capsules are to be dispersed. For some applications (e.g., interposition between two fixed electrodes), monodispersed capsule radii are desirable.
  • An encapsulation technique that is suited to the present invention involves a polymerization between urea and formaldehyde in an aqueous phase of an oil/water emulsion in the presence of a negatively charged, carboxyl-substituted, linear hydrocarbon polyelectrolyte material.
  • the resulting capsule wall is a urea/formaldehyde copolymer, which discretely encloses the internal phase.
  • the capsule is clear, mechanically strong, and has good resistivity properties.
  • the related technique of in situ polymerization utilizes an oil/water emulsion, which is formed by dispersing the electrophoretic composition (/. e. , the dielectric liquid containing a suspension of the pigment particles) in an aqueous environment.
  • the monomers polymerize to form a polymer with higher affinity for the internal phase than for the aqueous phase, thus condensing around the emulsified oily droplets.
  • urea and formaldehyde condense in the presence of poly(acrylic acid) (See, e.g., U.S. Patent No.
  • any of a variety of cross- linking agents borne in aqueous solution is deposited around microscopic oil droplets.
  • Such cross-linking agents include aldehydes, especially formaldehyde, glyoxal, or glutaraldehyde; alum; zirconium salts; and poly isocyanates.
  • the coacervation approach also utilizes an oil/water emulsion.
  • One or more colloids are coacervated (i.e., agglomerated) out of the aqueous phase and deposited as shells around the oily droplets through control of temperature, pH and/or relative concentrations, thereby creating the microcapsule.
  • Materials suitable for coacervation include gelatins and gum arabic. See, e.g., U.S. Patent No. 2,800,457.
  • the interfacial polymerization approach relies on the presence of an oil-soluble monomer in the electrophoretic composition, which once again is present as an emulsion in an aqueous phase.
  • the monomers in the minute hydrophobic droplets react with a monomer introduced into the aqueous phase, polymerizing at the interface between the droplets and the surrounding aqueous medium and forming shells around the droplets.
  • the resulting walls are relatively thin and may be permeable, this process does not require the elevated temperatures characteristic of some other processes, and therefore affords greater flexibility in terms of choosing the dielectric liquid.
  • FIG. 7A illustrates an exemplary apparatus and environment for performing emulsion- based encapsulation.
  • An oil/water emulsion is prepared in a vessel 76 equipped with a device
  • the aqueous continuous phase 88 may contain, for example, a prepolymer and various system modifiers.
  • FIG. 7B illustrates an oil drop 90 comprising a substantially transparent suspending fluid
  • the liquid phase may also contain some threshold/bistability modifiers, charge control agents, and/or hydrophobic monomers to effect an interfacial polymerization.
  • FIG. 7C illustrates a similar oil drop 98 comprising a darkly dyed suspending fluid 100 containing a dispersion of white particles 94 and appropriate charge control agents.
  • Coating aids can be used to improve the uniformity and quality of the coated or printed electrophoretic ink material.
  • Wetting agents are typically added to adjust the interfacial tension at the coating/substrate interface and to adjust the liquid/air surface tension.
  • Wetting agents include, but are not limited to, anionic and cationic surfactants, and nonionic species, such as silicone or fluoropolymer based materials.
  • Dispersing agents may be used to modify the interfacial tension between the capsules and binder, providing control over flocculation and particle settling.
  • Surface tension modifiers can be added to adjust the air/ink interfacial tension.
  • Polysiloxanes are typically used in such an application to improve surface leveling while minimizing other defects within the coating.
  • Surface tension modifiers include, but are not limited to, fluorinated surfactants, such as, for example, the Zonyl ® series from DuPont (Wilmington, DE), the Fluorod ® series from 3M (St. Paul, MN), and the fluoroakyl series from Autochem (Glen Rock, NJ); siloxanes, such as, for example, Silwet ® from Union Carbide (Danbury, CT); and polyethoxy and polypropoxy alcohols.
  • fluorinated surfactants such as, for example, the Zonyl ® series from DuPont (Wilmington, DE), the Fluorod ® series from 3M (St. Paul, MN), and the fluoroakyl series from Autochem (Glen Rock, NJ
  • siloxanes such as, for example, Silwet ® from Union Carbide (Danbury,
  • Antifoams such as silicone and silicone-free polymeric materials, may be added to enhance the movement of air from within the ink to the surface and to facilitate the rupture of bubbles at the coating surface.
  • Other useful antifoams include, but are not limited to, glyceryl esters, polyhydric alcohols, compounded antifoams, such as oil solutions of alkyl benzenes, natural fats, fatty acids, and metallic soaps, and silicone antifoaming agents made from the combination of dimethyl siloxane polymers and silica.
  • Stabilizers such as uv-absorbers and antioxidants may also be added to improve the lifetime of the ink.
  • acacia (Aldrich) is dissolved in 100.0 g of water with stirring at room temperature for 30 minutes. The resulting mixture is decanted into two 50 mL polypropylene centrifuge tubes and centrifuged at about 2000 rpm for 10 minutes to remove insoluble material. 66 g of the purified solution is then decanted into a 500 mL non-baffled jacketed reactor, and the
  • the oil phase prepared as described above, is slowly poured over about 15 seconds into the aqueous phase, also prepared as described above.
  • the resulting oil/water emulsion is allowed to emulsify for 20 minutes.
  • To this emulsion is slowly added over about 20 seconds 200 g of water that has been preheated to 40°C.
  • the pH is then reduced to 4.4 over five minutes with a 10% acetic acid solution (acetic acid from Aldrich).
  • the pH is monitored using a pH meter that was previously calibrated with pH 7.0 and pH 4.0 buffer
  • thermostat bath is then set to 40°C and allowed to stir for another 70 minutes.
  • the slurry is
  • the resulting capsule slurry from above is mixed with the aqueous urethane binder
  • NeoRez R-9320 (Zeneca Resins, Wilmington, MA) at a ratio of one part binder to 10 parts capsules.
  • the resulting mixture is then coated using a doctor blade onto about a 100 ⁇ m to about a 125 ⁇ m thick sheet of indium-tin oxide sputtered polyester film.
  • the blade gap of the doctor blade is controlled at 0.18 mm so as to lay down a single layer of capsules.
  • the coated film is
  • the dried film is hot laminated at 60°C to a backplane comprising about a 100 ⁇ m to about a 125 ⁇ m thick sheet of polyester screen printed with thick film silver and dielectric inks with a pressure of 15 psi in a hot roll laminate from Cheminstruments, Fairfield, OH.
  • the backplane is connected to the film using an anisotropic tape.
  • the conductive areas form addressable areas of the resulting display.
  • the resulting capsule slurry from above is mixed with the aqueous binder comprising a mixture of NeoRez R-966 (Zeneca Resins) and a 20% solution of Airvol 203 (a polyvinyl alcohol, Airvol Industries, AUentown, PA) at a ratio of one part Airvol 203 solution to one part NeoRez R-966 to five parts capsules.
  • the resulting mixture is then coated using a doctor blade onto about a 100 ⁇ m to about 125 ⁇ m thick sheet of indium-tin oxide sputtered polyester film.
  • the blade gap of the doctor blade is controlled to 0.18 mm so as to lay down an single layer of
  • the coated film is then dried in hot air (60°C) for 30 minutes. After drying, a thick film silver ink is then printed directly onto the back of the dried film and allowed to cure at
  • the conductive areas form the addressable areas of the display.
  • the binder typically is used as an adhesive medium that supports and protects the capsules, as well as binds the electrode materials to the capsule dispersion.
  • a binder can be non- conducting, semiconductive, or conductive. Binders are available in many forms and chemical types. Among these are water-soluble polymers, water-borne polymers, oil-soluble polymers, thermoset and thermoplastic polymers, and radiation-cured polymers.
  • water-soluble polymers are the various polysaccharides, the polyvinyl alcohols, N-methyl Pyrollidone, N-vinyl pyrollidone, the various Carbowax ® species (Union Carbide, Danbury, CT), and poly-2-hydroxyethylacrylate.
  • the water-dispersed or water-borne systems are generally latex compositions, typified by the Neorez ® and Neocryl ® resins (Zeneca Resins, Wilmington, MA), Acrysol ® (Rohm and Haas, Philadelphia, PA), Bayhydrol ® (Bayer, Pittsburgh, PA), and the Cytec Industries (West Paterson, NJ) HP line.
  • Neorez ® and Neocryl ® resins Zeneca Resins, Wilmington, MA
  • Acrysol ® Rohm and Haas, Philadelphia, PA
  • Bayhydrol ® Bayhydrol ®
  • Cytec Industries West Paterson, NJ
  • a typical application of a water-borne resin and aqueous capsules follows. A volume of particles is centrifuged at low speed to separate excess water. After a given centrifugation process, for example 10 minutes at 60 x gravity ("G"), the capsules 180 are found at the bottom of the centrifuge tube 182, while the water portion 184 is at the top, as shown in FIG. 8. The water portion is carefully removed (by decanting or pipetting). The mass of the remaining capsules is measured, and a mass of resin is added such that the mass of resin is, for example, between one eighth and one tenth of the weight of the capsules. This mixture is gently mixed on an oscillating mixer for approximately one half hour. After about one half hour, the mixture is ready to be coated onto the appropriate substrate.
  • G x gravity
  • the fhermoset systems are exemplified by the family of epoxies. These binary systems can vary greatly in viscosity, and the reactivity of the pair determines the "pot life" of the mixture. If the pot life is long enough to allow a coating operation, capsules may be coated in an ordered arrangement in a coating process prior to the resin curing and hardening.
  • Thermoplastic polymers which are often polyesters, are molten at high temperatures.
  • a typical application of this type of product is hot-melt glue.
  • a dispersion of heat-resistant capsules could be coated in such a medium. The solidification process begins during cooling, and the final hardness, clarity and flexibility are affected by the branching and molecular weight of the polymer.
  • Oil or solvent-soluble polymers are often similar in composition to the water-borne system, with the obvious exception of the water itself.
  • the latitude in formulation for solvent systems is enormous, limited only by solvent choices and polymer solubility.
  • Of considerable concern in solvent-based systems is the viability of the capsule itself - the integrity of the capsule wall cannot be compromised in any way by the solvent.
  • Radiation cure resins are generally found among the solvent-based systems. Capsules may be dispersed in such a medium and coated, and the resin may then be cured by a timed exposure to a threshold level of ultraviolet radiation, either long or short wavelength. As in all cases of curing polymer resins, final properties are determined by the branching and molecular weights of the monomers, oligomers and crosslinkers.
  • water-reducible monomers and oligomers are, however, marketed. In the strictest sense, they are not water soluble, but water is an acceptable diluent at low concentrations and can be dispersed relatively easily in the mixture. Under these circumstances, water is used to reduce the viscosity (initially from thousands to hundreds of thousands centipoise).
  • Water-based capsules such as those made from a protein or polysaccharide material, for example, could be dispersed in such a medium and coated, provided the viscosity could be sufficiently lowered. Curing in such systems is generally by ultraviolet radiation.
  • encapsulated electrophoretic displays include a dispersion of capsules in a polymeric binder.
  • the dispersion can include capsules in a carrier (rather than binder) or capsules without a binder or carrier.
  • the capsules contain an electrophoretically active suspension.
  • the capsule dispersion (or "slurry") typically is coated onto a flexible polymeric substrate that may be associated with a front electrode at some point in time, achieving a monolayer of capsules.
  • a binder with certain properties and/or altering a binder's physical characteristics with, for example, a change in pH or addition of a surfactant can be useful in depositing a monolayer of capsules.
  • This resulting film is then laminated to a rear substrate.
  • the rear substrate can be patterned in a single or multilayer electrode structure which may be printed or formed by other means on a polymeric (that can be flexible), a glass, and/or a metal substrate. While the invention is described in the context of a microencapsulated electrophoretic display, it can be relevant in the practice of any electronic display where the linking of a electrode (/. e. , a front surface that applies voltage to the display) to a rear electrode substrate is desired.
  • the capsule slurry is typically dewatered to achieve a target solids content.
  • Dewatering as described above, can be achieved through centrifugation, absorption, evaporation, mesh filtration, or osmotic separation.
  • This slurry is then mixed with a binder, for example, a polymer latex (such as an aqueous polyurethane dispersion), and agitated to ensure uniform distribution of the binder material.
  • a binder can have various fractions.
  • a certain portion of the binder can be a solid (“binder solid"), and a certain portion of the binder can be a liquid, such as water, that is capable of evaporating.
  • binder solid can include one or more types of solid in a particular binder (i. e. , the portion of solid(s) in the binder relative to other fractions in the binder).
  • the binder typically is an aqueous dispersion of latex particles.
  • the solid(s) can become integral with the film.
  • the ratio of binder solid mass to capsule mass should be kept as low as possible. Minimizing the amount of non- optically active material (such as binder) allows for good packing and results in good contrast between the white and dark state of a display. See, e.g., FIGS. 1A and IB.
  • the binder is in the film to provide structural integrity, creating a tension between desiring to reduce the amount of binder (for optical properties) and desiring to increase the amount to binder (for structural reasons).
  • a useful ratio of binder solid mass to capsule mass is in the range of about 1 :2 to about 1 :20, and preferably between about 1 :4 and about 1 : 12, and most preferably between about 1 :6 and about 1 :10.
  • the slurry of capsules in aqueous binder is coated on a substrate as a monolayer as described below.
  • the slurry is coated onto a polyester substrate with indium tin oxide ("ITO") disposed on the substrate, which will ultimately serve as the front transparent electrode and substrate.
  • ITO indium tin oxide
  • the substrate can be about 25 ⁇ m to about 500 ⁇ m thick.
  • This film typically is dried at about 60°C, evaporating the aqueous phase.
  • a slurry of capsules in aqueous binder, previously prepared, is coated in a monolayer.
  • the coating process involves metering the capsule/binder slurry through a slot die coating head.
  • a head 20 attached to a pump 21 meters a constant amount of capsule/binder slurry 22 through a tightly controlled gap 24.
  • the gap 24 allows only a single layer of capsules 26 to pass through and out of the head 20.
  • the flow rate of the slurry can be set such that, as the head 20 moves past the receiving substrate 28 that is placed on a roller 29, a continuous monolayer 25 is formed. The substrate 28 and the head 20 are moved relative to each other.
  • the substrate is moved either linearly (not shown) or on a roll 29 (FIG. 2).
  • the direction of movement of the roll 29 and the substrate 28 is shown as an arrow ⁇ .
  • the head 20 can be moved, typically linearly (FIG. 3).
  • the direction of movement is shown as an arrow ⁇ . It may be a continuous or a batch process.
  • the capsule/binder slurry typically is deposited at a rate of about 0.1 m/min to about 100 m/min, preferably at a rate of about 0.2 m/min to about 0.7 m min.
  • the fluid flow can be actively controlled, for example, to start and stop coating an area.
  • the pump 21 used to provide the metering flow can be a low shear pump, for example a peristaltic pump. A low shear pump can prevent capsule breakage during coating.
  • the slurry of capsules can be deposited in a monolayer by controlling the gap width to mean sphere diameter ratio.
  • the gap/mean sphere diameter ratio is the ratio of the width of the gap through which slurry moves to the mean of capsule diameters moving through the gap. This ratio can be based on the deformability and surface properties of the spheres as well as the flow properties of the coating fluid, but in one embodiment is between about 1 and about 2.5, and preferably between about 1.2 and about 1.6.
  • capsules are generally spherical during coating, they can vary slightly due to deformation during processing such that their diameter varies slightly at any given time. Thus, calculations based on the size of a capsule may vary slightly at any given time.
  • An equation that generally relates pump rate to coating width, relative die speed, and coating thickness is as follows.
  • the Coating Wet Thickness tends to deviate from a particular value in a monolayer formed with large, easily deformable particles because any deformation can change the thickness slightly.
  • a film that is slightly thicker than or slightly thinner than the diameter of one capsule may be desirable based on the capsule/binder ratio, how the capsules actually deform into a film, and/or the presence of any interstitial void, and the like. For example, the more compliant and/or resilient a capsule is, the thinner the film can be. The less compliant and/or resilient a capsule is, the thicker the film can be.
  • a film thickness is determined (e.g., empirically)
  • a change in Die Speed or Coat Width will relate directly to the equation above.
  • an air knife coater forms an encapsulated electrophoretic display having a monolayer of capsules.
  • Air knife coating has been used in a variety of coating applications, including carbonless paper and electroluminescence coatings, which both contain encapsulated materials. The use of an air knife in these applications is, however, used for thickness control, and is not used for forming a stable, durable monolayer of capsules.
  • a capsule slurry is applied to a substrate, which is either moving or still, by applying pressure so that the capsules in the slurry form a monolayer on the substrate.
  • a substrate can be a conductive material such as ITO sputtered polyester.
  • the pressure is applied to the mixture with a pressurized gas, typically air.
  • An air knife can be used to apply the pressure so as to uniformly distribute the slurry. Referring to FIG. 4, an air knife 30
  • the air knife 30 is held at an angle of from about 0° to about 90° (e.g. , shown in
  • FIG. 4 are three positions of the air knife 30a, 30b, 30c, although many more positions are possible) from the surface of the slurry 35.
  • a pressure source 34 provides pressure to the air knife 30. If conditions, such as gas pressure, distance from slurry, angle relative to the slurry, slurry viscosity, and relative speed between the air knife and the substrate on which the slurry is deposited are optimized, a monolayer can be formed. For example, the air knife can remove excess slurry as well as create a monolayer of capsules. When an air knife is used in conjunction with controlled amounts of capsule slurry, waste of the slurry can be limited. Also, because the air knife does not touch the slurry, the probability of scratching the substrate or breaking the capsules is reduced.
  • the gas being blown over the coating material can be other than air at ambient temperature.
  • the gas may be heated or cooled, changing the coatability and viscosity properties of the capsule slurry.
  • the gas may be blown on wet (e.g., a liquid in droplets) or dry, controlling evaporation of solvents in the capsule slurry. Temperature or addition of liquids can be controlled, for example, with a heater, refrigeration unit, liquid pump, and/or other devices known to those skilled in the art, as represented by a controller 33 in FIG. 4.
  • the gas may be mixed with solvents that help cure the capsule slurry and/or make the slurry easier to coat onto the substrate.
  • the solvent is chosen to be compatible with the substrate layer.
  • the solvent can be water or an alcohol.
  • Useful alcohols include isopropyl alcohol, methanol, and ethanol.
  • a compatible organic solvent can be mixed with the gas.
  • a butyl acetate substrate is coated with "acetate humidified" air.
  • Other useful organic solvents for use in methods of the invention include methylene chloride and chlorobenzene.
  • the suspending fluid inside the capsule is a halogenated hydrocarbon, such as tetrachloroethylene or poly(chlorotrifluoroethylene).
  • the evaporative binder in certain embodiments can be, for example, a polymer latex, an acrylic, urethane, poly(vinyl alcohol), or water-based binder. 3. Coating With Substantially No Binder
  • a capsule 50 has a capsule wall 52 that is constructed from a polymer.
  • the capsule can be formed from gelatin acacia, as described above.
  • the capsule wall 52 is heavily swelled with water and/or a polar solvent.
  • about 1% to about 90%, preferably about 5% to about 20%, of the capsule wall 52 can be formed from the polymer while about 10% to about 99%, preferably about 80% to about 95% can be formed from the water and/or polar solvent.
  • These capsules 50 are coated onto a substrate 54, as described above for the slurry.
  • the capsules 52 can be suspended in a carrier such as water or not suspended in any carrier.
  • a carrier such as water or not suspended in any carrier.
  • the water and/or polar solvent evaporates from the capsule walls 52 of the capsules 50 in the coated monolayer.
  • the capsule walls 52 intermingle with, associate with, and/or adhere to each other and/or the substrate 54.
  • a film is formed. Without a binder in the film, capsules can deform to a greater degree than with binder in the film, in some situations.
  • a capsule slurry is coated onto a front electrode on a flexible or rigid substrate (e.g., a polymeric material or glass), achieving a monolayer of microcapsules, this coated film is then laminated to a rear substrate (alternatively know as a "backplane").
  • the rear substrate can be, for example, a polymeric material (that can be flexible), glass, or metal.
  • the rear substrate can be patterned in a single or multi-layer electrode structure which may be printed or formed by other means on a second flexible polymeric substrate. While the present invention is described in the context of an encapsulated display, it can be relevant in the practice of any electronic display for linking a front active surface to a rear electrode substrate (either with or without additional layers between the front surface and rear substrate).
  • temperatures from about 40°C to about 150°C and more
  • a typical rear substrate is constructed from a base substrate either with or without an electrode layered on the base substrate.
  • a rear substrate is a polyester or polyimide base film and a set of patterned electrodes.
  • these electrodes are a single- or multi-layer conductor/insulator stack that can printed on the substrate.
  • the substrates can be a polymeric material (which can be flexible), glass, or a metal.
  • the conductors are conductive particles (e.g., carbon, silver, palladium, tin oxide, doped tin oxide, copper), doped polyesters, and vinyls which are screen printed and heat cured.
  • a rear substrate can have transistors (organic and/or silicon-based), diodes, and/or electrodes disposed on the substrate.
  • the film can be combined with the rear substrate in a variety of ways. Typically, the film
  • the binder 40 after being coated as a monolayer, contains voids and irregularities in the binder 44 between the capsules 42, irregular surfaces on the capsules 42, and/or irregular surfaces at the edge of the binder 44, as shown in FIG. 5 A.
  • the binder level in the slurry is kept as low as possible to maximize optically active area, leaving little binder to flow and absorb the stresses of lamination.
  • the capsule wall bears the majority of these stresses, which can result in capsule breakage.
  • the laminated product may have trapped air, or trapped vacuum packets, which can both change the mechanical stresses experienced by the film and affect the electrical characteristics (which may result in non-uniform switching).
  • an additional layer of material can be included between the film and the rear substrate to address the problem above.
  • This layer of material can be an adhesive which can flow at the lamination temperature.
  • the layer also may be tacky.
  • it may be a polymeric material identical or similar to that of the binder material coated onto the front substrate previously, or it may be a hotmelt adhesive sheet, which could be thermoplastic or thermoset.
  • it may be a material which is initially in liquid form at room temperature but forms a solid matrix after curing or crosslinking.
  • the additional layer of material 46 has filled the interstices (including, but without limitation, the voids between the capsules 42, the irregular surfaces of the binder 44 and the irregular surfaces of capsules 42 ) and adheres to a rear substrate 48.
  • the additional layer of material 46 can be initially coated onto the film 40 (i.e., the rear of the capsules) or onto the rear substrate 48, before the lamination procedure, or the layer 46 can be a hotmelt adhesive sheet (which can be thermoplastic or thermoset) introduced between the film and rear substrate during the lamination procedure.
  • this layer and/or the capsules and/or the substrate forms a uniformly thick stratum.
  • the stratum can be between about 10 ⁇ m thick and about 500 ⁇ m thick, preferably about 50 ⁇ m thick to about 300 ⁇ m thick.
  • certain capsules can be used without a binder, as described above. In that case, and referring to FIG. 9B, a final structure can be formed in which the interstices and irregular surfaces of capsules 50 on a substrate 54 are filled with a layer of material 56 that is adjacent a rear substrate 58.
  • the layer of material is initially coated on to the front film, it can substantially planarize the capsule film facing the rear substrate and/or provide a tacky surface to enable lamination to the rear substrate.
  • the capsule film is planar prior to lamination, and tacky front and rear substrates do not need to be stored separately, because only the front substrate is tacky.
  • a front film need not have a rear substrate.
  • a film that has been planarized with the layer of material can be operated with a stylus. This can occur with or without a rear substrate, and the layer of material need not be tacky if no rear substrate is used.
  • a semiconducting or anisotropically conducting adhesive can be used as the additional layer. This material will conduct an electric field from the backplane to the capsules with little loss of field strength.
  • An adhesive containing carbon particles, gold particles, aluminum particles, platinum particles, silver particles, plated polymer spheres, plated glass spheres, or ITO particles may be used.
  • conductive polymers such as polyacetylene, polyaniline, polypyrrole, P-DOT, or polythiophene can be used to dope the additional layer of material, causing it to conduct well in the Z-axis but not in the plane of the adhesive.
  • the adhesive sheet can be cast and then stretched in one or both axes.
  • the resistivity of the layer of material can be about 10 5 to about 10 15 ohm-cm, more preferably about 10 8 to about 10 13 ohm-cm.
  • an insulating layer of material can be used.

Abstract

La présente invention concerne un affichage par électrophorèse encapsulé, présentant une pluralité de capsules non sphériques disposées sensiblement sur une seule couche d'un substrat.
EP99950233A 1998-10-07 1999-10-06 Affichages par electrophorese encapsules pourvus d'une monocouche de capsules Ceased EP1118038A1 (fr)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
US10339898P 1998-10-07 1998-10-07
US103398P 1998-10-07
US11879499P 1999-02-04 1999-02-04
US118794P 1999-02-04
PCT/US1999/023313 WO2000020922A1 (fr) 1998-10-07 1999-10-06 Affichages par electrophorese encapsules pourvus d'une monocouche de capsules

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EP1118038A1 true EP1118038A1 (fr) 2001-07-25

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EP99950233A Ceased EP1118038A1 (fr) 1998-10-07 1999-10-06 Affichages par electrophorese encapsules pourvus d'une monocouche de capsules

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EP (1) EP1118038A1 (fr)
JP (2) JP5097316B2 (fr)
KR (1) KR100717556B1 (fr)
AU (1) AU6293699A (fr)
CA (1) CA2345619C (fr)
WO (1) WO2000020922A1 (fr)

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JP2002526812A (ja) 2002-08-20
KR20010085899A (ko) 2001-09-07
WO2000020922A1 (fr) 2000-04-13
CA2345619A1 (fr) 2000-04-13
CA2345619C (fr) 2008-04-08
JP5097316B2 (ja) 2012-12-12
KR100717556B1 (ko) 2007-05-15
AU6293699A (en) 2000-04-26
JP2011002844A (ja) 2011-01-06

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