Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-08-27
2001-07-17
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S085000, C349S086000, C359S296000, C204S606000
Reexamination Certificate
active
06262706
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electrophoretic displays, particularly encapsulated electrophoretic displays, and to materials useful in fabricating such displays.
BACKGROUND OF THE INVENTION
Electrophoretic displays have been the subject of intense research and development for a number of years. Electrophoretic displays have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption when compared with liquid crystal displays. Nevertheless, problems with the long-term image quality of these displays has, to date, prevented their widespread usage.
The recent invention of encapsulated electrophoretic displays solves many of these problems and offers additional advantages compared to liquid crystal displays. Some added advantages are the ability to print or coat the display material on a wide variety of flexible and rigid substrates. The clustering and settling problems, which plagued prior art electrophoretic displays and resulted in inadequate lifetimes for the displays are now overcome.
The purpose of this disclosure is to describe electrophoretic displays, especially encapsulated electrophoretic displays, and classes of materials, as well as some specific materials, which should be useful in their construction.
SUMMARY OF THE INVENTION
The successful construction of an encapsulated electrophoretic display requires the proper interaction of several different types of materials and processes. Materials such as a polymeric binder, a capsule membrane, and the 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.
In some cases, a separate encapsulation step of the process is not necessary. 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”. In such displays, 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.
In an encapsulated electrophoretic display, the binder material surrounds the capsules and separates the two bounding electrodes. This binder material must be compatible with the capsule and bounding electrodes and must 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.
The present invention provides electrophoretic displays, particularly encapsulated electrophoretic displays, and materials for use in such displays. The capsules may be spherical or non-spherical in shape. In electrophoretic displays, at least some of the particles are moved or rotated by application of electric fields. The electric field may be an alternating-current field or a direct-current field. The electric field may be created by at least one pair of electrodes disposed adjacent a binder material containing the particles. The particles may be absorbing pigments, scattering pigments or luminescent particles, for example. The particles may be made up of some combination of dye, pigment, polymer.
Such displays may also include, for example, one type of particle that retroreflects, or substantially retroreflects, light and another type that absorbs light. Application of an electric field may cause the particles in an encapsulated display to orient so that the capsule retroreflects, or substantially retroreflects, light. Application of another electric field may cause the particles to orient so that the capsule absorbs, or does not retroreflect, light. A display may also include a reflective substrate, so that orientation of one type of particle in a particular pattern causes light to pass through the capsule to the substrate, which reflects light. Orientation of a second type of particle in a particular pattern causes the capsule to absorb, or otherwise not reflect, light. Types of retroreflective and reflective materials that may be used in constructing a retroreflective or reflective substrates, respectively, include glass spheres and diffractive reflecting layers.
Another type of display has particles of differing colors. Such a display has at least two, and preferably at least, three different species of particles, with each type of particle having a different electrophoretic mobility. The different electrophoretic mobilities provide the particles with substantially non-overlapping electrophoretic mobilities, so that application of different electric fields causes different subsets of the colored particles to be viewed at the surface of the capsule.
Another type of display includes luminescent particles and a visible light-blocking medium, which may contain light-absorbing particles or dyes. Application of different electric fields may cause the particles to luminesce selectively or uniformly at the front (eyes see a bright pixel) or rear (fluid absorbs radiation) of the capsule. Application of different electric fields may cause either the luminescent particles or the light-blocking particles to rise to the capsule surface, resulting in either a light or a dark appearance to the capsule, respectively.
In another type of electrophoretic display, the particles may themselves be encapsulated pigments, dyes, pigment dispersions, dye solutions, or a combination of any of these. These particles are dispersed in a suspending fluid and are then encapsulated into capsules in a binder. The particles may be dispersed within a suspending fluid and may each contain a plurality of solid particles or a dye or both. The suspending fluid can be a single fluid or a mixture of two or more fluids. In one embodiment, the particles may have a diameter from between about 10 nm and about 5 &mgr;m, whereas the capsules may have a diameter from between about 5 &mgr;m and about 200 &mgr;m. In another embodiment, the particles may have a flexible outer surface or may be a polymeric layer surrounding a dye or dye solution.
The advantage of this system is that known emulsification or encapsulation techniques can be used to make improved particles, with better control of absorbance, optical properties, charge, mobility, shape, size, density, surface chemistry, stability, and processibility. There are vast numbers of dyes and/or particles and liquids of all polarities that can be used to gain a high level of control over the optical properties of the system. It is possible to create particles which are capsules containing dyes and/or particles in order to obtain properties difficult to achieve with pigments. The present invention relates to these encapsulated electrophoretic displays and the materials, such as dyes, pigments, binder, etc. that may be useful in their construction.
Encapsulated electrophoretic displays may include two or more different types of particles. Such displays may include, for example, displays containing a plurality of anisotropic particles and a plurality of second particles in a suspending fluid. Application of a first electric field may cause the anisotropic particles to assume a specific orientation and present an optical property. Application of a second electric field may then cause the plurality of second particles to translate, thereby disorienting the anisotropic particles and disturbing the optical property. Alternatively, the orientation of the anisotropic particles may allow easier translation of the plurality of second particles. The particles may have a refractive index that substantia
Albert Jonathan D.
Comiskey Barrett
Drzaic Paul
Feeney Robert
Jacobson Joseph M.
E Ink Corporation
Lewis David L.
Shalwala Bipin
Testa Hurwitz & Thibeault LLP
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