Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-10-06
2001-07-17
Ben, Loha (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C204S606000, C204S450000, C345S107000, C264S004000
Reexamination Certificate
active
06262833
ABSTRACT:
TECHNICAL FIELD
The present invention relates to electrophoretic elements, particularly encapsulated electrophoretic elements, and to methods and materials useful in fabricating such elements.
BACKGROUND
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 have, 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. Particle clustering and settling problems are reduced and service-life is increased.
The purpose of this disclosure is to describe electrophoretic elements and displays, especially encapsulated electrophoretic elements and displays, and classes of materials, as well as some specific materials, which are useful in their construction.
SUMMARY OF THE INVENTION
The present invention relates to capsules containing substantially immiscible liquids as the internal phase and methods for producing such capsules. Such capsules can be used, for example, in the fabrication of reflective, electrophoretic display devices. Throughout the Specification, the invention is described as a display for ease of description. However, the compositions and processes disclosed herein are equally applicable to “elements.” 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.
An electrophoretic display (EPID) can be formed by placing a capsule containing a dyed fluid and pigment particles between a pair of electrodes. The pigment particles move from one electrode to the other under the influence of an electric field situated between the electrodes. When viewing the device from the transparent (front) electrode, the display has a color of the pigment particles (for example, white titanium dioxide particles) when the polarity of that electrode is opposite to the charge on the particles. This state is referred to as the white state. When the electric field is reversed, the pigment particles migrate to the rear electrode, and the viewer sees only the color of the dyed liquid. This state is referred to as the dark state.
The presence of the dyed fluid in the spaces between the pigment particles degrades the appearance of the white state. For closely-packed, uniformly spherical particles, the space between particles accounts for 25% of the total volume occupied by the spheres, a significant amount. The present invention solves at least one problem associated with this generic type of display. Utilizing immiscible fluids, as more fully described below, allows the white state to be improved compared with the degraded white state of some other displays.
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 may be compatible with the capsule and bounding electrodes and may possess properties that allow for facile printing or coating. It also may 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.
In one aspect, the present invention relates to an encapsulated electrophoretic display element that includes a capsule that contains at least two substantially immiscible fluids. A first fluid includes an additive and a second fluid includes a plurality of particles. This aspect can have any of the following features. The additive can include a dye and/or a second plurality of particles. The dye can be substantially soluble in the first fluid and/or insoluble in the second fluid. At least a portion of the second particles can be substantially non-dispersible in the second fluid, and/or at least a portion of the second particles can have a surface treatment. At least a portion of the particles of the second fluid can be substantially non-dispersible in the first fluid, and/or at least a portion of the plurality of particles can have a surface treatment. The first and second fluids, respectively, can be selected from pairs of fluids including ethanol
-hexadecane, acetone
-hexadecane, low molecular weight silicone polymers/alkanes, low molecular weight fluorinated polymers/alkanes, perfluoroheptane
-dodecane, and perfluoroalkanes/hydrogenated alkanes. The second and first fluids, respectively, can be selected from pairs of fluids including ethanol
-hexadecane, acetone
-hexadecane, low molecular weight silicone polymers/alkanes, low molecular weight fluorinated polymers/alkanes, perfluoroheptane
-dodecane, and perfluoroalkanes/hydrogenated alkanes. The particles of the second fluid and/or the second particles are capable of moving under an electric field. The first fluid is capable of being displaced by the particles of the second fluid, and/or the second fluid is capable of being placed by the second particles. The particles of the second fluid can include at least two different species of particles, the species of particles differing in their size and/or their shape.
Another aspect of the invention relates to a process for creating an encapsulated electrophoretic display. The process includes the steps of forming a first mixture that includes an additive in a first fluid; forming a second mixture that includes a plurality of particles in a second fluid; combining the first mixture and the second mixture into a droplet such that the first and second mixtures are substantially separate; and forming a capsule around the droplet. This aspect of the invention can have any of the features described above including having an additive that includes a dye and/or a second plurality of particles.
Another aspect of the invention relates to an encapsulated electrophoretic display that includes at least one display element described above. Any display element can include any of the features described above, including having an additive that includes a dye and/or a second plurality of particles. The display also can include at least one electrode adjacent the display element.
REFERENCES:
patent: 2766478 (1956-10-01), Raley, Jr. et al.
patent: 2800457 (1957-07-01), Green et al.
patent: 3036388 (1962-05-01), Tate
patent: 3384488 (1968-05-01), Tulagin et al.
patent: 3389194 (1968-06-01), Somerville
patent: 3406363 (1968-10-01), Tate
patent: 3423489 (1969-01-01)
Comiskey Barrett
Loxley Andrew
Ben Loha
E Ink Corporation
Testa Hurwitz & Thibeault LLP
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