Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1998-03-05
2001-05-22
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C345S055000, C345S107000, C428S404000, C428S406000, C428S407000, C428S484100
Reexamination Certificate
active
06235395
ABSTRACT:
RELATED PATENT
Illustrated in U.S. Pat. No. 5,989,629, the disclosure of which is totally incorporated herein by reference, is a process for the preparation of bichromal spheres comprising (I) preparing monochromal spheres by the aggregation and coalescence of an emulsion resin with a first colorant and an inorganic salt; (ii) contacting the resulting monochromal spheres with an oxidizing agent, followed by a polymerization with a vinyl monomer and a free radical initiator; (iii) forming a of the resulting monochromal spheres on a substrate; and (iv) subjecting the resulting monochromal spheres to a vapor thermal deposition with a second colorant dissimilar than the first colorant to thereby coat one hemisphere of each of said monochromal spheres and resulting in bichromal spheres with dissimilar colors.
BACKGROUND OF THE INVENTION
This invention generally relates to displays, and the preparation, or fabrication of a display devices, and more specifically to robust and reflective flexible display devices, and sheets thereof comprised of small spheres encapsulated with a wax, for example, wherein small is for example, from about 2 to about 150 microns in volume average diameter as measured by the Coulter Counter, and more specifically wherein the wax encapsulated sphere is comprised of a bichromal sphere encapsulated within a hydrocarbon wax, and wherein the wax encapsulated spheres are dispersed in an elastomer or plastic membrane with a plastic conductive coating such as indium tin oxide.
The displays are useful in generating images, which can be stored or erased and more specifically the display devices or devices function by rotating a bichromal sphere by an external field to create the image.
PRIOR ART
Electric Paper or twisted ball panel display devices are known and are described, for example, in U.S. Pat. Nos. 4,126,854; 4,143,103; 4,261,653; 4,438,160; 5,389,945, the disclosures of each of which are totally incorporated herein by reference, and wherein the devices are generally comprised of an elastomer, such as a cured polysiloxane, sandwiched between two ITO coated substrates, such as glass or MYLAR®, and wherein the elastomer layer has closely packed cavities containing a bichromal sphere suspended in a dielectric liquid. The image is formed by the application of an electric field, which rotates the bichromal sphere differentiated by the different static properties induced by the pigment contained in the sphere and resulting in contrasting zeta potentials of the two colored hemispheres of the sphere. It is the difference in zeta potentials between the hemispheres of the ball which causes the ball to act like a dipole in the presence of an electrical field, causing the ball to rotate, until its dipole vector lines up with the direction of the electrical field established between opposed electrodes. In addition to the dipole charge distribution found on the bichromal ball in the presence of an electric field, there is also a monopole charge which is the net electrical charge of the entire ball. As a result of the monopole charge, the ball is caused to move in the direction of the electrical field and will rest and be retained against a cavity wall. In order for the ball to rotate easily in the liquid within the cavity, due to the dipole charge, it is moved from contact with the cavity wall. When at rest against the cavity wall, friction and other forces will prevent it from rotating until it has been moved away again, due to the monopole charge. It is this feature which primarily enables long term, that is indefinite image retention in the display device if undisturbed or not handled by force. However, the aforementioned electric paper devices are not believed to be robust and suffer with respect to image retention when handled. More specifically, the image formed on the above prior art displays can deteriorate by touching it, especially if the user has built up a static charge, by rubbing over the image, dropping the display device on a surface or by carrying it. This loss in image retention is caused by the insufficient lack of adhesion of the bichromal sphere onto the elastomer, and wherein the spheres detachment from the cavity surface suspends the bichromal sphere in a low viscosity medium thus allowing the sphere to rotate uncontrollably within the liquid cavity. The robust flexible display device of the present invention, possesses minimum, or substantially no image deterioration when handled by the user. More specifically, the display device of the present invention contains a solid wax encapsulating the bichromal sphere, hence not allowing for the sphere to move or minimizing movement within the cavity.
The fabrication of certain bichromal spheres is known, for example, the above mentioned U.S. Pat. No. 4,143,103, and wherein the sphere is comprised of black polyethylene. with a light reflective material, for example, titanium oxide, sputtered on hemisphere. Also in U.S. Pat. No. 4,438,160, the disclosures of which is totally incorporated herein by reference, a rotary ball is prepared by coating white glass balls of about 50 microns in diameter, with an inorganic coloring layer such as MgF
2
or Sb
2
S
3
by evaporation. In a similar process, there is disclosed in are article entitled “The Gyricon—A twisting Ball Display”, published in the proceedings of the S.I.D., Vol. 18/3 and 4 (1977), a method for fabricating bichromal balls by first heavily loading chromatic glass balls with a white pigment such as titanium oxide, followed by coating from one direction in a vacuum evaporation chamber with a dense layer of nonconductive black material which coats only one hemisphere.
Also in U.S. Pat. No. 4,810,431 by Leidner, there is disclosed a process for generating spherical particles by (a) coextruding a fiber of a semi-circular layer of a polyethylene pigmented white and a black layer of polyethylene containing magnetite, (b) chopping the resultant fiber into fine particles ranging from 10 microns to about 10 millimeters, (c) mixing the particles with clay or anti-agglomeration materials, and (d) heating the mixture with a liquid at about 120° C. to spherodize the particles, followed by cooling to allow for solidification.
There is also disclosed in U.S. Pat. No. 5,262,809, an apparatus for fabricating hemispherical bichromal balls, comprising a separator member having opposing first and second surfaces and an edge region in contact with both surfaces, and delivery means for flowing first and second colored hardenable liquid material over the first and second surfaces, respectively, so that the liquid materials arrive at the edge at substantially the same flow rate and form a reservoir outboard of the edge region. The reservoir comprises side-by-side regions of different colors which do not intermix. Further means is provided for propelling the first and second liquid materials away from the separator member and out of the reservoir into a fluid medium as a plurality of side-by-side bichromal streams whose forward ends become unstable and break up into droplets which form into spherical balls, each of the balls comprising hemispheres of differently colored hardenable liquids. These bichromal balls are from about 5 to 200 microns in diameter.
There is a need for a robust and reflective flexible display device which is reimageable multiple times, such as from about 10 to about 10,000 times and preferably from about 100 to about 10,000 times, which displays high reflectivity, such as from about 15 to about 100 percent or preferably from about 20 to about 50 percent, which displays high contrast ratios such as from about 3 to about 6, and is robust such that the device can be handled like paper without image deterioration or image loss.
SUMMARY OF THE INVENTION
It is a feature of the present invention to provide a method for the preparation of robust and flexible electric papers, gyricon or twisting Ball display devices.
In another feature of the present invention there is provided a process for the fabrication of wax encapsulated bichromal spheres.
In yet another fe
Mikkelsen, Jr. James C.
Sacripante Guerino G.
Le H. Thi
Palazzo E. O.
Xerox Corporation
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