U.S. patent number RE37,085 [Application Number 09/252,852] was granted by the patent office on 2001-03-06 for some uses of microencapsulation for electric paper.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Nicholas K. Sheridon.
United States Patent |
RE37,085 |
Sheridon |
March 6, 2001 |
Some uses of microencapsulation for electric paper
Abstract
Bichromal balls have two hemispheres, typically one black and
one white, each having different electrical properties. Each ball
is enclosed within a spherical shell and then a space between the
ball and shell is filled with a liquid to form a microsphere so
that the ball is free to rotate in response to an electrical field.
The microspheres can then be mixed into a substrate which can be
formed into sheets or can be applied to any kind of surface. The
result is a film which can form an image from an applied electrical
field.
Inventors: |
Sheridon; Nicholas K. (Los
Altos, CA) |
Assignee: |
Xerox Corporation (Stamford,
CT)
|
Family
ID: |
23449931 |
Appl.
No.: |
09/252,852 |
Filed: |
February 17, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
368120 |
Jan 3, 1995 |
05604027 |
Feb 18, 1997 |
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Current U.S.
Class: |
428/323; 264/4;
264/7; 428/320.2; 428/402.2; 428/402.21 |
Current CPC
Class: |
G02B
26/026 (20130101); G09F 9/372 (20130101); Y10T
428/249994 (20150401); Y10T 428/2985 (20150115); Y10T
428/2984 (20150115); Y10T 428/25 (20150115) |
Current International
Class: |
G02B
26/02 (20060101); G09F 9/37 (20060101); B32B
005/16 (); B32B 003/00 () |
Field of
Search: |
;428/320.2,323,402,402.2,402.21 ;264/4,7 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Chui, MIT Researcher Opens Volumes of Potential, MIT Researcher
Tries to Write New Chapter in Electronics, San Jose Mercury News,
Science & Technology Section, Jun. 18, 1996. .
Lee, A Magnetic-Particles Display, Proceeding of the S.I.D., vol.
16/3, Third Quarter 1975, pp. 177-184 (no month). .
Saitoh et al, A Newly Developed Electrical Twisting Ball Display,
Proceedings of the S.I.D., vol. 23/4, 1982, pp. 249-253 (no month).
.
Saxe et al, Suspended-Particle Devices, S.I.D., 1996, pp. 20-23 (no
month)..
|
Primary Examiner: Lam; Cathy F.
Attorney, Agent or Firm: McBain; Nola Mae
Claims
What is claimed is:
1. A display medium comprising:
a plurality of bichromal balls, each having two hemispheric
surfaces, one surface differing from the other in both color and
electrical characteristics
a layer of liquid surrounding each ball,
a skin of a first compound surrounding the layer of liquid to form
a microcapsule, and
a substrate of a second compound within which all of said
microcapsules are encapsulated.
2. The medium of claim 1 wherein said substrate is a solid.
3. The medium of claim 1 wherein said substrate is a liquid.
4. A display medium comprising:
a plurality of bichromal balls, each having two hemispheric
surfaces, one surface differing from the other in both color and
electrical characteristics
a layer of liquid surrounding each ball,
a skin of a first compound surrounding the layer of liquid, and
a substrate of a second compound within which all of said
microcapsules are encapsulated, which substrate is adapted to be
bonded to a surface.
5. The medium of claim 4 wherein said adhesive layer is
hardenable.
6. The medium of claim 4 wherein said adhesive layer is a
liquid.
7. The surface of claim 4 wherein said surface is flat.
8. The surface of claim 4 wherein said surface is not flat.
9. The surface of claim 4 wherein said surface is a
fabric..Iadd.
10. A display medium comprising:
at least one rotatable element having at least two portions,
wherein the two portions have both optical and electrical
characteristics such that the optical and electrical
characteristics of at least one portion of the at least two
portions differ from the optical and electrical characteristics of
at least another portion of the at least two portions,
a layer of liquid substantially surrounding the at least one
rotatable element,
a skin of a first compound surrounding the layer of liquid to form
a microcapsule containing a single rotatable element substantially
surrounded by a layer of liquid,
a substrate of a second compound at least partially surrounding the
microcapsule..Iaddend..Iadd.
11. The display medium of claim 10 wherein the at least one
rotatable element comprises a substantially spherical
element..Iaddend..Iadd.
12. The display medium of claim 10 wherein the at least one
rotatable element comprises two portions..Iaddend..Iadd.
13. The display medium of claim 12 wherein one of the portions is
colored black and the other portion is colored
white..Iaddend..Iadd.
14. The display medium of claim 12 wherein the at least one
rotatable element comprises at least one substantially spherical
element and each of the two portions substantially comprises a
hemisphere..Iaddend..Iadd.
15. The display medium of claim 10 wherein said substrate comprises
a solid..Iaddend..Iadd.
16. The display medium of claim 10 wherein said substrate comprises
a liquid..Iaddend..Iadd.
17. The display medium of claim 10 wherein said substrate
substantially surrounds the microcapsule..Iaddend..Iadd.
18. The display medium of claim 10 wherein said substrate
completely surrounds the microcapsule..Iaddend..Iadd.
19. The display medium of claim 10 wherein said substrate is
adapted to be bonded to a surface..Iaddend..Iadd.
20. The display medium of claim 18 wherein said substrate is an
adhesive..Iaddend..Iadd.
21. The display medium of claim 20 wherein said adhesive is a
liquid..Iaddend..Iadd.
22. The display medium of claim 21 wherein said adhesive is
hardenable..Iaddend..Iadd.
23. The display medium of claim 18 wherein the surface is
substantially flat..Iaddend..Iadd.
24. The display medium of claim 18 wherein the surface is
deformable..Iaddend..Iadd.
25. The display medium of claim 24 wherein the deformable surface
comprises a fabric..Iaddend..Iadd.
26. The display medium of claim 18 wherein the surface is
non-planar..Iaddend..Iadd.
27. The display medium of claim 10 wherein the at least one
rotatable element comprises a plurality of rotatable
elements..Iaddend.
Description
BACKGROUND OF THE INVENTION
A "twisting ball" medium for displaying an image comprising
internal bichromal balls that rotate to show either black or white
hemispheres in response to an externally applied electrical field,
and that are contained in individual liquid filled spherical shells
that are in turn dispersed in a transparent binder, which is
usually solid when used.
U.S. Pat. Nos. 4,126,854 and 4,143,103 describe a twisting ball
display and are incorporated by reference herein. These patents
describe a display system in which the display panel is comprised
of spherical balls which have an optical and an electrical
anisotropy due to each hemisphere surface having a different color
and electrical charge in contact with a liquid. These spherical
particles are imbedded in a solid substrate and a slight space
between each ball and the substrate is filled with a liquid so that
the balls are free to rotate, in a changing electrical field, but
can not migrate from one location to another. If one hemisphere is
black and the other is white, each pixel can be turned on and off
by the electrical field applied to that location. Each pixel can be
individually addressed, and a full page image can thus be
generated.
Most commonly the solid substrate used in this display is a gel,
typically a silicone gel. The purpose of using this material lies
in the remarkably large expansion in volume exhibited by gels when
soaked in certain liquids, which we refer to as plasticizing
liquids. 30% expansions are not uncommon when soaked in silicone
oils. The bichromal balls do not expand when contacted by the
plasticizing oil, so a spherical cavity opens up around each ball
when the gel is immersed in a plasticizing liquid. This space fills
with the plasticizing liquid.
After being soaked in plasticizer, the gel is soft and lacks
durability, and must be bonded between glass or plastic sheets for
protection. This process has the disadvantages that a large number
of steps are required for the fabrication, adding to the cost, and
that the final product lacks some of the optical and tactile
properties of paper, which it emulates in some embodiments. It will
be seen that significant advantages will further accrue when the
limitations to planar geometries are removed. A product that does
not require the use of bonding sheets would be desireable.
Historically there have been several approaches to the problem of
isolating twisting balls for displays. Lee (L. L. Lee,
"Matrix-Addressed Magnetic Particles Display", IEEE Trans. on
Elect. Devices, Vol. ED-22, No. 9, September 1975) created a
honeycomb type of structure in which the balls were contained in
separate compartments which were an integral part of the substrate.
Such a structure was inherently expensive to make and effectively
limited the ball sizes that could be used. Later, Saitoh et al (M.
Saitoh, T. Mori, R. Ishikawa, and H. Tamura, "A Newly Developed
Electrical Twisting Ball Display", Proc. of the SID, Vol. 23/4,
1982) developed an isolation technique in which the individual
balls were coated with a resin and subsequently dispersed in a poly
vinyl alcohol substrate. After the PVA was hardened it was immersed
in a solvent that had minimal effect on the PVA but that dissolved
the resin around the balls, leaving them free to rotate. Once
again, this is an expensive procedure that would be difficult to
implement on large scale. The most successful approach to date was
that of Sheridon, described in U.S. Pat. No. 4,143,103 referenced
above and described in the last two paragraphs.
SUMMARY OF THE INVENTION
The bichromal balls are individually enclosed in spherical shells
with the space between the two spherical surfaces filled with
dielectric liquid. The resultant capsules may be dispersed in a
second liquid, such as an optically clear epoxy, which may be
subsequently hardened. If the hardened liquid, now a solid, is of
sufficient strength no further protection is required. The
resultant display is then in the form of a thin, paper-like sheet
without the bulkiness and optical problems created by the
protective cover sheets as in the prior art. Alternatively, the
resultant display may be easily conformally coated on a non-planar
surface for even greater flexibility of applications.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross section of the prior art version of this twisting
ball display.
FIG. 2 is an enlarged view of the prior art bichromal ball
surrounded by plasticizing oil.
FIG. 3 shows a plurality of capsules dispersed in a substrate.
FIG. 4 is a cross section of a capsule of FIG. 3.
FIG. 5 is a bichromal ball before coating.
FIG. 6 is a bichromal ball after coating.
FIG. 7 shows a bichromal ball immersed in dielectric liquid.
FIG. 8 shows the finished microcapsule.
FIG. 9 shows one method of encapsulating bichromal balls.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a cross section of the prior art version of this twisting
ball display. A large number of bichromal balls 11 are mixed into
an uncured elastomer which is subsequently spread into a thin layer
10 and cured to form a solid sheet of elastomer. Next this
elastomer is soaked in a plasticizing oil which swells the
elastomer but generally does not effect the bichromal balls. The
result is that a spherical cavity 13 opens up around each bichromal
ball, and this cavity subsequently fills with the plasticizing
liquid. Finally the plasticized elastomer is bonded between two
protective, transparent sheets of plastic or glass, 12, one or both
of which might have a transparent .[.condicting.]. .Iadd.conducting
.Iaddend.coating. FIG. 2 is an enlarged view of the bichromal ball
15 surrounded by plasticizing oil 14 within a cavity in elastomer
16.
The substrate material used in the prior art twisting ball display
was largely limited to the class of elastomer materials, because
these materials undergo the greatest extent of swelling when
plasticized and thus form cavities of adequate size.
This invention is the improvement of using a separate encapsulating
shell to enclose both the bichromal ball and a sufficient thickness
of dielectric oil 14 to allow free rotation of the bichromal ball.
These capsules then constitute voltage sensitive members that may
be dispersed in any medium across which an electrical field may be
impressed. Most commonly this medium will be a solid, with the
balls dispersed in this solid while it is in a liquid phase. It
will be subsequently hardened, by chemical reaction, by cooling,
etc. The medium may also be a liquid, or a slurry consisting of a
liquid and solid particles, or solid particles whose purpose might
be to immobilize the capsules. Indeed, any medium might be used to
contain the capsules provided that it does not damage the
protective shell of the capsule or diffuse undesirable chemicals
across the shell. These voltage sensitive members will then
indicate the voltage condition at their locations. When used in
conjunction with an addressing means they can constitute an
information display. Other uses might include the visualization or
measurement of local electrical fields in test systems.
This invention allows the substrate material to be made from a very
large number of dielectric materials that are obtained by hardening
a liquid phase of the material into which the bichromal balls in
liquid-filled shells have been dispersed. In general the shells
will permit chemical isolation of the hardenable material from the
encapsulated liquid, providing great freedom in choosing the
substrate material.
The process of enclosing the bichromal balls and the oil layer in
individual capsules is a form of microencapsulation. There is a
rich scientific and patent literature on microencapsulation. It is
generally discussed in "Microcapsule Processing and Technology" by
Asaji Kondo, 1979, Marcel Dekker, Inc. Two particular methods that
are especially appropriate to this use are discussed here. An
individual capsule is illustrated in FIG. 4 and a plurality of such
capsules dispersed in a substrate is shown in FIG. 3.
A bichromal ball 15 as shown in FIG. 5 is coated uniformly to
result in a coated ball as shown in FIG. 6. The coating may be of
Parylene (a product of the Union Carbide Corp.) and take place in a
vacuum chamber. It may be a polymer which is dissolved in a solvent
and precipitated onto the ball by means of a temperature change, a
ph change, etc. A process such as this is discussed by Wei-Hsin Hou
in "Polymer-Encapsulated particles with Controlled
Morphologies:Preparation, Characterization and Application", PhD
Thesis, Lehigh University, 1991. UMI Disseration Service,
University Microfilms International, Ann Arbor, Mich. It may be a
hardenable liquid such as an epoxy and deposited as a mist or in a
tumbling situation such as in a fluidized bed. It may be a polymer
and deposited by means of an electrostatic painting process.
After the coating is applied, the bichromal balls are immersed in
dielectric liquid 14, as shown in FIG. 7, which has a chemical
affinity for the coating and plasticizes it, causing it to swell.
This process will also drive the liquid into the space between the
ball and the shell, at least partially filling it. Subsequently
placing the microcapsules thus formed into a second liquid that
diffuses more rapidly through the shell than the first liquid will
tend to more fully fill the space within the shell. The finished
product is shown in FIG. 8, and is ready to be mixed into the
hardenable substrate.
A second approach, discussed in Kondo's work, relies on the
well-known fact that when drops of certain liquids are placed in
other liquids, an interface skin will rapidly form between the two
liquids. A subset of this is called interfacial polymerization and
is used to fabricate certain polymers. One method of using this
phenomenon to encapsulate bichromal balls with a dielectric liquid
layer is shown in FIG. 9. On the left side of the apparatus the
balls 15 are mixed with the liquid 31 in the pipe 30. They are
ejected from the nozzle 32 under such conditions that each ball is
separate and is coated with the dielectric liquid to a
predetermined thickness. As these fall into the tank 33, the
chemical reaction between the dielectric liquid and the film
forming liquid creates a tough film over the fully encapsulates the
ball, including the dielectric liquid. These are removed from the
tank and dried for use.
The microcapsules formed by these processes need only be strong
enough to hold up to the process of being mixed with the hardenable
transparent material used to form the sheet of electric paper. Such
transparent materials include epoxies and polymers having an end
state as solids, gels and elastomers. In other cases, such as where
the microcapsules are used to determine electrical fields, stronger
structures may be required.
A particularly useful application of this technology is to mix the
capsules containing the bichromal balls with a transparent
hardenable material, such as a varnish, and to paint the resulting
dispersion onto a surface, which may be nonplanar. In this way one
may not only obtain display surfaces that conform to objects of any
shape, but one also obtains articles of decoration or camoflauge.
Simply applying electrical fields will cause such surfaces to
change color, inexpensively. Useful surfaces include structural
members and fabrics, especially articles of clothing. In addition
to being dispersed in the volume of a liquid that is subsequently
hardened, the microcapsules can also be adhered to adhesives that
are coated onto surfaces, typically forming monolayers. Thus, for
example, an article of clothing could be coated with an adhesive
and subsequently microcapsules could be adhered to the adhesive.
Thereafter the color of that article of clothing could be altered
by the application of electrical fields. Likewise, the surface of
an object that there is an intention to conceal could be coated
with a monolayer of microcapsules and a spatially varying voltage
could be applied to these microcapsules to control the pattern of
color on the surface of that object.
This invention is then highly advantaged over prior art methods of
providing isolation cavities for the bichromal balls used in
twisting ball displays to rotate. It is an inherently low cost
technique that allows a wide choice of substrate materials and that
can be applied to a large variety of planar and non-planar
surfaces. It will allow the fabrication of very thin sheets of
display materials having more paper-like properties than were
possible with prior art methods.
While the invention has been described with reference to a specific
embodiment, it will be understood by those skilled in the art that
various changes may be made and equivalents may be substituted for
elements thereof without departing from the true spirit and scope
of the invention. In addition, many modifications may be made
without departing from the essential teachings of the
invention.
* * * * *