U.S. patent application number 15/228625 was filed with the patent office on 2016-11-24 for electro-optic displays.
The applicant listed for this patent is E Ink Corporation. Invention is credited to Karl Raymond Amundson, Barrett Comiskey, Gregg M. Duthaler, Holly G. Gates, Alberto Goenaga, Anthony Edward Pullen, John E. Ritter, Michael L. Steiner, Russell J. Wilcox, Robert W. Zehner.
Application Number | 20160342065 15/228625 |
Document ID | / |
Family ID | 31978077 |
Filed Date | 2016-11-24 |
United States Patent
Application |
20160342065 |
Kind Code |
A1 |
Duthaler; Gregg M. ; et
al. |
November 24, 2016 |
ELECTRO-OPTIC DISPLAYS
Abstract
The invention provides an electrophoretic medium comprising at
least two types of particles having substantially the same
electrophoretic mobility but differing colors. The invention also
provides article of manufacture comprising a layer of a solid
electro-optic medium, a first adhesive layer on one surface of the
electro-optic medium, a release sheet covering the first adhesive
layer, and a second adhesive layer on an opposed second surface of
the electro-optic medium.
Inventors: |
Duthaler; Gregg M.;
(Needham, MA) ; Amundson; Karl Raymond;
(Cambridge, MA) ; Comiskey; Barrett; (Taipei,
TW) ; Gates; Holly G.; (Somerville, MA) ;
Goenaga; Alberto; (Houston, TX) ; Ritter; John
E.; (Westford, MA) ; Steiner; Michael L.; (New
Richmond, WI) ; Wilcox; Russell J.; (Newton, MA)
; Zehner; Robert W.; (Los Gatos, CA) ; Pullen;
Anthony Edward; (Tucson, AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
E Ink Corporation |
Billerica |
MA |
US |
|
|
Family ID: |
31978077 |
Appl. No.: |
15/228625 |
Filed: |
August 4, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14458513 |
Aug 13, 2014 |
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15228625 |
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12472486 |
May 27, 2009 |
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14458513 |
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10605024 |
Sep 2, 2003 |
7561324 |
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12472486 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02F 2001/1678 20130101;
G02F 1/1679 20190101; G02F 1/1334 20130101; G02F 1/167 20130101;
G02F 2201/52 20130101; G02F 1/16757 20190101; G02F 1/133516
20130101; G02F 1/1677 20190101; G02F 1/133348 20130101; G02F
2001/133354 20130101; G02F 2202/28 20130101; G02F 1/133514
20130101 |
International
Class: |
G02F 1/167 20060101
G02F001/167; G02F 1/1335 20060101 G02F001/1335; G02F 1/1333
20060101 G02F001/1333 |
Claims
1. A process for forming an electrophoretic medium, the process
comprising: mixing at least two pigments having differing colors to
form a mixed pigment; subjecting the mixed pigment to at least one
surface treatment; and dispersing the surface-treated mixed pigment
in a suspending fluid to form at least two types of particles
having substantially the same electrophoretic mobility but
differing colors.
2. A process according to claim 1 wherein the at least one surface
treatment comprises coating the mixed pigment with a coating
selected from silica and silica/alumina.
3. A process according to claim 1 wherein the at least one surface
treatment comprises forming a polymer on the mixed pigment.
4. A process according to claim 3 wherein the at least one surface
treatment comprises treating the mixed pigment with a silane
coupling agent to provide sites at which a polymer can be attached
to the mixed pigment, and thereafter treating the silylated mixed
pigment with at least one monomer and oligomer under conditions
effective to cause polymer for form of the mixed pigment
surface.
5. A process according to claim 1 further comprising encapsulating
the electrically charged particles and the suspending fluid within
at least one capsule.
6. An electro-optic display element comprising: an electro-optic
display medium; an optical biasing element arranged to modify an
optical characteristic of the electro-optic display element; and an
addressing electrode to address the electro-optic display medium,
wherein the color of the optical biasing element varies in
different portions of the electro-optic display element, so that
the optical biasing element forms a color filter.
7. An electro-optic display element according to claim 6 wherein
the electro-optic display medium is an electrophoretic medium
comprising a suspending fluid, a plurality of electrically charged
particles suspended in the suspending fluid and capable of moving
therethrough on application of an electric field to the suspending
fluid, and at least one capsule having a capsule wall surrounding
the suspending fluid and the electrically charged particles, the
display element optionally comprising a binder surrounding the
capsules and/or a lamination adhesive disposed adjacent the
electrophoretic medium and/or a front electrode disposed between
the electrophoretic medium and a viewing surface of the display,
and wherein the optical biasing element is disposed in at least one
of the capsule wall, the binder, the lamination adhesive and the
front electrode.
8. An electrophoretic medium comprising a plurality of capsules,
each capsule comprising a suspending fluid, a plurality of
electrically charged particles suspended in the suspending fluid
and capable of moving therethrough on application of an electric
field to the suspending fluid, and a capsule wall surrounding the
suspending fluid and the electrically charged particles, the medium
further comprising a color filter array having a plurality of
non-rectangular pixels.
9. An electrophoretic medium according to claim 8 wherein the
pixels of the color filter array are hexagonal, square, or
triangular.
10. An electro-optic display comprising a layer of a solid
electro-optic medium, at least one electrode arranged adjacent the
layer of electro-optic medium so as to apply an electric field
thereto, and a color filter array disposed between the
electro-optic medium and the electrode, the resistance of the color
filter array being not substantially greater than that of the layer
of electro-optic medium.
11. An electro-optic display according to claim 10 wherein the
color filter array has a volume resistivity not greater than about
10.sup.10 ohm cm.
12. A process for forming a color filter array, the process
comprising: imaging a photosensitive film to form a color filter
array pattern thereon; and thereafter depositing a conductive layer
on to the photosensitive film.
13. A process for forming an electrophoretic display, the process
comprising: providing a color filter array; providing an
electrophoretic medium comprising a plurality of capsules, each
capsule comprising a suspending fluid, a plurality of electrically
charged particles suspended in the suspending fluid and capable of
moving therethrough on application of an electric field to the
suspending fluid, and a capsule wall surrounding the suspending
fluid and the electrically charged particles; depositing the
electrophoretic medium on the color filter array to form a coated
color filter array; and thereafter laminating the coated color
filter array to a backplane comprising at least one pixel
electrode.
14. A process according to claim 13 wherein the surface of the
color filter array is surface treated prior to the deposition to
produce regions of varying surface energy on the surface.
15. A process for depositing an electrophoretic medium on an
electrode, the process comprising: providing an electrode;
providing an electrophoretic medium comprising a plurality of
capsules, each capsule comprising a suspending fluid, a plurality
of electrically charged particles suspended in the suspending fluid
and capable of moving therethrough on application of an electric
field to the suspending fluid, and a capsule wall surrounding the
suspending fluid and the electrically charged particles; surface
treating the electrode to produce regions of varying surface energy
thereon; and depositing the electrophoretic medium on the
surface-treated electrode.
16. A process for forming an electrophoretic display, the process
comprising: providing a front substrate; providing a backplane;
providing an electrophoretic medium comprising a plurality of
capsules, each capsule comprising a suspending fluid, a plurality
of electrically charged particles suspended in the suspending fluid
and capable of moving therethrough on application of an electric
field to the suspending fluid, and a capsule wall surrounding the
suspending fluid and the electrically charged particles; surface
treating a surface of the front substrate to promote wetting
thereof by the capsules; surface treating a surface of the
backplane to promote dewetting thereof by the capsules; assembling
the front substrate and the backplane together with the treated
surfaces thereof facing each other, and with a gap between the
treated surfaces; and introducing the electrophoretic medium into
the gap, whereby the capsules of the electrophoretic medium pack
against the treated surface of the front substrate.
17. An electro-optic display comprising, in this order: a backplane
comprising at least one electrode; a first layer of lamination
adhesive; a layer of electro-optic material; a second layer of
lamination adhesive; and a front substrate, wherein peripheral
portions of the first and second layers of lamination adhesive
extend outwardly beyond the edges of the layer of electro-optic
material, the peripheral portions of the first and second layers of
lamination adhesive contacting each other and thereby forming a
seal around the layer of electro-optic material.
18. An electro-optic display according to claim 17 further
comprising a protective layer provided on the opposed side of the
front substrate from the second layer of lamination adhesive.
19. An electro-optic display according to claim 17 wherein the
electro-optic material comprises a rotating bichromal member or
electrochromic material.
20. An electro-optic display according to claim 17 wherein the
electro-optic material comprises an electrophoretic material
comprising a plurality of electrically charged particles disposed
in a fluid and capable of moving through the fluid under the
influence of an electric field.
21. An electro-optic display according to claim 20 wherein the
electrically charged particles and the fluid are confined within a
plurality of capsules or microcells.
22. An electro-optic display according to claim 20 wherein the
electrically charged particles and the fluid are present as a
plurality of discrete droplets surrounded by a continuous phase
comprising a polymeric material.
23. An electro-optic display according to claim 20 wherein the
fluid is gaseous.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of copending application Ser.
No. 14/458,513, filed Aug. 13, 2014 (Publication No. 2014/0347718),
which itself is a division of application Ser. No. 12/472,486,
filed May 27, 2009 (Publication No. 2009/0225398, now abandoned),
which itself is a division of application Ser. No. 10/605,024,
filed Sep. 2, 2003 (Publication No. 2004/0155857, now U.S. Pat. No.
7,561,324), which claims priority from Provisional Application Ser.
No. 60/319,516, filed Sep. 3, 2002.
[0002] This application is related to copending application Ser.
No. 10/143,046 filed May 10, 2002 (Publication No. 2003/0011560,
now U.S. Pat. No. 7,256,766), which is a continuation-in-part of
application Ser. No. 09/140,862, filed Aug. 27, 1998 (now U.S. Pat.
No. 7,167,155). This application is also related to copending
application Ser. No. 10/145,861 (Publication No. 2002/0180688, now
U.S. Pat. No. 6,864,875), which is a continuation of application
Ser. No. 09/436,303, filed Nov. 8, 1999 (now abandoned), which is
turn is a divisional of copending application Ser. No. 09/289,507,
filed Apr. 9, 1999 (now U.S. Pat. No. 7,075,502), which claims
priority from Provisional Application Ser. No. 60/081,362, filed
Apr. 10, 1998. This application is also related to copending
application Ser. No. 10/249,957, filed May 22, 2003 (now U.S. Pat.
No. 6,982,178), which claims priority from Application Ser. No.
60/319,300, filed Jun. 10, 2002 and Application Ser. No.
60/320,186, filed May 12, 2003. The entire contents of all the
aforementioned applications, and of all patents and applications
referred to below, are herein incorporated by reference.
BACKGROUND OF INVENTION
[0003] This invention relates to electro-optic displays. More
specifically, this invention relates to components for use in
electro-optic displays, novel color filters for use in such
displays and methods for preparing such filters. This invention
also relates to novel methods for controlling the color of
electrophoretic displays.
[0004] Electro-optic displays comprise a layer of electro-optic
material, a term which is used herein in its conventional meaning
in the art to refer to a material having first and second display
states differing in at least one optical property, the material
being changed from its first to its second display state by
application of an electric field to the material. The optical
property is typically color perceptible to the human eye, but may
be another optical property, such as optical transmission,
reflectance, luminescence or, in the case of displays intended for
machine reading, pseudo-color in the sense of a change in
reflectance of electromagnetic wavelengths outside the visible
range.
[0005] Most aspects of the present invention are intended for use
with electro-optic displays containing an electro-optic medium
which is a solid (such displays may hereinafter for convenience be
referred to as "solid electro-optic displays"), in the sense that
the electro-optic medium has solid external surfaces, although the
medium may, and often does, have internal liquid- or gas-filled
spaces, and to methods for assembling displays using such an
electro-optic medium. Thus, the term "solid electro-optic displays"
includes encapsulated electrophoretic displays, rotating bichromal
member displays, electrochromic displays, microcell displays, and
other types of displays as discussed below.
[0006] One type of electro-optic display is a rotating bichromal
member type as described, for example, in U.S. Pat. Nos. 5,808,783;
5,777,782; 5,760,761; 6,054,071 6,055,091; 6,097,531; 6,128,124;
6,137,467; and 6,147,791 (although this type of display is often
referred to as a "rotating bichromal ball" display, the term
"rotating bichromal member" is preferred as more accurate since in
some of the patents mentioned above the rotating members are not
spherical). Such a display uses a large number of small bodies
(typically spherical or cylindrical) which have two or more
sections with differing optical characteristics, and an internal
dipole. These bodies are suspended within liquid-filled vacuoles
within a matrix, the vacuoles being filled with liquid so that the
bodies are free to rotate. The appearance of the display is changed
to applying an electric field thereto, thus rotating the bodies to
various positions and varying which of the sections of the bodies
is seen through a viewing surface.
[0007] Another type of electro-optic medium is an electrochromic
medium, for example an electrochromic medium in the form of a
nanochromic film comprising an electrode formed at least in part
from a semi-conducting metal oxide and a plurality of dye molecules
capable of reversible color change attached to the electrode; see,
for example O'Regan, B., et al., Nature 1991, 353, 737; and Wood,
D., Information Display, 18(3), 24 (March 2002). See also Bach, U.,
et al., Adv. Mater., 2002, 14(11), 845. Nanochromic films of this
type are also described, for example, in U.S. Pat. No. 6,301,038,
International Application Publication No. WO 01/27690, and in
copending application Ser. No. 10/249,128, filed Mar. 18, 2003.
[0008] Another type of electro-optic display, which has been the
subject of intense research and development for a number of years,
is the particle-based electrophoretic display, in which a plurality
of charged particles move through a suspending fluid under the
influence of an electric field. Electrophoretic displays can 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 prevented their widespread
usage. For example, particles that make up electrophoretic displays
tend to settle, resulting in inadequate service-life for these
displays.
[0009] Numerous patents and applications assigned to or in the
names of the Massachusetts Institute of Technology (MIT) and E Ink
Corporation have recently been published describing encapsulated
electrophoretic media. Such encapsulated media comprise numerous
small capsules, each of which itself comprises an internal phase
containing electrophoretically-mobile particles suspended in a
liquid suspension medium, and a capsule wall surrounding the
internal phase. Typically, the capsules are themselves held within
a polymeric binder to form a coherent layer positioned between two
electrodes. Encapsulated media of this type are described, for
example, in U.S. Pat. Nos. 5,930,026; 5,961,804; 6,017,584;
6,067,185; 6,118,426; 6,120,588; 6,120,839; 6,124,851; 6,130,773;
6,130,774; 6,172,798; 6,177,921; 6,232,950; 6,249,271; 6,252,564;
6,262,706; 6,262,833; 6,300,932; 6,312,304; 6,312,971; 6,323,989;
6,327,072; 6,376,828; 6,377,387; 6,392,785; 6,392,786; 6,413,790;
6,422,687; 6,445,374; 6,445,489; 6,459,418; 6,473,072; 6,480,182;
6,498,114; 6,504,524; 6,506,438; 6,512,354; 6,515,649; 6,518,949;
6,521,489; 6,531,997; 6,535,197; 6,538,801; 6,545,291; and
6,580,545; and U.S. Patent Applications Publication Nos.
2002/0019081; 2002/0021270; 2002/0053900; 2002/0060321;
2002/0063661; 2002/0063677; 2002/0090980; 2002/0106847;
2002/0113770; 2002/0130832; 2002/0131147; 2002/0145792;
2002/0171910; 2002/0180687; 2002/0180688; 2002/0185378;
2003/0011560; 2003/0011867; 2003/0011868; 2003/0020844;
2003/0025855; 2003/0034949; 2003/0038755; 2003/0053189;
2003/0076573; 2003/0096113; 2003/0102858; 2003/0132908;
2003/0137521; and 2003/0137717; and International Applications
Publication Nos. WO 99/67678; WO 00/05704; WO 00/38000; WO
00/38001; WO 00/36560; WO 00/67110; WO 00/67327; WO 01/07961; and
WO 01/08241.
[0010] Many of the aforementioned patents and applications
recognize that the walls surrounding the discrete microcapsules in
an encapsulated electrophoretic medium could be replaced by a
continuous phase, thus producing a so-called polymer-dispersed
electrophoretic display in which the electrophoretic medium
comprises a plurality of discrete droplets of an electrophoretic
fluid and a continuous phase of a polymeric material, and that the
discrete droplets of electrophoretic fluid within such a
polymer-dispersed electrophoretic display may be regarded as
capsules or microcapsules even though no discrete capsule membrane
is associated with each individual droplet; see for example, the
aforementioned 2002/0131147. Accordingly, for purposes of the
present application, such polymer-dispersed electrophoretic media
are regarded as sub-species of encapsulated electrophoretic
media.
[0011] An encapsulated electrophoretic display typically does not
suffer from the clustering and settling failure mode of traditional
electrophoretic devices and provides further advantages, such as
the ability to print or coat the display on a wide variety of
flexible and rigid substrates. (Use of the word "printing" is
intended to include all forms of printing and coating, including,
but without limitation: pre-metered coatings such as patch die
coating, slot or extrusion coating, slide or cascade coating,
curtain coating; roll coating such as knife over roll coating,
forward and reverse roll coating; gravure coating; dip coating;
spray coating; meniscus coating; spin coating; brush coating; air
knife coating; silk screen printing processes; electrostatic
printing processes; thermal printing processes; ink jet printing
processes; and other similar techniques.) Thus, the resulting
display can be flexible. Further, because the display medium can be
printed (using a variety of methods), the display itself can be
made inexpensively.
[0012] A related type of electrophoretic display is a so-called
"microcell electrophoretic display". In a microcell electrophoretic
display, the charged particles and the suspending fluid are not
encapsulated within microcapsules but instead are retained within a
plurality of cavities formed within a carrier medium, typically a
polymeric film. See, for example, International Applications
Publication No. WO 02/01281, and published US Application No.
2002-0075556, both assigned to Sipix Imaging, Inc.
[0013] Most types of electro-optic media have only a limited number
of optical states, for example a dark (black) state, a light
(white) state and, in some cases, one or more intermediate gray
states. Accordingly, to construct a full color display using such
media, it is common practice to place an electro-optic medium
adjacent a color filter having, for example, multiple red, green
and blue areas, and to provide a driving arrangement for the
electro-optic medium which permits independent control of the
medium adjacent each red, green or blue area. Certain applications
of color filters with electrophoretic displays are described in the
aforementioned application Ser. No. 09/289,507. The aforementioned
2003/0011560 describes ways for modifying the optical properties of
electrophoretic displays by incorporating an optical biasing
element in any one of several components of the display.
[0014] The present invention seeks to provide improvements in color
filters used in electro-optic displays, and in ways of generating
color in such displays.
SUMMARY OF INVENTION
[0015] In one aspect, the present invention provides an
electrophoretic medium comprising a plurality of electrically
charged particles dispersed in a suspending fluid, the particles
comprising at least two types of particles having substantially the
same electrophoretic mobility but differing colors. This aspect of
the invention may hereinafter be referred to as the "custom color"
electrophoretic medium.
[0016] In this custom color electrophoretic medium, the
electrically charged particles are desirably formed from an
inorganic pigment, which may be coated with a coating selected from
silica and silica alumina. The electrically charged particles may
be coated with a polymer. The electrically charged particles and
the suspending fluid may be held within at least one capsule.
[0017] This invention also provides a process for forming a custom
color electrophoretic medium of the invention. This process
comprises:
[0018] mixing at least two pigments having differing colors to form
a mixed pigment;
[0019] subjecting the mixed pigment to at least one surface
treatment; and
[0020] dispersing the surface-treated mixed pigment in a suspending
fluid to form at least two types of particles having substantially
the same electrophoretic mobility but differing colors.
[0021] In this process, the surface treatment may comprise treating
the mixed pigment with a silane coupling agent to provide sites at
which a polymer can be attached to the mixed pigment, and
thereafter treating the silylated mixed pigment with at least one
monomer and oligomer under conditions effective to cause polymer
for form of the mixed pigment surface.
[0022] In another aspect, the present invention provides an
electro-optic display element comprising:
[0023] an electro-optic display medium;
[0024] an optical biasing element arranged to modify an optical
characteristic of the electro-optic display element; and
[0025] an addressing electrode to address the electro-optic display
medium,
[0026] wherein the color of the optical biasing element varies in
different portions of the electro-optic display element, so that
the optical biasing element forms a color filter.
[0027] This aspect of the invention may hereinafter be referred to
as the "internal color filter" display element.
[0028] In such an internal color filter display element, the
electro-optic display medium may be an electrophoretic medium
comprising a suspending fluid, a plurality of electrically charged
particles suspended in the suspending fluid and capable of moving
therethrough on application of an electric field to the suspending
fluid, and at least one capsule having a capsule wall surrounding
the suspending fluid and the electrically charged particles, the
display element optionally comprising a binder surrounding the
capsules and/or a lamination adhesive disposed adjacent the
electrophoretic medium and/or a front electrode disposed between
the electrophoretic medium and a viewing surface of the display,
and the optical biasing element may be disposed in at least one of
the capsule wall, the binder, the lamination adhesive and the front
electrode.
[0029] Another, related aspect of the invention provides an
electro-optic display comprising a layer of a solid electro-optic
medium, at least one electrode arranged adjacent the layer of
electro-optic medium so as to apply an electric field thereto, and
a color filter array disposed between the electro-optic medium and
the electrode, the resistance of the color filter array being not
substantially greater than that of the layer of electro-optic
medium.
[0030] In such an electro-optic display, the color filter array
will typically have a volume resistivity not greater than about
10.sup.10 ohm cm.
[0031] In another aspect, this invention provides an
electrophoretic medium comprising a plurality of capsules, each
capsule comprising a suspending fluid, a plurality of electrically
charged particles suspended in the suspending fluid and capable of
moving therethrough on application of an electric field to the
suspending fluid, and a capsule wall surrounding the suspending
fluid and the electrically charged particles, the medium further
comprising a color filter array having a plurality of
non-rectangular pixels. In preferred forms of this electrophoretic
display, the pixels of the color filter array are hexagonal,
square, or triangular, preferably equilateral triangular.
[0032] In another aspect, this invention provides an article of
manufacture comprising:
[0033] a layer of a solid electro-optic medium having first and
second surfaces on opposed sides thereof;
[0034] a first adhesive layer on the first surface of the layer of
solid electro-optic medium;
[0035] a (first) release sheet disposed on the opposed side of the
first adhesive layer from the layer of solid electro-optic medium;
and
[0036] a second adhesive layer on the second surface of the layer
of solid electro-optic medium.
[0037] A preferred form of this article of manufacture further
comprises a second release sheet disposed on the opposed side of
the second adhesive layer from the layer of solid electro-optic
medium.
[0038] In this article of manufacture, the electro-optic medium may
be an electrophoretic medium comprising a plurality of capsules,
each capsule comprising a suspending fluid, a plurality of
electrically charged particles suspended in the suspending fluid
and capable of moving therethrough on application of an electric
field to the suspending fluid, and a capsule wall surrounding the
suspending fluid and the electrically charged particles. Also, the
first and second adhesive layers may extend beyond the periphery of
the layer of electro-optic medium; as described in more detail
below, this provides a convenient way for form an edge seal for the
display.
[0039] In another aspect, this invention provides an article of
manufacture comprising:
[0040] a layer of a solid electro-optic medium having first and
second surfaces on opposed sides thereof;
[0041] a first release sheet covering the first surface of the
layer of solid electro-optic medium; and
[0042] a second release sheet covering the second surface of the
layer of solid electro-optic medium.
[0043] The foregoing articles of manufacture may hereinafter be
referred to as the "double release film" of the invention.
[0044] This invention also provides a process for forming an
electro-optic display using the double release film of the
invention. This process comprises:
[0045] providing an article of manufacture comprising a layer of a
solid electro-optic medium having first and second surfaces on
opposed sides thereof, a first adhesive layer on the first surface
of the layer of solid electro-optic medium, a release sheet
disposed on the opposed side of the first adhesive layer from the
layer of solid electro-optic medium; and a second adhesive layer on
the second surface of the layer of solid electro-optic medium;
[0046] laminating the article to a front substrate via the second
adhesive layer, thereby forming a front subassembly;
[0047] removing the release sheet from the front subassembly;
and
[0048] laminating the front subassembly via the first adhesive
layer to a backplane comprising at least one electrode, thereby
forming the electro-optic display.
[0049] In this process, the front substrate may comprise an
electrode and/or a color filter array. The article of manufacture
may comprise a second release sheet covering the second adhesive
layer, and the process comprise removing the second release sheet
from the second adhesive layer prior to laminating the article to
the front substrate.
[0050] In another aspect, this invention provides a process for
forming a color filter array, the process comprising:
[0051] imaging a photosensitive film to form a color filter array
pattern thereon; and
[0052] thereafter depositing a conductive layer on to the
photosensitive film.
[0053] In another aspect, this invention provides a process for
forming an electrophoretic display, the process comprising:
[0054] providing a color filter array;
[0055] providing an electrophoretic medium comprising a plurality
of capsules, each capsule comprising a suspending fluid, a
plurality of electrically charged particles suspended in the
suspending fluid and capable of moving therethrough on application
of an electric field to the suspending fluid, and a capsule wall
surrounding the suspending fluid and the electrically charged
particles;
[0056] depositing the electrophoretic medium on to a color filter
array to form a coated color filter array; and
[0057] thereafter laminating the coated color filter array to a
backplane comprising at least one pixel electrode.
[0058] In this process, the surface of the color filter array may
be surface treated prior to the deposition to produce regions of
varying surface energy on the surface.
[0059] In another aspect, this invention provides a process for
depositing an electrophoretic medium on an electrode, the process
comprising:
[0060] providing an electrode;
[0061] providing an electrophoretic medium comprising a plurality
of capsules, each capsule comprising a suspending fluid, a
plurality of electrically charged particles suspended in the
suspending fluid and capable of moving therethrough on application
of an electric field to the suspending fluid, and a capsule wall
surrounding the suspending fluid and the electrically charged
particles;
[0062] surface treating the electrode to produce regions of varying
surface energy thereon; and
[0063] depositing the electrophoretic medium on the surface-treated
electrode.
[0064] Finally, this invention provides a process for forming an
electrophoretic display, the process comprising:
[0065] providing a front substrate;
[0066] providing a backplane;
[0067] providing an electrophoretic medium comprising a plurality
of capsules, each capsule comprising a suspending fluid, a
plurality of electrically charged particles suspended in the
suspending fluid and capable of moving therethrough on application
of an electric field to the suspending fluid, and a capsule wall
surrounding the suspending fluid and the electrically charged
particles;
[0068] surface treating a surface of the front substrate to promote
wetting thereof by the capsules;
[0069] surface treating a surface of the backplane to promote
dewetting thereof by the capsules;
[0070] assembling the front substrate and the backplane together
with the treated surfaces thereof facing each other, and with a gap
between the treated surfaces; and
[0071] introducing the electrophoretic medium into the gap, whereby
the capsules of the electrophoretic medium pack against the treated
surface of the front substrate.
BRIEF DESCRIPTION OF DRAWINGS
[0072] FIG. 1 of the accompanying drawings is a schematic
cross-section through part of an encapsulated electrophoretic
display in which a color filter array is provided in the capsule
walls;
[0073] FIGS. 2A, 2B and 2C show three different arrangements of
pixels in a color filter array of the present invention;
[0074] FIG. 3 is a schematic cross-section through a double release
film of the present invention; and
[0075] FIG. 4 is a schematic cross-section, similar to that of FIG.
3, through a second release film of the present invention provided
with an edge seal.
DETAILED DESCRIPTION
[0076] The present invention provides several different
improvements in color filters and other aspects of electro-optic
displays, and in ways of generating color in such displays. These
various improvements can be used alone or in various combinations
(for example, a single display might use a color filter array
having non-rectangular pixels produced by the imaging process of
the invention. For convenience, the various aspects of the present
invention will hereinafter be described separately, but it must
always be remembered that multiple aspects of the invention may be
used in a single electro-optic display or component thereof.
[0077] Part A--Custom Colors in Electrophoretic Displays
[0078] As discussed in some of the aforementioned E Ink and MIT
patents and published applications, in an electrophoretic display
one alternative to the use of color filters is to use multiple
types of capsules capable of displaying differing colors. For
example, the aforementioned 2002/0180688 shows, in FIG. 3I, one
pixel of an encapsulated electrophoretic display, this pixel
comprising three sub-pixels, each of which comprises a single
capsule capable of displaying three colors. Although these are not
the colors actually described with reference to this FIG. 3I, it
will readily be understood by those skilled in the technology of
electro-optic displays that a full color RGB display could be
produced using capsules capable of white/black/red,
white/black/green and white/black/blue optical states.
[0079] One major commercial application of electro-optic displays
is in advertising, and in advertising materials it is desirable to
be able to customize the colors displayed for particular customers.
For example, many major corporations have established corporate
practices which require that certain color logos and/or trademarks
be presented in an absolutely consistent manner, with the proper
colors of each portion of the relevant logo or trademark being
specified in terms of the Pantone ("PANTONE" is a Registered
Trademark) or a similar color system. Thus, such corporations may
require that (say) the blue state of an RGB electrophoretic display
be customized to render a blue portion of their corporate logo
accurately, even at the cost of some reduction in the color gamut
of the display (the range of colors capable of being displayed by
the display).
[0080] At first glance, such customization of colors in an
electrophoretic display appears to pose formidable obstacles.
Determining the type of particles to use in an electrophoretic
display is a complex process which needs to take account not only
of the color of the particle but also, inter alia, its ability to
maintain a consistent electrical charge (and thus a consistent
electrophoretic mobility), its tendency to aggregate, its color
fastness against light and its compatibility with other components
of the electrophoretic medium, for example the suspending fluid in
which the electrophoretic particles are suspended and the capsule
wall. Carrying out all the necessary tests is a time-consuming and
expensive process, which cannot economically be carried out every
time a customer requires a custom color in a display. Furthermore,
in practice it is found that organic pigments tend not to be useful
in electrophoretic displays because they degrade too rapidly, so
that commercial displays use metal oxide or similar inorganic
pigments, and it is far less easily to vary the exact color of such
inorganic pigments than it is organic pigments.
[0081] However, it has now been realized that, in an
electrophoretic display, all of the electrophoretic particles of a
particular type used to produce a particular color (for example,
the blue particles shown in the aforementioned FIG. 3I) need not be
of the same color, provided that all of the same type of particles
have similar electrophoretic mobilities so that they do not
segregate during operation of the display. The individual
electrophoretic particles, which typically have diameters of the
order of 1 .mu.m, are far too small to be visible to an observer of
the display. Accordingly, provided that the particles do not
segregate during operation of the display, an observer sees only
the average color of all the particles of a particular type. For
example, it is well known to those skilled in color mixing that the
apparent degree of saturation of many blues can be improved by
adding a small proportion of magenta to the blue. Accordingly, if
for example a particular customer required the blue state of the
aforementioned white/black/blue sub-pixels to have a degree of
saturation greater than could be achieved by the available blue
particles, the sub-pixel could contain a mixture of a major
proportion of blue particles and a minor proportion (say about 10
percent) of magenta particles.
[0082] This ability to use mixtures of differently colored
particles as a single type of electrophoretic particles greatly
simplifies the problem of customizing colors in an electrophoretic
display. If one prepares a set of three or four electrophoretic
particles having differing colors (say RGB, RGBK, CMY or CMYK) but
substantially the same electrophoretic mobility, pixels having any
desired color within the gamut available from the set can be
prepared by simply mixing and encapsulating appropriate amounts of
the various particles to form the desired color.
[0083] Thus, as already mentioned in one aspect the present
invention provides an electrophoretic medium comprising a plurality
of electrically charged particles dispersed in a suspending fluid,
the particles comprising at least two types of particles having
substantially the same electrophoretic mobility but differing
colors.
[0084] Although this aspect of the present invention is described
herein primarily with regard to full color displays, it is of
course not confined to such displays. For example, the present
invention may be useful in simple flashing displays in which a
layer of an electrophoretic medium is confined between two
electrodes, which apply drive pulses of alternating polarities to
the electrodes, and in which the layer of electrophoretic medium
comprises different types of capsules deposited in different areas,
each type of capsule having (say) a black optical state and a
second optical state of another color. Such a display may be used
to flash a corporate logo or other symbol.
[0085] Technology is available which substantially reduces the
difficulties of ensuring that electrophoretic particles formed from
different pigments have substantially the same electrophoretic
mobility. The aforementioned 2002/0185378 and the corresponding WO
02/093246 describe a process for forming electrophoretic particles
in which a pigment is first coated with a layer of silica (other
oxides may also be used) and then a polymer is formed chemically
bonded to the silica; the polymer may contain electrically charged
groups to enhance the electrophoretic mobility of the particle. In
such silica/polymer coated particles, the surface charge which is
responsible for the electrophoretic mobility of the particle is
essentially confined to the silica layer and/or the polymer, so
that the nature of the underlying pigment is essentially irrelevant
to the electrophoretic mobility of the particle. Accordingly,
provided that the particle size of the pigment is controlled, a
variety of pigments can be coated in this manner to produce
electrophoretic particles having substantially the same
electrophoretic mobility.
[0086] Furthermore, if the scale of production needed warrants it,
mixing of the different pigments required to produce a display with
a custom color can be effected at an early stage in the multi-stage
process required to produce the display, with the resultant mixture
of pigments thereafter carried as a single component through the
subsequent stages of the process. By way of example, consider the
preferred process for producing electrophoretic particles described
in aforementioned 2002/0185378 and the corresponding WO 02/093246.
This process comprises (a) forming a silica or silica/alumina shell
around a raw pigment; (b) treating the silica-coated pigment with a
silane coupling agent to provide sites at which a polymer can be
attached to the pigment; and (c) treating the silylated pigment
would at least one monomer or oligomer under conditions effective
to cause polymer to form on the pigment surface (certain preferred
forms of the process require multiple polymerization steps and/or
further processing to modify the chemical characteristics of the
polymer originally formed). In such a process, the blending of two
or more pigments to provide a custom color in the final display
could be effected at various stages, as follows:
[0087] 1. Blending of Raw Pigments:
[0088] Raw untreated pigments may be blended to obtain the desired
color before the first modification of the surface. The blended
pigment mixture is then coated with silica or silica/alumina
followed by the silane treatment and polymer formation steps.
[0089] At first glance, this might appear to be the most preferred
method to assure that the blended pigments have been treated in the
same manner under identical conditions thus leading to blended
pigments with identical surface chemistries. On the other hand, it
may be difficult to judge the color in the final display from that
obtained by raw pigment blending because of color alterations due
to the inorganic coating, pigment wetting when in the suspending
fluid (silica is used to coat pigments in paint applications to
prevent this wetting effect, but wetting must still be considered)
and alterations in the pigment color when placed behind the capsule
wall, conductive, binder, adhesive, filter layer and other layers
conventionally used in electrophoretic displays, as described in
the aforementioned E Ink and MIT patents and applications. These
color alterations may require repeated iterations of the blending
process and the production of displays from the blended pigment,
with considerable increase in expense and development time for
custom color displays.
[0090] 2. Blending of Pigments after Formation of Inorganic
Shell
[0091] In this route, raw pigments are first modified independently
with a silica or silica/alumina shell then blended to achieve the
desired color, and thereafter the blended pigment is subjected to
silane treatment and polymer formation.
[0092] 3. Blending of Pigments after Formation of Inorganic Shell
and Silane Treatment
[0093] In this route, raw pigments are first modified independently
with a silica or silica/alumina shell and silane treatment. The
pigments are then blended to obtain the desired color and the
blended pigments subjected to polymer formation.
[0094] 4. Blending of Pigments Formation of Inorganic Shell, Silane
Treatment and Polymer Formation
[0095] In this route, raw pigments are first modified independently
with a silica or silica/alumina shell, followed by silane treatment
and polymer formation. The pigments are then blended to achieve the
desired color.
[0096] This route ensures that the surface modification of the
pigments does not alter the color of the pigments because the
pigments are blended after all chemical modifications have been
completed. Nevertheless the color of the blended pigment may still
change after incorporation into an internal phase and placement
behind a capsule wall, binder, adhesive, and other layers as
discussed above. However, this route does may give rise to problems
in ensuring that the pigments in the final blend have been treated
in the same manner under identical conditions thus leading to
identical surface chemistries such as the thickness/coverage of the
silica or silica/alumina layer, coverage/quality/density of the
silane deposition and thickness/molecular weight/density of the
polymer.
[0097] Part B--"Internal" Color Filters
[0098] Conventional color filter arrays (CFA's) for use in
electro-optic displays comprise a layer of material colored in an
appropriate manner and disposed adjacent the viewing surface of the
display, "outside" the front electrode, i.e., between the front
electrode and the viewer. Such a conventional CFA is necessarily
separated from the electro-optic layer by at least the thickness of
the front electrode and possibly other layers, for example a
substrate on which the front electrode is mounted and/or a binder
in which electrophoretic capsules are held and/or the polymeric
matrix in a rotating bichromal member display. This separation
between the CFA and the electro-optic layer gives rise to parallax
problems, and these problems are exacerbated by the wide viewing
angles of many electro-optic displays. Such parallax problems
adversely affect the quality of an image on the display, especially
when the display is viewed at a large angle to the perpendicular to
the viewing surface thereof.
[0099] Another problem with conventional CFA's is aligning the CFA
with the pixel electrodes used to drive the display; it will be
appreciated that any misalignment between the CFA and the pixel
electrodes will cause cross-talk between the various color channels
of the image on the display. Alignment of CFA's with pixel
electrodes is more difficult in many types of electro-optic
displays than in liquid crystal displays, since in liquid crystal
displays the CFA and the pixel electrodes can be aligned optically
before the liquid crystal itself is introduced into the display,
whereas in, for example, electrophoretic or rotating bichromal
member displays, this approach is not possible since the normal
method for manufacturing such displays is to deposit the
electro-optic layer on to the CFA, and then to laminate the
combined electro-optic layer/CFA to a backplane containing the
pixel electrodes. Since an electrophoretic or rotating bichromal
member electro-optic layer is essentially opaque, the pixel
electrodes are not visible through the electro-optic layer during
the lamination procedure, thus precluding optical alignment of the
CFA with the pixel electrodes.
[0100] As already mentioned, the aforementioned 2003/0011560
describes ways for modifying the optical properties of
electrophoretic displays by incorporating an optical biasing
element in any one of several components of the display. It has now
been realized that this optical biasing element can serve as a
color filter for the display, provided that the optical biasing
element has varying colors in different areas of the display to
provide the necessary color filter elements.
[0101] The possible locations of such an optical biasing
element/color filter will vary with the type of electro-optic
display. For example, in an encapsulated electrophoretic display
the color filter may be provided (a) in the walls of the capsules;
(b) in the binder which surrounds the capsules; (c) in a lamination
adhesive used to secure the electrophoretic medium to a substrate
which forms the viewing surface of the display; or (d) in the front
electrode of the display. (Note that since an electrophoretic
medium is largely opaque, although the aforementioned 2003/0011560
describes optical biasing elements which lie "behind" the
electrophoretic medium, i.e., on the opposed side of the medium
from the viewing surface of the display, an optical biasing element
serving as a color filter needs to be located either within the
electrophoretic medium itself or between the electrophoretic medium
and the viewing surface of the display.) In a microcell
electrophoretic display, the color filter may be provided in the
front sheet which seals the microcells, or in locations
corresponding to (c) or (d) above. In a rotating bichromal member
display, the optical biasing element/color filter may be provided
in the polymeric matrix which surrounds the rotating members (this
matrix essentially corresponding to the binder of an encapsulated
electrophoretic display) or in locations (c) or (d) above.
[0102] FIG. 1 of the accompanying drawings is a schematic
cross-section through a preferred embodiment of the invention in
which a color filter is provided in the capsule walls of an
encapsulated electrophoretic display (generally designated 100).
The display 100 comprises an encapsulated electrophoretic medium
(generally designated 102) comprising a plurality of capsules 104,
104', 104'', each of which contains a suspending liquid 106 and
dispersed therein a plurality of positively charged black particles
108 and a plurality of negatively charged, white particles 116.
(The triangular shape of the particles 108 and the circular shapes
of the particles 116 are used purely by way of illustration to
enable the particles to be distinguished easily in the accompanying
drawings, and in no way correspond to the physical forms of the
actual particles, which are typically substantially spherical.)
[0103] The display 100 further comprises a common, transparent
front electrode 110, which forms a viewing surface through which an
observer views the display 100, and a plurality of discrete rear
electrodes 112, 112', 112'', each of which defines one pixel of the
display 100. For ease of illustration and comprehension, FIG. 1
shows only a single microcapsule forming the pixel defined by each
rear electrode, although in practice a large number (20 or more)
microcapsules are normally used for each pixel. The rear electrodes
112, 112', 112'' are mounted upon a substrate 114.
[0104] The display 100 is an RGB display with the red, green and
blue pixels arranged in cyclically repeating columns; it will be
appreciated that although only one electrode is shown in each
column in FIG. 1, in practice each column will contain a large
number of electrodes, the potential on each of which is
independently controlled by conventional active matrix drive
circuitry (not shown). There is no external color filter; instead,
an "internal" color filter is provided by dyeing the walls of the
capsules 104, 104', 104''. As indicated by the differences in
shading in FIG. 1, the walls of capsule 104 are dyed to transmit
red light, the walls of capsule 104' are dyed to transmit green
light and the walls of capsule 104'' are dyed to transmit blue
light.
[0105] FIG. 1 shows the display 100 with the rear electrodes 112
and 112'' held negative with respect to the common front electrode
110, but with the rear electrode 112' held positive with respect to
the common front electrode 110. Accordingly, in capsules 104 and
104'', the white particles 116 lie adjacent the viewing surface of
the display, so that these pixels appear red and blue respectively.
However, in capsule 104', the black particles 108 lie adjacent the
viewing surface of the display, so that this pixel appears
black.
[0106] It will be appreciated that displays of the type illustrated
in FIG. 1 do not need to use a RGB color scheme but could, for
example, use a CMY color scheme. Indeed, the latter may be
preferred for a reflective electro-optic medium, such as the
electrophoretic medium shown in FIG. 1, since a CMY color scheme
typically absorbs less of the incoming light and may thus produce
brighter colors.
[0107] Providing a CFA by dyeing the walls of microcapsules in an
electrophoretic display in the manner described above with
reference to FIG. 1 substantially eliminates the aforementioned
parallax problem in that there is no longer any separation between
the color filter array and the electro-optic layer of the display.
Similar advantages as regards parallax problems are achieved by
providing the CFA is the binder of an electrophoretic layer or in
the polymeric matrix of a rotating bichromal member layer.
[0108] A wide variety of techniques may be used to produce displays
with the internal CFA's of the present invention. These techniques
may be divided into two main groups, "preformed" CFA's, in which
the color is introduced into a display component before the
component is formed into a display, and "in situ" CFA's, in which
the CFA is formed in situ in the final display or in some
sub-assembly thereof. An example of a preformed CFA is dyeing (or
possibly treating with a pigment) capsules to form the red, green
and blue transmitting capsule walls as described above with
reference to FIG. 1, and then laying down the three types of
microcapsules in stripes aligned with the pixel electrodes to form
the display illustrated in FIG. 1. In general, however, in situ
CFA's may be more easily adaptable for mass production of displays.
It will be appreciated that, for example, in the display of FIG. 1,
all the capsules are identical apart from the staining of the
capsule walls, so that the display may be produced by coating a
uniform layer of capsules and then dyeing the capsule walls, and
optionally the surrounding binder. to produce the internal CFA.
Note that although such a process may result in a single capsule
extending across two adjacent electrodes, this has little or no
effect on the properties of the display, since it has been found
empirically that adjacent parts of the same capsule can have
differing optical states when exposed to differing electrical
fields.
[0109] In situ processes for the formation of CFA's may be divided
into two main types. In the first type, an external coloring agent
(for example, a dye or pigment, or a reagent which undergoes a
color-forming reaction with a component of the display in which the
CFA is to be formed) is applied imagewise to the display. For
example, capsule walls may be stained by a pigment or dye which may
be deposited using coating or printing techniques, such as
registered slot coating of colored stripes, spraying through a
mask, ink jet, offset, flexo-gravure or itaglio printing. In the
second type, color is developed in the component of the display in
which the CFA is to be formed using techniques based upon
photographic processes. For example, chemical additives may be
coated onto the capsule walls such that they resemble color film.
Then, by projecting a image of the desired CFA on to the capsule
coating, the capsules may be tinted to achieve proper coloration.
In using the term "photographic processes", we do not intend to
restrict the color-forming methods used to those based upon the
photosensitivity of silver halides, and indeed the use of
silver-based color formation will generally not be desirable since
there are substantial practical difficulties in removing silver and
silver halide from the CFA after the exposure. However, certain
color-forming reactions are known which are strongly sensitive to
wavelength, cf. U.S. Pat. No. 4,602,263, and such color-forming
reactions may be used to form the CFA's. For example, capsules
could be prepared in which the walls contain mixtures of red-,
green- and blue-dye forming compounds, these three compounds being
sensitive to three different wavelengths of radiation (typically
different infra-red wavelengths). After incorporation of the
capsules into the display, the relevant areas of the display are
exposed to radiation, preferably from lasers, of the different
wavelengths to turn these areas red, green and blue, thus forming
the CFA. Alternatively, the nanoparticle color-forming technology
described in U.S. Pat. Nos. 6,323,989 and 6,538,801 and in
copending application Ser. No. 10/065,617 (Publication No.
2003/0096113) may be used to produce the necessary color changes.
For example, this patent and application disclose tethered
nanoparticles which change color when the tether is broken by, for
example, ultra-violet or other radiation. By including tethered
nanoparticles into the capsule walls and then exposing the relevant
areas of the display to the tether-breaking radiation, the color
changes needed to form a CFA could be effected.
[0110] The in situ methods described above for formation of CFA's
may be carried out on an electro-optic layer on a double-release
film (see Section E below) rather than on an assembled display.
[0111] In situ formation of the CFA may be used to reduce or
eliminate the CFA alignment problem discussed above by using the
display itself to provide alignment marks needed for accurate
alignment of the CFA with the pixel electrodes. For example,
consider the aforementioned display containing capsules in which
the walls contain mixtures of red-, green- and blue-dye forming
compounds, these three compounds being sensitive to three different
wavelengths of radiation. Once such a display has been assembled
with an active matrix backplane, a portion of the backplane may be
activated to form an image on the display. For example, the
backplane might be activated such that the areas intended to be red
and green in the final CFA are dark in color, whereas the areas
intended to be blue are white. The resultant image can be used as
alignment marks to expose the white areas of the display to the
radiation needed to turn the capsules in these areas transmissive
of blue light. Next, for example, the blue and intended green areas
can be set dark, while the intended red areas are set white. It
will be apparent that the entire CFA may be produced in this manner
correctly aligned with the pixel electrodes.
[0112] In addition to the internal CFA's the displays of the
present invention my include any one or more of antireflective
coatings, microlens arrays, holographic filters, and brightness
enhancement films. It may also be desirable to incorporate a
barrier film onto the front of the display stack.
[0113] Part C--Color Filters with Non-Rectangular Pixels
[0114] Traditional CFA's used in liquid crystal displays are not
optimally suited for use in encapsulated electrophoretic displays.
An encapsulated electrophoretic medium tends to exhibit a slightly
degraded optical state near the boundaries between capsules (i.e.,
at the capsule walls) compared to the optical state exhibited near
the center of a capsule.
[0115] It has now been realized that these effects due to the
capsule walls can be minimized by careful choice of the shapes of
the pixels in the CFA; the pixel electrodes used to control the
display must of course match the shapes of the CFA pixels. Designs
which increase the likelihood that the capsule walls will lie in
the gaps between adjacent pixels, as compared with the (elongate,
non-square) rectangular pixels typically used in liquid crystal
displays are preferred. The CFA pixels may have the form of
hexagons (see FIG. 2A), squares (FIG. 2B) or triangles, preferably
equilateral triangles (FIG. 2C). In the accompanying monochrome
drawings, the colors of the various pixels have been indicated by
R, G and B for red, green and blue respectively. Although in theory
pentagonal pixels could be used, these and similar shapes, for
example octagonal pixels, are not favored because they do not close
pack on a surface. Hexagonal pixels are especially favored because
capsules ideally close pack in a hexagonal grid; square pixels are
also favorable.
[0116] Part D--Conductive Color Filters Between Electrodes
[0117] As already indicated, conventional CFA's developed for use
in liquid crystal displays comprise a layer of material colored in
an appropriate manner and disposed adjacent the viewing surface of
the display, "outside" the front electrode, i.e., between the front
electrode and the viewer. Such conventional CFA's are manufactured
on glass substrates and are formed from a plurality of films
(usually referred to as a "stack"), typically including a black
mask (usually formed of chromium), red, green and blue colored
photoresist layers and a conductive layer, typically formed of
indium-tin-oxide (ITO), which forms the front electrode of the
display.
[0118] Also as already indicated, certain types of electro-optic
display, especially encapsulated electrophoretic displays,
microcell displays and rotating bichromal member displays, have the
advantage that they can be formed on flexible substrates, such as
plastic films of poly(ethylene terephthalate) or poly(ethylene
naphthalate). While it is technically possible to use conventional
CFA's of the type described in the preceding paragraph with
electro-optic displays formed on plastic films, such conventional
CFA's are not well adapted for such use. A black chromium mask
poses difficulties on plastic substrates, since this metal is
typically patterned using etchants that tend to harm plastics;
accordingly, it is desirable to eliminate the black mask.
[0119] It is also desirable, the present inventors have realized,
if an "internal" CFA as described in Part B hereof is not employed,
to interchange the order of the colored layers and the conductive
layer. Such an interchange facilitates manufacturing, since plastic
films coated with conductive materials such as ITO are readily
available commercially and can be used as starting materials in the
process of manufacturing the CFA.
[0120] However, such an interchange necessarily places the colored
layers between the electrodes of the display and, at any given
operating voltage between the electrodes, reduces the voltage
across the electro-optic medium itself, since the voltage across
the electro-optic medium is equal to the operating voltage minus
the voltage drop across the colored layers. The reduced voltage
across the electro-optic medium typically slows the switching rate
of the medium. Although it is possible to compensate for the
reduced voltage across the electro-optic medium by increasing the
operating voltage, this is generally undesirable since it increases
the energy consumption of the display and may require modification
of electrical circuitry to produce and/or handle the increased
voltage. Furthermore, the electrical resistivity of many commercial
photoresists is so high that a very large, and often unacceptable,
increase in operating voltage would be required to compensate for
the presence of the colored layers between the electrodes.
[0121] Accordingly, it is desirable to increase the conductivity of
the material used to form the colored layers so that the resistance
of the colored layers does not substantially exceed that of the
electro-optic layer, and indeed is desirably less than that of the
electro-optic layer. Given the low conductivity of most types of
electro-optic media, the colored layers should have a volume
resistivity not greater than about 10.sup.10, and preferably not
greater than about 10.sup.9 ohm cm. The colored layers may be made
more conductive by doping with conductive nanoparticles, for
example nanoparticles of silver, gold, aluminum, platinum or
carbon; although these materials are opaque in bulk form, they can
be made into nanoparticles small enough (typically less than 10 nm
in diameter) that they do not substantially scatter light, and thus
do not interfere with the optical problems of the colored layers.
Other organic or inorganic pigments that have favorable electrical
and optical properties can also be used, as can conductive polymers
and other materials, although it is of course necessary to take
account of the overall optical properties of the display after
addition of these materials. The techniques described in the
aforementioned 2003/0011867 may be used to control the conductivity
of the colored layers. Also, since the colored layers are disposed
between the electrodes of the electro-optic display, the electrical
characteristics, and the variation of such characteristics with
environmental parameters such as temperature, may affect the
operating characteristics of the display in essentially the same
way as any other layer, for example a lamination adhesive, disposed
between the electrodes of the display. The reader is referred to
the aforementioned 2003/0025855 for a detailed summary of the
desirable characteristics of lamination adhesives used in
electro-optic displays; most of these characteristics are directly
applicable to colored layers used as internal color filter arrays
in accordance with the present invention.
[0122] Part E--Double Release Film
[0123] As already indicated, the methods used in liquid crystal
displays for incorporation of CFA's are not well adapted for use
with other types of electro-optic media. In particular, as already
indicated, the techniques used to assemble liquid crystal displays
do not transfer well for use with other types of electro-optic
media. In the conventional process for assembly of liquid crystal
displays, a front assembly is formed comprising a substrate, color
filter layers and a conductive layer, and this front assembly is
aligned with and secured to a rear assembly comprising pixel
electrodes and associated circuitry, a narrow cell gap being
maintained between the two assemblies by the use of spacers. This
cell gap is then evacuated and filled with the liquid crystal
material itself by dipping the combined assemblies into a bath of
the liquid crystal material.
[0124] Although in theory one could form an encapsulated
electrophoretic display in a similar manner, in practice this
assembly technique is highly undesirable because when injected into
a narrow cell gap, the capsules will not pack closely, as is
desirable for optimum optical performance of the resultant display.
Instead, it is desirable to coat or print the encapsulated
electrophoretic material combined with a polymeric binder in the
form of a slurry on to a substrate and then to dry and/or cure the
coated or printed layer to form the final layer of electrophoretic
medium. Although the coating or printing step can be performed
directly on the CFA, there may be problems with some CFA's in
achieving proper packing of the capsules and/or sufficient adhesion
of the capsules to the CFA.
[0125] In one aspect of this invention, the electrophoretic display
material, or other solid electro-optic material, is coated,
printed, or otherwise deposited on to a release sheet for later
transfer to a CFA or other substrate, for example a backplane (see
also the aforementioned copending application Ser. No. 10/249,957
and the corresponding International Application PCT/US03/16433).
The display material is desirably coated such that there is a thin
adhesive layer between the display material and the release sheet;
a second adhesive layer may be provided on the opposed side of the
display material capsules. To protect the coated composite material
during handling, it is desirable to apply a second release sheet
over the second adhesive layer.
[0126] A preferred double release sheet (generally designated 300)
of the present invention is shown in FIG. 3 of the accompanying
drawings. This sheet 300 comprises a central layer 302 of
electro-optic material, specifically in FIG. 3 a layer comprising
capsules 304 in a polymeric binder 306. The capsules 304 may be
similar to those described above with reference to FIG. 1. The
sheet 300 further comprises a first adhesive layer 308, a first
release sheet 310 covering the first adhesive layer 308, a second
adhesive layer 312 disposed on the opposed side of the layer 302
from the first adhesive layer 308, and a second release sheet 314
covering the second adhesive layer 312.
[0127] The sheet 300 may be formed by first coating a the release
sheet 310 with a layer of adhesive which is then dried or cured to
form the first adhesive layer 308. Next, a mixture of the capsules
304 and binder 306 is printed or otherwise deposited on the first
adhesive layer 308, and then the mixture is dried or cured to form
a coherent layer 302. Finally, a layer of adhesive is deposited
over the layer 302, dried or cured to form the second adhesive
layer 312, and covered by the second release sheet 314.
[0128] It will be apparent to those skilled in coating technology
that this sequence of operations used to form the sheet 300 is well
adapted for continuous production and that, by careful choice of
materials and process conditions, it may be possible to carry out
the entire sequence of operations in a single pass through
conventional roll-to-roll coating apparatus.
[0129] To assemble a display using a double release film such as
the film 300, one release sheet (typically that on to which the
electro-optic material was coated) is peeled away, and the
remaining layers of the double release film are attached to a CFA
or other front substrate using, for example a thermal, radiation,
or chemically based lamination process. Typically, the CFA or front
substrate will include a conductive layer which will form the front
electrode of the final display. The CFA and the conductive layer
may be in either order, but for reasons already discussed, it is
preferred that the CFA lie between the conductive layer and the
electro-optic layer. The front substrate may include additional
layers, such as a UV filter or a protective layer intended to
protect the CFA and/or the conductive layer from mechanical damage.
Thereafter, the other release sheet is peeled away, thereby
exposing the second adhesive layer, which is used to attach the
CFA/electro-optic material coating assembly to a backplane. Again,
a thermal, radiation, or chemically based lamination process may be
used. It will be appreciated that the order of the two laminations
described is essentially arbitrary and could be reversed, although
it practice it is almost always more convenient to laminate the
double release film to the CFA or other front substrate first, and
thereafter to laminate the resulting front subassembly to the
backplane.
[0130] As discussed above, in all CFA-based electro-optic displays,
it is desirable to make the distance from the color filter back
surface to the optically active layer as small as possible. This
minimizes optical losses and mitigates parallax problems. Thus, the
lamination adhesive on the front of the display and the capsule
wall should both be as thin as possible. It is conceivable that
these layers may be reduced to thicknesses approaching 1 .mu.m.
Furthermore, it is desirable for the capsules to deform during
coating and drying such that they present an effectively flat
surface against the color filter array. This will help minimize the
chance that light entering through one color pixel leaves through
an adjacent (differently colored) pixel after diffusely reflecting
form the optically active display material. Moreover, it is
desirable to match the index of refraction of all films used in
constructing the display stack.
[0131] Various display assembly techniques may be employed,
including but not limited to wet bond or hot melt lamination
processes. In some applications, it is preferable to use
repositionable adhesives or air soluble adhesives. In other
applications, it is preferable to use radiation, thermal, or
chemically curing adhesives. In each assembly technique, however,
it is essential to align the CFA sub-pixels to the TFT array
electronics on the backplane. In order to achieve high resolution
alignment (aligned within better than, say, 10-20 .mu.m), one can
use a standard optical alignment system that aligns fiducial marks
on the backplane to fiducial marks on the CFA. Once the fiducials
on these two substrates are aligned, they are brought together
without introducing misalignment and the lamination process takes
place. The lamination process may be based on 1. mechanical contact
(i.e. pressure sensitive adhesives, either repositionable or
otherwise), 2. thermal effects (e.g. hot melt, wet bond, vacuum
lamination, etc.), or 3. radiation-based methods (e.g. UV
cure).
[0132] It will readily be apparent to those skilled in the
technology of electro-optic displays that numerous changes and
modifications may be made in the process described for forming an
electro-optic display from a double release film. For example, in
each of the two laminations described, only one of the two
components being laminated together need carry an adhesive layer
and which component carries the adhesive layer is essentially a
matter of process engineering. Thus, in certain cases, it may be
convenient to omit one or both of the adhesive layers 308 and 312
from the sheet 300 and instead to place a similar adhesive layer on
the CFA, backplane or other substrate being used in the lamination.
Also, in some cases it may be possible to omit one release sheet
where this would not result in an adhesive layer being exposed to
contamination for an extended period. For example, if a double
release sheet such as the sheet 300 were formed on a continuous
production line and laminated to a color filter array or other
substrate a short time after the second adhesive layer 312 was
formed, application of the second release sheet 314 could be
omitted and the second adhesive layer used to laminate the sheet
300 to the color filter array.
[0133] It will also be apparent to those skilled in the technology
of electro-optic displays that the double release sheet of the
present invention may be regarded as a modified form of the front
plane laminate described in the aforementioned copending
application Ser. No. 10/249,957 and the corresponding International
Application PCT/US03/16433. This front plane laminate comprises, in
order, a light-transmissive electrically-conductive layer
(typically carried on a polymeric film substrate), a layer of a
solid electro-optic medium in electrical contact with the
electrically-conductive layer, an adhesive layer, and a release
sheet. The double release sheet of the present invention is
essentially a modification of such a front plane laminate derived
by replacing the electrically-conductive layer thereof with a
second release sheet, and optionally an associated second adhesive
layer. Accordingly, the double release sheet of the present
invention may include any of the optional features of the front
plane laminate described in the aforementioned copending
application Ser. No. 10/249,957 and the corresponding International
Application PCT/US03/16433. For example, the double release sheet
may have any one or more of (a) a conductive layer on one of both
of its release sheets to permit testing of the electro-optic medium
(see FIGS. 2-7 and the associated description of application Ser.
No. 10/249,957); (b) a conductor extending through the layer of
electro-optic medium (see FIGS. 9 and 10 and the associated
description of application Ser. No. 10/249,957); (c) an aperture
extending through the layer of electro-optic medium, which aperture
may later be filled with a conductive material to provide a
conductor as mentioned in (b) (see FIGS. 8 and 18 and the
associated description of application Ser. No. 10/249,957); (d) an
edge seal (see FIGS. 11-17, 19 and 20 and the associated
description of application Ser. No. 10/249,957); and (e) tabs in
which the release sheet extends beyond the layer of electro-optic
material to facilitate removal of the release sheet (cf. FIGS. 21
and 22 and the associated description of application Ser. No.
10/249,957).
[0134] Edge seals around the perimeter of a display are desirable
for display lifetime and ruggedness reasons. The edge seal material
may include UV, thermal, or chemically cured adhesives that are
compatible with the encapsulated electrophoretic display material.
The adhesive may be deposited around the edge of the display using
printing processes, automated pipette dispensing techniques, or
other similar techniques known by those skilled in the art. In a
traditional liquid crystal manufacturing process, this seal
material is cured before the liquid crystal is filled into the cell
gap. This is unacceptable for an encapsulated display because such
an edge seal locks voids (e.g. air gaps) into the laminated
display. There are several routes to eliminate this problem. First,
after lamination is complete one may fill the edge seal material
into the thin gap around the edge of the display. Second, one may
only position edge seal material around some fraction of the
display edges, perform the lamination, then fill in the remaining
edge seal material. These and other edge sealing techniques are
described in the aforementioned copending application Ser. No.
10/249,957. However, the double release film of the present
invention allows an additional method for providing an edge seal,
namely extending the adhesive layers lying on opposed sides of the
electro-optic layer beyond the edge of the electro-optic layer, but
not beyond the edge of the display. FIG. 4 illustrates an edge seal
formed in this manner. FIG. 4 illustrates a display (generally
designated 400) formed from a double release film, similar to as
the film 300 shown in FIG. 3, by the double lamination process
already described. The final display 400 comprises the
electro-optic layer 302, a backplane 316 and a CFA 318. The two
adhesive layers 308' and 310' extend beyond the edge of the
electro-optic layer, but not beyond the edge of the display, so
that after the two laminations, the two adhesive layers become
bonded together to form an edge seal, designated 320. Edge sealing
is often essential in providing a rugged electro-optic display
which can withstand wide variations in environmental conditions and
it is much simpler to use the existing adhesive layers in this
manner to form the required seal, rather than introducing a
separate seal material around the outer edge of the display.
[0135] Part F--Production of Color Filter Arrays by Photographic
Imaging
[0136] In another aspect this invention provides a process for
preparing a color filter for use in an electro-optic display. The
process comprises imaging a color filter pattern on to a
photosensitive film, processing the film (if necessary) to reveal
the image, then depositing a conductive layer on to the
photosensitive film to act as an electrode. The term
"photosensitive film" as used herein is not restricted to films
which rely upon silver halide chemistry, nor is it restricted to
films which are sensitive to visible wavelengths, but includes
films sensitive to electromagnetic radiation outside the visible
range. If the photosensitive film used is a conventional silver
halide film comprising a silver halide emulsion of a substrate, the
conductive layer will typically be deposited on the emulsion side
of the film. The result is a flexible color filter that can be used
as the top plane of an electro-optic display.
[0137] The need for preparing CFA's on flexible substrates, and the
problems encountered in attempting to modify the conventional
processes originally developed for forming CFA's on glass for use
with liquid crystal displays have already been discussed above. As
already noted, such processes are not well suited to flexible
substrates, and the cost of production is also high, comparable to
the cost of an amorphous silicon TFT backplane on quartz.
[0138] In one embodiment of the invention the image is transferred
by contact printing an existing color filter array on glass on to
the photographic film. The film is placed on a flat, non-reflective
surface with the emulsion side up. The color filter is then placed
dye side down on top of the film. The film is exposed with a light
source through the color filter. This method requires an existing
color filter to act as a master.
[0139] Another embodiment of the invention for producing a filter
uses a camera to image a pattern onto the film. The pattern could
be an existing color filter, in which case it would be backlit. In
this case, the camera would be set up to reproduce the image 1:1 on
the film. Alternatively, the master could be a large (poster-sized)
reflective object, e.g. a high-quality print on paper. In this
case, the master would be front-lit, and the camera would be set up
to reduce the image to the appropriate size on the film. This
method has the advantage of allowing the rapid construction of a
CFA from a macroscopic pattern, making it possible to change such
parameters as filter density, size of black mask, etc.
[0140] Another embodiment of the invention uses a linear array of
emissive elements translated across the film in a direction
perpendicular to the long axis of the linear array to produce a
pattern of stripes on the film. If a black mask is required in this
embodiment, the emissive elements could be toggled on and off at
the appropriate points to generate dark regions on the film.
[0141] In any of the above embodiments, the overall color cast of
the filter can be reduced (or enhanced) by applying an appropriate
color filter to the illumination source, or by placing filters over
the lens of the camera (when used). The density of the filter can
be adjusted by increasing or decreasing the film exposure. If the
film does not accurately reproduce one or more of the colors in the
filter (which is likely), then it will be necessary to adjust the
colors in the master. For any film, there will be an inverse
transform governed by the spectral response function of the
emulsion that will determine the proper colors to use in the master
to get the desired colors in the final display.
[0142] To complete the construction of a CFA, after one of the
processes described above, the film may be processed using the
appropriate chemical process. Then, a thin film of indium tin oxide
(ITO) or other conductive material can be evaporated on to the
emulsion side of the film. Alternately, a transparent conductive
polymer, e.g. Baytron (Registered Trade Mark), could be coated on
to this surface.
[0143] The present invention permits the inexpensive production of
CFA's on flexible substrates. Furthermore, using the reduction
technique described above, CFA's of arbitrary geometry and color
can be produced using very simple and easily available tools,
allowing for rapid prototyping of filter modifications.
[0144] Part G--Miscellaneous Processes for Production of Color
Filter Arrays
[0145] This invention relates to various methods for integrating
electrophoretic display materials into a CFA based electrophoretic
display. The manufacturing strategies of this invention are
markedly different from those used in the manufacture of liquid
crystal displays.
[0146] In a first aspect of the invention, an encapsulated
electrophoretic display material is coated directly onto the CFA
and the coated CFA is subsequently laminated to a backplane
containing pixel electrodes.
[0147] The deposition of the encapsulated electrophoretic display
material (i.e., a plurality of capsules) may be effected by slot
die, meniscus, curtain, or other coating methods directly on to the
color filter array. The color filter array may be comprised of a
glass or other optically clear substrate (including polymeric
substrates and thin, "flexible" glass), a plurality of red, green,
and blue color stripes, and a transparent conductor. In some
embodiments, the color filter array includes a "black mask", which
is a grid of opaque lines that are designed to conceal select
undesirable locations on the assembled electronic display. In still
other embodiments, the color filter array is comprised of a
plurality of red, green, and blue pixels, instead of stripes. The
black mask may be situated above or below the color stripes or
pixels. In another embodiment, the color filter may include stripes
or pixels that are optically clear instead of colored.
[0148] It is important to ensure that the encapsulated
electrophoretic display material is in intimate contact with the
CFA in order to ensure adequate optical coupling between the
display material and the color filter. At a minimum, it is required
that the distance between the color filter surface and the front
surface of the optically active material in the encapsulated
electrophoretic display material be substantially smaller than the
smallest dimensions of the pixels of the display. For example, for
pixels that are 100 .mu.m wide, one should ensure that the distance
from the surface of the color filter stripe to the front surface of
the optically active material be smaller than, say 10 .mu.m. This
gap may be filled with lamination adhesive, a polymeric binder,
capsule wall material, thin films above the tinted regions of the
color filter, and surface treatments applied to the color
filter.
[0149] A further aspect of the invention relates to methods for
generating regular surface energy patterns on the CFA to influence
the packing density of the capsules on the CFA. According to this
aspect of the invention, a surface treatment may be applied to a
CFA in order to influence the packing of capsules that are
subsequently coated directly onto the surface treated CFA.
Generally, it is desirable to design the color filter such that
there exists a regular surface energy pattern over the surface of
the color filter in contact with the encapsulated electrophoretic
display material. This helps to ensure that the capsules pack in a
way that improves the optical performance of the display.
[0150] Alternatively or in addition to such generation of regular
surface energy patterns, the surface may be prepared in such a way
as to uniformly increase or decrease wettability of this surface.
This may be effected by applying an adhesion promoter or suitable
surface chemistry, such as 1-propanamine, 3-(trimethoxysilyl) (more
systematically named 3-aminopropyl-trimethoxysilane),
3-aminopropyldimethyl-ethoxysilane, hexamethyldisilizane or other
such materials. Similar surface treatments may also be applied to
the surface of the backplane (or other surfaces where variation of
wettability is desired, as described below) in order to enhance
display properties.
[0151] In a particular embodiment of this invention, the CFA may be
constructed as follows: 1. pattern red, green, and blue stripes on
a substrate, 2. pattern a black mask above the color stripes (the
black mask is conventionally situated below the color stripes), and
3. treat the black mask surface such that it becomes non-wetting
and the color stripes wetting to the encapsulated electrophoretic
display material. Representative surface treatments include
octadecatrichlorosilane, a spectrum of other silane and thiol based
chemicals, various polytetrafluoroethylene agents, and other
materials known to those skilled in the art. The black mask may be
made receptive to these agents by including a surface treatment
receptive film on the topmost surface of the black mask. For
example, a thin gold film may be deposited as the topmost layer of
the black mask, and alkanethiols may be deposited onto the gold.
The thiol material may be engineered to have a markedly different
surface energy than the color stripes, thereby achieving the
desired effect.
[0152] A further aspect of the invention relates to methods for
using patterned surface treatments to influence the packing density
of the coated capsules on a continuous electrode. In this aspect, a
patterned surface treatment is deposited onto a continuous
electrode to influence the packing of subsequently deposited
capsules. A patterned surface treatment may be applied onto the
continuous electrode on top of the color filter by printing
techniques including microcontact, offset, intaglio, flexo-gravure,
or other printing techniques known to those skilled in the art.
This is an ideal application for printing, as perfect yield on the
local scale is not required; local defects are not catastrophic,
since proper packing of the capsules on the long range will tend to
organize the capsules correctly despite local defects.
[0153] In another aspect, this invention relates to the use of
monodisperse capsules (capsules that are substantially uniform in
size, for example in which at least about 95 percent of the
capsules have diameters which do not differ by more than about 20
percent, and preferably by not more than about 10 percent, from the
average diameter) in electrophoretic displays. The use of such
monodisperse capsules is especially desirable in conjunction with
the surface treatment aspects of this invention already discussed,
since with polydisperse capsules, regularly patterned surface
treatments become far less effective at reordering the deposited
film into a regular pattern, whether these surface treatments are
deposited onto a color filter black mask or onto a continuous
electrode.
[0154] These aspects of the present invention all serve to improve
the optical performance of a encapsulated electrophoretic display
by influencing the packing of capsules coated down onto a front
electrode. The surface treatments used to accomplish this task are
either built into the color filter black mask, or are printed
directly onto the continuous electrode in contact with the display
material.
[0155] Another aspect of the present invention relates to novel
surface treatments that enable filling a cell gap in between a CFA
and a backplane with encapsulated electrophoretic display material.
The novel surface treatment technique of the present invention
enables the use of more traditional liquid display manufacturing
techniques. In this aspect of the invention, a surface agent that
promotes capsule wetting is applied to the CFA, and a surface agent
that promotes capsule dewetting is applied to the backplane. Just
as in traditional liquid crystal manufacture, the color filter
array and the backplane are assembled with precision spacers in
between them, and the edges are sealed with epoxy or other
edge-sealing agent. The encapsulated electrophoretic display
material in then drawn into the space between the color filter
array and the backplane using pump, vacuum, or other similar
technique known to those skilled in the art. However, because of
the presence of the surface treatments on the CFA and the
backplane, the capsules preferentially pack tightly against the
front surface of the display (the color filter surface), and tend
to dewet and move away from the backplane surface. This invention
ensures that the encapsulated electrophoretic display material
packs against the front viewing surface, which provides for
markedly improved optical performance compared to techniques in
which the material packs against the backplane, or packs with no
preference for either the CFA or the backplane surface. Surface
forces are used to draw capsules to the front electrode, but other
forces including gravitational, electrophoretic, and magnetic may
be employed to accomplish this task.
[0156] This aspect of the present invention improves the optical
performance of the display by influencing the packing of capsules
injected into a cell gap formed between a front electrode and a
backplane. It enables the use of traditional display filling
technologies with encapsulated electrophoretic displays.
[0157] The electrophoretic media used in various aspects of the
present invention may be of any of the types described in the
aforementioned E Ink and MIT patents and applications, to which the
reader is referred for further information.
[0158] Those skilled in the part of electro-optic displays will
appreciate that numerous changes, improvements and modifications
can be made in the preferred embodiments of the invention already
described without departing from the scope of the invention.
Accordingly, the whole of the foregoing description is intended to
be construed in an illustrative and not in a limitative sense.
* * * * *