HK40087310A - Porous backplane for electro-optic display - Google Patents

Description

Permeable backplate for electro-optic displays

Related applications

This application is a divisional application of the application filed on March 27, 2018, with application number 201880016236.0 and invention title "Permeable Backplate for Electro-optic Display".

This application claims priority to U.S. Provisional Application No. 62/477,505, filed March 28, 2017, the entire contents of which are incorporated herein by reference.

Technical Field

This invention relates to backplates for electro-optic displays, particularly electrophoretic displays.

Summary of the Invention

The present invention provides a backplate for an electro-optic display, the backplate comprising at least one electrode disposed on a substrate, wherein the substrate or the electrode, or both, are liquid-permeable. The backplate may be, for example, water-permeable, and the substrate may be formed, for example, from cellulose or a similar hydrophilic polymer.

In the backplate of this invention, the electrodes ideally have a type of liquid that is permeable to the same liquid as the substrate, so that the electrodes do not form liquid-impermeable areas on the substrate. For example, when the liquid is water (or an aqueous solution), the electrodes can be formed of hydrophilic carbon black, which can be coated or screen-printed onto the substrate.

The present invention also provides an electro-optic display comprising: an electro-optic material layer comprising a continuous phase, the continuous phase comprising a liquid; and a backplate comprising at least one (backplate) electrode in contact with the electro-optic material layer and a substrate permeable to the liquid. The electro-optic material may be an electrophoretic material comprising a plurality of charged particles disposed in a fluid and capable of moving through the fluid under the influence of an electric field. The charged particles and fluid may be confined within a plurality of capsules or microunits. Alternatively, the charged particles and fluid may be presented as a plurality of discrete droplets surrounded by a continuous phase comprising a polymeric material.

The electro-optic display of the present invention may further include at least one (front) electrode that contacts the opposite side of the back electrode and the electro-optic material layer, and may further include a front substrate arranged to support the front electrode. Alternatively, the display may include a front substrate without a front electrode. At least one of the back electrode and the front electrode (usually the latter) should be light-transmitting (the term is used herein to mean that the layer transmits sufficient light to allow an observer to observe changes in the display state of the electro-optic medium through that layer), and if the front electrode is light-transmitting, any present front substrate should also be light-transmitting.

The present invention also provides a first process for forming an electro-optic display, the process comprising:

Provide an anterior substrate;

An electro-optic material layer comprising liquid is formed on the front substrate;

The exposed surface of the electro-optic material layer is brought into contact with a backplate comprising at least one electrode disposed on a substrate, the substrate being permeable to the liquid; and

Subsequently, conditions are applied to the combined assembly, including the front substrate, the electro-optic material layer, and the backplate, to effectively allow the liquid to diffuse through the permeable substrate and be removed from the combined assembly, thereby forming the electro-optic material layer as a coherent layer that anchors the front substrate and the backplate to each other.

The present invention also provides a second process for forming an electro-optic display, the process comprising:

Provide a front substrate having multiple cavities therein;

Electro-optic materials are arranged inside the cavity;

A sealing material layer is formed on top of the electro-optic material inside the cavity; the sealing material includes a liquid.

The exposed surface of the sealing material is brought into contact with a backplate comprising at least one electrode disposed on a substrate, the substrate being permeable to the liquid; and

Subsequently, conditions are applied to the combined assembly, which includes a front substrate, electro-optic material, sealing material, and backplate, to effectively allow liquid to diffuse through the permeable substrate and be removed from the combined assembly, thereby forming a coherent layer that secures the front substrate and backplate to each other.

The first and second processes of the present invention may include, after the removal of the liquid, an additional step of cutting the backplate substrate and the electrode into pieces to form a plurality of discrete electrodes.

Attached Figure Description

Figure 1 of the accompanying drawings is a schematic cross-section of the first step in the first process of the present invention and shows the electro-optic material layer formed on the front substrate.

Figure 2 is a schematic cross-section similar to that of Figure 1, but showing a schematic cross-section of the second step of the first process, in which the backplate contacts the exposed surface of the electro-optic layer.

Figure 3 is a schematic cross-section showing how the processes of Figures 1 and 2 can be performed on a roll-to-roll basis.

Figure 4 is a schematic cross-section similar to Figures 1 and 2, but showing a schematic cross-section of the first step of the second process of the present invention, in which electro-optic material is filled into a cavity in the substrate and a sealing material is applied.

Figure 5 is a schematic cross-section similar to that of Figure 3, but showing a schematic cross-section of the second step of the second process of the present invention, in which the backplate contacts the exposed surface of the sealing material.

Detailed Implementation

As indicated above, the present invention provides a backplate for an electro-optic display and a process for manufacturing such a display, the backplate comprising at least one electrode disposed on a liquid-permeable substrate, the electro-optic display comprising such a backplate.

This invention is designed to solve or mitigate certain problems that have long been encountered in the production of solid-state electro-optic displays, a term used herein to refer to a display in which the electro-optic material is solid in the sense that it has a solid outer surface, although the material may and often has internal spaces filled with liquid or gas. Therefore, the term "solid-state electro-optic display" includes rotating dual-color component displays, encapsulated electrophoretic displays, microcell electrophoretic displays, and encapsulated liquid crystal displays.

Extensive literature exists regarding such solid-state electro-optic displays and the processes used to manufacture them. For example, rotating dual-color component type displays are described in U.S. Patent 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 dual-color sphere" display, the term "rotating dual-color component" is preferred as it is more precise because, in some of the aforementioned patents, the rotating component is not spherical). Such displays utilize numerous small bodies (typically spherical or cylindrical) and internal dipoles, each body comprising two or more sections with different optical properties. These bodies are suspended within liquid-filled cavities within a matrix, allowing the bodies to rotate freely. The appearance of the display is changed by applying an electric field to the display, thereby rotating the subject to various positions and changing which part of the subject is seen through the observation surface.

Electrowetting displays are described in Hayes, R.A. et al., “Video-Speed Electronic Paper Based on Electrowetting”, Nature, 425, 383-385 (2003) and U.S. Patent No. 7,420,549.

Encapsulated and micro-unit electrophoretic and other electro-optic media are described in numerous patents and applications assigned to or in the name of MIT, E Ink, Inc., E Ink California LLC, and related companies. Encapsulated electrophoretic media comprise a plurality of small capsules, each capsule comprising an internal phase and a capsule wall surrounding the internal phase, wherein the internal phase contains electrophoretically mobile particles in a fluid medium. Typically, these capsules are held in a polymeric binder to form a coherent layer located between two electrodes. Typically, one of the electrodes is light-transmitting, i.e., the electrode transmits sufficient light to allow an observer looking through the electrode to observe changes in the displayed state of the electro-optic medium. In micro-unit electrophoretic displays, charged particles and fluid are not encapsulated within microcapsules but are held within multiple cavities formed within a carrier medium (typically a polymer film). Techniques described in these patents and applications include:

(a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814;

(b) Encapsulation, adhesives, and encapsulation processes; see, for example, U.S. Patents 6,922,276 and 7,411,719;

(c) Microunit structures, wall materials, and methods of forming microunits; see, for example, U.S. Patent Nos. 7,072,095 and 9,279,906;

(d) Methods for filling and sealing microcells; see, for example, U.S. Patent Nos. 7,144,942 and 7,715,088;

(e) Thin films and sub-assemblies comprising electro-optic materials; see, for example, U.S. Patent Nos. 6,825,829, 6,982,178, 7,112,114, 7,158,282, 7,236,292, 7,443,571, 7,513,813, 7,561,324, 7,636,191, 7,649,666, 7,728,811, 7,729,039, 7,791,782, 7,839,564, 7,843,621, 7,843,624, and 8,034. 209, 8,068,272, 8,077,381, 8,177,942, 8,390,301, 8,482,835, 8,786,929, 8,830,553, 8,854,721, 9,075,280, and 9,238,340, and U.S. Patent Application Publications Nos. 2007/0237962, 2009/0109519, 2009/0168067, 2011/0164301, 2014/0115884, and 2014/0340738;

(f) Backplanes, adhesive layers, and other auxiliary layers used in displays, and methods thereof; see, for example, U.S. Patent Nos. D485,294, 6,124,851, 6,130,773, 6,177,921, 6,232,950, 6,252,564, 6,312,304, 6,312,971, 6,376,828, 6,392,786, 6,413,790, 6,422,687, 6,445,374, 6,480,182, 6,498,114, 6,506,438, 6,518,949, 6,521,489, 6,535,197, 6,545,291, and 6,639,578. 6,657,772, 6,664,944, 6,680,725, 6,683,333, 6,724,519, 6,750,473, 6,816,147, 6,819,471, 6,825,068, 6,831,769, 6,842,167, 6,842,279, 6,84 2,657, 6,865,010, 6,873,452, 6,909,532, 6,967,640, 6,980,196, 7,012,735, 7,030,412, 7,075,703, 7,106,296, 7,110,163, 7,116,318, 7,148,12 8、7,167,155、7,173,752、7,176,880、7,190,008、7,206,119、7,223,672、7,230,751、7,256,766、7,259,744、7,280,094、7,301,693、7,304,780、7, 327,511, 7,347,957, 7,349,148, 7,352,353, 7,365,394, 7,365,733, 7,382,363, 7,388,572, 7,401,758, 7,442,587, 7,492,497, 7,535,624, 7,551, 346, 7,554,712, 7,583,427, 7,598,173, 7,605,799, 7,636,191, 7,649,674, 7,667,886, 7,672,040, 7,688,497, 7,733,335, 7,785,988, 7,830,592, 7,843,626, 7,859,637, 7,880,958, 7,893,435, 7,898,717, 7,905,977, 7,957,053, 7,986,450, 8,009,344, 8,027,081, 8,049,947, 8,072,675, 8,077 ,141、8,089,453、8,120,836、8,159,636、8,208,193、8,237,892、8,238,021、8,362,488、8,373,211、8,389,381、8,395,836、8,437,069、8,441,414 8,456,589, 8,498,042, 8,514,168, 8,547,628, 8,576,162, 8,610,988, 8,714,780, 8,728,266, 8,743,077, 8,754,859, 8,797,258, 8,797,633, 8,7 97,636, 8,830,560, 8,891,155, 8,969,886, 9,147,364, 9,025,234, 9,025,238, 9,030,374, 9,140,952, 9,152,003, 9,152,004, 9,201,279, 9,223,164, 9,285,648, and 9,310,661; and U.S. Patent Application Publications Nos. 2002/0060321, 2004/0008179, 2004/0085619, 2004/0105036, 2004/0112525, 2005/0122306, and 2005/012256. 3. 2006/0215106, 2006/0255322, 2007/0052757, 2007/0097489, 2007/0109219, 2008/0061300, 2008/0149271, 2009/0122389, 2009/0315044, 2010/ 0177396, 2011/0140744, 2011/0187683, 2011/0187689, 2011/0292319, 2013/0250397, 2013/0278900, 2014/0078024, 2014/0139501, 2014/0192000 Patents filed in the United States and Europe, including 2014/0210701, 2014/0300837, 2014/0368753, 2014/0376164, 2015/0171112, 2015/0205178, 2015/0226986, 2015/0227018, 2015/0228666, 2015/0261057, 2015/0356927, 2015/0378235, 2016/077375, 2016/0103380 and 2016/0187759; and International Application Publication No. WO 00/38000; European Patents Nos. 1,099,207B1 and 1,145,072B1;

(g) Color formation and color adjustment; see, for example, U.S. Patent Nos. 7,075,502 and 7,839,564;

(h) A method for driving a display; see, for example, U.S. Patent Nos. 7,012,600 and 7,453,445;

(i) Applications of displays; see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348; and

(j) Non-electrophoretic displays, as described in U.S. Patent No. 6,241,921 and U.S. Patent Application Publication No. 2015/0277160; and applications of packaging and microcell technologies other than displays; see, for example, U.S. Patent No. 7,615,325; and U.S. Patent Application Publication Nos. 2015/0005720 and 2016/0012710.

Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thus producing so-called polymer-dispersed electrophoretic displays, wherein the electrophoretic medium comprises a plurality of discrete electrophoretic fluid droplets and a continuous phase of polymeric material, and the discrete droplets of electrophoretic fluid in such polymer-dispersed electrophoretic displays can be regarded as capsules or microcapsules even without a discrete membrane associated with each individual droplet; see, for example, the aforementioned U.S. Patent No. 6,866,760. Therefore, for the purposes of this application, such polymer-dispersed electrophoretic media are considered as a subclass of encapsulated electrophoretic media.

Electro-optic displays typically comprise an electro-optic material layer and at least two other layers disposed on opposite sides of the electro-optic material, one of which is an electrode layer. In most such displays, both layers are electrode layers, and one or both electrode layers are patterned to define pixels of the display. For example, one electrode layer may be patterned as elongated row electrodes, while the other electrode layer is patterned as elongated column electrodes extending perpendicularly to the row electrodes, with pixels defined by the intersections of the row and column electrodes. Alternatively, and more commonly, one electrode layer has the form of a single continuous electrode, and the other electrode layer is patterned as a matrix of pixel electrodes, each pixel electrode defining one pixel of the display. In another type of electro-optic display, intended for use with a stylus, printhead, or similar movable electrodes detached from the display, only one layer among the layers adjacent to the electro-optic layer comprises electrodes, and the layers on opposite sides of the electro-optic layer are typically protective layers to prevent damage to the electro-optic layer by the movable electrodes.

Several different methods are used to produce such a three-layer structure. For example, U.S. Patent Nos. 6,839,158 and 6,982,178, and several other previously mentioned patents and applications, describe a process in which an encapsulated electrophoretic medium containing a capsule in a flowable adhesive is coated onto a flexible substrate containing an indium tin oxide (ITO) or similar conductive coating (which serves as an electrode of the final display) on a plastic film. The capsule/adhesive coating is dried to remove liquid (typically water) from the adhesive and form a coherent layer of electrophoretic medium firmly adhered to the substrate. Separately, a backplane is prepared, comprising an array of pixel electrodes and suitable conductor arrangements to connect the pixel electrodes to driving circuitry. To form the final display, a substrate with the capsule/adhesive layer on it is laminated to the backplane using a laminating adhesive. (By replacing the backplate with a simple protective layer (e.g., a plastic film), a very similar process can be used to fabricate electrophoretic displays that can be used with a stylus or similar movable electrodes that can slide on the protective layer.) In a preferred form of this process, the backplate itself is flexible and is fabricated by printing pixel electrodes and conductors onto a plastic film or other flexible substrate. A prominent lamination technique for mass-producing displays using this process is roll lamination using a laminating adhesive.

U.S. Patent Nos. 6,866,760 and 7,079,305 describe similar processes for forming electrophoretic displays with polymer dispersions. In this case, an emulsion of the inner phase (electrophoretic particles plus the dispersion medium) in an aqueous binder is used to form the initial coating. The binder is dried as described above, permanently encapsulating the inner phase and forming a coherent layer.

A variation of this process is described in U.S. Patent No. 7,561,324, a simplified version of the aforementioned U.S. Patent No. 6,982,178, which describes a so-called "dual-release sheet," specifically a front-plane laminate. One form of dual-release sheet includes a solid electro-optic dielectric layer sandwiched between two adhesive layers, one or both of which are covered by the release sheet. Another form of dual-release sheet includes a solid electro-optic dielectric layer sandwiched between two release sheets. Both forms of dual-release films are used in processes similar to those using the already described front-plane laminate but involving two separate laminations; typically, in the first lamination, the dual-release sheet is laminated to the front electrode to form a front sub-assembly, and then in the second lamination, the front sub-assembly is laminated to the backplane to form the final display, although the order of these two laminations can be reversed as needed. (When the form of dual-release sheet without an adhesive layer is used, the necessary adhesive layer must be provided on the electro-optic dielectric-facing surface of the front sub-assembly or backplane.)

Another variation of this process is described in U.S. Patent No. 7,839,564; this variation uses a so-called "inverted front-plane laminate"—a variation of the aforementioned front-plane laminate. This inverted front-plane laminate sequentially comprises at least one of a light-transmitting protective layer and a light-transmitting conductive layer, an adhesive layer, a solid electro-optic dielectric layer, and a release sheet. This inverted front-plane laminate is used to form an electro-optic display having a laminated adhesive layer between the electro-optic layer and the front electrode or front substrate; a second, typically thin, layer of adhesive may or may not be present between the electro-optic layer and the backplane. Such an electro-optic display can combine good resolution with good low-temperature performance.

Microcell displays are manufactured in a slightly different manner. First, a substrate is typically prepared by embossing an array of semi-solid polymer layers containing open cavities or recesses. The cavities are then filled with an electro-optical medium, usually by allowing a medium to flow across the substrate and removing excess medium with a scraper. A sealing layer is formed over the openings of the cavities and is dried or otherwise hardened to form a coherent sealing layer. Finally, an adhesive layer (typically supported on a release sheet) is laminated over the sealing layer. In a later step of this process, the release sheet (if present) is removed and the adhesive layer is laminated to a backing plate.

All these processes suffer from two problems. The first problem is that each process involves at least two, and in some cases three, lamination steps; at a minimum, there is one lamination step to attach the adhesive layer to the electro-optic layer and a second step to laminate the adhesive layer to the backing. These lamination steps are slow, typically performed at 0.5 ft/min (approximately 2.S mm/sec) and at high temperatures of 200–250°F (94–121°C). These lamination conditions can affect the moisture content in the laminated film in a somewhat unpredictable way, depending on the lamination conditions used as well as the ambient temperature and humidity, and the electro-optic properties of electrophoresis and other electro-optic displays are highly sensitive to the moisture content of the display. The second problem is that each process leaves at least one, and in some cases two, laminated adhesive layers between the electrodes in the final display. This laminated adhesive layer has a considerable resistance in series with the resistance of the electro-optic layer itself, such that a significant portion of the available voltage drop between the electrodes is “wasted” throughout the laminated adhesive and cannot be used to drive the electro-optic layer. The resistance of a laminating adhesive can be varied (see, for example, U.S. Patent No. 7,012,735, which describes adding an ionic dopant to a laminating adhesive to reduce its resistance), but such doping involves its own problems, such as unwanted migration of moving material outside the laminating adhesive layer, and in any case the resistance of the laminating adhesive layer cannot be reduced too much or lateral conduction within the laminating adhesive layer will affect the image produced on the electro-optic display.

An attempt was made to avoid the aforementioned problems by using a radiation-cured adhesive, which was applied via a roll lamination process after the electro-optic layer was coated and dried. However, this process still requires auxiliary lamination and leaves an adhesive layer between the electrodes in the final display, thus involving the voltage drop issue already discussed.

Attempts have been made to avoid the aforementioned problems by coating an electro-optic layer and an electrode onto a conductive film using various coating methods, including spraying. However, it is difficult to use spraying to coat many electro-optic layers (e.g., encapsulated electrophoretic layers) without leaving gaps or "pinholes" in the coated electro-optic layers. Furthermore, if an electrode layer is subsequently coated onto an electro-optic layer containing pinholes, the coated electrode layer will short-circuit with the conductive film, adversely affecting or damaging the electro-optic properties of the display. In addition, spraying an electrode layer onto a dried electro-optic layer inevitably involves rewetting the dried electro-optic layer with liquid, which can alter the liquid content of the electro-optic layer, leading to the problems discussed earlier.

It is known (see U.S. Patent Nos. 7,110,164 and 9,470,950) to provide encapsulated electrophoretic display layers with adhesives, which can also act as laminating adhesives. This requires an adhesive that flows at a temperature not exceeding approximately 150°C when dried. This greatly limits the range of adhesives that can be used and can therefore cause problems in finding an adhesive compatible with the other components of the electrophoretic layer. Furthermore, the process by which such adhesives are used to form an electro-optic display is very different from the process of the present invention. Electrophoretic layers including such adhesives are applied and dried in a normal manner. After drying and cooling, the electrophoretic display layer is then typically reheated in a hot laminator in contact with a backing plate to form the final display. In contrast, as already mentioned, in the first process of the present invention, an electro-optic layer containing an adhesive is applied, and the backing plate is in contact with this applied layer while it is still wet. Only after the backing plate is in place is the electro-optic layer dried to secure the backing plate to the electro-optic layer.

As already mentioned, the backplate of the present invention includes at least one electrode disposed on a liquid-permeable substrate. The liquid permeable to the backplate should be a liquid present in a continuous phase of the electro-optic material or sealing material, rather than a liquid that may be present in the cavities or microcapsules within the electro-optic material. For example, the continuous phase may include a water-soluble polyurethane whose viscosity (and conductivity) is a function of water content. Most electrophoretic materials use hydrophobic (and typically hydrocarbon) liquids present in an internal phase within cavities or microcapsules because such hydrophobic materials have high resistance (thus reducing power consumption of the display) and are less susceptible to electrolysis. The binder or continuous phase of such electrophoretic materials is typically aqueous, and therefore the backplate substrate should be water-permeable. Any of a variety of hydrophilic polymers (including cellulose and similar polysaccharides) can therefore be used as the backplate polymer.

It is obviously desirable for the backsheet to be as permeable as possible to liquid, as the presence of any impermeable areas can lead to uneven drying of the electro-optic material, consequently negatively impacting the uniformity of its electro-optic properties. Therefore, the presence of conventional metal electrodes on the backsheet should generally be avoided. Preferred types of electrodes comprise a large number of small particles of conductive, hydrophilic particulate materials (e.g., hydrophilic carbon black), formed by a coating or printing process that leaves a liquid-permeable electrode. Nevertheless, in some applications, transparent metal gate electrodes, such as etched high-transmittance metal meshes, perforated nanowire assemblies, and contact-printed nanoparticle films, can also be used as suitable permeable electrodes. In some embodiments, transparent metal gate electrodes will be combined with a separate initial rolling layer to produce a more uniform switching of the electrophoretic medium.

The front substrate used in the electro-optic display of the present invention can have any type known in the prior art, such as those described, for example, in the patents and published applications mentioned above. Typically, the front substrate will include a thin, transparent conductive layer (e.g., an indium tin oxide layer or similar ceramic often applied by sputtering; conductive organic polymers, graphite, or metal microfilaments may be used instead of ceramic) on a polymer film such as polyethylene terephthalate, although in some cases, such as in displays intended to be written to with a stylus or similar device, the conductive layer may be omitted. The coating of the electro-optic layer on the front substrate can be achieved using any method known in the prior art. Furthermore, any known sealing material can be used in the display of the present invention, assuming compatibility with the electrodes and the substrate material used in the backplate.

The exposed surface of the encapsulation electrophoretic material layer coated onto the front substrate is often non-planar because individual capsules tend to protrude above the adhesive surface, and in prior art electrophoretic displays, the adhesive or other layers in contact with the electrophoretic material layer are used to planarize the surface of the electrophoretic material. The backplate used in this process can achieve such planarization, but care should be taken to ensure that sufficient pressure is applied to the electrophoretic material layer to ensure that the electrophoretic material layer is planarized and that all portions of it are in contact with the backplate, as any gaps between these two layers can adversely affect the electro-optical performance of the display.

In the process of this invention, the removal of liquid from the electro-optic material or sealing material is achieved in principle in the same manner as in the prior art. However, it may be necessary to slightly adjust the conditions for liquid removal (e.g., by using longer drying times and/or higher drying temperatures) to take into account the need for the liquid to diffuse through the backplate substrate. It must also be ensured that the conditions for the drying step are compatible with the materials of the substrate used to form the electrodes and backplate, in order to avoid, for example, oxidation of the electrode or substrate materials during the drying step. If necessary, the drying step may be performed in an inert gas to avoid such oxidation.

Preferred embodiments of the invention will now be described with reference to the accompanying drawings (albeit by way of illustration only).

Figure 1 of the accompanying drawings is a schematic cross-section through a first step of the first process of the present invention, showing an encapsulation electrophoretic medium deposited on a substrate 108 by means of a slit-type coating apparatus (generally designated as 100). Apparatus 100 includes a coating die 102 through which a mixture of capsule 104 and adhesive 106 is coated onto the substrate 108, which is positioned from right to left relative to the die 102 as indicated by the arrows in Figure 1. As in prior art processes, the substrate 108 includes a polymer film and a conductive layer supported on its upper surface (as shown in Figure 1), but for illustrative purposes, this conductive layer is not shown separately in Figure 1. The capsule 104 and adhesive 106 are deposited onto the conductive layer of the substrate 108 to form a substantially uniform adhesive layer on the substrate 108.

Figure 2 illustrates a permeable backsheet applied to the coated substrate produced in Figure 2. As can be seen in Figure 2, the permeable backsheet comprises a continuous permeable electrode 120 (a plurality of discrete electrodes may alternatively be provided) preferably formed of hydrophilic carbon black and a permeable substrate 122 preferably formed of cellulose. Alternatively, the permeable electrode may be formed of a conductive hydrophilic polymer (e.g., polypyrrole) pre-patterned to have openings. Alternatively, the conductive hydrophilic polymer may be a doped polymer, such as poly(ethylene glycol) doped with a conductive material (e.g., carbon black, graphite, or conductive nanowires/nanotubes). Alternatively, the permeable substrate may be fiberglass or another inert textile material. The permeable backsheets 120, 122 are laminated under pressure to the exposed surfaces of the adhesive/capsule layers 104, 106. As shown in Figure 2, each capsule 104 comprises charged electrophoretic particles that move in the presence of an electric field. Techniques for forming capsules of charged electrophoretic media are described in the patents listed above. Charged electrophoretic particles can have different colors depending on the magnitude and polarity of their charge. The assembled components are then heated to approximately 60°C for a period sufficient to allow a considerable portion of the water present in the adhesive 106 to diffuse through the backplates 120, 122 and evaporate from their exposed surfaces, thereby drying the adhesive 106 and firmly adhering the backplate to the adhesive/capsule layer and the front substrate to form the completed display of the present invention.

In an alternative structure (i.e., a front-plane laminate), the substrate 108 may be a release sheet coated with an adhesive layer. In this structure, the resulting assembly comprises a continuous permeable electrode 120, a permeable substrate 122, and a mixture of a capsule 104 and an adhesive 106 coated on the substrate 108 (i.e., the release sheet). In this embodiment, it may be preferred that both the continuous permeable electrode 120 and the permeable substrate 122 are light-transmitting. For example, the continuous permeable electrode 120 and the permeable substrate 122 may be polyethylene terephthalate (PET) coated with indium tin oxide (ITO) including micron-sized holes drilled using a laser (i.e., direct-write laser patterning). Alternatively, patterned PET-ITO can be achieved using wet etching and photolithography. Thus, the permeable substrate 122 and the permeable electrode 120 constitute the front electrode, and the resulting front-plane laminate is coupled to an active matrix electrode backplane using the techniques described in the preceding patents.

The display thus formed, as shown in Figure 2, comprises only a single pixel because the permeable electrode 120 is continuous across the entire display. However, the substrate 122 and electrode 120 can later be sliced (cut or diced) into several pieces, as indicated by the thick dashed lines in Figure 2, to form a multi-pixel display. Slicing can be achieved by laser cutting or other suitable techniques. Connectors can then be provided to several discrete electrodes thus formed, for example, in the manner described in U.S. Patent No. 6,232,950. The resulting display will thus have various segmented electrodes, which can be independently controlled to provide, for example, designs, letters, numbers, or characters on the viewing side of the display.

It will be readily apparent to those skilled in the art of manufacturing electro-optic displays that the processes described above with reference to Figures 1 and 2 can be readily incorporated into a continuous roll-to-roll operation, as schematically illustrated in Figure 3. As shown in Figure 3, a front substrate 108 (e.g., comprising a light-transmitting front electrode and a substrate) removed from a roller (not shown) passes under a coating stage 302, which deposits a capsule/binder coating 304 onto the substrate 108. While still wet, the coating 304 contacts a continuous sheet of permeable backing 320 and then immediately passes through a clamping point between two rollers 322, 324 to secure the permeable backing 320 to the coating 304. The resulting substrate/coating/backing assembly passes through a drying zone 326 and is wound onto a roller 328. Clearly, additional operations (e.g., laser cutting to form discrete electrodes from the backing electrode, and the supply of conductors to the resulting discrete electrodes) can be performed between the drying zone 326 and the roller 328 if desired. Alternatively, the continuous display emerging from the drying zone 326 can be cut by a suitable cutting device (not shown) to form discrete displays, and the roller 328 can be replaced by a suitable stacking device for discrete displays.

Figure 4 schematically illustrates the filling of microcells with an electrophoretic internal phase. For background information on the formation, filling, and sealing of microcells, the reader refers to U.S. Patent Nos. 7,715,088 and 9,346,987. In Figure 4, the microcell substrate 402 (in which a plurality of cavities 404 are formed) is shown shifted from left to right as indicated by the arrows. The internal phase from the reservoir 406 flows downward and forms beads 408 on the surface of the substrate 402. Excess internal phase is removed by a scraper 410 to leave cavities 404 filled precisely flush with the top of the walls dividing these cavities.

The filled substrate produced in Figure 4 is then fed to the sealing stage shown in Figure 5, where the substrate again moves from left to right as indicated by the arrows. Flowable sealant from reservoir 412 forms beads 414 on the surface of the filled substrate. Instead of removing excess sealant with a scraper, as in the aforementioned U.S. Patent No. 7,715,088, the filled substrate coated with sealant immediately comes into contact with a permeable backing plate 416, and the sheet-filled substrate, sealant, and backing plate pass under roller 418, which controls the thickness of the sealant layer. The sheet can then be passed through a drying table as described above with reference to Figure 3 and then rolled up or cut in sheet form to form individual displays as previously described.

As will be seen from the foregoing, the present invention provides an electro-optic display in which an adhesive is not required between the electrodes, thus enabling the entire potential difference between the electrodes used to drive the electro-optic medium. The present invention also eliminates or reduces the need for a slow lamination step during the manufacture of the electro-optic display.

It will be apparent to those skilled in the art that many variations and modifications can be made to the specific embodiments of the invention described above without departing from the scope of the invention. Therefore, the entire foregoing description is to be interpreted in an exemplary sense rather than a limiting one.

Claims (20)

1. An electro-optical display, comprising: Front electrode that transmits light; An electro-optic material layer, disposed adjacent to the light-transmitting front electrode, the electro-optic material comprising: (a) a continuous phase comprising a polymer material and a liquid, and (b) a plurality of capsules containing charged particles and a fluid, wherein the charged particles are disposed in the fluid, the plurality of capsules are dispersed in the continuous phase, and the charged particles are capable of moving through the fluid under the influence of an electric field; and A backplate is arranged adjacent to the electro-optic material layer and opposite to the light-transmitting front electrode. The backplate includes a backplate electrode and a backplate substrate, wherein the backplate electrode is in contact with the electro-optic material layer, and the backplate substrate is permeable to the liquid. 2. The electro-optical display of claim 1, wherein the fluid is different from the liquid. 3. The electro-optical display of claim 1, wherein the fluid is hydrophobic. 4. The electro-optical display of claim 1, wherein the liquid comprises water. 5. The electro-optic display of claim 1, further comprising a front substrate arranged to support the light-transmitting front electrode. 6. The electro-optic display of claim 1, wherein the backplane substrate comprises a permeable hydrophilic polymer. 7. The electro-optic display of claim 6, wherein the backplate substrate comprises cellulose. 8. The electro-optic display of claim 1, wherein the backplate electrode comprises carbon black. 9. The electro-optic display of claim 8, wherein the backplane electrodes are coated or screen-printed onto the backplane substrate. 10. The electro-optic display of claim 1, wherein the backplate electrode is permeable. 11. The electro-optic display of claim 10, wherein the backplate electrode is a metal gate electrode. 12. The electro-optic display of claim 10, wherein the backplane electrode is selected from the group consisting of etched high-transmittance metal mesh, perforated nanowire assembly, contact-printed nanoparticle film and conductive polymer electrode. 13. An electro-optical display, comprising: Front electrode that transmits light; An electro-optic material layer, disposed adjacent to the light-transmitting front electrode, the electro-optic material comprising: (a) a continuous phase comprising a polymer material and a liquid, and (b) discrete droplets containing charged particles and a fluid, wherein the charged particles are disposed in the fluid, the discrete droplets of charged particles in the fluid are surrounded by the continuous phase, and the charged particles are capable of moving through the fluid under the influence of an electric field; and A backplate is arranged adjacent to the electro-optic material layer and opposite to the light-transmitting front electrode. The backplate includes a backplate electrode and a backplate substrate, wherein the backplate electrode is in contact with the electro-optic material layer, and the backplate substrate is permeable to the liquid. 14. A process for forming an electro-optic display, the process comprising: Provide an anterior substrate; An electro-optic material layer is formed on the front substrate. The electro-optic material comprises: a continuous phase including a polymer material and a liquid, and a plurality of capsules dispersed in the continuous phase. The plurality of capsules contain charged particles and a fluid, wherein the charged particles are arranged in the fluid and are capable of moving through the fluid under the influence of an electric field, wherein the fluid is different from the liquid. The exposed surface of the electro-optic material layer is brought into contact with a backplate comprising at least one backplate electrode disposed on a backplate substrate, the backplate substrate being permeable to the liquid; and Subsequently, a drying time and drying temperature are applied to the combined assembly including the front substrate, the electro-optic material layer and the backplate to effectively allow the liquid to diffuse through the permeable backplate substrate and be removed from the combined assembly, thereby forming a coherent layer in which the electro-optic material layer fixes the front substrate and the backplate to each other. 15. The process of claim 14, further comprising removing a portion of the liquid and cutting the backplate substrate and the backplate electrode into pieces to form a plurality of discrete backplate electrodes. 16. The process of claim 15, wherein the backplane substrate and the backplane electrodes are cut into pieces using a laser. 17. The process of claim 14, wherein the liquid comprises water. 18. The process of claim 14, wherein the backsheet substrate comprises a permeable hydrophilic polymer. 19. The process of claim 14, wherein the backplate electrode comprises carbon black. 20. The process of claim 14, wherein the backplate electrode is coated or screen-printed onto the backplate substrate.