Permeable backsheet for electro-optic displays

Abstract

A backplane for an electro-optic display includes electrodes and a substrate. The substrate can be permeable to a liquid such as water and can be formed of cellulose or a similar hydrophilic polymer. The electrodes desirably are also 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.

Description

[0001] Related Applications

[0002] This application is a divisional application of application number 201880016236.0, filed on March 27, 2018, having the title "Permeable Backplane for Electro-Optic Display".

[0003] This application claims priority to U.S. Provisional Application No. 62 / 477,505, filed March 28, 2017, the entirety of which is incorporated herein by reference. TECHNICAL FIELD

[0004] The present invention relates to backplanes for electro-optic displays, particularly electrophoretic displays. SUMMARY

[0005] The present invention provides a backplane for an electro-optic display, the backplane comprising at least one electrode disposed on a substrate, wherein either the substrate or the electrode or both are permeable to a liquid. The backplane can be, for example, permeable to water, and the substrate can be formed, for example, of cellulose or a similar hydrophilic polymer.

[0006] In the backplanes of the present invention, the electrode is desirably of a type that is permeable to the same liquid as the substrate, so that the electrode does not form a liquid- impermeable region on the substrate. For example, when the liquid is water (or an aqueous solution), the electrode can be formed of hydrophilic carbon black, which can be coated or screen-printed onto the substrate.

[0007] The present invention also provides an electro-optic display comprising: a layer of electro-optic material comprising a continuous phase, the continuous phase comprising a liquid; and a backplane comprising at least one (backplane) electrode in contact with the layer of electro-optic material and a substrate permeable to the liquid. The electro-optic material can 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 the fluid can be confined within a plurality of capsules or microcells. Alternatively, the charged particles and the fluid can be presented as a plurality of discrete droplets surrounded by a continuous phase comprising a polymeric material.

[0008] The electro-optic display of the present invention can also include at least one (front) electrode in contact with the layer of electro-optic material from the opposite side of the backplane electrode, and can also include a front substrate disposed to support the front electrode. Alternatively, the display can include a front substrate without a front electrode. At least one of the backplane and the front electrode, typically the latter, should be light-transmissive (the term is used herein to mean that the layer transmits enough light to enable a viewer to see changes in the display state of the electro-optic medium through that layer), and if the front electrode is light-transmissive, then any front substrate present should also be light-transmissive.

[0009] The present invention also provides a first process for forming an electro-optic display, the process comprising:

[0010] providing a front substrate;

[0011] forming a layer of electro-optic material comprising a liquid on the front substrate;

[0012] contacting an exposed surface of the layer of electro-optic material with a backplane comprising at least one electrode disposed on a substrate, the substrate being permeable to the liquid; and

[0013] subsequently applying conditions to the combined assembly comprising the front substrate, the layer of electro-optic material and the backplane effective to cause the liquid to diffuse through the permeable substrate and to be removed from the combined assembly, thereby causing the layer of electro-optic material to form a coherent layer securing the front substrate and the backplane to one another.

[0014] The present invention also provides a second process for forming an electro-optic display, the process comprising:

[0015] providing a front substrate having a plurality of cavities therein;

[0016] disposing an electro-optic material within the cavities;

[0017] forming a layer of sealing material over the electro-optic material within the cavities, the sealing material comprising a liquid;

[0018] contacting an exposed surface of the sealing material with a backplane comprising at least one electrode disposed on a substrate, the substrate being permeable to the liquid; and

[0019] subsequently applying conditions to the combined assembly comprising the front substrate, the electro-optic material, the sealing material and the backplane effective to cause the liquid to diffuse through the permeable substrate and to be removed from the combined assembly, thereby causing the layer of sealing material to form a coherent layer securing the front substrate and the backplane to one another.

[0020] The first and second processes of the present invention can include an additional step of dicing the backplane substrate and electrodes to form a plurality of discrete electrodes after removal of the liquid. BRIEF DESCRIPTION OF DRAWINGS

[0021] the Figure 1 is a schematic cross-section through the first step in the first process of the present invention and shows a layer of electro-optic material formed on a front substrate.

[0022] Figure 2 is a schematic cross-section similar to Figure 1 but shows the second step of the first process in which a backplane is contacted with an exposed surface of the electro-optic layer.

[0023] Figure 3 is a schematic cross-section showing Figure 1 and 2A schematic cross-section illustrating how the process can be performed on a roll-to-roll basis.

[0024] Figure 4 It is similar to Figure 1 and 2 The schematic cross-section shows a 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.

[0025] Figure 5 It is similar to Figure 3 The schematic cross-section shows a second step of the second process of the present invention, in which the backplate contacts the exposed surface of the sealing material. Detailed Implementation

[0026] 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.

[0027] 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.

[0028] 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.

[0029] Electrowetting displays are described in Hayes, RA et al., “Video-Speed ​​Electronic Paper Based on Electrowetting”, Nature, 425, 383-385 (2003) and U.S. Patent No. 7,420,549.

[0030] 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:

[0031] (a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814;

[0032] (b) Encapsulation, adhesives, and encapsulation processes; see, for example, U.S. Patents 6,922,276 and 7,411,719;

[0033] (c) Microunit structures, wall materials, and methods of forming microunits; see, for example, U.S. Patent Nos. 7,072,095 and 9,279,906;

[0034] (d) Methods for filling and sealing microcells; see, for example, U.S. Patent Nos. 7,144,942 and 7,715,088;

[0035] (e) Films and sub-assemblies containing electro-optic materials; see for example U.S. Patents 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; 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 Publication Nos. 2007 / 0237962; 2009 / 0109519; 2009 / 0168067; 2011 / 0164301; 2014 / 0115884; and 2014 / 0340738;

[0036] (f) Backplanes, adhesive layers, and other auxiliary layers used in displays and methods; 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; 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; 6,842,657; 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; 7,148,128; 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, 8,797,636, 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 Publication Nos. 2002 / 0060321, 2004 / 0008179, 2004 / 0085619, 2004 / 0105036, 2004 / 0112525, 2005 / 0122306, 2005 / 0122563, 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, 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 Patent Nos. 1,099,207 Bl and 1,145,072 Bl;

[0037] (g) Color formation and color adjustment; see for example U.S. Patent Nos. 7,075,502 and 7,839,564;

[0038] (h) Methods for driving displays; see for example U.S. Patent Nos. 7,012,600 and 7,453,445;

[0039] (i) Applications of displays; see for example U.S. Patent Nos. 7,312,784 and 8,009,348; and

[0040] (j) Non-electrophoretic displays, such as described in U.S. Patent No. 6,241,921 and U.S. Patent Application Publication No. 2015 / 0277160; and applications of encapsulation and microcell technology other than displays; see for example U.S. Patent No. 7,615,325; and U.S. Patent Application Publications Nos. 2015 / 0005720 and 2016 / 0012710.

[0041] Many of the foregoing patents and applications recognize that the wall surrounding a discrete microcapsule in an encapsulated electrophoretic medium can be replaced by a continuous phase, thus creating 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 the discrete droplets of electrophoretic fluid in such a polymer-dispersed electrophoretic display can be regarded as capsules or microcapsules even though there is no discrete capsule membrane associated with each individual droplet; see for example the aforementioned U.S. Patent No. 6,866,760. Thus, for the purposes of the present application, such a polymer-dispersed electrophoretic medium is regarded as a sub-class of encapsulated electrophoretic media.

[0042] Electro-optic displays generally comprise a layer of electro-optic material and at least two other layers, one of which is an electrode layer. In most such displays, both of the other layers are electrode layers and one or both electrode layers is patterned to define the pixels of the display. For example, one electrode layer can be patterned into elongate row electrodes, while the other electrode layer is patterned into elongate column electrodes extending at right angles to the row electrodes, the pixels being 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 into 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 or print head or similar movable electrode separate from the display, only one of the layers adjacent the electro-optic layer includes an electrode, the layer on the opposite side of the electro-optic layer typically being a protective layer to protect the electro-optic layer against the movable electrode.

[0043] Several different approaches are used to produce such three-layer structures. For example, in U.S. Patent Nos. 6,839,158 and 6,982,178 and several other previously mentioned patents and applications, a process is described in which an encapsulated electrophoretic medium comprising capsules in a flowable binder is coated onto a flexible substrate comprising an indium tin oxide (ITO) or similar conductive coating (which serves as one electrode of the final display) on a plastic film, the capsule / binder coating is dried to remove the liquid (typically water) from the binder 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 appropriate conductor arrangements to connect the pixel electrodes to drive circuitry. To form the final display, the substrate with the capsule / binder layer on it is laminated to the backplane using a lamination adhesive. (By replacing the backplane with a simple protective layer (e.g., a plastic film), a very similar process can be used to prepare an electrophoretic display that can be used with a stylus or similar movable electrode that can be slid over the protective layer.) In one preferred form of this process, the backplane itself is flexible, and is prepared by printing the pixel electrodes and conductors on a plastic film or other flexible substrate. The obvious lamination technique for mass production of displays by this process is roll lamination using a lamination adhesive.

[0044] U.S. Patent Nos. 6,866,760 and 7,079,305 describe a similar process for forming a polymer-dispersed electrophoretic display. In this case, an emulsion of the internal phase (electrophoretic particles plus dispersion medium) in a water-containing binder is used to form the initial coating. The binder is dried as before, permanently encapsulating the internal phase and forming a coherent layer.

[0045] A variation of this process is described in U.S. Patent No. 7,561,324, which describes a so-called "double release sheet", particularly a simplified version of the previously mentioned frontplane laminate of U.S. Patent No. 6,982,178. One form of double release sheet comprises a layer of solid electro-optic medium sandwiched between two adhesive layers, one or both of which is covered by a release sheet. The other form of double release sheet comprises a layer of solid electro-optic medium sandwiched between two release sheets. Both forms of double release sheet are used in a process that is generally similar to that using the previously described frontplane laminate but involves two separate lamination steps; typically, in the first lamination step, the double release sheet is laminated to the front electrode to form a front sub-assembly, and then, in the second lamination step, the front sub-assembly is laminated to the backplane to form the final display, although the order of these two lamination steps can be reversed if desired. (When the form of double release sheet that lacks adhesive layers is used, the necessary adhesive layers must be provided on the surfaces of the front sub-assembly or backplane that face the electro-optic medium.)

[0046] 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 front plane laminate described above. This inverted front plane laminate includes, in order, at least one of a light-transmissive protective layer and a light-transmissive conductive layer, an adhesive layer, a solid electro-optic medium 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, usually thin, layer of adhesive can or can 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.

[0047] Microcell displays are manufactured in a slightly different manner. A substrate is first prepared, usually by embossing a semi-solid polymer layer containing an array of open cavities or recesses. The cavities are filled with electro-optic medium, usually by flowing the medium across the substrate and removing excess medium with a doctor blade. 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 (usually supported on a release sheet) is laminated over the sealing layer. In a later step of the process, the release sheet (if present) is removed and the adhesive layer is laminated to the backplane.

[0048] All of 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 backplane. These lamination steps are slow, usually being carried out at 0.5 ft / min (about 2.5 mm / sec) and at high temperatures of 200-250°F (94-121°C). These lamination conditions can affect the moisture content in the laminated films in a somewhat unpredictable manner, depending on the lamination conditions used as well as the ambient temperature and humidity, and the electro-optic properties of electrophoretic 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 substantial resistance in series with the resistance of the electro-optic layer itself, so that a substantial fraction of the available voltage drop between the electrodes is "wasted" in the laminated adhesive and is not available to drive the electro-optic layer. The resistance of the laminated adhesive can be varied (see, for example, U.S. Patent No. 7,012,735, which describes the addition of ionic dopants to the laminated adhesive to reduce its resistance), but such doping involves its own problems, such as unwanted migration of mobile species outside the laminated adhesive layer, and in any case the resistance of the laminated adhesive layer cannot be reduced too much or transverse conduction within the laminated adhesive layer will affect the images produced on the electro-optic display.

[0049] Attempts have been made to avoid the aforementioned problems by using radiation-cured adhesives that are applied by a roll lamination process after the electro-optic layer is coated and dried. However, this process still requires auxiliary lamination and still leaves an adhesive layer between the electrodes in the final display, and thus involves the voltage drop problems already discussed.

[0050] Attempts have also been made to avoid the aforementioned problems by coating the electro-optic layer and one electrode by coating over the conductive film using various coating methods, including spraying. However, it is difficult to coat many electro-optic layers (such as encapsulated electrophoretic layers) using spraying without leaving some gaps or "pinholes" in the coated electro-optic layer, and if the electrode layer is then coated over the electro-optic layer containing pinholes, the coated electrode layer will short circuit with the conductive film, adversely affecting or destroying the electro-optic properties of the display. Furthermore, spraying of the electrode layer over the dried electro-optic layer inevitably involves re-wetting the dried electro-optic layer with a liquid, which can change the liquid content of the electro-optic layer, leading to the problems already discussed.

[0051] It is known (see U.S. Patents Nos. 7,110,164 and 9,470,950) to provide an encapsulated electrophoretic display layer with an adhesive that can also function as a lamination adhesive. This requires an adhesive that will flow at a temperature of no more than about 150°C when dried. This greatly limits the range of adhesives that can be used, and can therefore cause problems in finding an adhesive that is compatible with the other components of the electrophoretic layer. Furthermore, the process by which such a binder / adhesive is used to form an electro-optic display is very different from the process of the present application. The electrophoretic layer including such a binder / adhesive is coated and dried in the normal way. After drying and cooling, the electrophoretic display layer is then usually reheated in a hot laminator in contact with the backplane to form the final display. In contrast, as already mentioned, in the first process of the present application, the electro-optic layer containing the binder is coated, and the backplane is brought into contact with it while this coated layer is still wet. Only after the backplane is in place is the electro-optic layer dried to fix the backplane to the electro-optic layer.

[0052] As already mentioned, the backplane of the present application includes at least one electrode disposed on a liquid-permeable substrate. The liquid to which the backplane is permeable should be the liquid present in the continuous phase of the electro-optic material or the encapsulant, not the liquid which can be present in the internal cavities or microcapsules of the electro-optic material. For example, the continuous phase can comprise a water-soluble polyurethane, the viscosity (and conductivity) of which is a function of the water content. Most electrophoretic materials use a hydrophobic (and usually hydrocarbon) liquid in the internal phase present in the internal cavities or microcapsules, since such hydrophobic materials have a high resistance (thus reducing the power consumption of the display) and are less susceptible to electrolysis. The binder or continuous phase of such electrophoretic materials is usually aqueous, and thus the backplane substrate should be water-permeable. Any of a variety of hydrophilic polymers, including cellulose and similar polysaccharides, can thus be used as the backplane polymer.

[0053] It is clearly desirable that as large a portion of the backplane as possible be permeable to liquid, since the presence of any areas which are not permeable can result in non-uniform drying of the electro-optic material, with consequent adverse effects on the uniformity of its electro-optic properties. Thus, the presence of conventional metallic electrodes on the backplane should generally be avoided. Preferred types of electrode include a large number of small particles of electrically conductive, hydrophilic particulate material (e.g., hydrophilic carbon black), the electrode being formed by a coating or printing process which leaves a liquid-permeable electrode. Nonetheless, in certain applications, transparent metallic grid electrodes, such as etched high-transmission metal wire mesh, perforated nanowire assemblies and contact printed nanoparticle films can also be used as suitable permeable electrodes. In some embodiments, a separate roughing layer will be used in conjunction with a transparent metallic grid electrode to produce more uniform switching of the electrophoretic medium.

[0054] The front substrate used in the electro-optic display of the present application can be of any type known in the art, as described, for example, in the above-mentioned patents and published applications. Typically, the front substrate will include a thin, light-transmissive, electrically conductive layer (e.g., a layer of indium tin oxide or similar ceramic, often applied by sputtering; conductive organic polymers, graphite or metal micro-wires can be used instead of the ceramic) on a thin film of a polymer such as polyethylene terephthalate, although in some cases, such as displays intended to be written upon with a stylus or similar device, the conductive layer can be omitted. The application of the electro-optic layer to the front substrate can be effected in any manner known in the art. Moreover, any known encapsulant can be used in the display of the present application, provided that the encapsulant is compatible with the electrode and the substrate material used in the backplane.

[0055] The exposed surface of the encapsulated electrophoretic material layer coated onto the front substrate is often non-planar, as the individual capsules tend to protrude above the surface of the binder, and in prior art electrophoretic displays an adhesive or other layer in contact with the electrophoretic material layer is used to planarize the surface of the electrophoretic material. The backplane used in the present process can achieve such planarization, but care should be taken to ensure that the backplane is applied to the electrophoretic material layer with sufficient pressure to ensure that the electrophoretic material layer is planarized and that all parts of it are in contact with the backplane, as any voids between the two layers can adversely affect the electro-optical performance of the display.

[0056] In the process of the present application, removal of the liquid from the electro-optical material or the encapsulating material is in principle achieved in the same way as in the prior art. However, the conditions used for liquid removal can have to be slightly adjusted (e.g. by using longer drying times and / or higher drying temperatures) to take into account the need for diffusion of the liquid through the backplane substrate. It is of course also necessary to ensure that the conditions used for the drying step are compatible with the materials used for the formation of the electrodes and the substrate of the backplane, in order to avoid oxidation of the electrodes or the substrate material, for example, during the drying step. If necessary, the drying step can be performed in an inert gas to avoid such oxidation.

[0057] A preferred embodiment of the present application will now be described with reference to the accompanying drawings (although only by way of illustration).

[0058] The drawings Figure 1 is a schematic cross-section through the first step of the first process of the present application, showing deposition of an encapsulated electrophoretic medium onto a substrate 108 by means of a slot die coating apparatus, generally designated 100. The apparatus 100 comprises a coating die 102 through which a mixture of capsules 104 and binder 106 is coated onto the substrate 108, which is moved from right to left as indicated by the arrow, relative to the die 102, as shown. As in the prior art process, the substrate 108 comprises a polymer film supported on its upper surface (as shown), a conductive layer, which for the sake of illustration is not shown separately in the drawings, but which is present in the substrate 108. The capsules 104 and binder 106 are deposited onto the conductive layer of the substrate 108 to form a substantially uniform adhesive layer on the substrate 108. Figure 1 Figure 1 Figure 1

[0059] Figure 2 shows the application of a permeable backplane to the coated substrate produced in Figure 2 . As can be seen in Figure 2 ​​​As seen in the diagram, 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 / encapsulation layers 104, 106. Figure 2 As shown, each capsule 104 includes charged electrophoretic particles that move in the presence of an electric field. Techniques for forming capsules of the charged electrophoretic medium are described in the patents listed above. The 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 invention.

[0060] 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.

[0061] This is how it was formed. Figure 2 The display shown includes only a single pixel because the permeable electrode 120 is continuous across the entire display. However, the substrate 122 and the electrode 120 can be as follows: Figure 2The latter is indicated by the thick dashed line and is subsequently diced (sawn or cut) into pieces to form a multi-pixel display. The dicing can be accomplished by laser kiss cutting or other suitable technique. Connectors can then be provided to the several discrete electrodes thus formed, for example in the manner described in U.S. Patent No. 6,232,950. The resulting display will 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.

[0062] It will be readily apparent to one skilled in the art of the manufacture of electro-optic displays that the processes described above with reference to Figure 1 and 2 can readily be combined into a continuous roll-to-roll operation, and such an operation is schematically illustrated in Figure 3 . As shown in Figure 3 , a piece of front substrate 108 (e.g., comprising a light-transmissive front electrode and substrate) is taken off a roll (not shown) and passed under a coating station 302 which deposits a capsule / binder coating 304 onto the substrate 108. While still wet, the coating 304 is contacted with a continuous piece of permeable backsheet 320 and then immediately passed through a nip between two rollers 322, 324 to affix the permeable backsheet 320 to the coating 304. The resulting substrate / coating / backsheet assembly is passed through a drying zone 326 and wound onto a roll 328. Obviously, if desired, additional operations (e.g., laser cutting to form discrete electrodes from the backsheet electrodes, supply of conductors to the discrete electrodes thus produced) can be carried out between the drying zone 326 and the roll 328. Alternatively, the continuous piece of display emerging from the drying zone 326 can be sawn to form discrete displays by suitable cutting apparatus (not shown), and the roll 328 replaced by suitable stacking apparatus for the discrete displays.

[0063] Figure 4 A microcell is schematically shown being filled with an electrophoretic internal phase. For background information on the formation, filling and sealing of microcells, the reader is referred to U.S. Patent Nos. 7,715,088 and 9,346,987. In Figure 4 , a microcell substrate 402 (in which a plurality of cavities 404 are formed) is shown being moved from left to right as indicated by the arrow. Internal phase from a reservoir 406 flows downward and forms beads 408 on the surface of the substrate 402. Excess internal phase is removed by a doctor blade 410 to leave the cavities 404 filled exactly flush with the tops of the walls dividing the cavities.

[0064] The filled substrate produced in Figure 4 is then fed to Figure 5The sealing station is shown, where the substrate is again moved from left to right as indicated by the arrow. The flowable sealing material from reservoir 412 forms a bead 414 on the surface of the filled substrate. Rather than removing excess sealing material with a doctor blade, as in the previously mentioned U.S. Patent No. 7,715,088, the filled substrate coated with sealing material is immediately contacted with a permeable backsheet 416, and the sheet of filled substrate, sealing material, and backsheet is passed under rollers 418, which serve to control the thickness of the layer of sealing material. The sheet can then be wound up as a roll or cut into individual displays as described above with reference to FIG. 1. Figure 3 The sheet is then passed through a drying station and then wound up as a roll or cut into individual displays as described above with reference to FIG. 1.

[0065] It will be seen from the foregoing that the present application can provide electro-optic displays in which an adhesive need not be present between the electrodes, thus enabling the full potential difference between the electrodes for driving the electro-optic medium. The present application also eliminates or reduces the need for a slow lamination step during the manufacture of the electro-optic display.

[0066] It will be apparent to those skilled in the art that many modifications and variations can be made in the specific embodiments of the present application described above, while remaining within the scope of the present application. Thus, the foregoing description is to be construed in an exemplary rather than a limiting sense.

Claims

1. An electro-optic display, comprising: a light-transmissive front electrode; a layer of electro-optic material disposed adjacent to the light-transmissive front electrode, the electro-optic material comprising: (a) a continuous phase comprising a polymeric 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 backplane disposed adjacent to the layer of electro-optic material and opposite the light-transmissive front electrode, the backplane comprising a backplane electrode and a backplane substrate, wherein the backplane electrode is in contact with the layer of electro-optic material, and the backplane substrate and the backplane electrode are permeable to the liquid, the backplane substrate comprising a permeable hydrophilic polymer.

2. The electro-optic display of claim 1, wherein the fluid is different from the liquid.

3. The electro-optic display of claim 1, wherein the fluid is hydrophobic.

4. The electro-optic display of claim 1, wherein the liquid comprises water.

5. The electro-optic display of claim 1, further comprising a front substrate disposed to support the light-transmissive front electrode.

6. The electro-optic display of claim 1, wherein the backplane substrate comprises cellulose.

7. The electro-optic display of claim 1, wherein the backplane electrode comprises carbon black.

8. The electro-optic display of claim 7, wherein the backplane electrode is coated or screen printed onto the backplane substrate.

9. The electro-optic display of claim 1, wherein the backplane electrode is permeable.

10. The electro-optic display of claim 9, wherein the backplane electrode is a metal grid electrode.

11. The electro-optic display of claim 9, wherein the backplane electrode is selected from the group consisting of an etched high-transmission metal screen, a perforated nanowire assembly, a contact printed nanoparticle film, and a conductive polymer electrode.

12. An electro-optic display, comprising: a light-transmissive front electrode; a layer of electro-optic material disposed adjacent to the light-transmissive front electrode, the electro-optic material comprising: (a) a continuous phase comprising a polymeric material and a liquid, and (b) a plurality of 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 backplane disposed adjacent to the layer of electro-optic material and opposite the light-transmissive front electrode, the backplane comprising a backplane electrode and a backplane substrate, wherein the backplane electrode is in contact with the layer of electro-optic material, and the backplane substrate and the backplane electrode are permeable to the liquid, the backplane substrate comprising a permeable hydrophilic polymer.

13. A process for forming an electro-optic display, the process comprising: providing a front substrate; forming a layer of electro-optic material on the front substrate, the electro-optic material comprising: a continuous phase comprising a polymeric material, a liquid, and a plurality of capsules dispersed in the continuous phase, the plurality of capsules containing charged particles and a fluid, wherein the charged particles are disposed in the fluid, the charged particles being capable of moving through the fluid under the influence of an electric field, wherein the fluid is different than the liquid; contacting an exposed surface of the layer of electro-optic material with a backplane comprising at least one backplane electrode disposed on a backplane substrate, wherein the backplane substrate and the at least one backplane electrode are permeable to the liquid, the backplane substrate comprising a permeable hydrophilic polymer; and thereafter applying a drying time and a drying temperature to the combined assembly comprising the front substrate, the layer of electro-optic material, and the backplane effective to cause the liquid to diffuse through the permeable backplane substrate and to be removed from the combined assembly, thereby causing the layer of electro-optic material to form a coherent layer securing the front substrate and the backplane to one another.

14. The process of claim 13, further comprising removing a portion of the liquid, and dicing the backplane substrate and the backplane electrode to form a plurality of discrete backplane electrodes.

15. The process of claim 14, wherein the backplane substrate and the backplane electrode are diced with a laser.

16. The process of claim 13, wherein the liquid comprises water.

17. The process of claim 13, wherein the backplane electrode comprises carbon black.

18. The process of claim 13, wherein the backplane electrode is coated or screen printed onto the backplane substrate.

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