Electro-optic device having an electrophoretic medium comprising an electroactive organic compound

Abstract

An electro-optic device is disclosed that includes an electrophoretic medium that includes charged pigment particles, a charge control agent, an organic electroactive compound, and a nonpolar liquid. The electrophoretic medium is contained in a plurality of microcells. The composition of the electrophoretic medium is capable of reducing the residual voltage of the electro-optic device and reducing the wear of the electrodes and other components of the device even after operation using a direct current unbalanced waveform.

Description

[0001] Related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 535,471, filed August 30, 2023, which, along with all other patents and patent applications disclosed herein, are incorporated herein by reference in their entirety. Background of the Invention

[0004] This invention relates to an electro-optic device comprising an electrophoretic medium containing charged pigment particles, an organic electroactive compound, and a nonpolar liquid. The electrophoretic medium is contained within a plurality of microcells. Even after operation with a DC unbalanced waveform, the composition of the electrophoretic medium enables a reduction in the residual voltage of the electro-optic device.

[0005] The terms “bistable” and “bistable” are used herein in their conventional sense in the art to refer to a display comprising display elements having first and second display forms that are different in at least one optical property, and such that after any given element has been driven to present its first or second display form by an addressing pulse of finite duration, the state will persist for at least several times, for example, at least four times, the minimum duration of the addressing pulse required to change the state of the display element after the addressing pulse has terminated. U.S. Patent No. 7,170,670 shows that some particle-based electrophoretic displays capable of displaying grayscale are stable not only in their extreme black and white states but also in their intermediate gray states, and this is also true for some other types of electro-optical displays. This type of display is properly referred to as “multistable” rather than bistable; however, for convenience, the term “bistable” may be used herein to encompass both bistable and multistable displays.

[0006] When applied to materials or displays, the term "electro-optic" is used herein in its conventional meaning in the field of imaging to refer to a material having a first display state and a second display state that differ in at least one optical property, which changes from the first display state to the second display state by applying an electric field to the material. While the optical property is generally color perceptible to the human eye, it can be another optical property such as optical transmission, reflection, emission, or, in the case of a display intended for machine reading, pseudo-color in the sense of a change in reflectivity at electromagnetic wavelengths outside the visible range.

[0007] In terms of having a solid outer surface, some electro-optic media are solid, although these media may and often do have internal spaces filled with liquid or gas. For convenience, displays using solid electro-optic media will be referred to below as "solid-state electrophoretic displays".

[0008] Several types of electro-optic displays are known. One type is the rotating bicolor unit type, as described in, for example, U.S. Patents 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 bicolor sphere" display, the preferred term "rotating bicolor unit" is more accurate because in some of the aforementioned patents, the rotating unit is not spherical). Such a display uses a large number of small bodies (typically spherical or cylindrical) having two or more portions with different optical properties, as well as internal dipoles. These small bodies are suspended within liquid-filled bubbles within a matrix, allowing the small bodies to rotate freely. By applying an electric field to them, the display effect is altered, thus rotating the small bodies to different positions and changing the portion of the small body seen through the viewing surface. This type of electro-optic medium is typically bistable.

[0009] Another type of electro-optic display uses an electrochromic medium, such as an electrochromic medium in the form of a nanochromic film, which comprises an electrode at least partially formed of a semiconductor metal oxide and a plurality of dye molecules capable of reversible color changes 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. This type of nanochromic film is also described, for example, in U.S. Patents 6,301,038, 6,870,657, and 6,950,220. This type of medium is also typically bistable.

[0010] Another type of electro-optic display is the electrowetting display developed by Philips and described in Hayes, RA, et al., “Video-Speed ​​Electronic Paper Based on Electrowetting”, Nature, 425, 383-385 (2003). U.S. Patent No. 7,420,549 shows that such an electrowetting display can be fabricated to be bistable.

[0011] Electro-optic displays, a type of display that has been a focus of research and development for many years, are particle-based electrophoretic displays, in which multiple charged pigment particles move through a liquid under the influence of an electric field. Compared to liquid crystal displays (LCDs), electrophoretic displays offer advantages such as better brightness and contrast, wider viewing angles, bistable properties, and lower power consumption. However, long-term image quality issues have hindered their widespread application. For example, the particles constituting an electrophoretic display tend to settle, leading to a shorter lifespan for these displays.

[0012] As mentioned above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, this fluid is a liquid, but gaseous fluids can also be used to manufacture electrophoretic media; see, for example, Kitamura, T., et al., “Electrical toner movement for electronic paper-like display”, IDW Japan, 2001, Paper HCS1-1 and Yamaguchi, Y., et al., “Toner display using insulative particles charged triboelectrically”, IDW Japan, 2001, Paper AMD4-4). See also U.S. Patents 7,321,459 and 7,236,291. When the medium is used in a direction that allows particle settling, such as in a sign where the medium is set in a vertical plane, gas-based electrophoretic media exhibit susceptibility to the same type of problems due to such settling, as with liquid-based electrophoretic media. In fact, particle sedimentation appears to be a more serious problem in gas-based electrophoresis media than in liquid-based electrophoresis media because gaseous suspensions have lower viscosity than liquid suspensions, causing electrophoretic particles to settle more quickly.

[0013] Numerous patents and applications assigned to or attributed to MIT and E Ink describe various techniques used in encapsulated electrophoretic media and other electro-optic media. Such encapsulated media comprise a plurality of small capsules, each capsule containing an inner phase in a liquid containing electrophoretically moving particles and a capsule wall surrounding the inner phase. Typically, the capsules themselves are held within a polymer binder to form a coherent layer located between two electrodes. The techniques described in these patents and applications include:

[0014] (a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patents 7,002,728 and 7,679,814;

[0015] (b) Encapsulation, adhesives, and encapsulation processes; see, for example, U.S. Patents 6,922,276 and 7,411,719;

[0016] (c) Films and subassemblies containing electro-optic materials; see, for example, U.S. Patents 6,982,178 and 7,839,564;

[0017] (d) Backplanes, adhesive layers, and other auxiliary layers and methods used in displays; see, for example, 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; 6,657,77 2; 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; 6,8 65,010; 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; 7,176,88 0; 7,190,008; 7,206,119; 7,223,672; 7,230,751; 7,256,766; 7,259,744; 7,280,094; 7,327,511; 7,349,148; 7,352,353; 7,365,394; 7,365,733; 7,3 82,363;7,388,572;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;7,667,88 6;7,672,040;7,688,497;7,733,335;7,785,988;7,843,626;7,859,637;7,893,435;7,898,717;7,957,053;7,986,450;8,009,344;8,027,081;8,0 U.S. Patents Nos. 49,947; 8,077,141; 8,089,453; 8,208,193; 8,373,211; 9,726,957; 10,520,786; 10,585,325; and 11,513,414; and Nos. 2002 / 0060321; 2004 / 0105036;2005 / 0122306; 2005 / 0122563; 2007 / 0052757; 2007 / 0097489; 2007 / 0109219; 2007 / 0211002; 2009 / 0122389; 2009 / 0315044; 2010 / 0265239; 2011 / 0026101; 2011 / 0140744; 2011 / 0187683; 2011 / 0187689; U.S. Patent Application Publications Nos. 2011 / 0286082; 2011 / 0286086; 2011 / 0292319; 2011 / 0292493; 2011 / 0292494; 2011 / 0297309; 2011 / 0310459; and 2012 / 0182599; and International Application Publication No. WO00 / 38000; European Patents Nos. 1,099,207B1 and 1,145,072B1;

[0018] (e) Color formation and color adjustment; see, for example, U.S. Patent No. 7,075,502 and U.S. Patent Application Publication No. 2007 / 0109219;

[0019] (f) A method for driving a display; see, for example, U.S. Patents 7,012,600; 7,119,772; 7,453,445; and 10,475,396;

[0020] (g) Applications of displays; see, for example, U.S. Patents 7,312,784 and 8,009,348; and

[0021] (h) Non-electrophoretic displays, as described in U.S. Patent Nos. 6,241,921; 6,950,220; 7,420,549 and 8,319,759; and U.S. Patent Application Publication No. 2012 / 0293858.

[0022] 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, thereby producing what are known as polymer-dispersed electrophoretic displays, wherein the electrophoretic medium comprises a plurality of discrete droplets of electrophoretic medium and a continuous phase of polymeric material, and recognize that even if the discrete capsule membrane is not associated with each individual droplet, the discrete droplets of electrophoretic medium within such a polymer-dispersed electrophoretic display can be considered as capsules or microcapsules; see, for example, U.S. Patent No. 6,866,760 mentioned above. Therefore, for the purposes of this application, such polymer-dispersed electrophoretic media are considered a subtype of encapsulated electrophoretic media.

[0023] A related type of electrophoretic display is the so-called "microcell electrophoretic display." In a microcell electrophoretic display, charged pigment particles and fluid are not encapsulated within microcapsules, but rather retained within multiple cavities formed within a carrier medium, typically a polymer film. See, for example, U.S. Patents 6,672,921 and 6,788,449, both of which have been assigned to Sipix Imaging, Inc.

[0024] Although electrophoretic media are typically opaque (e.g., because in many electrophoretic media, particles essentially block the transmission of visible light through the display) and operate in reflective mode, many electrophoretic displays can be fabricated to operate in so-called “shutter modes,” where one display state is substantially opaque and the other is translucent. See, for example, U.S. Patents 5,872,552; 6,130,774; 6,144,361; 6,172,798; 6,271,823; 6,225,971; and 6,184,856. Dielectric electrophoretic displays, similar to electrophoretic displays but dependent on changes in electric field strength, can operate in a similar mode; see U.S. Patent 4,418,346. Other types of electro-optic displays may also be able to operate in shutter mode. Electro-optic media operating in shutter mode can be used in multilayer structures for full-color displays; in such structures, at least one layer adjacent to the viewing surface of the display operates in shutter mode to expose or hide a second layer farther from the viewing surface.

[0025] Encapsulated electrophoretic displays typically do not suffer from the aggregation and sedimentation failure modes of conventional electrophoretic devices and offer further advantages, such as the ability to print or coat displays on a variety of flexible and rigid substrates. The term "printing" is used to encompass all forms of printing and coating, including but not limited to: volumetric coating, such as patch die coating, slot or extrusion coating, ramp or step coating, curtain coating; roll coating, such as roller-blade coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing; electrostatic printing; thermal printing; inkjet printing; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques. Therefore, the resulting display can be flexible. Furthermore, because the display medium can be printed using a variety of methods, the display itself can be manufactured inexpensively.

[0026] Electro-optic displays typically include an electro-optic material layer and at least two other layers disposed on opposite sides of the electro-optic material layer, one of which is an electrode layer. In most such displays, both layers are electrode layers, and one or both of the electrode layers are patterned to define pixels of the display. For example, one electrode layer may be patterned as elongated row electrodes and the other electrode layer may be patterned as elongated column electrodes extending at right angles to the row electrodes, with the intersection of the row and column electrodes defining a pixel. 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, where each pixel electrode defines a pixel of the display. In another type of electro-optic display intended for use with a stylus, printhead, or similar movable electrode that is separate from the display, only one of the layers adjacent to the electro-optic layer includes an electrode, and the layer on opposite sides of the electro-optic layer is generally a protective layer designed to prevent the movable electrode from damaging the electro-optic layer.

[0027] The fabrication of a three-layer electro-optic display typically involves at least one lamination operation. For example, several of the aforementioned MIT and EInk patents and applications describe methods for fabricating encapsulated electrophoretic displays, wherein an encapsulated electrophoretic medium is coated onto a flexible substrate, the encapsulated electrophoretic medium comprising a capsule in an adhesive, the flexible substrate comprising an indium tin oxide (ITO) or similar conductive coating on a plastic film (which serves as an electrode of the final display), and the capsule / adhesive coating is dried to form a coherent layer of electrophoretic medium firmly adhered to the substrate. A backplane is fabricated separately, comprising a pixel electrode array and suitable conductor arrangements for connecting the pixel electrodes to drive circuitry. To form the final display, a substrate with the capsule / adhesive layer on it is laminated to the backplane using a lamination adhesive (a very similar method can be used to fabricate an electrophoretic display usable with a stylus or similar movable electrode by replacing the backplane with a simple protective layer such as a plastic film, on which the stylus or other movable electrode can slide). In a preferred form of such a method, the backplane itself is flexible and is fabricated by printing pixel electrodes and conductors onto a plastic film or other flexible substrate. The obvious lamination technique for mass-producing displays using this method is roll lamination using laminating adhesives. Similar manufacturing techniques can also be used for other types of electro-optic displays. For example, microcell electrophoretic media or rotating dual-color cell media can be laminated onto a backplane in essentially the same way as encapsulated electrophoretic media.

[0028] As discussed in the aforementioned U.S. Patent No. 6,982,178 (see column 3, lines 63 through 5, lines 46), many components used in solid-state electro-optic displays, as well as methods for manufacturing such displays, are derived from the technology used in liquid crystal displays (LCDs). LCDs are, of course, also electro-optic displays, although they use a liquid rather than a solid medium. For example, a solid-state electro-optic display may use an active matrix backplane comprising an array of transistors or diodes and corresponding pixel electrode arrays, and “continuous” front electrodes on a transparent substrate (in the sense of electrodes extending across multiple pixels and typically throughout the entire display), components substantially identical to those in an LCD. However, the methods used to assemble LCDs cannot be used for solid-state electro-optic displays. LCDs are typically assembled by forming a backplane and front electrodes on separate glass substrates, then bonding these components together, leaving small holes between them, placing the resulting assembly under vacuum, and immersing the assembly in a liquid crystal bath, allowing liquid crystal to flow through the holes between the backplane and front electrodes. Finally, with the liquid crystal in place, the holes are sealed to provide the final display.

[0029] This liquid crystal display assembly process cannot be easily transferred to solid-state electro-optic displays. Because the electro-optic material is solid, it must be placed between the backplate and the front electrode before the two components are fixed together. Furthermore, unlike liquid crystal materials, which are simply placed between the front electrode and the backplate without adhering to either, solid-state electro-optic media typically need to be fixed to both. In most cases, the solid-state electro-optic media is formed on the front electrode, as this is generally easier than forming the media on the backplate containing the circuitry. The front electrode / electro-optic media assembly is then laminated onto the backplate, usually by covering the entire surface of the electro-optic media with adhesive and laminating under heat, pressure, and possibly vacuum conditions. Therefore, most existing final lamination methods for solid-state electrophoretic displays are essentially batch processes, where the (typically) electro-optic media, lamination adhesive, and backplate are assembled immediately before final assembly, necessitating a method more suitable for mass production.

[0030] U.S. Patent No. 6,982,178 describes a method for assembling a solid-state electro-optic display (including an encapsulated electrophoretic display) that is well-suited for mass production. Essentially, the patent describes a so-called “front panel laminate” (“FPL”) comprising, in sequence: a light-transmitting conductive layer; a solid electro-optic dielectric layer electrically in contact with the conductive layer; an adhesive layer; and a release sheet. Generally, the light-transmitting conductive layer is carried on a light-transmitting substrate, which is preferably flexible, meaning that the substrate can be manually wound around a roller with a diameter of (reportedly) 10 inches (254 mm) without permanent deformation. The term “light-transmitting” in this patent and herein refers to a layer that transmits sufficient light to allow an observer viewing through the layer to observe changes in the display state of the electro-optic dielectric, which would typically be visible through the conductive layer and adjacent substrates (if present); where the electro-optic dielectric exhibits changes in reflectivity at non-visible wavelengths, the term “light-transmitting” should, of course, be interpreted as referring to the transmission at the relevant non-visible wavelengths. The substrate will generally be a polymer film and will typically have a thickness in the range of about 1 to about 25 mils (25 to 634 μm), preferably about 2 to about 10 mils (51 to 254 μm). The conductive layer is preferably a thin metal or metal oxide layer, such as a thin layer of aluminum or ITO. The conductive layer may contain a conductive polymer. Poly(ethylene terephthalate) (PET) films coated with aluminum or ITO are commercially available, for example, from El du Pont deNemours & Company of Wilmington, Delaware, under the name "aluminized Mylar" ("Mylar" is a registered trademark), and such commercial materials can be used in front panel laminates with good results.

[0031] Assembling an electro-optic display using such a front-panel laminate can be achieved by removing the release liner from the front-panel laminate and bringing the adhesive layer into contact with the backplate while effectively adhering the adhesive layer to the backplate, thereby fixing the adhesive layer, electro-optic dielectric layer, and conductive layer to the backplate. This method is well-suited for mass production because the front-panel laminate can be mass-produced, typically using roll-to-roll coating technology, and then cut into sheets of any size required for use with a specific backplate.

[0032] U.S. Patent No. 7,561,324 describes a so-called "dual release sheet," which is essentially a simplified version of the front-panel laminate of the aforementioned U.S. Patent No. 6,982,178. One form of the dual release sheet includes a solid electro-optic dielectric layer sandwiched between two adhesive layers, wherein one or both adhesive layers are covered by the release sheet. Another form of the dual release sheet includes a solid electro-optic dielectric layer sandwiched between two release sheets. Both forms of dual release sheets are intended for processes generally similar to those used for assembling electro-optic displays from the previously described front-panel laminate, but involving two separate lamination processes; generally, 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 backplate to form the final display, but the order of these two laminations can be reversed if desired.

[0033] U.S. Patent No. 7,839,564 describes a so-called "inverted front panel laminate," a variation of the front panel laminate described in U.S. Patent No. 6,982,178. This inverted front panel laminate may sequentially include: 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 panel 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, generally thin adhesive layer may or may not be present between the electro-optic layer and the backplate. Such an electro-optic display can combine good resolution with good low-temperature performance.

[0034] In high-resolution displays, each individual pixel must be addressable without interference from addressing adjacent pixels (regardless of whether the electro-optic medium used is bistable). One way to achieve this is to provide an array of nonlinear elements, such as transistors or diodes, with at least one nonlinear element associated with each pixel to produce an active matrix display, as mentioned above. The addressing (pixel) electrode that addresses a pixel is connected to a suitable voltage source via its associated nonlinear element. Conventionally, in high-resolution arrays, pixels are arranged in a two-dimensional array of rows and columns such that any particular pixel is uniquely defined by the intersection of a particular row and a particular column. The source electrodes of all transistors in each column are connected to a single column electrode, while the gate electrodes of all transistors in each row are connected to a single row electrode; the assignment of source electrodes to rows and gate electrodes to columns is conventional and can be reversed if desired. The row electrodes are connected to a row driver, which essentially ensures that only one row is selected at any given time, i.e., a voltage is applied to the selected row electrode to ensure that all transistors in the selected row are turned on, while a voltage is applied to all other rows to ensure that all transistors in these unselected rows remain off. Column electrodes are connected to column drivers, which apply selected voltages to each column electrode to drive the pixels in the selected row to their desired optical state. The aforementioned voltages are relative to a common front electrode, which is typically located on the side of the electro-optic medium opposite to the nonlinear array and extends across the entire display. After a preselection interval known as the “line addressing time,” the selected row is deselected, the next row is selected, and the voltage on the column drivers is changed so that the next row of the display is written. This process is repeated so that the entire display is written line by line.

[0035] In the following discussion, the term "waveform" will be used to refer to the entire voltage curve over time that influences the transition of a pixel from a specific initial gray level to a specific final gray level. Typically, such a waveform will contain multiple waveform elements; where these elements are inherently rectangular (i.e., where a given element contains the application of a constant voltage for a period of time); these elements may be referred to as "pulses" or "drive pulses." The term "drive scheme" refers to a set of waveforms sufficient to influence the possible transitions between all gray levels of a particular display. A display may use more than one drive scheme; for example, U.S. Patent No. 7,012,600 teaches that a drive scheme may need to be modified based on parameters such as the display's temperature or the time it has been operating during its lifespan. Therefore, a display may be equipped with multiple different drive schemes for use under conditions such as different temperatures. A set of drive schemes used in this way may be referred to as a "set of related drive schemes."

[0036] Prior art front electrodes for electrophoretic displays and similar electro-optic displays typically comprise an extremely thin (approximately 0.1 µm) ceramic layer, such as indium tin oxide or a similar mixed metal oxide layer (see the aforementioned U.S. Patent No. 6,982,178). This thin layer is typically formed by sputtering the ceramic onto a polymer film, typically polyethylene terephthalate. Prior art rear (pixel) electrodes can be formed in a similar manner, or can be formed from a thin metal film; naturally, the front electrode must be translucent so that the electro-optic layer can be seen, while for reflective electro-optic layers, the rear electrode can be opaque.

[0037] Despite years of large-scale commercial use, ceramic front electrodes still face numerous mechanical, optical, and electrical challenges. The tension and temperature used during the lamination process in display manufacturing can cause ceramic cracking, resulting in conductivity discontinuities and poor or inconsistent display switching. These cracked areas are also regions of high water vapor permeability, which can cause localized damage to humidity-sensitive electro-optic media (many of the aforementioned types are humidity-sensitive). In color displays using color filter arrays (CFAs), it is desirable to reduce parallax issues by using thin polymer films to bring the CFAs as close as possible to the electro-optic layer and reducing the thickness of the ITO-coated PET substrate. However, as the PET substrate becomes thinner, ITO-related cracking problems worsen due to the higher thermal shrinkage rate of the thinner matrix.

[0038] As discussed in detail in the aforementioned U.S. Patent No. 7,119,772, it has been found that for at least some types of electro-optic displays, it is desirable for the driving scheme at each pixel location to be DC balanced. In this sense, the algebraic sum of the pulses applied during any transition sequence that starts and ends at the same gray level is limited. It has been found that in some prior art displays, a precise DC-balanced waveform (i.e., a waveform in which the integral of the current of any particular pixel of the display with respect to time remains zero during long-term operation of the display) is required to maintain image stability, preserve symmetrical transition characteristics, and provide the longest possible effective operating life.

[0039] Ideally, all individual waveforms in a preferred drive scheme should be DC balanced, but this is practically difficult to achieve. Therefore, even if the drive scheme as a whole is DC balanced, a typical drive scheme is usually a mixture of DC balanced and DC unbalanced waveforms.

[0040] As discussed in U.S. Patent No. 7,119,772, the extent to which DC unbalanced drive affects electrophoretic displays or other electro-optic displays (presumably through the polarization of certain display components, as discussed in more detail below) can be determined by measuring the open-circuit potential (hereinafter referred to as "residual voltage") of specific areas of the display, such as pixels. A pixel is considered DC balanced when its residual voltage is zero. It is considered positively DC unbalanced if its residual voltage is positive, and negatively DC unbalanced if its residual voltage is negative. It has been found that non-zero residual voltage is associated with difficulties in accurate grayscale positioning.

[0041] The performance degradation caused by residual voltage is usually reversible, which can be achieved by leaving the display idle without further switching or by rebalancing the DC pulse through appropriate switching. However, in existing electrophoretic displays driven under extreme DC imbalance, the electrodes may suffer irreversible wear, presumably due to electrochemical reactions that consume the electrode material.

[0042] While DC-balanced drive waveforms effectively prevent the development of residual voltage and electrode wear, there are also problems associated with their use. Additional time must be allocated to provide the balancing pulse, sometimes resulting in update times that are two to three times longer than those possible with DC unbalanced drives. In some electrophoretic compositions, the time required for the optical transition from black to white differs from the time required for the optical transition from white to black. In DC-balanced waveforms, both transitions require the longer of the two switching times. Furthermore, during DC-balanced updates, display users may experience interfering optical transitions.

[0043] For example, as described in U.S. Patents 6,724,519 and 7,564,614, corrosion inhibitors can be added to electro-optic displays to prevent damage to electrodes caused by DC imbalance during display driving. U.S. Patents 9,726,957, 10,520,786, and 11,513,414 disclose an electrophoretic display having an electro-optic material comprising an encapsulated electrophoretic medium and an electro-optic material layer located between an electro-optic material layer and electrodes, wherein the polymer layer contains a redox compound. The redox material mitigates losses to display components caused by DC imbalance. This invention provides a more effective alternative method that prevents damage by including an organic electroactive compound in the electrophoretic medium. This invention also provides a method for effectively reducing the residual voltage of electro-optic devices. In the electro-optic device of this invention, the electrophoretic medium is in direct contact with a first electrode and at least one pixel electrode of the device. The organic electroactive compound is present in the electrophoretic medium in both oxidized and reduced forms. Its reduced form is oxidized at one electrode, and its oxidized form is reduced at another electrode, preventing damage to the electrodes and other components of the device. Invention Overview

[0045] Therefore, the present invention provides an electro-optic device comprising a first electrode layer including a light-transmitting electrode; a second electrode layer including a plurality of pixel electrodes; and a micro-unit layer disposed between the first electrode layer and the second electrode layer. The micro-unit layer includes a plurality of micro-units, each of which contains an electrophoretic medium in contact with at least one pixel electrode of the light-transmitting electrode of the first electrode layer and the plurality of pixel electrodes of the second electrode layer. The electrophoretic medium comprises: (a) charged pigment particles; (b) a nonpolar liquid; (c) a charge control agent; and (d) an organic electroactive compound. The organic electroactive compound exists in the electrophoretic medium in both oxidized and reduced forms. The oxidized form of the organic electroactive compound is electrochemically reduced at the surface of one of the first and second electrode layers. The reduced form of the organic electroactive compound is electrochemically oxidized at the surface of one of the first and second electrode layers. The oxidized and reduced forms of the organic electroactive compound are (i) soluble in the nonpolar liquid of the electrophoretic medium, or (ii) contained in a reverse micelle structure present in the electrophoretic medium. The oxidized form of the organic electroactive compound may have a reduction potential of no more than 1.0 V relative to a standard hydrogen electrode.

[0046] The molecular structure of the reduced form of the organic electroactive compound can be represented by formulas I to IX. R1 to R 39 It can be hydrogen, substituted or unsubstituted alkyl or aryl, and substituents R1 and R2 together, and / or R3 and R4, and / or R5 and R6, and / or R6 and R7, and / or R7 and R8, R9 and R 10 , and / or R 11 and R 12 , and / or R 14 and R 15 , and / or R 15 and R 16 , and / or R 16 and R 17 , and / or R 19 and R 20 , and / or R 21 and R 22 , and / or R 25 and R 26 , and / or R 26 and R 27 , and / or R 27 and R 28 A ring can be formed; and R 31 and R 32 At least one of them is aryl, R 33and R 34 At least one of them is aryl, and R 36 and R 37 At least one of them is an aryl group.

[0047]

[0048] Formula I Formula II

[0049]

[0050] Formula III Formula IV

[0051]

[0052] V-shaped VI-shaped

[0053]

[0054] Formula VII, Formula VIII, Formula IX

[0055] Groups R1 to R 39 It can be hydrogen, substituted or unsubstituted alkyl, alkenyl, or aryl. Substituents R1 and R2 are combined, and / or R3 and R4, and / or R5 and R6, and / or R6 and R7, and / or R7 and R8, R9 and R 10 , and / or R 11 and R 12 , and / or R 14 and R 15 , and / or R 15 and R 16 , and / or R 16 and R 17 , and / or R 19 and R 20 , and / or R 21 and R 22 , and / or R 25 and R 26 , and / or R 26 and R 27 , and / or R 27 and R 28 A ring can be formed. R 31 and R 32 At least one of them can be aryl, R 33 and R 34 At least one of them is aryl, and R 36 and R 37 At least one of them is an aryl group.

[0056] At least one of R1 to R4 in Formula I, at least one of R5 to R8 in Formula II, and R9 to R4 in Formula III 13At least one of them, R of formula IV 14 To R 18 At least one of them, R of formula V 19 To R 24 At least one of them, R of formula VI 25 To R 30 At least one of them, R of equation VII 31 and R 32 At least one of them, R of formula VIII 33 To R 35 At least one of them, and R of formula IX 36 To R 39 At least one of them can be an alkyl or alkenyl group having at least 10 carbon atoms.

[0057] R9 to R of Formula III 12 At least one of them, R of formula IV 14 To R 17 At least one of them, R of formula V 19 To R 22 At least one of them, R of formula VI 25 To R 28 At least one of them, R of formula VIII 33 and R 34 At least one of them, and R of formula IX 36 and R 37 At least one of them can be an alkyl or alkenyl group having at least 10 carbon atoms. The alkyl or alkenyl group can have from 10 to 100 carbon atoms. The alkyl or alkenyl group comprises an isoprene dimer or oligomer, the dimer or oligomer comprising 1 to 20 isoprene units (-CH2CH=C(CH3)CH2-). The alkyl or alkenyl group comprises an isoprene dimer or oligomer, the isoprene dimer or oligomer comprising 1 to 13 isoprene units (-CH2CH=C(CH3)CH2-).

[0058] The molecular structure of the reduced form of the organic electroactive compound can be represented by formula X. Groups R1, R2, and R3 can be hydrogen, alkyl, alkenyl, or alkoxy, and n can be an integer from 2 to 20. Groups R1 and R2 can both be methoxy, and R3 can be methyl. Groups R1 and R2 can both be methyl, and R3 can be hydrogen.

[0059]

[0060] Formula X

[0061] The reduced form of the organic electroactive compound can be panthenol-10.

[0062]

[0063] Panthenol-10.

[0064] The reduced form of the organic electroactive compound can be represented by formula XI.

[0065]

[0066] Formula XI

[0067] The molecular structure of the oxidized form of the organic electroactive compound can be represented by formula XII. Group R 40 R 41 R 42 R 43 and R 44 It can be hydrogen, alkyl, alkenyl, or alkoxy, and m can be an integer from 2 to 20.

[0068]

[0069] Formula XII

[0070] The molecular structure of the oxidized form of the organic electroactive compound can be represented by formula XIII or XIV. Group R 45 R 46 R 47 R 48 R 49 R 50 R 51 and R 52 It can be hydrogen, alkyl, alkenyl, or alkoxy, p can be an integer from 2 to 20, and q can be an integer from 2 to 20. The integer q can be selected from 3, 4, 7, and 9.

[0071] If the organic electroactive compound is represented by formula XIV, then the group R 48 R 49 R 50 and R 51 Both can be hydrogen, and R 52 It can be methyl.

[0072]

[0073] Formula XIII

[0074]

[0075] Formula XIV

[0076] On the other hand, the present invention provides a method for operating an electro-optic device, the method comprising: (a) providing the electro-optic device; and (b) driving the electro-optic device using a DC unbalanced waveform. The residual voltage of the electro-optic device may be lower than the residual voltage of a control electro-optic device, the control electro-optic device comprising a control electrophoretic medium that does not contain an organic electroactive compound. The electro-optic device comprises a first electrode layer including a transparent electrode; a second electrode layer including a plurality of pixel electrodes; and a micro-unit layer disposed between the first electrode layer and the second electrode layer. The micro-unit layer comprises a plurality of micro-units, each of the plurality of micro-units comprising an electrophoretic medium in contact with at least one pixel electrode of the transparent electrode of the first electrode layer and the plurality of pixel electrodes of the second electrode layer. The electrophoretic medium comprises: (a) charged pigment particles; (b) a nonpolar liquid; (c) a charge control agent; and (d) an organic electroactive compound. The organic electroactive compound exists in the electrophoretic medium in both oxidized and reduced forms. The oxidized form of the organic electroactive compound can be electrochemically reduced at the surface of one of the first and second electrode layers. The reduced form of the organic electroactive compound can be electrochemically oxidized at the surface of one of the first and second electrode layers. Both the oxidized and reduced forms of the organic electroactive compound are soluble in the nonpolar liquid of the electrophoretic medium or are contained in the reverse micelle structure present in the electrophoretic medium.

[0077] According to another aspect, the present invention provides an electro-optic device comprising a first electrode layer including a light-transmitting electrode; a second electrode layer including a plurality of pixel electrodes; and a micro-unit layer disposed between the first electrode layer and the second electrode layer. The micro-unit layer includes a plurality of micro-units, each of which contains an electrophoretic medium in contact with at least one pixel electrode of the first electrode layer and the plurality of pixel electrodes of the second electrode layer. The electrophoretic medium comprises: (a) charged pigment particles; (b) a nonpolar liquid; (c) a charge control agent; and (d) an organic electroactive compound. The organic electroactive compound is present in the electrophoretic medium in either an oxidized or reduced form. The oxidized form of the organic electroactive compound is electrochemically reduced at the surface of one of the first and second electrode layers. The reduced form of the organic electroactive compound is electrochemically oxidized at the surface of one of the first and second electrode layers. The oxidized and reduced forms of the organic electroactive compound are (i) soluble in the nonpolar liquid of the electrophoretic medium, or (ii) contained in a reverse micelle structure present in the electrophoretic medium. The oxidized form of the organic electroactive compound may have a reduction potential of no more than 1.0 V relative to a standard hydrogen electrode. Brief description of the attached diagram

[0079] Figure 1 is a side view of an electro-optic display from the prior art containing an electrophoretic medium encapsulated in a microcapsule.

[0080] Figure 2 is a side view of an electro-optic display from the prior art containing an electrophoretic medium encapsulated in microcells.

[0081] Figure 3A is a simplified schematic diagram of the movement of charged materials in the electrophoretic medium and adjacent layers of an electro-optic display in response to an electric field, which may lead to charge accumulation at the electrode interfaces and a reduction in the image quality of the display. This figure has been disclosed in the prior art.

[0082] Figure 3B is a simplified schematic diagram of the movement and transformation of important materials in the electrophoretic medium and adjacent layers of an electro-optic display in response to an electric field. This diagram has been disclosed in the prior art and is related to mitigating charge accumulation and residual voltage at electrode interfaces.

[0083] Figure 4 This is a side view of an example of an electro-optic device according to the present invention.

[0084] Figure 5 This is a schematic diagram of the redox reaction involving organic electroactive compounds.

[0085] Figure 6 Show the oxidized and reduced forms of panthenol-10, and the redox reactions involved in the conversion between these two forms.

[0086] Figure 7 It is a diagram of the redox reaction in the electrophoretic medium in the initial stage after the introduction of the reduced form of an organic electroactive compound.

[0087] Figure 8 It is a graph of the current flowing through the electrophoretic medium of the present invention (but excluding charged pigment particles) as a function of time under the condition that a DC voltage is continuously applied to the entire liquid over 48 hours.

[0088] Figure 9 It is a graph of the residual voltage across the electrophoretic medium of the present invention (but excluding charged pigment particles) as a function of time, measured after applying a DC voltage to the entire liquid and removing the applied voltage over 48 hours.

[0089] Figure 10 It is a graph showing the current flowing through the control electrophoretic medium and the electrophoretic medium of the present invention relative to the applied voltage, measured after using each DC voltage driving medium and removing the voltage.

[0090] Figure 11It is a graph of the residual voltage versus time of the control electrophoresis medium and the electrophoresis medium of the present invention, measured after using each DC voltage driving medium and removing the voltage.

[0091] Figure 12 It is a waveform applied to the medium of an electro-optic device to measure the color gamut of the corresponding electrophoretic medium.

[0092] Figure 13 It is the color gamut measured by the reference electro-optic device.

[0093] Figure 14 This is the color gamut measured by the electro-optic device of the present invention. Invention Details

[0095] This article uses the term "oxidized form" to refer to organic electroactive compounds, including both the fully oxidized form and other molecules with a higher degree of oxidation than the fully reduced form. This article also uses the term "reduced form" to refer to organic electroactive compounds, including both the fully reduced form and other compounds with a higher degree of reduction than the fully oxidized form.

[0096] The term "unsubstituted alkyl" refers to a branched or unbranched group containing one or more C-C single bonds and not containing C-C double or C-C triple bonds. The term "unsubstituted alkyl" includes cyclic groups containing C-C single bonds and not containing C-C double or C-C triple bonds or an aryl group. The term "unsubstituted alkenyl" refers to a branched or unbranched group containing one or more C-C double bonds. The term "unsubstituted aryl" refers to a group containing an aromatic ring. The term "substituted alkyl" refers to an alkyl group in which one or more hydrogen atoms are replaced by a substituent, which is not an alkyl group. The substituent can be alkenyl, aryl, or a group containing a heteroatom, which is an atom of Group V-VII of the periodic table. The term "substituted alkenyl" refers to an alkenyl group in which one or more hydrogen atoms are replaced by a substituent, which is not an alkenyl or alkyl group. The substituent can be aryl or a group containing a heteroatom, which is an atom of Group V-VII of the periodic table. The term "substituted aryl" refers to an aryl group in which one or more hydrogen atoms are replaced by a substituent. The substituent may be alkyl, alkenyl, aryl, or a group containing a heteroatom, wherein the heteroatom is an atom belonging to Groups V-VII of the periodic table. Non-limiting examples of heteroatoms include nitrogen, phosphorus, oxygen, sulfur, selenium, fluorine, chlorine, bromine, and iodine. Non-limiting examples of groups containing heteroatoms include hydroxyl, amino, alkoxy, carboxyl, thio, cyano, nitro, etc.

[0097] A typical electro-optic display may have an electro-optic material layer comprising an electrophoretic medium encapsulated in microcapsules or microcells, as described in U.S. Patent No. 6,982,178. Figure 1 shows a side view of a basic structural example of a portion of an electro-optic display with microcapsules. The electro-optic display 100 includes a front panel 116, a back panel 118, and an adhesive layer 110 connecting the front panel 116 and the back panel 118. The front panel 116 includes a front substrate 102, a light-transmitting conductive layer 104 (also referred to in the literature as a first electrode, top electrode, or common electrode), optionally including a polymer layer 106, and an electro-optic material layer 108. The back panel 118 includes a plurality of pixel electrodes 112 and a rear substrate 114. The adhesive layer 110 connects the electro-optic material layer 108 of the front panel 116 and the back panel 118. The light-transmitting conductive layer 104 serves as the front electrode of the display. The electro-optic material layer 108 includes a plurality of microcapsules. Each microcapsule has a microcapsule wall and contains an electrophoretic medium having charged pigment particles in a nonpolar liquid. Typically, multiple microcapsules are held within a polymer binder. A viewer can view the electrophoretic medium image of the electro-optic display 100 from the side of the front substrate of the display.

[0098] Figure 2 is a side view of a basic structural example of a portion of an electro-optic display with microcells. The electro-optic display 200 has a viewing surface 230 and includes a front substrate 202, a light-transmitting conductive layer 204, an electro-optic material layer 208, a sealing layer 209, and a backplate 218, the backplate containing multiple pixel electrodes. The electro-optic material layer 208 contains multiple microcells 230A-D. Each microcell 230A-D of the electro-optic material layer 208 contains an electrophoretic medium 220. The electrophoretic medium 220 contains charged pigment particles 225 in a non-polar liquid. Each microcell 230A-D has a bottom layer 231, a microcell wall 232, and an opening. The microcell wall 232 separates adjacent microcells from each other. The sealing layer 209 spans each opening of the microcell and seals the electrophoretic medium 220 within the microcell.

[0099] In the microcapsule-containing electro-optic display of Figure 1, the front substrate 102 is transparent. The front substrate 102 can be a plastic film, such as a polyethylene terephthalate (PET) sheet with a thickness of 25 to 200 µm. Although not shown in Figure 1, the front substrate 102 may also include one or more other layers, such as a protective layer that absorbs ultraviolet radiation, a barrier layer that prevents oxygen or moisture from entering the display, and an anti-reflective coating that improves the optical properties of the display. The same applies to the microcapsule-containing electro-optic display of Figure 2. That is, in the microcapsule-containing electro-optic display of Figure 2, the front substrate 202 is transparent. The front substrate 202 can be a plastic film, such as a polyethylene terephthalate (PET) sheet with a thickness of 25 to 200 µm. The front substrate 202 may also include one or more other layers, such as a protective layer that absorbs ultraviolet radiation, a barrier layer that prevents oxygen or moisture from entering the display, and an anti-reflective coating that improves the optical properties of the display.

[0100] In the microcapsule-containing electro-optic display of Figure 1, the light-transmitting conductive layer 104 can be a thin, continuous conductive material coating with minimal inherent absorption of electromagnetic radiation in the visible spectrum, such as indium tin oxide (ITO), poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT: PSS), graphene, etc. The same applies to the micro-unit-containing electro-optic display of Figure 2. That is, the light-transmitting conductive layer 204 can be a thin, continuous conductive material coating with minimal inherent absorption of electromagnetic radiation in the visible spectrum, such as indium tin oxide (ITO), poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT: PSS), graphene, etc.

[0101] The electrophoretic medium of the electro-optic display 100 in Figure 1 and the electro-optic display 200 in Figure 2 can contain two types of charged pigment particles. The electrophoretic medium of the display can contain three, four, five, or more than five types of charged pigment particles. Each type of charged pigment particle can have a different color. Each type of charged pigment particle can have a positive or negative charge. If the electrophoretic medium contains two types of charged pigment particles, namely a first type and a second type, the first type of charged pigment particles can be white and negatively charged (or positively charged), and the second type of charged pigment particles can be black and positively charged (or negatively charged). When an electric field is applied across the electro-optic material layer through the pixel electrodes of the transparent conductive layer and the backplate, the white particles in the electrophoretic medium move towards the positive electrode, and the black particles move towards the negative electrode, so that when an observer views the display from the viewing side (front substrate side), they see either a white or black display portion corresponding to the pixel electrode, depending on whether the transparent conductive layer is positive or negative relative to the pixel electrode.

[0102] As described in U.S. Patent No. 6,982,178, an adhesive layer 110 of the electrophoretic medium of an electro-optic display 100 is disposed between an electro-optic material layer 108 containing encapsulated electrophoretic medium and a plurality of pixel electrodes 112 of a backplate 118 (see FIG. 1). The adhesive layer 110 enables the electro-optic display to be constructed by combining two sub-assemblies, such as a front plate 116 and a backplate 118 as shown in FIG. 1. The adhesive layer 110 is formed by applying an adhesive composition to the surface of the electro-optic material layer 108, connecting the front plate 116 and the backplate 118, and then curing the adhesive composition by thermosetting or UV curing. In the case of the microcell electro-optic display of FIG. 2, a sealing layer 209 is disposed between a plurality of microcells containing electrophoretic medium 220 and pixel electrodes 212 of a backplate 218.

[0103] The adhesive layer 110 of the microcapsule electro-optic display 100 in Figure 1 and the sealing layer 209 of the micro-unit electro-optic display 200 in Figure 2 are located in the circuit separating the pixel electrodes and the light-transmitting conductive layer of the backplane. Therefore, the electrical properties of the adhesive layer of the microcapsule electro-optic display and the sealing layer of the micro-unit electro-optic display are important to the operation of the display and must be carefully designed. For example, in addition to polymer materials, the sealing layer may also contain conductive filler particles to adjust its volume resistivity.

[0104] The polymer layer 106 of the microencapsulated electro-optic display 100 of Figure 1 can be a laminated adhesive layer having properties similar to those described above with reference to the adhesive layer 110. However, since the polymer layer 106 is adjacent to the non-pixelated transparent common electrode 104, its conductivity may be higher than that of the laminated adhesive layer 110, which is adjacent to the pixelated backplane electrode 112, and cannot be too conductive such that during display switching, a large current flows from one backplane electrode to its adjacent portion when the backplane electrode and its adjacent portion are at different potentials. When the polymer layer 106 is an adhesive layer, it can be used to fix the electro-optic material layer 108 to the electrode layer 104 during the fabrication of the front panel, as described in detail in the aforementioned U.S. Patent No. 6,982,178.

[0105] Figure 3A is reproduced according to the prior art. Specifically, this figure is disclosed as Figure 2 of U.S. Patent No. 9,726,957. It is a simplified illustration of the movement of charged substances present in the electro-optic material layer and the electrophoretic medium of the electro-optic display 100 of Figure 1 in response to an electric field applied by means of electrodes 104 and 112. For convenience, only the polymer layer 106, the electro-optic material layer 108, and the adhesive layer 110 are shown, but it will be clear to those skilled in the art that other layers are present in the display. The movable charged substances in each layer are uniformly shown as positively charged substances A, C, and E, and negatively charged substances B, D, and F. Substances A and B in polymer layer 106 may originate from, for example, ionic dopants added to enhance the conductivity of polymer layer 106, or may be incidentally present in the material used to form polymer layer 106. For example, if water is present in polymer layer 106, substance A may correspond to protons generated by the ionization of water. Substance A may contain more than one movable cation. In this discussion, substances

[0106] Substance A refers to any mobile, positively charged substance in polymer layer 106. Similarly, substances E and F refer to positively and negatively charged mobile substances in adhesive layer 110, respectively. Substances C and D refer to mobile charged entities in the electrophoretic medium of electro-optic material layer 108; such entities include charged pigment particles whose movement alters the optical state of the display; and charged substances whose movement has no direct optical effect, such as micelle charges well known in the art.

[0107] Charged materials can cross the boundaries between the layers of the display. This is schematically shown in Figure 3A, where a positively charged material E is shown crossing the boundary between the adhesive layer 110 and the electro-optic material layer 108. Similarly, a negatively charged material B is shown crossing the boundary between the polymer layer 106 and the electro-optic material layer 108. If a charged entity is displaced within its respective layer and cannot cross the boundary between the layers, the charge accumulates at the impenetrable boundary, stored as in an electrolytic capacitor. After the applied electric field is removed and electrodes 104 and 112 are grounded, a discharge of the charge stored at the internal boundaries of the display occurs, altering the electric field experienced by the electrophoretic medium of the electro-optic material layer 108 and potentially changing the optical state of the display.

[0108] Even if mobile ionic charges could flow freely across the boundaries between layers within the display (without accumulating at internal boundaries), there remains a difficulty in crossing the boundaries between the internal layers of the display and electrodes 104 and 112. The only possible mechanism for charge transfer across these boundaries is electron transfer, i.e., oxidation / reduction chemical processes. If electron transfer between electrodes 104 and 112 and the internal layers is impeded, ionic charges will inevitably accumulate at the boundaries between electrode 104 and layer 106, and between layer 110 and electrode 112. If the display is driven using a DC unbalanced drive scheme, significant charge accumulation may occur at these locations. When the electrodes reach a common potential, the relaxation of the accumulated charge may cause charge carriers to flow through electro-optic material layer 108. This flow of charge carriers may lead to changes in the optical state of the display, which may be undesirable.

[0109] U.S. Patent No. 9,726,957 discloses a technique for mitigating charge accumulation problems by adding an electrochemically active compound to a layer adjacent to the electro-optic material layer of an electro-optic display. The electrochemically active compound is oxidizable or reducible. The invention of U.S. Patent No. 9,726,957 is schematically illustrated in FIG. 3B, which is disclosed as FIG. 3 of the patent. As shown in FIG. 3B, charge accumulation at the electrode interface is mitigated by an electrochemical oxidation / reduction reaction involving electron transfer from the electrodes of the electro-optic display of FIG. 1 to the material contained in polymer layer 106 and adhesive layer 110. At the cathode, electrons are transferred to reduce components in the adjacent layer (illustrated as reduction of neutral substance G to provide anion G⁻), while at the anode, electrons are transferred to the electrode, resulting in oxidation of components in the adjacent layer (showing electron transfer from neutral substance J to generate cation J⁺). The injected charge has the opposite sign to the charge displacement during the initial polarization of the display, thus mitigating charge accumulation at the electrode interface. As shown in Figure 3B, when a potential is applied to the electro-optic display 100 of Figure 1, the migration of ions towards the electrodes leads to the accumulation of charge in thin diffusion layers near the electrodes. These layers are on the order of the Debye shield length, as is well known in the field of electrochemistry. Within these diffusion layers, the potential gradient is very steep. After a certain period of time, the potential gradient becomes sufficient to trigger an electron transfer reaction. The ease of electron transfer is determined in particular by the redox potential and concentration of the material present near the electrodes.

[0110] As described above, in U.S. Patent No. 9,726,957, the electrochemically active compound used to control charge injection at the electrode interface is added to the outer phase layer of the display, i.e., a layer different from the electro-optic material layer containing the electrophoretic medium. However, it has been found that in practice, only those components within a sufficiently short distance for effective electron transfer to or from the electrode are effectively oxidized or reduced. Therefore, considering that the diffusion of typical electroactive compounds through the polymer is too slow to sustain a practical current in the display, the components undergoing electron transfer at the electrode are depleted much faster than the time required to replenish them by diffusion to the electrode surface. For this reason, the electro-optic device structure disclosed in U.S. Patent No. 9,726,957 is not optimal for mitigating the problem of charge accumulation at the electrode and the resulting residual voltage.

[0111] The inventors of this invention have surprisingly discovered that a micro-unit electro-optic device, in which the electrophoretic medium is in contact with at least one pixel electrode of a first electrode layer and a plurality of pixel electrodes, and the electrophoretic material comprises an organic electroactive compound, achieves an effective reduction in residual voltage after prolonged DC unbalanced driving. In another example, the electrophoretic medium is in contact with all of the pixel electrodes of the first electrode layer and the plurality of pixel electrodes. The electro-optic device of this invention comprises: (1) a first electrode layer comprising a light-transmitting electrode; (2) a second electrode layer comprising a plurality of pixel electrodes; and (3) a micro-unit layer disposed between the first electrode layer and the second electrode layer. The micro-unit layer comprises a plurality of micro-units, each of which comprises an electrophoretic medium in contact with the light-transmitting electrode of the first electrode layer and at least one pixel electrode (or more than one or all of the pixel electrodes of the second electrode layer) of the plurality of pixel electrodes of the second electrode layer. The electrophoretic medium comprises: (a) charged pigment particles; (b) a nonpolar liquid; (c) a charge control agent; and (d) an organic electroactive compound. The organic electroactive compound is present in the electrophoretic medium in both oxidized and reduced forms. The oxidized form of the organic electroactive compound can be electrochemically reduced at the surface of one of the light-transmitting electrodes in the first electrode layer and the pixel electrode in the second electrode layer. The reduced form of the organic electroactive compound can be electrochemically oxidized at the surface of one of the light-transmitting electrodes in the first electrode layer and the pixel electrode in the second electrode layer. Both the oxidized and reduced forms of the organic electroactive compound are soluble in the nonpolar liquid of the electrophoretic medium. Alternatively, both the oxidized and reduced forms of the organic electroactive compound are contained in a reverse micelle structure present in the electrophoretic medium.

[0112] The content of organic electroactive compounds in the electrophoresis medium can be 0.1-10% by weight, or 0.2-8% by weight, 0.3-6% by weight, 0.4-5% by weight, 0.5-4% by weight, 0.6-3% by weight, or 0.7-2% by weight, based on the weight of the electrophoresis medium.

[0113] An antimicelle structure in a nonpolar liquid (first liquid) is a droplet or dispersion (particles in a third liquid) of a second liquid surrounded by amphiphilic molecules. These droplets form the core of the antimicelle structure. An amphiphilic molecule is a molecule that simultaneously possesses both hydrophobic groups (heads) and hydrophobic groups (tails) in its molecular structure. Typically, the heads of the amphiphilic molecules face the core of each antimicelle structure, while the tails face the outer surface of the structure because the tails are hydrophobic and more compatible with the nonpolar liquid. The second or third liquid is less hydrophobic than the tails of the amphiphilic molecules and less compatible with the nonpolar fluid, and is more compatible with the heads of the amphiphilic molecules. The nonpolar liquid is referred to as the "continuous phase" of the antimicelle structure / nonpolar liquid mixture.

[0114] Figure 4 This is a side view of an example of an electro-optic device according to the present invention. The electro-optic device 300 includes a front substrate 202, a first electrode layer 204 having a light-transmitting electrode, an electro-optic material layer 208, and a second electrode layer 318. The electro-optic device 300 has a viewing side 230. The second electrode layer 318 includes a plurality of pixel electrodes 319. The electro-optic material layer 208 includes a plurality of microcells 230A-D. Each microcell 230A-D of the electro-optic material layer 208 contains an electrophoretic medium 320. The electrophoretic medium 320 contains charged pigment particles 225 in a non-polar liquid. Microcell walls 232 separate adjacent microcells from each other. In the electro-optic device 300, at least one of the light-transmitting electrodes of the first electrode layer 204 and at least one of the pixel electrodes 319 of the plurality of pixel electrodes of the second electrode layer 318 is in contact with the electrophoretic medium 320. More than one pixel electrode 319 of the plurality of pixel electrodes of the second electrode layer 318 may be in contact with the electrophoretic medium. All pixel electrodes 319 of the plurality of pixel electrodes in the second electrode layer 318 may be in contact with the electrophoretic medium 320. The second electrode layer 318 is typically part of a backplane that includes circuitry and a substrate. The fact that the electrophoretic medium is in contact with the light-transmitting electrodes of the first electrode layer and with the pixel electrodes of the second electrode layer means that the electro-optic device 300 may not include a sealing layer, which is present in commercially available microcell electro-optic displays containing electrophoretic media.

[0115] Figure 4The front substrate 202 of the electro-optic device 300 can be a plastic film, such as a polyethylene terephthalate (PET) sheet with a thickness of 25 to 200 µm. The front substrate 202 may also include one or more other layers, such as a protective layer that absorbs ultraviolet radiation, a barrier layer that prevents oxygen or moisture from entering the display, and an anti-reflective coating that improves the optical properties of the display.

[0116] Figure 4 The light-transmitting electrode of the first electrode layer 204 of the electro-optic device 300 can be a thin, continuous conductive material coating with minimal inherent absorption of electromagnetic radiation in the visible spectrum, such as indium tin oxide (ITO), poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT: PSS), graphene, etc.

[0117] Figure 4 The electrophoretic medium of the electro-optic display 300 may contain two types of charged pigment particles. The electrophoretic medium of the display may contain three, four, five, or more than five types of charged pigment particles. Each type of charged pigment particle may have a different color. Each type of charged pigment particle may have a positive or negative charge. If the electrophoretic medium contains two types of charged pigment particles, namely a first type and a second type, the first type of pigment particles may be white and negatively charged (or positively charged), and the second type of charged pigment particles may be black and positively charged (or negatively charged). When an electric field is applied across the electro-optic material layer through the light-transmitting electrode of the first electrode layer and the pixel electrode of the second electrode layer, the white particles in the electrophoretic medium move towards the positive electrode, and the black particles move towards the negative electrode, so that an observer viewing the display from the viewing side (the side of the front substrate) sees either a white or black display portion corresponding to the pixel electrode, depending on whether the light-transmitting electrode is positive or negative relative to the pixel electrode.

[0118] Figure 4 The electrophoretic medium of the electro-optic display 300 may further comprise one or more charge control agents (CCAs). CCAs may be low-molecular-weight surfactants, polymeric reagents, or blends of one or more components. CCAs are used to stabilize or otherwise alter the sign and / or magnitude of the charge on charged pigment particles. A CCA is typically a molecule containing ionic or other polar functional groups (head groups). At least one of the positive or negative ionic head groups is preferably attached to a nonpolar chain (tail group), which is typically a hydrocarbon chain. It is believed that CCAs form reverse micelle structures in the electrophoretic medium.

[0119] During the operation of electro-optic devices, organic electroactive compounds can exist in both oxidized and reduced forms in the electrophoretic medium. The oxidized form of the organic electroactive compound can be electrochemically reduced at or near the surface of the light-transmitting electrode in the first electrode layer or the pixel electrode in the second electrode layer. Conversely, the reduced form of the organic electroactive compound can be electrochemically oxidized at or near the surface of the light-transmitting electrode in the first electrode layer or the pixel electrode in the second electrode layer. In other words, the oxidized form is reversibly reduced to the reduced form electrochemically, and the reduced form is reversibly oxidized back to the oxidized form electrochemically. Both the conversion from oxidized to reduced form and from reduced to oxidized form occur through redox reactions. Therefore, organic electrochemically active compounds can also be referred to as redox raw materials.

[0120] While organic electroactive compounds capable of undergoing at least partially reversible redox reactions are superior to those capable of irreversible reactions, the ability to undergo fully reversible redox reactions is not an absolute requirement of this invention. The presence of sufficient concentrations of the reduced or oxidized form of the organic electroactive compound mitigates premature device degradation and reduces residual voltage over a period of time.

[0121] Figure 5 The diagram shows some important elements related to the operation of the electro-optic device of the present invention, including redox reactions at the electrodes. Figure 5 The diagram shows a cross-section of a microcell with two electrodes and an electrophoretic medium between them, the medium comprising charged pigment particles and an organic electroactive compound. Typically, the distance between the electrodes ranges from 5 to 25 µm. The electrophoretic fluid comprises a nonpolar liquid, typically with a low dielectric constant, and charged pigment particles (P... + and P - Symbol P + and P - This indicates that the electrophoretic medium contains positively charged pigment particles. In reality, the electrophoretic medium can contain more than two types of charged pigment particles, each carrying a different size of charge. Figure 5It was also shown that the electrophoretic medium contains charged reverse micelle structures M+ and M-. These reverse micelle structures can be formed by surfactant-like molecules such as CCA, which are added to the electrophoretic medium to promote and maintain pigment charging. When a voltage is applied across the microcells through the electrodes, positively charged pigment particles and positively charged reverse micelle structures migrate towards the more negatively charged electrode (hereinafter referred to as the cathode), while negatively charged pigment particles and negatively charged reverse micelle structures migrate towards the more positively charged electrode (hereinafter referred to as the anode). This charge migration can shield either the charged pigment particles or the charged reverse micelle structures present in the electrophoretic medium portion not near the electrodes from the electric field experienced by either. Therefore, a potential gradient may form in the electrophoretic medium. That is, due to the migration of charged pigment particles and charged reverse micelle structures, the potential near the electrode surface may be higher than the potential in the space far from the electrode surface, which allows electron transfer reactions involving the components of the electrophoretic medium to occur.

[0122] The organic electroactive compounds in the electrophoretic medium of this invention Figure 5 In electrophoretics, these are represented as Q (oxidized form) and QH2 (reduced form). The oxidized form Q and the reduced form QH2 of an organic electroactive compound form a redox pair in the electrophoretic medium. For example... Figure 5 As shown, QH2 loses two electrons at the anode to form Q and two protons. At the cathode, Q gains two electrons and gains two protons, forming the reduced form QH2. The current is maintained as the reduced form QH2 formed at the cathode diffuses to the anode, and the oxidized form Q formed at the anode diffuses to the cathode. These redox reactions at the electrodes prevent the redox pair from being depleted of Q / QH2.

[0123] Electro-optic devices must be bidirectionally actuated. That is, applying a voltage of one polarity should cause positively charged pigment particles to migrate to the viewing side, while applying a voltage of the opposite polarity should cause negatively charged pigment particles to migrate to the viewing side. In this invention, current is maintained regardless of the polarity used to drive the device. Specifically, protons formed at the anode will balance the negatively charged pigment particles and negatively charged antimicelle structures driven to the anode, while the protons are consumed at the cathode (or equivalently, anions that consume protons are generated at the cathode). Therefore, the electrochemical reactions at the electrodes can at least partially neutralize the charged pigment particles and charged antimicelle structures that have migrated to the electrodes during the initial polarization of the microcell. This charge neutralization leads to a reduction in residual voltage, which would otherwise cause electrostatic recoil and image drift when the display is grounded after being driven. Since the current in the electro-optic device of this invention can be maintained indefinitely, there is no reason to expect a significant increase in residual voltage after initial polarization and the establishment of a steady state. In fact, the inventors have surprisingly discovered that in a model system, current can be continuously applied to microcells containing the organic electroactive compounds of the present invention for 48 hours without a significant increase in residual voltage or electrode loss.

[0124] In this invention, any compound may be used that (a) has an oxidized and a reduced form that can be formed at least partially reversibly; and (b) is soluble in a nonpolar liquid of the electrophoretic medium or is part of a reverse micelle structure in a nonpolar liquid of the electrophoretic medium. Preferred compounds include substituted quinone / hydroquinone pairs (or corresponding catechols), wherein side reactions are minimized by appropriate substitution on one or more benzene rings. A particularly preferred compound pair is panthenol / panthenone, the structure of which is... Figure 6 As shown in the image. Panthenol, Figure 6 The structure above is the reduced form, while ubiquinone... Figure 6 The structure below is in its oxidized form.

[0125] The electrophoretic medium of the device may initially be packed in only one of two forms (oxidized or reduced forms of a redox pair) because the corresponding pairing compounds are generated when the device is driven. Figure 7 The diagram illustrates this reaction process. First, when the device is activated, the reduced form QH2 of the organic electroactive compound initially contained in the electrophoretic medium is converted to the oxidized form Q at the anode. Therefore, even if Q is initially absent at the cathode to sustain the current, another reduction reaction may occur, such as the reduction of protons from water to form hydrogen ions, as shown in the diagram. Figure 7As shown in the diagram. This reaction may not be reversible. However, as the reaction proceeds at the cathode, more oxidized form Q of the organic electroactive compound will be generated and accumulate in the microcell until a concentration sufficient to sustain a continuous current exists in the electrophoretic medium. Therefore, organic electroactive compounds can be added to the electrophoretic medium of the electro-optic device in their reduced form, their oxidized form, or a mixture of both. Furthermore, combinations of two (or more) organic electroactive compounds can be added to the electrophoretic medium. For example, an oxidized form of one organic electroactive compound A and a reduced form of another organic electroactive compound B can be used. In this case, it may be desirable for the standard reduction potential of the oxidized form of organic electroactive compound A to be less positive than the standard reduction potential of the oxidized form of organic electroactive compound B. This prevents reaction between the two organic electroactive compounds.

[0126] As described above, the reduced form of the organic electroactive compound used in this invention can be oxidized at the anode. However, it is preferable that the organic electroactive compound does not readily react with oxygen.

[0127] The molecular structures of the reduced forms of organic electroactive compounds can be represented by formulas I to IX. In these formulas, R1 to R... 39 It can be hydrogen, substituted or unsubstituted alkyl, alkenyl or aryl, and substituents R1 and R2 together, and / or R3 and R4, and / or R5 and R6, and / or R6 and R7, and / or R7 and R8, R9 and R 10 , and / or R 11 and R 12 , and / or R 14 and R 15 , and / or R 15 and R 16 , and / or R 16 and R 17 , and / or R 19 and R 20 , and / or R 21 and R 22 , and / or R 25 and R 26 , and / or R 26 and R 27 , and / or R 27 and R 28 A ring can be formed; and R 31 and R 32 At least one of them is aryl, R 33 and R 34 At least one of them is aryl, and R 36 and R 37 At least one of them is an aryl group.

[0128] At least one of R1 to R4 in Formula I, at least one of R5 to R8 in Formula II, and R9 to R4 in Formula III 13 At least one of them, R of formula IV 14 To R 18 At least one of them, R of formula V 19 To R 24 At least one of them, R of formula VI 25 To R 30 At least one of them, R of equation VII 31 and R 32 At least one of them, R of formula VIII 33 To R 35 At least one of them, and R of formula IX 36 To R 39 At least one of them can be an alkyl or alkenyl group having at least 10 carbon atoms.

[0129] R9 to R of Formula III 12 At least one of them, R of formula IV 14 To R 17 At least one of them, R of formula V 19 To R 22 At least one of them, R of formula VI 25 To R 28 At least one of them, R of formula VIII 33 and R 34 At least one of them, and R of formula IX 36 and R 37 At least one of them may be an alkyl or alkenyl group having at least 10 carbon atoms. The alkyl or alkenyl group may have 10 to 100 carbon atoms. The alkyl or alkenyl group comprises an isoprene dimer or oligomer, the isoprene dimer or oligomer comprising 1 to 20 isoprene units (-CH2CH=C(CH3)CH2-). The alkyl or alkenyl group may comprise an isoprene dimer or oligomer, the isoprene dimer or oligomer comprising 1 to 13 isoprene units (-CH2CH=C(CH3)CH2-).

[0130] The molecular structure of the reduced form of the organic electroactive compound can be represented by formula X. Groups R1, R2, and R3 can be hydrogen, alkyl, alkenyl, or alkoxy, and n can be an integer from 2 to 20. Groups R1 and R2 can both be methoxy, and R3 can be methyl. Groups R1 and R2 can both be methyl, and R3 can be hydrogen.

[0131] The reduced form of the organic electroactive compound can be panthenol-10. The reduced form of the organic electroactive compound can be represented by formula XI.

[0132] The molecular structure of the oxidized form of the organic electroactive compound can be represented by formula XII. Group R 40 R 41 R 42 R 43 and R 44 It can be hydrogen, alkyl, alkenyl, or alkoxy, and m can be an integer from 2 to 20.

[0133] The molecular structure of the oxidized form of the organic electroactive compound can be represented by formula XIII or XIV. Group R 40 R 41 R 42 R 43 and R 44 It can be hydrogen, alkyl, alkenyl, or alkoxy, p can be an integer from 2 to 20, and q can be an integer from 2 to 20. The integer q can be selected from 3, 4, 7, and 9. If the said organic electroactive compound is represented by formula XIV, then the group R 48 R 49 R 53 R 50 and R 51 It can be hydrogen, and R 52 It can be methyl.

[0134] The oxidized form of the organic electroactive compound may have a reduction potential of no more than 1.0 V relative to a standard hydrogen electrode. Preferably, the oxidized form of the organic electroactive compound has a reduction potential of no more than 0.2 V relative to a standard hydrogen electrode. Organic electroactive compounds satisfying this reduction potential criterion exist, and these compounds are soluble in the nonpolar liquid of the electrophoretic medium, allowing them to diffuse rapidly through the medium to participate in the electrochemical reaction at the electrode, thereby reducing the residual voltage observed after prolonged DC unbalanced drive.

[0135] It is believed that in the absence of the organic electroactive compound according to the invention, water oxidation to generate oxygen (a half-cell reaction with a standard reduction potential greater than 1V) may occur, although the invention is by no means limited to this view. Since the organic electroactive compound used in the invention is more readily reduced than water, when such an organic electroactive compound is present, less ionic polarization is required to generate a sufficiently steep potential gradient in the electrode bilayer for electron transfer, thus resulting in a lower residual voltage experienced by the electro-optic material.

[0136] As described above, according to the present invention, the use of organic electroactive compounds aims to control charge accumulation near the electrodes. Such charge accumulation is typically a reversible process. The present invention also seeks to control the nature of the Faraday reaction occurring at the electrode interface, thereby enabling DC unbalanced drive of the display without incurring irreversible electrode damage. The organic electroactive compounds of the present invention introduce a competitive redox pathway so that the Faraday reaction occurs at the electrode interface without electrode loss. Without the use of the organic electroactive compounds according to the present invention, undesirable Faraday reactions may occur, such as the electrolysis of water, resulting in the generation of byproducts such as hydrogen and oxygen. Even worse, the electrode material itself may participate in redox reactions. Some materials used for transparent electrodes are easily oxidized. For example, silver nanowires or meshes may be easily oxidized to silver cations. Other materials widely used for transparent electrodes are easily reduced. For example, conductive polymers such as PEDOT:PSS lose their conductivity upon reduction, and another common material used for transparent electrodes, indium tin oxide (ITO), can be irreversibly reduced to metallic tin or metallic indium, causing discoloration (yellowing) of the transparent electrode and ultimately leading to complete failure. This invention seeks to introduce competitive redox chemistry to enable Faraday reactions to occur at the electrode interface without electrode loss. In the case of ITO electrodes, it is desirable that the oxidized form of the organic electroactive compound used in this invention is more easily reduced than ITO. That is, preferential reduction of the organic electroactive compound protects the ITO electrode from irreversible electrochemical loss. On the other hand, it is desirable that the oxidized form of the organic electroactive compound is less easily reduced, i.e., its thermal redox form, unless such oxidation produces a new reduced form (i.e., a reduced form corresponding to the oxidized form).

[0137] The electro-optic device of the present invention can be operated by a method comprising the following steps: (a) providing the electro-optic device; (b) driving the electro-optic device using a DC unbalanced waveform. The residual voltage of the electro-optic device is reduced compared to the residual voltage of a control electro-optic device.

[0138] A control electro-optic device is a device comprising a control electrophoretic medium. The control electrophoretic medium is compositionally similar to the electrophoretic medium of the present invention, but does not contain an organic electroactive compound. The electro-optic device of the present invention comprises a first electrode layer including a transparent electrode; a second electrode layer including a plurality of pixel electrodes; and a micro-unit layer disposed between the first electrode layer and the second electrode layer. The micro-unit layer includes a plurality of micro-units, each of which contains an electrophoretic medium in contact with at least one pixel electrode of the transparent electrode of the first electrode layer and the plurality of pixel electrodes of the second electrode layer. The electrophoretic medium comprises: (a) charged pigment particles; (b) a nonpolar liquid; (c) a charge control agent; and (d) an organic electroactive compound. The organic electroactive compound exists in the electrophoretic medium in both oxidized and reduced forms. The oxidized form of the organic electroactive compound is electrochemically reduced at the surface of one of the first electrode layer and the second electrode layer. The reduced form of the organic electroactive compound is electrochemically oxidized at the surface of one of the first electrode layer and the second electrode layer. The oxidized and reduced forms of the organic electroactive compound are soluble in the nonpolar liquid of the electrophoretic medium, or are contained in the reverse micelle structure present in the electrophoretic medium. Example

[0139] Example 1

[0140] A solution was prepared comprising: (a) 1 wt% charge control agent, (b) 1 wt% panthenol, and (c) Isopar E. The charge control agent was prepared as described in Example 2 of U.S. Patent Application Publication No. 2020 / 0355978. Panthenol-10 was supplied by Biosynth of Staad, Switzerland. The solution was introduced into a battery comprising two opposing glass plates, each coated with an indium tin oxide (ITO) transparent conductive coating, spaced 25 μm apart, with a surface area of ​​6.5 cm². The battery was sealed with an epoxy resin composition and then driven at 15 V DC for 48 hours at 25 °C. During the drive, the current through the battery was continuously measured. After this time, the battery was driven at 0 V for 50 ms, then floated, and the residual voltage was measured.

[0141] Figure 8 The current flowing through it during the 48-hour drive period is provided. Figure 8 The graph shows the current measured relative to time. As can be seen from the graph, only a small decrease in current was observed during the 48-hour drive period. The battery remained transparent throughout the drive period, but under the same conditions, if a control solution was used, which contained only CCA in Isopar E (without organic electroactive compounds), ITO was depleted and the battery turned yellow. Figure 9 The graph shows the residual voltage during a 300-second float period following a brief 0V drive; it is a curve of the residual voltage versus time. In summary, this demonstrates that continuous DC current can be passed through a model composition containing the organic electroactive compound of the present invention without depletion of the electrodes or the model composition itself.

[0142] Example 2

[0143] An electrophoretic medium was prepared comprising a white pigment similar to pigment W1, a magenta pigment similar to pigment M1, and a cyan pigment similar to pigment C1, as described in U.S. Patent No. 10,678,111. The yellow pigment was a surface-treated pigment, Yellow 180, prepared by dispersion polymerization as described in Example 5 of U.S. Patent Application Publication No. 2023 / 132958. The electrophoretic medium also contained CCA as described in Example 1. The total amount of CCA in the electrophoretic composition was 1.8% by weight of the electrophoretic medium. The electrophoretic medium also contained 1% by weight of a polydimethylsiloxane polymer (PDMS DMS-T72, molecular weight approximately 700,000, supplied by Gelest Corporation) as an image stabilizer. Table 1 shows the weight percentage content of each pigment particle type by weight of the electrophoretic medium.

[0144] Table 1: Content of pigment particles in electrophoresis medium.

[0145]

[0146] Example 3

[0147] The electrophoresis medium of Example 2 was divided into two parts, 2A and 2B. Sample 2A was loaded into a battery similar to the one described in Example 1 above, except that the distance between the two electrodes was 10 μm and the surface area was 1 cm². Panthenol and ubiquinone (1% by weight of the electrophoresis medium and 1% by weight of the electrophoresis medium) were added to sample 2B to prepare sample 3B. Panthenol and ubiquinone were available from AmBeed, Illinois, USA. Sample 3B was loaded into a battery (the same type of battery as that loaded with sample 2A). The batteries containing samples 2A and 3B were driven with DC voltages of 1, 5, 15, and 30 V. Each voltage was applied for 240 seconds, followed by driving them at 0 V for 100 ms. The batteries were then floated while the residual voltage was measured. Figure 10 The measured currents for samples 2A and 3B are shown as a function of the applied voltage, while Figure 11The residual voltage measured during the final floating state is shown. It can be seen that: (i) the current through sample 3B (containing the organic electroactive compound) is higher than the current through sample 2A (control); (ii) the residual voltage measured in sample 3B (containing the organic electroactive compound) is lower than the residual voltage measured in sample 2A (control). That is, the electrophoretic medium containing the organic electroactive compound according to the invention exhibits improved performance (lower residual voltage).

[0148] The color gamut of electro-optic devices prepared from the electrophoretic media of sample 2A (control) and sample 3B (the present invention) was also measured. Figure 12 The waveform is the voltage applied to the backplane relative to the frontplane, used to probe the total color gamut (i.e., the range of all colors that the device can address). Figure 12 The waveform is used for testing purposes, although it is not the actual waveform used in commercial displays. This waveform is constructed from "dipoles," that is, pairs of pulses with opposite polarities, whose duration and amplitude are as follows: Figure 12 The dark envelope in the figure shows the systematic variation. The voltages studied were + / - 3.5, 6.1, 9.4, 13.4, 18.2, 23.7, and 30 V, and the pulse length durations were 50, 80, 120, 190, and 300 milliseconds. For each voltage pair (+, -), each pulse duration pair was visited once. This was done in such a way that the pulse duration pair in one dipole had exactly one value changed in the next dipole, and that value was adjacent in the ordered list of pulse duration values. Voltages were explored in a similar manner. In this way, the changes in the waveform are as smooth as possible because successive dipoles are as similar to each other as possible. The reflectance spectrum was obtained throughout the entire waveform (not just at its end) and converted to CIEL*a*b* units. Figure 13 The color gamut observed from an electro-optic device containing a control electrophoretic medium is shown. Figure 14 This displays the color gamut observed from an electro-optic device incorporating the electrophoretic medium of the present invention. From Figure 13 and Figure 14 As can be seen, the color gamut of the control device and the device of the present invention are very similar. That is to say, the organic electroactive compound of the present invention can be added to the electrophoretic medium without significantly affecting its electro-optic performance, but allows DC drive and reduces the accumulation of residual voltage.

[0149] Terms and Conditions

[0150] Clause 1: An electro-optic device comprising: a first electrode layer including a light-transmitting electrode; a second electrode layer including a plurality of pixel electrodes; and a micro-unit layer disposed between the first electrode layer and the second electrode layer, the micro-unit layer including a plurality of micro-units, each of the plurality of micro-units comprising an electrophoretic medium, the electrophoretic medium being in contact with at least one pixel electrode of the light-transmitting electrode of the first electrode layer and the plurality of pixel electrodes of the second electrode layer, the electrophoretic medium comprising: (a) charged pigment particles; (b) a nonpolar liquid; (c) a charge control agent; and (d) an organic electroactive compound, wherein...

[0151] The organic electroactive compound exists in the electrophoretic medium in both oxidized and reduced forms.

[0152] The oxidized form of the organic electroactive compound can be electrochemically reduced at the surface of one of the first and second electrode layers.

[0153] The reduced form of the organic electroactive compound can be electrochemically oxidized at the surface of one of the first and second electrode layers, and

[0154] The oxidized and reduced forms of the organic electroactive compound are (i) soluble in the nonpolar liquid of the electrophoretic medium, or (ii) part of a reverse micelle structure present in the nonpolar liquid of the electrophoretic medium.

[0155] Clause 2: The electro-optic device described in Clause 1, wherein the molecular structure of the reduced form of the organic electroactive compound is represented by formulas I to IX, wherein R1 to R... 39 It can be hydrogen, substituted or unsubstituted alkyl, alkenyl or aryl, and substituents R1 and R2 together, and / or R3 and R4, and / or R5 and R6, and / or R6 and R7, and / or R7 and R8, R9 and R 10 , and / or R 11 and R 12 , and / or R 14 and R 15 , and / or R 15 and R 16 , and / or R 16 and R 17 , and / or R 19 and R 20 , and / or R 21 and R 22 , and / or R 25 and R 26 , and / or R 26 and R 27 , and / or R 27 and R 28 A ring can be formed; and R 31and R 32 At least one of them is aryl, R 33 and R 34 At least one of them is aryl, and R 36 and R 37 At least one of them is an aryl group.

[0156] Clause 3: The electro-optic device described in Clause 2, wherein at least one of R1 to R4 of Formula I, at least one of R5 to R8 of Formula II, and R9 to R4 of Formula III are used. 13 At least one of them, R of formula IV 14 To R 18 At least one of them, R of formula V 19 To R 24 At least one of them, R of formula VI 25 To R 30 At least one of them, R of equation VII 31 and R 32 At least one of them, R of formula VIII 33 To R 35 At least one of them, and R of formula IX 36 To R 39 At least one of them is an alkyl or alkenyl group having at least 10 carbon atoms.

[0157] Clause 4: The electro-optical device described in Clause 2, wherein R9 to R of Formula III 12 At least one of them, R of formula IV 14 To R 17 At least one of them, R of formula V 19 To R 22 At least one of them, R of formula VI 25 To R 28 At least one of them, R of formula VIII 33 and R 34 At least one of them, and R of formula IX 36 and R 37 At least one of them is an alkyl or alkenyl group having at least 10 carbon atoms.

[0158] Clause 5: An electro-optic device according to Clause 3 or Clause 4, wherein the alkyl or alkenyl group has 10 to 100 carbon atoms.

[0159] Clause 6: An electro-optic device according to any one of Clauses 2 to 5, wherein the alkyl or alkenyl group comprises an isoprene dimer or oligomer, the isoprene dimer or oligomer comprising 1 to 20 isoprene units (-CH2CH=C(CH3)CH2-).

[0160] Clause 7: An electro-optic device according to any one of Clauses 2 to 5, wherein the alkyl or alkenyl group comprises an isoprene dimer or oligomer, the isoprene dimer or oligomer comprising 1 to 13 isoprene units (-CH2CH=C(CH3)CH2-).

[0161] Clause 8: An electro-optic device according to any one of Clauses 2 to 7, wherein the molecular structure of the reduced form of the organic electroactive compound is represented by Formula X, wherein R1, R2 and R3 can be hydrogen, alkyl, alkenyl or alkoxy, and n is an integer from 2 to 20.

[0162] Clause 9: The electro-optical device described in Clause 8, wherein R1 and R2 are methoxy groups and R3 is a methyl group.

[0163] Clause 10: The electro-optic device described in Clause 9, wherein the reduced form of the organic electroactive compound is panthenol-10.

[0164] Clause 11: The electro-optical device described in Clause 8, wherein R1 and R2 are methyl groups and R3 is hydrogen.

[0165] Clause 12: The electro-optic device described in Clause 11, wherein the reduced form of the organic electroactive compound is represented by formula XI.

[0166] Clause 13: In the electro-optic device according to Clause 1, the molecular structure of the oxidized form of the organic electroactive compound is represented by formula XII, wherein R 40 R 41 R 42 R 43 and R 44 It can be hydrogen, alkyl, alkenyl, or alkoxy, and m is an integer from 2 to 20.

[0167] Clause 14: The electro-optic device described in Clause 1, wherein the molecular structure of the oxidized form of the organic electroactive compound is represented by formula XIII or XIV, wherein R 45 R 46 R 47 R 48 R 49 R 50 R 51 and R 52 It can be hydrogen, alkyl, alkenyl or alkoxy, p is an integer from 2 to 20, and q is an integer from 2 to 20.

[0168] Clause 15: The electro-optic device described in Clause 14, wherein the molecular structure of the oxidized form of the organic electroactive compound is represented by formula XIV, R 48 R 49 R 50 R51 It is hydrogen, and R 52 It is a methyl group.

[0169] Clause 16: The electro-optical device described in Clause 15, wherein q is selected from 3, 4, 7 and 9.

[0170] Clause 17: An electro-optic device according to any one of Clauses 1 to 16, wherein the oxidized form of the organic electroactive compound has a reduction potential of not more than 1.0 V relative to a standard hydrogen electrode.

[0171] Clause 18: A method of operating an electro-optic device, the method comprising: (a) providing the electro-optic device according to Clause 1; and (b) driving the electro-optic device using a DC unbalanced waveform.

[0172] Clause 19: The method of operating the electro-optic device described in Clause 18, wherein the residual voltage of the electro-optic device is lower than that of a control electro-optic device, the control electro-optic device comprising a control electrophoretic medium that does not contain an organic electroactive compound.

[0173] Clause 20: An electro-optic device comprising: a first electrode layer including a light-transmitting electrode; a second electrode layer including a plurality of pixel electrodes; and a micro-unit layer disposed between the first electrode layer and the second electrode layer, the micro-unit layer including a plurality of micro-units, each of the plurality of micro-units comprising an electrophoretic medium in contact with at least one pixel electrode of the first electrode layer and the plurality of pixel electrodes of the second electrode layer, the electrophoretic medium comprising: (a) charged pigment particles; (b) a nonpolar liquid; (c) a charge control agent; and (d) an organic electroactive compound, wherein...

[0174] The organic electroactive compound is present in the electrophoretic medium in at least one of its oxidized or reduced forms.

[0175] The oxidized form of the organic electroactive compound can be electrochemically reduced at the surface of one of the first and second electrode layers.

[0176] The reduced form of the organic electroactive compound can be electrochemically oxidized at the surface of one of the first and second electrode layers, and

[0177] The oxidized and reduced forms of the organic electroactive compound are (i) soluble in the nonpolar liquid of the electrophoretic medium, or (ii) part of a reverse micelle structure present in the nonpolar liquid of the electrophoretic medium.

Claims

1. An electro-optic device, comprising: The first electrode layer includes a light-transmitting electrode; The second electrode layer includes multiple pixel electrodes; A micro-unit layer is disposed between the first electrode layer and the second electrode layer. The micro-unit layer includes a plurality of micro-units, each of which contains an electrophoretic medium. The electrophoretic medium is in contact with at least one pixel electrode among the light-transmitting electrode of the first electrode layer and the plurality of pixel electrodes of the second electrode layer. The electrophoretic medium comprises: (a) Charged pigment particles; (b) Nonpolar liquids; (c) Charge control agents; and (d) Organic electroactive compounds, in The organic electroactive compound exists in the electrophoretic medium in both oxidized and reduced forms. The oxidized form of the organic electroactive compound can be electrochemically reduced at the surface of one of the first and second electrode layers. The reduced form of the organic electroactive compound can be electrochemically oxidized at the surface of one of the first and second electrode layers, and The oxidized and reduced forms of the organic electroactive compound are (i) soluble in the nonpolar liquid of the electrophoretic medium, or (ii) part of a reverse micelle structure present in the nonpolar liquid of the electrophoretic medium. The molecular structure of the reduced form of the organic electroactive compound is represented by formula X. Formula X R1, R2, and R3 can be hydrogen, alkyl, alkenyl, or alkoxy, and n is an integer from 2 to 20.

2. The electro-optic device of claim 1, wherein R1 and R2 are methoxy groups and R3 is a methyl group.

3. The electro-optic device of claim 2, wherein the reduced form of the organic electroactive compound is panthenol-10.

4. The electro-optic device of claim 1, wherein R1 and R2 are methyl groups and R3 is hydrogen.

5. An electro-optic device, comprising: The first electrode layer includes a light-transmitting electrode; The second electrode layer includes multiple pixel electrodes; A micro-unit layer is disposed between the first electrode layer and the second electrode layer. The micro-unit layer includes a plurality of micro-units, each of which contains an electrophoretic medium. The electrophoretic medium is in contact with at least one pixel electrode among the light-transmitting electrode of the first electrode layer and the plurality of pixel electrodes of the second electrode layer. The electrophoretic medium comprises: (a) Charged pigment particles; (b) Nonpolar liquids; (c) Charge control agents; and (d) Organic electroactive compounds, in The organic electroactive compound exists in the electrophoretic medium in both oxidized and reduced forms. The oxidized form of the organic electroactive compound can be electrochemically reduced at the surface of one of the first and second electrode layers. The reduced form of the organic electroactive compound can be electrochemically oxidized at the surface of one of the first and second electrode layers, and The oxidized and reduced forms of the organic electroactive compound are (i) soluble in the nonpolar liquid of the electrophoretic medium, or (ii) part of a reverse micelle structure present in the nonpolar liquid of the electrophoretic medium. The molecular structure of the oxidized form of the organic electroactive compound is represented by formula XII. Formula XII Where R 40 R 41 R 42 R 43 and R 44 It can be hydrogen, alkyl, alkenyl, or alkoxy, and m is an integer from 2 to 20.

6. An electro-optic device, comprising: The first electrode layer includes a light-transmitting electrode; The second electrode layer includes multiple pixel electrodes; A micro-unit layer is disposed between the first electrode layer and the second electrode layer. The micro-unit layer includes a plurality of micro-units, each of which contains an electrophoretic medium. The electrophoretic medium is in contact with at least one pixel electrode among the light-transmitting electrode of the first electrode layer and the plurality of pixel electrodes of the second electrode layer. The electrophoretic medium comprises: (a) Charged pigment particles; (b) Nonpolar liquids; (c) Charge control agents; and (d) Organic electroactive compounds, in The organic electroactive compound exists in the electrophoretic medium in both oxidized and reduced forms. The oxidized form of the organic electroactive compound can be electrochemically reduced at the surface of one of the first and second electrode layers. The reduced form of the organic electroactive compound can be electrochemically oxidized at the surface of one of the first and second electrode layers, and The oxidized and reduced forms of the organic electroactive compound are (i) soluble in the nonpolar liquid of the electrophoretic medium, or (ii) part of a reverse micelle structure present in the nonpolar liquid of the electrophoretic medium. The molecular structure of the oxidized form of the organic electroactive compound is represented by formula XIII or formula XIV. Formula XIII Formula XIV Where R 45 R 46 R 47 R 48 R 49 R 50 R 51 and R 52 It can be hydrogen, alkyl, alkenyl or alkoxy, p is an integer from 2 to 20, and q is an integer from 2 to 20.

7. The electro-optic device of claim 6, wherein the molecular structure of the oxidized form of the organic electroactive compound is represented by formula XIV, R 48 R 49 R 50 R 51 It is hydrogen, and R 52 It is a methyl group.

8. The electro-optic device of claim 7, wherein q is selected from 3, 4, 7 and 9.

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